[Stoves] TLUD pellets stove with a venturi burner.

[Roberto Poehlmann]

 Julien,  thanks for your comments.


"Dear Roberto;

Thanks for the video.  That is an interesting idea for a burner.

I have found that it is a good idea to test a burner over a wide range of
gasification rates, because the patterns of air/fuel mixing and ratio can
change quite bit.

It would be interesting to see how well your burner turns down.  You
may find that there is a point in the pyrogas supply rate between very
low, and medium where the burner becomes a bit smokey, because there
is not quite enough secondary air from the lower holes, but secondary
air arriving above the concentrator ring is arriving too late, and/or
not mixing in properly."

RP> With an internal chimney, and primary and secondary air control
you can have a good turn down ratio. Because that only exists
secondary holes at the tube and at the cone, you can have a very low
blue flame, with flames starting only at the secondary holes of the
tube. For low rates, you can put a conde without holes.

"I once designed a burner that had a nice blueish flame but only in a
narrow range of gasification rates.  Another burner I have used a lot
shows a shift between the flame dancing over the top of the char bed
at low gasification rates, to a flame originating from the secondary
air holes. Between these two modes, there is a narrow zone in
gasification rate where neither mode is optimal."

RP> If you eliminate the secondary holes inside the combustion chamber
below the concentrator ring, and add a smaller tube with secondary
holes after the concentrator risk, you can have a continuos flame at a
lower gasification rates. You can put a cone without holes. Try it.

"At high gasification rates, you have a tall flame.  Is it possible
for you to increase the width of the burner to allow more horizontal
space for the flame?"

RP> It's a posibility. I can try with a 4 inch diameter tube for
example. I thing with a widther tube, i can produce a shorter flame at
more high power. But the lowest possible power will be higher than
with the 3 inch tube.

"
A question that I have been meaning to read-up on is the relative
strength of Venturi effects at the speed of air flow that we have in
TLUDs, and the pressure differential generated by draft.  My gut
feeling is that the Venturi effect is not quite as important as we
might think, and that the effects we see are largely driven by draft.
I am sure someone is going to have something to say about that."

RP> I thing that the draft produce negative pressure in the tube that
influence the production and velocity of the pyrolysis gases. The
velocity change in the tube due to the restriction, produce a drop in
pressure, that must be added to the total pressure that influence at
the secondary holes level.

Maybe with the helping of fluid dynamics, we can calculate the exact
influence of the venturi effect.

"
You have presented some through-provoking ideas.  Thanks for sharing.

Cheers,
Julien."

RP> Thanks Julien. MAny burners that i found in Internet have small
diameters, ¿why then in a typical TLUD burner the secondary air are
putting so distant or so far each other? With secondary holes at the
diameter of the combustion chamber you cannot have a stabilized flame
at a low gasification rates. With high gasification rates, the volume
of the gases is to much for the secondary air coming from the holes at
the perimeter. If the combustion chambers increase in diameter, the
area will grow quadraticaly and the perimeter linearly.


Cheers

Roberto Poehlmann
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20151009/c636f94b/attachment.html>