Steam drum

Steam drums are a regular feature of water tube boilers. It is a reservoir of water/steam at the top end of the water tubes in the water-tube boiler. They store the steam generated in the water tubes and act as a phase separator for the steam/water mixture. The difference in densities between hot and cold water helps in the accumulation of the "hotter"-water/and saturated-steam into the steam-drum.  

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Construction

Made from low Carbon Steel with high tensile strength and its working involves temperatures around 390^oC and pressures well above 350 psi(2.4MPa). The separated steam is drawn out from the top section of the drum and distributed for process. Further heating of the saturated steam will make superheated steam normally used to drive steam turbine. Saturated steam is drawn off the top of the drum and re-enter the furnace in through a superheater. Steam and water mixture enter the steam drum through riser tubes, drum internals consisting of demister separate the water droplets from the steam producing dry steam. The saturated water at the bottom of steam drum flows down through down comers pipe, normally unheated to headers and water drum. Its accessories include a safety valve, water level indicator and level controller. Feed water of boiler is also fed to the steam drum trough a feed pipe extending inside the drum, along the length of the steam drum. A steam drum is used without or in the company of a mud-drum/feed water drum which is located at a lower level.Boilers with both steam drum and mud/water drum is called a bi-drum boiler and boiler with only steam drum is called a mono drum boiler. The bi-drum boiler construction is normally intended for low pressure rating boiler while the mono drum is mostly designed for higher pressure rating.