Presenter: PART 75 SPAN & RANGE Manuel J Oliva Clean Air Markets Division U.S. Environmental Protection Agency
Instrument Span & Range PART 75 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.
Span & Range Defined u Range: Instrument Full-Scale ã “What the instrument is set up to measure” u Span: Highest concentration or flow rate that a monitor component is required to be capable of measuring. (§72.2) ã “What the rules require to be measured, Quality assured portion of the range” u “Rules of the Game” - Appendix A, §2 u Affected Parameters: SO 2, NO X, CO 2, O 2 and Flow Rate
Example of Span & Range Case 1: Span = Range Case 2: Span < Range 0 ppm500 ppm Span 0 ppm500 ppm Span 400 ppm
Range Settings u 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) ã 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 ã Exceptions: (SO 2 ) low sulfur fuel, (SO 2 /NO X ) emission controls and two span values, (SO 2 /NO X ) dual span unit Range Signal Noise Level Not Necessarily Linear at Extremes
Span Settings u Span Settings: Dependant on pollutant ã 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 ã “Simple” rule of thumb, range and span values can be equal
Setting the Span - SO 2 Monitors u Define MPC ã 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 u Define MEC if Appropriate ã Maximum Expected Concentration (MEC) is based on expected % SO 2 removal, fuel analysis or historical CEMS data ã MEC is appropriate for units with SO 2 controls or both high- sulfur and low-sulfur fuels, including blends
Setting the Span - SO 2 Monitors (Continued) u High Span* = MPC × 1.00 to MPC × 1.25 ã Rounded to nearest 100 ppm (or 10 ppm if SO 2 500 ppm) ã Full Scale Range Span Value u Low Span = 1.00 × MEC to 1.25 × MEC (If Required) ã Rounded to nearest 10 ppm (or 100 ppm as appropriate) ã Low Span Required if MEC < 20% of High Range (Controls or low sulfur fuels) ã Use the Low Span when SO 2 readings are expected to be below 20% of High Full-Scale Range * If unit has SO 2 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.
Setting the Span - NO X Monitors u Define MPC ã Maximum Potential Concentration (MPC) is based on the fuel (or blend) that gives highest uncontrolled NO X emissions. Options include: fuel based defaults, boiler type defaults, NO X emission test results, historical CEMS data or manufacturer data u Define MEC if Appropriate ã Maximum Expected Concentration (MEC) is based on expected NO X removal efficiency, NO X concentration testing, historical CEMS data, or permit limit ã Determine a separate MEC for each fuel (or blend)
Setting the Span - NO X Monitors (Continued) u High Span* = MPC × 1.00 to MPC × 1.25 ã Rounded to nearest 100 ppm (or 10 ppm if NO X 500 ppm) ã Full Scale Range Span Value u Low Span = 1.00 × MEC to 1.25 × MEC (If Required) ã Rounded to nearest 10 ppm (or 100 ppm as appropriate) ã Low Span Required if MEC < 20% of High Range (If more than one MEC, use MEC closest to 20% of High Range) ã Use the Low Span when NO X readings are expected to be below 20% of High Full-Scale Range * If unit has Add-On NO X 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.
Setting the Span - CO 2 & O 2 Monitors u Define MPC for CO 2 ã CO 2 Maximum Potential Concentration (MPC) is 14% CO 2 (boilers) or 6% CO 2 (turbines) default values, or determine based on historical CEMS data ã MPC is used only for substitute data purposes u Define Minimum Potential Concentration for O 2 ã O 2 Minimum Potential Concentration is determine based on historical CEMS data ã Minimum Potential Concentration is used only for substitute data purposes for units using flow monitors and O2 diluent monitors to determine Heat Input
Setting the Span - CO 2 & O 2 Monitors (Continued) u O 2 Span ã Between 15% and 25% O 2 ã Below 15% O 2 allowed with technical justification u CO 2 Span ã Between 14% and 20% CO 2 (for boilers) ã Between 6% and 14% CO 2 (for turbines)
Setting the Span - Flow Monitors u Define MPV ã 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) u Define MPF ã Maximum Potential Flow Rate (MPF) is equal to MPV × stack area ã Used only for substitute data purposes
Setting the Span - Flow Monitors (Continued) u Calibration Span = MPV* × 1.00 to MPV* × 1.25 ã Rounded up to at least two significant figures u Flow Rate Span = 1.00 × MPF to 1.25 × MPF ã Expressed in the units used for Part 75 reporting (scfh) ã Rounded to nearest 1000 scfh * MPV must be converted to the units of daily calibration (e.g. kscfm, inches of H 2 0, etc.)
Adjustments to Span and Range u Perform at least annual evaluation of the span and range settings (Appendix A, §184.108.40.206) DAHS
Summary Process Diagram RANGE 0 20 40 60 80 100 SPAN VALUE 20% to 80% of Full Scale Range (Majority of Data) Single Span (or High Span) Based on maximum potential concentration or flow rate Low Span (if Required) Based on maximum expected concentration ??