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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 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
??
Optimal Range