Abstract
The reaction characteristics, including hydration reaction rate and performance over repeated reaction cycles, of CaO extracted from different local limestone samples in Japan were examined to identify the optimal material to be used in chemical heat storage and pumps. The factors influencing the chemical reaction, including the chemical composition, crystal grain structure, collapse due to hydration/dehydration reactions of CaO/Ca(OH)2, specific surface area, and mean pore diameter, were compared and discussed. Based on the results, it was observed that CaO derived from limestone from Hiroshima, previously utilized by our research group, and Kawara CaO with a high purity exhibit similar reaction characteristics. Garou CaO, which has more impurities than that in the others tested, exhibits a lower initial hydration reaction rate and conversion change than those of Hiroshima/Okayama and Kawara CaO due to the presence of magnesium in Garou CaO as dolomite, which initially fills the pores. However, it was shown that Garou CaO can be used as a practical material for chemical heat storage and pumps with relatively high strength and reactivity compared with the other limestone samples because of its columnar joint texture and larger pore size following activation by four water vapor reaction cycles.
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