[Stoves] Low temperature vs high temperature charcoal?

[Carefreeland at aol.com]

Tom, Tom, Listers, 
    I would think that there would be a reduction in  tars in the higher 
temp chars. This might have some advantages in less surface  tension of water. 
The tars, on the other hand may have some beneficial use in  reducing, 
insects, fungus or bacteria growth in chars used for soil enhancement.  The 
chars created in a gasifier or less efficient system such as an open fire or  
various older systems of char making would all contain more ash. The extra ash 
 would have benefits as a nearly balanced fertilizer in the soil. Minus 
only  nitrogen. 
    It surprises me that higher temp chars  would have a lower surface 
area. Has anybody studied the  relationship between the time it takes to cook 
the char and the amount of  surface area created?  I would think the higher 
temperatures and faster  cooking would rupture the cell membranes violently 
and to a greater extent from  flashing steam. Would this create more or less 
surface area?  Would  carbonized cells have a greater CEC with tiny holes in 
them from slow cooking or  larger more accessible ruptures from fast 
cooking? Would some cells not rupture  completely?  or be blocked in large chunks 
of charcoal from acting to  absorb water and minerals?     
    Obviously, the type of biomass would  also be a great variable in the 
surface area equation as cells rupture  based on their design. Old gunpowder 
makers knew this from experience that is  why low ash, high surface area 
Willow and Dogwood were favored. The Dogwood for  dense, high octane powder and 
the Willow for light, fast burninig powder. 
    I think that nature already has figured this out in  a beautiful way- 
as usual. Char for soil is best created in hot but inefficient  forest fires. 
Char for use as a fuel for man is best created with a high yield  and lots 
of hydrocarbons in a closed retort system. All other uses fall on  a scale 
in between. The Biblical saying "Render unto God what is  God's" comes to 
mind. And you thought it was just about taxes! 
    I like to burn my brush in a big cut open tank in  the garden. All the 
ash flies out into the air and lands well distributed all  over the garden. 
This saves me the task of spreading the ash. In forest fires  the majority 
of the char forms underground or under ash. Again, Nature  is still one or 
many steps ahead of us. 
    Only questions, no answers as usual. No lab or even  a greenhouse 
anymore to experiment with.  Have fun all you college types.  Let me know what 
you find. I do still read some of the letters now and  then.
    Keep Charring and Stoving, 
    
    Dan Dimiduk 
    From the peanut gallery.  
    
In a message dated 6/16/2013 4:41:37 PM Eastern Daylight Time,  
tmiles at trmiles.com writes:

Stephen  Joseph should comment on the target "optimum" range set out by
Lehmann and  others of 450-550 C which seems to have guided most research.
According to  their work an increase in temperature to 500-700C would appear
to result in  slightly lower yield and surface area. pH and CEC would be
about the same.  Trials with different plants and soils since this early 
work
may tell us a  different story. 

We have had good results with limited use of higher  temperature pyrolysis
and gasifier chars, in the 500-700C range or even  higher, when used in
erosion control, filtration, vermiculture and  soil-less media. The main
drawback of a gasifier char is a lower char  yield.     

Tom Miles




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