Hydrogen production via thermochemical H2O splitting using CaSO4 – CaO redox reactions

Abstract

By applying the principles of the second law of thermodynamics and utilizing the HSC Chemistry software, the thermodynamic equilibrium and efficiency analysis of the CaSO4CaO water splitting cycle was performed in this investigation. The temperatures desirable and the equilibrium compositions allied with the thermal reduction of CaSO4 and the re-oxidation of CaO via water splitting reaction were estimated. The obtained results indicate that the thermal reduction temperature (TH) required to completely decompose the CaSO4 was decerased from 2220 to 1890 K due to the rise in the molar flow rate of (n˙Ar) from 1 to 50 mol/s. In addition, the consequence of the TH, n˙Ar, and the water splitting temperature (TL) on the process parameters such as total amount of solar energy needed, re-radiation losses, energy dissipated by the water splitting reactor and others associated with the CaSO4CaO water splitting cycle was scrutinized. By utilizing higher n˙Ar from 1 to 50 mol/s, the TH was decreased from 2200 to 1890 K. However, as the n˙Ar was increased from 1 to 50 mol/s, the amount of heat energy needed to heat the Ar was also upsurged from 12.5 to 625.6 kW. This rise in the Q˙Ar−heating, directly reflected into an increase in the Q˙solar−cycle from 1063.4 up to 2653.9 kW. The findings of this study further confirms that the maximum solar-to-fuel energy conversion efficiency (ηsolar−to−fuel) equal to 27.4% was realized by conducting the CaSO4CaO water splitting cycle at TH = 2220 K, n˙Ar = 1 mol/s, and TL = 1100 K. By using 50% of the recuperable heat, the ηsolar−to−fuel of the CaSO4CaO water splitting cycle can be enhanced up to 36.2%.