The kiln skin of cement rotary kiln is formed by clinker or dust changing from liquid or semi-liquid phase to solid. It is the main component of cement rotary kiln and plays an irreplaceable role in cement production. As a result, the peeling off of the cement rotary kiln skin will greatly reduce the overall performance of the cement rotary kiln equipment.
1. After the cement rotary kiln loses the protection of the kiln skin, when the heat load of the rotary kiln is too high, the hot surface layer matrix will melt at high temperature and migrate towards the cold surface layer, making the brick lining cold. The surface layer is densified, while the hot surface layer is loose and porous, making the cement rotary kiln less resistant to wear, impact, vibration and thermal fatigue, and prone to damage.
2. In the cement rotary kiln, there is no kiln skin protection for the brick belt. When the thermal system in the kiln is unstable, it is easy to produce a reduction flame or incomplete combustion, which causes reduction in the cement rotary kiln gas. The alternating changes with the oxidizing atmosphere cause the volume effects of shrinkage and expansion to occur repeatedly, causing holes in the bricks, weakening the structure, reducing strength, and chemical fatigue of the bricks.
3. When the kiln is not operating normally or the kiln skin is unstable, the alkaline bricks are easily damaged by thermal shock. The sudden collapse of the kiln skin causes the temperature of the brick surface to increase suddenly, causing great thermal stress in the bricks. At the same time, when the kiln skin falls, it takes away the broken bricks on the hot surface layer, causing the bricks to be continuously damaged.
Therefore, during the production process of the cement rotary kiln, attention should be paid to the protection of the rotary kiln skin, which will extend the normal service life of the cement rotary kiln.
Knowledge expansion:
Cement rotary kiln hanging kiln skin: The rotary kiln is the main equipment for cement production. The cement rotary kiln is an inclined, rotating cylinder placed on several pairs of supporting wheels through several wheel belts. The inner wall is inlaid with refractory bricks. The raw meal powder is fed into the kiln barrel from the feeding pipe at the high end of the kiln tail barrel. Due to the tilt and slow rotation of the kiln barrel, the material rolls along the circumferential direction and moves from high temperature to low temperature along the axial direction. It is a compound movement of end-to-end movement. The raw materials go through preheating, decomposition, firing and other processes in the kiln. After the cement clinker is burned, it is discharged from the bottom of the kiln barrel and enters the cooler. The fuel is injected from the kiln head and burned in the kiln. The heat emitted heats the raw meal, causing the raw meal to be calcined into clinker. The hot air formed during the exchange with the material enters the kiln system from the kiln feed end, and is finally ejected from the kiln. The chimney vents into the atmosphere.
The rotary kiln is mainly composed of the kiln barrel, transmission device, support device, wheel blocking device, kiln head sealing device, kiln tail sealing device, kiln head cover, etc. The cylinder of the cement rotary kiln is a cylinder made of steel plates. In order to protect the cylinder of the rotary kiln, a layer of refractory bricks is built inside it as the kiln lining.
The rotary kiln is an equipment that integrates fuel combustion, heat exchange, high-temperature chemical reaction and air flow to transport materials. Since the gas temperature in the kiln is much higher than the material temperature, it is often maintained in the container. At high temperatures above 1450°C, every time the kiln rotates, the kiln lining surface is subject to periodic thermal shocks, with a temperature change range of 150-250°C, which generates thermal stress within the 10-20mm surface layer of the kiln lining; the kiln lining also withstands the effects of rotation. The resulting alternating axial and radial mechanical stresses on the brickwork, as well as the erosion and wear of the calcined materials; because the silicate melt produced at the same time has a certain erosion effect on the refractory materials, it will cause the refractory materials to fall off, The surface temperature of the kiln body is too high or "red kiln".
The refractory bricks have limited refractory resistance and thickness. They cannot withstand the invasion of long-term high temperatures and the corrosion of chemical reactions of materials. In order to extend the service life of the refractory bricks, a solid layer is added to the surface. The protective layer is to hang a layer of clinker, which is called "kiln skin" by fire experts.
The purpose of hanging the kiln skin is to extend the service life of the fire bricks, protect the rotary kiln cylinder from damage, reduce heat loss outward, and improve thermal efficiency. Its specific functions are as follows:
1. Protect refractory bricks so that they are not directly exposed to high temperature and chemical erosion.
2. Store thermal energy, reduce heat loss from the kiln shell to the surroundings, and improve the thermal efficiency of the rotary kiln.
3. With sufficient heat transfer medium, when the kiln skin is exposed to the air and comes into contact with high-temperature air, it absorbs heat through radiation or convection. When the kiln skin contacts the material at the lower part, Heat is transferred to the raw material by conduction.
4. The surface of the kiln skin is rough, which can reduce the flow speed of the powder and prolong the reaction time of the material in the kiln.