Page 104 - Boiler plant and distribution system optimization manual
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Chapter 9
Boiler Tuneup
[The Importance of Operating Boilers with Minimum Excess Air]
Reducing excess air is one of the most ef- adding something new to a boiler if it can be cor-
fective boiler improvement techniques one can rected by maintenance and repairs or a tuneup.
apply without high capital cost. When excess air
is reduced, several things are accomplished:
A TUNEUP STARTS WITH
• When hot combustion gases leave a boiler,
AN INSPECTION AND TESTING
they have the potential to carry away a lot
of waste energy. The less volume of exhaust
Efficiency improvements obtained under a
gas, the less loss there is.
deteriorated state of the boiler can be substan-
• Flue gas velocity is reduced increasing the tially less than the improvements achieved under
time available for heat transfer in the boiler. proper working conditions. Therefore, it is essen-
• Flame temperature is raised, increasing ra- tial that the boiler be examined prior to testing
diant heat transfer in the combustion zone and that necessary repairs and maintenance be
walls. Heat transfer in the combustion or ra- completed.
diant heat transfer zone is very efficient and One of the first questions in tuning up an
becomes more efficient as flame temperature operating boiler is whether or not is necessary to
goes up. This increase of heat exchange effi- take the boiler out of operation and go through
ciency reduces stack temperatures. the expense of opening it up for a formal inspec-
tion.
• Pollution is reduced because less fuel is re- A preliminary efficiency test and review
quired to meet the same demands. of records might provide valuable information
about a boilers operating condition and whether
The increase in efficiency available from or not a more detailed inspection is necessary.
tuning up a boiler has three direct and related The condition of the burner system and
benefits: combustion process can be judged by the excess
(1) it saves fuel dollars, oxygen level. Boiler start up records and records
of previous tuneups provide a valuable reference
(2) it reduces the cost of energy at the point of
point for your tuneup program. Even a call to the
use and
manufacturer can provide useful information on
(3) it increases the steam output available from the boiler’s expected performance characteristics
a boiler (increased productivity). and minimum expected excess air levels.
The two important goals of a boiler tuneup
When evaluating boiler efficiency improve- are minimum excess air and stack temperature.
ment projects, cost and benefit calculations must Figure 9.1 shows the zone of highest efficiency
be based on the tuned up efficiency of the boiler where excess air [oxygen] is lowest and just be-
to prevent false estimates of benefits. It doesn’t fore carbon monoxide and combustibles, in the
make sense to attempt to correct a problem by form of carbon monoxide, hydrogen and un-
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