Fundamental Study On Reasonable Utilizating Of Raw Material Containing MgO In The Burden Of BF

In recent years, appropriate MgO content is required in the slag of BF with the increase of overseas iron ores. At the same time, it is the requirement of smelting low-Si hot meltal and smelting some special iron ores.Aim at this problem, effects of the materials containing MgO on sintering process, pellet process and the metallurgical properties of sinter and pellet were studied in this paper. By the EPMA, X-ray diffraction and thermodynamic analysis, existent shapes of MgO in iron ore before and during its reduction process were discussed. We also studied the melting properties of the slag containing MgO. On the basis of above study, softening and melting properties of three kinds of burden structure were conducted. We chosed the best burden structure for testing production. Then the technical index had been improved significantly.The main contents and achievements of the paper include:(1) MgO content is increased properly, the properties of fluidity, desulphurizing and excepting alkali are improved. MgO content should be about 8-10%.(2) With the increase of MgO content, utilization coefficient of sinter pot, the yield, strength and grade of sinter decrease. But the low-temperature disintegration properties can be improved. If the content of MgO is decreased, we should take some measures to restrain the disintegration of sinter.(3) A temperature range about high-pressure was defined in this paper. When the MgO content increases from 1.3% to 3.0%, the temperature range of sinter (R=1.36) increases from 50℃to 80℃, that of sinter (R=1.76) increases from 168℃to 218℃. Therefore, the sinter with high basicity and high MgO content will take a wide temperature range with bad gas permeability. Then the cohesive zone becomes thicken, and the airflow becomes foul-up. It isn't favourable to operation of BF.(4) The properties of pellet with MgO were studied in this paper. When the content of MgO is lower than 2.0%, MgO has no obvious effects on the strength and drum index of pellet, but it has obvious effects on metallurgical properties in high temperature. When the MgO content increases from 0.6% to 1.8%, RDI+3.15 increases from 62.2% to 75%, Ri increases from 45% to 53%(reduction condition:900℃, for 1 hour), and the position of cohesive zone can be declined. (5) The relative free-swelling properties was studied under the condition of Ri=40%. With the MgO content increases from 0.6% to 1.8%, the relative free-swelling index RSI decreases from 23% to 20% when magnesite or the fine ore with high MgO content is added. But RSI increases from 23% to 32% because of the effect of Ca when dolomite is added. So, though MgO can improve metallurgical properties of pellet, dolomite shouldn't be added in pellet production based on the above analysis.(6) Softening and melting properties of three kinds of burden structure were studyed in this paper. Thereinto, the best softening and melting properties is the burden structure (sinter with low MgO content and pellet with high MgO content are mixed). This kind of burden structure not only can improve metallurgical properties of sinter and pellet, but also can decrease the temperature range of cohesive zone (TD-T10) and high-pressure zone (T2-T1).(7) On the basis of laboratory researches, the burden structure (sinter with low MgO content and pellet with high MgO content are mixed) was tested in practical production. The results of testing production shows that technical index can be improved significantly with the decrease of MgO content in sinter raw material. Compare with the base period, utilization coefficient of sinter machine increases 1.46%, pressure of burden decreases 4.82%, and the production of BF increases 0.66% in the testing period.Summarizing the above results, it is founded that the burden structure (sinter with low MgO content and pellet with high MgO content are mixed) is the best favourable to modern operation of BF. The production of pellet with MgO can take the measure of adding magnesite or adding fine ores with high MgO content. In this paper, the result of research can not only ensure proper MgO content in slag, but also improve metallurgical properties of burden. It provides important reference value for the production of excellent iron ores, for improvement of metallurgical properties of slag, for reasonable process of adding MgO in BF, for optimizing ironmaking technology, and for achieveing integrated innovation.