Excess air
What reducing excess air in boilers and furnaces is worth: O₂, CO, stack losses, flame appearance and yearly fuel savings.
Simulator developed by José Geraldo da Silva Moreira · Energy-efficiency lab
What is reducing excess air worth?
Compare current operation with a proposal. The starting example is a natural-gas boiler with flue gas at 250 °C; use the buttons to compare with furnaces.
O₂ dry basis
Stack CO
Available heat
Fuel savings
Losses as a function of λ
Total lossStack gasUnburned (CO)
Flame appearance (current λ)
What to watch
- The total-loss curve has a minimum just above λ = 1. To the left, CO shoots up; to the right, excess air carries heat up the stack.
- Try the three buttons: the same O₂ point is worth little in a boiler with an economizer and a lot in a furnace without heat recovery.
- The real optimum sits away from the theoretical minimum: the margin covers mixing quality, fuel variation and analyzer reliability.
Stoichiometric balance per Nm³ of fuel; mean specific heats; CO from an illustrative industrial-burner correlation. Savings computed for the same useful heat.
Simplified teaching models with order-of-magnitude illustrative values. Do not use them for design or operating decisions without validation against plant data.