Effects Of Heating System And Reducing Atmosphere On Reduction Swelling Of Fluxed Pellets

Low consumption,high efficiency,emission reduction and low carbon can be realized by increasing the proportion of pellet,especially flux pellet.However,the reduction expansion of pellets has restricted the development of blast furnace charge structure.At present,most experimental studies on pellet expansion are carried out by isothermal standard test and isothermal constant CO atmosphere.The reaction path,thermodynamics and kinetics of pellets are different from the reaction conditions of blast furnace.Therefore,it is of great significance to simulate the expansion behavior of fluxing pellets under continuous temperature reduction conditions in traditional blast furnaces and future low hydrocarbon reduction blast furnaces and hydrocarbon free vertical furnaces.In this paper,pellets with different basicity（0.27-1.33）were prepared by pelletizing and roasting with magnetite concentrate,bentonite and hydrated lime as raw materials.Reduction expansion experiments were conducted on pellets with different basicity by changing the heating system and reducing atmosphere,and the changes of phase composition,reduction rate,reduction rate,reduction expansion rate and microstructure of pellets with different basicity were analyzed under different reaction conditions,and the following conclusions were drawn:（1）The reduction rate,reduction rate and reduction expansion rate of pellets increase first and then decrease with the increase of basicity.The binary basicity of flux pellets should be around 1.3,and the pellets with a basicity of 0.6-0.8 have the highest reduction expansion rate.As the increase of basicity leads to the increase of porosity and the increase of pellet reduction rate,the formation of iron whisker is the main reason for the increase of pellet reduction expansion rate.（2）Compared with constant temperature 900℃,the reduction rate of pellets with basicity 0.27-1.0 was increased by the two heating regimes（700-1100℃and 700-900-1100℃）.The reduction expansion rate of pellets with basicity of 0.83-1.0 was decreased.Under the condition of isothermal reduction,the reduction rate and reduction expansion rate of pellets with basicity R=0.83 and 1.0 increase with the increase of temperature.In the reduction of the two heating regimes,the pellet is softened by the continuous heating up to 1100℃,which reduces the porosity and leads to the reduction expansion rate of the pellet.（3）The addition of H₂ can effectively improve the reduction reaction rate and reduction rate of flux pellet,but has little effect on the reduction expansion rate.With the increase of H₂ ratio,the intensity of Fe phase peak increases and the number of iron whisker decreases gradually.The reduction expansion rate of pellets with different alkalinity is greatly affected by the reducing atmosphere,while that of pellets with the same alkalinity is less affected.