[Stoves] Fwd: [Biochar] An example of the exotherm during pyrolysis
Ronal Larson
rongretlarson at comcast.net
Sat Aug 8 17:43:02 CDT 2020
Stoves:
Somehow my computer remembered an out-of-date "stoves” address.
Ron
> Begin forwarded message:
>
> From: Ronal Larson <rongretlarson at comcast.net>
> Subject: Fwd: [Biochar] An example of the exotherm during pyrolysis
> Date: August 8, 2020 at 4:39:34 PM MDT
> To: Discussion of biomass <stoves at listserv.repp.org>
> Cc: Hugh McLaughlin <wastemin1 at verizon.net>, "Kevin McLean >" <info at sun24.solar>
>
> List: cc Hugh and Kevin
>
> I just sent this to the biochar list - but much/most of it relates to char-making stoves.
>
> Several useful cites below - all thanks to Hugh..
>
> Anyone able to help on the “retorts-as-parts-of-stoves” pmts of this message? More coming soon to this list on this corn cob topic.
>
> Ron
>
>
>> Begin forwarded message:
>>
>> From: "Ron Larson" <rongretlarson at comcast.net <mailto:rongretlarson at comcast.net>>
>> Subject: Re: [Biochar] An example of the exotherm during pyrolysis
>> Date: August 8, 2020 at 4:26:12 PM MDT
>> To: "main at biochar.groups.io <mailto:main at biochar.groups.io>" <main at Biochar.groups.io <mailto:main at Biochar.groups.io>>, Hugh McLaughlin <wastemin1 at verizon.net <mailto:wastemin1 at verizon.net>>
>> Cc: "Kevin McLean >" <info at sun24.solar <mailto:info at sun24.solar>>
>> Reply-To: main at Biochar.groups.io <mailto:main at Biochar.groups.io>
>>
>> Hugh and list:
>>
>> See inserts. (I will respond separately to later messages - mainly from/with John Hofmeyer)
>>
>>
>>> On Aug 7, 2020, at 7:43 PM, Hugh McLaughlin via groups.io <http://groups.io/> <wastemin1=verizon.net at groups.io <mailto:wastemin1=verizon.net at groups.io>> wrote:
>>>
>>> Hello List,
>>>
>>> I gave a webinar on July 23rd on the Greencarbonwebinar series where I discussed some concerns pertaining to the exotherm(s) that are lurking inside the nominally endothermic heating of biomass. I decided to see if I could create a simple example of the magnitude of the phenomenon, since I have several laboratory scale reactors, the associated measurement instruments, and have run many such experiments over the years.
>> [RWL1: I listened to that webinar then and again today. I strongly recommend it to most everybody on this list. See https://youtu.be/SsEKM1PaP4s?t=2772 <https://youtu.be/SsEKM1PaP4s?t=2772>. The part on exotherms is near the middle of your roughly 45 minutes. (That whole series is wonderful.).
>>>
>>> Even I was surprised by the magnitude and rapidity of the phenomenon, as show by the two attached powerpoint slides. One slide is the yield as a function of temperature for oxygen-free pyrolysis and the second is the lab data from a controlled heating of 627 grams of wood pellets from room temperature to 375C at 100 degrees per hour. The wood pellets were not dried before the experiment and the data shows the effect of removing the 7 wt% moisture removed in a separate drying of the same wood pellets.
>> [RWL2; Re your first slide and throughout your talk - I conclude that it is now better to say that biochar is NOT charcoal - it is a different and superior product. Hmm. This is a very powerful sales-pitch conclusion that I’ve been missing.
>>
>> Re the second slide, I hope you can do a few more such experiments (you now being retired). Some fascinating results there that can probably be expanded with other parameters that relate better to cookstoves - where the pyrolysis might be over in well less than an hour.
>>
>> I’ve added both your slides back in at the bottom.
>>>
>>> In summary, the exotherm raised the center of the reactor from 300C to 450C in less than 12 minutes, with a volatile generation of 40% of the initial biomass weight, which is more than the weight of the final biochar exiting the reactor (33.3 wt% in this experiment). The surge in exiting volatiles was obvious, but was only 250 grams in the lab because the reactor only contained 627 grams of wood pellets initially.
>> [RWL3: Could you forward the weight loss data behind the 40% statistic (and any other data you took at the same time)?
>> Did you mean 40% loss in 12 minutes (or longer)?
>> Do you feel most of the weight loss is always exothermic? It seems the exothermacity stop was “sudden” - at about 450 C. I wonder what variation there is in that number with different feedstocks?
>>>
>>> How this phenomenon manifests itself in any specific reactor geometry and size is difficult to predict, but it is clear that the exotherm is transversed as the pyrolysis temperature exits torrefaction conditions and by the temperatures associated with acceptable biochar properties.
>> [RWL4: Re “specific reactor geometry” - that is exactly why I find this most interesting. I have been working with Kevin McLean (being cc’d) on cookstoves optimized for corncobs. Being so lightweight, the cobs disappear (too?) quickly in a TLUD - suggesting the possible beneficial use of an associated retort. Having “violent” energy release in a retort is not what you want in a cook stove.
>> “Obviously”, this exothermic release is occurring in EVERY form of char-making. But it is well hidden in TLUD (and other) forms with a moving pyrolysis front. I have been assuming that most of the front movement was associated with radiant energy associated with the front - but now guess that the radiant energy frequency is lower (thermal - not optical wavelengths).
>> I hope you or anyone working with char-making who has any ideas on how to design retorts to make exothermicity more of a benefit than a problem will chime in on how to best use retorts for cooking. (The main virtue being to not use fossil fuels for cooking. Or disappearing biomass fuels. ).
>>
>>> As the saying goes, "Forewarned is forearmed". Please be careful when scaling up energy and vapor releases - because if the vessel cannot vent the pressure as it is generated, the kinetics often accelerate and the risk of catastrophic failure rises rapidly.
>> [RWL5: I have yet to see anything very technical on retorts used in cooking - but I believe the obvious need to get the pyrolysis gases to a combustion region (presumably always into a TLUD and/or Rocket region) will mean Your warning is NOT one needed for cookstoves employing a retort?
>>
>> Not directly related to anything you have reported, but I believe pressure differences associated with the moving pyrolysis front are important. Any chance any of your data includes pressure changes? (I mean low pressures - not high pressures.)
>>
>>
>> Should Kevin and I forget retorts as a help in furthering the replacement of fire woodd with corn cobs (now mostly left to rot in the field)?
>>
>> Again, thanks for both the webinar (cite above) and yesterday’s additional more recent experimental result (below).
>>
>> Thanks also for recommending the Green Carbon Joan Manya “book” you cited at the beginning of your webinar. I was surprised to find it is a freebie - at https://zenodo.org/record/3233733#.Xy8hchNKjGJ <https://zenodo.org/record/3233733#.Xy8hchNKjGJ> . I now have a lot to read.
>>
>> One last thanks Is for giving so much credit in your webinar talk to the pioneering (both charcoal and biochar) work of Mike Antal. He has been missed; I wish I had known him better.
>>
>> Ron
>>
>>>
>>> - Hugh McLaughlin, PhD, PE
>>> <Pyrolysis exotherm and volatile generation example.pptx>.
>>
>>
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