High-density and anti-clogging three-phase absorption heat storage with crystallization management

Abstract

Three-phase sorption heat storage can significantly enhance the energy storage density (ESD) through the crystallization of salt-water working pair. However, the crystals will cause the clogging of solution circulation, making it difficult to be realized in absorption heat storage with liquid absorbent. In this work, the crystal management strategy is proposed for three-phase absorption heat storage. By controlling the crystallization ratio, energy storage enhancement and clogging prevention can be achieved simultaneously. Both theoretical and experimental analyses were carried out. A detailed thermodynamic model of the three-phase absorption heat storage cycle was established, by considering the change of crystallization ratio. A prototype of LiBr-water three-phase absorption heat storage with crystallization management which includes crystal filtering, high-level solution intake, crystal fusion by electric heating rods, and water flushing, was designed and fabricated. The anti-clogging design ensures the circulation of solution, efficient vapor absorption and crystal dissolution in discharging process, thus achieving high energy storage density and stable heat output simultaneously. The three-phase absorption heat storage prototype demonstrated high ESD of 220 kWh/m3 and 178 kWh/m3 with crystallization ratio of 0.41 and 0.26 under the space heating and hot water supplying conditions, respectively. Comparing with the absorption heat storage prototype without crystallization, this represents ESD enhancement of 102% ∼ 210%, which confirms the feasibility and superiority of the proposed crystal management strategies.