In addition to workplace, protection gas cleaning devices are necessary to reduce or eliminate vapors and dust emissions from incinerators, power stations, cogenera- tion plants, and production facilities of the paper, cement, metallurgical, and other industries. This is to be in compliance with the environmental regulations of many countries. The systems include scrubbing systems, carbon adsorption, catalytic oxi- dizers, ceramic filters, and oxidizer systems. Some facilities use biofiltration, a tech- nique to remove odorous and other obnoxious components from a gas stream by passing the stream through a medium that has been inoculated with microorgan- isms that break down the offending components.
The fumes are often hot (up to 900°C) and corrosive. Fabric bag filters are often included as a prefilter to the cleaning system usually. According to Dickenson(165), “the development of heat and corrosion resistant fabric media, particularly modern treated needlefelts, has been one of the most significant advances in the dust extrac- tion and treatment of hot gases.” Needlefelts composed of polyamides, polypropylene, PTFE, aramides, glass, and mineral fibers have successfully been used in a wide range of hot gas filtration applications. Table 8.6 lists the properties of various filter fabrics.