PRINCIPLES OF NAVAL ENGINEERING 



connect the safety valves (not shown) to the 

 steam drum. 



The arrangement of internal fittings in a 

 double-furnace boiler with controlled superheat 

 is shown in figure 11-2. The dry pipe, the inter- 

 nal feed pipe, and the surface blow line are 

 about the same as the corresponding fittings in 

 the header-type boiler; but some of the other 

 fittings are different. 



The double-furnace boiler has no desuper- 

 heater, since auxiliary steam is taken directly 

 from the steam drum without passing first 

 through the superheater. 



Swash plates are not required in the water 

 spaces of the double-furnace boiler because this 

 type of boiler is always installed with the long 

 axis of the steam drum fore-and-aft rather than 

 athwartships. Surging of water, therefore, is 

 not a particular problem. 



The double-furnace boiler does not have a 

 separate chemical feed pipe. Instead, chemicals 

 for boiler water treatment come into the steam 

 drum with the feed water and are therefore dis- 

 tributed with the feed water through the holes 

 in the internal feed pipe. 



Perhaps the greatest difference in the inter- 

 nal fittings of the double-furnace boiler and the 

 header-type boiler is in the equipment provided 

 for the separation of moisture from the steam. 

 In the header-type boiler, a steam baffle helps 

 to separate the moisture from the steam before 



CYCLONE SEPARATORS 



NOZZLE PLATES OF 

 MANIFOLD BAFFLE 



■r INTERNAL FEED 



^ PIPE 



REMOVABLE APRON PLATES 

 OF MANIFOLD BAFFLE 



38.43 

 Figure 11-2.— Arrangement of internal fittings 

 in double-furnace boiler. 



the steam enters the dry pipe. In the double- 

 furnace boiler, cyclone steam separators are 

 used instead of a steam baffle. These separa- 

 tors utilize centrifugal force to separate water 

 and steam. There are usually 18 of these sepa- 

 rators installed in the steam drum of a double- 

 furnace boiler; half of them are installed on one 

 side of the drum and half on the other side. 



The cyclone steam separators are attached 

 to a manifold baffle which extends from just 

 forward of the generating tubes to just aft of 

 them. To avoid interference with boiler cir- 

 culation, the manifold baffle does not reach as 

 far as the downcomers. The manifold baffle 

 curves around inside the lower half of the steam 

 drum, passing just below the internal feed pipe 

 and leaving a space of about 3 inches between 

 the baffle and the steam drum. The baffle is 

 attached to the drum by means of two flat bars 

 which hang from the drum, one on each side. 

 The bars extend the full length of the baffle. 

 Each bar contains ports or openings, and a 

 cyclone steam separator is placed over each 

 port. 



The general arrangement of the manifold 

 baffle and the cyclone steam separators may 

 be seen in figure 11-2. Now let us examine 

 figure 11-3 and trace the flow of steam and 

 water through the steam drum. The generating 

 tubes discharge a mixture of steam and water 

 into the space between the manifold baffle and 

 the steam drum. From this space, the only 

 passage available for the steam and water is 

 through the ports which open to the cyclone 

 separators. As the mixture passes through the 

 separators, the steam passes upward and the 

 water is discharged downward. 



The cyclone steam separator is shown in cut- 

 away view in figure 11-4 and in plain view in 

 figure 11-5. The mixture of steam and water 

 enters the separator through the inlet connec- 

 tion, at a tangent to the separator body. Because 

 of its angle of entrance, the mixture of steam 

 and water acquires a rotary motion. As the 

 mixture whirls around, centrifugal force sepa- 

 rates the water from the steam. The water, 

 being heavier, is thrown out toward the sides 

 of the separator. The steam, being lighter, tends 

 to remain near the center. An internal baffle 

 further helps to deflect the steam to the center 

 and the water to the outside. The steam then 

 rises through the center of the separator and 

 passes through the scrubber element. The 

 scrubber consists of closely spaced corrugated 

 steel plates. As the steam passes through the 



278 



