Reverse osmosis module

The first reverse osmosis modules made from cellulose diacetate had a salt rejection of approximately 97—98%. This was enough to produce potable water (ie, water containing less than 500 ppm salt) from brackish water sources, but was not enough to desalinate seawater efficiently. In the 1970s, interfacial composite membranes with salt rejections greater than 99.5% were developed, making seawater desalination possible (29,30) a number of large plants are in operation worldwide. 

Developments and advances in both membrane materials and reverse osmosis modules have increased the range of appHcations to which RO can be apphed. Whereas the RO industry has developed around water desalination (9,53,73,74), RO has become a significant cornerstone in other industries. 

The success of EDR ia water demineralization has appareatly resulted from its greater tolerance of particulate and fouling matter compared to reverse osmosis greater forgivingness of process upsets greater tolerance for unskilled operators simplicity ia desiga and constmction of EDR stacks compared to reverse osmosis modules the abiHty to iaspect, clean, or replace one membrane at a time the existence of a comprehensive global sales and... 

A hollow-fiber reverse-osmosis module consists of a shell which houses the hollow fibers (Fig. 11.3). The fibers are grouped together in a bundle with one end sealed and the other open to the atmosphere. The open ends of the fibers are potted into Ml epoxy sealing head plate after which the permeate is collected. The pressurized feed solution (denoted by the shell side fluid) flows radially from a central porous tubular distributor. As the feed solution flows around the outer side of the fibers toward the shell perimeter, the permeate solution penetrates through the fiber wall into the bore side by virtue of reverse osmosis. The permeate is collected at the open ends of the fibers. The reject solution is collected at the porous wall of the shell. 

Designing systems of multiple reverse osmosis modules... 

H. 3 Designing Systems of Multiple Reverse Osmosis Modules... 

The task of synthesizing an optimal RON can be stated as follows For a given feed flowrate, Qf. and a feed concentration, Cp. it is desired to synthesize a minimum cost system of reverse osmosis modules, booster pumps and energy-recovery turbines Chat can separate the feed into two streams an environmentally acceptable permeate and a retentate (reject) stream in which the undesired species is concentrated. The permeate stream must meet two requirements ... 

The above equations show that for a reverse osmosis system specified In terms of y, 9, and X, any one of the six quantities (performance parameters) C], C2, C3, C3, X or X or T, and A uniquely fixes all the other five quantities (112). Further, since the relationships represented by the set of eq 34 to 41 Involve 8 equations with 12 unknowns, namely, y, 9, X, Z, A, C-j, C2, C2, C3, C3, C3 and X or X or T, by fixing any four Independent quantities Included In the above unknowns, eq 34 to 41 can be solved simultaneously to obtain the remaining 8 quantities. The utility of this approach to system analysis for reverse osmosis process design and predicting the performance of reverse osmosis modules Is Illustrated In detail In the literature (6d,105,107,108,111,112,113). 

Bundle Preparation. Packages of multifileiment yarns are backwound to prepare bundles necessary for the manufacture of a reverse osmosis module. A proprietary winder for this operation has been designed and constructed at Albany International Research Co. This device is capable of helically winding multifilament yarns into bundles around a mandrel. This is done in a manner such that the resulting bundle has uniform cylindrical dimensions and uniform fiber density. This minimizes channeling and optimizes exposure of membrane surface area. 

For water prepared by distillation and to be used as water for injection, the requirement is >80°C. Systems with built-in reverse osmosis modules and ultrafiltration devices must comply with the supplier specification. 

Fig 5. Hollow fiber reverse osmosis module used in desalination and other separation processes. Tmoho C o. Lnl.. Osaka, Japan)... 

Figure 3.45 By perforating the antitelescoping device, a small controlled bypass of fluid past the module seal is achieved to eliminate the stagnant area between the reverse osmosis module and the pressure vessel walls. This device is used in food and other sanitary applications of spiral-wound modules [115], Reprinted from Reverse Osmosis Technology, B.S. Parekh (ed.), Marcel Dekker, New York (1988), p. 359, by courtesy of Marcel Dekker, Inc.

Figure 3.47 A cross-flow hollow fiber module used to obtain better flow distribution and reduce concentration polarization (the Tyobo Hollosep reverse osmosis module). Feed enters through the perforated central pipe and flows towards the module shell...

In reverse osmosis, the commonly used modules are spiral-wound. Plate-and-frame and tubular modules are limited to a few applications in which membrane fouling is particularly severe, for example, in food applications or processing heavily contaminated industrial wastewater. The hollow fiber reverse osmosis modules used in the past have now been almost completely displaced by spiral-wound modules, which are inherently more fouling resistant, and require less feed pretreatment. 

As Figure 5.12 shows, Toray s PEC-1000 crosslinked furfuryl alcohol membrane has by far the best sodium chloride rejection combined with good fluxes. This explains the sustained interest in this membrane despite its extreme sensitivity to dissolved chlorine and oxygen in the feed water. Hollow fine fiber membranes made from cellulose triacetate by Toyobo or aromatic polyamides by Permasep (Du Pont) are also comfortably in the one-stage seawater desalination performance range, but the water fluxes of these membranes are low. However, because large-surface-area, hollow fine fiber reverse osmosis modules can be... 

FIG. 22-50 Cutaway view of high-pressure hollow-fine-fiber reverse-osmosis module. Courtesy DuPont.)... 

As mentioned, two membrane modules, Toray and Osmonics, were compared. The technical characteristics of these reverse osmosis modules are detailed in Table 41.3. 

The Monsanto hollow-fiber module Tor gas separation appears to be a compromise between the two preceding reverse osmosis module designs/ As shown in Fig, 20. [-4, the hollow fibers are closed at one and with an epoxy plug or similar devioe, and Teed enters at the side at one end, The feed then flows axially along Ibe fibers, and (he nor permeant exits at the opposite end from which the feed eaters. Permeant diffusing through the hollow-fiber wall into the bora moves con me (currently to the shell-side flow and unimeieiy is collected in the chamber where all the open ends of (he fibers terminate,... 

FIGURE 20.1-3 Sketch of a Purmasep hollow-fiber reverse osmosis module. Courtesy of E. I. Du Pont Co. 

AUegrezza A.E., Parekh B.S., Parise P.L., Swiniarski E.J., White J.L. (1987), Chlorine resistant polysulfone reverse osmosis modules. Desalination, 64, 285-304. 

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