What is the process of combustion in a boiler?

The correct answer highlights that combustion in a boiler is fundamentally the process of burning fuel in the presence of air, which generates heat. This heat is essential for the boiler's operation, as it raises the temperature of water, converting it into steam or hot water for various applications.

In a boiler system, fuel such as natural gas, oil, or coal is combined with air, and the combustion reaction produces heat energy. This generated heat is then used to transfer thermal energy to water or another medium, ultimately producing steam or heated water needed for heating or power generation.

Understanding combustion is crucial because it directly influences the efficiency of the boiler and the effectiveness of energy production. Factors like fuel type, air supply, and combustion temperature can affect how efficiently combustion takes place, ensuring optimal performance.

Other choices do not accurately capture the essence of the combustion process specific to a boiler's function. For instance, converting heat into mechanical energy pertains more to turbines or engines rather than the combustion process itself. Mixing water with fuel to create steam is a mischaracterization of how steam is produced in a boiler. Finally, cooling flue gases before venting is an important part of emissions management and efficiency but does not describe the combustion process.