Safety SAFETY WITH AMMONIA AND LOHCs AS HYDROGEN CARRIERS
Hydrogen is diffi cult to store and transport as a gas. As a liquid it is not much better. Given the challenges of handling hydrogen, much of the green hydrogen produced in the coming decades will be converted to ammonia to facilitate cost-eff ective supply chains.
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iquid organic hydrogen carriers (LOHCs) will also play a role in hydrogen storage and distribution. These are volatile
aromatic organic chemicals with physical properties like liquid hydrocarbon fuels such as gasoline or diesel. Flammable, and toxic, gas detection is required to use them safely.
Whichever way we look, fl ammable and toxic gases have been, are and will continue to be part of the hydrogen story. Getting to grips with gas detection is therefore essential for a safe energy transition.
Silyzer electrolyser for hydrogen production, Copyright Siemens Energy
electrochemical cell is also common. However, these sensors are easily poisoned and must be changed after exposure to an ammonia gas leak. Background traces of ammonia also desensitise the sensors over the long term.
Ammonia refrigeration compressor
Ammonia – the carbon-free hydrogen carrier
Ammonia gas detection builds on experience in the refrigeration industry where ammonia has been used as a refrigerant gas for decades. In refrigeration applications, the EN378 standard advocated detection limits at 5,000 and 30,000 ppm of ammonia to protect the plant from an ammonia explosion.
Whilst these high levels are appropriate to protect the equipment, employees must be protected at lower levels. For toxic detection the COSHH regulation specifi es a limit of 25ppm over 8 hours and 35 ppm over 15 minutes. These are the levels that are generally built into portable gas detectors that operators wear as part of their personal protective equipment.
Catalytic bead gas sensors can be used to detect ammonia. The
Hydrogenious benzyltoluol LOHC supplied to the HRS Erlangen, Copyright HyPlus
An increasingly popular mode of hydrogen storage and transportation is the use of a liquid organic hydrogen carrier (LOHC). Several aromatic organic chemicals, such as benzyltoluene, can perform as an LOHC.
Hydrogen is loaded into the LOHC using a chemical reaction called hydrogenation. The LOHC can then be shipped as a liquid. When required, the loaded LOHC can be dehydrogenated using heat and catalysts to release the hydrogen. The LOHC can then perform another round trip to transport hydrogen.
Liquid hydrogen storage
The physical properties of an LOHC are like that of diesel – a fl ammable liquid at room temperature and pressure. This enables
Liquid hydrogen distribution by road
The gas detection sensor control system should be mounted outside the area where the leak is expected to be. This allows the operator to safely examine the control system to understand what is happening in the room where the leak is being detected, without putting themselves at risk of toxic exposure.
Aromatic hydrocarbon gas detection for LOHCs
Ammonia storage
them to be used in storage and distribution equipment that has previously been aligned to refi ned products.
Gas detection for vapour leaks of the LOHC can be achieved using a PID detector. However, it is likely that the main areas of concern would be a hydrogen gas leak during hydrogenation and dehydrogenation of the LOHC. For the hydrogenation and dehydrogenation facility, using a pellistor hydrogen detector in parallel with a PID detector for the LOHC would be ideal.
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
WWW.PETRO-ONLINE.COM
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