As well as diluting the brine produced by desalination. Unclear if it's worthwhile though. As another commenter pointed out, you could treat the source of your low salinity water to produce fresh water instead and bypass a lot of this.
Japan seems to really be into osmotic pressure for whatever reason. It reminds me how in Splatoon, the reason given for why the character die when they touch water is osmotic pressure and there's a whole scientific explanation about it.[1] However, that all got cut out in the international localization for some reason.
Maybe there's a cultural reason why Japan is more aware this is a thing that exists? Dunno
They like reading random Wikipedia articles I think. It's normal in kids' stories for a character to do a cool technique and then a third character to explain how the cool technique worked based on the Wikipedia article the author just read.
It's routinely featured in Japanese equivalent of SAT tests. So anyone with a high school diploma at least have heard about it, most with a degree from a Japanese university have made attempts to solve a quiz involving it, and anyone with any degree from any of national universities have solved a question on that topic at least once.
This one is pretty annoying coz even if you support the idea of "kilowatt hours", it's common to discuss power station capacity in terms of Watts (plus for journalists the obligatory "this is enough to power N homes / a city the size of Coventry"). So it's like they're deliberately choosing to be obscure here!
What do you mean sensible units?
kW is instantaneous power whilst kWh is the amount of power created in a unit of time. In other words, this power plant generates 100kW of power and produce 876MWh in a year.
If you have an average of MWh a city needs, having MWh is a helpful metric, as well as kW to make sure you can power the city on peak consumption. No?
Does it generate enough electricity from freshwater to offset the energy used to desalinate more water? Would it be more efficient to just treat the freshwater that would have been used to run the plant for drinking water and desalinate less water?
If you're using water at the end of a process that's just going to get mixed anyway, you're just extracting waste energy from the mixing process. Basically the fresh, used water and the highly saline water are in a lower-entropy state, and normally we'd just dump both in the ocean and allow the entropy to increase without extracting energy. But in this case we allow their entropy to increase in a controlled environment and so we're able to extract some energy in that process.
No, the fresh water always produces less energy than it took to desalinate the fresh water to begin with. If the freshwater is recoverable, that will always be energetically better. But if you can't recover the fresh water for some reason, like say there is a particular contaminant that is impractical to remove, or it's going to be used for some application like irrigation or feeding a nature preserve where higher salinity is tolerable but you're never getting the water back, then it reduces the overall system losses.
On the other hand, there are often restrictions on how concentrated your brine can be when released so it doesn't cause environmental problems. If you have to dilute your brine anyways, might as well get a little energy back.
They really fail to explain a key point here. The reason you colocate this with a desalination plant is because you use the super-salty wastewater from desalination as the salty side of the osmosis power plant. Then you find some wastewater which is low in salt (such as semi-treated sewage), and use that as the fresh side of the osmosis power plant.
The end result is that the salty wastewater is partially diluted, which means it has a lower environmental impact when it is discharged to the ocean.
Yeah, this is the coolest part. The leftover brine from desalination is generally just a problem. It's harmful to the marine habitat if you just put it back into the ocean, and there isn't a lot else good to be done with it. (Basically you have to dilute it first.) But this way you get useful work out of the dilution!
The article also doesn't say if it produces more power than the attached desalination plant requires. I doubt it as you'd be getting close to a perpetual motion machine if so. In which case basically what you've got is a very energy efficient desalination plant, more than a power plant.
This sounds pretty awesome, recycling the waterwaste in a sort of feedback loop resulting in drinking water and power.
I am kind of curious on how much you can/should optimize this process until it becomes dangerous or unmaintainable. And can we do this on more places on this planet? For instance somewhere on a desert coast or something? Could be cool to build some of those between Sahara desert and the ocean, combined with solar panels or something.
1. I take a shower and produce non-salty waste water
2. That waste water and brine from a desalinization plant can be used in this plant.
3. The result is concentrated waste water and less salty brine and some power
4. The power can be used to (partially) power the desalinization plant produces fresh water from sea water and brine.
5. I get fresh water for my shower.
And the diluted brine from step 3 goes to the sea? Or can it be run through the desalinization plant again? Does concentrating the waste water in step 3 also help with the eventual treatment of it
The article mentions "partially treated wastewater", which I take to mean "water that we're ok with dumping into the ocean, but not ok with drinking". I think you can generally read this as a way of gaining some utility out of this partially-treated wastewater before you dump it into the ocean by mixing it with the extra-salty brine from the desalinization plant. The utility you get is:
- a bit of energy that would have just been wasted
- a more environmentally friendly product to dump in the ocean than just straight brine
I imagine someone out there does a cost-benefit analysis to compare this system to just fully treating and reusing the wastewater and thus needing to desalinate less saltwater.
The diluted brine goes out to sea. It's less harmful than dumping the concentrated brine you had before, with the bonus that you got some power out of it.
The concentrated waste probably gets disposed of rather than trying to get the remaining water. You treat it like the results of a waste treatment plant. You might dehydrate it a bit, just so you don't have to ship the water, but you probably won't try to recover any more water than you already have.
> While it is still an emerging technology being used only on a modest scale as yet, it does have an advantage over some other renewable energies in that it is available around the clock.
I notice the 'some' here, and the absence of the word 'nuclear' from the article, which of course is also available around the clock. Most readers will know something about Japan's troubled relationship with nuclear power and can fill in that context themselves, but to my eyes, it's a startling omission.
Exactly. Well not exactly. The desalinization plant produces brine (very salty water) as a waste product. Rather than disposing of it directly, they use the brine to generate electricity. This electricity is then used partly to run the desalinization plant.
As an imperfect car analogy, the way a turbocharger uses energy from the exhaust to inject energy into the intake, in the form of compressed air.
Neither is a perpetual motion engine, but both make the useful work more energy efficient.
This energy is not free. Solar cells and wind embody the cost of production of the device as the input cost along with cost of construction, and transmission, but the primary energy input is predicated on a real externality: Wind and Sun.
This system depends on using a LOT of energy to maintain an osmotic pressure gradient. That it turn depends on pumping water across a boundary. Energy has to be expended. Now, if you run a de-salination plant and/or waste water treatment you have to expend MOST of this cost anyway, so you are scavenging energy back from an unavoidable, non-externality cost.
This is a big difference. Wind and Solar bring energy in from the Sun and weather, outside human expenditure. This brings BACK some expended energy, doing another job.
I suppose hypothetically, given immensely saline water CLOSE to less saline water you could expend significantly less energy to arrive at the boundary condition but its for kilowatts, not gigawatts or even megawatts. The places which have these conditions might also have high sunlight or wind conditions no?
220 households, at say $2k/year of power bills is just under $500k/year revenue, plus whatever else from "disposing" of hypersaline water (if that's even a reverse stream?)
I hope this is just meant to be a tech demo, and doesn't have any advantages of scaling yet.
In 1998 when I was in high school I dreamt up this kind of power plant and asked my physics teacher where the power really came from. Not happy with his answer I asked a university physics Q&A service [1]. Not happy with their answer either I did a masters in engineering physics and kept asking this question whenever I got the chance. Never got a really good answer. But I’m glad to see it works.
The freshwater used in this osmotic power plant is produced by a wastewater treatment plant, and the high-salinity water used is the wastewater generated by a seawater desalination plant
So, if the freshwater produced by wastewater treatment plants is further processed into usable freshwater to replace the freshwater produced by seawater desalination plants, soon one water treatment plant could replace both the seawater desalination plant and the osmotic power plant, reducing steps. I believe this would greatly improve efficiency
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[ 3.2 ms ] story [ 67.6 ms ] threadMaybe there's a cultural reason why Japan is more aware this is a thing that exists? Dunno
[1] https://youtu.be/N3bn57twbHM?si=nmxVjFPaeaxlTqyk
100 kW, in sensible units.
If you have an average of MWh a city needs, having MWh is a helpful metric, as well as kW to make sure you can power the city on peak consumption. No?
See also, "Power is not Energy": https://youtu.be/OOK5xkFijPc
source: https://en.wikipedia.org/wiki/Osmotic_power
On the other hand, there are often restrictions on how concentrated your brine can be when released so it doesn't cause environmental problems. If you have to dilute your brine anyways, might as well get a little energy back.
The end result is that the salty wastewater is partially diluted, which means it has a lower environmental impact when it is discharged to the ocean.
The article also doesn't say if it produces more power than the attached desalination plant requires. I doubt it as you'd be getting close to a perpetual motion machine if so. In which case basically what you've got is a very energy efficient desalination plant, more than a power plant.
In fact, it almost seems that you could simple pull in sea water as the “low salt” water and still have a large enough delta against a brine solution.
Really interesting that it also solves the brining issue.
I am kind of curious on how much you can/should optimize this process until it becomes dangerous or unmaintainable. And can we do this on more places on this planet? For instance somewhere on a desert coast or something? Could be cool to build some of those between Sahara desert and the ocean, combined with solar panels or something.
But, if it’s in any way efficient, why not just use some of the fresh water you produce? Doesn’t that kinda become free power in a sense?
Using fresh water to power a desalinization plant just seems counterintuitive to me, I guess, but maybe (certainly) I’m misunderstanding something
1. I take a shower and produce non-salty waste water
2. That waste water and brine from a desalinization plant can be used in this plant.
3. The result is concentrated waste water and less salty brine and some power
4. The power can be used to (partially) power the desalinization plant produces fresh water from sea water and brine.
5. I get fresh water for my shower.
And the diluted brine from step 3 goes to the sea? Or can it be run through the desalinization plant again? Does concentrating the waste water in step 3 also help with the eventual treatment of it
I imagine someone out there does a cost-benefit analysis to compare this system to just fully treating and reusing the wastewater and thus needing to desalinate less saltwater.
The concentrated waste probably gets disposed of rather than trying to get the remaining water. You treat it like the results of a waste treatment plant. You might dehydrate it a bit, just so you don't have to ship the water, but you probably won't try to recover any more water than you already have.
I notice the 'some' here, and the absence of the word 'nuclear' from the article, which of course is also available around the clock. Most readers will know something about Japan's troubled relationship with nuclear power and can fill in that context themselves, but to my eyes, it's a startling omission.
1) It's expensive. Very very expensive.
2) It's dangerous when not operated properly, and I don't trust commercial interests operating hundreds of these due to this reason.
3) It's bad for the environment, both the mining to get the uranium and all of the processes to turn it into fuel.
4) There is no answer for spent fuel.
Whereas with solar or wind you can basically remove #1, #2, and #4, however you still have to mine and process the materials.
Anyways, nuclear will be great for some niche uses, I am sure, but it isn't the answer to our green energy prayers.
As an imperfect car analogy, the way a turbocharger uses energy from the exhaust to inject energy into the intake, in the form of compressed air.
Neither is a perpetual motion engine, but both make the useful work more energy efficient.
This system depends on using a LOT of energy to maintain an osmotic pressure gradient. That it turn depends on pumping water across a boundary. Energy has to be expended. Now, if you run a de-salination plant and/or waste water treatment you have to expend MOST of this cost anyway, so you are scavenging energy back from an unavoidable, non-externality cost.
This is a big difference. Wind and Solar bring energy in from the Sun and weather, outside human expenditure. This brings BACK some expended energy, doing another job.
I suppose hypothetically, given immensely saline water CLOSE to less saline water you could expend significantly less energy to arrive at the boundary condition but its for kilowatts, not gigawatts or even megawatts. The places which have these conditions might also have high sunlight or wind conditions no?
It's achieved by extracting some energy from the dilution process of waste salty brine with freshwater before dumping it to a river.
I hope this is just meant to be a tech demo, and doesn't have any advantages of scaling yet.
1. https://fragelada.fysik.org/index.php?amne=Energi&stage=&key...