Reverse spiral-wound

Spira.1- Wound Modules. Spiral-wound modules were used originally for artificial kidneys, but were fuUy developed for reverse osmosis systems. This work, carried out by UOP under sponsorship of the Office of Saline Water (later the Office of Water Research and Technology) resulted in a number of spiral-wound designs (63—65). The design shown in Figure 21 is the simplest and most common, and consists of a membrane envelope wound around a perforated central coUection tube. The wound module is placed inside a tubular pressure vessel, and feed gas is circulated axiaUy down the module across the membrane envelope. A portion of the feed permeates into the membrane envelope, where it spirals toward the center and exits through the coUection tube. 

In reverse osmosis, most modules are of the hollow-fine fiber or spiral-wound design plate-and-frame and tubular modules are limited to a few appHcations in which membrane fouling is particularly severe, for example, food appHcations or processing of heavily contaminated industrial wastewater. 

Hollow-fiber designs are being displaced by spiral-wound modules, which are inherently more fouling resistant, and require less feed pretreatment. Also, thin-film interfacial composite membranes, the best reverse osmosis membranes available, have not been fabricated in the form of hoUow-fine fibers. 

Reverse Osmosis. This was the first membrane-based separation process to be commercialized on a significant scale. The breakthrough discovery that made reverse osmosis (qv) possible was the development of the Loeb-Sourirajan asymmetric cellulose acetate membrane. This membrane made desalination by reverse osmosis practical within a few years commercial plants were installed. The total worldwide market for reverse osmosis membrane modules is about 200 million /yr, spHt approximately between 25% hoUow-ftber and 75% spiral-wound modules. The general trend of the industry is toward spiral-wound modules for this appHcation, and the market share of the hoUow-ftber products is gradually falling (72). 

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 earhest reverse osmosis and ultrafiltration units were based on flat membrane sheets ia arrangements similar to that of a plate and frame filter press. Siace then, mote efficient membrane configurations, ie, tubular, spiral wound, and hoUow fiber, have emerged (96—98). 

Reverse osmosis seawater Both hollow-fibres and spiral-wound modules... 

Reverse osmosis industrial Spiral-wound modules used almost exclusively fine fibres too... 

Configurations used include tubes, plate-and-frame arrangements and spiral wound modules. Spiral wound modules should be treated to remove particles down to 20 to 50. im, while hollow fiber modules require particles down to 5 im to be removed. If necessary, pH should be adjusted to avoid extremes of pH. Also, oxidizing agents such as free chlorine must be removed. Because of these restrictions, reverse osmosis is only useful if the wastewater to be treated is free of heavy contamination. The concentrated waste material produced by membrane processes should be recycled if possible but might require further treatment or disposal. 

Membrane module network design, in reverse osmosis, 21 666 Membrane modules, 15 818-824 21 636 hollow-fiber, 15 819-821, 823 plate-and-frame, 15 821 selecting, 15 821-824 spiral-wound, 15 818-819, 823-824 tubular, 15 821... 

Spiral-wound reverse osmosis membrane element, 26 75 Spiramycin... 

Membrane equipment for industrial scale operation of microfiltration, ultrafiltration and reverse osmosis is supplied in the form of modules. The area of membrane contained in these basic modules is in the range 1-20 m2. The modules may be connected together in series or in parallel to form a plant of the required performance. The four most common types of membrane modules are tubular, flat sheet, spiral wound and hollow fibre, as shown in Figures 8.9-8.12. 

A3/X°i, C° = X°3/X°, and 03= X 3/X°3. reverse osmosis system involving longitudinal feed flow pattern in the module (such as in spiral wound or tubular modules), let... 

Data of WRPC. The Water Reuse Promotion Center(WRPC) in JAPAN has been engaged in development of sea water desalination by reverse osmosis since 197. At IDEA meeting at Mexico city 1976,the first redults were reported with two types of modules, du Dont hollow fine fiber module B-10 and UOP s cellulose triacetate ultrathin spiral wound module,tested at their laboratory at Chigasaki beach. Then the WRPC has adopted two types of modules made in Japan, Toray new type of spiral wound module made from cellulose acetate and Toyobo s cellulose triacetate hollow fine fiber module. 

In current practice, turbulence promoters most often take the form of a net or screen material which also serves as a feed channel spacer between two membranes. For example, the familiar spiral wound modules (Figures 29) used extensively in reverse osmosis and to a lesser extent in ultrafiltration use a plastic screen material as the feed channel spacer. This is also used in some plate and frame systems (Figure 30). 

The greatest use of membranes is for reverse osmosis desalination of seawater and purification of brackish waters. Spiral wound and hollow fiber equipment primarily are applied to this service. Table 19.6 has some operating data, but the literature is very extensive and reference should be made there for details of performance and economics. 

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.

In some applications of reverse osmosis and ultrafiltration spiral-wound modules in the food industry, it may be desirable to allow a small portion of the feed solution to bypass the module to prevent bacteria growing in the otherwise stagnant fluid. One way of achieve this bypass is by perforating the ATD as illustrated in Figure 3.45 [115]. 

Figure 3.42 Exploded view and cross-section drawings of a spiral-wound module. Feed solution passes across the membrane surface. A portion passes through the membrane and enters the membrane envelope where it spirals inward to the central perforated collection pipe. One solution enters the module (the feed) and two solutions leave (the residue and the permeate). Spiral-wound modules are the most common module design for reverse osmosis and ultrafiltration as well as for high-pressure gas separation applications in the natural gas industry...

Figure 3.44 Schematic of a spiral-wound module [115] installed in a multimodule pressure vessel. Typically four to six modules are installed in a single pressure vessel. Reprinted from Reverse Osmosis Technology, B.S. Parekh (ed.), Marcel Dekker, New York (1988), p. 81, by courtesy of Marcel Dekker, Inc.

Reverse osmosis seawater Spiral-wound modules. Only one hollow fiber producer remains... 

Y. Kamiyama, N. Yoshioka, K. Matsui and E. Nakagome, New Thin-film Composite Reverse Osmosis Membranes and Spiral Wound Modules, Desalination 51, 79... 

S.S. Kremen, Technology and Engineering of ROGA Spiral-wound Reverse Osmosis Membrane Modules, in Reverse Osmosis and Synthetic Membranes, S. Sourirajan (ed.), National Research Council Canada, Ottawa, Canada, pp. 371-386 (1977). 

Equation (4.9) shows that concentration polarization increases exponentially as the total volume flow Jv through the membrane increases. This is one of the reasons why modem spiral-wound reverse osmosis membrane modules are operated at low pressures. Modem membranes have two to five times the water permeability, at equivalent salt selectivities, of the first-generation cellulose acetate reverse osmosis membranes. If membrane modules containing these new membranes were operated at the same pressures as early cellulose acetate modules, two to five times the desalted water throughput could be achieved with the same... 

The effect of concentration polarization on specific membrane processes is discussed in the individual application chapters. However, a brief comparison of the magnitude of concentration polarization is given in Table 4.1 for processes involving liquid feed solutions. The key simplifying assumption is that the boundary layer thickness is 20 p.m for all processes. This boundary layer thickness is typical of values calculated for separation of solutions with spiral-wound modules in reverse osmosis, pervaporation, and ultrafiltration. Tubular, plate-and-ffame, and bore-side feed hollow fiber modules, because of their better flow velocities, generally have lower calculated boundary layer thicknesses. Hollow fiber modules with shell-side feed generally have larger calculated boundary layer thicknesses because of their poor fluid flow patterns. 

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... 

A simplified flow scheme for a brackish water reverse osmosis plant is shown in Figure 5.24. In this example, it is assumed that the brackish water is heavily contaminated with suspended solids, so flocculation followed by a sand filter and a cartridge filter is used to remove particulates. The pH of the feed solution might be adjusted, followed by chlorination to sterilize the water to prevent bacterial growth on the membranes and addition of an anti-sealant to inhibit precipitation of multivalent salts on the membrane. Finally, if chlorine-sensitive interfacial composite membranes are used, sodium sulfite is added to remove excess chlorine before the water contacts the membrane. Generally, more pretreatment is required in plants using hollow fiber modules than in plants using spiral-wound modules. This is one reason why hollow fiber modules have been displaced by spiral-wound systems for most brackish water installations. 

Table 5.5 Advances in spiral-wound module reverse osmosis performance...

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