Abstract
The following reversible thermochemical reaction involving both an exothermic and an endothermic process was studied from the fundamental point of view of reaction kinetics in order to apply this reaction system to thermal energy storage by means of chemical reaction.
CaO + H2O _??_ Ca (OH) 2 + 104.2kJ/mol
Both the hydration of CaO and the dehydration of Ca (OH) 2 were studied in the chemical reaction control region by a thermogravimetric analysis (TGA) with the reactant solid particle size under 5 μm, the reaction temperature 356.2-723.2 K and the steam concentration 1.5-15.7vol%.
Reaction parameters such as rate constant, activation energy and reaction order of the individual reaction were determined by the obtained TGA experimental results on the basis of the Grain Model by assuming the presence of a reaction intermediate, CaO · H2O*, in the course of reaction.
It was found that the reaction orders of both the hydration of CaO and the dehydration of Ca (OH) 2 with respect to the concentration of solid reactant and the partial pressure of steam were 1.0. Further, it was found that the overall reaction rate constants of both reactions could be expressed in non-linear form, which gave a maximum value at about 473.2 K for the hydration of CaO.
