[ certification ] explosion and fire safety assessment as well as appropriate certification should also be conducted for electrolyser systems . performed on this revised system again to assess the emergence of new risks resulting from the design change .
HAZOP
A Hazards and operability study ( HAZOP ) is one of the methods widely used by industry for risk assessment . HAZOP provides a structured manner to review the design of the electrolyser system and identify possible hazards that may have been ignored during the general design phase . HAZOP is performed after the first design freeze , i . e ., when the first version of the P & ID ( piping and instrumentation diagram ) is defined , detailing the complete system layout with all existing components . HAZOP is conducted in several sessions where a core team of people with relevant skills brainstorm together . The sessions should be facilitated by a HAZOP moderator experienced with the HAZOP method as well as by a scribe who documents progress . The HAZOP moderator and the scribe need not be aware of the nitty-gritty of the system . Furthermore , the team should consist of engineers involved with the system design and the operator / user if possible .
During HAZOP , a system is divided into several nodes , depending on the complexity of the system , and hazards are identified for individual nodes with the help of standard guide terms and process parameters . For electrolysers , the most commonly used nodes are :
• Anode loop
• Cathode loop
• Coolant loop , if any
• Nitrogen loop , if any
• Gas separators
• External factors such as air intake and exhaust obstructions , rain , etc .
These nodes are just an example , and the actual nodes selection depends highly on the system design and complexity . The first HAZOP study will result in system design changes to eliminate or mitigate the risks identified . A risk assessment should be
Explosion and fire safety
Combustion requires three elements , commonly shown as the fire triangle : combustible , oxidant and ignition . In an electrolyser , all these three elements exist in close proximity to each other . The first common approach is to avoid ignition sources . This , however , is difficult for hydrogen due to its low ignition energy . A simple static spark is sufficient for ignition of a hydrogen-air mixture . As part of the explosion and fire safety assessment , the system design should be reviewed , also in a team of experienced engineers , to identify potential leak sources ( during normal operation as well as failure modes ).
Depending on the potential leaks , sufficient ventilation ( natural or mechanical ) should be sized and installed to dilute the formation of explosive mixture . EN-IEC 60079-10-1 : Classification of areas – explosive gas atmosphere provides a guideline on identifying and characterising potential leak sources , assessing the ventilation availability and accordingly defining the hazardous areas in the installation area . It is not always possible to eliminate the risk of explosion , especially in electrolysers .
A few common practices are suggested to be adopted for electrolysers to reduce the risk of explosion : 1 . Divide the system into two sections separated by a gas-tight wall – one section contains all the hydrogen-related equipment whereas the other container contains the electrical parts and control system .
2 . Install hydrogen-detecting equipment at the highest possible point in the system – at a location where the chances of hydrogen leakage and accumulation are highest . Programme this detection equipment to provide an alarm at 10 % LEL and automatically shut down the system at 25 % LEL detection .
Hydrogen Tech World | Issue 7 | December 2022 25