Combustion diagnostics – zirconia probe application A zirconia (zirconium oxide) probe installed in a furnace stack is used for continuous measurement of which parameter in flue gases?

Introduction / Context:
Optimizing combustion requires knowledge of excess air. Continuous oxygen monitoring enables tighter control of burners and improved fuel economy. Zirconia probes are the workhorses for O2 measurement in hot flue streams.

Given Data / Assumptions:

• Zirconia solid-electrolyte sensor exposed to hot flue gas and a reference gas (usually air).
• High-temperature operation is typical for accurate readings.
• Output is an emf related to oxygen partial pressure difference.

Concept / Approach:
Zirconia acts as an oxygen-ion conductor at elevated temperature. The Nernst equation relates cell emf to the ratio of oxygen partial pressures across the electrolyte. The instrument is thus a direct oxygen analyzer, not a generic CO2/CO meter nor a temperature probe.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer specifications list zirconia analyzers as excess oxygen monitors for combustion control loops (trim control), confirming the application.

Why Other Options Are Wrong:

• CO2/CO: Require infrared or electrochemical methods; zirconia is selective to oxygen via ionic conduction.
• Temperature: Although the probe is heated, it is not a temperature instrument.

Common Pitfalls:
Assuming flue gas analyzers are interchangeable. Each technology targets specific species; zirconia is specific to oxygen measurement.

Final Answer:
Oxygen in flue gases