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Damage Mechanism Of Carbon Bricks For Blast Furnace And Blast Furnace
Jan 21, 2019

As we all know, carbon refractories (such as carbon bricks) are widely used in blast furnace bottoms because of their high thermal conductivity, strong slag resistance, high temperature strength, good thermal shock resistance, and large size. It is important to determine the service life of the blast furnace, such as the hearth, to meet the requirements of the use conditions such as overhaul of 1600 °C.


 


The lining of each part of the blast furnace is different in operating conditions using carbon/graphite refractories, so the damage state is also different. Careful observation of the blast furnace damage characteristics of WISCO, made the following summary:


(1) The upper three layers of carbon bricks in the furnace carbon bricks are gradually eroded in the production with the high aluminum brick lining above the carbon bricks. When the furnace is overhauled, the residual thickness of the upper bricks is generally only 400~800mm. The carbon bricks in the fourth layer to the center line of the iron gate tend to erode less, but the carbon bricks around the slag iron gate are generally highly eroded.


(2) The erosion speed of the furnace carbon brick below the iron mouth is greatly accelerated, and the thickness of the residual carbon brick in the hearth is only 200~400mm when the mushroom erosion is overhauled.


(3) The interior of the hearth carbon brick lining generally has serious annular erosion joints. Some form annular cavities, and some annular seams with carbon bricks become powder, and some become loose, and the strength is greatly reduced. The width of the circumferential seam is generally 200~500mm. The width of the ring is narrow and narrow into a horn shape, and the lower part extends to the erosion line of the furnace bottom. Some of the holes are connected with the mushroom erosion zone of the hearth, and the slag iron can enter the ring seam zone.


(4) The erosion characteristics of the carbon brick at the bottom of the furnace are: the middle of the furnace bottom is protruded, and the carbon brick under the furnace brick lining is eroded into an annular groove, and the depth of erosion is 300~500mm deeper than the center to the water-cooled thin bottom of the full carbon brick. The maximum erosion depth is 2.3~2.5m.


(5) Among the brick joints with carbon bricks at the bottom of the furnace, there are many iron pieces with a thickness of 2~10mm and a depth of about 500mm, and the thickest is up to 40mm, which shows that this is also a kind of erosion phenomenon that cannot be ignored.


 


The reasons for the damage of the blast furnace lining carbon bricks are various, especially because the blast furnace lining carbon bricks increase the stress with the blast furnace efficiency. The blast furnace bottom and the furnace carbon lining reflect the comprehensive process. And it is composed of a combination of thermochemical erosion and thermomechanical erosion. The mechanism of erosion is:


(1) Metal penetration. The penetration of molten iron will change the physical parameters (performance) of the carbon brick material.


(2) Carbon bricks are dissolved. The carbon entering the melt causes the carbon brick to melt in the carbon-saturated molten iron.


(3) Flow of zinc and alkali molten products. This leads to an increase in mass transfer and thermal conductivity and a loss of carbon from the working surface.


(4) The deposition of stress metal causes an unstable heat flow in the lining, thereby forming cracks and causing flaking damage.


These mechanisms are not single, but integrated and mutually reinforcing, resulting in the destruction of carbon bricks.


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