Scotch marine boiler
A "Scotch" marine boiler (or simply Scotch boiler) is a design of
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 are many small-diameter
The Scotch boiler is a
Combustion chamber
The far end of the furnace is an enclosed box called the combustion chamber which extends upwards to link up with the firetubes.
The front wall of the combustion chamber is supported against steam pressure by the tubes themselves. The rear face is stayed by rod stays through the rear shell of the boiler. Above the combustion chamber and tubes is an open steam collecting space. Larger long rod stays run the length of the boiler through this space, supporting the ends of the boiler shell.
With multiple furnaces, there is a separate combustion chamber for each furnace. A few small boilers did connect them into one chamber, but this design is weaker. A more serious problem is the risk of reversing the draught, where exhaust from one furnace could blow back and out of the adjacent one, injuring the stokers working in front of it.
Origins
The first recorded boiler of comparable form was used in a railway locomotive,
Variants
Number of furnaces
Typical practice for ships was to have two furnaces in each boiler. Smaller boilers might only have one, larger boilers commonly had three. The limitation in boiler size was the amount of work each stoker could do, firing one furnace per man.[1] Larger ships (meaning anything above the smallest) would have many boilers.
As with the
Wet back and dry back
The typical design is the "wet back", where the rear face of the combustion chamber is water-jacketed as a heating surface.
The "dry back" variation has the rear of the combustion chamber as an open box, backed or surrounded by only a sheet-metal jacket.[4][5] This simplifies construction, but also loses much efficiency. It is used for only small boilers where capital cost outweighs fuel costs. Although the Scotch boiler is nowadays rarely the primary steam generator on a ship, small dry-back designs such as the Minipac[6] are still encountered, for supporting secondary demands whilst alongside in port with the main boilers cold.
One interesting variant of the dry-back design has been a patent for burning ash-prone fuels.[7] The rear of the combustion chamber is used as an access point for an ash separator, removing the ash before the small-diameter tubes.
Double-ended
The double-ended design places two boilers back-to-back, removing the rear wall of the boiler shell. The combustion chambers and firetubes remain separate. This design saves some structural weight, but it also makes the boiler longer and more difficult to install into a ship. For this reason they were not commonly used, although back-to-back arrangements of multiple single-ended boilers were common.[4]
Inglis
The "Inglis"[8] modification adds an extra combustion chamber where an additional single large flue returns from the rear to the front of the boiler. Flow through the multiple tubes is thus from front to back, and so the exhaust is at the rear. Multiple furnaces would share a single combustion chamber.[4]
The major advantage of the Inglis is the extra heating area it adds, for a comparable shell volume, of perhaps 20%.[9] Surprisingly this is not from the additional combustion chamber, but from lengthening the narrow firetubes. These can now run the full length of the boiler shell, rather than just the rather shorter distance from the inner combustion chamber to the front tubeplate. Despite this advantage, it is rarely used.
Use in ships
The Scotch marine boiler achieved near-universal use throughout the heyday of steam propulsion, particularly for the most highly developed piston engines such as the
Large or fast ships could require a great many boilers. The
Some motor ships, powered by internal combustion engines, also carried Scotch boilers. So-called exhaust-gas boilers were heated by the hot, exhaust gas of the main engines. An example is the diesel-powered, Monte-class passenger ships that were built in Germany in the 1920s and were each fitted with two boilers. The steam generated was used for auxiliary machinery.[11]
Shipboard working examples
Numerous Scotch boilers are in use on ships as of 2010, and new boilers can be built to replace life-expired ones. Examples of preserved steam boats employing Scotch boilers include:
- Steam Tug / Tender Daniel Adamson built 1903 fully restored and cruising on River Weaver in Cheshire and on Manchester Ship Canal has one coal fired Scotch Boiler fired by three furnaces.[12][13][14]
- Steam tug Mayflower, Bristol Industrial Museum
- Baltimore, of 1906, at the Baltimore Museum of Industry, is the oldest working steam tug in the US.[15]
- Steamship Shieldhall based in Southampton, UK, is fully operational and has two oil-fired Scotch boilers.[16]
- Steam-powered icebreaker Stettin, operating on two coal-fired boilers
- Steam-powered drifter Lydia Eva, based in Lowestoft or Great Yarmouth, Fully operational coal-fired Scotch boiler.[17]
- The steam tug Kerne built 1913. Operated out of Liverpool by the Steam Tug Kerne Preservation Society. One coal-fired wet back Scotch marine boiler with two furnaces. Max working pressure 180 pounds per square inch (1,200 kPa).[18]
- The steam ship Trafik built 1892 in Stockholm Sweden by Bergsunds Mekaniska Verkstad as a passenger and freight ship on the Swedisk lake Vättern and with homeport Hjo. The machinery and its boiler are the original ones made for the ship in Stockholm.[19]
- The oil-burning steam tug Canning, built in 1954. First based in Liverpool, but worked at Swansea Docks from 1966 and now part of the National Waterfront Museumthere.
References
Media related to Scotch marine boilers at Wikimedia Commons
- ^ Admiralty, via HMSO, via Eyre & Spottiswoode. 1901.
- ISBN 978-0582127937.
- ISBN 978-0071432023.
- ^ ISBN 978-0852423776.
- ^ Malek, Power Boilers, p.244
- ISBN 978-0117702233.
- ^ US 5558046, Schoppe, Fritz & Pröstler, Josef, "Fire-tube boiler", published 1996-09-24, assigned to Fritz Schoppe
- ^ "Business and History – John Inglis Co. Limited". University of Western Ontario. Archived from the original on 2010-01-12.
- ^ Milton, J.H. (1961) [1953]. Marine Steam Boilers (2nd ed.). Newnes.
- ISBN 978-1856484824.
- ^ "The Merchant Shipping Act, 1894 Report of Court (no. 7933)" (PDF). Local history & Maritime Digital Archive, Southampton City Council. 27 June 1954. Retrieved 20 April 2018.
- LCCN 2010525184. Retrieved 26 June 2020.
- ^ "Daniel Adamson". National Historic Ships UK. 2018. Retrieved 26 June 2020.
- ^ "The Danny — Full History". Daniel Adamson Preservation Society. 2020. Retrieved 26 June 2020.
- ^ "Steam Tug Baltimore".
- ^ "SS Shieldhall".
- ^ "Lydia Eva".
- ^ "s/s KERNE".
- ^ "S/S Trafik Hjo".