Horizon Reverse Osmosis Seafari Versatile SFC-1400-2 Owner'S Manual Download Page 21

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HRO

Systems

Horizon

Seafari

“Section C” Introduction

2. PRINCIPLES OF REVERSE OSMOSIS:

A. OSMOSIS:

Osmosis can be defined as the

spontaneous passage of a liquid from a dilute to a
more concentrated solution across an ideal semi-
permeable membrane which allows the passage
of the solvent (water) but not the dissolved solids
(solutes).

B. OSMOTIC PRESSURE:

The transfer of the water

from one side of the membrane to the other
continues until the head (pressure) is large
enough to prevent any net transfer of the solvent
(water) to the more concentrated solution. At
equilibrium, the quantity of water passing in
either direction is equal, and the pressure is then
defined as the Osmotic Pressure of the solution
having that particular concentration of dissolved
solids.

C. REVERSE OSMOSIS:

As described above, water

continues to flow from the pure water side of the
membrane to the saline solution side until the
pressure created by the high pressure pump on
the saline solution side of the membrane equals
the osmotic pressure. If the pressure of the saline
solution is increased until it exceeds the osmotic
pressure, water is forced to flow through the
membrane from the solution containing the
higher salt concentration into the solution with
the lower salt concentration. The process is
called Reverse Osmosis.

D. SPIRAL-WOUND MEMBRANE:

The spiral-

wound membrane consists of one or more
membrane envelopes each formed by enclosing a
channelized product water carrying material
between two large flat membrane sheets. The
membrane envelope is sealed on three edges with
a special adhesive and attached with the adhesive
to a small diameter pipe to form a cylinder 2, 4, 6,
8, or 12 inches in diameter and up to 40 inches in
length. A polypropylene screen is used to form
the feed water channel between the membrane
envelopes. A wrap is applied to the membrane
element to maintain the cylindrical configuration.
The center tube is also the permeate (product
water) collecting channel. Several elements may
be connected in series within a single or multiple
pressure vessel(s).

E. BOUNDARY LAYER CONCENTRATION

POLARIZATION:

When water permeates

through the membrane, nearly all the salt is left
behind in the brine channel. In any dynamic
hydraulic system the fluid adjacent to the wall of
the vessel is moving relatively slowly. Even
though the main body of the stream is turbulent, a
thin film adjacent to the wall (membrane) is
laminar. This thin film is called the boundary
layer. When the dissolved salts, at the Boundary
Layer become concentrated beyond permissible
limits then these salts adhere to the membrane
surface. This concentration of salts at the
membrane surface is referred to as Concentration
Polarization. Concentration Polarization is
caused by excessive recovery (percentage of
product water recovered from the feed water).

F. COMPACTION:

Some densification of the

membrane structure may take place while
operating at elevated pressures, above 1000 psi.
The change is known as compaction and is
accompanied by a reduction in the water
permeation rate.

G. WATER TEMPERATURE EFFECT

The

product water flow through the membrane is
significantly affected by the water temperature.
At any given pressure this flow increases with
increasing water temperature and is reduced at
lower temperatures.

H. PRESSURE:

The operating pressure has a direct

affect on product water quality and quantity.
Both factors increase as the system pressure
increases (within design limits). The system must
be operated at the lowest pressure required to
achieve the designed product water flow rate.
This parameter also affects compaction, which
proceeds at a faster rate at higher pressures as
well as at higher temperatures.

I. BRINE VELOCITY:

The brine flow over the

membrane surface is very important to both
product water quality and quantity. At low flows,
concentration polarization occurs, causing the
water quality to decline. In addition to inferior
product water quality, low brine flows can
increase the precipitation of sparingly soluble
salts, which foul the membrane surface. If this
occurs, the product water flux (production)
declines.

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