[Stoves] Increasing ND-TLUD riser height accelerates gasification and increases bed temperature

[Julien Winter]

Hi Jock;

Thanks for your comment "Tweak one [design parameter] and you tweak them
all".  The interactions in ND-TLUDs are interesting.  We don't see them so
much in FD-TLUDs because the fan overrides all.   I developed the burner I
am using with prototype tin-can TLUDs and found that the gasification rate
was higher over the whole power curve with moderately large secondary air
holes.  The size of the air holes can't be too large, however, because as
they become larger they structure the air jets less and less, and you also
end up with big gaps between the holes.  I have found that round holes are
better than rectangular holes, because the round holes are better at
self-regulating the flow of secondary air as the flame size changes.

Geometry and placement of secondary air holes can affect the distribution
of burner draft between primary and secondary air.  Paul Anderson made an
interesting comment to me the other day.  He wondered if as the size of the
gas flame increased, the flame became more fuel rich.  Perhaps he will
elaborate on this for us.

The burner I am using is simple and robust.  There are, of course, other
approaches to burners, as you and Kirk Harris have shown.


All the best,
Julien.

On Fri, Dec 12, 2014 at 8:19 AM, Jock Gill <jock at jockgill.com> wrote:

> Julien,
>
> If you increase draft  you will increase the "pull" on both secondary air
> and primary. This should allow you to reduce the size, amount, of the
> primary air holes.
>
> If you increase the amount of secondary air you will reduce the amount of
> primary air. It is easier to pull in secondary air than primary. The draft,
> primary and secondary air are all tightly coupled in a non linear system.
> It might be linear if the resistance in the fuel bed were a constant, but
> as the fuel is pyrolized the resistance is constantly changing.  And of
> course the variable amount of heat as the process progresses also
>  contributes to the non linearity of the system.
>
> Tweak one and you tweak them all.
>
> Cheers,
>
> Jock
>
> Jock Gill
> P. O. Box 3
> Peacham, VT 05862
>
> google.com/+JockGill
> <https://plus.google.com/_/notifications/emlink?emr=02164940119180120523&emid=CIn6jOiavboCFcgLTAodARYAAA&path=%2F102260924343967128597%2Fop%2Fu&dt=1383089746165&ub=50>
>
> Extract CO2 from the atmosphere!
>
> On Dec 11, 2014, at 7:20 PM, Julien Winter <winter.julien at gmail.com>
> wrote:
>
> Hi All;
>
> Attached is an "experimental vignette".  It is a report on a small
> experiment conducted to get a better understanding of natural draft TLUD
> design.
>
> The height of the riser above a gas burner was doubled.  The resulting
> increase in draft in the burner resulted in faster gasification rates and
> higher temperatures in the TLUD.   Besides riser height, I have found
> that a number of design elements of the gas burner can increase
> gasification rate such as the size of secondary air holes.
>
> I have a few more of these experimental vignette to come, such as how
> creating a vortex flame may not be a good idea, and how heat is lost from
> the side walls of the reactor, and a reasonable heap on reactor temperature
> for different fuels.  Now that snow is on the ground in Southern Ontario, I
> have more time to analyze data.
>
> All the best
> Julien
>
> --
> Julien Winter
> Cobourg, ON, CANADA
>
> <Height of gas burner riser.pdf>
>
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-- 
Julien Winter
Cobourg, ON, CANADA
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