Efficiency Enhancement Mechanism Of Fluorine-Free Steel-Making Dephosphorizer Made From Collected Dust And Its Harm Reducing Effect

The collected dust produced by iron and steel enterprises will pose a direct threat to the environment and production safety.Meanwhile,with the depletion of high-grade iron ore,the utilization of some high-phosphorus iron ore is easy to cause high phosphorus content in hot metal,resulting in cold brittleness and cracks in steel,which will affect product quality and reduce engineering reliability.In addition,the fluorine-containing slag used in dephosphorization will cau se lining erosion and environmental pollution.Therefore,how to use collected dust to prepare dephosphorizer for steelmaking and reduce the harm of fluoride on this basis is one of the difficult problems to realize the harmless steelmaking.In this paper,a high-efficiency fluorine-free dephosphorizer for steelmaking is developed from the steel-making collected dust from a steel plant.The mechanism of different substances in dephosphorization is explored to realize the internal recycling of collected dust and the fluorine-free dephosphorization of hot metal.First,a new dephosphorization and rephosphorization kinetic model was established based on the relative change in reactant concentration at the slag-iron interface.The comparative analysis of theoretical and experimental data shows that the[P]-t fitting deviation of the new dephosphorization model is significantly smaller than that of the traditional model,and the new rephosphorization model has high stability in mass transfer parameters.This improves the interface reaction theory of hot-metal dephosphorization.Then,using the collected dust as the raw material of dephosphorizer,a collected-dust based fluorine-free steel-making dephosphorizer was developed through the screening of fluorine-free flux and the optimization of the collected-dust ratio.The experimental analysis shows that the best technological parameters for decarbonization of collected dust are 1000°C and 100min;In the fluorine-free flux,Ca Cl₂ is not only higher than Ca F₂ in the flux effect,but also non-toxic and low-cost,which can temporarily replace Ca F₂;The best replacement ratio of collected dust is1.0,at which time[P]_f（final hot-metal phosphorus content）is as low as 0.031wt%,andη_P（dephosphorization efficiency）is as high as 87.6%.To realize stable and efficient dephosphorization,it is important to analyze the influence mechanism of carbon,silicon and calcium impurities in the collected dust on various factors in the dephosphorization process.The effect of carbon impurities on hot-metal dephosphorization is obvious.When the carbon content of the collected-dust based dephosphorizer is less than 2wt%,η_P can exceed 91.4%and[P]_f is lower than 0.025wt%.The effect of silicon substances on the hot-metal dephosphorization is complex.When the silicon content in hot metal is greater than 0.4wt%,η_P will exceed91%,[P]_f will be lower than 0.03wt%;the content of Si O₂ in dephosphorizer has no obvious effect onη_P;the presence of Ca Si O₃ can accelerate the dephosphorization reaction.To clarify the reaction mechanism of Ca Si O₃ accelerating dephosphorization,the mass transfer process of phosphorus was analyzed when silicon,Si O₂ and Ca Si O₃were used as the initial components of the experiment.In terms of the effect of Ca O derivatives on the hot-metal dephosphorization,Ca（OH）₂ has little effect onη_P,and[P]_f is concentrated at 0.015～0.021wt%;However,the increase in Ca CO₃ replacement ratio will make[P]_f decrease first and then increase.Through the experimental research on the mass transfer process of phosphorus when Ca O,Ca（OH）₂ and Ca CO₃are used as fixatives,the blocking mechanism of Ca（OH）₂ and Ca CO₃ on the hot-metal dephosphorization was clarified.The analysis and research on economy and safety show that the dephosphoriza-tion technology of hot metal based on collected dust and fluorine free can not only realize the utilization of internal circulation with high added value of collected dust,reduce production costs,reduce natural fluorite consumption,but also reduce furnace lining erosion and avoid the harm of fluorinated waste.