Development of a Mechanical Fluidized Bed Reactor for CaO/Ca(OH)2 Based Thermochemical Heat Storage

Kurzfassung

Due to development of renewable energies we also exploit more and more of the huge solar energy potential. During the summer season the surplus of PV electricity can present difficulties for network operators and lead to local grid instabilities. At the same time, at least in the regions with distinct seasons, there is a high demand for space heating during the winter time, which is usually based on fossil fuels. DLR therefore addresses the question how to store the available low-cost-renewable energy in the summer to provide space heating in the winter. The reversible CaO/Ca(OH)2 reaction is promising for a storing process, where we can use electricity for charging and provide heat during the discharge. The material has a high energy density, low material costs, is abundantly available and environmentally friendly. Due to the loss free storage principal a thermochemical process is suitable for mid- and long-term storage periods. Combined with renewable electricity it can achieve a year-round heat supply. Additionally, it can have positive effects on the power grids and on the CO2 emissions. One fundamental technological challenge, to make the storage system applicable for residential buildings, is to make the reactor compact and energy efficient. This is why we developed a novel kW scale reactor concept based on the mechanical fluidization of the storage material. The concept in principal allows a very high heat transfer into the material bulk and impedes material agglomeration and clogging. First operational tests revealed the successful charging and discharging of the storage material and proved the potential of high heat transfer rates. This presentation will outline the thermochemical energy storage concept based on unmodified CaO/Ca(OH)2 material and present the current modifications and performance data. The thermodynamic and heat and mass transfer performance of the reactor will be analyzed based on experimental data and implications for the overall storage system application will be derived and discussed.