Development and Evaluation of Hydrogen Energy System

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Hydrogen is an attractive fuel for the future because of its great flexibility as an energy carrier. It is also a clean fuel and does not contain S, N and C. The UT-3 (the University of Tokyo) cycle proposed by Kameyama and Yoshida is composed by for four solid-gas reactions consisting of Br, Ca and Fe compounds.A series of kinetic measurements and economical evaluation have been already conducted for this cycle, and a bench-scale plant was constructed and successfully operated to produce hydrogen continuously. In these studies the heat source was supposed to be a high-temperature gas reactor (HTGR). On the otherhand, an important use of solar energy in the future will be as the heat source for processes which produce fuels and chemicals. The means by which the solar heat source is coupled to the chemical process will strongly influence both the cost and efficiency of the overall system. Various studies of the solar heat-chemical process interface have been conducted in the USA.The UT- … More 3 cycle includes two endothermic hydrolysis reactions at high temperature. These reactions are parts of the thermochemical cycle and also act as a thermal storage system. Based on this view, we did jointly proposed a preliminary conceptual design of a solar thermochemical process using the UT-3 cycle for the production rate of 2000 Nm^3/h, and discusses the thermal performance of the steam heater and two endothermic fixed bed reactors.The plant consists of the following subsystems : (1) Heliostat field subsystem, (2) Solar receiver subsystem, (3) Thermochemical hydrogen plant subsystem using the UT-3 cycle, (4) Heat recovery subsystem using a chemical heat pump. The simulation results demonstrated the feasibility bf continuous operation in the transient state and showed that the control of steam flow rate was effective to compensate for changes of incoming solar heat. It was also shown that the hydrolysis reactors can work well both as a chemical storage system for the solar heat and as the parts of solar driven thermochemical cycle.The preliminary analysis of hydrogen production cost showed that it would be very favourable and that the UT-3 cycle may have a great potential to become a competitive process in combination with solar heat in the near future. Less