System efficiency for two-step metal oxide solar thermochemical hydrogen production – Part 2: Impact of gas heat recuperation and separation temperatures
KAUST DepartmentSABIC - Corporate Research and Innovation Center (CRI) at KAUST
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AbstractThe solar-to-hydrogen (STH) efficiency is calculated for various operating conditions for a two-step metal oxide solar thermochemical hydrogen production cycle using cerium(IV) oxide. An inert sweep gas was considered as the O2 removal method. Gas and solid heat recuperation effectiveness values were varied between 0 and 100% in order to determine the limits of the effect of these parameters. The temperature at which the inert gas is separated from oxygen for an open-loop and recycled system is varied. The hydrogen and water separation temperature was also varied and the effect on STH efficiency quantified. This study shows that gas heat recuperation is critical for high efficiency cycles, especially at conditions that require high steam and inert gas flowrates. A key area for future study is identified to be the development of ceramic heat exchangers for high temperature gas-gas heat exchange. Solid heat recuperation is more important at lower oxidation temperatures that favor temperature-swing redox processing, and the relative impact of this heat recuperation is muted if the heat can be used elsewhere in the system. A high separation temperature for the recycled inert gas has been shown to be beneficial, especially for cases of lower gas heat recuperation and increased inert gas flowrates. A higher water/hydrogen separation temperature is beneficial for most gas heat recuperation effectiveness values, though the overall impact on optimal system efficiency is relatively small for the values considered. © 2016 Hydrogen Energy Publications LLC.
CitationEhrhart BD, Muhich CL, Al-Shankiti I, Weimer AW (2016) System efficiency for two-step metal oxide solar thermochemical hydrogen production – Part 2: Impact of gas heat recuperation and separation temperatures. International Journal of Hydrogen Energy 41: 19894–19903. Available: http://dx.doi.org/10.1016/j.ijhydene.2016.07.110.
SponsorsThe authors would like to thank Dr. Ivan Ermanoski of Sandia National Laboratories for helpful discussion and comments about many aspects of the efficiency calculations. The authors are grateful for financial support from the U.S. Department of Energy Fuel Cell Technologies Program through the Solar Thermochemical Hydrogen (STCH) directive and the U.S. Department of Energy Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under Award Number DE-EE0006671 and the Saudi Basic Industries Corporation (SABIC). BDE and CLM gratefully acknowledge financial support from Award P200A120125 of the U.S. Department of Education Renewable and Sustainable Energy Graduate Assistance in Areas of National Need (GAANN) Program.