31
5
Electrostatic Precipitators
Bob Taylor
BHA Group, Inc., Kansas City, Missouri
5.1 DEVICE TYPE
Electrostatic precipitators are used for the purpose of removing dry particulate mat-
ter from gas streams. They basically apply an electrostatic charge to the particulate
and provide sufcient surface area for that particulate to migrate to the collecting
plate and be captured. The collecting plates are rapped periodically to disengage the
collected particulate into a receiving hopper.
5.2 TYPICAL APPLICATIONS AND USES
Dry electrostatic precipitators are used to remove particulate matter from ue gas
streams exiting cement kilns, utility and industrial power boilers, catalytic crack-
ers, paper mills, metals processing, glass furnaces, and a wide variety of industrial
applications (see Figure5.1).
An electrostatic precipitator is a constant pressure drop, variable emission par-
ticulate removal device offering exceptionally high particulate removal efciency.
There is a unique jargon involving electrostatic precipitators. If you contemplate
purchasing or studying the use of one, perhaps the following buzzword list will prove
helpful. It is in alphabetical order, so if you see a word that you do not understand,
just jump down the list to nd the offending word.
Air splitter switch: An air splitter switch is mounted at the high-voltage bushing
contained on the transformer rectier. The purpose of the switch is to iso-
late one of the two electrical sections served by the transformer rectier
while the other operates.
Antisneak bafe: A deector or bafe that prevents gas from bypassing the treat-
ment zone of the precipitator.
Arc: Arcs occur within the high-voltage system as a result of uncontrolled spark-
ing. If measurable current ow is detected, damage will occur to internal
components.
Aspect ratio: The treatment length divided by treatment height. A higher number is
more favorable for collection efciency.
Back corona: Occurs in high-resistivity dust applications. As a result of the dust resis-
tivity, a voltage drop occurs across the layer of dust on the collecting plates. The
application of current to the eld builds the charge on the surface of the dust
layer until the breakdown voltage of the dust is achieved. At this point a surge
32 Air Pollution Control Equipment Selection Guide
of current occurs from the surface of the dust to the collecting plate, causing
localized heating of the dust. The dust explodes back into the gas stream carry-
ing a charge opposite of the electrons and gaseous ions. This causes collection
efciency to degrade and dust reentrainment to increase.
Bus section: Smallest isolatable electrical section in the precipitator.
Casing: Gas-tight enclosure within which the precipitator collecting plates and dis-
charge electrodes are housed.
Chamber: Common mechanical eld divided in the direction of gas ow by a parti-
tion. The partition is either a gas-tight wall or open structural section.
Cold roof: This is the walking surface immediately above the hot roof section.
Collecting surface: Component on which particulate is collected. Also known as
collecting plate or panel.
Corona discharge: The ow of electrons and gaseous ions from the discharge elec-
trode toward the collecting plates. Corona discharge occurs after the dis-
charge electrode has achieved high enough secondary voltages.
Current-limiting reactor: This device provides a xed amount of inductance into
the transformer rectier circuit. Some current-limiting reactors have taps
that allow the amount of inductance to be varied manually when the circuit
is not energized.
Direct rapping: Rapping force applied directly to the top support tadpole or lower
shock bar of a collecting plate.
Discharge electrode: The component that develops high-voltage corona for the pur-
pose of charging dust particles.
Disconnect switch: A switch mounted in the high-voltage guard or transformer rec-
tier that allows the electrical eld to be disconnected from the transformer
rectier.
FIGURE5.1 Typical electrostatic precipitator in operation (BHA Group, Inc.).

Get Air Pollution Control Equipment Selection Guide, 2nd Edition now with the O’Reilly learning platform.

O’Reilly members experience live online training, plus books, videos, and digital content from nearly 200 publishers.