Reverse air collectors

In either type of collector, the location of the broken bag or bags has to be determined and corrective action taken. In a noncompartmentalized unit, this requires system shutdown and visual inspection. In inside collectors, bags often fail close to the bottom, near the tube sheet. Accumulation of dust on the tube sheets, the holes themselves, or unusual dust patterns on the outside of the bags often occurs. Other probable bag failure locations in reverse-air bags are near anticollapse rings or below the top cuff In shaker bags, one should inspect the area below the top attachment. Improper tensioning can also cause early failure. 

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. 

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. 

In dust collection, the laboratory test procedures are designed to support a particular theory. A more practical procedure, on the other hand, is described by Barlow and involves the construction of a pilot dust collector. The equipment houses four filter sleeves and is capable of operation in both reverse air and pulse cleaning... 

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. 

FIG. 17-60 Reverse-pulse fahric filter (a) filter cylinders (h) wire retainers (c) collars (d) tube sheet (e) venturi nozzle (f) nozzle or orifice (g) solenoid valve (h) timer (/) air manifold (k) collector housing (/) inlet (m) hopper (n) airlock (o) iipperplenum, (Mikropul Division, US. Filter Coip.)... 

Where reverse-pulse dust collectors are used for removing dust from dust extraction systems, they should usually be equipped with cartridge filters containing a compressed air lance, and be capable of continuous operation without interrupting the airflow. 

Dust control equipment includes collection hoods, fabric and fiber filters, reverse jet filters, wet and dry precipitators, cyclones, and scrubbers [27]. Selection depends on particle size and density of the material, volume and temperature of air to be treated, efficiency, economic considerations, and dust diaracteristics. Dusts that are sticky, fluffy, erosive, toxic, or combustible demand special consideration. The efficiencies of various types of collectors have been tabulated, along with a guide to selection for various applications [28]. This information is siunmarized in Tables 2-8 and 2-9. A combination of devices often will be more effective than a single t)q)e. 

Cleaning by reverse-flow pulses of high pressure air is normally applied to fabric filters and to pleated cartridge collectors alike. The high pressure pulses may be created by a pressure blower or come directly from a compressed air supply. In the latter case the type is normally called a pulse-jet filter. 

The containment model have been developed and constructed in scale 1 80 for the experimental investigation of the possible influence of the wind on the SPOT effectiveness. The investigations have been performed for the wind speed from 0 to 90 m/s (from the calm atmosphere to hurricane) at the wind direction from 0 to 360 degrees in relation to the reactor building axes. These experiments have shown the absence of the circulation reversal in the exhaust air stacks and have confirmed the design solution correctness, at which the SPOT trains are connected by the common inlet collector and the common outlet collector with the deflectors. 

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