In recent years, coal resources have become tense and price costs have risen. In order to save costs, cement plants have to reduce the quality of raw fuels, coupled with the gradual decline in limestone grades, resulting in simultaneous reductions in the output and quality of rotary kiln systems. In order to improve this situation, through in-depth analysis and research, the cement plant rotary kiln process has been optimized and improved, and the effect is remarkable.
First, main equipment configuration of cement production line and production before optimization and transformation
The main equipment of these two cement production lines is: double series cyclone preheater + TDF furnace, rotary kiln, high temperature fan, grate cooler and kiln burner. The main problems exist are as follows:
1. With the decline of the local limestone grade, the w(SiO2) value in the milled limestone is as high as 6.5%; the volatiles in the raw coal decrease, the moisture and ash increase, and the calorific value decreases. As a result, the heat consumption of the system clinker is as high as 870×4.18kJ•kg-1; the moisture of the coal powder entering the kiln is large (about 3%); the temperature of the exhaust gas in the kiln head is high. In addition, yellow clinker often appears in clinker, f-CaO fluctuates greatly, low weight rise, clinker clinking is poor, flying sand is serious, and 28d strength is not high.
2. The kiln tail chamber and the decomposition furnace are easy to crust, and the kiln is often thick and thick at 37~44m. When the kiln has a long thick kiln skin, the kiln tail often leaks; even if the raw material feed rate drops to 120t/h, there is still a large amount of leakage at the kiln tail. Leakage at the end of the kiln will adversely affect the service life of the kiln seal, while polluting the environment and increasing the labor intensity of employees.
3. The preheater collapses frequently, often causing the three-stage cylinder to block the material, and the kiln condition is unstable. For this reason, in the three-stage tube feeding tube which is easy to block the material, a compressed air tube is inserted as a material to guide the material, and although the blocking material is relieved, there is often a phenomenon of blocking material.
Second, the main problem analysis
The tight resources of limestone and bituminous coal have caused the quality of the raw fuel entering the plant to decrease, which has caused a series of problems. If the raw material is easily burnt, it is difficult to burn. If the coal quality deteriorates, the flame burning speed in the kiln is slow, the flame is dispersed, the high temperature is not concentrated, and the system working conditions are unstable; then the clinker is poor in material and the cooling effect is poor, resulting in kiln head exhaust gas and cooling clinker temperature. High; after the pulverized coal combustion, the preheater outlet temperature is high (up to 385 °C ± 10 °C), the temperature difference between the cylinders is small, and the heat exchange efficiency is low. Therefore, the heat consumption of the mature material is high, the strength of the clinker is lowered, the amount of the mixed material is decreased, the wearability is deteriorated, and the output of the cement mill is decreased, thereby greatly increasing the production cost of the enterprise. Therefore, the change in the quality of the raw fuel is the main reason.
In addition, the cement production line has been put into production for 5 years, the strength of the refractory material in the three air ducts has dropped significantly, and the top of the air duct is often red out. The emergency treatment is for the back casting, which causes the accumulation of refractory materials and fine clinker in the third duct to increase the third wind. The increase of pipe resistance and wind speed leads to unbalanced wind in the preheater system; in addition, the air leakage in each system is serious, and the circulation in the preheater is increased, which causes the airflow of the preheater to be disordered and collapsed frequently.
Third, the response measures
1. Strengthen contact with suppliers of limestone and bituminous coal, take pre-tests before entering the factory, strictly control the quality of raw materials into the factory, and reject the raw materials with poor quality. At the same time, strengthen the stacking management of the plant site, do a good job in the use of raw materials, and increase the stock level of the limestone homogenization warehouse, the coal homogenization warehouse and the raw material homogenization warehouse, and increase the sampling frequency of each process. , to achieve pre-control, improve the predictability of ingredients, and stabilize the chemical composition of raw materials.
2. Improve the burning speed of kiln coal powder and the burning rate of coal powder in the kiln tail decomposing furnace. The factors affecting the burning speed of pulverized coal mainly include moisture, ash, fixed carbon, fineness, and performance of the burner. According to the characteristics of low calorific value, high water content and low volatile content of coal powder, the countermeasures adopted are:
(1) Replace the damaged lifting plate in the drying chamber of the coal grinding system, reduce the average ball diameter of the second bin, clean the accumulated dust and accumulated materials of each pipe, etc., in order to increase the ventilation of the coal grinding system and ensure the fineness of the coal powder. The degree (80μm sieve) is controlled within 5%, and the moisture is controlled within 1.8%, which creates conditions for the full combustion of pulverized coal.
(2) In the case of the same process conditions such as equipment configuration, raw materials, and ingredients, the performance of the burner will affect the quality of the clinker. In order to reduce the amount of primary air, increase the utilization of high temperature secondary air, enhance the thrust of the burner, strengthen the carrying of the secondary air, increase the mixing of pulverized coal and combustion air, and increase the adjustment means for the air volume and wind speed of each channel. Increasing the burning rate, improving the thermal efficiency of the kiln system, making the flame shape and temperature field easy to control as needed, meeting the requirements of the current coal quality, and knowing more and replacing the new burner through multiple manufacturers. Compared with the old burner, the new burner has a shorter structure in the structure; the cross-sectional area of the outer and inner ducts is smaller; the cross-sectional area of the coal duct is larger. Therefore, after the new burner is put into use, it can increase the speed difference between the primary wind and the coal wind and the secondary air, so that the coal powder is fully mixed and has the ability to carry the high temperature secondary air, improve the adaptability to the coal quality, and promote the flame. More complete and more active, the pulverized coal is burned more completely, which improves the thermal strength of the kiln firing zone.
(3) Carefully inspected all aspects of the wind that affect the system to better adjust the process wind of the kiln system; cleaned the ventilation holes of the air chambers, pipes and rafts of the grate cooler to improve 篦The cooling effect of the cold machine reduces the temperature of the clinker and raises the secondary air temperature; cleans the accumulated material in the third air duct, and replaces the refractory material in the third air duct to ensure the air volume and wind speed of the third air duct. In addition, the air leakage points are thoroughly sealed and leaked, which can control the collapse phenomenon of the preheater system.
(4) Improve the heat exchange effect of the preheater system and reduce the heat consumption of the clinker. 80% of the heat exchange in the preheater is completed in the pipeline, and 20% is completed in the cyclone; the heat exchange efficiency is mainly affected by the dispersibility of the material in the pipeline, the dust collection efficiency of each cylinder, and the airflow of each cylinder. The speed difference of the material, the performance of the raw meal powder and other factors. In order to improve the heat exchange efficiency of the preheater, targeted transformation and adjustment measures were carried out:
First, the feeding angle of each sprinkling bin in the preheater is increased, and a material dispersing device is installed on the dispersing plate to forcefully disperse the material to improve the speed difference and dispersion effect of the material in the pipeline and the airflow;
The second is to increase the height of the inner cylinder of C4 and C5 to improve the dust collection efficiency of the two-stage cyclone;
The third is to check the clearance of each flap valve in the cutting tube and adjust the counterweight of the flap valve to ensure smooth and wind-locking effect during normal production.
Through the optimization and transformation of the above measures, the operating conditions of the rotary kiln system in the cement production line are stabilized, the number of occurrences of system process failures is reduced, the environmental pollution and the labor intensity of the employees are reduced, the output of the rotary kiln system is improved, and the quality is also significantly improved. In general, the transformation of the cement plant was more successful and has the significance of promotion.
