| Hot metal slag skimming is an essential technology to control the amount of slag entering the Basic Oxygen Furnace.It is also a key factor affecting the quality of molten steel and the cost of steelmaking.In order to improve the efficiency of traditional mechanical slag skimming technology,domestic and foreign scholars have developed a variety of hot metal ladle blowing assisted slag skimming process,and achieved excellent results in shortening slag skimming time in actual production.Among of them,the top lance blowing assisted slag skimming process has been widely used for its easy operation,safe and reliable.Although this process has achieved the goal of improving the effect of slag skimming in actual production,there still exists high slag-skimming iron loss,ladle wall wear,low blowing lance life and low slag skimming efficiency in application,which has seriously affected the stable production of high value-added low-sulfur steel in iron and steel enterprises.In view of the above problems,this paper has proved the slag-removing mechanism of the top lance blowing auxiliary slag skimming process through water model test and numerical simulation research.The influence of the process parameters of the top blowing lance and the structure of the nozzle on the slag-removing effect,the liquid surface slag entrapment and the wear of the ladle wall were systematically studied.Based on the above research,the optimal nozzle structure was designed.Based on the analysis of the damage mechanism of the top blowing lance,the performance requirements of the lance refractory were clarified.By introducing alumina bubbles into the mullite castable,the mechanical properties and thermal shock resistance of the lance castables are improved.Moreover,the mechanism of the effect of alumina bubble on the performance improvement of mullite castables was systematically studied.Based on the above research,an integrated technology of the top blowing lance was formed.Through industrial tests and applications,it has achieved excellent effects such as improved slag efficiency and lance life,and reduced slag iron loss and BOF sulphur re-enter,which guarantees large-scale stable and low-cost manufacturing of high value-added low-sulfur steel in iron and steel enterprises.The main conclusions obtained are as follows:1.The slag-removing mechanism of the top lance blowing auxiliary slag skimming process.The slag-removing mechanism of the top lance blowing auxiliary slag skimming process is the horizontal force directed to the slag mouth.Through the action of the horizontal driving force of the liquid level,the slag in the rear wall region of the ladle is gathered toward the slag mouth to achieve the purpose of assisting slag skimming.The horizontal driving force of the liquid surface comes from upward expansion of the blowing bubble and the restrain-steering effect of the ladle inclined wall on the floating bubble stream.2.The influence of the process parameters of the top-blowing lance on the comprehensive effect of driving the slag.As the flow rate of the blowing gas and the depth of lance insertion increase,the density of the stirring energy of the blowing gas increases continuously and the effect of driving the slag is continuously improved.However,when the flow rate of the blowing gas increases to a certain extent,there is a phenomenon of liquid level splashing and slag entrapment.As the insertion position of the lance is decreased,the restrain-steering effect of the back wall on the floating upper stream of the bubble is increased,which is favorable for driving the slag layer.The shearing force of the ladle is mainly distributed along the circumferential direction of the lance axis and the slag line.With the increase of the flow rate of the blowing gas and the lance insertion depth,the shearing force of the ladle continues to increase.As the insertion position of the lance increases,the maximum shearing force of the ladle wall is moved from the positive facing area of the lance to the circumferential side,and the maximum value is significantly reduced.3.The influence of the nozzle structure of the top blowing lance on the comprehensive effect of driving the slag and the design of the new nozzle structure.Increasing the number of nozzles of the lance can effectively reduce the height of the liquid level fluctuation and suppress the slag caused by the fluctuation.The nozzle arrangement has a large influence on the shape of the bare liquid surface,and the nozzle has a best included angle of 150°.The invention of two new structure lances,a circular four-nozzle and a slit-type nozzle,which change the flow field distribution of the molten pool,optimize the shape of the bare liquid surface,and suppress the wear of the refractory material of the ladle back wall and the liquid surface slag entrapment.Hence,the comprehensive effect of driving slag is significantly improved.4.Effects of alumina bubble addition on the properties of mullite castables for top blowing lance.Due to special spherical shape,the appropriate addition(4%)of alumina bubble is helpful to improve the flow values,BD,and thermal conductivity of castables.After heating,the inter locking network structure of mullite and anorthite grains has developed between the bubbles and the binding phases,which improve the mechanical strength of mullite castables.Due to the appropriate bonding at the alumina bubble/matrix interface,the appropriate amount of alumina bubbles is helpful to absorb the thermal shock crack propagation energy and improve castables' thermal shock resistance.5.Effects of alumina bubble particle size and surface pretreatment on the properties of mullite castables for top blowing lance.The relationships between the structure of alumina bubbles and the properties of castables are determined by using the grey relation analysis model.Under the experimental conditions,the most suitable particle size of the alumina bubble is 0.5-1 mm.The surface pretreatment of the bubbles helps to repair the defects of the alumina,increases the amount of mullite formed at the interface between the alumina bubble and the matrix,and further improves the performance of the castable.6.Industrial practice and application of new top blowing lance.Through the above research and industrial tests,the integrated technology of high-efficiency top blowing lance for auxiliary slag skimming process from hot metal ladle is formed and applied in a steelmaking plant.The service life of the new structure lance is 50 times and the highest is 67 times.Compared with the non auxiliary slag skimming process,the slag skimming efficiency is increased by 24.5%,the slag skimming time is shortened by 20.22%,and the slag iron loss is reduced by 14.71%.The life of the hot metal ladle remains unchanged.Significant economic and social benefits have been achieved. |
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