How To Optimize The Configuration Of Refractory Materials For New Dry Process Cement Kilns

How to optimize the configuration of refractory materials for new dry process cement kilns
The use of refractory materials in new dry process cement kilns is common, with materials for stationary equipment accounting for about 70% to 80% of the total. Different specifications of cement kilns and systems have different requirements for refractory materials, and suitable varieties must be selected for design matching; At the same time, the differences in the quality of raw materials, equipment conditions, and operating control habits used by various manufacturers objectively result in slightly different requirements for refractory materials.
1. Rotary kiln
The refractory castable used in rotary kilns, especially the refractory material at the front kiln mouth, not only has to withstand high temperatures above 1400 ℃ during use, but also suffers from mechanical stress, thermal stress, and chemical erosion. Therefore, the service life of the refractory castable at the front kiln mouth has a crucial impact on the operation cycle of the entire cement production line.
① As a dynamic equipment, the refractory castable at the front kiln mouth of the rotary kiln is subjected to two types of mechanical stresses during operation: 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. As the kiln diameter increases and the kiln speed accelerates, the periodic compression and loosening of the front kiln mouth intensify, and the damage to the radial shear stress borne by the refractory castable is also greater. The main reason for the axial compressive stress at the front kiln mouth is due to the 3.5% to 4% inclination of the kiln body with the horizontal line. During kiln operation, the materials inside the kiln move from the kiln tail to the kiln head direction. The poured materials at the front kiln mouth tend to move towards the kiln head direction under the combined action of the pushing force of the moving materials and the axial component force of the refractory bricks inside the kiln. Under the action of these two types of mechanical stresses, sufficient mechanical strength is required for the castable at the front kiln mouth.
② The data shows that during the operation of the rotary kiln, the temperature of the clinker outlet at the front kiln mouth reaches 1400 ℃, and the temperature of the secondary air entering the kiln reaches 1200 ℃. During the operation of the kiln body, the kiln skin hangs and falls frequently, and the temperature changes frequently. The resulting thermal stress is one of the main reasons for the damage of the castable at the front kiln mouth. With the trend of large-scale development in the cement industry, the kiln diameter is constantly increasing, and the discharge volume from the kiln mouth is also increasing. This not only increases mechanical stress, but also significantly improves the thermal strength inside the kiln. The thermal load per unit area of the castable also increases accordingly, and the destructive effect of thermal stress is more obvious. In this case, the castable at the front kiln should have better thermal shock stability.
③ Chemical erosion is one of the main reasons for the damage of refractory materials used in cement kilns. Due to the different grades of limestone and the quality of fuel used in each region, the content of harmful components such as alkali, * * *, and sulfur in the kiln also varies. The harmful components in raw ore and raw fuel evaporate at high temperatures, and these alkaline gases enter the kiln together with the raw materials. At an ambient temperature of 1350 ℃ to 1450 ℃ in the kiln, the harmful components and alkaline gases in the kiln materials have a strong chemical erosion effect with the pouring material at the front kiln mouth, forming expansive minerals that cause cracking and peeling, resulting in "alkali cracking" damage. Therefore, the castable at the front kiln mouth should have good alkali resistance.
In summary, the castable at the front kiln mouth should have sufficient fire resistance, mechanical strength, thermal shock stability, and alkali resistance in high-temperature environments. The pouring material at the front kiln has always been crucial in the refractory materials used in cement kilns. With the development of cement industry technology, the scale of cement kilns has gradually increased, and the pouring material at the front kiln has also undergone the development of high alumina, corundum, and dolomite refractory pouring materials. Our company's HR-PA80DT corundum mullite kiln mouth casting material was first used in the 2500t/d cement production line of Zhejiang Tongxing Group Cement Co., Ltd., which was built in 2001, with a service life of 8-10 months or more. Later, it was widely recommended for use in new dry cement production lines with a scale of 2500t/d and 5000t/d. Based on the actual working conditions of the new dry process cement production line, new standards have been proposed for the refractory materials at the front kiln mouth. We have developed HR-75MDT corundum mullite kiln mouth casting material, which has a service life of 10-12 months and meets the customer's requirements; The development of refractory materials is a new challenge for the construction of 5000t/d cement production line equipment. For the specific working conditions of the 5000t/d cement production line, we have also developed HR-75MTTF corundum mullite steel fiber high-strength kiln mouth casting material, which improves the mechanical strength and thermal shock stability of the material while considering the performance of HR-PA80DT and HR-75MDT.
2. Burner (coal injection pipe)
The working environment of the burner is around 1400 ℃, and its flame temperature is around 2000 ℃. It works in an alkaline atmosphere for a long time, and the temperature changes more frequently and the temperature difference is larger compared to the front kiln mouth. Therefore, it requires higher thermal shock resistance. The front end of the burner is always subject to air flow erosion inside the kiln, especially the lower part, which is more severe. Moreover, this air flow contains clinker dust inside the kiln, and the refractory castable of the burner needs sufficient wear resistance. Considering the above two points, the performance requirements for burner castable are higher than those for front kiln castable. Based on the operating conditions of the new dry process cement production line equipment, corresponding to the front kiln castable, we have developed HR-75MET, HR-75MEF, and HR-PA80ET coal injection pipe * * * materials with a service life of 5-8 months.
3. Kiln hood and grate cooler
The kiln hood and grate cooler are stationary equipment that suffer relatively little mechanical stress damage. Their operating temperature is generally lower than that inside the rotary kiln, and their requirements for refractory castables are relatively lower.
There are several special parts that need to be addressed: firstly, the refractory castable under the kiln hood is subjected to the rebound thermal impact of high-temperature clinker coming down from the kiln mouth. For some large cement kilns, the daily clinker production is large, and the heat load here is relatively high. If the curing and temperature control of the general high alumina refractory castable is not good, it is easy to burst and fall off. At the top of the kiln hood near the third air duct, the dust airflow is relatively severe, and the wear resistance of the casting material is good at high temperatures. The construction of the top casting material is difficult, and high requirements are placed on the flowability and early strength of the material. The second reason is that the top of the front end of the grate cooler is not only subjected to the rebound thermal impact of the clinker, but also has a relatively high and variable working temperature. The low walls on both sides of the front end have been damaged by certain mechanical and thermal stresses due to the high-temperature clinker that has been passing through the kiln mouth for a long time. The third is the turning point of the third branch, which is also prone to wear and tear under the erosion of dust airflow.
The use of refractory castables for the above-mentioned parts should be reasonably selected according to their respective working conditions. HR-DFB1 with early strength explosion-proof performance, HR-DFB with higher wear resistance, and HR-M66 mullite refractory castables with better thermal shock resistance are all suitable materials. When designing other parts, general high alumina refractory castables can meet the requirements of use.
4. Pre decomposition system
The raw material is gradually heated in the preheater, and harmful components such as alkali, * * *, sulfur in the raw material are constantly volatilized and condensed, repeatedly circulated and enriched, causing strong chemical erosion to the refractory castable and leading to "alkali cracking" damage. Therefore, high-strength alkali resistant castable is used in this area during design. Compared with the original raw material, the enrichment concentrations of alkali, * * *, and sulfur in the clinker of the * * thermal cyclone tube are as high as 5 times, 80-100 times, and 3-5 times, respectively. In the process of cement production, the pre decomposition system at the kiln tail often encounters the situation of crust blockage. The main parts of the pre decomposition system that are prone to crust blockage are the horizontal section from the rising flue to the C5 air duct, the C5 expansion joint, and the discharge pipe. The blockage is mainly caused by high-temperature bonding materials; The shrinkage and discharge slope of the kiln tail smoke chamber are mainly blocked by crust materials, which are hard and have high alkali content; The horizontal section of the C5-C4 air duct is mainly blocked by raw material sediment, which contains a lot of powder and is easy to clean; The cone of the decomposition furnace is mainly blocked by high-temperature molten coal ash. The chemical analysis of crust blockage and kiln ash by a certain cement enterprise shows that the high content of * * * is the fundamental reason for frequent crust blockage in the pre decomposition system, which is to some extent related to the grade of limestone used by the cement enterprise and the quality of raw materials and fuels.