[Stoves] burning wood gas

[Julien Winter]

Hi all;

I have a video of something similar to what Kirk is describing on Youtube.
https://youtu.be/xNBtQTyoS1s

It is an annular, cross-current burner.  Secondary air is introduced into
an annular gap from two directions (1) from the outside through holes in
the side-wall of the burner, and (2) from a central distributor.  The
central distributor is in the place of Kirk's bluff body.  This burner is
larger in diameter than the TLUD reactor, and the secondary air is not
preheated.

I am not sure how much air actually came through the central distributor,
because the path is a bit more tortuous than the side air holes, and the
intake is at slightly higher elevation.  The central burner is made out of
an inverted pet-food bowl with four vacuum cleaner tubes connecting it to
the outside.  A metal disk at the bottom of the bowel deflects the
secondary air sideways.  I tried to swirl the secondary air, but there was
no benefit.

I have attached a diagram of just the outer air holes.  There is a metal
ring placed above the air holes which helps to form the annular gap that
the flames must pass through.
Importantly however, I always use a metal ring above all types of air hole
burners because without it,
1) you can get small vertical flamelets rising up the sidewall of the
burner above the main horizontal flame jet.  These small vertical flamelets
often emit sooty smoke.
2) you can get unburned pyrolytic volatiles moving up the sidewall between
the air holes.
By using the deflection ring about the air holes, I ensure that all
reactants move horizontally toward the centre of the burner (before turning
upward).

Another important aspect of this burner is that at very low gasification
rates, the flame is below the burner and over the char.  Secondary air
sinks down from the air holes and is drawn towards a localized flame.  That
means that his burner works at low turndown, or in the final stages of
primary pyrolysis of the fuel.

This annular, cross-current burner worked very well for me, and I stopped
working on TLUD burners at that point (2015); not just because I thought I
had a good burner, but also because the University of Colorado had just
received a 1.1 million dollar grant to study natural draft TLUDs.  Surely,
I thought, if a university combustion engineering lab had that kind of
money, they would solve the problem … I was wrong.   They equipped their
lab with very expensive analytic equipment, and didn't spend time making
basic observations on ND-TLUDs.  "You have to learn to walk before you can
run."   What is the point of having a GC-mass spectrometer and lazers if
you don't know the right hypotheses to test?  So, when the UoCol failed to
make any advances, I started doing burner research again.

I have been trying to find simpler solutions than the annular,
cross-current burner.  The basic concentrator ring burner is easy to make
and use, and that is why, for practical reasons, it is chosen in rural
Bangladesh.  In some markets, an improved burner can't be too complicated
if it will successfully compete with a concentrator ring.  More elaborate
burners may be competitive in peri-urban communities.

Cheers,
Julien



-- 
Julien Winter
Cobourg, ON, CANADA
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