# RELATIVE ACCURACY TESTING

**OF AN X -**  **RAY BASED CONTINUOUS MERCURY**  **MONITOR**

**Contract No. DACA42 -**  **03 -**  **P -**  **0239 (TASK 2**  **)**

**FINAL REPORT**

**Prepared for** 

### U. S. Arm **y Corps of Engineers Engineer Research and Developm**  **ent Center Construction Engineering Research L**  **aboratory**

**Submitted By** 

### Cooper Environ **me ntal Services**  10170 SW Nimbus Ave Suite H5 Portland, Oregon 97223
September 30 , 2003

# RELATIVE ACCURACY TESTING OF AN X ****

**RAY BASED CONTINUOUS MERCURY MONITOR** 

**Contract No. DACA42 -**  **03 -**  **P -**  **0239**

**(TASK 2)**

**FINAL REP ORT** 

**Prepared by B.E. Johnsen, J.A. Cooper, M.Nakanishi, S. Fry, D. Barth, P. Ginochio** 

Cooper Environmental Services 11120 SW 124 th Place Portland, OR 97223

**Submitted to K. J. Hay**  U. S. Army

Corps of Engineers Engineer Research and Development Center Construction Engineering Research Laboratory P. O. Box 9005, CN
- E, Champaign, IL 61826
- 9005

September 30, 2003i



### EXECUTIVE SUMMARY Mercury has been identified by

the EPA as their air toxic of greatest concern (EPA, 2000 )

. Accordingl y, the EPA and Bush administration have proposed legislation such as the Clear Skies Act and Utilities MACT which have focused on mercury reduction and monitoring. To date, however, limited success with mercury Continuous Emissions Monitors (CEMs) has been achieved. Coop er Environmental Services (CES) was contracted b y the U.S. Army Corp of Engineers to test their Xact continuous mercury monitor during an EPA sponsored test at a coal

- fired power plant (CFPP) . The Xact extracts a representative emissions sample which is th en drawn through a reactive filter. The filter is advanced to an x

- ray fluorescence analyzer where total mercury mass is determined. Results are reported every 20 to 30 minutes with detection limits of better than 0.1 micrograms per dry standard cubic met er. For the tests, CES first evaluated the filter trapping efficiency and precision using a Mercury Speciation Cassette (MSC). The MSC consists of a stack of filters which measure s oxidized and elemental mercury

. The MSC tests were designed to compare the capabilities of the filter based approach relative to the EPA’s standard Ontario

- Hydro (OH) method for measuring mercury

. In general, the Xact and MSC performed very well relative to the OH , showing accuracy and precision that were on the same order as the standard method. Test results showed that: 1) The Xact total mercury relative accuracy

was 25%, which was essentially the same as the 22% RA between duplicate OH test runs. 2) The MSC total mercury relative accuracy

was 12% relative to the OH method , substantially

less than the 20% required for method equivalency

. 3) The MSC fractional mercury speciation was in excellent agreement with OH results showing an average of onl y 4% difference in the percent elemental mercury for all 12 OH runs. 4) The MSC relative preci sion was 30% better than the precision listed in the OH method for measurements less than 3 μg/dscm. This first Xact unit did develop cold spots which caused occasional water condensation and inconsistent results. This problem is being mitigated with more uniform heating. One of the largest problems for all candidate methods was the limited accuracy and precision of the EPA standard method at low mercury concentrations. C oncentrations for all but one OH run were below 3 μg/dscm. The OH has a listed precis ion of 34% under these low concentrations (ASTM, 1999 ) limiting its ability to evaluate the relative accuracy of the mercury

CEMs. In addition, mercury was almost exclusively

in the elemental form for all but one run. Since many C EM approaches are severel y impacted by oxidized mercury , the tests have limited applicability for CFPP which have significant concentrations of oxidized mercury

. Although additional testing is needed at varying mercury concentrations and speciation levels, the EPA tests demonstrat ed the feasibility of the Xact filter based approach to measure mercury in coal

- fired power plant emissions.1



### INTRODUCTION Cooper Environmental Services (CES) was contracted b y the U.S. Arm y C orp of Engineers to test their filter

- based Xact continuous mercury monitoring approach at an EPA sponsored test . The test, under the direction of the Midwest Research Institute (MRI) , was designed to evaluate various monitoring approaches for measuring mercury emissions from a coal

- fired power plant. MRI’s test occurred in two phases , an initial phase in May

2003 and a follow

- up phase in July

. During each phase, a series of twelve EPA standard Ontario

- Hydro (OH) reference method runs were conducted to evaluate the accuracy of candidate methods (Table 1)

. During the M RItests , CES conducted a series of grab

- sample test runs using its Mercury Speciation Cassette (MSC ). The purpose of the MSC testing during the first phase was to evaluate CES’ proprietary filter for trapping and speciating capabilities as well as its use as an alternative t o the EPA standard method (OH)

. During the second phase, CES conducted precision testing of the MSC and tested its Xact mercury monitor relative to the OH reference method. The Xact is a true continuous emissions monitor (CEM) for mercury and reports total mercury concentrations every 20 to 30 minutes

. This report summarizes the performance s of CES’ MSC and Xact relative to the EPA standard Ontario

- Hydro method

. **MERCURY SPECIATION CASSETTE TESTING** The MSC consists of a filter stack wi thin a Teflon coated stainless steel filter holder (Figure 1). The first filter traps particulate and gas phase reactive mercury . This filter is followed b y a filter for trapping elemental mercury and a back

- up carbon impregnated filter to ensure that bre akthrough was not occurring. The cassettes are small enough to fit in the palm of an operator ’ s hand and can be inserted directl y into the stack through a port that is 3 inches or larger in diameter

. For this test, an in

- stack approach was used since the s tack temperature was about 18 0° F. **Table 1. MRI Test Arrangement Figure 1. Mercury Speciation Cassette** 
**Phase Date**  **CES Test MRI Test**  I May-03 MSC-RA 12 OH Runs II Jul-03 Xact 12 OH Runs II Jul-03 MSC-Prec.
--2

The MSC approach offers a number of advantages over traditional standard methods including:

 Detection li mits of be tter than 0.1 micrograms/dscm for 50 minutes of sampling
 Sampling, anal ys is and sample recovery are completed without chemicals
 Sampling can be conducted by one operator
 Cassettes can be changed within five minutes
 Filter samples can be sent via FedEx for next day anal ys is
 Low per
- run anal ys is cost
 Routine analy sis turn

- around

- time is ty picall y less than one week
 Potential exists for in

- field XRF anal ys is for same day results
 XRF anal ys is is non

- destructive, so filters can be archived and reanal yz ed at a later date The results of the MSC testing during phase 1 are illustrated in the regression plot shown in Figure 2 and listed in Table 2

. A total of 12 OH runs were conducted with each run lasting two hours . For each OH run, two 50 minute MSC samples were collected by CES
. In general, the MSC and OH were in very good agreement with a relative accuracy of about 12 % (nine valid runs) , well within the 20% criteria for alternative methods specified b y EPA’s proposed Performance Specification 12. Three of the 12 OH test runs were o mitted from all candidate method comparisons. Runs 2 and 6 were omitted because of poor OH replication (>40% difference) and run 8 was omitted due to a plant upset and highl y variable mercury concentrations. For 11 of the 12 runs, the total mercury concentration ranged from about one to five μg/m3 with 90% in the form of elemental mercury . During run number 8, the stack gas temperatures increased significantly , total mercury increased to over 20 μg/m3 and averaged about 14 μg/m3 during the two hour OH test run. During this upset period, the elemental mercury concentration dropped from about 4 μg/m3 to about 2 μg/m3, but the oxidized mercury concentration increased about 300 fold; i.e., from about 0.04 μg/m3 to about 12 μg/m3, and represented about 85% of the total mercury

. The high correlation (r2 = 0.962) and low intercept of the MSC with the OH for the nine valid runs indicates good agreement between the two methods. **Figure 2. Correlation of MSC with OH During MRI Phase 1 Testing**
y = 0.908x + 0.152 R 2= 0.962

0 1 2 3 4 5 6

0 2 4 6

**OH (μg/dscm) M** **S C** **( μ** **g /** **d s** **c m** **)**3

**Table 2 . Reported MSC**  **and Ontario -**  **Hydro Results for Phase 1 Testing OH**  **MSC RUN**  **RUN START**  **STOP OXID**  **a ELEM.**  **TOT. AVG.**  **OH-1 OH-2**  **AVG. Valid**  **b MSC**  **OH % Diff** 

1A 1-May 13:20 14:15 <0.03 0.74 0.74 >95.9 1B 1-May 14:26 15:19 <0.04 1.42 1.42 >97.2 2A 2-May 10:20 11:11 0.12 2.77 2.89 96.0 2B 2-May 11:20 12:10 <0.08 2.59 2.61 >96.9 3A 2-May 14:41 15:31 0.10 1.63 1.74 94.0 3B 2-May 15:40 16:30 0.19 1.30 1.49 87.4 4A 5-May 10:00 10:50 <0.04 1.38 1.38 >97.1 4B 5-May
-- -- -- -- -- NM 5A 5-May 14:10 14:50 <0.05 1.75 1.75 >97.1 5B 5-May 15:00 15:50 <0.04 2.70 2.70 >98.5 6A 6-May 9:28 10:18 <0.04 4.58 4.58 >99.1 6B 6-May 10:27 11:17 <0.04 4.19 4.19 >99.0 7A 6-May 15:27 16:17 <0.04 3.35 3.35 >98.8 7B 6-May 16:26 17:16 <0.04 3.67 3.67 >98.9 8A 7-May 15:21 16:06 19.46 3.62 23.08 15.7 8B 7-May 16:13 17:03 11.80 3.12 14.91 20.9 9A 8-May 9:20 10:10 0.54 4.39 4.93 89.1 9B 8-May 10:17 11:07 0.34 4.22 4.56 92.5 10A 8-May 12:21 13:06 0.29 3.84 4.13 93.0 10B 8-May 13:16 14:06 0.29 4.01 4.30 93.2 11A 9-May 9:22 10:12 0.12 3.41 3.53 96.5 11B 9-May 10:21 11:11 0.18 3.04 3.21 94.5 12A 9-May 13:50 14:40 <0.08 3.57 3.57 >97.8 12B 9-May 14:49 15:39 0.18 4.09 4.27 95.8 -3.6 -2.4 **Percent Hg°**

99.1 99.2 94.1 96.5 99.2 15.2 98.9 99.4 2.6

-3.1 -8.4 -1.6 -1.0 -0.3 99.0 98.6

-0.4

20.3 94.2 99.5

-3.5

-3.5 5.24 4.26 3.35 3.88 9 10 11 12 5 6 7 8 1 2 3 4 1.88 5.57 4.14 14.27 1.33 4.20 1.64 1.50

4.75 4.22 3.37 3.92 2.23 4.39 3.51 19.00 1.08 2.75 1.61 1.38 **DATE MSC**  **(μg/dscm)**
1.36 1.29 5.34 3.05 1.64
-- 1.50 1.50 1.88
-- 6.91 4.22

4.26
-- 4.14
-- 14.27
--

3.33 3.36 3.88
-- Yes

Yes Yes **No** Yes Yes **OH TIME** 

Yes Yes Yes **No** Yes Yes

5.24
--

a) Includes particulate and vapor phase oxidized Hg b) Valid if OH Duplicates < 30% difference The MSC relative mercury speciation results (% Hg°) were also in excellent agreement with the OH results as shown in Table 2. The 12
- run average unsigned mean difference in the % Hg° from the two methods was 4.2%. The largest oxidized mercury concentration was observed during Run 8 in which the dominating oxidized mercury concentration was changing rapidl y. In addition, the OH and MSC were both stopped in the middle of the run due to the plant upset and the MSC runs covered only 100 of the 120 minutes of the OH run during which the mercury concentration was changing rapidly . Thus, the MSC clearl y demonstrated its responsiveness to changing relative mercury speciation and demonstrated a high degree of accuracy in the relative species apportionment. In addition to the stack tests, a series of runs were made comparing the MSC results to a direct injection of elem ental mercury from a Spectra Gases mercury canister (Table 3 , Figure 3 ) . The first two tests were conducted using a known concentration of 8 μg/dscm with MSC reported concentrations of 8.1 and 8.2 μg/dscm respectivel y. The MSC results are well within the Spectra Gases listed uncertainty of 20%. Following the initial tests, another series of three blind (unknown) tests were conducted by MRI with no CES personnel present. These blind tests used equivalent certified concentrations of 8, 19 and 19 μg/dscm resp ectivel y with the MSC resul ts closely correlated at 8.4, 18 .3, and 17.9 μg/dscm. The mean MSC recovery for the three blind tests was 98.4% with a standard deviation of 5.4% and a range from 94 to 105%. Again, the small percentage difference was well within the listed 20% uncertainty of the Spectra canister s .4

**Table 3 . Comparison of MSC Reported**  **Mercury Concentrations with Certified Spike Concentrations.**  **MSC Std.**  **μg/dscm μg/dscm**  STD. Known 1-May 8.1 8.0 STD. Known 1-May 8.2 8.0 STD. Blind 8-May 8.4 8.0 STD. Blind 8-May 18.3 19.0 STD. Blind 8-May 17.9 19.0 **Av erage**  **Standard Deviation**

**Da te**  **% Recovery** 101.0 **Injection Type**
102.5 104.6 96.4 94.3 99.8 4.3 A second series of 11 test runs were conducted using a pair of MSCs during p hase 2 of the MRIt ests (Table 4 ). Since the May tests had indicated good agreement with the standard method for the MSC, the July tests were limited to demonstration of the MSC precision relative to the ty

pical OH test run . According to the OH standard operating procedure, the OH has an 11% precision when concentrations are above 3 μg/dscm and a 34% precision when concentrations are less than 3 μg/dscm. Since only two MSC test runs during phase 2 were above 3 μg/dscm and all concentrations were below 3.3 μg/dscm, MSC precis ion could not be determined for high mercury concentrations. The MSC p recision for the 8 runs below 3 μg/dscm ranged fro m 0 to 37% with an average of 24 %, significantl y better than the OH listed precision. Itis believed that the MSC precision can be impro ved to about 5% with refinement

. **Table 4 . MSC Precision Tests During Phase 2 Testing** 

**MSC RUN**  **Total**

**(μg/m3) %** 

**Diff.** 1A 2.22 1B 2.21 2A 2.16 2B*
-- 3A 2.87 3B 2.43 4A 1.57 4B 2.25 5A 2.10 5B 3.06 6A 3.29 6B 3.01 7A 2.79 7B 3.24 8A 2.33 8B 2.77 9A 2.02 9B 2.55 10A 1.95 10B 2.51 11A 2.05 11B 2.90 **21.4**

**23.8** * 2B Omitted due to water contamination **Avg. (< 3 μg/dscm)** 0.4

-- 16.7 35.5 37.3 8.8 14.9 17.5 23.0 25.0 34.6 **Avg. (all)** 0 5 10 15 20

1 2 3 4 5

**Run No. H** **g C** **o n** **c (** **m i** **c r** **o g** **r a** **m s** **/ d** **s c** **m )**  Injected Conc MSC Results **Figure 3. MSC vs. Certified Mercury Concentrations for Spike Injection** 5

Overall, the MSC had better precision than the standard OH method under low mercury conditions, was able to effectivel y speciate the mercury concentrations, measured the standard gases to within 6 %, and had a relative accuracy of 12% compared to the OH method. However, since the MRItest site had limited opportunities to measure speciated mercury and rarel y had mercury concentrations above 3 μg/dscm, further testing un der a variety of stack conditions is recommended. 

### Xact **TESTING** The Xact mercury

monitor is designed to continuously measure total mercury concentrations and report data every 20 to 30 minutes with a detection limit of better than 0.1 μg/dscm (Figure 3)

. The monitor extracts a representative gas sample and concentrates the mercury on a reactive filter. The filter deposit is then advanced to an x

ray fluorescence (XRF) analyzer which determines mass concentrations. Minimal stack gas pretreatment is require d , which greatly simplifies the approach. Other advantages of the Xact include:

 Collection of total Hg including particulate , oxidized and elemental fractions
 Introduction of a f

resh filter with each sample

– no memory or blank bias
 Since XRF is non

- destr uctive, f ilters can be archived
 Solid

- phase Hg calibration minimizing use of expensive calibration ga ses  Since XRF is non

- destructive, results can be independently verified by another method
 Multi

- element sensor allow s for option of simultaneous monitoring for chromium, manganese, iron, cobalt, nickel copper, zinc, arsenic, selenium, bromine, and lead as well as mercury

.  Smoothly

varying theoretically

predictable sensitivities as a function of atomic number provides additional quality assurance . **Figure 3. Xact**  **Mercury Monitor**6



### Xact **Performance** During phase 2 testing, typ ical measured concentrations for both the Xact and the OH ranged from one to three micrograms per dry standard cubic meter (μg/dscm). Overall, the instrument ’ s relative accuracy (RA) compared to the OH was 25%, slightly higher than the 20% relative accuracy criteria set forth in the proposed pe rformance specification (Table 5 ) and similar to the other CEMs tested by MRI which had RA ranging from 15 to 40%. MRIused duplicate OH trains fo r all phase 2 testing. On average, the OH duplicate trains differed from each other by about 25% with three runs showing a difference of greater than 50%. According to the standard method, the OH precision is ty picall y about 34% when the mercury

concentrations are below 3 μg/dscm range so the MRI precision results were typical or slightl y better than historical OH precision levels . The magnitude of this imprecision , however, is on the same order as the desired relative accuracy . Thus, a large uncertainty ex ists in determining the relative accuracy results. For example, the RA of the OH duplicate trains compared to each other was 22%. **Any approach being compared to the OH could not expect to have a RA better than that of the**  **OH trains relative to**  **each other.** The Xact reported concentrations for 10 out of the 12 OH runs conducted during phase 2 tests. During run 1, the Xact experienced heater problems and developed a leak which was not repaired until the run had been completed. During run 7, the instrument was behaving appropriatel y prior to the run and following the run, but was turned off during the run. It is not known why

the instrument was turned off; however, it was located centrally in a very crowded room and could have been accidentall y turned off b y a by stander

. **Table 5 .**  **Reported Xact**  **and O ntario**  **- Hydro Results for Phase 2**  **Testing Xact**  **OH-1 OH-2**  **OH-A vg.**  **(μg/dscm) (μg/dscm)**  **(μg/dscm) (μg/dscm)**  1 7/24/2003 1010-1210
-- 1.44 1.32 1.38 2 7/24/2003 1420-1620 1.61 3.39 3.38 3.39 3 7/25/2003 0950-1150 2.07 2.27 2.38 2.33 4 7/25/2003 1425-1625 1.61 1.83 2.19 2.01 5 7/28/2003 1120-1320 1.27 1.53 1.26 1.40 6 7/28/2003 1525-1725 1.18 1.79 0.99 1.39 7 7/29/2003 0920-1120
-- 1.46 0.82 1.14 8 7/29/2003 1320-1520 1.69 1.56 1.24 1.40 9 7/30/2003 0915-1115 1.55 1.24 2.25 1.75 10 7/30/2003 1340-1540 1.51 1.17 1.63 1.40 11 7/31/2003 0915-1115 2.30 1.51 1.32 1.42 12 7/31/2003 1325-1525 1.72 1.25 1.20 1.23 **1.65 1.70**  **1.67 1.68**  **Run Date**  **Ti me** 

**Av g.** 7

In addition to the leak in run 1, the instrument experienced problems with heat tracing throughout the test s . The inlet tube immediately prior to the tape was heat traced but not thoroughl y insulated due to its close proximity to the x - ray

tube. The water content of the stack was higher than expected which led to periodic condensation in the tube with a resultant drop forming on the filter. Since the filter tape is hydroph ilic, the droplet would result in temporary

severe pressure drops and flow control issues. Although the droplets impact on pressure was severe, it is not certain that the condensation impacted the tape collection efficiency . However, the condensation on th e walls could be a potential sink for oxidized mercury . For this reason, any future Xact design needs to include a more thorough heat tracing of the inlet tube. Upon initial installation, a series of seven blind mercury standard gas tests were run with th e Xact . The Xact reported concentrations were within one percent of the certified standard concentration. Following OH testing, the Xact was again injected with the calibration gas, but the Xact response was significantly lower than expected. It is believe d that the Xact may

have experienced some problems with the calibration gas due to a heat tracing problem. On occasion, the Xact also reported blank concentrations of up to one μg/dscm. The high blank values could not be duplicated when the instrument was returned to CES and are currentl y being investigated. Overall, the prototype Xact was able to effectivel y measure the mercury for 10 of the 12 runs with a relative accuracy of 25%, approaching that of the replicate OH sample trains relative to each other (22%)

. The delivered unit was able to accurately measure the calibration gas and overall reported results correlated within uncertainty limits of the OH results. It is recommended, however, that the Xact be refined to improve transport and temperature control . It is also recommended that further reference method testing be conducted at a source with higher mercury

concentrations to better evaluate the Xact capabilities and potential accuracy . **CONCLUSION AND RECOMMENDATIONS** The MSC was able to effectivel y measure mercury concentration s with a relative accuracy of 12 % compared to EPA’s standard reference method. The MSC precision was better than the OH for the low concentrations present in the stack and the MSC was able to consistently determine concentrati ons to within 10% of the gas canister standards . Although onl y one OH run was present with significant oxidized mercury concentrations, the MSC and OH percentages of oxidized mercury were in good agreement for that run

. Overall, the MSC appears to be able to give comparable results to the OH at a fraction of the cost and effort. The Xact mercury

CEM had a relative accuracy of 25% in comparison to the OH method. Since the OH method’s precision for the test was also on the order of 25%, the Xact RA uncertainty

is limited by

the uncertainty in the OH method. The Xact was able to accuratel y measure the Spectra gas standard upon initial installation and was able to track changes in total mercury

concentrations relative to the OH method throughout the test.8

1) The MSC total mercury relative accuracy

was 12%, substantially

less than the 20% required for equivalency

. 2) The MSC fractional mercury speciation was in excellent agreement with OH results showing an average of onl y 4% difference for all 12 OH runs. 3) The MSC rel ative precision was 30% better than the precision listed in the OH method for measurements less than 3 μg/dscm. 4) The Xact total mercury relative accuracy

was 25%, which was essentially the same as the 22% RA between duplicate OH test runs. This first Xact unit did develop cold spots which caused occasional water condensation and inconsistent results. This problem is being mitigated with more uniform heating. One of the largest problems for all candidate methods was the limited accuracy and precision of the EPA standard method at low mercury concentrations. Concentrations for all but one OH run were below 3 μg/dscm. The OH has a listed precision of 34% under these low concentrations (ASTM, 1999) limiting its ability to evaluate the relative accuracy of the m ercury

CEMs. In addition, mercury was almost exclusively

in the elemental form for all but one run. Since many C EM approaches are severely impacted by oxidized mercury , the tests have limited applicability for CFPP which have significant concentrations of oxidized mercury

. Although the MSC and Xact performed well during the MRI tests, it is recommended that they be retested at a site that will provide high enough concentrations for precise OH measurements. It is further recommended that:

 The MSC be reen gineered for use in higher temperature stacks.
 The MSC undergo testing at a stack with significant quantities of both elemental and oxidized mercury

.  The MSC undergo testing at a stack with mercury concentrations greater than 3 μg/dscm.
 The Xact inlet should be reengineered for improved heat tracing and transport.
 The Xact should undergo testing at a stack with significant quantities of both elemental and oxidized mercury

. 

### ACKNOWLEDGEMENTS CES would like to acknowledge Pall Corporation and MetOne for their assistance with equipment development and the U.S. Army Corp of Engineers Construction Engineering Research Laboratory

for their sponsorship of this project.9



### REFERENCES EPA, 2000. EPA Fact Sheet Accompanyi ng EPA’s Decision to Regulate Mercury from Coal Fired Power Plants. December 14, 2000. Found on the web at http://www.epa.gov/ttn/oarpg/t3/fact_sheets/fs_util.pdf ASTM , 1999
. October 21, 1999. Standard Test Method for Elemental , Oxidized, Particle Bound and Total Mercury in Flue Gas Generated from Coal

- Fired Stationary Sources (Ontario

- Hydro Method). Found on the web at http://www.astm.org/cgi

bin/SoftCart.exe/DATABASE.CART/REDLINE_PAGES/D6784.htm?E+my store