Steam boilers are water-containing vessels that heat water to create steam that is emitted from the boilers for various functions, such as operating production equipment, sterilizing, heating, steam cleaning, and powering trains, ships, and boats.
Steam boilers are fueled by wood, oil or coal, or can be steam boilers gas fired. There are also electric steam boilers, which use resistance or immersion type heating elements.
Closed and open system steam boilers
"Closed system" steam boilers have enough energy to convert 100 percent of the steam they emit back to water. Because some processes can contaminate the steam emitted, it is necessary to also have “open system” steam boilers that do not return the condensation.
Types of steam boilers
Firetube steam boilers, or shell boilers, are the most commonly used. Firetube steam boilers gas fired send hot gases through the inside of tubes within the boiler shell. These tubes are surrounded by water and arranged in banks to allow gases to travel through steam boilers up to four times prior to going out the stack.
Watertube steam boilers gas fired direct fire or hot gases to and around the exterior of water-filled tubes that are set in a vertical position. Watertube steam boilers gas fired have a top drum where steam separates from water, and a bottom drum to collect sludge.
This is a useful information source about steam boilers.