[Stoves] Characteristics of biochar was Re: [biochar] grassifier & cedar chip char

Frank Shields frank at compostlab.com
Tue Feb 5 16:33:10 CST 2013


Paul,

 

My biggest problem with the term 'fixed carbon' is that it is not a
measurement of the carbon at all. Just the stuff left over after heating
that can contain Oxygen and hydrogen. 

 

Frank 

 

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
Paul Anderson
Sent: Tuesday, February 05, 2013 1:17 PM
To: Crispin Pemberton-Pigott; Discussion of biomass cooking stoves;
biochar at yahoogroups.com; Hugh McLaughlin; Ron Larson; Thomas Reed
Subject: Re: [Stoves] Characteristics of biochar was Re: [biochar]
grassifier & cedar chip char

 

Crispin,  

The influence of the coal industry on the testing is not a perfect match for
what biomass gasification is all about and the testing of biomass and
biochar.

Biomass can be 50% carbon, but with decay it will all go to CO2.      Fixed
carbon must be created in the carbonization process.

In Atlanta airport about to fly to Uganda for 3 weeks.   I hope that others
will comment, and not rely on me to reply.

Paul




Paul S. Anderson, PhD  aka "Dr TLUD"
Email:  psanders at ilstu.edu   Skype: paultlud  Phone: +1-309-452-7072
Website:  www.drtlud.com

On 2/5/2013 10:09 AM, Crispin Pemberton-Pigott wrote:

Dear Paul

 

1.     As far as I know, there is no "fixed carbon" in the biomass.   It is
fixed during the process of carbonization/pyrolysis.




That is the problem - it you give a sample of wood to a lab and they perform
a 'coal analysis test' on it you will get a report on the amount of 'fixed
carbon'. The point I was making is that it is a metric of convenience
arising from the test procedure, not a reference to a material property.

 


2.  Some biomass such as seeds have "oils" that vaporize or are volatile.
They are generally not pyrolyzed.   However, the lignin and other "stuff" in
biomass is what is pyrolyzed and gives off pyrolytic gases that are
volatile.   At low temperatures, the future volatiles are not yet in a form
that can be called volatile.   But they will volatize when subjected to
higher temperatures.

I will accept what the chemist eventually clarify for us.

 

The % Volatiles are defined as that fraction that will boil (literally) at a
given temperature. Choose you temperature. So when using a defined method,
the result changes with the temperature your use.

 

See for example http://www.sigmatest.org/Coal-Testing-India.html

 

"Proximate analysis - Moisture, Volatile matter, Ash and Fixed Carbon: 

"Proximate analysis indicates the percentage by weight of the Fixed Carbon,
Volatiles, Ash, and Moisture Content in coal. The amounts of fixed carbon
and volatile combustible matter directly contribute to the heating value of
coal. Fixed carbon acts as a main heat generator during burning. High
volatile matter content indicates easy ignition of fuel. The ash content is
important in the design of the furnace grate, combustion volume, pollution
control equipment and ash handling systems of a furnace."

This week we tried to get some tests of fuel content and were offered 'coal
analysis' tests. It all sounds good but if you look into the procedure, you
are not getting what you think - i.e. it is not an analysis of the elements
that we are used to talking about in the biomass fuel biz.

 

Getting a lab test result of this type using an instrument designed to do
ANSI/ASTM D3172 tests http://www.marsap.com/anamedinstru.com/coal.shtml  and
turning it into a 'standard' analysis is quite messy and I have a
spreadsheet for doing that if you need it. It was necessary for the Asian
Dev Bank (which built the SEET Lab) to do this because all that is available
is standard coal analyses, but the HTP test method is more scientific in the
sense that it uses the chemical composition of the fuel, not an
approximation of it.  It is also necessary to get the 'as received,
ash-free' heat content. Coal analysis methods gives AR (as received
moisture), AD (after drying but not 'actually dry') and FC (fixed carbon,
but not 'actual carbon' content). It also view some of the moisture as
'inherent'.

 

There are two things which come back 'wrong': the moisture content and the
carbon content. Finding out what the carbon content of the volatiles was is
nearly impossible. The right approach is XRD and XRF.

 

To give you an idea of how far wrong the method is for determining Carbon,
here is a standard test result of some coals and sawdust briquette. It is
well known that the sawdust contains about 50% Carbon. It was rated as
having 16% 'fixed carbon'. In other words it is basically a useless
measurement when it comes to biochar (or anything else).

 



 

Regards

Crispin

 

 

 

 

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