Factors that affect the heat exchange efficiency and dust collection efficiency of the preheater
First, the advantages of suspension preheating technology dry rotary kiln production of cement clinker, raw meal preheating, decomposition and firing process are completed in the kiln. As a firing equipment, rotary kiln can provide uniform temperature field of section temperature distribution, and can ensure that the material has enough residence time at high temperature, so it can still meet the requirements.
However, as a heat transfer equipment, the mass transfer equipment is not ideal, and the decomposition process is not suitable for the preheating which requires a large amount of heat. This is mainly due to the accumulation of materials in the kiln at the bottom of the kiln, the flow of air flow through the surface of the material layer, the small contact area between the air flow and the material, and the low heat transfer efficiency. At the same time, the decomposition belt powder in the kiln is in the layer. In the accumulation state, the area of carbon dioxide decomposed in the material layer is small, the resistance is large and the speed is slow, and the particles in the material layer are wrapped by carbon dioxide gas film, the partial pressure of carbon dioxide is large, and the decomposition temperature is high, which increases the difficulty of carbonate decomposition and reduces the decomposition rate. The breakthrough of suspension preheating technology fundamentally changes the heat transfer state of material preheating process, and the preheating and decomposition process of material accumulation state in kiln is moved to suspension preheater and calciner respectively. Because the material is suspended in the hot air flow, the contact area with the air flow increases greatly, so the heat transfer speed is very fast and the heat transfer efficiency is very high. High. At the same time, the raw material powder and fuel are mixed evenly in suspension state, and the combustion heat of fuel is transmitted to the material in time to decompose it rapidly. Therefore, due to the rapid heat transfer and mass transfer, the production efficiency and thermal efficiency are greatly improved. 2. The characteristics of suspension preheating kiln are that the suspension preheater is installed after the rotary kiln with short length, so that the material preheating and part of carbonate decomposition process carried out in the accumulated state in the kiln are moved to the suspension preheater in suspension state. Therefore, the suspended raw material powder can be in full contact with the hot air flow, the gas and solid phase contact surface is large, the heat transfer speed is fast and the efficiency is high, which is beneficial to improve the kiln's heat transfer speed and efficiency, so that the suspended raw material powder can fully contact with the hot air flow, the gas and solid phase contact surface is large, the heat transfer speed is fast and the efficiency is high, which is beneficial to improve the kiln. Production capacity, reduce clinker burning heat consumption. At the same time, it still has the advantages of less moving parts, not many ancillary equipment, simple maintenance, small occupation area, low investment cost and so on. Third, the composition and function of suspension preheater are mainly cyclone preheater and vertical tube preheater. Now the vertical tube preheater has tended to be eliminated. Cyclone preheater is used as preheating unit equipment in precalciner kiln. The heat exchange unit equipment which constitutes the cyclone preheater is mainly the connecting pipe between the cyclone tube and the cyclone tube (also known as the heat exchange pipe). The main function of suspension preheater is to make full use of the hot discharge from rotary kiln and calciner. The enthalpy of the air flow heats the raw meal to preheat and decompose part of the carbonate, and then enters the decomposition furnace or rotary kiln to continue to heat and decompose the clinker to complete the task of clinker firing. Therefore, it must have three functions: gas and solid phase can be fully dispersed and evenly distributed, rapid heat transfer, efficient separation and so on. Only by combining these three functions and making them as efficient as possible can we improve the heat transfer efficiency to the maximum extent and create conditions for the high quality, high efficiency, low consumption and stable production of the whole kiln system. The function of cyclone preheater lies in the dispersion, uniform distribution, gas-solid heat transfer and separation of materials in hot air flow.
Its performance is mainly manifested in whether it has a higher performance. Heat transfer efficiency, separation efficiency, low resistance and good sealing performance to reduce internal and external air leakage. Cyclone preheater is composed of cyclone tube and connecting pipe between upper and lower stage cyclone tube. The components of cyclone body are cylinder, cone, inlet pipe, outlet pipe, inner tube and feeding pipe. The upper part of the connecting pipe is connected with the inlet pipe of the superior cyclone tube, and the lower part is connected with the outlet pipe of the lower cyclone tube; the material pipe of the superior cyclone tube is connected with it in the appropriate part of the upper cyclone tube; and the air lock valve is installed in the appropriate part of the upper cyclone tube, which not only keeps the raw material separated from the superior cyclone tube open Overentry into the heat exchange pipe can prevent the hot gas flow from the lower cyclone tube from running into the superior cyclone tube to the maximum extent, resulting in the secondary flying of the separated raw material powder and reducing the separation efficiency of the superior cyclone tube. The result is that the hot gas flow from the lower cyclone tube can be short-circuited into the superior cyclone tube, resulting in the secondary flying of the separated raw material powder and reducing the separation efficiency of the superior cyclone tube. When the raw material powder from the upper cyclone tube enters the heat exchange pipe, the raw material powder from the upper cyclone tube is splashed on the heat exchanger, so that the raw material powder can be rapidly dispersed and distributed in the hot air flow out of the lower cyclone tube, so as to improve the heat transfer efficiency. The purpose of this paper is to make the raw material powder disperse rapidly and distribute it in the hot air flow out of the lower cyclone tube, so as to improve the heat transfer efficiency when the raw material powder from the superior cyclone tube enters the heat exchange pipe. Tracing back to the source, the cyclone tube, which is the main part of the cyclone preheater, It is developed on the basis of ordinary cyclone dust collector. The common denominator of the two is that they can have high gas-solid separation efficiency under low pressure loss. The difference is that the cyclone dust collector does not have the heat transfer function, but should have the highest gas-solid separation function as much as possible. For the cyclone tube of the main equipment in the cyclone preheater, because it is composed of multi-stage heat transfer unit, the material is heated step by the multi-stage preheating unit, so as long as the given gas-solid separation efficiency and a certain heat transfer effect are maintained, the due task is completed. So in the cyclone preheater system, depending on the different levels of the preheater, it has no The same gas-solid separation efficiency is the target, and the structure of the gas-solid separation is also different. So that the dust-containing gas stream is finally separated. The different physical properties of the air flow and the dust are mainly manifested in one of the gaseous substances, the quality is small, the deformation is easy, the other is a solid substance, the mass is large, and the dust is not easy to deform. Therefore, when the dust-containing gas flow is subjected to centrifugal force, when the dust-containing gas flow is concentrated to the inner wall of the cyclone cylinder, the centrifugal force it receives is larger than that of the gas, so that the dust is mechanically conditioned to extrude the air flow, and the air flow is concentrated on the cylinder wall, and the air flow is attached to the dust layer. When the dust-containing gas flow moves, the dust is applied to the air flow to locally change the motion state of the air flow; and The air flow also gives the dust a reaction force, which is the resistance of the air flow to the dust. The theoretical analysis and scientific experiments show that there are two main factors affecting the fluid resistance and separation efficiency of cyclone tube, one is the geometric structure of cyclone tube, the other is the physical properties of the fluid itself. As a cyclone used in suspension preheating device of cement industry, the physical properties of dust-containing air flow are roughly determined. Fourth, the factors that affect the thermal efficiency and dust collection efficiency 1. As an important equipment in the process of cement suspension preheating decomposition, the air leakage of cyclone tube is harmful and useless, whether it is internal air leakage or external air leakage. Pre The external air leakage of the thermal system directly influences the thermal efficiency and increases the power consumption of the exhaust fan, and the air leakage in the discharge pipe causes the separation efficiency of the cyclone to be reduced sharply, and the amount of fly ash in the system is increased, thus indirectly affecting the thermal efficiency of the preheater system. In the actual production process, the outside air leakage of the preheater system is easy to be found. Strengthen the management, improve the responsibility of the operator, and the external air leakage can be controlled. But the internal air leakage at the blanking pipe is generally judged by the experience of the operator, and is not easy to be found. At present, the discharge device of the flap valve is widely used, and in order to prevent the blockage and smooth discharge, a certain amount of gas is often allowed to leak into the discharging pipe from the turning plate, so the method Discharge of flap valve cannot completely eliminate internal air leakage. It is of great significance to study the influence of air leakage on the separation efficiency of cyclone and find effective measures to reduce the harm, which is of great significance for reducing fly ash and improving the thermal efficiency of preheater kiln system. The closer the air leakage point at the blanking pipe is to the discharge port of the cyclone, the greater the reduction in the separation efficiency of the cyclone caused by the air leakage. In the actual production process, the unloading of the flap valve cannot completely eliminate the internal air leakage. The separation efficiency of cyclone can be improved by extending the distance between the installation position of flap valve and the discharge port of cyclone. 2. The inlet wind velocity of cyclone affects different inlet wind speeds, with the cyclone. With the increase of the inlet wind speed, the air leakage at the feeding pipe leads to the decrease of the separation efficiency of the cyclone tube. If the air leakage volume is kept constant, the inlet wind speed has little effect on the decrease of the separation efficiency of the cyclone tube caused by the air leakage. 3. The effect of solid-gas ratio on solid-gas ratio is different, and the decrease range of separation efficiency of cyclone tube caused by air leakage at the feeding pipe is also different with the increase of solid-gas ratio, and the decrease range of separation efficiency of cyclone tube caused by air leakage at the feeding pipe is also increased. However, for a given air leakage rate, the difference of separation efficiency decreases with the increase of solid-gas ratio. The larger the ratio of solid to gas is, the more serious the phenomenon of shed material at the discharge port of cyclone tube is caused by the leakage of air in the discharge pipe. this It is possible that the larger the solid-gas ratio, the larger the separation efficiency of the cyclone can be reduced due to the air leakage at the discharge pipe. 4. The impact of the cone is well known. In the dust removal process, the cone has the function of reducing the loss of fly ash and improving the dust collection efficiency of the cyclone dust collector. The gas-to-gas ratio during the operation of the cement cyclone preheater is much larger than that of the cyclone dust collector. In order to study the role of the cone in the process of gas-solid separation, the cone plays an important role in reducing the separation efficiency of the cyclone cylinder due to the air leakage at the discharge pipe, which can be caused by the high separation efficiency of the cyclone. It is very difficult to improve the separation efficiency again. 5. the structure of cyclone tuyere is generally rectangular. Due to the change of structure type and the geometric shape of inlet, some of them are pentagonal or some are rhomboid, in order to guide the downward oblique movement of gas-solid flow into cyclone and reduce the resistance of cyclone. There are generally two kinds of inlet modes of cyclone, that is, the outer edge of the inlet air flow is tangent to the cylinder, and the inner edge of the air flow is tangent to the cylinder. Because the volute inlet can gradually narrow the air flow channel into the cyclone tube, it is beneficial to reduce the distance of particles moving to the cylinder wall and increase the gas. The distance from the flow to the exhaust pipe to avoid short circuit can improve the separation efficiency. At the same time, it also has the advantages of large air volume and small pressure loss, so it is often used. 6. The structure and size of exhaust pipe are also very important to the fluid resistance and separation efficiency of cyclone tube. If not designed improperly, a turbulent area will be produced near the lower end of the exhaust pipe, and the settled dust particles will be taken away to reduce the separation efficiency. It is generally believed that the diameter of the exhaust pipe decreases, the dust particles are removed, and the separation efficiency increases, but the resistance increases. In order to reduce the resistance, the diameter of the inner cylinder tends to expand, so the outlet wind speed also decreases. 7, with the insertion depth of the inner cylinder With the increase of degree, the resistance coefficient and separation efficiency increase in different ranges. In the range of the ratio of inner cylinder insertion depth to inlet height s/a=0.482-0.612, the resistance coefficient is low and does not change much, and the separation efficiency increases slightly, so to ensure a certain separation efficiency, it should be emphasized that the middle stage cyclone tube s ≥ a should be about 0.612, and it is better not to < 0.482 (the separation efficiency is reduced too much) and not > 0.816 (the resistance coefficient increases too much). The uppermost cyclone tube s / a, which emphasizes the separation efficiency, should be about 1.02, because when s ≤ a < 1.02, The separation efficiency decreased a lot. When s ≥ a > 1.02, the separation efficiency increased 8, and the resistance coefficient and separation efficiency decreased in varying degrees with the increase of inner cylinder diameter. When the inner cylinder diameter d ≤ D < 2 / 3, the resistance coefficient decreased rapidly, and when d ≥ D > 2 / 3, the resistance coefficient decreased slowly. For the separation efficiency, the separation efficiency is higher and the separation efficiency does not change much when the diameter of the inner cylinder D ≤ 0.6, and decreases rapidly when the diameter of the inner cylinder is d ≤ D > 0.6. Therefore, to ensure a certain separation efficiency, the diameter of the inner cylinder of the intermediate stage cyclone cylinder with resistance reduction should be emphasized. D ≤ D can be about 2 ≤ 3, and it is best not to do so. It is necessary to > 2 ≤ 3, otherwise the resistance coefficient does not decrease much and the separation efficiency decreases greatly; also do not < 0.6, otherwise the resistance coefficient increases too much, and the simple diameter in the upper stage cyclone cylinder, which emphasizes the separation efficiency, d ≤ D should be < 0.6, because when d ≥ D > 0.6, the separation efficiency decreases more. It is not large, but the resistance coefficient increases to a certain extent. 9. with the increase of the height of the cyclone tube, the resistance coefficient and separation efficiency of the cyclone tube decrease and increase in varying degrees, especially when the height and diameter of the cyclone tube is more obvious than that of H ≤ D < 2.282, but when H ≤ D > 2.28, the resistance coefficient and separation efficiency of the cyclone tube decrease and increase in varying degrees, especially when the height and diameter of the cyclone tube is more obvious than that of H ≤ D < 2.282. When 2, the drag coefficient and the separation efficiency decrease and increase with the increase of the cyclone cylinder height, respectively. Therefore, the high-diameter ratio of the cyclone can be ensured to be about 2.282 under the premise of considering the height of the kiln tail tower and the cost of one-time investment, because the separation efficiency is reduced when the height of the kiln tail tower is too low, and the resistance coefficient is increased. When too high, the separation efficiency and the drag coefficient are increased and reduced, respectively, while the cyclone cylinder height and the equipment cost are increased to a certain extent. V. Inspection and maintenance during normal production mainly includes the following aspects:
(1) the condition of the ash discharge valve during normal production;
(2) the sealing condition of the system;
(3) Decomposition furnace, cyclone tube and connecting pipe shell are abnormal (such as: observation shell domestic village falling off and red);
(4) whether the blowing blocking device of each cyclone tube is flexible (solenoid valve) and whether the blowing blocking pressure meets the standard;
(5) whether the manual plug removal tool is properly prepared;
(6) whether the system temperature measurement, whether the pressure measuring device is stable and reliable;
(7) whether the combustion of the combustor of the calciner is abnormal;
(8) whether the manual plugging tool is ready; (6) whether the pressure measuring device is stable and reliable;
(9) (9) whether the combustion of the calciner burners is abnormal; (8) whether the system safety protection measures are complete or not.
6. Inspection of preheater and calciner during kiln stoppage
7. (1) check whether brick or foreign body is dropped in cyclone tube and calciner and whether the inner cylinder is in good condition; whether brick is dropped in horizontal pipe The material and material shall be cleaned in time; if there is any brick in the rising pipe, the guide plate and the material spreading plate shall be in good condition.
(2) Check the lubrication of each ash discharge valve bearing, and conduct cleaning and oil filling if necessary; check whether the valve surface of each ash discharge valve is in good condition, such as serious or serious deformation of the valve surface, and replace it in time.
(3) Check whether the burner of the decomposition furnace is in good condition. If it is found that the burner is seriously or deformed, it shall be replaced.
(4) Check the end of the kiln, the smoke chamber and the tongue for skinning. If there is any skin, it shall be cleaned in a timely manner.
(5) After the overhaul of the system, thoroughly check whether the parts of the system are unblocked. No foreign body, ash discharge valve activity is flexible, after the inspection should close all observation holes and entry doors, do a good job of sealing the system.