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M.w. Kellogg Limited

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Operating Manual

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EST/JOB NO. CLIENT PROJECT LOCATION

5777 Kermanshah Petrochemicals Industries Co. Ammonia & Urea Complex Kermanshah, Iran

Managers

CLASS DOC. NO. PAGE: Revision

PROJ-PM-008 1 OF 312

5

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K.P.I.C

Operating Manual for 1200 MTPD Ammonia Plant

c: C-, V'~ PCS

MH

4

6/07/05

3

20/05/05

For Client Review

PCS

MH

2

10/08/04

For Internal Review

XU. B

ZH.G

Incorporating Client comments

DA

25/06/03

For Client Approval

JM

RL

Date

Reason for Issue

By

Checked

5

21/12/06

1

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w

It.

See Page 2 for list of revised pages Client Approved

0 Rev.

t- I MDV

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continuation sheet JOB NO.

SPEC. TYPE: CLASS DOC NO.

5777

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Revised Pages in Revision 5

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Page Number(s) 1 - 11 13-18 123 - 125 132 -135 160 174 180 - 181 190 216 298 - 306

Change Contents revised to reflect chanqes Re-Formatled Re-Formatled Re-Formatled Font corrected Spelling correction Note inserted Reference Corrected Font corrected Tables revised -- -------------

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. ...

TABLE OF CONTENTS

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1

INTRODUCTION

12

2

BASIS OF DESIGN

13

2.1

DUTY OF UNIT

13

2.2

FEED CHARACTERISTICS

13

2.3

PRODUCT SPECIFICATIONS

14

2.3.1 2.3.2

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Ammonia Product ............................................................................................... 14 Carbon Dioxide Product ....................................................................................... 14

2.4

MATERIAL AND ENERGY BALANCES

15

2.5

BATTERY LIMIT CONDITIONS [OPERATING TEMP. & PRESSURE]

16

2.6

DESIGN FEATURES

17

2.6.1 2.6.2 2.6.3 2.6.4 2.6.5 2.6.6 2.6.7 2.6.8

Feed Gas Compression and Purification .............................................................. 17 Air Compression Section ..................................................................................... 18 Reforming Section ............................................................................................... 18 Shift Conversion .................................................................................................. 18 CO 2 Removal ....................................................................................................... 18 Methanation ......................................................................................................... 19 Synthesis Gas Compressor ................................................................................. 19 Synthesis Loop Section ....................................................................................... 19

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Refrigeration Section ........................................................................................... 19 Steam System ..................................................................................................... 19 Utilities ................................................................................................................. 20 Catalyst Volumes ................................................................•................................ 20 20

Introduction .......................................................................................................... 20 Raw Synthesis Gas Preparation .......................................................................... 21 Synthesis Gas Purification ................................................................................... 24 Synthesis Gas Compression & Ammonia Synthesis ............................................ 28 Ammonia Refrigeration and Recovery ................................................................. 31 Ammonia Purge Gas Recovery System ............................................................... 32 Ammonia Storage & Loading Facilities (OSBL) .................................................... 32

3

DESCRIPTION OF UNIT CONTROL

34

3.1

UNIT CONTROL

34

3.1.1 3.1.2 3.1.3 3.1.4 3.1.5 3.1.6 3.2

3.3

Natural Gas Feed Preparation ............................................................................. 34 Raw Synthesis Gas Preparation .......................................................................... 38 Synthesis Feed Gas Purification .......................................................................... 44 Ammonia· Production ........................................................................................... 54 Refrigeration And Ammonia Product Purification .................................... :............ 59 Ammonia Storage & Loading (OSBL) .................................................................. 65

OPERATING CONDITIONS AND PROCESS VARIABLES 3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6

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Natural Gas Feed Preparation ............................................................................. 66 CO2 Removal ( aMDEA System) .......................................................................... 81 Methanation (R-21 06) .......................................................................................... 84 Ammonia Conversion ........................................................................................... 87 Ammonia Product Purification (Removal of Absorbed Gases) ............................. 98 Boiler Feed Water Deaeration (V-21 01 ) ............................................................. 101

CATALYST OPERATING CONDITIONS 3.3.1 3.3.2 3.3.3 3.3.4 3.3.5 3.3.6 3.3.7 3.3.8

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PROCESS FLOW DESCRIPTION 2.7.1 2.7.2 2.7.3 2.7.4 2.7.5 2.7.6 2.7.7

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103

Hydrogenator - R-2160 ..................................................................................... 103 Desulphurisers R-2108A1B ................................................................................ 104 Primary Reformer H-2101 .................................................................................. 105 Secondary Reformer R-2103 ............................................................................. 106 HT Shift Converter R-21 04 ................................................................................ 107 LT Shift Converter R-21 09 ................................................................................. 108 Methanator R-2106 ............................................................................................ 109 Ammonia Converter R-21 05 .............................................................................. 110

3.4

INSTRUMENT LIST

110

4

UTILITY I CHEMICAL REQUIREMENTS

111

4.1

UTILITY GENERATING CAPACITIES

111

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Deaerator V-21 01 .............................................................................................. 111 BFW Pumps P-21 04 AlB & BFW Distribution .................................................... 113 Steam Drum - D-21 01 ........................................................................................ 114 H.P. Steam Distribution ...................................................................................... 116 M.P. Steam System (42.5 Bara) ........................................................................ 118 L.P. Steam System (4.5 Bara) ........................................................................... 118 119

Surface Condenser - E-2140 ............................................................................. 119 Process Condensate Stripper- T-2150 ............................................................. 120 Process Condensate Drum D-2161 ................................................................... 121

4.4

COOLING WATER [SUPPLY & RETURN]

121

4.5

REFORMER COOLING WATER JACKETS

123

4.6

RAW WATER TREATMENT (OSBL)

124

4.7

SERVICE & POTABLE WATER (OSBL)

124

4.8

FLARE SYSTEM

124

4.9

AIR REQUIREMENTS

125

4.9.1 4.9.2

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STEAM CONDENSATE SYSTEMS 4.3.1 4.3.2 4.3.3

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STEAM REQUIREMENTS 4.2.1 4.2.2 4.2.3 4.2.4 4.2.5 4.2.6

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Instrument and Plant Air .................................................................................... 125 Combustion Air .................................................................................................. 126

4.10

NITROGEN SYSTEM

126

4.11

FUEL GAS

127

4.11.1 4.11.2 4.11.3 4.11.4 4.11.5 4.11.6

Arch Burners ...................................................................................................... 127 Superheater Burners ......................................................................................... 128 Tunnel Burners .................................................................................................. 129 Auxiliary Boiler Burners ...................................................................................... 129 H-2102 Start-up Heater ..................................................................................... 130 Pilot Gas Fuel .................................................................................................... 130

4.12

DIESEL FUEL REQUIREMENTS (OSBL)

130

4.13

ELECTRICAL REQUIREMENTS

130

4.14

CATALYST SPECIFICATIONS

131

4.14.1 4.14.2 4.14.3 4.14.4 4.14.5 4.14.6

Catalyst Specification for Hydrogenation Reactor R-2160 ................................. 131 Catalyst Specification for Desulphurisers R-21 08 A&B ...................................... 131 Catalyst Specification for H.T. Shift Converter R-21 04 ...................................... 131 Catalyst Specification for L.T. Shift Converter R-2109 ....................................... 131 Catalyst Specification for Primary Reformer H-2101 .......................................... 132 Catalyst Specification for Secondary Reformer R-2103 ..................................... 132

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Catalyst Specification for Methanator R-21 06 .................................................... 132 Catalyst Specification for Synthesis Converter R-2105 ................................... ,.. 132 133

CO2 Removal System (aMDEA) ......................................................................... 133 aMDEA System Antifoam Agent ........................................................................ 133 HP Steam System Treatment Chemicals (Estimated) ........................................ 133 Ammonia for Start-up ......................................................................................... 133 Oxygen Scavenger (such as Nalco 72100) ....................................................... 134 Phosphate ......................................................................................................... 134 Morpholine (or alternative such as Nalco 72310) ............................................... 135 Sodium Hydroxide [NaOH] ................................................................................ 135

5

PREPARATION FOR INITIAL STARTUP

137

5.1

INTRODUCTION

137

5.2

PRELIMINARY STARTUP PROCEDURES

138

·5.2.1 5.2.2 5.2.3 5.2.4 5.2.5 5.2.6 5.2.7 5.2.8 5.2.9 5.2.10 5.2.11 5.2.12 5.2.13 5.2.14 5.2.15

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CHEMICAL SPECIFICATIONS 4.15.1 4.15.2 4.15.3 4.15.4 4.15.5 4.15.6 4.15.7 4.15.8

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Unit Check-out Procedure .................................................................................. 138 Line Flushing Procedure .................................................................................... 139 Steam Blowing Procedure ................................................................................. 142 Air Blowing Procedure ....................................................................................... 147 Fuel Gas System Blow-out Procedure .............................................................. 148 Refractory/Heater Dry-out Procedures ............................................................... 148 Chemical Cleaning Procedure ........................................................................... 148 Catalyst Loading Procedures ............................................................................. 149 Catalyst Dusting Procedure ............................................................................... 149 Conditioning of CO 2 Removal System ............................................................... 150 Leak Testing Procedure ..................................................................................... 150 Commissioning HP Steam System .................................................................... 154 Check Relief Valve Settings ............................................................................... 155 Commissioning of Water Jacketing Systems ..................................................... 156 Precommissioning of NH3 Storage & Loading Facilities ..................................... 156

6

INITIAL START-UP PROCEDURE

158

6.1

INTRODUCTION

158

6.2

Instrument calibration

160

6.3

Surge system checking

160

6.4

test run of the machines

161

6.5

PRELIMINARY START-UP PROCEDURES

161

6.6

INITIAL UNIT START-UP PROCEDURE

163

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6.6.1 6.6.2 6.6.3 6.6.4 6.6.5 6.6.6 6.6.7 6.6.8 6.6.9 6.6.10 6.6.11 6.6.12

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6.6.13 6.6.14 6.6.15 6.6.16 6.6.17 6.6.18 6.6.19 6.6.20 6.6.21 6.6.22 6.6.23 6.6.24

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Commission DeaeratorV-2101 .......................................................................... 163 Reformer Start Up Sequence Logic Description ................................................ 164 Start Auxiliary Boiler........................................................................................... 171 Start E-2140 Surface Condenser (Refer to the Vendor drawings for E-2150) .... 172 Nitrogen Heating of Hydrogenator, Desulphuriser, Primary & Secondary Reformers and HTS Converter catalysts ............................................................ 175 Steam Heating of Primary, Secondary and HTS Catalysts ................................ 176 Reduction of Primary, Secondary and HTS Catalysts ........................................ 177 Establish Circulation of CO2 Removal System ................................................... 178 LTS Catalyst Reduction using Nitrogen as Carrier Gas ..................................... 178 Produce Desulphurised Feed Gas ..................................................................... 180 Introduce Desulphurised Feed Gas to the Primary Reformer. ............................ 181 Introduce Air to the Secondary Reformer and Complete Reduction and Desulphurisation of Catalysts ............................................................................. 181 Commission CO 2 Removal System .................................................................... 182 Complete Desulphurisation of the HTS Converter Catalyst... ............................. 184 Commission Methanator [R-21 06] .................................................................... 185 LTS Catalyst Reduction using Natural Gas Feed as Carrier .............................. 187 Commission LTS Converter ............................................................................... 188 Commission Refrigeration System ..................................................................... 189 Start Synthesis Gas Compressor ....................................................................... 191 Pressure Test of Synthesis Gas Loop ................................................................ 192 Start Up Heater, H-2102, Sequence Logic Description ...................................... 194 Synthesis Converter Catalyst Reduction ............................................................ 196 Commission Purge Gas Scrubber [T-2103] ....................................................... 202 Purge and Chilldown of NH3 Storage & Loading Facilities (OSBL) ..................... 203

6.7

START-UP LINES AND REQUIREMENTS

205

7

NORMAL OPERATION

208

7.1

INTRODUCTION

208

7.2

START-UP WITH ACTIVATED CATALYSTS

208

7.2.1 7.2.2 7.2.3 7.2.4 7.2.5

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Hydrogenator and Desulphurisers [R-2160 & R-21 08A/B] ................................ 208 Primary and Secondary Reformers [H-2101 & R-2103] .................................... 208 HTand LT Shift Converters [R-2104 & R-2109] ................................................ 209 Methanator [R-2106] ....................... :.................................................................. 209 Ammonia Converter [R-2105] ........................................................................... 210

7.3

RESTART OF CO2 REMOVAL SYSTEM

211

7.4

OPERATION AT 60% DESIGN CONDITIONS

212

7.5

WARM [37.5°C] AMMONIA PRODUCTION

212

7.6

COLD [-35°C] AMMONIA PRODUCTION

213

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NORMAL OPERATION OF NH3 STORAGE & LOADING FACILITIES (OSBL)

214

Normal Operation of NH3 Storage Tank ............................................................. 214 Normal Operation of Road Tanker Loading Station ........................................... 215 Normal Operation of Bottle Loading Station ....................................................... 215 Transfer of Warm NH3 Feed to Urea Unit from Storage Tank ............................ 216 Transfer of Ammonia to the Ammonia Unit for start-up ...................................... 216

7.9

Trouble shooting

216

8

SHUTDOWN PROCEDURE

217

8.1

NORMAL SHUTDOWN PROCEDURES

217

8.1.1 8.1.2 8.1.3 8.1.4 8.1.5 8.1.6 8.1.7 8.1.8 8.1.9 8.1.10 8.1.11 8.1.12 8.1.13 8.1.14 8.1.15 8.1.16 8.1.17 8.1.18 8.1.19 8.1.20 8.1.21

c 8.2

Summary of Shutdown ....................................................................................... 217 Reduction of Flow Rates .................................................................................... 218 Reduce Synthesis Section Feed Rate ................................................................ 219 Purge Gas Ammonia Recovery System shutdown ............................................. 219 Stop Ammonia Conversion ................................................................................ 220 Stop the Synthesis Gas Compressor [C-2103] ................................................. 221 Stop and Pump-out Refrigeration System .......................................................... 221 Depressurise and Purge Ammonia Converter .................................................... 222 Stabilisation of Ammonia Synthesis Catalyst ..................................................... 222 Methanator Shutdown ........................................................................................ 223 Methanator Catalyst Oxidation ........................................................................... 223 Shutdown of LT Shift Converter ......................................................................... 224 Shutdown of C02 Removal System ................................................................... 224 Shutdown of Process Condensate Stripper ....................................................... 225 Shutdown of Reforming Section ........................................................................ 225 Stop Feed to Primary Reformer ......................................................................... 226 Shutdown Desulphuriser Section ....................................................................... 226 Steam Oxidising of the Reformer Catalyst.. ....................................................... 227 Secure the Reformer Section .................. ,....................., .................................... 228 Shut Down and Secure the Steam System ........................................................ 228 Completing the Shutdown .................................................................................. 229

SPECIAL SHUTDOWN PROCEDURES 8.2.1 8.2.2 8.2.3

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7.8.1 7.8.2 7.8.3 7.8.4 7.8.5

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Removal of Ammonia Synthesis Catalyst .......................................................... 229 Oxidation of HT Shift Catalyst... ......................................................................... 230 Oxidation of LT Shift Catalyst ............................................................................ 231

9

EMERGENCY SHUTDOWN PROCEDURES

232

9.1

INTRODUCTION

232

9.2

AMMONIA CONVERTER

232

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9.3

LOW TEMPERATURE SHIFT CONVERTER

233

9.4

METHANATOR

234

9.5

LOSS OF FEED GAS

235

9.6

LOSS OF STEAM TO CARBON RATIO

237

9.7

LOSS OF PROCESS AIR

237

9.8

LOSS OF BOILER FEEDWATER TO STEAM DRUM 0-2101

238

9.9

LOSS OF PROCESS STEAM

240

9.10

HIGH H.P. STEAM SUPERHEAT TEMPERATURES

240

9.11

LOSS OF FIRING ON PRIMARY REFORMER/AUXILIARY BOILER

241

9.12

LOSS OF STEAM PRESSURE

241

9.13

INSTRUMENT AIR FAILURE

242

9.14

ELECTRIC POWER FAILURE

243

9.15

COOLING WATER FAILURE

243

9.16

FAILURE OF WATER TREATMENT SYSTEM

244

9.17

FAILURE OF AMDEA CIRCULATION

244

9.18

FAILURE OF REFORMER INDUCED DRAFT FAN

245

9.19

Loss of C-2112 Arch Burner FD Fan

247

9.20

Loss of C-2111 Aux Boiler FD Fan

247

9.21

LOSS OF HYDROGEN TO THE DESULPHURISER SECTION

248

9.22

LOSS OF PURGE GAS OR EXCESS SYN GAS TO H-2101 FUEL GAS

249

9.23

GENERAL EMERGENCIES

249

9.24

PRECAUTIONS TO BE OBSERVED TO PROTECT STEAM GENERATING EQUIPMENT

250

9.25

GENERAL PRECAUTIONS

250

10

SAFETY

251

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10.1

INTRODUCTION

251

10.2

FIRE/EXPLOSION HAZARDS

251

10.2.1 10.2.2 10.2.3 10.3

Plant Signs ........................................................................................................ 252 Consumables (Permits, Testing materials etc.) .................................................. 252 Notifications ....................................................................................................... 252

SAFETY SYSTEMS

253

10.3.1 Pressure Relief Valves ....................................................................................... 253 10.3.2 Rupture Discs .................................................................................................... 253 10.3.3 Alarms & Trips ................................................................................................... 253 10.3.4 The Firewater System ........................................................................................ 254

(' 10.4

PERSONAL SAFETY ASPECTS

255

10.5

NOISE

255

10.6

VESSEL ENTRY

255

10.7· ENVIRONMENTAL ASPECTS

256

10.7.1 Category 1- Exposure of Personnel ................................................................... 256 10.7.2 Category II - Pollution of the Environmenl... ....................................................... 256 10.8

10.8.1 10.8.2 10.8.3 10.8.4 10.8.5 10.8.6 10.8.7 10.8.8 10.8.9 10.8.10

c 10.9

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HAZARDOUS CHEMICALS

257

Natural Gas ....................................................................................................... 257 Nitrogen ............................................................................................................. 258 Carbon Monoxide............................................................................................... 258 Carbon Dioxide .................................................................................................. 259 Hydrogen ........................................................................................................... 259 Ammonia ........................................................................................................... 259 Oxygen Scavenger(such as Nalco 72100) ......................................................... 261 Condensate Conditioner (Morpholine or altemative such as Nalco 72310) ........ 261 Steam & Condensate ......................................................................................... 262 Catalysts ............................................................................................................ 262

RELIEF VALVES

263

10.10 SUMMARY OF RUPTURE DISCS

265

10.11 ALARM AND TRIP SETTING

265

11

INSTRUMENTATION

266

11.1

INTRODUCTION

266

11.2

COMPLEX LOOP INSTRUMENTATION

266

11.2.1

D-2101 Steam Drum Level Control .................................................................... 266

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11.2.2 11.2.3 11.2.4

HP Steam to MP Steam Letdown System .......................................................... 267 Auxiliary Boiler Combustion Air & Fuel Gas ControL .......................................... 269 Auxiliary Boiler Light-off Sequence .................................................................... 270 Arch Burner Light-off Sequence ......................................................................... 273 11.2.5 273 11.2.6 Superheater Burner Light-off Sequence ............................................................ 275 11.2.7 Tunnel Burner Light off sequence ...................................................................... 277 11.2.8 Start-up Heater Light-off Sequence ................................................................... 278 11.2.9 CO2 Absorber (T-21 01) Level Control ................................................................ 280 11.2.10 Instrumentation of the Compressor End of the Synthesis Gas Compressor ...... 280

C_.·

11.3

INTERLOCKS & SHUTDOWN DEVICES 11.3.1 11.3.2 11.3.3 11.3.4 11.3.5 11.3.6 11.3.7 11.3.8 11.3.9 11.3.10 11.3.11 11.3.12 11.3.13 11.3.14 11.3.15 11.3.16 11.3.17

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Shutdown 21-ESD-1203/1201 Low Steam/Carbon Ratio & Low Natural Gas Feed Rate ................................................................................................................... 281 Shutdown 21-ESD-1202 Low Low Process Steam Flow .................................... 283 Shutdown 21-ESD-21 06 Methanator Emergency Vent ...................................... 284 Shutdown 21-ESO-2102 Feed Gas Compressor ............................................... 285 Shutdown 21-ESD-21 01 Air Compressor ........................................................... 286 Shutdown 21-ESD-2103 Synthesis Gas Compressor ........................................ 286 Shutdown 21-ESD-21 05 Refrigeration Compressor........................................... 287 Shutdown 21-ESD-2112 Auxiliary Boiler ............................................................ 288 Shutdown 21-ESD-2113 Superheater Burner .................................................... 289 Shutdown 21-ESD-2111 Arch Burner ................................................................ 291 Shutdown 21-ESD-2114 Tunnel Burner. ............................................................ 293 Shutdown 21-ESD-2116 Startup Heater ............................................................ 293 Shutdown 21-ESD-1031 Fuel Gas High Calorific Value .................................... 294 Shutdown 21-ESD-1223 Steam Drum Low LeveL ............................................. 294 Interlock 21-ESD-1106 Boiler Feed Water Low Flow ......................................... 295 Shutdown 21-ESD-1003 Raw Gas Separator Low Level ................................... 295 Shutdown 21-ESD-1 069 Process Condensate Stripper High Differential Pressure .......................................................................................................................... 296 Interlocks for Auto Start of Pumps by FCS ........................................................ 296

11.4

ANALYSERS

296

12

EQUIPMENT LIST

297

13

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. LABORATORY ANALYSIS

297

13.1

INTRODUCTION

297

13.2

GENERAL LIST OF TARGET VALUES FOR CONTROL TESTS FOR AMMONIA PLANT AND ASSCOIATED SAMPLE AND ANALYSER POINTS

298

13.3

GENERAL LIST OF CONTROL TESTS FOR AMMONIA PLANT

303

13.4

CALIBRATION ROUTINES

306

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14

DRAWINGS

307

14.1

PLOT PLAN

307

14.2

PFDS & MATERIAL BALANCE TABLES

307

14.3

STEAM AND COOLING WATER BALANCES

307

14.4

PIPING AND INSTRUMENTATION DIAGRAMS

308

14.5

HAZARDOUS AREA CLASSIFICATION

308

14.6

INSTRUMENT LOGIC DIAGRAMS

308

14.7

INSTRUMENT INDEX. ALARM & SHUTDOWN SCHEDULE

308

Appendix I

Correction of Orifice, Averaging Pitot Tube and Venturi Flowmeters

Appendix II

Lower Heating Value (LHV) Calculations

Appendix III

Density of Liquid Ammonia

,

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INTRODUCTION This manual has been compiled to assist those charged with the responsibility and supervision of the initial start-up and subsequent operation of the 1200 metric tons per day ammonia plant for KERMAN SHAH PETROCHEMICAL INDUSTRIES COMPANY, IRAN. It's primary objective is to provide flow descriptions and discussions of the processes involved and related operating principles, together with suggested guideline procedures for the initial commissioning, start-up, normal shutdown and emergency shutdown of the plant. It may also serve as a basis for the preparation by supervisory personnel, of detailed operating instructions, which should include instructions as issued by the equipment manufacturers. Under no circumstances should operations deviate from safety regulations and practices followed throughout the industry. Operating conditions and techniques will evolve from actual operating experience and it is not possible to antiCipate and present herein all potential circumstances that may confront the operator during the commissioning, start-up, normal and emergency shutdown of the unit. Consequently, this operating manual must be recognised as a guide and that conditions stipulated are not rigid standards, unless specifically noted as such.

c

Whilst the main objective of the unit is to produce Ammonia product by the synthesis of nitrogen and hydrogen, it is stressed that the plant will only operate efficiently and economically if the same attention is paid to the various sub-sections and systems such as the HP Steam Generation and the CO2 Removal systems as is paid to the operation of the synthesis converter. Special attention must also be paid to the quality requirements of the boiler feed water as detailed in various sections of this manual and in ODS-148 - "Steam Generator Operation" included in the General Procedures Manual. Numerical values given in this manual are design figures indicating the ranges within which actual values may vary during normal operation and may need to be changed as a result of experience gained in the plant. Under no circumstances should these figures be regarded as guaranteed performance figures. Any and all information pertinent to the aMDEA® proprietary C02 removal process included in this Operating Instructions Manual is disclosed in confidence for use in accordance with agreement made between KERMAN SHAH PETROCHEMICAL INDUSTRIES COMPANY and BASF AKTIENGESELLSCHAFT and should be treated accordingly.

-~5'-;;':·.;>·

c

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Operating Manual

M.w. Kellogg Limited

continuation sheet JOB NO.

2

5777

SPEC. TYPE: CLASS DOC NO.

PROJ-PM-008

PAGE:

130F 312

REVISION:

5

BASIS OF DESIGN Where Block Valves are fitted on the inlet and discharge lines of unspared Relief Valves or, in the case of Relief Valves discharging to atmosphere to the inlet lines only, these valves must be locked open during plant operation.

It is the responsibility of the Plant Management to ensure that an administration system is in place, which will ensure that this condition is strictly observed

c 2.1

DUTY OF UNIT The Ammonia Unit is designed to produce 1200 tid of Ammonia and is based on the low energy natural gas reforming process licensed by the M.W.Kellogg Company. 1132 tid of the Ammonia product is sent as feed at approx. 37.5°C to the Urea Unit with the balance of 68 tid being sent, at _35°C, to the offsite Ammonia storage tank. Alternatively the Ammonia unit can produce 1200tld of cold product when the Urea Unit is not in operation. The Ammonia Unit is capable of producing 40% of design capacity for short periods of time (less than 7 days). To achieve this, some equipment will need to operate on kick-back and it will be necessary to burn some of the syngas as fuel or vent it. In addition, a high level of experienced supervision must be in attendance throughout this mode of operation. The Plant is designed also to produce 1494 tid of carbon dioxide, most of which is exported for use as a feed to the Urea Unit. The composition and conditions of the natural gas feedstock is given in Section 2.2.

c 2.2

FEED CHARACTERISTICS The natural gas specification is as follows: Composition

volume %

CH 4

96.85 1.23 0.216 0.085 0.054 0.042 0.041 0.15 0.242 1.09

C2Ha

c

C3 H8 n-C4H10 i-C4H10 n-C5H12 i-C5H12 C6 and heavier CO2

N2

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Operating Manual

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continuation sheet JOB NO.

5777

SPEC. TYPE: CLASS DOC NO.

PROJ-PM-008

Sulphur as organic Sulphur as inorganic Water MW Calorific Value

PAGE:

14 OF 312

REVISION:

5

20 ppmv 20 ppmv 150 ppmv 16.684 11,615 kcal/kg 8645.7 kcal/Nm3

Battery limit pressure, bara Design Winter (minimum) Maximum c~

17.0 10.0 70.0

Battery limit temperature, DC Minimum Normal I design Maximum 2.3

PRODUCT SPECIFICATIONS

2.3.1

Ammonia Product

20 Ambient 45

The product may be warm liquid to an adjacent urea plant, or cold liquid to storage, in any combination. The guarantee case is 1132 MTPD warm product and 68 MTPD cold product.

c 2.3.2

c

Ammonia content

min. 99.9 wt-%

Water content

max. 0.1 wt-%

Oil content

max. 5 ppmw

Warm product battery limit conditions

37 DC (max) at 25.5 bara

Cold product battery limit conditions

-35 DC

at

4.4 bara

Carbon Dioxide Product Carbon dioxide content

min. 98.9 vol-O/O, dry basis

H2/N2/CH4/Ar

max. 1.1 vol-O/O, dry basis

H2 content

max. 0.9 vol 0/0, dry basis

Water

Saturated at BL conditions

Temperature at B. L

43 DC

Pressure at B. L.

1.8 bara

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c

Operating Manual continuation sheet

JOB NO.

2.4

5777

SPEC. TYPE: CLASS DOC NO.

PROJ-PM-008

PAGE:

150F312

REVISION:

5

MATERIAL AND ENERGY BALANCES

The Material and Energy Balances are indicated on the following Process Flow Diagrams, steam and cooling water balances:

c

Air/Gas Compression <S Reduction Circuits Desulphurisation, Reforming & Shift Conversion CO2 Removal Methanation and Ammonia Synthesis Refrigeration (warm product case) Refrigeration (Cold product case) Ammonia Storage System Natural Gas Feed & Fuel Gas Steam Balance - Warm Product Case Steam Balance - Cold Product Case Steam Balance - C2101 Start-up Case Steam Balance - C2101 Restart Case Steam Balance - C2103 Start-up Case Steam Balance - C2103 Restart Case Steam Balance-Emergency Shut down Cooling Water Balance - Warm Product Case

DWG-060-D004 DWG-060-D005 DWG-060-D006 DWG-060-D007 DWG-060-D008 DWG-060-D009 DWG-060-D102 DWG-060-101 DWG-060-B001 DWG-060-B002 DWG-060-B003 DWG-060-B004 DWG-060-B005 DWG-060-B006 DWG"060-B007 DWG-060-B008

c

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continuation sheet

C JOB NO.

2.5

C~

c

c

5777

SPEC. TYPE: CLASS DOC NO.

PROJ-PM-008

PAGE:

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REVISION:

5

BATTERY LIMIT CONDITIONS [OPERATING TEMP. & PRESSURE]

LINE NO.

LINE SIZE

LINE SPEC

P&IONO.

FLOWING MEDIUM

FROM

TO

FLOW RATE KG/H

S.G. B.L. PRES~ TEMP OR @GRAOE 'C M.W. BARA

Al000

42"

lPl

62-0101

AIR

ATMOS.

C-2101

67890

28.6

39

0.88

A1401

6"

lPl

62-0101

AIR

C-2101

0·4101A

1980

28.6

39

2.03

AM1064

10"

lR1B

62-0118

NH3

TK-5101A1B

C-2105

1200

17.0

-11

0.9*

AM1023

6"

3Pl

62-0119

NH3

P-2113A1B

P-4104A1B

47167

0.585

37

25.5**

AM1034

4"

3R1B

62-0120

NH3

P-2124A1B/C

TK-5101A1B

51239

0.685

-35

4.4

AM1069

3"

lR1B

62-0120

NH3

0-2107

TK-4108

-

-

-

-

AM1098

8"

lPl

62-0117

NH3

E-4153

0-2122

10389

17.0

-3

3.9

B01025

3"

lSl

64·0101

CONDENSATE

0-2156

V-6201

1518

0.9

148

4.5

COl 004

20"

lPl

62-0122

CO2

T-2102

0-4101A

63618

42.5

43

1.8

CWR10l0

14"

W2

64-0109

COOLINGWAT.

HEADER

OSBL

-

0.992

42

3.4

CWR1013

24"

W2

64-0109

COOLING WAT.

HEADER

OSBL

-

0.992

42

3.4

CWR1016

24"

W2

64-0109

COOLING WAT.

E-4133

HEADER

41.8

3.4**

CWR1017

10"

Wl

64-0109

COOLING WAT.

E-4130

HEADER

216000

0.990

45

3.4**

CWR1018

12"

Wl

64-0109

COOLING WAT.

E-4132

HEADER

224000

0.990

45

3.4**

CWR1019

14"

Wl

64-0109

COOLING WAT.

E·4131

HEADER

192000

0.990

45

3.4**

CWR1024

4"

Wl

64·0109

COOLING WAT.

C-4102

HEADER

0.992

42

3.4

CWRll03

42"

W2

64-0109

COOLING WAT.

HEADER

OSBL

-

0.992

42

3.4

0.992

42

3.4

32

4.8

32

4.8

34.4

4.8

3281000 0.992

CWR1225

4"

Wl

64-0109

COOLINGWAT.

E-4135

HEADER

-

CWS10l0

14"

W2

64-0109

COOLING WAT.

OSBL

HEADER

-

0.995

CWS1012

42"

W2

64-0109

COOLING WAT.

OSBL

HEADER

-

0.995

CWS1016

24"

W2

64-0109

COOLING WAT.

HEADER

E·4133

3281000 0.994

CWS1017

10"

Wl

64-0109

COOLING WAT.

HEADER

E-4130

216000

0.995

32

4.8

CWS1018

12"

Wl

64-0109

COOLING WAT.

HEADER

E-4132

224000

0.995

32

4.8

CWS1019

14"

Wl

64-0109

COOLING WAT.

HEADER

E·4131

192000

0.995

32

4.8

CWS1024

4"

Wl

64-0109

COOLING WAT.

HEADER

C-4102

-

0.994

34.4

4.8

CWSl225

4"

Wl

64·0109

COOLING WAT.

HEADER

E-4135

-

0.995

32

4.8

OM1000

8"

W1J

62-0124

OEMIN. WATER

OFFSITES

E-21 06

245892

0.989

47

6.0

OR1061

4"

280X

64-0101

CONDENSATE

0-2156

A-9304

1518

0.919

148

4.5

OR1070

12"

280X

64-0106

CONDENSATE

V-21 01

A-9304

-

0.935

130

2.7

ORl175

2"

lP1J

62-0130

CONDENSATE

0-2161

V-6202

8100

0.972

76

0.88

OW1000

2"

W2W

63-0105

DRINK. WATER

OFFSITES

HEADER

5000

1

Amb

4

IA1000

3"

Zl

63·0105

INSTR.AIR

OFFSITES

HEADER

514

28.8

37

8

LPS100l

3"

lSl

64-0104

LPSTEAM

LP HEADER

J·4107AlB/C/O

850

18.0

227

4.5

LPS1200

3"

lS1

64-0104

LPSTEAM

OFFSITES

LP HEADER

-

-

-

-

LPS1305

20"

lS1

64-0104

LPSTEAM

LP HEADER

C-4102 IT)

17956

18.0

227

4.5

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M.W. Kellogg Limited

continuation sheet

C JOB NO.

·' C j

5777

SPEC. TYPE: CLASS DOC NO.

17 OF 312

REVISION:

5 S.G. B.L. PRESS TEMP OR @GRAOE ·C M.W. BARA

LINE NO.

LINE SIZE

LINE SPEC

P&IONO.

FLOWING MEDIUM

FROM

TO

FLOW RATE KG/H

M01019

1.5"

1P1J

62·0122

SOUR WATER

T-21 02

OFFSITES

·

·

·

·

MPS1200

10"

6S1

64·0103

MPSTEAM

UTILITY PLANT

MPHEAOER

50093

18.0

400

42.8

MPS1302

12"

6S1

64·0103

MPSTEAM

MPHEADER

C-4102T

89031

18.0

387

41.8

MPS1303

3"

6S1

64-0103

MPSTEAM

MPHEAOER

P-4130A (T)

387

41.8

N1000

3"

1P1

63·0105

NITROGEN

OFFSITES

HEADER

N1090

%"

1P1

63·0105

NITROGEN

HEADER

C-4102

· · ·

18.0

· ·

· ·

· ·

NG1000

12"

6P1

62·0102

NATURAL GAS

OFFSITES

0·2144

39114

16.7

40

17

NG1044

3"

6P1

62·0104

NATURAL GAS

C-2102

N·7101A1B/C

·

16.7

142

43.5

PA1001

2"

3P1

62·0101

PLANT AIR

C-2101

OFFSITES

3998

28.8

39

14.3

PA1002

3"

A1

63·0105

PLANT AIR

OFFSITES

HEADER

·

·

·

·

PC1012

4"

1S1

62·0121

STRIP. CONO.

E·2175

OFFSITES

52747

0.989

49

4.1

PC1034

2"

1P1J

62·0130

CONDENSATE

0-4130

1451

0.994

39

1.7

SC1003

6"

1S1

64·0105

CONDENSATE

P·2112A1B

0·2161 POL.lDEMIN. U

132788

0.989

51

4.0

SC1045

1.5"

1S1

64·0105

CONDENSATE

P·2112A1B

E-4133

6"

1S1

63·0106

CONDENSATE

HEADER

· ·

SC4005

6"

1S1

64-0105

CONDENSATE

P-4103A1B

0·6503 POL.lOEMIN. U

· ·

·

SC1100

· · 44172

0.989

51

4.0

SW1000

3"

W2

63·0105

SERV.WATER

OFFSITES

HEADER

·

·

·

·

V1046

16"

1P1

63·0104

NH3

HEADER

FLARE TIP

127288

17

100

2.0

V1050

20"

1P1

63·0104

SYNGAS

HEADER

FLARE TIP

195432

15.7

370

2.0

* Cold Product Case ** Warm Product Case

C 2.6

DESIGN FEATURES

2.6.1

Feed Gas Compression and Purification BIL Delivery Pressure (minimum) BIL Delivery Temperature Feed Gas Compressor Seal Loss Feed Gas Compressor Discharge Desulphurisation: ColMo Inlet Temperature ZnO Inlet Temperature Heat Loss Inlet H2

C

PROJ-PM-OOB

PAGE:

10.0 20-40

bara

°c

To Fuel

44.00

bara

371 371 11.0 2.B

°c °c °c

P:15777kermanshahISharedl· After OVOsIManualsIPROJ·PM·008·R5 ·NH3 Operating Manual.doc

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·

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Operating Manual

M.W. Kellogg Limited

continuation sheet

C JOB NO.

2.6.2

5777

SPEC. TYPE: CLASS DOC NO.

PROJ-PM-008

j

2.6.4

C

5

40 49 39.00 7.0

°c % bara

°c

3.2 605 36.5 17.0 17.0 91 10 616 605

°c bara °c °c % %

°c °c

Shift Conversion HTS Inlet Temperature CO Exit LTS (dry basis)

2.6.5

REVISION:

Reforming Section Steam/Carbon Ratio to Primary Reformer Crossover Temperature Primary Reformer A.P., Tube Exit Riser Temperature Rise Transfer Line Loss Primary Reformer Efficiency (LHV basis) Steam to Air Coil (Molar basis) Air Coil Exit Temperature Sec. Reformer Air Inlet Temperature

C'

18 OF 312

Air Compression Section Inlet Temperature Relative Humidity Discharge Pressure Air Cooling Approach

2.6.3

PAGE:

371 0.3

°c

1000

ppmv % % % % % %

mol%

CO 2 Removal CO 2 Leakage (dry basis) Lean Soln. Pump Efficiency Semi-lean Soln. Pump Efficiency Hydraulic Turbine Efficiency Lean Soln. Pump Capacity CO 2 Recovery Synthesis Losses to CO2 Removal

72 72 75 115 Max 0.3

c P:15777kermanshahISharedl· After DVDsIManualsIPROJ·PM·OO8-R5 ·NH3 Operating Manual.doc

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Operating Manual

M.W. Kellogg Limited

continuation sheet JOB NO.

5777

SPEC. TYPE: CLASS DOC NO.

PROJ-PM-008

PAGE:

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REVISION:

4

2.6.6 Methanation Methanator Inlet Temperature CO + CO2 Leakage (dry basis) Methanator Heat Loss (wet gas basis) H:JN2 Exit Methanator Methane Leakage (dry basis)

316 5.0 10.0 2.99 0.9

DC ppmv max. kcal/kmol mol%

2.6.7 Synthesis Gas Compressor

c

Suction Pressure Suction Temperature First Case - Stages/Nozzles Second Case-Stages/Nozzles

30.4 39.0 1/2 2/3

bara

DC

2.6.8 Synthesis Loop Section Pressure Exit Last Bed Inerts at Converter Inlet Exit Ammonia Recycle/Effluent Approach (E-2120) Loop Pressure Drop (A.P.) Primary Separator Temperature

139.3 8.0 15.75 10.0 7.55 -17.8

bara mol% mol%

DC

bara

DC

2.6.9 Refrigeration Section

C

Refrigeration Levels Utilised Exchanger (E-2120) Chiller Temperatures: 1st. Stage 2nd. Stage 3rd. Stage 4th. Stage

4

-35.0 -17.8 -2.2 16.7

DC DC DC DC

Warm Product Temperature Cold Product Temperature Warm Product Cold Product Alternate Cold Product Operation

37.5 -35 1132 68 1200

DC DC Vd Vd Vd

125.1

bara

2.6.10 Steam System HP Steam Drum Pressure

C.

p:15mkermanshah\Commisioning\Kermanshah NH3 op Man Final7.doc

Operating Manual

+M.W. Kellogg Limited

c

continuation sheet . JOB NO.

5777

SPEC. TYPE: CLASS DOC NO.

PROJ-PM-008

HP Steam Pressure to Turbines Superheat HP Steam Temp. to Turbines MP Export Steam Surface Condenser Pressure

120.4 505 45030 97

PAGE:

20 OF 312

REVISION:

4

bara

°c kg/h(warm case) mm Hg (abs)

2.6.11 Utilities CW Supply Temperature .CW Retum Temperature Rise (Overall) Exchanger CW Max. Outlet Temperature

c

32 10 50

°c °c °c

2.6.12 Ambient Conditions for design Barometric Pressure Min 851.6 Normal 877.6 Max. 881.2

mbar mbar mbar

Maximum Temperature Design for air coolers, compressors and fans Minimum ambient temperature Design Minimum temperature

44°C 40°C -27°C -25°C

.2.6.12 Catalyst Volumes Hydrogenation Reactor ZnO Desulphurisers Primary Reformer Secondary Reformer High Temperature shift Low Temperature Shift Methanator Ammonia Synthesis Converter

c 2.7

12.2 2x35.8 24.6 25.8 48.7 59.2 21.0 68.4

m3 m3 m3 m3 m3 m3 m3 m3

PROCESS FLOW DESCRIPTION

2.7.1 Introduction The ensuing discussion will describe in detail the main process flow through the unit together with all auxiliary systems that are pertinent to the process such as steam, boiler feed water, etc. The Operating Conditions and Process Variables will be discussed in detail in Section 3.0 of this manual. For the purpose of this description the process is divided into the following sections

C.

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Operating Manual continuation sheet

JOB NO.

5777

SPEC. TYPE: CLASS DOC NO.

PROJ-PM-008

PAGE:

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REVISION:

4

and the description of the process flows through the unit will be more readily understood if the Process Piping, Auxiliary and Utility Instrumentation Flow Sheets are referred to during study of this section.

• • • • •

Raw Synthesis Gas Preparation Synthesis Gas Purification. Purified Synthesis Gas Compression and Ammonia Synthesis. Ammonia Refrigeration System. Process Condensate Stripper and other facilities The process is illustrated in Process Flow Diagrams 060-0004 to 060-0008 and together with the Utility Flow Diagrams 061-B001 to 061-B008. These diagrams represent the operation of the plant using natural gas as feedstock to produce 1132 tid of warm product (37.5°C) plus 68 tid of cold product (-35°C). Process flow diagram 060-0009 illustrates the alternate refrigeration operation when the plant is producing 1200 tid of cold product. The following process description relates to the mode of operation of the plant for the feed gas composition shown on these process flow diagrams.

c

2.7.2 Raw Synthesis Gas Preparation The raw synthesis gas is produced from natural gas in four major steps

c 2.7.2.1

•

Compression, preheating and desulphurisation of the natural gas feed.

•

Steam reforming of the hydrocarbons in the feed to an intermediate level in the Primary Reformer furnace.

•

Autothermal reforming of the steam reformer effluent in the Secondary Reformer, where the Methane is reduced to a very low level while introducing the process air to provide Nitrogen in the proper ratio required for Ammonia synthesis.

•

Conversion of carbon monoxide and steam in the reformed gas to carbon dioxide and hydrogen in a shift converter. Supply & Compression of Natural Gas Feed Natural Gas is used for feedstock and fuel. Natural Gas Feed from the National Iranian Gas Company (NIGC) Metering Station enters the Offsites where a stearn heated Feed Gas Heater (E-1 001) is provided to prevent hydrate formation in the NH3 Unit feed gas/fuel gas and Offsites fuel gas systems. Three control valves located downstream of the heater E-1001 control the pressure of the Natural Gas supply to the Ammonia Unit and to the Offsites fuel gas system. After entering the NH3 Unit, the gas is passed through the Feed Gas Knockout Drum 0-2144, where entrained liquids and solids are removed. After the Knockout Drum,

c"

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continuation sheet JOB NO.

5777

SPEC. TYPE: CLASS DOC NO.

PROJ-PM-008

PAGE:

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REVISION:

4

feed and fuel streams are separated. The fuel stream provides most of the heating requirements in the Ammonia Plant reforming furnace and auxiliary boiler. The Natural Gas used as feed is compressed to 44 bara in a single case centrifugal Feed Gas Compressor, C-21 02. To protect the compressor over a wide range of operating conditions, it is provided with a Kickback Cooler, E-2133, which allows all or part of the discharge gas to be recycled back to the suction. When the pressure at the Ammonia Plant battery limit is above 44 bara a bypass is provided around C-21 02 to enable it to be shut down. To assist in this operation, Nat Gas Feed Preheater E-2171 is provided.

c

2.7.2.2

Preheating of Natural Gas Feed A small part of the purified hydrogen-rich synthesis gas is recycled to the process downstream of C-21 02, to give a hydrogen concentration of approx. 3% in the feed gas. The compressed feed gas is then heated to 371°C in the convection section of the primary reformer H-21 01, prior to sulphur removal by hydrogenation and desulphurisation.

2.7.2.3

Hydrogenation/Desulphurisation The heated feed gas then enters the Hydrogenation Reactor, R-2160, where the . organic sulphur compounds are hydrogenated to H2S over a bed of CobalV Molybdenum (Co-Mo) catalyst. Immediately downstream of the Hydrogenator are the Zinc Oxide (ZnO) Desulphurisers, R-2108A & B. The Hydrogen Sulphide in the gas reacts with and is retained by the Zinc Oxide producing an effluent stream containing less than 0.1 ppm H2S by volume. Normally the Desulphurisers operate in series, but provision is made in the installation to allow single reactor operation during catalyst change-out while the plant remains in operation. Based upon the content of sulphur compounds in the natural gas the Zinc Oxide in each desulphuriser is designed to be replaced every year.

c

The desulphurised feed is mixed with medium pressure (41.2 bara, 335°C) stearn added in a ratio of 3.2 moles of steam per mole of organic carbon. The feed Gas! steam mixture is further heated to 605°C in the convection section of the Primary Reformer, H-21 01, using heat recovered from the furnace flue gas. 2.7.2.4

Primary Reformer The purpose of the Primary Reformer is to begin the process of reforming the feed gas into the hydrogen needed for ammonia synthesis. The hot steam/gas mixture passes down through the nickel catalyst in the reformer catalyst tubes suspended in the radiant section of the furnace. Heat for the endothermic reforming reaction is supplied by fuel gas burners located between the rows of tubes. The down firing furnace burners develop a reformed gas temperature near 812°C at the outlet of the catalyst tubes. The outlet pressure of the catalyst tubes is 36.5 bara.

C

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Operating Manual

M.w. Kellogg Limited

continuation sheet 5777

JOB NO.

SPEC. TYPE: CLASS DOC NO.

PROJ-PM-008

PAGE:

23 OF 312

REVISION:

4

The reforming furnace incorporates the use of internal manifolding at the outlet of the catalyst section for heat conservation of the reformed gas. The reformed gas continues to pick up heat in the risers while exiting the Radiant section. This raises the gas temperature at the Primary Reformer exit to approximately 829°C. The reforming furnace is designed to maximise its thermal efficiency by recovering heat from the flue gases in the convection section. Flue gases consist of combustion products from the radiant section of the Reformer. The recovered heat is used for the following services: • • • • • •

C'

Steam / Gas mixed feed preheat Process air / steam preheating (two coils) Steam superheating (two coils) Natural gas feed 'preheat for desulphurisation High pressure BFW preheating Fuel Gas preheating

Heat is recovered from the Ammonia process by heating boiler feed water, generating high pressure steam, superheating high pressure steam and preheating the feed and fuel gas. The convection section and auxiliary boiler together with the Secondary Reformer Waste Heat Boiler, E-21 01, HP Steam Superheater E-21 02 , High Temperature Shift Effluent Waste Heat Boiler, E-21 03 , and the Ammonia Converter Effluent/Steam Generator, E-2123, will maintain the plant in steam balance. Normally, medium pressure steam will be exported to the Urea plant.

2.7.2.5

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Secondary Reformer

The process air supply for the Secondary Reformer is provided by a two case, steam turbine driven Air Compressor, C-21 01. The air is preheated to 616°C in order to transfer the maximum amount of the overall reforming conversion load to the Secondary Reformer. A small quantity of medium pressure steam is continuously .added to the preheat coil inlet to ensure a forward flow in the event of emergency shutdown of the Air Compressor. Air for the Urea Unit Hydrogen Converter and Passivation, as well as instrument and plant air for the Complex is taken at the required pressure levels from between compression stages of C-2101. A backup system is provided in the Utilities section of the Complex to provide compressed air when the Ammonia Unit is not in operation. The partially reformed gas from the Primary Reformer is mixed with the hot process air in the Secondary Reformer in stoichiometric proportions as required for the synthesis reaction. The combustion product is then directed downward through a bed of nickel catalyst. The gas temperature leaving the Secondary Reformer is approximately 994°C. The high temperature Secondary Reformer effluent is used to generate high pressure steam in Secondary Reformer Waste Heat Boiler, E-21 01, and to add superheat to

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the steam in HP Steam Superheater E-21 02. It exits E-21 02 at 371 the temperature required for the high temperature shift conversion. This Superheater provides only part of the steam superheat requirements, with the remaining portion fulfilled by a coil in the Primary Reformer convection section. A process gas bypass arrangement is provided between these exchangers to control the division of boiling and superheating duty according to the various operating demands of the steam system. 2.7.2.6

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Shift Converters Downstream of the E-21 02 are the High Temperature and Low Temperature Shift Converters, R-21 04 & R-21 09. The function of these Reactors is to convert the carbon monoxide in the gas stream to carbon dioxide for subsequent removal in the aMDEA® system. . In the shift conversion step, carbon monoxide reacts with steam to form equivalent amounts of hydrogen and carbon dioxide. The shift reaction is reversible and exothermic. High temperatures favour the reaction rate while low temperatures favour maximal conversion (equilibrium). For optimum performance, two stages of shift conversion are provided with the High Temperature Shift Effluent Waste Heat Boiler, E-21 03, located in between to moderate the gas temperatures and efficiently recover waste heat in the form of high pressure steam.

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The two single bed shift reactors are stacked vertically to save plot space and cost. Flow of the process gas is downward through the catalyst beds. Each shift reactor utilises a different catalyst material and each catalyst has its own distinct advantages. In the high temperature shift (HTS), a relatively cheap and more durable iron oxide catalyst produces the bulk of the shift conversion. A more favourable equilibrium is attained with the low temperature shift (LTS) copper catalyst, but it is more expensive and susceptible to poisoning from process impurities. The low CO leakage (0.3 dry mol%) obtained from this combination results in a reduction in plant feed requirements due to the more complete conversion of CO and steam to hydrogen and CO2 , It will be necessary to convert the oxidisedform of the LT Shift catalyst to the reduced form at start-up with hydrogen using either nitrogen or natural gas as a carrier gas. To assist in this operation, Start-up Cooler E-2173 has been provided. 2.7.3 Synthesis Gas Purification Raw synthesis gas from the LTS converter is processed to remove carbon dioxide and carbon monoxide yielding a highly pure hydrogen - nitrogen rich synthesis gas. Bulk removal of CO2 is accomplished by an aMDEA® system. This is a proprietary low energy process licensed by BASF. Final removal of residual carbon dioxide and carbon monoxide is accomplished in the Methanator by converting the carbon oxides to methane and water with hydrogen. The hot "shifted" gases from the bottom of the low temperature shift converter are cooled in the L.T. shift effluent train before entering the CO2 absorber T-2101. L.T.

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shift effluent gas is first cooled against boiler feed water in E-2131 and then provides reboil heat to the aMDEA@ system G02 Stripper T-21 02 via reboiler E-21 05 with final cooling against demineralised water in E-21 06 before entering Raw Gas Separator D2102 where condensed water is knocked out. Temperature control of the L.T. shift effluent gas and heat input to the aMDEA@ solution is effected by E-2131 boiler feed water bypass. An LP steam heated reboiler E-2111 provides further heat input to CO2 stripper T-21 02 . 2.7.3.1

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D-2102 - Raw Gas Separator Water vapour present in the process gas stream condensed in E-21 05 and E-21 06 is disengaged in the Raw Gas Separator D-21 02. The condensed process steam is withdrawn from the bottom of the separator and routed by pumps P-2121 AlB via exchanger E-2188 to the Process Condensate Stripper (T-2150) or when off specification or during short term upsets of D-21 02,to drain. The raw synthesis gas passes overhead from the separator D-21 02 and is directed to the CO2 absorber for the initial synthesis gas purification step. Pressure protection for the D-21 02 and upstream equipment is provided by relief valve PRV-D2102 on the Raw Gas Separator vapour outlet. A vent in the form of a manual by-pass of relief valve PRV-D2102 is provided on the vapour outlet from D-21 02 for start-up and emergency venting of process gas upstream of the CO2 Absorber, T -2101. A line from the vapour outlet of D-21 02 routes a nitrogen/hydrogen gas mixture to the Low Temperature Shift Converter inlet for catalyst reduction during start-up (Nitrogen circulation reduction step). A takeoff from the same line also supplies hydrogen at start-up to the suction of Feed Gas Compressor, C-21 02.

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2.7.3.2

T-2101 - C02 Absorber The raw synthesis gas with most of the water removed flows through an internal distributor into the bottom section of the CO2 Absorber column and then upward through two packed beds. Regenerated (C02 free) aMDEA@ solution is introduced through an internal distributor at the top of the column and flows downward through the beds. The downward flowing solution is contacted with the up-flowing gas in the bed packing and selectively absorbs the CO2 from the gas, the other components of the gas stream having very low solubility in the solution. The CO2 loaded (rich) solution collects in the bottom section of the column and exits under level control. A further bed of packing in the base of the column minimises gas entrainment in the solution. The rich solution at a pressure of about 32.5 bara is returned to the top of stripping column T -2102, which operates at a pressure of about 1.8 bara. Power is recovered from the flowing solution by passing it through a hydraulic turbine, which assists the P-21 07A Lean solution pump drive motor. A seal loop on the gas inlet line prevents backflow of solution in upset conditions.

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D-2103 - CO 2 Absorber Overhead KO Drum The aMDEA® solution absorbs essentially all of the CO2 that passes through the absorber. To knock out the bulk of any entrained solution the absorber tower also has a demisting pad in the top through which the gas passes before leaving the tower. The effluent gas from the absorber overhead flows to the CO2 Absorber Knockout Drum D-21 03 for final removal of any entrained solution. This solution is removed from the system manually to the sump system. Process gas leaving the top of D-21 03 then passes through the shell side of E-2114 (Methanator Feed/Effluent Exchanger) before flowing to the Methanator (R-21 06) top inlet.

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Piping is also provided from the outlet of D-21 03 to route process gas to: (i) Primary Reformer H-21 01 as excess synthesis gas to supplement the fuel gas (PG1 035-6");

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2;7.3.4

(ii)

to the suction of C-21 02 as start-up hydrogen (PG1038-3"), and

(iii)

to R-21 09 for LTS catalyst reduction during start-up(PG1019-1.5").

T -2102 - CO2 Stripper Regeneration of the Circulating solution by removing the absorbed carbon dioxide is accomplished by steam stripping in the CO2 Stripper T -2102 before the solution is recycled to the Absorber for reuse.

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The rich solution from the absorber is introduced into the LP flash section of Stripper T -2102 and flows downward through a bed of packing. Steam generated in the stripper section of the column passes upward through the bed and strips CO2 from the rich solution. The semi-lean solution is pumped from the base of the LP flash section by pumps P2108 AlB through exchanger E-2112A1B and returned to the top of the stripping section at boiling point. The solution passes downwards through the beds of packing in the stripping section and meets an upward flow of stripping steam generated by process gas reboiler E2105 and LP steam reboiler E-2111. The now fully regenerated solution at about 124°C exits the column through Lean/Semi Lean exchanger E-2112A1B where it is cooled and routed to the suction of pumps P-2107A1B. Pumps P-2107A1B return the lean solution to the top of the absorber column via exchangers E-21 09 and E2110 where it is further cooled to about 50°C. A slipstream is taken off the flow through filter F-21 04 to prevent a build up of particulate matter in the system. The CO2 released from the rich solution and stripping steam exit the top of the

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stripping column through the contact cooler section and demister. This section is supplied with cooled quench water by pumps P-2116 AlB via exchanger E-21 07 and has a demineralised water make up line DM1102-1". The contact cooler condenses the stripping steam and cools the CO2 to about 43°C before the major portion is exported from the plant for use in the production of Urea via CO2 Compressor C-41 02 located within the Ammonia Unit, with the balance being vented to atmosphere. The contact cooler also serves to remove any entrained aMDEA® solution from the CO2 before it is supplied to the Urea plant. Vacuum breakers SP-009 AlBIC I D&E and rupture disc SP-008 are also provided on the stripper overhead line.

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2.7.3.5

Auxiliary Equipment Auxiliary equipment for the CO2 removal system consists of a main aMDEA® Solution Storage Tank (TK-2114) an aMDEA® Solution Sump (TK-2115) to collect solution from various points in the system and a Collection Sump A-21 01 for collecting accidental spillage of solution, together with contaminated rainwater and wash water from bunded areas in the system. TK-2i 14 is used as the main storage tank for aMDEA® solution prior to start-up and if required to drain down the removal system during shutdowns. aMDEA® transfer Pump, P-2111 is used to transfer the contents to the CO2 removal system with P-21 07AlB being used to transfer from the removal system back to the tank. It should be noted that it is extremely important to ensure that the solution is regenerated and the Absorber depressurised before solution is transferred to TK-2114. Before TK-2114 is opened in any way it must be purged using the nitrogen connection at the sample point until suitable tests i.e. Drager, indicate that any hydrogen has been purged. If the tank is to be entered, then all the necessary precautions described in the Safety Manual for vessel entry must be strictly observed.

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Sump Pump P-2115 is used to circulate the recovered solution through the Sump Filter F-2115 or to transfer the recovered solution to TK-2114 either directly or via Sump Filter F-2115. There is also an aMDEA® Antifoam Injection System (V-21 09) for charging anti-foam inhibitor agent to the following two locations in the CO2 Removal system 1) P-21 07A(H) discharge line (Rich solution to Stripper). 2) P-21 07 AlB suction line. 2.7.3.6

C-4102 - CO 2 Compressor The CO2 product from the top of T -2102 CO2 Stripper together with a small amount of air from the 2nd stage suction of C-21 01, Air Compressor, is routed to D-41 01

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CO2 Compressor KO Drum. C-41 02, CO2 Compressor is a turbine driven two case/4 stage compressor on which the 1st, 2nd and 3rd stages are cooled in intercoolers and any entrained liquid condensed in the intercoolers is automatically level controlled to D-2161 Process Condensate Drum from separators provided downstream of each intercooler. A Hydrogen Converter, R-41 02 is located in the 2nd stage discharge piping of C-41 02 to remove any hydrogen present in the CO2 to less than 10 ppm(vol) by catalytic combustion. A portion of the air injected upstream of 0-4101 is used for this catalytic combustion.

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2.7.3.7

Methanation The synthesis gas from 0-2103 is heated to 316°C in the Methanator Feed/Effluent Exchanger E-2114. This exchanger recovers the heat in the Methanator effluent by heat exchange against the feed gas. A gas by-pass is provided around the exchanger to permit adequate control of the feed temperature. A separate highpressure steam heated Methanator Feed Heater E-2172 is provided for initial heating of the gas to normal operating temperature. E-2172 will also be required in normal operation when the LTS Shift catalyst is fresh and the heat of the Methanator reaction is not sufficient to provide the required temperature differential in E-2114. The Methanator R-21 06, contains a bed of Nickel catalyst that removes the remaining carbon oxides in the gas stream by promoting the reaction of carbon dioxide and carbon monoxide with hydrogen to form Methane and Water. The total amount of carbon oxides leaving the Methanator will be less than 5 ppm by volume, and the methane content about 0.9% (dry basis). Due to the highly exothermic nature of the methanation reactions, the synthesis gas temperature increases from 316°C at the inlet to about 347°C at the outlet.

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After heat exchange with the Methanator feed, the purified synthesis gas is air cooled to approximately 53°C in the Methanator Effluent Cooler E-2118 and further cooled against cooling water in E-2115 before delivery to the Synthesis Gas Compressor Suction Drum 0-2104 at about 39°C. The small amount of process condensate remaining in the synthesis gas, which disengages in 0-2104 and later 0-2105, is pumped to 0-2102 using the Low Pressure Condensate Pump P-2150, and is recovered for use as BFW with the other process condensate. 2.7.4 Synthesis Gas Compression & Ammonia Synthesis The purified synthesis gas, containing the stoichiometric ratio of hydrogen and nitrogen for ammonia synthesis, is compressed in a turbine driven centrifugal synthesis gas Compressor C-21 03. The compressor consists of two cases with intercooling between cases and a separate recycle wheel in the second case. From the discharge of the low pressure case, at approximately 67 bara a small portion of the synthesis gas is recycled back to the Primary Reformer feed gas preheat coil to

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provide hydrogen for the Co-Mo and ZnO desulphurisation. The make-up gas from the first case is first cooled by heat exchange with demineralised water in the Synthesis Gas Compressor Interstage/BFW Preheater E-2117. The gas is further cooled to 39°C against cooling water in the Synthesis Gas Compressor Intercooler E-2116, and then to 4.4°C with ammonia refrigeration in the Synthesis Gas Compressor Interstage Chiller E-2129. Condensate is separated from the synthesis makeup gas in the Synthesis Gas Compressor Interstage Separator 0-2105, and passed through an Oil Filter F-21 02, before it is directed back to 0-2104 for recovery.

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The cooled synthesis gas is compressed to the synthesis loop pressure in the makeup gas section of the high pressure compressor case. The fresh synthesis gas is mixed internally within the high pressure case of the compressor with recycle gas from the synthesis loop. After mixing, the pressure is boosted by the last wheel of the compressor. The combined flow to the synthesis loop is discharged from the compressor at approximately 144 bara and is cooled to 52°C in the Ammonia Synthesis Loop Cooler E-2124. Before the recycle gas (plus fresh feed) re-enters the converter, it is routed via E-2120 Unitised Chiller to condense out the net ammonia make produced on its previous pass through the converter. This specially designed chiller provides refrigeration of the synthesis gas through interchange of heat with ammonia vapours returning from the Secondary Flash Separator 0-2106 and boiling ammonia liquid at four different temperature levels (16.7°C, -2.2°C, -17.SoC and -35°C).

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The Unitised Chiller consists of multiple concentric tubes that run through the boiling ammonia compartments. Synthesis gas vapours from the Secondary Flash Separator 0-2106 pass counter-currently through the centre tubes and the compressor discharge flows through the annuli. Thus, the synthesis gas is being cooled from the outside by boiling ammonia and from the inside by recycle vapour from the Secondary Flash Separator. The final exit temperature of the Unitised Chiller is -17.SoC and the liquid ammonia product is disengaged from the synthesis gas immediately downstream. Liquid from the Secondary Flash Separator is flashed into the Ammonia Letdown Drum 0-2107. The flashed vapour, primarily gases released from solution, is mixed with the refrigeration system purge gas and sent to the Purge Gas Scrubber T-21 03. The liquid ammonia product is then split into several streams leading to E-2120 and to the purge gas cooler section of the Refrigerant Receiver 0-2109. The vapour from the Secondary Flash Separator 0-2106 is the Ammonia Synthesis Converter (R-21 05) feed. It contains near 2.7 vol% ammonia and is reheated to 42°C in the Unitised Chiller as described above. Before entering the Ammonia Synthesis .Converter the gas is preheated to 259°C in the Ammonia Converter Feed/Effluent Exchanger E-2121. This exchanger is provided with a feed gas bypass that controls R-21 05 feed temperature.

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Ammonia Converter - R-21 05 Product ammonia is synthesised from the hydrogen and nitrogen in the circulating gas stream over beds of catalyst in the horizontal, intercooled converter R-21 05. The converter contains a removable catalyst basket within the pressure shell and integrated with the basket is the internal heat exchanger E-2122. While there are only two adiabatic beds,there are three catalyst sections as the second stage is split into two sequential parts. Each catalyst bed contains a promoted iron magnetite catalyst supported on profile wire screens. A major portion of the feed gas is passed through the shell/basket annulus, thus preventing the pressure shell from being heated by the reaction, and enters the shellside of the internal exchanger, preheating the feed against hot effluent from the first bed. The remaining portion of the feed enters the converter via a bypass line and mixes with the other feed at the interchanger exit. The amount of bypass is varied to control the temperature of the process gas to the first catalyst bed. The feed gas is directed downward through the iron catalyst. The exothermic and equilibriurn governed reaction proceeds with a significant ternperature rise. Upon leaving the first bed, the partially reacted gas passes through the grid supporting the catalyst and into the space between the bottom of the bed and the basket wall. Frorn here it is routed to the tubeside of the E-2122 Interchanger and is cooled to the proper feed temperature to the second catalyst bed. There is no heat exchange between the two sections of the second adiabatic bed. Hot converter effluent from the last bed exits the converter via a special connection between the basket and pressure shell.

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The heat of reaction from the ammonia synthesis is recovered by the steam system in the Ammonia Converter Effluent Waste Heat Boiler E-2123 then used to preheat the feed in E-2121. A small portion of the reacted gas is taken from the synthesis loop at this point to prevent the build-Up in the synthesis loop of inert gases contained in the purified feed (e.g. CH 4 and argon). Chilling the vapour to -17.B lowers the ammonia content in this high pressure purge by ammonia refrigeration in the Purge Gas Chiller E-2125. The liquid ammonia condensed in this exchanger is removed in the Purge Gas Separator D-21 OB, and directed to the Ammonia Letdown Drum. The vapour from the separator is sent to the Purge Gas Scrubber T -2103, for recovery of the remaining ammonia and then used for fuel in the Primary Reformer furnace. A line is provided downstream of the converter effluent side of E-2121 to enable synthesis loop gas to be used as a secondary back-up supply of desulphurisation hydrogen in the event of a C-21 03 trip. The primary backup supply of desulphurisation hydrogen is synthesis gas from D-21 03 routed to the suction of the Feed Gas Compressor. The secondary back-up supply would only be required in cases when the Feed Gas Compressor is not running and the supply would only be available for a lirnited tirne, whilst the Feed Gas Compressor is started up, or C-21 03 is restarted. (It should be noted that the back-up supply should be switched to the injection point downstream of the pre-heat coil since the addition of NHs rich synthesis gas to the cold natural gas containing CO2 , could produce carbamates and cause line blockage.

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Start-up Heater - H-21 02 A gas fired Start-up Heater H-21 02 is provided for activating a fresh charge of catalyst in the Ammonia Converter and for heating the catalyst up to the required temperature during start-up.

2.7.5 Ammonia Refrigeration And Recovery

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A four stage ammonia refrigeration system provides refrigeration to condense ammonia product from the circulating gases in the synthesis loop to allow additional ammonia synthesis on recirculation of the gas stream through the converter. It also provides for recovery of ammonia from vented gases and for synthesis gas compressor makeup gas chilling. The four refrigeration levels operate at approximately 16.7°C, -2.2°C, -17.aoC and -35°C. The refrigeration system consists of a two-case centrifugal compressor (C-21 05) with two intercoolers, a refrigerant condenser, a refrigerant receiver, and evaporators. Provision is made for contact chilling and venting of any inert gases dissolved in the liquid ammonia from the synthesis loop. Additional provision is made to recover a small amount of ammonia vented from the atmospheric storage to the first stage suction of the Ammonia Refrigerant Compressor.

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Ammonia vapour from the second case of the Ammonia Refrigerant Compressor C-21 05 is cooled and condensed at 37.5° C in the Refrigerant Condenser E-2127, then sent to the Refrigerant Receiver 0-2109. Non-condensable gases with the residual ammonia vapour from the refrigerant receiver enter the contact chiller section on the top of the receiver where the ammonia is condensed and drains back to the vessel. The chilled vent gas from 0-2109 is mixed with the flash gases from 0-2107 and 0-210a before being senttothe Purge Gas Scrubber T-21 03 and ultimately to the fuel system. A small portion of the liquid ammonia from the Refrigerant Receiver 0-2109 is pumped by the Ammonia Injection Pump P-2120AlB for use as reflux to the Ammonia Stripper, T-21 04. Under normal operation, a major portion of the product ammonia is pumped from the receiver to the Urea unit via the Warm Product Pump P-2113A1B. The remainder of the liquid in 0-2109 is flash cooled to 16.7"C in the Fourth Stage Refrigerant Flash Drum 0"2123 where it provides cooling for the Unitised Chiller. A stream is taken from the warm Ammonia product line downstream of the pumps as cooling medium to the Urea Granulation Cooler E-4204 and Steam Condensate Chiller E-4153. The return frorn these is to the third stage Flash drum 0-2122. Some liquid ammonia frorn 0-2123 is used by the Synthesis Gas Compressor Interstage Cooler, E-2129. Other liquid from 0-2123 is let-down as required to the Third Stage Refrigerant Flash Orurn, 0-2122, flashing to -2.2°C. Liquid from the Third Stage Drum is flashed into the Second Stage Refrigerant Flash Drum, 0-2121, at -17.aoC.

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Liquid in the Second Stage Drum provides refrigeration directly to the second stage chiller section of the unitised exchanger. An additional flow of liquid ammonia is taken from this stage to provide the required refrigerant for the Purge Gas Chiller, E-2125. The net liquid from the Second Stage Drum is flashed into the First Stage Refrigerant Flash Drum D-2120 at -35°C. Liquid in the First Stage drum provides refrigeration directly to the first stage chiller section of the unitised exchanger and is also sent to the atmospheric storage tank via the Cold Ammonia Product Pump P-2124A1B/C.

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The vapours generated in the four refrigeration drums are fed to the appropriate stage of the two-case, steam turbine-driven centrifugal Ammonia Refrigerant Compressor. The vapours are compressed, condensed, and returned to the Refrigerant Receiver, thus completing the refrigerant cycle. The refrigerant compressor intercoolers E-2128 and E-2167 provide cooling between the second and third stages of compression. Boil off vapours from the ammonia storage are also routed to the first stage suction of the refrigerant compressor. They are thus condensed by the ammonia plant refrigeration system and a corresponding additional quantity of cold ammonia is routed to storage. 2.7.6 Ammonia Purge Gas Recovery System To prevent the build-up of inert gases such as argon & methane contained in the purified feed, a side stream of purge gas is taken from the loop. The high pressure purge gas from D-21 08, along with flashed gases from D-21 09 and D-21 07, are sent to the Purge Gas Scrubber T-21 03. Ammonia is absorbed by a water wash in a packed tower and the Primary Reformer burners use the low pressure absorber overhead gases as fuel gas.

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The solution leaving the absorber has an arnmonia concentration of about 11.17% wt. From the Purge Gas Scrubber it is pumped by the Purge Gas Scrubber Pump P-2130AlB, and heated to about 168. 7"C in the Ammonia Stripper Feed/Effluent Exchanger E-2161 by purified recycle water from the Amrnonia Stripper bottoms. The heated ammonia-water solution enters the Ammonia Stripper T-21 04 below a section of reflux packing. Liquid arnrnonia reflux to the top of the stripper column is provided from the refrigeration system frorn the Ammonia Refrigerant Receiver D-21 09 via the Ammonia Injection Pumps P-2120AlB. The ammonia vapour from the top of T-21 04 is vented to the Refrigerant Condenser E-2127 where it is recovered. The stripper heat is provided by the Ammonia Stripper Reboiler, which condenses mediUm pressure steam. A srnall amount of MP steam condensate is added to the system as rnake up for water losses in the scrubber overhead systern. 2.7.7 Ammonia Storage & Loading Facilities (OSBL) NOTE: The following description is based on the original Design Engineering package and to identify any later changes or modifications, reference should be made to the latest issue of the Offsites P&ID's.

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a) Storage Tank TK5101 is provided for the storage of Ammonia. The tank has a capacity of 1O,OOOMT operating at a pressure of 50 mbarg and a temperature of-35°C. b) Although well insulated, some heat leak into the ammonia tank occurs producing vapours, which must be removed by refrigeration. In general, refrigeration of the storage tank involves the removal of the ammonia vapours from the vapour space above the stored liquid ammonia by the Refrigeration Compressor, C-21 05 in the Ammonia Unit. If C-21 OS is shut down, the package Refrigeration Unit C-S1 01 will be in service maintaining storage tank temperature and pressure.

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c) A Road Tanker Loading Station is provided with two Loading Arms, V-S102 A & V-S102B each with a loading capacity of 2S000 Kg/hr. Ammonia liquid is transferred to the loading arms using the Ammonia Transfer Pumps, P-S101 AlB via the Ammonia Heater, E-S101 where the temperature control is set to obtain the required ambient temperature for loading the trucks with the displaced vapour being returned to the Ammonia Storage Tanks. d) Facilities are also provided to depressurise and fill bottles with ammonia. The loading is carried-out to an exact weight as specified for the bottle being filled, using the Ammonia Bottle Weight Scales, V-S103A1B e) A portable hydrostatic testing hand pump is provided to recertify used bottles when necessary.

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DESCRIPTION OF UNIT CONTROL 3.1

UNIT CONTROL This section of the manual will give the reader a clearer understanding of the unit control and can be more readily understood if the Process Piping, Auxiliary and Utility Instrumentation Flow Sheets are referred to during study of this section. Note that throughout this section instruments having the same number and designated AlBIC indicates that a two out of three voting system exists for the relevant interlock.

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3.1.1 Natural Gas Feed Preparation 3.1.1.1

Offsite Feed Gas Heater (E-1 001)

Natural Gas Feed from the NIGC Metering Station enters the Offsites where a steam heated Feed Gas Heater (E-1 001) is provided to prevent hydrate formation in the NH3 Unit feed gas and Offsites fuel gas systems. PI-1001 and TI-1001 monitor the pressure and temperature of the incoming gas. The temperature of the natural gas downstream of E-1001 and being supplied to the NH3 Unit is sensed by a temperature indicator controller located on the Offsites fuel gas system which resets the position of control valve PIC-1081 and regulates the flow of LP steam to the Feed Gas Heater.

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Should a low external supply pressure and ambient conditions allow, E-1001 can be totally by-passed. In the event of the supply pressure being raised to 44 bara it will be necessary to manually reset the temperature controller on the fuel gas supply line to prevent the formation of hydrates at the higher pressure. Three control valves located downstream of the Feed Gas Heater (E-1 001) control the pressure of the natural gas supply to the Ammonia Unit and to the Offsite fuel gas system. These operate under a split range pressure control system with the actual control valve positions dependent upon the external pipeline supply pressure. Should it be necessary to operate the system with a natural gas supply pressure in excess of 50 bara then for downstream protection, the two control valves (PV-1084B & C) must be blocked in and locked closed. Should the Natural gas supply pressure approach the minimum of 10 bara the feed gas compressor C-21 02 will not have sufficient capacity to supply both the Ammonia plant at full rate and the Offsites gas turbines. In this situation the Ammonia plant rate should be reduced and stabilised in good time to prevent an upset in the

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Reforming section. For over pressure protection, high/high pressure switches PSHH-1083A1B/C are located downstream of the pressure control assembly which in the event of an excessive high high pressure, will actuate an interlock which will close the shut-off valve XV-1041 on the natural gas feed line from the metering station and also the LP Steam supply to the Feed Gas Heater, E-1001. The same interlock may be manually actuated by the operator using shutdown switch HS-1041 located in the main control room (HS-1042 will reset shutdown switch HS-1041). The supply line to the Feed Gas KO Drum (0-2144) is further protected by relief valves PSV-1001A & B, which vent to atmosphere at a safe location.

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3.1.1.2

Feed Gas Knockout Drum (0-2144) Natural gas from the Feed Gas Heater (E-1 001) enters the ammonia plant battery limits on line NG-1 000-12" where the pressure and temperature of the incoming gas are monitored by pressure indicator (PI-1074) and temperature indicator (TI-1029). The flow is indicated on FR-1042 and integrated on FQI-1042. All these instruments are accessible to the operators on the FCS system in the control room. Any free water in the natural gas feed separates on entering 0-2144 Feed Gas KO Drum from where it may be drained for disposal. A high level alarm, LAH-1 002A will warn the operator of a high level and should the level continue to rise, LAHH-1212 on a 2 out of 3 voting system will actuate interlock ESO-21 02 which will shut down the Feed Gas Compressor C-21 02 and open the kickback valve UV-1015. Other causes of actuation of interlock ESO-2102 are described in detail in Section 11.3 of this manual. The main supply line from 0-2144, KO Drum routes feed gas to the Primary Reformer Feed Gas Preheat Coil, either directly or via the Feed Gas Compressor C-21 02, dependent on the pressure available from Offsites. There is also a branch line FG 1002-6", which supplies natural gas as fuel gas to the various burner users on the NHs Unit. These are described under "Utility Flows" later in this section. Another branch line FG1 076-2" before FR-1042 supplies fuel gas to the flare system with flow indicated on FI-1041.

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The supply pressure of natural gas feed to the Feed Gas Compressor is controlled by PRC-1187, which is provided with High and Low pressure alarms in the main control room. High high Pressure on PT-1191A1B/C and low low pressure on PT1192A1B/C will actuate interlock ESO-2102 (refer Section 11.3.4 of this manual for details) and shut down the Feed Gas Compressor should either of these conditions occur. 3.1.1.3

Feed Gas Compression The Feed Gas Compressor (C-21 02) is provided to compress the natural gas feed to the required pressure for the hydrogenation and desulphurisation reactions and subsequent reforming and conversion reactions through to the suction of the

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Synthesis Gas Compressor. C-21 02 is a centrifugal machine consisting of a single cased multi-stage compressor driven by a steam turbine using MP steam exhausting into the Surface Condenser E-2140 operating at a pressure of 97 mm Hg abs. Lubrication and governor oil for the compressor and turbine consists of a complete system shared with C-2101 Air Compressor as described later for C-21 01 Air Compressor. Alarms and shutdowns are also provided to alert personnel of abnormal operating conditions and for the protection of the machine itself.

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The compressor takes suction from the top of the knockout drum 0-2144 at a normal operating condition of 15.95 bara and 39.6°C and is discharged at 44 bara and 142°C through the feed preheat coil on Primary Reformer H-21 01. PRC-1 01 0 at the Oesulphuriser outlet, is provided to control the pressure being delivered from the compressor by regulating the speed of the steam turbine and which will go to minimum speed on minimum signal from PIC-1 01 O. HS-1202 is provided to allow manual trip of the steam turbine governor by actuating interlock ESO-21 02, together with reset switch HS-1058. The causes and effects of Interlock ESO-2102 are described in detail in Section 11.3.4 of this manual. A kickback system connecting the compressor discharge to the suction is provided to protect the machine from surging. This is controlled by FIC-1 015 on the compressor discharge and the kickback stream is cooled in Cooler E-2133 and any moisture is knocked-out in a piping pot fitted with a high level alarm LAH-1 077 and a manual drain to sewer. A tie-in to the kickback line PG1034-3" from 0-2103 is provided to supply hydrogen during start-up with flow indication by FI-1169A together with low flow alarm FAL-1169 in FCS and the flow also can be seen on FI-1169B locally with a manual globe valve installed in view.

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Local Indicators PI-1604 & TI-1609 together with temperature indicator (TI-1308) and a high temperature alarm (TAH-1308) plus a pressure recorder (PR-2205) and PAH in the main control room are provided on the compressor discharge. Relief valves PSV-C2102A & B set at 51.5barg and 54.1 barg protect the machine from an overpressure situation, which would relieve the compressor discharge to the vent system. With the possibility of natural gas being available at high pressures, a bypass round the Feed Gas Compressor C-21 02 has been provided to enable the NH3 Unit to be operated with this compressor shutdown. The minimum gas pressure at the battery limits required for this operation is 44 bara. When in this bypass situation, hand switch HS-1047A will be switched to route the signal from PIC-1 01 0, located on the natural gas feed to the Primary Reformer, to HV-1027 thereby controlling the pressure of natural gas to the Primary Reformer. In addition, when HS-1047A is switched in this position, it will cancel Interlock ESO-2102 which normally shuts down C-21 02. It is important that HS-1047 is correctly positioned when the machine is

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running to avoid running C-21 02 with the shutdown interlock ESD-2102 cancelled. To avoid the temperature of feed gas to H-2101 is too low with C-21 02 shutdown, the natural gas feed is preheated by LP steam in Nat Gas Feed Preheater E-2171, and the temperature of feed gas to H-21 01 is controlled by TIC-1197 via control valve TV1197 on the LP steam line. Note however that for start-up and shutdown of the NH3 Unit, the C-21 02 Feed Gas Compressor must be in service. This will require a battery limit supply pressure of natural gas of 14 bara to provide a sufficiently low pressure to enable the recycle of hydrogen rich gas back to the suction of C-21 02 for process purposes.

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3.1.1.4

Desulphurisation In normal operation and after compression, the natural gas feed stream is ioined by a hydrogen-rich gas stream from the first stage discharge of the Synthesis Gas Compressor (C-21 03). This mixture flows through the feed preheater coil on the Primary Reformer H-21 01. The flow of hydrogen-rich gas from C-21 03 is controlled by FIC-1 022. Temperature Controller TIC-1 093 located on the feed preheater bypass line provides a means of adjusting the inlet temperature to the Hydrogenator R-2160. Should it become necessary to use the back-up supply of hydrogen from the synthesis loop, then it is important to note that it should be routed downstream of the preheat coil using the interlocked bypass provided since the addition of NH3 rich synthesis gas to the cold natural gas containing CO2 could result in the formation of. carbamates and possible line blockage. During start-up and shutdown operations of the ammonia plant, hydrogen-rich gas for desulphurisation of natural gas and the desulphurisation and reduction of the Reformer and HTS shift catalyst, will be produced by dissociating ammonia in the Primary Reformer (see section 6.6.7). The hydrogen-rich gas so produced will be routed via a start-up line PG1034-3" from D-21 03 Absorber Overhead Drum back to the suction of the Feed Gas Compressor (C-2102). Hydrogen gas flow from C-21 03 to H-2101 is indicated on FIC-1022 and the combined hydrogen Inatural gas feed flow is indicated on FRC-1001. From these two indications, the Hydrogen to Feed Ratio may be calculated. The combined stream passes down through the Hydrogenator (R-2160) containing a bed of Cobalt Molybdenum catalyst. This vessel is provided with temperature indicators at the top (TI-1074), centre (TI-1075) and bottom (TI-1076) of the catalyst bed together with high temperature alarms (TAH-1075 and T AH-1076) at the centre and bottom of the bed. The temperature of the stream leaving R-2160 is indicated by TI-1067 (local) and TI-1 068 (on the main control panel). It then passes through the Desulphuriser reactors (R-21 08 A& B) containing Zinc Oxide pellets. Local temperature indicators are located on the outlet line from each vessel together with TI-1306 indicated on the main control panel.

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Pressure differential indicators are provided to indicate the pressure drop across each of the Hydrogenator and Desulphuriser catalyst beds and vessels. Sampling points are also located at intervals throughout each bed of Desulphuriser catalyst to enable catalyst activity to be monitored. A vent is provided on each Desulphuriser outlet line for use during start-up and shutdown together with a start-up line from the outlet line of R-21 08B for LT Shift catalyst reduction. 3.1.2 Raw Synthesis Gas Preparation Reformed gas is produced in successive process steps by reforming part of the hydrocarbons in the primary reformer furnace and additional reforming, with air addition for nitrogen requirements in the secondary reformer.

c 3.1.2.1

Primary Reformer - [H-2101] The desulphurised gas feed is flow controlled by FRC-1 001 and then mixes with process steam before passing to the mixed feed preheat coil located in the convection section of the Primary Reformer (H-21 01). The MP steam flow is controlled by FRC-1002 and both FRC-1001 and FRC-1002 are supplemented with low flow alarms FAL-1001 and FAL-1002 respectively. A further decrease in feed gas flow to the reformer will cause Low/low flow switch FSLL-1201 to actuate interlock ESD-1201 and ESD-2111, which is described in detail in Section 11.3.2 & Section 11.3.10 of this manual. Hand switch HS-1048 is provided to over-ride ESD1201 and ESD-2111 during start-up.

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The signal from natural gas flow transmitter FT-1201 is forwarded to relay FY-1201 together with a temperature/pressure compensated signal from relay FY-1202 on the Process Steam line. The two signals are divided to give the steam to carbon ratio which in the event of decreasing below a preset level and after a 5 second delay, will actuate Low Steam to Carbon Ratio Alarm FFAL-1201 and alert the operator to this condition. Should it decrease still further, then Lowllow Steam to Carbon Ratio switch FFSLL-1201 will actuate Interlock ESD-1203 and ESD-1211 to be described in detail in Section 11.3. Hand switch HS 1261 is provided as a start-up over-ride. The combined stream of steam and feed in a ratio of 3.2 mols steam per 1 mol of organic carbon, flows through the mixed feed preheat coil in H-2101 convection section at the exit of the radiant section of H-2101. When problems exist in the reforming section, HS-1202 may be used to manually actuate interlock ESD-1203 and ESD-1211 which will shut down gas feeds to the Primary and Secondary Reformers and open PIC-1169 vent control valve upstream of H-2101 thus allowing continued operations of the Hydrogenator and Desulphurisers. (HS-1059 will reset the interlock and HS-1261 over ride it on startup). From the main inlet header, the steam/gas stream is distributed to four

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sub-headers (harps) which are arranged in parallel rows across the top of the primary reformer arch. Each of the sub-headers distribute the flow via pigtail connections downward through 52 catalyst packed tubes in the radiant section of the primary reformer furnace. The total of 208 (4 x 52) catalyst packed tubes constitutes the primary reforming element of the process.

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The bottom of each row of 52 catalyst tubes terminates in collector headers located near the floor of the primary reformer furnace. There are four risers (centrally located), one on each of these collection headers, that return the flow to a water jacketed transfer line V-2150 located over the top of the arch of the radiant box. The transfer line directs the flow from the Primary Reformer to the process gas inlet of the Secondary Reformer (R-21 03). The primary reformer has various pressure gauges, temperature indicators and temperature recorders to observe process conditions. There is also pressure differential indicator (Pdl-11 01) for observing the pressure drop across the tubes and an analyser recorder (AR-1 001 A) recording the methane (CH 4) content of the process flow leaving the primary reformer. There are 110 fuel gas fired arch burners regulated by HIC-1 035 through 1039 located on the main panel together with 6 burners for providing additional heat to the convection section for superheating purposes. H-2101 also incorporates an independently fired auxiliary boiler of four burners for producing HP steam. The control systems for these arch, superheat and auxiliary boiler burners together with descriptions of associated shutdown devices and interlocks are contained in section 11.0 of this manual. To avoid overfiring during start-up and until normal process conditions are reached, special attention must be paid to the lower flows of fuel gas required until all burners are alight.

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The Primary Reformer fire box draft is provided by an induced draft fan C-211 0 and regulated by the Fan drive turbine speed which is controlled by the furnace box pressure controller PIC-1 019 adjusting the turbine governor speed setting. High/high pressure on PT-1 059A1B/C connected to interlocksESD-2111 , ESD2112andESD-2114 will shut down the arch burners, Aux. boiler burners and tunnel burners should a high pressure occur in the furnace box. The Aux. boiler combustion air is supplied by a turbine driven forced draft fan C2111. The air is supplied in ratio to the fuel by a leading air system that adjusts the fan drive turbine governor speed setting. PAHH-1060AlB/C located in the Aux. boiler firebox will shut down the Aux. boiler burners via interlock ESD-2112 should a high pressure occur in the firebox. The combustion air for the Arch burners is supplied by turbine driven fan C-2112. The air supply is regulated by five manually operated dampers in the combustion air ducts to the arch burners. The turbine speed is controlled by FIC-1181 , which adjusts the governor speed setting to regular the flow of combustion air.

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High pressure switch PSH-1058 located in the Arch burner fire-box and/or High pressure switch PSH-1057 located in the convection section at the suction of the ID Fan, will actuate interlock ESD-1058 which will cause Air Horn PAH-1058A to sound and Rotating Light PAH-1058B to light. These are both located in the Reformer penthouse and interlock ESD-1058 will also be actuated by Arch burner SID Interlock ESD-2111 and/or Aux. boiler burner SID ESD-2112 and/or tunnel burner SID ESD-2114. 3.1.2.2

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Process Air Compression Process air for the secondary reforming operation is delivered by C-21 01, Air Compressor,which is a four-stage, two case centrifugal compressor driven by turbine C-21 01 (T). C-21 01 (T) is a 6 stage, steam condensing turbine which is exhausted and condenses into surface condenser E-2140 operating at a pressure of 97 mm Hg abs. Lubrication, and governor oil for the compressor and turbine consist of a complete system, rnounted in a separate console 'and shared with C-21 02 Feed Gas Compressor. The console consists of a main reservoir together with individual compressor lube oil rundown tanks and control oil accumulators. Turbine driven lube oil purnps with electric motor standbys, together with coolers, filters, a pressure control system and ancillary piping are also provided. The coolers and filters are provided with valve linkages so that change over is accomplished without interrupting the oil flow but it should be noted that the standby cooler and filter must be completely filled with oil before being put into service.

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C-2101 takes suction through F-2101 Air Filter to remove dust and fine particles from the air stream. The air is compressed in the first stage of the LP case to 2.09 bara at 150°C and after being cooled in intercooler E-2141 to 39°C, enters the second stage of the LP case. The air is compressed in the second stage of the LP case to 4.9 bara at 150°C and then cooled in intercooler E-2142 to 39°C before entering the first section of the HP case. This section compresses the air to 14.4 bara at 185°C which is again cooled in an intercooler E-2143 to 39°C and then compressed in the final stage to 39 bara at 189°C for delivery to the process. The water knocked out in the intercoolers is sent to Process Condensate Drum D2161 for recovery. Local pressure and temperature indicators are provided wherever necessary for the checking of the process air conditions throughout the compressor system. A number of alarms and trips are also provided and alarm conditions should be corrected as quickly as possible. C-2101 may be shutdown manually by HS-1201A in the main control room panel or by HS-1201 B local shutdown switch. (both reset by HS-1057 in the main control room). Shutdown interlock ESD-2101 will shutdown the machine whilst interlocks ESD2102 (Feed Gas Cornpressor shutdown), ESD-1201 (Low Natural Gas Feed

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Rate),ESD-1223(Steam Drum Low level) and ESD-1203 (Low Steam to Carbon Ratio) will cause the machine to go to minimum speed. The causes and effects of all these interlocks are described in Section 11.3. of this manual. A supply of air to the Urea Plant is taken from the 2nd stage suction and instrument air to the Offsites is supplied from the 4th Stage suction. A branch line from the final discharge line is provided for line blowing and catalyst dusting during start-up.

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Additional piping from the final discharge line together with a return line to the LP case discharge line, is provided to enable circulation of nitrogen using the high pressure case of C-2101 in order to heat up the Primary Reformer catalyst at start-up. During these operations the LP case will be isolated from the HP case and vented to atmosphere from the interstage vent on the 2nd Stage discharge line. Piping is also provided from the HP case discharge line for Low Temperature Shift Converter reduction should it be decided to reduce the LTS catalyst using nitrogen as the carrier gas in a closed loop circulation as opposed to a once through reduction using desulphurised natural gas as the carrier medium. This includes a line from C-2101 final discharge together with a nitrogen tie-in and intermediate vent to atmosphere between the LP and HP cases. These procedures are discussed in the Start-up Section 6.0. of this manual. Process air flow to the Secondary Reformer from the final discharge of the compressor is controlled by FRC-1003 which regulates the speed of the C-21 01 turbine driver and will go to minimum speed on minimum signal from FRC-1003.

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FIC-1004 is an anti-surge controller provided to maintain the compressor flow above its minimum value (surge point) by venting air to atmosphere. Process airflow may be closed off to the Secondary Reformer by the operation of the valve HV-1006, which is part of the reformer feed shutdown circuit. HV-1006 is a inching valve on the 4th stage discharge line, which may be closed either by push button HS-1028 action, or as a result of one or more of the following interlocks being actuated:

• • • • • •

ESD-2101 ESD-1201 ESD-1223 ESD-2102 ESD-1203 ESD-1202

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C-2101 Air Compressor shutdown Low natural gas feed rate Steam Drum low level C-21 02 Feed Gas Compressor shutdown Low Steam to Carbon Ratio. Low Low Process steam

Any of these interlocks will also open HV-1023, the interstage vent to atmosphere and UV-1004, the vent to atmosphere on the 4th stage discharge. A 2-inch bypass is provided around HV-1 006 for use during initial start-up of the Secondary Reformer, which must be tight shut off during normal operation.

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Secondary Reformer (R-21 03) Downstream of HV-1 006,.the. process air is joined by a small flow of medium pressure steam, which is-c~ntrolled manually by the 4-rnch bypass valve on HV-1021 and metered by FI-1044. This steam flow is necessary for the protection of the preheat coil in the event of process air failure, with HV-1021 automated to initially open to a preset position on hand switch HIC-1021. This then allows further manual positioning of HV-1021 for excess cooling steam flow to the air heater coils when the solenoid holding HV-1006 is de-energised by an interlock and closes. A control valve (TV-1095) is located on a bypass line round the first (cold) process air preheat coil and is positioned by TIC-1 095 controlling the temperature downstream of the second (hot) process air coil where a high temperature alarm (TAH-1312) is also located. The preheated steam-air mixture enters at the top of the Secondary Reformer (R-2103) and is directed downward through a flow insert into the combustion zone of the reformer where the Primary Reformer effluent enters. Leaving the combustion zone of the reformer, the flow passes through the catalyst bed to enter a chamber at the bottom of the reformer. There are temperature recorders located at the top (TR-1052) and bottom (TR-1053) of the catalyst bed, and on the main outlet line from Secondary Reformer (TR-1334A and TR-1334B). Each of these recorders is provided with High temperature alarms. The entire vessel is encased in a water jacket with four metal temperature sensors (TE-1333A through D) attached to the shell at various points.

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Hot effluent gases from the Secondary Reformer are cooled in E-2101 (Waste Heat Boiler) and E-21 02 (HP Steam Superheater), then pass to the inlet of the High Temperature Shift Converter R-21 04. The temperature of the HP steam exiting E-21 02 is controlled by TIC-1 004 via control valve TV-1 004 located in Secondary Reformer Waste Heat Boiler E-2101 tube side which adjust the heat area of E-2101. The overall temperature drop across E-21 01 and E-21 02 from 994°C to 371°C is obtained by heating the boiler water from D-2101 that is thermo-circulating on the shell side of E-2101 and the HP steam passing through the tubes of E-21 02. The required inlet temperature to the HT Shift Converter of 343°C - 371°C is controlled by TIC-1010, which activates control valve TV-1010 located in the shell side of E-21 02. High (TAH-1336) and Low (TAL-1336) Temperature alarms are provided on the steam outlet line from E-21 02. An analyser for CH 4 (AE-1 001 B) together with a sample point (S-028), are located on the process gas line exit E-21 02. The primary reformer and secondary reformer systems including the waste heat boiler and steam Superheater, are protected against over-pressuring by Relief valves PSV-E2102A and PSV-E2102B at the "hot" outlet of E-21 02 HP Steam Superheater.

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Shift Conversion (High and Low Temperature) The shift converters are stacked one above the other with the upper vessel being the High Temperature Shift converter and first in the process flow from the Secondary Reformer.

3.1.2.4.1

R-2104 - HT Shift Converter The process flow enters the top of the High Temperature Shift Converter, passes through an inlet baffle and down through the shift catalyst and out through the outlet collector at the bottom of the converter. To monitor converter conditions, a pressure differential indicator (PDI-111 OA in FCS and local PDI-111 OB) across the catalyst bed together with temperature indicating points (TI-1340 through 1344) at intervals throughout the bed, are provided on the HTS converter. Piping provision is made for steam injection into the bottom of the HT Shift converter, which is routed up through the catalyst bed to a vent on the inlet line from E-21 02, for use during start-up and to keep the catalyst warm during brief shutdown periods. The steam flow is measured on FI-11 03 with a globe valve in view.

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The flow then enters the shell side of the HTS Effluent Waste Heat Boilers (E-2103A & B) to give up heat to boiler feed water for D-2101. A vent line is located on the process gas stream downstream of E-21 03B and is fumished to permit the manual venting of the high temperature shift converter effluent gas at start-up and in emergencies.

3.1.2.4.2

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R-2109 - L.T. Shift Converter After leaving the E-21 03A1B exchangers, the gas flows to the Low Temperature Shift Converter (R-21 09), passes through the low temperature catalyst bed and leaves via the bottom outlet. Analyser AR-1 022A is provided on the inlet line from E-21 03B to record the carbon monoxide content of the gas being fed to the LT Shift Converter. The low temperature shift converter may be bypassed during start"up or in emergencies by operating pushbutton HS-1004 which closes MOV-1008 in the L.T. shift inlet line and opens MOV-1009 in the bypass line. By "inching" HS-1009 or HS-1008, the two valves may be adjusted for partial bypass operation. The LTS inlet temperature is controlled by partial bypass of the boiler feed water to the tube side of exchanger E-21 03B. Controller TRC-1 011 positions control valve TV-1 011 which is located on E-21 03B tube side bypass and is used as a "forcing valve" through the tubes. Temperature indicators (TI-1046 through 1049) with high temperature alarm are

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provided at intervals throughout the LTS converter for monitoring of conditions together with a high temperature alarm (TAH-1350) at the catalyst bed exit. Temperature indicator TI-1 063 and analyser AR-1 022B located on the outlet line respectively indicate and record the temperature and carbon monoxide content of the gas exiting R-21 09.

3.1.3 Synthesis Feed Gas Purification 3.1.3.1

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The hot "shifted" gases from the bottom of the low temperature shift converter are cooled in the L.T. shift effluent train before entering the aMOEA CO2 Removal section. L.T. shift effluent gas is first cooled against boiler feed water in E-2131 and then' provides reboiler heat to the CO2 removal solution in reboiler E-21 05 with final cooling against demineralised water in E-21 06. Temperature control of the L.T. shift effluent gas and heat input to the aMOEA solution is effected by E-2131 boiler feed water bypass. A globe valve is installed on the water bypass line in view with local TI-1355 which indicate the outlet of E-2131 tube side temperature. The outlet temperature of E-2131 shell side is monitored on TI-1351 with TAL-1351 waming of low temperature. Temperature indicators are also provided on outlet lines of E-21 05 and E-21 06 hot side.

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3.1.3.1.1

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Carbon Oioxide Removal

0-2102 - Raw Gas Separator The cooled "shifted" gases enter the Raw Gas Separator 0-2102 where any water vapour present in the process gas stream and condensed in E-2105, E-2113 and E-2106, is disengaged. The condensed process steam is withdrawn from the bottom of the separator under control of LlC-1 003 and is routed directly to the Process Condensate Stripper (T-2150) via P-2121 AlB or when off specification or during short term upsets of 0-2102, to drain. High and Low level alarms LAH-1003 and LAL-1003 will wam personnel of these level conditions, and high level interlock 1-1003 will automatically start whichever pump is on standby P-2121 AlB should a high level occur. A low/low level on 0-2102 will also actuate an interlock ESO-1205 which will close valve LV-1003A on P-2121AlB discharge to T-2150 and close valve LV-1003B on the disposal line to the drain. (This interlock is further described in Section 11.0 of this manual). The raw synthesis gas passes overhead from the separator 0-2102 and is directed to the CO2 absorber T-21 01 for the initial synthesis gas purification step. Pressure protection for 0-2102 and upstream equipment is provided by relief valve PRV-02102 on the Raw Gas Separator vapour outlet. A vent in the form of a manual by-pass round relief valve PRV-02102 is provided on the vapour outlet from 0-2102 for start-up and emergency venting of process

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gas upstream of the CO2 Absorber T-21 01. The line PG1 034-3" from the vapour outlet of D-2102 routes a Nitrogen/Hydrogen gas mixture to the Low Temperature Shift Converter inlet for catalyst reduction during start-up (Nitrogen circulation reduction step). A takeoff from the same line also supplies hydrogen at start-up to the suction of Feed Gas Compressor C-21 02. 3.1.3.1.2

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T-2101 - Carbon Dioxide Absorber The raw synthesis gas with most of the water removed flows through an internal distributor into the bottom section of the column and then upward through two packed beds. The column oIJerates at about 32.5 bara, the column top and bottom temperatures being about 50'C and 82'C respectively. A seal lute on the gas inlet line prevents backflow of solution during upset conditions. Regenerated (C02 free) aMDEA solution is pumped by P-2107A1B from stripping colurnn T-21 02 and after cooling by E-21 09 and E-211 0 is introduced through an internal distributor at the top of the T-1201 absorber colurnn and flows downward through the beds. A slipstream is taken from this stream through Filter F-21 04 before it enters the column. The flow into the column is controlled by FIC-1005. Low flow alarm FAL-1005 will cut in the standby P2107 pump if there is not a low level in stripper T-21 02 bottom pan i.e. LALL-1043 on T-1202 is healthy. Low Low flow alarm FALL-1205 will trip the Methanator R-21 06 via interlock ESD-21 06 to prevent the excessive temperature rise which would ensue if aMDEA solution flow is lost or severely restricted.

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The downward flowing solution is contacted with the upward flowing gas in the bed packing and selectively absorbs the CO2 from the gas, the other components of the gas stream having very low solubility in the aMDEA solution. The CO2 loaded (rich) solution collects in the bottom section of the column and exits under level control LlC-1 004 with LAH and LAL. A further bed of packing in the base of the column minimises gas entrainment in the solution. A sight glass is provided on the bottom pan. The rich solution at a pressure of about 32.5 bara is returned to the top of stripping column T-21 02 which operates at a pressure of about 1.8 bara. Power is recovered from the flowing solution by passing it through a hydraulic turbine, which assists the P-21 07A Lean solution purnp drive rnotor via a clutch. The level in the bottom pan is controlled by LlC-1 004, which controls LV-1004A, and 1004-B on split range. LV-1004A operates frorn 0.2 - 0.6 bar and LV-1004B frorn 0.6 -1.0 bar. The hydraulic turbine P-2107(H) load is set by HIC-1 005. The hydraulic turbine load should be adjusted such that LV-1004A has sufficient throughput to rnodulate and control the absorber level. In the event of a hydraulic turbine trip LV-1 004A1B have . sufficient capacity to handle the total solution flow.

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LALL-1204 will trip LV-1004A1B, HV-1005 and XV-1105 closed via manual reset solenoids LY -1 004A1B, HY-1005 and XY-1105 to prevent breakthrough of high pressure gas to the stripping column if the liquid seal in the absorber is lost. These . solenoids must be reset manually in the field to resume control when the absorber level is re-established The differential pressure across the column is indicated on PDI-1 042, which is provided with a high alarm. An increased DP may indicate foaming problems or excessive liquid loading in the column.

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Anti-foam injection points are provided on the rich solution return line to T-21 02 and on the suction line to P-21 07A1B.Anti- foam is supplied from pump set V-21 09. 3.1.3.1.3

D-2103 - CO 2 Absorber KO Drum The aMDEA solution absorbs essentially all of the CO2 that passes through the absorber. The absorber tower also has a demisting pad in the top through which the gas passes before leaving the tower, to knock out the bulk of any entrained carbonate solution. The effluent gas from the absorber overhead flows to the CO2 Absorber Knockout Drum D-21 03, for final removal of any entrained solution. This solution is removed from the system manually to the sump system. A high level alarm (LAH-1132) is provided on the knockout drum to warn of an abnormal level condition. Process gas leaving the top of D-21 03 then passes through the shell side of E-2114 AlB (Methanator Feed/Effluent Exchanger) before flowing to the Methanator (R-21 06) top inlet. Pressure controller PIC-100510cated on the Process gas line from D-21 03 to E-2114 and the Methanator will vent excess pressure to the Front End Flare.

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Piping is also provided from the outlet of D-21 03 to route process gas to:

3.1.3.1.4

(i)

Primary Reformer H-21 01 as excess synthesis gas to supplement the fuel gas and the flow is controlled by FIC-1178. Low low Flow Alarm FAL-1278 in the main control room will actuate interlock ESD-1031 which is override by HS-1081 on start-up.

(ii)

to the suction of C-21 02 as start-up hydrogen, and

(iii)

to R-21 09 for LTS catalyst reduction during start-up.

T -2102

- Carbon Dioxide Stripper

Regeneration of the circulating solution by removing the absorbed carbon dioxide is accomplished by steam stripping in the Carbon Dioxide Stripper T -2102 before the solution is recycled to the Absorber for reuse.

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The rich solution from the absorber is introduced into the LP flash section of Stripper T -2102 where the reduction in pressure causes CO 2 to flash off the solution. The solution then flows downward through a bed of packing. Steam generated in the stripper section of the column passes upward through the bed and strips more CO2 from the rich solution. Solution is pumped from the base of the LP flash section by pumps P-21 OaAlB through exchanger E-2112 and returned to the top of the stripping section at boiling point.

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This pumped flow is normally controlled by FIC-l017 controlling FV-l017. Should, however, the level in the draw off pan go outside the limits set by LlC-l 041, LlC1041 will override the flow controller until the level is once more within the limits. A sight glass is provided. High and low alarms are provided on LlC-l041. A minimum stop is provided on FV1017 to give minimum flow protection to pumps P-21 OaAlB. FALL-l017 low/low flow alarm will start the stand by p-21Oa via Interlock 1-1017. FALL-1217 will trip the Methanator via interlock ESD-21 06 to prevent excessive catalyst bed temperature rise in the event of loss of, or restricted aMDEA solution flow.

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The solution passes downwards through the beds of packing in the stripping section and meets an upward flow of stripping steam generated by process gas heated reboiler E-21 05 and LP steam heated reboiler E-2111. The now fully regenerated solution at about 125'C exits the column through Lean/Semi Lean exchanger E-2112 where it is cooled and routed to the suction of pumps P-21 07. Flow of lean solution to the Absorber from P-21 07 is controlled by FIC-l005. Low/low flow FALL-l 005 will autostart the spare P-21 07 via Interlock 1-1005, however, LALL-1043 on the bottom draw off pan of the column prevents autostart of the standby P-21 07 if there is a Low Low level in the pan. A sight glass is provided. Pumps P-21 07 return the lean solution to the top of the absorber column via exchangers E-21 09 and E-211 0 where it is further cooled to about 50'C. E-2109 is a fin fan cooler consisting of 5 bays with 2 fans per bay. The louvers on each bay can be opened or closed manually. The fan blade pitch will be set manually on one fan and the pitch on the other will be controlled by TIC -1224 sensing the exit aMDEA temperature. A slipstream is taken off this flow through filter F-21 04 to prevent a build up of particulate matter in the system. PDI-ll02 and PDAH-ll 02 give warning that the filter elements need changing. Local flow indicator FI-1113B and flow indicator FI1113A in main control room indicate the flow through the filter. aMDEA draining can be recovered to Sump tank TK-2115 when changing filter elements. Seal flushing for pumps P-21 07AlB and p-210aAlB is provided from downstream of E-2110. This flushing and also the seal flush for P-2111 and P-2112A1B can also be supplied from BFW pumps P-2104A1B via cooler SP-167 during start up

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conditions. The normal supply to condensate pumps P-2112A1B and aMDEA transfer pump P-2111 will always be from this source. A pumpout line to TK-2114 MD1002-3" is provided downstream of E-211 O. This line MUST be kept spaded off during normal operations to prevent any possibility of over-pressurising TK-2114. Note that the minimum stop must be taken off the block valve downstream of pumps P-21 07AlB on MD 1020-16" when pumping out the system to prevent pumping solution back into T-2101.

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Note also that T-21 02 MUST be depressurised before removing the spade from pumpout line MD 1002-3" to remove any possibility of high pressure gas entering TK-2114. The CO2 released from the rich solution and stripping steam exit the top of the stripping column through the contact cooler section and demister. This section is supplied with cooled quench water by pumps P-2116A1B via exchanger E-21 07 and has a demineralised water make up facility. Temperature controller TIC-1 006 output adjusts the setpoint of FIC-1 016, which controls the water flow via FV-1 016 to maintain the required temperature exit the column. FALL-1016 Lowllow flow alarm starts the standby P-2116 pump via interlock 1-1016. High and low temperature alarms are provided on TIC-1006. The pump draw off pan is provided with a sight glass and level indication from LI-1 040 that has a high and low level alarm.

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The contact cooler condenses the stripping steam and cools the CO2 to about 43°C before the major portion is exported from the plant for use in the production of Urea via CO2 Compressor C-41 02 located within the Ammonia Unit, with the balance being vented to atmosphere. The contact cooler also serves to remove any entrained aMDEA solution from the CO2 before it is supplied to the Urea plant. Vacuum breakers SP-009A1B/CI D&E and rupture disc SP-008 are also provided on the stripper overhead line. The carbon dioxide flows through a demisting pad and out the top of the Stripper (T-2102) where it can be either vented to atmosphere or sent to the Urea plant with the stripper pressure controlled by PIC-11 04. The total flow of CO2 product to the Urea Unit is metered by FI-1162 and FQI-1162 and is controlled by FRC-1024, which controls the discharge flow of CO2 Compressor C-41 02 by regulating the speed of the turbine driver. High and Low pressure alarms PAH-1104 and PAL-1104 provide a warning of changes caused by the Urea Plant. The stripper normally operates under 1.8 bara. at the top, and about 1.6 bara. at the bottom and any excess pressure not absorbed in the flow to the CO 2 Compressor, will· be vented to atmosphere via PIC-11 04. The pressure drop across the stripper internals is measured by PDI-1043, which also incorporates a High DP

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alarm (PDAH-1043). 3.1.3.1.5

Auxiliary Equipment Auxiliary equipment for the CO2 removal system consists of a main aMDEA Solution Storage Tank (TK-2114) and aMDEA Solution Sump (TK-2115) to collect solution from various points in the system. TK-2114 is used as the main storage tank for aMDEA solution prior to start-up and if required to drain down the removal system during shutdowns. aMDEA transfer Pump, P-2111 is used to transfer the contents to the CO2 removal system with P-2107NBbeing used to transfer from the removal system back to the tank. P2111 can be used to circulate solution through filter F-2115 back to the tank to clean up the system inventory.

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TK-2114 is provided with a Nitrogen purge facility and vent, relief valve, temperature and level indication and low level alarm. It should be noted that it is extremely important to ensure that the solution is regenerated and the Absorber depressurised before solution is transferred to TK-2114. Before TK-2114 is opened in any way it must be purged using a nitrogen connection at the sample point until suitable tests i.e. Drager, indicate that any hydrogen has been purged. If the tank is to be entered, then all the necessary precautions described in the Safety Manual for vessel entry must be strictly observed. Sump Tank TK-2115 is provided with a Sump Pump P-2115, which is used to circulate the recovered solution in the Sump and to transfer the recovered solution to TK-2114 either directly or via Filter F-2115.

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A level switchLlC-6704 with LAL and LAH is provided on TK-2115.Low level in TK2115 will shut down P-2115 via Interlock 1-6704 and activate low level alarm LAL-6704 to wam the operator should this condition occur,. High level alarm (LAH-6704) will start P-2115 via Interlock 1-6704. Local level and temperature indications are provided. There is also an aMDEA Antifoam Injection System (V-21 09) for charging anti-foam inhibitor agent to two locations in the system. Anti-fo~m inhibitor injection is routed to: • • 3.1.3.1.6

P-21 07 NB suction line (Semi-lean solution to Absorber). P-21 07 A(H) discharge line (Rich solution to stripper). C-4102 - CO2 COMPRESSOR (in urea plant)

C-41 02 CO2 Compressor is a 4-case/16-stage compressor with a gearbox, which increases the speed of the 3rd & 4th stages. The compressor is driven by a 6 stage, steam condensing turbine (C-4102[T]) driven by MP steam which exhausts

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as extraction steam to 0-4110 Extraction Steam Saturator; and LP Steam exhausting .and condensing in Surface Condenser E-4133. C-4102[T] is also provided with a Gland Steam Condenser E-4135. Lubrication oil for the compressor and turbine consist of a complete system, mounted in the base plate. The console consists of a reservoir (TK-4120), a main steam driven lube oil pump P-4130A, a motor driven standby pump P-4130B, a pair of lube oil coolers E-4134A & B, a Lube Oil Tank Heater H-41 01, a Primary Oil Filter F-41 05 and a motor driven Oil Purifier V-4124. An Oil Filling Pump (air driven) P-4145 together with a Lube Oil Rundown Tank 0-4123 and a Control Oil Accumulator 0-4124 are also provided. A pressure control system and ancillary piping are also provided. The coolers and filters are provided with suitable valving and linkages so that change over is accomplished without interrupting the oil flow but it should be noted that the standby cooler and filter must be completely filled with oil before being put into service. The compressor is supplied with a number of alarms and trips which function, either to wam, or shutdown after previous warning, when potentially damaging conditions are approached. Any alarm condition will operate a common trouble alarm in the control room whilst the actual alarm will display on the local compressor alarm panel. Alarm conditions should be corrected as quickly as possible, especially those that are associated with a trip that operates if the condition is allowed to deteriorate. The design of the compressor is based on a mixture of Carbon Oioxide (87.9%), Oxygen (1.4%), Nitrogen (4.8%), Hydrogen (0.45%) & Water Vapour (4.8%) being supplied to the first stage from the CO2 Stripper T-21 02 on the Ammonia Unit together with a small amount of air from the 2nd stage suction of Air Compressor (C-2101).

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The compressor takes suction from 0-4101 Knockout Drum at 1.7 bara and 39.8°C. 0-4101 is provided with a level controller L1C-1 003, which disposes of any knocked out water to Process Condensate Drum 0-2161. In the event of a high level in 0-4101, the operator will be alerted by High Level alarm LAH-1003 and should the situation not be remedied, a High/High Level switch LSHH-1001 will actuate shutdown interlock 1-4102C and shut down the compressor. Similarly a Low/Low Pressure switch PSLL-1001 located on the suction line from 0-4101 will also actuate Interlock 1-4102C and shut down C-41 02. The compressed mixture exits the 1st stage at 6.7 bara and 177°C and after cooling in E-4130 Compressor first stage intercooler, enters the First Stage Separator 0-4130 where more moisture is knocked-out and disposed of by level controller L1C-1 012 to Waste Condensate Stripper T-2125. Again a High/High Level occurring in 0-4130 will actuate Interlock 1-4102C and shut down the compressor. The temperature leaving Intercooler E-4130 is controlled at 40°C by TIC-1013, which regulates the flow of gas through and round the intercooler.

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The CO2 mixture enters the second section of the LP case at 6.4 bara and here it is compressed to 24 bara at 1S0°C and routed to R-41 02 Hydrogen Converter where hydrogen and other combustibles present are reduced by catalytic reduction. Should over-reaction occur in R-41 02, then a High/High Temperature switch TSHH-1019 will actuate Interlock 1-1019F and cause C-41 02[T] to go to minimum speed. This interlock will be described in greater detail in a later section. In normal operation the temperature of the gas leaving R-41 02 will have increased to 24SoC and it is then cooled in E-4131 Second Stage Intercooler to 40°C (controlled by TIC-1022), before entering D-4131 Second Stage Separator. Any moisture is again knocked-out and discharged to T-2125 by Level Controller L1C-1023 and in the event of a HigJi/High Level in D-4131, Interlock 1-4102C will shutdown C-41 02.

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The CO2 mixture then enters the first section of the HP case of the compressor where it is compressed to 7S.5 bara and 170°C before cooling in Third Stage Intercooler E-4132 to 50°C (controlled by TIC-1035) and moisture removal in Third Stage Separator D-4132 prior to final compression in the 4th Stage to 146.4 bara and 114°C for delivery to the process. The turbine speed is controlled by FRC-1 024, which regulates the flow of carbon dioxide from the 4th stage discharge. FRC-1024 will control the turbine speed and on minimum signal from FRC-1024, will go to minimum speed. C-4102 may be shutdown manually by HS-1006A in the main control room or by local shutdown switch HS-1006B. (reset by HS-1007 in the main control room) which actuates shutdown device Interlock 1-41 02C to be described in detail in a later section. Valve XV-1 023 on the 4th Stage discharge line may be closed either by push button HS-1025 action, or as a result of one or more of the following interlocks being actuated: • • •

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1-4102C 1-1001H 1-1019T -

C-41 02 CO2 Compressor SID HP Ammonia Pump Shutdown Hydrogen Converter High Temperature

Actuation of any of these interlocks will also open the 2nd Stage Kickback to D-4101 and 4th Stage Kickback to D-4131 ; and close the valve on the main air supply line to the Urea Unit. 3.1.3.2

Process Condensate Drum D-2161 The condensate from the CO2 Compressor drums D-4130/1/2 together with condensate from D-4101 CO2 • Compressor Suction Knockout Drum, the condensate from C21 01 air compressor intercoolers and the overflow from R-21 03 water jackets is collected in Process Condensate Drum D-2161. The CO2 in the condensate from the CO2 compressor intercoolers is allowed to flash off . The condensate is then pumped to Offsites by pumps P-2161A1B for recovery. The level is controlled by L1C-1098. High and Low level alarms are provided.

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Process Condensate Stripper - T-2150 Process condensate from D-21 04 (Synthesis. Gas Compo Suction Drum) and D-21 05 (Synthesis. Gas Interstage Separator) is collected in the Raw Gas Separator, D-21 02 to be recovered and reused in the Ammonia plant. Process condensate can contain up to 1,000 ppm by wt. Ammonia; 3,000 ppm by wt. Carbon Dioxide, 500 ppm by wt. Methanol, and a trace of amines.

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Before it is exported to the offsite demineralisation plant, the condensate is stripped by counter current contact with medium pressure steam in the Process Condensate Stripper, T-2150. The recovered condensate will contain about 5ppmw ammonia, 5 ppmw carbon dioxide and 35 ppmw Methanol and higher alcohols. The condensate collected in the Raw Gas Separator D-21 02, is pumped by Condensate Pumps P-2121AlB to T-2150 via the Condensate Feed/EOffluent Exchanger E-2188 where it is preheated against stripped condensate leaving T -2150. It enters the stripper through a distribution pipe above two beds of slotted rings and heat for stripping is provided by MP Steam injection to the base of the tower under flow control of FIC-1019. In the event of a low/low level in D-21 02 Raw Gas Separator, sounding alarm LALL-1205 will warn the operators and the interlock ESD-1205 will be actuated which will close the level control valves on P-2121AlB discharge to T-2150 and on the Offsites disposal line.

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The condensate flows downward over the packing beds making intimate contact with the counter-flowing stripping steam and vapours of ammonia, CO2 etc. are liberated from the condensate by stripping action of the MP steam. The steam vapours exit the tower at the top and after being mixed with additional steam, is recycled back into the process via the mixed feed preheat coil as part of the mixed gas feed to the Primary Reformer. In the event of a high differential pressure across the two beds of slotted rings, interlock ESD-1069 will be actuated which will close control valve FIC-1 019 on the vapour line exiting the top of the tower. Interlock ESD-1 069 will also close the control valve on the discharge line of condensate pumps P-2121 AlB to E-2188. The stripped process condensate from the bottom of T-2150 flows to offsite storage after passing through the Feed/Effluent Exchanger E-2188 and then further cooled in Air Cooler E-2174. This flow is regulated by the stripper bottoms level controller LlC-1025 that is provided with High level alarm LAH-1025 and Low Level Alarm LAL-1025. An analyser AE-1017 is also provided downstream of E-2174 to indicate the conductivity of the condensate being routed to Offsites and to alert the operator if alarm AAH-1017 exceeds a preset limit and of the need to switch to alternative off-specification disposal. Air Cooler E-2174 has a one bay fitted with three fans and has a manual lever for louver adjustment. The fan blade pitch will be set manually on one fan and controlled

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automatically on the other two by TIC-1226. High (TAH-1652) & low (TAL-1652) temperature alarms are also provided on E-2174 outlet line.

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3.1.3.4

Methanation (Conversion of Carbon Oxides)

3.1.3.4.1

R-2106 - Methanator The preheated process gas from D-21 03 leaving the shell outlet of Methanator Feed/Effluent Exchanger E-2114 may be further heated in Methanator Feed Heater, E-2172 as necessary prior to entering the top inlet of the Methanator (R-2106). On pressure increase at the inlet, the "Anti-reset-wind-up" controller PIC-1005 upstream of exchangers E-2114 AlB will open and vent process gas to the Front End Flare. The temperature of the process gas entering the Methanator is controlled by TRC-1012 which is split ranged between a control valve TV-1012 located on the shell bypass of E-2114 and a control valve PV-11S0 on the HP steam supply to the Feed Heater E-2172. E-2172 may also be used during the start-up to heat the nitrogen being circulated during the reduction of the LT Shift catalyst. The flow passes through the Methanator high nickel base catalyst and leaves the vessel at the bottom outlet. If the process gas exiting the CO2 Absorber contains excess carbon oxides the temperature in the Methanator will become too high and activate high temperature alarms TAH-1357 through 1362. The Methanator is protected against dangerously high temperatures by shutdown switches TSHH-1200 through 1203, which actuate shutdown interlock ESD-2106. (This interlock is described in further detail in Section 11.0 of this manual).

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Should the bed temperature exceed the set temperatures of anyone switch TSHH-1200 through TSHH-1203,then interlock ESD-21 06 will be actuated and the two Methanator inlet valves HV-1034 and XV-1211 will close stopping all flow to the Methanator. As a result the pressure controller PIC-1005 in the inlet line will open to vent the feed gas to the Front End Flare. The Methanator trips should be set at approximately 27"C below the maximum allowable operating temperature set by the catalyst manufacturer. As a further protection against high run-away temperatures in the Methanator due to a CO2 breakthrough from the aMDEA system, Interlock ESD-2106 will also automatically shutdown the Methanator if the lean solution flow to the CO2 Absorber drops below a preset rate as sensed by lOW/low flow switch FSLL-1205 measured on FT-1205 or if the semi-lean flow from the LP flash section of the CO2 stripper drops below the preset rate as sensed by low/low switch FSLL-1217 measured on FT-1217. The Methanator may also be shutdown by activating push-button HS-1253 which also actuates interlock ESD-2106 and will shut HV-1034 and XV-1211 in the Methanator inlet line. Once tripped, the solenoid controlling XV-1211 needs to be manually reset before this valve can be opened. If the Methanator Feed Heater (E-2172) is in service, then interlock ESD-21 06 will also close the HP steam supply

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to the tubes. Upon a temperature excursion trip, the Methanator catalyst is cooled down by a manually initiated reverse nitrogen flow from the outlet line at the bottom to the atmospheric venton the inlet line. From the Methanator, the flow is first cooled in the tube side of the Methanator Feed/Effluent Exchanger E-2114 and then by a one bay Methanator Effluent Air Cooler E-2118 with 3 fans. The bay has a manual lever for louver adjustment and the fan blade pitch will be set manually on one fan and the other two will be, controlled automatfcally by TIC-1627 located on the outlet from E-2115 to 0-2104 on the other. Final cooling is by Methanator effluent trim cooler E-2115 using cooling water on the tube side. A high temperature alarm is provided on the outlet from E-2115to 0-2104 (TAH-1618).

c 3.1.3.4.2

0-2104 - Synthesis Gas Compressor Suction Orum From cooler E-2115, the flow goes to the Synthesis Gas Suction Orum (0-2104). Entrained water vapour in the process gas is separated in 0-2104 and pumped under level control of LlC-1008 (fitted with high and low alarms LAH/L 1008) by LP Condensate Pump P-2150NB to the Raw Gas Separator (0-2102) for onward treatment in the Process Condensate Stripper (T2150). Condensate from 0-2105, Synthesis Gas Compressor Interstage Suction Orum is also routed via Oil Filter F2102 into 0-2104. Facilities are also provided to drain 0-2104 to the oily water sewer. 0-2104 is also fitted with LT -1208NB/C and associated High/High level alarms, LAHH-1208NB/C. Through a voting system of 2 out of 3 of these alarms, interlock ESO-2103 will be actuated and will shutdown C-21 03, Synthesis Gas Compressor. (This interlock is described in further detail in Section 11.0 of this manual).

c

Gas to Synthesis Gas Compressor (C-21 03) exits from the top of 0-2104 through a demister pad. Pressure controller PRC-1006 on 0-2104 regulates C-21 03 turbine speed and synthesis gas from 0-2104 may also be routed to the ammonia vent via PIC-1 004 whenC-21 03 is shut-down or excess synthesis gas is vented. A manual sample point (S-014) together with analysers for total carbon oxides (AR-1 002), hydrogen (AR-1031), nitrogen (AR-1032) and methane (AR-1033) are located on 0-2104 outlet line to C-21 03. Prior to entering the 1st stage of C-21 03 compressor, the process gas stream from 0-2104 is joined by the L.P. case kickback flow controlled by FIC-1007. 3.1.4 Ammonia Production 3.1.4.1

Compression of Purified Synthesis Gas Compression of the purified synthesis gas by the Synthesis Gas Compressor

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(C-2103) is the first step in the liquid ammonia production phase of the process. C-21 03 compressor is a two-case mUlti-stage compressor driven by an extraction! condensing type turbine arranged with a drive shaft at each end connected to the two compressor case rotors. The turbine is driven by HP steam, which exhausts to the MP steam system with a small quantity going to the condensing stage, which then exhausts to the surface condenser E-2140.

c

The compressor cases and the turbine are provided with lube oil console which includes a turbine driven lube oil pump a motor driven auxiliary lube oil pump, a lube oil filter and a lube oil cooler. A low lube oil pressure alarm, auxiliary pump start-up, driver shutdown and shutdown alarm are provided. The compressor is fitled with dry gas seals. The compressor instruments are on a locally mounted board and in addition, a common trouble alarm is mounted on the control room panel. The low pressure compressor case receives gas from the suction drum 0-2104 at about 30.4 barg and 39°C and compresses the gas to about 67 bara at 150°C. The gas leaving the first case is cooled by BFW in preheater E-2117 and by cooling water in inter-cooler E-2116. The gas is then subcooled by ammonia refrigerant in . interstage chiller, E-2129 to 4.4°C before entering the high pressure case via 0-2105, Interstage Separator at about 66.B bara where it is compressed to about 144 bara From the last chiller (E-2129), the flow enters the Interstage Separator (0-2105) where all condensed liquid (mainly water) is returned via LP Condensate Oil Filter F-21 02 to 0-2104 for routing via 0-2102 to the Process Condensate Stripper and!or offsite disposal. 0-2105 is provided with high (LAH-1011) and low (LAL-1011) liquid level alarms and high/high level will actuate C-21 03 shutdown interlock ESO-21 03. (Oescribed in detail in Section 11.0 of this manual).

c

After passing through a demisting pad, the dry synthesis gas leaves the top of the separator and after being joined by the synthesis gas compressor H.P. case "kickback" flow controlled by FIC-1 OOB, enters the suction of the H.P. case machine. Gas from 0-2105 passes through twin check valves of dissimilar type (to reduce the likelihood of common mode failure) into the suction of the H.P. compressor case, round which there is a bypass line with a restriction orifice. When HV-1001 and HV-1031 trip closed, this bypass and orifice serves to depressurise the H.P. case to L.P. case pressure after compressor shutdown. From the top of the 0-2105 separator, a synthesis gas stream regulated by FIC-1007 directs gas back to the suction of the L.P. case machine for L.P. case "kickback" control. FIC-1007 in conjunction with FIC-100B is provided to enable the operator to keep the compressor out of "surge" condition by satisfying the machine's minimum flow requirements. Both FIC-1007 and 1008 are provided with "Anti-reset-wind-up" facilities and the line steam traced for their entire lengths to prevent condensation occurring.

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PROJ-PM-008

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In the H.P. case of the compressor the cooled synthesis gas (from the first stage separator) is further compressed and is joined by the recycle synthesis gas from the ammonia converter, which enters the side of the H.P. case machine at the 3rd Stage inlet. Since the amount of recycle stream received from the converter is much greater than the quantity of fresh feed, and since the instrumented kickback FIC-1008 satisfies only the first (make-up) wheels; the last wheel depends on the adjustment of the discharge - to - recycle bypass HIC-1030 until the compressor is running "all-ouf'. The 2 inch by-pass around valve HV-1 001 on the discharge line to E-2120, will be used for controlling the flow to the synthesis loop at start-up.

c

The main operating control for the synthesis gas compressor is via the governor of the driving turbine. The governor is reset by PRC-1012 which will regulate the amount of steam letting-down through the turbine into the MP steam header to control the HP steam header pressure; and by PRC-1 006 which adjusts the steam valves of the condensing stage to regulate the compressor speed as necessary for control of the pressure on the Compressor Suction Orum 0-2104. An HP steam to MP steam by-pass system round C-21 03[T] is provided which with the unit in normal operation, remains in a closed position. Activation of turbine trip system will, however, cause the valve to open. This HP to MP steam letdown valve may be actuated either automatically by Interlock ESO-2103 and ESO-21 05, or manually by the manual indicator controller HIC-1 028 and HIC-1029 located in the main control room during early periods of operation or unusual and emergency conditions. This HP to MP Steam let-down station will be described in more detail in a later section. Particular care should be taken during the conditioning of C-21 03[T] and C-21 05[T] turbines to be sure that the HP to MP steam let down valves are adjusted properly to pass the required steam flow when in the tripped position.

c

C-2103 may be shutdown manually by HS-1203A in the main control room or by local shutdown switch HS-1203B. A shutdown interlock ESO-2103 is also provided and this will be described in detail in a later section. The combined recycle and fresh feed stream discharged from the HP case to the synthesis loop is cooled in the tubes of the Ammonia Synthesis Loop Cooler E-2124 and as previously mentioned, the HP case anti-surge controller FIC-1008 routes a kickback flow from downstream of E-2124 to the HP case suction when necessary, to maintain the case suction flow above its minimum value. The L.P. case of the synthesis gas compressor is pressure protected by PSV-02105 set at 73.0 barg located at the outlet of the first stage separator (0-2105) and the H.P. case compressor by PSV-C2103 set at 154 barg in the discharge line of the H.P. case machine. The discharges of the low and high-pressure cases are provided with high temperature alarms, TAH-1364 and T AH-1367A respectively. The synthesis recycle

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suction is provided with a high (TAH-1366) and low (TAL-1366) temperature alarm. Pneumatically operated valves HV-1001 and HV-1 031 are provided in the H.P. case cooled discharge and synthesis gas recycle lines respectively. They are closed by action of C-21 03 shutdown interlock ;ESO-21 03 described in detail in Section 11.0 of this manual. The HV's 1001 and 1031 can be manually opened or closed by push buttons HIC-1001 and HIC-1031. 3.1.4.2

Conversion of Purified Synthesis Gas to Ammonia

3.1.4.2.1

E-2120 - Ammonia Unitised Chiller

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The high pressure synthesis gas after leaving the E-2124 Loop Cooler is further cooled in the "unitised" exchanger E-2120 by heat exchange with ammonia refrigerant from 0-2120, 0-2121, 0-2122 & 0-2123 and cooled vapours from 0-2106. In E-2120, ammonia refrigerant is routed to the four (4) shell sections from 0-2120, 0-2121, 0-2122 & 0-2123. The tube section consists of multiple concentric tubes with vapours from 0-2106 passing through the centre tubes and the synthesis gas and ammonia converter effluent from C-21 03/E-2124 passes through the annuli. Thus the converter effluent is being cooled from the outside by ammonia refrigerant and from the inside by vapour from the Secondary Flash Separator (0-2106). 3.1.4.2.2

c

0-2106 - Secondary Flash Separator The chilled stream enters the Secondary Flash Separator 0-2106 via a horizontal distributor. Ammonia from the recycle stream condenses out in the chillers and settles in 0-2106. The Separator is provided with High (LAH-1 013) and low (LAL-1013) level alarms and the presence of liquid can be checked locally by tricocks. An extra high level in 0-2106 will actuate C-21 03 compressor shutdown interlock ESO-21 03. (Refer to Section 11.0 of this manual for further details of this interlock). The synthesis recycle gas passes through the demisting pads at the top of the ammonia separator going to the ammonia synthesis system as a continuation of the synthesis recycle gas loop and comprises feed to the ammonia converter. Leaving the Secondary Flash Separator drum the recycle gas flow enters the tube centre inlet of the Unitised Chiller (E-2120) to take up heat from the process flow in the tube annuli. From the tube centre outlet of this exchanger the flow enters the tube side inlet of the Ammonia Conv. Feed/Effi. Exchanger (E-2121) and continues on to the inlet of the Ammonia Converter (R-21 05). The ammonia product that is separated from the synthesis gas loop in the Secondary Flash Separator, 0-2106, is sUb-cooled for maximum ammonia condensation before being level controlled by LlC-1013to 0-2107. This sub-cooling at the normal operating pressure of the synthesis gas loop will cause

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SPEC. TYPE: CLASS DOC NO.

PROJ-PM-008

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some gas (hydrogen, nitrogen, methane and argon) to be absorbed by the liquid and results in contaminated ammonia product. At the inlet of the tube side of E-2121, the synthesis gas is analysed for Hydrogen (AR-1041), Nitrogen (AR-1042), Methane (AR-1043), Argon (AR-1044) and Ammonia (AR-1045). 3.1.4.3

D-2107 - Ammonia Letdown Drum To remove the absorbed gases from the ammonia product it is first flashed in D-21 07, Ammonia Letdown Drum. D-21 07 receives its feed from D-21 06 where the net ammonia make has been separated from the synthesis gas, together with a small import flow from the Purge Gas Separator D-21 08. LlC-1 013 regulates the flow of liquid being letdown under pressure to D-21 07 from D-21 06.

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PIC-1108 releases the flash gas leaving D-21 07 to the Purge Gas Scrubber T-21 03 for the recovery of ammonia, but is set to hold design back-pressure to prevent over-flash. The liquid stream from D-21 07 is let down to two pOints in the refrigeration system under the level control of LlC-1012 with the actual routing being selected by the hand switch HS-1024. If this switch is set for "COLD" product operation, then approximately 74% of the liquid flow from D-21 07 will be let-down to the 1st Stage Refrigerant Flash Drum ( D-2120) with the balance being routed to D-2123 under the control of LlC-1012. If 'WARM" product operation is selected, then the liquid flow will be letdown to the 4th Stage Refrigerant Flash Drum ( D- 2123). In both cases tlash vapour is routed to the Ammonia Gas Scrubber via the Refrigerant Receiver D-21 09. (A more detailed description of the 'WARM" and "COLD" product operations is contained in Sections 7.5 and 7.6 of this manual). Control of the Ammonia Converter (R21 05) inlet temperature is by means of HIC-1026 on the main control panel, which regulates the flow of synthesis gas round the tube side of E-2121. After receiving some preheat from the converter effluent in E-2121, the synthesis gas enters the Ammonia Converter via main inlet valve SP-173 and bed quench valve HIC-1025. SP-006, a special rupture disc assembly, is located around SP-173 to protect E-2121 exchanger against excessive differential pressure if one side of the exchanger is depressurised by closure of SP-173 and/or the converter quench valves, HIC-1025.

c 3;1.4.4

R-2105 - Ammonia Converter Synthesis gas from E-2121 is introduced at one end of the external shell of the converter and flows along the annulus between the external pressure shell and catalyst basket towards the opposite end of the converter. This arrangement limits the temperature to which the external shell is exposed. On reaching the opposite end of the converter, the synthesis gas enters an opening in the end plate and flows across the external surfaces of E-2122 tubes. After passing across the outside surfaces of the tubes the synthesis gas enters a partitioned plenum where it is directed to the distributor above the first bed. On exiting bed no. 1, the synthesis gas re-enters the partitioned plenum where it is directed through the tubes of E-2122.

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SPEC. TYPE: CLASS OOCNO.

PROJ-PM-008

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REVISION:

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The synthesis gas exits E-2122 tubes and re-enters the plenum where it is directed through a distributor pipe to the top of bed no. 2A. The gas passes down through bed no. 2A and is then directed to the top of bed no. 2B. A further reaction takes place in bed 2B after which the gas exits the converter shell through an internal piping arrangement at the feed inlet end. Heat from the Ammonia synthesis reaction raises the gas temperature from the first bed to around 496°C. The effluent gas flows through the tube side of the interchanger, which cools the gas to about 387°C before passing over the second catalyst bed. The second catalyst bed is divided into two physical beds in series to ensure uniform flow over the catalyst. Further reaction in the second bed raises the converter outlet temperature to about 457°C and the ammonia concentration to 15.75 mol%. A bypass line around the converter, controlled by valve HIC-1025, is provided to permit introduction of feed gas to the first catalyst bed without preheating for temperature control. It is usually referred too as "quench".

c

The design feature of an intercooled converter has the advantages of producing a relatively high ammonia concentration per pass and making the heat available in the converter effluent at a temperature sufficient for the production of high pressure steam. 3.1.4.5

H-2102 - Start-up Heater The ammonia synthesis converter is equipped with a start-up heater (H-21 02). This heater is used to heat the converter catalyst up to reaction temperature during the start-up. The start-up heater feed flow is indicated on FI-1257and low/lowflow (FALL-1257) will actuate heater shutdown interlock ESO-2116 and shut down the heater burners. A high/high pressure on the inlet line to H-21 02 (PAHH-1196) will also actuate interlock ESO-2116. (A full description of interlock ESO-2116 is included in Section 11.0 of this manual)

c

There is a high temperature alarm (TAH-1689) located on the heater outlet line to the converter in addition to a high temperature alarm (TAH-1397) on the flue gas exiting the stack. High high temperature on the heater outlet line (TI-1396) will also actuate interlock ESO-2116 and TAHH-1396 will warn operator in main control room.

3.1.5 Refrigeration And Ammonia Product Purification 3.1.5.1

Removal of Inerts

A purge is taken from the synthesis loop to control the concentration of methane and argon in the loop since a build-up of these components is reflected in lower ammonia conversion. Part of the converter effluent gas exiting the shell side of E-2121 is therefore routed as purge gas which is chilled in Purge Gas Chiller E-2125 before entering the Purge Gas Separator 0-2108.

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0-2108 - Purge Gas Separator Purge gas exiting the top of 0-2108 is flow controlled by FIC-1 013 and routed to the bottom of Purge Gas Scrubber T-21 03. Analysers on the outlet line from 0-2108 to T-21 03 record the Hydrogen (AR-1061), Nitrogen (AR-1062), Methane (AR-1063), Argon (AR-1064) and Ammonia (AR-1065) contents in the gas. Liquid ammonia from 0-2108 is pressured to 0-2107 for recovery with controller LlC-1 014 with its associated high (LAH-1014) and low (LAL-1014) alarms controlling the liquid level in 0-2108.

3.1.5.1.2

c

C-2105 - Ammonia Refrigerant Compressor The Ammonia Refrigerant Compressor C-21 05 is a double case (four stage) machine with interstage coolers and driven by a non-condensing type steam turbine C-2105(T) exhausting to the MP steam system. Lubrication and governor oil for the compressor and turbine consist of a complete system shared with C-21 03 Synthesis Gas Compressor and as described previously for C-21 03. The compressor speed is set by the turbine governor in response to a signal from the compressor suction pressure controller PRC-100910cated on 0-2120 1st Stage Refrigerant Orum. The major duty on C-21 05 is the "unitised" exchanger E-2120 that takes up heat from the synthesis loop. The four sections of E-2120 operate at different pressure levels dictated by refrigerant flash drum temperature requirements. The ammonia refrigeration requirements for each section of E-2120 being proportional to the heat input from the synthesis gas tube side. Therefore there are intermediate suctions to the compressor that satisfy the pressure requirements of the 2nd (0-2121), 3rd (0-2122) and 4th (0-2123) Stage Refrigerant Orums.

c

There is a heat load on the third stage flash drum 0-2122 from the ammonia returned from the Urea Granulation cooler E-4204 and Steam condensate chiller E-4153. The first stage of the L.P. case recovers ammonia vapours from the 1st Stage Refrigerant Orum 0-2120 at 0.9 bara and -35°C together with any vapours being returned from the Storage tanks. At the entry to the second stage of the L.P. case, the first stage discharge is joined by ammonia vapour from the 2nd Stage Refrigerant Orum 0-2121. The discharge of the L.P. case is first cooled in inter-stage cooler E-2167 and then joined by the flash vapour from the 3rd stage Refrigerant Orum (0-2122) and passes into the H.P. case for compression in the third stage. The 3rd stage discharge is then cooled in inter-stage cooler E-2128, joined by the vapours leaving the 4th stage Flash Orum 0-2123 and enters the compressor for 4th stage compression and final discharge to the Refrigerant Condenser, E-2127 at about 15.6 bara.

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PROJ-PM-008

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To satisfy the compressor minimum flow requirements and to prevent compressor surge, a part of the compressor discharge flow must return to the flash drums 0-2120,0-2121,0-2122 & 0-2123 via the kickback controllers FIC-1012, FIC-1011, FIC-1010 and FIC-1009 respectively. These controllers regulate kickback ammonia vapour flows from each of the four discharge stages of the compressor to control surge whenever the system load is considerably less than design. C-21 05 compressor can be shut down by interlock ESO-21 05, which is either actuated manually by switch HS-1205A1B or automatically by various other devices necessary for full protection of the refrigeration machine. Interlock ESO-2105 is described in detail in Section 11 .0. of this manual.

c

A similar HP steam to MP steam by-pass system to that described previously for C-21 03 Synthesis Gas Compressor turbine is provided and described in detail in Section 11.0 of this manual. Particular care must be taken during the start-up of C-2105[T] and C-21 03[T] turbines to ensure that the HP to MP steam letdown valves are adiusted properly to pass the required steam flow when in the tripped position. 3.1.5.1.3

0-2109 - Refrigerant Receiver The compressed flash gases (ammonia plus inerts) that leave the Ammonia Compressor C-21 05 are sub-cooled in the Refrigerant Condenser E-2127 before being routed into 0-2109, Refrigerant receiver. Trapped inert gases from E-2127 are vented to 0-2109 via the purge connection located on the top of the condenser shell.

c

The inerts that flash from the subcooled ammonia in this drum in excess of pressure control requirements are routed to the Purge Gas Scrubber T-21 03 for ammonia recovery, under pressure control of PIC-11 09. When on 'WARM" ammonia production, a fixed flow of liquid ammonia will be pumped to the Urea Unit under control of FIC-1168 flow controller. The level in 0-2109 will then be held constant by level controller LlC-1 015 allowing the balance to flash down to the 4th Stage Refrigerant Drum, 0-2123. High (LAH-1 015) and low (LAL-1 015) are provided on 0-2109. On "COLD" ammonia production, the flow to the Urea Unit will be zero with 0-2109 total level being flashed down to D-2123. (A detailed description of the 'WARM" and "COLD" methods of operation is described in Sections 7.5 and 7.6 of this manual). The Ammonia Reflux Pumps P-2120AlB for the Ammonia Stripper T-21 04 also takes suction from 0-2109. These pumps are also used during start-up to route warm liquid ammonia to E-2124 shell inlet to prevent freezing of the water in the process side of E-2120 Chiller since an aqua ammonia solution has a freezing point well below the E-2120 operating temperature. Ammonia from 0-2109 also furnishes quench (required at start-up) to the 1st, 2nd,

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3rd and 4th Stage Refrigeration Drums and globe valves are provided in the individual quench lines to hand control the refrigerant flows. 3.1 .S.1.4

D-2120 - 1st Stage Refrigerant Flash Drum This Flash Drum serves the process in three ways: first, by a deep over-flash essentially all the inerts are removed from the ammonia product. Second, it serves as a "head drum" for the thermal circulating refrigerant that is removing heat from the synthesis gas loop via the "cold" section of E-2120. Third, it receives the flashed ammonia let down from the 2nd Stage Refrigerant Drum D-2121 via the Purge Gas Chiller E-212S.

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The pressure on D-2120 is controlled by PIC-1009, which regulates the speed of C-21 OS compressor driver. Liquid ammonia in D-2120 is circulated by thermoSyphon effect through the fourth section of the "Unitised" Exchanger, E-2120 . "COLD" product ammonia is routed to storage by Cold NH3 Product Pumps P-2124A!B/C under level control of LlC-1024 on D-2120. Should a high/high level condition occur, LAHH-1217A!B/C will activate on a 2 out of 3 voting system and interlock ESD-210S will shut down Refrigerant Compressor C-21 OS. 3.1.S.1.S

D-2121 - 2nd Stage Refrigerant Flash Drum As with the other Flash Drums, the pressure (and resulting temperature) of D-2121 is not variable as it floats on the suction of the first stage case of the Ammonia Compressor C-21 OS. Liquid in D-2121 is circulated by thermosyphon effect through the third section of E-2120. Refrigerant from D-2121 is also used to maintain a level in the shell side of the Purge Gas Chiller E-212S under the control of level controller LlC-1116 with the vapour being retumed to the 1st Stage Suction Drum D-2120. Excess liquid from D-2121 is then transferred to D-2120 under level control of LlC-1023, which incorporates high and low level alarms. Should a high/high level occur, then LAHH1216A!B/C, on a 2 out of 3 voting system will actuate ESD-21OS and shutdown C-21 OS.

c 3.1.S.1.6

D-2122 - 3rd Stage Refrigerant Flash Drum Again the pressure (and resulting temperature) of D-2122 is not variable as it floats on the suction to the second case of C-21 OS Ammonia Compressor. Liquid ammonia in D-2122 is circulated by thermosyphon effect through the second section of E-2120 with the level held constant by LlC-1022 routing excess liquid ammonia to the 2nd Stage Flash Drum D-2121. LlC-1022 also incorporates High (LAH-1022) & Low (LAL-1022) level alarms. Should a high/high level occur, then LAHH-121SA!B/C, on a 2 out of 3 voting system, will actuate ESD-21 OS to shutdown C-21 OS ..

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3.1.5.1.7

5777'

SPEC. TYPE: CLASS OOCNO.

PROJ-PM-008

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0-2123 - 4th Stage Refrigerant Flash Orum All of the ammonia that is not sent to the battery limits as "WARM" product from Refrigerant Receiver 0-2109 with the exception of the flow to 0-2120; together with ammonia from Ammonia Letdown Orum 0-2107, is routed to 0-2123. Liquid in 0-2123 is circulated by thermosyphon effect through the first section of E-2120 and also supplies Synthesis Gas Compressor Interstage Chiller E-2129. Excess liquid ammonia is transferred to 0-2122 under level control of L1C-1021 , which incorporates high and low level alarms. Should a high/high level occur, then LAHH-1214A1B/C, on a 2 out of 3 voting system, will activate ESO-2105 and shutdown C-21 05 and close valve LV-1 015 on the supply line from 0-2109 to 0-2123.

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The ammonia converter effluent stream is cooled by heat exchange giving up heat to boiler feed water in Waste Heat Boilers E-2123A & B, and to the converter feed in E-2121 before returning to the Recycle Gas Compressor C-21 03 to be recycled back to the converter. Before the recycle gas (plus fresh feed) re-enters the converter, it is routed via the unitised chiller system to condense out the net ammonia make produced on its previous pass through the converter. The synthesis gas loop has all the temperature indicators and recorders, pressure differential indicators and hand control valves (HCV's) to observe and control process conditions within the "loop". There are also special emergency valves that isolate the recycle compressor from the synthesis gas loop under certain conditions. These are described in Section 11 of this manual.

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3.1.5.2

Ammonia Recovery from Purge Gases

3.1.5.2.1

T-2103 - Purge Gas Scrubber Purge gases from the synthesis loop containing ammonia vapours are treated in the ammonia recovery section (T-2103 Purge Gas Scrubber and T-21 04 Ammonia Stripper) and ammonia vapours are returned to E-2127 Refrigerant Condenser and thus to 0-2109 Refrigerant Receiver. . Gases from 0-2107, 0-2108 & 0-2109 are routed to the base of the Purge Gas Scrubber (T-2103). The upflowing gases mix with a counter-current flow of water through a packed bed of stainless steel rings. The Scrubber purge gas feed, washed clean of arnmonia, passes through a demister pad and is routed to the Fuel Gas Preheat Coil in the Primary Reformer convection section under pressure control of PIC-1033. It should be noted that the loss of this flow of purge gas to the fuel gas system will have the effect of substantially increasing the calorific value of the feed gas being

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used by the Primary Reformer burners and will cause the tube outlet temperature to rise. Flow indicator FI-1258 together with low flow alarm FAL-1258 is therefore provided on the purge gas supply line to the fuel gas, which will alert the operator to the need to reduce the arch burner firing. Should the purge gas flow continue to fall, then interlock ESD-1 031 will be actuated. This interlock may also be actuated by 2 out of 3 low/low pressure switches located on the fuel gas supply line to each row of arch burners and set at 0.2 barg when firing on mixed gases. When Interlock ESD-1 031 is actuated by either of the above conditions, it will automatically close valve XV-1 031 on the purge gas supply line and XV-1030 on the excess synthesis gas supply line to H-2101 fuel gas system. At the same time it will automatically reduce the pressure setting of PIC-1 002, the main Arch bumer fuel gas pressure controller to 25% Note that due to the lower fuel gas supply pressure, manual adjustment to the arch burner firing will still be necessary.

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Water reflux to T-21 03 top is flow controlled by FIC-1 064 and to prevent freezing in the base of T-21 03 in the event of loss of liquid circulation, low flow alarm FAL-1064 and low level alarrn LAL-1026 warn of these conditions for reflux flow and bottoms level The flow from the bottom of T -2103 is measured by FT-1 065 and provides kick-back protection for the pumps, P-2130AlB through FIC-1065 controlling a flow back the the bottom of T-21 03. The Scrubber is also provided with high level alarm LAH-1026, and high (PDAH-1055) and low (PDAL-1055) pressure differential alarms across the packed bed. Over-pressure relief is provided by PSV-T2103 set at 13.0 barg. 3.1.5.2.2

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T-2104 - Ammonia Stripper An aqueous ammonia solution from the base of T -2103 is pumped to the top section of stripper T-21 04 after being heated by stripper bottoms in exchanger E-2161. This flow to T -2104 is controlled by LlC-1026 on the bottom section of T-21 03 and a manual bypass on the bottoms (shell) side of E-2161 controls the inlet temperature to the stripper. In T-21 04 the ammonia vapours are steam stripped across two lower beds of stainless steel rings. Steam for stripping is provided from a bottom reboiler E-2160 using MP steam flow controlled by FIC-1 027. The stripper bottom is provided with a level glass together with high (LAH-1027) and low (LAL-1027) level alarms. In the top section of T-21 04 the stripped arnmonia vapours are cooled against a manually controlled flow of ammonia reflux pumped by P-2120AlB from D-21 09 over a third bed of stainless steel rings. Ammonia vapours from the top of T-21 04 are released to Refrigerant Condenser E-2127 under pressure control of PIC-1034. Over pressure relief is provided by PSV-T2104 set at 20.5barg.

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3.1.6 Ammonia Storage & Loading (OSBL) When the ammonia unit is on "WARM" production, the greater part of the Ammonia Unit production is routed directly to the Urea Unit except for a small quantity of Cold ammonia being routed to the storage tank. When on "COLD" production, no ammonia is routed to the Urea Unit with the entire Ammonia unit production being continuously routed to the storage tank. Operational procedures for each of these cases are included in Section 7.5 & 7.6 of this manual. 3.1.6.1

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Ammonia Storage Tank TK- 5101 The Ammonia Storage Tank TK-51 01 is of the "double-integrity" type with double walls having th!'l annulus between the inner and outer tank filled with dry air. The annulus of the tank is supplied with instrument air controlled by 51 PIC-1 002 with associated high and low-pressure alarms. The bypass around 51 PIC-1 002 is fitted with a restriction orifice. The annulus is also fitted with a backpressure regulator 51 PCV-1 009 venting to atmosphere.and relief valves PSV-51007/8 A high liquid level alarm 51 LAH-1 001 and an analyser with a high NH3 in air alarrm are also provided in the annulus to warn the operator of ammonia leakage from the inner tank into the annulus. A number of Temperature sensors are located on the walls of the tank and on the under sides of the elevated concrete slabs for use during tank cool down. These sensors are indicated on local temperature indicators.

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It will be noted from Sections 7.5,& 7.6 of this manual that in both 'WARM" and "COLD" Ammonia production cases cold liquid ammonia is routed to the storage tank. In both cases, liquid ammonia @ -35.5°C is pumped from 0-2120 the 1st Stage Refrigerant Flash Drum on the Ammonia unit by Cold Ammonia Product Pumps P-2124NB/C into Storage Tank TK-5101. The flow rate to storage is regulated by LlC-1 024 to maintain a steady level in 0-2120 and monitored by Flow Recorder FR-1061 and Flow Integrator FQI-1 061 located on the Ammonia unit. The tank is equipped with two independent level indicators 51 LI-1004 and 51 LI-1005, the former is fitted with a high and low level alarm. In addition there are two alarms, a high/high alarm 51LAHH-1003 and a lowllow alarm 51LALL-1002. The lowllow alarm actuates interlock ESDI-5101 which will shut down the Ammonia Loading Pumps P-51 01 NB should tanker or cylinder loading be in progress when a lowllow level situation occurs and the Boil Off Gas compressor, in the package unit C-5101. The tank pressure is controlled by 51PIC-1004.Switch HS-1004 is used to direct the Ammonia vapour from the tank to either the Ammonia Unit Refrigeration system, or to the Boil Off Gas Compressor Package C-51 01. 51 PIC-1 004 is fitted with a high and low pressure alarm. Highlhigh pressure is indicated by 51 PAHH-1 006. 51 PIC-1 OOB is provided to vent excess pressure to the storage flare. A lowllow pressure switch 51 PALL-1007 is also provided which actuates interlock

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ESD-5101 to shut down the Ammonia Transfer Pumps should they be in use when a low/low pressure condition occurs and the Boil Off Gas compressor, in the package unit C-5101. A signal from 51 PT-1 OOB also goes to 51 PIC-1 049. The purpose of this controller is to cover the eventuality of a falling tank pressure when product rundown from the ammonia unit is minimal and tanker loading or cylinder filling is in progress. Should such a decrease in pressure occur, and to avoid ingress of air though the tank vacuum breakers, 51 PIC-1049 will open control valve 51 PV-1049 and route warm ammonia vapour from the outlet of Ammonia Heater E-5101. Once the unit is in steady operation, the ammonia vapour from the storage tanks due to heat leaks, vapour displacement and rundown, is returned to the Ammonia Unit Refrigeration systern for re-condensing. The Boil Off Gas Cornpressor Package, C-5101 is then shutdown.

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Arnrnonia Heater E-51 01 Liquid arnmonia frorn the storage tanks for loading tankers or cylinders is transferred by Arnrnonia Transfer Purnps P-51 01 AlB via Arnrnonia Heater E-5101. In E-51 01 , Methanol is heated by LP stearn and the Methanol vapours then transfer heat to the arnrnonia. Temperature controller 51 TIC-1 023 on the supply line to the tanker loading arms and cylinder filling system is set to obtain the required ambient temperature for loading or filling. It is fitted with a high and a low alarm 51 TAH/L1023. 51TIC-1023 will in turn resetthe pressure controller 51 PIC-1050 on E-5101, which regulates the amount of LP steam heating the Methanol. 51 PAH-1 050 will warn of high pressure. To avoid the Methanol pressure in E-51 01 continuing to rise when there is no-load on the heater, 51 PIC-1050 will close the valve PV-1050 when the Methanol pressure in the shell of E-5101 reaches 34.0 barg.

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Procedures for normal operation of the Loading arms and cylinder filling system are included in Sections 7.B.2 & 7.B.3 of this manual. Procedures for the transfer of warm ammonia from the storage tanks to the Urea unit and to the Ammonia unit for start-up are also, included in Sections 7.B.4 & 7.B.5. 3.2

OPERATING CONDITIONS AND PROCESS VARIABlES

3.2.1 Natural Gas Feed Preparation 3:2.1.1

Hydrogenation (Cobalt-Moly) & Desulphurisation (Zinc Oxide) The natural gas feed contains organic sulphur compounds, which must be removed since sulphur is a poison to the Primary Reformer catalyst. These compounds can best be removed by catalytic conversion to hydrogen sulphide (H2S) in the presence of excess hydrogen and subsequent removal of the H2S by reaction with zinc oxide. Natural gas feed, after compression to about 44 bara is mixed with a recycle stream

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of hydrogen-rich synthesis gas normally supplied from the first case discharge of the Synthesis Gas Compressor. Note that should the back-up hydrogen supply from the HP case recycle be used, then it should be routed downstream of the preheat coil since the addition of NH3 rich synthesis gas to the cold natural gas containing CO2 could result in the formation of carbamates and line blockage. The feed mixture, containing about 3.0% hydrogen first passes through the feed preheat coil located in the convection section of the Primary Reformer furnace, H-21 01, and then flows downward through the Hydrogenation reactor. This reactor contains cobalt-molybdenum catalyst, where the organic sulphur compounds are decomposed, the sulphur being hydrogenated to hydrogen sulphide ..

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The feed gas leaving the hydrogenator catalyst bed with essentially all of the contained sulphur in the form of H2S, then flows through the Desulphurizer reactor(s) containing zinc oxide pellets. All the sulphur that may be expected will be removed by reaction with the zinc oxide, forming zinc sulphide. As the feed gas may contain up to 5.0% CO2 , there is a possibility that a "methanation" reaction may take place in the hydrogenator reactor. In order to provide adequate design for this possibility, the operating temperature is reduced to 371°C. Particular attention for methanation should be made during start-up when gas containing up to 18% CO2 is recycled from 0-2102. The zinc oxide guard section is also designed to operate around 371°C with an exit temperature in the range of 360°C.

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I.

Catalyst: Both the cobalt molybdate and zinc oxide catalyst are mechanically strong and not difficult to handle. However, every effort should be made to prevent the formation of any condensation in the reactors, particularly at start-ups or shut-down, to avoid damaging the zinc oxide catalyst.

II.

Operating Variables: Important operating variables for the desulphuriser are, apart from the space velocity which is fixed by the flow rate, listed below in accordance to importance.

III.

Hydrogen/feed gas ratio: This is expressed in mols of hydrogen/mole of feed gas and design is for 0.03 mol/mol. Both the hydrogen content of the hydrogen-rich gas and the molecular weight of the natural gas feed gas must be known in order that the hydrogen/feed gas ratio can be accurately determined. In general, an increase in the hydrogen to feed gas ratio will improve the degree of desulphurisation obtained.

IV.

Temperature: Design is based on an outlet temperature from the feed preheat coil of about 371°C. Initially, and until some experience has been acquired, this temperature should not be exceeded. Generally, a slight increase in temperature will improve the degree of sulphur conversion.

V.

Pressure: The design is for an outlet pressure from the desulphuriser

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reactor of 41.2 bara. Under normal conditions, the primary reformer pressure level requires that this pressure level be maintained. Because the pressure is set at the value specified, it is not to be considered as an operating variable. However, it has been found that the higher the pressure, the better the desulphurisation. The only important side reaction, which might take place, is a gradual deposition of coke on the catalyst. 3.2.1.2

Primary Reforming After the sulphur compounds have been removed, it is desired to reform the feed gas under conditions that will produce hydrogen (H2 ) in an economical manner. This is . done by contacting the feed gas on nickel catalyst in a steam atmosphere at elevated temperature and pressure to promote (and favour) the desirable reactions. The reaction is endothermic and requires constant heat in-put from the primary reformer furnace to maintain the desired temperature level for proper primary reforming.

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The following discussions on reforming conditions should be thoroughly understood for the successful operation of the plant. Improper, or mal-operation at the front end of the unit can be (and is) reflected throughout the plant. 3.2.1.2.1

Reforming Reactions The catalysts promote two simultaneous equilibrium reactions in the primary and secondary reformers. These reactions are steam-methane reaction (higher homologues react in like manner):

CH 4 + H20

c

=

CO

+ 3H 2

and the carbon monoxide shift reaction: CO + H20

=

CO 2 +

H2

It would be preferable if these reactions went to completion to give an overall reaction:

CH 4 + 2H20

=

CO2

+ 4H2

but this is not the case and considerable CO occurs in the secondary reformer effluent Most of this unshifted CO is oxidised to CO2 in the shift converter thus increasing hydrogen yield. 3.2.1.2.2

Reforming Conditions •

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Temperature - The overall effect of increasing reforming temperature on the effluent gas composition is to reduce the methane and carbon dioxide content,

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and increase carbon monoxide and hydrogen content. On decreasing reforming temperatures, the effects are reversed.

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•

Pressure - The pressure of the system is so essentially fixed such that reforming pressure should be considered invariable. However, increasing pressure has an effect similar to reducing temperatures and reformer designs always represents a compromise in economics.

•

Steam to Carbon Ratio - Beyond the vital consideration of sufficient steam to prevent coking the catalyst, increasing steam-to-carbon ratio will shift both above equilibrium reactions to the right with a net effect of decreased methane and carbon monoxide and increased carbon dioxide and hydrogen in the reformed gas. At the same time, however, utility consumption will increase. For other than minor deviations, the unit operation is usually most economical at conditions closely approaching design steam-to-carbon ratio of 3.2 to 1. Whenever there is any doubt about the true steam-to-carbon ratio entering the furnace, the steam rate should be verified with a wet test meter method to determine the true conditions. It is of prime importance that the steam-to-gas ratio to the primary reformer is maintained at a value to ensure a steam-to-carbon ratio of 3.2 to 1 at all times. Should an operating or mechanical accident cause minor coke deposition on the reforming catalyst, the deposit may be removed and the catalyst activity restored by increasing steam-to gas ratio somewhat above normal for a period of time. If the catalyst coking is considerable, it may be necessary to shut down the unit for replacement of the catalyst.

3.2.1.2.3

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Primary Reformer Catalyst The primary reformer tubes are packed with a nickel reforming catalyst, in the form of rings, distributed equally to 208 tubes in the radiant section of the primary reformer furnace. The top section of the reforming tubes are loaded with alkalised (potash) catalyst, which will minimise the possibility of carbon laydown on the catalyst by the heavy hydrocarbons present in the feed. Top Section Potash is present in the top section catalyst in the form of a mixture of potassium aluminates and aluminosilicates such as Kalsilite (KAI Si04). In the reformer, these compounds hydrolyse slowly to form free potassium hydroxide on the catalyst surface. This free potash will prevent carbon deposition when reforming feedstock with heavy hydrocarbons, and will effectively protect the normal nickel reforming catalyst in the remainder of the catalyst tubes. Potassium hydroxide is slightly volatile in the presence of steam and there is a small loss of potash from the catalyst into the gas stream. This potash is replaced on the catalyst surface by more potash from the complex potassium compounds, and this maintains protection against carbon formation and laydown. The complex potassium

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compounds form a reservoir of potash, preventing potash loss from the surface, and giving adequate protection over the whole catalyst life. It should be noted that the rate of potash removal is increased by unsteady reformer operations and it is always greater on start-up.

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The hydrolysis of the potassium compounds is increased at temperatures below 700°C, and periods of steaming at such temperatures should therefore be avoided whenever possible. During plant start-up, however, steaming the catalyst at temperatures below 700°C is unavoidable while the plant is being heated to the temperature at which catalyst reduction is to be carried out. The hydrolysis caused by this steaming increases the amount of free potash in the catalyst, cau·sing a burst of potash release when the temperature reaches a level at which the potash is volatile. Transfer of potash, however, can be reduced if the process temperature, as measured at the reformer outlet, is raised slowly beyond 700°C, the objective being to allow recombination of free potash to take place before a temperature is reached where the vapour pressure becomes significant. This is particularly important if the reformer has previously been steamed for a long period below 700°C. To allow potash to recombine to the alumino-silicate form, it is suggested that the temperature be held at slightly over 704°C for about 3 hours, after which it is raised to 732°C for 3 hours and again raised in 28°C increments using the preceding heating schedule. This sequence of operations is continued until the desired steaming temperature is obtained. A similar procedure is suggested for a shutdown. Cooling down under a steam atmosphere below 704°C should be carried out reasonably fast, consistent with normal safe operating practice, to avoid leaving free potash on the catalyst. If possible, the steam should be replaced with nitrogen when the temperature reaches 538°C. If nitrogen is not available, steam cooling may be continued to within 38°C of the condensation temperature. If steam cooling is used, particular attention should be given to the soaking periods at 704°C, 732°C, and so on, on restarting the plant.

Lower Section Reformer (Lower Section) catalyst is a highly active steam hydrocarbon reforming catalyst composed of supported nickel oxide and is used for the primary reforming of methane and other light hydrocarbons in tubular reformers. After reduction of the nickel oxide to nickel, the catalyst normally operates in the range of exit temperatures up to 825°C, although higher exit temperatures are possible under favourable conditions. Normally, the exit temperature should be about 812°C at an operating pressure of 36.5 bara If a tube has abnormal differential pressure, overheating or insufficient reforming may occur, leading to improper operation and possible damage to radiant harp components. Catalyst reduction will be accomplished using ammonia (cracked in the primary

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reformer) to produce hydrogen, before natural gas feed is introduced. In this way, higher activity of the catalyst will be obtained. Before ammonia is injected into the primary reformer, the exit temperature should be as high as possible (SOO°C or more) to minimise the amount of ammonia which is not cracked. These procedures will be detailed in the Start-up section of this Operating Instructions Manual. After loading the catalysts in the primary reformer tubes, the tubes are mechanically vibrated to assure equal pressure drops, resulting in equal flow distribution through each tube. If a tube has abnormal DP (pressure differential), overheating or insufficient reforming may occur, leading to improper operation.

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Carbon Formation While running under normal operation conditions, primary reforming catalysts do not produce carbon. Plant incidents, such as power failures, instrument malfunctions and equipment failures can, however, bring about operating conditions under which carbon can be formed. The following reactions are possible: 2CO

=

c

+

CO2

CO + H2

=

C

+

H20

CH 4

=

C

+

2H2

CH

=

C

+

H2

Carbon formation can occur in two ways. Under certain conditions in the mixture of CO, CO2 , H2 , CH 4 and H20, free carbon is thermodynamically possible, and carbon can be formed from the first two reactions set out above. This carbon is usually referred to as thermodynamic carbon or Boudouard carbon. Carbon can also be formed as a result of thermo-cracking of hydrocarbons as set out in the last two reactions above. Thermodynamic carbon can produce the most difficult problems on a plant. There is a critical level of steam ratio depending on operating conditions, below which carbon from this reaction is formed instantaneously in the catalyst pores. This carbon deposit in the catalyst causes physical breakdown, and an immediate shutdown to change the catalyst will be necessary. The amount of carbon formed from hydrocarbon cracking depends on the relative rates of deposition and removal of carbon. The higher the number of carbon atoms in the hydrocarbon feed the faster the rate of decomposition, and, the higher the steam ratio the faster the rate of removal. Thus, the likelihood of carbon deposition occurring increases, with the molecular weight of the feedstock, and, as the steam ratio is decreased.

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The steam ratio level at which the amount of carbon deposited becomes significant depends on the feedstock composition. With a light feedstock, the level will be below the normal design minimum steam ratio of 2.5. As the amounts of heavier hydrocarbons present in the gas increases, so will the minimum operable steam ratio. With feedstock which are almost entirely heavier hydrocarbons, higher operating steam ratios are necessary and these levels must be maintained if long periods of trouble-free (that is carbon deposition-free) operation are to be obtained.

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Carbon, resulting from hydrocarbon cracking, does not usually form in the inner pores of the catalyst, and total breakdown of the rings does not therefore occur. The outer surface of the rings are, however, weakened, and the surface layers of the rings are often removed, either during operation, or on discharge. This gives the rings a characteristic eroded appearance, which, after the carbon is steamed off during operation or shutdown, is often the only indication of carbon formation. The Potash in the reforming catalyst promotes the removal of carbon from the catalyst, as stated previously, and this enables the catalyst to be used at steam ratios as low as 3.0:1, if required although the normal steam-to-carbon ratio for this unit is 3.2 to 1. Catalyst "regeneration", to recover activity, can be accomplished by steaming the catalyst, if only a minor amount of carbon deposition has occurred. This would be evident by reformer tube appearance and/or increased DP through the tubes. Reforming catalyst that has been reduced, must not be exposed to oxidising atmospheres at elevated temperatures, except under a carefully controlled condition. During the shutdown of the reformer the catalyst should be kept under a steam atmosphere until the temperature of the catalyst has been reduced to 204°C. The catalyst tubes should then be purged with nitrogen to sweep out the steam to prevent it from condensing.

(

Catalyst Poisons The poisons for primary reformer catalysts, normally encountered, are sulphur, chlorine and arsenic (lead will also poison and ruin these catalysts). The most common symptom is an increased reformer tube skin temperature. In very severe cases of poisoning, the methane content of the reformer effluent gas will also rise. If the catalyst activity is sufficiently reduced, methane cracking will occur at the inlet of the reformer instead of steam reforming, and carbon (in the form of graphite) will form, causing the activity of the catalyst to be lowered further. Any sUlphur compounds that break through the zinc oxide guard chamber to enter the primary reformer will reduce catalyst activity; however, this pOisoning is temporary and activity may be recovered by stripping the catalyst with sulphur - free gas. The catalyst itself may contain traces of sulphur as it is delivered from the manufacturer, but this sulphur is removed during early phases of the unit start-up.

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Chlorine, in small quantities, will be removed by the zinc oxide but less efficiently than sulphur. Chlorine poisoning is reversible, but it is more difficult to remove than sulphur. Steam stripping will remove minor amounts of chlorine, but in severe cases, the catalyst would have to be replaced. Chlorine may be introduced by the steam and so steam purity is especially important. In addition, cleaning solvents . containing chlorine should be avoided around the reformer. It is not anticipated that chlorine will be present to create any problems. Other poisons include arsenic and lead. The effects are usually irreversible, and the catalysts will be ruined and must be replaced, in addition to having to elaborately clean the reformer tubes and other pipework.

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The catalyst is shipped in the oxidised state. It is pre-shrunk at temperatures higher than those usually encountered in operation and shrinkage in service should be negligible. If water or wet steam should suddenly cool hot catalyst, breakage might occur, therefore this condition should be avoided. A catalyst loading procedure is included in the General Procedures Manual under "Catalyst Loading of Primary Reformer Tubes". The catalyst size may vary from the standard but has no effect on the loading procedure.

NOTE: Reforming catalyst that has been activated is placed in operational use in the reduced state and must not be exposed to oxidising atmospheres at elevated temperatures except under carefully controlled conditions. 3.2.1.2.4

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Fumace Operation In order to obtain the packed tube outlet temperature required (about 812°C) for the primary reforming, a flue gas temperature of about 101 OOC leaving the radiant section will probably be necessary. The firing must be carefully regulated to avoid "cold" banks of tubes and/or local overheating and special attention should be made to the note contained in Section 6.3.2.c - "Initial Start-up" of this manual. The hot flue gases pass downward through the radiant section of the box and enter ducts at the floor level. These ducts form the transition between the radiant and convection sections of the fumace and serve to keep the hot flue gases in efficient contact with the catalyst tubes, eliminating stagnant areas in the radiant section. Tunnel bumers are installed at Furnace floor level to allow adjustment of the furnace flue gas exit temperature to the Convection section if required. The draft necessary to cause the flue gases to flow is induced by the Induced Draft (I.D.) Fan, located at the base of the stack. The flue gases enter the convection section to give up heat, successively, to the following coils: - Mixed Feed preheat coil - Process air (and steam) heater coil (hot leg) - The steam Superheater (in two sections)

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- Natural Gas Feed preheat coil Process air ( and steam) preheater coil (cold leg) - The boiler feed water preheat coil - Fuel Gas preheat coil Flue gases from the auxiliary boiler enter the Auxiliary Boiler flue gas duct and join the main convection section of the fumace upstream of the steam Superheater coils. Superheater burners at the top of the convection section hot leg allow adjustment of the convection section cold leg temperatures.

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The cooled flue gases leave the convection section at a temperature of about 180°C and are discharged through the stack to atmosphere by the induced draft fan. Normal pressure in the radiant section of the fumace is -5 mm H20 (negative pressure) and is regulated by PIC-l 019, which controls the speed of the Induced Draft Fan turbine driver. High Pressure alarm PAH-l 019 which senses the pressure in the radiant box together with High pressure alarm, PAH-l057 measuring the pressure at the suction of the induced draft fan, will warn the operator of a pre-determined dangerously high pressure condition. The Aux. boiler combustion air is supplied by a turbine driven forced draft fan C2111.The air is supplied in ratio to the fuel by a leading air system which adjusts the Fan drive turbine govemor speed setting.

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The combustion air for the Arch burners is supplied by turbine driven fan C- 2112 . The air supply is regulated by five manually operated dampers in the combustion air ducts to the arch burners. The turbine speed is controlled by FIC-1181 which adjusts the Fan Turbine driver governor speed setting to hold a set pressure upstream of the dampers. The furnace has been designed to operate with excess air of 10% and a chart "Furnace Excess Air Determination Nomograph" has been included in the General Procedures Manual. This chart may be used in conjunction with occasional flue gas analyses (02 , CO2 & CO) as a check on firing efficiency. Observations of catalyst-tube skin temperatures should be made on a regular schedule using an optical pyrometer. Hot or brightly-coloured spots sornetimes indicate voids in the catalyst tube, or carbon deposits on the catalyst. The arch burners must be operated to avoid flarne impingernent on the tubes, as such mal-operation could result in early tube failure. A little experience and experimentation will indicate the optimum draft and burner air register adjustment to provide stable flame patterns and good heat distribution throughout the height of the fire box.

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Secondary Reforming The partially reformed gas from the primary reformer enters the Secondary Reformer (R-21 03) inlet chamber tangentially via a water jacketed transfer line. The temperature at the secondary reformer inlet will be about 829°C. The flow of gas is downward around a centrally located air inlet pipe and passes through a fixed straightening vane to enter the combustion zone of the reactor. Preheated process air (and steam) is introduced to the process flow through a nozzle located just below the straightening vane. This has the effect of intimately mixing the swirling process stream and air for rapid combustion and distributing the heat over the entire surface of the catalyst bed.

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From the combustion zone of the secondary reformer the flow passes through a bed of nickel catalyst to complete the reforming reaction. 3.2.1.3.1

Secondary Reformer Catalyst The catalyst bed consists of 25.8 cubic meters of nickel catalyst. The catalyst is supported on a bed of 25 dia. high alumina (low silica) content spheres laid on a bed of 50 mm tabular spheres of the same material. The support spheres and catalyst are supported by an arched brick dome located over the disengaging section of the secondary reformer. A catalyst loading procedure is submitted in the General Procedures Manual under "Catalyst Loading of the Secondary Reformer".

3.2.1.3.2

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Secondary Reforming Operation Maximum efficiency of the overall reforming operation requires that as much reforming as possible be done in this partial-combustion step. Utilisation of combustion energy reduces the fuel gas requirement in the primary reforming furnace. However, the amount of air charged to the secondary reforrner is set by the nitrogen requirernents for synthesis, so the degree of overall reforrning will be regulated by variation of prirnary reforrner temperatures. The design rnethane content of the secondary reformer effluent stream is 0.43 mol % (dry basis).Close control will be required on the ratio of hydrogen-to-nitrogen. If it gets very much olit of line, difficulties will be encountered at the ammonia converter, as will be discussed under the converter heading below. Gas analysers are provided to keep a running check on the synthesis gas to the synthesis gas compressor and on the gas being circulated through the synthesis loop. These instruments are normally a major reference for operation of the primary and secondary reformers. Sufficient air must be injected into R-21 03 to produce a HdN2 ratio of 3: 1 for the synthesis gas stream. Whenever the process air flow is altered, temperatures in the Secondary Reformer should be watched and compensating changes made as necessary. Increasing the air flow will raise the temperature, and a decreased firing rate in the primary reformer furnace should be used to compensate, as conditions

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dictate. When conditions are at an optimum and a change in feed gas flow is necessary, a proportional change (in the same direction) of the air rate will be required to maintain the hydrogen/nitrogen balance. Water jackets envelope the secondary reformer, transfer line, E-2101 & E-21 02 in order to keep the metal temperature low if heat leaks develop in the internal lining. 3.2.1.4

Waste Heat Boilers E-21 01 and E-2102 Raw synthesis gas with process steam at about 994°C leaves the bottom of the secondary reformer and is cooled bypassing through the tube sides of waste heat boiler E-21 01 and shell side of HP Steam Superheater E-21 02, to obtain the required inlet temperature to the HT Shift Converter R-21 04. E-2101 and E-21 02 are designed with "inner bypasses". The temperature of HP steam out of E-21 02 tube side is controlled by TIC-1 004 via control valve TV-1 004 installed on E-2101 tube side, which regulates the flow of the gas bypassing E-2101. The overall temperature drop across the E-21 01 and E-21 02 from 994°C to 371°C, is reflected as heat input to the boiler water from D-2101 that is thermo-circulating on the tube side of E-21 01 and to the HP steam passing through the tubes of E-21 02 respectively.

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The required inlet temperature to the HTS Converter of 343- 371°C, is controlled by TIC-1010 which activates control valve TV-1010 located in the shell side of E-21 02. 3.2.1.5

High Temperature Shift Converter [R-21 04] The HTS and LTS shift converters are constructed as a single stacked structure with the upper section being the HTS Converter R-21 04 consisting of one bed of high temperature shift catalyst containing about 48.7 cubic meters of catalyst. The High Temperature shift converter Fe30JCr203 catalyst will be either cylindrical or tablet form, depending on the vendor. A catalyst loading procedure is included in the General Procedures Manual and the size may vary from that quoted, but should have no effect on the loading procedure.

c 3.2.1.5.1

High Temperature Shift Converter Operation The gas-steam process flow enters the HT section of the shift converter at about 343-371°C, where a large percentage of the CO content will be oxidised in accordance with the following reaction:

CO+H20=

CO2 +

H2

This reaction is a reversible one, with "shifting" of the carbon monoxide (CO) favoured by low temperature. However, the rate of reaction is favoured by high temperature. To attain a specified CO conversion, the principal operating variables are temperature and steam-to-gas ratio. It is customary to maintain the operating temperature at design level (371°C) or lower. With new catalyst, it may be possible

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to obtain satisfactory conversion at an inlet temperature to the HT section of 343 to 357"C. The steam-to-gas ratio is usually maintained constant. However, in the event the LT shift converter is bypassed, and acceptable conversion has to be accomplished in the HT section of the converter, it will be necessary to reduce the feed gas rate to bring the steam-to-carbon ratio to the primary reformer to approximately 7.0:1.0. Temperature: If the reaction is near equilibrium, a decrease in temperature will likely improve conversion, and if it is not near equilibrium a temperature decrease will reduce the shifting reaction. Conversely, if the reaction is near equilibrium, an increase in temperature will result in a loss of conversion.

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The temperature conditions selected for the shift converter are based on a higher temperature for the HT section to take advantage of the higher reaction rate for the high CO content of the inlet gas, and comparatively lower temperature for the LT section, to take advantage of favourable equilibrium conditions for the lower CO concentrations in this section of the converter. NOTE: The design metal temperatures for the HT and LT shift converters are 480°C and 270°C respectively. The design metal temperatures of the converters should never be exceeded. Steam: Increasing the steam flow results in an increase of CO shifting if conversion is already near equilibrium, and a loss if not near equilibrium. It is important that at least 20% steam be present in the gas passing over the catalyst when at a temperature above 121°C, otherwise dehydration or change in the structure of the catalyst (with a loss of physical strength) may occur. Normal steam flows to the reforming section usually ensure this minimum steam flow to the shift converters, so this should not pose a problem.

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3.2.1.5.2

High Temperature Shift Catalyst Precautions Start-up with the new, unreduced, catalyst will follow the procedure outlined in Section 6.0. of this manual, utilising nitrogen for heating the HT shift catalyst initially to 107"C to minimise the formation of condensate, then continuing the heating with steam. For all subsequent startups from a "cold" condition, nitrogen warm up of the primary, secondary reformer and HT shift catalyst is also used. After shift catalysts have been exposed to reducing gases (i.e. hydrogen,carbon monoxide) they are pyrophoric and must not be exposed to oxygen (air) except under controlled conditions. Excessive temperatures resulting from too rapid oxidation of the reduced catalyst may cause catalyst and/or vessel damage. For this reason a heat-up with nitrogen, circulated via C-2101 Air Compressor is used until above the condensation temperature of steam, then steam will be used. If the catalyst is to be removed from the vessel, or if the vessel is to be entered, at

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the client's discretion, they may subject the catalyst to a controlled oxidation procedure to render it non-pyrophoric. However, it is recommended that oxidation of the catalyst be carried out only when necessary. Even though the procedure is followed carefully, some "dead spots" may occur where the oxidation was incomplete, and some overheating may occur upon exposure to air. Further, there is the probability that some loss of catalyst activity may occur following oxidation and re-reduction. A start-up with reduced catalyst must use inert gas (N 2) or a steam-gas mixture as the heating medium, taking all precautions possible to minimise formation of condensate, and keeping any water drained off. Water tends to weaken the binder used in the catalyst manufacture.

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When preparing to stop operations or expose reduced shift catalyst, the general procedures are as follows:

c 3.2.1.6

I.

If the process gas flow is to be interrupted for only a brief period time, the shift converter may be isolated under process gas pressure or under a positive steam pressure, keeping any condensate drained out of the vessel.

II.

If the shutdown is to be prolonged but the vessel is not to be entered or exposed at any time to oxygen, isolate it and maintain under a positive pressure with inert gas.

III.

If the catalyst is to be inspected by looking into a top manhole only, it may be cooled with steam to about 121°C. The steam should be purged out at this point with nitrogen. Open the manhole for inspection. Only a slight flow of inert gas is required to limit air diffusion. Inspectors should wear air masks.

IV.

Should it be necessary for a man to enter the shift converter, he should be equipped with an air or oxygen mask and a suitable hamess so that if oxygen supply fails he may be pulled from the vessel. However, the Safety Department of the plant should pass on the advisability of allowing a man to enter a vessel of unoxidised catalyst in an inert atmosphere.

Low Temperature Shift Catalyst Section The lower section of the stacked structure is the Low Temperature Shift Converter (R-21 09) containing one bed of CulZnO/AI20 3 catalyst. The total volume of catalyst is 59.18 cubic meters. The Low Temperature shift converter catalyst will be either cylindrical or tablet form, depending on the vendor. A catalyst loading procedure is included in the General Procedures Manual and the size may vary from that quoted, but should have no effect on the loading procedure. The top portion of this bed functions as a sulphur guard to absorb any trace amounts of H2S that may evolve from the HT shift section and have a poisoning effect on the LT shift catalyst. Most of the H 2S from the HT converter will be evolved during the

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first four to six hours at operating temperature. Therefore, the start-up procedure proposed in Section 6.0. of this manual recommends venting the HT shift effluent at the E-21 03 vent long enough to insure it is sulphur free. Never route the HT shift effluent forward from the E-21 03 vent until it is sulphur free. This will ensure a clean bed of top catalyst to act as a guard for the main bulk of the LT shift catalyst in the event of a sulphur breakthrough from the desulphuriser reactor zinc oxide guard bed during subsequent operations. During the initial start-up, having the HT shift effluent essentially free of sulphur will help insure that the aMDEA C02 removal solution will not be unnecessarily contaminated with an excessive amount of H2S.

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3.2.1.6.1

Low Temperature Shift Converter Operation The LT shift converter will normally be operated with an inlet temperature of 202°C. However, as Iowa temperature as possible is desirable for initial operation. Care must be taken not to operate too close to the dewpoint of the steam/gas mixture. Operating temperatures will be raised as the catalyst ages to sustain reaction, and to hold the CO level down. The maximum temperature to which the LT shift catalyst should be exposed is 260°C. The CO conversion in the LT shift converter responds in the same direction as the HT converter, to changes in, temperature, and steam-to-gas ratio. However, (as previously noted), the LT converter is run at a lower temperature level. This will ensure an effluent that is low in CO content and reduce the load on the Methanator.

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The temperature at the inlet to the LT shift converter is controlled by the heat exchange which takes place in the E-21 03 exchanger through which the HT shift effluent gas passes giving up heat to boiler feed water for HP steam generation. This reduces the temperature of the process gas entering the LT shift converter to the required'inlet temperature of 202°C. Panel-mounted push button (HS-1004) operates valves MV-1008 & MV-1009 to enable rapid bypassing of the LT shift converter in the event of conditions that may lead to excessive operating temperatures. The use of this emergency bypassing of the LT shift converter will require immediate reduction of feed gas to about 50% and reduction of firing rate to the primary reformer. This ensures that the CO conversion will be brought to a satisfactory level in the HT shift converter.

Caution: Do not fail to make a corresponding reduction in the process air rate to· the secondary reformer. If the reduction in feed rate is not made immediately before bypassing the LT shift converter, a high level of carbon monoxide (CO) will break through to the Methanator, resulting in excessive temperatures in this reactor. The above precautions are based on the assumption that the plant upset is of a minor nature and CO entering the Methanator can be maintained low enough to avoid a high temperature trip, by a rapid reduction in feed gas. However, the safest approach is to vent ahead of the Methanator before bypassing the LT shift.

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If the upset is due to loss of the air compressor, the latter procedure must be followed since reaction in the HT shift will be lost due to the sudden reduction in secondary reformer outlet temperature (HT shift feed temperature). 3.2.1.6.2

Low Temperature Shift Catalyst Precautions Start-up with the new, unreduced catalyst or reheating the reduced catalyst will follow the procedure outlined in Section 6.0. of this manual, using desulphurised natural gas or nitrogen for heating the catalyst to 177"C to 190°C.

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In the course of operation, particularly during the start-up stages, it may become necessary to purge and/or "blanket" the contents of the vessel after first isolating it. Purging or blanketing will be accomplished by the use of nitrogen to ensure that no ''wetting'' of the catalyst occurs: The nitrogen will be introduced into the top of the vessel and the contents displaced through the bottom reduction vent. When all hydrocarbon has been displaced, the vessel is left standing, "bottled up", under a positive pressure of nitrogen. Warning: Carbon dioxide, either in its wet or dry state, must never be used for purging and/or blanketing of the LT shift catalyst. Dry CO2 has an adverse effect on the activity of the catalyst and this is particularly so during the stages of activation. There is also some loss of activity, although to a somewhat lesser degree, when wet CO2 is used. The LT shift catalyst in the reduced stage is highly pyrophoric at any temperature, (due to chemically absorbed and mechanically absorbed hydrogen on the catalyst). Once reduced, therefore, the catalyst must never be exposed to, or contacted with air (oxygen), since rapid oxidation would occur resulting in excessive temperature and ultimate damage to the catalyst and/or the vessel.

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If the LT shift catalyst is to be salvaged it must be carefully deoxidised before exposing the catalyst to air (02). However, this is at client's discretion and those precautions regarding catalyst oxidation mentioned for the HT shift catalyst also apply here. If the catalyst is to be removed from the LT shift and there are no plans for salvaging, it may be unloaded from the shift converter under a nitrogen (N2 ) atmosphere without reoxidation. However, the catalyst should be cooled below 149°C before it is unloaded. If this latter procedure is used, the catalyst is permitted to flow into steel drums. The catalyst should be "spray wetted" as it leaves the converter and contacts air (02 ); this will prevent rapid reoxidation. The operators must be thoroughly familiar with the procedures for recovery or discarding of the catalyst. When carrying out procedures below normal operating pressures, do not exceed design velocities through the beds. Sudden pressuring and depressurising, and changes in rates of flow, should be avoided, to obviate "heaving" the beds. At all times, and particularly when hot, the catalyst should be protected from contact with

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water. Temperature of the catalyst bed should not be changed at a rate greater than 83°C/hr. 3.2.2 CO 2 Removal ( aMDEA System) The aMDEA CO2 removal system is a proprietary commercial process for CO2 removal from gas streams of high CO2 concentration 3.2.2.1

Flow of Gas and aMDEA Solution The reformed gas from the shift effluent separator enters the CO2 absorber through a branch distributor and flows upward through two beds of slotted ring packing. As the gases flow upward through the packed beds they are contacted by the downflowing solution which absorbs most of the CO2 .

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At normal design operating conditions it is expected that 773 MT/hr of the lean solution will be pumped through the distributor above the top bed The scrubbed gases pass through a demisting pad in the absorber top and in the overhead separator and out the top of the drum. The temperature of the gas leaving the top is expected to be about 50°C and the rich solution in the bottom of the tower at 82°C. It is expected that the gas from the top of the absorber will contain about 0.1 % CO2 by volume. The rich aMDEA solution is stripped of the CO2 in the CO2 stripper. The rich solution is pressured out of the absorber under level control. As the rich solution moves up the pipe toward the stripper inlet, more and more of the CO2 is flashed from the solution and separates from the liquid as it enters the stripper. The solution flows down the stripper over two beds of slotted rings in the LP flash section and into a trapout pan where the semi-lean pumps take suction. The P-21 08 semi-lean pumps pump the solution into the stripping section of the column via lean/semi-lean exchanger E-2112. The solution flows downwards through two beds of packing where it contacts the upflow of steam generated by reboilers E-21 05 and E-2111.The stripped solution is retumed to the absorber by lean solution pumps P2107 being cooled on route by exchangers E-2112, E-2109and E-2110

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A top contact cooler section washes out entrained carbonate from the CO2 product gas cools the stripper overhead gas and condenses the stripping steam. 3.2.2.2

Chemistry of the aMDEA Process aMDEA (Methyldiethanolamine) solution in water removes C02 from the gas stream by chemically bonding with the C02 to form bicarbonate. The bicarbonate is unstable and will decompose at reduced pressures and increased temperatures. The addition of an activator improves the rate of absorption. The quantity of activator can be varied to vary the characteristics of the solution between that of a physical and chemical solvent.

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The C02 is released from the solution in the stripping column by: 1. The reduction in pressure causing the C02 to flash off the solution in the LP Flash section. This removes the bulk of the C02 from the solution without significant heat input. 2. The addition of heat in the stripping section of the column. This decomposes the residual bicarbonate and reduces the C02 content of the solution to a level suitable for return to the C02 absorber for re-use.

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3.2.2.3

Solvent type and solution strength The aMDEA Solvent Systems are delivered as premix solutions, which consist of MDEA, the activator and a small water content. The solvent has to be diluted with demineralised water in the gas treatment unitup to 60 %(w/w) water and 40 %(w/w) amine. During operation the amine content has to be maintained between 37 and 45 % (w/w) by adjusting the make-up water flow rate.

3.2.2.3.1

Solvent make-up The annual solvent losses are approximately 5 to 10 % of the aMDEA premix inventory. The solvent losses are mainly caused by mechanical problems such as pump leakage, cleaning and change of filters or entrainment. Hence, the losses depend strongly on the maintenance and the measures taken to avoid entrainment. The aMDEA premix can be used as solvent make-up. However, the activator concentration drops slowly over months of operation since the vapour pressure of the activator is higher than of MDEA.

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Typical annual activator losses are around 10 - 15 % of the activator inventory which can be balanced by the addition of an enriched aMDEA make-up solution conSisting of 40%(w/w) MDEA, 40 %(w/w) activator and 20 %(w/w) water ("aMDEA 1: 1"). The activator make-up has to be added into the solvent loop, e.g. on the suction side of the lean solution pump. 3.2.2.3.2

Solvent storage Nitrogen blanketing is recommended if the solvent is stored for periods longer than three months. The continuous contact of the solvent with air turns the colour from light yellow to brownish (degradation products in the ppm-range). The absorption parameters of the a MDEA solvent, however, are not altered but the foam activity can be somewhat higher.

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Antifoam Agent The aMDEA solvent system is non-corrosive and therefore, no corrosion inhibitors are required. The only inhibitor, which has to be added to the solution, is a small amount of antifoam agent. The recommended defoamer is Amerel1500 .This is produced by Drew Ameroid Company but can also be ordered via BASF. The Amerel dosing rate depends strongly on the plant size, operating capacity and the impurities in the feed gas.

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Typical dosage rates of Amerel are as follows: • •

Natural gas: Synthesis gas:

1000 mllday for a plant capacity of 350,000 Nm3/h 100 mllday for a plant capacity of 100,000 Nm3/h

Amerel 1500 is a suspension of surface-mcidified Si02 in silicone oil. Therefore, it has to be stirred thoroughly before being added to the solution. The addition of Amerel can be carried out continuouslY,batchwise or only when increased foaming activity is predicated.

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•

Indications for a high foam activity are:

•

High differential pressure on the columns

•

Difficulties in controlling the bottom levels

•

High hydrocarbon content in the acid off-gas

•

High aMDEA-content in the reflux condensate or in knock-out drums

•

Results of the foam test outside specified range

In order to prevent foaming we recommend a regular discontinuous dosing of Amere11500, e.g. once per shift or once per day. For the initial start-up and when starting up after the pumps have been stopped, an extra quantity of antifoam agent should be added. 3.2.2.3.4

Filter Operation The filter deactivates the defoamer by the removal of the silicone particles. Therefore the filtered stream should not be higher than actually required.

3.2.2.3.5

Regular Solvent Analyses Solvent samples should preferably be taken from the lean solution line

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downstream the lean solution cooler. Further samples can be taken as required. The following regular analyses are recommended (see Analysis Manual for the BASF aMOEA Process). Once per shift:

water content by density measurement

Once per week:

total amine concentration

Once per month: 3.2.2.3.6

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MOEA content and activator content

Reduced Load Operation Solution rate can be reduced proportionally to the feed gas rate. Limitation: the liquid load of the absorber packing should be > 20 m3/m2/h A too low liquid loading might lead to mal-distribution and to a breakthrough of C02

3.2.3 Methanation (R-21 06) Process gas containing about 0.1 mol % of CO2 and about 0.36 mol % CO, flows from the top of the absorber through the absorber overhead demisting section where any entrained moisture will be removed in passage through the demisting pad contained therein. The gas then flows, in normal operation, to the Methanator R-21 06 via the Absorber Overhead. drum 0-2103 and the Methanator Feed/Effluent Exchanger E-2114 where it is preheated to 316°C.

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A gas by-pass is provided round E-2114 to permit adequate control of the feed temperature. A separate HP steam heated Methanator Feed Heater (E-2172) is provided for the initial heating of the gas to normal operating temperature during start-up. It will also be required during normal operation when the LT Shift catalyst is fresh and the heat of the methanation reaction is not sufficient to provide the required temperature differential in E-2114. The Absorber demisting section and the absorber overhead drum 0-2103 is provided as an additional protection for the catalyst in the Methanator. The hot Methanator catalyst would be damaged if contacted with liquid. Therefore, the absorber overhead should occasionally be checked to ascertain that liquid carryover is not excessive. Should the prospect of liquid carryover develop, steps should be taken to vent the Methanator feed gases and to close the Methanator inlet valve. This can be done by use of the emergency pushbutton (HS-1253) provided. Excessive carryover may be the result of foaming of the aMOEA solution or an excessive circulation rate of solution. Normally, the corrective step is self-evident. The objective of the methanation reaction is to complete the removal of the carbon oxides from the synthesis gas, since carbon oxides are pOison to the ammonia synthesis catalyst. Removal of the carbon oxides is accomplished by their

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conversion to methane, which acts as an inert gas in the ammonia converter. The methanation reaction is as follows:

co

+ 3H2

CO2 +

4H2

=

=

CH. + H20 + CH. + 2H20 +

Heat Heat

Both reactions are exothermic, causing a theoretical temperature rise of about 72°C for each mol percent carbon oxide in the inlet gas. Under normal operating conditions, with a carbon monoxide content of 0.36 mol % in the inlet gas, the expected temperature rise in the Methanator will be about 31°C resulting in an outlet temperature of about 347°C.

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Because of the highly exothermic nature of the methanation reaction, the Methanator is protected by automatic high temperature actuated, feed shutoff valving. The following temperature indicators and alarms measure the temperature at various pOints in the catalyst bed; TAH-1357,TAH-1358, TAH-1359, TAH-1360, TAH-1361 & TAH-1362A1B. High temperature alarms and Methanator shutoff trips TSHH-1200, TSHH-1201, TSHH-1202 & TSHH-1203 are located at intervals throughout the catalyst bed and are provided with thermocouple burn-out low temperature alarms. If the bed temperature exceeds the set temperature of anyone of alarms TAHH-1200 through TAH-1203, the solenoids provided on the two Methanator inlet valves will cause them to close, stopping all flow to the Methanator. As a result, the pressure controller (PIC-1 005) in the Methanator inlet line will open to vent the feed gas to atmosphere. The Methanator temperature trip should be set at a temperature of approximately 30°C below the Methanator vessel design temperature (455 C).

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As a further protection against high run-away temperatures in the Methanator due to a CO2 breakthrough from the CO2 absorber system, the Methanator will be shut-down automatically if the lean or semi-lean CO2 removal solution flows drop below preset values. Low low flow on FT-1205 & FT-1217 will activate the Methanator shut-down system in the same manner as activation of a high temperature trip from TSHH-1200 through TSHH-1203. If the Methanator feed valve is shut by the high temperature alarm system, determine and correct the cause before starting feed gas to the Methanator. When the feed gas total carbon oxides content has been reduced to normal or less, the feed gas may be restarted to the Methanator at a low rate with the inlet valve throttled manually. The inlet valve solenoid must be manually relatched. Gradually increase the feed rate until the inlet valve is wide open. Venting of the Methanator in the manner described above provides protection not only for the methanation catalyst but eliminates any chance of having a breakthrough of CO and CO2 into the synthesis loop which, of course, are poisons to ammonia conversion catalyst. With regard to CO2 , it should be mentioned that besides catalyst poisoning and degradation, this contamination can cause difficulty with the performance of the synthesis gas compressor. With relatively large amounts of residual CO2 from the Methanator, it is possible to deposit ammonium carbamate and/or ammonium

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carbonate in compressor internals as the result of contact with ammonia laden gases from the second case kickback of the C-21 03 synthesis gas compressor, that is, if the circuit is open during an emergency. This condition may create vibration problems in the compressor and/or stress corrosion of compressor internals. An emergency push button (HS-1253) has been provided on the control room board. This push button may be used to actuate the Methanator inlet valve solenoid on demand when desired. CAUTION: Never depressurise the Methanator below normal operating pressure while normal pressure exists upstream of the Methanator inlet valve. Such depressurising has caused extremely high temperatures in the Methanator because of inlet valve leakage, increased by the higher than normal inlet valve pressure differential. The Methanator design metal temperature is 455°C. This temperature must not be exceeded under any circumstances.

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The catalyst Loading procedures is described in the General Procedures Manual and once the catalyst has been placed in operation or reduced, it should not be exposed to air or to oxidising atmospheres. In a plant shutdown where Methanator entry is not anticipated, it should always be blocked in under an atmosphere of hydrogen or nitrogen. For removal of catalyst, it should first be at ambient temperature, then unloaded through the dropout under an atmosphere of nitrogen. The catalyst should be wetted down with water as it leaves the vessel to prevent rapid oxidation. Under certain conditions, carbon monoxide and nickel may react to form nickel carbonyl, Ni(CO)4, which is a highly toxic compound. Whenever men are going to enter (or open) the Methanator, tests should be made to assure that carbonyls are not present. The most likely time for nickel carbonyl formation is during start-up or shutdown, since these procedures involve the temperature range favourable for carbonyl formation, i.e. from ambient temperature conditions to about 177°C. A few simple precautions will suffice:

c 3.2.3.1

Shutting Down: The catalyst should never be permitted to cool down to ambient temperature in the presence of CO. When the process gas contains CO, the Methanator should be flushed with a CO-free gas before the temperature drops to 204°C.

3.2.3.2

Starting Up: The pressure on the Methanator should be kept as low as practicable when heating up on process gas, until the bed temperatures are above 177°C. This will help ensure a good flow distribution during initial heating of the catalyst bed. The catalyst should be brought up to normal operating temperature in as short a time as practicable to minimise the possibility of nickel carbonyl formation.

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3.2.4 Ammonia Conversion 3.2.4.1

Compression of Synthesis Gas and Water Removal The purified gas is compressed to about 67 bara in the first case of the synthesis gas and recycle compressor (C-21 03) and then chilled in three steps: first, by boiler feed water in the Synthesis Gas Compressor Interstage BFW Preheater E-2117; second, by cooling water in Synthesis Gas Compressor Intercooler E-2116 and then by ammonia refrigeration in the synthesis gas compressor interstage chiller E-2129. This chiller cools the gas to about 4.4°C and drops out most of the water in the first stage separator (0-2105).

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The low moisture content synthesis gas leaving the first stage separator (0-2105) goes to the second case of C-21 03 and the pressure is increased to about 144 bara to enter the synthesis gas loop. At an intermediate point (last wheel suction) of the second case of C-21 03 the synthesis gas is joined by the synthesis loop recycle gas. 3.2.4.2

Precautions Relative to Synthesis Gas Compressor The efficient operation of the Synthesis Gas Compressor, C-21 03, will require that the quality of the process gas entering the compressor be such that the CO2 content be maintained at the value specified (less than 10 ppm) at all times. It is important also that the temperature of the gas entering the suction of the high pressure case not be allowed to fall below aOc. Failure to observe these precautions when the machine is in operation can, under certain conditions, result in the formation of carbamate and/or ammonium carbonate at the first wheel location of the compressor second stage. This could have a damaging effect on the operation of the machine resulting in a progressive increase in vibration caused by an imbalance as the deposits build up.

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To eliminate the likelihood of this occurrence the following precautions must be followed once the compressor is in synthesis gas service: I.

The temperature of the gas entering the compressor second case must not be allowed to fall below the aOc temperature at any time in order to avoid conditions conducive to carbamate/carbonate formation. Formation of carbamate/carbonate is an inverse function of temperature; that is, decreasing temperatures increa$e the chances for formation of these compounds. With less than 10 ppm carbon oxides in the Methanator effluent, satisfactory operation can be expected with a compressor interstage temperature of aOc. Similarly, extremely low temperatures at the interstage location must be avoided because of the danger of freezing water of saturation in the synthesis gas at compressor suction locations, which can also cause wheel damage.

II.

Flow of steam to steam tracers on kickback lines will be turned on prior to starting. This is required in order to avoid liquid condensation in the kickback

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circuit particularly for removal of condensate to avoid situations which can cause slugs of liquid to enter the compressor and cause wheel damage. Prior to compressor start-up, the drains must be checked to make certain that no liquid is present in the kickback line. III.

Operate the compressor kickback (FIC-1008) on minimum kickback flow consistent with machine stability and, where feasible, with zero kickback. This is particularly desirable if there has been a sudden upset in the CO2 removal system causing a somewhat higher than normal breakthrough of CO2 from the Methanator. The second-casing kickback gas contains large amounts of ammonia vapour and this should not be allowed to contact the synthesis gas with a higher than normal CO2 content. If the kickback is closed or the kickback quantity is small during the upset, the possibility of formation of solids in the compressor is eliminated. It should be emphasised, however, that a breakthrough of CO2 resulting from an upset in the CO2 removal system will necessitate venting gas at the inlet to the Methanator (PIC-1005)

IV.

Satisfactory performance of the CO2 removal system requires that the analyser (AI-1002) which continuously analyses and monitors the total oxides in the synthesis gas stream be frequently checked and periodically calibrated. Accurate and dependable analyses of the stream will provide an early indication of higher than normal CO2 leakage and thus inform the operator when venting of the gas at the Methanator inlet or the suction drum (PIC-1004) is required.

V.

A major upset in the CO2 removal system resulting in an increase in the residual CO2 content of the gas leaving the absorber will make it necessary to vent gas at the Methanator inlet if the CO2 breakthrough is excessive (see "Methanation" Process and Operating Principles - Section 3.0). The push button switch (HS-1253) may be used to vent the gas at any time if the analyser recorder shows a tendency of a rise in the CO/C02 content.

VI.

Always maintain the normal design temperature on the gas outlet from E-2124. Temperature indicator (TI-1633) is installed for this purpose and the cooling water flow to the Loop Cooler should be adjusted to yield 50°C at this point. This will avoid condensation of ammonia and the return of liquid to the second case suction when the machine is on kickback operation.

VII.

The vibration measuring instruments should be checked frequently to determine levels of vibration on the compressors and the results recorded in the plant log. The vibration pattern should be checked often after an upset has occurred to determine if an increase has followed the upset. If excessive vibration patterns develop, the compressor must be shut down for inspection.

VIII.

If the backup hydrogen supply for feed as hydrogenation is taken from the synthesis loop, then it should be routed downstream of the preheat coil since the addition of NH3 synthesis gas to cold natural gas containing CO2 could

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result in carbamate formation and line blockage. If the precautions outlined above are observed, the likelihood of deposits of carbamate and/or carbonate formation occurring on the first wheel or situations involving build-up of liquid in the kickback circuit will be minimised. The 2 inch bypass valve around motor operated valve HV-1001 will be used for controlling the flow to the synthesis loop at start-up. 3.2.4.3

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Conversion of Synthesis Gas to Ammonia The synthesis converter (R-21 05) contains about 68.4 m3 of synthesis catalyst divided into three beds, bed no. 1 and beds no. 2A & 2B; each bed containing 22.8 3 m of catalyst. Prior to entering the Converter R-21 05, the synthesis gas receives some preheat from the converter effluent in E-2121. It is then introduced at one end of the external shell of the converter at 259°C and flows along the annulus between the external pressure shell and catalyst basket towards the opposite end of the converter. This arrangement limits the temperature to which the external shell is exposed. On reaching the opposite end of the converter, the synthesis gas enters an opening in the end plate and flows across the external surfaces of E-2122 tubes. After passing across the outside surfaces of the tubes the synthesis gas enters a partitioned plenum where it is directed to the distributor above the first bed. On exiting bed no. 1, the synthesis gas re-enters the partitioned plenum where it is directed through the tubes of E-2122. The synthesis gas exits E-2122 tubes and re-enters the plenum where it is directed through a distributor pipe to the top of bed no.2A. The gas passes down through bed no. 2A and is then directed to the top of bed no. 2B. A further reaction takes place in bed 2B after which the gas exits the converter shell through an internal piping arrangement at the feed inlet end. Heat from the Ammonia synthesis reaction raises the gas temperature from the first bed to around 496°C. The effluent gas flows through the tube side of the interchanger, which cools the gas to about 387"C before passing over the second catalyst bed. The second catalyst bed is divided into two physical beds in series to ensure uniform flow over the catalyst. Further reaction in the second bed raises the converter outlet temperature to about 457"C and the ammonia concentration to 15.75 mol%. A bypass line around the converter, controlled by valve HIC-1025 is provided to permit introduction of feed gas without preheating for temperature control to the first catalyst bed, usually referred to as "quench". The design feature of an intercooled converter has the advantages of producing a relatively high ammonia concentration per pass and making the heat available in the converter effluent at a temperature sufficient for the production of high pressure steam. The ammonia converter effluent stream at 448°C is cooled by heat exchange giving

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up heat to boiler feed water in steam generator E-2123 and to the converter feed in E-2121 before retuming to the Recycle Gs Compressor C-21 03 to be recycled back to the converter. Before the recycle gas (plus fresh feed) re-enters the converter, it is routed via the unitized chiller system to condense out the net ammonia make produced on its previous pass through the converter. A continuous vent or high pressure purge is maintained to remove excess inerts (mainly methane and argon) from the synthesis gas loop. This purge gas is chilled to -29°C for initial recovery of ammonia and then passes to the ammonia absorber for further recovery. If these inerts were allowed to build up to too high a level they would ultimately reduce ammonia production. However, excessive venting is to be avoided as a loss of yield by excessive loss of hydrogen/nitrogen synthesis gas will result.

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The following are discussions of factors affecting the operation of the synthesis converter. Conditions Influencing the Converter Reaction

3.2.4.4

The SyntheSiS Reaction, which is promoted by the catalyst, may be illustrated by the following equation: N2

+ 3H2

=

2NH3

The equilibrium point for this reaction is such that, at the proposed operating conditions, the ammonia content of the reactor effluent will be about 15.75 mol percent. The unconverted gases are recycled back through the reactor to achieve optimum production. 3.2.4.4.1

C

Temperature The effect of a change in temperature on the ammonia synthesis reaction is a double one, as it affects both equilibrium percentage and reaction rate. As the synthesis reaction is exothermic, a rise in temperature lowers the equilibrium percentage of ammonia and at the same time accelerates the reaction. This means that under conditions far from equilibrium, temperature rise will lead to higher conversion, while on the other hand for a synthesis system giving a conversion near the equilibrium percentage a rise in temperature will lead to a lower conversion. Efficiency always varies directly with temperature when catalyst deterioration. is not taken into account. Conversion efficiency is defined as the ratio of the actual percent NH3 in the converted gas to that theoretically possible under the conditions in question.

3.2.4.4.2

Pressure As the synthesis of ammonia involves a decrease in volume (decrease in the number of molecules), the equilibrium percentage of ammonia will increase with pressure. At the same time the reaction rate is accelerated by increaSing the pressure; therefore,

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the conversion will improve with higher pressure. Space Velocity

3.2.4.4.3

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At higher process gas rates (higher space velocity in the converter) the synthesis reaction has less time to operate and does not produce as high a concentration of ammonia in the converter effluent as is produced when the gas is moving through more slowly. However, the reduction in yield is far less than proportional to the percent increase in space velocity. The increased production of ammonia, due to the greater amount of gas put through the reaction zone, more than offsets the tendency toward decreased production due to less complete reaction (less residence time). Therefore, at normal or less than normal throughputs, an increase in gas rate to the converter will give increased production, provided that other conditions (temperature, pressure, HJN2 ratio) are unchanged. The usual method of changing space velocity is by altering the recycle (circulation) rate. With more circulation (if available) the temperatures will tend to drop in the converter beds, due to less conversion per pass; pressure will tend to drop because of more total production of ammonia. Circulation is increased by closing in on HIC-1030 Maximum circulation is attained when HIC-1030 is completely closed. 3.2.4.4.4

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Hydrogen to Nitrogen Ratio The fresh synthesis gas feed to the synthesis section should usually have a hydrogen-to-nitrogen ratio of about 3:1. This is the case because the combining of hydrogen with nitrogen to form ammonia is the ratio of 3:1. However, it should be recognised that the hydrogen-to-nitrogen ratio within the ammonia converter can be other than 3:1. It has been found that maximum conversion percentage is obtained at a 2.5 to 3:1 ratio of hydrogen-to-nitrogen in the converter. The ratio in the fresh gas feed may be altered slightly from 3:1 to obtain the optimum H2:N2 ratiO in the combined gas feed to the converter. Inert Gases

3.2.4.4.5

A continuous bleed of gas will be maintained from the recycle compressor suction header to the purge gas system. This purge stream is required to control the concentration of methane and other inert gases which would otherwise build up in the synthesis circuit, resulting in lower conversion, higher pressure and reduced production capacity. 3.2.4.4.6

Synthesis Gas Rate Increasing the synthesis feed gas rate alone produces more ammonia and has the following effects upon the conditions discussed above: (1) (2)

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The system pressure will increase. The catalyst bed temperature will increase.

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The inert gas content will rise. The H2:N2 ratio may change.

Conversely, decreasing the synthesis gas rate will have the reverse effects. Under normal operating conditions, the synthesis gas rate is determined by production requirements. An increase in gas feed to the synthesis section must be obtained by more production of gas in the front end of the plant. Control of the Synthesis Heaction Operation

3.2.4.5

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The synthesis system essentially rides on the line from the discharge of the synthesis gas compressor. Gas (H2 and N2 mixture of 3:1) is consumed as determined by the operating conditions, catalyst activity, and resultant capacity of the synthesis loop. The gas from the compressor keeps replacing the removed or converted gas. If excess synthesis gas is available, the production increases to the limit of the compressor; then raw synthesis gas is vented before the first stage of compression at 0-2104 suction drum. If there is insufficient gas, the compressor slows and the loop pressure drops until production of ammonia is reduced and comes in balance with the gas available. There are several variables, one or more of which may be changed to alter synthesis loop operation. The more important controlling variables are listed below:

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• • • • • • •

Synthesis feed gas rate Converter feed temperature Synthesis gas circulation rate Hydrogen-to-nitrogen ratio HP inert purge gas rate Purity of feed gas Converter bed temperature level

It will be noted that system pressure is not listed as a variable, which is available for control. The pressure frequently changes as a result of the manipulation of other conditions, but it is rare that a change would be made for the sole purpose of raising the pressure, to the exclusion of all other effects. The system is usually so operated that the pressure remains reasonably well below limits, while minimising the purge rate and while maintaining converter temperatures low enough to assure long catalyst life. Lower pressures usually indicate good operation, provided feed and purge rates are normal and the converter temperatures are satisfactory. Following are the factors affecting each of the synthesis loop conditions that the operators watch to detect changes for abnormalities in the process. If these factors are known, it is easier for an operator to explain a change in operating conditions. The operator can then manipulate one or more variables to make the necessary correction.

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Converter Pressure The main factors, which individually or collectively contribute to an increase in the synthesis loop pressure, are:

• •

An increase in the synthesis feed gas rate. A decrease in converter temperature level. A change in gas composition away from the optimum of 2.5 to 3:1 ratio of hydrogen to nitrogen in the synthesis gas loop. An increase in the ammonia content of the recycle gas. An increase in the inert gas (fixed gas) content of the circulating gas. A decrease in recycle gas circulation rate. Poisoning of the catalyst due to impure synthesis gas. Ageing of the catalyst.

•

• • • • •

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Conversely, a decrease in the pressure is caused by the reverse of the actions above.

3.2.4.5.2

Catalyst Temperature Level The main factors, which individually or collectively contribute to an increase in the catalyst temperatures, are: • • • • • • • •

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An increase in the synthesis feed gas rate. A decrease in recycle gas circulation rate. A closer approach to the optimum 2.5 to 3:1 hydrogen-to-nitrogen ratio. A decrease in the ammonia content of the circulating recycle gas. An increase in converter system pressure. A reduction in the cold gas bypass (quench) rate to the converter. A decrease in the inert gas content in the circulating synthesis gas. An increase in catalyst activity, following a temporary poisoning due to impure synthesis gas.

Conversely, the factors causing a decrease in the catalyst temperatures are the reverse of those mentioned above. The best temperature for steady operation is the lowest temperature that will give the maximum yield of ammonia product, yet high enough to provide stability in case of pressure surges. Excessive temperatures will age the catalyst and cause rapid reduction in catalyst activity.

3.2.4.5.3

Hydrogen-to-Nitrogen Ratio The main factors which individual or collectively contribute to a change in the H2:N2 ratio of the circulating gas are: •

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A change in the composition of the synthesis gas from the reforming and.

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purification systems A change in the synthesis feed gas rate. A change in the ammonia content of the circulating recycle gas. A change in the inert (fixed) gas content of the circulating gas.

The hydrogen-to-nitrogen composition of recycle gas to the converter is controlled to maintain about 2.5 to 3: 1 ratio. A rapid change of ratio will cause a rapid temperature change. Ammonia Content of the Circulating Gas

3.2.4.5.4

c.

Factors, which individually or collectively contribute to a change in the ammonia content of the gas entering the converter, are: • •

A change in cooling in the chillers before the ammonia separator D-21 06 The system pressure.

It is anticipated that the ammonia concentration of about 15.75% in the converter effluent will become 12.13% when the recycle and fresh feed gases are combined. After chilling and separation in D-21 06, it is expected that the ammonia concentration in the combined gas stream entering the converter will be about 2.69% after condensing out the ammonia make. 3.2.4.5.5

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Inert Gas Content of Circulating Gas The principal constituents, which contribute to the inert content of the circulating gas, are argon and methane. These gases tend to build up and raise pressure in the system, thus reducing the effective synthesis gas partial pressure. This is reflected in lower conversion per pass. The inert concentration in the system is controlled by withdrawing a stream of purge gas via E-2125 and the purge gas separator D-21 OS. Design is based on an inert gas (methane and argon) content of about 1.2 mol % in the feed gas. However, it may be found by experience that at higher concentrations overall ammonia production can be increased by conserving hydrogen, which would otherwise be removed from the system by excessive purge gas rates from the synthesis gas loop. From the preceding discussion of the ammonia synthesis operation it can be seen that the efficiency is affected by the controllable variables listed at the beginning of this subsection "(d)". All of these factors are interdependent and a change in one will have an effect on the others. Consequently, good operation will be a combination of operating experience and a recognition of the factors affecting the operation of the system. Thus, if a drastic change in one of the operating conditions occurs, experience will dictate those steps that should be taken to compensate for the change, so that the system will remain in good control. Any

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changes should be made slowly when possible, so as to avoid major disturbances.

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3.2.4.6

Converter Catalyst Characteristics

3.2.4.6.1

Catalyst Activation The synthesis catalyst is made from fused iron oxides containing potassium, calcium and aluminium oxides as stabilisers and promoters, and is charged to the ammonia converter in the oxidised state. The catalyst must be activated before production of ammonia will take place. The activation requires reduction of the iron oxide to practically pure elemental iron. Reduction of the synthesis catalyst will be accomplished during the initial start-up of the plant under the guidance of the catalyst vendor's representative and careful control of conditions during catalyst activation will result in uniform reduction which will prorr:lOte longer catalyst service. An outlined procedure, to be used as a guide, is described in Section 6.3.18. of this manual. During reduction, hydrogen is passed over the oxidised catalyst at progressively higher pressures and temperatures. The hydrogen combines with the oxygen from the iron oxide to form water. The water is removed (as much as possible) before the gas is recycled over the catalyst. The amount of water produced during the activation period is a good indication of the progress of the catalyst reduction. At the start of the reduction period, a small amount of water is formed and as reduction of the catalyst progresses, water formation increases. The reduction of the catalyst is aided by fairly high temperatures and controlled pressures. The water formation will reach a peak and then gradually taper off near the end of the reduction period.

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The reduction temperature should always be kept below that at which the catalyst is going to operate, so as to avoid deactivation due to the following: (1) high concentrations of water vapour in the circulating gas, (2) excessive heat. However, too Iowa temperature will cause catalyst reduction to move slowly; if temperatures drop low enough, reduction will stop. The effect of pressure and/or pressure change during catalyst reduction can be critical. If each catalyst bed is not activated uniformly as reduction moves downward, an increase in pressure may cause channelling. That is, the more reduced catalyst areas will promote the reaction of hydrogen and nitrogen to form ammonia in local sections of the bed. This reaction gives off heat and will cause catalyst bed temperatures to become higher and difficult to control in these localised areas. The pressure during catalyst reduction should be maintained at a point where reduction is symmetrical and temperatures in a horizontal section of the bed do not spread beyond a small range. Increasing the pressure will promote ammonia formation; lowering the pressure will retard ammonia formation. The catalyst can be reduced at fairly low gas rates; however, the higher the velocities through the catalyst the shorter will be the reduction period, and channelling through the beds may diminish at higher rates. It should also be noted that a minimum flow rate of 50,000 kglhr must be maintained through the annulus

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to avoid excessive temperatures between the top and bottom of the converter shell. Synthesis gas is recycled through the converter during catalyst reduction. When the reaction has started, it is very important that the circulating gas be cooled as much as possible to condense and remove the water vapour from the gas before recharging to the converter. Otherwise, gas with a high concentration of water vapour would enter the catalyst beds, which are already reduced. Water vapour will cause deterioration or poisoning of the reduced catalyst. In order to prevent freezing the water produced during the converter reduction, a stream of ammonia is injected to the discharge of the HP case of the synthesis gas compressor. This "anti-freeze" ammonia will prevent the water from freezing and damaging equipment. As soon as ammonia synthesis has started, the ammonia produced will lower the freezing pOint and permit water removal from the gas stream at lower temperatures and the ammonia injection will be discontinued.

c 3.2.4.6.2

Catalyst Thermal Resistance Even when operated on pure synthesis gas, ammonia catalysts do not retain their activity indefinitely. Some data indicate that when pure gas is being used, temperatures below 550°C do not affect the catalyst, whereas higher temperatures will harm the catalyst. These data also show that catalyst, which has suffered slightly from excessive temperatures, may show a loss of activity when tried out at 400°C, whereas the activity at 500°C may be unchanged. It Should, however, be emphasised that no definite temperature limit exists below which the catalyst is unaffected. At a fixed temperature level but under more severe conditions of pressure and space velocity, the deterioration of the catalyst should be expected to develop more rapidly. Degradation of the catalyst will first be apparent in reduced efficiency during operation at lower temperatures, higher pressure and/or higher gas rates. It has been observed that the more the catalyst activity has declined from the initial value, the more prolonged or severe will be the treatment required to produce further injury.

c 3.2.4.6.3

Catalyst Poisons Compounds which (when present in the synthesis gas) are capable of reducing catalyst activity and/or life are called poisons. Such substances normally form more or less stable compounds with the active materials of the catalyst. There are permanent poisons that cause lasting irreversible lowering of catalyst activity. They form stable surface compounds with active parts of the catalyst. Other poisons may cause a temporary decrease in activity; the initial effectiveness is restored in a relatively short time after removal of the poison compound from the gas.

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The most important group of poisons of ammonia synthesis catalyst are oxygen compounds. These cannot be classified as temporary poisons; neither are they permanent poisons. When an oxygen compound such as carbon monoxide is present in small quantities in the synthesis gas, some active areas of the catalyst combine with oxygen thus reducing catalyst activity. When the oxygen compound is removed from the synthesis gas, the catalyst again is fully reduced, but all the regenerated centres do not revert completely to the initial state or regain their initial activity. So the oxygen compounds cause a strong temporary and a small permanent decline in catalyst activity. The usual oxygen compounds that poison the catalyst are water vapour, carbon monoxide, carbon dioxide, and molecular oxygen. Other significant poisons are hydrogen sulphide (permanent) and oil spray deposits, which are not real poisons as this term is used here, but which are capable of lowering the activity of the catalyst by clogging the catalyst surface. 3.2.4.6.4

Catalyst Mechanical Strength The synthesis catalyst is mechanically strong. However, the operator should not expose it to excessive abuse. Mal-operation may cause very rapid temperature fluctuations, resulting in catalyst breakage. During the reduction period any rapid temperature changes should be carefully avoided; during this interval the catalyst is thought to be particularly sensitive to mechanical crushing and quick temperature variation A detailed catalyst loading procedure is presented in the General Procedures Manual under "Catalyst Loading of ammonia Synthesis Converter". Not covered in this procedure but of the utmost importance are the tests to which the catalyst must be exposed prior to loading in the converter. As later mentioned in the General Procedures Manual, chlorides in contact with the stainless steel converter basket may lead to stress corrosion cracking of this intemal vessel; therefore, the chloride content of each batch of catalyst must be checked before loading. The catalyst should have a maximum water soluble chloride content of 10 ppm. In the case of damaged catalyst containers that might have been exposed to contaminants, each container should be checked.

3.2.4.7

Separation of Anhydrous Liquid Ammonia from Synthesis Gas The ammonia that is produced in the synthesis reactor would quickly build to a level to interfere with the reaction so it has to be continuously removed from the synthesis recycle gas stream going to the converter. This is done by chilling the recycle stream via a combination of chillers/coolers in the unitized exchanger E-2120 to condense the net ammonia product that is produced in each pass through the converter. The temperature of the recycle gas stream is -17.SoC by the time it reaches the ammonia separator and the condensing / subcooling of the ammonia in the synthesis gas loop to this temperature, will reduce the ammonia in the recycle gas stream from 12.13 to 2.69%. The resulting chilled ammonia liquid collects in the ammonia separator (D-21 06) which is under L1C control (L1C-1013) The liquid ammonia leaving D-21 06 is the feed to the final product purification step of the process via D-21 07.

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3.2.5 Ammonia Product Purification (Removal of Absorbed Gases) As previously noted the liquid ammonia that is separated from the synthesis gas will contain a certain amount of absorbed gases that would result in a contaminated product and the purpose of the refrigeration system in the product purification step is twofold: First: the flash and reflash of liquid ammonia at lower pressure levels to release absorbed gases and direct them to the fuel gas/absorber system; & second: as an integral part of the refrigeration system, the process chillers in E-2120 remove heat from the synthesis gas in the synthesis gas loop to sub-cool the recycle gas to -17.BoC for the satisfactory separation and removal of the net ammonia make from the synthesis loop. These chillers are so located in the refrigeration system to take full advantage of the various pressure (and temperature) levels at which it is operated.

' C /

The ammonia refrigeration system is somewhat complex by nature; however, once the system is fully understood its operation is straight-forward and should operate very steadily. The following are descriptions of various items of equipment in the system, what they do, and how conditions are adjusted to give the desired results. For simplification the descriptions assume that essentially all ammonia product is withdrawn from the refrigerant receiver D-21 09. 3.2.5.1

Ammonia Let-down Drum (D-21 07) This let-down drum receives its feed from the ammonia separator (D-21 06) where the net ammonia make has been separated from the synthesis gas and in addition, a small import flow from the purge gas separator, D-210B. The D-21 07 pressure is controlled by PIC-110B at 17.6 bara and releases to the Ammonia Gas Scrubber, T-21 03. The liquid stream from D-21 07 is let down to two pOints in the refrigeration system under the level control of LlC-1 012 with the actual routing being selected by the hand switch HS-1024. If this switch is set for "COLD" product operation, then the liquid flow from D-21 07 will be let-down to the 1st Stage Refrigerant Flash Drum (D-2120). If 'WARM" product operation is selected, then the liquid flow will be let-down to the 4th Stage Refrigerant Flash Drum (D-2123). Any flash vapour from these two let down streams is routed to the Ammonia Gas Scrubber via the Refrigerant Receiver, D-21 09. The method of Unit Control when producing 'WARM" or "COLD" product is further described in Sections 7.6 & 7.7 of this manual.

c 3.2.5.2

First Stage Refrigerant Flash Drum (D-2120) This flash drum serves the process in three ways: first, by a deep over-flash essentially all of the inerts are removed from the ammonia product. Second, it serves as a "head drum" for the thermal Circulating refrigerant that is removing heat from the synthesis gas loop via the "cold" section of E-2120. Third, it receives the flashed ammonia let down from Second Stage Refrigerant Drum, D-2121 via the

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Purge Gas Chiller, E-2125. From 0-2120, the ammonia circulation rate through E-2120 is directly proportional to the heat input from the synthesis gas loop. The pressure on the drum is reduced to about 0.9 bara by the Refrigeration Compressor, C-21 05; pressure is controlled by PRC-1009, which regulates the speed of the machine. The temperature in the drum will be about -35°C as a result of the evaporating ammonia at 0.9 bara pressure. While producing a hot ammonia product as Urea plant feed from 0-2109 a smali portion of cold product is withdrawn from the 0-2120 to avoid an accumulation of water in the drum and the level in 0-2120 is held constant by level controller LlC-1024. Cold ammonia product pumps P-2124AlB/C are used for this disposal to the cold ammonia product system. It should be noted that when the Urea plant is in operation i.e. the NH3 Unit is on "WARM" product operation, only one pump will be in service with two on standby. When on "COLO" product operation, two pumps will be in parallel service with one pump on standby.

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Refrigerant Receiver (0-2109) All of the ammonia that has been flashed in the system, compressed by C-21 05 and sub-cooled in the ammonia condenser (E-2127) collects in this receiver. The pressure on this drum depends (indirectly) on the temperature and volume of cooling water flowing through the E-2127 condenser. The pressure is actually set by PIC-1109 (14.9 bara) that releases the inert gas (LP purge) to the Ammonia Gas Scrubber, T-21 03. The level of the receiver is held constant by level control LlC-1 015 The major portion of liquid ammonia from the refrigerant receiver is pumped by Warm Ammonia Product Pumps, P-2113AlB to the Urea Plant at a design temperature of 32.5°C at the battery limits. The remainder is flashed down to the Fourth Stage Refrigerant Flash Orum, 0-2123 at 16.~C. .

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Fourth Stage Refrigerant Flash Orum (0-2123) All of the ammonia that is not sent to battery limits as product from 0-2109 Refrigerant Receiver with the exception of the previously mentioned small stream from 0-2120, is reflashed in this drum. The pressure (and resulting temperature) of the Fourth Stage Flash Orum (0-2123) is variable, as it "floats" on an intermediate pressure of the second case of the ammonia compressor (C-21 05). This pressure is expected to be about 7.6 bara and the temperature of the evaporating ammonia in the flash drum will be about 16.~C. The level in 0-2123 flash drum is held constant by level control LlC-1021 controlling the let-down from 0-2123 into 0-2122. This drum serves as a "heads drum" and in addition to supplying refrigerant to 0-2122, also supplies ammonia refrigerant to two chillers: first, to the "hot" section of

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E-2120 by thermo-syphon circulation. As noted, this circulation rate is determined by the heat input to the chiller. Second, to E-2129 at a rate depending on the pressure differential between D-2123 and D-2122. The Interstage Chiller E-2129 is operated at a back pressure of about 3.4 bar (1°C) on the refrigerant side in order to prevent icing on the process side. 3.2.S.S

Third Stage Refrigerant Flash Drum (D-2122) The pressure (and resulting temperature) of the Third Stage Flash Drum is not variable, as it "floats" on the suction to the second case of the ammonia compressor (C-21 OS). This pressure is expected to be about 4.2 bara and the temperature of the evaporating ammonia in the flash drum will be about -2.2°C.

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Ammonia liquid is flashed directly into the Third Stage Refrigerant Flash Drum, D-2122 from D-2123 Fourth Stage Flash Drum by level control LlC-1021 and also via the Interstage Chiller, E-2129. Liquid from the Third Stage Flash Drum, D-2122 is circulated by thermosyphon effect through one of the two ''warm'' middle sections of unitized exchanger E-2120 in the synthesis loop. LlC-1022 controls the ammonia level in D-2122 by regulating the flow of liquid Ammonia from the Third Stage Flash Drum into the Second Stage Flash Drum, D-2121 3.2.S.6

Second Stage Refrigerant Flash Drum (D-2121) As with the other flash drums, the pressure (and resulting temperature) of the Second Stage Flash Drum is not variable, as it floats on the suction of the first stage case of the Ammonia Compressor, C-21 OS. This pressure is expected to be about 2.7 bara and the temperature of the evaporating ammonia in the flash drum will be about -17.SoC.

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Ammonia is also letdown from D-2121 into the First Stage Flash Drum, D-2120 through E-212S Purge Gas Chiller with the flow rate depending on the pressure differential between D-2121 and D-2120. . The liquid level in D-2121 is held constant by LlC-1 023, which delivers the excess to the First Stage Refrigerant Flash Drum D-2120. 3.2.S.7

Refrigerant Compressor (C-21 OS) The refrigeration compressor (C-21 OS) operates to serve the system in two ways: first, to maintain the desired pressure in the First, Second, Third and Fourth Stage Flash Drums (D-2120, D-2121, D-2122 & D-2123). This will ensure proper removal and separation of absorbed gases from the product stream. Second, to elevate the pressure of all flashed ammonia so the ammonia may be condensed and slightly sub-cooled with cooling water in the ammonia condenser E-2127 (1S.6 bara as read at PI-1641 on C-21 OS discharge.

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The condensing ammonia in E-2127 is subcooled approximately 2.2°C below the normal condensing temperature of ammonia as determined by the Compressor discharge pressure. This will ensure that pressure control of the compressor discharge is maintained by the release of absorbed gases to the Purge Gas Scrubber via PIC-11 09. Sub-cooling the condensed ammonia below this temperature will result in excessive absorbed gases in the refrigerant stream. On the other hand, sUb-cooling too close to the temperature could result in excessive ammonia in the purge gas stream. 3.2.6 Boiler Feed Water Deaeration (V-21 01)

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The preheated Demineralised water enters the top "stripping" section of the deaerator together with recovered condensate from the desuperheater steam traps and from the Ammonia Stripper Reboiler (E-2160) and C02 Stripper Stream Reboiler (E-2111). · The normal operating pressure of V-21 01 i~ 2.7 bara(1.7 barg), but during start-up however, the three preheat exchangers will not be in operation; therefore, the deaerator at this "cold water condition" may be operated at a lower pressure. · Oxygen content of the water can be reduced to 0.005 mg/litre or less by deaeration. · The requirements for .accomplishing this are: . · a) Having the water at tlie saturation condition; -i.e. at boiling temperature for the existing pressure b) Providing deaerator design that secures intimate contact between steam and water.

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0) Continuously venting a mixture of gases and steam from the deaerator. The deaerator design provides the intimatecontact of steam and water required. It is a tray type, wherein the preheated combined stream of makeup and condensate is sprayed into the steam compartment. -The water is spread out in a thin film as it flows down over the trays in continual contact with the steam and is heated to approximately saturation conditionS. A continual surplus of steam is used so that steam and the desorbed gases can be continually vented. This is accomplished by injecting sufficient LP steam under control of PIC-1031 which maintains the desired 2.7 bara operating pressure on the deaerator. The vent rate is set manually and it is sufficient that a moderate plume of steam be maintained from the vent since the volume of non-condensible gases desorbed is normally minute. The deaerated water flows down from the deaeration section into the storage section of the unit. The storage section holds water sufficient for about 20 minutes normal operation. Low level (LAL-1030) and high level (LAH-1030) alarms will warn the

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operator should either of these conditions occur so that corrective measures can be taken. A separate level controller L1C-1 031 is also provided which, on detection of a higher than normal level, will actuate control valve LV-1031 to dispose of the excess to the Equalisation Pond (A-9304) via a Blowdown pit. High/high level alarm (LAHH-1124) is also provided together with a Low/low alarm LALL-1125 which in addition to alerting the operator to this condition, will also actuate interlock ESD-1125 to automatically start the Offsite Deminineralised Water pump feeding the unit. There will be a slight (perhaps immeasurable) oxygen content from even the most efficiently operated deaerator. For this reason V-21 06 is provided to inject Oxygen scavenger to the water in the storage section.

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When boiler water is in contact with iron, some iron goes into solution as ferrous hydroxide. If there is no oxygen in the boiler water an equilibrium is soon reached. If oxygen is present in the water an insoluble compound, ferric hydroxide, is formed. Iron is lost from the system and a sediment is formed; if a continuing supply of oxygen is available, iron or steel continues to be lost from the piping and boiler systems. Ferrous hydroxide is an alkaline compound and its rate of solution depends upon the pH of the water. The lower the pH of the water, the more rapidly ferrous hydroxide goes into solution and in order to maintain the feed water at the desired pH range (8.8 to 9.2), morpholine is employed. A volume of morpholine is introduced into the injection tank V-21 07 to which steam condensate is supplied for dilution purposes and from where the morpholine injection pump takes suction and delivers the solution to the suction of the feed water pumps (P-2104A1B). It is anticipated that not more than 0.5 to 0.7 ppm of morpholine will be required to maintain the desired pH range of the BFW. Feed water is pumped from the storage section of the deaerator to the Steam Drum 0-2101 by Boiler Feed Water Pumps P-2104A1B via the preheaVwaste heat boiler systems as described previously.

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A line from P-2104A1B discharge also supplies B.FW. to the HP/MP Steam. Desuperheaters, the HP Steam Attemperator , the MP/LP Steam Desuperheater and desuperheater on E-2111 C02 Stripper Steam Reboiler LP steam supply. The feed water pumps are provided with manual and automatic low flow bypasses which retum a controlled amount of water to thedeaerator in order to avoid damage to the pumps if the steam drum level controller should shut completely. These flows are limited by auto recirculation valves from the pump discharge check-valves. The gate valves on the two lines must always be car-sealed open, (CSO).

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CATALYST OPERATING CONDITIONS

3.3.1 Hydrogenator - R-2160

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Stream Comgosition Methane Ethane Propane Butanes Pentanes C6+ Hydrogen Nitrogen Carbon dioxide Argon Water Total Flow H2S Sulphur (organic) Temperature Pressure

Unit kmol/hr kmol/hr kmol/hr kmol/hr kmol/hr kmol/hr kmol/hr kmollhr kmol/hr kmol/hr kmol/hr kmol/hr ppmv ppmv

°c bara

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Inlet 1452.4 18.4 3.2 2.1 1.2 2.2 45.0 31.3 3.6 0.2 0.1 1560.0 20 20 371 43.3

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3.3.2 Desulphurisers R-2108A1B

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Stream Comgosition Methane Ethane Propane Butanes Pentanes C6+ Hydrogen Nitrogen Carbon dioxide Argon Water Total Flow H2S Sulphur (organic) Temperature Pressure

Units Kmol/hr Kmol/hr Kmol/hr Kmol/hr Kmol/hr Kmol/hr Kmol/hr Kmol/hr Kmol/hr Kmol/hr kmol/hr kmol/hr ppmv ppmv

°c bara

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1452.4 18.4 3.2 2.1 1.2 2.2 45.0 31.3 3.6 0.2 0.1 1560.0 40.0 0.0 362 42.44

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3.3.3 Primary Reformer H-2101

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Stream Comj;losition Methane Ethane Propane Butanes Pentanes C6+ Hydrogen Nitrogen Carbon monoxide Carbon dioxide Argon Water Total Flow

Units Kmol/hr Kmol/hr Kmol/hr Kmol/hr Kmol/hr Kmol/hr Kmol/hr Kmol/hr Kmol/hr Kmol/hr Kmol/hr kmoVhr kmol/hr

Total Flow

Kg/h

Temperature Pressure

DC bara

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Outlet Inlet 1452.4 588.3 18.4 0 3.2 0 2.1 0 1.2 0 2.2 0 45.0 3292.5 31.3 31.3 0 460.3 3.6 482.1 0.2 0.2 4884.5 3467.2 6444.3 8321.9 113,533 113.533 605 39.9

811.9 36.5

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3.3.4 Secondary Reformer R-21 03

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Units Kmollhr Kmol/hr Kmol/hr Kmol/hr Kmollhr Kmol/hr Kmol/hr kmollhr kmolLhr

Feed 588.3 3292.5 31.3 460.3 482.1 0 0.2 3467.2 8321.9

Air/Steam

0 0 1626.6 0 0.6 437.5 19.6 208.4 2292.8

Outlet 31.6 4141.3 1658.0 963.1 536.6 0 19.8 3940.1 11290.4

Total Flow

Kg/h

113.533

64.132

177.665

Temperature Pressure

bara

812 35.6

605 36.3

994 35.1

Stream Coml2osition Methane Hydrogen Nitrogen Carbon monoxide Carbon dioxide Oxygen Argon Water Total Flow

°c

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3.3.5 HT Shift Converter R-21 04

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Stream Com[1osition Methane Hydrogen Nitrogen Carbon monoxide Carbon dioxide Argon Water Total Flow

Units Kmollhr Kmollhr Kmol/hr Kmol/hr Kmollhr Kmollhr kmollhr

Feed 31.6 4141.3 1658.0 963.1 536.6 19.8 3940.1 11290.4

Outlet 31.6 4828.6 1658.0 275.8 1223.9 19.8 3252.8 11290.4

Total Flow

Kg/h

177,665

177.665·

Temperature Pressure

bara

kmol/hr

°c

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371 34.2

434.4 33.9

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3.3.6 LT Shift Converter R-21 09

Stream Com[2osition, kmol/hr

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Methane Hydrogen Nitrogen Carbon dioxide Carbon monoxide Argon Water Total Flow, kmol/hr Total Sulphur, ppmv Temperature, DC Pressure, bara

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Inlet

Outlet

31.6 4828.6 1658.0 1223.9 275.8 19.8 3252.8 11290.4

31.6 5079.5 1658.0 1474.8 24.9 19.8 3001.9 11290.4

93°C at atmospheric pressure

4.15.8 Sodium Hydroxide [NaOH] • •

Grade: The alkali used should be high purity, low-salt caustic (mercury cell or rayon grade). Solution concentration (as used): 4 - 25% by weight.

The following is a typical rayon grade nominal 50 wt % sodium hydroxide solution analysis:

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Composition: NaOH NaZC03 NaCI NaCI03 Fe NazSO. SiOz Ab0 3 CaO MgO

51.2% bywt. 0.027% by wt. 0.002% by wt. 30 ppm 60 ppm