Draught
Draught is a small pressure difference causing flow of flue gas and air through the boilers. It is necessary for efficient combustion and to release the gases at sufficient height to avoid local pollution. There are mainly three types of draughts—induced draught, force draught, and natural draught.
Natural draught is pressure difference of hot gases column inside the chimney and cold air column of same height outside the chimney, whereas the artificial draught is created by means of mechanical fans. The fans used in boilers are induced draught, forced draught, and balanced draught.
Induced Draught
If a mechanical induced fan is used at the base of chimney to suck the air and flue gases from furnace, the draught created is known as induced draught.
Forced Draught
If a mechanical fan is installed at the gate of the furnace to force the air inside the furnace, the draught created is known as forced draught.
Balanced Draught
If both forced draught and induced draught fans are used in a boiler, the draught created is known as balanced draught.
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