[ethos] RE: [Stoves] Charcoal Stoves (Thomas Reed)

[Tom Miles]

John, Tom

Do we have any idea what the quality of charcoal is that is made largely in
the bush? It is only partially carbonized and therefore might have higher
volatiles throughout the structure? Does it then release the volatiles in a
more wood-like way? Are many charcoal stoves effectively burning wood? Then
is the GCV more like 19 MJ/kg and not 30 MJ/kg? Jean-Francois referred to
poor quality charcoal in Cambodia as high in volatiles. 
http://listserv.repp.org/pipermail/stoves/2006-June/011228.html

Are there field studies of charcoal quality that would show these
differences? 

Either way it looks like the techniques Dean has used to reduce CO (tall
insulated chimney - might improve CO and efficiency for a wide range of
charcoal qualities.

Tom 

 
-----Original Message-----
From: stoves-bounces at listserv.repp.org
[mailto:stoves-bounces at listserv.repp.org] On Behalf Of John Hofmeyr
Sent: Sunday, June 18, 2006 4:52 PM
To: stoves list
Subject: Re: RE: [ethos] RE: [Stoves] Charcoal Stoves (Thomas Reed)

Hi Tom and others,

In Message-ID: < <mailto:44948947.5070903 at comcast.net>
44948947.5070903 at comcast.net> Tom Reed wrote: 'The question of
"combustability" and efficiency is very complex.  Conventional charcoal made
for cooking represents a "buffered endpoint" in charcoal making.' 

 

Questions were raised about the CV and volatiles content of charcoal with
respect to its efficiency in cooking. I wonder whether the fixed carbon
content is maybe a more important consideration, because this is the value
which will translate into the utilisable energy, especially for grilling,
simmering and stewing. 

I introduce this idea, because, while the energy in the volatiles is
important for ignition, I think this energy is likely to be burnt off
rapidly? 

Therefore, would this energy only be useful, for example, to bring a pot to
the boil? 

If yes, would the energy from the glowing charcoal be recoverable more
efficiently and over a longer period?

And would this energy be maximised if the Fixed Carbon content of the
charcoal is maximised, but with balanced volatiles for ignition (about
12-15%%, dry basis)?

 

I think it is for this reason that the EU specifications for charcoal tend
to require a fixed carbon content above 80%, to ensure smokeless burning and
to avoid rapid burn-off  of volatiles.

 

Further, on  Sent: Monday, June 05, 2006 3:35 PM Dean wrote: "2/3rds of the
energy in wood is lost when making it into charcoal."

 

Properly-carbonised wood returns ~70% of its CV as solid, in the form of
biocharcoal with Fixed Carbon >80%.

By this I mean for example:

12000 tpa wood at 25% moisture equivalent to 9000 tpa bone dry at 19GJ/ton,
yields 4000 tpa biocharcoal (80%FC) at 30GJ/ton. 

 

Regards,    John in Joburg 

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