# Minnkota Power**~pr;]** 

# coo PER A T I V E, INC.
1822 Mill Road, P.O. Box 13200 • Grand Forks, ND 58208-3200 • Phone (701) 795-4000 November 9,2007

Mr. Terry O'Clair Director, Division of Air Quality North Dakota Department of Health 918 East Divide Avenue, 2nd Floor Bismarck, NO 58501-1947
Subject: Response to EPA's October4,2007 Letter
Dear Mr. O'Clair: Your Touchstone Energy" Partner 

# -

Enclosed, please find Minnkota's' comments in response to EPA's letter dated October 4,2007. Should you have any questions concerning our comments, please contact me at 701-795-4221.

# --b{~4--4V,-

# Z John T. Graves, P.E. Environmental Manager
C: David Sogard 

### wlo encl Luther Kvernen 

### wlo encl Craig Bleth 

### wlencl Kevin Thomas 

### wlo encl Stu Libby 

### wlo encl Tom Anseth 

### wlo encl Young Station File 

### wlencl

## Comment & 

## Response to EPA Region 8's October 4, 2007 Comment on NDDH BACT Determination at Milton R. Young Station
Minnkota Power Cooperative, Inc. and Square Butte Electric Cooperative (together "Minnkota") are pleased to provide their comments on the U.S. Environmental Protection Agency's ("EPA") October4, 2007, response to Minnkota's letters dated March 19,2007 and April 23, 2007 ("EPA Response"). After having exhaustively reviewed the EPA Response and Minnkota's original and supplemental submissions regarding the selection ofthe best available control technology ("BACT") at Milton R. Young Units 1 and 2, we have concluded that the administrative record fully supports a finding by the North Dakota Department ofHealth ("NDDH") that selective catalytic reduction technology is technically infeasible for electric generating units that include cyclone burners firing North Dakota lignite. We have summarized the bases for our conclusion below, and have responded in Appendix A to each ofEPA's October4, 2007 comments. 

## Minnkota has demonstrated that SCR technology is not available for use at Young Station EPA's 1990 Draft New Source Review Workshop Manuall ("Workshop Manual") concludes that a control technology is unavailable as BACT-and therefore technically infeasible-ifit is not commercially available for use at the source under consideration. Specifically, the Workshop Manual provides: "[It is not] expected that an applicant would be required to experience extended trials to learn how to apply a technology on a totally new and dissimilar
source type. Consequently technologies in the pilot scale testing stages ofdevelopment would not be considered available for BACT review."z.

It is indisputable that "there are no SCR installations in operation or planned on units that include cyclone burners firing North Dakota lignite with severe slagging and fouling tendencies combined with such high boiler economizer outlet gas temperatures (over 7

### SOOP) required for high-moisture fuel pre-drying systems and tubular air heaters.,,3 Cyclone burnerboilers firing

1 See Reference number 1. 2 Ibid, EPA NSR Workshop Manual at B.18 3 See Reference number 2 at Al-32.
1Minnkota Response to EPA Region 8 October 4,2007 Comments on NDDH BACT Determination at Milton R. Young Station

- DRAFT North Dakota lignite are in fact dissimilar from all other**~ommercial~scale** sources that have applied SCR, and Minnkota has described the facts supporting dissimilarity at length in its original and supplemental BACT reports. Indeed, this dissimilarity is apparent on its face in that the only sources ofinformation upon which Minnkota or EPA rely in their various discussions of technical feasibility for SCR on similar sources are from pilot scale testing. Any SCR catalyst vendor's willingness to guarantee performance on aNorth Dakota lignite-fired boiler will be very limited, requiring certain specific criteriato be met that are yet to be proven to exist orcapable ofexisting at MRYS. This limitation to the SCR catalyst guarantee is required by the vendor in orderto manage financial risks by specifying the limits oftheir system design in case ofpotential operating conditions that cause performance problems that prevent achievement ofguarantees and/or warranty claims. SCR catalyst vendors assume that the system suppliers have already solved (or will solve) the stated temperature problems, and proven solutions to these conditions have not been identified.
EPA attempts4 to minimize the significant dissimilarities in boiler operation and fuel source at cyclone burner-based units firing North Dakota lignite from other units utilizing SCR by citing a 1989 guidance document exploring the notion ofdissimilarity. The so-called dissimilarities scrutinized by the 1989 guidance are nothing like the real dissimilarities between Minnkota's units and other units using SCR.5 Moreover, Minnkota has followed the guidance in explaining very clearly in its original and supplemental BACT reports the impacts ofdifferent gas stream characteristics (in terms ofcontent and temperature) on an SCR add-on control. NDDH therefore has reasonable grounds upon which to conclude that Minnkota's units are dissimilar from other units that have successfully employed SCR.

EPA also attempts to close offdiscussion on the notion of"availability" by citing out ofcontext a single sentence in Minnkota's original BACT study6. Minnkota's original BACT study clearly noted at multiple points that the Young Station units are dissimilar from units at which SCR has

4 See Reference number 3, EPA October4, 2007 Response Enclosure at 2. 5 The 1989 guidance focuses on differences in unit size, less important differences in boiler design, and modest differences in fuel blends. As Minnkota has established in its original and supplemental reports, the cyclone burner design, high outlet temperatures, fuel type, and resultant gas streams are significant differences that result in dissimilarity for purposes ofBACT. 6 Ibid Reference number 3, EPA Response Enclosure at 31.

1119/2007 2Minnkota Response to EPA Region 8 October 4,2007 Comments on NDDH BACT Determination at Milton R. Young Station

- DRAFf been applied7• Though many ofthe same facts are relevant to a determination of"availability" and "applicability," Minnkota has clearly raised the issue ofavailability and NDDH may reasonably conclude that SCR is not available for Minnkota's units.
In summary, Minnkota has demonstrated that SCR is not commercially available for applications similar to Minnkota's Young Station units. NDDH may therefore reasonably conclude that SCR is not available as BACT, and characterize SCR as a technically infeasible technology that need
. not complete steps three through five ofthe top-down BACT analysis.


## Minnkota has demonstrated that 

## SeR technology is not applicable for use at Young Station The Workshop Manual concludes that an available control technology is "applicable" ifone of two conditions are satisfied: (1) "a commercially available control option will be presumed applicable ifit has been or is soon to be deployed on the same or a similar source type;" or (2) "[a]bsent a showing ofthis type, technical feasibility would be based on examination ofthe physical and chemical characteristics of the pollutant-bearing gas stream and comparison to the gas stream characteristics ofthe source types to which the technology had been applied previously."g Minnkota has demonstrated that SCR technology has not been nor soon will be deployed on a "same or similar source type"-that is, a cyclone burner-based unit firing North Dakota lignite. Accordingly, the presumption of"applicability" under the first condition is not met, and NDDH has a reasonable basis upon which to conclude under the first test that SCR is not applicable at Young Station.

7 Ibid Reference number 2, e.g., Minnkota BACT Report at AI-23-AI-24 ("There are, however, no existing fullscale SCR installations on units that fire North Dakota lignite."); id. at AI-26-AI-27 ("The question is whether SCR is a feasible technology for a unit firing North Dakota lignite."); id. at AI-28 (''There have been no installations of SCR systems (full-scale) on units that fire North Dakota lignite."); id. at AI-31 ("Catalysts for a conventional highdust, hot-side SCR system have not been installed nor successfully demonstrated in a full-scale installation ofan operating solid fuel-fired unit that are designed to continuously operate at the high temperatures (above 750 degrees F) that exist between the convection pass economizer and air heater on the Milton R. Young Unit I boiler."); id. at AI-32 ("However, there are no SCR installations in operation or planned on units that include cyclone burners firing North Dakota lignite with severe slagging and fouling tendencies combined with such high boiler economizer outlet gas temperatures (over 7500P) required for high-moisture fuel pre-drying systems and tubular air heaters."). 8 Ibid, Reference number I at B.18.

1119/2007 

### 3Minnkota Response to EPA Region 8 October4,2007 Comments on NDDH BACT Determination at Milton R. Young Station

- DRAFT Regarding the second condition, the Workshop Manual states "[d]eployment ofthe control technology on an existing source with similar gas stream characteristics is [a] generally sufficient basis for concluding technical feasibility barring a demonstration to the contrary.',9 In practice, the "similar gas stream characteristics" analysis compares the physical and chemical characteristics ofthe unit under review to the units at which the technology has been successfully applied, and analyzes how the a particular control technology (here SCR) responds to the different gas stream characteristics. Vendor guarantees provide an important insight into the ability ofan existing technology to be applied successfully on a unit with different gas stream

h .. 10 C aractenstlcs.
Minnkota has exhaustively described the significant physical and chemical differences between gas stream characteristics at Young Units 1 and 2 and other units at which SCR has been applied. Chiefamong these differences are the low and high flue gas temperatures that exist throughout the range ofboiler loads that vary with the extent ofboiler cleanliness; and an abundance offine sodium particles emitted from the boilers along with sulfur, calcium, and other alkali and alkaline earthelements that are in a physical and chemical form that will contaminate and rapidly
cause SCR catalyst to be ineffective. Moreover, Minnkota has provided detailed information regarding how SCR might react to these very different gas stream characteristics, and has cited a number oftechnical sources and pilot projects to illuminate the unresolvable technical difficulties precluding the successful deployment ofSCR to the Young Station. These unresolvable technical difficulties include: the inability to maintain catalyst effectiveness by avoiding severe micropore plugging by sodium-sulfur compounds that are present in the flue gas even after it has passed through an electrostatic precipitator and wet scrubber. Last, Minnkota has been unable-despite a detailed request for a guarantee document-to secure a detailed catalyst vendor's or supplier's guarantee covering a full-scale SCR system at Minnkota's units. While the lack ofa vendor guarantee is not dispositive oftechnical inapplicability, it is an important indication that the engineering companies that would be financially responsible for SCR performance are unwilling to take that risk. 11

9 Ibid, Reference number 1 at B.19. to Ibid, Reference number 1 at B.20. II EPA sidesteps the lack ofa vendor guarantee by describing Minnkota's request for a vendor guarantee as overly voluminous and having "a pessimistic tone." EPA Response at 5, 49. Minnkota disagrees with EPA's
11/912007 

### 4Minnkota Response to EPA Region 8 October4,2007 Comments on NDDH BACT Determination at Milton R. Young Station

- DRAFT

EPA has cited an opinion by Electric Power Research Institute (EPRI) issued on September7, 2006 that "SCR designs can accommodate fuel types never before used in practice on a full scale", and "While experience specifically with Texas lignite is limited, this should not prevent suppliers from providing an SCR system that meets these objectives
... ,,12 The ash chemical and physical properties ofTexas lignite (Wilcox formation) that TXU proposes to bum at the new Oak Grove powerplant do not represent all Texas lignites. This fuel also may be co-fired with Powder River Basin coal at TXU, which may mitigate some ofits less desirable characteristics. Texas lignites cited by the EPA do not represent what is fired in North Dakota, and its technical feasibility and expected performance in an SCR application is not transferable to North Dakota lignite-fired cyclone burner units due to the significant differences in ash chemical and physical properties.
EPA attempts to minimize these technical inapplicability arguments by suggesting that ifenough money were spent on an (experimental) SCR, Minnkota would find that the device could eventually be made to work, and that the BACT decision should therefore tum on costeffectiveness considerations. 13 This argument puts the cost-effectiveness cartbefore the technical feasibility horse. The top-down BACT process very clearly eliminates technically infeasible alternatives from the cost-effectiveness analysis. Minnkota has demonstrated that SCR is-under the definitions provided in the Workshop Manual relating to availability and applicability-technically infeasible. It is an invalid response to suggest that it may be cost effective for Minnkota to conduct an extended pilot test project or full-scale experimental construction and testing project when the definition ofa technically feasible control excludes those projects. EPA's suggestion that a technically infeasible, but hypothetically cost-effective control constitutes BACT is at odds with the Workshop Manual.

characterization and would respond by stating that the risks to technical feasibility that EPA so easily dismisses are an important part ofthe vendor guarantee process that adequately reflects the willingness ofthe vendor to "make good" any deficiencies in performance and provide an "evergreen warranty" that recognizes the importance of catalyst life over the SCR's lifespan. That these risks have dissuaded engineering companies from offering a guarantee is strong evidence that EPA is mistaken in its technical feasibility opinion. 12 Ibid Reference number 3, EPA Response Enclosure at 16-17. 13 Ibid Reference number 3, EPA Response Enclosure at 2-3.

111912007 

### 5Minnkota Response to EPA Region 8 October4, 2007 Comments on NDDH BACT Determin.ation at Milton R. Young Station

- DRAFT In the end, EPA's objections to Minnkota's voluminous submittals on BACT may be reduced to disputing Minnkota's characterization ofthe gas stream characteristics and the impacts ofthose characteristics on boiler and control operations. Certainly a final technicaljudgment will be required by NDDH regarding these issues, while Minnkota has provided a detailed and reasonable position regarding technical infeasibility. In the end, the administrative record would support a reasonable finding by NDDH that SCR is technically infeasible for application on North Dakota lignite-fired cyclone burner units at Young Station.

1 EPA New Source Review Workshop Manual, Prevention of SignificantDeterioration and NonattainmentArea Permitting, Draft October 1990 (The "NSR Manual"). 2 "NOx BestAvailable Control TechnologyAnalysis StudyforMilton R. Young Station Unit 1 Minnkota Power Cooperative, Inc." and a separate "NOxBestAvailable Control TechnologyAnalysis StudyforMilton R. Young Station Unit 2 Square Butte Electric Cooperative", October 2006, by Burns & McDonnell, submitted to EPA Region 8 and EPA Office ofRegulatory Enforcement. 3 United States Environmental Protection Agency (U.S. EPA orEPA) Region 8 letterby Martin Hestmark, Director, Air and Toxics Technical Enforcement Program, ECEJ to Terry L. O'Clair, North Dakota Department ofHealth, Environmental Health Section, Division ofAir Quality and David Sogard and John Graves, Minnkota Power Cooperative, Re: Transmittal of EPA's Response to Minnkota's Letters DatedMarch 19, 2007andApril23, 2007, Regarding the October2006NO x BACT Analysis Study Report forMilton R. Young Station, date stamped October4, 2007.

11/9/2007 6

### APPENDIX A MINNKOTA POWER COOPERATIVE, Inc. and SQUARE BUTTE ELECTRIC COOPERATIVE RESPONSES TO EPA and ERG COMMENTS REGARDING SCR TECHNICAL FEASIBILITY and NON-SCR CONCERNS MILTON R. YOUNG STATION UNIT 1 and UNIT 2 NOx BACT ANALYSIS STUDY November 6, 2007 Region 8 ofUnited States Environmental Protection Agency (U.S. EPA or EPA) has provided North Dakota Department ofHealth's, Environmental Health Section, Division ofAir Quality (NDDH) and Minnkota Power Cooperative Inc. ("Minnkota" or "MPC") with their comments regarding theirlreviewl4 ofMinnkota's letters dated March 

### 19,2007 15 and April 

### 23, 2007 16 regarding the October 

### 2006 Best Available Control Technology (BACT) Analysis Study reports 17 for control ofnitrogen oxides (NOx) emissions from existing Unit 1 and Unit 2 at Milton R. Young Station ("MRYS"). Additional comments from Eastern Research Group (ERG) (Christman) dated August 

### 20,2007 18
, and an Enclosure ofadditional EPA responsesl9
were also attached.

Burns & McDonnell was retained by MPC as an independentconsultant to perform the referenced NOx BACT Analysis Studies ofMinnkota's Unit 1 and Square Butte Electric Cooperative's Unit 2 at the Milton R. Young Station (MRYS) in accordance with the requirements ofa Consent Decree (CD)2o. Minnkota, along with Burns & McDonnell (B&McD), and Energy & Environmental Research Center (EERC) ofthe University ofNorth Dakota, have reviewed the referenced EPA and ERG letters which provided additional comments regarding selective catalytic reduction (SCR)

14 See Reference number 1, October4,2007. 15 See Reference number 2, March 19, 2007. 16 See Reference number 3, April 23, 2007. 17 See Reference number 4, October 2006. 18 See Reference number 5, August 20, 2007, provided with Reference number 1. 19 See Reference number 6, provided with Reference number 1. 20 See Reference number 7, April 24, 2006. 111912007 

### A-Itechnology feasibility and non-SCR concerns pertaining to the referenced NOx BACT Analysis Studies. The following are combined responses byEERC and B&McD to the comments by U.S. EPA Region 8 and ERG involving the referenced study reports for the two units at MRYS.
The following responses follow the outline ofthe attached ERG memorandum and Enclosure to the EPA's October4, 2007 letter. 

### ERG's Memorandum to U.S. 

### EPA, August 20, 200721 : "Core" Issue number I 

### Center Mine Ash Content Variability: ERG memorandum to EPA, August 20, 2007, page 2

. Original Reference: NDDH letter to Minnkota February 1,2007 request item number 1 and

EPA Region 8 letter to NDDH January 26,2007 request item number 4:

... "CenterMine coal does nothave unusual variability in ash contentand in no case has an ash contentfive times higher than PRB coal as B&McD has contended." [ERGAugust 20, 2007letter, page 2J EERC Response: The Center mine coal is extremely variable as compared to Powder River Basin (PRE) coals. Christman ignores information provided in the form ofresponses to comments and presentation that compares the ash percentages in PRE coals. This information was provided in detail in the document entitled "CenterLignites Minnkota Power Cooperative, Inc. and Square Butte Electric Cooperative

-- Responses to EPA Comments NOx BACT Analysis Study Milton R. Young Station Unit 1 and Unit 2 Regarding SCR Technical Feasibility," March 2007.
'Christman ignores the fact that the core data provides the actual variability ofthe lignite and focuses his attention on the 700 coals in the as-fired database for Unit 2, which have been affected by blending that occurs in the coal storage building and coal handling system. The true Center coal variability is represented in the coal core data. Unit I receives unblended coal. The levels ofash in the core samples range from 3.7 to 22.2 % on an as-received basis. This information was provided in the Responses to EPA comments March 2007. Recent stop belt

21 Ibid Reference number 5.
1119/2007 A-2sampling ofthe feed coal to Unit 1 has shown ash contents as high at 22.0 wt % on an as received basis. "Along with the generaldiscussion of ash variability, Dr. Benson introducedthe conceptof "acid-to-base ratio" of the ash (pages 

### 7-9, Minnkota, March 2007) as having relevance to the technical feasibility of SCR as appliedto North Dakota Lignite
.. .Dr. Benson does not, infact, make a direct connection between his discussion of base-to-acidratio and the functioning of an SCR system. B&M cD also only mentions impacton "operation of the boilers atMRYS" (page 9) andmakes no connection specifically to an SCR system. As a final note, Ihave been involved in one way oranother with SCR since the early 1970's and Ihave neverheardor readanything aboutacid-to-base ratio of ash in any SCR document ordiscussion, priorto Dr. Benson's introduction to the subject. " [ERGAugust20, 2007 memo, pages 2 and3

### J First ofall, it is the base-to-acid ratio, not the acid-to-base ratio. Unfortunately Christman is not aware ofthe importance ofthe use ofthe base-to-acid ratio. The base-to-acid ratio (B/ A=[NazO+MgO+CaO+ Kz O+FeO]/[SiOz +Alz03 +TiOz ]) provides a means ofsimply evaluating ash characteristics. The B/ A ratios are an effective way ofexamining variability and ash behavior impacts on power system performance. This relationship has several applications and in SCRs the application is the assessment ofpotential for sulfation. Coals that have a high B/ A ratios will produce entrained particulate and vapor phase species enriched in the basic components. The basic constituents are prone to form sulfate-based deposits that were found to plug and blind catalysts. The partitioning ofthe basic components into the vapor phase and small particle fractions is the greatest for cyclone-fired systems. This information has been provided on numerous occasions in writing and in presentations. The B/A ratio has been utilized for decades to evaluate ash behavior in combustion systems. I am surprised that Christman is unaware ofthe use ofB/A ratios since work supported by EPA in the area ofSCR and S03 reactions to form sulfates has been ongoing for several years. The following is a quote from a final report relevant to this issuezz: "Given the strong correlation between S03 uptake and the base:acid ratios ofthe ashes, it appears that chemi-sorption rather than physical adsorption dominates the process and that temperature plays a strong role as well." B&McD Response:

22 See Reference number 9, November 14,2006. 111912007 A-3Variations in the coal delivered and burned at MRYS have posed difficulties in maintaining consistent combustion and slag-formation and tapping conditions in the cyclones and lower furnaces ofthe boilers. Low BI A ratio correlates to undesirable cyclone operation. High viscosity ash, related to low BI A ratio, causes more incompletely burned coal and ash particles to be exhausted from the cyclone, which increases the amount offlyash that can create slagging and fouling problems in the furnace and convection passes ofthe boiler. This causes furnace exit gas temperatures to increase, requiring more aggressive heat transfer surface cleaning, which means higher gas temperatures with more ash and deposit fragments are exhausted from the boiler, which are problematic for potential blinding, deactivation, and longevity ofthe SCR catalyst.
"Core" Issue number 2 Catalyst deactivation by sodium and regeneration difficulties: ERG memorandum to EPA, August 20, 2007, page 3 Original Reference: EPA Region 8 January 26, 2007 letter to NDDH request item number 1: [Comments regarding Khodayari's work on SCR catalystdeactivation and regeneration due topoisoning by sodium andpotassium] [ERGAugust20, 2007memo, page 3] EERC Response: Christman appears to ignore key statements made by Khodayari in his thesis and other publications. The following is a quote from the abstract ofhis PhD thesis23 : "Potassium and sodium were found to be two ofthe worst poisons that had significant effects on the activity ofthe SCR catalyst due to their selective chemisorption on the Br¢nsted acid sites." [Comments regarding Beck's work on contributions of phosphorus, potassium and sodium]. "His subsequent work focused onphosphorus anddidnotaddress sodium atall. " [ERG August20, 2007memo, page 3] l. EERC Response: Beck and others focused on phosphorus because itwas at a higher concentration than sodium in the materials he was investigating.

23 See Reference number 10. 1119/2007 A-4... "University ofUtah andREIon application of SCR to low-rank coals
...butmasking by flyash is aproblem. The study further concludedthat thepoisoningpotential of the alkali materials rankedas: K>Na> Ca. " [ERGAugust20,2007memo, page 3] EERC Response: The University ofUtah studies did not consider high sodium coals in their testing. They examined lower sodium coals. We agree with the assessment that masking is a problem.
Christman brings up an importantpoint regarding the impacts ofpotassium on catalyst deactivation, but ignores its presence in lignite coals. Potassium can be as high as 2.3% in Center lignite. Potassium, like sodium, is prone to vaporize in combustion systems and condense to form small particles upon gas cooling.
Work was conducted at MRY Unit 1 to examine accumulations ofsticky ash at 300°F downstream ofthe ESP. Figure 1 shows a polished cross-section ofa deposit that has formed on a silicon dioxide surface when exposed to flue gas derived from the combustion ofCenter lignite. The red line shows the path ofa line scan where the composition was determined using x-ray microanalysis. Figure 1 also shows the change in chemical composition along the red line beginning at the outside and moving to the silicon dioxide for selected components. The results show levels ofpotassium (K) as high as 17% and sodium (Na) as high as 16% in the line scan. The material is highly sulfated as indicatedby the high levels ofsulfur (S). The deposit shown in Figure 1 formed at about 3000E In addition, potassium-rich materials were found in deposits plugging SCR catalysts at the Coyote Station as shown in Figure 2 and Table 1. Levels ofpotassiumranging from 2 to 8 elemental wt% were observed.

11/912007 A-5Cross-section ofa surface exposed to flue gas at about 3000 Fin MRY Unit 

### 1. 25.0 20.0 15.0 LOCATION (urn) 10.0 5.0 +---+----+--f---I-+--+--+--+--+---j-+--+--+--J.+--f---I-+--+--+--+--+--i-j_Na -Si**+--+--+-'---PI~",--",~"H---A.MP\-/.-----1LL--W++A----+-J-+--f---I-+--+--+--+--+--+** - S -K -Ca +--+--+--+--+-!---+--+--+--f---l-+----J!-I--+l--+--+--I-+--+--+--+--f---i-j_Fe 100%
90%
80%
70%
60% *-IJ: 50% e" iii 3= 40%
30%
20%
10%
0%0.0 Figure 1.

Figure 2. Ash accumulations in pores ofSCR catalyst exposed to Coyote flue gases for 4 months.

11/912007 A-62 ° F O 

### T hi 1 Ch ° 

### IA I ° f 

### Sit d POts 

### Sh

a 

### e ° ellllca nalYSIS 0 

### e ec 

### e om own 10**l~ure** ° 

## Point Locations, Elemental Wt 

## 0/0 Point 1 Point 2 Point 3 Point4 Point 5 

### Element

Na 5.09 1.88 0.58 2.68 2.04 Mg 2.49 0.88 4.23 4.38 1.39 Al 2.23 3.95 1.50 0.80 1.55 Si 4.86 1.79 4.67 5.82 4.42 P 0.00 0.85 0.06 0.10 0.00 S 32.51 29.43 31.35 30.33 27.55 CI 0.00 0.00 0.22 0.33 0.15 K 6.64 2.54 8.74 7.85 4.64 Ca 16.08 29.69 19.42 16.91 25.20 Ti 0.00 0.11 0.64 0.16 6.02 Cr 0.00 0.00 0.00 0.00 0.00 Fe 7.76 7.52 0.00 3.44 7.37 Ba 4.99 0.00 5.34 6.00 3.19 0 17.35 21.37 23.25 21.20 16.49 TOTAL 100.00 100.00 100.00 100,00 100.00
"While Dr. Benson concludes that the sodium levels in North Dakota Lignite ash are so high
...others atEERCdo notshare that opinion
... " [ERGAugust20,2007memo, page 3J EERC Response: The cited work conductedby Folkedahl (2006) was on a stoker-fired system and does not represent the partitioning that occurs in a cyclone or pulverized coal-fired system. They had significant problems during the testing because large pieces ofunburned biomass kept plugging the inlet to the slipstream system. Christman ignores work conducted by the EPA. Mussatti (2002) indicated in the "EPA Air Pollution Control Cost Manual- Sixth Edition" the following primary mechanisms for catalyst deactivation: "Poisoning

- Certain fuel constituents which are released during combustion act as catalyst poisons. Catalyst poisons include calcium oxide and magnesium oxide, potassium, sodium, arsenic, chlorine, fluorine, and lead. These constituents deactivate the catalyst by diffusing into active pore sites and occupying them irreversibly. Catalyst poisoning represents the main cause ofcatalyst deactivation."

111912007 A-7"BlindinglPlugging/Fouling

- Ammonia-sulfur salts, fly ash, and otherparticulate matter in the flue gas cause blinding, plugging or fouling ofthe catalyst. The particulate matter deposits on the surface and in the active pore sites ofthe catalyst. This results in a decrease ofthe number ofsites available for NOx reduction and an increase in flue gas pressure loss across the catalyst." "Since catalystdeactivation is due to alkaline materials
... This dependency isprobably not linear, since the overwhelming amount of ash in any installation does notdeposit on the catalyst(itpasses through the catalyst channels andends up in the ESP hopperor is emitted), but it is mostappropriate to consideraverage values of chemicalpoisons. This is because the total exposure will be less than the averagefor abouthalf the time andmore that average about halfthe time. The overall deactivation rate "averages out"." [ERG August20, 2007memo, page 4] EERC Response: These statements are an indication ofChristman's lack ofunderstanding ofpartitioning of alkali species during combustion and the transport ofthose species to catalyst surfaces and the importance ofvariability. During combustion the sodium, potassium, and other species vaporize and end up concentrated in the finer size fractions ofash. As the gas and entrained particles are transported through the catalyst channels the finer fraction ofash is deposited on the catalyst and in the pore via diffusion processes. Next to the surface ofthe catalyst there is a stagnant boundary layer where diffusion processes take place. The diffusion across the boundary layer results in selective accumulation ofthe problematic species such as sodium, potassium, sulfur, and other elements on the catalyst. Considering the average value ofpoisons is not appropriate; it does not average out. Values ofpoisoning higherthan the average will
cause rapid and irreversible plugging from which there is no recovery. "Although the high sodium content ofCenterMine coal ash is an economic issue (it will contribute to catalystdeactivation), Dr. Bensonprovides no evidence that itwill render SCR technically infeasible atMRYS". [ERGAugust20, 2007letter, page 4]

, B&McD Response: Catalyst activity for the severely plugged and blinded SCR catalystremoved from the Coyote pilot test was not able to be determined by the catalyst vendor who supplied it. Based on EERC's observation under a scanning electron microscope that every micropore ofthe entire
area ofthe Coyote pilot test SCR catalyst section analyzed was plugged, it could be inferred that the as-removed test catalyst activity would effectively be zero. The length ofexposure for plugging ofthe micropores in the Coyote pilot test for these results was less than or equal to

11/912007 A-8two months, as described in EERC's October 2005 referenced paper 24• The micropore plugging occurs when there is flyash and flue gas flow through that portion ofthe catalyst. It is reasonable to believe that the micropores would have become plugged prior to the observed ash accumulations. The gross ash deposits were found prior to the end ofthe six month test but
were not removed. These ash deposits subsequently caused high velocity flow through a portion ofthe test catalyst and consequently low or no flow through the portion where there are significant ash deposits.
"Core" Issue number 3 Downtime for catalyst cleaning and change out: ERG memorandum to EPA, August 20, 2007, page 4 Original Reference: EPA Region 8 January 26, 2007 letter to NDDH request item number 3: 

## "Ifone assumes a rather extreme short catalyst life of one yearand

### ifthe change out is coordinated with a boilercleaning outage, the SCR unitwouldonly contribute one ortwo days of downtimeperyear". [ERGAugust20, 2007letter, page 4] B&McD Response: The EPA's commenter's and the catalyst vendor's comments do not appear to recognize the impacts from isolating the high-dust SCR catalyst from the gas path during boiler cleaning outages. Ambient airflow through the boiler during the beginning ofa cleaning outage normally aids in the cooldown ofa hot-side SCR reactor. Keeping the SCR reactor inlet closed to prevent moisture and deposits liberated during off-line boiler fireside surface cleaning from entering the SCR reactor impairs the ability to cool the reactor after shutdown. The estimated amount oftime and difficulty in removing lignite ash accumulation from the SCR reactor(s), or replacing fouled catalyst with clean spare catalyst, depends on the volume ofcatalyst and ash requiring cleaning/removal and replacement, and the ability to access the reactor after cooldown. Performing such SCR maintenance outages during boiler cleaning outages is expected to require more boiler downtime than assumed by the EPA's commenter.
Because the EERC SCR pilot test at Coyote Station showed severe catalyst ash and micropore pluggage and fouling within two to four months ofexposure, the frequency offull-scale SCR catalyst cleaning and changeout events when exposed to the expected conditions in the gas

24 Ibid, included with Reference number 4. 11/912007 A-9path ofa North Dakota lignite-fired cyclone boiler could be more often than the boiler cleaning outage frequency. This was described in Minnkota's April 2007 letter to NDDH and EPA.
Documentation ofsuccessful on-line and off-line cleaning ofsuch severely plugged catalyst has not been found. Conventional on-line catalyst cleaning methods will be ineffective in removing the bulk ofthe small particles formed and bonded in a matrix observed throughout the Coyote catalyst (macro- and micropores). Catalyst regeneration will not be productive if the micropores ofthe catalyst cannot be adequately cleaned ofdeposits. Thus, the catalyst will become irreversibly contaminated and the level ofactivity and related NOx reduction performance is expected to diminish rapidly upon installation and short-term exposure during SCR operation.
The only effective countermeasure will be to frequently change-out the exposed catalyst with fresh catalyst. An SCR that needs to have its catalyst replaced every four months or less in order to maintain NOx control performance would be unreasonable to operate and maintain.
"Core" Issue number 4 

### Sticky ash: ERG memorandum to EPA, August 20, 2007, page Original Reference: ERG Letter to EPA, January 8,2007: "[would] soothlowing (steam orhorns) effectivelyprevent[SCR catalyst]pluggingfrom the ash that is normally entrained in theflue gas (notfalling accumulations)"
... [ERG August20, 2007letter, page 4] B&McD Response: The answer given (attributed to Sargent & Lundy during their May 24 presentation to NDDH and EPA) is presumably based on experience with PRE coal ash, not North Dakota lignite ash. As Dr. Benson has previously stated, the low melting temperature fouling deposits from North Dakota lignite cyclone firing can be extremely tenacious in their bonding characteristics. The EPA commenter's response appears to minimize what is likely to be·a significant operating and maintenance problem for SCR catalyst exposed to flue gas and flyash generated by cyclone boilers burning North Dakota lignite. Bums & McDonnell stands by their comments made in Minnkota's April 2007 response (pages 25-26) to the question ofmultiple engineering solutions suggested by the EPA's comment in the EPA's January 26, 2007 letter (page 2).

111912007 A-lO"Core" Issue number 5 EERC pilot test procedure/design: ERG memorandum to EPA, August 20,2007, page 4 Original Reference: EGR Letter to EPA and EPA Region 8 letter to NDDH, January 8, 2007: ".. In summary, the catalystshouldhave been cleaned with somefrequency so that it could be continuously exposed toflue gas. Tests at Coyote station were not useful in determining pluggingpotential and the attemptat simulating sootblowing was noteffective. By EERC's own admission
... theplugging was a result of ash accumulationsfalling onto the catalyst
... Mr. Hansen also confirmedthat the catalystpitch at Coyote (6 mm) was too small
....S&L presenters suggested that a 10 mmpitch mightbe requiredforNorth Dakota lignite applications." "[ERGAugust20, 2007letter, pages 

### 4 and5J
EERC Response: The reactor was sootblown based on recommendations ofthe catalyst vendors. Christman misinterpreted EERC's comments during the meeting at the North Dakota Department of Health (NDDH) in Bismarck. The ash that was on top ofthe surface ofthe catalyst shown in one ofthe images fell on the surface during dismantling the reactor and was not there during the testing. During cross sectioning ofthe SCR catalyst EERC specifically looked for evidence ofdeposit fragments plugging the catalyst. Numerous cross sections ofthe material plugging the catalyst were examined, and there was no evidence that deposit had fallen and accumulated. However, ash falling on the catalyst surface is possible. The slip stream reactors worked well at the Baldwin Station (cyclone PRB-fired) and Columbia (pulverized coal tangential PRB-fired) with minor to moderate fouling. The same reactor used at Baldwin was used at the Coyote Station. The pitch ofthe catalyst used at Coyote Station was 6 mm as recommended by Hansen at Haldor Topsoe. A comparison ofthe first 500 hours with both systems using fresh catalysts is shown in Figures 3 and 4 for Baldwin and Coyote Stations, respectively. Initially, at Baldwin there were some problems with startup and operation ofthe reactor because ofplant outages. The pressure drop at the end of500 hours averaged about 0.6 inches ofwater. The pressure drop for Coyote Station is shown in Figure 4, and at the end of 500 hours the pressure drop averaged about 0.85 inches ofwater. During these first 500 hours ofoperation the impacts ofany falling deposits would be minimal. In addition, after each 2 months ofoperation the ductwork upstream ofthe reactor was cleaned.

111912007 A-llBaldwin SeR Reactor First 500 hours 1.2 -,------,--------------------, S 1 -+---f"It---------j-,.,----------------j C'I 0.8 -+----+-+-------I----,--t-,- o 0.6 +:r---+-I--,-------,-- a. c I- 0.4 < (.J 0.2 -+---+---+t-f---------------------j I 0-+----=="'-+-'-------,r------,------.,------1 \ 0 100 200 300 400 500 

### I Runtime (hours) 

### L Figure 3. Pressure drop across SCR reactor during first 500 hours oftesting at Baldwin.

Coyote SeR Reactor First 500 Hours 1.2 -,...------------------------. 

## s 0.8 +-------,-,------jjrl;;lr;--- '0 0.6 

## 2i I- 0.4 0.2 -lftl--'-----------------------j
500 400 300 200 100 0-+-----....,.-------,-------,----...,.------1



### o Runtime (hours) Figure 4. Pressure drop across SCR reactor during first 500 hours oftesting at Coyote. B&McD Response: An increase in pressure drop is an indicator ofgross pluggage ofthe flue gas passages in the catalyst. Ash deposits that cause the pressure drop to significantly increase can also create maldistribution ofthe flue gas through the catalyst. Serious maldistribution causes some ofthe catalystpassages to be significantly underexposed to flue gas flow and ammonia, so they will not contribute to effective NOx control performance, regardless ofwhether there is a high level ofcatalytic activity or not. Likewise, catalyst that has severe micropore pluggage will be ineffective whether it is located within flue gas passages that are exposed to flue gas flow or

11/912007 A-12not. Prevention ofsignificant ash accumulation, flue gas flow maldistribution, and micropore pluggage needs to be effective in order to maintain high catalyst activity and subsequentNOx removal. Solving the first two conditions does not ensure that the last (most important) factor is also eliminated. In fact, it will contribute to reducing the amount oftime required to cause it.
It seems curious that the cause ofthe apparent failure ofthe pilot test at Coyote seems to be pointed at EERC, the design ofthe test, its equipment, and methods. It is difficult to believe that a consortium ofEERC, EPRI, USDOE, utilities, and three catalyst vendors would purposelydesign a test ofSCR technology with the expectation from the onset that it would fail dismally. The fact that it produced deactivation data at two ofthe three pilot test installations would appear to prove that failure (ofthe test to show the ability ofthe catalyst to survive the conditions) was not the intended goal. The SCR vendors that participated were advised ofthe nature ofNorth Dakota lignite and its challenges during the development oftest procedures and design ofthe equipment. The lack ofpositive results in the Coyote pilot test shows that the ability ofthe catalyst to overcome exposure to the testconditions was not as easy and assured as perhaps was initially believed by the SCR catalyst vendors.
"Core" Issue number 6 Split air preheater: ERG memorandum to EPA, August 20, 2007, page 5 Original Reference: EPA Region 8 letter to NDDH and EGR Letter to EPA, January 8,2007: "The discussion of the splitairpreheaterapproach
.. .seems a bitambivalent, implyingfirst that itcouldn'tbe done and laterstating that conceptually, it couldbe done. Further evidence isfound in thefact thatSCR retrofits a[tJNew Madrid (two large, PRB-fired cyclone boilers) included replacement of the tubularairpreheaters with new regenerative airpreheaters with enamel-coatedbaskets." [ERG October

### 4, 2007letter, page 5J B&McD Response: The ERG commenter's response appears to misinterpret B&McD's responses in Minnkota's March 2007 and April 2007 letters to comments made in ERG's January 2007 letter and subsequent request in the February 2007 request that included the EPA's January 26,2007 letter.
The arrangement and operation ofthe split air preheater concept proposed by ERG was flawed and would not work satisfactorily as described. Burns & McDonnell suggested alterations to

111912007 A-13the concept that would appear to satisfy the basic boiler air temperature requirements for proper lignite coal drying and combustion [March 2007 response page 15].
This is not the same as saying that a high-dust SCR would be technically feasible for installation on the subject units assuming that the alterations suggested to the split air preheater arrangement and operation to satisfy the basic boiler air temperature requirements for proper lignite coal drying and combustion were the only limitations to overcome.
The ERG and EPA comments still do not address the "relevant technical issues ofoperating the high-dust SCR effectively with such wide ranges offlue gas temperatures as shown in Minnkota's April 2007 response letter. Specifically, low load-clean boiler conditions have temperatures below the minimum at which conventional SCR catalysts are effective in coalfired applications. Operating MRYS Unit 1 and Unit 2 during such periods without effective post-combustion NOx emissions control by the high-dust SCR would have negative impacts on compliance with NOx emission limits required for consecutive 30-day rolling periods.
"Core" Issue number 7 B&McD low dust SCR assessment: ERG memorandum to EPA, August 20,2007, page 5 Original Reference: EPA Region 8 letter to NDDH and EGR Letter to EPA, January 8,2007:
"
...do notbelieve that resort to the low dustapproach is warranted
.... " [ERG memorandum to EPA, August20, 2007, page 5J B&McD Response: It is Burns & McDonnell's opinion that there are sufficient quantities ofsodium-rich particles that will be in the flue gas stream from a North Dakota lignite-fired cyclone boilerto pose significant catalyst pore blinding, pluggage, and deactivation problems to drastically inhibit effective NOx emissions control and catalystlife, regardless ofwhether it is placed in a highdust or low-dust SCR installation. See EERC's reply regarding this topic contained within the responses in this letter to the EPA's related comments [EPA October4 letter enclosure page 34].

111912007 A-14"Core" Issue number 8 Texas lignite assessment: ERG memorandum to EPA, August 20, 2007, page 5 Original Reference: EPA Region 8 letter to NDDH,and EGR Letter to EPA, January 8,2007: "George Offen's letterprovides some useful insights, particularly with regard to erosion. S&Lpersonnel confirmedthat Texas lignite ash is more erosive than North Dakota Lignite ash. This means that the TXUpilot test currently underway should resolve any concerns regarding erosion atafuture MRYS SCR installation." [ERGAugust20, 2007letter, page. 5] EERC Response: Texas lignites are prone to form silicate base deposits in the boilers and have more ofan abundance ofsilicate-rich entrained particles that can be erosive. However, the erosive nature ofthe ash is highly dependent upon the source ofTexas lignite. The coals fired at the TXU plants and others from the southern part ofTexas can be highly erosive.
For example, the coals in the Southern Jackson formation have high ash contents (range 6 to 48%, average 22%, as received basis) and produce a combination ofhighly porous ash particles and dense hard particles derived from quartz. The quartz materials will cause erosion. The porous particles will produce highly vesicular deposits ifthe ash accumulates on heat transfer surface. Large vesicular deposits are typically the origin ofpopcorn ash.
The coals from the Wilcox formation typically have lower ash contents (range 1.4 to 58.6, average 10.6% as received basis). The ash chemical and physical properties ofWilcox based ash materials are significantly different than the Southern Jackson. In addition, TXU co-fires Powder River Basin coal with the lignite. The Texas lignite fired at TXU is from the Wilcox formation and does not represent all Texas lignite. It also does not represent what is fired in North Dakota.
B&McD Response: Burns & McDonnell does not disagree that Texas lignite contains ash more abrasive than North Dakota lignite. Dr. Benson's discussion oflignite ash deposition in SCR catalyst (August 2007) indicates that small sodium-rich particles are more important in their impact than the large inorganic fraction ofthe entrained flyash. Burns & McDonnell stands by their comments in Minnkota's March 2007 response (pages 30-31).

111912007 A-15"Core" Issue number9 SCR vendor quote request: ERG memorandum to EPA, August 20, 2007, page 5 Original Reference: EPA Region 8 letter to NDDH, January 26,2007: "The ability toprovideflue gas at the appropriate temperature is notdiscussedandthe startup/shutdown requirements may be unreasonable. " [ERGAugust20, 2007 letter, pages 

### 5 and6] B&McD Response: Bums & McDonnell provided pertinent situation- and plant-specific data to the SCR system vendors and catalyst suppliers. The vendors need to be aware ofthe seriousness ofthe situation involving this request and the severity ofthe operating conditions imposed. The ability to successfully control SCR reactor inlet temperatures in a high-dust SCR application without impairing lignite pre-drying has not been confirmed. It would be inappropriate to assume these challenges have been solved or to request meaningful responses from vendors without advising them ofthe nature ofthe query and conditions involved.

1119/2007 A-16The following responses follow the outline ofthe Enclosure attached to EPA Region 8's October4,2007 letter25• Ie Introduction and Summary 

### ofEPA's Preliminary Analysis: EPA October4, 2007 letterEnclosure, page 6 Original Reference: EPA Region 8 January 26, 2007 letter to NDDH request item number 1: "Additionally, basedon a July 

### 2, 2004, conversation between Jim Standt of Andover Technology Partners andFlemming Hansen of Haldor Topsoe, the sudden buildup offly ash on the catalystsurface that oc:curredduring thepilot testing at Coyote Station was determined to be causedby the accumulation of ash upstream of the catalystandsudden dropping of thatash accumulatedash onto the catalyst face. " [EPA October

### 4, 2007letter Enclosure, page 

### 6J EERC Response: The increase in pressure drop across the catalyst was likely not solely due to ash falling in the reactor. The first 500 hours ofoperation previously shown in Figures 3 and 4 are likely due only to accumulation ofash materials on the catalyst surfaces. In addition, the ductwork was cleaned at two-month intervals. Jim Staudt and Flemming Hansen (Hansen) could not have reasonably determined that the pressure drop was due to ash deposits falling into the reactor. Neither ofthem was present to view the opening ofthe reactor or observed the deposits and accumulations in detail. Flow through the catalyst was maintained. See EERC's discussions in response to ERG's core issue number 5 above. "Clearly the twofacilities operating on PRB coal experiencedcatalystplugging that required extensive andaggressive cleaning measures.... " [EPA October

### 4, 2007letter Enclosure, page 

### 6J EERC Response: The accumulations at Baldwin and Columbia were minor or moderate in comparison to the results obtained at the Coyote Station. The fact that the reactor ran well for both the Baldwin and Columbia Stations are indications that the results for Coyote Station are valid. Similar testing protocol was initiated for both tests.
"EPA also spoke with Flemming Hansen regarding thefeasibility of an SCR installation at MRYS and the nature of the SCRpilot testing at the Coyote station conductedby EERC. " [EPA October

### 4, 2007letterEnclosure, page 

### 7J

25 Ibid Reference number 6. 11/912007 A-17EERCResponse: EPA discussion with Hansen seemed to not focus on one ofthe key issues we discussed with him. During EERC discussions with Hansen at Haldor Topsoe, his major concern was the soluble sodium. The fact that sodium is in a soluble form impacts the catalysts. No discussion with Hansen and EPA was held on the impacts ofthe high sodium in the soluble form. Much ofhis subsequent discussion was on plugging and not pore plugging.

"
...nothing has beenprovidedthatwoulddemonstrate that SCR wouldbe an ineffective means of NOx control atMRYS". [EPA October

### 4, 2007letterEnclosure, page 2J and "EPA believesB&McD's conclusions regarding the use of the "empirical data"from the Coyote Stationpilot-scale testing is not relevant for an analysis of technical feasibility, and fails to consider the observations on catalystmaintenancefrequency andpressure drop trendsfrom the Baldwin and Columbia Stationpilot tests. [EPA October4,2007 letterEnclosure, page 4

### Jand "For the Coyote Station, EPA agrees that theplugging andpressure drop observedduring thepilot testwere morepronouncedandoccurredquicker than whatwas observedat the twofacilities burning PRB coal. Additionally, basedon the deposition sampling, EPA agrees there is evidence thatsodium was afactor in theplugging at Coyote, where itdid notappearat the othertwofacilities. However, EPA disagrees that these test results can lead to a conclusion thilt extended forced outages wouldbe neededat two month intervals as statedby B&McD in Minnkota's March 19, 2007letter. "[EPA October4, 2007letter Enclosure, page 

### 5

### Jand "Basedon the above comparison, of thepilottesting results by EERC, it is unclearto EPA thatany definitive conclusions can be extrapolated from the results aboutSCR technical feasibility and/or timing orextentof SCR maintenance requirements andboileroutages

...as was done by B&McDforMRYS. Clearly the twofacilities operating on PRB coal experiencedcatalystplugging that requiredextensive andaggressive cleaning operation

.... " [EPA October4, 2007letterEnclosure, page 6J

"
...B&McD has notprovideda response to EPA's statements regarding normally observed pronouncedash deposition duringpilottesting, the small catalystpitch, usedat Coyote Station, andhow a largerpitch mighthave affectedthe test results, andhow the airpulsing didnotproperly representsootblowing capabilities on afull-scale SCR application." [EPA October

### 4, 2007letterEnclosure, page 7J
B&McD Response: Burns & McDonnell stands by their comments made in response to ERG's "core issue" number 2 and number 4 (herein), and Minnkota's April 2007 response (pages 25-26) to the question ofmultiple engineering solutions suggested bythe EPA's comment in the EPA's January 26, 2007 letter (page 2). Related additional information has subsequently been provided in EERC's discussion included in Minnkota's August, 2007 letter (page 22). 

## · ,

11/9/2007 A-18"Mr. Hansen saidthatHaldor Topsoe wouldnot rule outbidding on aproject that involvedNorth Dakota lignite
... they would lookat computermodelingfor the specific coal analysis andboiler
.... " [EPA October4, 2007letterEnclosure, page 8] EERC Response: Current computer models have difficulty in providing adequate information on the transport of submicron particles into the pore structure ofcatalyst, subsequent sulfation, bonding strength development, and removal potential.
"Mr. Hansen was unaware thatHaldor Topsoe sentemails to EPA Headquarters stating thatHaldor Topsoe (and two other catalyst vendors) couldprovide guaranteesfor the MRYS coal." [EPA October4, 2007letterEnclosure, page 9] B&McD Response: It is unclear what the referenced sentence is intended to convey. Burns & McDonnell continues to express concerns that any SCR catalyst vendor's willingness to guarantee performance on a North Dakota lignite-fired boiler will be very limited, requiring certain specific criteria to be met that are yet to be proven to exist or capable ofexisting at MRYS. This limitation to the SCR catalyst guarantee is required by the vendor in order to manage financial risks by specifying the limits oftheir system design in case ofpotential operating conditions that cause performance problems that prevent achievement ofguarantees and/or warranty claims. SCR catalyst vendors assume that the system suppliers have already solved (or will solve) the stated temperature problems, and proven solutions to these conditions have not been identified. Burns & McDonnell stands by their comments made in Minnkota's April 2007 response (pages 27-28).


### II. EPA Case-Specific Review ofBurns & 

### McDonnell & 

### EERC Technical Feasibility Analysis for Selective Catalytic Reduction A. High-Dust SCR 1. Ash Deposition Issue Raised by Burns & 

### McDonnell:

EPA October4, 2007 letter Enclosure, page 10 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH: "EPA is also notaware that any catalyst formulations have been developed to deal specifically with the issue of sodium. " [EPA October4, 2007letterEnclosure, page 10]

111912007 A-19EERC Response: Khodayari's major conclusion in his Ph.D. thesis was "Potassium and sodium were found to be two ofthe worst poisons that had significant effects on the activity ofthe SCR catalyst due to their selective chemisorption on the Bnzlnsted acid sites." A reference to the source for this thesis is provided in response to Christman's August 2007 comments.
"EPA askedMinnkota to look further into Engineering solutions currently available and determine whetherornot the macro-poreplugging issue described inthe EERC report couldbe effectively managed." [EPA October4, 2007letterEnclosure, page 10] EERC Response: During the discussions with Haldor Topsoe we asked ifthey had been pursuing developing SCR catalyst materials that would be less prone to the impact ofalkali and alkaline earth elements. They indicated that they had not pursued developing new catalysts or modifying current formulations that could be adapted for use with high base-to-acid ratio coal ash.
"EPA does notdispute EERC's description of the chemical andphysical fate of sodium in a cyclone boiler. " [EPA October

### 4, 2007letterEnclosure, page 

### 12] and "EPA acknowledges that the sodium contentof the CenterMine lignite is generally higher than PRB coals. EPA also recognizes thatashpartitioning in a cyclone boilerand resulting sodium depositionpresents certainproblems thatcouldpose engineering challenges to the design andoperation of an SCR system atMRYS. However, Minnkota has notprovidedany quantitative data thatshows that theplugging anddeactivation of the SCR system wouldbe an unresolvable technicalbarrierand/or the ability of the SCR to controlNOx wouldbe so limitedthatSCR wouldbe an ineffective control option." [EPA October

### 4, 2007letterEnclosure, page 

### 14] and "Due to the lackof NOx emission andcatalystdeactivation data, the Coyote Station study does notsupport utilizing any definitive conclusions, otherthan there was significant plugging, which also appearedatboth the Baldwin and Columbia Stations." [EPA October

### 4, 2007letterEnclosure, page 

### 15] and "EPA believes that the experience the utility industry has gained from the installations at PRBfacilities
... while Sargent & Lundy indicatedthat further datafrom well designedpilot study wouldenhance theirability to optimally design a more cost-effective SCR system.... " [EPA October

### 4, 2007letterEnclosure, pages 

### 15, 16] EERC Response: In recent discussions with Sargent & Lundy regarding the EERC SCR reactor testing, they
were unaware that 6 months oftesting occurred at the Baldwin Station using the same reactor

11/912007 A-20as was used at Coyote station. We recently advised Mr. DePriest ofSargent & Lundy that all the pores in the catalyst had plugged with sodium calcium and sometimes potassium sulfates and he indicated he had not been aware ofthis prior to our discussion. "The responsefrom EERCsimply restates theirposition regarding the high sodium content of the CenterMine lignite andhow this will cause both catalystporeplugging andgaspath plugging. EERC fails to consider the use of available engineering solutions to address theseproblems with operation of an SCR atMRYS." [EPA October

### 4, 2007letter Enclosure, page 

### 17] and

"
...aggressive on-line cleaning and/or frequent extendedoutages wouldbe required to remove ash accumulation or remove catalyst for cleaning
.... " [EPA October4, 2007letter Enclosure, page 18] "EPA acknowledges that the sodium content in North Dakota lignitepresents engineering challenges. EPA also thinks it ispossible that the "sodium-relateddeposition on SCR catalyst will shorten the time between outagesfor off-line cleaning
... Unfortunately, the pilot testing conductedat Coyote Station didnotprovide any quantitative results that could be used topredict the timeperiods between catalystcleaning/replacementon afull-scale application." [EPA October

### 4, 2007 letterEnclosure, page 

### 19] and EERC Response: Discussions on engineering solution have been conducted with catalyst vendors. None ofthem have indicated they have solutions for the sulfate based deposits in the pores ofthe catalyst that form by vapor phase and small particle diffusion and subsequentreaction to form sulfates.
B&McD Response: Bums & McDonnell stands by their comments made in response to ERG's "core issue" number 3 and number 4 (herein), and Minnkota's April 2007 response (pages 25-26) to the question ofmultiple engineering solutions suggestedby the EPA's comment in the EPA's January 26, 2007 letter (page 2). Related additional information has subsequently been provided in EERC's discussion included in Minnkota's August, 2007 letter (pages 22 and 23) and in the response immediately above. "The intentof referencing the EPRIletteron Texas lignite was not to imply thatNorth Dakota lignites are exactly the same as Texas lignites. The intent of referencing this letter was to show thata major utility research organization is of the opinion that the existing experience of SCR designers wouldgreatly help in designing SCR systemsfor accommodatingfueltypes neverbefore used inpractice on afull scale." [EPA October4, 2007letterEnclosure, page 18]

11/912007 A-21B&McD Response: The information included elsewhere in this letter and previously provided by EERC and B&McD shows that the obstacles to applying SCR on North Dakota lignite-fired cyclone boilers are much more problematic than those faced by designers for PRB or Texas lignitefired systems. None ofthe catalyst suppliers have developed proven solutions preventing or removing sodium- and sulfur-based deposits in the micropores ofthe catalyst that form by vapor phase and small particle diffusion and subsequentreaction to form sulfates that are bonded tightly to the catalyst surface. "However, the EPA cannot concurthat the qualitativepilot testing results at the Coyote Station cited in the EERC reportdemonstrate that afull-scale SCR installation atMRYS,
... wouldnot be technicallyfeasible
...EPApointedoutsome of the inherent limitations in the pilot testing thatmighthave contributedto the "failure" of that test. ... EPA questions the design andoperation of thepilot test in light of critical data obtained." [EPA October4, 2007letterEnclosure, page 20J EERC Response: Regarding EPA questioning the design and operation ofthe Coyote Station SCR testing, the design and operation was conducted at Columbia and Baldwin Stations prior to the testing at Coyote. Based on those results the project team that involved EERC, EPRI, USDOE, Haldor Topsoe, Cormetech, Hitachi, and associated utilities decided that the testing protocol should not be changed and testing at Coyote Station should go on even with the concerns about the high sodium lignite. The blinding and plugging was extremely rapid and severe as compared to testing at the PRB fired systems. It surprised the catalyst vendors and they did not have suggestions on how to minimize the impacts. They reviewed all publications and final reports, but did not provide any suggestions on further work to solve the problem.
B&McD Response: It appears that because ofthe lack ofquantifiable catalyst deactivation and NOx reduction data from the severely plugged pilot-scale SCR catalyst tested at Coyote Station, EPA discounts the observations resulting from short-term exposure ofSCR catalystto flue gas and flyash produced from burning North Dakota lignite in a cyclone-fired boiler. The Baldwin and Columbia Station pilot tests had significant ash deposition but still were able to be analyzed for catalyst deactivation while the Coyote catalyst was worse and could not be analyzed.

11/912007 A-22Reduction ofash deposition within the catalyst in the Coyote pilot SCR testing would have reduced the amount ofpressure drop increase through the catalyst layer. This is the "macroeffect" ofthe limitations ofthe pilot SCR testing to duplicate full-scale PRB cyclone and pulverized coal-fired boiler SCR installation experience because pilot-scale on-line ash cleaning and accumulation prevention measures were subsequently considered to be not as effective as the participants expected.
However, the plugging ofthe Coyote pilot catalyst micropores effectively prevents exposure of the catalyst to flue gas and ammonia so that NOx emissions reduction across the fouled catalyst cannot take place. The expected catalyst activity would essentially be zero and NOx reduction would be zero from a practical standpoint. This supposition is reasonable, based on the macroscopic and microscopic evidence.
EPA's statement ofMinnkota's arguments lacking "quantifiable data" appears to ignore this supposition. Such drastic, negative results from such a short amount oftime (4 months) of Coyote pilot SCR catalyst testing should be interpreted as an unsuitable application ofthe

.technology, sufficient to satisfy a technical assessment considering physical, chemical and engineering principles and/or empirical data showing the technology would not work on the emissions unit under review.

Burns & McDonnell stands by the comments in the October 2006 NOx BACT analysis, March 2007, April 2007, and August 2007 response letters, and the additional responses provided herein.



### 2. EPA Analysis ofthe "Popcorn Ash" Issue:

EPA October4, 2007 letter Enclosure, page 21 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH 

### "No response given to EPA's commentby EERC orB&McD. The topic was similarly addressed in the January 2007Christman Memo." [EPA October

### 4, 2007 letter Enclosure, page 21]

11/912007 A-23B&McD Response: Based primarily on one European power generating company's experiences (Steag, Babcock Power) referenced in ERG's January 8,2007 memo letter, there have been significant improvements in the design and implementation ofreliable and effective SCR inlet "popcorn" ash screens since the late 1990's/early 2000's. It is difficult to compare such experience with a hypothetical installation on a cyclone boiler firing North Dakota lignite, without knowing more specifics about the referenced boilers' operating conditions related to furnace and backpass surface slagging and fouling, and the means and frequency employed to clean such surfaces in association with the deployment ofthe large particle ash screens.

3. EPA Analysis ofthe Temperature Issue:

EPA October4, 2007 letter Enclosure, page 21 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH "No response given to EPA's commentby EERC orB&McD. The topic was similarly addressed in the January 2007 Christman Memo." [EPA October

### 4, 2007letter Enclosure, page 21J
B&McD Response: As stated in Minnkota's April 23, 2007 response to NDDH and EPA, and included in this letter in response to ERG core issue number 6, the suggested split airpreheater scheme does not raise the temperature exiting eitherboiler's primary superheater (PSH) section that is located upstream ofthe high-temperature pass ofthe tubular air preheater when the boiler is clean and the load is low. This PSH exit flue gas temperature is too low under these conditions for effective NOx reduction by a conventional hot-side SCR. We know ofno coal-fired utility boiler with a hot-side SCR using flue gas bypass around the primary superheater section. Reheating flue gas to acceptable temperatures for these conditions may be another solution, but this has been discounted due to the gross amount ofreheat fuel or steam required. Even ifsuch solutions were developed in more detail before they could be considered to be technically feasible and evaluated, it does not resolve the issues around catalyst micropore plugging and the fact that on-line cleaning measures have yet to be proven effective for SCRs on North Dakota lignite-fired cyclone boiler applications.

111912007 A-24

### 4. EPA Analysis ofthe Erosion Issue: EPA October4, 2007 letterEnclosure, page 21 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH "No response given to EPA's commentby EERC orB&McD. The topic was similarly addressed in the January 2007 Christman Memo." [EPA October4, 2007 letter Enclosure, page 21]

.B&McD Response: Various means ofresolving catalyst erosion were referenced in ERG's January 8, 2007 memo letter. Effective on-line catalyst cleaning ofdeposits seen in the Coyote pilot testing, especially in the micropores plugged with sodium-sulfur compounds, may not be achievable. Aggressive sootblowing using steam may damage the catalysteven with the suggested erosion prevention measures in place. It is difficult to comparecurrent experience with a hypothetical installation on a cyclone boiler firing North Dakota lignite, without knowing more specifics about the referenced catalysts surface and micropore fouling and cleaning operation conditions.



### 5. EPA Analysis ofthe Energy & 

### Environmental Research Center Report (Appendix B):

EPA October4, 2007 letterEnclosure, page 23 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH

"
... a better effort to keep the catalyst face clean. Mr. Hansen recalled the Coyote Station test reactorbecame quicklypluggedwithfly ash causing rapid increases inpressure loss causedmainly by wall ductash accumulations dropping on the catalyst face." [EPA October

### 4, 2007letterEnclosure, page 

### 23] and "Basedon the EERC response, the degree of catalystplugging observedat Coyote Station was the reason no deactivation testing on the catalystwas conducted. 

## if the testing were designedandconducted in a way thatcouldhave greatly reduced the effects of ash deposition on the catalyst face, presumably catalystdeactivation data couldhave been obtained. As statedpreviously, EPA questionsMinnkota's heavy reliance on the questionable resultsfrom the Coyote Stationpilottesting andcannotsupport using this data to draw definitive conclusions on thefeasibility of SCR atMRYS. " [EPA October4, 2007letterEnclosure, page 

### 23] EERC Response: Visual observations and the SEM analysis ofthe plugging materials do not support Hansen's suggestions that all the deposits came from walls ofthe vessel. Evidence offlow patterns in the plugging materials that were not consistent with the geometry ofthe catalyst was not observed. In addition, ifthe gases were not allowed to flow through the catalyst and they were
11/912007 A-25rapidly plugged begs the questions: Why were the pores being plugged in the middle and at the outlet regions ofthe catalysts? Why were deposits evident at the outlet ofthe catalyst and in the catalyst vessel as shown in Figure 5?

Figure 5. Plugging ofSCR catalyst and deposits formed downstream ofcenter section after removal from Coyote Station. The image at the left is the catalyst outlet after it was removed.

The image at the right is ofthe hard deposits that remained in the vessel at the outlet ofthe catalyst after the catalyst was removed. "In addition, Sargent & Lundy indicatedthat they were disappointed in how the Coyote Stationpilot test was carriedoutand found the results to be of very little valuefor evaluating an SCR systemfor facility burningNorth Dakota lignite." [EPA October4, 2007letterEnclosure, page 23

### J EERC Response: Sargent & Lundy was unaware that the same reactor was used for the Coyote testing as was used for the Baldwin testing, and that the testing at Baldwin occurred over a six-month period. They were also unaware ofthe degree ofblinding and plugging ofthe pores. The information from the Baldwin testing was used as input for the design ofSCR systems. Sargent & Lundy did not have an in depth appreciation ofthe challenges high sodium lignite has on SCR catalysts.

6. EPA Analysis ofthe Burns & McDonnell's Conclusion:

EPA October4, 2007 letter Enclosure, pages 25-31 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH26 "While thepilotstudy does suggest that catalystplugging atafacility burningNorth Dakota lignite would likely be more of a challenge than atafacility burning PRE coal,

26 Ibid Reference number 9.
11/9/2007 A-26EPA can notconclude that the test is determinative of whetheran SCR system wouldnot workatMRYS." [EPA October

### 4, 2007letterEnclosure, page 

### 25] and

"
... the qualitative information does notprovide meaningful conclusionsfor comparatively assessing SCR technical feasibilityforNorth Dakota lignite andPRB applications. The one exception wouldbe that the study shows lignite at Coyote Station showedmore sodium deposition and less calcium comparedto PRB coal. " [EPA October

### 4, 2007letter Enclosure, page 

### 28] and "Without representative catalystdeactivation testing orNOx control datafrom the Coyote Station, EPA does notbelieve thepilotstudyprovides meaningful results that couldlead to a definitive conclusion that SCR wouldbe infeasible atMRYS." [EPA October4,2007 letterEnclosure, pages 

### 28 and29Jand

"
... reactivity testingfor the catalyst. EERCdidnot test the catalystat Coyote Station, because the catalystwas allegedly tooplugged to conduct the testing. This appears to be a failure of thepilot test to meetthe original goalforNorth Dakota lignite.
... in light of substantial ash deposition on the catalyst face
... ". [EPA October4, 2007letterEnclosure, page 29J and

"The qualitative results of catalystpluggingfor thepilot testing at Coyote Station do not provide empirical evidence that SCR wouldbe ineffective at controlling NOx emissions, since there was no quantitative dataprovidedforeitherNOx reduction orcatalyst deactivation. As such, EPA is notconvincedthat the specific challengespresented for an SCR installation atMRYS is a matterof technical infeasibility andcouldnotbe overcome with a robust suite of ash (including sodium) mitigation measures and/ormaintenance measures." [EPA October4, 2007letterEnclosure, page 30] EERC Response: The deactivation testing was not conducted because the gas paths were severely plugged. Haldor Topsoe indicated that they would have to rod out the deposits to provide the catalyst activity testing. They indicated that the results ofreactivity testing wouldbe inclusive in the cleaned catalystbefore making the measurements. The conclusion that the plugging and blinding is largely due to upstream deposition is not correct. B&McD Response: Burns & McDonnell stands by the comments in the October 2006 NOx BACT analysis, March 2007, April 2007, and August 2007 response letters and the additional responses provided herein.

111912007 A-27B. Low-Dust SCR 1. EPA AnalYsis ofthe Catalyst Fouling and Deactivation Issue:

EPA October4, 2007 letter Enclosure, page 32 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH:

"
...general qualitative statements that the sodium-rich aerosols will cause blinding and deactivation do notnecessarily supportthe conclusion that a low-dust SCR system would be technically infeasible atMRYS. The effects of this blinding anddeactivation should either be quantifiedand usedwithin the economic analysis understep 

### 4 of the Top-Down BACTanalysis, ordescribed in sufficientdetail to demonstrate that theproblems associatedwith catalystblinding anddeactivation are unsolvable andwould result in the unsuccessful operation of a low-dustSCR. As statedonpage B.20 of the NSR Workshop Manual, "(p)hysicalmodifications neededto resolve technical obstacles do not in andof themselvesprovide ajustificationfor eliminating the control technique on the basis of technical infeasibility. However, the cost of such modifications can be considered in estimating costandeconomic impacts." [EPA October

### 4, 2007letterEnclosure, pages 32- 33J B&McD Response: As EERC has described previously and elsewhere in this document, effective solutions to prevent or remove micropore pluggage and blinding ofSCR catalyst from sodium-sulfur compounds evident in the flue gas stream exhausted from a North Dakota lignite-fired boiler, whether installed in a conventionalhot-side or cold-side application downstream ofa wet scrubber, have not been developed by SCR catalyst vendors. Burns & McDonnell previously discussed the estimated energy requirements for reheating flue gas upstream ofa low-dust and tail-end SCR in the October 2006 NOx BACT analysis and March 2007 response letters. Propane or fuel oil will certainly be more expensive to supply than pipeline natural gas, because ofthe additional over-the-road transportation requirements. These alternate fuels do nothing to address the fundamental issues ofthe composition ofthe flue gas and flyash being unsuitable for low-dust SCR applications. We believe these are credible arguments that adequately describe the reasons that preclude the**~uccessful** deployment ofthis technology on the cyclone boilers at MRYS.

2. EPA Analysis ofthe Site Space Constraint Issue:

EPA October4, 2007 letterEnclosure, page 33 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH:

1119/2007 A-28"EPA acknowledges that extensive work may be requiredfor installation of low-dust SCR
.. .basedon reasonable expected reheat fuel requirements, equipment installations, plant modifications
.... " [EPA October

### 4, 2007letterEnclosure, pages 33-34] B&McD Response: Bums & McDonnell believes it is appropriate to consider SCR technology for the cyclone boilers at MRYS to be technically infeasible and thus eliminated it during the Top-Down BACT analysis prior to the economic analysis step. The extensive plant modifications anticipated to deploy SCR at Unit 1 and Unit 2 at MRYS still do not resolve the catalyst micropore plugging and blinding problems evident in the Coyote Station pilot-scale testing.



### 3. EPA Analysis ofthe Burns & 

### McDonnell's Conclusion:

EPA October4,2007 letter Enclosure, page 34 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH: "B&McD appears to be saying that a significantportion of the sodium in thefly ash is in the vaporphase when it enters the ESP." [EPA October4, 2007letterEnclosure, page 34J EERC Response: EPA misinterpreted B&McD and EERC's response. B&McD and EERC do not suggest in any ofthe documentation that sodium is in the vapor phase at the temperatures ofthe SCR. Initially in cyclone-fired systems much ofthe sodium is vaporized. Vaporized sodium will condense upon gas cooling heterogeneously on entrained particles or homogeneously to form aerosols. The condensed material will react with other gas phase materials such as S02 and S03 to form sulfates. There is evidence ofsodium, potassium, calcium, and sulfur deposition downstream ofthe ESP as illustrated in Figure 1 presented in response to ERG Core Issue number 2.



### III. Additional Information Useful to Evaluating Technical Feasibility ofSCR atMRYS A. EPA Headquarters Believes SCR is the Correct Technology for MRYS in Developing the Clean Air Interstate Rule EPA October4, 2007 letterEnclosure, page 36 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH:

"
...EPA 's discussion with Flemming Hansen of Haldor Topsoe also revealed that despite the concerns aboutan SCR system subjected to the sodium environment
... Haldor Topsoe wouldnot rule outbidding such aproject." [EPA October4, 2007letterEnclosure, page 

### 37]

11/912007 A-29EERC Response: The most significantpart ofthe discussion with Haldor Topsoe is left out, and that was on the soluble form ofsodium. His indication that this form ofsodium is the worst kind relative to poisoning and would have a major influence on whether they would considerbidding or not. B&McD Response: As previously discussed in Minnkota's March 2007 response, SCR catalyst vendors willingness to bid on a project for applying SCR to aNorth Dakota lignite-fired cyclone boiler does not ensure that the identified issues will be satisfactorily resolved and that appropriate guarantees for catalyst performance and life will be agreed upon in the final contract. 

### B. SCR Technology is Presumptive BART for Cyclone Boilers in EPA's BART Guidelines EPA October4, 2007 letterEnclosure, page 37 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH:
"EPA is notsuggesting that the cost figures used in the BARTanalysis need to be used in the BACTanalysisforMRYS." [EPA October

### 4, 2007letterEnclosure, page 37J B&McD Response: Burns & McDonnell believes it is appropriate to consider SCR technology for the cyclone boilers at MRYS to be technically infeasible due to catalyst micropore plugging and blinding problems and thus eliminated it duringthe Top-Down BACT analysis prior to the economic analysis step.
C. February 27, 2006 Final Revisions to 40 CFR Part 60, Subpart Da, New Source Performance Standards for Electric Generating Units Set Final NOx Limit Based on Technical Feasibility ofSCR for Lignite-Fired Units EPA October4, 2007 letterEnclosure, page 38 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH:

"
... the new NSPS standards apply to affectedutility boilers that commence construction, reconstruction, ormodification afterFebruary 28, 2005. (EPA's original comments erroneously saidthat the standards only appliedto new units.) This would include any existing cyclone unitsfiring North Dakota lignite that undergo reconstruction or modification. The standards that wouldapply to.. .modifiedunits (1.4 lb/MWh or 0.15lb/MMBtu)
...EPA also agrees that there have been some recently-permitted units burning Texas lignite that haveproposedSCR and that there are some differences between

111912007 A-30North Dakota and Texas lignite. EPA believes these differences mightaffect the design and operation of an SCR systemfor the different lignites. EPA does notbelieve these differences indicate thatEPA didnot considerNorth Dakota lignite in revising the NSPS for utility boilers." [EPA October4, 2007letterEnclosure, pages 38 and 39J and

"Notwithstanding the differences between North Dakota lignite and Texas lignite, a modifiedcyclone boiler firing North Dakota lignite wouldstill needto meet the most recent NSPS Da limit for modified units, which is lower than the BACTlimitproposedby Minnkota. The likely choice to meet this limit of 0.15 lblMMBtu wouldbe SCR." [EPA October

### 4, 2007letterEnclosure, page 40 

## J

B&McD Response: B&McD concurs with EPA's analysis thatreconstructed or modified units would be required under the NSPS rules to meet emission limitations that are well below those proposed by Minnkota as BACT. However, these NSPS limits are not applicable in this case and the existence ofthe EPA's new NSPS standards is notproofthat Minnkota's October 2006 BACT analyses and subsequent responses are insufficient to meet the requirements ofthe process following the NSR Workshop Manual in accordance with the Consent Decree. B&McD continues to submit that there is no proven NOx control technology that is capable ofachieving these NSPS emission limits on cyclone-fired unit burning North Dakota lignite.
"EPA has reviewed the coal data submittedby EERCand, in general, agrees that the sodium content ofTexas lignites is lower than North Dakota lignites. However, itappears that the Jackson South Texas lignite has a somewhat comparable ash sodium contentabove 3%

... " [EPA October

### 4, 2007letterEnclosure, page 39J EERC Response: The lignite from the Jackson formation is a famous coal relative to the fate andbehavior of sodium. The sodium in the Jackson South and Yegua formations ofTexas is in the form ofa zeolite-type mineraL During combustion, most ofthe sodium is retained in the aluminosilicate meltphase and is not vaporized. As a result the sodiumreleased as a vapor for the Texas lignite is much less as compared to a North Dakota lignite from a cyclone-fire boiler. Therefore, making the comparison on a sodium mass per unit ofheat input (lb NalMMBTU) basis is not an accurate assessment ofsodium impacts from North Dakota lignite compared with the Texas lignites cited by EPA.

11/9/2007 A-31

### D. SCR and CatalystVendorInformation EPA October4, 2007 letter Enclosure, page 40, 41 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH: "EPA hadoriginally suggestedthatMinnkota "obtain information andproposals"from some of the othercompanies thatEPA hadlisted. EPA envisionedthis to include more of the level of detail describedby B&McD in theirMarch 19, 2007response." [EPA October 

### 4, 2007letterEnclosure, page 41J
B&McD Response: Burns & McDonnell provided pertinent situation- and plant-specific data to the SCR system vendors and catalyst suppliers. The vendors need to be aware ofthe seriousness ofthe situation involving this request and the severity ofthe operating conditions imposed. The ability to successfully control SCR reactor inlet temperatures in a high-dust SCR application without impairing lignite pre-drying has not been confirmed. It would be inappropriate to assume these challenges have been solved or to request meaningful responses from vendors without advising them ofthe nature ofthe query and conditions involved.



### EPA's Response to EERC and B&McD April 23, 2007 Letter to NDDH CommentsFebruary 1,2007 (Including Response to U.S. EPA Region 8 Comments -January 26, 2007): Requestfor Additional Information and the Non-SCR Comments from EPA IV. Minnkota's Responses to Additional Information Requested A. Center Mine Lignite Coal Ash Content and Variability EPA October 4, 2007 letterEnclosure, page 42 Original Reference: EPA Region 8 January 26, 2007 letterto NDDH: "EPA has reviewedthe coal data submittedbyMinnkota. EPA believesfuture coal data appears to show little changefrom the 2007cores." [EPA October

### 4, 2007letter Enclosure, page 

### 39

### J EERC Response: The challenges for the future are related to the decreased availability ofthe lower sodium coals. The abundance ofthe lower sodium coal depicted by the lower mode in Figure 

### 6 is decreasing in availability resulting in higher sodium levels. Historically, higher sodium means an increase in lower temperature sulfate based fouling problems in combustion systems.

11/912007 A-32350 300



### ,.... 250 T"" ('t) T"" II c 200 >. 0 c 150 CD :::J 0- 

# e u.. 100 50

0

### ~<t;>**~:/'** t<.(tr,**~.** EERC SB29240.CDR 2036-2045,2046-2055 

### Na2

### 0inAsh

_.__• BNI Core Database (2003-2006)

- - - 10-year averages

90th Percentile: 6.74wt%

Figure 6. Sodium oxide in ash frequency distribution for as-fired database compared to 10- year averages and weighted Core Database values


### B. High Economizer Exit Temperature EPA October 4, 2007 letterEnclosure, page 43
. Original Reference: EPA Region 8 January 26, 2007 letter to NDDH:
"EPA acknowledges that there are times when theflue gas temperature at theportion of the boilerwhere a high-dustSCR wouldbe located (primary superheater outlet for Unit 1 andpresumably the economizerexit for Unit 2) wouldbe higher than the temperature range typically suitablefor SCR. While B&McD seems to indicate in the March 19, 2007 letter that the dual-airpreheaterdesign suggested by ERG wouldbeproblematic, it later concedes that it conceptually couldwork, butwouldbe atadditional cost." [EPA October 4, 2007letterEnclosure, page 44

### J
B&McD Response: The EPA commenter's response appears to misinterpret B&McD's responses in Minnkota's March 2007 and April 2007 letters to comments made in ERG's January 2007 letter and subsequent request in the February 2007 request that included the EPA's January 26,2007 letter.

111912007 A-33The arrangement and operation ofthe split air preheater concept proposed by ERG was flawed and would not work satisfactorily as described. Bums & McDonnell suggested alterations to the concept that would appear to satisfy the basic boiler air temperature requirements for proper lignite coal drying and combustion [March 2007 response page 15].
This is not the same as saying that a high-dust SCR would be technically feasible for installation on the subject units assuming that the alterations suggested to the split air preheater arrangement and operation to satisfy the basic boiler air temperature requirements for proper lignite coal drying and combustion were the only limitations to overcome.
The ERG and EPA comments still do not address the relevant technical issues ofoperating the high-dust SCR effectively with such wide ranges offlue gas temperatures as shown in Minnkota's April 2007 response letter. Specifically, low load-clean boiler conditions have temperatures below the minimum at which conventional SCR catalysts are effective in coalfired applications. Operating MRYS Unit 1 and Unit 2 during such periods without effective post-combustion NOx emissions control by the high-dust SCR would have negative impacts on compliance with NOx emission limits required for consecutive 30-day rolling periods.
As stated in Minnkota's April 23, 2007 response to NDDH and EPA, and included in this letter in response to ERG core issue number 6, the suggested split air preheater scheme does not raise the temperature exiting eitherboiler's primary superheater (PSH) section that is located upstream ofthe high-temperature pass ofthe tubular air preheaterwhen the boileris clean and the load is low. This PSH exit flue gas temperature is too low under these conditions for effective NUx reduction by a conventional hot-side SCR. We know ofno coal-fired utility boiler with a hot-side SCR using flue gas bypass around the primary superheater section. Reheating flue gas to acceptable temperatures for these conditions may be another solution, but this has been discounted due to the gross amount ofreheat fuel or steamrequired. Even ifsuch solutions were developed in more detail before they could be considered to be technically feasible and evaluated, it does not resolve the issues around catalyst micropore plugging and the fact that on-line cleaning measures have yet to be proven effective for SCRs on North Dakota lignite-fired cyclone boiler applications.

11/9/2007 A-34

### C. Low-Dust SCR Fouling EPA October4, 2007 letterEnclosure, page 44 Original Reference: EPA Region 8 January 26, 2007 letter to NDDH: "While the relative effects of vaporized particlespassing through the ESP andcondensing priorto a low-dust SCR system mightbe morepronouncedcomparedto the non-vapor particles impacting a high dust environment, EPA maintains that the ESP will remove a very substantialportion of the ash that wouldaffecta high-dustSCR and the overall effects of catalystplugging anddeactivation in a high-dustapplication wouldbe greater than a low-dustapplication." [EPA October

### 4, 2007letterEnclosure, page 45] EERC Response: These materials are submicron sodium-rich aerosols that will cause problems in low dust operations. Please note the deposits that formed downstream ofthe ESP on MRY Unit 1 as previously illustrated in Figure 1. The chemical composition ofthe deposit is consistent with various pyrosulfates that have melting points as low as 530°F.


### D. SCR Deactivation EPA October4,2007 letter Enclosure, page 45, 47 Original Reference: EPA Region 8 January 26, 2007 letter to NDDH: "Meeting with Sargent & Lundy
... indicatedthat an SCR system couldtheoretically be designed to operate on North Dakota lignite... Sargent & Lundy representatives were of the opinion thata well-runpilot test wouldyieldvaluable information thatcouldbe used in conjunction withprevious SCR experience to evaluate anddesign an SCRfora North Dakota lignite application." [EPA October4, 2007letterEnclosure, page 47] EERC Response: Recent discussions with Mr. William DePriest (DePriest) from Sargent & Lundy indicated that he did not appreciate the challenges encountered due to high sodium lignite characteristics. We discussed reactor design and he was familiar with the oneused at the Baldwin Station. He did not know that the same reactor used at Baldwin wasused at Coyote Station. In addition, DePriest was not aware that the reactor was operated for six months at Baldwin Station.
B&McD Response: Bums & McDonnell stands by the comments in the October 2006 NOx BACT analysis, March 2007, April 2007, and August 2007 response letters and the additional responses provided herein.
11/912007 A-35E. 

### SCR Vendor Guarantees EPA October4, 2007 letterEnclosure, page 48 Original Reference: EPA Region 8 January 26, 2007 letter to NDDH: "The lettergoes into greatdetail about the worst-case nature ofCenterLignite coal. " [EPA October4, 2007letterEnclosure, page 48J EERC Response: EPA indicated that a worst-case nature ofCenter lignite was provided. Designs ofsystems must be able to accommodate the more challenging coals, and in this case, sodium oxide levels of6 to 8 % in the ash. The information provided was information that would be provided to any vendor ofequipment that would utilize Centerlignite coal. Specifically, the fuel compositional information provided included compositions for candidate design and performance coal compositions. Systems cannot be designed based on average coal properties.
"EPA has still notseen any vendor responses to the information request. EPA does note that the request seems to have been written with apessimistic tone... " [EPA October4, 2007letterEnclosure, pages 48-49

### J B&McD Response: Responses have not been provided by all ofthe SCR catalyst and system vendors that B&McD requested information from. Bums & McDonnell stands by the comments in the April 2007 response letter and the additional responses provided herein (e.g. ERG Core Issue number 9).


### F. MRYS Boiler Cleaning Outages EPA October4, 2007 letter Enclosure, page 50 Original Reference: EPA Region 8 January 26, 2007 letter to NDDH: "Flemming Hansen ofHaldor Topsoe
...gave a rough estimate thatan SCR systemfor North Dakota lignite couldbe designed (larger) to accommodate a catalyst replacement schedule of about everyyear. Mr. Hansen saidthatan SCR reactorcouldbe cooleddown within 24-36 hours (need for cool airdraft requires the boiler to be shutdown) and the catalyst layers rotated in about two of three days, three days all around." [EPA October 4, 2007letterEnclosure, page 50 

### J
B&McD Response: Burns & McDonnell continues to express concern that EPA and their discussions with the catalyst vendors have not emphasized the activities involving a boiler cleaning outage at
11/9/2007 A-36MRYS that are different than any other coal-fired boiler plant that may employ a hot-side SCR. The need for cool air draft immediately upon shutdown ofboiler fuel firing would require an alternate path from the SCR inlet to the stack that would not interfere with (or be contaminated by) the boiler interior cleaning flow, but which would provide simultaneous air flow through the reactor to aid in cooling the large mass ofcatalyst. We believe that the SCR catalyst vendor's estimates for replacement frequency and duration are optimistic, and significantly underestimate the conditions that are expected at MRYS which have been previously described and discussed.


### G. Hydrocarbon-Enhanced Selective Non-Catalytic Reduction (HE-SNCR) EPA October4, 2007 letter Enclosure, page 51 Original Reference: EPA Region 8 January 26, 2007 letter to NDDH: "The reasons given by B&McD to thispoint (high boiler fouling conditions andvarying gas temperatures and loads) appear themselves to be theoretical
.... EPA does notbelieve that whetherothernon-cyclonefired BARTapplicants includedan analysis of HE SNCR is evidence, in andby itself, that the technology is infeasible atMRYS." [EPA October4, 2007letterEnclosure, page 52]
B&McD Response: The high boiler fouling conditions and varying gas temperatures and loads at MRYS are actual, not theoreticaL The vendor's stated position that this technology is insensitive to fuel orburner types does not refute the lack ofexperience with HE-SNCR on boilers with such severe surface fouling and temperature conditions. Ifboiler conditions in the area where HE-SNCR distribution lances are located are not precisely known to be suitable and/or controlled for survival ofthe reagent, steam, and fuel injection hardware and effective NOx emissions reduction throughout the range ofoperation ofthe boiler in question continuously between startup and shutdown events, the supposition that the technology can "theoretically" be applied to any boiler and any fuel is not supported as fact. Any discussion with the HE SNCR vendor without providing the pertinent boiler conditions would be speculative and potentially misleading.
The point about non-cyclone fired North Dakota lignite burning boilers operated by other BART applicants not being evaluated for their potential application ofHE SNCR has been

11/9/2007 A-37missed. The intention was to show that EPA has been selective in their review comments towards Minnkota's BACT, which appearto be biased against whatevernon-SCR NOx control technology was evaluated for MRYS.


### H. Reburn with SNCR EPA October4, 2007 letterEnclosure, page 53 Original Reference: EPA Region 8 January 26, 2007 letterto NDDH: 

### "Ifthe technology has been demonstrated, it is consideredtechnologicallyfeasible without going throughfurther analysis
. ... B&McD alsopoints outthatnon-cyclone BARTeligible sources in North Dakota didnotprovide an analysis of Reburn with or withoutSNCR as a control alternative in theirBARTanalysis." [EPA October

### 4, 2007letterEnclosure, page 53J B&McD Response: EPA appears to say that differences in specific conditions ofthe MRYS boilers compared with the single unit where Reburn with SNCR has beendemonstrated are not pertinent to whether the control technology would be technically feasible. Successful implementation ofNOx controls is highly dependent on the specific configuration and process conditions that lend themselves to be compatible within the limits ofconstructability, survivability, and effectiveness. Just because a control technology is "technically feasible" based on EPA's interpretation ofthe NSR Manual does not mean it will work effectively at MRYS. These responses indicate that EPA has been selective in their review comments towards Minnkota's BACT, which appear to be biased against whatever non-SCR NOx control technology was evaluated for MRYS.


### I. Rich Reagent Injection (RRI) EPA October4, 2007 letterEnclosure, page 54 Original Reference: EPA Region 8 January 26, 2007 letter to NDDH: "Whilepredicting the exact level of NOx control forRR1 andMRYS may notbe possible
...EPA does notbelieve B&McD has demonstrated thatRRIshouldbe considered technically infeasible." [EPA October

### 4, 2007letterEnclosure, page 54J

111912007 A-38B&McD Response: EPA appears to ignore the arguments regarding the expected lack ofeffective NOx reduction from RRI ifit were applied at MRYS with modest cyclone air-staged combustion. Successful implementation ofNOx controls is highly dependent on the specific configuration and process conditions that lend themselves to be compatible within the limits ofconstructability, survivability, and effectiveness. Just because a control technology is "technically feasible" based on EPA's interpretation ofthe NSR Manual does not mean it will work effectively at MRYS. These responses indicate that EPA has been selective in their review comments towards Minnkota's BACT, which appear to be biased against whatever non-SCR NOx control technology was evaluated for MRYS.


### J. Rotating Opposed Fire Air (ROFA) EPA October4, 2007 letter Enclosure, page 55 Original Reference: EPA Region 8 January 26, 2007 letter to NDDH: "further consideration of ROFA is unnecessary." [EPA October

### 4, 2007letterEnclosure, page 55]
B&McD Response: We agree with EPA's response regarding ROFA.
K. Control Efficiency for SNCR EPA October4, 2007 letterEnclosure, page 55 Original Reference: EPA Region 8 January 26,2007 letter to NDDH: "EPA agrees that the 60% reduction citedat the upperendof the control range is likely notappropriateforMRYS. Itappears likely thatsomething closerto 30% than 60% would be reasonable." [EPA October4, 2007letterEnclosure, page 56]
B&McD Response: We stand by our use ofthe estimated levels ofNOx control for alternatives involving SNCR included in Minnkota's October 2006 MRYS BACT analysis.
L. Selection of30-day Average BACT Emission Limit EPA October 4, 2007 letter Enclosure, page 56 Original Reference: EPA Region 8 January 26, 2007 letter to NDDH:

11/912007 A-39"EPA
... now understands that the startupperiods didnot fall within the relevantbaseline period." [EPA October

### 4, 2007letterEnclosure, page 57J
B&McD Response: We stand by our use ofthe estimated levels ofNOx control included in Minnkota's October 2006 MRYS BACT analysis.
M. BACT Limit IS-Month Trial Period EPA October4, 2007 letterEnclosure, page 57 Original Reference: EPA Region 8 January 26, 2007 letter to NDDH: "EPA agrees this is an acceptable approach." [EPA October4, 2007letterEnclosure, page 58J
B&McD Response: Acknowledged.

111912007 A-40

### REFERENCES
1 United States Environmental Protection Agency (U.S. EPA orEPA) Region 8 letterby Martin Hestmark, Director, Air and Toxies Technical Enforcement Program, ECEJ to Terry L. O'Clair, North Dakota Department ofHealth, Environmental Health Section, Division of'Air Quality and David Sogard and John Graves, Minnkota Power Cooperative, Re: Transmittal of EPA's Response to Minnkota'

### s Letters DatedMarch 19, 2007andApril 23, 2007, Regarding the October2006NOx BACTAnalysis Study Report forMilton R. Young Station, date stamped October

### 4, 2007. 2 Minnkota Power Cooperative, Inc. and Square Butte Electric Cooperative "Response To EPA Region VIII Comments- January 8, 2007", March 19, 2007". 3 Minnkota Power Cooperative, Inc. and Square Butte Electric Cooperative "Response To NDDH Comments

- February 1,2007(Incl. Resp. to U.S. EPA Region 

### 8 Comments

- January 26, 2007)", April 23, 2007. 4 "NO x BestAvailable Control TechnologyAnalysis Studyfor Milton R. Young Station Unit 1 Minnkota Power Cooperative, Inc." and a separate "NOxBestAvailable Control TechnologyAnalysis StudyforMilton R. Young Station Unit 2 Square Butte Electric Cooperative", October 2006, by Burns & McDonnell, submitted to EPA Region 8 and EPA Office ofRegulatory Enforcement, and included with the "BART DETERMINATIONSTUDY forMilton R. Young Station Unit 

### 1 and

### 2 Minnkota Power Cooperative, Inc. Final Report, October2006" submittedby Minnkota to North Dakota Department ofHealth. 

### 5 Eastern Research Group (ERG) letterby Roger Christman, to U.S. EPA, Summary Discussion in Response to the Burns & McDonnell andEERCReports (Minnkota, March 19, 2007, andMinnkota, April 23, 2007), and the SubsequentMeeting on May 23, 2007, at the Offices of the Division of Air Quality, North Dakota Departmentof Health (NDDH), datedAugust20, 2007. 6 Enclosure, "Responses To EERCand C andB&McD's March 17,2007Letter Responding to EPA Region VIII Comments

- January 8,2007, and EPA's Response To EERCandB&McDApril 23, 2007Letter to NDDH Comments

- February 1,2007 (Including Response to U.S. EPA Region 

### 8 Comments

- January 26,2007): Requestfor AdditionalInformation andthe Non-SCR Commentsfrom EPA. (provided with reference number 

### 1 and reference number

### 3) 7 Consent Decree filed in the United States District Court ForThe District OfNorth Dakota, United States OfAmerica and State OfNorth Dakota, Plaintiffs, v. Minnkota Power Cooperative, Inc. and Square Butte Electric Cooperative, Defendants, Civil Action No.l:06-CV-034, filed April 24, 2006. 8 North Dakota Department ofHealth, Environmental Health Section, Division ofAir Quality letterby Terry L. O'Clair, P.E. to John Graves, Minnkota Power Cooperative,
11/912007 A-41Re: BACTDetermination Milton R. Young Station, dated February 1, 2007, with enclosure from United States Environmental Protection Agency Region 8, letter to Terry O'Clair, North Dakota Department ofHealth Division ofAir Quality, Re: Transmittal of EPA Non-SCR concerns andadditional information required for Minnkota BACT Analysis Study, dated January 26,2007. 9 Evaluation and Mitigation ofVisible Acidic Aerosol Plumes from Coal Fired Power Boilers, Final Report, by Peter M. Walsh, Joseph D. McCain, and Kenneth M. Cushing, EPA Contract No. EP-C-04,..056, Southern Research Institute Project No. 11402 November 14,2006. 10 PhD Thesis "Selective Catalytic Reduction ofNOx: Deactivation and Regeneration Studies and Kinetic Modeling ofDeactivation," 2001, by R. Khodayari, Dept. of Chemical Engineering II, P. O. Box 124, SE,..221 00 Lund, Sweden. 11 ERG Memorandum to EPA Region 8 and EPA Office ofRegulatory Enforcement, Review and Critique of the Bums & McDonnell NOx BACTAnalysisfor the Milton R. Young Station OperatedbyMinnkota Power (October2006), written by Roger Christman, Eastern Research Group, Inc., January 8, 2007, faxed by North Dakota Department ofHealth to Minnkota, January 9, 2007. and EPA Region 8 Preliminary Analysis of Burns 

### &McDonnell BACTAnalysis ForNitrogen Oxide atMilton R. Young Station, Units I and2 January 8, 2007faxed by North Dakota Department ofHealth to Minnkota, January 9, 2007. 12 "Appropriateness ofConducting Pilot Testing of Selective CatalyticReduction (SCR) Technology atMilton R. Young Station. Units I and

### 2, For Use InA NOx BACT Analysis", prepared for Minnkota Power Cooperative, Inc. by Dennis Arfmann, Hogan & Hartson, Steven A. Benson, Energy & Environmental Research Center, and Carl V. Weilert, Bums & McDonnell, August 14,2007.

11/9/2007 A-42