Pergamon Energy Convers. Mgmt Vol. 38, No. 10-13, pp. 1025-1033, 1997 © 1997 ElsevierScienceLtd All rights reserved. Printed in Great Britain PIl: S0196-891M(96)00132-X 0196-8904/97 $17.00 + 0.00 APPLICABILITY OF ZEOLITE FOR CO2 STORAGE IN A CaO-CO2 HIGH TEMPERATURE ENERGY STORAGE SYSTEM KYAW KYAW, T. SHIBATA, F. WATANABE, H. MATSUDA and M. HASATANI* Department of Energy Engineering and Science, Faculty of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-01, Japan Abstract--Many reversible thermal dissociation reactions have been reviewed for storing thermal energy at very high temperatures, such as high temperature heat from power plants. Among them, dissociation of CaCO3 seems very promising as the material can dissociate at 1098 K under atmospheric condition and the reactants involved are free from toxicity. One of the dissociation products, CO2 gas, requires a storage system. Three CO2 storage systems are being considered and the thermal operating efficiencies, COP, of the respective CaO--CO2 energy storage systems are evaluated. It is found that the system with a zeolite adsorbent for CO: storage becomes quite comparable to other systems when the adsorptivity of the adsorbent increases to higher values. The CO: adsorption characteristics of zeolite 13X and super activated carbon under a temperature range 303-573 K are studied. Based on the adsorption data, it is found that zeolite 13X adsorbent can be used as a CO: storage medium in a CaO-CO2 high temperature thermal energy storage system. © 1997 Elsevier Science Ltd. Thermal energy storage Upgraded temperature CO2 storage Calcium oxide Adsorptivity Zeolitel Activated carbon Coefficient of performance NOMENCLATURE COP = Coefficient of a heat pump k = A Freundich constant n = A Freundich constant q = Adsorptivity, wt of adsorbate/wt of adsorbent (kg/kg) P = Pressure of CO2 (kPa) Pe = Equilibrium dissociation pressure of CaCO3 (kPa) T = Absolute temperature (K) w = Weight of a sample (kg) t = Time (s) H = Higher level, higher value INTRODUCTION Generally, energy from primary energies is extracted as thermal energy in the form of high pressure steam or hot gases and is converted into electrical energy with 30-40% overall efficiency. Due to uneven demand, power plants which are structured to meet the peak demand usually operate at loads lower than the optimum design conditions which brings down the overall efficiency even lower. One of the main requirements for a power plant to attain maximum operating efficiency is a steady state operation where there is no load fluctuation. In connection with such requirements, energy storage systems can provide such benefits as base-load load following of power plants. Energy storage systems can also lead to increased substitution of renewable energies such as solar, wind and other intermittent energy systems for petroleum and natural gas. At present, it seems rather difficult to store large amount of electrical energy than to store thermal energy. A relatively low and middle temperature range thermal energy storage has been well studied *Corresponding author. 1025