Experimental Study On Sequestration Of CO₂ By Direct Aqueous Carbonation Of Alkaline Solid Waste

A large amount of CO₂ emission into the atmosphere has caused a series of environmental problems such as the greenhouse effect due to the utilization of fossil fuels such as coal.The CO₂ mineral carbonation technology is a very promising CO₂ emission reduction technology with the advantage of wide range of raw materials,low energy requirements,and the ability to achieve complete fixation of CO₂,which has important theoretical significance and research value.In this paper,the carbonation reaction characteristics of several kinds of alkaline solid wastes from different sources were studied.The effects of various factors on carbonation efficiency and CO₂ absorption and conversion rate were investigated in detail,in order to provide support for the practical application of CO₂ mineral carbonation technology in the future.Firstly,fruit tree ash was selected as raw material,and carbonation experiment was carried out under normal pressure conditions.The effects of reaction time,temperature,liquid to solid ratio and gas components on carbonation reaction were studied,and the reaction kinetics analysis was carried out.The results show that with the increase of reaction time,the degree of carbonation is continuously strengthened;the increase of reaction temperature will increase the carbonation efficiency in the early stage of the reaction,but it will have little effect on the final carbonation efficiency;the increase of liquid to solid ratio can be significant to accelerate the carbonation reaction process;under three atmosphere conditions,the carbonation efficiency was the highest under pure CO₂ conditions,followed by the oxyfuel combustion flue gas conditions,and finally the simulated flue gas conditions.The results of reaction kinetics analysis indicated that the dissolution and diffusion of Ca²⁺is the main process to limit the aqueous carbonation rate of fruit tree ash.Subsequently,chili pole ash was used as raw material for carbonation study under pressure.The carbonation reaction process was analyzed theoretically,and the effects of reaction time,temperature,liquid to solid ratio,pressure and gas components on the carbonation efficiency were investigated.The results show that the carbonation product of MgO was affected by the reaction temperature.Under the condition of 20?,the product mainly exists in the form of MgCO₃·3H₂O,and when the temperature exceeds 80?,its carbonation product mainly exists in the form of MgCO₃.The increase of reaction temperature will significantly increase the carbonation efficiency,and the increase of pressure will increase the concentration of CO₂ in the liquid phase so as to accelerate the process of carbonation reaction.The increase of liquid to solid ratio is also beneficial to improve the carbonation efficiency.The carbonation efficiency under pure CO₂ conditions is significantly higher than that of oxyfuel combustion flue gas conditions and simulated flue gas conditions.Then,three typical semi-dry desulfurization fly ash from waste power plants were used as raw materials,and a 100mL carbonation reactor was selected to carry out continuous carbonation experiment under simulated flue gas conditions.The changes of CO₂concentration at the outlet as well as the changes of inlet and outlet flow rates were monitored online.The effects of reaction temperature,liquid to solid ratio and ventilation rate on CO₂ absorption and conversion rate were investigated.The results show that during the carbonation reaction,the CO₂ concentration change at the reactor outlet can be divided into four stages.The absorption and conversion rate of CO₂ increases first and then decreases with the increase of temperature,and reaches the maximum at 60?;The larger or smaller liquid to solid ratio will reduce the absorption and conversion rate of CO₂,reaching the maximum at 10:1;and the lower the ventilation rate,the higher the absorption and conversion rate of CO₂.Finally,a typical steel plant semi-dry desulfurization ash was used as raw material,and a 1000mL carbonation reactor was selected to carry out a longer time continuous CO₂fixation study under the condition of simulated flue gas.The results showed that the duration of the equilibrium stage increased significantly.The order of CO₂ absorption and conversion rate under different temperature is:60?>40??80?>20?;The CO₂ absorption and conversion rate was highest when the liquid to solid ratio was 5:1;The lower the ventilation rate and liquid to solid ratio,the higher the absorption and conversion rate of CO₂.At temperature of 60?,liquid to solid ratio of 10:1,and ventilation rate of 300 mL/min,the slurry can continuously fix CO₂ for more than 66.6%of CO₂ absorption and conversion rate for 140 min,proved that the desulfurization ash can stably fix CO₂ for a long time with high efficiency under aqueous conditions.