Chapter 10- PROPULSION BOILERS 



SUPERHEATER 

 HEADERS 



SATURATED 

 ^ j STEAM 



o o " 

 o o o 1 



INLET 



DRAIN 



38.23 

 Figure 10-7. — Convection-type superheater 

 (double-furnace boiler). 



an access space or cavity is provided in the 

 middle of the superheater tube bank. The cavity, 

 which runs the full length and height of the 

 superheater, greatly increases the accessibility 

 of the superheater for cleaning, maintenance, 

 and repair. Some of the walk- in superheaters 



have U-shaped tubes. Others, such as the one 

 shown in figure 10-8, have W- shaped tubes. 



A few boilers of recent design have vertical, 

 rather than horizontal, convection-type super- 

 heaters. In these boilers, the U-bend super- 

 heater tubes are installed almost vertically, 

 with the U-bends near the top of the boiler; the 

 tubes are approximately parallel to the main 

 bank of generating tubes and the water screen 

 tubes. Two superheater headers are near the 

 bottom of the boiler, running horizontally from 

 the front of the boiler to the rear. 



Superheater tubes are generally identified by 

 loop number, name of tube bank, and number of 

 tube within the bank. In the case of horizontal 

 superheater tubes, as shown in figure 10-6, you 

 count from the bottom toward the top to get the 

 tube number. In the case of vertical superheater 

 tubes, you count from the front of the boiler 

 toward the rear. 



Desuperheaters 



On boilers with noncontrolled superheaters, 

 all steam is superheated, but a small amount of 

 steam is redirected through a desuperheater 

 line, the desuperheater can be located in either 

 the water drum or the steam drum, most gen- 

 erally the desuperheater will be found in the 

 steam drum below the normal water level. The 

 purpose of the desuperheater is to lower the 

 super-heated steam temperature back to or 

 close to saturated steam temperature for the 

 proper steam lubrication of the auxiliary ma- 

 chinery. The desuperheater is most generally 

 an "S" shaped tube bundle that is flanged to the 

 superheater outlet on the inlet side and the 

 auxiliary steam stop on the outlet side. 



Economizers 



An economizer is installed on practically 

 every boiler used in naval propulsion plants. 

 The economizer is an arrangement of tubes 

 installed in the uptake space from the furnace; 

 thus the economizer tubes are heated by the 

 rising gases of combustion. All feed water flows 

 through the economizer tubes before entering 

 the steam drum, and the feed water is warmed 

 by heat which would otherwise be wasted as 

 combustion gases pass up the stack. In general, 

 boilers operating at high pressures and tem- 

 peratures have larger economizer surfaces than 

 boilers operating at low pressure and tempera- 

 tures. 



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