The Thermal Chemical Energy Storage System Of Calcium Based

Thermal energy storage systems（TES）can effectively improve heat utilization efficiency of industrial production and renewable energy system.In solar thermal power generation system,TES can effectively overcome the inherent instability and intermittent of solar energy to ensure sustainable and stable supply of high level thermal energy.Among them,the Thermo-chemical energy storage system（TCS）of inorganic hydroxides can be widely applied to the energy supply systems of electric power production and other places that need thermal energy,because of its peculiarities such as high energy storage density,stability and safety,nontoxicity and easy availability,high reaction rate,controllable temperature and heat release rate and so on.And thereby,Thermochemical energy storage system can promote the development of solar thermal power generation technology.Ca（OH）₂/CaO+H₂O is a typical energy storage system of metal hydroxide.It stores thermal energy by absorbing external heat（such as solar,surplus heat of industry,waste heat）with the Ca（OH）₂ powder decomposing into CaO and H₂O（g）（endothermic reaction）,and releases the high grade thermal energy by combining water vapor with CaO（exothermic reaction）.The research evaluated the Ca（OH）₂/CaO+H₂O energy storage system through a packed bed apparatus,and 20 times circulation of the hydration-dehydration-rehydration processes were carried out under different hydration pressure.The results show that the highest temperature of releasing heat can be achieved at 150 kPa water vapor partial pressure is 504 ℃.In addition,when the hydration pressure is 70 kPa,110kPa,130 kPa respectively,the highest heat output temperature is 455 ℃,474 ℃,481 ℃ correspondingly.During the circulation process,reaction degree of both hydration and dehydration process were reduced with the increase of cycling times,and tended to be stable after the 10 th cycle.The mole reacted fraction of hydration is within the scope of 0.8⁰.9 and the mole reacted fraction of dehydration is about 0.1.The results also indicated that,the average grain diameter of the reactants is increased with the increasing hydration pressure and cycle index.However,the reactants still have a high activity after 20 times circulation;and high heat output can be achieved under high vapor partial pressures.Hydrates after 20 times circulation under different vapor pressure had been investigated in this paper.Multi-rate scanning method was used for thermal kinetic analysis of the hydrates.The results show that,two weight loss processes can be observed at temperature range of 300⁵40 ℃ and 540⁸₂0 ℃ in each TG curve.The first loss is caused by thermal decomposition of Ca（OH）₂,and the second loss is because of thermal decomposition of CaCO₃.Non-model approach is used to calculate apparent activation energy of the hydrates.And the average apparent activation energy is 111.60 kJ/mol,130.61 kJ/mol,137.01 kJ/mol and 157.78 kJ/mol respectively when the hydration pressure is 70 kPa,110 kPa,130 kPa and 150 kPa correspondingly.Besides,a linear relationship between the activation energy E and the natural logarithm of pre-exponential factor lnA is discovered under the experimental conditions.Decomposition kinetics model of the four kinds of hydrates under the experimental conditions turn out to be in accordance with the shrinking cylinder mechanism with surface reaction rate controlling,and the integral model function is G（α）=1-（1-α）^1/2,differential model function is f（α）=₂（1-α）^1/2.