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Fresh Air from atmosphere is
fed onto the surface of combustion chamber through
a statically & dynamically balance blower.
The shape of passage ensures to form an envelope
on the combustion chamber to extract maximum heat,
thus higher heat transfer efficiency. The air
continues to pass through outer surface of heat
exchanger, gaining heat & is collected at
the other end of hot air generator. The generation
of hot air is within minutes of its start.
Indirect fired hot air generator
types are,
a) Fuel fired HAG
This consists of multiple shell
in shell construction or shell and tube construction.
The process air does not come in contact with
the flame or the combustion gases. The combustion
gas path and process air paths are different.
The heat from flue gases is recovered for maximum
thermal efficiency. Thermal efficiency up to 88%
are easily achieved in these hot air generators.
Air temperatures up to 350 degree C are possible
in these types of heaters. The material of construction
of combustion chamber is SS 310 and the outer
shells are either made up of carbon steel and
spray galvanised or are made up of stainless steel.
For GMP plants the complete construction is in
stainless steel.
b) Steam/ Thermic Fluid heated
air heater
These consist of a bank of fin
tube radiators. The process air passes over the
fin tubes through which either steam or thermic
fluid flows. Thus indirect heating of air takes
place. Temperatures from 250 to 300 deg. C are
achievable depending upon the steam and thermic
fluid temperatures. The material of construction
of tubes is either carbon steel or stainless steel
depending upon process requirement. The mounting
of these heaters can be either horizontal or vertical.
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