Types of Boiler

Main Boiler Prop These are high-pressure water-tube boilers going up to pressures beyond 100 bars and temperatures of 513 degrees C.


Auxiliary Boiler Aids the propulsion in some way; e.g., heating of heavy fuel oil using a steam heater, necessary for propulsion would qualify the supplying boiler to be referred to as an auxiliary boiler.


Donkey Boiler A boiler used only for the “hotel” needs of the ship; e.g., supplying hot water to the galley.


Tank Boiler A boiler with a large water-carrying capacity where the shell is being used as the pressure vessel. Most low-pressure auxiliary boilers will come into this category.


Vertical Boiler Any boiler where the shell is upright and the furnace is usually contained within the shell at the lower half.


Horizontal Boiler This is also referred to as a cylindrical boiler. The boiler’s cylindrical shell lies across its length parallel to the structure of the ship or the ground level.


Exhaust Gas Boiler A boiler is operated by hot gas from an engine or other exhaust gas sources.


Exhaust Gas Boiler / composite boiler


Package Boiler Fully automatic, low-capacity boilers packaged inside a box-type casing, capable of quick steam production and flexible in being positioned anywhere; could be coil type or firetube type.


Boilers are classified depending on the flow of flue gases. They are:

  • Water-tube boilers
  • Fire-tube boilers


Water-tube Boilers Water-tube boiler consists of a series of tubes through which water flows. Hot flue gases pass over the tubes. The heat from the flue gas is transferred to Water tube boilers are classified according to their operating pressures:

  • Low-pressure boilers (0 to 7 bar)
  • Medium pressure (7 to 18 bar)
  • High pressure (18 to 64 bar)

Water tube boiler D Type


Fire-tube boilers In a fire-tube boiler, the flue gases flow through the tubes and water flows over the tubes. They are also called smoke tube boilers or scotch boilers. In a fire tube boiler, flue gas is produced by fuel combustion.


Flue gas flows through fire tubes, which are surrounded by water. The heat from the flue gas is transferred to water and steam is generated. Fire tube boilers are low-pressure boilers ranging up to 7 bar.  

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