Ultrafiltration spiral-wound

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]. 

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. 

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). 

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). 

Cross-flow is the usual case where cake compressibility is a problem. Cross-flow microfiltration is much the same as cross-flow ultrafiltration in principle. In practice, the devices are often different. As with UF, spiral-wound membranes provide the most economical configuration for many large-scale installations. However, capillary devices and cassettes are widely employed, especially at smaller scale. A detailed description of cross-flow microfiltration had been given by Murkes and Carlsson [Crossflow Filtration, Wiley, New York (1988)]. 

In a study of the bioaccumulation of metals as colloid complexes and free ions by the marine brown shrimp, Penaeus aztecus [29] the colloids were isolated and concentrated from water obtained from Dickinson Bayou, an inlet of Galveston Bay, Texas, using various filtration and ultrafiltration systems equipped with a spiral-wound 1 kDa cutoff cartridge. The total colloidal organic carbon in the concentrate was found to be 78 lmgdm 3. The shrimps were exposed to metals (Mn, Fe, Co, Zn, Cd, Ag, Sn, Ba and Hg) as radiolabelled colloid complexes, and free-ionic radiotracers using ultrafiltered seawater without radiotracers as controls. The experiments were designed so that the animals were exposed to environmentally realistic metal and colloid concentrations. 

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. 

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). 

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...

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. 

Figure 6.11 An illustration of the channel of a spiral-wound module showing how periodic turbulent eddies can dislodge deposited gel particles from the surface of ultrafiltration membranes...

Figure 12.5 Scheme of three different drinking-water production plants traditional (A) using ultrafiltration pretreatment and spiral-wound nanofiltration (B) and using capillary nanofiltration (Q [17]. 

Figure 431 ROCHEM ST module, a modified spiral wound module, showing a) a cross-section and b) the module within a pressure vessel housing. Courtesy ROCHEM Ultrafiltrations Systems GmbH.

Figure 16.4 Spiral wound ultrafiltration system. Courtesy of Koch Membrane Systems.

The difference between conventional dead-end filtration and cross-flow filtration is the configuration of the system. For large-scale operations, only cross-flow filtration will be used. The membranes for miocrofiltration as well as ultrafiltration are commonly utilized in a variety of filtration devices. There are three basic types of tangential flow filtration devices plate and frame, hollow fiber, and spiral wound membranes. 

Cheryan, M. and Kuo, K.P., Hollow fibers and spiral wound modules for ultrafiltration of whey Energy consumption and performance, J. Dairy Sci., 67, 1406, 1984. 

Kuo, K.P. and Cheryan, M., Ultrafiltration of acid whey in spiral-wound unit Effect of operating parameters on membrane fouling, J. 

FIGURE 35.4 Process diagram of CR ultrafiltration and spiral wound nanofiltration systems at M-Real Kirkniemi paper mill. (From Kreutzman, E. and Sutela, T., Ippta J., p. 15, 2004 Courtesy of Metso Paper. With permission.)... 

Pleated ultrafiltration module. The axial filter is convenient for experiments, in that volumes small relative to ordinary ultrafiltration systems can be studied and in that pumping of viscous solutions is limited to that necessary to replace filtrate or concentrate bled from the chamber, rather than that necessary to maintain desired cross flow velocities. There is no obvious reason it could not be scaled up to moderate sizes for practical separations, but so far as we know, no large-volume axial filters are available. For the operations of interest, any of the commercial ultrafiltration systems would be candidates. We have tested one module, recently developed by Gelman, which incorporates a pleated membrane (Figure 5), with somewhat more open feed passages than those of spiral-wound membranes, and which allows backwashing. Other applications of the module were discussed at this symposium by A. Korin in a paper coauthored by G. B. Tanny, and a written account is presumably in these proceedings. 

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