Andrew (cc 2 lists) See below ----- Original Message ----- From: [email protected] To: "Discussion of biomass cooking stoves" <[email protected]> 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 > > > > http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioener > >gylists.org > > > > or, via email, send a message with subject or body 'help' to > > [email protected] > > > > You can reach the person managing the list at > > [email protected] > > > > When replying, please edit your Subject line so it is more specific > > than "Re: Contents of Stoves digest..." ... and please try not to repost whole digests to the list. AJH _______________________________________________ Stoves mailing list to Send a Message to the list, use the email address [email protected] to UNSUBSCRIBE or Change your List Settings use the web page http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org for more Biomass Cooking Stoves, News and Information see our web site: http://www.bioenergylists.org/
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