NFPA World Safety presentation

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

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Introduction

• Part of Hydrogen Clearance Distances Project
  under Canadian Transportation Fuel Cell Alliance
  (CTFCA)
• RD 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

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International Fire Code, Section 2209
5
Thermal Level Standards for Hazard Assessment
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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.

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API Recommended Practice 521
8
Hydrogen Release from Vent Stack2000 CFM, 30
ft/s (9.14 m/s) wind
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Hydrogen Release from Vent Stack2000 CFM, 30
ft/s (9.14 m/s) wind
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Clearance Distances Based on Concentration
Envelopes
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Recommended Clearance Distances For Ignition
Sources Above Vent Stack Top
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Clearance Distances Based on Thermal Effects
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.
13
Recommended Clearance Distances Based on Thermal
Effects
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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