Thread Content
There are nearly 10,000 vertical kiln plants in my country with and without production licenses, and their annual cement production accounts for more than 80% of my country's total annual cement production. Based on my country's total cement output of 530 million tons in 1998, the output of shaft kiln plants was approximately 420 million tons or more. If the emission of shaft kiln dust is calculated as 4% of the output of the shaft kiln, the total annual emission of shaft kiln dust will be as high as 16 million tons. According to incomplete statistics, dust emissions from shaft kilns meet less than 2% of the standard. Although * * The Economic and Trade Commission has decided to eliminate more than 3,500 vertical kilns with a diameter of less than 2.2 meters in 1997, and to eliminate all vertical kilns with an annual output of less than 44,000 tons in 2000. However, there are still a considerable number of vertical kiln factories that are not included in the elimination. According to the requirements of the local environmental protection department, these factories must also meet the standards within a time limit, otherwise they will be ordered to stop production and close down. Faced with this severe situation, manufacturers are extremely anxious, so it is urgent to provide existing vertical kiln plants with dust removal equipment that has excellent performance, high efficiency, low price, and long-term safe operation. The current status of shaft kiln dust removal technology. Since the properties of shaft kiln flue gas and dust depend on the operating methods of the shaft kiln, the properties of raw materials and fuels, and process conditions, and the range of changes is large and rapid, it brings great difficulties to dust control. along with * * The emission standards formulated are becoming increasingly strict, and the environmental protection awareness of urban and rural people is increasing. Therefore, the dust removal of shaft kilns no longer uses a settling chamber with a simple structure, low investment, and a dust removal efficiency of less than 50%. This has prompted many scientific research and design units and environmental protection product manufacturers to develop new efficient and cheap dust removal devices. This is the main reason why various types of water dust collectors have mushroomed in vertical kilns in recent years. Of course, it is also related to the fact that the collected mud can be sent to the twin-shaft mixer with pre-added water pelletizing system, which solves the problem of secondary pollution. Compared with bag dust collectors and electrostatic precipitators, water dust removal facilities have the advantages of simple structure and low investment. However, according to the test results of manufacturers equipped with water dust removal facilities, the dust emission concentration is very unstable and it is difficult to maintain the emission concentration less than 150 mg per standard cubic meter for a long time. It is even more difficult to achieve the emission concentration less than 100 mg per standard cubic meter. In addition, the fatal weakness of water dust removal is that it can only remove dust but not eliminate smoke. For example, shaft kiln plants in Tongchuan, Shaanxi Province all burn bituminous coal with high sulfur content. Some plants are equipped with different forms of water dust removal devices. Although dust emissions are controlled to a certain extent, billowing yellow smoke is still emitted from the chimney. According to analysis, the yellow smoke emitted is not gas, but smoke with a particle size of less than 5 microns generated by the combustion of volatile matter in coal, which is essentially still classified as dust. These fine smoke cannot be removed by spraying or spraying water. Therefore, manufacturers using water dust removal facilities in Tongchuan area have a tendency to switch to bag dust removal or electrostatic dust removal. Since it is difficult for water dust removal to achieve the expected effect of vertical kiln dust removal, it is necessary to turn to bag dust removal or electrostatic dust removal with mature technology. Taking bag dust collectors as an example, due to improvements in body structure, dust cleaning methods and various valves, technological advances in filter materials, filter bags and dust cleaning control systems, and the application of auxiliary dust cleaning technology, the technology of using bag dust collectors in shaft kilns has become increasingly mature and perfect. In particular, the bag dust collector is not limited by the dust specific resistance and is also suitable for dust removal in shaft kilns. However, the resistance of the bag dust collector is relatively large, generally more than 1200 Pa on average. It is impossible to rely on natural exhaust from the vertical kiln chimney, so a separate exhaust fan needs to be configured. For example, for a vertical kiln with a diameter of 2.8×10 meters, the air volume is considered to be 55,000 cubic meters per hour. The power required for the main exhaust fan plus the back blower is about 80 kilowatts. Above, in addition, the filtration area of the filter bag is greater than 1,800 square meters. If the commonly used glass fiber filter material is used at 23 yuan/square meter, it will cost more than 40,000 yuan to replace the filter bag every two years. It also requires a relatively stable operating system of the vertical kiln, especially the operating temperature, because the temperature is too high and the bag is easy to burn, and the temperature is too low and the bag is easy to burn. Due to the above-mentioned shortcomings of the bag dust collector, and the high initial investment, its widespread promotion in vertical kilns is restricted. Especially in the northern region, the use of bag dust collectors in shaft kilns that burn bituminous coal must be cautious. The use of electrostatic precipitators and bag dust collectors in shaft kilns also has many lessons from failures. In addition to being restricted by the dust specific resistance, it is also affected by the operating conditions of the vertical kiln. However, in general, the operating conditions are not as high as the requirements of the bag dust collector, and the thermal pressure difference of the chimney can be used for natural exhaust. As long as the problems of over-temperature deformation and corrosion of the two poles are effectively solved, it is more reliable to use electric precipitator in shaft kiln. Although the one-time investment is large, it can at least be the same as bag dust collector. Advances in Shaft Kiln Electrostatic Precipitator Technology In the early 1980s, Qingdao Cement Plant was the first in my country to adopt horizontal electrostatic precipitators in mechanical shaft kilns. Since the vertical kiln flue gas has a high moisture content and a dew point of more than 50°C, the dust concentration in the flue gas is not high, generally less than 10 grams per standard cubic meter, and the dust particles are coarse, generally larger than 50 microns, accounting for more than 50%, so it is very suitable to use an electric precipitator, so the factory installed S After the HWB type electrostatic precipitator was put into operation, the dust collection efficiency was high. However, due to unstable working conditions, especially condensation in the electric field, the two poles were seriously corroded. The plate corrosion was almost completely corroded in less than two years. The daily cost of replacing it was very high, so it was eventually dismantled and replaced with a settling chamber. Subsequently, Jinan, Shaoguan and other cement plants also adopted this horizontal electrostatic precipitator, and its final fate was similar to that of the Qingdao plant. The cause of plate corrosion is generally believed to be acid corrosion caused by the sulfur contained in coal-fired shaft kilns, which produces sulfur dioxide during combustion and generates sulfuric acid when exposed to water. In fact, most of the sulfur in the coal is absorbed by the clinker, and only a small amount of sulfur generates sulfur dioxide. Only a small part of the vertical kiln flue gas is converted into sulfur trioxide, with a conversion rate of 0.5% to 3.0%. Because the conversion of sulfur dioxide into sulfur trioxide is mainly affected by the combustion temperature and the oxygen content in the flue gas. From this, it can be considered that the cause of corrosion of the shaft kiln electrostatic precipitator is not sulfuric acid but water corrosion. Later, when the mineralizer fluorspar (CaF) was added to the shaft kiln, the combustion of fluorspar would generate hydrogen fluoride, which would intensify the corrosion of the electrostatic precipitator. Whether it is corrosion caused by water or hydrofluoric acid, protective measures should be taken, otherwise corrosion will become an obstacle to the use of electrostatic precipitators in shaft kilns. In the 1980s, the Lanzhou Paint Research Institute tried to develop a paint that could be applied to the plates to be both anti-corrosive and conductive. It had achieved certain results in the laboratory, but the industrial test at the Liulihe Cement Plant was unsuccessful. In the late 1980s, the Hefei Cement Industry Research Institute applied conductive coating on the low-resistance corrugated electrode plates developed by the Hefei Cement Industry Research Institute, but the plates curled and fell off soon after being heated. In the early 1990s, the vertical kiln electrostatic precipitator developed by Tianjin Cement Industry Design Institute used 08AL as the plate material and was used in Beijing Yanshan Cement Plant. No significant results were achieved because the 08AL steel plate did not have anti-corrosion properties. Since the Tianjin Cement Plant uses aluminum alloy plates for dryer electrostatic precipitators and no corrosion has been seen for many years, the Tianjin Institute applied this result to shaft kiln electrostatic precipitators and did not obtain first-hand information. In the electrostatic precipitator of the shaft kiln of Guangzhou Chatou Cement Plant, nine different materials, including commonly used A3 steel plates, 08AL steel plates and aluminum alloy finished products, were hung in the electric field for corrosion resistance tests. After taking it out for inspection three months later, it was found that the aluminum alloy material had the best corrosion resistance. After wiping off the dust collected on the surface, the original luster was still revealed. Therefore, it was decided to use aluminum alloy plates in the renovation of the factory's electrostatic precipitator. However, it was a pity that the aluminum alloy plates were burned at high temperatures soon after. This gives inspiration to researchers engaged in the design of shaft kiln electrostatic precipitators. While solving the problem of anti-corrosion of shaft kiln electrostatic precipitators, they must also consider the problem of preventing the plates from being burned at ultra-high temperatures. In response to the above problems, Hefei Research Institute and Tianjin Research Institute have carried out a lot of research and development work in recent years, and breakthroughs have been made in vertical kiln electrostatic precipitator technology. For example, the JYC type extreme reduction electric field electrostatic precipitator researched by Hefei Research Institute passed technical appraisal in 1998 and was used in Lhasa and Shaanxi Qixing Cement Plant, both of which achieved good expected results. The new CDYL shaft kiln electrostatic precipitator developed by the Tianjin Institute has been used in the shaft kilns of Suzhou Yangcheng and Tianjin Cement Plant. Not only does the dust emission meet the standards, but it also solves the problem of yellow smoke when burning bituminous coal in the shaft kiln, relieving people's doubts that electrostatic precipitators can only remove dust but cannot eliminate smoke. Moreover, the products developed by these two companies have basically solved the existing problems of corrosion, overtemperature, condensation, explosion and other problems in shaft kiln electrostatic precipitators. While studying vertical kiln dry electrostatic precipitators, many scientific research institutions and manufacturers are also practicing wet electrostatic precipitators integrating water and electricity. Because wet electrostatic precipitators are not restricted by specific resistance, they have high dust removal efficiency and can also avoid the problems of over-temperature burnout and low-temperature condensation of shaft kiln electrostatic precipitators. Some magazines have published advertisements for similar successful products, but it is reported that many experiments ended in failure. If the mature experience of wet electrostatic precipitators in the chemical industry department is transplanted and combined with the actual situation of shaft kiln production, it will be completely successful to develop a wet electrostatic precipitator suitable for shaft kilns. Because the wet electrostatic precipitator consumes a large amount of water, such as the selection of nozzles, adjustment of water volume, sewage treatment, and recycling of clean water, especially how to reduce water consumption, must be gradually and properly solved. As long as the relevant units work together and persevere, the success of vertical kiln wet electrostatic precipitator will be just around the corner.