Stoves Archive for January 2001

Keith,

At our Chardust operation in Nairobi we don't yet make efficient use of the heat generated during the carbonisation process, but this is clearly wasteful and we are now experimenting with using it to pre-dry the feed stock (from around 50% to 15% in the case of sawdust). We are doing this by drawing air down through a bed of sawdust on a wire mesh and up through a pipe that is joined onto the outer sleeve of the carboniser chimney. The process is assisted by an 12V fan drawing air in through a side duct.

We cleanly flare the volatiles (white smoke) and the amount of heat produced is tremendous - approximately 40% of the energy value of the feedstock entering our carboniser.

There are obviously great opportunities to use the heat for space heating and plenty of other purposes. Our effort has been concentrated on getting efficient carbonisaton at low cost, and with an outfit made out of used oil drums we are a little limited in high-tech ducting and recycling options! Still, there is much we can and should be doing.

Some of the ideas we've had are:

- Firing bricks or other ceramics
- Making ice...(!) it can be done
- Drying or dehydrating crops ranging from grain to fruit
- Distilling potable water from polluted sources
- Transforming heat into mechanical energy - the Sterling Engine is one way
- Curing green wood

We don't have much call for heated greenhouses here in Kenya, but maybe in some parts of the world in the future we will see sawmill-carboniser-greenhouse combinations. I wonder how efficient that could be?

I expect other group contributors have much to say on this subject, especially in places with tighter emissions control (or any at all for that matter).

Matthew Owen and Elsen Karstad
Chardust Ltd.
Nairobi
Kenya
www.chardust.com

> ----- Original Message -----
> From: Keith Addison <keith@journeytoforever.org>
> To: <stoves@crest.org>
> Sent: Thursday, January 18, 2001 6:50 AM
> Subject: Re: Charcoal in East Africa
>
>
> > "A.D. Karve" <adkarve@pn2.vsnl.net.in> wrote:
> >
> > >Dear Matthew,
> > >you are right about the high cost and low calorific value of
> > >briquettes made out of compacted sawdust and other biomass.
> > >Charring it is simple and briquetting the char is also quite simple.
> > >Both can be done at a very low capital cost by a third world farmer.
> > >We have modified an old fashioned meat mincer into an extruder. We
> > >first operated the extruder manually, and after being satisfied with
> > >its performance, we are now fitting it with an electric motor, to
> > >increase its output. But the extruder is not obligatory, as one can
> > >just manually shape the charred biomass (after mixing it with a
> > >binder), into balls having a diameter of about 5 to 6 cm, and dry
> > >them in the sun. These balls can serve as fuel not only in a
> > >conventional charcoal burning stove but even in a pyromid stove.
> > >There is no real shortage of firewood in the rural areas of our
> > >state (Maharashtra, India), because of the availability of
> > >combustible agrowaste in the form of stalks of cotton and pegionpea,
> > >as well as abundant availability of Prosopis juliflora (mesquite)
> > >trees. The farmers have a lot of light biomass which is today not
> > >used as fuel (e.g. dried sugarcane leaves, wheat straw, stover of
> > >safflower, sunflower, sesame, mustard etc.), and often just burnt in
> > >situ, just to get rid of it. The farmers are not interested in
> > >making charcoal briquettes out of this biomass for their own use,
> > >but if somebody arranges to collect the charred biomass from the
> > >farmers, and produces them into briquettes, there is a good market
> > >for the latter in the cities. We have formed a cooperative, which
> > >would do just this. We do not see any difficulty in selling the
> > >char briquettes in the cities, because there exists a ban of the
> > >production of wood charcoal (as a measure of saving the trees). As a
> > >result of the ban, the charcoal prices have shot up to US$ 150 per
> > >tonne.
> > >Yours A.D.Karve
> >
> > Is there a way of charring the sawdust-biomass that gets some energy
> > use out of the process?
> >
> > Thanks
> >
> > Keith Addison
> > Journey to Forever
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