Solar fuel processing efficiency for ceria redox cycling using alternative oxygen partial pressure reduction methods

Abstract

a b s t r a c tSolar-driven non-stoichiometric thermochemical redox cycling of ceria for the conversion of solar energy into fuels shows promise in achieving high solar-to-fuel efficiency. This efficiency is significantly affected by the operating conditions, e.g. redox temperatures, reduction and oxidation pressures, solar irradiation concentration, or heat recovery effectiveness. We present a thermodynamic analysis of five redox cycle designs to investigate the effects of working conditions on the fuel production. We focused on the influence of approaches to reduce the partial pressure of oxygen in the reduction step, namely by mechanical approaches (sweep gassing or vacuum pumping), chemical approaches (chemical scavenger), and combinations thereof. The results indicated that the sweep gas schemes work more efficient at nonisothermal than isothermal conditions, and efficient gas phase heat recovery and sweep gas recycling was important to ensure efficient fuel processing. The vacuum pump scheme achieved best efficiencies at isothermal conditions, and at non-isothermal conditions heat recovery was less essential. The use of oxygen scavengers combined with sweep gas and vacuum pump schemes further increased the system efficiency. The present work can be used to predict the performance of solar-driven non-stoichiometric redox cycles and further offers quantifiable guidelines for system design and operation.

Solar thermochemical splitting of CO2 into separate streams of CO and O2 with high selectivity, stability, conversion, and efficiency

“…The trade-off between fuel purity and fuel yield is intrinsic to the dynamics of the oxidation step; optimization will be contingent upon the downstream processing of the fuel and the economics of the entire solar plant. As anticipated by thermodynamic analyses, 31,32 increasing the mass flow rate of the inert gas affected negatively Z solar-to-fuel because both Q inert and Q pump increased monotonically with : V Ar and additional energy was wasted for heating a larger Ar flow to the desired T reduction (ref. 50, Fig.…”

System efficiency for two-step metal oxide solar thermochemical hydrogen production – Part 3: Various methods for achieving low oxygen partial pressures in the reduction reaction

“…Some prior works [8,12] only considered a mixed gas system instead of a counter-flow arrangement, and the much higher inert gas flowrates calculated in this way tend to show that vacuum reduction is more efficient, even with limited pump efficiency values [12]. Other works compared counter-flow to perfect mixing [14] and parallel-flow [15,16] arrangements, and showed that the counter-flow was more efficient, but suggested that the final flow arrangement would be an intermediate state.…”

“…Others have suggested recycling inert gas, rather than producing it in an open-loop fashion [15,18]. Still others have suggested using both an inert sweep gas and vacuum pumping simultaneously [14]. In addition to the direct study of inter gas sweeping, other works have compared the energy required for inert gas and vacuum [14,19].…”

A transient heat transfer model for high temperature solar thermochemical reactors

“…The above relationship, Eq. (38), was also implemented in [45]. In the present work, we also use Eq.…”