[Stoves] Stoves Digest, Vol 14, Issue 17

[ajheggie at gmail.com]

On Sunday 16 October 2011 04:48:37 you wrote:

> RWL: I am sure this IBI guideline refers to everything in the
> "representative" char sample that one has been unable to remove by
> raising a 1 gram sample to 950C for a specified time period. But the
> detail is even more specific than that - including particle size
> distribution for the test.

Tom Miles has also raised the concern that this may limit what biochar can 
be made from and then used.

>
> I'd be careful about using the term "gasified" in the first sentence,
> it could be taken to mean using sufficient oxygen to deliberately
> gasify the fixed carbon in the husks. If this is done completely then
> the incinerated sample would be 100% ash.
>
> [RWL: Thanks for this reminder on "gasification". 

Yes sticking to "pyrolysis", "fixed carbon" and "labile carbon" makes 
sense to me when the aim is to have a char residue.
>
> [RWL: And the input biomass material. I suppose some input
> biomassmaterials may have an inherently difficult time achieving the
> 50% maximum ash limit , if they operate at high temperatures. This is
> agreeing with your next paragraph. ]

... and Tom's. In this case I was referring particularly to rice husks as 
their surface:volume ratio will differ substantially from stickwood and 
give less opportunity for redeposition of char internally.

> RWL: The ASTM testing talks about 950 C - and probably because little
> is happening even at 900 C. . I too hope to learn more. The experts do
> a lot of this testing with spectrographs. In Kyoto we heard one can
> learn a lot from light reflectivity tests. But indeed more graphene
> comes with higher temperatures. I haven't heard of any correlations
> with diamonds.

I wasn't suggesting there was, just pointing out that as carbon particles 
are heated they tended to form hexagonal graphene like bonds rather than 
linear, aliphatic, ones and this included the tetrahedral diamond lattice 
morphing to graphite at higher temperatures and low pressures.

Having attended two biochar meetings I have seen the references to these 
graphene like structure in secondary pyrolysis reactions as temperatures 
increased ( and means of detecting their presence by nuclear resonance 
and diffraction). What isn't clear to me yet is how these micro scale 
particles electrical properties will contribute to the biochar.


> My question is: why do you want fixed carbon? It is after all a small
> portion of normal charcoal.
>
> [RWL: Andrew - I was OK with your remarks up to here. I think the
> meaning is /was: let's pyrolyze and end up with char - rather than
> gasify and end up with mostly combustible gases. Can you clarify? We
> want fixed carbon (charcoal) for soil augmentation and carbon
> sequestration reasons (de-emphasizing energy). Ron

Just being devil's advocate, I'm still not clear in my mind what we are 
expecting of the char, it's clear we can make a controlled char now which 
will meet these premature standards but it is also plain that chars added 
to soils over the millenia were formed in a myriad of different ways, 
temperatures, feedstocks etc.

AJH