[Terrapreta] Long term durability of Low Temp Chars

[Sean K. Barry]

Hi Duane,

>From what I have read about pyrolysis reactions, the yield of carbon in charcoal being lower than the amount of carbon in the biomass feedstock is primarily lost through the production of producer gas (H2, CO, CO2, CH4, H2O, N2).  Pyrolysis reactions above, I think 250C, are exothermic, i.e. they produce heat.  It is enough heat for the reactions to be self sustaining, as long as additional feedstock and some oxygen (air) are continuously added.  So, there is no need to add energy to the process, once ignition has occurred.  If the air flow remains low, then the heated charcoal will pyrolize (partial combustion) the biomass chemicals into producer gas.  If the air flow is increased too much, then the chemicals in the biomass will fully combust, ejecting mainly CO2 and H2O.

Dr. Antal, uses a pressurized reaction vessel, which increases the speed of the pyrolysis reaction and can also increase the yield of charcoal (and fixed carbon) from the biomass feedstock.  The actual char yield depends much on air flow.

SKB
  ----- Original Message ----- 
  From: Duane Pendergast<mailto:still.thinking at computare.org> 
  To: 'Sean K. Barry'<mailto:sean.barry at juno.com> ; 'AJH'<mailto:ajh at sylva.icuklive.co.uk> 
  Cc: 'terrapreta'<mailto:terrapreta at bioenergylists.org> 
  Sent: Thursday, May 17, 2007 2:28 PM
  Subject: RE: [Terrapreta] Long term durability of Low Temp Chars


  Sean,



  I'm guessing a bit, but suspect that the yield may partly depend on how much of the energy to achieve the pyrolysis comes from the biomass itself. If an external source of energy, say electrical heating, is employed the yield might be increased.



  I'm sure Michael Anton or Danny Day is much better qualified than I to comment on this.



  Sincerely,



  Duane Pendergast



  -----Original Message-----
  From: terrapreta-bounces at bioenergylists.org<mailto:terrapreta-bounces at bioenergylists.org> [mailto:terrapreta-bounces at bioenergylists.org] On Behalf Of Sean K. Barry
  Sent: May 17, 2007 9:10 AM
  To: AJH
  Cc: terrapreta
  Subject: Re: [Terrapreta] Long term durability of Low Temp Chars



  Hi AJH,



  I've read, from work by Michael J. Antal, at the University of Hawaii, that the maximum theoretical amount of carbon, which can be retained in charcoal, after pyrolysis of biomass, is somewhere ~30-40% by weight of the feedstock biomass.  Achieving that is difficult and usual yields are more likely around 25% on a weight by weight basis charcoal/dry weight biomass feedstock, with charcoal being ~93-95% carbon.  Michael is a member of this list and he may be able to answer your questions better, so try to contact him  (maybe he will see this post and respond to you directly?).



  Regards,



  SKB

    ----- Original Message ----- 

    From: AJH<mailto:ajh at sylva.icuklive.co.uk> 

    To: Sean K. Barry<mailto:sean.barry at juno.com> 

    Sent: Thursday, May 17, 2007 9:56 AM

    Subject: Re: [Terrapreta] Long term durability of Low Temp Chars



    On Tue, 15 May 2007 16:21:51 -0500, Sean K. Barry wrote:

    >I don't think that it is doubted that anything less than a very high percentage of the original charcoal matter that was put into the soil over some thousands of years ago, is not still there.

    Nor I, I'm fairly confident all the fixed carbon will be there still
    but when the claim is made for carbon credits and there is ~18% of the
    weight in carbon-oxy-hydrogen compounds how much weight of carbon is
    sequestered?

    AJH


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