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Gas analyzer calibration

These are practical field notes from calibrating and troubleshooting extractive gas analyzers (Fuji ZRJ/ZFK and ABB Magnos/Uras series) on kiln inlet and coal mill applications — the kind of reference numbers that don't usually make it into a manufacturer's manual but matter when you're standing at the panel with a calibration gas cylinder in hand.

Zero and Span Calibration

Zero calibration: Set gas flow to 0.60 L/min. Zero gas depends on the parameter being calibrated:

  • For Oxygen — 1% CO in nitrogen balance is used as the zero gas
  • For CO and NOx — 21% Oxygen (essentially clean air) is used as the zero gas

Span calibration: A gas with a known, maximum-range concentration of the parameter being calibrated is used:

  • Oxygen span — 21%
  • CO span — 1%
  • NOx span — 2000 PPM

Calibration Gas Reference

Gas Mixture Cylinder Volume Weight Fill Pressure
1% CO, N&sub2; balance 3.4 6.2 kg 150 bar
Dry air, >90% (zero air) 3.4 6.2 kg 150 bar
1% O&sub2;, N&sub2; balance 3.4 6.2 kg 150 bar
2000 ppm NOx, N&sub2; balance Disposable cylinder — —
Pure N&sub2; (zero/purge gas) 3.4 6.2 kg 150 bar

Fuji-specific reference: O2 span = 1%, zero gas is balanced nitrogen.

ABB EL3020-specific reference: Zero gas is NO2. Typical span reference values: SO2 4946 mg/cm², CO 1913 mg/cm², NO 2991 mg/cm².

Common Faults in Gas Analyzers

  • Probe choked with dust or buildup
  • Primary stainless-steel filter choked
  • Mist filter choked
  • Membrane filter damaged or choked
  • Sample flow reading low
  • Drain pot water level low
  • Leakage somewhere in the sampling system
  • Sample pump faulty
  • Calibration drifted out of tolerance
  • Solenoid-operated valve (SOV) faulty
  • Purge MOV leaking through

NO2/NO Converter Notes

Standard NDIR cells respond to NO but not NO2, so a catalytic converter ahead of the analyzer converts NO2 in the sample back to NO for accurate total-NOx measurement. This converter's catalyst temperature must be maintained at 220°C — if the temperature drifts out of range, the NOx reading will be inaccurate. If the analyzer shows Error 15 during calibration, this typically indicates the sensor needs cleaning. Control voltage on Fuji systems is 110V AC, so all associated components are rated accordingly.

Zirconia Oxygen Cell and Cooler Temperatures

  • Zirconia oxygen analyzer cell operating temperature: 800°C
  • ABB sample cooler temperature: maintained at 2–5°C
  • Heated sampling line temperature: maintained at 100°C to prevent moisture condensation in the line

Field Case Notes

Kiln Inlet Analyzer

Probe pipe outer diameter at the kiln inlet body: 130 mm. Typical PID settings for the oxygen temperature controller (Fuji PXR4): P = 12, I = 51, D = 10.

Coal Bag House Analyzer

One recurring fault: the oxygen analyzer going offline due to a faulty temperature controller. Fix: replace the controller, re-tune the PID settings, and confirm the output contact is configured normally open. Thermocouple type used: Type R.

Typical Operating Ranges (Cement Kiln Inlet)

Fuel O&sub2; CO NOx
Normal running (general) 2–3% 0.001% 1200–1300 ppm
Coal firing 10–12% 0.002% —

Reading the numbers: Excess oxygen above the target range indicates heat losses from over-aeration; oxygen running low indicates unburnt fuel, which increases fuel cost. Excess CO likewise points to unburnt fuel. NOx should be kept within its target band — too high indicates a pollution/compliance concern, while unusually low NOx combined with high CO can point to incomplete combustion rather than "cleaner" burning.

The Bottom Line

Most gas analyzer problems in the field trace back to the sample conditioning train rather than the analyzer cell itself — chokes, leaks, and temperature drift in the probe, filters, and heated line cause more downtime than actual analyzer faults. Keep the sample dry, keep the line at temperature, and confirm flow before assuming the analyzer needs recalibration.

  

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