TM 5-815-1/AFR 19-6
d. Wood refuse boiler applications. It is not recom-
to 550 degrees Fahrenheit, which is below the
flue gas temperature of most incinerator
mended that a baghouse be installed as a particulate
installations
collection device after a wood fired boiler. The pos-
(2) Collection of condensed tar materials
sibility of a fire caused by the carry over of hot glowing
(typically emitted from incinerators) could
particles is to great.
lead to fabric plugging, high pressure drops,
9-8.
Performance
and loss of cleaning efficiency
Significant testing has shown that emissions from a
(3) Presence of chlorine and moisture in solid
fabric filter consist of particles less than 1 micron in
waste leads to the formation of hydrochloric
diameter. Overall fabric filter collection efficiency is 99
acid in exhaust gases, which attacks fiberglass
percent or greater (on a weight basis). The optimum
and most other filter media
operating characteristics attainable with proper design
(4) Metal supporting frames show distortion
of fabric filter systems are shown in table 9-3.
above 500 degrees Fahrenheit and chemical
attack of the bags by iron and sulphur at tem-
9-9.
Advantages and disadvantages
peratures greater than 400 degrees Fahrenheit
a. Advantages.
contribute to early bag failure. Any fabric
(1) Very high collection efficiencies possible
filtering systems designed for particulate con-
(99.9 + percent) with a wide range of inlet
trol of incinerators should include:
grain loadings and particle size variations.
-- fiberglass bags with silica, graphite, or teflon
Within certain limits fabric collectors have a
lubrication; or nylon and, teflon fabric bags
constancy of static pressure and efficiency,
for high temperature operation, or stainless
for a wider range of particle sizes and con-
steel fabric bags,
centrations than any other type of single dust
-- carefully controlled gas cooling to reduce
collector.
high temperature fluctuations and keep the
(2) Collection efficiency not affected by sulfur
temperature above the acid dew point,
content of the combustion fuel as in ESPs.
-- proper baghouse insulation and positive seal-
(3) Reduced sensitivity to particle size distribu-
ing against outside air infiltration. Reverse air
tion.
should be heated to prevent condensation.
(4) No high voltage requirements.
(5) Flammable dust may be collected.
primarily use electrostatic precipitators for air pollution
(6) Use of special fibers or filter aids enables sub-
control, but some installations have been shown to be
micron removal of smoke and fumes.
successful with reverse air and pulse-jet baghouses.
(7) Collectors available in a wide range of config-
The primary problem encountered with baghouse
urations, sizes, and inlet and outlet locations.
applications is the presence of sulphur in the fuel which
b. Disadvantages.
leads to the formation of acids from sulphur dioxide
(1) Fabric life may be substantially shortened in
the presence of high acid or alkaline
Injection of alkaline additives (such as dolomite and
atmospheres, especially at elevated tem-
limestone) upstream of baghouse inlets can reduce SO2
peratures.
present in the exhaust. Fabric filtering systems
(2) Maximum operating temperature is limited to
designed for particulate collection from boilers should:
550 degrees Fahrenheit, unless special fabrics
-- operate at temperatures above the acid dew
are used.
point,
(3) Collection of hygroscopic materials or con-
-- employ a heated reverse air cleaning method,
densation of moisture can lead to fabric plug-
-- be constructed of corrosion resistant material,
ging, loss of cleaning efficiency, large
-- be insulated and employ internal heaters to
pressure losses.
prevent acid condensation when the
(4) Certain dusts may require special fabric treat-
installation is off-line.
ments to aid in reducing leakage or to assist in
c. SO2 removal. The baghouse makes a good control
cake removal.
device downstream of a spray dryer used for SO2
(5) High concentrations of dust present an explo-
removal and can remove additional SO2 due to the pas-
sion hazard.
sage of the flue-gas through unreacted lime collected
(6) Fabric bags tend to burn or melt readily at
on the bags.
temperature extremes.
9-11
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