The Babcock & Wilcox Water-Tube Marine Boiler
This boiler consists in the main of an arrangement of inclined tubes forming the bulk of the heating surface, a horizontal steam and water drums, and a mud drum at the lower front end of the elements.
The tubes are expanded at both ends into wrought steel boxes or headers, and thus form sections vertically. By means of connections with the steam and water drum at the top of these headers the steam generated in the tubes passes into the drum, and the water supplied descends to take its place.
The furnace is underneath the nest of tubes and the gases come into intimate contact with all the heating surface, as is shewn by the direction of the arrows in the illustration (below). The furnace is lined with firebricks, or in cases where weight is a very important consideration fire tiles are used in their place, which are bolted to the side plates. The whole boiler is encased in an iron casing, lined with non-conducting material, this casing being fitted with doors for the removal of soot. Opposite the ends of the tubes are internal doors, the joints being made on the inside of the header by means of asbestos rings, and the door being drawn up to its face by means of an outside nut on a bolt with crossbar. All the steam mountings are attached to the steam and water drum, and blow-off valves are fitted to the mud drum.
The steam generated in the tubes of the boiler rises vertically through the rear headers into the steam and water drum, whence the water returns to the tubes through the short connection between the drum and the front headers, so that there is a continuous circulation of water in one direction, giving the boiler as far as possible an equal temperature in all its parts so as to avoid undue strain.
Source: Jane's Fighting Ships 1906 - 07 ed. (London: Sampson, Marston & Low, 1906), 452.
The Babcock, or B&W, boiler, shewn above, has the casing removed to show the arrangement of the tubes, which are of solid drawn steel. The tubes connecting the headers and cross-boxes together are 1-13/16 inches diameter; those between the headers are 7 feet 6 inches long, and those in the cross-boxes are 7 feet 4¾ inches long. The heating-surface is 2,356 square feet.
In a test of this boiler when burning 16.19 lbs. of coal per square foot of the area of the fire-grate per hour, 10.91 lbs of water were evaporated, as from and at 212°F per pound of coal; and 7.65 lbs of water were evaporated, as from and at 212°F per square foot of heating-surface per hour. The evaporation was 15,516 lbs of water per hour.
A smaller water-tube marine boiler of a similar type is shown in Fig. 331. It consists of a number of straight tubes placed at an inclination of 1 in 4 over the fire-grate, and connected to sinuous headers communicating by short tubes with a steam receiver, 3 feet 6 inches diameter. The water circulates down the back header, along the tubes into the front headers,and through their connecting-pipes into the steam-receiver. The sides of the boiler are formed of tubes connected with the circulating system. The tubes are 9 WG in thickness, and 1-7/8 inches external diameter, with the exception of those of the bottom row, which are of 4 inches' diameter.
The sides of the furnace are of fire-brick, lined with fire-tiles. The boiler is enclosed by a light casing, formed of two thin flanged plates, with asbestos millboard between them, on the outside of which is a light cleading having an air-space between it and the casing proper. The front and rear casings are in the form of doors to permit inspection of the headers. The heating-surface of the boiler is 1,000 square feet; the area of the fire-grate is 24 square feet; and the ratio of the fire-grate surface to the heating-surface is 1 to 41.7. This boiler is suitable for a triple-expansion engine of 270 indicated horse-power.
When supplying steam to triple-expansion engines, 3¾ square feet of heating-surface are usually provided in this boiler per indicated horse-power: and from 11 to 12 indicated horse-power are assumed to be developed per square foot of fire-grate surface per hour with natural draught.
When supplying steam to compound, or double-expansion engines, from 4½ to 5 square feet of heating-surface are usually provided per indicated horse-power; and from 9 to 10 indicated horse-power are assumed to be developed per square foot of fire-grate surface per hour with natural draught.
With forced draught, or an air-presure from 1 to 1½ inches of water, the area of the fire-grate is proportional to a coal-consumption of from 30 to 40 lbs per square foot of fire-grate surface per hour; and 6 lbs of water may be evaporated per square foot of the heating-surface of this boiler per hour.
The weight of this type of marine boiler, including casings, water, mountings, fire-bars, and other furnace materaials, but not including the foundation, the uptake, or the funnel, is on an average from 70 to 90 lbs per indicated horse-power developed by triple expansion engines.
Source: Walter S. Hutton, Steam-Boiler Construction: A Practical Handbook (London: Crosby Lockwood, 1903).
Some Babcock Success Stories
Perhaps the most famous battleship of all time, HMS Dreadnought of 1906 was powered entirely by B&W boilers.
An American all-big-gun ship laid down while the Dreadnought was still under discussion, USS Michigan also used B&W boilers.
The American super-dreadnought Texas running trials in 1913, her B&W boilers operating under forced draft.
Texas' sister ship USS New York seen from a balloon directly overhead, 1920.