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Full-Scale Evaluation of Mercury Control with Sorbent
Injection and COHPAC at Alabama Power E.C. Gaston
C. Jean Bustard a , Michael Durham a , Charles Lindsey a , Travis Starns a , Ken Baldrey a
,
Cameron Martin a , Richard Schlager a , Sharon Sjostrom b , Rick Slye b , Scott Renninger c
Larry Monroe d , Richard Miller e & Ramsay Chang f
,
a ADA-ES, LLC , Littleton , Colorado , USA
b Apogee Scientific , Englewood , Colorado , USA
c U.S. Department of Energy , National Energy Technology Laboratory , Morgantown , West
Virginia , USA
d Southern Company , Birmingham , Alabama , USA
e Hamon Research Cottrell, Inc. , Walnutport , Pennsylvania , USA
f EPRI , Palo Alto , California , USA
Published online: 27 Dec 2011.
To cite this article: C. Jean Bustard , Michael Durham , Charles Lindsey , Travis Starns , Ken Baldrey , Cameron Martin ,
Richard Schlager , Sharon Sjostrom , Rick Slye , Scott Renninger , Larry Monroe , Richard Miller & Ramsay Chang (2002) Full-
Scale Evaluation of Mercury Control with Sorbent Injection and COHPAC at Alabama Power E.C. Gaston, Journal of the Air &
Waste Management Association, 52:8, 918-926, DOI: 10.1080/10473289.2002.10470832
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Bustard et al.
TECHNICAL PAPER
ISSN 1047-3289 J. Air & Waste Manage. Assoc. 52:918-926
Copyright 2002 Air & Waste Management Association
Full-Scale Evaluation of Mercury Control with Sorbent Injection
and COHPAC at Alabama Power E.C. Gaston
C. Jean Bustard, Michael Durham, Charles Lindsey, Travis Starns, Ken Baldrey, Cameron Martin,
and Richard Schlager
ADA-ES, LLC, Littleton, Colorado
Sharon Sjostrom and Rick Slye
Apogee Scientific, Englewood, Colorado
Scott Renninger
National Energy Technology Laboratory, U.S. Department of Energy, Morgantown, West Virginia
Larry Monroe
Southern Company, Birmingham, Alabama
Richard Miller
Hamon Research Cottrell, Inc., Walnutport, Pennsylvania
Ramsay Chang
EPRI, Palo Alto, California
ABSTRACT
Gaston Unit 3 was chosen for testing because COHPAC
represents a cost-effective retrofit option for utilities with
existing electrostatic precipitators (ESPs). COHPAC is an
EPRI-patented concept that places a high air-to-cloth
ratio baghouse downstream of an existing ESP to improve
overall particulate collection efficiency. Activated carbons
were injected upstream of COHPAC and downstream of the
ESP to obtain performance and operational data.
Results were very encouraging, with up to 90% removal
of Hg for short operating periods using powdered activated
carbon (PAC). During the long-term tests, an average Hg
removal efficiency of 78% was measured. The PAC injection
rate for the long-term tests was chosen to maintain COHPAC
cleaning frequency at less than 1.5 pulses/bag/hr.
The overall objective of this project was to determine the
cost and impacts of Hg control using sorbent injection
into a Compact Hybrid Particulate Collector (COHPAC)
at Alabama Power’s Gaston Unit 3. This test is part of a
program funded by the U.S. Department of Energy’s
National Energy Technology Laboratory (NETL) to obtain
the necessary information to assess the costs of control-
ling Hg from coal-fired utility plants that do not have
scrubbers for SO2 control. The economics will be devel-
oped based on various levels of Hg control.
IMPLICATIONS
Sorbent injection technology represents one of the sim-
plest and most mature approaches to control Hg emis-
sions from coal-fired boilers. However, no application
experience was available from actual full-scale installa-
tions in the U.S. power industry. A field test program rep-
resenting the initial step toward defining technology to
be used by power-generating companies in meeting new
Hg regulations is being conducted for the NETL. The first
full-scale test was completed in the spring of 2002 on a
unit that burns a low-sulfur bituminous coal and uses a
COHPAC baghouse to collect the carbon and fly ash.
INTRODUCTION
In December 2000, the U.S. Environmental Protection
Agency (EPA) announced their intent to regulate Hg emis-
sions from the nation’s coal-fired power plants. Draft leg-
islation indicates that new regulations may require
removal efficiencies as high as 90% from existing sources.
In anticipation of these regulations, a great deal of re-
search has been conducted during the past decade to char-
acterize the emission and control of Hg compounds from
the combustion of coal. The U.S. Department of Energy,
918 Journal of the Air & Waste Management Association
Volume 52 August 2002

Bustard et al.
EPA, and EPRI funded much of this research. The results
are summarized in the comprehensive 1999 Air & Waste
Management Association Critical Review article.1 As a re-
sult of these efforts, the following was determined: (1)
trace concentrations of Hg in flue gas can be measured
relatively accurately, (2) Hg is emitted in a variety of forms,
(3) Hg species vary with fuel source and combustion con-
ditions, and (4) control of Hg from utility boilers will be
both difficult and expensive.
This latter point is one of the most important and dra-
matic findings from the research conducted to date. Because
of the large volumes of gas to be treated, the low concentra-
tions of Hg, and the presence of difficult-to-capture species
such as elemental Hg, some estimates show that 90% Hg
reduction for utilities could cost the industry as much as
$5 billion per year.1 Most of these costs will be borne by
power plants that burn low-sulfur coal and do not have wet
scrubbers as part of their air pollution equipment.
With regulations rapidly approaching, it is important
to concentrate efforts on the most mature retrofit control
technologies. Injection of dry sorbents such as powdered
activated carbon (PAC) into the flue gas and further col-
lection of the sorbent by electrostatic precipitators (ESPs)
and fabric filters commonly is used in municipal waste
incinerators for Hg control and represents the most ma-
ture and potentially most cost-effective control technol-
ogy for power plants.
sorbent to achieve similar removal efficiencies;
(3) capital costs for COHPAC are less than other op-
tions, such as replacing the ESP with a full-sized
baghouse or larger ESP;
(4) COHPAC requires much less physical space than
either a larger ESP or full-size baghouse system;
and
(5) outage time can be reduced significantly with
COHPAC systems in comparison with major ESP
rebuilds/upgrades.
E.C. GASTON SITE DESCRIPTION
The E.C. Gaston Electric Generating Plant, located in
Wilsonville, AL, has four 270-MW balanced-draft and one
880-MW forced-draft coal-fired boilers. All units fire a
variety of low-sulfur, washed, eastern bituminous coals.
The primary particulate control equipment on all units is
a hot-side ESP. Units 1 and 2 and Units 3 and 4 share
common stacks. In 1996, Alabama Power contracted with
Hamon Research-Cottrell to install COHPAC downstream
of the hot-side ESP on Unit 3. This COHPAC system was
designed to maintain the stack opacity levels of Units 3
and 4 at less than 5% on a 6-min average.5
The COHPAC system is a hybrid pulse-jet type
baghouse, designed to treat flue gas volumes of 1,070,000
acfm at 290 ºF (gross air-to-cloth ratio of 8.5 ft/min with
on-line cleaning). The COHPAC baghouse consists of four
isolatable compartments—two compartments per air-
preheater identified as either A- or B-side. Each compart-
ment consists of two bag bundles, each having a total of
544 23-ft-long polyphenylene sulfide (PPS) felt filter bags,
18-oz/yd2 nominal weight. This results in a total of 1088
bags per compartment, or 2176 bags per casing.5 The evalu-
ation was conducted on half of the gas stream, nominally
135 MW. The side chosen for testing was B-side. A-side
was monitored as the control unit.
Under a U.S. Department of Energy National Energy
Technology Laboratory (NETL) cooperative agreement,
ADA-ES is working in partnership with PG&E National
Energy Group (NEG); Wisconsin Electric, a subsidiary of
Wisconsin Energy Corp.; Alabama Power Co., a subsid-
iary of Southern Company; and EPRI on a field evalua-
tion program of sorbent injection upstream of existing
particulate control devices for Hg control.2 The test pro-
gram, which will take place at four different sites during
2001 and 2002, is described in detail in the July 2001 EM.3
Other organizations participating in this program as in-
dustry cost-share participants include Ontario Power Gen-
eration, First Energy, TVA, Kennecott Energy, Hamon
Research-Cottrell, EnviroCare, and Norit Americas.
Gaston Unit 3 was chosen as the first test site, be-
cause Compact Hybrid Particulate Collector (COHPAC)
represents a cost-effective retrofit option for utilities with
ESPs. The COHPAC is an EPRI-patented concept that places
a high air-to-cloth ratio baghouse downstream of an ex-
isting ESP to improve overall particulate collection effi-
ciency. The advantages of this configuration are
The hot-side ESP is a Research-Cottrell weighted wire
design. The specific collection area (SCA) is 274 ft2/1000
acfm. Depending on the operating condition of the hot-
side ESP, nominally 97–99+% of the fly ash is collected in
the ESP. The remaining fly ash is collected in the COHPAC
system. The average inlet particulate mass concentration
into COHPAC between January 1997 and April 1999 was
0.0413 gr/acf.5 Hopper ash from both the ESP and the
baghouse are sent to a wet ash pond for disposal. A
hydrovactor system delivers the fly ash to the pond.
Figure 1 shows a diagram of the location of the vari-
ous components of the air pollution control train. De-
sign parameters obtained from Alabama Power for
Gaston Unit 3 are presented in Table 1. For the Hg con-
trol program, carbon-based dry sorbents were injected
upstream of COHPAC and downstream of the ESP over
an 8-week period.
(1) sorbents are mixed with a small fraction of the
ash (nominally 1%), which reduces the impact
on ash reuse and waste disposal;
(2) pilot plant studies and theory4 indicate that com-
pared with ESPs, baghouses require one-tenth the
Volume 52 August 2002
Journal of the Air & Waste Management Association 919

Bustard et al.
were made using a semi-continuous emissions monitor
(S-CEM) designed and operated by Apogee Scientific. This
instrument was developed with EPRI funding to facilitate
EPRI research and development efforts.6 The locations of
the analyzers are shown in Figure 1. The S-CEMs oper-
ated continuously for more than 7 weeks providing spe-
ciated, vapor-phase Hg concentrations at the inlet and
outlet of COHPAC. Norit Americas supplied a portable
dilute-phase pneumatic injection system that is typical
of those used at municipal solid waste facilities for Hg
control with activated carbon. ADA-ES designed the dis-
tribution and injection components of the system.
Sorbent requirements for various levels of Hg control
were predicted based on empirical models developed
through EPRI funding.4 The values used were based on a
uniform sorbent size of 15 µm (size of commercially avail-
able PAC) and a bag cleaning frequency of 2 pulses/bag/
hr (it was also assumed all bags were cleaned at the same
time when, in practice, the bags are cleaned in sections or
rows). Rates used to design equipment for the Gaston test
are presented in Table 2. The system was sized for a maxi-
mum injection rate of 100 lb/hr.
Figure 1. Flow schematic of Gaston Unit 3, showing injection and
measurement locations.
TEST EQUIPMENT
The critical elements of the program were the actual field
tests and measurements, which relied on accurate, rapid
measurements of Hg concentration and an injection sys-
tem that realistically represented commercially available
technology. Near-real-time vapor-phase Hg measurements
Figure 2 shows the portable injection skid supplied
by Norit Americas and installed for use at Plant Gaston
Unit 3B. Activated carbon delivered to the plant in 900-lb
supersacks was loaded onto the skid by a hoist. The sor-
bent was metered by a variable speed screw feeder into
the conveying line. A blower/eductor provided the mo-
tive air to carry the sorbent ~100 ft to the injection point.
Sorbent was pneumatically transported via flexible
hose from the feeder to a distribution manifold at the
injection level and injected into the flue gas through six
injection probes (three/duct). Figure 3 shows the distri-
bution manifold. The injection system operated without
plugging while injecting carbon-based products with D50
particle size of 18 µm. The distribution system plugged
once while feeding a finer material with a D50 of 6–7 µm.
Table 1. Site description summary, Gaston Unit 3.
Parameter Identification
Description
Boiler manufacturer
Burner-type
B&W wall-fired
B&W XCL
Yes
Low NOx burners
NOx control (post-combustion)
Temperature (APH outlet)
None
290 ˚F
Coal (Typical—This Unit Fires a Variety of Coals)
Type
Eastern bituminous
Heating value (Btu/lb)
Moisture (%)
Sulfur (%)
Ash (%)
13,744
6.9
TEST RESULTS
0.9
Pre-Baseline Tests
The first field measurements were made prior to installing
the injection equipment. The objectives for the pre-baseline
13.1
0.06
0.03
Hg (µg/g)
Cl (%)
Control Device
Table 2. Predicted injection rates for FGD carbon on B-side of COHPAC.3
Type
Hot-side ESP with COHPAC
Hamon Research-Cottrell
Weighted wire
Target Hg Removal
Efficiency (%)
Predicted Injection
Concentration
(lb/Mmacf)
Predicted
Injection Ratea
(lb/hr)
ESP manufacturer
Design
Specific collection area (ft2/1000 afcm)
Flue gas conditioning
Baghouse manufacturer
Design
274
None
50
75
90
0.5
1.5
3.0
<30
45
Hamon Research-Cottrell
Pulse-jet, low-pressure–high-volume
8.5:1 (gross), on-line cleaning
90
Air-to-cloth ratio (acfm/ft2)
aInjection rate based on nominal flow at full load of 500,000 acfm.
920 Journal of the Air & Waste Management Association
Volume 52 August 2002

Bustard et al.
Table 3. Pre-baseline Hg measurement results (S-CEM).
Location
Total Hg µg/dncm @
Oxidized Hg %
a
3% O2
ESP inlet
7–10
7–10
7–10
0%
5–33
29–51
52–76
ESP outlet/COHPAC inlet
COHPAC outlet
Mercury removal across ESP
Mercury removal across COHPAC
0%
aNormal: T = 32 ºF
Hg measurements during the pre-baseline tests in January
on Unit 3. Two analyzers were used for these tests. The
analyzers were set up to measure simultaneously across ei-
ther the hot-side ESP or COHPAC. Because the hot-side ESP
outlet and the COHPAC inlet are the same sampling ports,
this analyzer was not moved. Flue gas temperatures were
nominally 650 ºF at the inlet to the hot-side ESP and be-
tween 240 and 270 ºF at the COHPAC inlet and outlet.
The results show that vapor-phase Hg varied between
7 and 10 µg/dncm at all three locations. These variations
appeared to be caused by changes in coal, because there
was no measurable removal of vapor-phase Hg across ei-
ther the hot-side ESP or COHPAC. These results are com-
parable to those made during the EPA information
collection request (ICR) measurements in 1999 on Unit 1
for total Hg concentrations and removal efficiencies. The
ICR measurements showed total Hg concentrations be-
tween 6.0 and 7.5 µg/dncm and no Hg removal across
the hot-side ESP.7
Figure 2. Carbon injection skid installed at Plant Gaston.
tests were to (1) document Hg emissions across COHPAC,
and (2) perform screening tests for Hg adsorption charac-
teristics of several activated carbons that were candidate
sorbents for the full-scale tests. Table 3 presents vapor-phase
No Hg removal was measured across COHPAC with-
out the addition of sorbents. A review of data collected
through the ICR at other plants shows that there was sig-
nificant natural Hg capture on units with conventional-
type baghouses when firing bituminous coals.7 This
natural collection is assumed to occur because of expo-
sure of the flue gas to ash on the bag dustcake. Ash samples
from both the hot-side ESP and COHPAC were tested for
loss-on-ignition carbon and Hg adsorption capacity by
URS Corp. Analysis of the ash showed high carbon con-
tent throughout the total size distribution and an adsorp-
tion capacity that indicates the ash should be capable of
collecting Hg. However, because COHPAC is downstream
of the hot-side ESP and the ESP was in excellent condi-
tion at the time of the tests, the inlet loading to COHPAC
was very low (0.04 g/acf on average and less than 0.01
g/acf during the tests), so there was a relatively small
amount of ash present on the bags to react with the Hg.
The portion of vapor-phase Hg in the oxidized state
increased in the direction of flow. There was a greater
percentage of elemental Hg at the hot-side inlet (econo-
mizer outlet) than there was at either the COHPAC inlet
Figure 3. Distribution manifold for injection lances at Plant Gaston.
Volume 52 August 2002
Journal of the Air & Waste Management Association 921

Bustard et al.
or outlet. The most significant oxidation occurred across
the COHPAC baghouse. Similar phenomena have been
documented across baghouses with fiberglass and PPS
fabric bags.8
of oxidized Hg was 61%, and it increased to 77% at the
outlet. Flue gas temperatures during these tests were nomi-
nally 255 ºF.
Parametric Tests
Baseline Tests
A series of parametric tests was conducted to determine
the optimum operating conditions for several levels of
Hg control up to 90% Hg removal, for several activated
carbon products. The NETL scope of work required that
only commercially available sorbents should be consid-
ered in these technology demonstration tests. Norit Ameri-
cas lignite-based PAC, Darco FGD, was chosen as the
benchmark sorbent. Sorbent type and injection concen-
tration for the long-term tests were chosen based on re-
sults from these tests.
In all, 15 different parametric conditions were tested.
The primary variables were carbon type and target Hg re-
moval level. Other variables included COHPAC cleaning
settings and flow through the baghouse. Although lower
flue gas temperatures have been correlated with increased
Hg removal, temperature was not a key variable during
these tests, because normal operating temperatures at this
plant were between 250 and 270 ºF, which is cool enough
for acceptable removal. Results from laboratory and pilot
plant tests suggest Hg capture is more difficult at tem-
peratures greater than 300 ºF. A summary of the paramet-
ric tests is presented in Table 5. Unless noted, all tests
were conducted with the boiler at full load conditions
and COHPAC cleaning at a drag initiate set point of 0.6
in. w.c./ft/min. A description of the different carbons used
in these tests is presented in Table 6.
After equipment installation and checkout, a set of
baseline tests was conducted immediately prior to the first
parametric test series to document current operating con-
ditions. During this test, boiler load was held steady at
“full-load” conditions during testing hours, nominally
7:00 a.m.–7:00 p.m. The Hg across the B-side of the
COHPAC was measured using two separate methods:
S-CEMs and modified Ontario Hydro method.
In addition to monitoring Hg removal, it was also
important to document the performance of COHPAC
during sorbent injection. The primary COHPAC perfor-
mance indicator at this site was cleaning frequency. Pres-
sure drop/drag is controlled by the cleaning frequency. It
was expected that cleaning frequency would increase with
the increased particulate loading from sorbent injection.
Cleaning frequency was monitored before, during, and
after sorbent injection.
Results from the Ontario Hydro tests conducted by
Southern Research Institute are presented in Table 4. Simi-
lar to pre-baseline measurements, there was no measur-
able Hg removal across COHPAC. The average of the inlet
and outlet total Hg measurements was ~15 µg/dncm. Coal
analyses showed Hg levels in the three coal samples var-
ied between 0.06 and 0.17 µg/g. Because Gaston burns
coals from several different coal sources each day, it is
difficult to correlate Hg level in the coal to a specific flue
gas measurement; however, the higher coal Hg values
correlate well with Hg measured in the flue gas. For ex-
ample, a coal Hg level of 0.17 µg/g is equivalent to an Hg
concentration of 15.0 µg/dncm in the flue gas.
Parametric tests measured Hg removal as a function of
injection concentration and sorbent type and the impact
of sorbent injection on COHPAC performance. Feedback
from the S-CEMs was invaluable in making timely, real-
time decisions on test conditions. Examples of the data
provided from the S-CEMs are presented in Figure 4. These
data are from the first week of parametric tests 1–4, with
Darco FGD. Reduction and recovery of outlet
The Ontario Hydro measurements also showed oxi-
dation across COHPAC. At the inlet, the average fraction
Hg concentration can be seen to correlate with
Table 4. Baseline Ontario Hydro measurements at COHPAC inlet and outlet.
relative injection rates.
Date/Location Particulate
Oxidized
Elemental
Total
Percent
Oxidized
Figure 5 presents Hg removal efficien-
cies as activated carbon injection concentra-
tions were varied during the parametric tests
for several activated carbons (see Tables 5 and
6 for description of test conditions). This fig-
ure shows that Hg removal increased nearly
linearly with injection rate up to 2 lb/Mmacf,
and then leveled off at ~90% removal with
higher injection providing no additional ben-
efit. This figure also shows that there was no
measurable performance difference between
the different PACs.
(µg/dncma)
(µg/dncma)
(µg/dncma)
(µg/dncma)
3/6/2001 inlet
3/6/2001 inlet
3/7/2001 inlet
Average inlet
0.0
0.0
0.2
0.1
0.0
0.0
0.0
0.0
11.6
8.0
6.6
7.0
4.3
5.9
4.6
3.0
2.4
3.3
18.2
15.0
13.5
15.6
14.8
15.5
13.3
14.5
63
53
67
61
69
81
82
77
9.0
9.5
3/6/2001 outlet
3/6/2001 outlet
3/7/2001 outlet
Average outlet
10.2
12.5
10.9
11.2
aNormal: T = 32 ºF
922 Journal of the Air & Waste Management Association
Volume 52 August 2002

Bustard et al.
Table 5. Summary of parametric test conditions.
Test
Carbon Name
Efficiency (%)
Target Hg
Removal
Non-Standard
Conditions
Series
1–5
6–9
10
Darco FGD
Norit PAC2B
None
50, 75, and 90
Standard
Standard
50, 75, and 90
Baseline
90
Standard
Figure 4. S-CEM Hg measurements during the first week of parametric
tests with Norit Darco FGD PAC.
11
Darco Insul
HydroDarco-C
Darco FGD
Standard
12
90
Standard
13 a–c
75
Change to pressure
drop initiate clean
Lower A/C to 4 ft/min
Compare to test 14 with
A/C = 7 ft/min
Similar to the baseline test series, Hg was measured
by both the S-CEMs and manual methods (Ontario Hy-
dro). The COHPAC performance, coal and ash samples,
and plant CEM data were collected. During these tests, an
EPA audit of the manual measurements was performed.
The long-term tests started on April 18, and carbon
was injected continuously until April 26. Full-load boiler
conditions were held between the times of 7:00 a.m. and
8:00 p.m., with load under dispatch control at other times
for the first 5 days. During the three days when the Ontario
Hydro tests were conducted, full load was maintained 24
hr/day. At the beginning of this test series, time was needed
to work out a COHPAC cleaning logic issue, and there
was a short period when load was lowered to fix a mill
problem. The final 7 days of the test were conducted at
the optimized PAC feed rate and COHPAC cleaning logic.
Three sets of Ontario Hydro measurements were made
at three locations: (1) inlet of the hot-side ESP, (2) COHPAC
inlet, and (3) COHPAC outlet. Arcadis G&M Inc. con-
ducted the hot-side measurements using an experimen-
tal in-duct, quartz thimble to minimize sampling artifacts
often seen with this method. Artifacts have been known
to occur when the particulate collected on the filter cap-
tures vapor-phase Hg, resulting in higher particulate-phase
Hg than is actually present. Sampling artifacts from par-
ticulate on the filter were not as much of a concern at the
other two locations, because either the hot-side ESP or
COHPAC already had removed most of the particulate.
14
15
Darco FGD
Darco FGD
50
50
Carbon injection significantly increased the cleaning
frequency of the COHPAC baghouse. Figure 6 presents
actual cleaning frequencies at different carbon injection
concentrations. At an injection concentration of 2.0 lb/
Mmacf, the cleaning frequency increased from 0.5 to 2
pulses/bag/hr, or a factor of 4. Acceptable cleaning fre-
quencies at this site to maintain long-term bag life are
considered to be less than 1.5 pulses/bag/hr.
Long-Term Tests
Long-term testing at “optimum” plant-operating condi-
tions as determined from the parametric tests was planned
to gather data on Hg removal efficiency over time, the
effects on COHPAC and balance of plant equipment of
sorbent injection, and operation of the injection equip-
ment to determine the viability and economics of the
process. During these tests, carbon was injected continu-
ously 24 hr/day, for 9 days. Based on results from the para-
metric tests, Darco FGD activated carbon was chosen as
the sorbent for these tests. Injection rate was determined
taking into consideration both Hg removal and the pro-
jected increase in COHPAC cleaning frequency. An injec-
tion concentration of 1.5 lb/Mmacf was chosen to
maintain COHPAC cleaning frequency at less than 1.5
pulses/bag/hr.
Table 6. Description of Norit carbons used in parametric tests.
Name
Description
Particle Size Distributiona
D95
D50
D5
Darco FGD
Norit PAC2B
Darco Insul
Lignite AC
Subbit/Bit blend AC
Fine chemically washed
specialty product
Coarser FGD
52
52
25
15–20
15–20
6–7
<3
<3
<2
HydroDarco-C
100
30
3
Figure 5. The Hg removal trends across COHPAC as a function of
PAC injection concentrations. Measurements made during parametric
tests, March 2001.
aPercent of particles less than size in µm.
Volume 52 August 2002
Journal of the Air & Waste Management Association 923

Bustard et al.
Ontario Hydro tests. This correlates well with the manual
measurements. However, it is important to note that the
S-CEMs showed that the average Hg removal efficiency
over the multi-day time period was 78%, with variations
from 36 to more than 90%. This difference is probably
caused by varying coal and operating conditions over time.
Figure 7 also shows that, during this 5-day period, inlet
Hg concentration varied by nearly a factor of 5. Outlet
concentrations can be seen to follow the inlet, and there
are times during these transitional periods when removal
efficiencies are fairly low. During the period when the
Ontario Hydro tests were run, inlet Hg levels were low
and fairly steady. These tests were conducted under ideal
conditions and may show the best-case condition for Hg
control at this injection rate.
During the test program, sorbent was injected at a
constant rate, with no attempt to increase sorbent when
the inlet Hg concentration increased. However, the data
in Figure 7 highlight the importance of having CEMs
to use as process control for a permanent Hg control
system. The most challenging time for COHPAC per-
formance was during the period with continuous full-
load operation and PAC injection. The cumulative
cleaning frequency increased to a high of 1.3 pulses/
bag/hr, but was mostly maintained at levels less than
1.0 pulse/bag/hr.
Figure 6. COHPAC cleaning frequency in pulses/bag/hr as a function
of PAC injection concentration. Measurements made during parametric
tests, March 2001.
Table 7 presents the results from each of the Ontario
Hydro measurements. These data show that the inlet to
the hot-side ESP and the inlet to COHPAC have similar
average Hg concentrations and speciation. The outlet Hg
concentrations show the effect of carbon injection with
overall low Hg emissions for all species. Table 8 presents
average speciated Hg removal across COHPAC. The over-
all average reduction in total Hg is 90%. At the outlet, the
predominant species of Hg is the oxidized form; however,
it is still 85% less than what was present upstream of PAC
injection.
Coal and Ash Characterization
Figure 7 presents inlet and outlet Hg concentrations
as measured by the S-CEMs, boiler load, and PAC injec-
tion concentration during the last 5 days of the long-term
test. Periods when Ontario Hydro measurements were
made are also identified. The S-CEMs indicate that Hg
removal was nominally 87, 90, and 88% during the
Coal and ash samples were collected daily during the
baseline, parametric, and long-term tests. Gaston fires a
variety of washed, low-sulfur eastern bituminous coals.
Because several different coals can be fired in a day, the
daily coal samples provide relative Hg concentrations
but may not be representative of specific test periods.
Standard ultimate and proximate analyses
were conducted, as were measurements for
Table 7. Long-term Ontario Hydro measurements at hot-side ESP inlet, COHPAC inlet, and COHPAC outlet.
Hg, Cl, and S.
Ash samples were collected from the
Date/Location
Particulate Oxidized
Elemental
Total
Percent
(µg/dncma) (µg/dncma) (µg/dncma) (µg/dncma) Oxidized
hot-side ESP, control-side (A-side) COHPAC,
and test-side (B-side) COHPAC hoppers. Ash
generated from the E.C. Gaston Plant is im-
pounded using a wet ash handling system.
The ash is not currently beneficially reused;
therefore, ash characterization testing con-
centrated on measuring Hg and carbon con-
tent. Archived ash samples will be submitted
for leaching tests at a later date.
4/24/2001 ESP inletb
0.5
0.0
0.1
0.2
0.1
0.4
0.2
0.2
0.1
0.2
0.1
0.1
2.9
7.3
6.2
5.5
4.9
5.6
8.5
6.3
0.9
0.9
0.9
0.9
5.6
3.7
9.0
11.0
9.3
32
66
66
55
48
60
62
56
91
78
93
87
4/25/2001 ESP inletb
4/26/2001 ESP inletb
3.0
Average ESP Inlet
4.1
5.2
9.8
10.3
9.4
4/24/2001 COHPAC inlet
4/25/2001 COHPAC inlet
4/26/2001 COHPAC inlet
Average COHPAC Inlet
4/24/2001 COHPAC outlet
4/25/2001 COHPAC outlet
4/26/2001 COHPAC outlet
Average COHPAC Outlet
3.4
5.2
13.9
11.2
1.0
4.6
0.1
The Hg content of coal samples taken
during the long-term tests varied between
0.09 and 0.21 mg/g. This is consistent with
flue gas Hg measurements that showed con-
siderable variability in Hg concentration.
This variability has implications on how Hg
0.1
1.1
–0.0
0.1
1.0
1.0
aNormal: T = 32 ºF; bTests conducted by Arcadis using an in-stack (heated) quartz thimble.
924 Journal of the Air & Waste Management Association
Volume 52 August 2002

Bustard et al.
Table 8. Average Hg removal efficiencies across COHPAC as measured with Ontario Hydro method.
CONCLUSIONS
A full-scale evaluation of Hg control using
activated carbon injection upstream of
a COHPAC baghouse was conducted at
Alabama Power Co.’s Plant Gaston Unit 3.
Results and trends from these relatively short-
term tests were encouraging.
Sampling Location
Particulate
Oxidized
Elemental
Total
(µg/dncma)
(µg/dncma)
(µg/dncma)
(µg/dncma)
COHPAC inlet
0.2
0.1
50
6.4
0.9
86
4.6
0.0
99
11.2
1.1
90
COHPAC outlet
Removal efficiency (%)
•
Effective Hg removal, up to 90% effi-
aNormal: T = 32 ºF
ciency, was obtained for short operating pe-
riods (8 hr) by injecting PAC upstream of
COHPAC.
control technologies will be implemented. The B-side
ash, mixed with sorbent, showed ~30% carbon content
as compared with 12% in the A-side ash. The sorbent-
ash mixtures from the B-side had ~30 times the Hg of
the A-side hopper ash, indicating removal of Hg by the
sorbent across COHPAC.
•
A significant increase in the cleaning frequency
of the COHPAC baghouse occurred with the in-
jection of activated carbons. At this site, the maxi-
mum acceptable cleaning frequency and pressure
drop limited the amount of sorbent that could
be injected and, therefore, the maximum Hg re-
moval actually achievable. Based on these results,
it will be necessary to take into consideration the
sorbent injection rate in the design of future
COHPAC baghouses and perhaps design the
baghouses more conservatively.
PAC ANNUAL COSTS
The requirements and costs for full-scale, permanent, com-
mercial implementation of the necessary equipment for
Hg control using PAC injection technology are being fi-
nalized for Gaston Unit 3. Preliminary capital and sor-
bent costs for 80% Hg removal have been developed. The
estimated uninstalled cost for a sorbent injection system
and storage silo for the 270-MW Unit 3 is $575,000 ± 30%.
Sorbent costs were estimated for nominally 80% Hg con-
trol based on the long-term PAC injection concentration
of 1.5 lb/Mmacf. For Gaston Unit 3, this would require
an injection rate of nominally 80 lb/hr. Assuming a unit
capacity factor of 80% and a delivered cost of $0.50/lb for
PAC, the annual sorbent cost for injecting PAC into the
existing COHPAC baghouse would be about $300,000.
Additional cost information is being developed for bal-
ance of plant impacts.
•
•
On average, ~78% Hg removal was obtained when
PAC was injected into COHPAC 24 hr/day during
long-term tests. The Hg removal varied through-
out the period and ranged from 36 to 90%.
To verify S-CEM measurements during the long-
term tests, Hg removal across COHPAC was mea-
sured following the draft Ontario Hydro method.
Results show an average 90% removal for the
three test periods. These results confirm the high
Hg removal measured with the S-CEMs.
•
Actual Hg removals were in reasonably close
agreement with theoretical model predictions for
Figure 7. Inlet and outlet COHPAC Hg concentrations, boiler load, and PAC injection concentration during long-term tests, April 2001.
Volume 52 August 2002
Journal of the Air & Waste Management Association 925

Bustard et al.
7. The U.S. Environmental Protection Agency Web site: http://
www.epa.gov/ttn/atw/combust/utiltox/utoxpg.html; accessed 2001.
8. Sjostrom, S.M.; Bustard, J.; Durham, M.; Chang, R. Hg Removal Trends
in Full-Scale ESPs and Fabric Filters. Presented at A&WMA’s Specialty
Conference on Hg Emissions: Fate, Effects, and Control, Chicago, IL,
August 21–23, 2001.
9. Hassett, D.J.; Pflughoeft-Hassett, D.F.; Laudal, D.L.; Pavlish, J.H. Hg
Release from Coal-Combustion Byproducts to the Environment. Pre-
sented at the Mercury in the Environment Specialty Conference, Min-
neapolis, MN, September 15–17, 1999.
80–90% removal (1.5–2 vs. 3 lb/MMacf), consid-
ering that the model is based on a uniform PAC
particle size of 15 µm when, in fact, the actual
FGD carbon used has a wide size distribution with
significant numbers of particles less than 15 µm.4
The model also assumed a cleaning frequency of
2 pulses/bag/hr (all bags cleaned at the same
time), whereas the bags were actually cleaned at
~1–2 pulses/bag/hr [bags cleaned 15 (one row) at
a time] during the tests.
•
Additional testing over longer periods (up to a
year) must occur to determine the impact of car-
bon injection on bag life (pressure drop and bag
strength) and outlet particulate emissions.
About the Authors
C. Jean Bustard (corresponding author) is executive vice
president, Michael Durham, Ph.D., is president, Charles
Lindsey is specialist, Travis Starns is project engineer, Ken
Baldrey is director of product development, Cameron Mar-
tin is director of engineering, and Richard Schlager is vice
president of contract research and development at ADA-
ES, LLC, 8100 South Park Way, B-2, Littleton, CO 80120.
Sharon Sjostrom is director of pollution control technology
development and Rick Slye is an engineering specialist at
Apogee Scientific, 2875 W. Oxford Avenue, Suite 1,
Englewood, CO 80110. Scott Renninger is program man-
ager at the National Energy Technology Laboratory, U.S.
Department of Energy, Collins Ferry Road, P.O. Box 880,
Morgantown, WV 26507-0880. Larry Monroe, Ph.D., is prin-
cipal research engineer at Southern Co., 600 North 18th
St., Birmingham, AL 35203. Richard Miller is sales manager
at Hamon Research Cottrell, Inc., 4589 Lehigh Drive,
Walnutport, PA 18088. Ramsay Chang, Ph.D., is a manager
at EPRI, P.O. Box 10412, Palo Alto, CA 94393-0813.
REFERENCES
1. Brown, T.D.; Smith, D.N.; Hargis, R.A.; O’Dowd, W.J. Mercury Mea-
surement and Its Control: What We Know, Have Learned, and Need
to Further Investigate; J. Air & Waste Manage. Assoc. 1999, 49, 1-97.
2. Durham, M.D.; Bustard, C.J.; Schlager, R.; Martin, C.; Johnson, S.;
Renninger, S. Field Test Program to Develop Comprehensive Design,
Operating, and Cost Data for Hg Control Systems on Non-Scrubbed
Coal-Fired Boilers. Presented at the Annual Conference and Exhibi-
tion of A&WMA, Orlando, FL, June 24–28, 2001.
3. Durham, M.D.; Bustard, C.J.; Schlager, R.; Martin, C.; Johnson, S.;
Renninger, S. Controlling Hg Emissions from Coal-Fired Utility Boil-
ers: A Field Test; EM 2001, July, 27-33.
4. Meserole, F.B.; Chang, R.; Carey, T.R.; Machac, J.; Richardson, C.F.
Modeling Hg Removal by Sorbent Injection; J. Air & Waste Manage.
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5. Miller, R.; Harrison, W.; Corina, B.; Cushing, K.; Chang, R. COHPAC:
The Next Generation in Particulate Control Technology at Alabama
Power Co.’s E.C. Gaston Units 2 and 3, A Success Story. Presented at
the EPRI-DOE-EPA Combined Utility Air Pollution Control Sympo-
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Richardson, R.; Chang, R.; Meserole, F. Assessing Sorbents for Hg
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926 Journal of the Air & Waste Management Association
Volume 52 August 2002