The preheater increases the temperature of air entering the furnace by using waste heat from flue gases. It consists of tubes through which hot flue gases pass, heating the air circulated around the tubes in a zig-zag pattern. Preheating the air accelerates combustion and allows inferior coal grades to burn efficiently, reducing fuel consumption by 15% and improving combustion efficiency.

1. PREHEATER
ROSHAN
MATHEW
SE MECH A
R.NO- 39
9699351643

2. INTRODUCTION
 The function of the pre-heater is to increase the
temperature of the air before it enters the
furnace .
 It is generally placed after the economiser ; so
the flue gases pass through the economiser and
then to the air pre-heater
 Pre- heated air accelerates the combustion and
facilitates the burning of the coal

3. WORKING
 After leaving the boiler or the economiser
the gaseous products of the combustion
travel through the inside of the tubes of the
air pre- heater
 The plate type consists of number of
parallel plates
 The hot gases are passed through the
tubes and air circulates around them

5.  Air is forced to deflect by using baffles and
are compelled to move in a zig-zag path for
number of times
 This increases the period of contact
between the air and the hot surface
 Hence air is effectively heated

6.  Thus the gases gets initially heated before
being supplied to the furnace .
 A soot hopper is fitted at the bottom of air
heater casing to collect the soot

7. ADVANTAGES
 Waste heat from the flue gases is recovered
for heating air and reduces the fuel
consumption by 15%
 Inferior grades of coal can be burnt efficiently
with pre- heated air
 Combustion can be more efficient and an
intense flame can be achieved in the furnace