WEST Associates’ Assessment of Hg MACT Floor Variability

CAAAC Mercury MACT

Working GroupWashington, 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 EnergyTri-State G & T

NV Nevada Power Co/ Sierra Pacific Power Co.

CO Colorado Springs UtilitiesXcel EnergyPlatte River Power AuthorityTri-State G & T

UT PacifiCorp/Utah Power and LightWY 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 MACTData 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 MACTData 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)

SOURCES OF UNCERTAINTY

MEASUREMENTERROR

DIFFERENTFACILITIES

FUEL VARIABILITY

OPERATIONS

WORSTCIRCUMSTANCES

(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.):

Fabric Filter/Spray Dryer Absorber

Frem = 1 - 0.8188*exp(-0.002164*Cl(ppm)); R2=0.935

00.10.20.30.40.50.60.70.80.9

1

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Chlorine (ppm)

Fra

cti

on

Hg

Re

mo

ved

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:1. If good correlation (from step 3), correlation equation used to calculate Hg

removal fraction2. 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

Distribution of National Bituminous Coal Hg Content

0102030405060708090

100

0.00 0.10 0.20 0.30 0.40 0.50

Hg Content in Coal (ppm)

Cu

mm

ula

tive

Fre

qu

en

cy

(%)

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):

Mecklenburg#GEN1

0.00.10.20.30.40.50.60.70.80.91.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

lb Hg/TBtu

Cu

mm

ula

tiv

e F

req

ue

nc

y

Elements of VariabilityNot 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 Floorsfor 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

Fabric Filter (No SO2 Control)

Frem = 1 - 0.33664*exp(-0.001101*Cl(ppm)); R2=0.0794

-0.2-0.1

00.10.20.30.40.50.60.70.80.9

1

0 200 400 600 800 1000 1200 1400

Chlorine (ppm)

Fra

ctio

n H

g R

em

ove

d

Multi-variable Method:5 Step Analytical Process

• STEP 3 (cont.): Figure 3

Hot Side Wet Scrubber

Frem = 1 - 0.7931*exp(-0.00089*Cl(ppm)); R2=0.2533

-0.3-0.2-0.1

00.10.20.30.40.50.60.70.80.9

0 200 400 600 800 1000

Chlorine (ppm)

Fra

ctio

n H

g R

em

ove

d

Multi-variable Method:5 Step Analytical Process

• STEP 3 (cont.):Figure 4

Hot Side (No SO2 Control)

Frem = 1 - 1.1289*exp(-0.0004021*Cl(ppm)); R2=0.389

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0 200 400 600 800 1000 1200 1400

Chlorine (ppm)

Fra

ctio

n H

g R

em

ove

d

Multi-variable Method:5 Step Analytical Process

• STEP 3 (cont.):Figure 5

Cold Side ESP

Frem = 1 - 0.6752*exp(-0.0001805*Cl(ppm)); R2=0.0827

-1

-0.5

0

0.5

1

0 1000 2000 3000 4000

Chlorine (ppm)

Fra

cti

on

Hg

Re

mo

ve

d