Spiral wound membrane modules membranes

Low polarity plasticizers, 74 479 Low power package, 74 863 Low pressure catalytic processes, 20 151 Low pressure chemical vapor deposition (LPCVD), 5 807, 811-812 Low-pressure gas separation, spiral-wound membrane modules for, 75 823-824 Low pressure hollow-fiber membranes, 76 24-26... 

Figure 19.4. The spiral wound membrane module for reverse osmosis, (a) Cutaway view of a spiral wound membrane permeator, consisting of two membranes sealed at the edges and enclosing a porous structure that serves as a passage for the permeate flow, and with mesh spacers outside each membrane for passage of feed solution, then wound into a spiral. A spiral 4 in. dia by 3 ft long has about 60 sqft of membrane surface, (b) Detail, showing particularly the sealing of the permeate flow channel, (c) Thickness of membranes and depths of channels for flows of permeate and feed solutions.

Four to six spiral-wound membrane modules are normally connected in series inside a single pressure vessel (tube). A typical 8-in.-diameter tube containing six modules has 100-200 m2 of membrane area. An exploded view of a membrane tube containing two modules is shown in Figure 3.44 [115]. The end of each module is fitted with an anti-telescoping device (ATD) which is designed to... 

Figure 4.9 Derivation of the mass transfer coefficient by Wilson s method. Toluene/water enrichments are plotted as a function of feed solution superficial velocity in pervaporation experiments. Enrichments were measured at different feed solution superficial velocities with spiral-wound membrane modules [15]...

Table 4.1 Representative values of the concentration polarization modulus calculated for a variety of liquid separation processes. For these calculations a boundary layer thickness of 20 im, typical of that in most spiral-wound membrane modules, is assumed...

The industry is extremely competitive, with the manufacturers producing similar products and competing mostly on price. Many incremental improvements have been made to membrane and module performance over the past 20 years, resulting in steadily decreasing water desalination costs in inflation-adjusted dollars. Some performance values taken from a paper by Furukawa are shown in Table 5.5. Since 1980, just after the introduction of the first interfacial composite membranes, the cost of spiral-wound membrane modules on a per square meter basis has decreased seven-fold. At the same time the water flux has doubled, and the salt permeability has decreased seven-fold. Taking these improvements into account, today s membranes are almost 100 times better than those of the 1980s. This type of incremental improvement is likely to continue for some time. 

The UF pretreatment (spiral-wound membrane module with a molecular weight cutoff of 50-100 kDa) allows a reduction of suspended solids (84%) and fat substances (71%) [23]. 

First multi-leaf spiral wound membrane module developed by Don Bray and others at Gulf General Atomic, under US Patent no. 3,417,870, "Reverse Osmosis Purification Apparatus," December, 1968. A multi-leaf spiral configuration improves the flow characteristics of the RO module by minimizing the pressure drop encountered by permeate as it spirals into the central collection tube. 

Recovery (sometime referred to as "conversion") is a term used to describe what volume percentage of influent water is "recovered" as permeate. Generally, RO system recoveries range from about 50% to 85%, with the majority of systems designed for 75% recovery. (Individual spiral wound membrane module recoveries vary from about 10% to 15%—see Chapter 4.3). A system recovery of 75% means that for every 100 gpm influent, 75 gpm will become permeate and 25 gpm will be retained as concentrate. 

Spiral wound membrane modules are the most common type of module used for RO today. The major advantage of a spiral wound module is that the packing density is fairly high, about 150 - 380 ft2/ft3,... 

Figure 4.14 Eight-inch diameter spiral wound membrane module. Courtesy of Dow Water and Process Solutions.

Focusing on spiral wound membrane modules as the most common type of membrane modules used in industry today, an RO array or "skid" or "train" consists of a number of pressure vessels arranged in specific patterns. Figure 5.1 shows an array of 3 pressure vessels. The pressure vessels are arranged into 2 sets, with 2 pressure vessels in parallel followed by 1 single pressure vessel. The 2 sets of pressure vessels are in series. Each set of pressure vessels in parallel (even if there is only 1 vessel) is called a STAGE. 

FIGURE 4.20 A spiral wound membrane module. (From Mulder M., Basic Principles of Membrane Technology. 2nd ed. Dordrecht, Kluwer Academic Publishers, 1996. With permission.)... 

Schwinge J., Wiley D.E., and Fletcher D.F., A CFD study of unsteady flow in narrow spacer-filled channels for spiral-wound membrane modules. Desalination 146 2002 195-201. 

Pilot-scale NF experiments were carried out with intermittent feed dilution using spirally wound membrane modules to extract at least 98% of NaSCN free of most impurities. Among the membrane types tested, PERMA-250 gave optimum results and was chosen for detailed studies. Pilot-plant data were consolidated and fed into a simulation software developed in Microsoft Excel to provide design of a commercial NF plant capable of handling 8 m /day of 10% NaSCN feed solution containing 2% % impurities. 

Figure 7 Detail of spiral wound membrane module. Reproduced with the permission of the American Institute of Chemical Engineers. 1982 AlChE. All rights reserved.

FIGURE 7.21 A spiral-wound membrane module. (From Mulder,... 

Net-type spacer Widely used in spiral wound membrane modules... 

The unexpected results of Sablani et al. [17] (i.e., less turbulence with smaller spacer thickness) may be best explained by an excellent paper by Schwinge et al. [82], The latter employed computational fluid dynamics (CFD) in a study of unsteady flow in narrow spacer-filled channels for spiral-wound membrane modules. The flow patterns were visualized for different filament configurations incorporating variations in mesh length and filament diameter and for channel Reynolds numbers, Re y, up to 1000. The simulated flow patterns revealed the dependence of the formation of... 

P. J. Hickey and C. H. Gooding, Modeling spiral wound membrane modules for pervaporative removal of volatile organic compounds from water. J. of Membrane Science, 88 (1994) 47-68. 

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