[Stoves] Smokeless transition

[Ray Menke]

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
>
>
> ________________________________
>
> _______________________________________________
> Stoves mailing list
>
> to Send a Message to the list, use the email address
> stoves at lists.bioenergylists.org
>
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
>
> for more Biomass Cooking Stoves,  News and Information see our web site:
> http://stoves.bioenergylists.org/
>
>
> _______________________________________________
> Stoves mailing list
>
> to Send a Message to the list, use the email address
> stoves at lists.bioenergylists.org
>
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
>
> for more Biomass Cooking Stoves,  News and Information see our web site:
> http://stoves.bioenergylists.org/
>
>



-- 
Ray  Menke