MinnkotaPower ~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 October 4,2007 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")

October 4, 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 of the 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 of Health ("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 of EPA's October 4, 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-if it 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 of development 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 7SOOP) required for

high-moisture fuel pre-drying systems and tubular air heaters.,,3 Cyclone burner boilers firing

1 See Reference number 1.

2 Ibid, EPA NSR Workshop Manual at B.18

3 See Reference number 2 at Al-32.

1
Minnkota 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~scalesources 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 of information 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 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 of existing at

MRYS. This limitation to the SCR catalyst guarantee is required by the vendor in order to manage

financial risks by specifying the limits of their system design in case of potential operating conditions that

cause performance problems that prevent achievement of guarantees 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 of dissimilarity. 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 of different gas stream

characteristics (in terms of content 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 off discussion on the notion of "availability" by citing out of context

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 October 4, 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 of BACT.

6 Ibid Reference number 3, EPA Response Enclosure at 31.

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

Young Station - DRAFf

been applied7

• Though many of the same facts are relevant to a determination of "availability"

and "applicability," Minnkota has clearly raised the issue of availability 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 of the 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" if one of

two conditions are satisfied: (1) "a commercially available control option will be presumed

applicable if it has been or is soon to be deployed on the same or a similar source type;" or (2)

"[a]bsent a showing of this type, technical feasibility would be based on examination ofthe

physical and chemical characteristics ofthe 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 of an

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 7500

P) required for high-moisture fuel pre-drying systems and tubular air heaters.").

8 Ibid, Reference number I at B.18.

1119/2007 3
Minnkota Response to EPA Region 8 October 4,2007 Comments on NDDH BACT Determination at Milton R.

Young Station - DRAFT

Regarding the second condition, the Workshop Manual states "[d]eployment of the 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 of the 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 of an 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.

Chief among these differences are the low and high flue gas temperatures that exist throughout

the range of boiler loads that vary with the extent of boiler cleanliness; and an abundance of fine

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 of technical sources and pilot projects to illuminate the unresolvable technical

difficulties precluding the successful deployment of SCR 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 of a vendor guarantee is not dispositive of technical 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 of a 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 4
Minnkota Response to EPA Region 8 October 4,2007 Comments on NDDH BACT Determination at Milton R.

Young Station - DRAFT

EPA has cited an opinion by Electric Power Research Institute (EPRI) issued on September 7,

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 of Texas 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 of its 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 if enough

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 cart before 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 of a 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 of the vendor guarantee process that adequately reflects the willingness of the 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 5
Minnkota Response to EPA Region 8 October 4, 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 of those

characteristics on boiler and control operations. Certainly a final technical judgment 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 ofSignificant Deterioration and

Nonattainment Area Permitting, Draft October 1990 (The "NSR Manual").

2 "NOx Best Available Control Technology Analysis Study for Milton R. Young Station

Unit 1 Minnkota Power Cooperative, Inc." and a separate "NOx Best Available Control

Technology Analysis Study for Milton R. Young Station Unit 2 Square Butte Electric

Cooperative", October 2006, by Burns & McDonnell, submitted to EPA Region 8 and

EPA Office of Regulatory Enforcement.

3 United States Environmental Protection Agency (U.S. EPA or EPA) Region 8 letter by

Martin Hestmark, Director, Air and Toxics Technical Enforcement Program, ECEJ to

Terry L. O'Clair, North Dakota Department of Health, Environmental Health Section,

Division of Air Quality and David Sogard and John Graves, Minnkota Power

Cooperative, Re: Transmittal ofEPA's Response to Minnkota's Letters Dated March 19,

2007 and April 23, 2007, Regarding the October 2006 NOx BACTAnalysis Study Report

for Milton R. Young Station, date stamped October 4, 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 of United States Environmental Protection Agency (U.S. EPA or EPA) has provided

North Dakota Department of Health's, Environmental Health Section, Division of Air Quality

(NDDH) and Minnkota Power Cooperative Inc. ("Minnkota" or "MPC") with their comments

regarding theirlreviewl4 of Minnkota's letters dated March 19,200715 and April 23, 200716

regarding the October 2006 Best Available Control Technology (BACT) Analysis Study

reports 17 for control of nitrogen 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 20,200718, and an Enclosure of additional EPA responsesl9

were also attached.

Burns & McDonnell was retained by MPC as an independent consultant to perform the

referenced NOx BACT Analysis Studies of Minnkota's Unit 1 and Square Butte Electric

Cooperative's Unit 2 at the Milton R. Young Station (MRYS) in accordance with the

requirements of a Consent Decree (CD)2o.

Minnkota, along with Burns & McDonnell (B&McD), and Energy & Environmental Research

Center (EERC) of the University of North Dakota, have reviewed the referenced EPA and

ERG letters which provided additional comments regarding selective catalytic reduction (SCR)

14 See Reference number 1, October 4,2007.

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-I
technology 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 of the attached ERG memorandum and Enclosure

to the EPA's October 4, 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:

... "Center Mine coal does not have unusual variability in ash content and in no case has

an ash contentfive times higher than PRB coal as B&McD has contended." [ERG August

20, 2007 letter, 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 of responses to comments and

presentation that compares the ash percentages in PRE coals. This information was provided

in detail in the document entitled "Center Lignites 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 of the 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 of ash 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-2
sampling of the feed coal to Unit 1 has shown ash contents as high at 22.0 wt % on an as

received basis.

"Along with the general discussion ofash variability, Dr. Benson introduced the concept of

"acid-to-base ratio" ofthe ash (pages 7-9, Minnkota, March 2007) as having relevance to

the technicalfeasibility ofSCR as applied to North Dakota Lignite.. .Dr. Benson does not,

in fact, make a direct connection between his discussion ofbase-to-acid ratio and the

functioning ofan SCR system. B&McD also only mentions impact on "operation ofthe

boilers at MRYS" (page 9) and makes no connection specifically to an SCR system. As a

final note, I have been involved in one way or another with SCR since the early 1970's and

I have never heard or read anything about acid-to-base ratio ofash in any SCR document

or discussion, prior to Dr. Benson's introduction to the subject. " [ERG August 20, 2007

memo, pages 2 and 3J

First of all, it is the base-to-acid ratio, not the acid-to-base ratio. Unfortunately Christman is

not aware of the importance of the use of the base-to-acid ratio. The base-to-acid ratio

(B/A=[NazO+MgO+CaO+ KzO+FeO]/[SiOz+Alz03+TiOz]) provides a means of simply

evaluating ash characteristics. The B/A ratios are an effective way of examining variability

and ash behavior impacts on power system performance. This relationship has several

applications and in SCRs the application is the assessment of potential 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 of the 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 of the use ofB/A ratios since work supported by EPA in the area of SCR

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 of the 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-3
Variations 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 of the boilers. Low BIA ratio correlates to undesirable cyclone operation. High

viscosity ash, related to low BIA ratio, causes more incompletely burned coal and ash particles

to be exhausted from the cyclone, which increases the amount of flyash that can create

slagging and fouling problems in the furnace and convection passes of the 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 of the 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 catalyst deactivation and regeneration

due to poisoning by sodium and potassium] [ERG August 20, 2007 memo, 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 of his PhD thesis23 :

"Potassium and sodium were found to be two of the worst poisons that had significant

effects on the activity of the SCR catalyst due to their selective chemisorption on the

Br¢nsted acid sites."

[Comments regarding Beck's work on contributions ofphosphorus, potassium and

sodium].

"His subsequent workfocused on phosphorus and did not address sodium at all. " [ERG

August 20, 2007memo, page 3]

l.

EERC Response:

Beck and others focused on phosphorus because it was at a higher concentration than sodium

in the materials he was investigating.

23 See Reference number 10.

1119/2007 A-4
... "University ofUtah and REI on application ofSCR to low-rank coals ...but masking by

flyash is a problem. The study further concluded that the poisoning potential ofthe alkali

materials ranked as: K>Na>Ca. " [ERG August 20,2007 memo, page 3]

EERC Response:

The University of Utah 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 important point regarding the impacts of potassium 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 of sticky ash at 300°F

downstream of the ESP. Figure 1 shows a polished cross-section of a deposit that has formed

on a silicon dioxide surface when exposed to flue gas derived from the combustion of Center

lignite. The red line shows the path of a 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 of potassium (K) as high as 17% and sodium (Na) as high as 16% in the

line scan. The material is highly sulfated as indicated by the high levels ofsulfur (S). The

deposit shown in Figure 1 formed at about 3000

E 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 of potassium ranging from 2 to 8 elemental wt% were observed.

11/912007 A-5
Cross-section of a surface exposed to flue gas at about 3000 Fin MRY Unit 1.

15.0 20.0 25.0

LOCATION (urn)

5.0 10.0

+---+----+--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:

e" 50%

iii

3=

40%

30%

20%

10%

0%

0.0

Figure 1.

Figure 2. Ash accumulations in pores of SCR catalyst exposed to Coyote flue gases

for 4 months.

11/912007 A-6
° F 2 O

Tahie 1° Chellllca ° IA I nalYSIS° 0 f Sit e ec ed POts om Shown 10 l~ure °

Point Locations, Elemental Wt 0/0

Point 1 Point 2 Point 3 Point 4 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 at EERC do not share that opinion... " [ERG August 20,2007 memo, page 3J

EERC Response:

The cited work conducted by 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 of unburned 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 of catalyst deactivation."

111912007 A-7
"BlindinglPlugging/Fouling - Ammonia-sulfur salts, fly ash, and other particulate matter in

the flue gas cause blinding, plugging or fouling of the catalyst. The particulate matter

deposits on the surface and in the active pore sites ofthe catalyst. This results in a decrease

of the number of sites available for NOx reduction and an increase in flue gas pressure loss

across the catalyst."

"Since catalyst deactivation is due to alkaline materials ... This dependency is probably

not linear, since the overwhelming amount ofash in any installation does not deposit on

the catalyst(it passes through the catalyst channels and ends up in the ESP hopper or is

emitted), but it is most appropriate to consider average values ofchemical poisons. This is

because the total exposure will be less than the average for about halfthe time and more

that average about halfthe time. The overall deactivation rate "averages out"." [ERG

August 20, 2007 memo, page 4]

EERC Response:

These statements are an indication of Christman's lack of understanding of partitioning of

alkali species during combustion and the transport of those species to catalyst surfaces and the

importance of variability. During combustion the sodium, potassium, and other species

vaporize and end up concentrated in the finer size fractions of ash. As the gas and entrained

particles are transported through the catalyst channels the finer fraction of ash 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 of the problematic species such as sodium,

potassium, sulfur, and other elements on the catalyst. Considering the average value of poisons

is not appropriate; it does not average out. Values of poisoning higher than the average will

cause rapid and irreversible plugging from which there is no recovery.

"Although the high sodium content ofCenter Mine coal ash is an economic issue (it will

contribute to catalyst deactivation), Dr. Benson provides no evidence that it will render

SCR technically infeasible at MRYS". [ERG August 20, 2007 letter, page 4] ,

B&McD Response:

Catalyst activity for the severely plugged and blinded SCR catalyst removed 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 of the 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 of exposure for

plugging of the micropores in the Coyote pilot test for these results was less than or equal to

11/912007 A-8
two 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 of the 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 of the 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:

"If one assumes a rather extreme short catalyst life ofone year and ifthe change out is

coordinated with a boiler cleaning outage, the SCR unit would only contribute one or two

days ofdowntime per year". [ERG August 20, 2007 letter, 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 of a cleaning outage

normally aids in the cooldown of a 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 of catalyst 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 of exposure, the frequency of full-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-9
path of a 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 of the 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 of deposits. Thus, the catalyst will

become irreversibly contaminated and the level of activity 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 or horns) effectively prevent [SCR catalyst] pluggingfrom

the ash that is normally entrained in the flue gas (notfalling accumulations)"... [ERG

August 20, 2007 letter, 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 of multiple 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 catalyst should have been cleaned with some frequency so that it could

be continuously exposed to flue gas. Tests at Coyote station were not useful in determining

plugging potential and the attempt at simulating sootblowing was not effective. By EERC's

own admission ...the plugging was a result ofash accumulationsfalling onto the catalyst...

Mr. Hansen also confirmed that the catalyst pitch at Coyote (6 mm) was too small....S&L

presenters suggested that a 10 mm pitch might be requiredfor North Dakota lignite

applications." "[ERG August 20, 2007 letter, pages 4 and 5J

EERC Response:

The reactor was sootblown based on recommendations of the 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 of the surface of the catalyst shown in

one of the images fell on the surface during dismantling the reactor and was not there during

the testing. During cross sectioning of the SCR catalyst EERC specifically looked for evidence

of deposit 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 of the catalyst used at Coyote Station was 6 mm as

recommended by Hansen at Haldor Topsoe. A comparison of the 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 start up and operation of the

reactor because of plant outages. The pressure drop at the end of 500 hours averaged about 0.6

inches of water. 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 of water. During these first 500 hours

of operation the impacts of any falling deposits would be minimal. In addition, after each 2

months of operation the ductwork upstream of the reactor was cleaned.

111912007 A-ll
Baldwin 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 of testing 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

100 200 300 400 500

0-+-----....,.-------,-------,----...,.------1

o

Runtime (hours)

Figure 4. Pressure drop across SCR reactor during first 500 hours of testing at Coyote.

B&McD Response:

An increase in pressure drop is an indicator of gross pluggage ofthe flue gas passages in the

catalyst. Ash deposits that cause the pressure drop to significantly increase can also create

maldistribution of the flue gas through the catalyst. Serious maldistribution causes some of the

catalyst passages to be significantly underexposed to flue gas flow and ammonia, so they will

not contribute to effective NOx control performance, regardless of whether there is a high level

of catalytic 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-12
not. Prevention ofsignificant ash accumulation, flue gas flow maldistribution, and micropore

pluggage needs to be effective in order to maintain high catalyst activity and subsequent NOx

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 of time required to cause it.

It seems curious that the cause of the apparent failure ofthe pilot test at Coyote seems to be

pointed at EERC, the design of the test, its equipment, and methods. It is difficult to believe

that a consortium of EERC, EPRI, USDOE, utilities, and three catalyst vendors would

purposelydesign a test of SCR 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 (of the test to show the ability of the catalyst to

survive the conditions) was not the intended goal. The SCR vendors that participated were

advised of the nature of North Dakota lignite and its challenges during the development of test

procedures and design of the equipment. The lack of positive results in the Coyote pilot test

shows that the ability of the catalyst to overcome exposure to the test conditions 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 ofthe split air preheater approach.. .seems a bit ambivalent, implying first

that it couldn't be done and later stating that conceptually, it could be done. Further

evidence isfound in the fact that SCR retrofits a[tJ New Madrid (two large, PRB-fired

cyclone boilers) included replacement ofthe tubular air preheaters with new regenerative

air preheaters with enamel-coated baskets." [ERG October 4, 2007 letter, 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 of the split air preheater concept proposed by ERG was flawed

and would not work satisfactorily as described. Burns & McDonnell suggested alterations to

111912007 A-13
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 of operating the

high-dust SCR effectively with such wide ranges of flue 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 not believe that resort to the low dust approach is warranted.... " [ERG

memorandum to EPA, August 20, 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 boiler to pose

significant catalyst pore blinding, pluggage, and deactivation problems to drastically inhibit

effective NOx emissions control and catalyst life, regardless of whether 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 October 4 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 letter provides some useful insights, particularly with regard to erosion.

S&L personnel confirmed that Texas lignite ash is more erosive than North Dakota Lignite

ash. This means that the TXU pilot test currently underway should resolve any concerns

regarding erosion at afuture MRYS SCR installation." [ERG August 20, 2007 letter, page.

5]

EERC Response:

Texas lignites are prone to form silicate base deposits in the boilers and have more of an

abundance ofsilicate-rich entrained particles that can be erosive. However, the erosive nature

of the ash is highly dependent upon the source of Texas lignite. The coals fired at the TXU

plants and others from the southern part of Texas 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 of highly porous ash

particles and dense hard particles derived from quartz. The quartz materials will cause erosion.

The porous particles will produce highly vesicular deposits if the ash accumulates on heat

transfer surface. Large vesicular deposits are typically the origin of popcorn 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 of Wilcox 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 of lignite 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 number 9

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 to provide flue gas at the appropriate temperature is not discussed and the

startup/shutdown requirements may be unreasonable. " [ERG August 20, 2007 letter, pages

5 and 6]

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 of the seriousness of the

situation involving this request and the severity of the 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 of the nature of the query and conditions involved.

1119/2007 A-16
The following responses follow the outline ofthe Enclosure attached to EPA Region 8's

October 4,2007 letter25•

Ie Introduction and Summary of EPA's Preliminary Analysis:

EPA October 4, 2007 letter Enclosure, page 6

Original Reference: EPA Region 8 January 26, 2007 letter to NDDH request item number 1:

"Additionally, based on a July 2, 2004, conversation between Jim Standt ofAndover

Technology Partners and Flemming Hansen ofHaldor Topsoe, the sudden build up offly

ash on the catalyst surface that oc:curred during the pilot testing at Coyote Station was

determined to be caused by the accumulation ofash upstream ofthe catalyst and sudden

dropping ofthat ash accumulated ash onto the catalystface. " [EPA October 4, 2007 letter

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 of operation previously shown in Figures 3 and 4 are likely due

only to accumulation of ash 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 of the 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 two facilities operating on PRB coal experienced catalyst plugging that

required extensive and aggressive cleaning measures.... " [EPA October 4, 2007 letter

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 the feasibility ofan SCR installation at

MRYS and the nature ofthe SCR pilot testing at the Coyote station conducted by EERC. "

[EPA October 4, 2007 letter Enclosure, page 7J

25 Ibid Reference number 6.

11/912007 A-17
EERC Response:

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 of the high sodium in the soluble form. Much

of his subsequent discussion was on plugging and not pore plugging.

"...nothing has been provided that would demonstrate that SCR would be an ineffective

means ofNOx control at MRYS". [EPA October 4, 2007 letter Enclosure, page 2J and

"EPA believesB&McD's conclusions regarding the use ofthe "empirical data" from the

Coyote Station pilot-scale testing is not relevantfor an analysis oftechnicalfeasibility,

andfails to consider the observations on catalyst maintenance frequency and pressure

drop trendsfrom the Baldwin and Columbia Station pilot tests. [EPA October 4,2007

letter Enclosure, page 4Jand

"For the Coyote Station, EPA agrees that the plugging and pressure drop observed during

the pilot test were more pronounced and occurred quicker than what was observed at the

two facilities burning PRB coal. Additionally, based on the deposition sampling, EPA

agrees there is evidence thatsodium was afactor in the plugging at Coyote, where it did

not appear at the other two facilities. However, EPA disagrees that these test results can

lead to a conclusion thilt extendedforced outages would be needed at two month intervals

as stated by B&McD in Minnkota's March 19, 2007 letter. "[EPA October 4, 2007 letter

Enclosure, page 5J and

"Based on the above comparison, ofthe pilot testing results by EERC, it is unclear to EPA

that any definitive conclusions can be extrapolatedfrom the results about SCR technical

feasibility and/or timing or extent ofSCR maintenance requirements and boiler outages

...as was done by B&McD for MRYS. Clearly the twofacilities operating on PRB coal

experienced catalyst plugging that required extensive and aggressive cleaning operation

.... " [EPA October 4, 2007 letter Enclosure, page 6J

"...B&McD has not provided a response to EPA's statements regarding normally observed

pronounced ash deposition during pilot testing, the small catalyst pitch, used at Coyote

Station, and how a larger pitch might have affected the test results, and how the air pulsing

did not properly represent sootblowing capabilities on afull-scale SCR application." [EPA

October 4, 2007 letter Enclosure, 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 of multiple engineering solutions suggested by 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 (page 22).

· ,

11/9/2007 A-18
"Mr. Hansen said that Haldor Topsoe would not rule out bidding on a project that

involved North Dakota lignite ... they would look at computer modeling for the specific

coal analysis and boiler .... " [EPA October 4, 2007 letter Enclosure, page 8]

EERC Response:

Current computer models have difficulty in providing adequate information on the transport of

submicron particles into the pore structure of catalyst, subsequent sulfation, bonding strength

development, and removal potential.

"Mr. Hansen was unaware that Haldor Topsoe sent emails to EPA Headquarters stating

that Haldor Topsoe (and two other catalyst vendors) could provide guaranteesfor the

MRYS coal." [EPA October 4, 2007 letter Enclosure, 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 of existing 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 of potential operating

conditions that cause performance problems that prevent achievement of guarantees 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 October 4, 2007 letter Enclosure, page 10

Original Reference: EPA Region 8 January 8, 2007 letter to NDDH:

"EPA is also not aware that any catalystformulations have been developed to deal

specifically with the issue ofsodium. " [EPA October 4, 2007 letter Enclosure, page 10]

111912007 A-19
EERC Response:

Khodayari's major conclusion in his Ph.D. thesis was "Potassium and sodium were found to be

two of the 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 asked Minnkota to look further into Engineering solutions currently available and

determine whether or not the macro-pore plugging issue described in the EERC report

could be effectively managed." [EPA October 4, 2007 letter Enclosure, page 10]

EERC Response:

During the discussions with Haldor Topsoe we asked if they had been pursuing developing

SCR catalyst materials that would be less prone to the impact of alkali 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 not dispute EERC's description ofthe chemical and physical fate ofsodium in a

cyclone boiler. " [EPA October 4, 2007 letter Enclosure, page 12] and

"EPA acknowledges that the sodium content ofthe Center Mine lignite is generally higher

than PRB coals. EPA also recognizes that ash partitioning in a cyclone boiler and

resulting sodium deposition presents certain problems that could pose engineering

challenges to the design and operation ofan SCR system at MRYS. However, Minnkota has

not provided any quantitative data that shows that the plugging and deactivation ofthe

SCR system would be an unresolvable technical barrier and/or the ability ofthe SCR to

control NOx would be so limited that SCR would be an ineffective control option." [EPA

October 4, 2007 letter Enclosure, page 14] and

"Due to the lack ofNOx emission and catalyst deactivation data, the Coyote Station study

does not support utilizing any definitive conclusions, other than there was significant

plugging, which also appeared at both the Baldwin and Columbia Stations." [EPA

October 4, 2007 letter Enclosure, page 15] and

"EPA believes that the experience the utility industry has gainedfrom the installations at

PRB facilities... while Sargent & Lundy indicated thatfurther data from well designed pilot

study would enhance their ability to optimally design a more cost-effective SCR system.... "

[EPA October 4, 2007 letter Enclosure, pages 15, 16]

EERC Response:

In recent discussions with Sargent & Lundy regarding the EERC SCR reactor testing, they

were unaware that 6 months of testing occurred at the Baldwin Station using the same reactor

11/912007 A-20
as was used at Coyote station. We recently advised Mr. DePriest of Sargent & 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 of this prior to our discussion.

"The response from EERC simply restates their position regarding the high sodium content

ofthe Center Mine lignite and how this will cause both catalyst pore plugging and gas path

plugging. EERCfails to consider the use ofavailable engineering solutions to address

these problems with operation ofan SCR at MRYS." [EPA October 4, 2007 letter

Enclosure, page 17] and

"...aggressive on-line cleaning and/orfrequent extended outages would be required to

remove ash accumulation or remove catalystfor cleaning.... " [EPA October 4, 2007 letter

Enclosure, page 18]

"EPA acknowledges that the sodium content in North Dakota lignite presents engineering

challenges. EPA also thinks it is possible that the "sodium-related deposition on SCR

catalyst will shorten the time between outagesfor off-line cleaning... Unfortunately, the

pilot testing conducted at Coyote Station did not provide any quantitative results that could

be used to predict the time periods between catalyst cleaning/replacement on a full-scale

application." [EPA October 4, 2007 letter Enclosure, page 19] and

EERC Response:

Discussions on engineering solution have been conducted with catalyst vendors. None of them

have indicated they have solutions for the sulfate based deposits in the pores of the catalyst that

form by vapor phase and small particle diffusion and subsequent reaction 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 of multiple engineering solutions suggested by 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 intent ofreferencing the EPRI letter on Texas lignite was not to imply that North

Dakota lignites are exactly the same as Texas lignites. The intent ofreferencing this letter

was to show that a major utility research organization is ofthe opinion that the existing

experience ofSCR designers would greatly help in designing SCR systemsfor

accommodating fuel types never before used in practice on afull scale." [EPA October 4,

2007 letter Enclosure, page 18]

11/912007 A-21
B&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 of the catalyst suppliers have developed proven solutions preventing or

removing sodium- and sulfur-based deposits in the micropores of the catalyst that form by

vapor phase and small particle diffusion and subsequent reaction to form sulfates that are

bonded tightly to the catalyst surface.

"However, the EPA cannot concur that the qualitative pilot testing results at the Coyote

Station cited in the EERC report demonstrate that a full-scale SCR installation at MRYS, ...

would not be technically feasible...EPA pointed out some ofthe inherent limitations in the

pilot testing that might have contributed to the "failure" ofthat test. ... EPA questions the

design and operation ofthe pilot test in light ofcritical data obtained." [EPA October 4,

2007 letter Enclosure, page 20J

EERC Response:

Regarding EPA questioning the design and operation of the 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 of the lack of quantifiable 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 of SCR catalyst to 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-22
Reduction of ash deposition within the catalyst in the Coyote pilot SCR testing would have

reduced the amount of pressure drop increase through the catalyst layer. This is the "macroeffect" of the 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 of the 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 of Minnkota's arguments lacking "quantifiable data" appears to ignore this

supposition. Such drastic, negative results from such a short amount of time (4 months) of

Coyote pilot SCR catalyst testing should be interpreted as an unsuitable application of the

.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 of the "Popcorn Ash" Issue:

EPA October 4, 2007 letter Enclosure, page 21

Original Reference: EPA Region 8 January 8, 2007 letter to NDDH

"No response given to EPA's comment by EERC or B&McD. The topic was similarly

addressed in the January 2007 Christman Memo." [EPA October 4, 2007 letter

Enclosure, page 21]

11/912007 A-23
B&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 of reliable 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 of the large particle ash screens.

3. EPA Analysis of the Temperature Issue:

EPA October 4, 2007 letter Enclosure, page 21

Original Reference: EPA Region 8 January 8, 2007 letter to NDDH

"No response given to EPA's comment by EERC or B&McD. The topic was similarly

addressed in the January 2007 Christman Memo." [EPA October 4, 2007 letter

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 air preheater scheme does not raise

the temperature exiting either boiler's primary superheater (PSH) section that is located

upstream of the high-temperature pass of the 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 of no 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 of reheat fuel or steam required. Even if such

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 of the Erosion Issue:

EPA October 4, 2007 letter Enclosure, page 21

Original Reference: EPA Region 8 January 8, 2007 letter to NDDH

"No response given to EPA's comment by EERC or B&McD. The topic was similarly

addressed in the January 2007 Christman Memo." [EPA October 4, 2007 letter

Enclosure, page 21]

.B&McD Response:

Various means of resolving catalyst erosion were referenced in ERG's January 8, 2007 memo

letter. Effective on-line catalyst cleaning of deposits 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 compare current 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 of the Energy & Environmental Research Center Report (Appendix B):

EPA October 4, 2007 letter Enclosure, page 23

Original Reference: EPA Region 8 January 8, 2007 letter to NDDH

"... a better effort to keep the catalystface clean. Mr. Hansen recalled the Coyote Station

test reactor became quickly plugged withfly ash causing rapid increases in pressure loss

caused mainly by wall duct ash accumulations dropping on the catalystface." [EPA

October 4, 2007 letter Enclosure, page 23] and

"Based on the EERC response, the degree ofcatalyst plugging observed at Coyote Station

was the reason no deactivation testing on the catalystwas conducted. ifthe testing were

designed and conducted in a way that could have greatly reduced the effects ofash

deposition on the catalystface, presumably catalyst deactivation data could have been

obtained. As stated previously, EPA questions Minnkota's heavy reliance on the

questionable resultsfrom the Coyote Station pilot testing and cannot support using this

data to draw definitive conclusions on the feasibility ofSCR at MRYS. " [EPA October 4,

2007 letter Enclosure, 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 of the vessel. Evidence of flow patterns in

the plugging materials that were not consistent with the geometry of the catalyst was not

observed. In addition, if the gases were not allowed to flow through the catalyst and they were

11/912007 A-25
rapidly plugged begs the questions: Why were the pores being plugged in the middle and at the

outlet regions of the catalysts? Why were deposits evident at the outlet of the catalyst and in

the catalyst vessel as shown in Figure 5?

Figure 5. Plugging of SCR catalyst and deposits formed downstream of center 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 of the hard deposits that remained in the vessel at the outlet of the

catalyst after the catalyst was removed.

"In addition, Sargent & Lundy indicated that they were disappointed in how the Coyote

Station pilot test was carried out andfound the results to be ofvery little value for

evaluating an SCR system forfacility burning North Dakota lignite." [EPA October 4,

2007 letter Enclosure, page 23J

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 of the degree of blinding and plugging ofthe pores. The information

from the Baldwin testing was used as input for the design of SCR systems. Sargent & Lundy

did not have an in depth appreciation of the challenges high sodium lignite has on SCR

catalysts.

6. EPA Analysis of the Burns & McDonnell's Conclusion:

EPA October 4, 2007 letter Enclosure, pages 25-31

Original Reference: EPA Region 8 January 8, 2007 letter to NDDH26

"While the pilot study does suggest that catalyst plugging at afacility burning North

Dakota lignite would likely be more ofa challenge than at afacility burning PRE coal,

26 Ibid Reference number 9.

11/9/2007 A-26
EPA can not conclude that the test is determinative ofwhether an SCR system would not

work at MRYS." [EPA October 4, 2007 letter Enclosure, page 25] and

"... the qualitative information does not provide meaningful conclusionsfor comparatively

assessing SCR technicalfeasibility for North Dakota lignite and PRB applications. The

one exception would be that the study shows lignite at Coyote Station showed more sodium

deposition and less calcium compared to PRB coal. " [EPA October 4, 2007 letter

Enclosure, page 28] and

"Without representative catalyst deactivation testing or NOx control datafrom the Coyote

Station, EPA does not believe the pilot study provides meaningful results that could lead to

a definitive conclusion that SCR would be infeasible at MRYS." [EPA October 4,2007

letter Enclosure, pages 28 and 29J and

"... reactivity testing for the catalyst. EERC did not test the catalyst at Coyote Station,

because the catalyst was allegedly too plugged to conduct the testing. This appears to be a

failure ofthe pilot test to meet the original goal for North Dakota lignite. ... in light of

substantial ash deposition on the catalystface ... ". [EPA October 4, 2007 letter Enclosure,

page 29J and

"The qualitative results ofcatalyst plugging for the pilot testing at Coyote Station do not

provide empirical evidence that SCR would be ineffective at controlling NOx emissions,

since there was no quantitative data providedfor either NOx reduction or catalyst

deactivation. As such, EPA is not convinced that the specific challenges presentedfor an

SCR installation at MRYS is a matter oftechnical infeasibility and could not be overcome

with a robust suite ofash (including sodium) mitigation measures and/or maintenance

measures." [EPA October 4, 2007 letter Enclosure, 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 of reactivity testing would be inclusive in the

cleaned catalyst before 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-27
B. Low-Dust SCR

1. EPA AnalYsis of the Catalyst Fouling and Deactivation Issue:

EPA October 4, 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 not necessarily support the conclusion that a low-dust SCR system would

be technically infeasible at MRYS. The effects ofthis blinding and deactivation should

either be quantified and used within the economic analysis under step 4 ofthe Top-Down

BACT analysis, or described in sufficient detail to demonstrate that the problems

associated with catalyst blinding and deactivation are unsolvable and would result in the

unsuccessful operation ofa low-dust SCR. As stated on page B.20 ofthe NSR Workshop

Manual, "(p)hysical modifications needed to resolve technical obstacles do not in and of

themselves provide a justification for eliminating the control technique on the basis of

technical infeasibility. However, the cost ofsuch modifications can be considered in

estimating cost and economic impacts." [EPA October 4, 2007 letter Enclosure, 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 of SCR catalyst from sodium-sulfur

compounds evident in the flue gas stream exhausted from a North Dakota lignite-fired boiler,

whether installed in a conventional hot-side or cold-side application downstream of a wet

scrubber, have not been developed by SCR catalyst vendors. Burns & McDonnell previously

discussed the estimated energy requirements for reheating flue gas upstream of a 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 of the composition of the 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 of this technology on

the cyclone boilers at MRYS.

2. EPA Analysis of the Site Space Constraint Issue:

EPA October 4, 2007 letter Enclosure, 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 oflow-dust

SCR...based on reasonable expected reheatfuel requirements, equipment installations, plant

modifications.... " [EPA October 4, 2007 letter Enclosure, 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 of the Burns & McDonnell's Conclusion:

EPA October 4,2007 letter Enclosure, page 34

Original Reference: EPA Region 8 January 8, 2007 letter to NDDH:

"B&McD appears to be saying that a significant portion ofthe sodium in the fly ash is in

the vapor phase when it enters the ESP." [EPA October 4, 2007 letter Enclosure, page 34J

EERC Response:

EPA misinterpreted B&McD and EERC's response. B&McD and EERC do not suggest in any

of the documentation that sodium is in the vapor phase at the temperatures of the SCR.

Initially in cyclone-fired systems much of the 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 of sodium, potassium, calcium, and sulfur deposition

downstream of the ESP as illustrated in Figure 1 presented in response to ERG Core Issue

number 2.

III. Additional Information Useful to Evaluating Technical Feasibility of SCR at MRYS

A. EPA Headquarters Believes SCR is the Correct Technology for MRYS in

Developing the Clean Air Interstate Rule

EPA October 4, 2007 letter Enclosure, page 36

Original Reference: EPA Region 8 January 8, 2007 letter to NDDH:

"...EPA 's discussion with Flemming Hansen ofHaldor Topsoe also revealed that despite

the concerns about an SCR system subjected to the sodium environment... Haldor Topsoe

would not rule out bidding such a project." [EPA October 4, 2007 letter Enclosure, page

37]

11/912007 A-29
EERC Response:

The most significant part 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 consider bidding 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 a North 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 October 4, 2007 letter Enclosure, page 37

Original Reference: EPA Region 8 January 8, 2007 letter to NDDH:

"EPA is not suggesting that the costfigures used in the BART analysis need to be used in

the BACT analysisfor MRYS." [EPA October 4, 2007 letter Enclosure, 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 during the 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 of SCR for Lignite-Fired Units

EPA October 4, 2007 letter Enclosure, page 38

Original Reference: EPA Region 8 January 8, 2007 letter to NDDH:

"...the new NSPS standards apply to affected utility boilers that commence construction,

reconstruction, or modification after February 28, 2005. (EPA's original comments

erroneously said that the standards only applied to new units.) This would include any

existing cyclone unitsfiring North Dakota lignite that undergo reconstruction or

modification. The standards that would apply to...modified units (1.4 lb/MWh or

0.15lb/MMBtu)...EPA also agrees that there have been some recently-permitted units

burning Texas lignite that have proposed SCR and that there are some differences between

111912007 A-30
North Dakota and Texas lignite. EPA believes these differences might affect the design and

operation ofan SCR system for the different lignites. EPA does not believe these

differences indicate that EPA did not consider North Dakota lignite in revising the NSPS

for utility boilers." [EPA October 4, 2007 letter Enclosure, pages 38 and 39J and

"Notwithstanding the differences between North Dakota lignite and Texas lignite, a

modified cyclone boilerfiring North Dakota lignite would still need to meet the most recent

NSPS Da limitfor modified units, which is lower than the BACT limit proposed by

Minnkota. The likely choice to meet this limit of0.15 lblMMBtu would be SCR." [EPA

October 4, 2007 letter Enclosure, page 40J

B&McD Response:

B&McD concurs with EPA's analysis that reconstructed 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 of the EPA's new NSPS standards is not proof that Minnkota's October 2006 BACT

analyses and subsequent responses are insufficient to meet the requirements of the 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 of achieving

these NSPS emission limits on cyclone-fired unit burning North Dakota lignite.

"EPA has reviewed the coal data submitted by EERC and, in general, agrees that the

sodium content ofTexas lignites is lower than North Dakota lignites. However, it appears

that the Jackson South Texas lignite has a somewhat comparable ash sodium content above

3%... " [EPA October 4, 2007 letter Enclosure, page 39J

EERC Response:

The lignite from the Jackson formation is a famous coal relative to the fate and behavior of

sodium. The sodium in the Jackson South and Yegua formations of Texas is in the form of a

zeolite-type mineraL During combustion, most of the sodium is retained in the aluminosilicate

melt phase and is not vaporized. As a result the sodium released 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 of heat input (lb NalMMBTU)

basis is not an accurate assessment of sodium impacts from North Dakota lignite compared

with the Texas lignites cited by EPA.

11/9/2007 A-31
D. SCR and Catalyst Vendor Information

EPA October 4, 2007 letter Enclosure, page 40, 41

Original Reference: EPA Region 8 January 8, 2007 letter to NDDH:

"EPA had originally suggested that Minnkota "obtain information and proposals" from

some ofthe other companies that EPA had listed. EPA envisioned this to include more of

the level ofdetail described by B&McD in their March 19, 2007 response." [EPA October

4, 2007 letter Enclosure, 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 of the seriousness of the

situation involving this request and the severity of the 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 of the nature of the 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): Request for 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 letter Enclosure, page 42

Original Reference: EPA Region 8 January 26, 2007 letter to NDDH:

"EPA has reviewed the coal data submitted by Minnkota. EPA believesfuture coal data

appears to show little change from the 2007 cores." [EPA October 4, 2007 letter

Enclosure, page 39J

EERC Response:

The challenges for the future are related to the decreased availability ofthe lower sodium

coals. The abundance of the 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-32
350

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2036-2045,2046-2055

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(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 letter Enclosure, page 43 .

Original Reference: EPA Region 8 January 26, 2007 letter to NDDH:

"EPA acknowledges that there are times when the flue gas temperature at the portion of

the boiler where a high-dust SCR would be located (primary superheater outletfor Unit 1

and presumably the economizer exitfor Unit 2) would be higher than the temperature

range typically suitable for SCR. While B&McD seems to indicate in the March 19, 2007

letter that the dual-airpreheater design suggested by ERG would be problematic, it later

concedes that it conceptually could work, but would be at additional cost." [EPA October

4, 2007 letter Enclosure, page 44J

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-33
The arrangement and operation of the 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 of operating the

high-dust SCR effectively with such wide ranges of flue 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 either boiler'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 NUx reduction by a conventional hot-side SCR. We know of no 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.

11/9/2007 A-34
C. Low-Dust SCR Fouling

EPA October 4, 2007 letter Enclosure, page 44

Original Reference: EPA Region 8 January 26, 2007 letter to NDDH:

"While the relative effects of vaporized particles passing through the ESP and condensing

prior to a low-dust SCR system might be more pronounced compared to the non-vapor

particles impacting a high dust environment, EPA maintains that the ESP will remove a

very substantial portion ofthe ash that would affect a high-dust SCR and the overall effects

ofcatalyst plugging and deactivation in a high-dust application would be greater than a

low-dust application." [EPA October 4, 2007 letter Enclosure, 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 of the ESP on MRY Unit 1 as

previously illustrated in Figure 1. The chemical composition of the deposit is consistent with

various pyrosulfates that have melting points as low as 530°F.

D. SCR Deactivation

EPA October 4,2007 letter Enclosure, page 45, 47

Original Reference: EPA Region 8 January 26, 2007 letter to NDDH:

"Meeting with Sargent & Lundy ... indicated that an SCR system could theoretically be

designed to operate on North Dakota lignite... Sargent & Lundy representatives were of

the opinion that a well-run pilot test would yield valuable information that could be used in

conjunction with previous SCR experience to evaluate and design an SCRfor a North

Dakota lignite application." [EPA October 4, 2007 letter Enclosure, 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 was used 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-35
E. SCR Vendor Guarantees

EPA October 4, 2007 letter Enclosure, page 48

Original Reference: EPA Region 8 January 26, 2007 letter to NDDH:

"The letter goes into great detail about the worst-case nature ofCenter Lignite coal. "

[EPA October 4, 2007 letter Enclosure, page 48J

EERC Response:

EPA indicated that a worst-case nature of Center lignite was provided. Designs ofsystems

must be able to accommodate the more challenging coals, and in this case, sodium oxide levels

of 6 to 8 % in the ash. The information provided was information that would be provided to

any vendor of equipment that would utilize Center lignite 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 not seen any vendor responses to the information request. EPA does note

that the request seems to have been written with a pessimistic tone... " [EPA October 4,

2007 letter Enclosure, pages 48-49J

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 October 4, 2007 letter Enclosure, page 50

Original Reference: EPA Region 8 January 26, 2007 letter to NDDH:

"Flemming Hansen ofHaldor Topsoe...gave a rough estimate that an SCR systemfor

North Dakota lignite could be designed (larger) to accommodate a catalyst replacement

schedule ofabout every year. Mr. Hansen said that an SCR reactor could be cooled down

within 24-36 hours (need for cool air draft requires the boiler to be shutdown) and the

catalyst layers rotated in about two ofthree days, three days all around." [EPA October

4, 2007 letter Enclosure, page 50J

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-36
MRYS 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 of boiler 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 of catalyst. 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 October 4, 2007 letter Enclosure, page 51

Original Reference: EPA Region 8 January 26, 2007 letter to NDDH:

"The reasons given by B&McD to this point (high boilerfouling conditions and varying

gas temperatures and loads) appear themselves to be theoretical.... EPA does not believe

that whether other non-cyclone fired BART applicants included an analysis ofHE SNCR is

evidence, in and by itself, that the technology is infeasible at MRYS." [EPA October 4,

2007 letter Enclosure, 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 or burner

types does not refute the lack of experience with HE-SNCR on boilers with such severe surface

fouling and temperature conditions. If boiler 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 of operation 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 of HE SNCR has been

11/9/2007 A-37
missed. The intention was to show 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.

H. Reburn with SNCR

EPA October 4, 2007 letter Enclosure, page 53

Original Reference: EPA Region 8 January 26, 2007 letter to NDDH:

"Ifthe technology has been demonstrated, it is considered technologically feasible without

going through further analysis. ... B&McD also points out that non-cyclone BART eligible

sources in North Dakota did not provide an analysis ofReburn with or without SNCR as a

control alternative in their BART analysis." [EPA October 4, 2007 letter Enclosure, page

53J

B&McD Response:

EPA appears to say that differences in specific conditions of the MRYS boilers compared with

the single unit where Reburn with SNCR has been demonstrated are not pertinent to whether

the control technology would be technically feasible. Successful implementation of NOx

controls is highly dependent on the specific configuration and process conditions that lend

themselves to be compatible within the limits of constructability, survivability, and

effectiveness. Just because a control technology is "technically feasible" based on EPA's

interpretation of the 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 October 4, 2007 letter Enclosure, page 54

Original Reference: EPA Region 8 January 26, 2007 letter to NDDH:

"While predicting the exact level ofNOx controlfor RR1 and MRYS may not be

possible...EPA does not believe B&McD has demonstrated that RRIshould be considered

technically infeasible." [EPA October 4, 2007 letter Enclosure, page 54J

111912007 A-38
B&McD Response:

EPA appears to ignore the arguments regarding the expected lack of effective NOx reduction

from RRI if it were applied at MRYS with modest cyclone air-staged combustion. Successful

implementation of NOx controls is highly dependent on the specific configuration and process

conditions that lend themselves to be compatible within the limits of constructability,

survivability, and effectiveness. Just because a control technology is "technically feasible"

based on EPA's interpretation of the 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 October 4, 2007 letter Enclosure, page 55

Original Reference: EPA Region 8 January 26, 2007 letter to NDDH:

"further consideration ofROFA is unnecessary." [EPA October 4, 2007 letter Enclosure,

page 55]

B&McD Response:

We agree with EPA's response regarding ROFA.

K. Control Efficiency for SNCR

EPA October 4, 2007 letter Enclosure, page 55

Original Reference: EPA Region 8 January 26,2007 letter to NDDH:

"EPA agrees that the 60% reduction cited at the upper end ofthe control range is likely

not appropriate for MRYS. It appears likely that something closer to 30% than 60% would

be reasonable." [EPA October 4, 2007 letter Enclosure, page 56]

B&McD Response:

We stand by our use of the estimated levels of NOx control for alternatives involving SNCR

included in Minnkota's October 2006 MRYS BACT analysis.

L. Selection of 30-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 startup periods did notfall within the relevant baseline

period." [EPA October 4, 2007 letter Enclosure, page 57J

B&McD Response:

We stand by our use of the estimated levels of NOx control included in Minnkota's October

2006 MRYS BACT analysis.

M. BACT Limit IS-Month Trial Period

EPA October 4, 2007 letter Enclosure, page 57

Original Reference: EPA Region 8 January 26, 2007 letter to NDDH:

"EPA agrees this is an acceptable approach." [EPA October 4, 2007 letter Enclosure,

page 58J

B&McD Response:

Acknowledged.

111912007 A-40
REFERENCES

1 United States Environmental Protection Agency (U.S. EPA or EPA) Region 8 letter by

Martin Hestmark, Director, Air and Toxies Technical Enforcement Program, ECEJ to

Terry L. O'Clair, North Dakota Department of Health, Environmental Health Section,

Division of'Air Quality and David Sogard and John Graves, Minnkota Power

Cooperative, Re: Transmittal ofEPA's Response to Minnkota's Letters Dated March

19, 2007 and April 23, 2007, Regarding the October 2006 NOx BACTAnalysis Study

Reportfor Milton 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 "NOx Best Available Control Technology Analysis Study for Milton R. Young Station

Unit 1 Minnkota Power Cooperative, Inc." and a separate "NOx Best Available Control

Technology Analysis Study for Milton R. Young Station Unit 2 Square Butte Electric

Cooperative", October 2006, by Burns & McDonnell, submitted to EPA Region 8 and

EPA Office of Regulatory Enforcement, and included with the "BART

DETERMINATION STUDYfor Milton R. Young Station Unit 1 and 2 Minnkota Power

Cooperative, Inc. Final Report, October 2006" submitted by Minnkota to North Dakota

Department of Health.

5 Eastern Research Group (ERG) letter by Roger Christman, to U.S. EPA, Summary

Discussion in Response to the Burns & McDonnell and EERC Reports (Minnkota,

March 19, 2007, and Minnkota, April 23, 2007), and the Subsequent Meeting on May

23, 2007, at the Offices ofthe Division ofAir Quality, North Dakota Department of

Health (NDDH), dated August 20, 2007.

6 Enclosure, "Responses To EERC and C and B&McD's March 17,2007 Letter

Responding to EPA Region VIII Comments - January 8,2007, and EPA's Response To

EERC and B&McD April 23, 2007 Letter to NDDH Comments - February 1,2007

(Including Response to U.S. EPA Region 8 Comments - January 26,2007): Requestfor

Additional Information and the Non-SCR Commentsfrom EPA. (provided with

reference number 1 and reference number 3)

7 Consent Decree filed in the United States District Court For The District Of North

Dakota, United States Of America and State Of North 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 of Health, Environmental Health Section, Division of Air

Quality letter by Terry L. O'Clair, P.E. to John Graves, Minnkota Power Cooperative,

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Re: BACT Determination 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 of Health Division of Air Quality, Re:

Transmittal ofEPA Non-SCR concerns and additional information requiredfor

Minnkota BACTAnalysis Study, dated January 26,2007.

9 Evaluation and Mitigation of Visible 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 of NOx: Deactivation and Regeneration

Studies and Kinetic Modeling of Deactivation," 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 of Regulatory Enforcement,

Review and Critique ofthe Bums & McDonnell NOx BACTAnalysisfor the Milton R.

Young Station Operated by Minnkota Power (October 2006), written by Roger

Christman, Eastern Research Group, Inc., January 8, 2007, faxed by North Dakota

Department of Health to Minnkota, January 9, 2007. and EPA Region 8 Preliminary

Analysis ofBurns & McDonnell BACTAnalysis For Nitrogen Oxide at Milton R. Young

Station, Units I and 2 January 8, 2007 faxed by North Dakota Department of Health to

Minnkota, January 9, 2007.

12 "Appropriateness ofConducting Pilot Testing ofSelective Catalytic Reduction (SCR)

Technology at Milton R. Young Station. Units I and 2, For Use In A 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