Thermodynamic evaluation of solar assisted ZnO/Zn thermochemical CO2 splitting cycle

Abstract

The solar thermochemical CO2 splitting (CDS) is scrutinized via a redox ZnO/Zn cycle. The second law efficiency analysis is carried out by acquiring the required thermodynamic data from HSC Chemistry software. The main focus of this study is to explore the influence of reduction temperature (Tred), molar flow rate of inert sweep gas (n˙inert), and energy required for the gas separation on the solar-to-fuel energy conversion efficiency (ηsolar−to−fuel) of the ZnO/Zn cycle. All the calculations are conducted at a constant gas-to-gas heat recovery effectiveness (εgg) equal to 0.5. n˙inert required is recorded to be too high (5050 mol/s) at Tred equal to 1500 K and moderately low (15 mol/s) for Tred equal to 2000 K. The amount of thermal energy required to heat the inert/O2 gas mixture (from CDS temperature to separator-1 temperature) and inert sweep gas (from separator-1 temperature to reduction temperature) has a significant impact on the total thermal energy requirement of the cycle (Q˙TC). The rise in Tred from 1500 K to 2000 K shows a considerable decline in Q˙TC from 77417.5 kW to 1161.8 kW, respectively. Consequently, the highest ηsolar−to−fuel (17.0%) is recorded for Tred equal to 2000 K.