A Clever New Approach To Desalination 128
jbeaupre writes "The Economist reports on progress by a company called Saltworks on using saline gradients to do the heavy lifting of desalination. In essence, Saltworks uses solar energy or waste heat to concentrate sea water. They then use the ionic gradient between the concentrated brine and two sea-water streams to pull ions from from a 3rd sea-water stream. It appears to work with entropy by trading the reduced entropy of the desalinated water against the increased entropy of 'mixing' the brine and the other sea-water streams. The article only discusses Na and Cl, but even just removing these ions is a step in the right direction."
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Does the word "nigger" actually personally offend you? Or do you avoid it and frown on its use because you feel like you're supposed to? Real question, and maybe as an AC you can give a truly honest answer.
The word doesn't offend me. I avoid it because I realize that others may be offended by it, and I do not understand the complex history of its word. Besides, there are plenty of other ways to refer to other human beings besides the color of their skin. Consider their first and last name, for instance.
It's also,important to remember that it does not have to denote a race or skin color. I tend to evaluate people based on their actions, and I have learned that the epithet could be applied to many of the people that post flamebait as AC. You are what you do, this is your hood, and your question is just some more mostly worthless graffiti. I say mostly worthless because it DOES show YOUR true color, no matter your race.
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That's the beautiful thing about water based catastrophie! Too much is as bad as too little.
Making Dew (Score:3, Interesting)
http://video.google.com/videoplay?docid=-524069894840499801# [google.com] (A/V's not synced)
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simpler way to get fresh water (Score:1)
1) use the sun to create sea salt.
2) sell it
3) buy fresh water.
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Thank you thank you thank you! Christ, I spent *years* trying to remember the name of that damn show!
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Likewise! Of course, it'll take another 10 years for me to even think of it again, by which time I'll have forgotten. Again.
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Wow! Thank you for taking me back to 6th grade!! I loved that series!
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Watched this in 4th grade (way back in '99). Damn, I couldn't remember the name of that show for the life of me.
Maybe (Score:2, Interesting)
Re:Maybe (Score:5, Informative)
Electricity is the flow of charge, not electrons.
If your statement was accurate, your computer would not work as it depends upon semiconductors which function in part based on the flow of positively charged holes in the electron structure of the material. (see p-n junctions, etc.) The Hall effect can be used to verify the charge of the moving carrier within a current. It can be either positive or negative.
Note that this desalinization mechanism works very similarly to a fuel-cell which also involves ion flow as part of an electric circuit.
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You do not know what you are talking about. An ion is an atom (or group of atoms) that have more protons than electrons. Maybe you should spend a few hours on wikipedia boning up on your basic chemistry.
Maybe you should spend some more time on wikipedia.
There DO NOT need to be more protons than electrons, they just need to be a non-equal quantity so that there is a net charge, making it a negatively OR positively charged atom/molecule.
Now, what you were saying would be correct if you were referring to cations specifically, which DO have more protons than electrons.
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Re:Maybe (Score:5, Informative)
Be that as it may, atoms are not ions, which is what the attempt at an article states.
The article doesn't state that atoms are ions. Rather, it states that ions are electrically charged atoms, which is totally correct. Here is the exact quote, in context:
I don't find any incorrect statement in the above quote regarding ions.
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Nope. For every hole moving through the semiconductor from positive to negative terminal, there's an electron that leaves the positive terminal and a corresponding one that arrives at the negative. You have electron-hole pair creation at the positive terminal and annihilation (through recombination) at the negative, but the holes pass through the semiconductor and the electrons through the rest of the circuit.
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A stream of alpha particles would have a well-defined current, despite the lack of electrons.
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Re:Maybe (Score:5, Insightful)
No, it's not inaccurate, unless you're claiming that protons don't have a charge. The ions here are nothing like wires. In a wire, the atoms (nuclei and nonconductive electrons) are fixed in position while the conduction band electrons are free to move from atom to atom. But in this desalinization process, the nuclei themselves actually move -- that's what makes it desalinization. The sodium and chlorine ions are true charge carriers. Ion conduction is not uncommon. Here's some more info on that:
http://amasci.com/amateur/elecdir.html [amasci.com]
Offtopic (Score:2)
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"True believer" is often used as a derogatory term for a person whose beliefs are fixed beyond all reason. Some people who claim to be open-minded throw the phrase around very recklessly. I feel that this is arrogant. Discovering new facts using rigorous methodologies is difficult and time-consuming. Everyone uses heuristics most of the time -- hearsay, incomplete evidence, confirmation bias, etc. IMHO, to wildly criticize others (especially when it's millions of people you've never met) for not wanting to
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what if they collected the fresh water vapour that is evaporating off the salt water as well?
TFA says they make fresh water by heating salt water with electricity so why not just heat it mostly with the sun and then a bit of electricity.
TFA is a bit light on details: why do Na+ ions go to one stream and CL- to the other? Have they got membranes that are impervious to CL- and NA+?
Re:Maybe (Score:5, Informative)
what if they collected the fresh water vapour that is evaporating off the salt water as well?
I'm guessing this would require active refrigeration unless they're in a colder climate?
TFA is a bit light on details: why do Na+ ions go to one stream and CL- to the other? Have they got membranes that are impervious to CL- and NA+?
Yes. From TFA:
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I'm guessing this would require active refrigeration unless they're in a colder climate?
You just put a roof over it and collect whatever condenses.
But unless you have a lot of surface area, the water you collect will be negligble in comparison to the main distillation process.
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Yeah, you "just" put a roof over it. As though that wouldn't 10x the construction and maintenance costs of the evaporation ponds. :P
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We should release carbon dioxide into the atmosphere! It is a greenhouse gas so it will help us make the earth one big greenhouse! Then everyone will have lots of fresh water! Damn, I need more exclamation points to qualify...
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I'm guessing this would require active refrigeration unless they're in a colder climate?
You just put a roof over it and collect whatever condenses.
But unless you have a lot of surface area, the water you collect will be negligble in comparison to the main distillation process.
One fractal green house coming up ...
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Re:Maybe (Score:5, Funny)
True. Too bad greenhouses are impossible.
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(to the music of Queen) - Black-bottomed pool you make the salty ions get found!
Sorry, couldn't resist
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If it's on Earth, then it is a colder climate. Colder than 100 degrees centigrade. Or as you probably call it, 212 degrees-F.
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what if they collected the fresh water vapour that is evaporating off the salt water as well?
I'm guessing this would require active refrigeration unless they're in a colder climate?
If it's on Earth, then it is a colder climate. Colder than 100 degrees centigrade. Or as you probably call it, 212 degrees-F.
Exactly. Just get a really long Aluminum pipe for the "waste steam", slightly angle it down, and you've got a water condenser. Run the "waste" pipe next to the input water pipe, and you've got increased efficiency on both heating and cooling.
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If it's on Earth, then it is a colder climate. Colder than 100 degrees centigrade. Or as you probably call it, 212 degrees-F.
Very funny, please go read up on "vapor pressure".
All that's needed to get some condensation is a surface that's colder than the pool, and in the same enclosed area. The trouble is, the rate of condensation and evaporation depends on the temperature differential between the condenser and the pool. So if your ambient temperature is 90 F and your pool is heated to 100 F you won't see very much evaporation compared to if you just exhaust your waste humidity into the (presumably comparatively dry) environment.
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come on now, steel pipes aren't THAT expensive...neither are pumps.
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And what if they let the water vapour, that is lighter than air, rise, and cool off by rising, to the point where it would condense again?
And if the rising force of the water vapour was used to drive some fans or turbines?
Or they could just release enough water vapour, letting it rise, so that there would be more precipitation downwind of the site. All of these would
generate power, and more fresh water, as well.
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what if they collected the fresh water vapour that is evaporating off the salt water as well?
Or better yet, collect the billions of gallons of condensate that falls out of the sky every day. Then you don't have to worry about all those silly ions, electrons and membranes.
Re:Maybe (Score:5, Funny)
Dr. Flammond: "A year ago, I was close to perfecting the first magnetic desalinization process. So revolutionary, it was capable of removing the salt from over a million gallons of sea water a day! Do you realise what that could mean to the starving nations of the earth?"
Nick Rivers: "My God, they'd have enough salt to last forever!"
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Current is by definition the flow of charge. In the case of your muscles, there is an electrical current along the muscle cell membrane that is caused by a change in the amount of cations allowed into the cell.
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Exactly. They built a perpetuum mobile that requires less than 1 kWh.
Re:Anyone else think... (Score:5, Informative)
Yeah, pretty much, for all practical purposes, but not quite, because sooner or later the fucking sun will in fact burn out.
You didn't need to read TFA. It's in the summary. Second sentence.
Re:Anyone else think... (Score:5, Funny)
Yeah, pretty much, for all practical purposes, but not quite, because sooner or later the fucking sun will in fact burn out.
Or get bought out by Oracle after giving away all its energy for Free.
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There ain't no such thing as a free Sun.
I feel like a single-celled organism subsisting on a decomposing lunch for only a few seconds.
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T
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Not really. The article clearly indicates that heat input is required (i.e. it doesn't purport to be a system that produces more energy than is put into it). The beauty of this system is that this energy is obtained from a source we don't have to pay for (i.e., the sun).
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(i.e. it doesn't purport to be a system that produces more energy than is put into it)
"Perpetual motion" doesn't produce necessarily "more" energy than is put into it. It simply doesn't require energy at all apart from the initial "push". And that is, of course, absolute rubbish, thanks to friction, diminishing returns, and any other number of physical laws that favor entropy.
I just don't understand how this project is meant to work. Maintaining those "concentrati
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Seems pretty simple to me. The ions flow down their concentration gradients creating opposite charges in streams that were once regular seawater, through some sort of bridge that only allows Cl ions into one stream and Na ions into the other stream. Then the seawater that needs to be desalinized is connected, the ions can't escape the charged streams due to their bridges, but the ions from the seawater to be desalinized travel to the charged streams. After that, you dump the charged streams and start over
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Yes I got THAT part. What I don't get is how they plan on maintaining this potential difference across the membrane. In the human body it's done by Na/K ATPase pumps that trade 2 sodium atoms for 1 potassium atom. But these pumps are working all the time (even during depolarization, when the Na gates open), and consuming ATP all the time. It's ACTIVE transport, and requires a lot of energy. That's why neurons die when deprived of oxygen after only 4 minutes, while other tissues can survive hours.
I find it h
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Your body has to pump the salt because it's going from a low concentration gradient (blood) to a high concentration gradient (urine). Obviously. This is just the opposite. In each side, one ion is going down a *major* concentration gradient (20% to 3.5%), while the other ion is going up a *minor* concentration gradient (0% to 3.5%). So entropy favors the reaction, and it will continue until the ions run out from the freshwater; you're ending in both a lower entropy and energy state. The key is that you
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Other than the fact that they are consuming not producing energy, yeah exactly like that...
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anyone else think this looks suspiciously like: http://en.wikipedia.org/wiki/Perpetual_motion [wikipedia.org]
Only if you can't read.
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I was thinking, "In this house we obey the laws of thermodynamics!"
It's probably the wave of the future (pun intended (Score:1)
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Why would the Poles want more ice? (Score:3, Funny)
The winter in Poland is already plenty cold enough...
:-P
Cheers,
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Ice displaces water, which will just make the sea level even higher, you bloody fool !
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Well... Then we'll stack it up on the continents!
Vancouver saves the world? (Score:3, Interesting)
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If you have the first one, the second one becomes redundant. Loads of problems just go away if you have cheap, abundant, clean energy.
-Peter
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But most people might be on space colonies before that scenario becomes likely.
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But most people might be on space colonies before that scenario becomes likely.
If we're lucky it might stave off the next Ice Age, due to begin this millennium. Then we have 10,000 years to figure the rest out.
General Confusion (Score:2, Interesting)
Thank you for that link to General Confusion. Made my day. Check out the freshman T-rex with his lava lamp and the sordid diatripe:
http://www.generalfusion.com/fossil_fuel_crisis.php [generalfusion.com]
The planet was covered with dense clouds and the atmosphere contained a high concentration of carbon dioxide, producing tropical conditions north of the 45th parallel. For example, many dinosaur fossils were excavated in Alberta, Canada. As the earth's crust cooled down, volcanic activity reduced.
Riddle of Burgess Shale's fossil-rich deposits solved [canada.com]
The site, close to the B.C.-Alberta border, is considered crucial to understanding the so-called Cambrian "explosion" of life - a time when the future Canadian land mass was drifting in tropical climes close to the Earth's equator.
In my historical atlas, the equator is considerably south of the 45th latitude. The dinosaur fossils in Alberta are equatorial in origin. But hey, if you can't get that right, no obstacle to solving the fusion problem. Like it's not a hard problem or anything. The typ
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You're right that the equator is considerably south of the 45th parallel. However, you forget that continents move around, given enough time. So in the Cambrian North America (Laurentia) was near the equator - here's a map [scotese.com]. Fast forward 320 million years to when the dinosaurs began to rule the earth, and North America is approaching where it is today - here's another map. [scotese.com] Note how Alberta is approaching the 45th parallel, where it is found in your atlas.
You need to get yourself a different atlas if you'r
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ion bridges cost? Consumable? (Score:3, Insightful)
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In their diagram, they have this schematic in the critical location:
[Salt water]<----(+)----[Brine]----(-)----->[Salt water]
Chemically, that "equation" just doesn't balance without an input of energy. It doesn't matter what kind of "ion bridges" they put into place between the brine and salt water reservoirs, or what the concentration of salt exists in the brine or salt water, it will require some energy to offset the entropy increase
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The energy was input by the sun before the different solutions were brought together.
delta S > 0 for a closed system as a consequence of the second law of the thermodynamics. No need for additional energy. The entropy of a the concentrated solution is less than the entropy of the dilute solution, hence dilution happens spontaneously, much like osmosis.
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The brine is created from a portion of the sea water. They use the sun to heat it and evaporate some of the H2O. This is the primary energy input.
Re:ion bridges cost? Consumable? (Score:4, Informative)
More important than the cost is the question of effectiveness.
In their diagram, they have this schematic in the critical location:
[Salt water]<----(+)----[Brine]----(-)----->[Salt water]
Chemically, that "equation" just doesn't balance without an input of energy.
The article DOES explain this, the salt imbalance makes
a kind of battery.
It's brilliant! Solar energy concentrates a brine, which
then (just as dissimilar metals make a thermocouple)
causes current and builds an electric potential
when connected via a membrane (impermeable
except to Na+ ions) to a less-concentrated brine.
So, the difference in concentration of ions between two
channels results in a diffusion from more-concentrated to
less-concentrated, OF A CHARGED ION. That means
electric current flows, until the charge buildup raises
the electric potential enough to stop the diffusion.
The solar input concentrates the brine, the resulting
(small) voltage then is electrically applied to the to-be-desalinated
channel, and (in the absence of a concentration difference)
the electric field causes the ions to leave the
to-be-desalinated stream.
Thus, it's a solar-concentration-of-salt that makes
the desalination occur. The electricity caused by the
diffusion is active ALL NIGHT until the concentration
of salt goes down, so the concentrated brine is
an effective load-leveling device for the whole plant.
The 'electric input' part of the process is entirely for
pumping the brines around, so it can be a small fraction
of the brute-force desalination energy requirement.
Heck, you could use wave or wind power for that.
Solar collectors for this kind of gizmo are just open-air
trays of brine. Can't get any more cost-effective than
THAT.
Re:ion bridges cost? Consumable? (Score:5, Informative)
You missed the other side of the reaction. It is charge neutral because the +/- charges in the two side pools are then balanced with -/+ charges from the water to be desalinated.
The charges flow apart in the first place because the central pool is highly concentrated - so it contains far more + and - charges than anything else in the system.
This kind of approach would never yield completely drinkable water, but that isn't the point. The goal is to get rid of a lot of the ion load before using more expensive processes to get rid of the rest.
Desalination is a marvel of process optimization. Multiple stages of purification are used - each one being more expensive than the last but more effective. The early steps get rid of a huge mass of dissolved matter for dirt cheap, so even if their product isn't drinkable it GREATLY reduced the cost of the later stages.
If you don't care about cost then desalination is trivially easy. Just run any kind of water you like through a H+ exchange resin followed by an OH- exchange resin, and then run it trough activated charcoal. The resulting water will be as clean as clean can be and the system would be remarkably simple. The catch is that those resins cost a small fortune to make, and if you run seawater into them then they're probably going to last all of 5 minutes. It might be a good approach for a camper to use to obtain water (the resin is a lot lighter than the amount of water that it could clean), but it is not a cost-effective method overall. Also - the purity it would achieve would be massive overkill. This is drinking water - we're not manufacturing CPUs.
Re:ion bridges cost? Consumable? (Score:4, Informative)
[Salt water]<----(+)----[Brine]----(-)----->[Salt water]
Chemically, that "equation" just doesn't balance without an input of energy. It doesn't matter what kind of "ion bridges" they put into place between the brine and salt water reservoirs, or what the concentration of salt exists in the brine or salt water, it will require some energy to offset the entropy increase.
This is exactly backwards; energy input is required in order to decrease entropy of (part of) a system. Entropy increases come for free. Consider if you fill one half of a fish tank with fresh water and the other half with brine, do you get a fish tank full of somewhat salty water or do the fresh and salt water separate out?
Re:ion bridges cost? Consumable? (Score:5, Informative)
No, the key piece of work is the idea. Ion bridges have been around forever.
This has to permit the travel of one kind of ion but not the other, i.e. Na+ or Cl-. Looks like this material could be expensive.
So you use, for instance, a polymer electrolyte (ionomer) with negatively charged side-chains for one bridge and a polymer with positively charged side-chains on the other. Only the counterions are mobile. The article says they're using modified polystyrene. This is not new, or terribly expensive. Similar things are already being used in industrial desalination technology for ion exchange columns.
It might plug up need to be periodically replaced.
Plug up with what? You naturally would have a mechanical filter to keep the crap out. It's not a major problem.
How expensive these are? How non toxic these are? What is needed to manufacture them? These are the questions we need to ask.
No, they're the questions asked by someone who doesn't know s--t about chemistry/chemical engineering. I happen to have a degree in the subject, but damnit, I learned about (used, even) polymer ion exchange columns in high school. If you want answers to your questions, go get Coulson & Richardson or some other chemical engineering textbook, and find the relevant section.
This technology is certainly very clever, but it does not make use of any new technology. The only question I think is worth asking here is whether or not it turns out to be more efficient or not.
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The only question I think is worth asking here is whether or not it turns out to be more efficient or not.
I detect a little unnecessary redundancy there.
Re:ion bridges cost? Consumable? (Score:4, Insightful)
Not everyone reading Slashdot has a degree in chemistry or chemical engineering. I appreciated OP's questions since I had the same ones. I appreciate your answers but not the attitude that I had to endure when reading your post.
Plug up with what? You naturally would have a mechanical filter to keep the crap out. It's not a major problem.
You answered the dumb question but failed to answer the smarter one. Does the ion bridge ever somehow lose its effectiveness after a good amount of use? If it does, it will need to be replaced. How often does this happen? How much water can one of them desalinate before needing replacement? If it never needs replacement because of *use* (not mechanical crap getting in the way), then that's great, but I don't know the answer. Again, I do not have a degree in any of this stuff, so please enlighten me.
Re:ion bridges cost? Consumable? (Score:5, Insightful)
The attitude of the GP was the problem. "These are the questions we need to ask", as if they were non-obvious and revolutionary. Whenever there is a post about an invention on /. the easiest way to get "+5 (Group-Wank)" is to write that it will never work because the inventors overlooked an issue a drunk chimpanzee could come up with. Then a thread ensues where everyone congratulates themselves on saving the world yet again.
You are right, the GP's questions were interesting and should have been answered in the article (which is for laypersons) and because they weren't it's good that someone answered them here on /.
The problem is that the GP posed the question in a way that implied he knew what he was talking about and was making a statement about the invention, instead of admitting that he had no idea and was asking for clarification. jm2c
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This technology is certainly very clever, but it does not make use of any new technology. The only question I think is worth asking here is whether or not it turns out to be more efficient or not.
If it's miniaturizable technology and sturdy enough to be permanently mounted on the deck of a ship unlike this [landfallnavigation.com] then I think it's got a future.
Maxwell's Demon (Score:1)
Reverse osmosis? (Score:2, Interesting)
Isn't this a large-scale demonstration of the same principle used in home reverse-osmosis systems? It sure sounds familiar.
Re:Reverse osmosis? (Score:5, Insightful)
No. It does look a bit similar but it isn't. In reverse osmosis the water has to pass through the membrane, driven by high pressure pumps, leaving its impurities behind.
In this version the impurities pass through the membrane (two separate membranes in fact) driven by an electrical current. Cleverly, the electrical current itself is generated by the salt passing through other membranes out of the highly concentrated brine that you made in your solar ponds.
One thing I've been wondering about for a while... (Score:2)
... is if it would be possible to combine solar-thermal power generation with desalination.
Build Fresnel-lens solar concentrators and stick them near a source of seawater. Boil the water using the sunlight, and use it as the working fluid in an ordinary steam-turbine-type power generator. But instead of recycling the same water once the steam recondenses, realize that you've just made a giant distiller: drink the water and use "new" seawater.
Re:One thing I've been wondering about for a while (Score:1)
Not an expert, but from what I've seen (on shows like World's Toughest Fixes, etc.), modern steam turbines are very sensitive to impurities. Even the size of water droplets matters. Running seawater vapor through one would probably not work without a redesign.
But what happens to the waste steam from the brine (Score:1, Redundant)
So I read the thing.
The process concentrates sea water to brine by an evaporation method. So why waste this low grade stream it is still has high in moisture content. There is already a condenser in this system. I'm thinking this can somehow boost output of clean water.
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I think the answer is cost. Near where I live a company makes table salt. They have acres and acres of these shallow ponds, and when the tide comes in they open the valves, filling up the ponds. Then they close the valves and wait for a few days for it all to dry into this muddy slush that gets scooped up by heavy machinery and, I hope, purified.
Aside from the land itself the entire operation is so cheap it's almost free. Sure, you could somehow trap that water vapor and cool it enough to change it bac
Old idea, misrepresented, tried and failed (Score:1)
Energy from salinity gradients (Score:2)
Just like it takes energy to desalinate water the opposite is also true: energy can be produced from salinating water.
See http://en.wikipedia.org/wiki/Osmotic_power [wikipedia.org]
What this system does is to concentrate seawater by evaporation and then use the salinity gradient between that concentrated brine and normal seawater to produce energy. This energy is then used to desalinate another stream of seawater. In principle, there is no reason to use this energy specifically for desalination. It could also be fed to the
Question about desalination. (Score:1)
I've long wondered about a few things when it comes to desalination, desert areas etc.
If it's cheap to make water with this process and remove the salt - would it be a good idea to create a huge bunch of these machines in desert-areas, pumping desalinated water into fields to promote vegetation to grow, fighting back the desert? I would think this wouldn't require the water to be further cleaned, after removing the salts..
Am I completely off my rockers, or is it a maybe-sort-of workable idea?
Powered by Evaporation (Score:2)
The source of the energy to evaporate the water is irrelevant, solar works just as well for either process. Assuming an essentially unlimited supply of seawater for cooling to the distillation step, I don't see how they can make enough concentrated brine to filter the seawater more cheaply.