BART DETERMINATION 

SUPPORT DOCUMENT FOR

TRANSALTA CENTRALIA GENERATION LLC POWER PLANT

CENTRALIA, WASHINGTON

Prepared by

Washington State Department of Ecology

Air Quality Program

August 2009

Revised April 2010

Revised November 2011

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 20111
Table of Contents 

Executive Summary

Section 1.0 Introduction 

 1.1 The BART Analysis Process

 1.2 Basic Description of the TransAlta Centralia Generation LLC Power Plant

 1.3 BART Eligible Units and Pollutant at TransAlta Centralia Generation LLC Power 

Plant

1.4 Visibility Impact of BART Eligible Units at TransAlta Centralia Power Plant

 1.5 Relationship to 1997 RACT Analysis and Determination

Section 2.0 Summary of TransAlta Centralia Power Plant’s BART Analysis

 2.1 NOx Controls Evaluated

 2.2 TransAlta’s Proposed BART

Section 3.0 Visibility Impacts and Degree of Improvement

Section 4.0 Ecology’s BART Determination

 4.1 NOx Control 

 4.2 Ecology’s Determination of the NOx Emission Controls That Constitute BART

Appendix A Coal Quality 

Appendix B Nitrogen Oxides Controls Evaluated in the 1997 Reasonably Available Control 

Technology Process

Appendix C References

Appendix D Modeling Result Information from June 2008 and January 2008 Best Available 

Retrofit Technology Modeling reports 

Appendix E Coal-Fired Electric Generating Unit BART Determinations in Western U.S. 

Appendix F TransAlta Centralia Power Plant Site Plans and Profiles

Appendix G Centralia BART Control Technology Analysis, Response to Questions 

Appendix H Additional Centralia Power Plant BART Modeling Simulations–Comparison of Flex 

Fuel and Flex Fuel plus SNCR 

Appendix I Establishing SNCR NOx Emission Limitation

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 20112
Executive Summary 

The Best Available Retrofit Technology (BART) program is part of the larger effort under the Clean 

Air Act Amendments of 1977 to eliminate human-caused visibility impairment in all mandatory 

Class I areas. Sources that are required to comply with the BART requirements are those sources 

that: 

1. Fall within 26 specified industrial source categories; 

2. Commenced operation or completed permitting between August 7, 1962 and August 7, 1977; 

3. Have the potential to emit more than 250 tons per year of one or more visibility impairing 

compounds; 

4. Cause or contribute to visibility impairment within at least one mandatory Class I area.

TransAlta Centralia Generation LLC Power Plant (TransAlta) operates a two-unit, pulverized coalfired plant near Centralia, Washington. Each unit of the plant is rated at 702.5 MW net output when 

using coal from the Centralia coal field. Current output capacity reported by TransAlta is 670 

MW/unit as a result of using coals from the Powder River Basin (PRB). Operation of a coal-fired 

power plant results in the emissions of Particulate Matter (PM), Sulfur Dioxide (SO2) and Nitrogen 

Oxides (NOx). All of these pollutants are visibility impairing. 

Pulverized coal plants such as the TransAlta facility are one of the 26 listed source categories. The 

units at the plant began commercial operation in 1971 and 1972. The units have the potential to emit 

more than 250 tons per year of SO2, NOx, and PM. As part of an approval of the Washington State 

Visibility State Implementation Plan (SIP) in 2002, Environmental Protection Agency (EPA) Region 

10 determined that particulate and SO2 controls installed as part of a 1997 Reasonably Available 

Control Technology (RACT) determination1

 issued by the Southwest Clean Air Agency (SWCAA)2

met the requirements for BART and constituted BART for those pollutants. EPA specifically did not 

adopt the NOx controls in the RACT order as BART. 

Modeling of visibility impairment was done following the Oregon/Idaho/Washington/EPA-Region 10 

BART modeling protocol.3 Modeled visibility impacts of baseline emissions show impacts on the 

8th highest day in any year (the 98th percentile value) of greater than 0.5 Deciviews (dv) at the 

twelve Class 1 areas within 300 km of the plant. The highest impact was 5.55 dv at Mt. Rainier

National Park. Modeling showed that NOx and SO2 emissions from the power plant are responsible 

for the facility’s visibility impact. 

TransAlta prepared a BART technical analysis following Washington State’s BART Guidance.4

Future operation of the TransAlta facility is specifically addressed in Chapter 180, Laws of 2011 

(also known as E2SSB 5769). Under this law, the Governor is to enter a Memorandum of Agreement 

whereby the plant owners will bring the two coal-fired units into compliance with the greenhouse gas 

1 SWAPCA Order No. 97-2057R1 issued December 26, 1998. 2 Previously known as the Southwest Air Pollution Control Authority (SWAPCA).

3 Modeling protocol available at http://www.deq.state.or.us/aq/haze/docs/bartprotocol.pdf. 4 “Best Available Retrofit Technology Determinations Under the Federal Regional Haze Rule,” Washington State 

Department of Ecology, June 12, 2007. 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 20113
(GHG) emission performance standard in RCW 80.80.040.5

 The law also requires the plant owner to 

install and operate selective noncatalytic reduction (SNCR) for NOx by January 1, 2013. The 

schedule in the law for bringing the coal units into compliance with the GHG emission performance 

standard directs that one unit is to comply by December 31, 2020, and the other is to comply by 

December 31, 2025. Based on testimony at the legislature and in the press, it is expected that the 

units will comply with the GHG emission standard by being decommissioned. The law also states 

that the requirement to meet the GHG emission performance standard does not apply in the event the 

Washington State Department of Ecology (Ecology) determines as a requirement of state or federal 

law or regulation that the selective catalytic reduction (SCR) technology must be installed on either 

coal-fired unit. 

In accordance with this law and its effects on potential NOx emission controls, Ecology has revised 

its determination of BART. We now find that BART for NOx emissions is the current combustion 

controls, the Flex Fuels Project, the use of a sub-bituminous coal from the PRB or other coal that will 

achieve similar emission rates and the installation and use of SNCR. In addition to the 20 percent

reduction in NOx emissions by use of the Flex Fuels Project, SNCR will further reduce NOx 

emissions. 

The exact amount of NOx reduction attributable to SNCR at this plant is unknown. However, all 

analyses of the effects of the use of SNCR are based on an assumption of an additional 25 percent

reduction. The SNCR system is required to be installed and operating by January 1, 2013. Ecology 

has established an interim emission limitation of 0.21 lb/MMBtu that will be in effect after start-up of 

the SNCR system until the BART Order is revised in 2015. During calendar years 2013 and 2014,

TransAlta will be required to optimize the SNCR system to maximize the NOx reduction while 

maintaining an acceptable ammonia emission rate. 

The use of low sulfur PRB coal also reduces SO2 emission by about 60 percent from the same period. 

The NOx reduction anticipated from the revised BART controls selected by Ecology will result in a 

visibility improvement from the baseline impacts at Mt. Rainier National Park of approximately 1.99 

dv, with improvements of 0.67 to 1.65 dv at other affected Class I areas. We estimate that the 

visibility improvement from meeting the interim emission limitation will be approximately 1 dv at 

Mt. Rainier National Park. 

Looking to the future, the 2020 decommissioning of one coal unit will further decrease the visibility 

impacts and the final 2025 decommissioning of the other unit will eliminate all visibility impacts 

from the combustion of coal at this facility. Ecology considers the future decommissioning of the 

coal units to be reasonable progress elements of the Regional Haze State Implementation Plan.

5 RCW 80.80.040(3)(c)(i) A coal-fired baseload electric generation facility in Washington that emitted more than one 

million tons of greenhouse gases in any calendar year prior to 2008 must comply with the lower of the following 

greenhouse gas emissions performance standard such that one generating boiler is in compliance by December 31, 2020, 

and any other generating boiler is in compliance by December 31, 2025:

(A) One thousand one hundred pounds of greenhouse gases per megawatt-hour; or

(B) The average available greenhouse gas emissions output as determined under RCW 80.80.050.

(ii) This subsection (3)(c) does not apply to a coal-fired baseload electric generating facility in the event the department 

determines as a requirement of state or federal law or regulation that selective catalytic reduction technology must be 

installed on any of its boilers.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 20114
1.0 INTRODUCTION 

This document is to support Ecology’s determination of the BART for the TransAlta coal-fired power 

plant located near Centralia, Washington. 

The TransAlta plant is a coal-fired power plant rated to produce a net of 702.5 MW per unit. The 

plant has two tangentially fired pulverized coal units currently using PRB sub-bituminous coals for 

fuel. 

In a letter dated October 16, 1995, the National Park Service (NPS) notified Ecology certified that 

there was uniform haze visibility impairment at Mt. Rainier National Park. The NPS expressed their 

belief that some or all of the haze was attributable to emissions from the Centralia coal-fired power 

plant. 

In 1998, the SWCAA issued a RACT, Order No. 97-2057R1, for compliance with the requirements 

of Chapter 70.94.153 Revised Code of Washington. This order established emission reductions for 

SO2 and NOx emissions from the coal-fired boilers at the plant. The emission limitations in the 

Order were the results of a negotiation process involving SWCAA, the plant’s ownership group, 

NPS, U.S. Forest Service, Ecology, and EPA Region 10. 

On June 11, 2003, EPA Region 10 approved Ecology’s Visibility State Implementation Plan 

(Visibility SIP) submitted on November 9, 1999.6 Ecology included the RACT emission reductions 

for Centralia as evidence of further progress in meeting the national visibility goals, but not as BART 

since no determination of attribution had been made as was required by the visibility rules in place in 

1997. The Federal Register notice approving this 1999 submittal notes that while the NPS had 

certified visibility impairment at Mt. Rainier National Park, “The State of Washington has not 

determined that this visibility impairment is reasonably attributable to the Centralia Power Plant

(CPP).” 

The EPA approval of Ecology’s 1999 Visibility SIP submittal included a determination by EPA that 

the SO2 and PM limits and controls required by the 1997 RACT Order issued by SWCAA met the 

requirements of BART. EPA’s determination that SO2 and PM emissions were BART level of 

control were based on an analysis performed by Region 10 staff and an example analysis in the 

Technical Support Document issued by SWCAA. 

In the Federal Register notice, EPA specifically did not include the NOx emission limit in the RACT 

Order as BART stating “while the NOx emission limitation may have represented BART when the 

emission limits in the RACT Order were negotiated, recent technology advancements have been 

made. EPA cannot say that the emission limitations in the SWAPCA7 RACT Order for NOx

represent BART.”

6 68 Federal Register 34821, June 11, 2003. 7 At the time, SWCAA was known as the Southwest Air Pollution Control Agency (SWAPCA).

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 20115
As a result of the June 11, 2003, approval of the Washington State Visibility SIP, the TransAlta plant 

is subject to BART under the Regional Haze (RH) program only for its NOx emissions.

8

1.1 The BART Analysis Process 

TransAlta and Ecology used EPA’s BART guidance contained in Appendix Y to 40 CFR Part 51, as 

annotated by Ecology, to determine BART. The BART determination for coal-fired power plants 

greater than 750 MW of total output must follow the process in BART guidance. The BART analysis 

protocol reflects utilization of a five-step analysis to determine BART. The five steps are:

1. Identify all available retrofit control technologies.

2. Eliminate technically infeasible control technologies.

3. Evaluate the control effectiveness of remaining control technologies. 

4. Evaluate impacts and document the results

5. Evaluate visibility impacts.

The BART guidance limits the types of control technologies that need to be evaluated in the BART 

process to available control technologies. Available control technologies are those which have been

applied in practice in the industry. The state can consider additional control techniques beyond those 

that are “available,” but is not required to do so. This limitation to available control technologies 

contrasts to the Best Available Control Technology (BACT) process where innovative technologies 

and techniques that have been applied to similar flue gases must be considered. 

In accordance with the EPA BART guidance, Ecology weighs all five factors in its BART 

determinations. To be selected as BART, a control has to be available, technically feasible, cost 

effective, provide a visibility benefit, and have minimal potential for adverse non-air quality impacts. 

Normally, the potential visibility improvement from a particular control technology is only one of the 

factors weighed for determining whether a control constitutes BART. However, if two available and 

feasible controls are essentially equivalent in cost effectiveness and non-air quality impacts, visibility 

improvement becomes the deciding factor in the determination of BART.

1.2 Basic Description of the TransAlta Centralia Generation LLC Power Plant

The TransAlta plant is a two-unit, pulverized coal boiler based power plant that currently uses PRB

coal. The boilers were initially commissioned in 1971 and 1972. Each unit is currently rated at 702.5 

MW (net) output capacity when using coal from the Centralia coal field. The units are physically 

identical, tangentially fired, wet bottom units designed by Combustion Engineering. 

TransAlta also operates two other generating resources that are part of the Centralia Power Plant 

complex. Operating under the name of Centralia Gas is a group of four combined cycle combustion 

turbines producing 248 MW. The combustion turbines were built in 2002 and were subject to 

Prevention of Significant Deterioration (PSD) permitting requirements. They are currently operated 

as peaking units. The combined cycle turbines are electrically and physically separate from the coal 

8 Mahbubul Islam, EPA Region 10, “Best Available Retrofit Technology Applicability for the TransAlta Centralia Power 

Plant,” letter, addressed to Robert Elliott, SWCAA, and Phyllis Baas, Ecology, September 18, 2007.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 20116
units. There is also a one MW hydropower facility located at TransAlta’s Skookumchuck River Dam 

and Reservoir. 

In addition to the above electricity generating units, the plant includes numerous other units, 

including an oil-fired auxiliary boiler used for cold starting of the coal-fired boilers and steam 

turbines. The auxiliary boiler is a 170 MMBtu/hr, oil-fired unit permitted to operate on #2 distillate 

oil (with less than 0.5 percent sulfur by weight) for a maximum of 600,000 gallons per year. The SO2

emissions from fuel oil combustion in this unit are included in the coal boiler SO2 emission 

limitation. The potential to emit of NOx from this unit is 7.2 ton/year and SO2 of 77 ton/year.

SO2 control on the two coal-fired boilers is provided by a wet limestone, forced oxidation wet 

scrubber system. This system removes over 95 percent of SO2 in the flue gas from the boilers. The

SO2 controls were installed in the 1999–2002 time period. 

Particulate control is provided by two electrostatic precipitators in series followed by the wet 

scrubber system. The first electrostatic precipitators were part of the original construction of the 

plant. The second precipitators date from the late 1970s. 

Current NOx control is provided by combustion modifications incorporating Alstom concentric 

firing, low NOx burners with close coupled and separated over-fire air.

9

 These combustion 

modifications are collectively known as Low NOx Combustion, Level 3 (LNC3).” The controls were 

installed in the 2000–2002 time period in response to the RACT Order. The combustion controls 

were designed and optimized to suit Centralia Mine coal. 

For a variety of reasons, TransAlta stopped active mining at the Centralia Coal Mine and now 

purchases all coal from PRB coal fields. To accommodate the change, the company has modified the 

rail car unloading system to handle up to 10 coal unit trains per week. Additional modifications are 

focused on the boilers. The boilers have been modified to reduce temperatures in the flue gas to 

accommodate the higher Btu coal now being combusted. Additional changes include the 

reinstallation of specific soot blowers and installation of new soot blowing equipment (steam lances) 

necessary to accommodate the different ash characteristics of the PRB coals. Improved fire 

suppression equipment has been installed to accommodate the increased potential of PRB coals to 

catch fire spontaneously. 

The use of PRB coals has resulted in the derating of the output capacity of the facility. TransAlta 

reports on their corporate internet pages that the Centralia facility is rated at 1340 MW or 670 MW 

per unit. 

Prior to 2010, TransAlta anticipated operating the plant until at least 2030. They acknowledge that to 

operate beyond 2025 will require significant plant upgrades to assure safe and reliable operation into 

the future. 

On May 21, 2009, the Governor of Washington State issued Executive Order 09-05, Washington’s 

Leadership on Climate Change. This Executive Order contained provisions that affected the 

9 This set of combustion controls are the basis of the presumptive BART limits of 0.15 lb NOx/MMBtu in Section 4.E of 

EPA’s BART Guideline. 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 20117
remaining useful lifetime of the coal units at the plant. This Executive Order has now been 

superseded by amendments to Chapter 80.80 RCW contained in Chapter 180, Laws of 2011. These 

amendments require the coal units at the plant to come into compliance with the GHG emission 

performance standard established in RCW 80.80.040. One unit is required to be in compliance by 

December 31, 2020, while the other is required to comply by December 31, 2025. The amendments 

also provide that if Ecology determines that state or federal law or regulations require the installation 

of SCR on the coal units, that the requirement to comply with the GHG emission standard will not 

apply. 

The power plant is subject to the federal Clean Air Act's Title V permitting program. The plant 

operations are covered by Air Operating Permit No. SW98-8-R3, issued September 2009 by 

SWCAA. 

Ecology received a BART analysis from TransAlta in February 2008, which was revised and 

resubmitted in July 2008 and supplemented in December 2008 and March 2010. The original BART 

determination was issued June 2010. 

The Revised BART Order is based on the above materials supplemented by additional BART 

decision information and material submitted by letter from Bob Nelson, Plant Manager, to Alan 

Newman of Ecology on August 8, 2011. This letter responded to a preliminary draft of the Revised 

BART Order and a Revised BART Determination Support Document that was developed for review 

and comment by the company, environmental group representatives, and EPA Region 10. 

1.3 BART Eligible Units and Pollutant at TransAlta Centralia Power Plant

The TransAlta facility located near Centralia, Washington, includes a number of different operations 

and units. Emissions from the plant are primarily generated and emitted by the two coal-fired boilers 

of the main power plant. The oil-fired auxiliary boiler is operated infrequently and is permitted to 

use a limited number of gallons of diesel fuel oil each year. The auxiliary boiler is used during cold 

start-up of the coal boilers to heat the boiler water to prevent thermal shock and failure of cold boiler 

tubes and for preheating of the steam turbines. Emissions from the auxiliary boiler were not 

evaluated for BART. 

As noted above, NOx is the only pollutant addressed in this BART analysis. As required by the 

BART guidance and modeling protocol, the maximum day emission rate in the calendar 2003 to 2005 

period was determined. The hourly NOx emissions on the day with maximum emissions during the 

baseline period (2003–2005) were 2,474 lb/hr (0.302 lb/MMBtu) for Unit 1 and 2,510 lb/hr (0.306 

lb/MMBtu) for Unit 2.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 20118
1.4 Visibility Impact of BART Eligible Units at TransAlta Centralia Power

Plant

Class I area visibility impairment and improvement modeling was performed by TransAlta using the 

BART modeling protocol developed by Oregon, Idaho, Washington, and EPA Region 10.10 This 

protocol uses three years of metrological information to evaluate visibility impacts. As directed in 

the protocol, TransAlta used the highest 24-hour emission rates for NOx, SO2, and PM/PM10 that 

occurred in the 3-year period to model its impacts on Class I areas. The modeled SO2 and PM/ 

Coarse Particle Matter (PM10) emission rates complied with their respective emission limits. The 

modeling indicates that the emissions from this plant cause visibility impairment on the 8th highest 

day in any one year and the 22nd highest day as all mandatory federal Class I areas within 300 km of 

the power plant.11 For more information on visibility impacts of this facility, see Section 3 below.

1.5 Relationship to 1997 RACT Analysis and Determination

As noted previously, in 1997 the SWCAA finalized a determination of RACT for the Centralia Power 

Plant. As part of the technical analysis that led to the determination of RACT for NOx emissions 

from this plant, 37 different emission control alternatives were evaluated (see Appendix B for the 

list). The analysis documents produced by the plant’s owners reviewed many alternative techniques 

potentially applicable to the facility. The list of controls reviewed ranged from proven methods of 

combustion control to methods that had only been proven to work in the laboratory. The alternate 

technologies evaluated at that time included methods such as natural gas reburn, SNCR, SCR, and 

several options which could control NOx and SO2 with the same control system. 

As discussed in the company’s analysis and the SWCAA support document, these technologies were 

not selected as RACT for NOx emissions in favor of the installation of the package of combustion 

modifications that are now recognized as LNC3. 

Since the 1997 RACT determination, Ecology has tracked development and installations of NOx

control technologies. Based on the large list of emission controls that had been reviewed to support 

the RACT determination, the relatively slow development of some techniques, and disappearance of 

some other techniques, Ecology allowed TransAlta to use the evaluation from the 1997 RACT

determination to narrow the list of potential control technologies appropriate for this BART review. 

The BART analysis by TransAlta focused on those controls that are available and have been 

implemented on coal-fired boilers of the general size of the plant. For more details on the control 

options evaluated for the RACT analysis, please refer to the RACT report by PacifiCorp for the 

Centralia Power Plant and the SWCAA Technical Support Document supporting the RACT 

determination. 

10 A copy of the modeling protocol is available at http://www.deq.state.or.us/aq/haze/docs/bartprotocol.pdf. 11 A source causes visibility impairment if its modeled visibility impact is above 1 dv, and contributes to visibility 

impairment if its modeled visibility impact is above 0.5 dv.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 20119
2.0 SUMMARY OF TRANSALTA CENTRALIA POWER PLANT’S BART 

ANALYSIS

The TransAlta’s BART technology analysis was based on the 5-step process defined in BART 

guidance and listed in Section 1.1 of this report. This section is an overview of TransAlta’s BART 

analysis and supplemental material provided by the plant’s owner. 

2.1 NOx Controls Evaluated

The plant already has installed combustion controls to reduce NOx emissions from thermal NOx. 

The controls currently installed are considered the base case from which the effects of other controls 

are evaluated. 

Table 2-1 Nitrogen Oxides Controls Evaluated 

Control Technology Control Efficiency Technically Feasible?

Low NOx burners with close coupled and 

separated over-fire air (LNC3) -- Yes, already installed under RACT

Flex Fuels Project—Existing LNC3 

combustion controls plus change in fuel to 

PRB coal and boiler modifications to 

accommodate use of PRB-type coals

Yes, LNC3 already installed, Unit 

2 Flex Fuel modifications 

completed and both units are 

operating in compliance with the 

original BART Order signed June 

18, 2010

SCR Up to 95% 

reduction Yes

SNCR 20%-40% reduction Yes

ROFA/RotaMix Unknown No

Neural net controls Up to 15% Yes

Low NOx Combustion, Level 3

As noted above, the combustion controls known as Low Nitrogen Oxides Combustion, Level 3, 

(LNC3) are currently installed on each of the coal-fired boilers at the plant. These controls have 

demonstrated an ability to meet the current NOx emission limit of 0.30 lb NOx/MMBtu using 

Centralia Mine coal and PRB coals. 

The Centralia Power Plant’s implementation of the LNC3 technology was included in EPA’s control 

effectiveness evaluations leading to its determination of the presumptive BART limits of 0.15 lb 

NOx/MMBtu in Section 4.E of EPA’s BART Guideline. In 2004 in connection with its adoption of 

the final BART Guidelines, EPA found that of the 17 boilers in the U.S. with the boiler design of the 

Centralia Power Plant’s (tangential-fired) that burn sub-bituminous coal, two of the units with LNC3 

installed prior to 1997 did not meet the presumptive BART limit. Seven of the units with pre-1997 

design did meet the presumptive limit. Of the remaining eight units with LNC3 technology installed 

in 1997 or after, the two Centralia boilers were the only two that did not meet the presumptive limit 

(EPA-HQ-OAQ-2002-076-0446(1) TSD). 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201110
Subsequent to the public comment period on the proposed BART determination, TransAlta was 

requested to supply additional information on the installation of LNC3 at this facility. This additional 

detail is contained in a March 31, 2010, report from CH2M HILL to Mr. Richard Griffith (Appendix 

G). 

The LNC3 system installed met its original design intent of a one-third reduction in NOx from the 

boiler. 

Subsequent to the initial burner installation, the company reports no additional analyses or boiler 

tuning operations beyond what is done in the normal course of operating the boilers. 

Flex Fuels Project

TransAlta has proposed its Flex Fuels Project as an addition to the currently installed LNC3 

combustion controls for consideration as BART emission control. The Flex Fuels Project is a series 

of actions being undertaken by the company to accommodate the exclusive use of sub-bituminous 

coals with ash, nitrogen and sulfur contents similar to PRB sub-bituminous coals. Combustion 

modeling of the boilers performed by Black & Veatch using EPRI’s Vista model using a 

representative PRB coal has indicated that the proposed changes will result in a reduction of the 

hourly and annual emission rate for NOx. 

TransAlta decided to rely on PRB coal after suspending mining operations for Centralia subbituminous coal at the end of 2006. PRB coals have a number of characteristics that differ 

significantly from the Centralia coal the plant was designed to use. Important characteristics that 

affect the boilers’ operation are the net heat content, the quantity of ash, and the abundance of 

sodium. Appendix A contains tables showing the important characteristics of typical PRB coals and 

the Centralia coal. 

The most important differences between the coals is the heat content British Thermal Units Per 

Pound (Btu/lb), lower fuel nitrogen, lower sulfur content, the moisture content, and the concentration 

of sodium. Centralia coal is very low in sodium, higher in fuel nitrogen and sulfur content, and much 

higher in water content than the PRB coals. The difference in sodium content changes the ash that 

deposits on the boiler tubes from light and fluffy (Centralia) to glassy and sticky (PRB). 

The boiler tube slagging and fouling characteristics of PRB coal increase the heat rates of the boilers 

compared with Centralia Mine coal. The Flex Fuels Project incorporates physical changes to the 

pressure parts in each boiler’s convective pass that improve heat transfer by reducing the boiler’s 

susceptibility to ash deposition. The major individual pressure part changes include: (a) reheater 

replacement to maximize soot blower cleaning effectiveness on the tube assembly surface areas, and 

(b) additional low temperature superheater and economizer heat transfer surface area to result in

higher boiler efficiency and a lower flue gas exit temperature. Other significant changes associated 

with this project are reinstallation of some of the original soot blowers and installation of new ‘soot 

blowing’ equipment specifically designed to remove the now sticky and glassy soot from the boiler 

tubes. These changes allow for more efficient heat transfer within the boiler. Additional discussion 

of this project’s effects and the combustion thermodynamic modeling performed to estimate the 

emissions decrease from the project can be found in the BART Analysis Supplement by TransAlta 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201111
dated December 2008 and the TransAlta Centralia Boiler Emissions Modeling Study by Black & 

Veatch, dated September 2007. 

No changes to the fuel delivery equipment (other than adding fire suppression equipment), burners, 

combustion air system, or steam turbine are being made. The Flex Fuels Project allows the boilers to 

burn PRB coal more efficiently, but does not increase the boilers’ potential steam generating 

capacity.

The lower nitrogen content of the PRB coals combined with the lower total quantity of fuel required 

to produce the same heat input rate to the boilers after the project has been completed on both units. 

The reduction in total fuel combusted will reduce the emissions of NOx by approximately 20 percent

from the rates during 2003–2005 period. The emission rates during that baseline period averaged 

0.304 lb NOx/MMBtu and at the completion of the Flex Fuels Project are expected to be below 0.24 

lb/MMBtu. 

Annual average NOx emissions from December 1, 2003 through November 31, 2005 were 15,695 

tons. Based on the proposed BART rate of 0.24 lb/MMBtu, the BART limit would reduce emissions 

by 3,139 tons/year to 12,556 tons/year. 

The estimated capital to implement Flex Fuels on both units is $101,808,663, based on the actual 

costs to implement the Flex Fuels Project on Unit 2 and the expected costs of installation on Unit 1. 

The annualized cost of the Flex Fuels Project is $11,184,197. Based on the estimated NOx

reductions of 3,139 tons/year, the cost effectiveness of the Flex Fuels Project is $3,563/ton of NOx

reduced. Since the Flex Fuels Project also reduces SO2 emissions by an estimated 1,287 tons/year, 

TransAlta has calculated that the overall cost effectiveness of the Flex Fuels Project as $2,526/ton of 

NOx plus SO2 reduced.

12

Neural Net Controls 

Neural net controls for boilers are a relatively new technique. It is based on using a number of 

different boiler operational information and using that information to continuously optimize the 

combustion efficiency of the boiler. While numerous vendors will provide this technology, 

TransAlta received detailed information from NeuCo, Inc. (NeuCo). NeuCo offers several neural net 

optimization products. Two of their products, CombustionOpt and SootOpt, provide the potential for 

NOx reduction at some facilities. Both CombustionOpt and SootOpt are control-system-based 

products. CombustionOpt provides for optimized control of fuel and air to reduce NOx and improve 

fuel efficiency. SootOpt improves boiler soot blowing by proportioning heat transfer and reducing 

“hot spots” resulting from ineffective cleaning. NeuCo stated that these products can be used on 

most boiler control systems and can be effective even in conjunction with other NOx reduction 

technologies. 

NeuCo predicts that generally CombustionOpt can reduce NOx by 15 percent, and SootOpt can 

provide an additional 5 to 10 percent. Expected NOx reductions are very unit-specific, and actual 

results may vary greatly. Previously received budgetary prices for CombustionOpt and SootOpt were 

12 Because the Flex Fuels Project is not being implemented for the primary purpose of emissions reduction, these cost 

effectiveness values are not directly comparable to those for installation of a control technology.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201112
$150,000 and $175,000, respectively, with an additional $200,000 cost for a process link to the unit 

control system.

Because NeuCo does not guarantee NOx reduction, the estimated emission reduction levels provided 

are not considered as reliable projections. In light of the uncertain and unquantifiable emission 

reductions, TransAlta considers a neural net system as a potential supplementary or polishing 

technology, but not as an applicable NOx technology for this BART analysis. Because of the 

potential NOx reductions and cost effectiveness, TransAlta is continuing to investigate use of this 

technique at this plant. 

Selective Noncatalytic Reduction 

SNCR is generally used to achieve modest NOx reductions. It is often chosen to augment 

combustion controls on older coal-fired boiler units, which are generally smaller units (units with 

heat input less than 3,000 MMBtu/hr) and industrial boilers. With SNCR, an ammonia or urea 

solution is injected into a location in the furnace that provides a temperature range of 1,600 degrees 

Fahrenheit (°F) to 2,100°F and provides a minimum detention time for the reaction to occur. Within 

this temperature range, the ammonia or urea reduces NOx to nitrogen and water. NOx reductions of 

up to 60 percent have been achieved, although 20 to 40 percent is more realistic for most 

applications. 

Reagent utilization, which is a measure of the efficiency with which the reagent reduces NOx, can 

range from 20 to 60 percent, depending on the amount of reduction to be achieved, unit size, 

operating conditions, and allowable ammonia slip. If the temperature in the boiler at the location of 

the ammonia injection is too high or too much ammonia is injected, the ammonia or urea is oxidized 

to NOx. With low reagent utilization, low temperatures, or inadequate mixing, ammonia slip occurs, 

allowing unreacted ammonia to create problems downstream. 

There are a number of potential adverse impacts due to ammonia slip. Unreacted ammonia can 

contaminate the fly ash collected in the ESPs that is sold for making concrete. If the ammonia 

concentration in the fly ash is high enough, it will render the fly ash odorous and unsaleable.

13 If the 

fly ash is unsaleable to make concrete, it would require disposal in a landfill or could be sold to a 

cement plant as a raw material to make cement. If used to make cement, the heating of the fly ash in 

a cement kiln will release any mercury that may be contained in the fly ash.

Two additional issues with ammonia slip are that ammonia is listed as a toxic air pollutant by 

Ecology, and its discharge from the stack may result in additional impacts. The unreacted ammonia 

may also react with sulfur oxides to generate ammonium sulfate or bisulfate to foul economizer, air 

preheater, and other duct surfaces. At facilities where there is no wet scrubber system included, 

excess ammonia may also create a visible stack plume. Since the TransAlta plant has a wet scrubber, 

no additional plume visibility would be anticipated.

13 Fly ash is reported to lose its desirability as a concrete admixture if the ammonia content is high enough that detectable 

levels of ammonia will be volatilized from the fly ash when it is mixed into the wet concrete. Ammonium on or in the fly 

ash is converted to ammonia when the pH of the mixture rises. At a pH of 12, essentially all the ammonium is converted 

to ammonia in solution. Based on Ecology’s review of the available literature, it is unlikely that a properly controlled 

SNCR system will cause any adverse impacts to fly ash sales due to ammonia slip.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201113
The control effectiveness of SNCR is a function of many variables, including the uncontrolled 

emissions concentrations, physical conditions, and operational conditions. A study by Harmon14

(1998) indicates that a large coal fired, tangentially fired unit equipped with a low NOx SNCR has 

the potential to reduce NOx emissions by only 20 to 25 percent with an ammonia slip of less than 10 

ppm. The EPA Office of Air Quality Planning and Standards’ EPA Air Pollution Control Cost 

Manual (EPA, 2002) states, “SNCR systems applied to large combustion units (greater than 3,000 

MMBtu/hr) typically have lower NOx reduction efficiencies (less than 40 percent), due to mixing 

limitations.” The Centralia Power Plant units have heat input rates of much greater than 3,000 

MMBtu/hr (above 7,000 MMBtu/hr15). After considering the above factors and a reasonable 

compliance factor, TransAlta selected a control effectiveness of 25 percent for its evaluation. 

TransAlta’s cost analysis uses a urea-based SNCR system providing a nominal 25 percent reduction 

in NOx levels with a 5 ppm ammonia slip. A 5 ppm ammonia slip is the maximum recommended 

taking into account the flue gas sulfur levels to avoid problems with ammonium sulfate and bisulfate 

fouling of the air heater. To achieve the proposed reduction, multiple nozzle lances are proposed to 

handle load changes from 50 to 100 percent. 

Retrofit costs to incorporate SNCR at this facility are included in the cost estimate. These retrofit 

costs are higher than for other similarly sized facilities due to an extremely tight boiler outlet 

configuration, limited available space for new equipment, probable modifications to boiler tubes to 

accommodate the urea injection lances, construction access difficulties to install SNCR injection 

equipment, and location of urea storage and solution preparation equipment. 

TransAlta has estimated that use of SNCR on their units would consume about 700 kW-h of 

electricity per unit, or a total of 1.4 MW-h for both units. 

The anticipated 25 percent reduction in emissions from the installation of SNCR would result in an 

emissions limitation of 0.225 lb/MMBtu and an emission reduction of 3,923 tons/year. TransAlta has 

estimated that the estimates of capital cost including the retrofit costs, adding SNCR to both units at 

the plant would cost $33.2 million with a cost effectiveness of $2,258/ton NOx reduced.

Subsequent to the public comment period on the proposed BART determination, TransAlta was 

requested to supply additional information on the use and cost of SNCR at this facility. The company 

had its contractor supply additional information related to the basis of its SNCR cost estimates. This 

additional detail is contained in a March 31, 2010, report from CH2M HILL to Mr. Richard Griffith

(Appendix G). The additional detail indicates the cost estimating approach utilized by CH2M HILL

on this BART analysis. 

The March 31, 2010, report indicates that the SNCR cost estimates in the June 2008 BART analysis 

were “budgetary estimates” supplemented by vendor quote of costs and NOx removal efficiency from 

Fuel Tech.

Selective Catalytic Reduction 

14 Harmon, A., et al, 1998, Evaluation of SNCR Performance on Large-Scale Coal-Fired Boilers, Institute of Clean Air 

Companies (ICAC) Forum on Cutting NOx Emissions, Durham, NC, March 1998. 15 2008 Acid Rain Program report lists the heat input rate at 8500 MMBtu/hr/boiler.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201114
SCR works on the same chemical principle as SNCR, but SCR uses a catalyst to promote the 

chemical reaction. Ammonia or urea is injected into the flue gas stream, where it reduces NOx to 

nitrogen and water. Unlike the high temperatures required for SNCR, the SCR reaction takes place 

on the surface of a vanadium/titanium-based catalyst at a temperature range between 580°F and 

850°F. Due to the catalyst, the SCR process is more efficient than SNCR resulting in lower NOx and 

ammonia emissions. Typically, an SCR system can provide between 70 and 95 percent reduction in 

NOx emissions. 

On coal-fired power plants, the most common type of SCR installation is known as the hot-side highdust configuration, where the catalyst is located downstream from the boiler economizer and 

upstream of the air heater and particulate control equipment. In this location, the SCR is exposed to 

the full concentration of fly ash in the flue gas that is leaving the boiler. An alternate location for an 

SCR system is downstream of the air heater or the particulate control device. In many cases, this 

location is compatible with use of a low temperature SCR catalyst or is within the low end of the 

temperature range of a conventional catalyst. Because the temperature of the flue gas leaving the air 

heaters and the Electrostatic Precipitators (ESPs) is too cool for the low temperature versions of SCR 

catalyst to operate, the high-dust configuration is assumed for TransAlta. 

In a new boiler installation or a retrofit installation where the existing boiler has minimal emission 

controls installed, the flue gases flow downward through the catalyst to aid in dust removal. In a 

retrofit situation, the SCR catalyst is often located in the existing gas duct, which may be expanded in 

the area of the catalyst to reduce flue gas flow velocity and increase flue gas residence time to 

maximize removal efficiency and minimize ammonia usage. As an alternate location, the catalyst 

bed in a retrofit situation may be installed in a “loop” of ducting. This loop may be horizontal or 

vertical in orientation, depending on how the flow in the duct that is intercepted is routed and 

available space to locate the catalyst bed. 

A new installation type SCR costing was used as the basis for analysis at the Centralia Power Plant

because of the limited space to install an SCR catalyst in the existing flue duct and the ability to 

design for a 90-plus percent reduction catalyst bed. The short distance between the boiler air heater

and the entrance to the first ESP does not provide the room required for a catalyst bed with 

reasonable temperatures or velocities to be inserted in the existing flue gas duct.16 The ducts from 

each boiler to the ESP have a relatively high velocity, such that the amount of catalyst that could fit 

into the unmodified duct would have minimal effectiveness due to the short residence time through 

the catalyst bed. 

As a result of electing to use a design capable of 90-plus percent NOx reduction, an adjustment was 

used for SCR cost estimates due to the Centralia Power Plant’s extremely tight boiler outlet ductwork 

configuration as shown in Figures 3-3, 3-4, and 3-5 of the June 2008 Revised BART Analysis and 

March 2010 supplement. As can be seen in the figures, installation of a full-scale SCR system 

requires reconfiguration of the flue ducts from the boilers, structural modifications of the first ESPs 

(or installation of all new structural support to hold the weight of the catalyst beds and ductwork) to 

accommodate the weight of the SCR catalyst and duct work, and realignment of the duct work from 

16 See Figures ES-1, 3.2, 3-4, and 3.5 of the BART Analysis for Centralia Power Plant, revised July 2008 and 

supplemented March 2010.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201115
the economizers to the air preheaters. The restricted site layout, support structure needs, intricate 

duct routing, limited construction space, and complexity of erection increases the capital cost.

Each boiler at the Centralia Power Plant has two exhaust gas ducts to aid in splitting the flow to the 

ESPs. As a result, each boiler would require two smaller, separate catalyst vessels instead of a single 

large catalyst vessel. The capital cost of installing dual catalyst vessels for each unit is slightly 

greater than a single catalyst vessel for units of similar size.

As in the case for SNCR, a potential adverse impact due to unreacted ammonia from the SCR system

is that it may render fly ash unsaleable. At facilities where there is no wet scrubber system included, 

excess ammonia could also create a visible stack plume. Again, TransAlta has a wet scrubber, so a 

visible stack plume from ammonia is not likely. 

As stated in TransAlta’s BART analysis, a SCR retrofit increases the electricity consumed by the 

existing flue gas fan system to overcome the additional pressure drop associated with the new 

catalyst, typically a 6- to 8-inch water gage increase.

17 The increase in pressure drop results in 

marginally higher operating costs. Since the BART analysis uses a planning level cost analysis, there 

has not been a more detailed engineering study of all components that may be affected by adding the 

SCR system. 

TransAlta evaluated twp options to use SCR at the plant. One option included SCR on only one unit 

to achieve the Presumptive BART emission limit of 0.15 lb NOx/MMBtu, both units averaged 

together. The other option included SCR on both units. 

The emissions reduction for installation of SCR (at a 95 percent removal rate) on one unit would be 

4,364 tons/year. The capital cost for including SCR on only one unit was estimated to be $290.1 

million with a cost effectiveness of $8,205/ton NOx reduced. 

The emissions reduction for installation of SCR (at a 95 percent removal rate) on both units would be 

7,855 tons/year. The capital cost for including SCR on both units would be double that for one unit 

with a cost effectiveness of $9,091/ton NOx reduced. 

Subsequent to the public comment period on the proposed BART determination, TransAlta was 

requested to supply additional information on the use and cost of SCR at this facility. 

In addition to the more readily readable drawings (Appendix F), the company had its contractor 

supply additional information related to the basis of its SCR cost estimates. This additional detail is 

contained in a March 31, 2010, report from CH2M HILL to Mr. Richard Griffith (Appendix G). The 

additional detail indicates the cost estimating approach utilized by CH2M HILL on this BART 

analysis. The approach described involved a company reevaluation of historical information updated 

with current equipment, material, and constructions costs, including cost estimates based on 

preliminary engineering sketches. The March 31 submittal indicates that a basic capital cost for a 

SCR system of $200/kW was used as the basis for the cost estimate. This basic cost was then scaled 

by CH2M HILL’s engineering judgment of the costs and complexity to install a SCR system on these 

boilers. As part of this additional analysis, the predicted TransAlta costs were compared to costs for 

17 Associated with providing a gas velocity through the catalyst beds below 20 ft/sec.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201116
other coal-fired power plants in the western U.S. (in Attachment 1 of the March 31, 2010 report). 

The cost analyses compared were performed by CH2M HILL and four other consulting firms. Many

have been determined to be BART by the various states. The cost for SCR at the Boardman OR plant

is listed as $382/kW versus $413/kW at Centralia. Both costs can be considered to be essentially 

equivalent since both are well within the +/-30% cost estimating range of the EPA Control Cost 

Manual and CH2M HILL’s +50%/-20% estimate range of each other’s cost analyses. 

The March 31, 2010, report also contains an improved description of how CH2M HILL envisioned 

the proposed SCR system to be installed and operated. Their proposal would have the SCR system 

installed in a “hot, dirty” location taking hot flue gas from the economizer and returning it to before 

the air preheater. The “hot, dirty” location in the flow path assures the catalyst bed would be at 

proper operating temperatures. The catalyst beds would be located above the first ESPs to avoid 

structural supports in the current access way under the divergent ducting between the air preheater 

and the ESP inlets. Structural supports would block plant operations and maintenance staff access to 

equipment and the ESPs. Locating the catalyst above the ESP would also provide the duct length to 

provide for lower velocities through the catalyst bed. The structural needs to support the weight of 

the ductwork and the catalyst beds were evaluated qualitatively.

In response to Ecology’s questions resulting from public comment, TransAlta had CH2M HILL

evaluate two other locations where SCR catalyst could be installed (Appendix G). 

One location evaluated an installation between the ESPs and the wet Flue Gas Desulfurization (FGD) 

system. The analysis indicates the anticipated difficulties due to changes in flue gas volume and 

velocity resulting from reheating the flue gas to 700°F and adding aqueous ammonia reagent. The 

potential adverse impacts of flue gas reheating (even through a regenerative system) on operation of 

the wet scrubbers were not evaluated. 

The other location is in the ESP inlet ducting after the air preheater. The air preheater outlet is 

300°F, well below the normal range for SCR catalysts. To increase the temperature of the gas exiting 

the air preheater would require changes to the plant thermodynamics (by reducing the temperature of 

combustion air) and would impact the overall plant heat rate and efficiency. In this location, CH2M 

HILL has estimated that the catalyst bed could be no more than 17 feet deep without requiring 

significant modifications to the ductwork from the economizer to the air heater. CH2M HILL

presents information that in this location, one layer of catalyst would provide a five percent decrease 

in NOx with a five inch water gauge pressure drop. A 2-layer system would increase removal to 12

percent at a pressure drop of 15 inches water gauge. The effects of an increased back pressure on the 

boilers or the ability of the induced fans to accommodate this much increase in pressure drop was 

outside of the scope of CH2M HILL’s contract.

Rotating Over-fire Air and Rotamix 

Mobotec markets Rotating Over-fire Air (ROFA) as an improved second-generation over-fire air 

distribution system. In their system, the combustion gases in the boiler are set in rotation with 

asymmetrically placed air nozzles. According to Mobotec installation information, the ROFA 

technology alone has not been installed on any tangentially fired coal unit greater than 175 MW. 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201117
The Mobotec Rotamix technology is a modification of the SNCR process. The ammonia or urea 

solution is added using lances in conjunction with the ROFA air nozzles to improve both the 

chemical distribution and lengthen the residence time for the reactions to occur. According to the 

Mobotec installation list, the largest tangentially fired coal unit using the Mobotec ROFA/Rotamix 

combination is 175 MW. The Rotamix SNCR system is anticipated to provide NOx reductions 

similar to conventional SNCR systems.

18

Based upon the BART guidance, Mobotec ROFA and Rotamix technologies are ‘available’ because 

they have been installed and operated successfully on tangentially fired pulverized coal boilers. 

TransAlta believes that while the ROFA and Rotamix technology are ‘available’ control technologies

as described in the BART guideline, the use of either ROFA as a replacement or addition to the 

current over-fire air injection system or installation of the Rotamix process are not technically 

feasible technologies due to unknown difficulties with installation on their boilers. Due to perceived 

risks of scale-up to their unit size, TransAlta believes that these technologies are not applicable to 

their facility.

2.2 TransAlta’s Proposed BART

The existing LNC3 combustion controls (low NOx burners, close coupled and separated over-fire air) 

currently installed at the plant and the Flex Fuels Project meeting an emission limitation of 0.24 lb

NOx/MMBtu, 30-day average, were proposed as BART for their facility.

Subsequent to TransAlta’s BART analysis submittals, which proposed the Flex Fuels Project as 

BART, TransAlta, the Governor’s office, environmental organizations, and state legislators 

negotiated a different set of emission control requirements. 

 

The end result of the negotiation and agreement was enactment of amendments to Chapter 80.80, 

Revised Code of Washington, which requires the coal units at the plant to implement SNCR control 

by January 1, 2013, and to meet the state GHG emission performance standard in 2020 and 2025. All 

parties of the negotiation anticipate compliance will be through decommissioning of the existing coal 

fired units at the Centralia Power Plant. 

3.0 VISIBILITY IMPACTS AND DEGREE OF IMPROVEMENT 

TransAlta modeled the visibility impairment for the baseline years per the modeling protocol and the 

potential improvement from the control scenarios that they evaluated as potential BART controls for 

their facility. In modeling the emissions, they followed the BART modeling guidance prepared for 

use by sources in Washington, Oregon, and Idaho. In accordance with the EPA BART guidance, this 

modeling protocol utilizes the CALPUFF modeling system and the ‘old’ Interagency Monitoring of 

Protected Visual Environments (IMPROVE) equation to convert modeled concentrations to visual 

impairment. This approach is consistent with most of the states included in the Western Regional Air 

Partnership for modeling individual source visibility impairment. The ‘old’ IMPROVE equation is 

used because it is included within the CALPUFF modeling system and is part of the EPA accepted 

18 The Mobotec combustion air injection techniques were not evaluated as part of the RACT process. Their development 

occurred after the RACT determination had been made.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201118
version of the model per 40 CFR Part 51, Appendix W. A new equation is available, but is not 

included within the version of the CALPUFF modeling system specified in the modeling protocol. 

The results of the TransAlta modeling are shown in Table 3-1 for all Class I areas within 300 km of 

the plant plus the Columbia River Gorge National Scenic Area. Table 3-1 shows the maximum day 

impairment due to TransAlta, the highest of the three 98th percentile days of each year modeled, and 

the 98th percentile day of all three years modeled. Also shown is the modeled visibility impairment 

resulting from the control scenarios modeled by TransAlta. The modeled dv impacts for the baseline 

condition and the three control scenarios for the 98th percentile day (22nd day over the 3-year period) 

are included in Table 3-1.19 

The emission rates modeled were derived from operating records for each boiler and reflect the 

highest 24-hour emission rate within the three years that were modeled. The proposed emission rates 

were applied to this maximum 24-hour operating rate and those rates were then used for modeling the 

visibility impairment/improvement that could be achieved through the use of the proposed controls. 

The modeled emission rates are shown in Table 3-1. 

The modeled visibility impairment indicates that the plant causes visibility impairment at all Class I 

areas within 300 km of the plant. The tables include modeled visibility levels for three alternative 

control scenarios, including the highest level of control considered by TransAlta to be available for 

the plant, SCR applied to both boilers. 

Ecology modelers have reviewed the modeling performed by TransAlta and have found that the 

modeling complies with the Modeling Protocol and produces a reasonable result. 

The modeled emission reductions from the control options modeled by the company result in

substantial reduction in the visibility impairment caused by the Centralia Power Plant in all Class I 

areas modeled and in the Columbia River Gorge NSA. For example, Table 3-120 shows that at the 

three most heavily impacted Class I areas, Olympic National Park, Mt. Rainier National Park, and the 

Goat Rocks Wilderness, TransAlta’s proposed BART controls would provide 1.13 to 1.45 dv 

reduction in visibility impairment in each of these areas. All Class I areas within 300 km of the plant 

are modeled to have visibility improvements of at least 0.2 dv from the NOx emission reduction from 

use of SNCR or Flex Fuels. Combined with the effects of the reduction in SO2 from implementation 

proposed BART controls, the minimum visibility improvement is 0.67 dv. 

The initial modeling for the control scenarios in the table evaluated only the NOx reduction impacts. 

Effects of SO2 reductions, which would occur as a result of implementing the Flex Fuels Project, 

were not initially evaluated by TransAlta. 

The actual SO2 emission rates from usage of PRB coals are anticipated to result in an additional 

reduction of about 1,287 tons/year from the baseline emission rates. Subsequent to the public 

19 See the BART Determination Modeling Analysis, TransAlta Centralia Generation Power Plant by Geomatrix 

Consultants, Inc, June 2008, for additional information on the modeling results for the other control scenarios evaluated. 

This report is part of the July 2008 BART analysis report.

20 Revised from the prior version of this document with the modeling results in the March 2010 modeling. This additional 

modeling was performed in response to public comments on the proposed BART determination.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201119
comment period, Ecology requested and TransAlta remodeled the Flex Fuels Project emissions to 

include the effect of the SO2 reduction from use of the PRB coals. The results of this remodeling are

portrayed in Table 3-1. Control Scenario 3 was not included in the table as presented during the 

public comment period but was available in TransAlta’s July 2008 BART Analysis Revision. 

In their review of the initial modeling results, TransAlta’s modeling consultant evaluated the 

modeling results to see if there were any patterns to the modeled impacts, such as season of the year, 

primary pollutant, or grouping of Class I area. Their review indicated that groups of Class I areas

exhibited similar patterns. They found that the 12 Class I areas fell into four groups, which coincide 

with both their physical locations and the modeled visibility effects. For their evaluation, see pages 8 

and 9 of the June 2008 BART modeling report. 

The important points to consider are that for the “East” group (Mt. Rainier National Park and Goat 

Rocks and Mt. Adams Wildernesses) most impacts occurred in the summer due to SO2 emissions. 

The expected high impacts due to NOx do not occur because the weather patterns transport the 

plant’s plume to other areas in the winter seasons. The impacts on Olympic National Park, (the sole 

member of the “Northwest” group) occur during wintertime stagnation episodes. While not 

mentioned in the report, this impact would be dominated by nitrates. For the “South” group (Mt. 

Hood, Mt. Jefferson, and Three Sisters Wildernesses) there are summertime impacts, but the highest 

potential visibility changes occur in the winter during wintertime stagnation episodes. Again, the 

wintertime events are dominated by nitrates. At the remaining four Class I areas (the “Northeast” 

group), there was no obvious seasonality or trends. The figures in Appendix D graphically depict this 

information for some of the Class I areas. 

Overall, the visibility impacts from the plant’s emissions on Class I areas are dominated by nitrates. 

The tables in Appendix D21 depict the chemical species contributions to visibility impairment for the 

baseline case, the Scenario 2 Flex Fuels case and the Scenario 1 SNCR case as predicted by 

CALPUFF. Again, consistent though not identical with the evaluation by TransAlta’s modeling 

consultant, at most nearby Class I areas, the visibility impairment on the 98th percentile worst days is 

primarily caused by the nitrate resulting from the plant’s emissions. These worst days primarily 

occur in the September through June time period. Conversely, at the more distant Class I areas, the 

visibility impairment is more variable, but the 98th percentile days usually occur in the June through 

September period and are dominated by sulfates. For more details, please refer to the modeling 

reports supplied by TransAlta. 

As noted above, TransAlta was requested to remodel the emissions from the project as a result of 

public comment on the proposal. They remodeled two scenarios using the same modeling protocol as 

used in the initial modeling. The two scenarios were the Flex Fuels and the Flex Fuels plus SNCR 

control options. The emission rates are consistent between the scenarios, with only the NOx rate 

changing to reflect the anticipated 25 percent reduction in NOx from the application of SNCR to the 

emissions from the Flex Fuels Project. The modeling results are contained in a report attached to a 

March 26, 2010, e-mail from Ken Richmond of Environ to Alan Newman and Clint Bowman of 

Ecology (Appendix H). 

21 From Geomatrix BART Modeling Reports, June 2008 and January 2008.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201120
The visibility impacts depicted in Table 3-1 have been updated to reflect the results of the revised 

modeling. The maximum 24-hour emission rate for SO2 in the revised Control Scenario 2 and new 

Control Scenario 3 is based on the ratio of the average sulfur content of Jacobs Ranch PRB coal to 

the average of the Centralia Mine coal used in the 2003–2005 time period. The maximum 24-hour 

NOx emission rate used in the Flex Fuels only control scenario is as modeled previously. The NOx

rate for Flex Fuels plus SNCR is a 25 percent reduction from the Flex Fuels only rate. 

Ecology did not request that TransAlta remodel their SCR control scenarios reflecting the use of low 

sulfur PRB type coals. The modeling results assume that TransAlta would return to using Centralia 

coal as a primary fuel for the boilers. Based on the modeling performed on Flex Fuels and Flex Fuels 

plus SNCR, there would be additional visibility improvements were PRB coal continued to be used 

by the facility and SCR added.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201121
Table 3-1 Three-Year Delta Deciview Ranking Summary

Class I Area Visibility Criterion

Baseline 

Emissions

Control 

Scenario 1: 

SNCR 

Control 

Scenario 

2: Flex 

Fuel

Control 

Scenario 3: 

Flex Fuel

plus SNCR

Control 

Scenario 4: 

SCR on 

both units

Alpine Lakes 

Wilderness Max 98% value (8th high) in any year 4.871 4.393 3.564 2.949 3.057

3-yrs Combined 98% value (22nd high) 4.346 3.844 2.994 2.598 2.531

Glacier Peak

Wilderness Max 98% value (8th high) in any year 3.615 3.209 2.403 2.049 2.036

3-yrs Combined 98% value (22nd high) 2.622 2.294 1.905 1.532 1.562

Goat Rocks 

Wilderness Max 98% value (8th high) in any year 4.993 4.398 3.676 3.069 3.137

3-yrs Combined 98% value (22nd high) 4.286 3.708 3.108 2.637 2.385

Mt. Adams 

Wilderness Max 98% value (8th high) in any year 3.628 3.118 2.646 2.194 1.984

3-yrs Combined 98% value (22nd high) 3.628 3.152 2.591 2.147 1.934

Mt. Hood 

Wilderness Max 98% value (8th high) in any year 3.471 3.051 2.346 1.978 2.082

3-yrs Combined 98% value (22nd high) 2.830 2.388 1.997 1.665 1.543

Mt. Jefferson 

Wilderness Max 98% value (8th high) in any year 2.079 1.784 1.399 1.150 1.159

3-yrs Combined 98% value (22nd high) 1.888 1.596 1.267 1.053 1.061

Mt. Rainier 

National Park Max 98% value (8th high) in any year 5.447 4.774 4.318 3.606 3.359

3-yrs Combined 98% value (22nd high) 5.489 4.743 4.225 3.501 3.275

Mt. Washington 

Wilderness Max 98% value (8th high) in any year 2.027 1.756 1.323 1.106 1.170

3-yrs Combined 98% value (22nd high) 1.414 1.248 0.872 0.737 0.855

North Cascades 

National Park Max 98% value (8th high) in any year 2.821 2.496 1.852 1.570 1.658

3-yrs Combined 98% value (22nd high) 2.212 1.887 1.486 1.228 1.183

Olympic National 

Park Max 98% value (8th high) in any year 4.645 4.040 3.192 2.695 2.506

3-yrs Combined 98% value (22nd high) 4.024 3.456 2.991 2.486 2.339

Pasayten 

Wilderness Max 98% value (8th high) in any year 1.954 1.701 1.287 1.075 1.160

3-yrs Combined 98% value (22nd high) 1.482 1.318 0.999 0.822 0.864

Three Sisters 

Wilderness Max 98% value (8th high) in any year 2.172 1.910 1.333 1.139 1.172

3-yrs Combined 98% value (22nd high) 1.538 1.328 0.993 0.819 0.902

Class II area modeled per the Modeling Protocol

Columbia River 

Gorge National 

Scenic Area Max 98% value (8th high) in any year 2.545 2.193 1.748 1.446 1.347

3-yrs Combined 98% value (22nd high) 2.353 1.942 1.657 1.378 1.182

Modeled Rates 

(lb/hr) Both units added together

NOx --> 4,984 3,738 3,936 2,952 1148

SO2 --> 4,522 4,522 1,854 1,854 4,522

The 8th day in any year or the 22nd day over the 3 year period, are the 98th percentile days.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201122
4.0 ECOLOGY’S BART DETERMINATION 

Ecology has reviewed the information submitted by TransAlta. The following discussions present 

our rationale for our determination. 

4.1 NOx Control

The BART analysis reports and supplemental material provided by TransAlta indicate that the Flex 

Fuels Project and SNCR are the only feasible controls for use at the Centralia Power Plant. We 

concur with their opinion on controls. This concurrence is based on our evaluations of their 

submittals plus Ecology research on potential controls. 

4.1.1 Control options determined not to be feasible

Three available control technologies were evaluated and determined not to be feasible NOx controls 

for use at the Centralia Power Plant. In addition, one available control option, natural gas reburning, 

had been evaluated for the 1997 RACT determination, but was not reevaluated by TransAlta in their 

BART analysis. Ecology has determined that none of these control technologies are feasible controls 

of NOx at the Centralia Power Plant. 

Rotating Over-fire Air/RotaMix 

TransAlta did evaluate the installation of the Mobotec ROFA technology. Both Ecology and 

TransAlta found that this air injection technique has been neither tested nor demonstrated in 

tangentially fired coal boilers of this size. Similarly, the Mobotec RotaMix technique for SNCR has 

not been tested or demonstrated on boilers of this size. For both Mobotec technologies, the largest 

tangentially fired unit reported to have the equipment is 565 MW.22,23 This rating is below that of 

TransAlta’s units, which are rated at 700 MW each. 

Emissions information on the recent installation is not published. The technology remains untested 

or demonstrated on units the size of the TransAlta facility. With the current lack of information on 

the control efficiency on the 565 MW plant, there are questions about the capabilities of scaling the 

technology up to Centralia size. Under BART, facilities are not expected to assume large risk or 

expense for installing a new technology or technique on an untried size or type of facility.

24 As a 

result, Ecology concurs with TransAlta that these techniques are not yet technically feasible for use 

on this facility.

Neural Nets

22 As of 2009, The NALCO/Mobotec reports the largest tangentially fired pulverized coal unit using ROFA or Rotamix 

was 565MW, Minnesota Power’s Boswell Unit #4. The next two largest units listed by the company are a 424 MW wallfired unit and a 577 MW opposed fired unit achieving a 55% reduction to 0.25 lb NOx/MMBtu on bituminous coal. Jay 

Crilley (Nalco), telephone conversation, June 24, 2009.

23 In spite of the limited application of the Mobotec ROFA technology, EPA did evaluate in its analysis of control 

techniques when evaluating the presumptive BART limitations. Go to the EPA’s Regional Haze Rule Docket for EPAHQ-OAR-2002-0076-0446(1) TSD.xls. 24 40 CFR Part 51, Appendix Y, Section IV. D.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201123
This technique is an available control technology. However, Ecology agrees with TransAlta that the 

use of this technique at the Centralia Power Plant is not guaranteed to reduce emissions. TransAlta is 

likely to continue to evaluate the appropriateness of installation and use of a neural net combustion 

optimization process at the facility and may at a future date choose to include it for polishing and 

fine-tuning operations beyond what can be achieved by their human operators. 

Natural Gas Reburning

Natural gas reburning has the potential to reduce NOx emissions. Natural gas reburning is a 

technique where natural gas is injected into the boiler above the last over-fire air ports and additional 

over-fire air ports are added above the natural gas injection level. The natural gas has the effect of 

reducing part of the nitrogen oxides to nitrogen gas, carbon dioxide, and water. The technique has an 

estimated control effectiveness of 40 to 50 percent. 

Ecology has looked briefly at the use of natural gas reburning to reduce NOx from these boilers. A 

review of the EPA RACT/BACT/LAER Clearinghouse database does not include any listings of this 

technique being used on any coal-fired boiler of any size. The lack of any entries showing use of this 

technology for coal-fired boilers of any size or type leads us to question whether this control 

technique is truly available. A review of NOx control literature from the late 1990s indicates there 

was a lot of interest and evaluations of various methods to implement reburning, including the use of 

pulverized coal as the fuel. While there was much experimentation, it appears that low NOx

burner/combustion controls were the dominant technology being implemented at that time. 

A 2005 review of NOx control techniques available for coal fired boilers listed 26 plants that have 

installed or tested reburning25. Of these 26 plants, only 4 were indicated as still using reburning 

when the review was written. The report’s authors express the belief that the reason the control is not 

used on the plants where it is installed is simple economics; it is costly to operate the reburn process. 

The 4 largest units listed in the review article, bracket TransAlta in size, but none of them were 

operating their reburning equipment. The few NOx emission limitations listed for reburning have 

higher emission rates than the control level achievable by Flex Fuels or SNCR. Based on the limited 

published information on installation of reburning on units the size of Centralia, we question the 

ability of the technology to achieve a level of control comparable to Flex Fuels or SNCR. 

Natural gas reburning was not cost effective (compared to the installation of LNC3 combustion 

controls) in 1997. The cost of natural gas is the primary cost of using this technology. Natural gas 

costs in Washington State have increased significantly since 1997, while natural gas pipeline capacity

serving the part of Washington west of the Cascade Mountains has not expanded significantly. 

SWCAA determined in 1997 that this control technique was not cost effective. Ecology is of the 

opinion that reburning is still not cost effective for implementation at the plant.

25 See Reference 5 for details.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201124
4.1.2 Evaluation of controls determined to be feasible

Low NOx Combustion, Level 3/Flex Fuels

As described in Section 2, the Flex Fuels Project is to allow the boilers at this plant to utilize PRB 

coals and accommodate its potential increased fire hazard. These modifications are relatively simple 

and well known in the coal combustion industry. Compared to the Centralia Mine coal, PRB coal 

contains less nitrogen and has higher energy content. These two factors work together to reduce the

NOx emissions from the boilers. 

The estimated capital cost to TransAlta to implement the Flex Fuels Project is $101,808,663. The 

annualized cost of the Flex Fuels Project is $11,184,197. Based on the estimated NOx reduction of 

3,139 tons/year, the cost effectiveness of the Flex Fuels Project is $3,563/ton of NOx reduced. Since 

the Flex Fuels Project also reduces SO2 emissions by an estimated 1,287 tons/year, the cost 

effectiveness of the Flex Fuels Project is $2,526/ton of NOx plus SO2 reduced.

Selective Catalytic Reduction 

For new coal-fired power plants, SCR is the BACT control technology of choice to reduce NOx

emissions. In some cases, the use of SCR is being considered to be the technology to be 

implemented for BART. TransAlta has presented a number of technical difficulties to implementing 

SCR at the Centralia Power Plant. The primary difficulty identified is a lack of space for easy 

installation of the catalyst beds and ducts, leading to very high estimated construction costs that far 

surpass ranges of acceptable cost effectiveness. 

In response to public comment on the clarity of the plan and profile drawings supplied, Ecology 

acquired additional layout drawings from TransAlta with dimensions and elevations more readily 

discernable to reviewers (Appendix F). The drawings indicate that the location proposed for 

installation of a SCR system is on top of the first ESP bank. This is at an elevation of approximately 

80 feet in the air, above the precipitator. This is also the elevation of the air preheaters. The 

horizontal distance between the outlet of the air preheater and the ESP is 55 feet. As indicated in the 

drawings, in this 55 ft distance, the flue gas currently has to turn 90 degrees and spread it out across 

the full width of the ESP inlet. 

TransAlta also supplied an explanation of the anticipated flow routing for the proposed SCR 

installation. As described in CH2M HILL’s March 31, 2010, report to TransAlta (Appendix G), they 

envision a “hot, dirty” SCR installation. In other words, the flu gas would be intercepted on leaving 

the boiler economizer (located before/above the preheater), routed through the SCR unit, and returned 

to the air preheater inlet. 

A “hot, dirty” installation provides flue gas within the normal operating range of a SCR catalyst, but 

a high concentration of particulate matter. Installing a SCR catalyst after the air preheater or after the 

ESPs would require reheating the flue gas to SCR operating temperatures. 

The March 2010 report identified additional engineering analyses that would be required to improve 

the construction cost estimate. These additional analyses include a fluid dynamics evaluation for 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201125
each possible location, an evaluation of new structures needed to support ductwork and catalyst beds, 

consideration of maintenance access to the ESPs and other equipment in that area of the plant, and a 

construction difficulty evaluation. All of these additional analyses were outside the scope of work for 

CH2M HILL’s March 2010 report. 

At Ecology’s request, TransAlta had CH2M HILL evaluate two alternate SCR locations: in the 

diverging duct between the air preheater and the ESP and between the ESP and the wet FGD system. 

CH2M HILL acquired vendor information about the removal efficiency and head loss of a one and 

two layers of catalyst that could be installed within the duct between the air preheater and the ESP. 

Due to velocity and the limited depth of catalyst bed possible in this location, SCR removal seems to 

be limited to five percent for a single layer system and 12 percent for a 2-layer system. As a result of 

the low removal rates that would be provided by a catalyst system in this location, CH2M HILL did 

not evaluate the construction costs of this location. In Ecology’s view, there are significant questions 

if these ducts could support the added weight of the catalyst without additional structural support, or 

if the company could work around the loss of vehicle access for maintenance purposes to the 

equipment located on the ground under and around the air preheaters and ESPs. 

The other location evaluated was in the ductwork between the ESPs and the wet FGD system. As 

indicated by the drawings in Appendix F, the ductwork is of different lengths and, what is not clearly 

obvious from the drawings, they have different cross-sectional dimensions. CH2M HILL provided a 

qualitative analysis of what would be involved in installation of an SCR system between the ESPs 

and the wet FGD system (Appendix G). Ecology accepts their qualitative analysis as demonstrating 

the difficulties in retrofitting an SCR system in this location.

Subsequent to the finalization of the original BART order, EPA Region 9 received BART submittals 

for the Navajo Generating Station and the Four Corners Power Plant. Region 9 has proposed BART 

for the Four Corners plant and is continuing to evaluate additional submittals for the Navajo station. 

Separately, EPA Region 6 rejected New Mexico’s BART determination and is issuing its final BART 

determination for the San Juan Generating station. 

NPS provided Ecology a copy of a presentation made by the Navajo Generating Station plant owners 

to EPA and the FLMs. This presentation gives the result of a detailed construction evaluation and a 

design level construction cost estimate to install SCR at the Navajo Power plant. The units at the 

Navajo plant are approximately the same capacity as Centralia and the construction difficulties due to 

layout and previously installed emission controls present a similarly difficult construction project 

with three existing boilers with their existing particulate controls, SO2 scrubbers and stacks placed 

adjacent to each other with little space between them. The tight construction configuration results in 

SCR catalyst beds being installed above and to the sides of existing ESPs and FGD control systems, 

with the exact configuration depending on which unit is being looked at. Due to the more detailed 

design and construction evaluation developed by the owners of the Navajo plant, their estimated costs 

of construction are significantly lower than the Navajo plant owners originally proposed and lower 

than the estimates produced for Centralia. 

As part of the Four Corners Power Plant BART evaluation, EPA developed construction cost 

estimates for the installation of SCR. The EPA construction cost estimate for the Four Corners 

Power Plant units 4 and 5 is similar to the Navajo Generating Station estimate. 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201126
For the initial BART evaluation, Ecology concurred with TransAlta that the construction costs to 

overcome the technical difficulties of retrofitting an SCR system on its boilers, given its current 

configuration and installed emission controls, rendered this technology economically infeasible for 

implementation. As demonstrated in the next paragraphs, Ecology still agrees that installation of the 

technology is not cost effective as a NOx control at the Centralia Power Plant.

We have reevaluated the cost effectiveness of SCR at the Centralia Power Plant to include the limited 

remaining lifetime of the units. For purposes of this evaluation, we assume the design/build process 

would start about November 2012 and take four years to complete26 (resulting in starting operation in 

2016). Using this 2016 starting date, one unit (Unit A) would operate with SCR for only four years 

(calendar years 2017 through calendar year 2020) and the other (Unit B) would operate for nine 

years.27 Using the revised cost estimate provided by TransAlta in the March 2010 submittal, the cost 

effectiveness for SCR on Unit A would be $14,800/ton NOx reduced and Unit B would be $8,400/ton 

NOx reduced. 

Ecology also has used the cost estimate prepared by Sargent and Lundy for the Navajo Generating 

Station to estimate alternative cost effectiveness for the Centralia Power Plant. Based on the site 

description for the Navajo plant compared to the Centralia site, Ecology scaled the construction cost 

based on the gross MW output for a coal unit at each plant. For Unit A, Ecology used the cost 

estimate for Unit 2 at the Navajo station and for Unit B; Ecology used the Unit 3 cost estimate for the 

Navajo station. The estimate Ecology derived based on the Navajo estimate results in a cost 

effectiveness of $12,000/ton NOx reduced over the 4-year operating lifetime of the SCR installation 

on the Unit A and $6,400/ton NOx reduced over the 9-year operating lifetime of the SCR installation 

on the Unit B. 

These costs are both above cost effectiveness levels for NOx that Ecology has determined to 

represent Best Available Control Technology to any source type in recent years. For comparison, 

EPA Region 9 has proposed SCR as BART for NOx on Units 4 and 5 at the Four Corners Power 

Plant. Since EPA rejected the owner’s cost calculation, EPA developed a revised cost effectiveness 

estimate for Unit 4 of $2,622 and for Unit 5 of $2,908/ton NOx reduced.

28 Similarly, EPA disagreed 

with the BART determination of the state of New Mexico for the San Juan Generating Station and 

proposed SCR as BART with the cost effectiveness for the four units at that plant ranging from 

$1,579 to $1,920/ton NOx reduced. EPA has not yet proposed BART for the Navajo station. 

26 For illustration, a constructability analysis and proposed construction schedule for the Navajo Generating station 

indicates a construction time of 55 months (4.5 years) to install SCR and baghouses on two of the three units at the plant. 

This time period includes initial engineering design and equipment procurement for all three units ahead of the start of onsite construction. Construction at the Navajo site is difficult and the proposal includes significant demolition prior to 

installation of a construction crane between two of the three existing units to assist in construction. Centralia would not 

require this same degree of demolition or so sophisticated of a crane system.

EPA’s final BART determination for the San Juan Generating Station is allowing five years for the design and 

construction of the required SCR system. 

27 “Unit A” and “Unit B” are used here to designate the two coal units for this cost discussion. TransAlta has not yet 

identified to Ecology which unit (BW21 or BW22) would be the first to be decommissioned.

28 Ibid., Table 15.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201127
Based on this additional information, analyses performed, and especially considering the limited

remaining operating lives of the units, Ecology finds that SCR is not economically feasible to 

implement. 

Selective Noncatalytic Reduction 

SNCR has been commonly selected for BACT determinations on new and modified coal-fired power 

plants where SCR cannot be used, as a method to meet NOx reductions required to comply with the 

Clean Air Interstate Rule (CAIR) program, and for seasonal NOx control requirements. SNCR has 

been required to meet BART at a few facilities, although the most common BART determinations 

publically available from states to date is low NOx burner technology similar to that already installed 

at the Centralia Power Plant with SNCR or SCR added later as further progress emission reductions. 

We evaluated a 25 percent reduction from the use of SNCR, a level supported in the emission control 

literature reviewed. When this reduction is applied to the baseline emission rate of 0.304 lb 

NOx/MMBtu, the resulting emission limit becomes 0.23 lb NOx/MMBtu. This is marginally better 

than the limit of 0.24 lb NOx/MMBtu limit proposed for the Flex Fuels Project. 

As can be seen in June 2008 Modeling Report, visibility improvement resulting from the NOx

reductions from SNCR or Flex Fuels (Control Scenario SNCR and Control Scenario Flex Fuels)

provide essentially equal reduction in visibility impacts at all Class I areas within 300 km of the 

plant. In addition, the use of low sulfur sub-bituminous coals can also reduce SO2 emissions from the 

plant by up to 1,300 ton/year.29 The March 2010 modeling, which includes the effects of the reduced 

SO2 emissions from use of the Flex Fuels Project, indicates that Flex Fuels provides significantly 

better visibility improvement than SNCR alone. 

As can be seen by looking at Table 3-1, the visibility improvement modeled from the NOx reduction 

aspects of the Flex Fuels Project (Control Scenario 2) ranges from 1.13 to 1.45 dv at the three most 

heavily impacted Class I areas. This visibility improvement at the most heavily impacted Class I 

areas is significantly greater than that provided by the use of SNCR alone (Control Scenario 1). At 

the most impacted Class I area, the improvement in visibility from adding SNCR to Flex Fuels 

provides an additional 0.7 dv of improvement, while at the least impacted Class I areas the visibility 

improvement is about 0.2 dv. 

Ammonia slip from the use of an SNCR system is inevitable. TransAlta assumed a 5 ppm slip in its

BART analyses for calculating ammonia costs. An SNCR system of the type contemplated for 

installation on these boilers normally results in an ammonia slip of 5–10 ppm30, though a review of 

the EPA RACT/BACT/LAER Clearinghouse data indicates SNCR systems on coal-fired units with 

ammonia slip emission limits as high as 41 ppm. As noted in Section 2’s discussion of SNCR, there 

are a number of potential adverse impacts that can result from ammonia slip. The higher the 

ammonia slip, the higher chance that one of the potential adverse impacts could occur. 

29 The effects of the SO2 reduction was modeled and included in the January 2008 BART report. However, the NOx and 

SO2 rates modeled for that report are not identical to those used in the June 2008 report or the December update. The 

March 2010 remodeling includes the SO2 reduction from Flex Fuels at the final anticipated reduction rather than the 

previous differing rates. Ecology is relying on the March 2010 analysis as the most accurate and consistent version for 

comparison purposes.

30 For comparison, actual monthly average SO2 emissions from this plant are currently under 20 ppm. 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201128
Ammonia can be a visibility impairing air pollutant and is a precursor to the formation of secondary 

Fine Particles (PM2.5). The presence of ammonia in the plant’s exhaust will tend to increase the total 

quantity of ammonia available for the formation of ammonium nitrate and sulfate in the plume and 

ultimately in the concentration of PM2.5 at downwind locations. This secondary PM2.5 is comprised 

of ammonium aerosols. These ammonium aerosols have been included in the dispersion modeling of 

the effects on Class I areas. The modeling assumes an unlimited supply of ammonia in the 

atmosphere available to react with NO2 and SO2 to produce ammonium compounds. 

Flex Fuels Plus Selective Noncatalytic Reduction

Ecology has also evaluated the impacts of utilizing the Flex Fuels Project and adding SNCR to 

further reduce NOx emissions. Assuming a 25 percent reduction in NOx to occur from adding SNCR 

to Flex Fuels, the resulting emission limit would be 0.18 lb NOx/MMBtu. The capital costs to add 

SNCR to Flex Fuels would increase by about one-third above Flex Fuels Project costs to an estimated

$135 million. The annual costs would increase by $6.2 million to about $17.3 million/year. The cost 

effectiveness of Flex Fuels plus SNCR is $2,162/ton NOx for a net reduction of 8,022 tons NOx per 

year. The annual cost increase is mostly to cover the cost of ammonia or urea, and to remove 

ammonium sulfate and bisulfite from boiler tubes and duct work downstream from the ammonia 

injection point. 

The Centralia Power Plant has already installed the LNC3 technology and the Flex Fuels Project, the 

cost of adding SNCR now is an incremental cost. The capital cost to add SNCR to Flex Fuels is the 

same as SNCR alone since the same equipment needs to be installed. The incremental cost of adding 

SNCR to both units at the facility is estimated to be $2,145/ton to remove an additional 2,890 tons31

NOx over Flex Fuels alone. 

The combination of Flex Fuels and SNCR would increase the level of visibility improvement at the 

three most heavily impacted Class I areas due to NOx reductions by 1.99 dv on the 98th percentile 

day, with improvement of 0.67 to 1.45 dv at other Class I areas modeled. 

Under the interim NOx emission limitation, visibility would also improve. We estimate that the 

improvement would be approximately midway between the projected improvements for Control 

Scenarios 2 and 3 in Table 3-1. At Mt. Rainier NP, this would be an improvement of approximately 

0.35 dv from the Flex Fuels impacts, and at the Three Sisters Wilderness approximately 0.1 dv 

additional improvement from the Flex Fuels impacts.

Subsequent to the passage of the amendments to Chapter 80.80 RCW, TransAlta issued a Request for 

Proposal and received responses from vendors for installation of a SNCR system. The TransAlta 

requested proposals from six SNCR system suppliers and received responses from two of them. 

None of the responses indicated an anticipated NOx reduction rate expected. TransAlta working with 

one SNCR system vendor to determine what emission reduction may actually be possible form the 

use of SNCR at this plant. The vendor is unwilling to set any guaranteed minimum level of removal 

until it has performed a through computational fluid dynamics (CFD) analysis of the boilers. The 

CFD modeling is unable to start until there are more detailed temperature and flow measurements 

31 Based on 78% capacity factor, which is below the company target rate of over 84 percent. 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201129
within the boilers to calibrate the models. As of the first week of August 2011, these measurements 

have not occurred. As a result of an oversupply of hydro and wind power within the BPA system, the 

two coal units had not been fired since the middle part of March 2011. Plant restart occurred in late 

August and the necessary measurements for the CFD modeling occurred shortly after the units 

resumed normal operation. As of early August 2011, TransAlta anticipated CFD modeling will be 

completed during October 2011. At that time, the vendor’s anticipated minimum NOx removal will 

be known. 

However, TransAlta and the vendor have identified several issues that may limit the amount of 

reduction possible while holding ammonia slip to a reasonable level. The items that cause concern 

are the location of the beginning of the SNCR reaction temperature zone, the presence of falling slag 

removed by the soot blowers from the superheater tubing, the anticipated short residence time at the 

SNCR reaction temperatures, and some concerns about inconsistent mixing provided by the separated 

over-fire air system (SOFA). The actual residence time at proper SNCR reaction temperatures is the 

only issue that is unique to the TransAlta boilers. All other issues have been addressed at other 

facilities. 

As presented by the company, based on temperature measurements inside the boiler, of the 

temperatures at bottom of the superheater pendants is higher than occurred when burning Centralia 

coal. This results in the beginning of the SNCR reaction zone being within the superheater zone. As 

a result, there is concern that inadequate reaction time is available. 

As explained by the company, the Centralia mine coal produced a slag on the boiler waterwall tubes 

that was a gray/dark color that aided heat absorption by the water in the waterwall tubes. This kept 

the temperature at the super heater lower than is now occurring. The burning characteristics of the 

Centralia mine coal also resulted in a boiler firebox configuration that is different than many eastern 

US boilers that have been designed for or converted to PRB coal combustion. The different furnace 

geometry affects the temperature at the superheater also.

The PRB coal now used by the plant produces a white slag on the waterwall tubes that impedes the 

heat transfer to the water in the waterwall tubes, resulting in higher temperatures at the superheater. 

The Flex Fuels Project did install additional boiler tubes to capture this excess heat, but the new tubes 

do not affect the combustion gas temperature at the superheater. 

The SNCR system vendor anticipates 3 levels of reagent injection to be installed in the boilers. 

These injection lances would be located within the elevation range of the superheater pendants. This 

location exposes the injection lances to slag falling off the superheater pendants and other boiler 

tubing located above the firebox leading to a recurring maintenance issue. This boiler tubing in this 

area has relatively constant soot blowing to remove the soot (slag) from the boiler tubes. Chunks of 

slag fall off the pendants and currently damage soot blowing lances (these lances are retractable to 

enable slag removal all along their length).

There is also a concern about competing combustion reactions as a result of the expected inconsistent 

mixing of secondary combustion air from the SOFA system in the firebox. The effect of poor 

mixing and competing reactions should be minimized by the location of the reagent injection lances 

based on the CFD modeling. 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201130
Based on the information from their vendors, a review of other BART decisions in the western U.S. 

where SNCR was selected as BART, TransAlta has proposed a modest additional reduction from 

Flex Fuels attributable to SNCR. TransAlta has proposed a starting NOx limit of 0.22 lb/MMBtu as 

a reasonable expectation.

Remaining useful life of the plant

There was an issue of the remaining useful life of the Centralia Power Plant. TransAlta’s investor 

information about its facilities has indicated that continued operation of the Plant beyond 2030 will 

require a substantial capital investment32 with decisions to be made by 2025. This projected lifetime 

is longer than the BART guidance would consider as a limiting factor for making a BART 

technology decision on economic grounds. 

However, since TransAlta made that statement in 2007, other circumstances that affect the remaining 

lifetime of this plant in its current configuration have occurred. On May 21, 2009, the Governor of 

Washington issued Executive Order 09-05, Washington’s Leadership on Climate Change. This 

Order would have ultimately resulted in the shutdown of the coal units at the plant by 2025. 

Governor’s Executive Order 09-05 has now been superseded by amendments to Chapter 80.80, 

Revised Code of Washington.33 Under the amendments to this law, the Governor is directed to sign a 

Memorandum of Agreement by January 1, 2012, whereby the plant owners will: 

• Install selective noncatalytic reduction for nitrogen oxides by January 1, 2013. 

• Bring the two coal-fired units into compliance with the GHG emission performance standard 

in RCW 80.80.040,34 one unit by December 31, 2020, and the other unit by December 31, 

2025. 

• Incorporate other specific requirements in the law into the Memorandum of Agreement. 

As noted in public testimony to the legislature and the press during development and passage of these 

amendments, the plant owners, the legislators sponsoring the bill, the Washington environmental 

community, and the Governor’s Office have all publically stated that compliance with the GHG

emission performance standard will be through decommissioning of the coal-fired units at the plant. 

The law also states that in the event Ecology determines as a requirement of state or federal law or 

regulation that the selective catalytic reduction technology must be installed on either coal-fired unit, 

the requirement to meet the GHG emission performance standard does not apply. This would then 

imply that the coal units would continue to operate indefinitely. 

The current GHG emission rate for the Plant is about 2,300 lb total GHGs/MW-hour (MWh) of 

electricity produced for sale. The emission performance standard in the RCW 80.80.040(1) is 

currently 1,100 lb total GHGs/MWh of electricity produced. Meeting that performance standard 

32 TransAlta Investor Day 2007, presentations published as PDF file on Nov. 17, 2007, Slide 38 of 101. 33 Enacted in Chapter 180, Laws of 2011.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201131
would require a GHG reduction in excess of 50 percent, on the order of 6–7 million tons of CO2 per 

year. The law (Chapter 80.80, RCW) also requires an evaluation of the GHG emission capabilities of 

natural gas fired combined cycle power plants every five years and a revision to this limitation based 

on that evaluation be established by rule. The revised emission performance standard is based on the 

capability of new combined cycle natural gas combustion turbines offered for sale and purchase in 

the U.S. Based on current offerings by the combined cycle combustion turbine industry, the first of 

the revised standards (due in 2012) is anticipated to be 850–920 lb/MWh. 

The effect of the ‘decommissioning process’ is to limit the economic lifetime of the units. Using a 

starting point of June 2011, the maximum remaining useful life of the units is reduced to 8 and 13 

years.

4.2 Ecology’s Determination of BART

Ecology has determined BART for the Centralia Power Plant to be the Flex Fuels Project plus SNCR

and the use of a sub-bituminous PRB coal or other coal that will achieve similar emission rates. This 

determination is based on the information synopsized above, information submitted by TransAlta, 

and additional materials collected by Ecology. 

Considerations in our decision include: 

• The Flex Fuels Project provides a 20 percent reduction from the 2003–2005 average 

emissions rate. The use of SNCR, as required by state law, will further reduce emissions by 

at least an additional 10 - 25 percent. 

• The Flex Fuels emission reductions are not exclusively NOx, but include SO2 reductions from 

ability to use PRB type coals. 

• The NOx emissions reduction from the use of Flex Fuels and SNCR will result in reduced 

visibility impairment at all Class I areas within 300 km of the plant.

• Additional NOx reductions from adding SNCR will start by January 1, 2013, less than 11⁄2 

years from June 2011. January 2013 is also approximately 13 months from the time the 

revised BART order is anticipated to be issued and submitted to EPA. 

• In order to meet the requirement of state law, TransAlta will be making significant financial 

and plant viability analyses of how best to comply with the GHG emission performance 

standard requirements of the law to be included in the Memorandum of Agreement. 

• The law provides that if Ecology determines that state or federal law or regulation requires the 

use of SCR to control NOx emissions from the plant, then the requirement to comply with the 

GHG emission performance standard (shut down the coal units) does not apply and the plant 

can operate beyond 2025. 

The emission limitation and coal quality limitation reflecting Ecology’s determination of BART for 

NOx from the Centralia Power Plant is provided in Table 4-1 below. A coal meeting the nitrogen and 

sulfur content of the Jacobs Ranch Upper Wyodak coal depicted in Appendix A, Table A-2 is 

considered to be a PRB coal or equivalent coal. Additional discussion on the basis for selecting the 

initial NOx emission limitation is contained in Appendix I.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201132
Table 4-1 Ecology’s Determination of the Emission Controls That Constitute BART

BART Control Technology Emission Limitation

Flex Fuels Project plus SNCR

0.21 lb NOx/MMBtu, 30 operating day rolling 

average, both units averaged together 

Fuel Quality Requirements 

Coal used shall be a sub-bituminous coal from the 

Powder River Basin or other coal that will achieve 

similar emission rates

SNCR optimization 

Optimize SNCR operation for lowest NOx reduction 

while minimizing ammonia slip. Revise the NOx

emission limitation to reflect that optimization.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201133
Appendix A—Coal Quality 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201134
Table A-1 Summary of Key Centralia Mine and Powder River Basin Coal Characteristics

 

TransAlta Centralia Mine Coal Powder River Basin Coal

Low Sulfur 

(<1.2%)

High Sulfur 

(>1.2%)

Mean Max Mean Max Mean Max From

Btu/lb 7,681 8,113 7,930 8,121 8,414 8,800

Jacobs Ranch Upper 

Wyodak

Sulfur (%) 0.69 0.84 1.89 2.14 0.40 0.88

Jacobs Ranch Upper 

Wyodak

Ash (%) 15.44 16.44 14.43 16.46 6.21 13.04 Special K Fuel

Carbon (%) 44.95 47.37 45.63 46.45 49.11 51.26

Jacobs Ranch Upper 

Wyodak

Nitrogen 

(%) 0.76 0.80 0.71 0.75 0.67 0.8

Jacobs Ranch Upper 

Wyodak

Coal characteristics on an "as received" basis.

Table A-2 Powder River Basin Coal Characteristics, from Best Available Retrofit Technology 

Analysis for the Centralia Power Plant, July 2008

Coal Sources and Characteristics

Coal Quality Data

Units

Bucksk

in

Caballo 

8500

Cordero 

Rojo

Jacobs Ranch 

Upper 

Wyodak

Rawhid

e

Special 

K Fuel

Belle 

Ayr

Eagle 

Butte

Proximate Analysis

(As-Received Basis)

Higher Heating 

Value Btu/lb 8400.00 8500.00 8456.00 8800.00 8300.00 7907.00 8500.00

8400.0

0

Moisture % 29.95 29.90 29.61 26.45 30.50 25.74 30.50 30.50

Volatile Matter % 30.25 31.40 30.71 32.50 30.40 28.76 30.40 31.92

Fixed Carbon % 34.65 33.80 34.22 34.35 34.20 32.46 34.20 32.93

Ash % 5.15 4.90 5.46 6.70 4.90 13.04 4.90 4.65

Fixed Carbon to 

Volatile Matter 

(Fuel) Ratio 1.15 1.08 1.11 1.06 1.13 1.13 1.12 1.03

Ultimate Analysis

(As-Received Basis)

Carbon % 49.00 49.91 49.16 51.26 48.58 45.82 50.01 49.17

Hydrogen % 3.24 3.56 3.43 3.89 3.34 3.07 3.43 3.42

Nitrogen % 0.63 0.71 0.71 0.80 0.63 0.56 0.67 0.67

Sulfur % 0.35 0.36 0.32 0.88 0.37 0.28 0.26 0.38

Ash % 5.15 4.90 5.46 6.70 4.90 13.04 4.90 4.65

Moisture % 29.95 29.90 29.61 26.45 30.50 25.74 30.50 30.50

Chlorine % 0.00 0.00 0.00 0.01 0.01 0.00 0.01 0.01

Oxygen % 11.68 10.66 11.31 10.01 11.68 11.49 11.12 11.20

Note: Special K Fuel is blend of Spring Creek and Kaolin coals

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201135
Appendix B—Nitrogen Oxides Controls Evaluated in the 1997 

Reasonable Available Control Technology Process

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201136
Table B-1 Nitrogen Oxides Controls Evaluated in the 1997 Reasonable Available Control 

Technology Process

Screening Criteria used in 1997 Review

Technically 

Feasible

Increase 

other 

Emissions

Safety? Reduce 

Product 

Marketability

Cost 

Competitive 

compared to 

LNB?

Mets or 

Exceeds 

CDM 

Emission 

Level

Comments

Boiler 

Modifications

1 Boiler Tuning Yes No

2 Low Excess Air Yes No Already Optimized

3 Burners-out-ofService (BOOS)Constrained 

by mill 

capacity

4 Fuel & Air Tip 

Replacement

Yes Meets New tip 

developments may 

provide capability 

to meet LNB 

levels of NOx

5 Close Coupled 

Over-fire Air 

(CCOFA)

Increased 

UBC 

potential

Yes Meets

6 Separated Overfire Air (SOFA)Increased 

UBC 

potential

Yes Meets

7 ABB Advanced 

TFS-2000 

System (2 levels 

of SOFA)

Furnace 

height/spacing 

at Centralia 

reduces 

applicability

Increased 

UBC 

potential

Yes Meets Limited 

commercial 

demonstration of 

this technology, 

furnace specific

8 CCOFA plus 

SOFA

May 

necessitate 

pressure part 

modifications

Increased 

UBC 

potential

Yes Exceeds

9 Selective 

Noncatalytic 

Reduction 

(SNCR) 

Not 

demonstrated 

on Centralia 

sized unit

Ammonia 

slip

Ammonia Ammonia 

contamination 

of fly ash

resulting in 

lost sales

No Exceeds High reagent 

cost/limited 

reduction 

capability

10 SNCR plus Air 

heater SCR 

(Hybrid) 

Only one 

partial unit 

coal-fired 

utility 

demonstration

; no 

demonstration

s on Centralia 

sized unit

Ammonia 

slip

Ammonia Ammonia 

contamination 

of fly ash

resulting in 

lost sales

No Exceeds High reagent & 

O&M cost

11 Selective 

Catalytic 

Reduction (SCR)

Ammonia 

slip

Ammonia Ammonia 

contamination 

of fly ash

resulting in 

lost sales

No Exceeds Extremely high 

capital and O&M 

cost

12 Natural Gas cofiringReduced ash 

sales

No Meets # 14 is a better 

variation on this 

option

13 Natural Gas 

Conversion

No ash to sell No Meets Very High Fuel 

cost

14 Natural gas 

Reburn (1st

Not 

demonstrated 

Reduced ash 

sales

No Meets High variable cost 

of operation

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201137
Screening Criteria used in 1997 Review

Technically 

Feasible

Increase 

other 

Emissions

Safety? Reduce 

Product 

Marketability

Cost 

Competitive 

compared to 

LNB?

Mets or 

Exceeds 

CDM 

Emission 

Level

Comments

Generation) on Centralia 

sized unit

15 Natural Gas 

Reburn (2nd

Generation)

No 

Commercial 

Application

Reduced ash 

sales

No Meets Natural Gas 

Expensive

Combined SO2/

NOx Controls

16 UOP/PETC 

Fluidized Bed 

Copper Oxide

Pilot level or 

limited use

No Exceeds

17 Rockwell 

Moving-Bed 

Copper Oxide 

Process

Pilot level or 

limited use

No Exceeds

18 NOXSO Process Pilot level or 

limited use

No Exceeds

19 Mitsui/BF 

Activated Process

Pilot level or 

limited use

No Exceeds

20 Sumitomo/EPDC 

Activated Char 

Process

Pilot level or 

limited use

No Exceeds

21 Sanitech 

Nelsorbent SOxNOx Control 

Process

Pilot level or 

limited use

No Exceeds

22 NFT Slurry with 

NOXOUT 

Process

Pilot level or 

limited use

No Exceeds

23 Ebara E-Beam 

Process

Pilot level or 

limited use

No Exceeds

24 Karlsruhe 

Electron 

Streaming 

Treatment

Pilot level or 

limited use

No Exceeds

25 ENEL PulseEnergization 

Process

Pilot level or 

limited use

No Exceeds

26 California 

(Berkeley) 

Ferrous Cysteine 

Process

Pilot level or 

limited use

No Exceeds

27 Haldor Topsoe 

WSA-SOX 

Process

Pilot level or 

limited use

No Exceeds

28 Degussa 

DESONOX 

Process

Pilot level or 

limited use

No Exceeds

29 B&W SOx/

NOx/ROx/Box 

(SNRB) Process

Pilot level or 

limited use

No Exceeds

30 Parsons Flue Gas 

Cleanup Process

Pilot level or 

limited use

No Exceeds

31 Lehigh 

University LowTemperature 

Pilot level or 

limited use

No Exceeds

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201138
Screening Criteria used in 1997 Review

Technically 

Feasible

Increase 

other 

Emissions

Safety? Reduce 

Product 

Marketability

Cost 

Competitive 

compared to 

LNB?

Mets or 

Exceeds 

CDM 

Emission 

Level

Comments

SCR Process

32 IGR/Hellpump 

Solid-State 

Electrochemical 

Cell

Pilot level or 

limited use

No Exceeds

33 Argonne HighTemperature 

Spray Drying 

Studies

Pilot level or 

limited use

No Exceeds

34 PETC Mixed 

Alkali Spray 

Dryer Studies

Pilot level or 

limited use

No Exceeds

35 Battelle ZnO 

Spray Dryer 

Process

Pilot level or 

limited use

No Exceeds

36 Cooper Process Pilot level or 

limited use

No Exceeds

37 ISCA Process Pilot level or 

limited use

No Exceeds

Controls Evaluated in Detail as part of 1997 RACT Evaluation 

 1997 Anticipated NOx Emission

Emission Reduction Technology Rate (lb/MMBtu)

Boiler Tuning 0.40 to 0.44

Fuel and Air Tip Replacement 0.40 to 0.44

LNB & Close Coupled Over-fire Air (CCOFA) 0.38 to 0.42

LNB & Separated Over-fire Air (SOFA) 0.30 to 0.34

Selective Noncatalytic Reduction (SNCR) 0.29 to 0.33

LNB with CCOFA plus SOFA 0.26 to 0.30

Hybrid (SNCR plus air heater SCR) 0.24 to 0.28

Gas Reburning 0.20 to 0.25

Selective Catalytic Reduction (SCR) 0.10 to 0.15

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201139
Appendix C—References 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201140
1. CH2M HILL, BART ANALYSIS FOR CENTRALIA POWER PLANT at Centralia 

Washington, January, 2008, Revised July 2008, Supplemented December 2008 and March 

2010 

2. TransAlta Centralia Boiler Emissions Modeling Study by Black & Veatch, dated 

September. 2007, Attachment to September 10, 2007 Air Permit Applicability Analysis for 

TransAlta Centralia Generation, LLC., Fuel Conversion Project. 

3. Raytheon Engineers and Constructors, Inc. and Easter Research Group, Inc., COAL 

UTILITY ENVIRONMENTAL COST (CUECost) WORKBOOK USERS MANUAL

and Excel Spreadsheet, Version 1.0, 1998, Provided by EPA.

4. Air and Waste Management Association, Editors, Anthony Buonicore and Wayne Davis, 

AIR POLLUTION ENGINEERING MANUAL, Von Nostrand Reinhold, 1992 

5. Srivastava, Ravi K., Hall, Robert E., et al, Nitrogen Oxides Emission Control Options for 

Coal-Fired Electric Utility Boilers, Journal of the Air & Waste Management Association, 

Sept. 2005 

6. Comparato, J. R., NOx Control Technologies: Focus SNCR, Presented at Western Coal 

Council, Burning PRB Coal Seminar, Presentation TPP-550 

7. Cardone, Carol, Kim, Ann, & Schroeder, Karl, Release of Ammonia from SCR/SNCR Fly 

Ashes, 2005, http://www.flyash.info/2005/68car.pdf. 

8. EPRI project summary, Evaluation of an SNCR Trim System on a 720 MW Tangential 

Design Coal-Fired Utility Boiler, May 2003, EPRI report 1008029 

9. Southwest Air Pollution Control Agency, 1997 Technical support Document for RACT 

Order No. 97-2057

10. Harmon, A., et al, Evaluation of SNCR Performance on Large-Scale Coal-fired Boilers., 

Institute of Clean Air Companies Forum on Cutting NOx emissions, March 1998 

11. US EPA, Air Pollution Control Cost manual, 6th Edition, January, 2002, EPA/452/B-02-

001 

12. New Mexico Dept. of Environment, Discussion of Nalco-Mobotec ROFA and Rotamix,

evaluation for application at San Juan Generating Station, March 29, 2008, 

http://www.nmenv.state.nm.us/aqb/reghaz/documents/03292008DiscussionofNalcoMobotecROFAandRotamixRev080329.pdf

13. SNCR Committee, White Paper: Selective Non-Catalytic Reduction (SNCR) for 

Controlling NOx Emissions., Institute of Clean Air Companies, February 2008 

14. TransAlta Investor Meeting presentations, September, 2007, 2007 Investor Day Presentations 

(produced Nov. 2007) 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201141
15. Letter to Lewis Dendy, North Dakota Department of Health, from Debra Nelson, Great River 

Energy, February 9, 2010, including attachments, concerning Fly Ash usage and properties 

related to ammonia

BART Analyses from other states, such as:

16. Black and Veatch, Public Service Company of New Mexico, San Juan Generating 

Station Best Available Retrofit Technology Analysis, June, 2007

17. CH2M HILL, BART Analysis for Jim Bridger Unit 1 {also Units 2 – 4}, January 2007 

18. Black & Veatch, Portland General Electric Boardman Plant Best Available Retrofit 

Technology (BART) Analysis, November, 2007 

19. Northern States Power Co. d/b/a Xcel Energy – Sherburne County Generating Plant Units 

1 and 2 Best Available Retrofit Technology Analysis, October, 2006 

20. Pinnacle West, Arizona Public Services, Four Corners Power Plant, BART Analysis 

Conclusions, January, 2008 

21. BART analyses by Region 9 for the 4 Corners Power Plants as included in federal rule 

docket EPA-R009-OAR-2010-0683 supporting Federal Implementation Plan proposal 

published in the Federal Register February 25, 2011 

22. Salt River Project and Sargent & Lundy, Presentation to EPA Region 10 and Federal Land 

Managers for the Navajo Generating Station, July 20, 2010. 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201142
Appendix D—Modeling Results

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201143
Modeling Result Information 

Table D-1 is copied from the June 2008 BART Modeling Report, Table D-2 is from the Dec. 

2008 Flex Fuels Addendum, and Table D-3 is from the January 2008 report. 

Tabled D-1, D-2, and D-3 show the percent contribution to visibility impairment on the days 

listed, the specific day, and the modeled visibility on those days. The days shown are the 98th

percentile for each year and the three years modeled. Since the same metrological information is 

used for each different emission scenario, the only thing that changes is the emission rate and 

percentage of total visibility attributable to each chemical species. This information is from the 

referenced report. The modeling addendum received in March 2010 did not extract this 

information from the model results.

Table D-1 June 2008 Report

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201144
Table D-2 December 2008 Flex Fuels Addendum

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201145
Table D-3 January 2008 Report 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201146
Figures D-1 through D-5 graphically depict the seasonality of visibility impacts from the 

TransAlta facility. Five different Class I areas are depicted in order to indicate how the 

seasonality of impacts changes somewhat based on season of the year. 

Figure D-1 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201147
Figure D-2 

Figure D-3

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201148
Figure D-3 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201149
Figure D-4 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201150
Figure D-5 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201151
Appendix E—Coal-Fired Electric Generating Unit BART 

Determinations in Western U.S. 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201152
Table of Coal-Fired Electric Generating Unit BART Determinations in Western U.S. 

All information presented is contained in Regional Haze State Implementation Plans available 

for public review or that have been submitted to EPA for approval, as of August 2011. 

Table E-1 

State Unit NOx Technology lb/MMBtu, 30 

day avg. 

Comments

EPA Region 6, 

New Mexico

San Juan Generating Station

SCR

0.05, 30 day 

rolling average, 

each unit

EPA Region 8, 

Montana

Colstrip

 

No final Decisions 

publicly available

EPA Region 9, 

Navajo 

Reservation

Navajo

SCR

No final Decision 

publicly available

Four Corners

SCR

0.11 plant wide

rolling 30 day 

average

Unit specific limits 

ranging from 0.11 

to 0.21

Proposed Decision, see 

Federal Register, Vol. 

76, No. 38, Friday, 

February 25, 2011

Arkansas Entergy Arkansas, Inc. White 

Bluff, Units 1 and 2

0.28 on 

bituminous coal 

0.15 on subbituminous coal

Controls not given. 

Limits in State 

Regulation 19.1505

SWEPCO Flint Creek Power 

Plant Unit 1

0.23 Controls not given. 

Limits in State 

Regulation 19.1506

California No Coal fired Units subject to 

BART

Colorado Martin Drake Units 5 - 7 Install over-fire air 

systems

0.39 Also limited to 0.35 

lb/MMBtu, annual 

Average

CENC (Trigen) Unit 4 Limited by rule to 

combustion 

controls, LNC3

115 lb/hr

CENC (Trigen) Unit 5 Limited by rule to 

combustion 

controls, LNC3

182 lb/hr

Craig Unit 1 Limited by rule to 

combustion 

controls, LNC3

0.39 Also limited to 0.30 

lb/MMBtu, annual 

Average

Craig Unit 2 Limited by rule to 

combustion 

controls, LNC3

0.39 Also limited to 0.30 

lb/MMBtu, annual 

Average

Public Service of Colorado, 

Comanche Units 1 and 2

Low NOx Burners 0.2 Also limited to 0.15 

lb/MMBtu annual 

average both units 

combined

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201153
State Unit NOx Technology lb/MMBtu, 30 

day avg. 

Comments

Public Service of Colorado, 

Cherokee Unit 4

Modify existing 

Low NOx burner 

and over fire air 

or install new 

burners

0.28

Public Service of Colorado, 

Hayden Unit 1

Modify existing 

Low NOx burner 

and over fire air 

or install new 

burners

0.39

Public Service of Colorado, 

Hayden Unit 2

Modify existing 

Low NOx burner 

and over fire air 

or install new 

burners

0.28

Public Service of Colorado, 

Pawnee Unit 1

Modify existing 

Low NOx burner 

and over fire air 

or install new 

burners

0.23

Public Service of Colorado, 

Valemont Unit 5

Modify existing 

Low NOx burner 

and over fire air 

or install new 

burners

0.28

Idaho No coal fired units

Kansas La Cynge Generating Station, 

Unit 1 and 2

SCR on Unit 1, 

Controls as 

needed on Unit 2

0.13, both units 

averaged 

together

Jeffrey Energy Center, Units 

1 and 2

Low NOx Burners 0.15

Minnesota MN Power, Taconite Harbor 

Boiler No. 3

ROFA/Rotamix 

(Mobotec)

0.13

MN Power, Boswell Boiler 

No. 3

LNB + OFA, SCR 0.07

Rochester Public Utilities, 

Silver Lake, Unit #3 boiler

No additional 

controls 

No Limit

Rochester Public Utilities, 

Silver Lake, Unit #4 boiler

ROFA/Rotamix 

(existing controls)

0.25

Xcel Energy, Sherco, Boiler 1 LNB 

+SOFA+Combusti

on Optimization

0.15

Xcel Energy, Sherco, Boiler 2 Combustion 

optimization

0.15

Xcel Energy, Allen S. King 

Boiler 1

SCR (existing 

controls)

0.1

Northshore Mining, Silver 

Bay, Boiler 1

LNB + OFA 0.41

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201154
State Unit NOx Technology lb/MMBtu, 30 

day avg. 

Comments

Northshore Mining, Silver 

Bay, Boiler 2

LNB + OFA 0.4

Iowa Used CAIR for BART

Louisiana Used CAIR for BART

Nebraska Gerald Gentleman, Units 1 

and 2

Existing LNC3 on 

Unit 2 New LNC3 

on Unit 1

0.23, both units 

averaged 

together

Nebraska City Station, Unit 1 LNC3 0.23

Nevada No Coal Fired BART units

New Mexico San Juan Generating Station No final Decision 

publicly available

North Dakota Olds Unit 1 SNCR plus overfire air0.19

(All Lignite units) Olds Unit 2 SNCR plus overfire air0.35

Coal Creek Units 1and 2 Additional overfire air plus LNB0.19

Stanton Unit 1 LNC3 plus SNCR 

for a 1/3 

reduction

0.29 a 1/3 reduction

Milton Young Station Unit 1 Advanced overfire air plus SNCR 

for a 58% 

reduction

0.36

Milton Young Station Unit 2 Advanced overfire air plus SNCR 

for a 58% 

reduction

0.35

Oregon Boardman LNC3 0.23 between 

July1, 2011 and 

Dec. 31, 2020.

Note Plant Closure by 

Dec. 31, 2020.

Oklahoma OG&E Muskogee Generating 

Station Units 4 and 5

0.15

OG&E Sooner Generating 

Station Units 1 and 2

0.15

AEP/PSO Northeastern 

Power Station Units 3 and 4 

0.15

Texas No Coal Fired BART units 

Subject to BART

Utah Hunter Power Plant, Units 1 

and 2

LNC3 0.26 Replacing LNC1 burners 

and add 2 levels of 

over-fire air under 

minor NSR program.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201155
State Unit NOx Technology lb/MMBtu, 30 

day avg. 

Comments

Huntington Power Plants, 

Units 1 and 2

LNC3 0.26 Replacing LNC1 burners 

and add 2 levels of 

over-fire air under 

minor NSR program.

Wyoming Naughton Unit 1 LNC3 0.26 Wyoming Long term 

strategy for this unit 

requires SCR @ 0.07 

lb/MMBtu by 2018.

Naughton Unit 2 LNC3 0.26

Naughton Unit 3 LNC3 plus SCR 0.07

Jim Bridger Units 1 - 4 LNC3 0.26

Dave Johnston Unit 3 LNC3 0.26

Dave Johnston Unit 4 LNC3 0.15

Wyodak Unit 1 LNC3 0.23

Basin Electric Units 1 - 3 LNC3 0.23

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201156
Appendix F—TransAlta Centralia Power Plant Site Plans and 

Profiles 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201157
These four drawings are large, and intended to be reproduced at 11” x 17” or larger scale for 

readability. The drawings are available from Ecology and are located on the Ecology website.

Drawing 1 is an overall site plan of the power plant including the plant office, wet scrubbers 

storm water lagoons, maintenance buildings, etc. It does not include the coal pile 

area.

Drawing 2 is a site plan of the boiler building, ESPs, and wet scrubber area of the plant. 

Drawing 3 is an elevation drawing looking from the south at the overall steam turbine/boiler 

building, ESPs and old stacks. 

Drawing 4 is an elevation drawing showing subset elevation indicated in Drawing 3 showing 

the plant boiler outlet area, and the ESPS. 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201158
Appendix G—Centralia BART Control Technology Analysis, 

Response to Questions

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201159
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201160
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201161
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201162
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201163
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201164
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201165
Appendix H—Additional Centralia Power Plant BART Modeling 

Simulations–Comparison of Flex Fuel and Flex Fuel plus SNCR

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201166
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201167
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201168
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201169
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201170
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201171
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201172
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201173
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201174
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201175
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201176
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TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201177
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201178
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201179
From: Ken Richmond [krichmond@Environcorp.com]

Sent: Friday, March 26, 2010 2:00 PM

To: Newman, Alan (ECY); Bowman, Clint (ECY)

Cc: RickLGrif@aol.com; Gary_MacPherson@TransAlta.com; 

Lori_Schmitt@transalta.com; richard_debolt@transalta.com

Subject: Additional Centralia Power Plant BART simulations

Attachments: flex-vs-flexwsncr.pdf

Al & Clint

I’ve attached the results from the additional BART simulations that you 

requested for the Centralia Power Plant. The results supplement the 

earlier BART simulations with 2 new cases.

Revised Flex Fuels: (PM10 242 lb/hr, NOx 3936 lb/hr & SO2 1854 lb/hr) The 

Flex Fuels SO2 emissions are based on the ratio of sulfur content of 

Jacobs Ranch (PRB) coal to Centralia Mine coal (41%) times the 2003-2005 

maximum 24-hr baseline rate of 4522 lb/hr.

Flex Fuels with SNCR: (PM10 242 lb/hr, NOx 2952 lb/hr & SO2 1854 lb/hr)

NOx emissions are reduced by 25% to 0.18 lb/MMBtu from the Flex Fuel 

factor of 0.24 lb/MMBtu.

In all respects the simulations were performed in the same manner as the 

original BART analysis. The results are summarized in the attached Tables 

that augment the tables from the original BART modeling analysis. How many 

copies of the modeling files do you want? As before the modeling files 

will contain spreadsheets with the extinction budgets for the top 8 days 

each year and top 22 days in three years for each Class I area of 

interest.

Regards,

Ken Richmond

Sr. Air Quality Scientist

ENVIRON International Corp.

19020 33rd Avenue W, Suite 310

Lynnwood, WA 98036

Phone: 425.412.1800

Direct: 425.412.1809

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BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201180
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201181
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201182
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201183
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201184
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201185
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201186
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201187
BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201188
Appendix I—Establishing SNCR NOx Emission Limitation for 

Revised Order

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201189
The 2011 amendments to RCW 80.80 require the Centralia Power Plant to install and operate 

SNCR by January 1, 2013. This SNCR technology is in addition to the emission reduction 

resulting from implementation of the Flex Fuels Project. 

A number of considerations are discussed below related to determining the most appropriate 

averaging period and initial NOx emission limitation for SNCR. Included is a discussion of the 

results expected from the SNCR optimization study.

What is the removal rate that can be expected by SNCR?

The literature contains a reasonable amount of information compiled for existing coal-fired 

utility boilers. The various sources all indicate that minimum expected removal rates of 20

percent with maximum removal for boilers above 500 MW of 35 percent. For boilers above 500 

MW, the most commonly reported removal rates are 25 to 35 percent. The following paragraphs 

are synopsis of three representative reviews. 

A 2003 EPRI report synopsis35 reported on an evaluation of a single level SNCR Trim system on 

a 720 MW tangential boiler. The single level system was operated over a load range from 40 to 

100 percent of the boiler maximum continuous rating. NOx reductions as measured at the 

economizer exit showed the highest levels of NOx reduction occurred in the furnace nearest the 

injectors. The system provided NOx reductions of 20 to 25 percent while the boiler operated at 

rates of 300–710 MW with an ammonia slip of 6–9 ppm. 

A 2008 report on SNCR by the Institute of Clean Air Companies supports SNCR on Centralia 

sized units producing 20 to 30 percent NOx reductions with ammonia slip as low as 5 ppm. The 

report notes that this level of NOx removal is anticipated for any installation, with the main 

criteria being able to adequately distribute the reagent within the reaction zone. The report 

indicates for various sizes of coal-fired utility boiler applications, the range of reduction is 20 to 

90 percent and the most commonly reported reduction is 25 percent. 

A 2005 report in the Journal of the Air and Waste Management Association36 evaluated NOx

controls systems in operation in the U.S. Table 3 of this report indicates that for larger coal-fired 

units, SNCR reduction of NOx can be anticipated in the range of 25 to 35 percent for units over 

200 MW. The data indicates smaller units can achieve higher removal rates. The units reviewed 

for this report had higher pre control emissions than Centralia, so the reported reductions may be 

more illustrative of the capability of SNCR in general rather than specifically applicable to 

TransAlta’s Centralia units. The article does not include information on ammonia slip. 

Based on SNCR vendor reluctance37 to provide a proposal to TransAlta, there is a reasonable 

doubt about the ability to achieve the 20 to 25 percent NOx reduction that is normally anticipated 

35 Evaluation of an SNCR Trim System on a 720 MW Tangential Design Coal-fired Utility Boiler, May 2003, 

Document #E214967, by R. Himes on EPRI Report #1008029, April 2003.

36 Nitrogen Oxides Emission Control Options for Coal-Fired Electric Utility Boilers, Ravi K. Srivastava, Robert E. 

Hall et al, Journal of the Air & Waste Management Association, Volume 55, September 2005. 37 TransAlta has noted that they sent out six requests for proposal and received two responses, each with two 

variations in return. Anecdotally, the system supplier with the greatest familiarity with the plant (Black and Veatch) 

did not submit a proposal.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201190
through the use of SNCR. Two SNCR system vendors supplied four proposals for SNCR 

systems. The vendors did not propose an ability to meet a specific NOx emission rate or removal 

percentage. The system vendors indicated that some small NOx removal would occur, but until 

they had completed modeling of the boilers, they would not be able to provide any guarantee of 

performance. Using the information supplied by the two vendors, TransAlta has proposed an 

initial NOx emission limit based on the use of SNCR of 0.22 lb/MMBtu (about a nine percent 

additional reduction). The rationale for this proposal is contained in the August 8, 2011, letter 

from Bob Nelson of TransAlta to Alan Newman of Ecology. In short, the company identifies 

operational and mixing issues resulting from the location of ammonia/urea injection lances 

within the superheater pendants, the end of the active combustion zone in the firebox at the 

bottom of the superheater pendants,38 and damage to injection lances from falling slag removed 

from the superheater tubes. Other normal operational problems are identified such as the 

formation of ammonium bisulfate and ammonium sulfate deposits in the air preheaters and 

economizer.

As part of the design for the SNCR system, TransAlta’s system vendor will be performing 

computational fluid dynamics modeling of the boilers. This modeling will determine a number 

of aspects of the SNCR system design, such as optimum locations for the injection system, the 

reaction time in the SNCR reaction temperature zone, and the anticipated nitrogen oxides 

emission rate and ammonia slip. Due to the lack of operation of the TransAlta coal boilers 

between mid February and mid August of 2011, the vendor was unable to acquire the 

temperature and flow rate information necessary to complete the modeling exercise. The earliest 

this information is expected to be available is the end of October 2011. 

The rationale presented to Ecology by TransAlta is very boiler specific. It is compelling 

information, but based on the literature on operation of SNCR in existing boilers, does not 

present many unexpected issues. The most unexpected issue is the higher temperatures at the 

super heater pendants when burning the PRB coal producing a smaller than anticipated size for 

the SNCR reaction zone. 

Based on literature reviewed, a reasonable minimum reduction rate to expect from the 

application of SNCR at this facility would be 25 percent as proposed by TransAlta in their 

BART analysis reports and as modeled by TransAlta to estimate the degree of visibility 

improvement that could be achieved. However, based on the recent information provided by 

TransAlta39 and the prospective SNCR system vendors, a lower minimum expected reduction 

rate on the order of 10 percent may be more reasonable as the basis for setting the initial NOx 

reduction rate.

Potential basis for emission limit

The proposed limitation is based on a 30-day rolling average, both units averaged together. This 

scenario tends to smooth out the hourly/daily variability in the NOx emissions from the boilers, 

especially when start-up emissions are included in the emission limitation. Thirty-day rolling 

38 The combustion zone ended well below the superheater pendants when using Centralia coal. The Centralia coal 

have a different volatility than the PRB coals, leading to the larger combustion zone.

39 Letter and attachments from Bob Nelson, Plant Manager, to Alan Newman, August 8, 2011.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201191
averages are used by other states for other coal-fired power plants and by EPA in its coal-fired 

boiler rules. 

Two approaches were used to evaluate the appropriate basis for setting the emission rate to apply 

the percent reduction from use of SNCR. One approach was to look at the available emissions 

data; the other was to utilize the basis used to set the current BART emission limitation.

Actual emissions rate based limitation

Rolling 30-day average emissions from the TransAlta plant were evaluated. These averages 

were based on the daily average values of NOx lb/MMBtu values for 2010 reported for the Acid 

Rain Program. The Acid Rain Program uses a different missing data substitution process for 

periods of start-up and extended monitor outages that result in higher values being inserted for 

missing data than the data substitution process in the BART Order. The data substitution process 

in the BART Order better reflects operating realities of the system than the process used in the 

Acid Rain Program.40 As a result, the use of this Acid Rain Program information is for 

illustrative purposes only and does not indicate compliance or noncompliance. This review is in 

an Ecology-generated spreadsheet titled CentraliaAnnualSummary2003-2010.xlsx. 

As a result of the Acid Rain Program missing data substitution, there were several 30-day 

periods where 30-day averages were above the current and proposed BART emission limitation. 

Upon inspection, these periods are almost entirely based on 30-day periods when only one boiler 

was in operation, when daily values were dominated by start-up of a boiler, or when Acid Rain 

Program substituted data was reported. There were no exceedances of the emission limitation 

contained in the current BART Order when the process contained in the BART Order was used 

for missing data substitution.

Prior to using the missing data process in the BART Order, all 30-day periods with emission 

averages above 0.24 lb/MMBtu (the NOx limit in the current BART Order) were dominated by 

the Acid Rain Program’s substitute data, especially when one unit was in start-up mode. 

The current limitation is based on a 30-day rolling average, both units averaged together. This 

scenario tends to smooth out the hourly/daily variability in the NOx emissions from the boilers. 

A 30-day rolling average is used by other states for other coal-fired power plants and by EPA in 

its coal-fired boiler rules. 

During the last three months of 2010, operation of the plant was consistent and continuous. 

During that 3-month period, the NOx emissions averaged 0.227 lb/MMBtu. A proposed NO2

emission limitation based on this 3-month period and a 25 percent reduction from SNCR would 

be 0.170 lb/MMBtu. A 10 percent reduction would result in limits of 0.204 lb/MMBtu. 

Emission limit reduction basis

40 The data substitution process in the Acid Rain Program is designed to estimate the maximum theoretical 

emissions during periods of time such as unit start-up and shutdown (when certified CEMs are not available for use), 

extended monitoring equipment outages, rather emissions that are more akin the unit actually operates.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201192
The current Flex Fuels emission limitation is based on a 20 percent reduction from the RACT 

emission limitation of 0.30 lb/MMBtu. The RACT limit value was conservatively set at 0.30 

lb/MMBtu to include a reasonable compliance margin. The current BART Order limit for Flex 

Fuels uses the RACT emission limit then applies the 20 percent reduction attributable to Flex 

Fuels (resulting in the current BART limit of 0.24 lb/MMBtu) continues to incorporate a 

reasonable compliance margin. Applying a further reduction resulting from the use of SNCR 

would result in a NOx limitation of 0.180 lb/MMBtu (25 percent reduction) or 0.21 lb/MMBtu 

(12 percent reduction). 

Operating day versus calendar day

We are proposing to use the concept of operating day rather than calendar day. The use of an 

operating day means that any day where neither coal unit is in operation (zero emissions) is not 

used to evaluate compliance with an emission limitation. 

Operating day is used in many EPA regulations for combustion units.41 An operating day has 

been defined as any day in which fuel is fired for any amount of time in either coal unit or a day 

where fuel is fired for more than a specified minimum amount of time (such as 4 or 8 hours). 

Recent revisions to EPA’s New Source Performance Standards for boilers have defined an 

operating day as any calendar day when fuel is fired at least one hour during the day. One 

rationale given by EPA to use the ‘any number of hours’ definition of operating day was 

specifically to include start-up and shutdown emissions in the 30 operating day rolling average 

emission limitation.

The same operating day concept is also used in some BART determinations that have been 

reviewed for this revision of the BART Order. Of most importance to this discussion is EPA 

Region 6’s use of a rolling 30 operating day average in its BART determination for the San Juan 

Generating station and proposed by Region 8 for coal-fired power plants in North Dakota. 

Alternately, EPA Region 9 has proposed to use a 30 calendar day average for the Four Corners 

Power Plant.

The Centralia Power Plant has a history of not operating for 2–6 weeks each year due to the 

availability of lower cost hydropower in the market. Operating records for the past several years 

indicate several time periods during each year where only one unit may be operating

continuously while the other unit operates for a few days at a time then be shut down or operate 

at minimum firing rate.

Another reason for considering the operating day concept is that Ecology and EPA are now 

requiring emissions during start-up and shutdown to be addressed specifically in permits and 

orders such as this. In the recent revisions to 40 CFR Part 60, Subpart DA, EPA retained the 

minimum hours of operation definition for operating day specifically for use in the preexisting 

NSPS requirements while using a definition of operating day that includes any hours where fuel 

is fired for use in the revised NSPS standard. 

41 In the EPA rules, both types of operating day have been used, though the most recent EPA rules have defined an 

operating day as any day when fuel is fired, regardless of the duration of fuel firing.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201193
Rather than going through the process of establishing emission limitations covering start-up and 

shutdown, Ecology is choosing to follow EPA’s lead on more recent emission standards of 

addressing start-up and shutdown emissions by establishing longer averaging period emission 

standards. The use of a 30 operating day averaging period that includes all days with fuel 

combustion in either coal unit addresses start-up and shutdown. 

Alternate form of the emission limitation

Ecology could change from the current emission standard expressed in terms of lb/MMBtu fired 

to an output based limitation such as lb of NOx per gross or net MWh produced. This approach 

would make the BART result more difficult to compare to other facilities. However, this form of 

emission limitation may be very appropriate for a new power plant or an existing plant 

undergoing significant renovation to assure maximum net efficiency in generating electricity. 

The approach of using lb/MWh has not been analyzed in detail, though based on information 

from some combined and simple cycle combustion turbines, it may not be adequate to address 

periods of low load and unit start-up and shutdown. 

An annual NOx emission limit in terms of tons per calendar year, like the current SO2 limit for 

the plant, could be established for the plant. One difficulty in this approach is the number of 

variables involved in setting the number. The current boilers have been modified and changed 

fuel from Centralia coal to PRB coal, all of which affect the plant heat input rate, NOx emissions 

from the boilers, and gross output rates. A result of these changes are that a number of values 

must be estimated or assumed such as the current design firing rate, controlled emission rate, 

plant capacity factor, and annual operating hours. 

Rationale for establishing the initial NOx emission limitation

Based on the above information, plus additional considerations explained below, Ecology 

proposes to establish an initial NOx emission limitation that will be achievable by the facility, 

low enough that use of the SNCR system on both units will be required to comply with the 

limitation, but not be so low as to result in an extensive SIP limit relaxation analysis by Ecology 

and EPA if the actual emissions from the power plant are unable to achieve the limitation.

The emission limitation selected is in the form of pounds of pollutant per million Btu heat input, 

30 operating day average. This is selected primarily for comparative purposes to other coal-fired 

power plants across the country, which commonly have emission limits in this form. This is also 

the unit of measure used in the federal New Source Performance Standard for utility boilers, and 

is the unit the plant is required to report its NOx emissions to EPA under the Acid Rain Program 

requirements. The use of a 30-day rolling average will also meet EPA guidance on setting 

emission limits that are enforceable in practice. 

For the numerical value of the NOx limit, several pieces of information were considered. One is 

that during periods of sustained operation, where neither unit is shut down or started up, 

emissions data indicate it is possible for the plant to demonstrate compliance with the 

Company’s proposed 0.22 lb/MMBtu limitation without operating the SNCR system. 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201194
As noted above there is a state law that affects the operation of this facility, Chapter 180, laws of 

2011 amending RCW 80.80.040. The specific requirement in RCW 80.80.040(3) says: 

(c)(i) A coal-fired baseload electric generation facility 

in Washington that emitted more than one million tons of 

greenhouse gases in any calendar year prior to 2008 must 

comply with the lower of the following greenhouse gas 

emissions performance standard such that one generating 

boiler is in compliance by December 31, 2020, and any other 

generating boiler is in compliance by December 31, 2025: 

(A) One thousand one hundred pounds of greenhouse 

gases per megawatt-hour; or 

(B) The average available greenhouse gas emissions 

output as determined under RCW 80.80.050. 

(ii) This subsection (3)(c) does not apply to a coalfired baseload electric generating facility in the event 

the department determines as a requirement of state or 

federal law or regulation that selective catalytic 

reduction technology must be installed on any of its 

boilers.

Ecology interprets subsection (3)(c)(ii) to mean that if the plant is required to install SCR to 

comply, that the requirement to meet the GHG emission performance standard goes away for 

both units. Such a requirement to install SCR can derive from a revised New Source 

Performance Standard , a requirement to comply with an emission limitation unachievable by 

SNCR in the BART order (as a requirement under state regulations), or after the BART order is 

included in the SIP (becoming a requirement of federal regulation too). It is in the interests of 

the state to see the coal units at the plant decommissioned. If the BART limitation is set at a 

level that SNCR cannot achieve, and would require the installation of SCR, then it is Ecology’s 

opinion that the decommissioning requirement in state law goes away. 

In comments to Ecology on a preliminary draft of the Revised BART Order, TransAlta 

suggested an initial emission limitation of 0.22 lb/MMBtu (a <9% reduction from the current 

emission limitation of 0.24 lb/MMBtu). As noted previously, our review of the Acid Rain 

Program data indicates that the units at the plant could achieve this proposed emission limitation 

without the operation of the required SNCR system during extended periods of consistent 

operation. 

In recent years, the Acid Rain Program report for the facility indicates plant operation has 

changed to lower capacity factors accompanied by more unit start-up and shutdown occurrences. 

During unit shutdown and start-up, emissions are higher on a pound/MMBtu basis than during 

consistent operation. For example, during 2011, the plant stopped producing electricity in 

February, and did not resume operations until August due primarily to two factors: an excess of 

hydropower from the Bonneville Power Administration system, and the large increase in electric 

generation from wind turbines, which receives preferential treatment by power purchasers. 

During 2010, the data also shows numerous unit shutdowns, periods of one unit operation and 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201195
periods of no operation. Historically, the plant has not operated in the late spring/early summer 

for periods of 2–4 weeks due to the availability of lower cost hydropower.42 

As a result of the increased number of unit start-ups with their relatively higher emissions, the 

potential for extended operation to comply with the company’s proposed initial NOx emission 

limitation without operating the SNCR system, and Ecology’s desire that the plant be required to 

utilize the system to comply while not triggering a requirement to install SCR, we propose to 

establish an initial NOx emission limitation a slightly lower emission limitation than proposal by 

the company. 

Projected Visibility Improvement as a result of implementing SNCR and ceasing to burn coal at 

the TransAlta Centralia plant

The following table depicts the projected visibility impacts at 3 future years resulting from the 

emissions reductions and coal unit decommissioning. SNCR is to be installed and operational in 

2013. It will then have a period of optimization to achieve the maximum NOx reduction; this 

will be achieved in 2015. By law, one unit must be decommissioned by the end of 2020 and the 

other coal unit by the end of 2025. These shutdowns are portrayed as starting in 2021 and 2026 

respectively.

The visibility improvement analysis assumes that the result of the SNCR optimization study will 

result in at least a 25% reduction in NOx emissions from the rates required for the Flex Fuels 

project (as reflected in the original BART Order). This reduction is projected to occur in 2015 

Based on this analysis, by 2015 when the results of the SNCR optimization study are required to 

be implemented, we anticipate the visibility improvement from SNCR will be at least 0.7 dv at 

all Class I areas within 300 km of the plant. By 2021 when the first unit will be decommissioned 

the visibility improvement is expected to be even more dramatic, leading to no impact by 2026 

when the second unit has been decommissioned. The following table indicates the visibility 

impacts and emission rates expected in the future.

Visibility Impacts from TransAlta Centralia Power Plant

Class I Area Visibility Criterion

Baseline 

(2002) 

Emissions 

2015 Flex 

Fuels and 

SNCR

2021, one unit 

decommissioned

2026, both units 

decommissioned

Alpine Lakes 

Wilderness Max 98% value (8th high) in any year 4.871 2.949 1.475 0

3-yrs Combined 98% value (22nd high) 4.346 2.598 1.299 0

Glacier Peak 

Wilderness Max 98% value (8th high) in any year 3.615 2.049 1.025 0

3-yrs Combined 98% value (22nd high) 2.622 1.532 0.766 0

Goat Rocks 

Wilderness Max 98% value (8th high) in any year 4.993 3.069 1.535 0

42 As a result of this known period of time when hydropower is available, the plant has routinely scheduled major 

maintenance for the late spring time period.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201196
Visibility Impacts from TransAlta Centralia Power Plant

Class I Area Visibility Criterion

Baseline 

(2002) 

Emissions 

2015 Flex 

Fuels and 

SNCR

2021, one unit 

decommissioned

2026, both units 

decommissioned

3-yrs Combined 98% value (22nd high) 4.286 2.637 1.319 0

Mt. Adams 

Wilderness Max 98% value (8th high) in any year 3.628 2.194 1.097 0

3-yrs Combined 98% value (22nd high) 3.628 2.147 1.074 0

Mt. Hood 

Wilderness Max 98% value (8th high) in any year 3.471 1.978 0.989 0

3-yrs Combined 98% value (22nd high) 2.83 1.665 0.833 0

Mt. Jefferson 

Wilderness Max 98% value (8th high) in any year 2.079 1.15 0.575 0

3-yrs Combined 98% value (22nd high) 1.888 1.053 0.527 0

Mt. Rainier 

National Park Max 98% value (8th high) in any year 5.447 3.606 1.803 0

3-yrs Combined 98% value (22nd high) 5.489 3.501 1.751 0

Mt. Washington 

Wilderness Max 98% value (8th high) in any year 2.027 1.106 0.553 0

3-yrs Combined 98% value (22nd high) 1.414 0.737 0.369 0

North Cascades 

National Park Max 98% value (8th high) in any year 2.821 1.57 0.785 0

3-yrs Combined 98% value (22nd high) 2.212 1.228 0.614 0

Olympic 

National Park Max 98% value (8th high) in any year 4.645 2.695 1.348 0

3-yrs Combined 98% value (22nd high) 4.024 2.486 1.243 0

Pasayten 

Wilderness Max 98% value (8th high) in any year 1.954 1.075 0.538 0

3-yrs Combined 98% value (22nd high) 1.482 0.822 0.411 0

Three Sisters 

Wilderness Max 98% value (8th high) in any year 2.172 1.139 0.570 0

3-yrs Combined 98% value (22nd high) 1.538 0.819 0.410 0

Columbia River 

Gorge National 

Scenic Area Max 98% value (8th high) in any year 2.545 1.446 0.723 0

3-yrs Combined 98% value (22nd high) 2.353 1.378 0.689 0

Modeled 

Emission Rates 

(lb/hr)

Both units added together

NOx --> 4,984 2,952 1476 0

SO2 --> 4,522 1,854 927 0

It is anticipated that there will at least 700 MW of replacement power generation located at the 

TransAlta site. This replacement power is anticipated to be provided by a new natural gas fired 

combined cycle combustion turbine facility that will have to receive a Prevention of Significant 

Deterioration permit. 

Proposed BART emission limitation

Based on the above analysis, Ecology proposes to establish an emission limitation of 0.21 

lb/MMBtu, 30 operating day rolling average as the initial NOx emission limitation. The 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201197
emission limitation will be revised in the future to reflect optimization of the installed SNCR 

system.

43 An operating day is any calendar day when a boiler was fired. A more precise 

estimate of the nitrogen oxides emission reduction achievable with the SNCR system could be 

made based on the upcoming computational fluid dynamics analysis of the boilers. However, the 

state law requires the installation of SNCR and the revision of the BART Order for this plant be 

completed prior before December 31, 2011, prior to the completion of that analysis. 

EPA has adopted the definition of operating day and 30 operating day averaging period for a 

number of its regulations and at least one BART determination established by Regions 6 and 9. 

The NSPS rules and BART determination intend covering unit start-up and shutdown emissions 

within the 30 operating day averaging period. Ecology agrees with EPA that a 30 operating day 

period is suitably long to moderate the effects of unit start-ups and low load operation. 

Based on the above review, Ecology proposes that the NOx emission limits for the Revised 

BART Order to be:

• Starting on date of order issuance, 0.24 lb/MMBtu, 30 operating day rolling average, both 

units averaged together. 

• Starting on the 31st operating day after January 1, 2013, 0.21 lb/MMBtu/hr 30 operating 

day rolling average, both units averaged together, 30-day rolling average. 

• A NOx reduction optimization program will be required. The initial NOx limitation 

based on the use of SNCR will be revised to reflect the NOx reduction rate derived from 

the required NOx reduction optimization program. 

The monitoring and emission calculation process in the Revised BART Order is based on the 

BART Federal Implementation Plans issued by EPA for coal fired power plants in North Dakota 

and New Mexico. Similar to EPA and other states in BART determinations, we do not propose 

to include tons of NOx per year, operating rate, or operating time limit in the BART Order. 

NOx Reduction Optimization Program

The goal of the SNCR optimization program is to determine the lowest NOx emissions that may 

be achievable and the lowest NOx emission rate that is paired with the lowest ammonia emission 

rate. The revised emission rate to be inserted in the Revised BART Order will be based on 

lowest NOx rate achievable with a minimum ammonia slip rate. The target of the optimization is 

not to determine how little ammonia injection is required to achieve the initial NOx emission 

limitation, but to determine the lowest NOx and ammonia rates achievable and that do not result 

in contamination of fly ash or gypsum44 produced by the FGD system that would render these 

byproducts unsalable. 

43 This revision will be submitted to EPA as a revision to the SIP emission limitations for this plant. 44 The use of fly ash to make concrete reduces the quantity of greenhouse gases and other air pollutants produced to 

make concrete by reducing the quantity of cement required. The use of gypsum to make wallboard for the local area 

reduces the pressure to mine natural gypsum in Mexico (the alternate gypsum source for the purchaser of the 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201198
The goal of the optimization process is to identify three operating points of the SNCR system:

• The lowest NOx emission rate that will meet an ammonia slip of less than 545 ppmdv. 

• The lowest NOx emission rate that will meet an ammonia slip of up to 20 ppmdv. 

• The lowest NOx emission rate that coincides with the lowest ammonia slip. 

• The ability to achieve a NOx emission rate no higher than 0.180 ppmdv, 30 operating day 

rolling average, each unit individually. 

To facilitate a true optimization of the SNCR system, the revised Order will allow a higher 

ammonia slip during part of the optimization period. This higher slip is necessary to allow 

excess ammonia to be injected to determine how much NOx emissions can be reduced. 

The Revised BART Order will then be revised again to incorporate the results of the 

optimization study. Based on the results of the study, the NOx limit will be revised to a lower 

limit. The ammonia slip limit may also be revised to a higher or lower limit, depending on the 

findings of the optimization study. Ecology intends to then submit the revision as an amendment 

to the Regional Haze portion of the Washington State Implementation Plan. 

TransAlta gypsum) or import wallboard from other countries. If these byproducts cannot be beneficially used the 

environmental and direct costs are more than simply the cost to TransAlta to landfill the materials. 

45 Change per request of Company during public comment. The 5 ppm value here and the 10 ppm limit in the Order 

are both 30 day averages.

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 201199
August 8, 2011 

Mr. Alan Newman 

Washington Department of Ecology 

Air Quality Program 

P.O. Box 47600 

300 Desmond Drive 

Lacey, WA 98504-7600 

Re: TransAlta Centralia Generation LLC’s Comments on Proposed Revisions to 

BART Order to Address SNCR 

Dear Mr. Newman: 

TransAlta Centralia Generation LLC (“TransAlta”) has reviewed the Department of Ecology’s 

proposed revisions to the Implementation Order that was issued in June of 2010 (“BART 

Order”) and we would like to provide the following comments. The issues of concern are 

described in this letter and suggested changes to address these concerns are made in attached 

red-line version of the draft BART Order. 

Nitrogen Oxides Limit (Condition 1.1.1) 

The draft Order proposes a nitrogen oxides (“NOx”) emission limit of 0.18 lb/MMBtu based 

on a presumed reduction factor of 25% of the Flex Fuels Project emission rate. However, for 

the following reasons, the 25% factor does not necessarily apply and is unlikely to be achieved 

in practice. 

 

As background, the CH2M Hill “BART Analysis for Centralia Power Plant,” p.3-6 (rev. July 

2008) cites a study by Harmon (1998) concluding that tangentially fired boilers are able to 

achieve a 20 to 25 percent reduction with the application of SNCR. Based on the study and 

other information, CH2M Hill’s 2008 BART Analysis applied the high end of the range, 25 

percent, to the baseline emission rate of 0.30 lb/MMBtu to derive an estimated emission rate of 

0.228 or 0.23 lb/MMBtu for the purpose of modeling visibility benefits from SNCR. (See 

Case 3 SNCR estimated emissions of 0.228 in 2008 BART Analysis). 

 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011100
Page 2 

8/8/2011 

Ecology’s BART Determination Support Document (rev. April 2010) concurred that the 25 

percent reduction factor was a reasonable assumption. TransAlta’s May 2008 response to 

Ecology’s comments on the January 2008 BART Analysis report reiterated the Harmon 

findings and implicitly acknowledged that the high end of the range from adding SNCR to 

existing LNC3 and Flex Fuels is 25%: 

 

“The control effectiveness of SNCR is a function of many variables including the 

uncontrolled emissions concentrations, physical conditions, and operational 

conditions. The greatest control effectiveness is generally achieved with high 

uncontrolled NOx concentrations, on new units that have been specifically designed 

for SNCR, and at a specific load ... In addition, a study by Harmon indicates that a 

large coal fired tangentially fired unit equipped with a low NOx SNCR has the 

potential to reduce NOx emissions by only 20-25 percent with an ammonia slip of 

less than 10 ppm....” 

The conclusion that 25 percent reduction is highest likely reduction is supported by PGE’s 

“Alternative BART Analysis for the Boardman Power Plant,” p. 3-4 (Aug. 27, 2010) concludes 

that SNCR achieves “emissions reduction levels of 15 to 25 percent for retrofit applications.” 

At Ecology’s request, in March 2010 TransAlta modeled the visibility benefits from adding 

SNCR to Flex Fuels. Based on the previous 25 percent reduction factor from the 2008 BART 

Analysis report, the 2010 visibility modeling assumed an emission rate of 0.18 lb/MMBtu 

based on the Flex Fuel Project rate of 0.24 lb/MMBtu. It is important to note that the 25 

percent assumption was not based on an engineering study or a vendor estimate. The emission 

reduction was not intended to be relied upon as a potential enforceable limit but only as an 

approximation of the visibility benefits. 

TransAlta did not begin to develop SNCR emission rates for use as an enforceable BART limit 

until the passage of SB 5769 earlier this year. In recent months TransAlta selected and is 

currently working with a SNCR system vendor to determine what NOx reduction efficiency 

and emission rates will be achievable with the proposed SNCR systems when they are installed 

on the TransAlta units. A computational fluid dynamics (CFD) model of each of the two 

Centralia furnaces must be generated as the first step in designing the optimal emissions 

reduction systems. This modeling and design must be completed before a construction 

contract for the systems can be issued and a warranty for the projected NOx reduction 

efficiency is obtained from the vendor. 

The creation and verification of CFD models allow the vendor’s technical experts to predict 

temperature distribution, gas flow paths and concentration and distribution of constituents 

including O2, CO, NOx, and unburned carbon within the boilers. The model is used to select 

the size, location and design of the SNCR system components and capabilities. The first step in 

the CFD modeling process is to generate a model based on the Plant’s engineering drawings 

for each boiler. The next step is to develop a baseline simulation at low & high boiler loads on 

each Centralia unit. This requires gathering operational data on temperature distribution, gas 

flow paths and concentration and distribution of constituents including O2, CO, NOx, and 

unburned carbon during operation of the units at different production levels. Since both units 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011101
Page 3 

8/8/2011 

were off-line from early March through late July, the testing to gather the required data is 

currently scheduled for August 2011. 

The data gathered in August will be used to calibrate the CFD models developed for each unit 

and estimate potential NOx reductions achievable over the anticipated operating range of the 

units. The information obtained from the CFD modeling will allow the selected vendor to 

finalize the design of the SNCR system equipment and warranty the design NOx removal 

efficiency of the SNCR systems in October 2011. 

Prior to completion of the CFD modeling and based on current information, the limit that can 

be achieved with reasonable assurance would be 0.22 lb/MMBtu, which is already a reduction 

of more than 25% from the pre-BART baseline emission levels. The study by Srivastava et 

al, Table 3, cited in the draft Determination Support Document lists 20 plants with SNCR that 

had emission rates ranging from 0.274 to 0.755, significantly higher than the 0.22 lb/MMBtu 

rate that TransAlta is proposing for Centralia. Although the removal rates may be higher, 

TransAlta understands that SNCR has diminishing efficiency at lower levels of baseline 

emissions, such as the Flex Fuel Project rates of the Centralia Plant. 

An emission rate of 0.22 lb/MMBtu is substantially lower than the median emission rate of 

0.27 for all the SNCR systems proposed as BART in the Western United States (see attached 

table). The attached table and the Department’s own draft BART Determination Support 

Document show that no coal-fired plant in the Western United States has been determined to 

be capable of achieving a BART emission rate less than 0.19 lb/MMBtu with SNCR 

technology and LNC3 combustion controls combined. 

Based on the foregoing information and TransAlta’s operating experience with LNC3 

technology, an emission rate of 0.22 lb/MMBtu should be achievable with the addition of 

SNCR technology to the current LNC3 technology and an ammonia slip of less than 5 ppm. 

This would result in a greater than 25 percent reduction from the pre-BART emissions. 

Operating experience will determine whether an additional emission reduction to a level of 

0.20 lb/MMBtu (a 33% reduction from 0.30 and 17% reduction from 0.24) is achievable with 

optimization of an SNCR system. However, as explained in the CH2M Hill BART Analysis, 

the reduction achievable depends upon many factors, including higher ammonia slip than the 

proposed limit. Achieving the Department’s proposed emission rate of 0.18 is considered very 

unlikely (see attached discussion). A discussion of the unique factors that influence NOx the 

installation of SNCR for NOx reduction in the TransAlta units is attached in the letter from the 

Centralia Plant engineer. 

In conclusion, it is necessary to complete the study required by Section 5 of the order to 

determine the lowest level that SNCR can reasonably achieve before a limit lower than 0.22 

lb/MMBtu is set. TransAlta proposes that, at the conclusion of the study required by Section 5, 

a lower emission limit (as low as 0.20 lb/MMBtu) will be requested if it is shown to be 

achievable by the result of the study. If the plant is able to optimize the systems to reach 0.20 

lb/MMBtu, this level would be among the lowest achieved by any plant in the Western U.S. 

utilizing SNCR with LNC3 technology. 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011102
Page 4 

8/8/2011 

Ammonia Emissions Limit 

Compliance with the ammonia emissions limit must be determined on the same 30-day rolling 

average time frame as the NOx limit. Without the flexibility to adjust ammonia addition rates 

as needed to operate the SNCR system optimally, we cannot assure that we can achieve 

compliance with the 0.22 lb/MMBtu NOx limit. 

Ammonia Emissions Monitoring 

We have not been able to find any CEMS for ammonia that will provide the required accuracy 

and repeatability on our plants when controlled by SNCR. A recent review of the technology 

confirms this (http://www.ladco.org/about/general/Emissions_Meeting/Greaves_032510.pdf). 

NDIR/FTIR ammonia analyzers have proven to be unreliable and inaccurate for measuring 

ammonia slip in the 5 ppm range. UV ammonia analyzers have also proven to be inaccurate 

for measuring ammonia slip in the desired range. TDLAS in-situ analyzers cannot be used on 

the saturated stack following the SO2 scrubber. 

The Differential NOx/NH3 Converter Method described on slide 8 of the presentation is the 

only technology that might be effective; however this type of system only works accurately 

when NOx emissions are at very low levels. For our process with SNCR the full scale of the 

analyzers must be set at levels approximately 200 ppm. The allowable 2.5% daily drift on an 

analyzer with a full scale of 200 ppm is 5 ppm. Since two analyzers are used to determine the 

ammonia concentration, the allowable drift of the two analyzers could compound the potential 

error to 10 ppm which is double the proposed limit for ammonia and would be unable to pass 

the proposed certification requirements. Based upon this review, it has been determined that 

monitors for ammonia that can be certified as CEMS are not available for our units. 

While we intend to install some type of process monitoring equipment on the SNCR system to 

provide necessary ammonia data for optimizing the SNCR operation, as we described above, 

the current technology cannot meet requirement for use as a CEMS. We therefore propose 

removing the ammonia monitoring requirements from the Order and replacing them with an 

annual compliance test. Once we determine the best system to monitor ammonia levels for the 

ammonia optimization study and where it can be installed to provide the most useful 

information (with assistance from the SNCR system supplier), we will include that information 

in the study plan required by condition 5.2. 

Greenhouse Gas Emissions 

Including SB 5769’s greenhouse gas (GHG) emission limitations is inappropriate. The GHG 

requirements are unrelated to the BART Order and the requirements of the Regional Haze SIP. 

SB 5769 provides that these requirements will be incorporated in an enforceable agreement 

between TransAlta and the State. There is no implication in the statute that the GHG limits 

should be incorporated in a BART determination. To the extent necessary to support the 

timelines used for the cost benefit calculations in the BART determination Support Document, 

State law establishes the enforceability of those timelines for EPA. 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011103
Page 5 Transt\lta 	 8/8/2011 

TransAlta believes that completely removing this section is appropriate; however, we have 

proposed alternative language if the Department cannot rely on State law to establish the 

enforceability of the timelines. The proposed language utilizes the language "cease burning 

coal" similar to the EPA approved Oregon BART language. 

Operating Days and Startup/Shutdown (Section 8.3) 

Removal of the 360 MW minimum operating rate references in the BART Order has 

essentially eliminated the startup/shutdown allowance from the existing Order. There must be 

an allowance for partial operating days or staJ1ups and shutdowns in the Order because the 

limits are based upon operation of the SNCR systems. These systems cannot operate under 

startup and shutdown conditions. EPA concurs that BART determinations may take into 

account higher emissions -during startup and shutdown. (Letter from EPA Region 8 to South 

Dakota Department of Environment and Natural Resources, Sept. 13,2010, p. 2, attached). If 

Ecology does not concur with the 360 MW minimum operating rate approach, then one 

alternative would be that an operating day with less than 8 hours of operation would have to be 

eliminated from the 30-day average since it will represent either startup or shutdown 

conditions. We propose that section 8.3 reflect that only days with 8 or more hours of firing 

coal would be averaged into the 30-day average. This is similar to the 8-hour startup 

allowance in our Title V permit condition M9 and we believe would exclude a portion of 

emissions that occur only during the beginning of a startup or ending of a shutdown from the 

30-day average. 

BART Determination Support Document (Section 4.2 and Appendix 1) 

We request that Ecology leave the BART determination as LNC3 and Flex Fuels. The 

installation of SNCR could be based on the technology needed to meet the State's Visibility 

Reasonable Progress goals. This approach would avoid the need to issue a new BART Order 

but would still accomplish the goal of setting a lower enforceable limit to improve visibility. 

Please contact Brian Brazil or Rick Griffith if you have any questions regarding these 

comments. 

Sincerely, 

5f'~ 

Bob Nelson 

Director, Centralia Operations 

TransAlta Centralia GenerationLLC 

cc: 	 Clint Lamoreaux, Southwest Clean Air Agency 

Rick Griffith 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011104
SNCR BART/RFP Determinations for Western Coal Plant Sources 

Emission Unit Assumed 

NOx Control 

Type 

NOx Emission 

Limit 

Assumed 

SO2 Control 

Type 

SO2 Emission 

Limit 

Reasonable 

Progress NOx 

Controls 

Alaska (http://www.dec.state.ak.us/air/anpms/rh/rhdoc/Section III.K.6.pdf)

GVEA Healy 

Unit 1 

existing LNB 

with OFA, 

SNCR 

required to be 

added 

0.20 lb/MMBtu existing dry 

sorbent 

injection 

system 

0.30 lb/MMBtu Will be 

evaluated if 

not shut down 

by 2024 

Colorado (http://www.cdphe.state.co.us/ap/regionalhaze.html) 

CENC 

Unit 5 

new LNB with 

SOFA, and 

SNCR 

0.19 lb/MMBtu 

Or 

0.26 lb/MMBtu 

Average for 

Units 4 & 5 (30-

day rolling) 

None 1.0 lb/MMBtu 

(30-day rolling) 

no 

TSG&T 

Craig 

Unit 1 

new SNCR 

System 

0.28 lb/MMBtu 

(30-day rolling) 

Wet 

Limestone 

scrubber 

0.11 lb/MMBtu 

(30-day rolling) 

BART is 0.27, 

0.28 allowed 

with SCR on 

Unit 2 

TSG&T 

Craig 

Unit 2 

(SNCR is 

BART) new 

SCR System 

for RP 

0.08 lb/MMBtu 

(30-day rolling) 

Wet 

Limestone 

scrubber 

0.11 lb/MMBtu 

(30-day rolling) 

BART is 0.27,

0.08 required 

for reasonable 

progress goal 

Nevada (http://deq.state.wy.us/aqd/308 SIP/309(g) SIP 1-7-11 Clean Final.pdf) 

NVE Reid 

Gardner 

Units 1 & 2 

ROFA with 

Rotamix 

0.20 lb/MMBtu

(12-month 

rolling) 

existing wet 

soda ash 

FGD 

0.15 lb/MMBtu 

(24-hr) 

no 

NVE Reid 

Gardner 

Unit 3 

ROFA with 

Rotamix 

0.28 lb/MMBtu

(12-month 

rolling) 

existing wet 

soda ash 

FGD 

0.15 lb/MMBtu 

(24-hr) 

no 

North Dakota (http://www.ndhealth.gov/AQ/RegionalHaze/Regional Haze Link Documents/Main SIP Sections 

1-12.pdf) 

BEPC 

Leland Olds 

Unit 1 

new LNB with 

SOFA and 

SNCR 

0.19 lb/MMBtu 

(30-day rolling) 

new Wet 

Limestone 

scrubber 

0.15 lb/MMBtu 

(30-day rolling) 

no 

BEPC 

Leland Olds 

Unit 2 

new LNB with 

ASOFA and 

SNCR 

0.35 lb/MMBtu 

(30-day rolling) 

new Wet 

Limestone 

scrubber 

0.15 lb/MMBtu 

(30-day rolling) 

no 

GRE 

Stanton 

Unit 1 

new LNB with 

OFA and 

SNCR 

0.29 or 0.23 

lb/MMBtu 

(30-day rolling) 

new Wet 

Limestone 

scrubbers 

0.24 or 0.16 

lb/MMBtu 

(30-day rolling) 

Note: limits on 

lignite and 

subbituminous 

MPC Milton 

R.Young 

Unit 1 

new LNB with 

ASOFA and 

SNCR 

0.36 lb/MMBtu 

(30-day rolling) 

new Wet 

Limestone 

scrubber 

0.15 lb/MMBtu 

(30-day rolling) 

no 

MPC Milton 

R.Young 

Unit 2 

new LNB with 

ASOFA and 

SNCR 

0.35 lb/MMBtu 

(30-day rolling) 

existing Wet 

Limestone 

scrubber 

0.15 lb/MMBtu 

(30-day rolling) 

no 

 

Average SNCR BART Limit 0.26 lb/MMBtu 

Median SNCR BART Limit 0.27 lb/MMBtu 

Lowest SNCR BART Limit 0.19 lb/MMBtu 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011105
July 28, 2011 

Mr. Brian Brazil 

Re: Selective Non Catalytic Reduction (SNCR) Technology implementation at 

Centralia Plant 

Brian: 

Station #1 & #2 boilers were retrofitted with Low NOx Burners (LNB) in 2002 and 2001, 

respectively. This modification, which included installation of Separate Over Fire Air (SOFA) 

and Close Coupled Over Fire Air (CCOFA) injection ports, allowed the NOx emissions to be 

lowered to 0.30 lbs/mm BTU. In 2008 as part of conversion to PRB fuels which are inherently 

lower in nitrogen content, and additional fine tuning of the boilers, the achievable NOx level 

was further reduced to 0.24 lbs/mm BTU. 

Earlier this year, we embarked on installation of SNCR technology on both boilers for 

additional reduction of NOx. In SNCR systems, a reagent is injected into the flue gas in the 

furnace within an appropriate temperature window. The reagent generates ammonia and the 

process reaction converts NOx to nitrogen and water vapor. The performance of an SNCR 

system depends on a variety of factors such as the furnace baseline oxygen and carbon 

monoxide concentrations, injected reagent quantity and distribution, residence time, and flue 

gas temperature. 

The influence of these parameters can have a significant impact on the performance of an 

SNCR system. The theoretical reduction for SNCR reaction is one mole of NOx to one mole of 

ammonia. However, experience has shown that a portion of ammonia can exit the boiler and 

cause numerous environmental and operational concerns such as formation of detached 

plumes, corrosion and boiler component pluggages. The unreacted ammonia reacts with other 

compounds in the flue gas to form ammonia compound such as NH4 HSO4 or NH4 Cl. These 

compounds are corrosive and can create blockages of the air preheater baskets that will lead to 

forced unit outages. Free ammonia also has the potential to contaminate the captured fly ash 

and the station SO2 control system’s by-products creating additional problem. 

Since the PRB fuels conversion at the plant we have had numerous issues unique to our 

boilers. These fireboxes, which were originally designed for combusting the native fuel from 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011106
Page 2 

7/25/2011 

the mine next door, are too short to allow sufficient heat adsorption from PRB fuels which 

generate higher radiant heat. This has resulted in excessive furnace exit gas temperature 

leading to non stratified isothermal planes. The excessive heat also generates fluid slag (due to 

high sodium PRB ash) on the walls that plug up observation ports and instrumentation taps on 

the boiler walls. The SOFA injection can also create pocket of high CO gas and unpredictable 

mixing zones for the reaction between the SNCR reagent and the NOx in the flue gas stream. 

These issues would significantly affect the performance of SNCR systems relying on injection 

above the furnace. 

The SNCR systems using multi nozzle lances injecting at the superheater pendant positions, 

rely on rotary insertion systems identical to our long lance IK soot blowers. These lances are 

unreliable, experience routine failures from clinker falls, and remain out of service on a regular 

basis. The long term viability of any SNCR system relying on multi nozzle lances is 

questionable. 

We have had multiple conversations with potential suppliers of SNCR technology and there 

appears to be a significant reluctance to offer an ironclad guarantee regarding the removal 

efficiency and the free ammonia slip stream at the boiler outlet. One of the contributors to this 

issue is the fact that we are already operating with extremely low NOx levels (0.24 lbs/mm 

BTU) that the actual realized system performance may be hard to predict. 

We are currently working with a SNCR system vendor to determine what NOx reduction 

efficiency and emission rates will be achievable with their proposed design of SNCR systems. 

We have also retained the services of an independent consulting firm specializing in modeling 

of SNCR components and their interaction with various parameters within a boiler. The 

outcome of these models will provide additional insight as to the performance of the SNCR 

system. 

The above mentioned concerns and due to the fact that the actual long term performance of any 

SNCR system can only be verified by post commissioning optimization, we do not anticipate 

to be able to achieve more than 19-20% NOX removal efficiency. However, it is our intention 

to push our system to its highest sustainable capability. 

Please feel free to contact me if you have any questions regarding these comments. 

Sincerely, 

Jim Khorsand, P.E. 

Plant Lead Engineer 

cc: Trevor Ebl 

BART Determination Document 

TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011107
Implementation of NH3 measurem

Combustion NOx Reduction S

LADCO WORKSHOP

March 24-25th, 2010

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
Ammonia Slip Measurement

Post Combustion NO

x Reduction:

3⁄4 Selective non-catalytic reduction (S3⁄4 Selective catalytic reduction (SCR)3⁄4 Common requirement: introduction 

4NO + 4NH 4NO + 4NH

3 + O

2

Æ 4N

2 + 6H

2NO

2 + 4NH

3 + O

2

Æ 3N

2 + 6

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
Ammonia Slip Measurement

Consequences of Ammonia Slip:z If over-titrated NH3 escapes – pollu

wastes

z Violates permit limit if applicablez If due to incomplete mixing – NOx z With high sulfur fuels ammonia sulf

bisulphate formed – can foul air pre

z Ammonia contaminates fly ash ma

hazardous

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
Ammonia Slip Measurement

SNCR Slip Monitor

Sta

SCR Slip Monitor

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
Ammonia Slip Measurement

Monitoring Methods:

z FULLY EXTRACTIVE (DRY BASIS)z FULLY EXTRACTIVE (HOT-WET BASISz DILUTION EXTRACTIVE (WET BASIS)z IN-SITU (CROSS STACK or PROBE)

Measurement Types:

z Chemiluminescence ,UV Absorption, FTz (TDLAS) 

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
z Analyzer Glossary

z Chemiluminescence: (Chemical Light) a measurement tech

measures the light given off as a result of the reaction betwelight output is proportional to the concentration of NO. NO2 is 

high temperature catalytic converter. NO2 does not react with 

converted to NO.

z UV Absorption: a measurement technique that uses a UV s

particular wavelength where the gas of interest absorbs (meawavelength where the gas of interest does not absorb (refere

SO2 measurement in high concentrations.

z Tunable Diode Laser Absorption Spectroscopy (TDLAS):

very narrow bandwidth in the IR region where no cross interfeabsorption of the IR source by the targeted gas is proportiona

concentration. 

z Fourier Transform-Infrared Spectroscopy (FTIR): This tec

absorption of infrared radiation by the sample gas versus waabsorption bands identify molecular components. 

z Differential Optical Absorption Spectroscopy (DOAS): is 

concentrations of trace gases by measuring their specific narstructures in the UV and visible spectral region 

Ammonia Slip Measurement

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
Ammonia Slip Measurement

Inlet/Outlet Differential NOx Methodz First method is based on the calculation of ammonia slip using 

differential NOx method along with ammonia flow rate and stac

method has been employed successfully in many EPA permitteSCAQMD and many other AQMD’s for control and compliance method is reliable and low in cost for sources where SCR inlet requirement.

z The inlet/outlet method is used where SCR control is also a req

the SCR inlet NOx and SCR outlet NOx are measured on a cooutlet measurement is usually the CEMS compliant system. Tha second probe mounted on the duct before the SCR and a se

z The NOx and NH3 react on a 1:1 basis. Therefore, the amount 

equal to the amount of NOx reduced in the SCR. The simplified 

NH3 slip = NH3 fed – (NOx in – NOx out)

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
Ammonia Slip Measurement

Differential NOx/NH3 Converter Method:

z An alternate ammonia method using direct measurement of d

stack. This method utilizes two (2) NOx analyzers on the outlammonia converter is included at the stack probe which conv

The sample line includes an additional sample tube to transp

sample stream to an additional NOx analyzer. 

z One analyzer is used to measure NOx emissions and the sec

measure the converted stream which includes the NOx and a

NOx for the ammonia slip calculations. The NOx analyzers manufacturer, model number.

z A special probe Is used to catalytically convert NH3 into NOx

that results is NH3 slip. The probe contains an electrically hewhere NH3 is oxidized with oxygen on the catalyst surface inwater, as follows:

4 NH3 + 5 O2 = 4 NO + 6 H2O

z The NH3 conversion process has an efficiency of 90-98% de

flowrates, age of converter, and NH3 concentrations. Conve

can be expected on typical combustion turbine applications.

NH3 slip (ppm) = NOx (ppm) (total converted) – NOx (

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
Ammonia Slip Measurement

Direct measurement of NH3:

z This can be done using several methods, both across 

measurement or Insitu probe type systems. 

z Typical across duct measurements use the Tunable D

DOAS monitor. 

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
In-Situ...Advantages:

No gas transport: Fast response time: No loss of components in a sample system: No filters, sample lines, pumps to clean

Lower planning expenses: Support for heated sample gas lines : Analysis container: Disposal of sample gas and condensateLower installation and operation cost: No Heated sample gas lines ( $50/ft ): Larger component Inventory and Replacement 

requirements

: Cost for shelter or space in existing analyzer rooms. 

Ammonia Slip Measurement

: Dan Kietzer June 30, 2009

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
LAS 

LAS Launch Optics

UCR TDL Test Cell

IR Laser Ligh

Process Gas

Scanner andLens

Legend

Fiber Optic Cable

Co-Ax CableBeam Path

Tunable Diode Laser Analyzer

Ammonia Slip Measurement

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
Ammonia Slip Measurement

TDLAS Ammonia slip Monitoring:• In-situ measurement avoids loss of sample integrity, t• Single Indicator of direct measurement of Slip for com

performance of DeNOx system 

• Fast response better then 60 seconds allows better fe

less violations.

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
Ammonia Slip Measurement

EXTRACTIVE : Sample delivered to analyzer mounted in typical 

cabinet , possibly integrated with CEMS.

 Useful for Dirty Applications such as certain Coal 

Fired Plants.

 Measurement type: Chemiluminescence, UV 

Absorption, FTIR

 Minimal performance at low concentrations Easy to calibrate, since standard calibration gas 

procedures are incorporated. 

 Not the most cost effective when equipment, install 

and maintenance costs are accounted for.

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
DEFOR, Dieter Deggim, September 

09

For measurement of 

1 to 3 UV components

Includiing O2

UV photometer

DEFOR

Ammonia Slip Measurement

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
Ammonia Slip Measurement

Certification of NH3 Slip Measurementsz There are no performance standards against which NH3 mon

and there are no adopted methodologies for the certification monitoring. 

z CTM-027 defines how best to obtain representative stack tes

of stack conditions, against which any analyzer system woul

z In addition, there are no NIST traceable Protocol calibration g

levels. The most accurate calibration gas for NH3 is a workinaccuracy of +/- 5%. Also, the lowest level that can be comme

z Spiking is an accepted method by which relative accuracy da

once again no standards are set on how to achieve this.

z Most Insitu analyzers have built in calibration standards eithe

gas cells. All have the ability to do self check zero and span, 

checked against a standard gas at a higher value working cla

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011
Ammonia Slip Measurement

SUMMARY:

 Until a clear acceptable method for accurate measure

lowest concentrations now seen (less than 2ppm) is coand one that can be applied to all applications, then Invendors to assist in meeting their needs whether it be process optimization.

 Insitu while giving the best accuracy will be considered 

most applications, but without the ability to do all applimeasurements will struggle for acceptability.

 Extractive surrogate measurements will continue to do

market for now because of the ease of acceptability as 

 Tunable Diode Laser technology is proving to be the m

but will have to wait until a suitable calibration methoo

and accepted.

BART Determination Document TransAlta Centralia Power Plant 

August 2009, Revised April 2010, Revised November 2011