NEWS CENTER

Technical Status and Prospect of Bag Filter


Release time:

Mar 15,2012

Preface China's energy structure is dominated by coal, China is the world's largest coal consumer, every year there are a large number of soot emissions, serious environmental pollution. Therefore, environmental protection requirements are becoming more and more stringent, and the state has put forward more stringent requirements for soot and S02 emissions. The Emission Standard of Air Pollutants for Thermal Power Plants (GB13223-2003) stipulates that since January 1, 2004, the maximum allowable mass concentration of soot emission is 50mg/m3 for new, expanded and rebuilt thermal power plant construction projects approved by the environmental impact report of the construction project. For the new standard, the current use of electrostatic precipitators

Foreword

China's energy structure is dominated by coal, China is the world's largest coal consumer, there are a large number of smoke and dust emissions every year, serious environmental pollution. Therefore, environmental protection requirements are becoming more and more stringent, and the state has put forward more stringent requirements for soot and S02 emissions. The Emission Standard of Air Pollutants for Thermal Power Plants (GB13223-2003) stipulates that since January 1, 2004, the maximum allowable mass concentration of soot emission is 50mg/m3 for new, expanded and rebuilt thermal power plant construction projects approved by the environmental impact report of the construction project. For the new standard, it is difficult to meet the above requirements even if the electrostatic precipitator is changed from four electric fields to five electric fields and six electric fields. At the same time, in order to reduce S02 emissions, many power plants will use low-sulfur coal or adopt corresponding desulfurization facilities, which will lead to a decrease in the dust removal efficiency of electrostatic precipitators, especially in power plants that use more than 85% of silicon and aluminum in coal. The mass concentration of soot emissions treated by electrostatic precipitators has fallen far short of national environmental protection requirements. According to the current development situation, coal-fired power plants will give priority to the use of bag dust collector, electrostatic precipitator for bag dust collector has been imperative.

1 Application status of dust collector

At present, in the construction of thermal power plants, the selection of high-efficiency dust removal devices is mainly based on electrostatic precipitators and bag filters. The application of electrostatic precipitators in China was earlier, and it has been applied to thermal power plants in the 1970 s, such as Jilin Thermal Power Plant and Baoding Power Plant. After years of development and application, electrostatic precipitator technology is mature, dust removal efficiency is high, has been widely used in electric power, metallurgy, chemical industry, building materials and other industries. The domestic 600MW thermal power units have all selected high-efficiency electrostatic precipitators.

Bag filter is widely used in some thermal power plants in the United States, Canada, Australia and Europe. The application of bag filter in coal-fired boilers is a mature technology, with a history of more than 30 years. Bag filter has been successfully applied in China's mining, building materials, food, pharmaceutical, metallurgy, chemical and other industries for many years, but in coal-fired boilers, it was not until 2001 in Hohhot Fengtai Power Plant that it was successfully applied for the first time. Up to now, the bag filter of more than 10 companies has been applied in different regions of the country, such as Tianjin Development Zone No. 5 heat source Plant, Zhangjiagang Free Trade Zone Thermal Power Plant, Jiaozuo Power Plant; moreover, the electrostatic precipitators of many thermal power plants have been transformed into bag filters, such as Hohhot Thermal Power Plant and Chifeng Fulong Thermal Power Co., Ltd. Thermal Power Plant.

2 Bag type dust collector

Principle of 2.1

Bag filter, also known as filter dust collector, is a dry and efficient dust collector. It uses bag filter elements made of organic fiber or inorganic fiber braid to filter out solid particles in dust-containing gas. It is used to collect non-adhesive and non-fibrous industrial dust. The principle of action is that the dust particles are intercepted when they are around the fibers of the filter cloth due to inertial force and fiber collision. Fine dust particles (particle size of 1um or less) are affected by the impact of gas molecules (Brownian motion) and constantly change the direction of movement, because the gap between the fibers is less than the free path of Brownian motion of gas molecules, the dust particles are separated by collision contact with the fibers. It has the advantages of high dust removal efficiency and stability, for more than 2um dust, its efficiency can reach more than 99.9, and the cost is low, simple management, easy maintenance. Therefore, it is a reliable dust removal equipment with excellent dust removal performance and can meet the strict requirements of the current Environmental Protection Law.

2.2 classification

The national standard "bag filter classification and specification performance representation method" (GB6719-97) has made clear provisions on the classification of bag filter. According to the different cleaning methods, it can be divided into five types: mechanical vibration, chamber blowback, nozzle blowback, pulse blowback and mechanical rotary blowback. Pulse jet bag filter is the most widely used dust removal device in the world because of its adjustable pulse jet intensity and frequency and good dust removal effect.

Improvement of 2.3 performance

In the past, the application of bag filter in domestic coal-fired boilers was unsuccessful. The following reasons were analyzed:(1) improper selection of filter material;(2) Failure to take corresponding technical protection measures according to the characteristics of coal-fired boiler flue gas as high-temperature acid gas, copying the successful operation experience of bag filter in metallurgy, building materials, chemical industry and other industries;(3) Poor manufacturing quality of dust collector itself and improper system operation control and protection measures.

Now these aspects have made great progress: first of all, the bag filter in the strength of the filter cloth, high temperature resistance, corrosion resistance, wear resistance and other aspects have been greatly improved. Foreign countries have screened out a special filter material suitable for backblowing bag filter-glass fiber, and a universal filter material suitable for pulse and backblowing bag filter-polyphenylene sulfide (PPS), polyimide (P84) and polytetrafluoroethylene (PTEE). Among them, polyimide (P84) and polytetrafluoroethylene (PTFE) have few users due to their high prices, and glass fiber has few users due to their high prices. Only polyphenylene sulfide (PPS), better performance, price, versatility, has been widely used.

Secondly, according to the characteristics of coal-fired boiler flue gas is high temperature acid gas, the corresponding technical protection measures are taken-flue gas filtration pretreatment process. Through the large cross-section structure, air flow uniform distribution device, grid-shaped inertial separator and other devices to reduce the flow rate of flue gas, remove large particles and smoke with fire, use dust pre-coating process to treat low-temperature flue gas, and use flue gas emergency spray cooling process to treat high-temperature flue gas.

Third, the manufacturing and installation level of the equipment has been significantly improved, the tooling and molding have been generally realized, and the installation level of the professional team has also been greatly improved. The system control has been automated, using PLC for automatic control, and monitoring the operating parameters in real time.

3 Bag dust collector and electrostatic precipitator technical and economic comparison.

3.1 electrostatic precipitator

(1) the advantages of dust removal efficiency is higher, up to more than 99%; small pressure loss, body resistance 100~200 Pa; with a wide range of temperature (from the dew point to the metal temperature limit); such as proper operation, the need for maintenance less work; mature technology, widely used.

(2) Disadvantages: Large equipment and large floor area; High voltage DC power supply system is required, and the one-time investment cost is high. Changes in boiler operating conditions and loads can affect its purification efficiency, resulting in unstable emission concentration. It is sensitive to changes in coal types and its dust removal efficiency is greatly affected by fly ash resistance. The level of manufacturing, installation and operation management is required to be high. Generally required during maintenance

Equipment stops running

3.2 bag filter

(1) Advantages The dust removal efficiency is very high, reaching more than 99.98%, and the discharged dust concentration is low, generally lower than 50mg/m3, even up to 10mg/m3; The discharged concentration is not affected by the specific resistance, concentration, particle size and other properties of dust. The change of boiler load and the fluctuation of flue gas volume have little effect on the discharge concentration at the outlet of bag filter. Strong adaptability, able to handle different types of particulate matter, especially for high specific resistance dust particles that are not easy to collect by electrostatic precipitator, it is also very effective. The suitable mass concentration range is large, and it also has certain stability to the change of flue gas flow rate. The structure and maintenance are relatively simple. Generally, the chamber structure is adopted, and there is room in the design, so that the dust collector can be alternately overhauled without affecting the operation of the boiler. The total investment and operation cost of bag remover is lower than that of electrostatic precipitator.

(2) Disadvantages The pressure loss is large, and the body resistance is 800~1500Pa; the application of large-scale units in China depends on imports.

Comparison of main economic indicators in 3.3 (see Table 1)

Parameters 75t/h 670t/h
Electrostatic cloth bag Electrostatic cloth bag
Equipment floor area/m2 300.8 58.6 836 305
Equipment investment/ten thousand yuan 660.8 195.0 1850 1155
Operation and maintenance fee/ten thousand yuan 52.6 24.0 154 99
Sewage charge/ten thousand yuan 5.1 3.2 86 28

4 Application prospect of bag filter

Although the application of bag filter in boilers in China is not much, but with the sustained and steady development of China's economy, coal-fired boiler flue gas treatment bag filter products will usher in a huge opportunity for development. Because:

(1) The increasingly stringent requirements for environmental protection have prompted the use of bag filters for boilers in China. At present, some industrial developed countries in the world in the coal-fired boiler dust removal application of bag filter is quite a lot. They have solved some problems of bag filter used in boilers, and the application of bag filter in boilers has become a mature technology and promoted.

(2) through engineering practice, thermal power plant boiler tail flue gas treatment using bag filter is completely feasible, the use of foreign boiler bag filter is quite common, the service life of the filter bag is also very long, generally more than 2a, and some even reach more than 6a.

(3) It has high dust removal efficiency, one-time investment, small equipment footprint (relative to the four electric field above the electrostatic precipitator), low operating costs and sewage charges. Especially in recent years, due to the development of manufacturing technology, the problems of filter bag corrosion and wear have been effectively solved, which provides a strong guarantee for the application of bag filter.

(4) Since the operation, fault and abnormal diagnosis of the dust collector adopt automatic monitoring and management, the operation management is relatively simple.

Therefore, the application of bag filter on coal-fired boilers to purify flue gas is technically mature and economically feasible. We believe that as long as the specific conditions of the boiler flue gas to adapt to the equipment components, operation methods and design, strict requirements on the manufacturing quality of the dust collector, strengthen the daily maintenance and management, the boiler application bag filter will certainly achieve good results.