Condensate and Feed Systems

The condensate and feed systems include all the piping that carries water from the condenser to the boilers and from feed tanks to the boilers, The condensate system includes the main and auxiliary condensers, pumps and piping. The boiler feed system includes the main feed pump, and the piping required to carry water from the deaerating feed tank to the boilers. Together, the condensate and feed systems begin at the condenser and end at the economizer of the boiler.

The main condenser is a heat exchanger in which exhaust steam is condensed as it comes in contact with tubes through which cool seawater is flowing. The steam enters at the top of the condenser and the water (now called condensate) collects at the bottom of the condenser, below the tubes. The main condenser is maintained under a vacuum of approximately 27 to 29.5 inches of mercury.

The condensate pump pumps the condensate from the condenser to the deaerating feed tank. As a rule, two condensate pumps are used for each condenser; under normal conditions, one pump is in use and the other is kept in standby condition.

The function of an air ejector is to remove air and other non-condensable gases from the condenser. An air ejector is a type of jet pump, containing no moving parts. The flow through the air ejector is maintained by a jet of high velocity steam passing through a nozzle.

Steam Systems

On many ships, the Main Steam System includes only the piping, which carries superheated steam from the boilers to the propulsion turbines, the turbo-generators, and the soot blowers. On some modern ships, the main steam system is more complex because more units use superheated steam.

For ahead operation, the superheated steam passes through the main steam strainer, a stop valve, and a throttle valve before entering the high pressure turbine.

From the high pressure turbine, the steam passes through a cross-over pipe to the low pressure turbine, then it exhausts to the condenser.

For astern operation, the superheated steam passes through the steam strainer and through a stop valve, then it goes to the steam chest of the astern turbine, which is located at one end of the pressure turbine.

Auxiliary Steam Systems supply saturated steam at the pressures and temperatures required .for the operation of many systems and units of machinery. Air compressors, whistles and sirens, fuel oil tank heating coils, air ejectors, forced draft blowers and pumps are typical of the systems and machinery that use auxiliary steam on most steam-driven ships.

On ships having single-furnace boilers, all steam goes through the superheater and the steam, which is required for auxiliary steam systems, is then desuperheated.

The Auxiliary Exhaust System receives exhaust steam from pumps, namely feed pumps, and other auxiliaries, which do not exhaust directly to a condenser. Auxiliary exhaust steam is used in various units, deaerating feed tanks, distilling plants, and turbine gland sealing systems. The pressure in the auxiliary system is maintained at 15 psig.

Gland sealing steam is supplied to the shaft packing glands of propulsion turbines and turbogenerator turbines to seal the shaft glands against two kinds of leakage: (1) air leakage into the turbine casings, and (2) steam leakage out of the turbine casings. Pressures in the gland seal system are low, ranging from about 3/4 psig to 2 psig, depending upon the conditions of operation.