Study On The Catalytic Mechanism Of Trace Additives For SO₂/NO_x Removal Process In Microwave Field

In process of iron and steel production,sulfur dioxide and nitrogen oxide emissions account for about 2/3 of whole process,which are the main pollutants of flue gas emissions.The development prospect of desulfurization and denitrification industry in 2021 was released by China's environmental desulfurization and denitrification commission.There is still a large gap between the amount of sulfur and nitrogen oxides discharged by the steel industry and the requirements of the Opinions on Promoting the Implementation of Ultra Low Emission in the Iron and Steel Industry.Therefore,it is the general trend of air pollution control in China to realize ultra-low emission and control of iron front process.Fly ash and carbide slag,as a common solid waste in industrial production process,face on many problems such as large volume,wide distribution and low utilization rate.The continuous production of fly ash and carbide slag will increase the operating cost of production enterprises and cause environmental pollution.The utilization of fly ash and carbide slag is still facing a serious situation.Therefore,fly ash and carbide slag was selected in this study to treat SO₂ and NO_x that produced in sintering production process,which is critical for the green development of Chinese iron and steel industry.In this study,the mixture of fly ash and carbide slag modified by microwave was used as the carrier(abbreviate as FC)during the preparation of catalysts with different active components.And the effects of different catalysts on the catalytic removal of SO₂ and NO_x were systematically studied.The results followed as:(1)The optimum preparation parameters and adsorption parameters of6%Fe₂O₃/FC catalyst was impregnation time 2 h,calcination temperature 550°C,microwave power 800 W,and reaction temperature 120°C.Under these conditions,the T_100%of simultaneous desulfurization and denitrification of the catalyst was 13min and 3 min,respectively.And the loading of active components changed the desulfurization and denitrification process from a single physical adsorption mode to a“chemical adsorption-based,supplemented by physical adsorption”mode.(2)6%Fe₂O₃/FC catalyst desulfurization and denitrification reaction mechanism and kinetic model fitting results showed that the loaded Fe₂O₃ can provide reactive oxygen species for simultaneous desulfurization and denitrification by changing the valence state of elements in the microwave field.In the desulfurization process,metal oxides are bound with the adsorbed SO₂ and SO₃,respectively,while in the denitrification process,metal oxides are bound with the adsorbed N₂O₅.The main products of these reactions were Ca SO₄,Ca SO₃ and Ca(NO₃)₂,and byproducts are Ca₅Si₂SO₁₂ and Ca CO₃.Under the optimal process parameters,the maximum adsorption capacities of SO₂ and NO were 0.0607 mmol/g and 0.0047 mmol/g respectively.The relationship between the fitting degree of the second-order kinetic model and the internal diffusion model is as follows:desulfurization(0.950<0.992)and denitrification(0.993<0.995).The fitting degree of the internal diffusion model is higher than that of the second-order kinetic model,and the internal diffusion link is the main speed-limiting link in the simultaneous desulfurization and denitrification process.(3)Under the condition of single alkaline active component,the presence of K₂O and Na₂O was able to promote the desulfurization and denitrification reaction.The desulfurization and denitrification performance of 6%K₂O/FC and 6%Na₂O/FC catalysts seemed to be ideal,the T_50%of desulfurization was 63 min and 73 min while the T_90%of denitrification was 7 min and 4 min.The desulfurization efficiency of the catalyst was better than its denitrification efficiency,and the loaded Na₂O and K₂O reduced the inhibition of SO₂ on denitrification.The main products of this reaction were Ca SO₃,Ca SO₄ and Ca(NO₃)₂,and the intermediate products were SNO₃,SNO₄,S₂N₃O₈ and S₂NO₉.In the case of composite active component,Fe-K catalyst and Fe-Na catalyst would inhibit the desulfurization process.