In the process of industrialization of human society, the earth has encountered atmospheric environmental problems. Frequent “visiting” of haze weather has seriously affected the residents’ daily lives and caused peoples’ deep concern about air quality problems.
What is PM2.5
PM2.5 Is the solid particles in the atmosphere with a diameter less than or equal to 2.5μm. Its diameter is less than 1/20 of the fineness of a human hair. Although the content of PM2.5 does not account for a large proportion of the atmospheric composition, according to the survey, the haze weather caused by PM2.5 is even more harmful to human health than sandstorms.
Solid particles with a particle size of more than 10μm will be blocked from the outside of the human nose; particles with a particle size of 2.5-10μm can enter the upper respiratory tract smoothly, but some can be excreted through sputum; Solid particles below 2.5μm can be easily inhaled into the lungs of creatures, and further enter the bronchi, thereby interfering with the gas exchange in the lungs. It can be seen that compared with other large particle sizes, PM2.5 has the characteristics of small particle size, large specific surface area, contain toxic substances (such as heavy metals), and long deposition time in the air. Therefore, it is really harmful to both human health and environmental quality.
The Source of PM2.5
PM2.5 has a wide range of sources and relatively complex composition. Its main source is human-made emissions, including emissions from coal-fired power plants, industrial exhaust gas, exhaust gas from human daily life, automobile exhaust, garbage incineration, fossil fuels, and Burning, etc. Besides, some of the emitted gas will be converted into PM2.5 through a series of chemical reactions. PM2.5 also has natural sources, including wind dust, volcanic ash, forest fires, floating sea salt, pollen, fungal spores, bacteria, etc.
What is PTFE
Polytetrafluoroethylene (PTFE) is a fluorine-containing polymer material with special properties, which made by polymerization of tetrafluoroethylene. Fluorine atoms are regularly and tightly packed to cover the entire polymer chain’s surface, which shields the carbon atoms of the skeleton. Therefore, PTFE has excellent high-temperature resistance, corrosion resistance, electrical insulation properties, sealing properties, etc., and its products can work for a long time at a temperature of -190 ~ 250 ℃. Except for molten sodium and liquid fluorine, PTFE is resistant to all other chemicals, even could be boiled in aqua regia. PTFE has been widely used in telecommunications cables, sealing, aerospace, and environmental protection with its outstanding performance.
PTFE Membrane Filter Bag
PTFE membrane filter bag is composed of PTFE base cloth and short fibers of different materials, which adopts unique acupuncture technology and heat setting process, supplemented by expanded polytetrafluoroethylene (PTFE) film treatment and made by sewing. It is one of the filter bags with the highest corrosion resistance and filtration accuracy. The PTFE microporous membrane has a uniform aperture size and is tightly covered on the surface of the needle felt made of short fibers.
The PTFE base fabric and short fibers provide a certain strength and support for the PTFE microporous membrane, and the PTFE microporous membrane provides a very high filtration accuracy. The PTFE base fabric and short fibers support the PTFE microporous membrane well, and the PTFE microporous membrane provides a higher filtration accuracy. Due to the accumulation of dust during use, the filter bag must be cleaned regularly, so the filter material’s folding resistance should be higher. Compared with the service life of glass fiber, PTFE filter media performs better.
Main Filtering Methods
There are two main filtering methods for filter media: deep filtration and surface filtration. The deep filtration of traditional filter media mainly relies on the “primary dust layer.” To ensure the continuous work of traditional filter media, the “primary dust layer” should be carefully protected when cleaning dust. In the filtration process, the deep filtration is only more efficient for a period of time, since it is always in the repeated state of “formation → stability → ash cleaning destruction → formation.” Moreover, the depth filtration has a low removal efficiency for particles below 1 μm, especially dust particles between 0.2 and 0.4 μm. Therefore, if the traditional filter media is used for filtration, the emission of dust particles below 1um is still high concentration, and the overall emission concentration range is about 40-80mg/m3.
Coated filter media belongs to surface filtration, which uses its micropore structure to change ordinary filter media’s filtration mechanism and transforms its deep filtration into surface filtration. In the coated filter material’s filtration process, the base cloth and needle felt only play a supporting role. Unlike traditional filter materials, which need to rely on the “primary dust layer” formed on the surface of the filter material for filtration, the PTFE membrane layer can replace the “primary dust layer.” In this way, the membrane filter is very efficient from the beginning. Membrane filter material mainly uses the microfiltration effect of the microporous membrane, which is the difference between the new type of membrane filter material and the traditional filter material.
Advantages of The Membrane Filter Bag
The application of PTFE membrane filter material in the control of PM2.5 has the following advantages:
- High filtration efficiency. The test result of ETS company in the United States shows that the emission concentration of PTFE membrane filter material to PM2.5 is 0, which can realize zero emission of PM2.5 in a true sense.
- Good dust removal effect and high stability. Since the PTFE coated filter material is surface-filtered and has deficient surface energy, it has better peelability from dust and has a smaller resistance loss than traditional filter materials.
- Good air permeability. The porosity of the PTFE microporous membrane is as high as 85%.
- Long service life. Due to the excellent acid and alkali resistance and high-temperature resistance, PTEE has a higher service life than other materials. Besides, due to better peelability from dust, reducing wear and tear from dust clean also greatly improves the service life.
- Low operating cost and low operating energy consumption.
The Main Application Areas of PTFE Membrane Filter Bags
1. Waste Incineration
Waste Incineration is one of the most important application areas of PTFE membrane filter bags. It will inevitably produce amount of pollutants, which have the following characteristics:
- There are particulate matter, acid gases, heavy metals, and highly toxic organic pollutants in the flue gas;
- The flue gas has high moisture content and high dew point temperature, which is easy to cause condensation on the filter;
- Interaction of high and low-temperature smoke;
- The particles produced by the deacidification treatment are easy to absorb moisture, which difficulty in cleaning dust and blockage of the pipeline;
- The flue gas is highly corrosive;
However, PTFE coated filter bags have good results in the flue gas purification of waste incineration power plants.
2. Coal-fired power plants
When coal is burned, large amounts of sulfur dioxide, nitrogen oxides and inhalable particulate matter are produced. The bag filter made of PTFE membrane and glass fiber needled felt composite material could greatly reduce the smoke and dust emissions of power plants in high-temperature environments.
3. Cement industry
In cement production, the bag filter made of needle felt and woven material surface composite PTFE membrane can reduce the emission of air pollutants, and can also recycle cement powder, which can increase production, reduce costs and save energy.
4. Laboratory purification
PTFE coated filter bags perform well in areas with higher air cleanliness in the biological, food, pharmaceutical, and medical industries. It has the characteristics of good stability, corrosion resistance and high filtration efficiency, can meet the requirements of high efficiency air filtration, and exert greater application value and economic and technical potential in these industries.