# s ...;> Minnkota, in its November 9, 2007 response to comments, provided evidence of sodium .and potassium compounds that deposited downstream of the electrostatic precipitator on Unit 1. This indicates that the electrostatic precipitator will not remove all .of

..the submicron sodium particles that are generated by the combustion of Center lignite. Given the high expected emission rate of sodium compounds (see Table 3), it appears a significant amount of sodium compounds, a catalyst poison, will enter a low dust or tail gas SCR system.
The deactivation issue for low-dust and tail-gas SCR remains as with the high-dust· SCR. The research, design and pilot testing needed to develop an SCR system that will have reasonable success makes this technology also not applicable at this time.
Site Constraints:
The NSR Manual 1 states: -Also a showing of unresolvable technical difficulty with applying the control would constitute a showing of technical infeasibility (e.g. size of the unit, location of the proposed site, and operating problems related to specific circumstances of the source). Where the resolution of technical difficulties is a matter of cost, the applicant should consider the technology feasible."
Minnkota has not indicated that the site constraints ,are unresolvable. Therefore, this issue appears to be an economic consideration instead of a technical feasibility issue.

56Tabl.e 3 HJ:STORICAL COAL EMJ:SS:ION RATE COMPAIUSON
CBN'rBR TEXAS WYOK[NG PO PA L1:GRJ:o;rB a L1:GH1:TE b SUBBIT'CKtI!lOUS b BX'l'maNOUS b Na20 (!$ of Ash) 4.4 0.5 1.6 0.3 CaO l!fi of Ash) 13.2 13.2 17.3 1.7 MgO (% of ash) 4.0 2.3 3.B 0.6 K

2 0 ('is of Ash) 1.3 0.5 0.5 1.9**~a20+CaO+MgO+K20** (% of Ash) 22.9 16.5 23.2 4.5
Ash Content 9.6 12.6 5.0 13.0 Heat Value (10' Btu/ton) 13.2 15.2 17.0 25.5
PM Emission Factor (lb/ton/1% Ash) 0'.4 Cyclone Boiler 9.4 6.7 2.0 2.0 Wall/Tangentially-fired Boiler (Pulverized) 5.8 5.B 10.0 10.0 PM Emissions (lb/10' Btu) Cyclone Boiler 6.84 5.55 0.59 1.02 Wall/Tangentially-fired Boiler (Pulverized) 4.22 4.81 2.94 5.10 Na20 Cyclone Boiler Emissions lb/ton 3.97 0.42 0.16 O.OB Ib/10' Btu 0.3008 0.0278 0.0094 0.0031 lb/dscf 3.05078-05 2.8164E-06 9.·62358-07 3.1276E-07 lb/wscf 2.5172E-05 2.3238E-06 8.8456E-07 2.8748E-07 Na20+CaO+MgO+K20 Cyclone Boiler Emissions lb/ton 20.66 13 .93 2.32 1.17 lb/10' Btu 1.5655 0.92 0.14 0.05 Ib/dscf 1.5878E-04 9.2941E-05 1.39548-05 4. 6914E-06 Ib/wscf 1.31018-04 7.6686E-05 1.28268-05 4.31238-06

21Table 3 Continued
CENTER 'l'BXAS WYOmNG PRB PA LIG!lJ:I'l'E • L:EGNJ:'l'B 1> SUBB:t'.rtJKINOUS I> BI'l'tJM:tNOUS b Ratio of ND Lignite Cyclone Emissions to Other Cyclones Na2 0 lb/ton 9.4 24.8 50.9 Ib/10' Btu 10.8 32.0 98.3 Ib/dscf 10.8 31.7 97.5 Ib/wscf 10.8 28.5 87.6 Na20+CaO+MgO+K20 Ib/ton 1.5 8.9 17.7 1b/10' Btu 1.7 11.5 34.1 lb/dscf 1.7 11.4 33.8 Ib/wsc,f 1.7 10.2 30.4 Comparison of ND Lignite Cyclone to Pulverized Units Na20 Emissions 1b/ton 3.97 0.37 0.80 0.39 1b/10' Btu 0.3008 0.0240 0.0471 0.0153 Ib/dscf 3.0507E-05 2.4381E-06 4. 8117E-06 1.5638E-OG Ib/wscf 2.5172E-05 2.0117E-06 4.4228E-06 1. 4374E-06 Na2 0+CaO+MgO+K2 0 Emissions 1b/ton 20.66 12.06 11.60 5.85 Ib/lO' Btu 1.5655 0.7933 0.6824 0.2294 Ib/dscf 1.5878E-04 8.0457E-05 6.9770E-05 2.3457E-05 lb/wscf 1.3101E-04 6.63B5E-OS 6.41309E-05 2.15613E-05 Ratio of ND Lignite Cyclone Emissions to Pulverized Units Na.20 Ib/ton 10.9 5.0 10.2 Ib/lO' Btu 12.5 6.4 19.7 Ib/dscf 12.5 G.3 19.5 lb/wscf 12.5 5.7 17.5

22**Tabl~** 3 Continued
OH'l'U 'l'BXAS WYOKERG PRB PA L:tGNJ:'.rB a LZGNZ'l'B » SUBBZ'l'OIaNOtrS » BZ'1'OMJ:HOtJS » Na20+CaO+MgO+K20 Ib/ton 1.7 1.8 3.5 Ib/lO' Btu 2.0 2.3 6.8 Ib/dscf 2.0 2.3 6.8 Ib/wscf 2.0 2.0 6.1

• Information from Minnkota's April 16, 2007 submittal.
b Data from the USGS National Coal Database and university of Wyoming.

c From AP-42, Compilation of Air Pollutant Emission Factors except for Minnkota whiCh is based on actual stack testing.

Emission factor for tangentially and wall-fired units burning lignite is the average of the AP-42 emission factors.

23

# Minnkota Power**~PCl** 

### COOPERATIVE, INC.
1822 Mill Road, P.O. Box 1320"0 • Grand Forks. NO 58208-3200 • Phone (701) 795·40DO**~ovember** 

### 9, 2007

Mr. Terry O'Clair Director, Division of Air Quality North Dakota Department of Health 918 East Divide Avenue, 

### 2nd 

### Floor Bismarck, 

### NO 58501-1947

Subject: Response to EPA's October 4,2007 Letter

Dear Mr. O'Clair: YourTouchstone Energy- Partner 

# -

Enclosed,**~ease** 

### find Minnkota's comments in response to EPA's letter dated October 

### 4, 2007. Should you have any questions concerning our comments, please contact me at 701-7954221.

.

# -M~~I'-~ John T. Graves, P.E. Environmental Manager
C: David Sogard 

### wlo enel Luther Kvernen 

### wlo encl

. ·Craig Bleth 

### wlencl

Kevin Thomas 

### wlo encl Stu Libby 

### wlo encl Tom Anseth 

### wlo encl Young Station File 

### w/enclVariations in the coal delivered andburned at MRYS have posed difficulties in maintaining consistent combustion and slag-formation and tapping conditions in the cyclones and lower furnaces ofthe boilers. Low 

### HIA ratio correlates to undesirable cyclone operation. High viscosity ash, related to low BIA ratio, causes more incompletely burned coal and ash particles tobe exhausted from the cyclone, which increases the amount offlyash that can create sJagging and fouling problems in the furnace 

### and convection passes ofthe boiler. This causes furnace exit gas temperatures to increase, requiring more aggressive heat transfer surface cleaning, which**me~ns** higher gas temperatures with more ash and deposit**frag~ents** are exhausted from the boilert' which are problematic for potential blinding, deactivation, and longevity ofthe SCR catalyst.

"Core" Issue number 2 

### Catalyst deactivation by sodium and regeneration difficulties: ERG memorandum to EPA, August 20, 2007, page 3 Original Reference: EPA Region 8 January 26,2007 letter to NDDH request item number I: [Comments regarding Khodayari's workon SCR catalystdeactivation andregeneration due topoisoning by sodium andpotassium] [ERGAugust20,2007memo, page 3] EERC Response: Christman appears to ignore key statements made by Khodayari in his thesis and other publications. The following is a quote from the abstract ofhis PhD thesis23:
"Potassium and sodium were found to be two ofthe worst poisons that had significant effects on· the activity ofthe SCR catalyst due to their selective chemisorption on the BrlZlnsted acid sites." [Comments regarding Beck's work on contributions of phosphorus, potassium and sodium]. "His'subsequent workfocusedonphosphorus anddidnotaddress sodiumat all." [ERG August20, 2007memo, pa8.e 3] EERC Response: Beck and others focused on phosphorus because it was at a higher concentration than sodium in the materials he was investigating.

23 See Reference number 10.
1119/2007 A-4••• II University ofUtah andREIon application of SCR to low-rank coals

...butmasking by jlyash is aproblem. The study further concludedthat thepoisoningpotential ofthe alkali materials rankedas: K>Na> Ca. " [ERGAugust20,2007memo., page 3] EERC Response: The University ofUtah studies did not considerhigh sodium coals in their testing. They examined lower sodium coals. We agree with the assessment that masking is aproblem

.



### .. Cltristman brings up an important pointregarding the impacts ofpotassium on catalyst deactivation, but ignores its presence in lignite coals. Potassium can be as high as 2.3% in

.Center lignite. Potassium, like sodium, is prone to vaporIze in combustion systems and condense to form small particles upon gas cooling.


# ----v Work was conducted at MRY Unit 1 to examine accumulations ofsticky ash at**300~F** downstream ofthe ESP. Figure 

### 1 shows a polished cross-section ofa deposit that has formed
on a silicon dioxide suiface when exposed to flue gas derived from the combustion ofCenter lignite. The red line shows the path ofa line scan where the composition was determined using x-ray microanalysis. Figure 1 also shows the change In chemical composition along the red

. . line beginning at the outside and moving to the silicon dioxide for selected components. The results show levels**ofpotassiu~** (K) as high as 17% and sodium (Na) as high as 16% in the line scan. The matenal.is highly sulfated as indicated by the high levels ofsulfur (S). The deposit shown in Figure 1 formed at about 300oP. In addition. potassium-rich materials were found in deposits plugging SCR catalysts at the Coyote Station as shown in Figure 2 and Table 1. Levels ofpotassium ranging from 2 to 8 elemental 

### wt% were observed.

11/912007 A-5**~'I-\-:-t-ft--+f-+--t---** ._- --" 

# I·

.**----~-** 

# ---!-------·---1-
+--.+--+-t---+--+---f--+-+---I-----l--_!_--+--+---I-l!'--_!_

- -. Na
- -51 -$

_ .. -K -Ca '-Fe

10.0 15.0 20,0 25.0 LOCATION (urn) 

### Figure 1. Cross-section ofasurface exposed to flue gas at about 3000 

### Fin MRY Unit 1.



### Figure 2. Ash accumulations in pores ofSCR catalyst exposed to Coyote flue gases for4 months.

111912007 A-6**)~f** ... ·l .'



### 2 . F' T bl 1 

### Ch • I A I . f 

### SIt d P

. 15 

### Sb



### a e 

# . emlca· nalYSIS 0 eec e om OWDm 

### tgure 

# . Point Locations, Elemental Wt 

## %

. Point 

### 1 Point 2' Point 3 Point 4 Point 5 

### Element

Na 5.09 1.88 0.58 2.68 2.04 Mg 2,49 0.88 4.23 4.38 1.39

.. 

### AJ 2.23 3.95 1.50 0.80 1.55 Si 4.86 1.79 4.67 .5.82 4.42 P 0.00 0,85 0.06 0.10 0.00 S 32.51 29.43 31.35 30.33 27.55 CI 0.00 0.00 0.22 0.33 0.15 K 6.64 2.54 8.74 7.85 4.64 Ca 16.08 29.69 19,42 16.91 25.20 Ti 0.00 0.11 0.64 0.16 6.02 Cr 0.00 0.00 0.00 0.00 0.00 

### Fe 7.76 7.52 0.00 3.44 7.37 

### Ba 4.99 0.00 '5.34 6.00 3.19 

### 0 17.35 21.37 23.25· 21.20 16.49 TOTAL 100.00 100.00 100.00 100.00 100.00

# :':·~/ 

# .

.

### , .

.

# .

"While Dr. Benson concludes that the sodium levels in North Dakota Lignite ash are so high

.. .others atEERCdo notshare that opinion

... " [ERGAugust20, 2007memo, page 3

### J EERC Response: The cited work conducted by Folkedahl (2006) "Yas on a stoker-fired system and does not represent the partitioning that occu,rs in a cyclone orpulverized coal-fired system. They had significant problems during the testing because large pieces ofunburned biomass kept plugging the inlet to the slipstream**syst~m.** Christman ignores work conducted by the EPA. Mussatti (2002) indicated in the "EPA Air Pollution Control Cost Manual

- Sixth Edition" the following primary mechanisms for catalyst deactivation: "Poisoning

- Certain fuel constituents which are released during combustion act ascatalyst poisons. Catalyst poisons include 

### calcium oxide and'magnesium oxide, potassium, 

### sodium. arsenic, chlorine. fluorine. and lead. These constituents deactivate the catalyst by diffusing into active pore sites and occupying themirreversibly. Catalyst poisoning represents the main cause ofcatalyst deactivation."

11/9/2007 A-7

# --? B. Low-Dust SCR 

### 1. EPA Analysis ofthe CatalystFouling and Deactivation Issue:

EPA October**4~** 2007 letterEnclosure, page 32 Original Reference: EPA Region 8 January 8. 2007 letter to NDDH:

"

.. .general qualitative statements that the sodium-rich aerosols will cause blinding and deactivation do notnecessarily support the conclusion thata·low-dustSCR system would be technically infeasible atMRYS.The.effects of this blinding anddeactivation should eitherbe quantified. and used within. the economic analysis understep 4 of the Top-Down BACTanalysis, ordescribed in sufficientdetail to demonstrate that theproblems associatedwith catalystblinding-anddeactivation are unsolvable and would result in the unsuccessful operation of a low-dustSCR. As stated onpage B.20of the NSR Workshop Manual, U(p)hysical modificationsneededto resolve technical obstacles do not in andof themselvesprovide ajustificationfor eliminating the control technique On the basis of technical infeasibility. However, the costof such modifications can be consideredin estimating costandeconomic impacts." [EPA October

### 4, 2007letterEnclosure, pages 32- 33J B&McD Response: As EERC has described previously and elsewhere in this document, effective solutions to prevent or removemicropore pluggage and blinding ofSCR catalyst from sodium-sulfur compounds evident in the flue gas stream exhausted from a North Dakota lignite-fired boiler, whether installed in a conventional hot-side 

### orcold-side application downstream ofa wet. scrubber, have not been developed by $CR catalyst vendors. Bums 

### & McDonnell previously discussed the estimated energy**requirement~** for reheating flue gas upstream ofa low-dust and**t~l-end** SCR in the October 2006 NOx BACT analysis and March 2007 response letters. Propane orfuel oil will certainly be more expensive to supply than pipeline natural gas, because ofthe additional over-the-road transportation requirements. These alternate fuels do nothing to address the fundamental issues ofthe composition ofthe flue gus and flyash being unsuitable for low-dust SCR applications. We believe these are credible arguments that adequately describe the reasons that preclude the successful deployment ofthis technology on the cyclone boilers at MRYS.



### 2. EPA Analysis ofthe Site Space ConStraintIssue:

EPA October4, 2007 letterEnclosure, page 33 Original Reference: EPA Region 8 January 8, 2007 letter to NDDH:

1119/2007 A-28" 

### ,. I' 'J



# ..

# ~/ "EPA acknowledges that extensive work may be required for installation of low-dust SCR

...basedon reasonable expected reheat fuel requirements, equipment installations, plant modifications

.... " [EPA October

### 4, 2007letterEnclosure, pages 33-34]

. B.&McD Response:

Burns & McDonnell believes it is appropriate to considerSCR technology for the cyclone boilers at MRYS to be technically infe.asible**an~thus** eliminated it during the Top-Down BACT analysis prior to the economic analysis step. The,extensive'plant modifications anticipated to deploy SCRat Dnit 1 and Unit 2 at MRYS still do not resolve the catalyst micropore plugging and blinding problems evident in the Coyote Station pilot-scale testing.



### 3. EPA Analysis ofthe Burns & 

### McDonnell's Conclusion:

EPA October4, 

### 2007 letterEnclosure, page 

### 34 Original Reference: EPA Region 8 January 8, 

### 2007 letter to NDDH: "B&McD appears to be saying thata significantportion of the sodium in the

### fly ash is in the vaporphase when it enters the ESP." [EPA October

### 4, 2007letterEnclosure, page 34]

. EERC Response:

EPA misinterpreted B&McD and EERC's response. B&McD and EERe do not suggest in any ofthe documentation that sodium is in the vaporphase at the temperatures ofthe SCR. Initially in cyclone-fired systems much ofthe sodium is vaporized. Vaporized sodium will condense upon gas cool,in.g heterogeneously on entrained particles Orhomogeneously to form aerosols. The condensed material 

### will react with othergas phase materials such as 

### S02 and S03 to form sulfates. There is**eVide~ce** ofsodium, potassium, calcium, and sulfur**depositiO~** • downstream ofthe ESP as illustrated in Figure 1 presented in response to ERG Core Issue number2.



### III. Additional Information Useful to Evaluating Technical Feasibility ofSCR at MRYS A. EPA Headquarters Believes SCR is the CorrectTechnology**~or** 

### MRYS in Developing the Clean Air Interstate Rule EPA October4, 

### 2007 letterEnclosure, page 36 Original Reference: EPA Region 8 January 

### 8,2007 letter to NDDH:

"

...EPA's discussion with Flemming Hansen ofNaldor Topsoe also revealed thatdespite. the concerns aboutan SCR system subjected to the sodium environment

... HaldorTopsoe wouldnot rule outbidding such aproject. "**{~PA** October

### 4, 2007letterEnclosure, page 

# 3n '

11/9/2007 A-29