[Stoves] [biochar-production] Re: Stoves Digest, Vol 14, Issue 17

Frank Shields frank at compostlab.com
Wed Oct 26 10:23:26 PDT 2011



Regarding the 50% ash value: 


I agree with this number. Biochar is made of two components: 1) light weight
carbon structure and 2) heavy mineral matter including dirt.  So 50% ash
will still 'look like' a lot of char and little ash because we look at it as
a volume basis. Also with many feedstocks like grasses etc a 50% ash content
may not be that unusual. And I think because we are using biochar as a soil
amendment the high ash is not necessarily undesirable as it contains
nutrients and liming effects. But a greater than 50% may mean dirt and sand
contamination. So I suggest keeping the 50% ash and then further
characterization of high, medium and low ash chars. 


Something like that.





Frank Shields

Control Laboratories, Inc.

42 Hangar Way

Watsonville, CA  95076

(831) 724-5422 tel

(831) 724-3188 fax

frank at compostlab.com





From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Tom Miles
Sent: Saturday, October 15, 2011 9:12 PM
To: biochar-production at yahoogroups.com; 'Discussion of biomass cooking
stoves'; 'Andrew Heggie'
Subject: Re: [Stoves] [biochar-production] Re: Stoves Digest, Vol 14,Issue


I can see it is time to look at the proposed test methods. The 50% ash looks
like a showstopper for many good substrates like manures or straws with high
nutrient contents.  


I would be interested in the reasoning behind the 50% ash level. That would
rule out a lot of manure ash and certainly the 50% ash (40% carbon) rice
husk char we saw in Kyoto.


You require 50% maximum ash, then to make the char work you add 1/3 clay and
1/3 poultry litter to make an organo-mineral complex (S Joseph) so you wind
up with 15% or less char and 80% ash? Or you make a biochar based fertilizer
(BBF, China) that probably also has more than 50% inorganic in the blend. 





From: biochar-production at yahoogroups.com
[mailto:biochar-production at yahoogroups.com] On Behalf Of
rongretlarson at comcast.net
Sent: Saturday, October 15, 2011 8:49 PM
To: Discussion of biomass cooking stoves; Biochar-production; Andrew Heggie
Subject: [biochar-production] Re: [Stoves] Stoves Digest, Vol 14, Issue 17



Andrew (cc 2 lists)

   See below  


From: ajheggie at gmail.com
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>
Sent: Saturday, October 15, 2011 5:31:07 AM
Subject: Re: [Stoves] Stoves Digest, Vol 14, Issue 17

On Saturday 15 October 2011 06:56:03 Ron Larson wrote:
> Trevor, Paul, and lists
>     See Table 1 on p 12 of the draft IBI guidelines, which states that
> the ash content shall be less than 50%.  If you think this is the wrong
> level, now is the time to speak up.
>    See
> http://www.biochar-international.org/sites/default/files/IBI_Guidelines

Ronal, does this refer to total ash after the sample has been incinerated 
and include ash in the char matrix as well as "free" ash in a partly 
incinerated air starved fire? I can see the desire to not have loose ash 
in a product sold as biochar.

   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.

   I should have given the further instructions from IBI's Table 1 for the
ash test - which says (in full):

"Apply loss on ignition (ASTM D1762-84) to ascertain
total non-carbonate ash, then add back inorganic
carbon as carbonate."

    This standard (like all ASTM standards) costs money.    Interested
individuals might find it available in a local library.   But if one googles
a little, you might find something on the web.  What I found and summarized
above may not be the most current.  In a Webinar last week, I heard that
alternative tests are not permitted - for ash or for anything else.  Bit
more below.  This not being my area of interest - I am uncertain on the
statement above about inorganics (carbonates) - which I don't find in the
ATM standard.  But the guidelines also call for that measurement - so I
think there may be some room for confusion here  (and so am including Kelpie
Wilson in this response as well)  Re inorganic carbon, the pertinent box
from Table 1, says:

"C, H, N analysis by dry combustion (Dumas method),
before (total C) and after (organic C) HCl addition;
inorganic C is the difference between total and organic

   This is undoubtedly clear to those doing this regularly.  An example is
on the last page of the guidelines.

> > If we gasified all volatile matter,
> > the fixed carbon content of the char would rise to about 43%,
> > and the ash content would rise to about 57%.
> > But typically rice hull biochar has an ash content of about 40%.
> > This means that there is still a lot of volatile matter that remains
> > in the biochar.
> >

I've still not seen rice husks so take my comments with a pinch of salt.

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".  IBI and biomass
community avoid the word "gasified" - unless they truly are talking about
the very small amount of material (mostly ash) when one is gasifying
(usually to put the gas into an engine) and to then get minimum char out.
I wouldn't go so far as to say that gasifiers give 100% ash - but gasifier
folk (and we have a sister list doing only that) certainly strive to
minimize char.

A pyrolysed sample would keep all the ash locked in a char matrix. The 
amount of char would depend on the rate of temperature rise ( which we 
could expect to be high in the thin, low mass hulls) and the final 
temperature attained in the treatment

   [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.]

A typical gasifier would still have some fixed carbon in the ash because 
the air supply is restricted to below that necessary to react out all the 
carbon, because things are not perfect and it is better to discard char 
than have any free oxygen downstream of the gasification process. This is 
the opposite of the internal combustion process where a slight excess air 
is necessary to prevent soot and CO being carried into the exhaust. 

> > In the case of rice hulls,
> > the amount of volatile matter that remains in the biochar is
> > determined by the rate of gasification. At times the yield in rice
> > hull biochar by weight is as low as 30%. At times the yield is as
> > high as 50%.

Yes, this I would expect, biochar will consist of two parts, the fixed 
carbon ( which usually  is usually dependant largely on lignin content of 
the feedstock and soots redeposited from secondary reactions) and the 
higher temperature tars. These latter are volatilised as temperature 

   [RWL:  And the Biochar community refers to the volatile not-so-permanent
part as the labile component.]

> > If the rate of gasification is high, high temperatures within the
> > reactor are reached. With high temperatures, more volatile matter is
> > gasified.

Yes, the heat of burning the carbon raises the temperature and this 
volatilises any surviving tars.
> >
> > We need operating temperatures well beyond 1000 C before fixed carbon
> > gets gasified. 

Well the fixed carbon will remain static above 900C in an airless 
environment but if any oxygen is present it will continue to react with 
any carbon it meets but some carbon will have changed from an amorphous 
form to less reactive graphene like clumps. I'd like to learn more about 
how carbon graphitises with increased temperatures, we know diamond will 
do this but I see little about how biomass derived carbon might undergo 
this change.

   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.


shows a phase diagram that suggests at low pressures and high temperatures 
graphite is favoured.

> > In my opinion it makes little sense to gasify fixed 
> > carbon.

Then keep air away and quench it fast.

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

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 ... and please try not to repost whole digests to the list.


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