In recent years, a large number of new dry-process cement clinker production lines have been built in China, but most cement companies have focused on the optimization of calcining and grinding process equipment and energy-saving and energy-saving. Even some newly-built enterprises have not fully considered drying, so that the drying process is backward and the equipment selection is unreasonable, which has become a bottleneck restricting the entire production line.
According to the urgent needs of the market, Nanjing Rotary Heavy Duty Machine has developed an upgraded product of traditional rotary dryer and vertical dryer â€“ high-yield energy-saving dryer. On the basis of simple process and high equipment operation rate, the rotary dryer has the advantages of high output, low coal consumption and reliable operation. It can increase the output by 60%~100% on the basis of the original rotary dryer. The effect is very significant.
1. Problems with traditional rotary dryers
The output is not high, and the average drying power consumption and coal consumption are high. The material does not dry, and the final moisture exceeds the control index, resulting in low mill output, high grinding power consumption, and serious jamming and grinding accidents. The dryer has a large amount of maintenance, and the head of the dryer is easily burned and deformed, especially the feeding part, which needs to be replaced frequently, which seriously affects the normal production of the dryer. Exhaust gas purification system of drying operation is prone to condensation and wet bottom, which not only affects production, but also shortens the service life of equipment and increases maintenance costs.
In order to achieve the control index to achieve the final moisture content of the drying material, some users themselves lengthen the length of the drying cylinder, which not only increases the weight, power consumption and investment of the equipment, but also increases the civil construction investment and construction period, resulting in on-site process layout. Difficult and crowded.
2. Adopting a downstream process to eliminate the countercurrent process
The downstream process means that the flow direction of the material and the hot air in the dryer is the same, and the countercurrent process means that the flow of the material and the hot air in the dryer is opposite. The countercurrent process is simple in operation, and the dust concentration of the machine is low, which is convenient for dust collection. However, the following defects are insufficient, which seriously restricts the normal production of the drying materials, especially the slag.
It is not easy to seal, and the sticking phenomenon is serious: during the drying process, the power of the flue gas flow is formed by the negative pressure gradient of the induced draft fan. Since the feed port of the counter-current drying system and the exhaust gas outlet, the discharge port and the hot air inlet are respectively in the same position, the air leakage is serious, the system cannot form a stable negative pressure, and the induced draft fan cannot form a stable negative pressure power, resulting in the heating system. The hot air is difficult to enter the dryer to participate in the heat exchange to the maximum extent; on the other hand, the countercurrent drying material has the highest water content in the low temperature section, and the surface is baked to the crust for too long during the creeping process. Strong adhesion to each other, movement is not smooth, and it is easy to cause blockage when feeding continuously.
The influence of the contact mode of materials and flue gas on the cooking performance of the material: the moisture of the drying material is the largest, and the moisture of the machine is the lowest. The temperature trend of the countercurrent drying process is the lowest when the moisture content of the material is the highest, and the highest when the moisture content is the lowest, that is, when the material is in the high temperature section, the internal moisture is low, the evaporation intensity is low, and the dry burning state is close. Therefore, certain physical and chemical properties (activity, crystal structure, etc.) of the material are easily changed, such as the loss of heat loss of the coal when the coal is dried. Due to the high outlet temperature of the material, a large amount of heat is taken away, which increases the heat consumption of the material, and the drying energy consumption increases. The downstream process just avoids the above situation, and the temperature change adapts to the high to low drying requirements of the material moisture, and the process is simple. The drying efficiency is relatively high and the thermal efficiency is high.
3. Using high temperature fast boiling furnace technology
The combustion of a boiling furnace is a combustion method between layered combustion and suspended combustion. The combustion condition is: the fuel violently tumbling up and down in the height of the furnace layer, as if the water boiled in the pot, Boiling state. The boiling furnace has the advantages of enhanced combustion, good heat transfer effect, simple structure and easy mechanization operation. Basically, it can use inferior coal that cannot be burned by other hot stoves, such as coal gangue and oil shale with a calorific value of 4000kcal/kg, and the burn-up rate is over 95%.
4. Major improvements have been made in the structural function of the rotary dryer
Adopting transmission gear mosaic structure: Compared with the traditional transmission spring steel plate adjustable gear structure, the dryer cylinder is processed, the gear is embedded on the cylinder, the concentricity is higher, the dryer stiffness is better, and the operation is more stable. The structure that the small dryer must use for small vibration.
The dryer feeds in the front of the dryer: the traditional dryer feeds in the upper part of the boiling furnace, feeding through the heat-resistant feeding tube, because the temperature of the boiling furnace of the dryer is very high, even under the heat-resistant steel casting The material tube is also easy to burn out and frequently replaced, which seriously affects the normal operation of the dryer. In the front part of the dryer, the material is fed through a special device, and the feeding tube can be omitted, and there is no problem of replacing the feeding tube at all. At the same time, the feeding tube is eliminated, the ventilation inside the dryer is more smooth, and the drying effect is better.
Adopting speed-regulating motor: In order to meet the different requirements of different materials for the speed of the dryer, when the conditions permit, the speed of the dryer is increased appropriately, and the height of the dryer is increased, which can better throw the material and dry. Better results. Replace the Y series motor with the speed control motor. The speed range is between 132 rpm and 1320 rpm. The frequency conversion speed can also be used. The speed of the dryer can be controlled from 0 rpm to 6 rpm, which can fully meet the production needs.
5. Adopt new type of combination lifting plate and center X type lifting plate
According to the nature and specific conditions of the drying material, a suitable lifting device is designed and the proper shape and layout are determined to ensure the hot air heat exchange of the materials in the machine. For specific and specific drying operation systems, while ensuring effective drying time, measures to shorten the residence time in the dryer are taken to create conditions for improving the throughput of the dryer.
At present, the internal lifting devices of most rotary dryers in China adopt ordinary arc-shaped lifting plates, which have the characteristics of simple structure and strong adaptability to materials. However, the spread of the lift material is low and the uniformity is poor, and the ideal curtain cannot be formed. In addition, some lattice type lifting plates are also used, which can make the lifting part more uniform, but the lifting plate is easily deformed by heat, the weld is cracked, and it is not easy to clean and maintain, especially not suitable for drying and sticking. Block material. The new combined lifting plate has a large lifting angle and good material throwing performance. It can be adjusted according to the material in the different drying areas of the dryer, combined with the production of a new type of lifting plate structure. The residence time in the dryer realizes the accelerated drying, constant-speed drying and slow-speed drying of the material in the dryer, which greatly increases the evaporation speed and strength of the water, which is the output of the dryer. Key measures.
The center X-type lifting plate is installed in the middle of the dryer, and the material entering the dryer is first brought to a certain height by the circumferential lifting plate, and then the material is thrown away, and the backward material is thrown into the middle X-shaped lifting plate, the material The upper X-shaped lifting plate is thrown again to the lower X-shaped lifting plate, thereby forming a layer of falling material, and the material has a rain-like curtain in the drying section, thereby avoiding the existence of a hot cavity in the dryer, and Orientation, current sharing and resistance. As the material is continuously thrown in the X-shaped lifting plate, the residence time of the material in the X-shaped lifting plate is prolonged, the opportunity of material exchange with hot air is increased, and the heat exchange efficiency in the dryer is improved. At the same time, as the material is repeatedly thrown in the X-lifting plate, it plays a certain crushing effect, and the drying effect is greatly improved.
6. Problems in the high-yield and energy-saving technical transformation of slag dryer
Pay attention to the choice of air volume of the dust collector: the ventilation effect of the dust collector directly affects the output of the dryer. If you want high production, you must choose a dust collector with a large air volume. It is necessary to ensure that the dryer has a certain negative pressure, and the high-temperature gas generated by the boiling furnace is sucked into the dryer in time to quickly exchange heat with the drying material and eliminate it in time, so as to reduce the temperature of the exhaust gas in the dryer as much as possible. The purpose of drying. The selection of the air volume for the exhaust gas of the dryer bag filter should be based on the specifications of the dryer, the type of the dried material, and the size of the water. After detailed calculation, the shape is selected reasonably, the output of the dryer is high, and the internal resistance is large. In the past, dust collectors were generally designed to be small, twice as much as conventional dryers.
Pay attention to the balance of wind and fire materials: Whether the dryer can be high-yield, the key is to balance the "wind, fire, material". First determine the ventilation capacity of the dust collector and the specifications of the dryer, and then determine whether the heating capacity of the high temperature boiling furnace is appropriate. Secondly, it is necessary to strengthen the operation, the feeding should be uniform, the water fluctuation should not be too large, the heat source temperature should be adjusted in time, the furnace temperature and the exhaust gas temperature should be stable, and the ventilation and dust removal should ensure the air volume and the wind pressure are normal. Only by doing these things can we achieve high winds, large materials and fires, and achieve high yield and low consumption.
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