[Stoves] Alternative to charcoal

[Andreatta, Dale A.]

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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