Exploration and Solution of the Problem of Blast Furnace High Aluminum Slag

December 20, 2019

[China Aluminum Industry] blast furnace production practice shows that the slag Al2O3 content of more than 16% will have a greater adverse effect on the stability of the furnace condition, and even cause the blast furnace to malfunction. For example, No. 7 blast furnace of Wuhan Iron and Steel Company is a 3200m3 large-scale blast furnace with advanced equipment. After it was put into production, it has achieved very good operational indicators. However, as of June 2009, due to large fluctuations in the composition of raw materials, the quality of sintering deteriorated, and the content of Al2O3 in ores was high. The fluidity of iron deteriorated, and the slag iron could not be discharged in time, resulting in deterioration of the furnace condition, resulting in an abnormal condition of the furnace and causing a great loss to the blast furnace production. To this end, Wuhan Iron & Steel strives to explore effective measures to solve the problem of blast furnace high aluminum slag.

According to experience in production practice, when the Al2O3 content reaches 18% or more, it is not feasible to rely on high MgO slag to reduce the slag viscosity, because increasing the slag MgO content depends on increasing the proportion of the dolomite and other flux in the sinter, when the sinter When the content of MgO increases, the fluidity of the binder phase deteriorates. If the fuel consumption does not increase, the strength of the sintered ore will inevitably decrease. The conclusion of the laboratory study is that the content of MgO in the sinter is preferably 2.5%. Exceeding this range, the sinter index will tend to decrease. Therefore, it is necessary to study the appropriate blast furnace slagging system in order to cope with the excessively high Al2O3 content caused by uncontrolled raw material sources. There are two ways to reduce the viscosity: manganese plus manganese (MnO) and fluorite (CaF2). Since the addition of manganese will affect the content of Mn in pig iron, the method of adding the amount of fluorite should be studied.

In July 2009, the BF slag No. 7 blast furnace slag Al2O3 content was as high as 18.6% throughout the day and 22.81% higher, which seriously affected the fluidity of slag iron and the separation of slag iron, which directly led to the difficulty of slag iron discharge. Although many measures have been taken, such as adding manganese ore and hot-washing furnaces, due to the serious accumulation of hearths, the furnace condition has not improved for a long time and it was later decided to use fluorite to wash the furnace. From July 24 to July 28, 2009 and August 3 to 7, fluorspar was added. After the fluorspar was used up, the Mn ore was used again. A large amount of net coke is added during the washing to supplement the heat of the hearth. Judging from the effect of using, fluorite has a significant effect on the scrubbing of the shaft and the handling of the stacking of the furnace. After the addition of fluorite, the melting point of the slag is significantly reduced, the flowability of the slag is improved, and the slag removal effect is significant for the iron in front of the furnace, which plays a very important role in the recovery of the furnace condition.

It should be pointed out that although the addition of fluorite helps to improve the slag fluidity, fluorite has a serious effect on the cooling wall of the hearth furnace hearth, so the use of fluorite washing furnace should be very careful. When WISCO processed the piles of the 7th blast furnace in July 2009, fluorite was evenly added into the furnace through the charge. Fluorite was distributed throughout the material surface. The fluorite was in contact with the cooling system of the hearth and hearth at a large area. Caused a lot of damage to the tuyere, delayed the recovery time, and should be improved later when dealing with the accumulation of furnace slag caused by high Al2O3 in the slag.

Practice shows that CaF2 can reduce the viscosity of high Al2O3 slag, but CaF2 also damages the refractories in the blast furnace. Therefore, the use of CaF2 is generally due to the high Al2O3 content, large viscosity causing the hearth to be inactive, the furnace vats to accumulate, etc. use. In the case where the average daily Al2O3 content in the slag of Wuhan Iron & Steel is less than 18%, the CaF2 content is about 2.0%. If CaF2 is added for a long time during normal production, it is necessary to consider the problem of the refractory capacity of the blast furnace.

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