MIL-HDBK-1003/6
c)
Decreased efficiency,
d)
Increased power factor.
The reverse effect may be expected with voltage above normal.
Other design criteria such as frequency, voltage regulations, etc., further
affect performance and must be coordinated with the primary power supply.
The designer shall obtain suppliers data on final motor selection
for the following:
a)
Maximum load torques,
b) Starting, pull-up and breakdown torques greater than the
respective torque values of the load speed-torque curves,
c)
Accelerating capacity to meet maximum allowable time to come to
speed,
d)
Maximum starts per hour to protect motor winding,
e) Motor efficiencies at various speeds and loads for multispeed
and variable speed motors,
f) Requirements for explosion-proof, dustproof or waterproof
installations.
8.5
Economizers
General. Economizers use the relatively low temperature flue gas
8.5.1
leaving the boiler to heat the feedwater entering the boiler. Economizers
will increase boiler efficiency by approximately 1 percent for every 10
degrees F (5.6 degrees C) increase in feedwater temperature or for a 40
degree F (22.2 degrees C) reduction in exit gas temperature.
Applications. Economizers may be furnished as an integral part of
8.5.2
the steam generator, as an accessory in the flue gas system of the original
installation or as a subsequent retrofit item. Economizers are not
practically applied to HTW boilers because of the low flue gas exit
temperatures. When applicable to steam generators consideration must be given
to all factors affecting design. These considerations include:
a) Type of fuel and sulfur content. The dew point and rate of
corrosion increase as the sulfur content increases. See Figure 37.
b) Operating pressure and temperature. The flue gas temperature
must be higher than the steam temperature in a boiling tank for heat transfer
to take place. Therefore economizers are better suited for high pressure
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