Dale and all,
Thank you for your input, especially the quantitative parts. I confirm
and agree with your comments, such as about 1 inch maximum of diameter
of wood in the residential size TLUDs.
I hope that more people will be considering alternatives to charcoal.
Paul
Paul S. Anderson, PhD aka "Dr TLUD"
Email: [email protected] Skype: paultlud Phone: +1-309-452-7072
Website: www.drtlud.com
On 4/8/2013 4:09 PM, Andreatta, Dale A. wrote:
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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