Reducing Operating Costs and Risks of Hg Control with
Fuel Additives
Paper #89
Presented at the
Power Plant Pollutant Control and Carbon Management “MEGA” Symposium
August 16-19, 2016
Baltimore, MD
Constance Senior,1 Sharon Sjostrom,1 Gary Mitchell,2 David Boll2; 1ADA-ES, Highlands
Ranch, CO, 2AmerenUE, St. Louis, MO
ABSTRACT
Under the MATS rule, coal-fired boilers have many options for mercury control. Once in
compliance, plants will need to keep the operating costs of mercury control systems in check.
Coal additives are used to increase the oxidation of mercury in the flue gas and improve the
effectiveness of activated carbon. Bromine is currently the most commonly used coal additive.
While effective, bromine addition has been associated with balance-of-plant problems. ADA’s
M-Prove™ coal additive has been used successfully on PRB- and lignite-fired boilers to increase
mercury oxidation and reduce PAC consumption for mercury control. The paper presents a case
study on the successful demonstration of M-Prove combined with powdered activated carbon at
a subbituminous-fired boiler with a cold-side ESP to achieve mercury emissions below the
MATS limit in order to reduce carbon consumption and minimize balance-of-plant impacts.
INTRODUCTION
Air emissions from coal-fired boilers and industrial sources are regulated under the federal Clean
Air Act as well as under state rules. On December 16, 2011, the EPA issued the final Mercury
and Air Toxics Standards (MATS) rule, which took effect on April 16, 2012. Almost all affected
units had to be in compliance on April 16, 2016. For coal-fired boilers firing bituminous or
subbituminous coal, the MATS emission limit for mercury is 1.2 lb/TBtu, computed on a 30-day
rolling average basis. This is a multi-pollutant rule, which can increase the complexity of finding
a compliance solution. The control of particulate matter (PM) must be accomplished while
controlling both acid gases and mercury (Hg).
There are only two pathways by which mercury can be removed from coal-fired boilers:
collection of mercury that has been adsorbed on surfaces (e.g., fly ash, sorbents) and absorption
of oxidized gaseous mercury species (collectively, Hg2+) in aqueous media. Any mercury
control strategy must utilize one or both of these pathways, either by removing particulate-bound
Hg using the particulate collection device or by removing gaseous Hg2+ in a flue gas
desulfurization (FGD) scrubber.
Halogen compounds have long been identified as the most important species for oxidizing
mercury in coal combustion systems. Chlorine is the most abundant halogen in coal. The
1
chlorine contents of coals from the U.S. span two orders of magnitude,1 and this large variation
resulted in the observation that coal chlorine content had a strong influence on the oxidation state
of mercury in the flue gas, as well as the removal of mercury in certain air pollution control
devices.
The presence of halogen compounds in the flue gas promotes mercury adsorption by activated
carbon. With low concentrations of halogens in the flue gas, powdered activated carbon (PAC)
is not very effective at adsorbing mercury in coal-fired boilers. The effectiveness of activated
carbon in low-halogen flue gas is increased by either adding halogen to the flue gas or by
pretreating the activated carbon with a halogen.
When additional mercury oxidation is needed in the flue gas, bromine has typically been the
halogen used. However, there are balance-of-plant effects of bromine addition that have been
noted after several years of bromine usage at coal-fired utility boilers, including: corrosion in the
flue gas path, selenium partitioning in the flue gas, and potential discharges of bromide in
scrubber wastewater.
An ongoing study by EPRI4,5 on the balance of plant effects of bromine addition (including
direct bromine addition and injection of brominated PAC) has, to date, identified corrosion as the
major observed impact. The most commonly reported corrosion locations in the EPRI study
associated with bromine addition were the cold-end baskets of air preheaters (APHs). This
corrosion was only observed on boilers firing subbituminous coals or subbituminous-bituminous
blends. Furthermore, most of the corrosion identified in boilers in which bromine was added to
the fuel took place in boilers with bromine addition rates greater than 100 μg Br/g coal.
ADA’s patented M-Prove Technology was developed to provide the benefits of halogen addition
for mercury control without the negative impacts that have been observed with bromine.
Leveraging years of research and technical expertise, ADA has secured 13 patents incorporating
M-Prove Technology, with more pending in the US and foreign patent offices. ADA’s portfolio
includes patents that cover the combined use of halogen-based coal additives and mercury
sorbents, including activated carbon. Typically, eight to ten times less M-Prove additive is
required to achieve similar oxidation and Hg removal results as with bromine. This mitigates
risk from balance-of-plant impacts associated with bromine injection at higher levels while
achieving similar mercury control benefits. The proprietary liquid coal additive product for
enhanced mercury oxidation and removal in coal-fired boilers can be applied at various stages of
the coal feed process. More than 100 million tons of coal have been treated with the M-Prove
additive with no reported balance-of-plant impacts.
This paper provides an example of the mercury control capabilities of the M-Prove Technology.
The objective of the demonstration discussed here was to evaluate different options for
controlling Hg emissions on a boiler firing a low-halogen subbituminous coal using a cold-side
ESP. The demonstration included the following mercury control technologies: standard
brominated and non-brominated PAC and ADA’s proprietary M-Prove coal additive. The
brominated sorbents and M-Prove coal additive were tested to assess the potential of higher
vapor-phase mercury removal through increased mercury oxidation.
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EQUIPMENT AND METHODS
Unit Description
Labadie Unit 3 is a Combustion Engineering tangentially fired, dry-bottom boiler with a
nominal rating of 630 MWG, and was commissioned in 1971. The unit was originally
configured to burn Illinois bituminous coal and switched to subbituminous Powder River Basin
(PRB) coals in the 1990s. Table 1 summarizes the plant and air pollution control device (APCD)
operation and Figure 2 provides the location of major equipment and the locations of reagent
addition and sampling points.
Unit 3 is fitted with low-NOx burners, LNCFS™ Level III, and utilizes SOFA for NOx control.
No post-combustion NOx or SO2 control devices are installed on this unit. A feedwater heater
was out of service for the entirety of testing. The resultant economizer outlet temperature was on
the order of 100˚F higher than in months past. Gas from the Unit 3 economizer splits
(50%/50%) between two runs of ducting which each contain a Ljungström air preheater (APH).
Particulate control is accomplished with three parallel ESPs. The original ESPs (A- and B-) are
Research-Cottrell designs and are configured in a chevron pattern. Each system consists of three
collection fields with four bus sections per field. The C ESP, which was added in the early
1980s, is a Flakt design that consists of four collection fields with four bus sections per field.
Normally the plant injects SO3 upstream of the ESPs for flue gas conditioning (FGC). During
the testing reported here, however, ADA’s RESPond™ flue gas conditioning (FGC) agent was
used instead of SO3 FGC. RESPond FGC does not have any impact on the performance of PAC
for mercury control.
Table 1. Labadie Unit 3 Unit Description.
Parameter Identification
Boiler Manufacturer
Furnace Type
Nominal Unit Rating
NOx Control
SOx Control
Particulate Matter Control Device
Units
°F
Unit 3
Combustion Engineering
Tangential Firing
630
LNCFS™ Level III, SOFA
Low Sulfur Coal
Cold Side ESPs
“A” & “B” Research-Cottrell;
“C” Flakt
325-355
°F
730
MMacfm
2.2
SO3 or RESPond FGC
<0.5
MWEG
ESP Manufacturer
Typical ESP Operating Temperature
Typical APH Inlet Operating
Temperature
Flue Gas Flow Rate at Stack
Flue Gas Conditioning Agent
LOI
wt%
3
U 3 Layo
out.
Figure 1. Labadie Unit
Flue Ga
as Mercurry Measurrements
Economiizer Outlet
ADA insstalled and op
perated two Thermo Fish
her Mercuryy Freedom S
System™ conntinuous
emission
ns monitoring
g systems (H
Hg-CEMS). One of the H
Hg-CEMS ssampled from
m the econom
mizer
outlet (A
APH inlet) B--duct and thee other samp
pled from thee Unit 3 stacck. The Hg-CEMS
measurem
ments were the
t basis for the test merrcury measurrements andd emission prrofile
characterrization for the
t duration of the test prrogram. Equuipment verrifications weere conducteed on
completion of installation of each
h Hg-CEMS
S in accordannce with AD
DA’s Qualityy
Assurancce/Quality Control
C
(QA/QC) Protoco
ol.
The Hg-C
CEMS operaated continuo
ously and un
nmanned thrroughout thee test period. The vapor-phase meercury data collected
c
durring baselinee, parametricc, and long-tterm testing at the
economizzer outlet provided a reaal-time trend
d for current levels of meercury in the coal being
combusteed. This info
formation waas valuable to
o provide innsight on the required ratte of injectioon of
mercury control sorb
bents and waas also used to
t determinee if the stackk Hg-CEMS was trendingg
properly..
Stack
ADA also installed and
a operated a Thermo Fisher
F
Hg-CE
EMS in Unitt 3 stack in a non-RATA
A
dedicated
d port. Equiipment verifiications were conductedd on complettion of installlation in
accordan
nce with ADA
A’s Quality Assurance/Q
Quality Conttrol (QA/QC
C) Protocol.
4
The Hg-CEMS operated continuously and unmanned throughout the test period. The total
vapor-phase mercury emissions data collected during baseline, parametric, and long-term testing
were used to assess unit response to injected sorbents and reagents. The economizer outlet
mercury numbers in comparison to stack mercury numbers provide a characterization of percent
mercury removal during each phase of testing.
Method 30B Comparison
Clean Air Engineering (CAE) conducted EPA Method 30B testing to determine relative accuracy
of the Hg-CEMS installed at the Unit 3 stack. Method 30B runs were conducted at the same
elevation as the Hg-CEMS at the RATA sample ports.
Solids Sampling
Coal samples were collected by the plant downstream of coal mill 3F. Ultimate, proximate,
mercury, and chlorine analyses were performed on these coal samples. Ash samples were also
collected by the plant from Unit 3 ESP A fields 10 and 11 as well as composites of the inlet
fields of ESP A, ESP B, and ESP C. Ash samples were analyzed for Loss-On-Ignition (LOI).
Powered Activated Carbon (PAC) Injection
ADA installed temporary ACI equipment to inject PAC upstream of the air preheaters. The
injection equipment consisted of a total of twelve lances with six in each side of the split flue gas
path. The lances were staggered in length across the width of the 9-foot deep duct, consisting of
(2) one-third, (2) one-half, and (2) two-third lance lengths for better distribution of PAC in the
flue gas path.
Several different PACs were evaluated in the test program. PAC A was a standard lignite-based
non-brominated PAC used for mercury capture. PAC A is typically used with high-chlorine
containing coals or in combination with an oxidizing agent. PAC B was an enhanced nonbrominated PAC used for mercury capture. PAC B had a smaller particle size than PAC A
which can result in more collection surface area on the activated carbon particles. PAC C was
treated with bromine to promote mercury oxidation and capture. It is specifically designed for
flue gas mercury capture in low-halogen applications such as Powder River Basin coals.
The convention for describing the injection concentration of injected sorbent is “pounds of
sorbent per million actual cubic feet of flue gas”, or “lb/MMacf”. The actual mass flow rate of
sorbent is therefore dependent on the total volumetric flow of flue gas at the point of injection.
The actual injection concentrations presented in this report are calculated from the actual sorbent
feed rates on a pound-per-hour basis and the actual stack flow data recorded by the plant DCS
reported in units of “thousand standard cubic feet per minute” (KSCFM). This standard
volumetric flow rate was converted to an actual volumetric flow rate at stack conditions.
Coal Additive Injection – Mercury Oxidizer
ADA’s proprietary M-Prove Technology increases the presence of halogens in the flue gas
which helps oxidize vapor-phase mercury and increase the capture efficiency of injected mercury
sorbents.
ADA installed a temporary coal additive system consisting of a pump skid and a chemical tote
containing ADA’s proprietary M-Prove coal additive (Figure 2). The skid and tote were located
on the turbine deck, adjacent to the coal feeder deck. The M-Prove additive was pumped from
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Figuree 2. M-Prov
ve Coal Add
ditive Pump
p Skid.
the tote throough the pum
mp skid and
through 3/88-in tubing innto coal feedder
3F using a 33/8-in stainleess steel lancce
inserted intoo a port on thhe top of thee
coal feeder.. The flow w
was metered by
the pump w
which was set to sufficienntly
treat the enttire unit.
RESULT
TS
Parametric testing was conducted bby
injecting thee sorbents att targeted
injection cooncentrationss. ADA’s
approach too parametric testing is to
begin low aand increase injection wiith
subsequeent test runs. Although not
n always achieved, thee intent for thhe Labadie U
Unit 3 tests w
was
to provid
de at least thrree mercury removal datta points neaar the MATS
S mercury em
missions lim
mit:
one abov
ve, one at, an
nd one below
w the emissio
on limit. Forr ease of com
mparison to baseline datta,
these testts were cond
ducted at as near
n to full unit
u load as ppossible for each test dayy.
Coal an
nd Ash Co
omposition
ns
Coal sam
mples were co
ollected dailly during thee first week oof testing (T
Table 2). Thee moisture
content of
o the coal saamples as-m
measured appeared to be hhigher than ttypical as-firred coal, whhich
might be a consequen
nce of how the
t coal sam
mples were haandled. Theerefore, the ccoal analysess
were corrrected to 27%
% H2O, whiich is typicall of the as-fiired coal. Baaseline ash ssamples had losson-ignitio
on (LOI) vallues in the raange of 0.24 wt% to 0.3 1 wt%.
Table 2. Coal Comp
positions (As-Received Basis, correected to 27%
% H2O).
Date
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6
Day 7
Day 8
Ash,
wt%
4.80
4.81
4.36
4.47
4.53
4.72
4.67
4.63
S, wt%
Btu/lb
B
Hg, lb/TBtu
C
Cl, µg/g
0.30
0.27
0.23
0.22
0.24
0.28
0.32
0.28
8,858
8
8,831
8
8,806
8
8,868
8
8,791
8
8,854
8
8,836
8
8,851
8
5.7
5.81
4.88
6.02
4.64
5.48
5.88
7.11
< 15
< 15
< 15
< 15
< 15
< 15
< 15
< 15
Baselin
ne Hg Testting
Measurem
ments of meercury at the economizerr outlet and sstack during baseline perriods are shoown
in Table 3. Baseline removal of mercury waas low, refleccting the low
w halogen coontent of the coal
ow amount of
o unburned carbon in th
he ash (meassured as LOII).
and the lo
6
Table 3. Baseline Hg Emission Rates and Removal.
Hg Emission Rate [lb/TBtu]
Date
Day 1
Day 2
Day 3
Econ.
8.8
7.4
9.1
Stack
6.6
5.4
9.9
Hg Removal Based on
CEMS [%]
Stack vs. Econ.
25.0
27.0
-8.8
Activated Carbon Parametric Testing
Both non-brominated PACs (PAC A and PAC B) showed similar performance for mercury
removal (Figure 5). PAC injection rate is shown in terms of lb/MMacf; M-Prove addition rate is
shown in terms of parts per million by weight (ppmw) of halogen added to the coal. When the
non-brominated PACs were combined with the M-Prove Technology, the amount of nonbrominated PAC required for a certain level of mercury reduction was cut in half, a very
significant reduction in PAC usage.
Figure 2. Comparison of Mercury Removal with and without 5 ppmw M-Prove
Technology as a Function of PAC Injection Rate.
100%
Hg Removal
80%
60%
PAC A
40%
PAC B
20%
PAC A with M‐Prove
PAC B with M‐Prove
0%
0
1
2
3
4
lb/MMacf PAC
5
6
7
Figure 6 compares the performance of brominated PAC (PAC C) with the combination of nonbrominated PACs plus the M-Prove additive. At a fixed PAC injection rate, the M-Prove
Technology plus non-brominated PAC performed the same as the brominated PAC.
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Figure 3. Comparison of Brominated PAC (PAC C) with M-Prove Technology (5 ppmw)
Plus Non-Brominated PAC.
100%
Hg Removal
80%
60%
40%
PAC A with M‐Prove
Pac B with M‐Prove
20%
PAC C
0%
0
1
2
3
4
lb/MMacf PAC
5
6
7
Halogen species in the flue gas affect mercury by oxidizing elemental mercury (Hg0), resulting
in increased gas-phase oxidized mercury (Hg2+), and by promoting adsorption on carbon,
resulting in more particulate-bound mercury (Hgp). Oxidation of Hg0 by halogens takes place in
the gas phase or on certain catalytic surfaces like carbon. In some boilers, there might be
sufficient unburned carbon in the fly ash to provide good mercury oxidation, although the
unburned carbon content of the fly ash at Labadie Unit 3 was very low and probably did not
contribute significantly to mercury oxidation.
At Labadie Unit 3, the fraction of Hg2+ in the flue gas increased from the APH inlet to the ESP
outlet (Figure 4). Low levels of Hg2+ were observed at the APH inlet and increased slightly with
M-Prove additive level: from about 10% Hg2+ to about 20% Hg2+. The M-Prove Technology
had a greater impact on mercury oxidation in the flue gas at the ESP outlet, particularly when
PAC was injected: Hg2+ increased to more than 80% at the ESP outlet with 2.2 lb/MMacf PAC
injection and M-Prove additive.
The fraction of oxidized mercury at the outlet of the ESP doesn’t provide sufficient insight into
the effectiveness of the additive to enhance capture in the ESP, since some of the mercury that is
oxidized is captured. Furthermore, at boilers with a wet flue gas desulfurization (FGD) scrubber
after the ESP, an important metric is the amount of elemental mercury at the ESP outlet, since
wet FGD scrubbers remove ~95% of the inlet oxidized mercury but little or no elemental
mercury. As long as the scrubber does not have significant re-emission of absorbed oxidized
mercury, the amount of Hg0 at the scrubber inlet is indicative of the stack emissions of mercury.
Figure 5 illustrates the ability of the M-Prove Technology in conjunction with carbon to drive
elemental mercury concentrations to low levels at the ESP outlet.
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Figure 4. Mercury Speciation as a Function of PAC Addition and M-Prove Technology
Rates.
100
80
ESP
Outlet
% Hg2+ 60
40
20
APH Inlet
0
0
2
4
6
M‐Prove Rate, ppmw
APH Inlet
No PAC
1.1 lb/MMacf
2.2 lb/MMacf
8
Figure 5. Elemental Mercury Concentrations as a Function of PAC Addition and M-Prove
Technology Rates.
Elemental Hg , lb/TBtu
8
7
APH Inlet
6
5
4
3
ESP
Outlet
2
1
0
0
2
4
6
M‐Prove Rate, ppmw
APH Inlet
No PAC
1.1 lb/MMacf
8
2.2 lb/MMacf
9
Stack Testing Results
The combination of M-Prove Technology and non-brominated PAC was able to reduce stack
emissions at Labadie below the MATS limit of 1.2 lb Hg/TBtu. Data collected during the
Method 30B test runs are summarized in Table 4. There is good agreement between the Method
30B mercury measurements and ADA mercury CEMS measurements. The relative accuracy
between the Method 30B and Hg-CEMS measurements were all within an absolute difference of
1.0 µg/m3 as well as within 15%. A relative accuracy of less than 20% is considered good
agreement. There does not appear to be a bias, high or low, between the CAE and ADA data
sampled.
Table 4. Comparison of Method 30B and CEMS Mercury Measurements.
Test Condition
Reagent
M-Prove Coal
Mercury
Injection Ratio
Additive
(Method 30B)
[lb/MMacf]
Rate,1 ppmw
[lb/TBtu]
Mercury
(Hg-CEMS)
[lb/TBtu]
Baseline Day 1
0.00
0
6.652
6.93
Baseline Day 2
0.00
0
5.592
5.03
0.57
3
3.29
3.4
1.11
3
2.26
2.4
2.25
3
1.13
1.2
1.11
7
2.26
1.9
2.22
7
1.28
1.1
Injection of PAC B +
M-Prove Day 3
Injecion of PAC B +
M-Prove Day 4
1
Parts per million of halogen added to coal
Averaged Method 30B data for all runs of that day. Based on Fc Factor.
3
Averaged CEMS total vapor-phase emission rate data from beginning of first run through last run of that day. Based on Fc Factor.
2
CONCLUSIONS
ADA’s M-Prove Technology enhanced the effectiveness of non-brominated PAC at Labadie
Unit 3, cutting in half the amount of non-brominated PAC required for a given level of mercury
removal. The performance of M-Prove Technology plus non-brominated PAC was comparable
to the performance of a brominated PAC. For plants that sell fly ash, reducing the amount of
PAC in the fly ash can enhance the byproduct value of the ash.
The combination of M-Prove Technology and PAC decreased the amount of elemental mercury
at the ESP outlet dramatically. For plants that have flue gas desulfurization scrubbers
downstream of the ESP, low levels of elemental mercury at the scrubber inlet generally translate
to low mercury stack emissions.
Very low levels of M-Prove additive were needed to give good mercury removal. Such low
levels reduce long-term corrosion risks to cut maintenance and repair costs and to enhance
system reliability. M-Prove Technology also reduces additional halogen that could leach from
fly ash or be present in the wastewater treatment system of a scrubbed unit.
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Key benefits of M-Prove are as follows:

Effective at extremely low chemical treatment rates, typically eight to ten times lower
than those used with bromine;

Significantly reduces the balance-of-plant risks, including corrosion, attributed to
other halogen-based coal treatments;

Minimizes ancillary halogen emissions in the stack, fly ash, and wastewater;

Reduces sorbent consumption for ACI systems;

Facilitates enhanced mercury removal by other downstream pollution control devices
(ESP, FF, FGD);

Minimal capital investment.
REFERENCES
1. Kolker, A.; Senior, C.L.; Quick, J.C. Mercury in coal and the impact of coal quality on
mercury emissions from combustion systems. Applied Geochemistry, 2006, 21, 1821-1836.
2. Vosteen, B.W.; Kanefke, R.; Köser, H. Bromine-enhanced Mercury Abatement from
Combustion Flue Gases - Recent Industrial Applications and Laboratory Research. VGB
Power Tech, March, 2006, pp. 70-75.
3. Kolker, A.; Quick, J.C.; Senior, C. L.; Belkin, H. E. Mercury and halogens in coal- Their
role in determining mercury emissions from coal combustion. USGS Fact Sheet 2012-3122,
2012.
4. Dombrowski, K.; Aramasick, K.; Srinivasan, N. Balance of Plant Impacts of Bromine for
Mercury Control. Presented at Air Quality IX Conference, Arlington, VA, October 2013.
5. Dombrowski, K.; Srinivasan, N. Bromine Balance of Plant Study. Presented at Reinhold
NOx Conference, Salt Lake City, UT, February 18-19, 2013.
KEYWORDS
Mercury Control, Activated Carbon, Halogen
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