In the simplest terms, a dry electrostatic precipitator ( ESP )
is a large box. Particulate control begins when the dust laden gases are drawn into
one side of the box. Inside, high voltage
electrodes impart a negative charge to the particles entrained in the gas.
These negatively charged particles are then attracted to a grounded collecting
surface which is positively charged. The gas then leaves the box up to 99.9%
cleaner than when it entered.
The particulate control process continues inside the box,
as the particles from the continuous flow build up on the collecting plates. At
periodic intervals, the plates are rapped causing the particles to fall into hoppers.
The particles collected during the particulate control process are then removed from
the hoppers by a rotary screw conveyor.
The negatively charged rigid type discharge electrodes
are accurately centered between the collecting surfaces and supported from
high voltage insulators located in insulator compartments.
One of the most important considerations in design and operation
of the dry electrostatic precipitator ( ESP ) is the removal of the collected material
from the collecting surfaces without re-entraining it in the gas stream, this ensures
compliance with MACT. On PPC dry electrostatic precipitator devices ( ESP ), material
removal from the plates is accomplished by electromagnetic rappers installed on the
roof section. These rappers deliver hammer blows
of preset intensity at preset intervals to the plate headers. A vertical shock
wave is created in each plate causing the collected material to shear off
and fall into the hopper. The rapping intensity and interval is dictated by
the characteristics of the deposited material. These adjustments are made
to the rapper system to suit the requirements of each installation and are
a part of the dry electrostatic precipitator ( ESP ) start up service provided by PPC.
As opposed to dry electrostatic precipitator ( ESP ) hoppers,
the PPC dry precipitator hoppers have integral, support members which simplifies support steel fabrication
and structural steel erection. Additionally this allows shop installation
of insulation and heaters at substantial savings. PPC dry electrostatic precipitator hopper openings are
a minimum of 18" wide to allow free flow of ash and eliminate bridging.
Hopper depth is kept to a minimum to reduce cooling of ash and subsequent
Maximum effectiveness of the dry electrostatic precipitator particulate control
system occurs when the voltage supply output reaches the sparking threshold.
Variation in gas volume, dust loading and other factors, however affect the
sparking threshold level. Employing an advanced electrical control system, an automatic control circuit regulates each high voltage power supply output for maximum dry electrostatic precipitator ( ESP ) efficiency regardless of process variation. Sparking causes the power supply to "notch down" slightly with the automatic controls bringing it right back up to sparking potential. Modern digital electronic controls automate this process and assure the ESP particulate control device operates a peak performance levels at all times, ensuring compliance with MACT guidelines as set forth by the EPA.