Effect of diameter on the stability of granulated Ca(OH)2 during thermochemical cycling in a fixed bed reactor

Abstract

One solution to reduce CO2 emissions and advance climate protection in the heat sector is the utilization of thermochemical energy storages (TCES) based on the material Ca(OH)2 to store waste heat or surplus electricity. In contrast to powdered materials, the material in granular form has a lower tendency to be affected by agglomeration effects and provides higher energy density and thermal conductivity. This results in enhanced durability, stability, and efficiency of the storage, making the storage material Ca(OH)2 in granular form more suitable for TCES applications. This work investigates the performance of a chemically unmodified granular sample over 15 storage cycles in a test fixed bed reactor and evaluates whether its performance and durability are already sufficient for potential applications without further modification. In addition, different granule samples with different diameters were also cycled to determine whether the selection of certain diameter sizes can improve the stability of the granules. Furthermore, different methods were used in the pre- and post-analyses to assess the stability of the samples. The comparison of three tested granular samples with different diameters reveals that the sample with a diameter of 2–4 mm has the highest durability and reactor performance. Despite a decrease in mechanical strength, this configuration could be suitable for applications with a small number of storage cycles, such as seasonal storages.