[Stoves] Pyrolysis: No Air?

[mtrevor at mail.mh]

Funny I always sort of thought is was gasification. I guess that came from reading Mother Earth News by candle light half a century ago.





From: Dean Still 
Sent: Sunday, May 17, 2015 1:10 PM
To: Discussion of biomass cooking stoves 
Subject: Re: [Stoves] Pyrolysis: No Air?

Hi All, 

Seems to me that the word gasification might fit the TLUD process better? The primary air controls the amount of oxygen, the rate of reaction? 
There is no pyrolysis in a Rocket or an open fire?


Gasification is a process that converts organic or fossil fuel based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide. This is achieved by reacting the material at high temperatures (>700 °C), without combustion, with a controlled amount of oxygen and/or steam.


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".


Best,


Dean

On Sat, May 16, 2015 at 4:58 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com> wrote:

  Dear Alex, Dean
  That Reed reference is a good one. As biomass is about 40% oxygen by mass, there is a real chance one can have some combustion without any air at all. There is almost enough oxygen to burn all the hydrogen ‎in most biomass. That is a heat source that could leave all the carbon behind, in theory. In practise there will always be CO and H2 in the output from a retort. 
  Regards Crispin 


  Dean, 
  There being oxygen in the chemical structure of biomass and oxygen in the spaces and cracks, a strict abstinence is difficult. In one of the Reed/Das handbooks there is a graph of the pyrolysis-gasification-combustion continuum, where the x axis goes from say zero to %200 of stoichiometric oxygen/air. I think ( always roughly) gasification fit in the %20-%80 range with pyrolysis below and combustion above. The char and gas yield % was in there too. I'm sure folks could argue endlessly about where exactly to place the demarcations.
  Alex

  On Sat, May 16, 2015 at 6:50 PM, Dean Still <deankstill at gmail.com> wrote:

      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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