[Stoves] Pyrolysis: No Air?

kgharris kgharris at sonic.net
Mon May 18 15:43:28 CDT 2015


Dean,

I am sorry, I failed to communicate clearly.  The primary air is continuous but it is continuously used up by part of the continuous supply of wood gas before any air reaches the majority of solid fuel, and so most of the fuel is heated without air.  If air was present here, then there would be more ash in the char.  My thought is that you are correct about gasification, but that gasification is a more general term which includes several processes including dehydration, pyrolysis and combustion.

Concerning the question about pyrolysis in a rocket stove.  I believe that wood gas is produced by pyrolysis.  The presence of oxygen burns the wood gas immediately after pyrolysis rather than later like in a TLUD.  In any fire, the wood does not burn, but rather the wood gas produced by the heat is what burns.  Yes, pyrolysis is present in a rocket stove or any other wood fire.

My responses may not be completely right, but I have read your questions several times, each time trying to come closer to understanding your intent.  I have attempted to respond to your questions rather than wander into other related topics with statements that do not actually address your question.  I very much appreciate this when others respond to my questions, and I feel that actually addressing the question is an act of respect.

Kirk


  ----- Original Message ----- 
  From: Dean Still 
  To: Discussion of biomass cooking stoves 
  Sent: Saturday, May 16, 2015 10:07 PM
  Subject: Re: [Stoves] Pyrolysis: No Air?


  Kirk, 


  That's very interesting! Thanks! 


  You say:


  "The small amount of added air supports the combustion of a small amount of the gas to produce heat, but that air is soon used up and most of the fuel pyrolyzes without added air."


  I experience that a constant supply of air is needed to keep the TLUD going. Without added air I see the gas making eventually stop so I've wondered if the word gasification is a better descriptor. I agree that it is a small amount of primary air which, if too much, makes too much gas and then produces visible smoke since the mixing/time can't handle the overly rich mixture. 


  Too little primary air and the reactions stop? You experience that no primary air is needed to continue the reactions?


  What about a Rocket or an open fire? No pyrolysis? Always has oxygen?


  Best,


  Dean



  On Sat, May 16, 2015 at 8:34 PM, kgharris <kgharris at sonic.net> wrote:

    Dean,

    Thank you for bringing this up.  I have never really thought about there being a difference between pyrolysis and gasification.  The definition of gasification in Wikipedia, "This is achieved by reacting the material at high temperatures (>700 °C), without combustion, with a controlled amount of oxygen and/or steam", is different from the definition of pyrolysis which is without additional oxygen.  Your statement seems correct according to this.  

    As I read further in Wikipedia, there is a section on chemical reactions.  Here there are 5 different processes which the fuel undergoes, pyrolysis being one of those.  This would lead me to believe that pyrolysis is part of the more general process of gasification.  Rather than it being one or the other, a TLUD would include both.  The small amount of added air supports the combustion of a small amount of the gas to produce heat, but that air is soon used up and most of the fuel pyrolyzes without added air.  The combination, including pyrolysis, would be gasification.

    I will look further to see if Christa Roth adresses this question in her Micro-gasification manual.  

    Kirk
      ----- Original Message ----- 
      From: Dean Still 
      To: Discussion of biomass cooking stoves 
      Sent: Saturday, May 16, 2015 3:50 PM
      Subject: [Stoves] Pyrolysis: No Air?


        1.. Hi All,
      When I look up the word pyrolysis I find the following:
        1.. Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen (or any halogen). It involves the simultaneous change of chemical composition and physical phase, and is irreversible. The word is coined from the Greek-derived elements pyro "fire" and lysis "separating".
        2.. However, I think that folks use it to describe what happens in a TLUD, etc? Isn't that gasification not pyrolysis because of the presence of some air?
      Best,


      Dean


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