Diffusion limited hydration kinetics of millimeter sized salt hydrate particles for thermochemical heat storage

Abstract

Potassium carbonate is a promising salt for thermochemical heat storage. For an application mm-sized salt hydrate particles are manufactured to be loaded inside a reactor. The step towards larger particles is necessary to prevent a large pressure drop over the reactor bed during hydration/dehydration in a given air flow. Therefore, in this work a systematic study on the hydration kinetics of mm-sized disc shaped salt hydrate (K2CO3) particles is presented for the first time. The effect of density, primary particle size and driving force on the hydration kinetics was evaluated using a 1D diffusion model. The main conclusions are that the hydration kinetics of mm-sized salt hydrate particles is diffusion limited and that the particle density (porosity) and tortuosity are the main parameters controlling its performance. On the contrary, the primary powder size did not affect the particle performance in any way. It is shown that the calculated transport mechanism is unaffected by changes in driving force whereas the power output decreases with decreasing driving force. Lastly shape and size optimization is discussed which can possibly improve the hydration kinetics of salt hydrate particles in view of thermochemical heat storage. Since the particle hydration is expected to be similar for various other salts, the model from this work offers opportunities to predict and optimize particles made from different salts as well.