Solar UT-3 thermochemical cycle for hydrogen production

Abstract The UT-3 thermochemical hydrogen producing cycle is a four step process developed at the University of Tokyo. In the process, only solid and gas reactants/products are used and the maximum temperature is 1033 K. The process has been developed to be coupled with gas cooled nuclear reactors (HTGR). In this article, a new UT-3 process is conceived to be coupled with a solar heat source. In the new process, all four reactions are carried out in a adiabatic equipment where steam (or steam + nitrogen) can be used as a vector. The operation of the process is done continuously. During sunshine hours, the energy to the process is supplied directly from the solar receiver. During cloudy periods and nights, it is supplied from a thermal storage system where the necessary high temperature heat is stored during sunshine hours. The solar UT-3 process has been evaluated using the ASPEN-PLUS code. It is found that the overall thermal efficiency is 49.5%, the exergetic efficiency is 52.9% and the process can be realized using conventional materials. Sizing of a solar hydrogen plant producing 2000 Nm3 per hour hydrogen has been carried out and operation of various equipment has been discussed.