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Development and Prospect of Bag Filter

Date: 2010-08-10 | Hits:
Bag filter is the most widely used in the cement industry, a dust collector. Its fine dust particles (1 ~ 5μm) efficiency of more than 99%, but also can remove 1μm or 0.1μm dust particles. Bag filter is relatively strong, not affected by the dust resistance, there is no other pollution problems, in the selection of the appropriate filter aid conditions, the gas can be simultaneously removed solid and gas two pollutants. Due to this feature, a bag filter is basically used at all dust discharge points in the cement industry.

1. Bag filter development

    Bag filter early with artificial or mechanical rapping dust, and thus its application is limited. Since 1950, due to the counter-blowing (blow hair) and pulse-type invention and application of the bag filter and cleaning to achieve a continuous operation, and the resistance is stable, high air velocity, internal no moving parts, with the new , Durable, corrosion-resistant, high temperature (up to 300 ~ 400 ℃), low pressure loss, easy to clean the application of filters, especially the non-woven polymer filter and wire fabric mixture filter development, making it increasingly widespread , Become the main high-efficiency dust collector.

    Bag filter depends mainly on the following aspects: (1) gravity settling: dust-containing gas into the bag filter, the larger particles, the larger the proportion of dust settling down under the action of gravity, which is the role of sedimentation chamber Exactly the same. (2) Sieve: When the particle diameter of the dust is larger than the gap between the fibers of the filter or the space between the dust on the filter, the dust is blocked when the airflow passes through. (3) Inertial force: air flow through the filter cloth can be passed around the fiber, and larger dust particles in the inertia force, still according to the original direction of movement, then collided with the filter was captured. (4) thermal movement: light body small dust movement with the air flow, very close to the air line, can bypass the fiber. But after they collide with gas molecules that are hot (ie, Brownian) when heated, they change their original direction of motion. This increases the chances of dust coming into contact with the fiber, allowing the dust to be captured.

    Bag dust collector ash collection methods: (1) Vibrating bag method: to give a slight vibration at the top of the bag, prompting the filter bag ash layer collapse. (2) anti-hair wind method: This method makes the bag due to the difference between the air pressure inside and outside the bag and received deflated, so that the adhesion of the gray layer loose down. (3) pulse jet method: Every 3s with 700000Pa compressed air to the pulse valve compartment air chamber blows, the pulse of high-speed expansion of the air blast to produce shock wave, filter bag deflection to remove the adhesion Gray layer. (4) Sonic cleaning method: This method uses a sonic generator to generate low-frequency sound waves to vibrate the filter bag, and combines the blow hair to make the dust particles adhered to the surface of the filter bag shake off.

    Filter bag filter material: (1) natural fiber: the main cotton fiber, wool fiber and cotton wool blended fiber. (2) inorganic fiber: the main glass fiber material. (3) Synthetic fiber: Mainly nylon fiber, polyester fiber, acrylic fiber, vinylon fiber, Teflon fiber and so on.
From the early 1990s, in the face of the increasingly stringent environmental regulations and public awareness of environmental protection, dust collector manufacturers in the developed countries of the western countries began to search for new breakthrough points for dust collection. After a comprehensive assessment, they considered that the technical feasibility and manufacturing cost competition Aspects, bag filter most promising. Prior to this pulse pulse cleaning bag filter has been born, but the processing capacity is limited. On this basis, the gas box pulse bag dust collector developed is close to the electrostatic precipitator's handling capacity, but the high temperature working condition is still a misunderstanding of ordinary filter media. The early 90s of last century, the domestic hospital in Nanjing as the representative of the development of a glass fiber filter bag, but the filter mechanism is still in the filter bag after the formation of deep-filtering dust cake, glass fiber density than chemical fiber blended woven high, with The filter bag has a metal frame, and the bending strength of the glass is very low, so the use of the process either the effect or the life cycle are poor, can not be promoted.

    Truly make the bag filter revolutionary technology revolution is DuPont pioneered the development of PTFE [(C2F4) n, TEFLON] that PTFE membrane technology. PTFE is a polymer compound, chemical stability, acid and alkali resistance, especially better acid resistance, high temperature, the physical and chemical properties below 300 ℃ stable above 300 ℃ instability activity. Polytetrafluoroethylene film used for bagging is not pure polytetrafluoroethylene. In order to ensure the proper thickness of the film and to control the air permeability, additives of other components are added. When the actual working temperature is below 260 ℃, instantaneous Temperature up to 280 ~ 290 ℃, more than 300 ℃ physical and chemical structure will be destroyed.

    Teflon coating revolutionary significance is that it can block the dust through the PTFE membrane, which in the filter cake is not formed, the traditional deep filter into a surface filter, as long as the surface dust stripping timely, filter media The permeability will not be significantly reduced, the pressure loss will be small. Teflon film coated on glass fiber can be used in the temperature below 260 ℃ conditions, and the ideal electrostatic precipitator temperature between 180 ~ 220 ℃, and thus have a wider temperature than the electrostatic precipitator Use range.

    Represented by FULLER in the United States, a big bag dust collector was developed to replace the electrostatic precipitator in the late 1980s. However, due to the shortcomings of glass fiber filter (NOMEX NOMAX filter is only applicable to 200 ℃ below the temperature) and sub-room control technology is imperfect, has not been promoted.

    In the early 1990s, the control technology of the sub-chamber was switched by PLC control solenoid valve. With the support of Teflon coating technology, the technology of back-blowing big bag and gas box pulse has been greatly developed. Can completely replace the electrostatic precipitator. The Lafarge cement plant in Dujiangyan started construction in 2000 and has adopted a bag filter. The acceptance inspection results in 2002 show that the emission concentration of all the dust collectors is controlled below 20mg / Nm3. The discharge from the big bag filter of the kiln exhaust gas treatment Concentration control in the following 10mg / Nm3, basically reached the concept of industrial zero emissions.

    At present, it can be maturely applied to big bag anti-hair dust collector under high temperature conditions. All the production technologies are in the hands of several companies in the United States. The property right of Teflon film belongs to Dupont Company. The best fiberglass fabric technology By the United States BGF company, and the big bag of hair dryer dust belongs to the United States Fuller technology company, even if the Teflon film to the base cloth paste technology only a few of the more mature foreign companies, the domestic Filter manufacturers using hot lamination and plastic coating technology and foreign technology is still a big gap. Domestic equipment manufacturers have been doing the overall introduction of technology, but the high cost of technology, it is difficult to spread in the country.

    In addition to the big bag filter, the small single-pulse pulse cleaning cloth bag dust collector and pulse box bag filter is more common in China, the domestic filter manufacturers polyester, polypropylene or acrylic-based cloth covered PTFE membrane Has been able to meet the cement needs of low temperature filtration conditions, due to the increase of domestic technology after the coating less costly, and thus has become the membrane filter cloth bag filter cement plant main media.

    In the use of the surface PTFE membrane filter, due to the thin surface film, once the membrane is damaged, its surface filtration mechanism will disappear, for the chemical fiber cloth surface filtration mechanism disappears or weakened after the depth of filtration can play a very Good filtration, but for the fiberglass fabric is fatal, thin glass fiber fabric and warp and weft than the chemical fiber fabric, it is difficult to form a good dust cake. Therefore, a new type of PTFE filter material --- PTFE needle felt has been recently developed. The principle is that PTFE is treated on the base fabric before the filter material is formed, so that the PTFE exists not only in the surface layer of the filter material but also in the depth of the base fabric Layer or even a dozen layers of PTFE, the final filter is still forming surface filtration mechanism, but also eliminates the surface film is damaged defects. More mature is PTFE polyimide fiberglass filter instead of PTFE, at present there is no one factory to use, but has begun to promote the use of foreign countries. Due to its high cost, the current use is generally limited to replacing PTFE glass fiber media. In short, the development of bag filter dust collector is basically the development of filter media, filter material category to promote the development of mechanical structure and control means.

    In recent years due to the wide application of dry desulfurization technology, the use of bag filter more and more. In particular, the improvement of the filter material in recent years has increased the service life of the bag and broadened the application range of the bag filter. Foreign main progress is: Packaged, tubular folded bag filter, substantially increase the same volume of filter area; Pre-attached layer technology to reduce drag to increase wind speed; The use of flue gas conditioning technology to improve the efficiency of dust removal; Improve the bag filter system of leak detection technology, such as show full dust and monochrome irradiation technology applications; new filter high temperature, corrosion resistance, good performance; the United States, Japan, Australia, Germany and other countries to electrostatic technology and bag filter Combined with the development of the "electrostatic bag filter", to improve bag filter performance, improve the collection efficiency, improve the filter cleaning ability and reduce the dust particle filtration rate and system resistance have a significant effect.

2 bag filter technology outlook
    2.1 Technology Innovation Trends. At present, all major cement environmental protection equipment enterprises are very concerned about the development of advanced technologies in the world, such as the host of standardization, different welding assembly; nano-technology used in filter media to produce nanoscale fibers, filter quality greatly improved; Membrane technology used in rigid filter media, the surface of the sprayed metal film greatly improve the filter material and anti-cleaning effect and so on. With the continuous expansion of production scale, product technology, product quality, product variety adaptability have been improved, bag filter applications and technological development will also be a new era.

   2.2 large-scale trend of the whole machine. With the acceleration of structural adjustment of the domestic cement industry, the launch of high-tech and large-scale cement kiln lines in succession and the improvement of national atmospheric dust emission standards will inevitably promote the application and promotion of large-scale bag filters, especially the pulse bag type , The trend of large-scale low-pressure bag dust collector obvious, performance has reached the international advanced level. Such as Hebei Xianxian environmental dust removal plant design and manufacture of large gas box pulse bag dust collector in Beijing Cement Plant, Lurgi improved large bag dust collector in Inner Mongolia Winterthur power plant put into use, the emission test records are significantly lower In the national emission standards, reached the international advanced level.

    2.3 to promote high temperature, high concentration bag dust collector trend. In the "Tenth Five-Year" period, to adapt to high temperature, high dust concentration bag filter will be further promoted. This bag dust collector can directly handle the temperature up to 300 ℃, dust concentration of 1400g / m3 of gas, than in the past to improve the number of times, and stable discharge standards.

    2.4 more widely used. Foreign countries such as the United States, Australia, Canada, Europe and many other countries are widely used bag filter, and the emergence of the trend of electricity to change bags, technically and economically more successful. As the state attaches great importance to the increasing impact of air pollution, environmental standards, strict requirements on fuel composition, the superiority of bag dust collector is more obvious. Vigorously promote the application of bag filter, and gradually increase the bag filter market share, in the next few years will become China's cement industry environmental protection equipment market is an indisputable fact.

    China started the implementation of "pollution control standards for domestic solid waste incineration" on June 1, 2000. It formulated ten indicators for pollution discharge and clearly stipulated that the dust collection equipment must use a bag filter. Some bag collection enterprises in our country have also started to involve in the flue gas treatment of waste incineration. Some enterprises have also participated in international cooperation and the dust collector has been sold to foreign countries. Hebei Xianxian environmental dust removal plant has been successfully developed and has in Taiwan, Hebei and other places the use of garbage incinerator, and achieved good results.

    The biggest advantage of bag filter is the dust collection efficiency, up to 1mg / Nm3 in the laboratory. This is the bag filter mechanism determines the mechanism of this mechanism is the filter, so that the dust attached to the filter bag, the dust involved in the dust filter. Therefore, the bag filter dust collection efficiency is high. In our country to implement the strategy of sustainable development, vigorously strengthen environmental protection, the implementation of total pollutant control, "a control double standard" case, bag dust collector in the control of smoke, dust, sulfur dioxide, dioxins and other pollutants Will get great application.
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