MHD Energy Recovering Systems from Liquid Hydrogen

The realization and connection to the electrical grid of large scale renewable generating plants exploiting sources such as solar or wind can be prevented by problems of grid stability and power management due to fluctuating and poorly predictable resource availability. One of the most promising and studied means for long storage of energy in chemical form is the production of hydrogen by electrolysis of water, which can be stored in liquid form when large storage is required. The liquefaction process is high power consuming, but part of the energy consumption can be recovered if the Liquid Hydrogen (LH2) is used in order to improve the performance of some of the devices which make part of the global system. This paper describes advanced systems for reconversion of LH2 into Gaseous Hydrogen (GH2) at the end of the transport chain, which is necessary if end-users actually requires GH2 or if the LH2 has to be converted into electric energy. Working with Liquid Hydrogen (LH2) at 20 K as cold sink and making use of MHD generator with high combustion temperatures, these systems achieve very high thermodynamic efficiencies, actually allowing the recovering of part of liquefaction energy when compared with traditional systems. Different Gas Turbine, MHD, and combined systems are proposed and compared with available conventional thermo-electric and fuel cell systems in terms of output electric energy and Gaseous Hydrogen (GH2) for unit mass of input LH2. The higher electric energy output for the same consumed hydrogen can be seen as the re-covering of part of the energy spent for liquefaction.