Study On Controlling Pollutants In Flue Gas Cycle Sintering Based On Biomass Fuel

The iron and steel industry is one of the key industries supporting the development of the national economy,in addition to being a resource-and energy-intensive industry that produces high levels of pollution.The high levels of energy consumption,resource consumption,and environmental load have become the bottleneck restraining factors related to upgrading and sustainable development in the industry.Reducing the emissions of sintering flue gas pollutants is the top priority related to air pollution control in the iron and steel industry.In the face of increasingly stringent environmental protection policies,it is difficult to meet the emission requirements for flue gas pollutants with a single flue gas pollutant terminal treatment.In this paper,the results of research on both source control of pollutants from biomass fuel and process control via circulating sintering flue gas are presented,in accordance with the concept of synergistic treatment of the whole sintering process.In addition,potential options forusing existing terminal treatment technology for sintering flue gas pollutants to realize the synergistic treatment of pollutants are presented.(1)Study on replacing coke with biomass fuel for sintering:Comparing industrial analysis,calorific value and pore structure of three biomass fuels(sawdust,peanut hulls,and corn stalks)with bituminous coal and coke powder.Biomass fuels are typically characterized by low fixed carbon contents,low calorific values,loose and porous interiors,large specific surface areas,and good fuel reaction performances.In view of such fuels having low calorific values and reaction rates that were too fast,briquetting and carbonization experiments of biomass fuel were carried out to increase fixed carbon content and calorific value.A sinter performance evaluation system was constructed using Fluent,and it was estimated that the optimum addition amount of biomass fuel during the sintering process was 30%.The major factors restricting the application of biomass fuel sintering were fast reaction rates and low layer temperatures.The modification experiment of biomass fuel was carried out to reduce the reactivity of biomass fuel.As a result of the fuel modifications,the fuel reaction rate was significantly reduced,the reaction temperature increased to 422?,and the reaction temperature further increased to 462? with package granulation.In view of the low temperature of the material layer,the experiment on rational blending of sintered raw material,the FactSage thermodynamic simulation,melting performance experiment,and DSC experiment were carried out by adjusting the sintering mixture basicity,MgO content,and Al2O3 content.It was determined that suitable conditions were:a basicity of 2.0;a MgO content of 1.0%;and an Al2O3 content of 2.7%.Based on these sintering raw material conditions,the sintering cup experiment was carried out with modified sawdust carbon.It was found that it would be possible to replace 40%of the coke powder with biomass fuel while still maintaining sintering index and performance(2)Study on the formation mechanism and emission law of flue gas pollutants in different sintering layers:The sintering layers were simulated under conventional sintering conditions and flue gas circulation conditions using three high temperature tube furnaces.Comparing sawdust carbon and coke as sintering fuels,the formation mechanisms and emission laws of SO2 and NOx in different sintering layers were studied.The S and N in the sinter ore layer had reacted completely at high temperature,so there was no effect on the formation of SO2 and NOx.However,under the action of CO and calcium ferrate in flue gas circulating sintering,part of the NO.in the flue gas could be reduced to N2.At the same time,the solvent remained in the part of the SO2 adsorbed to the sinter ore layer,which reduced the emission of pollutants.In the sintering combustion layer,the fuel began burning intensely,the temperature of the sintering layer increased,the raw material containing S and N began to decompose and oxidize,and large amounts of SO2 and NOx were generated.This caused the concentration of SO2 and NOx in the flue gas to increase significantly.In the preheated drying layer,the material containing S and N combined with oxygen to generate part of the SO2 and NOx with increasing temperature.However,the fluxes would absorb part of the SO2 in the preheated drying layer,and SO42-would exist in the preheated drying layer,but there was no adsorption on NOx in the flue gas.In the overdamp layer,there was basically no SO2 and NOx formation Due to the higher concentrations of pollutants in the circulating flue gas,fluxes in this layer adsorbed more SO2 in the flue gas,thus reducing SO2 emissions.However,there was no effect on NOx emissions.Due to the high concentration of pollutants in the circulating sintering flue gas,the emissions of flue gas pollutants were higher,but pollutants were adsorbed and reduced with the increasing material layers.When sawdust carbon was used as sintering fuel,the content of S and N was low,so the SO2 and NOx of flue gas pollutants produced by sawdust carbon were lower than that of coke.Thus,the use of sawdust carbon could provide source control of sintering flue gas pollutants.(3)Study on the control of pollutants from flue gas circulating sintering based on biomass fuel:Based on optimized ore matching conditions,modified charcoal was used instead of coke to carry out the flue gas circulating sintering experiment.The effects of oxygen content,temperature,SO2 content,and NOx content on the sinter ore properties and the emission law of pollutants from the sintering flue gas were studied.At the saiiie time,a suitable substitution amount of modified charcoal under the circulating flue gas conditions was studied.When a part of coke was replaced with modified charcoal for circulating flue gas sinterings the suitable flue gas content was 14.9%,the SO2 concentration was less than 500 ppm,the effect of NOx on the sintering performance index was small,and the higher the NOx concentration in the flue gas was,and the greater the reduction in emissions of NOx in the flue gas was.Under flue gas condition/'of 200? and 0.85%CO,the charcoal content,instead of coke,was increased from 40%to 50%on the premise of ensuring sinter ore performance,and the emission reductions of SO2 and NOx in the sintering flue gas pollutants were 42.6%and 65.8%,respectively,which reduced the required amount of flue gas terminal treatment.The goal of comprehensive utilization of waste heat for sintering flue gas and control of sintering flue gas pollutants was achieved.