Application of Zn-ferrite towards thermochemical utilization of carbon dioxide: A thermodynamic investigation

Abstract

This study reports a thermodynamic analysis of ZnFe2O4 based CO2 splitting cycle. The model developed is evaluated by using HSC Chemistry software. Effects of the influence of the ratio of the molar flow rate of inert sweep gas to the molar flow rate of ZnFe2O4, thermal reduction temperature, and gas-to-gas heat recovery effectiveness on thermal energy required to drive the cycle and the solar-to-fuel energy conversion efficiency are investigated at reduction nonstoichiometry of 0.1. The decrease in the reduction temperature is significant when the ratio of the molar flow rate of inert sweep gas to the molar flow rate of ZnFe2O4 increases from 10 to 30. At a steady gas-to-gas heat recovery effectiveness equal to 0.7, a rise in the ratio of the molar flow rate of inert sweep gas to the molar flow rate of ZnFe2O4 from 10 to 90 is responsible for an increase in the thermal energy required to drive the cycle above 184.9 kW by a factor of 1.45 and decrease in the solar-to-fuel energy conversion efficiency by 4%. At gas-to-gas heat recovery effectiveness equal to 0, the difference between the thermal energy required to drive the cycle at the ratio of the molar flow rate of inert sweep gas to the molar flow rate of ZnFe2O4 equal to 10 and 100 is 346.5 kW. However, as the gas-to-gas heat recovery effectiveness increases to 0.9, this difference decreases to 11.8 kW. Because of this, the reduction in the solar-to-fuel energy conversion efficiency also drops to 0.6%. Therefore, a maximum possible solar-to-fuel energy conversion efficiency equal to 16.8% can be achieved.