Page 121 - Boiler plant and distribution system optimization manual
P. 121
106 Boiler Plant and Distribution System Optimization Manual
may also affect conditions at other firing excess oxygen levels for both fuels at all firing
rates. In such cases, choose the settings that rates. Based on information gained from the tune-
give the best performance over a wide range up procedure, a judgment can be made as to the
of firing rates. A trial-and-error approach, best conditions which are practical.
one involving repeated tests, may be neces-
sary. Evaluation of the New Low O Settings
2
If energy gains are to be realized, the new
Many experts agree that it generally is best low O settings must be realistic and they must
2
not to make any adjustments to your control be maintained. Pay extra attention to furnace
system in the lower control range of your boiler and flame patterns for the first month or two
without being very careful. Air flow requirements following implementation of the new adjust-
at low-fire conditions usually are dictated by ments. Thoroughly inspect the boiler during the
flame ignition characteristics and stability rather next shutdown. To assure high boiler efficiency,
than by efficiency. Air/fuel ratios at low loads periodically make performance evaluations and
and at or near light off conditions are very sensi- compare with the results obtained during the test
tive and any changes may jeopardize safe light- program.
off characteristics. If boiler load requirements
force a boiler to operate at low loads much of the
time, check with the boiler manufacturers service REVIEW OF THE FINE TUNING PROCESS
group or a qualified combustion consultant be-
fore establishing excess-oxygen levels. It is sometimes possible during the optimi-
zation program to lower the CO or smoke limits,
10. Verify that the new settings can accommo- to achieve even lower excess air levels achieving
date the sudden load changes that may occur greater efficiency gains. If the burner and fuel
in daily operation without adverse affects. systems are not functioning properly your best
Do this by increasing and decreasing the efforts at lowering excess air may be wasted. The
load rapidly while observing the flame and approach to this procedure is to insure that every-
stack. If you detect undesirable conditions, thing is in conformance with the manufacturers
reset the combustion controls to provide a recommendations and then conduct organized
slightly higher level of excess oxygen at the “trial-and-error” (Table 9.2) adjustments in such a
affected firing rates. Next verify these new way that meaningful comparisons can be made.
settings in a similar fashion. Then make sure Items that may result in lower minimum ex-
that the final control settings are recorded at cess O levels include:
2
steady-state operating conditions for future
reference. • Burner register settings
• Oil gun tip position
Repeat these checks at frequent intervals un- • Diffuser position
til it becomes obvious that the boiler is not having • Fuel oil temperature
problems that cause it to exceed smoke or CO lim- • Fuel oil atomizing pressure
its or that control, burner or fuel system problems • Coal spreader adjustments
are not causing unsafe conditions to develop. It is • Coal particle size
easy to hide such problems my making high ex-
cess oxygen adjustments. Trying to optimize per- The effect of these adjustments on minimum
formance will cause these problems to reemerge. O are variable from boiler to boiler and difficult
2
When an alternative fuel is burned, perform to predict.
these same tests and adjustments for the second The principal method used for improving
fuel. It is not always possible to achieve optimum boiler efficiency involves operating the boiler at
