Membrane and Desalination Technologies - TCE Moodle Website

572 J.P. Chen et al.
Shell
Feed
Tube Sheet
Product-Water
Header
Product Water
Fig. 13.3. Schematic drawing of a hollow fiber module.
Hollow Fibers
and flows radially around the fiber bundle toward the outer permeator pressure shell. Water
permeates through the outside wall of the fibers into the hollow fiber bore and is removed
from the tube sheet end of the fiber bundle.
An increase in permeate flux will increase the delivery rate of ions to the membrane
surface and increases salt concentration on the membrane surface, whereas an increase in
feed flow increases turbulence and reduces the thickness of the high concentration layer near
the membrane surface. For a hollow fiber module, the permeate water flow per unit area
of membrane is generally low, and therefore, the concentration polarization is not high on the
membrane surface. Furthermore, the feed water flow must exceed a minimum reject value in
order to minimize concentration polarization and maintain even flow distribution through the
fiber bundle. Typically, a single hollow fiber permeator can be operated at up to half recovery
and meet the minimum reject flow required.
Systems based on this configuration are extremely compact and require relatively little
space because of its extremely high packing density. Its primary disadvantage is that the
configuration is highly susceptible to fouling and is difficult to clean effectively because of
the very small spacing between fibers in the bundle. Thus, extensive pretreatment is required
even on relatively clear feed waters.
3.1.2. Spiral-Wound
The spiral-wound configuration (Fig. 13.4) consists of several flat membranes separated by
the permeate collector channel materials to form a leaf. The edges of the leaf are sealed on