| Calcium-based materials have the characteristics of high heat storage density,low cost and environmental friendliness.CaO/Ca(OH)2 cycle heat storage of calcium-based materials has become one of the most potential thermochemical heat storage for concentrated solar thermal power generation.Improving the heat storage reaction characteristics and cycle stability of calcium-based materials is the key to obtain higher heat storage performance.In this paper,various methods were developed to enhance the CaO/Ca(OH)2 cycle heat storage performance.In this paper,the CaO/Ca(OH)2 cycle heat storage performance of hollow structure CaO was studied.The mechanism of Mn modification and Ce modification to strengthen the CaO/Ca(OH)2 cycle heat storage reaction was studied by density functional theory calculation.The CaO/Ca(OH)2 cycle heat storage performance of CaO under fluidization was proposed,and the methods of SiO2 modification and coupled calcium-looping heat storage were proposed to improve the CaO/Ca(OH)2 cycle heat storage performance under fluidization respectively.The mechanism of strengthening the CaO/Ca(OH)2 cycle heat storage performance was revealed by microstructure analysis,particle size distribution analysis and density functional theory calculation,which provided theoretical guidance for the industrial application of thermochemical heat storage of calcium-based materials.In order to improve the chemical reaction rate of CaO,a hollow-structured CaO for calciumlooping decarburization coupled with CaO/Ca(OH)2 cycle heat storage was prepared by a hydrothermal carbon template method.The formation process of the hollow structure and the effect of preparation condition were analyzed by microscopic characterization.The carbonation reaction and hydration reaction performance of the hollow-structured CaO were investigated.The mechanism of the hollow structure improving the heat storage reaction characteristics of CaO was analyzed and the optimal preparation conditions were determined.The interaction mechanism of calcium-looping decarburization and heat storage was discussed.The microscopic morphology and pore structure evolution mechanism of hollow-structured CaO in calcium-looping decarburization and CaO/Ca(OH)2 cycle heat storage were analyzed.The mechanism of heat storage cycle to rapidly alleviate CaO sintering during calcium-looping decarburization was revealed.When the hydrothermal temperature is 170℃ and the hydrothermal time is 6 h,the prepared hollow-structured CaO have higher calcium-looping decarburization and heat storage performance.After 10 calcium-looping decarburization cycles,the carbonation conversion and the highest hydration conversion of hollowstructured CaO reaches 57.3%and 80.8%,respectively,which are 1.7 and 1.3 times as high as that of calcined limestone.In order to increase the hydration exothermic rate of CaO,Mn-modified and Ce-modified CaO were prepared by wet mixing method.The CaO/Ca(OH)2 cycle heat storage performance of CaO/Ca(OH)2 of Mn-modified and Ce-modified CaO were investigated.Mn modification and Ce modification improved the hydration exothermic reaction rate of CaO.The hydration exothermic reaction process of Mn-modified and Ce-modified CaO was investigated by density functional theory calculations.The effects of Mn modification and Ce modification on the geometric structure and electronic properties of CaO hydration exothermic reaction process were analyzed from the atomic scale.The mechanism of Mn modification and Ce modification promoting the hydration exothermic reaction characteristics of CaO was elucidated.When the hydration exotherm time is 30 s,the hydration conversion of Mn-modified CaO reaches 83.3%,which is 1.09 and 1.13 times as high as that of Ce-modified CaO and pure CaO,respectively.Mn modification and Ce modification reduce the activation energy of CaO hydration exothermic reaction.Mn modification has the strongest promotion effect and the activation energy of hydration exothermic reaction of Mn-modified CaO is 0.013 eV,which is only 44.8%of that of Ce-modified CaO.The CaO/Ca(OH)2 cycle heat storage characteristics of CaO under fluidization were studied.The hydration exothermic and cyclic heat storage performance of CaO under fluidization were obtained.The effects of particle size,fluidization number,water vapor concentration,cycle times and type of carrier gas on the CaO/Ca(OH)2 cycle heat storage performance of CaO under fluidization.By comparing the exothemic characteristics and particle morphology of CaO under different gas-solid flow patterns in the fixed bed reactor and the bubbling fluidized bed reactor,it is found that CaO under fluidization did not exhibit obvious particle agglomeration.The stability of cycle heat storage of CaO under fluidization is significantly improved.The influence mechanism of various factors on the hydration exothermic performance of CaO under fluidization was revealed and the wear characteristics of CaO in cyclic heat storage was investigated.It is found that the rapid expansion of CaO in multi-cycle heat storage is the main reason for the decrease of its cyclic heat storage stability.In order to suppress the rapid expansion of CaO,it was proposed to use silica sol and limestone as precursors to prepare SiO2-modified CaO composites.The influence mechanism of CaO/SiO2 mass ratio and pre-calcination temperature on the cyclic heat storage performance of SiO2-modified CaO was investigated.The promotion mechanism of SiO2 modification on the hydration exothermic performance of CaO was revealed.After 10 cycles,the expansion rate of SiO2-modified CaO is 124%,which is only 45.4%of that of pure CaO,and the volume energy density of SiO2-modified CaO is 691.5 MJ/m3,which is 33.2%higher than that of pure CaO.By introducing the calcium-looping heat storage(CaO/CaCO3 cycle heat storage)process,a calcium-looping heat storage coupled with CaO/Ca(OH)2 cycle heat storage process of CaO under fluidization was proposed.The heat storage performances of CaO in different process flow were studied.Calcium-looping heat storage and CaO/Ca(OH)2 cycle heat storage performance of CaO in the multi-stage coupled heat storage process were obtained.The wear characteristics of CaO in the coupled heat storage process were investigated.The interaction between the CaO/Ca(OH)2 cycle heat storage and the calcium-looping heat storage and the particle evolution mechanism were revealed.The study found that CaO has higher coupled heat storage performance in the mode of first entering the CaO/Ca(OH)2 cycle heat storage.It is found the mutual promotion between the calcium-looping heat storage and CaO/Ca(OH)2 cycle heat storage and the mutual promotion mechanism was revealed through microstructure analysis and particle size distribution analysis.The carbonation conversion of CaO increased by 64.7%and the carbonation exothermic time is prolonged by 31.7%after 10 CaO/Ca(OH)2 heat storage cycles.The volumetric energy density of CaO in hydration stage increases by 1.9 times after 10 calcium-looping heat storage cycles. |
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