# Presentation: 417588

## WEST Associates’ Assessment of Hg MACT Floor Variability

**CAAAC Mercury MACT**
**Working Group**
- Washington, DC
- March 4, 2003

## Who Is WEST Associates?

**AZ****	**Arizona Electric Power 	Cooperative
- 	Pinnacle West Capital Corp.
- 	Salt River Project
- 	Tucson Electric Power Co.
**CA****	**Glendale Public Service Dept.
- 	Los Angeles Dept. of Water 	& Power
- 	Southern California Edison
**OR**	PacifiCorp
**ID****	**Idaho Power Company
**ND**	Basin Electric Power

**NM****	**Public Service Co of NM,
- 	Xcel Energy
- 	Tri-State G & T
**NV****	**Nevada Power Co/ Sierra Pacific Power Co.
**CO**	Colorado Springs Utilities
- 	Xcel Energy
- 	Platte River Power Authority
- 	Tri-State G & T
**UT****	**PacifiCorp/Utah Power and 	Light
**WY **Basin Electric,
**	**PacifiCorp,
- 	Xcel Energy
- 	Tri-State G & T

## WEST Associates efforts to-date

- September 2002:
- Mercury Emissions from Western Coal-fired Power Plants: Nature, Extent, and Fate
- Unique Western Concerns Related to the Role of Chlorine contents of Coal on Hg Emissions
- Recommended that MACT standard reflect these issues.
- Statistical Analysis to address coal chemistry issues

## WEST’s Hg MACTData Analysis Goals

- Determine from 80 unit source test ICR III database, statistically robust datasets for potential MACT subcategories (ENSR ANOVA Study)
- Coal rank (bit., sub-bit., & lignite)
- Coal Hg content
- Hg/Cl ratio
- Develop a statistically valid approach to integrate operational variability using the ICR II fuel chemistry database to calculate Hg MACT floors

## WEST’s Hg MACTData Analysis Goals

- This study used the regulatory framework:
- “...the average emission limitation achieved by the best performing twelve percent of existing sources” _*and*_
- “... is achievable under the most adverse circumstances which can reasonably be expected to recur.”

## Variability in MACT Floor Determinations(Conceptual Illustration)

- (Hg, Cl, & Btu Content)

- (Soot blowing, load following)t

## 80 Unit Source Test ICR III Does Not Capture Variability

- Three 1-hr source tests are only a “snapshot” in time taken under steady state operations
- Three 1-hr source tests _do not represent actual emissions_ over any longer operating time
- Based only on limited coal chemistry, and operational variability occurring during the 3 tests
- ICR III source tests represent only a fraction of total variability

## WEST’s Multi-variable Method

- Uses ICR III source test and control effectiveness data from 12% best performing units by coal rank, plus annual coal chemistry data from ICR II
- Integrates key drivers of variability:  Coal Hg, Cl, & Btu content (annual variability)
- Multi-variable Method is based on a 5 step statistical analytical process

## Multi-variable Method:5 Step Analytical Process

**STEP 1**
- 80 source test units _sorted by coal rank_
- FBC units; petroleum coke units; combination fuel units removed (15 total)
- Leaves 29 bit. Units; 26 subbit. units; 10 lignite units
**STEP 2**
- Within each coal rank, units sorted in ascending order of stack tested Hg emissions (# Hg/TBtu)
- _Best performing 12% of units_ = the 5 units with lowest emissions in each coal rank
_**Note**_:  Significant differences occur in averages of Cl (ppm) and Hg (#/TBtu) between coal ranks.

## Multi-variable Method:5 Step Analytical Process

**STEP 3**
- To account for _“intra-unit” variability_, correlation equations were developed to relate Hg emissions to coal chlorine content
- For each control configuration (e.g., FF/SDA, etc.) determined relationship between Hg removal % and coal Cl concentration using ICR III stack test database for all tested units (not only the best performing units)

## Multi-variable Method:5 Step Analytical Process

-  **STEP 3 (cont.):**

**Figure 1**

## Multi-variable Method:5 Step Analytical Process

**STEP 4:**
- For each best performing unit, “controlled” Hg emissions calculated by multiplying “uncontrolled” Hg emissions by (1-Hg removal fraction)
- ICR II test data (Btu and Hg content) used to calculate uncontrolled emissions
- Hg removal fraction derived in one of two ways:
- If good correlation (from step 3), correlation equation used to calculate Hg removal fraction
- If poor correlation, ICR III source test Hg removal fraction used
- Process repeated for each set of measured coal composition data from ICR II database (I.e., Hg, Btu and Cl measurements) _yielding a range of Hg emissions for each unit over time_

## Variability in Coal Hg Content

## Multi-variable Method:5 Step Analytical Process

**STEP 5:**
- For each best performing unit, calculated mercury emissions sorted from smallest to largest to obtain a frequency distribution
- 95% value of this distribution assumed to represent the operation of the unit _under the most adverse circumstances reasonably expected to recur_ for each unit
- The 95% upper confidence limit (UCL) of the mean of these adverse-case emissions is reported as the Hg MACT floor

## Multi-variable Method:5 Step Analytical Process

-  **STEP 5 (cont):**

## Elements of VariabilityNot Captured by this Method

- Analysis of fuel variability accounts for some, but not all, of the variability in the stack testing of each unit in ICR III
- Stack test measurement error (+/- 20-25%)
- Intermittent maintenance events (e.g., operation of air heater soot blowers) affect Hg emission rates
- Source tests conducted at static load; load following can change results

## Results of Multi-variable Hg MACT Floor Method

| Coal Rank | MACT Floor (lb Hg/TBtu) |
| --- | --- |
| Bituminous | 2.26 |
| Subbituminous | 5.75 |
| Lignite | 10.15 |

-  **Potential national Hg reduction:  15 t/yr; 31%**

## Statistical Rationale for Alternate MACT Floors

- Could replace Coronado with Comanche in list of top 5 best performing sub bituminous plants
- Hg rate for Coronado is only 6% less than Comanche
- Measured Hg removal data for Comanche show much less scatter than data for Coronado
- The % removal for Coronado was found to be _negative_ for all 3 source tests
- Could use simple average of top 5 best performing lignite units (5 out of 10 units).
- Need for 95% UCL for inter-unit variability among 10 units is less

## Alternate Hg MACT Floorsfor Subbituminous & Lignite

| Coal Rank | MACT Floor (lb Hg/TBtu) |
| --- | --- |
| Bituminous | 2.26 |
| Subbituminous | 4.15 |
| Lignite | 8.20 |

-  **Potential national Hg reduction:  17 t/yr; 36%**

## Conclusions of Multi-variable Method Hg MACT Floor Study

- Multi-variable method uses the maximum amount of information from both ICR II and ICR III databases in the determination of variability in a MACT floor
- First known study to comprehensively bridge between the ICR III source test, and ICR II annual coal chemistry data
- Our MACT Floor levels represent statistically robust estimates of the variability of Hg emissions as a result of annual variability of coal chemistry
- Variability of coal chemistry accounts for only one driver of variability.  The MACT Floor results likely underestimate most adverse circumstances which can reasonably be expected to recur at a unit meeting a mercury MACT limit.
- This technical analysis conforms to regulatory requirements

## Supplemental Slides

- Additional
- Correlation Equations

## Multi-variable Method:5 Step Analytical Process

-  **STEP 3 (cont.):**

-  **Figure 2**

## Multi-variable Method:5 Step Analytical Process

-  **STEP 3 (cont.):**

**Figure 3**

## Multi-variable Method:5 Step Analytical Process

-  **STEP 3 (cont.):**

**Figure 4**

## Multi-variable Method:5 Step Analytical Process

-  **STEP 3 (cont.):**

**Figure 5**