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Tank Storage Istanbul 2011 29-30 November 2011 Grand Cehavir Hotel, Istanbul, Turkey



News regarding venting of atmosheric and low-pressure storage tanks



News regarding use of flame arresters

(why do p/v-vents not function as flame arrester?)

Dipl.-Ing. Axel Sommer PROTEGO® – Braunschweiger Flammenfilter GmbH

1

New International Standard: Venting of atmospheric and low-pressure storage tanks ISO 28300

API 2000 5th edition

ISO 28300 Petroleum, petrochemical and natural gas industries – Venting of atmospheric and low-pressure storage tanks

EN 14015 Annex L

TRbF 20

API 2000 6th edition 2

Background and development of ISO 28300 Standard 

ISO 28300 was mainly developed based on the API 2000 standard 1998 6th Edition and the EN 14015 Standard Annex L and the German TRbF 20



Contradiction towards the venting requirements for normal venting



Contradiction towards the use of vents as flame arresters

Committee goal: 

This standard shall consider all state of the art knowledge concerning tank venting and safety and provide best practice to the user

3

Why new calculation methods for determining normal venting requirements? 

Prof. Salatino from the University of Napoli predicted that the calculation method of API 2000 may underpredict thermal breathing



The German TRbF 20 standard developed by Dr. Hans Foerster from the Federal Institute if Physiks (PTB) also results in higher values for thermal breathing



The EN 14015 Standard developed by Dr. Wheyl from BASF also results in higher breathing values



All the above methods depend on a detailed thermodynamic model and provide higher inbreathing rates than the API 2000 standard 4

Validation of results for inbreathing Prof. Salatino Model calculation at University of Napoli, 1999 • • • •

Tank: V = 63000 m3; D = 70 m; H = 15 m Δ T = 40 °C Water (rain) flow density Refined model calculation - Dynamic simulation (pressure differential at vent) - Different start temperatures of roof, shell and product

5

Validation of results for inbreathing

API 2000 TRbF 20 ISO 28300

Prof. Salatino Model calculation at University of Napoli, 1999

6

Validation of results for inbreathing Life field tests and model calculation at Hoechst in 1980 and 1981 • Tank: V = 617 m3; D = 8,5 m; H = 10,6 m • 17 °C ≤ Δ T ≤ 26 °C • Water (rain) flow density: about 60 kg/m2h • TRbF-model calculation

7

Validation of results for inbreathing

8

Summary 

The new section is based on the European EN 14015 Standard.



The approach used is more general than API (the API approach is centered around hexane or similar services).



Calculated vent rates with the new approach can be substantially higher for certain tank sizes than what is shown in API-2000.



A research paper from Prof. Salatino and research results from Hoechst in Frankfurt, which had been provided by Dr. Hans Foerster from the PTB justified this change.



An advantage of the new calculation method is that it does allow to consider full and partial insulation of the tank for normal in- and out-breathing.

9

ISO 28300 venting requirements Normal out-breathing and normal inbreathing flows are defined as the combination of tank vent flows due to: 

Liquid flows into and out of the tank



Ambient weather (thermal) effects

 =V   V + V out thermal− out pump −in

 =V   V + V in thermal−in pump − out 10

Liquid filling capacities - out-breathing out-breathing rate = filling rate

special calculation have to be done for spike products, and at storage temperature > 40°C and vapour pressure > 50 mbar: 11

Liquid filling capacities - inbreathing in-breathing rate = discharging rate

12

Basis: Model calculations for a fixed roof above ground storage tank of steel General assumptions and approximations: 

Uniform (time dependent) temperatures of wall, tank atmosphere, ambient air and rainwater-film



Primary result is the temperature of the tank atmosphere in dependence on time ; volume flow rates are then deduced by an isobaric approach (constant ratio of volume to temperature)



Tank atmosphere is air at ambient pressure



Wall thickness is according to common tank standards ( ≥ 4 mm)



No heat flux via tank bottom 13

Determining of normal & emergency venting requirements

General Basic Equation for ISO 28300 Model:

V dTg  ⋅ V= Tg dt Energy balance to describe temperature distribution with respect to time

dTg  Q = k ⋅ A ⋅ (Tg − Ts ) = V ⋅ ρ g ⋅ c g ⋅ dt 14

Heat flows during heating by solar radiation (outbreathing) solar irradiation far IR radiation loss

convection

convection

15

Solution if solving differential equation: 80

ϑW

Maximum volume flow

30

Volume Flow V in m3/h

25 40 VG,B 20 20

Maximum volume flow occurs at maximum delta T 0

0

900

1800

2700

3600 Time t in s

4500

5400

6300

15 7200 16

Temperature ϑ in oC

ϑG

60

Thermal out-breathing simplified as in ISO 28300 0,9  = V C V R in thermal− out out T

Cout = 0,2

latitude : > 58°

Cout = 0,25

latitude : 58°-42°

Cout = 0,32

latitude : < 42°

Rin = reduction factor insulation Vt = tank volume 17

Heat flows during cooling by rain (inbreathing) Rain water flow to wall

conduction

convection and evaporation

convection

Rain water drain from wall 18

Solution if solving differential equation: Maximum volume flow

300

55 VG,B 45

Temperature ϑ in oC

Volume Flow V in m3/h

240

ϑG

180

35 120

ϑW

25

Maximum volume flow occurs

60

at maximum delta T 0

0

180

360

Time t in s

540

720

15 900 19

Thermal - inbreathing 0,7  Vthermal−in = Cin VT R in vapour pressure

Cin latitude > 58° 42° - 58° < 42°

higher than hexane, or unkown storage temperature < 25 °C ≥ 25°C < 25 °C ≥ 25°C 2,5 4 4 4 3 5 5 5 4 6,5 6,5 6,5 haxane or similar

Rin = reduction factor insulation Vt = tank volume

20

Calculation – Examples Tank 1 Tank: 

Height: 5m



Diameter: 7m



Tank volume: 192.4 m3



Pump in rate: 96 m3/h



Pump out rate: 96 m3/h



Vertical tank



No insulation



MAWP: + 7.5 mbar



MAWV: - 2.5 mbar 21

Inbreathing Requirements (Total) for Tank 1 Inbreathing requirements Tank 1 400

Venting requirements [m3/h]

350 300 250 200 150 100 50 0 API 2000

EN 14015, North, VP Hexane

EN 14015, North, VP> Hexane

EN 14015, 42- EN 14015, 4258, VP Hexane 58, VP> Hexane Pump out

EN 14015, South, VP Hexane

EN 14015, South, VP> Hexane

TRbF 20

Thermal

22

Outbreathing Requirements (Total) for Tank 1 Outbreathing requirements Tank 1 250

Venting requirements [m3/h]

226 200

150

116

117

123

130

H/D = 0.71

118

100

H/D = 0.5 H/D = 2

122 109

50

0 API 2000, FP =37.8C

EN 14015, North

EN 14015, 4258 Pump in

EN 14015, South

TRbF 20

TRbF 20-2

TRbF 20-3

Thermal

23

Calculation – Examples Tank 2 Very Large Size Tank (outside of scope of API 2000): 

Height: 15 m



Diameter: 75 m



Tank volume: 66,268 m3



Pump in rate: 1,400 m3/h



Pump out rate: 1,400 m3/h



Vertical tank



No insulation



MAWP: + 7.5 mbar



MAWV: - 2.5 mbar 24

Inbreathing Requirements (Total) for Tank 2 Inbreathing requirements Tank 5 18000

Venting requirements [m3/h]

16000 14000 12000 10000 8000 6000 4000 2000 0 API 2000

EN 14015, North, VP Hexane

EN 14015, North, VP> Hexane

EN 14015, 42- EN 14015, 4258, VP 58, VP> Hexane Hexane Pump out

EN 14015, South, VP Hexane

EN 14015, South, VP> Hexane

TRbF 20

Thermal

25

Outbreathing Requirements (Total) for Tank 2 Outbreathing requirements Tank 5 10000

Venting requirements [m3/h]

9000 8000 7000 6000 5000 4000 3000 2000 1000 0 API 2000, FP =37.8C

EN 14015, North

Pump in

EN 14015, 42-58

EN 14015, South

TRbF 20

Thermal

26

Calculation example considering insulation: • • • • • •

Tank volume Stored liquid Pump in Pump out Insulation Insulation thickness

592,000 barrel (94.120 m³) Bitume 4542 barrel/h (722 m³/h) 5458 barrel/h (867 m³/h) Calciumsilicate 2”

27

Overview Venting Requirements (API 2000, ISO 28300) API 2000 (without consideration of insulation): • Inbreathing: • Outbreathing:

6.600 Nm3/h 4.200 Nm3/h

ISO 28300 (without consideration of insulation): • Inbreathing: • Outbreathing:

16.020 Nm3/h 7.920 Nm3/h

28

How to consider insulation during thermal inand out-breathing Reduction factor for insulation according to ISO 28300

RIN =

1+

1 h ⋅ LIN

λ IN

λ

= heat conduction coefficient

h

= heat transfer coefficient

LIN

= thickness of insulation

Here: RIN = 0.2145 29

Overview Venting Requirements (API 2000, ISO 28300) API 2000 (without consideration of insulation): • Inbreathing: • Outbreathing:

6.600 Nm3/h 4.200 Nm3/h

ISO 28300 (with insulation): • Inbreathing: • Outbreathing:

4.140 Nm3/h (vs. 16.020 Nm³/h) 2.280 Nm³/h (vs. 7.920 Nm³/h)

30

How to determine inert gas blanketing rates ISO 28300 Annex F provides guidance for inert gas blanketing of tanks for flashback protection 

This guidance is based on the German TRbF 20 standard



The concept has provided proven safety to the industry for decades



It is simple way to assure sufficient inert gas blanketing levels



The amounts result from the inbreathing rates of the ISO 28300 equations 31

3 different levels of inert gas blanketing 

Level 1 minimum inert gas blanketing requirements in combination with a specific flame arrester classification



Level 2 more stringent inert gas blanketing requirements with different flame arrester classification



Level 3 the highest inert gas blanketing requirements with no flame arrester

32

Tank inbreathing needs to be considered 

inbreathing due to changes in weather



inbreathing due to emptying of tank

Inert gas supply needs to be determined 

minimum amount of inert gas volume flow



amount of reserve inert gas

VI

VI 33

Inert gas level 1: 0,7  VI = 0,1× C × VT + Vpe

= VI 0, 04 × VT

expressed in m3/h expressed in m3

Additional conditions: 

monitor inert gas supply



alarm shall be triggered when set pressure of the vacuum vent is reached.



inside of the tank can be classified as Zone 1 (according to the IEC)



An end-of-line flame arrester shall be installed which has been tested for atmospheric deflagration and endurance burning for IEC explosion group IIA (NEC Group D) vapours. 34

Inert gas level 2: 0,7  VI = 0, 2 × C × VT + Vpe

= VI 0, 08 × VT

expressed in m3/h expressed in m3

Additional conditions: 

The alarm specified under inert gas stage 1 shall activate the shutdown of the liquid outflow.



At this level of inert gas blanketing the inside of the tank can be classified as Zone 2 in accordance with IEC 60079-10.



An end-of-line flame arrester shall be installed which has been tested for atmospheric deflagration for IEC explosion group IIA (NEC Group D) vapours. 35

Inert gas level 3: 0,7  VI = 0,5 × C × VT + Vpe = VI 0,12 × VT

expressed in m3/h expressed in m3

Additional conditions: 

The tank pressure shall be kept above atmospheric pressure and the monitoring system shall have redundancy in the design.



The inert gas supply shall be kept above the tank pressure and in particular the required flow rate of shall be achieved with a tank pressure at least equal to the atmospheric pressure.



The trip pressure at which the liquid outflow will be shut down shall be set above atmospheric pressure. (Pump Shut Off)



Alarms shall be triggered at the trip pressure.



At this level of nitrogen blanketing the inside of the tank can be classified as Zone 2 in accordance with IEC 60079-10. At this level of inert gas blanketing no additional protection against flame propagation from the outside to the inside of the tank is required. 36

Why conservation vents do not function as flame arresters:

37

Why conservation vents do not function as flame arresters: 

API 2000 5th Edition 1998: A flame arrester is not considered necessary for use in conjunction with a pressure vacuum valve venting to atmosphere because flame speeds are less than vapor velocities across the seat of the pressure vacuum valve



TRbF 20 (German standard): clearly calls for flame arresters for tanks that contain liquids that can create an explosive atmosphere



Factory Mutual (Insurance and approval company) requires installation of flame arresters on tanks which store liquids with a flash point at or below 43 ◦C or on tanks which heat the stored liquid to its flash point 38

Conclusion for ISO 28300 committee regarding atmospheric explosion protection of storage tanks: 

Research work is needed due to contradicting standards and opinions on the ISO 28300 committee



ISO 16852 shall apply as test standard



Two types of test are needed: A) atmospheric deflagration test B) continuous burn test

39

5 major vent manufacturers where tested

pressure pallet

vacuum pallet

40

Typical settings for API 650 tanks set pressure: 10 mbar ( 4.0 in WC)

set vacuum: -2 mbar

(-0.8 in WC) 41

Atmospheric Deflagration - Test set-up 1 ignition source 2 plastic bag Ø 1,2 m, length 2,5m foil thickness >0,05 mm 3 conservation vent 4 explosion proof container 5 mixture inlet with shut-off valve 6 mixture outlet 7 bursting diaphragm

atmospheric deflagration test of end-ofline flame arrester as described in ISO 16852 part 7.3.2.1 and EN 12874 part 6.3.2.1 42

Atmospheric Deflagration - Test set-up 1 ignition source

6

2 plastic bag Ø 1,2 m, length 2,5m foil thickness >0,05 mm

2

3 conservation vent 4 explosion proof container

1

5 mixture inlet with shut-off valve 3

6 mixture outlet 7 bursting diaphragm

5

7

4 43

44

Atmospheric Deflagration – Test No 1

P/V VALVE – 4,2 vol% propane in air – 28.03.2007

45

Atmospheric Deflagration – Test No 2

P/V VALVE – 5,5 vol% propane in air – 28.03.2007

46

Atmospheric Deflagration – Test No 3

P/V VALVE – 6,0 vol% propane in air – 28.03.2007

47

High Velocity Burning - Test set-up 1 continuous flame 2 pressure vacuum valve 3 explosion proof container 4 mixture inlet 5 bursting diaphragm 7 pilot flame 10 shut-off valve

Flame transmission test for high velocity vent valves as described in ISO 16852 part 9.2. and EN 12874 part 9.2. 48

High Velocity Burning – Test No 4 P/V VALVE stoichiometric propane air mixture V= 85 m³/h 28.03.2007

49

High Velocity Burning – Test No 5 P/V VALVE stoichiometric propane air mixture V= 100 m³/h 28.03.2007

50

Recommendation of ISO 28300 regarding explosion prevention: 

Different tank selection



Inert gas blanketing



Flame arresters



Flame propagation through pressure/vacuum valves (4.5.4) Testing has demonstrated that a flame can propagate through a pressure vacuum valve and into the vapour space of the tank. Tests have shown that ignition of a PV's relief stream (possibly due to a lighting strike) can result in a flash back to the PV with enough overpressure to lift the vacuum pallet causing the flame to enter the tank's vapour space. Other tests have shown that, under low flow conditions, a flame can propagate though the pressure side of the PV. 51

Summary - p/v valves cannot stop an atmospheric deflagration - p/v valves are not able to stop a flame by dynamic effects hence: - p/v valves cannot substitute flame arresters - p/v valves are not high velocity vent valves - only devices approved according flame arrester standards* are flame arresters * ISO 16852, EN 12874, USCG 33 CFR part 154, CSA Z343-98 52

Thank you very much for your attention !

Any questions?

53