How To Solve The Problems Of Refractory Materials in Cement Rotary Kiln
During the operation of cement rotary kiln, there are often faults such as egg formation, flying sand, snowman making and ring formation. These faults not only affect the operation of the kiln, but also affect the service life of the furnace lining refractory. To solve these problems, we must understand the formation mechanism of these faults, destroy the formation conditions of faults, so as to achieve the purpose of high yield, high quality and low consumption.
Today we will talk about the circle of cement rotary kiln. The former and the latter are divided into three types. Among them, the most difficult to deal with is the back ring.
1. Sulfur base cycle
The thioalkali ring is a circle formed in the decomposition zone, which not only contains a large number of volatile components, but also some characteristic minerals, such as 2c2s. CaSO4 and 2c2s? CaCO3.
The formation mechanism of thioalkali ring is that a large number of volatile components act as adhesives. When C2S is stable or converted to 2c2s? CaSO4 and 2c2s? In CaCO3, the transformation of β-C2S-γ-C2S does not occur, nor does it accompany the transformation to produce powder phenomenon, and there is a sulfur-alkali cycle.
Therefore, the prevention and control methods of the sulfur-alkali cycle are as follows:
① Control the sulfur and alkali content of raw materials and fuels;
② Slow down the enrichment of sulfur and alkali in the kiln;
③ The sulfur-alkali ring was destroyed by hot firing method.
2. Front ring
The front ring is the ring connected to the cooling zone. When the material in the kiln enters the cooling zone from the firing zone, a part of the clinker that cannot be completely solidified on the kiln skin is formed on the surface. If it is not handled in time, it will accumulate higher and higher and develop into a front ring.
Some experience in handling preforming loops
When the current ring forming position is far away from the discharge port, it is mainly due to the ring formed in front of the coal injection pipe for a long time. In the process of treatment, the coal injection pipe is pulled out and the temperature of the kiln head is properly raised to make the front ring burn.
When the current ring forming position is close to the discharge port, it is mainly due to the ring formed after the long-term setting of the coal injection pipe. In the process of treatment, the coal injection pipe is pulled out, the internal flow air and secondary air volume are appropriately increased, and the secondary air temperature is increased. This can increase the calcination temperature, make the firing zone move forward, and increase the front ring temperature. When the current ring forming temperature rises and the liquid phase viscosity is lower than the kiln material, the front ring is gradually ground by the kiln material after 2-3 hours.
(3) If the former method cannot burn the front ring, the amount of coal, the amount of coal and the secondary air volume can be appropriately reduced. When the tail temperature is low, pull the coal injection pipe to the outermost, and the nozzle is aimed at the solid combustion. After the poorly pre-fired material at the kiln end enters the firing zone, the flame can be shortened and the front ring is forced to burn.
④ Before treatment, we should often observe the treatment, pay attention to the changes of incoming materials, increase or decrease the coal consumption according to the calcination situation, adjust the flame shape, and prevent damage to the kiln skin, loss of raw materials or burn out refractory materials or mechanical and electrical equipment.
3. Back ring
The latter is a ring formed at the junction of the launch and transition zones. There is a close relationship between the kiln back ring and the low melting point material in the kiln. It is also closely related to coal ash. Therefore, the latter ring is also called the pulverized coal ring.
When the transition zone material enters the firing zone, it will be blocked by the kiln skin. Some materials stay for a certain time before entering the kiln belt. Due to the rising temperature of the kiln material or the presence of some low-melting material, this part of the material may adhere to the front of the kiln skin, forming a ring root. After the formation of the rear ring, its protruding part can hinder the flow of gas in the kiln, and adhere to the pulverized coal in the kiln gas to form a pulverized coal ring. If the back ring strength is low, when the back ring length is large, the insulation effect will be enhanced, the kiln body temperature near the back ring will be reduced, the kiln body contraction will create pressure on the lining, and may damage the back ring due to pressure. If a large number of unstable C2S are present in the back ring, a β-C2S-γ-C2S transition occurs when the temperature is reduced to a suitable value, resulting in pulverization and collapse. However, if the ring is not damaged for various reasons, it will develop into a difficult fault to deal with.
The latter is related to coal, especially the ash content and ash melting point of coal. According to Zhang Yanwei's research, when using Dengfeng No. 2 coal with a ash flow temperature of 1388℃, the cement kiln often forms a circle. If Jincheng coal with a flow temperature higher than 1500℃ is used, the formation of the back ring can be avoided.
If the back knot doesn't self-destruct, it'll be longer and taller. If it develops to a certain extent, manual treatment is required. The ring formation after treatment is usually accomplished by hot firing and cold flash. According to Zhang Gaofei's experience, the far circular combustion is mainly cold, and the near circular combustion is mainly hot.
① When the kiln skin is long and thick or has a slight ring root in the kiln, the coal injection pipe should be pulled out to move the position of the firing belt forward, reduce the solid temperature, change the location of the ash settlement, and make the thick and long kiln skin gradually collapse. At the same time, adjust the combination of air and coal, accelerate the combustion of pulverized coal, so that the low temperature part at both ends of the high temperature zone is not extended, and prevent the growth of ring roots.
When the thick and long kiln skin in the kiln is treated improperly or not in time, it will lead to the rapid growth of the kiln skin cycle, so that the thick kiln skin develops into a back ring. First determine the position and thickness of the ring and the accumulation after the ring, and then reduce the feed amount, increase the flame temperature, strengthen the pre-firing, gradually accelerate the kiln speed, maintain the rapid rotation of the kiln, and part of the accumulation after the ring. At this time, it is not appropriate to reduce the temperature of the coal entering the coal ring, thereby reducing the temperature of the flame. After 4-5 hours of combustion, the coal injection pipe is pulled out and repeatedly burned, so that the ring body collapses due to temperature changes. In order to ensure the complete combustion of pulverized coal and prevent the development of ring formation, it is necessary to appropriately change the composition of raw materials, reduce the liquid phase content of materials, appropriately change the coal quality, and use high-volatile and low-ash coal.
In general, it is difficult to form rings after sintering. Sometimes the ring body is very hard, if the ring is burned for too long, it will burn the kiln skin and lining, or in the transition zone the kiln skin is long and thick, and then a second ring is formed behind the ring body. Therefore, be careful when treating. Under the premise of protecting the kiln skin, both before and after, careful operation to avoid excessive concentration of flame, avoid burning the kiln skin and lining, resulting in greater losses.
4 Use refractories to slow the formation of rings
In order to slow the formation of rings, refractories can be used in addition to controlling raw materials and fuels, improving the burnability of raw materials, improving combustion, using thin material quick turn operation and stabilizing thermal systems.
The test results show that the thioalkali ring can be alleviated by using bricks containing SiC or ZrO2, the thioalkali ring can be alleviated by using square magnesia-alumina spinel brick, and some kilns can also be alleviated by silica fume brick. This is mainly through the selection of refractory materials to reduce the binding strength of refractory materials and kiln materials, so that the attached kiln materials are easier to fall off. However, cement clinker and various cement kiln refractories are silicate materials. Therefore, the use of refractory materials can only reduce, but not completely avoid the bonding between kiln lining and kiln material.
JIYGO REFRACTORY & ABRASIVE LIMITED
