•
Inertial Collection
– Dust particles strike the fibers placed perpendicular to the airflow direction
instead of changing direction with the air stream.
•
Interception
– Particles that do not cross the fluid streamlines come in contact with fibers because of
the fiber size.
•
Brownian Movement
– Sub-micron particles are diffused, increasing the probability of contact
between the particles and collecting surfaces.
•
Electrostatic Forces
– The presence of an electrostatic charge on the particles and the filter can
increase dust capture.
A combination of these mechanisms results in formation of the dust cake on the filter, which eventually
increases the resistance to air flow. The filter must be cleaned periodically. A balance must be
maintained between having some dust cake formation to improve efficiency and an acceptable increase
in pressure drop. A timer controller or magnehelic gauge, monitoring the differential pressure (DP) and
pulsing accordingly, can maintain the dust cake with minimal increase in pressure. By pre-coating your
filter with a special dust at start-up, you can increase initial efficiency of your collector (see Section 360 –
PRECOATING OF FILTERS).
400.2 Filter Cleaning
The
Gold Cone
cartridge elements are sequentially cleaned by back flushing with air. This momentary
airflow reversal is induced by a short burst of compressed air. The air is released from the compressed air
reservoir by a fast-acting, high-flow diaphragm valve. This “pulse” of air dislodges the accumulated dust
from the filter element. The dislodged dust then drops into the hopper or collection drawers. Each pulse
cleans one row of filter cartridges leaving the remaining cartridges available to continue filtering the
ventilation air. This allows the cleaning to take place without the need to stop the ventilation system.
Figure 400.2.1 shows a
Gold Cone
cartridge in normal operation. Figure 400.3.1 demonstrates the pulse
of compressed air cleaning a cartridge.
32
Figure 400.2.1 – Normal
Gold Cone Operation
