The boiler

1. A boiler (or steam generator, as it is commonly called) is a closed vessel in which water, under pressure, is transformed into steam by the application of heat.
2. Open vessels and those generating steam at atmospheric pressure are not considered to be boilers.
3. In the furnace, the chemical energy in the fuel is converted into heat, and it is the function of the boiler to transfer this heat to the water in the most efficient manner.
4. Thus the primary function of a boiler is to generate steam at pressures above atmospheric by the absorption of heat that
   is produced in the combustion of fuel.
5. With waste-heat boilers, heated gases serve as the heat source, e.g., gases from a gas turbine.
6. A steam electric power plant is a means for converting the potential chemical energy of fuel into electrical energy.
7. In its simplest form it consists of a boiler supplying steam to a turbine, and the turbine driving an electric generator.