Appendix C to Part 75 -- Missing Data Estimation Procedures

1. Parametric Monitoring Procedure for Missing SO2 Concentration or NOX Emission Rate Data

1.1      Applicability

The owner or operator of any affected unit equipped with post-combustion SO2 or NOx emission controls and SO2 pollutant concentration monitors and/or NOx continuous emission monitoring systems at the inlet and outlet of the emission control system may apply to the Administrator for approval and certification of a parametric, empirical, or process simulation method or model for calculating substitute data for missing data periods. Such methods may be used to parametrically estimate the removal efficiency of the SO2 of postcombustion NOx emission controls which, with the monitored inlet concentration or emission rate data, may be used to estimate the average concentration of SO2 emissions or average emission rate of NOx discharged to the atmosphere. After approval by the Administrator, such method or model may be used for filling in missing SO2 concentration or NOx emission rate data when data from the outlet SO2 pollutant concentration monitor or outlet NOx continuous emission monitoring system have been reported with an annual monitor data availability of 90.0 percent or more.

Base the empirical and process simulation methods or models on the fundamental chemistry and engineering principles involved in the treatment of pollutant gas. On a case-by-case basis, the Administrator may pre-certify commercially available process simulation methods and models.

1.2      Petition Requirements

Continuously monitor, determine, and record hourly averages of the estimated SO2 or NOX removal efficiency and of the parameters specified below, at a minimum. The affected facility shall supply additional parametric information where appropriate. Measure the SO2 concentration or NOX emission rate, removal efficiency of the add-on emission controls, and the parameters for at least 2160 unit operating hours. Provide information for all expected operating conditions and removal efficiencies. At least 4 evenly spaced data points are required for a valid hourly average, except during periods of calibration, maintenance, or quality assurance activities, during which 2 data points per hour are sufficient. The Administrator will review all applications on a case-by-case basis.

1.2.1      Parameters for Wet Flue Gas Desulfurization System

1.2.1.1      Number of scrubber modules in operation.

1.2.1.2      Total slurry rate to each scrubber module (gal per min).

1.2.1.3      In-line absorber pH of each scrubber module.

1.2.1.4      Pressure differential across each scrubber module (inches of water column).

1.2.1.5      Unit load (MWe).

1.2.1.6      Inlet and outlet SO2 concentration as determined by the monitor or missing data substitution procedures.

1.2.1.7      Percent solids in slurry for each scrubber module.

1.2.1.8      Any other parameters necessary to verify scrubber removal efficiency, if the Administrator determines the parameters above are not sufficient.

1.2.2      Parameters for Dry Flue Gas Desulfurization System

1.2.2.1      Number of scrubber modules in operation.

1.2.2.2      Atomizer slurry flow rate to each scrubber module (gal per min).

1.2.2.3      Inlet and outlet temperature for each scrubber module ( °F).

1.2.2.4      Pressure differential across each scrubber module (inches of water column).

1.2.2.5      Unit load (MWe).

1.2.2.6      Inlet and outlet SO2 concentration as determined by the monitor or missing data substitution procedures.

1.2.2.7      Any other parameters necessary to verify scrubber removal efficiency, if the Administrator determines the parameters above are not sufficient.

1.2.3      Parameters for Other Flue Gas Desulfurization Systems

If SO2 control technologies other than wet or dry lime or limestone scrubbing are selected for flue gas desulfurization, a corresponding empirical correlation or process simulation parametric method using appropriate parameters may be developed by the owner or operator of the affected unit, and then reviewed and approved or modified by the Administrator on a case-by-case basis.

1.2.4      Parameters for Post-Combustion NOx Emission Controls

1.2.4.1      Inlet air flow rate to the unit (boiler) (mcf/hr).

1.2.4.2      Excess oxygen concentration of flue gas at stack outlet (percent).

1.2.4.3      Carbon monoxide concentration of flue gas at stack outlet (ppm).

1.2.4.4      Temperature of flue gas at outlet of the unit ( °F).

1.2.4.5      Inlet and outlet NOx emission rate as determined by the NOx continuous emission monitoring system or missing data substitution procedures.

1.2.4.6      Any other parameters specific to the emission reduction process necessary to verify the NOx control removal efficiency, (e.g., reagent feedrate in gal/mi).

1.3      Correlation of Emissions With Parameters

Establish a method for correlating hourly averages of the parameters identified above with the percent removal efficiency of the SO2 or post-combustion NOX emission controls under varying unit operating loads. Equations 1-7 in §  75.15 may be used to estimate the percent removal efficiency of the SO2 emission controls on an hourly basis.

Each parametric data substitution procedure should develop a data correlation procedure to verify the performance of the SO2 emission controls or post-combustion NOx emission controls, along with the SO2 pollutant concentration monitor and NOx continuous emission monitoring system values for varying unit load ranges.

For NOx emission rate data, and wherever the performance of the emission controls varies with the load, use the load range procedure provided in section 2.2 of this appendix.

1.4      Calculations

1.4.1      Use the following equation to calculate substitute data for filling in missing (outlet) SO2 pollutant concentration monitor data.

Mo = Ic (1-E) (Eq. C-1) where,

Mo = Substitute data for outlet SO2 concentration, ppm.

Ic = Recorded inlet SO2 concentration, ppm.

E = Removal efficiency of SO2 emission controls as determined by the correlation procedure described in section 1.3 of this appendix.

1.4.2      Use the following equation to calculate substitute data for filling in missing (outlet) NOx emission rate data.

Mo = Ic (1-E) (Eq. C-2) where,

Mo = Substitute data for outlet NOx emission rate, lb/mmBtu.

Ic = Recorded inlet NOx emission rate, lb/mmBtu.

E = Removal efficiency of post-combustion NOx emission controls determined by the correlation procedure described in section 1.3 of this appendix.

1.5      Missing Data

1.5.1      If both the inlet and the outlet SO2 pollutant concentration monitors are unavailable simultaneously, use the maximum inlet SO2 concentration recorded by the inlet SO2 pollutant concentration monitor during the previous 720 quality assured monitor operating hours to substitute for the inlet SO2 concentration in equation C-1 of this appendix.

1.5.2      If both the inlet and outlet NOx continuous emission monitoring systems are unavailable simultaneously, use the maximum inlet NOx emission rate for the corresponding unit load recorded by the NOx continuous emission monitoring system at the inlet during the previous 2160 quality assured monitor operating hours to substitute for the inlet NOx emission rate in equation C-2 of this appendix.

1.6      Application

Apply to the Administrator for approval and certification of the parametric substitution procedure for filling in missing SO2 concentration or NOx emission rate data using the established criteria and information identified above. DO not use this procedure until approved by the Administrator.

2. Load-Based Procedure for Missing Flow Rate and NOX Emission Rate Data

2.1      Applicability

This procedure is applicable for data from all affected units for use in accordance with the provisions of this part to provide substitute data for volumetric flow rate (scfh), NOX emission rate (in lb/mmBtu) from NOX-diluent continuous emission monitoring systems, and NOX concentration data (in ppm) from NOx concentration monitoring systems used to determine NOX mass emissions.

2.2      Procedure

2.2.1      For a single unit, establish ten operating load ranges defined in terms of percent of the maximum hourly average gross load of the unit, in gross megawatts (MWge), as shown in Table C-1. (Do not use integrated hourly gross load in MW-hr.) For units sharing a common stack monitored with a single flow monitor, the load ranges for flow (but not for NOX) may be broken down into 20 operating load ranges in increments of 5.0 percent of the combined maximum hourly average gross load of all units utilizing the common stack. If this option is selected, the twentieth (uppermost) operating load range shall include all values greater than 95.0 percent of the maximum hourly average gross load. For a cogenerating unit or other unit at which some portion of the heat input is not used to produce electricity or for a unit for which hourly average gross load in MWge is not recorded separately, use the hourly gross steam load of the unit, in pounds of steam per hour at the measured temperature (°F) and pressure (psia) instead of MWge. Indicate a change in the number of load ranges or the units of loads to be used in the precertification section of the monitoring plan.

      Table C-1--Definition of Operating Load Ranges for Load-based
                      Substitution Data Procedures
------------------------------------------------------------------------
                                                             Percent of
                                                               maximum
                                                            hourly gross
                                                               load or
                   Operating load range                        maximum
                                                            hourly gross
                                                             steam load
                                                              (percent)
------------------------------------------------------------------------
1.........................................................       0-10
2.........................................................  <ls-thn-eq>1
                                                                 0-20
3.........................................................  <ls-thn-eq>2
                                                                 0-30
4.........................................................  <ls-thn-eq>3
                                                                 0-40
5.........................................................  <ls-thn-eq>4
                                                                 0-50
6.........................................................  <ls-thn-eq>5
                                                                 0-60
7.........................................................  <ls-thn-eq>6
                                                                 0-70
8.........................................................  <ls-thn-eq>7
                                                                 0-80
9.........................................................  <ls-thn-eq>8
                                                                 0-90
10........................................................  <ls-thn-eq>9
                                                                    0
------------------------------------------------------------------------

2.2.2      Beginning with the first hour of unit operation after installation and certification of the flow monitor or the NOX-diluent continuous emission monitoring system (or a NOX concentration monitoring system used to determine NOX mass emissions, as defined in §  75.71(a)(2)), for each hour of unit operation record a number, 1 through 10, (or 1 through 20 for flow at common stacks) that identifies the operating load range corresponding to the integrated hourly gross load of the unit(s) recorded for each unit operating hour.

2.2.3      Beginning with the first hour of unit operation after installation and certification of the flow monitor or the NOX-diluent continuous emission monitoring system (or a NOX concentration monitoring system used to determine NOX mass emissions, as defined in §  75.71(a)(2)) and continuing thereafter, the data acquisition and handling system must be capable of calculating and recording the following information for each unit operating hour of missing flow or NOX data within each identified load range during the shorter of: (a) the previous 2,160 quality assured monitor operating hours (on a rolling basis), or (b) all previous quality assured monitor operating hours.

2.2.3.1      Average of the hourly flow rates reported by a flow monitor, in scfh.

2.2.3.2      The 90th percentile value of hourly flow rates, in scfh.

2.2.3.3      The 95th percentile value of hourly flow rates, in scfh.

2.2.3.4      The maximum value of hourly flow rates, in scfh.

2.2.3.5      Average of the hourly NOX emission rate, in lb/mmBtu, reported by a NOX continuous emission monitoring system.

2.2.3.6      The 90th percentile value of hourly NOX emission rates, in lb/mmBtu.

2.2.3.7      The 95th percentile value of hourly NOX emission rates, in lb/mmBtu.

2.2.3.8      The maximum value of hourly NOX emission rates, in lb/mmBtu.

2.2.3.9      Average of the hourly NOX pollutant concentrations, in ppm, reported by a NOX concentration monitoring system used to determine NOX mass emissions, as defined in §  75.71(a)(2).

2.2.3.10      The 90th percentile value of hourly NOX pollutant concentration, in ppm.

2.2.3.11      The 95th percentile value of hourly NOX pollutant concentration, in ppm.

2.2.3.12      The maximum value of hourly NOX pollutant concentration, in ppm.

2.2.4      Calculate all monitor or continuous emission monitoring system data averages, maximum values, and percentile values determined by this procedure using bias adjusted values in the load ranges.

2.2.5      When a bias adjustment is necessary for the flow monitor and/or the NOX-diluent continuous emission monitoring system (and/or the NOX concentration monitoring system used to determine NOX mass emissions, as defined in §  75.71(a)(2)), apply the adjustment factor to all monitor or continuous emission monitoring system data values placed in the load ranges.

2.2.6      Use the calculated monitor or monitoring system data averages, maximum values, and percentile values to substitute for missing flow rate and NOX emission rate data (and where applicable, NOX concentration data) according to the procedures in subpart D of this part.

[58 FR 3701, Jan. 11, 1993, as amended at 60 FR 26547, 26548, May 17, 1995; 63 FR 57313, Oct. 27, 1998; 64 FR 28652, May 26, 1999]