Page 64 - Boiler plant and distribution system optimization manual
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Distribution System Efficiency 49
ly and often predicts that insulating bare pipe will ———————————————————————
pay off in less than a month. 120
—————— = 11.7%
1204 x 0.85
———————————————————————
MEASURING INSULATION LOSSES
A useful way to measure insulation losses is ExTERNAL STEAM LEAKS
to weigh the condensate produced by a section
of piping under study. This is sometimes called External steam leaks are usually visible and
the barrel test as it requires a barrel, a scale and the length of the plume can be measured by eye.
a drain connection to the discharge end of the The following chapter on steam systems has more
steam trap. If the piping being tested is typical information on this. In our example system there
of the entire system, then an overall estimate of are 4 visible steam leaks, two 6 foot plumes and
system performance is possible. The effectiveness two 8 foot plumes. This works out to an $84,000
of insulation under different conditions can also a year loss plus the cost of water, chemicals and
be studied by the change in condensate formed fuel wasted heating make up water to operating
when the piping is exposed to variable conditions temperature.
of weather such as changing temperatures, hu-
midity, rain and wind conditions.
INTERNAL STEAM LEAKS
CONDENSATE SYSTEM LOSSES Internal steam leaks are hard to detect but
common sense indicates there could be many
Recycling hot condensate for reuse as boiler such leaks. Steam traps are installed with bypass
feed water is an important way to maintain the valves which can be opened in the event there is
efficiency of the system. The energy used to heat a problem with the trap. The bypass valves are
cold make-up water is a major part of the heat often opened on start up or when water hammer
delivered for use by the steam system. becomes a problem in the system. Steam driven
For example, in the system under study, the equipment such as turbines and pumps often
condensate should return at 182 F [83 C], but if it have drains and warm up systems and these can
returns to the boiler plant at 127 F [53 C]; 55 F [30 be left open too. In our example 10 traps had par-
C] cooler, it will cause a loss of 5 million Btu/hr, a tially open bypass valves averaging 75 pounds
4.8% energy loss costing $242,000 a year. per hour. This was costing $26,500 a year.
If no condensate is returned to the plant and
62 F [17 C] make-up water is used instead, this
will cause a 11.4% loss costing $581,000 a year. STEAM TRAP MALFUNCTIONS
In this example we can see that heating cold
make-up water requires a significant energy in- It is not unusual to find that half of the steam
vestment; 11.7% of the heat in the steam. traps in a plant aren’t functioning properly. They
The formula below illustrates this point: work in a harsh environment and have an uncer-
tain lifetime measured from 3 to 5 years. In our
a. Heat loss 120 Btu/lb, using 62 F water rather example we have uncovered 35 defective traps
than 182 F condensate return. wasting on the average of 50 pounds of steam per
hour costing about $62,000 a year. [See chapter on
b. Heat in Steam 1204 Btu/lb steam traps]
c. Boiler Efficiency 85%
