Material Transfer And Return Process In The Gas-based Direct Reduction Shaft Furnace

As a new ironmaking equipment,gas-based direct reduction shaft furnace uses gases such as hydrogen,carbon monoxide and methane as reductant,and its product sponge iron is a good substitute for scrap steel,it can not only solve the problem of the shortage of scrap resources in our country,but also effectively reduce the emission of harmful gases,which is in line with the environment of energy saving and emission reduction.On the basis of previous studies,the charging operation on the burden distribution,the discharge of the screw feeder and the chemical reaction process in the reduction section of the shaft furnace are studied through the combination of thermodynamics analysis and numerical simulation.It provides valuable theoretical guidance and reference for the further application of gas-based direct reduction shaft furnace.Firstly,according to the discrete element method?DEM?,the pellets are simplified into spherical particles of different sizes,and the three-dimensional models of the screw discharging machine and the whole shaft furnace are established.The distribution law of burden descending velocity along the radial direction of shaft furnace is obtained by simulation in EDEM software.In order to obtain the descending velocity of the burden similar to the"piston flow",by reducing the diameter and pitch of the first few helical blades,it is found that reducing the pitch of the screw discharging can really play the role of uniform material falling speed.But the effect is much smaller than that of reducing the diameter of the helical blade.It is suggested that the minimum diameter of spiral blade in this model should not be less than 600m considering the existence of dead burden pile at the bottom of shaft furnace and the actual production.Then the discrete element method is also used to simulate the shrunk shaft furnace and chute feeder model and the spherical particles close to the size of the real pellets.The radial distribution of voids is studied when the chute angle is 10°?20°?30°and the thickness of burden layer is 0.12 m?0.14 m?0.16 m.Furthermore,the unit pressure drop in the material layer is calculated according to the voidage,and the distribution of air flow in the shaft furnace under different distribution operation is preliminarily understood.Finally,based on the study of the burden descending velocity and the porosity distribution,the UDF program of the porosity is compiled,and the sliding grid technique is used.The finite volume method is used to simulate the chemical reaction process of Fe by reducing Fe2O3 material by H₂ under the two-dimensional axisymmetric model of shaft furnace in Fluent software.The distribution law of Fe mass fraction in shaft furnace height and along radial direction was obtained under different discharging operation.It is found that in the early stage of reduction reaction,the effect of porosity on the radial Fe mass distribution of shaft furnace is relatively obvious,and in the late stage of reduction reaction,the influence of voidage on the mass distribution of radial Fe of shaft furnace is very weak,almost negligible.