What is required for complete combustion to occur in a boiler?

Complete combustion in a boiler requires a controlled air supply because the right amount of oxygen must be present to react with the fuel effectively. By controlling the air supply, engineers can ensure that there is just enough oxygen available for combustion, which maximizes efficiency and minimizes the formation of harmful emissions such as carbon monoxide and unburned hydrocarbons.

In practice, if there is insufficient air, incomplete combustion occurs, leading to waste of fuel and the production of harmful byproducts. On the other hand, too much air can also be counterproductive, as it can lower the combustion temperature and reduce efficiency without providing additional benefits.

Other options, like having excess air, can lead to inefficiencies by reducing the overall temperature of the combustion process, although it may contribute to safety by ensuring that all fuel combusts. Burning at high pressure does not inherently guarantee complete combustion, nor does it directly contribute to the efficiency of the reaction. A mixture of air and fuel in a specific ratio is a factor in combustion, but the emphasis here is on controlling the air supply to meet the requirements of complete combustion optimally.