United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-85/121 July 1986
f/EPA Project Summary
Evaluation of Pilot-Scale Air
Pollution Control Devices on a
Refuse and Coal-Fired Boiler
Fred D. Hall, John M. Bruck, and Diane N. Albrinck
This study, funded by the U.S. Envi-
ronmental Protection Agency (EPA),
Hazardous Waste Engineering Re-
search Laboratory (HWERL) was con-
ducted to evaluate prototype air pollu-
tion control devices on "waste-as-fuel"
processes. The site, Ames, Iowa, cofires
pulverized coal and refuse-derived fuel
(RDF) in a tangential-fired, suspension
boiler. A test program was imple-
mented to evaluate a pilot electrostatic
precipitator (ESP), pilot venturi scrub-
ber, and pilot fabric filter in controlling
particulate and gaseous air pollutants.
Each device was slipstreamed ahead of
the plant's full-scale ESP, and operated
as a primary control device. The pilot
scrubber was also tested downstream
of the full-scale ESP, and was evaluated
as a secondary control device.
This Project Summary was devel-
oped by EPA's Hazardous Waste Engi-
neering Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
The nature and magnitude of atmo-
spheric pollutant emissions caused by
the thermal conversion of waste to en-
ergy are not yet well defined. Thus far,
pollutants identified in air emissions
from various resource recovery opera-
tions include particulates, metals, chlo-
rides, sulfur oxides (SOX), nitrogen ox-
ides (NOX), and polycyclic organic
materials (ROMs).
Fabric filters have been successfully
applied to preprocessing operations,
and ESPs are the most common air pol-
lution control equipment used on
cofired boilers and mass-burn incinera-
tors. Full-scale fabric filters have not
been applied to waste-as-fuel combus-
tion processes, and wet scrubbers have
been used on incinerators with less suc-
cess than ESPs. Since available infor-
mation indicated that state-of-the-art
devices proved effective in controlling
pollutants of concern from waste-as-
fuel processes, alternative devices such
as wet ESPs, and jet ejector scrubbers
were not considered for this study.
Test Plans and Results
Four different pollution control
devices were tested. The fabric filter in-
stalled at the Ames solid waste recovery
plant was sampled to evaluate particu-
late removal efficiency. The fabric filter
treats particulate-laden gas, at in-plant
temperature, from seven sources in the
plant—the air density separator/RDF cy-
clone exhaust, primary shredder, sec-
ondary disc screen, and a number of
conveyor transfer points. Results indi-
cate that the fabric filter effectively con-
trols particulates generated by various
sources in the plant. While no attempts
were made to optimize operation or
collection efficiency of the unit, it re-
moved an average of 97.8 percent of the
particulates.
A pilot ESP, pilot scrubber, and pilot
fabric filter were also tested. All the
devices were controlling combustion
gases from the cofired Boiler 7 at the
Ames Power Plant. The boiler burns pul-
verized coal and RDF in a tangential fir-
ing mechanism at different fuel ratios
ranging from 0 to 25 percent RDF on a
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Btu basis. Emissions are currently con-
trolled with an ESP.
Emissions were characterized by
simultaneously measuring selected pol-
lutants at the inlet and outlet of each
control device. The full range of boiler
fuel ratios was studied for each device.
Operating parameters that varied dur-
ing mobile venturi scrubber testing in-
cluded pressure drop across the venturi
throat, gas flow rate, and scrubbing
liquor flow rate. The gas flow rate in-
creased with the scrubber liquor flow
rate in such a manner that the liquid-to-
gas ratio remained constant. Testing
was performed at pressure drops of 2.5,
5.0, and 7.5 kPa (10, 20, and 30 in. H2O).
The operating parameters that were
varied during pilot ESP testing included
the number of energized fields, specific
collection area (SCA), and gas flow rate.
Tests were performed at 3, 4, and 5 en-
ergized fields and at SCAs of 16.4, 21.9,
and 27.3 m2 per m3/h (300, 400, and 500
ft2/acfm).
The pilot fabric filter was operated at
an air-to-cloth range of 0.46 to 0.91 m3/
min per m2 (1.5 to 3.0 acfm per ft2). The
unit was equipped with reverse air, me-
chanical shake, or a combination of the
two for cleaning the fabric.
Figure 1 shows the slipstream and
sampling locations. All the control
devices were slipstreamed into the sys-
tem upstream of the existing ESP. Addi-
tional scrubber tests were performed
while slipstreaming flue gas down-
stream of the full-scale ESP, thus repre-
senting a secondary control device.
Samples were taken at the inlet and out-
let of each pilot control device while
boiler conditions, fuel composition, and
control device operating conditions
were monitored. A Method 5 source
sampling train was used to sample each
Colorado
Coal
RDF
Boiler
Firing
RDF and
Pulverized
Coal
Sampling Locations:
ASH - ESP ASH Co/lection Hopper
C - Coal Mixture (Unpulverized)
El - ESP Inlet
EO - ESP Outlet
SI - Scrubber Inlet
SL - Unfiltered Scrubber Liquor
SO - Scrubber Outlet
Ft - Preprocessed RDF
FFI - Fabric Filter Inlet
FFO - Fabric Filter Outlet
Stack
Figure 1. Schematic of pilot control devices at Ames, Iowa.
2
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control device at the inlet and outlet.
These samples were analyzed for total
participate, halides, elemental analysis
(by spark source mass spectrometry),
and selected metals (by atomic absorp-
tion analysis).
Discrete grab samples of coal, RDF,
ESP ash, fabric filter ash, and scrubber
liquor were collected at the time of
emission testing. Coal samples were
taken before the pulverizer, and pro-
cessed refuse samples were collected at
the atlas storage bin before the fuel en-
tered the pneumatic feed to the boiler.
Tables 1 and 2 show the ultimate and
proximate analyses of coal and RDF
grab samples. Table 1 shows the results
of samples taken during ESP and scrub-
ber tests and Table 2 shows results of
fabric filter tests.
During all primary device tests, the
particulate removal efficiency was 99
percent. The efficiency remained
roughly the same for coal plus RDF tests
at all pressure drops, and efficiency de-
creased with increasing pressure drop
for the tests with coal only. This obser-
vation led to the conclusion that an op-
erating parameter other than pressure
drop affected removal efficiency to a
greater degree. Midwest Research Insti-
tute investigated this theory and re-
ported that the observed contradiction
in the data ".. .was due to the longer
residence time created by a lower pres-
sure drop and partly due to the fluctua-
tion of particle size distribution..."
Pressure drop in the scrubber was
maintained by adjusting gas and liquor
flow rates, not throat size. The results
also suggest that RDF input to the boiler
may enhance particulate collection in a
venturi scrubber. This observation is
somewhat misleading, however, be-
cause inlet particulate loading also ap-
pears to increase with RDF input. Chlo-
rides were also sampled and analyzed,
and the results are as follows:
Chloride emissions increase when fir-
ing RDF, when compared with coal
only tests.
A water/lime solution in a venturi
scrubber is highly effective in con-
trolling chloride emissions.
The secondary scrubber tests resulted
in particulate removal efficiencies rang-
ing from 75 to 95 percent.
The results of particulate testing on
the pilot ESP, specifically the effects of
SCA and fuel type on removal effi-
ciency, indicate the following:
The number of energized fields and
SCA, when increased within design
limits, tend to enhance particulate
Table 1. Average Fuel Analyses-Pilot Scrubber and ESP Test Runs Only (Values in Weight
Percent Except as Shown)
Coal3 RDF"
Fuel as received
Proximate analysis
Water
Ash
Volatile matter
Fixed carbon
Heating value, MJ/kg
(Btu/lb)
Dry fuel
Ultimate analysis
16.13
9.27
36.54
38.06
23.68
(10,180)
13.25
12.78
61.36
12.61
15.45
(6,644)
Ash
Carbon
Hydrogen
Oxygen b
Sulfur
Nitrogen
Heating value, MJ/kg
(Btu/lb)
11.06
73.53
1.38
9.73
3.13
1.17
28.21
(12,130)
14.83
50.31
3.97
30.37
.38
.14
17.80
(7,654)
aAverage of selected grab samples.
bCalculated by difference.
Table 2. Average Fuel Analyses-Pilot Fabric Filter Test Runs Only (Values in Weight Percent
Except as Shown)
Coal" RDF"
Fuel as received
Proximate analysis
Water
Ash
Volatile matter
Fixed carbon
Heating value, MJ/kg
(Btu/lb)
Dry fuel
Ultimate analysis
Ash
Carbon
Hydrogen
Oxygenb
Sulfur
Nitrogen
Heating value, MJ/kg
(Btu/lb)
16.06
15.96
31.53
36.50
21.25
(9,122)
18.92
61.81
4.13
9.60
4.38
1.16
25.32
(10,869)
5.74
9.64
70.57
14.05
17.38
(7,460)
10.23
46.83
6.16
36.17
.27
.34
18.44
(7,913)
aAverage of selected grab samples.
bCalculated by difference.
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collection efficiency regardless of the
coal and RDF mixture.
At a specific SCA, RDF input to the
boiler tends to decrease ESP collec-
tion efficiency; however, a further in-
crease in RDF input does not neces-
sarily continue to decrease ESP
performance.
The lead concentrations measured at
the ESP inlet and outlet show a definite
increase in lead emissions with in-
creased RDF; however, the highest lead
emission measured was less than 5 mg/
dry std. m3, and the overall average was
0.71 mg/dry std. m3.
For fabric filter tests, Figure 2 shows
the effects of pressure drop and type of
fuel on paniculate collection efficiency.
Significant trends cannot be recognized
within the collection efficiency range
shown. Regardless of pressure drop or
fuel type, paniculate collection effi-
ciency was 99 percent or greater.
The control of lead emissions was
shown to be very effective. Only one of
five outlet samples was above the de-
tectable limit of 0.007 mg/dry std. m3,
with a concentration of 0.03 mg/dry std.
m3. Lead emissions did, however, in-
crease with increasing RDF input.
Chloride emissions, again, increased as
RDF increased, with very little control
exhibited by the fabric filter (20 to 30
percent removal). Fluoride emissions
did not change significantly throughout
the range of operating conditions.
Conclusions
Total uncontrolled paniculate emis-
sions at the Ames test site were not sig-
nificantly different in tests of coal only
and of coal plus RDF. Some trace ele-
ments and gaseous chlorides increased
significantly when burning RDF. Lead
and zinc emission concentrations were
about three times higher and gaseous
chlorides about 10 times higher when
burning 25 percent RDF (Btu basis). Nei-
ther the scrubber, ESP, nor fabric filter
paniculate removal efficiencies
changed as the portion of heat input
supplied by RDF increased.
Conventional state-of-the-art air pol-
lution control devices were found to be
effective in controlling the pollutants in-
vestigated: paniculate, trace metals,
SOX, and halides. The fabric filter and
ESP were more efficient in controlling
paniculate emissions than gaseous pol-
lutants. A venturi scrubber was very ef-
fective in removing the gaseous pollu-
tants. Specific operating parameters,
which were varied on the respective
control devices, can optimize pollutant
removal efficiencies.
01 o
<=c u
« c
11
is
I
700
Co
to
98.5
Numbers Indicate Fabric
Fitter Run Number
38,39.40,
41,43,47
42,45,46,
48,51
Coal Only
Coa, & RDF
33.34,35.
37'44
• 25,26,27.28.
29,30,31,32,36
.5
1.0 1.5 2.0
Pressure Drop, kPa
2.5
Figure 2. Paniculate removal efficiency as a function of fabric filter pressure drop
4
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