Effect of oxygen-enriched combustion air in furnaces When fuel is burned with oxygen-enriched air, which key performance variable definitely increases?

Introduction / Context:
Oxygen enrichment raises the oxygen fraction in combustion air above ambient. This decreases inert nitrogen in the flame zone, alters flame structure, and can significantly improve thermal performance if managed correctly.

Given Data / Assumptions:

• Fuel composition and firing rate are otherwise comparable.
• We focus on direct cause-and-effect of oxygen enrichment.

Concept / Approach:
With higher oxygen content, less nitrogen dilutes the flame, increasing adiabatic flame temperature. Often, total flue-gas volume decreases (less N2), and for the same duty, fuel consumption can drop rather than increase. Stack losses can also decrease if excess air is optimized and heat recovery is effective.

Step-by-Step Solution:

Verification / Alternative check:
Adiabatic flame temperature calculations show higher values as oxygen fraction rises, confirming the direct correlation.

Why Other Options Are Wrong:

Common Pitfalls:
Ignoring increased NOx potential with very hot flames; staged firing or dilution may be necessary.

Final Answer:
flame temperature