How much energy does it take to desalinate ocean water?

<div class='quotetop'>QUOTE(burritos @ Jul 18 2007, 03:16 PM) [snapback]481104[/snapback]</div>

It'd probably require more energy to pump it inland from the coast than it would take to desalinate it.

 

Israel employs this technology on a fairly broad scale.

http://www.water-technology.net/projects/israel/

Wonder if they're able to sell the salt to generate an offsetting income?

 

As a teenager, I drew sketches for an offshore desalination plant. It was a floating geodesic dome, using sunshine to evaporate the surface water, deeper water to cool the surface of the dome so the vapour would condense, and wave action to power the pumps. Sea salt was a byproduct that could be picked up by barge. Are these in use anywhere?

 

Desalizination, using reverse osmosis (saline fluid pushed through a membrane) is energy intensive. There are large amounts of brine and salt left over to deal with.

Desalizination, using the south Pacific evaporation glass "tent" method is powered by the sun and requires no other energy. This method works best in high air temperatures (40 °C +) and works worst in low air temperatures (lower evapotranspiration)

 

Hyosilver, check this:

http://www.irc.nl/page/24010

 

Has anybody else noted how almost unbelievably cheap these processes are? The thread now has references to several plants with costs in the neightborhood of 0.2 cents per gallon. So, clearly the purchased energy inputs to these processes are tiny. I mean, if the entire cost were for energy, and you burned gasoline to get it, that 0.2 cents would amount to ... 22 (k)calories per gallon. So in fact the entire purchased energy input has to be less than that. Whereas (if I did the math right) it takes 1600 kcalories to turn a gallon of water (at boiling) into steam. I understand that they recover a lot of what would otherwise be waste energy, but that still strikes me as pretty cheap. I have a friend with a water distiller and he figures it takes about 40 cents a gallon to run (at 10 cents per KWH). I pay 0.5 cents/gallon for municipal water but most of that is the sewage rate (and I suppose in fact most of the rest is the amortized value of the infrastructure). But even if the town had to switch to desalinated water, it strikes me that the increase in the water rates would be pretty modest.

 

<div class='quotetop'>QUOTE(tochatihu @ 2007 July 18 11:28 PM) [snapback]481460[/snapback]</div>

Thanks, tochatihu, that's very interesting. This could provide clean, cheap water to millions.

Now, about power generation. Is there yet any such thing as a solar steam engine? I'm thinking of a shiny parabolic trough with a metal tube at the focal point, oriented to the sun. If I put water in one end of the tube, how big does the apparatus have to be to get steam out the other end? Would there be enough steam to generate a reasonable amount of electricity?

 

<div class='quotetop'>QUOTE(hyo silver @ Jul 19 2007, 12:59 PM) [snapback]481731[/snapback]</div>

Are you kidding? That's impossible. :lol: :lol:

Yeah, you've just described Concentrated Solar Power. it's the cheapest form of solar power. Typical plants are basically a Rankine Cycle Natural Gas fired power plant but with concentrators and heat exchangers added in. Apparently, these things can heat water to about 3000 deg C!

 

<div class='quotetop'>QUOTE(hyo silver @ Jul 18 2007, 02:48 PM) [snapback]481134[/snapback]</div>

I also saw something on this concept on the Science channel, or Discovery, a couple weeks ago, about a plan to build a large-scale curved wall. But this was one of things to happen off in the future sometime. Sounded very promising, and wouldn't require an energy source. Seems like a no-brainer to me.