Vapor-collection technology saves water while clearing the air(news.mit.edu)
news.mit.edu
Vapor-collection technology saves water while clearing the air
https://news.mit.edu/2021/infinite-cooling-nuclear-0803
25 comments
If you find this interesting, there are other technologies either proposed or used to collect atmospheric water.
Air wells: https://en.wikipedia.org/wiki/Air_well_%28condenser%29
Fog collection: https://en.wikipedia.org/wiki/Air_well_%28condenser%29
Air wells: https://en.wikipedia.org/wiki/Air_well_%28condenser%29
Fog collection: https://en.wikipedia.org/wiki/Air_well_%28condenser%29
You've got an accidental double link to the same air condenser article -- here's fog collection for the lazy: https://en.wikipedia.org/wiki/Fog_collection
Thank you!
If this became widespread wouldn’t this negate some of the positive side-effects of creating more light reflection on earth? https://www.bbc.com/future/article/20190220-how-artificially...
Water vapour potentially works as a greenhouse gas too though, although it’s debated how much effect it has - https://www.nasa.gov/topics/earth/features/vapor_warming.htm...
That’s actually one reason I’m quite excited about wind and solar as a power source. Apart from the CO₂ that coal and gas pants emit (and the fugitive methane emissions from coal, oil and gas production), it seems like an improvement to be able to generate electricity without having to pump so much waste heat into the atmosphere with all that water vapour.
That’s actually one reason I’m quite excited about wind and solar as a power source. Apart from the CO₂ that coal and gas pants emit (and the fugitive methane emissions from coal, oil and gas production), it seems like an improvement to be able to generate electricity without having to pump so much waste heat into the atmosphere with all that water vapour.
This is ultimately almost useless because the minerals in the water are more important than the water itself.
This seems like a roundabout way to achieve a closed-loop cooling cycle. Why do this vs a water-to-air heat exchanger and never evaporate the water in the first place?
It does still evaporate, it just condenses back to liquid shortly after. I don't understand the thermodynamics very well, but isn't the point of steam to carry heat _away_ from the plant? I'm wondering if the catch is that the plant would then have to deal with hot water removal instead of just venting straight up and out.
Also,
> What’s more, in many arid coastal areas power plants are cooled directly with seawater. This system would essentially add a water desalination capability to the plant, at a fraction of the cost of building a new standalone desalination plant, and at an even smaller fraction of its operating costs since the heat would essentially be provided for free.
This seems like a no-brainer and it's surprising to me that it doesn't already work this way.
Also,
> What’s more, in many arid coastal areas power plants are cooled directly with seawater. This system would essentially add a water desalination capability to the plant, at a fraction of the cost of building a new standalone desalination plant, and at an even smaller fraction of its operating costs since the heat would essentially be provided for free.
This seems like a no-brainer and it's surprising to me that it doesn't already work this way.
Oh sure, there's cases where the output is more valuable than the input. I agree that desalination is possibly quite worthwhile. Though I'd imagine that in the ocean water case that the flow rate is high enough that little water is heated to the point of evaporating. Probably don't want to produce brine or salt residue.
But much of the article talks about how 40% of lake, river, and well water goes into evaporative power plant cooling. Recovering that already-salt-free water via condensation vs just not evaporating it in the first place seems silly. Your car doesn't use evaporative cooling, it uses a heat exchanger. So too could a power plant.
Though if the working fluid is steam I guess we'd call it a condenser rather than a radiator. That said, if you have steam to exhaust you have energy left to extract. My home water heater condenses the steam out of combustion exhaust to achieve good efficiency.
But much of the article talks about how 40% of lake, river, and well water goes into evaporative power plant cooling. Recovering that already-salt-free water via condensation vs just not evaporating it in the first place seems silly. Your car doesn't use evaporative cooling, it uses a heat exchanger. So too could a power plant.
Though if the working fluid is steam I guess we'd call it a condenser rather than a radiator. That said, if you have steam to exhaust you have energy left to extract. My home water heater condenses the steam out of combustion exhaust to achieve good efficiency.
It's all about the surface area. The evaporative chiller couples the heat to a much larger volume of air, much more quickly, than a water-air convective heat exchanger. This is due to the high enthalpy of evaporation of water. The hyperbolic towers get an extra boost due to convection.
Once it evaporates to steam, it mixes with more air, which cools it and the steam condenses to fog. But at this point, this heat transfer is of no consequence to the power plant. You can collect this fog without affecting the thermal efficiency of the plant.
But you can't skip that evaporation step because it's the high surface area of the sprayed droplets evaporating that does all the work. You also can't have the collector too close because then you just have a still, and the collector plate heats up from the condensation until it equilibrates. You need the air mixing.
Basically TFA describes a cheap way to get a much larger effective surface area.
Once it evaporates to steam, it mixes with more air, which cools it and the steam condenses to fog. But at this point, this heat transfer is of no consequence to the power plant. You can collect this fog without affecting the thermal efficiency of the plant.
But you can't skip that evaporation step because it's the high surface area of the sprayed droplets evaporating that does all the work. You also can't have the collector too close because then you just have a still, and the collector plate heats up from the condensation until it equilibrates. You need the air mixing.
Basically TFA describes a cheap way to get a much larger effective surface area.
So... cost, basically? A condenser or heat exchanger will be more capex but consuming fresh water is more opex. And something like these water capture panels might be a way to pick an operating point somewhere in the middle: lose a bit of water, but capture a lot of it for low up-front expenditure?
> isn't the point of steam to carry heat _away_ from the plant?
The point of steam is to turn a generator, these plants are basically steam engines using heat to produce steam for driving a turbine.
Edit: I think I'm wrong in that the steam loop for driving the turbines is isolated from the loop including the cooling towers which is strictly for cooling the closed generation circuit via heat exchangers to condense the steam... you're right.
The point of steam is to turn a generator, these plants are basically steam engines using heat to produce steam for driving a turbine.
Edit: I think I'm wrong in that the steam loop for driving the turbines is isolated from the loop including the cooling towers which is strictly for cooling the closed generation circuit via heat exchangers to condense the steam... you're right.
The process of evaporation of water takes a massive amount of energy, which is exactly what's needed if you're trying to get rid of heat from a data center or industrial processes.
To do the same with a heat exchanger would need a much much bigger heat exchanger, and some of these evaporation systems are already pretty big.
To do the same with a heat exchanger would need a much much bigger heat exchanger, and some of these evaporation systems are already pretty big.
Actually steam and fog are different things. Fog is already condensed steam that consists of small water droplets. This technology captures the condensed water droplets and at this point no no extra latent energy from steam is released.
I wonder if this tech could be applied to evaporative cooling systems for data centers in hot regions to capture the water that is otherwise lost.
I know many of the big data centers use a ton of water in areas that don’t exactly have water to spare.
I know many of the big data centers use a ton of water in areas that don’t exactly have water to spare.
What hot regions use evap systems in data centers? Seems the humidity wouldn’t be worth it and once you dehumidify you might as well use an a/c in the first place.
Does a compressor use more energy than a dehumidifier? Seems like there might still be some savings by avoiding the compressor
I thought dehumidifiers contain compressors.
There you go then! In my head, I was envisioning a humidifier, so I guess that's not going to work at all.
> ...vapor collection could be made much more efficient by first zapping the tiny droplets of water with a beam of electrically charged particles, or ions, to give each droplet a slight electric charge. Then, the stream of droplets passes through a wire mesh, like a window screen, that has an opposite electrical charge. This causes the droplets to be strongly attracted to the mesh
Woah, this seems really simple and possibly applicable to other situations where you're trying to condense a vapor.
Woah, this seems really simple and possibly applicable to other situations where you're trying to condense a vapor.
That's how cars are painted :)
[1] https://en.wikipedia.org/wiki/Electrostatic_coating
[1] https://en.wikipedia.org/wiki/Electrostatic_coating
So the summary is that some evaporation systems waste water by letting condensed water droplets escape rather than water vapor. Those water droplets aren't carrying away much heat like the vapor is, so are effectively just wasted water. This system recaptures those water droplets.
Would having two meshes of opposite charge work?
Will it be something like the ones used for binary load lifters?