107
11
Mechanically Aided
Scrubbers
11.1 DEVICE TYPE
Mechanically aided scrubbers are dened as devices that use a moving mechanism
in the gas stream to achieve the desired particulate or contaminant gas removal.
Mechanically aided scrubbers are generally used for dust control involving par-
ticulate larger than approximately 10 μm diameter and at low loadings (below 5
grains per dry standard cubic foot). They have been used to control dusts from load-
ing and unloading facilities, fugitive dusts from storage facilities, wet coating opera-
tions, and numerous other applications. They were particularly popular in the 1970s
in the mining industry for dust control where a wet product was required and are
still used for that purpose. They are noted for their low cost, compact size, and
reliability. Ever-tightening codes have shifted the focus to low- to medium-energy
Venturi scrubbers on many applications that had been dominated by mechanically
aided designs.
11.2 TYPICAL APPLICATIONS AND USES
These designs are used to control high dust loadings of relatively large dust where it
is desirable to recover the dust wet. Controlling dust from conveyors, blenders, mull-
ers, mills, and other high-dust-loading sources are areas where this type scrubber
has been used. In these applications, the dust is usually returned to the process as wet
slurry or is separated in a pond or clarier.
They are effective on particles 10 μm or larger. They are not used as much where
the particulate is hygroscopic and may build up on the scrubber inlet. Similarly, they
are not used for gas absorption, although they may be used ahead of a gas absorption
device (such as a packed tower).
These scrubbers have been applied to the control of emissions from dissolving
tank (smelt tank) vents in the paper industry. Some have been enhanced through
the addition of a Venturi reverse spray scrubber ahead of the mechanically aided
scrubber. Some recovery boiler suppliers routinely supply mechanically aided
scrubbers for use on the dissolving tank vents. In recent years, packed towers have
been added after the mechanically aided scrubber for additional gas absorption and
odor control.
Their compact size and low cost make them attractive, where codes allow, for
general dust control applications.

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