On June 16, 2021, a blast furnace in a steel plant was equipped with three ball-type hot blast furnaces. The hot blast temperature continued to show a downward trend, the high-alumina balls were seriously bonded, and the resistance of the pebble bed increased.
1. Bonding degree of high aluminum ball
When the ball was poured for the first time, it was found that there was pulverization in the lower part of the pebble bed, and the bonding in the middle and upper parts was serious, and the higher the upper part, the more serious the bonding. The bonding body is large and is semi-circular along the furnace wall, the castable cannot slide off by itself, and supports the upper pebble bed, and the high-alumina ball cannot slide off by itself. In view of this situation, after research, it was decided to blast the bonded body and break it into zero. Even so, among the high-alumina balls cleaned out, the maximum diameter of the bond body is 30cm, which shows that the degree of bonding of the pebble bed is relatively serious. When blasting, it is necessary to consider that blasting may cause damage to the internal structure of the hot blast stove, especially the burner and the vault, so the blasting force is not easy to be too large. In the cleaned high-alumina balls, the roundness of some balls is seriously damaged, and the surface of the balls has many facets and pits. This part of the high-aluminum balls with serious deformation cannot be reused. Judging from the previous inverted balls, the amount of new balls added each time is about 1/3 of the total amount of balls.
2. Reason analysis
After discussion and analysis, the main reason for high alumina ball slag formation is that the dust removal system bag is damaged, resulting in a large amount of dust in the net gas. Using this kind of gas burning furnace naturally brings more gas ash into the hot blast stove. The reason for the damage of the bag has a lot to do with the material of the bag. The refractory castable material used in our factory is Fumex composite needle felt. The common temperature of this kind of bag is 260~280℃, and the highest temperature can reach 300℃ in an instant. Second, the temperature of semi-clean gas entering the bag box is too high.
The temperature of the top of the furnace exceeds the capacity of the cloth bag, causing the cloth bag to burn out. A large amount of unfiltered waste gas is directly used to burn the furnace. The gas ash contained in the waste gas enters the hot blast stove. At high temperature, CaO and SiO2 in the gas ash undergo chemical reaction. To produce substances with low susceptibility points, wear-resistant castables block voids or wrap high-alumina balls, and high-alumina balls are bonded to each other. After the above situation occurs, the gap between the high-alumina balls becomes smaller, which leads to an increase in the resistance of the pebble bed, and at the same time, the heat-exchange area of the high-alumina balls decreases, and the heat storage capacity decreases, which is directly manifested as insufficient air supply capacity.
The old balls poured out of the hot blast stove are re-installed into the hot blast stove through manual screening, and the old balls with smooth surface, no deformation and no cracks are put back into the hot blast stove for use. The total ball volume of the three hot blast stoves is about 580 tons. very large. According to the experience of pouring balls, about 65 tons of new balls need to be added to a hot blast stove each time the balls are poured, accounting for about one third of the total balls. The new balls are usually installed on the top of the ball bed.
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