[Stoves] pre-mix of wood-smoke with air? and how?

[Boll, Martin Dr.]

Dear Jeff, Paul, Frank,

I like your answers. It is a little bit difficult for me to respond, because
your proposals and questions touch somehow a lot of problems in this field,
which I wanted to mill down one by one. 

Possibly I started form the wrong point, that is, from the end of the
process, from finally woodgas-burning.

I made a long way of thinking, and it would be too much to point that out at
once; and it would be not understandable to give only key-words.

So I describe starting from the end:

With the normal gas-burner in mind and the pictures of Paul's T-LUD, Tom's
camping-stove and others I asked myself:

Would it be better or easier to burn a pre-mixture of smoke and air, as it
is done by the known gas-burners (butane etc.), instead of making all the
mixture in the burning point.

 I thought about possible difficulties: 1.-false mixture-ratio, 2.-too low
temperature for good ignition and quick burn, 3.-too high temperature and by
that too early ignition and burn (burn before the nozzles) 4.-Too slow
flame-speed to cause self-outblow (I know from old experiments), or too high
flame-speed to cause "Rueckschlag" (=retro-burn?? By gas-burners a roaring
flame just on top of the mixing-nozzle). 5.- The fear of condensation and
with that: problems with the burner-nozzles and tar in whole the system.

( to complete the burner-thoughts: Must there be a "Prallplatte" (baffle?)

If I knew about that, I wanted to see, if the smoke and/of air has to be
pre-heated or not; even if it is necessary to cool-down the smoke for no
self-ignition.

The idea is:

- If there must be a strong preheating of air, it can be reached by cooling
the out-streaming burned gasses by radial-vertically fins, reaching from the
burning gasses on top down into the air-admission-area and transfer so heat
by that fins to the air. -Naturally there must be a separation-lamella for
exhaust and air, as well as a heat-isolation to stop most radiation to the
outside.

- If there must be a mild preheating of the fresh air, it could possibly
reached by cooling down the smoke, especially if the smoke had a temperature
that would lead to self-ignition, when in contact with air (that is not
desired before the gas-burner-nozzles)

- If preheating is not necessary and self-ignition-temperature of the smoke
is not reached, the only advantage of air-preheating is a certain natural
draft, which is even desired, to spare/avoid artificial draft. 

The question to make artificial blow/draft or not is then the main question;
with gradual solutions:

 from starting with only natural draft, to chimney, to partly-natural draft,
to partly few- or partly sometime-blow  (handmade, if low-tech??) to full
artificial blow at the other end.

If I knew a lot about the possibilities, the advantages and the negative
points I wanted to decide, if I could manage with some natural draft or have
to make it work with a blower. I have not in mind to work with a T-LUD- or a
Camping-stove-like burning, because I would like not to work with a
fuel-stack but to re-fuel on top, but I think it must be somehow a
gasifier-burner, because I don't believe to get a real good burn without
premixing smoke and air. 

-Therefore my premixing questions.

I hope that was not too unclear-explained stuff.

 

Jeff wrote:

>It's a good idea to use some of the waste heat to pre-heat the air. Hot gas
or cool gas has been a big subject >starting back in 1900 or earlier.

Do you have some papers of that? The old ones are possibly in German or
French. -I did forget the name of a man experimenting in Austria about that,
I think it was before coal was used to be gasified.

Jeff wrote:

>ABOUT 50:50. Woodgas varies greatly.

Fits that ratio 50:50 to be blowed through the multiple nozzles of a gas
burner (which mixes a lot of more air into the flame, by forming a jet?) to
burn without forming sooth? -It does not matter if burning blue or yellow,
if that was the reason of preheating the air.-

In fact I saw simple woodgas, (without air) streaming out of a hole of a can
approx 2 or 3mm diameter, that I could not ignite, because of blowing out
the igniting flame. Therefore I think there had to be used a "Prallplatte"
(=baffle?) to have somewhere inbetween the nozzle and the baffle the right
speed to form a stable flame or/and to re-ignite. (I saw that theme
discussed and described later on in the wing-stove-page. In:   ......)

 

Jeff wrote:

>I try to condense as much as possible. Cleaner gas!

For only burning purpose, and not for gas-engines, I think all smoke burns
to clean burning gasses, if there is the right ratio and the right burning
temperature, depending as well on the temperature of the un-burnt smoke and
the air for burning.

 

Paul wrote:

By pre-mixing, I am assuming that there is some additional time and space
allowed for the pre-mixing in the interval between the creation of the
wood-smoke (wood-gas or pyro-gas) and the final combustion.

Isn't the premixing by butane-burners the reason for clean burning? Couldn't
that be the same by woodgas?

Or does woodgas need so much less air, to burn clean without sooth in
comparison with propane/butane, which has to be (??) pre-mixed to burn
without sooth by burning in a low pressure-jet/nozzles?

 

Paul wrote:

>The only exception that I know of is the successful work of Alexis Belonio
who can move at least several meters the >gases made from TLUD gasification
of rice husk to the final burner.  I am quite sure that in that case he does
not >have any pre-mixing of air with the combustible gases.

As far as I have seen Alexis Belonios pictures, the burning-gasses are moved
with much more pressure. I think/guess/feel the pressure made by a fan
produces a comparable pressure that makes the jets of a propane/butane
camping-stove-burner. But take this with the famous corn of salt: If the
flame-speed is far less, the jet has to be slower. Possibly is the lower
caloric-worth of woodgas helpful to burn the jet with lower pressure/mix
completely.

 

Paul wrote:

>I believe that the people working on pyro-gas (wood-smoke, wood-gas,
rice-gas, agri-gas, etc) are focused on >getting good mixing of the gas with
the air precisely at the area of the final combustion.

I think the pressure of the jet must be high enough, that it works, but how
is that with natural draft? -Needing possibly a chimney after the heating
work, to create such good-mixing jets? 

My idea was to premix smoke and air, and by this to create a better natural
draft. Naturally the mixing-area must be heat-isolated in order to stay the
heat in the system.

 

Paul wrote:

>In summary, in my opinion, gases that contain condensible volatiles should
not be pre-mixed with air.

Is the fact of condensation not mainly question of the temperature of the
air/smoke-mixture; and if this mixture can be kept hot enough (possibly by
preheating the air from burnt gasses, however it is made) condensation could
not be a/the problem?

 

Pardon to all, for my long sermon.

 

Regards

 

Martin