Shake collectors

In practice, it is normal to manufacture the tubes in quite long lengths, for example 100 m, after which the individual sleeves can be cut to the ordered size in preparation for the next stage of fabrication, hi the case of reverse air and shake collectors, this may involve the fitting of anti-collapse rings and possibly metal caps - attachments by which the filter sleeve can be suspended in the filter. Other reinforcements may also be included to enable the sleeve to withstand the effect of frequent flexing. 

FIGURE 53.3 Fabric filters (a) large, multicompartment fabric filter cleaned by mechanical shaking. (Courtesy of Wheelabrator-Shint.) (b) Envelope-type fabric filter cleaned by reverse flow. (Courtesy of Shinto Dust Collector.)... 

Fabric dust collectors are usually classified according to their cleaning mechanism, these being shake, reverse air, and jet pulse. Whichever mechanism is employed, it is important that a programme is devised to provide an optimum level of dust removal. In other words, the cleaning should not be so excessive as to destroy the porous structure formed by the dust, which could lead to emission problems, but not so ineffective as to lead to an unacceptable pressure drop. 

Shake cleaning, as the name implies, involves switching off the exhaust fan and flexing the filter elements (or sleeves) with the aid of a shaking mechanism, either manually, as in traditional units, or automatically. In both cases the effect is to release the dust, which then falls into a hopper for collection and removal (Fig. 3.3). In this type of collector, the filter sleeves, which may be up to 10 m in length, are suspended under controlled tension from the arm of a flexing mechanism, which effects the cleaning action. 

Many large fabric filters are self-cleaning. For some, agitation or motion shakes off the collected material and cleans the filters. Some use reverse air flow to knock material loose. During a cleaning cycle and cleaning action, exhaust system air must divert from the exhaust system to an alternate collector. 

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