[Stoves] IBI Draft Guidleines for Biochar Specifications

[Crispin Pemberton-Pigott]

Dear Tom and All

 

Picking up on your point as to why things have been chosen, and also on Andrew and Ron’s points about what was chosen, I toss in my observations after three frustrating years of trying to get the coal industry standard analysis (methods) to somehow agree with the biomass industry norms.

 

There are so many differing ways fuels are analysed, and they are so functionally useless when it comes to accurately characterising stove performance, that we had to develop our own approach. The closest and most sensible are the approaches taken by the biomass/stoves community because they are the closest to ultimate analysis at any stage of processing.

 

Obviously in Ulaanbaatar we are working mostly with coal and we were given reams of tests from coal companies about their products. To my surprise the actual carbon, hydrogen and oxygen content is not really known at any stage of the analysis. Even now, no one can tell what the hydrogen content of the volatiles is for any of the dozen or so coals available.

 

The discussion of the char analysis seems to be proceeding along the same path and the importance of the issue of carbon, how much in each form, will probably dominate future correspondence. Obviously the labile portion of the char is important for agricultural application of bio-active char. If the conditions of char production are not known, variability in the result is guaranteed. It is not ‘char’ that is needed, it is some inert carbon and some labile carbon and the ratio is determined by the condition of the soil. Wow. 

 

When it comes to ‘carbon’ in a fuel there is the total atomic content, the amount that is locked in forms that amount to being included in the ash, the carbon that comes out easily with the volatiles (which are never, or hardly ever analysed). There is the carbon that is left after coking – supposedly the ‘fixed’ portion.

 

There is no such this as ‘fixed’ carbon in the way people think of it. It is merely a way of stating the amount of carbon that remains after heating using a particular protocol. If you use a different protocol, you get a different value. In all the ‘carbon’ remaining, there are volatiles and H2. So it is hardly ‘fixed carbon’ because some of it will come out if you heat it farther.

 

Here is an example (and it is by no means the only approach taken)

 

The technician heats the sample to 105 C for 1 hour and the mass loss determined to get the nominal moisture content. It is not the total water content because some water will still emerge at a higher temperature. If you crush the coal to <2mm before doing this it will give you a higher % moisture for the very same fuel because moisture can be hard to get out. [Some protocols use ‘air dried’ with no specification whatsoever as to what the conditions are.] Then it is heated again (sometimes) to a higher temperature and the moisture loss calculated again. That is classed as ‘inherent moisture’ and it is sometimes higher than the ‘moisture’. Bizarre. With biomass we think only of total moisture which is the second important number for any fuel after the LHV.

 

Following this it is again heated to perhaps 420 C in a closed container with a small hole to allow out the volatiles. This is used to calculate the ‘volatiles’ content. Whatever is missing is volatile. 

 

Then it is heated again to 830 (or another number) and air is supplied. The ‘fixed carbon’ (which contains hydrocarbons and sulphur) burns off leaving ‘ash’. Whatever remains is considered to be the ash content, even if it contains carbon.

 

The process is arbitrary. There is no definitive science suggesting that only a certain approach should be used. As the coal (or biomass) is heated, more and more of the content evaporates or burns depending on the conditions. What I have learned is that the ‘moisture content’ is not accurate. The ‘volatiles’ is almost arbitrary as what is left has lots of volatiles. The ‘fixed carbon’ is a meaningless name because some of the carbon left already and some is left and after burning it there is still some left. On top of this, the final % of content given for fixed carbon, volatiles and ash do not include the sulphur content which is simply ignored even if the content is 3 or 4%. You could not make up a stranger set of numbers.

 

None of them are useful for calculating the performance of a stove because whatever you use from them is inaccurate, often significantly so. Significant in the scientific sense.

 

I suggest that you insist that all analyses be done with ultimate analysis as a format, and that you try to get other to do the same. At least then you can work out what energy you have, what SO2, CO2 and H2O to expect during a test, and what the HHV and LHV are.

 

When it comes to charcoal for agricultural uses, it is necessary to use fluorescence and diffraction methods to determine what the form of carbon is, because inert carbonates are not the only things to subtract from the total carbon. It will be available in several forms which are labile or relatively inert and perhaps still in the form of volatiles hydrocarbons. Complex stuff, this.

 

Regards

Crispin

 

++++++

 

Ref: http://bit.ly/biocharguidelines

 

The Guidelines represent a substantial and very useful effort on the part of IBI and its advisors. After an initial reading I would suggest that IBI provide more discussion or justification for the choices that have been made.  While there is a long list of references the reasons for the IBI selection may not be apparent. 

 

1.       Methods of analysis

a.       What alternate methods that are used in other countries such as the CEN or ISO apply?

b.      Explain reasons for selecting each method.

c.       Fixed Carbon and Volatile Carbon are not included in the Level 1 characterization. Why? They are typically included in a proximate analysis for fuels (MC, Ash, FC, VC)

2.       Maximum values

a.       Why are “maximum”  values indicated for  Level 1 (Characterization) for ash (L1), H:C (L1)? 

3.       Where are the biochar reference databases used to developing these guidelines? For example, EPA provides reference databases for fuels, or analyses for hundreds of fuels when recommending a procedure or rule.  These are often referenced in whitepapers.

4.       What commercial and non-commercial laboratories have been consulted?

5.       What is the typical cost for each level of analysis in commercial labs?

Tom

 

 

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
>_for_Specifications_of_Biochars_for_October_2011_Public_Review.pdf
>

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
C."

   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 
increases.

   [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.

 http://www.bris.ac.uk/Depts/Chemistry/MOTM/diamond/cphased.gif

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.

AJH



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