[Stoves] Air power Re: Burning saw dust in TLUD stove

[Marc Pare]

Crispin, Doc, et al.,

Some details from very recent work to add detail to this comment:

>2.  We need feet of chimney height to equal what a small fan can
accomplish, and a blower gives even more power.

Well, how much is actually needed? We need to break out the combustion
analysers again and get the readings.

Dr. Belonio has a good analysis of this question for rice husk gasification
stoves in his handbook.<http://www.bioenergylists.org/stovesdoc/Belonio/Belonio_gasifier.pdf>

His approach is to take the necessary equivalence ratio and cook time
desired to calculate a desired mass flowrate. He converts that into a
superficial velocity, which, can be used to find the pressure drop through
the bed of fuel (in his case, rice husk) via the Ergun equation.

Down in Northwest GA, we can get natural draft rice husk stove to run with 1
meter of chimney. We are hoping to reduce the amount of chimney needed, but
it's going to take better understanding of the first issue Doc brought  up:
correctly splitting the primary and secondary air.

One advantage of pushing air through the bed of fuel is that it provides the
syn gas more time to carbonize (I'm not sure that's the right term) as it
filters through the bed of char. In practice, this means that we observe
blue flames when using a fan on a rice husk stove but yellow/orange flames
in the natural draft versions. Both are smokeless, but I am very curious as
to whether one is cleaner than the other.

Hope this is interesting to folks on the list. I'm working on these
questions actively, would be happy to speak to others that are, too. Seems
like there's some real opportunity for some engineering here since the
tipping point between getting a natural draft stove working with a chimney
is right on the verge of what's possible with appropriate materials...

Marc Paré
B.S. Mechanical Engineering
Georgia Institute of Technology | Université de Technologie de Compiègne

my cv, etc. | http://notwandering.com


On Tue, Jan 18, 2011 at 11:09 AM, Crispin Pemberton-Pigott <
crispinpigott at gmail.com> wrote:

> Dear Paul
>
> Thanks for the reply.  I continue with:
>
> >1.  One pull needs to serve both the primary and secondary air, and to
> separate the pull into two paths is difficult and interrelated (increase
> one
> will diminish the other).
>
> So far we are doing fine with several fuels. Just reporting....
>
> >2.  We need feet of chimney height to equal what a small fan can
> accomplish, and a blower gives even more power.
>
> Well, how much is actually needed? We need to break out the combustion
> analysers again and get the readings. How much is used v.s. actually
> needed.
> If the stove is venting into the room, there is no different to vent the
> chimney into the room. If it accomplishes the same thing, there is no
> problem. Just because it has a chimney does not mean it HAS to go outside.
> Just sayin'.....
>
> >3.  In the context of sawdust or even rice husks, nobody has successfully
> pulled (via a chimney) the primary air through such fine materials,
> especially with small cookstove sizes that could finish cooking before a
> substantial chimney gets sufficiently hot to give a stable draft.
>
> Yeah, well, OK, but who said it has to be pulled through the fuel? There is
> more than one way to burn a pile of sawdust. So let's look broadly at how
> to
> burn fuel without pulling it through the whole volume of it. The fact that
> most of the designs rapidly copied from the Campstove says nothing about
> other designs that work differently.
>
> I am about to suggest to Rok and Richard that they make a no-hole briquette
> stove that uses counter-flow air like the Lion/Tau/Libhubesi stoves to
> avoid
> the erosion of walls problem common to stoves with all the air coming from
> one side. Still working on the briquette-tube wall gap.
>
> >4.  (Opinion) Fans and blowers will enter the cookstove efforts in major
> ways in the coming few years.
>
> Chimneys will be favoured if they work as well and have no moving parts for
> the simple reason that you can't make your own fan. A lot of metal stoves
> are still made at home or by a neighbour.
>
> >We Stovers are just scratching the surface of applications of FA into
> cookstoves.
>
> And innovative uses for chimneys!
>
> >The topic of FA is integrated into the content of the BEF Gasifier Stove
> Camps ...
>
> Cool. May the fans fill your sails!
>
> Regards
> Crispin
>
>
>
>
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