BART FIVE FACTOR ANALYSIS  ASH GROVE CEMENT

MONTANA CITY, MONTANA

VERSION 0 

Prepared by: 

TRINITY CONSULTANTS

9777 Ridge Drive 

Suite 380 

Lenexa, Kansas 66219 

(913) 894-4500 

June 2007 

Project 071601.0069 
Ash Grove Cement Company i Trinity Consultants 

BART Analysis 

TABLE OF CONTENTS

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

2. INTRODUCTION AND BACKGROUND.................................................................... 2-3

3. BART APPLICABILITY DETERMINATION........................................................... 3-5

4. SO2 BART EVALUATION .................................................................................... 4-1

4.1 IDENTIFICATION OF AVAILABLE RETROFIT SO2 CONTROL TECHNOLOGIES .......... 4-1 

4.2 ELIMINATE TECHNICALLY INFEASIBLE SO2 CONTROL TECHNOLOGIES ................ 4-2 

4.2.1 FUEL SUBSTITUTION ...........................................................................................4-2

4.2.2 RAW MATERIAL SUBSTITUTION .........................................................................4-2

4.2.3 LIME SPRAY DRYING ..........................................................................................4-3

4.2.4 WET LIME SCRUBBING .......................................................................................4-3

4.3 RANK OF TECHNICALLY FEASIBLE SO2 CONTROL OPTIONS BY EFFECTIVENESS .. 4-4 

4.4 EVALUATION OF IMPACTS FOR FEASIBLE SO2 CONTROLS..................................... 4-4 

4.4.1 WET LIME SCRUBBING .......................................................................................4-5

4.4.2 FUEL SUBSTITUTION ...........................................................................................4-9

4.5 EVALUATION OF VISIBILITY IMPACT OF FEASIBLE SO2 CONTROLS .................... 4-12 

4.6 PROPOSED BART FOR SO2 ..................................................................................... 4-1 

5. NOX BART EVALUATION................................................................................... 5-3

5.1 IDENTIFICATION OF AVAILABLE RETROFIT NOX CONTROL TECHNOLOGIES......... 5-3 

5.2 ELIMINATE TECHNICALLY INFEASIBLE NOX CONTROL TECHNOLOGIES............... 5-4 

5.2.1 LOW-NOX BURNER IN THE ROTARY KILN .........................................................5-4

5.2.2 FLUE GAS RECIRCULATION ................................................................................5-6

5.2.3 CEMENT KILN DUST INSUFFLATION ...................................................................5-6

5.2.4 MID-KILN FIRING OF SOLID FUEL (TIRES) WITH MIXING AIR FAN....................5-7

5.2.5 SELECTIVE NONCATALYTIC REDUCTION............................................................5-8

5.2.6 SELECTIVE CATALYTIC REDUCTION...................................................................5-9

5.3 RANK OF TECHNICALLY FEASIBLE NOX CONTROL OPTIONS BY EFFECTIVENESS 5-12 

5.4 EVALUATION OF IMPACTS FOR FEASIBLE NOX CONTROLS ................................. 5-13 

5.4.1 SNCR AND LNB ...............................................................................................5-13

5.5 EVALUATION OF VISIBILITY IMPACT OF FEASIBLE NOX CONTROLS ................... 5-14 

5.6 PROPOSED BART FOR NOX.................................................................................. 5-15 

6. PM BART EVALUATION..................................................................................... 6-1
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BART Analysis 

LIST OF TABLES

TABLE 1-1. VISIBILITY IMPAIRMENT IMPROVEMENT AT GATES OF THE MOUNTAINS WILDERNESS 

AREA ......................................................................................................................................1-2

TABLE 3-1. SUMMARY OF U.S. EPA REGION 8 BART APPLICABILITY MODELING RESULTS...........3-6

TABLE 3-2. SUMMARY OF MODELING METHOD DIFFERENCES BETWEEN EPA AND AGC ...............3-7

TABLE 3-3. KILN EMISSION RATES IN BART DATA SUBMITTAL VS. 2006 ANALYZER DATA...........3-8

TABLE 3-4. EXISTING MAXIMUM 24-HOUR SO2,NOX, AND PM10 EMISSIONS (AS HOURLY 

EQUIVALENTS) .......................................................................................................................3-8

TABLE 3-5. SUMMARY OF EXISTING STACK PARAMETERS ................................................................3-9

TABLE 3-6. EXISTING VISIBILITY IMPAIRMENT ATTRIBUTABLE TO MONTANA CITY PLANT KILN AND 

CLINKER COOLER...................................................................................................................3-9

TABLE 4-1. EXISTING ACTUAL MAXIMUM 24-HOUR SO2 EMISSION RATES......................................4-1

TABLE 4-2. AVAILABLE SO2 CONTROL TECHNOLOGIES.....................................................................4-2

TABLE 4-3. RANKING OF TECHNICALLY FEASIBLE KILN SO2 CONTROL TECHNOLOGIES BY 

EFFECTIVENESS ......................................................................................................................4-4

TABLE 4-4. COST ANALYSIS FOR WET LIME SCRUBBING ..................................................................4-6

TABLE 4-4. COST ANALYSIS FOR WET LIME SCRUBBING (CONTINUED)............................................4-7

TABLE 4-4. COST ANALYSIS FOR WET LIME SCRUBBING (CONTINUED)............................................4-8

TABLE 4-5. SUMMARY OF COST EFFECTIVENESS FOR FUEL SUBSTITUTION....................................4-11

TABLE 4-6. SUMMARY OF EMISSION RATES MODELED IN SO2 CONTROL VISIBILITY IMPACT 

ANALYSIS .............................................................................................................................4-12

TABLE 4-7. SUMMARY OF MODELED IMPACTS FROM SO2 CONTROL VISIBILITY IMPACT ANALYSIS4-1

TABLE 4-8. SUMMARY OF COST EFFECTIVENESS OF SO2 CONTROL TECHNOLOGIES ........................4-1

TABLE 5-1. EXISTING ACTUAL MAXIMUM 24-HOUR NOX EMISSION RATES.....................................5-3

TABLE 5-2. POSSIBLE NOX CONTROL TECHNOLOGIES ......................................................................5-4

TABLE 5-3. RANKING OF TECHNICALLY FEASIBLE KILN NOX CONTROL TECHNOLOGIES BY 

EFFECTIVENESS ....................................................................................................................5-13
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BART Analysis 

TABLE 5-4. SUMMARY OF EMISSION RATES MODELED IN NOX CONTROL VISIBILITY IMPACT 

ANALYSIS .............................................................................................................................5-15

TABLE 5-5. NOX CONTROL VISIBILITY IMPACT ANALYSIS...............................................................5-15

TABLE 6-1. EXISTING MAXIMUM 24-HOUR PM10 EMISSION RATE....................................................6-1

TABLE 6-2. VAP VISIBILITY IMPAIRMENT CONTRIBUTIONS AT GATES OF THE MOUNTAINS............6-1
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BART Analysis 

1. EXECUTIVE SUMMARY

This report documents the determination of the Best Available Retrofit Technology (BART) as 

proposed by Ash Grove Cement Company (AGC) for the Portland cement manufacturing plant 

located in Montana City, Montana (Montana City plant). There are two emission units at the 

Montana City plant for which AGC has made a BART determination: the kiln and the clinker cooler. 

Currently, particulate matter emissions from the kiln are controlled by an electrostatic precipitator. 

Particulate matter emissions from the clinker cooler are controlled by a baghouse. The Montana City 

plant has other lesser emitting BART-eligible emissions units, but the negligible visibility impairment 

attributable to these sources concludes that no additional controls are necessary to satisfy the 

requirements of the BART rule.1 

AGC used the U.S. Environmental Protection Agency’s (EPA’s) guidelines2 in 40 CFR Part 51 to 

determine BART for the kiln and clinker cooler. Specifically, AGC conducted a five-step analysis to 

determine BART for SO2, NOX, and PM10 that included the following: 

1. Identifying all available retrofit control technologies; 

2. Eliminating technically infeasible control technologies; 

3. Evaluating the control effectiveness of remaining control technologies; 

4. Evaluating impacts and document the results; 

5. Evaluating visibility impacts 

Based on the five-step analysis, AGC proposes the following as BART: 

Kiln: 

• PM10 – AGC proposes that the existing electrostatic precipitator constitutes BART. This 

control device is the most effective for controlling PM10 from a wet kiln. 

• NOX – AGC proposes to comply with a BART emission limit of 227.25 lb/hr on a 30-day 

rolling basis by installing and operating a direct-fired low-NOx burner (LNB) and a selective 

noncatalytic reduction (SNCR) system. Compliance with the emission limit will be 

demonstrated by continuous emissions monitoring. 

• SO2 – AGC proposes that no additional SO2 controls are required for BART compliance. 

Additional SO2 controls would provide little visibility improvement and require significant 

expenditures. 

Clinker Cooler: 

 1 AGC submitted an inventory of all of the BART-eligible emission sources to the Montana Department of 

Environmental Quality. EPA Region 8 subsequently evaluated the kiln and clinker cooler to determine the applicability of 

BART to the Montana City plant. Trinity Consultants conducted two BART applicability visibility modeling analyses for 

the Montana City plant. One modeling analysis included all of the BART-eligible sources at the plant. The other modeling 

analysis included the kiln and clinker cooler only. The difference in the modeled visibility impact predicted for the two 

scenarios was negligible; thus, it was concluded that the contribution of the non-kiln and clinker cooler sources to visibility

impairment is negligible, and controlling these sources would not improve any existing visibility impairment. 

2 40 CFR 51, Regional Haze Regulations and Guidelines for Best Available Retrofit Technology (BART) 

Determinations 
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BART Analysis 

• PM10 – AGC proposes that the existing baghouse constitutes BART. This control device is 

the most effective for controlling PM10 from a clinker cooler. 

The proposed BART control strategies will result in reductions of the visibility impacts attributable to 

the Montana City plant. A summary of the visibility improvement at the Gates of the Mountains 

Class I area based on the existing emission rates and proposed BART emission rates is provided in 

Table 1-1. 

TABLE 1-1. VISIBILITY IMPAIRMENT IMPROVEMENT AT GATES OF THE MOUNTAINS 

WILDERNESS AREA

 

98% Impact 

(Δdv) 

Existing 2.874 

BART 1.377 

Improvement 52.09% 
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BART Analysis 

2. INTRODUCTION AND BACKGROUND

On July 1, 1999, the U.S. EPA published the final Regional Haze Rule (RHR). The objective of the 

RHR is to improve visibility in 156 specific areas across with United States, known as Class I areas. 

The Clean Air Act defines Class I areas as certain national parks (over 6000 acres), wilderness areas 

(over 5000 acres), national memorial parks (over 5000 acres), and international parks that were in 

existence on August 7, 1977. 

On July 6, 2005, the EPA published amendments to its 1999 RHR, often called the Best Available 

Retrofit Technology (BART) rule, which included guidance for making source-specific BART 

determinations. The BART rule defines BART-eligible sources as sources that meet the following 

criteria: 

(1) Have potential emissions of at least 250 tons per year of a visibility-impairing pollutant, 

(2) Began operation between August 7, 1962 and August 7, 1977, and 

(3) Are included as one of the 26 listed source categories in the guidance. 

A BART-eligible source is subject to BART if the source is “reasonably anticipated to cause or 

contribute to visibility impairment in any federal mandatory Class I area.” EPA has determined that a 

source is reasonably anticipated to contribute to visibility impairment if the 98th percentile visibility 

impacts from the source are greater than 0.5 delta deciviews (∆dv) when compared against a natural 

background. Air quality modeling is the tool that is used to determine a source’s visibility impacts. 

Once it is determined that a source is subject to BART, a BART determination must address air 

pollution control measures for the source. The visibility regulations define BART as follows: 

“...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 cost of compliance, the energy and non air quality environmental impacts of 

compliance, any pollution control equipment in use or in existence at the source, the 

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

may reasonable be anticipated to result from the use of such technology. 

Specifically, the BART rule states that a BART determination should address the following five 

statutory factors: 

1. Existing controls 

2. Cost of controls 

3. Energy and non-air quality environmental impacts 

4. Remaining useful life of the source 

5. Degree of visibility improvement as a result of controls 

Further, the BART rule indicates that the five basic steps in a BART analysis can be summarized as 

follows: 

1. Identify all available retrofit control technologies; 
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BART Analysis 

2. Eliminate technically infeasible control technologies; 

3. Evaluate the control effectiveness of remaining control technologies; 

4. Evaluate impacts and document the results; 

5. Evaluate visibility impacts 

A BART determination should be made for each visibility affecting pollutant (VAP) by following the 

five steps listed above for each VAP. 

BART applicability was determined for the Montana City plant based on a combination of an 

applicability analysis performed by U.S. EPA Region 8 and a refined applicability analysis performed 

by AGC. Both analyses determined that the kiln and clinker cooler are subject to BART. The details 

of the applicability determination can be found in Section 3. 

Subsequently, AGC performed an analysis to determine BART for each VAP for the kiln and clinker 

cooler. The VAPs emitted by the kiln and clinker cooler include NOx, SO2, and particulate matter 

with a mass mean diameter smaller than ten microns (PM10) of various forms (filterable coarse 

particulate matter [PMc], filterable fine particle matter [PMf], elemental carbon [EC], inorganic 

condensable particulate matter [IOR CPM] as sulfates [SO4], and organic condensable particulate 

matter [OR CPM] also referred to as secondary organic aerosols [SOA]). The BART determinations 

for SO2, NOX, and PM10 can be found in Sections 4, 5, and 6, respectively. 
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BART Analysis 

3. BART APPLICABILITY DETERMINATION

As stated in Section 2, a BART-eligible source is subject-to-BART if the source is “reasonably 

anticipated to cause or contribute to visibility impairment in any federal mandatory Class I area.” 

EPA has determined that a source is reasonably anticipated to contribute to visibility impairment if 

the 98th percentile of the visibility impacts from the source is greater than 0.5 ∆dv when compared 

against a natural background. U.S. EPA Region 8 (EPA) conducted air quality modeling to predict 

the existing visibility impairment attributable to the Montana City plant in the following Class I areas: 

• Gates of the Mountains Wilderness Area 

• Scapegoat Wilderness Area 

• Anaconda – Pintler Wilderness Area 

• Bob Marshall Wilderness Area 

• Mission Mountains Wilderness Area 

• Selway – Bitterroot Wilderness 

• Yellowstone National Park 

• Red Rock Lakes Wilderness Area 

• Glacier National Park 

• North Absaroka Wilderness Area 

• Washakie Wilderness Area 

• Teton Wilderness Area 

Based on this modeling, EPA concluded that the Montana City plant was subject to BART since the 

98th percentile of the visibility impacts attributable to the kiln and clinker cooler are greater than 0.5 

Δdv when compared against a natural background for one Class I area: Gates of the Mountains 

Wilderness Area. The results of the applicability modeling are summarized in Table 3-1. 
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BART Analysis 

TABLE 3-1. SUMMARY OF U.S. EPA REGION 8 BART APPLICABILITY MODELING RESULTS 

Minimum 

Distance 

98th Percentile Visibility 

Impact for Each Year 

(∆ dv) 

Overall 

98th 

Percentile 

Visibility 

Impact 

Class I Area (km) 2001 2002 2003 (∆ dv) 

Gates of the Mountains 30 2.17 1.82 2.52 2.17 

Scapegoat 80 0.36 0.42 0.26 0.34 

Anaconda - Pintler 113 0.09 0.09 0.07 0.08 

Bob Marshall 116 0.39 0.30 0.18 0.30 

Mission Mountains WA 162 0.05 0.06 0.04 0.05 

Selway-Bitterroot Wilderness 173 0.01 0.01 0.01 0.01 

Yellowstone NP 175 0.00 0.01 0.01 0.01 

Red Rock Lakes 207 0.00 0.00 0.00 0.00 

Glacier NP 223 0.10 0.04 0.04 0.05 

North Absaroka Wilderness 228 0.00 0.00 0.00 0.00 

Washakie Wilderness 276 0.00 0.00 0.00 0.00 

Teton Wilderness 289 0.00 0.00 0.00 0.00 

AGC verified EPA’s results by performing a refined modeling analysis for the Class I area located 

closest to the Montana City plant: Gates of the Mountains Wilderness Area. The modeling methods 

used by AGC and EPA Region 8 differed slightly and are summarized in Table 3-2. 
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TABLE 3-2. SUMMARY OF MODELING METHOD DIFFERENCES BETWEEN EPA AND AGC 

Processor/Model Parameter Ash Grove (AGC) Modeling Analysis EPA Region 8 (EPA) Modeling 

Analysis 

CALMET Surface Stations AGC included all the 36 surface stations 

listed in the MDEQ Draft Protocol 

("protocol”) in the CALMET 

processing. 

EPA included all the 36 surface 

stations listed in the MDEQ Draft 

Protocol as well as 3 additional surface 

stations in the CALMET processing. 

CALMET Precipitation Stations AGC included 146 precipitation stations 

in the CALMET processing. 

EPA did not include precipitation 

stations in the CALMET processing. 

CALMET Surface Station for 

Surface Temperature 

AGC used the Helena Regional Airport 

surface station for the surface 

temperature, as this is the surface station 

nearest the Montana City plant (7.6 km). 

EPA used the Billings Logan Airport 

surface station for surface temperature. 

This station is 272.4 km from the 

Montana City plant. 

CALPUFF Puff Splitting AGC included puff splitting, per the 

protocol. 

EPA did not include puff splitting. 

CALPUFF Coordinate System AGC used Lambert Conformal 

Coordinates. The following are the 

reference coordinates: 

Reference Latitude: 43.1861N 

Reference Longitude: -116.2657 W 

Latitude 1: 43 N 

Latitude 2: 49 N 

EPA used Lambert Conformal 

Coordinates. The following are the 

reference coordinates: 

Reference Latitude: 44.29 N 

Reference Longitude: -109.5 W 

Latitude 1: 45 N 

Latitude 2: 49 N 

False Easting: 600 meters 

CALPUFF Grid Size AGC used a grid size of 2 km. This 

smaller grid size was selected due to the 

distance of the closest Class I area to the 

Montana City plant (Gates of the 

Mountains, 30 km). 

EPA used a grid size of 6 km. 

CALPUFF Background Ozone AGC used default background ozone 

concentrations of 30 parts per billion 

(ppb) for October through May and 50 

ppb for June through September. 

EPA used a default background ozone 

concentration of 80 ppb for the entire 

year. 

CALPOST Monthly Relative 

Humidity 

Adjustment Factor 

AGC used the monthly relative humidity 

adjustment factors based on the 

representative IMPROVE site location 

for the Class I area, as shown in the 

MDEQ protocol. 

EPA used the monthly relative 

humidity adjustment factors based on 

the centroid of the Class 1 Area. 

In addition to different modeling methods, AGC also modeled slightly different NOX and SO2

emission rates for the kiln. EPA modeled the Montana City plant based on emissions data that AGC 

had submitted to MDEQ (and, subsequently, EPA) for the BART applicability analysis. The kiln 

NOX and SO2 emissions data provided in that submittal was from stack testing performed in April of 

2006. In May of 2006, a SO2/NOX analyzer was installed on the kiln exhaust and AGC has collected 

additional data on SO2 and NOX emissions from the kiln. The data from May 2006 through the end of 

2006 show that the maximum actual SO2 and NOx emission rates from the kiln are higher than the 

SO2 and NOx emission rate originally submitted to MDEQ. The emissions data are summarized in 

Table 3-3. 
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TABLE 3-3. KILN EMISSION RATES IN BART DATA SUBMITTAL VS. 2006 ANALYZER DATA

Pollutant 

BART Data 

Submittal to 

MDEQ 

(lb/hr) Comment 

2006 Analyzer 

Data 

(lb/hr) Comment 

SO2 285.83 Stack Test Data, 

April 2006 

473.87 2006 Maximum Actual 24-

Hour SO2 Emission Rate 

From Analyzer Data (Hourly 

Equivalent) 

NOX 439.17 Stack Test Data, 

April 2006 

848.74 2006 Maximum Actual 24-

Hour NOX Emission Rate 

From Analyzer Data (Hourly 

Equivalent) 

PM10 37.17 Stack Test Data, 

April 2006 

37.17 Stack Test Data, April 2006 

AGC updated the emission rates used in the refined BART applicability modeling to the emission 

rates based on the analyzer data. Table 3-4 summarizes the emission rates that EPA and AGC 

modeled for SO2, NOX, and PM10, including the speciated PM10 emissions. The total PM10 emission 

rates include both the filterable and condensable fractions and are speciated into the following: 

▲ Coarse particulate matter (PMC) 

▲ Fine particulate matter (PMf) 

▲ Sulfates (SO4) 

▲ Secondary organic aerosols (SOA) 

▲ Elemental carbon (EC) 

TABLE 3-4. EXISTING MAXIMUM 24-HOUR SO2,NOX, AND PM10 EMISSIONS (AS HOURLY 

EQUIVALENTS) 

Model Source SO2 NOX Total 

PM10 

SO4 PMc PMf SOA EC 

(lb/hr) (lb/hr) (lb/hr) (lb/hr) (lb/hr) (lb/hr) (lb/hr) (lb/hr) 

EPA Region 8 Kiln 285.83 439.17 37.17 6.80 7.28 21.35 0.93 0.82 

Applicability Clinker Cooler 0.00 0.00 6.00 0.00 0.00 5.94 0.00 0.06 

AGC Refined Kiln 473.87 848.74 37.17 6.80 7.28 21.35 0.93 0.82 

Applicability Clinker Cooler 0.00 0.00 6.00 0.00 0.00 5.94 0.00 0.06 

Table 3-5 summarizes the stack parameters that were used to model the kiln and clinker cooler. 
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BART Analysis 

TABLE 3-5. SUMMARY OF EXISTING STACK PARAMETERS

 Kiln Clinker Cooler 

Latitude (degrees) 46.544 46.539 

Longitude (degrees) -111.921 -111.922 

Stack height (ft) 100 50 

Stack Diameter (ft) 9 4 

Exhaust Velocity (ft/s) 47 54 

Exhaust Temperature (K) 384 132 

The results of AGC’s refined modeling verified EPA’s BART determination; the results are 

summarized in Table 3-6. The 98th percentile of the visibility impacts attributable to the kiln and 

clinker cooler are greater than 0.5 Δdv when compared against a natural background for the Gates of 

the Mountains Wilderness Area. 

TABLE 3-6. EXISTING VISIBILITY IMPAIRMENT ATTRIBUTABLE TO MONTANA CITY PLANT KILN 

AND CLINKER COOLER

Class I Area 

Minimum 

Distance 

98th Percentile Visibility 

Impact for Each Year 

(∆ dv) 

Overall 

98th 

Percentile 

Visibility 

Impact 

 (km) 2001 2002 2003 (dv) 

Gates of the Mountains 30 2.736 2.874 3.038 2.874
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BART Analysis 

4. SO2 BART EVALUATION

Sulfur, in the form of metallic sulfides (pyrite), sulfate, or organosulfur compounds, is often found in 

the raw materials used to manufacture cement and in the solid and liquid fuels burned in cement 

kilns.3 The raw materials and fuels for the Montana City plant are no exception. Sulfur dioxide can 

be generated by the oxidation of sulfur compounds in the raw materials and fuels during operation of 

the pyroprocess. Constituents found in fuels, raw materials, and in-process materials, such as the 

alkali metals (sodium and potassium), calcium carbonate, and calcium oxide often react with SO2

within the pyroprocess to limit emissions of SO2 as much of the sulfur leaves the process in the 

principle product of the kiln system called clinker. 

The kiln is the only BART source which emits SO2, thus an SO2 BART evaluation was performed 

only for the kiln. The maximum actual 24-hour kiln SO2 emission rate that was modeled for the 

BART applicability determination is summarized in Table 4-1. The SO2 24-hour maximum actual 

emission rate was determined from analyzer data for 2006. 

TABLE 4-1. EXISTING ACTUAL MAXIMUM 24-HOUR SO2 EMISSION RATES

 SO2 24-Hour 

Emission Rate 

SO2 Hourly Equivalent 

Emission Rate 

 (ton/24-hr) (lb/hr) 

Kiln 5.69 473.87 

4.1 IDENTIFICATION OF AVAILABLE RETROFIT SO2 CONTROL 

TECHNOLOGIES

Step 1 of the BART determination is the identification of all available retrofit SO2 control 

technologies. A list of control technologies was obtained by reviewing the U.S. EPA’s Clean Air 

Technology Center, publicly-available air permits, applications, and technical literature published by 

the U.S. EPA, state agencies, and Regional Planning Organizations (RPOs). 

The available retrofit SO2 control technologies are summarized in Table 4-2. 

 3 Miller, F. MacGregor and Hawkins, Garth J., ”Formation and Emission of Sulfur Dioxide from the Portland Cement 

Industry”, Proceedings of the Air and Waste Management Association, June 18-22, 2000. 
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BART Analysis 

TABLE 4-2. AVAILABLE SO2 CONTROL TECHNOLOGIES

SO2 Control Technologies 

Fuel Substitution 

Raw Material Substitution 

Lime Spray Dryer 

Wet Lime Scrubbing 

4.2 ELIMINATE TECHNICALLY INFEASIBLE SO2 CONTROL TECHNOLOGIES

Step 2 of the BART determination is to eliminate technically infeasible SO2 control technologies that 

were identified in Step 1. 

4.2.1 FUEL SUBSTITUTION

AGC uses a mixture of coal and petroleum coke as the primary fuels for the kiln; natural 

gas is combusted during startup. The 2006 fuel usage breakdown, on an energy input 

basis, was 58 percent petroleum coke, 41 percent coal, and 1 percent natural gas. The 

sulfur content of the petroleum coke is approximately 4.5 percent and the sulfur content of 

the coal is approximately 0.8 percent. 

The design of the long wet kiln system is such that much of the SO2 resulting from fuel 

combustion is emitted. Therefore, if AGC reduces sulfur in fuel input to the kiln, a 

corresponding reduction in SO2 emissions from the kiln would be expected. Fuel sulfur 

content could be reduced by burning a different blend of coal and coke which results in a 

lower overall sulfur content. Therefore, AGC anticipates that lowering the input of sulfur 

through fuel substitution would be an effective and technically feasible SO2 control 

technology for the kiln. 

4.2.2 RAW MATERIAL SUBSTITUTION

Sulfide sulfur in the raw materials, usually in the form of iron pyrite, is thermally 

decomposed and oxidized or “roasted” to form SO2. The pyritic sulfur reacts with oxygen 

according to the following reaction: 

4FeS2 + 11O2 Æ 2Fe2O3 + 8SO2

Using raw materials with lower pyritic sulfur content can reduce the potential for SO2

emissions from a wet kiln system. While pyrites are present in the limestone and other raw 

materials used at the Montana City plant, the concentrations of sulfide sulfur in these 

materials are already very low. With rare exceptions, cement plants are built at or near a 

source of limestone, the primary raw material for cement manufacture. To do otherwise is 

an economic penalty that would cause most plants, including Montana City plant, to be 

economically infeasible. During the production of cement clinker, the limestone loses 

about one-third of its weight as CO2. The shipping costs for the “lost” weight in the 

limestone often can be economically prohibitive. 
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BART Analysis 

Since material substitution would result in a negligible reduction in SO2 for the kiln, raw 

material substitution is not considered an SO2 control technology for the kiln and is 

removed from further consideration as BART. 

4.2.3 LIME SPRAY DRYING 

Lime spray drying (LSD) consists of injecting an aqueous Ca(OH)2 suspension in fine 

droplets into the flue gas. The Ca(OH)2 reacts with SO2 in the flue gas stream to create 

fine particles of CaSO3 or CaSO4. The moisture evaporates from the particles, and the 

particles are collected in the particulate matter control device (PMCD) serving the kiln. 

For optimum effectiveness, the reaction of Ca(OH)2 with SO2 must have adequate gas 

retention time and must be followed by a PMCD for capturing the sulfates created by the 

reaction. 

Unlike a preheater/precalciner kiln system that provides by its design a natural location for 

a spray dryer type control system to be utilized between the top of the preheater tower and 

the PMCD, a wet kiln does not have that attribute. In other words, the back-end of a wet 

kiln has a relatively short retention time between that and it’s associated PMCD. 

Additionally, the PMCD in place was not designed for the additional loading or for the 

increased water vapor that would need to be moved through the system to accommodate 

adequate lime spray drying control. It is also expected that with the added moisture 

generated from the wet process slurry that rates of evaporation for spray drying to occur 

could be retarded as compared to other combustion systems that might employ this type of 

system. 

Lastly, the added gas cooling that would result from the injection of slurry prior to the 

PMCD would have the potential for undesirable acid dewpoint conditions to occur in the 

PMCD that could reduce its effectiveness. For these reasons and as there are no known 

applications of lime spray dryers on wet cement kilns, this technology considered is 

technically infeasible and is removed from further consideration as BART. 

4.2.4 WET LIME SCRUBBING

Wet lime scrubbing (WLS) is a name for a traditional tailpipe wet scrubber. This process 

involves passing the flue gas from the main PMCD through a sprayed aqueous suspension 

of Ca(OH)2 or CaCO3 (limestone) that is contained in an appropriate scrubbing device. In 

the case of the Montana City plant, the basic underlying economics would dictate the use 

of ground limestone as the scrubbing reagent. In WLS, the aqueous suspension of 

scrubbing reagent is not taken to dryness as it is in LSD. The SO2 reacts with the 

scrubbing reagent to form CaSO3 that is collected and retained as aqueous sludge. 

Typically, the sludge is dewatered and disposed in an on-site landfill. In some cases 

involving cement plants, the CaSO3 sludge could be oxidized to CaSO4 and used in the 

finish mills as a substitute for purchased gypsum for regulation of the setting time of the 

cement product. 
Ash Grove Cement Company 4-4 Trinity Consultants 

BART Analysis 

Typically, WLS is considered to have a scrubbing efficiency of up to 90 percent of the SO2

in the flue gas treated by the scrubber.4 WLS is a high maintenance process with high 

rates of downtime expected as the scrubber matures and corrosion of components becomes 

a serious problem. Conceivably, a pair of wet scrubbers ultimately would be required so 

that one is in operation while the other is repaired. 

Despite these identified drawbacks, WLS is considered a technically feasible BART 

option. 

4.3 RANK OF TECHNICALLY FEASIBLE SO2 CONTROL OPTIONS BY 

EFFECTIVENESS

The third step in the BART analysis is to rank the technically feasible options according to 

effectiveness. Table 4-3 presents potential SO2 technically feasible control technologies for the kiln 

and the associated SO2 emission levels. 

TABLE 4-3. RANKING OF TECHNICALLY FEASIBLE KILN SO2 CONTROL TECHNOLOGIES BY 

EFFECTIVENESS

Pollutant Control Technology 

Effectiveness 

SO2 Emissions Level 

(lb/hr) 

SO2 

 Wet Lime Scrubbing 25.35 lb/hr as a 30-day rolling average†

 Fuel Switching 126.76 lb/hr as a 30-day rolling average * 

†Based on a 90% removal efficiency from the 2006 average 24-hour emission rate hourly equivalent (253.52 lb/hr). The 

90 percent reduction was applied to the 2006 average 24-hour SO2 emission rate rather than the maximum 24-hour SO2

emission rate to best reflect the performance of the control on a 30 day rolling basis. 

*Based on a fuel switching scenario that reduces sulfur emissions by 50% from the 2006 average 24-hour emission rate 

hourly equivalent (253.52 lb/hr). The 90 percent reduction was applied to the 2006 average 24-hour SO2 emission rate 

rather than the maximum 24-hour SO2 emission rate to best reflect the performance of the control on a 30 day rolling 

basis. 

4.4 EVALUATION OF IMPACTS FOR FEASIBLE SO2 CONTROLS 

Step four for the BART analysis procedure is the impact analysis. The BART determination 

guidelines list the four factors to be considered in the impact analysis: 

• Cost of compliance 

• Energy impacts 

• Non-air quality impacts; and 

• The remaining useful life of the source 

 4EPA Air Pollution Control Technology Fact Sheet – Flue Gas Desulfurization (FGD) Wet, Spray Dry, and Dry 

Scrubbers. A control efficiency of up to 95% is listed. However, at an uptime of 95%, the actual annual control efficiency 

would be 90.2% 
Ash Grove Cement Company 4-5 Trinity Consultants 

BART Analysis 

AGC has conducted an impact analysis for the two control options with the highest SO2 control 

efficiencies: WLS and fuel switching. 

4.4.1 WET LIME SCRUBBING

Cost of Compliance 

AGC obtained a site-specific WLS proposal from a vendor and performed an economic 

analysis to determine the annualized cost for WLS. AGC divided the annualized cost of 

WLS by the annual tons of SO2 reduced to determine the cost effectiveness for WLS. The 

“annual tons reduced” were determined by subtracting the estimated controlled annual 

emissions from the existing annual emissions. The existing annual emissions are based on 

the average 24-hour SO2 emission rate (hourly equivalent) in 2006, as recorded by the gas 

analyzer, multiplied by the 2006 operating hours. The estimated controlled annual 

emissions were calculated by applying the 90 percent control efficiency to the existing 

annual emissions. Table 4-4 provides the cost effectiveness analysis related to WLS. Note 

that the cost effectiveness analysis does not include the cost to construct a new exhaust 

stack, which would be needed to employ the WLS technology. 
Ash Grove Cement Company 4-6 Trinity Consultants 

BART Analysis 

TABLE 4-4. COST ANALYSIS FOR WET LIME SCRUBBING

 Direct Costs 

 Purchased Equipment Costs 

 Wet Scrubber Unit $5,687,500 

 Instrumentation (10% of EC) $568,750 

 Sales Tax (3% of EC) $170,625 

 Freight (5% of EC) $284,375 

 Subtotal, Purchased Equipment Cost (PEC) $6,711,250 

 

 Direct Installation Costs 

 Foundation (6% of PEC) $402,675 

 Supports (6% of PEC) $402,675 

 Handling and Erection (40% of PEC) $2,684,500 

 Electrical (1% of PEC) $67,113 

 Piping (30% of PEC) $2,013,375 

 Insulation for Ductwork (1% of PEC) $67,113 

 Painting (1% of PEC) $67,113 

 Subtotal, Direct Installation Cost $5,704,563 

 

 Site Preparation N/A 

 Buildings N/A 

 

 Total Direct Cost $12,415,813 

 

 Indirect Costs 

 Engineering (10% of PEC) $671,125 

 Construction and Field Expense (10% of PEC) $671,125 

 Contractor Fees (10% of PEC) $671,125 

 Start-up (1% of PEC) $67,113 

 Performance Test (1% of PEC) $67,113 

 Contingencies (3% of PEC) $201,338 

 Total Indirect Cost $2,348,938 

 

 

 Total Capital Investment (TCI) $14,764,750 

 
Ash Grove Cement Company 4-7 Trinity Consultants 

BART Analysis 

TABLE 4-4. COST ANALYSIS FOR WET LIME SCRUBBING (CONTINUED) 

 Direct Annual Costs 

 Hours per Year (365 days per year, 24 hours per day) 8,760 

 

 Operating Labor 

 Operator (0.5 hr/shift, 3 shifts/day, 365 d/yr, $16/hr) $8,760 

 Supervisor (15% of operator) $1,314 

 Subtotal, Operating Labor $10,074 

 

 Maintenance 

 Labor (0.5 hr/shift, 3 shifts/day, 365 d/yr, $16/hr) $8,760 

 Material (100% of maintenance labor) $8,760 

 Subtotal, Maintenance $17,520 

 

 Utilities 

 Electricity 

 Pump (kW) 380.48 

 Cost ($/kW-hr) $0.0537 

 Subtotal, Electricity $179,082 

 

 Limestone Slurry 

 Amount Required (ton/yr) 2,847 

 Cost ($/ton) $15.00 

 Subtotal, Lime $42,705 

 

 Water 

 Amount Required (gpm) 31.0 

 Cost ($/1000 gallons) $3.075 

 Subtotal, Water $50,101 

 

 Sludge Disposal 

 Amount Generated (tpy) 5,913 

 Disposal Fee ($/ton) $23.00 

 Subtotal, Sludge $135,999 

 

 Subtotal, Utilities $407,887 

 

 Total Direct Annual Costs $435,481 

 
Ash Grove Cement Company 4-8 Trinity Consultants 

BART Analysis 

TABLE 4-4. COST ANALYSIS FOR WET LIME SCRUBBING (CONTINUED) 

Indirect Annual Costs 

 Overhead (60% of sum of operating, supervisor, maintenance labor & materials) $153,839 

 Administrative (2% TCI) $295,295 

 Property Tax (1% TCI) $147,648 

 Insurance (1% TCI) $147,648 

 Capital Recovery (10 year life, 7 percent interest) $2,102,168 

 Total Indirect Annual Cost $2,846,597 

 

Conclusion 

 

 Total Annualized Cost $3,282,078 

 Pollutant Emission Rate Prior to Scrubber (tons SO2/yr) 981 

 Pollutant Removed (tons SO2/yr) 883 

 Cost Per Ton of Pollutant Removed $3,716 

 

Energy Impacts 

A wet scrubber requires an additional fan of considerable horsepower to move the flue gas 

through the scrubber. 

Non Air-Quality Impacts 

WLS may lead to an increase in PM emissions because some particles of limestone or 

CaSO3 will be entrained in the flue gas and subsequently be emitted from the scrubber. 

WLS is also known to increase emissions of sulfuric acid mist.5 A frequent steam plume 

can be expected at the discharge of the wet scrubber that would result in visual impairment 

in the area. 

Utilization of a wet scrubber would require the use of a significant amount of water. An 

appropriately sized wet scrubber would consume approximately 16 million gallons of 

water per year. Most of this water would be emitted as vapor with a small portion in the 

sludge that would be generated by the control device. 

In addition to the consumption of a large amount of water, the WLS technology would also 

generate a large amount of sludge. Disposal or treatment of WLS sludge presents 

additional environmental impacts. 

Remaining Useful Life 

 5 Innovations in Portland Cement Manufacturing, Portland Cement Association, 2004, pg. 660 & 669 
Ash Grove Cement Company 4-9 Trinity Consultants 

BART Analysis 

The remaining useful life of the kiln does not impact the annualized cost of WLS because 

the useful life is anticipated to be at least as long as the capital cost recovery period, which 

is 10 years. 

4.4.2 FUEL SUBSTITUTION

Cost of Compliance 

The cost of fuel substitution was determined by calculating the cost of the current 

coal/coke fuel blend and determining the increased cost of switching to combusting a fuel 

blend that would reduce fuel sulfur content by 50 percent from the 2006 levels. The 

proposed solution discussed in this evaluation would equate to reducing coke usage from 

the proportions used in 2006. At this time, AGC has not fully evaluated the potential fuel 

blends that could be used to reduce fuel sulfur content. 

The current coal/coke fuel blend costs are based on 2006 fuel usage and cost data for the 

Montana City plant. The fuel switching costs are based on a switch to an 18.5% coke and 

81.5% coal blend, where the specific coal and coke assumed for the blend are the coal and 

coke that are currently burned at the plant. This fuel blend results in an approximate 50% 

reduction in fuel sulfur content from the fuel blend used in 2006. Again, AGC has not 

fully evaluated all potential fuel blends that would result in a 50% reduction in fuel sulfur 

content; this fuel blend was used only for costing purposes. In practice, AGC may utilize 

higher quality coal or lower sulfur coke to meet the energy requirements of the kiln. It was 

assumed in this analysis that fuel switching will not require any capital expenses. 

The total annual cost of fuel switching was divided by the annual tons of SO2 reduced to 

determine the cost effectiveness for fuel switching. The “annual tons reduced” were 

determined by subtracting the estimated controlled annual emissions from the existing 

annual emissions. The existing annual emissions are based on the average 24-hour SO2

emission rate (hourly equivalent) in 2006, as recorded by the gas analyzer, multiplied by 

the 2006 operating hours. The estimated controlled annual emission rates were calculated 

by reducing the existing annual emission rate by 50%. The sulfur content of the existing 

coal/coke fuel blend is 2.09 percent; this is calculated based on the sulfur contents of the 

fuels (3 percent for coke and 0.8 percent for coal) and the 2006 fuel usage (by MMBtu). 

The calculation for the sulfur content of the coal/coke fuel blend is as follows: 

905,045 Coke MMBtu 4.5% Sulfur + 643,376 Coal MMBtu 0.8 % Sulfur = 2 96 % Sulfur 

1,548,421 Total MMBtu 1,548,421 Total MMBtu 

The sulfur content of the fuel switching scenario is calculated based on a 11% coke and 

89% coal blend. The calculation of the sulfur content of the fuel blend and the reduced 

emissions are shown below: 

286,458 Coke MMBtu 4.5% Sulfur + 1,261,963 Coal MMBtu 0.8 % Sulfur = 1.48 % Sulfur 

1,548,421 Total MMBtu 1,548,421 Total MMBtu 
Ash Grove Cement Company 4-10 Trinity Consultants 

BART Analysis 

2.96 % Sulfur - 1.48% Sulfur = 50 % 

2.96 % Sulfur 

253.52 lb 7,741 hr ton 50 % = 491 ton SO2 Reduced 

hr yr 2,000 lb yr 

The cost of fuel switching is summarized in Table 4-5. 
Ash Grove Cement Company 4-11 Trinity Consultants 

BART Analysis 

TABLE 4-5.

SUMMARY OF 

COST 

EFFECTIVENESS FOR 

FUEL 

SUBSTITUTION

Existing 

Annual 

Emissions 

Controlled 

Annual 

Emissions 

Reduced 

Annual 

Emissions 

Existing 

Annual 

Energy 

(Coal/Coke) 

Usage 

Existing 

Coal/Coke 

Cost* 

Average 

Heating Value 

Annual Fuel 

Usage Cost 

Annual 

Fuel Cost 

(tons/yr) (tons/yr) (tons/yr) (MMBtu/yr) ($/yr) Btu/lb Tons/yr $/ton ($/yr) 

981 492 490 1,548,421 $1,860,967 14,582 (Coke) 9,822 (Coke) 16.38 (Coke) 2,814,066 

8,426 (Coal) 74,885 (Coal) 35.43 (Coal) 

*

The existing coal/coke cost is based on 2006 actual usage data (31,033 tons coke * $16.38/ton + 38,178 tons Coal * 35.43/ton = $1,860,967).
Ash Grove Cement Company 4-12 Trinity Consultants 

BART Analysis 

Energy Impacts and Non Air-Quality Impacts 

There are no energy or non-air quality impacts associated with fuel switching. 

Remaining Useful Life 

The remaining useful life of the kiln does not impact the annualized costs for fuel 

switching, since, for this analysis, it is assumed that fuel switching will not require any 

capital costs. 

4.5 EVALUATION OF VISIBILITY IMPACT OF FEASIBLE SO2 CONTROLS 

A final impact analysis was conducted to assess the visibility improvement for existing emission rates 

when compared to the emission rates of WLS and fuel switching. The existing emission rates and 

emission rates associated with WLS and fuel switching were modeled using CALPUFF. The existing 

emission rates are the same rates that were modeled for the BART applicability analysis. The SO2

emissions rates associated with WLS and fuel switching are the proposed BART emission limits in 

lb/hr based on reductions from the 2006 average 24-hour emission rate (as an hourly equivalent). 

The SO2 emission reductions from the WLS and fuel switching control options were applied to the 

2006 average 24-hour SO2 emission rate rather than the maximum 24-hour SO2 emission rate because 

the BART limit is proposed as a 30-day rolling average. Had the reductions been applied to the 

maximum 24-hour SO2 emission rates, the controlled emission rates would be much higher than what 

AGC anticipates could be achieved by the WLS and fuel switching control options on a 30-day 

rolling basis. The emission rates are summarized in Table 4-6. 

TABLE 4-6. SUMMARY OF EMISSION RATES MODELED IN SO2 CONTROL VISIBILITY IMPACT 

ANALYSIS 

 Emission Rate Scenario Emission Rate 

 SO2 NOX PM10 

 (lb/hr) (lb/hr) (lb/hr) 

WLS 25.35 848.74 37.17 

Fuel Substitution 126.76 848.74 37.17 

Comparisons of the existing visibility impacts and the visibility impacts based on WLS and fuel 

switching for the Gates of the Mountains Wilderness Area are provided in Table 4-7. The visibility 

improvement associated with WLS and fuel switching are also shown in Table 4-7; this value was 

calculated as the difference between the existing visibility impairment and the visibility impairment 

for the controlled emission rates as measured by the 98th percentile modeled visibility impact. 
Ash Grove Cement Company 4-1 Trinity Consultants 

BART Analysis 

TABLE 4-7. SUMMARY OF MODELED IMPACTS FROM SO2 CONTROL VISIBILITY IMPACT 

ANALYSIS

 

98% Impact 

(Δdv) Improvement 

Existing 2.87 --

Fuel Switching 2.70 6.05% 

WLS 2.63 8.39% 

As shown in Table 4-7, the installation of a WLS on the kiln results in an 8.39 percent improvement 

to the existing visibility impairment. Fuel switching results in a 6.05 percent improvement to the 

existing visibility impairment. Therefore, utilization of WLS as compared to fuel switching results in 

only a 2% incremental improvement (0.07 Δdv). The minimal visibility improvement was expected 

due to the low contribution of sulfates to the existing visibility impairment when compared to nitrates. 

4.6 PROPOSED BART FOR SO2

In order to determine BART for SO2, AGC evaluated each control option’s cost of compliance, 

energy impacts, and non-air quality impacts, as well as the remaining useful life of the kiln. Table 4-

8 summarizes the cost effectiveness for each control option based on the tons of SO2 reduced and the 

visibility improvement in deciviews. The cost effectiveness for the fuel switching is $1,947 per ton 

of SO2 reduced and $5.5 million per deciview of visibility improvement. This corresponds to a 

nominal visibility improvement from 2.87 Δdv to 2.70 Δdv. The cost effectiveness for the WLS is 

$3,716 per ton of SO2 reduced and $13.6 million per deciview of visibility improvement. This 

corresponds to a nominal visibility improvement from 2.87 Δdv to 2.63 Δdv. The incremental cost of 

utilizing WLS as opposed to fuel switching is $33,271,129 per deciview. 

TABLE 4-8. SUMMARY OF COST EFFECTIVENESS OF SO2 CONTROL TECHNOLOGIES

 Existing 

Emissions 

Controlled 

Emissions 

Reduced 

Annual 

Emissions 

Annual Cost Cost 

Effectiveness

 (tons/yr) (tons/yr) (tons/yr) ($/yr) ($/ton) 

Fuel Switching 981 492 490 953,099 1,947 

WLS 981 98 883 3,282,078 3,716 

 Base 98th 

Percentile 

Impact 

98th Percentile 

Impact 

98th 

Percentile 

Improvement 

98th 

Percentile 

Improvement 

Cost 

Effectiveness 

 (DV) (DV) (DV) (%) ($/DV) 

Fuel Switching 2.87 2.70 0.17 6.05 5,477,581 

WLS 2.87 2.63 0.24 8.39 13,618,583 
Ash Grove Cement Company 4-2 Trinity Consultants 

BART Analysis 

Based on the five step analysis outlined by EPA, fuel switching and WLS were identified as the two 

technically feasible technologies. Cost, energy and environmental impacts were assessed for both 

technologies and the visibility improvements associated with both options were evaluated against 

existing conditions. This analysis demonstrates that the cost of compliance associated with both 

control options is high while the visibility impact analysis demonstrates that the visibility 

improvements associated with both control options are nominal due to the fact that the percentage of 

visibility impairment attributable to SO4 is relatively low. As a result, AGC has determined that 

additional SO2 control technologies (fuel switching and WLS) would provide little visibility 

improvement and require significant expenditures. Therefore, AGC proposes that limiting the kiln to 

the existing levels of SO2 emissions constitutes BART for the kiln. 
Ash Grove Cement Company 5-3 Trinity Consultants 

BART Analysis 

5. NOX BART EVALUATION

In Portland cement kilns, the NOx that is generated is primarily classified into one of two categories, 

i.e., thermal NOx or fuel NOx

6. Thermal NOx occurs as a result of the high-temperature oxidation of 

molecular nitrogen present in the combustion air. Fuel NOx is created by the oxidation of 

nitrogenous compounds present in the fuel. It is also possible for nitrogenous compounds to be 

present in the raw material feed and become oxidized to form additional NOx referred to as feed NOx. 

Due to the high flame temperature in the burning zone of the rotary kiln (3400o F), NOx emissions 

from the kiln tend to be mainly comprised of thermal NOx. Although NOx emissions from cement 

kilns include both nitrogen oxide (NO) and nitrogen dioxide (NO2), typically, less than 10% of the 

total NOx in the flue gas is NO2.7

The kiln is the only BART source which emits NOx, thus a NOx BART evaluation was performed 

only for the kiln. The maximum actual 24-hour kiln NOx emission rate that was modeled for the 

BART applicability determination is summarized in Table 4-1. The NOx 24-hour maximum actual 

emission rate was determined from analyzer data for 2006. 

TABLE 5-1. EXISTING ACTUAL MAXIMUM 24-HOUR NOX EMISSION RATES

NOx 24-Hour 

Emission Rate 

NOx Hourly Equivalent 

Emission Rate 

 (ton/24-hr) (lb/hr) 

Kiln 10.18 848.74 

5.1 IDENTIFICATION OF AVAILABLE RETROFIT NOX CONTROL 

TECHNOLOGIES

Step 1 of the BART determination is the identification of all available retrofit NOX control 

technologies. A list of control technologies was obtained by reviewing the U.S. EPA’s Clean Air 

Technology Center, control equipment vendor information, publicly-available air permits, 

applications, and technical literature published by the U.S. EPA and the RPOs. 

The available retrofit NOX control technologies are summarized in Table 5-2. 

 6 NOx Formation and Variability in Portland Cement Kiln Systems, Penta Engineering, December 1998. 

7 IBID. 
Ash Grove Cement Company 5-4 Trinity Consultants 

BART Analysis 

TABLE 5-2. POSSIBLE NOX CONTROL TECHNOLOGIES

Kiln Control Technologies 

Low NOx Burner 

Flue Gas Recirculation 

CKD Insufflation 

Mid-Kiln Firing of Tires 

Selective Noncatalytic Reduction 

Selective Catalytic Reduction 

5.2 ELIMINATE TECHNICALLY INFEASIBLE NOX CONTROL TECHNOLOGIES

Step 2 of the BART determination is to eliminate technically infeasible NOX control technologies that 

were identified in Step 1. 

5.2.1 LOW-NOX BURNER IN THE ROTARY KILN

Low NOx burners (LNBs) reduce the amount of NOx formed at the flame. The principle of 

all LNBs is the same: stepwise or staged combustion and localized exhaust gas 

recirculation (i.e. at the flame). As applied to the rotary cement kiln, the low-NOx burner 

creates primary and secondary combustion zones at the end of the main burner pipe to 

reduce the amount of NOx initially formed at the flame. In the high-temperature primary 

zone, combustion is initiated in a fuel-rich environment in the presence of a less than 

stoichiometric oxygen concentration. The oxygen-deficient condition at the primary 

combustion site minimizes thermal and fuel NOx formation and produces free radicals that 

chemically reduce some of the NOx that is being generated in the flame. 

In the secondary zone, combustion is completed in an oxygen-rich environment. The 

temperature in the secondary combustion zone is much lower than in the first; therefore, 

lower NOx formation is achieved as combustion is completed. CO that has been generated 

in the primary combustion zone as an artifact of the sub-stoichiometric combustion is fully 

oxidized in the secondary combustion zone. 

The EPA has indicated that a 14% reduction in NOx emissions may be anticipated in 

switching from a direct-fired standard burner to an indirect-fired LNB8. This is based on a 

study conducted on an indirect-fired LNB at the Dragon Product Company cement kiln at 

the plant located in Thomaston, Maine. However, the EPA has also determined that the 

[emission reduction] contribution of the LNB itself and of the firing system conversion 

[direct to indirect] can not be isolated from the limited data available9. The terms direct 

and indirect firing have unique meaning in the context of kiln firing (unlike the more 

general meanings where direct firing implies that the products of combustion contact the 

 8 NOX Control Technologies for the Cement Industry, EC/R Incorporated, Chapel Hill, NC, USA, U.S. EPA 

Contract NO. 68-D98-025, U.S. EPA RTP, September 19, 2000. 

9 USEPA, Office of Air Quality Planning and Standards. Alternative Controls Technology Document - NOx 

Emissions from Cement manufacturing. EPA-453/R-94-004, Page 5-5 to 5-8. 
Ash Grove Cement Company 5-5 Trinity Consultants 

BART Analysis 

process materials whereas indirect firing involves a heat transfer medium). In kiln firing, 

direct and indirect firing describes the manner in which pulverized fuel is conveyed from 

the fuel grinding mill to the burner. 

In the direct firing configuration, fuel is pneumatically conveyed directly from the coal mill 

to the burner. The quantity of air introduced to the primary combustion zone is dictated by 

the minimum air requirements of the coal mill and the conveyance system, rather than the 

optimum flame requirements. The Montana City plant kiln uses a direct firing system. 

In the indirect firing configuration, the coal mill air is separated from the pulverized fuel 

which is stored in a tank before being fed to the kiln. The pulverized fuel is then conveyed 

to the burner with the quantity of air that is optimum for flame considerations. There have 

been no controlled studies conducted on cement kilns that verify that this method of 

burning solid fuel reduces the formation of NOx. 

The AGC Midlothian, Texas plant, which also operates direct-fired wet kilns, utilizes a 

direct fired LNB system that consists of a plugged annual burner pipe. In this design, the 

burner pipe has a central plug, which reduces the pressure at the core of the jet. As a result, 

the pressure of the primary air jet is relieved inward, reducing the rate of the expansion of 

the flame. This produces a non-divergent flame that minimizes surface area of the flame 

and maintains the fuel concentrated in the core of the flame. The annual burner pipe is 

shown in Figures 5-1 and 5-2. 

FIGURE 5-1 ANNUAL BURNER PIPE WITH CONTRACTED FLAME

FIGURE 5-2 SCHEMATIC OF ANNUAL BURNER PIPE 

When compared to simple free jet burners without the annual nozzle, these burners 

enhance NOX control by reducing flame turbulence, delaying fuel/air mixing, and 
Ash Grove Cement Company 5-6 Trinity Consultants 

BART Analysis 

establishing a fuel rich core in the flame for initial combustion. Low-NOx burners are 

considered to be a technically feasible option for NOX control. 

5.2.2 FLUE GAS RECIRCULATION

Flue gas recirculation involves the use of oxygen-deficient flue gas from some point in the 

process as a substitute for primary air in the main burner pipe in the rotary kiln. Flue gas 

recirculation (FGR) lowers the peak flame temperature and develops localized reducing 

conditions in the burning zone through a significant reduction of the oxygen content of the 

primary combustion “air.” The intended effect of the lower flame temperature and 

reducing conditions in the flame is to decrease both thermal and fuel NOx formation in the 

rotary kiln. 

While FGR is a practiced control technology in the electric utility industry, AGC is not 

aware of any attempt to apply FGR to a cement kiln because of the unique process 

requirements of the industry, i.e., a hot flame is required to complete the chemical reactions 

that form clinker minerals from the raw materials. The process of producing clinker in a 

cement kiln requires the heating of raw materials to about 2700°F for a brief but 

appropriate time to allow the desired chemical reactions that form the clinker minerals to 

occur. A short, high-temperature flame of about 3400°F is necessary to meet this process 

requirement. The long/lazy flame that would be produced by FGR would result in the 

production of lower or unacceptable quality clinker because of the resulting undesirable 

mineralogy. Clinkering reactions must take place in an oxidizing atmosphere in the 

burning zone to generate clinker that can be used to produce acceptable cement. FGR 

would tend to produce localized or general reducing conditions that also could 

detrimentally affect clinker quality. Due to these important limitations on the application 

of FGR and the lack of a successful demonstration on a cement kiln in the United States, 

FGR is not a technically feasible control option for NOx control at this time. 

5.2.3 CEMENT KILN DUST INSUFFLATION

Cement kiln dust (CKD) is a residual byproduct that can be produced by any of the four 

basic types of cement kiln systems. CKD is most often treated as a waste even though 

there are some beneficial uses. However, as a means of recycling usable CKD to the 

cement pyroprocess, CKD sometimes is injected or insufflated into the burning zone of the 

rotary kiln in or near the main flame. The presence of these cold solids within or in close 

proximity to the flame has the effect of cooling the flame and/or the burning zone thereby 

reducing the formation of thermal NOx. The insufflation process is somewhat 

counterintuitive because a basic requirement of a cement kiln is a very hot flame to heat the 

clinkering raw materials to about 2700o F in as short a time as possible. Because there is an 

increased requirement for thermal energy in the burning zone when insufflation is 

employed, it is not an attractive technology for recirculation of CKD in wet kiln systems. 

Other, more efficient procedures are available. Therefore, this option is removed from 

consideration for BART. 
Ash Grove Cement Company 5-7 Trinity Consultants 

BART Analysis 

5.2.4 MID-KILN FIRING OF SOLID FUEL (TIRES) WITH MIXING AIR FAN

Secondary combustion is defined as follows: a portion of the fuel is fired in a location 

other than the burning zone. This reduces thermal NOx generation because the temperature 

in the secondary combustion zone is less than 2100 °F. Mid-kiln firing (MKF) of solid 

fuels, such as used tires, is an example of secondary combustion. MKF allows part of the 

kiln fuel to be burned at a material calcination temperature (secondary combustion zone) 

which is much lower than the clinker burning temperature. 

The Cadence feed form MKF technology was first introduced in 1989. It is comprised of 

three primary components: (1) a staging arm or “feed fork,” that picks up the fuel modules 

and positions them for entry into the kiln, (2) two pivoting doors that open to allow the fuel 

to drop into the kiln, and (3) a drop tube that extends through the side wall of the kiln. In 

addition to these basic components, feed fork technology also requires a delivery system 

which positions the fuel models so they can be picked up by the feed fork and a mechanism 

for opening the doors so the fuel can enter the kiln. Due to rotation of the kiln, fuel can 

only be injected once per revolution from the top, as shown in Figure 5-3. 

FIGURE 5-3. MID-KILN FIRING SCHEMATIC10

High-pressure air, in the range of a 2-10 percent replacement of the primary combustion 

air, could be injected through the shell of the rotary kiln and into the calcining zone to 

where a mixing air fan mixes the air with the gas and fuel within the rotary kiln for more 

complete combustion of the solid fuel. 

By adding fuel mid-kiln, MKF changes both the flame temperature and flame length. 

These changes should reduce thermal NOX formation by burning part of the fuel at a lower 

temperature and by creating reducing conditions at the mid-kiln fuel injection point which 

may destroy some of the NOX formed upstream in the kiln burning zone. 

 10 NOX Control Technologies for the Cement Industry, EC/R Incorporated, Chapel Hill, NC, USA, U.S. EPA 

Contract NO. 68-D98-025, U.S. EPA RTP, September 19, 2000. 
Ash Grove Cement Company 5-8 Trinity Consultants 

BART Analysis 

The discontinuous fuel feed from MKF may also result in increased carbon monoxide (CO) 

emissions. To control CO emissions, the kiln may have to have increased combustion air 

which can decrease production capacity. 

AGC currently utilizes MKF of tires on three wet kilns at the Midlothian, Texas plant; 

approximately 4 million tires are burned each year for the three wet kilns. This accounts 

for about 20% of the fuel usage (BTU basis) at the Midlothian plant. It is estimated that 

approximately 1.3 million tires would be required at Montana City to achieve the same fuel 

replacement and equivalent NOX reductions. A study by the Montana Environmental 

Quality Council11 estimated that between 527,400 and 879,000 waste tires are generated 

each year in Montana. Therefore, in order for the Montana City plant to obtain the 

required amount of tires, tires would likely need to be imported from surrounding states. 

Furthermore, the Holcim Trident cement plant located in Three Forks, Montana, is 

currently seeking approval from MDEQ to burn up to 1,137,539 tires per year as 

supplemental fuel. In the Draft Environmental Impact Statement submitted by Holcim to 

MDEQ in July 2006, Holcim states that it will transport tires from out of state to 

supplement the number of tires available in Montana. This would create an additional 

strain on the supply of tires available in the region for the Montana City plant. 

Transportation of tires from surrounding states would increase the cost associated with 

MKF and generate additional air pollutant emissions for motor vehicle transportation and 

fugitive dust from traffic at the Montana City plant. Therefore, while MKF of tires is 

technically feasible, AGC proposes to eliminate this control option from further 

consideration as BART due to the supply shortage of tires. 

5.2.5 SELECTIVE NONCATALYTIC REDUCTION

In the relatively narrow temperature window of 1600 to 1995°F, ammonia (NH3) reacts 

with NOx without the need for a catalyst to form water and molecular nitrogen in 

accordance with the following simplified reactions. 

4NO + 4NH3 + O2 Æ 4N2 + 6H2O 

2NO2 + 4NH3 + O2 Æ 3N2 + 6H2O 

As applied to NOx control from cement kilns and other combustion sources, this 

technology is called selective noncatalytic reduction (SNCR). Above this temperature 

range, the NH3 is oxidized to NOx thereby increasing NOx emissions. Below this 

temperature range, the reaction rate is too slow for completion and unreacted NH3 may be 

emitted from the pyroprocess. This temperature window generally is available at some 

location within the rotary kiln. The NH3 could be delivered to the kiln shell through the 

use of anhydrous NH3, or an aqueous solution of NH3 (ammonium hydroxide) or urea. 

 11 Status of and Alternatives for Management of Waste Tires in Montana: Report to the 56th Legislature, 

Montana Environmental Quality Council, October 1998. 
Ash Grove Cement Company 5-9 Trinity Consultants 

BART Analysis 

A concern about application of SNCR technology is the breakthrough of unreacted NH3 as 

“ammonia slip” and its subsequent reaction in the atmosphere with SO2, sulfur trioxide 

(SO3), hydrogen chloride (HCl) and/or chlorine (Cl2) to form a detached plume of PM10 –

PM2.5. 

SNCR is currently being used successfully as an independent technology on wet cement 

kiln systems in Europe and recently, authorization was granted to AGC to test SNCR at its 

wet kiln in Midlothian, Texas. AGC installed a full scale SNCR system on one of its wet 

kilns and the system has been running for several months; it is achieving a 35 to 40% NOx 

reduction on a consistent basis. 

As SNCR is currently being operated on one of AGC’s wet cement kiln at the Midlothian 

Texas plant, it is considered a technically feasible NOx control option for the Montana City 

plant 

5.2.6 SELECTIVE CATALYTIC REDUCTION

Selective Catalytic Reduction (SCR) is an add-on control technology for the control of 

emissions of the oxides of nitrogen (NOx) from a combustion process. SCR has been 

successfully employed in the electric power industry. The basic SCR system consists of a 

system of catalyst grids placed in series with each other within a vessel that is located in a 

part of the process where the normal flue gas temperature is in the required range. An 

ammonia-containing reagent is injected at a controlled rate upstream of the catalyst grids 

that are designed to ensure relatively even flue gas distribution within the grids, to provide 

good mixing of the reagent and flue gas, and to result in minimum ammonia (NH3) slip.12 

The NH3 reacts with NOx compounds (i.e., NO and NO2) on the surface of the catalyst in 

equal molar amounts (i.e., one molecule of NH3 reacts with one molecule of NOx). 

Common reagents include aqueous NH3, anhydrous NH3 and urea [(NH2)2CO]. In the 

presence of the catalyst, the injected ammonia is converted by OH-

 radicals to ammonia 

radicals (i.e., NH2

-

), which, in turn, react with NOx to form N2 and H2O. The SCR catalyst 

enables the necessary reactions to occur at lower temperatures than those required for 

Selective Non-Catalytic Reduction (SNCR). While catalysts can be effective over a larger 

range of temperatures, the optimal temperature range for SCR is 570 - 750o F. 

The catalyst system used in SCR applications usually consists of (1) a porous honeycomb 

of a ceramic substrate onto which catalyst has been attached to the surface of the ceramic 

material, or (2) a flat or corrugated plate onto which catalytic material has been deposited 

on the surface. A porous metal oxide with a high surface area-to-volume ratio acts as a 

catalyst base. On this base, typically titanium dioxide (TiO2), one or more metal oxide 

catalysts are deposited in various concentrations. In SCR applications, the active catalyst 

material typically consists of vanadium pentoxide (V2O5), tungsten trioxide (WO3), and 

molybdenum trioxide (MoO3) in various combinations. The composition, also known as 

the catalyst formulation, is tailored by the catalyst vendor to best suit a particular SCR 

 12 Slip refers to the quantity of unreacted reagent that exits the SCR reactor. 
Ash Grove Cement Company 5-10 Trinity Consultants 

BART Analysis 

application. Catalyst deactivation through poisoning, fouling, masking, sintering and 

erosion are common problems for SCR catalysts that, without careful process design and 

operation, could be exacerbated. If not fouled by sulfur dioxide (SO2), the catalysts used 

in SCR have a propensity to oxidize sulfur dioxide (SO2) in the flue gas to sulfur trioxide 

(SO3), a more undesirable pollutant. 

Because the reaction rate of NH3 and NOx is temperature dependent, the temperature of the 

flue gas stream to be controlled is the most important consideration in applying SCR 

technology to any combustion source. The optimum temperature range for SCR 

application is about 300o C (570o F) to 450o C (840o F). This range of normal process 

temperature may be found in the exhaust gas from the wet kiln at the PMCD inlet. 

SCR has not been applied to a cement plant of any type in the United States. SCR has 

been applied successfully at a cement plant in Solnhofen, Germany. The Solnhofen plant 

has a kiln with a preheater tower as opposed to the wet kiln system at AGC’s Montana City 

plant. SCR has also been successfully applied at a cement plant in Moncelice, Italy; 

however, this plant is also a preheater plant as opposed to the wet cement kiln system at 

Montana City. 

Earlier this year, as part of permitting a new cement plant to be located on the Moapa 

Pauite Indian Reservation in Nevada (Moapa Paiute plant), AGC carefully assessed all of 

the publicly available information regarding SCR application at Solnhofen to determine (1) 

whether the Solnhofen testing indicates that the SCR technology exceeds the performance 

of SNCR and (2) whether the technology is commercially available for 

preheater/precalciner system such as that intended for AGC’s proposed Moapa Paiute 

plant. In order to ensure a comprehensive review, AGC engaged an independent expert in 

SCR technology to conduct an extensive analysis of SCR and its availability in relation to 

the Moapa Paiute plant. This analysis determined that the SCR system at Solnhofen does 

not result in a lower NOx emission rate than that which can be gained from SNCR.13 The 

study also concluded that the cost and time required for pilot testing to select the 

appropriate catalyst and SCR size/configuration needed to achieve the same emission 

levels achievable by SNCR is unknown. In the draft Moapa Paiute PSD permit put out for 

public comment this spring, EPA Region 9 concluded that SCR did not constitute BACT 

for cement kilns as it could not be demonstrated to outperform SNCR (that permit is 

expected to be issued upon completion of the Endangered Species Act consultation). 

The major SCR vendors have also indicated that SCR is not commercially available for 

cement kilns at this time. The St. Lawrence Cement Company recently issued a Request 

for Proposals (RFP) for SCR for the company’s proposed new cement kiln in Greenport, 

New York. Of the four major vendors contacted, two, Lurgi PSI Inc. (Lurgi) and Babcock 

& Wilcox, did not provide any proposal, with Lurgi stating that their technology was not 

yet ready for commercial release. A third with relevant experience from the Solnhofen 

 13 Schreiber, Robert J., Evaluation of Suitability of Selective Catalytic Reduction for Use in Portland Cement 

Manufacturing, 2006 
Ash Grove Cement Company 5-11 Trinity Consultants 

BART Analysis 

demonstration plant, KWH,14 indicated that technical uncertainties prevented them from 

designing an SCR system without pilot plant testing. Only Alstom provided a proposal 

that suggested SCR could be supplied to a cement kiln system. However, careful review of 

the Alstom proposal, indicated that the Alstom proposal did not identify a commercial SCR 

system that would be viable for a cement kiln system application 

AGC has reviewed the publicly available SCR assessments and vendor documents related 

to the Greenport plant. Ash Grove believes that the Greenport vendor evaluation continues 

to be relevant and supports the conclusion that an SCR system is not commercially 

available as defined in the NSR Workshop Manual, pages B.17 and B.18, which states that: 

...Two key concepts are important in determining whether an 

undemonstrated technology is feasible: “availability” and 

“applicability.“ 

 As explained in more detail below, a technology is considered "available" if it can be 

obtained by the applicant through commercial channels or is otherwise available within the 

common sense meaning of the term. An available technology is “applicable” if it can 

reasonably be installed and operated on the source type under consideration. A technology 

that is available and applicable is technically feasible. Availability in this context is further 

explained using the following process commonly used for bringing a control technology 

concept to reality as a commercial product: concept stage; research and patenting; bench 

scale or laboratory testing; pilot scale testing; licensing and commercial demonstration; and 

commercial sales. 

A control technique is considered available, within the context presented above, if it has 

reached the licensing and commercial sales stage of development. A source would not be 

required to experience extended time delays or resource penalties to allow research to be 

conducted on a new technique. Neither is it expected that an applicant would be required 

to experience extended trials to learn how to apply a technology on a totally new and 

dissimilar source type. Consequently, technologies in the pilot scale testing stages of 

development would not be considered available. An exception would be if the technology 

were proposed and permitted under the qualifications of an innovative control device 

consistent with the provisions of 40 CFR 52.21(v) or, where appropriate, the applicable 

SIP [in which case it would be considered available]. 

Commercial availability by itself, however, is not necessarily sufficient basis for 

concluding a technology to be applicable and therefore technically feasible. Technical 

feasibility, as determined in Step 2, also means a control option may reasonably be 

deployed on or "applicable" to the source type under consideration. (NSR Page B.18) 

As SCR would require pilot scale testing, Ash Grove concluded that SCR was not 

“available” with respect to the Moapa Paiute plant because it was not commercially 

 14 KWH teamed with Elex, a German engineering firm who was responsible for some aspects of the Solnhofen 

installation. Elex holds a patent covering certain applications of SCR to cement kilns in the United States. 
Ash Grove Cement Company 5-12 Trinity Consultants 

BART Analysis 

available. This determination has also been the finding of the Florida DEP as recently as 

March 2005, which in a BACT determination for Florida Rock Industries, Newberry Plant, 

concluded that “there has been no pilot study conducted in the United States, and there 

have been no indications that a pilot plant will be constructed to test SCR by any Portland 

cement facilities in the United States.” Further, “...Some additional time would be needed 

to conduct tests to determine the correct catalyst formulation” and, “The Department does 

not consider SCR necessary to achieve a BACT level of control in Florida.”15.

In conclusion, AGC has determined that SNCR is as good as SCR based on Solnhofen and, 

due to commercial unavailability that AGC determined for the Moapa Paiute plant and 

since there is no known application of SCR on a wet kiln system, SCR is eliminated from 

further consideration as BART for NOx control at the Montana City plant. 

5.3 RANK OF TECHNICALLY FEASIBLE NOX CONTROL OPTIONS BY 

EFFECTIVENESS

The third step in the BART analysis is to rank the technically feasible options according to 

effectiveness. Table 5-3 presents potential NOx technically feasible control technologies for the kiln 

and the associated NOx emission levels. The emission rates are largely based AGC’s experience with 

wet kiln NOX control technologies at AGC’s Midlothian, Texas plant. 

 15 Air Permit No: 0010087-013-AC; PSD-FL-350 - BACT Determination, Comment written by Al Linero, 

Florida DEP, 3/30/2005, Pages BD-10 and BD-11. 
Ash Grove Cement Company 5-13 Trinity Consultants 

BART Analysis 

TABLE 5-3. RANKING OF TECHNICALLY FEASIBLE KILN NOX CONTROL TECHNOLOGIES BY 

EFFECTIVENESS

Pollutant Control Technology Effectiveness 

NOX Emissions Level 

(lb/hr) 

NOX 

LNB and SNCR 227.25 lb/hr (~35 % control)†

SNCR 295.36 lb/ hr (~35 % control) §

LNB 422.59 lb/ hr (~7% control) ††

†The effectiveness level for SNCR and LNB corresponds to a 50% NOX reduction from the 2006 average 24-hour 

emission rate as an hourly equivalent (454.50 lb/hr). The 90 percent reduction was applied to the 2006 average 24-hour 

NOx emission rate rather than the maximum 24-hour NOx emission rate to best reflect the performance of the control on a 

30 day rolling basis. 

§ The effectiveness level for SNCR corresponds to a 35% NOX reduction from the 2006 average 24-hour emission rate as 

an hourly equivalent (454.50 lb/hr). The 90 percent reduction was applied to the 2006 average 24-hour NOx emission rate 

rather than the maximum 24-hour NOx emission rate to best reflect the performance of the control on a 30 day rolling 

basis. 

††The effectiveness level for the direct-fired LNB system is based on AGC’s experience with a system at the Midlothian, 

Texas plant. The effectiveness corresponds to a 7% NOX reduction from the 2006 average 24-hour emission rate as an 

hourly equivalent (454.50 lb/hr). The 90 percent reduction was applied to the 2006 average 24-hour NOx emission rate 

rather than the maximum 24-hour NOx emission rate to best reflect the performance of the control on a 30 day rolling 

basis. 

5.4 EVALUATION OF IMPACTS FOR FEASIBLE NOX CONTROLS 

Step four for the BART analysis procedure is the impact analysis. The BART determination 

guidelines list four factors to be considered in the impact analysis: 

• Cost of compliance 

• Energy impacts 

• Non-air quality impacts; and 

• The remaining useful life of the source 

5.4.1 SNCR AND LNB 

Cost of Compliance 

Since AGC is proposing the most stringent control option as BART, the cost of compliance 

is not evaluated. 

Energy Impacts and Non Air-Quality Impacts 

SNCR systems require electricity to operate the blowers and pumps. The generation of the 

electricity will most likely involve fuel combustion, which will cause emissions. While the 

required electricity will result in the emissions, the emissions should be small compared to 

the reduction in NOx that would be gained by operating an SNCR system 
Ash Grove Cement Company 5-14 Trinity Consultants 

BART Analysis 

Ammonia slip from SNCR systems occurs either from ammonia injection at temperatures 

too low for effective reaction with NOx, leading to an excess of unreacted ammonia, or 

from over-injection of reagent leading to uneven distribution; which also leads to an excess 

of unreacted ammonia. Based on AGC’s experience at the Midlothian, Texas plant, we 

believe that ammonia slip will be less than 10 ppm above baseline emissions. While the 

presence of ammonia slip is recognized here as an impact attributable to SNCR systems, it 

is an air-quality impact and so is legally not part of the BART analysis process. 

Remaining Useful Life 

The remaining useful life of the kiln does not impact the annualized costs of SNCR 

because the useful life is anticipated to be at least as long as the capital cost recovery 

period, which is 10 years. 

5.5 EVALUATION OF VISIBILITY IMPACT OF FEASIBLE NOX CONTROLS 

The final impact analysis was conducted to assess the visibility improvement for existing emission 

rates when compared to the emission rates of the SNCR and LNB combined control option. The 

existing emission rates and emission rates associated with SNCR and LNB were modeled using 

CALPUFF. The existing emission rates are the same rates that were modeled for the BART 

applicability analysis. 

The NOx emission rate associated with the SNCR and LNB control option is the 2006 average 24-

hour NOx emission rate (hourly equivalent) reduced by 50 percent. This 50 percent reduction was 

applied to the 2006 average 24-hour NOx emission rate rather than the maximum 24-hour NOx

emission rate because the BART limit is proposed as a 30-day rolling average. Had the 50 percent 

reduction been applied to the maximum 24-hour NOx emission rate, the controlled emission rate 

would be much higher than what AGC anticipates could be achieved by the SNCR and LNB on a 30-

day rolling basis. The emission rates are summarized in Table 5-4. 
Ash Grove Cement Company 5-15 Trinity Consultants 

BART Analysis 

TABLE 5-4. SUMMARY OF EMISSION RATES MODELED IN NOX CONTROL VISIBILITY IMPACT 

ANALYSIS

Unit Emission Rate Scenario Emission Rate 

 SO2 NOX PM10

 (lb/hr) (lb/hr) (lb/hr) 

Kiln SNCR and LNB 473.87 227.25 37.17 

 Existing 473.87 848.74 37.17 

Comparisons of the 98th percentile existing visibility impacts and the visibility impacts based on LNB 

and SNCR for the Gates of the Mountains Wilderness Area are provided in Table 5-5. The visibility 

improvement associated with LNB and SNCR are also shown in Table 5-5; this was calculated as the 

difference between the existing visibility impairment and the visibility impairment for the remaining 

control options as measured by the 98th percentile modeled visibility impact. 

TABLE 5-5. NOX CONTROL VISIBILITY IMPACT ANALYSIS

 

98% Impact 

(Δdv) Improvement 

Existing 2.874 - 

SNCR and LNB 1.377 52.09% 

As seen in Tables 5-5, the SNCR and LNB result in a visibility improvement of 52.09 percent. 

5.6 PROPOSED BART FOR NOX 

Based on the five step analysis outlined by EPA, SNCR with LNB was identified as the sole 

technically feasible add-on control technology. Cost, energy and environmental impacts were 

assessed for this technology and the visibility improvements were evaluated against existing 

conditions. Consistent with EPA guidance, economic impacts were not assessed as AGC was willing 

to utilize the highest ranked control technology. The visibility impact analysis demonstrates that the 

utilization of SNCR and LNB to achieve a 227.25 lb/hr NOx emission rate results in significant 

visibility improvements. Neither non-air quality nor energy impacts associated with this control 

technology are material and so do not present a basis for eliminating SNCR/LNB in favor of retaining 

the existing rates as BART. Therefore, AGC proposes that a direct-fired LNB system with SNCR is 

BART for NOx. AGC proposes to comply with a BART emissions limit of 227.25 lb/hr on a 30-day 

rolling basis. Compliance with the emission limit will be demonstrated by continuous emissions 

monitoring. 
Ash Grove Cement Company 6-1 Trinity Consultants 

BART Analysis 

6. PM BART EVALUATION

PM is generated by the kiln and clinker cooler. The PM emissions are from the kiln are currently 

controlled by an ESP, and the PM emissions from the clinker cooler are controlled by a baghouse. 

The maximum daily PM10 emission rates that were modeled for the BART applicability determination 

are summarized in Table 6-1. 

TABLE 6-1. EXISTING MAXIMUM 24-HOUR PM10 EMISSION RATE

 PM10 24-Hour 

Emission Rate 

PM10 Hourly 

Emission Rate 

 (ton/24-hr) (lb/hr) 

Kiln 0.45 37.17 

Clinker Cooler 0.07 6.00 

A comparison of Table 6-1 with Table 4-1 and Table 5-1 shows that the current PM10 emission rates 

for the kiln and clinker cooler are much less than the current emission rates of SO2 and NOX for the 

kiln. The low PM10 emission rates correspond to low visibility impacts attributable to PM10 when 

compared to the impacts attributable to SO2 and NOX, as shown in Table 6-2. 

TABLE 6-2. VAP VISIBILITY IMPAIRMENT CONTRIBUTIONS AT GATES OF THE MOUNTAINS

98th Percentile 

Impact 

Visibility Impairment 

Attributable to SO4

1

Visibility Impairment 

Attributable to NO3

2

Visibility Impairment 

Attributable to PM103

 (∆ dv) (%) (%) (%) 

2.16 23.1 66.5 10.4 

1 The visibility impairment attributable to SO4 is primarily from SO2 emissions. A very small portion is from SO4 emitted 

as condensable particulate. 

2 The visibility impairment attributable to NO3 is entirely from NOX emissions. 

3 The visibility impairment attributable to PM10 is the sum of the visibility impairment attributable to all modeled primary 

PM species (PMc, PMf, EC, and SOA). 

As mentioned, the kiln has an existing ESP for particulate matter control. The ESP is the most 

effective particulate matter control device for a wet kiln, due to the temperature of the exhaust exiting 

the kiln. The exhaust from the kiln is well over 5000

F at times under normal operations and would 

require an extensive gas conditioning system to operate a fabric filter PMCD properly. 

Also, as mentioned, the clinker cooler has an existing baghouse for particulate matter control. A 

baghouse is currently the best device for controlling particulate matter from a source. 

As no particulate control devices were identified that are more effective than the existing PMCDs, 

AGC proposes that no additional PM control technologies are required for either the kiln or clinker 

cooler for BART. AGC believes that the existing controls are the best, most technically feasible 

controls for these types of sources. Because AGC is proposing to retain the most effective particulate 
Ash Grove Cement Company 6-2 Trinity Consultants 

BART Analysis 

control devices on the two BART units, there is no need to evaluate other impacts in establishing 

these control technologies as BART.