Research On The Gas-solid Two Phase Flow In Oxygen Blast Furnace By Physical And Mathematical Simulation

As the problems of global wanning,environmental degradation and energy resources shortage become more and more serious,the governments around the world have made the increasingly strict environmental protection and emission reduction policy.Especially,the steel industry is facing enormous pressure because of its high energy consumption and high pollution.The energy conservation and emissions reduction in blast furnace ironmaking process is one of the important way to reduce energy consumption,CO2 and other pollutant emissions.The energy saving capacity of top gas recycling-oxygen blast furnace ironmaking technology(Abbreviated as OBF)has been verified by theoretical calculations and industrial tests.The shaft gas injection is one of the key characteristics of the OBF.In this thesis,the gas-solid two phase flow in the OBF is studied by the combination of experimental physical model and DEM-CFD coupling mathematical model.The factors influencing the shaft injected gas distribution characteristics in the furnace are also studied.At last,put forward the future development direction of blast furnace DEM-CFD coupling mathematical model.Firstly,a reduced-scale OBF two-dimensional(2D)cold physical model is built according to the similarity principle.The gas-solid flow behaviors under different operating conditions of blast furnace especially under OBF conditions are carried out.The results show that:The solid flow characteristics obtained from physical model in OBF are consistent with that in TBF which can also be divided into four zones;With the increasing of the batch weight,the shape of stagnant zone tends to be short and fat;The plug flow zone in the upper part of the shaft has no significant change under different conditions;With the increase of the shaft injected gas proportion the stagnant zone gradually become thin and high.Next,the pre-processing of 2D and 3D OBF DEM-CFD coupling mathematical model are finished.It mainly includes the abstract processing of actual furnace,data processing of geometric model,mesh generation,local special treatment of the model,determination of the control equation and so on.Then,the 2D DEM-CFD coupling model corresponding to the physical model is established.The physical model is simulated by it simply.The simulation results show that:Consistent with the experimental results,the solid flow characteristics can also be divided into four zones;The shaft injected gas(SIG)has little influence on the solid flow from the numeral results,and the simulation results can reflect the real situation more accurate;The compressive force acted on the particles in the fast moving zone is small,but in the deadman and shaft lumpy zone is big which will cause the particles in these two areas extrude with each other serious,pulverization and poor permeability.The characteristics of gas-solid two phase flow in OBF under different factors are studied by the 2D DEM-CFD coupling mathematical model further.The influence factors such as the particle diameter,shaft tuyere size and specific value of shaft injected gas flowrate to total gas flowrate on shaft injected gas permeation are evaluated.The results show that:As the particle movement reaches a steady state in the furnace,a gas channels is generated in the furnace center which is beneficial for the center gas development;In the shaft injection level the penetration distance of injected gas is short,but with the upward flow it gradually penetrates into the furnace center;The specific value has significant impact on the shaft injected gas distribution;The essential factor affecting the SIG penetration depth is pressure difference between upper and lower of the shaft tuyere level,if the pressure difference is small,the SIG can easily penetrate into the furnace center.Next,the 3D DEM-CFD coupling model is performed to analyze the gas-solid flow in an OBF.The important features such as melting zone and raceway are taken into consideration.The particle number is closer to the actual blast furnace by improving the coupling method.Three kinds of the shaft tuyere arrangement are calculated and compared.The optimal configuration is put forward.The results showed that:The 3D DEM-CFD model can eliminate the wall effects of 2D models.The burden above the melting zone is mostly in the plug flow zone;The solid volume fraction at the furnace edge is larger than that at the center in addition to the raceway and its nearby which is conducive to the center gas development;The solid phase volume fraction attains a maximum value above the melting zone,and the gas pressure in the furnace drops rapidly and the direction of the gas flow changes in this zone;When the horizontal velocity of the SIG reaches to a large value,as a result of the violent collisions between the upward gas and the SIG,it will force the SIG to flow downward which is not conducive to the full use of the injected gas;The optimal configuration of the shaft tuyere is that the number of shaft tuyeres and hearth tuyeres are equal and the shaft tuyere is located between the hearth tuyeres which produces a reasonable heat distribution throughout the OBF.By taking the 3D model modeling ideas into the 2D slot model the complex OBF 2D DEM-CFD coupling model is established.The burden size is reduced further.The results show that:The solid phase volume fraction is larger in complex 2D model than that in the 3D model.The permeability of the furnace becomes worse;In the upper part of the shaft the two charges have a stratification phenomenon which is consistent with 3D model,but this phenomenon disappears earlier in the middle and lower part of the shaft.Under the same SIG ratio it is more difficult for the SIG to penetrate into the furnace center in the complex 2D model than that in the simple 2D model.The edge is just the opposite.The simulation results from complex 2D model are more close to the actual state of the OBF than the other two models.The future development of the furnace DEM-CFD coupling model should be the following aspects:The model and control equation of gas-solid heat transfer,particle size change process,particle shrinkage in soft-melting zone and so on which are closer to the actual blast furnace should be gradually added in the future model;The liquid phase,gas-solid-liquid phase reaction and reaction process-particle parameters coupling model should be taken into consideration in the future advanced DEM-CFD model.The improvement of the furnace simulation model can not depart from the data support of the laboratory research and industrial test,also depends on the development of the calculation method and computer ability.