Hobo stoves, tin cans and braziers

[ESpy]

please keep us updated on your progress re: Calcium Acetate.

Well, I finally used some of it. It took ages to evaporate adequately - cold windowsill - but evaporate it did. I was left with some clumps of white crystalline deposits, that I ground up a bit to powder them. Dissolved 1/2 a film can-full in the same volume of water (or tried to), then added 1 1/2 film cans of meths. A gel formed almost instantly on the top; after a few minutes, the rest of it gelled. The instructions say to add the alcohol slowly - I didn't (OK, I slipped) and it took longer than the instructions suggested.

Other points - the stuff will dissolve far more readily in hot water than cold (naturally); also, I could do with grinding it to a finer powder. This is a thixotrope, so stirring it doesn't help much in maing it - you're persuading it to stay liquid.

But it does work... :twisted:

 

[Stew]

So it burns well then?

You'll have to give us a more detailed account of what you did! ie how many eggshells, amount of vinegar, etc.
:bu:

 

[Adi007]

How many eggshells did you need to get that much calcium acetate?

please keep us updated on your progress re: Calcium Acetate.

Well, I finally used some of it. It took ages to evaporate adequately - cold windowsill - but evaporate it did. I was left with some clumps of white crystalline deposits, that I ground up a bit to powder them. Dissolved 1/2 a film can-full in the same volume of water (or tried to), then added 1 1/2 film cans of meths. A gel formed almost instantly on the top; after a few minutes, the rest of it gelled. The instructions say to add the alcohol slowly - I didn't (OK, I slipped) and it took longer than the instructions suggested.

Other points - the stuff will dissolve far more readily in hot water than cold (naturally); also, I could do with grinding it to a finer powder. This is a thixotrope, so stirring it doesn't help much in maing it - you're persuading it to stay liquid.

But it does work... :twisted:

 

[ESpy]

I'd estimate I used about 250ml of strong vinegar (the pickling stuff); I kept dropping eggshells in until they didn't dissolve any more. Maybe 6 or 7 eggshells, depends on the size of the eggs. It isn't precision stuff, it is really just using up as much of the acid as possible. Chalk would work, as would marble, but I had eggshells on hand.

One other point - yes, it burns well, and leaves a white deposit in the burning container. Given that calcium acetate decomposes above 160C (to form acetone vapour and calcium carbonate, apparently), I would imagine that this is just calcium carbonate (which could be reacted with vinegar again).

Safety data: http://www.intox.org/databank/documents/chemical/calcacet/cie671.htm
(there are probably others worth readig too)

This reaction works with isopropanol, too.

 

[Roving Rich]

Hi Espy,
I am a bit lost with this one could you possibly start a new thread outlining the process :bu:
Thanks Rich

 

[Adi007]

I might have to try this with glacial acetic acid (the pure stuff!) :f:

 

[ESpy]

Nice if you can get it, but that moves away from my kitchen chemistry approach of subverting household goods :twisted:

Unless glacial acetic is something you keep under the sink? I shouldn't be surprised, after all, I have 98% sulphuric under mine...

 

[Adi007]

I don't keep it at home ... I just have "access" to some!

 

[Andy]

if you put abit of foil under the grateof your stove you don't burn the ground.

 

[Les Marshall]

Because funds are short, I adapted an old mettle paint kettle by drilling holes round the bottom and fill it with charcoal, over which I sprinkle meths and stike a light with my fire steel, this burns hot and for a long time. I have used it under a lean too bivvy and found that I was snug as a bug. :f:

 

[Keith_Beef]

I made one of these at the weekend...

I took two coffee cans, a small awl and my Leatherman SuperTool.

I used the awl to punch a lot of small holes and also a blade to cut out two larger holes in the bottom of one can, then used a can opener on the SuperTool to take out what is a perforated disc.

On the other can, I used the awl again to punch a lot of holes, over a height of about 2" from the bottom.

Then, in three places around the can, I cut out a V shape, and folded this inwards. These serve as brackets to hold up the grate, which will be around 3" above the base of the can, and also allow in more air, and allow me to light the fuel resting on the grate from below (one of the larger holes in the grate lines up with a hole in the side).

I had to crease the grate slightly to fit it into the can, but with the brackets sticking about 1/2" inside, there's no way it can fall right to the bottom. OK, so if I tried, I suppose I could have done that. But even I'm not that clumsy at four in the afternoon. Not usually.

So now that the stove was finished, I threw some paper and tinder in the bottom, then kindling, then slightly thicker stuff (nothing revolutionary there, then).

A match poked in under the grate made the paper catch, then the rest, and in a short while there were nice yellow and blue flames coming out of the top.

But as for cooking on it, no chance!

I was looking forward to making some proper coffee, but my coffee pot must have been trapping too much smoke inside. I just got a tar-like deposit on the bottom of the pot, tepid water inside it, and some charcoal...

OK, so the optimist in me says I have got myself a charcoal kiln. Or maybe even a producer-gas generator, if I tweak it... But really what I want is a hobo stove.

Back to the drawing board, I suppose.


Keith.

 

[Keith_Beef]

I've made a new "double-wall" stove; a coffee can inside a beer can.

The idea came from looking at high-efficiency woodburning stoves for use in countries where deforestation (from collecting firewood) is a very severe problem.

Fuel is chemical energy. Burning the fuel converts the chemical energy to thermal energy (heat). There is some loss of energy at this stage, though not too much.

The big problem is transfering the heat to the food to cook it.

Cooking over an open fire, only around 5% of the heat goes to the pan containing the food.

Over a primitive stove, this improves to perhaps 15%, but over an improved stove, this can reach 25% to 30%.

Here are two sites (among the many that I looked at recently) that discuss improved stoves:
http://www.solutions-site.org/kids/stories/KScat2_sol60.htm
http://journeytoforever.org/at_woodfire.html

I decided that I could put a coffee can inside a beer can and fill the space between the two with wood ash as an insulator. The combustion chamber is in the bottom of the coffee can; the heat is trapped in there, hot gases must rise up to the base of the pan and around the sides before escaping into the air.

I realised quite soon that my sheet-metal skills are not quite up to such a complicated construction, so the first attempt doesn't have any insulation between the two cans, other than air. But this should still give a little boot to effifciency.

I tried it this morning, but had problems with the pan smothering the fire. I think I need to cut a flue hole near the top of the combustion chamber, or find a smaller pan.

I also had a problem with the latch for closing the fuel door. The flange of pop-rivet I used is too small, the latch comes off and the stove is too hot to put it back on.

I'll replace it with a small machine screw, like the one on the door.

A list of images (unsorted and without comments, for now) should be here:
http://mysite.verizon.net/keith_beef/Hobo_stove/In_construction/list

I think that I could put a shelf around the outer chamber, to hold the insulating ash, as the design sketch shows.


K.