what are the factors that affect the service life of rotary kiln lining?

2023-11-15

The firing zone of a rotary kiln is a place where the materials used in the kiln lining are strictly controlled. The main factors affecting the service life of refractory bricks in the kiln zone are as follows:

1、 The influence of advantages in physical performance indicators on refractory bricks

Slag resistance refers to the ability of refractory materials to resist chemical erosion. When the initial layer of the kiln skin is formed in a rotary kiln, and when the material viscosity is too high or local high temperatures cause the kiln skin to fall off, slag resistance is very important.

Porosity and thermal conductivity play an important role in forming the initial layer of the rotary kiln skin, and refractory materials with higher porosity and thermal conductivity are helpful for timely repair of the kiln skin when it falls off locally. But at the same time, it may also exhibit a significant destructive effect, causing the thin layer of refractory bricks to peel off.

During the production process of refractory bricks, their physical and chemical changes generally do not reach the equilibrium state of calcination temperature and time, and there are also refractory bricks that are not fully calcined. Therefore, when they are no longer subjected to high temperature during the use of rotary kilns, most refractory bricks undergo irreversible re firing shrinkage due to the generation of their own liquid phase and the filling of pores. Therefore, the stability of the volume of refractory bricks at high temperatures should be considered when selecting fired refractory bricks.

Layered peeling on the hot surface is the main form of damage to the lining of the rotary kiln after thermal shock. If local peeling occurs simultaneously, it greatly shortens the service life of refractory bricks.

2、 The influence of calcination and fuel nozzle on refractory bricks.

When using coal as fuel, the volatile and ash content of coal play a decisive role and directly affect the shape of the flame. Coal powder with high volatile content and low ash content can shorten the black flame and form low-temperature long flame calcination. It is generally beneficial for protecting the kiln lining, but if the volatile content is too high, if the flame is fast, the temperature of the kiln clinker can reach 1260 degrees Celsius or above. When the secondary air temperature exceeds 900 degrees Celsius, it is easy to burn out the coal nozzle, causing it to deform or burn out, and even create gaps, resulting in a disordered flame shape. The kiln lining is already damaged before it is replaced. The volatile content of coal is too low (less than 20%), the ash content is too high (more than 28%), and a large amount of coal powder cannot be completely burned. It will settle in the material, and the large amount of heat released by combustion will also damage the kiln skin.

The structure of coal spray nozzles is often not given enough attention in production. The shape of the nozzle and the size of the outlet mainly affect the degree of mixing of coal powder with the same primary air and the spraying speed. In order to strengthen the mixing of wind and coal, it is also possible to install air wings inside the nozzle. However, it should be noted that excessive rotation radius of the swirl air can easily damage the kiln skin.

3、 The impact of fluctuations in raw material composition on refractory bricks in rotary kilns.

The fluctuation of the chemical composition of raw materials not only affects the roasting quality of clinker, but also causes significant damage to the rotary kiln lining. When the aluminum content is too high and the liquid viscosity is high for a long time, the kiln lining will collapse in large quantities, which is difficult to control in operation and is not conducive to protecting the kiln lining. In production practice, the aluminum rate is generally controlled between 1.3-1.6; When high saturation, high silicon content, and low liquid phase batching are adopted, it is easy to produce cohesive material erosion, abrasion of the kiln skin, thinning of the kiln skin, and in severe cases, damage to the kiln lining. In production practice, when the silicon content is controlled at 2.5, the saturation ratio should not exceed 0.92. When the silicon content is controlled at 2.8, the saturation ratio should not exceed 0.9

The fluctuation of raw material feeding amount poses a significant threat to the lining of rotary kiln. When there is too much feed in the kiln, the exhaust air volume at the kiln tail is generally reduced, and the amount of coal powder is increased for strong burning, resulting in a rapid increase in heat load during firing, which in turn causes serious damage to the kiln lining. When there is too little incoming material in the kiln, the coal powder flame significantly decreases, and the kiln skin in this area will fall off and become thinner at high temperatures, rushing towards the thinner material layer. If the air volume and coal consumption are not adjusted in time, it is easy to burn the kiln skin and refractory bricks. In addition, fluctuations in the amount of raw material feeding can lead to instability in the thermal system inside the kiln, and high temperatures can cause the kiln skin to fall off or be damaged.

In the actual operation of rotary kilns, damage to the kiln lining is inevitable. Pay attention to the above aspects and take reasonable measures, which can help extend the service life of rotary kilns and reduce economic burden.