Submitted by MiloFrank76 t3_10paoln in explainlikeimfive
dkf295 t1_j6ja1cf wrote
Desalination itself is super easy. Take salt water, evaporate and recondense it to separate the salt and other minerals/etc from the water. You can do it yourself on a stovetop or a campfire.
The problem is that there's no way to scale it easy for the massive demands of human use (personal, industrial, and agriculture). It takes a decent amount of energy to heat up water, and you need to do something with all of the salt you've got left over - no matter where you dump it, you're going to cause environmental problems. Salt is also corrosive so there's longevity problems with equipment/piping/etc but those are relatively minor problems with partial solutions. You can't ignore physics, or just make giant piles of salt disappear.
Thoscellen t1_j6jac5d wrote
Are not some power plant near the sea for heating the water?
RhynoD t1_j6jb07i wrote
That explanation is good but I think it underestimates just how much energy it takes to evaporate water, especially at scale. Yeah, you can use a power plant but we're already struggling to generate the power that we need in ways that aren't destructive to the environment.
konwiddak t1_j6jmd3k wrote
In any real world plant that operates via evaporation, most of the energy used to boil off the water is re captured via the heat exchangers used to condense the steam back into water. This heats the incoming water. (Most are multi stage running different parts at different temperatures/pressures.) Overall its a pretty efficient process, with reverse osmosis a bit more efficient.
However the amount of water that we use for not drinking purposes, irrigation, washing e.t.c is massive.
dkf295 t1_j6jbd75 wrote
Most power plants do use water in their power generation, but it's largely a closed loop and freshwater is used. Fossil fuels/trash/radioactive decay is used to heat water which evaporates into steam and turns turbines, then cools and gets used in the cycle again.
If you decided to use saltwater in this process, the salt would be super super hard on the powerplant, piping, etc and dramatically reduce the lifespan and increase the maintenance costs of the power plant. You also wouldn't be able to generate water safe for use, as the water would likely be contaminated. You're better off with a dedicated power plant and a dedicated desalination plant.
Finally, you still need to figure out what to do with all that salt. If you dump it back in the ocean, you're going to kill off wildlife en masse and just generate more and more salt over time, as the salt concentration in the water you're pumping in increases. You can't dump it on land, it will completely destroy the ecosystem and you will need a TON of space. Unlike landfills, it won't decompose over time - just wash away (which means you're killing things elsewhere). You could potentially use old mines and such, but those aren't reliably structurally sound and you're still risking runoff or even worse, getting massive amounts of salt into the water table.
Caucasiafro t1_j6jde4j wrote
Regarding "what to do with the salt" wouldn't we be able to just use the salt from desalination plants and have that replace salt mining?
Obviously the concept is killed before even getting to this problem but I'm just wondering.
Envelope_Torture t1_j6jl40g wrote
Most large scale desalination is reverse osmosis, which produces a very salty brine rather than solid deposits of anything. Further processing and refining of minerals from this would also be very resource intensive as well as complex. There is a lot of research going on in this area as well.
VelocityDuck t1_j6ka986 wrote
No. They are near large bodies of water for cooling. The ways which is turned to steam is rather pure water to start with.
MiloFrank76 OP t1_j6jlufl wrote
Thank you. Do you think the need for fresh water increases in the future, that we'll figure out something?
c00750ny3h t1_j6ku1l0 wrote
The only thing I can figure out is to conserve water or eat less meat which uses more water per edible calorie compared to vegetables.
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