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Post by spinifex on Jul 28, 2019 10:05:49 GMT 10
Completed a 1 hour test run with my 'improved' model 2 water desalination/sterilisation still. I got 1.6 litres of perfectly clean fresh water from seawater. Mod 2 is very similar to my first design but with some important refinements. Evolution of design and learnings from tests are provided below.  Model 1. My first attempt I had trouble with steam escaping from around the lid of the boiler. I also had an unsupported/unframed condenser coil with poor orientation. The poorly oriented coil meant that water condensing in the tube would create blockages in sections where there was no downward gradient in the coil loops. The steam leaks around the lid meant insufficient pressure inside the system to push the little water blockages in the tube through and out into the jar for receiving the fresh distilled water. The output on the first test was zero. I fixed the pressure leaks around the boiler lid by wrapping about 4 layers of pink plumbing tape around the rim of the lid. The and test 2 yielded a decent amount of water. Accurate measurement of the output was hard as liquid came out as a series of spurts due to the poorly oriented coil.  This is model 2. I didn't want to be reliant on 'consumable' plumbers tape to get a good seal on the boiler lid so I paid $6 for a length of rubber channel to fit to the top edge of the pot. (The black rim). The channel is very precisely cut with a box cutter to get a perfect join where the two ends of the rubber meet - this is important to prevent pressure leaking when the lid is on. The condenser coil now has an external frame attached to give correct orientation of all the loops so water flows unimpeded down through the coil and out into the collection jar. The frame is made from a section of adjustable shelving rail. The coil is attached to the frame with zip ties. The spot where the condenser tube exits the cooling bath is sealed up with gutter sealant.  The Model 2 being given a test run. The tests are being run with a gas burner but the boiler is intended to be heated with a small wood fire. Compared to model 1 I added a system to enable addition of cold water into the bottom of the cooling bath that allows the really hot water at the top of the cooling bath to flow out into a collection bucket via a short 25mm pvc overflow. On long runs it is vital to be able to add cold water and remove hot water from the cooling bath to keep the condenser tube cold. Cold water is poured into the black funnel, travels down a length of 25mm to the bottom of the cooling bath and enters the cooling bath through a T piece that helps the cold and hot water layers to not mix too much - this helps with efficiency. I now put the lid on upside down to get a good seal. (The old system of plumber tape on the lid rim is visible.) The distilled water now comes out (into the blue bucket) in a steady little trickle. |
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Post by spinifex on Jul 28, 2019 10:41:45 GMT 10
Additional learnings to guide future designs:
1. Heat is currently wasted by water vapour and steam condensing on the upper sides and lid of the boiler. I think this is a significant loss of efficiency and freshwater output. The upper part of the boiler should be well insulated against heat loss. Even just adding a 4-5 cm thick layer of dry sand onto the lid would be a help. As would winding a broad strip of wool blanket or other insulation around the sides of the boiler. The more heat loss in the boiler can be prevented the less firewood has to be collected to feed the system. Also the rate of steam generation should rise creating more gas flow through the condenser coil and more freshwater output.
2. Generating fresh water using a coil relies on boiling water to generate pressure to force water bearing gasses through the coil. That's a high energy system. I think a design that condenses low temperature water vapour (not steam) on a sloped overhead plate and collects via a gutter would probably generate more fresh water from much less firewood. I am thinking about a new 'A frame' design made from simple items to test this concept.
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Post by WolfDen on Jul 28, 2019 12:36:40 GMT 10
I’m looking to do some research on how the old timers set up their stills in regards to cutting on steam vapour leakage. Very interested in how they dealt with it. There’s always an unfortunate cost with purchasing insulation tape for each cook.
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Tim Horton
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Post by Tim Horton on Jul 29, 2019 5:18:17 GMT 10
It has been too many years ago, but in Hydronics, Power Steam class there were charts from the late 1700s, early 1800s about evaporation rates and fuel consumption from the old Scottish whiskey distillers. Info is still relevant, hardware is much better I'm sure.
There should be info about worm size compared to boiler size and efficiency that will be helpful.
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myrrph
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trying to figure out how to change my nick :P
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Post by myrrph on Jul 29, 2019 13:41:45 GMT 10
Thanks Spinifex! this thread is so good!
I have been wondering how to get the distillation, not just for seawater, but maybe even grey water. what is the residue like after distallation?
Can show pics?
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Post by spinifex on Aug 3, 2019 17:08:01 GMT 10
The third test I did (1hr long on model 2) left about 2 litres of clear, presumably very saline water in the boiler.
My impression is that the evaporation rate of the water during boiling slows down as the water left in the boiler gets more and more salty.
My next test will be a 1 hour run starting with 6 litres of sea water and I'll end the experiment if I meet my target of 4 litres of distilled water per hour - leaving 2 litres of highly saline water in the boil. I think I read somewhere that boiling hypersaline water can dissolve aluminium and my boiler at the moment is an aluminium pot.
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Post by spinifex on Aug 4, 2019 15:50:45 GMT 10
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Post by spinifex on Aug 4, 2019 16:20:36 GMT 10
I tried a new design today (Model 3). Took about an hour to put together. Zero cost as its all scrounged materials I had laying around. The sheet metal is actually the roof of an old rusted out raintank. A copper dome condenser. This one is air cooled at the moment. I'm going to modify it next week to be water cooled and this should greatly improve the rate of output of distilled water. I had to use a different boiler as the handles on my other pot got in the way of the base-plate the dome sits on. The best I could get from this one was 600ml per hour. It did use much less energy input to make that water compared to my Model 2 coil type condenser. It requires so little energy to operate that it was producing at 600ml per hour (ie its peak rate) for 20 minutes after I shut off the burner. A coil condenser will not do that - they stop as soon as the flame is put out. I'm contemplating attaching one or more coil condensers to a water cooled version of this dome in order to acheive my desired 4 litre per hour target output.    |
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Post by spinifex on Aug 9, 2019 15:38:27 GMT 10
 Linear condenser on the 15 litre boiler.  The End Game: my 80 litre wood fired boiler, copper dome, with my original 3m coil condenser. The hard part with this one is keeping up the supply of cold water to cool the condenser coil. |
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Post by Joey on Aug 9, 2019 16:45:46 GMT 10
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Post by Joey on Aug 9, 2019 17:12:01 GMT 10
Another quick thought, would putting a neoprene or similar hose insulator on the pipe between the burner and the cooling pot help at all?
Now you got me wanting to make one lol
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Post by spinifex on Aug 9, 2019 18:51:37 GMT 10
Yes, using actual sea water. Mainly because it has other things in it besides just table salt. Wolfden put me on to the concept of discarding the first part of the distilation run (about 100ml) as it tends to contain some kind of volatile impurity that makes it have a faintly bitter after-taste. The water after that is pristine tasting. With practice a person could learn to take the left over hyper-saline water and do fractional crystalisation to recover medically useful iodine, potassium, magnesium and calcium salts and maybe even a bit of nitrate for preserving meat as well as 'table' salt for curing meat.
My thinking is that any insulation mainly needs to be on the top and upper sides of the boiler just to help keep the heat in the pot and generating steam and not losing it to the air. Mostly a fuel efficiency measure but it might help increase steam generation too.
They are a good bit of kit. Oz is surrounded by sea and much of the inland groundwater is saline too. One of these rigs opens up a lot of possibilities for travelling away from the more visited fresh water terrain features. Worth your effort to experiment!
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Post by Joey on Aug 9, 2019 19:32:01 GMT 10
Might turn it into a weekend science experiment with the young ones.
Willing to try pee in the tub and boil that off? lol
I once did a survival training course and they had a much more agricultural setup of the evaporative water purification on a small hose leading from the boiler covered by some dirt along the way into the collection pot. They had us all try the water, then they showed us where they got the water from.. A small cattle dam that the cows had shit and pissed in as they do when drinking lol
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Frank
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Post by Frank on Aug 9, 2019 20:28:01 GMT 10
Awesome thread. I am no where near the sea, but can see the benefits for some of the possible water sources around me. Good work
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Post by spinifex on Aug 11, 2019 12:30:29 GMT 10
I tell you folks ... it pays to test and experiment. I ran mod 4 (linear 1.5 metre length of 12mm copper tube with a 1m length cooling jacket) today. And learned some things.  1. It yielded 2.9 litres of fresh water per hour starting from sea water. The fresh water coming out is quite cold so it means the condenser tube has the cooling capacity to be able to stoke more heat under the boiler to generate more steam and generate an even higher rate of fresh water production. (When warm condensate starts coming out the system is nearing its limits to condense steam back to water.) 2. New cooling water MUST be trickled into this design constantly or: 3. The temperature of the cooling water at the end closest to the boiler rapidly gets to near boiling. 4. The pvc pipe cannot hold up against boiling water - it goes soft and deforms. 5. The silastic used to seal the copper tube into the pvc doesn't like high temperature either and fails. (I'll use high temp gasket glue next time). I think expansion of the copper tube inside the jacket as it heats up also contributes to the seal failure. 6. Lots of major leaks form in the cooling jacket! 7. Experiment aborted after 12 minutes due to excessive leakage. |
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Post by spinifex on Aug 11, 2019 12:42:33 GMT 10
General thoughts about designs.
1. A well made coil in bucket is a nice compact item easy to move without getting damaged. In my case it fits neatly inside the boiler pot which both protects it and takes up less space.
2. The copper coil does not require the use of high temperature sealants or any high temp components at all - unlike the linear design.
3. It seems that the biggest factor in getting a high rate of fresh water production is how much steam the system can generate and push through the condenser. I used a much bigger burner for the most recent test and got a higher rate of output. All my condensers have had cold water coming out of them which means they have lots of reserve capacity to handle more steam.
4. Always use a boiler that can let excess pressure escape through the lid. Screwtop or clamped lid boilers without pressure release valves can become highly dangerous steam bombs.
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kelabar
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Post by kelabar on Sept 3, 2019 21:40:08 GMT 10
Great topic with excellent info. A couple of thoughts spring to mind for the coil type.
The boiler could be tilted so the exit to the coil is slightly lower. This would hopefully cause the condensate on the lid/top to run downward. If a small funnel or tray could somehow direct this runoff into the coil this might help increase production. It may require some sort of customisation to the boiler but it might be worth it. Or custom make a boiler with a sloping lid or top.
With the coolant water getting hot at the top of the condenser, compress the coil to about half of the condenser height and have the coil enter about halfway down the side of the condenser. But still have coolant to near the top of the bucket. This might get the coolant moving by convection and even out the coolant temperature. It would require sealing around where the coil enters the compressor, make that condenser, though. But I don't know how this might affect the efficiency.
For a more permanent installation the boiler could be topped up by a feed from the coolant as it will be preheated. Similarly adding cold water to keep the coolant level up would help condensation. Not a great efficiency increase probably but worth consideration. Possibly a pump or one-way valve would be required Not sure. Haven't thought it through but other plumbing-minded members may have ideas.
From my experience with camping and rocket stoves it would be very worthwhile adding a sheath around the boiler to hold in heat. Something like a 20 litre drum or similar with the top and bottom cut out. Cut a hole or holes at the bottom to allow air feed to the fire (and to allow fuel to be added if solid fuel is used) and place the drum over both the heat source and boiler. If there is a one or two inch gap between the boiler and the drum this forces the heat into the boiler (or stops it dissipating away, same thing) to a greatly increased extent. Once again only for a more permanent setup or if easily done.
Thanks for posting this info. |
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Model 1. My first attempt I had trouble with steam escaping from around the lid of the boiler. I also had an unsupported/unframed condenser coil with poor orientation. The poorly oriented coil meant that water condensing in the tube would create blockages in sections where there was no downward gradient in the coil loops. The steam leaks around the lid meant insufficient pressure inside the system to push the little water blockages in the tube through and out into the jar for receiving the fresh distilled water. The output on the first test was zero.
This is model 2. I didn't want to be reliant on 'consumable' plumbers tape to get a good seal on the boiler lid so I paid $6 for a length of rubber channel to fit to the top edge of the pot. (The black rim). The channel is very precisely cut with a box cutter to get a perfect join where the two ends of the rubber meet - this is important to prevent pressure leaking when the lid is on. The condenser coil now has an external frame attached to give correct orientation of all the loops so water flows unimpeded down through the coil and out into the collection jar. The frame is made from a section of adjustable shelving rail. The coil is attached to the frame with zip ties. The spot where the condenser tube exits the cooling bath is sealed up with gutter sealant.
The Model 2 being given a test run. The tests are being run with a gas burner but the boiler is intended to be heated with a small wood fire. Compared to model 1 I added a system to enable addition of cold water into the bottom of the cooling bath that allows the really hot water at the top of the cooling bath to flow out into a collection bucket via a short 25mm pvc overflow. On long runs it is vital to be able to add cold water and remove hot water from the cooling bath to keep the condenser tube cold. Cold water is poured into the black funnel, travels down a length of 25mm to the bottom of the cooling bath and enters the cooling bath through a T piece that helps the cold and hot water layers to not mix too much - this helps with efficiency. I now put the lid on upside down to get a good seal. (The old system of plumber tape on the lid rim is visible.) The distilled water now comes out (into the blue bucket) in a steady little trickle. 
