Assessment Process

Indiana-Kentucky Electric Corporation

Clifty Creek Station

Evaluation for 720 Operating Hour Site Rolling Average SO2 Mass Emissions Limits Using Flue Gas 

Desulfurization (FGD)

Step 1: Facility Description and Modeled Limits

The Indiana-Kentucky Electric Corporation’s (IKEC’s) Clifty Creek Station has six coal-fired electric 

generating units (Units 1 through 6) that were placed into commercial operation in 1955 and 1956. All 

six units have pulverized-coal, front-wall-fired, wet-bottom boilers and a nameplate generating capacity 

of approximately 217 megawatts.

Prior to being exhausted to the atmosphere, the flue gases from Units 1, 2, and 3 are combined and 

scrubbed for SO2 removal in a jet-bubbling reactor (JBR) scrubber. The scrubber for Units 1, 2 and 3 is 

referred to as JBR13, and the combined scrubbed flue gases from these three units is exhausted through 

Common Stack CS013 (also known as Flue 13). The flue gases from Units 4, 5, and 6 are combined and 

scrubbed in JBR46 prior to being exhausted through Common Stack CS046 (also known as Flue 46). The 

two flues associated with each scrubber are contained in one stack shell (Stack 14), and the emissions 

from each flue are represented of the combined scrubbed emissions from all six units. The scrubbers 

were designed to allow the Clifty Creek Station to use local Illinois Basin coal with sulfur content in the 5 

lb per mmBtu range.

For modeling purposes, IKEC identified an appropriate mass emissions limit as a site average for the 

Clifty Creek Generating Station that smodels attainment of the 2010 1-hour primary NAAQS for SO2.

Per the request of IKEC), Mr. Dave Long - at American Electric Power (AEP) performed modeling using 

the representative Clifty Creek Station post scrubber emissions data supplied to him by OVEC. Based on 

numerous modeling runs, Mr. Long determined that an emission value of 2,624.6 lbs/hour as a SITE

average emissions rate as averaged over a 30 day period will assist the Indiana Department of 

Environmental Management (IDEM) in complying with the 2010 SO2 NAAQS. 

Step 2: Compile Representative Emissions Data Set

Data was obtained for hourly SO2 mass emissions (lbs/hour) for each stack at the Clifty Creek Station 

from June 1, 2013 00:00 hour through December 31, 2015 23:00 hour. This starting date was chosen 

based upon the startup dates for each of the two JBR scrubbers that were placed into service at the 

Clifty Creek Station in 2013 (CS013: 3/20/2013, CS046: 5/15/2013). Since a site limit was developed for 

the entire Clifty Creek Generating Station, the following criteria were used to “clean up” the data set:

1. At least one unit on each stack had to be operating. Periods when only one single stack was in 

operation was discarded.

2. The data from each stack was obtained using either the primary or backup certified SO2 

monitoring system. Hours when either stack had data generated using the missing data 

algorithm was discarded.

3. Two data sets were generated. One data set included all data meeting criteria 1 & 2 from June 1, 

2013 00:00 hour through December 31, 2015 23:00 hour. The second data set included data 
meeting criteria 1 & 2, but only for the years 2014 and 2015, which IKEC believes is more 

representative based on fuel source and operational mode. The coal blend consumed in 2013 

included a significant proportion of residual Powder River Basin coal, which is no longer 

consumed at the Clifty Creek Generating Station. This fuels source was still being consumed 

during 2013 due to contractual obligations in place prior to the commencement of scrubber 

operation. Utilization of the data from this time period could result in a low biasing of SO2 

emissions, which would not have been representative of future operations, nor of the design 

criteria for scrubbers themselves. The data for 2014 & 2015 was not impacted to a significant 

degree by any PRB fuel blending and therefore is more representative of expected longer term 

fuel source and future operations.

Step 3: Calculate 720 Operating Hour Site Rolling Average

After summing the hourly mass emissions for SO2 from each stack, this data was then used to calculate a 

720 Operating Hour Site Rolling Average mass emission value for each hour in the data collection period. 

The “cleaned up” data set resulted in a 720 Operating Hour Site Rolling Average that did not include 

hours where valid data was not available from both stacks and did not include hours where only one 

stack was operating. It should be noted that there are no values calculated for the first 720 hours of the 

data set.

Step 4: Calculate the 99th Percentile Values

The 99th percentile values were calculated for the 1-hour site emissions data set and the 720 Operating 

Hour Site Rolling Average. The Site 1 Hour Data set the 99th Percentile value was determined to be 2,394 

lbs/hour. The 720 Operating Hour Site Rolling Average data set the 99th Percentile Value was 

determined to be 1,346 lbs/hour.

Step 5: Calculate the Ration of the 99th Percentile Values

Dividing the 99th percentile value of the 720 Operating Hour Site Rolling Average by the 99th percentile 

value for the Site 1-Hour Data yields a quotient of 56.2%.

1,346 lbs/hour / 2,394 lbs/hour *100%= 56.2%

Discussion

The attached graph shows the 720 Operating Hour Site Rolling Average and the 2,624.5 lbs/hour 

modeled value trended alongside the 99th percentile value for this particular data set. 

IKEC proposes that the value of 2,624.5 pounds per hour (2,624.5 lb/hr) Site Average mass SO2 emission 

rate be utilized for the IDEM Commissioner’s Order. This compliance value would be an unweighted 

average calculated by IKEC using data collected by existing certified CEMS. Data used for determining 

this compliance value will be unbiased data. Additionally, data generated the using Part 75 Missing Data 

Algorithms will not be used to determine compliance. This is analogous to the manner in which data is 

handled under the existing Part 60 and MATS programs, which are utilized by IKEC for Title V and MATS 

compliance demonstration. The hourly data should be calculated as a 720 operating hour site rolling 

average. IKEC also believes the Commissioner’s Order should state that IKEC is not out of compliance 

during periods where the certified CEMS is not producing valid data for both stacks if the scrubber 

parametric data remains within the limits listed below:
Normal operation of either JBR reactors shall be deemed to be 

(a) Slurry level at or between the range of 19.33 to 21.06 feet, and;

(b) Slurry pH at or between 4.0 S.U. to 6.5 S.U.
0

1000

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7000

8000

9000

10000

Hourly Site SO2 Mass Emissions(pounds) from January 1, 2014 through December 31, 2015

Sum of Plant

SO2 lbs/hr

Emissions

99th Percentile

Value of Hourly

Data

Proposed Limit

5,000 lbs/hr

Figure 4

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24 Hour Rolling Average SO2 Mass Emissions(pounds) from January 1, 2014 through December 31, 2015

24  Hour

Rolling Average

99th Percentile

Value of 24

Hour Rolling

Average Data

Figure 5

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1000

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720 Hour Rolling Average SO2 Mass Emissions(pounds) from January 1, 2014 through December 31, 2015

720 Hour

Rolling Average

99th Percentile

Value of 720

Hour Rolling

Average Data

Figure 6
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2000

4000

6000

8000

10000

12000

14000

16000

Hourly Site SO2 Mass Emissions (pounds) from June 1, 2013 through December 31, 2015

Sum of

Plant SO2

lbs/hr

Emissions

99th

Percentile

Value of

Hourly Data

Figure 1

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1000.0

2000.0

3000.0

4000.0

5000.0

6000.0

7000.0

8000.0

24 Hour Rolling Average SO2 Mass Emissions (pounds) from June 1, 2013 through December 31, 2015

24  Hour Rolling

Average

99th Percentile Value

of 24 Hour Rolling

Average Data

Figure 2

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

1400.0

1600.0

720 Hour Rolling Average SO2 Mass Emissions (pounds) from June 1, 2013 through December 31, 2015

720 Hour Rolling

Average

99th Percentile Value

of 720 Hour Rolling

Average Data

Figure 3