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

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part 75 span range

PART 75SPAN & RANGE

Manuel J Oliva

Clean Air Markets Division

U.S. Environmental Protection Agency

slide2

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.

span range defined
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
slide4

Example of Span & Range

Span

Case 1: Span = Range

0 ppm

500 ppm

Span

Case 2: Span < Range

400 ppm

0 ppm

500 ppm

range settings

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
slide6

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
slide7

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
slide8

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.

slide9

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)
slide10

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.

slide11

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
slide12

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)
slide13

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
slide14

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.)

slide15

Adjustments to Span and Range

  • Perform at least annual evaluation of the span and range settings (Appendix A, §2.1.2.5)

DAHS

slide16

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