Water Flashcards
Reviewing how water is made and where it is used
Explain the primary purpose of desalination in naval engineering.
The primary purpose of desalination is to produce fresh water for personnel consumption, engineering plant use, steam plant operations, electronic cooling, and other applications.
Describe the principle of operation for a flash-type distilling plant.
In a flash-type distilling plant, feed water is heated and then introduced into stages with decreasing pressure. As the water enters each stage, a portion flashes into vapor, which is then condensed to produce freshwater.
How does a reverse-osmosis distilling plant operate?
In reverse-osmosis distilling plants, feed water is pumped at high pressure through a semi-permeable membrane that allows pure water to pass while restricting the flow of impurities. The purified water is then sterilized and filtered before storage.
Why is high pressure required in reverse-osmosis distilling plants?
High pressure is needed to force water molecules through the semi-permeable membrane, overcoming the natural osmotic pressure that resists the flow of water.
What safety considerations must be taken when using desalinated water within 4 miles of land?
Within 4 miles of land, water may be contaminated by oil, chemicals, and other wastes.
How is water sterilized to ensure it is safe for consumption?
Water must be heated to at least 165°F for 7 seconds or longer to be considered sterilized. Bromine or chlorine is used to sanitize the water.
Explain the role of salinity cells in desalination plants.
Salinity cells are strategically placed throughout the desalination plant to monitor the salinity levels of the fresh water continuously. This ensures that the water remains within acceptable salinity limits and activates auto flow shutoff using solenoid valves if necessary.
What is the significance of “Navy showers” in water conservation efforts?
“Navy showers” are a water conservation technique where water is turned off while lathering and only used for rinsing. This helps conserve limited freshwater resources onboard ships.
What is the role of the feed heater in a flash-type distilling plant?
The feed heater preheats the seawater (feed water) before it enters the distillation stages to improve the efficiency of the distillation process.
Why is reverse osmosis considered more efficient for producing potable water compared to other methods?
Reverse osmosis is considered more efficient because it uses a semi-permeable membrane to remove impurities, requires less energy compared to distillation, and produces water with lower salinity levels suitable for drinking.
What is the purpose of the main condensate system in a naval ship?
o condense steam from the turbines back into liquid and pump the condensate from the main condenser to the main feed system.
What is condensate depression, and why is it important?
It is the amount of subcooling of condensate in the hotwell of the main condenser. Proper condensate depression is important to prevent cavitation in the pumps and to maintain efficiency.
What are the main components of the main feed system?
The components include the Deaerating Feed Tank (DFT), surge tanks, booster pumps, feed regulation valves, main feed pumps, and economizer.
Explain the principle of operation for the level control system in the main feed system.
It uses a closed-loop feedback principle where the actual output is measured, compared with the desired output, and corrections are made as necessary.
Describe how air ejectors work in the main condensate system.
They function as jet pumps powered by auxiliary steam to generate a vacuum (remove air) and non-condensable gases from the main condenser.
