[Gasification] [biochar] Pine char gasification

Jeff Davis jeffdavis0124 at gmail.com
Mon Dec 23 19:17:25 CST 2013

"char-philia" that's what drove me away from biochar ! ! I can see some 
things never change.


On 12/23/2013 06:36 PM, Tom Miles wrote:
> Ron,
> I didn't mean anything quite so personal. :-/
> Most of the biochar research has focused on pyrolitic char and not on 
> combustion or gasification char. There is a clear bias toward 
> pyrolysis, or low temperature char. Can anyone really say this is the 
> way that the Amazonians, or anyone else, created the charcoal that we 
> find in the terra preta soils? Or was it smoldering combustion, staged 
> combustion (a la Alex English), or a combination of pyrolysis, 
> gasification and combustion? I know that I have had a lot of bad slash 
> and straw burns that have left a lot more char on the ground than ash. 
> Are there "signatures" in the terra preta char that point specifically 
> to pyrolysis, gasification or combustion?
> I see biochar production growing in stages. For the time being a large 
> quantity of char that is sold as Biochar is actually char from 
> gasification. As biochar markets grow we might expect to find more 
> pyrolytic char made "for purpose" but now we have some pyrolitic char 
> and byproducts of gasification (including TLUDs) and combustion.
> The "high temperature" gasifier char performs very well and in some 
> applications better than pyrolytic char. Several studies (and some 
> commercial producers) have found that conditioning the char through 
> partially oxidation (to higher temperature) enhances nutrient 
> retention. These products are for improving soil fertility , not 
> necessarily to replace activated carbon. So why not consider CO2 
> gasification as a possible process step?
> One major producer of char in California uses a downdraft gasifier. In 
> a downdraft gasifier wood devolatilizes at or above the oxidation 
> zone. Volatile carbon is oxidized by the air injected from nozzles to 
> make CO2. The hot CO2 reacts with the char to form CO and H2. This 
> occurs in the "reduction zone". The reduction zone is often shown as a 
> deep bed of carbon but in fact it is usually only a couple of inches 
> thick. Large chips reduce to powdered char in less than 2 inches where 
> gas temperatures are 800-900C. The resultant producer gas is a mixture 
> of this CO from reducing char and the devolatilized gas. Taking CO2 
> and reacting it with charcoal at 800-900C as Purdue has done is not a 
> lot different so the qualities of the char should be similar.
> I think we need to explore all avenues of producing char and energy
> 1.Slow pyrolysis -- 25%-30% char; 30% oil+gas
> 2.Fast pyrolysis -- 15% char; 60% oil
> 3.Gasification -- 5%-25% char; 75%-95% energy
> 4.Combustion -- 1-5% char; 95% heat
> Tom
> *From:*biochar at yahoogroups.com [mailto:biochar at yahoogroups.com] *On 
> Behalf Of *Ronal W. Larson
> *Sent:* Monday, December 23, 2013 2:53 PM
> *To:* Biochar; Tom Miles
> *Cc:* Crispin Pemberton-Pigott; Gasification-Request
> *Subject:* Re: [biochar] Pine char gasification
> Tom etal:
>    1.   I'm not sure I want to accept the "philia" part of this 
> message  ("philia" goes with "abnormal" and pedophilia at one google 
> site).  I found the word agape - but that sounds presumptuous.  But I 
> do admit to being at the non-sensical end of the char spectrum.  Maybe 
> charphilia is apt.
>   2.  I know close to zero about any part of gasification, but I can 
> understand why one would promote the idea of recycling the CO2 to get 
> more gas (eventually the Purdue group wants liquid, it seems).  But 
> that has to result in less char - and apparently leaves much higher 
> temperature char.  Eventually it is almost all CO2, for gasification, 
> but I worry that the char produced this (high temperature) way might 
> only be suited to replace AC = activated carbon.
>   3.  Since Alex English name came up today, we should note that he 
> also recycles CO2.
>   4.  The dogma of the cult I am in says more char beats more heat, 
> gas or liquid, so I will look forward to some proof that is not correct.
>  Good luck to the Purdue folk.
> Ron
> On Dec 23, 2013, at 12:58 PM, Tom Miles <tmiles at trmiles.com 
> <mailto:tmiles at trmiles.com>> wrote:
> Ron,
> This work is very important for both the biochar and gasification 
> lists. Biochar will be produced at the large, or even small, scale as 
> a co-product of energy (liquid fuels and/or power). The most efficient 
> way to generate power from the gases and vapors from slow pyrolysis 
> (50% of the energy) is probably through charcoal gasification (e.g. 
> run the pyrolysis gases through a charcoal gasifier). There are 
> commercial systems under development to make char and power in this 
> way. There are also commercial systems under development to make 
> liquid fuels through combinations of pyrolysis and gasification. The 
> char products from these and fast pyrolysis processes run from 0% to 
> about 15% of fuel input. I don't know the fuel or char yield for Cool 
> Planet.
> This particular study prepared the char with high temperature (826 C) 
> nitrogen.  Wood particles (chips, sawdust) and resultant char 
> particles in this study are larger than for other char studies. Obs
> ervations about BET surface area, particle size and the char 
> morphology are very interesting. The char morphology looks different 
> than the SEM images that we typically see. From gasification and 
> pyrolysis we know that pine carbonizes differently than hardwood so it 
> is interesting to see the shredded fibrous appearance of the pine char 
> in this study compared to the neat geometric structures that we often 
> see, which is probably from hardwood chars. The authors observe that 
> the macropore volume is significantly greater than the mesopore or 
> micropore volume of the char. They observe "numerous wide tunnel 
> protruding into the char particles. . . [that] may provide pathways 
> for bulk transport of CO2 into the particle."
> Char conversion numbers are interesting. Only 10-12% of the char was 
> gasified at 726 C (BET 391 m3/g) while 98-100% was converted at 896 C. 
> Surface area increased with conversion but not much greater than the 
> 35-47% conversion at 776 C so CO2 gasification could be used to 
> increase surface area at the expense of half of char (660 m3/g). Meso 
> and micro pore volume doubles at the higher rate but stays pretty 
> constant above 776 C. Researchers conclude that a significant 
> proportion of the pore volume is within macro pores although the 
> majority of the internal surface area is within micro pores.  They 
> point out that the mass loss with surface gasification occurs within 
> the smaller pores leading to pore widening.
> Researchers explain that the char gasification process involves three 
> steps: (1) adsorption of the gas-phase species to the char surface, 
> (2) surface reactions, and (3) desorption of the gasification products 
> from the surface. The latter is the rate limiting process.
> Recycling CO2 from gasification to gasify the char is an interesting 
> concept that may apply to modifying char properties (e.g. increase 
> surface area) from pyrolysis or recovering energy (heat, power, 
> syngas) in an industrial setting.
> There is very little information about gasification or combustion 
> chars. Sometimes it helps to step back from our char-philia (and 
> gaso-phobia) to see what products combined pyrolysis and gasification 
> can produce.
> Tom
> *RL>*don't see any relevance to the biochar list.  (Except if this 
> work shows that char is more valuable in the ground and/or that an 
> approach like Cool Planet's is more efficient.)  On the biochar list, 
> we should want BOTH high value fuels and charcoal.
>    This Purdue work is all about gasification of char - not pyrolysis. 
>   I am not sure whether the topic is appropriate for "gasification" 
> either, since that list seems to want gases for engines, not liquids.
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