RE: [Biochar] Energy utilization from process

Dear Steve,

My approach is to not get in the way of others who try variations of TLUD devices.   Things can be learned when making changes, and different circumstances might benefit from changes.

However, you have asked a specific question and your favorable comment implies that  you might copy what you see in  the video.  Please do not.   To assist you (and to be constructive for others) I make these comments about the  barrel-size
TLUDs for biochar production:

A.  I have found no evidence that a second barrel (an inner barrel) provides advantages, and the disadvantages include:

                1.  Double the cost of materials

                2.  Extra weight to transport to and from locations, or to lift at the location of use.

                3.  Eventual failure of the bottom of the inner barrel could mean that the entire arrangement might be discarded, whereas if that bottom were to be fully visible, a repair might be accomplished, resulting in additional usage.

B.  While I am at it, I will also point out the propagation of an error (in my opinion) in the 2009 video by Peter Hirst (who is a valued friend of mine and who does good work, but not this one time).   The site is
https://www.youtube.com/watch?v=RXMUmby8PpU  and it has 234,237 views.  The method is not good.   The TLUD function  is only in the annulus (ring) of biomass placed around the inner barrel that is to
function as a retort.   This method does not work because

                1.  Retorts need to be heated externally.   The TLUD ring of fuel is only heating the part of the retort barrel that is at or above the level  of the descending MPF (migrating pyrolytic front), which at the half way point
of the TLUD operation is only the upper half of the retort barrel.

                2.  Even worse, the TLUD process is creating woodgas (and biochar) and those gases are not even combusted until they reach the upper part of the TLUD barrel where the secondary air enters and  where the flames start.   The
vast majority of the flames and heat go up the chimney and have no impact on the retort (except to heat the top lid of the closed retort barrel, with minimal impact).  

For whatever reasons that “errors” or steps backward occur, they can impact negatively a great many people who follow those sub-optimal leads.  

So, what is recommended?

There are many variations of barrel-size TLUD stoves.   See:

https://www.drtlud.com/?resource=prt12001    which is also at:

https://www.drtlud.com/wp-content/uploads/2012/10/ETHOS-2012-Barrel-Size-Micro-gasification.pdf      (Note:  The   www.drtlud.com 
contents are be gradually incorporated into my  www.woodgas.com     comprehensive website, but that will take some  time.)

Of those shown in that document, my recommendation is a lid variation on the JR Oven (page 2) by Karl Frogner, with more details at:  
http://biochar.bioenergylists.org/node/1749   .   Karl volunteered at the Shafer’s Warm Heat Worldwide  which has excellent training videos.   See

https://warmheartworldwide.org/biochar-training-videos/       Warm Heart in Thailand had the world’s larger biochar project with TLUD barrels.  

The recommended lid variation on those simple but excellent TLUD barrels is to have a larger top with a  downward lip of 4 to 6 inches that makes the lid loosely fit down over the barrel and guide in the secondary air.   The purpose is
three-fold:  1) The downward lip helps prevent cross draft under the lid and  2) the lip gives secure placement of the two cross bars that create the gap between the lid and the top lip of the TLUD barrel while 3) providing four handles to be able to lift
safely the lid/top with the chimney attached. 

There
are at least two ways to make such a lid/top with lip.  One is to make a “new” lid such as the improvised one from scrap metal seen in Section 1.f. of that document (photo with Art Donnelly in Costa Rica in 2011-12).  The other is to use the inner disk of
a barrel end (not including the rolled edge of the barrel).   You increase the radius about 2+ inches (5 cm) with a long strip of metal about 8 inches or 20 cm wide, that is folded 90 degrees, with cuts on one side so that it can be curved to make a ~4 inch
downward circular strip / ring that is longer than the circumference.   [Make the strip 95 inches long to have some overlap at the closure of the ring.  Sorry that I cannot find right now a photo of one made in Kenya about 10 years ago.]

Also please note that the description in that Section 1.f. points out that there is no need for a bottom to the  TLUD barrel if care is taken to create an air pocket and ample air inlet(s) at the bottom of the fuel in the barrel.  The air
pocket could be under a separate metal grate or even be a temporary “grate” of firm biomass that could then be pyrolyzed at the end of the TLUD operational cycle.

The global climate crisis and the need for biochar for carbon dioxide removal might stimulate more use of TLUD barrel kilns.   We want them to choose the most beneficial designs.  Unfortunately messages such as this are rather short lived
and reach fewer people than do videos.  I will  assist if anyone wants to make a video of the  recommended TLUD  barrel design.

Paul