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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.
> 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.
They do hint at it at end:
> “It is also noteworthy that the Japanese plant uses concentrated seawater, the brine left after removal of fresh water in a desalination plant, as the feed, which increases the difference in salt concentrations and thus the energy available.”
And the "fresh" water is also "treated wastewater". That could mean a bunch of things but in most cases it's water that's released into the environment by the water treatment plant. Its quality can be as good as clean water, but most municipalities wouldn't feed that right back to the consumer, they dump in a river or lake instead.
Basically this is like the recouperator on early heat engines, but with a liquid gradient instead of a thermal one.
It's making desalination more efficient and the effluent a bit easier on the ecosystem.
Goes nicely with the "pressure exchanger" which recovers the pressure of the high pressure brine waste stream. Lots of heat exchanger analogies!
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.
Fukuoka's desalination plant treats about 16400 m^3 of water per day. Assuming 3kWh per m^3 of water, this works out to a time-averaged power consuption of ~2000kW.
The osmotic power plant generates about 100kW, so it's about 5% of the total desalination energy requirement.
explains your username, explain like im like 17
thanks
> it is expected to generate about 880,000 kilowatt hours of electricity each year
100 kW, in sensible units.
*An average of 100kW assuming 100% duty cycle.
Expecting it to operate most of the time is a safer bet than expecting it to have a peak output that’s substantially higher than the average. It’s be smart to try to align it with power usage, but in truth it’ll lag behind peak water usage by however long it takes to top off the tanks. I don’t know when that is but I would suspect before morning rush hour.
Probably this thing peaks at 120-150KW which isn’t going to fix the grid.
It's going to partially offset the power usage (and the effluent brine) of the desalination plant that feeds it.
It is expected to have about 8760 hours each year.
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?
It seems like it would have to be more efficient to further treat the semi-treated wastewater. However there is often resistance to putting treated waste-water into reservoirs.
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.
So let me get this straight:
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.
This french startup has a pilot osmotic plant near Marseille : https://www.sweetch.energy/
It must be very wasteful in water - nearly all low-salinity water is easy to recycle, but here is wasted for a tiny powerplant.
Fukouka isn't particularly in short supply of access to water, it's just not convenient for them.
The region is humid and rainy for over half the year and it's only particularly dry for about a quarter of the year. And they have a comprehensive system for evacuating stormwater during the rainy season as well.
So I'd reason a guess that they have a waste water excess 1/2 to 3/4 of the year but still need the baseload capacity of the desalination plant for the remaining chunk of the year. And while you could probably switch over to plain seawater for the portion where you are running negative, it may not be worth the added maintenance/cleanup cost of having to deal with salt or brackish water for only a small portion of the year. So instead you just eat the losses for that window in exchange for the increased efficiency/lower complexity/lower operating costs.
It uses high salinity brine that's a byproduct of desalination.
Your parent is talking about the "fresh" (treated wastewater) side.
It sounds like this recovers some of the energy that the desalination plant used to create fresh water and brine from ocean water?
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.
People are willing to waste energy to avoid drinking their own (treated) sewage, before it's temporarily mixed in the ocean.
> 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.
I love nuclear power and know a lot about operating them, however:
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.
1) It's actually not that expensive, but the regulations made it so. I remember something from titans of nuclear or some Jordan Peterson podcast. I'll try to write the gist of it here:
There was some rule, that the cost of safety (like how thick concrete should be in some places), could be so high, that the usually cheaper fission energy would be equal in cost with the other sources (like burning oil). Then came the oil crisis of the 70's in USA. The safety margins got boosted to crazy levels, without any realistic gains. Moving from 99.999% to 99.9999% safety (just an example).
When the oil prices dropped, safety standards stayed and now fission energy is expensive. At least in USA and EU. Not in France or South Korea, which streamlined the regulations.
2) not with the modern technology, it isn't. And there are even safer alternatives like marble balls reactors that can't meltdown even if cooling is shut down.
3) not using it is bad for the environment. Fuel requirements are minimal compared to other plants. Even some types of renewables pollute more per W of energy produced. Like wind turbines that will fill up landfills at some point.
4) Thorium reactors. If we just give the fission energy some research & development, we can burn all the spent fuel up in thorium reactors.
Some other *renewable* energies. Nuclear isn't generally considered renewable.
But it's inexhaustible. Sun will die at some point and moon will fall down to earth. Then we'll have no solar and no waves.
Nuclear is quite exhaustible. If we use it to power everything, we have about 100 years worth. It's just another kind of fossil fuel, storing energy that was captured long ago.
Coverage readable (although most images are missing) without JavaScript: https://www.independent.co.uk/climate-change/news/japan-osmo...
Wait... so they have made a plant run by the power of mixing fresh and salt water so it can separate the salt out again?
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.
Is there a more ironic way to power a desalination plant?
It has a pleasant symmetry to it, I think.
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
Crafted by Rajat
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