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Pocket Rocket For Water Distillation/Purification?  RSS feed

 
Sean Murphy
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Hey guys, I'm thinking about a university project I'm going to be working on in a few weeks where I have to purify 1L of water in 30 minutes with a budget of $100. The water is going to contain soil, bacteria and salt. Soil and bacteria are pretty easy to take care of but the only real way I know of to remove salt is distillation, which obviously requires boiling. Unfortunately, boiling a litre of water DRY in 30 minutes would take an enormous amount of energy. Even a gas stovetop probably wouldn't be enough. But then I remembered reading something about rocket mass heaters and thought it might have a chance. So I've been reading a lot about them in the past few hours and thought I'd post here for some advice.

I think this has potential after reading page 16 of this document (boiling 2.5L of water in ~25 minutes): https://www.engineeringforchange.org/static/content/Agriculture/S00069/Rocket%20Box%20Design%20Document.pdf

But as for a design, I'm pretty much clueless at the moment. All it really needs to be is small and as hot as possible. Efficiency is pretty much irrelevant but it would be nice I guess. Any tips?
 
C.J. Murray
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Location: 5,500 ft. desert. 13" annual precip.
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Start by looking at this: http://www.oldjimbo.com/survival/kellystove.html

And this guy's videos. I think he has posted here before: http://www.youtube.com/user/bs4872
 
Sean Murphy
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C.J. Murray wrote:Start by looking at this: http://www.oldjimbo.com/survival/kellystove.html

And this guy's videos. I think he has posted here before: http://www.youtube.com/user/bs4872


Hmm... bs4872's water heater is just that, a large volume, low temperature water heater. I'm looking more for a low volume, high temperature boiler. I guess there isn't much of a design difference though, so it does show promise. The Kelly Kettle seems a little less practical... just not large or powerful enough. It doesn't use the "reburn" that makes rocket heaters so powerful.

However, I did find this somewhat inspiring: http://www.youtube.com/watch?feature=endscreen&NR=1&v=ati_6roaTOA

Still a lot of research to be done. There are a lot of ways this could go.
 
C.J. Murray
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Location: 5,500 ft. desert. 13" annual precip.
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I’m thinking I was simply pointing out the double wall feature. The diameter, height, double wall volume and amount of water put in it is at the user’s discretion. I highly recommend the use of a rocket heater for simplicity sake and cost of materials. The parameters are easy to change.

If the Kelly Kettle’s volume is too little then increase it..

If the Kelly Kettle’s height does not take advantage of the reburn then make it taller.

If bs4872’s water container holds to much water then don’t fill it up. He certainly has enough heat being generated.

Is this an exercise for an engineering class of some type?

Since there is time to scrounge for used materials utilizing a piece of used double wall stove pipe should be considered.
 
Ernie Wisner
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Does it have to be a single distill? you could use small diameter pipe and do a high heat distill then An evap and distill. by the end of the process you should have about as pure water as you could get. it should do it well under 30 min. if you balance your feed speed you should be able to pull live steam off the pipe and recondence it into an evaporation retort then recondence that into your product. A small pocket rocket should give plenty of heat to perform both operations with little of no slowdown.
 
Sean Murphy
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Ernie Wisner wrote:Does it have to be a single distill? you could use small diameter pipe and do a high heat distill then An evap and distill. by the end of the process you should have about as pure water as you could get. it should do it well under 30 min. if you balance your feed speed you should be able to pull live steam off the pipe and recondence it into an evaporation retort then recondence that into your product. A small pocket rocket should give plenty of heat to perform both operations with little of no slowdown.

I'm not sure I follow... are you saying double distillation? What do you mean by an evap and distill? I was thinking just boil it all once, capture the vapour and condense it into another vessel. Do you think it would make a difference whether a low volume of water is being slowly dripped onto the rocket or a large volume is surrounding it? Also, would an open top with a pot sitting on top of it be better or worse than another cylinder over the top, with a pot sitting on that? And yeah, I'm hoping a pocket rocket will suffice... it's an utterly enormous amount of energy though. How big do you think it will need to be? Tin-can size or much bigger?
 
Ernie Wisner
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I am picturing a 5 gal pocket rocket, with 1/4 inch or 3/8ths pipe wrapped around it, and somewhat high flow, so you get live steam just as it gets to the end of the pipe. The supply tank would be up relatively high, so you can run a loop of pipe down and back up without too much chance of steam-locking the pipe.
Then the steam gets put through a condenser (cold pipe, can be metal or glass, usually coiled up in an ice bath or cool water bath). In my version, that condenser would drip into an evaporation chamber on the stovetop, with another condenser that drips into your final collection beaker.

If I understand correctly, you are looking for a very fast way to distill water, and get the purest product you can. Some salts and minerals will only come out when the water is evaporated the second time, just boiling it can spit minerals into your distillate. If you are just looking to create drinkable water, you might be able to use the boiled-off results.

You might also look at prices for a reverse-osmosis filtration system. There are some on the market for under $100, but they might not meet the 30-minute deadline.

If you pre-filter all the guck with cheap materials you should have a much easier time with either distillation or osmosis.
(Cheesecloth, coffee filters, worn cotton; Erica remembers somebody suggesting 4 layers of an old cotton sari will remove most waterborne parasites in the Ganges if you don't have anything else).

As far as the pots, direct contact just above the flame path will give you good heat transfer, but if you are picturing an open-flame type rocket cookstove, you also have to keep the soot and smoke out of your setup. See if you can find Erica's illustration of the J-tube pocket rocket; it's a contained fire that gives good access to both high- and low-temperature heat without messing up your fire's burn by making the fire itself too cold.

A drip gives control; but it's slow. A big hot bath (maybe with a towel or something to speed evaporation) might be faster, but could give too much pressure unless your condenser is set up to accept all that steam at once. A pipe with fixed diameter, and controlling the flow by raising or lowering the source tank, lets you put a fair amount of material through quickly but stay within the limits of your condenser. You'd definitely have to pre-filter it though, or risk blowing the pipe.
 
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