Desalination ratio

Feed solution used in all experiments contained sodium chloride at a concentration level of 5,000 ppm. Membrane salt rejection is evaluated from conductance measurements of product water and expressed as percent rejection, %R, or desalination ratio, D. . These units are defined by the following equations in which Cp and Cf are sodium chloride concentrations in feed and product respectively. Note that D. is very sensitive to concentration changes and expands rapidly as 100% rejection is approached. 

In the above definitions, C,yis the moiar concentration of i in the initial uniform mixture. For the desalination ratio, i is usually 2, corresponding to salt, which concentrates in region 2, whereas water concentrates in region 1 (ice in example II, Figure 1.1.2 purified water in example I, Figure 1.1.3). For the decontamination factor used with radioactive or surfactant impurities in solvents (or particles in air filtration), i is the impurity and j is the region for the purified solvent. These definitions need not be restricted to salt or a radioactive or surfactant impurity. They are... 

If x,i 7 x,2 and both are different from Xyt the single-entry separator has achieved some separation. How much separation has been attained can be estimated by suitable descriptors, indices of separation. The simplest of these indices bear the name of specific separation processes where they are extensively used the desalination ratio Dr the solute rejection R and the decontamination factor Df. 

Example 8.1.21 Determine the extent of desalination achieved in terms of the desalination ratio in an ED stack in which the diluate chamber liquid velodly is 10 cm/s, the diluate chamber cell thickness is 0.1 cm, tjjp = 0.9, the membrane length along the diluate flow path is 250 cm and (i/Mdii) has the value of lOOOmilliamp-liter/cm -gm-equiv. The feed brine concentration is 3000 ppm. 

Fig. 4. The 341,000-m /d multistage flash (MSF) evaporation desalination plant A1 Taweelah B in Abu Dhabi, United Arab Emirates. Courtesy of Italimpianti SpA. It is a dual-purpose plant, composed of six identical power and desalination units. The desalination units at 56,800 m /d each are currently (1997) the largest ia the world. They have 17 recovery and 3 reject stages and a Performance Ratio of 8 1. The plant also produces 732 MWe of...

The performance ratio of ME plants is just slightly lower than the number of effects, which is deterrnined as an optimized compromise between energy efficiency and capital cost. Six effects ate typical, although plants with as many as 18 effects have been built. Eurther detail about ME desalination can be found in (56,59). 

The pressure to be used for reverse osmosis depends on the salinity of the feedwater, the type of membrane, and the desired product purity. It ranges from about 1.5 MPa for low feed concentrations or high flux membranes, through 2.5—4 MPa for brackish waters, and to 6—8.4 MPa for seawater desalination. In desalination of brackish or sea water, typical product water fluxes through spiral-wound membranes are about 600—800 kg/m /d at a recovery ratio RR of 15% and an average salt rejection of 99.5%, where... 

The fluxes in hoUow-fiber membranes used in seawater desalination are 20—30-fold smaller, but the overall RO system size does not increase because the hoUow-fiber membranes have a much larger surface area per module unit volume. In use with seawater, their RR is about 12—17.5% and the salt rejection ratio is up to 99.5%. 

Long term experiments of one pass seawater desalination using our module have been carried out at Chigasaki Laboratory of Water Reuse Promotion Center under the supervision of Ministry of International Trade and Industry, Japan (4). A continuous long term test for 12,000 hours was successfully conducted with the m-value of 0.02. Another demonstration plant with an 800 m3/D capacity has also been operating over 3,000 hours at the recovery ratio of using the feed water of F.I. value of about 4. 

Module performance and energy consumption were estimated in the case for the desalination of U.2% salinity seawater under high pressure of 75 Kg/cm2c at different recovery ratios. The results are shown in Table 4. 

In summary, the NS-300 membrane system actually comprises a family of membranes, with reverse osmosis properties determined by the isophthallc trimesic ratio. Exceptionally high fluxes are possible at high retentivity levels for dissolved salts containing polyvalent anions. This membrane type may find applications in the desalination of brackish sulfate ground waters or industrial... 

A schematic of a batch parametric pumped adsorption process is sketched in Figure 15.22(a), and Figure 15.22(b) shows the synchronized temperature levels and flow directions. At the start, the interstices of the bed and the lower reservoir are filled with liquid of the initial composition and with the same amount in both. The upper reservoir is empty. The bed is kept cold while the liquid is displaced from the interstices into the upper reservoir by liquid pumped from the lower reservoir. Then the temperature of the bed is raised and liquid is pumped down through the bed. Adsorption occurs from the cold liquid and desorption from the hot liquid. For the system of Figure 15.22(c), the separation factor is defined as the ratio of concentrations of the aromatic component in the upper and lower reservoirs very substantial values were obtained in this case. Data of partial desalination of a solution with an ion exchange resin are in Figure 15.22(d), but here the maximum separation ratio is only about 10. 

Clearly, the absolute amount and ratio of restricted water to bulk-like water will depend inversely on the pore-size of the porous glass desalination membrane (see column 6, Table I). By normalizing the samples, an average thickness of an annulus of the first adsorbed layer, t (in angstroms can be estimated by t = Vn, X lOVS 0CJ water Table I t (sample 2) = 0.024x10 /... 

N NaCl has been used. Conversely, for brackish water desalination a 0.1 N NaCl/membrane/0.2 N NaCl may be used. The membrane potential is measured using a potentiometer or high impedance voltmeter (more than 2 MQ). In general, the membrane potential is high when the ratio of the concentration of the concentrated side solution to that of the dilute side solution is high and becomes low when salt solutions of high concentration are used. Transport numbers are calculated by Eq. (4.1) when a 1 1 valence electrolyte solution is used and the potentials between the probe electrodes and their ambient solutions are subtracted ... 

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