[Terrapreta] torrefaction vs. Carbonization---------Char Hydrophobic / Hydrophilic characters

[Sean K. Barry]

Hi Greg,

I believe temperature has a greater impact on VM content.  All biomass consists of differing amounts of the carbohydrate polymers; cellulose, lignin, and hemi-cellulose.  These three pyrolyze at different temperatures.  As the temperature in a pyrolysis reaction rises hemi-celluloses begin to pyrolyze at 120C and break down at ~200-250C.  Cellulose (the largest biomass component) follows by breaking down at temperatures from ~250-350C, and last, lignin, from ~280-500C.

Pyrolysis within a charcoal bed is really a two phase process.  The raw biomass at first flames, producing hot gases, volatiles, and charcoal.  As the feedstock sinks into the bed, where it is prevented from getting as much oxygen, then a reaction begins where the hot gases and volatiles interact with the charcoal to produce even more pyrolysis products; gases, volatiles, and charcoal (this is the 2nd phase).  The 1st pyrolysis phase proceeds somewhat slowly and temperatures are lower.  The 2nd pyrolysis phase occurs at a high rate.  Once the 2nd phase has driven most the gases and the volatiles out of the charcoal bed, then further decomposition of the bed occurs at a very much slowed rate.  A very limited amount of oxygen can actually quench the reaction at this point and it will stop.

If feedstock and charcoal are only allowed to reach lower temperatures before they are ejected from the reactor, then the charcoal will contain a higher percentage of volatiles.  Even if the charcoal is allowed to reach a higher temperature, it does take some time to complete the pyrolysis of the original molecules in the biomass, breaking them to the smaller gaseous molecules in "producer gas"; H2, CO, CO2, H2O, CH4, N2, and trace others.  If the feedstock goes through a high temperature state at a high rate and is allowed to cool, then it also could contain a higher VM%.  The 2nd pyrolysis phase is very rapid though and that rate can be increased by pressurizing the reactor (see the work by Michael J. Antal).

So, temperature and time combine somewhat to dictate the VM% content, but on the whole, I think temperature impacts this more.
I could cite you some papers which I have read on this subject, if you like, but I am not now near where I have that information.  What I have said comes from my head, based on memory, which may have some faults?


Regards,

Sean K. Barry
Principal Engineer/Owner
Troposphere Energy, LLC
11170 142nd St. N.
Stillwater, MN 55082-4797
(651)-285-0904 (Work/Cell)
(651)-351-0711 (Home/Fax)
sean.barry at juno.com<mailto:sean.barry at juno.com>
  ----- Original Message ----- 
  From: Greg and April<mailto:gregandapril at earthlink.net> 
  To: Undisclosed-recipients:<mailto:Undisclosed-recipients:> 
  Cc: terrapreta at bioenergylists.org<mailto:terrapreta at bioenergylists.org> 
  Sent: Tuesday, December 11, 2007 11:49 AM
  Subject: Re: [Terrapreta] torrefaction vs. Carbonization---------Char Hydrophobic / Hydrophilic characters


   
  Someone please answer me this if you can:

  Which has a bigger effect of the % and types of VM, temperature or time?

  Say for example getting the core temperature up to 600* or holding it at 450* for 6 hours.

  Greg H.
    ----- Original Message ----- 
    From: Tom Miles<mailto:tmiles at trmiles.com> 
    To: 'Edward Someus'<mailto:edward at terrenum.net> ; 'Nikolaus Foidl'<mailto:nfoidl at desa.com.bo> ; 'Gerald Van Koeverden'<mailto:vnkvrdn at yahoo.ca> ; 'Sean K. Barry'<mailto:sean.barry at juno.com> 
    Cc: terrapreta at bioenergylists.org<mailto:terrapreta at bioenergylists.org> 
    Sent: Sunday, December 09, 2007 12:09
    Subject: Re: [Terrapreta] torrefaction vs. Carbonization ---------Char Hydrophobic / Hydrophilic characters


     
    < SNIP >

     

    Instead of carbonization temperature is volatile matter (%VM) a better measure of the degree of carbonization and hence the level of toxic compounds? 

    Tom

     

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