[Stoves] Natural draft TLUD turn-down

Crispin Pemberton-Pigott crispinpigott at outlook.com
Mon May 19 18:38:41 CDT 2014


Dear Roberto

I agree with your analysis. There is a lot of merit in keeping the secondary flame in close proximity to the top of the fuel bed. The most important is that the secondary flame is harder to put out with a slight breeze (because it relights). The second is that when the primary air is turned down to control the power, the secondary flame is able to remain hot enough to stay alight. Combined with external, down-drafting secondary air preheating (not like the Peko Pe) one can maintain the secondary air feed ration under different primary air conditions.

Read and heed! TLUD's are not succeeding in meeting the turndown ratios required by ordinary cooking. To burn clean at different burn rates, whatever the fuel, you have to control both the primary and secondary air flows.

While a 'double controller' can work, turning the secondary air down at exactly the same time as the primary leads to a 2-3 minute period of very high PM and or CO and VOC's because of the retained heat in the fuel bed and stove body. This is worse if the combustion chamber is ceramic or cast iron.

If the secondary air feed it an automatic, buoyancy-driven ‎supply, it will draw in additional air as required during the cooling-off period. This explains the strange layout of the air supply in a Vesto Stove which tried to address the problems inherent in David Hancock's (very advanced at the time) 1984 Tsotso Stove (which is still in production).

Regards
Crispin in Seoul enjoying spring

BBM 2B567C3
From: Roberto Poehlmann
Sent: Tuesday, May 20, 2014 02:28
To: stoves at lists.bioenergylists.org
Reply To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Natural draft TLUD turn-down


Kirk,
this is a very interesting document, thanks to share it.

The method 2 is like the 12 holes configuration of the Peko Pe design in
page 9 of the following document:

http://www.adansonia-consulting.ch/document/Grass%20Cooker%20handbook_print.pdf?PHPSESSID=3d064accc3efbdafd3b1133a13129f9a

Maybe this is the reason that the Peko Pe stove don't need an internal
chimney to operate. This 12 holes function also like 12 pilot flames,
maintaining the secondary flame hot.

I have replicated this design of the Peko Pe, and in operation, you can see
the pilot flames attached to the 12 holes.

Maybe the 4 holes concept in the middle of the combustion chamber can also
helps to maintain a slow power consumption. When the pyrolysis front reach
the middle of the combustion chamber, this "primary air" start to combust
the charcoal, adding heat to also support the flame.

Roberto Poehlmann
Valdivia Chile.


"
All,

Dr. Ron Larson, Dr. Paul Anderson and I have been working on the problem of
lack of turn-down in natural draft TLUD cook stoves.  We have found
considerable success.  Attached is a document introducing the results of
our labors.  All information is in the public domain.

K Harris
Santa Rosa, CA. USA

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