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 Milt on 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 impact s on SCR performance include a substantial amount of “chaff” that has no bearing on the S CR 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 de tails presented was a discussion of how a cyclone partitions the ash between fly ash an d 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 condensatio n processes related to ash formation, ash particle formation, ash deposition, and soot blowing cycles. An understanding of what happens in the boile r 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 processe s 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 comp osition of the ashes derived from lignite andsubbituminous coals have similarities in the t ypes of elements present. However, the

abundance of elements in that ash betwee n 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 Rive r 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 ha ve 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 pr oblems. As indicated in Figure 2 the boiler is firing some very high sodium containing co als 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’swebsite 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 sodi um 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 discussion s 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 th e 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 load ing 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 th em to Haldor Topsoe and they indicated that they were too plugged and deactivati on 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 plan ts. Coupon te sts 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 30.00Illinois #6Utah BlindCoal CreekPeabody Big SkyDietzNorth Decker 2WyodakColstripShercoNorth Decker 1Spring CreekBT-Co. BlendBeulahJacobs RanchSarpy CreekRochelleBuckskinCorderoBlack ThunderSmith-RolandCIT EBNanticoke PRBCaballo RojoEagle ButteShoshoneCaballoNorth AntelopeDry ForkAntelopeBelle AyrRaw Hide

CoalMass % CaO Na2O ASH

Figure 1. Ash Co d as equivalent ntent (as received) and s odium and calcium expresse 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 350Frequency, 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

1 0- 11 11-12

1 2- 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

oals in the as-fired database. c1. 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 rem ove 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 bot h 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 45081898 11081898 13081898 15081898 17120298 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

DateAsh (moisture free)

5400 5600 5800 6000 6200 6400 6600 6800 7000 7200Cyclone 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 1.40081898 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

DateBase/Acid

5400 5600 5800 6000 6200 6400 6600 6800 7000 7200Cyclone Performance

igure 3. Base-to-Acid ratio of as-f ired coal samples showing variability. F% Ash

0.00 2.00 4.00 6.00 8.00 10.00 12.00

B Blend Colstrip

o . Blen d

PR BT-C abody Big Sk y North Decker 1 North An te lope

No

rth

D

e c k e r 2

W y o d ak CIT E B Eag

l e Bu

tt e

Ca

ba

l lo Roj o Be ll e A

yr

Co

al

C

r eek Smith-Rola nd

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 lig nite 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. Ch ristman 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

C atalyst Erosion

Christman appears to have misundersto od 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 proble m

— 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 pr opensity to produce deposits on the convective pass heat exchanges surfaces and when that ma terial 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 st ation 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. Pluggi ng of SCR catalyst and de posits 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

B linding During Coal Combustion

a test

i ng and blinding due to deposit formation mited our ability to obtain activity data. The SCR catalysts from Otter Tail Power’s Coyo te 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

liRegarding 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 cataly st vendors have not addressed th em. Mr. Christman curiously

d id 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

Ja nuary 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 leve ls 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 ind icated that they had som experience and found significant d eactivation of in coupon samples after 6000 e to 7 s of sodium. 00 0 hours of operation with a coal having elevated level

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 hig h sodium coals regarding ad vanced formulations, catalyst regeneration

nd he was not aware of any work that had advanced SCR systems for high sodium a 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 proble ms 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 depositi on 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 mate rials (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 th e 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 bi omass fuels that contain high potassium and r the

sodium and found rapid deactivation in the SCR catalyst. They indicate that the sodiu m or potassium resembles the ammonium ion and bl ocks 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 organi cally 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: En vironmental 49(2004)15-25) established

th at sodium correlates with catalyst deacti vation activity and that pore condensation of

s odium 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

w ill cause plugging in addition to the reac tions 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 so dium that causes the deposition

opcorn Ash issue Raised by Burns & McDonnell P

EPA Analysis of the Erosion Issue

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

EPA believes that there may be inherent lim itations with the pi lot 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 pre ssures and felt it would be sufficient to w testing that included Haldor Tops oe, 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 pr oblems 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

s odium deactivation work conducted by Haldor Topsoe (Slabiak and Envoldsen, ), PreussenElektra Engineering (G utberlet 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 i mportant unresolvable technical difficulty is the impact of sodium on e formation of bonded sulfate phases that plug and mask the catalyst and on the ability th of sodium to deactivate the catalyst.

Low Dust SCR

Sodi um-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 t o 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 co als and SCR does not have direct applica tion to the lignite coal s because of the high sodium content of the lignite. The experience with German brown coals does no t 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 sy stems 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 wa s not aware of the details of the levels o

sodium and the form of sodium in f

the coal wh en 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 60 00 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.