An example of the exotherm during pyrolysis


Hugh McLaughlin
 

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.

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.

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.

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.

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.

- Hugh McLaughlin, PhD, PE


Tom Miles
 

Thanks Hugh. This illustrates a difficulty that several people have reported with controlling torrefaction, especially during scaleup.


Tom  

 

From: main@Biochar.groups.io <main@Biochar.groups.io> On Behalf Of Hugh McLaughlin via groups.io
Sent: Friday, August 07, 2020 6:43 PM
To: Biochar Group <main@biochar.groups.io>; Hugh McLaughlin <wastemin1@...>
Subject: [Biochar] An example of the exotherm during pyrolysis

 

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.

 

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.

 

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.

 

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.

 

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.

 

- Hugh McLaughlin, PhD, PE


John Hofmeyr
 

Thanks for a useful clarification, Hugh.
For the questions below I have assumed that your reactor was electrically heated. My questions come in two parts.
PART A:
Please clarify the relatively straight line of the wall temperature track against time:
(a) How was the wall temperature controlled after the exotherm begins to take effect? i.e. Was your reactor fitted with both heating and cooling apparatus? 
(b) Was the biomass in the reactor mixed / agitated?
It would be interesting to see the power consumption for heating plotted against time.
(c) Would that show a decrease in demand as more of the required energy is gradually contributed by the exotherm?
PART B:
Does the above line of thinking lead to an exacerbated potential danger for mixed bed configurations (rotary or fluidised)? 
That question is derived from the following:
If your reactor was a fixed-bed configuration, would the biomass closest to the wall begin to contribute exotherm before the biomass lying close to the centreline?
If yes, then would there be a gradual contribution of exotherm energy to maintain a uniform the rate of increase of the wall temperature?
Again if yes, in the case of a mixed-bed reactor (rotary or fluidised) should one expect all of the biomass to begin contributing exotherm at the same time? (i.e. a less gradual contribution) leading to a runaway thermal spike?


John Hofmeyr
 

(1) Sorry, I have now seen "fixed bed' on the graph. 
(2) please clarify your sentence "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."
Is this a reference to the point of inflection in the centreline temperature curve at 90 minutes / 100deg C?


Hugh McLaughlin
 

Replying to John Hofmyer's questions:

PART A:
Please clarify the relatively straight line of the wall temperature track against time: - Controller is a ramping controller and the heat is provided to maintain a ramped wall temperature.

(a) How was the wall temperature controlled after the exotherm begins to take effect? i.e. Was your reactor fitted with both heating and cooling apparatus? The unit loses heat to the ambient and the controller provides what is needed to maintain the temp ramp.

(b) Was the biomass in the reactor mixed / agitated? No

It would be interesting to see the power consumption for heating plotted against time. - Excessive heat loss to ambient masks the magnitude of the exotherm - it is only 600 grams of biomass

(c) Would that show a decrease in demand as more of the required energy is gradually contributed by the exotherm? Yes, if it cold be resolved

PART B:
Does the above line of thinking lead to an exacerbated potential danger for mixed bed configurations (rotary or fluidised)? It is an issue to be addressed in a specific design.

That question is derived from the following:

If your reactor was a fixed-bed configuration, would the biomass closest to the wall begin to contribute exotherm before the biomass lying close to the centreline? - that is correct, and that was the phenomenon I was demonstrating.

If yes, then would there be a gradual contribution of exotherm energy to maintain a uniform the rate of increase of the wall temperature? The exotherm augments the additional heat to ramp the wall temperature.

Again if yes, in the case of a mixed-bed reactor (rotary or fluidised) should one expect all of the biomass to begin contributing exotherm at the same time? (i.e. a less gradual contribution) leading to a runaway thermal spike?Yes, that would be what happens and what is observed.

2) please clarify your sentence "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."

Is this a reference to the point of inflection in the centreline temperature curve at 90 minutes / 100deg C? Yes

- Hugh



On Saturday, August 8, 2020, 2:44:02 PM EDT, John Hofmeyr <john-h@...> wrote:


(1) Sorry, I have now seen "fixed bed' on the graph. 
(2) please clarify your sentence "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."
Is this a reference to the point of inflection in the centreline temperature curve at 90 minutes / 100deg C?


John Hofmeyr
 

Thanks for clarifications.
/John


Ron Larson
 

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 <wastemin1@...> 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.  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 .  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>.    


Paul S Anderson
 

I reply to Ron (and Kevin), and with thanks to Hugh for his scientific explanations about pyrolysis.

 

Ron wrote: 

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)?

 

IMBO   (In My Biased Opinion).   I would says “Yes, forget retorts.”   Now in need to explain my thinking.

 

1.  A retort does not provide a uniform supply of heat which cooks desire.   Retorts do not give combustible gases from the very early minutes.   And, as shown in Hugh’s research, when the heat does come, it will be much in a relatively short time (again, not good for cooking).

 

2.  From  the little that I saw of Kevin’s simple (very low cost) TLUD, there was minimal or no attempt to restrict the entry of the primary air.  The result has two disadvantages:

 

A.  There was a faster than desired release of the gases (and the resultant cooking flame).  

B.  The created char was subjected to too much O2 (in the surplus air) and subsequently burned (char-gasified) to the point that you are lamenting the low yield of char.

 

3.  Based on 2 above, the there is some solution to both problems when there is actual control of the entry of primary air.   Such control come with an extra cost.   IMO, that cost (for a mostly sealed container and control of air supply) is what makes the TLUDs stoves successful.  Success with  TLUD technology is closely tied with air control.   

 

4.  My experience with dry maize cobs as fuel is quite successful.   Cobs are less dense than woody stuff,  so the TLUD fuel chamber needs to be larger.   That, unfortunately, also adds to the cost.  

 

5.  Sorry, the above is not good new when a major criterium of success is to have ultra-low cost of the physical stove.   My counter argument that is to justify the extra cost of air control is to bring to the stove users (the cooks and their families) the financial benefits of producing biochar/charcoal that can be sold and/or bring in some revenue as carbon offsets/removals.

 

6.  Tying this back to Hugh’s work with exothermic boost of heat, that boost does take place in TLUD stoves, but it is occurring at a consistent rate in each millimeter of the descending migratory pyrolytic front. (MPF). 

 

Paul

 

Doc / Dr TLUD / Paul S. Anderson, PhD --- Website:   www.drtlud.com

         Email:  psanders@...       Skype:   paultlud

         Phone:  Office: 309-452-7072    Mobile & WhatsApp: 309-531-4434

Exec. Dir. of Juntos Energy Solutions NFP    Go to: www.JuntosNFP.org 

Inventor of RoCC kilns for biochar and energy:  See  www.woodgas.com

Author of “A Capitalist Carol” (free digital copies at www.capitalism21.org)

         with pages 88 – 94 about solving the world crisis for clean cookstoves.

 

From: main@Biochar.groups.io <main@Biochar.groups.io> On Behalf Of Ron Larson via groups.io
Sent: Saturday, August 8, 2020 5:26 PM
To: main@biochar.groups.io; Hugh McLaughlin <wastemin1@...>
Cc: Kevin McLean > <info@...>
Subject: Re: [Biochar] An example of the exotherm during pyrolysis

 

[This message came from an external source. If suspicious, report to abuse@...]

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 <wastemin1@...> 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.  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 .  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>.    

 


 

Yes Paul, this discussion fits with my practical experience.  I compensate by loosening the material inside.  Partly, by that, I mean I have layers inside, and mix materials types, like chips and small fairly even sized branches for example.  Perhaps because of some good luck, our cooks are consistent in timing and final product.  And yes we have had them get to what I think is too hot. (1100 F) That is rare, and of course I attempt control  of oxygen.

David




David R Derbowka             Chief Executive Officer

Passive Remediation Systems Ltd.
Tel: +1 250 306 6377 | 
eMail: david.derbowka@... |Web: prsi.ca |



On Sat, Aug 8, 2020 at 8:14 PM Paul S Anderson <psanders@...> wrote:

I reply to Ron (and Kevin), and with thanks to Hugh for his scientific explanations about pyrolysis.

 

Ron wrote: 

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)?

 

IMBO   (In My Biased Opinion).   I would says “Yes, forget retorts.”   Now in need to explain my thinking.

 

1.  A retort does not provide a uniform supply of heat which cooks desire.   Retorts do not give combustible gases from the very early minutes.   And, as shown in Hugh’s research, when the heat does come, it will be much in a relatively short time (again, not good for cooking).

 

2.  From  the little that I saw of Kevin’s simple (very low cost) TLUD, there was minimal or no attempt to restrict the entry of the primary air.  The result has two disadvantages:

 

A.  There was a faster than desired release of the gases (and the resultant cooking flame).  

B.  The created char was subjected to too much O2 (in the surplus air) and subsequently burned (char-gasified) to the point that you are lamenting the low yield of char.

 

3.  Based on 2 above, the there is some solution to both problems when there is actual control of the entry of primary air.   Such control come with an extra cost.   IMO, that cost (for a mostly sealed container and control of air supply) is what makes the TLUDs stoves successful.  Success with  TLUD technology is closely tied with air control.   

 

4.  My experience with dry maize cobs as fuel is quite successful.   Cobs are less dense than woody stuff,  so the TLUD fuel chamber needs to be larger.   That, unfortunately, also adds to the cost.  

 

5.  Sorry, the above is not good new when a major criterium of success is to have ultra-low cost of the physical stove.   My counter argument that is to justify the extra cost of air control is to bring to the stove users (the cooks and their families) the financial benefits of producing biochar/charcoal that can be sold and/or bring in some revenue as carbon offsets/removals.

 

6.  Tying this back to Hugh’s work with exothermic boost of heat, that boost does take place in TLUD stoves, but it is occurring at a consistent rate in each millimeter of the descending migratory pyrolytic front. (MPF). 

 

Paul

 

Doc / Dr TLUD / Paul S. Anderson, PhD --- Website:   www.drtlud.com

         Email:  psanders@...       Skype:   paultlud

         Phone:  Office: 309-452-7072    Mobile & WhatsApp: 309-531-4434

Exec. Dir. of Juntos Energy Solutions NFP    Go to: www.JuntosNFP.org 

Inventor of RoCC kilns for biochar and energy:  See  www.woodgas.com

Author of “A Capitalist Carol” (free digital copies at www.capitalism21.org)

         with pages 88 – 94 about solving the world crisis for clean cookstoves.

 

From: main@Biochar.groups.io <main@Biochar.groups.io> On Behalf Of Ron Larson via groups.io
Sent: Saturday, August 8, 2020 5:26 PM
To: main@biochar.groups.io; Hugh McLaughlin <wastemin1@...>
Cc: Kevin McLean > <info@...>
Subject: Re: [Biochar] An example of the exotherm during pyrolysis

 

[This message came from an external source. If suspicious, report to abuse@...]

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 <wastemin1@...> 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.  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 .  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>.    

 


Hugh McLaughlin
 

All,

Paul Anderson has nicely addressed the issue of retorts and Tluds. I concur that interfacing retort heat release profiles with cooking dynamics is unlikely to improve on easier and established approaches (natural and fan-assisted Tluds).

My discussion of exotherms is directed at larger devices, where the potential and actual energy releases represent legitimate causes for concern about safety and mechanical integrity of the devices.

I often tell a story about the Wright Brothers in my talks. I note they were very good engineers, if not overly schooled. They took data, scaled it and succeeded where others had failed. However, even they never addressed the issue of how to land an airplane until they successfully took off - which left them with 9 seconds to address the challenges. This is why I urge everyone to think through the entire sequence of events - to the extent they are known - and have a plan of action for the predictions. Life is full of enough surprises without ignoring the foreseeable.

- Hugh



On Saturday, August 8, 2020, 11:14:12 PM EDT, Paul S Anderson <psanders@...> wrote:


I reply to Ron (and Kevin), and with thanks to Hugh for his scientific explanations about pyrolysis.

 

Ron wrote: 

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)?

 

IMBO   (In My Biased Opinion).   I would says “Yes, forget retorts.”   Now in need to explain my thinking.

 

1.  A retort does not provide a uniform supply of heat which cooks desire.   Retorts do not give combustible gases from the very early minutes.   And, as shown in Hugh’s research, when the heat does come, it will be much in a relatively short time (again, not good for cooking).

 

2.  From  the little that I saw of Kevin’s simple (very low cost) TLUD, there was minimal or no attempt to restrict the entry of the primary air.  The result has two disadvantages:

 

A.  There was a faster than desired release of the gases (and the resultant cooking flame).  

B.  The created char was subjected to too much O2 (in the surplus air) and subsequently burned (char-gasified) to the point that you are lamenting the low yield of char.

 

3.  Based on 2 above, the there is some solution to both problems when there is actual control of the entry of primary air.   Such control come with an extra cost.   IMO, that cost (for a mostly sealed container and control of air supply) is what makes the TLUDs stoves successful.  Success with  TLUD technology is closely tied with air control.   

 

4.  My experience with dry maize cobs as fuel is quite successful.   Cobs are less dense than woody stuff,  so the TLUD fuel chamber needs to be larger.   That, unfortunately, also adds to the cost.  

 

5.  Sorry, the above is not good new when a major criterium of success is to have ultra-low cost of the physical stove.   My counter argument that is to justify the extra cost of air control is to bring to the stove users (the cooks and their families) the financial benefits of producing biochar/charcoal that can be sold and/or bring in some revenue as carbon offsets/removals.

 

6.  Tying this back to Hugh’s work with exothermic boost of heat, that boost does take place in TLUD stoves, but it is occurring at a consistent rate in each millimeter of the descending migratory pyrolytic front. (MPF). 

 

Paul

 

Doc / Dr TLUD / Paul S. Anderson, PhD --- Website:   www.drtlud.com

         Email:  psanders@...       Skype:   paultlud

         Phone:  Office: 309-452-7072    Mobile & WhatsApp: 309-531-4434

Exec. Dir. of Juntos Energy Solutions NFP    Go to: www.JuntosNFP.org 

Inventor of RoCC kilns for biochar and energy:  See  www.woodgas.com

Author of “A Capitalist Carol” (free digital copies at www.capitalism21.org)

         with pages 88 – 94 about solving the world crisis for clean cookstoves.

 

From: main@Biochar.groups.io <main@Biochar.groups.io> On Behalf Of Ron Larson via groups.io
Sent: Saturday, August 8, 2020 5:26 PM
To: main@biochar.groups.io; Hugh McLaughlin <wastemin1@...>
Cc: Kevin McLean > <info@...>
Subject: Re: [Biochar] An example of the exotherm during pyrolysis

 

[This message came from an external source. If suspicious, report to abuse@...]

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 <wastemin1@...> 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.  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 .  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>.    

 


James Bledsoe
 

So, are you saying that a spherical retort completely filled with small wood chips or wet pellets  would be prone to explosions?


On Fri, Aug 7, 2020 at 6:45 PM Hugh McLaughlin via groups.io <wastemin1=verizon.net@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.

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.

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.

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.

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.

- Hugh McLaughlin, PhD, PE


Geoff Thomas
 

Hi Hugh, this hails to my experience with my Pyramid flame cap kiln, - there comes a period, where the air is really trying to get in, (can one say that?) and you are poking/shoving wood into every opening yet still you have almost lost control, it is so hot inside, and the kiln is almost roaring, - unless you have a very large supply of various smaller pieces of wood, you have no alternative but  to quench it right then,- even though the job wasn’t quite done.

Speaking back to the Australian Bushfires of last season, could there be Plasma effects occurring?

Cheers,
Geoff.

On 8 Aug 2020, at 11:43 am, Hugh McLaughlin via groups.io <wastemin1@...> 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.

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.

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.

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.

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.

- Hugh McLaughlin, PhD, PE
<Pyrolysis exotherm and volatile generation example.pptx>


Roger Faulkner
 

I am a polymer scientist. I used to work at the Forest products laboratory. The exotherm you describe it's probably initiated by thermal decomposition of cellulose. In the crystalline state cellulose is very stable. if I remember correctly it has no known melting temperature. But at some point it bus go through a thermal melting and when that occurs the cellulose is suddenly way more chemically reactive.


On Sat, Aug 8, 2020 at 11:36 PM, Hugh McLaughlin via groups.io
<wastemin1@...> wrote:
All,

Paul Anderson has nicely addressed the issue of retorts and Tluds. I concur that interfacing retort heat release profiles with cooking dynamics is unlikely to improve on easier and established approaches (natural and fan-assisted Tluds).

My discussion of exotherms is directed at larger devices, where the potential and actual energy releases represent legitimate causes for concern about safety and mechanical integrity of the devices.

I often tell a story about the Wright Brothers in my talks. I note they were very good engineers, if not overly schooled. They took data, scaled it and succeeded where others had failed. However, even they never addressed the issue of how to land an airplane until they successfully took off - which left them with 9 seconds to address the challenges. This is why I urge everyone to think through the entire sequence of events - to the extent they are known - and have a plan of action for the predictions. Life is full of enough surprises without ignoring the foreseeable.

- Hugh



On Saturday, August 8, 2020, 11:14:12 PM EDT, Paul S Anderson <psanders@...> wrote:


I reply to Ron (and Kevin), and with thanks to Hugh for his scientific explanations about pyrolysis.

 

Ron wrote: 

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)?

 

IMBO   (In My Biased Opinion).   I would says “Yes, forget retorts.”   Now in need to explain my thinking.

 

1.  A retort does not provide a uniform supply of heat which cooks desire.   Retorts do not give combustible gases from the very early minutes.   And, as shown in Hugh’s research, when the heat does come, it will be much in a relatively short time (again, not good for cooking).

 

2.  From  the little that I saw of Kevin’s simple (very low cost) TLUD, there was minimal or no attempt to restrict the entry of the primary air.  The result has two disadvantages:

 

A.  There was a faster than desired release of the gases (and the resultant cooking flame).  

B.  The created char was subjected to too much O2 (in the surplus air) and subsequently burned (char-gasified) to the point that you are lamenting the low yield of char.

 

3.  Based on 2 above, the there is some solution to both problems when there is actual control of the entry of primary air.   Such control come with an extra cost.   IMO, that cost (for a mostly sealed container and control of air supply) is what makes the TLUDs stoves successful.  Success with  TLUD technology is closely tied with air control.   

 

4.  My experience with dry maize cobs as fuel is quite successful.   Cobs are less dense than woody stuff,  so the TLUD fuel chamber needs to be larger.   That, unfortunately, also adds to the cost.  

 

5.  Sorry, the above is not good new when a major criterium of success is to have ultra-low cost of the physical stove.   My counter argument that is to justify the extra cost of air control is to bring to the stove users (the cooks and their families) the financial benefits of producing biochar/charcoal that can be sold and/or bring in some revenue as carbon offsets/removals.

 

6.  Tying this back to Hugh’s work with exothermic boost of heat, that boost does take place in TLUD stoves, but it is occurring at a consistent rate in each millimeter of the descending migratory pyrolytic front. (MPF). 

 

Paul

 

Doc / Dr TLUD / Paul S. Anderson, PhD --- Website:   www.drtlud.com

         Email:  psanders@...       Skype:   paultlud

         Phone:  Office: 309-452-7072    Mobile & WhatsApp: 309-531-4434

Exec. Dir. of Juntos Energy Solutions NFP    Go to: www.JuntosNFP.org 

Inventor of RoCC kilns for biochar and energy:  See  www.woodgas.com

Author of “A Capitalist Carol” (free digital copies at www.capitalism21.org)

         with pages 88 – 94 about solving the world crisis for clean cookstoves.

 

From: main@Biochar.groups.io <main@Biochar.groups.io> On Behalf Of Ron Larson via groups.io
Sent: Saturday, August 8, 2020 5:26 PM
To: main@biochar.groups.io; Hugh McLaughlin <wastemin1@...>
Cc: Kevin McLean > <info@...>
Subject: Re: [Biochar] An example of the exotherm during pyrolysis

 

[This message came from an external source. If suspicious, report to abuse@...]

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 <wastemin1@...> 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.  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 .  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>.    

 


Paul S Anderson
 

David,

 

Thank you for your comments.   Please describe or include images of the stove type to which you refer.   Information about your cooks and their experiences would also be appreciated.

 

Paul

 

Doc / Dr TLUD / Paul S. Anderson, PhD --- Website:   www.drtlud.com

         Email:  psanders@...       Skype:   paultlud

         Phone:  Office: 309-452-7072    Mobile & WhatsApp: 309-531-4434

Exec. Dir. of Juntos Energy Solutions NFP    Go to: www.JuntosNFP.org 

Inventor of RoCC kilns for biochar and energy:  See  www.woodgas.com

Author of “A Capitalist Carol” (free digital copies at www.capitalism21.org)

         with pages 88 – 94 about solving the world crisis for clean cookstoves.

 

From: main@Biochar.groups.io <main@Biochar.groups.io> On Behalf Of David R Derbowka via groups.io
Sent: Saturday, August 8, 2020 10:33 PM
To: main@Biochar.groups.io Group Moderators <main@biochar.groups.io>
Cc: Hugh McLaughlin <wastemin1@...>; Kevin McLean > <info@...>
Subject: Re: [Biochar] An example of the exotherm during pyrolysis

 

[This message came from an external source. If suspicious, report to abuse@...]

Yes Paul, this discussion fits with my practical experience.  I compensate by loosening the material inside.  Partly, by that, I mean I have layers inside, and mix materials types, like chips and small fairly even sized branches for example.  Perhaps because of some good luck, our cooks are consistent in timing and final product.  And yes we have had them get to what I think is too hot. (1100 F) That is rare, and of course I attempt control  of oxygen.

 

David

 

 

 

David R Derbowka             Chief Executive Officer

Passive Remediation Systems Ltd.
Tel: +1 250 306 6377 | 

eMail: david.derbowka@... |Web: prsi.ca |

Image removed by sender.

 

 

On Sat, Aug 8, 2020 at 8:14 PM Paul S Anderson <psanders@...> wrote:

I reply to Ron (and Kevin), and with thanks to Hugh for his scientific explanations about pyrolysis.

 

Ron wrote: 

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)?

 

IMBO   (In My Biased Opinion).   I would says “Yes, forget retorts.”   Now in need to explain my thinking.

 

1.  A retort does not provide a uniform supply of heat which cooks desire.   Retorts do not give combustible gases from the very early minutes.   And, as shown in Hugh’s research, when the heat does come, it will be much in a relatively short time (again, not good for cooking).

 

2.  From  the little that I saw of Kevin’s simple (very low cost) TLUD, there was minimal or no attempt to restrict the entry of the primary air.  The result has two disadvantages:

 

A.  There was a faster than desired release of the gases (and the resultant cooking flame).  

B.  The created char was subjected to too much O2 (in the surplus air) and subsequently burned (char-gasified) to the point that you are lamenting the low yield of char.

 

3.  Based on 2 above, the there is some solution to both problems when there is actual control of the entry of primary air.   Such control come with an extra cost.   IMO, that cost (for a mostly sealed container and control of air supply) is what makes the TLUDs stoves successful.  Success with  TLUD technology is closely tied with air control.   

 

4.  My experience with dry maize cobs as fuel is quite successful.   Cobs are less dense than woody stuff,  so the TLUD fuel chamber needs to be larger.   That, unfortunately, also adds to the cost.  

 

5.  Sorry, the above is not good new when a major criterium of success is to have ultra-low cost of the physical stove.   My counter argument that is to justify the extra cost of air control is to bring to the stove users (the cooks and their families) the financial benefits of producing biochar/charcoal that can be sold and/or bring in some revenue as carbon offsets/removals.

 

6.  Tying this back to Hugh’s work with exothermic boost of heat, that boost does take place in TLUD stoves, but it is occurring at a consistent rate in each millimeter of the descending migratory pyrolytic front. (MPF). 

 

Paul

 

Doc / Dr TLUD / Paul S. Anderson, PhD --- Website:   www.drtlud.com

         Email:  psanders@...       Skype:   paultlud

         Phone:  Office: 309-452-7072    Mobile & WhatsApp: 309-531-4434

Exec. Dir. of Juntos Energy Solutions NFP    Go to: www.JuntosNFP.org 

Inventor of RoCC kilns for biochar and energy:  See  www.woodgas.com

Author of “A Capitalist Carol” (free digital copies at www.capitalism21.org)

         with pages 88 – 94 about solving the world crisis for clean cookstoves.

 

From: main@Biochar.groups.io <main@Biochar.groups.io> On Behalf Of Ron Larson via groups.io
Sent: Saturday, August 8, 2020 5:26 PM
To: main@biochar.groups.io; Hugh McLaughlin <wastemin1@...>
Cc: Kevin McLean > <info@...>
Subject: Re: [Biochar] An example of the exotherm during pyrolysis

 

[This message came from an external source. If suspicious, report to abuse@...]

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 <wastemin1@...> 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.  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 .  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>.    

 


 

Dear Paul and everyone
When I built it; I had in mind about how to facilitate VOCs escape easily.   If I put in 18 inch clonal cuttings dried, (1/2 inch thick clonal cuttings that did not sell) so voc 'flames up' right away after heat startup.  (I use throw away pallets to start up).  So cuttings also provide a "looseness" in the oven for easy escape.  Cottonwood chips keep things under control, or provide "body", if you will.  This is my best guessing about how this one works.  It makes great product, which I process to perfect size with a "mouldy oldie" grain grinder.  

See pictures attached.

Cheers
David Derbowka




David R Derbowka             Chief Executive Officer

Passive Remediation Systems Ltd.
Tel: +1 250 306 6377 | 
eMail: david.derbowka@... |Web: prsi.ca |



On Sun, Aug 9, 2020 at 6:23 AM Paul S Anderson <psanders@...> wrote:

David,

 

Thank you for your comments.   Please describe or include images of the stove type to which you refer.   Information about your cooks and their experiences would also be appreciated.

 

Paul

 

Doc / Dr TLUD / Paul S. Anderson, PhD --- Website:   www.drtlud.com

         Email:  psanders@...       Skype:   paultlud

         Phone:  Office: 309-452-7072    Mobile & WhatsApp: 309-531-4434

Exec. Dir. of Juntos Energy Solutions NFP    Go to: www.JuntosNFP.org 

Inventor of RoCC kilns for biochar and energy:  See  www.woodgas.com

Author of “A Capitalist Carol” (free digital copies at www.capitalism21.org)

         with pages 88 – 94 about solving the world crisis for clean cookstoves.

 

From: main@Biochar.groups.io <main@Biochar.groups.io> On Behalf Of David R Derbowka via groups.io
Sent: Saturday, August 8, 2020 10:33 PM
To: main@Biochar.groups.io Group Moderators <main@biochar.groups.io>
Cc: Hugh McLaughlin <wastemin1@...>; Kevin McLean > <info@...>
Subject: Re: [Biochar] An example of the exotherm during pyrolysis

 

[This message came from an external source. If suspicious, report to abuse@...]

Yes Paul, this discussion fits with my practical experience.  I compensate by loosening the material inside.  Partly, by that, I mean I have layers inside, and mix materials types, like chips and small fairly even sized branches for example.  Perhaps because of some good luck, our cooks are consistent in timing and final product.  And yes we have had them get to what I think is too hot. (1100 F) That is rare, and of course I attempt control  of oxygen.

 

David

 

 

 

David R Derbowka             Chief Executive Officer

Passive Remediation Systems Ltd.
Tel: +1 250 306 6377 | 

eMail: david.derbowka@... |Web: prsi.ca |

Image removed by sender.

 

 

On Sat, Aug 8, 2020 at 8:14 PM Paul S Anderson <psanders@...> wrote:

I reply to Ron (and Kevin), and with thanks to Hugh for his scientific explanations about pyrolysis.

 

Ron wrote: 

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)?

 

IMBO   (In My Biased Opinion).   I would says “Yes, forget retorts.”   Now in need to explain my thinking.

 

1.  A retort does not provide a uniform supply of heat which cooks desire.   Retorts do not give combustible gases from the very early minutes.   And, as shown in Hugh’s research, when the heat does come, it will be much in a relatively short time (again, not good for cooking).

 

2.  From  the little that I saw of Kevin’s simple (very low cost) TLUD, there was minimal or no attempt to restrict the entry of the primary air.  The result has two disadvantages:

 

A.  There was a faster than desired release of the gases (and the resultant cooking flame).  

B.  The created char was subjected to too much O2 (in the surplus air) and subsequently burned (char-gasified) to the point that you are lamenting the low yield of char.

 

3.  Based on 2 above, the there is some solution to both problems when there is actual control of the entry of primary air.   Such control come with an extra cost.   IMO, that cost (for a mostly sealed container and control of air supply) is what makes the TLUDs stoves successful.  Success with  TLUD technology is closely tied with air control.   

 

4.  My experience with dry maize cobs as fuel is quite successful.   Cobs are less dense than woody stuff,  so the TLUD fuel chamber needs to be larger.   That, unfortunately, also adds to the cost.  

 

5.  Sorry, the above is not good new when a major criterium of success is to have ultra-low cost of the physical stove.   My counter argument that is to justify the extra cost of air control is to bring to the stove users (the cooks and their families) the financial benefits of producing biochar/charcoal that can be sold and/or bring in some revenue as carbon offsets/removals.

 

6.  Tying this back to Hugh’s work with exothermic boost of heat, that boost does take place in TLUD stoves, but it is occurring at a consistent rate in each millimeter of the descending migratory pyrolytic front. (MPF). 

 

Paul

 

Doc / Dr TLUD / Paul S. Anderson, PhD --- Website:   www.drtlud.com

         Email:  psanders@...       Skype:   paultlud

         Phone:  Office: 309-452-7072    Mobile & WhatsApp: 309-531-4434

Exec. Dir. of Juntos Energy Solutions NFP    Go to: www.JuntosNFP.org 

Inventor of RoCC kilns for biochar and energy:  See  www.woodgas.com

Author of “A Capitalist Carol” (free digital copies at www.capitalism21.org)

         with pages 88 – 94 about solving the world crisis for clean cookstoves.

 

From: main@Biochar.groups.io <main@Biochar.groups.io> On Behalf Of Ron Larson via groups.io
Sent: Saturday, August 8, 2020 5:26 PM
To: main@biochar.groups.io; Hugh McLaughlin <wastemin1@...>
Cc: Kevin McLean > <info@...>
Subject: Re: [Biochar] An example of the exotherm during pyrolysis

 

[This message came from an external source. If suspicious, report to abuse@...]

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 <wastemin1@...> 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.  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 .  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>.    

 


Kirk Harris
 

Roger,

Thank you for this probable explanation of the source of the exotherm.  I assume that a "thermal melting" is a change in chemical structure, making the cellulose more reactive.  The size of the exotherm might depend on how evenly the fuel is being pyrolysed, the more uniform, the greater and shorter the exotherm.  A less uniform pyrolysing would make a continuously small exotherm, which would be not so noticeable (flatten the curve). 

The interior of a wood stove, such as a TLUD, is below atmospheric pressure.  The interior of a retort will be above atmospheric pressure.  Would a pressure difference change the temperature at which this "thermal melting" occurs, like it changes the temperature of vaporization?  Would this effect the quality of the biochar?  Would a sturdy retort that operates at a higher pressure because of this exotherm, produce a different quality of biochar than a lower pressure retort or TLUD?

Kirk H.

On 8/9/2020 4:07 AM, Roger Faulkner via groups.io wrote:
I am a polymer scientist. I used to work at the Forest products laboratory. The exotherm you describe it's probably initiated by thermal decomposition of cellulose. In the crystalline state cellulose is very stable. if I remember correctly it has no known melting temperature. But at some point it bus go through a thermal melting and when that occurs the cellulose is suddenly way more chemically reactive.


On Sat, Aug 8, 2020 at 11:36 PM, Hugh McLaughlin via groups.io
All,

Paul Anderson has nicely addressed the issue of retorts and Tluds. I concur that interfacing retort heat release profiles with cooking dynamics is unlikely to improve on easier and established approaches (natural and fan-assisted Tluds).

My discussion of exotherms is directed at larger devices, where the potential and actual energy releases represent legitimate causes for concern about safety and mechanical integrity of the devices.

I often tell a story about the Wright Brothers in my talks. I note they were very good engineers, if not overly schooled. They took data, scaled it and succeeded where others had failed. However, even they never addressed the issue of how to land an airplane until they successfully took off - which left them with 9 seconds to address the challenges. This is why I urge everyone to think through the entire sequence of events - to the extent they are known - and have a plan of action for the predictions. Life is full of enough surprises without ignoring the foreseeable.

- Hugh



On Saturday, August 8, 2020, 11:14:12 PM EDT, Paul S Anderson <psanders@...> wrote:


I reply to Ron (and Kevin), and with thanks to Hugh for his scientific explanations about pyrolysis.

 

Ron wrote: 

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)?

 

IMBO   (In My Biased Opinion).   I would says “Yes, forget retorts.”   Now in need to explain my thinking.

 

1.  A retort does not provide a uniform supply of heat which cooks desire.   Retorts do not give combustible gases from the very early minutes.   And, as shown in Hugh’s research, when the heat does come, it will be much in a relatively short time (again, not good for cooking).

 

2.  From  the little that I saw of Kevin’s simple (very low cost) TLUD, there was minimal or no attempt to restrict the entry of the primary air.  The result has two disadvantages:

 

A.  There was a faster than desired release of the gases (and the resultant cooking flame).  

B.  The created char was subjected to too much O2 (in the surplus air) and subsequently burned (char-gasified) to the point that you are lamenting the low yield of char.

 

3.  Based on 2 above, the there is some solution to both problems when there is actual control of the entry of primary air.   Such control come with an extra cost.   IMO, that cost (for a mostly sealed container and control of air supply) is what makes the TLUDs stoves successful.  Success with  TLUD technology is closely tied with air control.   

 

4.  My experience with dry maize cobs as fuel is quite successful.   Cobs are less dense than woody stuff,  so the TLUD fuel chamber needs to be larger.   That, unfortunately, also adds to the cost.  

 

5.  Sorry, the above is not good new when a major criterium of success is to have ultra-low cost of the physical stove.   My counter argument that is to justify the extra cost of air control is to bring to the stove users (the cooks and their families) the financial benefits of producing biochar/charcoal that can be sold and/or bring in some revenue as carbon offsets/removals.

 

6.  Tying this back to Hugh’s work with exothermic boost of heat, that boost does take place in TLUD stoves, but it is occurring at a consistent rate in each millimeter of the descending migratory pyrolytic front. (MPF). 

 

Paul

 

Doc / Dr TLUD / Paul S. Anderson, PhD --- Website:   www.drtlud.com

         Email:  psanders@...       Skype:   paultlud

         Phone:  Office: 309-452-7072    Mobile & WhatsApp: 309-531-4434

Exec. Dir. of Juntos Energy Solutions NFP    Go to: www.JuntosNFP.org 

Inventor of RoCC kilns for biochar and energy:  See  www.woodgas.com

Author of “A Capitalist Carol” (free digital copies at www.capitalism21.org)

         with pages 88 – 94 about solving the world crisis for clean cookstoves.

 

From: main@Biochar.groups.io <main@Biochar.groups.io> On Behalf Of Ron Larson via groups.io
Sent: Saturday, August 8, 2020 5:26 PM
To: main@biochar.groups.io; Hugh McLaughlin <wastemin1@...>
Cc: Kevin McLean > <info@...>
Subject: Re: [Biochar] An example of the exotherm during pyrolysis

 

[This message came from an external source. If suspicious, report to abuse@...]

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 <wastemin1@...> 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.  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 .  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>.    

 


Virus-free. www.avg.com