PLANTSERV® Process and Plant Safety: Expert Series
Special Edition: Cold H2 Vent Stack – Three Key Safety Factors
Are you aware of the typical H2 safety risks in vent stacks?
In this edition of our expert series, we focus on the safe disposal of hydrogen, specific hydrogen hazards in cold vent systems and some design considerations for process safety.
1. Safe disposal of hydrogen
- Systems using pressurized hydrogen (H2 ) must be safeguarded against overpressure
- Vent, depressurization and pressure safety valve (PSV) outlet lines need to be routed to a safe disposal system
- H2 is typically vented to the atmosphere since it is non-toxic and lighter than air
- If H2 is mixed with toxic gases or hydrocarbons, it must be routed to flare
- Typical systems using a cold H2 vent stack:
- Hydrogen trailer filling stations
- Electrolyzers
2. Specific H2 hazards in cold vent systems
- Potential explosion in header due to air ingress
- Risk of harm if the vent stack outlet is not safely routed due to:
- H2 dispersion cloud
- heat radiation
- overpressure from gas cloud explosion
- High temperature if H2 self-ignites
- Potential noise emissions
- Potential explosion in stack due to air ingress
- Potential process condensate or rainwater
3. Design considerations
- Safe location:
- Vent height, location and direction must consider
- H2 vapor cloud extension (explosive atmosphere)
- Heat radiation from H2 flame (ignites easily!)
- Dynamic pressure from ignition of vapor cloud that has formed
- Vent height, location and direction must consider
- Material for vent tip must be selected to allow for the high temperature
- Air ingress might lead to internal explosion in header:
- Safety-relevant purge of header must be provided; or
- Detonation-proof header design
- Detonation-proof stack design
- Condensate handling:
- High level buildup from condensates in stack is an issue
- Explosive atmosphere at automatic drains is also a risk
- Potential back-firing into header if vent gas is flammable (electrolysis H2 might contain O2 )
As the above illustrates, there are many safety factors to be taken into consideration when designing vent stacks for H2 trailer filling stations, electrolyzers and similar.
Here at PLANTSERV® our experts have extensive experience in the safe disposal of H2.
We can help you identify potential hydrogen hazards in your cold vent system and put the appropriate safety mechanisms in place.
Contact us for more information.
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