Matching And Usage Methods Of Refractory Materials For Pre Decomposition Kiln

Matching and usage methods of refractory materials for pre decomposition kiln
During the operation and use of rotary kilns, refractory bricks mainly bear two types of mechanical stresses: radial shear stress of the kiln and axial compression stress along the direction of the kiln barrel.
The radial shear stress mainly comes from the mechanical deformation generated during the operation of the rotary kiln. The kiln barrel will undergo elliptical deformation, and the centerline of the barrel will no longer be a straight line; On the other hand, in the area near the supporting wheel belt, the kiln body will undergo elliptical deformation. Continuous measurements of the running kiln body using testing methods show that the relative difference between the horizontal and vertical diameters of the body can reach 0.3 ‰, and even 0.6 ‰ to 0.7 ‰ on older kilns. As the diameter of the elliptical kiln increases and the kiln speed accelerates, the periodic compression effect on the kiln body intensifies. The refractory bricks will be subjected to greater radial shear stress damage, and the firing zone and upper transition zone are the areas of radial shear stress * *.
There are two main aspects to the generation of axial compressive stress. One reason is that the materials inside the kiln move from the kiln tail to the kiln head during operation, and the refractory bricks inside the kiln tend to move towards the kiln head under the combined action of the pushing force of the moving materials and the axial force of the bricks' own gravity; The second is the expansion force generated by the heating of refractory bricks. The expansion coefficient of refractory bricks at 1400-1450 ℃ is 1.4 ‰ -1.6 ‰. The commonly used length of each brick is 198mm, and the measured expansion is 2.8-3.2mm. If the heating rate is too fast during kiln drying, the expansion rate of the kiln barrel will be relatively slow compared to the bricks, which will limit the further expansion of the refractory bricks and generate significant stress, even leading to brick cracking. The harsh working environment inside the kiln requires refractory bricks to have sufficient mechanical strength. At the same time, reasonably reserving expansion joints during kiln brick masonry can also effectively alleviate the damage caused by these two stresses.
Thermal stress damage: The test results show that the surface temperature of the kiln lining changes by more than 400 ℃ during one rotation of the kiln, and the resulting thermal stress is one of the main reasons for the damage of refractory bricks. With the trend of large-scale development in the cement industry, the diameter of the external decomposition kiln has increased (the kiln diameter of the 10000 t/d production line reaches 6m), and the output of the kiln increases to the third power with the increase of kiln diameter. The volumetric output has increased to more than three times that of traditional kilns, reaching 5t/(m3. d). This not only increases the mechanical stress, but also significantly enhances the thermal strength inside the kiln. The unit heat load on the refractory bricks also increases, and the thermal stress damage intensifies. In addition, the kiln speed is also increased (3-4 r/min), which greatly increases the frequency of periodic temperature differences experienced by the kiln lining, requiring refractory bricks to have better thermal shock stability.
Chemical erosion damage: Chemical erosion is one of the main causes of refractory material damage. At an ambient temperature of 1350-1450 ℃ inside the kiln, clinker with strong alkalinity will cause strong chemical corrosion to the kiln lining. The liquid phase substances in the clinker will react with the salt based substances in the brick to form intermediate phases with a bottom melting point (sulfates, potassium sodium salts, etc.), which will deposit deep into the brick body at a depth of 40-50mm. This will cause the structure of the brick to become brittle, hard, loose, and prone to peeling. The key to overcoming the damage caused by chemical erosion is to prevent the penetration of certain components in cement (SiO2, CaO, KCI, etc.). In addition, harmful components such as alkali, chlorine, and sulfur in raw materials can also cause serious erosion and damage to the kiln lining. The sulfates and chemicals of alkali are continuously enriched through volatilization, condensation, and repeated circulation in the preheater system. Usually, compared with the original raw material, the concentration of alkali, chlorine, and sulfur enrichment in the hot material of the * * thermal cyclone tube reaches 5 times, 80-100 times, and 3-5 times respectively. The refractory material is eroded by alkali compounds from the kiln material and kiln gas, forming expansive minerals that cause cracking and peeling, resulting in alkali cracking and damage.
Reasonable use of refractory materials: When ordering refractory materials, it is important to ensure their long-term safe use. Firstly, consider the qualifications and production processing capabilities of the manufacturer, and pay attention to the quality and after-sales service of the refractory materials. When ordering refractory materials, requirements should be made for the packaging and transportation of the supplied products. If there is no solid and sturdy packaging, reliable transportation can easily cause damage and directly affect the service life. For refractory materials with shelf life (such as some castables), long-term storage should be avoided. Refractory bricks should be moisture-proof and stacked in an orderly manner to avoid confusion. Improving the quality of masonry construction: The quality of kiln lining is one of the main factors determining the kiln operation cycle, and the quality of masonry construction is a key link in ensuring the quality of kiln lining. The "Regulations on the Use of Refractory Materials for Cement Rotary Kilns" promulgated and implemented in 1995 provided a basis for standardized construction. Enterprises should provide training for furnace construction personnel, comprehensively learn and promote the application of the "Regulations on the Use of Refractory Materials for Cement Rotary Kilns", in order to improve the technical level of construction personnel. However, due to various reasons, there is often a phenomenon of non-compliance during construction, which requires work to be done in strengthening management. During the masonry construction process, attention should be paid to the following issues: controlling the amount of water added as required. Although a large amount of water is convenient for construction, it greatly reduces the strength performance of the casting material. Pay attention to post construction maintenance. The common situation is that construction units, in order to catch up with the schedule, cement companies, in order to start production early, rarely manage to properly maintain the casting materials according to the required time. This will inevitably directly affect its performance. When heating and baking the poured material after construction, the setting of exhaust holes should be fully considered, especially in the kiln hood area. In most cases, there is no separate baking process at this location, and the temperature of the hot clinker entering the kiln hood rises sharply from around 400 ℃ to around 1100 ℃. If the exhaust hole is not properly set, the risk of refractory material bursting is extremely high. During masonry, the lining bricks should not have any suspended points or surfaces. The big head should be pressed tightly against the cylinder, and the uneven weld seam should be polished flat. The deformed part of the cylinder should be leveled and aligned with clay pads. Leave expansion joints according to the expansion coefficient of the bricks. Leaving excessive gaps can lead to brick drawing and even brick dropping accidents, while leaving insufficient gaps can exacerbate the stress damage of the bricks. The use of adjusting iron plates should be standardized. The dosage should not be excessive, and it is strictly prohibited for colleagues with large heads and small heads to adjust, and it is not allowed to sew and add continuously; The iron plate should not be inserted halfway into the brick joint, causing the small end joint to be tight and the large end joint to be loose; When inserting the iron plate, do not forcefully smash it, and do not forge or bend the iron plate to damage the brick surface. Use a rubber hammer or wooden hammer to strike the brick surface, ensuring that the bricks are in solid contact with each other. Reasonable use and operation, kiln heating operation. **Firstly, based on the performance of refractory bricks, a reasonable baking temperature curve should be developed and the heating rate should be strictly controlled (usually 30-50 ℃/h) to effectively reduce the damage of bricks caused by thermal stress; At the same time, strictly implement the kiln heating and turning system to reduce the mechanical stress damage caused by the mechanical deformation of the kiln barrel to the bricks. When the new kiln lining is baked, it is difficult to control the transition from oil baking to oil coal co firing, which can easily cause the heating rate to lose control and accelerate, leading to thermal stress damage.