Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGMost ships that have 600-psi main steamsystems have a 600-psi auxiliary steam systemand a 150-psi auxiliary steam system, plussome lower pressure service systems. The600-psi auxiliary steam system serves somemachinery directly and also supplies the 150-psisystem through reducing valves or reducingstations. The 150-psi auxiliary steam systemserves some units directly and also providesauxiliary steam for units or systems that requireauxiliary steam at even lower pressures.Figure 9-16 shows part of a 600-psi auxiliarysteam system for the two forward plants (No. 1and No. 4) on a heavy cruiser of the CA 139class. Note that the system is arranged inloop form, with cross connections at requiredintervals and with branch lines serving thevarious units and systems. Note, also, thatthe auxiliary steam system is, like the mainsteam system, basically rather simple.Ships that havea 1200-psi main steam systemhave a 1200-psi auxiliary steam system, a600-psi auxiliary steam system, a 150-psiauxiliary steam system, and several constantand intermittent steam service systems. Theauxiliary steam systems of the DLG 14 andDLG 15 are described here in some detail asexamples of auxiliary steam systems on shipshaving 1200-psi main steam systems.The 1200-psi and the 600-psi auxiliary steamsystems for the forward plant of the DLG 14and DLG 15 are shown in figure 9- 17. A similararrangement exists in the after plant. The1200-psi auxiliary steam system for each plantis entirely separate and independent; the 600-psi systems can be cross-connected but arenot normally operated that way. Each plant hastwo boilers, both of which supply steam to the1200-psi auxiliary steam system of that plant.The steam comes from the desuperheater outletof each boiler; it is desuperheated fromapproximately 950° F (the operating temperatureat the superheater outlet) to approximately700° F. Note that the steam in this auxiliarysteam system still has something more than200° F of superheat, so it is not strictly"saturated" steam. The 1200-psi auxiliarysteam lines from each boiler are interconnectedso that either boiler can provide steam foreverjrthing served by this system.The 1200-psi auxiliary steam system suppliessteam directly to the soot blowers, theforced draft blowers, and the reducing stationsthat reduce the pressure from 1200 to 600 psig;it also supplies augmenting steam at 12 psigto the auxiliary exhaust system, when necessary.The 600-psi auxiliary steam system suppliessteam at 600 psig and approximately 650° F toboth fireroom and engineroom equipment. Inthe fireroom, the 600-psi system suppliessteam to the fuel oil service pumps, the mainfeed booster pump, the fire pump, and thereducing stations that reduce the pressure from600 to 150 psig. In the engineroom, the 600-psi system supplies steam to the standby lubeoil service pump, the main condensate pump,the main circulating pump, and a reducingstation that reduces the pressure from 600 to150 psig.The 150-psi and the 50-psi auxiliary steamsystems for the after plant of the DLG 14 andDLG 15 are shown in figure 9-18. The forwardplant has similar systems.The 150-psi auxiliary steam system in eachplant provides all machinery, equipment, andconnections which require 150-psi steam. Thissystem also supplies steam to other reducedpressure systems, via reducing stations, andmay deliver steam to other ships or receivesteam from outside sources through specialpiping and deck connections. Another functionof the 150-psi system is to augment the auxiliaryexhaust system; in fact, this function isnormally performed by the 150-psi system,although it may be performed directly by the1200-psi auxiliary steam system when necessary.Steam for the 150-psi system in the fireroomis supplied from the reducing stations thatreduce the pressure from 600 to 150 psig. Thereare two such stations ineachfireroom. A spraytypedesuperheater reduces the temperatureof the fireroom 150-psi system to 400° F. Servicesand auxiliaries operated from the 150-psi system in the fireroom include superheaterprotection steam, 5 service steam systems,oil heating systems, boiler casing steamsmothering systems, fireroom bilge steamsmothering system, bilge and fuel oil tankstripping pumps (in No. 1 fireroom and No. 2engineroom only), steam for burner cleaningservice, and hose connections for boiling outboilers. In emergencies, the fireroom 150-psiauxiliary steam system can also supply steamfor some units that are normally supplied bythe engineroom 150-psi system.Superheater protection steam is discussed in chapter10 of this text.210