Economiser

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An economiser is a device fitted to a boiler which saves energy by using the exhaust gases from the boiler to pre-heat the cold water used the fill it (the feed water).

The first successful design of economiser was used to increase the steam-raising efficiency of the boilers of stationary steam engines. It was patented by Edward Green in 1845, and since then has been known as Green's economiser. It consisted of an array of vertical cast iron tubes connected to a tank of water above and below, between which the boiler's exhaust gases passed. This is the reverse arrangement to that of fire tubes in a boiler itself; there the hot gases pass through tubes immersed in water, whereas in an economiser the water passes through tubes surrounded by hot gases. The most successful feature of Green's design of economiser was its mechanical scraping apparatus, which was needed to keep the tubes free of deposits of soot.

Economisers were eventually fitted to virtually all stationary steam engines in the decades following Green's invention. Some preserved stationary steam engine sites still have their Green's economisers although usually they are not used. One such preserved site is the Claymills Pumping Engines Trust in Staffordshire, England, which is in the process of restoring one set of economisers and the associated steam engine which drove them.

Modern-day boilers (such as those in coal-fired power stations) are still fitted with economisers which are descendants of Green's original design. In this context they are often referred to as feedwater heaters and heat the condensate from turbines before it is pumped to the boilers.

[edit] References

• Richard L. Hills (1989). Power from steam: A history of the stationary steam engine. Cambridge University Press. ISBN 0-521-45834-X.