Assessment of inherently safer technologies for hydrogen storage

Hydrogen storage is a particularly critical issue, due to the physical and chemical properties of this substance: operating conditions and processes are critical to manage, pressures may be higher than those of usual storage processes (tens of MPa) and temperatures may be lower than other cryogenic processes (only tens of Kelvin). Moreover the flammability limits are wider and the ignition energy much lower than other flammable substances. Thus, several alternative technologies were proposed for hydrogen storage. Besides the conventional compression and storage in pressured vessels in the gas state and the cryogenic storage in vacuum insulated vessels, innovative technologies as adsorption on solid or liquid matrices were proposed. A relevant increase in the use of hydrogen as an energy vector and in advanced refining technologies is expected in the next years. The increase in the number and in the potentialities of hydrogen production plants will thus require the improvement of hydrogen storage technologies. Moreover, the use of hydrogen as an energy carrier may cause a spread of hydrogen storage installations also in vulnerable contexts, such as residential and commercial areas. In this framework, the further development of hydrogen storage technologies requires a thorough examination of the safety issues. As a matter of fact, risk reduction in hydrogen storage may be a key issue influencing the development of new or improved storage technologies. The present study was dedicated to the safety assessment of alternative technologies for hydrogen storage. Reference schemes for “small”, “medium” and “large” size hydrogen storage systems were defined. The safety analysis of the alternative storage technologies was thus performed, aimed to the identification of critical safety issues. Since the alternative technologies are at different stages of process development (research, pilot plant, industrial application), an inherent safety approach was applied. A specific methodology for the quantitative assessment of the inherent safety of the alternative storage technologies was developed and applied. Besides the identification of critical elements with respect to safety for each alternative technology, the methodology allowed the achievement of preliminary indications on the inherently safer systems for hydrogen storage and on the expected safety performances of alternative technologies.