United States
Environmental Protection
 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

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).

  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
Filter Media
  The filter media used in the baghouses at
Kerr included:
  (1) Teflon®  felt,  style  2663,   a
    tetrafluoroethylene (TFE)
  (2) Gore-Tex® (GT), an expanded Teflon
    (polytetrafluoroethylene-PTFE) with in-
    terfacing air-filled pores;

   (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-
   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

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.

  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
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

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.


Filter Media
   • Teflon felt is extremely durable and will
    withstand removal,  manual cleaning,
    and  long-term usage (longer than 3
   • 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
   • 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
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.
Multiplied by    Yields Metric
                                      •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
   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

United States
Environmental Protection
Official Business
Penalty for Private Use $300
Center for Environmental Research
Cincinnati OH 45268
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