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A watertube boiler[1] (also spelled water-tube and water tube) is a type of boiler  in which water

circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot

gas which heats water in the stea-generating tubes. !n saller boilers, additional generating

tubes are separate in the furnace, while larger utility boilers rely on the water-filled tubes that

a"e up the walls of the furnace to generate stea.

#he heated water then rises into the stea dru. $ere, saturated stea is drawn off the top of the

dru. !n soe ser%ices, the stea will reenter the furnace through a superheater  to becoe

superheated. &uperheated stea is defined as stea that is heated abo%e the boiling point at a

gi%en pressure. &uperheated stea is a dry gas and therefore used to dri%e turbines, since water

droplets can se%erely daage turbine blades.

'ool water at the botto of the stea dru returns to the feedwater dru %ia large-bore

downcoer tubes, where it pre-heats the feedwater supply. (!n large utility boilers, the

feedwater is supplied to the stea dru and the downcoers supply water to the botto of the

waterwalls). #o increase econoy of the boiler, exhaust gases are also used to pre-heat the air blown into the furnace and war the feedwater supply. &uch watertube boilers in theral power

stations are also called steam generating units.

#he older fire-tube boiler  design, in which the water surrounds the heat source and gases fro

cobustion pass through tubes within the water space, is a uch wea"er structure and is rarely

used for pressures abo%e .* +a (/ psi). A significant ad%antage of the watertube boiler is

that there is less chance of a catastrophic failure0 there is not a large %olue of water in the boiler 

nor are there large echanical eleents subect to failure.

https://en.wikipedia.org/wiki/Water-tube_boiler#cite_note-1https://en.wikipedia.org/wiki/Boiler_(steam_generator)https://en.wikipedia.org/wiki/Furnace#Industrial_furnaceshttps://en.wikipedia.org/wiki/Furnace#Industrial_furnaceshttps://en.wikipedia.org/wiki/Steamhttps://en.wikipedia.org/wiki/Steamhttps://en.wikipedia.org/wiki/Steam_drumhttps://en.wikipedia.org/wiki/Steam_drumhttps://en.wikipedia.org/wiki/Superheaterhttps://en.wikipedia.org/wiki/Thermal_power_stationhttps://en.wikipedia.org/wiki/Thermal_power_stationhttps://en.wikipedia.org/wiki/Fire-tube_boilerhttps://en.wikipedia.org/wiki/Boiler_(steam_generator)https://en.wikipedia.org/wiki/Furnace#Industrial_furnaceshttps://en.wikipedia.org/wiki/Steamhttps://en.wikipedia.org/wiki/Steam_drumhttps://en.wikipedia.org/wiki/Superheaterhttps://en.wikipedia.org/wiki/Thermal_power_stationhttps://en.wikipedia.org/wiki/Thermal_power_stationhttps://en.wikipedia.org/wiki/Fire-tube_boilerhttps://en.wikipedia.org/wiki/Water-tube_boiler#cite_note-1

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