How to recycle high-performance filter materials？
With the upgrading of emission standards in the environmental protection industry, ultra-low emissions of 10mg/m3 or even 5mg/m3 have become the industry norm. As the most effective technology to control industrial smoke and dust in China, bag filter has been widely used in coal-fired power plants and industrial boilers, cement, steel, waste incineration, chemical industry, non-ferrous metallurgy and other industries.
As a consumable, the filter bag needs to be replaced in about 4~5 years, which will produce a large amount of high-performance fiber waste. These discarded filter bags are not only difficult to degrade, but also contain different kinds of dust on the surface and inside. Some of them contain heavy metals or other hazardous substances. If they are not recycled, they will cause secondary pollution to the environment.
According to different application fields, the materials of high-temperature filter bags are different. For example, the coal industry mainly uses pure PPS fiber or PPS+PTFE composite fiber filter materials, the cement industry mainly uses aramid, polyimide, glass fiber and glass fiber composite filter materials, the steel industry mainly uses pure aramid, polyester, glass fiber composite filter materials, and the garbage incineration industry mainly uses PTFE fiber filter materials.
The primary recovery process of filter bags is to collect, remove dust, disperse and crush the waste filter bags and then make them into primary building materials, well covers, thermal insulation materials and other products through rough washing, pressing and thermal setting processes. It is suitable for the recovery of pure filter materials such as PPS, aramid, polyimide and glass fiber.
Although the primary recovery process is simple, the equipment investment is low, and it is easy to operate, the added value of the product is low, which does not give full play to the advantages of high-performance fiber materials. On this basis, the intermediate recovery process of the filter bag needs to add a deep cleaning process. The dust on the filter material fiber is completely removed by physical methods, and then it is melted, resin granulated, or processed into other injection molding materials, such as special engineering plastics, vehicle shells, brake pads, chemical reactor fillers, temperature/corrosion/toughness bolts, etc. The product has the advantages of heat resistance and corrosion resistance. However, this method is only suitable for pure fusible fiber materials, such as PPS filter bags in coal fired power plants, and is not suitable for aramid, polyimide and other non melting point fiber materials.
In fact, in order to improve the performance of filter materials to adapt to complex application environments, filter materials are usually made of a variety of materials, such as PPS+PTFE hybrid filter materials in the coal-fired field. PTFE mixed in the filter material will seriously affect the quality of regenerated PPS. How to separate and purify various materials in the filter material is still a problem in the industry. Professor Liu Jingxian's research group of Northeastern University has studied the advanced recovery technology route of hybrid filter materials that can separate and purify PPS and PTFE hybrid filter materials. Through performance strengthening, PPS can recover its original performance and be made into high-level resins, fibers and other products. It was found that the cleaned waste filter material was put into the prepared chlorine based solution. After heating and maintaining for a certain time, PPS was dissolved while PTFE was still solid. After filtering, PPS solution was obtained. After cooling and purification, PPS solid could be made.
For other non melting point high-performance fibers used for high-temperature filter media, such as the recycling technology of aramid fiber, there is no report on the industrial production line in China. Although Teijin Group has established a aramid fiber recycling system, it mainly aims at the waste materials in the production and processing process, as well as the waste protective articles such as fire clothing and cutting gloves, which are recycled into pulp Short fiber or short fiber yarn and other products. There are also companies and institutions specialized in the recycling of aramid protective clothing in developed countries such as Europe and the United States. The recycled fiber products also include fiber particles, fan wheels and other engineering materials. In contrast, the waste filter material has a lot of dust or dangerous substances, and the fiber is usually damaged by high temperature and chemical substances, so the recovery cost is higher and more difficult