Page 56 - Boiler plant and distribution system optimization manual

Basic Boiler Plant Efficiency
These cold air purges act to cool down the boiler
wasting energy.
The cause of unusually hot boiler rooms usu-
ally this heat from hot surfaces. Good design and
maintenance can reduce this loss significantly.
Figure 4.10—How infrared measurements of boiler
surface temperatures and radiation heat loss mea-
surements can be used evaluate conditions. This is a
chart of one such survey.
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Figure 4.11—As boiler load decreases the percent-
age of losses increase. These losses remain relatively
constant but because the percentage loss is a func-
tion of the actual load, the percentage loss increases
as the load goes down. A 2% surface loss is illustrat-
ed above to show the relationship more dramatically.
AS-FOUND EFFICIENCY
The largest boiler losses are stack losses, boil-
er surface losses and blowdown losses. In our ex-
ample boiler, shown in Figure 4.12, they add up to
22% giving an efficiency of 78%. These losses are
not all of the losses but they represent the major
losses that can be measured easily and corrected
economically.
Figure 4.12—When the percent losses are subtracted
from 100% an approximation of efficiency is possi-
ble.