[Stoves] Stoves Digest, Vol 103, Issue 16

Wed Mar 20 16:05:27 CDT 2019

Kirk, I totally agree with your assessment of clean burning TLUDs. That is
the way my TLUDs operate. Cannot wait to get to Apro this summer and do
more testing.

Norm

On Wed, Mar 20, 2019 at 10:01 AM <stoves-request at lists.bioenergylists.org>
wrote:

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>    1. Re: A Premix Burner (Kirk H.)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 19 Mar 2019 13:01:23 -0700
> From: Kirk H. <gkharris316 at comcast.net>
> To: Discussion of biomass cooking stoves
>         <stoves at lists.bioenergylists.org>
> Subject: Re: [Stoves] A Premix Burner
> Message-ID:
>         <
> mailman.2.1553101202.24431.stoves_lists.bioenergylists.org at lists.bioenergylists.org
> >
>
> Content-Type: text/plain; charset="utf-8"
>
> This is a festinating discussion about pre-mixing and flame color.  I do
> have some things to add here.  I don?t know that I will add anything to
> pre-mixing technology in this discussion.
>
> Pre-mixing is excellent for burning clean.  It is not necessary, but it is
> excellent.  I believe it is restricted to TLUD-FA stoves.  My design goal
> for higher power in TLUD-ND stoves is rapid mixing and burning.  This is
> fairly easy to achieve.  If the burner is designed to provide lots of
> surface contact between the wood gas and air as they meet, and yet keeps
> the gasses concentrated and hot, the result can be a very fast and clean
> flame.  Adding a little late secondary air (adding secondary air twice) can
> clean the flame even more.  One must be careful not to add to much
> secondary air overall.  My thinking is that the first secondary flame uses
> the heat from the easy to burn gasses to crack the long chain hydrocarbons,
> and adding a little more late secondary air burns the newly cracked
> hydrocarbon gasses.  Things I look for in my large burners are; providing
> lots of immediate surface contact between the wood gas and air,
> concentrating the heat into a heat reservoir (with high enough temperature
> to drive the cracking of the hydrocarbons and enough quantity of heat to
> feed the endothermic cracking reaction), allowing time for the hydrocarbons
> to crack, adding a little late secondary air to burn the new hydrocarbon
> gasses, allowing time for these new gasses to burn, using the pressure
> difference between the atmospheric air and lower pressure wood gas to its
> fullest potential, and enhancing the pressure difference between the wood
> gas and air to help drive them into each other.  This arrangement works
> fast and effectively for my TLUD-ND designs, so the more difficult to
> achieve pre-mixing is not necessary for clean burning.
>
> The color of the flame has some barring on my designs.  For a TLUD-ND I
> look for a yellow flame.  Yellow indicates a flame that is hot enough to
> burn the carbon particulates, and yet is fairly easy to achieve.  Dean
> Still at Aprovecho has said that a yellow to orange flame can be very clean
> burning.  I have found this to be true, and it is much easier to achieve in
> a hydrocarbon flame than blue.  Attached is a picture of a yellow flame
> that is very clean.  Note that it finishes burning while it is still hot
> inside the stove (minimal soot, smell, and smoke).
>
> I am looking forward to learning more about pre-mixing in a TLUD.  Perhaps
> my views will change.
>
> Kirk H.
>
> Sent from Mail for Windows 10
>
> From: Andrew Heggie
> Sent: Saturday, March 16, 2019 1:41 PM
> To: Discussion of biomass cooking stoves
> Subject: Re: [Stoves] A Premix Burner
>
>   forwarded a message from wmknauss
>
> The two short video clips were too large for the list server but I
> have included a screenshot.
>
> Andrew
> >
> > Subject: A Premix Burner
> >
> >
> >
> > I have tried everything I can think of to add some very short video
> > clips as a reply to all from either my iPhone or tablet.  Nothing
> > seems to work so I am sending my videos and comments directly to you.
> >
> > Before I read Gordon`s email I burned my 7 year old barrel TLUD in the
> > shop shop side by side with the new barrel TLUD I had recently
> > completed. This was the first time I had burned the old TLUD inside.
> > Outside in the daylight the only indication that it is burning is the
> > heat waves rising from the top.
> >
> > The design of both TLUD's is very similar except the old one has a
> > secondary combustion chamber that is made from 20ga stainless steel,
> > no insulation, and is about a quarter of the size of the new one.  The
> > primary difference with the  new one is that the larger seconddary
> > combustion chamber is lined with refractory fiber insulation.
> >
> > Much to my surprise the videos clearly show a nice blue turbulent
> > flame in th old TLUD and a light yellow flame in the new one.  The
> > pecan shell feedstock was identical in both units with around 13%
> > moisture.
> >
> > I have no idea if one of the TLUD's was burning cleaner than the
> > other, but if anyone has any ideas what is going on I would sure would
> > like to hear it. My first thought is that Paul Olivier has the most
> > experience with controlling the flame color and has probably done some
> > testing that suggests it is a cleaner flame.
> >
> > On the subject of premixing the pyrolysis gas with air it occurs to me
> > that the premixer must be separated from the combustion chamber with a
> > tube or orifice that is small enough to increase the velocity of the
> > cooler mixture and long enough to prevent the premixed from becoming
> > too hot, for the purpose of prevent the secondary flame from
> > backfiring into the premixed chamber.  A good illustration of the
> > problem is when you try to adjust an acetylene torch to a low
> > intensity flame and it backfires into the torch. That is not something
> > you want to happen in a TLUD or a torch.
>
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> End of Stoves Digest, Vol 103, Issue 16
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