Risk Management in a Containerized Metal Hydride Storage System

HyCARE project, supported by the Clean Hydrogen Partnership of the European Union, deals with a prototype of hydrogen storage tank using a solid-state hydrogen carrier. Up to 40 kilograms of hydrogen are stored in twelve tanks at less than 50 barg and less than 100 °C. The innovative design is based on a standard twenty-foot container including twelve TiFe-based metal hydride (MH) hydrogen storage tanks, coupled with a thermal energy storage in phase change materials (PCM). This article aims at showing the main risks related to hydrogen storage in a MH system and the safety barriers considered, based on HyCARE’s specific risk analysis.
Regarding the TiFe MH material used to store hydrogen, experimental tests showed that the exposure of the MH to air or water did not cause spontaneous ignition. Furthermore, an explosion within the solid MH cannot propagate due to internal pore size. Additionally, in case of leakage, the speed of hydrogen desorption from the MH is self-limited, which is an important safety characteristic since it reduces the potential consequences from the hydrogen release scenario.
Regarding the integrated system, the critical scenarios identified during the risk analysis were: explosion due to release of hydrogen inside or outside the container, internal explosion inside MH tanks due to accidental mix of hydrogen and air, and asphyxiation due to inert gas accumulation in the container. This identification phase of the risk analysis, allowed to pinpoint the most relevant safety barriers already in place and recommend additional ones if needed to further reduce the risk that were later implemented.
The main safety barriers identified were: material and component selection (including the MH selected), safety interlocks, safety valves, ventilation, gas detection and safety distances.
The risk management process based on risk identification and assessment contributed to coherently integrate inherently safe design features and safety barriers.