Thermal Reduction of Iron Oxide under Reduced Pressure and Implications on Thermal Conversion Efficiency for Solar Thermochemical Fuel Production

Abstract

Successful implementation of solar thermochemical metal oxide water splitting cycles is dependent upon the ability to reach low partial pressures of oxygen during the thermal reduction step. Low partial pressures of oxygen are required to provide a thermodynamic driving potential for the thermal reduction reaction and avoidance of recombination. Achieving low partial pressures of oxygen (e.g., < 10–2 bar) may require a nontrivial energy input to the solar-to-fuel conversion process, negatively impacting the solar to fuel energy conversion efficiency. Three different strategies to reduce the partial pressure associated with oxygen generated during an iron oxide thermal reduction process were investigated using an open system thermodynamic analysis. These strategies include vacuum pumping, purging with an inert gas, and purging with steam. If the difficult to achieve solid-phase heat recuperation is neglected, open-system thermodynamic simulations show that vacuum pumping will have over twice the overall cy...