What is the effect of high temperature increase in cement kiln on refractory materials?

Cement is fired at high temperatures, so refractory materials are used as furnace linings.

1. Wear and tear. Due to the mechanical action of moving solids, the loss of the material surface is caused;

2. Erosion. Surface erosion due to chemical action of external media;

3. A lava hole. The maximum diameter, minimum diameter and depth of the depression formed by the melting of the brick surface can be measured;

4. Creep. Isothermal deformation of refractory materials with time under a certain stress;

5. Erosion. Erosion of the surface of the refractory material due to the mechanical action of the fluidized substance, which may or may not contain solid material;

6. Peeling. Fracture or cracking that causes the surface of the refractory to fall off in flakes.

The speed of a conventional cement kiln is 1r min, but the speed of a large pre-calciner kiln is as high as 3 4r min. On the high-temperature, high-speed and large-diameter pre-calciner kiln, the working environment of the kiln body and kiln lining is much more harsh than that of the traditional co-rotor kiln.

The simplified warp wheel of the cement rotary kiln is supported on the tugboat. The simplified body has a large dead weight, and is affected by the gravity of refractory bricks, kiln skins and kiln materials, and the cross-section of the simplified body between the wheels and belts will produce a large radial deformation. Continuous measurement of the kiln body in operation with a simplified measuring instrument can show that the dimensional difference between the horizontal and vertical diameters of the cylinder can be reached and sometimes even reached.

During operation, the curvature of the simplified body will change again and again every time the kiln body rotates, and the refractory lining will inevitably be damaged under the action of fatigue load due to the periodic extrusion pressure of the simplified body and the balancing stress inside the brick ring.

In addition, the error of manufacturing and installation, improper withering of the tugboat and the uneven settlement of the kiln foundation can also make the bending of the kiln body exceed the allowable value, so that the simplified body loses linearity and roundness. If the bending occurs at the end, it will cause the end body to jump, resulting in air leakage at the kiln head and kiln tail, and damage to the sealing device and refractory materials. If it occurs at the transmission gear, the meshing of the large and small gears will be uneven, causing vibration, resulting in loosening, drawing lots, falling bricks or being damaged by excessive mechanical stress of the refractory material.

With the expansion of production capacity, the diameter of the cylinder of the new dry cement rotary kiln continues to increase, from 3300mm to 6400mm today, which is almost a double increase. At present, there are two main types of bricks used in cement rotary kilns, among which the alkaline bricks generally use VDZ series brick type (international general series, the middle width is constant, and the sintered silicon-aluminum refractory bricks generally use ISO series brick type (international general series, the width of the large head is constant 103mm). The height and thickness of the refractory bricks are relatively fixed, and there is not much room for adjustment.

If the height of the refractory brick is too low, the thermal insulation performance of the refractory brick is too poor, and the hot end of the brick is slightly damaged, the temperature of the kiln body will rise above the upper limit, resulting in the kiln being stopped and replaced with bricks; If the height of the refractory bricks is too high, the quality of the bricks will increase, which will cause the kiln body to produce overfire deformation, and will also damage the refractory bricks.

The increase of kiln diameter, the increase of speed, especially the speed of the technologically advanced second-gear kiln is higher, reaching 5r min, which is easy to cause the increase of the ovality of the simplified body, and the corresponding compressive stress of the refractory bricks has higher requirements, so the compressive strength of the refractory bricks is required to be high. In particular, the wheel belt part is simplified, and it is required to use refractory bricks with the same characteristics as far as possible near the wheel belt part.

With the expansion of the kiln diameter, the refractory brick corresponding to the center angle will become smaller, the stress of the refractory brick will increase, and the size tolerance of the refractory brick also puts forward more demanding requirements at the same time, the diameter of the cylinder of the 10,000-ton cement kiln reaches the height of the refractory brick in the kiln, and the refractory brick with large size deviation is prone to accidents such as drawing lots off the brick in the process of masonry and use, which seriously endangers the normal operation of the cement kiln.

The new dry kiln system is far more complex than the traditional cement rotary kiln. The new dry kiln system is composed of several parts, such as the preheater system, the calciner furnace, the kiln tail smoke chamber, the rotary kiln body, the kiln door cover, the burner, the cooler, the tertiary air duct, the fan, the humidification tower, the electric dust collector, etc., and any part of the problem may lead to the production stop.

The structure of the new dry process cement kiln system is complex, and different parts require the use of different types and specifications of refractory materials. There are more than 100 types of bricks on the 4000t d pre-calcining kiln, and the production and construction management are extremely complex. Therefore, it is necessary to standardize the kiln lining design, modernize the manufacturing process and standardize the construction process.

First of all, try to avoid complex brick types, and try to combine complex masonry structures with bricks of a few shapes. For example, CAD technology is used to simplify the design of kiln linings, and as many amorphous refractories are used as much as possible to reduce the project cost. Secondly, the use of advanced management and modern equipment to manufacture high-quality, stable performance of refractory materials, so that the material has good high temperature resistance, erosion resistance, thermal shock resistance, moderate mechanical strength and other properties and accurate dimensions.

Third, in strict accordance with the regulations for the construction of refractory brick masonry and castables, reasonable maintenance of refractory materials, and the elimination of incorrect storage, transportation, construction and maintenance methods. In this way, the material can be fully exploited and the kiln lining life can be maximized.

To prolong the life of the refractory in the cement kiln, we must first understand the cause of the damage to the refractory

1. Melt loss; 2. Gas loss; 3. Permanent shrinkage; 4. Structural peeling; 5. Mechanical stripping; 6. Thermal peeling and softening damage.

There are corresponding prevention methods for these causes of damage, such as dissolution, which can be refractory materials with low porosity and low air permeability and good firing, refractory materials with low melting degree and high viscosity of dissolved products to the melt chain, or refractory materials that are not easy to be eroded by melt next to the melt shed as much as possible.

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Mechanical stress, axial expansion extrusion stress, and production operation should be done well.