Performance of Dust Collectors

Many types of particulate collection devices are available commercially (see Table 53.2). Each operates on a different principle for accomplishing removal of particulates from the gas stream. Four basic types are common in drying systems (1) the drying vessel itself (in the case of vessel dryers), (2) cyclones, (3) bag filters, and (4) wet scrubbers. Electrostatic precipitators (ESPs) are not used widely in drying installations in spite of their low-pressure drop and high collection performance. The initial cost of purchase and construction is high. For this reason, the emphasis in Section 53.3 will be on the three most widely used devices, e.g., cyclones, fabric filters, and wet scrubbers. For a concise discussion of various types of solid-gas separation equipment and guidelines for selection of dust collectors,... 

Measurements of the concentrations and characteristics of dust dispersed in air or other gases may be necessary (1) to determine the need for control measures, (2) to establish compliance with legal requirements, (3) to obtain information for collector design, and (4) to determine collec tor performance. 

Pressure loss through the cyclone is also a key performance parameter, and this depends mainly on the design of the cyclone. In general, the pressure drop across the cyclone collector is small compared with most other dust collectors, but the higher the collection efficiency required, the larger the pressure drop and hence the energy consumption required. 

The details of specifications for bag filter dust collectors are important to a proper and operable design selection. There are many variables which must be furnished by the manufacturer so that the user can understand how the unit operates mechanically and the unit s dust loading capabilities. The larger the air/cloth ratio for the unit, the smaller will be its physical dimensions and generally, cost however, the higher will be the frequency of cleaning. This can be quite troublesome, therefore low values of this ratio are preferable, consistent with the analysis of overall performance. 

The drilling operation, which provides a recess for the installation of a fuse in a 155mm shell, was performed in building 1619. An air driven drill is used to put a recess in the Composition B that has been encased in the nose. The dust generated from this operation is removed by suction through a 5.1 cm (2.0 in) line to a Hoffman primary dust collector. Downstream of the primary collector is a secondary collector used to take any excess not trapped in the primary collector. Two sample areas were selected for study as shown in Figure 5. 

Particulate Scrubbers Wet collectors, or scrubbers, form a class of devices in which a liquid (usually water) is used to assist or accomplish the collection of dusts or mists. Such devices have been in use for well over 100 years, and innumerable designs have been or are offered commercially or constructed by users. Wet-film collectors logically form a separate subcategory of devices. They comprise inertial collectors in which a film of liquid flows over the interior surfaces, preventing reentrainment of dust particles and flushing away the deposited dust. Wetted-wall cyclones are an example [Stairmand, Tram. lmt. Chem. Eng., 29,356 (1951)]. Wet-film collectors have not been studied systematically but can probably be expected to perform much as do equivalent dry inertial collectors, except for the benefit of reduced reentrainment. 

Gravity vessels are suitable for low-, medium-, and high-temperature operation in the last case, the housing will be lined completely with refractory brick. Dust-recovery equipment is minimized in this type of operation since the bed actually performs as a dust collector itself, and dust in the bed will not, in a successful application, exist in large quantities. 

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