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 O ffice of Regulatory Enforcement ot Provide technical assistance to EPA Region 8 in ev aluating the Report on the B4st Available Control Technology (BACT) Analysis for Milto n R. Roung Station Units 1 & 2, prepared by Burns & McDonnell and the appended As h 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 lowe r 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 betw een fly ash and slag and how these processes for lignite coals can enhance lower temperatures r eactions where SCRs are operated. The combustion processes of importance that take pl ace in the boiler that are critical to ash behavior downstream include: vaporization and condensation proce sses related to ash formation, ash particle formation, ash depos ition, 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 impor tant for lignite since the low temperature ash deposition processes related to alkali a nd alkaline earth elements are much more challenging for high sodium lignite coal s as compared to other coals.

GENERAL BACKGROUND

Cyclone fired units – Christman indicates that the cyclones are impor tant even though his initial statements indicated what happens in the boiler is not important and the cyclones are part of the boiler. The chemical com position 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 between most subbituminous coals and lignite are different. Shown in Figure 1 is the abunda nce of sodium and calcium presented as equivalent oxides and ash content of primar ily subbituminous coals. There are several additional coals including bituminous coal s 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 significan t fouling problems and is a coal that was indicated to cause problems a ssociated 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 distribut ion 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 probl ems. As indicated in Figure 2 the boiler is firing some very high sodium containing co als that can cause signi ficant problems. In addition, the sodium in the Cent er lignite is organically asso ciated or sometime referred to as water or acid soluble components a nd based on publications on Haldor Topsoe’swebsite causes catalyst deactivation (T. Slabiak and S. Enevoldsen, Topsoe’s Corrugatedtype DeNOx Catalysts – Characteris tics and Operating Experience, http://www.topsoe.com/site.nsf/vALL WEBDOCID/KVOO-5PGF7F/$file/Cat%20- %20Topsoe's%20corrugated-t ype%20DeNOx%20Catalysts.pdf ). On December 6, 1999 Dr. Heinz Gutberlet and Jürgen Brandenste in from PreussenElektra Engineering of Germany visited the EERC to discuss sodium reactions with SCR catalysts. They expressed their concern regardi ng deactivation. Latter that year they pr esented 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 system s. The species that end up in the flyash for a cyclone as compared to pc wall or ta ngential unit are enriched in the inorganic or ash species that are more volatile such as s odium. 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 lo ading may be less but the melting point and the stickiness of the fly ash is greater for th e 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 ga s from Coyote Stations were completely plugged. EERC offered to send them to Haldor Topsoe and they indicated that they were too plugged and deactiva tion testing could not be conducted. Thisdiscussion was held between Jason Laumb of the EERC and Flemming Hansen of Haldor Topsoe.

Figure 1. Ash Content (as received) and sodi um and calcium expressed as equivalent

oxides in the ash in coals from EERC’s database.

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

coals in the as-fired database. 0 50 100 150 200 250 300 350

< 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-

1 1 11 - 12 12 - 13 13-14Frequency, N=1317 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% 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 ASH1. No comment

2. Center Lignite is extremely variable in ash content and the constituents that make up the ash. Christman focuses attention on averages. Typically it is not the average coal that causes ash related pr oblems 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 base-to-acid ratio (B/A=(Na2O+MgO+CaO+K2O+FeO )/(SiO2+Al2O3+TiO2)).

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

Figure 3. Base-to-Acid ra tio of as-fired coal sa mples showing variability. 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

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

SPECIFIC ISSUES

SCR Applicabiltiy

High Dust SCR

Catalyst Deactivation

Christman ignores the primary deactivation mechanism associated with lignite and that is sodium. He focused on the impacts of calcium. Sodium is much highe r in Center lignite than nearly all PRB coals with the excep tion 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 sulfate alone. Christman rightly brings up the other problem of sodium and that is by deactivating individual reaction sites. Ch ristman appears to miss the major problem and

that is sodium.

Regeneration has been attempted in Europe with SCR catalysts exposed to biomass as with high K (similar in chemistry to Na) and they had some significant problem in recovering reactivity.

Catalyst Erosion

Christman appears to have misunderstood the problem with ash deposition and reentraining the deposit fragments that can ca use erosion. The primary superheater and economizer in cyclone fired boilers are prone to significant fouling that requires frequent sootblowing. This deposition problem is not related to the partitioning that occurs in cyclones. The species that are in the fly ash have more calcium and sodium than the bulk % Ash

0.00 2.00 4.00 6.00 8.00 10.00 12.00

PRB Blend Colstrip

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n dcoal ash. This results in more sticky mate rials that create dense deposits these lower temperature convective pass heat transfer su rfaces. 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 mate rial is soot blown it is entrained and the entrained deposit fragment can cause erosion. The entrained deposits are greater due to the high ash deposition propensity of the Ce nter lignite it is not the ash content

Catalyst Plugging

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 bulk of the problem was sodium, calcium and sulfur rich fine particles. That cause severe bonding after 2 to 6 months of operation.

Figure 6. Plugging of SCR catalyst and deposit s formed downstream of catalyst section

after removal.

High economizer outlet temperature

No Comment

Low Dust SCR

North Dakota Industrial Commission project Evaluation of Potential SCR Catalyst Blinding During Coal Combustion

The SCR catalysts from Otter Tail Power’s Coyot e Station were too pl ugged to run a test on deactivation. Flemming Hansen did not se e 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 pl ugging and blinding due to deposit formation limited our ability to obtain activity data.

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 HaldorTopsoe. They all approved the design of th e reactor, sootblowing system, and operating parameters. They also provided the catalys t. The vendor selected the pitch of the catalysts.

CONCLUSIONS

The conclusions do not address the high sodium levels but a ppears to focus again on the

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 the reports submitted.

EPA REGION 8 Preliminary Analysis of Burns & McDonnell BACT Analysis for Nitrogen Oxide at Milton R. Youn Station, Units 1 and 2 January 8, 2007

I. Introduction and Summary of EPA’s Preliminary Analysis

a. Summary of EPA’s Preliminary Analysis

We spoke to Haldor Topsoe and after desc ribing the issues related to sodium they were very concerned regard ing 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 th e organically associated form. They indicated that they had some experience and found significant d 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

II. EPA Case-Specific Review of Burns & McDonnell & EERC Technical Feasibility Analysis for Selective Catalytic Reduction

a. High Dust SCR

EPA Analysis of the Ash Deposition Issue:

EPA states that the high amount of ash materials causing blin ding of macro-pores in the catalyst is real but solvable. Strides in catalyst formulations, catalyst management system, and recently, catalyst regeneration pr ocesses, have all combined to lower the overall cost of both initial and replacem ent catalyst in modern SCR systems.

We spoke to a catalyst vendor regarding what has been done to deal with the problems of high sodium coals regarding a dvanced formulations, catalyst regenerationand 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 significan tly different from PRB coals. EPA indicates that the probl ems of deposition will decrease because the cyclones take out some of the ash but for lignites removing some of the ash but for lignites cyclones create additional deposit ion problems downstream. The cyclones partition the more refractory ash component s into the slag and the more volatile components into the fly ash. The fly ash beco mes enriched in components that vaporize and subsequently condense upon gas cooling to form liquid phases and small particles that are very reactive to gas phase component s that cause bonding.

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

also discuss the formation of calcium sulfat es the can plug pores in catalysts and also discuss the impacts of other alkaline materi als (potassium, sodium, and magnesium) and their potential to deactivate in dividual sites rather than blinding pores. They fail to recognize the formation of combined phases su ch 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 recogni ze that cyclones partiti on the ash increasing the proportion of sodium in the smaller particle s resulting in increa sed propensity for the 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 biom ass fuels that contain high potassium and 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 organica lly 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 a nd is not soluble. More recently work conducted by Beck and ot hers, 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 sodi um and calcium rich fine particulate plugging pores of the catalyst.

Other Ash Deposition Problems on Downstream ComponentsNote 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 &Environmenta l Research Center Report (Appendix B):

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

will address EPA’s comments. The followi ng vendors were involved in the design and testing that included Haldor Tops oe, Cometech, and Hitachi.

1) The pulsing system was designed with th e assistance of the catalyst vendors. They provided suggestions on the sootblowing pre ssures and felt it would be sufficient to remove the deposits.

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

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

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

Haldor Topsoe was the only catalyst vendor willing to provide catalyst for the lignite testing.

We agree that the EERC pilot scale tes ting should not alone be the deciding considerations when evaluating SCR tec hnical feasibility at MRYS. The EERC comparisons of catalyst blindi ng for lignite and subituminous coal testing as well as the sodium deactivation work conducted by Haldor Topsoe (Slabiak and Envoldsen, ), PreussenElektra Engineering (Gutberlet and others, ), J. Beck and others (2004)

EPA Analysis of Burns & McDonnell Conclusions

EPA did not examine the report in deta il. The deposition and plugging was much more pronounced for the Coyote Station test ing as compared to the Columbia and Baldwin Station. The pressure drop increased much more rapidly and the soot blowing was not as effective. The conclusions made by EPA that the accumulations are similar

are incorrect.

The most important unresolvable technical difficulty is the impact of sodium on the formation of bonded sulfate phases that pl ug 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 known to be present in high sodium coal co mbustion flue gases. These species are known to produce pyrosulfates.

III. Additional Information Useful to Evalua ting Technical Feasibility of SCR at

MRYS

a. EPA Headquarters Believes SCR is the Correct Technology for MRYS in Developing the Clea n Air Interstate Rule (CAIR)

The experience from subbituminous coals and SCR does not have direct application to the lignite coals because of th e 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 Hal dor 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 wa s not aware of the deta ils of the levels of

sodium and the form of sodium in the coal wh en he was asked before . He indicated that the sodium in the lignite was a major concer n and that it causes d eactivation, especially

the acid soluble form. He indicated that they had some experience and found significant deactivation of SCR coupon samples after 6000 to 7000 hours of operation with a coal having elevated levels of sodium.

b.

c.

d. SCR and Catalyst Vendor Information

Some of the websites discuss the problems of sodium and deactivation. However, EPA has not provided a review of that information.