Application of pinch-analysis to the charging and discharging processes of Thermo-Chemical Energy Storage for Concentrated Solar Power plants

Over recent years, large scale energy storage applications have been proposed in order to increase the solar energy penetration into the electricity grid with a view to limit the fossil fuels utilization in the energy sector. Among renewable energy technologies, Concentrated Solar Power (CSP) plants have a great potential for integration with Thermal Energy Storage (TES) systems. Thermochemical energy storage (TCES) is a less mature and considerably higher energy density among TES technologies and potentially capable of decoupling energy production and demand both for short and long term. In this framework, the TCSE at large scale investigated in this work is based on the Calcium Looping (CaL) process, which exploits the reversible calcination -carbonation reactions of calcium carbonate and calcium oxide. The CaL technology was initially studied for its potential in the field of post-combustion CO2 capture, however it shows interesting characteristics in the CSP integration systems, such as the high inversion temperature, the high energy density volumetric and the low cost of natural CaO. In this project several plant layouts are explored in order to improve the performance of the CaL-CSP integration, focusing on the opportunities for heat recovery. Firstly, the main characteristics of the components used in the CaL-CSP integration and the power cycle adopted are presented. Afterwards, the design of the heat exchanger network capable of fostering the heat recovery is discussed. Given the time dependency of the charging and discharging phases of the thermochemical storage system, the Pinch-Analysis for batch-processes was carried out in order to create a feasible heat exchangers configuration that allows the correct operation of the integrated CaL-CSP system. The optimized CaL-CSP integration layout as well as showing better characteristics from the heat recovery point of view, allows to reduce the investment costs of the heat exchangers network.