- Time:Dec 30, 2022
A. What is hanging kiln coating
A rotary kiln is the main equipment for cement production. A cement rotary kiln is an inclined, rotating cylinder placed on several pairs of pallets by a number of belts, with refractory bricks inlaid on its inner wall. The raw material powder is fed into the kiln from the feeding pipe at the high end of the kiln barrel. Due to the inclination and slow rotation of the kiln barrel, the material produces a compound movement that rolls along the circumference and moves from high temperature to low end along the axial direction. The fuel is sprayed in from the kiln head and burned in the kiln, the heat issued heats the raw material and makes it calcined into clinker. The hot air formed in the process of exchanging with the material enters the kiln system from the kiln feed end and is finally discharged into the atmosphere by the chimney.
Rotary kiln mainly consists of kiln cylinder, transmission device, support device, wheel stopper device, kiln head sealing device, kiln tail sealing device, kiln head cover and so on. The cylinder of cement rotary kiln is a cylinder made of steel plate. To protect the cylinder of rotary kiln, a layer of refractory bricks is set on its inner side as kiln lining.
Rotary kiln is an equipment integrating fuel combustion, heat exchange, high-temperature chemical reaction and conveying material airflow. As the gas temperature inside the kiln is much higher than the material temperature he, a high temperature of more than 1450℃ is often maintained in the vessel, and the surface of the kiln lining is subjected to periodic thermal shock with a temperature change of 150-250℃ for every rotation of the kiln, which produces a thermal stress within the surface layer of 10-20mm of the kiln lining. Thermal stress; kiln lining is also subjected to alternating changes in brick masonry axial and radial mechanical stress due to rotation, as well as calcined material scouring wear; due to the simultaneous production of silicate melt has a certain erosion effect on the refractory material, will cause the refractory material off, so that the kiln surface temperature is too high or "red kiln".
Refractory brick refractoriness and thickness is limited, can not stand long time high temperature attack and material chemical reaction of corrosion, in order to extend the service life of refractory bricks, so in its surface plus a layer of solid protection layer, that is, hanging on a layer of clinker, see fire workers called it "kiln coating".
The purpose of hanging kiln coating is to extend the service life of fire bricks, so that the rotary kiln barrel is not damaged, and can reduce the heat loss to the outside and improve thermal efficiency. Its specific role is as follows.
1. Protect the refractory bricks from direct high temperature and chemical erosion.
2. Store heat energy, reduce the heat loss from the kiln shell to the surrounding area, and improve the thermal efficiency of the rotary kiln.
3. Adequate heat transfer medium, where the kiln coating is exposed to air and in contact with hot air, absorbs heat by radiation or convection, and when the kiln coating is in contact with the material in the lower part, transfers heat to the raw material by conduction.
4. The surface of kiln coating is rough, it can reduce the flow speed of powder and prolong the reaction time of material in the kiln.
B. The principle of hanging kiln coating
According to the material in the calcination has the adhesive properties and surface melt refractory bricks combined together to hang kiln coating characteristics. After the material enters the firing zone, the liquid phase appears and increases with the temperature rise. When the surface of the refractory bricks slightly molten, with the rotation of the kiln, the clinker with certain adhesive properties will be pressed under the refractory bricks, and absorb a certain amount of heat from the refractory bricks to make them stick together, and chemical reactions, with the temperature drop to form the first layer of kiln coating, with the kiln running time longer kiln coating thicker and thicker, the surface temperature of the kiln coating is also getting higher and higher, the number of sticky and fallen kiln coating equal, and then by firing, the kiln coating solid and dense.
C. How to hang kiln coating
New dry kiln general hanging kiln coating steps are as follows.
When the kiln tail temperature reaches about 950 degrees, the vortex decomposition chamber temperature reaches 650-700 degrees, and the fire brick at the kiln head starts to shine and turn white, the raw material fed first will enter the firing zone soon. At this time, the kiln head stays on fire to maintain a high enough temperature in the firing zone and restore the 2 C4 ash discharge valves that are lifted. Open the valve of the third air duct to about 10%, open the valve of the vortex combustion chamber and decomposition chamber, and start to spray light diesel fuel and a small amount of coal dust into the vortex decomposition chamber. When the temperature of C1 outlet reaches 400-450 degrees, open the cold air valve placed on the exhaust gas pipe from C1 outlet to the high temperature fan, and mix in cold air to adjust the exhaust gas temperature and protect the high temperature fan. When the gas temperature of C5 outlet reaches 900 degrees, open the valve of the three air ducts appropriately and then feed the material. The feeding amount is 30-40% of the design capacity, and gradually close the cold air valve to appropriately increase the amount of coal feeding and system exhaust air, turn the kiln slowly and start to hang kiln coating; the system is normal and the decomposition furnace temperature is stable, you can remove the ignition nozzle; if burning anthracite coal, you should appropriately extend the use of the ignition nozzle, but the amount of oil can be reduced to play a role in the smokeless combustion. The key to hang the kiln coating is to adjust the coal feeding and kiln speed in time when the raw material arrives at the firing zone to ensure that the temperature of the firing zone is stable and the kiln speed is compatible with the feeding amount, so that the thickness of the kiln coating is consistent and flat. If the temperature is too high, the hanging kiln coating is easy to be burned down, raw material is easy to burn flow, refractory bricks are seriously eroded; if the temperature is suddenly reduced will run raw material, the formation of the kiln coating loose sandwich, easy to collapse. Generally, it takes 3-4 shifts to hang the kiln coating.
D. Influencing factors of hanging kiln coating
1. Chemical composition of raw material
The so-called hanging kiln coating is the process of liquid phase solidification to the surface of refractory bricks. Therefore, the amount of liquid phase of clinker firing liquid phase viscosity directly affects the formation of kiln coating, and the chemical composition of raw material directly affects the amount of liquid phase and its viscosity. In the past for wet kiln, people advocate that the silica rate of raw material during the hanging kiln coating should be lower, and the saturation ratio should be higher. However, for the precalciner kiln, the kiln head is currently using three ducts or four ducts burner, rotary kiln normal operation, the primary air volume is small, and the secondary air temperature is very high. Therefore, the coal powder combustion rate and flame temperature are much higher than those of wet process kilns. If the silicic acid rate is reduced, the amount of liquid phase increases accordingly, the material is easy to burn flow, and the hanging kiln coating is easy to fall off without fire. So it is generally advocated that the raw material hanging kiln coating should be the same as the normal raw material composition is good.
2. Firing temperature and flame control
The main factors to hang a good firing belt kiln coating in addition to a certain amount of liquid phase and liquid phase viscosity, but also a proper temperature, airflow, material and refractory bricks between a certain temperature difference. Generally should be controlled at the firing temperature during normal production. Grasp the clinker nodules fine and uniform, not burning large pieces more can not burn flow, strictly prohibit running raw material. The weight is controlled within the normal production index. To keep the firing temperature stable, kiln speed stable, flame shape integrity, smooth. This hanging out of the kiln coating thickness consistent, flat, uniform and solid.
3. Feed rate and kiln speed
A stable kiln thermal regime is a prerequisite for a solid, even and flat kiln coating. Stable feeding amount and stable kiln speed are essential during kiln coating hanging. Too much feeding or kiln speed is too fast, the kiln temperature is not easy to control, and the kiln coating hanging sticky is not flat, not solid. Therefore, the first time the new kiln hanging kiln coating starting feeding amount and kiln speed is best to control the design output of about 35%. Hang to a certain extent and then gradually increase slowly depending on the kiln coating sticky hanging situation. This can keep the material layer from thin to thick, the temperature from lower to higher, the material in the kiln residence time from longer to shorter, in order to keep the fire power in the middle and stable, sticky hanging good kiln coating and burn good clinker. As the kiln coating continues to thicken, gradually reduce the residence time of the material in the kiln, thicken the material layer, improve the firing belt fire, which is also a measure to prevent the kiln coating from hanging fast and loose.
4. Nozzle position during kiln coating hanging
In general, the nozzle position should be as far forward (pulled outward) as possible, while the bias material, the flame should be short rather than long. This is more concentrated in the high-temperature area, high-temperature point forward, so that the kiln coating from the front of the kiln gradually advance towards the kiln. With the gradual increase in the amount of raw feed, the nozzle should move to the kiln accordingly. When the kiln output increases to the normal condition, the nozzle also moves to the normal production position. Do not hang the kiln coating during the flame is too long, otherwise the high-temperature area is not concentrated, the kiln coating hanging far or before the thin after the thick, or even appear in front of the kiln coating has not yet been hung, the back has formed a knotted circle and other unfavorable circumstances.
5. The new kiln should have a three-day operating time to hang the kiln coating
In the process of hanging kiln coating, the kiln coating is required to gradually thicken, not too fast, in order to avoid hanging the kiln coating loose, not strong, affecting the long-term safe operation of the rotary kiln in the future. To judge whether the kiln coating is flat, firstly, according to the barrel temperature scan, see whether there is a peak in the curve fluctuation; secondly, according to the kiln law curve, see whether there is a wide and narrow periodic change; in addition, the site in the kiln head with a fire mirror can also see the kiln coating color slightly white, flat before and after, one color, no convex and concave and bright and dark phenomenon, it indicates that the kiln coating is flatter.
E. How to protect the kiln coating
To protect the kiln coating, the following points should be noted.
1. First of all, we have to hang the kiln coating well, and there is protection in the hanging, and there is hanging in the protection.
2. Establish and build a complete kiln lining material storage and bricklaying responsibility system, improve the quality of lining materials and bricklaying, each with kiln lining should be matched accordingly.
3. Strengthen the control of calcination, avoid burning large fire, burning top fire, strictly prohibit burning flow or birth material, to ensure that the clinker particles fine and uniform.
4. Improve the structure of the coal spray nozzle, maintain the complete flame shape, frequently move the position of the coal spray nozzle, and adjust the high temperature zone.
5. Strictly prevent the knotted circle, found knotted circle to deal with in time.
6. Take timely measures when you find that the kiln coating is not good.
7. Strengthen equipment maintenance and reduce the number of kiln stops to avoid the kiln coating falling off due to sudden cold and heat.
According to the material in the calcination of the adhesive properties and the surface of the molten refractory bricks combined with the characteristics of hanging kiln coating, pay attention to the amount of feeding when hanging kiln coating, kiln speed, flame length and hanging kiln coating time and other points, taking into account all factors, hanging a good kiln coating can reduce heat loss to the outside, improve thermal efficiency, extend the service life of refractory materials, the rotary kiln has a very positive impact. In addition, equipment maintenance should be strengthened, and measures should be taken in time to protect the kiln coating when it is found to be bad.
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