False air and O₂ trim
Cold air leaking through doors and joints fools the O₂ probe: the trim cuts burner air, the flame goes rich and fuel use rises.
Simulator developed by José Geraldo da Silva Moreira · Energy-efficiency lab
The analyzer says there is excess air. The flame says there isn't.
Cold air enters through doors, sight glasses and joints downstream of the burners and reaches the O₂ probe at the furnace exit.
O₂ trim
O₂ measured by the probe
what the control “sees”
Actual λ at the burners
Overall λ
burners + infiltration
Extra fuel
vs. a tight furnace at the same O₂
Furnace, side view
What to watch
- With trim on and 20% false air, the control cuts burner air until measured O₂ meets the setpoint. The flame goes sub-stoichiometric.
- A double penalty: false air enters cold (it bypasses the recuperator) and the rich flame leaves CO in the furnace atmosphere.
- The fix: slightly positive furnace pressure control, sealing, and CO measured alongside O₂.
Assumes false air mixes with the flue gas before the probe and that the CO formed does not fully burn before measurement.
Simplified teaching models with order-of-magnitude illustrative values. Do not use them for design or operating decisions without validation against plant data.