Research Of Dephosphorization And Technology Optimization In Big Converter

As the increasingly strict requirements on phosphorus in steel, low phosphorus steel production of large converter becomes the critical control factor of clean steel steelmaking. With advantages of high efficiency and good dynamics conditions of combined-blowing converter, the study that researches on selective oxidation of elements, dephosphorization law of thermodynamics, slagging characteristics and effect factors of Lp, and formulates optimization of converter dephosphorization process, is beneficial to the optimization of converter smelting process. It greatly improves the efficiency low phosphorus clean steel production of converter, and has important significance to realize stable low phosphorus clean steel production.Based on the large combined-blowing converter low phosphorus steel steelmaking as the research object, through methods of element selective oxidation, dephosphorization law of thermodynamics, dynamics simulation experiment, thermodynamic calculation, process model calculation and field test, it established the system of low cost high efficiency dephosphorization technology with conditions of conventional dephosphorization of converter, low silicon low cost hot metal and less slag ultra-low phosphorus steel smelting practice. It achieved good effect through process optimization. The main research work is as follows:(1) The rule research of elemental selective oxidation and dephosphorization in converter steelmaking processThe industrial test results in large converter showed that the apparent dephosphorization rate fluctuated between 0.00088%/min and 0.02448%/min during smelting. The early and late periods of smelting were the main stages of dephosphorization, and the dephosphorization rates were 16 and 6.7 times of the whole smelting progress, respectively. The early and late periods of smelting were the main stages of slag formation by studying the slag formation characteristic, and the slag quantity were 54.79% and 28.88% of the total slag, the slaging rate were 7.35 and 6.11 times of the middle stage respectively.It studied elements selective oxidation rule during large converter smelting process. Elements oxidation controlled by oxygen level, elements with low oxygen level was oxided first. Desilication reaction was prioritized at smelting beganning when the silica oxygen level minimum; As the desilication reaction, when [Si]= 0.1% or less, dephosphorization oxygen level was minimum under the condition of suitable slag, which was preferential oxidation; Early decarburization oxygen level was a little higher than desiliconization and dephosphorization oxygen level, desiliconization and dephosphorization priority happened; Decarburization oxygen level was minimum at middle smelting process, decarburization reaction was preferred; When [C]= 0.33% or less in late smelting, decarburization into carbon mass transfer control, oxygen decarburization oxygen level increased rapidly, which below the dephosphorization oxygen level, dephosphorization oxygen level was minimum, then dephosphorization reaction was preferred.It obtained dephosphorization regularity of large converter steelmaking process. Dephosphorization reaction occured on the surface of steel and slag (steel slag pool interface, interface and slag sinosteel drops in steel slag interface); Reasonable control of CaO, FeO, MgO content of slag could reduce reaction zone P2O5 activity coefficient, whch reducing dephosphorization oxygen level and promoting dephosphorization reaction is preferred; The oxygen in dephosphorization reaction area affected by oxygen in molten pool. Phosphorus competed with carbon, silicon reacted with oxygen during smelting process. Dephosphorization in early stage of smelting was mainly restricted by silica oxygen level.At the beginning of the smelting, the dephosphorization had good thermodynamic condition, but limited by insufficient conditions of reaction kinetics and reaction time, which made apparent phosphorus distribution (Lp) off balance far in early stage; At late stage, dephosphorization reaction approached the thermodynamic equilibrium. It concluded large converter smelting end apparent Lp calculation formula by data regression analysis:(2) Dynamics experimental study of the converter steelmaking processThe large converter cold simulation study showed that the main factor influencing the molten pool blending time was bottom blowing stirring. The relationship of mass transfer coefficient of steel slag with molten pool was linear regressive. The linear relationship of steel slag mixing and mass transfer coefficient could be ka∝-(εB+0.09εT)-0.4. Bottom blowing stirring was main technological means to promote molten pool blending and mass transfer between steel and slag.(3) Efficient dephosphorization technology research of large-scale converterAnalysis results of the production data of conventional large converter dephosphorization showed that Lp was the main indicators of slag dephosphorization efficiency. It obtained the large converter system of high efficiency low phosphorus steel smelting technology through the studies above, and by which achieved stability of [P]< 0.010% low phosphorus steel production.(4) Research of low-cost converter dephosphorization processOn the basis of the dephosphorization analysis, experiment and technics research, it put forward low cost less slag smelting process model. Model technology analysis showed that slag quantity needed of dephosphorization had quantitative relationship with phosphorus distribution ratio between steel and slag, molten iron phosphorus content and phosphorus content. It had realized low cost less slag smelting through the application process. Lime consumption reduced by 30%. Smelting process dephosphorization rate increased from 83.90% to 90.08%. The average Lp at the end of smelting increased from 57.2 to 112.1, the end phosphorus content from 0.0161% down to 0.0133%.(5) Research of super low-phosphorus steel and slag less steelmaking technology of large converterIt found that semisteel phosphorus and phosphorus distribution ratio of steel-slag was a key factor controlling slag quantity of decarburization convertor by studying the decarburization converter slag smelting process. To realize less slag low phosphorus steel smelting, it required semisteel [P]=0.03% or less, the Lp=100 or higher. To realize super low phosphorus steel smelting, it required semisteel [P]=0.025% or less, the Lp =110 or higher, the lime quantity is 20 kg/t and 2 times furnace slugging with 52kg/t or higher slag weight.It did achieve the low phosphorus steel and ultra-low phosphorus steel slag smelting through process optimization. The average smelting end [P] was 0.007% of low phosphorus steel after decarburization furnace, and average smelting end [P] was 0.00256% of ultra-low phosphorus steel after decarburization furnace, which had realized ultra-low phosphorus smelting of [P] 0.004% or less.