Hydration of magnesium carbonate in a thermal energy storage process and its heating application design

Abstract

First ideas of applications design using magnesium (hydro) carbonates mixed with silica gel for day/night and seasonal thermal energy storage are presented. The application implies using solar (or another) heat source for heating up the thermal energy storage (dehydration) unit during daytime or summertime, of which energy can be discharged (hydration) during night-time or winter. The applications can be used in small houses or bigger buildings. Experimental data are presented, determining and analysing kinetics and operating temperatures for the applications. In this paper the focus is on the hydration part of the process, which is the more challenging part, considering conversion and kinetics. Various operating temperatures for both the reactor and the water (storage) tank are tested and the favourable temperatures are presented and discussed. Applications both using ground heat for water vapour generation and using water vapour from indoor air are presented. The thermal energy storage system with mixed nesquehonite (NQ) and silica gel (SG) can use both low (25-50%) and high (75%) relative humidity (RH) air for hydration. The hydration at 40% RH gives a thermal storage capacity of 0.32 MJ/kg while 75% RH gives a capacity of 0.68 MJ/kg.