AS an approximate measure of the attractiveness of CaOCa (OH) 2 as a heat storage material, when CaO is hydrated with low pressure exhaust steam, ~44xl0 6 J of heat are obtained at a constant and high temperature level (430-540°C) from 0.028 m3 of CaO in bulk storage. Experimental results obtained to date on the CaO-Ca(OH)2 material include material characterization (chemical composition, particle size and surface area, and porosity) before and after reaction cycling. Three 8-g Ca(OH)2 samples were alternately dehydrated and hydrated up to, in one case, 1171 times, and the degree of completion of the reaction was measured periodically. The activation energy and the heat of reaction were measured using a pressure differential scanning calorimeter and were found to correspond closely with reported values. System studies were conducted on selected CaO-Ca(OH)2 thermochemical energy storage systems for a 100-MW commercial, solar-powered, thermal-electric generating station. Results indicate that, for the storage concepts considered, the CaO-Ca(OH)2 storage system is more complex and higher in cost than a high temperature (593 °C) sensible heat storage system using liquid sodium (unless long storage times of ~ 14 h or more are needed), but is lower in cost than a low temperature (316°C) sensible heat storage system such as hot rocks and HT-43 oil. Contents The experimental work deals primarily with the characterization of the properties of CaO-Ca(OH)2 under conditions typical of a fixed-bed reactor system. An apparatus was designed and constructed for performing multiple reaction cycles. The temperature of 8-g of Ca(OH)2 powder is raised to ~550°C. The water vapor driven off is condensed, and the volume is measured as a function of time. For the hydration cycle, boiling water at about 110°C supplies the water vapor. Table 1 shows selected results of cycling one of the samples to 1171 cycles. Gradual losses of utilization were observed at intervals during the course of the experiment, but it was found that a rapid re-evacuation of the apparatus immediately restored the utilization of the material to the 90% level or greater. This behavior is hypothesized to be the result of the accumulation of noncondensibl es, largely from air in-leakage, and some of which may be generated from a corrosion
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Rosemary et al. (1979) studied this question.