Boiler (power generation)

Any remaining heat in the combustion gases can then either be evacuated or made to pass through an economiser, the role of which is to warm the feed water before it reaches the boiler.

For the first Newcomen engine of 1712, the boiler was little more than large brewer's kettle installed beneath the power cylinder.

Smeaton further lengthened the path of the gases by means of a spiral labyrinth flue beneath the boiler.

A longer version on a rectangular plan was developed around 1775 by Boulton and Watt (wagon top boiler).

An early proponent of the cylindrical form was the British engineer John Blakey, who proposed his design in 1774.

[1][2] Another early proponent was the American engineer, Oliver Evans, who rightly recognised that the cylindrical form was the best from the point of view of mechanical resistance and towards the end of the 18th century began to incorporate it into his projects.

Due to space and weight considerations the latter were one-pass exhausting directly from fire tube to chimney.

From 1804 onwards Trevithick produced a small two-pass or return flue boiler for semi-portable and locomotive engines.

A significant step forward came in France in 1828 when Marc Seguin devised a two-pass boiler of which the second pass was formed by a bundle of multiple tubes.

Prior to the Rainhill trials of 1829 Henry Booth, treasurer of the Liverpool and Manchester Railway suggested to George Stephenson, a scheme for a multi-tube one-pass horizontal boiler made up of two units: a firebox surrounded by water spaces and a boiler barrel consisting of two telescopic rings inside which were mounted 25 copper tubes; the tube bundle occupied much of the water space in the barrel and vastly improved heat transfer.

Old George immediately communicated the scheme to his son Robert and this was the boiler used on Stephenson's Rocket, outright winner of the trial.

The design formed the basis for all subsequent Stephensonian-built locomotives, being immediately taken up by other constructors; this pattern of fire-tube boiler has been built ever since.

The problem was producing big enough plates, so that even pressures of around 50 psi (344.7 kPa) were not absolutely safe, nor was the cast iron hemispherical boiler initially used by Richard Trevithick.

Once-through monotubular water tube boilers as used by Doble, Lamont and Pritchard are capable of withstanding considerable pressure and of releasing it without danger of explosion.

The source of heat for a boiler is combustion of any of several fuels, such as wood, coal, oil, or natural gas.

This is because natural draught is subject to outside air conditions and temperature of flue gases leaving the furnace, as well as chimney height.

In a Stephensonian firetube locomotive boiler, this entails routing the saturated steam through small diameter pipes suspended inside large diameter firetubes putting them in contact with the hot gases exiting the firebox; the saturated steam flows backwards from the wet header towards the firebox, then forwards again to the dry header.

Superheating only began to be generally adopted for locomotives around the year 1900 due to problems of overheating of and lubrication of the moving parts in the cylinders and steam chests.

The term "boiler" should not be used for a supercritical pressure steam generator, as no "boiling" actually occurs in this device.

The most common options for demineralization of boiler feedwater are reverse osmosis (RO) and ion exchange (IX).

At best, this increases energy costs and can lead to poor quality steam, reduced efficiency, shorter plant life and an operation which is unreliable.

While variations in standards may exist in different countries, stringent legal, testing, training and certification is applied to try to minimize or prevent such occurrences.

Failure modes include: The Doble steam car uses a once-through type contra-flow generator, consisting of a continuous tube.

This means that every particle of water and steam must necessarily pass through every part of the generator causing an intense circulation which prevents any sediment or scale from forming on the inside of the tube.

[7] Similar forced circulation generators, such as the Pritchard and Lamont and Velox boilers present the same advantages.