On the Design of a Reactor for High Temperature Heat Storage by Means of Reversible Chemical Reactions

Kurzfassung

This work aims on the investigation of factors influencing the discharge characteristics of a heat storage system, which is based on the reversible reaction system of Ca(OH)2 and CaO. As storage, a packed bed reactor with embedded plate heat exchanger for indirect heat transfer is considered. The storage system was studied theoretically by means of finite element analysis of a corresponding mathematical model. Parametric studies were carried out to determine the influence of reactor design and operational mode on storage discharge. Analysis showed that heat and gas transport through the reaction bed as well as the heat capacity rate of the heat transfer fluid affect the discharge characteristics to a great extent. To obtain favourable characteristics in terms of the fraction of energy which can be extracted at rated power, a reaction front perpendicular to the flow direction of the heat transfer fluid has to develop. Such a front arises for small bed dimensions in the main direction of heat transport within the bed and for low heat capacity rates of the heat transfer fluid. Depending on the design parameters, volumetric energy densities of up to 309 kWh/m3 were calculated for a storage system with 10kW rated power output and a temperature increase of the heat transfer fluid of 100 K. Given these findings, this study is the basis for the dimensioning and design of a pilot scale heat exchanger reactor and will help to evaluate the technical feasibility of thermo-chemical heat storage systems.