[Stoves] Why doesn't charcoal burn in the Champion TLUD?

Fri Oct 17 16:08:15 CDT 2014

Hi Christa,

Thank you.  I read the GIZ-HERA Manual.  It is one of the best documents I
have encountered on the subject.  Your additional comments are helpful.  

I would definitely like to know more details of the prototype you did in
Madagascar.  People in Besongabang (where we are working) generally don't
use charcoal so adapting to existing charcoal stoves would be completely new
for them (i.e. They don't have charcoal stoves now).  The feeling amongst
our team as we have been discussing this (but haven't built any prototypes
yet, will do in the next few weeks) is that people would rather burn the
charcoal than save it for later use as either fuel or soil amendment.

What puzzled me about the TLUD is that there is heat to create the gases
which are then burnt with the secondary air.  Why isn't this heat enough to
burn the carbon (charcoal)?  I can see that you can slow burning by
controlling the primary air but I'm still puzzled by why, if there is enough
primary air to support a fire to produces gases why isn't it enough to burn
carbon?

I could imagine wood in an airtight container that was heated so that gases
were emitted but there is no air to burn anything.  If the gases were
released and contacted air then the gases could burn.  If that heat could
then be used to continue heating the air tight container you could keep
making gases and charcoal.  And the heat could be used for cooking.  But for
the way I'm describing it I don't see how you would direct the heat back to
the airtight container.

Anyway, I'm just trying to describe what puzzles me in this.   I did
understand your explanation of how more primary air will burn the charcoal.

I will study your comments further.

Thanks,

Huck

From: CHRISTA ROTH [mailto:stoves at foodandfuel.info] 
Sent: Friday, October 17, 2014 9:20 AM
To: Discussion of biomass cooking stoves
Cc: Sujatha Srinivasan
Subject: Re: [Stoves] Why doesn't charcoal burn in the Champion TLUD?

Huck, in the GIZ-HERA manual microgasification:
https://energypedia.info/wiki/File:Micro_Gasification_2.0_Cooking_with_gas_f
rom_dry_biomass.pdf  you find most of your answers. 

See  pages 12 onwards, where we tried to describe in an easy-enough way
step-by-step the processes happening when burning biomass and how the
principles are put to work in different stoves/burners. You may find the
visualisation helpful, where heat-driven pyrolysis and oxygen-driven
char-burning and gas-combustion are separated.  AS Paul Anderson already
pointed out, 'TLUD' is not a device but rather an operation mode. 

The figure on page 24 of the manual explains how to switch from TLUD
(top-lit up-draft) mode to Bottom-burning  UD mode, if you can deliberately
control primary air so you can add sufficient air at the end to burn the
char (from whichever side the air gets in bottom and/or side burning).

any stove/burner that provides the option to increase primary air at the end
of the char-making pyrolysis process should be able to burn the char. The
air control and the configuration of the air-holes matter most: with forced
air or substantially increased air flow on the hot char, the char will burn
to ash. The configuration of the air-holes will determine, how the char is
burnt: wherever an air-hole leads oxygen on the char, you find an increase
in the glowing intensity which indicates that the 'char is burnt'.

the TChar concept (8b in the figure) is also explained in more detail on
pages 28-30 and again page 60.

Two weeks ago we made an interesting prototype in Madagascar with a simple
accessory to an existing charcoal stove. Much easier and cheaper than
developing a gasifier from scratch. and a lot safer to use, as you don't
need to transfer hot charcoal, you simply lift the accessory up and replace
the pot. 

can give you more details if you are interested.

Hope that helps. 

regards

Christa

Am 15.10.2014 um 21:49 schrieb Paul Anderson <psanders at ilstu.edu>:

Huck,

In  general, data about the operational aspects and results of use of some
stoves (you named two) are not readily available.  You said "seem to burn".
That is different for making direct claims, or of implying that there are no
negative effects of burning the char inside the gasifiers.   Some claim to
have superior materials, as in the fuel chamber.   You can  ask them
directly.

But unless reasons and differences are clarified and documented, I would
agree with the comments by Ray and Julien and Kirk and others, which say:
It is not good practice to burn the charcoal in the TLUD stove that made it.
I thank them all for sending replies, a sure sign that everyone knows that
questions to  the Listserv are to everyone, not just to a few who get named
in the opening line.

HOWEVER, there are two exceptions because of differences in the TLUD
designs:
A.   The TChar concept.    See documents at my website and elsewhere.   This
has not been implemented (as far as I know) in any particular project with
20 or more stoves, in part because of the difficulty of joining WELL
(safety, leaks of primary air, workmanship, variability of charcoal stoves
to serve as the bottom base, etc.).

B.  The charcoal burner insert for the Servals Champion TLUD. See:

http://www.drtlud.com/2012/09/06/servals-charcoal-burning-attachment-for-cha
mpion-tlud-stove/

I am sure that Sujatha of Servals (a member of this Listserv) will answer
specific questions.   None of these inserts is in the USA, as far as I know.
I do not have one.

Comments on A and B:  The concept is quite appropriate, but both do involve
movement, transfer, possible spillage, etc of hot charcoal.    That is
similar to the third "option" C.

C.  Simply pour the hot char into an appropriate stove that is made to burn
charcoal, and then continue cooking.    Please note that the char from TLUDs
tends to be in smaller pieces than the standard charcoal sold on the
streets.   And the existing charcoal stoves are mainly for the street-vendor
size charcoal (which is inherently wasteful, but that is not the question
being discussed.)

Huck, because you are initiating a new housing project with kitchens
included, you are able to offer to the residents whatever combination of
stoves you make available.   We all are anxious to have your results
reported back to this Listserv.

Paul

Doc  /  Dr TLUD  /  Prof. Paul S. Anderson, PhD
Email:  psanders at ilstu.edu
Skype: paultlud      Phone: +1-309-452-7072
Website:  www.drtlud.com

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