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Optimized configuration of refractory materials for new dry process cement kiln

The new dry-process cement kiln has more refractory materials, and the materials of static equipment account for about 70%-80% of the total. Different types of cement kiln and different parts of the system have different requirements for refractory materials. When designing and matching, it is necessary to select the varieties that are suitable for them; at the same time, the quality of raw materials used, the equipment status, operation control habits, etc. The differences in terms of objectively have slightly different requirements for refractory materials. This paper mainly describes the configuration of unshaped refractory materials on cement kiln.

Rotary kiln

The refractory castables for rotary kiln, especially the refractory materials of the front kiln mouth, in addition to being subjected to high temperature above 1400 °C, are also subject to mechanical stress, thermal stress and chemical corrosion, so the front kiln refractory castable The service life has a crucial impact on the operating cycle of the entire cement production line.

1 Rotary kiln as dynamic equipment, during the operation and use, the refractory castable of the front kiln mouth is subjected to two kinds of mechanical stress: one is the radial shear stress of the kiln, and the other is the axial compressive stress along the direction of the kiln cylinder. . The radial shear stress is mainly derived from the mechanical deformation generated in the operation of the rotary kiln. As the kiln diameter increases, the kiln speed increases, the periodic compression and loosening of the front kiln mouth is intensified, and the radial shear of the refractory castable is The damage of the shear stress is also greater. The main reason for the axial crushing stress of the front kiln is that the kiln cylinder and the horizontal line are inclined by 3.5% to 4%. The material in the kiln moves from the kiln to the kiln in the kiln operation, and the front kiln is castable. Under the combined action of the thrust of the moving material and the axial component of the refractory brick in the kiln, there is a tendency to move toward the kiln head. Under the action of these two mechanical stresses, sufficient mechanical strength is required for the front kiln castable.

2The data shows that during the operation of the rotary kiln, the clinker outlet temperature of the front kiln reaches 1400 °C, and the secondary air temperature of the kiln reaches 1200 °C. During the operation of the kiln, the kiln skin hangs and the temperature changes frequently. The thermal stress generated is one of the main causes of damage to the cast-in-place slag. With the development trend of large-scale cement industry, the kiln diameter is also increasing, and the discharge amount of the kiln mouth is also increasing, which not only increases the mechanical stress, but also greatly increases the thermal strength in the kiln. The thermal load is also increased accordingly, and the damage of thermal stress is more obvious. In this case, the front kiln castable should have better thermal shock stability.

3 Chemical corrosion is one of the main reasons for the damage of refractory materials used in cement kiln. Due to the different grades of limestone in each area, the quality of the fuel, such as alkali, chlorine and sulfur, is different. Raw ore and original The harmful components in the fuel volatilize at high temperature. These alkaline gases enter the kiln along with the raw materials. At the ambient temperature of 1350 ° C ~ 1450 ° C in the kiln, the harmful components and alkaline gases in the kiln are poured into the front kiln. The material produces strong chemical attack, forming a swelling mineral to cause cracking and spalling, and "alkali cracking" occurs. Therefore, the front kiln castable should have good alkali resistance.

In summary, the front kiln castable should have sufficient refractoriness, mechanical strength, thermal shock stability and alkali resistance in a high temperature environment. The former kiln castables have always been the key in cement kiln refractories. With the development of cement industry technology, the scale of cement kiln has gradually increased, and the former kiln castables have also experienced high aluminum, corundum and moxisite. Development of refractory castables. Our company's HR-PA80DT corundum-Mulley kiln special castables were first used in the 2500t/d cement production line of Zhejiang Tongxing Group Cement Co., Ltd., which was built in 2001, with a period of 8 to 10 months or more. It is recommended to use a new dry process cement production line of 2500t/d and above 5000t/d. According to the actual working conditions of the new dry process cement production line, a new standard has been proposed for the kiln refractory material. We have developed the HR-75MDT corundum-mullite kiln special castable, which has a service life of 10 to 12 months. The customer's use requirements; for the construction of 5000t / d cement production line equipment, the development of refractory materials is a new challenge. For the specific working conditions of the 5000t/d cement production line, we have developed the HR-75MDTF corundum-mullite steel fiber high-strength kiln special castable. Based on the performance of HR-PA80DT and HR-75MDT, the material has been improved. Mechanical strength and thermal shock stability.

2. Burner (spray pipe)

The working environment of the burner is around 1400 °C, and the flame temperature is about 2000 °C. It works in an alkaline atmosphere for a long time. Compared with the temperature change of the front kiln mouth, the temperature difference is more frequent and the temperature difference is larger. Therefore, the thermal shock resistance is higher. . The front end of the burner is always flushed by the airflow in the kiln, especially the lower part is subjected to the scouring, and the airflow is sandwiched by the clinker dust in the kiln, and the refractory castable of the burner needs sufficient wear resistance. In view of the above two points, the performance requirements of the burner castables are higher than those of the former kiln castables. According to the working conditions of the new dry process cement production line equipment, we have developed HR-75MET, HR- corresponding to the former kiln castables. 75MEF and HR-PA80ET special materials for coal injection pipe, the service period is 5-8 months.

3. Kiln hood and grate cooler

The kiln head cover and the grate cooler belong to the static equipment, and the mechanical stress damage is relatively small. The working temperature is lower than the temperature in the rotary kiln, and the requirements for the refractory castable are relatively lower.

There are several special parts that need to be proposed: First, the refractory castables in the lower part of the kiln cover are rebounded by the high temperature clinker from the kiln mouth. For some large cement kilns, the daily output of clinker is large, and the heat load here is relatively high. High-aluminum refractory castables are prone to bursting if the curing temperature is not well controlled. The top of the kiln hood is close to the 3rd air duct. The dust flow is relatively severe. The wear resistance of the castable at high temperature is good. The construction of the top castable is difficult, and the fluidity and early strength of the material are relatively high. Second, the top of the front end of the grate cooler is not only subjected to the rebound thermal shock of the clinker, but the working temperature is relatively high and varies greatly. The high temperature clinker that has passed through the kiln mouth for a long time on both sides of the front end is damaged by certain mechanical stress and thermal stress. The third is the bend of the 3 times of the pipe, which is also easy to wear under the scouring of the dust airflow.

The use of refractory castables in the above-mentioned parts should be reasonably selected according to the respective working conditions. HR-DFB1 with early strength and explosion-proof performance, HR-DFB with higher wear resistance, and HR-M66 mullite with better thermal shock resistance. Castables are suitable materials. When other parts are designed, the general high-aluminum refractory castables can meet the requirements of use.

4. Pre-decomposition system

The raw raw material is heated step by step in the preheater, and the harmful components such as alkali, chlorine and sulfur in the raw material are continuously volatilized and agglomerated, and the cycle is continuously enriched, which causes strong chemical attack on the refractory castable, and the occurrence of alkali cracking occurs. "Destruction, so this part of the design uses high-strength alkali-resistant castables. Compared with the original raw materials, the enrichment concentration of alkali, chlorine and sulfur in the clinker of the hottest-grade cyclone cylinder is 5 times, 80-100 times and 3 to 5 times, respectively. In the cement production process, the kiln tail pre-decomposition system often encounters crust blockage. The pre-decomposition system is prone to crust blockage. There are mainly rising flue to C5 duct horizontal section, C5 expansion joint and cutting tube. The blockage is mainly a high-temperature bonded material; the kiln tail smoke chamber shrinkage and the blanking slope, the blockage is mainly crust material, the hardness is hard, the alkali content is high; the C5-C4 air duct horizontal section, the blockage is mainly raw material Sediment, many powders, easy to clean; decomposition furnace cone, the blockage is mainly high-temperature melting of coal ash. According to the chemical analysis of the crust blockage and kiln dust of a cement enterprise, the high chlorine content is the root cause of the frequent crust blockage of the pre-decomposition system, which is to some extent related to the grade and raw material of the limestone used by the cement enterprise. The quality of the fuel is related.