DRAFT, 2/06/07 

EERC Response 

Roger Christman, Eastern Research Group, Inc. on Review and Critiquie of the 

Burns&McDonnell, NOx BACT Analysis for the Milton R. Young Station Operated by 

Minnkota Power (October 2006). 

EPA Preliminary Analysis of B&M NOx BACT Analysis (January 8, 2007. 

INTRODUCTION 

ERG was asked to review the U.S. EPA Office of Regulatory Enforcement ot Provide 

technical assistance to EPA Region 8 in evaluating the Report on the B4st Available 

Control Technology (BACT) Analysis for Milton R. Roung Station Units 1 & 2, prepared 

by Burns & McDonnell and the appended Ash impacts on SCR Catalyst Perfomance 

(Benson, 2005) prepared by the EERC. 

REVIEW RESULTS 

Christman indicates the reports on ash impacts on SCR performance include a substantial 

amount of “chaff” that has no bearing on the SCR issue. Specifically he indicates that 

what happens in the boiler has no relevance to what happens in lower temperatures of the 

boiler downstream of the economizer. However, what happens inside the boiler defines 

the flux of material that will be carried back into the lower temperature regions of the 

furnace. Of specific importance in the details presented was a discussion of how a 

cyclone partitions the ash between fly ash and slag and how these processes for lignite 

coals can enhance lower temperatures reactions where SCRs are operated. The 

combustion processes of importance that take place in the boiler that are critical to ash 

behavior downstream include: vaporization and condensation processes related to ash 

formation, ash particle formation, ash deposition, and soot blowing cycles. An 

understanding of what happens in the boiler defines the flux of materials (vapors, 

particles, deposit fragments) that will be transported through the boiler with the flue 

gases. These phenomena are especially important for lignite since the low temperature 

ash deposition processes related to alkali and alkaline earth elements are much more 

challenging for high sodium lignite coals as compared to other coals. 

GENERAL BACKGROUND 

Cyclone fired units – Christman indicates that the cyclones are important even though his 

initial statements indicated what happens in the boiler is not important and the cyclones 

are part of the boiler. The chemical composition of the ashes derived from lignite and 
subbituminous coals have similarities in the types of elements present. However, the 

abundance of elements in that ash between most subbituminous coals and lignite are 

different. Shown in Figure 1 is the abundance of sodium and calcium presented as 

equivalent oxides and ash content of primarily subbituminous coals. There are several 

additional coals including bituminous coals such as Illinois #6, Utah Blind Canyon 

(Wasatch Basin), and Shoshone (Green River Formation); blends; and Beulah lignite 

(Fort Union of North Dakota). Based on these analyses only the Spring Creek 

subbituminous coal has a high level of sodium that is typical of North Dakota lignite. 

Spring Creek coal is known to cause significant fouling problems and is a coal that was 

indicated to cause problems associated with sodium deactivation of SCR catalyst coupons 

at a Michigan power plant as indicated by Flemming Hansen (Personal Communication 

February 2007). All of the other PRB coals have sodium oxide levels of less that 2 to 

3%. Figure 2 shows the distribution of sodium oxide in Center lignite. The results of the 

analysis show that the sodium content is on average of 4.4% however, there is a 

multimodal distribution of sodium levels in the coal ash. Using average compositions 

can be misleading related to ash deposition problems. As indicated in Figure 2 the boiler 

is firing some very high sodium containing coals that can cause significant problems. In 

addition, the sodium in the Center lignite is organically associated or sometime referred 

to as water or acid soluble components and based on publications on Haldor Topsoe’s 

website causes catalyst deactivation (T. Slabiak and S. Enevoldsen, Topsoe’s Corrugatedtype DeNOx Catalysts – Characteristics and Operating Experience, 

http://www.topsoe.com/site.nsf/vALLWEBDOCID/KVOO-5PGF7F/$file/Cat%20-

%20Topsoe's%20corrugated-type%20DeNOx%20Catalysts.pdf). On December 6, 1999 

Dr. Heinz Gutberlet and Jürgen Brandenstein from PreussenElektra Engineering of 

Germany visited the EERC to discuss sodium reactions with SCR catalysts. They 

expressed their concern regarding deactivation. Latter that year they presented their work 

on sodium deactivated catalysts from coals that contain higher soluble sodium (Gutberlet, 

NETL SCR 2000 Conference). In discussions with Haldor Topsoe has indicated that 

soluble sodium is the worst kind. 

Christman indicates for a typical cyclone that about 30% of the ash ends up as fly ash and 

the remaining ash ends up as slag. This is not the case for lignite where about 45 to 50 

percent of the ash forming components end up as fly ash. Because more of the ash 

forming components in the lignite is organically associated more of the species end up in 

the fly ash. Christman does not discuss the enrichment of sodium and other volatile 

species in the fly ash from cyclone fired systems. The species that end up in the flyash 

for a cyclone as compared to pc wall or tangential unit are enriched in the inorganic or 

ash species that are more volatile such as sodium. In wall or corner fired systems the 

enrichment of sodium in the fly ash is not as significant because of the dilution of the 

other ash forming components. The ash loading may be less but the melting point and 

the stickiness of the fly ash is greater for the cyclone units as compared to the pc units. 

This creates more deposits in the boiler and downstream surfaces. 

The SCR catalysts sections that were exposed to the flue gas from Coyote Stations were 

completely plugged. EERC offered to send them to Haldor Topsoe and they indicated 

that they were too plugged and deactivation testing could not be conducted. This 

Comment [REJ1]: Gutberlet’s paper is very 

general in nature. At that time, the SCR market was 

still in shock over Gutberlet’s claim that SCR would 

not work on PRB fired plants. Coupon tests at New 

Madrid showed dismal results. Gutberlet was in the 

middle of all this because PreussenElektra and KWH 

catalysts were owned by the same company. 

Gutberlet was the leading authority to the US market 

for KWH. The referenced paper only mentions that 

sodium is known to deactivate catalysts and 

primarily deals with arsenic. 

It is also well known that soluble sodium will 

deactivate an active site. This occurs when the 

sodium can dissociate from the fly ash if it is wetted. 

At operating conditions, sodium is not generally 

regarded as a significant deactivating mechanism. 

Comment [REJ2]: No flue gas across the 

catalysts means the catalyst is not subject to typical 

deactivating mechanisms.
discussion was held between Jason Laumb of the EERC and Flemming Hansen of Haldor 

Topsoe. 

Comparison of Coal Data (CaO sorted)

0.00

5.00

10.00

15.00

20.00

25.00

30.00

Illinois #6

Utah Blind

Coal Creek

Peabody Big Sky

Dietz

North Decker 2

Wyodak

Colstrip

Sherco

North Decker 1

Spring Creek

BT-Co. Blend

Beulah

Jacobs Ranch

Sarpy Creek

Rochelle

Buckskin

Cordero

Black Thunder

Smith-Roland

CIT EB

Nanticoke PRB

Caballo Rojo

Eagle Butte

Shoshone

Caballo

North Antelope

Dry Fork

Antelope

Belle Ayr

Raw Hide

Coal

Mass %

CaO Na2O ASH

Figure 1. Ash Content (as received) and sodium and calcium expressed as equivalent Comment [REJ3]: What is the sodium content in 

the coal on a ppmw basis? oxides in the ash in coal om EERC’s database. s fr

0

50

100

150

200

250

300

350

Frequency, N=1317

<0.5

0.5-1

1-2

2-3

3-4

4-5

5-6

6-7

7-8

8-9

9-10

10-11

11-12

12-13

13-14

Na2O in ash

10th Percentile:

1.99 w t%

50th 

Percentile:

 4.4 w t%

55th 

Percentile:

4.61 w t%

45th 

Percentile:

4.09 w t%

90th Percentile:

6.74 w t%

Figure 2. Distribution of sodium (expressed as equivalent oxide) in ash derived from the 

coals in the as-fired database. 
1. No comment 

2. Center Lignite is extremely variable in ash content and the constituents that m

up the ash. Christman focuses attention on averages. Typically it is not the 

average coal that causes ash related problems and it is those excursions that 

impact the formation of difficult to remove deposits on surfaces exposed to flue 

gases. Figure 3 and 4 show actual data from the MRY plant on lignite variability

that shows the extreme variability in both the ash content and baseake to-acid ratio 

(B/A=(Na2O+MgO+CaO+K2O+FeO)/(SiO2+Al2O3+TiO2)). 

0

5

10

15

20

25

30

35

40

45

081898 11081898 13081898 15081898 17 120298 01120298 09120298 17121598 07121598 07121598 07121598 07122698 07122698 05122798 19122798 17122798 15011699 09011699 09011699 09040699 09040699 15040699 21040799 03050499 15050699 05050599 07050599 09050499 17050699 21071199 21071099 05071299 09071099 11071299 21071099 17071399 09

Date

Ash (moisture free)

5400

5600

5800

6000

6200

6400

6600

6800

7000

7200

Cyclone Performnace

Figure 3. Moisture free ash content of as-fired coal samples showing variability. 

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

081898 11081898 15081898 19081898 23120298 09120298 19120198 23121598 21121598 23121698 01121698 03122798 05122798 05122798 05122798 05011699 01011699 03011699 05040699 07040699 15040699 23040799 07050499 21050699 13050599 17050599 21050599 11071099 15071399 09071199 01071499 05071199 17071099 05071299 13

Date

Base/Acid

5400

5600

5800

6000

6200

6400

6600

6800

7000

7200

Cyclone Performance

Figure 3. Base-to-Acid ratio of as-fired coal samples showing variability. 
% Ash

0.00

2.00

4.00

6.00

8.00

10.00

12.00

B Blend

Colstrip

o. Blend

PR

BT-C

abody Big Sky

North Decker 1

North Antelope

North Decker 2

Wyodak

CIT EB

Eagle Butte

Caballo Rojo

Belle Ayr

Coal Creek

Smith-Roland

Pe

igure 5. Ash contents of selected subbituminous coals (as-received basis). 

PECIFIC ISSUES 

CR Applicabiltiy

F

S

S

igh Dust SCR 

atalyst Deactivation

H

C

Christman ignores the primary deactivation mechanism associated with lignite and that is 

sodium. He focused on the impacts of calcium. Sodium is much higher in Center lignite 

than nearly all PRB coals with the exception of Spring Creek a Northern PRB coal. 

Sodium combines with sulfur and calcium to produce low melting point sulfate phases 

that plug pores and is much more aggressive in plugging pores that just calcium su

alone. Christman rightly brings up the other problem of sodium and that is by 

deactivating ind

lfate 

ividual reaction sites. Christman appears to miss the major problem and 

at is sodium. 

s 

hemistry to Na) and they had some significant problem in 

covering reactivity. 

Comment [REJ4]: Is this a hypothesis or a fact? 

Is there any data that shows %sodium by weight on 

an SCR catalyst from a ND lignite? How can it be 

stated so conclusively? 

th

Regeneration has been attempted in Europe with SCR catalysts exposed to biomass a

with high K (similar in c

re

Catalyst Erosion

Christman appears to have misunderstood the problem with ash deposition and 

reentraining the deposit fragments that can cause erosion. The primary superheater and 

economizer in cyclone fired boilers are prone to significant fouling that requires frequ

sootblowing. This deposition problem is not related to the partitioning that occurs in 

ent 

Comment [REJ5]: Catalyst erosion is a function 

of flue gas velocity and fly ash velocity vectors at 

the face of the catalyst. Localized pluggage, if 

severe enough, has been known to change both sets 

of vectors and to cause erosion. Only in the most 

unusual of circumstances have sootblowers caused 

erosion. Catalyst pluggage was also feared on PRB 

applications. Because some PRB coals fouled heat 

transfer surfaces, this was extrapolated for SCRs. In 

a well operated SCR, pluggage has not been a 

problem—wall fired, T-fired or cyclone fired boilers.
cyclones. The species that are in the fly ash have more calcium and sodium than the b

coal ash. This results in more sticky materials that create dense deposits these lower 

temperature convective pass heat transfer surfaces. Related to ash deposition for high 

sodium lignites cyclones make it worse not better as Christman appears to think. It is 

not the ash content that counts, it is the propensity to produce deposits on the convective 

pass heat exchanges surfaces and when that material is soot blown it is entrained and the 

entrained deposit fragment can cause erosion. The entrained deposits are greate

ulk 

r due to 

e high ash deposition propensity of the Center lignite it is not the ash content 

atalyst Plugging

th

C

The catalysts that were tested at Coyote station were completely plugged and deposits 

were forming at the exit of the catalyst. These deposits were highly consolidated and 

bonded by sulfates and are shown in Figure 6. The ash that was responsible for the bu

of the problem was sodium, calcium and su

lk 

on

lfur rich fine p

ding after 2 to 6 months of operation. 

articles. That cause severe 

Comment [REJ6]: Slipstream tests can be 

problematical because wall effects distort flue gas 

and fly ash vectors. My opinion: this was a flawed 

test and the results should not be used to draw any 

conclusions other than that a full scale system design 

needs to be done very carefully.

b

Figure 6. Plugging of SCR catalyst and deposits formed downstream of catalyst section 

fter removal. 

 outlet temperature 

o Comment 

ow Dust SCR 

n project Evaluation of Potential SCR Catalyst 

a

High economizer

N

L

North Dakota Industrial Commissio

Blinding During Coal Combustion

 a test 

ing and blinding due to deposit formation 

mited our ability to obtain activity data. 

The SCR catalysts from Otter Tail Power’s Coyote Station were too plugged to run

on deactivation. Flemming Hansen did not see any point in trying to get values of 

catalyst activity. The aim of the project was to determine the rate of loss of catalytic 

activity. However, the challenges of plugg

li
Regarding the design and operation of the slip stream system – the design and operation 

of the slip stream reactor was conducted with input from Cormatech, Hitachi, and H

Topsoe. The

aldor 

y all approved the design of the reactor, sootblowing system, and operating 

arameters. They also provided the catalyst. The vendor selected the pitch of the 

 on the 

p

catalysts. 

CONCLUSIONS 

The conclusions do not address the high sodium levels but appears to focus again

lower calcium levels. None of the sodium issues have been resolved. Sodium is a 

problem in the formation of deposits and in deactivation as indicated by several 

investigators. The catalyst vendors have not addressed them. Mr. Christman curiously 

did not address the challenges of sodium even though it is the major problem identified in 

e reports submitted. 

Preliminary Analysis of Burns & McDonnell BACT Analysis for 

itrogen Oxide at Milton R. Youn Station, Units 1 and 2 

ary Analysis 

y 

th

EPA REGION 8 

N

January 8, 2007 

I. Introduction and Summary of EPA’s Prelimin

a. Summary of EPA’s Preliminary Analysis 

We spoke to Haldor Topsoe and after describing the issues related to sodium the

were very concerned regarding guaranteeing performance. It was evident that EPArepresentatives may have not indicated the levels of sodium and the form of sodium in 

the coal. They indicated that the sodium in the lignite was a major concern and that it 

causes deactivation, especially the organically associated form. They indicated that they 

had som experience and found significant d e eactivation of in coupon samples after 6000 

to 7000 hours of operation with a coal having elevated levels of sodium. 

b. Relevant Language from Consent Decree 

eview of Burns & McDonnell & EERC Technical 

Feasibility Analysis for Selective Catalytic Reduction 

II. EPA Case-Specific R

a. High Dust SCR

EPA Analysis of the Ash Deposition Issue:

EPA states that the high amount of ash materials causing blinding of macro-po

in the catalyst is real but solvable. Strides in catalyst formulations, catalyst ma

res 

nagement 

ystem, and recently, catalyst regeneration processes, have all combined to lower the 

overall

s

 cost of both initial and replacement catalyst in modern SCR systems. 

Comment [REJ7]: Is the extent of deactivation 

from sodium any different than that from arsenic or 

calcium? Can EERC specifically state the 

magnitude of sodium deactivation? Based on the 

information received from Alstom, which included 

proposals from catalyst suppliers based on the 

known data, the conceptual design included a 

conservatively high deactivation rate. As mentioned 

before, sodium is a known deactivating element. 

Just because it is mentioned in general presentations 

does not make it a significantly different deactivating 

mechanism than others.

Comment [REJ8]: Coupon analyses can also be 

problematical. Due to the positioning within a duct, 

these are generally subject to different velocity and 

fly ash vectors than seen in an SCR reactor. It is 

well known within the catalyst industry that coupons 

are not reliable indicators of deactivation rates. 
We spoke to a catalyst vendor regarding what has been done to deal with the 

problems of high sodium coals regarding advanced formulations, catalyst regeneration 

and he was not aware of any work that had advanced SCR systems for high sodium 

applications. 

Comparison of MRYS to SCR Systems Operating on Power River Basin coals

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

PRB coals. EPA indicates that the problems of deposition will decrease because the 

cyclones take out some of the ash but for lignites removing some of the ash but fo

lignites cyclones create additional deposition problems downstream. The cyclones 

partition the more refractory ash components into the slag and the more volatile 

components into the fly ash. The fly ash becomes enriched in componen

r 

ts that vaporize 

nd subsequently condense upon gas cooling to form liquid phases and small particles 

at are

a

th very reactive to gas phase components that cause bonding. 

 EPA discusses ash loadings and the potential impacts on SCR performance. They

also discuss the formation of calcium sulfates the can plug pores in catalysts and also

discuss the impacts of other alkaline materials (potassium, sodium, and magnesium) and

their potential to deactivate individual sites rather than blinding pores. They fail to 

recognize the formation of combined phases such as sodium calcium sulfates those low 

melting points that are very reactive and can both block pores and deactivate individual 

sites in catalysts. They also fail to recognize that cyclones partition the ash increasing the 

proportion of sodium in the smaller particles resulting in increased propensity fo

formation of the complex sulfate phases. Topsoe presented at the DOE NETL meeting 

on SCR-SNCR on (http://www.netl.doe.gov/publications/proceedings/99/99scrsncr/enevolds.pdf) testing conducted with biomass fuels that contain high potassium and

r the 

sodium and found rapid deactivation in the SCR catalyst. They indicate that the sodium 

or potassium resembles the ammonium ion and blocks access to the active sites. They

indicate that this occurs most readily where the alkali elements are soluble. In North 

Dakota lignite most of the sodium is organically associated and is in a soluble form. 

Topsoe goes on to indicate that the alkali in coal is not soluble but they only looked at 

potassium. Potassium is associated in the coal with clay minerals and is not soluble. 

More recently work conducted by Beck and others, 2004 (J. Beck, J. Brandenstein, S. 

Unterberger, K. Hein, Applied Catalysis B: Environmental 49(2004)15-25) established 

that sodium correlates with catalyst deactivation activity and that pore condensation of 

sodium is the major deactivation mechanism. 

Engineering Solutions for SCR Applications at High Ash Facilities

 

 The issue is not high ash it is high sodium. The issue is a high potential for ash 

deposition in lower temperature convective pass surfaces such as the economize and

primary superheater that require continuous cleaning and the resulting deposit fragments 

will cause plugging in addition to the reactions of the sodium and calcium rich fine 

particulate plugging pores of the catalyst. 

Comment [REJ9]: Do these melting 

temperatures exist within the SCR catalyst pores? 

What is the temperature range?

Comment [REJ10]: Sodium and potassium 

deposition within the catalyst will generally 

deactivate catalysts. The real question is how 

quickly and how manageable is the rate? On 

biomass applications and some gas turbine plants, K 

and Na deposition is high mainly because there is no 

or little fly ash on which these elements can react. Is 

this true on a lignite fired boiler? 

Comment [REJ11]: Is an SCR catalyst surface at 

the same temperature as these heat transfer surfaces?
Other Ash Deposition Problems on Downstream Components

 Note that it is not the ash loadings it is the sodium that causes the deposition 

Popcorn Ash issue Raised by Burns & McDonnell

EPA Analysis of the Erosion Issue

EPA Analysis of the Energy &Environmental Research Center Report (Appendix B):

EPA believes that there may be inherent limitations with the pilot study. The following 

ill address EPA’s comments. The following vendors were involved in the design and 

 was designed with the assistance of the catalyst vendors. They 

rovided suggestions on the sootblowing pressures and felt it would be sufficient to 

w

testing that included Haldor Topsoe, Cometech, and Hitachi. 

1) The pulsing system

p

remove the deposits. 

2) The 6 mm pitch was recommended by the vendors. 

3) If the first layer plugs the gases cannot get to the subsequent layers. 

4) Deposition and plugging are significant problems that impact the reliability of the 

aldor Topsoe was the only catalyst vendor willing to provide catalyst for the lignite 

s the 

MRY facility. 

H

testing. 

We agree that the EERC pilot scale testing should not alone be the deciding 

considerations when evaluating SCR technical feasibility at MRYS. The EERC 

comparisons of catalyst blinding for lignite and subituminous coal testing as well a

sodium deactivation work conducted by Haldor Topsoe (Slabiak and Envoldsen, ), 

PreussenElektra Engineering (Gutberlet and others, ), J. Beck and others (2004) 

E nalysis of Burns & McDonnell Conclusions PA A

 EPA did not examine the report in detail. The deposition and plugging was much

more pronounced for the Coyote Station testing as compared to the Columbia and 

Baldwin Station. The pressure drop increased much more rapidly and the soot blowing 

as not as effective. The conclusions made by EPA that the accumulations are similar 

re inc

w

a orrect. 

Comment [REJ12]: 6mm pitch from Cormetech 

is much different than that for Topsoe or Hitachi. 

The real issue is open area, which is much smaller 

for the honeycomb catalyst.

Comment [REJ13]: I don’t believe the 

references cited in this letter detail such work. 

Sodium is only mentioned. 
 The most important unresolvable technical difficulty is the impact of sodium on 

the formation of bonded sulfate phases that plug and mask the catalyst and on the ability 

of sodium to deactivate the catalyst. 

Low Dust SCR 

Sodium-rich aerosols are a problem that can get through the ESP. These aerosol are 

know t in high sodium coal combustion flue gases. These species are 

know

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

n to be presen

n to produce pyrosulfates. 

MRYS 

a. EPA Headquarters Believes SCR is the Correct Technology for 

MRYS in Developing the Clean Air Interstate Rule (CAIR)

The experience from subbituminous coals and SCR does not have direct 

application to the lignite coals because of the high sodium content of the lignite. The 

experience with German brown coals does not have direct application to ND lignite 

because of the lower sodium levels. 

We spoke to Flemming Hansen of Haldor Topsoe on February 2, 2007 about the 

issues associated with high sodium North Dakota lignite. They have experience with 

sodium and potassium from biomass fired systems and their experience has not been 

good. After describing the issues related to sodium he was very concerned regarding 

guaranteeing performance. It was evident he was not aware of the details of the levels o

sodium and the form of sodium in 

f 

the coal when he was asked before. He indicated that 

e sodium in the lignite was a major concern and that it causes deactivation, especially 

e aci ble form. He indicated that they had some experience and found significant 

eactivation of SCR coupon samples after 6000 to 7000 hours of operation with a coal 

vels of sodium. 

d. SCR and Catalyst Vendor Information

th

th d solu

d

having elevated le

 b. 

c. 

Some of the websites discuss the problems of sodium and deactivation. However, 

EPA has not provided a review of that information. 

Comment [REJ14]: References? Any known 

data for an SCR application? 

Comment [REJ15]: But it has relevance to 

system design. 

Comment [REJ16]: See previous comments re: 

K and Na issues.