(a) If you demonstrate continuous compliance using a CEMS for measuring NOX emissions, excess emissions are defined as the applicable compliance period for the stationary combustion turbine (either 4-operating-hours, 30-operating-days, or 12-calendar-month), during which the average NOX emissions from your affected facility measured by the CEMS is greater than the applicable maximum allowable NOX emissions standard specified in § 60.4320a as determined using the procedures specified in this section that apply to your stationary combustion turbine.

(b) The NOX CEMS data for each operating hour as measured according to the requirements in § 60.4345a must be used to determine the hourly average NOX emissions. The hourly average for a given operating hour is the average of all data points for the operating hour. However, for any periods during which the NOX, diluent, flow, watt, steam pressure, or steam temperature monitors (as applicable) are out-of-control, the data points are not used in determining the hourly average NOX emissions. All data points that are not collected during out-of-control periods must be used to determine the hourly average NOX emissions.

(c) For each operating hour in which an hourly average is obtained, the data acquisition and handling system must calculate and record the hourly average NOX emissions in units of lb/MMBtu or lbs, as applicable, using the appropriate equation from EPA Method 19 in appendix A-7 to this part. For any hour in which the hourly average O2 concentration exceeds 19.0 percent O2 (or the hourly average CO2 concentration is less than 1.0 percent CO2), a diluent cap value of 19.0 percent O2 or 1.0 percent CO2 (as applicable) may be used in the emission calculations.

(d) Data used to meet the requirements of this subpart shall not include substitute data values derived from the missing data procedures of part 75 of this chapter, nor shall the data be bias adjusted according to the procedures of part 75. For units complying with the 12-calendar-month mass-based standard, emissions for hours of missing data shall be estimated by using the average emissions rate of non-out-of-control hours within ±10 percent of the hour of missing data within the 12-calendar-month period. If non-out-of-control data is not available, the maximum hourly emissions rate during the 12-calendar-month period shall be used.

(e) All required fuel flow rate, steam flow rate, temperature, pressure, and megawatt data must be reduced to hourly averages. However, for any periods during which the flow, watt, steam pressure, or steam temperature monitors (as applicable) are out-of-control, the data points are not used in determining the appropriate hourly average value.

(f) Calculate the hourly average NOX emissions rate, in units of the emissions standard under § 60.4320a, using lb/MMBtu or ppm for units complying with the input-based standard, using lbs for units complying with the mass-based standard, or lb/MWh or kg/MWh for units complying with the output-based standard:

(1) The gross or net energy output is calculated as the sum of the total electrical and mechanical energy generated by the combustion turbine engine; the additional electrical or mechanical energy (if any) generated by the steam turbine following the heat recovery steam generating unit; the total useful thermal energy output that is not used to generate additional electricity or mechanical output, expressed in equivalent MWh, minus the auxiliary load as calculated using equations 1 and 2 to this paragraph (f)(1):

Equation 1 to Paragraph (f)(1) Where: P = Gross or net energy output of the stationary combustion turbine system in MWh; (Pe)t = Electrical or mechanical energy output of the combustion turbine engine in MWh; (Pe)c = Electrical or mechanical energy output (if any) of the steam turbine in MWh; PeA = Electric energy used for any auxiliary loads in MWh (only applicable to owners/operators electing to demonstrate compliance on a net output basis); Ps = Useful thermal energy of the steam, measured relative to ISO conditions, not used to generate additional electric or mechanical output, in MWh; Po = Other useful heat recovery, measured relative to ISO conditions, not used for steam generation or performance enhancement of the stationary combustion turbine; and T = Electric Transmission and Distribution Factor. Equal to 0.95 for CHP combustion turbine where at least 20.0 percent of the total gross useful energy output consists of electric or direct mechanical output and 20.0 percent of the total gross useful energy output consists of useful thermal output on an annual basis. Equal to 1.0 for all other combustion turbines. Equation 2 to Paragraph (f)(1) Where: Ps = Useful thermal energy of the steam, measured relative to ISO conditions, not used to generate additional electric or mechanical output, in MWh; Qm = Measured steam flow in lb; H = Enthalpy of the steam at measured temperature and pressure relative to ISO conditions, in Btu/lb; and 3.413 × 10 6 = Conversion factor from Btu to MWh.

(2) For mechanical drive applications complying with the output-based standard, use equation 3 to this paragraph (f)(2):

Equation 3 to Paragraph (f)(2) Where: E = NOX emissions rate in lb/MWh; (NOX)m = NOX emissions rate in lb/h; BL = Manufacturer's base load rating of turbine, in MW; and AL = Actual load as a percentage of the base load rating.

(g) For each stationary combustion turbine demonstrating compliance on a heat input-based emissions standard, excess NOX emissions are determined on a 4-operating-hour averaging period basis using the NOX CEMS data and procedures specified in paragraphs (g)(1) and (2) of this section as applicable to the NOX emissions standard in table 1 to this subpart.

(1) For each 4-operating-hour period, compute the 4-operating-hour rolling average NOX emissions as the heat input weighted average of the hourly average of NOX emissions for a given operating hour and the 3 operating hours preceding that operating hour using the applicable equation in paragraph (g)(2) of this section. Calculate a 4-operating-hour rolling average NOX emissions rate for any 4-operating-hour period when you have valid CEMS data for at least 3 of those hours (e.g., a valid 4-operating-hour rolling average NOX emissions rate cannot be calculated if 1 or more continuous monitors was out-of-control for the entire hour for more than 1 hour during the 4-operating-hour period).

(2) If you elect to comply with the applicable heat input-based emissions rate standard, calculate both the 4-operating-hour rolling average NOX emissions rate and the applicable 4-operating-hour rolling average NOX emissions standard, calculated using hourly values in table 1 to this subpart, using equation 4 to this paragraph (g)(2).

Equation 4 to Paragraph (g)(2) Where: E = 4-operating-hour rolling average NOX emissions (lb/MMBtu or ng/J); Ei = Hourly average NOX emissions rate or emissions standard for operating hour “i” (lb/MMBtu or ng/J); and Qi = Total heat input to stationary combustion turbine for operating hour “i” (MMBtu or J as appropriate).

(h)(1) For each combustion turbine demonstrating compliance on an output-based standard, you must determine excess emissions on a 30-operating-day rolling average basis. The measured emissions rate is the NOX emissions measured by the CEMS for a given operating day and the 29 operating days preceding that day. Once each day, calculate a new 30-operating-day average measured emissions rate using all hourly average values based on non-out-of-control NOX emission data for all operating hours during the previous 30-operating-day operating period. Report any 30-operating-day periods for which you have less than 90 percent data availability as monitor downtime. If you elect to comply with the applicable output-based emissions rate standard, calculate the measured emissions rate using equation 5 to this paragraph (h)(1) and calculate the applicable emissions standard using equation 6 to this paragraph (h)(1). If you elect to comply with the applicable output-based emissions rate standard and determine the heat input on an hourly basis, calculate the 30-operating-day rolling average NOX emissions rate using equation 5, and determine the applicable 30-operating-day rolling average NOX emissions standard, calculated using values in table 1 to this subpart, using equation 6. Hours are not subcategorized by load for the purposes of determining the applicable output-based standard. The emissions standard for all hours, regardless of load, is the otherwise applicable full load emissions standard.

Equation 5 to Paragraph (h)(1) Where: E = 30-operating-day average NOX measured emissions rate combustion turbines (lb/MWh or ng/J); Ei = Hourly average NOX emissions rate or emissions standard for non-out-of-control operating hour “i” (lb/MMBtu or ng/J); Qi = Total heat input to stationary combustion turbine for non-out-of-control operating hour “i” (MMBtu or J as appropriate); Pi = Total gross or net energy output from stationary combustion turbine for non-out-of-control operating hour “i” (MWh or J); and n = Total number of operating non-out-of-control hours in the 30-operating-day period. Equation 6 to Paragraph (h)(1) E = 30-operating-day rolling NOX emissions standard (lb/MWh or kg/MWh); ENG = 30-operating-day emissions standard for natural gas-fired combustion turbines (lb/MWh or kg/MWh); Enon-NG = 30-operating-day emissions standard for non-natural gas-fired combustion turbines (lb/MWh or kg/MWh); HNG = Hours of operation combusting natural gas during the 30-operating-day period; Hnon-NG = Hours of operation combusting non-natural gas fuels during the 30-operating-day period; and HT = Total hours of operation during the 30-operating-day period.

(2) If you elect to comply with the applicable output-based emissions rate standard and elect to not determine the heat input on an hourly basis, the applicable 30-operating-day emissions rolling NOX standard is the most stringent standard applicable to the combustion turbine. The 30-operating-day rolling NOX emissions rate is determined as the sum of the hourly emissions divided by the sum of the gross or net output over the 30-operating-day period.

(i) For each combustion turbine demonstrating compliance on a mass-based standard, you must determine excess NOX emissions on both a rolling 4-operating-hour and rolling 12-calendar-month basis using the NOX CEMS data and procedures specified in paragraphs (i)(1) through (4) of this section as applicable to the NOX emissions standard in table 2 to this subpart. In addition, during system emergencies each combustion turbine must determine excess NOX emissions using the procedures specified in paragraph (i)(5) of this section.

(1) For each 4-operating-hour period, compute the 4-operating-hour rolling NOX emissions as the sum of the hourly NOX emissions for a given operating hour and the 3 operating hours preceding that operating hour. Calculate a 4-operating-hour NOX emissions rate for any 4-operating-hour period when you have valid CEMS data for at least 3 of those hours (e.g., a valid 4-operating-hour rolling NOX emissions rate cannot be calculated if 1 or more continuous monitors was out-of-control for the entire hour for more than 1 hour during the 4-operating-hour period).

(2) Calculate the applicable 4-operating-hour rolling NOX emissions standard, calculated using hourly values in table 2 to this subpart, using equation 7 to this paragraph (i)(2).

Equation 7 to Paragraph (i)(2) Where: E = 4-operating-hour rolling NOX emissions (kg or lbs); and Ei = Hourly NOX emissions rate or emissions standard for operating hour “i” (kg or lbs).

(3) For each 12-calendar-month period, compute the 12-calendar-month rolling NOX emissions as the sum of the hourly NOX emissions for a given month and the 11 calendar months preceding the calendar month. Emissions during system emergencies are not included when calculating the 12-calendar-month emissions rate.

(4) Calculate the applicable 12-calendar-month rolling NOX emissions standard, calculated using hourly values in table 2 to this subpart, using equation 8 to this paragraph (i)(4). Heat input during system emergencies is not included when calculating the 12-calendar-month emissions standard.

Equation 8 to Paragraph (i)(4) Where: E = 12-calendar-month rolling NOX emissions (tonnes or tons); ENG = 12-calendar-month emissions standard for natural gas-fired combustion turbines (tonnes or tons); Enon-NG = 12-calendar-month emissions standard for non-natural gas-fired combustion turbines (tonnes or tons); HNG = Hours of operation combusting natural gas during the 12-calendar-month period; Hnon-NG = Hours of operation combusting non-natural gas fuels during the 12-calendar-month period; and HT = Total hours of operation during the 12-calendar-month period.

(5) During system emergencies during which the owner or operator elects to not include emissions or heat input in the 12-calendar month calculations, the applicable average natural gas-fired emissions standard is 0.83 lb NOX/MW-rated output (1.8 lb NOX/MW-rated output when firing non-natural gas) or the current emissions rate necessary to comply with the 12-calendar month natural gas-fired emissions standard of 0.48 tons NOX/MW-rated output (0.81 tons NOX/MW-rated output when firing non-natural gas) whichever is more stringent. For example, if a combustion turbine operated for 4,000 hours during the current 12-calendar month period the applicable average natural gas-fired emissions standard during the system emergency would be 0.24 lb NOX/MW-rated output and the applicable average non-natural gas-fired emissions standard during the system emergency would be 0.41 lb NOX/MW-rated output.