Design and Configuration of Membrane Modules 12421 Preliminary Remarks

The following informations are valid generally for all possible applications. There are several very different ways to construct membrane modules by the arrangement of the inlet and outlet streams. For example, a three-end module for cross-flow configuration consists of a frame construction for the selected membrane

Table 12.4 Characteristics, advantages and disadvantages of plate and tubular membrane

modules (MUNLV 2003; VDMA 2005).

Tubular membranes

Plate membranes

Tubular module

Capillary module

Hollow fiber module

Plate and frame module

Spiral wound module

Membrane cushion

Active layer

Inside

Out-/inside

Out-/inside

Outside

Outside

Outside

Internal diameter

5.5-25 mm

0.25-5.5 mm

0.04-0.25 mm

Membrane surface area-volume ratio

ca. 80 m2 m~3

ca. 1000 m2 m-3

ca. 10000 m2 m-3

40-100 m2 m-3

ca. 1000 m2 m-3

400 m2 m-3

Configuration

Cross flow

Dead end/cross flow

Dead end

Cross flow

Dead end/cross flow

Dead end/cross flow

Advantages

Low blocking, low pressure drop, gel layer controlled

High surface area-volume ratio, low design costs, permeate back-washing

Very high surface area-volume ratio, low specific membrane costs, stable against high pressure

Simple exchange of membranes, low blocking

High surface area-volume ratio, fewer seals, low design costs

Low pressure drop, low fouling

Disadvantages

Low surface area-volume ratio

Low compression strength

Blockage, pressure drop

Many seals, low surface area-volume ratio

Long permeate ways, no mechanical cleaning, high blockage danger

Low surface area-volume ratio, many seals

Fig. 12.6 Membrane modules in submerged mode. (a) Kubota flat panel, submerged in an unit with bubble dififusor. (b) Zenon hollow fiber module, with air bubbling and a hollow fiber in detail.

Fig. 12.6 Membrane modules in submerged mode. (a) Kubota flat panel, submerged in an unit with bubble dififusor. (b) Zenon hollow fiber module, with air bubbling and a hollow fiber in detail.

material with connections to one inlet (feed) and two outlet streams (permeate and concentrate) and a pump providing the driving pressure. Modules with tubular or plate membranes are described in Table 12.4.

Five principle configurations are commonly found (Stephenson et al. 2000):

• Plate-and-frame modules, commonly known from electrolysis stacks, are often used for micro- and ultrafiltration and less often for reverse osmosis (e.g. Kubota flat panel; Fig. 12.6a). Similarly, there are membrane cushions with permeate spacers and support plates welded together with the plate membranes.

• Spiral-wound modules are the standard configuration for reverse osmosis and nanofiltration modules.

• Membrane cushions are although used in ultra- and nanofiltration modules.

• Hollow fine fiber (Zenon; Fig. 12.6b) and capillary membranes are self-supporting membranes with out-to-in flow direction for hollow fibers and in-to-out flow direction for capillary ones.

• Tubular membranes are used for high turbulence and good cleaning characteristics (Berghof 2005; Fig. 12.7a). An example for a complete process is the Wehr-le ultrafiltration plant in Fig. 12.7b.

Module design has to fulfil the following requirements:

• High ratio of membrane area to module bulk volume.

• Low pressure drop, low energy demand.

• High degree of turbulence on the feed side to promote mass transfer.

• Low costs per unit membrane area.

• Good cleaning management.

Fig. 12.7 Membrane modules in cross-flow mode. (a) Berghof tubular module and membranes. (b) Wehrle, MBR, ultrafiltration plant for the food industry.

Fig. 12.7 Membrane modules in cross-flow mode. (a) Berghof tubular module and membranes. (b) Wehrle, MBR, ultrafiltration plant for the food industry.

For the treatment of a feed with a high suspended solids concentration, the demands for a high membrane area: volume ratio together with a design that facilitates cleaning is inconsistent and a compromise is necessary. Furthermore, hydro-philic behavior, attainable permeate volume flux, cut-off and operational life of the membrane have to be taken into account. Configurations such as dead-end, submerged and cross-flow mode are used for ultra- and microfiltration.

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