There are many parts of refractories used in new dry process cement kilns, of which the materials of static equipment account for 70% - 80% of the total. Different specifications of cement kilns and different parts of the system have different requirements for refractories, so the varieties should be selected when matching the design. At the same time, the quality of raw materials used by various manufacturers, equipment conditions, operating control habits and other aspects of differences, objective requirements for refractories are also slightly. Different. This paper mainly describes the configuration of unshaped refractory in cement kiln.
1. rotary kiln

The refractory castables used in rotary kiln, especially the refractories used in front kiln mouth, are destroyed by mechanical stress, thermal stress and chemical erosion besides the high temperature above 1400. Therefore, the service life of the refractory castables in front kiln mouth has a vital influence on the operation cycle of the whole cement production line. .

(1) As a dynamic equipment, the refractory castable at the front kiln mouth bears two kinds of mechanical stresses: one is the radial shear stress of the kiln, the other is the axial extrusion stress along the direction of the kiln tube. The radial shear stress mainly comes from the mechanical deformation during the operation of rotary kiln. With the increase of kiln diameter and kiln speed, the periodic compression and loosening of the front kiln mouth intensifies, and the radial shear stress of refractory castable suffers more damage. The main reason of axial compression stress in front kiln mouth is that the inclination of kiln barrel and horizontal line is 3.5%-4%. The material in kiln moves from kiln tail to kiln head when it is running. Under the combined action of the thrust of the material in front kiln mouth and the axial component force of refractory brick in kiln, the material in front kiln mouth moves toward the kiln head. Under these two mechanical stresses, sufficient mechanical strength is required for the castables of the front kiln.

(2) The data show that the outlet temperature of the clinker at the front kiln mouth reaches 1400 C and the secondary air temperature reaches 1200 C during the operation of the rotary kiln. During the operation of the kiln body, the kiln skin hangs down and the temperature changes frequently. Thermal stress is one of the main reasons for the damage of the castable at the front kiln mouth. With the development trend of large-scale cement industry, the diameter of kiln is also increasing, and the output of kiln is also increasing. This not only makes the mechanical stress bigger, but also the thermal strength of kiln is greatly improved. The thermal load of castable per unit area is also increased correspondingly, and the damage of thermal stress is more obvious. In this case, the castables of the front kiln should have better thermal shock stability.

(3) Chemical erosion is one of the main reasons for the damage of refractories used in cement kilns. Because of the grade of limestone in each area and the quality of fuels used, the contents of harmful components such as alkali, chlorine and sulfur in the kilns are different. The harmful components in raw ores and fuels volatilize at high temperatures. These alkaline gases are combined with raw materials. When entering the kiln, the harmful ingredients and alkaline gases in the kiln materials produce strong chemical erosion with the castable at the front kiln entrance under the ambient temperature of 1350 ~1450 C, forming expansive minerals to make it crack and spall, and causing "alkali cracking" damage. Therefore, the castables of the front kiln should have good alkali resistance.

In conclusion, the front kiln gate castable should have enough fire resistance, mechanical strength, thermal shock stability and alkali resistance under high temperature environment. With the development of cement industry technology, the scale of cement kiln increases gradually, and the castable of front kiln mouth has also experienced the development of high alumina, corundum and mullite refractories. The HR-PA80DT corundum-mullite kiln mouth castable for our company was first used in the 2500t/d cement production line of Zhejiang Tongxing Group Cement Co., Ltd. which was put into operation in 2001. The usage period was more than 8-10 months. Later, it was widely recommended to be used in the 2500t/d and 5000t/d new dry process cement production line. According to the actual working conditions of the new dry-process cement production line, a new standard for refractories at the front kiln entrance is put forward. We have developed HR-75MDT corundum-mullite castable for kiln entrance. The service life of the castable reaches 10-12 months, which meets the customer's requirements. For the construction of 5000t/d cement production line equipment, the development of refractories is also in progress. This is a new challenge. In view of the specific working conditions of 5000t/d cement production line, we have developed HR-75MDTF corundum-mullite steel fiber high-strength kiln gate castable. On the basis of considering the properties of HR-PA80DT and HR-75MDT, the mechanical strength and thermal shock stability of the castable are improved.

2. burner (coal injection pipe)

The working environment of the burner is about 1400 C, the flame temperature is about 2000 C, and the burner works in alkaline atmosphere for a long time. Compared with the front kiln mouth, the temperature changes more frequently and the temperature difference is bigger, so the thermal shock performance of the burner is required to be higher. The front end of the burner is always scoured by the air flow in the kiln, especially the lower part is scoured more seriously, and the air flow holds the clinker dust in the kiln, so the refractory castable of the burner needs enough wear resistance. In view of the above two points, the performance requirements of burner castables are higher than that of front kiln nozzle castables. According to the operating conditions of new dry cement production line equipment and corresponding front kiln nozzle castables, we have developed special materials for HR-75MET, HR-75MEF and HR-PA80ET coal injection nozzles, and the service life is up to 5-8 months.

3. kiln head and grate cooler

The kiln head cover and grate cooler belong to static equipment, which suffer less mechanical stress damage. The working temperature is generally lower than that in rotary kiln, and the requirement for refractory castable is relatively lower.

Several special parts need to be put forward: First, the refractory castable under the kiln head cover is subjected to the rebound heat shock of the high-temperature clinker from the kiln mouth. For some large cement kilns, the daily output clinker is large, and the heat load is relatively high here. If the general high-alumina refractory castable is not well controlled, it is easy to burst and drop the block. . Close to the top of the kiln hood three times the air duct, dust flow erosion is relatively serious, castable at high temperature wear resistance is better, the construction of top castable is more difficult, the material flow and early strength requirements are higher. Secondly, the top of the front end of the grate cooler is not only impacted by the rebound heat of clinker, but also the working temperature is relatively high and varies greatly. The high temperature clinker coming down from the kiln mouth on both sides of the front wall is damaged by certain mechanical stress and thermal stress. The three is the 3 turning point, which is also easy to wear under the scouring of dust airflow.

The use of refractory castables in 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, ordinary high-alumina refractory castables are used. It can meet the requirement of use.

4. predecomposition system

Raw meal in the preheater step by step, alkali, chlorine, sulfur and other harmful ingredients in raw meal volatilization, condensation, repeated cycle and enrichment, on refractory castable produce strong chemical erosion, occur "alkali cracking" damage, so the design of this part of the use of high-strength alkali-resistant castable. Compared with raw meal, the concentration of alkali, chlorine and sulfur in clinker of the hottest cyclone cylinder is 5 times, 80-100 times and 3-5 times respectively. In the cement production process, the pre-decomposition system at the end of the kiln often encounters the situation of crust blockage. The main parts of the pre-decomposition system are easy to crust blockage, such as ascending flue to the horizontal section of the C5 air duct, C5 expansion joint and blanking pipe, and the blockage is mainly high-temperature bonded materials; the shrinkage of the flue chamber at the end of the kiln and the slope of the blanking material, and the blo Skin material, hard, high alkali content; C5-C4 duct horizontal section, clogging material is mainly raw material sediment, powder, easy to clean up; decomposition furnace cone, clogging material is mainly coal ash high temperature melt. The chemical analysis of crust plugging and kiln ash in a cement enterprise shows that the high chlorine content is the basic reason for frequent crust plugging in the pre-decomposition system, which is related to the grade of limestone and the quality of raw materials and fuels adopted by the cement enterprise to a certain extent.

According to the requirement of this working condition, our company has developed HR-50S and HR-60S anti-crust castables, in which the main raw material silicon carbide not only has very good anti-chemical corrosion performance, but also has oxidation reaction at high temperature, and produces SiO2 glass-like smooth material layer on the surface of the material, which more effectively prevents harmful gases from casting refractory. Chemical erosion of the injection material, in addition, silicon carbide has a strong wear resistance, in the discharge pipe and other parts can meet the requirements of a large number of raw materials. [author]: Yao Jianming