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Safety for hydrogen vent systems
Hydrogen vent systems play an essential role in ensuring hydrogen safety . For many applications , it is common practice to connect all normal hydrogen piping vent points , including relief valves , to a vent system . Evaluating this system during the facility hazard review is essential . This evaluation is often missed , and there have been numerous incidents in which improper vent stack design or operation caused injuries and property damage . This article addresses critical safety issues in vent system design and operation for liquefied ( LH2 ) and gaseous ( GH2 ) hydrogen .
By Thomas G Witte , CEO of Witte Engineered Gases , and Nick Barilo , Executive Director of Center for Hydrogen Safety
Vent systems are used to safely release hydrogen during normal and abnormal events such as high-flow relief device operation . When properly designed and installed , these systems reduce the effects of fire , asphyxiation , and fog ( cold gas released from a liquefied hydrogen tank ) on people , equipment , and the environment . Vent system designs are based on the properties of hydrogen . For example , because hydrogen is extremely buoyant , has low ignition energy , and can condense water vapor in the air from LH2 , vent systems are designed to move hydrogen away from ground level for safety purposes . Typical equipment connected to a vent system can include pressure relief devices , purge and vent valves , bleed valves , and any opening that can vent hydrogen under operation or maintenance .
• Materials of construction
• Supports
• Location
• Hydrogen operations
• Vent outlet piping design
• Expansion / contraction
• Flares or flame arrestors
• Grounding
• Purge gases
These design considerations are critical to the safe operation of the vent system and preventing vent system failure . Additionally , the design parameters ( e . g ., vent diameter , vent supports , interaction with other streams ) must be evaluated for each process stream entering the vent system .
Unfortunately , the configuration of hydrogen vent systems may not be considered during the initial design or not included in the process hazard assessment ( PHA ). This can lead to vent stack damage or failure and hydrogen being discharged to undesired locations . It is essential that vent systems be designed by qualified engineers or designers . Designers need to consider the following :
• Process flow parameters ( including maximum pressure , peak flow , maximum or minimum temperature , and composition )
Improper designs that can cause vent system failure include :
• Incorrect supports
• Incorrect piping expansion / contraction
• Joints or vent system components with melting points below the hydrogen flame temperatures
• Undersizing the vent system
• Incorrect vent stack termination
Failures include :
• Overpressurization
• Plugging the vent system
34 Hydrogen Tech World | Issue 7 | December 2022