Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERING'RECIRCULATING f^MAKEUP FEED 'AIR EJECTOR*CONNECTION CONNECTION SUCTIONEXHAUST STEAM IFROM PROPULSION CTURBINES !CIRCULATING-WATER OUTLABSOLUTEPRESSURE GAGEVACUUM GAGECONNECTIONCONDENSATEOUTLETFigure13-1.— Cutaway view of main condenser.47.70Xunder the tube bundle is condensed by the condensatedripping from the condenser tubes. Inthis process, the condensate (which has beensubcooled by its contact with the cold tubes) tendsto become reheated to a temperature which approachesthe condensing temperature correspondingto the vacuum maintained in the hot well.The difference between the temperature of thecondensate discharge and the condensing temperaturecorresponding to the vacuum maintainedat the exhaust steam inlet to the condenser iscalled the condensate depression . One measureof the efficiency of design and operation of anycondenser is its ability to maintain the condensatedepression at a reasonably low value underall normal conditions of operation. Excessivecondensate depression decreases the operatingefficiency of the plant because the subcooled condensatemust be reheated in the feed system, witha consequent expenditure of steam. Excessivecondensate depression also allows an increasedabsorption of air by the condensate, and this airmust be removed in order to prevent oxygen corrosionof piping and boilers.Main condensers have various internal bafflearrangements for the purpose of separating airand steam so that the air ejectors will not beoverloaded by having to pump large quantities ofsteam along with the air. Air cooling sectionsand air baffles may be seen in figure 13-3.In some installations the condenser is hungfrom the low pressure turbine in such a way thatthe turbine supports the condenser. Where thistype of installation is used, sway braces are usedto connect the lower part of the condenser shellwith the ship's structure. Spring supports are350