Study On Reaction Kinetics Mechanism And Flow Field Of Ammonia Direct Reduction In Shaft Furnace

In response to China’s goal of"carbon compliance and carbon neutralization",carbon reduction in the iron and steel industry is urgent.At present,the research on carbon reduction in the steel-making industry in the world is based on the gas-based shaft furnace direct reduction technology,which uses the reduction gas:CO and H₂mixture.Because co will produce a large amount of CO₂in the reduction process,which is not in line with the current trend of steel-making and carbon reduction.Although the reduction product of H₂is a clean product,at present,the storage and transportation technology of H₂is not perfect,its gas density is small,it is difficult to store a large amount,resulting in high costs.Therefore,NH₃is selected as the main reduction gas in this thesis.Compared with the first two gases,NH₃has the advantage of easy liquefaction,strong H storage capacity and pollution-free products.This thesis will carry out a series of basic research on NH₃reduction of iron oxide,and use the research results to simulate the industrial gas shaft furnace,so as to provide reference for the actual industrial production.The kinetic parameters of Fe₂O₃reduction by NH₃were explored by using a shaft high temperature electric furnace.The kinetic parameters of each stage of Fe₂O₃reduction by NH₃at different NH₃concentrations（20%,40%,100%）were solved by fitting the data with the mechanism function.It is concluded that the mechanism function of the first stage（Fe₂O₃→Fe₃O₄）reduction process of Fe₂O₃by conforms to the chemical reaction model,which is controlled by the chemical reaction,and its reaction order is n=2/3.The mechanism function of the second stage（Fe₃O₄→FeO）reduction process conforms to the random nucleation and subsequent growth model,and its reaction order is n=3/4.The mechanism function of the third stage（FeO→Fe）reduction process conforms to the three-dimensional diffusion model,and its reaction order is n=1/2.The simulation of industrial gas-based shaft furnace is continued by using fluent fluid simulation software and the dynamic parameters obtained in this experiment.The reduction parameters of the cooling section and the reduction section at the flow rates of reducing gas（15m/s,30 m/s,45 m/s,60 m/s）and cooling gas（5 m/s,10 m/s,15 m/s,20 m/s,25 m/s）were investigated.The following conclusions were obtained:increasing the reduction gas flow rate can improve the conversion of pure Fe,and when the reduction gas flow rate is too large,the conversion of pure Fe will be reduced.Increasing the cooling gas flow rate can reduce the temperature of the solid phase at the outlet and slightly increase the reduction efficiency.In addition,this thesis also optimizes the furnace body and draws a conclusion.When the overall flow rate of the cooling gas is constant,the temperature of the solid phase at the outlet can be reduced by increasing the number of inlet ports.In order to explore the mechanism of Fe₂O₃reduction by NH₃at low temperature,this thesis carried out a basic study on the reduction of Fe₂O₃under different NH₃concentrations and different inert gases.The following conclusions are drawn:when Fe₂O₃is reduced by NH₃at low temperature,pure Fe₃O₄can be obtained at400℃;Pure fe₃n can be obtained when NH₃concentration exceeds 40%at 500℃;Pure Fe can be obtained at 600℃.At 500℃,Fe₃N will be generated when N₂is used as inert gas,and Fe₄N with low N content will be generated when AR is used as inert gas.At the same time,experiments were designed to explore the reaction path of NH₃reducing Fe₂O₃.It was concluded that at 400℃,the reduction path of NH₃reducing Fe₂O₃was Fe₂O₃→Fe₃O₄;at 500℃,the reaction path of NH₃and Fe₂O₃is Fe₂O₃→Fe₃O₄→Fe₃N;the reduction path of NH₃reducing Fe₂O₃is Fe₂O₃→Fe₃O₄→FeO→Fe at 600℃,...