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ABU DHABI GAS INDUSTRIES LTD.

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PROCESS ENGINEERING

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DESIGN MANUAL

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COMPAGNIE t=RAN(AISf: DES PETROTIS c--.

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PROCESS ENGINEERING DESIGN MANUAL

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Page No

X

TEP'DP/EXPISUR Date:

1.

DESIGN CONDITIONS

2. VESSELS (vapour-liquid separa tors)

.

Horizontal Vertical

.

3. COLUMNS

. .

Tray Packed

4. HEAT EXCHANGERS

.

.

Shell + tube Air coolers

Plate exchangers Furnaces

5. PUMPS

. .

Centrifugal Reciprocating

6. DRlVERS

. .

Gas turbines Electric drivers

. Steam turbines

7. COMPRESSORS g. EXPANDERS 9. FLARE SYSTEMS

10. PIPES VALVES + FITTINGS . Line sizing . Piping classes

. 6 P through valves and .ii ttings . Control valves - sizing and selection

11. PIPELINES

. Pressure and temperature drops 12. PACKAGE UNITS

Dehydra tion Refrigeration

. Gas sweetening

13. UTILITIES

Water Nitrogen

Air Drainage

14. COMPUTER PROGRAMS 15. DATA 16. PROCESS CALCULATION SHEETS 17. PROCESS OAT A SHEETS

• L-_____________________________________________________________________________ ~

ReVISIon

0

Page No

FORE WORD TO REVISION 0

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~_T_EP_I_O_P_/E_X_P_I_SU__R~~________________________________~______-L_D_a_te_'___2_/_&_5__~__________

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The purpose ot this manual is to present in a practical way the process design methods to be used by TEP personnel for quick calculations as well as detailed ones. They have been carefully

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selected by the most experienced engineers of the Process and Operations Department (TEP/DDP/DIP/EXP/SUR).

The physical presentation is different from that of the othh TEP/DDP/DIP manuals in order to get an easily transportable document as well as one which i~ convenient for photocopies.

Chapter 15 gives a selection of basic data which is

I

I I

Most methods are illustrated by selected examples.

.1

sUfficie~t for

most calculations.

Chapters 16 and 17 consist of blank calculation sheets and! Process data sheets that can easily be photocopied. !

Blank pages a 100

MOP .. 596

Vessels subject to vacuum during operation shaH be designed for the maximum external operating pressure plus a margin of 0.15 bar. If the-internal pressure is 0.35 bar a or less the vessel will be designed for full vacuum.

D-esign pressure for pump discharges shaH be calcuIa!ted by taking 120 96 of the normal pump ~ P when operating at design conditions.

I I I I I I I I I I

Page No

DESIGN CONDITIONS

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PROCESS ENGINEERING DESIGN MANUAL

ReYI~ion :

Date

2/&5

I

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2.

VESSELS

, i

I

•

.

Pa.. f'- - f'v

'f'·2-3

)

r

Equation 3 is then used to calculate Vs.

4.2.

LIQUID-LIQUID SETTLING VELOCITY

-l. , (

(based on Stokes law of terminal settling)

Co"

l)

,1

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c,t- ~' ,J

- \ C ,-'

The following equation can be used for calculating the settling velocity of water in oil or the upwards "settling" of oil in water. The important fact is to use the viscosity of the continuous phase i.e : fo~oJI settling ':lpwards through water use the water v}~cosity, for water settling in oil use the oil viscosity.

Ut = 3" D

18

c..

~ (f ... - fl.)

10

)lc.

Ut =

terminal velocity

m/s

g =

gravitation accel

m/s2

density heavy fluid

kg/m3

I'h =

o

,:/1

=

density light fluid

kg/m3

)'C

=

viscosi ty (continuous)

kg/m.s

.;1 ('

D=

particle diameter m Setting the particle size to 125 microns and using more useful units gives: (5)

Ut: 0.5108 (

.f~ f~)

Ut in

Ie. f

mm/min

in centipoise in kg/m3

The above equation is valid for RE YNOLDS number of 0.1 _ 0.3 If calculated settling velocity is 4.3.

> 250 mm/min use 250 max.

.

j"

"J

/((

'-'

Iii-'

---/

U.

VESSEL VOLUMES

Partial volumes of a horizontal cylinder can be calculated using the partial volume charts in Figure 3 or estimated using the following equations: (for vessels wi th a diameter < 1.2 m ignore ~ead volumes)

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0

Page No

2/85

2.4

RevIsion'

I I I I I I I

VAPOUR - LIQUID SEPARA TORS Date:

(see page 2.13 for sketch)

HORIZONTAL CYLINDER Arccos 2 DISHED HEADS 2 ELLIPTICAL HEADS 2 HEMISPHERICAL HEADS

in radians

Vdh = 0.21543 h 2 (1.5 D - h) m3 Veh = 0.52194 h 2 (1.5 D -: h) m 3 (most common) Vhh = 1.047 h 2 (1 •.5 D - h) m 3 (gives extra vol)

VOLUME UP TO BAFFLE (see page 2.23) =

fordepthh (elliptical heads)

0.52194h..z. (1 •.5D-h)+ AL.B 2

These formula are accurate enough for general design and are easily programmed on to a calculator for time saving. More accurate formula are available, see ref list, but are often too complicated to be useful for multiple calculations. For greater accuracy the length L should be the tan-tan length and not the flowpath length between nozzles. This is especially true with large vessels and a tight design. 4.4.

CALCULA TION PROCEDURE VERTICAL VESSEL (vapour-liquid separation) A guide for filling in the attached calculation sheet. Decide if Figure I can be applied i.e P [f

< 50

bara,

j1 < 0.0 I cp

applicable use the .500 micron curve to evaluate settling velocity (this assumes

a mist eliminator will be installed) or 150 micron with no mist eliminator. It is recommended to instaCl a mist eliminator for most applications. If not calculate Vs using equ 3. Derate the calculated settling velocity by 85 96 design margin to give a maximum allowable vapour velocity. Calculate drum

internal diameter and round to nearest 50 mm. (further

adjustment of 10 : 00 can be made to suit standard head dimensions).

r

Check if wall thickness is less than 100 mm (See para 4.8). .J

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r----------r-_______ .___ ._.... _____________.-______-.-____~ 0

RevISion

Page No.

VAPOUR - LIQUID SEPARA TORS

•

2/85

Date.

2.5

calculate vessel height based on following criteria:

v

TL

hI : max (15 % of

0 or 400 mm)

(L}

~

)_

'q,)( ..

h2 : 100 mm if mesh selected

hI

150 mm for compressor KO

h2

h3 : max (50 % of

0 or 600 mm)

l'

"

.

hl F

If no mesh use hi + h2 + h3 :: 60 %

~ or 800 mm

h4 III-'

h4 : 400 mm

hS

+

d/2 : d = inletl nozzle

0

IJLL

h6

- -HLL

u.r..

h5 : calculate based on 1-21inutes residence time at maximum liquid inflow (Imin 200 mm)

h7 I

IoU

/,

h6 : base on following hold up times: (min 350)

h8 TL

reflux drums

4 min

product drums

5 min

with pump

3 min

no pump

L

heater feed

8 min

HP sep. to lP sep.

4 min

h7 : 1-2 min residence time (rr!linimum 150 mm) I

h8 : 150 mm for bottom connebted lC 300 mm for side connecteb LC Note:

,

For compressor suction drums that are nlormally dry set Hll at 450 mm I

above tan line and use bottom connect¢d lC. This will reduce ves5el height if required. ,'10 specific Hll-LLL IhOld up time required.

I

RevIsIon

0

P.Jge No

2/85

2.6

VAPOUR - LIQUID SEPARATORS

g

Date"

4.5.

CALCULA TlON PROCEDURE HORIZONTAL VESSEL (2 phase) A guide on how to fill in the attached calculation sheet.

f

1. Calculate settling velocity Vs for par tical size 500

(use Fig. I or equ. 3.)

2. Derate this by F = 0.85 and calculate required vapour velocity V mls

"' Vm = F x Vs x (LID) mls

use LID of 3 to 4 max (J firs test)

3. Evaluate required vapour cross sectional area, Av 4. Assume drum is 70 % full i.e hiD = .7 and evaluate drum ~ to give required Av (to nearest 50 mm). For "dry" vessels use hiD = .35 5. For required liquid surge volume, calculate vol at HLL, if insufficient adjust 0 or L (note if LID changes significantly recheck Av using new Vm). 6. Set position of LLL in drum and confirm required surge vol between HLL-LLL. If volume is insufficient increase 0, Lor h. Include volumes in heads. 7. When setting LLL height take into account any LSLL, LSL alarms and vortex breakers which may set minimum value usable. Usually 300-350 mm. 8. Rationalise all heights and dimensions to nearest 10 mm.

I

NOTES: For high volumetric flows of gas with small liquid volumes consider using split flow arrangement. Design is as above but with half vapour volume flow. Normal design is with top entry, exit nozzles. However if space is limiting (primarily offshore) head mounted nozzles can be used to "increase flowpath. L is designated as the flow path length i.e distance between inlet and outlet nozzle. L' is the tangent-tangent length. For 1st estimates L' = L 0i ~ inlet nozzle diameter

+

1.5 0i

+

1.5 ~2

02 = outlet nozzle diameter

"Normal" liquid levels are taken as midway between the high and low levels. "I

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I I I I I I I I I I I I I I I I I

n

EY8'WP

VA PO lm - LIQ UID SEP AR A TOR S Dat e·

4.6 .

2/8 5

2.7

CA LC UL AT ION PRO CED UR E HO RIZ ON TAL VESSEL 3 PHA SE (S~e Fig ure 4) Suf fici ent resi den ce tim e to allo w sep ara tion of the oil- wat er mix ture as wei ! as the oil sur ge and vap our flow are as mu st be pro vid ed. 1. Pro cee d wit h step s I to 4 as for a two pha se sep ara tion . Use LID = 3 (l st est ima te) and eva lua te L. 2.

Pro visi on now has to be mad e to acc om mo dat e bot h oil and wat er sur ge vol um es. Use Tan -Ta n len gth L' and not noz z-n ozz dis tan ce L.

3. Cal cul ate LLL req uire d to giv e app rox 4 min s oil sur ge cap aci ty (mi nim um ). Ins pec tion wil l rev eal whe the r suf fici ent hei ght exi sts belo w LLL to inc lud e the inte rfa ce lev els. If not , adj ust the ves sel 00r L to giv e suf fici ent roo m. No te:

If the wat er cut is ver y sma ll, con side rati on may be giv en to usin g wa ter boo t inst ead of a baf fle arra nge me nt see step 10.

~

4. Hav ing det erm ine d HLL and LLL now set bot h pos itio n and hei ght of baf fle. Cal cul a te term ina l sett ling vel oci ty of wat er dro ple t (eq u ') sec t 4.2} and set tlin g tim e at bot h HL L and LLL . Vol um etri c flow of liqu id is in bot h cas es the oil plu s the wa ter. Cal cul ate fall dis tan ce of a dro ple t acr oss len gth of the dru m. Baf fle hei ght and pos itio n can now be set not ing : the baf fle sho uld be at lea st 75 mm belo w the LLL the baf fle sho uld be at lea st 2/3 dow n the len gth of the dru m from the inle t in som e cas es the wat er dro ple ts will set tle to the floo r in a sho rt dis tan ce. The baf fle sho uld stil l be set at a min imu m of 2/3 ~long the ves sel. 5. Set the HIL at baf fle hei ght - 75 mm . The LlL acc ord ing to hei ght det erm ine d by vor tex bre ake r -to LSLL use a min imu m of 300 -35 0 mm . 6. Che ck if an oil dro ple t will rise thro ugh the wat er lay er (fro m dru m floo r) to LlL bef ore rea chi ng wat er out let. Use are a at LlL wit h nor mal oil + wat er flo wra tes . (Th is crit eria is ver y rare ly gov ern ing but mu st be che cke d). 7. Cal cul ate wa ter surg e tim e bet wee n HIL and LILt and resi den ce tim e bet wee n NIL and out let. Rem em ber to use only one hea d vol ume , and leng"th of dru m upt o baf fle. Min imu m acc ept abl e tim es are 4-5 min s. If cal cul ate d tim es are ver y lon g con sid er usin g a wat er boo t arra nge me nt. 8. Rat ion alis e all dim ens ion s and "tid y" leve ls to stan dar d valu es if pos sibl e I.e 150 mm , 200 , 250 , 300 etc . Thi s allo ws use of stan dar d disp lace rs. 9. Rec alc ula te ail resi den ce tim es bas ed on "tid ied" lev els (if req uire d). No te: In cal cul atin g tPe fina l resi den ce tirn es mak e sur e tha t the ves sel tan tan len gth is use d and not the noz zle to noz zle dist anc e L.

• 0

RevIsion

a

Page No

VAPOUR - LIQUID SEPARA TORS

« ••

Date:

2/85

2.8

10. Boot calculation (See Fig. 5)

If the water volumetric flow is so small as to ryot warrant a separate baffled settling compartement as detailed above a water boot should be used instead. To design proceed as follows:

1. Proceed as previous upto step 3. 2. Calculate settling distance of water droplet when vessel is operating at LLL. Water droplet should reach floor of drum before oil outlet. Remember that the oil exit nozzle will be raised above the floor as a standpipe.' Adjust drum ~ or L to achieve settling.

3. Check that settling is also possible when operating at HLL, droplet to fall below drawoff nozzle level. 4. Size water drawoff boot

~

(try to use standard pipe diameters). Calculate

rising velocity of the oil in water, set downward velocity of water in boot at 90 % of this and evaluate boot 0. Boot length by inspection (use standard displacers). Note

Boot" must be less than 35 % of vessel" When heavy walled vessels are used a remote boot may be more economical to prevent large cuts in the main vessel.

NOZZLE SIZING (see section I 0.0 also)

4.7.

Inlet nozzle Size based on normal volumetric flow + 10 % (liquid + vapour flow) Limit inlet velocity to 7 - 13 m/s Round nozzle diameter up or down to nearest standard size Gas outlet

Normal flow + 10 %

Velocity limit 15-30 m/s

Velocity limit

Manholes: 450 mm or 600 4.&.

Liquid outlet

Size on normal flow

I-J m/s HC 2-4 m/s water

Min. diameter = 2" (avoid plugging)

VESSEL WALL THICKNESS Calculate vessel wall thickness using the ASME VIII dive 1 formula. The wall thickness should be calculate9 immediatly < 100 mm.

t

after

0

is known

to confirm

if

r

2.11

I EQUIP\lENT 01 0

1)

I

2)

Calr:ulate settling veloc::ity Vs

~

Cakulate vessel diarneter required tor droplets separation:

I

01

Y.

=4

Qg

lr. VS.

I

1/

.,

F. (LTD)

I

3)

Cakula te vessel diameter required for suffic:ient liquid residence time:

02

V-

=

6 QI

I 4)

Select 0

I,

= max (D 1,

I

~

I

02). Round to Upper value

= QI = Ys = 0 = LID = F =

security fac:tor (O.85)

tres =

liquid residenc:e time

Qg

r

I

t,.,

311'" (LID)

(

I I I

gas flowrate at P, T

m 3 /s

total liquid flowrate

m 3 /s

settling velocity

m/s

vessel diameter

m vessel design ratio (LID = 3-4) _

.

s

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i

.

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t I

... ~ 8y

I

1

CHI(

I

PROCESS CALCULATION SHEET

SHOR T CUT METHOD HORIZONTAL DRUM

R

DATE

1

!

I

ITEM

No lOf! Tift[

l08No ~!"

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I I

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I 2. I 3

CALCULA TlON SHEET FOR VERTICAL TWO PHASE SEPARA TOR

.D

EQUIPMENT N°

It3~

MOr

l>EGASSING.

0eerating data: Pressure (operating)

bara

Temperature (operating)

°C

Gas MW Gas flow rate Gas density

kg/h (T,P)

kg/m3

Ac:tual volume flow Qg

m3/s

= 1.01. = 3~ = $'"1. It = 1i~o = ~.I = o.9"l

Liquid desc:ription : C Ilv~£ o;t... Liquid flow rate

kg/h

Liquid densi ty (T ,P) kg/m3 Actual volume flow m3/min Partide size

CS):

Mesh pad

No

= 106'\0 = 210 = O.~~ = IS"O

mic:rons

Estimate Vs using Figure I and 500 mic:ron c:urve

:

If P

< 50

If P

> 50 bar or

~

bar and

< 0.0 I

use Fig. I and 150 mic:rons

! ) 0.0 I use c:akulation for Vs

1. Vapour-liquid settling velocity: from Fig I/cel "let! d.