MIL-HDBK-1003/6
6.2
Fabric Filter Dust Collectors
6.2.1
Application. Fabric filter dust collectors (baghouses) are
becoming increasingly popular because of their compatibility with acid gas
scrubbers. The addition of an acid gas scrubber upstream of a baghouse allows
the unit to be used with virtually any type of combustion process because the
scrubber removes all burning flyash particles.
Fabric filters cannot be used downstream from a wet scrubber, or
anytime the emissions are damp, because moisture will blind (clog) the
filters.
If an acid gas scrubber is not required, the possibility of burning
flyash carryover (or unburned fuel that may blind or smolder on the surface of
the bag) must be considered.
Advantages. The major advantages of fabric filter dust collectors
6.2.2
over electrostatic precipitators are: lower initial cost, modular construction
(permits on-line maintenance), no high voltage requirements, simplicity, wide
economical capacity range, and a high collection efficiency (99 percent plus)
that is not appreciably affected by such variables as inlet grain loading,
particle size distribution, turndown, or fuel constituents.
Disadvantages. The fabric filter is sensitive to flue gas
6.2.3
temperature and the flue gas temperature must be controlled for maximum bag
life and preventing bag blinding (clogging). Operation with flue gas
temperatures below the dew point will blind the baghouse filters within a
short operating period and shorten fabric filter life. Operation above the
temperature limits of the fabric filter will result in fabric failure. See
para. 6.2.9, for minimum requirements to prevent temperatures below the dew
point and those temperatures above the specified limit from entering the
baghouse.
The 2.0-5.0 inch water gauge (in. w.g.) (0.25 to 1.25 kPa) pressure
drop across a baghouse is high compared to the typical 0.5-1.0 in. w.g.
pressure drop across an electrostatic precipitator. This puts a higher stress
on the ducting between the baghouse outlet and the induced draft fan. The
horsepower requirements of the fan are much higher and add to the annual
operating cost of the unit.
6.2.4
Types
6.2.4.1
Reverse Air Collector. This type fabric filter is sometimes called
the inside bag collector type because the fly ash is collected on the inside
of the fabric filter bag. The casing is divided into two parts by a tube
sheet with the upper or clean air side containing the fabric filter bags. The
fly ash hopper is located beneath the tube sheet. This type fabric filter
collector is cleaned by reversing the gas flow through the fabric using clean
flue gas.
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