Chapter 10- PROPULSION BOILERS 



■FLAME AND GASES ■ 



147.83 

 Figure 10-1.— Natural circulation (free type). 



installed between the steam drum and the water 

 drums. These large tubes, called downcomers , 

 are located outside the furnace and away from 

 the heat of combustion, thereby serving as path- 

 ways for the downward flow of relatively cool 

 water. When a sufficient number of downcomers 

 are installed, all small tubes can be generating 

 tubes, carrying steam and water upward, and all 

 downward flow can be carried by the down- 

 comers. The size and number of downcomers 

 installed varies from one type of boiler to an- 

 other, but some are installed on all modern naval 

 boilers. 



Controlled circulation boilers are, as their 

 name implies, quite different in design from the 

 boilers that utilize natural circulation. Con- 

 trolled circulation boilers depend upon pumps, 

 rather than upon natural differences in density, 

 for the circulation of water within the boiler. 

 Because controlled circulation boilers are not 

 limited by the requirement that hot water and 

 steam must be allowed to flow upward while 

 cooler water flows downward, a great variety of 

 arrangements may be found in controlled circu- 

 lation boilers. 



Controlled circulation boilers have been used 

 in a few naval ships during the past few years. 

 In general, however, they are still considered 

 more or less experimental for naval use. 



Arrangement of Steam and 

 Water Spaces 



Natural circulation boilers are classified as 

 drum-type boilers or as header-type boilers, 

 depending upon the arrangement of the steam 

 and water spaces. Drum-type boilers have one 

 or more water drums (and usually one or more 

 water headers as well). Header-type boilers 

 have no water drum; instead, the tubes enter a 

 great many water headers. 



What is a header, and what is the difference 

 between aheader andadrum? The term HEADER 

 is commonly used in engineerlngto describe any 

 tube, chamber, drum, and similar piece to which 

 a series of tubes or pipes are connected in such a 

 way as to permit the flow of fluid from one tube 

 (or group of tubes) to another. Essentially, a 

 header is a type of manifold. As far as boilers 

 are concerned, the only distinction between a 

 drum and a header is the distinction of size. 

 Drums are larger than headers, but both serve 

 basically the same purpose. 



Drum-type boilers are further classified 

 according to the overall configuration of the 

 boiler, with particular regard to the shape 

 formed by the steam and water spaces. For 

 example, double-furnace boilers are often called 

 "M-type boilers" because the arrangement of 

 tubes is roughly M-shaped. Single-furnace 

 boilers are often called "D-type boilers" be- 

 cause the tubes form (rouglily) the letter D.3 



Number of Furnaces 



All boilers that are now commonly used in 

 the propulsion plants of naval ships may be 

 classified as being either single-furnace boilers 

 or double-furnace boilers. The D-type boiler is 

 a single-furnace boiler; the M-type boiler is a 

 double-furnace (or divided-furnace) boiler. 



Furnace Pressure 



Recent developments in naval boilers make it 

 convenient to classify boilers on the basis of the 



An interesting variation in this terminology occurred 

 when the single-furnace or D-type boiler became 

 standard for steam-driven destroyer escorts and thus 

 subsequently became known as a "DE-type boiler." 

 The term "DE-type boiler" is still used rather freely; 

 its use should be discouraged, however, as this gen- 

 eral type of boiler is now installed on many ships 

 other than destroyer escorts. 



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