| Solar energy can be converted into electricity by means of concentrating solar thermal power technology, which can not only reduce the consumption of fossil fuels but also ease greenhouse effect caused by CO2 problems. However, because the solar energy is intermittent and is easily affected by environmental factors, how to ensure the continuous supply of solar energy has become the key of solar thermal power generation technology. A feasible method is the development of thermal energy storage system, which will store heat during the sunshine periods and release it during the periods of weak or no solar irradiation.At present, three kinds of thermal energy storage methods exist: sensible heat storage, latent heat storage and chemical heat storage. Due to the high energy density and negligible heat loss, thermochemical energy storage method has attracted widespread researches. In several available thermochemical heat storage systems, the Ca(OH)2/Ca O system has become one of the most studied systems because of high energy storage density, faster reaction kinetics, safe, nontoxic and low price.The heat and mass transfer performance of reaction bed during the endothermic and exothermic reaction processes, as well as the cyclical stability of reactants after 20 cycles had been investigated in this paper. The results show that: when the reaction bed temperature rises to 400 ℃, the dehydration reaction occurs rapidly and the mole reacted fraction of the reactants reduces to 0.06 after dehydration 180 minutes; The dehydration reaction proceeds faster with the increase of dehydration temperature; During the hydration process, the temperatures within the reaction bed increase rapidly and then begin to decrease. Temperatures inside the reactor bed are higher than that of the outer periphery; Mole reacted fraction is 0.95 at the end of the hydration process and no significant performance decay is observed after 20 cycles.The reactor bed heat storage capacity gradually increases with increasing dehydration temperature during the endothermic reaction process; Heat storage capacity after dehydration 90 minutes is equivalent to 33.6% of that during the whole dehydration process; With the increase of dehydration temperature, heat storage capacity of reaction bed increases at the same time; During exothermic process, the gross heat output after hydration 30 minutes is equivalent to 91.7% of the total heat output throughout the exothermic process; the heat storage capacity and total heat output at the same time decrease with the increase of cycle number, however, little changes are found in overall.Multi-rate scanning method was used in this paper to explore the decomposition kinetics parameters of Ca(OH)2 in nitrogen atmosphere and different heating rates, the results show that two weight loss processes are observed during the thermal decomposition of Ca(OH)2 at a temperature range of 623.15~773.15 K and 873.15~973.15 K; The resulting kinetic parameters are related to the reaction conversion rate, the heating rate and the selection of model approach; When the conversion rate is equal to 0.2~0.8, the obtained apparent activation energy using non-model approach is 115~140 k J/mol and the pre-exponential factor ln(A/s-1) is between 12 and 19; The decomposition kinetics model of Ca(OH)2 under the experimental conditions is proved to be shrinking cylinder mechanism with surface reaction rate controlling, and the integral mechanism function is G(α) =1-(1-α)1/2; Besides, a linear relationship between the activation energy E and the natural logarithm of pre-exponential factor A is discovered under different heating rates. |
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