Spiral wound membrane geometry

Spiral Wound The spiral-wound membrane geometry in MF and UF is not widely used in surface water treatment because spiral-wound membranes cannot be backwashed, and extensive pretreatment is therefore required to keep the membrane from clogging. However, there are some applications in groundwater treatment where surface water UF membranes are applied to remove color (Nystrom et al., 1999). In the spiral-wound configuration, two flat sheets of membrane are separated with a permeate collector channel material to form a leaf. This assembly is sealed on three sides, with the fourth side left open for permeate to exit. A feed/brine spacer material sheet is also included in the leaf assembly. A number of these assemblies or leaves are wound around a central plastic permeate tube. This tube is perforated to collect the permeate from the multiple leaf assemblies (Hydranautics, 2001). Most commercial lengths are 1 or 1.5 m and 20 cm in diameter (Fig. 6.7). 

Membranes are manufactured in a diverse range of geometries they include flat, tubular, and multi-tubular, hollow-fiber, and spiral-wound membranes. The type of geometry the membrane is manufactured into depends on the material the membrane is made from. Ceramic membranes, generally, come in tubular, multi-tubular and flat geometries, whereas spiral-wound and hollow-fiber membranes seem, for the most part (with a few notable examples), to be made from polymers. 

Common types of membrane materials used are listed in Table 3. This gets us into the concept of geometry. There are three types of modules generally used, namely Tubular, Spiral wound, and Hollow fiber. A comparison of the various geometries is given in Table 4. 

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. 

Design of the membrane module system involves selection of the membrane material the module geometry, eg, spiral-wound or hollow-fiber product flow rate and concentration solvent recovery operating pressure and the minimum tolerable flux (9,11). The effects of these variables can be obtained from laboratory or pilot experiments using different membranes and modules. The membrane module as well as the solvent recovery can be chosen to minimize fouling. Spiral-wound modules are widely used because these offer both high surface area as well as a lower fouling potential. 

A comprehensive presentation of all membrane types, modules and geometries is beyond the scope of this chapter, reference available membrane books for details [12,17, 55, 60, 71, 77,90]. The examples in Figure 16.2 are an illustration of a typical membrane module and installation. The most widespread FS membrane system is mounted as a spiral-wound (SW) unit. In the SW example the actual membrane module is shown together with how they are mounted inside a pressure vessel. A typical installation is shown where several pressure vessels are subsequently mounted in a stack. Pressurized HF units are typically operated as a crossflow system. In the example shown the HF modules are mounted vertically and arranged in a skid. Several variations of the theme can be found depending on the type of module and the manufacturer, where Figure 16.2 is not specific to a particular item. 

Liquid impregnated (or immobilized) in the pores of a thin microporous sohd support is defined as a supported liquid membrane (SLM or ILM). The SLM may be fabricated in different geometries. Flat sheet SLM is useful for research, but the surface area to volume ratio is too low for industrial applications. Spiral-wound and hoUow-fiber SLMs have much higher surface areas of the LM modules (103 and 104 m /m, respectively [23]). The main problem of SLM technology is the stability the chemical stability of the carrier, the mechanical stability of porous support, etc. 

A further generality of the MDPE is that knowledge of the actual shape and geometry of the membrane within the MCS is not necessary. The equation is not restricted, and can be applied to any chosen shape (plate module, hollow fiber, spiral wound, and so on). 

Depending on their geometry, the membranes can be subdivided in tubular, hollow fibre, spiral wound saAflat sheet [10] ... 

The performance of membrane processes also relies on the use of correct module configurations (Zhou Smith, 2002). Typical commercial manbrane geometries are flat sheet and mbular. There are five module types plate-and-flame and spiral-wound modules, based on flat membranes, and tubular, capillary and hollow-fibre modules, based on tubular membrane geometries (Basile, 2013). A qualitative comparison amongst some of the different model configurations is presented in Table 20.7. 

Membranes can be subdivided into four categories according to their geometry tubular, hollow fiber, spiral wound and flat sheet (Basile et al, 2011). Tubular membranes are used most frequently, even though they require relatively high volumes and involve high costs. 

Supported Liquid Membranes. A SLM can be fabricated in at least three different geometries. Planar or flat sheet SLMs are very useful for laboratory research and development purposes, but the surface area to volume ratio of flat sheets is too low for industrial applications. Spiral wound and hollow fiber geometries can... 

In all these endeavors, rigorous or approximate, transport parameters play a key role and must be addressed first. They are dependent on a number of variables, including flow conditions, membrane and module geometry, and the specific membrane process being addressed. Thus, the flow can be laminar or turbulent, involve gases or liquids, or take place in hollow-fiber or spiral-wound geometries. We listed some of these features and the resulting transport parameters in Table 8.8. 

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