PART 75 SPAN & RANGE

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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 75SPAN & 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?

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
• 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

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

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

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

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

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.

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)

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.

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

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)

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

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.)

Adjustments to Span and Range

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

DAHS

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