United States
Environmental Protection
Agency
Industrial Environmental
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA 600/S7-84-037 May 1984
Project Summary
Continued Assessment of a High
Velocity Fabric Filtration System
Used to Control Fly Ash
Emissions
John D. McKenna, John M. Ross, Joyce M. Foster, and Rodney A. Gibson
In a full-scale investigation of m
modified pulse-jet fabric filtration, per-
formance of a variety of filter media pro-
vided technical and economic informa-
tion under high-velocity conditions (high
gas/cloth ratio). The fly ash emission
studies demonstrated that woven fiber-
glass fabrics and felts made from Teflon
and Gore-Tax laminate were capable of
meeting the State emission code re-
quirements at gas/cloth ratios of 4/1 to
6/1. The economic analysis showed
that, in terms of annualized cost, the
gas/cloth ratio, initial bag cost, and bag
life represents the greatest potentials for
cost reduction. Pressure drop reduc-
tions can lower operating cost, but they
have only a secondary impact on an-
nualized cost. The analysis compares
the effects of incremental changes in
bag life, gas/cloth ratio, and bag price
on total annualized cost.
This Project Summary was developed
by EPA'* Industrial Environmental Re-
search Laboratory. Research Triangle
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 ordering
information at back).
Introduction
This report summarizes a technical and
economical evaluation of the application of
high-velocity fabric filtration to coal-fired
boiler fly ash control. The evaluation is based
on data from a full-scale field industrial
boiler/baghouse operation.
Two independent baghouses of similar
size were used to control emissions from dif-
ferent boilers burning essentially the same
low sulfur bituminuous coaf.
Performance screening of a variety of
semi-commercial and commercial filter media
was performed in an attempt to determine
the better techno-economic alternatives and
also provide information on the technical
feasibility of operating such a system and
filter media at higher filtering velocities. The
use of fabric filter baghouses to control fly
ash emissions from coal-fired boilers became
widespread in the late 1970s. Utility
gas/cloth ratios (filtering velocity) normally
are about 2/1 (ft/min*), while industrial
boilers often operate at about 4/1. Opera-
tion at 6/1 or greater can significantly reduce
both the capital cost and the space re-
quirements; therefore, both the technical
feasibility and economic impact were
evaluated. (This report is a follow-on to work
reported in EPA-600/7-79-094.) Note that the
baghouses were initially at the Kerr Finishing
plant in Concord, NC; in 1979 these bag-
houses were moved to a plant in Travelers
Rest, SC, after a fire destroyed the plant in
Concord.
Filter Media
The filter media used in the baghouses at
Kerr included:
(1) Teflon® felt, style 2663, a
tetrafluoroethylene (TFE)
fluorocarbon;
(2) Gore-Tex® (GT), an expanded Teflon
(polytetrafluoroethylene-PTFE) with in-
terfacing air-filled pores;
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(3) Globe Albany 22.5 oz/yd2 woven glass
with Q-78 finish (GA-22.5);
(4) Globe Albany 15 oz/yd2 woven glass
with Q-78 finish (GA-15);
(5) P&S 26 oz/yd2 woven glass with 10
percent Teflon B finish (PS-26);
(6) Nomex felt, a high-temperature-
resistant nylon fiber (polyamide); and
(7) Huyck experimental felted glass.
Teflon felt has been used exclusively in
Baghouse No. 1 at Kerr. These bags proved
to be very durable and able to withstand
repeated manual removal and vacuuming. It
was not until after about 1-% years of ser-
vice did any appreciable failures occur. After
4 years of operation (less about 8 months
because of a fire), 85 of 648 bags (13 per-
cent) were replaced. This performance is
somewhat remarkable in light of the ex-
perimental nature of the program which
resulted (by design) in the exposure of these
bags to a variety of severe operating con-
ditions.
Baghouse No. 2 was initially outfitted with
Gore-Tex PTFE laminate bags. One complete
cell (36 bags) was replaced with Huyck ex-
perimental glass bags in March 1977; another
cell was outfitted with Globe Albany 22.5
oz/yd2 woven glass bags in May 1977.
Neither of these cells has failed to date.
The Gore-Tex bags, with a replacement
rate of 10 percent during the first year's
operation, began to fail at an accelerated rate
and, in August 1978, were completely re-
placed with 26 oz/yd2 woven glass bags with
Teflon B finish. Many of the Gore-Tex
failures may be attributed to damage caused
by manual cleaning and handling of the
bags. The 26 oz bags held up well for the
6 months of operation before the fire. After
being in operation at Travelers Rest for about
3 months, many failures occurred. It is
believed that the cleaning, handling, and
storage of these bags during the move was
the primary cause of failure. After the failure
of the 26 oz bags, a decision was made to
install 15 oz woven glass in combination with
mesh cages. While the experience at Kerr in-
dicated better life with heavier weight glass,
some commercial success, when mesh
cages with 15 oz glass and pulse jets were
used, led to the above decision.
The 36 Huyck felted glass bags tested
proved to be very durable. These bags were
in place for more than 3 years, and visual in-
spection indicated no failures.
Two other filter media, Nomex felt and 15
oz/yd2 woven glass, were tested in Bag-
house No. 2 and found to be lacking in en-
durance for this particular application and set
of operating conditions. It appears that the
heavier weight woven glass fabric is more
durable than the 15 oz/yd2 fabric. The
- Nomex failed in less than 10 days.
In summary, the bag life study indicated
that the Teflon felt bags were very durable
and 4 years after start-up, 87 percent of the
original bags were still in use. The Huyck
glass felt bags, while not tested for as long
a period, also proved to be very durable; they
were in place for over 3 years. Heavier
weight (26 oz/yd2) woven glass was more
durable than lighter weight (15 oz/yd2)
woven glass for this particular application
and set of operating conditions. Nomex felt
was found to fail rapidly, as had also been
observed in the Kerr pilot study. Gore-Tex
bags, which had shown 10 percent failure
in the first year of operation, failed at an ac-
celerated rate in the second year and were
changed out. The bags tested were Gore-
Tex laminate on Gore-Tex woven backing.
It is expected that the laminate on a different
backing, such as a felt, would provide longer
life.
Emission Control Evaluations
The tests performed on baghouse inlets
and outlets at Kerr consisted of EPA
Methods 1-5 (substituting a medium porosity
alundum thimble for a heated glass filter in
some tests) and particle sizing tests using
Andersen and Brink cascade impactors. In
addition, some parameters were continu-
ously monitored by recorders in the bag-
house facility control room. Only a limited
amount of emission data was obtained dur-
ing this program. The data acquisition pro-
gram required that the units be operated in
a relatively stable mode; unfortunately,
shortly after the desired stability was
achieved at Concord, the plant was
destroyed by fire. Moving the baghouses to
Travelers Rest resulted in a repeat of the
unstable operation and the need once again
to determine the stable operating mode.
For Teflon felt and Gore-Tex, the Method
5 results also indicated that these two filter
media met the State compliance require-
ments. The lowest outlet emission mea-
sured, 0.0087 gr/scf, was obtained on Teflon
felt when the house was in Concord. The in-
let grain loading averaged about 0.5 gr/scf
for House No. 1 and about 0.1 gr/scf lower
for House No. 2. While the Gore-Tex bags
were undamaged, their emission perfor-
mance was similar to that of the Teflon.
Characterization of the particle size
distribution at the outlet of each house
showed that each medium (Teflon felt.
Globe Albany 22.5 oz/yd2 woven glass, and
Gore-Tex/Gore-Tex PTFE laminate) emits
essentially the same range of particle sizes.
All comparisons were made at a G/C ratio
of 6/1 afrn.
In summary, the emission studies demon-
strated that Teflon fete, Gore-Tex laminate
on a woven backing, and woven glass are
all capable of meeting the State emission
code requirements at gas/cloth ratios of 4/1
to 6/1.
Economics
To better direct the development program,
an economic study of the impact of various
costs was undertaken. Key parameters eval-
uated included bag cost, pressure drop cost,
and gas/cloth ratio. Unlike the earlier
economic evaluations of Kerr, where specific
bag cost and /or measured pressure drops
were used, the current study was done in a
generalized manner so that the cost benefit
of achieving a yet untested operating mode
could be evaluated.
The approach was specific to Kerr in that
a fixed gas volume of 70,000 acfm was used.
However, the results will provide some
general economic insights valid for from half
to twice this volume, thus suitable for many
industrial boiler applications. The main
variables studied and the range covered for
each are shown in Table 1.
Table 1. Variables Studied in Economic
Evaluation
Variable Range
Pressure Drop, in. H20
Bag Costs
Interest, %
Bag Replacement, %/yr
Gas/Cloth Ratio
3 to IS
$10 to $100
5 to 20
25 to 100
2 to 10
The economic analysis indicated that, in
terms of annualized cost, the gas/cloth ratio
and bag life represented the greatest poten-
tial for cost reduction. Bag cost could also
be important if the cost reduction increment
is greater than about $1/ft2 of cloth. The
analysis indicates that, all else being equal,
in order for a $50 bag to compete with a $20
bag, it requires four times longer life.
Pressure drop reductions (1 in. increments),
while reducing operating costs significantly,
do not have as large an impact on annualized
costs as do bag cost, gas/cloth ratio, or bag
life, when considering increments of
$10/bag, 1 ft/min, and 1 year, respectively.
Additive Program
The Apollo Chemical Company manufac-
tures an additive called Coaltrol X-1 (here-
after referred to only as Coaltrol), a
powdered solid that, according to the
manufacturer, neutralizes S03 but does not
react with S02. Tests were performed in co-
operation with Apollo in which varying
amounts of the Coaltrol additive were in-
jected into the flue gas stream entering Unit
1 but not Unit 2. Samples of ash collected
in Unit 1 were analyzed for free acid,
reported as milligrams of H?SO4 per gram of
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ash, during Coaltrol addition, as well as dur-
ing normal operation without Coaltrol in
order to establish the effectiveness of the
Coaltrol additive.
During the period of Coaltrol addition, a
limited program to evaluate the effects of the
Coaltrol additive on fabric swatch aging and
metal corrosion was performed. Two dif-
ferent metals and five different filter media
were tested.
The results of a short duration study in-
dicated that such injection was effective in
reducing pressure drop, metal corrosion, and
fabric deterioration. An extended duration
program, along with a cost/benefit analysis,
would provide valuable additional data.
Conclusions
Filter Media
• Teflon felt is extremely durable and will
withstand removal, manual cleaning,
and long-term usage (longer than 3
years).
• Woven glass can be used at a 5/1
gas/cloth ratio, but it appears that
heavier weights (>20 oz) may be re-
quired to obtain long life.
• Gore-Tex PTFE laminate on PTFE
woven backing is not structurally
durable enough to make it a practical
alternative. This does not rule out the
possibility that the Gore-Tex laminate
may be suitable on some other more
durable backing.
• Huyck's felted glass proved to be very
durable. The bags tested were not very
flexible and therefore were somewhat
difficult to install. These bags were
made early in the commercial develop-
ment of this product, and inspection of
subsequent material indicated it to be
somewhat more flexible.
• Nomex is not suitable for use in this ap-
plication and will fail in a matter of
weeks.
• The Teflon felt, Gore-Tex, and 26 oz
woven glass were capable of controll-
ing emissions to the level needed to
meet the State code. No emission per-
formance evaluations were possible for
the other filter media tested for life.
Additive Injection
• The injection of Coaltrol into the inlet
gas stream resulted in significant reduc-
tion of free acidity.
• Reduced metal corrosion occurred due
to the injection of Coaltrol.
• In some cases, the strength of certain
filter media is retained at higher levels
due to the injection of Coaltrol.
• Longer term studies should confirm the
above.
Conversion Factors
Readers more familiar with the metric
system may use the following factors to con-
vert to nonmetric units that were used in this
Summary for convenience.
Nonmetric
Multiplied by Yields Metric
ft
ft2
ft3
gr
in.
oz
yd
0.305
0.093
28.317
0.0648
2.54
28.35
0.914
m
m2
I
g
cm
g
m
•ft U S GOVERNMENT PRINTING OFFICE; 1984 - 759-015/7684
J. McKenna. J. Ross, J. Foster, and R. Gibson are with ETS. Inc., Roanoke, VA
24018-4394.
Louis S. Hovis is the EPA Project Officer (see below).
The complete report, entitled "Continued Assessment of a High-Velocity Fabric
Filtration System Used to Control Fly Ash Emissions," (Order No. PB 84-169
598; Cost: $15.OO, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC27711
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United States
Environmental Protection
Agency
Official Business
Penalty for Private Use $300
Center for Environmental Research
Information
Cincinnati OH 45268
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