United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-86/030 Dec. 1986
x°/EPA Project Summary
Demonstration, Operation,
and Testing of a Fabric Filter
on an Industrial Boiler for an
Extended Period of Time
Gary P. Greiner, Jeffrey K. Smith, John M. Ross, and John D. McKenna
A number of fabric filters were evalu-
ated in baghouses controlling particu-
late emissions from industrial coal-fired
stoker boilers. Various techniques were
employed to achieve higher gas-to-
cloth (G/C) ratios and longer bag life, rt
was found that off-line, high energy,
pulse jet cleaning was necessary for
long term pressure drop stability at G/C
ratios greater than 5/1. Cleaning energy
dramatically affected filter perform-
ance, but cleaning frequency had only a
minor effect. A felted fabric combina-
tion of Teflon and glass exhibited excel-
lent performance, life, and stability.
This Project Summary was devel-
oped by EPA's Air and Energy Engineer-
ing Research Laboratory, Research Tri-
angle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Project Report or-
dering information at back).
Introduction
Previous pilot and full-scale programs
had shown that fabric filters could be
successfully used in a baghouse con-
trolling the particulate emissions from
coal-fired industrial boilers, but that
gas-to-cloth (G/C) ratios and bag life
needed improvement. A program for
this purpose was instituted in March
1981, at Kerr Finishing Co., Travelers
Rest, SC, where two tandem baghouses
were in operation and controlling the
particulate from industrial coal-fired
boilers. These boilers produced steam
for a textile finishing plant where load
requirements fluctuated often and
rapidly, and harsh cycling conditions of
start-up and shutdown produced fre-
quent dewpoint excursions in the bag-
houses.
One of the baghouses was a pulse jet
dust collector with on- and off-line
cleaning capability. The other baghouse
had high volume, low pressure (10 in.
w.g.; 2.49 kPa), reverse-flush cleaning
which provided a cleaning energy less
than a pulse-jet but higher than conven-
tional reverse-air cleaned baghouses.
This report summarizes the results of
this program, which was terminated in
November 1982.
Baghouse Details
Both baghouses contained 648 bags,
5 in. (12.7 cm) in diameter and 104 in.
(264.2 cm) long, providing a total filtra-
tion area of 6800 ft2 (631.7 m2). Each
house was divided into six cells.
Normal operation of the pulse jet bag-
house was to take a cell off-line during
pulse cleaning. All fabric in this house
was a form of Teflon felt, with each cell
having bags of the same material. Felts
of varying weight and construction
were evaluated.
The second house was cleaned by air
plenum pulse, rather than pulse jet.
Four fabric sets were evaluated in this
house: three woven glass sets with
varying finishes, and one Nomex felt set
with an acid resistant finish.
Parameters Studied
Parameters studied as having an ef-
fect on the gas-to-cloth ratio were:
(1) cleaning energy—pulse jet vs. re-
-------
verse air vs. combinations; (2) cleaning
mode—on vs. off-line; (3) cleaning fre-
quency; and (4) fabric type and style.
Operational Stability
The criterion for stable operation of a
baghouse cell was the "drag," defined
as the average tubesheet differential
pressure (AP) during a filtering cycle, di-
vided by the G/C of the cell. When no
consistent upward movement in drag
was observed over a 2 to 3 day period,
a cell was considered to have short-
term stability.
AP across the cells was equalized, and
the cell flows were monitored. G/C ra-
tios, which fluctuated with steam load,
typically varied from 5 to 8.
Emissions Testing
Method 5 testing for outlet paniculate
concentrations vs. evaluation variable
was not done because of budget con-
straints. Both baghouses passed stand-
ard state compliance testing.
Fabric Evaluation
Fabric properties were evaluated by
removing bags from the baghouses and
testing them in the laboratory for tensile
strength, Mullen burst strength, MIT
flexes, loss on ignition, and permeabil-
ity. Visual and microscopic inspections
were also performed.
Fabric permeabilities determined in
the laboratory as part of the fabric eval-
uation program were compared on a
relative basis, since removal of a bag
from the baghouse must alter the cake
properties on the fabric.
Bag Conditioning
Bags were conditioned for 4 weeks at
G/C ratios of 1.5 to 2.5 with flow, tem-
perature, and cell AP carefully moni-
tored. Bags were also visually inspected
periodically.
Fabric Properties vs. Time
Part of the program involved fabric
property tests performed on bags from
the plenum pulse baghouse after
1 hour, 24 hours, 1 week, 1 month,
3 months, 5 months, and 7 months of
service. The material tested was woven
fiberglass with acid resistant Teflon B
and an experimental Teflon finish, and
Nomex felt with an acid resistant finish.
These tests provided the first documen-
tation of how rapidly strength charac-
teristics change with time.
Conclusions
High G/C Study
Pulse jet cleaning of felted fabric was
necessary for long term pressure drop
stability at G/C ratios higher than 4/1.
There were indications that woven fab-
rics could not operate stably above 4/1
on a long term basis.
Off-line pulse jet cleaning was re-
quired for stable operation at G/C ratios
above 4-5/1.
A new Teflon felt consisting of Teflon
and glass fibers performed very well
throughout the test period at G/C ratios
of 7-9 and with stable pressure drops.
This fabric exhibited the potential of op-
erating at G/C ratios 50% or more above
those in practice today. Additional long
term studies are warranted.
Effect of Cleaning on Drag
Fabric drag was found to be a strong
function of cleaning energy. An in-
crease of 50% in energy decreased the
drag by 30%. However, the effect of
cleaning frequency, which varied from 6
to 20 minutes, was slight.
Fabric Life
Woven glass bags with either 7%
Teflon B or acid resistant finishes sur-
vived about 2 years in the low cleaning
energy baghouse. These bags were not
tested in the pulse jet house.
Nomex bags failed within 6 months of
normal operation because of the high
sulfur trioxide.
Teflon felt proved very durable. A cell
of original bags was still functioning af-
ter 5 years, and no major failure rates
occurred on any of the other Teflon con-
structions except for an asymmetrical
felt construction.
G. Greiner. J. Smith, J. Ross, and J. McKenna are with ETS, Inc., Roamoke,
VA 24018.
Louis S. Hovis is the EPA Project Officer, see below.
The complete report, entitled "Demonstration, Operation, and Testing of a Fabric
Filter on an Industrial Boiler for an Extended Period of Time," (Order No.
PB 87-111 134/AS; Cost: $13.95. subject to change) will be available only
from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 221611
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park. NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S7-86/030
Q000329
------- |