| To build a highly efficient and low-cost clean steel production platform,Shougang Jingtang designs and builds a new generation recyclable steel manufacturing process.However,some problems were still encountered in the practical production process of desulfurization-desilication/decarburization(hereinafter referred to as De[S]-De[Si]/[P])Technology of Iron and Steel.Chiba,2004.pretreatment,posing is a big concern to the ferrous metallurgy industry and hence needs to be settled urgently.Based on the regulation status of hot melt mass flow in the De[S]-De[Si]/[P]pretreatment of Shougang Jingtang's steelmaking process,theories related to Metallurgical Process Engineering(MPE)were employed in this paper to conduct an analysis and simulation study on the basic parameters of mass flow(time,temperature,and mass quantity).Through this,the two key technical issues restricting the proportion of De[S]-De[Si]/[P]pretreatment were studied:scrap melting and the cost of BOF auxiliary material.The mass flow operational status in the De[S]-De[Si]/[P]pretreatment of the steelmaking process was analyzed in this paper,and the result revealed that the proportion,cost control,composition control,as well as time and temperature controls of the De[S]-De[Si]/[P]pretreatment had failed to fulfill the design requirements.There was a certain disparity between its control level and that of other steel mills.To address the problems concerning the De[S]-De[Si]/[P]pretreatment,more emphasis should be placed on the building a clean steel production platform to comprehensively regulate the basic parameters of mass flow by optimizing the whole steelmaking process in an all-round way.By analyzing the operational time length of the mass flow,it was found that the productivity of BOF is low and the idle time of the empty furnace is long,with an average idle time of empty dephosphorization furnmace and decarburization furmace being 19.86 min to 15.91 min.The process has low continuation degree due to the slow pace of the production,resulting in a large portion of the time being wasted in the inter-process waits.By analyzing the operational temperature of the mass flow,it was found that the hot melt tapping temperatures of ultra-low carbon steel and low carbon steel were 1680? and 1666? respectively,higher than that of steel mills of the same kind.The reason lies in its slow production pace,which causes the temperature to drop quickly during material transportation because a large portion of time has been wasted in the inter-process waits.Therefore,higher temperatures of hot melt tapping should be kept to secure the temperature of continuous casting tundish.Fluent was used to simulate the thermal condition of an empty BOF,wherein the thermal dissipation of BOF varies from 0.89 to 7.85×107kJ due to the empty furnace idle time;when the idle time is increased by 30 min,the thermal dissipations of dephosphorization furnace and decarburization furnace increase by 2.34×107kJ and 4.13×107kJ respectively.Within a certain smelting time length,the temperature drops of hot melt from dephosphorization furnace,decarburization furnace,and BOF increase by 12.5?,15? and 17? respectively,while the additions of scrap steel for duplexing sruelting and conventional smelting decrease by 0.93%and 0.75%respectively.Plant Simulation was employed to build a simulation model for the operational quantity of mass flow,and the result indicated that the proportion of De[S]-De[Si]/[P]pretreatment grows from 33%to 100%,the continuation degree of the process also improves,and the average idle time for material transportation of BOF casting decreases by 5-14 min,which is equivalent to a temperature drop of 4.9-13.7? of the hot melt tapping.The average idle time for the transportation of DeP-DeC decreases by about 10.14 min,the average idle time for transportation of KR-DeP decreases by about 11.62 min,equivalent to a temperature increase of 1.93oC for the hot melt in the decarburization furnace and an increase of 2.21? in the dephosphorization furnace.Due to the acceleration of the pace of production,the productivity of BOF rises from the current 50%to 60%-70%.The thermal dissipation reduces due to a reduction in the empty furnace idle time,which translates to a temperature drop of 12.5? for the hot melt in the dephosphorization furnace,and a drop of 15? in the decarburization furnace,hence further lowering the production cost.As for scrap melting,the calculation of material balance and thermal balance was conducted to the dephosphorization furnace,the result of which shows that heat is not a limiting factor to scrap melting,while both temperature and composition of hot melt are sufficient for melting the scrap steels of the current proportion.Whether or not the scrap steel can be molten on time is dependent on its melting rate,blowing time of BOF,and its thickness.A melting rate model and melting thickness model of scrap steel were built,and simulated under the temperature of 1360?,when the carbon content in the molten pool increases from 4.5%to 5.0%,the melting rate of scrap steel increases by 43%to 63 mm;when the carbon content is less than 4.5%,and the temperature of molten pool is increased from 1350? to 1400?,the melting rate of scrap steel increases by 60%to 70 mm.When the scrap steel is heated from room temperature to 800?,the crust thickness on its surface reduces,but the influence on melting rate is still negligible.Moreover,long blowing time can further increase the melting thickness of scrap steel.However,the allowable size in which the scrap steel can be molten in a dephosphorization furnace is limited.Regarding the eost of BOF auxiliary materials,C#language was employed to develop an interface of the calculation model for the auxiliary material addition.In the current mass flow condition,it can be learned through the calculation model that the cost of BOF auxiliary product is highly related to the temperature,the silicon content,and the carbon content in the hot melt.In this paper,the cost of auxiliary materials added into De[S]-De[Si]/[P]pretreatment and conventional smelting were compared under different conditions;when the proportion of De[S]-De[Si]/[P]pretreatment reaches 100%,the cost of auxiliary product added into De[S]-De[Si]/[P]pretreatment declines compared to conventional smelting for the current hot melt and target steel grade.When it comes to the smelting of low-carbon steel when the hot melt's carbon content is 4.1%,the silicon content is 0.1%,and the temperature is 1330?,the average cost of auxiliary material per ton of steel reduces by RMB 0.13-4.63. |
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