Chapter 10- PROPULSION BOILERS 



External fittings and instruments used on 

 naval boilers may include drains and vents; 

 sampling connections, feed stop and check 

 valves; steam stop valves; safety valves; soot 

 blowers, watergage glasses and remote water 

 level indicators; pressure and temperature 

 gages; superheater temperature alarms; super- 

 heater steam flow indicators; smoke indicators; 

 and various items used for the automatic control 

 of combustion and water level. 



TYPES OF PROPULSION BOILERS 



Now that we have examined the basic com- 

 ponents used in most naval propulsion boilers, 

 let us put these components together, so to 

 speak, to see how they are arranged to form the 

 types of boilers now used in the propulsion plants 

 of naval ships. The order of presentation is 

 more or less historical, starting with the 

 header-type boiler (which is probably the oldest 

 boiler design still in service), going on to 

 double-furnace boilers and to both older and 

 newer types of single-furnace boilers, and end- 

 ing with the recently installed pressurized- 

 furnace boiler. 



Header-Type Boilers 



Sectional header boilers, commonly called 

 header-type boilers, are installed in many 

 auxiliary ships. The basic design of this type of 

 boiler is shown in figures 10-15 and 10-16. 



Header-type boilers normally operate at 450 

 to 465 psig and are designed for a maximum 

 superheater outlet temperature of 740° to 750° F. 

 In capacity, they range from about 25,000 to 

 about 40,000 pounds of steam per hour. 



Header-type boilers are sometimes referred 

 to as cross-drum boilers because many of them 

 were designed to be installed with the steam 

 drum athwartships rather than fore and aft. How- 

 ever, some header-type boilers are not of the 

 cross-drum type. 



Header-type boilers are also referred to 

 occasionally as side-fired boilers. This term 

 is used to indicate the location of the burners 

 with respect to the position of the steam drum. 

 However, the term "side-fired" tends to be 

 misleading because the surface of aboiler along 

 which the burners are installed is generally re- 

 garded as the front of the boiler. In this discus- 

 sion, we will take as the front of the boiler the 

 surface along which the burners are installed. 

 From this point of view, then, the steam drum is 



installed lengthwise along the top of the boiler 

 front. 



The header-type boiler gets its name from 

 the header sections which are connected by the 

 generating tubes. There may be 12, 14, or 16 of 

 these header sections, depending upon the size 

 of the boiler. Half of the header sections are 

 installed under the steam drum, at the front of 

 the boiler. The other half are installed at the 

 rear of the boiler, at a somewhat higher level. 

 The header sections are installed at a slight 

 angle fromthe vertical, leaning somewhat toward 

 the front of the boiler. The angle of inclination 

 of the headers allows the straight generating 

 tubes (which enter the headers normal to the 

 header surfaces) to slope slightly upward from 

 the front of the boiler toward the rear, thus al- 

 lowing free natural circulation within the boiler. 



The header sections installed under the 

 steam drum at the front of the boiler are known 

 as downtake headers. Each downtake header is 

 connected to the steam drum by a short down- 

 take nipple. The lower end of each downtake 

 header is connected to the junction header 

 (sometimes called the mud drum ) by a short 

 nipple. 



The header sections installed at the rear of 

 the boiler are known as uptake headers. Each 

 uptake header is connected to the steam drum 

 by a large circulator tube which enters the 

 steam drum slightly above the normal water 

 level. 



As shown in figures 10-15 and 10-16, the 

 generating tubes in this type of boiler are 

 straight rather than curved. The generating 

 tubes connect the downtake headers at the front 

 of the boiler with the uptake headers at the rear 

 of the boiler. 



The superheater consists of U-bend tubes, 

 an upper superheater header, and a lower super- 

 heater header. The superheater tubes are in- 

 stalled at right angles to the generating tubes, 

 between the main bank of generating tubes and 

 the water screen tubes. 



The steam drum of a header-type boiler 

 usually has a manhole at each end. The steam 

 drum contains the internal fittings, including a 

 desuperheater. 



The furnace of a header-type boiler has four 

 vertical walls and a flat floor. The side walls 

 are water cooled, being covered by water wall 

 tubes which form a part of the circulation sys- 

 tem of the boiler. There are two water wall 

 downtake headers, one at each corner of the 

 boiler front, installed vertically in the space 



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