Civil Engineering Reference
In-Depth Information
Fig. 6.12
Variation in boiler efficiency losses with changes in boiler firing rate with natural gas in
two operating conditions (O
2
% is kept constant to roughly 3 % in volume—see Table
6.8
—over
the load range by means of combustion control; O
2
% increases linearly as load is reduced if
combustion control is not installed)
6.9
Auxiliary Equipment
Auxiliary equipment can be divided into heat recovery systems and water treatment
systems.
6.9.1 Heat-Recovery Systems
Flue gas going up the stack contains a considerable amount of thermal energy, part
of which can be recovered by installing air preheaters and economizers.
Air preheaters are used to transfer heat from the stack flue gas to the incoming
combustion air. In this way boiler efficiency is improved because of (1) reduction of
stack gas temperature (2) reduction of excess air due to improved burner combus-
tion conditions if preheated air is supplied.
