DIFFERENT TYPES OF CHIMNEYS

VIKAS CHINNAPPA

The draught system is the most essential system of a thermal power plant

A chimney is a vertical tubular structure of masonry, concrete or steel

It is built to enclose a column of hot gases to produce the draught

To produce required flow of air through boiler, economiser, preheater, chimney, pressure differential are needed

Supplies required quantity of air and removes burnt gases from furnace

CHIMNEYS

Draught

Natural/Chimney

Artificial

Steamjet

Induced

Forced

Mechanical

Induced

Balanced

forced

Obtained by a tall chimney or a stack Small capacity boilers It is created by the density difference between

the atmospheric air and hot gas in the stack It produces draught and air flows through the

fuel bed, furnace, boiler passes. It discharges effluents at a certain height to

prevent air pollution Creation of chimney draught requires hotter

flue gases which reduce the efficiency of the power plant

NATURAL OR CHIMNEY DRAUGHT

ADVANTAGES No external power Low maintenance cost Long life Less investmentDISADVANTAGES Low pressure difference Draught created is at the expense of

thermal efficiency Poor combustion and increases fuel

consumption Not flexible for variable loads

A fan is used to deliver air to the furnace Pressure in the furnace is higher than

atmospheric pressure As pressure is higher it s known as positive

draught Draught produced by chimney is not

significant

FORCED DRAUGHT SYSTEM

Created by fan and chimney to produce a draught

Pressure in the furnace is below atmospheric Fan is located at the base of the stack and

has to handle hot flue gases Requires higher power and has to handle

corrosive action and fly ash Gases can be discharged at the lowest

possible temperature using heat recovery units

INDUCED DRAUGHT SYSTEM

It is a combination of forced and induced draught

The forced draught fan delivers air into the furnace and an induced draught fan removes gas from the unit

Opening the furnace for inspection or firing is not possible

BALANCED DRAUGHT