Retrotec USACE User Manual
Page 180
D50 ENERGY & PROCESS ASSESSMENT PROTOCOL
boiler. For effi cient operation, carbon monoxide is the best (but the most
expensive) monitor. Carbon dioxide works well if only one fuel type is in
use. The sensing of oxygen may give false readings due to air leaks into the
fl ue. Based on a fl ue gas temperature of 350° F, the following are good op-
erating conditions for effi cient operation:
Fuel
Excess Air
Oxygen
Carbon Monoxide
Carbon Dioxide
Natural gas
7%
1.5%
<100 ppm
11%
#2 fuel oil
10%
2%
<100 ppm
14.1%
D.4.1.11 Boiler Tubes Not Cleaned in Two Years (Ineffi ciency)
Figure D82. Inside of boiler, showing heat
exchanger tubes.
Most large boilers are of a water tube design; in boilers of this design,
water is heated in tubes that surround the combustion chamber (Figure
D82). Even with the best water treatment, dirt and slag can form on
the inside of these tubes, which limits the heat transfer and can lead to
overheating the tubes. Poor heat transfer results in poor boiler efficiency,
while tube overheating can result in leaks due to tube failure. Because of
these concerns, boilers are normally opened for inspection and cleaning
once a year. The inside of the boiler tubes are scrubbed with brushes at
this time. If this cleaning has not taken place in two years, it should be a
point of concern.