Water-tube boiler 1

Water-tube boiler

Schematic diagram of a marine-type water tube boiler

A water tube boiler is a type of boilerin which water circulates in tubesheated externally by the fire. Fuel isburned inside the furnace, creating hotgas which heats water in thesteam-generating tubes. In smallerboilers, additional generating tubes areseparate in the furnace, while largerutility boilers rely on the water-filledtubes that make up the walls of thefurnace to generate steam.

The heated water then rises into thesteam drum. Here, saturated steam isdrawn off the top of the drum. In someservices, the steam will reenter thefurnace through a superheater to become superheated. Superheated steam is defined as steam that is heated above theboiling point at a given pressure. Superheated steam is a dry gas and therefore used to drive turbines, since waterdroplets can severely damage turbine blades.

Cool water at the bottom of the steam drum returns to the feedwater drum via large-bore 'downcomer tubes', where itpre-heats the feedwater supply. (In 'large utility boilers', the feedwater is supplied to the steam drum and thedowncomers supply water to the bottom of the waterwalls). To increase economy of the boiler, exhaust gases arealso used to pre-heat the air blown into the furnace and warm the feedwater supply. Such water tube boilers inthermal power station are also called steam generating units.The older fire-tube boiler design – in which the water surrounds the heat source and the gases from combustion passthrough tubes through the water space – is a much weaker structure and is rarely used for pressures above 350 psi(2.4 MPa). A significant advantage of the water tube boiler is that there is less chance of a catastrophic failure: thereis not a large volume of water in the boiler nor are there large mechanical elements subject to failure.

Applications

StationaryModern boilers for power generation are almost entirely water-tube designs, owing to their ability to operate athigher pressures. Where process steam is required for heating or as a chemical component, then there is still a smallniche for fire-tube boilers.

MarineTheir ability to work at higher pressures has led to marine boilers being almost entirely water-tube. This changebegan around 1900, and traced the adoption of turbines for propulsion rather than reciprocating (i.e. piston) engines– although water tube boilers were also used with reciprocating engines.

Water-tube boiler 2

RailwayThere has been no significant adoption of water-tube boilers for railway locomotives. A handful of experimentaldesigns were produced, but none of these were successful or led to their widespread use.[1] Most water-tube railwaylocomotives, especially in Europe, used the Schmidt system. Most were compounds, and a few uniflows. TheNorfolk and Western Railway's Jawn Henry was an exception, as it used a steam turbine combined with an electrictransmission.[2]

•• LMS 6399 FuryRebuilt completely after a fatal accident

•• LNER 10000 "Hush hush"Using a Yarrow boiler, rather than Schmidt. Never successful and re-boilered with a conventional boiler.[3]

Hybrids

A slightly more successful adoption was the use of hybrid water-tube / fire-tube systems. As the hottest part of alocomotive boiler is the firebox, it was an effective design to use a water-tube design here and a conventionalfire-tube boiler as an economiser (i.e. pre-heater) in the usual position.One famous example of this was the USA Baldwin 4-10-2 No. 60000, built in 1926. Operating as a compound at aboiler pressure of 350 psi it covered over 100,000 successful miles. After a year though, it became clear that anyeconomies were overwhelmed by the extra costs and it was retired to become a stationary plant.[4] A series of twelveexperimental locomotives were constructed at the Baltimore and Ohio Railroad's Mt. Clare shops under thesupervision of George H. Emerson, but none of them was replicated in any numbers.[5]

Brotan boiler

The only railway use of water-tube boilers in any numbers was theBrotan boiler, invented in Austria in 1902 by Johann Brotan and foundin rare examples throughout Europe. Hungary, though, was a keen userand had around 1,000 of them. Like the Baldwin, this combined awater-tube firebox with a fire-tube barrel. The original characteristic ofthe Brotan was a long steam drum running above the main barrel,making it resemble a Flaman boiler in appearance.[6][7]

Road

While the traction engine was usually built using its locomotive boileras its frame, other types of steam road vehicles such as lorries and carshave used a wide range of different boiler types. Road transportpioneers Goldsworthy Gurney and Walter Hancock both usedwater-tube boilers in their steam carriages around 1830.

Most undertype wagons used water-tube boilers. Many manufacturersused variants of the vertical cross-tube boiler, including Atkinson,Clayton, Garrett and Sentinel. Other types include the Clarkson 'Thimble tube' and the Foden O-type wagon'spistol-shaped boiler.[8]

Steam fire-engine makers such as Merryweather usually used water-tube boilers for their rapid steam-raisingcapacity.Many steam cars used water-tube boilers, and the Bolsover Express company even made a water-tube replacementfor the Stanley Steamer fire-tube boiler.[9]

Water-tube boiler 3

Design variations

D-type boilerThe 'D-type' is the most common type of small- to medium-sized boilers, similar to the one shown in the schematicdiagram. It is used in both stationary and marine applications. It consists of a large steam drum vertically connectedto a smaller water drum (a.k.a. "mud drum") via multiple steam-generating tubes. These are surrounded by wallsmade up of larger water-filled tubes, which make up the furnace. M-Type Boilers Two fireboxes with a controlsuper-heater

Low Water ContentThe 'Low Water Content' boiler has a lower and upper header connected by water tubes that are directly impingedupon from the burner. This is a "furnace-less" boiler that can generate steam and react quickly to changes in load.

Babcock & Wilcox boiler

Babcock & Wilcox boiler

Designed by the American firm of Babcock and Wilcox, this type has asingle drum, with feedwater drawn from the bottom of the drum into aheader that supplies inclined water-tubes. The water tubes supplysteam back into the top of the drum. Furnaces are located below thetubes and drum.

• Foster-Wheelers•• Combustion Engineering

This type of boiler was used by the Royal Navy's Leander classfrigates.

Stirling boiler

The Stirling boiler has near-vertical, almost-straight watertubes that zig-zag between a number of steam and waterdrums. Usually there are three banks of tubes in a "four drum" layout, but certain applications use variationsdesigned with a different number of drums and banks.

They are mainly used as stationary boilers, owing to their large size, although the large grate area does alsoencourage their ability to burn a wide range of fuels. Originally coal-fired in power stations, they also becamewidespread in industries that produced combustible waste and required process steam. Paper pulp mills could burnwaste bark, sugar refineries their bagasse waste.

Water-tube boiler 4

Yarrow

End-view of a Yarrow boiler

Named after its designers, the then Poplar-based Yarrow Shipbuilders,this type has three drums in a delta formation connected by watertubes. The drums are linked by straight water tubes, allowing easytube-cleaning. This does however mean that the tubes enter the drumsat varying angles, a more difficult joint to caulk. Outside the firebox, apair of 'cold-leg' pipes between each drum act as 'downcomers'.[10]

Due to its three drums, the Yarrow boiler has a greater water capacity.Hence, this type is usually used in older marine boiler applications. Itscompact size made it attractive for use in transportable powergeneration units during World War II. In order to make it transportable,the boiler and its auxiliary equipment (fuel oil heating, pumping units,fans etc.), turbines, and condensers were mounted on wagons to betransported by rail.

White-Forster

The White-Forster type is similar to the Yarrow, but with tubes that are gradually curved. This makes their entry intothe drums perpendicular, thus simpler to make a reliable seal.[10]

Thornycroft

End-view of a Thornycroft boiler

Designed by the shipbuilder John I. Thornycroft & Company, theThornycroft type features a single steam drum with two sets of watertubes either side of the furnace. These tubes, especially the central set,have sharp curves. Apart from obvious difficulties in cleaning them,this may also give rise to bending forces as the tubes warm up, tendingto pull them loose from the tubeplate and creating a leak. There are twofurnaces, venting into a common exhaust, giving the boiler a wide basetapering profile.[10]

Forced-circulation boiler

In a forced-circulation boiler, a pump is added to speed up the flow ofwater through the tubes.[11]

Other types

•• O-type•• A-type•• Flex-tube boiler•• M-Type Control superheater

Water-tube boiler 5

References[1] "High Pressure Steam Locomotive Technology." (http:/ / www. aqpl43. dsl. pipex. com/ MUSEUM/ LOCOLOCO/ hptech. htm). Loco

Locomotive gallery. .[2] "The Jawn Henry" (http:/ / www. trains. com/ trn/ default. aspx?c=a& id=349). Trains Magazine. . Retrieved 2008-10-28.[3] "LNER 10000 High Pressure Locomotive" (http:/ / www. aqpl43. dsl. pipex. com/ MUSEUM/ LOCOLOCO/ LNER10000/ 10000. htm).

Loco Locomotive gallery. .[4] "Baldwin 60000" (http:/ / www. aqpl43. dsl. pipex. com/ MUSEUM/ LOCOLOCO/ USAhp/ USAhp. htm). Loco Locomotive gallery. .[5] See chapter on "Experimentals" in Sagle, Lawrence W. (1964). B&O Power. Staufer. p. 288 ff.[6] "Brotan" (http:/ / www. aqpl43. dsl. pipex. com/ MUSEUM/ LOCOLOCO/ brotan/ brotan. htm). Loco Locomotive gallery. .[7] "Brotan" (http:/ / erojr. home. cern. ch/ erojr/ Content/ phylo/ BROTAN. HTM). .[8] Kelly, Maurice A. (1975). The Undertype Steam Road Waggon. Cambridge: Goose and Son. ISBN 0-900404-16-7.[9] Harris, K. N. (1967). Model Boilers and Boilermaking. Hemel Hempstead: Model Aeronautical Press.[10] Stokers' Manual ((1912 edition) ed.). Admiralty, via HMSO, via Eyre & Spottiswoode. 1901.[11] http:/ / www. enggcyclopedia. com/ 2012/ 01/ boilers-circulation-systems-natural-circulation-forced-circulation/

External links• Robertson, Leslie Stephen Water-tube boilers; based on a short course of lectures delivered at University college,

London (http:/ / www. archive. org/ details/ watertubeboiler01robegoog) (1901) from the Internet Archive

Article Sources and Contributors 6

Article Sources and ContributorsWater-tube boiler  Source: http://en.wikipedia.org/w/index.php?oldid=526355465  Contributors: A2Kafir, Adamrush, Alex Alex Lep, Andy Dingley, Archimedes, Bellhalla, Benea, Bermicourt,Biscuittin, Bluezy, Capecodeph, Carmen56, Chinakow, Dore chakravarty, EdJogg, Email4mobile, Emoscopes, Gaius Cornelius, Globbet, GraemeLeggett, HamburgerRadio, Hellbus,Hooperbloob, JHunterJ, Jdonohue41, Jll, Ka34, Keilana, Lasta, Mangoe, Mb1000, Morven, Pinethicket, Planvi, Pluggy06, Postrach, Pterre, Quackdave, RP459, Tagishsimon, TheAMmollusc,Trekphiler, Wuhwuzdat, ZooFari, 66 anonymous edits

Image Sources, Licenses and ContributorsImage:Water tube boiler schematic.png  Source: http://en.wikipedia.org/w/index.php?title=File:Water_tube_boiler_schematic.png  License: Creative Commons Attribution-Sharealike 2.5 Contributors: User:EmoscopesImage:Brotans boiler.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Brotans_boiler.jpg  License: Creative Commons Attribution-ShareAlike 3.0 Unported  Contributors: stanislavJelenImage:Babcock and Wilcox boiler (Heat Engines, 1913).jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Babcock_and_Wilcox_boiler_(Heat_Engines,_1913).jpg  License:unknown  Contributors: A7N8X, Andy Dingley, Cirt, El.Image:Yarrow boiler end section (Stokers Manual 1912).jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Yarrow_boiler_end_section_(Stokers_Manual_1912).jpg  License:unknown  Contributors: Andy DingleyImage:Thornycroft boiler end section (Stokers Manual 1912).jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Thornycroft_boiler_end_section_(Stokers_Manual_1912).jpg License: unknown  Contributors: Andy Dingley

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