H2 generation via solar assisted CaO/Ca thermochemical H2O splitting cycle

Abstract

This investigation reports the thermodynamic evaluation of a solar assisted CaO-based H2O splitting (Ca-WS) cycle. An HSC Chemistry 9.9 software was utilized for performing the thermodynamic equilibrium as well as efficiency analysis. Results associated with the equilibrium analysis indicate that the thermal reduction of the CaO (TR-Ca) was improved from 0 to 100% with an upsurge in the thermal reduction temperature (TH) from 1900 K to 2230 K. The water splitting (WS) reaction was feasible at all temperatures above 300 K. However, to keep the Ca in the solid phase it was carried out at TH = 1050 K. Due to the rise in the individual enthalpies of the Ca and O2, the solar energy required to run the reactor (Q˙solar−reactor−Ca−WS) and heater (Q˙solar−heater−Ca−WS) was increased by 775.5 kW and 69.5 kW as the TH rose from 1900 K to 2230 K. The solar energy required to run the Ca-WS cycle (Q˙solar−cycle−Ca−WS) was also enhanced by 1568.2 kW due to the similar increment in the TH. The solar-to-fuel energy conversion efficiency associated with the Ca-WS cycle (ηsolar−to−fuel−Ca−WS) was first increased up to 19.5% and then decreased to 17.1% as a function of the rise in TH from 1900 K to 2230 K. Overall, the Ca-WS cycle can achieve the maximum possible ηsolar−to−fuel−Ca−WS (19.5%) at TH and TL equal to 2040 K and 1050 K. For the identical operating conditions, the ηsolar−to−fuel−Ca−WS was further increased up to 38.5% due to the employment of heat recuperation.