Condensate and Feed Systems
WATER SYSTEMS
The condensate system and the boiler feed system,
Generally speaking, there are two classes of water:
together, are usually known as the feedwater system.
fresh water and seawater. The term fresh water is used
The condensate system includes all the apparatus and
on board ship to refer to potable water, feedwater,
piping used to collect and condense steam. The
reserve potable water, and reserve feedwater. Potable
condensate system includes the main and auxiliary
water is water known to be of drinking water quality.
condensers, a pump or a combination of pumps, and the
Feedwater is water known to be suitable for use in the
piping required to carry the condensate from the
ship's boilers.
The principal difference between fresh water and
condensers recover feedwater by condensing exhaust
seawater is salinity. This difference leads to many other
steam from propulsion turbines, generator turbines, and
differences in characteristics. For example, under
various auxiliary machinery units.
normal atmospheric pressure fresh water freezes at 32F
The boiler feedwater system includes the DFT, the
and boils at 212F. Under the same pressure, seawater
freezes at 27F and boils at 213 1/2F. Seawater and
feed booster pump, the main feed pump, and the piping
fresh water also differ in specific weight and in specific
required to carry the feedwater from the DFT to the
boilers. A small amount of additional water, called
heat in Btu. (A Btu is the amount of heat required to
raise 1 pound of a substance 1F.) Fresh water is the
makeup feed, is usually required to make up for any loss
that occurs in the cycle. This makeup feed is taken from
standard of comparison for specific gravity and specific
heat, and therefore has a specific gravity of 1 and a
the reserve feedwater tanks. All lines that carry water
specific heat of 1. These factors will vary with the
to the boilers, either from DFTs or the reserve feed
salinity of seawater. On the average, though, seawater
tanks, are part of the feedwater system.
weighs about 64 pounds per cubic foot (specific gravity
Steam and Freshwater Drains
varies from 1.0043 to 1.0463) compared with 62.4
pounds per cubic foot for pure fresh water. The specific
Most of the feedwater in a shipboard steam plant is
heat of seawater varies from 0.903 to 0.980, depending
recovered so that it can be used over and over again for
on salinity.
the generation of steam. As steam is condensed in the
The properties of water are influenced by
temperature and pressure. For example, specific weight
returned to the feed system. Also, the steam exhausted
and viscosity of water change with temperature. The
from auxiliary machinery is collected in the auxiliary
boiling and freezing points of water vary with pressure.
exhaust system and is returned to the feed system. But
At atmospheric pressure, fresh water boils at 212F, but
steam is used throughout the ship in a good deal of
at an absolute pressure of 10 psi (equivalent to a vacuum
machinery, equipment, and piping that does not exhaust
of 9 l/2 inches of mercury) water boils at 193.1F. At
either to a condenser or to the auxiliary exhaust system.
an absolute pressure of 30 psi, the boiling point is 250F.
Therefore, steam and freshwater drain systems are
At an absolute pressure of 900 psi, the boiling point is
provided so that water can be recovered and put back
531.9F.
into the feed system after it has been used (as steam) in
fuel oil heaters, distilling plants, steam catapult
Water exists as a solid, a liquid, and a gas--that is,
systems, water heaters, whistles and sirens, and many
as ice at low temperatures and as steam at high
temperatures. One of the peculiar characteristics of
other units and systems throughout the ship. The
systems of piping that carry the water to the feed
water is that it expands from 8.5 to 10 percent in volume
systems, and also the water carried in the systems, are
when it freezes, and creates a pressure that would burst
known as drains.
most piping and equipment. We have said that the
specific weight of fresh water is 62.4 pounds per cubic
There are four steam and freshwater drain systems
foot. This is its maximum specific weight. At a
on ships built to Navy specifications: (1) high-pressure
temperature above or below 39.1F, assuming 1
steam drainage systems, (2) service steam drainage
atmosphere pressure, the specific weight of fresh water
systems, (3) freshwater drain collecting systems, and
is less than 62.4 pounds per cubic foot.
(4) contaminated drainage systems. Most drain lines
are fitted with steam traps to keep steam from passing
into the drain systems. High-pressure drains are
generally a mixture of steam and water, even after they
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