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 When the load fluctuates, automatic starting and stopping by means of level
c o n t r o l is usually employed.
1.5 Filling and Emergency Pump. Often, the size of the makeup feedwater pump
i s inadequate to fill the system in a reasonable time. A c o l d w a t e r f i l l i n g
pump, with a capacity ranging from 100 to 200 gpm, is used in those cases to
f i l l t h e s y s t e m . T h i s pump delivers cold water from the treated cold water
tank to the expansion tank; connections are also made to the boiler and pipe
l i n e s f o r f i l l i n g p u r p o s e s . When used for emergency feeding, or as a standby
for the makeup pump, suction must also be connected to the feedwater heater or
t o the storage tank. For emergency makeup, the pump should be sized to
d i s c h a r g e stored makeup water into a boiler circulating system to feed one
b o i l e r for approximately 10 minutes at full steaming capacity. This will make
u p for steam lost in the lowest set safety valve on the expansion tank in the
e v e n t it is stuck open.
2 CONDENSATE RETURN. T h e following practices are important in the operation
of condensate return systems.
(a) Ensure the maximum amount of condensate is returned to the central
b o i l e r p l a n t . This practice saves heat and reduces makeup water
I n turn, both the investment costs for water treatment
requirements.
equipment and the costs of treating makeup water are reduced.
( b ) Condensate losses should be minimized. Losses of condensate lead to
increased costs for makeup water. Poorly operating traps may waste steam,
causing losses which must be replaced by makeup water to the boilers. B o i l e r
blowdown operations should be reduced to the minimum required to control
s o l i d s in boiler water within speci f i e d l i m i t s . Excessive blowdown results in
h e a t waste and requires additional m a k e u p water to replace that lost through
blowdown.
( c ) To avoid possible contam ination, condensate from some sources should
b e discarded rather than returned. If such condensate is to be discharged
i n t o a terra cotta or concrete sewer, i t should first be piped through a
cooling basin or sump, or a proper arrangement should be used to lower its
T h i s will prevent damage to the sewer. Do not return condensate
temperature.
f r o m any source likely to produce contamination, such as: pickling tanks,
e l e c t r o p l a t i n g baths, decreasing equipment, or open steam cookers.
( d ) Monitor system regularly for acid corrosion. In general, condensate
i s pure water with no salts or causticity. However, carbon dioxide (CO2),
w h i c h enters the boiler system with the feedwater, carries over with the steam
a n d dissolves in the condensate, making it acidic. A l s o , oxygen often leaks
in at pipe connections and glands. Acid corrosion caused by CO2 usually
r e s u l t s in grooving or channeling along the bottom of the pipe, or in a
u n i f o r m thinning of the metal. T h i s produces initial failure at threaded
j o i n t s where the piping is thin and where stress may accelerate the attack.
T h i s condition exists just after the traps of hot water generators or
r a d i a t o r s . O x y g e n corrosion is characterized by general pitting over the
c i r c u m f e r e n c e of the pipe.
4-18
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