| Vanadium is a typical rare metal,and it is wildly used in steelmaking,aerospace,chemical and medical industries.So vanadium is a strategic resources and known as?modern industrial MSG‘.Moreover,the rigid requirement that vanadium micro-alloying for aseismic ribbed bar in steelmaking industry,which has made the quantity demanded of vanadium resource became much more bigger.Oxygen blow smelting in converter has the efficient ability of recovering vanadium from v-bearing hot metal,which makes it becomes the most wildly used method.However,vanadium extraction smelting process in converter requires not only maximum vanadium recovery to form v-enriched slag,but also to ensure enough high carbon content in semi-steel,which is the other product of vanadium extraction process,to ensure subsequent steel-making process.So,vanadium extraction process needs?deep devanadium‘and?minimum carbon loss‘simultaneously.There are two 200t combined blown vanadium extraction converter in Pangang Group Steel Vanadium and Titanium Co.,Ltd.,and they are the biggest ones in china.The goal of vanadium extraction process are residual vanadium in semi-steel must remain low,mostly under0.05 wt%;and carbon content in semi-steel needs to above 3.4 wt%.To ensure highly efficient vanadium extraction process,the following problems must be settled.First,figuring out the removal characteristics of vanadium and carbon during smelting process and reasonable final point temperature control is necessary to realize double hitting?deep devanadium‘and?minimum carbon loss‘simultaneously and automation of vanadium extraction process.Second,oxidation of elements in v-bearing hot metal is indirect and oxygen is transferred by ferric oxide.So,reasonable melting and rheological must be ensured to enhance the kinetic condition for mass transfer.However,the blast furnace smelting in Pansteel belongs to middle-high titanium type,which lead to the low content of[Si]in hot metal.So,a reasonable strategy of adding ingredients silica sand is necessary to ensure reasonable?SiO2?content in slag.Third,combined blown converter has much better kinetic condition than other types.However,vanadium enrich slag is very sticky and tapping must ranks each three heats,which lead to residual slag is easy to block bottom blown devices and reduce the stirring effect.So,promoting the status of top blowing in the premise of avoiding excessive carbon removal by increase top flow becomes necessary.Fourth,slag splashing is a key technology to extend the service life of converter and reduce the costs.However,slag splashing has not been applied on vanadium extraction converter due to the acid slag composition.It is necessary to carry out research on modification of vanadium slag to make it be fit for slag splashing.In this paper,studies focused on problems mentioned above based on 200t combined blown converter were carried out to enhance vanadium recovery with minimum carbon loss.The conclusions are summarized as follow.?1?Thermodynamic analysis combined industrial experiments were applied to study the oxidation behaviors and scales of vanadium and carbon to develop a reasonable strategy for temperature control.The new strategy employed Tsl?the selective oxidation temperature between carbon and vanadium?and Teq?the equilibrium temperature of vanadium oxidation and reduction?for the earlier and middle-late smelting respectively.Industrial experiments showed a great deal of[V]?56.9wt%?was removed with only 5.6wt%carbon loss in the earlier smelting,and30wt%[V]was removed with 13.4wt%carbon loss in the middle-late smelting.Applicability analyses have confirmed Teq as the high-limit temperature for final point.Vanadium removal remains low and carbon loss climbed up significantly when the molten bath temperature exceeded Teq.?2?A theoretical model based on metal droplet generation and Gibbs free energy minimum has been built to study the dynamics during vanadium extraction smelting process in converter.Oxidation of elements in v-bearing hot metal can be divided into three groups,[Ti]and[Si]removed at the earliest period,[V]and[Mn]followed,[C]removal go through all smelting and goes rapid at later period.No available slag layer has formed at the beginning of smelting,ferric oxide enriched coolant could be added before smelting to accelerate oxidation of[Ti]and[Si].The slag consist of FeO-SiO2-TiO2 ternary system at the earlier period of smelting,and turn to FeO-SiO2-MnO-V2O3-TiO2 system at the mid-later period.Coolant addition has lead to drastic vibration of slag composition,but it also lead to gently temperature rise.To satisfied the smelting goal of?deep vanadium‘and?minimum carbon loss‘,sufficient coolant should be added in batches,exorbitant[Ti]and[Si]content in hot metal and intensity of oxygen blowing must be avoid.?3?A new adjustment strategy has been proposed based on SiO2/V2O3 ratio and FeO content of vanadium slag to solve the problem of addition of ingredients silica sand.The melting temperature of vanadium slags depended on BI'and SiO2/V2O3 ratio.With the increase of SiO2/V2O3 ratio and constant FeO content,FeO·Fe2O3 decreased and2FeO·SiO2 increased,the melting temperature of vanadium slag decreased first,then increased due to the generation of SiO2.With the increase of FeO content,the SiO2/V2O3 ratio increased when the melting temperature was the lowest.With the increase of SiO2/V2O3 ratio,the variation trend of viscosity with various temperatures became more gently,the viscosity of meltdown vanadium slag increased,and viscosity has became much higher with low temperature.Synthesizes the influence of viscosity on metal-slag interface reaction and reducing slag loss,SiO2/V2O3 ratio should controlled as 0.7 when FeO=44%.Adjustment of vanadium slag composition should figure out the addition of coolant based on composition and temperature of hot metal,then the FeO content in vanadium slag could be deduced,addition of silica sand to suit reasonable SiO2/V2O3 ratio can be deduced by[Si]and[V]contents in hot metal.?4?Optimization on parameters of oxygen lance nozzle was proposed in the premise of do not increase top blowing flow and avoid excessive carbon loss to improve the stirring of molten pool.Angle,hole number and Ma number of nozzle were optimized by building a physical simulation system of 200t combined blowing converter.The mixing time decreased and 1/3 big waves increased with the hole angle decreased first,and these two turned to opposite trend when the angle below 12°.The mixing time of 12°nozzle was 4.17%smaller than original 13°nozzle,and 1/3 big waves was4.21%bigger.The mixing time and 1/3 big waves of 5-hole-nozzle were 1.88%and3.35%smaller than 4-hole-nozzle respectively,and conductivity measurements showed there existed dead zone in the molten pool of 5-hole-nozzle.The mixing time of nozzle with Ma number 2.10 and 2.20 were 7.36%and 14.31%smaller than nozzle with Ma number 1.99,and 1/3 big waves were 8.68%and 14.75%bigger.The order of the affection extent of each parameter was as followed Ma number>Nozzle hole angle>Nozzle hole number,and the optimization results turned to be more outstanding when the bottom blowing flux remains low.The parameters of optimized nozzle are 4 holes,12°and Ma 2.10.?5?Industrial experiments have been taken place on 4#200t vanadium extraction converter of Pangang Group Steel Vanadium and Titanium Co.,Ltd.to apply the research results of temperature strategy,dynamics,vanadium slag and optimization of oxygen lance nozzle,and great efficiency has been archived.In order to combine the research results with operation parameters during smelting,a software has been built based on VB language,and it has showed good accuracy rate.?6?Component modification of MgO addition and iron oxides reduction was proposed to make vanadium slag suit for slag splashing.Crystallization behaviors were expectantly optimized on the premise of reducing corrosion and ensuring reasonable melting temperature.The results showed[FeO4]-tetrahedral increased from 0 to 19.1%in the slag structure with the increase of MgO content,and MgO played a role in motivating FeO change into Fe2O3.Pleonaste?MgO.Fe2O3?and solid solution?MgO-FeOss?with high melting temperature generated and FeO.V2O3 precipitation weakened.The melting temperature increased with the increase of MgO content and decreased with the decrease of TFe content.MgO addition reduced the polymerization degree of slag and TFe decrease reduced the precipitation of crystalline phases,which led to decreasing of crystallization activation energy.Vanadium slag with MgO=12wt%and TFe=16%satisfied the demands on melting temperature and crystallization tendency for slag splashing.Microstructure changed from dispersed distribution to blocky crystals combined with banded solid solution which greatly promoted the corrosion resistance of slag splashing layer. |
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