According to the different parts of refractory used in the kiln, the main requirements of rotary kiln for kiln bricks are as follows:
- Strong high temperature resistance. No matter the firing condition in the kiln is good or bad, the temperature in the kiln is above 1000 ℃, which requires that the refractory brick cannot melt at high temperature and maintain a certain strength below the melting point. At the same time, it also has the characteristics of fixed volume after being exposed to high temperature for a long time.
- Good thermal vibration stability, i.e. good ability to resist drastic changes in kiln temperature without being damaged. When the kiln is stopped, opened and the operation of the rotary kiln is unstable, the temperature in the kiln changes greatly, which requires that the kiln bricks cannot crack or peel off when the blast degree changes sharply. This also requires that the kiln temperature be as stable as possible during operation.
- Strong chemical corrosion resistance. When fired in the rotary kiln, the ash, dissolved slag and steam formed will greatly erode the kiln bricks
- Good wear resistance and mechanical strength. The sliding of feed in the kiln and the friction of dust in the air flow will cause great wear to the kiln bricks. Especially in the early stage of kiln opening, especially when there is no kiln skin protection in the kiln. Kiln bricks also bear the expansion stress at high temperature and the stress caused by elliptical deformation of kiln shell. Kiln bricks are required to have certain mechanical strength.
- The kiln brick has good performance of hanging kiln skin. The kiln skin is hung on the kiln brick, which has a great protective effect on the kiln brick. If the kiln brick has good performance of hanging kiln skin and the kiln skin can be maintained for a long time, the kiln brick can not be eroded and worn.
- The porosity should be low. If the porosity is high, it will cause corrosive kiln gas to penetrate into the kiln bricks, condense and destroy the kiln bricks, especially alkaline gas.
- Good thermal expansion stability. Although the thermal expansion coefficient of kiln shell is greater than that of kiln brick. However, the kiln shell temperature is generally about 280-450 degrees, while the kiln brick temperature is generally more than 800 degrees. In the firing zone, the temperature is more than 1300 degrees. In this way, the thermal expansion of kiln brick is still larger than that of kiln shell, and kiln brick is easy to peel off due to compressive stress.
2、 The type and selection of refractory brick, whether the quality and fire resistance characteristics of refractory brick are consistent, and the quality of brick laying will affect the service life of kiln brick. The service life of refractory brick will directly affect the maintenance cost and output of rotary kiln. This shows the importance of refractory bricks. When selecting kiln bricks, they are generally selected according to the temperature and load of each belt. It should be noted that the expansion coefficient of kiln bricks and kiln barrel should be relatively close. The greater the thickness of the kiln brick, the better the effect of heat insulation of the kiln shell, but the effective cross-sectional area in the kiln will be reduced, which will reduce the output of the kiln. The thinner the kiln brick is, the larger its effective volume is, but the more harmful the heat dissipation of the kiln shell is. The damage of high temperature to equipment and the waste of energy are relatively large. At present, two series of bricks are used most in the world, namely ISO system (International Standard) and vdz system (German standard). In fact, the materials of both are the same, but the specifications and sizes are different. The bricks of ISO system are larger and thicker, with less brick joints, but it is inconvenient to handle and operate. The bricks of vdz system are relatively small and thin, which is convenient for operation and easy to squeeze, but the strength is small and there are many brick joints. The ISO system shall be used to unify the specifications as much as possible, with a height of 220mm and a width of 200mm, which can reduce the amount of spare parts and save investment. Refractory bricks can be divided into the following types according to their different materials: 1. Clay brick (thermal insulation brick): used in the area of preheating calcination belt, the fire resistance is below sk35. 2. High alumina brick: its main component is Al2O3. The higher the content, the higher the fire resistance of refractory brick, and the better the spalling resistance, thermal conductivity, mechanical strength and chemical corrosion resistance. However, high alumina brick has great reversible expansion, and its slag resistance is worse than that of base fire brick. It is generally used in calcining belt (transition belt). The commonly used fire resistance index is sk37. Use sk37 or 36 in the cooling zone. 3. Basic firebrick: basic firebrick has high chemical resistance to ash and slag at high temperature, good hanging performance of kiln skin, and the kiln skin is firmly attached. Because the bricks and kiln skin are integrated, if the kiln skin falls, part of the kiln bricks will also fall with the kiln skin, with high spalling resistance and poor aluminum bricks.
It mainly has two kinds of bricks:
a. Dolomite brick: the main component of dolomite brick is periclase (MgO), and its component is close to that of raw meal. Therefore, this kind of brick has good kiln skin hanging performance and will not react with raw meal. It has high fire resistance and volume stability, but when the kiln skin falls, part of the kiln brick may fall together with the kiln skin. Be careful to prevent ashing when using. Special attention shall be paid to waterproof when kiln bricks are transferred and stored.
b. Magnesia chrome brick: the main component of magnesia chrome brick is chrome ore. It has good spalling resistance and mechanical strength. It is generally used in the firing belt of rotary kiln. In the firing zone, it needs three conditions: thermal stress, mechanical stress and chemical erosion. Therefore, the requirements for kiln bricks in this belt are relatively strict. In the past, chrome magnesia brick was generally used, which has the advantages of high fire resistance, good alkaline chemical corrosion resistance and so on. However, the content of chromium in magnesium chromium brick is relatively high. When the fire brick is discarded, the chromium metal will be lost together with water and enter the environment to cause pollution. At present, the amount of chrome magnesia brick is gradually decreasing and has been replaced by spinel brick. Hualien plant will place the waste kiln bricks in the mine and mix them with limestone, which will be recycled as raw materials in the plant to reduce waste and pollution.
- Types of refractory mud refractory mud can be mainly divided into the following categories: A. castable fire mud: also known as gas curable fire mud. It is used in the burner at the kiln head as a protective refractory layer and in some parts of the preheating machine as refractory materials, which are generally constructed by grouting. B. insulating fireclay: it is used for repairing and leveling the deformed plane of the kiln shell, or for thermal insulation of the roof of the cooler. C. refractory clay: also known as thermal setting fireclay, it is mainly used in bricklaying and when using refractory clay, Glass water must be added for stirring (sodium silicate, water, NaSiO3, H2O). Generally, didotect135 (high temperature resistance above 1350 ℃), sk34 is used at the kiln tail. Didotect150 (high temperature resistance above 1500 ℃), sk35couprit160h is used at high temperature, which is mainly used in kilnburnerhead couprit135h, which is mainly used in preheater and cooler.
- Selection of kiln refractory bricks A. selection of refractory bricks in the kiln #1 kiln use high alumina bricks after 35m, use high alumina bricks in the outlet cooling zone, and use magnesia chrome bricks or spinel bricks in other places# High alumina bricks are used in kiln 2 after 43M, and magnesia chrome bricks or spinel bricks are used in other places# High alumina bricks are used in kiln 3 after 35m, and magnesia chrome bricks or spinel bricks are used in other places. Refractory mud is used in the #3 kiln outlet cooling zone. Near the tire ring, in order to avoid excessive heat transmission and lead to the thermal expansion of the kiln shell, which causes the kiln shell to bear large mechanical stress. The firebrick here is made of two layers of high alumina brick and protective layer brick. b. Selection of refractory bricks inside the cooler
For medium fire resistant bricks, the temperature of clinker in the front section is different from that in the rear section. The temperature in the front section is higher and the temperature in the rear section is lower. The selected refractory bricks are also different. The high brick is mainly used in the thermal insulation section, and the high brick is mainly used in the thermal insulation section. In the cooler, where the fire brick contacts and rubs with the material layer, the fire brick is more vulnerable to high temperature and friction, and the quality requirements of fire brick are more strict. c. Selection of refractory materials in the preheating machine. The main refractory materials are insulating bricks and cast mortar of the same grade. In the preheating machine, the refractory material requires light material, enough fire resistance and fire resistance. In the preheating machine, the air flow entrains powder and wears the inner wall of the cyclone, especially at the corner or direction change of the air duct. The bottom of the hammer body of the cyclone also has deacidification high-temperature raw material in contact with the cylinder wall. There is coal injection in the rising pipe of kiln gas and the tertiary air pipe for the decomposition of carbonate in the preheater. The temperature is also relatively high, and the requirements for refractory materials here are more strict.