Air Pollution Control Equipment Selection Guide, 2nd Edition

91

9

Filament (MeshPad)

Scrubbers

9.1 DEVICE TYPE

Filament or mesh pad type absorbers have proven themselves very effective in

the absorption of water-soluble gases. When constructed in a sufciently dense

medium panel, they can be used for the collection of airborne bacteria and spores.

These devices typically use woven or layered lamentaceous mesh layers onto

which a spray of liquid is administered. The contaminant gases, particulate, or

both pass through these layers of mesh wherein the contaminant and liquid are

brought into intimate contact, thereby promoting gas absorption. Various vendors

have developed proprietary designs of this generic type with hundreds of success-

ful installations.

9.2 TYPICAL APPLICATIONS

Filament and mesh pad type scrubbers are often used to collect inorganic acid vapor

emissions from process reactors or storage tank vents. They are also used after par-

ticulate removal devices to enhance the absorption of gases. Laboratory hoods and

point of use scrubbers often use wetted lament or mesh pad scrubbers.

They are often used on large gas cleaning systems, for example, for acid concen-

tration and capture. Figure9.1 shows a multistage wet scrubber on a superphosphate

fertilizer plant for the recovery of uosilicic acid. This system consists of a Venturi

scrubber for particulate control, a multistage wetted Kimre pad unit for stepwise acid

gas concentration, and a preformed spray scrubber for polishing the emission using

pond water. The water ows upstream from the preformed spray scrubber to the la-

ment type absorber. The uosilicic acid is concentrated in three sprayed stages in the

lament type scrubber, which is housed in the rectangular box on the left (ahead of

the fan). The mesh pad type scrubber is shown in the foreground of Figure9.2.

Another common application is in the control of gases and mist from chemical

reaction vessels. These vessels may incorporate an acid (or base) feed system that

injects the chemical(s) into a vented, agitated tank. Given the agitation and chemi-

cal reaction, some absorbable gases may be evolved along with droplets. Often, the

mesh pad type device drains back into the reaction vessel, thus serving to capture

and recycle the mist and chemicals.

Filament or mesh pad type scrubbers are generally not used where insoluble par-

ticulate is present or where a precipitate can form during chemisorption.

92 Air Pollution Control Equipment Selection Guide

FIGURE9.2 Crossow meshpad type scrubber in foreground (Bionomic Industries, Inc.).

FIGURE9.1 Multiple stage superphosphate plant system (Bionomic Industries, Inc.).