14.1 DEVICE TYPE
Spray tower scrubbers use spray nozzles to extend the surface area of the scrubbing
liquid to enhance mass transfer of contaminant gas(es) into the liquid. They are pri-
marily used for gas absorption.
Spray scrubbers include designs that use spray nozzles (hydraulically or air or
steam atomized) to absorb gases and control larger diameter (+10 μ) particulate.
14.2 TYPICAL APPLICATIONS AND USES
Spray tower scrubbers are often used on wet ue gas desulfurization (FGD) systems
at public and industrial power generation facilities. These FGD systems use lime
or limestone slurries as the scrubbing liquid. Their open vessel design is an advan-
tage where plugging or scaling may occur. The simplicity of the design makes them
a lower cost alternative for high gas volume scrubbing applications (over 100,000
actual cubic feet per minute [acfm]).
They are also used as part of quenching and gas conditioning systems wherein the
gas must be brought to saturation or near saturation with water.
Most spray towers are countercurrent in design wherein the gas ows vertically
upward and the liquid falls downward through the ascending gases. Some units, used
for odor control, are horizontally oriented using a multiplicity of concurrent spray
sections in series. Often, a series of bafes is incorporated into the scrubber vessel
to change the direction of the gas stream and to provide intimate contact of the spray
and the contaminant gas.
Some spray tower designs have been modied to act as direct contact condensers
in applications wherein packed devices may plug with solids. Though not as mechan-
ically efcient in that application as pure countercurrent designs (such as a packed
tower), the ability to resist plugging and therefore provide greater on-line availability
can make the spray tower condenser attractive.
Spray scrubbers cover a wider variety of designs. These vary from devices as
simple as a spray header in a duct to cyclonic type devices (often called preformed
14.3 OPERATING PRINCIPLES
A common characteristic of this type of scrubber is the use of spray nozzles to extend
the liquid surface and produce target droplets.
At least one spray zone is produced in a spray tower using at least one spray
nozzle in a containing vessel. In practice, however, most spray towers use multiple
spray zones to achieve the required gas cleaning efciency. Figure 14.1 shows a