[Terrapreta] Charcoal properties

[danny day]

Tom:

The difference in porosity of materials depends on many factors which are
well documented and I have to beg off on the references right now (use
carbonnegative.info for help if needed).  A new one that you may not have
run into is:

Nathasak Boonmee's (2004)THEORETICAL AND EXPERIMENTAL STUDY OF AUTOIGNITION
OF WOOD, Univ. of Md.

His work is excellent showing orientation of heat applied to the wood fiber
in situ and the differences created.  The ability to simulate natural fire's
impact on charcoal is a fascinating study and lots to incorporate into our
energy/soil productivity practices.  Bob Hawkins will be presenting an oral
presentation on testing to optimize char's effects at the upcoming
conference in Australia.  I hope everyone can invest in the airfare to
attend who is really interested.

Danny


On 3/4/07, Tom Miles <tmiles at trmiles.com> wrote:
>
> Michael, Danny,
>
> Is there a difference in the morphology of wood and agricultural charcoals
> with different volatile contents such as pore size or porosity? Can it be
> seen in scanning electron microscopy (SEM) photos or measured with
> absorption techniques?
>
> See images in J. Skjemstad, "Charcoal Carbon in US Agricultural Soils"
> linked at:
> http://terrapreta.bioenergylists.org/Skjemstadus
>
> Thanks
>
> Tom
>
>
>
>
> -----Original Message-----
> From: terrapreta-bounces at bioenergylists.org
> [mailto:terrapreta-bounces at bioenergylists.org] On Behalf Of Michael J.
> Antal, Jr.
> Sent: Friday, March 02, 2007 12:29 PM
> To: terrapreta at bioenergylists.org
> Subject: [Terrapreta] Charcoal properties
>
> Dear friends: terra preta is fascinating in part because it involves so
> many
> disciplines.  My viewpoint is that of a fuel scientist/chemical engineer.
> My laboratory produces well-characterized charcoals for a wide variety of
> research endeavors, including carbon fuel cell studies, metallurgical
> charcoal applications, activated carbon production, and terra preta
> research
> (with my colleagues Dr. Goro Uehara, Dr. Jonathan Deenik, and Tai
> McClellan
> in the University of Hawaii's College of Tropical Agriculture and Human
> Resources).  With this message I wish to call your attention to the
> elementary properties of charcoal that I think about when I am producing a
> charcoal for one of our research endeavors.
>
> Both the feedstock and the process (i.e. pyrolysis) conditions influence
> the
> properties of the charcoal product.  For example, oak wood has little ash;
> consequently its charcoal also has little ash.  On the other hand, rice
> hulls have much ash (nearly pure silica), and so does its charcoal.
> Likewise corncobs produce a highly macroporous charcoal, whereas sucrose
> charcoal lacks a macroporous structure.  But unfortunately, the properties
> of the feedstock do not completely determine the properties of the
> charcoal.
> For example, if pyrolysis is carried out at a high temperature, some of
> the
> volatile ash components leave the charcoal.  In our work it is not unusual
> to find that the charcoal contains as little as 20% of the amount of ash
> that we expected on the basis of the feedstock ash content.  One carbon
> company produces an ash-free carbon for metallurgical applications by
> simply
> heating a fossil carbon (usually coal) to such a high temperature that
> virtually all the minerals in the fossil carbon vaporize.
>
> Likewise the pyrolysis temperature (usually called the "heat treatment
> temperature" or HTT) exerts a big influence on the properties of the
> carbon.
> Fuel scientists employ proximate analysis to measure this
> influence.  Let's
> be clear: there is nothing approximate about proximate
> analysis!  Proximate
> analysis determines the moisture content (mc), volatile matter (VM)
> content,
> fixed carbon (fC) content, and ash content of a charcoal (or fossil
> carbon).
> A good barbeque charcoal will have a VM content of 25 – 30%, whereas a
> charcoal destined for metallurgical use often has VM content below 10%.
> Increasing HTT lowers the VM content of the charcoal, but there is not a
> simple relationship between the HTT and the charcoal's VM content.  Why?
> The simplest explanation is that the thermocouple used to measure the HTT
> measures the temperature of the pyrolysis environment: it does not measure
> the temperature of substrate during pyrolysis!  Pyrolytic reactors
> designed
> to maximize "oil" (or gas) yields - and minimize the charcoal yield -
> employ
> high heating rates.  Under these conditions the pyrolysis reactions are
> endothermic; consequently there is a large temperature difference between
> the charcoal and its environment (i.e. the temperature of the charcoal can
> be hundreds of °C lower than its environment).  On the other hand, a
> pyrolytic reactor that is designed to maximize the charcoal yield will
> evoke
> exothermic pyrolysis reactions in the substrate, since the reactions that
> form charcoal are exothermic.  In this case the temperature of the
> charcoal
> can be much higher than its HTT.  I can provide some interesting papers on
> this subject for anyone who is interested.
>
> In summary, both the feedstock and the pyrolysis process conditions
> influence the properties of the charcoal product, but they do not
> determine
> the properties (i.e. knowing the feedstock and process conditions is not
> enough to predict the properties of the charoal).  The only way to
> determine
> the charcoal's properties is to actually measure them.  We do proximate
> analyses of all our charcoals.  Often we do gas sorption measurements to
> determine the carbon's surface area and pore volume
> distribution.  Sometimes
> we obtain an elemental analysis of the carbon, or an analysis of its ash
> content.  For our carbon fuel cell work we measure the carbon's electrical
> conductivity, and with colleagues in the Hungarian Academy of Sciences we
> do
> temperature-programmed desorption of biocarbons used in our fuel cell.  We
> have done XRD, NMR, ESR, and MALDI-TOF MS analyses of some of our
> charcoals.
> We have plans to expand our analysis capabilities into other areas soon.
>
> Tests by my colleague Professor Goro Uehara and his co-workers in CTAHR
> have
> shown that the addition of some charcoals to the soil can be harmful to
> plant growth.  Our analyses of the properties of this "harmful" charcoal
> indicate that it would have been perfect for barbeque.  This illustrates
> the
> dangers of working with an uncharacterized charcoal purchased from your
> local grocery store.  Professor Uehara and his co-workers will have more
> to
> say on this subject in the near future.  In the meantime I emphasize that
> our understanding of charcoal's beneficial and detrimental effects on
> plant
> growth must rest (in part) upon measurements of the charcoal's properties.
> This is not an easy job and there are no short cuts that I can find.
>
> Like most of you, at present my terra preta research is not funded, so the
> best I can do is provide well-characterized charcoals to my colleagues
> here
> at UH.  In the future I may have the resources to provide
> well-characterized
> charcoals to other terra preta researchers as well.  I will let you know
> when this becomes possible.
>
> Best wishes, Michael.
>
> Michael J. Antal, Jr.
> Coral Industries Distinguished Professor of Renewable Energy Resources
> Hawaii Natural Energy Institute School of Ocean and Earth Science and
> Technology (SOEST) 1680 East-West Rd., POST 109 University of Hawaii at
> Manoa Honolulu, HI 96822
>
> Phone: 808/956-7267
> Fax: 808/956-2336
> http://www.hnei.hawaii.edu
>
>
>
>
>
>
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-- 
Danny Day
President
EPRIDA
404-202-6105 Cell
706-621-7651 Office
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