[Terrapreta] Charcoal properties

[Sean K. Barry]

Hi Michael,

Thank you for your very interesting comments.  By what you have said in your post, ...

"Tests by my colleague Professor Goro Uehara and his co-workers in CTAHR have
shown that the addition of some charcoals to the soil can be harmful to
plant growth.  Our analyses of the properties of this "harmful" charcoal
indicate that it would have been perfect for barbeque."

and ...

"A good barbeque charcoal will have a VM content of 25 - 30%, whereas a
charcoal destined for metallurgical use often has VM content below 10%."

... would it be fair to infer, then, that relatively high volatile matter content (25 - 30%) in charcoal probably does not make a good agricultural use charcoal?  Has anyone tested metallurgical use charcoal (@ <10% VM) as an AgChar?  What are the pyrolysis conditions under which metallurgical use charcoal is made (feedstock, temperature, oxygen or air supply level, etc.)?  Are there any simple methods (not involving expensive gas chromatographs and/or other equipment) to test for VM content?  Like, maybe does low VM charcoal combust at a lower or higher temperature the higher VM charcoal?  Do they have a different densities?

You say, "This is not an easy job and there are no short cuts that I can find."  So maybe my questions seem like naivete, but what I am interested in learning from you is if a fuel scientists/chemical engineer like you really does maybe know some possible simple methods to do proximate analysis of charcoal or maybe some parts of it.  Not everyone interested in testing or making Terra Preta has your kind of background, nor access to the kinds of scientific equipment you do.  But, I suspect that there are low tech ways to accomplish some of the things you are doing with your analysis of charcoal properties.  Hopefully, you may be willing to at least discuss the possibilities.

Would you be willing to put your papers online for the group?  I'm interested, so if you like, send them to me.


Thank you and regards,

Sean K. Barry
Principal Engineer/Owner
Troposphere Energy, LLC
11170 142nd St. N.
Stillwater, MN 55082
(651) 351-0711 (Home/Fax)
(651) 285-0904 (Cell)
sean.barry at juno.com<mailto:sean.barry at juno.com>
  ----- Original Message ----- 
  From: Michael J. Antal, Jr.<mailto:mantal at hawaii.edu> 
  To: terrapreta at bioenergylists.org<mailto:terrapreta at bioenergylists.org> 
  Sent: Friday, March 02, 2007 2:28 PM
  Subject: [Terrapreta] Charcoal properties


  Dear friends: terra preta is fascinating in part because it involves so many
  disciplines.  My viewpoint is that of a fuel scientist/chemical engineer.
  My laboratory produces well-characterized charcoals for a wide variety of
  research endeavors, including carbon fuel cell studies, metallurgical
  charcoal applications, activated carbon production, and terra preta research
  (with my colleagues Dr. Goro Uehara, Dr. Jonathan Deenik, and Tai McClellan
  in the University of Hawaii's College of Tropical Agriculture and Human
  Resources).  With this message I wish to call your attention to the
  elementary properties of charcoal that I think about when I am producing a
  charcoal for one of our research endeavors.

  Both the feedstock and the process (i.e. pyrolysis) conditions influence the
  properties of the charcoal product.  For example, oak wood has little ash;
  consequently its charcoal also has little ash.  On the other hand, rice
  hulls have much ash (nearly pure silica), and so does its charcoal.
  Likewise corncobs produce a highly macroporous charcoal, whereas sucrose
  charcoal lacks a macroporous structure.  But unfortunately, the properties
  of the feedstock do not completely determine the properties of the charcoal.
  For example, if pyrolysis is carried out at a high temperature, some of the
  volatile ash components leave the charcoal.  In our work it is not unusual
  to find that the charcoal contains as little as 20% of the amount of ash
  that we expected on the basis of the feedstock ash content.  One carbon
  company produces an ash-free carbon for metallurgical applications by simply
  heating a fossil carbon (usually coal) to such a high temperature that
  virtually all the minerals in the fossil carbon vaporize.

  Likewise the pyrolysis temperature (usually called the "heat treatment
  temperature" or HTT) exerts a big influence on the properties of the carbon.
  Fuel scientists employ proximate analysis to measure this influence.  Let's
  be clear: there is nothing approximate about proximate analysis!  Proximate
  analysis determines the moisture content (mc), volatile matter (VM) content,
  fixed carbon (fC) content, and ash content of a charcoal (or fossil carbon).
  A good barbeque charcoal will have a VM content of 25 - 30%, whereas a
  charcoal destined for metallurgical use often has VM content below 10%.
  Increasing HTT lowers the VM content of the charcoal, but there is not a
  simple relationship between the HTT and the charcoal's VM content.  Why?
  The simplest explanation is that the thermocouple used to measure the HTT
  measures the temperature of the pyrolysis environment: it does not measure
  the temperature of substrate during pyrolysis!  Pyrolytic reactors designed
  to maximize "oil" (or gas) yields - and minimize the charcoal yield - employ
  high heating rates.  Under these conditions the pyrolysis reactions are
  endothermic; consequently there is a large temperature difference between
  the charcoal and its environment (i.e. the temperature of the charcoal can
  be hundreds of °C lower than its environment).  On the other hand, a
  pyrolytic reactor that is designed to maximize the charcoal yield will evoke
  exothermic pyrolysis reactions in the substrate, since the reactions that
  form charcoal are exothermic.  In this case the temperature of the charcoal
  can be much higher than its HTT.  I can provide some interesting papers on
  this subject for anyone who is interested.

  In summary, both the feedstock and the pyrolysis process conditions
  influence the properties of the charcoal product, but they do not determine
  the properties (i.e. knowing the feedstock and process conditions is not
  enough to predict the properties of the charoal).  The only way to determine
  the charcoal's properties is to actually measure them.  We do proximate
  analyses of all our charcoals.  Often we do gas sorption measurements to
  determine the carbon's surface area and pore volume distribution.  Sometimes
  we obtain an elemental analysis of the carbon, or an analysis of its ash
  content.  For our carbon fuel cell work we measure the carbon's electrical
  conductivity, and with colleagues in the Hungarian Academy of Sciences we do
  temperature-programmed desorption of biocarbons used in our fuel cell.  We
  have done XRD, NMR, ESR, and MALDI-TOF MS analyses of some of our charcoals.
  We have plans to expand our analysis capabilities into other areas soon.

  Tests by my colleague Professor Goro Uehara and his co-workers in CTAHR have
  shown that the addition of some charcoals to the soil can be harmful to
  plant growth.  Our analyses of the properties of this "harmful" charcoal
  indicate that it would have been perfect for barbeque.  This illustrates the
  dangers of working with an uncharacterized charcoal purchased from your
  local grocery store.  Professor Uehara and his co-workers will have more to
  say on this subject in the near future.  In the meantime I emphasize that
  our understanding of charcoal's beneficial and detrimental effects on plant
  growth must rest (in part) upon measurements of the charcoal's properties.
  This is not an easy job and there are no short cuts that I can find.

  Like most of you, at present my terra preta research is not funded, so the
  best I can do is provide well-characterized charcoals to my colleagues here
  at UH.  In the future I may have the resources to provide well-characterized
  charcoals to other terra preta researchers as well.  I will let you know
  when this becomes possible.

  Best wishes, Michael.

  Michael J. Antal, Jr.
  Coral Industries Distinguished Professor of Renewable Energy Resources
  Hawaii Natural Energy Institute
  School of Ocean and Earth Science and Technology (SOEST)
  1680 East-West Rd., POST 109
  University of Hawaii at Manoa
  Honolulu, HI 96822

  Phone: 808/956-7267
  Fax: 808/956-2336
  http://www.hnei.hawaii.edu<http://www.hnei.hawaii.edu/>






  _______________________________________________
  Terrapreta mailing list
  Terrapreta at bioenergylists.org<mailto:Terrapreta at bioenergylists.org>
  http://tech.groups.yahoo.com/group/biochar/<http://tech.groups.yahoo.com/group/biochar/>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: /pipermail/terrapreta_bioenergylists.org/attachments/20070302/2ef8bcd3/attachment-0001.html