GAS-L: Pellet stove combustors and lambda sensors

["Tom Reed" <tombreed@attbi.com>]

Dear Doug, Paul and All:

I have long been interested in the automatic pellet heating stoves and
believe it is not a gasifier stove in the sense I like to use the term.
(There was a discussion here last week about close-coupled gasifiers.  It is
NOT one.)

The action is as follows:

Pellets fall onto the 3 to 4 inch diameter grate and are ignited
electrically, while a combustion air fan comes on and provides excess air.

As the first layer of pellets burn they produce volatiles and charcoal in a
process I call "flaming combustion".  Since there is a great excess of air,
all the volatiles and characoal are burned with the excess air and no
identifyable gas is created except locally down in the mass.

If too deep a pile is made, all the excess air will be consumed and you will
have CO and HC emissions.  If it is really deep you will have an updraft
gasifier.  So the controls are careful to maintain the correct depth so that
excess air is present.


~~~~~~~~~
Excess air reduces efficiency of heating and burning, so it can't be too
much.  It is my impression that in Europe there are now pellet stoves that
incorporate lambda (air/fuel) meter sensors and regulate pile depth to
minimize excess air and maximize efficiency and clean combustion.  I haven't
heard that any pellet stoves in the U.S. do this.  Any comments?

Yours truly,                TOM REED


> Doug and all,  ( am sending to the Stoves list also because this topic is
> at the interface of interests between the two groups.)
>
> Yes, the discussion is fruitful.
>
> One thing I learned in your message below is just how different our
> definitions can be.
>
> For example, the web link you provided went to a site about what we call
in
> America "pellet stoves".  Although gasification of wood mass takes place
> (as it does in ALL burning), I and others on the Stoves list have not
> thought of pellet stoves as being "gasifiers" and we on Stoves list do NOT
> discuss much those heating device for the developed world.
>
> When I refer to "small gasifying units", I mainly think of the size of 2
of
> one-gallon cans or maybe as big as a 5 gallon (20 liter) bucket.   and
with
> no moving parts except possibly adding on a very small fan for forced
> convection.
>
> So I feel that the issue of "gasification for domestic use in small
stoves"
> is still very much a valid topic for the Gasification list.  The problems
> of NOx and other such things are very important to domestic "burning
units"
> whether for cooking (stoves) or for heating (space heater or water
heater).
>
> Thanks very much for the document on the small gasifier that you have
> designed (described as " 5 - 10 kW " on the Figure 4.2.3) .   At first I
> did not realize that what I wanted was the "Download the Pioneer Class
> gasifier design article" that is in the "Anniversary project" archive
file.
> http://www.fluidynenz.250x.com/
>
> And now that I have the document, I will need to study it to understand
> well your design.  But I can tell right from the start that I like the
size
> of it.   For me, your design is on the "large-side of the small-size
> gasifiers".   In comparison, my stuff is in the "micro-gasifier size" and
> so much smaller.
>
> This leads me to additional questions, but I leave them for a later
message.
>
> Paul
>
>
> At 08:20 PM 6/28/02 +1200, Graeme Williams wrote:
> >Dear Paul & Colleagues,
> >
> >It's pleasing to see the Gasification List come alive again, and what's
more
> >unveiling the issues that each of us in our own way are trying to
resolve.
> >With such healthy input, surely our gasification technologies can be
> >presented in an orderly fashion to the less informed, and where possible
> >support those who strive on our behalf behind the scenes.
> >
> >I have to say that in our debate on small gasifiers, the addition of
stoves
> >just doesn't fit right in my mind, although you could call them process
heat
> >gasifiers and try and find them in the "Yellow Pages".
> >
> >Here in New Zealand there is a healthy market for such stoves and there
must
> >have been 20 - 30 different models and sizes on a display I saw a few
weeks
> >ago.  I know the KENT brand was sold in the USA a few years ago, and they
> >made a big thing out of the emissions being far less than the US
standards.
> >Possibly these types of stoves are a New Zealand development, as I know a
> >lot of work was done to perfect their design principle in the old DSIR
> >laboratories.
> >
> >To read a nice explanation with diagrams, check this web page -
> >www.energywise.co.nz/content/pdf/demo59.pdf and hope the whole discussion
on
> >these wood burners can be passed back to "Stoves".
> >
> >The gasifier design that I mentioned can be found on the Fluidyne
Archive -
> >www.fluidynenz.250x.com
> >
> >I hope this clarifies some of the issues
> >
> >Doug Williams
> >FLUIDYNE GASIFICATION
> >
> >
> >-
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> >
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>
> Paul S. Anderson, Ph.D.,  Fulbright Prof. to Mozambique 8/99 - 7/00
> Rotary University Teacher Grantee to Mozambique >10 mo of 2001-2003
> Dept of Geography - Geology (Box 4400), Illinois State University
> Normal, IL  61790-4400   Voice:  309-438-7360;  FAX:  309-438-5310
> E-mail: psanders@ilstu.edu - Internet items: www.ilstu.edu/~psanders
>
>
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>
> Gasification List Moderator:
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> www.webpan.com/BEF
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> http://www.crest.org/articles/static/1/1011975339_7.html Gasification
> http://www.crest.org/articles/static/1/1011975672_7.html Carbon
>
>



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Gasification List Moderator:
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www.webpan.com/BEF
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http://www.crest.org/articles/static/1/1011975339_7.html Gasification
http://www.crest.org/articles/static/1/1011975672_7.html Carbon