Precautions of Coal Gangue Brick in Roasting Process of Tunnel Kiln

The sintering of coal gangue sintered brick can be understood:

Under the action of high temperature, the high temperature stable crystal phase is formed and grows up, and the amount of liquid phase formed during the formation and sintering of new crystals is as followsAbout 2% is appropriate, the existence of excessive liquid phase will make the product produce plastic deformation, but also make the product strength decreased, brittleness increased, and produce moisture expansion and other defects.

The necessary conditions for the sintering process: 1/calcination temperature; 2/sintering time; 3/atmosphere properties.

1/, Observation Analysis and Regulation

The normal operation of the coal gangue sintering tunnel kiln is continuous. Under the condition of the same speed, the pressure, temperature and atmosphere of the three zones must be in a relatively stable level state, and the fluctuation range is not allowed to exceed the requirements of the thermal system.

Temperature and pressure are important issues that should be mastered in roasting operations. The temperature system serves the yield and quality requirements of roasted products, while the pressure system serves the temperature system.

In order to ensure the normal operation of the tunnel baking kiln, the firing workers must observe and analyze some changing factors frequently so as to control them in time.

2/Relationship between preheating zone and roasting zone

The preheating zone and the roasting zone are not completely separated, and the two zones have the continuity of preheating, heating and firing. In terms of temperature, the preheating zone temperature is the basic temperature of the roasting zone temperature, and the temperature of the previous parking space is also the basic temperature of the next parking space.

The basic temperature is directly related to the roasting temperature. In turn, the burning intensity of the roasting zone affects the base temperature of the preheating zone. It can be seen that the relationship between the two belts is extremely close, mutual restriction and mutual influence. Therefore, in the operation, we must look forward to see its development trend, so as to adjust and control the loss.

There is a relationship of interdependence and mutual restriction between the preheating zone and the roasting zone. When the car speed is faster, the temperature of the preheating zone is lower, and the preheating zone moves backward, thus affecting the roasting maximum temperature point to move backward, and the roasting zone also moves backward. When the speed of entering the car is slow, the front section of the preheating zone heats up, and the temperature of the preheating zone is higher. Therefore, the highest temperature point affecting the roasting moves forward, and the roasting zone also moves forward.

3/. Burning intensity and air supply

The firing temperature, the number of high-temperature vehicles and the high-temperature point are all directly related to the combustion intensity of the brick in the kiln. The combustion intensity is strong and weak, and is closely related to the air supply. Production practice has proved that the air supply should be able to meet the full combustion of brick, and in the high temperature zone can also ensure a certain amount of excess air. This contributes to the formation of a strong oxidizing atmosphere in the firing zone, thereby improving the combustion intensity. Part of the excess air enters the preheating zone through the roasting zone, which is also conducive to the slow heating and combustion of the second half of the brick blank in the preheating zone.

Excessive air supply is not conducive to the firing state in the kiln, which will cause the temperature of the cooling zone to drop sharply and make the product cold crack. At the same time, the temperature of the roasting zone and the preheating zone will also decrease. If the air supply is too small, the cooling zone will cool down slowly, the initial rotation temperature will be too high, and the products will easily burst due to extreme cold from the outside. At the same time, the roasting zone forms a reducing atmosphere and the image firing quality; The temperature of the roasting zone is low, which makes the preheating effect of the preheating zone poor. It can be seen that unreasonable air supply will lead to a chain reaction in the three zones of the tunnel roasting kiln, resulting in unstable kiln operation, and even a vicious circle that affects the firing yield and quality.

Whether the air supply is appropriate can be observed from the coal hole in actual operation. After opening the coal hole and putting in a small amount of firewood, cover the hole cover. When opening the coal hole cover after 1min, if the fire of firewood is very good, it means that there is enough air supply. If the firewood is not on fire when the coal hole cover is opened and the firewood is not on fire after waiting for a few minutes, this indicates that the air supply there is insufficient. The reason why firewood catches fire after opening the coal hole cover is that the kiln is in a negative pressure state. When the hole cover is opened, the wind enters the kiln from the coal hole to support combustion. The formation of a reducing atmosphere in the second half of the firing zone and the preheating zone should be avoided.

4/Kiln car yard blank quantity

Coal gangue fired brick is internal combustion firing, the temperature of the kiln energy from the brick itself contains the heat. Due to different batches of coal gangue calorific value is different, as well as the actual proportion of ingredients fluctuations, so, different batches of mud calorific value may be very different, generally with the mud in the aging pool to determine its calorific value, so, easy to operate and manage. Therefore, it is necessary to adjust the amount of the yard blank of the kiln car according to the actual calorific value of the mud to ensure that the temperature in the kiln will not fluctuate due to the calorific value of the mud. A standard calorific value of mud can be determined according to the roasting system, and then the total calorific value of the brick blank of the whole vehicle can be calculated as the standard heat of the unit kiln car. In order to make the calorific value of each car brick blank basically consistent, it is necessary to adjust the loading quantity of kiln car code blank.

5/Sand seal

In order to avoid or reduce air leakage during the operation of the tunnel baking kiln car, sand sealing is an important measure in addition to the requirement that the kiln car is not deformed and the docking is tight, as well as the pressure balance. The problem that should be paid attention to for sand sealing is the selection and use of sand for sand sealing. According to the operation experience of refractory tunnel baking kiln, bean sand is best used for sand sealing. This kind of sealing performance and fluidity are better, sand sealing is tight, and the resistance to kiln car lining plate is small. Therefore, the load of hydraulic jacking machine is relatively small when entering the car. In addition, the sand at the exit end is taken out of the kiln by the kiln car sand sealing liner, which needs to be recovered in time and finely screened for use.

6/2. Kiln body sealing

The sealing quality of tunnel kiln has a great influence on the pressure and temperature in the kiln. The use of time is not long kiln, kiln sealing is generally better. The part that should be paid attention to frequently is the sealing of the kiln door at the inlet end. Generally, although the kiln body adopts double kiln doors, once air leakage occurs, it will have a greater impact on the kiln parking space. The negative pressure here is the largest. The cold air outside can easily enter the kiln from the periphery of the kiln door, which will reduce the temperature of the parking space. The moist air outside the kiln will enter the kiln, causing net cracks on the brick surface. According to the operating procedures of the double kiln door, the car should be entered so as not to affect the temperature in the kiln and the pumping force of the smoke extractor due to air leakage of the girder.

7/, black heart brick

Bricks that are not thoroughly burned have some black hearts inside, so they are called black heart bricks. This part has no sintered black heart, which seriously affects the strength of the brick. There are many organic compounds in the brick, and a strong oxidizing atmosphere and a long time should be maintained in the medium temperature stage, so that the carbide in the brick can be fully oxidized and burned, which is the most effective measure to prevent the production of the black core brick products.

The raw material of the black-core brick is due to the lack of oxidation atmosphere in the medium temperature stage, the oxidation time period, and the carbide of the organic substance is not completely burned. If the temperature of the brick blank is too fast in the medium temperature stage, especially the kiln temperature rises to 800 ℃, the thicker layer on the surface of the brick blank starts to produce liquid phase. When the liquid phase closes the capillary gaps between particles, it will prevent the full burning of carbides at high temperature, thus forming black hearts. It is easy to find in production that sometimes some kiln cars are fired at lower temperatures. Although the products coming out of the kiln are a little short of fire, there, there, there is no black hearts, this fully proves that the generation of black-core bricks is not necessarily caused by the low temperature of the baking zone. Once the products form black-core in the medium temperature stage, and when the high temperature stage is reached, the timely baking temperature is as high as 1050 ℃, and black-core will inevitably appear. This is an effective measure to prevent black bricks. The coal gangue porous brick must adopt the flat code method. If the flat code method is adopted, the black core embossing is easy to appear on the surface, which not only affects the appearance quality of the masonry wall, but also because the black core embossing part is not sintered, its strength, freeze-thaw performance is poor, and it is easy to fall off.

8/, white-headed brick

Products out of the kiln, if the surface of the brick pink white phenomenon, it is called white brick.

The reason for the production of white head bricks is that the bricks contain sulfides. When these sulfides are burned and produced during roasting, sulfur dioxide and sulfur dioxide continue to be oxidized in an oxidizing atmosphere to generate sulfur trioxide. Sulfur trioxide is absorbed by the surface of the brick in the humid flue gas to generate sulfate, so the surface of the product appears pink white.

measures to prevent white head brick:

First, reduce the moisture content of the brick or reduce the density of the code blank;

Secondly, shorten the preheating zone to prevent condensation and moisture regain;

Then increase the smoke exhaust force, so that the generated sulfur-containing flue gas can be discharged out of the kiln in time.