[Terrapreta] volatile matter and char

[bakaryjatta]

Dear TP list members,

All these posts about the unknown qualities of  TP are confusing. I have
been making char from tree trimmings, mixed in crop residues like sorghum
stalks, elephant grass and sticks up to 45 mm thick. My retort is a standard
200 liter drum with a fairly tight lid. There is a piece of pipe allowing 
the
volatile gasses to blow into the firebox under the drum that is lying
horizontal. The contraption is partly enclosed with mud blocks and sheeting
to keep the heat from dissipating into the landscape. Once the temperature
is high enough for the volatile gasses to effectively take over the firing,
we just wait until the process finishes and let it sit until cool enough to
open the lid. When opened we find the larger material properly charred and
the smaller stuff reduced to grit. There is no evidence of tar like when we
botched up some of the first batches.

Seeing there is no way of testing and have nothing to compare it with
anyway, we use it after reducing the chunks with a peanut sheller. The
rougher pieces are then put through a hand corn mill. I have been using it
in my garden patch mixed with the effluent from a biogas digester and urine.
I thought I was having good results, but maybe I should worry that I am  not
doing it right? Ah, that is useles, let me leave well enough alone, but keep
watching. If I get negative results I will report it. Don't want to be a
spoiler of this part of the world you know!

I agree, it will be nice if one knows exactly what one should do. But trial
and error has been the learning method for many generations. Vegetables grow
quite fast, so results will show quick enough. My crop of Sorghum which had
the char mix tretment did quite well last season. I will continue the
production of char, one drum at a time, and increase the area where it will
be applied.

Thanks for feeding me information. I will have to check out the news that a
biochar project in West Africa includes Senegal and the Gambia.

Warm regards,

Bakary Jatta
Bwiam village,
The Gambia.


>Gerald Van Koeverden wrote:

> From the McClellan, Deenik, Uehart, Antal study  (Effects of Flashed
> Carbonized? Macadamia Nutshell Charcoal on Plant Growth and Soil
> Chemical Properties)
>
> Its conclusions:  "High volatile matter content charcoal has a
> detrimental effect on plant growth.   BUT!  Low volatile matter
> charcoal may have a beneficial effect on plant growth, especially
> when combined with fertilizer."
>
>
> What is the source/cause of high volatile matter in char?  Does this
> VM (since it is 'volatile') decrease/volatize by itself over a short
> time?
>
> According to the article "VM" content is "a measure of the
> susceptibility of charcoal to further decompose and form carbon when
> heated."
>
> Translation, please??
>


Sean K. Barry wrote

> Hi Gerrit,
>
> What is the source/cause of high volatile matter in char?  Does this VM
> (since it is 'volatile') decrease/volatize by itself over a short time?
>
>
> According to the article "VM" content is "a measure of the susceptibility
> of charcoal to further decompose and form carbon when heated."
>
>
> Translation, please??
>
> We've asked Dr. Michael J. Antal this very question, when he was
> subscribed to the list.  He was vague about what VM actually is then, too.
> It is measurable as the percent weight (VM%) of a charcoal sample (this is
> done using a "proximate analysis" test), but its chemical analysis is a
> mystery.  Some others have recently mentioned VM has an insecticidal
> effect (Dr. Reddy).  Edward Someus also says high VM% content on charcoal
> is a problem in soil.  People working with Eprida, Danny Day, Dr.
> Christoph Steiner, etc., were wondering if the VM% was a benefit as "food
> for microbes".
>
>>From what I have read about pyrolysis reactions, the VM% content is be
>>dictated primarily by maximum internal particle temperature in the char
>>bits (this can be somewhat related to residence time in the reactor).  Low
>>VM% is obtained at high temperatures, basically.  Higher temperatures
>>produce a more "activated" charcoal too ("activated" charcoal has a high
>>adsorption surface area).  Now, charring biomass on a forest floor or in
>>the soil will not likely allow such high temperatures (~1000C) to be
>>achieved, so one wonders how the original Terra Preta soil was made with
>>low temp char and does not suffer from toxicity.  Perhaps any toxicity in
>>fresh low temperature charcoal is lost over time once it is in the soil.
>
> As you suggest, VM is "volatile", so I imagine it does dissipate somewhat
> off the surface of the charcoal, through reduction by oxygen from the air,
> or water.  This has been recognized as a "storage" problem for fresh
> charcoal.  Fresh charcoal can spontaneously ignite!  THis occurs when the
> VM reacts and creates heat).  Another question I had was,  ... What about
> charcoal from natural forest fires that are quenched out by rain, for
> instance?.  Wouldn't these be low temperature and leave toxins in the
> soil?  But, as has been observed, soils on which forest fires have run
> across do not stop plant growth.  In fact, there is a "bloom" of new
> growth.  So, what's up? (with this "toxicity of of high VM% on low
> temperature charcoal" scare).
>
> I think this premise needs testing.  I think no none who has provided any
> "field results of using charcoal in soil" here yet, has known that the
> charcoal they used was low VM% or even what temperature the char was made
> at (no data on this presented).  I can make charcoal with my reactor and
> control the max temperature inside the reactor core.  I can do a
> "proximate analysis" test on any charcoal produced and make measurements
> of VM%.  I cannot discover any ways yet to characterize the chemical
> analysis of the VM in any way.  Dr. Antal got short with me when I asked
> him about doing this.  He told me, like in the paper, Volatile Matter is
> only quantifiable, not characterize-able.  (Who gets to say, "That's
> bunk!" to a PhD?).
>
> It may be that the processes required to produce low VM% charcoal are more
> expensive than otherwise, so these producers are trying to play up the
> value of their product.  I think the premise needs testing.  I think most
> testing occurring now is NOT seeing this detriment in their plant growth
> results.
>
> Carry on.
>
> Regards,
>
> SKB
>