Boil-off recovery of LH2 infrastructure using metal hydrides

Kurzfassung

Liquid hydrogen (LH2) storage can be one option to store large amounts of energy in small volume for stationary applications as well as for mobile applications with high energy density needs, e.g. in airplanes. Due to the required energy for liquefaction – up to 30% of heating value of hydrogen – every hydrogen molecule stored in the liquid phase is very precious. However, in the process chain of LH2 along transportation, filling and storage, heat input is inevitable. This effect leads to energy losses due to boil-off H2 to the ambient. State of the art recovery systems for boil-off H2 include reliquification plants, which are reasonable for existing large-scale stationary applications. However, with H2 infrastructure spreading, there is a need for simple recovery systems in smaller scale. Metal hydride systems can be used to buffer the H2 released at few mbar above ambient and release it at an elevated pressure level, when required. In this application, the feature of thermal compression using metal hydrides offers a very energy efficient and simple way to save H2, thus energy and cost. The contribution will present experimental results for thermal boil-off H2 compression achieving pressure ratios of 3 to 6 when using temperatures between 0 and 70 °C.