Tubular membrane modules applications

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). 

The tube-and-shell, or tubular, membrane module is easily adapted for use with drawn tubular membranes as well as membranes that are made by depositing a thin permselective metal layer onto a porous tube support. There are three significant variants to this module design. One is based on the membrane tubes fixed to a header at each end of the membrane tube. The second is similar in that both ends of the membrane tubes are fixed to a header, but to the same header. In the second design, the membrane tubes are bent into a U shape, which can be easily done with small diameter metal tubes. The third is based on a single header, to which open sides of closed-one-ended membrane tubes are fixed. The closed-ends of the membrane tubes are suspended freely. This latter design is more common for commercial applications, due to free thermal expansion and greater membrane durability (see above discussion), whereas laboratory test-and-evaluation practices favor the first variant for its ease of assembly. If the membrane is a drawn, thin-walled tube, the membrane tube will usually be brazed to the header. This is more difficult if the membrane tubes are to be fixed at both ends to head-... 

The added-particle effect is also evident in the application of fluidized beds to provide turbulence promotion. Figure 10.46 is a schematic diagram of a combined tubular membrane-fluidized bed system. It consists of a tubular membrane module, fluidized particles, a feed pump, and the feed storage tank. During the operation, the particles are fluidized... 

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). 

Shell-and-tube modules (Fig. 3b) seem to be more promising than flat-membrane ones, since they can develop up to 250 mVm [13]. Indeed, most of the recent literature on membrane reactors concerned tubular membranes. The lower the tube diameter, the higher the specific surface areas attainable. However attempts to manufacture hollow-fiber supported ceramic membranes were not completely satisfactory owing to the unacceptable brittleness of the obtained membranes from the practical application viewpoint [16-18]. 

The heat in the exit gas is recovered downstream the tubular reformer, usually by the production of steam, preheating of boiler feed water, etc. The final separation into the desired product compositions depends on the application. Pressure swing adsorption (PSA) is in most cases used if pure hydrogen is desired. Pure carbon monoxide can be obtained by cryogenic separation in a cold box. Adjustment of the H2/CO ratio can be accomplished by polymer membrane modules with different selectivities for permeation of the two compounds. 

Membrane bioreactors have been modelled using approaches that have proven successful in the more conventional catalytic membrane reactor applications. The simplest membrane bioreactor system, as noted in Chapter 4, consists of two separate units, a bioreactor (typically a well-stirred batch reactor) coupled with an external hollow fiber or tubular or flat membrane module. These reactors have been modelled by coupling the classical equations of stirred tank reactors with the mathematical expressions describing membrane permeation. What makes this type of modelling unique is the complexity of the mecha-... 

For industrial applications, large surface areas are obtained using modules with many tubular or hollow-fiber membranes or by using large sheets in a spiral-wound arrangement. Tubular membranes are 5 to 25 mm inside diameter and up to 3 m long. Hollow-fiber UF membranes have diameters of 0.2 to 2 mm, and thousands of fibers are sealed in each cylindrical module. Spiral-wound modules of the type used for RO are widely used for UF. 

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