Thermochemical heat storage is a promising technology for improving energy efficiency through the utilization of low-grade waste heat. The formation of a SrCl 2 ammine complex was selected as the reaction system for the purpose of this study. Discharge characteristics were evaluated in a packed bed reactor for both the gas-solid reaction and the liquid-solid reaction. The average power of the gas-solid reaction was influenced by the pressure of the supplied ammonia gas, with greater powers being recorded at higher ammonia pressure. For the liquid-solid reaction, the obtained average power was comparable to that obtained for the gas-solid reaction at 0.2 MPa. Moreover, the lower heat transfer resistance in the reactor was observed, which was likely caused by the presence of liquid ammonia in the system. Finally, the short-term durability of the liquid-solid reaction system was demonstrated over 10 stable charge/discharge cycles.

Thermochemical heat storage is a promising technology for improving thermal energy efficiency. In this study, CaCl2 and H2O were selected as the reactant and working medium, respectively, assuming the utilization of low-grade waste heat. To investigate the durability of the CaCl2/H2O reaction, 1000 repetitive operations were conducted at the same 110 °C charging and discharging temperatures. During the long-term repetitions, a decrease in the average volumetric power density was observed. The peak value in repetitions 901–1000 was 11% lower than the peak value in the initial 50 repetitions. This trend was mainly caused by a decrease in the heat transfer rate; it was observed after the repetitive experiments that reactant particles had moved out of the heat exchanger. Although a decreasing trend in the power density was observed, a peak value of Q = 320 kW/m3 and a conversion ratio of approximately 0.7 were observed in repetitions 901–1000. In addition, approximately 90% of the stored heat was released in all 1000 repetitions. Thus, using long-term repetitions (1000), this study confirmed the durability of the CaCl2/H2O reaction for thermochemical heat storage.

Thermochemical heat storage is a promising technology for improving thermal energy efficiency. To investigate the durability of the CaO/Ca(OH) 2 reaction and develop a reactivation method, repetitive charging/discharging operation of a packed bed reactor with a thick packed bed was conducted, and variations in the discharging behavior, final conversion, and reactant activity were investigated. Owing to the formation of a deactivated sintered reactant block, the discharging time halved and the final conversion ratio decreased by the 53rd discharging operation. To enhance durability, a reactivation method using high-pressure vapor was implemented during the 54th discharging operation. Following reactivation, the final conversion increased 15%, and the discharging time tripled when compared with the discharging operation before reactivation, confirming the success of this simple reactivation method.

A heat storage system that is used to generate steam directly by exploiting the dissolution phenomenon between CaBr 2 and water was studied. The performance of the system in terms of the coefficient of performance (COP) or volumetric heat capacity (VHC) yielded maximal values for the amount of water supplied. The COP was 0.072 to 0.115 for steam pressures of 20-50 kPa at x ¼ 7.5. VHC values recorded were 177.2 to 250.1 kJ/l for steam pressures of 20-50 kPa at x ¼ 7.5. This calculation was validated by comparing the calculated value with the experimental result. The pressure settled at the equilibrium state for a very short duration at the heat release step, proving that the dissolution phenomenon involved a high mass transfer rate and was able to transform the heat of dissolution into enthalpy of steam. The amount of steam generated in the experiment conformed very well to the calculations, thus validating the calculation method. V C 2014 AIP Publishing LLC.

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