TM 5-815-1/AFR 19-6
CHAPTER 9
FABRIC FILTERS
9-1.
Fabric filtration
more difficult. A closed suction system is
illustrated in figure 9-2.
Fabric filters are used to remove particles from a gas
b. Filter shape and arrangements.
stream. Fabric filters are made of a woven or felted
(1) The cylindrical filter is the most common
material in the shape of a cylindrical bag or a flat
filter shape used in fabric filtration. The
supported envelope. These elements are contained in
principal advantage of a cylindrical filter is
a housing which has gas inlet and outlet connections, a
that it can be made very long. This maximizes
dust collection hopper; and a cleaning mechanism for
total cloth area per square foot of floor space.
periodic removal of the collected dust from the fabric.
Cylindrical filters are arranged to
In operation, dust laden gas flows through the filters,
accommodate each of the basic flow
which remove the particles from the gas stream. A
configurations shown in figure 9-3.
typical fabric filter system (baghouse) is illustrated in
(2) A panel type filter consists of flat areas of
figure 9-1.
cloth stretched over an adjustable frame. (See
figure 9-3.) Flow directions are usually
9-2.
Types of filtering systems
horizontal. Panel filters allow 20 to 40
The mechanisms of fabric filtration are identical
percent more cloth per cubic foot of collector
regardless of variations in equipment structure and
volume and panels may be brushed down if
design. In all cases, particulates are filtered from the
dust build-up occurs. However, panel-type
gas stream as the gas passes through a deposited dust
filters are not widely used in boiler and
matrix, supported on a fabric media. The dust is
incinerator applications.
removed from the fabric periodically by one of the
c. Cleaning methods. A fabric cleaning mechanism
available cleaning methods. This basic process may be
carried out by many different types of fabric filters with
must impart enough energy to the cloth to overcome
a variety of equipment designs. Filtering systems are
particle adhering forces without damaging the cloth,
differentiated by housing design, filter arrangement,
disturbing particle deposits in the hopper; or removing
and filter cleaning method.
too much of the residual dust deposit on the filter. The
cleaning period should be much shorter than the filter-
a. Housing design. There are two basic housing con-
ing period. The correct choice of cleaning method for
figurations which apply to boiler and incinerator flue
a particular application will greatly enhance the perfor-
gas cleaning. These are closed pressure, and closed
mance of the fabric filter system. An incorrectly
suction.
matched cleaning method can result in high pressure
(1) The closed pressure baghouse is a completely
drops, low collection efficiency, or decreased bag life.
closed unit having the fan located on the dirty
A performance comparison of the various cleaning
side of the system. Toxic gases and gases with
methods is given in table 9-1.
high dew points are handled in this type of
(1) Mechanical shake. Some baghouses employ
baghouse. Fan maintenance problems arise
a type of mechanical shaking mechanism for
due to the fact that the fan is in the dirty gas
cleaning. Bags are usually shaken from the
stream before the baghouse. The floor of the
upper fastenings, producing vertical, horizon-
unit is closed and the hoppers are insulated. A
tal, or a combination of motions, on the bag.
closed pressure baghouse is illustrated in
All bags in a compartment may be fastened to
figure 9-2.
a common framework, or rows of bags are
(2) The closed suction is the most expensive type
attached to a common rocking shaft. After the
of baghouse, with the fan being located on the
bags have been shaken, loosened dust is
clean gas side. The closed suction baghouse
allowed to settle before filtration is resumed.
is an all-welded, air-tight structure. The floor
The entire cleaning cycle may take from 30
is closed, and the walls and hopper are
seconds to a few minutes. Some designs
insulated. Fan maintenance is less than with
incorporate a slight reversal of gas flow to aid
the pressure type, but inspection of bags is
in dust cake removal and settling, as any
9-1
Previous Page
