[Terrapreta] medium-size charcoal making - the tools?

[Sean K. Barry]

Hi Andrew,

Did you say you used a ring kiln?  Is that kiln something like the FAO (TPI) kiln?  (two stacked 1 m high x 2 m diameter cylinders, a semi flat conical roof, four stacks set over onto 8 inlet/outlet stubs around the base)?  I've read that two men can use two of those kilns and pyrolyze ~20-23 tons per week from wood feedstock.  That would require preparing wood feedstock of about ~80-100 tons of wood (perhaps 30-50 cords green, depending on the species), then loading ~80-100 cords dry wood feedstock and unloading ~20-23 tons of charcoal every week.

I wonder what you would think of a similar kiln that had an exhaust manifold built to set onto those 8 inlet/outlet stubs ?  It could be built to capture and use the heat and BTUs in the combustible flue gases.  The exhaust gases could be used to supply sensible heat, perhaps fuel an internal combustion engine, or drive a turbine and supply electricity or air pressure.  The compressed air could be used to suck the exhaust flow through the manifold with venturi produced vacuum pressure.  This could clean the emissions (especially Methane-CH4 and particulates), which are normally products from conventional charcoal making.  At the same time, the system could potentially also provide some renewable bio-energy.

There is no reason that "wood gas" or pyrolysis product gas from any biomass source cannot be fired into a combined cycle turbine and make electricity as efficiently and cleanly as a big power company's combined cycle generation system.  The heat alone from burning the combustible product gases (and the excess heat from the pyrolysis reaction as well) can be put to use (e.g. drying feedstock, heating winter green houses, heating farm animal buildings, heating anerobic digesters).

Another important advantage of using this kiln is that it is designed to be "portable".  The "power manifold" can be made removable and transportable as well.  With enough feedstock, the kiln can clean its own emissions "flaring" its own producer gas output.  It may even perhaps be possible with electronically controlled valves, temperature and lambda (oxygen) sensors, to run the kiln at the exact stoichiometric to produce maximum charcoal yield in the minimum amount of time.  All done with no extra input of external energy.  All the required energy would come from the pyrolysis feedstock itself.  The producer gas would run an air compressor and or generator.  The compressed air and valve controls would provide the flow control, with the temperature sensors and lambda sensors providing feedback.

Once there is a "portable" and "clean" way to make charcoal, then charcoal can be made with field residue, then the kiln moved to a new field when its done.  The charcoal could be made and applied right on the same site, removing all the cost and energy required for transporting the biomass feedstock and the charcoal.

Regards,

SKB

I 
  ----- Original Message ----- 
  From: andrew<mailto:list at sylva.icuklive.co.uk> 
  To: terrapreta at bioenergylists.org<mailto:terrapreta at bioenergylists.org> 
  Sent: Sunday, December 23, 2007 5:14 AM
  Subject: Re: [Terrapreta] medium-size charcoal making - the tools?


  On Saturday 22 December 2007 21:45, Gerald Van Koeverden wrote:
  > Is there any open-source do-it-
  > yourself technology that is ready to be made and used locally by
  > communities on the medium level scale?

  This all depends on what your resource is and how much it costs. If 
  you are going to add the char to the soil then soil contamination is 
  not an issue. You note that offgas can be polluting and the most 
  straightforward way to do this is to flare it, effectively losing 
  half the energy in the wood. Flaring is easy if the biomass is dry.

  I've successfully made a lot of char in a short period (8m3 bulk in 
  2hrs using a mechanical loader) in UK using forest waste (lop and 
  top) using both a ring kiln and a simple pit. The technique was used 
  in Tudor times but is quite wasteful compared with traditional 
  methods.

  Firstly the resource needs to be small diameter and having dried out 
  substantially. Waste from a hardwood thinning is <50mm diameter and 
  if winter felled in UK is dry enough by mid May.

  Find a container or dig a trench wide enough for your needs and long 
  enough for the branches. Build a small fire at the bottom and slowly 
  add small branches whilst maintaining a good flame. Keep adding 
  branches such that there is always sufficient offgas to flare and 
  prevent any oxygen getting to the pyrolysing wood. If you can see 
  white surface on the sticks then the char has started to oxidise and 
  either the wood is not dry enough or you have not added enough. 
  Heavy smoke indicates too much wood or too much moisture.

  Once the trench has filled with char and the flare is dying cover the 
  trench and seal with earth and consider dowsing it with water.

  AJH

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