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

[Greg and April]

This brings to mind something that I have had bouncing around in the back of my head for a while.


It's one thing if the size is small to facilitate movement ( and speed of reaction ) through a faster pyrolysis reactor, but it is something else if someone is trying to accomplish the same thing in a low tech setting with a retort / kiln.    A small wood partial size, in such a method, might actually increase the time needed to char the biomass, and actually cause a issue with the ability for the VM to leave the biomass - as it might pack together acting as a single large piece rather than many smaller pieces.

If this is the case, would it not be better to use a larger partial size that would have more space between them ( for heat and gasses to move about more easily?    If so, what would be an optimum size?    2 - 4 cm+?


Greg H.

  ----- Original Message ----- 
  From: Sean K. Barry 
  To: Greg and April 
  Sent: Friday, December 14, 2007 22:15
  Subject: Re: [Terrapreta] torrefaction vs. Carbonization---------Char Hydrophobic / Hydrophilic characters


  Hi Greg,

  Yes.  The particle size of the feed material in the reactor is very critical, as if effects the core and surface temperatures of the feedstock particle and the differences between these.  Tom Reed at the Biomass Energy Foundation (http://woodgas.com) studied this with a pyrolysis reactor built of transparent glass, with gold lining as thermal insulation.

  I think Tom showed that 1 cm x 1 cm x 0.3 cm particle size of wood "chip" had some a more ideal size characteristics for producing non-condensable and condensable fuel and combustion product gases.  Particle size can control the ratios between these gases; concentrating on more useful fuel gases and less combustion gases in the reaction products.  These "larger" sizes particles create a "fixed bed"  of charcoal (or "slowly moving bed").  It also can yield more solid charcoal, with variable "volatile matter" %, depending on maximum particle temperature, and the residence time in the reactor, before the charcoal is dumped and solid feedstock is replenished.

  "Fast pyrolysis" reactors produce more liquid and gases than soild by-products.  I think the particle size in "Fast pyrolysis" feeds are much smaller; 1-3 mm x 1-3 mm x 1-3 mm (like sawdust).  The pyrolysis reaction proceeds more quickly because all of the fuel particles, being smaller, are consumed to quenching more quickly.  The solid biomass fuel is converted to product materials in liquid and gas phases, the heat generating reaction is over, the products exit the reactor, and then new solid feed is introduced into the "fluidizied bed".

  Regards,

  SKB
    ----- Original Message ----- 
    From: Greg and April 
    To: Sean K. Barry 
    Sent: Thursday, December 13, 2007 11:14 AM
    Subject: Re: [Terrapreta] torrefaction vs. Carbonization---------Char Hydrophobic / Hydrophilic characters


     
    It also sounds like the size of the biomass would play an important part, with smaller pieces ( and the mass as a whole ) playing a critical part in how long a given piece is at a critical temperature.

    Greg H.

      ----- Original Message ----- 
      From: Sean K. Barry 
      To: Greg and April 
      Cc: terrapreta at bioenergylists.org 
      Sent: Tuesday, December 11, 2007 12:20
      Subject: Re: [Terrapreta] torrefaction vs. Carbonization---------Char Hydrophobic / Hydrophilic characters


      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
        ----- Original Message ----- 
        From: Greg and April 
        To: Undisclosed-recipients: 
        Cc: 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 
          To: 'Edward Someus' ; 'Nikolaus Foidl' ; 'Gerald Van Koeverden' ; 'Sean K. Barry' 
          Cc: 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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