CaO/Ca?OH?₂ Heat Storage Performance Of Carbide Slag Experienced Calcium Looping Cycles For CO₂ Capture

The instability of solar radiation make solar heating can not be carried out continuously.CaO/Ca(OH)2 thermochemical heat storage can effectively avoid the time and geographical limitations of solar energy utilization.Carbide slag is a kind of calcium-based industrial waste mainly composed of Ca(OH)2,which can capture CO2 in coal-fired power plants.However,CO2 capture activity of carbide slag decreases with the number of carbonation/calcination cycles.The carbide slag with low activity is discharged eventually from CO2 capture system.To reuse the spent carbide slag,a novel process coupling CO2 capture and CaO/Ca(OH)2 heat storage based on carbide slag was proposed in this paper.The carbide slag experienced multiple CO2 capture cycles is used for CaO/Ca(OH)2 heat storage cycles to store heat form solar energy.The stored heat can be used to heat feed water in coal-fired boiler.It breaks through the traditional way that using steam turbine exhaust to heat feed water,which is expected to reduce coal consumption.In order to provide theoretical guidance and data support for the novel process,CaO/Ca(OH)2 heat storage performance of carbide slag experienced CO2 capture were studied.The direct heat storage performance of carbide slag in CaO/Ca(OH)2 system was studied.The dehydration and hydration performances of carbide slag were discussed.And the effects of types of carbide slag and the number of heat storage cycles on the direct heat storage performance were studied.The decay mechanism of the direct heat storage performance of carbide slag was revealed.It was found that after 10 heat storage cycles,the heat storage conversions of carbide slag with Cl and without Cl remain above 0.7,which indicates that the two types of carbide slag have good direct heat storage performance in CaO/Ca(OH)2 system.CaO grains in carbide slag are broken during the heat storage cycles,which decreases the pore in the range of 20-100 nm in diameter.It hinders the diffusion and absorption of water vapor in CaO.In addition,due to the air transportation,a small amount of Ca(OH)2 in carbide slag react with CO2 in the air to generate CaCO3,which blocks the hydration exothermic reaction of CaO.Therefore,the direct heat storage performance of carbide slag decrease with the number of heat storage cycles.The CaO/Ca(OH)2 heat storage performance of carbide slag experienced CO2 capture was studied.The effects of the number of CO2 capture cycles and CO2 capture conditions on the heat storage performance of carbide slag experienced CO2 capture were discussed.And the interaction mechanism between cyclic CO2 capture and cyclic heat storage of carbide slag was revealed.It was found that the heat storage performance of carbide slag experienced CO2 capture is slightly lower than the direct heat storage performance of carbide slag.However,CO2 re-capture during the heat storage process can contribute to the decomposition of undehydrated Ca(OH)2 and CaCO3 inert impurities into CaO at high temperature.And the pore structure of carbide slag becomes better.Therefore,CO2 capture during the heat storage process can improve the heat storage capacity of carbide slag by over 30%.In addition,the heat storage during the CO2 capture process can break the sintered CaO grains and increase the pore in the range of 2-100 nm in diameter,which is benefical for the absorption and diffusion of CO2 in CaO.Therefore,the heat storage during the CO2 capture process can improve the CO2 capture capacity of carbide slag by about 50%.It indicates that the cyclic CO2 capture and cyclic heat storage of carbide slag can promote each other,which shows that the novel process based on carbide slag can reach to good CO2 capture capacity and heat storage capacity at the same time.The method of glycerol combustion modification was proposed to improve the heat storage performance of carbide slag in this work.The effects of types of carbide slag on the direct heat storage performance of combustion-modified carbide slag were studied.The effects of the number of CO2 capture and CO2 capture during the heat storage process on the heat storage performance of combustion-modified carbide slag experienced CO2 capture were discussed.The results showed that after 30 direct heat storage cycles,the hydration and dehydration conversions of combustion-modified carbide slag is higher than carbide slag by 63%and 68%,respectively.CO2 capture during the heat storage process can maintain the heat storage conversions of combustion-modified carbide slag experienced CO2 capture cycles above 0.6.It indicates that the glycerol combustion modification can significantly improve the direct heat storage performance and the heat storage stability of carbide slag.The CaO/MgO-based composite material was prepared using carbide slag and dolomite.The effects of the mass ratio of CaO to MgO on the direct heat storage performances of the composite material was studied.And the effects of the number of CO2 capture cycles on the heat storage performances of the composite material experienced CO2 capture were discussed.It was found that the optimum mass ratio of CaO and MgO for the direct heat storage of the composite material is 90:10.After 30 heat storage cycles,the heat storage conversions of the composite material experienced CO2 capture are still higher than 0.45,indicating that the heat storage performance and heat storage stability of the composite material experienced CO2 capture are significantly higher than those of carbide slag and combustion-modified carbide slag.Therefore,the CaO/MgO-based composite material has the most application value in the novel process proposed in this work.