Reverse osmosis capacity

Figure 4.1 shows that the rate of growth in reverse osmosis capacity was slow between 1970 and 1973. From 1974 through 1980, there was an accelerated rate of growth during which time the reverse osmosis capacity increased from 62,500,000 GPD to 412,500,000 GPD or an increase of 560% in the 7-year period. Between 1981 and 1984 (4 years), the total operating capacity increased from 412,500,000 to 524,000,000 GPD, an increase of 27%. 

Co-location is not be suitable for all desalination plants. This process only becomes feasible if the volume of cooling water discharged from the power plant is at least three to four times greater than the capacity of the desalination plant (Voutchkov 2004). Furthermore, corrosion from power plant heat exchangers may elevate the levels of metal in the feed to the desalination plant, which may then damage the reverse osmosis membrane units (Voutchkov 2004). 

All commercial types of processes, with the exception of freezing, namely, distillation, reverse osmosis and electrodialysis, are being applied in the above units with various kinds of distillation processes being used for seawater desalting. Two of them, horizontal tube multieffect distillation and vapor compression units were developed and manufactured locally by the Israel Desalination Engineering Ltd. Recently, two small RO units with a combined capacity of approx. 100 cu. m/day were also used to desalt seawater. The main aim of these units is to test and demonstrate the feasibility of this new technology. 

Srinivasan and Tien (18) have made an analytical study on the mass-transfer characteristics of reverse osmosis in curved tubular membranes. The increase in mass-transfer due to secondary flow resulted in a substantial reduction in the wall concentration (the polarization modulus) for Np =100 and a/R=0.01 (see Figure 39). Further, the production capacity (permeation rate) was markedly increased (see Figure 40). 

Fig. 8. Portion of reverse osmosis (ROl desalination plant in a Singapore power station. Capacity is 2.IXX) lons/day. (Toyobn Co., Lot., Osaka. Japan)...

Currently, approximately one billion gal/day of water are desalted by reverse osmosis. Half of this capacity is installed in the United States, Europe, and Japan, principally to produce ultrapure industrial water. The remainder is installed in the Middle East and other desert regions to produce municipal drinking water from brackish groundwater or seawater. In recent years, the interfacial composite membrane has displaced the anisotropic cellulose acetate membrane in most applications. Interfacial composite membranes are supplied in spiral-wound module form the market share of hollow fiber membranes is now less than... 

Table 5.3 Operating costs for large brackish water and seawater reverse osmosis plants [49]. Capital costs are approximately US 1.25 per gal/day capacity for the brackish water plant and US 4-5 per gal/day capacity for the seawater plant...

The operating pressure of brackish water reverse osmosis systems has gradually fallen over the past 20 years as the permeability and rejections of membranes have steadily improved. The first plants operated at pressures of 800 psi, but typical brackish water plants now operate at pressures in the 200- to 300-psi range. Capital costs of brackish water plants have stayed remarkably constant for almost 20 years the rule of thumb of US 1.00 per gal/day capacity is still true. Accounting for inflation, this reflects a very large reduction in real costs resulting from the better performance of today s membranes. 

The main methods used in desalination units are reverse osmosis and multi-effect distillation. The energy consumption of a desalination plant using the technology of reverse osmosis depends on its size, the contents of sea water and the desired quality of the produced water and usually ranges between 5-7 kWh/m3 when sea water is used. When well water in coastal regions is used for desalination the energy consumption is less than half of the above. The nominal capacity of small-size desalination units for rural housings is of the order of 400 W. 

FPG-type deep cartridge filtering elements of 20 pm and 5 pm filtering capacity are used in microfilters. Element ERU-100-1016 (filtering capacity 10 nm) at a pressure < 0.3 MPa is used in ultrafilters in reverse-osmosis filters element ERO-KM-100-1016 (selectivity for NaCl 95-99%) at a pressure <7.0 MPa is used. Ion-exchange filters are... 

Electrodialysis is a well-proven technology with a multitude of systems operating worldwide. In Europe and Japan, electrodialysis dominates as a desalting process with total plant capacity exceeding that of reverse osmosis and distillation [3]. Electrodialysis with monopolar membranes is applied to different food systems, to demineralization of whey [5-8], organic acids [9], and sugar [10,11], separation of amino acids [12] and blood treatments [13], wine stabilization [14—16], fruit juice deacidification [17-19], and separation of proteins [20-22]. These applications use the sole property of dilution-concentration of monopolar lEMs in a stack of as many as 300 in an electrodialysis cell. 

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