Pulse Jet Collector. This type is also called the outside bag
collector since the fly ash is collected on the outside of the fabric filter
bag. The tube sheet is in the upper part of the casing and the fabric filter
bags extend down into the dirty side of the casing. The bags are supported by
a wire cage which prevents the bag from collapsing under flow conditions.
This type fabric filter collector is cleaned by pulses of compressed air
injected down inside and through the fabric filter bags. Cleaning may be done
off-line by isolating modules or on-line.
General. To properly apply their equipment, the fabric filter
collector manufacturer must know the expected inlet gas conditions over the
range of inlet conditions. For applications which are operationally sensitive
at reduced load, i.e., stokers and incinerators, upset partial load conditions
should also be included. This information can best be supplied by the boiler
or incinerator manufacturer; compensation must be made for the effects on any
system components between the boiler or incinerator outlets and the fabric
filter collector inlet.
In determining the inlet gas conditions for existing installations,
source testing should be performed to determine the gas flow and contents.
Gas volume determination should be made using a Pitot tube in accordance with
IGCI Bulletin 101, Test Procedures. This publication incorporates ASME PTC
27, Dust Separating Apparatus. For particulate loading, an actual sample
should be taken and analyzed in accordance with ASME PTC 28, Determining the
Properties of Fine Particulate Matter.
For new installations, the inlet gas conditions should be obtained
from the manufacturer. If inlet gas conditions are not available, the inlet
and outlet gas contents must be estimated. When estimates are made, the
emission factors and handbook data should be taken from EPA AP-42, Compilation
of Air Pollutant Emission Factors.
Source testing should be conducted in accordance with the
applicable portion of EPA 40 CFR 60, Appendix A, Reference Methods.
Reverse Air Collector
General. This type of cleaning action is much gentler than pulse
jet cleaning. The collector operates at a lower air to cloth ratio than pulse
jet collectors which results in a higher initial cost. The filter fabric
usually lasts 2 to 3 times longer in the reverse air unit. The reverse air
collector is commonly used for larger flue gas systems. For flue gas flows
from 50,000 ACFM up to 100,000 ACFM, a life cycle cost analysis should be made
to determine the proper selection. For flue gas flows above 100,000 ACFM, the
reverse air collector is the preferred type.
Design Criteria. For a conservatively sized reverse air fabric
filter fly ash dust collector the design gas flow must be carefully selected
for the actual expected operating conditions.