Evaporator (marine)
An evaporator, distiller or distilling apparatus is a piece of ship's equipment used to produce fresh
Early evaporators on sailing vessels
Although distillers are often associated with
At first, only larger warships and some exploratory ships were fitted with distilling apparatus: a warship's large crew naturally needed a large supply of water, more than they could stow on board in advance. Cargo ships, with their smaller crews, merely carried their supplies with them. A selection of documented systems is as follows:
- 1539. Blasco de Garay.[2][3][4]
- 1560. "Jornada de Los Gelves".[5]
- 1578. Martin Frobisher. According to some authors, obtained fresh water from frozen seawater.[6]
- 1717. A doctor from Nantes, M. Gauthier, proposed a still (not working well on the sea, with the rocking of the ship).[7]
- 1763. Poissonier. Implemented a countercurrent water condenser.[8][9]
- 1771. Method of Dr. Charles Irving, adopted by the British Royal Navy.[10]
- 1771. Cook's Pacific exploration ship HMS Resolution carried a distiller[11] and did tests to check: coal consumption vs. amount of fresh water produced.[12][13]
- 1783. Louis Antoine de Bougainville.[14]
- 1805. Nelson's HMS Victory was fitted with distilling apparatus in her galley.[15]
- 1817.
- 1821. Publication of the details of an apparatus for distilling aiguardente in continuous process, by the Catalan Joan Jordana i Elias. This still had many advantages over the previous ones and was quickly adopted in Catalonia.[19]
Boiler feedwater
With the development of the marine steam engine, their boilers also required a continual supply of feedwater.
Early boilers used seawater directly, but this gave problems with the build-up of
The distillation system for boiler feedwater at this time was usually termed an evaporator, partly to distinguish it from a separate system or distiller used for drinking water. Separate systems were often used, especially in early systems, owing to the problem of contamination from oily lubricants in the feedwater system and because of the greatly different capacities required in larger ships. In time, the two functions became combined and the two terms were applied to the separate components of the system.
Potable water distillers
The first water supply by distillation of boiler steam appeared on early
Evaporators
Combined supply
The first distilling plants that boiled a separate water supply from that of the main boiler, appeared around 1867.[15] These were not directly heated by a flame, but had a primary steam circuit using main boiler steam through coils within a steam drum or evaporator.[23] The distillate from this vessel then passed to an adjacent vessel, the distilling condenser.[23] As these evaporators used a 'clean' seawater supply directly, rather than contaminated water from the boiler circuit, they could be used to supply both feedwater and drinking water. These double distillers appeared around 1884.[15] For security against failure, ships except the smallest were fitted with two sets.[23]
Vacuum evaporators
Evaporators consume a great deal of steam, and thus fuel, in relation to the quantity of fresh water produced. Their efficiency is improved by working them at a partial vacuum, supplied by the main engine condensers.
Scale
One of the greatest operational problems with an evaporator is the build-up of
Despite the obvious salinity of seawater,
A greater problem for scaling is the deposition of
To further control scale formation, equipment may be provided to automatically inject a weak citric acid solution into the seawater feed. The ratio is 1:1350, by weight of seawater.[28]
Compound evaporators
Operation of an evaporator represents a costly consumption of main boiler steam, thus fuel. Evaporators for a warship must also be adequate to supply the boilers at continuous full power when required, even though this is rarely required. Varying the vacuum under which the evaporator works, and thus the boiling point of the feedwater, may optimise production for either maximum output, or better efficiency, depending on which is needed at the time. Greatest output is achieved when the evaporator operates at near atmospheric pressure and a high temperature (for
If condenser vacuum is increased to its maximum, evaporator temperature may be reduced to around 72 °C. Efficiency increases until the mass of feedwater produced almost equals that of the supplied steam, although production is now restricted to 86% of the previous maximum.[24]
Evaporators are generally installed as a set, where two evaporators are coupled to a single distiller.[29] For reliability, large ships will then have a pair of these sets.[29] It is possible to arrange these sets of evaporators in either parallel or in series, for either maximum or most efficient production.[24] This arranges the two evaporators so that the first operates at atmospheric pressure and high temperature (the maximum output case), but then uses the resultant hot output from the first evaporator to drive a second, running at maximum vacuum and low temperature (the maximum efficiency case).[29] The overall output of feedwater may exceed the weight of steam first supplied, as up to 160% of it. Capacity is however reduced, to 72% of the maximum.[24]
Evaporator pumps
The unevaporated seawater in an evaporator gradually becomes a concentrated brine and, like the early steam boilers with seawater feed, this brine must be intermittently blown down every six to eight hours and dumped overboard.
Flash distillers
A later form of marine evaporator is the flash distiller.[31] Heated seawater is pumped into a vacuum chamber, where it 'flashes' into pure water vapour. This is then condensed for further use.
As the use of vacuum reduces the vapour pressure, the seawater need only be raised to a temperature of 77 °C (171 °F).[i] Both evaporator and distiller are combined into a single chamber, although most plants use two joined chambers, worked in series. The first chamber is worked at 23.5 inHg (80 kPa) vacuum, the second at 26–27 inHg (88–91 kPa).[31] Seawater is supplied to the distiller by a pump at around 20 pounds per square inch (140 kPa). The cold seawater passes through a condenser coil in the upper part of each chamber before being heated by steam in an external feedwater heater. The heated seawater enters the lower part of the first chamber, then drains over a weir and passes to the second chamber, encouraged by the differential vacuum between them. The brine produced by a flash distiller is only slightly concentrated and is pumped overboard continuously.[31]
Fresh water vapour rises through the chambers and is condensed by the seawater coils. Baffles and catchment trays capture this water in the upper part of the chamber. Vacuum itself is maintained by steam ejectors.[31]
The advantage of the flash distiller over the compound evaporator is its greater operating efficiency, in terms of heat supplied. This is due to working under vacuum, thus low temperature, and also the regenerative use of the condenser coils to pre-heat the seawater feed.[31]
A limitation of the flash distiller is its sensitivity to seawater inlet temperature, as this affects the efficiency of the condenser coils. In tropical waters, the distiller flowrate must be throttled to maintain effective condensation.[31] As these systems are more modern, they are generally fitted with an electric salinometer and some degree of automatic control.[31]
Vapour-compression distillers
Where no adequate steam supply is available, a
Seawater is pumped into an evaporator, where it is boiled by a heating coil. Vapour produced is then compressed, raising its temperature. This heated vapour is used to heat the evaporator coils. Condensate from the coil outlet provides the fresh water supply. To start the cycle, an electric pre-heater is used to heat the first water supply. The main energy input to the plant is in mechanically driving the compressor, not as heat energy.[33]
Both the fresh water production and the waste brine from the evaporator are led through an output cooler. This acts as a
Submarines
Vapour-compression distillers were installed on US submarines shortly before World War 2.[34] Early attempts had been made with evaporators running from diesel engine exhaust heat, but these could only be used when the submarine was running at speed on the surface. A further difficulty with submarines was the need to produce high-quality water for topping up their large storage batteries. Typical consumption on a war patrol was around 500 US gallons (1,900 litres) per day for hotel services, drinking, cooking, washing[ii] etc. and also for replenishing the diesel engine cooling system. A further 500 gallons per week was required for the batteries.[34] The standard Badger model X-1 for diesel submarines could produce 1,000 gallons per day. Tank capacity of 5,600 gallons (1,200 of which was battery water) was provided, around 10 days reserve.[34] With the appearance of nuclear submarines and their plentiful electricity supply, even larger plants could be installed. The X-1 plant was designed so that it could be operated when snorkelling, or even when completely submerged. As the ambient pressure increased when submerged, and thus the boiling point, additional heat was required in these submarine distillers, and so they were designed to run with electric heat continuously.[34]
See also
- Chaplin's Patent Distilling Apparatus with Steam Pump
- Scuttlebutt
Notes
- ^ A temperature of at least 71 °C (160 °F) is required, for sterilisation purposes.
- ^ Although German U-boats relied on saltwater soap, US practice was to fit adequate distilling plant.
References
- ^ The Repertory of Arts, Manufactures, and Agriculture. 1818. pp. 313–.
- ^ Salvador Canals (1926). Nuestro tiempo.
- ISBN 978-2-7108-1076-6.
- ISBN 978-84-8102-565-1.
- ISBN 978-84-00-05288-1.
- ^ Encyclopedie Methodique. 1791. pp. 709–.
- ^ Bulletin du Musée de l'industrie. Bruylant-Christophe. 1845. pp. 11–.
- ISBN 90-04-00617-6.
- ^ Observations et Memoires sur la Physique. 1779. pp. 316–.
- ^ "Log book of HMS Resolution". Cambridge Digital Library. Retrieved 23 July 2013.
- ^ James Cook; Esq. George William ANDERSON (1820). Voyages round the World, performed by Captain James Cook ... [The abridgment of G. W. Anderson.] Embellished with engravings. J. Robins & Company; Sherwood, Neely & Jones. pp. 368–.
- ^ James Cook (1809). The Voyages of Captain James Cook Round the World: Printed Verbatim from the Original Editions, and Embellished with a Selection of the Engravings. R. Phillips. pp. 251–.
- ^ Sholto Percy (1835). Mechanics' Magazine and Journal of Science, Arts, and Manufactures. Knight and Lacey. pp. 296–.
- ^ a b c d e f Rippon, Vol.1 (1988), pp. 78–79.
- ^ World (1839). Voyage autour du monde ... exécuté sur les corvettes de s.m. l'Uranie et la Physicienne, pendant les années 1817,1818,1819 et 1820, publ. par L. de Freycinet. pp. 1387–.
- ^ Jöns Jakob Berzelius (Friherre); Olof Gustaf Öngren (1838). Traité de chimie. A. Wahlen et Cie. pp. 167–.
- ^ Jacques Arago (1823). Narrative of a Voyage Round the World, in the Uranie and Physicienne Corvettes, Commanded by Captain Freycinet, During the Years 1817, 1818, 1819, and 1820. Treuttel & Wurtz, Treuttal, jun. & Richter. pp. 20–.
- ^ Francisco Carbonell Bravo (1830). Nuevo aparato para mejorar la cosecha del vino, o sea, Suplemento: al arte de hacer y conservar el vino. Imp. de la Vda. é Hijos de A.Brusi. pp. 5–.
- ^ a b Rippon, Vol.1 (1988), p. 30.
- ^ a b Rippon, Vol.1 (1988), p. 60.
- ^ a b c Rippon, Vol.1 (1988), p. 164.
- ^ Admiralty, via HMSO, via Eyre & Spottiswoode. 1901. pp. 42–45.
- ^ a b c d e f g Rippon, Vol.1 (1988), pp. 160–164.
- ^ a b c d Drover, Engineer-Captain F.J., RN (1925). Marine Engineering Repairs. Chapman & Hall. pp. 105–106.
{{cite book}}
: CS1 maint: multiple names: authors list (link) - ^ Naval Marine Engineering Practice (1971), p. 227
- ^ Machinery Handbook (1941), pp. 156–166
- ^ Naval Marine Engineering Practice (1971), pp. 225–226
- ^ a b c Machinery Handbook (1941), pp. 159–160
- ^ Rippon, Vol.1 (1988), p. 161
- ^ a b c d e f g Naval Marine Engineering Practice (1971), pp. 212-215
- ^ Milton, J. H. (1961) [1953]. Marine Steam Boilers (2nd ed.). Newnes. pp. 119–137.
- ^ a b c Naval Marine Engineering Practice (1971), pp. 230-232
- ^ a b c d Fleet Submarine, Distilling Systems
Bibliography
- Rippon, Commander P.M., RN (1988). The evolution of engineering in the Royal Navy. Vol. 1: 1827–1939. Spellmount. ISBN 0-946771-55-3.)
{{cite book}}
: CS1 maint: multiple names: authors list (link - Rippon, Commander P.M., RN (1994). "5: Evaporator and Distilling Machinery". The evolution of engineering in the Royal Navy. Vol. 2: 1939–1992. Spellmount. pp. 40–44. ISBN 0907206476.)
{{cite book}}
: CS1 maint: multiple names: authors list (link - Smith, E.C. (1937). "Introduction of Auxiliary Machinery". A Short History of Marine Engineering. Cambridge University Press, for Babcock & Wilcox. pp. 220–225.
- BR 77 Machinery Handbook. later replacement for the Stokers Manual. Admiralty, via HMSO. 1941.
- Naval Marine Engineering Practice. later replacement for the ISBN 011-770223-4.
- Submarine Distilling Systems. The Fleet Type Submarine. Vol. 5. Bureau of Naval Personnel. January 1955. Navpers 16170. Archived from the original on 2012-03-18. Retrieved 2011-06-28.