High temperature heat storage and temperature upgrading above 1273 K by means of CaO/CO{sub 2} reversible reactions

For storing thermal energy at high temperature around 773-1273 K like from concentrated solar energy and nuclear power plant, many thermal decomposition reactions have been investigated in terms of thermodynamic, reaction equilibrium and physical properties of the involved reactants. Among them CaO/CO{sub 2} system seems very promising because: decomposition of CaCO{sub 3} can occur at 1098 K under 101 kPa with very high enthalpy and the reactants are free from toxicity and corrosiveness. Three methods for storing the dissociation product CO{sub 2} gas are considered and the Coefficient Of Performance COP against the upgraded temperature are evaluated. From repeated carbonation/decarbonation of CaO carried out in thermogravimetric-analysis (TGA) it was found that pore surface area and volume of Cao is closely related to conversion and that the reactivity can be enhanced by the presence of water vapor in the carbonating gas. The possibility to generate high temperature heat around 1300 K by the CaO-CO{sub 2} heat storage system is verified by means of carbonating a packed bed of CaO at 773 K under CO pressures of 400-700 kPa in a lab-scale adiabatic reactor. The sets of reaction temperature and pressure observed agree fairly well with the equilibrium relationships. Such issues asmore » the enhancement of reactivity of CaO, heat and mass transfer in the reactor packed with CaO particles are also under study for realizing this Cao/CO{sub 2} heat storage system from a practical point of view. 3 refs., 9 figs.« less