| Reasonable distribution of blast furnace gas flow plays an important role in long campaign,high efficiency,low consumption and high quality of blast furnace.The gas flow of blast furnace reaches the stock surface through tuyere,cohesive zone and lumpy zone.The charging equipment and system of furnace top have an important influence on burden distribution of stock surface,burden distribution of lumpy zone and cohesive zone.At present,bell-less top system of blast furnace is mainly divided into parallel hopper type and serial hopper type.Because of the high feeding ability of the bell-less top system,it is adopted by most of the large blast furnaces in China,such as Baosteel 1#4966 m3 blast furnace,Meisteel 5#4070 m3 blast furnace,Shougang Jingtang 1#,2#and 3#5500 m3 blast furnace.It is found that the charging process of bell-less top blast furnace with parallel hopper will produce falling point segregation,flux segregation,size segregation and basicity segregation,which will affect the of gas flow distribution in the lumpy zone,thus affecting the preheating and reduction of the burden in lumpy zone,further affecting the cohesive zone,and finally affecting the long campaign and stability of the blast furnace.The above segregation is affected by the structure of bell-less top equipment and charging system.The throat diameter of large blast furnace is larger.Once the structure of bell-less top equipment and the charging system are unreasonable,it will lead to more serious falling point segregation,flux segregation,size segregation and basicity segregation.Therefore,it is very important to optimize the equipment structure and charging system of the bell-less top blast furnace.In this paper,a three-dimensional geometric model of 5500 m3 blast furnace bell-less top system with parallel hopper is established,which includes ore and coke bunker,main feeding belt,switching chute,left and right hopper,Y-shaped tube,central throat tube,rotating chute and throat.The influence of bell-less top equipment structure and charging system on the falling point segregation,flux segregation,size segregation and basicity segregation in the charging process of blast furnace is studied by the Discrete Element Method simulation and 1:1 model experiment.The main research contents and results are as follows:The results of 1:1 model experiment are consistent with Discrete Element Method simulation,which verifies the accuracy and reliability of Discrete Element Method simulation results.The effects of the hopper outlet position(the hopper outlet is on the left,the hopper outlet is on the middle and the hopper outlet is on the right),the hopper outlet tilting angle(50°,60 0 and 70°),and the switching chute tilting angle(35°,45 0 and 55°)on the falling point segregation,flux segregation and size segregation are analyzed by the Discrete Element Method simulation.The results show that the hopper outlet position,the hopper outlet tilting angle and the switching chute tilting angle have little effect on the falling point segregation and flux segregation.When the hopper outlet is on the middle,the hopper outlet tilting angle is 70 0 and the switching chute tilting angle is 55°,the burden size in the center of the stock surface is larger,and the burden size distribution in the radial direction of stock surface is more conducive to the development of the central gas flow.The influences of the central throat diameter(600 mm,650 mm and 730 mm)and the rotating chute structure(smooth circular rotating chute,rough circular rotating chute,smooth rectangular rotating chute and rough rectangular rotating chute)on the falling point segregation,flux segregation and size segregation are analyzed by the Discrete Element Method simulation.The results show that the central throat diameter and the rotating chute structure have little effect on the size segregation.Reducing the central throat diameter and using the rectangular rotating chute can effectively reduce the falling point segregation and flux segregation.The influence of the feeding time sequence of different type iron ore(lump ore is located in the feeding time sequence head,lump ore is located in the feeding time sequence middle,lump ore is located in the feeding time sequence end and lump ore occupies the whole feeding time sequence)on the flux segregation,size segregation and basicity segregation is analyzed by Discrete Element Method simulation.The results show that different feeding time sequence has little effect on flux segregation and size segregation.When the lump ore is located in the feeding time sequence head,the comprehensive burden basicity distribution in the radial direction of the stock surface is most evenly.The effect of the proportion of pellets(30%,40%,50%and 60%)on the falling point segregation,flux segregation,size segregation and basicity segregation is analyzed by Discrete Element Method simulation.The results show that the proportion of pellets has little effect on the falling point segregation and flux segregation.With the increase of pellet proportion,the burden average size increases,the comprehensive burden basicity distribution in the radial direction of stock surface becomes uneven,the porosity of burden layer increases,and the permeability of burden layer becomes better.In order to study the factors that affect the distribution of blast furnace gas flow further and realize the control of gas flow.In this paper,a three-dimensional geometric model of 5500 m3 blast furnace body is established.The effects of cohesive zone tilting angle(30°,45° and 60°),cohesive zone root height(9.6 m,12.6 m and 15.6 m)and ore layer thickness(1 m,1.2 m and 1.4 m)on gas-solid two-phase flow and distribution in the furnace are analyzed by the Discrete Element Method and Computational Fluid Dynamics coupling simulation.The results show that:(1)The increase of the cohesive zone tilting angle and its root height and the decrease of the ore layer thickness can reduce the pressure drop of blast furnace.(2)With the increase of the cohesive zone tilting angle and its root height,the gas flow velocity in the top area(blast furnace center)of the cohesive zone also increases.(3)The increase of the cohesive zone tilting angle and its root height will result in the decrease of deadman size in the furnace.(4)With the increase of the cohesive zone tilting angle and its root height,the stress on the coke particles in the deadman decreases,and the particles on the surface of the deadman are easy to enter the raceway and be consumed.In a word,by optimizing the bell-less top equipment structure and charging system of the blast furnace with parallel hopper,realizing the reasonable size segregation in the burden layer,and avoiding the falling point segregation,flux segregation and bascity segregation,combining with the metallurgical properties of raw materials and other blast furnace operating systems,maintaing the proper cohesive zone tilting angle and its root height and the burden layer thickness,which is benefit to realizing the long campaign,high efficiency and green production of blast furnace. |
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