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United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-89/016 Jan. 1990
&EPA Project Summary
Baghouse Efficiency on a
Multiple Hearth Incinerator
Burning Sewage Sludge
R. C. Adams, L. E. Keller, E. V. Robb, M. C. Vancil and Joseph B. Farrell
A pilot-scale fabric filter
(baghouse) was evaluated for its
performance in removing 23 metals
and sulfur as well as total particles
when fitted to a multiple hearth
incinerator burning sewage sludge.
The small-scale baghouse was
installed to take a slipstream of about
3% of the total Incinerator emissions.
Particle size fractions were collected
from the gas streams entering and
leaving the baghouse. Each particle
size fraction was analyzed for the 24
elemental species, and baghouse
performance was evaluated for
overall removal efficiency, size
fraction removal efficiency, and for
selective removal of specific metals.
Total concentrations of each element
In the controlled emission stream
were determined as well as the
proportionate concentrations of
species in the solid and volatile
states. Concentrations of each metal
in the emission stream were
compared with the concentrations In
a sludge residue. To obtain compar-
isons of baghouse performance with
a more typical emission control
device, the performance of the
incinerator's full-scale wet scrubber
was also evaluated.
The efficiency of the baghouse for
collection of total particles was 99%
compared with 94% for the wet
scrubber system. Its collection
efficiency was superior for cadmium,
but the wet scrubber was much more
efficient for collection of sulfur.
This Project Summary was
developed by EPA's fl/sfc Reduction
Engineering Laboratory, Cincinnati,
OH, to announce key findings of the
research protect that is fully
documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction
This research project was undertaken
to determine the particulate removal
efficiency of a fabric filter emissions
control system installed on a multiple
hearth furnace burning sewage sludge.
Of particular interest was the fate of
metals found in a city/industrial type of
sludge when incinerated and subjected to
fabric filter (baghouse) air pollution
control. A pilot-scale baghouse was
temporarily fitted to an existing multiple
hearth furnace burning digested and
dewatered sewage sludge. A slipstream
of incinerator exhaust gas, amounting to
about 3% of the total incinerator exhaust,
was taken from the top hearth of the
incinerator. This afforded an opportunity
to compare baghouse performance with
the particulate removal performance of
the incinerator's wet scrubber.
Procedure
The full-scale, six hearth, multiple
hearth incinerator was fitted with ducting
to take a slipstream of uncontrolled
emissions. The slipstream was fed to the
baghouse at temperatures averaging
411 °F. The top hearth temperature of the
incinerator averaged 747"F during
baghouse operation.
Emission tests were first conducted at
the inlet and the outlet of the incinerator's
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wet scrubber; these were followed by
tests of the baghouse performance. A
Source Assessment sampling train
(SASS) was used to collect particle size
fractions of diameters of >10 jim
(micrometer), 3 to 10 urn, and <1 urn. To
collect volatile metals, impingers
(bubblers) were located downstream of
the particle sizing part of the train. The
impingers were immersed in an ice bath.
A weak solution of nitric acid was used to
facilitate capture of the metals.
Metals were analyzed by the
inductively coupled argon plasma method
(ICAP). The concentrations of 23 target
metals plus sulfur were determined in
each particle size fraction and in the
impinger catches. From these results,
concentrations of each metal in the
controlled and uncontrolled emission
streams, in each particle size fraction,
and in the impinger catches were
determined, as were overall efficiencies
of the emission control devices and
removal performance of the individual
metals and the specific particle fractions.
Results and Discussion
In addition to assessing the fate of the
metals in the uncontrolled and controlled
emissions from the incinerator, the
baghouse and the scrubber system were
compared. The devices were not tested
simultaneously, which lessens the value
of the comparison, but differences were
so great that results can be viewed with
confidence. The baghouse proved to be
much more effective for removing total
particulates than did the scrubber
system. Baghouse efficiency averaged
99.1% for the three baghouse runs
whereas the average efficiency for the
scrubber runs was 94.3% (Table 1). An
examination of collection efficiencies for
individual particle size fractions shows
that the scrubber was inefficient in
collecting particles finer than 1 nm; the
baghouse was efficient for all fractions.
Both devices showed 100% efficiencies
for the 3-nm and l-pm catches. This
does not necessarily reflect their
performance for these fractions. For an
unknown reason, the uncontrolled
emissions contained very little mass in
these size fractions. Because recovery
downstream of the air pollution control
devices Was negligible for these fractions,
efficiencies were calculated as 100%.
Contamination reduced the value of
the results for several elements, most
particularly chromium and aluminum.
Effects of contamination were most
pronounced for the controlled emissions
because mass collected for the SASS
train fractions was small and a small
amount of contamination produced a
large effect. Contaminants in the filter
paper affected results for several metals
in the <1 urn catch, and dissolution of
stainless steel contaminated the
impingers (bubblers) as well as the
"probe + 10-iirn" catch. Only results
unaffected by these problems are
reported below.
Uncontrolled particulate emissions
showed substantial enrichment for three
metals: cadmium, lead, and tin. These
metals also were present in unusually
high proportion in the finest fraction (<1
|im). These metals may volatilize during
combustion and condense to fine
particles or adsorb on the finest p
leaving the incinerator.
In the controlled emissions, a
removal efficiency averaged 82%
wet scrubbing system and 98.5%
baghouse. Efficiency was low for 1
scrubber because the scrubber eff
was low for the < 1 pm filter
fraction, and most of the cadmium
this fraction.
The enrichment ratio for ca
increased from 25.6 for uncon
emissions to 75.4 at the scrubbei
and to 47.1 at the baghouse outlc
concentration of cadmium in the
fraction combined with poor col
efficiency for the finest fn
accounted for the large incree
enrichment ratio for the scrubbei
increase was not as large fc
baghouse because collection effii
for the finest fraction was only :
lower than that for the other fraction
The scrubber showed a 99% n
for sulfur whereas the baghouse rei
very little sulfur. If SO2 remo
important, a baghouse would have
preceded or followed by at least
pressure drop wet scrubber.
Visual observation showed a c
plume, which indicated significant o
emission, and condensation of a
layer on surfaces. Pressure drop i
the filter bags rose slowly durin
tests, indicating that the bags requ
more vigorous cleaning procedure
baghouse supplier noted that
samples from the bag were high in
volatiles" (water and/or volatile oi
compounds).
Table 1. Particulate Removal Efficiency by S4SS Size Fraction
Baghouse
Run 6
Run?
Run 8
Average
Probe +
10 itm
99.3760
99. 1 470
97.3230
98.6150
3 pm
Cyclone
100.0000
100.0000
100.0000
100.0000
1 ton
Cyclone
100.0000
100.0000
100.0000
100.0000
Filler
Catch
97.7570
98.7090
99.4260
90.6370
Total
99.4660
99.4300
98.4180
99.1050
Scrubber
Run 2
Run3
Run 4
Average
94.7800
98.9140
99.3110
97.6680
100.0000
100.0000
100.0000
100.0000
100.0000
100.0000
100.0000
100.0000
54.6930
64.2670
58.3740
59.1110
91.9460
95.7600
95.1460
94.2820
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elusions and
ommendations
e superiority of the baghouse over
wet scrubber system for collecting
particles and most metals was
ly established. On the other hand,
et scrubber system collected sulfur
h more efficiently than did the
ouse.
The colored plume, an oily layer on
some surfaces, and the presence of
"early volatiles" in the dust collected on
the filter bags indicated the presence of a
substantial proportion of unburned
hydrocarbons, which could adversely
affect the long-term performance of a
baghouse. Use of an afterburner would
obviate this problem, but if an after-
burner were not to be used, a long-term
test of a bag filter would be advisable to
verify that the filters would not be
clogged by oily discharges.
The full report was submitted in
fulfillment of Contract No. 68-03-3148 by
Radian Corporation under the
sponsorship of the U.S. Environmental
Protection Agency.
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R. C. Adams, L. E. Keller, E. V. Robb, and M. C. Vancil are with Radian Corp.,
Research Triangle Park, NC 27709. The EPA author, Joseph B. Farrell, is
also one of the EPA Project Officers (see below)
Howard Wall and Joseph B. Farrell are the EPA Project Officers (see below).
The complete report, entitled "Baghouse Efficiency on a Multiple Hearth
Incinerator Burning Sewage Sludge" (Order No. PB 89-190 318/AS; Cost:
$28.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officers can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S2-89/016
UNOFFICIAL MAIL:
MtCTER
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5 0 2 5 H
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