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Open AccessArticle

Possibility of Calcium Oxide from Natural Limestone Including Impurities for Chemical Heat Pump

1
Graduate School of Science and Engineering, Chiba University, 1-33, Yayoi-cho, Inage, Chiba 263-8552, Japan
2
Central Research Laboratory, Taiheiyo Cement Corporation, 2-4-2, Osaku, Sakura 285-8655, Japan
*
Author to whom correspondence should be addressed.
Energies 2020, 13(4), 803; https://doi.org/10.3390/en13040803
Received: 24 December 2019 / Revised: 28 January 2020 / Accepted: 6 February 2020 / Published: 12 February 2020
Improving energy recycle is an important way to save energy resources and preserve the global environment. Chemical heat pump (CHP) is a technology for saving energy, which utilizes chemical reactions to store thermal energy such as waste heat and solar heat, then release it to provide heat for heating/cooling/refrigeration. For a practical CHP, it is necessary to find cheaper and more stable supply materials. In order to evaluate the possibility of calcium oxide from natural Ofunato natural limestone including impurities, we compare Ofunato limestone with Kawara natural limestone and Garou natural limestone from Japan. These calcium oxides worked as a reactant for CaO/H2O/Ca(OH)2 CHP by repeated hydration/dehydration reaction cycle experiments in a thermogravimetric analyzer. As a result, Ofunato CaO exhibits a high hydration reaction rate after decarbonization at 1223 K for 5 h. The reactivity increased by the repeated hydration reaction although the first hydration rate was low. Furthermore, the sintering of impurities in Ofunato limestone occur easier than that in Kawara limestone with lower impurities. The impurities adhered to the surface of the CaO particle to make specific surface area of CaO particle smaller, which could inhibit hydration reaction of CaO particle. Even if Ofunato limestone contains some impurities, it can be utilized as a raw material for chemical heat pumps. View Full-Text
Keywords: chemical heat storage; Ofunato limestone; hydration reaction; CaO; Ca(OH)2; CaCO3 chemical heat storage; Ofunato limestone; hydration reaction; CaO; Ca(OH)2; CaCO3
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Lai, L.; Imai, T.; Umezu, M.; Ishii, M.; Ogura, H. Possibility of Calcium Oxide from Natural Limestone Including Impurities for Chemical Heat Pump. Energies 2020, 13, 803.

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