MinnkotaPower ~Pc;j coo PER A T I V E, INC.

1822 Mill Road· P.O. Box 13200 • Grand Forks, NO 58208-3200 • Phone (701) 795-4000

February 20, 2009

Mr. Terry O'Clair

Director, Division of Air Quality

North Dakota Department of Health

918 E. Divide Avenue, 2nd FI

Bismarck, ND 58501-1947

Your Touchstone Energy'" Partner

-

RE: Supplemental information for the North Dakota Department of Health's Best

Available Control Technology Determination for Control of Nitrogen Oxides for

M.R. Young Station Units 1 and 2, dated June 2008

Dear Mr. O'Clair:

In response to the Department's request for additional information concerning the use of

Low Dust SCRs and Tail End SCRs at Milton R. Young Station, please find enclosed

the report titled "Supplemental Information for Consideration Regarding NOx BACT for

M.R. Young Units 1 and 2: Technical Feasibility Issues for TESCR or LDSCR Retrofit,

February 20,2009".

Minnkota continues to believe the NDDH's preliminary BACT determination dated June

2008 to be correct and appropriate.

Should you have any questions concerning this submittal, please contact me at 701-

795-4221.

Sincerely,

POWER COOPERATIVE, INC.

John T. Graves,

~~P.E.

Environmental Manager

C: David Sogard
Supplemental Information for Consideration by NOOH

Regarding NOx BACT for M.R. Young Units 1 and 2:

Technical Feasibility Issues for TESCR or LOSCR Retrofit

prepared for

Minnkota Power Cooperative, Inc.

And

Square Butte Electric Cooperative

February 20, 2009

prepared by

Burns & McDonnell Engineering Company, Inc.

Kansas City, Missouri

and

Steve Benson, PhD

Department of Chemical Engineering,

University of North Dakota

Project No. 31777
Supplemental Information for Consideration

Regarding NOx BACT for M.R. Young Units 1 and 2:

Technical Feasibility Issues for TESCR or LOSCR Retrofit

February 20, 2009

1. Purpose

Bums & McDonnell (B&McD), along with Steve Benson ofthe Department ofChemical

Engineering at the University ofNorth Dakota1

, have reviewed the technical literature provided

by the North Dakota Department ofHealth (NDDH) regarding submicron particle collection and

penetration for dry electrostatic precipitators (ESPs), and have prepared this document in

response. The information and commentary provided herein are being submitted to NDDH for

consideration relative to selective catalytic reduction (SCR) technology infeasibility for control

ofnitrogen oxides emitted from Milton R. Young Station Units I and 2. Issues related to the

technical infeasibility of SCRs located in both the low-dust configuration (LDSCR) and the tailend configuration (TESCR) are addressed. [Refer to the basic schematic diagrams below].

Low Dust

Tail End

1 formerly employed by Energy & Environmental Research Center (EERC) ofthe University ofNorth Dakota.

Supplemental Information

For Consideration by NDDH

1 February 20, 2009
We continue to believe that the administrative record fully supports a fmding by the NDDH that

separated over-fIre air (SOFA) in conjunction with selective non-catalytic reduction (SNCR)

technology is Best Available Control Technology (BACT) for NOx control for electric

generating units that utilize cyclone burners fIring North Dakota lignite.

2. Scope

The following sections address specifIc topics pertaining to the NDDH's Preliminary NOx

BACT Detennination for Nitrogen Oxides for Milton R. Young Station Units 1 and 2, dated June

2008 (NDDH, 2008)

• SignifIcance ofsubmicron aerosol particle removal by ESPs and wet FGD

• Evaluation ofsubmicron particle penetration data provided by NDDH

• Sodium-rich aerosol fonnation and penetration through ESP and FGD at M. R. Young

Station fIring North Dakota lignite

o Fonn ofsodium in Center lignite

o Vaporization ofsodium in the high temperature cyclones' combustion process

o Condensation ofsodium and concentrating in the submicron size fraction

o Electrostatic precipitator collection effIciency

o Aerosol capture efficiency in scrubbers

o Powerspan testing at MRYS

o MRYS sulfate aerosol sampling

• Detennination of Sodium Loading Adversely Affecting SCR Catalyst Performance

• Alkali Aerosol Loading and Catalyst Deactivation

• Experience ofESPIFGD equipped utility plants co-fIring biomass and coal with TESCR

• Relevance ofrecent TESCR investigations at We Energies' South Oak Creek Station

• Relevance ofongoing LDSCR installation at We Energies' South Oak Creek Station

• Relevance of existing LDSCR installation at PSEG Mercer Station

• Additional technical feasibility issues for TESCR at MRYS

• Summary and Conclusions

Supplemental Information

For Consideration by NDDH

2 February 20, 2009
3. Significance of Submicron Aerosol Particle Removal by ESPs and

WetFGD

The removal percentage ofsubmicron or aerosol particles by an ESP or any other device is not

important. The key is not what is removed, but rather the quantity that is not removed. The

amount (mass and number) ofsubmicron and ultrafme particles, as well as the speciation ofthe

particles which pass through the ESP, are extremely important. These particles have the

following detrimental characteristics:

• Condensed vapor phase species concentrate in the less than I J.1m size fraction and are in

the range ofparticle sizes where ESPs and wet flue gas desulfurization systems (FGDs)

are ineffective in capturing them

• Small particles that can penetrate deep into catalyst pores

• Highly reactive, because of chemistry [rich in sodium (Na), potassium (K), sulfur (S),

phosphorus (P)], which results in poisoning sites

• Highly reactive, because of physical characteristics - high surface area can react with gas

phase species, which results in blinding ofpores

• Highly concentrated because ofthe removal oflarger particles by cyclone and air

pollution control devices

• Highly concentrated aerosols (not diluted by large particles) that upon accumulation can

efficiently bond together causing catalyst blinding and are available to poison active sites

4. Evaluation of Submicron Particle Penetration Data provided by

NDDH

The NDDH provided publications on the efficiency ofESPs and scrubbers to remove particulate

as well as penetration of aerosol particles through the devices. The following are some ofthe

key conclusions that can be drawn from the review ofthe information described in these papers.

The information provided indicates poor collection efficiency ofsubmicron particles:

• The particulate collection efficiencies for the coarse fraction particles or particles larger

than I to 5 J.1m in ESPs are generally very good (99.9%).

Supplemental Information

For Consideration by NDDH

3 February 20, 2009
• For particles less than 1 J.1m, the collection efficiency drops offsignificantly.

• Particles in the finer size fractions are largely composed of condensed vapor phase

species such as sodium, potassium, chlorine (CI), and sulfur.

• Higher combustion temperatures result in more vaporization and increased levels of

submicron particles.

• Emission rates downstream ofESPs described in the reports range from 4,500 to 50,000

J.1g1Nm3• The particulate are dominated by aerosols rich in sodium and potassium.

NOTE: The level of22,500 J.1g1Nm3 ofsodium and potassium rich fly ash derived from

biomass resulted in catalyst deactivation of40 % in 1500 hours (Kling and others, 2007).

Specific observations and/or comments on each ofthe documents provided by NDDH are

presented below:

Mohr, M., Ylatalo, S., Klippel, N., Kauppinen, E.L, Riccious, 0., and Burtscher, H.,

Submicron Fly Ash Penetration through Electrostatic Precipitators at Two Coal Power Plants,

Aerosol Science and Technology 24:191-204(1996)

Measurement ofthe size distribution offme particulate (diameter less than 0.5J.1m) at the inlet

and outlet ofthe ESP for two full scale pulverized coal fired power plants was conducted. The

coals fired consisted of high volatile bituminous coals from South Africa and Columbia. The

characteristics ofthese coals are summarized in Table 1. The analysis indicates very low levels

ofsodium as well as other alkali and alkaline earth elements [I(, calcium (Ca), and magnesium

(Mg)]. The potential for formation of alkali rich aerosols from these coals is extremely small

because ofthe form ofthe alkali and abundance.

Supplemental Information

For Consideration by NDDH

4 February 20, 2009
Table 1. Coal analysis (Mohr and others, 1996)

COAL

~try South Colombia South

Africa .Africa

Coal field Klein Eldorado Klein

KDpie . Kopie

Location ofbuming Plant A Plant A PlantB

Date 9.5.94 17.5.94 11.8.93

Proximate analysis

Total moisture % 9.9 13.5 7.4

dryweight bases

Ash 9fJ 17.1 10.2 16.2

Volatile matter % 20.7 35.5 23

fixed carbon % 62.2 54.2 60.9

Omss calorific value MJ/kg 27.42 29.99 27.34

Ultimate analysis

Caibon % 70.3 73.4 68.4

Hydrogen % 3.4 4.6 1.S

N'atrogen % L7 1.5 3.5

Osysen % 7 9.4 9.9

Sulfur % 0.43 0.81 o.s

Coal ash

P20, % 1.2 0.3 1.2

Si02. % 45.3 55.7 47.7

P~03 % 3.5 7.3 3.1

Al20 3 % 31.4 21.0 33.2

nOt % 1.6 0.9 1.1 Cao % 7.3 4.1 6.2 Mao % 1.7 2.1 1.4

SO, % 5.4 3.1 4.8

K20 9& 1.0 2.1 0.7

Ha20 % 0.3 0.6 0.2

Li20 % 0.0 0.0 0.0

By comparison, Table 2 summarizes the average lignite properties relevant to MRYS. It can be

seen that the characteristics ofthe MRYS coals are very different and will produce significantly

different size distributions of ash than the coals fired in the plants reported by Mohr and others,

1996.

Table 2. Average Center lignite and ash composition (moisture, ash, sulfur, and heating value

expressed on an as-received basis; and ash composition expressed as weight percent equivalent

oxide ofthe ash).

Average 37.13 9.64 0.98 6578 11.68 0.52 13.15 8.90 3.99 0.12 1.33 36.04 4.40 18.39

This testing has little relevance to the collection of ash in the MRY boilers for two primary

reasons. The first is the firing type. The boilers are pulverized coal (PC)-fired and partitioning

to the finer ash fraction will be much lower than that observed for cyclone-fired boilers. The

Supplemental Information

For Consideration by NDDH

5 February 20, 2009
second reason is coal type. The coals tested are bituminous coals. The ash fonning components

in the bituminous coals are mineral grains with no organically associated elements (Na, K, Ca

and Mg). The fraction ofthe elements in an easily vaporizable fonn is much lower in the

bituminous coals producing lower levels of ash in the smaller sized fractions.

Nobrega, S. W:, Falaguasta, M.c.R., and Coury, LIt, A Study ofa Wire-Plate Electrostatic

Precipitator Operating in the Removal ofPoly dispersed Particles, Brazilian Journal of

Chemical Engineering, Vol 21, No. 02, pp 273-284, April-June 2004.

This paper is a laboratory and computer modeling effort that examined the perfonnance ofESPs.

The precipitators tested were small scale laboratory systems. A phosphatic concentrate was used

as particulate. Computational models for predicting fme particle removal in ESPs were

improved. However, the relationship to particulate collection from coal ftred power systems is

small.

Power Station Emissions Handbook, Cooperative Research Centre for Coal in Sustainable

Development, http://www.ddsd.biztpSE Handbook/5/6/5/index.cfm accessed 11/24/2008.

This document states:

"Wet scrubbers can remove more than 90% for particles with diameters above 10 microns.

Efficiencies for smaller particles will be signiftcantly lower."

"The size distribution ofthe dust influences the overall ESP collection efficiency. Particles in the

range of 0.1 to 1.0 Jlm are the most difficult for an ESP to collect. "

"ESP collection efficiency is particularly affected by several factors including coal ash

resistivity, gas temperature, chemical composition and particle size distribution (Wu 2001)."

There is no discussion on fly ash types that are collected. Only general data is provided.

Application to high sodium lignite derived coal ashes is not apparent from the website.

Supplemental Information

For Consideration by NDDH

6 February 20, 2009
ICACInstitute ofClean Air Companies, Particulate controls,

http://www.icac.com/i4a/pages/index.cfm?pageid=3398

This website states:

"Precipitator collection efficiencies will be somewhat lower for particles with diameters near 0.3

microns. The reason for a minimum in collection efficiency for 0.3 micron particles is that both

particle charge and the resistance ofthe gas to particle motion both increase with particle size.

Near 0.3 micron, the particle charge is low enough and the resistance to particle motion is high

enough that particles are collected relatively poorly."

These conclusions indicate that aerosols can penetrate through ESPs.

Lind, T., Hokkinen, J., and Jokiniemi, J.K., Saarikoski,S., and Hillamo, R., Electrostatic

Precipitator Collection efficiency and Trace Element Emissionsfrom Co-Combustion of

Biomass andRecovered Fuel in Fluidized-bed Combustion, Environmental Science and

Technology, 2003, 37, 2842-2846.

This paper describes the removal efficiency of ash particles produced in a 66 megawatt (MW)

biomass-fired bubbling bed fluidized bed combustion (FBC) system. Fluidized bed combustion

systems operate at lower temperatures (1400 to 1600 OF) than conventional pulverized coal-fIred

or cyclone-fired utility boilers. The bed material in the FBC was sand. The fuel was mixture of

peat and wood wastes. Fluidized bed systems typically have significant levels of entrained ash

particles that provide sites for condensation ofvaporized species. The particles that penetrated

the ESP were found to contain mostly alkali salts (Na, K, Cl, and S04). The quantity of

materials penetrating the ESP was 4.5 to 9 mg/Nm3 (4,500 to 9,000 flg/Nm3).

The 2003 paper by Lind references her earlier work on ash formation mechanisms (Lind, and

others, 2000). This paper describes in detail the mechanisms offormation ofthe aerosol

particles and that they are enriched in alkali salts (Na, K).

Supplemental Information

For Consideration by NDDH

7 February 20, 2009
Ohlstrom, M., Jokiniemi, J., Hokkinen, J., Makkonen, P., and Tissari, J., Combating

Particulate Emissions in Energy Generation and Industry, Tekes, VTT Technical Research

Centre ofFinland, 2006.

This paper also describes the concentrating of vaporized elements such as sodium and potassium

in the fme (less than 1 ~m) size fraction. The authors also state "higher combustion temperatures

typically increase the amount offme particle released." In addition, they discuss the fact that

"Electrostatic precipitators are at their least efficient when handling particle sizes between 0.1

JlIll to 1 ~m." They indicated in Table 8 on pg 29 ofthe report that the emission rates ranged

from 15 to 50 mg/Nm3(15,000 to 50,000 ~g/Nm3) from the ESP. This paper also shows that

scrubbers are extremely ineffective in removing aerosols.

5. Sodium-Rich Aerosol Formation and Penetration Through ESP and

FGD at M. R. Young Station Firing North Dakota Lignite

As described above, the fly ash penetration derived from the preceding described literature is not

fully relevant to MRYS due to the significant differences in the sodium content ofthe fuels fired

and the differences in the fuel firing mechanism employed in the plants tested. The following

discussion will briefly review the following topics:

• Form ofsodium in Center lignite

• Vaporization ofsodium in the high temperature cyclones' combustion process

• Condensation ofsodium and concentrating in the submicron size fraction

• Electrostatic precipitator collection efficiency for fme particulate and relationship to ash

produced from Center lignite

• Aerosol capture efficiency in scrubbers

• Powerspan testing at MRYS

• MRYS sulfate aerosol sampling.

Form of Sodium in Center Lignite

Sodium is associated with the organic matrix in Center lignite. That means the sodium is

atomically dispersed in the organic matrix. The sodium is associated with a carboxylic acid

groups (ion exchange sites). The carboxylic acid groups act as bonding sites for various

Supplemental Information

For Consideration by NDDH

8 February 20, 2009
elements such as Ba, Ca, Mg, and Sr along with minor amounts ofK. Figure I illustrates the

bonding ofsodium to the organic fraction ofthe coal and the association ofother coal impurities.

Included Minerals

Excluded Minerals

OrganicS

..•/_.

. •...

HzOwith Water Soluble Minerals

•Present in minor amounts

•NazSO. and other soluble salts

are the most common types.

Minerals GraIns

•Included in coal particles

•Excluded in coal particles

o

Na'O·11:)

o

J.l )=0 0·0

Ca++

o

II )_ .......... - 0·0

Mg++

Organically Associated Elements

•Bound as salts ofcarboxylic acids

•Organically associated sulfur

•Coordination complexes Aj3+and Fe3

+

Figure 1. Form ofsodium in coal (Benson and Laumb, 2008).

Vaporization of Sodium in the High Temperature Cyclones' Combustion Process

Sodium is a volatile element and is in the easily volatilized organic form in Center lignite and

will be transformed into a gas upon combustion. The vaporization ofsodium during the

combustion oflignite is a very well known fact that has been examined by numerous

investigators, including work conducted by MIT, CalTech, Sandia National Laboratory, National

Energy Technology Laboratory, University ofUtah, and others (see review by Lighty and others,

2000). For example, research conducted by Senior and others (2000) reported that relative to

Supplemental Information

For Consideration by NDDH

9 February 20, 2009
other coals, North Dakota lignite produced more vaporized ash. The actual amount vaporized for

ND lignite is double the level vaporized as compared to subbituminous and lignite coals from

Montana as illustrated in Figure 2.

7

ID Calculated II Actual I

I

i

..

aI

.....

I

i

r 1

0

Figure 2. Ash vaporized during combustion oflignite and subbituminous coals (Senior and

others, 2000).

Work conducted at the MRY plant related to the vaporization ofsodium from a cyclone fIred

system is illustrated in Figure 3. The results show over two thirds ofthe sodium is not retained

in the slag and is vaporized in the high sodium lower ash coals 1-3. In the low sodium high ash

coals 4-5, very small amounts ofthe sodium was vaporized.

Supplemental Information

For Consideration by NDDH

10 February 20, 2009
14JJO r-----------------------------...,

0.00

IIffI MAY MAY

CDaI ColI Slag

444

C5O.rheJ

Figure 3. Comparison ofsodium levels in Center lignite coal and slag samples.

Condensation of Sodium and Concentrating in the Submicron Size Fraction

EPA has evaluated the literature on particle fonnation during combustion and from other sources

and incorporated it into an educational module that was found on the following website:

(http://www.epa.gov/apti/bces/module3/fonnationffonnate.htm). The classification ofparticle

types shown by EPA is illustrated in Figure 4. The EPA classification is consistent with the

review conducted by Lighty and others (2000). Vaporized species can condense

heterogeneously on surfaces ofother entrained coarse ash particles and can condense

homogeneously to fonn the fme and ultrafme particles. The distribution ofparticles depicted in

Figure 4 is shown on a "frequency percent particles by mass" basis. The number of particles

versus size is also important. A comparison ofthe number of particles and particle size is

summarized in Table 3. The number of aerosol particles is significant. These particles have high

surface areas and are very reactive.

Supplemental Information

For Consideration by NDDH

11 February 20, 2009
0.1 1.0 10

Particle diameter (Dp), IJm

0.002

Ultrafine

0.01

Fine cOarse Supercoarse

100 1000

Figure 4. Particle size categories used to classify particles.

(http://www.epa.gov/apti/bces/module3/category/category.htm)

Figure 5 provides a comparison ofthe mass distribution and particle number distribution. As the

particle size decreases the number ofparticles in the size fraction increases. In addition, as

illustrated in Table 3, the surface area increases significantly with decreasing particle resulting in

the opportunity for reactive gases such as sulfur oxides to react, forming sticky phases that bond

particles together.

Table 3. Particle size, number ofparticles, and surface areal

(http://www.epa.gov/apti/bces/module3/category/category.htm)

T_ • 1

" • d "PIIiIl:1W 1'1III_-- .... ....'- 1.'.--_ (11II) ... .-aJ

..... .- IJ

.- 'I

-

1... 11 2.-

- -

- ..

1 .. I

&, •

Supplemental Information

For Consideration by NDDH

12 February 20, 2009
10

:============~~:1~=i.ITSP .. ..'PM • .. ..'PM' 10 I

....:::=::;:;;;;;;;;;:..!11JIrIdMPM : 2.S: : ~.. .'NInopIrIcIeI : ;:: 100 _---.;.----.;------i---i--....;..-., ,

1

I

~MnIeal

AlJIId CombuIlIanPM

SoaI , ....

,

,

, PIinaryComIIuI1IoI'I .....

SoaI

Fume from 1tIItt VlIflCIIlDl!On

....._---------------...I04ITSP _-------------:--_~'PM I

:::======::;;;;;;;Pi.--:"jPMU "! 10 :

10.000;'.~::;~~~~~.J-----~:--~: ,Soat, ......Md -~:~-..,

:Acld NucleIMod!' I

I

Col1lllUIlIon em-t ~Mo* ,

,

I

I

Figure 5. Comparison ofMass Distribution and

Particle Number Distribution for Combustion Derived

Particles and Aerosols (Lighty and others, 2000).

Particle size distributions for fly ash collected upstream and downstream of an ESP are

illustrated in Figure 6. This work was conducted by Markowski and others (1980) specifically

aimed at characterizing the submicron aerosol mode offly ash formation. Figure 6B shows the

penetration offme particulate through the ESP.

Supplemental Information

For Consideration by NDDH

13 February 20, 2009
2.Il

Q.lO

.I, 1

- IIolPACTOR 2.4 30 ---IMPACroRUPPfRBOUND

l , I -~

i \ / 0." 2.0 ; , , '"

f\ "'"' 1/ 0 0 0 r

- 1.6 a" ,.. 20

~! 12

.~ -IMPl\C1OR

~! 15

I \ ----IMI'I\C'roRUPP"JlIIOUIID I \ -EM I \

0.8 0 EMEJlRlIRESTIIMTE 10 f \

! I

i \ OA j i.,/

,,-

lbii, 0.1 1 10 00•

01 0.1 10

GEOMflRIC AEROSOI.I*MfTER (jIIIl) A. GEOMElRIC AaIOSOl. DIAMETER IlJml B.

Figure 6. Typical differential mass distributions of particulate collected upstream

(A) and downstream of an ESP (b) (Markowski and others, 1980).

Fly ash produced upon the combustion of high sodium lignites in a pulverized coal (PC) fired

system shows significant enrichment ofsodium in the smaller size fractions as shown in Figure

7. This figure illustrates the increase in the sodium content in the fmer size fractions of ash as a

result offiring high sodium lignite. The sodium and sulfur content ofthe less that 3 micrometer

size fraction ofthe sampling train approached 20% Na20, and 25% S03. The form ofthe

sodium is likely sodium oxide and sulfate.

Supplemental Information

For Consideration by NDDH

14 February 20, 2009
/'

_______11Pa .J. ••• ten MgO

....--------·I---~p.I_n=­ O.....----f--~:.:-=--=-=i-=--=---·---------or_-ZW'5

>10 10-3 <3

MuItkydone size pm

Figure 7. Composition distribution of ash particles during

combustion ofNorth Dakota Lignite (Benson and others, 1984).

Electrostatic Precipitator Collection Efficiency

The classical curve for ESP particle collection efficiency is shown in Figure 8. This curve is

typical ofwell behaved ash materials that do not present significant problems in collection. The

collection efficiency is very good for particles greater than 5 to 10Jlm and the collection

efficiency decreases with decreasing particle size, with a minimum collection efficiency between

Supplemental Information

For Consideration by NDDH

15 February 20, 2009
0.2 to 211m in diameter. The collection efficiencies vary significantly because ofparticle size

and composition.

Low collection efficiency for difficult to collect particles is between 0.1 to 1 11m in particle

diameter. Figure 9 provides an illustration ofthe range of collection efficiencies. Based on EPA

education modules (http://www.epa.gov/apti/bces/module3/collect/collect.htm). no air pollution

control device shows high collection efficiency in this range (0.1 to 1.0 11m) due to inherent

limitations ofthe collection devices and particle characteristics. The following mechanisms of

particle capture are impacted by the size ofthe particles. The impact ofthese mechanisms are

described

-Inertial impaction and interception

-Brownian diffusion

-Gravitational settling

-Electrostatic attraction

-Thermophoresis

-Diffusiophoresis

The EPA has indicated that based on a number ofstudies of actual "sources stationary sources

generating high concentrations ofparticles in the 0.1 to 0.5 micrometer range may be an

especially challenging control problem. '" The gap is most noticeable in wet scrubbers and

electrostatic precipitators." A generalized plot showing the range of collection efficiencies is

shown in Figure 9. Overlaid on the diagram is the mass size distribution ofparticles collected

downstream ofthe ESP wet FGD at the MRYplant (Markowski and others, 1983). This shows

that ash produced in the MRY plant have a particle size that pass through the scrubber and that

these particles are rich in sodium as previously shown in Figure 7.

Supplemental Information

For Consideration by NDDH

16 February 20, 2009
D.2 0.3 Q.5Q,7 1 23457

PartkIe cIfameIer, JU'"

99.9 .----,....--,----r---r~T"T""TT"-_._-,..._ __..........,.~OJJD1

.. cum

.,,9J:1

?}9U

I~I:

•

95

IJ

10 L..L:~~~uL___..JL_L_l_LJLU..J3

0.1

Figure 8. Typical ESP Collection efficiency curve for removal of

particulate from gas streams

(http://www.epa.gov/apti/bces/module3/collect/collect.htm).

.,. 75

1.0 i f .~.\. .~ g

Iso • \ .~ c ... .' j \./

0.1 I B 25

100 r----,---:::~=:p=:=--..,

1.0 1QD 100.0

PartIcle diameter, lAIn

01....----"'-----"'-------'

0.1

Figure 9. Particulate control efficiency for difficult to control particulate

combined with the mass distribution ofparticulate collected downstream of

the scrubber at MRYS (Markowski and others, 1983 and

(http://www.epa.gov/apti/bces/module3/collect/collect.htm).

Supplemental Information

For Consideration by NDDH

17 February 20, 2009
Aerosol Capture Efficiency in Scrubbers

As indicated by EPA (Woodward, 1998), scrubbers do not effectively remove particulate less

than 1~m in diameter. There is significant evidence that sodium-rich aerosols penetrate ESPs as

well as scrubbers at full-scale power plants when firing high-alkali-containing fuels. An

example is a biomass fired system using a tower type scrubber where the removal efficiency of

the smaller size fraction of ash is low, as shown in Figure 10 (Ohlstrom and others, 2006).

I

-- Wood, grate boiler, scrubber inlet I

- I

- - - - Wood, grate boiler, scrubber outlet I

I ... ,- •

I

.- I ...... .

I

,- I

,- I \ I

I

- I

- I r.\. I

- .. .~ ! - I , \\ , cut-alf I F , I. I D50=-3um - •

I , \\ i ,

, ~A , '. .-

/ M'," -- ; ............•• I

'-- -~ .... -- ·-L.~ ... 0 ..- I I I

1

0.1 1

Dp[Jlml

10 100

Figure 10. Removal offme aerosols using a scrubber on a wood fired combustor (Ohlstrom and

others, 2006).

Minnesota Power's Boswell Energy Station found that when it fired high-sodium, lower-ash

northern Powder River Basin subbituminous coal (7% Na20 in the ash), it experienced increases

in opacity. Hurley and Katrinak (1992) conducted a field-testing project on Unit No.4, a

pulverized coal-fIred boiler equipped with a venturi wet scrubber, to better understand the

reasons for the opacity problems. During the field testing, sampling ofthe coals, flue gases, and

scrubber materials was conducted. The particulate in flue gases downstream ofthe scrubber was

aerodynamically classified using multicyclone followed by an impactor and a Nucleopore filter.

Supplemental Information

For Consideration by NDDH

18 February 20, 2009
The sized fractions were weighed and analyzed to detennine the abundance and composition of

the submicron-sized fractions. The mass loadings in the various size bins are plotted in Figure

11, showing that the scrubber is quite effective in removing the larger particles. However, the

scrubber is not very effective in removing the aerosols less than 1 micrometer in diameter for

both the blended coal and the high sodium coal (Coal A).

1

10.1

f

j 0.01

0.001 Blend -inlet Blend - outlet Coal A-Inlet Coal A- outlet

e D50 == a.o microns ~D50 == 25 microns .050-0.7 microns 1IBD50 <0.7 mla'ons

OYeraH mass size dIstrIbutfons for entrainedash SImples.

Figure 11. Mass loadings and size for particulate collected upstream and downstream ofthe wet

venturi scrubber at Clay Boswell plant (Hurley and Katrinak, 1992)

The results ofthe study indicated that the particulate collected downstream ofthe scrubber was

coal-related and caused by the high sodium content ofthe coals. Vapor-phase sodium condenses

in the boiler's convective pass to fonn fme sodium-rich aerosols or other Na species that later

react with ash particles. Pure Na2S04 particles are too small to be removed by such scrubbing.

Figure 12 shows the spikes ofthe ash material collected on Stage 10 ofthe impactor. This

impactor accumulation represents particles ofless than 0.7 to 2.5 micrometer size fraction ofthe

Supplemental Information

For Consideration by NDDH

19 February 20, 2009
submicron aerosol. The spikes are made up ofsubmicron particulate matter, and the chemical

analyses ofthe spikes and ash particles collected on the Nucleopore filters downstream ofthe

impactor plates are shown in Table 4. Both samples are dominated by sodium and sulfur that are

likely in the form ofsodium sulfate. These sulfate materials exhibit highly cohesive tendencies.

Figure 12. Scanning electron microscope images ofspikes formed on impactor plates when

high-sodium subbituminous coal is combusted (the picture on the right is a close-up ofthe spike)

(Hurley and Katrinak, 1992).

Supplemental Information

For Consideration by NDDH

20 February 20, 2009
Table 4. Chemical Composition ofthe Spike Shown in Figure 12 and the Filter

(weight percent expressed as equivalent oxide).

100% Coal A

Oxide Spike Filter

NazO 35.1 17.3

MgO 1.4 7.8

Alz0 3 2.0 9.8

SiOz 9.1 10.6

PzOs 0.4 0.2

503 39.7 28.0

KzO 2.6 1.5

CaO 6.2 15.7

TiOz 0.2 1.8

CrZ03 1.4 0.1

Fez03 0.9 2.9

BaO 0.5 2.6

In addition to the aforementioned testing results, penetration ofsubmicron particles through ESP

and scrubbers has been reported by numerous researchers (Markowski and others, 1983, and

Lighty and others, 2000). Figure 13 shows the penetration ofparticulate from ND lignite to be

the highest ofthe combustion systems tested as part ofthe DOE field test program.

Supplemental Information

For Consideration by NDDH

21 February 20, 2009
•

.

-~

! t-------r-----J~_R_-_+___t ----IIIIIIJ

I • CMIInaI I ...-------!---I--+---"""',r-.-f 1.-_-._-_-_COII __OMk _ ...

0.1 t 10 100

Plant Description Slack Emissions

Bailly 345 MW, Cyclone Burner 60 kg/hr

Dry scrubber. ESP

Illinois high-sulfur bituminous

Cardinal 615 MW, well-mounted cell burner 100 kg/hr

ESp, no sulfur removal

Pittsburgh No.8 bituminous

Coal Creek 550 MW, tangential-fired 260 kg/hr

Wet scrubber, ESP

North Dakota lignite

Figure 13. Nonnalized differential particle mass distributions measured in the stack for a

sample of coal-fIred power plants using different burner and gas-cleaning technologies

(Lighty and others, 2000).

Supplemental Information

For Consideration by NDDH

22 February 20, 2009
Powerspan Testing at MRYS

The Powerspan slipstream electrocatalytic oxidation (ECO) reactor system was designed by

Powerspan and the EERC (Tolbert and Benson, 2008). The slipstream system was installed by

the EERC at Minnkota Power Company's Milton R. Young Station Unit 1 downstream ofthe

ESP where the flue gas temperature ranged from 300°F to 350°F. The dielectric barrier

discharge (DBD) reactor has quartz electrode rods inside where electric current is passed in order

to generate the plasma used to oxidize nitrogen oxide (NO) to nitrogen dioxide (N02). The

temperature ofthe quartz electrodes was approximately 100°F higher than the gas temperature.

The system at MRYS was commissioned on July 3,2007, and it operated for 107 days.

Operational performance ofthe system was monitored and data were archived for post

processing. A pair of electrodes was extracted and replaced on a bi-weekly basis. Each pair of

electrodes was shipped to Powerspan for testing in their laboratory reactor for NO conversion

testing. Tested electrodes were then shipped to the EERC for scanning electron microscopy

imaging and x-ray microanalysis. Measurement ofNOx conversion in the field by the slipstream

system was not possible due to the nitric acid production ofthe DBD reactor. Aerosols passing

through the ESP at MRY Unit 1 resulted in significant accumulation on Powerspan's slipstream

ECO barrier discharge reactor rods resulting in significant degradation in performance.

The operational observations, performance results, and lab testing showed that the system was

adversely affected by ash fouling. NOx conversion by ash covered electrodes was significantly

reduced. Figure 14 visually compares a clean unexposed quartz rod to one exposed to flue gas

and aerosols downstream ofthe ESP at MRY Unit 1. The abundance ofsodium in lignite coal

fired during the Powerspan testing at MRYS is shown in Figure 15. The results show sodium

levels measured by the full stream elemental analyzer (FSEA) ranged from 3.5 to 6 % Na20 in

ash. Figure 16 shows the degradation in NO conversion measured during subsequent lab testing

at EERC using the exposed quartz rods removed from the slipstream test ECO DBD reactor at

MRYS as a result ofbeing coated with aerosols. The NO conversion was severely impacted.

Supplemental Information

For Consideration by NDDH

23 February 20, 2009
A. Clean quartz rod. B. Dirty rod exposed to flue gas downstream ofthe

ESP at MRYS Unit 1 for 16 days.

Figure 14. Comparison ofa clean quartz rod and rod exposed to flue gas.

SODIUM

FULL STREAM ELEMENTAL ANALYZER

3 July -18 October, 2007

9.00

8.00

7.00

.. 6.00 c

CII

5.00 ·S

cr

w -4.00

i 3.00

2.00

I

I-Na20 I~ I -AvgTrend

-- ~I 1\ f-- -

V I U tJ i-" - I-

~Ir II \ N " 1-- Itr' "\ f-J 1'\

\

1.00

0.00

3-Jul 17-Jul 31-Jul 14-Aug 28-Aug 11-Sep 25-Sep 9-0ct

Date

23-0ct

Figure 15. Sodium levels in lignite delivered during testing ofthe Powerspan barrier discharge reactor

at MRYS Unit 1.

Supplemental Information

For Consideration by NDDH

24 February 20, 2009
SAMPLING SCHEDULE

SAMPLING LOCATION REMOVE DAYS IN REPLACE DAYS IN

DATE ROD# REACTOR WITH ROD REACTOR

3-Jul START

TESTING

19-Jul F 6 16 15 91 K 11 16

1-Aug M 13 29 17 78 8 2 18

16-Aug H 8 44 19 63 D 4 20

3O-Aug C 3 58 81 49 J 10 82

13-Sep I 9 86 83 35 G 7 84

27-Sep E 5 100 85 21 L 12 86

11-0ct NU oAM'"'L :0 I:A I t(j\..; I I:U uut: U IHt: " ... 11 T I U

THE FINAL SAMPLING.

A 1 iAll Of me e1ectroaes IIstea

18-0ct 107 abOve will be removed for N 14 lab testing and analysis.

Lignite Pilot Electrode Performance

100

90

80

70

60

50

40

30

20

10

o

£.6 All' £. .. 0_ aA -

11III ..I!I! ... .. """ III

o III '11II

8 10 12 14 16 18 20

Energy Density (watts/scfm)

AEERC #7 - CL 0 EERC #5 - D1Y AEERC #3 - CL ABurger - CL

/:"EERC #9 - CL III EERC #12 - D1Y IIIEERC#10 - D1Y

Figure 16. NO conversion for clean (CL) and dirty (DTY) for quartz tube exposed the flue gas

during the MRYS testing. Burger is a slipstream pilot ECO system in Ohio used for reference.

Supplemental Information

For Consideration by NDDH

25 February 20, 2009
Examination ofthe quartz rodsremoved from the slipstream ECO DBD reactor at MRYS (crosssectioned to expose coating thickness) by EERC using scanning electron microscope equipped

with an x-ray analyzer showed significant elemental sodium, sulfur, and calcium in the ash

coating the tubes after only 16 days oftesting. The data is reported on Figure 17. The thickness

ofthe layer was approximately 25 /lrn. A sonic hom was used for in-service cleaning ofthe rodtube deposits. Images ofthe reactor and coatings on the electrodes are shown in Figure 18.

Tag Na Mg AI Si P S CI K ca Ti Fe Sa

1 35.38% 0.98% 14.10% 4.68% 0.00% 35.75% 0.00% 1.42% 6.61% 0.02% 1.07% 0.00%

2 0.00% 0.00% 0.22% 98.52% 0.00% 0.00% 0.07% 0.89% 0.00% 0.30% 0.00% 0.00%

3 0.00% 0.00% 0.61% 98.11% 0.00% 0.00% 0.00% 1.05% 0.00% 0.00% 0.22% 0.00%

4 0.00% 0.00% 0.20% 98.33% 0.00% 0.00% 0.00% 1.19% 0.00% 0.00% 0.27% 0.00%

5 0.00% 0.00% 0.00% 98.70% 0.00% 0.00% 0.00% 1.24% 0.00% 0.00% 0.06% 0.00%

6 0.00% 0.00% 0.25% 97.26% 0.00% 0.00% 0.27% 1.70% 0.00% 0.00% 0.36% 0.16%

7 0.00% 0.00% 0.00% 97.93% 0.00% 0.00% 0.00% 1.55% 0.00% 0.00% 0.47% 0.05%

Figure 17. Example of SEM point analysis on electrode #11 (removed from slipstream ECO

reactor at MRYS after 16 days ofservice).

Supplemental Information

For Consideration by NDDH

26 February 20, 2009
Figure 18. Images oftop ofslipstream ECO DBD reactor at MRYS showing ash accumulations

on electrodes and reactor surfaces.

Conclusions gained by this work are:

1.) Sodium rich aerosols and small ash particles that had penetrated the ESP accumulate and

become bonded on the surface ofthe silica electrodes despite using a sonic hom as

recommended by Powerspan.

2.) Ash accumulations adversely affected the NOx conversion.

3.) The adverse impact occurs within a two week time period.

Supplemental Information

For Consideration by NDDH

27 February 20, 2009
MRY Sulfate Aerosol Sampling

The penetration of aerosols through ESP and wet scrubbers is well known and has been studied

since the mid 1970s (McCain and others, 1975; Ensor and others, 1975). As a result ofthese

challenges, the quantity oftotal aerosols and sulfate aerosols was measured at MRYS by

Markowski and others, 1983. Markowski and others (1983) collected EPA method 17

particulate samples and size segregated the particles using an impactor that aerodynamically

separates particles and allows for the characterization of each fraction. The results ofthe EPA

method 17 samples conducted over a four day period. The mass concentrations of aerosols as

determined by EPA method 17 sampling are illustrated in Figure 19 for the inlet and out ofthe

scrubber. At the inlet aerosol mass concentrations ranging from a high ofover 10,000 /lg/m3 to a

low of4000 /lg/m3

• Significant levels were also found at the scrubber outlet ranging from 8800

to 2500 /lg/m3

• The removal efficiency varied from -25 to 66%. Markowski and other (1983)

offered no explanation ofthe differences in the levels of aerosols measured in the flue gas and

removal efficiency. They did not consider that the ash content ofthe coal varied significantly

during the testing. Results oftesting at MRYS have shown significant differences in the quantity

vaporized for coals that have different ash contents (see Figure 3). The variations in ash content

shown in Figure 19 reflect changing coal characteristics that resulted in differences in aerosol

mass concentration.

Supplemental Information

For Consideration by NDDH

28 February 20, 2009
12000

:§ 10000

Q

:::L

C 8000

.2

-

ns

.. 6000 -

c

CII

u

c 4000 0

v

In

In

ns 2000 ::i

0

• Inlet

• Outlet

6/10/1981 6/11/1981 6/12/1981 6/13/1981

8.41% 12.12% 18.87% 5.74%

Sampling Date and Ash Content (as received)

Figure 19. Mass Concentration of Aerosol Collected at MRYS Unit 2 at the

Scrubber Inlet and Outlet (Markowski and others, 1983).

The results ofthe measurements of aerosol capture are illustrated in Figure 20. The results show

that aerosols less than one micrometer in diameter are not effectively captured in the wet FGD at

the MRY facility. The graph also indicates the penetration ofthe particles through the FGD as a

function ofparticle size. The penetration is the outlet size distribution divided by the inlet size

distribution. (Penetration = 1- efficiency). Markowski and others (1983) showed that the

"metallic" sulfate aerosols (sodium sulfate) penetrated the FGD much more effectively than the

larger particulate materials.

Supplemental Information

For Consideration by NDDH

29 February 20, 2009
100.-------"""r"------"""r"-------,1000

10 '0

0.1 0.,

"---",,~ i ""

", -

Q ,.0 1.0 .B'

II

A.

"

0.0'0.....,------,....0------.... '0-----,:°1

ACTUAL DIAME'lER (MICROMETBlS)

Figure 20. Penetration through the MRYS Unit 2 wet scrubber (Markowski and others, 1983).

The mass of each ofthe impactor size fractions for the aerosols collected at the inlet and

the outlet ofthe wet FGD upstream and downstream ofthe MRYS Unit 2 scrubber are illustrated

in Figure 21 and 22 with the results tabulated in Table 5. The total mass distributions are

summarized in Figure 21 and the sulfate mass distribution is illustrated in Figure 22. Based on

the impactor data the total mass ofparticulate that penetrates the scrubber is 5990 J.lg/m3

(Markowski and others, 1983). These ash materials consist of a combination ofsulfates and

Supplemental Information

For Consideration by NDDH

30 February 20, 2009
oxides ofsodium, calcium, and sulfur. Much ofthe aerosol is present in the >14 J.lm size

fraction. There are also significant mass in the less than 1 J.lm size fraction that has the potential

to penetrate the pores ofthe catalyst. In addition, there is a significant mass in the <0.26 Ilm

fraction. This fraction represents the ultrafme component that has been implicated as the most

significant contributor to catalyst poisoning (Kling and others, 2007).

Table 5. Size segregated total and sulfate particulate collected upstream and downstream ofthe

MRYS FGD (Markowski and others (1983).

Inlet Outlet Inlet Outlet

Total, Total, Sulfate, Sulfate,

Size, ~m ~g/m3 ~gfm3 ~gfm3 ~m3

<0.26 1910 769 436 602

0.26-0.52 401 640 164 274

0.52-1.1 883 1410 293 459

1.1-2.5 1020 265 291 69.2

2.5-6.7 337 154 173 94

6.7-14 300 367 100 103

>14 700 2390 439 46.2

Total 5550 5990 1896 1650

>1.1 2357 3176 1003 312.4

<1.1 3194 2819 893 1335

Percent

>1.1 42.5% 53.0% 52.9% 18.9%

<1.1 57.5% 47.1% 47.1% 80.9%

Supplemental Information

For Consideration by NDDH

31 February 20, 2009
3000

Total Particulate

- 2500 Q

:::L

r: 2000

0

..III

...

.. 1500 c

u

c 1000 II Inlet 0

v

III

III 500 II Outlet III

:E

0

Size, Jlm

Figure 21. Total particulate removal across scrubber at MRYS.

700

600 -

Q

:::L 500 r:

0

.. 400 III

.....

c 300 u

c

0 200 v

III

III

III 100

:E

Sulfate Particulate

II Inlet

II Outlet

Size, Jlm

Figure 22. Sulfate particulate removal across scrubber at MRYS.

6. Determination of Sodium Loading Adversely Affecting SCR

Catalyst Performance

Alkali metals such as potassium and sodium are known poisons and blinding agents for SCR

catalysts used for NOx emissions control. As previously discussed (Burns & McDonnell and

others, November 2008) and repeated above, there will be submicron sodium, likely in sulfate

Supplemental Information

For Consideration by NDDH

32 February 20, 2009
form, emitted from the dry ESPs at MRYS that will contaminate SCR catalyst located in a lowdust or tail-end configuration. The first fundamental issue is "how to estimate the amount (mass

rate) ofsodium and in what size range could be emitted from the boilers at MRYS, for the

purposes ofa BACT analysis". Because BACT analyses on existing sources are not common,

we also presume them to be "studies on paper using available information". We do not consider

BACT analyses as research projects requiring design of experiments, site-specific testing, and

development engineering for the control technique being considered. Thus, this first issue is a

significant challenge.

The second fundamental issue is "for the purposes of a BACT analysis, what rate of catalyst

deactivation is likely to occur as a result of exposure to the expected particle or aerosol size

range and concentration ofsodium emitted from a boiler over a given period oftime?"

Only by assuming that these fundamental issues can be resolved with the degree of certainty

required for purposes of a BACT analysis, can such a comparison then be performed that could

lead to a basis oftechnical feasibility oflow-dust and tail-end SCR technology for MRYS.

Because most coals fired in utility boilers do not have the high sodium content ofNorth Dakota

lignite, and because cyclone boilers fire at high temperatures which promotes the emission of

submicron sodium aerosols, there is not much published technical information that is available to

help answer these fundamental questions. We can gain some insight into what might happen to

SCR catalyst exposed to flue gas containing significant amounts of alkali salts by looking at the

impact of co-firing biomass such as straw or switchgrass with coal. This is increasingly

important to utilities that have chosen to pursue such a fuel mix strategy who also employ SCR

technology on their boilers. We have previously commented on the high-dust SCR catalyst

experience at the Avedore plant (Burns & McDonnell and others, November 2008) and the high

frequency of catalyst washing performed to counteract the apparent highly negative impacts of

biomass cofrring.

7. Alkali Aerosol Loading and Catalyst Deactivation

There is evidence that alkali aerosol loading in the flue gas streams results in catalyst

deactivation. The total and sulfate aerosol mass loading measurements were conducted by

Markowski and others (1983) at the inlet and outlet ofthe wet FGD scrubber at MRYS Unit 2.

Supplemental Information

For Consideration by NDDH

33 February 20, 2009
The key data obtained by Markowski and others (1983) is illustrated in Figure 23 as well as the

size fractionated data in Figures 21 and 22 provide information on loadings. The data provided

shows a range ofmass concentrations up to 8800 J.lg/m3 at the outlet ofthe scrubber based on

EPA method 17. Based on results in mass size distribution ofthe aerosol, 47 to 80% ofthe

aerosols that pass through the scrubber are less than 1.1 J.lm. Much ofthis material is in the

ultrafine fraction. These materials have the potential to penetrate into the catalyst, causing

plugging, and can react with active components in the catalyst. There are numerous publications

supporting these mechanisms. Kling and others (2007) found that the rate of catalyst

deactivation was related to the accumulation ofsodium and potassium on the catalyst as shown

in Figure 24 and 25. The work by Kling and others (2007) is consistent with the work conducted

by Khodayari, 2001 illustrated in Figure 26 where he shows that the deactivation rate is more

significant for PC-fired systems as compared to fluidized beds. The work based on Kling and

others (2007) when applied to PC and cyclone-fired systems will likely underestimate the degree

of catalyst deactivation because ofthe firing methods.

12000

...

E 10000 -Ol

::.

c' 8000

0

-.;::

III

..... 6000 C

41

u

c 4000 0

V

III

III

III 2000 :;:

0

III Inlet

III Outlet

6/10/1981 6/11/1981 6/12/1981 6/13/1981

8.41% 12.12% 18.87% 5.74%

Sampling Date and Ash Content (as received)

Figure 23. Mass Concentration of particulate collected at MRYS using EPA Method 17

(Markowski and others, 1983).

Supplemental Information

For Consideration by NDDH

34 February 20, 2009
n

cq u

.. <> ... <>A

A • A

.....

.....

o FR (season_C)

• B+30%DW(season B)

o P+15%W(season_B) OP (season_C)

mFR+S (season C A FR+S (season 0

100%

95%

90%

85%

80%

75%

70%

65%

60%

55%

50%

0,00 0,05 0,10 0,15 0,20 0,25 0,30

Accumulation of alkali (potassium+sodium] on catalyst sample

[weight percent]

Figure 24. Catalyst deactivation compared to accumulation of potassium and sodium on the

catalyst surface (Kling and others, 2007).

o;e 60% i:..

..... &: .. . 50%

~.e 40%

>. 15"c ... 30% u.s

~e-::::s 20% !s

uao

.-c.

M 10%

.I!

.::::s ,90 0%

.c

Ii

~<; ~iii' .-. <; iii' 6 6' u ~.-. ~~

#. c l

a. i' • en c l f/) c' 0<1 om #.C o::c o::c o::c ~§ c l

~~+ aI

100

...

+ aI

fIl aI u.~aI u.~aI u.~aI ~~ ~~ IO fIl ~~ U.l U.l .-tll Mal a.! a.! ! i i ! + i + i ...... ...... m...... mFigure 25. Loss in catalyst activity when exposed to flue gases containing vaporized Na and K

when combusting biomass in a fluidized bed combustion system (Kling and others, 2007).

Supplemental Information

For Consideration by NDDH

35 February 20, 2009
1:IM-r-------------------------..,

.CFB .CFB

eCFB

OPe

OPe

OPe

APe .. L--I_----I-_--I-_--1-_--1-_--I-_-\-_-+-==+==~

o - 1C1OO 1500 2alID 25IJD 3IIJD !SUD 4lIXI 450D 5CXIJ

Op uantllne'"

Figure 26. Comparison ofpoisoning of catalysts in a CFB boiler fIring forest residues and in a

PC fIring pulverized wood (Khodayari, 2001).

There is a direct relationship to the concentration ofsodium and potassium in the flue gas with

accumulation on the catalyst and subsequent deactivation. The deactivation shown in Figures 24

and 25 directly relates the accumulation ofsodium and potassium on the catalyst with

deactivation. Deactivation rates of40 to 55 percent (considering the error bars) was measured on

catalyst that had accumulated 0.25 wt % sodium and potassium on the catalyst surface when

exposed to flue gas containing 22,500 ~g/m3 sodium and potassium for only 1500 hours. The

flue gas downstream ofthe scrubber at the MRYS Unit 2 has been shown to contain aerosols at

levels of 8800 ~g/m3 with about 50% ofthe mass being less than 1.1 ~m. The ash that exits the

ESP on Unit 1 is dominated by sodium and sulfur based on the results from the Powerspan

testing. The quartz elements exposed to the flue gases for 16 days (384 hours) were completely

covered with sodium and sulfur rich ash (see Figure 17). These elements were exposed to

cleaning using a sonic hom. The sodium and sulfur rich ash produced a dense layer on the

surface ofthe quartz rods approximately 25 ~m thick in 384 hours. The MRYS results along

with research efforts conducted in Europe show that masking and poisoning of SCR catalysts

from flue gases containing alkali aerosols is a significant problem that has not been overcome by

SCR catalyst vendors.

Supplemental Information

For Consideration by NDDH

36 February 20, 2009
8. Experience of ESP/FGD Equipped Utility Plants Co-Firing Biomass

and Coal with TESCR

In previous communications to NDDH, it was stated that no recent TESCR installations had been

completed on utility boilers anywhere in the world. Burns & McDonnell subsequently learned

about the Amager facility currently under construction in Copenhagen, Denmark that will

involve a TESCR system on a multiple fuel-fired boiler that is expected to burn combinations of

pulverized coal, wood pellets, straw, and fuel oil. A technical paper written by Haldor Topsoe

described the design efforts for SCRs on biomass (straw)-frred boilers (Crespi, and others, 2008)

and indicated that the TESCR configuration was chosen specifically to address the concerns

about catalyst poisoning due to the constituents ofthe straw (notably potassium). Follow-up

communications were initiated by Bums & McDonnell with Haldor Topsoe, which supplied the

catalyst for Amager's TESCR reactor; Alstom, which was the supplier ofthe SCR reactor system

and the Flowpac wet FGD system (see attached project summary); and a plant engineer for the

boiler's operator (Vattenfall A/S) (Bums & McDonnell personal communications, 2009). These

personal communications provided the following information about this installation:

a. The boiler is wall-fired and can be frred with oil (start-up), coal and wood- and straw-pellets.

Coal and bio-pellets are pulverized in mills [prior to firing in the boiler], with full flexibility

from 0 to 100 % straw. It is expected to frre 100% biomass most ofthe time. Maximum heat

input to the boiler is 350 MW during coal and oil fIring and 300 MW during wood/straw

pellets fIring.

b. Danish regulations on emission include an emission fee ($/ton ofS02 or NOx emitted),

therefore the utility looks for the best compromise between low cost fuel and low emissions.

The utility wants to be able to fire any mixture as specified above for the flexibility of cost

and availability ofboth straw and coal. This is common for European customers who have to

balance carbon dioxide (C02) emissions. When a new plant is built, the utility wants to make

sure it can fire any fuel that may come on the market in the coming years without being

limited by his boiler and cleaning equipment. Ofthe biofuels, straw is considered to be the

most difficult as compared to woodchips, saw dust, paper, etc. The situation is the same in

Sweden, Holland and some other countries.

Supplemental Information

For Consideration by NDDH

37 February 20, 2009
c. At the planning stages ofthe Amager project it was expected to co-fire biomass and coal in

the boiler. Now, ifbio-mass fuels are not available, 100% coal will be fired. When bio-mass

is fired, NOx emissions are expected to be low, so the utility is allowed to bypass the flue gas

cleaning system. According to European regulations, the NOx emission limit with bio-mass

is 300 mglNm3 (dry 6% 02). Both the FGD and the SCR systems will be bypassed, ifNOx in

the flue gas emitted from boiler is below 300 mglNm3

• No dampers are installed upstream of

the TESCR. There is a global by-pass of both FGD and TESCR systems. The wet FGD and

TESCR are mainly needed for any coal firing flue gas cleaning. When pure straw/ biomass is

fired the whole wet FGD and SCR system can be bypassed, saving a lot ofoperating cost as

both SOx and NOx will be within the limits from the authority. The client was not sure that

they could get enough ofstraw available at an acceptable price, so the boiler had to have great

fuel flexibility.

Based on this information, it appears that the Amager plant's TESCR system will typically be

bypassed when the fuel firing conditions are most difficult for the SCR catalyst with regard to

poisons. Consequently, Burns & McDonnell does not believe the Amager facility project under

construction provides any indication that TESCR technology is technically feasible for

application to MRYS.

9. Relevance of Recent TESCR investigations at We Energies' South

Oak Creek Station

Recently, in response to a Consent Decree that requires the installation ofSCR technology on

Units 5, 6, 7 and 8 at its South Oak Creek Generating Station in Oak Creek, Wisconsin, We

Energies (Wisconsin Electric) has investigated the use ofTESCR technology. The investigation

ultimately led to the determination that the TESCR approach would not be used. Based on

information obtained by Burns & McDonnell from the engineering consultant and the technology

vendor for that project (Bums & McDonnell personal communications, 2009), the decision not to

use TESCR technology was based on economics. However, the fact that TESCR systems were

considered to be feasible for specific application at the South Oak Creek units is not indicative

that the same technology would be technically feasible for application at MRYS. This is due to

Supplemental Information

For Consideration by NDDH

38 February 20, 2009
the substantial differences between the South Oak Creek boilers and the MRYS boilers, as

summarized in the Table below:

Table 6. Comparison ofBoilers for South Oak Creek and Milton R. Young Station

South Oak Creek Milton R. Young

Fuel Type PRB Coal ND lignite

(low ash, very low sulfur)

FGD Design Fuel Sulfur Content, 1.15 3.95

SOzlb/mmBtu

Firing Type PC wall-fired (Units 5 & 6) Cyclone fired (Units 1 & 2)

PC tangential (Units 7 & 8) (slagging-type, wet bottom)

(dry bottom)

Design Boiler Outlet NOx 0.15 0.51 (Unit 1 w/ASOFA)

Ib/mmBtu 0.49 (Unit 2 w/ASOFA)

Consent Decree NOx Limit 0.10 TBD

Ib/mmBtu

The significant differences in the ash characteristics, especially with regard to the sodium

content, between PRB coal and North Dakota lignite have been explained in previous submittals

to NDDH (Burns & McDonnell and others, 2007 and 2008). The effect that cyclone firing has

on the partitioning ofsodium has been explained previously, and reiterated in this document. In

addition, it can be seen from the tabulation above that the S02 content ofthe flue gas will be up

to four times as high at MRYS as at South Oak Creek, either before or after the FGD system.

This means that the potential for deposition of ammonium bisulfate on the SCR catalyst, due to

the reaction between the ammonia reagent and the S03 that fonns within the SCR reactor when

catalytic S02 oxidation occurs, will be proportionally much greater for the application ofTESCR

technology to MRYS than it would have been at South Oak Creek. Finally, it should be noted

that compliance with the Consent Decree for NOx emissions in the case of South Oak Creek

required only a moderate degree of emission reduction in the SCR systems, meaning that the

design was not particularly challenging from a percentage reduction standpoint.

Supplemental Information

For Consideration by NDDH

39 February 20, 2009
10. Relevance of Ongoing LDSCR Installation Project at We Energies'

South Oak Creek Station

Following the elimination ofTESCR systems from further consideration for the SCR retrofits

required by the Consent Decree, We Energies is proceeding with the installation ofLDSCRs at

Units 5, 6, 7 and 8 at South Oak Creek. Again, as shown in Table 6, the significant differences

between the fuel, firing type, sulfur content and NOx reduction requirement support the

contention that installation ofLDSCR systems under construction at South Oak Creek does not

constitute a demonstration that LDSCR technology is technically feasible for MRYS.

11. Relevance of Existing LDSCR Installation at PSEG Mercer Station

In response to a January 2002 Consent Decree that required the installation of SCR technology

on Units I and 2 at its coal-fired electric generating station in Mercer County, New Jersey, PSEG

Fossil (PSEG) has installed and operated LDSCR systems at this site since 2004 (Unit 2) and

2005 (Unit 1). However, the fact that LDSCR was considered to be feasible for specific

application at the Mercer units is not indicative that the same technology would be technically

feasible for application at MRYS. This is due to the substantial differences between the Mercer

boilers and the MRYS boilers, as summarized in the Table below:

Table 7. Comparison ofBoilers for Mercer and Milton R. Young Station

Mercer Milton R. Young

Fuel Type Low-sulfur bituminous coal NO Lignite

(Venezuelan and eastern u.s. blend)

Firing Type PC wall-fired, slagging-type (wet Cyclone fired (slagging-type,

bottom) wet bottom)

Design Boiler Outlet NOx 1.40 (prior to controls) 0.51 (Unit 1 w/ASOFA)

Ib/mmBtu (see note below) 0.49 (Unit 2 w/ASOFA)

Consent Decree NOx Limit 0.10 TBO

Ib/mmBtu

Mercer has demonstrated and employed various NOx reduction techniques before LOSCR installation in

2004, primarily SNCR, with and without fuel-lean gas reburn, and in-duct SCR.

Supplemental Information

For Consideration by NOOH

40 February 20, 2009
The significant differences in fuel type and firing type between these two plants would create

very different flue gas characteristics ofthe flue gas entering the LDSCR, especially with regard

to the sodium aerosol. The significant differences in the ash characteristics, especially with

regard to the sodium content, between bituminous coal and North Dakota lignite have been

explained in previous submittals to NDDH. The effect that cyclone firing has on the partitioning

ofsodium has also been explained previously, and reiterated in this document.

12. Additional Technical Feasibility Issues for TESCR at MRYS

As noted in previous submittals to NDDH (Burns & McDonnell and others, September and

November, 2008), there are no existing or planned TESCRs on coal-fired utility power plants in

the U.S. A review ofthe TESCR applications on German coal-fired power stations has indicated

that these installations are configured basically as shown in the diagram on page 1 ofthis

document. That is, flue gas from the outlet ofthe wet flue gas desulfurization (FGD) system

absorber is reheated prior to entering the TESCR system, using a regenerative (Ljungstrom type)

gas-to-gas heat exchanger (GGH) that supplies heat that was extracted from the flue gas

upstream ofthe FGD. According to consultation with the designers ofthe LDSCR systems for

South Oak Creek, the expected leakage through this type of heat exchanger will be at least 5.0

percent. When flue gas leaks across this "FGD GGH" from the inlet to the outlet flue gas

stream, it effectively bypasses the FGD absorber, meaning that no S02 removal takes place from

this slipstream ofthe total flue gas.

In the case ofboth MRYS Unit 1 (in the CD) and Unit 2 (in the proposed BART), NDDH has

indicated that 95% S02 removal is required. This will preclude the use ofthis type ofGGH,

because, as leakage around the FGD system approaches five percent, it becomes impossible to

achieve 95% overall S02 removal. This was not an issue for the German FGD systems, which

were not required to achieve the same high level of S02 removal efficiency that is dictated by the

MRYS CD and the proposed S02 BART.

Supplemental Information

For Consideration by NDDH

41 February 20, 2009
This leakage could be avoided ifthe saturated flue gas from the FGD system absorber were sent

directly to the "SCR GGH" upstream ofthe TESCR reactor as shown in the diagram on page 1.

However, according to the engineering consultant who performed the evaluation ofTESCR

technology at South Oak Creek (as described in Section 9 above), "Saturated flue gas tends to be

corrosive and there is virtually no experience with Ljungstrom GGH handling corrosive saturated

gas. Saturated gas from the absorber tower carries gypsum slurry droplets, which tend to plug

the cold end ofthe GGH with gypsum deposits that are extremely difficult to clean on-line."

Another aspect ofthe TESCR approach that appears infeasible at MRYS is that the flue gas

would enter the new fiberglass reinforced plastic (FRP) ductwork leading to the respective

chimneys, and Unit 2's FRP chimney liner, at a normal temperature above the 200°F design

limit, due to the TESCR reactor's outlet temperature being above 500 OF entering the treated-side

ofthe SCR GGH.

Based on these considerations, the only way to apply TESCR technology to the units at MRYS

while providing high S02 removal would be to employ a flue gas reheating technology which

has not been proven in the application to a TESCR system at any full scale power plant

installation. This indicates that TESCR technology is technically infeasible for application to the

Units at MRYS.

13. Summary and Conclusions

• Because ofthe unique properties ofFort Union Lignites, they produce more vaporized

ash (Na and other elements) that other coals including PRB and bituminous coal.

• Higher combustion temperatures associated with cyclone firing result in more ash

vaporization and increased levels ofsubmicron fine and ultrafme aerosol particles.

• Cyclones reduce the quantity of coarse flyash particles in the flue gas available to provide

sites for sodium condensation and to dilute the bonding effects ofthe aerosols once

deposited on a surface.

• The particle collection efficiencies for fine particles less than 1 J.lm are poor for both ESP

and wet FGD, such as those utilized at MRYS.

• The number offlue gas particles per gram increases ten times for 1 J.lm versus 10 J.lm and

another ten times for 0.1 J.lm versus 1 J.lm (diameter), so the fme and ultrafme aerosols are

plentiful in number because ofpenetration through ESPs and scrubbers. These fine

particles have high surface areas, are highly reactive, and readily bond together because

of high surface energies.

Supplemental Information

For Consideration by NDDH

42 February 20, 2009
• Particles in the 0.1 to 1.0 J.1m size fractions are largely composed of condensed vapor

phase species such as sodium, potassium, and sulfur.

• Sodium-rich aerosol particles present in flue gas downstream ofthe ESP at MRYS Unit 1

significantly impacted the performance ofthe Powerspan slipstream ECO barrier reactor

system in less than two weeks of exposure.

• Sodium- and sulfur- rich coatings on the surface ofthe Powerspan quartz rods were

dense, continuous, and difficult to scrape off. These sodium and sulfur rich layers were

produced in only 384 hours and were 25 J.1m thick.

• Emission rates downstream ofESP described in the reports provided by the NDOH range

from 4,500 to 50,000 J.1g1Nm3

• The particulate emitted are dominated fine and ultra fme

aerosols rich in sodium and potassium. NOTE: The level of 22,500 J.1g/Nm3 ofsodiumand potassium-rich fly ash derived from biomass firing resulted in catalyst deactivation of

30 to 40 % in 1500 hours (King and others, 2007).

• These are no TESCR installations in the U.S. on utility coal-fired boilers, and there are no

examples ofTESCR technology being applied worldwide on any coal-fIred boilers

having the same high percentage S02 removal requirements that are applicable at MRYS.

The heat exchanger technology that has been employed on other TESCR systems for

bituminous coal-fIred boilers located in Germany, ifapplied at MRYS, will preclude

compliance with the established S02 removal requirements.

• The expected outlet temperature from the TESCR and downstream gas-to-gas heat

exchangers will be too high for the fiberglass flue gas ductwork exhausting the chimneys

atMRYS.

• The existing LOSCR installations in the U.S. are on units fIring coals and using coal

fmng technology that will not produce the same high level of catalyst poisons in the flue

gas as would be the case at MRYS, where both units are cyclone furnaces firing highsodium lignite.

Conclusions

In the end, arguments regarding the technical feasibility oftail-end and low-dust SCR technology

at Milton R. Young Station are reduced to disputing the characterization ofthe gas stream

characteristics and the impacts ofthose characteristics on boiler and emissions control

operations. Those who suggest that these impacts can be resolved by the use ofLOSCR and

TESCR, and that such technology will work at MRYS without failure, cannot point to relevant

data showing success at other coal-fIred boiler SCRs which have such high levels ofsodium in

the fuel and the flue gas stream.

Considering the findings and conclusions presented above and previously, low-dust and tail-end

SCR technology would not be available to apply to Units 1 and 2 at MRYS without extensive

long-term pilot-scale testing and design development efforts. As BACT is not the selection of a

pollution reduction technology that requires such research and development in order to determine

Supplemental Information

For Consideration by NDDH

43 February 20, 2009
ifit can be successfully deployed for full-time, full-scale operation, we believe that low-dust and

tail-end SCR technology is not technically feasible at MRYS for Unit 1 and Unit 2 NOx

emissions control (Arfmann and others, 2007).

Supplemental Information

For Consideration by NDDH

44 February 20, 2009
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Supplemental Information

For Consideration by NDDH

47 February 20, 2C09