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Stupid question time, why not expose the sea water over a larger area and expose to sunshine? There's plenty of room in the UAE for this, somebody is even building a wall that could hold the water which could be dual purpose and act as cooling via evaporation...
Larger area than the oceans?
Earlier quoted context omitted.
In an operation like that, do they heat the syrup under low pressure to reduce the boiling point of water?
I'd guess that if anything they'd increase the pressure to raise the boiling point. That way things dissolve in it faster and the water doesn't evaporate away.
Probably very dumb idea, but would it be feasible to just pump and sprinkle sea-water on hot, dry desert and let it naturally evaporate, and then collect it as fresh rainwater back? i.e. how much water would you need to evaporate to have a noticeable increase in rainfall?
Can I shower in salt water? Then all I need to do is desalinate drinking water. “Distributed” home desalination for drinking water seems like the best approach in my mind, then people can pay as much or as little they need, but I have no real data to back this up.
You at least need special soap: https://en.wikipedia.org/wiki/Saltwater_soap
Earlier quoted context omitted.
In an operation like that, do they heat the syrup under low pressure to reduce the boiling point of water?
I'd guess that if anything they'd increase the pressure to raise the boiling point. That way things dissolve in it faster and the water doesn't evaporate away.
I am not a physicist but let me give it a stab: except for a few specialized steps like UV or oxidizing heavy metals, most filtration is mechanical. A series of filters with smaller and smaller pores capture more and more of the mess in the water like bacteria and particulates while UV breaks down viruses, the oxidizer precipitates out metals, and so on.
None of those methods work with salt. Salts in general disassociate through ion-dipole interactions - the water dipoles essentially rip the ionic compound apart and surround each ion in what is called a hydration shell. They're bigger than bare water molecules but not much bigger - much too small to target with pore size. This shell also puts them in a thermodynamically stable state and it takes energy to "jostle" the water molecules away from the ions either through evaporation, distillation, or through another chemical reaction that precipitates out the ions.
As it turns out, doing that takes a lot of energy, so we use reverse osmosis as a cheaper alternative: we exploit the hydration shell of the ions by putting them behind a semi-permeable membrane with very small pores, "nanopores" if you will. The pores are too small for water to cross normally, but under high pressures bare water molecules can be forced through the pores while the ions trapped in their shells remain and concentrate into a brine. It takes less energy but produces a concentrated liquid waste stream that must be disposed of.
Someone please correct any mistakes I've made
Can I shower in salt water? Then all I need to do is desalinate drinking water. “Distributed” home desalination for drinking water seems like the best approach in my mind, then people can pay as much or as little they need, but I have no real data to back this up.
It's not difficult. It's just energetically uphill. Undoing entropy costs energy. Second Law of Thermodynamics.
The thing is, it doesn't have to be. The energy released by mixing salt into water is small, around 3.9kJ/mol. Molar mass of salt is 58g/mol, and the average sea water salinity is around 3.6% So a cubic meter of sea water will have 1000*0.036/0.058=620 moles of salt, and it'll require 2.4MJ of energy to remove the salt in a perfect desalinator. In more common units, 2.4MJ is about 0.75 kWh. Around here electricity is…
> A thousand liters takes about 3kwh.
So, if those numbers are right, desalination is currently at about 25% of theoretical energy efficiency. Is that correct?