Ultrafiltration membranes spiral wound 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). 

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...

A variation of the basic plate-and-frame concept is the spiral-wound module, which is widely used today in reverse osmosis, ultrafiltration, and gas separation. Its basic design is illustrated in Figure 1.33 (c). The feed flow channel spacer, the membrane, and the porous membrane support are rolled up and inserted into an outer tubular pressure shell. The filtrate is collected in a tube in the center of the roll. 

Membrane Process for Recovery of Alkanesulfonates. Many attempts have been made over the years to reduce the wastewater load—which represents a loss of product—by a number of different methods. These include evaporation, extraction, reverse osmosis, and ultrafiltration. All of these processes have the disadvantage of high equipment cost and high energy requirements, and the space-time yield is low. The first breakthrough came with the development of new types of membrane with a definite separating efficiency and a large surface area, so-called spiral-wound modules. 

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. 

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. 

Mainly four types of membrane modules are used plate-and-frame, spiral-wound, tube-in-shell, and hollow fiber. The plate-and-frame module consists of a series of membranes (10-500 pm thick) sandwiched between spacers that act as flow channels (Figure 5.69). (The membranes are often laminated on a porous support that offers no flow resistance.) The feed flows in one set of channels and the permeate, with or without carrier fluid, flows in alternate channels. Plate-and-frame modules find use in ultrafiltration and dialysis applications which include hemodialysis and electrodialysis. 

A case study of a natural gas production site covering various technical issues related to selection of an appropriate RO system is presented [59], As part of the pretreatment selection, two types of ultrafiltration (UF) membrane modules, namely, spiral wound and hollow fiber, with molecular weight cutoff (MWCO) of 8,000 and 50,000 Da, respectively, were tested in parallel with NF membranes of the spiral-wound type with MWCO 200 Da. The NF plant with 50% capacity gave a recovery of 75%, and the RO plant gave a recovery of 60% in... 

Commercial membrane separation processes include reverse osmosis, gas permeation, dialysis, electrodialysis, pervaporation, ultrafiltration, and microfiltration. Membranes are mainly synthetic or natural polymers in the form of sheets that are spiral wound or hollow fibers that are bundled together. Reverse osmosis, operating at a feed pressure of 1,000 psia, produces water of 99.95% purity from seawater (3.5 wt% dissolved salts) at a 45% recovery, or with a feed pressure of 250 psia from brackish water (less than 0.5 wt% dissolved salts). Bare-module costs of reverse osmosis plants based on purified water rate in gallons per day are included in Table 16.32. Other membrane separation costs in Table 16.32 are f.o.b. purchase costs. 

Figure 3 Membrane modules for microfiltration and ultrafiltration, (a) Tubular membrane module. (From Zeman and Zydney, 1996.) (b) Cassette membrane assembly. (From Perry et al., 1997.) (c) Spiral wound membrane module. (From Purchase, 1996.) (d) Hollow fiber membrane module. (From Zeman and Zydney, 1996.)...

Spiral-wound membrane modules, with hydrophilic membranes, are suited for water-based paint recovery in spray paint installations, and also for electrocoat paint filtration. Figure 4.32 shows a schematic for an ultrafiltration system for treating spray booth waste. 

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