This document discusses boiler draught, which refers to the pressure difference needed to move air and flue gases through a boiler. It describes three types of draught: natural draught created by chimney effect; forced draught using a fan at the boiler's base; and induced draught using a fan at the chimney top. Balanced draught, a combination of forced and induced, helps overcome issues like blowback when opening furnace doors. Artificial draught provides better control and efficiency than natural draught. Losses occur due to friction in moving air and gases through the boiler system.

1. BOILER
DRAUGHT
By-
Umesh Ghuge 64
(11920115)
Ahmed Shah 69
(11920152)

2. BOILER
DRAUGHT
To move the air through the fuel bed and to
produce a flow of hot gases through the boiler,
economizer, preheater and chimney require a
difference of pressure.
The difference of pressure for maintaining the
constant flow of air and discharging the gases
through the chimney to atmosphere is known as

3. TYPES OF
DRAUGHT
Natural Draught
Artificial Draught
•Forced
•Induced
•Balanced

4. NATURAL DRAUGHT
The Draught
required is
created by
Chimney
It does not require
any external
power for
producing the
draught.

5. LIMITATION
S OF
NATURAL
DRAUGHT
The maximum pressure is limited to
15 – 20 mm of water (196 N/m sq.)
under normal atmospheric temp.
The draught decreases with increase
in outside air temperature.
Combustion is very poor.

6. ARTIFICIAL
DRAUGHT
Natural Draught provides insufficient
head and lack of flexibility hence
Artificial Draught is used.
The requirement of draught in actual
power plant is high (300 mm of water)
and to meet high draught
requirements, some other system
must be used.

7. FORCED DRAUGHT
In a forced draught
system, a blower is
installed near the
base of the boiler
and air is forced to
pass through the
furnace, flues,
economizer, air-
preheater and to
the chimney.
The chimney is only
used to discharge
gases high in the
atmosphere to
prevent the
contamination.

8. INDUCED DRAUGHT
The blower is located
near the base of the
chimney The air is
sucked in the system
by reducing the
pressure through the
system below
atmosphere pressure.
The induced draught
fan sucks the burned
gases from the furnace
and the pressure inside
the furnace is reduced
below atmosphere and
induces the
atmospheric air to flow
through the furnace.
The draught produced
is independent of the
temperature of the hot
gases.

9. DISADVANT
AGES OF
FORCED
AND
INDUCED
In the forced draught the furnace cannot be
opened either for firing or inspection
because of high-pressure air inside the
furnace which will try to blow out suddenly
and there is every chance of blowing out the
fire completely and furnace stops.
In the induced draught the furnace cannot
be opened either for firing or inspection
because the cold air will try to rush into the
furnace as the pressure inside the furnace is
below atmospheric pressure.

10. BALANCED DRAUGHT
To overcome
drawbacks a balanced
draught is used, which
is a combination of
forced and induced
draught.
The forced draught
overcomes the
resistance of the fuel
bed therefore sufficient
air is supplied for
proper and complete
combustion.
The induced draught
maintains pressure in
the furnace just below
atmosphere. This helps
to prevent the blow-off
when the doors are
opened as the leakage
of air is inwards.

11. BENEFITS
OF
ARTIFICIAL
DRAUGHT
It is better in control and more
economical than natural draught.
The rate of combustion is high.
The air flow can be regulated
according to the requirement.
It prevents the formation of smoke
as complete combustion is possible

12. LOSSES IN
BOILER
DRAUGHT
Frictional resistance offered to the
flow of flue gases.
Bends in gas flow, offer flow
resistance.
Loss due to friction head in grate,
economizer, super heater etc.
Loss due to flow resistance offered
by chimney.

13. THANKS!!
Any questions?