Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGsoot blowers. On some recent ships (both 600-psi and 1200-psi) the main steam system suppliessuperheated steam to several other unitsas well. For example, some carriers use superheatedsteam to supply steam catapult systems;also, some carriers and other ships usesuperheated steam to operate forced draftblowers, main feed pumps, main circulatingpumps, and other auxiliaries. The soot blowersare not supplied from the main steam systemon some ships that have 1200-psi main steamsystems; instead, steam for the soot blowers istaken from the 1200-psi auxiliary steam system,as discussed later in this chapter.Figure 9-12 illustrates the main steam systemfor the forward plant (No. 1 fireroom andNo. 1 engineroom) of a steam-driven destroyerescort. The after plant (No. 2 fireroom and No.2 engineroom) main steam system is very similar.There is one boiler in each fireroom. Eachboiler is provided with a boiler stop valve whichcan be operated either locally from the fireroomor remotely from the main deck. A secondline stop valve in each fireroom providestwo-valve protection for the boiler when it isnot in use, and permits effective isolation incase of damage. This type of two-valve protectionis standard for all boilers installed in U.S.Navy ships.For ahead operation, the superheated steampasses through a main steam strainer, a guardingvalve, and a throttle valve before enteringthe high pressure turbine. From the high pressureturbine, the steam passes through a crossoverpipe to the low pressure turbine; then itexhausts to the condenser. For astern operation,the superheated steam passes through thesteam strainer and through a stop valve; thenit goes to the steam chest of the astern element,which is located at one end of the low pressureturbine.The forward and after main steam systemsare connected by cross-connection piping betweenthe forward engineroom and the afterfireroom. By means of this piping, either boilercan be used with either or both propulsion unitsand turbogenerators. Thus the two propulsionplants can be operated either independently(split-plant) or together (cross-connected).Soot blowers are devices for removing soot from theboiler firesides while the boiler is steaming. Sootblowers are discussed in chapter 11 of this text.Note that superheated steam for the sootblowers goes from the superheater outlet pipinginto a soot blower steam header. 4 Branchesgo from the header to the individual soot blowers.A 600-psi main steam system is shown infigure 9-13. This is the main steam system forthe two forward plants (No. 1 and No. 4) on aheavy cruiser of the CA 139 class. Although thisdrawing is more complicated, the system itselfis still basically simple.A 600-psi main steam system for destroyersof the DD 445 and DD 692 classes is shown infigure 9-14. A later modification was made onthese ships to provide a separate superheatedsteam supply to the turbogenerators. With thismodification, this main steam system is typicalof most destroyers, even those that are considerablymore recent than the DD 445 and DD 692classes.For comparison, figure 9-15 shows a 1200-psi main steam system for the forward plant ofthe frigates DLG 14 and DLG 15. Note that the1200-psi main steam system does not supplysteam to the soot blowers but that it does supplysteam to the main feed pumps. In both of theserespects, the 1200-psi system differs from theDD 445 and DD 692 main steam system describedabove.AUXILIARY STEAM SYSTEMSAuxiliary steam systems supply steam at thepressures and temperatures required for the operationof many systems and units of machinery,both inside and outside the engineering spaces.Although auxiliary steam is often called "saturated"steam, it has some degree of superheatin some auxiliary steam systems. Constant andintermittent service steam systems, steamsmothering systems, whistles and sirens, fueloil heaters, fuel oil tank heating coils, air ejectors,forced draft blowers, and a wide variety ofpumps are typical of the systems and machineryThe term header is commonly used in engineeringtodescribe any tube, chamber, drum, or similar piece towhich a series of tubes or pipes are connected in sucha way as to permit a flow of fluid from one tube (orgroup of tubes) to another. In essence, a header is akind of manifold. In common usage, a distinction ismade between drums and headers on the basis of size:a large piece of this kind is likely to be called a drum,a smaller one a header.206