Fabric filters applications

Because of their inherently high efficiency on dusts in all particle-size ranges, fabric filters have been used for collection of fine dusts and fumes for over 100 years. The greatest limitation on filter application has been imposed by the temperature limits of available fabric materials. The upper limit for natural fibers is about 90°C (200°F). The major new developments in filter technology that have been made since 1945 have followed the development of fabrics made from glass and synthetic fibers, which has extended the temperature limits to about 230 to 260°C (450 to 500°F). The capabihties of available fibers to resist high temperatures are still among the most severe limitations on the possible applications of fabric filters. 

The selection of the optimum type of particulate collection device (i.e., ESP or fabric filter oaghouse) is often not obvious without conducting a site-specific economic evaluation. This situation has been brought about by both the recent reductions in the allowable emissions levels and advancements with fabric filter and ESP technologies. Such technoeconomic evaluations can result in application and even site-specific differences in the final optimum choice (see Piecip New.sLetter, 220, June, 1994 and Fabric Filter Newsletter, 223, June, 1994). 

Fabric filters have had a long history in performing effectively in a wide variety of applications. Common applications using pulse-jet cleaning systems include ... 

It is important to note that these applications are typical, but not at all definitive. Fabric filters can be used in almost any process where dust is generated and can be collected and ducted to a centralized location. In general, fabric filters come in many different sizes and configurations. In older plants one can find makeshift operations. See Figures 7 and 8 for examples of common configurations and characteristics. 

Practical application of fabric filters requires the use of a large fabric area in order to avoid an unacceptable pressure drop across the fabric. Baghouse size for a... 

Fabric filters can be more costly to operate and maintain than electrostatic precipitators, cyclones, and scrubbers however, fabric filters are more practicable for filtration of specific dusts. For example fabric systems are the typical control method for toxic dusts from insecticide manufacturing processes, salt fumes from heat treating, metallic fumes from metallurgical processes, and other applications. Any other control method may not be as efficient, nor economically feasible for such applications. 

The cast grids are made into battery anode and cathode plates by the application of a lead oxide paste of 70 percent lead oxide (PbO) and 30 percent metallic lead. Lead ingots are tumbled in a ball mill with airproducing lead oxide and fine lead dust (referred to as leady oxide ). Leady oxide particulates are entrained in the mill exhaust air, which is treated sequentially by a cyclone separator and fabric filter. The used fabric filter bags are shipped to a RCRA-permitled commercially operated ha2ardous waste landfill located in Colorado. The leady oxide production process does not produce wastewater. 

Design and application of fabric filters are covered in various references. " ... 

Goodfcilow, H. D., R. J. Geren,, and E. F. C. Foord. Applications of Fabric Filters at High Air-to-Cloth Ratios on Metallurgical Fumes. In The User and Fabric Filtration F.qmpment 111, APCA Specialty Conference Proceedings, Buffalo, NY (Oct. 1-3, 1978). 

The gas entering the filter must be kept above its dewpoint to avoid water-vapor condensation on the bags, which will cause plugging. However, fabric filters have been used successfully in steam atmospheres, such as those encountered in vacuum dryers. In these applications, the housing is generally steam-cased. 

Eliminate from consideration any bags that are patently unsatisfactory. Bag D is eliminated because its recommended maximum temperature is below the operating temperature for this application. Bag C is also eliminated, because a pulse-jet fabric-filter system requires that the tensile strength of the bag be at least above average. 

Dry cyclones are the primary collection equipment used to capture the detergent dust in the spray dryer exhaust and recycle it back to the crutcher. The dry cyclones can remove up to 90 percent by weight of the detergent product fines from the exhaust air. Fabric filters have been used after cyclones but have limited applicability, especially on efficient spray dryers, because of condensing water and organic aerosols binding the fabric filters [4, 21]. 

Until recently, air filtration for clean rooms uses dead-end fabric filters. They are not efficient in the particle diameter range of 0.1 to 0.5 pm and also suffer in many cases from two of the most important problems in clean room gases applications particle shedding and gas reactivity (or called hydrocarbon outgassing). Some ceramic membranes such as alumina membranes have made a visible entry into the clean room market as in-line gas filters. 

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