[Stoves] Alternative to charcoal/ cut to length split on site

Tue Apr 9 10:29:52 CDT 2013

Dale and Stovers,

How about wood cut to a length, that works for a typical household stove, maybe 3 to 6" long, it could be a large diameter or a small diameter, and let the end user split the wood to the right size for their stove, with a hatchet.

Wood dries quicker when cut to a shorter length and it is easy to split, easy to handle, and easy to weigh, and the wood is more compact to ship, also the wood dries quicker.

I have been burning red oak, pallet oak, spruce 2x4 and limbs cut to about 6" long, and split to size with a hatchet. I used a chain saw for the disk and a hand saw to cut the limb and 2x4. If the wood is longer than you need, and you do not have a chain saw, split the wood first and then use a hand saw to cut it to length. I usually cut a typical "fire wood" length in 3 pieces.

Wood, Short Lengths, Split to Size.

Lanny

  ----- Original Message ----- 
  From: Andreatta, Dale A. 
  To: Discussion of biomass cooking stoves 
  Sent: Monday, April 08, 2013 5:09 PM
  Subject: [Stoves] Alternative to charcoal

  At the recent ETHOS conference Paul Means and Chris Lanning gave a very thought-provoking talk about an alternative to charcoal.  The basic idea was to use a gasifying stove with prepared wood fuel.  The prepared wood fuel would be bought by the user instead of charcoal, and the supply chain would be similar to charcoal.  The big advantage is that the very inefficient step of charcoal production is eliminated.  The stove would hopefully be easy to use and would smoke very little, so as to retain the benefits of a charcoal stove.  

  Their proposed fuel was crumbled wood, which would work well, but seemed to me to require a lot of big machinery and capital.  How could one go from a tree to a fuel that would burn well in a gasifier with as little work as possible, and without too much costly equipment?  The fuel  should be as low or lower in cost than charcoal per unit of food cooked, and give a better ratio of food cooked per unit of tree.  

  I did some preliminary experiments.  With 779 g of natural wood from the trees in my yard, I used a Paul Anderson Champion gasifier and boiled 5 liters in 21.4 minutes (corrected).  After an easy light the stove burned steadily with no attention, other than turning down the primary air when boiling started.  About 10 minutes after boiling the pyrolysis ended and I transferred 123 grams of char sticks, glowing only weakly, into a charcoal stove, and continued simmering until nearly 2 hours after the start of boiling.  I had good turndown on the charcoal stove and a lid on the pot.  There was a little smoke during the pyrolysis phase, but not too much.  This seems like excellent stove performance.  

  Had I used a very good charcoal stove to perform a similar task, it might have taken 240 g of charcoal.  This would take about 1800 g of wood if the charcoal were made efficiently, or 3000 g if it were made normally.  (Reference Means and Lanning on the efficiency of charcoal production.)

  The wood I started with was about 1 inch diameter (2.5 cm) by 6 inches (15 cm) long, cut from my trees and dried outdoors but under cover for some months.  I didn't measure the moisture content, but a previous oven-drying test with similar wood showed about 12-14% moisture.  A previous test with larger diameter wood didn't go well, so I think this is about the maximum possible diameter.  I don't know how long it took to get to this moisture content, not months I'm sure, but at least some number of days.  

  The production method for this alternative to charcoal would be to use a chain saw to cut wood into convenient lengths while in the forest, then take it to a central place.  Here, use electric saws and/or hydraulic  splitters to cut the wood to the appropriate size.  Give the wood a modest amount of drying in the sun, or in some simple oven.  The wood might have to finish drying at the place of use.  I expect that split wood would dry faster than cut sticks, since the moisture doesn't have to pass through the bark.  Alternatively, use a chain saw and engine powered splitter to cut the wood to size in the forest, then transport to a central place for drying.  When fairly dry, transport the wood to the users as with charcoal.  During transport, the energy per unit weight would be lower than charcoal, but the energy per unit volume would be similar.  The user might be given the option of buying shorter sticks for cooking smaller meals, or longer sticks for larger meals.  

  In comparing the economics of this method to charcoal, I would think of the cost of the fuel as coming from 5 elements; the cost of the trees, the cost of the processing equipment, the cost of the labor, the cost of the transportation and distribution, and the cost of the stove.  If the trees are free, then the fact that you don't cut as many trees doesn't help much.  If the trees must be paid for, then this method looks more attractive.  The processing equipment for charcoal is virtually free, but hopefully this method doesn't take too much equipment.  The labor for this method might be similar to charcoal, but it might be less because you are cutting and processing a lot fewer trees to serve the same number of customers.  Transportation would be more expensive, since you are shipping more mass, though not a lot more volume.  This method would require a gasifier or T-Char stove, which would be an expense, though hopefully not a lot compared to the annual cost of fuel.  

  Thus, if the trees must be paid for, this method might be attractive to the consumer of the fuel, the producer of the fuel, and to the forest.  If the trees are not paid for, this method looks less attractive, though the forest would still benefit and some outside subsidy might be available.

  Dale Andreatta, Ph.D., P.E.  

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