TM 5-815-1/AFR 19-6
(1) Venturi scrubbers. The venturi scrubber uti-
good for particles larger than a micron in
lizes a moving gas stream to atomize and
diameter. Gas absorption efficiency is low
accelerate the liquid droplets (figure 7-4). A
because of the co-current nature of the gas
convergent-divergent nozzle is used to
and liquid flow. Liquid pumping power
achieve a gas velocity of 200 to 600 feet per
requirements are high and capacity is low
second (ft/ sec) which enhances liquid
making this type impractical for boiler or
atomization and particulate capture.
incinerator emissions control.
(3) Dynamic (wetted fan) scrubber This
Collection efficiency in a gas atomized
venturi scrubber increases with pressure
scrubber combines a preformed spray,
drop. Pressure drops of 25 inches water
packed bed or centrifugal scrubber with an
gauge or higher are utilized to collect sub-
integral fan to move the gas stream through
micron particles. Scrubbers of the gas
the scrubber. Liquid is also sprayed into the
atomized type have the advantage of adjust-
fan inlet where the rotor shears the liquid
ment of pressure drop and collection
into dispersed droplets. The turbulence in
efficiency by varying gas velocity. The gas
the fan increases liquid/ gas contact. This
velocity is controlled by adjusting the area of
type of scrubber is effective in collection of
the venturi throat. Several possible methods
fine particulate. Construction of this
for doing this are illustrated in figure 7-5.
scrubber is more complex due to the neces-
This can be used to control performance
sity of the fan operating in a wet and possibly
under varying gas flow rates by maintaining
corrosive gas stream. The design must
a constant pressure drop across the venturi
prevent build-up of particulates on the fan
throat. Due to the absence of moving parts,
rotor.
c. Dry scrubbers. Dry scrubbers are so named
scrubbers of this type may be especially
suitable for the collection of sticky particles.
because the collected gas contaminants are in a dry
Disadvantages include high pressure drop
form.
(1) Spray dryer. The spray dryer is used to
for the collection of sub-micron particles and
limited applicability for gas absorption.
remove gaseous contaminants, particularly
(2) Ejector venturi. The ejector venturi scrubber
sulfur oxides from the gas stream. An
utilizes a high pressure spray to collect parti-
alkaline reagent slurry is mechanically
cles and move the gas. High relative velocity
atomized in the gas stream. The sulfur
between drops and gas aids in particle
oxides react with the slurry droplets and are
collection. Particle collection efficiency is
absorbed into the droplets. At the same time,
7-3
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