Theoretical Basis And Process Research On High Efficiency Dephosphorization Of Converter By Double Slag And Slag-remaining

The control requirements for phosphorus content in steel are becoming more and more stringentas phosphorus is a harmful element in most steel types.The low-phosphorus smelting technology of converters has become the key in the entire steelmaking process.Based on the above analysis of the current situation,combined with theoretical calculations,laboratory experiments,industrial experiments,the paper studied the double slag retention slag process,the converter hot slag recycling technology,the limestone steelmaking and iron ore smelting reduction technology which are beneficial to high-efficiency dephosphorization.Through industrial experiments,the relationship between the composition of dephosphorization slag,slag phase and dephosphorization rate in converter smelting process was studied by means of staged sampling.The specific research work is as follows:(1)The activity calculation model of Ca O-Si O₂-Fe O dephosphorization slag was established by the theory of molecular ion coexistence.The effects of Si O₂,Fe O content and temperature on dephosphorization of slag were analyzed.The dephosphorization kinetics and dephosphorization restriction were analyzed by two-mode theory.During smelting,the slag composition should be controlled to have a lower viscosity.After dephosphorization,the furnace temperature is controlled between 1380?1450°C,the slag basicity is controlled at 1.3?1.6,and the slag(Fe O)is controlled at 15?20%.The slag(Mg O)is controlled at 4 to 8%.(2)Through the process dephosphorization test,it is found that adding suitable iron ore to the molten pool can improve the oxidization of the slag and greatly accelerate the dephosphorization reaction of 3?12 min.The Fe O content in the slag of 6?12 min is 15%.Between?23%,the slag basicity is between 2.5 and 2.8.The formation of solid phase dicalcium silicate particles during the slagging process plays an important role in accelerating the dephosphorization reaction.The results of double slag dephosphorization test showed that the slag basicity was 1.5?1.8 when smelting was4min,the Fe O content in slag was 15?20%,and the dephosphorization effect was the best when the slag temperature was 1410?1450°C.By adjusting the alkalinity of slag during smelting for 4 min,the dephosphorization rate was increased by 12%;the Fe O content in the slag was adjusted to increase the dephosphorization rate by 22%when smelting for 4 minutes;and the dephosphorization rate was increased by adjusting the slag temperature by 15%.(3)The use of limestone for secondary rapid slagging can change the problems caused by the traditional lime slagging process.Industrial tests show that pure iron smelting can be used.The average amount of limestone in the slag-forming material can reach 23.66kg/t steel instead of lime.The amount of 13.26kg/t steel can reduce CO₂ emissions by 10.42 kg/t steel.Temperature,iron ore density,iron ore ratio have an effect on the dissolution time of lime,and the temperature effect is most significant.At a temperature of 1400°C,as the proportion of iron ore increases,the complete dissolution time of lime gradually decreases.(4)The dephosphorization rate of the pre-and end points of the furnace with the addition of the end slag is much better than that of the non-end slag.The dephosphorization rate of the first stage and the end point of the one-time addition of the slag-forming material is better than that of the batch-added slag-making material.In the case of one-time feeding,the initial steel and slag reaction interface has a higher oxygen potential value,and the dephosphorization reaction rate in the early low temperature condition is greatly improved,and the slag in the early stage is more in the liquid phase,and the kinetic conditions are better.The dephosphorization effect is better than batch feeding.(5)When the whole amount of slag is used,the circulation process is difficult to control.When the slag discharge rate is controlled by the constant slag retention amount,the continuous slag continuous circulation can be realized by controlling the slagging rate and the dephosphorization rate.When the dephosphorization rate is 50%and the residual slag amount is 6t,the slag discharge rate is 40?50%,can achieve continuous circulation of less slag smelting process;when the dephosphorization rate is 65%and the residual slag amount is 6t,the slagging rate is guaranteed to be40?60%,which can achieve continuous circulation of less slag smelting process.(6)The static control model of converter steelmaking was developed.The industrial site verification showed that the average lime consumption was 20.44 kg/t from January to June 2018,the average limestone consumption was 1.94 kg/t,and the average light burn dolomite consumption was 18.48 kg/t.The total consumption of lime decreased by 13.46 kg/t,and the CO2 emission was reduced by 10.58 kg/t.The reduction of slag amount reached the requirement,and the reduction of iron-steel ratio could save 6.56 kg/t of standard coal.The innovations of the paper are as follows:(1)Based on the composition and phase analysis of dephosphorization slag in the double slag process of converter,it was found that the formation of C₃P-C₂S solid solution is beneficial to improve the dephosphorization efficiency.(2)Proposed and verified the process route to control the(Fe O)content in the dephosphorization slag of the converter through the control of the reduction degree of iron ore.(3)The model of de-phosphorization of double slag residue in converter was developed,and the dephosphorization hit rate reached a satisfactory level.