Hollow fiber modules configuration

Table 16.3 Summarizes the advantages and limitations of tubular, spiral wound and hollow fiber module configurations.

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. 

Let us consider the following case of removing an inorganic salt from an aqueous stream. It is desired to reduce the salt content of a 26 m /hr water stream (Qf) whose feed concentration, Cp, of 0.035 kmol/m (approximately 2,000 ppm). The feed osmotic pressure (rrp) is 1.57 atm. A 30 atm (Pp) booster pump is used to pressurize the feed. Sixteen hollow fiber modules are to be employed for separation. The modules are configured in parallel with the feed distributed equally among the units. The following properties are available for the HFRO modules ... 

Configurations used include tubes, plate-and-frame arrangements and spiral wound modules. Spiral wound modules should be treated to remove particles down to 20 to 50. im, while hollow fiber modules require particles down to 5 im to be removed. If necessary, pH should be adjusted to avoid extremes of pH. Also, oxidizing agents such as free chlorine must be removed. Because of these restrictions, reverse osmosis is only useful if the wastewater to be treated is free of heavy contamination. The concentrated waste material produced by membrane processes should be recycled if possible but might require further treatment or disposal. 

Ultrafiltration hollow-fiber modules are usually made with a shell and tube configuration. The fibers are potted at both ends of the module with the fiber lumen open for recirculation of the process stream (Figure 21). Naturally, strainers or prefilters must be utilized to eliminate plugging of the fibers. At Nude-pore, it has been shown that larger diameter hollow fibers, 1.5 to 3mm in i.d., are much less prone to fouling. Fortunately, all UF hollow fiber systems can be back-washed and are amenable to a number of cleaning techniques. 

Bocquet, S., Viladomat, E.G., Nova, C.M., Sanchez, J., Athes, V. and Souchon, I. (2006) Membrane-based solvent extraction of aroma compounds Choice of configurations of hollow fiber modules based on experiments and simulation. Journal of Membrane Science, 281, 358. 

Membrane technology is a well-established technology for the immobilization of enzymes [233] since Degussa [234] introduced a continuous acylase process employing an enzyme-membrane reactor for the enantiomeric production of pure L-amino acids in 1981. Polymer membranes configured into hollow-fiber modules are, by far, the most widely used membrane where the enzyme is held back by the low cutoff of the membrane. 

FIGURE 14.6 Configuration of Microza hollow-fiber module. 

A hollow fiber module is conceptually similar to the capillary module, but differs in dimensions. In this case the diameter of the tubular membrane varies between 50 and 100 pm and several thousand of fibers can be placed in the vessel. The hollow fiber module is the configuration with the highest packing density (with values up to 30,000 m m ). 

While the previously described three membrane modules required flat sheet membrane material for their preparation, special membrane configurations are needed for the preparation of the tubular, capillary, and hollow fiber modules. The tubular membrane module consists of membrane tubes placed into porous stainless steel or fiber glass reinforced plastic pipes. The pressurized feed solution flows down the tube bore and the permeate is collected on the outer side of the porous support pipe, as indicated in Figure 1.33 (d). The diameters of tubular membranes are typically between 1-2.5 cm. In some modules, the membranes are cast directly on the porous pipes and in others they are prepared separately as tubes and then installed into the support pipes. 

Depending on the process application, one or the other of these requirements is of primary importance and, for this reason, a number of different modules have been designed. The most important designs are the plate and frame, the spiral wound and the hollow fiber module. Optimization procedure and some of its results will be discussed for only one module configuration, the hollow fiber module-and for only one application-RO. 

In the case of reverse osmosis, the relative flow configuration does not affect the performance to any large extent. As already indicated, the situation is quite different for gas permeation. While countercurrent flow improves the separation efficiency of hollow fiber modules in reverse osmosis only slightly, as far... 

Microza is the tradename of Asaihi Kasei Corporation FIGURE 14.7 Configuration of Microza hollow-fiber module. 

However, for practical purposes, membrane configurations with higher surface-area-to-volume ratio, such as spiral wound and hollow-fiber modules, are required. In hollow-fiber modules, the IL is confined, by capillarity, within the pores of the hollow fibers, and the aqueous feed and strip solutions circulate by each side of the fiber thus, the solid membrane serves both as a support for the IL and as a uniform barrier between the aqueous solutions, which usually circulate within the inner (feed solution) and the outer (strip solution) of the fiber. This results in two aqueous/IL interfaces with well-defined transfer areas. This configuration has been... 

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