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Utility MACT Working Group

Negative Removals -- A Review

Bill Maxwell, OAQPS/ESD

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Purpose

To present a review of test reports from units showing negative mercury removals during ICR speciated mercury emissions tests

Not to definitively answer all questions

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Background - All testsNegative mercury removals were

indicated at 31 test sites when calculated either from coal-to-stack or across the tested control device 12 sites showed negative removals only

when calculated from coal-to-stack Because of differences in test

methodologies, for this analysis, this is not a calculation that we feel should be used

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General theories -- coal to stackRepresentativeness of sample

For some sites, coal analyses during testing did not match similar ICR analyses for surrounding period

Method and location of sample acquisition different than that for ICR samples

Timing of coal sampling vs. when that flue gas gets to stack sample train

Does not negate usefulness of coal-to-stack analyses overall

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Background -- Control device only19 remaining test sites indicated negative

removals across the tested control device Reviewed each test report in greater detail Cannot definitively say “here is the reason”

for any site Have plausible theories for most sites that are

felt to reasonably account for, or at least contribute strongly to, the negative removalsSome sites fall under more than one theory

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General theories - control device

Coal typeLow level of mercury presentNormal sampling distribution around

“0”Use of hot-side ESPSampling locationsTest/analytical method problems

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Coal type15 of the 19 sites burned

subbituminous or lignite coals Generally have higher proportion of

elemental mercury in flue gas Not expected to be removed Subject to loss during sample handling

Ontario-Hydro method has been modified to add stabilizer to permanganate solution that inhibits loss of elemental mercury

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Low level of mercury presentOntario-Hydro method validated at 2 ug/m3

For units having emissions near this level (may vary somewhat between labs), small variations in numerical measurements lead to large variations in percentages

Indicates care must be taken in use of significant figures and in precision of any standard

Also creates problems with non-detect values

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Normal sampling distribution around “0”Normal variability in sampling would

lead one to expect a distribution of results around any value When that value is “0” -- normal distribution

may indicate negative removals Normal sampling/analytical variability in

each sample exacerbates problem more at low removal levels than at higher removal levels

Would apply to coal-to-stack values also

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Example for tests with +/- 30% error: Poor mercury control

Gas concentrations, ug/dscminlet outlet

30% high 13 13average 10 1030% low 7 7

There are nine combinations for these 6 values above Gas concentrations, ug/dscm

inlet outlet % control1 13 13 0.0%2 10 13 -30.0%3 7 13 -85.7%4 13 10 23.1%5 10 10 0.0%6 7 10 -42.9%7 13 7 46.2%8 10 7 30.0%9 7 7 0.0%

This example illustrates that negative reported values of percent removal are expected when there is poor mercury control in the unit.

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Example for tests with +/- 30% error: Good mercury control

Gas concentrations, ug/dscminlet outlet

30% high 13 1.3average 10 130% low 7 0.7

There are nine combinations for these 6 values above Gas concentrations, ug/dscm

inlet outlet % control1 13 1.3 90.0%2 10 1.3 87.0%3 7 1.3 81.4%4 13 1 92.3%5 10 1 90.0%6 7 1 85.7%7 13 0.7 94.6%8 10 0.7 93.0%9 7 0.7 90.0%

This example illustrates that negative reported values of percent removal are not expected when there is good mercury control in the unit.

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Use of hot-side ESP

5 of 19 units utilized hot-side ESP controls Not expected to exhibit effective

mercury removal due to relatively high temperatures

Adds to problem of normal distribution of data around “0” removal

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Sampling locationSeveral sites had multiple inlet and/or

scrubber by-pass configurations Multiple modules for control devices complicate

inlet duct configurations and sampling locationsInlet sites in general were less adequate than outlets

Scrubber by-pass to meet SO2 requirements May be biasing the inlet data +/- Indicates that “percent removal” format may not

be appropriate if taken across control

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Test/analytical method problemsOntario-Hydro, at the time of testing,

was a new test method with few testing or analytical firms familiar with its use Is not an “easy” method and requires strict

adherence to procedures, QA/QC, etc. Some test contractors indicated problems

with blank levels, lost samples (dropped impingers, etc.), etc.

Sample hold times sometimes exceeded

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How the theories fit the units

Following slides fit tested sites to the theories noted earlier

Some sites fit more than one theoryGenerally cannot say “Eureka”

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Negative removal coal to stack only Cliffside Unit 1 Clifty Creek Unit 6 Columbia Unit 1 Gibson Unit 3 (both

sets of tests) Leland Olds Unit 2 Limestone Unit LIM1

Navajo Unit 3 Newton Unit 2 Rawhide Unit 101 Sherburne County

Unit 3 Stanton Station Unit

10 Wyodak Unit BW91

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Coal type

Big Brown Unit 1Cholla Unit 2Cholla Unit 3Clay Boswell Unit 4Colstrip Unit 3Coronado Unit U1BGeorge Neal South

Unit 4GRDA Unit 2

Laramie River Unit 3Lawrence Unit 4Monticello Unit 1Nelson Dewey Unit 1Platte Unit 1Sam Seymour Unit 3Stanton Station Unit 1

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Low level of mercury present

Bay Front Unit 5 . . . . . Cholla Unit 3. . . . . . . .Clay Boswell Unit 4 . . .Coronado Unit U1B . . .Laramie River Unit 3 . .Lawrence Unit 4 . . . . .Nelson Dewey Unit 1 .Presque Isle Unit 9 . . .Valley Unit 2. . . . . . . .

2.5 - 4 ug/m3

1 - 2 ug/m3

5 - 6 ug/m3

2.5 - 3 ug/m3

2.5 - 3.5 ug/m3

~5 ug/m3 (+ non detects)2 - 3 ug/m3

1 - 2 ug/m3

1 - 2 ug/m3

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Normal sampling distribution around “0” GRDA Unit 2 . . . . . . . . . . . . . . . . . Lawrence Unit 4. . . . . . . . . . . . . . . Platte Unit 1 . . . . . . . . . . . . . . . . . Big Brown Unit 1 . . . . . . . . . . . . . . Cholla Unit 2 . . . . . . . . . . . . . . . . . Coronado Unit U1B. . . . . . . . . . . . . Nelson Dewey Unit 1. . . . . . . . . . . . Presque Isle Unit 9 . . . . . . . . . . . . . Stanton Station Unit 1. . . . . . . . . . . Valley Unit 2. . . . . . . . . . . . . . . . . .

+18 to - 24% - 2 to - 34%+27 to - 33%+ 1 to - 13%+23 to - 33% - 11 to - 21%+ 2 to - 23%+ 0 to - 6%+ 2 to - 9%+ 6 to - 25%

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Use of hot-side ESP

Cholla Unit 3Gaston Unit 1Nelson Dewey Unit 1Platte Unit 2Presque Isle Unit 9

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Sampling locations

Big Brown Unit 1Clay Boswell Unit 4Colstrip Unit 3Coronado Unit U1B

(scrubber by-pass)George Neal South

Unit 4

Laramie River Unit 3

Lawrence Unit 4Sam Seymour Unit

3 (also scrubber by-pass)

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Contractor/method problems Bay Front Unit 5 . . . . . . . .

Cholla Unit 2. . . . . . . . . . . Cholla Unit 3. . . . . . . . . . . Gaston Unit 1 . . . . . . . . . . George Neal South Unit 4. . Laramie River Unit 3 . . . . .

Reported “suspect” elemental data for 2 of 3 of outlet runsNumerous problemsNumerous problemsPossible sample hold problemPossible bad test runPossible sample hold problemProbable bad test run

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ConclusionsNegative removals are expected for

some tests on units with poor mercury removal Negative removals are primarily a

combined function ofActual low removal efficienciesInherent variability in test and analytical

procedures Other factors may also be involved but

believed to be of lessor importance

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Conclusions - MoreNegative removals are not expected

for tests on units with good mercury removal Test data with good mercury removal

used for setting emission standardsAdditional testing would not impact final

MACT levels

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So where does this leave us...Ontario-Hydro method is not inherently

flawed Nothing in the data to so indicate Modifications have been made to stabilize

elemental mercury in permanganate solution Data do indicate caution in setting level of

standardTruly positive removal numbers are validMercury is not being generated

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Examples

Laramie River Unit 3Coronado Unit U1B

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Laramie River Unit 3Uses subbituminous coalSample storage conditions (~20 °C) and

holding times (> 45 days) may have been violated prior to analysis

Low mercury valueMultiple inlet ductsOne inlet run considerably different from

5 other runs at same or similar site

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Laramie River Unit 3 -- cont.Inlet concentration,

ug/ dscmOutlet concentration,

ug/ dscmLaramie River Unit 1: 1 4.593 2.835

Laramie River Unit 1: 2 5.055 3.501

Laramie River Unit 1: 3 4.562 3.286

Laramie River Unit 3: 1 0.389 2.368

Laramie River Unit 3: 2 5.263 2.761

Laramie River Unit 3: 3 5.621 3.281

Laramie Units 1 and 3 are same type of boiler, burn the same coal, and in similar quantities

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Coronado Unit U1B

Uses subbituminous coalLow mercury valueUses scrubber by-pass as part of SO2

control Sampled inlet upstream of by-pass duct Sampled outlet upstream of by-pass duct Actual impact on percent removal

calculations is unknown

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List of Units Exhibiting Negative Removals Across Control or Coal-to-Stack

Facility/ Unit Coal type Control Removal coal-to-stack, %

Removal acrosscontrol, %

Bay Front 5 Bit Mech collector -47.4 -57.1

Big Brown 1 Lignite CSESP/ FF 10.0 -8.1

Cholla 2 Sub Wet scrub 24.5 -4.4

Cholla 3 Sub HSESP 64.2 -36.3

Clay Boswell 4 Sub Wet scrub 11.4 -21.9

Cliffside 1 Bit HSESP -12.4 30.4

Clifty Creek 6 Sub HSESP -30.5 34.0

Colstrip 3 Sub Wet scrub 14.7 -7.8

Columbia 1 Sub HSESP -25.2 12.0

Coronado U1B Sub Wet scrub 30.6 -15.2

Gaston 1 Bit HSESP -40.0 -17.2

George Neal South 4 Sub CSESP 21.9 -9.6

Gibson 3 (both sets of tests) Bit CSESP -201; -16.9 5.0; 35.7

GRDA 2 Sub SDA/ CSESP -1.0 -2.8

Laramie River 3 Sub SDA/ CSESP 70.4 -78.5

Lawrence 4 Sub Wet scrub -23.2 -17.4

Leland Olds 2 Lignite CSESP -12.8 4.9

Limestone LIM1 Lignite Wet scrub -7.5 51.0

Monticello 1-2 Lignite Fabric filter -20.4 -21.3

Navajo 3 Bit Wet scrub -20.5 21.0

Nelson Dewey 1 Sub HSESP 55.6 -9.0

Newton 2 Bit CSESP -19.2 8.2

Platte 1 Sub HSESP -67.5 -2.9

Presque Isle 9 Bit/Pet coke HSESP 9.9 -3.6

Rawhide 101 Sub SDA/FF -25.6 31.8

Sam Seymour 3 Sub Wet scrub 56.2 -20.3

Sherburne County 3 Sub SDA/FF -9.7 4.5

Stanton 1 Lignite CSESP 44.1 -3.6

Stanton 10 Lignite SDA/FF -7.0 1.5

Valley 2 Bit FF -109 -6.8

Wyodak BW91 Sub SDA/ CSESP -144 43.5