Principles of naval engineering - Historic Naval Ships Association

Chapter 10- PROPULSION BOILERSSPRAYER ATOMIZER DISTRIBUTOR NOZZLEPLATE NUT HEAD BODYDISHED AND ROUNDED FACEOIL LEAVING WHIRLING OIL RETURNORIFICE CHAMBEROILSUPPLY38.74Figure 10-13.—Two kinds of standard sprayerplates.pressure. The amount of oil burned in the furnaceis controlled by regulating the oil returnpressure. The supply oil enters through thetube-like opening down the middle of the atomizerbarrel and passes through the sprayer plate.The tangential slots or grooves in the sprayerplate cause the oil to enter the whirling chamberwith a rotary motion. As the oil reaches thereturn annulus, centrifugal force causes a certainamount of the oil to enter the return annulis.The amount of oil thus returned is determinedby the back pressure in the return line;the back pressure is in turn determined by theextent to which the return line control valve isopen. The oil which is not returned emergesfrom the orifice in the form of a hollow conicalspray of atomized oil. The amount of oil burnedis the difference between the amount of oil suppliedand the amount returned.The straight-through-flow atomizers and thereturn-flow atomizers just described are bothconsidered to be mechanical atomizers of thepressure type. The steam-assist atomizer, nowin use on some new ships, operates on differentprinciples. The fuel oil enters a steam-assistatomizer at relatively low pressure and is veryfinely atomized by a jet of steam. Combustion airis supplied by forced draft blowers, just as it isin other installations.A steam-assist atomizer has two supply linescoming into it, one for fuel oil and one for steam.These two lines make the atomizer look a gooddeal like a return-flow atomizer. However, thesteam-assist atomizer does not return any fueloil; instead, all oil supplied to the atomizer isburned in the boiler furnace. Sprayer plates andother parts are somewhat differently shaped insteam-assist atomizers than they are in38.75Figure 10-14.—Return-flow atomizer.straight-through-flow atomizers and returnflowatomizers.One reason why steam-assist atomizers havenot been used for naval propulsion boilers untilquite recently is that they use a considerableamount of steam which cannot be recovered andreturned to the feed system. However, they havesome advantages that tend to make up for thisdisadvantage. A major advantage is that the firingrange of steam-assist atomizers is muchgreater than the firing range of other types ofatomizers. This characteristic makes thesteam-assist atomizer particularly useful fornaval service, since it means that large changesof load can be made merely by varying the fueloil supply pressure, without cutting burners inand out. The fuel oil supply pressure can bevaried between 8 and 350 psi.AIR REGISTERS.— The main parts of an airregister are (1) the movable air doors, (2) thediffuser, and (3) the stationary air foils. Theseparts are shown in figure 10-10. The movableair doors allow operating personnel to open andclose the register. When the air doors are open,air rushes in and is given a whirling motion bythe diffuser plate. The diffuser thus serves tomake the air mix evenly with the oil, and alsoto prevent flame being blown back from theatomizer. The stationary air foils guide themajor quantity of air and cause it to mix withthe larger oil spray beyond the diffuser.Furnaces and RefractoriesA boiler furnace is a space provided for themixing of air and fuel and for the combustion ofthe fuel. A boiler furnace consists of a more orless rectangular steel casing which is lined on243