Most auxiliary machinery operates on saturated
steam. Reciprocating machinery, in particular,
requires saturated steam to lubricate internal
moving parts of the steam end. Naval boilers,
therefore, produce both saturated steam and
The EXPANSION area of the main steam
system is that part of the basic steam cycle in
which steam from the boilers to the main turbines
is expanded. This removes the heat energy stored
in the steam and transforms that energy into
mechanical energy of rotation.
The main turbines usually have a high-pressure
(HP) turbine and a low-pressure (LP) turbine. The
steam flows into the HP turbine and on into the
LP turbine. Area B of figure 3-1 shows the
expansion area of the main steam system. This
portion of the main steam system contains HP
and LP turbines.
Each ship must produce enough feedwater for
the boilers and still maintain an efficient
engineering plant. Therefore, feedwater is used
over and over again.
As the steam leaves or exhausts from the LP
turbine, it enters the CONDENSATE system. The
condensate system is that part of the steam cycle
in which the steam is condensed back to water.
Then it flows from the main condenser toward
the boilers while it is being prepared for use as
The components of the condensate system are
(1) the main condenser, (2) the main condensate
pump, (3) the main air ejector condenser, and
(4) the top half of the deaerating feed tank (DFT).
These components are shown in area C of figure
The main condenser receives steam from the
LP turbine. It condenses the steam into water. We
will explain this process in the next chapter on
boilers. The main condensate pump takes suction
from the main condenser hot well. It delivers the
condensate into the condensate piping system and
through the main air ejector condenser. As its
name implies, the air ejector removes air and
noncondensable gases from the main condenser
that leak or are discharged into it during normal
operation. The condensate is used as a cooling
medium for condensing the steam in the inter and
after condensers of the main air ejector.
The DFT (fig. 3-2) is the dividing line between
condensate and feedwater. The condensate enters
the DFT through the spray nozzles and turns
into feedwater in the reservoir section of the DFT.
The DFT has three basic functions:
l To remove dissolved oxygen and non-
condensable gases from the condensate
. To preheat the water
. To act as a reservoir to store feedwater to
take care of fluctuations in feedwater
demand or condensate supply
The condensate enters the DFT through the
condensate inlet. There it is sprayed into the dome
of the tank by nozzles. It is discharged in a fine
spray throughout the steam-filled top. The fine
spray and heating of the condensate releases
trapped air and oxygen. The gas-free condensate
falls to the bottom of the tank through the water
collecting cones, while the air and oxygen are
exhausted from the tank vent.
The collected condensate in the storage
section of the DFT is now called feedwater and
becomes a source of supply for the main feed
booster pump. The main feed booster pump takes
suction from the DFT and maintains a constant
discharge pressure to the main feed pump.
The main feed pump receives the water
(delivered from the booster pump) and discharges
it into the main feed piping system. Area D of
figure 3-1 shows the path of the water from the
DFT to the economizer. The discharge pressure
of the main feed pump is maintained at 100 to
150 psig above boiler operating pressure on
600-psi plants. On 1200-psi plants, it is maintained
at 200 to 300 psig above boiler operating pressure.
The discharge pressure is maintained throughout
the main feed piping system. However, the
quantity of water discharged to the economizer
is controlled by a feed stop and check valve or
automatic feedwater regulator valve.
The economizer is positioned on the boiler to
perform one basic function. It acts as a preheater.
The gases of combustion flow around the
economizer tubes and metal projections that
extend from the outer tube surfaces. The tubes
and projections absorb some of the heat of
combustion and heat the water that is flowing
through the economizer tubes. As a result, the
water is about 100 °F hotter as it flows out of the
economizer to the boiler.