Thermochemical Heat Storage Performance Of Co-doped Modified Carbide Slag In CaO/CaCO₃ Cycles

CaO/CaCO3 heat storage is considered a competitive technology in concentrated solar power plants due to its high energy density,high operating temperature and low cost.The main defects of CaO/CaCO3 heat storage technology are its performance attenuation in multiple heat storage cycles and its low absorption rate to solar radiation.In this paper,industrial calcium-based solid waste carbide slag is used as calcium source,aiming to prepare composite materials with high heat storage performance and high cyclic stability.Based on macroscopic experiments and microscopic simulation,the heat storage performance of various additives co-doped modified carbide slag is studied and its related mechanism is revealed,providing a new idea for the design and preparation of materials in the application of the third-generation concentrated solar power plants technology.To improve the heat storage performance of carbide slag,Mn/Ce co-doped modified carbide slag was prepared.The effects of Mn/Ce doping amount and carbonation pressure on the heat storage performance of Mn/Ce co-doped carbide slag were studied in a double fixed-bed reactor.The reaction kinetics of carbonation heat release of Mn/Ce co-doped carbide slag was explored.Also,the mechanism of Mn/Ce improving the heat storage performance of carbide slag was revealed.It is found that the combined addition of Mn and Ce has a synergistic promoting effect on the heat storage performance of carbide slag.The material with a mass ratio of carbide slag/Mn/Ce of 100:5:2.5 shows better heat storage performance after 30 heat storage cycles at atmospheric pressure.The effective conversion after 30 cycles is 0.67,which is 3.3 times that of carbide slag.The excellent heat storage performance can be attributed to the great sintering resistance of CaMnO3 and the synergistic promotion effect of Mn/Ce.That is,the electron transfer process(Mn3+Ce4+?+Mn4++Ce3+)promotes the transfer of O2-and the generation of CO32-,resulting in heat thermal storage performance.To simultaneously improve the cyclic stability and optical absorption of carbide slag in cyclic heat storage,red mud/Mn/high alumina cement co-doped modified carbide slag was prepared using industrial solid waste red mud as iron source and high alumina cement as aluminum source.The effects of the addition of high alumina cement and red mud/Mn on the heat storage capacity,cyclic stability,and optical absorption of carbide slag were investigated.The heat storage/release rate of red mud/Mn/high alumina cement co-doped carbide slag was discussed.The phase composition and microstructure evolution during the cyclic heat storage were analyzed.The modified carbide slag exhibits excellent heat storage capacity and optical absorption.The Ca3Al2O6 and CaMnO3 inhibit the growth of CaO grains.FeMnO3 and Ca2Fe2O5 possess high optical absorption properties.The additions of Mn and red mud enhance the heat storage rate and basicity of carbide slag.the effective conversion and optical absorptance of modified carbide slag are 0.62 and 58%after 30 cycles,respectively,which are 3.1 and 6.5 times as high as that of the untreated carbide slag.Based on density functional theory,the mechanism of high alumina cement/Mn co-doped modified calcium carbide slag with high heat storage performance was revealed from the microscopic atomic level.The effects of Ca3Al2O6 and Mn on the heat storage performance of CaO-based materials were studied.The structure of CO2 adsorbed on CaO supported by CaO(001),Ca3Al2O6(110)and Mn-Ca3Al2O6(110)surfaces were built.And the structural changes,adsorption energy,charge transfer and density of states of each adsorption system were analyzed.In Ca3Al2O6 supported CaO structure,the adsorption energy of Ca3Al2O6 surface on CaO cluster is 2.4 times that of CaO structure.Therefore,Ca3Al2O6 effectively improves the sintering resistance of CaO-based materials.The adsorption energy of Mn-Ca3Al2O6 supported CaO for CO2 adsorption significantly increased,which is 2.2 times that of Ca3Al2O6 supported CaO structure.The results show that Mn doping promotes the adsorption of CO2 by Ca3Al2O6,making it easier for electrons to transfer to the O atoms in the CaO cluster,which effectively improves the heat storage performance of modified materials.