Tubular membrane modules

Membrane module Tubular, hollow fiber Tubular, hollow fiber. Tubular, spiral wound, plate Tubular, spiral wound. 

Tubular membranes Tubular modules Tubular reactors Tubulates b-Tubulin Tubulin Tuffs Tufperm Tufprene... 

Tubular Modules. Tubular modules are generally limited to ultrafiltration appHcations, for which the benefit of resistance to membrane fouling because of good fluid hydrodynamics overcomes the problem of their high capital cost. Typically, the tubes consist of a porous paper or fiber glass support with the membrane formed on the inside of the tubes, as shown in Figure 24. 

Membrane systems consist of membrane elements or modules. For potable water treatment, NF and RO membrane modules are commonly fabricated in a spiral configuration. An important consideration of spiral elements is the design of the feed spacer, which promotes turbulence to reduce fouling. MF and UF membranes often use a hollow fiber geometry. This geometry does not require extensive pretreatment because the fibers can be periodically backwashed. Flow in these hollow fiber systems can be either from the inner lumen of the membrane fiber to the outside (inside-out flow) or from the outside to the inside of the fibers (outside-in flow). Tubular NF membranes are now just entering the marketplace. 

If the pressure drop across a tubular membrane is 2.8 bars, determine the permeat velocity across the membrane module. The thickness and the porosity of the deposit are 2 mm and 40 %, respectively. The average diameter of the partices is 5 microns. The initial membrane resistance is estimated to be 1.7 X 10 1/m. 

The concept of cross-flow microfiltration is shown in Figure 16.11, which represents a cross-section through a rectangular or tubular membrane module. The particle-containing fluid to be filtered is pumped at a velocity in the range 1-8 m/s parallel to the face of the membrane and with a pressure difference of 0.1-0.5 MN/m2 (MPa) across the membrane. The liquid penneates through the membrane and the feed emerges in a more concentrated form at the exit of the module.1617 All of the membrane processes are listed in Table 16.2. Membrane processes are operated with such a cross-flow of the process feed. 

Industrial membrane plants often require hundreds of thousands of square metres of membrane to perform the separation required on a useful scale. Before a membrane separation can be used industrially, therefore, methods of economically and efficiently packaging large areas of membrane are required. These packages are called membrane modules. The areas of membrane contained in these basic modules are in the range 1-20 m2. The modules may be connected together in series or in parallel to form a plant of the required performance. The four most common types of membrane module are tubular, spiral, wound and hollow fibre. 

Membrane module network design, in reverse osmosis, 21 666 Membrane modules, 15 818-824 21 636 hollow-fiber, 15 819-821, 823 plate-and-frame, 15 821 selecting, 15 821-824 spiral-wound, 15 818-819, 823-824 tubular, 15 821... 

Tubular loop reactors, 25 710 Tubular membrane modules, 25 821 Tubular pervaporation modules,... 

Figure 19.3. Tubular and plate-and-frame membrane modules for reverse osmosis and ultrafiltration, (a) Construction and flow pattern of a single 1 in. dia tube with membrane coating on the inside in Table 19.4, the Ultracor model has seven tubes in a shell and the Supercor has 19 [Koch Membrane Systems (Abcor)]. (b) Assembly of a plate-and-frame ultrafiltration module (Danish Sugar Co.), (c) Flow in a plate-and-frame ultrafiltration module.

Spiral-wound modules were used in a number of early artificial kidney designs, but were fully developed for industrial membrane separations by Gulf General Atomic (a predecessor of Fluid Systems, Inc.). This work, directed at reverse osmosis membrane modules, was carried out under the sponsorship of the Office of Saline Water [112-114], The design shown in Figure 3.42 is the simplest, consisting of a membrane envelope of spacers and membrane wound around a perforated central collection tube the module is placed inside a tubular pressure vessel. Feed passes axially down the module across the membrane envelope. A portion of the feed permeates into the membrane envelope, where it spirals towards the center and exits through the collection tube. 

Both Mitsui [26] and Sulzer [27] have commercialized these membranes for dehydration of alcohols by pervaporation or vapor/vapor permeation. The membranes are made in tubular form. Extraordinarily high selectivities have been reported for these membranes, and their ceramic nature allows operation at high temperatures, so fluxes are high. These advantages are, however, offset by the costs of the membrane modules, currently in excess of US 3000/m2 of membrane. 

Salts rejected by the membrane stay in the concentrating stream but are continuously disposed from the membrane module by fresh feed to maintain the separation. Continuous removal of the permeate product enables the production of freshwater. RO membrane-building materials are usually polymers, such as cellulose acetates, polyamides or polyimides. The membranes are semipermeable, made of thin 30-200 nanometer thick layers adhering to a thicker porous support layer. Several types exist, such as symmetric, asymmetric, and thin-film composite membranes, depending on the membrane structure. They are usually built as envelopes made of pairs of long sheets separated by spacers, and are spirally wound around the product tube. In some cases, tubular, capillary, and even hollow-fiber membranes are used. 

In Table 16.2 some of the typical characteristics of the various types of membranes and configurations are given. In MBR systems SW membrane modules are not used as the channels within the spiral are prone to clogging when the feed water has high suspended-solids concentrations. Tubular membrane systems are not common either as they tend to become very expensive due to the low area to volume ratio. Commercial MBR systems today are normally based on immersed FS configurations or H F/CT configurations. 

FIGURE 5 Membrane module design, (a) Spiral-wound (Koch Membrane Systems) (b) hollow-fiber (Du Pont) (c) tubular (generic) (d) plate-and-frame (c) pleated cartridge (Millipore). [Figure 2(d) from Strathmann and Chmiel (1985)]. 

There are four basic forms for RO membrane modules Plate and frame, tubular, spiral wound, and hollow fine fiber. These four configurations are summarized in Table 4.3 and discussed below. Additionally, some manufacturers have developed other module configurations that are briefly discussed in Chapter 4.3.5. 

Figure 4.13 Tubular RO membrane module. Membrane tubes are placed in series in the housing.

Most tubular membrane modules are used for specialty microfiltration (MF) and ultrafiltration (UF) applications rather than RO due to the lower packing density of this type of module and because MF and UF typically treat higher-solids feed water (see Chapter 16.1). 

Microfiltration and UF membranes are available in tubular, spiral wound, and hollow fiber membrane module configurations. Tubular and spiral MF and UF modules are similar to RO tubular and spiral wound membrane modules described in Chapters 4.3.2 and 4.3.3. However, while the thickest feed spacer in a spiral RO module is 34-mil, UF and MF modules nominally have up to a 45-mil spacer due to the relatively high concentration of suspended solids these membranes are called upon to treat (TriSep Corporation offers a special 65-mil spacer for dairy applications). 

Hollow fiber membrane modules can be backwashed to remove foulants whereas tubular and most spiral configurations cannot be backwashed. Backwashing of traditional spiral-wound modules would break the glue lines holding the membrane leaves together or cause blistering and delamination of the membrane from the backing in both spiral and tubular modules (TriSep Corporation has recently developed a back-washable, spiral-wound module (SpiraSep—US patent 6,755,970), that is used in immersed systems see below). 

Membranes are used to separate gaseous mixtures or liquid mixtures. Membrane modules can be tubular, spiral-wound, or plate and frame configurations. Membrane materials are usually proprietary plastic films, ceramic or metal tubes, or gels with hole size, thickness, chemical properties, ion potential, and so on appropriate for the separation. Examples of the kinds of separation that can be accomplished are separation of one gas from a gas mixture, separation of proteins from a solution, dialysis of blood of patients with kidney disease, and separation of electrolytes from non electrolytes. 

Yoshino, Y., Suzuki, T., Nair, B.N., Taguchi, H., and Itoh, N., Development of tubular substrates, silica based membranes and membrane modules for hydrogen separation at high temperature, Journal of Membrane Science, 267, 8-17, 2005. 

Two types of connection (and therefore sealing) are involved in assembling membrane modules. The first type connects tubular or monolithic membrane elements in bundles using header plates at the ends and, in some cases, in the middle of the module length. The second type provides sealing between the plates and the module housing. 

Figure 3 Possible module configurations for IMRs. (a) Flat membranes (b) tubular membranes.

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