Nstm 531 Volume 3

Front 1

Navy reverse osmosis (RO) desalination plants are designed for service where ____pressure
steam or waste heat is unavailable or the quantities are insufficient to operate distillers. As with vapor
compression distillers,

Back 1

low

Front 2

There are, however, three important differences between RO and conventional
filtration processes:

Back 2

1. osmotic pressure( high in RO)
2. Crossflow operation ( 20 to 30% passes through the membrane)
3. Particle size( ions are seperated because of the limited diffusion

Front 3

Several types of membrane elements are
available commercially in a variety of membrane materials. The two main element types are ?

Back 3

hollow fiber and
spiral wound.

Front 4

At this time, all Navy RO units use what substance for the membrane?

Back 4

polyamide membrane material.

Front 5

The two primary performance characteristics of RO membranes are?

Back 5

salt rejection and water flux.

Front 6

Performance characteristics of RO membranes are affected by?

Back 6

feed temperature, pressure, and salinity.

Front 7

Raising the feed temperature of an RO does what?

Back 7

increases the output of the module

Front 8

For seawater RO, an osmotic pressure of _____ to _____pounds per square inch
(psi) exists across the membrane, requiring fairly high pressures (700 to 1000 psi) of operation

Back 8

350 to 400

Front 9

Conventional
filtration processes typically operate from ___ to ___ psi?

Back 9

10 to 25 psi.

Front 10

If the weaker solution is pure water (solvent) and the concentrated solution is seawater, the resulting
osmotic pressure will be about ____ psi.

Back 10

350

Front 11

a pressure of ____ to ____ psi is required to obtain an acceptable flow of water through the membrane.

Back 11

700 to 1000

Front 12

The currently available RO units usually yield a product water containing less than ____ percent of
the total dissolved solids (TDS) entering with the seawater feed.

Back 12

1%

Front 13

Raising the temperature of the feed _____the output of a module.

Back 13

increases

Front 14

An RO unit can produce boiler quality water by either _____ or _______

Back 14

continuous or batch processing

Front 15

3 types of fouling in an RO system

Back 15

a. Membrane element plugging
b. Membrane scaling
c. Colloidal (biological) fouling.

Front 16

Before entering the RO unit pretreatment system, the seawater is filtered through a _______that removes marine animals and large debris.

Back 16

sea chest strainer

Front 17

In the RO unit, the seawater is first cleansed of the larger and heavier suspended particles by a
______. This removes most particles larger than ____ microns.

Back 17

cyclone seperator, 75 microns

Front 18

The remaining suspended particles down to ____ microns are removed by a series of cartridge filters, each with elements consisting of successively smaller
filter media.

Back 18

3

Front 19

The permeate for potable use is ____ to ensure that it is free of harmful
organisms.

Back 19

brominated

Front 20

After the ship-installed duplex strainer, the entering feed passes through a thermostatically controlled
heater that maintains a feed temperature above ______.

Back 20

35° F

Front 21

The feed next enters the _____ where
the larger and heavier debris, sand and silt, is removed to prevent premature plugging of the cartridge filters.
From the centrifugal separator, the feed then flows through the ____________positioned
for normal operation. The feed then enters the cartridge filters, 20- and 3-micron filter media in series, to remove
the remaining suspended particles that could foul the membrane.

Back 21

centrifugal separator, three-way feed selector valve (V-2),

Front 22

The cleaned feed next enters the high-pressure (HP) pump, which increases the pressure to approximately
_____.

Back 22

800 psi

Front 23

The permeate leaves the module from the center collection port and passes by the ________,
which measures salinity.

Back 23

conductivity cell

Front 24

If the permeate is out of specification, (that is, greater than ____________) it is automatically
dumped to the bilge.

Back 24

1,000 micromhos/cm

Front 25

The centrifugal separator
is designed to remove _____ percent, by weight, of separable solids 200 mesh (74 microns, or 0.003 inch) and
larger.

Back 25

98%

Front 26

The heater prevents freezing on the freshwater side of the membrane modules when the
seawater temperature is below _____.

Back 26

32° F

Front 27

The heater contains a built-in thermostat that activates the heating element when the
seawater temperature drops below _______ and deactivates the element when the temperature rises above _____.

Back 27

35° F,38° F

Front 28

The activated carbon filter removes the _______ or __________, which is harmful to the polyamide membrane, from the freshwater in the storage tank before it is used for flushing or
cleaning the RO unit.

Back 28

bromine or chlorine