# Presentation: 495549

## Utility MACT Working Group

- Negative Removals --
- A Review
*Bill Maxwell, OAQPS/ESD*

## 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

## Background - All tests

- Negative 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

## General theories -- coal to stack

- Representativeness 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

## Background -- Control device only

- 19 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 removals
- Some sites fall under more than one theory

## General theories - control device

- Coal type
- Low level of mercury present
- Normal sampling distribution around “0”
- Use of hot-side ESP
- Sampling locations
- Test/analytical method problems

## Coal type

- 15 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

## Low level of mercury present

- Ontario-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

## 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

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

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

## 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

## Sampling location

- Several sites had multiple inlet and/or scrubber by-pass configurations
- Multiple modules for control devices complicate inlet duct configurations and sampling locations
- Inlet 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

## Test/analytical method problems

- Ontario-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

## How the theories fit the units

- Following slides fit tested sites to the theories noted earlier
- Some sites fit more than one theory
- Generally cannot say “Eureka”

## 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

## Coal type

- Big Brown Unit 1
- Cholla Unit 2
- Cholla Unit 3
- Clay Boswell Unit 4
- Colstrip Unit 3
- Coronado Unit U1B
- George Neal South Unit 4
- GRDA Unit 2

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

## 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

## 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%

## Use of hot-side ESP

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

## Sampling locations

- Big Brown Unit 1
- Clay Boswell Unit 4
- Colstrip Unit 3
- Coronado Unit U1B (scrubber by-pass)
- George Neal South Unit 4

- Laramie River Unit 3
- Lawrence Unit 4
- Sam Seymour Unit 3 (also scrubber by-pass)

## 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 runs
- Numerous problems
- Numerous problems
- Possible sample hold problem
- Possible bad test run
- Possible sample hold problem
- Probable bad test run

## Conclusions

- Negative removals are expected for some tests on units with poor mercury removal
- Negative removals are primarily a combined function of
- Actual low removal efficiencies
- Inherent variability in test and analytical procedures
- Other factors may also be involved but believed to be of lessor importance

## Conclusions - More

- Negative removals are not expected for tests on units with good mercury removal
- Test data with good mercury removal used for setting emission standards
- Additional testing would not impact final MACT levels

## 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 standard
- Truly positive removal numbers are valid
- Mercury is not being generated

## Examples

- Laramie River Unit 3
- Coronado Unit U1B

## Laramie River Unit 3

- Uses subbituminous coal
- Sample storage conditions (~20 °C) and holding times (> 45 days) may have been violated prior to analysis
- Low mercury value
- Multiple inlet ducts
- One inlet run considerably different from 5 other runs at same or similar site

## Laramie River Unit 3 -- cont.

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

## Coronado Unit U1B

- Uses subbituminous coal
- Low mercury value
- Uses 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

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