Page 132 - Boiler plant and distribution system optimization manual
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Over 100 Ways to Improve Efficiency 117
2. Steam system pipe temperatures are lower shell losses become higher percentage of fuel use
3. Steam leaks are less and frequent “on” and “off” cold air purge cycles
4. Steam trap flash losses are less send a lot of valuable heat out the exhaust. Boilers
typically have very poor efficiency at low loads
Possible Disadvantages so this type of operation can be quite inefficient.
1. Excessive piping velocities due to higher Often boilers with measured efficiencies over 80%
volume of steam flow have been found to be operating at less than 60%
2. Pressure to emergency pumps and genera- efficiency on an annual basis.
tors may not be high enough There are many solutions to this problem,
which usually starts with the original design
3. Boiler priming [dangerous slugs of water
where large safety factors were employed to in-
entering the steam system]
sure against inadequate steam supply on the cold-
4. Noisy steam valves [essential element of
est windiest day of the year. However, insulation
steam valve design]
improvements, energy conservation measures
5. Temperature sensitive traps may start to and mild weather can put these over-designed
blow through steam high capacity systems into the energy wasting
6. Cavitation noises in feedwater valves mode.
7. Atomizing steam pressure may be too low The answer to managing boilers efficiently is
simply stated: “You have to know the efficiency
8. Differential pressure across steam traps
of your boilers at all firing rates and you have to
may change capacity of some types of
take into account these standby losses.”
traps
9. Steam traps will have to handle more con- Advantages/Disadvantages
densate Knowing the losses incurred at each level
10. Pumping capacity of original design may of operation and having a plan to minimize the
change inefficient levels is a good management practice.
11. Calibration of flow meters may change Although it may be take extra effort to get the real
time performance data required for true operat-
One way to approach lowering steam pres- ing efficiencies of boiler systems, it must be done
sure is to do it gradually over a period of time if energy dollars are to be saved. In some cases a
and watching for changes in system operation continuous computerized monitoring of the sys-
and correcting them if possible.. tem may be required.
7. AVOID LOW FIRING RATES 8. MAINTAIN LOW
BOILER ExHAUST TEMPERATURES
Some boiler plants are oversized for their
current loads, or small boilers are not available Figure 10.11 and 10.12 show the influence of
to handle light loads of summer or partial plant exhaust temperature on efficiency. Boilers usually
production schedules. This is caused by the boil- run 24 hours a day month after month running
er cycling on and off continually because of the up very expensive fuel bills. Keeping a watchful
low load factor. Each time the boiler starts up or eye on shifts in exhaust temperature can really
shuts down cold air is blown through it to purge pay off. Heating oil and heavy fuel oils are espe-
out any possible accumulations of unburned fuel cially prone to fouling which retards heat transfer
as a safety precaution. This plus normal heat pushing temperatures up. This can happen very
loss to the environment can add up to a signifi- quickly, within a few hours and staff must be alert
cant percent of its operational fuel demand. The for this.
