Modules spiral wound

Spiral wound modules were originally developed for RO but are capturing an ever increasing share of the UF market. They currently provide one of the least expensive UF modules available in terms of cost per unit of membrane area. 

Permeate Collection Material Membrane Feed Channel Spacer 

Spiral-wound modules cannot be unwrapped for cleaning lest the glue line seal rupture and most cannot be autoclaved. They are more prone to fouling than tubes and some plate and frame units (depending on the type of feed channel spacer), but they are more resistant to fouling than hollow fibers. 

Membrane Replacement cost (not including labor) High Moderate Low Moderate/ Low 

Flux (6SFD) Good Fair/Poor Excellent/ Good Good 

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, 

Influent that enters the spiral wound module does so tangentially to the membrane surface and the reject exits the module at the end opposite of the influent. Water that permeates the membrane does so perpendicularly to the surface of the membrane and is collected 

Spiral wound modules are typically covered in fiberglass to protect the leaves (exceptions being sanitary modules, see Chapter 4.4.2.6). Because of the materials of construction (namely the adhesives used) and the potential for annealing the membrane, the maximum operating water temperature is limited to 45°C.27 

Characteristics of spiral wound modules are described below. 

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

O-rings can roll upon installation into membrane modules, thereby 

Feed water feed water Feed water and 

The standard spiral woimd module is 8 inches in diameter with a 40-inch length. There are also 4-inch and 18-inch diameter industrial membrane modules available (2.5-inch diameter modules are available for tap water or home-use applications). Koch Membrane Systems also makes a 60-inch long, 8-inch diameter module called a Magnum and an 18-inch diameter by 60-inch length module called a MegaMagnum  

Similar considerations are vahd for organic-organic separation. Spiral-wound modules have thus been used in pilot plants for the removal of methanol and ethanol from dry organic mixtures or for the removal of aromatic from aliphatic components. The stabihty of the material for the feed-side spacer and the glue 

There has been a development on spiral-wound modules for dehydration applications, too. So far this did not lead to apphcations in industrial plants. Chemical-stabihty problems of the components and too high pressure losses in the permeate-side spacer could not be solved satisfactorily, and the costs of the modules and for the installation in a plant were not reaUy lower than those for plate modules. 

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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. 

Fig. 22. Multileaf spiral-wound module, used to avoid excessive pressure drops on the permeate side of the membrane. Large, 30-cm diameter modules may have as many as 30 membrane envelopes, each with a membrane area of about 2 m. ...

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. 

For ultrafiltration appHcations, hollow-fine fibers have never been seriously considered because of their susceptibiUty to fouling. If the feed solution is extremely fouling, tubular or plate-and-frame systems ate still used. Recentiy, however, spiral-wound modules with improved resistance to fouling have been developed, and these modules are increasingly displacing the more expensive plate-and-frame and tubular systems. Capillary systems are also used in some ultrafiltration appHcations. 

Spiral-wound modules are much more commonly used in low pressure or vacuum gas separation appHcations, such as the production of oxygen-enriched air, or the separation of organic vapors from air. In these appHcations, the feed gas is at close to ambient pressure, and a vacuum is drawn on the permeate side of the membrane. Parasitic pressure drops on the permeate side of the membrane and the difficulty in making high performance hollow-fine fiber membranes from the mbbery polymers used to make these membranes both work against hollow-fine fiber modules for this appHcation. 

Pervaporation operates under constraints similar to low pressure gas-separation. Pressure drops on the permeate side of the membrane must be small, and many prevaporation membrane materials are mbbery. For this reason, spiral-wound modules and plate-and-frame systems ate both in use. 

Plate-and-frame systems are competitive in this appHcation despite their high cost, primarily because they can be operated at high temperatures with relatively aggressive feed solutions, for which spiral-wound modules might fad. 

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). 

Both hollow-fiber and spiral-wound modules are used ia gas-separation appHcations. Spiral-wound modules are favored if the gas stream contains oil mist or entrained Hquids as ia vapor separation from air or natural gas separations. 

Solids nd Colloids. Suspended soHds can accumulate at the membrane surface, creating an additional resistance to flow through the membrane as well as a possible feed channel, such as that for a spiral-wound module plugging and subsequently a decrease in flux. Prevention of this type of fouling lies in the removal of the suspended soHds, which can be accompHshed using filters and screens prior to arrival at the RO unit. 

Modules Eveiy module design used in other membrane operations has been tried in peivaporation. One unique requirement is for low hydraulic resistance on the permeate side, since permeate pressure is veiy low (O.I-I Pa). The rule for near-vacuum operation is the bigger the channel, the better the transport. Another unique need is for neat input. The heat of evaporation comes from the liquid, and intermediate heating is usually necessary. Of course economy is always a factor. Plate-and-frame construc tion was the first to be used in large installations, and it continues to be quite important. Some smaller plants use spiral-wound modules, and some membranes can be made as capiUaiy bundles. The capillaiy device with the feed on... 

RO membrane performance in the utility industry is a function of two major factors the membrane material and the configuration of the membrane module. Most utility applications use either spiral-wound or hollow-fiber elements. Hollow-fiber elements are particularly prone to fouling and, once fouled, are hard to clean. Thus, applications that employ these fibers require a great deal of pretreatment to remove all suspended and colloidal material in the feed stream. Spiral-wound modules (refer to Figure 50), due to their relative resistance to fouling, have a broader range of applications. A major advantage of the hollow-fiber modules, however, is the fact that they can pack 5000 ft of surface area in a 1 ft volume, while a spiral wound module can only contain 300 ftVff. 

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

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

Ultrafiltration Tubular, capillary and spiral-wound modules all used. Tubular generally limited to highly fouling feeds (automotive paint), spiral-wound to clean feeds (ultrapure water). 

Spiral-wound modules consist of several flat membranes separated by turbulence-promoting mesh separators and formed into a Swiss roll (Figure 16.18). The edges of the membranes are sealed to each other and to a central perforated tube. This produces a cylindrical module which can be installed within a pressure tube. The process feed enters at one end of the pressure tube and encounters a number of narrow, parallel feed channels formed between adjacent sheets of membrane. Permeate spirals roward the perforated central tube for collection. A standard size spiral-wound module has a diameter of about 0.1m, a length of about 0.9 m and contains about 5 m2 of membrane area. Up to six such modules may be installed in series in a single pressure tube. These modules make better use of space than tubular or flat sheet types, but they are rather prone to fouling and difficult to clean. 

Modules and Housings Modern gas membranes are packaged either as hollow-fiber bundles or as spiral-wound modules. The former uses extruded hollow fibers. Tube-side feed is preferable, but it is limited to about 1.5 MPa. Higher-pressure applications are usually fed on the shell side. A large industrial permeator contains fibers 400 pm by 200 pm i.d. in a 6-inch shell 10 feet long. Flat-sheet membrane is wound into spirals, with an 8- by 36-inch permeator containing 25 of membrane. Both types of module are similar to those illustrated in Background and Definitions. Spiral modules are useful when feed... 

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. 

Multileaf spiral-wound modules, 15 819 Multilevel 157-nm resist systems, 15 188-189... 

Membrane gas-separation systems have found their first applications in the recovery of organics from process vents and effluent air [5]. More than a hundred systems have been installed in the past few years. The technique itself therefore has a solid commercial background. Membranes are assembled typically in spiral-wound modules, as shown in Fig. 7.3. Sheets of membrane interlayered with spacers are wound around a perforated central pipe. The gas mixture to be processed is fed into the annulus between the module housing and the pipe, which becomes a collector for the permeate. The spacers serve to create channels for the gas flow. The membranes separate the feed side from the permeate side. 

Figure 8.11. Schematic diagram of spiral-wound module...

The geometries for asymmetric mixed-matrix membranes include flat sheets, hollow fibers and thin-fihn composites. The flat sheet asymmetric mixed-matrix membranes are formed into spirally wound modules and the hollow fiber asymmetric mixed-matrix membranes are formed into hollow fiber modules. The thin-film composite mixed-matrix membranes can be fabricated into either spirally wound or hollow fiber modules. The thin-film composite geometry of mixed-matrix membranes enables selection of different membrane materials for the support layer and low-cost production of asymmetric mixed-matrix membranes utilizing a relatively high-cost zeolite/polymer separating layer on the support layer. 

In 1968 we started investigations of RO applications for desalting brackish water. In the course of the investigations, we have found the spirally wound module of asymmetric cellulose acetate RO membrane shows excellent durabilities against fouling materials and free chlorine. 

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. 

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