CHAPTER 16 



AUXILIARY STEAM TURBINES 



Auxiliary steam turbines are used to drive 

 many auxiliary machinery units aboard steam- 

 driven ships. Turbine-driven auxiliaries located 

 in the engineering spaces include ship's service 

 generators, forced draft blowers, air compres- 

 sors, and a number of pumps such as main con- 

 densate pumps, main condenser circulating 

 pumps, main feed pumps, feed booster pumps, 

 fuel oil service pumps, and lubricating oil serv- 

 ice pumps. 



In many cases, the turbine-driven auxiliaries 

 are duplicated by electrically driven units for in- 

 port or cruising use. Although the motor-driven 

 units have a comparatively high efficiency, their 

 capacity is not sufficient (on some ships, at least) 

 to meet the demands of the engineering plant at 

 high speeds. A further advantage of auxiliary tur- 

 bines is their greater reliability; in general, 

 there is greater possibility of interruption or 

 loss of electric power supply than of steam sup- 

 ply. In addition, the use of auxiliary turbines im- 

 proves the overall plant efficiency because ex- 

 haust steam from the auxiliary turbines can be 

 utilized in various ways throughout the plant. 



The basic principles of steam turbine design, 

 classification, and construction discussed in 

 chapter 12 of this text apply in general to auxil- 

 iary turbines as well as to propulsion turbines, 

 except for specific differences noted in the re- 

 mainder of this chapter. 



TYPES OF AUXILIARY TURBINES 



Many auxiliary turbines are of the impulse 

 type. Reduction gears are used with most auxil- 

 iary turbines^ to increase efficiency. Since 

 space requirements frequently demand relativ- 



Direct drive, rather than geared drive, units include 

 forced draft blowers, high speed centrifugal pumps, 

 and some recent ship's service turbogenerators. 



ely small units, auxiliary turbines are usually 

 designed with comparatively few stages— often 

 only one. This means a large pressure drop and 

 a high steam velocity in each stage. To obtain 

 maximum efficiency, the blade speed must also 

 be high. With auxiliary turbines, as with propul- 

 sion turbines, reduction gears serve to reconcile 

 the conflicting speed requirements of the driving 

 and the driven units. 



Until about 1950, many generator turbines 

 were designed and installed in such a way that 

 they could be operated on steam from either su- 

 perheated or saturated steam lines at full boiler 

 pressure. Most of the other auxiliary turbines at 

 this time operated on saturated steam at full 

 boiler pressure. During the early 1950's, a few 

 ships were built in which all auxiliary turbines 

 were designed to operate on steam at full super- 

 heat and full boiler pressure. On most oil-fired 

 ships built since 1953, steam at full superheat 

 and full boiler pressure is supplied to the auxil- 

 iary turbines for generators, main feed pumps, 

 and forced draft blowers; the other auxiliary tur- 

 bines on these ships usually operate on steam at 

 reduced temperature and pressure (about 50° F 

 of superheat and 600 psig). On nuclear ships, all 

 turbines (propulsion and auxiliary) are designed 

 to operate on wet steam— usually, steam which 

 contains about 1 percent moisture. The auxiliary 

 turbines on nuclear ships operate over a wide 

 pressure range which varies according to the 

 type of nuclear propulsion plant. For more recent 

 nuclear submarines, the pressure range is from 

 285 to 750 psig; on the nuclear carrier USS En- 

 terprise, the pressure range is from approxi- 

 mately 585 to 1025 psig under normal operating 

 conditions. The generator turbines usually ex- 

 haust to their own separate auxiliary condensers; 

 on recent submarines, however, they exhaust to 

 the main condenser. Most other auxiliary tur- 

 bines exhaust to the auxiliary exhaust system. 

 The auxiliary exhaust system imposes a back 



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