span and range

Presenter:

PART 75SPAN & RANGE

Manuel J OlivaClean Air Markets DivisionU.S. Environmental Protection Agency

Instrument Span & Range

PART75

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 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

Case 1: Span = Range

Case 2: Span < Range

0 ppm 500 ppm

Span

0 ppm 500 ppm

Span

400 ppm

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

Range

Signal Noise Level

Not Necessarily Linear at Extremes

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

Summary Process DiagramRANGE

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 rateLow Span

(if Required)Based on maximum

expected concentration

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Optimal Range