ABSTRACT
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 (gypsum)/ water reaction system for effective waste energy utilization. The CHPs can store thermal energy in the form of chemical energy by endothermic reactions and release it at various temperature levels for heat demands by exo/endothermic reactions. The CHP system using CaSO4.1/2H2O hydration/dehydration reaction can use low-temperature level thermal energy effectively in many processes. In general, the natural gypsum CaSO4.2H2O is well known as an inexpensive and safe material. The natural gypsums, however, are used in many fields, and 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. In this study, we collected some usable gypsum for CHPs; natural gypsums in different place of production, variety of composite gypsum, plaster fertilizer, recycled gypsums etc. We examined the hydration/dehydration conversions, reaction rates etc. by Thermogravimetry (TGA-50, Shimazu corp.) or Differential Thermogravimetry (DTG-60 (TG/DTA), Shimazu corp.). We prepared two types of particles. The one (A) is a just crushed natural gypsum (710- 1000μm), and the other (B) is a granulated same size particles by fine particles (<10μm).
As a result, the changes of conversion and reaction rate showed some differences depending on the place of material production. It was probably caused by impurities in the gypsums to some extent. The impurities may have affected the stability of the data and the final conversions etc. The conversions of 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) and the same size natural gypsum (A) did
not show distinctive difference on reproducibility and stability. We need to design the reaction materials from the view points of the purity and the heat/mass transfer characteristics in order to meet the chemical heat pump performance.
Keywords: Calcium sulfate, Gypsum, Thermogravimetry, Hydration, Dehydration.
