| In recent years, the power industry of our country is developing quickly, and the power capacity had exceeded 440 million kilowatts till the end of 2004, 75 percent of which was from coal-fired plant. The micro-particle of fly ash which produced from the coal fired is one of the primary factors of the air pollution. The emission standard of air pollutant for thermal power plant (GB 13223-2003) stipulates that the highest allowed dust emission concentration of the new coal-fired plant after 2005 and the old coal-fired plant before 2010 should be 50 mg/m3. For the gross emission limit, it is strictly stipulated in many cities that the dust emission concentration must be below 30 mg/m3.The filter media is one of the pivotal technologies of the bag filter, and the bag filter was used unsuccessfully in 1980s due to the unsophisticated technology of filter media. The bag filter using on dust control of core-fired plant was bogged down for 20 years, and meanwhile the electrostatic precipitator was used widely. But there are technical difficulty and economical stress to meet the new emission standard if the electrostatic precipitator goes on to be used, especially for city coal-fired plant.The experience of international application over 20-odd years and the results of projects introduced into our country show that it can meet the new emission standard by using the bag filter. But the source of filter media depends on importing, and the price is very high. Because of the ingredient of the core, the boiler and the managing condition, the ingredient of the gas is more complex. All of the above-mentioned are the bottle-neck of extending extensively the bag filter nationally.This paper is for the project of GUODIAN First Coal-fired Plant's No. 13 boiler which uses bag filter to replace the old three electric fields' electrostatic precipitator in Tianjin. The project requires that the dust mission concentration is lower than 30 mg/m3, which are the request of Tianjin local environmental protection. The challenge of this paper is how to extend the bag filter from the plant boiler burning low sulfur core to the plant boiler burning high sulfur core, which requires the filter media technology must be advanced.Aiming at the request of the project, the measure to ameliorate filter media is advanced in this paper, and the emphases are ameliorating the filter media's structure, material and technics of production. The filter media's echelon structure is that the surface layer adopts microfibre and the thicker fibre is used in next layers. The filter layer adopts the fibre of PTFE and PPS, and the bottom layer and the substrate adopt the fibre of PTFE and fibre glass. Furthermore, the needle filter media is steeped by PTFE, and the surface layer of the fibre is conglutinated PTFE membrane. It is signality for the antisepsis, hot resistant and the water-refuse. This filter media is named after HUABOTE echelon filter media (for short, HBT echelon filter media).By dint of the means of scanning electron microscope, the structure of HBT echelon filter media is analyzed. The characteristics of this filter media are that the surface layer adopts microfibre and that the hydro-channels of the filter media's structure are narrow in the front and wide in the back. The traditional filter media is produced by the fibre of the same measure andvariety, and this structure alters the traditional filter media's structure which is the same width hydro-channel. This solved the problem that the filter resistance ascends along with the filter media used. Because the HBT echelon filter media's surface layer adopts microfibre and assimilates the excellence of the membrane media's surface filter, it forms the characteristic of top layer filter which has longer service life.The testing device for filter performances of filter media under normal temperature is designed, after referring to domestic and international testing standards for filter performance of filter media. The testing device adopts Grimm Environmental Dust Monitor instrument. It not only can test the filter efficiency of filter media for PM10, PM2.5, and PM1.0, but also can test the grade filter efficiency for dust whose particle diameter is under 10 u m (the particle diameter range is from 0 to 10 u m, divided into 13 steps, and the lowest measure is 0.3 u m). Because of having adopted the circumstance aerosol to test the filter efficiency of clean filter media, the efficiency difference of different filter media is obvious, and it can test quickly.The 13 kinds high-temperature filter media for dust separation are divided into three species by the different filter ways (surface layer filter, top layer filter, and deep layer filter), and their filter performances are tested.. The testing result shows that the order of the filter efficiency of clean filter media for the circumstance aerosol from high to low is surface layer filter media (membrane filter media), top layer filter media (echelon filter media), and deep layer filter media (traditional filter media);the order of the filter resistance for circumstance air from low to high is deep layer filter media, top layer filter media, and surface layer filter media. The HBT echelon filter media's performance is not only close to membrane filter media's high filter efficiency, but also close to P84's low filter resistance. It can be used for dust separation of boiler burning high sulfur core, after especial disposing, for example, antisepsis and hot-resistant.The reversed filter performances of filter media are tested, for realizing the effect of counterblast when clearing dust. The result shows that the efficiency of obverse filter media is higher than the efficiency of reverse;the "echelon" compound filter media and membrane filter media have different two-faced filter efficiency, but their reversed filter efficiency are still higher compared with other traditional filter media, for example P84.The boiler capacity of Tianjin First power plant is 220T/h, and the emission concentration of the electrostatic precipitator before reformed is 444.56mg/Nm3 which exceeds the standards badly. The design parameters are that the gas capacity is 400,000m3/h, the gas temperature is 150°C, and the sulphur content is 4530mg /m3. The filter velocity of bag filter is 0.96m/min, and the filter bag is made of HBT echelon filter media, whose filter area is 6900 m2. After three months' using, the running result tested by Tianjin Environmental Testing Station shows that the dust mission concentration is blow 30 mg/m3 and the running resistant is about 1100 Pa. Now the running status satisfies the design request, but the service life waits for the testing of using time.
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