Construction. The casing including tube-sheet, hoppers, and ducts
should be of a minimum 7 gage ASTM A36 steel designed to withstand the maximum
static conditions of the draft system at the maximum temperature limits of the
fabric filter. It is not uncommon to see these conditions set at plus or
minus 20 in. w.g. at 550 degrees F (287.5 degrees C). The module outlet
dampers and reverse air dampers must be of zero leakage design. Properly
fabricated poppet dampers have proven satisfactory for this service and are
Pulse Jet Collector
Design Conditions. A pulse jet collector uses dry high pressure
compressed air from 80 to 100 psig (552 to 690 kPa) depending on the fabric
filter supplier's recommendation as a cleaning medium to back-pulse the bags.
To assist in cleaning, the tops of the bags are usually provided with a
venturi which inducts secondary air into the bag. High quality solenoid
valves are required in the compressed air lines as pulse times are usually
measured in fractions of a second.
For fly ash collection applications, off-line cleaning with module
isolation is preferred by most to extend fabric filter life and some
manufacturers prefer to omit the venturi. Both woven and felted fabric may be
used. Felted fabric has shown a longer life but with a higher cost. With the
higher air-to-cloth ratios this collector will probably require less space
than a reverse air collector. The pulse jet collector is a more simply
designed unit with fewer moving parts and a much less complicated control
system than the reverse air collector.
Design Criteria. The following criteria can be used as a guide for
off-line cleaning pulse jet collectors.
a) Collector should be a compartmental design with sufficient
compartments so that construction and performance criteria are met with one
compartment cleaning and one off-line for maintenance.
b) Maximum gross air to cloth ratio to be 3.5 to 4.5 actual cubic
feet per minute per square foot of filter area.
c) Maximum net air-to-cloth ratio with one or more modules off-
line for cleaning and or service to be not more than 5.0 actual cubic feet per
minute per square foot (1.524 m) of filter area.
d) The above air-to-cloth ratios are for woven fabric.
felted fabric manufacturers may consider slightly higher ratios.