With the continuous progress of the cement industry, rotary kiln, as the core cement equipment of cement production line, is developing towards a large scale. Compared with the traditional rotary kiln, its technology is more complex, and the requirements for rotary kiln design and accessories are higher. The rotary kiln refractory lining is a layer of refractory material installed inside the kiln cylinder, which plays a protective role in many aspects, and is an important part of cement rotary kiln.
- It can prevent direct damage to the kiln cylinder by high-temperature flame or high-temperature airflow.
- It prevents erosion of the kiln body by harmful substances (CO, SO2), materials, or airflow.
- It reduces the temperature of the kiln body and protects the kiln from being oxidized and corroded.
- It has the function of heat preservation and can reduce heat loss.
Refractory brick is a kind of rotary kiln lining. At the early time, due to the small size of the kiln body and low calcination temperature, we mainly used high-alumina brick and clay brick as the lining. In the 1960s, the kiln lining at high-temperature zone was replaced by alkaline bricks. With the large-scale of rotary kiln, its sintering temperature increases, meanwhile, the cylinder rotating speed and the diameter also increase, all of which cause certain damage to the rotary kiln refractory brick. Besides, the corrosion of alkali, sulfur, chlorine, and other volatile substances, as well as some erosive wear, aggravate the wear degree of refractory bricks inside the kiln body. After a summary, they can be respectively classified as chemical damage, mechanical stress damage, and thermal stress damage. In most cases, they act on the refractory lining in combination.
Chemical Damage: It is caused by the erosion of silicate, ferrate, and alkali salt, accounting for 36%.
Mechanical Stress Damage: It is caused by the deformation of kiln body and thermal expansion of bricks, accounting for 37%.
Thermal Stress Damage: It is caused by overheating or thermal shock, accounting for 27%.
Therefore, if we want to ensure the smooth running of cement rotary kiln and prolong its service life, we should select the right kind of refractory bricks according to their damage mechanism in different parts of the rotary kiln body.
How To Choose Cement Rotary Kiln Refractory Bricks?
Through our research on the damage mechanism of the rotary kiln refractories, we conclude that the refractory lining brick with high quality should meet the following conditions:
- Strong resistance to high-temperature clinker and alkali salt erosion.
- Good structural toughness against thermal stress and mechanical stress.
- The brick ingredients meet environmental requirements.
In addition, we should combine the structure of cement rotary kiln to choose the refractory brick. The cement rotary kiln can be generally divided into preheating zone, lower transition zone, upper transition zone, sintering zone, and cooling zone. The length, temperature, and function of each zone are different, so the selection of refractory lining brick should meet the requirements of each area.
Preheating Zone: phosphate high-alumina brick, anti-stripping alumina brick, and alkali-resistant brick are generally used in this zone.
Lower Transition Zone: the temperature in this area is relatively low, so the thermal conductivity of the refractory brick is required to be low. Both anti-stripping alumina brick and silicon mullite brick are frequently used in this zone. Of the two bricks, the performance of silica mullite brick is superior, its service life is about 1 time longer than the anti-spalling high alumina brick, but the price is about 1.5 times higher.
Upper Transition Zone: the coating formation in this zone is unstable, the kiln lining is required to has good thermal shock resistance, low thermal conductivity, and strong wear resistance. Magnesia alumina spinel brick is a good choice, but its thermal conductivity is relatively high. By contrast, the wear resistance and overall performance of the silica-alumina brick are equivalent to the magnesia alumina spinel brick, and its thermal conductivity is low.
Sintering Zone: the sintering zone has a high calcining temperature and intense chemical reaction, the lining brick in this area should have a strong ability to resist the erosion of clinker, SO3, and CO2. Magnesia-chrome brick has a poor performance and is easy to react with clinker to produce Cro3, resulting in short service life. The commonly used magnesia iron spinel brick has a great effect but a high cost. Therefore, comprehensive consideration, we had better choose periclase spinel compound brick in this area.
Cooling Zone: the temperature fluctuates greatly in this zone and the coating formation is unstable. The rotary kiln refractory lining should be wear-resisting and has excellent thermal shock resistance and low thermal conductivity. In recent years, we usually use silicon mullite bricks and anti-stripping abrasive brick.
According to the above analysis, we can select suitable refractory bricks for the cement rotary kiln, but the raw materials and fuels of each cement kiln may be different, we should make appropriate adjustments according to the characteristics of our rotary kiln.