Optimizing Study Of De-P Steelmaking Process In ShouGangJingTang

Shougang Jingtang Iron & Steel Co., Ltd. uses the desulfuration dephosphorization and desilicication pretreatment process to produce clean steel. The prototype dephosphorization converter is a 16-hole bottom blown converter, where many molten steel flow zones in a bath affect the reaction; the bottom blowing tuyere always are plugged, resulting in low bottom blown effect; low temperature in the dephosphorization converter leads to steel sticking to the coverter wall, incomplete scrap melting, etc. during smelting, and dephosphorization rate of semi-steel index not reaching advanced level. Thus, this paper focuses on the systemic study on dephosphorization technologies for dephosphorization converter, such as bottom blowing tuyere layout, furnace lining maintenance technology, material balance and heat balance, re-use of the slag from the decarburization converter, etc. In 300t dephosphorization converter of Shougang Jingtang Iron & Steel Co., Ltd., and gives process-improving measures, which have been taken to achieve ideal results in industrial test and production. This paper has the following main innovations and work.According to the structure and combined blown parameters of 300t dephosphorization converter of Shougang Jingtang Iron & Steel Co., Ltd., the 1:12 water simulation experiments were performed in a lab. The optimal number and layout of bottom blowing tuyeres in the converter were analyzed by the single-factor double-index. The optimal process parameters were obtained by analyzing the effects of bottom blown flow, top blown flow and oxygen lance position on the mixing time and interface mass transfer rate in the converter. The optimal parameters of 300t dephosphorization converter of Shougang Jingtang Iron & Steel Co., Ltd. were as follows:incompletely symmetrical central layout of eight bottom blowing tuyeres in an inner ring with the shortest mixing time and the highest mass transfer rate; top blown flow of 14.35 Nm3/h (corresponding to 18000 Nm3/h in the prototype); the oxygen lance at 128 mm (corresponding to 2400 mm in the prototype); bottom flown flow of 2.74 Nm3/h (corresponding to 3673 Nm3/h in the prototype). The problems of smaller semi-steel output, scrap sticking to fconverter bottom, etc. were solved by studying the movement of different types and sizes of scraps in bath at different top blown flows and bottom blown energy, determining the suspending energy of scrap with different single weight in the bath (stirring energy required when the scrap was suspending in the bath) and defining the rational scrap steel type and size in semi-steel melting in the dephosphorization converter The scrap consumption of less than 10% was recommended because the big size scrap steel had longer mixing time than small size scrap; maximum single weight of not more than 1.5t (corresponding to the suspending energy of 14989 W/m3) when scrap steel was suspended in the bath at the top blown flow of 3000 Nm3/h (the oxygen lance at 2000 mm) and bottom blown flow of 4010 Nm3/h in combined blown melting.To further study the effects of converter bottom blown tuyere arrangement and top and bottom combined blowing parameters on molten steel flow in the dephosphorization converter bath, the research on gas-liquid two-phase flow in the dephosphorization converter by numerical simulation showed that the layout of eight bottom blown tuyeres in an inner ring provided uniform molten steel rate distribution, big area of "mass transfer renewing zone", and small area of "mass transfer stagnation zone" in the bath. Thus, it was the optimal bottom blown tuyere arrangement. The molten steel flow rate was bigger and the mass transfer renewing zone had bigger area at the bottom flow of 3500 Nm3/h, with the oxyen lance at 2000 mm, at top oxygen flow of 35000 Nm3/h and bottom flow of 35000 Nm3/h, therefore favorable for dephosphorization reaction.A model of prediction of FeO content of the slag from converter was created in consideration of material balance and heat balance models for converting at low temperature in the dephosphorization converter, and production data, and used to predict the FeO content of the converter slag, instruct the oxygen lance position and top oxygen flow. The results showed that the calculated FeO content of the converter slag matched the measured value very well, i.e. over 80% of the calculated FeO content values had the absolute error of ±2% and relative error of less than 10%.Comparative of the slags from decarbonization converter and dephosphorization converter shows that hot slag from decarbonization converter could be reused in the dephosphorization furnace. The hot slag from decarbonization converter was reused in the dephosphorization furnace to further enhance the slag melting and dephosphorization effect in the dephosphorization converter and achieve none material consumption in the dephosphorization converter by developing a new-type hot slag pot. After hot slag from the decarbonization converter was reused in dephosphorization converter, the final phosphorus content was reduced by 0.006%, and TFe content of final slag from the converter was reduced by about 3.4%. The hot slag experiments achieved zero lime consumption, zero light burning dolomite consumption, etc.The industrial test results showed that the optimized layout of bottom blown tuyeres increased the dephosphorization rate from 65.3% to 72.2% and decreased the final phosphorus content from 0.039% to 0.0316%. resulting in improved dephosphorization effect; lining maintenance by conventional method or washing method could effectively control the thickness of steel sticking to converter lining, enhance dephosphorization effect and prolong the service life. It was found during scrap melting experiment in the converter, such as medium-size scrap, steel strap, hot rolled steel cuttings, etc., that only medium-size scrap could be used in the dephosphorization converter; for big size scrap such as steel strap, hot rolled steel cuttings, etc., the scrap melting rate was enhanced by prolonging the blowing time and enhancing the temperature in the converter bath, etc.