Spiral wound membrane modules advantage

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,... 

What is an advantage and a disadvantage of a spiral-wound membrane module ... 

Membrane processes are used to filter liquids. Instead of conventional filter materials (e.g. filter cloth, filter candles,) microporous membranes are employed with molecular size pores. First the industry had to learn how to manufacture membranes with controlled pore sizes. To optimise the filtration capacities specific filter structures had to be designed in which the liquid followed well defined flow patterns on one side of the membrane. Many different systems were developed for the varied applications, all having their advantages and also disadvantages, i.e. plate modules, tubular modules, spiral wound membranes, etc. Research and development in this field is far from being exhausted. Today membrane systems are available which are sufficiently resistant to chemical, mechanical and thermal stress. They are produced from plastic... 

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. 

Modules Every module design used in other membrane operations has been tried in pervaporation. One unique requirement is for low hydraulic resistance on the permeate side, since permeate pressure is very low (0.1-1 Pa). The rule for near-vacuum operation is the bigger the channel, the better the transport. Another unique need is for heat 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 construction 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 capillary bundles. The capillary device with the feed on the inside of the tube has many advantages in principle, such as good vapor-side mass transfer and economical construction, but it is still limited by the availability of membrane in capillary form. 

Each membrane/module type has advantages and disadvantages [2,7]. Hollow fine fibers are generally the cheapest on a per-square-meter basis, but it is harder to make very thin selective membrane layers in hollow-fiber form than in flat-sheet form. This means the permeances of hollow fibers are usually lower than flat-sheet membranes made from the same material. Also, hollow fine fiber modules require more pretreatment of the feed to remove particulates, oil mist and other fouling components than is usually required by capillary or spiral-wound modules. These factors offset some of the cost advantage of the hollow fine fiber design. 

The major advantage of the spiral configuration over a plate-and-frame configuration is that there is minimal leakage associated with the spiral configuration. The spiral wound module does not require periodic tightening of nuts and bolts to prevent leaks, unlike plate-and-frame modules. Limitations of the spiral configuration include inferior current and flow distribution relative to plate-and-frame modules, as well as difficulty in assembly and field membrane replacement.17... 

Microfiltration units can be configured as plate and frame flat sheet equipment, hollow fiber bundles, or spiral wound modules. The membranes are typically made of synthetic polymers such as Polyethersulfone (PES), Polyamide, Polypropylene, or cellulosic mats. Alternate materials include ceramics, stainless steel, and carbon. Each of these come with its own set of advantages and disadvantages. For instance, ceramic membranes are often recommended for the filtration of larger particles such as cells because of the wider lumen of the channels. However, it has been shown that spiral wound units can also be used for this purpose, provided appropriate spacers are used. 

The objective in membrane design is to pack as much permeation surface area into as small a space as possible to minimize operation requirements. Depending on the application, various membrane designs are used, such as flat sheet, disc tube, hollow fiber, spiral wound, and ceramic (17). Module design has a measurable effect on the hydrodynamic performance of the cross-flow membrane device. The advantages and disadvantages of different membrane modules are summarized in Table 1. 

The two most common RO membrane configurations used in water treatment today are spiral-wound and hollow fiber. The spiral-wound elements can operate at a higher pressure and at a higher silt density index (SDI) than the hollow fiber type, and thus may require less pretreatment (and are more tolerant of pretreatment upsets). They also are easier to clean than the hollow fiber type. The main advantage of the hollow fiber configuration is that it has the highest amount of membrane area per unit volume, thus requiring less space. Since there is only one hollow fiber element per pressure vessel, it is easier to troubleshoot, and it is easier to replace membrane modules. 

Hie three major membrane configurations, flat sheet, spiral wound, and hollow fiber, each having advantages and limitations, will he reviewed briefly prior to considering the detailed analysis of these devices. Some of these issues include relative magnitudes of active membrane area per unit separator volume, mtninrizakm of pressure buildup in the permeant stream, membrane integrity, and the ease of module manufacture and membrane replacement. 

The membrane is in the form of a hollow fiber (see Fig. 109), which has the advantage of reduced outer dimensions together with a large membrane area. The membrane module consists only of the hollow fiber bundle and the module housing. Such a simple structure can avoid difficulties encountered with other membrane module designs, such as sealing of flat seat type and spiral-wound type membranes and furthermore can reduce not only the volume and the weight of the modules, but also the total system size. 

The majority of a membrane system cost is associated with the large compressors required to pressurize the permeate stream and feed pretreatment operations required to remove heavy hydrocarbon and water vapor impurities only about 10%-25% of the total system cost is associated with the membrane module [27]. Membranes for CO2 removal applications are typically fabricated in either hollow fiber or spiral wound format. Hollow fiber approach has the advantage of greater membrane area per unit volume and greater operational flexibility and module fabrication cost [28]. 

The relatively low cost of hollow-fiber modules is their principal advantage. A key disadvantage is that the polymer membrane must perform the separation required as well as withstand the pressure driving force across the membrane. Preparing membranes that meet both requirements is difficult Thus, producing membranes that have high selectivities and high fluxes and that are mechanically stable is more difficult in hollow-fiber form than with the flat sheets used in spiral-wound modules. As a result, membranes used in spiral-wound mod-... 

A filtration device consists of a filtrate outlet structure and a membrane unit in which a specific membrane surface area is housed, the membrane module. There are four types of membrane modules that are used for RO plate and frame, tubular, spiral wound and hollow fiber. A brief description about these membrane modules and their functions is given in the following sub sections. Several advantages and disadvantages of all these membrane modules are also discussed in Table 4.1. 

Design of Membrane Modules for Gas Separations The advantages of spiral-wound modules are ... 

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