AEP Flint Creek draft BART analysis - EPA R6 comments

Dayana Medina to: pettyjohn 11/01/2012 10:36 AM

Cc:

mac, rheaume, "Brown, Derrick", Spencer, Stuart, Stuart, "Davis, 

Anthony", Guy Donaldson, Michael Feldman, Joe Kordzi, Barbara 

Nann

From: Dayana Medina/R6/USEPA/US

To: pettyjohn@adeq.state.ar.us

Cc: mac@adeq.state.ar.us, rheaume@adeq.state.ar.us, "Brown, Derrick" 

<brownd@adeq.state.ar.us>, Spencer, Stuart <SPENCER@adeq.state.ar.us>, Stuart 

<SPENCER@adeq.state.ar.us>, "Davis, Anthony" <DavisA@adeq.state.ar.us>, Guy 

Hi Mary, 

Here are Region 6's comments on the AEP Flint Creek draft BART analysis. We appreciate the 

opportunity to comment during the BART evaluation process. Our comments below are provided in the 

hope that the SIP revision provided by the State of Arkansas will be fully documented and approvable. We 

appreciate Arkansas' attention to these concerns. Please don't hesitate to call me or Guy Donaldson if 

you have any questions. 

1. Appendix Y to Part 51 provides that if a source commits to a BART determination that consists of the 

most stringent controls available, then there is no need to complete the remaining steps in the BART 

analysis. This is assuming that the most stringent level of control is selected as BART. Although we 

agree that wet scrubbers and NID systems are the two most effective technologies for control of SO2 

emissions, it is not clear that 95% is the most stringent level of control achievable by these two 

technologies. Wet scrubbers have been demonstrated to achieve up to 98% control efficiency. In 

Appendix C of the TSD for our Oklahoma BART FIP, we explained that wet scrubbers on units 

burning low sulfur coal can achieve 97% - 98% removal efficiency or an outlet SO2 of 0.04 lb/MMBtu. 

CEMS data shows that this level of performance has been demonstrated by wet scrubbers at EGUs 

of comparable size to the AEP Flint Creek unit and burning low sulfur coal such as that burned at this 

unit. Furthermore, AEP states in the revised BART analysis that NID technology is capable of 

achieving up to 95% control efficiency. However, Alstom states its NID system is capable of achieving 

up to 98% removal efficiency, which is considerably higher than the control level that AEP’s proposed 

SO2 emission limit of 0.06 lb/MMBtu corresponds to. If the reason why AEP did not consider a lower 

SO2 emission limit for the NID system is because it was not able to get a vendor guarantee for a 

lower emission limit, then proper documentation of this should be provided in the analysis. If AEP Flint 

Creek is not able to document the highest level of control available for SO2 BART is being utilized, the 

remaining steps of the BART analysis must be completed for the wet scrubber option. We note that in 

our Oklahoma BART FIP, we analyzed wet scrubbers at 0.04 lb/MMbtu and ultimately determined that 

the additional cost of wet scrubbers was not justified when compared to the cost and visibility 

improvement due to dry scrubbers at 0.06 lb/MMBtu. 

2. As you may know, EPA filed a request for a re-hearing en banc on the CSAPR. As the outcome of this 

is as of yet uncertain, we only provide comment on the NOx BART analysis and determination but do 

not, at this time, provide comment on any reliance on CAIR or CSAPR for NOx BART. 

3. There appears to be an inconsistency in the calculation of emissions for visibility modeling which 

results in an under estimate of the visibility benefit anticipated by the controls. The modeled emission 

rate for the controlled case with NID is based on the anticipated emission rate and the maximum heat 

input. This represents a 92% reduction in emissions from the 4728.4 lb/hr SO2

 modeled in the 

baseline to 379.4 lb/hr modeled for the control case, rather than the 95% control efficiency estimated 

by AEP. The actual 24-hr maximum emission rate for the baseline corresponds to an emission rate of 

0.87 lb/MMBtu. Following the methodology outlined on page 5-6, this emission rate should be 

multiplied by the maximum boiler heat input to obtain a baseline emission rate for visibility modeling to 
be compared with the controlled cases. As explained above, the controlled case emission rate should

be based on the maximum anticipated control efficiency for that control technology. Similarly, the 

maximum 24-hr emission rate for NOx corresponds to an emission rate of 0.32 lb/MMBtu. We note a 

discrepancy in the calculation of NOx emissions for the SNCR case. The listed emission rate on page 

6-11 is 1777.74 lb/hr NOx, the modeled emission rate for SNCR was 1277.4 lb/hr for NOx (CALPUFF 

input files) and the calculated rate based on 0.21 lb/MMBtu and the maximum heat input (6324 

MMBtu/hr) is 1328 lb/hr.

4. The analysis notes that SCR is capable of 80-90% control and EPA analysis shows that NOx 

continuous emission monitor (CEM) data from the EPA Clean Air Markets Division (CAMD) 

demonstrate that SCR retrofits routinely result in 90% removal efficiency. However, the control 

efficiency of SCR examined in this analysis of 0.067 lb/MMbtu only represents an approximately 80% 

reduction from the baseline. For SNCR, there is limited explanation concerning the control 

effectiveness of SNCR and the selection of 10% reduction beyond combustion controls given the 

10-20% range for improvement over LNB/OFA and the range of achievable emission rates of 

0.18-0.23 cited in the analysis. Furthermore, the references cited for control efficiencies of SCR and 

SNCR date from 1994 and 2001 and may not be representative of the control efficiencies achievable 

with these technologies today. As discussed above with respect to SO2

 controls, proper 

documentation and thorough examination supporting all the NOx control efficiencies evaluated should 

be provided in the analysis.

 

5. AEP assumed a 15 year equipment life for the NID system in the cost analysis for SO2 BART and for 

SNCR in the cost analysis for NOx BART. Unless AEP provides proper documentation to 

demonstrate that the anticipated equipment life of the NID system is limited to 15 years, we believe 

that an anticipated 30 year equipment life would be more appropriate to use in the cost analysis. The 

OAQPS Control Cost Manual (CCM) assumes an economic lifetime of 20 years for an SNCR system. 

Therefore, unless AEP provides proper documentation to demonstrate that the anticipated equipment 

life is limited to 15 years, AEP should assume a 20 year equipment life for SNCR. Since the capital 

costs are annualized over a period of time equal to the anticipated equipment lifetime, and then added 

to the annual operating costs to obtain the total annualized costs, we believe that a NID system is 

actually more cost-effective than AEP’s estimate of $4288/ton SO2 removed and that a combination 

of LNB/OFA/SNCR is actually more cost-effective than AEP’s estimate of $3,391/ton NOx removed.

6. The cost analyses provided in Appendix A for the NID system, LNB/OFA, and SCR controls only 

provide Total Capital Investment (TCI) estimates. A breakdown of all the direct and indirect costs 

associated with purchasing and installing the equipment is needed to properly review the cost 

analysis and determine whether the analysis follows the OAQPS Control Cost Manual (CCM) and that 

the TCI estimates only include costs allowed by the CCM. 

7. AEP is proposing to use a NID system to satisfy SO2 BART, which will involve switching out the 

existing electrostatic precipitators (ESPs) and replacing with a baghouse. This will likely result in a 

higher PM removal efficiency than currently achieved by the existing ESPs. Although we approved 

ADEQ’s determination for PM BART for this unit in our March 12, 2012 final action on the Arkansas 

Regional Haze SIP (77 FR 14604), in light of the above, we encourage the source to consider 

re-evaluating the emission limit for PM. 

Thank you, 

Dayana Medina

U.S. Environmental Protection Agency, Region 6

Multimedia Planning and Permitting Division 

Air Planning Section (6PD-L)

1445 Ross Avenue
Dallas, TX 75202

214-665-7241

medina.dayana@epa.gov