Chapter 10- PROPULSION BOILERS 



SPRAYER ATOMIZER DISTRIBUTOR NOZZLE 

 PLATE NUT HEAD BODY 



DISHED AND ROUNDED FACE 



38.74 

 Figure 10-13.— Two kinds of standard sprayer 

 plates. 



pressure. The amount of oil burned in the fur- 

 nace is controlled by regulating the oil return 

 pressure. The supply oil enters through the 

 tube-like opening down the middle of the atomizer 

 barrel and passes through the sprayer plate. 

 The tangential slots or grooves in the sprayer 

 plate cause the oil to enter the whirling chamber 

 with a rotary motion. As the oil reaches the 

 return annulus, centrifugal force causes a cer- 

 tain amount of the oil to enter the return an- 

 nulis. The amount of oil thus returned is deter- 

 mined by the back pressure in the return line; 

 the back pressure is in turn determined by the 

 extent to which the return line control valve is 

 open. The oil which is not returned emerges 

 from the orifice in the form of a hollow conical 

 spray of atomized oil. The amount of oil burned 

 is the difference between the amount of oil sup- 

 plied and the amount returned. 



The straight-through-flow atomizers and the 

 return-flow atomizers just described are both 

 considered to be mechanical atomizers of the 

 pressure type. The steam-assist atomizer, now 

 in use on some new ships, operates on different 

 principles. The fuel oil enters a steam-assist 

 atomizer at relatively low pressure and is very 

 finely atomized by a jet of steam. Combustion air 

 is supplied by forced draft blowers, just as it is 

 in other installations. 



A steam-assist atomizer has two supply lines 

 coming into it, one for fuel oil and one for steam. 

 These two lines make the atomizer look a good 

 deal like a return-flow atomizer. However, the 

 steam-assist atomizer does not return any fuel 

 oil; instead, all oil supplied to the atomizer is 

 burned in the boiler furnace. Sprayer plates and 

 other parts are somewhat differently shaped in 

 steam-assist atomizers than they are in 



OIL LEAVING WHIRLING OIL RETURN 

 ORIFICE CHAMBER 



OIL 

 SUPPLY 



38.75 



Figure 10-14.— Return-flow atomizer. 



straight-through-flow atomizers and return- 

 flow atomizers. 



One reason why steam-assist atomizers have 

 not been used for naval propulsion boilers until 

 quite recently is that they use a considerable 

 amount of steam which cannot be recovered and 

 returned to the feed system. However, they have 

 some advantages that tend to make up for this 

 disadvantage. A major advantage is that the fir- 

 ing range of steam-assist atomizers is much 

 greater than the firing range of other types of 

 atomizers. This characteristic makes the 

 steam-assist atomizer particularly useful for 

 naval service, since it means that large changes 

 of load can be made merely by varying the fuel 

 oil supply pressure, without cutting burners in 

 and out. The fuel oil supply pressure can be 

 varied between 8 and 350 psi. 



AIR REGISTERS.— The main parts of an air 

 register are (1) the movable air doors, (2) the 

 diffuser, and (3) the stationary air foils. These 

 parts are shown in figure 10-10. The movable 

 air doors allow operating personnel to open and 

 close the register. When the air doors are open, 

 air rushes in and is given a whirling motion by 

 the diffuser plate. The diffuser thus serves to 

 make the air mix evenly with the oil, and also 

 to prevent flame being blown back from the 

 atomizer. The stationary air foils guide the 

 major quantity of air and cause it to mix with 

 the larger oil spray beyond the diffuser. 



Furnaces and Refractories 



A boiler furnace is a space provided for the 

 mixing of air and fuel and for the combustion of 

 the fuel. A boiler furnace consists of a more or 

 less rectangular steel casing which is lined on 



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