Study On Desulfurization Of Composite-Powder Staged Injection Based On Kinetic Model

As requirements of steel quality turn higher and higher,as well to reduce the load of the following refinement processes,the desulfurization through injection powder in the hot metal pre-treatment stage plays an important role in the steel production process and it has attracted more and more studies.Generally speaking,for the high-temperature environment of powder-injected desulfurization,the chemical reaction is not a rate-limited part of the desulfurization process,but the mass transfer controls the desulfurization performance of the reactor.The factors that enhance the agitation,the properties and behavior of the sprayed powder,and their dispersion degree in the slag/metal bulk determine the efficiency of process and the utilization of the powder,thus the reactor performance and production cost.Just under this background,this study explores through establishing a kinetic model to investigate desulfurization process,particularly focusing on the effects of process parameters on desulfurization efficiency and powder utilization.Based on the difference of CaO and Mg powder desulfurization kinetics characteristics,several staged injecting schemes are proposed and discussed to improve the powder utilization rate and desulfurization efficiency.the focus of the research include the establishment of a kinetic model of composite powder injected into hot metal desulfurization and the different staged injecting schemes also investigated,Specifically discuss as followed:(1)Kinetic model of desulfurization through composite powders injected into hot metalBased on the characteristics of different powders(calcium oxide,magnesium),as well as considering of the features of distinct slag zone(regular top slag and entrapped slag droplet)in the process of desulfurization,a comprehensive kinetic model was built.This model includes the influence of mixing time,residence time,powder penetration ratio.After the model though plant practical data was validated,it was applied to investigate the effect of process parameters,including carrier gas flow rate,immersion depth of injected lance and injecting rate,on desulfurization efficiency and the powder utilization rate.The following results were obtained:(a)As the carrier gas flow rate increases,the end content of the sulfur increases and the utilization of magnesium increases.(b)As the immersion depth increases,the end content of the sulfur decreases and the utilization of magnesium increases.(c)As the powdering rate increases,the end content of sulfur decreases and the utilization of magnesium decreases.(2)Study on process route of staged-injected powderBased on the established mathematical model,it is found that in the desulfurization process,the desulfurization rate of magnesium and calcium oxide is not constant,the rate change with the change of the sulfur content of the hot metal,which is manifested by the faster desulfurization rate of calcium oxide in the early stage.Then as the sulfur content decreases,the rate is slower in the later period.On the other hand,considering the magnesium is present in the form of steam or magnesium bubbles,thus,the rate of desulfurization by the magnesium powder in the early stage is slow,and as the magnesium content increases in the hot metal,the desulfurization rate will become fast.While in the later stage,the sulfur content is lower,and the rate becomes slow again.In view of this rule,the composite powder staged injected based on different ratios was proposed to maximize the utilization of magnesium powder and reduce the production cost under the premise of ensuring the goal of desulfurization.This study consider the production practical situation,the injecting process was divided into four stages.Further,the carrier gas flow rate,immersion depth,injecting rate and the ratio of calcium oxide and magnesium powder in the four injection stages were investigated.The main results of the study are as follows:In the same end content of sulfur,the increasing immersion depth,reducing the carrier gas flow rate and lowering the powder injecting rate will increase the utilization rate of magnesium powder.Also,the proposed staged route can the utilization of magnesium to be 5%higher than the initial injection scheme.Furthermore,the optimized staged injecting route was applied to the practice of a steelmaking plant.The model calculation end point sulfur content and the actual one can be well matched.More importantly,the amount of magnesium(magnesium consumption)consumed based on the removal of unit sulfur is reduced by 1%to 4%using the proposed route.The study shows that the proposed staged injection composite powder method is beneficial to achieve the effective utilization of magnesium powder and improve the performance of the reactor,which is conducive to the goal of cost reduction and efficiency improvement in enterprise production.