Power generation based on the Ca(OH)2/ CaO thermochemical storage system – Experimental investigation of discharge operation modes in lab scale and corresponding conceptual process design

Abstract

Thermochemical storage systems offer in theory promising advantages for a wide range of applications. In particular the reversible reaction of calcium hydroxide to calcium oxide and water vapour is intensively discussed as an alternative storage solution for concentrated solar power plants. The material is cheap, environmentally friendly and discharge temperatures of the reaction of 600°C and above fit to the operating range of today’s power plants. However, experimental data on the operation of the system in lab scale and at load conditions comparable to the real application is rarely reported.Therefore the thermal discharge of the reaction system at vapour pressures between 4 and 470kPa and temperatures between 280 and 600°C is experimentally investigated in this study. In particular the influence of the cooling load at various vapour pressures on the achievable discharge temperatures is analysed. The presented data complements the experimental characterisation of the reaction system in the complete temperature and pressure range which is relevant for real process applications. Based on this knowledge the applicability of the storage for various processes can now be assessed more accurate. By means of the experimental results a first integration option of the thermochemical system in a CSP plant is proposed in this work and thermodynamically analysed. The analysis revealed that, when the required steam production during discharge is thermally integrated into the Rankine steam cycle, a high storage efficiency of up to 87% can be reached compared to only 60% in the reference case.