SAFETY ON HYDROGEN REFUELLING STATIONS 10 Gas Detection


Hydrogen refuelling stations (HRS) are static systems and the leak points for hydrogen are most likely to be valves, connectors, and the fl exible hoses. It is advisable to use fi xed gas or fl ame detection equipment sited close to these locations.


P


ublic HRS stations are likely to be in the open air to enable the free movement of vehicles. In these cases, the natural wind may blow a hydrogen leak in one direction


or another. Therefore, multiple gas detectors may be required to ensure the leak is sensed whatever the wind conditions. For indoor bus depots or hydrogen refuelling of indoor forklift truck fl eets, variable wind direction is less likely to be a factor that must be addressed.


Flame detection can be used as a second line of defence, in combination with gas detectors. Using multiple gas detection devices and fl ame detectors, the operator can use a ‘voting system’ to escalate the system response from a visual alarm to an audible alarm and ultimately to an automated system shutdown, according to the number of gas and fl ame detectors that have been activated. This can help to minimise disruptive ‘false-alarms’ and simultaneously ensures that a truly hazardous situation is fl agged as quickly as possible.


High pressure is unavoidable on the HRS


On a hydrogen refuelling station (HRS) there generally be an inventory of hydrogen at high pressure. Even if there is on-site hydrogen production using an electrolyser, storage of hydrogen is required to ensure that there is suffi cient gas available to fi ll the tank of an incoming vehicle rapidly.


The buffer storage of hydrogen must be at high pressure. The reason is that there needs to be a driving pressure from the storage to the bus. When the bus tank is ‘full’ it will be at 350 bar. The pressure in the storage will need to be a minimum of 400 bar to ensure a 50 bar pressure gradient to transfer the hydrogen into the bus rapidly. In essence, the static storage on the HRS is ‘empty’ at 400 bar.


High pressure is itself a hazard. Additionally, the higher the pressure of the gas, the more hydrogen inventory exists. Since a moderate inventory of high-pressure hydrogen is an operational requirement of the HRS, the focus must be placed on mitigating the risk in ways other than reducing the pressure or inventory.


Engineering design may specify gas


and fl ame detection Appropriate engineering and design of hydrogen systems requires the use of established safety processes such as Layers


IET JANUARY / FEBRUARY 2023


of Protection Analysis (LOPA), Hazard Analysis (HAZAN), Risk Assessment (RA), and Hazard and Operability Study (HAZOP). Using these tools will call for the implementation of appropriate mitigating actions.


Many of the actions that result from these studies will be focused on avoiding leaks of hydrogen. To add to the layers of protection, gas and fl ame detection are also often specifi ed. These safety devices cannot avoid leaks, but they can reduce the severity of a leak and thereby reduce the size of the hazard.


Gas detection, for example, can shut off a valve to prevent a small leak developing into a larger one. For some gas alarms a simple response such as closing an actuated valve may be suitable to eliminate the hazard. Or a full emergency shut down of the process and evacuation may be required if the combination of alarms indicates an extremely hazardous situation.


Doubling up with dis-similar sensors


improves system integrity Electrochemical and catalytic sensors can be used for hydrogen gas detection. For maximum safety, it is recommended to use two different technologies to detect any type of gas, and the same applies to hydrogen.


The benefi t of doubling up detection with dis-similar technolgies is stonger than duplicating the same technology. This is because there may be adverse environmental conditions which impact one of the two gas sensor technologies, but the other type of sensor may continue to function normally.


Author Contact Details Stephen B. Harrison • sbh4 GmbH • Address: Kranzlstraße 21, 82538 Geretsried, Germany • Tel: +49 (0)8171 24 64 954 • Email: sbh@sbh4.de • Web: www.sbh4.de


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44