The main function of the rotary kiln refractory lining is to protect the barrel of the rotary kiln from high-temperature gas and high-temperature materials and to ensure normal production. According to the different types of calcined materials, the use conditions of kiln linings are also different. For cement rotary kiln, dolomite rotary kiln, active lime rotary kiln, alumina rotary kiln, chemical waste rotary kiln, a layer of stable kiln crust should be hung on the burning zone of rotary kiln to protect the rotary kiln bricks. However, there is no need to hang the kiln crust on the rotary kiln refractory lining which calcined metalized pellet and oxidized pellet. In addition, to use refractory bricks made of wear-resistant refractory materials, measures such as preventing ring formation and repairing should be considered to protect the inner rotary kiln brick lining.
Refractory Lining in Cement Rotary Kiln
Cement rotary kiln is a typical type of rotary kiln that needs to hang kiln crust. Kiln crust refers to the protective layer that materials adhere to the surface of the lining bricks of the rotary kiln. It can prevent chemical erosion and mechanical wear of high-temperature materials, and play the role of heat insulation and heat preservation, which is an important factor to improve the rotary kiln refractory lining’s service life.
The formation of a kiln crust is a complicated physical and chemical process. When the material is close to the burning zone, the flame will gradually shorten, appropriately increase the exhaust and burning volume, control the high-temperature flame, and burn the refractory bricks into a semi-melted state so that the chemical components in the bricks and the chemical components in the clinker react and bond with each other. When the temperature decreases, the product after reaction forms a block with the brick and forms kiln crust.
This process requires that the grain size of the kiln crust should be small and uniform, with good integrity and firmness without falling off. If the kiln crust of the rotary kiln refractory lining cannot be hung, the semi-melted material will corrode the inner lining very seriously. If the kiln crust is not hung firmly and falls off frequently, the inner rotary kiln brick lining will be subjected to rapid cold and heat, which will be severely damaged.
Protection of Rotary Kiln Bricks in Operation
In industrial production, the use cycle of refractory bricks installed on the burning zone of the rotary kiln is very short. The damage of rotary kiln brick often leads to planned out of kiln maintenance, which is the key factor affecting the good, high yield, low consumption, and annual operation rate of sponge iron kiln, carbon kiln, and other rotary kilns.
Erosion causes of rotary kiln bricks
- Whether it is a wet process kiln or a new dry process rotary kiln, during the material calcination process, the surface of the refractory lining in cement rotary kiln is subjected to periodic thermal shocks, and thermal stress will damage the refractory bricks on the lining of the rotary kiln.
- The kiln lining also bears the alternating radial and axial mechanical stresses of the brickwork caused by the rotation of the kiln, as well as the erosion and wear of the calcined materials.
- During the production process of the rotary kiln, silicate melt will be produced, which will interact with the surface of the rotary kiln refractory lining refractory brick to form an initial layer in a high-temperature environment. The silicate melt penetrates into the interior of the refractory brick and bonds with it, thereby changing the chemical composition and phase composition of the refractory brick and reducing the technical performance of the rotary kiln brick lining.
How to avoid the corrosion of rotary kiln bricks
- Slag resistance refers to the ability of refractory materials to resist chemical attack. The slag resistance is very important when the initial layer of the kiln crust is formed and when the material is highly viscous or when the local high temperature causes the kiln crust to fall off.
- Porosity and thermal conductivity play an important role in forming the initial layer of kiln crust. When the kiln crust on the rotary kiln refractory lining is partially peeled off, the refractory with higher porosity and thermal conductivity will help the kiln crust to be repaired in time. But at the same time, it may show a great destructive effect, causing the thin layer of refractory bricks to peel off.
- The fluctuation of the raw material feed rate is more harmful to the kiln linings. When there is too much material in the kiln, the exhaust air volume at the tail of the rotary kiln has to be reduced, and the amount of pulverized coal is increased for forced firing, which will increase the heat load of the burning zone rapidly and cause serious damage to the kiln lining. When there is too little incoming material in the kiln, the pulverized coal flame will tilt down significantly, and the kiln crust in this area will fall off and become thinner at high temperatures. If the air volume and coal consumption are not adjusted in time, the kiln crust and refractory bricks are easily burnt.
|Regular magnesia-chrome brick||Semi – directly bonded magnesia-chrome brick||Direct-bonded magnesia-chrome bricks|
|Refractoriness under load/ ℃||≥ 1530||≥ 1550||≥ 1580|
|Compressive resistance/Mpa||≥ 20||≥ 35||≥ 40|
|Volume density//kg·m -3||2850||2900||≥2980|
|Apparent porosity/%||23~24||20~22||≤ 19|
|MgO/%||55~60||≥ 65||≥ 70|
|SiO2/%||≤ 5.5||≤ 4.0||≤ 3.0|