How does excessive air affect combustion efficiency in a boiler?

Excessive air in a boiler negatively impacts combustion efficiency primarily because it can lead to incomplete combustion. When more air is introduced than is required for optimal combustion, it dilutes the fuel-air mixture and can carry away heat, resulting in lower temperatures within the combustion chamber. This dilution can hinder the chemical reactions necessary for efficient combustion, causing some fuel to remain unburned.

Moreover, with too much air present, the flue gases contain a higher concentration of nitrogen and excess oxygen, which do not contribute to heating the system and instead absorb energy without providing any benefit to the combustion process. This ultimately leads to a loss of overall thermal efficiency as more energy is required to achieve the same level of heat output. Therefore, the presence of excessive air not only decreases combustion efficiency but can also increase fuel costs and reduce the overall effectiveness of the boiler operation.