de-salinastion?

[ridgey]

Hi.

Would it be possible to desalinate water using the weight ot the ocean as power? If there was a stucture deep in the ocean covered with a semi-permiable membrane, and a pipe and pump to take the fresh water to the surface, and reduce the presure inside the structure. The weight of the water providing the power.

I think they use around 800 p.s.i pressure in some comercialy available desalination units. Thats about the pressure is at a depth of around 562 meters.

Any ideas.

cheers

[Externet]

Ok, that means one side of the membrane has 800 psi more than its other side...

The top of the membrane would have the ocean column pushing water down, and you have to make vacuum under the membrane to obtain 0 psi for the pressure differential.

The pump under the membrane would have to be 800 psi anyway for its outlet to reach the surface. Work on that.

Miguel

[ridgey]

As fresh water is boyant in salt water, could it be "packaged" and float to the surface for collection? Would it require a great amount of energy to maintain the vacume, given the fairly slow flow rate of the membrane?

cheers

[insane_alien]

packaging the water would be inefficient.

 

the main problem with using the weight of the ocean to drive this is that you have to pump the water back up with a pump that is much more powerful than the pump you'd need for a normal surface de salinisation plant.

[ridgey]

By package, i'm thinking something like a giant balloon, that would float to the surface when full, and sink back down when empty. let gravity fill the balloon, and flotation carry it to the surface.

[insane_alien]

ridgey, its still less efficient than a pipe. it may seem like a good idea but your still going to need a pump to fill it and its not just going to sink fast enough on its own. a pipe would be better.

[Klaynos]

As I see it maintaining the pressure differential is a big problem here :\

[insane_alien]

couple of stages of centrifugal pumps would handle it nicely

[Klaynos]

couple of stages of centrifugal pumps would handle it nicely

 

And how energy efficient would that be?

[insane_alien]

well, they're more efficient than reciprocal pumps would be in that application. maybe 78% -ish. with a reciprocal pump you would only need one pump to handle the pressure differential but it would only be about 50% efficient maybe less.

[SilverStar]

It would be best to just lay a large sheet of plastic over a frame on floats. as the water evaporates it is condensed on the plastic sheet. Basic physics states that as water evaporates it take nothing with it. By using only the Sun's rays you get fresh water that is safer to drink than the best purifiers can make. you only need to get the water to land. However you can simply use soler panels to provide the power, still the Sun.

[insane_alien]

yeah but the whole point of this is reverse osmosis rather than distillation. the former requires less energy.