Flue gas diagnostics – indicator of incomplete combustion losses When incomplete combustion losses are high in a furnace or boiler, which component will be present in unusually large amounts in the flue gas analysis?

Introduction / Context:
Stack gas analysis provides rapid feedback on combustion quality. Complete combustion of carbon to carbon dioxide maximizes heat release. When combustion is incomplete, chemical energy remains in partially oxidized products, especially carbon monoxide (CO), indicating losses and safety concerns.

Given Data / Assumptions:

• Fuel contains carbon and possibly hydrogen, sulphur, etc.
• Combustion air and mixing may be suboptimal (deficient oxygen or poor turbulence).
• Flue gas analyzer measures CO2, CO, O2 (and often NOx, SO2), and sometimes unburnt hydrocarbons and opacity.

Concept / Approach:
Incomplete combustion of carbon forms CO when oxygen supply or mixing is inadequate, or when quenching occurs. CO represents unliberated chemical energy because C → CO releases less heat than C → CO2. Therefore, elevated CO in flue gas is the most direct indicator of incomplete combustion loss. High soot can appear, but opacity alone is not a reliable quantitative measure of heat loss; CO2 generally drops when CO rises because carbon is not fully oxidized; excess O2 may simultaneously be high if mixing is poor rather than oxygen-deficient globally.

Step-by-Step Solution:

Verification / Alternative check:
Combustion tuning aims to minimize CO at acceptable excess O2; efficiency calculations penalize CO and unburnt hydrocarbons in loss accounting.

Why Other Options Are Wrong:

• CO2: Typically decreases when incomplete combustion rises.
• O2: Can be high due to excess air, but does not by itself indicate losses.
• C (soot): May increase, but CO is the standard quantitative indicator.

Common Pitfalls:
Assuming zero O2 implies perfect combustion—low O2 can also imply oxygen deficiency and more CO. Balance both CO and O2 for optimal tuning.

Final Answer:
CO