[Stoves] Traditonal Charcola Making Process / retort

[Crispin Pemberton-Pigott]

Dear Paul

I was not going to consider a kiln type until I learned more about the type
of gases produced, the heat content in them, problems I might face running
it for a long time and the economic of the firing and the charcoal.

Energy is quite expensive at $0.14 per KWH in Maputo - if you are using
electricity.  I don't yet know the cost of wood when bought in bulk.
Charcoal is $12 for 70 Kg retail, roughly 2000 MJ = 544 KWH or $0.02 a KWH.

Wood is probably 1/2 the price or less (remember that transport is
expensive).

Turning wood into charcoal is a big business so diverting wood to make
woodgas and charcoal would be more efficient than traditional methods (which
yield about 15%).  The problem is the charcoal is not worth much so it might
be better simply to use wood to fire the kiln, but I like the idea of
turning out a large amount of charcoal if I can.  It has a huge market.  It
will displace inefficiently produced competition.

If I get 0.75 Kg of charcoal per stove fired and I produce 500 stoves a day
at each of 10 locations, I get 3.75 tons of charcoal a day.  That will take
14 tons of wood a day.  While this sounds like a lot, it is a pittance
compared with what is going on in the rural areas now to provide 300 tons a
day.

If I can buy 14 tons of wood and make 5000 stoves, and still turn out $640
worth of charcoal, as well as save 3.5 x 5000 KWH in electricity = $2450.
Saving $2450 and generating $640 leave a lot of money to buy 14 tons of
wood.  In fact I could afford to pay more than $0.20 a kg which is more than
the charcoal costs retail!

This means that it is very attractive to use biomass to fire the stoves.
Now...check this out!  Each stove put into the market saves about 60% of the
charcoal which means that to save the energy in biomass that was used to
create it will take only about a day.  To save the purchaser the price of
the stove takes about 3 weeks.  That is a pretty good deal all round.

It also means that promoting the use of biomass to fire modern charcoal
stoves is environmentally defensible from every point of view.

The main question is what temperature I can get the kiln to, and maintain,
using a gasifier.  This affects the chemistry chosen for the mixture.  If I
can maintain 1250, a full 80 degrees higher than I am using now, I can use
less feldspar, lower the cost and still get a low thermal expansion product
- probably even get a lower expansion value.

So that is my reasoning and present view.

Thanks
Crispin