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 (e) corrosion can be minimized by the following methods:
( 1 ) Proper Operation. Since carbon dioxide and oxygen are the main
offenders, any operating method that reduces the content of carbon dioxide
a n d / o r oxygen will reduce the corrosive effects. Operate nonaerating heaters
at the temperatures, pressures, and ratings recommended by the manufacturer
for proper release of noncondensible gases (mainly CO2 and oxygen).
( 2 ) External Treatment. Different types of pretreatment of makeup
water may be required, as for example: l i m e - s o d a softening, hot lime zeolite
s o f t e n i n g , acid-cycle softener, a n d the salt splitting process. The choice of
any of these methods depends on the economics of the individual case and the
c h a r a c t e r i s t i c s of the available water. A l l types reduce the quantity of
C O 2 or bicarbonate fed to boilers, thus reducing return line corrosion.
( 3 ) Internal Treatment. Corrosion of return piping can be
controlled by the use of amines. Amines are chemical compounds that raise the
a l k a l i n i t y of the water. Some of the simpler types are soluble and volatilize
f r o m boiler water. A m i n e s inhibit corrosion by protecting the surface of the
m e t a l , as well as by raising the pH (increasing the alkalinity) of the
I n the concentrations required for protection of condensate
condensate.
piping, amines do not affect nonferrous metals, are nontoxic, and are stable
at temperatures approximating 765F.
2.1 Condensate Return Systems. Condensate may return to the boiler plant by
gravity or by the use of mechanical means.
2 . 1 . 1 Gravity Return. I n gravity return systems, condensate returns to the
boiler under its own hydraulic head. The elevation of the steam-using units
above the boiler waterline must be sufficient to overcome pressure drops
c a u s e d by flow, as well as operational pressure differentials.
2 . 1 . 2 Mechanical Return. Condensate pumps are used to return condensate from
Figure 4-4 illustrates
a building or group of buildings to the boiler plant.
a typical condensate return unit. T h e unit consists of a receiver with a
water gauge, a motor driven centrifugal pump, and a f l o a t c o n t r o l . The pump
o p e r a t e s intermittently under the action of the flo a t control switch.
P e r f o r m the following procedures for HTW pump
3 OPERATION OF HTW PUMPS.
operation.
3 . 1 Startup Inspection. When starting a new unit, o r a f t e r a g e n e r a l
o v e r h a u l , make sure the following requirements are fulfilled.
( a ) A l l i n s t a l l a t i o n , r e p a i r , and cleanup work is completed.
(b) Installation is tested for leaks.
(c) Unit is aligned.
( d ) Unit is lubricated with an approved lubricant.
(e) Pump is turned over by hand to make sure that it is free.
4-19
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