Study On Performance And Mechanism Of High Efficiency Calcium Based Desulfurizer For Low Concentration SO₂ Removal

Sulfur dioxide（SO₂）is one of the major atmospheric pollutants that causes serious harm to human health and ecological environment.At present,wet desulfurization is the most effective desulfurization technology for high concentration SO₂ flue gas generated by burning fossil fuels such as coal and oil.For low concentration SO₂ flue gas,dry/semi-dry desulfurization technology is more suitable in terms of economy,etc.However,the efficiency of dry/semi-dry desulfurization is relatively low due to the performance of desulfurizer.Therefore,it is important to develop a high-efficiency and low-cost low-concentration SO₂ absorber.In this paper,we studied the effects of different additives on the performance of calciumbased desulfurizers from the perspective of modification of calcium-based desulfurizers,and prepared a new type of calcium-based composite desulfurizer by the coupled effect of multicomponent additives.The desulfurization reaction mechanism was explored through scanning electron microscopy,X-ray diffraction,and other methods.Furthermore,some relevant reaction models were established at the molecular scale by density functional theory（DFT）,and the reaction mechanism was revealed by combining microscopic simulation and macroscopic experiments.The main study contents and findings are as following:Firstly,the effects of transition metal oxides（MnO₂/Fe₂O₃/CeO₂）,fly ash,hygroscopic agents,surfactants,and other additives on the sulfur capacity and breakthrough time of calciumbased desulfurizers were investigated.The results showed that the sulfur capacity of the desulfurizer could be increased by 51.8%by adding only 0.125%of the MnO₂ precursor.The sulfur capacity of the desulfurizer could be further improved by 19.80%through the volcanic ash reaction between fly ash and Ca（OH）₂.Hygroscopic agents had an inhibitory effect on the performance of the calcium-based desulfurizer prepared in this paper.The specific surface area of the desulfurizer could be increased by 87.67%and the sulfur capacity could be further improved by 24.72%by controlling the growth of Ca（OH）₂ with surfactants.Finally,a new type of composite desulfurizer based on Ca（OH）₂/CaCO₃,modified by the coupled effect of MnO₂ and surfactants,was determined.Secondly,various analysis methods such as phase analysis,morphology analysis,infrared spectroscopy,and element valence were used to study the mechanism of the reaction system in this paper.It was found that there were various oxides of Mn in the newly synthesized calciumbased composite desulfurizer,among which MnO₂ played a major role in catalytic oxidation,and some Mn₂O₃ also played a role.Thirdly,the effects of reaction conditions（temperature,particle size,water vapor content,and SO₂ concentration）on the newly prepared calcium-based composite desulfurizer were investigated,laying a foundation for practical application.The results showed that the decrease in temperature and the increase in water vapor content would increase the relative humidity and absolute humidity inside the reactor,which was beneficial to the desulfurization reaction.Both particle size and SO₂ concentration had threshold values that need to be noted in practical applications.In addition,the application value of the prepared desulfurizer was validated through a comparative experiment under the same conditions with the commercially available calcium-based desulfurizer.Furthermore,the surface reaction and internal diffusion mechanisms of desulfurizer particles were investigated through gas-solid reaction kinetics.Relevant reaction models were established,and it was discovered that the most stable adsorption site for SO₂/SO₃ was the Otop site of CaO.The reaction pathway for the catalytic oxidation of SO₂ by MnO₂ and reaction of SO₂ on Ca-Mn surface were explored based on Ma-vK and E-R catalytic oxidation mechanism,and the reaction mechanism was revealed through a combination of molecularscale simulations and particle-scale experiments.The experimental data and theoretical support provided in this study are significant for the modification of dry/semi-dry calcium-based desulfurization technology.This research has important guiding significance for achieving efficient and cost-effective removal of lowconcentration SO₂.