Dephosphurization Process Development In 120t Combined Blown Converter At Tonghua Steel

Converter steel-making is to decarburizatie, heat, dephosphorizate, desulphurizate and purify of molten steel mainly through the oxygen supply and reasonable slagging. The conventional steelmaking process is of a large quantity of slag, high FeO content in slag, and much more iron beads contained in slag, which causes higher consumption of steel and iron material. In order to reduce consumption of steel and iron material and slag material, improve the overall economic benefits, through the analysis of the present situation of raw materials, technology and equipment, the key project of dephosphorization in 120t combined blown converter at steelmaking and rolling plant, Tonghua Steel, is carried out.Through the theorial study of remaining slag splashing in hot metal charging, dephosphorization mechanism, sufficient deslagging at dephosphorization-stage end, lining maintenance, etc., the industrial experiments on dephosphurization process in 120t converters at Tonghua steel were conducted in three stages. The first stage is for converter end-point slag solidification and safe charging of hot metal, mainly involved the precondition suitable for implementation of dephosphourization through remaining slag, slag solidification process after slag splashing, and addition of cooling material, slag solidification effect and temperature of slag, hot metal charging time. The second stage is for the dephosphorization effect of smelting process with "remaining slag", influnce factors of dephosphorization, raw material consumption and cost reduction per ton, and effect of slag on the lining maintenance. The third stage is for the practice of SGRS(Slag Generation Reduced Steelmaking)smelting process, mainly involved dephosphorization rates of dephosphurization stage and converter, influence factors on dephosphorization, factors affecting deslagging amount of dephosphorization stage, raw material consumption and cost reduction per ton, effect of slag on the lining maintenance.The results from convert end-point slag solidification and safe hot metal charding research show that slag splashing reaction in hot metal charging due to remaining slag can be controlled effectively for safety through controlling oxygen content less than 600×10-6 at converter end-point, lowering end-point temperature, splasing slag by adding MgO balls containing carbon and increasing slag splashing time in order to steadily control slag temperature less than 1350℃ and FeO content in slag less than 20%.Industry experiments of "the remaining slag mothod" smelting process shows that "the remaining slag method" smelting process greatly reduces the consumption of lime. With comparison to the conventional dephoshurization process, the process uses 39.36 kg/t lime comsuption, reduceing the consumption of lime by 18.77%,75.01 kg/t slag amount, decreasing it by 11.43%. Dolemite and oxygen gas consumption are also reduced. Raw material containing iron increases by 0.57 kg/t. Average dephosphorization and desulfurization degrees are 76.96% and 19.29%, a little higher than those in conventional process.Industrial experiments of SGRS smelting process shows that average dephosphorization and desulfurization degrees of SGRS smelting process are 80.05% and 12.62%, a little higher than those in conventional process, with 1.4-1.6 end-point slag basicity,1370-1420℃ end-point temperature, and 11%～13% TFe content in end-point slag during dephosphorization stage. The SGRS process can satisfy the necessity of smelting most steel grades and decrease further steelmaking cost at the same time. In comparison with conventional process, consumption of lime reduced 14.96kg/t, lowering by 29.38%, dolomite consumption reduced 4.94kg/t, decreasing by 35.12%, converter slag consumption reduced 20.88kg/t, lowering by 27.48%, steel and iron material consumption reduced 1.55kg/t.. These data suggest that SGRS smelting process can greatly reduce the smelting cost without affecting the smelting effect and lining life, and the SGRS smelting process has excellent popularization and application value.