Energy & Fuels XXXX, xxx,
A
Experiences in Long-Term Evaluation of Mercury Emission
Monitoring Systems
Chin-Min Cheng,* Hung-Ta Lin, Qiang Wang, Chien-Wei Chen, Chia-Wei Wang,†
Ming-Chung Liu,† Chi-Kuan Chen,† and Wei-Ping Pan
Institute for Combustion Science and EnVironmental Technology, Department of Chemistry, Western
Kentucky UniVersity, 2413 NashVille Road, Bowling Green, Kentucky 42101
ReceiVed NoVember 10, 2007. ReVised Manuscript ReceiVed May 5, 2008
Six mercury continuous emission monitoring (CEM) systems provided by two leading mercury (Hg) CEM
system manufacturers were tested at five coal combustion utilities. The linearity, response time, day-to-day
stability, efficiency of the Hg speciation modules, and ease of use were evaluated by following procedures
specified in the Code of Federal Regulation Title 40 Part 75 (40 CFR Part 75). Mercury monitoring results
from Hg CEM systems were compared to an EPA-recognized reference method. A sorbent trap sampling
system was also evaluated in this study to compare the relative accuracy to the reference method as well as
to Hg CEM systems. A conceptual protocol proposed by U.S. EPA (Method 30A) for using an Hg CEM
system as the reference method for the Hg relative accuracy (RA) test was also followed to evaluate the
workability of the protocol. This paper discusses the operational experience obtained from these field studies
and the remaining challenges to overcome while using Hg CEM systems and the sorbent trap method for
continuous Hg emission monitoring.
Introduction
Mercury (Hg) is one of the 189 hazardous air pollutants listed
in the 1990 Amendments to the Clean Air Act. Coal-fired power
generation is the largest anthropogenic source of Hg in the U.S.
and is responsible for the annual release of approximately 50
tons of Hg into the atmosphere.1,2 The U.S. Environmental
Protection Agency (EPA) announced the Clean Air Mercury
Rule (CAMR) in 2005, which capped mercury emissions from
coal-fired power utilities and established a mercury cap-andtrade program. Although the rule was vacated by the District
of Columbia Circuit in February 2008, a more restrictive Hg
emission regulation is expected to be implemented by the EPA
using Maximum Achievable Control Technology (MACT)
standards.
To ensure the Hg emission reduction goals can be met, the
implemented mercury emission regulation will also require
affected electric utility units to continuously monitor mercury
(Hg) mass emissions using available monitoring techniques [e.g.,
Hg continuous emission monitoring (CEM) system and sorbent
trap method]. Any applied monitoring system will be subject
to restrictive certification and quality assurance/quality control
(QA/QC) procedures, which are currently described in the 40
CFR Part 75.
The Institute for Combustion Science and Environmental
Technology (ICSET) at Western Kentucky University (WKU),
* To whom correspondence should be addressed. E-mail: chin-min.cheng@
wku.edu.
† Current address: Department of Chemical Engineering, Ming-Chi
University, Taipei, Taiwan.
(1) U.S. Environmental Protection Agency. Mercury study report to
Congress. Volume II: An inventory of anthropogenic mercury emissions
in the United States. Technical Report, EPA-452/R-96-001b, Office of Air
Quality Planning and Standards, Washington, D.C., 1996.
(2) Brown, T. D.; Smith, D. N.; Hargis, R. A., Jr.; O’Dowd, W. J. J.
Air Waste Manag. Assoc. 1999, 49, 628–640.
in conjunction with Electric Power Research Institute (EPRI)
and Illinois Clean Coal Institute (ICCI), conducted six field
studies to evaluate using the Hg CEM systems and sorbent trap
method for measuring Hg emissions.
The study was carried out under a wide variety of coal-fired
power generation operation conditions. Two types of pulverized
coal (PC) boilers (i.e., wall-fired and cyclone) and a circulating
fluidized bed (CFB) combustion system were studied. Bituminous, powder river basin (PRB) sub-bituminous, and lignite
coals were burned by these tested facilities. Combinations of
various air pollution control devices were also included in the
study to provide comprehensive evaluation results.
In these field studies, the initial certification and data quality
assurance and quality control (QA/QC) procedures specified in
the 40 CFR Part 75 were carried out to evaluate the capability
of the tested Hg CEM systems to pass compliance requirements,
as well as the data integrity and system stability during
operation.
Relative accuracy (RA) of the test Hg CEM systems was
determined using the Ontario Hydro (OH) method. A sorbent
trap method for monitoring the Hg emission was also tested
following the procedures and data QA/QC criteria specified in
the Appendix K of 40 CFR Part 75. In addition, a conceptual
protocol (Method 30A) proposed by EPA for using Hg CEM
systems as a reference test method for conducting RA testing
was also carried out to evaluate the workability of the protocol.
During the field study 1 (FS-1), stratification tests, using NOx,
SO2, and O2 as substitutes for Hg, were also performed.
This paper discusses the results obtained from instrument
certification and data QA/QC verification tests, relative accuracy
tests, and emission monitoring. This paper also discusses the
10.1021/ef7006744 CCC: $40.75  XXXX American Chemical Society
Published on Web 07/22/2008
B
Energy & Fuels, Vol. xxx, No. xx, XXXX
Cheng et al.
Table 1. Configurations of Test Sites
field test
number
facility
FS-1
FS-2
FS-3
FS-4
FS-5
FS-6
boiler
types
APCD
configurations
Hg in
coala (µg/g)
Hg in stack
gas (µg/dscm)
CEM
participatedb
14 ( 3f,g
0.19 ( 0.15f
1.9 ( 0.3f
2.3 ( 1.6g
0.70 ( 0.16g
1.41 ( 0.18g
NA
A2 and B2
B1
A1
boiler
fuel types
capacity
(MWe)
T
S
C
unit 4
unit 123
unit 31/32
lignite
bituminous
bituminous
650
115
90
PCc
CFBh
Cyclone
ESPd + FGDe
SNCRi + FFj
SCRk + ESP + FGD
0.20 ( 0.04
0.067 ( 0.009
0.072 ( 0.016
S
C
M
unit 4
unit 33
unit 2
bituminous
bituminous
PRBl
173
205
140
Cyclone
PC
PC
SCR + ESP + FGD
SCR + ESP + FGD
ESP
0.087 ( 0.007
0.068 ( 0.015
NA
A1
B1
A3 and B3
a Dry based. b CEM A1 and B1 were provided by ICSET, and the others were provided by the facilities. c Pulverized coal. d Electrostatic precipitator.
Flue gas desulfurization. f Non-ozone season. g Ozone season. h Circulation fluidized bed. i Selective noncatalytic reduction. j Fabric filter. k Selective
catalytic reduction. l Powder river basin.
e
Table 2. Concentration of Hg Gases Generated by CEM A1
Verified by OH and Sorbent Trap Methods
Hg concentration (µg/N m3)
Ctargeted ) 10.2 µg/N m3
RD (%)
Ontario Hydro
sorbent trap
9.3 ( 0.2
91.2
10.1 ( 0.8
99.0
Table 3. Evaluation of Hg Calibration Gases
Hg calibration
source
response
CEM
CEM A-1
CEM A-1
cylinder
cylinder
CEM B-3
CEM A-3
CEM
CEM
CEM
CEM
CEM
CEM
A-2
B-2
A-2
B-2
A-3
B-3
targeted
concentration
(µg/dscm)
response
concentration
(µg/dscm)
RD (%)
14.78
14.78
9.5
9.5
10.0
10.0
15.1 ( 0.8
19.8 ( 0.4
8.06 ( 0.16
9.12 ( 0.05
8.02 ( 0.07
12.7 ( 0.5
102
134
85
96
80
127
operational experience obtained from these field studies and the
remaining challenges to be overcome.
Experimental Section
Testing Site. Evaluation studies were conducted at five coal
combustion facilities. The configurations of each test unit are
summarized in Table 1. As shown in the table, the five units tested
in this study represented a wide range of operational configurations
in terms of fuels, boiler types, and combinations of air pollution
control devices (APCDs).
The Hg concentrations in the coal used by the test boilers ranged
from 0.067 to 0.2 µg/g. The averages of Hg concentration in the
flue gases of the test units during the evaluation period ranged from
0.19 to 14 µg/dscm. The results were determined by the OH method,
which is one of the EPA reference methods for flue gas Hg
measurement.
Hg Continuous Emission Monitoring (CEM) Systems. Six Hg
CEM systems were tested. Three of the systems were provided by
manufacturer A and are referred to as A1, A2, and A3 in the Results
and Discussion. The other three systems were provided by
manufacturer B and are referred to as B1, B2, and B3 in the
following section. Table 1 illustrates what Hg CEM system was
used in each field evaluation.
For a given Hg CEM system, the configuration includes an
atomic fluorescence spectroscopy Hg analyzer, a calibration unit
for providing elemental Hg gases, a sampling probe, a heated
umbilical line for transporting flue gas samples and sampling
parameters, and a gas conditioner for converting ionic Hg to
elemental Hg in the flue gas and for removing acidic gas
components.
All Hg CEM systems used fast loop, inertial type sampling
probes allowing for ash-free flue gas to be extracted from the stack.
This type of probe extracts the flue gas by a stream of compressed
air passing through an eductor installed at the exit end of the flue
gas sampling loop. The movement of the compressed air creates a
pressure differential across the eductor, which generates an axial
flue gas flow in the sampling loop with high velocity. After being
extracted, flue gas containing fly ash particles continue to travel in
a straight direction. A sample stream is withdrawn from the main
flue gas flow by a vacuum created by a second eductor at a very
low filter face velocity, which separates the sample stream from
fly ash. High velocity axial gas flow and low radial velocity prevent
particles entrained in the flue gas from depositing on or penetrating
into the porous filter wall. The sample stream was diluted with
zero air before it was transported to the analyzer. The dilution ratios
of the participating Hg CEM systems ranged from 28-41, which
were adjusted on the basis of calibration results.
For Hg CEM systems from manufacturer A, the diluted gas
sample was transported through a heated umbilical line (180 °C)
to a conditioner located more than 100 m away from the sampling
probe. In the conditioner, the gas sample was separated into two
streams: i.e., Hg(0) and Hg(T). The Hg(0) stream delivered a gas
sample containing only elemental Hg and other insoluble components to the analyzer after passing through a scrubber, in which
ionic Hg and acidic components in the gas were removed. The
Hg(T) stream passed a catalyst tube where ionic Hg was reduced
to elemental Hg at a temperature of 700 °C. After removing acidic
components in another scrubber, the Hg(T) stream was sent to the
analyzer. A chiller (5 °C) was used to remove excess moisture in
the conditioned sample gas. For Hg CEM systems from manufacturer B, the sample conditioning unit was located in the probe
assembly. The flue gas sample was immediately treated after being
diluted. Instead of using deionized water, the system used sorbent
material to remove acidic components from the sample stream.
Both A and B Hg CEM systems used atomic fluorescence
spectroscopy as the Hg detector. The difference between the two
types of analyzers was the application of gold traps. Two parallel
gold traps were used by the analyzers in the Hg CEM systems from
manufacturer A to selectively capture the elemental mercury in the
sample gas prior to the detector. Elemental mercury in the sample
gas formed an amalgam with the gold surface. Once loaded, the
trap was heated and flushed to the detector with ultra pure argon.
One complete adsorption and desorption cycle took approximately
150 s. In the case of Hg CEM systems from manufacturer B, flue
gas was continually delivered into the detector without passing
through gold traps and, therefore, generated continuous Hg readings.
The B Hg CEM systems were set to provide a 5 min average
reading every 1 min.
Only compressed air was required to operate the Hg CEM
systems from manufacturer B. In the case of the A Hg CEM
systems, in addition to compressed air, supplies of ultra high purity
argon and deionized water were also required.
Sorbent Trap Mercury Sampling System. A sorbent trap
sampling system provided by Apex Instruments, Inc. (FuquayVarina, NC) was used in this study. A known volume of dry flue
gas was extracted from the stack through paired sorbent traps with
a constant flow rate of 0.2-0.6 L/min. Each trap consisted of three
sections of activated carbon. The first section was designed to
capture Hg in the flue gas. The second and third sections were used
for sampling and analytical QA/QC purposes. After sampling, each
section of the trap was analyzed for Hg using an RP-M324 mercury
analyzer (Ohio Lumex, OH). The analyzer decomposes the sorbent
with a known mass at a temperature between 600 and 800 °C. The
EValuation of Mercury Emission Monitoring Systems
Energy & Fuels, Vol. xxx, No. xx, XXXX C
Table 4. Summaries of Hg CEM Setup, Certification, and Data Validation Results
CEM
CEM
CEM
CEM
A-1 (FS-1)c
B-1 (FS-2)
A-2 (FS-1)
B-2 (FS-1)
CEM A-1 (FS-3)
CEM B-1 (FS-4)
CEM A-1 (FS-5)
total study
duration
setup/ adjustment
durationa (day)
95
72
95
95
5
21
14
17
53
68
68
system down
timeb (day)
7 day
calibration
error check
Observed from Field Studies 1 and 2
68/90
NA
10/51
2/24
35/74
0/2
32/71
1/2
Observed from Field Studies 3, 4, and 5 after Modification
2
0/51
2/2
3
0/65
2/2
2
2/66
2/2
linearity
check
system
integrity
check
cycle time
check (min)
NA
2/2
4/4
5/6
NA
1/1
2/2
2/3
NA
13
12.5
8
1/1
1/1
1/1
1/1
1/1
1/1
10
8
10
a The duration is the days required since the system was powered up to the day when the first test of the 7 day calibration error check was started. It
excludes the time required for umbilical line installation and infrastructure construction. b System down time reports the days that the system was
brought offline for maintenance. c FS ) field study.
Hg concentration was determined by measuring the mercury vapor
released during the decomposition using a Zeeman atomic adsorption spectroscopy.
Sampling Location. For a given test, the sampling location for
the Hg CEM system was above the nearest flow restriction by a
distance of greater than 10 duct diameters and away from the flue
gas outlet by at least 22 duct diameters. The gas sample (treated or
untreated depending upon the CEM systems) was transported to
the analyzer through a heated umbilical line (100-125 m in length).
While carrying out OH method sampling, the stack gas was
collected at either 90° or 180° from the Hg CEM sampling probe
with the exception of field test 5 (FS-5). In the FS-5 test, the flue
gases were extracted from the two flue gas desulfurization (FGD)
unit outlet ducts for OH method sampling.
Certification Tests. A series of inertial certification tests
described in the Appendix A of 40 CFR Part 75 were carried out
(with the exception of FS-6), which included a 7 day daily
calibration error check, linearity check, system integrity check, and
cycle time test. The relative accuracy of a given evaluated Hg CEM
system (except for FS-6) with respect to the OH method results
was also determined. A total of 12 runs of paired OH method
sampling were carried out for the relative accuracy test. The data
QA/QC procedures provided in Appendix B of Part 75 were also
followed to evaluate the stability of the CEM systems.
Inertial Certification Test. Detailed procedures for each test can
be seen in Appendix A of 40 CFR Part 75. In summary, the 7 day
calibration error test was to evaluate the accuracy and stability of
the calibration of the Hg gas monitor over an extended period of
operation. For the linearity check test, three concentration levels
of elemental Hg gases, which were chosen based on the fuel burned
by the coal combustion utility, were measured by an Hg CEM
system to determine whether the response of a gas monitor is linear
across its range. Instead of using elemental Hg, three levels of ionic
Hg gases were used in the system integrity check to verify the
effectiveness of the sample gas conditioning unit. The cycle time
test was to measure whether a gas monitoring system is capable of
completing at least one cycle of sampling, analyzing, and data
recording every 15 min.
RelatiVe Accuracy Test. The relative accuracy (RA) test was
performed using the OH reference method. Detailed RA test
procedures are described in Appendix A of 40 CFR Part 75. In
short, while an RA test was conducted in this study, 12 runs of
OH method samplings were carried out within a period of 96
consecutive unit operating hours. The evaluated Hg continuous
monitoring system remained operating during the OH method
sampling. No system adjustment was performed during the RA test.
After the RA test, at least 9 sets of the OH method data were chosen
based on the criteria specified in the procedures and those data were
used as the reference values. A total of 9-12 sets of Hg monitoring
results from the test CEM system, which were the mean values of
the Hg readings collected from perspective OH method sampling
periods, were compared to the reference values. If the instrument
passed the RA test, the bias test was performed to determine whether
the monitoring system was biased low with respect to the OH
reference method.
Data QA/QC Procedures. Three types of tests (i.e., daily
calibration error check, weekly one point system integrity check,
and linearity check) were performed on the test CEM after the first
RA test was completed. Testing procedures were very similar to
the tests described in the initial certification tests.
Instrumental Reference Method (EPA Method 30A). The procedures described in the conceptual method using the Hg CEM system
as a reference method for conducting relative accuracy testing were
evaluated in field study 1 (FS-1). Both CEM A2 and B2 were used
as the IRM systems.
Results and Discussion
Calibration Gas Evaluation. The National Institute of
Standards and Technology (NIST)-traceable gas standards and
protocols for mercury gas generators and cylinders were not
available when the studies were conducted. To evaluate the Hg
gas provided by the calibration units of the CEM A and B
systems, a series of comparison tests were performed. Two
concentration levels of Hg gas cylinders provided by Spectrum
Gases, Inc. (West Branchburg, NJ) were also used. First, the
Hg gas from the CEM A2 calibration unit was evaluated by
three runs of the OH method test. The concentration was also
evaluated by the sorbent trap method. The results are summarized in Table 2, where the relative deviation (RD, %) is
calculated by the following equation:
RD (%) )
Cmeasured
× 100%
Ctargeted
(1)
The results shown in the table have been corrected to 20 °C.
As can be seen in the table, the target values of the evaluated
Hg gas was 9.7 and 0.9% higher than the averages of the three
OH method and sorbent trap method measurements, respectively. The relative standard deviations of the three OH method
and sorbent trap method results were 2.2 and 7.9%, respectively.
The test illustrated that the Hg gas generated from the calibration
unit of the A1 Hg CEM system was somehow close to the
reference value.
The second test of the series consisted of measuring the Hg
gas from the A1 calibration unit using the A2 and B2 systems.
While doing measurements, the A1 Hg gas was delivered
through the calibration gas line, inertial filter, sample conditioner, heated sample delivery line, and the analyzer of the two
measuring Hg CEM systems. In addition, a Hg cylinder gas
(9.5 µg/N m3) provide by Spectra Gases (West Branchburg, NJ)
was also used. Results obtained from the study are listed in
Table 3.
D
Energy & Fuels, Vol. xxx, No. xx, XXXX
Cheng et al.
Table 5. Summary of Operation Difficulties of Mercury CEM Systems in Field Tests
period
problem observed
solutions
A1 in FS-1
7/30-8/8
8/12-9/25
1.
2.
1.
2.
3.
incorrect umbilical line temperature
no sample flow incorrect orifice differential pressure
unstable proportion valve operation
unstable loop flow rate
incorrect absolute venture pressure
replaced umbilical line
1. cleaned sampling loop
2. sampling loop and calibration line were found
reversely connected to the stingers.
A2 in FS-1
7/19-7/28
8/20-8/22
9/13-9/25
1. probe was not heated
2. low Hg2+ readings
incorrect probe pressure response
1. low Hg2+ conversion rate
2. low sampling flow rate
3. software crash
7/18-7/29
low calibration recovery
8/23-9/9
low calibration recovery
9/14-9/17
1. drifting issue of the analyzer
11/17-12/9
12/20-12/22
1.
2.
3.
1.
12/25-1/14
1. unstable and negative Hg readings
1. replaced heating elements
2. replace catalyst
brushed sampling loop frequently
1. replaced catalyst
2. replaced peristaltic pump tubings
3. upgraded instrument software
B2 in FS-1
B1 in FS-2
incorrect probe temperature high zero air background
low sample flow
unstable calibration gas flow rate
unstable calibration results and Hg readings
It was found that the response of the A2 system to the A1
Hg gas was within 2% of standard deviation. The response of
the B2 system to the A1 Hg gas was 34% higher than the target
value. Using the Hg gas cylinder, the response of the B2 system
was closer than the response from the A2 system. According
to the test results, in general, the response from Hg CEM
systems provided by manufacturer B were systematically higher
than the results from the A systems.
The observed discrepancy was due to the concentration
bias between the Hg calibration gases generated from the
two units. At a specified concentration, the calibration gas
generated from the A calibration units was higher than the
Hg gas provided by the B units. The conclusion is illustrated
by field study 6 (FS-6), in which Hg gases from the
calibration units of A3 and B3 were measured against each
other. As can be seen in Table 3, an approximate 20% of
disagreement was observed between the tag value and the
response of the measuring Hg CEM.
Mercury CEM System Setup, Certification, and Operation. The observations during the system setup and initial
certification period are discussed. Table 4 provides an overview
of the evaluation results from four Hg CEM systems (A1, A2,
B1, and B2). It was found that during the FS-1 and FS-2 studies,
except for CEM A1, the systems required at least 2 weeks for
setup and performance adjustment before the first day of the 7
day calibration error check began. The setup and adjustment
duration did not include the time spent on umbilical line
installation and infrastructure construction (e.g., compressed and/
or argon gas lines, deionized water supply, power supply, and/
or instrument shelter).
Although the A1 system started the inertial certification test
after 5 days of setup and adjustment, a combination of multiple
operational difficulties, including heated umbilical line malfunc-
1.
2.
3.
4.
5.
6.
7.
1.
2.
1.
replaced probe stinger
replaced heating element
replaced calibration unit
replaced lamp
added a humidifier in the calibration gas path
cleaned umbilical line
replaced catalyst
replaced inertial filter
adjusted calibration unit
controlled reaction cell temperature
1.
2.
3.
1.
2.
1.
2.
3.
replaced probe
cleaned umbilical line
removed blockage found in the S2 valve in the analyzer
replaced the lamp with a heating element
upgraded instrument software
installed nitrogen generator
used nitrogen as carrier gas for the analyzer
replaced the calibration unit
tion and probe blockage, prevented the A1 system from
participating in the test after approximately 2 weeks of operation.
The probe blockage was later found because of a reversed
connection of the sampling loop and calibration gas loop at the
heated probe tip.
A summary of the operational difficulties found during the
testing period can be seen in Table 5. As demonstrated in
the table, Hg CEM systems A2, B1, and B2 all encountered
multiple system malfunctions during the first two field studies,
i.e., FS-1 and FS-2. In the case of the A2 system, the catalyst
in the sample conditioner was replaced twice during the
testing period because low conversion efficiencies were
observed. However, no catalyst was replaced for the A1
system in the FS-3 and FS-5 studies, in which the system
was evaluated for a longer operational time. The observed
different lifetime of the catalyst might be due to the presence
of certain element(s) or/and compound(s) in the flue gases.
For example, the lignite coal used in the FS-1 study contained
a much higher Se concentration level (8.1 ( 0.9 µg/g)
compared to the Se contents (ranging from 0.08 to 0.2 µg/g)
in the coals used in the FS-3 and FS-5 studies. However, the
effect of flue gas compositions on the lifetime of the catalyst
needs further investigation.
In general, sampling loop blockage and contamination,
electronic parts failure, and malfunctions of the calibration unit
were the most commonly found problems causing unsatisfactory
calibration results. When the system encountered operational
difficulties, various corrective actions (e.g., parts replacement,
probe cleaning and maintenance, operational software update,
changing unit, to maintain the Hg CEM) were taken. Similar
operational difficulties were also found by the other testing
EValuation of Mercury Emission Monitoring Systems
Figure 1. Effect of lamp temperature on the stability of the B1 Hg
CEM system observed in the FS-2 study.
group. In a 10 month long-term field evaluation conducted by
EPA,3 similar operational problems were also reported.
In addition, significant drifting was observed on the B1 system
tested in the FS-2 study (Figure 1), where the average stack Hg
concentration was 0.35 µg/dscm. As shown in Figure 1, the
stack Hg readings fluctuate between 1.8 and -1.2 µg/dscm
within a 10 h period. The drifting and high background noise
problems were found to be correlated to the variation of lamp
temperature and inappropriate carrier gas for the Hg analyzer,
which both affected the intensity stability of the Hg lamp. The
problems were improved by using N2 as the carrier gas and
controlling the lamp temperature at 35 °C. The monitoring
results after the modification remained relatively constant at a
level of 0.4 µg/dscm (Figure 1), which was very close to the
OH method measurement results.
Before the modification, the system used purified compressed
air as the carrier gas, which might reduce the sensibility of the
analyzer because of a quenching effect. Using an atomic
fluorescence spectroscopy detector for Hg analysis is based on
the measurement of fluorescence emanating from excited
mercury atoms contained in the gas sample. However, fluorescence can be quenched quickly through the collision of excited
mercury atoms with other components of the sample gas,
especially oxygen, which affected the monitoring readings.
After modifications and maintenances in the FS-1 and FS-2
studies, the CEM A1 and B1 systems later participated in three
other field studies (FS-3, FS-4, and FS-5). Different from the
operational experiences of the FS-1 and FS-2 studies, both
systems required much less time (less than 3 days) to setup
and perform adjustments before precertification tests began.
During approximately 2 months of operation, no downtime was
required for system maintenance.
The operational stability of Hg CEM systems A1 and B1 after
modification are demonstrated by the daily calibration error
check results from the FS-3, FS-4, and FS-5 studies (Figure 2).
As shown in the figure, both A1 and B1 passed every daily
calibration error check performed in the FS-3 and FS-4 studies.
(3) U.S. Environmental Protection Agency. Long-term field evaluation
of mercury continuous emission monitoring systems: Coal-fired power plant
burning eastern bituminous coal and equipped with selective catalytic
reduction (SCR), electrostatic precipitator (ESP), and wet scrubber: Field
activities from November 2004 to September 2005. Final Report of EPA
Contract GS-10F-0127J, Office of Air Quality Planning and Standards Air
Quality Assessment Division, Research Triangle Park, NC, 2006.
Energy & Fuels, Vol. xxx, No. xx, XXXX E
In the FS-5 study, two problems (i.e., probe blockage and DI
water overflow) occurred during the 68 day operation, which
resulted in eight unsatisfactory daily calibration error checks.
The operational experiences obtained from these studies show
that the Hg systems provided by the two manufacturers were
still in the development stage during the testing period. Many
instrument parts had not yet been standardized or qualitycontrolled. The systems required a long time to install and
perform adjustments because both manufacturers needed to
search for suitable setups. The stability study demonstrates that
the Hg CEM systems were able to run without major maintenance for a period of time after the necessary modifications were
made.
Relative Accuracy and Bias Tests. During each field test,
two series of relative accuracy (RA) tests were performed on
every evaluated CEM system with the exception of the FS-5
and FS-6 studies. Only one series of RA tests was carried out
at the middle of the FS-5 study, and no test was performed on
the FS-6 study. For the other four field studies, the first series
of RA tests was conducted after the initial certification tests
were completed. The second series was carried out during the
last week of each field study. Results obtained from the RA
tests conducted in the four field tests are summarized in Table
6. The bias test results were also calculated and listed in the
table.
As shown in Table 6, the RA results of A2 and B2 were less
than 20%. In the other field studies, although the RA values
were greater than 20%, the evaluated Hg CEM systems also
passed the RA test because the differences between the mean
values of the CEM measurements and the OH method mean
values did not exceed 1.0 µg/dscm. According to the criteria
specified in the procedure, the results were acceptable when
the average of the Hg concentration measured by the OH method
during the RA test was less than 5.0 µg/dscm.
By comparing the CEM readings to the OH method results,
it was found that the two CEM systems provided by manufacturer A (i.e., A1 and A2) responded to lower Hg values, except
for the readings from the first series of the RA tests in the FS-3
study. In the five RA tests carried out at the CEM A1 system,
three sets of the results show the system was bias low. In the
case of the Hg CEM systems provided by manufacturer B, the
readings were consistently higher than the results from the OH
method.
The lower responses observed in the A Hg CEM systems
and higher responses observed in the B Hg CEM systems were
likely due to the bias caused by the Hg calibration gases
provided by the two systems. As discussed in the previous
section, the A Hg CEM systems were calibrated with a higher
concentration of Hg gas compared to the Hg gas provided by
the B systems with the same tag value. As a result, the A Hg
CEM systems responded with lower stack Hg monitoring results.
EPA Method 30A (IRM) Evaluation. An Hg CEM system
is required to meet a series of certification and data quality
assurance tests (specified in the EPA Method 30A) when it is
used as an instrument reference method for an RA test. Detailed
procedures for performing the tests are described in a draft
version of EPA Method 30A. Two Hg CEM systems, A2 and
B2, were used to evaluate how the two Hg CEM systems
respond to the tests specified in the method. The time required
to perform the IRM protocol was evaluated.
Table 7 summarizes the results obtained from the Hg0 and
Hg2+ calibration error check tests. As shown in the table, the
two evaluated CEM systems passed the two precertification tests.
The CEM B2 passed the Hg2+ system calibration error check
F Energy & Fuels, Vol. xxx, No. xx, XXXX
Cheng et al.
Figure 2. Daily calibration results of Hg CEM systems during operation: (a) B-1 at field study 2, (b) A-1 at field study 3, (c) A-1 at field study 4,
and (d) B-1 at field study 5.
Table 6. Results of RA and Bias Tests
field study
1
unit
A2
B2
series
1
2
1
OH method available runs
OHaveragea
CEMaveragea
RAb (%)
djc
|cc|d
conclusion
bias teste
9
11.89
10.65
20.0
1.23
1.14
pass
fail
9
15.24
13.67
18.1
1.57
1.18
pass
fail
9
11.89
11.88
14.1
0.01
1.67
pass
pass
STaveragef
RA (%)
dj
|cc|
conclusion
bias test
dCEMSg
12.92
23.7
-0.81
2.06
fail
17.93
16.0
-2.69
1.39
pass
pass
-4.26
12.92
23.7
-0.81
2.06
failed
-2.27
-1.04
2
Hg CEM
9
17.38
18.29
17.6
-0.91
2.14
pass
pass
2
3
4
5
B1
A1
B1
A1
1
2
1
System
10
0.12
NA
NA
NA
NA
NA
NA
12
0.10
0.34
311.5
-0.25
0.06
pass
pass
12
1.88
2.44
71.1
-0.56
0.16
pass
pass
0.04
143.4
0.12
0.11
pass
fail
0.30
2.20
35.1
-0.32
0.29
pass
pass
0.16
Sorbent Trap Method
17.93
NA
16.0
NA
-0.55
NA
1.39
NA
pass
NA
pass
NA
0.36
NA
2
1
2
1
11
1.93
1.64
33.9
0.29
0.36
pass
pass
12
1.41
1.74
38.5
-0.33
0.15
pass
pass
12
1.30
1.88
60.5
-0.58
0.21
pass
pass
12
0.70
0.49
40.6
0.21
0.08
pass
fail
2.21
16.8
0.04
0.34
pass
pass
-0.46
1.59
38.5
-0.18
0.27
pass
pass
0.15
1.35
60.55
-0.05
0.44
pass
pass
0.47
0.67
19.5
0.03
0.10
pass
pass
-0.18
Units of µg/dscm. b Relative accuracy ) ([difference arithmetic mean] + [confidence coefficient])/RM arithmetic mean × 100. c Difference
arithmetic mean. d Confidence coefficient. e Difference arithmetic mean should be less than the confidence coefficient to pass the bias test. f Average of
Hg monitoring results from the sorbent trap method. g CEMSaverage - STaverage.
a
on the second attempt after the system was recalibrated using
ionic Hg gases.
The system response time was determined by measuring the
time required for an evaluated system to respond 95% of the
stable value after the calibration gas was changed from a low
level to a high level. The results can be seen in Figure 2. The
response time for the CEM A2 and B2 was determined to be 5
and 4 min, respectively. Also shown in the figure is the time
required for each Hg CEM system to give a stable response at
each testing concentration level. It was found that the A2 system
responded to the elemental Hg gas approximately 2 times faster
than to the Hg2+ vapor. In the case of B2, no significant
difference was found.
The dynamic spiking (DS) test was performed on the tested
CEM systems after the systems passed both system calibration
error checks. The spiking Hg gas was delivered into the
sampling loop at a flow rate approximately 1/10 of the loop flow
rate. Two spiking levels were required. At the high-level spike,
the Hg concentration in the spiking ionic Hg vapor was
calculated so that the Hg concentrations in the spiked flue gases
EValuation of Mercury Emission Monitoring Systems
Energy & Fuels, Vol. xxx, No. xx, XXXX G
Table 7. Summaries of the Results Obtained from 3-pt Hg0 and Hg2+ System Calibration Error Checks
calibration gas level
certification
concentrationA
system
responseb
Hg0
A2
B2
A2
B2
absolute
difference|a - b|
calibration error
[|a - b|]/CS × 100
conclusion
Tcomplete (min)
low
mid
high
low
mid
high
3.7
11.09
18.47
4.00
10.00
18.00
3-pt
4.05
11.4
18.2
3.67
9.65
17.6
System Calibration Error Check
0.35
0.31
0.27
0.33
0.35
0.4
1.8
1.6
1.4
1.7
1.8
2.0
pass
pass
pass
pass
pass
pass
5
5
5
3
3
3
low
mid
high
low
mid
high
3.9
10.4
15.3
4.25
9.6
16.87
3-pt Hg2+ System Calibration Error Check
4.18
0.28
10.74
0.34
15
0.3
4.34
0.09
9.46
0.14
17.38
0.51
1.4
1.7
1.5
0.4
0.7
2.5
pass
pass
pass
pass
pass
pass
10
10
10
4
3
3
Table 8. Results Obtained from Dynamic Spiking Tests Performed on A2 and B2
target level
high
low
high
low
a
Qprobe
(lpm)
Qspike
(lpm)
actual Cspike value
(µg/dscm)
49.996
49.994
50.001
49.991
50.01
50.006
4.90
4.91
4.89
4.85
4.80
4.90
93.12
94.12
91.60
60.79
60.29
56.66
31.22
31.22
31.22
31.22
31.22
31.22
3.22
3.22
3.22
3.80
3.80
3.80
113.50
115.20
119.29
113.5
115.20
119.29
expected Css
(µg/dscm)
Cnative (mg/m3)
actual Css
(µg/dscm)
pre
post
average
percent spike
recoveryya
CEM A2
18.2
18.4
18.5
15.7
15.8
15.0
16.71
16.9
16.83
14.40
14.64
13.66
10.91
10.72
11.22
11.02
11.67
11.47
10.72
11.22
11.42
11.67
11.47
10.32
10.82
10.97
11.32
11.34
11.57
10.90
76.15
75.81
73.86
70.58
72.33
69.07
CEM B2
24.4
25.2
25.4
26.3
27.1
27.4
27.54
26.80
28.18
27.54
26.80
28.18
13.8
14.6
14.5
13.8
14.6
14.5
14.6
15.1
14.8
14.6
15.1
14.8
14.20
14.85
14.65
14.20
14.85
14.65
126.47
113.45
122.25
109.07
98.12
105.47
y has to be within 95-105% to meet spike recovery criteria.
were 1.8-2.0 times higher than the native concentrations.
During the low-level spike, the Hg concentration in the flue
gas was elevated to a level that was 1.4-1.6 times higher than
the native concentration.
Figure 3 shows the temporal trends of the responses from
the A2 and B2 systems during the dynamic spiking tests. As
Figure 3. Temporal responses of Hg CEM systems on the 3-pt Hg0
and Hg2+ error checks.
shown in the figure, the time required for a stable response by
each spike was after about 10 min for A2 and 5-7 min in the
case of B2. Results obtained from the test are summarized in
Table 8. In the table, the Css and Cnative values were the averages
of the three readings after the responses of the systems were
stable. As shown in the table, the spike recoveries of the A2
system ranged from 69 to 76%. In the case of the B2 system,
it was approximately 120% at the high span and 104% at the
low span.
Neither test system passed the dynamic spiking test based
on the resulting recoveries, which all exceeded the 5% criterion
with the exception of the low span at the B2 system. It is
suspected that the observed low recoveries for the A2 system
were due to an incorrect dilution factor, which is the ratio of
sampling loop flow rate to the flow rate of the spiking gas. The
loop flow rate was one of the probe operational parameters
calculated on the basis of the temperature and pressure differential across a venture. Unlike the B2 system, the venture of
the A2 system was not calibrated before conducting the dynamic
spiking experiment. It is necessary to consider the effect of the
humidity on the flow rate while performing venture calibration.
For the B2 system, the higher than target response was likely
due to analyzer drifting. It was found that the B2 system tended
to respond high at a higher concentration level even after
calibration. Because the oxidized Hg vapor was prepared from
a 1.06 × 10-6 M HgCl2 solution, the moisture content of the
Hg vapor increased as the spiking concentration increased.
A series of experiments were conducted to evaluate the effect
of moisture content in the calibration gas generated by a
HovaCal system on the response of the B2 system. The system
was first calibrated by performing filter zero to correct Hg(T)
H
Energy & Fuels, Vol. xxx, No. xx, XXXX
Figure 4. Temporal responses of Hg CEM systems during dynamic
spiking.
background and filter span to adjust the dilution factor using
its own calibration unit. After calibration, three levels of oxidized
Hg vapor were prepared from HgCl2 solutions with 4 HgCl2
concentrations, i.e., 2.12 × 10-6, 1.06 × 10-6, 5.03 × 10-7,
and 2.40 × 10-7 M. The moisture content in the generated Hg
vapor ranged from 2.9 to 36.04%. Figure 6shows the study
results. As can be seen, the response of the test CEM system
increased as the moisture content in the calibration gas increased.
Substitutes for Hg in Stratification Tests. To test for Hg
stratification, we must use the CEM system to measure the Hg
concentration at the 12 or fewer traverse points located as
specified in the EPA Method. However, the current probe design
does not allow easy movement of the sampling probe 12 times
within the required time. Therefore, a stratification test was
carried out in the first field test to investigate the potential of
using other gas components, e.g., SO2, NOx, O2, and CO2, or
CO, as a substitute.
The Hg concentration was measured by a CEM system
provided by PS Analytical (PSA) (Deerfield Beech, FL). Other
gas components (i.e., NOx, O2, CO2, SO2, and CO) were
measured by an integrated continuous, multi-emission monitoring system provided by Teledyne Instruments (San Diego, CA).
One 15 ft Apex Instrument Method 5 probe setup was used to
collect flue gas from the stack for both Hg and gas analyses.
Flue gas was transported to a wet-chemistry speciation module
immediately after being extracted from the stack using a 2 ft
insulated Teflon tube. The speciation modules sit on a fourwheel cart, which travels along with the probe. A 100 m heated
umbilical line (130 °C) was used to transport gas samples to
the analyzer after the speciation module.
Cheng et al.
Figure 6. Effect of moisture content in oxidized mercury vapor on the
response of the Hg CEM system.
Table 9. Correlation Coefficients of Hg(T) as a Function of
Other Flue Gas Componentsa
Hg concentration
a
SO2
CO2
NOx
O2
CO
0.63
0.72
0.49
0.69
0.42
Unit of µg/dscm.
Figure 4 shows the correlation between Hg(T) and five other
gas components (i.e., SO2, NOx, CO2, O2, and CO) in the stack
gas. Each data point represents the averages of the readings
collected from one traverse point. Readings were collected at
least 20 min before the move to the next traverse point. The
correlation coefficients are summarized in Table 9. As can be
seen, there is no significant correlation between Hg and other
gas components. The highest correlation coefficient was found
to be 0.72 for CO2 followed by O2 and SO2 (0.69 and 0.63,
respectively). None of the concentrations of the selected flue
gas components were found to be well-correlated (with a
correlation coefficient greater than 0.8) with the Hg concentration in flue gas (Figure 5).
Sorbent Trap for Hg Monitoring. Using a sorbent trap
method as an alternative to the Hg CEMS was also evaluated.
Both short (1-2 h) and long (5-16 days) term studies were
carried out. In the short-term study, paired sorbent trap sampling
was simultaneously conducted with the OH method sampling.
Comparisons of Hg monitoring results from short-term
sorbent trap sampling to the OH method and CEM system can
be seen in Table 6. Except for the FS-1 study, the sorbent trap
method passed all of the RA tests. In the 11 RA tests, the
averages of sorbent trap sampling results were all greater than
the results from the OH method, except the second series from
the FS-3 study. The average of 12 1-h runs sorbent trap sampling
Figure 5. Correlation between the concentrations of Hg and other flue gas components.
EValuation of Mercury Emission Monitoring Systems
Energy & Fuels, Vol. xxx, No. xx, XXXX I
Table 10. MDL of RP-M324 Hg Analyzer
averages of the Hg data from Hg CEM systems collected during
the same sorbent trap sampling period. Detailed sampling
duration and results can be seen in Table 11. For a given
sampling event, two sorbent traps were installed at the tip of
the sampling probe. Two types of sampling devices [i.e., regularand inertial-type probe (modified by ICSET)] were used to
investigate the effect of moisture and fly ash on sampling
operations.
As shown in Table 11, the results from the sorbent trap were
consistently about 1 order of magnitude lower than the CEM
average readings in the FS-2 study. Results from the sorbent
trap method seem to be more reliable compared to the results
from the Hg CEM system. In a 7 day sampling, the sorbent
trap collected approximately 4 dscm of stack gas. More than
100 ng of Hg was collected in a sorbent trap after each sampling,
which is well above the detection limit of the RP-M234 analyzer.
In the case of the Hg CEM B1, after dilution, the Hg
concentration in the sample gas delivered to the analyzer was
lower than 20 ng/dscm, which is very close to the background
noise of the instrument (about 4 ng/dscm).
Using a regular probe in FS-3, it was found that the sorbent
trap results were consistently higher than the Hg CEM results.
Unlike the FS-2 study, deposition of ash at the sorbent tip was
found. The deposition caused high vacuum during sampling and
interrupted the sampling several times. To eliminate the potential
ash effect, an inertial-type probe was used in the FS-4. The
sorbent trap results were found to be either slightly less (<0.3
µg/dscm) or slightly higher (<0.02 µg/dscm) than the Hg CEM
results. No deposition or operation difficulty was found.
A side-by-side comparison of the results from regular- and
inertial-type sampling setups was carried out at the FS-5 study.
No significant difference was found between the results from
the sorbent trap and the A1 Hg CEM system, with the exception
of the first series. One of the two sorbent traps showed a much
higher value, resulting in a higher relative deviation (>21%).
In the other two series, the sorbent trap results were greater
than the results from the A1 Hg CEM system (<0.32 µg/dscm).
No ash deposition was found in any of the traps after a weeklong sampling.
The relative deviation (RD, %) was calculated by dividing
the absolute value of the difference between the results from
run number
IR (ng)
1
2
3
4
5
6
7
standard deviation, S
MDL ) 3.143S
MDL ) t(n - 1, 1 - R ) 0.99) (S)
18.0
19.0
21.0
19.0
19.0
18.0
20.4
1.12
3.5
was 0.04 µg/dscm, which is much less than the OH method
(0.1 µg/dscm) and Hg CEM results (0.34 µg/dscm). It was likely
due to a low Hg concentration level in the flue gas. Short
sampling duration resulted in the amount of Hg adsorbed in
the sorbent trap being very close to the analytical detection limit.
The detection limit of the sorbent trap method during the RA
tests can be estimated by conducting the method detection limit
(MDL) measurement for the RP-M324 (Ohio Lumex, OH)
analyzer, which was used for sorbent trap Hg analysis in the
tests. MDL is defined as the minimum concentration of a
substance that can be measured and reported with 99%
confidence that the Hg concentration is greater than zero and is
determined from analysis of a sample in a given matrix
containing Hg.
To calculate MDL, the RP-M324 analyzer measured seven
prespiked sorbent traps, which all had an Hg concentration level
5 times higher than the estimated MDL. The estimated MDL,
which was 4 ng in the test, was 5 times that of the instrument
noise. The instrument MDL was then determined by multiplying
the standard deviation of the seven measurement results by a t
test value, which was 3.141, with a sample size of seven. The
MDL of the analyzer was determined to be 4 ng (Table 10).
For a given 1 h sorbent trap sampling run, approximately
0.025 m3 of dry flue gas was collected. As the result, the
detection limit of the sorbent trap method for a 1 h run was 0.2
µg/dscm, which was higher than the results obtained from the
OH method.
Long-term (5-16 days) sampling was carried out to evaluate
the operational feasibility of using the sorbent trap method.
Results from the sorbent trap method were compared to the
Table 11. Comparison of Long-Term Hg Monitoring Results from the Sorbent Trap Method and Hg CEM Systems
field study
2a,b
3a,b
4a,c
Hg CEM unit
B1
A1
B1
series
1
2
3
1
2
3
4
5
1
sampling duration (days)
sorbent trap
RDd (%)
spike recovery6 (%)
CEMS datag
dCEMSh
6
0.02
3.5 (pass)
48.4 (fail)
0.79
0.77
6
0.03
0.3 (pass)
4.0 (fail)
0.18
0.15
7
0.03
5.0 (pass)
19.2 (fail)
0.46
0.43
7
2.73
1.2 (pass)
93.7 (pass)
1.95
-0.78
7
2.43
5.0 (pass)
93 (pass)
1.95
-0.48
8
2.84
1.1 (pass)
86.8 (pass)
1.57
-1.27
10
3.66
5.8 (pass)
93.7 (pass)
1.98
-1.68
7
2.83
12 (pass)
84.8 (fail)
1.59
-1.24
7
1.71
6.6 (pass)
NAf
1.93
0.22
field study
5a-c
Hg CEM unit
A1
series
sampling duration (days)
CEMS datae
sampling device
sorbent trap
RDd (%)
spike recovery (%)
dCEMSf
1
7
0.23
regular
0.28 (passe)
86.8 (pass)
-0.05
2
inertial probe
1.85 (pass)
21.6
87.3 (pass)
-1.52
7
0.25
regular
0.53 (pass)
10
98.7 (pass)
-0.28
2
3
11
16
1.69
2.07
11.9 (pass) 35.9 (passe)
NAf
NAf
1.99
2.05
0.3
-0.02
3
inertial probe
0.67 (pass)
0.1
97.9 (pass)
-0.32
7
0.37
regular
0.51 (pass)
1.7
96.0 (pass)
-0.18
inertial probe
0.65 (pass)
12.1
100.5 (pass)
-0.28
a Unit of µg/dscm. b Regular sorbent trap probe was used for sampling. c Ash-free inertial probe was used. d RD (%) ) [(|C
trap 1 - Ctrap 2|)/(Ctrap 1 +
Ctrap 2)] × 100%. e The difference between the results from OH and sorbent trap methods was less than 1.0 µg/dscm. 6 Spike recovery ) [Cmeasured/
Cspiked] × 100%. f A spike test was not performed. g Averages of monitoring results during sorbent trap sampling. h CEMSaverage - STaverage.
J
Energy & Fuels, Vol. xxx, No. xx, XXXX
the two traps by the sum of the results from the two traps. On
the basis of the criteria, the RD should be less than 10% to
validate the sampling results. As can be seen in Table 10, in a
total of 14 sampling runs, 5 did not pass the criteria. Another
data QA/QC parameter specified in the Appendix K procedures
is spike recovery. For field sample analyses, the recovery is
required to be within 25% of the spiked concentration. It was
found that the recovery was far below the satisfactory criteria
with the exception of the FS-4 study. No spike test was
performed.
Conclusions
Results from a series of calibration gas comparison tests
showed that, with the same tag values, the elemental Hg gases
provided by the calibration units of the Hg CEM systems from
manufacturer A were approximately 20% higher than the
elemental Hg gases from the calibration units of manufacturer
B. The discrepancy of calibration gases resulted in the disagreements observed between the Hg monitoring results from the
Hg CEM systems of the two leading manufacturers when both
measured the same Hg source.
The observations from the FS-1 and FS-2 studies indicate
that the evaluated Hg systems provided by the two manufacturers were still in the development stage during the testing period.
Many parts had not yet been standardized or well-qualitycontrolled, which resulted in many part replacements and system
modifications. After replacing broken parts and performing
needed services, the Hg CEM systems provided by the two
manufacturers were able to be operated without serious maintenance (FS-3, FS-4, and FS-5).
The most challenging procedure in certifying an Hg CEM
system was conducting a system integrity check. During the
five field studies, a HovaCal system was used to provide
oxidized Hg vapors. The oxidized Hg gas setup was not
available for the tested Hg CEM systems provided by the two
manufacturers. Because the HovaCal system was not integrated
into the testing systems, extra cautions were taken while
performing the test. For example, the whole oxidized Hg vapor
line was kept above 180 °C to prevent the formation of “cold
spots”. Glass-coated connection unions were used for gas line
connections. The concentrations of the HgCl2 solutions used
for producing oxidized Hg vapors were verified by cold vapor
atomic adsorption spectroscopy before use. The delivering Hg
concentrations were corrected for temperature before being
compared to the CEM responses.
In summary, the Hg CEM system from manufacturer A
needed more attention and supplies to carry out the monitoring
task (e.g., supplies of ultra high purity argon and DI water,
peristaltic pump tubings, cleaning and replacement of gold traps,
and frequent lamp voltage adjustments). In the case of the Hg
CEM system of manufacturer B, the analyzer encountered a
noticeable drifting problem. It also had a less stable calibration
unit and user-friendly interface to operate the system.
When using a Hg CEM system as an instrumental reference
method for a RA test, dynamic spiking was the most crucial
and difficult step to certify the system. Factors such as dilution
Cheng et al.
factor measurement, variation of native concentration, loop flow
measurement, and stability of the instrument can greatly affect
the recovery of the dynamic spiking.
The criteria of passing the IRM depend upon the selection
of the calibration span, which depends upon the stack gas Hg
concentration (i.e., the native concentration). The higher the
calibration span, the larger the error allowed. In the case of the
FS-1 study, concentrations up to 40 µg/N m3 can be selected
as the calibration span, which allows 0.8 and 2 µg/dscm of error
for the 3-pt system Hg0 calibration error and 3-pt system Hg2+
calibration error checks, respectively. For utilities in the other
four field studies, which all had native concentrations less than
5 µg/N m3, the differences between the reference and measured
values were be less than 0.2 or 0.5 µg/N m3 for the 3-pt system
Hg0 calibration error and 3-pt system Hg2+ calibration error
checks, respectively.
Using SO2, CO, CO2, or NOx as the substitute for in the Hg
stratification test was not feasible. There was no strong
correlation between the concentrations of Hg and the other four
selected gas components in the duct.
Results from sorbent trap studies showed promise for using
this technique as an alternative to the Hg CEM for coal
combustion utilities. However, deposition of ash at the tip of
the sorbent traps was found in the FS-3 study, which interfered
with the sampling operation and possibly resulted in the bias
results. Further systematic investigation is desired to further
explore the feasibility of using this sorbent trap method with
respect to different sample digestion and analytical methods,
sampling devices, long-term operations, and comparison of longterm monitoring results with Hg CEM.
Acknowledgment. This report was prepared by Chin-Min Cheng
and ICSET of Western Kentucky University with support, in part,
by grants made possible by the Illinois Department of Commerce
and Economic Opportunity through the Office of Coal Development
and the Illinois Clean Coal Institute. Neither Chin-Min Chen and
ICSET of Western Kentucky University, nor any of its subcontractors, nor the Illinois Department of Commerce and Economics
Opportunity, Office of Coal Development, the Illinois Clen Coal
Institute, nor any person acting on behalf of either (A) makes any
warranty of representation, express or implied, with respect to the
accuracy, completeness, or usefulness of the information contained
in this report, or that the use of any information, apparatus, methods,
or process desclosed in this report may not infringe privately owned
rights; or (B) assumes any liabilities with respect to the use of, or
for damages resulting from the use of, any information, apparatus,
method or process disclosed in this report. Reference herein to any
specific commercial product, process, or service by trade name,
trademark, manufacturer, or otherwise does not nesessarily constitute or imply its endorsement, recommendation, or favoring; nor
do the views and opinions of authors expressed herein necessarily
state or reflect those of the Illinois Department of Commerce and
Economic Opportunity, Office of Coal Development, or the Illonois
Clean Coal Institute. The authors acknowledge valued assistance
from Mr. Martin Cohron during the field studies. The authors thank
Spectrum Gases for providing Hg calibration gas cylinders.
EF7006744