Boiler is a kind of energy conversion equipment. The energy input to the boiler includes chemical energy in fuel, electric energy, heat energy of high-temperature flue gas and other forms. After boiler conversion, steam, high-temperature water or organic heat carrier with certain heat energy are output. It is mainly used in thermal power plants, ships, locomotives and industrial and mining enterprises.

The working medium of the steam boiler is water, and the output working medium is steam. Steam can be divided into saturated steam and superheated steam. The working medium of the hot water boiler is water, and the output working medium is unsaturated hot water. Boiler with special working medium Other chemical fluids other than water, such as mercury vapor boiler.