Re: Fundamental facts about TLUDs #technology #tlud

Paul S Anderson

To Hans Erken,      Thanks for the photo.   Nicely done.   TLUDs for making char, two sizes.  No evident intent to cook, which forces cookstove TLUDs to have other characteristics that add cost and can be inconvenient when char is the objective.


To Hugh,


Thanks for those statements about TLUDs.   The “systematic view” too often gets pushed to the side.  


Your comments apply to both the char-making and the cookstove objectives.


I agree with Hugh about the destabilizing influence of increasing the  diameter of TLUD devices.   A 200 L barrel (55-gallon drum) is about a large as is reasonably reliable (assuming attention is given to the dryness, size, consistency, etc. of the biomass).   There are numerous variations of the single barrel TLUD.   Changes are in the top for the secondary air and draft and in the bottom (including with no bottom at all) for the primary air entry.  


Unfortunately, the message (suggestion) of what not to do is taken by some as a challenge, so they then  prove to themselves that it is not a good idea to make it substantially larger. 


I am not sure I agree with Hugh’s statement that     “forced convection tends to exacerbate the imbalance.”    But you have only said “tends to” and I can accept that as true.   The full advantages of forced air (FA-TLUD) have not been completely explored, mainly because such additions add cost, but cost reduction is so important when dealing with cookstoves. 



But I have recently watched the 2017 video about the large char-maker by Biochar Now of Colorado.      41 minutes long, but you can go to about minute 25 until minute 30 to get the info about the char making equipment.    


The presenter (James Gaspard, owner of Biochar Now) never says it is with top lighting or TLUD principles or whatever process goes on inside.   But this system has forced air in several places, certainly in the sophisticated chimney/burner.     IF (I wrote   IF  ) this is TLUD or a derivative of basic TLUD principles, then Gaspard has shown how forced air can make a big difference AND how the diameter of a TLUD can be increased.   And he spent lots of money and he has patents that cover his discoveries.  


I am sending a blind copy of this message to James Gaspard, and we should hope that someone at Biochar Now is a subscriber to this Biochar Discussion Group.   So my hopes are high for a reply  that will tell  us what is happening inside that char maker.


For those readers who got started with char making after 2007, they might not realize that TLUD is a quite recent arrival to the char making stable of technologies.  Even until about 2015, the name “TLUD” usually needed to be explained to newcomers.   And maybe that is still the case, but simply as “TLUD” without explaining “Top-Lit UpDraft”.   The paper “Origins and History of TLUD…..” is found in the Quick Picks section (tab) of my website:   




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

         Email:  psanders@...       Skype:   paultlud

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

Exec. Dir. of Juntos Energy Solutions NFP    Go to: 

Inventor of RoCC kilns for biochar and energy:  See

Author of “A Capitalist Carol” (free digital copies at

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


From: <> On Behalf Of Hans Erken via
Sent: Sunday, September 13, 2020 12:19 AM
Subject: Re: [Biochar] Fundamental facts about TLUDs


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For me it is all about the chimney.  I developed the TLUD in this image some years ago and it works very well and I can’t improve on it.  I have played with TLUDs that are more portable but I find lower build and less draught can easily cause the fire to lose ignition if the fuel is not perfectly dry and sized.  My design is very forgiving and we have been using it for years.


Maleny, Qld


From: [] On Behalf Of Hugh McLaughlin via
Sent: Sunday, 13 September 2020 11:37 AM
To: Biochar Group
Subject: [Biochar] Fundamental facts about TLUDs


Dear list,


The basics of Tlud's are well established, if not well organized. Let me share a few of my hunches, developed over the years:


1) Tlud's are not chaotic. This means they follow the same path if started from the same starting point. This may seem obvious, but it is in fact a wonderful quality. It allows study and prediction of behavior. Lacking this, few studies will get far at predicting the future.


2) Tlud's scale linearly, but become less stable as the many amplified variables become less deterministic. This is essentially academic gibberish, but it means that the scaled predictions  are linear, but the results become less stable due to additional effects taking over.


3) For example, Tlud's become less stable the bigger they are - in that the linear progression of the pyrolytic front in the z-axis become less stable in the x-y axis, leading to unstable (uneven) progression of the hot zone down the fuel stack. At some point, the flame zone expands under a section of fuel and the pyrolysis become unstable, resulting in traditional combustion of the fuel to ash.


4) Tlud's make great stoves, due to relatively small scale and good heat transfer across the fuel bed. What is an acceptable temperature gradient across 150 mm become an unstable zone across 600 mm. At 2 meters, all stability is lost and the unit becomes a bonfire, not a controlled source of heat and biochar.


5) Significant instabilities in Tlud's are observed at 200l vessels, and forced convection tends to exacerbate the imbalance. Bigger is only worse.


6) What Tlud's do well they do brilliantly, beyond that, they are inferior to other designs.


I urge other to weigh in on the Tlud and it's calling.




Hugh McLaughlin, PhD, PE



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