[Terrapreta] the pyrogenic nature of pyrolytic charcoal

[Rebecca Oglesby]

Michael,

Bob Hawkins posted our understanding of this subject awhile back. I have
copied it below:

   It was mentioned that char can spontaneously combust, and since then,
several questions about this have been asked.  Below, is an explanation for
why this occurs and how to prevent it.  I hope this answers everyones
concerns.


   We collect the char in an air-tight barrel as it falls out of our
pyrolysis unit. Char fresh from the machine is still hot and it only takes a
little bit of oxygen to get it glowing hot and burn up all its surroundings,
reducing the char to ashes. If no oxygen is present, it won't continue to
burn once it is out of the reactor. This reactivity is caused by several
factors and is easily preventable, however.  The freshly produced char has
never been exposed to oxygen, and during the pyrolysis process, reactive
organic species are created on the surface of the char (this includes the
surface of the pore structure).
These organic compounds react exothermically with oxygen, and when char is
fresh and in a big pile, there is enough heat in the char pile to start
these reactions. Once these reactions begin, and there is air getting to the
char, the coals are no lit, so to speak. Also, when the char is collected in
an air-tight container, there is still enough heat in the char as it exits
the pyrolyzer for small amounts of volatiles to enter the gas phase. When
the char totally cools, these volatiles will re-condense in and on the char.
 If there still exists gas-phase volatile organic compounds in the char
pile, and they are exposed to oxygen, they react exothermically, providing
enough heat to get the char going.

   This can be prevented by a few methods.  The char has to be exposed to
air at somepoint, so never allowing it to come in contact with oxygen is not
really
practical.  The trick is to expose the char to air slowly, and while not in
a big pile.  Usually, just transferring the char from its collection
container into a separate storage container will prevent the
char from igniting.  The reason for this is that the volatile organic gasses
trapped in the char pile are allowed to escape, and the highly reactive
surfaces on the char are allowed to react with the air, but in the process
of moving from one container to another, the heat from the reaction can
escape and does not cause the char to heat up.  After the char has been
transfered, grinding the char into smaller pieces repeats the process just
mentioned, and further prevents the char from igniting.

   One thing to remember, char contains energy that is released as heat when
it reacts with oxygen.  Char, or charcoal, can catch fire at any time if it
is hot enough and there is enough air. So, if you are storing the char in a
huge container (industrial size storage), and it is 100 degrees   outside,
and there is air drafting through the container (maybe from a hole
somewhere), it is possible that the char may catch fire, much like a pile of
compost/wood waste gets hot enough to burn..  Therefore, careful attention
must be paid to storage of char.

I hope this helps

Regards,
~Rebecca



> Date: Thu, 6 Sep 2007 18:59:47 +1000
> From: "Michael Bailes" <michaelangelica at gmail.com>
> Subject: Re: [Terrapreta] the pyrogenic nature of pyrolytic charcoal
> To: "Gerald Van Koeverden" < vnkvrdn at yahoo.ca>,  terrapreta
>         <terrapreta at bioenergylists.org>
> Message-ID:
>         < 7dcba7be0709060159o2b92cfaj16903fabca8b751f at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-1"
>
> On 04/09/07, Gerald Van Koeverden <vnkvrdn at yahoo.ca > wrote:
> >
> > Dr. Antal,
> >
> >         Charcoal produced by pyrolysis, as Adriana Downie writes, tends
> to
> > be highly pyrogenic.  In an earlier message, she described charcoal
> > stored in plastic pails as melting the containers.  I know two
> > instances (another company) when such pyrolytic charcoal being
> > transporting have started combusting.  This makes storage (under
> > nitrogen?), handling, and shipping (flammable materials licensing,
> > etc.) rather problematic.  Is the charcoal produced by flash
> > carbonization pyrogenic?  If so, how have these difficulties been
> > solved?
> >
> > Gerrit
>
>
>
> I find this hard to believe unless the char has only just been made and
> not
> properly extinguished. Here it is mostly stored in paper bags, so we
> should
> have fires everywhere.
> I have seen pallets of them and no spontaneous fires.
>
> (I have seen spontaneous fires of oily rags in a factory dustbin.)
>
> There are no government warnings or regulations coving char
> safety  either.
> Chemist shops should have little fires on their charcoal tablet counter
> It should also be impossible to put out a bushfire.
>
> --
> Michael the Archangel
>
> "You can fix all the world's problems in a garden. . . .
> Most people don't know that"
> FROM
> http://www.blog.thesietch.org/wp-content/permaculture.swf
> -------------- next part --------------
> An HTML attachment was scrubbed...
> URL:
> /pipermail/terrapreta_bioenergylists.org/attachments/20070906/6cac37b6/attachment-
> 0001.html
>
> ------------------------------
>
>


-- 
Eprida, Inc
1151 E. Whitehall Rd.
Athens, GA 30605
(706) 316 - 1765 ext 645
http://www.eprida.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: /pipermail/terrapreta_bioenergylists.org/attachments/20070906/e72b978d/attachment.html