Let's talk about de-salinization... [Archive] - Glock Talk


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04-01-2012, 10:27
I have a relatively infinite supply of salt water nearby (assuming my 17k gallons of stored water runs out).

What are some approaches to De-Salinization besides boiling water under a peaked plastic tent and collecting non-salted water at the edge?

What are some better approaches? As always, cheaper is better, simpler is better, less moving/irreplaceable parts is better.

04-01-2012, 11:01

Use a big pot or basin with a domed lid. Put the lid on upside down with a collection cup in the middle. This wouldn't require any fuel, provided ambient temperature was acceptable, and minimal tending.

Scale size/quantity to desired production. Freezing would be an issue.

04-01-2012, 11:03
I recollect this question coming up recently?

My vote is for a solar still. Infinitely sustainable, no moving parts.

I think I posted my portable "busser's tray" solar still on here, didn't I? It was a hybrid design that put the evaporation tray to the top and let the distillate fall down below. Very efficient. But it looks like the S/P forum only keeps the most recent 4 pages of the forum?

Anyway, I am considering purchasing a solar oven, which I would modify into double duty as a solar still desal device. Should be very efficient.

04-01-2012, 11:37
Volume is the issue I have with both of those. Any solar still examples?

I may have posted this and forgot...

04-01-2012, 11:57
But it looks like the S/P forum only keeps the most recent 4 pages of the forum?

Change your display options at the bottom of the page from 1 month to something longer.

04-01-2012, 12:09
Thanks Gimmejr.

Here's the "bus tub cookie sheet still" thread (my first post here) but the photos are now gone. See if I can hunt them up.

It is based on the commonly seen "busser's tray" used to clear tables at restaurants, and a teflon-coated cookie sheet. The unique part of this design is the tray-up-top, wich steals from Jordanian and Iranian designs that put the brack-water tray near the top for peak efficiency, and the distillate falls below the tray and into the tub. The entire tub is tilted to match the angle of the sun. You do have to construct (of wire rod) a tray holder that offsets the tub angle so the tray stays level.

The expensive part for me was asking the glass cutter to make me a piece of glass with smooth curved corners, that was $30. If I'd done that myself from scrap glass I could have kept the cost down to about $25. With the custom cut glass it was $55.

I've had two important suggestions for improvement: (1) place dark dyed sponges in the brack tray to decrease the potential of spillage (a danger with a tray-up-top design) and (2) to construct a way to siphon off the distillate as soon as it appears. This would be some sort of hose that would suck the distillate off the bottom of the tray, which has the advantages of (1) not re-distilling the already distilled water and (2) removing the clean water without needing to remove the tray, which has a spill potential. Both are good suggestions to be incorporated in my next version.



04-01-2012, 12:26
Improved solar still: http://survivalblog.com/2012/03/the-extreme-solar-still-concept-by-jim-d.html

Or standard whiskey still, you just have to run it a little hotter. If you have a goos source for fire.

They Katadyn lifeboat desalinators come up surplus from time to time, but still $$$$$.

04-01-2012, 12:51
Footnote: I messed around with "hole-in-the-ground" designs for some time, and they all suffered from the same problem: the plastic sheeting would drop most of the distillate within a couple of inches of its origin. So most "clean" water would drop back into the brackish water, and very little would flow all the way down to the drop point.

The design posted above at survivalblog has an exceptionally long "run" which would be challenging.

After reading several dozen practical & academic articles on this, I discovered that "early release" is a very common and serious problem for virtually all plastic-sheet covered solar stills, and one of the main reasons for their inefficiency. The only fix I'm aware of for typical plastic sheeting is to increase the slope of it (requiring a deeper hole), and perhaps to coat it with something slick (maybe wax or vegetable oil? Haven't experimented with that yet.)

Somebody solved the problem by using a specialty type of sheet plastic for the cover...I think it might have been a DuPont product...which acted more like glass. (Glass is so slick lets even the most distant drops slide all the way down to the bottom. Also it is a thicker, better insulator. That's why I used it in my design. A double-pane of glass would work even better.)

But now I can't remember the specific name of the special plastic sheeting that was recommended. If anyone knows, please post.

All the types of sheeting I tried from the big box stores were pretty bad.

Footnote #2: I think you could make a really efficient solar still / desalinator out of a solar oven. That's where I'm headed next. The hotter you can get it inside the "box" the more efficient the still.

Notice how similar in shape this solar oven (http://www.sunoven.com/) is to the bus-tub concept. It's just nicer all the way around, and I'm sure it's a LOT hotter. All you'd need to fabricate is a wire frame to hold a tray.

04-01-2012, 13:30
Now that I see the pictures, it makes a lot more sense. That is a really good design, Bolster.

I also would put a supply line in so you can fill the brack tray without opening the lid. Much less danger of contamination if you never have to actually touch it.