[Stoves] [Terrapreta] How to make charcoal

[Robert Flanagan]

Hi All,

 

I've just been playing around with my natural draft stove to see how easy it
would be to use it for cooking and making charcoal
http://www.youtube.com/watch?v=sZZDtXOiGLE .

I fed some extra fuel in the side so show the pyrolysis reaction taking
place.

 

So at the start I light a fire on top of the biomass to build this hot
carbon layer, it's during this start up period that we get smoke coming out
the flue. But when the whole top layer is on fire (So to speak) and we've
got our hot carbon layer then all gasses coming up must pass through this
layer and they get broken down and become combustable. The biggest problem
is always moisture (biomass should have a moisture content of less then 25%)
and typically we get a white smoke but when water passes through hot carbon
it reacts to give us H2O+C = H2+CO (Syngas) so we actually burn water along
with the woodgas. Gasification allows a small amount of fresh air to pass
through the unburned biomass up to the flaming pryolysis zone and this is
where get the exothermic reaction to take place. Then the oxygen lean gas
travels up until it meets the secondary air where it finally has the
air:fuel ratio correct for complete combustion. 

 

The reason I was left with just charcoal at the end of the clip is because
of the restricted amount of air passing up through the charcoal. When we
have a mix of hot charcoal and unburned biomass the air will always react
with the unburned wood first so there is no oxygen left to break down the
carbon. Now at the end I could have opened the bottom and side door and the
flow of fresh air meeting the hot charcoal would have raised the temperature
and reduced the charcoal to ash (But then I'd have no charcoal to play
with!)

 

This is very very different to pyrolysis where the biomass is typically high
in moisture (50%) and the oxygen is restricted. Here the moisture content in
the gas is way to high to combust so unless the biomass was pre-dried the
gas typically has to go through a condenser to produce vinegar and bio-oil,
then the non-condensables should be combustible. 

 

Regards,

Rob.

-- 
Robert Flanagan
Chairman & President
Hangzhou Sustainable Agricultural Food & Fuel Enterprise Co., Ltd.

Skype "saffechina"
Tel:   86-571-881-850-67
Cell:  86-130-189-959-57 

 

Forwarded from the terra preta discussion list
http://terrapreta.bioenergylists.org/