1. Determination of Clearance Distances for Venting of Hydrogen Storage Andrei Tchouvelev, Pierre Benard, Vlad Agranat and Zhong Cheng

2. Acknowledgements Work partially supported by –Natural Resources Canada (NRCan) CTFCA Clearance Distance Project –Natural Sciences and Engineering Research Council of Canada (NSERC) Industrial Research Fellowship

3. Introduction 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

4. International Fire Code, Section 2209

5. Flux (kW/m 2 )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 melts1st degree burns in 10 sec 9.5 Immediate skin reactions 4.7 (1,500 BTU/ft 2 ) Pain threshold 1.6 (500 BTU/ft 2 ) Safe level Thermal Level Standards for Hazard Assessment

6. API 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”.

7. API Recommended Practice 521

8. Hydrogen Release from Vent Stack: 2000 CFM, 30 ft/s (9.14 m/s) wind Flow rate0.949 m 3 /sec / 2000 SCFM Stack height3.658 m / 12 ft IFCDistance 1D7.92 m – 10.97 m / 26 – 36 ft Lot line 1.25D9.9 m – 13.7 m / 32.5 ft – 45 ft Leak typeChokedSubsonic Stack diameter25 mm / 1”50 mm / 2” CFD 2% vol. extent5.5 m / 18.0 ft9.7 m / 31.8 ft 4% vol. extent2.0 m / 6.6 ft4.0 m / 13.1 ft

9. Hydrogen Release from Vent Stack: 2000 CFM, 30 ft/s (9.14 m/s) wind Flow rate 0.949 m 3 /sec / 2000 SCFM Stack height 3.658 m / 12 ft IFCDistance 1D7.92 m – 10.97 m / 26 – 36 ft Lot line 1.25D9.9 m – 13.7 m / 32.5 ft – 45 ft Leak typeChokedSubsonic Stack diameter25 mm / 1”50 mm / 2” CFD 2% vol. extent 5.5 m / 18.0 ft9.7 m / 31.8 ft 4% vol. extent 2.0 m / 6.6 ft4.0 m / 13.1 ft FlameNet length3.17 m3.32 m Max diameter1.01 m1.30 m At 1.8 m level Max radiation4.22 kW/m 2 6.93 kW/m 2 Dis. to max flux2.31 m2.18 m Distance to 1.6 kW/m 2 7.81 m9.69 m Distance to 4.7 kW/m 2 --4.78 m Pain Threshed CalculationsMax radiation flux at ground level: 4.7 kW/m 2 PainStack height3.46 m4.46 m Distance to max flux2.18 m2.58 m Distance to 1.6 kW/m 2 7.94 m9.33 m

10. Clearance Distances Based on Concentration Envelopes Flow, CFM5001000200050001000020000 Flow, m 3 /s0.250.512.54.759.5 2% extent (sonic), m2.645.59.214.419.5 2% extent (subsonic), m5.579.713.51621.5 4% extent (sonic), m0.81.223.45.98.9 4% extent (subsonic), m2.5346.27.19.7 Vent Diameter, mm25 25-5025-7550-7575

11. Recommended Clearance Distances For Ignition Sources Above Vent Stack Top Approach: Applying Subsonic DataReasonably Conservative (Metric Units) Flow, CFM5001000200050001000020000 Flow, m 3 /s0.250.512.54.759.5 2% LFL extent (subsonic), m 5.579.713.51621.5 4% LFL extent (subsonic), m 2.5346.27.19.7 Clearance Distance, m 3.13.85.07.39.012.0 Vent Diameter, mm25 25-5025-7550-7575

12. Clearance Distances Based on Thermal Effects Sonic + Subsonic Flow - Imperial Units H2 Flow Rate 2,000 CFM5,000 CFM 10,000 CFM 20,000 CFM Vent Diameter, in1221133233 Height, ft11.41214.61718.21717.81920.922.3 Distance to 1,500 BTU/ft 2, ft7.215.78.516.711.118.313.21616.222.3 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/ft 2 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.

13. Recommended Clearance Distances Based on Thermal Effects Approach: Averaging Sonic and Subsonic Data, Reasonably Conservative (Imperial Units) Flow, CFM5001000200050001000020000 H, ft111315182124 D, ft6810141823 Vent Dia, in111 - 21 - 32 - 33

14. Summary 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