Appendix A. NPS Comments on Milton R. Young Station (MRYS) Baseline 

Emissions 

Minnkota p4-3: 4.1 RANK OF NOX CONTROL OPTIONS BY EFFECTIVENESS 

The first step in this supplemental “top-down” BACT evaluation is to determine the 

expected control effectiveness of the hypothetical application of tail end and low-dust 

SCR technology alternatives, so that they may be compared and ranked relative to the 

technically-feasible NOX control techniques and technologies included from the initial 

NOX BACT Analysis Study report. To do this, we start with the basis for determining the 

NOX emissions control effectiveness, which is the historic baseline emissions expressed 

in pounds per million Btu of heat input from the five-year lookback period. 

NPS: Use of historic baseline emissions is permissible only if they are documented and 

do not determine the outcome of the analysis/or constraints are enforceable, and provided 

that the cost-effectiveness is compared to similar sources using similar approaches. 

According to the NSR Workshop Manual [emphasis added]: 

“...baseline emissions are essentially uncontrolled emissions, calculated using realistic 

upper boundary operating assumptions.” 

“...in developing a realistic upper boundary case, baseline emissions calculations can also 

consider inherent physical or operational constraints on the source. 

Such constraints should accurately reflect the true upper boundary of the source's ability to 

physically operate and the applicant should submit documentation to verify these 

constraints. If the applicant does not adequately verify these constraints, then the 

reviewing agency should not be compelled to consider these constraints in calculating 

baseline emissions. In addition, the reviewing agency may require the applicant to 

calculate cost effectiveness based on values exceeding the upper boundary assumptions to 

determine whether or not the assumptions have a deciding role in the BACT determination. 

If the assumptions have a deciding role in the BACT determination, the reviewing 

agency should include enforceable conditions in the permit to assure that the upper 

bound assumptions are not exceeded.

In addition, historic upper bound operating data, typical for the source or industry, may be 

used in defining baseline emissions in evaluating the cost effectiveness of a control option 

for a specific source. For example, if for a source or industry, historical upper bound 

operations call for two shifts a day, it is not necessary to assume full time (8760 hours) 

operation on an annual basis in calculating baseline emissions. For comparing cost 

effectiveness, the same realistic upper boundary assumptions must, however, be used for 

both the source in question and other sources (or source categories) that will later be 

compared during the BACT analysis.” 
MRYS #1 Baseline Emissions 

Minnkota p4-4: Unit 1 boiler’s baseline pre-control emissions at Milton R. Young 

Station are based upon the same highest rolling 12-month average unit emission rate 

(lb/mmBtu) and corresponding highest rolling 12- month average gross heat input rate 

(mmBtu/hr) that were reported in 2001-2005: 

• MRYS Unit 1’s highest 12-month NOX mass emissions averaged 0.849 lb/mmBtu 

at a corresponding average unit heat input rate of 2,744 mmBtu/hr and unit gross 

electrical output of 244.5 MWg. 

• During this lookback time period, Unit 1 at Milton R. Young Station was typically 

operated in a base-loaded manner. 

NPS: MRYS #1’s highest annual NOX mass emissions averaged 0.866 lb/mmBtu in 

1995 and 0.843 in 2004. MRYS #1’s highest annual average unit heat input rate of 2,761 

mmBtu/hr occurred in 2003. MRYS #1’s highest annual availability of 97% occurred in 

2001 and again in 2004. 

In its 2009 BART determination, NDDH stated that MRYS #1 had a Boiler Rating of 

3,200 x 106

 Btu/hr, with 2000 – 2004 NOx emissions averaging 8,665 tons/year (tpy) and 

0.81 lb/mmBtu. NDDH used a baseline emission rate of 9,032 tpy. The subsequent 

NDDH BART permit again stated the rated capacity as 3,200 mmBtu/hr and limited 

NOx emissions to 0.36 lb/mmBtu on a 30-day rolling average; there were no limits on 

annual emissions. 

In its 2010 BACT determination, NDDH stated that MRYS Unit 1 had a heat input of 

2,728 mmBtu/hr and 2003 – 2007 NOx emissions averaging 9,081 tpy and 0.840 

lb/mmBtu. NDDH calculated a maximum emission rate of 9,676 tpy and used a baseline 

emission rate of 9,934 tpy. ASOFA would achieve 0.513 lb/mmBtu. 

According to Tom Bachmann of NDDH (4/26/10 e-mail), “the Title V Permit to 

Operate limits NOx emission from Unit 1 to 2752 lb/hr... This effectively caps 

annual emissions...” to 12,054, tpy at 8760 hr/yr operation which is equivalent to 0.86 

lb/mmBtu @ 3,200 mmBtu/hr @ 100% utilization. It is clear that NDDH is using 3,200 

mmBtu/hr heat input, 100% utilization, and 0.86 lb/mmBtu in conducting its BART 

analyses and developing its Title V permit. 

2
In the absence additional constraints, baseline emissions for the purpose of 

evaluating the cost-effectiveness of additional NOx controls should be estimated at 

0.86 lb/mmBtu and SCR cost-effectiveness should be assumed at 0.513 lb/mmBtu @ 

3,200 mmBtu/hr with 100% capacity utilization.1

 This yields a baseline NOx

emission rate of 12,054 tpy for the uncontrolled situation and 7,190 tpy for the 

emissions into the SCR. 

MRYS #2 Baseline Emissions 

Minnkota p4-4: Unit 2 boiler’s baseline pre-control emissions at Milton R. Young 

Station are based upon the same highest rolling 12-month average unit emission rate 

(lb/mmBtu) and corresponding highest rolling 12- month average gross heat input rate 

(mmBtu/hr) that were reported in 2001-2005: 

• MRYS Unit 2’s highest 12-month NOX mass emissions averaged 0.786 lb/mmBtu at a 

corresponding average unit heat input rate of 4,885 mmBtu/hr and unit gross electrical 

output of 440 MW. 

• During this lookback time period, Unit 2 at Milton R. Young Station was typically 

operated in a base-loaded manner. 

NPS: MRYS #2’s highest annual NOX mass emissions averaged 0.856 lb/mmBtu in 

2007. MRYS #2’s highest annual average unit heat input rate of 5,230 mmBtu/hr 

occurred in 1997. MRYS #2’s highest annual availability of 95% occurred in 2000 and 

again in 2008. 

In its 2009 BART determination, NDDH stated that MRYS #2 had a Boiler Rating of 

6,300 x 106

 Btu/hr, with 2000 – 2004 NOx emissions averaging 14,705 tons/year and 

0.81 lb/mmBtu. NDDH used a baseline emission rate of 15,507 tpy. The subsequent 

NDDH BART permit again stated the rated capacity as 6,300 mmBtu/hr and limited 

NOx emissions to 0.35 lb/mmBtu (excluding startup) on a 30-day rolling average; there 

were no limits on annual emissions. 

In its 2010 BACT determination, NDDH stated that MRYS #2 had a heat input of 4,691 

mmBtu/hr and 2003 – 2007 NOx emissions averaging 14,858 tons/year and 0.835 

lb/mmBtu. NDDH calculated a maximum emission rate of 15,818 tpy and used a baseline 

emission rate of 15,793 tpy. ASOFA would achieve 0.489 lb/mmBtu. 

 

1

 According to the NSR Workshop Manual, “For comparing cost effectiveness, the same realistic upper 

boundary assumptions must, however, be used for both the source in question and other sources (or source 

categories) that will later be compared during the BACT analysis.” In its Table 8, NDDH has used costeffectiveness data from permits issued by Wyoming to Basin Electric for its Dry Fork PC boiler and to Black 

Hills Power for its Wygen 3 PC boiler. Because both of those cost-effectiveness analyses were based upon 

100% utilization of the PC boilers, NDDH must use the same 100% capacity utilization for comparison to MR 

Young. (At 97% availability, the historic maximum availability for MRYS #1, the baseline NOx emission 

rates would be 11,704 tpy for the uncontrolled situation and 6,982 tpy for the emissions into the SCR.) 

3
4

 

According to Tom Bachmann of NDDH (4/26/10 e-mail), “the Title V Permit to 

Operate limits NOx emission...to...5418 lb/hr from Unit 2. This effectively caps 

annual emissions...” to 23,731, tpy at 8760 hr/yr operation which is equivalent to 0.86 

lb/mmBtu @ 6,300 mmBtu/hr @ 100% utilization. It is clear that NDDH is using 6,300 

mmBtu/hr heat input, 100% utilization, and 0.86 lb/mmBtu in conducting its BART 

analyses and developing its Title V permit. 

In the absence additional constraints, baseline emissions for the purpose of 

evaluating the cost-effectiveness of additional NOx controls should be estimated at 

0.86/b/mmBtu and SCR cost-effectiveness should be assumed at 0.489 lb/mmBtu @ 

6,300 mmBtu/hr with 100% capacity utilization.2

 This yields a baseline NOx

emission rate of 23,731 tpy for the uncontrolled situation and 13,493 tpy for the 

emissions into the SCR. 

2

 At 95% availability, the historic maximum availability for MRYS #2, the baseline NOx emission rates 

would be 22,652 tpy for the uncontrolled situation and 12,880 tpy for the emissions into the SCR.)