Industrial boilers are pressure vessels which utilize combustion or heat from a process to heat water. The steam or heated water are used for various processes applications.

There are two primary configurations of industrial boilers:

Fire Tube Boilers

A fire-tube boiler is a type of boiler in which hot gases from a fire pass through tubes that are inside of a pressure vessel and are covered with water. The heat from the hot gases are exchanged with the water through the walls of the tubes. The heat and material balance for these boilers is such that the tubes are always submerged in water. The heat input from the hot gases balances the heat required to boil off the water and maintain a desired output steam pressure.

Water Tube Boiler

By flipping around the process of a fire-tube boiler one gets a water tube boiler. A water tube boiler circulates water inside tubes and heats the tubes externally by the fire. Water tube boilers are used for high-pressure boilers. Fuel is burned inside the furnace, creating hot gas which heats water in the steam-generating tubes.

The heated water running through the tubes goes into a steam drum. In the steam drum, saturated steam is drawn off the top of the drum.