Stack gas measurements indicate an excess air level of 44.9% with a flue gas minus combustion air temperature of 400°F. From the table, the boiler combustion efficiency is 78.2% (E1). Tuning the boiler reduces the excess air to 9.5% with a flue gas minus combustion air temperature of 300°F. The boiler combustion efficiency increases to 83.1% (E2).
Excess Air Coefficient - an overview | ScienceDirect Topics
The sectional superficial gas velocity is limited somewhat concerning its ability to maintain fast fluidization in the furnace. The excess air coefficient at the furnace exit of a typical CFB boiler is 1.2, and the sectional superficial gas velocity is 5∼6 m/s at 850°C, so the furnace cross section heat release rate is 3.6∼4.4 MW/m 2.
Mar 15, 2019 · With those measurements, the following formulas can be used to calculate excess air: For example, if the oxygen dry reading in flue gas is 2.5%, then the excess-air calculation would be: 0.895 x 0.025 / (0.21-0.025) = 12.1% excess air. Too much excess air leads to lower flame temperature. That means less heat gets into the system.
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Typical excess air to achieve the highest possible efficiency for some common fuels: 5 - 10% for natural gas. 5 - 20% for fuel oil. 15 - 60% for coal. Carbon dioxide - CO2 - is a combustion product and the content of CO2 in a flue gas is an important indication of the combustion efficiency.