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Desalination Technology
Sun, 06/29/2008 - 22:29 — Wayne Gramlich
Does anybody know what the current state-of-the art for fresh water extraction is for sea going boats. For example, if you own an ocean going sail boat, is there some sort of reverse osmosis or vacuum desalination technology that you buy to help top off the fresh water tanks. How about for cargo ships? Do that just have large fresh water tanks that they fill up at port, or do they have some sea water to fresh water technology that they use. Are there off-the-shelf desalination solutions that can be purchased that are sized appropriate to a boat?
Reverse osmosis for boats
This will let you see some of the stuff boat people are using:
http://www.westmarine.com/webapp/wcs/stores/servlet/SiteSearchView?catal...
Watermakers
I just found that page on my own. I kept typing "reverse osmosis" and "desalination" into Google and kept getting inappropriate hits. If I had typed "watermaker" I would have found them all. I should have looked at the west marine catalog from the start. They are sort of the the definition of "off the shelf" when it comes to marine products. Thanks for the link.
Watermakers
Reverse osmosis (RO) is the practical choice for a vessel that does not have waste heat to produce steam or the capability of using cold, deep ocean water. Generally, RO is pretty power hungry. Spectra Watermakers is most likely the most efficient you’ll find in the 1,000 gallon per day (GPD) range. Using multiple units for the desired capacity is probably the best way to go for redundancy, maintenance, and power conservation. Energy recapture technology for larger units (>5,000GPD) is not quite off the shelf. Spectra’s technology is.
(Note: I have 4 years experience installing, servicing, and building watermakers.)
I knew big ships use RO, but
I knew big ships use RO, but i didnt know RO equipment scaled all the way down like that. Neat.
Free water from the sky
What we do in Anguilla is collect water from the roof. To do this you want a cistern that is almost big enough to hold a years worth of water. If you have salt water handy, the cost of this tank might make solar panels and reverse osmosis not look so bad. In some seastead designs it might be possible to use part of the structure without needing to spend extra for a tank and then storage could be very reasonable.
You have to take life as it happens, but you should try to make ithappen the way you want to take it. - German Proverb
Essentially desalination is
Essentially desalination is just turning seawater to steam, separating water vapors from salt, then letting the vapor cool into a separate place sounds simple... wouldn't it be cheaper to just build something ourselves?
Dehumidification
Just out of interest, does anyone have information on the methods and their efficiency of gathering air humidity and converting it into liquid water?
The Wikipedia [url=http://en.wikipedia.org/wiki/Atmospheric_water_generator]article[/url] on the closest topic seems to be more of a commercial resource, offering some comparisions, but a more conclusive source would be welcome.
Id say that would require a
Id guess that would require a lot of surface area, which we do not have.
Water is everywhere. In the
Water is everywhere. In the ocean, in the air, in the ground. Producing potable water is just a matter of energy. If you have plenty of energy it is a non-issue.
Disentropy, rather than energy
I'd like to point out that the concept of "energy" is often misunderstood by the layman. What you really need in order to produce useful work is really disentropy (negative entropy), which is an unbalance of something that tends to balance itself. Temperature differential rather than raw heat, altitude differential, speed differences rather than raw velocity, pressure or density or concentration differentials (partial pressure in gases and osmotic pressure in liquids count, too), lighting differentials (between day and night, even), all these can be harnessed.
So, yes...
With what Jesrad is stating, we will have plenty of oppurtunities to harness disentropic sources out on the surface of an ever-changing seascape.
Deep cold water
That is correct, you need disentropy. That is why I think pulling that 40F water from the deep may still be worthwhile even if you use no OTEC at all. That cold water can be used for airconditioning, improving the efficiency of refrigeration and, most importantly, can be used in the making of fresh water by condensing water from saturated air. Solar can be used to heat surface ocean water, even if it is just passive. Then use the cold sea water to condense freshwater out. Using a vacuum pressure can make the process faster/more efficient. The only question then is the economical feasiblity of pulling the deep cold water to the surface and the cost of the pipe.
Reverse osmosis is good, but you will need a LOT of fresh water and I don't think it would be cost effective for the amount needed. It would be nice to get some numbers on this.
I understand that this deep water may have other valuable uses, as it is mineral rich.