In the process operation of the rotary kiln in the cement plant, many problems are often encountered. This article summarizes some knowledge about ignition operation, operation of hanging kiln skin, handling operation of unstable incoming material, handling operation of flying sand material, handling operation of balling in the kiln, etc. I hope that when you encounter problems, you can Find a solution fast!

1. Ignition operation of rotary kiln

Whether it is new construction or put into production after maintenance, ignition will be encountered. Before ignition, the entire combustion system should be linked for trial operation to avoid unfavorable conditions such as excessive temperature of the preheater system, blockage of the cyclone pipe and the feeding pipe. Either with firewood or diesel ignition. The dampers of all high-temperature fans should be closed, and the ignition chimney should be opened appropriately according to the situation, so that the kiln head is in a state of slight negative pressure to prevent the wind from being too strong and difficult to ignite. When spraying pulverized coal, try to ensure the combustion rate of pulverized coal, do not spray too much, and add coal slowly; and rotate the kiln at a certain time interval, and the kiln is rotated at 1/4 each time, so as to avoid the bending deformation of the cylinder. When the temperature reaches above 700℃, the auxiliary transmission continuous rotary kiln should be used, the high temperature fan should be activated according to the situation, and the opening of the damper should be adjusted appropriately; when the temperature reaches 900℃, the main transmission rotary kiln can be used. If the diesel ignition is not busy, all oil pumps should be closed, but the valve opening can be appropriately reduced; after feeding, after the material reaches the combustion zone, the oil supply can be stopped. The feeding time is determined according to the temperature of the kiln tail and the outlet temperature of the preheater; the initial feeding amount of the kiln should be relatively high, generally not less than 60% of the designed output, and then slowly increase the feeding amount. The feeding range should be small and not large. up to the normal feed rate; in addition, the run time at low feed rates should be kept as short as possible, as the preheater system is prone to collapse and plugging during this time.

2. Hanging kiln skin of cement rotary kiln

After changing bricks (here only refers to the firing zone), the kiln should be properly baked to avoid temperature rise. First of all, the hanging kiln skin has certain requirements on the raw material composition, especially the amount of liquid phase and the fire resistance of the material. If the amount of liquid phase is large, it is easy to form kiln skin, but it is also easy to collapse, not strong, and cannot withstand high temperature calcination; if the amount of liquid phase is small, the material is refractory, and it is difficult to form kiln skin. The formed kiln skin is quite strong, but if there is a collapse, it is not easy to repair. According to my years of experience, it is recommended to use raw material powder during normal production, which is conducive to the formation of kiln skin. Because in the calcination process, the kiln skin is a kind of dynamic balance, even if there is a small part of the collapse, it is easy to make up in time, but when hanging the kiln skin, do not run out of raw material and under-fire.

3. How to deal with unstable incoming materials

In normal production, the amount of raw material feed fluctuates, but the fluctuation range is small. However, when there are some problems with the equipment, or the raw material water is not easy to control in the rainy season, and the raw materials are easy to agglomerate on the top of the warehouse or on the wall of the warehouse, resulting in poor feeding, there will be a large fluctuation range. In this case, the operator needs to observe and adjust frequently, but also with a certain degree of predictability. The amount of material is judged according to the current change of some conveying equipment. Take action in advance to reduce adverse effects on production, quality and equipment.

(1) When the material is small, do not extend the coal injection pipe, open the large exhaust gas, and elongate the flame, so that the temperature of the kiln tail rises sharply, and the furnace is decomposed. The temperature of the cyclone pipe will also rise rapidly, which is easy to cause the cyclone pipe or the blanking pipe to stick or even block, and the kiln tail smoke chamber and the precalciner are also easy to peel off, increasing the system resistance. When there is less material, the correct operation method is: properly exit the coal injection pipe, close the small exhaust gas, reduce the amount of coal in the precalciner and the kiln head, control the temperature of the kiln tail and the cyclone pipe, use short smoke to burn, and wait for the material arrival.

(2) When there are many raw materials, the kiln head will have positive pressure, and the temperature of the outlet of the cyclone tube and the decomposition furnace will drop sharply. At this time, the kiln speed should be appropriately reduced, the feed amount should be reduced, the large exhaust gas should be opened, and the coal injection pipe should be extended to increase the temperature of the kiln tail and enhance the pre-burning effect of the material. Create a reducing atmosphere and reduce the temperature in the kiln. When the current of the main transmission motor of the kiln drops rapidly, the kiln speed should be reduced, the coal injection pipe should be withdrawn, and the exhaust gas should be appropriately reduced. At this point, a short flame can be used to bring it back to normal. When the working conditions in the kiln are normal, the feeding material is not allowed to be heated, so that the operation is in a passive state, and the production quality is difficult to guarantee.

4. Why fly sand? how to deal with it

There are three main reasons for the formation of flying sand material. One is the improper composition of raw materials, resulting in high silicon rate SM, high aluminum rate IM, low iron content, low calcined liquid phase, and increased liquid viscosity, making it difficult to form calcium silicate (C3S) and form flying sand; second, in order to reduce cost, some manufacturers use pozzolan and fly ash as the calibration raw material, and it is easy to form flying sand; third, the cooler effect is poor, forming flying sand.

When the flying sand material appeared, some people took the method of opening the big exhaust. Increase the kiln end temperature. I think that opening the large exhaust gas can indeed enhance the pre-firing of the material, but when the material reaches the solid phase reaction zone, the liquid phase of the material is not enough, the firing zone is difficult to granulate, and it is easier to form flying sand, which will also affect the entire firing zone. The stability of the kiln skin is not conducive to the kiln conditions and thermal system. After several years of practice and exploration, we have taken measures to withdraw from the coal injection pipe, properly close the exhaust volume (in severe cases, the output can be appropriately reduced), use short smoke combustion, reduce the temperature of the kiln tail, weaken the pre-burning effect of materials, and try to make the liquid phase form as much as possible. , to form C3S more effectively. Although the formation of flying sand materials cannot be completely avoided, it can effectively reduce or weaken the flying sand materials. Except for the partial damage of the kiln skin at the front end of the kiln, it will not affect the stability of the kiln skin of the entire firing zone. It can be replenished in time after the ingredients are improved.

5. Treatment method of ball formation in rotary kiln

The main reasons for the formation of balls in the kiln are: fluctuation of raw material composition and excessive liquid phase; unstable feeding, resulting in high and low temperature at the kiln end, which is difficult to control; high equipment failure rate and frequent shutdown; harmful components such as sulfur, chlorine and alkali in the raw fuel High content; large fluctuation of pulverized coal quality, poor homogenization effect; uneven mixing of kiln dust; negligence of operators, improper temperature control or slow running for a long time. The balling in the kiln can be prevented and treated by taking the following measures.

(1) Preventive measures. First, an appropriate dosing scheme can be selected to stabilize the raw ingredients. Generally, a high lime saturation coefficient is used. High-silicon raw materials are not easy to form balls, and the quality of clinker is good, but it is refractory and requires high operation. If the lime saturation coefficient is low, the aluminum ratio is low, the sintering range is narrow, the liquid phase is large, and the grains are coarse, a little carelessness will lead to ball formation. Therefore, in the production, try to choose the ingredient scheme with two highs and one medium, namely high KH, high SM, and medium IM, which is easy to operate and the quality of clinker is relatively stable. The second is to use raw fuels with lower harmful components as much as possible, especially coal; strengthen the homogenization of coal combustion, reduce the fineness of coal powder as much as possible, and meet production requirements; strengthen the mixing of wind coal during the calcination process to avoid excessive coal powder. Incomplete combustion; if pulverized coal with lower volatility is used, the combustion time is slow and the fire intensity is not concentrated, so the fineness and moisture of the pulverized coal should be reduced as much as possible.

(2) Treatment measures. If pellets have formed in the kiln, analyze, sample and test the reasons for the formation of pellets, and conduct chemical analysis on the core and shell respectively to find out the reasons and prescribe the right remedy. If the pellets are relatively small, the ventilation in the kiln should be appropriately increased to make the flame stable, but attention must be paid to the control of the temperature at the end of the kiln, so that it should not be too high; it can slightly reduce the coal used in the kiln head, but must ensure complete combustion of pulverized coal , Appropriately reduce the feed amount, slightly reduce the kiln speed, so that the material balls in the kiln roll into the firing zone; after the material balls reach the firing zone, the kiln speed can be reduced, and the fire can be burned or reduced in a short time to avoid entering the cooling zone. block or smash the grate plate, but pay special attention to the kiln skin at this time. If the ball is large, it can be treated alternately with cold and heat; when the material ball in the transition zone is not easy to enter the firing zone, it can be extended into the coal injection pipe to appropriately reduce the feeding amount. After burning for 1~2 hours, pull out the coal pipe, and burn for 1~2 hours, again and again, until the pellets break; if it cannot be broken, you can stop the kiln to cool for 1~2 hours, and then ignite and heat, so that the pellets are Excessive temperature difference and rupture. During the treatment process, be careful not to let the large pellets roll into the cooler, otherwise it will cause great damage to the cooler; in addition, the temperature at the end of the kiln should not be too high to prevent the small pellets from appearing one after another.