Study On Charge Assimilation Of Bottom Oxygen Gas-Injection BF Process

Pulverized coal injection (PCI) into BFis one of effective technologies to reduce the cost and enhance competitiveness of BF process, but it brings a series of troubles to BF operation. The Bottom Oxygen Gas-Injection BF Process was put forward, which the reducing gas produced by coal in a gasifier is injected to BF from tuyeres. Whole charge assimilation of the new process was studied under the simulative conditions, the influences of H₂ content on RDI_-3.15, reduction rate, melt-dropping of iron ore, slag formation and coke transformation were determined. The conclusions are as follows:Temperature is the principal factors which influence on the low temperature reduction degradation index (RDI) of charge, the RDI_-3.15 reaches the maximum at 500℃, and it decreases as the temperature increases from 500℃to 900℃, the charge degradation finishes at 900℃. At the same condition, the RDI_-3.15 increases as the H₂ content increases, decreases with the CO₂ content increases, and the RDI_-3.15 of sinter is higher than that of pellet and crude iron ore. It is found that the mechanism of the low temperature reduction degradation is caused by volume expansion when hematite was reduced to magnetite.The reduction ratio of iron ore increases with reduction temperature and time increase, they present linear relationship. The reduction ratio of iron ore increases obviously with H₂ content of gas increasing, the indirect reduction is mainly carried out in lumpy zone of BF, and it has decisive effect to strengthen the smelting process and reducing energy consumption. The carbon loss ratio of coke increases with the H₂ ratio increases, the properties of coke is deteriorated, it has higher request to coke which act as frame in BF.When the H₂ ratio increases, the dropping temperature, maximum negative pressure and the maximum pressure drop of charge falls significantly, thus the ironmaking process could be carried out at lower temperature, the energy consumption could be reduced. The BF cohesive zone becomes thin or even disappeared, and the gas permeability of charge is improved, it is beneficial to BF smooth operation.The formation of primary slag is related to charge species. The primary slag formed by pellet and crude iron ore is composed by a large number of aluminosilicate and FeO; the primary slag formed by sinter is an acid slag system of CaO-Al₂O₃-MgO-SiO₂. In the course of primary slag descend, FeO is reduced and CaO and MgO in sinter are absorbed, then the final slag formed finally. Contrast to PCI BF process, the acidic materials entering BF tuyeres decrease sharply in the new BF technology, thus the basicity of charge loaded from furnace top decreases, the slag ratio decreases sharply; there are not unburned coal in slag, the formation of primary slag and bosh slag become well. The fluidity of BF slag was improved, it is helpful to form reasonable operating furnace profile, strengthen smelting process. Reasonable slagging system could enhance the metallurgical properties of slag, the trouble could be solved that caused by slag quantity deceases; high quality hot metal could be produced.The results reveal that the new technology is completely feasible. The complex combustion and gasification of coal in tuyeres were transferred to outside BF in the new technology, the iron-making process in BF was simplified, and rich hydrogen metallurgy was achieved. The top gas could be recycled by gasifier, the emission of CO₂ and energy consumption could be reduced, the BF process could use large number of normal coal instead of metallurgical coke. The new technology is in accordance with the needs of current metallurgical industry, it has obvious advantages.