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A B C D E F G H I J K L M N O P Q R S
Saddle supports, for heat exchangers, Safety factors, Safety, of heat exchangers: Salicyl aldehyde: Salts, heat transfer, as heat transfer media, Sand roughness, equivalent, Santotherm, heat transfer media, Sastri and Rao correlation for surface tension, Saturated boiling: Saturated density: Saturated fluids, tables of physical properties, Saturation pressure, Saturation temperature, Saunders, E A D Sauer, H J Jr, Scale formation in heat exchangers, Scaling approximations, in nonisothermal gas radiation, Scattering bed models, for radiative heat transfer from surfaces, Scattering, interaction phenomena with, Scattering coefficient, Schack wide-band model, for gas radiation properties, Schick and Prausnitz method, for critical volume of mixtures, Schlunder, E U Schmidt, F W Schmidt correlation, for heat transfer in in-line banks of high fin tubes, Schmidt number, Schneider, G E, Schrock and Grossman correlations, for forced convective heat transfer in two-phase flow, Schunk, M Schwier, K, Scraped surfaces: Scaling devices, in shell-and-tube heat exchangers, Seawater physical properties, Seider-Tate equation, for heat transfer in heat exchangers, Selection of heat transfer equipment: Semiconductors, thermal conductivity, Separated flow model: Separation, exergy analysis for, Separators, for use in association with evaporators, Series solutions, for one-dimensional transient conduction, Serrated fins, in plate fin heat exchangers, Shah correlation for boiling, Shah correlation, for boiling in horizontal tubes, Shape factor, in radiative heat transfer between diffuse surfaces, Shear flow, of non-Newtonian fluids, Shear free flow, of non-Newtonian fluids, Shear rate, in fluid, Shear stress: Sheffield, J W, Shelf dryer, Shell-and-tube heat exchanger: Shell-to-baffle clearance, in shell-and-tube heat exchangers, Shells, for shell-and-tube heat exchangers: Sherwood number Shipes, K V, Short-tube vertical evaporator, Sigma phase embrittlement, of stainless steels, Silicate scales, in heat exchangers, Silicone oils, as heat transfer media, physical properties of, Silver method, for calculation of multicomponent condensation, Similarity theory, Simonis, V, Single-phase fluid flow: Single stage flash evaporation (SSF): Singularities, two-phase gas-liquid pressure drop across, Sink, in radiation: Skid-mounted units, specification of, Skin friction coefficient, Skrinska, A, Slab: Sleeves, internal, for expansion bellows, Slot: Slug flow: Slugging, in fluidized beds, Smith, A A, Smith, R, Smith, R A Smith, O, Snell's law, in radiation, Software, for code design, Solar absorber, Solar reflector, Soldered fins, in double pipe exchangers, Solid fuels, properties of, Solids circulation, in fluidized beds, Solid-gas flow: Solid-liquid flow: Solidification: Solids: Solids circulation, in fluidized beds, Soot blowing, Sound velocity: Source, in radiation: Spacers, in shell-and-tube heat exchangers, Spalding, D B, Sparging: Specific enthalpy, Specific entropy: Specific heat capacity, Specific internal energy, Specific volume: Specification of heat exchangers, Spectral absorptivity: Spectral emissivity, in gases, Specular surface, Specular-walled passages, radiative heat transfer in, Spheres: Spherical coordinates, for finite difference equations for conduction, Spherical shells: Spheroids (oblate and prolate), free convective heat transfer from, Spine fins: Spiral heat exchanger: Spirally fluted tubes: Sponge rubber balls, in fouling mitigation, Spray dryers, Sprays, in heat exchangers, Square ducts: Stable equilibrium, of vapor and liquid, Staggered tube banks: Stainless steels, Stanton number Startup: State diagram, for fluidized beds, Static mixers, in heat exchangers, Statically stable foams, Steam, dropwise condensation of, Steam tables, Steam turbine exhaust condensers, Steels, as material of construction, Stefan-Boltzmann constant, Stefan's law, for blackbody radiation, Stegmaier, W, Steiner and Taborek correlation, for forced convective boiling, Stephan and Korner correlation, for boiling of binary mixtures, Stiffeners, PD5500 code guidelines for, Stiffeners, against external pressure, EN13445 guidance on, Stirred beds, heat transfer to, Stirred reactor model, for furnaces, Stone's strongly implicit method, Straight fins (longitudinal fins): Stratified gas-liquid flow: Stratified liquid-liquid-gas flow: Steam analysis methods, for shell-side heat transfer and pressure drop in shell-and-tube heat exchangers, Stress, compressive, in heat exchanger tubes, Stress corrosion cracking, of stainless steels, Stress equation models, for turbulent boundary layers, Stress-strain curve, for solids, Stress tensor: Stresses: Strip baffles, in tube bundles with longitudinal flow, Strouhal number, Subchannel analysis, for critical heat flux in rod bundles, Subcooled boiling: Subcooling: Sublayer, viscous, Submerged combustion, Successive over-under relaxation method for solution of implicit equations, Suction: Suction line exchangers in refrigeration, Sulfur: Sulfur compounds (organic): Sulfur dioxide: Sulfur hexafluoride: Sulfur trioxide: Supercritical fluids: Superficial velocity, in multiphase flow, Superheated gases: Superheated liquid, in metastable state, Superheated vapor, condensation of, on vertical surface, Supersaturation, as cause of fogging in condensers: Suppression of nucleate boiling, Surface catalysis, in augmentation of heat transfer, Surface condensers, Surface finish: Surface, hydraulically smooth, Surface material, effect on fouling, Surface models, in radiative heat transfer, Surface modification for drag reduction, Surface temperature, effect on fouling, Surface tension: Surfactants, in drag reduction, Suspension, radiation interaction phenomena in, Sutherland formula, for viscosity variation with temperature, Sutterby fluid (non-Newtonian), free convective heat transfer to, Swirling flow, in augmentation of heat transfer, Synthetic heat transfer media, Synthetic mixture heat transfer media,
T U V W X Y Z

Flash Desalination Processes

DOI 10.1615/hedhme.a.000384

3.22 FLASH EVAPORATION
3.22.2 Flash desalination processes

On an industrial scale the flash desalination process has a multistage configuration for flash evaporation. The main elements of the process include the brine heater and the flashing stages. Other process units include the feed intake, brine disposal lines, deaerator, chemical dosing, pumping station, vacuum ejectors, and the control room. The most common industrial process is the multistage flashing process with brine circulation (MSF). On the other hand, the once through multistage flashing process (MSF-OT) is found on a very limited scale. Also, it should be noted that the single stage flashing system (SSF) combined with a brine heater is not used on industrial scale because of its low performance. However, discussion of the SSF process and development of a mathematical model for it are necessary to have better understanding of the more complex processes found in the multistage flashing systems.

The most characteristic feature of the flash desalination process is that vapor formation takes place within the liquid bulk instead of the surface of hot tubes. The hot brine is allowed to flow freely and flash in a series of chambers; this feature keeps the hot and concentrated brine from the inside or outside surfaces of heating tubes. This is a major advantage over the original and simple concept of thermal evaporation, where submerged tubes of heating steam are used to perform fresh water evaporation. The performance of submerged tubes was far from satisfactory, where salt scale is formed progressively on the outside surface of the tubes. The formed scale has a low thermal conductivity and acts as an insulating layer between the heating steam and the boiling seawater. Consequently, the evaporation rate is drastically reduced and cleaning becomes essential to restore the process efficiency.

Earlier designs of the flash desalination process were developed on commercial scale in the early 1950’s. Silver (1970) modified these earlier designs and devised the MSF process, where the number of flashing stages was much larger than the thermal performance ratio. The development optimized the system heat transfer area and the number of flashing stages. Since the establishment of the process in the late fifties, a huge amount of field experience has been accumulating in process technology, system design, construction practice, operation, and maintenance. Developments addressed several operational problems that include scale formation, foaming, fouling, and corrosion. The experience gained has led to use of inexpensive construction material capable of withstanding the harsh conditions at high seawater salinity. The MSF system does not include moving parts, other than conventional pumps. Construction of the MSF plants is simple and contains a small number of connections, which limits leakage problems and simplifies maintenance work. It is believed that the MSF system has remained the optimum choice for large capacity plants for desalination of seawater for the following reasons:

  • The conservative nature of the desalination owner.

  • The product is a strategic life-supporting element.

  • Extensive experience in construction and operation.

  • Process reliability.

  • Limited experience, small database, and unknown risks with new technologies.

Since inception, several developments have been achieved in system design and operation. These developments include the following:

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