PART 75 SPAN & RANGE

1. PART 75SPAN & RANGE Manuel J Oliva Clean Air Markets Division U.S. Environmental Protection Agency

2. PART 75 Instrument Span & Range Question: Aren’t Span and Range the Same? Answer: Under Part 75 Span and Range can be equal in value, but are not the same. However, the range value must always be  the span value.

3. Span & Range Defined • Range: Instrument Full-Scale • “What the instrument is set up to measure” • Span: Highest concentration or flow rate that a monitor component is required to be capable of measuring. (§72.2) • “What the rules require to be measured, Quality assured portion of the range” • “Rules of the Game” - Appendix A, §2 • Affected Parameters: SO2, NOX, CO2, O2 and Flow Rate

4. Example of Span & Range Span Case 1: Span = Range 0 ppm 500 ppm Span Case 2: Span < Range 400 ppm 0 ppm 500 ppm

5. Range Not Necessarily Linear at Extremes Signal Noise Level Range Settings • Select a range so majority of readings obtained during typical unit operation are kept within 20 to 80 percent of instrument full scale range (to extent practicable) • Importance: Avoid signal to noise problems at low end of range, and inaccuracies or exceedance at high end of range. Accuracy of measured values is objective • Exceptions: (SO2) low sulfur fuel, (SO2/NOX) emission controls and two span values, (SO2/NOX) dual span unit

6. Span Settings • Span Settings: Dependant on pollutant • Importance: Concentrations of calibration gases used for daily QA and linearity checks, as well as daily control limits for gas and flow monitors are expressed as % span • “Simple” rule of thumb, range and span values can be equal

7. Setting the Span - SO2 Monitors • Define MPC • Maximum Potential Concentration (MPC) is based on analysis of highest sulfur fuel burned (max % sulfur and min GCV, or max % sulfur/GCV ratio) or historical CEMS data • Define MEC if Appropriate • Maximum Expected Concentration (MEC) is based on expected % SO2 removal, fuel analysis or historical CEMS data • MEC is appropriate for units with SO2 controls or both high-sulfur and low-sulfur fuels, including blends

8. Setting the Span - SO2 Monitors(Continued) • High Span* = MPC × 1.00 to MPC × 1.25 • Rounded to nearest 100 ppm (or 10 ppm if SO2 500 ppm) • Full Scale Range  Span Value • Low Span = 1.00 × MEC to 1.25 × MEC (If Required) • Rounded to nearest 10 ppm (or 100 ppm as appropriate) • Low Span Required if MEC < 20% of High Range (Controls or low sulfur fuels) • Use the Low Span when SO2 readings are expected to be below 20% of High Full-Scale Range * If unit has SO2 control it can forgo high span and report a “default high range value” of 200% of MPC during hours when low range is exceeded. Full scale of low range cannot exceed five times MEC.

9. Setting the Span - NOX Monitors • Define MPC • Maximum Potential Concentration (MPC) is based on the fuel (or blend) that gives highest uncontrolled NOX emissions. Options include: fuel based defaults, boiler type defaults, NOX emission test results, historical CEMS data or manufacturer data • Define MEC if Appropriate • Maximum Expected Concentration (MEC) is based on expected NOX removal efficiency, NOX concentration testing, historical CEMS data, or permit limit • Determine a separate MEC for each fuel (or blend)

10. Setting the Span - NOX Monitors(Continued) • High Span* = MPC × 1.00 to MPC × 1.25 • Rounded to nearest 100 ppm (or 10 ppm if NOX 500 ppm) • Full Scale Range  Span Value • Low Span = 1.00 × MEC to 1.25 × MEC (If Required) • Rounded to nearest 10 ppm (or 100 ppm as appropriate) • Low Span Required if MEC < 20% of High Range (If more than one MEC, use MEC closest to 20% of High Range) • Use the Low Span when NOX readings are expected to be below 20% of High Full-Scale Range * If unit has Add-On NOX control it can forgo high span and report a “default high range value” of 200% of MPC during hours when low range is exceeded. Full scale of low range cannot exceed five times MEC.

11. Setting the Span - CO2 & O2 Monitors • Define MPC for CO2 • CO2 Maximum Potential Concentration (MPC) is 14% CO2 (boilers) or 6% CO2 (turbines) default values, or determine based on historical CEMS data • MPC is used only for substitute data purposes • Define Minimum Potential Concentration for O2 • O2 Minimum Potential Concentration is determine based on historical CEMS data • Minimum Potential Concentration is used only for substitute data purposes for units using flow monitors and O2 diluent monitors to determine Heat Input

12. Setting the Span - CO2 & O2 Monitors (Continued) • O2 Span • Between 15% and 25% O2 • Below 15% O2 allowed with technical justification • CO2 Span • Between 14% and 20% CO2 (for boilers) • Between 6% and 14% CO2 (for turbines)

13. Setting the Span - Flow Monitors • Define MPV • Maximum Potential Velocity (MPV) is based on equations in Appendix A (F-factors, heat input, diluent concentration and moisture concentration), or Highest values from traverse testing (Ref. Method 2) • Define MPF • Maximum Potential Flow Rate (MPF) is equal to MPV × stack area • Used only for substitute data purposes

14. Setting the Span - Flow Monitors(Continued) • Calibration Span = MPV* × 1.00 to MPV* × 1.25 • Rounded up to at least two significant figures • Flow Rate Span = 1.00 × MPF to 1.25 × MPF • Expressed in the units used for Part 75 reporting (scfh) • Rounded to nearest 1000 scfh * MPV must be converted to the units of daily calibration (e.g. kscfm, inches of H20, etc.)

15. Adjustments to Span and Range • Perform at least annual evaluation of the span and range settings (Appendix A, §2.1.2.5) DAHS

16. 0 20 40 60 80 100 Summary Process Diagram RANGE  ?? SPAN VALUE Single Span (or High Span) Based on maximum potential concentration or flow rate 20% to 80% of Full Scale Range (Majority of Data) Low Span (if Required) Based on maximum expected concentration

17. Optimal Range