Determination of Clearance Distances for Venting Determination of Clearance Distances for Venting of Hydrogen Storage of Hydrogen Storage

Andrei Tchouvelev, Pierre Benard, Vlad Agranat and Zhong ChengAndrei Tchouvelev, Pierre Benard, Vlad Agranat and Zhong Cheng

AcknowledgementsAcknowledgements

• Work partially supported by– Natural Resources Canada (NRCan) CTFCA

Clearance Distance Project– Natural Sciences and Engineering Research

Council of Canada (NSERC) Industrial Research Fellowship

IntroductionIntroduction• Part of Hydrogen Clearance Distances Project under Canadian

Transportation Fuel Cell Alliance (CTFCA)• R&D study with practical application: contribute to development of

model codes and engineering guidelines for design of vent stacks for hydrogen venting under conditions of a hydrogen energy station

• Innovative approach:– Clearance distances related to venting of hydrogen storage were

differentiated between distances to people and equipment (at 1.8 m above ground) and distances to air intakes and ignition sources (located above the top of a vent stack)

– Recommended clearance distances are based on extents of 100% LFL hydrogen concentration envelopes plus 25% safety factor

• Obtained tables and graphs were based on CFD modeling of hydrogen releases and dispersion, implemented through the PHOENICS software package and on thermal effects analysis using TNO “Yellow Book” recommendations

International Fire Code, Section 2209International Fire Code, Section 2209

Flux (kW/m2) Damage to Equipment

Damage to human beings

37.8 Damage to process equipment

1% mortality in 10 sec

25.0 Minimum energy required to ignite wood at indefinitely

long exposure

Significant injury in 10 sec

12.6 Plastic tubing melts 1st degree burns in 10 sec

9.5 Immediate skin reactions

4.7 (1,500 BTU/ft2) Pain threshold

1.6 (500 BTU/ft2) Safe level

Thermal Level Standards for Thermal Level Standards for Hazard AssessmentHazard Assessment

API Recommended Practice 521API Recommended Practice 521

• “Flame length varies with emission velocity and heat release. Information on the subject is limited and is usually based on VISUAL observations in connection with emergency discharges from flares. Figures 8 and 9 were developed from some PLANT-SCALE experimental work on flame lengths covering relatively high release rates of various mixtures of hydrogen and hydrocarbons”.

API Recommended Practice 521API Recommended Practice 521

Hydrogen Release from Vent Stack:Hydrogen Release from Vent Stack:2000 CFM, 30 ft/s (9.14 m/s) wind2000 CFM, 30 ft/s (9.14 m/s) wind

Flow rate 0.949 m3/sec / 2000 SCFMStack height 3.658 m / 12 ftIFC Distance 1D 7.92 m – 10.97 m / 26 – 36 ft

Lot line 1.25D 9.9 m – 13.7 m / 32.5 ft – 45 ftLeak type Choked SubsonicStack diameter 25 mm / 1” 50 mm / 2”CFD 2% vol. extent 5.5 m / 18.0 ft 9.7 m / 31.8 ft

4% vol. extent 2.0 m / 6.6 ft 4.0 m / 13.1 ft

Hydrogen Release from Vent Stack:Hydrogen Release from Vent Stack:2000 CFM, 30 ft/s (9.14 m/s) wind2000 CFM, 30 ft/s (9.14 m/s) wind

Flow rate 0.949 m3/sec / 2000 SCFM

Stack height 3.658 m / 12 ft

IFC Distance 1D 7.92 m – 10.97 m / 26 – 36 ft

Lot line 1.25D 9.9 m – 13.7 m / 32.5 ft – 45 ft

Leak type Choked Subsonic

Stack diameter 25 mm / 1” 50 mm / 2”

CFD 2% vol. extent 5.5 m / 18.0 ft 9.7 m / 31.8 ft

4% vol. extent 2.0 m / 6.6 ft 4.0 m / 13.1 ft

Flame Net length 3.17 m 3.32 m

Max diameter 1.01 m 1.30 m

At 1.8 m level

Max radiation 4.22 kW/m2 6.93 kW/m2

Dis. to max flux 2.31 m 2.18 m

Distance to 1.6 kW/m2 7.81 m 9.69 m

Distance to 4.7 kW/m2 -- 4.78 m

Pain Threshed Calculations Max radiation flux at ground level: 4.7 kW/m2

Pain Stack height 3.46 m 4.46 m

Distance to max flux 2.18 m 2.58 m

Distance to 1.6 kW/m2 7.94 m 9.33 m

Clearance Distances Based on Concentration Clearance Distances Based on Concentration EnvelopesEnvelopes

Flow, CFM 500 1000 2000 5000 10000 20000

Flow, m3/s 0.25 0.5 1 2.5 4.75 9.5

2% extent (sonic), m 2.6 4 5.5 9.2 14.4 19.5

2% extent (subsonic), m 5.5 7 9.7 13.5 16 21.5

4% extent (sonic), m 0.8 1.2 2 3.4 5.9 8.9

4% extent (subsonic), m 2.5 3 4 6.2 7.1 9.7

Vent Diameter, mm 25 25 25-50 25-75 50-75 75

Extents of 2% and 4% vol. concentration envelopes for sonic and sub-sonic flows

R2 = 0.9963

R2 = 0.9978

R2 = 0.9927R2 = 0.9975

0

5

10

15

20

25

0 1 2 3 4 5 6 7 8 9 10Hydrogen flow rate, m3/s at NTP

Hor

izon

tal e

xten

t, m

0

5

10

15

20

25

2% extent (subsonic), m 4% extent (sonic), m4% extent (subsonic), m 2% extent (sonic), mPow er (2% extent (subsonic), m) Pow er (4% extent (sonic), m)Pow er (4% extent (subsonic), m) Pow er (2% extent (sonic), m)

Recommended Clearance Distances For Ignition Recommended Clearance Distances For Ignition Sources Above Vent Stack TopSources Above Vent Stack Top

Approach: Applying Subsonic Data Reasonably Conservative (Metric Units)

Flow, CFM 500 1000 2000 5000 10000 20000

Flow, m3/s 0.25 0.5 1 2.5 4.75 9.5

2% LFL extent (subsonic), m 5.5 7 9.7 13.5 16 21.5

4% LFL extent (subsonic), m 2.5 3 4 6.2 7.1 9.7

Clearance Distance, m 3.1 3.8 5.0 7.3 9.0 12.0

Vent Diameter, mm 25 25 25-50 25-75 50-75 75

Clearance Distances for Air Intakes and Ignition Sources Located Above the Top of Hydrogen Vent Stacks

3.13.85.0

7.39.0

12.0

R2 = 0.997

0123456789

10111213

0 1 2 3 4 5 6 7 8 9 10Hydrogen Flow Rates, m3/s at NTP

Cle

aran

ce D

ista

nce,

m

Clearance Distances Based on Thermal EffectsClearance Distances Based on Thermal EffectsSonic + Subsonic Flow - Imperial Units

H2 Flow Rate 2,000 CFM 5,000 CFM 10,000

CFM 20,000

CFM

Vent Diameter, in 1 2 2 1 1 3 3 2 3 3

Height, ft 11.4 12 14.6 17 18.2 17 17.8 19 20.9 22.3

Distance to 1,500 BTU/ft2 , ft 7.2 15.7 8.5 16.7 11.1 18.3 13.2 16 16.2 22.3

Sonic flows correspond to lowest stack diameter in each flow rate range. It is interesting that the best sonic (coloured green) and subsonic (coloured yellow) results in terms of distances to 1,500 BTU/ft2 for each flow rate range are quite close to each other. This indicates that if an appropriate height of the vent stack is selected, the stack orifice will not materially affect the clearance distance.

Recommended Clearance Distances Based on Recommended Clearance Distances Based on Thermal EffectsThermal Effects

Approach: Averaging Sonic and Subsonic Data, Reasonably Conservative (Imperial Units)

Flow, CFM 500 1000 2000 5000 10000 20000

H, ft 11 13 15 18 21 24

D, ft 6 8 10 14 18 23

Vent Dia, in 1 1 1 - 2 1 - 3 2 - 3 3

Minimum Vent Stack Height and Separation Distance vs Hydrogen Flow RateImperial Units

1113

1518

24

68

10

14

18

2321

y = 3.0166x0.2101

R2 = 0.9992y = 0.6457x0.3611

R2 = 0.9994

0

5

10

15

20

25

30

0 5000 10000 15000 20000

Hydrogen Flow Rate, CFM at NTP

Vent

Sta

ck H

eigh

t (H

) or S

epar

atio

n D

ista

nce

(D),

ft

H, ft D, f t Pow er (H, f t) Pow er (D, f t)

SummarySummary• Clearance distances related to venting of hydrogen

storage were derived using both thermal effects and concentration envelope approaches

• Obtained tables and graphs were based on thermal effects analysis using TNO “Yellow Book” recommendations and CFD modeling of hydrogen releases and dispersion, implemented through the PHOENICS software package

• Obtained results provide comprehensive guidance to both design engineers and regulatory authorities to design and provide regulatory approvals for placement of hydrogen storage systems vent stacks