Research On High-Efficiency Dephosphorization Process Of Converter Based On Flue Gas Analysis And Multiphase Slag Theory

Dephosphorization is one of the most important tasks in steelmaking.In order to achieve high-efficiency dephosphorization effect,it is necessary to do "three highs and one low" in thermodynamics during the steelmaking process,and at the same time supplement it with good kinetic conditions.However,in recent years,with the increasingly stringent requirements for environmental protection and low carbon emission,converters have gradually adopted fluorine-free steelmaking to meet the environmental protection requirements of fluorine-free emissions,resulting in poor slag melting effect,at the same time,it is necessary to use less slag steelmaking to meet the environmental requirements of reducing slag discharge,and the temperature of molten iron has to be increased to meet the requirements of low carbon emission and negative energy consumption steelmaking requirements,which have brought huge pressure to converter dephosphorization.In addition,domestic converters generally adopt a long converter serving life and weak bottom blowing intensity process,and at the same time adopt a slag splashing process to protect the refractory lining,which leads to the "regular" rise of the bottom of the furnace,which eventually causes the bottom blowing tuyeres to be blocked,and ultimately affects the bottom blowing effect,leading to poor kinetic conditions for dephosphorization.At the same time,breakthroughs have been made in some new steelmaking technologies,such as converter flue gas analysis technology,which can monitor chemical reactions in the converter in real-time based on converter flue gas information,allowing for more accurate judgment of various stages of converter decarbonization reaction,making it possible to dynamically adjust the converter blowing process.In addition,with the in-depth study of multi-phase slag dephosphorization theory,researchers found that P₂O₅ generated by molten steel dephosphorization finally exists stably in the form of 2CaO·SiO₂-3CaO·P₂O₅ solid solution in slag.If the converter slag system is controlled to be dominated by 2CaO·SiO₂-3CaO·P₂O₅ solid solution slag system,the amount of converter slag can be greatly reduced.In order to fully utilize flue gas analysis technology and multiphase slag dephosphorization theory to study the dephosphorization reaction in the converter,and solve the problem that dephosphorization reaction dynamics conditions are difficult maintain due to the bottom blowing stirring effect is difficult to ensure for the long converter serving life,weak bottom blowing intensity and slag splashing technology,some experimental works were done.In this paper,the 210t converter of S plant is used to carry out technical research around the converter dephosphorization process and bottom blowing process.Theoretical analysis,industrial experiments,physical simulations,numerical simulations,and other means were used to conduct experimental research on efficient dephosphorization of converter based on flue gas analysis,industrial exploration of multiphase slag dephosphorization of converter,and research on the influence of bottom blowing design on the flow characteristics of high-temperature melt.The main work is summarized as follows:Based on the results of thermodynamic analysis and converter flue gas analysis,the concept of "window period" for dephosphorization in the early stage of converter blowing was proposed.Its start time is when the oxidation reaction of the[Si]element in the molten pool is nearly completed,and its end time is when the converter blowing reaction enters the second stage of decarburization,and is affected by the amount of scrap steel added in converter,the temperature of molten iron added in the converter,and the[Si]content of molten iron and other parameters.And it is found that prolonging the duration of the first stage of decarburization is beneficial to prolonging the "window period" of dephosphorization.Through process optimization,the average converter dephosphorization rate of conventional steel grade has increased from 86.4%to 90.2%,and the average dephosphorization rate of low phosphorus steel grades has increased from 90.3%to 96.5%.In order to achieve the effect of less slag steelmaking,based on the multiphase slag dephosphorization theory,the Rp index based on the product of the ratio of 2CaO·SiO₂-3CaO·P₂O₅ solid solution area to the total slag area and the P₂O₅ content in the solid solution was defined.It was found that increasing Rp requires controlling the CaO content in the CaO-FeO-SiO₂ ternary system to around 60%,and the FeO content should be controlled to 20%～30%,while ensuring CaO saturation.The restrictive steps of dephosphorization were studied by using the multiphase slag dephosphorization theory,and key control points such as increasing the bottom blowing intensity and increasing the FeO content of slag in the early stage of converter blowing were proposed.In order to improve the kinetic conditions of converter dephosphorization reaction,a water simulation experiment platform suitable for 210t converter was built in this paper,and a three-dimensional full-scale two-phase flow mathematical model was established for it.Water model and numerical model research were carried out,and found that the stirring ability of the bottom blowing stream to the melt pool corresponding to the bottom blowing stream when the bottom blowing tuyeres were installed at an angle of 10° was better than that of the bottom blowing stream when the bottom blowing tuyeres were installed vertically.The uniform time shows an increasing trend with the increase of the thickness of the slag splashing layer.Based on actual production,a precise control technology for the thickness of the slag splashing layer has been developed to achieve stable bottom blowing effect under the conditions of slag splashing and low bottom blowing intensity,even when the converter life is around 6500 heats.Based on the theory of flue gas analysis and multiphase slag dephosphorization,this article studies the theory and process of efficient dephosphorization in the converter,clarifies the mechanism of improving the dephosphorization effect in the converter,and proposes relevant process improvement measures,which has guiding significance for guiding the production practice of efficient dephosphorization in the converter.