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Multi-Technology, Mercury Abatement Program, Implementation and Performanceat Nova Scotia Power
Technical PaperBR-1844
Authors:
D. McLellan
Nova Scoa Power Incorporated
Haifax, Nova Scoa, Canada
B.J. Jankura
Babcock & Wilcox
Power Generaon Group, Inc.
Barberton, Ohio, U.S.A.
M. MacKenzie
R. Ojanpera
Babcock & Wilcox Canda
Cambridge, Ontario, Canada
Presented to:EPRI Power Plant Air Pollutant
Control Mega Symposium
Date:
August 30 - Sept. 2, 2010
Locaon:
Balmore, Maryland, U.S.A.
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Babcock & Wilcox Power Generation Group 1
Multi-Technology, Mercury Abatement Program, Implementation and Performance at Nova Scotia Power
B.J. Jankura
Babcock & Wilcox
Power Generation Group, Inc.
Barberton, Ohio, U.S.A.
BR-1844
Abstract
Nova Scotia Power Incorporated (NSPI) has installed
mercury capture technologies on seven coal-red boilers to
comply with provincial regulations for mercury emissions.
To achieve with the 2010 provincial cap of 65 kg/yr, a
multi-technology approach consisting of enhanced mercury
oxidation followed by halogenated activated carbon injec-
tion, has targeted 70% coal-to-stack reduction from existing
total mercury emissions. This paper discusses programimplementation and performance test results at seven NSPI
boilers using the combination of calcium chloride injection
technology with Powdered Activated Carbon (PAC) injec-
tion upstream of the particulate collection devices. Both
systems were installed on several different plant congura-
tions, including both front and tangentially red boilers, with
electrostatic precipitators and one unit with a baghouse. The
design and performance issues with novel “hot-side” PAC
injection lances before the air preheater and performance
with Colombian, bituminous coal are included.
Introduction Nova Scotia Power Incorporated is a regulated, vertically-
integrated, electric utility. The company supplies over 97%
of the generation, transmission and distribution of electrical
power to 460,000 customers in the province of Nova Scotia,
Canada. NSPI owns 2,293 megawatts (MW) of generation
capacity, fuelled by a mix of coal and petroleum coke (55%),
oil and natural gas (27%) and hydro, tidal and wind (18%).
Mercury regulation development
The development of a mercury regulation in Nova Scotia,
leading to the implementation of mercury emission controls
at Nova Scotia Power, was over a relatively short timeframe.
Canadian coal red utilities participated in a collective
program administered through the Canadian Electricity As-
sociation to gain an understanding of mercury measurement
and capture (REF1). The information gathered in this program
was then reviewed and supported decision making in theCanada Wide Standard process completed by the Canadian
Council of Ministers of the Environment (REF2).
In 2005, a 168 kg annual mercury cap came into effect
in Nova Scotia. This was achieved through fuel switching
and intensive monitoring. However, following the release
of the Canada Wide Standard for Mercury and subsequent
revision to the Nova Scotia Air Quality Regulations reducing
the annual cap to 65 kg, the required reduction could not
be met by fuel switching alone (REF3). At this point, NSPI
completed a test program to assess if the 2010 cap could be
met by commercially available control technology.
Following the testing, a procurement process and work
order submission to the regulator were immediately initiatedto meet the aggressive implementation schedule. Figure 1
gives an overview of the events leading to the implementa-
tion of mercury control systems.
Summary of NSPI units with installedsystems
There are four solid-fuel burning thermal stations in
the NSPI eet, and it was at three of these stations that the
mercury control equipment was installed. This includes a
Presented to:
EPRI Mega Symposium 2010
August 30 - Sept. 2, 2010Baltimore, Maryland, U.S.A.
M. MacKenzie
R. Ojanpera
Babcock & Wilcox Canada
Cambridge, Ontario, Canada
D. McLellan
Nova Scotia Power Incorporated
Halifax, Nova Scotia, Canada
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2 Babcock & Wilcox Power Generation Group
total of seven boilers at the three stations. Relevant details
of the plants are discussed below and summarized in Table 1.
Lingan - This plant is the largest in the thermal eet
and currently operates four (4) 150 MW tangentially red
units. The units are of the same manufacture and vintage,
and have been retrotted with low NOx systems, including
separated overre air. Particulate collection is by means of
an electrostatic precipitator.
Point Tupper - Pt Tupper Unit 2, the remaining unitoperating at the plant, was converted from a heavy oil red
unit in the 1980’s. Unit 2 is a 150 MW tangentially-red
boiler and has also been retrot with a low NO x combustion
system including separated overre air. Particulate collec-
tion is by means of an electrostatic precipitator.
Trenton - This plant currently operates two (2) units.
Unit 5 is 150 MW, constructed in the late 1960’s, and has
the original circular register burners. A baghouse was added
in 2009 to supplement the original electrostatic precipita-
tor. Unit 6, with nameplate capacity of 160MW, went into
service in 1991 and has an electrostatic precipitator for
particulate collection.
Test fuel
Nova Scotia Power has burned a variety of fuels and
fuel blends over the last number of years as local supplies
became less available. These blends are tested and adjusted
accordingly to meet environmental and operational con-
straints. When identifying the fuel that would be used to
complete testing on the new mercury abatement systems, a
low-sulfur Colombian coal with a higher heating value av-
eraging around 10,300 Btu/lb was selected since it would be
readily available for the testing and used for the rst several
months of operation.
Mercury control technology selectionFollowing the revision of provincial regulations to set the
2010 mercury cap, NSPI completed a review of commer-
cially available technologies that could be used to meet the
required emission reduction. This review led to pilot scaletesting of activated carbon injection and sorbent enhance-
ment additives.
After a review of the test results, NSPI made the deci-
sion to initiate a procurement process that would lead to
the purchase and installation of seven mercury abatement
systems. Results indicated that activated carbon injection
could meet an emissions reduction of almost 70% and the
use of brominated activated carbon or sorbent enhancement
additives would provide additional margin to meet the
regulation. Also a consideration when selecting the control
Fig. 1 Timeline of development and regulatory milestones.
Fig. 2 MercPlus™ system storage system.
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Babcock & Wilcox Power Generation Group 3
technology, were the long term opportunities to minimize
operation and maintenance costs and have exibility in the
use of future fuels at each station.
MercPlus™ system
Mercury control at the NSPI plants is accomplished by
a combination of two technologies. The rst technology is
the MercPlus™ front-end fuel additive system from Babcock
& Wilcox Power Generation Group, Inc. (B&W PGG) to
enhance the oxidation of mercury in the boiler. The system
is composed of liquid solution storage tanks, pumping/
metering skid(s), coal injectors, and DCS interface control-
lers. The storage tanks at NSPI are berglass construction
to allow for the various sizes and congurations required
at the multiple locations. There is one pumping/metering
skid for each boiler. The skids have multiple pumps with asingle pump dedicated to each coal feeder injection point.
The pumps are sized sufciently that should one pump need
to be taken down for service, the remaining pumps can au-
tomatically increase their rates to keep the overall injection
rate for each boiler at the proper level.
The MercPlus system sprays a CaCl2 solution on the coal
prior to combustion. This is advantageous because oxidized
mercury can be captured with relatively high efciency. The
additive is injected directly onto the coal as a 30% solution
of CaCl2 (20% chlorine), which is commercially readily
available from multiple suppliers. It is stored in tanks that
can be either inside the boiler building or outside without
freeze protection. Figure 2 shows pictures of the MercPlus
storage system. The physical properties of the solution of –55F freeze point do not require heat tracing on any of the
equipment or piping even in the very low temperatures typi-
cally experienced in the plant locations.
The solution is pumped by the skids from the storage
tanks to the coal feeder deck in the boiler building where it
is sprayed onto the coal in each of the operating coal feed-
ers upstream of the pulverizers. Figure 3 shows the solution
ow control skids.
Figure 4 shows the coal feeder injector piping. The in-
jection rate is metered to the feeders as a function of feeder
speed, which is proportional to coal ow, to achieve the de-
sired additive stoichiometry. As opposed to furnace reagent
injection, or coal silo injection, this is a very simple system,which affords fewer injection points, good reagent mixing,
even distribution among burners, and a quick response time.
The injection rate of the chloride solution additive was
automatically controlled by the DCS system with logic pro-
vided by B&W PGG. The equipment operator could directly
select the required injection rate for unattended operation.
The chloride addition rate is based on a ratio to the coal ow
measured in pounds of chlorine per million pounds of coal
to the boiler – dry basis (ppmd).
Table 1
Summary of Nova Scotia Plant Designs
Plant Lingan Point Tupper Trenton 5 Trenton 6
Unit Nameplate Capacity 4 @ 150 MW 1 @ 150 MW 1 @ 150 MW 1 @ 160 MW
Combustion System
Corner red,
low NOx with
Overre Air
Corner red, low NOx
with Overre Air
Front Wall red,
original burners
Front Wall red,
low NOx burners
and overre air
Particulate Collection Device(s) Cold Side ESP Cold Side ESPCold Side ESP
and BaghouseCold Side ESP
ESP Details
Total Collecting Area (sq. ft) 130,159 120,960 103,500 173,430
# of electrical elds 6 3 4 3
# of mechanical field 3 3 3 3
Baghouse Details
Air/Cloth Ratio -------- -------- 3.46 --------
Net Cloth Area (sq. ft.) -------- -------- 166,445 --------
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4 Babcock & Wilcox Power Generation Group
Activated carbon addition system
Injection of Powdered Activated Carbon (PAC) into the
ue gas is the primary technology used for mercury control
at NSPI. Each boiler has a dedicated system which includes
storage silo, blower, feeder, piping, splitters, distribu-
tion bottles and lances. Each silo contains one redundant
blower (i.e. two blowers/silo, one operating at any point in
time) and eductor. Figure 5 shows the four PAC silos at the
Lingan Plant.
While the nominal ratings of the seven plants are similar,
there are four distinct plant designs which required speciclayout and equipment specications. A summary of the
signicant design parameters of the carbon injection equip-
ment is shown in Table 2.
PAC is pneumatically transferred from the silo to the
injectors through a series of rigid piping and exible hoses.
The transfer piping was custom designed for each instal-
lation to enable minimum transport distances and number
of ow direction changes. Figure 6 shows the pneumatic
transfer piping for the Trenton 5 plant. Trenton 5 was the
only outdoor installation with injection after the existing
ESP into the top ue going to the baghouse. The return ue
form the baghouse is the lower one.
The PAC injection rate was automatically controlled by
the DCS system. The equipment operator could directly
select the required injection rate for unattended operation.
The carbon addition rate is based on a ratio of pounds of
carbon per million actual cubic feet of ue gas at the air
heater outlet (lb/Macf).
Computational Fluid Dynamics (CFD) was utilized in thedesign of individual components as well as to establish injec-
tion locations. The major goals of the CFD analyses were:
• To verify as built piping pressure drop;
• Achieve uniform PAC distribution to each bottle;
• To achieve target distribution of PAC to each lance via
distribution bottles;
• To be able to inject predicted quantities at two elevations
along a given lance; and,
• To achieve desired mixing of PAC in ue gas prior to
particulate collection
Figure 7 shows typical results of PAC particle paths in
the distribution bottle. The biggest issue for the design was
accounting for the high particle momentum. Several bottle
styles were investigated with the bottom fed arrangement
producing the most even distribution. This was also an
advantage for the installation arrangement of the rigid and
exible piping. CFD modeling provides the exibility to
easily customize the distribution bottle design for different
number of lances and preferential distribution as required
for specic applications.
Figure 8 shows the results of PAC ow in an individual
lance. For comparison a photo from wind tunnel testing is
also presented. The CFD model accurately reproduced the
major ow features found in the wind tunnel test. The use
of CFD modeling provides the exibility to easily custom-ize the lance design for multiple/varying levels and varying
amounts per level.
For each plant detailed models of the ue system were
developed including, where appropriate, injection lances,
airheater and particulate collection device. These models
Fig. 3 MercPlus™ injection system equipment.
Fig. 4 MercPlus™ solution injector system.
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Babcock & Wilcox Power Generation Group 5
were used to optimize PAC distribution in the ue gas at the
entry point to the particulate collection devices. A typical
result is shown in Figure 9.
Mercury removal performance testing
Methodology
Mercury concentrations were measured using U.S. EPA
Reference Method 30B “Determination of Total Vapor Phase
Mercury Emissions From Coal-Fired Combustion Sources
Using Carbon Traps”. To determine mercury mass emission
rates and the mercury reduction efciency of the mercury
removal systems, EPA Methods 3 (O2/CO2), 4A (moisture
content), and coal ow were also used (except at Trenton
Unit 5 where coal ow data was not available). The testing
included one-hour sampling runs conducted at the outlet lo-cations. Inlet sampling at Trenton Unit 5 included 20 minute
sampling runs conducted during the one-hour sampling runs
collected at the outlet location. The outlet testing consisted
of sampling of ue gas at the locations described below:
• Lingan Units 1 and 2 - breeching prior to entering the
combined stack
• Lingan Units 3 and 4 - breeching prior to entering the
combined stack
• Trenton Units 5 and 6 – stack; and Point Tupper Unit
2 - stack.
Fuels and PAC properties
Performance testing was conducted during November – December 2009. Colombian coal was red during these
tests. The as-red fuel data are provided in Table 3.
At the time of testing, the coal also had a relatively low
mercury concentration ranging from 0.035 to 0.060 ppm
which is generally more consistent than when blended fuels
are used. The chlorine content of this coal was also low
compared to some of the previous fuels used, ranging from
80 to over 300 ppm, but mostly under 200 ppm.
Fig. 5 Lingan Plant powdered activated carbon silos and feeders. Fig. 6 NSPI Trenton 5, activated carbon distribution piping.
Table 2
Carbon Injection Equipment Selected Design Features
Plant Lingan Point Tupper Trenton 5 Trenton 6
Unit Nameplate Capacity 4 @ 150 MW 1 @ 150 MW 1 @ 150 MW 1 @ 160 MW
Injection Location Economizer outlet Economizer outlet
ESP outlet/
Baghouse Inlet Economizer outlet
# of ues 2 1 1 2
# of PAC distribution bottles 2 1 1 2
# of lances 2 x 6 = 12 1 x 6 = 6 1 x 6 = 6 2 x 5 = 10
# of injection points 24 12 12 20
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6 Babcock & Wilcox Power Generation Group
Two different PAC products were used. For condential-
ity reasons they are described as PAC-1 and PAC-2. ThePAC media is a nely ground, high performance brominated
activated carbon that is specically manufactured for the
removal of both elemental and oxidized mercury from the
ue gases of coal-red boilers. The particle size and den-
sity of this bulk powder are presented in Table 4- Selected
PAC Properties. The particle size distributions of the bulk
powders are presented in Figure 10.
While PAC is a commercially available specialty chemi-
cal, NSPI found that an initial effort was involved in logistics
of co-coordinating fuel burn rate and carbon injection rates
during the testing.
Results and discussion
NSPI conducted guarantee mercury reduction perfor-
mance testing on all seven of its coal-red boilers. Using
the combined technologies of chloride injection to the coal
and PAC injection before the particulate collector, an aver-
age of 70% mercury reduction from the coal potential to
the stack was required. Tests were conducted on all seven
units between November 18 and December 18, 2009. The
purpose of the testing was to verify the percentage of mer-
cury capture at specied MercPlus and PAC injection rates.
Mercury capture was determined by one of two methods:
• On Trenton 5 mercury sampling was performed at theeconomizer inlet to establish untreated mercury emis-
sion rates. These levels were then compared to samples
from the stack.
• On the remaining units, untreated mercury emissions
were calculated from coal composition and coal feeder
data. These levels were then compared to samples from
the stack.
The coal potential mercury emissions ranged from
3.5 – 5.1 lb/TBtu.
The MercPlus solution injection was established based
on augmenting the inherent coal chlorine to reach a target
of 700 ppmdry. For the coal chlorine in the test coals, thechloride addition ranged from 300 – 600 ppmdry. If the
inherent coal chlorine had been high enough, then no solu-
tion would have been required.
PAC injection rates were set to obtain 4 lb/Macf for
Trenton 5 and 6 lb/Macf for the remaining units. The lower
injection rate for Trenton 5 reects the use of a baghouse for
particulate collection, which has much higher contact time
when compared to an electrostatic precipitator, between the
activated carbon and ue gas. Even with 1/3 less PAC, Tren-
ton 5 had the highest capture (~98%) consistent with mercury
Table 3
Test Fuel Properties
Plant Lingan 1 Lingan 2 Lingan 3 Lingan 4 Point
Tupper Trenton 5 Trenton 6
Ultimate Analysis
(% by weight)
C 60.54 59.20 62.29 64.22 63.51 64.81 62.52
S 0.93 0.72 0.97 0.72 .60 0.67 0.72
H2 4.02 3.84 4.2 4.19 4.36 4.04 4.06
N2 1.23 1.21 1.23 1.27 1.35 1.23 1.14
O2 9.22 8.91 9.26 7.82 7.50 3.52 4.50
Moisture 18.34 19.0 15.94 15.7 14.31 14.77 17.74
Ash 5.88 7.12 6.08 6.1 8.38 10.99 9.35
Cl (ppmd) 81.83 81.0 336 169 175 127.5 127.5
Hg(ppmd) 0.065 0.050 0.050 0.058 0.045 0.046 0.050
HHV (Btu/lb) 10,361 10,152 10,834 10,758 11,004 10,506 10,350
Fixed Carbon 44.11 42.52 45.29 45.58 44.26 42.70 41.57
Volatile Matter 31.68 31.36 32.69 32.62 33.05 31.54 31.34
FC/VM 1.39 1.36 1.38 1.40 1.35 1.35 1.33
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Babcock & Wilcox Power Generation Group 7
capture performance on units equipped with a baghouse.
Performance test parameters and results on the aver-
age of several individual test runs are presented in Table
5. The average system-wide capture over the seven plants
of approximately 80% compared well to the performance
target of 70%.
PAC-1 showed a signicant variation in capture efcien-
cies. As it was only used at Lingan, plant design variation
can be ruled out as a contributing factor. It was noted that
the rst two tests (conducted on Lingan 3 and 4) were done
with only a few hours of initial conditioning. It was also
noted that the capture percentage increased as the test period
progressed. Based on this, a minimum 24 hour “seasoning” period was, therefore, established for subsequent tests. Cor-
respondingly, overall capture was signicantly higher on
Lingan 1 and 2 tests. This is indicative of actual performance
on the Lingan units.
PAC 2 was utilized on Trenton 5, Trenton 6 and Point
Tupper. The latter two units are equipped with electrostatic
precipitators and thus can be reasonably compared to each
other. Despite signicant differences in the boiler design,
PAC system and electrostatic precipitators the capture ef-
ciencies are almost equal.
The eetwide mercury reduction measured during the
guarantee testing is summarized in Figure 11. The overall
eetwide mercury reduction of 80% compares well to the
guarantee of 70%.
Mercury removal sorbent costs
Sorbent injection is considered one of the simplest and
most mature technologies for mercury control with relatively
low capital costs (REF 4). However, the operating costs arerelatively high, especially if the system does not include
other air pollutant removal equipment, such as SCR or FGD.
Since the NSPI mercury reduction relies solely on injection
followed by particulate collection, the injection rates and
costs of the mercury control sorbents are relatively high.
For condentiality reasons, NSPI could not include the
actual delivered cost for the mercury sorbents. However,
using a typical basis of $USD1.00 for the cost of calcium
chloride solution per gallon and $USD1.00 for the cost of
PAC per pound the cost for the chloride and carbon sorbents
as a ratio of the plant power output with a range from 1.42
to 2.03 $USD/MW h. When FGD is included the sorbent
requirements are greatly reduced and operating costs aresubstantially less. For example, The Newmont Mining TS
power plant utilizes a spray dry/baghouse FGD system that
operates with only 0.3 lb/Macf Br-PAC and 100 ppm CaCl2
for an average cost of $0.13/hr (REF 5).
Fig. 7 CFD simulation of PAC flow in the distribution bottle.
Table 4
Selected PAC Properties
PAC Product Mean Particle
Size (microns)
Bulk Density
(lb/ft 3 )
PAC 1 12.14 30.1
PAC 2 17.82 21.6
Fig. 8 Comparison of CFD simulation and wind tunnel testing of
individual lances.
Fig. 9 Lingan Plant CFD for PAC distribution at the ESP inlet.
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8 Babcock & Wilcox Power Generation Group
The majority of the cost is for the brominated PAC,
which averaged 89%. Depending on the overall boiler
eet utilization, and coal chlorine content, the total annual
cost for mercury sorbents could range from about $USD
10,000,000 – 15,000,000 annually based on this available
commercial information.
Conclusions
The installation of seven mercury abatement systems
was successfully installed and tested in 2009 at Nova Scotia
Power. These projects were initiated in response to the pend-
ing provincial annual cap not to exceed 65 kg of mercury.
The two components of these installations were enhanced
mercury oxidation using calcium chloride application to the
fuel feedstock in combination with a brominated PAC. An
interesting feature of the systems installed on the six units
without a baghouse is the novel hot-side PAC injection lance
system located before the air preheater.
Following construction, tests completed at all unitsyielded results that exceeded the targeted 70% mercury
capture and positioned NSPI to meet the provincial regula-
tion in 2010.
References
1. Canadian Electricity Association (CEA) Mercury
Program. Retrieved June 13, 2010, from http://www.
ceamercuryprogram.ca/EN/program_overview.html
2. Canada-Wide Standards for Mercury Emissions from
Coal-Fired Electric Power Generation Plants, Endorsed by CCME Council of Ministers, October 11, 2006
3. Schedule C of the Air Quality Regulations. Environ-
ment Act of Nova Scotia. Amended September 25, 2007
4. Institute of Clean Air Companies, Sorbent Injection
Technology for Control of Mercury Emissions From
Coal-Fired Boilers, ICAC Fact Sheet 051506.pdf
5. Jankura, B.J, et.al, Cost Effective Mercury Emissions
Control At The Newmont TS Power Plant, Electric
Power May, 2010, Rosemont, Ill
Key words
Calcium Chloride
Powdered Activated Carbon
Mercury Control
Nova Scotia Power
The Babcock & Wilcox Company
Fig. 10 PAC particle size distribution. Fig. 11 NSPI fleet-wide mercury reduction.
Tables 5
NSPI Plant Mercury Removal Performance
Plant Particulate
Control
Cl
Addition
ppmd
PAC
Addition
lb/Macf
PAC
Type
Boiler
Load
MWg
Coal
Cl
ug/g
Coal
Hg
ng/g
APH
Tin
F
APH
Tout
F
Coal
Hg
g/hr
Stack
HgT
M30B
g/hr
Stack
HgT
M30B
lb/TBtu
Hg
Removal
Eff %
Lingan 1 ESP 600 6 PAC-1 161 82 65 N/A 331 2.61 0.27 0.31 92
Lingan 2 ESP 600 6 PAC-1 149 81 50 745 319 2.54 0.67 0.95 75
Lingan 3 ESP 300 6 PAC-1 165 336 50 713 340 3.12 1.09 1.85 59
Lingan 4 ESP 300 6 PAC-1 162 269 58 713 340 3.36 1.26 2.10 58
Point Tupper ESP 500 6 PAC-2 157 175 45 672 329 2.76 0.41 0.58 84
Trenton 5 BGH 550 4 PAC-2 118 127 46 N/A 302 3.34 0.04 0.04 99
Trenton 6 ESP 550 6 PAC-2 158 127 50 703 267 2.91 0.38 0.60 86
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