Simulation Study On Burden Movement In COREX Melter Gasifier

COREX process,which consists of a shaft furnace for prereduction and a melter gasifier for final reduction,is the earliest industrialized smelting reduction ironmaking process.Compared with the traditional blast furnace iron-making process,COREX process has advantages of using non-coking coal and low pollutants emission.Baosteel has firstly introduced the COREX-3000,which provides a new way of non-blast furnace ironmaking.As the amplification of industrial-scale,many problems have been arisen in actual production,such as small raceway,non-active furnace center,and slow renewal velocity of burden,low temperature,poor reduction and separation of slag-iron,unsmooth furnace operation and poor permeability of burden and so on.The burden movement determines the gas distribution in the melter gasifier and the reasonable gas distribution is a crucial factor to smooth furnace operation,improve productivity and reduce fuel consumption.Aiming at the existing problems of COREX melter gasifier,the fundamental cause of these problems is lack of understanding and grasp about the burden movement and its interaction mechanism.In order to solve these problems in melter gasifier,it is necessary to be clear with the burden movement and gas distribution in melter gasifier.This study has been done from four aspects,which are cold model study,thermal model study,discrete element method(DEM)and mathematical simulation of gas distribution in detail.Up to now,the study about burden movement of COREX melter gasifier remains blank.Base on the study of blast furnace burden movement and using the theory of geometric similarity,a cold model of burden movement in COREX 3000 melter gasifier has been established.To ensure the similarity of burden movement in model and prototype,the similarity criteria of burden movement are deduced by similarity theory,and the experimental program is determined.The polyethylene particles and compressed air are employed,which are served as the coke and oxygen,respectively.The method of joining tracer particles has been adopted to study the burden movement from the macroscopic level.The burden flow pattern,trajectories and resident time under different operation conditions are obtained through this cold model.The enlargement of melter gasifier hearth diameter leads to furnace center inactivity.To improve the furnace operation and refer to blast furnace that different charging patterns are adopted to adjust the burden structure,a method that adding some cokes is proposed to improve the gas distribution.A thermal model of gas distribution in melter gasifier has been established.The paraffin particles,corn particles and hot air are employed,which are served as the direct reduction iron,coke particles or lump coal and CO,respectively.Firstly,a pre-experiment is carried out,which provide references and basis for the assumption of cohesive zone in DEM.Then,the gas distribution under different coke charging patterns in melter gasifier has been studied,that the method of using thermal couple to measure the temperature distribution is employed.In addition,the results can provide references and basis for determining reasonable coke charging pattern and improving gas distribution.Based on the self-compiled C program,the discrete element model of melter gasifier has been established to study the burden movement of melter gasifier with or without cohesive zone conditions and different coke charging patterns.The burden movement is also investigated under different cohesive zone shapes.The microscopic information including velocity,normal force and voidage distribution has been obtained.In mathematical simulation about gas distribution under different coke charging patterns,a mathematical model is established based on the slot physical model.The gas distribution under different coke charging patterns has also been analyzed by using the information of voidage distribution obtained from DEM and porous media model.With the coke column added,the gas velocity overall increased by 0.4 m·s-1 and the gas velocity in coke charging position increased obviously,which is about 1.1-1.6 m·s-1.Compared with the mixed charging pattern,the mass flux distribution in radial direction increased by 1.08 kg·s-1·and 0.88 kg·s-1·m-2 under center coke charging pattern and intermediate coke charging pattern,respectively.The mass flux distribution in axial direction increased by 1.62 kg·s-1·m-2.The gas permeability of melter gasifier is improved when coke column is added.However,the coke charging amount should be well controlled to avoid the gas flow overdevelopment,which affects the gas utilization.