Encyclopedia of Environmental Science and Engineering, Volume I and II

218 DESALINATION

5. freezing operates, practically only at the freezing
   point of the final solution, and there can be no mul-
   tistaging to reuse the latent heat of phase transition.

However, the major disadvantage of the freezing processes

is the necessity of washing the ice crystals from adhering

brine, an operation which inevitably consumes part of the

product water.

As in all refrigeration, there are two types of processes

for desalination of seawater:

1. mechanical compression of vapors, and


2. absorption of vapors by a hydrophylic liquid which
   then uses heat energy for desorption by evaporation.
   Both may use other refrigerants in either direct or
   indirect heat transfer relation.

MEMBRANE

TUBE

BOLT

CLEANING FLANGE

FEED

DIAPHRAGM

SUPPORT

DIAPHRAGM

PLATE

FRESH WATER (PERMEATE)

MEMBRANE

MEMBRANE

FILTER PAPER

FILTER PAPER

PLATE

SAMPLING

PERMEATE

MEMBRANE

SUPPORT TUBE

MEMBRANE

TUBE

PRESSURE

SUPPORT TUBE

MEMBRANE

SUPPORT

CONCENTRATE

B

A

FEED

MEMBRANE

FIGURE 18 Schematic diagram of the reverse osmosis and ultrafiltration modules. A, the tube mod-

ule arrangement. B, the plate and frame module arrangement. In the tube module membranes are

formed as tubes with the active layer either inside the tube or the membrane support tube. In the plate

and frame arrangement the membranes are flat sheets put onto the flat support diaphragms.

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