A high pressure watertube boiler (also spelled water-tube and water tube) is a type of

boiler A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central h ...

in which water circulates in tubes heated externally by the fire. Fuel is burned inside the

furnace A furnace is a structure in which heat is produced with the help of combustion. Furnace may also refer to: Appliances Buildings * Furnace (central heating): a furnace , or a heater or boiler , used to generate heat for buildings * Boiler, used t ...

, creating hot gas which boils water in the steam-generating tubes. In smaller boilers, additional generating tubes are separate in the furnace, while larger utility boilers rely on the water-filled tubes that make up the walls of the furnace to generate

steam Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization ...

. The heated water/steam mixture then rises into the

steam drum A steam drum is a standard feature of a water-tube boiler. It is a reservoir of water/steam at the top end of the water tubes. The drum stores the steam generated in the water tubes and acts as a phase- separator for the steam/water mixture. The d ...

. Here, saturated steam is drawn off the top of the drum. In some services, the steam passes through tubes in the hot gas path, (a

superheater A superheater is a device used to convert saturated steam or wet steam into superheated steam or dry steam. Superheated steam is used in steam turbines for electricity generation, steam engines, and in processes such as steam reforming. There ar ...

) to become superheated. Superheated steam is defined as steam that is heated above the boiling point at a given pressure. Superheated steam is a dry gas and therefore is typically used to drive turbines, since water droplets can severely damage turbine blades. Saturated water at the bottom of the steam drum returns to the lower drum via large-bore 'downcomer tubes', where it pre-heats the feedwater supply. (In large utility boilers, the feedwater is supplied to the steam drum and the

downcomer Boilers for generating steam or hot water have been designed in countless shapes, sizes and configurations. An extensive terminology has evolved to describe their common features. This glossary provides definitions for these terms. Terms which re ...

s supply water to the bottom of the waterwalls). To increase economy of the boiler, exhaust gases are also used to pre-heat combustion air blown into the burners, and to warm the feedwater supply in an

economizer Economizers (US and Oxford spelling), or economisers (UK), are mechanical devices intended to reduce energy consumption, or to perform useful function such as preheating a fluid. The term economizer is used for other purposes as well. Boiler, po ...

. Such watertube boilers in

thermal power station A thermal power station is a type of power station in which heat energy is converted to electrical energy. In a steam-generating cycle heat is used to boil water in a large pressure vessel to produce high-pressure steam, which drives a stea ...

s are also called ''steam generating units''. The older

fire-tube boiler A fire-tube boiler is a type of boiler in which hot gases pass from a fire through one or more tubes running through a sealed container of water. The heat of the gases is transferred through the walls of the tubes by thermal conduction, heating t ...

design, in which the water surrounds the heat source and gases from combustion pass through tubes within the water space, is typically a much weaker structure and is rarely used for pressures above . A significant advantage of the watertube boiler is that there is less chance of a catastrophic failure: there is not a large volume of water in the boiler nor are there large mechanical elements subject to failure. A water tube boiler was patented by Blakey of England in 1766 and was made by Dallery of France in 1780.

Applications

"The ability of watertube boilers to be designed without the use of excessively large and thick walled pressure vessels makes these boilers particularly attractive in applications that require dry, high-pressure, high-energy steam, including steam turbine power generation". Owing to their superb working properties, the use of watertube boilers is highly preferred in the following major areas: * Variety of process applications in industries * Chemical processing divisions * Pulp and Paper manufacturing plants * Refining units Besides, they are frequently employed in power generation plants where large quantities of steam (ranging up to 500 kg/s) having high pressures i.e. approximately and high temperatures reaching up to 550 °C are generally required. For example, the Ivanpah solar-power station uses two Rentech Type-D watertube boilers for plant warmup, and when operating as a fossil fueled power station.

Stationary

Modern boilers for power generation are almost entirely water-tube designs, owing to their ability to operate at higher pressures. Where

process steam A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include: Business and management *Business process, activities that produce a specific se ...

is required for heating or as a chemical component, then there is still a small niche for fire-tube boilers. One notable exception is in typical Nuclear power stations (Pressurized Water Reactors), where the steam generators are generally configured similar to firetube boiler designs. In these applications the hot gas path through the "Firetubes" actually carries the very hot/high pressure primary coolant from the reactor, and steam is generated on the external surface of the tubes.

Marine

Their ability to work at higher pressures has led to marine boilers being almost entirely water-tube. This change began around 1900, and traced the adoption of

turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating e ...

s for propulsion rather than reciprocating (i.e. piston) engines – although watertube boilers were also used with reciprocating engines, and firetube boilers were also used in many marine turbine applications.

Railway

There has been no significant adoption of water-tube boilers for railway locomotives. A handful of experimental designs were produced, but none of these were successful or led to their widespread use. Most water-tube railway locomotives, especially in Europe, used the Schmidt system. Most were

compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with defensive struct ...

s, and a few uniflows. The

Norfolk and Western Railway The Norfolk and Western Railway , commonly called the N&W, was a US class I railroad, formed by more than 200 railroad mergers between 1838 and 1982. It was headquartered in Roanoke, Virginia, for most of its existence. Its motto was "Precisio ...

's '' Jawn Henry'' was an exception, as it used a

steam turbine A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam turbin ...

combined with an electric transmission. *

LMS 6399 Fury The London Midland and Scottish Railway (LMS) No. 6399 ''Fury'' was an unsuccessful British experimental express passenger locomotive. The intention was to save fuel by using high-pressure steam, which is thermodynamically more efficient than l ...

: Rebuilt completely after a fatal accident * LNER 10000 "Hush hush" : Using a

Yarrow boiler Yarrow boilers are an important class of high-pressure water-tube boilers. They were developed by Yarrow & Co. (London), Shipbuilders and Engineers and were widely used on ships, particularly warships. The Yarrow boiler design is characteristic ...

, rather than Schmidt. Not successful and re-boilered with a conventional boiler.

Hybrids

A slightly more successful adoption was the use of hybrid water-tube / fire-tube systems. As the hottest part of a locomotive boiler is the

firebox Firebox may refer to: *Firebox (steam engine), the area where the fuel is burned in a steam engine *Firebox (architecture), the part of a fireplace where fuel is combusted *Firebox Records, a Finnish 8101705801record label * Firebox.com, an electro ...

, it was an effective design to use a water-tube design here and a conventional fire-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 Under the Whyte notation for the classification of steam locomotives by wheel arrangement, represents the arrangement of four leading wheels, ten powered and coupled driving wheels and two trailing wheels. In South Africa, where the wheel arra ...

No. 60000, built in 1926. Operating as a

at a boiler pressure of it covered over successfully. After a year though, it became clear that any economies were overwhelmed by the extra costs and it was retired to a museum display at the Franklin Institute in Philadelphia, Pennsylvania. A series of twelve experimental locomotives were constructed at the

Baltimore and Ohio Railroad The Baltimore and Ohio Railroad was the first common carrier railroad and the oldest railroad in the United States, with its first section opening in 1830. Merchants from Baltimore, which had benefited to some extent from the construction of ...

's Mt. Clare shops under the supervision of George H. Emerson, but none of them was replicated in any numbers. The only railway use of water-tube boilers in any numbers was the Brotan boiler, invented in Austria in 1902 by

Johann Brotan Johann Brotan (24 June 1843 – 20 November 1918) was an Austrian mechanical engineer, specialising in locomotive construction.Kirsche (1978), p. 144. Biography Johann Brotan was born in Klattau, now Klatovy in the Czech Republic. He studied at t ...

and found in rare examples throughout Europe. Hungary, though, was a keen user and had around 1,000 of them. Like the Baldwin, this combined a water-tube firebox with a fire-tube barrel. The original characteristic of the Brotan was a long steam drum running ''above'' the main barrel, making it resemble a

Flaman boiler There have been a vast number of designs of steam boiler, particularly towards the end of the 19th century when the technology was evolving rapidly. A great many of these took the names of their originators or primary manufacturers, rather than a m ...

in appearance.

Road

While the

traction engine A traction engine is a steam engine, steam-powered tractor used to move heavy loads on roads, plough ground or to provide power at a chosen location. The name derives from the Latin ''tractus'', meaning 'drawn', since the prime function of any t ...

was usually built using its

locomotive boiler A fire-tube boiler is a type of boiler in which hot gases pass from a fire through one or more tubes running through a sealed container of water. The heat of the gases is transferred through the walls of the tubes by thermal conduction, heating t ...

as its frame, other types of steam road vehicles such as

lorries A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construction ...

and

cars A car or automobile is a motor vehicle with wheels. Most definitions of ''cars'' say that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people instead of goods. The year 1886 is regarded as t ...

have used a wide range of different boiler types. Road transport pioneers

Goldsworthy Gurney Sir Goldsworthy Gurney (14 February 1793 – 28 February 1875) was an English surgeon, chemist, architect, builder, lecturer and consultant. He was a prototypical British gentleman scientist and inventor of the Victorian era. Amongst many acc ...

and

Walter Hancock Walter Hancock (16 June 1799 – 14 May 1852) was an English inventor of the Victorian period. He is chiefly remembered for his steam-powered road vehicles, but also received a patent for preparing and cutting natural rubber into sheets. He ...

both used water-tube boilers in their steam carriages around 1830. Most undertype wagons used water-tube boilers. Many manufacturers used variants of the vertical cross-tube boiler, including

Atkinson Atkinson may refer to: Places *Atkinson, Nova Scotia, Canada * Atkinson, Dominica, a village in Dominica *Atkinson, Illinois, U.S. * Atkinson, Indiana, U.S. *Atkinson, Maine, U.S. *Atkinson Lake, a lake in Minnesota, U.S. *Atkinson, Nebraska, U. ...

, Clayton, Garrett and

Sentinel Sentinel may refer to: Places Mountains * Mount Sentinel, a mountain next to the University of Montana in Missoula, Montana * Sentinel Buttress, a volcanic crag on James Ross Island, Antarctica * Sentinel Dome, a naturally occurring grani ...

. Other types include the Clarkson ' thimble tube' and the Foden O-type wagon's pistol-shaped boiler. Steam fire-engine makers such as

Merryweather Merryweather may refer to: People * Alice Merryweather (born 1996), American alpine skier * Andrew Merryweather (born 1961), Australian rules footballer * George Merryweather (1794–1870), English inventor of the tempest prognosticator, a leech-ba ...

usually used water-tube boilers for their rapid steam-raising capacity. Many steam cars used water-tube boilers, and the Bolsover Express company even made a water-tube replacement for the

Stanley Steamer The Stanley Motor Carriage Company was an American manufacturer of steam cars; it operated from 1902 to 1924. The cars made by the company were colloquially called Stanley Steamers, although several different models were produced. Early history ...

fire-tube boiler.

Design variations

D-type boiler

The ' D-type' is the most common type of small- to medium-sized boilers, similar to the one shown in the schematic diagram. It is used in both stationary and marine applications. It consists of a large steam drum vertically connected to a smaller water drum (a.k.a. "mud drum") via multiple steam-generating tubes. These drums and tubes as well as the oil-fired burner are enclosed by water-walls - additional water-filled tubes spaced close together so as to prevent gas flow between them. These water wall tubes are connected to both the steam and water drums, so that they act as a combination of preheaters and downcomers as well as decreasing heat loss to the boiler shell.

M-type boilers

The M-type boilers were used in many US World War II warships including hundreds of ''Fletcher''-class destroyers. Three sets of tubes form the shape of an M, and create a separately fired superheater that allows better superheat temperature control. In addition to the mud drum shown on a D-type boiler, an M-type has a water-screen header and a waterwall header at the bottom of the two additional rows of vertical tubes and downcomers.

Low water content

The ''low water content'' boiler has a lower and upper header connected by watertubes that are directly impinged upon 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 Babcock & Wilcox is an American renewable, environmental and thermal energy technologies and service provider that is active and has operations in many international markets across the globe with its headquarters in Akron, Ohio, USA. Historicall ...

, this type has a single drum, with feedwater drawn from the bottom of the drum into a header that supplies inclined water-tubes. The watertubes supply steam back into the top of the drum. Furnaces are located below the tubes and drum. This type of boiler was used by the

Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...

's ''Leander''-class

frigate A frigate () is a type of warship. In different eras, the roles and capabilities of ships classified as frigates have varied somewhat. The name frigate in the 17th to early 18th centuries was given to any full-rigged ship built for speed and ...

s and in

United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

New Orleans-class cruiser The ''New Orleans''-class cruisers were a class of seven heavy cruisers built for the United States Navy (USN) in the 1930s. These ships participated in the heaviest surface battles of the Pacific War. ''Astoria'', ''Quincy'', and ''Vincenne ...

Stirling boiler

The

Stirling boiler The Stirling boiler is an early form of water-tube boiler, used to generate steam in large land-based stationary plants. Although widely used around 1900, it has now fallen from favour and is rarely seen. Design Stirling boilers are one of the ...

has near-vertical, almost-straight watertubes that zig-zag between a number of steam and water drums. Usually there are three banks of tubes in a "four drum" layout, but certain applications use variations designed 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 also encourage their ability to burn a wide range of fuels. Originally coal-fired in power stations, they also became widespread in industries that produced combustible waste and required

. Paper pulp mills could burn waste bark, sugar refineries their

bagasse Bagasse ( ) is the dry pulpy fibrous material that remains after crushing sugarcane or sorghum stalks to extract their juice. It is used as a biofuel for the production of heat, energy, and electricity, and in the manufacture of pulp and building ...

waste. It is a horizontal drum type of boiler.

Yarrow

Named after its designers, the then Poplar-based

Yarrow Shipbuilders Yarrow Shipbuilders Limited (YSL), often styled as simply Yarrows, was a major shipbuilding firm based in the Scotstoun district of Glasgow on the River Clyde. It is now part of BAE Systems Surface Ships, owned by BAE Systems, which has also o ...

, this type of

three-drum boiler Three-drum boilers are a class of water-tube boiler used to generate steam, typically to power ships. They are compact and of high evaporative power, factors that encourage this use. Other boiler designs may be more efficient, although bulkier, an ...

has three drums in a

delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D (NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may also re ...

formation connected by watertubes. The drums are linked by straight watertubes, allowing easy tube-cleaning. This does, however, mean that the tubes enter the drums at varying angles, a more difficult joint to

caulk Caulk or, less frequently, caulking is a material used to seal joints or seams against leakage in various structures and piping. The oldest form of caulk consisted of fibrous materials driven into the wedge-shaped seams between boards on w ...

. Outside the firebox, a pair of cold-leg pipes between each drum act as

s. Due to its three drums, the Yarrow boiler has a greater water capacity. Hence, this type is usually used in older

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

boiler applications. Its compact size made it attractive for use in transportable

power generation Electricity generation is the process of generating electric power from sources of primary energy. For utilities in the electric power industry, it is the stage prior to its delivery ( transmission, distribution, etc.) to end users or its stor ...

units during

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

. In order to make it transportable, the boiler and its auxiliary equipment (fuel oil heating, pumping units, fans etc.),

turbines A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful Work (physics), work. The work produced by a turbine can be used ...

, and

condensers __NOTOC__ Condenser may refer to: Heat transfer * Condenser (heat transfer), a device or unit used to condense vapor into liquid. Specific types include: ** HVAC air coils ** Condenser (laboratory), a range of laboratory glassware used to remove ...

were mounted on wagons to be transported by

rail Rail or rails may refer to: Rail transport *Rail transport and related matters *Rail (rail transport) or railway lines, the running surface of a railway Arts and media Film * ''Rails'' (film), a 1929 Italian film by Mario Camerini * ''Rail'' ( ...

White-Forster

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

Thornycroft

Designed by the shipbuilder John I. Thornycroft & Company, the Thornycroft 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, tending to pull them loose from the tubeplate and creating a leak. There are two furnaces, venting into a common exhaust, giving the boiler a wide base tapering profile.

Forced circulation boiler

In a

forced circulation boiler A forced circulation boiler is a boiler where a pump is used to circulate water inside the boiler. This differs from a natural circulation boiler which relies on current density to circulate water inside the boiler. In some forced circulation boile ...

, a

pump A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they u ...

is added to speed up the flow of water through the tubes.

Other types

O-type boiler An O-type boiler is a form of water-tube boiler. It is named, like the D-type and A-type boilers, from the approximate shape of its tubes. They are characterised by single steam and water drums vertically above each other, with curved vertical ...

A-type boiler A type or type A may refer to: * A-type asteroid, a type of relatively uncommon inner-belt asteroids * A type blood, a type in the ABO blood group system * A-type inclusion, a type of cell inclusion * A-type potassium channel, a type of voltage-gat ...

* Flex-tube boiler * M-type control superheater

References

External links

* {{steam engine configurations Boilers