Causes of Damage to Hot Blast Furnace Lining

The cause of damage to the hot blast furnace lining is that when the dust content and operating temperature are constant, the choice of clay bricks reflects the relatively low melting temperature of the product, which produces a thin glass layer on the surface of the bricks and penetrates deep into the interior through the capillary tube, with a larger Corrosion depth; the maximum static load at the bottom of the regenerator checker brick is up to 8kg/cm, and the static load at the bottom lining of the combustion chamber is up to 4~5kg/cm. The pressure the furnace roof arch foot bricks bear is 02~20kg/cm². Under the load of mechanical equipment and continuous high temperature, the brickwork will produce shrinkage deformation and industrial cracks, endangering the service life of the hot blast furnace.

The structural types of hot air stoves are different, and the damage to the lining is also different. The most easily damaged part of the internal combustion hot blast stove is the partition wall, while the external combustion hot blast stove is the vault and bridge between the two rooms. The root causes of damage mainly include the following three aspects:

1. The effect of thermal stress. A hot air stove is a heat exchanger. When heating, the combustion chamber temperature is very high, and the furnace top temperature can reach 1500~1560℃. The temperature slowly drops from the vault along the furnace walls and checker bricks; during air supply, high-speed cold air is blown in from the bottom of the regenerator and gradually heated. Therefore, the lining of the hot air stove and the checkered brick room are often subject to rapid changes in cooling and heating. Under the influence of thermal stress, the masonry can crack, crack, and fall off. In particular, the partition walls of internal-combustion hot blast furnaces are prone to loosening and toppling of masonry, leading to “short circuit failures” and forcing the furnace to be shut down for repairs.

When the structural design is unscientific or the operation is improper, the destructive effect of thermal stress is higher. For example, if the heating cycle is too long and the temperature of the bottom checker bricks and furnace walls is too high, the temperature will drop during the air supply, that is, the temperature difference between hot and cold alternating is too large, resulting in cracking of the refractory brick masonry, deformation of the furnace grate, and even column movement.

2. Chemical attack. There are certain amounts of alkaline oxides in the gas and combustion air. The ash after combustion contains 20% iron oxide, 20% zinc oxide, and 10% alkaline oxide (mainly potassium oxide). Most of these substances are expelled from the oven, but some components remain adhered to the masonry surface and penetrate the brickwork. Over the years, its depth has reached around 20mm. At the same time, these substances undergo chemical changes with the components of refractory bricks to produce attenuating aluminosilicates, which change the volume of the bricks, destroy the structure, crack, reduce strength, and sustain high-temperature application performance.

It should be pointed out that at the upper end of the regenerator, chemical corrosion is severe, and the degree of damage varies depending on the dust content, operating temperature, and materials. When the dust content and working temperature are constant, the choice of clay bricks reflects the relatively low melting temperature of the product. A thin glass layer is produced on the surface of the bricks and diffuses into the interior through the capillary depth. The corrosion depth is relatively large; the choice of high when using aluminum bricks, the melting temperature of the product is relatively high, adhering to the brick surface and continuing to grow; when choosing silica bricks, the reaction product is easy to volatilize, the brick surface is smooth, and there is less corrosion. In addition, because the checker brick is heated on all sides, it is affected by chemical corrosion

In recent years, due to the selection of new gas cleaning machines, the dust content of gas has been reduced to 10mg/m³. Therefore, the degree of chemical corrosion has been reduced to a certain extent. At the same time, the widespread use of high-quality refractory bricks has also improved the ability to resist chemical corrosion.

3. The effect of mechanical equipment load. A hot air stove is a high-rise building. The maximum static load at the bottom of the regenerator checker bricks is 8kg/cm, the maximum static load at the bottom lining of the combustion chamber is 4~5kg/cm, and the pressure of the furnace top arch foot bricks is 0.2~2.0kg/cm². Under the load of mechanical equipment and continuous high temperature, the brickwork will produce shrinkage deformation and industrial cracks, endangering the service life of the hot blast furnace.