Basic Research On Efficient Utilization Of Scrap In Converter Steelmaking

With the increase of scrap generation year by year in recent years,as well as the national requirements for carbon peaking and carbon neutrality in the steel industry,the more efficient use of scrap has become an important development direction for converter steelmaking.Scrap is one of the main raw materials for converter,and due to its cold material properties,the melting process of scrap has a very important impact on the stable control of the melt pool temperature and the smooth production of the converter.However,there is still a lack of research on scrap melting in the converter,and there are relatively few quantitative studies on the effects of scrap ratio on the converter process,cost and pollutant emissions,which limit the efficient use of scrap in the converter.Therefore,in this paper,the melting principle of scrap was analyzed,based on which a single scrap melting model was established.And the model that can simulate the scrap melting in the converter blowing process was obtained by combining the converter melt pool temperature and composition model.The calculation model of converter material consumption was established according to the mechanism model,and the model parameters were classified and regressed using the actual production data,which effectively improved the prediction accuracy of the model.Based on the carbon balance principle,the carbon emission model was established by reasonably dividing the calculation boundary of blast furnace and converter processes.The influence of the change of scrap ratio on the converter material consumption,converter cost and pollutant emission were systematically studied by using the above model.The scrap melting process was investigated by thermal simulation experiments,and the control links of scrap melting under different melting bath conditions were determined.And a scrap melting model was established based on the scrap melting mechanism.The speed and control links of scrap melting under the conditions of molten pool in the early,middle,and later stages of converter blowing were determined.The influence of carbon content and temperature in the molten pool on scrap melting was determined.The mechanism of the influence of scrap size and temperature on the melting process of scrap was analyzed.In the early and middle stages of converter smelting,increasing the melt pool carbon content and temperature can promote scrap melting,and in the late stages of converter smelting,increasing the melt pool temperature is more important to promote scrap melting.Reducing the scrap size and increasing the scrap temperature can effectively reduce the scrap melting time.Based on the three-stage decarburization theory,a continuous prediction model for the carbon content was established.The prediction model of phosphorus content and manganese content of converter was established by using multiple linear regression method.A temperature prediction model was established based on the converter heat balance combined with the regression statistics.Based on the composition and temperature models,a converter scrap melting model was established based on the principle of scrap melting using the finite difference method to simulate the scrap melting process in the converter blowing process and to analyze the influencing factors of the maximum size of the scrap.Increasing the hot metal temperature and reducing the scrap ratio can increase the maximum size of scrap allowed into the furnace.Taking the 130 t converter of a certain steel plant as an example,the maximum scrap size can be increased by about 0.1 m by increasing the hot metal temperature by 25℃.Decreasing the scrap ratio by 2.5%increases the maximum size of scrap by about 0.13 m.The influence of scrap ratio on slag basicity,flux consumption,and oxygen consumption was analyzed.A static model was established based on the mechanism and classification regression method to calculate the consumption of lime and oxygen,clarifying the impact of scrap ratio on lime and oxygen consumption.Based on the heat balance of converter,a model was established to calculate the scrap addition,and the factors affecting the scrap ratio of converter were investigated.When the phosphorus content of scrap and molten steel is the same,a 5%increase in 130 t converter scrap ratio can reduce the basicity by 0.31,the lime consumption by 241 kg and the oxygen consumption by 189.63 Nm3.Increase the temperature of the hot metal,the carbon and silicon content of the hot metal,and reduce the temperature of the molten steel can improve the scrap ratio,of which the silicon content of the hot metal has the greatest impact.In actual production,the scrap ratio can be determined according to the silicon content of the hot metal and the temperature of the hot metal.The composition of converter cost was analyzed,and a converter cost calculation model was established to clarify the influence law of raw material conditions,steel conditions,scrap composition and scrap ratio on the converter ton steel cost.Taking the 130 t converter as an example,a 0.1%increase in carbon content of scrap increases the cost of converter ton of steel by about 3.095 yuan.Scrap silicon content increased by 0.1%,the converter ton steel cost increased by about 1.2 yuan.An increase of 0.01%in phosphorus content of scrap increases the cost of converter tonne by about 0.32 yuan.There is a scrap price at which the impact of changes in scrap ratio on converter costs is minimal when there is excess heat in the converter.By constructing a process carbon emission model,the quantitative effect of scrap ratio on carbon emission of blast furnace-converter process was obtained.Increasing the scrap ratio can reduce the carbon emission of the converter process.When there is residual heat in the converter,a 5%increase in the scrap ratio can reduce the carbon emission per ton of steel in the converter process by about 7.1%,the carbon emission per ton of steel in the blast furnace process can be reduced by about 5.97%,and the carbon emission per ton of steel in the blast furnace and converter processes can be reduced by about 6.11%.When the converter heat is insufficient,the scrap ratio increases by 5%,and the carbon emissions per ton of steel in the blast furnace and converter process can be reduced by about 4.67%.