What are the working conditions and damage factors of refractory brick linings in various parts of the blast furnace?

The refractory bricks used in the blast furnace lining are the key to the life of the entire blast furnace. The operating mechanisms of each part of the blast furnace are different, their working environments are different, and the selection of refractory bricks for the furnace lining is very different.

01 furnace bottom

The working conditions of the furnace bottom are extremely harsh, and its durability is the decisive factor in the life of a generation blast furnace. The blast furnace bottom is under high temperature and high pressure conditions for a long time. The damage to the furnace bottom can be divided into two stages. In the early stage of opening the furnace, molten iron penetrated and floated the bricks to form a pan-shaped deep pit. The second stage was chemical erosion after the sintered layer was formed.

The conditions for molten iron to penetrate: first, it must bear the gravity of the slag iron and the material column, and the gas pressure; second, the existence of joints and cracks in the masonry bricks. When molten iron penetrates into the gap under high pressure, it cools slowly and solidifies at 1150°C. During the condensation of molten iron, graphite carbon is precipitated, and the volume expands, causing the gap to expand. In this way, the molten iron can penetrate very deep, and the bricks will float under the static pressure of the molten iron.

When the furnace bottom is eroded to a certain depth, the slag iron erosion gradually weakens. Under long-term high temperature and high pressure, the bricks lining the pit are partially softened and recrystallized to form a sintered layer with a thickness of about 700~1400mm. Small blast furnaces are as thin as many. The sintered layer can resist the penetration of molten iron, and the main cause of furnace lining damage is the reduction of SiO2 in the brick lining by [C] in the molten iron, but this chemical erosion rate is very slow.

02 hearth

The lower part of the furnace is where the slag and molten iron are stored. Its working conditions are similar to those of the upper part of the furnace bottom. The periodic accumulation and discharge of molten slag and the erosion of the furnace lining by high-temperature gas flow are the main damaging factors. In particular, slag iron often flows through the furnace lining near the slag mouth and taphole, causing more serious erosion. Furnace slag tends to be alkaline while commonly used aluminum silicate refractory bricks tend to be acidic, so chemical slag formation occurs at high temperatures, which is also an important destructive factor for the furnace lining.

In the tuyere zone above the hearth, high temperature is the main factor causing the damage of refractory bricks. This is the highest temperature area of the entire blast furnace, and the inner surface temperature of the furnace lining often reaches 1300~1900°C, so the high temperature resistance of the brick lining and the corresponding cooling measures are crucial.

03 hearth

The furnace bosh is located above the tuyere. This part is subject to strong thermal stress. Not only is the inner surface temperature of the furnace lining high, but the thermal shock caused by temperature fluctuations is very destructive. It also bears the slag and molten iron falling into the furnace hearth from above and the high-speed The erosion, chemical erosion and oxidation of the upward moving high-temperature gas flow, coupled with the pressure and friction of the charge and the huge impact force when the material collapses. In fact, a few months after the furnace was opened, the furnace lining here was quickly replaced by solidified slag skin. During normal production, this area is mainly protected by slag skin. The thickness of the furnace bosh slag skin mostly fluctuates in the range of tens to 100mm.

04 furnace waist

The furnace waist is close to the furnace belly, and the erosion effect is similar. The primary slag here contains a large amount of FeO and MnO, so the erosion effect of the slag is more prominent. Judging from the furnace shape, there are folded corners up and down the furnace waist, so the airflow scouring effect is stronger than other parts. If the edges are excessively developed and there is a lot of raw material powder, the destructive effect will be greater. The hearth waist structure generally has thick hearth waist, thin hearth waist and transitional form, and the degree of damage is also different.

05 furnace body

Since the height of the furnace body is relatively large, the factors causing damage to the lining of the upper and lower parts of the furnace body are also different. Mainly withstands: mechanical wear of furnace charge and gas flow; carbon deposition damage; damage of alkali metals and other harmful elements; erosion of fusible compounds, etc. Overall, the working conditions gradually deteriorated from top to bottom, and the degree of damage gradually intensified.

The temperature of the lower part of the furnace body is relatively high, so the influence of thermal stress is greater, and it is also corroded by the newly formed slag liquid. The temperature in the middle part of the furnace body has dropped, and the main factor that damages the furnace lining is the friction and erosion of the gas and the charge. In addition to being affected by this factor, the upper part of the furnace body is also affected by the impact of the charge. In addition, carbon deposition and alkali metal oxidation will seriously damage the entire furnace brick lining.

06 furnace throat

The furnace throat is subject to frequent collisions with furnace materials and erosion by high-temperature dusty coal gas flow. If the furnace lining at the furnace throat is damaged, the distribution and gas flow distribution will be out of control. In order to maintain its cylindrical shape from being damaged, it should have good impact resistance, so the furnace throat protection plate (also called steel brick) must be made of metal. Even so, it will still lose strength at high temperatures and undergo thermal deformation due to uneven temperature distribution. The damage is more serious when the gas leakage in the furnace is frequent.

From the overall perspective of the blast furnace lining, the lower part of the furnace body is currently the weakest link of the blast furnace. Although the working conditions here are better than those in the lower part, the service life is shorter because there is no protection from the slag skin. Our country's blast furnaces often use silicon-aluminum linings in this part, and the lining corrosion is serious, which becomes the main factor affecting the service life of the blast furnace. Often an intermediate repair is required between two major repairs to repair the furnace lining.