Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc i 

## Northshore Mining Company Analysis of Best Availabl e Retrofit Technology (BART)

Table of Contents

1. Executive Summary..................................

................................................... ........................................iv
2. Introduction.......................................

................................................... .................................................1 2.A BART Eligibility...................................

................................................... ...................................3 2.B BART Determinations ................................

................................................... .............................4
3. Streamlined BART Analysis ..........................

................................................... ...................................9 3.A Indurating Furnaces ................................

................................................... .................................9 3.B PM-Only Taconite MACT Emission Units ...............

................................................... ..............9 3.C Sources of fugitive PM that are subject to MACT sta ndards............................................. .......10 3.D Non-MACT Units and Fugitive Sources (PM only)......

................................................... ........10 3.E Other Combustion Units .............................

................................................... ...........................10 3.F Visibility Impact Modeling for Negligible Impacts..

................................................... .............11
4. Baseline Conditions and Visibility Impacts for BART Eligible Units .................................... ...........13 4.A MPCA Subject-to-BART Modeling ......................

................................................... ................13 4.B Facility Baseline Modeling.........................

................................................... ...........................14 4.C Facility Baseline Modeling Results .................

................................................... ......................19
5. Full BART Analysis for BART Eligible Emission Units

................................................... ................21 5.A Indurating Furnace.................................

................................................... ................................21 5.A.i Sulfur Dioxide Controls............................

................................................... ................ 22 5.A.i.a STEP 1 – Identify All Available Retrofit Control Te chnologies ................. 22 5.A.i.b STEP 2 – Eliminate Technically Infeasible Options.. .................................. 22 5.A.i.c STEP 3 – Evaluate Control Effectiveness of Remainin g Control Technologies.......................................

................................................... ...... 27 5.A.i.d STEP 4 – Evaluate Impacts and Document the Results. .............................. 28 5.A.i.e STEP 5 – Evaluate Visibility Impacts............... ........................................... 30 5.A.ii Nitrogen Oxide Controls............................

................................................... ............... 30 5.A.ii.a STEP 1 – Identify All Available Retrofit Control Te chnologies ................. 31 5.A.ii.b STEP 2 – Eliminate Technically Infeasible Options.. .................................. 31 5.A.ii.c STEP 3 – Evaluate Control Effectiveness of Remainin g Control Technologies.......................................

................................................... ...... 43 5.A.ii.d STEP 4 – Evaluate Impacts and Document the Results. .............................. 44 5.A.ii.e STEP 5 – Evaluate Visibility Impacts............... ........................................... 45 5.B External Combustion Sources........................

................................................... ........................47 5.B.i Sulfur Dioxide controls............................

................................................... ................. 47 5.B.i.a STEP 1 – Identify All Available Retrofit Control Te chnologies ................. 47 5.B.i.b STEP 2 – Eliminate Technically Infeasible Options.. .................................. 47Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc ii 5.B.i.c STEP 3 – Evaluate Control Effectiveness of Remainin g Control Technologies.......................................

................................................... ...... 51 5.B.i.d STEP 4 – Evaluate Impacts and Document the Results. .............................. 51 5.B.i.e STEP 5 – Evaluate Visibility Impacts............... ........................................... 53 5.B.ii Nitrogen Oxide Controls............................

................................................... ............... 54 5.B.ii.a STEP 1 – Identify All Available Retrofit Control Te chnologies ................. 54 5.B.ii.b STEP 2 – Eliminate Technically Infeasible Options.. .................................. 54 5.B.ii.c STEP 3 – Evaluate Control Effectiveness of Remainin g Control Technologies.......................................

................................................... ...... 61 5.B.ii.d STEP 4 – Evaluate Impacts and Document the Results. .............................. 62 5.B.ii.e STEP 5 – Evaluate Visibility Impacts............... ........................................... 64
6. Visibility Impacts.................................

................................................... ............................................67 6.A Post-BART Modeling Scenarios.......................

................................................... .....................67 6.B Post-BART Modeling Results .........................

................................................... ......................67
7. Select BART........................................

................................................... ............................................71

List of Tables

Table 3-1 Summary Table of BART-Eligible Units Subject to a S treamlined BART Analysis ....12 Table 4-1 Baseline Conditions Modeling Input Data and the Bas is for 24-hour Emissions Data..15 Table 4-2 Baseline Visibility Modeling Results...............

................................................... ........20 Table 5-1 Indurating Furnace SO 2 Control Technology – Availability, Applicability, and

Technical Feasibility ..............................

................................................... .................27 Table 5-2 Indurating Furnace SO 2 Control Technology Effectiveness.................. .......................27 Table 5-3 Indurating Furnace SO 2 Control Cost Summary .............................. ............................29 Table 5-4 Indurating Furnace NO x Control Technology – Availability, Applicability, and

Technical Feasibility ..............................

................................................... .................43 Table 5-5 Indurating Furnace NO x Control Technology Effectiveness .................. ......................43 Table 5-6 Indurating Furnace NO x Control Cost Summary .............................. ...........................44 Table 5-7 Backup Process Boiler SO 2 Control Technology – Availability, Applicability, and

Technical Feasibility ..............................

................................................... .................51 Table 5-8 Backup Process Boiler SO 2 Control Technology Effectiveness .................. .................51 Table 5-9 Backup Process Boiler SO2 Control Cost Summary..... ...............................................52 Table 5-10 Backup Process Boiler NO x Control Technology – Availability, Applicability a nd

Technical Feasibility ..............................

................................................... .................61 Table 5-11 Backup Process Boiler NOx Control Technology Effect iveness ..................................61 Table 5-12 Backup Process Boiler NO x Control Cost Summary.............................. ......................62 Table 5-13 Backup Process Boiler NO x Control Technology – Other Impacts Assessment..... .......63 Table 5-14 Backup Process Boiler NO x Post- BART Emission Rates for Emission Unit EU003 and

EU004..............................................

................................................... .......................64 Table 5-15 Backup Process Boiler Post-BART Modeling Scenarios . ............................................65 Table 5-16 Backup process Boiler Post-BART NO x Modeling Scenarios - Modeling Input Data ..66Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc iii Table 5-17 Backup Process Boiler Post-BART NO x Modeling Scenarios - Visibility Modeling

Results ............................................

................................................... ........................66 Table 5-18 Backup Process Boiler Post-BART NO x Modeling Scenarios – Comparison of

Visibility Modeling Results to Baseline Modeling Re sults..........................................66 Table 6-1 Post-BART Modeling Scenarios .......................

................................................... .......69 Table 6-2 Post-BART Modeling Scenarios - Visibility Modeling Results ...................................70 Table 6-3 Post-BART Modeling Scenarios – Comparison of Visibi lity Modeling Results to

Baseline Modeling Results ..........................

................................................... ............70

List of Figures

Figure 2-1 Minnesota’s BART Geography.........................

................................................... .........2

List of Appendices

Appendix A Control Cost Analysis Spreadsheets Appendix B Changes to MPCA BART Modeling Protocol Appendix C Visibility Impacts Modeling Report Appendix D Applicable and Available Retrofit Techno logies for Indurating Furnaces Appendix E Clean Air Interstate Rule (CAIR), Cost-E ffective Air Pollution Controls Appendix F Applicable and Available Retrofit Techno logies for Process BoilersY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc iv 

# 1. Executive Summary

Northshore Mining Company (NMC) is located in north ern Minnesota, with mining facilities located at Babbit and a taconite processing plant located a t Silver Bay. This report describes the background
and methods for the selection of the Best Available Retrofit Technology (BART) as proposed by NMC for its taconite processing plant.

Minnesota Pollution Control Agency MPCA identified 36 pieces of equipment at NMC that were installed within the time window (1962-1977) that m akes them subject to BART. The equipment includes two straight-grate indurating furnace line s (Furnaces 11 and 12) and two backup steam process boilers ( Process Boilers 1 and 2) that use natural gas and oil for fuel, as well material handling and/or storage units for ore, product, and additives. Preliminary visibility modeling conducted by the Minnesota Pollution Control Agency MPCA found that air emissions from NMC “cause or contribute to visibility impairment” in a federally protected Class I area, therefore making the facility subject to BART.

Guidelines included in 40 CFR §51 Appendix Y and MP CA Attachments 2 and 3 were used to propose BART. The existing pollution control equip ment on the furnace lines includes a wet walled electrostatic precipitator (WWESP) designed to cont rol of particulate matter (PM) and sulfur dioxide (SO 2 ). A dispersion modeling sequence of CALMET, CALPU FF, and CALPOST was used to assess the visibility impacts of the baseline emissions an d after the application of candidate BART controls. Visibility impacts were evaluated in the selection of BART. Other criteria that the BART rules require to be considered include the availability o f technology, costs of compliance, energy and environmental impacts of compliance, existing pollu tion control technology in use at the source, and the remaining useful life of the source.

Based on consideration of all of the above criteria , NMC proposes the following as BART:

• SO 2 emissions will be controlled by the existing WWESP s on the taconite furnaces. The process boilers will have no additional controls. NO x emissions will be controlled by good combustion practices for the taconite mining proces s for the furnaces and process boilers.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc v • PM emissions at the furnaces will be controlled as prescribed by the taconite maximum achievable control technology (MACT) standard 1 . The existing WWESPs adequately control
PM emissions from the furnaces to meet the MACT sta ndard. The process boilers will have
no additional controls.

The CALPUFF model is conservative, resulting in an over prediction of impacts 2 . This modeled high impact from the BART eligible sources is 1.1 d eciviews (dV), slightly above perceptible levels of one to two dV. The modeling also shows that the se sources do affect Class I area visibility at les s than 10 percent of the time based on the model pred icting an impact greater than 0.5dV only 34 to 38 days per year. Real impacts to the Class I areas f rom NMC are expected to be even less than these modeled impacts. NMC will continue to evaluate en ergy efficiency projects and other mechanisms to reduce their visibility impairment pollutants em ission rates.

1 40 CFR 63 Subpart RRRRR-and DDDDD NESHAPS: Taconit e Iron Ore Processing and Industrial Commercial and Institutional Boilers and Process Heaters 2 Federal Register 70, 128 (July 6, 2005): 39123Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 1 

# 2. Introduction

Northshore Mining Company (NMC) is located in north ern Minnesota, with mining facilities located at Babbit and a taconite processing plant located a t Silver Bay.. This report describes the backgroun d
and methods for the selection of the Best Available Retrofit Technology (BART) as proposed by NMC for its taconite processing plant.

To meet the Clean Air Act’s requirements, the U.S. Environmental Protection Agency (U.S. EPA) published regulations to address visibility impairm ent in our nation’s largest national parks and wilderness (“Class I”) areas in July 1999. This ru le is commonly known as the “Regional Haze Rule” [64 Fed. Reg. 35714 (July, 1999) and 70 Fed. Reg. 39104 (July 6, 2005)] and is found in 40 CFR part 51, in 300 through 309.

Within its boundary, Minnesota has two Class I area s – the Boundary Waters Canoe Area Wilderness and Voyageurs National Park. In addition, emission s from Minnesota may contribute to visibility impairment in other states’ Class I areas, such as Michigan’s Isle Royale National Park and Seney Wilderness Area. By December 2007, MPCA must submi t to U.S. EPA a Regional Haze State Implementation Plan (SIP) that identifies sources t hat cause or contribute to visibility impairment in these areas. The Regional Haze SIP must also inclu de a demonstration of reasonable progress toward reaching the 2018 visibility goal for each of the s tate’s Class I areas.

One of the provisions of the Regional Haze Rule is that certain large stationary sources that were put in place between 1962 and 1977 must conduct a Best Available Retrofit Technology (BART) analysis. The purpose of the BART analysis is to a nalyze available retrofit control technologies to determine if a technology should be installed to im prove visibility in Class I areas. The chosen technology is referred to as the BART controls, or simply BART. The SIP must require BART on all BART-eligible sources and mandate a plan to achieve natural background visibility by 2064. Figure 2-1 illustrates the BART-eligible facilities and the two Class I areas in Minnesota. When reviewing Figure 2-1, it is important to note that Minnesota Steel Industries (MSI) and Mesabi Nugget (Nugget), which are illustrated in the figur e, are not currently in operation. The SIP must also include milestones for establishing reasonable progress towards the visibility improvement goals and plans for the first five-year period. Upon subm ission of the Regional Haze SIP, states must make the requirements for BART sources enforceable throu gh rules, administrative orders or Title V permit amendments.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 2 Figure 2-1 Minnesota’s BART Geography The Minnesota SIP will address the 2 PSD Class I Ar eas [Voyageurs National Park (VPN) and Boundary Waters Canoe Area (BWCA)] and BART-eligible units i llustrated above. Facilities indicated in yellow ar e future facilities. (Source MPCA BART-Strategy October 4, 2005)

By U. S. EPA’s definition, reasonable progress mean s that there is no degradation of the 20 bestvisibility days, and the 20 worst-visibility days m ust have no more visibility impairment than the 20 worst days under natural conditions by 2064 3 . Assuming a uniform rate of progress, the default glide path would require 1 to 2 percent improvement per y ear in visibility on the 20 worst days. The state must submit progress reports every five years to es tablish their advancement toward the Class I area natural visibility backgrounds. If a state feels it may be unable to adopt the default glide path, a slower rate of improvement may be proposed on the b asis of cost or time required for compliance and non-air quality impacts.

3 See the preamble to the final BART and Regional Ha ze Rules, 70 FR No. 178, pp. 39104-39172Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 3 Note that the improvements required under the Regio nal Haze regulations are different from the BART requirements. Facilities subject to BART are not required to make all of the reasonable progress towards improving regional haze in Class I areas. Rather, BART is but one of many measures which state may rely upon in making ‘reaso nable progress” towards regional haze improvement goals. 

## 2.A BART Eligibility BART eligibility is established on the basis on thr ee criteria. In order to be BART-eligible, sources must meet the following three conditions:

1. Contain emission units in one or more of the 26 lis ted source categories under the PSD rules (e.g., taconite ore processing plants, fossil-fuel- fired steam electric plants larger than 250 MMBtu/hr, fossil-fuel boilers larger than 250 MMBtu /hr, petroleum refineries, coal cleaning plants, sulfur recovery plants, etc.);
2. Were in existence on August 7, 1977, but were not i n operation before August 7, 1962;
3. Have total potential emissions greater than 250 ton s per year for at least one visibilityimpairing pollutant from the emission units meeting the two criteria above.

Under the BART rules, large sources that have previ ously installed pollution-control equipment required under another standard (e.g., MACT, NSPS a nd BACT) will be required to conduct visibility analyses. Installation of additional con trols may be required to further reduce emissions o f visibility impairing pollutants such as PM, PM 10 , PM 2.5 , SO 2 , NO x , and possibly Volatile Organic Compounds (VOCs) and ammonia. Sources built before the implementation of the Clean Air Act (CAA), which had previously been grandfathered, may also have to conduct such analyses and possibly install controls, even though they have be en exempted to date from any other CAA requirements.

Once BART eligibility is determined, a source must then determine if it is “subject to BART.” A source is subject to BART if emissions “cause or co ntribute” to visibility impairment at any Class I area. Visibility modeling conducted with CALPUFF or another U.S. EPA -approved visibility model is necessary to make a definitive visibility impair ment determination (>0.5 deciviews). Sources that do not cause or contribute to visibility impairment are exempt from BART requirements, even if they are BART-eligible.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 4 

## 2.B BART Determinations Each source that is subject to BART must determine BART on a case-by-case basis. Even if a source was previously part of a group BART determination, individual BART determinations must be made for each source. The BART analysis takes into accou nt six criteria and is analyzed using five steps. The six criteria that comprise the engineering anal ysis include: the availability of the control technology, existing controls at a facility, the co st of compliance, the remaining useful life of a source, the energy and non-air quality environmenta l impacts of the technology, and the visibility impacts. 4 The five steps of a BART analysis are:

Step 1 - Identify all Available Retrofit Control Technologie s

The first step in the analysis is to identify all r etrofit control technologies which are generally available for each applicable emission un it. Available retrofit control technologies are defined by U.S. EPA in Appendix Y to Part 51 (Guidelines for BART Determinations Under the Regional Haze Rule) as fol lows:

Available retrofit technologies are those air pollu tion control technologies with a practical potential for application to the e missions unit and the regulated pollutant under evaluation. Air pollutio n control technologies can include a wide variety of available methods, system s, and techniques for control of the affected pollutant. Technologies re quired as BACT or LAER are available for BART purposes and must be include d as control
alternatives. The control alternatives can include not only existing controls for the source category in question, but also take into account technology transfer of controls that have been applied to simi lar source categories or gas streams. Technologies which have not yet been appl ied to (or permitted for) full scale operations need not be considered as ava ilable; we do not expect the source owner to purchase or construct a process or control device that has not been demonstrated in practice. 5

Step 2 - Eliminate Technically Infeasible Options

In the second step, the source-specific technical f easibility of each control option identified in step one is evaluated by answering th ree specific questions:

4 40 CFR 51 Appendix Y 5 Federal Register 70, No. 128 (July 6, 2005): 39164Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 5 1. Is the control technology “available” to the specif ic source which is undergoing the BART analysis?

The U.S. EPA states that a control technique is con sidered “available” to a specific source “if it has reached the stage of licensing an d commercial availability. 6 ” However, the U.S. EPA further states that they “do not expect a source owner to conduct extended trials to learn how to apply a tec hnology on a totally new and dissimilar source type. 7 ”

2. Is the control technology an “applicable technology ” for the specific source which is undergoing the BART analysis?

In general, a commercially available control techno logy, as defined in question 1, “will be presumed applicable if it has been used on the same or a similar source type. 8 ” If a control technology has not been demonstrate d on a same or a similar source type, the technical feasibility is determine d by “examining the physical and chemical characteristics of the pollutant-bearing s tream and comparing them to the gas stream characteristics of the source types to w hich the technology has been applied previously. 9 ”

3. Are there source-specific issues/conditions that wo uld make the control technology not technically feasible?

This question addresses specific circumstances that “preclude its application to a particular emission unit.” This demonstration typi cally includes an “evaluation of the characteristics of the pollutant-bearing gas st ream and the capabilities of the technology 10 .” This also involves the identification of “un-re solvable technical difficulties.” However, when the technical difficu lties are merely a matter of increased cost, the technology should be considered technically feasible and the technological difficulty evaluated as part of the e conomic analysis 11

.

6 Federal Register 70, No. 128 (July 6, 2005): 39165 7 IBID 8 IBID 9 IBID 10 IBID 11 IBIDY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 6 It is also important to note that vendor guarantees can provide an indication of technical feasibility but the U.S. EPA does not “co nsider a vendor guarantee alone to be sufficient justification that a control optio n will work.” Conversely, the U.S. EPA does not consider as “sufficient justification that a control option or emission limit is technically infeasible. In general, the d ecisions on technical feasibility
should be based on a combination of the evaluation of the chemical and engineering analysis and the information from vendor guarantees 12

.
Step 3 - Evaluate Control Effectiveness

In step three, the remaining controls are ranked ba sed on the control efficiency at the expected emission rate (post BART) as compared to t he emission rate before addition of controls (pre-BART) for the pollutant of concern

.
Step 4 - Evaluate Impacts and Document Results

In the fourth step, an engineering analysis documen ts the impacts of each remaining control technology option. The economic analysis co mpares dollar per ton of pollutant removed for each technology. In addition it include s incremental dollar per ton cost analysis to illustrate the economic effectiveness o f one technology in relation to the others. Finally, Step Four includes an assessment o f energy impacts and other non-air quality environmental impacts.

Economic impacts were analyzed using the procedures found in the U.S. EPA Air Pollution Control Cost Manual – Sixth Edition (EPA 452/B-02-001). Equipment cost
estimates from the U.S. EPA Air Pollution Control C ost Manual or U.S. EPA’s Air Compliance Advisor (ACA) Air Pollution Control Tech nology Evaluation Model
version 7.5 were used. Vendor cost estimates for th is project were used when applicable. The source of the control equipment cos t data are noted in each of the control cost analysis worksheets as found in Append ix A.

Step 5 - Evaluate Visibility Impacts

The fifth step requires a modeling analysis conduct ed with U.S. EPA -approved models such as CALPUFF. The modeling protocol 13 , including receptor grid, meteorological data, and other factors used for this part of the a nalysis were provided by the Minnesota

12 IBID 13 MPCA. October 10, 2005. Best Available Retrofit Technology (BART) Modeling Protocol to Determine Sources Subject to BART in the State of Minnesota

.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 7 Pollution Control Agency. The model outputs, includ ing the 98th percentile dV value and the number of days the facility contributes mor e than a 0.5 deciview (dV) of visibility impairment at each of the Class I areas, are used to establish the degree of improvement that can be reasonably attributed to ea ch technology.

The final step in the BART analysis is to select th e “best” alternative using the results of steps 1 through 5. In addition, the U.S. EPA and MPCA guid ance states that the “affordability” of the controls should be considered, and specifically sta tes:

1. Even if the control technology is cost effective, t here may be cases where the installation of controls would affect the viability of plant ope rations.

2. There may be unusual circumstances that justify tak ing into consideration the conditions of the plant and the economic effects requiring the use of a given control technology. These effects would include effects on product pric es, the market share, and profitability of the source. Where there are such unusual circum stances that are judged to affect plant operations, you may take into consideration t he conditions of the plant and the economic effects of requiring the use of a control technology. Where these effects are judged to have severe impacts on plant operations y ou may consider them in the selection process, but you may wish to provide an economic an alysis that demonstrates, in sufficient detail for public review, the specific e conomic effects, parameters, and reasoning. (We recognize that this review process must preserve the confidentiality of sensitive business information). Any analysis may also consider whether competing plants in the same industry have been required to i nstall BART controls if this information is available. 14

To complete the BART process, the analysis must “es tablish enforceable emission limits that reflect the BART requirements and requires compliance withi n a reasonable period of time 15 .” Those limits must be developed for inclusion in the state implem entation plan (SIP) that is due to U.S. EPA in December of 2007. In addition, the analysis must i nclude requirements that the source “employ techniques that ensure compliance on a continuous b asis 16 .” which could include the incorporation of other regulatory requirements for the source, inclu ding Compliance Assurance Monitoring (40 CFR

14 MPCA. March 2006. Guidance for Facilities Conducting a BART Analysis . Page 20. 15 MPCA. March 2006. Guidance for Facilities Conducting a BART Analysis . Page 23. 16 MPCA. March 2006. Guidance for Facilities Conducting a BART Analysis . Page 23.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 8 64), Periodic Monitoring (40 CFR 70.6(a)(3)) and Su fficiency Monitoring (40 CFR 70(6)(c)(1)). If technological or economic limitations make measurem ent methodology for an emission unit infeasible, the BART limit can “instead prescribe a design, equipment, work practice, operation standard, or combination of these types of standard s 17 .”

Compliance with the BART emission limits will be re quired within 5 years of U.S. EPA approval of
the Minnesota SIP.

17 MPCA. March 2006. Guidance for Facilities Conducting a BART Analysis . Page 23.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 9 

# 3. Streamlined BART Analysis

Within the preamble to the final federal BART rule, U.S. EPA explicitly encouraged states to include a streamlined approach for BART analyses 18 . The streamlined approach will allow both states a nd the
facilities to focus their resources on the main con tributors to visibility impairment. This section of the report follows the MPCA approved streamlined BA RT analysis for taconite facilities and presents the results of the streamlined approach.


## 3.A Indurating Furnaces The indurating furnaces are sources of three visibi lity impairing pollutants: NO x , SO 2 , and PM. The indurating furnaces is subject to the taconite MACT standard 19 for the PM emissions. MPCA’s guidance for conducting a BART review states that “ MPCA will rely on MACT standards to represent BART level of control for those visibilit y impairing pollutants addressed by the MACT standard unless there are new technologies subseque nt to the MACT standard, which would lead to
cost-effective increases in the level of control.” [Attachment 2, March 2006, page 2]. Since the MACT standard was established very recently and bec omes effective in 2006, the technology analysis is up-to-date. As a result, BART will be presumed to be equivalent to MACT for PM and no further analysis will be required to establish BART for PM for this source.

A full BART analysis will be conducted for NO x and SO 2 where applicable. 

## 3.B PM-Only Taconite MACT Emission Units In addition to the indurating furnaces, the taconit e MACT standard also regulates PM emissions from Ore Crushing and Handling operations, Pellet Cooler s, and Finished Pellet Handling operations. These sources operate near ambient temperature, onl y emit PM, and do not emit NO x or SO 2 . The Ore Crushing and Handling sources and the Finished Pellet Handling sources operate with control equipment to meet the applicable MACT limits (0.008 gr/dscf for existing sources and 0.005 gr/dscf for new sources). The Pellet Cooler sources are ex cluded from additional control under the MACT
standard due to the large size of the particles and the relatively low concentration of particle
emissions [FR, December 18, 2002, page 77570]. Therefore, t he emissions from the pellet coolers are considered to have a negligible impact on visib ility impairment, and no control requirements
under the MACT standard is consistent with the inte ntion of the BART analysis.

18 Federal Register 70, no. 128 (July 6, 2005): 39107 and 39116 19 40 CFR 63 Subpart RRRRR-NESHAPS: Taconite Iron Ore ProcessingY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 10 Since the MACT standard was established recently an d will become effective in 2006, the technology analysis is up-to-date. Again, for these units sub ject to a MACT standard, BART will be presumed to be equivalent to MACT according to MPCA guidance

.
No further analysis will be required to establish B ART for these sources. 

## 3.C Sources of fugitive PM that are subject to MACT standards The taconite MACT standard also regulates fugitive PM emissions (fugitive PM emissions from nonMACT sources are addressed in section 3.D). No equ ipment that emits fugitive PM has been identified at NMC as potentially BART-eligible equi pment, so these sources are not required to be addressed. Therefore, no further analysis will be required to establish BART for these sources. 

## 3.D Non-MACT Units and Fugitive Sources (PM only) A few sources of PM emissions and sources of fugiti ve PM are not subject to a MACT standard. They include units such as:

• Bentonite storage and handling

• Additive storage and handling

• Concentrate storage and handling
Considering all PM emissions which are subject to t he BART standard, the PM emissions from the above units typically represent less than 2.5% of P M emissions from the facility, which are subject to
BART.

The point source emission units are controlled by b aghouses, which is a technology that achieves a high level of control for PM. Since these units al ready have control equipment for PM emissions,
and since the PM emissions from these sources are s mall relative to the total PM emissions that are subject to the BART standard, additional control of these sources can be presumed to have minimal impact on visibility improvement in Class I areas. Existing controls will be considered BART consistent with direction from MPCA in the May 18, 2006 meeting.

No equipment that emits fugitive PM has been identi fied at NMC as potentially BART-eligible equipment, so these sources are not required to be addressed. No further analysis will be required to
establish BART for these sources.



## 3.E Other Combustion Units
The combustion units are sources of three visibilit y impairing pollutants: NO x , SO 2 , and PM.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 11 NMC facility has two process boilers that are subje ct to the boiler MACT 20 . Since the boiler MACT standards were established recently and become effe ctive in 2007, the technology analysis is up-todate. For the units subject to the boiler MACT sta ndard, BART will be presumed to be equivalent to MACT for PM according to MPCA guidance. A full BAR T analysis will be conducted for NO x and
SO 2 .
The Northshore facility also has a powerhouse which will require a full BART analysis. That analysis is provided in a separate report. 

## 3.F Visibility Impact Modeling for Negligible Impac ts The streamlined BART approach allows for a screenin g modeling demonstration of negligible visibility impacts for fugitive sources and combust ion units other than indurating furnaces and process boilers. NMC does not have any potentially BART eligible sources that require screening modeling.

20 40 CFR 63 Subpart DDDDD-NESHAPS: ICI Boilers and P rocess HeatersY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 12 Table 3-1 Summary Table of BART-Eligible Units Subj ect to a Streamlined BART Analysis

Emission Unit # Emission Unit Description VisibilityImpairing Pollutant Applicable

Limit 1 gr/dscf Maximum Daily

lbs/day 2 3.A Indurating Furnaces EU 100 Furnace 11 Hood Exhaust PM 0.01 272 EU 100 Furnace 11 Hood Exhaust PM 0.01 272 EU 100 Furnace 11 Hood Exhaust PM 0.01 272 EU 104 Furnace 11 Waste Gas PM 0.01 255 EU 104 Furnace 11 Waste Gas PM 0.01 255 EU 110 Furnace 12 Hood Exhaust PM 0.01 272 EU 110 Furnace 12 Hood Exhaust PM 0.01 272 EU 110 Furnace 12 Hood Exhaust PM 0.01 272 EU 114 Furnace 12 Waste Gas PM 0.01 255 EU 114 Furnace 12 Waste Gas PM 0.01 255 3.B PM-Only Taconite MACT Emission Units EU 008 East Car Dump PM 0.008 32 EU 010 Fine Crusher Bin Storage – East PM 0.008 45 EU 016 Crushed Ore Conveyors – East PM 0.008 12 EU 017 Fine Crushing Line 101 PM 0.008 8 EU 018 Fine Crushing Line 102 PM 0.008 8 EU 019 Fine Crushing Line 103 PM 0.008 8 EU 020 Fine Crushing Line 104 PM 0.008 8 EU 031 Concentrator Transfer Bin – East PM 0.008 8 EU 044 Concentrator Bin - Section 101 PM 0.008 18 EU 045 Concentrator Bin - Section 102 PM 0.008 18 EU 046 Concentrator Bin - Section 103 PM 0.008 18 EU 047 Concentrator Bin - Section 104 PM 0.008 18 EU 048 Concentrator Bin - Section 105 PM 0.008 18 EU 049 Concentrator Bin - Section 106 PM 0.008 18 EU 050 Concentrator Bin - Section 107 PM 0.008 18 EU 051 Concentrator Bin - Section 108 PM 0.008 18 EU 052 Concentrator Bin - Section 109 PM 0.008 18 EU 053 Concentrator Bin - Section 110 PM 0.008 18 EU 120 Furnace 11 Discharge PM 0.008 95 EU 121 Furnace 12 Discharge PM 0.008 95 EU 122 Furnace 11 Screening PM 0.008 95 EU 124 Furnace 12 Screening PM 0.008 95 3.D Non-MACT Emission Units and Fugitive Sources (PM-On ly) EU 077 Furnace 11 Day Bin Collector PM 0.01 4 EU 078 Furnace 11 Air Slide Collector PM 0.01 4 EU 079 Furnace 12 Day Bin Collector PM 0.01 4 EU 080 Furnace 12 Air Slide Collector PM 0.01 4 EU 081 East Pelletizer Bentonite Storage - Bin 3,4 PM 0.01 4 EU 082 East Pelletizer Bentonite Storage - Bin 5,6 PM 0.01 4 EU 083 Bentonite Unloading Collector PM 0.01 4 EU 084 Supplemental Bentonite Unloading Collector P M 0.01 10 3.E Other Combustion Units lb/mmBtu EU 003 Process Boiler #1 PM 0.6 45 EU 004 Process Boiler #2 PM 0.6 45 1 PM – Filterable PM only as measured by U.S. EPA Met hod 5 including the applicable averaging and groupi ng provisions, as presented in the MACT regulation, ef fective October 26, 2006. 2 Based on baseline flow rates.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 13 

# 4. Baseline Conditions and Visibility Impacts for BART Eligible Units

As indicated in U.S. EPA’s final BART guidance 21 , one of the factors to consider when determining BART for an individual source is the degree of visi bility improvement resulting from the retrofit technology. The visibility impacts for this facili ty were estimated using CALPUFF, an U.S. EPA approved model recommended for comparing the visibi lity improvements of different retrofit control
alternatives 22 (REFERNECE FED. GUIDANCE PREAMBLE pages 39127 – 39 129 as appropriate). However it is important to note that CALPUFF is a c onservative model that over estimates real impacts. Therefore, although the CALPUFF baseline modeling results are important to comparing control alternatives on a relative basis they are d o not accurately predict real impacts.

The CALPUFF program models how a pollutant contribu tes to visibility impairment with consideration for the background atmospheric ammoni a, ozone and meteorological data. Additionally, the interactions between the visibili ty impairing pollutants NO x , SO 2, PM 2.5 and PM 10 can play a large part in predicting impairment. It is therefore important to take a multi-pollutant approach when assessing visibility impacts.

In order to estimatedetermine the visibility improv ement resulting from the retrofit technology, the
source must first be modeled at baseline conditions . Per MPCA guidance, the baseline, or pre-BART conditions, shall represent the average emission ra te in units of pounds per hour (lbs/hr) and reflect
the maximum 24-hour actual emissions 23

. 

## 4.A MPCA Subject-to-BART Modeling In order to determine which sources are “Subject-to -BART” in the state of Minnesota, the MPCA completed modeling of the BART-eligible emission un its at various facilities in Minnesota in accordance with the Regional Haze rule. The modeli ng by MPCA was conducted using CALPUFF,
as detailed in the “Best Available Retrofit Technol ogy (BART) Modeling Protocol to Determine Sources Subject-to-BART in the State of Minnesota,” finalized in March 2006. The modeling by MPCA was conducted using emission rate information submitted by the facility. The emissions were

21 Federal Register 70, no. 128 (July 6, 2005): 39106

. 22 Federal Register 70, no. 128 (July 6, 2005): 39125 23 MPCA. March 2006. Best Available Retrofit Technology (BART) Modeling Protocol to Determine Sources Subject-to-BART in the State of Minnesota. Page 8.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 14 reported in units of pounds per hour (lbs/hr) and w ere to reflect the maximum actual emissions during a 24-hour period under steady-state operatin g conditions during periods of high capacity utilization. The results of the modeling were pres ented in the document titled “Results of Best Available Retrofit Technology (BART) Modeling to De termine Sources Subject-to-BART in the State of Minnesota ,” finalized in March 2006. The modeling conducted by MPCA demonstrated that this facility is subject-to-BART. 

## 4.B Facility Baseline Modeling Prior to re-creating the MPCA visibility impairment model, the modeling protocol was re-revaluated.
On behalf of NMC and the other Minnesota taconite f acilities, Barr Engineering proposed changes to the modeling protocol. The changes, as submitted t o MPCA on May 16, 2006 are presented in Appendix B.

In addition, the maximum 24-hour emission rates wer e re-evaluated internally within NMC to confirm that the emission rates represent the maxim um steady-state operating conditions during periods of high capacity utilization. The maximum 24-hour emission rates were not adjusted.

The facility baseline data is summarized in the Tab le 4-1. The full modeling analysis is presented in Appendix C.Y:\23\00 MN Taconite BART (2006)\Facility BART Reports\NMC\NMC Furnace-Process Boiler\NMC Furnace BARTReport_9-6-2006.doc15Table 4-1 Baseline Conditions Modeling Input Data and the Basis for 24-hour Emissions DataEU #EUDescriptionSO2Maximum24-hrEmissionRate(lbs/day)Basis forSO2 24-hourActualEmissionNOxMaximum24-hrEmissionRate(lbs/day)Basis forNOx 24-hourActualEmissionPM2.5Maximum24-hrEmissionRate(lbs/day)Basis forPM2.524-hourActualEmissionPM10Maximum24-hrEmissionRate(lbs/day)Basis forPM1024-hourActualEmissionSV #StackEasting(utm)StackNorthing(utm)Height ofOpeningfromGround(ft)BaseElevationof Ground(ft)Stacklength,width, orDiameter(ft)FlowRate atexit(acfm)ExitTemp(oF)EU003ProcessBoiler #1402 279 45 SV003 631471.5 5238482.8 131 611 6.5 59900 450EU004ProcessBoiler #2402 279 45 SV003 631471.5 5238482.8 131 611 6.5 59900 450EU008East CarDumpNA NA NA NA 32 SV008 631224.7 5238953.7 83 8705.0 62600 77EU010FineCrusherBinStorage -EastNA NA NA NA 45 SV010 631316.0 5238925.9 101 7676.0 90100 77EU016CrushedOreConveyors - EastNA NA NA NA 12 SV016 631314.1 5238884.6 69 7673.3 22400 77EU017FineCrushingLine 101NA NA NA NA 8 SV017 631322.8 5238896.8 69 767 2.7 15,000 77EU018FineCrushingLine 102NA NA NA NA 8 SV018 631328.6 5238905.9 69 767 2.7 15,000 77EU019FineCrushingLine 103NA NA NA NA 8 SV019 631334.4 5238915.1 69 767 2.7 15,000 77EU020FineCrushingLine 104NA NA NA NA 8 SV020 631341.2 5238924.2 69 767 2.7 15,000 77EU031ConcentratorTransferBin -EastNA NA NA NA 8 SV031 631455.6 5238785.1 83 696 2.7 18000 77EU044Concentrator Bin -Section101NA NA NA NA 18 SV044 631473.1 5238808.5 93 7163.3 29200 77EU045Concentrator Bin -Section102NA NA NA NA 18 SV045 631486.7 5238828.7 93 7163.3 29200 77Y:\23\00 MN Taconite BART (2006)\Facility BART Reports\NMC\NMC Furnace-Process Boiler\NMC Furnace BARTReport_9-6-2006.doc16EU #EUDescriptionSO2Maximum24-hrEmissionRate(lbs/day)Basis forSO2 24-hourActualEmissionNOxMaximum24-hrEmissionRate(lbs/day)Basis forNOx 24-hourActualEmissionPM2.5Maximum24-hrEmissionRate(lbs/day)Basis forPM2.524-hourActualEmissionPM10Maximum24-hrEmissionRate(lbs/day)Basis forPM1024-hourActualEmissionSV #StackEasting(utm)StackNorthing(utm)Height ofOpeningfromGround(ft)BaseElevationof Ground(ft)Stacklength,width, orDiameter(ft)FlowRate atexit(acfm)ExitTemp(oF)EU046Concentrator Bin -Section103NA NA NA NA 18 SV046 631501.3 5238849.0 93 7163.3 29200 77EU047Concentrator Bin -Section104NA NA NA NA 18 SV047 631514.8 5238870.3 93 7163.3 29200 77EU048Concentrator Bin -Section105NA NA NA NA 18 SV048 631529.4 5238890.7 93 7163.3 29200 77EU049Concentrator Bin -Section106NA NA NA NA 18 SV049 631544.0 5238911.0 93 7163.3 29200 77EU050Concentrator Bin -Section107NA NA NA NA 18 SV050 631557.6 5238932.3 93 7163.3 29200 77EU051Concentrator Bin -Section108NA NA NA NA 18 SV051 631572.1 5238952.6 93 7163.3 29200 77EU052Concentrator Bin -Section109NA NA NA NA 18 SV276 631590.6 5238980.0 93 7163.3 29200 77EU053Concentrator Bin -Section110NA NA NA NA 18 SV053 631605.2 5239000.3 93 7163.3 29200 77EU077Furnace11 DayBinCollectorNA NA NA NA 4 SV077 631274.7 5238341.3 97 670 0.8 1,800 77EU078Furnace11 AirSlideCollectorNA NA NA NA 4 SV078 631315.5 5238399.2 97 670 0.8 1,800 77EU079Furnace12 DayBinCollectorNA NA NA NA 4 SV079 631276.6 5238344.4 97 670 0.7 1,800 77Y:\23\00 MN Taconite BART (2006)\Facility BART Reports\NMC\NMC Furnace-Process Boiler\NMC Furnace BARTReport_9-6-2006.doc17EU #EUDescriptionSO2Maximum24-hrEmissionRate(lbs/day)Basis forSO2 24-hourActualEmissionNOxMaximum24-hrEmissionRate(lbs/day)Basis forNOx 24-hourActualEmissionPM2.5Maximum24-hrEmissionRate(lbs/day)Basis forPM2.524-hourActualEmissionPM10Maximum24-hrEmissionRate(lbs/day)Basis forPM1024-hourActualEmissionSV #StackEasting(utm)StackNorthing(utm)Height ofOpeningfromGround(ft)BaseElevationof Ground(ft)Stacklength,width, orDiameter(ft)FlowRate atexit(acfm)ExitTemp(oF)EU080Furnace12 AirSlideCollectorNA NA NA NA 4 SV080 631318.4 5238402.2 97 670 0.8 1,800 77EU081EastPelletizerBentoniteStorage -Bin 3,4NA NA NA NA 4 SV081 631311.2 5238408.2 129 6700.7 1,800 77EU082EastPelletizerBentoniteStorage -Bin 5,6NA NA NA NA 4 SV082 631318.0 5238419.3 130 6700.7 1,800 77EU083BentoniteUnloadingCollectorNA NA NA NA 4 SV083 631320.9 5238422.4 127 6700.7 1,300 77EU084SupplementalBentoniteUnloadingCollectorNA NA NA NA 10 SV084 631331.9 5238426.5 117 6701.7 4,900 77EU100Furnace11 HoodExhaust284 410 272 SV101 631339.1 5238341.2 121 636 6.0 70700 142EU100Furnace11 HoodExhaust284 410 272 SV102 631344.3 5238338.3 121 636 6.0 74300 142EU100Furnace11 HoodExhaust284 410 272 SV103 631348.4 5238335.3 121 636 6.0 77400 142EU104Furnace11 WasteGas142 1498 255 SV105 631343.4 5238298.9 134 6366.0 93,000 140EU104Furnace11 WasteGas142 1498 255 SV104 631334.2 5238298.9 134 6366.0 93,000 140EU110Furnace12 HoodExhaust284 410 272 SV111 631361.5 5238372.7 121 636 6.0 70700 142Y:\23\00 MN Taconite BART (2006)\Facility BART Reports\NMC\NMC Furnace-Process Boiler\NMC Furnace BARTReport_9-6-2006.doc18EU #EUDescriptionSO2Maximum24-hrEmissionRate(lbs/day)Basis forSO2 24-hourActualEmissionNOxMaximum24-hrEmissionRate(lbs/day)Basis forNOx 24-hourActualEmissionPM2.5Maximum24-hrEmissionRate(lbs/day)Basis forPM2.524-hourActualEmissionPM10Maximum24-hrEmissionRate(lbs/day)Basis forPM1024-hourActualEmissionSV #StackEasting(utm)StackNorthing(utm)Height ofOpeningfromGround(ft)BaseElevationof Ground(ft)Stacklength,width, orDiameter(ft)FlowRate atexit(acfm)ExitTemp(oF)EU110Furnace12 HoodExhaust284 410 272 SV112 631365.6 5238369.7 121 636 6.0 74300 142EU110Furnace12 HoodExhaust284 410 272 SV113 631370.7 5238366.8 121 636 6.0 77400 142EU114Furnace12 WasteGas142 1498 255 SV114 631354.5 5238331.4 134 6366.0 93,000 140EU114Furnace12 WasteGas142 1498 255 SV115 631362.7 5238325.5 134 6366.0 93,000 140EU120Furnace11DischargeNA NA NA NA 95 SV120 631383.5 5238300.6 91 6363.8 48000 150EU121Furnace12DischargeNA NA NA NA 95 SV121 631405.9 5238332.1 91 6363.8 48000 150EU122Furnace11ScreeningNA NA NA NA 95 SV122 631387.6 5238297.7 91 6363.8 48000 150EU124Furnace12ScreeningNA NA NA NA 95 SV124 631380.9 5238282.5 91 6363.8 48000 130Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 19 

## 4.C Facility Baseline Modeling Results The Minnesota BART modeling protocol 24 describes the CALPUFF model inputs, including the meteorological data set and background atmospheric ammonia and ozone concentrations, along with the functions of CALPOST post processing.. The CALP OST output files provide the following two methods to assess the expected post-BART visibility improvement:

• 98 th Percentile: As defined by federal guidance and as stated in the MPCA’s document which identifies the Minnesota facilities that are subjec t to BART 25 , a source "contributes to visibility impairment” if the 98 th percentile of any year’s modeling results (i.e. 7 th highest day) meets or exceeds the threshold of five-tenths (0.5) of a deciview (dV) at a Federally protected Class I area receptor.

• Number of Days Exceeding 0.5 dV: The severity of t he visibility impairment contribution, or reasonably attributed visibility impairment, can be gauged by assessing the number of days on which a source exceeds a visibility impairment t hreshold of 0.5 dV.

A summary of the baseline visibility modeling is pr esented in Table 4-2. As illustrated in the table, this facility is considered to contribute to visibi lity impairment in Class I areas because the modele d
98 th percentile of the baseline conditions exceeds the threshold of 0.5 dV However, the results also indicate that the highest modeled impact may not ex ceed human perceptibility which is on the order of one to two dV. In addition, the modeling shows that these emission sources cause or contribute to visibility impairment less than 10 % of the time, b ased on the modeling results predicting 34 to 38 days annually above 0.5dV. The results of this mode ling are also utilized in the post-BART modeling analysis in section 6 of this document.

The full modeling analysis is presented in Appendix C.

24 MPCA. March 2006. Best Available Retrofit Technology (BART) Modeling Protocol to Determine Sources Subject-to-BART in the State of Minnesota. Page 8. 25 MPCA. March 2006. Results of Best Available Retrofit Technology (BART ) Modeling to Determine Sources Subject-to-BART in the State of Minnesota.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 20 Table 4-2 Baseline Visibility Modeling Results

2002 2003 2004 2002 – 2004 Combined

Class I Area with Greatest Impact Modeled

98 th Percentile Value (deciview) No. of

days exceeding 0.5 deciview Modeled

98 th Percentile Value (deciview) No. of

days exceeding 0.5 deciview Modeled

98 th Percentile Value (deciview) No. of

days exceeding 0.5 deciview Modeled

98 th Percentile Value (deciview) No. of

days exceeding 0.5 deciview BWCA 1.1 34 1.1 34 1.3 38 1.1 106Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 21 

# 5. Full BART Analysis for BART Eligible Emission Units

BART eligible sources at NMC can be divided into gr oups based upon type of process.


## 5.A Indurating Furnace The primary function of taconite indurating furnace s is to convert magnetic iron concentrate to a more highly oxidized iron in the form of a pellet t hat is sold to metallic iron and steel production facilities. “Soft” or “green” pellets are oxidized and heat-hardened in the induration furnace. The induration process involves pellet pre-heating, dry ing, hardening, oxidation and cooling. The process requires large amounts of air for pellet oxidation and cooling. Process temperature control in all parts of the furnace is critical to minimize produc t breakage in the initial process stages, allow required oxidation reactions to occur, and adequate ly cool the product prior to subsequent handling steps. Directed air flow, heat recovery and fuel c ombustion are critical to controlling temperature and product quality in all parts of the furnace. N MC uses a straight grate furnace, in which pellets move through the entire furnace on a traveling grat e. The pellet hardening and oxidation section of the induration furnace is designed to operate at 2, 400 oF. This temperature is required to meet taconite pellet product specifications. Direct-fire d fuel combustion in the induration furnace is carried out at 300 % to 400 % excess air required t o provide sufficient oxygen for pellet oxidation.

Air is used for combustion, pellet cooling, and as a source of oxygen for pellet oxidation. Due to the high-energy demands of the induration process, indu ration furnaces have been designed to recover as much heat as possible using hot exhaust gases to he at up incoming pellets. Pellet drying and preheat zones are heated with the hot gases generated in th e pellet hardening/oxidation section and the pellet cooler sections. Each of these sections is designed to maximize heat recovery within process constraints. The pellet coolers are also used to pr eheat combustion air so more of the fuel’s energy i s directed to the process instead of heating ambient air to combustion temperatures.

NMC process has two straight-grate furnaces, Line 1 1 and Line 12 that are subject to BART. Line 11 and 12 are permitted to burn natural gas and fue l oil. Both line’s emissions are controlled by wet walled electrostatic precipitators (WWESP) using ca ustic reagent. The existing WWESP already provides excellent control and removal of PM and SO 2 .

Emissions of SO 2 result from low amounts of sulfur present in the o re and potentially from fuel oil use. Stack testing using natural gas fuel has demo nstrated the WWESP effectively removes SO 2 toY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 22 one to two parts per million in the exhaust from th e WWESPs. A recent BACT analysis for a similar
furnace at NMC established an emissions limit of 10 parts per million SO2 using existing WWESPs.

NO x is controlled through furnace design. The NMC fur naces emit the lowest tons of NO x /long ton product of any taconite producer making similar pel lets. NMCs furnaces are of an early vintage. Furnaces 11 and 12 have numerous burners critically located to supply heat to the various furnace sections. The burner layout limits production capa bility for the size of the furnace. This furnace design is not used by any other taconite producer.

The primary source of SO2 emissions in taconite pro duction is from trace amounts of sulfur in the iron concentrate and binding agents present in the green balls. Sulfur is also present in distillate fuel oil that is one of the permitted fuels.



### 5.A.i Sulfur Dioxide Controls

5.A.i.a STEP 1 – Identify All Available Retrofit Co ntrol Technologies See Appendix D for a comprehensive list of all pote ntial retrofit control technologies that were evaluated. Many emerging technologies have been id entified that are not currently commercially available. A preliminary list of technologies was submitted to MPCA on May 9 with the status of the technology as it was understood at that time. As w ork on this evaluation progressed, new information became apparent of the limited scope an d scale of some of the technology applications. Appendix D presents the current status of the avail ability and applicability of each technology.

5.A.i.b STEP 2 – Eliminate Technically Infeasible O ptions Step 1 identified the available and applicable tech nologies for SO 2 emission reduction. Within Step 2, the technical feasibility of the control op tion is discussed and determined. The following
section describes retrofit SO 2 control technologies that were identified as avail able and applicable in the original submittal and discusses aspects of tho se technologies that determine whether or not the technology is technically feasible for indurating f urnaces.
Wet Walled Electrostatic Precipitator (WWESP) An electrostatic precipitator (ESP) applies electri cal forces to separate suspended particles from the flue gas stream. The suspended particles are given an electrical charge by passing through a high voltage DC corona region in which gaseous ions flow . The charged particles are attracted to and collected on oppositely charged collector plates. P articles on the collector plates are released by rapping and fall into hoppers for collection and re moval.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 23 A wet walled electrostatic precipitator (WWESP) ope rates on the same collection principles as a dry ESP and uses a water spray to remove particulate ma tter from the collection plates. For SO 2 removal, caustic is added to the water spray system, allowin g the WWESP spray system to function as an SO 2 absorber. WWESPs are designed to remove emissions to levels less than 10 parts per million SO2 .

The SO 2 control efficiency for a WWESP is dependent upon v arious process specific variables, such
as SO 2 flue gas concentration, fuel used, and ore composit ion. NMC currently employs a WWESP designed for removal of particulate matter and SO 2 . The addition of a secondary WWESP would act as a polishing scrubber and would experience reduce d control efficiency due to lower SO 2 inlet concentrations. A control efficiency as a polishing WWESP ranges from 30-80% dependent upon the process specific operating parameters.

Based on the definitions contained within this repo rt, a polishing WWESP is considered an available technology for SO 2 reduction for this BART analysis. The existing WW ESP already removes SO 2 to a very low concentration. No other improvements ar e available to enhance the removal efficiency of the existing controls. Installation of a secondary WWESP is carried forward in this analysis.

Wet Scrubbing (High and Low Efficiency) Wet scrubbing, when applied to remove SO 2 , is generally termed flue-gas desulfurization (FGD ). FGD utilizes gas absorption technology, the selecti ve transfer of materials from a gas to a contacting liquid, to remove SO 2 in the waste gas. Crushed limestone, lime, or caus tic are used as scrubbing agents. Most wet scrubbers recirculate the scrubbin g solution, which minimizes the wastewater discharge flow. However, higher concentrations of s olids exist within the recirculated wastewater.

For a wet scrubber to be considered a high efficien cy SO 2 wet scrubber, the scrubber would require designs for removal efficiency up to 95% SO 2 . Typical high efficiency SO 2 wet scrubbers are packed-bed spray towers using a caustic scrubbing s olution. Whereas, a low efficiency SO 2 wet scrubber could be as low as 30% control efficiency. A low efficiency SO 2 could be a venturi rod scrubber design using water as a scrubbing solvent. Venturi rod scrubbers, which are frequently used for PM control at taconite facilities, will also re move some of the SO 2 from the flue gas as collateral
emission reduction.

Limestone scrubbing introduces limestone slurry wit h the water in the scrubber. The sulfur dioxide is absorbed, neutralized, and partially oxidized to ca lcium sulfite and calcium sulfate. The overall reactions are shown in the following equations:Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 24 CaCO 3 + SO 2 → CaSO 3 • 1/2 H2O + CO 2 CaSO 3 •1/2 H 2 O + 3H 2 O + O 2 → 2 CaSO 4 •2 H 2 O

Lime scrubbing is similar to limestone scrubbing in equipment and process flow, except that lime is a more reactive reagent than limestone. The reactions for lime scrubbing are as follows:

Ca(OH) 2 +SO 2 → CaSO 3 • 1/2 H 2 O + 1/2 H 2 O Ca(OH) 2 + SO 2 + 1/2 O 2 + H 2 O → CaSO 4 •2 H 2 O

When caustic (sodium hydroxide solution) is the scr ubbing agent, the SO 2 removal reactions are as
follows:

Na+ + OH- + SO 2 + → Na 2 SO 3 2Na+ + 2OH- + SO 2 + → Na 2 SO 3 + H 2 O

Caustic scrubbing produces a liquid waste, and mini mal equipment is needed as compared to lime or
limestone scrubbers.. If lime or limestone is used as the reagent for SO 2 removal, additional equipment will be needed for preparing the lime/lim estone slurry and collecting and concentrating the resultant sludge. Calcium sulfite sludge is wat ery; it is typically stabilized with fly ash for la nd filling. The calcium sulfate sludge is stable and e asy to dewater. To produce calcium sulfate, an air injection blower is needed to supply the oxygen for the second reaction to occur.

The normal SO 2 control efficiency range for SO 2 scrubbers on coal-fired utility boilers with exces s oxygen of 2-3% is 80% to 90% for low efficiency scr ubbers and 90% to 95% for high efficiency scrubbers. The highest control efficiencies can be achieved when SO 2 concentrations are the highest. Unlike coal-fired boilers, indurating furnaces oper ate with maximum excess air to enable proper oxidation of the pellet. The excess air dilutes the SO 2 concentration as well as creates higher flow rates to control. Additionally, the varying sulfur concentration within the pellet causes fluctuations of
the SO 2 concentrations in the exhaust gas stream. This co uld also impact the SO 2 control efficiency
of the wet scrubber.

As stated in the beginning of this section, WWESPs are currently in place on the furnace exhausts
and are believed to remove 80 to 95% of the SO 2 in the exhaust. Taking into consideration of the
removal of SO 2 from the existing primary WWESP as well as a high efficiency SO 2 polishing wet scrubber, an overall efficiency of the control trai n would then be well over 90%.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 25 Based on the information contained within this repo rt, a secondary wet scrubber is considered an available technology for SO 2 reduction for this BART analysis.

Dry Sorbent Injection (Dry Scrubbing Lime/Limestone Injection) Lime/limestone injection is a post-combustion SO 2 control technology in which pulverized lime or limestone is directly injected into the duct upstre am of the fabric filter. Dry sorption of SO 2 onto the lime or limestone particle occurs and the solid par ticles are collected with a fabric filter. Further SO 2 removal occurs as the flue gas flows through the fi lter cake on the bags. The normal SO 2 control efficiency range for dry SO 2 scrubbers is 70% to 90% for coal fired utility boi lers.

Induration waste gas streams are high in water cont ent and are exhausted at or near their dew points. Gases leaving the induration furnace are currently treated for removal of particulate matter using a WWESP. The exhaust temperature is typically in the range of 100 °F to 150 °F and is saturated with water. For comparison, a utility boiler exhaust op erates at 350 °F or higher and is not saturated wit h water. Under induration furnace waste gas condition s, the baghouse filter cake would become saturated with moisture and plug both the filters a nd the dust removal system. Although this may be an available and applicable control option, it is n ot technically feasible due to the high moisture
content and will not be further evaluated in this r eport.
Spray Dryer Absorption (SDA) Spray dryer absorption (SDA) systems spray lime slu rry into an absorption tower where SO 2 is absorbed by the slurry, forming CaSO 3 /CaSO 4 . The liquid-to-gas ratio is such that the water evaporates before the droplets reach the bottom of the tower. The dry solids are carried out with the gas and collected with a fabric filter. When used t o specifically control SO 2 , the term flue-gas desulfurization (FGD) may also be used.

Under induration furnace waste gas conditions, the baghouse filter cake would become saturated with moisture and plug both the filters and the dust rem oval system. In addition, because of the moisture in the exhaust, the lime slurry would not dry prope rly and it would plug up the dust collection system. Similarly to the dry sorbent injection cont rol option, this is an available and applicable control option, but is not technically feasible due to the high moisture content. This option will no t be further evaluated in this report.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 26 Energy Efficiency Projects Energy efficiency projects provide opportunities fo r a company to reduce their fuel consumption, which results in lower operating costs. Typically reduced fuel usage translates into reduced pollutio n emissions. An example of an energy efficiency proje ct could be to preheat incoming make-up air or pellet feed. Each project is very dependent upon t he fuel usage, process equipment, type of product and many other variables.

Due to the increased price of fuel, the facilities have already implemented energy efficiency projects

. Each project carries its own fuel usage reductions and potentially emission reductions. It would be impossible to assign a general potential emission r eduction for the energy efficient category. Due to the uncertainty and generalization of this category , this will not be further evaluated in this report

. However, it should be noted that facilities will co ntinue to evaluate and implement energy efficiency projects as they arise.

Alternate Fuels As described within the energy efficiency descripti on, increased price of fuel has pushed companies
to evaluate alternate fuel sources. These fuel sou rces come in all forms – solid, liquid and gas. To
achieve reduction of SO 2 emissions through alternative fuel usage, the sour ce must use fuels with lower sulfur content. NMC has the capability to on ly burn natural gas and distillate fuel oil in its furnaces. Therefore this option is not applicable for SO 2 reductions at NMC.

It is also important to note that U.S. EPA’s intent is for facilities to consider alternate fuels as t heir option, not to direct the fuel choice. 26

However, NMC will continue to evaluate and implemen t alternate fuel usage as the feasibility arises.

26 Federal Register 70, no. 128 (July 6, 2005): 39164Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 27 Coal Processing
Since NMC does not burn coal in Furnaces 11 and 12, this option is not applicable for SO 2 reductions
at NMC.

Step 2 Conclusion Based upon the determination within Step 2, the rem aining SO 2 control technologies that are available and applicable as secondary controls to t he existing indurating furnace WWESPs are identified in Table 5-1. The technical feasibility as determined in Step 2 is also included in Table 5 -1.

Table 5-1 Indurating Furnace SO 2 Control Technology – Availability, Applicability, and Technical Feasibility

SO 2 Pollution Control Technology Available? Applicable? Technically Feasible? Secondary Wet Scrubbing (High

Efficiency) Yes Yes Yes
Secondary Wet Scrubbing (Low

Efficiency) Yes Yes Yes
Secondary Wet Walled Electrostatic Precipitator (WWESP) Yes Yes Yes
Dry sorbent injection Yes Yes No Spray Dryer Absorption (SDA) Yes Yes No Alternative Fuels Yes No No Energy Efficiency Projects Yes Yes No Coal Processing Yes No No

5.A.i.c STEP 3 – Evaluate Control Effectiveness of Remaining Control Technologies Table 5-2 describes the expected control efficiency from each of the remaining feasible control options. The WWESP and high efficiency wet scrubbin g control options listed in Table 5-2 would be considered a polishing scrubber since a highly effe ctive SO2 control WWESP currently exists.

Table 5-2 Indurating Furnace SO 2 Control Technology Effectiveness

SO 2 Pollution Control Technology Approximate Control Efficiency Secondary Wet Walled Electrostatic Precipitator (WW ESP) 80

Secondary Wet Scrubber 60Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 28 5.A.i.d STEP 4 – Evaluate Impacts and Document the Results As illustrated in Table 5-2 above, the technically feasible control remaining provide varying levels o f emission reduction. Therefore, it is necessary to consider the economic, energy, and environmental impacts to better differentiate as presented below.

Economic Impacts Table 5-3 details the expected costs associated wit h installation of a secondary WWESP after the existing WWESP on each stack. Equipment design was based on the maximum 24-hour emissions, vendor estimates, and U.S. EPA cost models. Capita l costs were based on a recent vendor quotation.
The cost for that unit was scaled to each stack’s f low rate using the 6/10 power law as shown in the following equation:

Cost of equipment A = Cost of equipment B * (capac ity of A/capacity of B) 0.6

Direct and indirect costs were estimated as a perce ntage of the fixed capital investment using U.S. EPA models and factors. Operating costs were based on 93% utilization and 8339 operating hours per year. Operating costs of consumable materials, such as electricity, water, and chemicals were
established based on the U.S. EPA control cost manu al 27 and engineering experience, and were adjusted for the specific flow rates and pollutant concentrations.

Due to space considerations, 60% 28 of the total capital investment was included in th e costs to account for a retrofit installation. After a tour of the facility and discussions with facility staff , it was determined the space surrounding the furnaces is co ngested and the area surrounding the building supports vehicle and rail traffic to transport mate rials to and from the building. Additionally, the structural design of the existing building would no t support additional equipment on the roof. Therefore, the cost estimates provide for additiona l site-work and construction costs to accommodate the new equipment within the facility. A site-speci fic estimate for site work, foundations, and
structural steel was added to arrive at the total r etrofit installed cost of the control technology. The site-specific estimate was based on Barr’s experien ce with similar projects. See Appendix C for an aerial photo of the facility. The detailed cost ana lysis is provided in Appendix A.

27 U.S. EPA, January 2002, EPA Air Pollution Control Cost Manual, Sixth Editio n

. 28 U.S. EPA, CUE Cost Workbook Version 1.0 . Page 2.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 29

Table 5-3 Indurating Furnace SO 2 Control Cost Summary

Control Technology Installed

Capital Cost (MM$) Operating Cost

(MM$/yr) Annualized

Pollution Control Cost ($/ton) Incremental

Control Cost ($/ton) Secondary Wet Scrubber Furnace 11 Hood Exhaust $16,952,864 $2,401,349 $139,872 NA
Furnace 11 Waste Gas $15,859,420 $2,201,975 $384,034 NA
Furnace 12 Hood Exhaust $16,952,864 $2,401,349 $152,149 NA
Furnace 12 Waste Gas $15,859,420 $2,201,975 $417,742 NA Secondary Wet Walled Electrostatic Precipitator (WW ESP) Furnace 11 Hood Exhaust $23,617,556 $4,188,875 $182,993 NA
Furnace 11 Waste Gas $21,846,389 $3,799,211 $496,949 NA
Furnace 12 Hood Exhaust $23,617,556 $4,294,171 $204,058 NA
Furnace 12 Waste Gas $21,846,389 $3,764,113 $535,575 NA

Based on the BART final rule, court cases on cost-e ffectiveness, guidance from other regulatory bodies, and other similar regulatory programs like Clean Air Interstate Rule (CAIR), cost-effective air pollution controls in the electric utility indu stry for large power plants are in the range $1,000 to $1,300 per ton removed as illustrated in Appendix E . This cost-effective threshold is also an indirec t measure of affordability for the electric utility i ndustry used by USEPA to support the BART rulemaking process. For the purpose of this taconite B ART analysis, the $1,000 to $1,3000 cost effectiveness threshold is used as the cutoff in pr oposing BART. The taconite industry is not afforded the same market stability or guaranteed co st recovery mechanisms that are afforded to the electric utility industry. Therefore, the $1,000 t o $1,300 per ton removed is considered a greater business risk to the taconite industry. Thus it is reasonable to use it as a cost effective threshold for proposing BART in lieu of developing industry and s ite specific data.

The annualized pollution control cost value was use d to determine whether or not additional impacts analyses would be conducted for the technology. If the control cost was less than a screening threshold established by MPCA, then visibility mode ling impacts, and energy and other impacts are evaluated. MPCA set the screening level to elimina te technologies from requiring the additionalY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 30 impact analyses at an annualized cost of $8,000 to $12,000 per ton of controlled pollutant 29

. Therefore, all air pollution controls with annualiz ed costs less than this screening threshold will be evaluated for visibility improvement, energy and ot her impacts.

The incremental control cost column in Table 5-3 is intended to present the incremental value of each technology as compared to the next most effective a lternative. Since none of the secondary SO 2 control technologies are cost effective, the increm ental cost is not applicable.

Energy and Environmental Impacts

Because the cost of SO 2 controls for the NMC furnaces is so high and does not meet a reasonable definition of cost effective technology, these tech nologies are removed from further consideration in this analysis.

5.A.i.e STEP 5 – Evaluate Visibility Impacts As previously stated in section 4 of this document, states are required to consider the degree of visibility improvement resulting from the retrofit technology, in combination with other factors such as economic, energy and other non-air quality impac ts, when determining BART for an individual source. The baseline, or pre-BART, visibility impa cts modeling was presented in section 4 of this document. The economic impacts of additional, seco ndary controls for SO 2 are not reasonably cost effective, so visibility impacts were not modeled f or SO 2 controls. Refer to Table 4-2 for a summary
of the modeled 24-hour maximum emission rates and t heir computational basis for the existing
controls for SO 2 .
Visibility impacts with NO x controls are presented in section 6. Table 6-1 pr ovides a summary of the
SO 2 , NO x , and PM 10 emissions for each modeling scenario.


### 5.A.ii Nitrogen Oxide Controls

To be able to control NO x it is important to understand how NO x is formed. There are three mechanisms by which NO x production occurs in the furnaces: thermal, fuel a nd prompt NO x .

• Fuel bound NO x is formed as nitrogen compounds in the fuel is oxi dized from fuel
combustion.

29 Minnesota Pollution Control Agency (MPCA). Air Pe rmit for Cenex Harvest States Cooperative Soybean Processing Plant, Fairmont, MN Permit 09100059-002

.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 31 • Thermal NO x production arises from the thermal dissociation of nitrogen and oxygen
molecules within the furnace. Combustion air is the primary source of nitrogen and oxygen. In taconite furnaces, thermal NO x production is a function of the residence time, fr ee oxygen, and temperature, primarily in the flame area of the furnace.

• Prompt NO x is a form of thermal NO x which is generated at the flame boundary. It is t he result of reactions between nitrogen and carbon rad icals generated during combustion. Only
minor amounts of NO x are emitted as prompt NO x .
The majority of NO x is emitted as NO. Minor amounts of NO 2 are formed in the furnaces.

The NMC furnaces are first and second generation st raight-grate furnaces that were built with lower grade steel and less refractory lining than the new er generations. As a result, the furnaces cannot survive the higher temperature conditions (both fla me temperature and roof air conditions) achieved in newer indurating furnaces. Consequently, the am bient air in the ignition and combustion zone is much cooler, leading to lower thermal NO x generation.

5.A.ii.a STEP 1 – Identify All Available Retrofit C ontrol Technologies With the understanding of how NO x is formed, available and applicable control techno logies were evaluated. See Appendix D for the current status of the availability and applicability of retrofit control technologies.

5.A.ii.b STEP 2 – Eliminate Technically Infeasible Options Step 1 identified the available and applicable tech nologies for NO x emission reduction. Within Step 1, the technical feasibility of the control op tion was also discussed and determined. The following describes retrofit NO x control technologies that were identified as avail able and applicable in the original submittal and discusses aspects of those technologies that determine whether or not the technology is technically feasible for indurati ng furnaces.

External Flue Gas Recirculation (EFGR) External flue gas recirculation (EFGR) uses flue ga s as an inert material to reduce flame temperatures thereby reducing thermal NO x formation. In an external flue gas recirculation s ystem, flue gas is
collected from the heater or stack and returned to the burner via a duct and blower. The flue gas is
mixed with the combustion air and this mixture is i ntroduced into the burner. The addition of flue gas reduces the oxygen content of the “combustion air” (air + flue gas) in the burner. The lower oxygen level in the combustion zone reduces flame temperat ures; which in turn reduces NO x emissions. ForY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 32 this technology to be effective, the combustion con ditions must have the ability to be controlled at the burner tip.

The normal NO x control efficiency range for EFGR is 30% to 50%.

Application for EFGR technology in taconite indurat ion is problematic for three reasons:

1. The waste gas in an induration furnace typically ha s near atmospheric oxygen vs. a boiler which has 2% - 3% oxygen. In a boiler, the flue ga s is relatively inert so it can be used as a diluent for flame temperature reduction. Taconit e waste gas has much higher oxygen level; thus use of taconite waste gas for EFGR woul d be equivalent to adding combustion air instead of an inert gas.

2. The oxidation zone of induration furnaces needs to be above 2,400 o F in order to meet product specifications. Existing burners are desig ned to meet these process conditions. Application of EFGR would reduce flame temperatures . Lower flame temperatures would reduce furnace temperatures to the point that product quality could be jeopardized.

3. Application of EFGR technology increases flame leng th. Dilution of the combustion
reactants increases the reaction time needed for fu el oxidation to occur; so, flame length increases. Therefore, application of EFGR could re sult in flame impingement on furnace components. That would subject those components to excessive temperatures and cause equipment failures.

Although this may be an available and applicable co ntrol option, it is not technically feasible due to the high oxygen content of the flue gas and will no t be further evaluated in this report.

Low- NO x Burners

Low- NO x burner (LNB) technology utilizes advanced burner d esign to reduce NO x formation through the restriction of oxygen, flame temperatur e, and/or residence time. LNB is typically a staged combustion process that is designed to split fuel combustion into two zones, primary combustion and secondary combustion. This analysis utilizes the staged fuel design in the cost analysis because lower emission rates can be achiev ed with staged fuel burner than with a staged air
burner.

In the primary combustion zone of a staged fuel bur ner, NO x formation is limited by a rich (high fuel) condition. Oxygen levels and flame temperatur es are low; this results in less NO x formation. InY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 33 the secondary combustion zone, incomplete combustio n products formed in the primary zone act as reducing agents. In a reducing atmosphere, nitrogen compounds are preferentially converted to molecular nitrogen (N 2 ) over nitric oxide (NO). The estimated NO x control efficiency for low NO x burners in high temperature applications is 10%. L ow NO x burners have been installed to the preheating section of a straight grate furnace at a nother taconite plant. If LNB were to be applied in the indurating section of the furnace, the reduced flame temperatures associated with LNB would adversely affect taconite pellet product quality. Low NO x burners have not been applied to the indurating section of any straight grate taconite f urnace.

However, NMC has a completely different combustion design compared to other furnaces. NMCs furnace design does not separate the preheat zone f rom the combustion zone and temperature control becomes a controlling variable for operation. Beca use the temperature in the indurating zone is critical to product quality, and because this is de pendent on the preheat zone operation, it is not practical to control the furnace conditions in the preheat zone adequately to make low NOx burners a feasible option at NMC.

It is also important to note that there are other m ethods being developed for low NO x burners which are not yet commercially available. Some incorpora te various fuel dilution techniques to reduce flame temperatures; such as mixing an inert gas lik e CO 2 with natural gas. Water injection to cool the burner peak flame temperature is also being inv estigated. This technique has already been successfully used for reducing NO x emissions from gas turbines and a straight grate t aconite indurating furnace in the Netherlands. The water i njection technique shows promise for high temperature applications, but will not be further i nvestigated in this report as the technology is sti ll in the development phase.

Induced Flue Gas Recirculation Burners Induced flue gas recirculation burners, also called ultra low- NO x burners, combine the benefits of flue gas recirculation and low- NO x burner control technologies. The burner is designe d to draw flue gas to dilute the fuel in order to reduce the flame temperature. These burners also utilize staged fue l combustion to further reduce flame temperature. Th e estimated NO x control efficiency for IFGR burners in high temperature applications is 25-50%.

As noted above, taconite furnaces are required to o perate at high oxygen levels.. At these oxygen levels, flue gas recirculation is ineffective at NO x reduction, and it would adversely affect combustion because excessive amounts of oxygen woul d be injected into the flame pattern. InY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 34 addition, IFGR relies on convective flow of flue ga s through the burner and requires burners to be up-fired; meaning that the burner is mounted in the furnace floor and the flame rises up. Furthermore, IFGR is not feasible because the reduc ed flame temperatures associated with IFGR would adversely affect taconite pellet product qual ity.

Although this may be an available and applicable co ntrol option, it is not technically feasible due to the high oxygen content of the flue gas and will no t be further evaluated in this report.

Energy Efficiency Projects Energy efficiency projects provide opportunities fo r a company to reduce their fuel consumption. Typically reduced fuel usage translates into reduce d pollution emissions. An energy efficiency project could be preheat incoming make-up air or pe llet feed. Each project is very dependent upon the fuel usage, process equipment, type of product and so many other variables.

Due to the increased price of fuel, the facilities have already implemented energy efficiency projects

. Each project carries its own fuel usage reductions and potentially emission reductions. It would be impossible to assign a general potential emission r eduction for the energy efficient category. Due to the uncertainty and generalization of this category , this will not be further evaluated in this report

. However, it should be noted that facilities will co ntinue to evaluate and implement energy efficiency projects as they arise.

Ported Kilns Ported kilns are rotary kilns that have air ports i nstalled at specified points along the length of th e kiln for process improvement. The purpose of the p orts is to allow air injection into the pellet bed as it travels down the kiln bed. Ports are installed a bout the circumference of the kiln. Each port is equipped with a closure device that opens when it i s at the bottom position to inject air in the pelle t bed, and closed when it rotates out of position.

The purpose of air injection is to provide addition al oxygen for pellet oxidation. The oxidation reaction extracts enough heat to offset the heat lo ss associated with air injection. Air injection reduces the overall energy use of the kiln and prod uces a higher quality taconite pellet. Air injectio n also prevents carry over of the oxidation reaction into the pellet coolers.

Ported kilns are applicable to grate kilns but not to straight grate indurating furnaces, as are prese nt at NMC. Therefore, the ported kilns are not an applic able technology for this facility.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 35 Alternate Fuels As described within the energy efficiency descripti on, increased price of fuel has moved companies
to evaluate alternate fuel sources. These fuel sou rces come in all forms – solid, liquid and gas.
Reduction of NO x emissions through alternative fuel usage has been achieved at taconite grate kilns through the use of solid fuel. In these cases the reduction resulted due to changes from pulverized solid fuel dispersal in the kiln that results in lo wer flame temperature compared to other fuels. Switching from natural gas or oil to solid fuel has a potential drawback in that it can exchange one visibility impairment pollutant (NO x ) for another (SO 2 ). More importantly, the design of the straight grate furnaces at NMC does not allow the use of sol id fuels. Therefore, this option will not be further evaluated in this report.

It is also important to note that U.S. EPA’s intent is for facilities to consider alternate fuels as t heir option, not to direct the fuel choice. 30

However, similar to energy efficiency, facilities w ill continue to evaluate and implement alternate fuel usage as the feasibility arises.

Process Optimization with NO x CEMS or Other Parametric Monitoring MPCA guidance lists “NO x CEMS” as a work practice/operational change for co ntrolling NO x emissions 31 . Parametric monitoring is a possible derivative o f this alternative.

Based on conversations with MPCA staff, this work p ractice would include process adjustments, or optimization, to minimize NO x emissions. The impact of the process adjustments would be measured using the NO x CEMS. This approach has been used in the electric utility industry to fine tune NOx
emissions from boilers.

One taconite plant has installed NOx CEMS to monito r emissions but not to optimize NOx emissions through process fine tuning. That plant has experi enced some reduction in NOx emissions but these encompass multiple variables and are not directly a ttributed to process fine tuning with the NOx CEMS. Therefore, this alternative has not been dem onstrated in the taconite industry.

30 Federal Register 70, no. 128 (July 6, 2005): 39164

31 MPCA. March 2006. Guidance for Facilities Conducting a BART Analysis . Page 4.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 36 There are several concerns with utilizing process o ptimization as an available, applicable and technically feasible control option for the taconit e industry:

• Taconite furnaces are designed and operated to conv ert magnetite to hematite in the presence of excess oxygen and require heat input to initiate the reaction which is exothermic and
releases heat once initiated. Fuel combustion is o nly part of the process and therefore this process is different from a boiler.

• The quality of the process feed materials to the fu rnace is variable at some taconite operations and product quality may be compromised b y attempting to fine tune heat input to
minimize NOx formation.

• At some operations, the operating parameters which generally influence the rate of NO x generation such as flame temperature, fuel usage an d excess air are relatively constant during operation of the furnace, independent of process op eration variability. This indicates that NO x formation may not be dependent upon controllable op erating parameters. In the absence of controllable parameters, process optimization would not be effective at controlling NO x emissions.

Based upon this information, there is no indication that further emission reductions would be achieved through the use of the process optimizatio n, using NO x CEMS or other parametric monitoring, as a control technology. Therefore, pr ocess optimization as a control option will not be evaluated further in this report.

Post Combustion Controls

NO x can be controlled using add-on systems located dow nstream of the furnace area of the combustion process. The two main techniques in com mercial service include the selective non catalytic reduction (SNCR) process and the selectiv e catalytic reduction (SCR) process. There are a number of different process systems in each of thes e categories of control techniques.

In addition to these treatment systems, there are a large number of other processes being developed and tested on the market. These approaches involve innovative techniques of chemically reducing, absorbing, or adsorbing NO x downstream of the combustion chamber. Examples of these alternatives are nonselective catalytic reduction (NSCR) and Low Temperature Oxidation (LTO). Each of these
alternatives is described below.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 37 Non-Selective Catalytic Reduction (NSCR) A non-selective catalytic reduction (NSCR) system i s a post combustion add-on exhaust gas treatment system. NSCR catalyst is very sensitive t o poisoning; so; NSCR is usually applied primarily in natural gas combustion applications.

NSCR is often referred to as “three-way conversion” catalyst because it simultaneously reduces NO x , unburdened hydrocarbons (UBH), and carbon monoxide (CO). Typically, NSCR can achieve NO x emission reductions of 90 percent. In order to oper ate properly, the combustion process must be near stoichiometric conditions. Under this condition, i n the presence of a catalyst, NO x is reduced by CO, resulting in nitrogen (N 2 ) and carbon dioxide (CO 2 ). The most important reactions for NO x removal

are:

2CO + 2NO → 2CO 2 + N 2 (1)

[UBH] + NO → N 2 + CO 2 + H 2 O ( 2)

NSCR catalyst has been applied primarily in clean c ombustion applications. This is due in large part to the catalyst being very sensitive to poisoning, making it infeasible to apply this technology to th e indurating furnace. In addition, we are not aware of any NSCR installations on taconite induration furnaces or similar combustion equipment. Therefore , this technology will not be further evaluated in this report.

Selective Catalytic Reduction and Regenerative Sele ctive Catalytic Reduction SCR is a post-combustion NO x control technology in which ammonia (NH 3 ) is injected into the flue gas stream in the presence of a catalyst. NO x is removed through the following chemical reaction :

4 NO + 4 NH 3 + O 2 → 4 N 2 + 6 H 2 O (1)
2 NO 2 + 4 NH 3 + O 2 → 3 N 2 + 6 H 2 O ( 2)

A catalyst bed containing metals in the platinum fa mily is used to lower the activation energy required for NO x decomposition. SCR requires a temperature range of about 570°F – 850°F for a normal catalyst. At temperature exceeding approxima tely 670oF, the oxidation of ammonia begins to become significant. At low temperatures, the forma tion of ammonium bisulfate causes scaling and corrosion problems.

A high temperature zeolite catalyst is also availab le; it can operate in the 600 °F – 1000°F temperature range. However, these catalysts are ver y expensive.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 38 Ammonia slip from the SCR system is usually less th an 3 to 5 ppm. The emission of ammonia increases during load changes due to the instabilit y of the temperature in the catalyst bed as well as at low loads because of the low gas temperature.

Regenerative Selective Catalytic Reduction (RSCR) a pplies the Selective Catalytic Reduction (SCR) control process as described below with a preheat p rocess step to reheat the flue gas stream up to SCR catalyst operating temperatures. The preheatin g process combines use of a thermal heat sink (packed bed) and a duct burner. The thermal sink r ecovers heat from the hot gas leaving the RSCR and then transfers that heat to gas entering the RS CR. The duct burner is used to complete the preheating process. RSCR operates with several pac ked bed/SCR reactor vessels. Gas flow
alternates between vessels. Each of the vessels alt ernates between preheating/treating and heat

recovery.

The benefits of RSCR are:

• Its high energy efficiency allows it to be used aft er SO 2 and particulate controls.

• RSCR has a thermal efficiency of 90% - 95% vs. stan dard heat exchangers which have a thermal efficiency of 60% to 70%.

• Application of RSCR after SO 2 and PM controls significantly reduces the potentia l for problems associated with plugging and catalyst pois oning and deactivation.

There are several other concerns about the technica l feasibility and applicability of RSCR on an indurating furnace:

• The composition of the indurating furnace flue gas is significantly different from the composition of the flue gas from the boilers that u tilize RSCR;

• The taconite dust is highly erosive and can cause s ignificantly equipment damage. RSCR has a number of valves which must be opened and closed frequently to switch catalyst/heat recovery beds. These valves could be subject to ex cessive wear in a taconite application due to the erosive nature of the taconite dust;

• RSCR has not been applied downstream of a wet scrub ber. Treating a stream saturated with water may present design problems in equipment sizi ng for proper heat transfer and in corrosion protection;Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 39 • RSCR catalyst had been shown to oxidize mercury. O xidized mercury can be absorbed by the local environment and have adverse impact. The impact of RSCR on mercury emissions
needs to be studied to determine whether or not mer cury oxidation is a problem and to identify mitigation methods if needed.

To date, RSCR has been applied to wood-fired utilit y boilers. Application of this technology has not been applied to taconite induration furnaces, to ai rflows of the magnitude of taconite furnace exhausts, nor to exhaust streams with similar, high moisture content. Using RSCR at a taconite plant would require research, test runs, and extended tri als to identify potential issues related to catalys t selection, and impacts on plant systems, including the furnaces and emission control systems. It is not reasonable to assume that vendor guarantees of performance would be forthcoming in advance of a demonstration project. The timeline required to p erform such a demonstration project would likely be two years to develop and agree on the test plan, obtain permits for the trial, commission the equipment for the test runs, perform the test runs for a reasonable study period, and evaluate and report on the results. The results would not be av ailable within the time window for establishing emission limits to be incorporated in the state imp lementation plan (SIP) by December 2007.

Recalling U.S. EPA’s intention regarding “available ” technologies to be considered for BART, as mentioned in Section 2.B, facility owners are not e xpected to undergo extended trials in order to learn how to apply a control technology to a comple tely new and significantly different source type. Therefore, RSCR is not considered to be technically feasible, and will not be analyzed further in this BART analysis.

SCR with reheat through a conventional duct burner (rather than using a regenerative heater) has been successfully implemented more widely and in hi gher airflow applications and will be carried forward in this analysis as available and applicabl e technology that is reasonably expected to be technically feasible.

Low Temperature Oxidation (LTO) The LTO system utilizes an oxidizing agent such as ozone to oxidize various pollutants including
NO x . In the system, the NO x in the flue gas is oxidized to form nitrogen pento xide (equations 1, 2, and 3). The nitrogen pentoxide forms nitric acid v apor as it contacts the water vapor in the flue gas (4). Then the nitric acid vapor is absorbed as dil ute nitric acid and is neutralized by the sodium hydroxide or lime in the scrubbing solution forming sodium nitrate (5) or calcium nitrate. TheY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 40 nitrates are removed from the scrubbing system and discharged to an appropriate water treatment system. Commercially available LTO systems include Tri-NO x ® and LoTOx®.

NO + O 3 → NO 2 + O 2 (1)

NO 2 + O 3 → NO 3 + O 2 (2)

NO 3 + NO 2 → N 2 O 5 (3)

N 2 O 5 + H 2 O → 2HNO 3 (4)

HNO 3 + NaOH → NaNO 3 + H 2 O (5)

Low Temperature Oxidation (Tri-NO x ® ) This technology uses an oxidizing agent such as ozo ne or sodium chlorite to oxidize NO to NO 2 in a primary scrubbing stage. Then NO 2 is removed through caustic scrubbing in a secondary stage. The
reactions are as follows:

O 3 + NO → O 2 + NO 2 (1)

2NaOH + 2NO 2 + 1⁄2 O 2 → 2NaNO 3 + H2O (2)

Tri-NO x ® is a multi-staged wet scrubbing process in industr ial use. Several process columns, each assigned a separate processing stage, are involved. In the first stage, the incoming material is quenched to reduce its temperature. The second, ox idizing stage, converts NO to NO 2 . Subsequent stages reduce NO 2 to nitrogen gas, while the oxygen becomes part of a soluble salt. Tri-NO x ® is typically applied at small to medium sized sources with high NO x concentration in the exhaust gas (1,000 ppm NO x ). NO x concentrations in taconite exhaust at HTC are typi cally less than 200 ppm. Therefore, Tri-NO x ® is not applicable to taconite processing and will not be analyzed further in this BART analysis.

Low Temperature Oxidation (LoTOx ® )

BOC Gases’ Lo-TOx ® is an example of a version of an LTO system. LoTOx ® technology uses ozone
to oxidize NO to NO 2 and NO 2 to N 2 O 5 in a wet scrubber (absorber). This can be done in the same scrubber used for particulate or sulfur dioxide rem oval, The N 2 O 5 is converted to HNO 3 in a scrubber, and is removed with lime or caustic. Ozo ne for LoTOx ® is generated on site with an electrically powered ozone generator. The ozone ge neration rate is controlled to match the amountY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 41 needed for NO x control. Ozone is generated from pure oxygen. In order for LoTOx ® to be economically feasible, a source of low cost oxygen must be available from a pipeline or on site generation.

The first component of the technical feasibility re view includes determining if the technology would apply to the process being reviewed. This would in clude a review and comparison of the chemical and physical properties required. Although it appe ars that the chemistry involved in the LTO technology may apply to an indurating furnace, the furnace exhaust contains other ore components that may participate in side reactions. This techn ology has not been demonstrated on a taconite pelle t indurating furnace. This raises uncertainties abou t how or whether the technology will transfer to a different type of process.

The second component of the technical feasibility r eview includes determining if the technology is commercially available. Evaluations of LTO found t hat it has only been applied to small to medium sized coal or gas fired boiler applications, and ha s never been demonstrated on a large-scale facility

. For example, the current installations of LoTOx ® are on sources with flue gas flow rates from 150 – 35,000 acfm, which is quite small, compared to the indurating furnace flue gas flow rates of over 400,000 acfm. Therefore, the application of LTO wo uld be more than an order of magnitude larger than the biggest current installation. This large scale-up is contrary to good engineering practices and could be problematic in maintaining the current removal efficiencies.

In addition, only two of BOC’s LoTOx ® installations are fully installed and operational applications. Therefore, although this is an emerging technology, the limited application means that it has not been demonstrated to be an effective technology in wides pread application.

There are several other concerns about the technica l feasibility and applicability of LTO on an indurating furnace:

• The composition of the indurating furnace flue gas is significantly different than the composition of the flue gas from the boilers and pr ocess heaters that utilize LTO;

• The taconite dust in the flue gas is primarily magn etite (Fe 3 O 4 ) which would react with the ozone to form hematite (Fe 2 O 3 ); since the ozone injection point would be before the scrubber, there can be more than 400 pounds per hour of tacon ite dust in the flue gas which could consume a significant amount of the ozone being gen erated which may change the reactionY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 42 kinetics; consequently, this would necessitate eith er an increase in the amount of ozone generated or a decrease in the estimated control ef ficiency;

• The ozone that would be injected into the flue gas would react with the SO 2 , converting the material to SO3 which could result in the generatio n of sulfuric acid mist from the scrubber;

• Since LTO has not been installed at a taconite plan t, it is likely that the application of LTO to an indurating furnace waste gas could present techn ical problems which were not encountered, or even considered, in the existing LT O applications;

• An LTO system at a taconite facility would also be a source of nitrate discharge to the tailings basin which would change the facility wate r chemistry which could cause operational problems and would likely cause additional problems with National Pollutant Discharge Elimination System (NPDES) discharge limits and req uirements.

Application of this technology has not been applied to taconite induration furnaces, to airflows of th e magnitude of taconite furnace exhausts, nor to exha ust streams with similar, high moisture content. Using LTO at a taconite plant would require researc h, test runs, and extended trials to identify potential issues related to design for high airflow s and impacts on plant systems, including the furnaces and emission control systems. It is not r easonable to assume that vendor guarantees of performance would be forthcoming in advance of a de monstration project. The timeline required to perform such a demonstration project would likely b e two years to develop and agree on the test plan, obtain permits for the trial, commission the equipment for the test runs, perform the test runs for a reasonable study period, and evaluate and rep ort on the results. The results would not be available within the time window for establishing e mission limits to be incorporated in the state implementation plan (SIP) by December 2007.

Recalling U.S. EPA’s intention regarding “available ” technologies to be considered for BART, as mentioned in Section 2.B, facility owners are not e xpected to undergo extended trials in order to learn how to apply a control technology to a comple tely new and significantly different source type. Consequently, the technical feasibility of LTO on a n indurating furnace is technically infeasible for this application and will not be evaluated further.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 43 Step 2 Conclusion Based upon the determination within Step 2, the rem aining NO x control technologies that are available and applicable to the indurating furnace process are identified in Table 5-4. The technical feasibility as determined in Step 2 is also include d in Table 5-4.

Table 5-4 Indurating Furnace NO x Control Technology – Availability, Applicability, and Technical Feasibility

NO x Pollution Control Technology Available? Applicable? Technically Feasible? External Flue Gas Recirculation (EFGR) Yes Yes No

Low- NO x Burners Yes Yes No Induced Flue Gas Recirculation Burners Yes Yes No Energy Efficiency Projects Yes Yes No Ported Kilns Yes No No

Alternative Fuels Yes Yes No Process Optimization using NO x CEMS Yes No No Non-Selective Catalytic Reduction (NSCR) Yes No No Selective Catalytic Reduction (SCR) with conventional reheat Yes Yes Yes

Regenerative SCR Yes No No Selective Non-Catalytic Reduction (SNCR) Yes No No Low Temperature Oxidation (LTO) Yes No No

5.A.ii.c STEP 3 – Evaluate Control Effectiveness of Remaining Control Technologies Table 5-5 describes the expected control efficiency from each of the remaining technically feasible control options as identified in Step 2.

Table 5-5 Indurating Furnace NO x Control Technology Effectiveness

NO x Pollution Control Technology Approximate Control Efficiency SCR with Conventional Reheat 80%Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 44 5.A.ii.d STEP 4 – Evaluate Impacts and Document the Results Table 5-6 details the expected costs associated wit h installation of Low NO x burners. Capital costs
were calculated based on the maximum 24-hour emissi ons, U.S. EPA cost models, and vendor estimates. Vendor estimates for capital costs base d on a specific flow rate were scaled to each stack’s flow rate using the 6/10 power law to accou nt for the economy of scale. Operating costs were based on 93% utilization and 8339 operating house p er year. Operating costs were proportionally adjusted to reflect site specific flow rates and po llutant concentrations.

After a tour of the facility and discussions with f acility staff, it was determined the space surround ing the furnaces is congested and the area surrounding the building supports vehicle and rail traffic to transport materials to and from the building. A sit e-specific estimate for site-work, foundations, and structural steel was added based upon the facility site to arrive at the total retrofit installed cost of the control technology. The site specific estimate was based on Barr’s experience with similar projects. See Appendix C for a site plan of the facility. Add itionally, the structural design of the existing building would not support additional equipment on the roof. The detailed cost analysis is provided in Appendix A.

Table 5-6 Indurating Furnace NO x Control Cost Summary

Control Technology Installed Capital Cost (MM$) Total Annual Cost (MM$/yr) Annualized

Pollution Control Cost ($/ton) Incremental

Control Cost ($/ton) Selective Catalytic Reduction (SCR) With Reheat Furnace 11 Hood Exhaust $25,735,488 $11,314,358 $155,784 NA

Furnace 11 Waste Gas $23,344,084 $8,274,322 $46,771 NA

Furnace 12 Hood Exhaust $25,912,320 $11,387,084 $162,309 NA

Furnace 12 Waste Gas $24,026,527 $10,442,659 $61,107 NA

Based on the BART final rule, court cases on cost-e ffectiveness, guidance from other regulatory bodies, and other similar regulatory programs like Clean Air Interstate Rule (CAIR), cost-effective air pollution controls in the electric utility indu stry for large power plants are in the range $1,000 to $1,300 per ton removed as illustrated in Appendix E . This cost-effective threshold is also an indirec t measure of affordability for the electric utility i ndustry used by USEPA to support the BART rule-Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 45 making process. For the purpose of this taconite B ART analysis, the $1,000 to $1,300 cost effectiveness threshold is used as the cutoff in pr oposing BART. The taconite industry is not afforded the same market stability or guaranteed co st recovery mechanisms that are afforded to the electric utility industry. Therefore, the $1,000 t o $1,300 per ton removed is considered a greater business risk to the taconite industry. Thus it is reasonable to use it as a cost effective threshold for proposing BART in lieu of developing industry and s ite specific data.

The annualized pollution control cost value was use d to determine whether or not additional impacts analyses would be conducted for the technology. If the control cost was less than a screening threshold established by MPCA, then visibility mode ling impacts, and energy and other impacts are evaluated. MPCA set the screening level to elimin ate technologies from requiring the additional impact analyses at an annualized cost of $8,000 to $12,000 per ton of controlled pollutant 32

. Therefore, all air pollution controls with annualiz ed costs less than this screening threshold will b e evaluated for visibility improvement, energy and ot her impacts.

The incremental control cost column in Table 5-6 is intended to present the incremental value of each technology as compared to the technology with the n ext most effective alternative. Since none of the
NO x reduction technologies are cost effective, the inc remental cost is not applicable.

Energy and Environmental Impacts

Because the cost of NO x controls for NMC furnaces is so high and does not meet a reasonable definition of cost effective technology, this techn ology is removed from further consideration in this analysis.

5.A.ii.e STEP 5 – Evaluate Visibility Impacts As previously stated in section 4 of this document, states are required to consider the degree of visibility improvement resulting from the retrofit technology, in combination with other factors such as economic, energy and other non-air quality impac ts, when determining BART for an individual source. The baseline, or pre-BART, visibility impa cts modeling was presented in section 4 of this document. The economic impacts of controls for NO x are not reasonably cost effective, so visibility impacts were not modeled for NO x controls. Refer to Table 4-2 for a summary of the modeled 24- hour maximum emission rates and their computational basis for the existing controls for NO x .

32 Minnesota Pollution Control Agency (MPCA). Air Pe rmit for Cenex Harvest States Cooperative Soybean Processing Plant, Fairmont, MN Permit 09100059-002

.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 46 Visibility impacts with SO 2 controls are presented in section 6. Table 6-1 pr ovides a summary of the
SO 2 , NO x , and PM 10 emissions for each modeling scenario,Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 47 

## 5.B External Combustion Sources Two natural gas and fuel oil fired process boilers require BART analysis. These boilers are back-up boilers to the main NMC Power House boilers to prov ide steam required to operate the taconite plant during Power House outages. These boilers are only permitted to use gas and distillate oil for fuel.



### 5.B.i Sulfur Dioxide controls
Sulfur in the fuel is the only source of SO 2 emissions from these boilers. The boilers only ha ve low
emissions of SO 2 due to the low sulfur content of the permitted fue ls.

5.B.i.a STEP 1 – Identify All Available Retrofit Co ntrol Technologies See Appendix F for a comprehensive list of all pote ntial retrofit control technologies that were
evaluated.

5.B.i.b STEP 2 – Eliminate Technically Infeasible O ptions Step 1 identified the available and applicable tech nologies for SO 2 emission reduction. Within Step 2, the technical feasibility of the control op tion is discussed and determined. The following
section describes retrofit SO 2 control technologies that were identified as avail able and applicable and discusses aspects of those technologies that de termine whether or not the technology is technically feasible for the process boilers.

Wet Walled Electrostatic Precipitator (WWESP) An electrostatic precipitator (ESP) applies electri cal forces to separate suspended particles from the flue gas stream. The suspended particles are given an electrical charge by passing through a high voltage DC corona region in which gaseous ions flow . The charged particles are attracted to and collected on oppositely charged collector plates. P articles on the collector plates are released by rapping and fall into hoppers for collection and re moval.

A wet walled electrostatic precipitator (WWESP) ope rates on the same collection principles as a dry ESP and uses a water spray to remove particulate ma tter from the collection plates. For SO 2 removal, caustic is added to the water spray system, allowin g the WWESP spray system to function as an SO 2 absorber.

The SO 2 control efficiency for a WWESP is dependent upon v arious process specific variables, such
as SO 2 flue gas concentration and fuel used. Based on the definitions contained within this report, a WWESP is considered an available technology for SO 2 reduction for this BART analysis.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 48 Wet Scrubbing (High and Low Efficiency) Wet scrubbing, when applied to remove SO 2 , is generally termed flue-gas desulfurization (FGD ). FGD utilizes gas absorption technology, the selecti ve transfer of materials from a gas to a contacting liquid, to remove SO 2 in the waste gas. Crushed limestone, lime or Caust ic is used as scrubbing agents.

Limestone scrubbing introduces limestone slurry wit h the flue gas in a spray tower. The sulfur dioxide is absorbed, neutralized, and partially oxi dized to calcium sulfite and calcium sulfate. The overall reactions are shown in the following equati ons:

CaCO 3 + SO 2 → CaSO 3 • 1/2 H2O + CO 2 CaSO 3 •1/2 H 2 O + 3H 2 O + O 2 → 2 CaSO 4 •2 H 2 O

Lime scrubbing is similar to limestone scrubbing in equipment and process flow, except that lime is a more reactive reagent than limestone. The reactions for lime scrubbing are as follows:

Ca(OH) 2 +SO 2 → CaSO 3 • 1/2 H 2 O + 1/2 H 2 O Ca(OH) 2 + SO 2 + 1/2 O 2 + H 2 O → CaSO 4 •2 H 2 O

When that caustic (sodium hydroxide solution) is th e scrubbing agent, the SO 2 removal reactions are
as follows:

Na+ + OH- + SO 2 + → Na 2 SO 3 2Na+ + 2OH- + SO 2 + → Na 2 SO 3 + H 2 O

Caustic scrubbing produces a liquid waste, and mini mal equipment is needed as compared to lime or
limestone scrubbers. If lime or limestone is used a s the reagent for SO 2 removal, additional equipment will be needed for preparing the lime/lim estone slurry and collecting and concentrating the resultant sludge. Calcium sulfite sludge is wat ery; it is typically stabilized with fly ash for la nd filling. The calcium sulfate sludge is stable and e asy to dewater. To produce calcium sulfate, an air injection blower is needed to supply the oxygen for the second reaction to occur.

The normal SO 2 control efficiency range for SO 2 scrubbers on coal fired utility boilers is 80% to 90% for low efficiency scrubbers and 90% and more for h igh efficiency scrubbers. The highest control
efficiencies can be achieved when SO 2 concentrations are the highest. The process boile r exhaust would not have a high SO 2 concentration, so the low end of the efficiency ra nge would be expected.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 49 Dry Sorbent Injection (Dry Scrubbing Lime/Limestone Injection) Dry sorbent injection involves the injection of a l ime or limestone powder into the exhaust gas stream. The stream is then passed through a baghous e or ESP to remove the sorbent and entrained
SO 2 . The process was developed as a lower cost FGD opt ion because the mixing occurs directly in the exhaust gas stream instead of in a separate tow er. Depending on the residence time and gas stream temperature, sorbent injection control effic iency is approximately 55%. Therefore DSI is technically feasible.

Spray Dryer Absorption (SDA) Spray dryer absorption (SDA) systems spray lime slu rry into an absorption tower where SO 2 is absorbed by the slurry, forming CaSO 3 /CaSO 4 . The liquid-to-gas ratio is such that the water evaporates before the droplets reach the bottom of the tower. The dry solids are carried out with the gas and collected with a fabric filter. The normal SO2 control efficiency range for SDA is up to 90%.

Based on the information contained with this report , SDA is considered an available technology for
SO 2 reduction for this BART analysis.

Energy Efficiency Projects Energy efficiency projects provide opportunities fo r a company to reduce their fuel consumption, which results in lower operating costs. Typically reduced fuel usage translates into reduced pollutio n emissions. Due to the increased price of fuel, the facilities have already implemented energy efficiency projects. Each project carries its own f uel usage reductions and potentially emission reductions. It would be impossible to assign a gene ral potential emission reduction for the energy efficient category. Due to the uncertainty and gene ralization of this category, this will not be furth er evaluated in this report. However, it should be no ted that facilities will continue to evaluate and implement energy efficiency projects as they arise.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 50 Alternate Fuels As described within the energy efficiency descripti on, increased price of fuel has pushed companies
to evaluate alternate fuel sources. These fuel sou rces come in all forms – solid, liquid and gas. To
achieve reduction of SO 2 emissions through alternative fuel usage, the sour ce must use fuels with lower sulfur content. NMC has the capability to on ly burn low sulfur fuels, natural gas and distillat e oil, in these process boilers. Therefore this opti on is not applicable to the process boilers.

It is also important to note that U.S. EPA’s intent is for facilities to consider alternate fuels as t heir option, not to direct the fuel choice. 33

Therefore, due to the limited fuel burning capabili ties of the boilers and the fact that BART is not intended to mandate a fuel switch, alternative fuel s as an air pollution control technology will not b e further evaluated in this report.

However, similar to energy efficiency, facilities w ill continue to evaluate and implement alternate fuel usage as the feasibility arises.

Coal Processing Since NMC process boilers are not capable of burnin g solid fuel, this option is not applicable for SO 2 reductions at NMC.

STEP 2 Conclusion Based upon the determination within Step 2, the rem aining SO 2 control technologies that are available and applicable to the process boilers are identified in Table 5-7. The technical feasibility as determined in Step 2 is also included in Table 5-7.

33 Federal Register 70, no. 128 (July 6, 2005): 39164Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 51 Table 5-7 Backup Process Boiler SO 2 Control Technology – Availability, Applicability, and Technical Feasibility

SO 2 Pollution Control Technology Available? Applicable? Technically Feasible? WWESP Yes Yes Yes Wet Scrubber Yes Yes Yes Spray Dry Absorption (SDA) Yes Yes Yes Dry Sorbent Injection (DSI) Yes Yes Yes Energy Efficiency Projects Yes Yes No Alternative Fuels Yes Yes No

5.B.i.c STEP 3 – Evaluate Control Effectiveness of Remaining Control Technologies Table 5-8 describes the expected control efficiency from each of the remaining feasible control options when burning liquid fuels.

Table 5-8 Backup Process Boiler SO 2 Control Technology Effectiveness

SO 2 Pollution Control Technology Approximate Control Efficiency Wet Walled Electrostatic Precipitator (WWESP) 80% Wet Scrubbing (High Efficiency) 80% Dry Sorbent Injection 55% Spray Dryer Absorption 90%

5.B.i.d STEP 4 – Evaluate Impacts and Document the Results As illustrated in Table 5-8 above, the technically feasible control remaining provide varying levels o f emission reduction. Therefore, it is necessary to consider the economic, energy, and environmental impacts to better differentiate as presented below.

Economic Impacts Table 5-9 details the expected costs associated wit h installation of a WWESP, wet scrubber, DSI and SDA on each stack. Equipment design was based on th e maximum 24-hour emissions, vendor estimates, and U.S. EPA cost models. Capital costs were based on a recent vendor quotation. TheY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 52 cost for that unit was scaled to each stack’s flow rate using the 6/10 power law as shown in the following equation:

Cost of equipment A = Cost of equipment B * (capac ity of A/capacity of B) 0.6

Direct and indirect costs were estimated as a perce ntage of the fixed capital investment using U.S. EPA models and factors. Operating costs were based on 93% utilization and 7650 operating hours per year, which is very conservative, considering t hese are backup boilers. Operating costs of consumable materials, such as electricity, water, a nd chemicals were established based on the U.S.
EPA control cost manual 34 and engineering experience, and were adjusted for the specific flow rates and pollutant concentrations.

See Appendix C for an aerial photo of the facility. The detailed cost analysis is provided in Appendix
A.

Table 5-9 Backup Process Boiler SO2 Control Cost Su mmary

Control Technology Installed Capital Cost ($) Total

Annual Cost ($/yr) Annualized

Pollution Control Cost ($/ton) Incremental

Control Cost ($/ton) Wet ESP $11,808,857 $2,247,725 $36,558 NA Wet Scrubber $13,618,522 $1,869,933 $31,845 NA Dry Sorbent Injection and Baghouse $4,890,063 $1,409,010 $22,917 NA Spray Dryer and Baghouse $16,134,577 $2,751,525 $44 ,752 NA

Based on the BART final rule, court cases on cost-e ffectiveness, guidance from other regulatory bodies, and other similar regulatory programs like Clean Air Interstate Rule (CAIR), cost-effective air pollution controls in the electric utility indu stry for large power plants are in the range $1,000 to $1,300 per ton removed as illustrated in Appendix E . This cost-effective threshold is also an indirec t measure of affordability for the electric utility i ndustry used by USEPA to support the BART rulemaking process. For the purpose of this taconite B ART analysis, the $1,000 to $1,300 cost effectiveness threshold is used as the cutoff in pr oposing BART. The taconite industry is not afforded the same market stability or guaranteed co st recovery mechanisms that are afforded to the electric utility industry. Therefore, the $1,000 t o $1,300 per ton removed is considered a greater

34 U.S. EPA, January 2002, EPA Air Pollution Control Cost Manual, Sixth Editio n

.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 53 business risk to the taconite industry. Thus it is reasonable to use it as a cost effective threshold for proposing BART in lieu of developing industry and s ite specific data.

The annualized pollution control cost value was use d to determine whether or not additional impacts analyses would be conducted for the technology. If the control cost was less than a screening threshold established by MPCA, then visibility mode ling impacts, and energy and other impacts are evaluated. MPCA set the screening level to elimin ate technologies from requiring the additional impact analyses at an annualized cost of $8,000 to $12,000 per ton of controlled pollutant 35

. Therefore, all air pollution controls with annualiz ed costs less than this screening threshold will b e evaluated for visibility improvement, energy and ot her impacts.

The incremental control cost column in Table 5-9 is intended to present the incremental value of each technology as compared to the next most effective a lternative. Since none of the technologies are cost effective, the incremental control cost is not applicable.

Energy and Environmental Impacts

Because the cost of SO 2 controls for the NMC process boilers is so high an d does not meet a reasonable definition of cost effective technology, these technologies are removed from further consideration in this analysis.

5.B.i.e STEP 5 – Evaluate Visibility Impacts As previously stated in section 4 of this document, states are required to consider the degree of visibility improvement resulting from the retrofit technology, in combination with other factors such as economic, energy and other non-air quality impac ts, when determining BART for an individual source. The baseline, or pre-BART, visibility impa cts modeling was presented in section 4 of this document. The economic impacts of controls for SO 2 are not reasonably cost effective, so visibility impacts were not modeled for SO 2 controls. Refer to Table 4-2 for a summary of the modeled 24- hour maximum emission rates and their computational basis for the existing controls for SO 2 .
Visibility impacts with NO x controls are presented in Section 6. Table 6-1 pr ovides a summary of
the SO 2 , NO x , and PM 10 emissions for each modeling scenario.

35 Minnesota Pollution Control Agency (MPCA). Air Pe rmit for Cenex Harvest States Cooperative Soybean Processing Plant, Fairmont, MN Permit 09100059-002.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 54 

### 5.B.ii Nitrogen Oxide Controls

To be able to control NO x it is important to understand how NO x is formed. There are three mechanisms by which NO x production occurs: thermal, fuel and prompt NO x .

• Fuel bound NO x is formed as nitrogen compounds in the fuel is oxi dized in the combustion

process.

• Thermal NO x production arises from the thermal dissociation of nitrogen and oxygen
molecules within the furnace. Combustion air is the primary source of nitrogen and oxygen.
Thermal NO x production is a function of the residence time, fr ee oxygen, and temperature.

• Prompt NO x is a form of thermal NO x which is generated at the flame boundary. It is t he result of reactions between nitrogen and carbon rad icals generated during combustion. Only
minor amounts of NO x are emitted as prompt NO x .
The majority of NO x is emitted as NO. Minor amounts of NO 2 are formed in the heater.

5.B.ii.a STEP 1 – Identify All Available Retrofit C ontrol Technologies With the understanding of how NO x is formed, available and applicable control techno logies were evaluated. See Appendix F for the current status of the availability and applicability of retrofit control technologies.

5.B.ii.b STEP 2 – Eliminate Technically Infeasible Options Step 1 identified the available and applicable tech nologies for NO x emission reduction. Within Step 2, the technical feasibility of the control op tion was discussed and determined. The following
describes retrofit NO x control technologies that were identified as avail able and applicable and discusses aspects of those technologies that determ ine whether or not the technology is technically feasible for the process boilers.

External Flue Gas Recirculation (EFGR) External flue gas recirculation (EFGR) uses flue ga s as an inert material to reduce flame temperatures thereby reducing thermal NO x formation. In an external flue gas recirculation s ystem, flue gas is
collected from the heater or stack and returned to the burner via a duct and blower. The flue gas is
mixed with the combustion air and this mixture is i ntroduced into the burner. The addition of flue gas reduces the oxygen content of the “combustion air” (air + flue gas) in the burner. The lower oxygen level in the combustion zone reduces flame temperat ures; which in turn reduces NO x emissions. ForY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 55 this technology to be effective, the combustion con ditions must have the ability to be controlled at the burner tip. Process boilers 1 and 2 do not have the capability of control at the burner tip. Therefore, this option is not technically feasible and will not be further evaluated in this report.

Low NOx Burners (LNB)

Low- NO x burner (LNB) technology utilizes advanced burner d esign to reduce NO x formation through the restriction of oxygen, flame temperatur e, and/or residence time. LNB is a staged combustion process that is designed to split fuel c ombustion into two zones. In the primary zone, NOx formation is limited by either one of two metho ds. Under staged air rich (high fuel) condition, low oxygen levels limit flame temperatures resultin g in less NOx formation. The primary zone is then followed by a secondary zone in which the inco mplete combustion products formed in the primary zone act as reducing agents. Alternatively, under staged fuel lean (low fuel) conditions, excess air will reduce flame temperature to reduce NO x formation. In the secondary zone, combustion products formed in the primary zone act to lower the local oxygen concentration, resulting in a decrease in NO x formation. Low NO x burners typically achieve NO x emission reductions of 25% - 50% for process boilers.

Overfire Air (OFA)

Overfire air diverts a portion of the total combust ion air from the burners and injects it through separate air ports above the top level of burners. OFA is a NO x control technology typically used in boilers and is primarily geared to reduce thermal N O x . Staging of the combustion air creates an initial
fuel-rich combustion zone for a cooler fuel-rich co mbustion zone. This reduces the production of
thermal NO x by lowering combustion temperature and limiting th e availability of oxygen in the combustion zone where NOx is most likely to be form ed. OFA is considered compatible with the LNB and is a technically feasible option for furthe r NO x reduction. However, due to the small size and number of burners, OFA is not desirable alterna tive for NMC process boilers and will not be considered for further BART analysis.

Induced Flue Gas Recirculation Burners Induced flue gas recirculation burners, also called ultra low- NO x burners, combine the benefits of flue gas recirculation and low-NO x burner control technologies. The burner is designe d to draw flue gas to dilute the fuel in order to reduce the flame temperature. These burners also utilize staged fue l combustion to further reduce flame temperature. Th e estimated NO x control efficiency for IFGR burners in high temperature applications is 50-75%.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 56 Energy Efficiency Projects Energy efficiency projects provide opportunities fo r a company to reduce their fuel consumption. Typically reduced fuel usage translates into reduce d pollution emissions. An energy efficiency project could be preheat incoming make-up air or pe llet feed. Each project is very dependent upon the fuel usage, process equipment, type of product and so many other variables.

Due to the increased price of fuel, the facilities have already implemented energy efficiency projects

. Each project carries its own fuel usage reductions and potentially emission reductions. It would be impossible to assign a general potential emission r eduction for the energy efficient category. Due to the uncertainty and generalization of this category , this will not be further evaluated in this report

. However, it should be noted that facilities will co ntinue to evaluate and implement energy efficiency projects as they arise.

Alternate Fuels As described within the energy efficiency descripti on, increased price of fuel has pushed companies
to evaluate alternate fuel sources. These fuel sou rces come in all forms – solid, liquid and gas. To
achieve reduction of NO x emissions through alternative fuel usage, the sour ce must be currently burning a high NOx emitting fuel relative to other fuels. The boilers are only capable of burning natural gas and distillate oil. Therefore the use of alternate fuels is not a viable option for the p rocess boilers and will not be considered further in this analysis.

It is also important to note that U.S. EPA’s intent is for facilities to consider alternate fuels as t heir option, not to direct the fuel choice. 36

Therefore, due to the limited boiler fuel capabilit ies and the fact that BART is not intended to mandate a fuel switch, alternative fuels as an air pollution control technology will not be further evaluated in this report

However, similar to energy efficiency, facilities w ill continue to evaluate and implement alternate fuel usage as the feasibility arises.

36 Federal Register 70, no. 128 (July 6, 2005): 39164Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 57 Post Combustion Controls

NO x can be controlled using add-on systems located dow nstream of the combustion process. The two main techniques in commercial service include t he selective non catalytic reduction (SNCR) process and the selective catalytic reduction (SCR) process. There are a number of different process systems in each of these categories of control tech niques.

In addition to these treatment systems, there are a large number of other processes being developed and tested on the market. These approaches involve innovative techniques of chemically reducing, absorbing, or adsorbing NO x downstream of the combustion chamber. Examples of these alternatives are nonselective catalytic reduction (NSCR) and Low Temperature Oxidation (LTO). Each of these
alternatives is described below.

Non-Selective Catalytic Reduction (NSCR) A non-selective catalytic reduction (NSCR) system i s a post combustion add-on exhaust gas treatment system. NSCR catalyst is very sensitive t o poisoning; so; NSCR is usually applied primarily in natural gas combustion applications.

NSCR is often referred to as “three-way conversion” catalyst because it simultaneously reduces NO x , unburdened hydrocarbons (UBH), and carbon monoxide (CO). Typically, NSCR can achieve NO x emission reductions of 90 percent. In order to oper ate properly, the combustion process must be near stoichiometric conditions. Under this condition, i n the presence of a catalyst, NO x is reduced by CO, resulting in nitrogen (N 2 ) and carbon dioxide (CO 2 ). The most important reactions for NO x removal

are:

2CO + 2NO → 2CO 2 + N 2 (1)

[UBH] + NO → N 2 + CO 2 + H 2 O ( 2)

NSCR catalyst has been applied primarily in clean c ombustion applications. This is due in large part to the catalyst being very sensitive to poisoning, making it infeasible to apply this technology to liquid fuels. Therefore, this technology will not b e further evaluated in this report.

Selective Catalytic Reduction and Regenerative Sele ctive Catalytic Reduction SCR is a post-combustion NO x control technology in which ammonia (NH 3 ) is injected into the flue gas stream in the presence of a catalyst. NO x is removed through the following chemical reaction :Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 58 4 NO + 4 NH 3 + O 2 → 4 N 2 + 6 H 2 O (1)
2 NO 2 + 4 NH 3 + O 2 → 3 N 2 + 6 H 2 O ( 2)

A catalyst bed containing metals in the platinum fa mily is used to lower the activation energy required for NO x decomposition. SCR requires a temperature range of about 570°F – 850°F for a normal catalyst. At temperature exceeding approxima tely 670oF, the oxidation of ammonia begins to become significant. At low temperatures, the forma tion of ammonium bisulfate causes scaling and corrosion problems.

A high temperature zeolite catalyst is also availab le; it can operate in the 600 °F – 1000°F temperature range. However, these catalysts are ver y expensive.

Ammonia slip from the SCR system is usually less th an 3 to 5 ppm. The emission of ammonia increases during load changes due to the instabilit y of the temperature in the catalyst bed as well as at low loads because of the low gas temperature.

Regenerative Selective Catalytic Reduction (RSCR) a pplies the Selective Catalytic Reduction (SCR) control process as described below with a preheat p rocess step to reheat the flue gas stream up to SCR catalyst operating temperatures. The preheatin g process combines use of a thermal heat sink (packed bed) and a duct burner. The thermal sink r ecovers heat from the hot gas leaving the RSCR and then transfers that heat to gas entering the RS CR. The duct burner is used to complete the preheating process. RSCR operates with several pac ked bed/SCR reactor vessels. Gas flow
alternates between vessels. Each of the vessels alt ernates between preheating/treating and heat

recovery.

The benefits of RSCR are:

• Its high energy efficiency allows it to be used aft er SO 2 and particulate controls.

• RSCR has a thermal efficiency of 90% - 95% vs. stan dard heat exchangers which have a thermal efficiency of 60% to 70%.

• Application of RSCR after SO 2 and PM controls significantly reduces the potentia l for problems associated with plugging and catalyst pois oning and deactivation.

To date, RSCR has been applied to wood-fired utilit y boilers. Application of this technology has not been applied to liquid and natural gas fired boiler s. Using RSCR would require research, test runs,Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 59 and extended trials to identify potential issues re lated to catalyst selection, and impacts on plant systems. It is not reasonable to assume that vendo r guarantees of performance would be forthcoming in advance of a demonstration project. The timeline required to perform such a demonstration project would likely be two years to develop and agree on t he test plan, obtain permits for the trial, commission the equipment for the test runs, perform the test runs for a reasonable study period, and evaluate and report on the results. The results wo uld not be available within the time window for establishing emission limits to be incorporated in the state implementation plan (SIP) by December
2007.

Recalling U.S. EPA’s intention regarding “available ” technologies to be considered for BART, as mentioned in Section 2.B, facility owners are not e xpected to undergo extended trials in order to learn how to apply a control technology to a comple tely new and significantly different source type. Therefore, RSCR is not considered to be technically feasible, and will not be analyzed further in this BART analysis.

Selective Non-Catalytic Reduction (SNCR) In the SNCR process, urea or ammonia-based chemical s are injected into the flue gas stream to convert NO to molecular nitrogen, N 2 , and water. SNCR control efficiency is typically 25% - 60%. Without a catalyst, the reaction requires a high te mperature range to obtain activation energy. The
relevant reactions are as follows:



### NO + NH 3 

### + 1⁄4O 2 

### → N 2 

### + 3/2 

### H 2 

### O (1)

NH 3 

### + 1⁄4O 2 

### → NO + 3/2H 2 

### O (2)

At temperature ranges of 1470 to 1830 ° F reaction (1) dominates. At temperatures above 200 0 ° F, reaction (2) will dominate. This control option is considered feasible.

Low Temperature Oxidation (LTO) The LTO system utilizes an oxidizing agent such as ozone to oxidize various pollutants including
NO x . In the system, the NO x in the flue gas is oxidized to form nitrogen pento xide (equations 1, 2, and 3). The nitrogen pentoxide forms nitric acid v apor as it contacts the water vapor in the flue gas (4). Then the nitric acid vapor is absorbed as dil ute nitric acid and is neutralized by the sodium hydroxide or lime in the scrubbing solution forming sodium nitrate (5) or calcium nitrate. The nitrates are removed from the scrubbing system and discharged to an appropriate water treatment system. Commercially available LTO systems include Tri-NO x ® and LoTOx®.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 60 NO + O 3 → NO 2 + O 2 (1)

NO 2 + O 3 → NO 3 + O 2 (2)

NO 3 + NO 2 → N 2 O 5 (3)

N 2 O 5 + H 2 O → 2HNO 3 (4)

HNO 3 + NaOH → NaNO 3 + H 2 O (5)

Low Temperature Oxidation (Tri-NO x ® ) This technology uses an oxidizing agent such as ozo ne or sodium chlorite to oxidize NO to NO 2 in a primary scrubbing stage. Then NO 2 is removed through caustic scrubbing in a secondary stage. The
reactions are as follows:

O 3 + NO → O 2 + NO 2 (1)

2NaOH + 2NO 2 + 1⁄2 O 2 → 2NaNO 3 + H2O (2)

Tri-NO x ® is a multi-staged wet scrubbing process in industr ial use. Several process columns, each assigned a separate processing stage, are involved. In the first stage, the incoming material is quenched to reduce its temperature. The second, ox idizing stage, converts NO to NO 2 . Subsequent stages reduce NO 2 to nitrogen gas, while the oxygen becomes part of a soluble salt. Tri-NO x ® is typically applied at small to medium sized sources with high NO x concentration in the exhaust gas (1,000 ppm NO x ).

Low Temperature Oxidation (LoTOx ® )

BOC Gases’ Lo-TOx ® is an example of a version of an LTO system. LoTOx ® technology uses ozone
to oxidize NO to NO 2 and NO 2 to N 2 O 5 in a wet scrubber (absorber). This can be done in the same scrubber used for particulate or sulfur dioxide rem oval, The N 2 O 5 is converted to HNO 3 in a scrubber, and is removed with lime or caustic. Ozo ne for LoTOx ® is generated on site with an electrically powered ozone generator. The ozone ge neration rate is controlled to match the amount
needed for NO x control. Ozone is generated from pure oxygen. In order for LoTOx ® to be economically feasible, a source of low cost oxygen must be available from a pipeline or on site generation.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 61 In addition, only two of BOC’s LoTOx ® installations are fully installed and operational applications. Therefore, although this is an emerging technology, the limited application means that it has not been demonstrated to be an effective technology in wides pread application. Consequently, the technical feasibility of LTO as technically infeasible for th is application and will not be evaluated further.

Step 2 Conclusion Based upon the determination within Step 2, the rem aining NO x control technologies that are available and applicable to the process boilers are identified in Table 5-10. The technical feasibilit y as determined in Step 2 is also included in Table 5 -10.

Table 5-10 Backup Process Boiler NO x Control Technology – Availability, Applicability a nd Technical Feasibility

NOx Pollution Control Technology Available? Applicable? Technically Feasible? External Flue Gas Recirculation (EFGR) Yes Yes No Low-NOx Burners Yes Yes Yes Overfired Air Yes Yes No Induced Flue Gas Recirculation (IFGR) Yes Yes Yes Energy Efficiency Projects Yes Yes No Alternative Fuels Yes Yes Not required Non-Selective Catalytic Reduction (NSCR) Yes Yes No Selective Catalytic Reduction (SCR) Yes Yes Yes Regenerative SCR Yes Yes No Selective Non-Catalytic Reduction (SNCR) Yes Yes Ye s Low Temperature Oxidation (LTO) Yes No No

5.B.ii.c STEP 3 – Evaluate Control Effectiveness of Remaining Control Technologies Table 5-11 describes the expected control efficienc y from each of the remaining technically feasible control options as identified in Step 2.

Table 5-11 Backup Process Boiler NOx Control Techno logy Effectiveness

NOx Pollution Control Technology Approximate Control Efficiency Low-NOx Burners 50% Low-NOx Burners with IFGR 75%
SCR 90% Selective Non-Catalytic Reduction (SNCR) 50%Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 62 5.B.ii.d STEP 4 – Evaluate Impacts and Document the Results Table 5-12 details the expected costs associated wi th installation of NO x controls. Capital costs were calculated based on the maximum 24-hour emissions, U.S. EPA cost models, and vendor estimates. Vendor estimates for capital costs based on a speci fic flow rate were scaled to each stack’s flow rate using the 6/10 power law to account for the economy of scale. Operating costs were based on 93% utilization and 7650 operating hours per year, whic h is extremely conservative, since they are backup boilers. Operating costs were proportionally adjust ed to reflect site specific flow rates and pollutan t concentrations.

After a tour of the facility and discussions with f acility management, it was determined the space surrounding the boilers is congested and the area s urrounding the building supports vehicle and rail traffic to transport materials to and from the buil ding. A site-specific estimate for site-work, foundations, and structural steel was added based u pon the facility site to arrive at the total retrof it installed cost of the control technology. See Appe ndix C for a site plan of the facility. Additionall y, the structural design of the existing building woul d not support additional equipment on the roof. The detailed cost analysis is provided in Appendix A.

Table 5-12 Backup Process Boiler NO x Control Cost Summary

Control Technology Installed

Capital Cost ($) Operating Cost

($/yr) Annualized

Pollution Control Cost ($/ton) Incremental

Control Cost ($/ton) Low NOx Burner $90,775 $14,915 $723 NA Low NOx Burner / IFGR $518,713 $330,367 $10,675 $30,626 Selective Catalytic Reduction (SCR) $5,563,529 $1,120,061 $30,160 NA
Selective NonCatalytic Reduction (SNCR) $925,876 $250,181 $12,126 NA

Based on the BART final rule, court cases on cost-e ffectiveness, guidance from other regulatory bodies, and other similar regulatory programs like Clean Air Interstate Rule (CAIR), cost-effective air pollution controls in the electric utility indu stry for large power plants are in the range $1,000 to $1,300 per ton removed as illustrated in Appendix E . This cost-effective threshold is also an indirec t measure of affordability for the electric utility i ndustry used by USEPA to support the BART rulemaking process. For the purpose of this taconite B ART analysis, the $1,000 to $1,300 costY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 63 effectiveness threshold is used as the cutoff in pr oposing BART. The taconite industry is not afforded the same market stability or guaranteed co st recovery mechanisms that are afforded to the electric utility industry. Therefore, the $1,000 t o $1,300 per ton removed is considered a greater business risk to the taconite industry. Thus it is reasonable to use it as a cost effective threshold for proposing BART in lieu of developing industry and s ite specific data.

The annualized pollution control cost value was use d to determine whether or not additional impacts analyses would be conducted for the technology. If the control cost was less than a screening threshold established by MPCA, then visibility mode ling impacts, and energy and other impacts are evaluated. MPCA set the screening level to elimin ate technologies from requiring the additional impact analyses at an annualized cost of $8,000 to $12,000 per ton of controlled pollutant 37

. Therefore, all air pollution controls with annualiz ed costs less than this screening threshold will be evaluated for visibility improvement, energy and ot her impacts.

The incremental control cost listed in Table 5-12 r epresents the incremental value of each technology as compared to the technology with the next highest level of control.

Energy and Environmental Impacts The energy and non-air quality impacts for LNB and LNB with IFGR are presented in Table 5-13. Because the cost of the remaining NO x control technologies for the NMC process boilers i s so high
and does not meet a reasonable definition of cost e ffective technology, these technologies are removed from further consideration in this analysis

.
Table 5-13 Backup Process Boiler NO x Control Technology – Other Impacts Assessment
Control Option Energy Impacts Other Impacts
LNB - Minimal energy impacts - Increase in CO emissions

- Potential for steam tube wastage due to longer combustion flame IFGR/LNB - Minimal energy impacts. - Increase in CO emissions

- Potential for steam tube wastage due to longer combustion flame.

37 Minnesota Pollution Control Agency (MPCA). Air Pe rmit for Cenex Harvest States Cooperative Soybean Processing Plant, Fairmont, MN Permit 09100059-002.Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 64 5.B.ii.e STEP 5 – Evaluate Visibility Impacts As previously stated in section 4 of this document, states are required to consider the degree of visibility improvement resulting from the retrofit technology, in combination with other factors such as economic, energy and other non-air quality impac ts, when determining BART for an individual source. The baseline, or pre-BART, visibility impa cts modeling was presented in section 4 of this document. This section of the report evaluates the visibility impacts of BART NO X control and the resulting degree of visibility improvement.

Predicted 24-Hour Maximum Emission Rates Consistent with the use of the highest daily emissi ons for baseline, or pre-BART, visibility impacts, the post-BART emissions to be used for the visibili ty impacts analysis should also reflect a maximum 24-hour average project emission rate. In the visibility impacts NO X modeling analysis, the emissions from the sources undergoing a full BA RT NO X analysis were adjusted to reflect the projected 24-hour maximum NO X emission rate when applying the control technologi es that met the threshold requirements of steps 1 – 4. The emissio ns from all other Subject-to-BART sources were not changed. Table 5-14 provides a summary of the modeled 24-hour maximum emission rates and their computational basis for the evaluated NO X control technologies. Table 5-15 provides a summary of the SO 2 , NO X , and PM 10 emissions for each modeling scenario, and Table 5- 16 provides a summary of the modeling input data.

Table 5-14 Backup Process Boiler NO x Post- BART Emission Rates for Emission Unit EU003 and EU004

Control Scenario SV # Emission Unit Description NO x Control Technology % NO x

Reduction NO x

Annual Emission Rate (tons/year) NO x

24-hour Maximum Emission Rate (lb/day)
1 SV003 Process Boiler 1 Low Nox Burners 50% 25.5 279

1 SV003 Process Boiler 2 Low Nox Burners 50% 25.5 279Y:\23\00 MN Taconite BART (2006)\Facility BART Reports\NMC\NMC Furnace-Process Boiler\NMC Furnace BARTReport_9-6-2006.doc65Table 5-15 Backup Process Boiler Post-BART ModelingScenariosScenarioControl Scenario TechnologyModeling Emission Rate InputSO2NOxPM2.5/PM10SO2NOxPM%Reduced24-hr Maxlb/hr%Reduced24-hr Maxlb/hr%ReducedPM2.5 24-hr Max.lb/hr%ReducedPM2.5-1024-hr Max.lb/hr0Base Base BaseSV003ProcessBoilers1 & 20 33.5 0 23.3 0 0 1.91BaseLNBwithIFGRBaseSV003ProcessBoilers1 & 20.0% 33.5 50.0% 11.6 0 0 1.9Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-

2006.doc 66 Table 5-16 Backup process Boiler Post-BART NO x Modeling Scenarios - Modeling Input Data

Control Scenario SV # Emission Unit Stack Easting LCC (km) Stack Northing

LCC (km) Height of

Opening from Ground (m) Base

Elevation of Ground (m) Stack

Diameter (m) Flow Rate

at exit (acfm) Exit

Temp ( o F)
1 SV003 Process

Boilers 1 & 2 631471.5 5238482.8 131 611 6.5 59900 450

Post-BART Visibility Impacts Modeling Results Results of the post-BART visibility impacts modelin g for NO X for the process boilers are presented in Table 5-17. The results summarize 98th percenti le dV value and the number of days the facility contributes more than a 0.5 dV of visibility impair ment at each of the Class I areas. The comparison of the post-BART modeling scenarios to the baseline conditions is presented in Table 5-18.

Visibility impacts with SO 2 controls are presented in section 6.

Table 5-17 Backup Process Boiler Post-BART NO x Modeling Scenarios - Visibility Modeling Results

2002 2003 2004 2002 – 2004 Combined

Scenario # Class I

Area with Greatest Impact Modeled

98 th Percentile Value (deciview) No. of

days exceeding 0.5 deciview Modeled 98 th

Percentile Value (deciview) No. of days

exceeding 0.5 deciview Modeled 98 th

Percentile Value (deciview) No. of days

exceeding 0.5 deciview Modeled 98 th

Percentile Value (deciview) No. of days

exceeding 0.5 deciview 0 BWCA 1.1 34 1.1 34 1.3 38 1.1 106 1 BWCA 1.1 33 1.1 34 1.3 38 1.1 105

Table 5-18 Backup Process Boiler Post-BART NO x Modeling Scenarios – Comparison of Visibility Modeling Results to Baseline Modeling Re sults

2002 2003 2004 2002 – 2004 Combined

Scenario # Class I

Area with Greatest Impact Improved

Modeled 98 th Percentile Value ( ∆ -dV ) Decreased

No. of days exceeding 0.5 deciview Improved

Modeled 98 th Percentile Value ( ∆ -dV ) Decreased

No. of days exceeding 0.5 deciview Improved

Modeled 98 th Percentile Value ( ∆ -dV ) Decreased

No. of days exceeding 0.5 deciview Improved

Modeled 98 th Percentile Value ( ∆ -dV ) Decreased

No. of days exceeding 0.5 deciview 0 BWCA 1.1 34 1.1 34 1.3 38 1.1 106 1 BWCA 0.0 1 0.0 0 0.0 0 0.0 1Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 67 

# 6. Visibility Impacts

As previously stated in section 4 of this document, states are required to consider the degree of visibility improvement resulting from the retrofit technology, in combination with other factors such as economic, energy and other non-air quality, when determining BART for an individual source. The baseline, or pre-BART, visibility impacts model ing was presented in section 4 of this document. The visibility impacts of individual control techno logies were presented in Step 5 of section 5 of thi s document. This section of the report evaluates the various BART control scenarios utilizing both
SO 2 and NO x controls, and estimates the resulting degree of vi sibility improvement. 

## 6.A Post-BART Modeling Scenarios Steps 1-4 of the BART analysis identified the contr ol technologies that were:

• Available and applicable;

• Technically feasible; and

• Below the screening cost threshold for further BART analysis.

Step 5 of the BART analysis evaluated the visibilit y impacts of each of the control technologies that met the requirements of the screening analysis of s teps 1-4.

However, because there are limited control options available that meet the above criteria, there are limited available control combinations, or control scenarios, that must be considered. Additionally, the interactions between the visibility impairing p ollutants NO x , SO 2 and PM 10 can play a large part in predicting impairment. It is therefore important to take a multi-pollutant approach when assessing visibility impacts. Accordingly, this visibility i mprovement analysis evaluates several operating
control scenarios that account for the various comb inations of available SO 2 and NO x controls. In addition, two site-specific scenarios were develope d so that the evaluation includes other operating scenarios and conditions that would improve visibil ity impairment. The post-BART modeling scenarios, including those presented in Step 5 of s ection 5, are presented in Table 6-1. 

## 6.B Post-BART Modeling Results Results of the post-BART modeling scenarios are pre sented in Table 6-2. The results summarize 98th percentile dV value and the number of days the facility contributes more than a 0.5 dV ofY:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 68 visibility impairment at each of the Class I areas. The comparison of the post-BART modeling scenarios to the baseline conditions is presented i n Table 6-3.

While the cost per ton of low NO x burners is $723, and is below the threshold of $1,0 00 to $1,300 per ton, they result in essentially no visibility impro vement to the Class I areas. In the three years, additional controls would result in only one fewer day with a visibility impact of greater than 0.5 dV and the change in the modeled worst day (98 th percentile) is 0.007 deciviews, which is less than 1% of the total modeled BART impact. The cost of this marginal improvement is $4.3 million per deciview, considering the capital cost of $91,000 a nd the total annual cost of $15,000.Y:\23\00 MN Taconite BART (2006)\Facility BART Reports\NMC\NMC Furnace-Process Boiler\NMC Furnace BARTReport_9-6-2006.doc69Table 6-1 Post-BART Modeling ScenariosScenario Control TechnologySO2NOxParticulate MatterControlScenarioSV #Emission UnitSO2NOx%ReductionMax24-hour lbs/hr% ReductionMax24-hourlbs/hrPM10Max 24-hrlbs/hrPM2.5Max 24-hrlbs/hrPMcoarseMax 24-hrlbs/hr0Base(existingdesign)Base(existingdesign)SV101Furnace 11 Hood Exh--- 11.8 --- 17.1 11.3SV102Furnace 11 Hood Exh11.8 17.1 11.3SV103Furnace 11 Hood Exh11.8 17.1 11.3SV104Furnace 11 Waste Gas--- 5.9 --- 62.4 10.6SV105Furnace 11 Waste Gas5.9 62.4 10.6SV111Furnace 12 Hood Exh--- 11.8 --- 17.1 11.3SV112Furnace 12 Hood Exh11.8 17.1 11.3SV113Furnace 12 Hood Exh11.8 17.1 11.3SV114Furnace 12 Waste Gas--- 5.9 --- 62.4 10.6SV115Furnace 12 Waste Gas5.9 62.4 1.6SV003Process Boilers 1 & 233.5 23.3 1.91 BaseBase oninduratingfurnace andLow NOxBurners onthe backupprocessboilersSV101Furnace 11 Hood Exh11.8 --- 17.1 11.3SV102Furnace 11 Hood Exh11.8 17.1 11.3SV103Furnace 11 Hood Exh11.8 17.1 11.3SV104Furnace 11 Waste Gas5.9 --- 62.4 10.6SV105Furnace 11 Waste Gas5.9 62.4 10.6SV111Furnace 12 Hood Exh11.8 --- 17.1 11.3SV112Furnace 12 Hood Exh11.8 17.1 11.3SV113Furnace 12 Hood Exh11.8 17.1 11.3SV114Furnace 12 Waste Gas5.9 --- 62.4 10.6SV115Furnace 12 Waste Gas5.9 62.4 1.6SV003Process Boilers 1 & 233.5 50.0% 11.6 1.9Y:\23\00 MN Taconite BART (2006)\Facility BART Reports\NMC\NMC Furnace-Process Boiler\NMC Furnace BARTReport_9-6-2006.doc70Table 6-2 Post-BART Modeling Scenarios - Visibility Modeling Results2002200320042002 – 2004CombinedScenario #Class I AreawithGreatestImpactModeled98thPercentileValue(deciview)No. of daysexceeding0.5deciviewModeled 98thPercentileValue(deciview)No. of daysexceeding 0.5deciviewModeled 98thPercentileValue(deciview)No. of daysexceeding 0.5deciviewModeled 98thPercentileValue(deciview)No. of daysexceeding 0.5deciview0 BWCA 1.1 34 1.1 34 1.3 38 1.1 1061 BWCA 1.1 33 1.1 34 1.3 38 1.1 105Table 6-3 Post-BART Modeling Scenarios – Comparisonof Visibility Modeling Results to Baseline Modeling ResultsModeling Results02002200320042002-2004ScenarioLimiting Class I AreaImprovedModeled98thPercentileValue(∆-dV)DecreasedNo. of Daysexceeding 0.5dVImprovedModeled 98thPercentileValue(∆-dV)DecreasedNo. of Daysexceeding0.5 dVImprovedModeled 98thPercentileValue(∆-dV)DecreasedNo. of Daysexceeding0.5 dVImprovedModeled98thPercentileValue(∆-dV)DecreasedNo. ofDaysexceeding0.5 dV0 BWCA 1.1 34 1.1 34 1.3 38 1.1 1061 BWCA 0.0 1 0.0 0 0.0 0 0.0 1Y:\23\00 MN Taconite BART (2006)\Facility BART Repo rts\NMC\NMC Furnace-Process Boiler\NMC Furnace BART Report_9-6-2006.doc 71 

# 7. Select BART

BART for NMC is proposed to be as follows:

Indurating Furnaces
For SO 2 , polishing add-on controls are not cost effective. Therefore, BART is proposed to be existing controls. The corresponding SO 2 emissions limit would be 2.0 lbs/mmBtu, which equa tes to 300 lb/hr per furnace based upon each furnace heat input rating of 150 mmBtu.

For NO x , add on control are not cost effective. Therefore , BART is proposed to be the existing furnace design and permitted fuels. The correspond ing NO x limit would be 176 lb/hr for each
furnace.

For PM, requirements compelled by the upcoming MACT standard constitute BART. The corresponding emissions limit would be 0.01 grains per dscf for the furnaces.

Process Boilers The process boilers are backup boilers for steam pr oduction normally supplied to the taconite plant from the power boilers. For SO 2 , add-on controls are not cost effective. Therefor e, BART is proposed to be existing design and permitted fuels. The corresponding SO 2 emissions limit would be
0.6 lb/mmBtu for each boiler.

For NO x , add-on controls would not accomplish a meaningful improvement in visibility. Therefore, BART is proposed to be existing design and permitte d fuels. The corresponding NO x limit would be
0.17 lb/mmBtu for each boiler.

Other Taconite Sources

For PM, requirements compelled by the upcoming MACT standard constitute BART. The corresponding emissions limit would be equivalent t o the MACT limit.

The schedule for implementation of these limits is within the 5-year time-frame required for BART implementation.