Marine Steam Boilers J H Milton Pdf Viewer
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The Johnson boiler is a water-tube boiler used for ship propulsion.[1]
The Johnson design was developed by the British engineer J. Johnson in the late 1920s.[2] A patent was granted in 1931,[3] and one of these boilers was installed in the RMS Empress of Britain.[2] This was a time when water-tube boilers were being adopted in fast turbine ships, such as naval warships and passenger liners. There was also a shift to oil firing rather than coal burning. Oil had several advantages for a fast ship, particularly a warship that needed to combine both efficiency for long range with the ability to generate high power on demand when full speed was needed. Oil required fewer stokers, and a smaller crew required less space aboard given over to mess spaces. Refuelling was also quicker and cleaner with oil than with coal.[4]
The Johnson boiler was the first of the O-type boilers, a class of water-tube boilers characterised by single steam and water drums vertically above each other, with curved vertical water tubes to the sides forming an overall cylindrical volume. There is no grate at the base of this furnace space, so they are fired by liquid burners, rather than a solid fuel furnace producing ash.[4]
The large radiant heating area available allows a combustion rate, for a given furnace volume, of around twice that for a contemporary boiler, such as the Yarrow.[5] The end walls of the furnace may be either water walls with more tubes, or else simple firebrick. The small amount of brickwork for the Johnson design, without requiring a furnace base, was seen as an advantage by the Navy.[5]
The Royal Navy trialled a Johnson boiler in 1936, when the H-class destroyerHMS Hyperion was built with two Admiralty 3-drum boilers and a Johnson, rather than the three Admiralties used for the rest of the class.[5][6] This boiler had a water wall at the non-firing end. The initial design had poor circulation until external cold downcomers were added, increasing the weight by 10%.[5]
Babcock-Johnson boilers[edit]
The Babcock-Johnson is the developed form of the Johnson design, constructed by Babcock. The end walls of the furnace are tube-walled and there are large external downcomers.[7] Installing osmo software upgrade roomba 400 troubleshooting guide.
The boiler and its exhaust uptake is enclosed in an overall downward air duct, supplied through an air preheater in the exhaust stack.[7]
Early versions of this design used a thick tube nest, split into two layers and with the superheater placed as axially-parallel tubes between these.[7]
Later designs had thinner tube nests of only four rows of tubes, with the superheater placed in the uptake to the funnel. Working conditions would be '850/850', with a working pressure of 850 pounds per square inch (59 bar) and a steam temperature of 850 °F (454 °C).[7] The superheater would be placed in one side of the uptake, with a reheater between the high and low pressure turbines placed in the other.[7]
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Fairfield-Johnson boilers[edit]
The Fairfield-Johnson boiler is a further development of the Babcock-Johnson type. The working pressure of the boiler is reduced from around 58 bar to 30 bar, but the steam temperature after the supheater remains the same at around 825 °F (441 °C).[8]
The engineering change for these boilers is to reduce the work done in the boiler's steam generating tubes, in favour of increased superheating. Radiant heating of the boiler tubes is the same, but there is less convective heat transfer, giving a higher superheater gas inlet temperature.[8]
References[edit]
- ^Smith, Edgar C. (2013) [1937]. A Short History of Naval and Marine Engineering. pp. 313–315. ISBN1107672937.
- ^ abSmith (1937), p. 313.
- ^US 1816780, 'Water tube boiler'
- ^ abMilton, J. H. (2013) [1953]. 'Chapter 4: Water Tube Boilers'. Marine Steam Boilers (4th ed.). London: Newnes. pp. 150–153. ISBN1483102289.
- ^ abcdRippon, Commander P.M., RN (1998). The evolution of engineering in the Royal Navy. Vol 1: 1827-1939. Spellmount. pp. 245–246. ISBN0-946771-55-3.
- ^'G- and H-class Destroyers'. Grey Funnel Line. Archived from the original on 2016-04-25.Cite uses deprecated parameter
deadurl=(help) - ^ abcdeMilton, Marine Boilers, pp. 150–151.
- ^ abMilton, Marine Boilers, pp. 152–153.
A steam generator is a form of low water-content boiler, similar to a flash steam boiler. The usual construction is as a spiral coil of water-tube, arranged as a single, or monotube, coil. Circulation is once-through and pumped under pressure, as a forced-circulation boiler.[1] The narrow-tube construction, without any large-diameter drums or tanks, means that they are safe from the effects of explosion,[note 1] even if worked at high pressures.[2] The pump flowrate is adjustable, according to the quantity of steam required at that time. The burner output is throttled to maintain a constant working temperature. The burner output required varies according to the quantity of water being evaporated: this can be either adjusted by open-loop control according to the pump throughput, or by a closed-loop control to maintain the measured temperature.
They are used as auxiliary boilers on ships.[3]
- 1Types
Types[edit]
Stone-Vapor[edit]
One of the best-known designs is the Stone-Vapor.[3][4] The inner casing of the boiler forms a vertical bell, with an outer airtight cylindrical casing. The oil or gas burner is mounted at the top, above the coils, and facing downwards. The heating element is a single tube, arranged into a number of helical cylinders. The first helices (in the flow direction) are small-diameter tubes, wrapped in large diameter turns. Succeeding turns are coiled inside this and the tube is of progressively increasing diameter, to allow for a constant flow rate as the water evaporates into steam and forms bubbles. The steam outlet is from the final turn at the bottom of the inner helix. The outlet is approximately 90% steam (by mass)[4] and residual water is separated by passing it through a steam-water separator. The exhaust gases turn upwards and flow over the outside of the bell, usually passing additional helices that are used as an initial feedwater heater.
Clayton[edit]
The Clayton steam generator is similar to the Stone-Vapor, but the burner and flow directions are reversed. The heating coil is mounted within a simple cylindrical casing. Rather than helical, cylindrical layers, the Clayton coils are arranged as layers of flat spirals. Water is pumped into the top layers and forced downwards. Again, the tube diameter increases in steps, as evaporation takes place. The final turns form a single closely spaced helical cylinder around the burner as a water-wall furnace and is heated by radiant heat. The steam output is passed through a centrifugal separator and a dry steam quality of 99.5% is claimed.[1]
See also[edit]
References[edit]
- ^This safety from explosion is due to two causes. Firstly, small diameter tubes are inherently stronger than large tubes of the same construction, as was first appreciated by William Fairbairn in the mid-19th century. Secondly, the low water-content means that there is relatively little volume of water per area of heating surface (i.e. boiler power). As the destructive energy of a boiler explosion is largely due to the sudden release of this energy, and proportional to water volume, a low water-content boiler has a more favourable ratio of useful power (from its area) to risk (from its volume).
- ^ ab'Principle of Operation of a Clayton Steam Generator'.
- ^Milton & Marine Steam Boilers, p. 212
- ^ abNaval Marine Engineering Practice. Vol 1. Royal Navy, via HMSO. 1971 [1959]. pp. 8–10. ISBN0-11-770223-4.
- ^ abMilton, J. H. (1961) [1953]. Marine Steam Boilers (2nd ed.). Newnes. pp. 209–214.