[Stoves] Pyrolysis: No Air?

[Dean Still]

Paul,

Clean Rockets have a secondary combustion chamber above the primary
combustion chamber as in a TLUD (the Rocket has the vertical tube above the
fire). A TLUD without a secondary chamber can make smoke but adding the
'burn out chamber' like in your and Kirk's stoves cleans up combustion. In
the same way, lots of folks are adding jets of air in a Rockets vertical
tube to increase mixing and decrease escaping emissions.

In a TLUD, especially when the fuel is low in the combustion chamber there
is a definite distance between gas creation and gas burning but as you say
it seems that in many ways"the various chemical and physical processes are
the same" in a Rocket and TLUD. The big advantage of the TLUD, I think, is
that all of the gases go into the flame which is not true in a Rocket. So
the Rocket is dependent on jets of forced air to create a zone of mixing
but a natural draft TLUD can be as clean as a forced air TLUD.

Best,

Dean
On Sat, May 16, 2015 at 9:08 PM, Paul Anderson <psanders at ilstu.edu> wrote:

>  Dean,
>
> Any solid biomass that is burning is undergoing the same various chemical
> and physical processes.   But in gasifiers the processes are somewhat
> separated (make gases and burn them later in a different location, even if
> the later is only a few milli-seconds and the location is only a few
> centimeters away).   In contrast, the fires in Rocket stove and bonfires,
> etc, have the processes occurring virtually simultaneously and
> intermingled, some at essentially the same location (or with mixing).
>
> In a standard fire (Rocket, etc.) that the relatively cool secondary air
> (needed to burn the gases) is entering at or close to the fuel, resulting
> in some cooling of fuel that needs to be hot to create the gases.   This is
> a fundamental difference that allows gasifiers to be burning gases
> separately from where the gases are being created, with benefits of cleaner
> combustion (if done properly).
>
> In somewhat simplistic terms, carbonization and pyrolysis are two sides of
> the same coin (or process).  Carbonization creates char (focus is on the
> resultant char) and Pyrolysis creates gases (focus is on the gases).   Both
> relate to "burning".
>
> Remember also that the char (once it is created) is hot and IF exposed to
> oxygen will itself "char-oxidize" or "char-gasify" (into CO or CO2) and
> therefore will "disappear" in a regular fire.   But in a TLUD the char just
> sits there, being hot but without any O2 (unless fans, etc bring in
> sufficient air with O2 to reach the surface of the char.)
>
> Terminology:  Pyrolysis is by HEAT.   The heat can be with FIRE present or
> not (retort).  There is oxic pyrolysis (oxygen present / coming in) and
> anoxic pyrolysis (no oxygen from outside the biomass).
>
> Paul
>
> Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
> Email:  psanders at ilstu.edu
> Skype: paultlud      Phone: +1-309-452-7072
> Website:  www.drtlud.com
>
> On 5/16/2015 10:34 PM, kgharris 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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