HIGH TEMPERATURE HEAT STORAGE USING GAS-SOLID REACTIONS

Abstract

Thermal heat storage systems are used to improve energy efficiency of power plants and the use of process heat. They are also required for continuous energy supply in solar thermal applications. Thermo-chemical reactions offer an option for high temperatures where common sensible or phase change materials are not available. In the framework of a major research project, DLR research is focused on the temperature range from 300 to 1000°C, while the University of Stuttgart (Institute for Thermodynamics and Thermal Engineering) will investigate low-temperature reactions for long-term heat storage. Because of their high energy density and low cost gas-solid reactions are promising candidates for such systems, especially decomposition reactions of metal hydroxides and carbonates. Main concerns are the correct integration of the complex energy and mass flows into the thermo-chemical system, structural changes of materials, and heat transfer restrictions due to low thermal conductivity. In an initial study, the system requirements and suitability of various materials were identified. However, problems with cycling stability of calcium hydroxide and carbonate were observed during the first thermo-gravimetric measurements. To understand mechanisms and limitations on transport in a packed bed reactor, a 3D-model solved by Finite-Element-Method has been developed to describe heat and mass transfer during the reactions. It was implemented into a simulation tool to compare different design concepts. This presentation reports on the influence of the main parameters in the packed bed. Possibilities for enhancing the thermal conductivity in case of indirect and direct heat transfer concepts are evaluated based on simulation results.