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The furnace wall (cylinder) carbon brick is damaged
At present, the blast furnace walls (cylinders) used in our country are basically divided into three categories: one is the introduction of foreign carbon bricks and related technologies to ensure that the service life of the furnace walls (cylinders) meets the basic requirements of enterprise production. For example, Baosteel No. 1 blast furnace uses Japanese large carbon Bricks, the first generation furnace is more than ten years old, but it still needs to use vanadium-titanium ore to protect the blast furnace walls; the second is to use a composite furnace bottom that combines high alumina bricks with large roasted carbon bricks, which is among the backbone steel companies in my country. Generally speaking, due to the intensification of production capacity and the enlargement of furnace capacity, the service life of this kind of furnace wall (cylinder) is only 2 to 7 years; the third is the self-baking carbon brick furnace wall (cylinder), which is widely used in many small and medium-sized blast furnaces. The furnace age can reach 6 to 10 years, which can basically meet the production needs of enterprises. The damage to the composite furnace bottom combining high alumina bricks and large roasted carbon bricks and the furnace wall (cylinder) of roasted carbon bricks has two prominent features, namely, annular fracture and abnormal erosion.
01Mechanical flushing
When the molten iron comes into contact with the carbon bricks, the penetration of the molten iron into the carbon bricks, the mechanical erosion of the molten iron, and the dissolution of the carbon will occur. Fluctuations in furnace temperature lead to embrittlement and cracking, which damages the structure of the carbon bricks, leading to erosion.
02Thermal stress
Since there is a break point in the furnace shell at the hearth and the roasted carbon bricks are large in size, the temperature difference between the outer two sides of the furnace lining is large after the blast furnace is opened, causing thermal stress in the carbon bricks in the furnace lining. The hot end of the carbon brick is affected by thermal expansion, the cold end is restricted by the furnace shell, and the difference in the expansion coefficient of the carbon brick and the high alumina brick in the composite furnace bottom also causes its thermal stress to increase. The interaction of various thermal stresses causes ring fracture (ring cracking). An investigation was conducted on the damage to the blast furnace wall (cylinder) after the furnace was shut down for maintenance. The results showed that the hot end side of the carbon brick was broken upward. Judging from the fracture surface, it is obviously damage caused by mechanical action. The fracture of this kind of ring seam is relatively clear, and it is obviously a crack caused by mechanical damage, not a crack caused by embrittlement.
03alkali metals
Alkali metals also have a great damaging effect on it. The main locations where it occurs are the outside of the ring crack, the cooling stave and the leakage location of the tuyere. The investigation of multiple damage to the blast furnace wall (cylinder) showed that the carbon bricks outside the ring crack were in the form of loose powder, and there were caves in them.
04The quality of brick lining and construction is poor
In recent years, due to various reasons, the quality and construction quality of blast furnace brick linings have been unsatisfactory. As a result, the erosion and shedding of the brick lining are accelerated under the combined action of multiple factors. For example, a certain steel plant had many abnormalities only half a year after its overhaul and had to stop production for maintenance. During the maintenance process, not only was it discovered that the furnace wall (cylinder) was severely eroded, but also a large area of brick lining fell off the furnace body.