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The role and selection conditions of rotary kiln refractory

 

  Rotary kiln refractory brick, also called kiln brick, is a layer of refractory material filled inside the kiln cylinder. Its main functions are:

  1. Reduce the chemical corrosion and mechanical wear of the high temperature gas and materials on the cylinder and protect the kiln shell.

  2. Acting as a heat transfer medium The kiln brick can absorb a part of the heat from the gas and transmit it to the material in different conduction and radiation ways.

  3. Kiln bricks can also be insulated and heat-reduced to reduce heat loss in the kiln.

  Refractory bricks can be divided into the following categories according to their materials:

  1. Clay brick (insulation brick): used in the area of ​​preheating calcination belt, the refractoriness is under SK35;

  2. High-aluminum brick: Its main component is Al2O3. The higher the content, the higher the refractoriness of the refractory brick, and the better the peeling resistance, thermal conductivity, mechanical strength and chemical corrosion resistance. However, high alumina bricks have a large reversible expansion and are more resistant to slag than salt-based fire bricks. Generally used in calcination zones (transition zones). The commonly used fire resistance index is SK37. Use SK37 or 36 for the cooling belt.

  3. Salt-based fire bricks: Salt-based fire bricks have high chemical resistance to ash and slag at high temperatures, have good performance of hanging kiln skin, and the kiln skin is relatively firm. Because the brick and the kiln skin are integrated into one body, if the kiln skin is falling, some of the kiln bricks will fall with the kiln skin, and the aluminum slabs with higher peeling resistance are worse.

  Whether the type of refractory bricks and the quality and fire resistance of the selected refractory bricks are appropriate, the quality of the bricks will affect the life of the kiln bricks. The life of the refractory brick will directly affect the cost of the rotary kiln maintenance and the level of production. This shows the importance of refractory bricks.

  According to the different parts of the refractory used in the kiln, the main requirements of the rotary kiln for the kiln brick are:

  1. High temperature resistance, the temperature in the kiln is above 1000 °C, which requires that the refractory brick can not be melted at high temperature, and must maintain a certain strength under the melting point. At the same time, there are still long-term exposure to high temperature and still have a fixed volume and other characteristics.

  2. The thermal vibration stability is good, that is, the ability to resist the violent change of the kiln temperature without being damaged. In the case of unstable operation of the kiln, the open kiln and the rotary kiln, the temperature change in the kiln is relatively large, which requires the kiln brick to be cracked or peeled off under the condition of drastic changes in temperature. This also requires that the kiln temperature be stabilized as much as possible during operation.

  3. It is resistant to chemical attack. When it is fired in a rotary kiln, the ash, slag and steam formed will cause great erosion to the kiln brick.

  4. The wear resistance and mechanical strength are good, the sliding of the feed in the kiln and the friction of the dust in the airflow will cause great wear on the kiln brick. This is especially true in the early days of the kiln, when there is no kiln skin protection in the kiln. The kiln bricks are also subjected to the expansion stress at high temperatures and the stress caused by the elliptical deformation of the kiln shell. Kiln bricks are required to have a certain mechanical strength.

  5. The kiln brick has good performance in hanging kiln skin. The kiln skin is hung on the kiln brick and has a great protective effect on the kiln brick. If the kiln brick has good kiln skin performance and the kiln skin can maintain a long time, the kiln brick can be protected from erosion and wear.

  6. The porosity is low. If the porosity is high, the corrosive kiln gas will penetrate into the kiln brick to condense and destroy the kiln brick, especially the alkaline gas.

  7. Thermal expansion stability is better. The thermal expansion coefficient of the kiln shell is greater than the thermal expansion coefficient of the kiln brick. However, the temperature of the kiln shell is generally around 280-450 °C, and the temperature of the kiln brick is generally above 800 °C, and the temperature in the firing zone is more than 1300 °C. In this way, the thermal expansion of the kiln brick is still larger than that of the kiln shell, and the kiln brick is easily peeled off by compressive stress.

  When selecting refractory bricks, it is generally selected according to the temperature and load of each belt. It should be noted that the expansion coefficients of kiln bricks and kiln cylinders are 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 is also reduced, which will reduce the output of the kiln. The thinner the kiln brick is, the larger the effective volume is, and the heat dissipation of the kiln shell is also more harmful. The damage of high temperature to the equipment and the waste of energy are relatively large. At present, the most used in the world are two series of bricks, ISO series (international standard) and VDZ series (German standard). In fact, the materials of both are the same, but the specifications are different. The ISO series of bricks are larger and thicker, with fewer brick joints and are not convenient to handle and operate. The VDZ series of bricks are relatively small and thin, which is conducive to operation and easy to squeeze, but the strength is small and the brick joints are more. In general, the ISO series of refractory bricks can be used to uniform specifications, which can reduce the amount of spare parts and save investment.

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