High-end Filter Material Challenges PM2.5

By Yang Cheng, Changchun Hipolyking Co., Ltd.

With the high speed development of China’s economy, the heavy chemical industry based on the resource and energy consumption has also developed rapidly. However, it is accompanied by the serious problems of environmental pollution, especially the air pollution problem being particularly serious. In recent two years, haze has appeared frequently. Every year, the number of days of haze is more than 100 in the Beijing-Tianjin-Hebei region, the Yangtze River Delta and the Pearl River Delta, or even more than 200 days in some cities. Haze has become a focus of public attention in China. According to the research, fine particulate matter (PM2.5) is the culprit of haze, and the industrial smoke and dust is one of the major sources of PM2.5.

The bag type dust collector stands out from competing equipment

At present, the mainstream flue gas dust removal equipment is the electrostatic precipitator and the bag type dust collector. Compared with the electrostatic precipitator, the bag type dust collector features high efficiency of dust removal, high filtration accuracy, stable operation, simple technical structure and convenient maintenance, etc. Therefore, the application proportion of the bag type dust collector has increased year-on-year in recent years, and the bag type dust collector has become the first choice for dust removal systems.
In order to effectively control the emission of PM2.5, China must strictly control the dust emission concentration, and strengthen the popularization of dust removal systems. Through extensive study, bag type dust removal technology is proved that it can effectively control the fine particles of dust, really realize the high accurate filtration and reduce the content of fine particles in emissions. As the key material of the bag type dust collector, the performance of filter material determines the efficiency of the dust removal system. To cope with PM2.5 pollution, the domestic research institutes and enterprises are also actively engaged in the research of new filter materials. In 2013, prominent technical progress has been made in spunlaced filter materials, membrane filter materials and fine surface layer filter materials.

High-end filter material distinguishes itself

The smoke and dust generated in different industrial sectors have different properties. If the workplace is high temperature, high humidity, or contain corrosive acid or alkali, the filter bag materials can be fatally damaged. In addition to good mechanical properties, filter material should also have features like excellent chemical resistance and hydrolysis resistance under the high temperature environment to ensure the service life and dust removal efficiency of the filter bag.
High-end filter materials for the bag type dust collector have developed rapidly in China, and they mainly include polyimide (PI) fiber, poly-m-phenyleneisophthalamide (MPIA) polysulfone amide (PSA), polytetrafluoroethene (PTFE) fiber and polyphenylene sulfide (PPS) fiber. Most-frequently used inorganic filter material is glass fiber.

1. PI fiber

The prominent characteristic of PI fiber with excellent comprehensive performance is the high temperature resistant grade. Its thermal decomposition temperature is as high as 570 degrees centigrade and heat shrinkage rate is only 0.3%. PI fiber can be used for a long time at 280 degrees centigrade and for an instant at 360 degrees centigrade. It is currently a filter material with the highest application temperature, and can used for a variety of workplaces with high temperature and harsh environment such as cement kiln, waste incineration plant and power plant.

2. PTFE fiber

PTFE fiber, which is a filter material with the best chemical corrosion resistance, is mostly used in workplaces with strong corrosion like waste incineration plant. PTFE fiber can be used for a long time at 250 degrees centigrade and for an instant at 290 degrees centigrade. Owing to flexible groups in its molecular backbone, PTFE fiber has shortcoming like  low strength and easy to creep. Therefore, it is often used with other filter materials together in bay type dust collectors. In addition, due to difficulties in fiber processing, PTFE can only be produced in several companies including Shanghai Lingqiao Environmental Protection Equipment Works Co., Ltd., Shanghai Dagong New Materials Co., Ltd. and Zhejiang Kertice Environmental Protection Special Material Technology Co., Ltd. in China. Therefore, the application of PTFE filter material is constrained by the high price of PTFE fiber.

3. PSA

PSA is a high temperature resistant fiber developed in China. PSA and MPIA are both aromatic polyamide fibers, and their chemical resistance is similar. The main chain of PSA contains sulfonyl group, endowing PSA good heat resistance and dyeing performance. PSA can be used for a long time at 250 degrees centigrade, and due to its low strength, it is mostly used with other filter materials together to ensure a long service life of the filter bag. PSA in China is mainly produced by Shanghai Tanlon Fiber Co., Ltd., which has a capacity of 1 kt/a.

4. PPS

The chemical resistance of PPS fiber is only weaker than PTFE fiber. The long-term tolerant temperature of PPS fiber is 160 degrees centigrade and its instant tolerant temperature is 190 degrees centigrade. PPS fiber features good acid/alkali resistance and hydrolysis resistance. However, its oxidation resistance is poor. When meeting the high temperature and high oxygen content, its mechanical strength will accelerate to decline, causing the directly broken of filter bag. PPS filter bag is generally used in power plants. Sichuan Deyang Science and Technology Co., Ltd. and Jiangsu Ruitai Science and Technology Co., Ltd. are China’s major PPS fiber enterprises with a capacity of 1 kt/a each. Major foreign production enterprises include Toray Industries and Toyobo of Japan. The price of domestic products is lower, but their quality is not as good as products of Toray Industries.

5. MPIA

The R&D and production of MPIA was firstly conducted by DuPont. MPIA has a thermal decomposition temperature of 427 degrees centigrade. However, its acid/alkali resistance and hydrolysis resistance are not as good as PTFE. MPIA filter materials are used in the filtration of flue gas with complete desulfurization or low sulfur content. MPIA can be used for a long time at 200 degrees centigrade and for an instant at 240 degrees centigrade. At present, major MPIA fiber producers include DuPont of the United States, Yantai Tayho Advanced materials Co., Ltd., Shanghai SRO Group and Guangdong Charming Co., Ltd., etc.

6. Glass fiber

Glass fiber is a high performance inorganic nonmetallic material. Due to its outstanding heat resistance and corrosion resistance, glass fiber is used in the industrial and mining enterprises with higher smoke and dust temperature. For example, it is used as filter material for blast furnace gas. The glass fiber filter materials can be used for a long time at 260-280 degrees centigrade and for an instant at 350 degrees centigrade. Because of its shortcomings like brittleness, poor abrasion resistance and weak bending resistance, in the industrial and mining application, ash will cause a severe damage to the glass fiber filter materials and significantly affect the service life of the filter materials. Compared with organic high performance fibers, the price of glass fiber is lower. So it is widely used in many enterprises.

Conclusion

As the government gives more and more emphasis on environmental issues, the requirements on the energy-saving, consumption reduction and environmental protection in all sectors will improve constantly. For the bag type dust removal sector, it is not only an opportunity, but also a challenge. China’s filter material enterprises should continuously improve quality, reduce costs, produce series products and further promote the bag dust removal technology to make a contribution to the domestic environmental protection.