[Stoves] Pyrolysis: No Air?

Mon May 18 16:20:15 CDT 2015

Hi Kirk,

Thanks for the very clear explanation. I very much value your thoughts.

 Here's what I think I see:

Primary air rises up through the batch of fuel and controls the rate of
reactions on top.

The secondary air is needed for clean combustion of the made gas and flame
and powers the jets for mixing.

Today Art is here with his new TLUD and he turns down the primary air until
the burn is clean.

The fuel under the burn zone has air passing through it but it's not much
(so small an amount!) to get a clean burn.

The TLUD needs to keep only the top of the batch burning to meter the
correct amount of gas flowing into the flame for complete combustion.

If the burn zone is too active (too much primary air) the emissions rise as
the air/fuel mixture gets too rich. The batch is making too much wood gas.

I don't know whether this should be called gasification or pyrolysis but a
rose by any name is sweet!

Great to look at Art's new stove with so many Harris/Anderson/Wendelbo
features.

Best,

Dean

On Mon, May 18, 2015 at 1:43 PM, kgharris <kgharris at sonic.net> wrote:

>  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 <deankstill at gmail.com>
> *To:* Discussion of biomass cooking stoves
> <stoves at lists.bioenergylists.org>
> *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 <deankstill at gmail.com>
>> *To:* Discussion of biomass cooking stoves
>> <stoves at lists.bioenergylists.org>
>> *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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