Physical And Numerical Simulation Study On Burden Distribution In COREX Melter Gasifier

COREX is the earliest industrialized smelting reduction ironmaking process.It is featured with shorter route,less operation and lower environmental pollution as a result of the removal of sintering and coking processes.COREX process mainly consists of two reactors:a reduction shaft(RS)and a melter gasifier(MG).There are two types of distributors in the MG:the Gimbal distributor to charge lamp coal and the DRI-flap distributor to charge DRI from RS.The distributor structure,raw materials properties and charging pattern are all significantly different from that in traditional blast furnace.At present,only a few studies are dedicated to the burden distribution in the MG,mainly due to the short history of the process and limited industrial facilities.As the mixed charging pattern directly affects the coal and DRI distributions in the MG and then determines the further gas flow distribution,and the gas flow distribution is a crucial factor to improve production efficiency and reduce fuel consumption,it is of great importance to investigate the burden distribution in the MG.In this work,taking the COREX-3000 MG charging system as the research object,physical experiment,numerical simulation and mathematical modelling were conducted to study the burden distribution under the independent and mixed charging conditions.The main contents are as follows.Based on the similarity theory,a physical model of 1:7.5 scaled COREX-3000 MG burden distribution system was constructed,and real coal,coke,pellet and sinter were used for the physical simulation experiments.At first,the independent and mixed charging processes of the two type distributors were investigated.The results show that,when the Gimbal distributor works independently,the burden stream width increases,the burden pile moves to the furnace wall and its thickness decreases with the increase of chute inclination angle.The voidage shows a U-shape distribution profile in the radial direction,meaning that it is smaller at the apex than that near the side of burden pile.When the DRI-flap distributor works independently,the burden stream width increases,the burden pile moves to the furnace wall and its thickness decreases with the decrease of flap inclination angle.Influenced by the flap shape,uneven distribution of pellet particles in the circumferential direction was observed with more pellets accumulated in the area between two flaps and less pellets in the area below the flap.When the Gimbal distributor and DRI-flap distributor work together,the burden surface profile is higher in the center and lower near the wall.The radial ore-to-coal(coke)ratio is significantly affected by charging pattern group and burden material,while the charging pattern in a same group and the stockline have less effect.Besides,particle size segregation was observed along the radial direction during both independent and mixed charging.Smaller particles tend to accumulate in the center areas while large ones segregate near the wall.DEM and DEM-CFD coupled approach were adopted to investigate the independent and mixed charging and gas-solid flow in the MG on the particle scale.The effects of chute inclination angle,rotational speed,flap inclinational angle and shape,particle shape,gas velocity at the tuyere and charging pattern on burden distribution were discussed in details.The results show that when Gimbal distributor works independently,an intrinsic asymmetrical pile was observed that the inner angle of repose is larger than the outer one.This is mainly due to the horizontal velocity of coal particles when they flow out of the chute.In addition,the effect of the rotational speed on the coal distribution is minor.To solve the problem of uneven distribution of pellets in the circumferential direction,the shape of the flap was optimized,and the arc shaped flap is capable to attain uniform distribution of pellets in the circumferential direction.Besides,when non-spherical particles were used to simulate the DRI reduced from lump ore,the particles are distributed more evenly in the circumferential direction and the bed pressure drop increased with increasing the fraction of non-spherical DRI particles.During the mixed charging in the MG,it is hard to form a layered structure of coal and DRI in the packed bed like that in a blast furnace.Although the upper bed structure has negligible effect on the raceway shape and size,the gas velocity distribution in the bed is affected by the burden distribution,which has less fluctuation in the region where the burden is evenly distributed.The particles above the raceway region descend faster than that near the center and the wall.The interparticle force in the region of low particle velocity is larger,indicating stronger and more stable interactions between particles.Furthermore,with increasing the gas velocity,a stable raceway is gradually formed in front of the tuyere and the raceway size increases accordingly.The raceway depth is larger than its height.Besides,the particles make a circumnutation flow in the raceway under the combined action of gravity and gas drag force.A COREX MG burden distribution mathematical model was established based on the physical experimental and numerical simulation results.When using the mathematical model to calculate the burden surface profile and the burden pile structure,it shows that the burden surface profile is higher in the center and lower near the wall.The burden surface profile and radial ore-to-coal ratio agree well with the experimental results.Hence,this mathematical model is capable to effectively predict the mixed charging process in the COREX MG,and provide reference data for adjusting the charging operation in practice.