[Terrapreta] pulverizing charcoal

[Greg and April]

Some where I read that at extreme temperatures, the pores in char near the surface, can glaze over ( my understanding ), actually leading to pieces being less porous.    

Here it is - Dr Michael Antal sent me several PDF's last march and the following in purple is from:    The Art, Science, and Technology of Charcoal Production

Marsh and co-workers
observed a maximum in the surface area (500 m2/g) of
a cellulose char that was carbonized at 900 °C. 106
Masters and McEnaney107 reported a strong falloff in
the open micropore volume of carbons derived from
cellulose at heat-treatment temperatures (HTTs) above
1000 °C. Raw biomass charcoal prepared at a low
temperature (400 °C) has a negligible surface area and
an iodine number below 50. 108  Baileys and Blankenhorn 109 
reported an increase in total porosity with
increasing peak temperatures up to 500 °C (the highest
temperature studied). On the other hand, Khalil 110 
observed very low surface areas and iodine numbers for
carbons from a wide variety of lignocellulosic materials
charred at 550 °C. Without specific references to the
literature, Wenzl stated that the micropore volume
reached a maximum at relatively high temperatures
(800-850 °C), whereas the mesopore volume did not
increase at temperatures above 550 °C.  39  MacKay and
Roberts  72  found that microporosity was established near
500 °C and further heating volatilized residual material
that blocked micropores,  41  thereby increasing the micropore
volume somewhat. Blankenhorn and co-workers  99
observed a maximum in the total porosity of black
cherry wood near 700 °C. In the case of redwood,
MacKay and Roberts  72  reported pore volumes in the
range of 0.18-0.23 mL/g. Corn stover char evidenced
lower micropore volumes because its high content of
inorganic materials partially filled or blocked access to
the micropores. At temperatures near 900 °C, McKay
and Roberts  72  observed shrinkage of the micropore
structure leading to a reduction in open porosity.
Precursor composition and heating rate had little influence
on char microporosity.  72   Corroborating these findings,
Dai and Antal  108  reported a decrease in iodine
number from 181 to 129 for macadamia nut shell
("macshell") charcoal carbonized at 750 and 900 °C,
respectively. They attributed this decrease to the loss
of free sites, defects, and edges that results from thermal
annealing.  107,111  The 900 °C carbonized charcoal had a
surface area of about 100 m2/g and a pore volume of 0.06
mL/g. Using the same macshell charcoal carbonized at
950 °C, Conesa et al. measured an iodine number of 154
and a surface area of 193 m2/g. De-ashing of the biomass
feedstock often increases the surface area of its carbon
derivative.  53  In our experience, the surface area and
pore properties of a carbon can be dramatically affected
by the presence or absence of gas flow during carbonization
and any inadvertent exposure of the carbon to air
during carbonization.


Does this explain why a piece of char may be in the ground and not get saturated?    This may be reason to make the char in larger pieces and then crush - to get past the surface glazing.

Greg H.

  ----- Original Message ----- 
  From: MFH 
  To: 'Larry Williams' 
  Cc: 'Miles Tom' ; 'folke Günther' ; 'bakaryjatta' 
  Sent: Wednesday, May 21, 2008 3:13
  Subject: Re: [Terrapreta] pulverizing charcoal


  "Is it possible that pieces of charcoal can be in the ground for a year and not get saturated? Why?"

   

  As per a previous comment, my guess is that some charcoal will have pores so fine that a surfactant is needed in the water to enable penetration. The surfactant could be fertilisers such as urea and ammonium sulphate, probably urine, and maybe runoff from animal manure. Char from different sources will have different pore sizes.

   

  Max H

   


------------------------------------------------------------------------------

  From: Larry Williams [mailto:lwilliams at nas.com] 
  Sent: Wednesday, 21 May 2008 6:58 PM
  To: MFH
  Cc: folke Günther; Miles Tom; bakaryjatta
  Subject: Re: [Terrapreta] pulverizing charcoal

   

  This photograph, taken by Richard Haard, in a garden situation seems to support the idea that the critters and the plant roots help to break charcoal apart. The larger dry piece of charcoal which the knife point is laying on was in the ground for nearly one year and it does not resemble the smaller piece of charcoal which had one small white flat worm (the white oval spot) and apparent plant roots attached to it. The larger dry piece of charcoal indicates little biological activity.

   

  I can only suggest that the dry charcoal was buried just after it was made. Likely it was a product of last spring's earthen mound kiln with no special attempt to wet, size, fertilize or inoculate it. Is it possible that pieces of charcoal can be in the ground for a year and not get saturated? Why?

   

  In my gardening activities, I have found a considerable number of charcoal pieces that, I believe, have been compacted by foot traffic during home construction. Usually this charcoal is found when draining systems are installed or repaired. These photographs are examples (here, here and here), also taken by Rich. These specific pieces could have been in the ground since the land was cleared for construction of the home some ninety years ago and were 4-6" (10-15 cm) below the surface. This charcoal was 18" (45 cm) from an aged moss covered brick wall with no  noticeable fire markings suggesting that the charcoal was buried for a period of time that was closer to the construction of the home than of recent origin.

   

  From my perspective, the placement of charcoal in the soil needs to meet certain requirements for it to interact with the soil's biology. I agree with Max and Folke that the charcoal is broken up by the local biology in due course. Soil compaction may likely stall the break up of charcoal (till the next ice age? I live in a location where the last ice age was fifteen thousand years ago and was a mile... 1600 meters thick ice sheet).

   

  Keep your eyes open for there is charcoal in more places than you might believe, just under your foot-------Larry (in the wet Pacific NW)

   

   

  -------------------------------------  

  On May 20, 2008, at 3:26 PM, MFH wrote:





  Worms feed by "sucking" moist particles of organic matter. They have no teeth. It appears that fine grains of soil or sand or char are ingested to assist in the breakdown of the organic matter in the worm's intestines.

   

  It seems unlikely that worms could be directly involved in breaking down large char pieces. That doesn't mean that there isn't a link. If the moisture conditions are suitable and there is ample organic matter then there will be worms, and worms will improve the soil, and improved soil will mean more plant vigour, which will mean more plant roots. And more plant roots will mean greater breakdown of charcoal lumps, as the roots penetrate holes and gaps seeking nutrients and moisture. The forces generated by expanding roots is considerable, as evidenced domestically by broken concrete paths and damaged pipes.

   

  And there are lots of roots. A mature rye plant has a total of around 600 km. of roots.

   

  Max H

   

   


------------------------------------------------------------------------------

  From: terrapreta-bounces at bioenergylists.org [mailto:terrapreta-bounces at bioenergylists.org] On Behalf Of folke Günther
  Sent: Wednesday, 21 May 2008 8:01 AM
  To: Greg and April
  Cc: terrapreta at bioenergylists.org
  Subject: Re: [Terrapreta] pulverizing charcoal

   

  I don't know what happens if you have very large amounts, but if you add a reasonable (>a kilo per sq. m) amount of unsorted (up to 4-5 cm pieces) char to he soil, and wait for a year, then all char will be very soft and easily split up in smaller pieces. I think the plant roots do most of the on, and he worms will hunt for bacteria in the char.

  2008/5/20 Greg and April <gregandapril at earthlink.net>:

  Are you sure about that ?

   

  We already have some evidence that when char level get above a certain level in worm bins, they don't do very well - probably because it's so abrasive.

  If you add amounts of char in the worm-bin, the organic material will disintegrate rather fast, the microbes will be eaten by the worms, an after some time (faster than you think), almost only the char will be left. It is evident that the worms don't thrive very well there!

     

    If it's abrasive enough to keep worm levels down, what makes you think that the worms can make big pieces small?

     

    I'm not trying to be rude, I'm just pointing out that we may have some evidence that what you said may not be true.

     

     

    Greg H.

     

     

      ----- Original Message ----- 

      From: folke Günther 

      To: May Waddington 

      Cc: terrapreta at bioenergylists.org ; Roy Lent 

      Sent: Tuesday, May 20, 2008 2:17

      Subject: Re: [Terrapreta] pulverizing charcoal

       

      The worms and the plant roots  will do the job. After a year, all pieces are conveniently small.
      FG




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