[Stoves] Smokeless transition

[Dean Still]

Hi All,

We added more bottom air until all the wood had turned to charcoal so there
was no smoke at the transition.

Best,

Dean

On Fri, Dec 12, 2014 at 4:32 AM, Ray Menke <ray.menke at gmail.com> wrote:
>
> If the fuel is not dry, or doesn't let enough air through, the stove
> will need more primary air.  A small computer fan mounted in the
> bottom of a tin can or 2 liter juice bottle will provide that excess
> air.  (I use an old motorcycle battery with clip-clip leads.)  Most of
> the time, it is not needed, but it does solves the problem in a hurry.
> It also melts grates and the walls of the burn chamber.  A sacrificial
> burn chamber liner from scrap metal or old stovepipe works well, and
> grates can be made from 1/8" thick steel.
> Another solution might be to mix some pencil size torrefied wood in
> with the almond husks.  (one or two inches in length.)  The torrefied
> wood is guaranteed dry, and will loosen the packing of the husks so
> more air can enter.
> My stoves are based on Paul Anderson's Champion TLUD design, and have
> a 2" tube at the bottom for primary air.  A funnel to direct air into
> the tube can be made by taping tin or cardboard around the open end of
> the olive can.
> Ray
>
> On Fri, Dec 12, 2014 at 4:57 AM, kgharris <kgharris at sonic.net> wrote:
> > Marc,
> >
> > I have also been struggling with this transition problem.  It has become
> > more pronounced since the rains started, so humidity may be a
> contributing
> > factor.  Also, the ND-TLUD I am using has turn-down capability and the
> > transition problem seems to share some similarities with turn-down
> problems.
> > This makes sense because in both cases the wood gas production is being
> > reduced and the temperature of the flame is lower.  This made me think
> that
> > perhaps the problem could be addressed in the same way that turn-down is
> > addressed, with either hot char or pilot flame support.  This has so far
> not
> > worked with pilot flame support.  What has helped is giving the stove
> lots
> > of primary air to get the char hot before the flame reduces.  Entering
> this
> > phase with the stove turned to a low setting always results in smoke.
> This
> > is in keeping with something that Crispin wrote about, using paper to
> cover
> > excess primary holes.  When the pyrolysis front reaches the bottom, it
> burns
> > the paper and lets extra primary air in to heat the char, which helps get
> > through this phase without smoke.  It might be a pain to add this paper
> to
> > each burn.
> >
> > Fuel depth may have some input here.  With a large load the char will
> start
> > burning at the bottom and will not be near the decreasing wood gas to
> heat
> > and ignite it.  Directing air down onto the top of the char and heating
> some
> > of it to red hot may help.  This is one of the methods of supporting
> > turn-down by using red hot char.  Julian Winter once suggested a purched
> > char method for turn-down which did work.  Placing a small amount of
> char or
> > wood which will become char in a wire basket inside the reactor just
> below
> > the secondary air inlet provides red hot char to support the secondary
> flame
> > during turn-down.  This would have the deminishing transition wood-gas
> > passing through red hot char to be heated and ignited.  This might work
> for
> > the transition and also provide turn-down.
> >
> > The primary air in this phase will be used mainly for the last bit of
> > pyrolysis and the char will gradually increase burning as the pyrolysis
> > slows down.  This produces a temperature low point before the char heats
> up.
> > Excess primary air just before this phase can heat the char to keep the
> > temperature up.  Keeping the temperature up is important.
> >
> > Please post anything you might learn.
> >
> > Kirk
> > Santa Rosa, CA. USA
> >
> > ----- Original Message -----
> > From: Marquitusus
> > To: stoves at lists.bioenergylists.org
> > Sent: Friday, December 12, 2014 1:01 AM
> > Subject: [Stoves] Smokeless transition
> >
> > Hi Stovers,
> >
> > There is a point in the TLUD process that I find specially difficult to
> > understand and control: the transition from wood gasification to char
> > gasification. Maybe you can help me to do it.
> >
> > At this point,  when the hydrocarbon fuel is near to finish, my
> experiments
> > with almond husks as fuel for ND-TLUD shows 2 possible endings:
> >            1- The flames in the burner turns to blue color (due to high
> CO
> > presence in gases) and the char pyrolisis continues until ashes. No smoke
> > present.
> >            2- The flames in the burner extinguishes and the smoke
> appears.
> >
> > I made a lot of tests, with variations in ND-TLUD design (riser height,
> > quantity of primary and secondary air, type of concentrator, etc.)  and
> > still I'm not able to say which factor combination is the answer for a
> > smokeless transition. Sometimes I have smoke, and sometimes I don't.
> >
> > I suspect the answer has to do with chemical fuel composition, as when I
> use
> > wood pellets, almost never have smoke.
> >
> > So this is the point where I am today. When char gasification begins, I
> have
> > to lower the primary air? Lower the secondary air? How I can ensure the
> > flame won't extinguish?
> >
> > It would be very useful for me to read your comments about this.
> >
> > Thanks very much,
> >
> > Marc
> >
> >
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>
>
> --
> Ray  Menke
>
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