[Stoves] Is there a role for combining torrefaction and char-making stoves?

Mon Feb 27 18:32:13 CST 2012

Frank, Hugh etal 

Few reply comments below. I use "TBM" to mean "torrefied biomass material". 

----- Original Message -----
From: "Frank Shields" <frank at compostlab.com> 
To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org> 
Cc: "Hugh McLaughlin" <wastemin at charter.net> 
Sent: Monday, February 27, 2012 3:12:34 PM 
Subject: Re: [Stoves] Is there a role for combining torrefaction and char-making stoves? 

Ron, 

I am not involved in the web site and my work is well beyond what is in it at the moment. 

[RWL1: I look forward to seeing updates.] 

I was wrong in thinking the tongue depressor was a measure of heat. Rather a measure of percent pyrolyzed (or inverse torrefied) when surface area or weight is used. Other measurements are Color change (shades of gray) at low temperatures determine temperature, change in pressure to break with description of the break determine structure breakdown and , perhaps FTIR when I learn more about what it can do. So all the above can be calibrated using simple equipment (except FTIR). 

[RWL2: I had always taken the tongue depressor changes to be a potential calibrator of max temperature reached (with some time element) - as in your sentence #2. 

At the Kyoto meeting (and elsewhere) there was quite a lot on using FTIR for this temperature determination purpose. But I still think the use of tongue depressors could/might be very helpful in the field - if there is still room for dimension changes when the desired temp is around 250-280 oC. You sound like the perfect person to give that answer. Maybe Hugh also? 

I have added Dr. David Rutherford (USGS) to this dialog as he has also recently obtained an FTIR for this purpose] 

It seems to me that to determine if it is worthwhile to torrefy before making char that we need to know which feature change occurs that may make it worthwhile. Plot a curve of trucking cost vs. weight of biomass. Or cost of energy making pellets vs. torrefication temperatures. Things like that. Then making the new partial torrefied biomass we plot the temperature/time needed against weight loss for transportation and degree of torrefaction required to make pellets at low cost. Then a smart person could overlap the expenses of doing all this and see if they overlap showing it worthwhile. Being able to control the temperature and time during the process will be a challenge IMO as so much happens between 250c and 450c. 

[RWL2: Agreed that we need all this. I am most of the way done in something like this - prepared in response to something recent from AD Karve. In talking with others, I see that volume changes are perhaps as important as weight changes (in case anyone has that data) - if one is trying to minimize transportation costs (which I am). 

I don't think that 450 is the right upper limit for the term "torrefaction" - I think even 280 oC might be too high an upper limit. Saying this because I think we want to keep as much energy gas in the product as possible. Some of the first useful gases coming out are not exothermic - and so we don't mind losing them. We certainly shouldn't ever mind the big water weight loss. 

One value you haven't mentioned is that torrefaction (always?) means that there are chemical/structural changes that change the TBM from hydrophilic to hydrophobic. I think this can be a/the key benefit for getting TBM into developing country urban charcoal use - to switch from charcoal use to TBM-turned-into-Biochar. 

The whole idea of torrefaction is confusing to me. Once wood loses weight after moisture it should be ‘torrefied’ up to weight becoming stabilized (~450c). where it is now biochar IMO. I’m just learning how to spell the words and trying to understand what they mean. That’s harder for me than developing a test to determine degree of torrefication. 

[RWL3: Still confusing to me also - but more dialog is helping a lot (thanks). But I have to repeat that a temperature of 450 is ready to use as a soil amendment. I am OK with that if the gases have been productively used. But I am trying to wean urban cooks off of charcoal use - to be replaced by charcoal-making. My first economics are saying that the economics can be favorable - since the per kilo price of TBM should be appreciably less than the price of char (if not transported too far) - and its energy content is getting close. Charcoal using stoves are not that efficient - and there is no chance for an output as valuable as is Biochar.] 

And any correction of my spelling and meaning of these words is very well appreciated. 

[RWL4: Only that I have not seen anything on "inverse" torrefaction; maybe better to not try to insert that concept - as the forward direction is hard enough to explain? 

Ron 

Regards 

Frank 

Frank Shields 

42 Hangar Way 

Watsonville, CA 95076 

(831) 724-5244 tel 

(831) 724-3188 fax 

frank at bioCharlab.com 

From: stoves-bounces at lists.bioenergylists.org [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of rongretlarson at comcast.net 
Sent: Saturday, February 25, 2012 12:46 PM 
To: Discussion of biomass cooking stoves 
Cc: Hugh McLaughlin 
Subject: Re: [Stoves] Is there a role for combining torrefaction and char-making stoves? 

Frank: (and ccs) 

I'm enjoying this dialog. I see why you are thinking dimensions rather than weight - but change in total weight still seems to be a statistic of interest to torrefaction researchers.. Your suggestion (last time) for using tongue depressors for char-making stove development is very useful. 

I have now (for the first time) wandered around your several test description pages. You have an amazingly diverse wet of tests and client-types. On this list, I think it OK for you to describe (promote) your business a little more, if I initiate the question. 

Nowhere did I see the words "Torrefaction testing". Have you been describing in this thread the development of some new (independent lab) test needs for (I now see, presumably) many emerging torrefaction companies? 

Any comments on the appropriateness in developing countries of torrefied (and maybe pelletized) materials for char-making stoves? Do you think it possible that women with such stoves could in some circumstances make rather than expend money while cooking? Or better to think that with unprocessed input fuels only (I'm thinking transport costs as well). 

Ron 

----- Original Message -----

From: "Frank Shields" < frank at compostlab.com > 
To: "Discussion of biomass cooking stoves" < stoves at lists.bioenergylists.org > 
Cc: "Hugh McLaughlin" < wastemin at charter.net > 
Sent: Saturday, February 25, 2012 1:01:47 PM 
Subject: Re: [Stoves] Is there a role for combining torrefaction and char-making stoves? 

Ron, 

<snip> 

I think shape is better as it can fine tune the variation in temperature along the TD. Also weights of tars that may collect on the stick will not be an error if size is the measure. 

It seems from the links that it will come to a constant size (or weight) if given enough time. But for shorter burst of a temperature it will not be accurate (as you suggest). I guess it is an average temperature for a given time. 

Regards 

Frank 

Frank Shields 

42 Hangar Way 

Watsonville, CA 95076 

(831) 724-5244 tel 

(831) 724-3188 fax 

frank at bioCharlab.com 

1. I agree that the tongue depressor changes in shape sound like a very useful (and cheap at not much more than 1 cent each) diagnostic tool at these low temperatures. Especially they seem useful in identifying temperature differences at different retort locations. But after that problem is solved, it would seem that weight loss (as opposed to dimensions) should be a fairly direct indicator of temperature. Have you tried and can report weights for some of your temperatures near torrefaction levels? 

2. I have found a fairly robust (and free) technical literature on torrefaction. The first two I have read are: 

a. http://www.bioenergytrade.org/downloads/grazkleinschmidtpaper2011.pdf 

Its Table 1 (I couldn't copy, sorry) shows significant (factor of 3?) potential benefits for torrefied pellets over charcoal in volumetric energy density terms. Also benefits over wood and wood pellets in other measures. Although not written for charcoal-making stoves, and specific temperatures are not recommended, I take this paper to be positive towards charcoal-making stove use. 

b. http://www.dcf.ufla.br/CERNE/artigos/08-01-2010625209%20artigo%20686.pdf 

This one is much more technical - and show results for applied temperatures of 220, 250, and 280 degrees C. Exothermicity is not seen at 220, but is at 250 and more at 280. There is a good bit more weight loss at the higher temperature - and possibly there is some advantage in terms of pelletizing. But if one can avoid pelletizing (by starting with short pellet-shaped branch or chip material), It seems like the 250 C temperature could be fine as well - from the authors' perspectives. 

Re Frank's tongue depressors, the change in weight (and dimensions) is seen to be dependent on time as well as temperature - so simply knowing weight loss is not going to provide a unique temperature. Still weight loss is a valuable start - and will give some data. If a retort wall temperature reads 250 C and there has been little weight loss, one will need to wait longer and/or reach a outside higher wall temperature.. 

3. I see lots of other responses (thanks) - going to next. (and so truncate this one) So far it lstill ooks like there could be a good application of torrefaction to char-making. Hope someone is trying it out. 

Ron 

From: "Frank Shields" < frank at compostlab.com > 
To: "Discussion of biomass cooking stoves" < stoves at lists.bioenergylists.org >, "Paul Olivier" < paul.olivier at esrla.com > 
Cc: "Hugh McLaughlin" < wastemin at charter.net > 
Sent: Friday, February 24, 2012 1:01:54 PM 
Subject: Re: [Stoves] Is there a role for combining torrefaction and char-making stoves? 

Dear Paul and stovers interest in torrefication or degree of torrefication, 

I have been experimenting with my pipes filled with tongue depressors at 
different temperatures. Still trying to get a way to verify the temperature 
reached the range I want. I use McKesson Medi-Pak Standard 6" (15cm) X 0.69" 
wide. 

http://www.allegromedical.com/browse/browseProducts.do?searchPhrase=tonque+d 
epressors 

These are amazing. They start to shrink at 250c and at 450c are a fraction 
the size they started. Then they still shrink some and start to curl. But 
they keep their shape so measurements (length and width) can be made. If the 
furnace has uneven heat one end will be wider than the other. Best 
temperature gauge within the torrefied range I have found. My plan is to add 
one with each biomass or biochar I am charring. First I need to accurately 
calibrate them. Meaning I need to make sure the ovens are at a constant 
temperature of my chosen. Using these sticks are showing that is not as easy 
as I thought with my old ovens. 

Regards 

Frank 

Frank Shields 
42 Hangar Way 
Watsonville, CA 95076 
(831) 724-5244 tel 
(831) 724-3188 fax 
frank at bioCharlab.com 

-----Original Message----- 
From: stoves-bounces at lists.bioenergylists.org 
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Paul S. 
Anderson 
Sent: Thursday, February 23, 2012 6:23 PM 
To: Discussion of biomass cooking stoves; Paul Olivier 
Cc: Hugh McLaughlin 
Subject: Re: [Stoves] Is there a role for combining torrefaction and 
char-making stoves? 

Ronal and all, ( I do not know if other Listservs should be sent a copy.) 

Great topic. I have a little different twist to it. 

<snip> 

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