1. Bag dust removal – the mainstream technology of industrial dust removal
At present, China’s electric dedusting technology has reached a stage of mature application, and bag dedusting technology is in a period of rapid development. However, as the country’s requirements for industrial smoke pollution control are continuously increasing, electrostatic dedusting technology can no longer fully meet the requirements, and bag dedusting technology is used. The use of electric dedusting as an alternative to electric dedusting has become the mainstream.
Bag type dust removal mechanism: using special fibers made of filter bags, the dust gas is injected into the filter bag, and the filter bag is used to filter and trap dust. The filtering effect depends on the quality of the filter bag.
2. High-temperature filter material – core material for bag dust removal
The filter effect of the bag filter is achieved through the filter material. It can be equipped with resistance to normal temperature (below 130°C), high temperature resistance (above 130°C), corrosion resistance, water and oil repellent, explosion-proof and explosion-proof, and long life (2~4 years ) Various filter bags with different properties are used to achieve different filtering effects. There is also a strong correlation between changes and innovations in bag dust removal technologies and changes in filter media.
At present, high-temperature filter fibers for flue gas treatment at home and abroad mainly include PPS (polyphenylene sulfide), Nomex (aromatic polyamide), P84 (polyimide), PTFE (polytetrafluoroethylene), and glass fiber. PSA (aryl sulfone) fibers, etc., are often used in practical applications with a variety of fibers. The production process includes needle felt, surface coating, emulsion impregnation, etc., which can achieve the effect of surface filtration and gradient filtration. It not only improves the dust collection capacity, but also reduces pressure loss, facilitates cleaning and saves energy.
3. Introduction of main high temperature filter
(1) Polyphenylene sulfide (PPS) – currently the most widely used high temperature filter
Introduction: Polyphenylene sulfide fiber, with stable chemical properties, high melting point (285 °C) and excellent heat resistance, its flame retardant, chemical resistance and stability is also extremely outstanding, mainly used in municipal waste Incinerators, utility boilers, coal-fired boilers, hospital incinerators, and pulse bag filters on cogeneration boilers are currently the most widely used high-temperature filter media.
From a global perspective, PPS is mainly used in the automotive sector in 2012. 33% of Japanese PPS and 50% of European PPS are consumed in this area. China’s consumption structure is dominated by environmental protection industries (filter bags), accounting for about 30% of the total, followed by auto parts and electronic and electrical industries.
(2) Polyimide fiber (P84) – dust removal material with the highest temperature rating
Introduction: Polyimide fiber, also known as aromaticimide fiber, is a high-performance fiber obtained by polymerization of pyromellitic dianhydride and aromatic diamine to obtain polyamic acid prepolymer and then spinning through solution. .
Polyimide fiber was first developed by the Austrian Lancense Company under the trade name “P84”. The monopolistic product is now part of Germany’s Evonik. It is mostly used in dust bags and is known as the “gold wire”.
Polyimide fiber has excellent comprehensive performance, high temperature resistance, good filterability, and acid and alkali resistance, and can be used in high temperature environments such as cement kiln tail, garbage incineration and power plants.
In addition, for the polyimide fiber product, it has a unique fiber structure – irregular blade-like cross-section, which increases the surface area by 80% compared to the general circular cross-section, and brings two major advantages:
Enhanced ability to capture dust
Irregular fiber cross-section due to the different size of its internal stress, uneven distribution and natural curling of the fiber, so that the fiber has a strong cohesion entanglement. Therefore, by adding polyimide fibers to the glass fiber composite needled felt, even if the wind speed increases, the felt layer does not easily fall off.
(3) Polytetrafluoroethylene fiber – dust removal material with the best corrosion resistance
Description: PTFE fiber, also known as “Kevlar” in China. It was first developed by DuPont in 1953 and achieved industrial production in 1957. Polytetrafluoroethylene fiber is a synthetic fiber made of polytetrafluoroethylene as a raw material, which is produced by spinning or making a film and cutting or fibrillating it. At present, there are four main production methods for PTFE fibers, including emulsion spinning and paste extrusion spinning.
PTFE fiber inherits many advantages such as good chemical stability, wide temperature range, atmospheric aging, radiation resistance, low permeability, etc., mainly used as high temperature dust filter bag, strong corrosion resistance Filtration materials for filtering gas or liquids, fillers for pumps and valves, sealing tapes, self-lubricating bearings, reinforcing materials for alkali-produced perfluorinated ion exchange membranes, and rags for rocket launchers.
Polytetrafluoroethylene dust filter bag has two forms: one is PTFE fiber coated on other fabric (polyphenylene sulfide fiber, P84 polyimide fiber, glass fiber, etc.) made of the base cloth And the other is the use of polytetrafluoroethylene fiber for the film and base fabric, processed into needle felt. 100% PTFE fiber filter bags have better performance. Despite its superior performance, the high price of PTFE fiber is an obstacle to its wide-range promotion.
(4) Aramid fiber – the most widely used dust removal material
Introduction: Aramid fiber is a kind of high-performance synthetic fiber. It was first developed by DuPont and has excellent properties such as ultra-high strength, high modulus and high temperature resistance, acid and alkali resistance, light weight, heat-resistant flame retardant, etc. It has a wide range of applications. The aramid varieties commercialized on the market today include meta-aramid and para-aramid, as well as a small amount of modified products such as aramid II and aramid III.
Meta-aramid with high temperature, flame retardant, insulation properties, mainly used in high-temperature protective clothing, electrical insulation and high temperature filtration. The application of para-aramid is mainly to use its high-strength and high-model points, applied to individual protection, anti-ballistic armor, mechanical rubber products, high-strength cables, and asbestos substitutes.
High-temperature dust removal is the most important consumer market for meta-aramid. As the price/performance ratio is not superior to glass fiber and PPS, Kevlar fiber currently accounts for only about 5% of the high temperature filtration industry. Compared with other fibers, the outstanding performance of aramid fiber filter bag is its very low shrinkage rate in high temperature applications. It can still maintain a shrinkage of 1% at 1000°C for 1000 hours.
(5) Introduction of aryl sulfone
Introduction: Aryl sulfone belongs to the para-aramid series. Its scientific name is polyphenyl sulfone terephthalamide fiber. It is an aromatic polyamide fiber containing a sulfone group (-SO2-) in the polymer main chain. Ternary random copolymer.
The aryl sulfone is an excellent material for bag filter bag making, not only has good heat resistance, but also has excellent stability against thermal aging, small heat shrink, good dimensional stability and good resistance. Acid properties, etc., can be used at high temperatures for a long period of time. It is very suitable for high-temperature filter materials, and the price is relatively low compared to P84, PPS, and Nomex. In addition, aryl sulfone fiber friction coefficient is small, with its filter bag cleaning easy; because aryl sulfone temperature is high, so it can be PTFE (curing temperature 260 °C) heat pressure bonding made of good filtering effect And stable coated media.
(6) Glass fiber – the most economical high temperature filter material
Introduction: Glass fiber is a kind of traditional filter material, and it is also the most widely used filter material for dust removal in medium and high temperature flue gas. According to different glass components, glass fibers can be classified into two major categories: C (internal alkali) glass fiber filter materials and E (non-alkali) glass fiber filter materials.
Glass fiber is outstanding in high temperature performance and can work for a long time at a temperature of 260°C (alkali)/280°C (alkali free). Instant temperature up to 350 °C. High strength, low elongation rate, its tensile strength is higher than other natural and synthetic fibers, excellent corrosion resistance, resistance to most of the acid (except hydrofluoric acid) corrosion. The glass fiber surface is smooth, and the filtration resistance is small, which is favorable for dust stripping. It does not burn or deform. Glass fibers treated with different surface treatments have the advantages of softness, smoothness, hydrophobicity, anti-condensation and low shrinkage. Glass fiber has prominent dimensional stability, high tensile breaking strength, strong corrosion resistance, smooth surface, breathable water, easy to remove dust, good chemical stability, because of its low cost, when the user requirements are low, dust removal equipment Manufacturers also use glass fiber filters for pulse bags.