Sunday, September 21, 2008

A biomass cooker

One of the things one is faced with when trying to pare back a budget is this: the majority of really cheap food is fuel intensive to cook. Sure, we all like a good bean soup or locally, good poi, but the fact is that boiling away for hours when the doing so requires the consumption of expensive electricity, liquid or gaseous fuels--suddenly things become much less frugal. It can cost 5 bucks to cook a dollars worth of food, and this hardly makes sense. Suddenly you're better off to have a steak.

So, in the quest for simplicity, I built a simple updraft charcoal/wood cook stove of the type modeled on the "volcano" stove and a zillion others. There's a lot of designs, they all work, some built out of paint cans--mine is a little nicer built out of 6 inch well casing about 15 inches long and a piece of plate stock.

There isn't much to it. Weld them together. Drill a few holes in the top and bottom(of the sides of the thing, of course) and give it a test burn. With no pot on the top the stove should burn hot and quickly generate very hot coals in the tube. Once you're at this point, you can put a pot on top, which caps the major draft and now you're burning charcoal, which will simmer along for hours. Burn quality dry fuel in this device or your wasting your time. For an experiment, plain old grocery store charcoal is good for practice.

Start out with 4 .5 inch holes in the top and bottom of your can or tube. If the fire burns too low once the pot is on, or goes out, punch a few more. You want a very low flame that burns for several hours with a slow cook process. Don't worry over much about bugs getting into the stew, as the small amount of smoke from the thing drives them off.

A very useful and practical device, and cooking a pot of chickpeas on the equinox is a fairly idyllic experience.


subgenius said...

Back when I lived in the countryside instead of the city I used to make Ianto Evans-style rocket stoves - similar to yours, but its a J shape with a downdraft air flow and a horizontal burn tube.

The advantage (for colder climes) is that it creates positive pressure in the chimney (long part of the J) so you can drop a large cap over (we used 55gal oil drums with the bottom cut off). The pressure inside this means that you can push the flue HORIZONTALLY - we ran them through floors and thermal mass formed into furniture. The top of the upturned drum makes a great hotplate too. If you want to cook you insulate the vertical part of the drum, if you just want a heater you leave it uninsulated and use as a radiator.

subgenius said...

oh yeah - the impartance of the horizontal flue is that you can trap a HUGE percentage of the heat normally lost through the stack and store it in the thermal mass of the building.

jaywfitz said...

I look to build a proper rocket stove for cooking at some point on that porch. In the interior I've got a nice jotul stove. I don't have the same requirements as many have for winters here in Hawaii. While it might get down to the high 30's at night in the winter, it's not like dealing with winter elsewhere. The main issue is keeping things sensibly dry, and moving great amounts of air is key.

I by no means am short on biomass!