[Stoves] Natural draft TLUD turn-down

[Roberto Poehlmann]

 Crispin and all:

For method 3, y also think that the same objective can achieved with a
downdraft stove.

This is an example of a japanese downdraft camping stove. It have a wire
grate or basket to contain the pellets.

https://www.youtube.com/watch?v=GV0WDudP538

I think that this stove operates like a rocket stove. The stove produce a
very strong and orange flame because it have to much primary air. The stove
produce a lot of smoke at ignition.

This "downdraft rocket stove", with a few modifications, can operate like a
method 3 "TLUD" stove. The challenge is to ignite the stove and achieve the
secondary flame without smoke. I think this is possible.

Crispin, ¿how is the ignition of the BLDD 6 stove?


Cheers
Roberto Poehlmann
Valdivia, Chile


"
Dear Kirk



This is the sort of detailed analysis that really helps the whole field of
advanced stoves. I really appreciate your taking the time to put it into
writing.



Method three, turned upside down, is a downdraft stove with preheated
secondary air and it is a very good way to burn biomass, especially pellets
which are predictable. There is no need to elevate the fuel because gravity
handles that. I can recommend that anyone trying it use a wire grate, not
bars. This is a development of the BLDD stoves from the SeTAR Centre where
considerable success has been achieved in reducing PM emissions burning
semi-bituminous coals and again in Mongolia burning wet lignite, both with
extremely low emissions.



Method 2 - using flamelets to maintain the main fire is a useful idea that
can be added to many stoves to overcome some debilitating shortfalls (ie
make them practical devices).



Can I assume, based on your report, that you do not own a combustion
analyser?  You have long ago reached the stage where you need one to be able
to make better prototypes and to be able to make more generalised
statements. Some of the things said in the document are only correct in
certain cases. In nearly all stove layouts, if there is air entering from
below and exiting the top, the excess air level is too high to get really
good results save in narrow circumstances (low variability). If you want to
have high turndown, you have to control the EA in order to have a flame
remain viable.



In the case of the flamelets, part of the reason for your success is that
the flamelets are compensating for too much excess air in a turned down
condition. If the EA was lower, the flamelets would perhaps be 'less
necessary'.



You described having up to three controllable air sources. What I have been
suggesting is that the control of the secondary air can be made automatic if
the bottom-in-top-out architecture is abandoned in favour of downdrafted
preheating. You are correct, you need three controls, but if the structure
is correct, that happens automatically because the heat inside controls the
amount of air entering. With a bottom-to-top air path, there is nearly no
hope of getting that to happen automatically.



With the downdraft layout, there is a lot to be gained in terms of automatic
control because all air is downdrafted to the fire chamber. A combination
would be downdrafting secondary air, possible the pilot flame air as well,
in the amounts needed to cover the range of power envisaged. The draft
calculator available on the Stoves website can assist with this while only
having a thermocouple to measure gas temps with. You divide the stove into
sections and enter the temps are the top and bottom of each and it will
calculate the total draft. You can either check the draft of something that
works well, or predict what temps or heights you need in order to generate
the draft necessary to run the stove at that power.



I really encourage you to get or borrow a combustion analyser and read the
article in Boiling Point on how to use and calculate the necessary numbers
that provide guidance.



Regards

Crispin
"
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20140526/703295cd/attachment.html>