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28 Cards in this Set
- Front
- Back
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, |
low
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There are, however, three important differences between RO and conventional
filtration processes: |
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 |
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Several types of membrane elements are
available commercially in a variety of membrane materials. The two main element types are ? |
hollow fiber and
spiral wound. |
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At this time, all Navy RO units use what substance for the membrane?
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polyamide membrane material.
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The two primary performance characteristics of RO membranes are?
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salt rejection and water flux.
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Performance characteristics of RO membranes are affected by?
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feed temperature, pressure, and salinity.
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Raising the feed temperature of an RO does what?
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increases the output of the module
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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 |
350 to 400
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Conventional
filtration processes typically operate from ___ to ___ psi? |
10 to 25 psi.
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If the weaker solution is pure water (solvent) and the concentrated solution is seawater, the resulting
osmotic pressure will be about ____ psi. |
350
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a pressure of ____ to ____ psi is required to obtain an acceptable flow of water through the membrane.
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700 to 1000
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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. |
1%
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Raising the temperature of the feed _____the output of a module.
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increases
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An RO unit can produce boiler quality water by either _____ or _______
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continuous or batch processing
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3 types of fouling in an RO system
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a. Membrane element plugging
b. Membrane scaling c. Colloidal (biological) fouling. |
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Before entering the RO unit pretreatment system, the seawater is filtered through a _______that removes marine animals and large debris.
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sea chest strainer
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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. |
cyclone seperator, 75 microns
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The remaining suspended particles down to ____ microns are removed by a series of cartridge filters, each with elements consisting of successively smaller
filter media. |
3
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The permeate for potable use is ____ to ensure that it is free of harmful
organisms. |
brominated
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After the ship-installed duplex strainer, the entering feed passes through a thermostatically controlled
heater that maintains a feed temperature above ______. |
35° F
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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. |
centrifugal separator, three-way feed selector valve (V-2),
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The cleaned feed next enters the high-pressure (HP) pump, which increases the pressure to approximately
_____. |
800 psi
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The permeate leaves the module from the center collection port and passes by the ________,
which measures salinity. |
conductivity cell
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If the permeate is out of specification, (that is, greater than ____________) it is automatically
dumped to the bilge. |
1,000 micromhos/cm
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The centrifugal separator
is designed to remove _____ percent, by weight, of separable solids 200 mesh (74 microns, or 0.003 inch) and larger. |
98%
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The heater prevents freezing on the freshwater side of the membrane modules when the
seawater temperature is below _____. |
32° F
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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 _____. |
35° F,38° F
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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. |
bromine or chlorine
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