| Among the solar energy storage technologies,the CaO/Ca(OH)2 system has been considered as one of the most promising energy storage systems due to the high energy storage density,low energy storage loss,high energy storage rate and non-toxicin.The calcium-looping technology utilizes the cyclic carbonation/calcination reaction of CaO to capture CO2 produced from coal-fired power plants,and it has been considered as one of the most promising large-scale CO2 capture technologies,while massive CaO with low activity is usually exhausted from the calciner.In this work,a coupled system with cyclic CO2 capture and hydration/dehydration process for energy storage was proposed based on calcium-based materials,which uses calcium-based materials that experienced multiple CO2 capture cycles as the heat storage material.This process makes full use of calcium-based materials,and it is expected to simultaneously achieve calcium-looping capture of CO2 and thermochemical heat storage.The heat storage performances of limestone after cyclic carbonation/calcination were studied in this paper.The effects of hydration conditions,dehydration conditions and particle size on heat storage performances of CaO were studied,and the optimal hydration and dehydration conditions were determined.It has been found that the most optimal hydration condition is at 400 C and for 5 min,and the most optimal dehydration condition is at 550 C and for 10 min.After 10 heat storage cycles,the hydration conversion of CaO was as high as 0.83 mol/mol.With the increase of the number of heat storage cycles,the heat storage performance of CaO is reduced because the crystal grains of CaO were broken during the heat storage process,which limited the absorption and diffusion of steam.Besides,volume of pores that distributed in the range of 30-100 nm in diameter decreased,which might be the key range for the hydration reaction of CaO,so that the heat storage performance of CaO graduately decreased.In order to improve the heat storage performance of limestone,modification of acetic acid solution on limestone was proposed.The effects of calcination conditions and carbonation conditions on the heat storage performance of acetic acid modified limestone were studied.It has been found that acetic acid modified limestone achieves higher heat storage performance than limestone.After 10 CO2 capture and 10 heat storage cycles,the hydration conversion of acetic acid modified limestone is as high as 0.79 mol/mol,which is 20%higher than that of limestone.The acetic acid modification method can improve the pore structure of CaO,which gives rise to higher surface area and pore volume.With the modification of acetic acid,the volume of pores distributed in the range of 30-100 nm increases,which is beneficial for the hydration reaction.As a result,acetic acid modified limestone achieves higher heat storage performance than limestone,and the heat storage performance of acetic acid modified limestone is improved with the support of CO2 capture cycles.Ce modified limestone was prepared with acetic acid,limestone and cerium nitrate.The effect of CaO/CeO2 mass ratio on the heat storage performance of Ce modified limestone was studied.When the mass ratio of CaO/CeO2 is 90/10,the heat storage performance of Ce modified limestone is the highest.After 10 CO2 capture and 10 heat storage cycles,the heat storage performance of Ce modified limestone as high as 0.85 mol/mol,which is 11%higher than acetic acid modified limestone.CeO2 achieves higher sintering resistance and functions as the support material,thus the heat storage performance is improved.After several CO2 capture cycles and heat storage cycles,pore structure of Ce modified limestone is improved,and surface area and pore volume increases,especially in the range of 10-100 nm in diameter,which is an important range for heat storage of CaO.As a result,Ce modified limestone is a good CO2 capture and heat storage material. |
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