Reverse Osmosis: Modern Alternative for Shipboard Water Production
Every ship is installed with fresh water production unit which produces fresh water from sea water. The efficient water production unit of the ship helps the vessel owner to save on additional fresh water expenses that are incurred by purchasing water from port suppliers.
Two popular methods for production of fresh water on ships include:
- Reverse osmosis process.
Reverse osmosis is one of the modern methods used by the shipping industry to produce fresh water from sea water. This method of water production does not use waste heat source, unlike fresh water generator, to desalinate the sea water to convert it into fresh water with low salt ppm.
Principle of Reverse Osmosis
As the name suggest, this methods works on reversing the osmosis principle.
When a chemical solution is separated from pure water by a semi permeable membrane (allowing passage of water not salt) then the pure water flows through the membrane until all the pure water has passed through or until the hydrostatic pressure head of the salt solution is sufficiently big enough to arrest or stop the process.
Reverse osmosis is the use of this phenomenon in reverse direction. This results in water being forced through the membrane from the concentrated solution toward the more dilute one. This is achieved by applying pressure of the osmotic pressure of the concentrated solution.
Working
The osmotic pressure of sea water is 28 bars but to overcome system losses and the fact that the sea water concentration increases as it passes through the length of the membrane, much higher pressure around 40-70 bar, depending upon the plant size, is required.
A triplex plunger pump is popularly used to produce high pressure across the membrane. The membrane used has a very fine barrier of dense holes which only allows water and gases to pass through, while preventing the passage of solutes such as salt and other impurities.
The fresh water produced after this stage is treated with chemicals and ultraviolet treatment to make it drinkable and useful for other purpose.
You may also like to read-Sewage Treatment Plant on a Ship Explained
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Disclaimer :
The information contained in this website is for general information purposes only. While we endeavour to keep the information up to date and correct, we make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, suitability or availability with respect to the website or the information, products, services, or related graphics contained on the website for any purpose. Any reliance you place on such information is therefore strictly at your own risk.
In no event will we be liable for any loss or damage including without limitation, indirect or consequential loss or damage, or any loss or damage whatsoever arising from loss of data or profits arising out of, or in connection with, the use of this website.
About Author
An ardent sailor and a techie, Anish Wankhede has voyaged on a number of ships as a marine engineer officer. He loves multitasking, networking, and troubleshooting. He is the one behind the unique creativity and aesthetics at Marine Insight.
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Hi Anish,
For our exams, the surveyors ask us the pressures in the various stages of a R.O plant.
Do you have any drawing of a multi stage RO plant?
Ashok
I actually had no idea you could use reverse osmosis on sea water to make it drinkable. Ever since I was a kid I thought it was impossible to make sea water drinkable! You learn something new every day 🙂
What is the regulation for using fresh water maker, that is at wht distance from coast it should be used
basically you can produce any quantity onboard the ships. it depends on that design how many quantities of permeated you actually required.
To know more about the calculation, please contact me and i can help to calculate for you.
jonaluhXXXXX@XXXXX.com
Im working for a company that builds these plants we are very busy. Just had a order of 60 plants for South African army.