What serves as the heating source for the economizer?

The economizer is a component in a steam generation system that recovers waste heat from the flue gas leaving the boiler. The primary function of the economizer is to preheat the feedwater entering the boiler, which improves the overall efficiency of the steam generation process.

Combustion gases are the correct answer because they provide a significant source of heat as they exit the combustion chamber. The economizer uses these hot gases to transfer heat to the feedwater, thereby reducing the amount of fuel necessary to achieve the desired steam output. By harnessing the heat energy from combustion gases, the economizer enhances efficiency, conserves fuel, and leads to lower operational costs.

In contrast, thermal oil, electric heaters, and high-pressure steam may serve other purposes in various systems or applications but do not specifically function as the heating source for an economizer in the context of steam generation.