Step 5: Useful Byproducts
At the brine chamber as more and more water gets vaporized, the concentration of the brine solution increases ie. the salt content in the chamber increases. As more and more water is desalinated, the liquid in the chamber soon becomes saturated brine. This can be tapped off periodically. What use is saturated brine?
1. It is used to preserve vegetables, fish, meat etc.
2. Brine is also a common fluid used to transfer heat in large refrigerator installations.
3. It can be used to manufacture common salt (who can live without it?). Just wait till the brine becomes completely saturated. Since the solution cannot dissolve more salt, it starts depositing at the bottom as a residue. Just tap it out.
4. Brine solution is used as the electrolyte in manufacture of Chlorine, Sodium Hydroxide, Hydrogen by electrolysis. Potassium and calcium compounds can also be obtained.
1. It is used to preserve vegetables, fish, meat etc.
2. Brine is also a common fluid used to transfer heat in large refrigerator installations.
3. It can be used to manufacture common salt (who can live without it?). Just wait till the brine becomes completely saturated. Since the solution cannot dissolve more salt, it starts depositing at the bottom as a residue. Just tap it out.
4. Brine solution is used as the electrolyte in manufacture of Chlorine, Sodium Hydroxide, Hydrogen by electrolysis. Potassium and calcium compounds can also be obtained.
Remove these ads by
Signing Up
Visit Our Store »
Go Pro Today »
Since most coastlines are heavily populated the desalination plant could be located inland with 3 pipes running to it, bunch the pipes together and wrap them with insulation. This would be your heat exchanger with 2 of the pipes going into the ocean (sea water in and slightly saltier sea water out) and the 3rd pipe branching off to be distributed into the public water distribution.
In a place like California where inland also means higher elevation then the entire system would run under a natural vacuum due to the weight of the water. The entire desalination plant would have to run as a closed system, with the only openings being at the lower end of each of the 3 pipes for this to work.
The only problem I am having with it in my head is how to reliably clear the brine.
I want to have an inverted Y with the fork right at the edge of the vacuum so the salt water comes up one side and the brine goes down the other with the vapor going up and over to the fresh side. But if the temperature rises then the pressure of the vacuum goes up (from say 0.1 atmospheres to 0.11 atm) the the level will drop below the fork and the brine will be trapped. (and as I said before, dissolved gases coming out of solution and contaminating the vacuum which would have the same effect)
If someone could solve those two problems you could have a completely passive desalination plant. Anyone could walk down to the beach next to the 40 ft tall tower and pour themselves a glass of free, pure water.
Could you please explain how:
- you assume a 33ft head over the sea level will produce allow boiling at ambient temp. on what principal is this based?
- you propose to produce a vacuum with this height difference. Is it more a "suction" imparted by the flow of stored sea water from 33ft down to sea level again? I know that 10m of head (about 33ft) = 1 bar or 14PSI in pressure when measured at the base, but are you saying that the opposite, draw, would produce a -1Bar vacuum?
Thanks!!!
- water production could be slow, just a couple of gallons a day would be fine, most second residences are not used that often
- the unit would be small enough to be almost portable, at least would fit in a car. The feeds and returns would be the standard black plastic water pipe, very cheap.
- ideally it would be 100% solar powerable with less than a 100W panel, this enabling small DC pumps (or vacuum pumps) to run in daylight hours = no accumulation battery
It has to do with vapor pressure. As you heat a liquid its vapor pressure rises and the rate at which it evaporates goes up. When the vapor pressure equals the pressure pressing down on it can evaporate from the middle. We call this boiling.
Now, if the pressure pressing down on the liquid is lower then it doesn't need to be as hot to overcome the atmospheric pressure. People who live on mountains know this because they have to boil their eggs longer or add stuff to the water to raise its boiling point back up to 100C.
If you reduce the atmospheric pressure enough then the water will boil at room temperature. You can see demonstrations of this on YouTube.
Now, boiling takes energy, no matter how low the pressure is, so you still have to heat it or it will get colder and stop boiling. But you only need to keep it at room temperature.
re. your second question, take a glass and stick it in a sink full of water. Turn it upside-down and slowly lift it out of the sink. Why does the water stay in the glass? Why does it get heavier the higher you lift it? It has nothing to do with flow.
Sorry I am getting too tired to think. If the rest doesn't come to you then I will explain another day.
Good night,
Gordie.
I get it now, and some youtube videos really helped :) indeed by flow and vacuum we were talking of the same thing: with a pump fill a tank 50feet up, shut off the flow, and the water will drop to 33ft, the space above will be a vacuum.
The problem I now see is how to extract the water vapor to be condense else where, or the water itself if condensed in the upper vacuum chamber space, without braking the vacuum!! One solution mounts the fresh water collection at sea level (0 feet), which would work when the condenser was installed in the upper vacuum space (www.vacuumdesalination.com), but requires a second pump, and more energy, to return the water where it is to be used (a small tank at about 33ft).
but with a few improvements.
I like your idea of the pump. You would only need about 25 PSI pump which should be cheaper than a vacuum pump.
Then you use a solar collector to heat the salt water and put the fresh water tube in the shade with fins on it. The solar collector doesn't have to be very big, just enough to raise the temperature a few degrees above the air temperature at the condenser.
As you mention, a small capilary solar water heater (pool type) would produce a few more degrees for a stronger boil.
There's only one vacuum chamber. It separates the salt water from the fresh water. You only need one vacuum pump to keep it 'clean' of air.
I guess I should make a sketch to be clear...
Check out this:
http://www.eng.usf.edu/~abutayeh/Files/Solar%20Flash%20Desalination%20under%20Hydrostatically%20Sustained%20Vacuum.pdf
(for some reasion the link meses up, but google "Solar Flash Desalination under Hydrostatically Sustained Vacuum.pdf" and you'll find it