Modules hollow fiber

Hollow-fiber module Hollow-fiber reactor Hollow fibers... 

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.

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

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. 

Major problems inherent in general applications of RO systems have to do with (1) the presence of particulate and colloidal matter in feed water, (2) precipitation of soluble salts, and (3) physical and chemical makeup of the feed water. All RO membranes can become clogged, some more readily than others. This problem is most severe for spiral-wound and hollow-fiber modules, especially when submicron and colloidal particles enter the unit (larger particulate matter can be easily removed by standard filtration methods). A similar problem is the occurrence of concentration-polarization, previously discussed for ED processes. Concentration-polarization is caused by an accumulation of solute on or near the membrane surface and results in lower flux and reduced salt rejection. 

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 ... 

Hermans, J. J. (1978). Physical aspects governing the design of hollow fiber modules. Desalination, 26, 45-62. 

Hollow fiber modules, or permeators, are precisely machined units containing bundles of fine hollow fibers, positioned parallel to and around a perforated center FW tube, with only one or two bundles per pressure vessel. They are widely used for brackish and seawater supply applications. Hollow fiber modules exhibit a low flux rate (permeate flow per unit membrane per unit time) and foul easily, but... 

Figure 10.8 (a) Ceramic hollow-fiber module of Hyflux... 

Equations (20-66) and (20-67) present single-pass formulas relating retentate solute concentration, retentate crossflow, permeate flow, and membrane area. For relevant low-feed-concentration applications, polarization is minimal and the flux is mainly a function of pressure. Spiral or hollow fiber modules with low feed channel and permeate pressure drops are preferred. 

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. 

Shell-side feed hollow-fiber modules,... 

The geometries for asymmetric mixed-matrix membranes include flat sheets, hollow fibers and thin-fihn composites. The flat sheet asymmetric mixed-matrix membranes are formed into spirally wound modules and the hollow fiber asymmetric mixed-matrix membranes are formed into hollow fiber modules. The thin-film composite mixed-matrix membranes can be fabricated into either spirally wound or hollow fiber modules. The thin-film composite geometry of mixed-matrix membranes enables selection of different membrane materials for the support layer and low-cost production of asymmetric mixed-matrix membranes utilizing a relatively high-cost zeolite/polymer separating layer on the support layer. 

Figure 5. Characteristics of Toyobo s hollow fiber modules over a long period Hollowsep 5 modules used for the first stage (6).

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. 

Figure 21. Nuclepore hollow-fiber module end potting...

Naruse et al. proposed another bioreactor design [22,23], in which porcine hepatocyte spheroids are immobilized on non-woven polyester fabric. This device allows more direct contact between hepatocytes and perfused medium and improves, therefore, the mass transfer capacity. The non-woven fabric module expressed better metabohc and synthetic functions at 24 hours than a hollow fiber module containing spheroids in suspension culture. Longer term results are not yet available and the immunoexclusion properties of this fabric have not been addressed. 

Hollow fiber modules and the micro encapsulation of progenitor cells have been used in hematopoietic culture with less success [69, 70]. Furthermore, these approaches do not fit the chnical requirements, as the harvest of the cells is almost impossible. 

The mass transfer coefficient can be calculated from the slope of the line obtained by plotting the solute concentration ratio (In [AC/AC ]) from Eq. (7) vs time. This iCjn is related to Eqs. (5) and (6). However, the parameters in the above Eqs. (5)-(7) are quite complicated functions. Hence, the gas absorption equations developed by Yang and Cussler [181] in hollow fiber contactors have been extended for liquid-liquid systems. The overall mass transfer resistance in hollow fiber modules is given by [2,182] ... 

RO membrane modules are available from many manufacturers including, for hollow-fiber modules, DuPont and Dow/FilmTec Corporation, and for spiral-wound modules, UOP Inc., Millipore Corporation, Nitto-Denko America, Inc., Toray Industries Inc., Dow/FilmTec Corporation, and DuPont. 

Hollow fiber refers to a membrane tube of very small diameter (e.g., 200 pm). Such small diameters enable a large membrane area per unit volume of device, as well as operation at somewhat elevated pressures. Hollow-fiber modules are widely used in medical devices such as blood oxygenators and hemodialyzers. The general geometry of the most commonly used hollow-fiber module is similar to that of the tubular membrane, but hollow fibers are used instead of tubular membranes. Both ends of the hollow fibers are supported by header plates and are connected to the header rooms, one of which serves as the feed entrance and the other as the retentate exit. Another type of hollow-fiber module uses a bundle of hollow fibers wound spirally around a core. 

Figure 19.5. The Permasep hollow fiber module for reverse osmosis, (a) Cutaway of a DuPont Permasep hollow fiber membrane module for reverse osmosis a unit 1 ft dia and 7 ft active length contains 15-30 million fibers with a surface area of 50,000-80,000 sqft fibers are 25-250 pm outside dia with wall thickness of 5-50pm (DuPont Co.), (b) The countercurrent flow pattern of a Permasep module.

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