EPA REGION 8PRELIMINARY ANALYSIS OF

BURNS & McDONNELL BACT ANALYSIS FOR NITROGEN OXIDE

AT MILTON R. YOUNG STATION, UNITS 1AND 2

January 8, 2007

I. Introduction and Summary ofEPA's Preliminary Analysis·

A. Summary ofEPA's Preliminary Analysis

After ~view ofthe October 2006 report by Burns & McDOnnell (B~M). "NO" Best Available

Control Techliology Analysis ~'tody" forthe Milton R. Young Station (MRY~), Units 1and 2, and after

review ofother pertinent infonnation and studies cited below, EPA's prelitnlnary analysis is that the

B&M study lacks sufficient infonnation witbin the BACTanalysis. Specifically. dIe study excludes

Selecti-y6 Catalytic Reduction (SCR) as a technically feasible control option at step 2 ofthe five-step TopDown analysis. While not. presenting NOx control effectiveness Ot catalyst actlvlty"data.. As a result,

B&M fails to rank SCR against other control options in terms ofcontrol effectivelless' at step 3, and fails

to analyze costs ofSCR versus other conlTol options al stepA. EPA questionS the reaSonS cited by B&M

fat tcchnica.1 infeasibility ofSCR. Furthcrmol'c, based 011 a survey ofSCR venda!',. described later in this

repOlt, EPA found there are vendorsthat will offer performance guarantees for this type ofapplication. .

FUlthct jnrorma~ion should he requested, to snpportthe analysis with respect:to SCR. .

B. Relevant Langgage trom ConsentDecree

Under a Federal Consent Decree flIed April 24,2006 in U.S. DistrictCourt in North Dakota,

Minnkota Power Cooperative Inc. and Square Butte Electlio Cooperative ("Defendants") are required,

within six months after entry ofthe Consent Decree, to submit to the North Uakota Department ofHealth

(NDDH) for review and approval. and to EPA for review, a NOl[ Top-Down BACT Analysis for each

eXisting coal-tired Unit at the MRYS. The Analysis shall include all informa~on necessary for NDDH to

make a BACTdetennination, and an)' additional infonnation requested by EPA'a!)d NDDI-1. 11le

Analysis Shall include an evaluation ofSCR, SelectiveNon..catalytic Reduction (SNClt), Over-fire Air

(OFA), as well as other NOll control technologies. (Decree at Paregraph 65.)

NDDH shall review the Analysis and sha.1l devolop 1m BACT detern1inationi whioh shall be

pl'eSented to all Parties after consultation with EPA. 1lte determination l:IhaU:be subjeetto the dispute

resolution process set forth in Paragraph 147 ofthc Decree. (Decree at Paragraph 66.)

IT. EPA Case-Specific Reyiew ofBurns & McDonnell & EERC Technicalll'easibilitx

AnalYBis for Sclcdivc Catalytic Reduction

A. High-Dust SCR

B&M has eliminated High-Dust SCR a.c: technically infeasible due to issuesdescribed below.

B&M's analysis utilizes a report by the Hnergy &Environmental Research Qelltea' (EERC). EPA's.

reSponse on each issue is also described below.

EPAPrclirninKfY Amllysis ofB&MNO.

aACT Analysis at MRYS

lanuary S. 2007

Ash Deposition Issae Raised by Burns & McDonnell:

B&M state.o; that North Dakota lignite contaiJ.ls a vmiable ~d complexvariety ofinorganic

compounds dUl.t conlnDute1:0 ash deposition. B&M statesthat this fuel pi'Oduccs ash with severe

deposition cJ.laracteristic~ that are not typical with otJler coals. Wh~n exposed to the beat ofthe

combustion process inside the cyclone bumers. the m4iority ofthe fuel aSh b~mcs molten and flows

into me boUX>m orthe furoaCe. A significant portion oithe fuel ash is entraiJied into the flue gas exiting

the cyclone barrels at high velocity, where it comes in1D Contact with the.lower furnace waterwalls. The

portion that is canied with the rising flue gas cools and some.is deposited on hQat ft'ansfer surfaces in the

upperf'Urnace HDd boiler convection pass. B&M sta:(l:)s thst ash deposition oil heat1ransfersurfaces is a

substantial problem for units that fire North Dakota lignite, and that the problem is so severe at Milton R.

Young that the Unit I boiler must be sbut down at 120~day intervals to allow;for cleaning ofash depObits

from the boilel' heat transfersUlfaces. in orderto restore reasonable ftlrnace exit gas velocities and

temperatures.

B&M also states that sodium is. a significant contributol' to the "stickiness" ofthe ash produced

tj'om firing North Dakota lignite. Sodium content ofthe lignite ush averages approximately 4.4%, and

can nearly double this valuc forsome ofthe lignite produced from the Center min~. Powd~rRiver Basin

(PRE) coal typically averages around 1.5% sodium content. Boilers firing North Dakota lignite typically

have a 2.5% higher heat rate (million Btu per kilowatt ofelectric generation) than ~. typical boiler firing

PRB coal, thus requiring more heat input and firiilg more £liel per megawatt ofelectricity output B&M

states that a cyclone boilerfiring North Dakota ligniw also convcl'ts appl'oximately 50% oftile fuel ash to

flyash,compared with a 35% eonvel'Sion rate for· PRB coal-fired cyclone boilers. Overall, B&M states,

this results ill an amount Ofsodium emitted from a cycione·boiJer firing North Dakota lignite of

app~x~~t~ly7_.3 Ib~~hr compared with_<!.~ !bs/MW-hI'for a P~-fired cycl0l'le boiler.

B&M further stutes that the oatalysts in coal-fired boiler SCR reactors are hlghly susceptible to ash

deposition. III a typical conventional highwdustSeR reactol~ tile flue gas typically passes through two to

four layers ofcatalyst mod\lIes. The catalyst modules ha.ve riumerous narrow p88~ages to provide

intimate Contact between the flue gas. ammonia and oatBlyst, TIle clearance (pitch) in these passages is

typically 6-10 milJimeters. A typical catalyst layer is approximately 1 to ·1.5metel's deep. '111e catalysts

in coal-fired boiler SCRreaotors must he oleaned frequently using soot blowers and/orsonic homs. This

is true even on units firing fuels that do Dot produce a stiol-y 8llh tba.t OOiltribtites to ash deposition. B&M

states that ash deposition on the catalyst in a high-dustsea application would be severe fur a unit firing.

Norlb Dakota lignite.

Sulfur in the coal is mcidized during excess air combustion to form sulfur dioxide (S02), and a small

amount ofsulfur trioxide (S03). Some ofthe ammonia-based reagent iluected up~trl(am ofthe SCR

reactor will combine with 803 to fot'ln ammonium bisulfate. The catalyst in the SCR reactor will also

oxidize a portion ofthe SOlto SOl. Excess unreacted ammonia reagentcarryovert'ammonia slip") from

the SCR reactor will a.lso react with these sulfurie acid compounds in a similar fashion. B&M states that

the deposition <:hamcwristics for a unit bunling North Dakota lignite will crelfte difficult-to-re.move ash

deposits and pluggage ofit conventional high-dust catalyst, and increase the probabilitY thut tilt air

pl'cllea.ter downstream and flue gas ductwork will bt pronc to accumulations which could be severe.

B&M further states that high-dust SCR perfonnance and cat"dlyslUfe will be severely impacted, and that

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J:.l'APreli!!linnry Analysis of13&M NO~

BACT Analysis at MRYS

Junulfry 8. 2007

it is anticipated that ahigh-dust SCR's catalyst life will be shortened from 3-6 years (typical) to as little as

2-12 months, requiring extended. frequent outages for replacement .

I3&M also ~tes that hot"$ide air pl·eheat.el·s a.:e,susceptible to fouling.' Tubular air pre heaters

originally supplied with all cyclone boilers also tc~rate moderate dust loadings. since their height and

size make them difficult to maintain cleanliness.teak tightness ofthc· air preheater is impor'tant on

cyclone.fired boilel'S with .-elatively high forced draftfan discharge (combustion .air supply) pressures. A

high dust SCI{ installation. says B&M, will be prone to air preheatertube fouling and pluggage, I'equil'ing;

extended, frequent outagesfor QI~ing.. ... '.

EPA AnQlysis ofthe Ash DePositiop Issue;

The concern about high amounts of ash material causing blinding ofmacro-pores in the catalyst is

real butsolvable. Strides in catalystformulations, catalyst management systems, and re::ently, catalyst

regenetat.on processes, have all combined to lower the overdlI cost conlribution ofboth initial and .

replacement catalyst in modem SCRsysrems. .

CorJ'lP-arison ofMKrS /tJ SCR Systems Operating onPowdeiRiver Ba~inSjg.J,.

The B&M BACT analysis contends that the higher ash content ofNol'th Dakota lignite used at

MRYS (Center Mine coal) makes the comparison of SCR feasibility at MRY;S to Powder River Basin

(PRB) sub-bituminous coal SCR experience not relevant, Even though the chemical compositions of

PRE ash and Center Mine coal ash arc very simils!', particularly for the specific constituents ofconcern

for catalyst deactivation, the quanlity ofash in the Center Mine coal is more than twice as higb on a per

M~tu basis, However, for a cyclone b~i1el', only about 30-50% ofthe ash ends up as fly ash at full load

(less at tower loads) and for a wall on:omer-flrcd pulverized coal boiler(PC boiler), about 80% ofthe ash

ends up as fly ash.· Tho l'esiJlt isthat SCRcatalyst in a l'C boiler PRB applic~tioo ;is C)(posed to similar

quantities ofthe m<\ior constituents of conoel'n'<~lkalulematerial) as a catalyst would be expo$ed to at

MRYS. (FOI' purposes ofthis analysis, we will refer to wall alld cornel' fired boilers as"PC bo!lers,"

Even though cyclone boilers are sometimes referred to· as PC boilers, for thi~ docum.ent when that term is

used, we are not referring to cyclone boilers.) .The B&M analysis ~lso $Uggests that n linear comparison

oftheoretical total ash or ash constituentratesto SCR catalyst deactivation rates ~an be made. Although

EPA does not believe this to be the case and l3&M has not presented any evidej\cc.9f a quantitative

relationship between ash loading and SCR catalyst deactivation rates, BPA IrcJs nevertheless examined

B&M's arguments related to ash loading. . .

Table 1 below shows a comparison ofth~ total asll loading for different bOiler designs for No.th

Da1<ota lignite, assuming a re:rerence unit ofl.O IbIMMBtu forlignite, lignite will have twice the I\.sh

content on a per Btu ba...ia, and the conversion.to flyash will be 30..50% for cyclone boilers and 80% for .

PC boilers, As elm be seen from this compariSon, the theoretical flyash loading for a PC boiler firing.

PRB. boiler (O.4IbIMMBtu) will be in the same range as what would be expected fora cyclone boiler

firing Norlh Dakota lignire (O..3~O.S Ib/MMBtu). There are several PC boilers operatIng with SCR to

comply with the NOx SIP Call that bUl1l PRB coal in PC boilers. As we will. disctlss later, catalyst

deactivation due to calcium and other alkaline materials isa «chronic," rather tIl/in "acute" phenomenon.

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~PA :I'!'eliminary AnalyRiR oiB&M NOx

BACT Analysis at MRYS

Janull!Y 8. 2001

Deactivation depends on the tot'ililime and mass exposure, 8l\d the PRB PC l:ioiler data are extremely

relevant to evaluating SCR feasibility tOr North Dakota lignite.

TABLEt

Comparison ofAsh Loading fo)" North Dakota Ligllite V!l- Powder River Basin Coal

Total Flyash Loading Total Flyash Total Flyash

Total fuel C."yclone 'Boiler at Loadjns .Cyclone Loading PC

Coal Type Ash Loading 30% Conversion Boiler at 50% Boller 80%

(lblMlVIBtu) (lblMMBtu) Conversion, Conversion

(lbIMMBtu) (lb/MMBtu) .. North Dakota Lignite 1.0 0.3 0.5 0.8 -- I .~-

Powder River Basin 0.5 0.15 0.2-5 0.4 -. ;

, . .

There at'e a couple ofimportant omissions in the quantitative comparisOll ofsodium ash loading

presented in the B&M BACT analysis. Pirst, the B&M quantitative sodium loading analysis pl'esented ill

the application does not make a comparison ofNortli Dakota Lignite on oycl9ne boilers to PC boilers

using PRE coal, which, as discussed above, would have hIgher a"$h loading Uian cyclone boilers buming

PRB coal. Furthermore, the sodium loading analysis does not take into account en1lre range of

alkaline material that would affect ash loading exiting the boiler tiiat is relevant to catalyst plugging. The

B&M quantitative analysis appearsto f'Ocus on the Jowe.,;ttype offlyash-emi~ring boiler design for PRB

coal (cyclone) and the alkaline constituent (sodium) that is higher fur North Dakota lignite compared to

PRB coal. As shown in Table I and explained further below, these ash-loading differences are not as

pronounced when evaluating all alkaline materials fur PC boilers burning PRB coal. In fdct, Table I

shows that, on a Ib/MMBtu basis, totallheoretical tlyash loading at the economizer exit ofa cyclone

boilel' firing lignite would very similarto that ofa PC boilerfiring PRBcoaL,

Another alkaline constitllent that ha.c; been a concern is calcium, which can react with SO] to plug

pores as CaSO... This has been a much-studied problem and the mechanism involves the calciumcontaining proticle getting «cHught" in a maoro-pore ofthe catalyst and sUbSf!quently reacting with S03 in

the flue gas. The resulting CaSOd particle is larger in volume than the Cao particle and, in essence,

swells to fill the pore. The rdW determining step is the oliginal capture oftha ~lcium-containing particle;

varying concentrations ofS~ and 80] have little effect On the overall ntl"e of calcium blinding by the

ciogging ofmacro-pores. This, again, points to the relevancy ofongoing, lower sulfttr }'RB SCR

operating experience. PRB coal has been shown to have approximately 300/0: mOle calcium in its ash

compared to North Dakota. lignite. (Reference: Table 4 from the EERC paper. SCR Catalyst

Performance in FliJe Oases Derived from Subbituminousand Lignite Coals published in Fuel ProcesSing

Technology.) When considering this difference and tll'e fuel to flyash conversion Ia"tCS for cyclone versus

PC boilers) the SCR catalyst at a futul'e MRYS SCR system would see a catcjum environmentsimilaJ' to a

PC boiler PRB coal SCR installation and theref'Ore would have a similar catalyst deactivation rate.

Other alkaline materials (potassium, sodium and magnesium) deactivate catalysts by deactivating

individual reaction sites rather than the blinding by macro-pore plugging that was described for Calcium.

The average CenterMine coal ash contentfor these alkaline constituents is about 9%. (Reference:

-4-
HI'A Jlreliminaty Analysis ofB&M NO~

BACT Analysis at MRYS

JtUlllllry 8. 2007

November 3D, 2002 EERC Report: Asb Impacts on Sel{Calalyst Performance. Note that no average.

Center Mine lignite ash constituent values wel'e given in the October 2006 BACT;'application, Only wide

ranges were given in the October 2006 submittaL These ranges are oflittle u~ for making meaningful

ash loading comparisons.)'This percentage is OOJnewhat lowel' than most PRB cQlilsand within the

envelope of experience ofEuropean installations. One ofthe references cited in the Appendix B EERC

report, Cichanowicz & Muzio (200I), places the range ofEuropeml SCR exPerience with these alkaline

constituents at 8% to 15% ofash. ThuS, the c:oal.llsed at MRYS has slmilac poisoning potential compared

to other coals in use at SCRwequipped boilersin Europe and the U.s.

In their2001SCRsurvey paper, Cichanowicz and Mu~o go further in sayiQg; "Short-tenn

explorcitory tests suggested the extreme calcium content ofPRB coals promotes ~H poisoning.

However. not all catalystsuppliersshare this view. and the first commercial i~8talIa1ion with PRB coal

has not incurred any noticeable deactivation." In a May 2002 SCRtechnology slUveypaper presented at

DOE's SClVSNCR conference. authors Sanyaltmd Ellison concluded; "Evolved from two genel'ations of

design in the late 70s to the early 80s ill Japan and mid 80s ill Germany, 2 X.265 MW ofCamey's l)oint

and 375 MW ofMerl'imack are seen to bl;l pioneers of coal fired SCR Installations in the USA. Since

then, SCR technology has made great strides attaining 93% NOx removal efficiency, 3 ppm ofammonia

slip and 0.5% S02 to SO.. eonversion. SCR units on bolleJ'S with all three firing modes - cyclone, wall and

cornet·, dry as well as wet bottom, have been successfully commissioned and arc if! commercial operation.

High dust application ofSCR technology has becn demonstrated oi. units firing b.mu~illollS coal with near

to 4% sulfur and PRB coal containing over 25% calcium oxide:'

The concern about high amounts ofalkaline matetials in Center Mine coal expressed ill B&:,M'g

BACT analysis and described in the Appen.di~ B BERC report is real, though not necessarily unlike

operating SCR systems oope boilers burning PRB oo9J. As explained abov~. we believe there is value in

successful operating experielice realized at current SCR installal.ion at PRB-f!l-ed power plants. The

problems cited in the BACT analysis ate being dealt with at several NO", SIP CaJ1SCR installations

today. In addition, the analysis presents no quantitative analytical information derived from the ftring of

lignite coal on SCR catalyst deactivation tojustii)r tbe fmding that Selt is infeasil)le~

Engineerillg SoJuti011.Y lor. SCRA1!P-1jcations at High-Ash Fqcilities

Plugging ofSCR catalysts by fly ash ar.:c~ulation and bridging of paSsages in honeycomb

catalysts and between plates in plate-type catalysts has been a problem for d~signers a.od catalyst vendors

since the fil'Sf: coal-fired installations in I:he 197.Qs. The primary response bas ~n more sootblowing, onJine cleaning equipment, and larger catalyst pitch for honeycomb configurations and·wideI' plate spacing

for plate-type contigUlutions. These measures. combined with periodic cleaning <lurillg boiler outages

have, by-nnd-large, reduced catllly~1. plugging to a manageable SCR Jl'0blem.- Agai~'because the MRYS

units are cyclone fired, the potential for plugging is similarfor these units with their high ash coat

compared toPe boilers buming a moderate ash coal. Also, the fact thatthe ~R.ys units are brought

down for planned boiler deposit cleaning at 120-day intervals provides more opportunity fOl' catalyst,

cleaning maintenance than is available at the t.Y.pical power plant.

Further demonstrating the ability GfSCR designer.! to use existing knowledge and experience

with SCR installations for high ash fuels., the Electric Power Research Institute (EPRl) has advised clients

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EPA Prl;liminllr.Y Analysis ofB&M NO.

BACT Anltl}'l>is at MRYS

January 8, 2001

that based on industly experience on a wide range ofSeR installations overthe year:s5SCI{ designs can

accommodate fuel types never before used in practice O'n a full scale. In a S~ptember 7, 2006lettel'

addressed to TXU Power' > EPRI stated, "While experience specificallywith .Texas lignite is limited, this

should not preventsuppliers from providing all SCR ~'Ystem that m~ts these. objectives; dealing with a

new fuel is similarto the challenge faced by U;S. utilities and their SCR suppliors when tirst installing

SCR systems on plants til'ing high sulfur bituminous or PRB·coals. Neither suppliers nor utilities had

prior experience with these fuels, which produce flue gas properties that are Vel)~ different fr~rn those in

the Japanese and European plants where SCR has been installed before. Therefore, SCR designel'S had to

rely upon their knowledge, engineeringjudgment, and experience with theseol.her coa.ls to design SCR

systems suitable for these new applications. While some ofthe firSt U.S. SCR in$l!ationS 6Xpelienced

problems (e.g;. accelerated cat'dlyst; activity decay due to arsenic poisoning i~ die absence ofsufficient

calcium in the coal. and catalyst pluggage due·to large Particle ash)~ none ofthese problems prevented the

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

oftlle catalysts." .' .

Other Asn Deposition Problema on DO'Wn§h-egTn Components

In regards to B&M's concerns I'elated to ash deposits on other downstream boiler components, we

have already pointed out that ash loading ofmedium ash coals (PRB) fU'ed in PC boilers would be

comparable to the ash loading at the MRYS units. Also, as noted above, the;factthat the MRYS units are

already brought down for planned boiler deposit cleaning at 12O-d1l.y. intervals would provide additional

opportunity to clean these accumulatlons. B&M'sdlscussion ofthese "other" potential accumulation

problems does not reach any definitive conclusions related l.O the .technical feasibility ofSCR, so I)PA

does notsee this as a technical ba.'l·iCJ'to instalJing SCR at the MRYS units.

Accounting tor C'ata'~ & Performance in Top-Down BACT4nalysis .

Finally; the conclusion reached in the B&M BACTanalysis that ash d~posjtion and catalyst

pluggagc will adversely affect SCR J)erformance'(we assume this means cO$ol efficiency) and catalyst

life does not necessarily support a conclusion that the technology is technicallY infeasible and that SCR

should be eliminated atstep 2 ofthe Top-Down BACT analysis. Furtbennore, the B&M analysis

presents no quantitative data rela.ted to SCR perfolmarice and catalyst life to.support such a conclusion.

Although the catalyst deactivation rdtes ma.y be somewhat higher than the rates eXperienced at eastern

bituminousflIed SeR installations, strides in catalyst fonnulations and designs. catalyst management

systems, and catalyst regeneration processes~ have all combined to lowerthe opc~tional challenges and

overdll cost contribution ofbolli initial and replacement catalyst in modern SCRSystems. However, SCR

performance and any real construction and openrtional(;osl.sare factors that woulQ ~e accounted for under

thc economic impactstage related to cost effectiveness ofSCR (step 4) und~ tlIe Top-Down BAC.'T

analysis.

I http://www.reliabletcxaspower.com/pdfloglltr_eprt9_1_06.pdf

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EPA. Prclinlinarv..An.-uvsis of B&M NOx

BACT Analysis ilt MRY~

. JanulIry8. 2007

"Pom:orn Ash" Issue Raised by Burns & Mc:DollneJl:

A second consideration in the application ofconventional hi~dust SCR.teclui910gy on a lignite:.

fired \tni~ says B&M, is the potential ofthe SCRreactOr oatalyst pluggage rosultirtg fi'Om carlY over of

"popcorn ash" from the boiler, B&M statesthat bailersfiring·N(nth Dakota·ligon,: have severe problems

with ash deposition onboilersurfaces. North Dakota lignite has a bigh propensity', says B&M, to form

deposits on the boiler's furnace alld convection pass fireside swfaces. For Iigniie-f~d units, the boiler's

heat transfersurfaces must be cleaned by sootbJowlng and othel' methods (e.g. water lances) fi'equently to

maintain satisfactory boiler operation. Some ofthe removed deposits released by the cleaning action

within the boiler andc:onvection passes form "popcorn ash", whioh will be enlIoained in tbe flue gas.

B&M statesthat carryover ofhoiler ash deposits will cOntribute to l)luggage afthe "popcorn ash" screen

ahead ofthe top layer ofSCR reactor catalyst. This ca.n causedistortions in gas distribution

("channeling")through the ~CR reactor, which will aggravate erosion in the high velocity areas and

ineffective perfotmance ofthe catalyst.

EPA Analysis QUite "Popeorn Ash" Issue:

The "popC01'l1" ash mentioned ill the ~&M BACT analysis and the Appendix B EERC repOlt ha.s

.surfaced in the past few years as SCR units on lower rank coals; including those burning PRB coals, have

come on line. It is being addressed by increasing sootblowing frequency al'ldj in SQtne cac;es, installing a

large mesh screen above the first catalyst layer. In addition. the Japanese approach ofusing It hard

ceramic "dummy" layerwould also aid in dealing with this material. Catalyst layers are now provided

.with hardened or erosion-resistant leading edges. Japanese catalyst vendors prov19c a"dmnmy" layer of

ceramic material with the same cell size (pitch) as tile real catalyst layers beneaih.· The '~dumJnY" layer

not only pro1.oots the undel'lying oatalystfrom erosion, but also permits more VigoIDussootblowing to

deal with the catalyst plugging problems. Additionally, new licreen designs now 'being successfully

installed and operdted with on-line cleaning to deal with popcorn ash deposition. ,./, .

Temperature Issue raised by Burns & MeDonnelh

A third issue tha.t impacts the feasibility ofinstalling high-dust SCR technology on the NOlth

Dakota·lignite-tired units, according to B&M. is catalyst operating tempel·atlJre. T~e.perfurmance ofany

seR catalyst is highly dependent on tile temperature ofthe flue gas passingthrough the reactor.

Typically, a temperdture of600 - 750 degrees F is l'eCJuired to obtain sntisfltctoJ)t QPeration of an SCR

reactor. Opea'ation ofcommonly supplied catalyst Suill\ble for a high-(Illst SCR reactor at temperatures

above 750 degrees results in severe and rapid deterioration ofthe cataly!>( and SCR 1'eac1or's NOx

emission reduction perfonnam:e. For bi~uminous andsub"bituminous coal-fired units, boiler flue gas

passing between the economizer outlet and air heater inlet is generally withIn. a temperature range

acceptable for conventional SCR catalysts without additional heating or cooling ofthe flow stream.

North Dakota lignite-fired cyclone boilers, including those atMiltol1 R. YOl!ng Station, ha.....e high

temperatures at the economizer's flue gas outlet by design. 13&M lItllle81hat the hi.QN:st gas temperatures·

downstream ofthe convection pass ec:onomizer:sections and upstream ofthe air h~ter inlets in Milton R.

Young Unit l·s boiler are much hig.ler.than 750 degrees. '
EPA'Prclimitlat'Y Analy;:is ofB&M NO~

BACf AnalysisIII MRYS

Ianmuy 8.2001

High gastemperatures at the air heater inlet are required to: produce the higl1 air temperatures

(700°F) needed for the pre-combustion lignite drying system. along with primary and secondary

combustion air supplied to the cyclones. Such air preheater arrangements and .bilities have been

taken into account in the design ofthe North Dakota lignite-fired cYclone boilers. :B&M states that

reducing tbis higb gas temperature to accommodate 'conventional catalystsfor ~nventional high..clust

8CRreactor would result in pre-combusiion air temperatures &It.are tOQ loW to provide satisfactory

dJying and ra.pid ignition ofthe high-moisture fuel. B&M further states that this will seriously impact

reliable combustion, slag formation and tapping in the cyclone burners. Consequently. says B&M. it is

not feasible to modify the Milton it Young Unit l's boilerto operatewith the Jower·cconomi7.er outlet

flue gas temperdtm:e.

B&M also states that catalyststor a eonv~)tional high.:c.ust, hot-side SCR ~:ysq,m have not been

.installed norsuccessfully demonstrated in a full-scale installation ofan operlltingl$olid fuelufired unit that

are designed to continuollsly operate at the high temperatul'es (above 150 degl'c;:e~ F);that exist between

the convection pass economizer and air heater on th~ Milton It. Young Unit j·s boiler.

EPA Analvsis ofthe Tempernture Issue:

The economi:ler exit temperature for MRYS units will be higher than that ofa atypical·' coal-fired

utility boller SCR installation, which normally involves an economizer exit temperature ofabout 750°F

when the boiler is opemting at full load. When a "typical" unit iii operating at.-educed IQad,.the design

problem ~lat must be overcome is flue gas that istoo cool, perhaps as low as 60Qor. This istypically

handled by installing an economizer bypass duel. with a damper that is gradually 9pened when boiler-load

drops below a preset point. The hot bygassed flue gas is mixed with the rem~il'iing economizer exit flue

gas to maintain the desired 700° to 750 Ftemperdture at the catalyst inlet. Reliable operation ofthese

high-tempeJ'a~lTedampers has been problematj~ aodcareful design is neeessiuy to achieve good mixing

ofthe bypass flue gas and the economizer flue gas over- the load l'angc. The p~tentia1 engineering

challenge a.t MRYS may actually present a bettersituation for high-dust SCR soccess than the ''typical''

designs employed on unitS where the high economizer exit temperatures do not exist. .

At MRYS it would be possible to install a small air preheater ahead of'the S;CR catalyst vessel and ,

. split the primary airflow between ~ir pl"benters before and after tho catalyst., .By a.djusting the proportion

ofprimary air passing through eaeh air preheater, the temperature offlue"gas' entering the catalyst could

be maintained at the optimum temperature fOT the parl:icul81' catalyst formulation selected i:mdthc full

amount of heat needed for the Direct-firing Pre-drying Bypass System wOlll~ be extracted. The costs

associated with the two air preheaters would 'be partially offset by the eliminat~(m oCthe air preheater

bypass'and damper and by the fact lhat the two ail' pl'eheaters would each be somewhat smallerthall a

single preheater. This approaoh also elimimites the problem thatsome installations ~re having with

inadequate mixing ofeconomizer bypass flue gas. From an operating standpoin~ the two air pl'eheater

approach should be superior to the cu....ent, "typical" $CR systems.

Erosion Issue raised by Buns & McDonnell:

Another consideration. according to B&M, on whether hot-side, high-dust SC'R techno]ogycan be

.sllccessf'Ul on aNorth Dakota lignite-fired unit. is the potential for erosion ofthe seR catalyst .North

-8-
BPAJ'rllJilllinary Aoalysis oi13&M NO.

BACT Analysis at MRVS

}llIlllllJ)' 8. 2007

Dakota lignite supplied from the Centet· mine has an avel'age fuel ash content of IPS%, and can have an

ash content up to 25.5%. PRB coal fuel ash conl-ent typically averages approximately 5 percent. As

previously stated by B&M, a cyclone boiler firing North Dakota lignIte con~erts a significantly greater

amount offlyash than B PRS-fired cyclone boiler. Overall, says ~&M, this results in a flyash output rate

. from a cyclone boilerfiling North Dalc:ota lignite ofapproximately 83 IbsIMWhr compared with 21

IbsIMW-hrfor a PRB-fired cyclone boiler. High ash contents In.the flue gas *ea.m; says B&M. can

result in physical erosion oftbe catalyst. In addition~ says·B&M,.effective On-iDle cleaning ofthe highdust catalyst will likely require steam Orcompressed airsootblowing. B&M states that cleaning cycles of

the catalyst will be required muchmore frequently th!lf\ a typical conventional SCR jnstallation due to the

ash deposition characteristics oftbe North Dakota lignitE) and the expocted buildup and pluggage resulting

from the carry over of"popc.om ash." F'requentsootblowing.ofthe catalyst t:u remoVe fouling deposits

and ash aCcumulations will contribute to erosion 'and decreased catalyst:life..There is some European

ex.perience with higb ash browri coals that catalyst manufacturers wiJl be able 10 draw upon. This

expel"ience. hciwever, will nQt be directly applicable to these United States units, SIJ.YS B&.M; oocause of

the severe deposition characterl~1:ics orthe North Dakota lignite ash compared to brown coal.

EPA AIUtlysjS ofthe Erosion Issue:

.'

The high ash content oftbe Center Mine coal does, in fact. mean that the a$ l()adings at the

economizer exit ofthe MRYS units will be fairly high, but, as discussed ab9Ye, it would be \"Oughly tile

same as typically seen in PC-fired PRB units that are cummtly fitted with SC:R. Sootblowing is common

to all coal-fired units and particularly high rates ofsootblowim~ arc characteristic ofslagaing coals and

cyclone firing. SCR vendors have provided a llumber of~1easures.to avoid the erosion problems lh~t

were seen in early Japanese and German installations. First, ca.ta.lyst layers!ire now provided with

hardened or erosion-resistWlt leading edg~s, including providing "dummt'layer, previously

discussed u'nder the POPCOI1l ash section. Finally, today's sea designers are much more sophisticated in

design measuresthat insure a more even aue gas velocity distribution across'the .cat~yst layet' surface.

Although this is driven by the desire for unifol111 reaction rates across theca1alys1,~ to achieve the low

ammonia slip guarantees reqUired today, it has th~ additional benefit of eIim~natingareas oferosion due

to high ash velocity and improper "angle ofattack". .

Energy & EnvirODmental'Reseal'Ch Center Report (APUendix B): :

As part ofthe BACT analysis by B&M, a report authored by the Bnergy & Environmental Research

Center (EERC1 entitledUAsh Impacts on SCR Catalyst Perfonnance" was inclad~d as Appendix B. The

B&M analysis relies on a passage from the HERe t'\:lportM paltofits determinatibn.tliat SCR would be

technically infeasible for the MRYS units. The passage is as foll~ws. «the mosts,gnlficant problems tllat

ptOhibit tbe successful operation ofSCR catalyststo lignite coal is the fonn~tion. allow-temperature

sodium-ca.lcium-magnesium sulfates alld phosphates that will form all the sUrfaces ofcatalysts and the

.carryover of deposits that will plug the catalyst openings, resulting in increased pressure dt'Op and

decreased efficiency." . .

The BBRe report included in the MRYS BACT analysis relies heavily on pilot testing that was

conducted by EERC at two PRB-fired plants and one North Dakota lignite-tIred plant. The MRYS

BACT analysis also references this test and the accompanying technical paper, "Ash and Mercury

-9-
EPA 1.'relillljn~I'Y Ano.lY$iS ofB&M NO~

BACf Annlysisllt MRYS

JaJiuary 8. 2007

Behaviour in SCR Catalysts When Firing Subbilumino\ls and Lignite Coals" by the EERC tilat was

published in the Febnlaty 200S issue ofFuel Processing Technology magazine. The majority ofB&M's

technical argtunents related to technical difficulties ofhigh-dust SCRfor North Dakota lignite appear to

have their origin with the results ofthis pilot testing. It is worth noting thai: page 578 ofthe original

Februmy 2005 article cited above has nearly identical lancouagc to that used in tlle Appendix B EBRC

report, except the conclusions differ on the successful application QfSCRapplication ofSCR catalyststo

lignite coal. '

. "The most It;gniticant problem that limitsthe suQcessful application ofSClt catalyststo lignite coal

is tbe fOl'Dlation oflow-temperature sodium-calcium-magnesium sulfates, phosphates. and possibly

carbonates that will f01111 on the surfaces ofeatalystsand the canyover ofdeposits that will plug the

catalyst openings. resulting in increased pressure drop and decreased cfficiency [3.11-14]. 'l11e degree of

the ash ofthe ashwrelated inipacts on SCR catalyst performance depends upon the composition oftlle coal,

the type offiring systems, fhle gas 1emperawl'e, and catalyst design." (Emphasis added)

EPA Analysis oCtIle Energy & Environmental Re.searcII Center lummi <Augend.),: B):

It is interesting that.~;ERC characterizedthe technical problems associated SCRapplication lo

lignite-fired boileIS as being "limns" in thistechnical paper, but say that the problems "prohibit' the

successful use ofSCR ill the MRYS BACT analysis AppendixB report. While the former language

suggests sucCessful operation ofSCR is possible, tho later language appears to be crafted specifically for

addressing technical feasibility in .thc context ofBACr. However, the conclusions reached in the

Appendix B report do not address some ofthe engineering solutions previously cited and explained below

that arc a.vailable for full-scale SCRapplications. Furthermore, EPA Region 8 believesthat there may be

inherent limitations witb tile pilotstudy (that wasthe basis for both BERC I'ej>orts) th~ drdws into

question the validity ofdirectly applying those conclusions to tlle range ofpossi\;lIe SCR designs ofa fl\lI~

scale application at NlRYS. Statements Rom three majol' SCR catalyst mamifactill'ers (including Haldor

Topsoe. the catalyst manufacturer involved in the pilot testing for North Dakota lignite) suggest that the

Ct'Italyst deposition and plugging problems experienced dW'ing the pilot testing may be exaggerating on a

pilot scale .md can be solved in a full-scale design snd application. This is eXPlained in more detail in

Section HI ofthis report.

Othet inherent problems associallld with directly applying the results oftlle EBRC pilot testing at

Coyote Station on North Dakota lignite include: .

l) The air pulse used to clear deposits during the pilot test is a poorsimulation ofsootblowing and

is much less effective. Sootblowers essentially "blast" the deposits offthe leading edges ofthe catalyst

with jets ofsteam or air. TOO test rig used in this project merely blewair into the space above the catalyst

face, resulting in a pulse ofhigher velocity. which is much less direct than sdotblOwlng. Most new

comml;ll'Cial SCRinstallations aloe a.pplying acoustic horns in lieu ofsootbJowtflg and are found to be vel)'

effective.

2) The 6mm pitch catalyst used for the pilottesting at Coyote Station is much smaIJer than

currently being specified for coal·fired installations. Vendors are now supplying 9mm, 10mm ur even

I Imm pitch catalysts. As discussed earlier. larger catalyst pitch is one ofseveral engineering solutions to

-10-
· EPA Prcliminmy Analysis ofB&M NO.

BACT Analysis at MRYS

.lfUluary 8, 2007

address the problem ofcatalyst plugging for higher ash coal. This current industry pl'~ctice makesthe

EBRC results based on 6 II;Im pitch catalyst essentially obsolete, .

3) 1'he one meter depth oftbe catalyst used in tbepilottest is equivalent to one layer ofcatalyst in

a commercial in~tallation. Conirnerolal systems aimed at high rcmovais have three laYers, each about

three feet thi~ and, at various times in the catdlystIDlIlU\gement'Cycle, incorporate fOllr layers. BERG's

test, the11, only simulaled the lOp layer of a mUltiyIaycr system. The top layel' of any SCRsystem always

takes the lion's share ofthe abuse from the ash.and the activity degrades at a much faster rate than the

seCOlld and third layel'. The top layer continues to protecttho lowerlayers even when its activity has been

severely degraded, This is why the IJIStstep in most catalyst maJiagomentsohemes usually involves

adding a fburth layer and leaving the badly degraded t9p Ia.yerin place for the second opcl'ating period.

BERe's project provides no real insight into the effectiveness and survivabil~ o.fa second or third layer,

4) The scale oftcstil'lg carded out ill this project is usually associatecl'withobserving catalyst life

prospects (01' said another way. the rate ofloss in catalyst activity) rather than physical processes of

deposition or plugging, This is because the deactivation mechanisms operdte on a micrOwscalc and can lle

accurately simulated at this small seale, but the plugging and deposition are influenced by larger

processes, such as flow imbalance and countemleasures (sootblowing, homs~ screens, baffles, etc.) and

are not duplicated on the small scale.

For these reasons, EPA Region 8 questions the direct app1ic~tion of th~ results ofthe BERG pilot

testing at Coyote Station and the accompanying Appendix B EERG report for p~os~ ofthe BACT

technioal feasibility analysis of SCR at MRYS, The experience and opinions ofthe SCR supplierthat·

participated in the BERC pilot test indicate that the problems encountered du:ritlg the pilot test are not

determinate ofwhethersea plugging experienced during the pilottest would be unresol"able by

vendors, To the contrary7 statementsfi'OIn HaldorTopsoe off-eringtheir SCRcatalystfor installation on

lignife..fired boilers indicates that the fulJ.·scaIQ differences and engineering sOlutions lIvaUjililc today

provide evidence that the BERC pilottesting results should not alone be the deciding consideration when

evaluating SeR teclmical feasibility at MRYS.

BUI'ns & Mcnonnellts Conclnsio•• on Technical Feasibility ofHigh~Dmd SCR:

B&M notes that EPA's 'NSR Manual St"dtes that for a technology to be feasible it must "available

and applicable", The question is whcthel' SCR technology is ~'applicable" for a unit firing N0I1h Dakota

lignite.

B&M further notes that, in accordance with EPA's NSR Manual, a techll0logy is. :Capplicable" ifit

has been jns~lIed on a "similar unit:' Hot-side, high-dust SCR technology has ~en relrOfitted on coalw

fired units featuring cyclone boilers. However, B&M states, thereare.no SCR installations in operation

or planned on units that include cyolone burners tiring 'Nolth Dakota lignite wiLli'severe slagging and

f'Ouling tendencies combined with such high boiler economizcr outlet gas temperatures (over 7500P)

required for high-moisture fuoJ proolying systems and tubular air preheaters.

B&M notesthat the NSR Manual also states a technology may be detelmined to be not applicable if

4'a. rechnical assessment considering physical, chemical and engineering pt'inciples and/or empilical data

-11-
EPA Preliminary Analysis of B&M NO.

BAcr Analysis at MltYS

JIll1llIU'Y 8. 2007

showing tile technology would 110t wol'lc. on the emissions unit undcl'review or that unsolvable technical

difficulties would preclude the successful deployment ofthe technique." In this SCR.tecllnology

application. says B&M. it appean that II utility power plant firing North Da~tlllignlte would experience

extended time delays, 01' ~e required to devote significant inmrnal resources and engage outside research,

followed by extended field trials. to Jearn how to llpply a conventiQlli),1 higb-dust, hot-side SCll

technology on a such a fuel source. '

EPA Anulysils of theBurns & McDonnell's ConcluSion:

EPA notes that there is considerable experience in the industry to show that u~e orseR on North

D-dkota lignite is technically feMible, EPA has previously artiCtllated this b~Jiefm a number ofnational

rnlemakings, including dIe Clean Air Interstate Rule (CAJR). the Best Available Retrofit Technology

(BART) GuideJines. and revisions to the New Source Pcrfol'mance Standards(NSPS) for Electric Uti!ity

Steam Generating Units(finalized on Febroary 27.2006). These 1'!1lemakings are discussed in more

detail in Section III ofthis report,. Furthermore, B&M's assertion that MR~ would not be considel'ed

"similal'" to those PRB facilities that have successfulJy installed SCR is notsupported by comparing total

alkaline ash loading at MRYS to PRB-fired PC units that convert 80% oftIle ruel"ash to flyash.

EPA understandsfrom the HERC pilot study at Coyote Station llsing North Dakota lignite, there

was noticeable ash build lip on the catalyst and concerns· with catalyst plugging d~ril18 the test. While

TIERe notes that ash deposition problems were most pronounced .at Coyote Stalion. compared to the two

test facilities burning PRB coal, it also states generally that all ofthe coals in the pilot shldy "produced

ash that had significant accumulations ofash on the catalyst On both macroscopic and In icr08copic

levels." Thus. the conclusions ofthe study appear to be that deposition issue,! might be somewhat greater

for North Dakota lignite than for PRB coal. Since significant accumulations ofash on the catalyst was

also observed during pilot ~esting atthose facilities burning PRB ~a1 and thcre arc numerous examples of

PRB coal-fired power plants 8ucccssftJlly operating SCR systems. the qualitative results ofthe pilot

testing described by B&M and HERe would not appear to predude successful operation ofSCR on a

power plant burning North Dakota lignite. The EERe study does not appear toq4antify the effect that the

ash acculnulation had on microscopic catalyst deactivation rates or overall ~lalyst perfonnance. Absent

such information that reflects lhe use of currently available full-scale ash loqrling mitigation designs, pilot

testing results may not be evidence thatsuccessful implementation ofSCR on North Dakota fired units

"is going to be impossible." as stated in the Appendix B EERC report.

As noted abovf? due to the inherent pi[ot~scale littJ.itations i.nvolved in this testinS1 dil'ect applical:ion

ofthe effects and/or magnitude ofash deposition during the EERC pilotstudy should not be used as the

primary basis for detennining technical feaSibility ofSCR at MRYS. Tn tIle full-seale installations. th~se

conoerns al'eaddressed dtninglhe SCRdesign stage, While combustion ofNorth,Dal<ota lignite in

cyclone boile1'S might presentsome additional engineering challenges for SCltdesigners. l;hel"e are

multiple credible solutions that Minnkota should have evaluated before concluding that SCR is not

technically feasible.

The October 1990 EPA drctft New Source Review Manual (NSR Manual) statesthat a

"demonstration oftcchnical infeasibility is based on a technical.nssessmen1 considering physical,

chemical m1d engineering principles. and/or empirical data showing that the tcchl10lo~y would not work

-12~
EPAPrclimimu)' Analysis ofB&M NO.

BACT Analysisll1 MRYS

Janullry 8.20crl

on the emissions unit under review, orthat unresolvable tecbnic!1l difficulties would preclude the·

successful dep~oyment oftbe technique. Physical modifications needed to resolve technical obstacles do

not in and ofthemselves provide ajustification for eliminating the control technique on the basis of

teohnical infcasibilify. However, the cost ofsuch modlfications caR be consideredin estimating cost and

ecoilomic impacts, which, in tum. may fonn the basis for elIminating a ootitrolteehnQlogy." (Page 8.20)

(Bmphasis added) Based on the aVailable·infonnation, the problems'Cited by B&M for·appHcation of

SCR at MRYS (ash depOSition, "popcorn ash", rompcrawre, and erosion) are: rc.so~vable through the

engineering solutions discussed above. While such engineering Solutions may be a cost burden to

Minnkota, as noted above,step 2 is not the properstage ofthe Top-Down BACT' 3ru~tysis to account for

th~e costs. As described in the NSR Manual, "where the resolution ofteclulical difficulties is a matter of

coSt, the applicantshould considerthe technolOgy as technically feasible. The economic feasibility ofa

control alternative is reviewed in the economic impacts portion ofihe BA(.'T selection process." (Pages

B,19uB.20) Many ofthe technical feasibility arguni~nts presented in the BACT analysis are centered on

decreased catalyst life and perfonnance. increased maintenance and outage time, and plant differences .

unique to MRYS that preclude SCR feasibility at MRYS. Consistent with the NSR Manual. lhese

concems are incorrectly incorpol"'dted into the TOp"Down BACT analysis atstep 2. and really should be

accounted tOr as additional costs per ton ofpollutant removed at step 4 ofthe a~aly.sis,

Furthennore, the NSR Manual states, '~:Vendor guarantees may·providean indication of

commercial availability llI1d the technical feasibiHty ofa control technique nnd·could contribute to·a

determination afteohnical feasibility orrechnical infectsibility. depending on circuml'tallces. However,

EPA does not consider a vendor guarantee alone to be sufficientjuStification:that a control optiOtl will

work. Conversely, lack ofavendor guarantee by itselfdoes not presentsufficientjustification that a

control option or anemissions limit istechnically.infeasible. Generally, decisions about technical

feasibility will be based on cbemioal and engineering analyses (as discu~ed. above) in conjunction with

infOI'luation about vendor guarantees." (page B.20) So; while EPA does not consider vendor guarantees

by themselves to bedetermin8te in making technical fea:sibility decisions, they an~a ;contributing tactor in

making these decisions. EPA is aware ofthree catalyst vendors (Haldor-Topsoe,.Cormetech, and

Argillion) who would be willing to prOVide performance guarantees for ligniteuflred boilers applications.

Based on the criteria discussed above, Minnkota and B&D should hav4 fur610r explored both the

full-scale engineering solutions used to address the problems cited in their analysis in c.:onjunction with

information from SCRlcata1yst vendors to offer perfonnancc guaranteesto design and instaU an SeH. unit

at MRYS. The BACT analysis fol' MRYS that was submitted relies heavily on the technical problems

experienced during the BERe pilot testing at Coyote Station in conjunction with the fact that SCR has not,

been installed on a cyclone boilerthat bums North Dakota lignite. We do not believe that this analysis

adequately addresses the criteria citw above. As such. it appeal's that the case-speCific NOx BACT

analysis submitted for Minnkota MRYS is deficient in terms ofimproperly eliminatingSCR from

consiqeration at step 2·ofthe BACT analysis for technical feasibility.

B. J...ow-Dost SCR

Burns & McDonnell has eliminated Low-Dust SCR astechnically infeasible due to il:>sues

described below. EPA's response on each issue is also described below .

-13-
EPA Preliminary Al1alysis of B&M NO.

BACT AnHly~is III MRYS

Janual)' 8. 2007

Catalyst Fouling and Deactivation Issue U.aised by Burns & McDonnell:

B&M states that an existing electrostatic precipitfttor(ESP) upstream of a low dust SCR reactor will

still expose the catalystto the acid gas content and fine particulate containing trace metals and the high

alkali miner.u content ofthe entrained lignite flyash not removed by the ES}l upstream. Although the

total amount offlyash carryover into the LD-SCR reactor is greatly reduced co~pared with a high-dust

design. it is antioipated, says B&M, that the low-dust SeRcatalyst life wifl still be tmacceptably short.

The small particle flyash passing into the reactor will be sltfficient'to calise plLiggage ofthe catalyst pores,

Says B&M, resulting in deactivlltioo ofthe oataly~ The tiring oflignimcoal produceS fine (less dUlIl 5~

pm diameter)flyash particles. which are also least likely to be removed by the existing particulate

colJectioncquipment (e.g. ESP) upstream of a low-dust SCR- This creates conditions, says B&M, that

allow these smaU flyash particles to enter!he pores oIthe catalyst, reactwith SOl in ,the flue gas, and

for!n sulfil.tes }vhich bind other a,'\hparticles into a matrix ofsodiulD-, calcium-. and sulfur-rich materials

(likely in a fonn of calc:illm sulfate). B&M states that once such a matrix fonns wltbin the catalyst, it can

be extremely tenacious and difficult to remove.B&M notesthat one catalyst vendor has stated it is their

"experience that lowudust catalyst is more difficult to clean than that from higl}.dust~ B&M concludes

that low-dust SCR performance and catalyst lif-e could be seven:ly negatively impacted. and that'

shortened'lifespans ofthe LD SCR catalyst will require premature, extended, frequent outagesfOl'

repla-cement.

, El~AAna1Y8is uribe CntalvstFuuling and Deactivation Issue:

A few SCR systems installed on coaJ-fil'C~d boiler~have been designed with ,th!3 SCR catalyst

installed after the ES1' or baghouse. This approach elil11ina.tes virtually all ofthe poisoning, pluggillg and

erosion problems that have been associated with SCR catalyst. (Chris1::nlan MemQ,'2/18l03) For the same

reasons noted ab~ve under the high-dust SCRanalysis, the catalystfouling and deactivation'problems

may be J'esolvable technical pl'Oblems that do not warrant elimination oflow-dust SeR under step 2 ofthe

Top-Do\¥tl BACT analysis. In a recent PSD permittillgaction torthe Desel'et Bonanza II 0 MW Waste

Coal-FiredCirculating Fluidized Bed project, EPA Region 8 did l19trule out-iow-dust SCR based on

unresolvable technical feasibility issues Witll catalyst fouling and deactivation. Similarly.,pemlit

applicationsfur three recentCirculating Fluidized Bed projects in Nortb Dakota (MDU WestmOQreland

Gascoyne, South H~rt, and Gascoyne 500MW) did'not eliminate low"Dust SCR based on unresolvable

technic.al feasibility issues with catalystfouling and deactivation. While there would be inherent costs

associated with preheat, other possible physical modifications to the plant to a~modate low-dust

SCR, and engineering designs to min'mi?G and manage catalyst fouling and deactivation, these factors,

consistent with the NSR Manual, should be accounted for when considering the economic impacts ofthe

technology.

Site Space CODstraint IssueRuised bv Burns & Me.Donnell:

The installation of a low-dustSCR system with flue gas reheat requires a substantial amount of

space for installation and operation. A low-dust SCR system will likely use 0. regenerlitive gas-to-gas heat

exchanger(reheater) to raise the temperdture ofthe flue gas at tile SCR inlet. A g~s-:to-gas heat

exchanger(GTG HE) will transfer heat from the flue gas at the SCR rea<:tor outlet 10 the flue gas entering

the SCR reactor irl orderto rn inimi7..e the supplemental SCR energy usage. The GTG HH dictates lh~

footprint ofthe cold-side low-dust SCR system. Space is required for the GIG HE and for ductwork in

-14-
EM }>reliminal')' Analysis of B&:M NO~

BACT Anllly~is III MRYS

January 8, 2007

and out ofthe rehellter. Sufficient free space around the reheater and SCR is also required fol'

maintenance.

The ~,rea around Units I and 2 at the M.R. Young station is ¢)(ttemely congested,says B&M. ill the

areas where low..cJust SCR sylitems must be located. The situation,Is paJ!ioul!U"ly SeVCI'C, says B&M, for

Unit No.2. Equipment that. impactsthe feasibility ofinsta,llIng alow"dust SCR system on Units 1 and 2

includes the Unit 2 absorbers, Unit 2 flue gas desulfurization (FOD) dewatering equipment, fly ash

handling e,quipment,ftlel storage and transfer equipment, ~acks) failS and ductwork. It would be

extremely disruptive to the continued economic operation 6fboth boilers, says B&M. to relocate all the

mentioned equipmentto create space for the low-dust SCR systems at the M.R. Young Station. Stacks.

fans and ductwork and the Unit 2 FGD system cannotbe readily relocated due to adjacentstructures and

the need to continue operation while constructing the retrofit installations. 'ryle fuel handling equipment

includes a coal storage bam and the main conveyors supplying lignite to the mlful~ Relocating the coal

handling equipment currently occupying space needed tor the low dust SCRsystem.s would be quite

difficult, says B&M> given the site configuration. It is conceivable that the tiy ash equipment located·

west ofUnit 1could be relocated to provide some oflhe space needed for the low-dust SCR. However.

lite availability oftbisspace is doubtful, says B&M,since aVoiding the.Jikelihood ofsevcrc SCR catalyst

sulfate fouling will require a new Unit 1FGDsystem to be instlllled. If a.newFGDsystem is installed for

Unit 1. the FOD system would need to occupy the space that can be made available by relocating ash

handling equipment. B&M concludes tha.t this space subsequently would not be available for a low-dust

SCRsystem. . .

EPA Analysis ofthe Site Space Constraint lssue:

While the extent ot'thc physical plant modifications necessary to accommodate Iowwdust SCR at the

MRYS is not entirely clear, the above description- does not iildicate that the site space constraints at

~RYS would necessarily preclude the possible installation oflow-dust SCR. It does sound like m4ior

and costly equipment relocatiol1 may be necesSary to provide the space necessary fOI'low~dl1st SCR.

However, consistent with the.NSR'Manual. «physical modifications needed to resolve technical obstacles

do not in alld ofthemselves provide ajustification for eliminating the contro' technique on the basis of

technical infeasibility.;' 'lnese Costs should be accounted for whtm estimating the cost and economic

impacts oflow-dust SCR. butshould not be used as a basis for eliminating the technolOgy as t.echnically infeasible. .. .

Bums & McDonnell's Conclusion on Technical Feasibility ofLow-Dust BCR:

Based upon a technical Msessment tllat looked at the various design and operational issues

associated with the installation oflow-dust 8CR technology on a North Dakota lignite-fired steam-electric

generating unit, B&M concludes that this control option should be considere~techniea11yinfeasible for

the Milton R. Young Station ·Unit 1's boiler. '

El'A Analysis ofthe BonIS & McDonnell's Conelu..orion:

As explained above, EPA Region 8 believesthat the inherent challenges with installing and

opeJ"ating low-dust SCR at MRYS are resolvable ona technical basis. The fact that a few low"dust SCR

applications are currently used in practice indicatesthat the small-particle catalyst fouling and

-15-
EPA Preliminnry Annlysis ofB&.M NO~

BACT Analysis at MRYS

1anuaI)' 8, 2007

deactivation problem described would not preclude the use oflow-dust SClt.~ In &et, EPA Region 8

believes that the dust-loading problemsthat can be efl'eetively addressed through ~ngineeril18 solutions in

a high-dust environment are less problematic than in a low-dw.1: enviromnenti B&D's statement's that

"Iow-dust SCR perfOI'lnance and catlllyst life could be severely negatively impacted resulting in

premature, extended. frequent "oUlages for replacement" can be minimized by proper SCR design and online cleaning. As stated previously, any real costs assooiated witli ~e construCtion and maintenance

required to operate the low-dust SCR should be accounted for under the economic impacts stage ofthe

Top-Down BACT analysis(&'Wp 4). Similarly, physical plant modifications that Would be required to

accommodate the low-dust SCR (and auxiliary ~uipment) shQuld be consi~red iylthe economic impact

evaluatioll, rather than used as evidence oftechnical infuasibility. '

III. Additional Information Usefnl to Evalnating Technical Feasibility ofSCR at MRYS

A. EPA Headquarters Believes sea is the Correct Tecbnology for MRYS in

Dcvcloning the Clean Air Interstate Rule (CAIR)

During the preparation ofthe CAIR ru)~ EPA developed a scenario tOl' best controls across coalfired units in the United States based on all assessment of bcHler type, fuel t:Y1;le', and existing controls.

This assessment recommended that SCRtechnology would be the best technology forthe two units at

MRYS.

Several commenters- Mon(anawDakota Utilities Co. (VI.G-0754); Otter-Tail Power Co. (VI.C0628); Lignite Energy Council (VI.C-0935); Lloyd. Oosselink, Blevins. Rochelle, Baldwin & ToWnsend,

P.C. for Texas Lignite Coalition (VI.C-I037); and Basin Electric Power Cooperative (VI.B-0690)-~

argued that SCRtechnology is not feasible fOJ' application on lignite-fired boilers. Some oftltese

"oommenters claimed that an SCR pilot test on a slipstream from a boiler "fil'lng ligtlite had shoWn catalyst

plugging and "blinding. One commenteJ' attributed this problem to ~ulfates ofcaJciumand sodium. which

arc present in the flue gas stream entering the SeR, as uesultoftifing oflignite in the boiler, One of

lhr;:se COmmcmtcrs also claimed"that SCR was not feasible for boilersfiring $l.lb--bifurilinous. . . . ,

In its response at VI.13. ofthe CAIR docket, EPA noted that there is considerable exp~rien¢e 11'1 the

industry to show that use ofseR on sl1b-bitundnous coals and lignite is technioally feasible. SCR is

currently in lise on sever-dl subwbituminous coaMired boilers in the U.S. firing PowderRiver Basin coal.2

Regarding the use ofSCR on" boilers firing lignite, EPRl testing ofSeR catalyst in a slipstream at the

Martin Lake plantshowed acceptable results from Texas Lignite.' Furthermore, the technology suppliel's

report that SCR bas been successfully used on lignite and brown coal boilers in Europe." from this

experience. it can be concluded that SCR can be used on sub-bituminoLls coal and lignite boilers in the ,

It "SCR Lowest NOx Ranking, 3111 Quarter 2003," Mcnvaine Website, www.mcilva;~~ornparty.com. accessed on

December 23,2003 (dockct no. OAlt-2003-<lOS3-1940) "

"Impact; ofTexas l.igniteCoal On SCR Catalyst Life and Perfo1ll1ance: Field Data fium TXU's Martin Lake

Planl," EPRl Website, www.eprLcom, accessed on December 11,2003 (docket no: OAR-2003-Q053-1944)

4 Email from J. Staudt to S. Khan. Lignite hlstalllltion List, July S, 2004.(dockul nO. OAR-2003-00SJ-1946)
•

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EPAPreliminary Analysis ofB&.M NOx

BACT Anulysis al MRYS

JanUaIJI 8. 2007

U.S. and catalyst supplie1's have indicated that they will offer performance guarantees on these

applications ill the U.S.s . . ,. .

In the docket information regarding this issue, oDe ofthe SCR catalyst vendor::;, Argillon. provided

a list a sea installations at EOUs in Europe that bum lignite orsbnilarrank ~oal. including:

• Riedersbaeh install81ions in 19~5 and 2001(hard coalllignite)

• Voitsbet'g (lignite)

• DOl."DlUgen installations in 1994 and 1996 (lignite)

EPA a.lso noted that the commontcl'$ llave not provided any details of1116 pilot test that has been

mentioned with regardsto the plugging lUld blinding ora. catalyst'ftom lignite-generated fuel galles.

Without this information, this part ofthe comment cannot be addressed properly. The El)A'5 own

investigations show that the main reason for this problem was ash build up On the catalyst, witich is a

problem commonly experienced in pilot test f~i1itics,(1 Tn the t\JJI"scale installations, 111is concem is .

addressed during the SCR design stage. The methods used to avoid this problem include duct design to

promote ash fallout prior to the SCR. catalyst reactor design to avoid ash buiid up. and on-line cleaning

methods (sootblowers and sonic horns). '

In addition, the following catalyst vendors stated that they could provide .catalysts/SCR for Iigniteu

fired boilers: .

HaJdor-Topsoe. ~[c."ln confinn·that on a general basis Htldol'-Topsoe calland will offer our SeR

catalyst for use in lignite--tirod boilers, to be installed either before or aft¢r ash colloot'OI'S.'·

Connetech. "Cormetech has no reservations in pl'Oviding perf0l1nance.guarant-ees for application

of 8CR for NOx reduction all lignite-fired utility boilers."

Argilloll."Generally speaking. yes, ArgiJlon would provide perfoml1mce guarantees on seR

catalyst on a lignite-tired boiler~ In fact, we were recentl)' asked Ifwc would do so for a specific

'.'_" __ ._. _. _.__ . __ .Q!!U~t and w~~ed~.w~J~~!i~e _@~at our expcrI~nc~~~~.~.!.1~DE.~.~lign.i!e.~~~_k!,~~!e~~_~ ~~~ .__. __._ _.. __.. _ . the characteristics ofthe two types orus lignite, our overall experience with many fuels,

combined with our in-house flow modeling capability prOVide us with enough information to

design camlyst that perfonns as specified."

Email From J. Staudt to S. Khan, Response to CommenL'I. ·IAQR. July 2, 2004 (docket 110. OAR-2003-0053-1945)

6 Email From J. Staudt to S. Khan, 8CR on NO Lignite, August 20~ 2004(doclc.etnd. OAR~2003.0053.1947)

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EPA:Preliminnry Analysis of B&M NO.

BACTAnalysis at MRYS

January 8, 2007

In ll. memo dated August 20, 2004, .Tim Staudt ofAndover Technology Pat1nel'S to Sikandcl' Khan of

EPA CAMD. discussed both the EERC pilot testing results and ~ome ofthe negative issues raised by

B&M and documented how Haldor Topsoe was aWll'e ofthese iS~es, but nevertheless felt ·comfortable

providing SCR catalyst.

"Re: SCRcatalyst testing on NO Lignite

Yesterday Ispoke wilh Mr. Flemming Hansen ofHaldorTopsoe l-egal'ding their experience

testing Baldo!Topsoe's SCR catalyst on North Dakota Lignite. Haldor Topsoe participated in a

progratn with the University ofNorth Dakota's BERe and·OtterTail Power. In this program

their catalyst was tested on a pilotfacility bumil1g lignite coal. Flemming's recollection WdS that

the test ran sevel'at thousand hours- possibly around 4,000-6,000 hours. Ca;talyst testing was

performed roughly every two thousand hours. .

Flemming's recollection was that sudden fly ash build up on the ~yst race occurred during the

test. The cause ofthis sudden build up" was determined to be accumtilation orash upstream oftIle

catalyst mId sudden dropping ofthat accumulated ·ash Ol'\to the CatalYst face. l11is.. he explained.

is a problem that frequently occurs in pilot fucilities. but tends to be far less ofa concem for much

larger. filii-scale systems. He explained that this behavior is also similar to that exhibited by PRB

coal fly ash, whieh shares some physical characteristics with Lignite fly ~h,

. As you are aware, SCR system.suppliers perform extensive work - physical·and computer flow

modeling - to design the SCR reactor to minimize ash buildUp in fulluscaJe systems. Moreover,

cleaning d~vices are always installed to clean the catalyst on-line. So there are engineering

solutions to address fly ash build \Jp. And, f1S experienced with SCR-equipped boilers that fire

PRB coal, SCR systems call be designed to acoommodatethis fly-ash behavior while providing

reliable operation in 'elecnic utility plants, .

Recall thatHaldor Topsoe provided a statementsaying that they would offer their SCR catalyst

for installation on Lignite-fired boilers either before or after particle collection. l1tis statement

was provided on JuJy 2, 2004, after their plllticipation·in the pilot test on l·ignite-fired coal. So,

this statement was made, no doubt, with knowledge ofthis program." .. .

B. SCR Technology is l~rcSumptivcBART for Cyclone Boilers in EPA's BART Guidelines

EPA made a specific and informed decision in its BART Guidelin.es regarding oyclone-fired utility

boilers. For all other boilertypes, some fonll ofcombustion control was deemed to be the presumptive

level ofcontrol. However, for cyclone units burning any type.ofcoal (bituminous, subbiturninotls, or

lignite), presumptive BART is SCR. SCR was selected because the technology is·feasihle and costeffective, especially considering the high baseline flue gas NOX concentrations (e.g.~ 0.8 IbIMMBtu). The

spreadsheet that was used to tabulate BART source control costs for the BART rule showed low SCR

costs for MRYS (about $550/0011),

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EPAPteliminary Analysis ofB&M NOx BACT Analysis at MRYS

. January 8. 2007

C. February 27. 20061i"malRevisioDs tg 40 emPart· 60, SubAAttDa, New Source

!JerformaD'le'Stnn,danlsfur Eledrit Utility Steam Generating ll!ifs Set Final NOx

l.imit na~ed ·011 TeclJnical Feasibility ofseu for ~:iitpyFjre~.uDits~

In its response to public comments on the February 28,2005 dra1fNSPS, Subpart Da. proposal,

EPA rejected comments received on NCh. con~~requiremcnts futJignito-:fll-ect units: Speoifically, EPA

took the same position as it did in the CAlRaitd BART ndes. rejtlcting commenters' concerns that SCR

would not be feasible for lignite units. No legal challengeS were made to the finall'lJle regarding EPA's

response to the lignite concerns. While the revisedNSP8, ~bpart Da wouJdappJY o~y to new lmits. it is

fulther evidence that EPA t~Jmical experts believe that SCRean':successfOUy be:applied to lignite

facilities. The B&M BAct. analysis essentially makes the same teChnicat arf;ume~'t$. that EIJA l'ejected in

this rule package. " ,

D. 8m and Catalvst Vendor Information

As noted above, the following catalyst vendors were comfortable .providing:c;atalys(s/SCRfor

lignite-fired boilers: . . .

• Haldor..:.Topsoo

• Connetech

• A.rgilloll

In addition, the above-cited memo dated August 20, 2004,Jim Staudt ofAndoverTechnology

Partnersto Sikander Khan ofEPA CA~, discussed both the EERC pilottesting results and some ofthe

negative issues l'8.ised by B&M and documented how Haldor TQpsoe was lI.wa:~ ofthese issues, but

.nevertheless ~Jt comfortable providing SCR catalyst.

EPA R~gion 8 also contacted the Instittne ofClean Air Companies website fo:obtain the

following list of21 companles offering "SqR Systems, Equipment, Supplies and Services;"'

• ALSTOM POWER

• Argillon LLC

• Babcock & Wilcox , Babcock Power Inc.

• BASF ,

• Conn~toch, lne.

• Coming Incotporated

• CRl Cattlyst Company ,

CSM Worldwi~ Inc. .. •

• EpconIndustriaJ Systems. N.V.

• Fuel Tech. Inc.

, . GB Energy Services

• Haldol' Topsoe. Inc.

• Hamon Research-Cottrell, Inc.

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":,

EP:A,Prclhriinary Analysis ofB&M NO~

BACT Analy$ill at MRYS

.1(1iJUllry 8. 2007

'" Hitachi Power Systems America.. ·Ud..

'" Hitz America Inc; ,

III Johnson Matthe}! Stg,tionaiy Source Emissions Coritrol '" Millennium Chemicals . ':". '.,: ..

• Mitsubishi Power Systems AmenSf¥, hie.

• SClt-'fech

'" Wheelabrator Air Pollution Control; Inc

';i

.' . EPA Region ghas visited most otthe vendol'S~ websites ll'O,d rourid"~any vendors with experience

that would be gennane to the MRYS Situation, (Others are not vendo~ for hirge power plants.)'rhe

experience ofthese companies should be used to supplementthe endorsement by three ofthe SCR

catalyst vendors used by EPA in the backgrou,nd research fOl' the CAIR, BART, and NSPS rules. We

believe it would be prudent for Minnkota to ob~in ·information mi~ proposa.!sfrom more than one vendor

and involve the NDDH and EPA in tJleir findill~;s .

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