Effect of slag ratio on 5 500 m³ BF smelting

Since May 2019,the proportion of pellets fed has been successfully increased from 25% to 50%-70% on the 5 500 m³blast furnace in Shougang Jingtang Iron and Steel Co.,Ltd. The pre iron system has not only reduced the emission of pollutants such as particulate matter, SO₂ and NO_x by 24%, the emission of CO₂ per ton of iron by 10%, but also the slag ratio has reduced from 300 kg/t to 210 kg/t, which greatly promoted the improvement of blast furnace smelting level. The influence of slag ratio on the main parameters of blast furnace smelting is studied, which can provide technical reference for blast furnace smelting with low slag iron ratio in the future.It is found through the statistics of production data that after the slag iron ratio decreases from 300 kg/t to 230 kg/t, on the one hand, the main indicators have been significantly improved. The utilization coefficient has been increased from 2.25 to more than 2.50, the permeability index has been increased from 4 100 to more than 4 300, the coke ratio has been reduced from 295 kg/t to less than 265 kg/t, and the coal ratio has been increased to 200-220 kg/t. On the other hand, the reduction of slag ratio also brings about the reduction of slag desulfurization and alkali discharge capacity. Under the conditions of 3.80-3.90 kg/t sulfur load and 2.60 kg/t alkali load, in order to meet w(S)<0.050% in molten iron and the slag alkali discharge rate is greater than 75%, the optimal slag iron ratio control center line of 230 kg/t is proposed.In the future, if the the slag ratio is further reduced, it should start with reducing harmful elements and optimizing slag composition to minimize the circulation and enrichment of harmful elements in the furnace, so as to ensure that the furnace conditions are high and stable.In addition, after the slag ratio decreases significantly, the flow rate of molten iron increases significantly, and the tapping times decrease. The tapping system should be optimized and adjusted in time to meet the smelting requirements of low slag ratio.