Otter Tail Power Company

Big Stone Generating Station

Unit 1

Best Available Retrofit 

Technology Analysis

November 2, 2009

Project 53777
 i 11/2/2009 

Otter Tail Power Company 

Big Stone Plant 

Unit I 

Best Available Retrofit Technology Analysis

Table of Contents

LIST OF TABLES ...........................................................................................................iii 

 EXECUTIVE SUMMARY ........................................................................................ES-1 

1.0 INTRODUCTION ............................................................................................................1

1.1 BACKGROUND ................................................................................................ 2 

1.2 BART ANALYSIS PARAMETERS.................................................................. 3 

1.3 APPROACH ....................................................................................................... 5 

1.3.1 IDENTIFICATION OF RETROFIT CONTROL TECHNOLOGIES............... 6 

1.3.2 FEASIBILITY ANALYSIS................................................................................ 6 

1.3.3 EVALUATE TECHNICALLY FEASIBLE CONTROL OPTIONS BY 

EFFECTIVENESS.............................................................................................. 6 

1.3.4 IMPACT ANALYSIS......................................................................................... 6 

1.3.5 METHODOLOGY FOR ESTIMATED COSTS................................................ 7 

1.3.6 METHODOLOGY FOR VISIBILITY IMPACTS DETERMINATION .......... 9 

1.3.7 ADDITIONAL APPROACH METHODS....................................................... 10 

1.4 THE ROLE OF MODELING AND CALPUFF IN A BART ANALYSIS ..... 10 

1.4.1 CALPUFF MODELING METHODOLOGY................................................... 11 

1.4.2 MODELING SCENARIOS.............................................................................. 11 

2.0 NOX BART EVALUATION ..........................................................................................13

2.0.1 BART GUIDELINE NOX LIMITS FOR CYCLONE-FIRED BOILERS ....... 13 

2.1 IDENTIFICATION OF RETROFIT NOX CONTROL TECHNOLOGIES .... 13 

2.2 TECHNICAL DESCRIPTIONS AND FEASIBILITY ANALYSIS OF NOX

CONTROL TECHNOLOGIES ........................................................................................ 14 

2.2.1 FEASIBILITY OF COMBUSTION NOX CONTROLS.................................. 14 

2.2.2 FEASIBILITY OF POST-COMBUSTION NOX CONTROLS....................... 15 

2.2.3 RESULTS OF FEASIBILITY ANALYSIS ............................................................ 16 

2.3 CONTROL EFFECTIVENESS EVALUATION OF NOX CONTROL 

TECHNOLOGIES ............................................................................................................ 16 

2.4 EVALUATION OF IMPACTS FOR FEASIBLE NOX CONTROLS............. 18 

2.4.1 COST IMPACTS OF NOX CONTROLS ......................................................... 18 

2.4.2 ENERGY IMPACTS OF NOX CONTROL ALTERNATIVES ...................... 25 

2.4.3 NON AIR QUALITY AND OTHER ENVIRONMENTAL IMPACTS OF NOX

CONTROL ALTERNATIVES......................................................................... 27 

2.4.4 VISIBILITY IMPAIRMENT IMPACTS OF NOX CONTROLS .................... 28 

2.4.5 SUMMARY OF IMPACTS OF NOX CONTROLS – BSP UNIT I ................ 30 

3.0 SO2 BART EVALUATION............................................................................................32

3.0.1 BART GUIDELINE SO2 LIMITS FOR CYCLONE-FIRED BOILERS ........ 32 
 ii 11/2/2009 

3.1 IDENTIFICATION OF RETROFIT SO2 CONTROL TECHNOLOGIES ..... 32 

3.2 TECHNICAL DESCRIPTION AND FEASIBLITY ANALYSIS .................. 33 

3.2.1 PRE-COMBUSTION FUEL TREATMENTS - FUEL SWITCHING ............ 33 

3.2.2 POST-COMBUSTION FLUE GAS DESULFURIZATION ........................... 33 

3.2.3 RESULTS OF FEASIBILITY ANALYSIS ..................................................... 34 

3.3 EVALUATE TECHNICALLY FEASIBILE SO2 CONTROL OPTIONS BY 

EFFECTIVENESS............................................................................................................ 35 

3.4 EVALUATION OF IMPACTS FOR FEASIBLE SO2 CONTROLS .............. 36 

3.4.1 COST ESTIMATES ......................................................................................... 36 

3.4.2 ENERGY IMPACTS........................................................................................ 43 

3.4.3 NON-AIR QUALITY ENVIRONMENTAL IMPACTS................................. 43 

3.4.4 VISIBILITY IMPACTS ................................................................................... 44 

3.4.5 IMPACT SUMMARY...................................................................................... 45 

4.0 PARTICULATE MATTER BART EVALUATION...................................................46

4.1 IDENTIFICATION OF AVAILABLE RETROFIT PM CONTROL 

TECHNOLOGIES ............................................................................................................ 46 

4.2 TECHNICAL DESCRIPTION AND FEASIBLITY ANALYSIS .................. 47 

4.2.1 FABRIC FILTER (FF) ..................................................................................... 47 

4.2.2 COHPAC .......................................................................................................... 47 

4.2.3 ELECTROSTATIC PRECIPITATOR (ESP)................................................... 48 

4.3 RANK OF TECHNICALLY FEASIBLE PM CONTROL OPTIONS BY 

EFFECTIVENESS............................................................................................................ 48 

4.4 EVALUATION OF IMPACTS FOR FEASIBLE PM CONTROLS – UNIT I49 

4.4.1 VISIBILITY IMPACTS ................................................................................... 49 

5.0 BART RECOMMENDATIONS....................................................................................49

5.1 NOX BART ....................................................................................................... 50 

5.2 SO2 BART ........................................................................................................ 50 

5.3 PM BART ......................................................................................................... 51 

5.4 COMBINED BART.......................................................................................... 52 

Appendix A 

 Technical Feasibility Assessment Details for NOX Controls (A1) 

 Summary of CUECost Inputs (A2) 

 Summary of Modeling Results (A3) 

Appendix B 

 Technical Description of SO2 Controls (B1) 

Appendix C 

 Technical Description of Particulate Matter Controls (C1) 

 

Appendix D 

 Visibility Modeling and Impairment Improvement Analysis Details (D1) 
 iii 11/2/2009 

List of Tables

1.2-1 – Unit Design and Operating Parameters 

1.2-2 – Coal Parameters 

1.2-3 – Economic Factors 

1.4-1 – Big Stone Plant Modeling Scenarios 

2.1-1 – Potentially Available NOX Control Alternatives Identified for BART Analysis 

2.2-1 – NOX BART Feasibility Analysis Results 

2.3-1 – Evaluated NOX Control Technologies 

2.3-2 – Estimated Control Options NOX Emission Rates Evaluated 

2.4-1 – Unit Capital Cost Factors of Feasible NOX Control Options 

2.4-2 – Estimated O&M Costs for NOX Control Options 

2.4-3 – Capital and Annualized Costs Estimated for NOX Control Alternatives 

2.4-4 – Estimated Annual Emissions and LTAC for NOX Control Alternatives 

2.4-5 – Estimated Incremental Annual Emissions and LTAC for NOX Control Alternatives 

2.4-6 – Visibility Impairment Impacts from Emission Controls 

2.4-7 – Cost for Incremental Visibility Improvement 

2.4-8 – Impacts Summary for BSP Unit I NOX Controls 

3.1-1 – SO2 Control Technologies Identified for BART Analysis 

3.2-1 – SO2 BART Feasibility Analysis Results 

3.3-1 – SO2 Control Technologies Identified for BART Analysis 

3.4-1 – First Year O&M Cost Estimate for BSP FGD Systems 

3.4-2 – Capital and Annualized Costs Estimated for SO2 Control Alternatives 

3.4-3 – Estimated Annual Emissions and LTAC for SO2 Control Alternatives 

3.4-4 – Estimated Incremental Annual Emissions and LTAC for SO2 Control Alternatives 

3.4-5 – Energy Requirements of SO2 BART Alternatives 

3.4-6 – Visibility Impairment Impacts from Emission Controls 

3.4-7 – Cost for Incremental Visibility Improvement 

3.4-8 – Impacts Summary for BSP Unit I SO2 Controls 

4.1-1 – PM Control Technologies Identified for BART Analysis 

4.2-1 – PM BART Feasibility Analysis Results 

5.4-1 – Visibility Impairment Impacts from Combined Emissions
 ES-1 11/2/2009 

EXECUTIVE SUMMARY 

The U.S. Environmental Protection Agency (EPA) finalized the Regional Haze Regulations and 

Guidelines for Best Available Retrofit Technology (BART) Determinations in 2005 (40 CFR 51, Subpart 

P; 40 CFR 51, App. Y). BART is defined as “an emission limitation based on the degree of reduction 

achievable through the application of the best system of continuous emission reduction for each pollutant 

which is emitted by a BART-eligible source. The emission limitation must be established, on a case-bycase basis, taking into consideration the technology available, the costs of compliance, the energy and 

non-air quality environmental impacts of compliance, any pollution control equipment in use at the 

source, the remaining useful life of the source, and the degree of improvement in visibility which may 

reasonably be anticipated to result from the use of such technology” (40 CFR 51.301). This document 

presents the BART analysis for each of three major pollutants (nitrogen oxides (NOX), sulfur dioxide 

(SO2), and particulate matter (PM)) for Otter Tail Power Company’s (OTPC’s) Big Stone Plant (BSP) 

Unit I located near Big Stone City, South Dakota. Otter Tail Power Company is operating agent for the 

Big Stone Plant co-owners: NorthWestern Energy, Montana-Dakota Utilities, Co., a division of MDU 

Resources Group, and Otter Tail Power Company. 

BSP is a steam electric generating plant with one generating unit burning Powder River Basin coal and a 

net electrical output of 475 MW. Particulate control for Unit I is provided by a conventional pulse-jet 

fabric filter installed in 2007. Nitrogen oxides (NOx) emissions from the unit are controlled with an overfire air system (OFA). The unit does not have controls for sulfur dioxide emissions other than firing lowsulfur Powder River Basin coal. Unit I began operation in 1975 and is presumed to be subject to the 

requirements for BART analysis under the Regional Haze Rule absent a formal determination to the 

contrary from the DENR. 

The BART analysis steps 1 through 5 for NOX, SO2 and PM emissions from BSP are described in this 

report. Potentially applicable control technologies are first identified. A brief description of the 

processes and their capabilities are then reviewed for availability and feasibility. Subsequently, those 

available technologies deemed feasible for retrofit application are ranked according to control capability. 

The impacts analysis then reviews the estimated capital and O&M costs for each alternative, the energy 

impacts and non-air quality impacts. The impact based on the remaining useful life of the source is 

reviewed as part of the cost analysis. In the final step of the analysis, feasible and available technologies 

are assessed for their potential visibility impairment impact reduction capability via visibility modeling 

results. The results of the impact analyses are tabulated and potential BART control options are listed. 
 ES-2 11/2/2009 

The final result of this analysis is a recommendation of the Best Available Retrofit Technology (BART) 

based upon the detailed analysis conducted in this report. For NOX, five control alternatives were 

identified and evaluated using the 5 steps. Over-fire air (OFA), separated over-fire air (SOFA), Selective 

Non-Catalytic Reduction (SNCR) with SOFA and Selective Catalytic Reduction (SCR) with SOFA were 

the technologies that remained after completing steps 1 though 4 of the analysis. To reduce visibility 

impacts due to NOX emissions below a discernable level of 0.5 dV, SOFA is recommended as BART for 

BSP Unit I. Application of SOFA for NOX control translates into a BART emission rate of 2,804 pounds 

per hour. 

For SO2, three control alternatives were identified and evaluated using the 5 steps. Wet FGD and semidry FGD at two levels of control were selected for visibility impacts evaluation after completing steps 1 

though 4 of the analysis. To reduce visibility impacts due to SO2 emissions below a discernable level of 

0.5 dV, semi-dry FGD is recommended as BART for BSP Unit I. Application of semi-dry FGD for SO2

control translates into a BART emission rate of 505 pounds per hour. 

For the PM evaluation, three post combustion control technologies were selected for evaluation in 

addition to the existing pulse-jet fabric filter. BSP Unit I currently uses a pulse-jet fabric filter (installed 

in 2007) that is the best technology available for particulate control, the impact review was abbreviated 

and maintaining the existing pulse-jet fabric filter is recommended as BART for BSP Unit I. The 

corresponding BART emission rate for the existing fabric filter is 84.1 pounds per hour 

Modeling to determine visibility impairment was performed using the recommended BSP Unit I BART 

emission rates for NOX, SO2, and PM. The 98th percentile results are provided in Table ES-1. 
 ES-3 11/2/2009 

TABLE ES-1 – Visibility Impairment Impacts from Combined Emissions 

Control Technique 

NOX

Emission 

Rate

(lb/hr) 

SO2

Emission 

Rate

(lb/hr) 

PM 

Emission 

Rate

(lb/hr) 

Visibility 

Impairment 

Impact 

(dV)

BART 2,804 505 84.1 0.493 

The modeling showed that the proposed BART emissions rates for NOX, SO2 and PM caused no Class I 

area to exceed 0.5 dV for predicted visibility impairment impact (98th percentile) with Boundary Waters 

Canoe Area Wilderness (Boundary Waters) showing the highest predicted visibility impairment impact at 

0.493 dV for the 2007 modeled year. 
 1 11/2/2009 

1.0 INTRODUCTION 

The EPA finalized the Regional Haze Regulations and Guidelines for Best Available Retrofit Technology 

(BART) Determinations in 2005 (40 CFR 51, Subpart P; 40 CFR 51, App.Y). BART is defined as “an 

emission limitation based on the degree of reduction achievable through the application of the best system 

of continuous emission reduction for each pollutant which is emitted by a BART-eligible source. The 

emission limitation must be established, on a case-by-case basis, taking into consideration the technology 

available, the costs of compliance, the energy and non-air quality environmental impacts of compliance, 

any pollution control equipment in use at the source, the remaining useful life of the source, and the 

degree of improvement in visibility which may reasonably be anticipated to result from the use of such 

technology” (40 CFR 51.301). This document presents the BART analysis for each of three major 

pollutants (nitrogen oxides (NOX), sulfur dioxide (SO2), and particulate matter (PM)) for Otter Tail Power 

Company’s (OTPC’s) Big Stone Plant (BSP) Unit I located near Big Stone City, South Dakota. Otter 

Tail Power Company is operating agent for the Big Stone Plant co-owners: NorthWestern Energy, 

Montana-Dakota Utilities, Co., a division of MDU Resources Group, and Otter Tail Power Company. 

A BART eligible source is one that meets three criteria identified by EPA: (1) source is BART eligible if 

operations fall within one of 26 specifically listed source categories, (2) the source entered into service 

between August 7, 1962 and August 7, 1977, and (3) the source has the potential to emit 250 tons per year 

or more of any air (40 CFR 51.301)). The South Dakota Department of Environment & Natural 

Resources (DENR) reviewed the sources within South Dakota and independently determined which 

sources are BART eligible. The DENR classified the electric generating unit (EGU) at Big Stone Plant as 

BART eligible. Once a source is determined to be eligible, baseline modeling is performed to determine 

if the source “contributes” to visibility impairment by exceeding EPA’s recommended 0.5 deciView (dV) 

threshold. Baseline modeling results show that Unit I at BSP exceeds the 0.5 dV impact threshold and is 

subject to a BART analysis. 

The EPA has established guidelines for states to follow when determining BART. These guidelines are 

discretionary for sources other than 750 MW power plants (40 CFR 51.308(e); 40 CFR 51, App, Y, I.H). 

Per EPA’s guidelines, the general steps for determining BART for each pollutant are (40 CFR 51, Appy. 

Y, IV.D.): 

STEP 1 - Identify all available retrofit control technologies (within the BART Guidelines). 

STEP 2 - Eliminate technically infeasible options. 
 2 11/2/2009 

STEP 3 - Evaluate control effectiveness of remaining control technologies. 

STEP 4 - Evaluate the following impacts for each feasible control technology and document results: 

• The cost of compliance. 

• The energy impacts. 

• The non-air quality environmental impacts. 

• The remaining useful life of the source. 

STEP 5 – Evaluate the visibility impacts. 

OTPC retained Burns & McDonnell to assist in the completion of the Best Available Retrofit Technology 

analysis for Big Stone Plant (BSP) Unit I.i

 This report includes steps 1 through 5 of the BART 

Determination for emissions from Unit I at BSP. Section 1 of the report summarizes the plant conditions, 

provides the parameters used in the analysis and discusses the approach to the BART Determination. The 

BART analysis for each pollutant (NOX, SO2 and PM) is provided in Sections 2 through 5. Within the 

section for each pollutant, the results of each step of the BART analysis are summarized for the unit. 

Summaries are provided at the end of the report that communicate the results of each step in the analyses, 

that combine results obtained for each pollutant and that develop permit limit recommendations based 

upon a 30 day rolling average. 

1.1 BACKGROUND 

Otter Tail Power Company operates the Big Stone Plant near Big Stone City, South Dakota. BSP is a 

steam electric generating plant with one Babcock & Wilcox (B&W) cyclone-fired steam generating unit 

burning Powder River Basin coal and a net electrical output of 475 MW. Particulate control for Unit I 

was originally provided by an electrostatic precipitator. In 2001, a new developmental technology, the 

Advanced HybridTM system, was installed. The Advanced HybridTM technology used both an 

electrostatic precipitator and a fabric filter (baghouse) for exhaust gas particulate removal. However, the 

demonstration technology encountered operational problems during its testing phase, which resulted in 

decreased fabric filter life, decreased particulate removal efficiencies, and limited plant operations. 

Consequently, the Advanced HybridTM system was deemed unacceptable for particulate emissions control 

and was removed and replaced with a conventional pulse-jet fabric filter in 2007. The Advanced 

HybridTM system is not currently used in any coal-fired power plant. Nitrogen oxides (NOx) emissions 

 

i

 Burns & McDonnell plans, designs and constructs electric generating facilities and has been providing 

environmental services to the power industry since the 1970s. As a result of its long history providing these 

services, Burns & McDonnell has extensive experience in permitting, Best Available Control Technology (BACT) 

studies, BART analysis and control technology analysis. 
 3 11/2/2009 

from the unit are controlled with an over-fire air system (OFA). The unit does not have controls for sulfur 

dioxide emissions other than firing low-sulfur Powder River Basin coal. Unit I began operation in 1975 

and is presumed to be subject to the requirements for BART analysis under the Regional Haze Rule 

absent a formal determination to the contrary from the DENR. 

1.2 BART ANALYSIS PARAMETERS 

Table 1.2-1 contains the design and operating parameters for BSP Unit I used in the analysis. Typical 

coal parameters used in the BART analysis are provided in Table 1.2-2. The economic factors for this 

study are presented in Table 1.2-3. 

TABLE 1.2-1 – Unit Design and Operating Parameters

 

Unit Characteristics

 Unit I 

Parameters 

Boiler Type Cyclone 

Boiler Manufacturer B&W 

Boiler Heat Input Capacity (descriptive), mmBtu/hr 5,609 

Unit Generator Output Capacity, MW (net) 475 

NOX Emissions 

lb/mmBtu 0.86 

lb/hr1 4,854.8 

SO2 Emissions 

lb/mmBtu 0.86 

lb/hr1 4,832.2 

PM Emissions 

lb/mmBtu 0.015 

lb/hr2 84.1 1

Highest 24-hour actual average emission rates during 2001-2003 as recommended 

 by the BART Guideline. The SO2 emission rate does not correspond to fuel sulfur content. 2

Highest achievable 24-hour average emission rate based on the existing control 

 technology emission rate and the unit heat input
 4 11/2/2009 

TABLE 1.2-2 – Coal Parameters 

 

Ultimate Coal Analysis (% by mass): 

PRB 

Typical 

 Moisture 29.75 

 Carbon 49.30 

 Hydrogen 3.32 

 Nitrogen 0.66 

 Chlorine 0.01 

 Sulfur 0.33 

 Ash 4.63 

 Oxygen 12.00 

 Total 100.00 

Higher Heating Value, Btu/lb 8,547 

Ash Mineral Analysis (% by mass): 

 Silica 35.51 

 Alumina 17.11 

 Titania 1.26 

 Calcium Oxide 26.67 

 Magnesium Oxide 5.30 

 Sodium Oxide 1.68 

 Iron Oxide 6.07 

 Sulfur Trioxide 1.56 

 Potassium Oxide 2.87 

 Phosphorus Pentoxide 0.97 

 Strontium Oxide not reported 

 Barium Oxide not reported 

 Manganese Oxide not reported 

 Total 99.00 
 5 11/2/2009 

TABLE 1.2-3 – Economic Factors

Total Possible Operating Hours per Year 8,760 

Amortization Life, Years 30 

Discount Rate 9% 

Construction Cost Escalation 3% 

O&M Escalation 2% 

Auxiliary Electric Power Cost, $/MW-hr $25 

Fly Ash Disposal Cost ($/ton) $2 

Bottom Ash Disposal ($/ton) $3.50 

Gypsum Waste Disposal ($/ton) $1 

Operating Labor Rate, $/hr $48 

Lime Cost ($/ton delivered) $145 

Limestone Cost ($/ton delivered) $24 

Urea Cost, ($/ton delivered) $380 

Ammonia Cost ($/ton delivered) $325 

1.3 APPROACH 

The purpose of the Regional Haze Rule is to address visibility impairment in mandatory Class I areas that 

results from the emission of SO2, NOX, PM, Volatile Organic Compounds (VOCs) and ammonia from 

certain major sources. The visibility impact of VOCs and ammonia are considered negligible and are not 

addressed further in this report. Before the actual BART analysis can begin, a basis must be defined for 

establishing emission rates to be used for BSP Unit I. For NOX and SO2, the highest 24-hour actual 

average emission rates for 2001-2003 were used for the basis as recommended by the BART guideline. 

For PM, the achievable emission rate for the fabric filter installed in 2007 was used as the basis of the 

study. A sulfuric acid mist (SAM) emission rate of 3.604 pounds per hour as approved in the Modeling 

Protocol was used for the baseline evaluation and for all control scenarios. 

In Part IV of the Guidelines for BART Determination, and discussed in Section 1.0 of this report, the

EPA provides five basic steps for a case-by-case BART analysis although states have the discretion to 

adopt approaches that differ from the guidelines for sources other than 750 MW power plants. The 

format of this report follows these basic steps. The approach used to complete each step is summarized 

below. 
 6 11/2/2009 

1.3.1 IDENTIFICATION OF RETROFIT CONTROL TECHNOLOGIES 

The initial step in the BART determination is the identification of retrofit control technologies. In order 

to identify the applicable control technologies, several reference works are consulted. A preliminary list 

of control technologies and their estimated capabilities is developed. 

1.3.2 FEASIBILITY ANALYSIS 

The second step of the BART process is to evaluate the control processes that have been identified and 

determine if any of the processes are technically infeasible. The BART guidelines discuss consideration 

of two key concepts during this step in the analysis. The two concepts to consider are the “availability” 

and “applicability” of each control technology. 

A control technology is considered available, “if the source owner may obtain it through commercial 

channels, or it is otherwise available in the common sense meaning of the term” or “if it has reached the 

stage of licensing and commercial availability.” On the contrary, a control technology is not considered 

available “in the pilot scale testing stages of development.” (70 FR 39165) When considering a source’s 

applicability, technical judgment must be exercised to determine “if it can reasonably be installed and 

operated on the source type.” The EPA also does not “expect a source owner to conduct extended trials to 

learn how to apply a technology on a totally new and dissimilar source type.” (70 FR 39165) “A 

technology that is available and applicable is technically feasible.” (70 FR 39165) 

1.3.3 EVALUATE TECHNICALLY FEASIBLE CONTROL OPTIONS BY 

EFFECTIVENESS 

The third step in the BART analysis is to evaluate the control effectiveness of the technically feasible 

alternatives. During the feasibility determination in step 2 of the BART analysis, the control efficiency is 

reviewed and presented with the description of each technology. The evaluation of the technically 

feasible BART alternatives concludes with the alternatives ranked in descending order of control 

effectiveness. 

1.3.4 IMPACT ANALYSIS 

Step four in the BART analysis procedure is the impact analysis. The BART Guidelines lists four factors 

to be considered in the impact analysis: 

• The costs of compliance; 

• Energy impacts; 
 7 11/2/2009 

• Non-air quality environmental impacts; and 

• The remaining useful life of the source. 

The first three of the four factors considered in the impact analysis are discussed in the associated 

pollutant section. The remaining useful life of the source is included as part of the cost of compliance. 

Due to the complexity involved with estimating costs, additional discussion is provided below. 

1.3.5 METHODOLOGY FOR ESTIMATED COSTS 

The economic evaluations of each control alternative are presented together for each pollutant in the 

respective sections of the report. Capital and O&M cost estimates for each control alternative are 

presented. The Levelized Total Annual Cost (LTAC) and Unit Control Costs for the control alternatives 

are calculated and presented. The Levelized Total Annual Cost (LTAC) represents the levelized annual 

cost of procurement, construction and operation over a 30 year design life in current (2009) dollars. As a 

minimum, the design life for any alternative was taken to be that recommended by “The EPA Air 

Pollution Control Cost Manual”, Sixth Edition, January 2002, EPA/452/B-02-001. 

The LTAC is used to calculate the average annual and incremental cost effectiveness of each alternative. 

The differences between alternatives are also presented graphically in the form of a plot of the LTAC 

versus the annual emissions reduction (tpy) for each alternative. This form of plot graphically depicts the 

cost effectiveness (in $/ton of pollutant reduction) of each alternative relative to all of the others. The 

average cost effectiveness is defined as the LTAC divided by the annual emissions reduction (ton/yr). 

The area on the plot indicated by the various data points represents the cost effectiveness envelope for the 

alternatives under consideration. A smooth line is drawn on this plot connecting the rightmost points 

(those with the lowest cost for a given level of emissions reduction). This line is referred to as the 

Dominant Control Curve (DCC). The DCC defines the right hand boundary of the envelope 

encompassing all of the alternatives considered. The DCC is used as a screening tool between considered 

alternatives. Those alternatives whose plotted position is above and/or to the left of the DCC are not as 

cost effective as those forming the line and thus can be eliminated from further analysis. An example 

DCC chart was provided in the BART Guidelines. 
 8 11/2/2009 

To more accurately compare alternatives having different costs and control efficiencies; the incremental 

cost effectiveness is also determined for those alternatives on the DCC. The incremental cost 

effectiveness is defined as the LTAC of a given control option minus the LTAC of an alternative, divided 

by the difference between the annual emissions reduction (tpy) of the given control option and the 

alternative being evaluated. The combination of these two economic analyses can be used as an argument 

for the elimination of control technologies with significantly greater marginal control costs than the given 

case. The equation used for the incremental cost effectiveness is shown below. 
 9 11/2/2009 

( )

( )

1 2

1 2

AE AE

LTAC LTAC ICF −

− =

Where, 

ICF = Incremental cost effectiveness ($/incremental ton removed) 

LTAC1 = Levelized Total Annual Cost of control alternative No. 1 ($/yr) 

LTAC2 = Levelized Total Annual Cost of control alternative No. 2 ($/yr) 

AE1 = Control option No. 1 Annual Emissions Reduction (ton/yr) 

AE2 = Control option No. 2 Annual Emissions Reduction (ton/yr) 

(The higher cost, more effective control option is subscript 1 in this equation.) 

The economic analyses presented in this report include not only the estimated capital and O&M costs for 

each alternative, but also the LTAC for economic comparison of the various alternatives. In addition, the 

average cost effectiveness is presented for each alternative. Finally, a comparison between alternatives, 

in the form of the incremental cost effectiveness, is presented in both numerical and graphical form. Thus 

a comprehensive comparison of the economic impacts of each alternative, as well as the differences in 

economic impact between alternatives is clearly presented. 

1.3.6 METHODOLOGY FOR VISIBILITY IMPACTS DETERMINATION 

In the BART Determination Guidelines, and discussed in Section 1.0 of this report, the EPA provides five 

basic steps for a case-by-case BART analysis. The fifth step involves evaluating visibility impacts 

utilizing dispersion modeling. Visibility impairment impacts for modeled baseline (pre-control) and postcontrol emission levels and visibility improvements are to be assessed in deciViews (dV). The BART 

guidelines describe the thresholds for visibility impairment as: 

“A single source that is responsible for a 1.0 dV change or more should be considered to “cause” 

visibility impairment; a source that causes less than a 1.0 dV change may still contribute to 

visibility impairment..... any threshold that you (the States) use for determining whether a source 

“contributes” to visibility impairment should not be higher than 0.5 dV.” (70 FR 39161) 

This study follows the EPA’s Regional Haze Rule threshold recommendations and thus, 0.5 dV is the de 

minimis threshold level of visibility impairment impact for an otherwise BART-eligible source. In other 

words, a BART-eligible source for which modeling predicts a visibility impairment impact of greater than 

0.5 dV is deemed to contribute to a visibility impairment impact and thus is subject to a case-by-case 

BART analysis. A BART-eligible source for which the modeling predicts less than a 0.5 dV impact 
 10 11/2/2009 

would be deemed to not have a visibility impairment impact, and thus could be exempted from a case-bycase BART analysis on that basis. Most noticeably, the EPA fails to address the question of whether or 

not a difference in visibility impairment impact improvement of less than 0.5 dV between two BART 

alternatives would constitute equivalency under the visibility analysis, or if any difference in the model 

results, no matter how slight, should be interpreted as ranking one solution over the other. 

The approach taken in the BART analysis for BSP incorporates the visibility analysis results as part of the 

decision making process. If two alternatives have an identical potential for visibility improvement, the 

remaining criteria identified for consideration as part of the impact analysis are then used to differentiate 

between the two alternatives. Where similar visibility improvement potentials are identified for two or 

more alternatives, the incremental cost to achieve the slightly greater visibility improvement is 

determined and evaluated against incremental costs for the next most stringent alternative. This approach 

identifies the more effective BART alternative in terms of regional haze considerations, not in terms of 

the most stringent control alternative, as would happen if a strictly top-down approach had been 

implemented. 

1.3.7 ADDITIONAL APPROACH METHODS 

In addition to the steps discussed above, the presumptive limits and their application to power plants 

smaller than 750 MW in size warrant mention due to their effects on the contents of the report. For power

plants greater than 750 MW in size, the EPA requires state agencies to apply the presumptive limits for 

BART as a floor for NOX or SO2 control. However, for power plants smaller than 750 MW in size, the 

presumptive limits are described as being “generally cost-effective” but not set as a minimum 

performance requirement (see, e.g., 40 CFR 51, App. Y, IV.E.4). Thus, EGUs at power plants smaller 

than 750 MW in size, like BSP, are not required to meet the presumptive BART limits. This BART 

analysis for BSP will evaluate potential control options that can attain presumptive limits on typical 

EGUs. However, based upon the feasibility analysis, the recommended control options may not achieve 

the EPA’s presumptive BART limits for specific pollutants. 

1.4 THE ROLE OF MODELING AND CALPUFF IN A BART ANALYSIS 

The BART guidelines list visibility impact at a Class I area as one of the factors in a BART 

determination. For Class I areas more than 50 km from a source, the EPA has identified CALPUFF as a 

guideline model for long-range transport that is suitable for predicting potential changes in visibility. 
 11 11/2/2009 

CALPUFF is a non-steady-state meteorological and air quality dispersion modeling system used to assess 

long-range transport of pollutants. Seven Class I areas have been identified for inclusion in the visibility 

analysis for BSP. These are the Theodore Roosevelt National Park (NP), the Lostwood National Wildlife 

Refuge (WR), Voyagers NP, Isle Royal NP, Boundary Waters Canoe Area Wilderness, Badlands NP, and 

Wind Cave NP, the closest of which is more than 400 km (248 miles) from BSP. 

1.4.1 CALPUFF MODELING METHODOLOGY 

The specific version of CALPUFF, coordinate grid points, wind field options, terrain, dispersion options, 

receptor coordinates and plume characteristics and other model parameters approved by the DENR were 

used for modeling. Meteorological data for the years 2002, 2006 and 2007 were used for the modeling. 

In order to predict the change in light extinction at the Class I areas, SO2, NOX, and PM were modeled 

with CALPUFF using pre-control (baseline) and post-control emission scenarios. A variety of postcontrol scenarios were modeled to determine the reduction in visibility impact for each control 

technology. 

The BART guideline states that a visibility improvement is based upon the modeled change in visibility 

impacts, measured in deciViews, for the pre-control and post-control emission scenarios. The comparison 

should be made for the 98th percentile days (40 CFR 51, App. Y, IV.D.5). In other words, visibility 

impacts should be compared on an annual basis using the eighth highest day for comparison (365 * (1-

.98) ≈ 7 days of acceptable exceedance). Therefore, the visibility impairment impact reduction presented 

for each control scenario in this section is based on the 98th percentile value or eighth highest day. 

1.4.2 MODELING SCENARIOS 

Since a BART analysis is based on the degree of visibility impairment reduction achieved by the 

application of control technologies, the CALPUFF analysis examined multiple emission scenarios based 

upon the feasible control technologies identified for each pollutant. These scenarios represent the 

emissions of SO2, NOX, and PM under the following conditions: 

• Baseline NOX, SO2 and PM emissions

• PM emissions based upon existing controlled baseline conditions, and NOX and SO2 emissions 

based upon application of several control technologies 

The modeled emission rates in each scenario are presented in Table 1.4-1. 
 12 11/2/2009 

TABLE 1.4-1 – Big Stone Plant Modeling Scenarios 

Unit I 

Scenario

NOX

(lb/h)

SO2

(lb/h)

PM 

(lb/h)1 

0 Baseline 4,854.8 4,832.2 84.1 

1 Over-fire Air (OFA) 

Presumptive Dry FGD 3,645.9 841.4 84.1 

2 OFA 

Presumptive Wet FGD 3,645.9 841.4 84.1 

3 OFA 

Dry FGD at 90% Control 3,645.9 504.8 84.1 

4 OFA 

Wet FGD at 95% Control 3,645.9 241.2 84.1 

5 Separated OFA (SOFA) 

Presumptive Dry FGD 2,804.5 841.4 84.1 

5A SOFA 

Dry FGD at 90% Control 2,804.5 504.8 84.1 

5B SOFA 

Wet FGD at 95% Control 2,804.5 241.2 84.1 

6 SNCR with SOFA 

Presumptive Dry FGD 1,963.2 841.4 84.1 

7 RRI+SNCR with SOFA 

Presumptive Dry FGD 1,121.8 841.4 84.1 

8 SCR with SOFA 

Presumptive Dry FGD 560.9 841.4 84.1 

 1 – The PM technology for all modeling scenarios is the existing pulse-jet fabric filter. 

These scenarios represent the range of emissions evaluated for consideration in making a BART 

determination. The baseline scenario is based on the historical, highest 24-hour actual average SO2 and 

NOX emission rates for BSP between 2001 and 2003. The emission rate for PM is the achievable 

controlled emission rate for the existing fabric filter. Due to the number of variations involved for each 

pollutant, the scenarios are discussed in the section related to the controlled pollutant. 
 13 11/2/2009 

2.0 NOX BART EVALUATION 

The BART analysis steps 1 through 5 for NOX emissions from BSP are described in this section. 

Potentially applicable NOx control technologies are first identified. A brief description of the processes 

and their capabilities are then reviewed for availability and feasibility. A detailed technical description of 

each control technology is provided in Appendix A1. Subsequently, those available technologies deemed 

feasible for retrofit application are ranked according to nominal NOx control capability. The impacts 

analysis then reviews the estimated capital and O&M costs for each alternative, including Balance Of 

Plant (BOP) requirements. Following the cost determination, the energy impacts and non-air quality 

impacts are reviewed for each technology. The impact based on the remaining useful life of the source is 

reviewed as part of the cost analysis. In the final step of the analysis, feasible and available technologies 

are assessed for their potential visibility impairment impact reduction capability via visibility modeling 

results. The results of the impact analyses are tabulated and potential BART control options are listed. 

2.0.1 BART GUIDELINE NOX LIMITS FOR CYCLONE-FIRED BOILERS 

EPA’s presumptive limit for emissions of nitrogen oxides from cyclone-fired boilers, which does not 

apply to BSP, was established in the final BART Guidelines1

: 

“The use of SCRs at cyclone units burning bituminous coal, sub-bituminous coal, and lignite 

should enable the units to cost-effectively meet NOX rates of 0.10 lbs/mmBtu. As a result, [the 

EPA] are establishing a presumptive NOx limit of 0.10 lbs/mmBtu based on the use of SCR for 

coal-fired cyclone units greater than 200 MW located at 750 MW power plants. ” [70 FR 39172] 

40 CFR 51, App. Y, IV.E.5. While Unit I at BSP is greater than 200 MW output, it is not located at a 750 

MW power plant. Thus, Unit I is not subject to presumptive limits. 

2.1 IDENTIFICATION OF RETROFIT NOX CONTROL TECHNOLOGIES 

The first step in the BART evaluation for NOx emissions is to identify potentially applicable retrofit 

control alternatives. A comprehensive literature search was performed, with sources including technical 

papers and presentations made by parties involved with design, construction, and testing of NOX control 

techniques at conferences sponsored by nationally-recognized technical organizations, plus hardware 

supplier experience lists. 
 14 11/2/2009 

There are two basic categories of NOX emission control alternatives: 

• Combustion controls; and 

• Post-Combustion controls. 

A summary of the potentially available alternatives identified for NOX emissions control on coal-fired 

cyclone units is shown in Table 2.1-1. 

TABLE 2.1-1 – Potentially Available NOX Control Alternatives 

Identified for BART Analysis 

Combustion Controls 

Low-NOX Burners (LNBs) 

Over-fire Air (OFA) 

Separated Over-fire Air (SOFA) 

Post-Combustion Controls

Selective Non-Catalytic Reduction (SNCR) 

Rich Reagent Injection (RRI) 

Selective Catalytic Reduction (SCR)

2.2 TECHNICAL DESCRIPTIONS AND FEASIBILITY ANALYSIS OF NOX

CONTROL TECHNOLOGIES 

The second step of the BART process is to evaluate the control processes that have been identified and 

eliminate any that are technically infeasible for application at the source. The following paragraphs 

summarize the evaluation of the processes for technical feasibility for BSP Unit I NOX controls. A detailed 

description of the various NOX control technology retrofits and their technical feasibility is included in 

Appendix A1, with the associated references for technical literature. 

2.2.1 FEASIBILITY OF COMBUSTION NOX CONTROLS 

The following combustion controls are potentially feasible technologies that are applied to a cyclone-fired 

boiler. 

• An over-fire air (OFA) system has already been implemented on the Unit I boiler with the ability to 

significantly lower NOX emissions. Implementation of more stringent operational procedures to 
 15 11/2/2009 

maintain significantly lower NOX emissions with the existing OFA system was considered a 

feasible application at BSP for Unit I. 

• Separated over-fire air (SOFA) systems have been retrofit to many cyclone boilers for combustion 

NOX control. 2,3,4,5,6 SOFA offers the highest performing version of this technology for cyclone 

boilers, and may include relocating vent ports and/or flue gas recirculation ports. SOFA is a 

feasible technology for BSP Unit I and is included in the control effectiveness analysis for 

additional NOX. The NOX control improvements through use of SOFA on Unit I will be limited by 

potential adverse impacts on cyclone operation associated with air-staged (sub-stoichiometric 

air/fuel) cyclone operation, which are described in Appendix A1. 

Low-NOX burners (LNBs), while commonly applied to pulverized coal-fired boilers, are not applicable to 

cyclone fired units since initial combustion occurs in the barrel-shaped cyclone and not in the furnace 

chamber as is the case for the pulverized coal-fired boiler. Therefore, they will not be considered further. 

2.2.2 FEASIBILITY OF POST-COMBUSTION NOX CONTROLS 

Post-combustion controls involve technologies that are applied to the flue gas after the combustion 

process. Typically these processes involve the use of a reagent to chemically react with NOX. These are 

summarized as follows; for more details, refer to the technical feasibility evaluation included in Appendix 

A1: 

• SNCR has been applied on several cyclone-fired boilers since 1995 and its installation on the Unit I 

cyclone boiler is considered feasible. 7,8,9 Because BSP Unit I already has OFA for NOX control, 

SNCR will be evaluated in conjunction with the existing OFA or SOFA. 

• Rich Reagent Injection (RRI) injects aqueous urea into the high-temperature lower furnace zone 

and requires an “air-starved” atmosphere to avoid creating instead of reducing NOX. RRI has been 

developed and demonstrated with application intended only on cyclone boilers.9,10,11,12 RRI has 

been installed and is commercially available. 

o RRI is susceptible to impairment due to fouling by ash slag deposits and heat-related damage of 

injection nozzles, which are located near the cyclones in the lower furnace. 

o RRI is considered feasible for application on cyclone boilers operating under substoichiometric 

conditions with advanced forms of SOFA and in combination with SNCR for NOX control at BSP 

Unit I. 

• Selective Catalytic Reduction (SCR) technology has been installed on 22 cyclone-fired boilers in 

the U.S., burning bituminous or sub-bituminous coals, and its installation on BSP Unit I for 
 16 11/2/2009 

additional NOX control is considered technically feasible. 34 As with SNCR, SCR will be evaluated 

in conjunction with the existing OFA or SOFA. 

2.2.3 RESULTS OF FEASIBILITY ANALYSIS 

The results of the evaluation of the identified BART alternatives following the feasibility analysis are 

summarized in Table 2.2-1. 

TABLE 2.2-1 – NOX BART Feasibility Analysis Results 

Control Technology 

In service on 

Existing Utility 

Boilers 

Commercially 

Available 

Technically 

Applicable To Big 

Stone Plant 

Over-fire Air (OFA) Yes Yes Yes 

Separated OFA (SOFA) Yes Yes Yes 

Selective Non-catalytic Reduction (SNCR) 

with OFA or SOFA

Yes Yes Yes 

Rich Reagent Injection (RRI) + SNCR with 

SOFA 

Yes Yes Yes 

Selective Catalytic Reduction (SCR) with 

OFA or SOFA 

Yes Yes Yes 

2.3 CONTROL EFFECTIVENESS EVALUATION OF NOX CONTROL 

TECHNOLOGIES 

Control options that offer zero or very small additional control performance at a significant cost impact 

were not included in impact analysis. Alternatives that are equally effective in predicted emission 

reduction percentage but are more expensive to install and operate, or have more substantial operational 

limitations compared to other feasible alternatives, were also eliminated from further analysis. Table 

2.3-1 lists the feasible control technologies and indicates the technologies evaluated in the analysis. 
 17 11/2/2009 

TABLE 2.3-1 – Evaluated NOX Control Technologies 

Control Technology

Approximate 

Control 

Efficiency Evaluated

Over-fire Air (OFA) 25 Yes

Separated OFA (SOFA) 42 Yes 

Selective Non-catalytic Reduction 

(SNCR) with OFA 60 No1

SNCR with SOFA 60 Yes 

Rich Reagent Injection (RRI)+SNCR 

with SOFA 77 Yes 

Selective Catalytic Reduction (SCR) 

with OFA 

88 

No2 

SCR with SOFA 88 Yes

1 – Due to an estimated $1,810,000 increase in levelized annual costs for the same level of control as 

SNCR with SOFA, this technology would be above the dominant controls curve and are not evaluated 

further as described in Section 1.3.5. 

2 – Due to an estimated $140,000 increase in levelized annual costs for the same level of control as SCR 

with SOFA, this technology would be above the dominant controls curve and are not evaluated further as 

described in Section 1.3.5 

Available NOX emission control options considered feasible for BSP Unit I boiler are listed in Table 2.3-2 

in descending order of control effectiveness. Ranking of the alternatives in Table 2.3-2 assumes that the 

baseline level of NOX emissions for the BSP Unit I boiler is associated with the emission rate of 0.86 

lb/mmBtu. 

The emission reduction (control effectiveness) percentages developed for the feasible alternatives shown 

in Table 2.3-2 are estimates based upon engineering judgments with considerations of: 

• the general combustion properties of Powder River Basin (PRB) coal; 

• published and available emission reduction performance achieved at other similar utility power 

plants (wet-bottom cyclone-fired boilers); and 

• inclusion of performance margins to allow for variations in fuel, weather, equipment condition, 

and other factors that prevent the ultimate peak short-term performance from being reliably 

sustained over the course of long-term operation. 

The potential operational limitations mentioned in the detailed feasibility discussions included in 

Appendix A1 for deeply air-staged cyclones associated with separated over-fire air and Rich Reagent 

Injection alternatives are expected to limit the amount of NOX control potential possible compared to 

other boiler types where this technique or technology was applied. 
 18 11/2/2009 

TABLE 2.3-2 – Estimated Control Options NOX Emission Rates Evaluated

NOX Control Technique 

Emission 

Rate

(lb/mmBtu) 

Control 

Percentage

Hourly 

Emission 

(lb/hr) 

SCR w/ SOFA 0.10 88 560.9 

Rich Reagent Injection 

(RRI)+SNCR w/ SOFA 0.20 77 1,121.8 

SNCR w/ SOFA 0.35 60 1,963.2 

Separated Over-fire Air (SOFA) 0.50 42 2,804.5 

Over-fire Air (OFA) 0.65 25 3,645.9 

Baseline 0.86 -- 4,854.8 

2.4 EVALUATION OF IMPACTS FOR FEASIBLE NOX CONTROLS 

The fourth step of a BART analysis is to evaluate the following impacts of feasible emission controls: 

• The cost of compliance. 

• The energy impacts. 

• The non-air quality environmental impacts. 

• The remaining useful life of the source. 

The purpose of the impacts evaluation is to determine if there are any energy, economic, non-air quality 

environmental reasons, or aspects of the remaining useful life of the source, which would eliminate the 

remaining control technologies from consideration for BSP Unit I. 

2.4.1 COST IMPACTS OF NOX CONTROLS 

An evaluation was performed to determine the compliance costs of installing various feasible NOX control 

alternatives on BSP Unit I boiler. This evaluation included estimates for: 

• Capital costs; 

• Fixed and variable operating and maintenance (O&M) costs; and 

• Levelized total annual costs to engineer, procure, construct, install, startup, test, and place into 

commercial operation a particular control technology. 
 19 11/2/2009 

 

The results of this evaluation are summarized in Tables 2.4-1 through 2.4-6. 

2.4.1.1 CAPITAL COST ESTIMATES FOR NOX CONTROLS 

The capital costs to implement the various NOX control technologies were largely estimated from unit 

output capital cost factors ($/kW) published in technical papers discussing those control technologies. 

Anticipated costs unique to BSP that are necessary for installation of the control technology were also 

identified. In the cases involving SNCR or RRI, vendor budgetary cost information was obtained and 

used in place of, or to adjust, the published unit output cost factors. These cost estimates were considered 

to be study grade, which is + or – 30% accuracy. 

A review of the unit capital cost factor and associated capital costs for the feasible NOX emission 

reduction technology evaluated for BSP are presented in Table 2.4-1. 

TABLE 2.4-1 – Unit Capital Cost Factors of 

 Feasible NOX Control Options 

NOX Control Technique 

Unit Capital 

Cost1

($/kW) 

Capital Cost 

($1000)

SCR with SOFA 1722 81,800 

RRI + SNCR with SOFA 343

 16,200 

SNCR with SOFA 25 11,900 

Separated Over-fire Air (SOFA) 10 4,800 

Over-fire Air (OFA) Existing Existing

1 – Unit capital cost factors ($/kW) of these individual technologies were combined by simple addition. Actual 

installed costs may differ due to positive or negative synergistic effects. 

2 – Estimate taken from CUECost adjusted to reflect Burns & McDonnell project experience included in 

Appendix A2. 

3 – RRI estimate is taken from the DOE report, “Field Testing of Advanced Layered Technology Approach 

(ALTATM) for NOx Control in Sioux Unit 1”. 

2.4.1.2 OPERATING AND MAINTENANCE COST ESTIMATES FOR NOX

CONTROLS 

The operation and maintenance costs to implement the NOX control technology evaluated for BSP Unit I 

were largely estimated from cost factors established in the EPA’s Air Pollution Control Cost Manual 
 20 11/2/2009 

(OAQPS), and from engineering judgment applied to that control technology. These cost estimates were 

considered to be study grade, which is + or – 30% accuracy. 

Fixed and variable operating and maintenance costs considered and included in each NOX control 

technology’s O&M costs are estimates of: 

• Auxiliary electrical power consumption for operating the additional control equipment; 

• Reagent consumption, and reagent unit cost for SCR, SNCR and RRI alternatives; 

• Catalyst replacement for SCR; and 

• General operating labor, plus maintenance labor and materials devoted to the additional emission 

control equipment and its impact on existing boiler equipment. 

A review of the estimated operation and maintenance costs for the feasible NOX emission reduction 

technology evaluated for BSP are presented in Table 2.4-2. 

TABLE 2.4-2 – Estimated O&M Costs for NOX Control Options 

NOX Control Alternative 

First Year 

O&M 

Cost

($1,000) 

SCR with SOFA 4,110 

RRI+SNCR and SOFA 7,260 

SNCR with SOFA 2,120 

Separated Over-fire Air (SOFA) 152 

Over-fire Air (OFA) 106 

In order to compare a particular NOX emission reduction alternative during the cost of compliance impact 

analysis portion of the BART selection process, the basic methodology defined in the BART Guidelines

was followed. The Levelized Total Annual Cost (LTAC) of these NOX control alternatives was 

calculated based on the same economic conditions and a 30 year project life (see Section 1.3.5 of this 

BART evaluation for methodology details). Estimated capital costs were split evenly over a two year 

construction period for all alternatives and a present value was calculated. Table 2.4-3 shows the 

estimated present value capital cost and annualized cost values for the various feasible NOX emission 

reduction technologies. These are listed in order of control effectiveness, with the highest ranked options 

at the top. 
 21 11/2/2009 

TABLE 2.4-3 – Capital and Annualized Costs Estimated for 

NOX Control Alternatives 

NOX Control Alternative 

Capital Cost1

($1000)

Present Value

Capital 

Cost

($1,000) 

First Year 

O&M 

Cost

($1,000) 

Levelized 

Cost2 

($1,000) 

SCR with SOFA 81,800 76,800 4,110 13,210 

RRI+SNCR and SOFA 16,200 15,200 7,260 11,390 

SNCR with SOFA 11,900 11,200 2,120 3,990 

Separated Over-fire Air 

(SOFA) 4,800 4,500 152 650 

Over-fire Air (OFA) 0 0 106 140 

1 – Installed capital cost is estimated for determination of total capital cost for a control technology, assuming 

maximum unit output capacity is based on 475,000 kW. 

2 – Levelized Total Annual Cost = Annualized Installed Capital Cost + Levelized Annual O&M cost. 

The Annualized O&M cost factor = 1.361 and the Capital Recovery Factor = 0.0991 

The average cost effectiveness was then determined as the LTAC divided by baseline annual tons of 

pollutant emissions that would be avoided by implementation of the respective alternative. Table 2.4-4 

shows the average cost effectiveness comparison for the NOX control technologies. The feasible control 

alternatives were also compared by calculating the change in LTAC per incremental ton of pollutant 

removed for the next most stringent alternative (incremental cost effectiveness). This identified which 

alternatives produced the highest increment of expected pollutant reduction for the estimated lowest 

average LTAC increment compared with the pre-control baseline emission rate. The expected annual 

number of tons of pollutant removed versus estimated LTAC for each remaining control alternative was 

then plotted. 
 22 11/2/2009 

TABLE 2.4-4 – Estimated Annual Emissions and LTAC for NOX Control Alternatives 

NOX Control Alternative 

Annual 

NOX

Emissions1 

(Tons/yr) 

Annual NOX

Emissions 

Reduction1 

(Tons/yr) 

Levelized 

Total 

Annual 

 Cost

($1,000) 

Average 

Cost 

Effectiveness

($/ton) 

SCR with SOFA 2,090 16,000 13,210 825 

RRI+SNCR and SOFA 4,180 13,910 11,390 818 

SNCR with SOFA 7,310 10,780 3,990 197 

Separated Over-fire Air (SOFA) 10,440 7,640 650 85

Over-fire Air (OFA) 13,570 4,510 140 31 

Baseline 18,080 - - - 

1 – Annual NOX emissions and control level based upon 8,760 hours of operation and 85% capacity 

factor. 

The comparison of the cost-effectiveness of the control options evaluated for BSP is shown in Figure 

2.4-1. The estimated annual amount of NOX removal (emission reduction) in tons per year is plotted on 

the abscissa (horizontal axis) and the estimated LTAC in thousands of U.S. dollars per year on the 

ordinate (vertical axis). 
 23 11/2/2009 

Figure 2.4-1 – NOX Control Cost Effectiveness 

SNCR/ SOFA

SCR / SOFA

SOFA

OFA

RRI/SNCR/SOFA

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

- 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

Emissions Reduction (tpy)

Total Levelized Costs ($1000)

The purpose of Figure 2.4-1 is to show the range of control and cost for the evaluated NOX reduction 

alternatives and identify the least-cost controls so that the Dominant Controls Curve (DCC) can be created. 

The DCC is the best fit line through the points forming the lower rightmost boundary of the data zone on a 

scatter plot of the LTAC versus the annual NOX removal tonnage for the various remaining BART 

alternatives. Points distinctly to the left of and above this curve are inferior control alternatives per the 

BART Guidelines on a cost effectiveness basis. Following a “bottom-up” graphical comparison approach, 

each of the NOX control technologies represented by a data point to the left of and above the least cost 

envelope should be excluded from further analysis on a cost efficiency basis. Of the highest-performing 

versions of the technically feasible NOX control alternatives evaluated for cost-effectiveness, the data point 

for RRI/SNCR/SOFA is seen to be more costly for fewer tons of NOX removed than for SCR with SOFA. 

This appears to be an inferior control, and thus should not be included on the least cost and DCC boundary. 

Figure 2.4.2 provides the DCC. 
 24 11/2/2009 

Figure 2.4-2 – NOX Control Cost Effectiveness and 

Dominant Control Cost Curve 

OFA

SOFA

SCR / SOFA

SNCR / SOFA

$0

$2,000

$4,000

$6,000

$8,000

$10,000

$12,000

$14,000

- 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

Emissions Reduction (tpy)

Total Levelized Costs ($1000)

The next step in the cost effectiveness analysis for the BART NOX control alternatives is to review the 

incremental cost effectiveness between remaining least-cost alternatives. Table 2.4-5 contains a repetition 

of the LTAC and NOX control information with RRI+SNCR/SOFA removed, and shows the incremental 

cost effectiveness between each successive set of least-cost NOX control alternatives. The incremental 

NOX control tons per year, divided by the incremental levelized annual cost, yields an incremental control 

cost effectiveness ($/ton). 
 25 11/2/2009 

TABLE 2.4-5 – Estimated Incremental Annual Emissions and LTAC 

for NOX Control Alternatives 

NOX

Control Technique 

Levelized 

Total 

Annual 

Cost

($1,000) 

Annual 

Emission 

Reduction1 

(Tons/yr) 

Incremental 

Levelized 

Total 

Annual 

Cost2

($1,000) 

Incremental 

Annual 

Emission 

Reduction1,2 

(Tons/yr) 

Incremental 

Control Cost 

Effectiveness 

($/ton)3

SCR with SOFA 13,210 16,000 9,220 5,220 1,766 

SNCR with SOFA 3,990 10,780 3,340 3,140 1,063 

SOFA 650 7,640 510 3,130 163 

OFA 140 4,510 140 4,510 31 

1 – Annual NOX emissions and control level based upon 8,760 hours of operation and 85% capacity factor. 

2 – Increment based upon comparison between consecutive alternatives (points) from lowest to highest. 

3 – Incremental control cost effectiveness is incremental LTAC divided by incremental annual emission reduction (tons per 

year). 

In the final BART Guidelines, the EPA does not propose hard definitions for reasonable or unreasonable 

average or incremental cost effectiveness values. As can be seen from a review of Table 2.4-4, the 

average levelized control cost effectiveness of control alternatives ranges from $31/ton to $825/ton. 

The incremental cost effectiveness is a measure of the increase in marginal cost effectiveness between 

two specific alternatives. The incremental cost analysis indicates that from a cost effectiveness 

viewpoint, the most costly alternative is SCR with SOFA. This control option is considered technically 

feasible for BSP, but incurs a significant annual (levelized) incremental cost compared to the other 

feasible NOX control techniques.

2.4.2 ENERGY IMPACTS OF NOX CONTROL ALTERNATIVES 

The feasible NOX control alternatives were reviewed for significant or unusual energy penalties or 

benefits associated with their use. There are several basic kinds of energy impacts for NOX emissions 

controls: 

• Potential increase or decrease in power plant energy consumption resulting from a change in 

thermal (heat) energy to net electrical output conversion efficiency of the unit, usually expressed 

as an hourly unit heat rate (Btu/kW-hr). This may or may not change the net electrical output 
 26 11/2/2009 

(MW) capacity of the EGU depending on if there are physical or imposed limits on the total heat 

input to the boiler or electrical power output. 

• Potential increase or decrease in net electrical output of the unit resulting from changes in 

physical operational limitations imposed on the ability to sustain a fuel heat input rate 

(mmBtu/hr), which results in a potentially lower or higher unit net electrical output (MW) 

capacity. This is effectively a change in net electrical output (MW) capacity of the EGU. 

• Potential increase or decrease in net electrical output of the unit resulting from changes in 

auxiliary electrical power demand and usage (kW, kW-hrs). This is effectively a change in net 

electrical output (MW) capacity of the EGU. 

• Potential increase or decrease in reliability and availability to generate electrical power. This 

results in a change to the number of hours of annual operation, not necessarily a change in net 

electrical output (MW) capacity of the EGU. 

There should not be a major impact on energy consumption by the operation of the variations of an overfire air (OFA) system, such as separated over-fire air (SOFA). An OFA system does not significantly 

change the total amount of air introduced into the boiler, only the location where it is introduced. 

Combustion air damper actuators’ electrical power demand would be an insignificant (+ 1 kW) change in 

net electrical power consumption. For cyclone boilers, providing effective volumes and velocities of 

separated over-fire air at the injection ports should not require higher forced draft fan power consumption 

resulting from higher fan discharge pressure. Higher vent ductwork pressure drop impacts of the OFA 

system on the forced draft fans’ auxiliary electrical power consumption are expected to be negligible (less 

than 1% of the annual auxiliary power consumed by these fans) so that unit net electrical output (MW) 

capacity is essentially the same as the current nameplate rating. 

Boiler furnace exit gas temperature and superheater steam / reheater steam outlet temperatures may be 

slightly elevated during air-staged cyclone operation with OFA. This impact on the boiler’s operation is 

typically small, and within the design capabilities of the boiler from a heat transfer and mechanical stress 

standpoint. This small negative impact (much less than 1%) on the plant unit heat rate (higher Btu/kWhr) was not quantified, as the historical variation in coal heat content that influences plant unit heat rate is 

expected to have more significant impacts. 

OFA is not expected to significantly reduce unit reliability and availability to generate electrical power, 

once the amount of secondary combustion air that can be withdrawn from the cyclones is established for 

consistent combustion and continuous slag tapping under substoichiometric air/fuel operating conditions. 
 27 11/2/2009 

There may be some changes in the degradation rate of the boiler’s furnace waterwall tubes resulting from 

exposure of more area of the furnace walls to slightly air-starved conditions during OFA operation. Such 

conditions can promote corrosion from sulfur compounds in the furnace gases being created above the 

cyclones and below the OFA injection ports. Due to the relatively small amounts of sulfur content in the 

PRB coal and the modest amount of air-staging of the existing cyclones during OFA operation, the 

expected change in corrosion rate of the boiler tubes should be minor. This degradation is expected to 

occur over many years of operation, and normally requires periodic replacement of the deteriorated 

sections of boiler furnace waterwall tubes to avoid forced outages to repair tube leaks or failed sections. 

The potential change in the frequency of furnace wall tube failures and changeouts is difficult to estimate, 

and has not been quantified. 

For SNCR-related NOX control alternatives, the injection of a diluted urea solution requires some 

additional auxiliary power for heating and pumping the liquid, and using compressed air for atomization 

and cooling the reagent injection nozzles/lances, on the order of 150 to 400 kW. The injection of water 

(used for urea dilution) into the boiler flue gas also has a small negative impact on the plant heat rate 

(higher Btu/kw-hr), which is approximately equal to the heat released from the reaction of the reagent 

with NOX or oxygen. The impact of additional flue gas created by operation of an SNCR-related system 

on induced draft fan power consumption should be insignificant. 

For the SCR NOX control alternative, the system requires the same 150 to 400 kW of auxiliary power for 

heating and pumping the reagent (ammonia) as SNCR, and using compressed air for atomization and 

cooling the reagent injection nozzles/lances, on the order of 150 to 400 kW. If a urea based reagent feed 

system is used, an additional 400 kW of auxiliary power is required to convert the urea to ammonia. 

However, the major consumer of auxiliary power for a SCR is additional induced draft fan power needed 

to overcome the additional 6 to 9 inches of water column pressure drop created by the addition of catalyst 

and ductwork. In most cases, the addition of an SCR would require replacement of the induced draft fans 

and depending upon the fan and motor efficiency additional 400 to 1000 kW of auxiliary power. 

2.4.3 NON AIR QUALITY AND OTHER ENVIRONMENTAL IMPACTS OF NOX

CONTROL ALTERNATIVES 

Operation using OFA or SOFA systems for NOX emissions control will increase the amount of unburned 

carbon in the flyash produced by the boiler and collected for disposal by small increments. The potential 
 28 11/2/2009 

changes in the annual amounts of flyash disposal rates are expected to be inconsequential, and have not 

been quantified. 

Operation of an SCR or SNCR system will normally create a small amount of unreacted ammonia or urea 

to be emitted into the flue gas. The amount of ammonia slip produced depends on the amount of reagent 

utilization and location of the injection points. Higher NOX reduction performance involves greater 

amounts of reagent usage and ammonia slip. This is typically controlled to less than 10 ppmvd, 

especially since the possible formation of sulfates such as ammonium sulfate [(NH4)2SO4] and ammonium 

bisulfate [NH4HSO4] will be more problematic at higher slip levels. Sulfur trioxide (SO3) can also be 

formed during combustion in the boiler or conversion in the SCR to combine with ammonia during 

passage through the flue gas ductwork to form the sulfates. 

Some of the unreacted ammonia and other compounds discussed above will be collected with the flyash 

in the pulse-jet fabric filter. If a scrubber is installed, some of the ammonia and other compounds will be 

captured. These collected materials may impact the disposal of fly ash or scrubber blow down. 

Storage of ammonia reagent on-site creates the potential for accidents, leaks, and subsequent releases to 

air, ground, and surface water immediately surrounding the facility. Regulation of storage and 

containment of such reagents s will be under the requirements of various federal Acts. 

2.4.4 VISIBILITY IMPAIRMENT IMPACTS OF NOX CONTROLS 

The final impact analysis conducted was to assess the visibility impairment impact reduction for the NOX

control technologies. The analysis used a baseline NOX emission rate which assumed the highest 24-hour 

actual emission rate for 2001-2003 as recommended by the BART guideline and listed in the Modeling 

Protocol. Four CALPUFF model runs for BSP were conducted with the constant SO2 emission rate of 

0.15 lb/mmBtu, constant PM emission rate of 0.015 lb/mmBtu, and various levels of NOX control. Table 

2.4-6 shows the modeled emission rates.

The difference between the modeled impacts at the 98th percentile level from various controlled emission 

rates represents the visibility impairment impact reduction in deciViews (dV). Table 2.4-6 shows the 

results of the visibility impact modeling attributable to NOx reductions while maintaining PM and SO2

emissions constant. A table containing the 98th percentile results for all modeled years and Class I areas 

is included in Appendix A3. Combined impacts from all pollutants are addressed later in the report. 
 29 11/2/2009 

TABLE 2.4-6 – Visibility Impairment Impacts from Emission Controls 

NOX Control 

Technique 

Emission 

Rate

(lb/mmBtu) 

Visibility 

Impairment 

Impact 

(dV)

Visibility 

Impairment 

Reduction 

(Δ dV)1

Technology 

Incremental 

Reduction 

(Δ dV) 

SCR with SOFA 0.10 0.170 0.487 0.218 

SNCR with SOFA 0.35 0.388 0.269 0.136 

Separated Over-fire Air 

(SOFA) 0.50 0.524 0.133 0.133 

Over-fire Air (OFA) 0.65 0.657 - - 

Baseline 0.86 1.079 - - 

1 – Impairment reduction is from OFA levels. 

The results of the baseline visibility impairment modeling for BSP showed that NOX emissions caused a 

Class I area to exceed 0.5 dV for predicted visibility impairment impact (98th percentile). Modeled 

visibility impairment impacts decreased with the addition of NOX controls. 

The 0.5 dV value is the lowest visibility impairment impact that is considered discernible by the human 

eye and the EPA set this threshold as the point where a given source is considered a “contributing source” 

(40 CFR 51, App. Y, III.A.1.). Thus, an impairment impact of less than 0.5 dV is considered visibly 

indiscernible. The difference in impacts between OFA (lowest control level) and SCR (highest control 

level) is less than 0.5 dV, which is visibly indiscernible. To assess the cost effectiveness of the various 

controls with respect to visibility improvement, the incremental cost to achieve the visibility improvement 

is determined and evaluated against incremental costs for the next most stringent alternative. Table 2.4-7 

shows the costs to achieve the incremental reduction in visibility impairment. 
 30 11/2/2009 

TABLE 2.4-7 – Cost for Incremental Visibility Improvement 

NOX Control Technique 

Incremental 

Levelized Total 

Annual Cost1

($)

Impairment 

Reduction 

(Δ dV) 

Incremental 

Reduction 

(Δ dV) 

Cost for 

Incremental 

Improvement 

($/dV) 

SCR with SOFA 9,220,000 0.487 0.218 42,290,000 

SNCR with SOFA 3,340,000 0.269 0.136 24,560,000 

Separated Over-fire Air (SOFA) 510,000 0.133 0.133 3,830,000 

Over-fire Air (OFA) 140,000 - - - 

1 – Increment based upon comparison between consecutive alternatives (points) from lowest to highest.

2.4.5 SUMMARY OF IMPACTS OF NOX CONTROLS – BSP UNIT I 

Table 2.4-8 summarizes the various quantifiable impacts discussed in Sections 2.4.1 through 2.4.4 for the 

NOX alternatives evaluated for BSP Unit I. 

 

TABLE 2.4-8 – Impacts Summary for BSP Unit I NOX Controls 

NOX Control 

Technique 

Emission 

Rate

(lb/mmBtu) 

Levelized 

Total 

Annual 

Cost

($1,000) 

Incremental 

Levelized 

Total 

Annual Cost1

($1,000) 

Visibility 

Impairment 

Impact 

(dV)

Visibility 

Impairment 

Reduction 

(dV) 

Technology 

Incremental 

Reduction 

(Δ dV) 

SCR with SOFA 0.10 13,210 9,220 0.170 0.487 0.218 

SNCR with SOFA 0.35 3,990 3,140 0.388 0.269 0.136 

Separated Over-fire 

Air (SOFA) 0.50 650 510 0.524 0.133 0.133 

Over-fire Air (OFA) 0.65 140 140 0.657 - - 

Baseline 0.86 - - 1.079 - - 

1 – Increment based upon comparison between consecutive alternatives (points) from lowest to highest.
 31 11/2/2009 

NOX SECTION REFERENCES: 

1. “Regional Haze Regulations and Guidelines for Best Available Retrofit Technology (BART) 

Determinations”; Environmental Protection Agency; Federal Register, Volume 70, No. 128; July 6, 2005. 

2. “The State of the Art in Cyclone Boiler NOX Reduction”, by O’Connor, Dave, Himes, Rick, and Facchiano, 

Tony (Electric Power Research Institute), presented at the EPRI-DOE-EPA Combined Utility Air Pollutant 

Control Symposium, Atlanta, GA, August 16-20, 1999. 

3. “B&W’s Advances on Cyclones NOX Control Via Fuel and Air Staging Technologies”, by Farzan, H., 

Maringo, G., Johnson, D. W., and Wong, D.K. (Babcock & Wilcox, Co.), Beard, C.T. (Eastman Kodak 

Company), and Brewster, S.E. (Tennessee Valley Authority), presented at the EPRI-DOE-EPA Combined 

Utility Air Pollutant Control Symposium, Atlanta, GA, August 16-20, 1999. Available at B&W’s internet 

website: http://www.babcock.com/pgg/tt/pdf/BR-1683.pdf

4. B&W experience list September 18, 2002. 

5. “Reburning Projects in the Department of Energy’s Clean Coal Technology Demonstration Program”, by 

Mann, Al and Ruppel, Tom (Parsons Corporation), and Sarkus, Tom (National Energy Technical 

Laboratory), presented at the 2004 DOE-NETL Conference on Reburning for NOX Control, Morgantown, 

WV, May 18, 2004. A reburn-related document (an updated version of a poster from the May 18 

Conference) is titled “Scorecard on Reburning 6/1/2004” by Al Mann and Tom Ruppel, Parsons Corporation, 

available on-line at: 

http://www.netl.doe.gov/publications/proceedings/04/NOx/posters/Reburning%20Scorecard.pdf

6. GE Energy (formerly GE-EER) experience list September 29, 2005. 

7. “Demonstration of Rich Reagent Injection for NOX Control in AmerenUE’s Sioux Unit 1” by Cremer, Marc 

A. and Adams, Bradley R. (Reaction Engineering International), Boll, David E. (AmerenUE), and O’Connor, 

David C. (Electric Power Research Institute), presented at the US DOE Conference on SCR/SNCR for NOX

Control, Pittsburgh, PA, May 15-16, 2002. 

8. “Evaluation of Cost Effective Non-SCR Options for NOX Control in PRB Fired Cyclone Boilers” by Cremer, 

Marc A., Wang, David H. and Adams, Bradley R. (Reaction Engineering International); Boll, David E. and 

Stuckmeyer, Kenneth B. (AmerenUE), presented at the Western Fuels Symposium, 19th International 

Conference on Lignite, Brown, and Subbituminous Coals (formerly Low-Rank Fuels), October 12-14, 2004, 

Billings, MT. 

9. “NOX Emissions Below 0.15 lb/Mbtu Achieved in a Cyclone-Fired Boiler Using In-Furnace Control”, by 

Cremer, M., Adams, B., and Chiodo, A., (Reaction Engineering International); Giesmann, C., Stuckmeyer, 

K., and Boyle, J. (AmerenUE), presented at the Powergen International 2005 conference, December 6-8, 

2005, Las Vegas, Nevada. 

10. RJM experience list September 3, 2004. 

11. “Design and Demonstration of Rich Reagent Injections (RRI) Performance For NOX Reduction at 

Connectiv’s B.L. England Station” by Cremer, Marc A. and Adams, Bradley R. (Reaction Engineering 

International); O’Connor, David C. (Electric Power Research Institute); Bhamidipati, Venkata (Conectiv B.L. 

England Station), and Broderick, R. Gifford (RJM Corporation), presented at the 2001 US EPA/DOE/EPRI 

MEGA Symposium on SCR and SNCRs, Chicago, IL, August 20-23, 2001. (available from REI’s internet 

website http://www.reaction-eng.com/donwloads/rri_mega.pdf) 

12. “Improved Rich Reagent Injection (RRI) Performance For NOX Control In Coal Fired Utility Boilers” by 

Cremer, Marc A. and Wang, Huafeng D. (Reaction Engineering International), Boll, David E. (AmerenUE), 

Schindler, Edmund (RJM Corporation), and Vasquez, Edmundo RMT, Inc. (Alliant Energy Corp.), presented 

at 2003 U.S. DOE Conference on SCR and SNCR for NOX Control, Pittsburgh, PA, October 29-30, 2003.
 32 11/2/2009 

3.0 SO2 BART EVALUATION 

In this section, steps 1 through 5 of the BART determination for BSP are described for SO2. Potentially 

applicable SO2 control technologies are first identified. A brief description of the processes and their 

capabilities are then reviewed for availability and feasibility. A detailed technical description of each 

control technology is provided in Appendix B1. Subsequently, those available technologies deemed 

feasible for retrofit application are ranked according to nominal SO2 control capability. The impacts 

analysis then reviews the estimated capital and O&M costs for each alternative, including Balance Of 

Plant (BOP) requirements. Following the cost determination, the energy impacts and non-air quality 

impacts are reviewed for each technology. The impact based on the remaining useful life of the source is 

reviewed as part of the cost analysis. In the final step of the analysis, feasible and available technologies 

are assessed for their potential visibility impairment impact reduction capability via visibility modeling 

results. The results of the impact analyses are tabulated and potential BART control options are listed. 

3.0.1 BART GUIDELINE SO2 LIMITS FOR CYCLONE-FIRED BOILERS 

EPA’s recommended limit for emissions of sulfur dioxides from cyclone-fired boilers was established in 

the final BART Guidelines: 

“You [meaning States] must require 750 MW power plants to meet specific control levels for SO2

of either 95 percent control or 0.15 lbs/mmBtu, for each EGU greater than 200 MW that is 

currently uncontrolled unless you determine that an alternative control level is justified based on a 

careful consideration of the statutory factors.” 

40 CFR 51, App. Y, IV.E.4. While Unit I at BSP is greater than 200 MW output, it is not located at a 750 

MW power plant. Thus, Unit I is not subject to presumptive limits. 

3.1 IDENTIFICATION OF RETROFIT SO2 CONTROL TECHNOLOGIES 

The initial step in the BART determination is the identification of retrofit SO2 control technologies. In 

order to identify the applicable SO2 control technologies, several reference works were consulted, 

including “Controlling SO2 Emissions: A Review of Technologies (EPA-600/R-00-093, October 2000) 

and the RACT/BACT/LAER Clearinghouse (RLBC). From these and other literature sources, a 

preliminary list of control technologies and their estimated capabilities was developed. 
 33 11/2/2009 

Removal of SO2 from flue gas can either be accomplished prior to combustion, or post combustion. The 

primary method for pre-combustion controls is fuel switching. Post combustion methods include wet 

Flue Gas Desulfurization (FGD) typically using limestone reagent and semi-dry FGD technologies using 

lime reagent. Following are descriptions and technical analyses of the identified technologies for 

application to BSP Unit I. Table 3.1-1 contains the results of this effort. 

TABLE 3.1-1 – SO2 Control Technologies Identified for BART Analysis 

Control Technology 

Fuel Switching 

Semi-Dry Flue Gas Desulfurization 

Wet Flue Gas Desulfurization 

3.2 TECHNICAL DESCRIPTION AND FEASIBLITY ANALYSIS 

The second step in the BART analysis procedure is a technical feasibility analysis of the options 

identified in Step 1. The two concepts to consider are the “availability” and “applicability” of each 

control technology. The technical and feasibility analysis is presented below for each identified option. 

3.2.1 PRE-COMBUSTION FUEL TREATMENTS - FUEL SWITCHING 

Fuel switching can be a viable method of fuel sulfur content reduction in certain situations. The PRB coal 

listed in Table 1.2-2 is one of the lower sulfur coals available in the U.S. and switching to a different 

lower sulfur coal (if available) would achieve little to no additional reduction in SO2 emissions. 

Therefore, for the purpose of this BART analysis, fuel switching is not considered a viable option for SO2

control for BSP Unit I. 

3.2.2 POST- COMBUSTION FLUE GAS DESULFURIZATION 

Two different post combustion processes for reducing SO2 emissions were evaluated as BART 

alternatives in this analysis. These include two well established Flue Gas Desulfurization (FGD) 

processes, wet and semi-dry. Commercially-available wet and semi-dry FGD processes achieve SO2

removal by absorption of the SO2 into an aqueous slurry which contains a neutralizing agent, normally 

either lime or ground limestone. Chemical reaction(s) between the SO2 and the neutralizing agent convert 

the SO2 to a stable compound that can be readily sold or disposed of in a permitted facility. 
 34 11/2/2009 

3.2.2.1 WET FLUE GAS DESULFURIZATION 

Wet FGD technology utilizing lime or limestone as the reagent and employing forced oxidation to 

produce gypsum (calcium sulfate dihydrate, CaSO4 2H2O) as the byproduct is commonly applied to coalfired boilers. Absorbed SO2 is converted to calcium sulfite and then oxidized to calcium sulfate dihydrate 

(gypsum) which is filtered from the scrubber solution and either disposed of in a permitted disposal 

facility, or possibly sold for wallboard production. 

Based on commercial availability and applicability, wet FGD systems were found to be an acceptable 

BART alternative for SO2 emission control. 

3.2.2.2 SEMI-DRY FLUE GAS DESULFURIZATION 

The most common semi-dry FGD system is the lime Spray Dryer Absorber (SDA) using a fabric filter for 

downstream particulate collection. This report addresses the spray dryer FGD process. Two other 

variations, the Novel Integrated Desulfurization (NID TM) and Circulating Dry Scrubber are similar 

technologies that achieve similar levels of control effectiveness. They primarily differ by the type of 

reactor vessel used, the method in which water and lime are introduced into the reactor and the degree of 

solids recycling. Due to similar nature of the different semi-dry technologies and the similar levels of 

control efficiency achieved by all the technologies, semi-dry technologies are grouped together for the 

analysis. Technical characteristics associated with the semi-dry technologies are described in Appendix 

B1. 

Based upon availability and applicability, semi-dry FGD is considered a viable alternative for SO2

emission control. 

3.2.3 RESULTS OF FEASIBILITY ANALYSIS 

The results of the evaluation of the identified BART alternatives following the feasibility analysis are 

summarized in Table 3.2-1. 

TABLE 3.2-1 – SO2 BART Feasibility Analysis Results 

Control 

Technology 

In service on 

Existing 

Utility Boilers 

Commercially 

Available 

Technically Applicable 

To Big Stone Plant 

Fuel Switching Yes Yes No 

Wet FGD Yes Yes Yes 

Semi-dry FGD Yes Yes Yes 
 35 11/2/2009 

3.3 EVALUATE TECHNICALLY FEASIBILE SO2 CONTROL OPTIONS BY 

EFFECTIVENESS 

The third step in the BART analysis procedure is to evaluate the control effectiveness of the technically 

feasible alternatives. 

Historically, wet FGD systems have operated with SO2 control efficiency anywhere from 70% to in 

excess of 95%. For the purposes of this study, wet FGD performance was evaluated at presumptive 

BART limit of 0.15 lb/mmBtu and also at the 95% SO2 control as representative of the performance of 

this technology on PRB coal. Further technical characteristics associated with wet FGD are described in 

Appendix B1. 

No variation of semi-dry FGD systems has clearly demonstrated the ability to achieve SO2 removal levels 

similar to wet FGD systems in the U.S. Table B-1, in Appendix B, lists many of the recent lime spray 

dryer system installations in the U.S. The information in Table B-1 was obtained from the 

RACT/BACT/LAER Clearing House. Burns & McDonnell completed a study of the emission reduction 

performance of existing, electric utility, semi-dry FGD systems.3

 Information utilized for the evaluation 

was derived from EIA coal quality data and EPA SO2 stack emissions and heat input data. The evaluation 

determined that the highest SO2 removal efficiency maintained by semi-dry FGD on a continuous basis 

was just above 90%. No unit was able to maintain an efficiency of 95%. Semi-dry FGD is considered a 

viable alternative to achieve the presumptive SO2 BART level, but the upper bound on SO2 removal 

efficiency was set at 90% based on a review of the historic performance of this technology. 

Table 3.3.1 presents the remaining BART alternatives following the feasibility analysis ranked in 

descending order according to their effectiveness in SO2 control. 
 36 11/2/2009 

TABLE 3.3-1 – SO2 Control Technologies Identified for BART Analysis 

SO2 Control Technique 

Emission 

Rate

(lb/mmBtu) 

Control 

Percentage

Hourly 

Emission 

(lb/hr) 

Wet Limestone FGD 0.043 95 241.2 

Semi-dry Lime FGD 0.09 90 504.8 

Presumptive Wet Limestone FGD 0.15 83 841.4 

Presumptive Semi-dry Lime FGD 0.15 83 841.4 

Baseline 0.86 -- 4,832.2 

3.4 EVALUATION OF IMPACTS FOR FEASIBLE SO2 CONTROLS 

Step four in the BART analysis procedure is the impact analysis. The BART Guidelines lists four factors 

to be considered in the impact analysis. 

• The costs of compliance; 

• Energy impacts; 

• Non-air quality environmental impacts; and 

• The remaining useful life of the source. 

Three of the four impacts required by the BART Guidelines are discussed in the following sections. The 

remaining useful life of the source was determined to be greater than the project life definition in the 

EPA’s OAQPS Control Cost Manual (EPA/453/B-96-001) and thus had no impact on the BART 

determination for BSP. In addition, the visibility impairment impact of each alternative was evaluated as 

part of the impact analysis. 

3.4.1 COST ESTIMATES 

Cost estimates for the wet and semi-dry (including SDA and fabric filter) SO2 control technologies were 

completed utilizing the Coal Utility Environmental Cost (CUECost) computer model (Version 1.0) 

available from the EPA. The CUECost model is a spreadsheet-based computer model that was 

specifically developed to estimate the cost of air pollution control technologies for utility power plants 

within +/- 30 percent accuracy. The EPA released the version of the model used for this study in 
 37 11/2/2009 

February 2000. The model is available for download from the EPA website at 

http://www.epa.gov/ttncatc1/products.html. 

The user must specify the design parameters for the air pollution control technologies in CUECost. Unit 

costs for consumables, labor, and other variables can be modified by the user to fit the specific situation 

under evaluation. Because these models are in spreadsheet form, the calculation procedures and 

assumptions can be readily determined and adjusted by the experienced user as necessary to fit the unique 

requirements of the evaluation being conducted. The program itself is also somewhat user adjustable to 

compensate for local conditions. The CUECost default case is a generic facility located in Pennsylvania. 

Burns & McDonnell has adjusted the CUECost spreadsheets as described in the following sections to 

account for known facility and local conditions. 

Operating information utilized as input into the model for the purpose of cost estimating is listed in 

Tables 1.2-1 and 1.2-2. Economic information utilized as input into the model is given in Table 1.2-3. 

The model was run with 2008 designated as the cost basis year because equipment cost estimating in the 

model is based on the Chemical Engineering Cost Index and the composite 2008 index is the latest 

version available. Following completion of the estimating on a 2008 cost basis year, all costs were 

escalated to a 2009 basis year utilizing the inflation rates designated in Table 1.2-3. 

3.4.1.1 WET FGD CAPITAL COST ESTIMATE 

The capital cost estimate for the wet FGD system includes the SO2 control system and major support 

facilities. This capital cost estimate for wet FGD applies to either evaluated emission rate as the accuracy 

of the estimate cannot account for the cost differential due to minor equipment differences. The SO2

control system cost is representative of a typical furnish and erect contract by a wet FGD system supplier. 

The “typical” furnish and erect contract would not include costs for foundations. The wet FGD system 

cost estimated by CUECost is broken down into the major subsystems of reagent preparation, SO2

absorption tower, dewatering systems, flue gas handling systems (booster fans and ductwork) and support 

systems. The estimated capital cost associated with a wet FGD system is $171,800,000 or a unit capital 

cost of $362/kW. 

3.4.1.2 SEMI-DRY FGD CAPITAL COST ESTIMATE 

Estimated direct costs for the semi-dry FGD system include the absorbers and major support facilities. It 

was assumed that the existing fabric filter can be used to collect the reaction products from the semi-dry 

FGD absorber. The SO2 control system cost is representative of a typical furnish and erect contract by a 
 38 11/2/2009 

lime semi-dry FGD system supplier. This capital cost estimate for semi-dry FGD applies to either 

evaluated emission rate as the accuracy of the estimate cannot account for the cost differential due to 

minor equipment differences. The “typical” furnish and erect contract would not include costs for 

foundations. The system costs estimated by CUECost are broken down into the major subsystems of 

reagent preparation, absorber, waste handling systems, flue gas handling systems (booster fans and 

ductwork) and support systems. The estimated capital cost associated with a semi-dry FGD system is 

$141,300,000 or a unit capital cost of $297/kW. 

3.4.1.3 O&M COST ESTIMATE 

The annual operating and maintenance costs (O&M) costs are comprised of fixed costs (maintenance and 

labor) and variable cost (consumables). These costs were developed as part of the CUECost model and 

include operating labor, administrative and support labor and maintenance. Table 3.4-1 summarizes the 

O&M cost estimates for the wet and semi-dry FGD systems. 

TABLE 3.4-1 – First Year O&M Cost Estimate for BSP FGD Systems 

SO2 Control System 

Fixed Costs 

($1000/yr)

Variable Costs 

($1000/yr)

Total O&M 

($1000/yr) 

Wet FGD $7,000 $2,600 $9,600 

Presumptive Wet FGD $7,000 $2,490 $9,490 

Semi-dry FGD $4,500 $3,160 $7,660 

Presumptive Semi-dry FGD $4,490 $2,990 $7,480 

3.4.1.4 LEVELIZED TOTAL ANNUAL COST 

In order to compare a particular SO2 emission reduction alternative during the cost of compliance impact 

analysis portion of the BART selection process, the basic methodology defined in the BART Guidelines

was followed [70 FR 39167-39168]. The Levelized Total Annual Cost (LTAC) for these SO2 control 

alternatives was calculated based on the same economic conditions and a 30 year project life (see Section 

1.3.5 of this BART evaluation for methodology details). Estimated capital costs were split evenly over a 

two year construction period for all alternatives and a present value was calculated. Table 3.4-2 shows 

the estimated present value capital cost and the annualized cost for the two feasible SO2 emission 

reduction technologies. These are listed in order of control effectiveness, with the highest ranked options 

at the top. 
 39 11/2/2009 

TABLE 3.4-2 – Capital and Annualized Costs Estimated for 

SO2 Control Alternatives 

SO2 Control Alternative Capital Cost1

($1000) 

Present Value

Capital 

Cost

($1,000) 

First 

Year 

O&M 

Cost

($1,000) 

Levelized

Cost2 

($1,000) 

Wet FGD 171,800 161,400 9,600 29,050 

Presumptive Wet FGD 171,800 161,400 9,490 28,900 

Semi-dry FGD 141,300 132,700 7,660 23,570 

Presumptive Semi-dry FGD 141,300 132,700 7,480 23,330 

 1 – Installed capital cost is estimated for determination of total capital cost for a control 

technology, assuming maximum unit output capacity is based on 475,000 kW. 

 2 – Levelized Total Annual Cost = Annualized Installed Capital Cost + Levelized Annual O&M 

cost. The Annualized O&M cost factor = 1.361 and the Capital Recovery Factor = 0.0991 

The average cost effectiveness was then determined as the LTAC divided by the annual tons of pollutant 

emissions that would be avoided by implementation of the respective alternative. Table 3.4-3 shows the 

average cost effectiveness comparison for the SO2 control technologies. The feasible control alternatives 

were also compared by calculating the change in LTAC per incremental ton of pollutant removed for the 

next most stringent alternative (incremental cost effectiveness). This identified which alternatives 

produced the highest increment of expected pollutant reduction for the estimated lowest average LTAC 

increment compared with the pre-control baseline emission rate. The expected annual number of tons of 

pollutant removed versus estimated LTAC for each remaining control alternative was then plotted. 

TABLE 3.4-3 – Estimated Annual Emissions and LTAC for SO2 Control Alternatives 

SO2 Control Alternative 

Annual SO2

Emissions1 

(Tons/yr) 

Annual SO2

Emissions 

Reduction1 

(Tons/yr) 

Levelized 

Total 

Annual 

 Cost

($1,000) 

Average 

Cost 

Effectiveness

($/ton) 

Wet FGD 900 17,100 29,050 1,699 

Semi-dry FGD 1,880 16,120 23,570 1,462 

Presumptive Wet FGD 3,130 14,870 28,900 1,944 

Presumptive Semi-dry FGD 3,130 14,870 23,330 1,569 

Baseline 18,000 - - - 

1 – Annual SO2 emissions and control level based upon 8,760 hours of operation and 85% capacity 

factor. 
 40 11/2/2009 

The comparison of the cost-effectiveness of the control options evaluated for BSP is shown in Figure 3.4-

1. The estimated annual amount of SO2 removal (emission reduction) in tons per year is plotted on the 

abscissa (horizontal axis) and the estimated levelized total annual cost in thousands of U.S. dollars per 

year on the ordinate (vertical axis). 

Figure 3.4-1 – SO2 Control Cost Effectiveness 

Presumptive Semi-dry 

FGD

Wet FGD

Semi-dry FGD

Presumptive Wet FGD

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

- 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

Emissions Reduction (tpy)

Total Levelized Costs ($1000)

The purpose of Figure 3.4-1 is to show the range of control and cost for the evaluated SO2 reduction 

alternatives and identify the least-cost controls so that the Dominant Controls Curve (DCC) can be created. 

The DCC is the best fit line through the points forming the lower rightmost boundary of the data zone on a 

scatter plot of the LTAC versus the annual SO2 removal tonnage for the various remaining BART 

alternatives. Points distinctly to the left of and above this curve are inferior control alternatives per the 

BART Guidelines on a cost effectiveness basis. Following a “bottom-up” graphical comparison approach, 

each of the SO2 control technologies represented by a data point to the left of and above the least cost 

envelope should be excluded from further analysis on a cost efficiency basis. Of the highest-performing 

versions of the technically feasible SO2 control alternatives evaluated for cost-effectiveness, the data point 

for presumptive wet FGD is seen to be more costly for the same tons of SO2 removed than for presumptive 
 41 11/2/2009 

semi-dry FGD, semi-dry FGD or wet FGD. The presumptive wet FGD appears to be an inferior control, 

and thus should not be included on the least cost and DCC boundary. Figure 3.4.2 provides the DCC for the 

SO2 Controls 

Figure 3.4-2 – SO2 Control Cost Effectiveness and 

Dominant Cost Control Curve 

Semi-dry FGD

Wet FGD

Presumptive Semi-dry 

FGD

$0

$5,000

$10,000

$15,000

$20,000

$25,000

$30,000

$35,000

- 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000

Emissions Reduction (tpy)

Total Levelized Costs ($1000)

The next step in the cost effectiveness analysis for the BART SO2 control alternatives is to review the 

incremental cost effectiveness between remaining least-cost alternatives. Table 3.4-4 contains a repetition 

of the levelized total annual cost and SO2 control information with presumptive wet FGD removed, and 

shows the incremental cost effectiveness between each successive set of least-cost SO2 control 

alternatives. The incremental SO2 control tons per year, divided by the incremental levelized annual cost, 

yields an incremental average unit cost ($/ton). 
 42 11/2/2009 

TABLE 3.4-4 – Estimated Incremental Annual Emissions and LTAC 

for SO2 Control Alternatives 

SO2

Control 

Technique 

Levelized

Total 

Annual 

Cost

($1,000) 

Annual 

Emission 

Reduction1 

(Tons/yr) 

Incremental

Levelized 

Total 

Annual 

Cost2

($1,000) 

Incremental 

Annual 

Emission 

Reduction1,2 

(Tons/yr) 

Incremental 

Control Cost

Effectiveness

($/ton)3

Wet FGD 29,050 17,100 5,480 980 5,592 

Semi-dry FGD 23,570 16,120 240 1,250 192 

Presumptive 

Semi-dry FGD 23,330 14,870 23,330 14,870 1,569 

1 – Annual SO2 emissions and control level based upon 8,760 hours of operation and 85% capacity factor. 

2 – Increment based upon comparison between consecutive alternatives from lowest to highest. 

3 – Incremental control cost effectiveness is incremental LTAC divided by incremental annual emission reduction (tons per 

year). 

As can be seen from a review of Table 3.4-4, the incremental levelized control cost effectiveness of 

control alternatives ranges from $192/ton to $5,592/ton. In the final BART Guidelines, the EPA state 

that: 

“For example, you may be faced with a choice between two available control devices at a source, 

control A and control B, where control B achieves slightly greater emission reductions. The 

average cost (total annual cost/total annual emission reductions) for each may be deemed to be 

reasonable. However, the incremental cost (total annual cost A – B/total annual emission 

reductions A – B) of the additional control B may be very great. In such an instance, it may be 

inappropriate to choose control B, based on its high incremental costs, even though its average 

cost may be considered reasonable.” (40 CFR 51, App. Y, IV.D.e.5.) 

The incremental cost effectiveness is a measure of the increase in marginal cost effectiveness between 

two specific alternatives. The incremental cost analysis indicates that from a cost effectiveness 

viewpoint, the most costly alternative is wet FGD. The wet FGD control option is considered technically 

feasible for BSP, but incurs a significant annual (levelized) incremental cost compared to the other 

feasible SO2 control techniques and is an inappropriate control option based upon high incremental costs. 
 43 11/2/2009 

3.4.2 ENERGY IMPACTS 

The energy impacts of each alternative, in terms of both estimated kW of energy usage and the percent of 

total generation, are given in Table 3.4-5. The primary energy impact of the wet FGD alternative consists 

of the additional electrical load resulting from pumps, blowers, booster fans, ball mills for limestone 

grinding and vacuum pumps for byproduct slurry dewatering. The largest energy users for the semi-dry 

alternatives are pumps, atomizers and booster fans. Building HVAC and interior and exterior lighting 

loads are also included, but the major energy consumption is due to the primary systems described above. 

TABLE 3.4-5 Energy Requirements of SO2 BART Alternatives 

 

BART 

Alternative 

Energy 

Demand 

(kW) 

Percent of 

Nominal 

Generation 

Wet FGD 9,500 2.0% 

Semi-dry FGD 3,325 0.7% 

3.4.3 NON-AIR QUALITY ENVIRONMENTAL IMPACTS 

Non-air quality environmental impacts of the installation and operation of the various BART alternatives 

include solid and aqueous waste streams, and salable products that could result from the implementation 

of various BART alternatives. Captured mercury would be present in the solid waste stream from any 

post combustion alternative as a trace contaminant in the solid waste. Under current regulation, the 

presence of trace amounts of mercury would not affect its disposal. 

A wet FGD system for BSP Unit I is estimated to produce approximately 6 tons per hour of solid waste. 

The waste stream would be composed of gypsum solids and inerts at approximately 15% moisture. Over 

the course of a year, the total solid waste quantity is estimated to be approximately 44,700 tons of gypsum 

solids which would need to be landfilled. 

The annual quantity of aqueous waste that would be produced by a wet FGD system is difficult to 

quantify because the blowdown rate from a wet FGD system is primarily a function of the dissolved 

chloride levels in the absorber reaction tank. Most of the chloride reaching the scrubber is in the form of 

hydrochloric acid which is readily absorbed and neutralized. Based upon the use of relatively low 

chloride coal, one can assume the chlorides to be removed via the blowdown stream as CaCl2 and would 

leave the plant in the entrained moisture in the solid waste. No blowdown specifically for chloride 

disposal or special treatment of the waste would be required under these conditions. 
 44 11/2/2009 

3.4.4 VISIBILITY IMPACTS 

The final impact analysis conducted was to assess the visibility impairment impact reduction for the SO2

control technologies. The analysis used a baseline SO2 emission rate which assumed the highest 24-hour 

actual emission rate for 2001-2003 as recommended by the BART guideline and listed in the Modeling 

Protocol. Three CALPUFF model runs for BSP were conducted with the constant NOX emission rate of 

0.65 lb/mmBtu, constant PM emission rate of 0.015 lb/mmBtu, and various levels of SO2 control applied. 

Table 3.4-6 shows the modeled emission rates.

The modeling for this analysis was performed using CALPUFF. The difference between the modeled 

impacts at the 98th percentile level from various controlled emission rates represents the visibility 

impairment impact reduction in deciViews (dV). Table 3.4-6 shows the results of the visibility impact 

modeling attributable to SO2 reductions while maintaining NOX and PM emissions constant. The 

modeling results with combined impacts from all pollutants are addressed later in the report. 

 

TABLE 3.4-6 – Visibility Impairment Impacts from Emission Controls 

SO2 Control 

Technique 

Emission 

Rate

(lb/mmBtu) 

Visibility 

Impairment 

Impact 

(dV)

Visibility 

Impairment 

Reduction1

(Δ dV) 

Technology 

Incremental 

Reduction 

(Δ dV) 

Wet FGD 0.043 0.611 0.046 0.009 

Semi-dry FGD 0.09 0.620 0.037 0.037 

Presumptive Semi-dry 

FGD 0.15 0.657 - - 

Baseline 0.86 1.079 - - 

1 – Impairment reduction is from presumptive semi-dry FGD levels. 

The results of the baseline visibility impairment modeling for BSP showed that SO2 emissions caused a 

Class I area to exceed 0.5 dV for predicted visibility impairment impact (98th percentile). Modeled 

visibility impairment impacts decreased with the addition of all SO2 controls. 

As previously discussed, the 0.5 dV value is the lowest visibility impairment impact that is considered 

discernible by the human eye and the EPA set this threshold as the point where a given source is 

considered a “contributing source”. Thus, an impairment impact or a difference in impairment impacts of 
 45 11/2/2009 

less than 0.5 dV is considered visibly indiscernible. Because the difference in impacts between semi-dry 

FGD and wet FGD are 0.009 dV apart, the visibility improvement resulting from these controls is 

considered indiscernible. Where visibility improvement between alternatives is indiscernible, the 

incremental cost to achieve the indiscernible visibility improvement is determined and evaluated against 

incremental costs for the next most stringent alternative. Table 3.4-7 shows the costs to achieve the 

incremental reduction in visibility impairment. 

TABLE 3.4-7 – Cost for Incremental Visibility Improvement 

SO2 Control Technique 

Incremental 

Levelized Total 

Annual Cost1

($)

Impairment 

Reduction 

(Δ dV) 

Incremental 

Reduction 

(Δ dV) 

Cost for 

Incremental 

Improvement 

($/dV) 

Wet FGD 5,480,000 0.046 0.009 608,900,000 

Semi-dry FGD 240,000 0.037 0.037 6,500,000 

Presumptive Semi-dry FGD 23,330,000 - - - 

1 – Increment based upon comparison between consecutive alternatives (points) from lowest to highest.

3.4.5 IMPACT SUMMARY 

Table 3.4-8 summarizes the various quantifiable impacts discussed in Sections 3.4.1 through 3.4.4 for the 

SO2 alternatives evaluated for BSP Unit I. 

TABLE 3.4-8 – Impacts Summary for BSP Unit I SO2 Controls 

SO2 Control 

Technique 

Emission 

Rate

(lb/mmBtu) 

Levelized 

Total 

Annual 

Cost

($1,000) 

Incremental 

Levelized 

Total 

Annual Cost1

($1,000) 

Visibility 

Impairment 

Impact 

(dV)

Visibility 

Impairment 

Reduction 

(dV) 

Technology 

Incremental 

Reduction 

(Δ dV) 

Wet FGD 0.043 29,050 5,480 0.611 0.046 0.009 

Semi-dry FGD 0.09 23,570 240 0.620 0.037 0.037 

Presumptive Semidry FGD 0.15 23,330 23,330 0.657 - - 

Baseline 0.86 - - 1.079 - - 

1 – Increment based upon comparison between consecutive alternatives (points) from lowest to highest.
 46 11/2/2009 

4.0 PARTICULATE MATTER BART EVALUATION 

In this section, steps 1 through 5 of the BART determination for BSP Unit I are described for PM. All 

PM control technologies are first identified. A technical description of the processes and their capabilities 

are then reviewed to determine availability and feasibility. Subsequently, those available technologies 

deemed feasible for retrofit application are ranked according to nominal PM control capability. The 

impacts analysis then reviews the estimated cost, energy, and non-air quality impacts for each technology. 

The impact of the remaining useful life of the source is reviewed as part of the cost analysis. In the final 

step of the analysis, the remaining technologies are assessed for their potential visibility impairment 

impact reduction capability via visibility modeling results. The results of the complete analyses are 

tabulated and possible BART control options are listed. 

The BART guidelines published in the Federal Register on July 6, 2005 (70 FR 39104) do not specify 

presumptive BART levels for particulate matter (PM) emissions. The guidelines suggest the use of PM10

as the indicator for all PM2.5, because all PM2.5 is encompassed within the PM10 emissions fraction. (40 

CFR 51, App. Y, II.A.3.) The BART guidelines specify the distinction between coarse (PM10 minus 

PM2.5) or fine (PM2.5) PM in determining visibility impacts, which was made during the CALPUFF 

visibility modeling. 

 

The BART Guidelines indicate that one of the evaluated emission limits must be at least as stringent as 

the New Source Performance Standard (NSPS) requirement for the source (40 CFR 51, App. Y, IV.D.1). 

The BSP pulse-jet fabric filter meets the current NSPS emission rate 0.015 lb/mmBtu as required of new 

sources under 40 CFR § 60.42Da(c). All of the evaluated control technologies used a PM emission rate 

of 0.015 lb/mmBtu. 

4.1 IDENTIFICATION OF AVAILABLE RETROFIT PM CONTROL 

TECHNOLOGIES 

The initial step of the BART determination is the identification of available retrofit PM control 

technologies. In order to produce a list of control technologies and their estimated capabilities, sources 

such as the RACT/BACT/LAER Clearinghouse (RBLC) were used. The results of the investigation 

determined that the removal of PM from flue gas is accomplished using post combustion technology. The 

two most common post combustion technologies used to control PM emissions include fabric filters (FF) 
 47 11/2/2009 

and electrostatic precipitators (ESPs). The existing BSP configuration contains a pulse-jet fabric filter 

that was installed in 2007. Table 4.1-1 contains the results of the available PM control technologies. 

TABLE 4.1-1 PM Control Technologies Identified for BART Analysis 

Control Technology 

Existing Fabric Filter 

New Fabric Filter 

COHPAC Baghouse 

Electrostatic Precipitator 

4.2 TECHNICAL DESCRIPTION AND FEASIBLITY ANALYSIS 

The second step in the BART analysis procedure is a technical feasibility analysis of the options 

identified in Step 1. This analysis is presented below for each identified option. 

4.2.1 FABRIC FILTER (FF) 

A fabric filter or baghouse removes particulate by passing flue gas through filter bags. A pulse-jet fabric 

filter (PJFF), a common type of fabric filter, consists of isolatable compartments and a tube sheet which 

separates the particulate laden flue gas from the clean flue gas. The flue gas passes through the PJFF by 

flowing from the outside of the bag to the inside up the center of the bag through the hole in the tube sheet 

and out the PJFF. Fly ash particles are collected on the outside of the bags and the cleaned gas stream 

passes through the bag to the outlet of the fabric filter. Each filter bag alternates between relatively long 

periods of filtering and short periods of cleaning. During the cleaning period, fly ash that has 

accumulated on the bags is removed by pulses of air and falls into a hopper for disposal. 

The existing fabric filter on BSP Unit I can achieve a filterable PM emission rate of 0.015 lb/mmBtu. 

Therefore, continuing the use of the existing fabric filter is a technically feasible option. Replacement of 

the existing fabric filter with a new fabric filter is feasible, but would provide little to no increase in 

removal efficiency or reduction in emission rate. 

4.2.2 COHPAC 

A COmpact Hybrid PArticulate Collector (COHPAC) is a high air-to-cloth ratio pulse jet fabric filter 

located downstream of an existing ESP. The COHPAC acts as a polishing device for control of 

particulate emissions. The difference between a COHPAC and the fabric filter described above is that a 

COHPAC is installed after an ESP. Because Big Stone Plant does not have an ESP and already uses a 

fabric filter for particulate control, the use of a COHPAC is not considered further. 
 48 11/2/2009 

4.2.3 ELECTROSTATIC PRECIPITATOR (ESP) 

ESPs are commonly used as the primary filterable PM control device on coal fired units. The ESP 

discharge electrodes generate a high voltage electrical field that gives the particulate matter an electric 

charge (positive or negative). The charged particles will then be collected on a collection plate. 

Technical characteristics associated with ESPs are described in Appendix C1. 

It is anticipated that a new ESP installed at BSP could achieve a PM emission rate of approximately 0.015 

lb/mmBtu. Therefore, the use of a new electrostatic precipitator is a technically feasible option. 

Replacement of the existing fabric filter with a new ESP is feasible, but would provide little to no 

increase in removal efficiency or reduction in emission rate. 

The results of the feasibility analysis for the available BART alternatives are summarized in Table 4.2-1. 

TABLE 4.2-1 – PM BART Feasibility Analysis Results 

Control 

Technology 

In Service on 

Existing 

Utility Boilers 

Commercially 

Available 

Technically Applicable 

To Big Stone Plant 

Existing Fabric Filter Yes Yes Yes 

New Fabric Filter Yes Yes Yes 

COHPAC Baghouse No1 Yes No 

New ESP Yes Yes Yes 

1 – While COHPAC has been installed on existing EGUs, it has not been installed in 

conjunction with an existing fabric filter. 

4.3 RANK OF TECHNICALLY FEASIBLE PM CONTROL OPTIONS BY 

EFFECTIVENESS 

The third step in the BART analysis procedure is to rank the technically feasible alternatives. However, 

because BSP Unit I currently uses a pulse-jet fabric filter that is the best technology available for 

particulate control and can achieve similar emission rates to new versions of the same technology or a 

new ESP replacing the existing fabric filter with new particulate control is inappropriate. Thus, the 

existing fabric filter is the highest ranked and only option evaluated further. 
 49 11/2/2009 

4.4 EVALUATION OF IMPACTS FOR FEASIBLE PM CONTROLS – UNIT I 

Step four in the BART analysis procedure is the impact analysis. The BART Guidelines list four factors 

to be considered in the impact analysis: 

• The costs of compliance; 

• Energy impacts; 

• Non-air quality environmental impacts; and 

• The remaining useful life of the source. 

Because Big Stone Plant Unit I currently uses a pulse-jet fabric filter that is the best technology available 

for particulate control and can achieve similar emission rates to new versions of the same technology 

replacing the existing fabric filter with new particulate control is inappropriate. Reviewing the four 

impacts listed above would provide no additional information regarding the type of technology to be 

selected to best achieve visual emissions improvement. However, as described in Section 1.3.6, the 

visibility impairment impacts due to particulate matter were included as part of the analysis. 

4.4.1 VISIBILITY IMPACTS 

A visibility analysis specifically for PM was not conducted due to the selection of the existing fabric filter 

and the conclusion that the alternatives would result in the same emission rate. Per the BART Guidelines, 

because BSP has “elected to apply the most stringent controls available...you need not conduct, or require 

the source to conduct, an air quality modeling analysis for the purpose of determining its visibility 

impacts.” (40 CFR 51. App. Y, IV.D.5.) 

5.0 BART RECOMMENDATIONS 

The presented emission rates in this section are the BART recommendation. However, because the 

accuracy of the cost estimate is + 30% and in some cases is greater than the variance of the estimated 

costs between control alternatives, the technology selected by Big Stone Plant to meet the BART 

recommendation may change. This section summarizes the analysis performed for each pollutant. 
 50 11/2/2009 

5.1 NOX BART 

Five types of NOX control processes were identified for evaluation. Over-fire air (OFA), separated overfire air (SOFA), Selective Non-Catalytic Reduction (SNCR), Rich Reagent Injection (RRI), Selective 

Catalytic Reduction (SCR) and combinations these technologies were evaluated for control effectiveness. 

Of these alternatives, stand alone SNCR and SCR were eliminated from further impacts analysis as BSP 

already has an OFA system in operation. A cost analysis of the remaining technologies eliminated 

RRI/SNCR/SOFA due to the operating costs. 

Predicted visibility impairment impacts decreased significantly with the NOX control technologies. The 

largest incremental impact reduction came from the application of SCR. However, the difference in 

impacts between OFA (lowest control level) and SCR (highest control level) is less than 0.5 dV, 

which is visibly indiscernible. The modeling also shows that SOFA must be applied to reduce 

visibility impacts due to the NOX contribution below a discernable level of 0.5 dV. An analysis of the 

incremental cost-effectiveness of consecutively more stringent controls was performed for BSP Unit I. 

Installing and operating any control technology beyond SOFA would cost more than 24 million dollars 

per dV of visibility impairment improvement and would only improve predicted visibility impacts by an 

amount that is not discernable to the human eye. 

Based on the analysis, SOFA is recommended as BART for BSP Unit I. Application of SOFA for NOX

control translates into a BART emission rate of 2,804 pounds per hour (0.50 pounds per million Btu of 

fuel heat input at 5,609 mmBtu/hr). The emission rate of 2,804 pounds per hour is recommended as the 

permit limit based upon a 30 day rolling average. 

5.2 SO2 BART 

Three types of SO2 control processes were identified for evaluation. While evaluating each process for 

BSP SO2 control, fuel switching was eliminated due to the current use of low sulfur PRB coal. Wet FGD 

and semi-dry FGD at two levels of control were selected for further evaluation. A cost analysis of the 

remaining technologies eliminated wet FGD at the presumptive emissions rate due to the higher cost for 

achieving the same emission rate as semi-dry FGD. 

The difference in impacts between semi-dry FGD and wet FGD are 0.009 dV apart, which is visibly 

indiscernible. The modeling also shows that semi-dry FGD at 90% control must be applied to reduce 
 51 11/2/2009 

visibility impacts due to the SO2 contribution below a discernable level of 0.5 dV. An analysis of the 

incremental cost-effectiveness of consecutively more stringent controls was performed for BSP Unit I. 

Installing and operating wet FGD over semi-dry FGD would cost 608 million dollars per dV of visibility 

impairment improvement and would only improve predicted visibility impacts by an amount that is not 

discernable to the human eye. 

Based on the analysis, semi-dry FGD is recommended as BART for BSP Unit I. Application of semi-dry 

FGD for SO2 control translates into a BART emission rate of 505 pounds per hour (0.09 pounds per 

million Btu of fuel heat input at 5,609 mmBtu/hr heat input). The emission rate of 505 pounds per hour is 

recommended as the permit limit based upon a 30 day rolling average. 

5.3 PM BART 

For the PM evaluation, three post combustion control technologies were selected for evaluation in 

addition to the existing pulse-jet fabric filter. While evaluating each technology for BSP Unit 1 PM 

control, a COHPAC baghouse was eliminated from the evaluation. A new fabric filter and ESP were 

eliminated in the analysis because the existing fabric filter provides a similar level of control effectiveness 

without the additional capital costs. 

Because BSP Unit I currently uses a pulse-jet fabric filter that is the best technology available for 

particulate control and is the only technology remaining in the analysis, the impact review can be 

abbreviated. 

Reviewing the cost of compliance, the energy and non-air quality environmental impacts, other pollution 

control equipment in use at the source, and the remaining useful life of the source would provide no 

additional information to change technologies from the existing fabric filter. The modeling was 

conducted with a constant PM emission rate of 84.1 pounds per hour. 

Based upon selection of the best available PM control technology, maintaining the existing pulse-jet 

fabric filter is recommended as BART for BSP Unit I. The corresponding BART emission rate for the 

existing fabric filter is 84.1 pounds per hour (0.015 pounds per million Btu of fuel heat input at 5,609 

mmBtu/hr heat input). The emission rate of 84.1 pounds per hour is recommended as the permit limit 

based upon a 30 day rolling average. 
 52 11/2/2009 

5.4 COMBINED BART 

As indicated previously, this report presents the analysis of control technologies for NOX, SO2, and PM 

for BSP Unit I. The BART control technology recommendations for the individual pollutants are based 

upon the steps outlined in the EPA guideline. Modeling to determine visibility impairment was 

performed using the recommended BSP Unit I BART emission rates for NOX, SO2, and PM. The 98th

percentile results are provided in Table 5.4-1. 

TABLE 5.4-1 – Visibility Impairment Impacts from Combined Emissions 

Control Technique 

NOX

Emission 

Rate

(lb/hr) 

SO2

Emission 

Rate

(lb/hr) 

PM 

Emission 

Rate

(lb/hr) 

Visibility 

Impairment 

Impact 

(dV)

BART 2,804 505 84.1 0.493 

The results of the visibility impairment modeling for BSP showed that the proposed BART emissions 

rates for NOX, SO2 and PM caused no Class I area to exceed 0.5 dV for predicted visibility impairment 

impact (98th percentile) with Boundary Waters Canoe Area Wilderness (Boundary Waters) showing the 

highest predicted visibility impairment impact at 0.493 dV for the 2007 modeled year. Modeled visibility 

impairment impacts decreased significantly with the addition of the BART controls. 
 A-1 

APPENDIX A 

Technical Feasibility Assessment Details for NOX Controls (A1) 

CUECost Input Summary (A2) 

Summary of Modeling Results (A3) 

 
 A-2 11/2/2009 

A1 Technical Feasibility Assessment of NOX Control Alternatives 

Uncontrolled NOX emissions from a coal-fired electric generating unit are highly dependent on type of 

firing method, amount of solid fuel fired per unit time and furnace volume, and the fuel’s basic 

combustion properties and elemental composition. The methods for reduction of such emissions: 

• either prevent pollution, i.e., use inherently lower-emitting processes/practices which produce 

fewer NOX emissions during the power generation process; or 

• involve improvements to, or provide new add-on controls that, reduce emissions after they are 

produced before they are emitted from the facility; or 

• are combinations of inherently lower-emitting processes and add-on controls. 

There are two basic categories of NOX emission control alternatives: 

• Combustion controls; and 

• Post-Combustion controls. 

A significant number of the identified control options have been commercially-available, installed, and 

operating in many full-scale, permanent installations in the United States for five years or more. 

Similar to the dependency of the uncontrolled emissions being based on the unit type, the applicability of 

the control technologies are also dependent upon the type of coal-fired unit. 

Combustion controls, such as over-fire air (OFA) or separated over-fire (SOFA) air are applicable to 

cyclone fired units. Low-NOX burners (LNBs), while commonly applied to pulverized coal-fired boilers, 

are not applicable to cyclone fired units since initial combustion occurs in the barrel-shaped cyclone and not 

in the furnace chamber as is the case for the pulverized coal-fired boiler. 

Selective Catalytic Reduction (SCR) and Selective Non-Catalytic Reduction (SNCR) are post-combustion 

technologies that have been applied on bituminous or sub-bituminous coal-fired boilers. Others, mostly 

comprised of a combination of available control technologies, are often referred to as “hybrid” or “layered” 

control technologies. Variations of SNCR, such as more recently developed “Rich Reagent Injection” (RRI) 

technology, have only been demonstrated on a limited number of cyclone-fired boilers. In most of the 

“layered” control combination and emerging control cases, the NOX control technology has been 

demonstrated to be capable of controlling the targeted pollutant(s) on either: 

• a full-scale basis, but only with temporary equipment; or 
 A-3 11/2/2009 

• a full-scale basis, with permanent equipment but in a limited number of installations. 

A1.1 Combustion Controls 

Nitrogen oxides (NOX) are produced when nitrogen in the fuel and combustion air are exposed to high 

temperatures. Nitrogen oxide (NO) is the most predominant form of NOX emissions, along with nitrogen 

dioxide (NO2). The formation of these compounds in utility powerplant boilers is sensitive to the method 

of firing and combustion controls utilized. The techniques employed for mixing the combustion air and 

fuel, which creates flames and high temperature combustion products, results from the rapid oxidization 

of carbon, hydrogen, and other exothermic reactions. Cyclone-fired boilers, by design, create intense heat 

release rates to melt and fluidize the coal ash introduced into the barrel-shaped furnaces. This produces 

very high uncontrolled NOX emissions. 

Combustion controls employ methods that reduce the amount of NOX emissions created in the 

combustion zone of the boiler prior to exhausting the flue gases from the furnace (upstream of the 

convective heat transfer zones). This results in fewer emissions that may require subsequent reduction 

from applicable post-combustion techniques. 

A1.1.1 Low-NOx Burners (LNB) 

LNBs are not applicable to cyclone-fired boilers1. This is due to the physical constraints imposed by the 

cyclone furnaces’ (barrels) length and diameter, and the incompatibility with the amount of heat released 

and flame dispersion patterns, and insufficient amount of fine coal particles required to sustain stable 

combustion associated with air-staged firing of coal using low-NOX burners with pulverized fuel. This 

alternative was eliminated from consideration for potential additional NOX emissions reductions from Big 

Stone’s boiler. 

A1.1.2 Over-fire Air (OFA) or Separated Over-fire Air (SOFA) 

Over-fire Air (OFA) and Separated overf-ire air (SOFA) systems are commonly-applied, combustionrelated NOX emission reduction technology. Separated Overfire Air (SOFA) is an air-staging NOX

reduction technique that is usually based on withholding 15 to 20 percent of the total combustion air 

conventionally supplied to the firing zone. It is believed that Big Stone’s boiler would be a suitable 

candidate for the installation of SOFA and for additional NOX control, if this is necessary. 
 A-4 11/2/2009 

For typical cyclone coal-fired boilers, the operation of SOFA involves diverting approximately 20 percent 

of the secondary combustion air from the burner barrels, forcing the cyclones to operate fuel-rich. The 

diverted combustion air is then injected in the upper furnace, where combustion is completed. 

SOFA can achieve significant NOX reduction, typically 30 to 70 percent on typical cyclone coal-fired 

boilers with this typical amount of air staging. A summary of several of the first OFA retrofits to 

cyclone-fired boilers is described in published technical papers1,2. At least thirty nine existing cyclonefired boilers, firing eastern bituminous, midwestern bituminous, and western subbituminous (“Powder 

River Basin”) coals in units ranging in size from 50 to 1150 MW, have been retrofitted with commercial 

SOFA since 19983

. Additional cyclone-fired boilers have installed separated overfire air systems in 

conjunction with commercial fuel reburn retrofit projects4

. Other NOX emission reduction demonstration 

projects, primarily sponsored by U.S. Department of Energy National Energy Technology Laboratory’s 

Clean Coal Technology Program5

, and other fuel reburn retrofit projects6 have also installed separated 

overfire air on cyclone boilers. 

A basic form of separated overfire air (SOFA) can be applied and installed on Big Stone. There are 

potential impacts and limitations unique to cyclone boilers firing PRB that should be recognized as part of 

this emission reduction technology application. 

A key aspect of successfully applying and operating separated overfire air on a cyclone-fired boiler is the 

ability to maintain adequate molten coal ash (slag) formation and flow within the barrels and slag taps. 

As secondary combustion air is diverted, less heat is released during air-staged combustion from the 

intentional formation of carbon monoxide, and temperatures within the cyclones decreases. The degree to 

which the cyclones can be operated with less than theoretical (stoichiometric) combustion air directly 

contributes to less NOX formation and further in-furnace emission reduction but also risks solidification 

of the molten coal ash. There are several challenges anticipated for implementing SOFA, primarily 

involving the ability to route large SOFA ductwork for diverting secondary air from the windboxes. 

These are believed to be solvable. Using a basic SOFA system, assuming a sustainable level of NOX

emissions control with the operation of modestly air-staged cyclone furnaces with suitable combustion 

controls, is considered feasible for Big Stone. 

 
 A-5 11/2/2009 

A1.2 Post-Combustion Controls 

Post-combustion controls deal with techniques that thermally or chemically-treat the flue gases to reduce 

NOX emissions after they have exited the boiler’s lower furnace. In the case of Big Stone Unit I, this 

primarily involves forms of selective catalytic reduction (SCR) and selective non-catalytic reduction 

(SCR) technologies. 

A1.2.1 Selective Non-Catalytic Reduction (SNCR) 

Selective Non-Catalytic Reduction (SNCR) technologies are all post-combustion types of boiler NOX

emission controls. These technologies promote NOX reduction with chemical reactions that are 

insensitive to the specific fuel types whose combustion products are being treated. While the large 

majority of boiler applications to date have been on pulverized coal-fired units burning eastern 

bituminous fuels, SNCR has been used to reduce NOX emissions on utility boilers burning eastern 

bituminous coal, midwestern bituminous coal, and, to a lesser extent, western subbituminous coal. SNCR 

has also been used with fuel oil and natural gas-fired units. SNCR (and hydrocarbon-enhanced SNCR) 

technologies can each be applied to fossil fuel-fired boilers with or without the use of a SOFA system. 

The ability to apply SNCR does not appear to be dependent directly on the type of burners (wall-fired, 

tangentially-fired, and cyclone-fired) employed in the boilers where it has been installed, with or without 

overfire air in full operation. Operation at these plants has demonstrated that SNCR can decrease NOX

emissions as much as 15-40% at full load, most typically between 25-35%.7, 8, 9 

In the conventional SNCR process, urea or ammonia is injected into the boiler in a region where the 

combustion gas temperature is in the 1700 to 2100 degrees F range. Under these temperature conditions, 

the urea reagent [CO(NH2)2 ] or ammonia [NH3 ] reacts with the nitrogen oxides [NOX], forming 

elemental nitrogen [N2 ] and water, reducing NOX emissions. 

SNCR can be applied and installed on the Big Stone boiler in combination with basic or separated form of 

over-fire air (OFA). 

A1.2.2 Rich Reagent Injection (RRI) 

Rich Reagent Injection (RRI) is a NOX control technology that has been developed and demonstrated 

specifically for use on cyclone boilers. Rich Reagent Injection is an SNCR process that involves the 

injection of urea into the lower furnace between the cyclones and the SOFA ports. RRI targets a high 
 A-6 11/2/2009 

temperature, fuel-rich zone within the boiler-furnace environment immediately adjacent to the cyclone 

burners, and requires temperatures in the range of 2400 to 3100 degrees F. The combustion gases must be 

essentially devoid of free oxygen, in order to avoid oxidizing the nitrogen contained in the injected 

reagent, which would create NOX emissions instead of reducing them. 

The RRI process for NOX reduction must be used in conjunction with air-starved (substoichiometric 

staged-air) cyclone combustion resulting from the installation and operation of an OFA system. The 

cyclones’ air/fuel stoichiometry must be carefully controlled to maintain fuel-rich conditions for the RRI 

process to be effective. This introduces oxygen in the same vicinity as the reagent injection ports, and 

will disrupt the beneficial action of the fuel-rich zone and amine reagent to significantly reduce NOX

emissions. Without SOFA, RRI will not contribute positively to NOX emissions control on Big Stone 

Unit I boiler. This places a large emphasis on the expected performance of SOFA in order for RRI to be 

successful in producing significant additional NOx emissions reduction on PRB-fired cyclone boilers. 

The three zones of a Rich Reagent Injection SNCR application on a boiler with separated overfire air are 

shown as a sectional side elevation view of the furnace11 in Figure A.1-4. 
 A-7 11/2/2009 

Figure A.1-4 Rich Reagent Injection Application on Boiler With Overfire Air10 

The Rich Reagent Injection (RRI) process has been successfully demonstrated on at least two cyclonefired boilers, with the most recent installation at Ameren’s Sioux Unit I, a 500 MW boiler firing a blend 

of PRB and midwestern bituminous coals. 

The NOX emission reduction reagent injection for RRI processes must be precisely located and carefully 

controlled to be effective. Operation outside of the required operating ranges can even result in increased 

NOX emissions. Extensive computational fluid dynamic (CFD) simulations are needed to determine the 

optimum injection points. Boiler operating conditions will change with unit load and varying fuel 

characteristics. The RRI process control systems must be able to adjust for these changing conditions. 

2400-3100oF

NOx

N2

Chemical

Injection

NHi NCO

Staged

Combustion 

Zone

Fuel Rich Zone

Burnout Zone OFA

Fuel

2400-3100oF

NOx

N2

Chemical

Injection

NHi NCO

Staged

Combustion 

Zone

Fuel Rich Zone

Burnout Zone OFA

Fuel
 A-8 11/2/2009 

RRI has the potential to provide a moderate degree of NOX reduction on coal-fired cyclone boilers. Rich 

Reagent Injection can be applied and installed on Big Stone boiler only with separated over-fire air 

(SOFA). 

A1.2.3 Selective Catalytic Reduction (SCR) 

The lowest NOx emission levels from coal-fired utility boilers are typically achieved by installing and 

operating selective catalytic reduction (SCR) technology. In the SCR process, the gas stream is passed 

through a catalyst bed in the presence of ammonia to reduce NOX to molecular nitrogen and water. The 

process is termed “selective” because the ammonia preferentially reacts with the NOX rather than with the 

oxygen in the flue gas. A catalyst is used to enhance NOX reduction and ammonia utilization at 

appropriate flue gas temperatures. SCR is usually applied to flue gas in the 600°F to 750°F temperature 

range. There are variations in the SCR process for coal-fired boilers that mostly involve locations in the 

flue gas path where the catalyst is placed in order to promote the desired NOX emission reduction effect. 

These are described below. 

For coal-fired boilers, a conventional SCR reactor utilizes readily-available catalyst materials and reagent 

in the form of ammonia. A conventional SCR reactor is commonly installed in a high-dust, hot-side 

arrangement, located between the economizer outlet and air heater inlet, where the flue gas temperature is 

within the desired operating range for the SCR catalyst. 

A schematic graphic diagram for a conventional high-dust, hot-side SCR system on a boiler with a flue 

gas desulfurization system and stack gas reheat is provided in Figure A.1-5. 
 A-9 11/2/2009 

Figure A.1-5 Conventional SCR Arrangement 

with FGD Scrubber Outlet Reheat 

(figure copied from Wheelabrator Air Pollution Control literature) 
 A-10 11/2/2009 

SCR technology has been installed on several pulverized coal and cyclone boilers firing bituminous and 

subbituminous coal in the United States. The installation of SCR systems has been completed on 

approximately 22 cyclone units. Several SCR installations have been retrofit on existing cyclone-fire 

boilers burning western subbituminous coal (or PRB blended with midwestern bituminous coal). For 

cyclone coal-fired utility boilers retrofitted with SCR technology, all were originally designed to burn 

bituminous coal. 

Two byproducts from the high-dust, hot-side SCR process are ammonia slip and SO3: 

• Ammonia Slip: Slip is ammonia that is unreacted in the NOx emission reduction process. 

Maximum ammonia slip for a gas fired unit is usually 10 ppmvd whereas, on a coal fired unit, 

ammonia slip below 2 ppm is desired. For certain applications, this concentration can be 

problematic, therefore requiring more catalyst to reduce slip. Most new SCR applications have 

ammonia slip guaranteed at a 2 ppmvd maximum for an initial operating period, and are expected to 

continue to operate at these low ammonia slips levels beyond the end of the initial period. 

• SO3: Due to the composition of typical SCR catalysts, a small percentage of inherent SO2 will be 

oxidized to SO3. This oxidation can be controlled by catalyst selection and can be less than 1%. 

SO2 to SO3 oxidation must be carefully controlled to avoid creating SO3 levels sufficiently high to 

raise the possibility of air heater fouling. A unit firing high-sulfur coal with SCR technology is 

especially vulnerable to SO2 oxidation and ammonia slip-related fouling problems. The deposition 

and fouling is due to formation of solid ammonium sulfate ((NH4)2SO4) and liquid ammonium 

bisulfate (NH4HSO4). The most important design variable is optimizing the catalyst selection and 

amount of catalyst that will reduce NOX emissions, control ammonia slip, and minimize SO2

oxidation. 

As posted on Electric Power Research Institute Inc.’s (EPRI’s) website regarding the impact of coal type 

on SCR catalyst life and performance, a recent EPRI study11 produced field data analyzed from an “InSitu Mini SCR Reactor” system installed in a typical “high-dust” location at seven different test sites, 

including four firing PRB coal, one firing Texas lignite, one firing high-sulfur eastern bituminous coal, 

and one firing a PRB/eastern bituminous coal blend. The PRB/bituminous coal blend test was performed 

at AmerenUE’s Sioux Station, on one of the two 500 MW cyclone-fired boilers. This study found that 

the cyclone unit firing the PRB/bituminous coal blend exhibited the fastest rate of catalyst activity 

degradation. Also, the higher deactivation rates seen at this site were due to economizer exit flue gas 

temperatures being significantly higher than at the other sites. A comparison of the Texas lignite and one 
 A-11 11/2/2009 

of the PRB-fired sites of two different catalysts’ deactivation was more a function of trace elements in the 

flue gas and flyash than the specific catalyst type or formulation. 

Based upon this technical assessment that looked at the various design and operational issues associated 

with the installation of hot-side, high-dust SCR technology, SCR is considered a feasible option for Unit I 

at Big Stone. 
 A-12 11/2/2009 

References for Appendix A1: 

1. “The State of the Art in Cyclone Boiler NOx Reduction”, by O’Connor, Dave, Himes, Rick, and 

Facchiano, Tony (Electric Power Research Institute), presented at the EPRI-DOE-EPA Combined 

Utility Air Pollutant Control Symposium, Atlanta, GA, August 16-20, 1999. 

2. “B&W’s Advances on Cyclones NOx Control Via Fuel and Air Staging Technologies”, by Farzan, 

H., Maringo, G., Johnson, D. W., and Wong, D.K. (Babcock & Wilcox, Co.), Beard, C.T. (Eastman 

Kodak Company), and Brewster, S.E. (Tennessee Valley Authority), presented at the EPRI-DOEEPA Combined Utility Air Pollutant Control Symposium, Atlanta, GA, August 16-20, 1999. 

Available at B&W’s internet website: http://www.babcock.com/pgg/tt/pdf/BR-1683.pdf

3. Burns & McDonnell internal database for NOX reduction projects. 

4. B&W experience list September 18, 2002. 

5. “Reburning Projects in the Department of Energy’s Clean Coal Technology Demonstration 

Program”, by Mann, Al and Ruppel, Tom (Parsons Corporation), and Sarkus, Tom (National 

Energy Technical Laboratory), presented at the 2004 DOE-NETL Conference on Reburning for 

NOx Control, Morgantown, WV, May 18, 2004. A reburn-related document (an updated version of 

a poster from the May 18 Conference) is titled “Scorecard on Reburning 6/1/2004” by Al Mann and 

Tom Ruppel, Parsons Corporation, available on-line at: 

http://www.netl.doe.gov/publications/proceedings/04/NOx/posters/Reburning%20Scorecard.pdf

6. GE Energy (formerly GE-EER) experience list September 29, 2005. 

7. Fuel Tech experience list dated 1/28/2005. 

 

8. SNCR “White Paper”, Institute of Clean Air Companies, Inc. (ICAC), SNCR Committee, May 

2000, Fuel Tech website http://www.fueltechnv.com/pdf/TPP-534.pdf. 

9. RJM experience list September 3, 2004. 

10. “Improved Rich Reagent Injection (RRI) Performance For NOx Control In Coal Fired Utility 

Boilers” by Cremer, Marc A. and Wang, Huafeng D. (Reaction Engineering International), Boll, 

David E. (AmerenUE), Schindler, Edmund (RJM Corporation), and Vasquez, Edmundo RMT, Inc. 

(Alliant Energy Corp.), presented at 2003 U.S. DOE Conference on SCR and SNCR for NOx 

Control, Pittsburgh, PA, October 29-30, 2003. 

11. “Ash Impacts on SCR Catalyst Performance”, Energy & Environmental Research Center (EERC) 

of the University of North Dakota”, Benson, Steven A., Ph.D., October 2005. 
 11/2/2009 

A2 CUECost Input Summary 
CUECost - Air Pollution Control Systems Economics Spreadsheet

APC Technology Choices

Description Units Case 1 Case 2 Case 3

FGD Process Integer 1 1 1

 (1 = LSFO, 2 = LSD)

Particulate Control Integer 1 1 1

 (1 = Fabric Filter, 2 = ESP)

NOx Control Integer 1 1 1

 (1 = SCR, 2 = SNCR, 3 = LNBs, 4 = NGR)

INPUTS

Description Units Case 1 Case 2 Case 3

General Plant Technical Inputs

Location - State Abbrev. SD SD SD

MW Equivalent of Flue Gas to Control System MW 475 475 475

Net Plant Heat Rate Btu/kWhr 11,809 11,809 11,809

Plant Capacity Factor % 85% 85% 85%

Total Air Downstream of Economizer % 120% 120% 120%

Air Heater Leakage % 10% 10% 10%

Air Heater Outlet Gas Temperature °F 320 320 320

Inlet Air Temperature °F 70 70 70

Ambient Absolute Pressure In. of Hg 28.75 28.75 28.75

Pressure After Air Heater In. of H2O -15 -15 -15

Moisture in Air lb/lb dry air 0.013 0.013 0.013

Ash Split:

 Fly Ash % 80% 80% 80%

 Bottom Ash % 20% 20% 20%

Seismic Zone Integer 0 0 0

Retrofit Factor Integer 1.5 1.5 1.5

 (1.0 = new, 1.3 = medium, 1.6 = difficult)

Select Coal Integer 1 1 1

Is Selected Coal a Powder River Basin Coal? Yes / No Yes Yes Yes

Economic Inputs

Cost Basis -Year Dollars Year 2008 2008 2007

Sevice Life (levelization period) Years 30 30 30

Inflation Rate % 3% 3% 3%

After Tax Discount Rate (current $'s) % 9% 9% 9%

AFDC Rate (current $'s) % 11% 11% 11%

First-year Carrying Charge (current $'s) % 10% 10% 10%

Levelized Carrying Charge (current $'s) % 10% 10% 10%

First-year Carrying Charge (constant $'s) % 10% 10% 10%

Levelized Carrying Charge (constant $'s) % 10% 10% 10%

Sales Tax % 6% 6% 0%

Escalation Rates:

 Consumables (O&M) % 3% 3% 3%

BSGS 102709 CUECost Rev15PrelimR4.XLS, Input & Calculation Summary 1 11/2/2009, 1:01 PM
CUECost - Air Pollution Control Systems Economics Spreadsheet

 Capital Costs:

 Is Chem. Eng. Cost Index available? Yes / No Yes Yes Yes

 If "Yes" input cost basis CE Plant Index Integer 575.4 575.4 575.4

 If "No" input escalation rate. % 3% 3% 3%

Construction Labor Rate (Not Used N Calc) $/hr $35 $35 $35

Prime Contractor's Markup % 3% 3% 3%

Operating Labor Rate $/hr $48 $48 $48

Power Cost Mills/kWh 25 25 25

Steam Cost $/1000 lbs 3.5 3.5 3.5

Limestone Forced Oxidation (LSFO) Inputs

Any By-Pass around the scrubber 2 2 2

 (1 = yes, 2 = no)

Percent of By-Passed Gas % 0.0% 0.0% 0.0%

SO2 Removal Required % 95.0% 83.0% 95.0%

L/G Ratio gal / 1000 acf 125 125 110

Design Scrubber with Dibasic Acid Addition? Integer 2 2 2

 (1 = yes, 2 = no)

Adiabatic Saturation Temperature °F 132 132 135

Reagent Feed Ratio Factor 1.05 1.05 1.03

 (Mole CaCO3 / Mole SO2 removed)

Scrubber Slurry Solids Concentration Wt. % 15% 15% 15%

Stacking, Landfill, Wallboard Integer 2 2 3

 (1 = stacking, 2 = lanfill, 3 = wallboard)

Number of Absorbers Integer 1 1 1

 (Max. Capacity = 700 MW per absorber)

Absorber Material Integer 1 1 1

 (1 = alloy, 2 = RLCS)

Absorber Pressure Drop in. H2O 6 6 6

Reheat Required ? Integer 2 2 2

 (1 = yes, 2 = no)

Amount of Reheat °F 0 0 0

Reagent Bulk Storage Days 60 60 30

Reagent Cost (delivered) $/ton $24 $24 $12

Landfill Disposal Cost $/ton $4 $4 $30

Stacking Disposal Cost $/ton $2 $2 $6

Credit for Gypsum Byproduct $/ton $0 $0 $0

Maintenance Factors by Area (% of Installed Cost)

 Reagent Feed % 3% 3% 3%

 SO2 Removal % 3% 3% 3%

 Flue Gas Handling % 3% 3% 3%

 Waste / Byproduct % 3% 3% 3%

 Support Equipment % 3% 3% 3%

Contingency by Area (% of Installed Cost)

 Reagent Feed % 20% 20% 20%

 SO2 Removal % 20% 20% 20%

 Flue Gas Handling % 20% 20% 20%

 Waste / Byproduct % 20% 20% 20%

 Support Equipment % 20% 20% 20%

General Facilities by Area (% of Installed Cost)

 Reagent Feed % 10% 10% 10%

 SO2 Removal % 10% 10% 10%

BSGS 102709 CUECost Rev15PrelimR4.XLS, Input & Calculation Summary 2 11/2/2009, 1:01 PM
CUECost - Air Pollution Control Systems Economics Spreadsheet

 Flue Gas Handling % 10% 10% 10%

 Waste / Byproduct % 10% 10% 10%

 Support Equipment % 10% 10% 10%

Engineering Fees by Area (% of Installed Cost)

 Reagent Feed % 10% 10% 10%

 SO2 Removal % 10% 10% 10%

 Flue Gas Handling % 10% 10% 10%

 Waste / Byproduct % 10% 10% 10%

 Support Equipment % 10% 10% 10%

Lime Spray Dryer (LSD) Inputs

SO2 Removal Required % 90% 83% 90%

Adiabatic Saturation Temperature °F 132 132 135

Flue Gas Approach to Saturation °F 20 20 25

Spray Dryer Outlet Temperature °F 152 152 160

Reagent Feed Ratio Factor 0.92 0.85 0.92

 (Mole CaO / Mole Inlet SO2)

Recycle Rate Factor 30 30 30

 (lb recycle / lb lime feed)

Recycle Slurry Solids Concentration Wt. % 35% 35% 35%

Number of Absorbers Integer 2 2 1

 (Max. Capacity = 300 MW per spray dryer)

Absorber Material Integer 1 1 2

 (1 = alloy, 2 = RLCS)

Spray Dryer Pressure Drop in. H2O 5 5 5

Reagent Bulk Storage Days 60 60 30

Reagent Cost (delivered) $/ton $145 $145 $60

Dry Waste Disposal Cost $/ton $4 $4 $30

Maintenance Factors by Area (% of Installed Cost)

 Reagent Feed % 2% 2% 2%

 SO2 Removal % 2% 2% 2%

 Flue Gas Handling % 2% 2% 2%

 Waste / Byproduct % 2% 2% 2%

 Support Equipment % 2% 2% 2%

Contingency by Area (% of Installed Cost)

 Reagent Feed % 20% 20% 20%

 SO2 Removal % 20% 20% 20%

 Flue Gas Handling % 20% 20% 20%

 Waste / Byproduct % 20% 20% 20%

 Support Equipment % 20% 20% 20%

General Facilities by Area (% of Installed Cost)

 Reagent Feed % 10% 10% 10%

 SO2 Removal % 10% 10% 10%

 Flue Gas Handling % 10% 10% 10%

 Waste / Byproduct % 10% 10% 10%

 Support Equipment % 10% 10% 10%

Engineering Fees by Area (% of Installed Cost)

 Reagent Feed % 10% 10% 10%

 SO2 Removal % 10% 10% 10%

 Flue Gas Handling % 10% 10% 10%

 Waste / Byproduct % 10% 10% 10%

 Support Equipment % 10% 10% 10%

BSGS 102709 CUECost Rev15PrelimR4.XLS, Input & Calculation Summary 3 11/2/2009, 1:01 PM
CUECost - Air Pollution Control Systems Economics Spreadsheet

Particulate Control Inputs

Outlet Particulate Emission Limit lbs/MMBtu 0.015 0.015 0.015

Fabric Filter:

 Pressure Drop in. H2O 9 9 9

 Type (1 = Reverse Gas, 2 = Pulse Jet) Integer 1 2 1

 Gas-to-Cloth Ratio ACFM/ft2 2.3 3.5 2.3

 Bag Material (RGFF fiberglass only) Integer 1 3 1

 (1 = Fiberglass, 2 = Nomex, 3 = Ryton)

 Bag Diameter inches 12 6 12

 Bag Length feet 30 26 30

 Bag Reach 3 3 3

 Compartments out of Service % 10% 10% 10%

 Bag Life Years 5 3 5

 Maintenance (% of installed cost) % 5% 5% 5%

 Contingency (% of installed cost) % 20% 20% 20%

 General Facilities (% of installed cost) % 10% 10% 10%

 Engineering Fees (% of installed cost) % 10% 10% 10%

ESP:

 Strength of the electric field in the ESP = E kV/cm 10.0 10.0 10.0

 Plate Spacing in. 12 12 16

 Plate Height ft. 36 36 36

 Pressure Drop in. H2O 3 3 2

 Maintenance (% of installed cost) % 5% 5% 5%

 Contingency (% of installed cost) % 20% 20% 20%

 General Facilities (% of installed cost) % 10% 10% 10%

 Engineering Fees (% of installed cost) % 10% 10% 10%

NOx Control Inputs

Selective Catalytic Reduction (SCR) Inputs

NH3/NOX Stoichiometric Ratio NH3/NOX 0.8 0.8 0.800641299

NOX Reduction Efficiency Fraction 0.80 0.84 0.70

Inlet NOx lbs/MMBtu 0.5 0.65 0.15

Space Velocity (Calculated if zero) 1/hr 0 0 0

Overall Catalyst Life years 2 2 3

Ammonia Cost $/ton 325 325 325

Catalyst Cost $/ft3 150 150 150

Solid Waste Disposal Cost $/ton 11.48 11.48 11.48

Maintenance (% of installed cost) % 1.5% 1.5% 1.5%

Contingency (% of installed cost) % 20% 20% 20%

General Facilities (% of installed cost) % 5% 5% 5%

Engineering Fees (% of installed cost) % 10% 10% 10%

Number of Reactors integer 2 2 2

Number of Air Preheaters integer 2 2 2

Selective NonCatalytic Reduction (SNCR) Inputs

Reagent 1:Urea 2:Ammonia 1 1 1

Number of Injector Levels integer 3 3 3

Number of Injectors integer 18 18 18

Number of Lance Levels integer 0 0 0

BSGS 102709 CUECost Rev15PrelimR4.XLS, Input & Calculation Summary 4 11/2/2009, 1:01 PM
CUECost - Air Pollution Control Systems Economics Spreadsheet

Number of Lances integer 0 0 0

Steam or Air Injection for Ammonia integer 1 1 1

NOX Reduction Efficiency Fraction 0.30 0.60 0.46

Inlet NOx lbs/MMBtu 0.5 0.5 0.65

NH3/NOX Stoichiometric Ratio NH3/NOX 2 4 2

Urea/NOX Stoichiometric Ratio Urea/NOX 2 4 2

Urea Cost $/ton 380 380 380

Ammonia Cost $/ton 325 325 325

Water Cost $/1,000 gal 0.407 0.407 0.407

Maintenance (% of installed cost) % 1.5% 1.5% 1.5%

Contingency (% of installed cost) % 20% 20% 20%

General Facilities (% of installed cost) % 5% 5% 5%

Engineering Fees (% of installed cost) % 10% 10% 10%

Low NOX Burner Technology Inputs

NOX Reduction Efficiency fraction 0.35 0.35 0.35

Boiler Type T:T-fired, W:Wall T T T

Retrofit Difficulty

L:Low, A:Average, 

H:High A A A

Maintenance Labor (% of installed cost) % 0.8% 0.8% 0.8%

Maintenance Materials (% of installed cost) % 1.2% 1.2% 1.2%

Natural Gas Reburning Inputs

NOX Reduction Efficiency fraction 0.61 0.61 0.61

Gas Reburn Fraction fraction 0.15 0.15 0.15

Waste Disposal Cost $/ton 11.48 11.48 11.48

Natural Gas Cost $/MMBtu 2.31 2.31 2.31

Maintenance (% of installed cost) % 1.5% 1.5% 1.5%

Contingency (% of installed cost) % 20% 20% 20%

General Facilities (% of installed cost) % 2% 2% 2%

Engineering Fees (% of installed cost) % 10% 10% 10%

Sulfuric Acid Mist Control Inputs

BSGS 102709 CUECost Rev15PrelimR4.XLS, Input & Calculation Summary 5 11/2/2009, 1:01 PM
 11/2/2009 

A3 Summary of Modeling Results 
Modeling Report for a BART 

Assessment of the Big Stone I 

Coal-Fired Power Plant, 

Big Stone City, South Dakota 

Part 2 – BART Controls 

October 2009 

Prepared For: 

Big Stone I 

Otter Tail Power Company, 

Big Stone City, South Dakota 

Prepared By: 

TRC Environmental Corporation 

650 Suffolk Street 

Lowell, Massachusetts 01854 

(978) 970-5600 
i 

TABLE OF CONTENTS 

Page 

1. INTRODUCTION .......................................................................................................................... 1-1

2. SOURCE DESCRIPTION ............................................................................................................ 2-1

3. GEOPHYSICAL AND METEOROLOGICAL DATA, AIR QUALITY MODELING 

OPTIONS ........................................................................................................................................ 3-1

4. RESULTS ....................................................................................................................................... 4-1

5. REFERENCES ............................................................................................................................... 5-1

LIST OF FIGURES 

Page 

Figure 3-1. Terrain elevations for the CALMET and CALPUFF modeling domain at 4 km 

resolution. The locations of the Big Stone facility and Class I areas are also shown. ..... 3-3 

LIST OF TABLES 

Page 

Table 2-1: Point Source Parameters and Emission Rates .................................................................. 2-2 

Table 2-2: PM10 Size Distribution ..................................................................................................... 2-3 

Table 2-3: PM10 Speciation and Size Distribution ............................................................................. 2-4 

Table 4-1. Visibility Impacts for 2002 .............................................................................................. 4-2 

Table 4-1. Visibility Impacts for 2002 (continued). .......................................................................... 4-3 

Table 4-2. Visibility Impacts for 2006. ............................................................................................. 4-4 

Table 4-2. Visibility Impacts for 2006 (continued). .......................................................................... 4-5 

Table 4-3. Visibility Impacts for 2007. ............................................................................................. 4-6 

Table 4-3. Visibility Impacts for 2007 (continued). .......................................................................... 4-7 
Introduction 1-1 

1. INTRODUCTION 

TRC Environmental Corporation has conducted a site-specific BART (Best Available Retrofit 

Technology) modeling assessment of the Big Stone I coal-fired power plant facility located near 

Milbank and Big Stone City in South Dakota to determine if this facility is subject to BART 

controls on emissions. Part I of the October 2009 report presented a modeling assessment of 

baseline emissions from the Big Stone I power plant facility to determine whether the facility is 

subject to BART controls. This report (Part 2) represents the results of 10 emission control 

scenarios. 

On July 6, 2005 the U.S. Environmental Protection Agency (U.S. EPA) published in the Federal 

Register the “Regional Haze Regulations and Guidelines for Best Available Retrofit Technology 

(BART) Determinations” (40 CFR Part 51). The regional haze rule requires States to submit 

implementation plans (SIPs) to address regional haze visibility impairment in 156 Federallyprotected parks and wilderness areas, commonly referred to as “Class 1 Areas”. The final rule 

addresses BART-eligible sources, which are defined as sources that have the potential to emit 

250 tons or more of a visibility-impairing air pollutant, were put in place between August 7, 1962 

and August 7, 1977 and whose operations fall within one or more of 26 specifically listed source 

categories, of which Coal-Fired Power Plants are one. 

The modeling described in this report is consistent with modeling described in baseline report. 

All CALMET/CALPUFF switches used in this BART analysis are identical with the switches 

used and described in previous report. In this report, ten BART control scenarios were analyzed 

and results of these modeling presented. 

The purpose of the modeling is to assess the visibility impacts of sulfur dioxide (SO2), particulate 

matter (PM) and nitrogen oxides (NOx) emissions from the Big Stone I boiler and compare the 

impacts to the 0.5 change in deciview threshold at all the federally mandatory Class I areas. Since 

there is no Class I area within the 300 km radius usually applied, the South Dakota Department of 

Environment and Natural Resources requested that the Class I areas between 300 km and up to 

625 km away from the Big Stone I facility sources be modeled. A total of eight Class I areas are 

located between these distances: two wilderness areas: Boundary Waters Canoe Area Wilderness 

and Rainbow Lake Wilderness, one National Wildlife Refuge (NWR): Lostwood and five 

National Parks: Voyageurs NP, Theodore Roosevelt NP, Badlands NP, Wind Cave NP and Isle 

Royale NP. However, Rainbow Lake Wilderness is one of two Class I areas where the visibility 

analysis is not required (http://www.dnr.state.wi.us/org/aw/air/modeling/ psd.htm), so it is not 

included in the modeling analysis. The MM5 datasets distributed by WRAP did not extend far 

enough in the East to include the Isle Royale NP or cover all of the Boundary Waters Class I area. 

The re-extracted MM5 data for 2002 and new MM5 domains for 2006 and 2007 include these 

areas. 

The CALMET and CALPUFF non-steady-state models (Scire et al., 2000a,b) are recommended 

by the U.S. EPA (Federal Register, 6 July 2005) to perform source-specific subject-to-BART 
Introduction 1-2 

screening. The CALPUFF system was therefore used for this modeling analysis. The U.S. EPA 

has promulgated the CALPUFF modeling system as a Guideline Model for Class I impact 

assessments and other long range transport applications or near field applications involving 

complex flows (U.S. EPA, 2000), and the model is recommended by both the Federal Land 

Managers (FLM) Air Quality Workgroup (FLAG, 2000) and the Interagency Workgroup on Air 

Quality Modeling (IWAQM, 1998). The CALPUFF modeling system is also recommended in 

new proposed guidance by the FLMs (FLAG, 2008). On August 31, 2009 EPA issued new 

recommendations on CALMET switch settings. The current modeling is based on the August 

2009 recommendations. 

The Big Stone I BART modeling analysis was performed with the EPA-approved Version 5.8 of 

the CALMET and CALPUFF models. Version 6.221 of CALPOST was used because it contains 

the FLM-approved implementation of Method 8 (FLAG, 2008), but in other respects is identical 

to the EPA-approved Version 5.6394. 

CALMET is a diagnostic meteorological model that produces three-dimensional wind fields 

based on parameterized treatments of terrain effects such as slope flows and terrain blocking 

effects. Normally, meteorological observations are blended with gridded data from the NCARPSU Mesoscale Model, Version 5 (MM5). For this evaluation, MM5 data were generated by 

TRC with a 12-km grid spacing for two years (2006 and 2007) to define the initial guess wind 

fields. For 2002, 12-km MM5 data were re-extracted from the EPA MM5 dataset to cover entire 

region including the Isle Royale NP to the east. 

CALPUFF is a non-steady-state puff dispersion model. It accounts for spatial changes in the 

CALMET-produced meteorological fields, variability in surface conditions (elevation, surface 

roughness, vegetation type, etc.), chemical transformation, wet removal due to rain and snow, dry 

deposition, and terrain influences on plume interaction with the surface. CALPUFF contains a 

module to compute visibility effects, based on a humidity-dependent relationship between 

particulate matter concentrations and light extinction, as well as wet and dry acid deposition 

fluxes. The meteorological and dispersion modeling simulations were conducted for three years 

(2002, 2006 and 2007). SO2, SO4, PM, and NOx, emissions and their secondary products resulting 

from chemical conversions from the Big Stone I facility were modeled and their impacts on 

visibility evaluated at receptors in the Class I areas. Visibility impacts were estimated with the new 

FLM-recommended visibility algorithm and monthly average relative humidity adjustment factors 

(Method 8 in Version 6.221). 

This report outlines the techniques and data sources used in the BART analyses. In Section 2, a 

general description of the source configurations for the baseline case and 10 control scenarios are 

provided. Section 3 refers to the baseline report where descriptions of the site characteristics and 

data bases (meteorological, geophysical, and aerometric) were provided, as well as an overview 

of the CALMET and CALPUFF models settings and parameters that were used in the analysis. 

The results of the control scenario evaluations are summarized in Section 4. 
Source Description 2-1 

2. SOURCE DESCRIPTION 

The 450-megawatt Big Stone I facility is a coal-fired power plant situated close to Big Stone City and 

Milbank in Grant County, South Dakota, at the border of Minnesota State. A BART applicability 

analysis was completed for the facility to determine those sources subject to the BART controls. The 

BART-eligible source is the Big Stone I cyclone-fired boiler with one stack 152 meters (498 feet) high. 

The proposed emissions for the BART analysis were described in a Modeling Protocol dated June 2009. 

These emissions were reviewed and approved by SD DENR. In addition, 10 different control scenarios 

were modeled. Table 2-1 shows the source parameters and emission rates for the source considered in 

this report both for the baseline case and ten control scenarios. The highest 24-hour average actual 

emission rates of SO2, NOx and PM under normal conditions over the 2001-2003 period were used for 

the baseline case in this analysis. 

As shown in Table 2-2, the filterable PM10 are divided into a particle size distribution based on AP-42, 

Table 1.1-6 for baghouse controlled emissions because the facility currently uses a fabric filter for PM 

control. Approximately 57.6% of the filterable mass is in the fine (PM2.5) size category, and 42.4% in 

the coarse (2.5 to 10 μm diameter) size range. Each of the particle size categories was modeled as a 

separate PM species in CALPUFF. The filterable PM10 emission rate is reported by the facility at 

10.48 g/s (83.2 lb/hr). Based on AP-42 Table 1.1-5, the total condensable PM10 is approximately 

0.01 lb/mmBtu based on approximately 0.4% sulfur coal or 7.07 g/sec (56.1 lb/hr) assuming an heat 

input of 5609 mmBtu/hr. This estimate is consistent with the stack test data (August, 2006) at Otter Tail 

Power’s Hoot Lake Plant, Unit 2, (which burns PRB coal) where the ratio of the filterable/total PM10

ratio was 0.66, resulting in a 2/3 filterable and 1/3 condensable split to the total PM10.

1

Elemental Carbon (EC) emissions were assumed to be 3.7% of the fine filterable fraction based on U.S. 

EPA (2002) and were assigned to the smallest particle size category. The primary H2SO4 emissions are 

0.454 g/s (3.604 lb/hr) based on annual emission inventories and Toxic Release Inventory reports. The 

remaining condensable emissions were assigned to organic carbon and distributed equally into the two 

smallest particle size categories. 

Table 2-3 provides a summary of the PM10 speciation and size distribution. 

Note that since all Class I areas are more than 50 km away from the facility, as recommended by the 

Federal Land Managers (FLMs) (US Fish and Wildlife, National Park Service and U.S. Forest Service), 

no downwash computations was performed. 

 

1

 AP-42 Table 1.1-8 was not used to estimate the particulate matter size distribution for Big Stone I because the emission 

factors were derived for cyclones burning bituminous coal, not sub-bituminous coal which is burned at Big Stone I. 
Source Description 2-2 

Table 2-1: Point Source Parameters and Emission Rates 

Main Stack 

LCC1

East 

(km) 

LCC1

North 

(km) 

Stack 

Ht 

(m) 

Base 

Elevation 

(m) 

Stack 

Diameter 

(m) 

Exit 

Velocity 

(m/s) 

Exit 

Temp. 

(K) 2

SO2

Emission

Rate 

(g/s) 

H2SO4 

Emission 

Rate 

(g/s) 

E

Baseline Case 38.141 587.875 151.79 328.90 7.37 20.14 423.1 608.9 0.454 Control 1 Over-fire Air (OFA) 

Presumptive Dry FGD '' '' '' '' '' 19.57 352.6 106.0 '' 

Control 2 OFA 

Presumptive Wet FGD '' '' '' '' '' 18.23 330.4 106.0 '' 

Control 3 OFA 

Dry FGD at 90% Control '' '' '' '' '' 19.57 352.6 63.6 '' 

Control 4 OFA 

Wet FGD at 95% Control '' '' '' '' '' 18.23 330.4 30.4 '' 

Control 5 Separated OFA (SOFA) 

Presumptive Dry FGD '' '' '' '' '' 19.57 352.6 106.0 '' 

Control 5a SOFA 

Dry FGD at 90% Control '' '' '' '' '' 19.57 352.6 63.6 '' 

Control 5b SOFA 

Wet FGD at 95% Control '' '' '' '' '' 18.23 330.4 30.4 '' 

Control 6 SNCR with SOFA, 

Presumptive Dry FGD '' '' '' '' '' 19.57 352.6 106.0 '' 

Control 7 RRI+SNCR with SOFA 

Presumptive Dry FGD '' '' '' '' '' 19.57 352.6 106.0 '' 

Control 8 SCR with SOFA 

Presumptive Dry FGD '' '' '' '' '' 19.57 352.6 106.0 '' 

1 Lambert Conformal Projection with an origin of 40.0N, 97.0W and standard parallels at 33N and 45N. Datum is NWS-84. 2 The PM technology for all modeling scenarios is the existing pulse-jet fabric filter. 
Source Description 2-3 

Table 2-2: PM10 Size Distribution1 

Particle Size2

(μm) 

Cumulative Mass 

(PM) 

(%) 

Cumulative Mass 

(PM10) 

(%) 

15 97 - 10 92 100 

6 77 83.7 

2.5 53 57.6 

1.25 31 33.7 1.00 25 27.2 

1 From AP-42, Table 1.1-6, Cumulative particle size distribution and size-specific emission factors for dry bottom boilers burning 

bituminous and subbituminous coal. 2 Expressed as aerodynamic equivalent diameter. 
Source Description 2-4 

Table 2-3: PM10 Speciation and Size Distribution 

input Data: H2SO4 PM10 PM2.5

 g/s g/s g/s 

PM10 and H2SO4 Emissions 

(g/s) 0.454 17.550 13.106 

filterable 

condensable % 59.7% 

 g/s 

 10.480   AP-42, Table 1.1-6  coarse coarse soil soil soil soil EC H2SO4 OC  PM800 PM425 PM187 PM112 PM081 PM056 PM056 PM081 

6.00 - 

10.00 2.50-6.00 

1.25-

2.50 

1.00-

1.25 0.625-1.00 

0.50-

0.625 0.50-0.625 

0.625-

1.00 

16.3% 26.1% 23.9% 6.5% 12.0% 15.2% 57.6% 50.0% 

EC % of filterable 96.3% 3.7% 1

inorganic % of g/s g/s g/s g/s g/s g/s g/s g/s g/s 

condensable 1.708 2.735 2.412 0.656 1.211 1.534 0.223 0.454 3.308 

 inputs to POSTUTIL: 

Extinction coefficient 0.6 0.6 1 1 1 1 10 3*f(RH) 4 

coarse coarse soil soil soil soil EC H2SO4 OC 

PM800 PM425 PM187 PM112 PM081 PM056 PM056 PM081 

g/s g/s g/s g/s g/s g/s g/s g/s g/s 

1.708 2.735 2.412 0.656 1.211 1.534 0.223 0.454 3.308 
Geophysical and Meteorological Data 3-1 

3. GEOPHYSICAL AND METEOROLOGICAL DATA, AIR QUALITY 

MODELING OPTIONS 

The South Dakota Department of Environment and Natural Resources requested that the eight Class I 

areas shown in Figure 3-1 be considered in the BART analysis. Rainbow Lake Wilderness is one of two 

Class I areas where the visibility analysis is not required so it has been removed from the present 

analysis (see http://www.dnr.state.wi.us/org/aw/air/modeling/psd.htm). The MM5 dataset for this 

analysis were extended to include the Isle Royale National Park as well as all of the Boundary Waters 

Class I area. 

Processing of the topography and land use for the domain shown in Figure 3-1 was described in detail in 

Section 3 of the October 2009 Big Stone Report (Report). In the same Report, all meteorological data 

and ozone data used in the modeling have been discussed. Locations of the stations were presented in 

Figures 3-3 and 3-4 of the Report. 

CALMET was run with 4-km grid resolution using 12-km MM5 data for initial guess fields. CALMET 

and CALPUFF use terrain-following coordinates. In order to cover a large enough area for the refined 

analysis covering all seven Class I areas within a single domain, and including a buffer of at least 50 km 

around each Class I area, the domain dimensions of 1250 km x 720 km were used. For a 4-km grid 

spacing, this amounts to 313 x 181 grid cells. In the vertical, a stretched grid was used with finer 

resolution in the lower layers and somewhat coarser resolution aloft thus allowing adequate 

representation of the mixed layer. The ten vertical levels were centered at: 10, 30, 60, 120, 240, 480, 

920, 1600, 2500 and 3500 meters. 

CALMET and CALPUFF were run for three years, 2002, 2006 and 2007. A network of discrete 

receptors derived from the list of receptors developed by the National Park Service (NPS) are located 

within the boundaries of the seven Class I areas modeled: Boundary Water Canoe Area Wilderness, 

Voyageur National Park, Badlands National Park, Wind Cave National Park, Lostwood National 

Wildlife Refuge, Theodore Roosevelt National Park and Isle Royale National Park. 

Meteorological modeling options including initial guess fields and step 1 and 2 wind fields, dispersion 

modeling options and visibility calculations were all described in Section 4 of the October 2009 report. 

Calculations of the impact of the simulated plume particulate matter component concentrations on light 

extinction were carried out with the CALPOST postprocessor following the new proposed FLAG 

(2008) guidance. A revised new IMPROVE algorithm to compute the extinction (1/Mm) has been 

developed by the IMPROVE steering committee for estimating light extinction from particulate matter. 

That algorithm provides a better correspondence between the measured visibility and that calculated from 

particulate matter component concentrations (Tombach, 2006): 

To represent background natural conditions, monthly background concentrations must be entered into 

the CALPOST input control file for all aerosols defining the background. The WRAP Protocol (2006) 

recommendations for natural conditions background are to use all three types of EPA default Natural 

Conditions: Best 20% Days, Annual Average and Worst 20% Days. In “Guidance for Estimating 

Visibility Conditions Under the Regional Haze Rule” (EPA, 2003), these three default values are 

defined only by their extinction coefficient in Mm-1. For CALPOST Method 8, explicit background 
Geophysical and Meteorological Data 3-2 

concentrations are required to allow the computation of the small and large sulfate particulates, nitrate 

particulates and organic carbon. So, in this analysis, the annual averaged background conditions were 

used to define the natural background for each of the seven Class I areas, following FLAG (2008). The 

concentrations used as background for each of the seven Class I areas are summarized in Table 4-2 of 

the October 2009 report. These concentrations were used to compute the natural background light 

extinction following the revised IMPROVE formulae described above, for each of the Class I areas. 

Tables 4-3, 4-4, and 4-5 in October 2009 report, provide the monthly f(RH) values for each of the seven 

Class I areas, that are used to compute extinction coefficients for hygroscopic species, respectively for 

small ammonium sulfate and ammonium nitrate particles, large ammonium sulfate and ammonium 

nitrate particles, and sea salt particles. 

The 8th highest (98th percentile) predicted light extinction change for each year modeled was compared 

to the threshold value of 0.5 deciview. 
Geophysical and Meteorological Data 3-3 

Figure 3-1. Terrain elevations for the CALMET and CALPUFF modeling domain at 4 km resolution. The locations of the 

Class I areas are also shown. 

-500 -400 -300 -200 -100 0 100 200 300 400 500 600 

LCC x (km), NWS-84

300400500600700800900

1000

LCC x (km), NWS-84

Projection:LCC; Center: 40N, 98WStandards: 20N, 60NDatum: NWS-84

FACILITY

WindCave

Badlands

TheodoreRoosevelt

Lostwood

Voyageurs Boundary

Waters

Isle R
Results 4-1 

4. RESULTS 

The results for the BART analysis for the Big Stone I facility are presented in this section. The analysis 

consists of evaluating the visibility impact (percent change in light extinction due to the sources 

measured in deciview) at all the Class I areas modeled. The results are presented in three tables for the 

baseline case and ten control scenarios, each table gathering the impact at seven Class I areas for each of 

the years modeled: Table 4-1 for 2002, Table 4-2 for 2006 and Table 4-3 for 2007. The change in light 

extinction due to the source is compared to the annual average natural background light extinction. The 

interpretation of the results is done by comparing the 98th percentile of delta deciview for each year to 

the 0.5 delta deciview threshold. Analysis is performed by using CALPOST Method 8. 
Results 4-2 

Table 4-1. Visibility Impacts for 2002 

Park Max Delta 

Deciview 

4th Highest 

(99%) 

8th Highest 

(98%) 

Nb. 

Exceed. 

> 5% 

Nb. 

Exceed. 

> 10% 

Baseline 

Boundary Waters 1.315 0.837 0.574 14 1 

Voyageurs 2.162 0.690 0.623 9 3 

Wind Cave 0.873 0.475 0.305 3 0 

Theodore Roosevelt 1.390 0.555 0.215 4 1 

Lostwood 0.564 0.388 0.232 2 0 

Badlands 0.762 0.671 0.452 7 0 

Isle Royale 1.182 0.789 0.629 10 2 

Control 1 

Boundary Waters 0.685 0.563 0.330 5 0 

Voyageurs 1.252 0.541 0.329 4 1 

Wind Cave 0.485 0.258 0.101 0 0 

Theodore Roosevelt 0.530 0.298 0.092 1 0 

Lostwood 0.329 0.171 0.111 0 0 

Badlands 0.462 0.342 0.223 0 0 

Isle Royale 0.780 0.471 0.377 2 0 

Control 2 

Boundary Waters 0.716 0.639 0.360 5 0 

Voyageurs 1.191 0.586 0.349 5 1 

Wind Cave 0.417 0.262 0.095 0 0 

Theodore Roosevelt 0.476 0.278 0.099 0 0 

Lostwood 0.320 0.155 0.118 0 0 

Badlands 0.549 0.315 0.234 1 0 

Isle Royale 0.809 0.497 0.367 3 0 

Control 3 

Boundary Waters 0.647 0.542 0.319 5 0 

Voyageurs 1.210 0.534 0.307 4 1 

Wind Cave 0.473 0.244 0.093 0 0 

Theodore Roosevelt 0.453 0.287 0.087 0 0 

Lostwood 0.317 0.150 0.109 0 0 

Badlands 0.441 0.326 0.219 0 0 

Isle Royale 0.758 0.448 0.363 2 0 

Control 4 

Boundary Waters 0.687 0.593 0.350 5 0 

Voyageurs 1.121 0.574 0.312 4 1 

Wind Cave 0.379 0.237 0.080 0 0 

Theodore Roosevelt 0.421 0.260 0.084 0 0 

Lostwood 0.298 0.138 0.103 0 0 

Badlands 0.505 0.281 0.225 1 0 

Isle Royale 0.762 0.456 0.351 2 0 
Results 4-3 

Table 4-1. Visibility Impacts for 2002 (continued). 

Park Max Delta 

Deciview 

4th Highest 

(99%) 

8th Highest 

(98%) 

Nb. 

Exceed. > 

5% 

Nb. 

Exceed. > 

10% 

Control 5 

Boundary Waters 0.551 0.449 0.264 2 0 

Voyageurs 0.997 0.426 0.263 3 0 

Wind Cave 0.385 0.206 0.083 0 0 

Theodore Roosevelt 0.458 0.237 0.076 0 0 

Lostwood 0.263 0.144 0.089 0 0 

Badlands 0.370 0.272 0.169 0 0 

Isle Royale 0.618 0.375 0.298 2 0 

Control 5a 

Boundary Waters 0.513 0.428 0.250 2 0 

Voyageurs 0.955 0.419 0.249 3 0 

Wind Cave 0.372 0.191 0.074 0 0 

Theodore Roosevelt 0.380 0.227 0.069 0 0 

Lostwood 0.251 0.124 0.085 0 0 

Badlands 0.349 0.256 0.165 0 0 

Isle Royale 0.595 0.355 0.285 2 0 

Control 5b 

Boundary Waters 0.537 0.465 0.274 2 0 

Voyageurs 0.876 0.449 0.244 2 0 

Wind Cave 0.296 0.184 0.063 0 0 

Theodore Roosevelt 0.325 0.204 0.066 0 0 

Lostwood 0.234 0.109 0.081 0 0 

Badlands 0.396 0.219 0.174 0 0 

Isle Royale 0.594 0.357 0.274 2 0 

Control 6 

Boundary Waters 0.418 0.335 0.200 0 0 

Voyageurs 0.740 0.309 0.196 2 0 

Wind Cave 0.283 0.154 0.072 0 0 

Theodore Roosevelt 0.384 0.176 0.063 0 0 

Lostwood 0.196 0.118 0.075 0 0 

Badlands 0.278 0.203 0.120 0 0 

Isle Royale 0.464 0.275 0.221 0 0 

Control 7 

Boundary Waters 0.285 0.221 0.137 0 0 

Voyageurs 0.481 0.192 0.130 0 0 

Wind Cave 0.180 0.104 0.070 0 0 

Theodore Roosevelt 0.309 0.115 0.050 0 0 

Lostwood 0.129 0.085 0.051 0 0 

Badlands 0.187 0.135 0.090 0 0 

Isle Royale 0.310 0.174 0.142 0 0 

Control 8 

Boundary Waters 0.198 0.143 0.097 0 0 

Voyageurs 0.309 0.125 0.086 0 0 

Wind Cave 0.119 0.072 0.053 0 0 

Theodore Roosevelt 0.262 0.074 0.036 0 0 

Lostwood 0.085 0.053 0.037 0 0 

Badlands 0.127 0.102 0.079 0 0 

Isle Royale 0.207 0.113 0.092 0 0 
Results 4-4 

Table 4-2. Visibility Impacts for 2006. 

Park Max Delta 

Deciview 

4th Highest 

(99%) 

8th Highest 

(98%) 

Nb. 

Exceed. 

> 5% 

Nb. 

Exceed. 

> 10% 

Baseline 

Boundary Waters 2.572 1.183 0.790 16 5 

Voyageurs 1.578 0.862 0.574 11 2 

Wind Cave 0.454 0.302 0.120 0 0 

Theodore Roosevelt 2.232 0.772 0.459 6 3 

Lostwood 1.110 0.662 0.385 5 1 

Badlands 1.002 0.519 0.481 7 1 

Isle Royale 1.806 0.635 0.506 8 2 

Control 1 

Boundary Waters 1.375 0.799 0.548 9 3 

Voyageurs 1.262 0.554 0.399 5 1 

Wind Cave 0.273 0.162 0.024 0 0 

Theodore Roosevelt 1.234 0.469 0.247 3 1 

Lostwood 0.619 0.355 0.168 2 0 

Badlands 0.504 0.319 0.176 1 0 

Isle Royale 1.010 0.467 0.296 2 1 

Control 2 

Boundary Waters 1.405 0.830 0.546 11 3 

Voyageurs 1.549 0.594 0.494 7 2 

Wind Cave 0.266 0.162 0.027 0 0 

Theodore Roosevelt 1.116 0.454 0.244 3 1 

Lostwood 0.588 0.366 0.171 3 0 

Badlands 0.482 0.326 0.199 0 0 

Isle Royale 1.014 0.462 0.273 3 1 

Control 3 

Boundary Waters 1.319 0.780 0.534 8 3 

Voyageurs 1.218 0.540 0.391 5 1 

Wind Cave 0.260 0.150 0.023 0 0 

Theodore Roosevelt 1.196 0.455 0.234 3 1 

Lostwood 0.594 0.339 0.153 2 0 

Badlands 0.482 0.308 0.172 0 0 

Isle Royale 0.983 0.454 0.287 2 0 

Control 4 

Boundary Waters 1.313 0.793 0.521 10 3 

Voyageurs 1.469 0.571 0.464 6 1 

Wind Cave 0.244 0.139 0.025 0 0 

Theodore Roosevelt 1.052 0.431 0.230 3 1 

Lostwood 0.554 0.335 0.144 2 0 

Badlands 0.443 0.306 0.191 0 0 

Isle Royale 0.966 0.440 0.250 3 0 
Results 4-5 

Table 4-2. Visibility Impacts for 2006 (continued). 

Park Max Delta 

Deciview 

4th Highest 

(99%) 

8th Highest 

(98%) 

Nb. 

Exceed. > 

5% 

Nb. 

Exceed. > 

10% 

Control 5 

Boundary Waters 1.109 0.635 0.433 6 2 

Voyageurs 1.013 0.440 0.314 2 1 

Wind Cave 0.216 0.132 0.019 0 0 

Theodore Roosevelt 0.987 0.372 0.199 2 0 

Lostwood 0.494 0.281 0.136 0 0 

Badlands 0.401 0.252 0.137 0 0 

Isle Royale 0.804 0.366 0.235 2 0 

Control 5a 

Boundary Waters 1.051 0.615 0.419 6 2 

Voyageurs 0.967 0.426 0.306 2 0 

Wind Cave 0.204 0.120 0.018 0 0 

Theodore Roosevelt 0.948 0.358 0.186 2 0 

Lostwood 0.468 0.265 0.124 0 0 

Badlands 0.378 0.242 0.133 0 0 

Isle Royale 0.777 0.355 0.226 2 0 

Control 5b 

Boundary Waters 1.036 0.622 0.407 6 2 

Voyageurs 1.160 0.449 0.365 3 1 

Wind Cave 0.189 0.109 0.019 0 0 

Theodore Roosevelt 0.827 0.336 0.180 2 0 

Lostwood 0.430 0.259 0.114 0 0 

Badlands 0.344 0.237 0.147 0 0 

Isle Royale 0.758 0.342 0.195 1 0 

Control 6 

Boundary Waters 0.837 0.468 0.318 3 0 

Voyageurs 0.759 0.325 0.228 2 0 

Wind Cave 0.161 0.103 0.016 0 0 

Theodore Roosevelt 0.736 0.274 0.150 1 0 

Lostwood 0.369 0.209 0.103 0 0 

Badlands 0.297 0.186 0.098 0 0 

Isle Royale 0.595 0.268 0.174 1 0 

Control 7 

Boundary Waters 0.560 0.299 0.202 1 0 

Voyageurs 0.502 0.204 0.157 1 0 

Wind Cave 0.107 0.071 0.014 0 0 

Theodore Roosevelt 0.479 0.176 0.101 0 0 

Lostwood 0.244 0.138 0.082 0 0 

Badlands 0.227 0.120 0.066 0 0 

Isle Royale 0.382 0.169 0.115 0 0 

Control 8 

Boundary Waters 0.373 0.186 0.136 0 0 

Voyageurs 0.328 0.128 0.107 0 0 

Wind Cave 0.071 0.047 0.012 0 0 

Theodore Roosevelt 0.306 0.111 0.070 0 0 

Lostwood 0.162 0.092 0.064 0 0 

Badlands 0.188 0.079 0.060 0 0 

Isle Royale 0.239 0.104 0.077 0 0 
Results 4-6 

Table 4-3. Visibility Impacts for 2007. 

Park Max Delta 

Deciview 

4th Highest 

(99%) 

8th Highest 

(98%) 

Nb. 

Exceed. 

> 5% 

Nb. 

Exceed. 

> 10% 

Baseline 

Boundary Waters 3.574 1.351 1.079 25 9 

Voyageurs 2.062 1.376 0.724 19 5 

Wind Cave 1.671 0.591 0.325 4 2 

Theodore Roosevelt 0.744 0.491 0.322 3 0 

Lostwood 0.959 0.722 0.409 6 0 

Badlands 2.202 0.698 0.471 6 2 

Isle Royale 1.224 0.745 0.665 13 2 

Control 1 

Boundary Waters 2.018 0.874 0.657 9 2 

Voyageurs 1.260 0.750 0.460 7 2 

Wind Cave 0.950 0.334 0.130 3 0 

Theodore Roosevelt 0.393 0.211 0.190 0 0 

Lostwood 0.547 0.415 0.245 1 0 

Badlands 1.292 0.395 0.241 3 1 

Isle Royale 0.665 0.436 0.339 2 0 

Control 2 

Boundary Waters 1.959 0.890 0.667 11 2 

Voyageurs 1.232 0.768 0.521 8 2 

Wind Cave 1.030 0.355 0.130 2 1 

Theodore Roosevelt 0.395 0.228 0.161 0 0 

Lostwood 0.558 0.426 0.253 2 0 

Badlands 1.369 0.440 0.254 2 1 

Isle Royale 0.720 0.439 0.323 2 0 

Control 3 

Boundary Waters 1.944 0.848 0.620 9 1 

Voyageurs 1.225 0.717 0.450 7 1 

Wind Cave 0.902 0.317 0.120 2 0 

Theodore Roosevelt 0.380 0.204 0.173 0 0 

Lostwood 0.520 0.394 0.226 1 0 

Badlands 1.234 0.378 0.230 2 1 

Isle Royale 0.641 0.418 0.323 2 0 

Control 4 

Boundary Waters 1.844 0.840 0.611 10 1 

Voyageurs 1.171 0.705 0.502 8 1 

Wind Cave 0.938 0.323 0.117 2 0 

Theodore Roosevelt 0.373 0.197 0.138 0 0 

Lostwood 0.509 0.381 0.234 1 0 

Badlands 1.261 0.405 0.234 2 1 

Isle Royale 0.677 0.406 0.290 2 0 
Results 4-7 

Table 4-3. Visibility Impacts for 2007 (continued). 

Park Max Delta 

Deciview 

4th Highest 

(99%) 

8th Highest 

(98%) 

Nb. 

Exceed. > 

5% 

Nb. 

Exceed. > 

10% 

Control 5 

Boundary Waters 1.630 0.699 0.524 8 1 

Voyageurs 0.997 0.602 0.364 4 0 

Wind Cave 0.763 0.268 0.106 1 0 

Theodore Roosevelt 0.311 0.175 0.156 0 0 

Lostwood 0.439 0.328 0.211 0 0 

Badlands 1.039 0.315 0.191 2 1 

Isle Royale 0.525 0.349 0.272 2 0 

Control 5a 

Boundary Waters 1.554 0.671 0.493 6 1 

Voyageurs 0.961 0.569 0.354 4 0 

Wind Cave 0.715 0.251 0.096 1 0 

Theodore Roosevelt 0.299 0.160 0.141 0 0 

Lostwood 0.412 0.314 0.178 0 0 

Badlands 0.979 0.298 0.180 2 0 

Isle Royale 0.503 0.331 0.256 1 0 

Control 5b 

Boundary Waters 1.459 0.667 0.478 6 1 

Voyageurs 0.915 0.554 0.393 6 0 

Wind Cave 0.735 0.253 0.091 1 0 

Theodore Roosevelt 0.291 0.155 0.108 0 0 

Lostwood 0.399 0.301 0.182 0 0 

Badlands 0.991 0.316 0.182 2 0 

Isle Royale 0.527 0.319 0.227 1 0 

Control 6 

Boundary Waters 1.233 0.520 0.388 4 1 

Voyageurs 0.737 0.454 0.267 3 0 

Wind Cave 0.575 0.202 0.085 1 0 

Theodore Roosevelt 0.230 0.143 0.121 0 0 

Lostwood 0.331 0.241 0.157 0 0 

Badlands 0.781 0.236 0.143 1 0 

Isle Royale 0.388 0.259 0.199 0 0 

Control 7 

Boundary Waters 0.825 0.339 0.256 2 0 

Voyageurs 0.501 0.304 0.176 1 0 

Wind Cave 0.389 0.137 0.071 0 0 

Theodore Roosevelt 0.149 0.112 0.080 0 0 

Lostwood 0.223 0.155 0.101 0 0 

Badlands 0.524 0.157 0.099 1 0 

Isle Royale 0.268 0.172 0.134 0 0 

Control 8 

Boundary Waters 0.549 0.217 0.170 1 0 

Voyageurs 0.383 0.205 0.123 0 0 

Wind Cave 0.265 0.093 0.055 0 0 

Theodore Roosevelt 0.102 0.090 0.064 0 0 

Lostwood 0.152 0.122 0.063 0 0 

Badlands 0.352 0.105 0.070 0 0 

Isle Royale 0.189 0.124 0.098 0 0 
References 5-1 

5. REFERENCES 

FLAG, 2000. Federal Land Manager' Air Quality Related Values Workgroup (FLAG). 

Phase I Report. U.S. Forest Service, National Park Service, U.S. Fish and 

Wildlife Service. 

FLAG, 2008. Federal Land Manager' Air Quality Related Values Workgroup (FLAG). 

Phase I Report -Revised. U.S. Forest Service, National Park Service, U.S. Fish 

and Wildlife Service, June 27, 2008, Draft. 

Scire, J.S., D.G. Strimaitis, and R.J. Yamartino, 2000a: A User’s Guide for the 

CALPUFF Dispersion Model (Version 5). Earth Tech, Inc., Concord, MA 

Scire, J.S., F.R. Robe, M.E. Fernau, and R.J. Yamartino, 2000b: A User’s Guide for the 

CALMET Meteorological Model (Version 5). Earth Tech, Inc., Concord, MA. 

Tombach, I, 2006: Instructions: A Postprocessor for Recalculating CALPOST Visibility 

Outputs with the New IMPROVE Algorithm, Version 2, 14 October, 2006. 

U.S. EPA, 1998: Interagency Workgroup on Air Quality Modeling (IWAQM), Phase 2 

Report: Summary Report and Recommendation for Modeling Long Range 

Transport and Impacts on Regional Visibility. EPA-454/R-98-019. 

U.S. EPA, 2000: Federal Register Notice dated April 21, 2001. 

U.S. EPA, 2003: Guidance for Estimating Natural Visibility Conditions Under the 

Regional Haze Program. EPA-454/B-03-005, September 2003. 

U. S. EPA, 2005: Regional Haze Regulations and Guidelines for Best Available 

Technology (BART) Determinations. Fed. Reg./Vol. 70, No. 128/Wed. July 6, 

2005, Rules and Regulations, pp. 39104-39172. 40 CFR Part 51, FRL-7925-9, 

RIN AJ31. 

U.S. EPA, 2009: Clarification on EPA-FLM Recommended Settings for CALMET. EPA 

Memo by T. Fox dated August 31, 2009. 

WRAP Air Quality Modeling Forum RMC, 2006: CALMET/CALPUFF Protocol for the 

BART Exemption Screening Analysis for Class I Areas in the Western United 

States, August 15, 2006. 
 B-1 11/2/2009 

APPENDIX B 

Technical Description of SO2 Controls (B1)
 B-2 11/2/2009 

B1 Technical Description of SO2 Controls 

B1.1 Fuel Switching 

Fuel switching can be a viable method of fuel sulfur content reduction in certain situations. The PRB 

burned by BSP Unit I is one of the lower sulfur coals available in the U.S. and switching to a lower 

sulfur coal (if available) would achieve little to no additional reduction in SO2 emissions. Therefore, 

for the purpose of this BART analysis, fuel switching is not considered a viable option for SO2

control. 

B1.2 Wet Flue Gas Desulfurization 

Wet FGD technology utilizing lime or limestone as the reagent and employing forced oxidation to 

produce gypsum (calcium sulfate dihydrate, CaSO4·2H2O) as the byproduct, is commonly applied to 

coal-fired boilers. The gypsum byproduct is either landfilled or sold for commercial reuse. 

A flow diagram of the wet FGD process is provided in Figure B-1. In the wet FGD process, a slurry 

of finely ground limestone (CaCO3) in water is recirculated through an absorber tower where it is 

brought into turbulent contact with the flue gas. The contact between the flue gas and the slurry cools 

and saturates the gas via evaporation of water from the slurry. SO2 is simultaneously absorbed into 

the slurry where it forms sulfurous acid which reacts with the limestone, forming calcium sulfite 

hemihydrate (CaSO3•1⁄2H2O) which can then be disposed of as a waste product or oxidized to calcium 

sulfate dihydrate or gypsum (CaSO4•2H2O) before disposal or for commercial reuse. No commercial 

uses for sulfite waste products have been identified. 
 B-3 11/2/2009 

Figure B-1. Wet FGD Process Flow Diagram 

Chemical reactions between the limestone and the absorbed SO2 take place within the slurry in the 

absorber, and in the absorber reaction tank, resulting in the formation of particles of CaSO3·1⁄2 H2O. 

Some of the oxygen in the flue gas may participate in the reaction, resulting in the formation of 

particles of CaSO4•2H2O as well. Air may be injected into the absorber sump to promote the 

formation of gypsum and minimize the formation of calcium sulfite solids where a gypsum product is 

desired, either for ease of disposal or commercial use. The resultant slurry is then processed in a 

dewatering system prior to disposal or commercial use. 

As the limestone reagent in the recirculating slurry is depleted, it is replenished with fresh slurry 

prepared by wet grinding of crushed limestone using reclaimed liquid from the dewatering system. 

Fresh water is also required to replace water lost to evaporation in the flue gas cooling process. Fresh 

water is often used to wash the mist eliminators, devices located at the scrubber exit to capture slurry 

droplets entrained in the exiting flue gas stream and return them to the scrubber. The mist eliminator 

wash removes accumulated materials from the mist eliminator chevrons, thus preventing solids 

buildup and pluggage. In addition, depending upon the mineral content of the coal, a portion of the 

reclaimed liquid from the dewatering process may be blown down, or disposed of, to prevent 

excessive accumulation of mineral salts in the slurry which could result in mineral scaling within the 

absorber equipment. The blow down rate varies with each plant. Fresh water makeup, both through 

the mist eliminator wash system and in the limestone grinding process, replaces the blow down and 

evaporative losses. 

 

Stack

Flue Gas

from Air Heater

ESP

Booster Fan

Recycle 

Pump

Water

Limestone

Oxidation Air To Dewatering System

Reaction 

Tank

Absorber

Tower 

Mist Eliminators
 B-4 11/2/2009 

Lime scrubbers are very similar to limestone scrubbers. The use of lime rather than limestone can 

reduce the liquid-to-gas ratio and/or absorber size required to achieve a given SO2 removal rate. 

Lime is sometimes used in wet FGD systems where extremely high SO2 removal rates are desired or 

where limestone is not readily available. However, since lime is more expensive than limestone, the 

reagent cost is much higher for a lime system. Therefore, the vast majority of wet FGD systems are 

designed to use limestone as the neutralizing reagent. 

Tow advantages of the wet FGD systems include lower reagent costs, primarily due to the ability to 

use limestone instead of lime as a reagent and the production of a salable by-product and high 

removal efficiency. Also, wet FGD systems have a high turndown capability and plant operational 

flexibility is not hindered to the same degree as the semi-dry processes. This last advantage is 

important where wet FGD systems are applied to load following units. Disadvantages of wet FGD 

systems include corrosion due to a wet environment with corrosive chemicals including salts of 

sulfurous and sulfuric acid and hydrochloric acid. Also, because the wet systems are more 

mechanically complex, they typically require larger maintenance staff than the semi-dry, CFB and 

FDA alternatives. The greater mechanical complexity also contributes to a greater capital cost for 

wet FGD systems. Finally, because wet FGD systems completely saturate the flue gas stream, nearly 

all the SO3 or H2SO4 vapor in the entering flue gas is condensed into aerosol droplets which are too 

small to be efficiently captured in the scrubber. Fifty percent or more of these droplets pass right 

through the scrubber. Where units are burning high sulfur fuels, this can cause a plume opacity 

problem. Wet FGD systems commonly achieve 95% percent SO2 removal efficiencies in commercial 

applications. 

 

B1.3 Semi-Dry Flue Gas Desulfurization 

As an alternative to wet FGD technology, the control of SO2 emissions can be accomplished using 

semi-dry FGD technology. The most common semi-dry FGD system is the lime Spray Dryer 

Absorber (SDA) using a fabric filter for downstream particulate collection. The semi-dry FGD 

process became popular in the U.S. beginning in the late 1970s as a way to comply with the New 

Source Performance Standards (NSPS) for electric utility steam generating units for which 

construction commenced after September 18, 1978 (40 CFR Part 60, Subpart Da). These standards 

require that all new coal-fired electric utility boilers be equipped with a “continuous system of 

emission reduction” for SO2. However, the standards allowed SO2 removal efficiency as low as 70 
 B-5 11/2/2009 

percent for facilities burning low-sulfur coal. The semi-dry FGD process could meet this 

requirement, and was often selected as the SO2 control technology for many new coal-fired power 

plants that were built in the 1970s and 1980s and designed to burn low-sulfur western coal. In the 

late 1980s and through the 1990s, most of the new coal-fired boilers built in the U.S. were for small 

Independent Power Producer (IPP) projects, and many of these also selected the semi-dry/lime FGD 

process. 

There are several variations of the semi-dry process in use today. This section addresses the spray 

dryer FGD process. Two other variations, the Novel Integrated Desulfurization and Circulating 

Fluidized Bed absorber are similar processes. They primarily differ by the type of reactor vessel 

used, the method in which water and lime are introduced into the reactor and the degree of solids 

recycling. They are considered similar technologies and are not discussed further. 

A schematic diagram of the spray dryer FGD process is provided in Figure B-2. In the spray dryer 

FGD process, boiler flue gas is introduced into a Spray Dryer Absorber (SDA) into which hydrated 

lime (calcium hydroxide, Ca(OH)2) and water are added as dispersed droplets. The Ca(OH)2 reacts 

with SO2 that has been absorbed into the water to form primarily calcium sulfite and some calcium 

sulfate. The heat from the flue gas causes the water to evaporate, cooling the gas and drying the 

reaction products. Because the total water feed rate is much lower than that of the wet FGD process, 

the reaction products are dried in the SDA and the flue gas is only partially saturated. The amount of 

water added to the process is carefully controlled so that the flue gas temperature is maintained well 

above the saturation, or dewpoint, temperature (typically 30-40 0

F above saturation) to avoid 

corrosion problems. Cooling the gas to this point significantly increases the SO2 control efficiency 

over injection into hot, dry flue gas. The reaction product leaves the SDA as fine dry particles 

entrained in the flue gas. The flue gas enters the SDA at the top and flows downward, co-current with 

the introduced neutralizing agent. This characteristic is the opposite of the wet FGD system which 

introduces flue gas into the bottom of the absorber, countercurrent to the falling slurry spray. 
 B-6 11/2/2009 

Figure B-2 Spray Dryer FGD Process Flow Diagram 

In the lime spray drying process, quicklime (CaO) is slaked with water to form lime slurry which is 

then injected into the SDA along with additional water through a rotary atomizer or dual fluid nozzle 

or similar apparatus. Recycled PM from the PM control equipment downstream of the SDA is often 

mixed with the lime slurry before injection into the SDA to provide additional surface area for SO2

absorption. The flue gas is introduced into the SDA in a manner designed to maximize the contact 

between the gas and the droplets and to prevent slurry impingement on the walls of the SDA. The 

turbulent mixing of the flue gas and the slurry droplets promotes rapid absorption of SO2 into the 

water of the slurry droplets. The chemical reactions between the absorbed SO2 and the calcium 

hydroxide take place within the droplet as the flue gas moves through the SDA. The flue gas is 

cooled and partially humidified as the water evaporates, leaving a mixture of fly ash and dry 

powdered reaction product entrained in the flue gas. Some of the solid particles fall to the bottom of 

the reactor and are collected by a waste handling system. Entrained particles are collected in an 

electrostatic precipitator (ESP) or fabric filter (FF) downstream of the SDA. 

An additional distinguishing characteristic of the SDA is that it must be located upstream of a 

particulate control device, as opposed to the wet FGD process which is normally the last flue gas 

treatment process before discharge to the stack. For new plants, this point is not of such great 

importance. However, when retrofitting FGD equipment to an existing coal-fired plant, which 

Flue Gas

from Air Heater

Lime Slurry

Preparation

Lime

Water

Spray

Dryer

To Solids Recycling

Fabric Filter

To Solids Recycling

or Disposal

Stack

I.D. Booster Fan

Water or Ash

Recycle Slurry
 B-7 11/2/2009 

already has particulate control equipment installed, this becomes an important point. If a suitable 

location exists for the insertion of a new SDA upstream of an existing PM control device, and if the 

performance of the existing PM control device would not be overly degraded by the additional PM 

loading, then the retrofit process would consist only of installation of the SDA, reagent preparation 

and waste handling systems. However, many times one, or both, of these conditions do not exist and 

the choice to utilize an SDA requires the installation of a new PM control device, such as an ESP or 

fabric filter. Where this situation exists, the capital cost of the SDA option increases significantly. 

Semi-dry processes have some notable advantages compared to wet FGD processes including a dry 

byproduct which can be handled with conventional ash handling systems. Because the semi-dry 

system does not have a truly wet zone, corrosion problems in the SDA are eliminated, or significantly 

reduced, to the point exotic materials of construction are not required. Spray dryer systems utilize 

less complex equipment resulting in a reduced capital cost and allowing somewhat smaller operations 

and maintenance staff. Where a fabric filter is utilized as the downstream particulate control device 

for a semi-dry process, the lime content of the filter cake on the fabric filter reacts with condensed 

SO3 in the flue gas stream capturing and neutralizing the acid aerosol. Consequently, semi-dry FGD 

options, paired with a fabric filter for PM control, have virtually zero emissions of acid aerosols. 

The primary disadvantages of the lime spray dryer process make it less likely to be applied to large 

power plant boilers, especially those firing high-sulfur coal. The lime spray dryer requires the use of 

lime, which is much more expensive than limestone. While lime contains approximately 1.8 times 

more calcium than limestone on a mass basis, lime can cost up to five times more than limestone on a 

mass basis. Therefore, reagent costs for a lime based process are typically higher than a limestonebased process for a given application. 

Wastes from semi-dry processes have very limited possibility for reuse due to fly ash contamination. 

Also, where fly ash might be sold for other uses, contamination with the semi-dry FGD reaction 

products typically eliminates commercial options for reuse. Where fly ash sales are to be maintained, 

a second PM control device would be required for the semi-dry FGD system exhaust stream, 

increasing both capital and O&M costs. 

SDAs have much more stringent size limitations than wet FGD scrubbers. Typically units larger than 

250 to 300 MW will require at least two SDAs, thus driving up capital costs and system complexity 

for larger units, while wet FGD systems can handle up to 1000 MW in a single absorber module. 
 B-8 11/2/2009 

SDAs do not have the same turndown capabilities as wet FGD absorbers, further limiting 

applicability for load following units. Finally, lime spray dryer systems do not have the same level of 

experience with high SO2 removal requirements in high sulfur applications that wet FGD systems 

have. 

No variation of semi-dry FGD systems has clearly demonstrated the ability to achieve SO2 removal 

levels similar to wet FGD systems in the U.S. Table B-1 lists many of the recent lime spray dryer 

system installations in the U.S. The information in Table B-1 was obtained from the 

RACT/BACT/LAER Clearing House. As can be seen in the column titled Efficiency, two units were 

permitted with an SO2 removal efficiency of 94.5% and one with 95%. However, these units 

typically use a lower sulfur fuel and achieve an emissions limit in the range of 0.12 to 0.17 lb 

SO2/mmBtu. 
 B-9 11/2/2009 

Table B-1 – Recent Dry FGD Permits From RBLC 

RBLC 

ID Facility Process Fuel Size Unit Control Device 

Emission 

Limit 

(lb/mmBtu

*NE0018 Whelan Energy Center 

Unit 2 Utility Boiler PRB coal 2,210 mmBtu/hr 

Spray Dryer Absorber (SDA) 0.12 

AR-0074 Plum Point Energy 

Boiler , Unit 1 - SN-01 Bituminous Coal 800 MW 

Dry Flue Gas Desulfurization 0.16 

MT-0022 

Boiler, PC No. 1 Coal 390 MW 

Dry Flue Gas Desulfurization (FGD) 0.12 

MT-0022 

Bull Mountain, No. 

1, LLC - Roundup 

Power Project Boiler, PC No. 2 Coal 390 MW Dry Flue Gas Desulfurization (FGD) 0.12 

IA-0067 

MidAmerican Energy Company 

CBEC 4 Boiler PRB Coal 7,675 mmBtu/hr 

Lime Spray Dryer Flue Gas Desulfurization 0.1 

KS-0026 Holcomb Unit #2 Boiler, PC 

Subbituminous Coal 660 MW 

Dry Flue Gas Desulfurization 0.12 

WY0057 WYGEN 2 500 MW PC Boiler Subbituminous Coal 500 MW Semi-Dry Lime Spray Dryer Absorber 0.1 MO0050 

Kansas City Power & Light Co. - Hawthorn Station PC Boiler, Coal 384 T/H 

Dry Flue Gas Desulfurization 0.12 

WY0039 

Two Elk Generation Partners, Limited Partnership 

PC Fired Boiler Coal 250 MW 

Lime Spray Dry Scrubber 0.17 

WY0047 

Encoal CorporationEncoal North Rochelle Facility 

PC Fired Boiler 

Subbituminous Coal 3,960 mmBtu/hr Lime Spray Dryer 0.2 

WY0048 Wygen, Inc. - Wygen Unit One Boiler, PC Subbituminous Coal 80 MW Circulating Dry Scrubber 0.2 PA-0133 

Mon Valley Energy Limited Partnership 

PC Fired Boiler Bituminous Coal 966 mmBtu/hr Spray Dry Absorption 0.25 
 B-10 11/2/2009 

Table B-1 – Recent Dry FGD Permits From RBLC (cont.) 

RBLC 

ID Facility Process Fuel Size Unit Control Device 

Emission 

Limit 

(lb/mmBtu

VA-0213 SEI Birchwood, Inc. 

PC Fired Boiler Coal 2,200 mmBtu/hr 

Lime Spray Drying System (FGD System) 2

WY0046 Black Hills P&L Neil Simpson U PC Fired Boiler Coal 80 MW Circulating Dry Scrubber 0MI-0228 

Indelk Energy Services Of Otsego 

Boiler (Coal) Coal 778 mmBtu/hr Dry Scrubber 0

NC-0057 

Roanoke Valley Project Ii 

Boiler, PCFired Coal 517 mmBtu/hr Dry Lime Scrubbing 0.1

SC-0027 

Boiler, PCFired Unit No. 1 Coal 385 MW Spray Dryer Absorber 0

SC-0027 

PC-Fired Boiler, Unit No. 2 Coal 385 MW Spray Dryer Absorber 0

SC-0027 

South Carolina 

Electric And Gas 

Company 

PC-Fired Boiler, Unit No. 3 Coal 385 MW Spray Dryer Absorber 0

NJ-0015 

Keystone Cogeneration Systems, Inc. 

PC-Fired Boiler 

Coal, Bituminous 2,116 mmBtu/hr Spray Dryer Absorber 0

NC-0054 

Roanoke Valley Project 

Boiler, PCFired Coal 1,700 mmBtu/hr Dry Lime FGD 0.2

NJ-0014 

Chambers Cogeneration Limited Partnership 

2 PC-Fired Boilers Coal 1,389 

mmBtu/hr (each) Spray Dryer Absorber 0

VA-0176 Hadson Power 13 Boiler Coal 30,228 lb/hr coal Lime Spray Dryer 0.1VA-0171 

Mecklenburg Cogeneration Limited Partnership 

PC Fired, Boiler, 4 Units Bituminous Coal 834.5 mmBtu/hr 

Spray Dryer, Fabric Filter 0.1
 C-1 11/2/2009 

APPENDIX C 

Technical Description of Particulate Matter Controls (C1)
 C-2 11/2/2009 

Appendix C1 – Technical Description of Particulate Matter Controls 

C1.0 FABRIC FILTER (FF) 

A fabric filter or baghouse removes particulate by passing flue gas through filter bags. A pulsejet fabric filter (PJFF) unit (like the current Big Stone PM controls) consists of isolatable 

compartments with common inlet and outlet manifolds containing rows of fabric filter bags. The 

filter bags are made from a synthetic felted material that are suspended from a tube sheet mounted 

at the top of each fabric filter compartment. The tube sheet separates the particulate laden flue 

gas from the clean flue gas. This tube sheet is a flat sheet of carbon steel with holes designed to 

accommodate filter bags through which the bags are hung. The flue gas passes through the PJFF 

by flowing from the outside of the bag to the inside, up the center of the bag through the hole in 

the tube sheet and out the PJFF. Fly ash particles are collected on the outside of the bags, and the 

cleaned gas stream passes through the fabric filter and on to the chimney. A long narrow wire 

cage is located within the bag to prevent collapse of the bag as the flue gas passes through it. 

Each filter bag alternates between relatively long periods of filtering and short periods of 

cleaning. During the cleaning period, fly ash that has accumulated on the bags is removed by 

pulses of air and then falls into a hopper for storage and subsequent disposal. 

Cleaning is either initiated at a preset differential pressure across the tubesheet or based on a 

maximum time between cleanings. Bags in a PJFF are cleaned by directing a pulse of pressurized 

air down the filter bag countercurrent to the flue gas flow to induce a traveling ripple (pulse) in 

the filter bag. This pulse travels the length of the bag, deflecting the bag outward and separating 

the dust cake as it moves. 

An advantage of a fabric filter over an ESP is that a fabric filter is not dependent on the resistivity 

of the fly ash. Since the fabric filter uses bags instead of an electric charge to remove the 

particles, the resistivity of the particles is not an issue. Fabric filters also have a lower 

dependence on particle size than ESPs. A disadvantage of fabric filters is that they have a 

tendency to corrode and clog with high sulfur coal applications. The high sulfur coals produce 

more SO3, which tends to create problems with the fabric filters. Therefore, ESPs are typically 

used on high sulfur coal applications instead of fabric filters. Another disadvantage of fabric 

filters is the associated pressure drop. The bags, which collect a cake of particles, create an 

obstruction to the gas path. Fabric filters typically have approximately three times the pressure 
 C-3 11/2/2009 

drop of an ESP. Fabric filters have been proven to control PM removal efficiency in excess of 

99%. 

C1.1 ELECTROSTATIC PRECIPITATOR (ESP) 

ESPs are commonly used as the primary filterable PM control device on coal fired units. The 

ESP discharge electrodes generate a high voltage electrical field that gives the particulate matter 

an electric charge (positive or negative). The charged particles will then be collected on a 

collection plate. A rapper or hammer system will be utilized to vibrate the collected particles off 

of the plates so they can fall into the hoppers for storage and subsequent disposal. 

The advantages of an ESP include the fact that an ESP can be applied to high sulfur coals, and the 

pressure drop across an ESP is relatively low compared to other alternatives such as a fabric 

filter. Unlike the fabric filter, which uses bags as the filter media, an ESP does not contain 

elements that can plug in the presence of SO3. The unobstructed design of the ESP results in a 

pressure drop that is approximately 1/3 of a corresponding fabric filter. The disadvantage of the 

ESP is that its effectiveness to remove particulate is dependant on the resistivity of the fly ash and 

particle size. ESPs have been proven to control PM removal efficiency in excess of 99%. 

C1.1 COMPACT HYBRID PARTICULATE COLLECTOR (COHPAC)

A COmpact Hybrid PArticulate Collector (COHPAC) is a high air-to-cloth ratio pulse jet fabric 

filter located downstream of an existing ESP. The COHPAC acts as a polishing device for 

control of particulate emissions. The difference between a COHPAC and the fabric filter 

described above is that a COHPAC is installed after an ESP. The ESP prior to the COHPAC will 

remove the majority of the fly ash. This allows the COHPAC to have a higher air-to-cloth ratio 

than a typical fabric filter. The air-to-cloth ratio for a COHPAC unit is typically greater than or 

equal to 6 ACFM/ft2

 while the air-to-cloth ratio for a typical pulse jet fabric filter is 

approximately 3.5 to 4.0 ACFM/ft2

. Because Big Stone Plant does not have an ESP and already 

uses a fabric filter for particulate control, the use of a COHPAC is not considered further.