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

[rongretlarson at comcast.net]

Frank: 

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 

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