Fresh Water Makers Flashcards
Which of the following desalination plants will always require a sterilizer when providing water to a potable water system? A Titanium plate type unit B Multi-stage flash type unit C Submerged tube type unit D Reverse osmosis type unit
D Reverse osmosis type unit
In order for a reverse osmosis fresh water generator to be able to overcome the osmotic pressure without damaging the spiral-wound membrane modules, the pressure must be controlled. What is the location of the pressure regulator?
Brine outlet from the membrane modules.
Which of the following fresh water generators has an operating principle that evaporates pre-heated sea water by causing it to undergo a pressure drop into a vacuum? A Submerged tube unit B Flash type unit C Titanium plate unit D Reverse osmosis unit
B Flash type unit
A high reading is only indicated at the salinity cells labeled “W” and “6” shown in the illustration. This would be the probable result of __________. GS-0053
a faulty cell at location “6” and a tube leak in item “I”
If a reverse-osmosis freshwater generating unit has a high salinity alarm associated with the freshwater outlet, what should be done?
The membrane modules should be flushed and cleaned.
What is the BEST indication that the pre-treatment filter (or filters) of a reverse- osmosis freshwater generator must be serviced by cleaning or replacement?
An excessive pressure drop across the pre-treatment filter.
What is the BEST indication that the membrane module is damaged and is no longer semi-permeable and allowing the solute to pass through?
High freshwater outlet salinity.
A high reading at a salinity cell located in the loop seal between two stages of a flash type evaporator would indicate __________.
carryover in the first-stage
A high reading is indicated at the salinity cells labeled “Y”, “Q”, and “6” shown in the illustration. This would be the probable result of __________. GS-0053
carryover from “III”
The quantity and density of brine discharged from the last effect of a flash type evaporator should be kept at a constant value so as to __________.
ensure distillate quality and distilling plant efficiency
Which of the listed problems could produce a high absolute pressure within a flash type evaporator? A seawater feed temperature below 165*F B a cracked distillate pump vent line C production of high salinity distillate D a leak in the first stage demister
B a cracked distillate pump vent line
If the demister used in the device shown in the illustration is improperly installed, which of the following will occur? See Illustration MO-0110
There will be an increase of chlorides measured at the distillate pump salinity cell.
Which of the following conditions can cause high salinity of the distillate due to sea water leakage in the illustrated device. MO-0110
Failure to properly tighten the bolts of the condenser heat exchanger.
Which of the conditions listed would indicate a large condenser tube leak within the distiller shown in the illustration? See Illustration MO-0111
The activation of the salinity monitoring equipment’s annunciator circuit.
A salinity indicator is used to determine the __________.
location of salt water contamination
A salinity indicating system functions on the basic principle of measuring the __________.
electrical conductivity of water
In a flash-type evaporator, an electrical salinity cell would be installed in the __________.
A distillate outlet from the distillate cooler
B distillate inlet to the distillate cooler
C condensate drains from the distiller feed water heater
D all of the above
D all of the above
Which of the following statements represents the basic principle of operation of an electrical salinity indicator?
A Measures the hydrogen ion concentration.
B Measures the voltage of the chloride ions.
C Measures the electrical resistance of the water.
D Determines the conductivity of the dissolved oxygen.
C Measures the electrical resistance of the water.
A salinity indicator system such as that used to measure the salt content of potable water systems and boiler feed and condensate systems uses what technology?
a salinity cell that senses the electrical conductivity of water
If the salinity indicator periodically registers high salinity in the main hot well, the cause may be __________.
a contaminated distilled water tank
Indicated high salinity of the distillate discharged from a flash-type distilling plant will be a result of __________.
leaks in the demister baffles
Regarding a freshwater generator of the reverse-osmosis type, what statement is true?
A The solute is salt and the solvent is fresh water.
B The solute is fresh water and the solvent is salt.
C The solute is saltwater and the solvent is salt.
D The solute is salt and the solvent is saltwater.
A The solute is salt and the solvent is fresh water.
reverse-osmosis freshwater generators usually feature multiple membrane modules, typically of the spiral-wound membrane type. How are these multiple membrane modules piped?
The multiple membranes may be connected in series, parallel, or in some combination of series and parallel.
Regarding a reverse-osmosis type freshwater generator using multiple spiral-wound membrane modules, what statement is true?
A Modules may be piped in series to increase the freshwater throughput.
B Modules may be piped in series to increase the freshwater purity.
C Modules may be piped in parallel to increase the freshwater purity.
D Modules may be piped in series to decrease the likelihood of fouling.
B Modules may be piped in series to increase the freshwater purity.
To ensure potable water of drinking quality, chemical treatment is required for reverse- osmosis freshwater generators. What is the purpose of chemical pre-treatment?
Chemical pre-treatment sterilizes the sea water entering the unit to prevent bacteria from becoming resident in the reverse-osmosis unit filters and membrane modules.
Regarding the operating principle of a reverse-osmosis type freshwater generator, what statement is true?
External pressure is applied to the side of strong concentration forcing freshwater through the semi-permeable membrane to the side of weak concentration.
Regarding the high-pressure pump of a reverse-osmosis freshwater generator, what statement is true?
The high-pressure pump is typically a multiple-cylinder reciprocating pump, but may be a multi-stage centrifugal pump.
For the successful operation of a reverse-osmosis freshwater generator, why is the high pressure pump required to operate in the 750 to 1200 psig range for a discharge pressure?
To overcome the osmotic pressure generated by the difference in solution concentrations.
For the successful operation of a reverse-osmosis freshwater generator, the setting of the brine back pressure regulator is critical. What statement regarding the set point of this regulator is true?
If the regulator setting is set too high, the membrane modules may be damaged. If the regulator setting is too low, the freshwater production will be too low.
What component of a reverse-osmosis freshwater generator could be isolated and replaced with the unit remaining in service?
A parallel-connected membrane module.
Under what conditions would the pre-treatment capabilities of a reverse-osmosis freshwater generator MOST likely be overloaded, and as a result, these conditions should generally be avoided?
Entering harbors.
When a reverse-osmosis freshwater generator is shutdown, what must be accomplished?
The unit must be flushed with freshwater and treated with an anti-bacterial growth inhibitor.
Which of the freshwater generators listed below is operated without a source of heat? A Titanium plate type B Flash type C reverse-osmosis type D Submerged tube type
C reverse-osmosis type
Which of the following freshwater generators has an operating principle that requires it to run under a substantially positive pressure? A Submerged tube unit B Titanium plate unit C reverse-osmosis unit D Flash type unit
C reverse-osmosis unit
In which of the following freshwater generators would an air ejector be unnecessary? A reverse-osmosis unit B Submerged tube unit C Titanium plate unit D Flash type unit
A reverse-osmosis unit
Which of the freshwater generators listed below requires a source of heat and evaporates sea water at a location other than a heat exchanger surface? A Submerged tube type B reverse-osmosis type C Titanium plate type D Flash type
D Flash type
If a reverse-osmosis freshwater generator has fouled membrane modules, what statement is true?
The freshwater production rate would be lower than normal, and the feed pressure would be higher than normal.
In a two-stage flash evaporator, the sea water feed temperature is increased as it passes through the \_\_\_\_\_\_\_\_\_\_. A first-stage distilling condenser B second-stage distilling condenser C salt water feed heater D all of the above
D all of the above
In a flash evaporator, heated water under pressure is converted into vapor by suddenly __________.
decreasing its pressure
If the orifice in the loop seal of a flash evaporator were to become significantly enlarged through erosion, the __________.
evaporator absolute pressure could eventually equalize in both stages to that of the second stage
Other than taking a scale thickness through a zinc plug opening of the water box of a feed water heater of a flash evaporator, what would be the BEST indication for a need to remove scale build-up?
A rise in the feed water heater shell temperature and a rise in the feed water heater shell absolute pressure (decrease in vacuum).
What procedure can be used to reduce the rate of scale formation on the heating surfaces of a flash evaporator while still maintaining the desired rate of distillate production?
Chemically treating the incoming feed water.
Where a two-stage air ejector set is used in a two-stage flash evaporator, the first-stage air ejector takes suction from the second stage of the evaporator, and the second stage air ejector __________.
takes suction from the first stage ejector discharge
A fixed orifice plate is generally installed in the live steam supply to a flash evaporator. One of the functions of this orifice is to control the quantity of the supplied steam. A second function is to __________.
reduce pressure fluctuations of the steam supply in the salt water feed heater
The thickest deposit of scale in a flash evaporator is most likely to occur in the tubes of the __________.
saltwater feed heater
In a flash evaporator, scale as a result of higher than normal temperatures is most likely to occur in the __________.
saltwater feed heater
If a higher than normal water level is observed through the inspection port of a flash evaporator, you should suspect __________.
a malfunctioning brine pump
Irregular feeding or surging of the feed water supply to a flash evaporator may be attributed to __________.
a dirty strainer in the salt water feed pump suction line
A multistage flash evaporator will be unable to produce consistently pure distillate if the __________ .
vacuum is fluctuating
An excessively high brine level in a flash evaporator can be caused by __________ .
failure of the brine pump
In a two stage flash evaporator, heated feed water is vaporized in the __________ .
first and second stage flash chambers
In which of the areas listed would you expect to find the highest salt concentration in a flash evaporator? A Distiller air ejector cooling medium B Saltwater heater discharge C First-stage internal feed box D Second-stage internal feed box
D Second-stage internal feed box
In which of the following types of evaporators is the control of brine density least important? A Solo shell evaporators B flash evaporators C Submerged tube evaporators D Basket evaporators
B flash evaporators
Irregular feeding or surging of the feedwater supply to a flash evaporator may be attributed to __________ .
a dirty strainer in the saltwater feed pump suction line
Less scale formation occurs in a flash evaporator than in a submerged tube evaporator because __________ .
no boiling occurs on heat transfer surfaces
One distinct advantage of flash type evaporators, as compared to most other evaporators, is that in a flash evaporator shell __________ .
scale formation is not a severe problem
The condensers located in the various stages of a flash evaporator are cooled by __________ .
seawater
The distillate produced by a flash evaporator has a salinity of 0.21 grains per gallon, with a feed water temperature entering the first-stage of the evaporator at 170°F. Under these conditions the three-way solenoid valve will __________.
direct distillate to the freshwater tanks
The first stage feedwater temperature and shell absolute pressure in a multistage flash evaporator is __________ .
higher than the second stage feedwater temperature and shell absolute pressure
Tube leaks in the distillate cooler of a two stage flash evaporator will result in __________ .
contamination of the distillate
Vapor is produced in a flash evaporator by introducing __________.
heated water into a low pressure area
What is the main reason that live auxiliary steam is normally attemporated before entering the feed heater of a flash evaporator?
To reduce the rate of scale formation on heating surfaces.
When a flash evaporator is being operated in extremely cold water, you may need to throttle the seawater supply to __________.
maintain the feedwater temperature above the required minimum input temperature
Which of the listed conditions will cause the feed water, that has not flashed to vapor in the first-stage of a flash evaporator, to flow into the second-stage?
Higher vacuum in the second-stage
While in operation, the function of the orifice in the flash evaporator loop seal is to __________ .
maintain the absolute pressure difference between the first and second stages
Small droplets of water entrained in the flashed vapor produced in a flash-type evaporator are removed by the __________.
demisters
In order to prevent salt water contamination of the distillate in a flash-type evaporator, it is important to provide a positive seal around the __________ .
demisters
The demisters installed in a flash-type evaporator serve to __________.
remove small water droplets entrained in the flashed vapor
The process of boiling seawater in order to separate it into freshwater vapor and brine is usually defined as __________.
evaporation
Which of the following statements is correct relative to distillation plant operation?
Distillation is the process of boiling seawater to produce vapor which is condensed into fresh water.
The efficiency of a flash type evaporator can be increased by __________.
decreasing the absolute pressure of each stage
Diesel engine jacket water is used in the fresh water distillation process as the __________.
means of heating the feed water
The brine level in the second-stage of a flash-type evaporator is determined in part by the feed rate, the rate of evaporation in both stages, and the __________.
throughput of the brine overboard pump
What is the BEST indication that the membrane module is damaged and is no longer semi-permeable and allowing the solute to pass through?
High freshwater outlet salinity.
In a two-stage flash-type distilling plant, the mesh-type vapor separators function to __________ .
improve distillate purity
The vapor separators installed in some distilling plants consist of several rows of vertical hooked vanes which remove entrained moisture from the vapor by __________ .
abruptly changing the direction of vapor flow
