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 combustion and endothermic evaporation of shell type boiler are completed in a cylinder, which can be divided into horizontal type and vertical type, such as the early Lanzhou Development and firecracker furnace. Water tube boiler is a boiler whose main heating surface is tubes, which is a major improvement of early boilers, and its safety and reliability are greatly improved.