Turbulence promoters, membrane cleaning

Spiral-wound modules consist of several flat membranes separated by turbulence-promoting mesh separators and formed into a Swiss roll (Figure 16.18). The edges of the membranes are sealed to each other and to a central perforated tube. This produces a cylindrical module which can be installed within a pressure tube. The process feed enters at one end of the pressure tube and encounters a number of narrow, parallel feed channels formed between adjacent sheets of membrane. Permeate spirals roward the perforated central tube for collection. A standard size spiral-wound module has a diameter of about 0.1m, a length of about 0.9 m and contains about 5 m2 of membrane area. Up to six such modules may be installed in series in a single pressure tube. These modules make better use of space than tubular or flat sheet types, but they are rather prone to fouling and difficult to clean. 

The spiral-wound configuration tFigure 17-lQ is more conplicated but has a significandy higher surface area per unit volume. With proper design of the channels there will be significant turbulence at the membrane surface that promotes mass transfer. These systems have been used for carbon dioxide recovery, UF of relatively clean solutions and RO. 

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