Technical And Theoretical Study On Controlling SO₃ Concentration In Copper Smelting Flue Gas

A large amount of SOx will be produced in the copper pyrometallurgical process with sulfide ore as raw material.These Sox are mainly SO₂ and contain a small amount of SO₃.When SO₃ concentration in flue gas exceeds a certain level,it will affect normal production.The existence of SO₃ will cause corrosion of waste heat boiler and dust collection equipment,affect waste heat recovery and dust collection efficiency,affect mercury removal and increase the amount of waste acid.Nowadays,most of the technologies for controlling SO₃ in flue gas are concentrated in coal-fired power plants.The basic compounds containing calcium and magnesium are used to control SO₃ in coal-fired power plants,and these technologies have achieved good results in coal-fired power plants.One of the characteristics of copper smelting flue gas is the high concentration of SO₂.Moreover,the properties of SO₂ and SO₃ are similar.If the method of controlling SO₃ in coal-fired power plant is adopted,a large amount of SO₂ loss and consumption of alkaline compounds will be caused,and the loss of SO₂ will greatly reduce the benefit of the plant in the acid production process.At present,the method used to control SO₃ concentration in flue gas can not remove SO₃ in flue gas while retaining SO₂,and there are technical problems such as high energy consumption,high investment cost,secondary pollution,and difficult to deal with desulfurization products in varying degrees.Therefore,it is imperative to carry out the research on controlling SO₃ in copper smelting flue gas.In this paper,the effects of temperature and gas phase components on the formation of SO₃ were first analyzed by FactSage thermodynamic calculations.It is found that the lower the temperature is,the more favorable it is for the formation of SO₃.The content of O₂ in the gas phase is the key factor controlling SO₃.Therefore,this paper proposes a technical route to control the content of SO₃ in the flue gas by injecting sphalerite and galena into the flue during the flue gas treatment process.According to thermodynamic calculations,it is found that the related reactions between ZnS and PbS and O₂ take precedence over the oxidation reaction of SO₂,and the inhibitory effect of ZnS is stronger than that of PbS at high temperature.In this paper,a gas-solid reaction experimental platform was built by the laboratory.Firstly,the soot catalytic oxidation experiment was carried out.It was found that SO₃ generated only by gas phase is very limited,and most of SO₃ generated by smelting soot catalytic.The temperature range of sulfur trioxide in flue gas can be divided into three temperature ranges:high temperature zone（above 800℃）,medium temperature zone（600～800℃）,low temperature zone（below 600℃）.Among them,sulfur trioxides are relatively less in the low temperature zone and high temperature zone,and the middle temperature zone is the main temperature range of sulfur trioxides.Since the temperature of flue gas treatment in smelting process is from high to low,it is concluded that ZnS and PbS should be added before HRSG.Secondly,the experiments of PbS and ZnS were carried out in the simulated flue gas environment.It was found that PbS and ZnS had a good inhibition effect on the formation of sulfur trioxides under different oxygen content and sulfur dioxide atmosphere.After adding PbS and ZnS,The content of SO₃ did not exceed 0.6%,and the inhibitory effect of ZnS on SO₃ was stronger than that of PbS under the same conditions.In addition,the oxidation kinetics of ZnS and PbS was analyzed,and the oxidation kinetic parameters of ZnS and PbS were obtained.It was found that the reaction mechanism of ZnS oxidation was three-dimensional diffusion,and the reaction mechanism of PbS oxidation was first-order reaction.Finally,the flow field of HRSG is simulated by ANSYS discovery live.The best injection position of ZnS and PbS is on the wall of the lower half of HRSG inlet.