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  • Three-drum boiler


    Three-drum boiler, casing removedThree-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, and so the three-drum pattern was rare as a land-based stationary boiler. The fundamental characteristic of the "three-drum" design is the arrangement of a steam drum above two water drums, in a triangular layout. Water tubes fill in the two sides of this triangle between the drums, and the furnace is in the centre. The whole assembly is then enclosed in a casing, leading to the exhaust flue. Firing can be by either coal or oil. Many coal-fired boilers used multiple firedoors and teams of stokers, often from both ends.

  • Scotch marine boiler


    German example. Note the steam dome, a typically German feature, and also the corrugated furnaces. A "Scotch" marine boiler (or simply Scotch boiler) is a design of steam boiler best known for its use on ships. Sectional diagram of a "wet back" boiler The general layout is that of a squat horizontal cylinder. One or more large cylindrical furnaces are in the lower part of the boiler shell. Above this is a large number of small-diameter fire-tubes. Gases and smoke from the furnace pass to the back of the boiler, then return through the small tubes and up and out of the chimney. The ends of these multiple tubes are capped by a smokebox, outside the boiler shell. The Scotch boiler is a fire-tube boiler, in that hot flue gases pass through tubes set within a tank of water. As such, it is a descendant of the earlier Lancashire boiler, and like the Lancashire it uses multiple separate furnaces to give greater heating area for a given furnace capacity. It differs from the Lancashire in two aspects: a large number of small-diameter tubes (typically diameter each) are used to increase the ratio of heating area to cross-section. Secondly, the overall length of the boiler is halved by folding the gas path back on itself.

  • Stirling boiler


    Five-drum form, section. Note the chain-grate automatic stoker (left) 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.

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