Module Shell

Other areas of corrosion concern are the membrane seals. If the seals are composed of flexible graphite, a preferred sealing material as discussed above, then corrosion by the common feed stream constituents is not a problem. However, with any metal seal - whether it be a brazed, welded, or soft-metal gasket seal - it is prudent to evaluate the potential for corrosion specifically at the seal. This evaluation is complicated by the fact that with brazed and welded seals, the metallurgy of the seal is influenced by the addition of the membrane alloy to the liquid braze alloy or weld pool. Experience has shown that welded seals to Pd—40Cu membranes, in which the membrane is welded to either Monel or 304L stainless steel, rapidly fail when subjected to 50 ppm hydrogen sulfide at 400 °C. 

In contrast, tube-and-shell type membrane modules do not have these engineering challenges with deflection and compromise of seal integrity. For this reason, tubular membrane modules will generally be lighter in construction relative to stacked planar membrane modules of comparable membrane area. However, a drawback to the tubular membrane module is that the packing density of the membrane is often substantially less than that which can be achieved with the stacked planar designs. 

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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...

Spiral-wound module) (Shell side feed)... 

Shell Membrane module shell side referred to... 

Figure 5.14 Cross-section of a membrane module showing weld joining of a Pd-40Cu membrane to a Monel module shell. The weld is to the far left of the module. The horizontal line in the middle is where the top and bottom half of the membrane module meet at the membrane.

At the start of the development, it had been intended use an expert system shell to implement this tool, however, after careful consideration, it was concluded that this was not the optimum strategy. An examination procedure can be considered as consisting of two parts fixed documentary information and variable parameters. For the fixed documentary information, a hypertext-like browser can be incorporated to provide point-and-click navigation through the standard. For the variable parameters, such as probe scanning paths, the decisions involved are too complex to be easily specified in a set of rules. Therefore a software module was developed to perfonn calculations on 3D geometric models, created fi om templates scaled by the user. 

Since it was required by LM Glasfiber that the scanner should be able to inspect joints between the shells and the iimer beams on each side and also the joints between the shells on the leading and trailing edge of the rotor blades, the X-Unit module was designed with three different set-ups for the Y-modules, which perform the movement of the probes transverse the length of the blade. The three different set-ups of the Y-modules are ... 

When the scanning of the adhesive bonded joint between the shells on the leading edge is complete, the rotor blade is rotated 180° and another special designed Y-module is applied for inspection of the trailing edge of the rotor blade in set-up 3, illustrated on figure 5. 

The axial filter (Oak Ridge National Laboratory) (30) is remarkably similar to the dynamic filter in that both the rotating filter element and the outer shell are also cylindrical. An ultrafiltration module based on the same principle has also been described (31). Unlike the disk-type European dynamic filters described above, the cylindrical element models are not so suitable for scale-up because they utilize the space inside the pressure vessel poorly. 

Fig. 23. Two types of hollow-fiber modules used for gas separation, reverse osmosis, and ultrafiltration applications, (a) Shell-side feed modules are generally used for high pressure appHcations up to - 7 MPa (1000 psig). Fouling on the feed side of the membrane can be a problem with this design, and pretreatment of the feed stream to remove particulates is required, (b) Bore-side feed modules are generally used for medium pressure feed streams up to - 1 MPa (150 psig), where good flow control to minimise fouling and concentration polarization on the feed side of the membrane is desired.

The second type of hoUow-fiber module is the bore-side feed type illustrated in Figure 23b. The fibers in this type of unit are open at both ends, and the feed fluid is usually circulated through the bore of the fibers. To minimize pressure drops inside the fibers, the fibers often have larger diameters than the very fine fibers used in the shell-side feed system and are generally made by solution spinning. These so-called capillary fibers are used in ultrafiltration, pervaporation, and in some low to medium pressure gas appHcations. Feed pressures are usually limited to less than 1 MPa (150 psig) in this type of module. 

N. Shell side of microporous hollow fiber module for solvent extraction... 

Air Backflush A configuration unique to microfiltration feeds the process stream on the shell side of a capillaiw module with the permeate exiting the tube side. The device is rim as an intermittent deadend filter. Eveiw few minutes, the permeate side is pressurized with air. First displacing the liquid permeate, a blast of air pushed back-... 

FIG. 22-75 Air fractionation by membrane. O2 in retentate as a function of feed fraction passed tbrougb tbe membrane (stage cut) showing tbe different result with changing process paths. Process has shell-side feed at 690 kPa (abs) and 298 K. Module comprised of hollow fibers, diameter 370 im od X 145 im id X 1500 mm long. Membrane properties (X = 5.7 (O2/N2), permeance for O2 = 3.75 X 10 Barrer/cm. Coutiesy Innovative Membrane Systems/ Fraxair)... 

The molecular basis for quasi-equivalent packing was revealed by the very first structure determination to high resolution of a spherical virus, tomato bushy stunt virus. The structure of this T = 3 virus was determined to 2.9 A resolution in 1978 by Stephen Harrison and co-workers at Harvard University. The virus shell contains 180 chemically identical polypeptide chains, each of 386 amino acid residues. Each polypeptide chain folds into distinct modules an internal domain R that is disordered in the structure, a region (a) that connects R with the S domain that forms the viral shell, and, finally, a domain P that projects out from the surface. The S and P domains are joined by a hinge region (Figure 16.8). 

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. 

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