Seawater potable water from

Seawater Evaporators The production of potable water from saline waters represents a large and growing field of application for evaporators. Extensive work done in this field to 1972 was summarized in the annual Saline Water Conversion Repoi ts of the Office of Sahne Water, U.S. Department of the Interior. Steam economies on the order of 10 kg evaporation/kg steam are usually justified because (1) unit production capacities are high, (2) fixed charges are low on capital used for pubhc works (i.e., they use long amortization periods and have low interest rates, with no other return on investment considered), (3) heat-transfer performance is comparable with that of pure water, and (4) properly treated seawater causes httle deterioration due to scahng or fouhng. 

Leading Examples Electrodialysis has its greatest use in removing salts from brackish water, where feed salinity is around 0.05-0.5 percent. For producing high-purity water, ED can economically reduce solute levels to extremely low levels as a hybrid process in combination with an ion-exchange bed. ED is not economical for the produc tion of potable water from seawater. Paradoxically, it is also used for the concentration of seawater from 3.5 to 20 percent salt. The concentration of monovalent ions and selective removal of divalent ions from seawater uses special membranes. This process is unique to Japan, where by law it is used to produce essentially all of its domestic table salt. ED is very widely used for deashing whey, where the desalted product is a useful food additive, especially for baby food. 

In summary, the FT-30 membrane is a significant improvement in the art of thin-film-composite membranes, offering major improvements in flux, pH resistance, and chlorine resistance. Salt rejections consistent with single-pass production of potable water from seawater can be obtained and held under a wide variety of operating conditions (ph, temperature, pressure, and brine concentration). This membrane comes close to being the ideal membrane for seawater desalination in terms of productivity, chemical stability, and nonbiodegradability. 

Reverse osmosis membranes can be divided into subclasses according to their solute/water selectivity and operating pressure regimes. Figure 30 shows a number of commercial membranes developed for seawater and brackish desalination, and for nanofiltration. These include cellulose ester and polyamide asymmetric membranes available since the 1960s, and high-performance composite membranes developed in the 1970s. Collectively, they make it possible to produce potable water from virtually all saline water sources. 

Desalination — is a process to produce clean (potable) water from brackish or seawater. This is done mainly by... 

Currently another process for the production of potable water from seawater is becoming established reverse osmosis (RO). The RO-process is particularly suitable for small plants. Therefore almost 70% of all plants operate according this principle, but they account for only 35% of the desalination capacity. In osmosis, water permeates... 

Production of potable water from brackish water or seawater by reverse osmosis ... 

Membrane research and development started in Du Pont in 1962 and culminated in the introduction of the first B-9 Permasep permeator for desalination of brackish water by reverse osmosis (RO) in 1969. The membrane in this B-9 Permasep module consisted of aramid hollow fibers. In 1969, proponents of RO technology had ambitious dreams and hopes. Today, RO is a major desalination process used worldwide to provide potable water from brackish and seawater feeds. Du Font s membrane modules for RO are sold under the trademark Permasep permeators. The RO business is a virtually autonomous profit center that resides in the Polymer Products Department. The growth and success of the Permasep products business is a direct result of Du Font s sustained research and development commitment to polyamides, a commitment that dates back to the 1930 s and the classic polymer researches of Wallace H. Carothers. Since 1969, improved and new Permasep permeators have been introduced six times, as shown in Table I. 

In a parametric study on seawater RO, Soo-Hooel al.5 estimated the capital cost for a stand-alone seawater RO plant to produce 400 kL/dey of potable water from seawater to be [,100,000 (1981). Energy requirements were halwean 9 W- h/L for a high-pressure plant with no energy recovery, and 3 W h/L for a lower pressure plant with energy recovery. Membrane replacement costs were approximately 40,000/year. 

Normally, in evaporation the thick liquor is the valuable product and the vapor is condensed and discarded. In one specific situation, however, the reverse is true. Mineral-bearing water often is evaporated to give a solid-free product for boiler feed, for special process requirements, or for human consumption. This technique is often called water distillation, but technically it is evaporation. Large-scale evaporation processes have been developed and used for recovering potable water from seawater. Here the condensed water is the desired product. Only a fraction of the total water in the feed is recovered, and the remainder is returned to the sea. 

General quality improvement of present supplies Upgrade total municipal supply Potable water from degraded supplies Brackish water desalination Seawater desalination... 

Seawater Evaporators The production of potable water from... 

A list of RO apphcations is given in Table 1.9. Several case studies are discussed in Chapter 3. RO plays a major role in providing potable water, defined as <1000 mg/1 total dissolved solids (TDS) by the W.H.O. or <500 mg/1 TDS based on U.S. EPA criterion. Desalination of seawater (50—100 bar g 35,000 mg/1 TDS) and brackish water (15-25 bar g 1000—10,000 ppm TDS) are the largest applications of RO. The highest rejection RO membranes are those that can make potable water from seawater using multi-staged, single-pass RO units. 

In Section 9.1, Figure 9.1, we have seen that adjacent to a charged surface there is an excess of counterions and a deficit of co-ions. Both contribute to the neutralization of the surface charge. Let us now focus on the expulsion of the co-ions. The expulsion of co-ions implies a reduced volume available for electrolyte, or, in other words, there is an excluded volume with respect to the presence of electrolyte. This is known as the Donnan effect. For the same reason salt (= electrolyte) cannot penetrate in narrow capillaries and pores having charged walls. Based on this phenomenon, porous membranes that are permeable for water but not for salt may be used in reversed osmosis (also called ultrafiltration). Practical applications of reversed osmosis are found in, for example, the production of potable water from seawater, in hemodialysis using artificial kidneys, and in the concentration of solutions such as fruit juices. 

Reverse osmosis (RO) desalination technology has become established over a number of yeat for producing potable water from various natirral waters, including seawater. While some RO systems utihze nonmetaUic construction materials for the pressirre vessels to contain the membrane Ccinridges, metallic materials are desired where higher pressirres and/or enhauiced fire resistance are required. 

The desalination plant to produce potable water from seawater feedstock (assumed at 25°C) is a feed forward Multi-Effect-Distillation (MED) design, which is driven by the heat recovered in cooling the SC-CO2 from 100°C down to the SC-CO2 critical temperature of 31°C. The brine from the desalination plant is rejected at 35°C. 

Today polymeric membranes are widely used to produce potable water from seawater, treat industrial effluents, for controlled drug delivery systems, separate common gases, pesticide release systems, and in prosthetic devices for humans, among others (76). Most of these methods require the separation of two or more components. Membrane-based separation processes are environmentally green, economic, and frequently more efficient than conventional methods. 

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