Dust filter bag is an important equipment for separating gas and dust solids in industrial flue gas treatment. The filter bag captures particles through inertial collision, electrostatic adsorption, diffusion, sieving and gravity filtration mechanisms. Due to the objective conditions of the flue gas, specific post-treatment processes are required for the dust filter bags to make them more efficient and longer service life.
Impregnation is one of the post-treatment processes, which can improve the performance of the filter media by impregnation, making the needle felt more water and oil resistant and corrosion resistant under high temperature.
I. Process of needle felt production
The process mainly includes fiber opening, carding, auxiliary net, pre-felting, main felting, felting, burnishing, rolling, impregnating PTFE, drying, shaping, and coiling.

II. Composition of PTFE emulsion
Impregnation is to immerse PTFE emulsion into the needle felt, so that PTFE granules are coated on the fiber surface and embedded into the pores, thus improving the surface and structural properties of the needle felt. PTFE emulsion is made of TFE emulsion polymerization, consisting of PTFE particles, non-ionic surfactant (to disperse PTFE particles and increase wettability), PFOA (perfluorooctanoic acid ammonium), ammonia (to prevent pH too low, non-ionic surfactant is engulfed by bacteria) and deionized water.

III. Preservation methods of PTFE emulsion
1、The correct preservation method
(1) After opening the barrel, the remaining emulsion should be sealed and stored to prevent the evaporation of ammonia, which will lower the pH value and cause the non-ionic surfactants to be devoured by bacteria, resulting in the instability of the emulsion; secondly, it can prevent the surface water of the emulsion from evaporating and crusting.   
(2) When long-term storage is needed, it must be stored at room temperature from 10℃ to 25℃ for at least 10 days to 14 days once, return to 20℃ to 25℃ and slowly shake the container to make it redispersed. The freezing of the dispersion, violent stirring, the addition of water-soluble solvents and electrolytes, etc. will cause irreversible coagulation.
2、The necessity of slow stirring
The specific gravity of PTFE particles is greater than water, and the particles have a tendency to settle when stored at rest for a long time, so it is necessary to stir or oscillate slowly at regular intervals to redistribute PTFE particles evenly.
3、The recovery of emulsion
After long-term storage, the bottom part of the barrel emulsion is sticky, can be dispersed again by slow stirring method. If the bottom of the barrel appears difficult to flow caking material, it can not be dispersed again, need to use filter or filter cloth to remove.

IV. Advantages of PTFE impregnation treatment
PTFE impregnation treatment can make all the fibers coated with PTFE fine particles, which increases the corrosion resistance of the fibers and thus improves the service life of the filter media.

PTFE impregnation treatment can improve the overall chemical performance of PPS needle felt, can improve the PPS needle felt oxidation resistance, can relatively improve the use of PPS needle felt temperature, can better meet the use of working conditions. At the same time after PTFE impregnation treatment is also more beneficial to the filter bag cleaning.

Five, the difference between water repellent treatment and impregnation treatment
Water repellency treatment of needle felt and PTFE immersion treatment, the two use different chemical treatment agents after impregnation, rolling, high-temperature drying and baking and achieve different treatment effects, the production process of the two is basically the same.
The differences are.
(1) the active ingredients of the treatment agent is different. Water repellent treatment is generally used fluorine water repellent, water repellent components is a perfluorinated alkyl acrylate copolymer, baked at high temperatures, can form a layer of very small surface tension in the fiber surface film, so that its fabric surface tension is less than water and oil, and so achieve a good water repellent oil repellent effect. And PTFE immersion treatment is PTFE powder made of suspension dispersion, in the high temperature baking PTFE solidified in the fiber and filter surface.
(2) chemical treatment after the product grammage changes are different. Water repellent treatment of chemical active ingredient generally makes the needle felt gram weight increase 0.5%-1%, while PTFE immersion treatment of chemical active ingredient generally makes the needle felt weight increase 3%-5%.
3) The surface state of the needle felt after chemical treatment is different. Water repellent treatment of the needle felt surface structure basically no change, PTFE immersion treatment of the needle felt surface has obvious treatment agent attached, changing the original surface structure of the needle felt, so that the surface of the needle felt smoother, smaller pores.
4) The difference in use function.

Water repellent treatment is focused on improving the performance of dust filter bag water repellent solution, the use of anti-condensation role. PTFE impregnation treatment has a certain water repellent performance, mainly to improve the dust filter bag corrosion resistance, while the surface of the needle felt becomes smooth and pore size reduction, to a certain extent to improve the filtration and ash cleaning performance of the needle felt.

Anhui Yuanchen Environmental Technology Co., Ltd (hereinafter referred to as "Yuanchen Technology") is a high-tech enterprise integrating R&D, production and sales of dust removal bags and denitrification catalysts. Over the past sixteen years, Yuanchen Technology has been focusing on environmental protection field, and now has 4 international PCT patents, 26 authorized invention patents, 60 utility model patents, 21 software copyrights, 27 drafted and participated standards, 1 national achievement appraisal, and 17 new products in Anhui Province. Among them, many products such as "dust removal and denitrification integrated technology products" were awarded the Scientific Progress Award of Anhui Province. The dust removal bags (mainly PPS, PTFE, P84 and composite series needle felt) and SCR denitrification catalysts have been widely used in cement, steel, glass kilns, waste incineration power generation, biomass power generation, non-ferrous metal smelting and other industries.

In the future, Yuanchen Technology will be guided by "becoming the guardian of global ecological environment", always rooted in environmental protection, and insist on the great cause of guarding the blue sky and white clouds. Leveraging on the national ecological civilization construction pattern, we will continue to deepen technology, optimize management, strengthen brand, refine industry and solidify advantages, and create synergistic value for industry through comprehensive and integrated governance and services.