Study On Dissolution Behavior Of Lime Particles During Top-Bottom Combined Blowing Converter

In order to reduce the free calcium oxide content in steel slag and promote the resource cycle of steel slag,the lime dissolution behavior in the steelmaking process of top-bottom combined blowing converter was studied.Firstly,the dissolution behavior of lime in the slag was studied under laboratory conditions,comparing the difference in the dissolution ratio of CaO-Si O₂-FeO synthetic slag with different FeO content and different lime particle size and the limitation of lime dissolution process had identified.Based on the computational fluid dynamics theory,flow field,temperature distribution and particle tracks in the furnace was calculated by ANSYS Fluent software.With the help of DPM user-defined scalar equations,the dissolution and reaction behavior of lime particles in the converter was studied coupling the lime dissolution and reaction model.Through the statistical analysis of the discrete phase simulation results,the variation of the residual content of lime particles after dissololved in the slag was obtained.The main conclusions are as follows:（1）Small particle size lime maintained high dissolution ratio.The slag conponents had a greater impact on the lime dissolution ratio with various FeO content.When the lime with 10 mm diameter dissolved for 180 s,the solubility of lime samples in slag with FeO content of 40 wt.%was 69.9%,which was greater than that in slag with FeO content of 25and 31 wt.%.In addition,FeO could reduce the viscosity of the slag and improve the external diffusion mass transfer kinetics conditions of the lime dissolution process.（2）Lime dissolution was controlled by boundary layer dissolution in the slag with FeO content of 40 and 25 wt.%.However,diffusion through product layer was the rate controlling step in the slag with FeO content of 31 wt.%.With increasing the FeO content,the apparent rate constant increased from 1.09×10^-4to 1.29×10^-3.the diffusion coefficient through boundary layer D_Caoincreased from 1.84×10^-4m²/s to 2.76×10^-5m²/s,and the effective diffusion coefficient through product layer product D_ewas 1.78×10^-4m²/s when lime was dissolved in slag with FeO content of 31 wt.%.（3）The dissolution reaction ratio was unevenly distributed during the movement of particles,and the great majority of the particles were unchange after launching into the slag layer at the beginning due to not reach the dissolution temperature,while the diameter of lime particles near the center of the converter changed rapidly.The lime particles with smaller diameter remained the high dissolution reaction ratio,and the reaction utilization rate showed a trend of first increasing and then decreasing,reaching a maximum of 86%.（4）The slag with low CaO and high FeO content was conducive to improving the driving force of the dissolution behavior of lime particles and the phosphorus distribution ratio between slag and steel.Maintaining low lime addition achieved low CaO content in the slag and accelerate the lime dissolution ratio.After dissolved in the S3 slag,the remaining free calcium oxide content is the lowest,about 9%,and the free calcium oxide content dissolved in the other slags is S2,S1 and S4 arranged in increasing order.However,it is not conducive to the dephosphorization reaction under low CaO content conditions in the slag during actual steelmaking process.The influence of the dynamic variation of CaO content in the slag caused by the amount of lime addition on the dephosphorization reaction needs to be further studied.