Reaction characteristics of various gypsum as chemical heat pump materials

From the viewpoints of energy savings and environmental impacts, the authors have been studying on Chemical Heat Pump (CHP) systems such as a calcium sulfate/water reaction system for effective waste energy utilization. The CHP system using hydration of CaSO4/dehydration of CaSO4·1/2H2O reaction can use low-temperature level thermal energy effectively in many processes. The reaction material CaSO4 is prepared from original material: gypsum (CaSO4·2H2O). Although the natural gypsum is used in many fields; an enormous amount of resources has become waste. We are trying to solve the problems of the energy consumption, environmental pollution and waste material at the same time by the CHPs using CaSO4·1/2H2O hydration/dehydration reaction.More studies on the reaction characteristics of various CaSO4 materials are necessary for the CHP reaction system in different conditions. We examined the hydration/dehydration conversions, reaction rates etc. of several CHP materials. We prepared two types of original particles. The one (A) is a just crushed natural gypsum (710–1000 μm), and the other (B) is a granulated same size particles by fine particles (<10 μm).As a result, the changes of conversion and reaction rate showed some differences. It was probably caused by impurities in the gypsum to some extent. The impurities may have affected the stability of the data and the final conversions etc. The hydration conversions of CaSO4 from the natural gypsum which contains some of impurities such as Thailand one were lower than 85%, and the conversions of the natural gypsum which contains fewer impurities such as Australia or Morocco one were higher than 90%. The granulated particle (B) has some effect of adsorption because of the wider specific surface area. We need to design the reaction materials from the viewpoints of the purity and the heat/mass transfer characteristics in order to meet the chemical heat pump performance.