Particle Properties of CaO/Ca(OH)2 Throughout Cyclisation in a Fluidized Bed for Thermochemical Energy Storage – Consequences for Fluidization

Calciumoxide/Calciumhydroxide is a promising storage material system for thermochemical energy storage at temperatures between 400 °C and 600 °C. Its main advantages are a high storage density, broad abundance, low cost, nontoxicity and chemical stability. The low heat conductivity of the material is challenging. It restricts the power in- and output of the system. But it can be maximized by using fluidized bed technology. This results in special requirements regarding material stability throughout storage cycles. Decreasing mechanical stability of the material limits the applicability of the fluidized bed technology. Particle breakage with increasing number of storage cycles leads to an increasing share of fines in the fluidized bed and therefore an increasing risk of defluidization. This knowledge on particle properties and their changes throughout the storage cycles is crucial for reactor design. Of the numerous particle properties relevant in fluidization technology, in this work especially the Sauter mean diameter 𝑑3,2 and the particle density 𝜌𝑝 are accounted for. Both parameters are studied experimentally in laboratory and pilot-scale reactors. The laboratory reactor has a fluidized bed volume of up to 1.8 L and a height to diameter ratio of up to 4. The pilot-scale system has a reactor volume of up to 30 L at a height to diameter ratio of up to 2.3. The results are analyzed regarding fluidization charachteristics based on Geldart classification and theoretical minimal fluidization velocity. A theoretical transition from Geldart A to C through B is observed accompanied by decreasing minimal fluidization velocities. However, due to the broad particle size distributions in the system, solely Geldart B fluidization behavior is observed in the reactor systems. High deviations in calculated theoretical minimal fluidization velocities and theoretical bed porosities at minimal fluidization impede further experimental investigation.     «

Calciumoxide/Calciumhydroxide is a promising storage material system for thermochemical energy storage at temperatures between 400 °C and 600 °C. Its main advantages are a high storage density, broad abundance, low cost, nontoxicity and chemical stability. The low heat conductivity of the material is challenging. It restricts the power in- and output of the system. But it can be maximized by using fluidized bed technology. This results in special requirements regarding material stability through...     »