Answer / vinoth

when water is converted into steam, huge quantity of
dissolved salts are residues of this conversion. They
normally settle down in the bottom of the Boiler drum. In
CBD, we continuously remove this dissolved salts otherwise
it will get carry over with steam and damage the blades of
turbine. Where as IBD is to remove Excess feed water which
crosses the Seperator level inside the boiler drum.so IBD is
to prevent carry over water with steam where CBD is to
prevent carry over of scales with steam.
with above description, we can easily predict why IBD is
in higher elevated than CBD.

Answer / shahnawaz ahmad

Intermittent blowdown better known as bottom blowdown or mud drum blowdown is done to remove undissolved solids from the mud drum of a boiler or from the bottom of the shell of a fire tube boiler. Some boilers operated at high pressure with super clean water dont need this very often. The pipe from the mud drum goes to a tank the purpose of which is to reduce the pressure to atmospheric and to reject heat so that the water/mud mixture is cool enough not to damage the sewer lines or whatever fixtures it flows to. This tank is the intermittent blowdown tank or the atmospheric blowdown tank since it is vented to atmosphere.

The continuous blowdown tank is a flash tank used to collect heat from the water that is continuously drawn from the steam drum in order to control the dissolved solids. As water is boiled off to steam in the steam drum anything that will not evaporate is left behind and this will increase the concentration of dissolved solids in the boiler water. This is bad because the solids will precipitate out and form scale which must be removed chemically and water with high solids concentration will start to foam which will cause level control problems and will also result in material carrying over with the steam resulting in deposits in the superheater tubes and headers. To control this some of the high concentration boiler water is drawn off and replaced with lower concentration feed water.

This flows to a tank at a lower pressure than that in the drum and some of the water flashes to steam, which can be used to heat feedwater or what have you. The liquid left over can be used in a heat exchanger to heat make-up water or it can flow through a standby boiler to keep it warm and to maintain the chemicals in the water or to the circulating water in a cooling tower or to the atmospheric blow down tank.

Answer / anikettech

Remember, CBD is mounted at Boiler water level while IBD is mounted at bottom of Boiler. Therefore, inlet vent of CBD is always at higher elevation than inlet vent of IBD.

Answer / tarun

intermeediate blow down is higher elevation than cbd for releasing high pressure to air vent to atmosphere

Answer / randhir singh

CBD uses to remove floating impurites which collectes on top of water and IBD uses to remove TDS which collects in bottom (mud drum). So CBD vent kept at higher elevation than IBD vent.

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