Page 267 - Boiler plant and distribution system optimization manual
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252 Boiler Plant and Distribution System Optimization Manual
External Steam Leaks If it can be returned to the boiler feed system,
Steam leaks to the atmosphere are usually it can be recycled with little further treatment. By
visible, audible or both. Because of the safety haz- reusing the condensate, you avoid the need for
ard they present, they are usually fixed quickly, more raw water to be purchased and treated and
However many leaks seem to go on being neglect- you can avoid the sewage costs which can be in-
ed for years. Their large plumes are hard to hide curred when condensate is allowed to run to the
and can be seen for long distances (Table 13.6). drain. Also, this condensate contains valuable
heat energy that was paid for in the boiler fuel;
Table 13.6—Steam leak energy loss estimates based energy that an efficient condensate recovery sys-
on steam plume length. tem will conserve.
The efficiency of a condensate return system
can be improved, sometimes dramatically. For
example, Table 13.7 shows annual dollar savings
from improving condensate return. Savings are
based on steam generation cost of $6.00 per 1,000
lbs. Make up improves from 100% to just 10%, a
90% reduction. Annual dollar savings for three
boiler sizes listed include water cost, chemical
treatment and energy savings.
Table 13.7—Annual cost reduction from
improving condensate return.
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Internal Steam Leaks
100 BHP 250 BHP 500 BHP
Steam plumes are easy to spot. What about
the steam leaks you can’t see? Leaks inside steam
$21,900 $54,750 $109,500
systems are invisible.
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Valves in bypasses around steam taps are
prime candidates for this type of leakage. They
The Basic Challenge
are often opened to assist system start up or to
The condensate system is perhaps the most
vent excessive air and can easily be forgotten or
ignored and least understood system in a steam
only closed partially or develop leaks over time.
using facility. An examination of the dollar sav-
The need for bypasses should always be
ings listed in Table 13.7 suggests that it might be
questioned. If they are needed for startup it is
profitable to spend some time studying your con-
likely that their real purpose is the discharge of
densate systems.
non-condensible gasses faster than a steam trap
One of the most useful instruments for this
can handle them. An automatic air vent can do the
job is a makeup water meter. It can be used to de-
job better and more economically. A trap could be
tect system leaks, malfunctioning system compo-
installed in the bypass line as a back up in case re-
nents as well provide an excellent basis for calcu-
pairs are required for the main trap or to provide
lating wasted energy.
more capacity during high loads. This way the li-
ability of internal steam loss can be prevented.
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The rule of thumb on condensate return
Condensate Return System Losses
energy is:
Condensate is certainly not waste water. It
is water that has been preheated, softened, made
For each 11°F the water temperature is cooled,
suitable for use as boiler feedwater, and then dis-
it loses 1% of efficiency for the system.
tilled.
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