Optimisation of salt impregnated matrices for open thermochemical heat storage through material characterisation and hygrothermal cyclic analysis

This work sought to narrow the selection of raw material sorbents suitable for domestic ‘open’ thermochemical heat storage to those that had a high affinity of each working pair to each other, were environmentally stable with low raw material costs, a low regeneration temperature, a high reaction temperature lift, high cyclic efficiency and high energy density. This was achieved through characterisation of the pore geometry and hygrothermal properties of the materials. The pore geometry and structure was mapped using N2 physisorption, gas pycnometry and gravimetric testing. The hygrothermal properties were characterized using modified transient plane source, differential scanning calorimetry and modified dynamic vapour sorption (DVS) techniques. A custom built testing rig was used to test the cyclic behaviour through analysis of output and regeneration temperatures, material mass and cycle times with a comparative analysis of all materials also undertaken. Vermiculite with impregnated calcium chloride or lithium bromide appeared to have significantly higher storage potential when compared to the other materials with a low regeneration temperature. Vermiculite with impregnated lithium nitrate had less temperature rise but had a significantly longer temperature dwell time. A combination system comprising these three materials may be the most suitable candidates for an open thermochemical storage system.