(737d) Preliminary Reactor Design for High Temperature Discharge of Solid-State Thermochemical Energy Storage Particles

The increased interest in harvesting and storing solar energy has led to the development of multiple Thermochemical Energy Storage (TCES) materials that enable the accumulation of solar energy in the form of chemical energy. In addition to the TCES materials, suitable reactors for the charging and discharging processes must be developed. The use of Concentrating Solar Power (CSP) enables the use of heat transfer fluids (HTF) at high temperatures, which then can be used to run thermal power plants or can also be used to charge TCES materials by means of endothermic reduction reactions, allowing the conversion and storage of thermal energy into chemical energy. Moreover, the discharge of TCES can be carried out as high temperature exothermic oxidation reactions, returning the stored chemical energy in the form of thermal energy. Higher temperature discharge allows for higher power generation efficiency, at the expense of more difficult process conditions. Presented here is a preliminary concept development of a reactor for high temperature (≥900 °C) oxidation of solid particles used for thermochemical storage of solar energy. An analytical hierarchy process was performed to ponder the main design criteria, such as flowability, heat transfer, fabricability and reliability, among others. Reactor concepts such as packed bed, moving bed, fluidized bed, and combinations thereof were then evaluated based on the criteria. The ‘hybrid’ design presented here consists of a top moving bed, a middle fluidized bed with heat exchanger and a bottom moving bed. The top and bottom moving beds will serve as heat recuperation devices, and the middle fluidized bed with heat exchanger will be used to carry out the oxidation reaction and to transfer the heat of reaction to the HTF. The results indicate that the hybrid concept surpasses its contenders in flowability and heat transfer parameters, but it had low scores in fabricability, control and operation aspects. Additionally, a preliminary design of a hybrid reactor for the oxidation of relatively large TCES particles (1 mm or greater) is presented with a focus on enhancing the heat transfer between the particles and the walls, as well as improving the solids flow within the reactor for better residence time distributions. A heat output of 1 kW is used as basis to design the oxidation reactor and heat exchanger and moving beds. The preliminary modelling results indicate that pressure has a significant effect on heat transfer and fluidization. Also, under specific conditions, particle preheating is feasible in the top and bottom moving beds, and a working fluid outlet temperature of 800 °C or greater is achievable.