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

[Frank Shields]

Dear Crispin, Tom,

I think we need to define a minimum *carbon* content for a material to be
called *biochar*. We can't call something a biochar if it has less than 1%
carbon for example. So where do we draw the line? We need to include all
natural biomass made into biochar like rice hulls. The material needs to
have enough carbon to be useful. So I say 50% carbon a minimum to be
'excellent' biochar knowing that most all natural, clean biomass will
produce a biochar with greater than 70% carbon. But open to other values to
make a scale. This makes it a product with enough value for a grower to
purchase and spread. 

I think the product should have the carbon content defined for quality (not
DAF). We should not include the oxygen and hydrogen and ash. We should
calculate the percent carbon content on the biochar sample dry weight (200
deg C). If we base quality on percent fixed matter (C-H-O) after subtracting
the ash I think there is a mistake. Because we 'make' more ash when we
change the cations into carbonates (increasing weight) during the process.
More cations from vegetative matter the more the problem. And this quantity
of ash is not what we are spreading on the field. Also the carbon trapped in
the ash (as CO3) is not included in the fixed carbon fraction - it should be
because it comes from the organic carbon in the raw sample. These are just
details and perhaps not that important. To do what I think is needed we must
determine the carbon using a Leco CHN analyzer. More work with expensive
equipment. But if we want to get carbon credits in the future we need to
start off accurately measuring the potential CO2 we are fixing. When money
is involved these details need to be addressed. Now is the time or we will
be back here again at a later time. 

Just because the carbon content is 0.1% and the ash is 99.9% doesn't mean
the product is not beneficial for an ag field. But I don't think we should
call it biochar even if someone did add a spoonful into a soil mix. This
rating has nothing to do with benefit to a field. That is site specific. It
has something to do with label on the bag (or may in the future). 


Regards
Frank








Vegatative plant material is 10 to 20 percent. We test a lot for nutrients.
It is very hard to get the customer to bring us a clean sample as it takes
so very little dust and dirt to bring the ash concentration up. I think
harvesting biomass for biofuel and one will not be careful to harvest clean
samples. 

If you have 15% ash in a dry organic material. Loose 60% of the organic
fraction during pyrolysis you have something like 20+ percent ash. And, as
you point out, there can be biomass with much greater than 20% ash. 

I suggested the 50% thinking this would be high enough to include most all
biomass that is made into biochar. Thinking we need some limit that if there
is less than 50% carbon  

  




Frank Shields
Control Laboratories, Inc.
42 Hangar Way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com
 
 

-----Original Message-----
From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Crispin
Pemberton-Pigott
Sent: Wednesday, October 26, 2011 12:42 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] [biochar-production] Re: Stoves Digest, Vol 14,Issue
17

Dear Frank

Apart from the special case of rice hull, how could you get a 50% ash level
in char?  Trees are about 0.5% ash. There is not much left of the fuel if
the char is 1% of the initial mass. 

Regards
Crispin

Frank,
 
I see the ash/carbon content as a sliding scale with relative changing
benefits rather than a threshold level. If biochar has less carbon than ash
is there still an agronomic benefit?
 
It is not clear how the IBI guidelines will be used. The guidelines should
list those components that should be measured. The recommended levels of
those components for different purposes could be separate recommendations
from IBI to a certification agency.
 
If the purpose is stability and carbon sequestration why limit counting
recalcitrant carbon even if it is 0.1% carbon or, 99.9% ash?
 
Tom
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