Simulation Study On Bath Mixing And Mass Transfer Between Slag-steel In 200t Top And Bottom Combination Blown Converter

The top and bottom combination blown converter steelmaking method combines the advantages of the smelting advantages of the top-blown steelmaking method and the bottom-blowing steelmaking method.The smelting efficiency and the quality of molten steel are closely related to the mixing of the bath and the mass transfer of slag-steel in such converters.In order to obtain reasonable and efficient blowing process parameters,and to investigate the fluid flow behavior in the converter bath,in this study,a 200 t top and blown combination blown converter in a steel plant was used as the research prototype to study the effects of different process parameters on the mixing and the mass transfer between the slag-steel in the bath.The main contents and results obtained are as follows:(1)Based on the similarity principle,a physical converter model with a geometric similarity ratio of 1:12 was established in the laboratory.The effect of top tuyere height,scrap weight unmetled in the bath,number and arrangement of different bottom tuyeres,bottom gas flowrate,bottom non-uniform gas supply and top blowing flowrate on the mixing and mass transfer were studied,and the results show that:1)Under the conditions of this study,there are more options of bottom blowing schemes with 8?12 bottom tuyeres in the 200t top-blown converter than those with 4?6 tuyeres.Asymmetric bottom tuyere arrangements can achieve smaller bath mixing time compared to symmetrical bottom tuyere arrangements.When there is scrap unmelted in the converter bath,it has a hindrance to the mixing,and the fluid flow velocity is reduced.Increase in the bottom gas flowrate is beneficial to shorten the bath mixing time.2)The optimization of the combination blwon process for the 10-32 bottom tuyere arrangement shows that the minimum mixing time is 23.2 s with the bottom gas flowrate of 1.14 m3/h,the top gas flow of 107 m3/h and the top lance height of 200 mm.Under the conditions in the study,it is considered that 200 mm(prototype 2.4 m)top lance height in the top and bottom combination blowing can obtain a shorter bath mixing time.In the pure bottom blowing,the bath stirring effect is better,and the mixing time is lower with the bottom gas flow rate of 0.91 m3/h.3)Studies on non-uniform bottom gas supply show that the linear non-uniform bottom gas supply mode(M1 and M5),compared with the uniformbottom gas supply,can improve the stirring capacity of bottom gas and reduce the bath mixing time.The non-uniform bottom gas supply with reduction in 1/2?3/4 bottom blowing flowrate on one side of the trunnion has little effect on the mixing,and the dispersing bottom tuyere arrangement is better than the concentrated bottom tuyere arrangement in non-uniform bottom gas supply.4)The research on the influence of different bottom tuyere failures on the bath stirring with 8-30 bottom tuyere arrangement shows that in the case of bottom tuyere feilure,if the unblocked bottom tuyere arrangement is dispersed or symmetrical,the bloked bottom tuyere should be replaced or the gas flow should be increased to strengthen the stirring.(2)Influence of different number and arrangement of bottom tuyeres,bottom blowing flow rate and non-uniform bottom gas supply on the slag flow in the model and volumetric mass transfer coefficient between slag-steel was studied.The behavior of mass transfer between slag-steel under different experimental conditions is as follows:1)The restrictive step in mass transfer between slag and steel is diffusion.Intensifying stirring is helpful to promote mass transfer.And the slag emulsion formed under the action of top-blowing gas moves downward along the furnace wall.When the bottom gas flow rate is 0.57 m3/h,the slag-steel interface is stable,and the slag can be moved downward to 45 mm from the bottom of the furnace.2)Under the same experimental conditions,the volume mass transfer coefficients with arrangements of 4?6 bottom tuyeres are significantly lower than those with arrangements of 8?12 bottom tuyeres.When the bottom gas flow rate is 0.57?2.86 m3/h,the volume mass transfer coefficient increases with the increase in the bottom gas flow rate,and the mass transfer coefficient begins to decrease after the bottom gas flow rate is 3.42 m3/h.The mass transfer coefficient with bottom tuyere arrangement 10-25 at the bottom gas flow rate of 2.86 m3/h is the largest one,being 1.7×10-3 s-1.3)Under the experimental conditions in the study,the non-uniform gas supply at the bottom blowing has little effect on the volume mass transfer coefficient between the slag-steel.(3)A mathematical model of gas-liquid two-phase flow in the top and blown combination blown converter was established and numerically calculated with the finite element analysis software FLUENT.The effects of different number and arrangement of bottom tuyeres,bottom gas flowrate and non-uniform bottom gas supply on fluid flow in the bath and "dead zone" in the bath were studied.The experimental results are as follows:1)The mathematical simulation results of gas-liquid two-phase flow in the top and blown combination blown converter show that the fluid velocity at the bottom of the 8?12 bottom tuyeres is larger.In the arrangements of 4?6 bottom tuyeres the "dead zone" in the bath is larger,while the 8?12 bottom tuyere schemes have obvious center circulation at the 2/3 height of the bath.The more concentrated bottom tuyere configurations can obtain larger total bath velocity and total turbulent kinetic energy,and smaller "dead zone".2)The asymmetric arrangement of the bottling tuyeres forms an asymmetric flow in the bath,and the 4 vortex cores with different heights in the vertical direction can agitate a larger area,which can reduce the "dead zone" volume by 50%compared with the symmetric arrangement.3)When the bottom gas flow rate is 1.14m3/h,the "dead zone" volume of the non-uniform bottom gas supply schemes(M1 and M5-1)whose bottom gas flow rate linearly increase along the trunnion is below 4%,in the bottom of the fluid bath,a large circulation flow is formed,and the fluid flow zone in the horizontal direction increases,which is conducive to promoting the stirring and mixing in the bath.4)In top-blowing,the shape and depth of the impact cave formed by the interaction between the top lance jet and the bath liquid constantly chang.The formation of surface waves on the liquid surface exacerbates the instability of the bath.5)The increase in the number of tuyeres is conducive to reducing the erosion of the lining.When the number of tuyeres is small,the velocity at the bottom of the bath is significantly reduced.