During the operation of the cement rotary kiln, there are often failures such as egg formation, sand flying, snowman building, and circle formation. These failures not only affect the operation of the kiln, but also the service life of the refractory lining material. In order to solve these problems, it is necessary to understand the formation mechanism of these faults and destroy the formation conditions of the faults, so as to achieve the purpose of high yield, high quality and low consumption.
Today we will talk about the problem of the ring of cement rotary kiln. The former and the latter are divided into three types. Among them, the most difficult to deal with is the rear ring.
Henan refractory brick manufacturers, refractory ball manufacturers, lightweight insulation bricks, Henan Liwei Metallurgical Materials Technology Co., Ltd
1. Sulfur-alkali cycle
The sulfur-alkali ring is a circle formed in the decomposition zone, which not only contains a large number of volatile components, but also contains some characteristic minerals such as 2C2S? CaSO4 and 2c2s? CaCO3。
The formation mechanism of sulfur-alkali rings is that a large number of volatile components act as binders. When C2S stabilizes or converts to 2c2s? CaSO4 and 2c2s? In the case of CaCO3, there is no conversion of β-C2S-γ-C2S, and there is no chalking phenomenon with the conversion, and there is a sulfur-alkali cycle.
Therefore, the prevention and control methods of sulfur-alkali cycle are as follows:
(1) Control the sulfur-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 the hot burning method.
2. a front ring
The front ring is a ring that connects 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 not dealt with in time, it will accumulate higher and higher, and develop into a front ring.
Sun Hung Kai Refractories Co., Ltd. has summarized some of the experience of ring formation before treatment
(1) When the current ring-forming position is far away from the discharge port, it is mainly due to the ring formed for a long time in front of the coal injection pipe. In the process of treatment, the coal injection pipe is pulled out, and the temperature of the kiln head is appropriately increased, which can make the front ring burn.
(2) When the current ring-forming position is close to the discharge port, it is mainly due to the ring formed after the coal injection pipe is set up for a long time. During the treatment process, the coal injection pipe is pulled out, the internal air and secondary air volume are appropriately increased, and the secondary air temperature is increased. This increases the calcination temperature, moves the firing zone forward, and increases the temperature of the front ring. When the current ring-forming temperature rises and the viscosity of the liquid phase is lower than that of the kiln material, after 2-3 hours, the front ring is gradually ground by the kiln material.
(3) If the front ring cannot be burned by the former method, the amount of coal feed, the amount of coal feed and the amount of secondary air can be appropriately reduced. When the tail temperature is low, pull the coal injection pipe to the outermost side, and the nozzle is aimed at the solid combustion. After the poorly pre-fired material at the kiln tail enters the firing zone, the flame can be shortened and the front ring is forced to burn.
(4) Before treatment, the treatment should be observed frequently, pay attention to the change of incoming materials, increase or decrease coal consumption according to the calcination situation, adjust the flame shape, and prevent damage to the kiln skin, loss of raw materials or burning of refractory materials or mechanical and electrical equipment.
3. a rear ring
The latter is a ring formed at the junction of the launch zone and the transition zone. The kiln back ring has a close relationship with 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 clogged by the kiln skin. Some of the materials stay for a certain amount of time before entering the kiln belt. Due to the increase in the temperature of the kiln material or the presence of certain materials with low melting points, this part of the material may adhere to the front of the kiln casing, forming a ring root. After the rear ring is formed, 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 strength of the back ring is low, when the length of the back ring is large, the thermal insulation effect will be enhanced, the temperature of the kiln body near the back ring will decrease, and the shrinkage of the kiln body will put pressure on the inner lining, and the back ring may be damaged due to the pressure. If there is a large amount of unstable C2S in the rear ring, when the temperature is lowered to a suitable value, the β-C2S-γ-C2S transition will occur, resulting in pulverization and collapse. However, if the ring is not damaged for various reasons, it can develop into a failure that is difficult to deal with.
The latter is related to coal, specifically the ash content and ash melting point of coal. According to Zhang Yanwei's research, when Dengfeng No. 2 coal with an ash flow temperature of 1388 °C is used, the cement kiln often forms a loop. If Jincheng coal with a flow temperature higher than 1500°C is used, the formation of a rear ring can be avoided.
If the posterior knot does not self-destruct, it will be longer and higher. If it progresses to a certain level, artificial treatment is required. Ring formation after treatment is usually done by hot burning and cold flashing. According to Zhang Gaofei's experience, the far circle is mainly cold when burning, and the near circle is mainly hot when burning.
(1) When the kiln skin in the kiln is long and thick or has a slight ring root, the coal injection pipe should be pulled out to move the position of the firing zone forward, reduce the solid temperature, change the position of coal ash settlement, and gradually collapse the thick and long kiln skin. At the same time, adjust the wind-coal mix to accelerate the combustion of pulverized coal, so that the low-temperature parts at both ends of the high-temperature zone are not lengthened to prevent the growth of ring roots.
(2) When the thick and long kiln skin in the kiln is not properly treated or not timely, it will lead to the rapid growth of the kiln skin cycle, so that the thick kiln skin will develop into a back ring. First, determine the position and thickness of the ring and the accumulation behind the ring, then reduce the amount of feed, increase the flame temperature, strengthen the pre-firing, gradually increase the kiln speed, maintain the rapid rotation of the kiln, and discharge part of the accumulation behind the ring. At this time, it is not advisable to reduce the temperature of the coal entering the coal ring, thereby reducing the temperature of the flame. After 4-5 hours of burning, the coal injection pipe is pulled out and burned repeatedly, causing the ring body to collapse due to temperature changes. In order to ensure the complete combustion of pulverized coal and prevent the development of circles, it is necessary to appropriately change the composition of raw materials, reduce the liquid phase content in the materials, appropriately change the coal quality, and use coal with high volatile content and low ash content.
In general, it is difficult to form rings after sintering. Sometimes the ring body is very hard and if the ring is burned for too long, it will burn out the kiln skin and lining, or in the transition zone the kiln skin is long and thick, and then a second ring is formed after the ring body. Therefore, be careful while treating. On the premise of protecting the kiln skin, it is necessary to take into account the front and back, operate cautiously, avoid excessive concentration of flames, and avoid burning the kiln skin and lining, resulting in large losses.
4. Use refractory materials to slow down the formation of rings
In order to slow down the formation of rings, refractories can be used in addition to controlling feedstocks and fuels, improving the flammability of raw meals, improving combustion, employing thin material rapid rotation operation, and stabilizing thermal systems.
The test results show that the sulfur-alkali ring can be alleviated by using bricks containing SiC or ZrO2, the sulfur-alkali ring can be alleviated by using galatus-magnesium-aluminum spinel bricks, and some kilns can also be alleviated with silica fume bricks. This is mainly through the selection of refractory materials to reduce the bond 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 cannot completely avoid, the bonding of the kiln lining and the kiln material.
