Energy Storage of Low Potential Heat using Lithium Hydroxide Based Sorbent for Domestic Heat Supply

Abstract

With the increasingly energy consumption and environmental degradation, the recovery of low-grade industrial waste heat and the development and utilisation of renewables have become urgent needs. At present, the recovery of waste heat is mainly at high temperature, and the recovery rate of waste heat at medium and low temperatures is low. Adsorption thermochemical energy storage (TCES) is a pivotal technology applied for long-term thermal energy storage based on the reversible gas-solid reaction at mid-to low-temperature. LiOH·H2O is a potential thermochemical material (TCM) candidate because of the high energy storage density (ESD). In this paper, the expanded graphite (EG) is used as supporting matrix to impregnate LiOH to further improve its heat and mass transfer. The water vapour adsorption properties such as sorption capacity and sorption isotherms of the consolidated composite sorbents with EG contents of 0, 5, 8, 12, and 15 wt% were tested. It was found that the samples with 5% and 8% wt% EG have superior sorption capacity and kinetics at various relative humidities (RHs), and the maximum water uptake substantially decreased with increasing temperature. The cyclability results showed 90% and 92% of the original ESDs are retained after 12 cycles for the samples with 8% and 15% wt% EG, suggesting good stability of composite sorbent. The ad/desorption isobars processes also proved the existence of the sorption hysteresis loop, and this phenomenon is more obvious at low pressure. The data fitting results revealed that the kinetics coefficient of the promising composite sorbent containing 8 wt% EG is 0.01671 s – 1 at 30 °C with 58% RH. Compared with the sensible or latent energy storage, the heating temperature produced from the sorbent is adjustable for different purposes. Considering the low emissions and pollution of LiOH-based heat production compared to the coal-fire system, i.e., 1262 kg pollutants are theoretically reduced for a household per year, it is a clean alternative for the residential heat supply.