| Solar energy is a widely distributed renewable energy.Solar thermal power generation technology converts thermal energy into electrical energy through thermal power conversion.Its advantage lies in the thermal storage system,which can achieve continuous and stable power generation.The redox reaction of metal oxides has the advantages of large energy storage density and high storage/exothermic temperature,which is very suitable for application in solar thermal power generation systems.In this paper,two kinds of metal oxides,Co3O4/CoO system and CuO/Cu20 system,were used as heat storage medium,and the metal oxide oxidation/reduction kinetics,heat storage material formulation optimization and porous honeycomb heat storage module and other aspects were systematically studied.The effects of heating/cooling rate,reaction temperature and partial pressure of oxygen on the reaction kinetics of two kinds of metal oxide heat storage mediums were analyzed with thermal analysis equipment,and the corresponding kinetic mechanism models were fitted and analyzed afterwards.The results showed that the Co3O4/CoO system had favorable reaction kinetics,high cycle stability,and the ability of achieving complete redox conversion under high oxygen concentration.Additionally,the oxygen concentration can change the reaction conversion temperature.When the oxygen concentration changed from 30%to 70%,the reduction/oxidation conversion temperature increased from 942.25 ?/894.35 ? to 961.57 ?/925.91 ?;the temperature difference of oxidation and reduction conversion under high oxygen concentration became smaller,and under different oxygen concentrations,the corresponding reaction mechanism function of the redox conversion process would change accordingly.As for the CuO/Cu2O system,it is difficult to achieve complete reoxidation due to its slow reoxidation process.The optimum reoxidation temperature was found to be 980? after multiple experiments.With the temperature continuing to increase,the reaction rate decreased rapidly.Moreover,doping CuO with a suitable proportion of Al2O3 can significantly improve its reoxidation kinetics.The reaction rate increases with the increasing of Al2O3 doping ratio.During the cooling stage,when the mass fraction of CuO decreased from 100%to 90%,the reoxidation ratio increased from 61.25%to 89.67%.After that,if the Al2O3 doping proportion was continuously increased,the reoxidation rate did not obviously enhance.The main reason for the reoxidation kinetics of the CuO/Cu2O system is the presence of the complex metal oxides Al2CuO4 and Cu2Al4O7 in the doped samples.If the temperature is higher than the melting point of CuO,the structure of the complex metal oxide in the doped samples would be destroyed,resulting in a decrease of the reactivity.The metal oxide particles were added into porous honeycomb heat storage module,and the self-designed heat storage test systems were used to analyze the reaction condition under electric heating and radiation heating respectively.The results showed that the reoxidation rate of Co3O4 porous honeycomb in two heating/cooling cycles under electric heating were 90.46%and 97.93%,respectively,and the thermal storage module maintained good structural stability.The doping of Al2O3 can significantly increase the reoxidation rate of the Cu0/Cu20 system,but the increase of Al2O3 doping ratio will reduce the structural stability of the Al2O3-doped porous honeycomb.The storage/exothermic performance test was carried out on a porous honeycomb with a stable structure of 90%CuO+10%Al2O3,of which the reoxidation conversion was 85.7%.Co3O4 was tested as a sample for the redox conversion of metal oxide under concentrated radiation heating.The results showed that the reduction and oxidation reaction rates of porous honeycomb structure were higher than those of solid particles.The reoxidation rate of porous honeycomb under radiation heating is about 79.59%,indicating that most of the reduced Co3O4 can be reoxidized during temperature decrease.And the porous honeycomb is a suitable thermal storage structure for metal oxide. |
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