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93-681: The four main components of an evaporator assembly are: Heat is transferred to the liquid inside the tube walls via conduction providing the thermal energy needed for evaporation. Convective currents inside it also contribute to heat transfer efficiency. There are various evaporator designs suitable for different applications including shell and tube, plate, and flooded evaporators, commonly used in industrial processes such as desalination, power generation and air conditioning. Plate-type evaporators offer compactness while multi-stage designs enable enhanced evaporation rates at lower heat duties. The overall performance of evaporators depends on factors such as

186-400: A vacuum inside the vessel, achieving partial evaporation. The vapor then passes through a demister before reaching the condenser section. Seawater is pumped through the condenser section to cool the vapor sufficiently for condensation. The distillate gathers in a tray, from where it is pumped to the storage tanks. A salinometer monitors salt content and diverts the flow of distillate from

279-481: A European directive) is not allowed. In practice, a fraction of the living bacteria pass through RO through membrane imperfections or bypass the membrane entirely through leaks in seals. A solar-powered desalination unit produces potable water from saline water by using a photovoltaic system to supply the energy. Solar power works well for water purification in settings lacking grid electricity and can reduce operating costs and greenhouse emissions . For example,

372-430: A concentration of two and a half times, this is not a problem in service. A greater problem for scaling is the deposition of calcium sulphate . The saturation point for this compound decreases with temperature above 60 °C (140 °F), so that beginning from around 90 °C (194 °F) a hard and tenacious deposit is formed. To further control scale formation, equipment may be provided to automatically inject

465-421: A controlled phase change process. Some air conditioners and refrigerators use compressed liquids with a low boiling point that vaporizes within the system to cool it, whilst emitting the thermal energy into its surroundings. Evaporators are often used to concentrate a solution. An example is the climbing/falling film plate evaporator , which is used to make condensed milk . Similarly, reduction (cooking)

558-486: A flame, but had a primary steam circuit using main boiler steam through coils within a steam drum or evaporator . The distillate from this vessel then passed to an adjacent vessel, the distilling condenser . 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. For security against failure, ships except

651-469: A highly porous and much thicker substrate region. John Cadotte, of Filmtec corporation , discovered that membranes with particularly high flux and low salt passage could be made by interfacial polymerization of m -phenylene diamine and trimesoyl chloride. Cadotte's patent on this process was the subject of litigation and expired. Almost all commercial RO membrane is now made by this method. By 2019, approximately 16,000 desalination plants operated around

744-482: A low pressure or slight vacuum, according to design. As the evaporator works at pressure, not under vacuum, boiling may be violent. To avoid the risk of priming and a carry over of saltwater into the vapour, the evaporator is divided by a bubble cap separator. Vapour-compression distillers were installed on US submarines shortly before World War 2. Early attempts had been made with evaporators running from diesel engine exhaust heat, but these could only be used when

837-490: A lower operating cost and the ability to avoid heat-treatment, which makes it suitable for heat-sensitive substances such as protein and enzymes . RO is used in the dairy industry to produce whey protein powders and concentrate milk. The whey (liquid remaining after cheese manufacture) is concentrated with RO from 6% solids to 10–20% solids before ultrafiltration processing. The retentate can then be used to make whey powders, including whey protein isolate . Additionally,

930-434: A manual scaling hammer. This also has a risk of mechanical damage to the tubes, as the slightest pitting tends to act as a nucleus for scale or corrosion. It is also common practice to break light scaling free by thermal shock, by passing steam through the coils without cooling water present or by heating the coils, then introducing cold seawater. In 1957, the trials ship HMS  Cumberland , an obsolete heavy cruiser ,

1023-795: A membrane that is either nonporous or uses nanofiltration with pores 0.001 micrometers in size. The predominant removal mechanism is from differences in solubility or diffusivity , and the process is dependent on pressure , solute concentration, and other conditions. RO requires pressure between 2–17 bar (30–250 psi ) for fresh and brackish water, and 40–82 bar (600–1200 psi) for seawater. Seawater has around 27 bar (390 psi) natural osmotic pressure that must be overcome. Membrane pore sizes vary from 0.1 to 5,000 nm. Particle filtration removes particles of 1 μm or larger. Microfiltration removes particles of 50 nm or larger. Ultrafiltration removes particles of roughly 3 nm or larger. Nanofiltration removes particles of 1 nm or larger. RO

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1116-496: A pair of these sets. It is possible to arrange these sets of evaporators in either parallel or in series, for either maximum or most efficient production. 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). The overall output of feedwater may exceed

1209-416: A relatively large surface area. The plates are usually corrugated and are supported by the frame. During evaporation, steam flows through the channels formed by the free spaces between the plates. The steam alternately climbs and falls parallel to the concentrated liquid. The steam follows a co-current, counter-current path with the liquid. The concentrate and the vapor are fed into the separation stage, where

1302-540: A seawater feed. A level of 500 ppm is generally the upper limit for drinking water, while the US Food and Drug Administration classifies mineral water as water containing at least 250 ppm. Energy recovery can reduce energy consumption by 50% or more. Much of the input energy can be recovered from the concentrate flow, and the increasing efficiency of energy recovery devices greatly reduces energy requirements. Devices used, in order of invention, are: The desalinated water

1395-467: A solar-powered desalination unit designed passed tests in Australia's Northern Territory . Sunlight's intermittent nature makes output prediction difficult without an energy storage capability. However batteries or thermal energy storage systems can provide power when the sun does not. Larger scale reverse osmosis water purification units (ROWPU) exist for military use. These have been adopted by

1488-429: A vacuum pump to create a low pressure over a solvent while simultaneously rotating the liquid flask to increase surface area and decrease bubble size. Typically, the vapor is passed over a cold finger or coil so that the vaporized material does not damage the pump. The rotary evaporator is best used for removing solvent from solutions containing the desired product that will not vaporize at the operating pressure to separate

1581-424: 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: 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

1674-469: A waste of heated seawater. The optimum operating salinity was thus fixed at three times that of seawater, and so the brine pump had to remove at least one third of the total feedwater supply rate. These pumps resembled the steam-powered reciprocating feedwater pumps already in service. They were usually produced by the well-known makers, such as G & J Weir . Vertical and horizontal pumps were used, although horizontal pumps were favoured as they encouraged

1767-401: A weak citric acid solution into the seawater feed. The ratio is 1:1350, by weight of seawater. 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

1860-437: 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. 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. The advantage of

1953-414: Is distilled multiple times to ensure that it does not leave deposits on the machinery or cause corrosion. RO is used to clean effluent and brackish groundwater . The effluent in larger volumes (more than 500 m /day) is treated in a water treatment plant first, and then the effluent runs through RO. This hybrid process reduces treatment cost significantly and lengthens membrane life. RO can be used for

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2046-399: Is a paper by-product membrane bonded to a synthetic layer that allows contact with chlorine in the water. These require a small amount of chlorine in the water source to prevent bacteria from forming on it. The typical rejection rate for CTA membranes is 85–95%. The cellulose triacetate membrane rots unless protected by chlorinated water , while the thin-film composite membrane breaks down in

2139-420: Is a process of evaporating liquids from a solution to produce a "reduced" food product, such as wine reduction. Evaporation is the main process behind distillation , which is used to concentrate alcohol , isolate liquid chemical products, or recover solvents in chemical reactions. The fragrance and essential oil industry uses distillation to purify compounds. Each application uses specialized devices. In

2232-720: Is around 3 kWh/m (11,000 J/L), with the development of more efficient energy recovery devices and improved membrane materials. According to the International Desalination Association , for 2011, RO was used in 66% of installed desalination capacity (0.0445 of 0.0674 km /day), and nearly all new plants. Other plants use thermal distillation methods: multiple-effect distillation , and multi-stage flash . Sea-water RO (SWRO) desalination requires around 3 kWh/m , much higher than those required for other forms of water supply, including RO treatment of wastewater, at 0.1 to 1 kWh/m . Up to 50% of

2325-468: Is important for any ship. Although distillers are often associated with steam ships , their use pre-dates this. Obtaining fresh water from seawater is a theoretically simple system that, in practice, presented many difficulties. While there are numerous effective methods today, early desalination efforts had low yields and often could not produce potable water. At first, only larger warships and some exploratory ships were fitted with distilling apparatus:

2418-416: Is in the final category of membrane filtration, hyperfiltration, and removes particles larger than 0.1 nm. Around the world, household drinking water purification systems, including an RO step, are commonly used for improving water for drinking and cooking. Such systems typically include these steps: In some systems, the carbon prefilter is replaced by a cellulose triacetate (CTA) membrane. CTA

2511-409: 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. Evaporators are generally installed as a set, where two evaporators are coupled to a single distiller. For reliability, large ships will then have

2604-447: Is limited by conductivity, organics, and scaling inorganic elements such as CaSO 4 , Si, Fe and Ba. Low organic scaling can use two different technologies: spiral wound membrane, and (for high organic scaling, high conductivity and higher pressure (up to 90 bars)), disc tube modules with RO membranes can be used. Disc tube modules were redesigned for landfill leachate purification that is usually contaminated with organic material. Due to

2697-424: Is normally made under vacuum conditions to maximize ∆T while maintaining the most favorable product temperature so that the product only sees equilibrium conditions inside the evaporator and can maximize volatile stripping and recovery. Technical problems can arise during evaporation, especially when the process is used in the food industry. Some evaporators are sensitive to differences in viscosity and consistency of

2790-613: Is popular among reef aquarium keepers, and is preferred above other water purification processes due to the low cost of ownership and operating costs. Where chlorine and chloramines are found in the water, carbon filtration is needed before RO, as common residential membranes do not address these compounds. Freshwater aquarists also use RO to duplicate the soft waters found in many tropical waters. While many tropical fish can survive in treated tap water, breeding can be impossible. Many aquatic shops sell containers of RO water for this purpose. An increasingly popular method of cleaning windows

2883-485: Is sometimes used to prevent formation of mineral deposits on the surface of electrodes . Many reef aquarium keepers use RO systems to make fish-friendly seawater. Ordinary tap water can contain excessive chlorine , chloramines , copper , nitrates , nitrites , phosphates , silicates , or other chemicals detrimental to marine organisms. Contaminants such as nitrogen and phosphates can lead to unwanted algae growth. An effective combination of both RO and deionization

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2976-698: Is stabilized to protect downstream pipelines and storage, usually by adding lime or caustic soda to prevent corrosion of concrete-lined surfaces. Liming material is used to adjust pH between 6.8 and 8.1 to meet the potable water specifications, primarily for effective disinfection and for corrosion control. Remineralisation may be needed to replace minerals removed from the water by desalination, although this process has proved to be costly and inconvenient in order to meet mineral demand by humans and plants as found in typical freshwater. For instance water from Israel's national water carrier typically contains dissolved magnesium levels of 20 to 25 mg/liter, while water from

3069-449: Is susceptible to fouling (loss of production capacity). Therefore, pretreatment is a necessity for any RO or nanofiltration system. Pretreatment has four major components: The high pressure pump pushes water through the membrane. Typical pressures for brackish water range from 1.6 to 2.6 MPa (225 to 376 psi). In the case of seawater, they range from 5.5 to 8 MPa (800 to 1,180 psi). This requires substantial energy. Where energy recovery

3162-448: Is the "water-fed pole" system. Instead of washing windows with conventional detergent, they are scrubbed with purified water, typically containing less than 10 ppm dissolved solids, using a brush on the end of a pole wielded from ground level. RO is commonly used to purify the water. Treatment with RO is limited, resulting in low recoveries on high concentration (measured with electrical conductivity ) and membrane fouling. RO applicability

3255-438: Is the flash distiller. 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). Both evaporator and distiller are combined into a single chamber, although most plants use two joined chambers, worked in series. The first chamber

3348-412: Is the world's largest. The typical single-pass SWRO system consists of: Pretreatment is important when working nanofiltration membranes due to their spiral-wound design. The material is engineered to allow one-way flow. The design does not allow for backpulsing with water or air agitation to scour its surface and remove accumulated solids. Since material cannot be removed from the membrane surface, it

3441-608: Is then fed through a high-pressure piston pump into a series of RO vessels. 90.00–99.98% of the raw water's total dissolved solids are removed and military standards require that the result have no more than 1000–1500 parts per million by measure of electrical conductivity . It is then disinfected with chlorine . RO-purified rainwater collected from storm drains is used for landscape irrigation and industrial cooling in Los Angeles and other cities. In industry, RO removes minerals from boiler water at power plants . The water

3534-426: Is typically 3 bar/50 psi less than the feed pressure, and thus retains much of the input energy. The desalinated water purity is a function of the feed water salinity, membrane selection and recovery ratio. To achieve higher purity a second pass can be added which generally requires another pumping cycle. Purity expressed as total dissolved solids typically varies from 100 to 400 parts per million (ppm or mg/litre) on

3627-485: Is used in industrial processes and the production of potable water . RO retains the solute on the pressurized side of the membrane and the purified solvent passes to the other side. The relative sizes of the various molecules determines what passes through. "Selective" membranes reject large molecules, while accepting smaller molecules (such as solvent molecules, e.g., water). RO is most commonly known for its use in drinking water purification from seawater , removing

3720-414: Is used, part of the high pressure pump's work is done by the energy recovery device, reducing energy inputs. The membrane assembly consists of a pressure vessel with a membrane that allows feedwater to be pushed against it. The membrane must be strong enough to withstand the pressure. RO membranes are made in a variety of configurations. The two most common are spiral-wound and hollow-fiber . Only part of

3813-412: Is useful in concentrating solutions. The operation is very similar to that of a calandria where the liquid is boiled inside vertical tubes by applying heat to the outside of the tubes. The produced solvent vapor presses the liquid against the walls of the tubes forming a thin film that moves upwards with the vapor. The vapor may be released from the system while the liquid may be recirculated through

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3906-449: Is usually restricted to seven because, after that, the equipment cost approaches the cost savings of the energy-requirement drop. Two types of feeding can be used when dealing with multiple-effect evaporators: In recent years, multiple-effect vacuum evaporator (with heat pump ) systems have come into use. These are well known to be energetically and technically more effective than systems with mechanical vapor recompression (MVR). Due to

3999-422: Is very high and is most of the cost for an evaporation system. Putting together evaporators saves heat and thus requires less energy. Adding one evaporator to the original decreases energy consumption by 50%. Adding another effect reduces it to 33% and so on. A heat-saving-percent equation can estimate how much one will save by adding a certain number of effects. The number of effects in a multiple-effect evaporator

4092-429: Is worked at 23.5  inHg (80  kPa ) vacuum, the second at 26–27 inHg (88–91 kPa). 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

4185-489: The Ashkelon plant has no magnesium. Ashkelon water created magnesium-deficiency symptoms in crops, including tomatoes, basil, and flowers, and had to be remedied by fertilization. Israeli drinking water standards require a minimum calcium level of 20 mg/liter. Askelon's post-desalination treatment uses sulfuric acid to dissolve calcite (limestone), resulting in calcium concentrations of 40 to 46 mg/liter, lower than

4278-639: The United States armed forces and the Canadian Forces . Some models are containerized , some are trailers, and some are themselves vehicles. The water is treated with a polymer to initiate coagulation . Next, it is run through a multi-media filter where it undergoes primary treatment, removing turbidity . It is then pumped through a cartridge filter which is usually spiral-wound cotton. This process strips any particles larger than 5 μm and eliminates almost all turbidity. The clarified water

4371-594: The University of California at Los Angeles (UCLA) first investigated osmotic desalination . Researchers at both UCLA and University of Florida desalinated seawater in the mid-1950s, but the flux was too low to be commercially viable. Sidney Loeb at UCLA and Srinivasa Sourirajan at the National Research Council of Canada , Ottawa, found techniques for making asymmetric membranes characterized by an effectively thin "skin" layer supported atop

4464-467: The volatile components of a mixture from non-volatile materials. Natural circulation evaporators are based on the natural circulation of the product caused by the density differences that arise from heating ( convection ). A chamber containing a solution is heated, and the vaporized liquid is collected in a receiving flask. This type of evaporator is generally made of 4–8 m (13–26 ft) tubes enclosed by steam jackets. The uniform distribution of

4557-498: The 45 to 60 mg/liter found in typical Israeli fresh water. Post-treatment disinfection provides secondary protection against compromised membranes and downstream problems. Disinfection by means of ultraviolet (UV) lamps (sometimes called germicidal or bactericidal) may be employed to sterilize pathogens that evade the RO process. Chlorination or chloramination (chlorine and ammonia) protects against pathogens that may have lodged in

4650-583: 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. Reverse osmosis Reverse osmosis ( RO ) is a water purification process that uses a semi-permeable membrane to separate water molecules from other substances. RO applies pressure to overcome osmotic pressure that favors even distributions. RO can remove dissolved or suspended chemical species as well as biological substances (principally bacteria ), and

4743-399: The boiler, avoiding the engine and its lubricants, was led to them. With the development of steam heating jackets around the cylinders of engines such as the trunk engine , the exhaust from this source, again unlubricated, could be condensed. The first distilling plants that boiled a separate water supply from that of the main boiler, appeared around 1867. These were not directly heated by

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4836-451: 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 saturated steam this will be at a limit of 100 °C), which may then have an efficiency of 0.87 kg of feedwater produced for each kg of steam supplied. If condenser vacuum

4929-417: The build-up of brine and scale . For efficiency, as well as conserving feedwater, marine engines have usually been condensing engines . By 1865, the use of an improved surface condenser permitted the use of fresh water feed, as the additional feedwater now required was only the small amount required to make up for losses, rather than the total passed through the boiler. Despite this, fresh water makeup to

5022-815: The case of desalination of seawater or in Zero Liquid Discharge plants, the reverse purpose applies; evaporation removes the desirable drinking water from the undesired solute/product, salt. Chemical engineering uses evaporation in many processes. For example, the multiple-effect evaporator is used in Kraft pulping, the process of producing wood pulp from wood. Large ships usually carry evaporating plants to produce fresh water, reducing their reliance on shore-based supplies. Steamships must produce high-quality distillate to maintain boiler -water levels. Diesel engine ships often utilize waste heat as an energy source for producing fresh water. In this system,

5115-465: 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. Both the fresh water production and the waste brine from the evaporator are led through an output cooler. This acts as a heat exchanger with the inlet seawater, pre-heating it to improve efficiency. The plant may operate at either

5208-428: The cross-flow, it is given a flow booster pump that recirculates the flow over the membrane between 1.5 and 3 times before it is released as a concentrate. High velocity protects against membrane scaling and allows membrane cleaning. Areas that have limited surface water or groundwater may choose to desalinate . RO is an increasingly common method, because of its relatively low energy consumption. Energy consumption

5301-410: The de-aeration of feedwater. Electrically powered rotary centrifugal pumps were later adopted, as more efficient and more reliable. There were initial concerns whether these would be capable of pumping brine against the vacuum of the evaporator and so there was also a transitional type where a worm gear -driven plunger pump for brine was driven from the rotary shaft. A later form of marine evaporator

5394-406: The dilute solution. These evaporators could work inefficiently because of a loss of circulation. The pump of an evaporator may need to be changed if the evaporator needs to be used to concentrate a highly viscous solution. Fouling also occurs when hard deposits form on the surfaces of the heating mediums in the evaporators. In foods, proteins and polysaccharides can create such deposits that reduce

5487-519: The distiller flowrate must be throttled to maintain effective condensation. As these systems are more modern, they are generally fitted with an electric salinometer and some degree of automatic control. Diesel -powered motorships do not use steam boilers as part of their main propulsion system and so may not have steam supplies available to drive evaporators. Some do, as they use auxiliary boilers for non-propulsion tasks such as this. Such boilers may even be heat-recovery boilers that are heated by

5580-488: The efficiency of heat transfer. Foaming can also create a problem since dealing with excess foam can be costly in time and efficiency. Antifoam agents are used, but only a few can be used when food is being processed. Corrosion can also occur when acidic solutions such as citrus juices are concentrated. The surface damage caused can shorten the long life of evaporators. The quality and flavor of food can also suffer during evaporation. Overall, when choosing an evaporator,

5673-409: The engine exhaust. Where no adequate steam supply is available, a vapour-compression distiller is used instead. This is driven mechanically, either electrically or by its own diesel engine. 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

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5766-405: The engine-cooling water is passed through a heat exchange, where it is cooled by concentrated seawater. Because the cooling water, which is chemically treated fresh water, is at a temperature of 70–80 °C (158–176 °F), it would not be possible to flash off any water vapor unless the pressure in the heat exchanger vessel is dropped. A brine-air ejector venturi pump is then used to create

5859-406: The evaporator is adjusted as seawater temperature changes and shuts down altogether when the ship is maneuvering. An alternative in some vessels, such as naval ships and passenger ships, is the use of the reverse osmosis principle for fresh-water production instead of using evaporators. Evaporation , or vaporization , is an endothermic phase transition process that is thoroughly understood in

5952-436: The evaporator to further concentrate the solute . In many cases, the tubes of a rising film evaporator are usually between 3–10 metres (9.8–32.8 ft) in height with a diameter of between 25–50 millimetres (0.98–1.97 in). Sizing this type of evaporator requires a precise evaluation of the actual level of the liquid inside the tubes and the flow rates of the vapor and film. Climbing and falling-film plate evaporators have

6045-450: The feedwater system of a large warship under full power could still require up to 100 tons per day. Attention was also paid to de-aereating feedwater, to further reduce boiler corrosion. 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

6138-456: The field of thermodynamics . It is intimately related to the vapor pressure of the liquid and surrounding pressure, in addition to the enthalpy of vaporization. Evaporators work using the same principle design. A heat source is in contact with the liquid causing it to evaporate. The vapor is removed entirely (like in cooking), or it is stored for reuse (like in a refrigerator) or a product for isolation (essential oil). Rotary evaporators use

6231-419: 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. 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,

6324-536: The heat transfer coefficient, tube/plate material properties, flow regime, and achieved vapor quality. Advanced control techniques, such as online fouling detection, help maintain evaporator thermal performance over time. Additionally, computational fluid dynamics (CFD) modeling and advancements in surface coating technologies continue to enhance heat and mass transfer capabilities, leading to more energy-efficient vapor generation. Evaporators are essential to many industries because of their ability to separate phases through

6417-427: The increasing complexity of surface condensers demanded better feedwater quality, a pump became part of the evaporator equipment. This pump had three combined functions as a seawater feed pump, a fresh water delivery pump and a brine extraction pump, each of progressively smaller capacity. The brine salinity was an important factor in evaporator efficiency: too dense encouraged scale formation, but too little represented

6510-434: The lower boiling temperature, they can handle highly corrosive liquids or liquids which are prone to forming incrustations. Agitated thin-film evaporation has been very successful with difficult-to-handle products. Simply stated, the method quickly separates the volatile from the less volatile components using indirect heat transfer and mechanical agitation of the flowing product film under controlled conditions. The separation

6603-437: The lower portion. As they are entirely submerged, they avoid the most active region for the deposition of scale, around the waterline. Each coil consists of one or two spirals in a flat plane. Each coil is easily removed for cleaning, being fastened by individual pipe unions through the side of the evaporator. A large door is also provided, allowing the coils to be removed or replaced. Cleaning may be carried out mechanically, with

6696-423: The mechanism of fluid flow is reversed, as the solvent crosses membrane, leaving the solute behind. The predominant removal mechanism in membrane filtration is straining, or size exclusion, where the pores are 0.01 micrometers or larger, so the process can theoretically achieve perfect efficiency regardless of parameters such as the solution's pressure and concentration. RO instead involves solvent diffusion across

6789-519: The permeate, which contains lactose , is concentrated by RO from 5% solids to 18–total solids to reduce crystallization and drying costs. Although RO was once avoided in the wine industry, it is now widespread. An estimated 60 RO machines were in use in Bordeaux , France, in 2002. Known users include many of elite firms, such as Château Léoville-Las Cases . In 1946, some maple syrup producers started using RO to remove water from sap before boiling

6882-789: The presence of chlorine. The thin-film composite (TFC) membrane is made of synthetic material, and requires the chlorine to be removed before the water enters the membrane. To protect the TFC membrane elements from chlorine damage, carbon filters are used as pre-treatment. TFC membranes have a higher rejection rate of 95–98% and a longer life than CTA membranes. To work effectively, the water feeding to these units should be under pressure (typically 280 kPa (40 psi) or greater). Though Portable RO Water Purifiers are commercially available and extensively used in areas lacking cleaning potable water, in Europe such processing of natural mineral water (as defined by

6975-455: 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. The first water supply by distillation of boiler steam appeared on early paddle steamers and used a simple iron box in the paddle boxes, cooled by water splash. A steam supply direct from

7068-422: The production of deionized water . In 2002, Singapore announced that a process named NEWater would be a significant part of its water plans. RO would be used to treat wastewater before discharging the effluent into reservoirs. Reverse osmosis is a more economical way to concentrate liquids (such as fruit juices) than conventional heat-treatment. Concentration of orange and tomato juice has advantages including

7161-420: The qualities of the product solution must be taken into careful consideration. Evaporator (marine) An evaporator , distiller or distilling apparatus is a piece of ship's equipment used to produce fresh drinking water from sea water by distillation . As fresh water is bulky, may spoil in storage, and is an essential supply for any long voyage, the ability to produce more fresh water in mid-ocean

7254-475: The salt and other effluent materials from the water molecules. As of 2013 the world's largest RO desalination plant was in Sorek, Israel , outputting 624 thousand cubic metres per day (165 million US gallons per day). A process of osmosis through semi-permeable membranes was first observed in 1748 by Jean-Antoine Nollet . For the following 200 years, osmosis was only a laboratory phenomenon. In 1950,

7347-492: The sap to syrup . RO allows about 75–90% of the water to be removed, reducing energy consumption and exposure of the syrup to high temperatures. When beer at typical concentration is subjected to reverse osmosis, both water and alcohol pass across the membrane more readily than other components, leaving a "beer concentrate". The concentrate is then diluted with fresh water to restore the non-volatile components to their original intensity. For small-scale hydrogen production , RO

7440-564: The seawater input can be recovered as fresh water, though lower recovery rates may reduce membrane fouling and energy consumption. Brackish water reverse osmosis (BWRO) is the desalination of water with less salt than seawater, usually from river estuaries or saline wells. The process is substantially the same as SWRO, but requires lower pressures and less energy. Up to 80% of the feed water input can be recovered as fresh water, depending on feed salinity. The Ashkelon desalination plant in Israel

7533-431: The smallest were fitted with two sets. 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. On modern diesel-powered ships, this vacuum can instead be produced by an ejector , usually worked by the output from the brine pump. Working under vacuum also reduces

7626-431: The solution is important when using this type of evaporator. The solution enters the evaporator and gains velocity as it flows downward. This gain in velocity is attributed to the vapor being evolved against the heating medium, which also flows downward. This evaporator is usually applied to highly viscous solutions, so it is frequently used in the chemical, sugar, food, and fermentation industries. This type of evaporator

7719-446: The storage tanks if the salt content exceeds the alarm limit. Sterilization is carried out after the evaporator. Evaporators are usually of the shell-and-tube type (known as an Atlas Plant) or of the plate type (such as the type designed by Alfa Laval ). Temperature, production and vacuum are controlled by regulating the system valves. Seawater temperature can interfere with production, as can fluctuations in engine load. For this reason,

7812-412: 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 etc. and also for replenishing the diesel engine cooling system. A further 500 gallons per week

7905-411: The system in which the difference in solvent concentration between the sides of a membrane is reduced. This is called osmotic pressure. It reduces as the solvent moves into the more concentrated solution. Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications. RO differs from filtration in that

7998-525: The temperature required to boil seawater and thus permits evaporators to be used with lower-temperature waste heat from the diesel cooling system. One of the greatest operational problems with an evaporator is the build-up of scale . Its design is tailored to reduce this, and to make its cleaning as effective as possible. The usual design, as developed by Weir and the Admiralty , is for a vertical cylindrical drum, heated by steam-carrying drowned coils in

8091-521: The vapor is sent to a condenser. This type of plate evaporator is frequently applied in the dairy and fermentation industries since they have spatial flexibility. A negative point of this type of evaporator is its limited ability to treat viscous or solid-containing products. There are other types of plate evaporators that work with only climbing film. Unlike single-stage evaporators, these evaporators can be composed of up to seven evaporator stages (effects). The energy consumption for single-effect evaporators

8184-424: The water pumped onto the membrane passes through. The left-behind "concentrate" passes along the saline side of the membrane and flushes away the salt and other remnants. The percentage of desalinated water is the "recovery ratio". This varies with salinity and system design parameters: typically 20% for small seawater systems, 40% – 50% for larger seawater systems, and 80% – 85% for brackish water. The concentrate flow

8277-427: The weight of steam first supplied, as up to 160% of it. Capacity is however reduced, to 72% of the maximum. 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. Early evaporators were simply mounted high-up and dumped their brine by gravity. As

8370-460: The world's largest low-pressure RO plant, producing 56.8 million liters (15 million US gal) per day (MGD). In (forward) osmosis , the solvent moves from an area of low solute concentration (high water potential ), through a membrane, to an area of high solute concentration (low water potential). The driving force for the movement of the solvent is the reduction in the Gibbs free energy of

8463-468: The world, producing around 95 million cubic metres per day (25 billion US gallons per day). Around half of this capacity was in the Middle East and North Africa region. In 1977 Cape Coral , Florida became the first US municipality to use RO at scale, with an initial operating capacity of 11.35 million liters (3 million US gal) per day. By 1985, rapid growth led the city to operate

8556-471: Was required for the batteries. 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. 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

8649-405: Was used for the first tests of the 'flexing element' distiller, where non-rigid heating coils flexed continually in service and so broke the scale free as soon as it formed a stiff layer. Despite the obvious salinity of seawater, salt is not a problem for deposition until it reaches the saturation concentration . As this is around seven times that of seawater and evaporators are only operated to

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