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The influencing factors of refractory service life of rotary

Date:2019-07-22 14:50     writer:cement editor     Views:

There are many factors that affect the service life of refractory brick in kiln.Through theoretical analysis combined with practical production experience, it is considered that there are mainly three aspects: mechanical stress, thermal stress and production operation.

1. Influence of mechanical stress on the service life of firebrick

Mechanical stress is the internal force that interacts with each other in the body due to external factors when the body deforms, so as to resist the external factors and try to make the body return from the position after deformation to the position before deformation.When the mechanical stress of refractory brick in kiln exceeds its own strength, partial or total damage occurs under the action of stress.

The main causes of mechanical stress are as follows:


(1) elliptic deformation.

Due to the combined factors of lining brick, kiln material and cylinder body weight, the cylinder body is deformed, and the circular section of the cylinder body becomes elliptic under the action of gravity and thermal load.When the kiln is running, the ellipse causes mechanical stress on the brick, and the greater the ellipticity, the greater the mechanical stress.The shear stress caused by the change of ellipticity ACTS on the tangent direction of each ring brick, which results in the ring spalling of the brick.Generally, the thickness of the peel is uniform and hard.

(2) axis deviation of rotary kiln.

Rotary kiln is supported by belting leather, roller, roller, the axis of each section shall be kiln circle center attachment and in a straight line, but in the kiln shell after installation and partial cylinder cut change, or run over a period of time after the kiln body and the furnace thermal system is not stable, in under the action of heat load and load, the axis of the kiln body produces deviation.After that, after a long period of operation, the wear of the belt and roller, the outer deviation and inner deviation of the roller, the load conditions of each fulcrum will change. Especially, when the load of the fulcrum is too large, it is easy to cause the burning loss of the roller roller shingles, abnormal peeling or cracks on the surface of the belt and roller, which will further aggravate the axis deviation of the kiln body.As a result, the brick will be crushed and deformed, causing it to break or fall off.The shape of the firebrick varies after it is damaged.

2. The influence of thermal stress on the service life of firebrick

Thermal stress refers to the stress produced by an object which cannot expand and contract completely freely due to the external constraints and the mutual constraints between the internal parts when the temperature changes.High temperature thermal expansion can easily cause axial expansion and extrusion stress of refractory brick, which is one of the important reasons for flaking and breakage of refractory brick in cement rotary kiln.Take magnesium-chrome or spinel brick as an example, the expansion rate of 1400℃ can be calculated by 1.6%, the expansion of 198mm firebrick can reach 3.17mm, such a large expansion, if not properly left in the gap, too large or too small will make the firebrick draw lot, brick, peeling, seriously shorten the service life of the firebrick.

3. Influence of production operation on service life of refractories


The influence mechanism of production operation on the service life of firebrick is complex and there are many factors.


(1) brick damage caused by too high calcination temperature.

The flame temperature in the new dry pre-decomposition kiln can reach more than 1700℃, and the working temperature of the transition zone, firing zone, cooling zone, kiln head cover, the throat and high temperature area of the cooling machine and the outside part of the nozzle is also much higher than that of the corresponding part of the traditional kiln.Even with high quality refractory materials, the lining life of transition belt, firing belt and cooling belt of large rotary kiln is generally 0.5 ~ 1 year, and even 3 ~ 5 months.The service life of kiln mouth and nozzle liner is usually only 0.5 ~ 1 year, or even shorter.The life of kiln head cover and throat lining of cooling machine is about 2 years.In the trial production stage, usually the rotary kiln's operating rate is only 70% ~ 75% or even lower, very few can reach 85% ~ 90%.If coupled with the poor operation of preheater and decomposing furnace, the decomposing degree of materials into kiln is very unstable, the position of each process belt in kiln will change frequently, which will lead to unstable operation of kiln and faster damage of kiln lining.For example, if the temperature of calcining is too high, the refractory bricks in the kiln will damage the melting pit.

(2) brick damage caused by fast kiln speed.

The rotating speed of the new dry pre-decomposition kiln is usually 3 ~ 3.7r /min, even up to 4 r/min, and the linear speed of the rotary kiln cylinder reaches over 1m/s.In the new dry kiln with high rotating speed, large diameter and high temperature, the comprehensive damage effect of thermal stress, mechanical stress and chemical erosion on the kiln lining is much larger than that of the traditional kiln.This requires that the lining of the new dry kiln must have sufficient strength and stability in both cold and hot conditions.

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