Boilers:

Two distinct heat sources used for boilers are electric probes and burned fuel (coal, oil, etc.) This theory will use fuel boilers to describe the typical design of boilers. Refer to Figure during the subsequent discussion.

The boiler has an enclosed space whereas the fuel combustion takes place, commonly referred to as the furnace or combustion chamber. Air is supplied to merge along with the fuel, resulting in combustion. A heat of combustion is absorbed through the water within the risers or circulating tubes.

The density difference among hot and cold water is the driving force to circulate the water back to the steam drum. Ultimately the water will absorb enough heat to generate steam. A Steam leaves the steam drum through a baffle that causes any water droplets being carried through the steam to drop out and drain back to the steam drum. The steam might then travel by a superheater if superheated steam is required. A hot combustion gasses from the furnace will heat the steam by the superheater's thin tube walls. A steam then goes to the steam supply system and the several steam loads.

A few boilers have economizers to improve cycle effectiveness through preheating inlet feedwater to the boiler. An economizer uses heat from the boiler exhaust gasses to raise the temperature of the inlet feedwater.

Figure: Typical Fuel Boiler