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Misunderstanding of New Dry Process Cement Kiln Operation

Date:2019-12-25 16:44     writer:admin     Views:

China's new dry cement technology, from the introduction of foreign technology to independent research and development, design, manufacturing, installation, after more than 20 years of exploration, summary and continuous innovation, has gone abroad. Regardless of process design, assembly level or installation capacity, it has reached the international advanced level. However, in terms of new dry cement production management, due to the rapid development of domestic new dry cement, enterprise integration steps are relatively diffuse, and human resources are relatively lacking. Many companies have insufficient understanding of new dry cement production. There is no scientific and reasonable standard for dry cement production management, equipment management and quality control, especially there are still many misunderstandings about the operation of the rotary kiln in the central control room, and there is nothing to do about the process failure.

1 Determinants of kiln operation level


The control and operation of the new dry cement production line kiln is the most important link to finally realize the design intent, excavate the equipment capacity, and improve the efficiency of the enterprise. The level of kiln operation lies in its knowledge of the new dry cement process; whether it is familiar with the site and whether it can accurately determine the status of stable kiln conditions; and whether it adopts corresponding effective and proficient according to different raw fuel materials The adjustment of the coal injection pipe, the control of the kiln tail temperature, the control of the caster cooler, the balanced matching of wind, coal, material and kiln speed, and the optimization of the operating parameters of the system
 

2 Misunderstanding of new dry cement kiln operation


The main misunderstandings of the new dry cement kiln operation are: the higher the saturation ratio, the higher the clinker strength; the lower the temperature in the kiln, the higher the free calcium, and the slower the kiln speed; The internal wind of the coal injection pipe reduces the external wind and the flame shortens; increasing the external wind of the coal injection pipe reduces the internal wind and the flame extends; the position of the coal injection pipe in the third quadrant is better.
 

2.1 About saturation ratio and clinker strength


There are kiln operations in many factories, especially the process technicians believe that the higher the saturation ratio, the higher the clinker strength. The author believes that the clinker saturation ratio exceeds 0.93, and the clinker strength cannot be improved. Because the new dry-type kiln is different from other kiln types such as Huaxin (343.75 yuan / ton, 0%) kiln, Lipor kiln and hollow kiln, the length of the kiln is relatively small, generally 4-10, and even the length-diameter ratio is about 12. The two-support short kiln, the preheating and decomposition of materials are completed in the preheating and precalcining system. The rotary kiln is only a clinker satin firing process. If the clinker saturation ratio is high, it is necessary to increase the thermal strength in the kiln, increase the thermal load of the kiln, increase the amount of coal sprayed at the kiln head, and reduce the kiln speed appropriately. In this way, the capabilities of the preheater, decomposition furnace, caster cooler and rotary kiln will be mismatched, the system will be disordered, and the phenomenon of collapse and crust will easily occur. The thermal system in the kiln will be difficult to stabilize, which will not ensure stability and high maturity Material strength. According to the author's debugging experience of different kiln types from 1000t / d to 5000t / d, it is reasonable to control KH = 0.90 ± 0.02. The system is stable and easy to control, which can ensure the long-term safe and stable operation of the rotary kiln, while maintaining high process technical indicators. And environmental protection indicators, and truly achieve high quality, high output, low consumption and safe and environmentally friendly operation.
 

2.2 About low temperature in front of the kiln


The temperature in front of the kiln is low, and severe free calcium is high in severe cases. Many operators are accustomed to head coal and reduce kiln speed. If the filling rate in the kiln is not large, it is still possible to add a little bit of coal or slightly reduce the kiln speed, and it can also increase the front temperature. However, the low temperature in front of the new dry process kiln is often caused by poor ventilation in the kiln. For example, the opening of the three-way air main valve is too large, necking, skinning of the smoke chamber, and the negative pressure of the preheater system rises as a whole. It can be sure that the ventilation in the kiln is poor. In severe cases, adding coal will cause the tail temperature to drop and the inlet temperature of the decomposition furnace to rise. At this time, the more coal is added, the faster the kiln speed drops, and the free calcium will be higher; at the same time, lowering the kiln speed will also cause the kiln tail sealing ring to dump. The correct operation method should be to appropriately reduce the feeding amount and reduce the filling rate in the kiln. After that, check whether the main air valve is broken three times. If the negative pressure of the kiln tail increases or decreases, the overall negative pressure of the preheating system should be immediately cleared to eliminate the causes of poor ventilation in the kiln and return the kiln to normal. Of course, low secondary air temperature, low decomposition rate, and poor pre-burning of materials also cause low temperature in front of the kiln. Regardless of the reason, as long as the cause of the low temperature before the kiln can be accurately judged, the operation adjustment is relatively simple.
 

2.3 About Kiln Skin


In the past, there were special operations for hanging the kiln skin, such as special low material with high liquid phase, slow kiln speed, and stipulated that the pulverized coal injection pipe of the kiln head was moved 3 to 4 times in one shift. Although this operation method is not adopted now, many operators are concerned that the flame of the kiln head is strong and the kiln skin is easily damaged. It is customary to lengthen the kiln head flame and hang the kiln skin with a soft flame. Especially when the kiln skin is not very good and the barrel temperature is high, the operator naturally reduces the primary air pressure and lengthens the kiln head flame. The author believes that the kiln operation of the new dry process cement does not require special kiln hanging operations, and there is no need to worry about the kiln skin being damaged by the kiln head flame. As long as the stable thermal system in the kiln is maintained and the kiln condition is maintained, the kiln skin will grow naturally and intact. However, when the refractory brick is thin and the temperature of the cylinder is high, you can appropriately lengthen the flame and move the coal injection pipe according to the location of the high temperature of the cylinder. The flame was readjusted to make the flame lively and powerful, and the high temperature point was concentrated. The coal injection pipe gradually returned to the original position, and the high temperature kiln skin was replaced. During this period, a stable thermal system and good kiln conditions must be guaranteed. The strong flame of the kiln head will not only damage the kiln skin, but also facilitate the growth of the kiln skin. As long as the flame does not diverge and is lively and powerful, it will not damage the kiln skin. Only when the flame shape is good, the high temperature point is concentrated, and the kiln skin hung under the condition of high flame intensity is strong, long-lasting, and not easy to fall off.
 

2.4 About Kiln Head Flame


Regarding the adjustment of the coal injection pipe, the author found that many operators simply increased or decreased the internal wind or external wind of the coal injection pipe in order to shorten or extend the flame. Many product descriptions of coal injection pipes and some textbooks are basically this view. However, the author believes that the adjustment of the coal injection pipe must ensure that the flame is lively and powerful, short but not scattered, and long and not thin. If only the internal or external wind is adjusted, the flame shape cannot reach the ideal state. Whether it is a two-channel, three-channel or four-channel coal injection pipe, the length of its flame depends on the burning rate of pulverized coal. The larger the burning rate, the shorter the flame; the smaller the burning rate, the longer the flame. The combustion rate v of pulverized coal is a function of the oxygen content O2 and the temperature T: V = f (O2, T). The stronger the cyclone wind (also called the inner wind), the better the pulverized coal mixes with the air. The greater the oxygen content in the flame, the greater the combustion rate and the shorter the flame. At the same time, because of the strong cyclone wind and the high rotation rate, the flame is easy to diverge. . The stronger the jet wind (also called the external wind), the greater the injection rate, the greater the negative pressure in the negative pressure zone of the coal injection pipe outlet, the more high-temperature secondary air absorbed, and the higher the temperature of the pulverized coal combustion air, the greater the combustion rate. , The flame will be shortened; it is also because of the high jet velocity, the strength of the wrapped flame, the flame is slender. Therefore, adjusting the flame of the coal injection pipe should adjust the internal and external wind at the same time, which can ensure the effective mixing of pulverized coal and the combustion air and fully absorb the high temperature secondary air, so that the flame is lively and powerful, short but not scattered, and long and thin.
 

2.5 About the position of the coal injection pipe


Many enterprises will determine the position of the coal injection pipe before the ignition of the new kiln, which is generally the third quadrant and the coordinates are (-30, -50). This approach is personally considered undesirable. The position of the coal injection pipe should be positioned according to different kiln types and different raw fuel material components to stabilize the thermal system in the kiln. The small kiln has a small kiln diameter, low output, small amount of coal, and relatively small flames, so the cold positioning of the coal injection pipe is preferably centered or the first quadrant. The large kiln has a large kiln diameter, high output, and high coal consumption. The flame is relatively large and the flame is relatively thick, so the cold positioning of the coal injection pipe is preferably centered or the third quadrant. The thermal position of the coal injection pipe should be adjusted in consideration of the composition of the raw materials, the temperature gradient in the kiln, the clinker pellets, and the length and thickness of the kiln skin. For example, potassium, sodium, chlorine, sulfur, magnesium and other harmful components in raw materials are high, clinker grains are coarse, and it is easy to produce core material, and coal injection pipe is suitable for partial deviation; otherwise, the center of coal injection pipe is better. it is good.
 

The hot-state positioning of the pulverized coal injection pipe finally takes the length of the kiln skin B as 4.5-5.2 times the diameter D of the rotary kiln, that is, L = (4.5-5.2) × D, the kiln skin is uniformly thick, and the clinker agglomeration is uniform.
 

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