Durability Enhancement of CaSO4 in Repetitive Operation of Chemical Heat Pump

Authors: Y. Shiren, M. Masuzawa, H. Ohkura, T. Yamagata, Y. Aman, N. Kobayashi

Abstract:

An important problem for the CaSO4/CaSO4･1/2H2O Chemical heat pump (CHP) is that the material is deactivated through repetitive reaction between hydration and dehydration in which the crystal phase of the material is transformed from III-CaSO4 to II-CaSO4. We investigated suppression on the phase change by adding a sulfated compound. The most effective material was MgSO4. MgSO4 doping increased the durability of CaSO4 in the actual CHP repetitive cycle of hydration/dehydration to 3.6 times that of undoped CaSO4. The MgSO4-doped CaSO4 showed a higher phase transition temperature and activation energy for crystal transformation from III-CaSO4 to II-CaSO4. MgSO4 doping decreased the crystal lattice size of CaSO4･1/2H2O and II-CaSO4 to smaller than that of undoped CaSO4. Modification of the crystal structure is considered to be related to the durability change in CaSO4 resulting from MgSO4 doping.

Keywords: CaSO4, chemical heat pump, durability of chemical heat storage material, heat storage.

Digital Object Identifier (DOI): doi.org/10.5281/zenodo.1338301

References:

[1] COCN, (Leading-edge technology to be applied to energy network), 2014, http://www.cocn.jp/common/pdf/thema63-L.pdf (accessed Jan 6th 2015)
[2] Energy Conservation Center, Japan, (Survey Research of factories waste heat), 2001, pp. 14.
[3] Society of Inorganic Materials, Japan ed., Cement ･Gypsum･Lime Handbook, Giho-do, 1995, pp. 142-143.
[4] J. J. Gardet, B. Guilhot, M. Soustelle, Cement and Concrete Research. Vol. 6, 1976, pp. 193-200.
[5] Jun-Hee Lee, H. Ogura, S. Satoh, App. Term. Eng., Vol. 63, 1, Feb. 2014, pp. 192-199.
[6] H. E. Kissinger, Anal. Chem., Vol. 29, 11, pp. 1702-1706, 1957
[7] T. Kotoyori, “Energy of Activation for Oxidative Pyrolysis of Several Plastics”, Research Report of the Research Institute of Industry Safety, RR-19-4. 1971, https://www.jniosh.go.jp/publication/doc/rr/RR-19-4.pdf (accessed Jan 6th 2015).