Research On Particle Descending Velocity Distribution And Reducing Gas Flow Field In Gas-based Direct Reduction Shaft Furnace

Gas-based direct reduction shaft furnace is considered as an effective way to reduce the energy consumption and the dependency on coal,and cut down the pollution emission and carbon dioxide emission in ironmaking.The essence of the gas-based direct reduction shaft furnace is a gas-solid counter-current heat exchange equipment.Therefore,the reducing gas distribution and the particle descending velocity distribution have a great influence on the shaft furnace,which directly affect the production index and further the shaft furnace normal smelting.The reducing gas distribution and the particle descending velocity distribution are directly dominated by the furnace profile,the charging operation,the chemical reaction of the pellets,etc.To solve the above problems,some research works have been done as follows:In order to obtain the effect of the furnace profile and the gas flow on the particle descending velocity distribution,a three dimensional model(3D)is established based on the discrete element method(DEM)and computation fluid dynamic(CFD).The effect of the gas flow in the shaft furnace,the height,the diameter,the bosh angle and the stack angle of the shaft furnace on the particle descending velocity distribution during discharging process is investigated by the model and analyzed based on the granular dynamic theory and Janssen theory.It is helpful to provide theoretical support for the shaft furnace design.In order to investigate the effect of charging operation on the burden distribution and the porosity distribution inside the shaft furnace,the 3D models of the flap distributor and the gimbal distributor are established based on DEM.The influence rules of the different influencing factors in the distributors on the burden distribution and the porosity distribution inside the shaft furnace are investigated by the models.It is found that the porosity distribution can not be obtained directly by the burden distribution,and only investigating the burden distribution has certain limitations.The certain relationship between the burden distribution and the porosity distribution is obtained through comprehensive comparative analysis.It provides a reference for subsequent researches.To investigate the coupling problem of fluid and solid,the flow field in the shaftfurnace is calculated based on CFD.The pellets in the shaft furnace are simplified as porous media in this simulation.The law of change of the reduction ratio and the reduction swelling ratio of the pellets with time under the simulated shaft furnace atmospherethe are obtained through experiment.The porosity distribution is calculated through the hypothesis,the experimental results and the research results of the above two aspects.The regression equations of the viscous drag coefficient distribution and the inertial resistance coefficient distribution are calculated and transferred into the calculation model.The flow field in the shaft furnace with the consideration of the charging operation,the particle descending velocity distribution and the chemical reaction of the pellets is obtained.According to the above research results,gas-based shaft furnace with two reduction sections is proposed.The gas consumptions for reduction reaction and the heat balance and the minimum gas flow rate in the bottom of the auxiliary reduction section are calculated.The flow field in the reduction section of the gas-based shaft furnace with two reduction sections under different conditions and compared with that in the traditional shaft furnace.The results indicate that the pressure at the gas inlet and the effective power of the blowers are effectively reduced in the shaft furnace with two reduction sections.In addition,the flow field in the shaft furnace with two reduction sections can be adjusted in a certain extent.