I •••



### Via 

### CertifiCd Mail .. Mr. 

### TenyO'Clair Director, Division ofAir Qualjty 

### North DakotaDepartment ofHealth 918 

### E. 

### Divide Avenue Bismarck, ND 58501-1943. 

### Ref: 8ENF-L UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION 8 1595 Wynkoop street DENVER, CO 80202-1129 Phone 800-227-8917 .

. http://www.epa.gov/region08 

## OCT - 4 2007

Mr. 

### David Sogard, General Counsel John**Grav~s~** 

### Envirotiinental Manager 1822 

### State Mill Road . P.O. Box 13200 

### ·Grand Forks, NorthDakota 58208-3200 

### Re: Transmittal ofEP A's Response to 

### Mirinkota's Letters Dated March 19, .2007· 

### and April 

### 23, 2007, 

### Regarding the OCtober 2006 

### NOx

### BACTAnalysis Study Report fOf

. Milton R 

### Young Station Dear Teny, David and John:

. . . .


### . .the United States Environmental ProtectiOn AgencY,. Region 8 

### (EPA) subinitsthis letter and the Enclosure to respond,to**l~s** 

### dated March 

### 19, 20Q7 

### and 

### April 23, 2007 

### m;tthored by . Minnkota Power COOperative, Incorporated (Minnkota) regarding the Burns & McDonnell , .(B&McD) Best Available Control TechnoI8gy{BACT) Analysis for**Nitrog~n** 

### Oxides (NUx) 

### at

Milton 

## It. Young Station (MRYS), Units 1 and 2, prepared by B&McD for Minnkota (Minnkota BACTAnalysis). The 

### above identified two letters were submitted by Minnkota iIi 

### response to . letters sent byEP A to North DakotaDepartmentofHealth (NDD:a), dated 'anuary. 8 

### and 26,**2007~** 

### and.were also in**resp~nse** 

### to a letter from the NDDH dated February 1; 2007 .. 

### EPA appreciates theongoing dialogue and exchange ofinformation with NDDH and Minnkota on these 

# very complex and important issues related to the appropriate NOx 

### control technology to**b~** 

### installed at MRYS Units· 1 

### and 2. 

### The meeting in aismarck on 

### May- 23, 2007 

### with representatives ofMinnkota was very useful. EPA also**appreciat~s** 

### the efforts by you and. your staffto seek a well-informe<l decision on thiS matter. The Enclosure contains a response from·EPA's consUltant, Roger Christman 

### of Eastern

### Research Group, on technical issues related to Selective 

### Cata:Iytic Reduction (SCR) (Christman August 20,2007 Memo). The :Enclosure also

. contamsEPA's detailed response 

### to Minnkota's letters datedMarch 19,2007 

### and April 23,

### 2007.

### To briefly sutrimarizethe Enclo·sure, the MinnkotaBACT Analysis is incomplete, and the

.determinations oftechnica1 infeasibility for·the mgh-dust SCR, Low-dust SCR, Hydrocarbon . Enhanced Selective Non-Catalytic Reductiori (HE 

### SNCR), Reburn with SNCR and Rich Reagent Injection NOx control technologies are incorrect. Mitinkotahas inCorrectly interpreted and tnisa,pplied Chapter B ofEP A's ''New Source Review Workshop Matiual- Prevention of Significant Deterioration and Non-attainment Area Permitting" (Draft 

### October 1990) (NSR

· .Workshop 

### Manwd) in its determination that 

### these control technologies are**t~hnica1ly** 

### infeasible.

·Furthermore, Mitinkotahas incorrectly utilized the results ofthe pilottesting conducted· at 

### the· Coyote Station by the Energy & 

### Enviromilental Research Center

### to find that SCRis inapplicable. . .

.Minnkotamust evaluate these coptrol technologies beyond step 2 

### ofthe proeess outlinedin the NSR Workshop 

### Manual. . The operational problems assOciated with the . Coyote Station pilot test 

### andthe . lack·of cat3Iyst deactivation data greatly dimiIiish the usefulness ofthe test I;esults in analyzing the technical feasibility ofSCR at MRYS.EPA maintains thatthe resUlts of the Coyote Station pilot test do not demonstrate technical infeasibility ofSeRTor utility bollers firing North Dakota lignite. Minnkota has not provided informationandlor data in the original Minnkota BACT.

·Analysis or in any. ofthe subsequently delivered letter responses demonstrating that the

·differences between North Dakota lignite and other solid fuels would prevent the 

### successful application ofSCR at

### MRYS, EPAfinds that 

### the wealth ofexPerience in the utility industry applying SeRto solid fuel utility boilers creates a presumption of

### technical feasibility at MRYS. ---------.-lMinnkOtailas 

### not overcome**thispr~t~resently** 

### finds**that·th~t~--** 

### ..**-,~---.** 

### BACT Analysis.is**incomple~e,** 

### has noiheen 

## carried out 

### in accordatice with ChapterB ofEPA's . NSR Workshop Manual, does not provide

# an ofthe information necessary for NDDH to 

### make a BACT deteimination and does not contain all ofthe information· requestoo by EPA· ..

. EPA has received NDDH's letter dated September 21, 2007 

### transmitting Minnkota's paper entitled**"'Approp~ness** 

### ofConducting Pilot Testing ofSelective Catalytic RedUction (SCR)

..Technology at Milton

### R Young Station Units 1 .and 2, for lise in a NOx

### BACT Analysis" and ·is planning to 

### review it. EPA·remams committed to moving the BACT process forWard sothat Minnkota can meetihe deadlines specified inthe Consent Decree. Forthe BACT process to

·proceed, EPAbelieves NDDH·should move past the question oftechnica1 feasibility for SCR . and the other incorrectly determined technically**inf~ible** 

### control technologies and require

·Minnkota to 

### cOmplete the Top-Down BACT analysis. for SCR apd ihe othel' controltechnologies

·in accordance with paragraphs 24 and 65· ofthe Consent Decree.. If

### you would like tQ discuss any ofthese matters, please Call 

### me at (303) 312-6776. . .

# ~tLo+-~ Martin Hestmark, Director, Air and Toxics Technical Enforcement Program, ECEJ . 2

### .EncloSure cc: Eddie Sierra,. Deputy Assistant Regional Administrator, ECEJ

. JeffKodish, OECA Ron Rutherford,. OECA 

### ·Adam Kushner, OECA 

### Brenda Morris,EPA Douglas Latimer, EPA Mike Owens, EPA Hans Buenning, EPA

.Jerry MacLaughlin, DOJ



### 3 

# * Printed on RecycledPaperI 

## MEMORANDUM TO: . 

### Hans Buenning, Albion Carlson, Doug Latimer, Martin Hestmark, Brenda Morris, EPA Region 8 . . Sounjay Gairola, Ron Rutherford,EPAlORE HQ FROM: 

### Roger Christman, Eastern Research Group, Inc. DATE: ..

### August 20,2007 SUBJECT: . 

### Summary Discussion in Response to the Bums & 

### McDonnell'and EERC Reports (MiIlJl1(ota,March 19, 2007 and Minnkota, April 23, 2007) and the Subsequent Meeting on May 23, 2007, at the Offices ofthe Division ofAir Qu'ality, North Dakota Department ofHealth (NDDH). INTROQUCTION

, . 

### ERG has been tasked by the 

## U.S. EPA Office ofRegulatory Enforcement to provide technical assistance-to EPA Region 8 in evaluating a series. ofdocunients**prepar~d** 

## by Bums & 

### McDonnell (B&McD), and the'Energy & 

### Environmental Research Center (EERC) at the ,UniversitY ofNorth Dakota, .on behalfofMinnkota Power Cooperative, Inc: m'respense totlie sti6missiori, in .'" '" October of2006, ofa BACT Analysis for Milton R. 

### Yourig Station (MRYS) and the appended
,Ash Impacts on 

## sci? Catalyst Performance 

### (Benson, October 2005), I prepared a memo

(Christman, January 2007) addressing issues raised in**~e** 

### BACT Analysis**~d** 

### theBenson**p~per** 

### that were cited by Minnkota as renclering. SC!t technically**infe~ible** 

### at MRYS. My memo,.along with EPA Region .8 

### and NDDHquestions and requests for additional. informatiori were forwarded to Minnkota., ' .. Minnkota provided a response to the ERG memo (Minnkota, March 19, 200?) and additional responses' and Information about a**~onth** 

### later (Minnkota,**Apri123~** 

### 2007). These**rriaterial~** 

### were reviewed by Region 8 personnel and ERG in preparation for'a meeting with Minnkota at NDDH**o~** 

### May. 23, 2007. A list ofnine unresolved "core" issues**w~re** 

### identified and were subsequently discussed at the May meeting. They are addressed f?elow. Also, some ofthe discussion during a meeting 'on May 24, 2007., that included an SCR/North Dakota Lignite presentation by Sargent & 

### Lundy (S&L),corioborated much ofthe EPA arid ERG positions and will also be,noted in the' discussion'here. Issues that app.ear to have been resolved prior to, or at the May 23-'meeting are not discussed (e.g., popcorn. ash). '

PRIVILEGED ENFORCEMENT INFORMATION Not for Release Under FOIA or Other Information Release Statutes 1The nine "core"**is~ues** hiclude: 1. Center Mine. ash content variability 2. Catalyst deactivation by sodium and regeneration difficultie$. 

### 3. Downtime for catalyst cleaning andchange· out. . 

## 4.· Sticky ash. . 5..**EE~C** pilot test procedures/design. 

### 6.. Split ·air preheater. 7.. B&McD low dust SCR assessment.·

... 8. Texas Lignite comparison.



### . 9. SCR vendor· quote request. DISCUSSION 

### 1. Center Mine ash content variability. At the May meeting, B&McD representatives and Dr. Benson continued to refer to the .extreme coal variability, both in proximate. analysis and ash constituep.t concentrations and. continued to refer to ash contents as high as 25.5%. An examination ofthe actual data (analyses ofmore than 700 as-fired coal samples provided by Minnkota in 2003) shows that.the coal ash content is not particularly variable, with more than 95% ofthe samples having an ash content between 7% and 15% .. Well over 50% ofthe samples fall between 8% and 11.%. The actual maximum content

### i~ ' .

.just under 16%, not 25.5% as 'stated by B&McD. rhe higher figure is based on a single sample·

WIth none offfie more than 

### 700 otner samples**eX1immnguan~1'i** cornent gfeaterthan**t~;·**

"
. Along with the general discussion ofash variability, Dr. Benson introduced the concept of variability in the**"acid-to-b~e** ratio" ofthe ash**(pages7~9,.** Minnkota,Marc.h**~007)** as having' relevance to thetechnical.feasibility ofSCR as applied to North**D~ota** Lignite.· He included two ·figures that display· moisture and Base/Acid and an undefined "Cyclone Performance".· The accompanying text refers to slag freezing events and the

### n~ed to provide

### ~uppl.emental fuel. Although the ash fusion temperatufe·andthe ash viscosity at cyclone barrel temperatures (>2,500

. ·F) are· functions ofash composition and thus are sensitive to· varhlti6ns in that composition with.

time; there should be no impact on that ash behavior downstream at SCR temperatures. Dr. . ..

. Benson does· not, in fact, make a direct coimection between his discussion ofbase-to-acid ratio

.and the functioning ofan SCR system. B&McD also .only**m~ntions** impact on "operation ofthe boilers at MRYS" (page 9) and makes .no connection specifically to an SCR system. As a final

. note, 

### 1 have been involved in one way or another with SCRsince ·the early 1970's and I have PRIVILEGED**ENFORCEMt~T** INFORMATION . NoHor**R~lease** Under FOIA or Other Information Release Statutes 

### 2

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

### Of discussion, prior to, Dr. Benson's introduction ofthe subject.

, ' 

### '2.**Catalys~** 

### deactivation by'sodium and regeneration**diffi~ulties.** 

### Dr. Benson.cited a paper by'Khodayarl as evidence that catalyst ppisoned 'by potassium

### c~uld not be regenerated and that the same would be true ofsodium-poisoned catalyst (reference 12', Minnkota, March 2007)., A careful reading ofthe paper shows that Khoqayari**~chieved** 

### 90% to '110% recovery ofthe originalteactivity ofthe catalyst. Further,' Khodayari's PhD dissertation states that potassium" not total alkali, is the problemfor SCR application to ,biofuelcombustion. ,A paper authored by engineers involved in the application ofSCR to biomass fuels cites' 'Khodayari's work as evidence that catalyst activity can'berecovered by washing and wi,ll result in reduced cost for biomass applications (Alstom, lindated,'-2006). . ,

. . . . . 

### Dr: Benson further states that work by Beck (reference**16~** 

### Minnkota, March 2007) established a

.. deactivation correlation with 'sodium in ash. Again, a careful reading'ofthe paper shows that

sodium is only mentioned 'when the discussion addresses total alkali and 

# Beck actUally cite$ potassium and phosphorQs as the prim8l'y poisons associated with 

### a range ofbio-materials that are burned for energy recovery; He concludes that-additional research is needed to detennirie the relative' contributions ofphosphorus, potassium an,d sodium. His**subseque~t wo~k**  

### focused" , 'entirely 'on phosphorus and did not address'sodium at all. ,A 2006 presentation covering work conducted by the Uniyersity ofUtah and REI on the , application ofSCR to low-rank coals concluded that "chemical,poisoning is'not irriportant" for , I()w-raiik.' coals;

# out mask1ng oy**nyaslils~f** 

### prooIem. 'IIre sfilOy"fUi'ttier conetutletl"'thatthe" , '



### poisoning'potential of the alkali materials ranked as: K.>Na>Ca. While Dr. Benson ctmcludes that the

### sodi~ 'levels in North Dakota Lignite ash are so high as to , ,render 

### sC:k technically infeasible; apparently others atEERC do'not share that opinion and have researched the co-firing ofbiofueI,s with low-rank coal's (EERC, Folkedahl; 20(6). The intent of the,study was to determine'ifthe higher levels ofalkali materials'in the biofuel would**acce~~rate** 

### ' the deactivation rate' (which Dr. Benson concludes is already mtolerably high). The final report states: ','However"little is knoWn ofbiomass firing with low-ranked coals, such as North Dako,ta Lignites and Powder River Basin coals." The report concludes that)**a~thotigh** 

### they experienced operating diffic,u1ties, the deactivation rate appears to be 1.7% to 2.6% every 1000 hours. In'summary, Dr. Benson misread the work ofKhodayari regarding regeneration of.a1kalipoisoned catalysts. Both a careful reading .ofthe cited Khodayari paper and some ofhis, other , pUblicrttions confinn this, as does the Alst6ni paper and several recent papers by the, catalyst regeneration vendors (Full-Scale Catalyst Regeneration Experienye at the, Coal-fired Indiantoyvn

.GeI1eration Plant, Bullockand Hartenstein, October 2003· and Regeneration Advances, McMahon, May 2006) and a comprehensive SCR technology survey (The First 100 GW ofSCR in the 

## 0.s.- What Have'We Learned?, Cichanowicz, Muzio and Hein,**~006).** 

### He also misread the' Beck paper which, upon careful reading, does not shed much light on sodium poisoning, but rather, has a major focus?n phosphorus and potassium. Work by the Uniyersity ofUtah and REI' PRIVILEGED ENFORCEMENT INFORMATION Not for Release Under: FOIA or Other Information Release Statutes ,3

### further implicates potassium as having a greater poisoning.potential than sodium. Although the high sodium .content ofCenter Mine 'coal'ash is an economic issue (it will contribute to catalyst deactivatioIi); Dr. Benson provides no evidence that it will render SCR technically infeasible 

## at MRYS. . As a final note,.**sinc~** 

### catalyst deactivation due to alkaline materials is a "chronic," rather than . "acute" phenomenon, deactivation depends on the total time and mass exposure. This. dependency is probably not linear, since the overwhelming.amount ofash in anyinstallation does not deposit on the catalyst (it passes through the catalyst channels and ends up in the ESP hoppers 

### Or is emitted), but it is most appropriate to consider average values ofchemical poisons. 'Qrls is becausethe total exposure will be less tli,an the average for about halfthe time .and more than the average about halfthe.time. The overall deactivation rate "averages out" .. . .



### .. 3. Downtime for catalyst cleaning and change out.



### a boiler cleanirig outage, the SCR unit would only contribute one or tWo days" ofdoWntime per year.. Although the downtime durations for boiler cleaning cited by Minnkota are not long enough to permit a complete catalyst change out, they do in some cases approach the J 

### day turnarol,1nd that Flemming Hansen cited in the April 16, 2007 phone conversation with Region 

## 8personnel. Additionally, the boiler cleailing outages would afford the opportunitY for some cleaning ofthe' catalyst four times a year; a luxury not available at most year-roUnd SCR installations. This·.

. would contribute to both catalyst'life and lower pressure drop. Also·, during**discuss~ons** 

### with**S&L~** 

### their engineers pointed outthat the system can be designed to facilitate faster catalyst "

change out by providing wider than nonnal platforms at each catalyst layer level, thereby allowing replacement modules to be pre,,:,positioned as the spent modules are removed. Ifone assumes' a ratfiefextfemesfiotfcata1yst lIfe of

### one "yearamt tfthe 

### change-out iSCOOldiImtedwith 

### 4.' Stic.ky ash. 

### :Much light was shed on the topic ofsticky ash during the S&L presentation and discussi<?n. Sticky ash (in PRB applications) was described as having a steeper angle ofrep'ose (less slump) and thus tended to accurilUlate in large amounts on structural members and subsequen,tly falling. onto the tops ofthe catalyst layers in piles. These piles can not be readily broken down by· ·.soQtblowing (steam or horns) and eventually require shutdown for manual cleaning.. S&L's, engineering response. has been to eliminate flat, horizontal surfaces (weld

# an inverted vee 'on the tops·ofI-beams arid.angle-ironmembers that are .above the catalyst layers) and aim sonic**~oms** 

### at areas prone to ash accumulation.. When asked directly ifsootblowing (steam or horns) would effectively prevent plugging from the ash that is normally entrained··in the flue gas (not falling" accumulations) the answer given was "yes". 5.**EE~C** 

### pilot test procedures/design. 

### Page 7 ofmy previous memo (Christman, January 2007) contains a detailed discussion ofthe

. EERC test at the Coyote Station, all ofwhich remains valid. In summary, the catalyst**s~ould** PRIVILEGED ENFORCEMENT INFORMATION NoHor Release Under FOIA or Other Information Release Statutes 

### 4have· been clearied:with somefrequericy so that it could be continuously exposed to

### fluegas~ Tests ofthe scale at Coyote' are not useful in determining plugging potential and the attempt at

. simul;:t.ting sootblowing was liot effective. By EERC's own admission (and confirmed by Hansen' .

.dUring the April 16, 2007 call) the plugging was a

### r~sult ofash accUmulations faIling onto the catalyst (see "sticky ash", above). 

### Mr. Hansen also confirmed that

# the catalyst pitch at Coyote (6 mm) was too small. S&L presenters suggested' that a '1 0 mm pitch might be required for North . Dakota Lignite applications;' .' . 

### In my January memo and at the May 2Jd meeting, 

### I stated that 

### the Coyote test was' so·.flawed that 

### it did not provide any meaningful data bearing on the issue oftechnical feasibility.' During the . 8&1., disctission on May 24 t1\ Bill DePriest was asked, by an NDDH-participant, what he thought ofthe EERC test at. Coyote. Even though he was clearly uncomfortable criticizing the work of another organization, he stated that the test produced no useful information. 

### 6. Splitair preheater. The discussi(;:m ofthe .spl.it air preheater approach contained in the Minnkota March 

### 19th document seems a bit ambivalent,**imply~ng** first that it couldn't be done·and later stating that conceptually, it could be done (page 15, Minnkota, March·2007). Further evidence that it is not

. infeasible 

### is found in'the Hict that the SCR retrofits a New Madrid (two large,**PRB~fired** cyclone

boilers) included replacement ofthe tubular air preheaters with new regenerative air preheaters . with enamel-coated baskets. 

### I do not believe that B&McD·indicated infeasibility**d~ng** the meeting on May**23~d,** but they did insist that BACT would not reqUire substantial rebuild of the source (boiler). 

### 7.B&McD low.dust 8CR 

### assessment. I 

### am**~ot** qualified to comment on the B&McD discussion ofthe steam'extraction forflue gas. reheat for the low 'dust application. 

### I do not ,believe that resort to the low dust approach is warranted, since ash issues should be manageable. 

### 8.**Texa~** 

### Lignite comparison. George .Offen's letter (EPRI,September 7,2006) provides some useful insights, particularly with

. regard to erosion. S&L**p~rsonnel** confirmed that Texas Lignite ash is more erosive that North

Dakota Lignite 

### ·ash. This :means that the TXU pilot test currently underway should resolve any concerns regarding erosion at a future MRYS SCR installation.. 

### 9. SCR 

### vendor quote request..

. . The volume'ofinformation provided in the B&McD vendor quote request will be troubling to the vendor's sales staffsince they are not likely to invest a great deal oftime in something that is . clearly not meant to generate a sale in the foreseeable futi.rre. Also, by including a discussion on . the enforcement situation, it is clear that the requestor is looking for support for the technical. infeasibility argument. The ability to provide flue gas at the appropriate temperature is not PRnnLEGED ENFORCEMENT INFORMATION Notfor Release Under FOIA or Other Information Release Statutes 

### 5

### discussed and**t~e** 

### startup/shutdown requirements 

### may be unreasonable. I dQ not expect the exercise to produce any meaningful results.

PRMLEGED ENFORCEMENT INFORMATION Not for Release Under FOIA or Other Information Release Statutes 

### 6.

### ENCLOSURE RESPONSE TO ·EERC AND C AND B&McD's MARCH 17, i007 LETTER RESPONDING TO EPA REGION 

### VIIi COMMENTS JANUARY 

### 8, 2007 1. Introduction

### au"dSu~mary of

### EPA's Preliminary Analysis



### .EPA's January 8, 

### 2007 Comment:.

. . . EPA isprei,minary analysis is that the'B&Mstudy lacks sufficient information within the BACT analysis. Specifically, the study excludes Selective Catalytic**R~duction($CR)** as a technically feasible control option at step. 2 ofthefive-stepTop-Down analysis, while notpresentingNO x conirol effectiveness or catalyst activity data. As a result, .B&M fails to rankSCR against other control options in terms of control effectiveness at step3, andfails' to analyze costs ofSCR versus other control options at step 4. EPA questions the reasons citedby B&Mfor technical infeasibilityofSCR Furthermore, based' (In a survey ofSCR vendors described later in this report, EPAfound there are vendors that will offer' performance guaranteesfor this type of application. Further information shouldbe requested, to support the analysis with resp(fct to SCR

. .' . 

### B&McD's March 13; 

### 2007Response:

... ,... The EPA's NSR Manual does not;pecijically define

## rheoperatlngpara~eter orpeiformance . measure that aparticular NO x control technique or technology would have to achieve to satisfY "a technicg!**ass.r~s§rnent** coilsidering..JJ.hx.,slcgl", chemicaland£Engineering 12rincjple§. qnd/or**eml!iri~al** data showing the technology wouldnotwork on the emissions urlii under review or that unsolvable technical difficulties wouldpreclude 

### the successful'deployment of the**tech~ique"** in order for said alternative to be excluded 

## [rom further consideration. . . . . '. .

. The severe accumulation of ash andblinding in the Coyote station slipstream SCR catalyst field test after 2 months was documented in Dr. Benson's referencedtechnicalpaper . .The evident failure of the Coyote slipstream SCRcatalystfield test to avoidsevere-.catalystfouling andash accumulation ledBurns & McDonnell to believe that ifsuch results wereroutbiely encounteredat afull-scale high-dust SCR catalyst installation during operation on a North 'Dakota lignite-fired cyclone boiler, aggressive on-line cleaning and/orfrequent extendedforcedoutages wouldbe neededto remove ash accumulation or. remove the catalystjor cleaning in ordertorestorefull unit output andcatalJl$tNO x reduction effectiveness. Either or both of these maintenance activities coulddamage the catalyst and/or require it . to be frequently replaced. .

Two monthsbetwe.e.n SCR c.atalyst maintenance activities

### wo~k/be 

## an extremely short operating' cycle time comparedto 36 months typically experiencedat other. $CR installations. Burns & McDonnell interpreted these field test results 

## as "empirical data showing the technology wouldnot work on the. emissions unit under review" for technical infeasibilitypurposes. Eliminating technically':'infeasible . alternativesprior to rankingthefeasible controls based upon control effectiveness, andthen evaluating the impacts'of implementingonly feasible control techniques and technologiesfollows the BACT .**process~.;** .... ,

EPA Response to MinnkotaComment Letters from March 19, 2(l07 and April 23, 2007 BACT Analysis at MRYS 

### EPA Response: 

# As articulated inthe Jamiary26, 2007 letter related to other widely-used NOx control .. options that were eliminated in Minnkota's BACT analysis'based on technical ip.feasibility, EPA, believes the Minnkota BACT analysis for SCR should begin with the presumption that SCR is technically feasible, since the technology haS been widely demonstrated on utility boilers.. This presumption is. based oil the "techno,togy transfer" discussion· in lhe NSR Wo.rkshop Manual,,)

. other-EPA**guidancedo~timents,2** andOthe' facfthat'hundreds ofSCR systems have been .

successfullyinstalled on utility boilers worldwide. ,The NSR Workshop Marillal and

### oth~r EPA .. guidance clearly piaces a substantial bl!fden ofproofon the applicant to show that, based 

# oua . comparison ofthe .:physical and**chemi~al** characteristics ofthe exhaust gas stream under -review . and the sources to which the technology had**be~n** previously applied, the technology would be technically infeasible. 

### EPA agrees that the NSR 'Workshop Manual does notspecificaliy define.. the operating parameter or perfotrilance measure that a partIcular NOx contiol technology or

. technique would have to meet in order to satisfy the criterion. However, given the sheer number
, ofsuccessful SCR systems in operation at utility boilers today; EPA believes this burden ofproof

is cOD:siderable onthe part ofMinnkota and should include quantitative 'evidence that such. unresolvahle differences do exist that would renderthe technology unsuccessful at controlling 

## NOx• .

. The qualit.ative evidence provided to date by:B&McD and EERC demonstrates that there. are certain factors relevant. to MRYS that will requireengirieering design considerations to make

· an SCR installation workable; however,'considering ea,ch SCR system design for**a~pecifiC**

facility has tobe customized to some extent, this situation is hardly unIque. Additionally, rl9thing has beenprovided that would demonstrate that SCRwould be an ineffective means of NOx control at MRYS. 'B&McD's beliefis that the pilottest results from Coyote Station show, that a full-scale SCR installation at MRYS would require "aggressive on-line cleaning and/or 1 See NSR Workshop ManualpageB.19: "Unless significant differences betWeen source tYpes exist that are pertinent to the successful,operation ofthe control device, the control option is presumed to be technically feasible unless the source can present information to',the contrary." (Emphas,is added) . ,.' , 2 See June 15,.1989 letter from Gary McCutchen (EPA Office ofAir Quality Planning and Standards, New Source Review Section Chief) to John Daniel (Department ofAir Pollution Control, Commonwealth 'of Virginia): "Another

. point worth mentionjng is the area oftechnology transfer. We have heard that some applicants are attemp.ting to

· define gas streams and source types far more narrowly than common sense would dictate irian effort to avoid certain controls. For example,an applicant might saythatNOx controls have been applied to a 30 and 70 MW coal boiler, but not a 45 MWcoal boiler; thatthe control. technology has been applied to pulverized and fluidized.bed linits; but ' not to spreader stokers; or thatthe technology has never been applied to the particular mix of, say wpod and coal planned for that unit. Such arguments should be closely scrutinized and the applicant should explain fully not only ,what is different about the gas stream (ifthecontr<>l tecbnologybeing analyzed is an add-on¢ontrol), but also why'

·that difference pre.cludes transfer of that controltechnology to the proposed source, .

## The burden ofproofshould be relatively high in order to prevent circumvention ofreasonable technology transfer by the selection ofSome slightly different unit." http://www.epa.gov/Region7/programs/artd/air/nsr/nsnnemos/finlbact.pdf 

### -2- " I,EPA Response to Minnkota Comment Letters from March 19,2007 and April 23, 2007 BACT Analysis at MRYS frequent extended forced outages." While this may·or may not be the case, such conditions do not undennine the conclusion that SCR should still be considered technically feasible. 3 EPA did ackrtowledge that such real costs associated Withoperational realities ofthe boiler and-"fuel type in an SCR application at MRYS can be accounted for through the costevaluationunder step 40f the BACT analysis. 4 .EPA does not view additional

### mainten~ce and operational measures that would be required at MRYS· compared to other·facilities to bejustificatiqn oftechriical infeasibility. Again, the bUrden ofproofis considerable in the case ofdemonstrating infeasibility ·ofSCR for autility boiler due to the large number ofSystems currently in operation at utility

· boilers. . B&McD has apparently interpreted the pilot testing experience at Coyote Station to mean that an SCR installation at. MRYS would require "SCR catalyst maintenance activities" every . two months and thatthis constitutes "empirical data showing the-technology would not work on the emissions unit under review."s B&McD states that this time period "would be an extremely short operating cycle time compared to 

### 36 months typically experienced at other SCR installations." EPA d.oes not believe B&McD' s· use ofthe Coyote Station pilot testing ·.maintenance requirements is an accurate means ofpredicting· full-scale maintenance . .**requirements~** The EERC·report indicates that aggressive catalyst cleaning and maintenance

measures were also taken at the Baldwin and Columbia Stations during the initial months ofthe pilot testing and that significant ash acc.umulation, catalyst plugging,. and pressure drop increases occurred during the c(;rurse ofthe six-month test at both facilities. Baldwhi and Columbia·**Statipn~** both bum·P·Iill**co~l1,·** which·is also·humedat

# many· full-scaleutilityhoilers currently o-perati·ng SCR systems. with typical maintenance cycles.· EPAbdieves B&McD'g conclusions regarding the use ofthe "empirical data" from the Coyote Station pilot-scale testing is not relevant fOf an anaiysis oftechnica:I feasibility, and fails to consider the observations on catalyst niaintenance frequency and pressure drop trends from the Baldwin and Columbia Station pilot tests. A comparison ofthesefindillgs for all three facilities is presented below'...

. .

.During the testing at the Baldwin Station, "(a)t 2-month intervals, a section ofcatalyst was . removed and replaceCi with a new one.,,6 The nan-ative indicates that catalyst plugging at .

· Baldwin had also occurred during the first two months, as the "pressure drop steadily

·**incre~ed."** 7 The report describes that during the remainder ofthe test (months 2-6), pressure drop was highly variably but maintained within a range of

### 0.6 and 

### 0.8 inches ofwater "due to the installation offresh catalyst section and leaving two thirds ofthe catalysts in place that were :3 -See pages B.l9and B.20 ofthe NSR Workshop Manual:**~'Where** the resolution oftechnical difficultie!! is a matter ofcost, the applicant should consider the technology as technically feasible." . 4 See page 6 ofEPA Region 8 Preliminary Analysis ofBums and McDonnell BACT Analysis for Nitrogen Oxide at Milton R. Young Station, Units 1 and 2, January 8, 2006. 5 See page B.20 ofthe NSR Workshop Manual which indicates empirical data can be used in making determinations oftechnical feasibility., 6 See Appendix B, Page 19 ofOctober 2006 Minnkota BACT Analysis Study for MRYS. 7 See Appendix B, Page 19 ofOctober 2006 Minnkota BACT Analysis Study for MRY8. 

### -3-EPA Response to Minilkota CommentLetters from ' March 19, 2007 and April 23; 2007 BACT Analysis at MRYS partially plugged. The gas veloCitY inthe single

### ~e~tion ofnew, clean catalystwas high because ofchanneling, and the result pfthe high gas,flow was less deposition and accumulation. Gas "

### veloc~ty has a significant

### ir.npa~t**~n** the

### ~otentlal for deposits to fomi.

### ~owe~,er, at high

### ga~ velOCIty, low NOxconverSIon IS lIkely." Hence, based on B&McD's reasomng, the SCR pIlot testing at Baldwin would provide' empirical evidence demonstrating that a full..scale SCR '
, installation on PRB facilities wouid be infeasible, especially at the typical 36.:monthoperatini '

cycles for majormalntel1ance. 

### IIi. fact, the EERCrepoi1: suggests that when a section ofcatalyst at Baldwin was changed**ou~** every two months to deal with the increase in pressure drop caused ,by plugging, low NOxconversion for the SCR would be likely. Based ori the'catalyst maintenance requirements and pressure drop data, B&McDwould presumably concludethat the pilot testing at Baidwin Station showed that

# a SCR system, operating()n

### PRB~oal would require, significant and frequent catalyst**maint~nance** and replacement and**tha~** the NOxreduction would be limited, much like the results ofthe Coyote Station testing. ' The final test report describes the catalyst reactivity test results forcata:Iyst samples at 2,**4~** and 6 months ofoperation at Baldwin Station. 9 The two month sample "had no noticeable loss ofreactivity compared to the reference catalyst. After four months,'the reactivity was 96% ofthe reference, and aftersixmo'nths, therea.ctivity had ,dropped to 84% of the reference catalyst" 

### It does not appear thetels any real correlation between the pressure'drops observed at Baldwin Station and the measured activity ofthe catalyst. The pressure drop did not steadily Increase as the reactivity decreased during. the 4 anq. 6 month**intervals~** while there were some temporary variations, the pressure drop throughout the test was in the range of0.6-0.8 inches ofwater. The most prolonged period during which the pressure drop was higher than 0.8 inches ofwater was

.during the 'first two mOriths, when no deactivation occurred: ' , For the ColUmbia Station, there was also aggressive reactor Cleaning and catalyst' replacement within the six-month period ofthe test. The EERCreport 'in Appendix B' ofthe Minnkota BACT Analysis does notprovide as much information as is contained in the 

### Fuel Processing Technology article describing the same pilot testing. 

### ThePuelProcessing' , Technology article includes a graph ofpressure drop for the entire' six months oftesting, whereas'

. the Appendix BEERC report only shows the pressure drop graph for the first two months of

testing. It is unclearwhy this additional data was not part ofthe Appendjx B report,but the entire data set does show there were significant increases in pressure drop after the first two months ofthe test. According to 

### the:Fuel Processing Technology article, there Was "a rapid increase in pressure drop across**~he** catalystat about 3000 h .ofoperation, and aggressive pulsing brought it doWn to·O.4 in. ofwater until the catalyst section was changed out at about 3200h. After cleaning the reactor and replacing one catalyst section, the pressure drop**~as** about 0.3 but 8 See Appendix B, Page 19 ofOctober 2006 Minnkota BACT Analysis Study for MRYS. . 9 Final Report for JV TaskJ I - Evaluation ofPotential SCR Catalyst Blinding During Coal Combustion and' AddOn: Impact ofSCR Catalyst on MeI:cury Oxidation in Lignite-Fired Combustions Systems, November 29; 2004,

. page4I. ' 

## -4-EPA Response to Miririkota Comment Letters from March 19, 2007 and April 23, 2007 BACTAnalysis at MRYS 

# . increased to over 0.6 in of:water up to about 4100 h. There 'Yasan outage at the.plant, and . aggressive pulsing ofthe reactor was conducted; the pressure drop was brought back down to 0.3 but rapidly increasedto over 0.5 in. ofwater within 500 h."IO Most ofthis paragraph describing the entire 

### 6 months ofthe test does appear in Appendix B ofthe EERC report; with the exception ofthe first sentence; . 

### In any caSe, it :appears as though significant plugging aiso occurred during. the Columbia Station pilot test that.required aggressive on-line Cleaning and 'catalyst . replacement. The problems first appeared at about fo"!ll' months and then reoccurred in much shorter time intervals. These time frames, while longer than that observed at Coyote Station, are . obviously much shorter than the 36-month operating cycle described by. B&McD for normal SCR maintenance. . . Additionally, Columbia Station catalyst reactivity testing showed 93% reactivity at two months, 90% at four months and 90% at six months. 11**Agai~** there does not seem t.o be'a clear correlation between pressure drop readings through the six months ofpilot testing at Columbia Stationand the catalyst reactivity testing. During the first two months, pressure drop readings weregenerallybetweenOA and 0.6 inches ofwater. During months two through four, pressure 'drop was generally**higher~** between0.6 and 0.8 inches ofwater. During the final two months, pressure drop was more varied, but generally between 0.4 and 0.6 inches ofwater. It does not appear that there was anY .clear relationship between degree ofpressure drop and the level of**re~ctivity** retained by the catalyst. Furthermore, while the "Columbia Station showed more . signifiCant accumulationandplugging

### th~the Baldwin Station,',12 the catalystreactiyityfor Baldwin Station"decreased morethan at Columbia Station over the courseOnneslX iriontns**of~·~~·~· ._-.-.~~_**  ..... pilot testing (84% vs.90%). Again, itdoes notappear that the qualitative observations from the pilot:studyfor.Baldwin andColtimbia Stations correlate well with the catalyst reactivity testing

.results, which were not included in Appendix B ofthe MinnkotaBACt analysis. For the Coyote Station, EPA agrees that the plugging and**pres~uie'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 that sodium was afactorin the plugging 'atCoyote, where

### itdid not appear at the other two facilittes.· However,· EPA disagrees that these test results can lead to a conclusion that . extended forced outages would be needed at two month intervals as stated by B&McD in· . Minrikota's 'March 19, 2007**letter~** 13 The results ofthe catalyst deactivation testing at Baldwin

. . .' . . 10 See Page 594, Fuel Processing Technology 86 (2005) 577-613, "SCR Catalyst Performance in Flue Gases· . Derived from SUbbituminous and Lignite Coals" (Accepted July 2004) . .. II BabCock-Hitachi K.K "Test Results of Catalyst Samples for Energy & Environmental**Rese~ch** Center", April, 2005, Table 3. '. 12 Final Report for N Task 31- Evaluation ofPotential SCR Cataiyst-Blinding During Coal Combustion and AddOn: hnpact ofseR Catalyst on Mercury Oxidation in Lignite:"Fired Combustions Systems, Noveinber 29,2004, .**~~.** . 13 page AI-30 ofOctober 2006 Minnkota BACT Analysis Study for MRYS**indic~tes** that the anticipated catalyst life for SCR at MRYS would be 2-12 months, "requiring extended, frequent outages for replacement." 

### -5-, ' '
EPA Response to Minnkota Comment. Lett,ers from March 19,2007 lind April 23, 2007 , BACT Anil1ysis at MRYS ' 

### and

### 'Coillinbi~**~tations** showed no clea,r correlationbetween magnitude ofpressure drop and the
, degree ofca,talyst deactivation 

### at each plant. Also,**th~** 

### qualitative. observations on catalyst,',·

plugging did not correlate to the degree ofcaJalyst deactivationfor..Baldwin and Columbia Stations relative to one another. Furthermore, given**th~tthe** 

### two facilitiesbtuning PRE cmil required $imilar maintenance measures and schedules to Coyote**Station~** 

### EPA questions how the .maintenance activities' (and their tllneframes) required during the pilot testing at Coyote Station

. 'can be significantly distinguished from the BaldwiIi and Columbia Stations burning 

### PR.J;J coal.. '

EPA does not agree that it is correct to defIne catalyst replacement requirements associated with·' full-scale SCR at MRYS based on the pilot testing expenence at Coyote 'Station. ' Additionally, based on a July 2, 2004 conversation between Jim Stalldt ofAndover . Technology Partners and FlemmingHanse.n**ofH~l1dor** 

### Topose, the sudden build up offlyash on the catalyst face that occurred during the piiottesting.at Coyote Station was ,determined 

# to be caused by theaccumulatjon. ofash upstream ofthe catalyst and sl\dden dropping orthat ' accumulated ash onto the catalyst fac.e. 14 

### Thus, the initial pressure drop experienced' during the pilot test atCoyQte Station might have been.largely due to cOl1ditions that would notexist,and/or could be avoided through design, on a full-scale application ofa**SC~** 

### system. This further calls intoquestion the applicability ofthe**pres~ure** 

### drop**trendsexperi~nced** 

### during the pilottestingto . full..scale SCR applications and their catalyst maintenance requirements. . Based on the above comparison orthe pilot testing results presented by EERC, it is unclear.. to EPAthat any definitive conelusions cali be extrapolated from the results about SCRtechnical feasibility aridlof the timing or extent. ofSCR maintenance**requir~ments** 

### and boiler, outages for . these threefacilities, as waS done 

# by B&McD for MRYS. Clearly, the two facilities operating on PRB coal experienced catalyst plugging that required extensive

# and aggressive cleaning . measures within timeframes that, ifapplied directly to anticipated maintenance at full..scale operation, would not be consistent with real full scale experience at ntmlerous.boilers burn,ing . PRB coal. EPA'knows that there are**suc~essful ~pplications**  

### ofSCR systems to**~tility** 

### boilers burning PRB coal. Hence,EPA does not believeit is reasonable to directly apply the catalyst maintenance and replacement experience fronl the**pilo~** 

### test to ,a**full~scale** 

### . application at MRYS.· . Based on B&McD;s assertions about

## expe~tedmairite~ancer~quireril~nts and schedules for MRYS based on the Coyote results, a facilitybuming PRB would also be expected to encounter significant plugging, which would require aggressive on':linec1eaniilg, catalyst replacement, and forced boiler outage periods within the initial months ofinstallation: EPA knows from experience that the issues facing facilities burning PRB coal, while real and significant, have been dealt with successfully. Therefore, 

### EPAbelieves the pilot testing was either designed in a way that does not accuratelyreflect full-scale SCR catalystpluggingandlor mitigation measures 14 August 20, 2004 Memorandum from 

### Jim Staudt (Andover Technology 'Partners) to Sikander Khan (EPA), "SCR catalyst testing on ND Lignite" 

### -6-EPA Response.to MinnkotaComment Letters from , March 19, 2007 and April 23, 2007 , BACT Analysis at MRYS 

### currently khown to exist, or that additional measures could have been. taken beyond what was attempted'during the pilot testing to keep the catalyst face clean and mitigate the'effects of catalyst plugging. To that end,**a~thoJ1gh** 

### it was mentioned in the preliminary EPA comments; B&Mcb**h8$notprovicl~d** 

### a response to EPA's statements regarding the normally observed pronounced ash deposition during pilot ·testing, the small catalyst pitch used at Coyote Station alid how a larger pitch might**hav~affected** 

### the test results,. and how the air pulsing did not properly represent sootblowing capabilities on a full-scale SCR application. In sumriiaiy, EPA ' does not agree with conclusions drawn from the pilot testing presented in Minnkota; s March 17, 2007 letter related to catalyst maintenance and replacement.requirements and the related forced boiler outages to accommodate these activities. As an alternative to relying on these pilot test results, it would be preferable for Minnkota to work with catalyst**~d** 

### SCR design companies to analyze how the sodium deposition at MRYS would affect catalyst maintenance and replacement requirements and schedules. " . 

### EERCMarch 19,2007Response:

. . .... . . 'We spoke to Flemming Hansen of Haldor Topsoe, an SCR catalyst vendor, regardingproviding performance 'guarantees. After,describing the characteristics ofCenier lignite, specifically issues related to sodium, they were very concerned regarding guaranteeingperformance. Basedon the conversation, it

.became evident that EPA representatives may hdv.e not indicatedthe levels of sodium and the form of sodium in the coal. Haldor Topsoe indicatedthat the sodium wasa major concern and that it causes**~~~~~. rldeactivati~peciaH)rlhevrganicaHj"tlss(}eiaterJ-for~ky1ndieated~lhttt--therhaehom~)tperienee~~~**  and found significant deaCtivation of coupon samples after 6000 to 7000 hours of operation with a coal having elevated levels of sodium. 

### EPA Response: ,

, EPA also spoke with Flemming Hansen regarding the feasibility ofan SCR installation at MRYS andthe nature oftheSCR pilot testing at the Coyote Station condllcted by EERC., EPA asked Mr. Hansen about the effects ofsodium onBCR catalyst**performance~** 

### Mr. Hansen said the sodium ion can poison catalyst because it prevents the ammonia from interacting 'with it. He also estimated that sodium catalyst poiSoning limits the life ofthe catalyst to roughly one year. At that point, the catalyst wbuld need to bereplaced 'or washed/rejuvenated. ' 

### ,Mr. Hansen inditated**th~t** 

### the only exp.erience"Haldor-Topsoehas had with lignite coal was the pilot testing performed at the Coyote Station conducted by EERC. However, they did run some catalyst ''test coupons" at the Wisconsin Electric Power**(~Energies)** 

### Presque Isle Station, which bUrns Powder River Basin coal with sodium levels similar to North Dakota lignite. Mr. Hansen recollected that there was a significant difference in the deactivation ofthe test coupons upstream 

## ofthe particulate' control device,.(ESP) compared to downstream ofthe' ' ESP at Presque Isle. 

### -7-EPA Response to Minnkota Comment Letters from March 19, 2007 and April 23, 2007 ..

. BACTAnalysis at MRYS· 

### Mr. Hansen said he recalled there were problems during the Coyote Station pilot test' , 'lJeci:uise,the reactor became quicklyplugged with flyashcausiDg rapid iricreases in pressure' drop.,
, Mr. ,Hansen said that the pressure drop was mainly caused by diu::t-:wallashaccumulations, . , dropping on the catalyst face. 'Mr. Hansen**recall~d** 

### that problems with tlle,sodlum poisoning
,**'~ere'secoridary** 

### compared to the ash plugging problems.**H~,stated** 

### that ash plugging is,a·"

problem of**pllot~scale** 

### testing and would not be a real full,;,s¢ale application Issue. He, said thafhe was aware, that actual operations at plants buiiling PRB coal peffonn much',better than the pilot ' tests would indicate. " " ' Mr. Hansen said that, in hindsight, the pilot test sh6uld have been performed differently. Mr. Hatlsen stated that" changes to the pilot test at Coyote Station, 'such as the use'ofa higher pitch catalyst, could have helped reduce, but not entirely elIminate, the impacts ofash plugging: Additionally, he said the pilottest d,id,not have good simulation offull-scale sootbloWIng. 'Ifthe ' test were to be redone, a better effort could also be made to keep the catalyst face dean.

. Mr. Hansen said the pilot testing at Coyote Station was inconclusive in terms of determining Whether SCRwould be technically feasible on North Dakota lignite. Mr. Hansen

. saidthatpilot te$ts often have problems that can be**o~ercome** 

### at the full scaie. Mr. Harisen said', that Haldor Topsoe wouldnot'rule out bidding ona project that involved North Dakota lignite and that they would primarily look at the computer flow modeling for the specific coal analysis and boiler and evaluate whether there are available mitigatIon options to address,any significant ' technical issues indicated by the analysis. Mr. Hansen said that there "are niany tools in the toolkit" to address SCR technical issues. For North Dakota lignite, with 'its high ash and sodiUm content,**Mr.,H~lJiSen** 

### said that Haldor Topsoe would likely consider,such options as screens, very , good soot blowing (steam assisted) and a high catalyst pitch. Mr. Hansen said and/or implied

that an SCR could be designed to work with the specific characteristics ofNorth Dakota lignite through proper reactor**sizing~pitch** 

### sizing, steam soot blowing, and proper regeneration schedule: ,He 'gave a rough estimate that the SCR system could be designed (larger) to '
, accommodate'a catalyst replacement schedule, ofabout every-year. 

### EPA asked Mr. Hansen how he would weighthe results ofthe pilot testing at Coyote ' '
, Station.**Mr~** 

### Hansen said that he would have to go back and look at the Coyote Station test ,

results and see ifthere was any useful information to consider. Mr. Hansen**~mid** 

### and/odmplied that the coal profile, information and the results ofcomputer flow modeling would be more, ' critical than the Coyote, Station pilot test results in**~y,** 

### evaluation 'ofbidding a project With North Dakota lignite. . ",



### -8-EPA**Re~ponse** to Minnkota Comment Letters from March 19,2007 and April 23; 2007 BACT Analysis at MRYS 

## Mr. Hansen was unaware that Haldor 'Topsoe sent

## em~ils to' EPA HeadqUarters stating that Haldor Topsoe (and two other catalyst vendors) could provide guaraIitees for the MRYS coal.. However, he sent an email t9 a consultant to EPA in 2004 statmg in general they could propose SCR catalysts for North Dakotalignite assuniing certain criteria are met. He had also talked With that consult(,liit at that time about the fact that pilot plants have problems that full-scale SCR systems do not. . . .... . 

### II. EPA Case-Specific Review ofBurns & McDoimell &'EERC Technical FeasibilitY Analysis for Selective. Catalytic Reduction**'A~** 

### High-Dust SCR B&M has eliminated

### Uigh~Dust SCR as technically irlfeasible due to issues described below. B&M'sanalysis utilizes a report by the Energy & Environmental Research Center (EERC). EPA's response on each issue isalso presented below. 

### 1. 

### Ash Deposition Issue Raised by Burns & 

### McDonnell: EPA's January8, 2007 Comment: The concern about high amounts of 

# ash material causingblinding of macro-pores in the catalyst is real but solvalJle.8trides incatalystformulations, catalystmimagement systems. andrecently, catalyst regeneration processes, have all combinedto lower the overall cost contribution of both initial and replacement catalyst in modeni SCR systems. . . . 

### EERCMarch 19, 

### 2007Response: EPA states that the high anlOunt of ash materials causing blinding of macropores in the catalyst is real but solvable. We spoke to Flemming Hansen of Haldor Topsoe, a catalyst vendor, regarding what has been done to deal with theproblems of high-sodium coals with regard to advancedfotmulations and catalyst regeneration, andhe was not aware of any work thathadadvancedSCR systems for hlgh-soc(tum applications.. .

.. Regeneration 

### h4s been attempted in Europe 'with SCR catalysts exposed/o biomass with high'K

_ (similar in chemistry to Na), andthey hadsome significqntproblem In recovering reactivity.



### -9-EPA**Resp~nse** to Minnkotit Comment Letters from· March 19,2007 and April 23, 2007 BACT Analysis at MRYS



### · B&McD March 

### 19, 2007

### Response:

. It is unclear whetherEP A 's claimedSCR catalyst improvements citedwould translate i1'lto preventing the catalyst layersfrom being susceptible to macro-pore blinding and plugging by calciumbasedcompounds 

### andthe impact on the individual catalyst reaction sitesjromsodium:'basedcompounds· discUssed in Dr. Benson's referenced technicalpaper.· The EPA cites nopublishedtechnical literature . that describes the results of testing that definitively documents how longcurrently available SCR

· catalysis c(m survive and provide effective NOx reduction when exposedio thejlue gas and jlyash constituents exhaustedfrom combustion cmd.operation of any cyclone boiler firing North Dakota lignite, particularly one located in a high-dust, hot-side application such as would be the case atMilton R. Young Station.· .



### . . EPA Response: . As described earlier, the burden ofproofis on Minnkota to demonstrate SCR would

### b~ technically infeasible at MRYS. The BACT process does not requirethat the reviewing agency demonstrate that a technology would work for the exact type ofinstallation under review, especially when the technology has been well documented to be technically feasible for the

· source category under review. EPA had asked

### Minnkota.t~ look ii.n1her into the engineering solutioriscurrently available anddetertnine**whet~et** 

### or not the macro-pore plugging issues described in the EERC report could be effectively managed. It 

### does not appear that these engineering solutions were given

.. rriuch consideration. Without addressing the available engineeririgsolutions to deal with·macfo-:·

· pore blinding and plugging, MlnnkQta has not met the significant burden ofproofdemonstration

EPA believes is requiredfor showing SCR is nota technically feasible contro(option forNOx 

### at MRYS. .... 

### a. . Comparison ofMRYS to SCR Systems Operating on Powder RiverBasin Coal

. . .



### EPA's .January 9,2007 

### Comment: Even though the chemical compositions of PRB ash and CenterMine coal ash are very similar, particularly for the specific constitl!ents of concernfor catalyst deactivation, the quantity of ash in the Center Mine coal is more than twice as high on aper MMBtit basis. However, for a cycloneboiJer, only**-lO~**EPA Response to Minnkota Comment Letters, from
, March 19,2007 and April 23, 2007 BACT Analysis at MRYS

. ., . about 30-50%'of the ash ends up as fly ash at full load (less atlower loads) and for a wall or corner-jired pulverizedcoal boiler (PC boiler); about 80% of the ash ends up asflyash. 'The result is thatSCR catalyst in a PC boiler PRB application is exposedto similar quem/ities of the major constituents of ' concern (alkaline material) as a catalystwould be exposedto atMRYS. The B&Manalysis also suggests that a linear comparison of theoretical total ash or aSh constituent rates to SCR catalystdeactivation " rates can be made. AlthOl,fgh EPA does not believe this to be the case andB&Mhas not presentedany evidence of a quantitative relationship between ash loading andSCR catalyst deactivation rates, EPA has, nevertheless examinedB&M's argUments related td ash loading.

, Table 1 below shows a comparison of the total ash loadingfor different boiler designs for North' Dakota lignite, assuming a reference unit of 1.0 IblMMBtufor lignite, lignite 

### will have twice the ash ' content 

## on a per Btu basis, and the conversion toflyash will be 30-50% for cyclone boilers and80% for PC boilers. As can be seen from this comparison, the theoretiealflyash loadingfor aPC boiler firing , ,PRB boiler (OAlbIMMBtu) will be in the same range as what woitldbe expectedfor a cycl(1ne boiler firing North Dakota lignite (0.3-0.5IbIMMBtu) .... ;.. Deactivation depends on the total time andmass exposure, and the PRB PC boiler data are extremelyrelevant to evaluating SCRfeasibility for North Dakota lignite ... :.... Table 1 shows that; on a IblMMBttl basis, total theoreticalflyash loading at the economizer exit of d cyclone boiler firing lignite would be very similar to thalola PC boiler firing PRB coaL ' Another alkaline constituent that has been a concern is calcium, whiCh can react with S03 toplug' pores 

### dS caS04 • This has been q much-studied problem and the mechanism involves the calcium- ,**~~~~~cOJ:JtainilJgp.adick.gettjl1g** "(;fJJ,JgbLlnJLm£lC,ro·pore-fJithe ,catal)!.standsubsequentl)!. reacting with SO; , in theflue gas. ' The 'resulting CaSO4particle is larger in volume than the CaOparticle a;u!, in essence, swells tofill thepore PRBcoal has been shown to have approximately 30% more caldum in its
, ash comparedto North Dakota lignite Other alkaline materials (potassium, sodium and

magnesium) deactivate catalysts by deactivating individual reaction sites'rather.'than the blinding by macro-poreplugging that was described for calcium. The average Center Mine coal ash content for these alkaline constituents is about 9%.. : Thispercentage is somewhai!Qwer than mostPRB coals andwithin the envelope of experience of European installations; One of the referf!.nces cited in the Appendix B EERC report, Cichariowicz & Muzio (2001), places the range of European SCR experience with these alkaline constituents at 8% to 15% of ash. Thus, the coal usedat MRYS has similarpoisoning potentfalcompared to othercoals in use at,SCR-equipped boilers in Europe andthe U.S... .. .. , ..... The concern about high amounts of alkaline materials in Center Mine coal expressed in B&M's BACTanalysis anddescribed in the AppendixB EERC repor,t isreal, though notnecessarily unlike ' operating SCR systems on PC boilers burning PRB coal. As explainedabove, we believe there is value in successful operating experience realizedat currentSCR instal/aNon at PRB-fired powerplants. The problems cited in the BACTanalysis are being dealt with at severalNO x'SIP Call SCR installations today. In addition, the analysispresents no quantitative analytical information derived from the firing of lignite coal on SCR catalyst deactivation tojustify thefinding that SCR is l1ifeasible.



### -11-. . EPA Response to Mi",nkota Comment LetteJ;S from March 19, 2007 and April 23, 2007

. BACT Analysis at MRYS 

### EERC's March 19, 2007Response:

. . . The sodium and.ash contents of Center lignite are significantly different from 

### P RB coais. EPA.
, indicates thdt theproblems.of deposition will decrease because the cyclones take out Some· of the ashas : slag but for "ligillte, cyclones create additiwuJIdepositionprob.lems downstream. The cyclones partition the more refrt;Jctoryash c(J!flP(Jnents into the slag andthe more volat!lecomponents into thejly ash. . Th(!! jlyash becomes enriched in c011Jponents that vCiporize and.. sZ!bsequently, condense upon gas cooling to, . form liquidphases andsmaltparticles that are very reactive to ga.s-phase components thcit'cause .. bonding.· .. . EPA· discusses ash loadings cmdthepotential impdcts on SCR

### performance~ They also d.iscuss the formation of calCium sulfates that canplugpores in catalysts as well as the impacts of other alkaline materials (potassium, sodium, andmagnesium) and theirp,otential to deactivate individual sites rather than blindingpores. . They fail ta recognize theformation of combined phasessuchas sodium cafC"ium sulfates with low meltingpoints that are·very reactive andcan both blockpores anddeactivate individual sites in catalysts. They alsofail to recognize that cyclonespartition the ash,· increasing the prop.ortionof sodium in the smallerparticles, resulting in increased propensity for the formation of the complex sulfate. phases. . . .. . Tops.oepresented apaper at the 

## u.s. DeparimentofEnergy (DOE) National Energy Technology Laboratory (NETL) meeting on SCR-selective non..;catalytic reduction (SNCR) on testing conductedwith biomass fuels ihat contain highpotassium andsodiuJn found rapiddeactivation in· the SCR catalyst. Their data stiggestsodiumorpotassium resembles. the ammonium.ion andblocks access to the active . sites in the catalyst . .They indicate that tMs occurs most readily where the alkali elements are in a soluble fbrm;Topsoe incorrectly assumes that all alkali incoalisriot sol't!ble because of work they did on

. potassium. Potassium is asso(;iated in the coal with clay minerals and is not soluble. Sodium in North

Dakota lignite is organically associated(solubleform) andis readily available for reactions with catalysts andflue gas spec.ies..More recent lYork conducted by Beck andothers (2004) established/hat sodium correlates with catalyst deactivation activity and thatpore condensation of sodium is th'e major deactivation. mechanism. / .•..

.. . , Sodizmllevels at MRYS have a multiinodal di$lribution,**a~d** assZ(ming the average sodiZ(m level in the ash

is not realistic ... :..... . .... . .. .. 

### EPA Response: .. EPA does not

### disputeEERC~s**d~scriptioit·** offuechemical and physical fate ofsodium in

### a '. cyclone boiler. Please.refer to the: August 20,2007 Christman Memo Item#2 for the response .

. on the effects ofsodiuni. on a SCRsystem and the apptopriateness· ofusing average coal

constituentvalues when evaluatiD:g !heireffect on anSCR system.



### -12:....EPA Response to Minnkota Comment Letters from March 19, 2007 and April 23, 2607 BACT Analysis atMRYS 

### EPA's original analysis was in response to B&McD's quantitative comparison ofsodium ash loading presented in the original BACT analysis. 15 

### This comparison uses**.aven~ge** 

### fuel ash
, and sodium values to calculate a sodium ash loading rate of7.31b/MW-hr :for North Dakota

lignite compared to 0.9Ib/MW-hr for a PRB-fired cyclone boiler. 16 

### 'One reason EPA provided a " comparison is that B&McD's analysis did not look at PC-fired**PRBtinits~** 

### whIch would have a higher ash loading rate than a cyclone unit. ThIs infotn;lation is relevant considering SCR systems 

### have been installed on PRB-fired PC units. B&McD's analysis assumes 35% '. conversion offueI-ash to flYaSh for PRB-fired cyclone units 

### arid 50% for ligirlte-fired cyclone

. units.. Using the 80% conversion offuel ashto flyash for a PRB-fired PC unit increases the

sodium loading presented by B&McD t02.11b/MW-hr. [(0.9Ib/MW-hr / 0.35) 

## = 2.57Ib/MWhr (sodium in the fuel ash fot PRB coal) 

## * 0.8 conversion offuel ash to flyash in 

# aPc boiler = . 

### 2.1Ib(MW-hr(0.9Ib/MW-hr·is the sodium loading for PRBcoal calculated by a&McD on a cyclone boiler assuming 35% conversion offuel ash to flyash)] The other reason EPAprovided this analysis was to include the entire Set ofash constituents'for the quantitative comparison. , EPA presented this comparison with some reservations, since, as stated in the comments, EPA does not believethat a linear comparison can be made between theoretical ash constituent . loading rates to SCR catalyst deactivation rates. Nevertheless, EPAwanted to demonstrate that B&McD's comparison oforily the sodium ash loading from lignite-fired cyclone units to PRB..: . , fired cyclone unitsignores the PRB-fired PC units which have the higher fuel ash to flyash ,

### .conversio!1~d()t1).e!~~hc:o~s~itllen!s,t~a!, <to effe<.;t

### ~_~,~**0Jlerati~ns:** ',On

### its_:s':lrfac~,}3~~~J?' s" . analysis portrays a.sodium loading**differen~e** 

### between North**Dakot~lignite** 

### and PRBcoal that is' greater thana factor 

## ofseven. this difference becomes less whenincluding PRB-fired PC units ' (about a factor ofthree difference) and other ash constituents (virtually zero). Agairi,EPA does

. not believ.e there is Ii 

### linear relationship between this ash loading and SCR deactivation rate. '

However, since B&McD presented a theoretical sodium loading comparison betWeen North,
, Dakota lignite and PRB coal fired cyclone units, with the apparent implication that the difference'

was significant in the.disc,ussion oftechnical feasibility ofSCR at MRYS; EPA wanted to 'include a more complete comparison.

15, See page A 1..29 ofOctober 2006 Minnkota BACT Analysis Study for MRYS. 16 In the March 19, 2007 response (page 28), EERC dist:J1isses EPA's analysis. "Sodium levels at MRYS have a multimodal distribution, and assuming the average sodium level in the ash in not realistic." Note that the analysis presented by B&McD uses average fuel characteristics for North Dakota lignite and PRB coal. . 

### -13-EPA Response to MinnkotaCoininent

### Lcitte~s from . ·.March 19,2001 and April 23; 2007 BACT Arialysis atMRYS

. .'
. . '.' '. . 

### EPA

## acknowledge~ that the' sodium content

### ofthe Center Mine lignite is

## gen~rallyhigher th&Ii 

### PRB ·coals.EP/\. also recognIzes that ash partitioning in a cyclone boiler and resultIng'**sodium·deposition·presentsceitain.problemsthatcouldpos~engineenllg ~hallenges**  

### to the design· and operation of

### aD. SCR system at MR**yS~** 

### H'owever,**Mi~ota** 

### haS not provided any . . quantitatIve data that shows that the'plugging'i,md deactivation of

## the· SCR system would.

## be an' .
·unresolvable technical harrier and/or the ability ofthe SCR to control NOx 

### would be:

# so limited that SCR would be 

## aD. ineffective control option. Ag13.in, EPA thiriks that both ofthese issues would be more**appropria~ely** 

### addressed at step 4 oftlle Top-Down BACT analysis: . '. . . . 

### The Topsoe 1999 paper referenced byEERC does observe that biomass

### having.~ high. percentage ofsoluble sodium .or potassium that was burned in an incinerator caused "rapid

·deactivation in the SCR catalyst." 

### .It is u.nclear how these soluble sodium or potassium . percenti:lges compare to the alkaline makeup ofCenter. Mine lignite. Furthermore, it is unclear what Topsoe meant by "rapid deactivation." The paper does not appear to indicate that the SCR was inoperable or ineffective for this test. 

### It is fnappropriatetodraw any meaningful. conclusions '. on technical feasibility based on these qualitative statements iIi Topsoe's paper. . .
. . . 

### B&McD's March**19~** 

### 2007Response:

. The discussion iii the EPA'spreliminary analjJsis ojMinnkota 's NOx BACT Analysis atMRYS ignores the BACTreports' statements that ihejiring 

### of lignite coal in acyc!one boilerspecifically.

·designed and built topre-dry and**bu~n** North Dcikota ligniteproducesfinejlyashparticles which wiil . enterthe poresoftheSCR catalYsi .. react with S03 ifl (hejlue gas, andform sulfates which bindoiher ash

. particles into the. matrix.' .

. When considering the much higher sodium content o/Center lignite coal.ash.(lb/mmBtu) compcll'ed . to PRE coal, the impact on tlze individual catalyst reaction sites from sodium-basedcompounds discuSsed' in Dr.**Benson~s** referencedtechnicalpaper has largely been ignored 

### bythe EPA;s' . commenters . The problems associated with sodium combined with calcium, sulfur; andother alkaline elements at

·any cyclone boiler firing North Dakota lignite appear

# to be unpreventCible for successful application of . SCR catalysts. There is no**full-~cale** long-term documentedand publisheddemonstrated experience .at commercial SCRbistallations on largecoal-jired boilers with similarly high sodium levels. .The tendency

. of s.mall sodium vaporparticles to be generatedduring the combustion'andslaggingprocesses of a North . Dakota lignite-fired cyclone boiler has no/been. adequately addressedby/he EPA c.ommenter's . . discussion.' . .



## -14-

# .. EPA Response to. Minnkota CommentLetters from . March 19, 2007 and April 23, 2007 BACT Analysis at MRYS The lack of publishedNOx control effectiveness and catalyst activity data for the Coyote slipstream 

### scR catalystfieldtestpreclu,dedBums & McDonnel/from evaluating or including it in the NOxBACT . Analysis Study rejJortsfor the Milton 

### R Young boilers Electric Power Research Institute, Inc. (EPRI)

.produceda recent study on the impactof coal type on SCR catalyst lift and performance... .. : ... This

.study found that the SioUxphnt 's cyclone unit firing the PRBlbituminous coal blendexhibitedthefastest rate of catalyst activity degradation. Also, the higher deactivation rates seen at this site were· due to economizer·exit flue gas temperatures being significantly higher than at the other sites.. Bums & McDonnell believes that theflue gas and flyash conditionsproducedduring the

· compustion andslaggingprocesses of a North Dakota lignite-fired cyclone boiler will be significantly moreproblematic than the tests at Sioux Station demonstrated.. ... 

### EPA Response: Please refer to the August 

### 20,- :2007 Christman Memo Item #2 for the response on the effects of.sodium on SCR. EPA's original comment does not largely ignore the statements in the Minnkota BACT analysis about higher sodium content and its impact on catalyst**deactivation~** EPA's analysis looked·at the combined percentages ofother alkaline materials (potassium, sodium, and magnesium) that would contribute to catalyst deactivation, instead of just focusing on sodium; These other constituents are ofimportance. See the expanded ahalysis and· . discussion above. B&McD states that E}>A has not adequately addressed high Center Mine lignite sodium issue and has provided no·documentedlorig;,.term experience at commercial SCR·installations on large coal-fired boilers with similarly high sodium levels. As discussed earlier, EPA believes that the burden ofproofin this·case is on Minrtkota to provide definitive qu;;mtitative evidence that SCR would be**technic~lly** infeasible atMRYS due to the high number ofSCR**syst~ms**
· currently in operation at utility boilers. Furthermore, a lack ofa full""scale long-term commercial

· SCR installation at a facility with similar sodium levels in the fuel is not evidence that SCRis .

technically infeasible at MRYS. While EPA agreesthat the sodium levels in North. Dakota . lignite are higher and 

### will require aggressive mitigation measures, SCR systemshave obviously been applie.d to new fuel types with unique characteristics over the history ofSCR installation,s. EPA has mentioned a number ofengineering solutions that could help manage the high sodium issue from a technical standpoint. .EPA does not believe that the qualitative information .

. presented thus far is sufficient to outweigh the vast amount pfSCR operating experience for

utility boilers to say that SCR would be technically infeasible at MRYS. Due to the lack ofNOx emission and catalyst deactivation data, the Coyote Station study does not sUPPQrt utilizing any . definitive conClusion, other than there was significant plugging, which also appeared at both the Baldwin and Columbia Stations. .. . EPA believes that the experience the utility industry has gained from the installationS at .. 

### PRB facilities would be USeful in designing an SCR systemfor a cyclone unitburning North. 

### -15-:-EPA Response to Minnkota Comment Letters from March 19, 2007 

## and April 23, 2007 BACT Analysis at MRYS Dakota lignite. According 'to

### th~ presehtation given In Bismark on May

### 23~2007to NDOH and ". EPA. by the utility design 

### firm, Sargent & Lundy, the successes and failures ofthePRB' . instaJlaticins would provide :'valuable infoiniation for designing an SCR system 

# pn a plant burnIng North Dakota lignite. 'Wliile'Sargent 

### & Lundy indicated that getting further data from a

### ~ell- ' designed pilot study would enhance'theirability'to optimally design a more cost-effective SCR system, they indicated that they would certainly draw uponthe 'experience gained through,the PRB installations. ' EPA does nothave access 

# to the EPR! study referenced that

### producedfield'dat~ from an "In-Situ Mini SCR Reactor" and showed that the fastest rate ofdeactivation was from the AmerenUE Sioux Station, which is a cyclone boiler burning a PRB/bituminous blend. B&McD appears to imply that this result demons.trates that an SCRinstallation on a cyclone boiler win experience faster deactivation, than art installation on a PC..fired, boiler because ofthe higher economizer flue gas exit temperatures. Since EPAdoes not have access to this data, EPA does not know how large ofa**differen~e** there was between the cyclone lInit and the PC-fired units.' , Without access to this data, it would in approprIate for EPA to place any reliance on assumptions or conclusions fromthis study. Furthermore, EPA is unsurehowthis relates'exactlyto the issue ofSCR technical feasibility at MRYS. This data might be useful in trying to predict catalyst cleaning / replacement requirements, but it is not relevant to demonstratingtIie technical ' feasibility ofSCR at MRYS.

. .'. "b. . Engineering

## S~lutions fOr SCR Applications

## atHigh~Ash Facilities 

### EPA 'sJanuary 9, 

### 2007 Co';'ment:

, Plugging of SCR catalystsby fly ash accumulation and bridging of passages in honeycomb ' catalysts and betWeenplates inplate-type catalysts h(;ls been aprobletnfordesigners Cind catalyst vendors. since'thejtrst coal-fired ins.tallations in the 1970s.Th'eprimary response has been more sootblowing" on-line cleaning ,equipment, 

### ctndlarger catalystpitch for honeycomb configurations and . widerplate spacingforplate-type configurations. These measures, combinedwithperiodic cleaning during boiler outages have, by-and-large, reducedc;atalystplugging to a manageable SCRproblem .. ... Also, theidet that the MRYS units are brought downforplanned boiler deposit cleaning at 120-day
, interval$provides more opportunity for catalyst cleaning maintenance than is available at the typical . powerplant. " . Further

### d~mo~trating the ability of SCR df;signers io use existing mowledge andexperience with SCR installatiansfor highashfuels, the. Electric PowerResearch Institute (EPRl) has advised' clients that basedon industry experience on a wide range of SCR ins.tallationsOver the years, SCR. ' " designs can accommodate fiiel types never before used inpractice on a full scale. In a September 7, :2006 letter addressedto TXUPower, EPRIstated, "While experience specifically.with Texas lignite is limited, this shouldnotprevent'suppliers from providing an SCR system that meets these objectives; dealing with a new fuel is similar to/he challenge faced by US. utilities andtheir SCR supplierswhen first installing SCR systems onplanisfiring high sulfur bituminous orPRE coals. Neithersuppliers nor utilities had 

## -16- "EPA Response to Minnkota Comment Letters from March 19, 2007 and April 23; 2007 BACT Analysis at MRYS prior experience with these fuels, whichproduce flue gasproperties'that are very different from those in the Japanese andEuropeanplants where SCR has been installed before. Therefore, SCR designers hadto rely upon their knowiedge, engineeringjudgment, andexperience with these other coals to design SCR systems suitable for these new applications. While some of the**j;rs~** 

### u.s. SCR installations experienced.

. problems (e.g., acceleratedcatalyst activity decay due .to arsenicpoisoning in the absence of sufficient calcium in the coal, andcatalystpluggage due to largeparticle ash), none of**the~e** problemsprevented

.the systems from achieving their NOx goals initially and, eventually, maintaining them over the expected

. life of the catalysts. 11 . 

### EERC's March 19, 

### 2007Response: . The issue isn'ot strictly the high ash content of North-Dakota lignite, it is the high sodium contentof this lignite's ash. The issuefor the application ofSCR on NorthDakotalignite,jiredcycloneboilers is a highpotential fOr ash deposition in lower-temperature convectivepass suifaces such as the economizer and primary superheater. The high ash deposition r.ates require continuous cleaning with-sootblowers,

. and the resulting liberateddepositfragments will cause catalystplugging. The depositfragments, along

with theformation of sulfatedsodium- ande.alcium-rich fine particulatepluggingpor(!s of the catalyst, causesplugging of gaspaths. . . 

### EPA Response: . The response

### fro~EERC simply restates their position regarding the high sodium

### conte~t**~~~~~o~f""tT""lie~-'7"C"""e~nt~e"';:r**

### 1\Iirie IigriiteaIid howtliiswillciruse botli-catalyst porepliiggirig-iiildUgas path' plugging. EERC Jails to consider the use ofavailable engineering solutions to address these problems with operation of

# an SCR at MRYS. . .... 

### B&McD'sMarch 19, 

### 2007Response: For a North Dakota lignite-jired cyclone boiler, aggressive on-line cleaning (mdlor frequent extended forced outages would be neededto remove the ash accumulation or remove the catalystfor cleaning in order to restorefull unit output qndcatalystNOx reduction effectiveness. Either or both of these'maintenance activities coulddamage the catalyst andlor require itto befrequenHy- . replaced the**e~timated** amount ofiime anddifficulty for MRYS boilers'SCR maintenance appears 

# to be insufficient to use boiler deposit cleaning outages toperform significant catalyst cleaning or " replacemeniwork without delaying startup. . EP RJ's statements do not conclusively support the technical feasibility of applying SCR wiiJi '. specific technical evidence that showsproof of the hypotheses, that it 

### will be successful on Texas lignitefired boilers.. It also does not suggest or imply that North Dakota lignites are similar to Texas lignites and therefore SCR shouldalso be successful on such applications. The high ash andmoisture content of a TexaS lignite-jired unit wouldresult in a different set of challenges for application of**high~dust** SCR technology. Possible solutions to deal with Texas lignite are not relevant to compare to North Dakota' cyclone boilers in this NOx BACTanalysisfor MRYS. Already-instaliedboiler and backendequipment designs on units firing TXvs ND lignites are significantly difJerent, reflective of the approaches the 

## -17-EPA Response to Minnkota Comment Letters from March 19, 2007 and April 23, 2007 BACT Analysis at MRYS . 

### origilialdesign

### ~ngineers took

# to**~tt~ch** these situations as separate

### p~obiems. OA comparison of the .. differences between TexascindNorth Dakota lignites is included in EERC's subsequent respo,!ie to the' . /iPA's comments regarding the NSPS revisions later in this response. document ..



### . EPA Resiumse: . This response states that aggressive on-line cleaning"andlor frequentexiended' ol,ltages would be required to remove ash accumulation or remove the catalyst for cleaning. The response seems to acknowledge that the SCRcould be used at MRYS, albeitwith potentia.llyhigher than normal maintenance requirements. This is not inconsistent with EPA's position, which is that the problems cited in the Minnkota BACT analysis appear to be. more a matter ofcostthan te.chnical feasibility.ltindeed necessary; the extended. outage times could be accounted for as additional operational cost (ifmore frequent catalyst cleaning is necessary and/or cannot be performed online) or accounted for, by adding additional catalyst layers to the SCR system. The. intent ofreferencing the EPRI letter on Texas

### lignit~' was not to' imply that North ,Dakota iignites are exactly the same as Texas lignites. The Interit ofreferencing this letter was to

show that a major utility**res~arch** 

### organizationis bfihe opinion that the**existii1gexperien<~e** 

### of the SCR designers WQuld greatly help in designing SCR systems for accolnmodatingfuel types. ,never before used in practice on

### a~full scale. This underscores EPA's position that, although the

. specific fuei and boIkrcharacteristics at MRYS may present chaUenges to an SCR installation, the significant iridustry experience with SCR for new fuel types in the past would serve'useful to. overcome the technical challenges described by**Minnkota~** 

### This again was reiterated by the design firm Sargent and Lundy in the'pre;sentation described above. '.

. , 

### c. . OtherAshDeposition Problems on Downstream

### Co~ponents EPA's January 9, 

### 20iJ.7 C;omment:

. B&M's discussion

## ofthese~'other" potential accumulationproblems does not reac.h 

## any definitive conclusions related(0 the technical feasibility of SCR, so EPA does. not**se~** 

### this as 

# a technic,al barrier to. . installing SCRat the MRYS units.

. . . . ' 

### EERCMarch 

### 19, 2007Response: Note that it 

### is not the ash loadings, iiis

### thesodium,.'~**ih~** lignite ash that causes

### th~ deposition.
, The $odium-relateddeposition on 

### SCR catalyst will shorte.n the time between 'outages for off-line**cleaning~** 

### . . ,,' ,



### -18-EPA Response to Minnkota Comment Letters from March 19, 2007 and April 23, 2007 BACT Analysis at MRYS 

### EPA's Response: EPA ac1aJ.owledges that the· sodium

### cont~nt in North Dakota lignite presents engineering

.challeng¢s. EPA also thinks it is possible that**~e** 

### "sodium-related deposition on SCR catalyst" will shorten the**tim~** 

### between outages fO,r off-line cleaning." As stated previously, the :**requiremen~** 

### for increased catalyst maintenance does not render the technology technically infeasible.' Any increaSed maintemince and unit downtime would result in added cost, which should be quantified at step 4 ofthe Top-down BACT analysis. Unfortunately, the piiot testing conducted at Coyote Station did not provide any quantItative results that could**b~** 

### used to predict the time periods between catalyst cleaning/replacement on 'a full-scale application. B&McD's March 19,2007Response: The higher amount of ash, sodium; andsulfur in North Dakota lignite combinedwith calcium and

. other alkaline elements along withammonia andS03 emittedfrom a high-dust SCR will exaggerate

. tubular airpreheater andeconomizer tube exterior surface fouling and plugging**problem~** at any cyclone boiler firing thisfuel comjJaredto bituminous or PRE coals. The tubular airpreheaters and the built-in economizers at MRYS are notequipped with sootblowersfor on-line gas-side surface deposit cleaning. NiJtingthatMRYS boilers' airpreheater andecimomizerswould be'downstream of the boilerbackpass outlets anda high-dust SCR,' isolClting these components during off-line boiler deposit cleaning or SCR cleaning outages from negative impacts of"dirty air would be chaliengingand expensive: Similar .

.**~~~~. effimClIed~(}ums---o.ftim~€md-aijjieultYf(}r-8ueh~ojf-line-downslFe{Jm-depos-ifepemovaf.s-wiIkH~~----_·**  -.**-~** unit startups following such outages ..... 

### EfA's Response: It 

### is unclear how the tubular air preheater and economizer tube exterior surface fouling alld piugging problemswould become exaggerated from the use ofan SCR system. As noted, ·in the August 20, 2007 Christman Memo, "the SCRretrofits at New Madrid (two large, PRB-fired cyclone boilers) included replacement ofthe tubular air preheaters with new regenerative air preheaters with enamel-coated baskets." This and other alternatives should have been consjdered in Minilkota's BACT analysis. The additional expense to clean these components. and isolating the SCR system are described as "challenging and expensive." As discussed
,**previously~** 

### these costs should be addressed under step 4 ofthe Top-Down BACT analysis, not at.

the technical feasibility stage. d. .. 

### Accoun!ingfOr CatalystLife & 

### PerfOrmance in Tdp;.Down BACT Analysis EPA's 

### January 9, 2007CiJmment: Finally, the conclusion reached in the B&MBACTanalysis that ash deposition andcatalyst pluggage will adversely affect SCRperformance (we assume this means .control e./ficiency) andcatalyst life does not necessarily support a conclUsion that 'the technology is technically infeasible andthat SCR 

### -19-. . EPA Response to Minnkota Comment Letters from

. . March 19,2007 and April 23, 2007 BACT Analysis at MRVS shouldbe eliminatedat step 

### 2 ojthe Top-Down BACT{lnalysis. Furthermore, the B&Manalysispresents, noqucrntitative data related

### t.o SCRperformance andcatalyst life to support such

# aconcliision ... .

..**~H(jwever,** SCRperjormtlrice tindany real construction and operational costs arejactors that would be . accounted/or under the economic impact stage related to cost effectiveness ojSCR (step 4) under the· . Top-Down BACTanalysis. 

### B&MdJMarch 

### 19,',2007Response: The reasonsjor the

## ~ssertion**~jtechnical** infeasibility ojSeRior iignite-jiredcyclone boilers were presented in the MRYStation Unit 1 and Uf?it 2 NOx BACTanalysis reports; withfUrther explanation. providedherein. The EPA'spreliminary analysis comments minimize the cfifficultiesposed by the higher amount of aSh,sod!um, andsulfur in NorthDakota lignite combinedwith calcium and otheralkaline· elements along with ammonia andS03 emitted from a high-dust SCR on the tWo existing North Dakota lignite-jir¢dcyclone boileratMRy-S; , The EPA cites nopublishedtechnicalliterature that describes....... as would be the case

# at Milton

. . . . . R. Young Station.

. . . ·.The evidentfailure of the Coyote

### slipst~eam SCR catalystfieldtest to ... .... ledBurns & McDonnell to believe these field testresults indicate ... . . .for technic(J1 infeasiMlitypurposes. 

### EPA 

### Response: . The majority ofthis coniment is addressed under EPA's response to the preliminary summary... EPA does not discount the challenge's that Center Mine lignite might posefor an SCR installation at MRYS. However, EPA cannot concur that the qualitative pilot testing results at .

. Coyote Station cited in the EERC report demonstrate thata rull-scale SCR installation at MRYS,

.that iQcluded the currently available engineering :design measures, would not be techniCally·· . feasible and offer substantial NOx**redil(~tions.** 

### EpAhas pointed out some ofthe inherent limitations in the pilot testing that might have contributed to the "failure" .ofthat test. B&McD and**EE~C's** 

### responses do not provIde much insight on whether thes.etests were desigriedto reasonably represent full-scale conditions, other than to say that EERC was notaione responsible·

..for the testing' s·**de~ign.** 

### EP**Aquestion~** 

### the design and operation ofthe Coyote ·Station pilot test. in light ofthe lack ofcritical data obtained. . EPA has also not found any deflnltivequautitative·results, taking intoaccoUllt

## th~ ash deposition and cat,alyst plugging counter· measures, that show the expected rate ofcatalyst. deactivation and off-line cleaning frequency that would be necessary for operation ofan SCR system at MRYS. As described in detail previously, EPA does not believe the pilot testing presented by EERCprovides an accurate estimate ofwhat type ofcatalyst maintenance and replacement-would be required. Without sllch quantitative information, EPA continues to believe that Minnkotahas not provided sufficient evidence oftechnical infeasibility for SCR at

. MRYS. EPA believes SCR is in fact technically feasible at MRYS. EPA**be~ieves** 

### under the 

### -20-:EPA Response to Minnkota Comment Letters from March 19, 2007 and April 23, 2007 BACT Analysis at MRYS

· Top-Down BACT analysis, any additional costs should 

### be accounted for under step 4.

·Furthermore, as explained previously, EPA believes the burden ofprooffor technical

. . .. infeasibility for SCR at MRYS is considerable giveri the large number orSCR systems currently in operation at utility boilers worldwide with vastly different fuel types and characteristics. Quite.simply, the record does ·not support Minnkota's conclusions. '

. . 

### 2. EPA Analysis ofthe "Popcorn Ash" Issue: '. , No ,response given to EPA's comment by EERC or B&McD. The topic was similarly addressed

· in tbe January 

### 2007 Christman Memo. 

### 3. EPA Analysis ofthe Temperature Issue: No response given to EPA's comment by EERC or B&McD. The topic was similarly addressed ' in.the January 

### 2007 Christman Memo. 

### 4. EPA Analysis ofthe Erosion Issue: No response given to EPA's commentby EERC or B&McD. The topic was similarly addressed in the January 

### 2007 Christman Memo. .**~~~~~~,~- ..~-~--~--.-.-.**  , 

### 5. EPA Analysis ofthe Energy & 

### Environmental Research Center Report (Appendix B): . EPA's January 9, 2007Comment:

. .

...... '" .However, the conClusions reached in the Appendix B report do not address some of the . engineering solutionspreviouslyciteilandexplained below that are**availabk~** for full-scale SCR ' , appiications. Furthermore, EPA. Region 8 believes. that there may be inherentlimitations with thepilot ' study (that was the basisfor bothEERC reportsfthat draws into question the validity of directly applying those conclusions to the range of possible SCR designs of afull-scale application at MRYS. Statem.ents from three major SCR catalyst manufacturers (including Haldor Topsoe, 'the catalyst manufacturer
, involved in thepilot testingforNorth Dakota lignite) suggest that the catalystdeposition and plugging problems experiencedduring thepilot testing may be exaggerating on apilot-scale andean be solved in a full-scale design andapplication . Other inherentproblems associatedwith directly applying the results af the EERCpilot testing at

. Coyote Station on North Dakota lignite include: ., .. 1) The airpulse usedto cleardeposits during thepilot test is apoor simulation of sootblawing and is much less effective... . 2) The6mmpitch catalyst usedfor thepilot testing at Coyote Station is much smaller than currently being specified for coal-fired installations. Vendors are now 'supplying 9mm, 10mni or even 

### -21-. EPA Response to Minnkota Comment LettersJrom ..

.March 19, 2007 and April 23, 2007 BA.CT Analysis at MRYS 11mmpitch catalysts .. , .:..•..... ;

. 3) The. one me.ier depth of the catalyst used in thepilot test is equivalent to one layer of catalyst in

· a commercial installation. CommerCial systems aimedat high removals haVe three layers, each about threeftet thick, alu1, at various times in the catalyst managemc?1ttcycle, incorporate four layers. EERC's,·

· test, then,. r,mlysimitlilied the top layer of a·multi-Iayer**system.~** This is why the first step in

.most cqtalyst management schemes usually involves adding afourth layer .andleaVing the badly degraded top layer inplace for the secondoperatingperiod EERC'sprojectprovides no real insight into the effectiveness andsurvivability of a secondor thirdlayer. . . 4). The. scale 

## ()i testing carried out in thisproject is usually associatedwith observing catalyst life prospects (or said another way, the rate of loss in catalyst activity) rather thanphysicalprocesses of

· .deposition orplugging. This is because the deactiva(ion mechanisms·operate on a micro-scale andcan·

be accurately simulatedat ihis small scale, but theplugging and deposition are influenced by larger processes, such as flow imbalance andcountermeasures. (sootblowing,. horns, screens, baffles, etc./and

· .are not duplicated on the small scale.· .

. For these reasons, EPA Region 8 questions the direct**applicati~n** of the results of the EERCpilot·' testing at Coyote Station and the accompanyingAppendix B EERC reportjorpurposes of the BACT technical feasibility analysis of SCR.at MRYS. The experience and opinions of the SCR supplier that participatedin the EERCpilot test indicate that theproblems 'encounteredduring thepilot. test are not determinate of whether SCRplugging experiencedduring the pilot test would be unresolvable by**venddrs~** To the contrary, statementsfrom Haldor Topsoe offeringthe.ir SCR catalyst/or installation on lignitefired boilers indicates that thefull-scale differences and engineering solutions available todayprovide evidence thatthe EERCpilot testing results shouldnot alone be the dec.iding consideration when

·**e~aluating** SCR technical feasibility at MRYS. . . .. 

### EERCMarch 19, 

### 2007Response:

... ..... The catalyst vendors, Haldor Topsoe;Cormetech andHiiachi, were all involved bi thedesiin· of the piiot-scaleslip, stream .testsystem and testingconditions..Thepulsing system was designed with the assistance of the catalyst vendors. .Theyprovidedsuggestions on the sootblowingpressures and felt it

· .would be s.ufficient to remove the**deposits~.** The 6mmpitch was recommended 

### by the vendors. 

### If thefirst layerplugs, the gases cannotget to'the subsequent laYers; Significant deposition was noteddownstream of the SCRcatalystsection instdlledDeposition al]d plugging aresiinificantproblems that impact/he .. ,
· reliability of the MRY facility. Haldor Topsoe was the only catalyst vendor willirzg toprovide catalystfor the lignite tesiing. . .

. . .' ," . . The EERCpilot-scale

### te~ting was a collaborative effort involving coal-ji;edutilities, EPRl, DOE, .
· andcatalyst vendors. All depisions on system design, plants for testing; an.d testing conditions were '

. reviewedandagreed

## upon byvimdors.The EERCcomparisons of catalystblindingfodignite and . , subbituminouscoal testing as well as the sodium deactivation work conductedby other research

organizations andcatalyst wmdors should be use(i in evaluating technicCilje(Jsibility ofSCRfOf'MRYS.



### -22-:-EPA Response to Minnkota Comment Letters from , March'19, 2007 arid April 23, 2007 , BACT Analysis at MRYS ' , 

### EPA Response:

, The results ofthe pilot testing were'examined in more detajl. EPA's observations on the test ilS 

### it relates to expected catalyst maintenance and replacement requirements at MRYS are' described 

### in detail under the EPA'response to the preliminary summary.

- . . . . 

### , EERC indicates that the catalyst vendQrs assisted in the design' ofthe air pulsing system for the Coyote Station pilot testing and recommended the 6 mm catalyst pitch. Flemming Hansen of Haldor Topsoe, the catalyst vendor for the Coyote Station pilot test, informed EPA Region 8' that, in hindsight, the pilottesting should have been conducteddifferently. Specifically, Mr. Hansen**~aid** 

### that changes to the test such as increased catalyst pitch could have helped reduce the impacts bfash plugging. AdditiomHly, Mr. Hansen said that pilot test's air pulsing system did not accurately simulate full-scale sootblowing and that ifthe test could be redone, a better effort 'could be made to keepthe'catalyst face clean. Mr. Hansen recalled that the Coyote Station test reactor became 'quickly plugged with flyash'causing rapid increases in pressure loss caused mainly by wall-duct ash accumulations dropping on the catalyst face. Mr. Hansen stated that this type ofasp deposition would not be a problem on a full-scale**appli~ation.** 

### Mr. Hansen's statements suppbrt EPA's original comments that there wereitilierent ' problems with the pilottesting that contributed to the degree ofcatalyst plugging during the**~~~~,CC"0yote** 

### Station pilottesting. In addition, experts frCJm Sargent& Lundy indicated that they were disappointed in how the Coyote Station pilot test was carried outand found the results to be of very little value for evaluating anSCR system for a facility burning North Dakota lignite. Based on the EERCresponse, the degree ofcatalyst plugging observed at Coyote Station was the.reason no deactivation testing on:. the catalyst was conducted. Ifthe testing were' designed and conducted in a way that could havegreatiy reduced the effects ofash deposition on the catalyst face, presumably catalyst deactivation data would have beenobtained. As stated**previ~usly~** 

### EPA questions Mlllnkota',s heavy reliance on the questionable results from the Coyote Station pilot testing and cannot support using this data to draw definitive conclusions on the feasibilityofSCR at MRYS. Furthennore,

### ~hether the design issues were originally attributable to the catalyst vendor or not, EPA does not believe that a pilot test designed and

. conducted under conditions unrepresentative offull-scale engineering capabilities is a fair measUre ofwhether the technology is technically feasible or not., Input from both Haldor Topsoe and Sargent and Lundy support this positIon. .



### -23-EPA Response to Minnkota Comment**Lett~rs** from . March 19, 2007 

## and Apri12J, 2007 BACT Analysis at MRYS



### .. 6. . EPA Analysis ofthe Burns & 

### McDonnell's Conclusion: EPA 'sJanuary 9, 

### 2007 Comment:

. . EPA notes that there is

### co~side~able experience in ihe industry to show that. Use. of SCR on North. Dqkota lignite is technically feasible.· EPA haspreviously articulatedthis belief in a number of national· rulemakings, including the Clean AirInterstate ·Rzile (CAIR),the BestAvailabieReirofit TechllOlogy. (BART) Guidelines, andrevisions to the New Source Performance Standards (NSPS)for ElectriciJtility . ··Steam Generating Units (finalized on feBruary 27,2006) ... .. ; .... ,. .... . 

# .. EPA understands from the EERCpilotstudy at Coyote Station usrng North Dakota lignite, there was noticeable ash build up on the catalyst.andconcerns with catalystplugging during the test . .While. EERC notes that ash depositionproblems were mostpronouncedat Coyote Stqtiofl, compared to the two . test facilities burning PRB coal, italso states generally that all of the coals in thepilot study "produced ash that hadsignificant accumulations of ash on the catalyston both macroscopic and microscopic levels." Thus, the conclusions of the study appear to be that depositionissues might be somewhatgreater for North Dakota lignite thanfor PRB coaL Since §ignificant accumulations of ash on the· catalyst wqs also observedduringpilot testing at thosefacilities burningP 

## RB coal and there are numerous examples

. of PRB coal-fired powerplants. successfully operating SCRsystems, the qualitative results of the pilot testing describedby B&Mand EERC wouldnot appear topreclude successful operation of SCR on a powerplant burning North Dakota lignite. The EERG study does not appear to quantify the effect that ihe .ash accimiulation hadon microscoplccaiqlyst deactivation rates or overall catalystperformance. Absentsuch Information that refleCts the use of currently available full-scale ash loading mitigation designs, pilot testing results may not be evidence that successful implementation of SCR on North Dakota firedunits: "is going to be impossible," as statedin the Appendix B.EERC report.. .

. . ' .

. The October 1990 EPA draft New

### Sour~e**Revie~** Manual (NSR Manual) states that

## a**"demo~sfration** of technicalinfeasibility is basedona technical assessment consideringphysical, chemical and engineerrrigprinciples, and/or empirical data showing that the technology wouldnot work

.on the emissions unit under review, .orthatunresolvable technical difficulties would preclude the . . successful deploymentojthe technique. Physical modifications neededto resolve technical obstacles do .

. not in and of themselvesprovide ajustificaiionfor eliminating the conirol technique on the· basis of

. technical infeasibility. However, the cost of such modificdtions can be considered in estzmating cost and . economic impacts, which, in turn, may form the basis for elfminating a control technology." (Page B.20) (Emphasis added). Basedon the available information, theproblems cited by B&Mfor application 

### oj SCR atMRYS (ash deposition, . "popcorn ash ", temperature; anderosion). are resolvablethrQugh the engineering solutions discussed above. .Whilesiti:h engineering solutions mciy be a cost burden to Minnkota,. as notedaQove, step 

### 1 is not theproper stage of the Top-Down .JJACTanalysis to accoUnt for these costs; As describedin the NSR Manual, "where the resolution of technical difficulties isa matter of cost, the applicant shouldconsider the technology as technically feasible. The economic feasibility of a· control alternative is reviewed in the economic impactsportion of the BACT.selectionproc(!ss." (Pages B.19-B.2.0/· Many of the technical feasibility argumentspresenied in the BACTanalysis are centeredon

. decreasedca.ialyst life and performance, increased maintenance andoutage time, and plant differences unique to MR.YS thatpreclude SCRfeasibility at MRYS. Consistent with the NSR Manual, these concerns

.are incorrectly incorporated into the Top-Down BACTanalysis at step 2 and really shouldbe accounted 

## -24-EPA Response to Minnkota Comment Letters from March 19, 2007 and April 23, 2007 BACT Analysis at MRYS for as additional costsper ton of pollutant removeda/step 4 of the analysis So, while EPAdoes not consider vendorguarantee.s by themselves to be determinate in making technical feasibility decisions; they are a contributing factor in making these**decisions~** EPA is aWare of three catalyst vendors (HaldorTopsoe, Cormetech,. andArgillion) who wouldbe willing toprovideperformance guaranteesfor lignite-

. fired boilers applications.

. Basedon the criteria discussedabove, MinnkotaandB&D shouldluwefurther explored both the full-scale engineering solutionS usedto address theproblems cited in their anqlysis in conjunction with informationJrom SCR/catalyst vendors to offerperformance guarantees to design and install an SCR unit 

### €IiMRYS. The BACTanalysisforMRYS thatwas submitted relies heavily on the technicalproblems

. experiencedduring the EERCpilot testing at Coyote Station in conjunction with the fact that SCR has not been installedon a cyclone boiler that burns North Dakota lignite. We do not believe that this analysis adequately addresses the criteria citedabove. As such, itappears that the case-specific NO xBACT analysis submittedforMinnicota MRYS is deficient in terms ofiinproperlyeliminating SCRJrom consideration at step 2 of the BACTanalysis for technicalfeasibilitjJ. 

### EERC's March 

### 19,2007Response: EPA did not examine·the EERC report in detail. The deposition andjJluggingwas much more pronouncedfor the Coyote Station testing ascompared to the Columbia andBaldwin Station. The

. pressure drop increased much more rapidly and the s.ootblowing was notas effective ..... The most

important unresolvabl(! technical difficulty is the impact.of sodium on theformation of bondedsulfate**~~~~~phases-cthtttfJht~and~maskth(7eatalyst-and-()n-the-ab#ity4f~()dium-lo-deae:tivate-..the.-cata/J1s1,,--------c---.** ._ 

### EPA Response: EPA's original assessment ofsome ofthe general statements on the results ofthe pilot testing conducted by EERC at the three power plants are.based O:Q 

### a direct quotation from the EERC report in Appendix B, which states that there was significant catalyst plugging at all three test sites. While it is true that the problems were most pronounced at the Coyote Station and the facili-ty experienced higher**pr~ssure** 

### drop during the test, the results from the three facilities taken . together do not demonstrate· whether SCR would be technicallyfeasible or infeasible at any or all ofthe.**fac~lities** 

### tested, since no quantitative 

## NOx 

### control or catalyst deactivation data was provided in the EERC report in Appendix B ofthe BACT analysis. While the pilot study does**~uggest** 

### that catalyst plugging. at a facility burning North Dakota lignite would likely be more of a challenge than at a facility burning PRR**co~il,** 

### EPA. can not conclude that the test is determinative ofwhether anSCR system would not**work,~t** 

### MRYS. See EPA's previous detailed analysis for more information. ,. . EPA has since received the background documents for project participants and reviewed quarterly progress reports. For reference, below is a summary ofsome ofthe relevant history and background information from the pilot study. 

### -25-EPA Response to Mirinkota Comment Letters from March 19, 2007 and April 23, 2007 BACT Analysis at MRYS.

. '" 

### Original goals'ofthe

## t<~st(2000 EERC'Proposal) '. .' 

### • . "Determine the mechanistic and fundamental causes of potential blinding or masking ofselective catalytic reduction (SCR) catalysts due to**flu~** 

### gas constituents in low-rank coals." (Objectives) • "Utilities will gain scientific and engineering information- related to potential

.fouling' ofSCR catalyst material and will be abl€ - to negotiate guarantees and performance criteria for SCR systems and materials, and SCR manufactllrers

. and distributors will gain 

## an appreciation forpotential challenges facing -

utiiities using low-rank coals that could cause SCR masking and will be able to adjust future systems." (Expected Resillts) _ . '. • "The testchamber will be constructed

# so that periodic

### s~ples ofthe catalyst can be removed to 

### assess the reactivity as afunction of time." (Eniphasis added) 

### (Task 4 - SCR Test Chamber Installation 'and Data Collection) • . "The endresult is that research is needed to determine the true extent of'

_ potential SCR blinding for**lower~rari.k** 

### coals. Ifindeed masking ofSCR catalystmaterial is an**issue~** 

### then SCR technology may not be the "best

. available" technology for NOx 

### control at North Dakota utility sites and the. EPA ruling (1998 NSPS limit) may need to be amended. Other options' may surface as result (sic). ofthis research include providing technological and fundamental science and engineering knowledge for manufacturing catalysts that resist blinding from low-rank coal-type ash material or designing SCR systems that can be cleaned on-line." (Rationale for the Project) Here are some relevant· excerpts**~akenfrom** 

### the fined results ofthe test. (November2004 Final Report for period November 1, 2004·;June30, 2004, with two exceptIonsnoted below)

. . 

### • Baldwin Station (cyclone boiler, PRB coal) catalyst reactivity testing at 2 months",:"" . 100%,4 months -.:.. 96%, and 6 months - 84%. 6 month sample showed "extensive sulfation ofalkaline-earth elements present in**the'deposits~"** 

### "Regions of the catalyst" where all ofthe pores were blocked anciamininialamourit ofdeposit on the surface ofthe catalyst." "Higher magnification view ofthe deposit that is filling the pore:';-

• Columbia Station (tangentialiy fired boiler, 

## PRB coal) catalyst reactivity testing at 2 months - 93%, 4 months - 90%, and 6 months :.- 90%. (December 22,2006 email . from Isato Morita, Hitachi Power Systems America Ltd. to Dr.. Steven Benson, . EERC) "The Columbia Station showed more**signifi~ailt** 

### accumuhliion and plugging than the Baldwin Station." "The six month sample from the Columbia Station showed particles adhering to the surface and filling pores in the catalyst." 

### -26- . ,.EPA Response to Minnkota Comment Letters from March 19, 2007 and April 23, 2007 BACT Analysis' at MRYS
• Coyote Station (cyclone boiler, ND lignite) - No catalyst testing conducted and no· NOx data submitted. "The mostsigniflcant accumulation was notedfor the Coyote Station." "The. Coyote Stationhad some large pieces ofash deposit material onthe' surface as well as plugging ofthe catalyst passages." "The six month sample from the Coyote Station showed particles adhering to the surface and filling pores 

### iIi the catalyst." Describing photos ofthe catalyst inlet after two months ofoperation, ''the left side ofthe catalyst is indicative ofthe amount offoullng present whereas the ash present on the right side·ofthe catalyst fell from the upstream flue section when the jointwas separated. Nev.ertheless, the entire surface appears coated with ash

.**deposits~and** some ofthe catalystchannels were plugged." (February 2004 Quarterly Report - not noted in the final report) (Note: The right side ofthe catalyst face looks FAR worse than the h::ft side in the photo.) • . Study Conclusions: "The pressure drop across the catalyst was found to· be the most significantfor the lignite-:-fired plant as. compared to the subbituminous-fired plants.. 

## Both coals had significantaccumulations ofash on the catalyst, on both macroscopic' andmicroscopic levels.;" .

. . t"This study suggests careful evaluation ofeach SCR installation 

### in applications using subbitunlinous and lignite coals. Improvements are needed to ensure technical

### ~~'---.-~~~**~~fi** 

### ..... "easibi1ily-o-eS12eciall}'" with

### Jignii.~tired**llilit~"** ..

### InsJallatiQn.s.invQj.YingJignjj;.eJilel~s ""w'-A!il ..... l

__

### ~~~ need**~dvanced** cleaning techniques to handle the high sodium and high dust loads .. aSsoCiated with burning most lignite fuels."

.. .... . Below i!)EPA's assessment ofthese additional background documents and reports received after the original comments were submitted on January 8; 2007 and January 26, 2007 and how to compare the :results from the three facilities tested during the pilot study. 1. Quantitative.Data Analysis

• EERC apparently did no catalyst reactivity testing' for the Coyote Station and did hot monitor NOx control performance ofthe SCR system during the test period. (Original test proposals from 2000 included mention of instrumentation "able to monitor whether NOx control "is occurring", but EERC has not provided this data to EPA, nor. is there further evidence that it . was ever collected.) • Pressure drop data for Coyote Station does not show gradual increase, btlt a sudden dramatic increaSe likely resulting from the ash dropping from upstream flue sections, as described int-he February 2004 Quarterly report. EPA's conversation with HaldorTbpsoe is consistent with this interPretatiOll.. -27-EPA Response to Minnl.cota Comment Letters from 'March 19,2007 and April 23, 2007 BACT Analysis at MRYS ' 

### ,'Pressure'drop data and comparisons to Columbia and Baldwin

## Station~ are

therefore not meaningful. ' 2:**Qu~litative** 

### Catalyst Analysis ,"

• While 'c.oyote Stationis described as having the most significant catalyst inlet ash accumulation, it is entirely possible that this is due in large part to the ash
,dropping from upstream flue sections. • The microscopic catalyst description for Coyote Station was notentirely unlike that ofthe Columbia Station, where both "showedparticles adhering to the surface and filling

### por~s**i~** the catalyst." ' ". Due to the upstream fluesectiori ash contribution at Coyote Station and the similarities between microscopic analyses presented by EERC between the ' North Dakota lignite and PRB coals (both showed particles adhering to the ,surface and filling catalyst-pores), the qualitative information does not provide meaningful conclusions forcomparative1y assessing SCR technical feasibility for North Dakota lignite and PRB coal applications. "The one exception would bethat the.study shows lignite at Coyote**Statio~** 

### showed more sodium deposition and less calcium compared 

### to PRB coal. It 

### is unclear what the" basis is (or EERC's statement that the sample at COYQte Station "shows
, , significant evidence ofsulfat"ion" after only 2 

### m,onthsofexposure arid was much more pronounced than the 2':month samples for theB;;tldwin and 'Columbia Stations." Even ifthis is based on visual observation ofthe SEM iinages, it is not quantitatively compelling'information. As stated in EERC's"

. final report, "both coals had significarit accumulations ofash on' the catalyst, , on both macroscopic and miCroscopic levels." ',. ",3. EPA's ConClusions ofthe EERC pilot Stqdy ,
• The quantitative data provided for catalyst deactivation for Baldwin (reduced, to 84%) and. Columbia (reduced to 90%) indicates that the visual observations from the pilot study,are not me'aningful ways to quantitatively represent the '**~h** 

### impacts on SCR systems.. In fact, the reactivity results 

### show the opposite
, trend as. would be expected when comparing the visual'observations' at

BaldWin and Columbia Station: "Columbia Station showed more significant' ,', accumulation and plugging than the BaldwInStation," but Columbia Station's "catalyst showed less deactivation than BaldWin Station's catalyst. .As such, it
, does not appear that a correlation can be made**,betw~en** 

### the visual , ' ' "obserVations and the effects On catalyst performailce. Without representative

catalyst deactivation testing or

## NOx 

### control: data from the Coyote Station, EPA 

### -28'- , "EPA Response to Minnkota Comment Letters from March 19, 2007 and April 23, 2007 BACT Analysis at MRYS 

### does not believe the pilot study provides meaningful results that could lead to 

# a

definitive conclusion that SCR would be infeasible at MRYS. ' •**Th~** 

### quantitative data on**pr~ssure** 

### drop is not compelling since it is not directly related to**c~talyst** 

### performance and is suspect for the**C~oteStationdue** 

### to ' upstream flue ash dropping on, to the catalyst face.' . . • The catalystanalysis on both micro and macroscopic-levels does support the'
,claim by EERC that catalyst deposits Will contain more sodium when exposed**to.lignit~** 

### comparedto PRB coal, but does notclearly support the assertion by

. BERC that SCRwould not work**on~** 

### lignite plant. In fact, EERC's . .

conclusions seem to question how well SCRwould work atPRB plants, which has been disproved with operating plants. • , IIi summary, the primary goal ofthe piloftest was to determine mechanistic and fundamental causes' ofpotential blinding or masking ofSCR catalysts due to flue gas cons,tituents in low-rank coals. In the test proposals, 

### it was clear that this included 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 meetthe originalgoal for North Dakota lignite. As explained**above~** 

### the plugging

. appears to be in largepaii, due to the upstream flue ash dropping onto the.

. catalyst face. As such, it is riot clear whether the catalyst testing would have**~~~~~~-'c-'~~~~~-,b"-"e=e#Il~c..,=b""n=du=c=t=ed=...,if"-1t"",h",,e.--"c=at=aI,YJ!twould** 

### have beenke12t cleaner.**Additionally~~** 

### ..**~~_~~_** 

### EPAunderstands that the catalyst deactivation testing still could have been conducted, itjust would not have provided a very'quality "data point" because .ofthe irregular catalyst exposure over time in light ofthe substantial. ash \ . -. . . . 

### deposition on the catalystface and the resulting high gas flows through the catalyst.· This effect may have also contributed to the differences in catalyst deactivation rates between Baldwin and Columbia Stations. 

### B&McD"s March 

### 19, 2007Response:

... ,.. The EPA's review offeredno specific documented and publishedsubstantive demonstrated experience '" ..... of any cyclone boiler firing North Dako{a lignite, particularly one locatedin a highdust, hot-slde application at Milton 

### R Young Sta#on. 'Burns & McDonnel/disagrees that the lack ofSCR catalyst deactivation data from the Coyote slipstream SCR. catalysts field te.st completely refutes (he premise of Dr. Benson's referenced technicalpaper and the Minnkota NOx BACT Analysis Study conclusions that SCRs are technically infeasible for !ignite-jiredcyclone boilers.

. 

### '.' The, EPA's NSR Manual does not.specifical/y define ..... ; in order for saidalternative to be excluded fromfurther consideration. When a BACTanalysis ispeiformedon a new unit, there has typically been significant conceptual anddetailed engineering anddesign workalreadyperformedthat forms the ba:sis of the subsequent 

### -29,EPA Respon!?e to**Minnkot~** CommentLetters from' March 19, 2007 and'April 23, 2007 ,BACT Analysis at MRYS



### , capital cost,estimate and

### a;soci~ted expected0 & 

### ,Mcosts for thepwticular emission control technologies to be employedor that were'consideredaspart of the overallprojecteffort. Performing a BACTanalysis on. an existing unit sl1ouk! notrequire'similar substantial resources to 4evelop conceptual designs andcreate technical details that determine the'estimaiedsite-specific retrofit costs for overcoming significant technical challenges that wouldotherwise,prechtde the 'abilityof the technique or technl?logy from successfully controlling the em.issions in question. The EPA's NSR Manual states: "A source wouldnot be, requiredto exper.ienceextendediime delays or resourcepenalties to allow research to be conductedon a new technique. " 'There eire no Citedexamples'where successfulsolutions to such challenges asposedl;y stich highly complex interactions b.etwe.enJlyash, Jl1,te gas, andgas temper.atures producedby lignite firingfor SCR coal{iredboiler applications**~.** 

### . ' 

### EPA Response:

. . .' . . 

### Again, EPA believes that in the case ofdeciding on technical infeasibility for SCR at a ' utility boiler, the bUrden ofproofis on the applicant and is considerable. EPA'sposit,ion is that the hundreds ofSCR installations at utility 'boilers worldwide demonstrate 

# a wealth of-experierice
, within the industry to address various factofsover a very wide range ofboiler designs and fuel

types., The qualitative resl;llts ofcatalyst phigging for the pilot testing at Coyote Station do not provide empirical 'evidence that SCR would be ineffective atcoIitrolling NOx 

### emissions, since there was no quantitative data provided for eitherNOx 

### reduction or catalyst**deactivation~** 

### As such, EPA is not convinced thatthe specific chaJlenges presented for 

## aD. SCR installation at MRYS is a matter of**technic~l** 

### infeasibility and could not**b~9vercome** 

### with a robust suite ofash (including sodium) mitigation ineasures and/or maintenance measures;' While EERC has had verbal contact with Haldor Topsoe, Minnkota's March 17,2007**r~sponse** 

### letter simply says that this vendor would have concerns 'about providing a perforri:lance guarantee in'light ofthe specific, sodium content ofthe lignite burned at MRYS. It is not clear based on this statement whether Raldor Topsoe would or would not in fact provide 

## a: performance guarantee '(or whatthe , guarantee would entail) for**~n** 

### SCR installation at MRYS. Also, as noted previously; during EPA's own discussion with Haldor Topsoe, Mr. Flemming Hanst:n did not rule out bidding on a project that involved North Dakota**lignite~** 

### " , ' ,

### B&McD'~ assertion thata BACT analysis for an existing 'unit "should not

### ~equir~slmilar , substantial resources to develop. conceptua.l designs and create technical, details, that determIne, '

the estimated site-specific retro-fit-costs for overcoming significant technicafchallenges that would otherwise preclude the ability ofthe technique or technology from successfully , controlling the emissions in question"**doe~** 

### notappear

### to' have a basis inEPA regulations or policy. Prevention ofSignificant Deterioration**(P~D)regulations** 

### make no distinction between BACT requirements for new and existing UJ1its undergoing PSD review. In**fact~EPA's** 

### position, has been that when it is discovered that a source avoided PSD review, but it was laterdetennined ,that PSD permitting requirements, including BACT, should have applied, the source would**n~ed** 

### to address the 'appropriate requirements "as ifconstruction had not yet commenced." I? , ' 17 See April 20, 1999 letter from RichardR.Long{EPA Region 8}to Dennis Myers (Colorado Department of 

### -30-EPA Response to Minnkota Comment Letters from-

- March 19, .i007 and April 23, 2007 BACT Analysis at MRYS In addition, B&McD's referellce to page·B.I8 ofthe

### NSRWorksh~p Manual is taken out ofcontext mid is. not relevant to their discussion on 'how a BACT anaIysis for an existing soUrce should be less rigorous than for a new source. The NSR Workshop Manual citation' is a discussion ofwhether a given control technology or ie'chnique should be considered**"ava~lable"**

_

in the context ofthe technical feaSibility analysis under step 2 of the Top-Down: analysis. IS There is little question ofwhether SCR is "available" for instaIiation at MRYS. hi fact; . Minllkota's original BACT ailalysiscontends that SCR- meets the criterion for being - "available".!9 So; it is inappropriate for B&McDto bring up this passage from the NSR Workshop Manual. The question has been whether SCR would be "applicable" (the second criterion under step 2). B&McD's reference on page B.18oftheNSR Workshop Manual would only apply for a "new: technique." Given the vast experience inthe utility industry. with SCR and the EPA policy on technology transfer considerations, EPA does not believe iOs reasonable to consider SCR as a "new technique" for MRYS, even ifthere are no SCR instaliations' . specifically operating on cyclone boilers burning North Dakota lignite.2o In conclusion, EPA does not believe Minnkota has satisfied the high threshold ofdemonstration that SCR would not be technically feaSible at MRYS. While EPA-agrees there are-engineering challenges with operating an SCRsystem atMRYS,EPAbelieves these would largely be a matter ofcost and

_ should be examined under step 4 ofthe Top-:Down BACT. analysis.**~--_** .._----'--- 

### : B.... . Low.,Dust SCR BOurns & McDonriell has eliminated Low.,Dust SCR as technically infeasible due to issues described below.. EPA's response on each issue is also described**~elow** -**1~** 

### EPA Analysis ofthe Catalyst Fouling and Deactivation Issue: 

### EPA's January 

### 9, 2007 Comment: . Afew SCRsystems installedon coal-fired boilers have.been designed with theSCR catalyst installedafter the ESP or baghouse; This approach- eliminates virtually all of thepoisoning, plugging and erosionproblems that have.been associatedwith SCR catalyst. '(Christman Memo, 2/18/03) For the same reasons notedabove under the high-dust SCR**analysi~,** the catalyst fouling anddeactivation . - prob"lems may be resolvable technicalproblems that do not warratitelimination of low-dust SCR under

.Public Health and Environment).http://epa.gov/region7/programs/artd/air/nsr/nsnnemos/amersoda.pdf

- 18 Page RI8 ofNSR Workshop Manual: "A control technique is considered available, within the context presented above, ifit has reached the licensing and .commercial sales stage ofdevelopment. A source would not be required to experience extended time delays or resource penalties to allow research to be conducted on a new technique." 19 See Page AI-32 ofOctober 2006 Minnkota BACTAnalysis Study for MRYS. 20 See June 15, 1989 letter from Gary McCutchen (EPA Office ofAir Quality Planning and Standards, New Source Review Section Chief) to John Daniel (DepaTtment ofAir Pollution Control, Commonwealth ofVirginia). htiP://www.epa.gov/Region7/programs/artd/air/nsr/nsnnemos/fmlbact.pdf 

### -31-EPA Response to Minnkota Comment Letters from·

. . March 19; 2007**~ndApriI23,2007** BAtT Analysis at MRYS. .



### ·step 2 

### ojthe .Top-:Down BACT**an~lysis** 

### Similarly, permit applications for three recent Circulating Fluid.izedBed projects in North Dakotd(MDU Westmooreland Gascoyne, South Hart, .andGascoyne· 500MW) 

### didnot.eltminate10w:.Dusi SCR basedon unresolvable . technical feasibility issues with catalyst jouling anddeactivation. While there wouldbe/Inherent costs associatedwith gas-reheat, otherjJossible

·physical modifications to iheplant to accommodate low-dust SCR, andengineering**~esignsto** 

### minimize· . andmanage catalyst fouling ariddeactivation, these factors, consistent with the NSR Manual, shouldbe. accol,lnted for ·when considering 

## ihe economic impacts of/he technology. 

### EERC's Marclt 19,2007Response:

. Sodium-r!ch aerosols are aproblem that can get through the ESP. These aerosols are known to be

.. present in high**~odiumcoal** 

### c0'!lbustion fuel gases.. These speciesare known toproducepyrosulfates. These will causeb/inding anddeactivation of the low-dust catalyst. EPA**Re~ponse:** As described previously, general qualitative statements thatthe

### scidiu~-rich aerosols will cause blinding and deactivation do not riecessarily support the conchlsion thata low-dust SCR system would be**technic~lly** .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**~ssociated** with catalyst blinding and deactivation are unsolvable andwouldresult 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 obstl:lc1es do not in and ofthemselves provide a justification for eliminating the**co~tro1"technique** on the basis oftechnical**infeasibi1ity~** However, the cost ofsuch modifications can be considered in estimating cost and economic impaCts."



### ·B&McD's March 19,2007Response: The needfor a majorsourceof heat to reheat thejlue gas stream clownstream oithe ESP in a low- . dustSCR application will require either an expensive naturalgas supplypipeline onm unac<;eptable . derate of the nei unit electrical output associqtedwiih extensive. modifications of the. components in steam

. cyclepowergeneration andbalance-ofpli:mt systems and, boilergas systems to supply highpressure,' .

. hightemperature steam as suggestedbythe EPA and their consultant . . The magnitude of such retrofit" . mod.ijicationsandrisks of failure in applying/ow-dust SCR technology at MRY.S are much**gr~ater** 

### than Is considell'edreasonable. '. .' . EPA 'Response: .

. . .

. B&McD contemplates

### ~he.useofnaturalgas (and associated COflstfuetionofanatural gas pipeline) and plant steam for flue gas reheat arid makes a 'general statement that the "magnitude: ofsuch retrofit"modificatiOJ,1s and risks offailure in applying low:-dust SCR technology atMRYS 

### -32-. EPA Response to Minnkotl Comment Letters from March 19, 2007 and April 23, 2007

. BACT Analysis at MRYS are much greater than is.considered reasonable." AbsenrfrOIll 8&McD's consideration for flue gas reheat are fuel oil**ait~** propane (instead ofnatUral gas and the associated pipeline). These

. options would likely require a less complex analysis. Based on their response, it is unclear if

.. B&McD is still eliminating low-dust SCR as technically infeasible or int is dismissing further

analysis as unreasonable as part ofthe ecc:>D.omical analysis under step 4 ofthe Top-Down BACT

. . analysis. While EPA acknowledges that the two options described by B&McD would require engineering and cost estimates, EPA does not agree that a cost analysis for low·dust SCR should· not be required. FUrthermore, as stated in EPA's original January 

### 8, 2007 comments, recent pennit actions issued by.both the North Dakota Department ofHealth and Region 

### 8 included a cost analysis for low-dust SCR. B&McD did not respond to this original corriinent. . 

### ·2. EPA Analysis ofthe Site.SpaceConstraintIssue: 

### EPA's January**~,2007** 

### Comment: While the extentof thephysicalplant modifications necessary to accommodate low-dust SCR at the MRYS is not entirelyclear, the above description does not indicate that the site space constraints at MRYS wouldnecessarilypreclude thepossible installation of low-dust 

### sci?. It does sound like major**a~d** costly equipment relocation may be necessary toprovide .the space necessaryfor low-dustSCR However, consistent wlttz the NSR Manual, "physical modifications needed to resolve technical obstacles do not in andof themselvesprovide ajusJificationforeliminating the control technique on the basis of**·~~~~~tHteehnieal-infeasibiJity~1'he8e-:c-&sts:-sh()uld-be-q~eountedf(J~hen-estima#ng4l~and-ee()n&1nie~. ~­** 

. impacts of low-dust SCR, but shouldnot be usedas a basis for eliminating the technology as techfJically mftaswk. . . 

### B&McD's March 19,2007Response: Significant engineering resources wouidneedto be devoted to investigate and estimate the capital costs of major boiler andairpollution·equipment relocations, facility additions, and boilerhouse building modifications required to implement low-dust SCR**t~chnoloiY** atMRYS. Burns & McDonnell believes the expected levelizedtota(antzual costs requiredfo apply low-dust SCR technology to North Dakota iignite-jired cyclone boilers are unacceptably high. . 

### EPA Response:

. IfB&McD "believes the expected levelized total annual costs required to apply low-dust SCR technology to North Dakotalignite-frr¢d· cyclone boilers are miacceptably high", more detail should be provided within step' 4**oftheTop~Down** BACT analysis•. EPA acknowledges

. that extensive work·may be required for installation oflow-dust SCR and the costs might turn out to be unacceptably high, but the NSR Workshop Manual does riot allow for dismissing a control. option based on unsubstantiated beliefs ab()ut costs. B&McD should do a cost estimate basedon reasonable expected reheat fuel requirements, equipment installations, plant . modifications, etc. A comprehensive analysis would .be unnecessary ifit is shown that costs of 

### ..,..33-. EPA Response to Minnkota Comment Letters from

. . March 19,2007 and April 23, 2007

. BACTAnalysis at MRYS 

### one or two aspe.cts 

# ofinstalling low-dust SCR (i.e; the reheat fuel costs) would be unacceptably.. high. Since there have**b~en** 

### low-dust Installations at utilitY boilers, EPA cannot concur 

## with the general aSsessment that the ·costs· are expected to be unacceptably high·for MRYS: .. 

### 3. EPA Analysis ofthe Burns & McDonilell'sConcluslon:



### ·EPA's January··9, 2007**Co~ment:** As explainedabove, EPA Region 8 believes

### th~t the inherent challenges with installing and . operating low-dust SCR at ·MRYS are· resolvable on a technical basis. Thefact that a few low-dust SCR applications are currently used inpractice indicates that the small-pariicle catalyst.fouling and . deactivationproblem described wouldnotpreclude the use of low-dust SCR ;. B&D's statement's that "low-dust SCRperformance andcatalystlife could be severely negatively impacted r.esulting in premature, extended,frequent outages for replace.ment" can be minimizedbyproperSCR design and online cleaning. As stated previously, any real costs associated with the construction and maintenance required to operate the low-dust SCR shouldbe accountedfor under the economic impacts stage· of the Top-Down BACTanalysis (step 4). Similarly, physicalplant modifications that would be required to· . accommodate the low-dust SCR (andauxiliary equipment) should be considered in the economic impact evaluation, rather than usedas evidence oftechnicaiinfeasibility ...



### ·B&McD's March 19, 

### 2007Response: . Asprevi(J1,Isly stated by the EERC; the EPAfdils to recognize that lignite-jired cyclonesjJartition the. ash, increasing theproportion of sodium in the slJlallerparticles, resulting in increased propensity for· theformatiori of the complexsulfatephases. the.fly ash becomes enriched in components that vaporize aruJ, subsequently, condense upon gas cooling toform liquidph(1ses andsmallparticles that are very .. reactive to gas-phase components that cause bonding, blinding, anddeactivation of individual catalyst .. reaction sites, even in a low-fjust SCR application.· .. . 

### EPA Response: 

### .:

- . .' .'.. . '. . . . . -

. . . . '. . 

### B&McD appears to be saying that a significant portion ofthe sodium in theflyash is irtthe vapor phase when itenters the ESP. Therefore, these smaller sodiuin particles would not be controlled by the· ESP and would condense: to a liquid at the temperature range for a low:"dust SCR. This results in bonding, blinding, .and deactivation ofindividual reaction sites ofthe catalyst. ...There is no ·qiIantificationofthe**·fly~h** 

### ·sodium in 

### the vapor phase that would cause the severe catalyst plugging**andblindi~g** 

### described under the high:"dust SCR portions ofthe BACT

· analysis. PresumablY,ifa sighificantpoi1ion ofthe flyashsodium is in vapor phase when it . would be entering the ESP, that same portion would also be in vapor phase When entering a highdust SCR and therefore 

## not affect the catalyst. EPAis not disputing that there may be some vapor phaseflyash sodium that will bypass the ESP arid deposit on the lcrw-dust SCR catalyst. Based ()n B&McD.and EERC'sasse.rtions that

# a high-dust SCR system atMRYS would see a .. sodium environment higher**th~~y** 

### other SCRsystem in the world, 

### it would seem that most 

### of 

## -34-EPA Response to Minnkota Comment Letters from March. 19, 2007 and April 23, 2007 BACT Analysis at MRYS 

### the flyash sodium is not expected to be in vapor phase at the temperature ofthe high-dust SCR

. aridESP. 

### Ifthis is the case; 

### EPA expects avery large portion ofthe flyash sodium would be.

removed by the ESP and not effect a low-dust SCR installation. . . . Additionally; during EPA's April. 16, 2007 phone conversation with Flemrriing

### H~sen of Haldor Topsoe, Mr. 

### Hansen indicated Haldor Topsoe did run some catalyst "testcoupons" at the Wisconsin Electric Power (WE Energies) Presque Isle Station, which burns Powder River· Basin coal with similar sodium levelsto North Oakota lignite. ·Mr. Hansen recollected that there· was a significant difference in the deactivation ofthe test coupons upstream ofthe.particulate control device (ESP) compared to downstream ofthe ESP at Presque Isle. Mr. Hansen did not offer a reason why or attempt to quantify the difference. The most obvious explanation for the . difference would be that the ESP·removed Ii 

### great deal ofmaterial that deactivates catalyst. This experience suggests that catalyst deactivation observed at 

# a low-dust SCR would be less than at a high-dustS CR.···· , III. Additional Information Useful to Evaluating Technical Feasibility ofSCR at MRYS A. EPA Headquarters Believes SCR is the Correct Technology for MRYS in Developing the Clean Air Interstate Rule (CAIR)

.. . During thepreparation of the CAIR rule, EPA developed a scenario for bestcontrols across coalfired units. in the UnitedStates basedon an assessment of boiler type, fuel type, and existing controls. . This assessment recommended that SCR technology would be the best technology for the two units at MRYS. Several commenters -- Montana-Dakota Utilities Co. (VLC.,0754); Otter-Tail Power Co. (YLC- . 0628); Lignite Energy Council (VLC-0935); Lloyd, Gosselink, Blevins, Rochelle, Baldwin 

### & Townsend, P.C.for Texas Lignite Coalition (VIC-1037); andBasin Electric Power Cooperative (VLB-0690)-- argued that SCR technology is not feasiblefor application on lignite-fired boilers. Some 

### of these· cOmmenters claimedthat an SCRpilot test on a slipstream from a boiler firing lignite hadshown catalyst plugging and blinding. One commenter attribuied thisproblem to sulfates of calcium andsodium, which arepresent in the.flue gas stream entering the SCR, asa result of firing of lignite in the boiler. One of these commenters also claimedthat SCR was notfeasiblefor boilersjiring sub-bituminous. In its response at VIB. of the CAfR docket. EPA·notedthat there is considerable experience in the industry to show that use of SCRon**sub~bituminous** coals and lignite is ,technically feasible. SCR is currently"in use on several sub-bituminous coal-firedboilers in the US. firing Powder RiverBasin coal. Regarding the USe ofSCR on boilersjiring lignite. EPRIiesting"ofSCR catalyst in a slipstream at the Martin Lakeplant showedacceptable resultsfrom Texas Lignite. Furthermore. the technology suppliers repor.t that SCR has been srlccessfully zisea'on lignite and brown coal boilers in Europe. From this

. experience. it can be concluded that SCR can be usedon sub-bituminous coal andlignite boilers in the 

### -35-" , EPA Response to Minnkota Comment Letters from March 19,2007 and April 23, 2007

. BACT Analysis at MRYS US: andcatalystsuppliers have

# i~dicated**~hat** they will offer

# perfor~ance**gu~rantees** on these',

. applications in the 

### u.s. . In, the docket information regarding this i;sue, one 

### .of the SCR catalyst vendors, Argillon, provided a list aSCR,in'stallations at EGUs·in Eu,ropethatburnligniteor'similar rank coal, including:.,

• Riedersbach installations in 1995 and2001 (hard coal/lignite) .• 'Voitsberg (lignite)

• Dormagfm installationS in 1994,'and 1996 (lignite) . EPA also noted that/he commeriters have notprovidedany details of thepilot test that has been mentionedwith regards to theplugging and blinding of a catalyst from lignite-generated fuel gases. .' Without this information, thispart of the comment cannot be a.ddressed properly. The EPA's oWfl. . investigations show that the main reason for thisproblem was ash build up on the catalyst, 'which is a problem commonly experienced inpilot test facilities. In the**full~scale** installations, this concern is , addressed. during the SCR design stage: The methods'usedto avoid thisproblem include duct design to promote ash falloutprior to the SCR, catalyst reactor design to avoidash build, up, 'and on-line cleaning methods (sootblowers'andsonic horns). In addition,. thefoilowing catalyst vendors statedthat they could provide catalysts/SCRforlignitefired boilers: Haldor-Topsoe Cormetecl:z Argilion :.. ' lit a memo datedAugust 20, 2004, Jim Staudt of Andover Technology Partners to Sikander Khan of EPA CAA,1D, discussedboth the EERCpilot testing results andsome of the negative issues raised by , B&Manddocumented how Haldor Topsoe was aware of these issues, but neverthfllessfelt comfortable providing SCR catalyst... ... ..... . EERC's 

### March 19,2007Response: EPA's cited experiencefrom subbituminous coals cmdSCR does not haVe direCt application to the North Dakota tignite-firedcyclone boilers a{MRYS because of the high sodium content of the lignite. The SCR experience withGerman brown coals does not have direct appiication to ND lignite because. of. the lower sodium levels of the German coals. "

. ., " ". EERC spoke to Flemming Hansen of HaldorTopsoe .. : on February2, 2007 about ihe issues' associated with high spdium North Dakota: lignite. Haldor Topsoe hits ?xperience with sodium and potassium from biomass fired systems and their experience has not belm good. After describing the issues related to sodium ....... after 60.00 to 7000 hours %peration with 

### ci coal having elevated/evels of sodium. 

### . ' 

### EPA Response: EPA's presentation ofsome U.S.' subbituminous coal and 

# Geiman broWn coal experience was intended to demonstrate that SCRsystems 1}ave,beert shown to work worldwide on lower-, ranked coals. While direct application ofSCR experience on these coals'may not be entirely. appropriate for North Dakota lignite, EPA did use this information (along with the other factors 

### -36- ,

### ..EPA Response to Minnkota Comment Letters from March 19,2007 and Aprit'23, 2007 , BACT Analysis at MRYS described in the January 8, 2007 comments) to conclude that SCR was technically feasible for lignite boilers in general. ' As described above, EPA's discussion with Fleriiming Hansen ofHaldor Topsoe also revealed that despite concerns about 

### ali SCR system subject to the sodium environment that would exist for a North Dakota lignite application, Haldor Topsoe would not rule out bidding such a project. 

### B. '. SCR Technology is PresuinptiveBART for Cyclone Boilers in EPA's BART Guidelines EPA's January 

### 9, 2007 Comment: EPA made a specific and informedde(:ision in its BARTdUidelinesregarding cyclone-fired utilitY boilers. For all other boiler types, some form of combustion control was deemed to be ihepresumptive ' level of contro/; However,jor cyclone units burningany, type of coal (bituminous,subbituminous, or lignite), presumptive BARTis SCR SCR was se(ectedbecause the technology 

## isfeasible andcosieffeCtive**~....** " ' 

### B&McD's March 

### 19, 2007Response:**~~~~~~** 'KP:A Ignored the n'umerous comments ree-ewe«jor**rh7rdrafrs-%~fi1TesTstmilllrtU1frat"7:ire-d~-u---~-~,-­** in the EPA's CAIR discussionfor thepreceding issue) about the infeasibility ofSCR appliedto North, Dakota llgnite. The unit capital cost capaciiy factor for SCR retrofitsappliedto cyclone boilers 'by the EPA i.n the cost-effectiveness analysis usedforestablishingpresumptive'BARTwas $1001kW. Burns & McDonnell believes the EPA 's

### cost~effeCtiveness analysis is inaccurate andsignificantly underestimates the expectedcapitalplus operating and maintenance costs required to apply high-dustor , low-dust SCR technology, to North Dakota lignite-jiredcyclone boilers.



### ,EPA Response: ,B&McD contends that EPA ignored numerous cornh1ents received on the draft BART guidelines about**infea~ibility** ofSCR applied to North Dakota lignite. As stated above, EPA
, weighed many different factors and concluded that SCR'is technically feasible for a plant fired on North Dalcota lignite. ' B&McD also contends that EPA underestimated the capital costs for SCR on cyclone boilers and that total cost ,estimates in the BART guidelines are inaccurate for applying SCR to North Dakota lignite-fired cyclone boilers. EPA is not suggesting that the cost figures used in the BART analysis need to be used in the BACT analysis for MRYS .. EPA has maintained that Minnkota should provide a cost analysis for Units 1 and 2 according to step 4 ofthe Top-Down BACT analysis. . . 

### -37-EPA Response to**Minriko~** Comment Letters from March 19, 2007 and Apri123, 2007 BACT Analysis at MRYS

, , , 

### C. February 27, 2006 Final Revisions to 40 CFR Part 60, SUbpart Da,

### N~w Source' Performance Standards for Electric Utility Steam Generating Units Set Final ' NOx 

### Limit Based on Technical FeasibilityofSCR for Lignite-Fired Units. EPA's 

### jiIn':l{iry 9, 

### 2007 

### Comment: In its response topublic comments on the February 28,2005 draft NSPS,Subpart .(Japroposal" EPA rejectedcomnientsreceivedon NOx control requirements for lignite-fired units. Specijic;ally, EPA took the sameposition as it did in the CAIR andBARTrules, rejecting commenters'concerns that SCR wouldnot befeasiblefor lignite units. No legalchallenges were made to thefinal rule regarding EP.A's response to the lignite concerns ... ... ....' , 

### B&McJ)'s March 19,2007Response:.

, , ' Burns & McDonnell rejects the EPA;s argument that the lack of a lawsuitprotesting the establishment of revisedNSPS limits for new electric utility steam generating units (EUSGUs) that require SCRsfor NOx control mea;"s that this is appropriate technology jor a BACTretrofit on existing lignite-fired cyclone boilers. Cyclone boilers are no longer commercially available, so there are, no new, cyclone boilers, beingpermittedand built. Utility owners of existing North Dakota lignite-Jiredboilers wouldnot be expected te c()mment on the. draft revisions to the NSPSproposedby the EPA because they apply only to new units with different methods of firing coalthan cyclone. boilers. It is doubtful that the ' EPA consideredjJringlignite in new cyclone boilers would be apossibllity when theyproposed the draft NSPS standards.. Anyrecently bulltorpermittedlignite-jired boilers have'beenpredominantly

### ci~culatingjluidized bed (CFB) type andhave not incorporated, SCR technologyforNOx emissions control. There havebeeTi receni permit applications filed for constructingpulverizedcoal boilers burning Texas lignite that , propose to jncludehigh-dust SCR teelmology. H9wever,. there are distinct differences betWeen North " Dakota and Texas lignites thatpreclude assuming that this supports the technicalfeasibilityof applying high-dust SCR technology to existing cyclone boilers burning North Dakota lignite. , ' , 

### EPA Response: B&McDcontends that since no

## ne~cycloneunits are

## b~ing**peimitt~d,&1d'built,.existi~g** , utility owners in North Dakota would not be expected

# to comment on draft reviSIOns to the NSPS , proposed by EPA be.cause they apply only to, new units with different methods offiring coal than cyclone boilers and that it

# was doubtful that 

### EPA consideredfiring lignite in new cyclones when proposing the draft NSPS standards., Actually, the new NSPS standards apply,to, affected utility, boilers that:commence

### constrUc~ioi1~**reconst~ction,** or modification after. Febiuary 28, 2005.21 , 

### (EPA's original comments erroneously said t.hat the standards only, applied to: new Units.) This would inClude any existing cyclone 

### units firing North Dakota lignite that undergo reconstruction 21 See 40 CFR §60.44Da(e) 

### -38-EPA Response to Minnkotll Comment Letters from

_ March 19, 2007 and April 23, 2007 BACT Analysis atMRYS or modification. -The standards**th~t** would apply to**recon~truc~ed** unjts (1.0 IbIMWh or 0.11 IbIMMBtuon a 30-day average) and modified units (lA-IbIMWh or 0.15 IbIMMBtu) are well below the BACT liinit proposed by NJ:innkota. Since these standards apply to modified and reconstructed affected units and notjl,1st new units, the exclusive construction ofnew circulating

_ fluidized bed (CFB) boilers -in North Dakota and the differences between Texas lignite-and

### North Dakota detailed by B&McD and EERC are not

### parti~ublrly relevant to 

## the revised NSPS. EPA does not disagree that all ofthe recently-pennitted utility boilers have been CFB boilers (although that does not rule outthepossibility ofa PC-fired unit inNorth Dakota in the future). EPA also agrees that there have been soine recently-pennitted units burning Texas lignite that have proposed SCR and that there are some differences in characteristics between 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 differencesindicate that EPAdid not consider North Dakota lignite in revising the NSPS for utility boilers. - 

### EERCResponse:

_

North Dakota lignites are substantially different than Texas lignites in composition andfouling tendencies. Thefollowing comparison shows the proximate analyses, sulfurcoritentsandheating values for various lignites, plus ash composttionet! analyses of Texas lignites Comparison o/North Dakota and Texas Lignites Table 3 summarizes ashcomposition analysis expressedas equivalent oxide. The compositional analyses show that t/:ze aSh has**relativ~lylow** sodium and lower calcium content than**·~-~-North~EJakota~fignite~'Fheproblems~of~SGR1JatalY9t-lJlintiing-tiue~t<'!~the-fopmati()nc.o.fs()tiiufnoC-aleium~-~-.:._.~-~-~-_.~~---- ._-~-­**  sulfates createdfrom thefiringofTexas lignites will be**mu~h** less severe/han/orNorth Dakota lignites. 

### EPA Response: EPA has reviewed the coal data submitted by EERC and, in general,**~grees** 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 sodlUIil content above 

### 3% (EPA

- assumes this is an average) compared to the average (or 59th perceiltile) value of4.4% forCeIiter

mine coal (per the April 23, 2007 coal analysis submitted by Minnk6ta). - Considering the high ash content ofthe Jackson South lignite (42% average) 

### and low heating value (3,972 Btullb as received), compared to the ash content (9.53% average) andheatingvalue_(6,572 Btullb) of Center Mine lignite, the Jackson South lignite ofTexas would actually have a much higher sodium loading (on average) than CenterMine lignite (by roughly a factor of

### 4). The Yegua East lig:nite with an ash content of 18% and a heating value of5,761 Btullb would have a sodium loading ofroughly 60% ofaverage Center Mine lignite. As explained in previous comments, EPA does not believe a strict linear comparison can be made from these loading levels, but it : -

appears that some Texas lignite has comparable sodium levels- on-a per Btu basis to Center Mine

- -lignite.
-39-EPA Response to MinnkoUl Comment Letters' from ". March 19; 2007 

## and April 23, 2007 BACT Analysis at MRYS NotWithstanding the

## difference~'betWeen NorthDakota lignikand

# Texas lignite; a modified cyclone boiler firing North Dakota lignite would still need to meet the most recent NSPS Da liniitfor modified'units, which is much lower than the BACT 'limit proposed 

### by Minnkota. The likely choice to meetthi& limito{O.15Ib/MMBtuwduldbe SCR.· 

### D. SCR

### ~nd Catalyst Vendor

### I~formation. EPA's January 9, 200tComment: As notedabove, the following catalystvendors were

### ~omfortablep.,roviding cataiystslSCR/or ligJ1itefired boilers: Haldor- Topsoe,Cormetech, andArgillon. . '.

. . In addition, the above-citedmemo datedAugust20, 2004, Jim Staudt of Andover**Te~hnology** . Partners to Sikander Khan of EPA CAMD, discussed both the EERCpilot te8ting results andsome of the negative issues raisedby B&Manddocumented how Haldor Topsoe was aware of these issues, but

.nevertheless felt comfortableproviding SCR catalyst. . ': .' . '. .' . EPA Region 8.also contaCtedthe

### Instii~te ofelean Air Companies website to obtain thefollowing list of 2 I companies offering "SCR Systef11s, Equipment; $uppti"es andServices: .. EPA Region 8 has visitedmostof the

### ve~dors 'websites.andfound many vendors with experience thatwould. be germane to the MRYSsituation .. ; ..... Webelieve itwoitld beprudentfor Minnkota to obtain information qndproposals.jrom more than onew!ndor and involve the NDDHandEPA in 'their findings.' EERC's March 

### 19, 2007Response:

.EERC has already includedsome. comments from discussions with Haldor Topsoe regarding'lheir .

. concerns about the sodium content in North Dakota lignite and its tendenciesfor catalyst deactivation..

Some of the. EPA-citedSCR catalyst vendors' web sites discUss theproblems of sodium anddeac.tivation. However, EPA has notprovideda ri!viewof that informaiion. . 

### EPA's Response:

. EPA has already

### disc~ssedits phone

### ~~nver~atiori with FleIIimingHansen ofHaldor Topsoe and how Mr. Hansen, while acknowledging some difficulty de.aling with the sodiuin . . .. issue with North Dakota lignite; did not dismiss that an SCR system might'be technically feasible' for

# a North Dakota lignite application, nor the possibility that Haldor Topsoe would bid on such:' a project: '" . . . B&McD March 

### 19, 2007Response: EPA's listing of21 suppliers of"seR Systems, EquiPment, Supplies, andServices " has not been screened to e.liminate companies that are not active in the U.S. coal-firedSCR market EPA 's 

### '-40-EPA Response to Minnkota ComrtlentLetters from , March 19, 2007 and April 23, 2007 , BACT Analysis at MRYS evidence of SCR catalyst vendor's willingness, to guarantee. performance on a lignite.1ired boiler is very general in nature anddoes not include typical qualifying statements reiated to (he client's needto adhere, to specifiedSCR design conditions, which are yet to be**~stablished...** ... ... '

... .•. .from Burns & McDonnell's experienc.e, what d vendor or supplier sayspre-biddoes not always match whOt they actually will offer in afirm contract..... a c.ommercial guarantee does not mean the systemproyidedby the vendor will work long term; all it means is that based 'on the language in the contractand the 'amountof money the supplier has allocatedto cover their risk or exposure, the vendor willguarantee the systemperformQ1lce commercial contraCtguarantees always have afinite life, which means the owner of the system orily benefits from the vendor's guaranteefor 3 years**~pically** .... EPA's cites SCR catalyst vendor statements lack substantive language that deais with mitigating

. the client's risks offailure to meet catalyst activiJy versus life guarantees, and the concerns recently

expressed by Haldor Topsoe when EERC described sodium components in thej/uegas. In Burns & McDonnell's opinion, SCR system vendors have notprovidedadequate documented and publishec! demonstrated catalyst experience with supporting technical inforination to support these claims. The vendors offeredno specificcompcirativepeer-revieweddata asproof that currently-available catalysts can survive and provide effective NOx reduction when exposed to thejlue gas and jlyash constituents exhaustedfrom combustion and operation of any cyclone boiler firing North Dakota lignite, particularly one located in a high-dust,**hot~side** application at Milton R Young Station. EPA Response:**,-~~---,._---. --,~_**  ..

## _-- EPA had originally suggested that Minnkota "obtain informatioil and proposals" from SOme ofthe other companies that EPA had listed. EPA erivisioned this to include more ofthe level of detail described by B&McD,in their March 19,2001 response. while B&McD seems to ' , discount the value ofa performance guarantee, EPA's 

### NSR Workshop Manual states that "(v)endorguarantees may provide an indication of commercial availability and 

### the, technical
, feasibility ofa control technique andcould contribute to a'determinati()n oftechnicalfeasibility or technical infeasibility, depending on the circumstances." While EPA does not believe the vendor guarantee is the solefactor in determining technical feasibility ofSCR for MRYS, EPA does believe it would be 'useful information to obtain for making the determination., '



### -41-EPA Response to Minnkota Comment Letters from" March 19, 2007 lind April 23, 2007 BACT Analysis at MRYS

## "EPA~s "RESPONSE .TOEERCAND B&McD APRIL

## 2~~ 2007 LETTER 

## TQ ND"DH " , COMMENTS - FEBllUARY 1, 

### i007 (lNCLUDINGRESPON'SE 

## TO 

# u.s. EPA REGiON 8" COMMENTS - JANUARY 

### 26,2001):" REQUEST 

### FOR ADDITIONAL INFORMATION"" 

## "ANi> THE NON-SCR COMMENTS FROM EPA " "

## IV~" MINNKOTA'S :RESPONSES TO ADDITIONALINFORMATIONREQUESTED " A. Center Mine Lignite Coal Ash Content and Variability 

### EPA's January 26,2007Request:

. . .' ..".. Please

## ~roVidedata currently available on the tenterMine coal

## ~onstiiuehts (presented in "Minnkota's October 2006NO x BACT Analysis), including all av.ailable**d~ta** samplingforjuture and presently-minedareas of the mine, Pleaseprovide the data in terms of averages, 'in additionio vqlue ranges. 

### EERCAprii 23, 

### 2007Response: The his.toriCal c/atabase was obtained from samples cqllecied for thepurpose of testing the

### imp~ct; of lignite characteristics onplantperformance. The database consists of13J. 7 as-firedsamples. "" The average. standard deviation,"maximuin, minimum andselectedpercentilesfor ash, sulfur, heating value, andselectedash constituents are includediiz Table 1. "

" "" 

### The use of

### averageco~l properties/or design and performance of coinbustionand

### en~jronm~ntal control systems"tYpically under"estimates adverseproblems such asjireside ash depositioil," opacity, 

### ahd" "" "" sulfur emissionS. Designs of powersystems must consider the challenging coal characteristics in"order

## to " " dewlop .,/esigns and'operatingparameters with sufficientflexibilitytharallow for. the combustion of coals "" thatert least represent the 9(jh arld 1(jhpercentile of selectedconstituents , Thefrequency .' "" " distributions a/components Qf the coalprovide better understanding

### of the**potentiall:hallenges~** ... The results of the analysis show that the lignite ash has 

# a4.4% average sodium content; however, there is 

## ci multimodal distribution of**~odium** levels in the coalash..... The averageproperties as well as the . " minimum andmaximum values do not adequately represent the characteristics of the

### fuel. As indicated in

. Fi/Wre 1, the MRYS boilers arejiringsome very high-sodium-containing coals that can cause significant . proble111swhen sodium .reacts with silicate, aluminosilicate, andsulfur species in the furnace and lower temperature regions of the·power plant." . . 

### EPA Respons"e: " EPA has revievved the coal data submitted by Minnkota. .EPA believesthe future coal data" " appears to show little change from the 

### 2007 core samples. EPA is·not sure what the basis is for

EERC's statementthat "s'odium levels have shoWn increased levels in the future coals that

# will "likely contribute to increased fouling

### challeng~s.,,22**"Th~** sodium oxide percentages from 

### 2007 22 See page 10 ofApril 23, 2007 letter from Minnkota to EPA, DOJ, and NDDH.· 

### -42-'EPA Response to Minnkota Comment Letters from March 19, 2007 and April 23; 2007. BACT**Analysi~** at MRYS 

### compare very closely to the 2009-2010 cores samples (Ave; = 

### 5.8% vs. 5.6%, Max 

## = 13.3% vs. 13.4%) as do the ash percentages (Ave. = 

### 7.9%'vs. 7,1%, Max 

### == 24.6% vs. 23.8%). As explained in great detail above, these differences 

## in coal characteriStics are useful tor making general comparisons with other fuel types, but it is unclear how these differences can be directly applied when making determinations on feasibility ofSeR atMRYS." ' 

### B. High Economizer ExitTemperature NDDH's February 

### 1, 200·7Request: The temperature between the economizer and the air heaters is described as "much higher than· 750 degrees". Pleaseprovide more spec;ijic data on the temperatures tl1Qt wouldbe· encounteredat the· location an SCR would be installed. " 

### B&McD's April 

### 23,2007Response: The primary superheat (PSH) outlet flue gas temperatures for Unit I areprovidedinsteadof the eco;'omizer outlet temperatures. Unit 1 at the MR. Young Station has a two-pass tUbular airpreheater (APH). The economizer for Unit 1**i~** situated between thefirst andsecond pass of the airpreheater. The flue gaspasses on the inside of the**~ubes** of the AP H... .. : ..... The configuration of the ·economizer and air .

. preheaterphysicallyprecludes locating a conventional high-dust SCR upstreatn of the eXisting air·**--~-P1:eheatei."ecorwmizer-OfLUniLLiJ:ilts.i:un:entlac-atiol1.JJ11dJ:f)lJJJgw...atioJ1,~TfzejlueiaS.1gmllerqllP~.g** is .. _ __._.._ . reduced by trcmsferring heat to the boiler 'sfeedwater and the boiler's combustion cmddrying system air streams; respectively. In addition, temperatures at the existing airpreheate-r outlet for Unit 1 arefar below the "temperatures neededfor operation of a conllentionalhot-side high-dtistSCR. The Unit No. 1 boiler is shut down/or cleaning at intervals rangingfromapproximately 90 to 120 days.. .The gas**temperatures~at** the PSHoutlet vary inversely with the boiler cleanlb:zess during each operating run Note that qt/ow loads and clean conditions, thePSH'outletjlue gas temperatures are 170-270 degrees F below the acceptable rangefor conventional hot-side high-dust SCRcatalyst .... Unit 1 's PSH full-load flue gas temperatures historically range between' 840Fand 960 F, depending upon the cleanliness of the boiler..... there have been instances when Unitl's PSHfull-loadaverageflue gas temperatures have exceeded 1000 F and individual temperature measuring elements have exceeded 1050 F ..

.A portion of MRYSUnit 2boilers' feedwater heating surface is iii 

## alocation normally occupiedby a traditional conventional econ01nizer section in the convection·pass of the boiler '" The configuration of the boiler's economizer and the airpreheaterphysicallyprecludes locating a conventional high-dUst SCR upstream of the existing**air~preheater/economizer** on Unit2 in its current location andconfiguration :. Unit 2 boiler is shut downfor cleaning at intervals rangingfrom approximately 80 to 110 days. . at low loads andclean conditions, boiler outlet flue gas temperatures are 170-270 degreesF below the acceptable range Unit 2 's boiler-exit economizer-outlet full-load flue gas temperatures historically rangefrom 780 to 880 F... :.there have been instances when Unit 2 's 

### -43-EPA Response to Minrikota Comment Letters from March 19,**~007** and April 23, 2007

. BACT Analysis at MRYS . average full-load economizer outlet }iuegas temperatures haVe exceeded

## 930Fand individual temperaturf! measuring elements have exceeded990 F. . 

### EPA Response: This inforniation that was requested by NDDH was reviewed by EPA. EPA acknowledges that there are times when the flue gas teniperatUie at the.portion pfthe boiler:where a high-dust . SCR would be located (primary superheat outlet for Unit 1 and presUmably the economizeiexit for Unit 2) would be higher than the temperature range typically ·suitable for 

### SCR.

. While B&McD seems to iiidicate in

# the March 19, 2007Jetter that the dual-air preheater design suggested by ERG**~ould** 

### be problematic, it later concedes thafitconceptually could work, but would be at an additional cost. EPA agrees that such a design would cost more than a . typical high dust SCR application. A more refined cost estimate that .·reflects real c·osts . associated with constructing and operating a split air heater design can certainly be submitted 

## by Minn.kota. EPA believes this would be conducted under step 4 ofthe Top-Down BACT analysis..

. For further information

## ~n this topic, please refer to the August 

### 2007 Christman Memo response regarding the split air. heater. . . . . C 

### Low-Dust**~CRFouling**



### .. NDDH's February 1, 2007Request: .

. Itis indicatedthat a low dust SCR wouldbe subject tl} the same fouling.problems as·a high dust SCR due the emissions of small

# « 5 micron) pariicles containbig sodium-calcium sulfur rich materials. Pleaseprovide any existing data on the composition of theparticulate matter exiting the electrostatic precipitators. 

### EERCApril23, 2007Response: Aspreviously discussed in responses to the EPA's January 8, 2007 commenis} the MRYS cyclone . b9i1ers 'fly ash becomes enriched in Components that vaporize and, subsequently, condense upon gas

. cooling to form. liquid phqses andsmqllpartiCles·:that are very reaCtive to.gas:'phqse components, resultingin!ormatio':'of compounds ihat cause bonding; blinding, anddeactivation ojindividualcatalysi reaction sites, even in a10w-dust SCR application. Sodium-richaerosokcan get through the electrosiaticprecipitator (ESP).. These aerosols at.e known to bepresent in**high~sodium** coal combustion flue gases. These**spe~ies** are known toproducepyrosulfates. These will cquse blinding anddeactivation of the low-dust catalyst. . . 

## -44-EPA Response to Minnkota Comment Letters from March 19, 2007 and April 23, 2007

. BACT Analysis at MRYS Stack sampling was conducteddownstream of the EPSand set FGD .on Unit 2 at the MRYplant. Theftlters were examined using scanning electron microscopy andx-ray microcmalysis to determine the microscopic features and chemical compositions , The chemical compositions of the analysis

. areas and points were determined through the use of energy dispersive x-ray microanalysis.... 

### EPA Response: This information that was requested by NDDH was reviewed by EPA. While the telative effects ofvaporized particles' passing through the ESP and condensing.prior to a 10w-dustSCR system .might be more pronoull<;ed compared to the non-vapor particles impacting a high-dust environnient, 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 ina" high-dl,lst application would be greater than.in a low-dust application. This is substantiated by EPA's discussion with Flemming Hansen ofHaldor Topsoe'and his experience with SCR test coupons at the WE Energies Presque Isle Station, as discussed above. EPA**acknowledg~s** 

### that there are other technical and cost issues related to low:-dust SCR that were discussed previously. 

### D. SCR DeactIvation EPA's January 26,2007Request:**~~~~~~.~~ .~**  ..**~." Please=-provide-T:lnranrh:tlI~(nlfld-~inf()rmCltir:m~ektted~t(Teatalyst-4fleaeffv€lti€m~1'(1tt!'9'€lnd~~~~-;~-_···_---**  ._".

. control effectiveness measuredat the threefacilities testedduring the "Ash Impacts on SCR Catalyst
, Performctnce" stiidy that is extensively referred to in the "EERC Report" includedas Appendix B of the Minnkota NOx BACTanalysis. This shouldinclude the originalproposal, all testplans, 'all raw catalyst deactivation andNO x control data collectedduring the test, andall final reports and conclusions that wereproducedfor the study'sparticipants. In addition, pleaseprovide a quantitative 'analysis of the application of the multiple engineering solutions (e.g. catalyst.rejuvenation and regeneration, acoustic horns, etc.) described by Roger Christman andEPA to address specific concerns highlighted in the BACT

. analysis andEERC Report and their effect on SCR catalyst deactivation rates andNO x control effectiveness at. MRYS. . 

### EERC'sApril23, 

### 2007Response:

" The EERC offeredto send them to Haldor Topsoefor evaluation; the catalyst vendor indicatedthat the Coyoie SCR test catalysts were toopluggedanddeactivation testing couldnot be conducted. The lack . of

publishedcatalyst activity dataior the Coyote slipstream SCR catalyst field test is a result of the severitj of the catalystfotllingfrom North Dakota lignite ash. The requesteddata is available; this information has been copied, compiled, anddue to its volume, will be submittedseparately. Information on catalyst deactivation rates andNOx reduction effectiveness for the Baldwin and Columbia Station slip-stream SCR catalyst fteld testing was determinedandsome of the information was in thefinal report. EERC recently received informationfrom Hitachi on catalystdeactivationfor the 

### -45-EPA Response to Minnkota Comment Letters from March 19, 2007 and April 23, 2007 BACT Analysis at MRYScatalysts at Columbta. This information is**rnclude~** inthe EERC datacompiledand being submittedto theNDDH.
:. . :.

. . .' .:
. . . Regeliera,;on has been attempted in Europe with SCR catalysts exposedto biomass 

## as with high potassium (elemental symbol K, similar in chemistry to sodium, Na), and they hadsome significant problem in recovering reactivity (KhodayariandOdenbrand, 2001). "



### ,EPA 

### Response: EPA has reviewed the background documents. Please see EP.A;s previous detailed analysis related to the review ofthe pilot study documents under the section,"EPA Analysis ofBums 

### & McDonnell's Conclusion" (responding to the March 19, 20071etter response.) 

### B&McD'sApril 23, 

### 2007Response: 'A qucmtitati;eanalysis on the application of the multiple

### e~gineeringsolutions suggested by the EPA's commenter mentionedabove has not beenperformed. Significantlymore time would be required. A definitive analysis would requirepilot-scale slipstream SCR reactor testing on thejlue'gas streams ' emitted from the boilers at MRYS over a significant length of time to**simula~e** real-time effects of gas and' 'flyash constituents andtheir interactions with the catalyst. Using assumptions of the effectiveness of sol1,ltions suggested by EPA's commenter basedon. use of theoretical data developedfrom laboratory testing and/or 'empirical data gathered from other high-dust SCR installations that do npt treat jlue gases producedjrom cyclone boilers firing North Dakota lignite coal wouldbe hypothetical, Such d theoretical quantitative analysis of EPA's claimedSCR catalyst improvements citedandwhether this .wouldactually be translatable intopreventing the catalyst layers from being suscepiible to macro-pore'blinding and ' plugging by calcium-basedcompounds and the impact on the individual catalyst reaction sitesfrom sodium-based compounds discussed in Dr; Benson's referenced technicalpaper would be speculative. Burns & McOonnidl believes it wouldllOt bf; accurate to burn lignite or

## ~e**jly~h** samples' ' collected from aMR,YS electrostaticprecipiiator l1(i{h artificialflue .gas to simulate c{;ltalyst fouling arid blindingphenomenon in a laboratory.:. orpilot-scalete.st setting Performing a quantitative analysis
,**wo~ld** require substantral resources to develop slip-stream SCR catalyst testequipment designs and'

operational conditions to 'address the significant technical challenges tl;at were. evident in therefere.nce field demonstration testing at Coyote station. It is unreasonable that the EPA expects ihat such. an 

### indepth investigation is required undera BACTanalysis. . ' Performin8 a BACTanalysjson. an existing, unit shouldnot require substantial resources. ..•. .

### ~~:'

, 

# .
-46-. EPA·Response to Minnkota Comment Letters· from March 19, 2007 and April 23, 2007 BACT Analysis at MRYS 

### EPA Response: Many ofthe concerns in this section have been previously presented verbatim byB&McD and have been largely addressed elsewhere in EPA's previous responses. See the March 19, 

### 2007 resp0Q.se to "North Dakota Industrial Commission project Evaluation ofPotential SCR Catalyst Blirtding During

### Co~ Combustion (from the. JanUary

### 8~ 

### 2007 ERG Memo

# r and "EPA

. Analysis ofBurns & McDonnell's Conclusion." ..' . B&McD's response indicates that a complete evaluation ofthe engineering solutions to

.address macro-pore plugging and individual catalyst site deactivation goes beyond the requirements ofa BACT analysis .and would be speculative withOlitdoing additional pilot testing. As noted previously, EPAbelieves that Minnkota faces a high threshold for demonstrating that a technology like .SCR, that has been widely-deployed in the same industry, is technically infeasible. While results from a well-designed and operated pilot test would certainly be useful in optimizing a potential SCR system to deal with the plugging, blinding, and deactivation issues, EPA is not convinced that it would be required ifa conservative design approach is· taken. . . In the previously mentioned meeting with**Sarge~t** & Lundy, LLC, Mr. WilliamDePriest, Senior Vice President and Director or Environmental Services, indicated that an SCR system**~~~~~c~oe-::u=ld** theoreticallyJ>e .designedto operate on North Dakotalignite, but indicated the. design**._~~.** __.._._ would likely have to be conservative in terms ofthe catalysfdeSIgn mid**sI2~rngofthereactor** and could result in significant maintenance requirements and associated outages. Sargent & Lundy representatives were ofthe opinion that a well-run pilot test would yield valuable information that could be used in conjunctionwith previous SCR experience to**evaluat~and** design an SCR system for-a North l)akota lignite application. . . In EPA's view, the unanswered questions related' to North Dakota lignite described by Sargent & Lundy would likely result in exaggerated .capital costs (conservative design) and/or potentially result in additional operational costs to Minnkota. EPA agrees itwould be preferable to have additional data related to catalyst deactivation on North Dakota lignite in order to'select the optimum catalyst design and reactor size. It is unfortunate thatthe pilottesting at Coyote Station.did not capture this information. However, the risks.involved in the capital and operational costs cannot be used as the basis for a determination oftechnical feasibility. The NSR Workshop Manual states that "(w)herethe resolution oftechnical difficulties is a matter of cost, the applicant should consider'the technology as technically feasible. ,,23 EPA believes that the cost for a conservativdy-designed SCR system at MRYS that minimizes 

## the associated**ris~** described and includes an anticipated catalyst operation and maintenance schedule can· be . estimated and accounted for under step' 4 of the Top-Down analysis.

. . 23 See NSR Workshop Manual page 8.19-20 

## -47-. EPA Response to Minnkota Comment Letters from· March 19, 2007 and Aptil23, 2007 BACT Analysis at MRYS 

### K SCR Vendor Guarantees EPA 

### ;s Jan'!!lry 

### 26, 2007Request: Although EPA 'stJraft'1990NSR Workshop'Manual recogniies thai vendor guarantees by themselves are not,sujJicient,to show that a technoloiY. is feasible, ve,ndorguarantees can contribute to a . technical feasibility determination in some situations. In light of statementsEPA has received from three SCR vendors (Haldor Topsoe, Cormetech, andArgillon) indicating they would providepeiformance guarantees on SCR lignite applications, pleaseprovide additionalvendor information,from multiPle vendors, thatMinnkota believes is more specific to MRYS them the statements received byEPA andcited in EPA's analysis submittedtoNorth Dakota on January 8, 2007. We would expect that the catalyst. suppliers citedabove would be among the vendors contacted by Minnkota. EERC's

### April 23" 

### 2007Response: EERC has alreadyinc!udedsome co;"mentsjr()m February 2007

### tel~phone discussiQns with Haldor Topsoe regarding their concerns about the sodium content in North Dakota lignite and its tendencies for catalyst deactivation. . 

### EPA Response: EPA has previously presented its 

### Owll discussions with Haldoi Topso.e. 

# .. .' B&McD's

### April 23,. 

### 2007Response:

, .A query

# 0;SCR catctlyst verid()r

## ~s willingness to

## guarant~e performance on a lignite-firedbOilerto ' .' address comments in EPA's citeddocuments mentionedabove has not been completed. AdditionaltimeJ$

required The information on SCRpeiformance guaranteesfor MRYS applications has been requested; 

### it will,be submittedseparately when iUs available. A copy o/the information request letter and

. attachments,issued to the SCR vendors'is attached (AppendixA). ' .

. . . ... .. . . . '
. . ..' , 'System andequipment vendors have ase/f:interest to 'sell technology that they offer, and to manage finanCial risks by specifyinglhe limits of their system design in case of potential operating condiiions that
, causepeiformanceproblems thatprevent**achievem~nt** of guarantees and/or warranty claims'" ....



### , , EPA Response:

, B&McD states obtaining this infomiation will require more

## tim~. They have

## s~nt a letter to four catalyst system suppliers and five catalyst suppliers. TheJetter goes into great detail about the worst-case nature ofCenter Mine coal·.' During the May 23, 2007 meeting, in Bismark with Minnkota and NDDH, B&McD indicated' that: they did get some feedback' from a few vendors, but were unable to disclose any written response at that time ,

### EPAhas still not seen any vendor
, responses to the information request. EPA does note: that the request**see~s** 

### to have been written 

### -48-EPA Response to Minnkota CommentLetters from March 19,2007 and April 23, 2007 BACT Analysis at MRYS with a pessimistic tone that would likely lead the vendor to believe that the requestor was not serious about obtaining 

# acontract for the described·SCR project.. There is also reference to . cornillents made by.EPA on the Minnkota MRYS BACT analysis,

### which·~o\Jld provide further

.disincentive on the**part.of~e** vendor to properly evaluate and give serious consideration to the request.· Because ofthis EPA·is suspect that the feedback might be negativ.ely biased and not provide'a realistic response to whether a vendor wQuld be interested in bidding a performance. guarantee on an SCRproject'at MRYS. . . 

### F. '. MRYSBoiler Cleaning Outages EPA's January"26, 2007

### Request: The Mimikota MRYS NO x BACTanalysis includes discussion of periodic boiler outages that are required to address the slagging effects of the Center Mine lignite. Pleaseprovide historical dates of . thesf! outage periods and their durationfor theprevious 10years. Also, pleaseprovide an estimate of · .boiler outage frequency that would be expecteddue to SCR maintenance, bas.ed on information collected in response to items 1 and2of this list. . .



### · B&McD'sApril 23, 

### 2007

### Response:'

. Information to estimate· MRYS boiler outagefrequency expected for high-dust SCR maintenance**~.** -.- .._.**~~9fjased** upon a**qlIerJl:7)fieIrcutalystverTdors-mentioned-in-ite"d~above-is~not~avail-able-aHhi~ttme~---'-·** .-.**~~~** Additional time"is required' . A revieWof historic outage data shows**t~at** over thepast 10years (1997-2.006), the typicalMRYS Unit1. boiler cleaning outage was between 67 and 82 hours in duration, but these clm be as short as 56

. ha,urs and as long as 206 hours.....**~Over** this same timeperiod, the typical MRYS Unit 2 boiler cleaning

. outage was between 64 and 102 hours in duration, but these can be as short 

### as 37 hours and as long as

244 hours A boiler fireside cleaningoutage is typically scheduledfor 96 hours (four days) duration. . . A high-dustSCR would need to be isolatedfrom the gaspath between the.boiler and the inlets to the electrostaticprecipitator during boiler cleaning outages to prevent the moisture anddeposits . liberatedduring boiler fireside surface cleaningfrom entering the SCR reactor. Beginning the work of removing ash accilmulation or catalyst from the SCR reactor(s) will be delayed by 48 to 60 hours after

·the start of the outages, depending on ambient temperatures, because the inside of the reai:tor(s)"will be too hot forpersonnel health andsafety. Because the length of the boiler cleaning outages is typically less . than 4 days (96 hours), that does not leave much time to do any significantcatalyst cleaning or replacement work without delaying boiler startup. The estimatedamount of 

## time anddifficulty in . removing lignite ash accumulation from ihe SCR reactor(s), or replacingfouledcatalyst with clean spare catalyst, is expectedto require at least 144 hours (6 days), plus 60 hours upfrontfor allowing the reactor to cool-down.. This is based upon the use of mobile industrial vacuum cleaning methods ("super-sucker" truck). The total SCR maintenance outage time will be around200 hours from boiler shutdown endto 

### -49-EPA Response to Minnkota Comment Letters from

. .March 19, 2007 

### and April 23, 2007

. BACT Analysis at MRYS beginning a/startup.

## rh~ frequency olsuch $CRmaintena1Jce outages are expectedto be requiredat least annually, .or more often. .. . .. . There were only two

## outagesoth~rthan major scheduled overhauls during the

## hist~ric**ten~y~ar** .. periodthat appeared to be of sufficient length (greater than 

### 8 days) lhatcouldhave lent themselVes to signijicantcatalyst cle.ariing or replacem.ent wor!rwithOutdelaying startup: one on: Unit 

### Ifandone. on Unit 2 .... ..There are basic concerns that using short boiler Cleaning outages as SCR catalyst maIntenance opportunities couldbe detrimental to catalystlife due to thermal stress.es cmd passing through various (Jewpoint**temperature~.** Bringing the very,large mass of ceramic catalyst material and the reactor structure down in temperature and then back up rapidly andany more frequently than absolutely· necessary should be avoided... :... . 

### EPA Response: EPA looks fQrward to reyiewing the infonnation obtained

## fro~ the vendor

## req~~~t; During the previously discussed phone conversation with Flemiliing Hansen ofHaldor Topsoe, Mr.: Hansen gave-a rough estimate that an SCR system for NorlhDakota lignite couldbe d;esigne(il (larger) to accommodate a catalyst replacement schedule ofabout every year. Mr. Hansen said that an SCR reactor could be cooled down within 24 to 36 hours (needfor the cool air draft requires the boiler to be. shut down) and the catalyst layers rotated in about two or three days,

.three days aflaround.. This is significantly less than the roughly 200 hours -(or eight days)· estimated by B&McD for catalyst replacement. This discrepancy would probably warrant· further examination ofboth figures inn the context ofa cost analysis. G';

### .Iiydrocarbon-E~hanced Selective Non-Catalytic.Reduction (HE 

### SNCR) EPA'sJanliari 26, 

### 2007 c,omment: Minnkota eliminates this.technoiogy irimarily based on the fact that ithas not been appiiedto .. cyclone boilers or units burning lignite**orhigh~slagging** western. subbituminous coals.**Th~re** are two full . scale installations of this technology on easternpulverizedcoal-fired boilers. There is some general . discussion about the slaggingproblems that ligniie wouldcause the HE SNCR techn(!logy, but it is unclear whether the vendor 

## of this technology would be able to overcome these issueS. 4t thispoint,· it is· .

. unclear whe.ther HESNCR is technically feasible. Minnkota, shou14provide ci more thorfJught;lnalysis· on whetherthiscontroloption is "available andapplicf;lble" (as described in the NSRM.anual) a{MRYS by examiningthephysical andchemical characteristics of**t~e** exhauststream in terms of teqhnical feasibility . andsoliciting vendor information. . A qu.antitatilleanalysis of Its techni(:al feasibillty.$hould beproyided .

.andsupported with 4ataand vendor statements..



## -50-EPA Response to Minnkota Comment Letters froll) March 19,2007 and Apri12J;2oo7 BACT Analysis at MRYS 

### B&Mc:o,'s April 23, 2007 Response: The October**200~** MRYS NOx B4CTanaiysis wasperformed using technical literature available in the public domain, proprietary vendor customer experience lnformation, and limited engagement of se'ected vendors for capital cost, operating and maintenance costs, andemissionsperformance estimates along

· with Burns & McDonnell's technical expertise. . This analysis approach meets the requirements of the' EPA. 's NSR Manual .

.' A detailed query of thepotential availability andapplicability of hydrocarbon-enhanced (HE) selective non-catalytic reduction (SNCR) on a tfgnite-jired cyclone boiler from the single vendor mentioned in the October: ,2006MRYSNOxBACT Analysis, reports has not beenperformed. Additional.' time wouldbe required, It is importcmtandappropriate to specify the composition of the Center lignite

· coal andash constituents and boiler configuration sufficiently toprovide a soundbasis for allowing the HE-SNCR vendors' reviews'and qualified responses. HE-SNCR design conditions that are reasonably . reflective ofactttal operating conditions and boiler fouling experience are yet to be established. The lack of detailed development of MRYS unit-specific HE-SNCR injection lance design schemes to deal with the high boiler fouling conditions and varying boilergas temperaturescmd loads will require HE-SNCR design operating conditions to be assumed before workable design concepts hqve been confirmed., .. Itis interesting to riote that other non-cyclone BART'-idigtble boilers burning North Dakota lignite did**~ot**
·mention or evaluate HE:·SNCR technology as apossible NOx control aliernative in their BARTanalyses.



### . EPA Response: EPA has simply asked Minllkota to get the vendor's input on the facility in question.· . Minnkota's original BACT analysis describes theoretical problems thatmight be encountered if

. HE SNCR is installed at MRYS and states that the lack ofexperience with cyclone boilers •

burning low·rank 'western coal satisfies a showing that HE SNCR is technically infeasible. The vendor who offers this technology states thatitis not sensitive to fuel type or bumers,so EPA still questions whether the·determination oftechnical infeasibility is valid without getting vendor input or substantiating data.

. . '.' . 

### EPA does not agree

### ~ith B&McD's

### i~teIpretation ofthe NSR Workshop Manual.

. B&McD' states that in order for the vendor to develop a realistic technical basis that would support estimated unit..:.specific HE SNCR performance, capital and operation and maintemmce costs, they would need specific customer data. B&McD claims this is not required 

### by an applicant because the**NS~** 

### Workshop Manlialstates, "a source would not be required to' experience extendedtime delays or resource. penalties to allow research to be conducted on a new technique;" This statement.is in the context**o~** 

### detennining whether the technology is "available." According to Minnkota's ;BACT analysis, the vendor ofthis technology believes the technology is not sensitive to fuel or burner types. As such, it would appear that, in general, this technology is "available" for MRYS .. therefore, the reference to the NSR Manual made by B&McD is only relevant ifthe vendor would not ()ffer thetechnology to 

# a customer based on specific conditions ofthe plant. Minnkota can go through this process 

### ifit believes the 

### -51-EP**ARespo~se** to Minnkota**C~mment** Letter:s from March 19, 2007 and April 23, 2007 BACT Analysisat MRYS

. .


### · technology is notavailable, but appareritly does not wishto do so. Hence, EPA believes the . technology is "available."·. IfB&McDdoesnot believe it is "applicable," further informatIon should be prOvided. The reaSons given·by B&McD to this point (high boiler fouling conditions and va,ryirig gas temperatures and loadsj'appear themselves to be theoretical. EPA believes·

.statementsJrom vendors or more quantitative Information might be helpful for hUlking this . determinatiop.

. . . . . '.' . 

### EPA does not believe that whether other non-cyclone fired BART applicants included an·

· analysis ofHE·SNCR**isevidence~** 

### in and by: itself, that the technology is infeasible at MRYS: 

## If

the technology is "available," it should .be evaluated. According to statements from the vendor in question, the technology is generally available to po.wer plants..**~..** 

### . 

### H. Reburn with SNCR EPA's: Jamuiry 

### 2.6, 2007

### Comment: While various.]orms of reburn systems were determined to be

### technicallYf~asible in the Minnkota . analysis, reburn combinedwith SNCR was ruled out basedon technical infeasibility. AlthoughJull scale

· pulverizedcoal installations of gas reburn with SNCR andoverfire air were found to exist, Minnkota did not analyze whether the technology combination would be "available and applicable" to MRYS, as described in the NSR manual. Instead, the application states, "(t)he lackof experience with these· combinations on a cyclone-fired boiler, especially for lignite-flring, makes the application for MRY·

· Station's boiler infeasible. " Minnkota should prOVide a 

# more thorough analysis ..... 

### B&McD Response:

" '., .'
. .

..A detailed query of thepqtential availability andapplicabilitju)j fuelreburn technqlogy combined·· . with SNCR on a lignite-fired cyclone boiler from the rebitrn technology vendors has not beenperformed .

·As mentioned in AppendixAl of the October 

### 2006MRYSNOx BA(:T Analysis reports, whikSNCR may . potentially be installeddownstream. of separated oveijire**a~r** andvarious types offuel reburn, "there is 

### a . lack of demonstrated experience of this .combination on cyclone boilers. Only one example of gas reburn . with SNCR,applied to 

## atangentially-fired boiler, was foun((l In available technical literature. Moreover .. the very high capital andO&Mco.sts't!lready estimated for coal andgas reburn tecknologies with . .

. ASOFA in Section 3 of the October 

### 2006MRYSNDxBACT Analysis reports showedthat

### s~cJi ..

· alternatives were sig"ificantlyabove the BACTDominant Controls Cost Curves forMRYS Unit rand .
· Unit 2. Thus, eveniffuelreburn technology com!JinedwithSNCR )vere availablea.nd.applicable to· .

lignite-fired cyclone boilers, the average .and incremental unit control co.sts ($per ton) wouldnot be .. ·expecte.dto be on theNOx BACTDominant-Controls Cost**C~rvesfor** MRYS Unit 1 andUnit 

### 2. Such reburn with SNCR alternatives would thus be consideredas "inferior", o,!dwouldnot be consideredtis .

. .BACT S"ubstantialresources wouldbe required... ./t is interesting to note thaIother non-cyclone BARTeligible boilers burning North Dakota lignite didnot mention or evaluate reburn wi/hor withoutSNCR technology aspossibleHOx control alternatives in·their BARTanalyses. 

### -52-EPA Response to Minnkota Comment Letters from



### . March 19,2007 andApril 

### 23, 2007 BACT Analysis at MRYS . 

### EPA Response:**B~McD.has** declined to perform an analysis ofwhether Rebum withSNCR would be

. "available and applicable" because·the technology haS not been "demonsirated" on cyclone

boilers. However, according. to theNSR Workshop Manual, the "available and applicable;' analysis is only required whenever the technology in question has not been demonstrated in practice. Ifthe technology has been deQ1onstrated, it is considered technologically feasible without goirig through further analysis. Hence, B&McD's logic for riot doing the "available and applicable" analysis appears to be contrary to the NSR Workshop Manual. ..

. B&McD also

### makes~he argument that the average and

### incrementa~ cost associated with .

Rebum with SNCR would not expected t9 be on the NOx BACT Dominant Control Cost Curves, so they would be eliminated on that basis, ifthey were found to be technically feasible: However, Reb1,1I11 with SNCR wouid offer greater NOx emissions reductions thanjust SNCR (assuming**e~ch** would also include ASOFA), SO this data point on the curve would be above and right ofthe data point for SNCR. EPA can not say with certainty that the average and. . . incremental cost effectiveness ofRebum with SNCR would be ruled out based on·cost because the analysis is not presente9: by B&McD. B&McD also points Qutthatnon-cyclone BART eligible sources in North Dakota did not provide an analysis ofRebum with or without**SNC~** as a control**altemati:y_~** in**th~ir BA,-R~T--,-~**  analysis. For the reasons cited above, EPA does not agree that Rebum with SNCR can be ruled·

.out baSed on technological infeasibility or cost effectiveness at this time.. 

### I. Rich Reagent Injection (RRI) 

### EPA's January 26, 

### 2007 Comment: ..

. Minnkota eliminates this technology because of the difficulty in achievingproper substoichiometric 'boiler conrJitions necessary to get effective NO x control. As described in the application, theproblem**occur~** because of the variable heat content of Center Mine lignite. While RRIhas been successfully demonstratedoi cyclone units burning blends of Powder River. Basin coal with Midwestern bituminous coal, Minnkota Ju;rs ruledRRIout as technically infeasible. However, there does not appear (0 be an analysls of whether RRImeets the "available andapp1icable" criteria described in the NSR Manual for elimination under step**2~** 

### If RRIwouldbe less effectivejor the· reasons cited in Minnkota's application,.that wouldresult in a·lowerrailking under step 3 and possible elimination under.step 4. At· this time, it does rIOt seem appropriate to eliminate RRIunder step 

### 2. Minnkota Shoilldprovidea more thorough analysis·..... .' . . . .



### -53-EPA Response to Minnkota Comment Letters from March 19,2007 and April 23;20(n,
, BACT Analysis at MRYS



### , B&McD Response: 'Since thepublication of the MRYS NOx BACT Analysis report;'two

### commerci~l Rich Redgent ,

.Injection $ystems "'ave completeddesign, fabrication, and installation 'in late 2006'atAmeren Sioux Unit I and Unit 

### 2. Full optimizedroutine operation is expectedto begin by early May, 2007. Although RRl NOx emissions reduction technology appears to satisfy the "available" criteria (as described in the NSR , Manualfortechnicalfeasibility)forpotential application on the cyclone boilers atMRYS,' the substll.ntive., issue is "applicability". The expected insurmountable difficulties in achieving consistent control " '
, effectiveness.; ...from this technology 

## if applied to modestly air-starvedcyclone combustion on these lignite-fired boilers and the reasons for technical infeasibility of 

### RK!at MRYS were included in Appendix Al of the October 2006NOx BACT Analysis reports. '. A query of the singleRR! licensee mentioned in the MRYS NOx BACTanalysis, anda quantitative' analysis of its technical feasibiiity for the expected boiler operating conditions has not beenperjormed. "
, The transient variabiliiyofthefiredlignite 'coal at MRYSwas discussed/n AppendiXAl of the October 2006NOx BACTAnciiysis reports. This variabilitYmakes it impossible to accuratelypredict realistica./ly achievable NOx emissions reductions even with sophisticatedcomputationalfluiddynamics (CFD) modeling'ofthe'MRYS boller cqmbzistion reactions and in-furnace NOx reductionprocesses·associated with 

### RRItechnology under reasonably realistic boiler operating conditions. This is duetd the statIc**(i.e~** steady-state) nature of the**boi~er** furnace operating conditions assumed to exist in order to simulate the performance ofmode.stlyair-sicirvedcyclone. combusti(.m on theselignite-fired boilers with varying heat and air inputs to individual cyclones usingCFD modeling techniques. Because of the dynamic wiriability of the higher heating value of thefuel burnec/'tmdthe lack of abilitjJ toprecisely control the actual stoichiometry in real-time on an individual cyclone basis, 

### R1UCFD modelpredictions would be unrealistic and thus these'vendor statements wouldnot be reflective of reatisti.callyachievable NOX
, emissions reductions. Substantial resources would be required .... .. 

### 'EPA Response:

,EPA believes that therecentinstallationofRRI at the Sioux 1 and 2 cyclone uriits is also strong evidence

### th~t the technology is "applicable" to MRyS. the 

### NSR ,Workshop 

### Manua1. ' states that**'~if** 

### the control techriology,has been installed and operated successfully 'on the type of source under review, it is 4emonstratedand it is technically feasible." While the'Sioux plant' does, not hum lignite, PRB coal is**al~o** 

### a low-ranking western coaL This indicates to'EPA that before ruling out 

### RRI as technically infeasible, detailed analysis shouldbe provided. ' "

, ' , , .



### . Wlllie predictiilg:the exaCtlevel ofNOx 

### control for 

### RRI

### ~d MRYSmay not

### bepossibl~; ,'. 

### EPA believes' some informed estimates could be made. Further" 

### EPA does not believe predicting, exaCt levels ofNOx 

### contr.ol is necessarily cruciarto whether a controloption is technically feasible. Hence, EPA does riot believe B&McD has demonstrated that 

## RRI should be considered
,technically infeasible; In fact, 

### EPA believes therecellt operation ofRRI at the Sioux plant' provides strong evidence that RRI would be, teclulically feasible**atMRYS~** 

### , 

## -54-EPA Response to Minnkota Comment Letters from March 19, 2007 and April 23, 2007 BACT Analysis at MRYS 

### J. Rotating Opposed Fire Air (ROFA) 

### EPA's January 26,2007 Comment: Minnkota eliminates this

### techn~logy becazise it "lacks demonstrated cyclone-firedexperience, and thus was considered infeasible.;' While a technology that has been demonstratedon the source type under review would.show it is technica!lyjeasible, lack of such demonstrationforthe specific type ojemission' '. unit does not necessarily lead to a conclUSion of infeasibility, Minnkotashouldprovide'a more thorough analysis.. : ... :. '. . 

### B&McD Response: A detailed query of the potential availability andapplicability of ROF A technology on a lignitefired cyClone boilerfrom the single vendor mentioned in the October2006 MRYS NOx BACT Analysis

. reports has not beenperformed. Burns & McDonnell h"as reviewedavailable ROF A technical literature, attendedsalespresentations andparticipated in discussions with ROF A vendorpersonnel regarding the application of ROFA to cyclone' boilers, inc/tiding lignite-fired units. As an engineer anddesign/builder

.of numerous commercia/separated over:fire air systemsspecijically designed/or cyclone-fired boilers, Burns cmdMcDonnell believes that ROF A ter;:hnology is not superior to the evaluated version of SOFA in the October 2006 MRYS NOxBACT Analysis towarrant stich a vendor query anda quantitative analysis

........ , ROF A does not offer any significant advantages in lignite-fired cyclone-specific application of separated overfire air technology.' ..**.~~~**

### EPA Response:

. '. 

### EPA does not currently have information to the contrary and will 

### agree that this option may not differ substantially from ASOPA or offer greater**NO~** 

### reduction on cyclone boilers. Since

. ASOFA has 1?een addressed elsewhere in the BACT analysis, further consideration ofROFA is

unnecessary. 

### K. Control Efficiency for SNCR 

### EPA's January26, 2007 Comment: Based on theproposedemission rate of0.36IbIMMBtu and the emission rate expectedfrom installingAdvancedSeparated Over:fire Air (ASOFA) alone (O.513lb/MMBtu), it appears as though the SNCR controls will only be achieving approximately 30% reduction. (po 3-18) AP-42 states that SNCR' can achieve NOx reductions between 30-60%. Many recent PSD**p~rmit** applications also include discussion ofSNCR being able to achieve NO x control in the 60%,range or higher. Considering that Minnkota:s cyclone 'boiler will have high uncontrolledNO x emissions (even considering the ASOF A), the highend of this range shouldhave been considered in the BACTanalysis. Minnkota's analysis really provides no technical discussion on whY it ruled out higher capabilities ofSNCR control and why they usedthe control efficiency that isproposed.**Usi~g** 60% control wouldyieldan emissions rate of 0.21 Ib/MMBtl!for a BACTlimit with ASOFA andSNCR. comparedtotheproposed 0.36.lb/MMBtu. 

### -55.:..EPA Response to Minnkota

### Co~ment Letters from March ]9,2007 and ApJi123, 2007 .

. BACT Analysis at MRYS . 

### B&McD'sApri/23, 2007Response: There werepertrnent references in AppendixAl of the MRYSNOx BACTanalysis discuSsing long- , term examples where SNCRhas been appliedforNOx emission controlon two cyclone-fired boilers, . achieving reductions around30percentfrom·high uncontrolled baseline levels. There 

### was also another relevant cyclone boilerSNCR demonstration test listed inAppendix.A2 of the MRYSNOx BACTanalysiS that controlledNOx in this same 3.0percentrange. NOx control ef!ectivenesi ofSNCR is highly boiler-:- . specific. It is important to note that PSJ)permit applications are for new boilers; there are no new cyclone boilers being built, andfew new boilers (other than CFB boilers) are required to**i~tall** and operate SiVCR. The citedAP-42 NOx emissions rate reductionpercentagefor SNCR application on**coal~·** fired boilers isn't applicable to the specific conditions expectedat the MRYS boilers ., ../Jurns & McDonnell estim(Jtedthe level ojemission reductions expectedfromSNCR bqsedon informationfrom an

· experienced urea-basedSNCR vendor. B&fvfcD believes that 60percent reduction o/NOx emissions is ..

inappropriate, andnot**rejlecti~e** or realistic for long-term levels of control at MRYS. 

### EPA Response: After further review 

# ofthe information provided, 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. . 

### L. Selection of30-day Average BACT Emission Limit 

### EPA's January 26, 

### 2007Comment:·

. .",.'. ....,' .- '. The baselli1e emission rateusedfor calculating theproposedBACTlimitis based:on the highest . NO x emission rate (0.884IbIMMBtu)duririg actual operations from 2001-2005.(p. ES-9) Thisperiod also includes the longest reportedstqriup event during thatperiod**(61hours)~** How does this 30-day . baseline compare with the rest of the historical data? Does this emission rate represent a realistic upper· bound value, or is it an outlier comparedwith the majority of the data? 

### Jf ihe d.atapoint does not . reasonably compare with the vast majority of the other data;"it does notmake sense· to set

# a BA CTlimit basedon an outlierdatapoint. Furthermore, the baseline emissions rate usedfor calculating the 30-day

· limitis baser! on the .highest30-dayperiodduring actual operations fiwn 2001-2005, which includedthe

· longest startup ev.ent. lfthis highest 30-dayperiodwas user! as the baseline to calculate the 30-day

average limit, and the worst-r:aSe startup event occurredduring this historic 30-dciyperiod,it is not necessary to inclu4e the recommended "startup aq;ustment"{+O ..D411blMMB,tu)per siartupevent with

. this limit. .. . 

### B&McD'sApril23,·;2007Response: According to MRYSUnit 1 's October 2006BACT Analysis; the control e.!frctiveness calculations were determined based upon the highest hlstorical12-month rollingNOx emission summation operating conditions for MiltonR Young Station boilers duringyears 2001-2005.....MRYS operating conditions 

### -56-EPA Response to MinnkotlComment Letters fro'm March 19, 2007 and Apri123, 2007 BACT Analysis at MRYS . during the highest historical 30-day rolling NOx emissionperiods foryears 2001-2005 were then comparedto the highest 12-morUh 'historicpre-control baselin.eperiodconditions. The average unitNGx emission rate (lb/mmBtu)from the- highest historicpre-con"trol 30-day baselineperiodwas comparedwith the average NOx emission rate (lb/minBtu)from the 12-consecutive monthperiodwith the highest historic unit NOx mass emissions (pounds) reportedfor actual operation during the same 5-year look-. backperiod It waS coincidental that the highest**historical30~day** rolling NOx emissionpe.riodforMRYS "Unit 1 (December 17, 2003'through January 15, '2004) was within the same highest I2-inonth historic . pre-control baselineperiod (ending on October 30, 2004). The longest indiVidual Uriit 1 startupperiod during actZ!al operation between January 1,2001 andDecember 31,2005 occurredduring the 61· consecutive hourperiodfrom June 27-29, 2005**.~** .... The highest historical 30-day rolling NOx emission

.period for MRYS Unit 2 (March 7, 2003 through April 5, 2002) was not within the same**hig~est** 12-month historicpre-control baselineperiod (ending April 30, 2004). The longest individual Unit 2 startupperiod during actualoperation between January 1, 2001 andDecember 31, 2005 occurredduring/he 115- consecutive hourperiodfrom October 25-30, 2001. Note that this did no(fa/l within either the 30-day or the 12-inonth highest historic rolling average NOx mass emissionperiods. ... ,.. The selectedhighest baselinepre-control 30-day rolling average NOx unit emission ratesfor MRYS Unit 1 and Unit 2 boilers are consideredto be realistic upper boUndcases, not "outliers"...... The recommended30-day Rolling,

. Aver.age unadjusted(i.e. ste.ady-state) BACTNOx emission rates do not include the impact of the worstcase startup events for eitherMRYS Unit 1 or Unit 2. The "startup**adjustment~'** as describedIn the October 2006MRYS Unit 1 and Unit 2 NOx BACT Analysis reports is appropriate as the recommended (unadjusted) 30-dayRollingAverage NOx Emission Ratepermit limitations basically reflect steady-state. rates.



### .EPA Response: EPA has reviewed B&Mc;sdetailed description ofhow it established the baseline emission rates and the startup/shutdown adjustment factor and· now understandsthat the startup periods did not fall within the relevant baseline period. EPA 

### will consider the startup adjustment concept to the extent it is relevant to NDDH's proposed BACT determination. 

### M. BACT Limit IS-Month TrialPeriod EPA's January 26,2007 Comment:" EPA has conc.ems with Minnkota isproposal for an 18-month trialperiod for establishing a final BACTlimit. (p. ES-ll) Thisproposal appears to be in direct conflict with thepr.ocessfor establishing and potentiallyrevisingthe NO x BACTlimits set/orth in Sections V. B & D of the Consent Decree. Therefore, EPA believes theproposed I8-month tria/"periodfor establishingafinal BACTlimit in Minnkota's BACTanalysis cannot be accepted

. . 

### B&McD'sApril 

### 26, 2007Response:

..... Paragraph 73 of the referenced Consent Decree states "The Settling Defendants shall submit anypetition for any Unit under this Paragraph no later than six (6) months after thefinal compliance 

### -57-EPA Response to Minnkota Com"ment Letters·from March 19, 2007 l,Uld April 23, 2007 BACT Analysis at MRYS date specijtedfor that Unit in Paragraph 

## 67". Paragraph 67requires that MRYS Unit land/Unit 2 shall .achieve andmaintain a Phase 1I30-Day RollingAverageNOx EmissionRate established·bythe NDDH through itsNOx BACTDeterminationbeginning no later than**Decemb~r** 31,2011 andDecember 31,: 20J0, respectively. This does not preclude anearly installation of ConsentDecree Phase IINOx emission reduction systems with associaiedcommissioning atMilton. R. Young Stationprior to the 

## CD .

. compliance datesfor.MRYS Unit J and Unit 2, respectively.- This couldallow Minnkota io gain· operating experience in advance of the June 30,20JiandJune 30, 20Jldeadlinesforsubmitting apetition. lfthe . Settling Defendants do not accelerate the schedule for Phase IINOx control implementation; recogn.izing·.·

. that the CD apparently does not allow an**18~month** trial demonstrationperiodfo.llowiJig the siatedjbial

. compliance dates; the applicant will 'have to make use 'ofthepetitionprocess as**de~cribedin** the CD in .

. this circumstance, if appropriate. . .. . . 

### EP

### A**Respons'~:** 

### . EPA agrees this.is 

# an acceptable approach.



# ,.

-58- . 

### .