Thermochemical heat storage system utilizing low-grade heat sources: combined investigations, material development, design and integration

Abstract

The cost of space heating is dependent on electricity prices because of its significant utilization of electricity. There was a 60% increase in the unit electricity price between 2005 and 2019 which is sure to further increase in the future. Thermochemical heat storage systems (THHS) can store heat in summer and provide space heating for households in winter, without major heat storage loss. THSS have the potential to control both temperature and humidity of residential houses, helping to tackle dampness in the house and reduce electricity consumption. This project focuses on a novel, thermochemical storage system with a multi-cyclic operation capability. To investigate the potential of the THSS, environment-friendly, non-toxic and harmless materials were selected. In order to solve the problem of a large pressure drop of moist air passing through fixed bed reactors, stainless steel tubes of 8 mm in diameter and 50 mm in length were filled with strontium bromide and installed with in-line and staggered layouts in the reactors. Hydration and dehydration cycles were carried out to test the operation of these tube-type reactors, under different operating temperatures. Additionally, to maximize the volumetric storage capacity, a spiral reactor design was also utilized. In order to enhance the heat storage capacity and reaction kinetics of strontium bromide and magnesium sulphate, composite pellets were prepared with supporting materials such as activated carbon, expanded natural graphite, molecular sieves, celite, etc. All samples were thermally characterized using thermogravimetric (TGA) and differential scanning calorimetry (DSC) techniques throughout the cyclic tests. The most promising pellet was utilized in a laboratory–scale fixed bed reactor to investigate the potential of the composite. This research is expected to make a valuable contribution to a better understanding of thermochemical heat storage systems with the analysis made on both the reactor configuration and the heat storage materials.