[Stoves] T-LUD with central core: derived from Dung Berry Fireballs

[Richard Stanley]

Paul Lanny et al.,
I think the chinese briquette machine the more or less classic 6"' 
diameter,  multi holed cylindrical briquette is what you're after.
Richard...
PS., Paul; Hows the stepper coming along ?


On Oct 31, , at 9:54 PM, Paul S. Anderson wrote:

> Stovers,
>
> Lanny's comment makes sense:
>>> The central combustion [hollow vertical core surrounded by fuel in a 
>>> canister] seems to keep the top gasses lit. Could this be
>>> the gasifier "spark plug" that is needed to keep top lit application
>>> flaming when burning dificult to burn fuel?
>
> Richard commented about
>> attempting to top lite the hollow core briquette in our briquette
>> gassifying experiements in south africa. Problem was that the hole was
>> too inviting and it would [end] up being a toplit, bottom-burned 
>> briquette..
>>
>> You are right about the need for a central air feed though. Something
>> is needed to supply air up through the center at least when you are
>> trying to gassify biomass to our experience.
>
> When a T-LUD is of small diameter (such as 4 inches -- 10 cm -- as in 
> the
> Woodgas Campstove) and there is a reasonable draft of primary and 
> secondary
> air, the sustaining of the combustion is not much of a problem.  But 
> when the
> diameters are 6 inches or 8 or larger, the gases (especially if at a 
> low
> turn-down setting) can be rather wispy and/or favoring one side more 
> than the
> others.  Therefore, especially in those cases, a "flame holder" or 
> "spark plug"
> could be of great assistance.
>
> Based on the comments from Lanny and Richard, I offer an idea that I 
> have not
> yet had a chance to try, but hope to do soon.  It involves a central 
> core, but
> a specific type:
>
> 1.  The core must not allow fire (via falling embers, etc) to fall to 
> the bottom
> and to cause a bottom-lit situation.  Therefore, the core is mostly 
> closed and
> rather small in diameter.  I envision a hollow metal tube perhaps 1 cm 
> in
> diameter with perhaps two of 1/8th inch holes (about 3 mm) placed at 1 
> cm
> vertical spacing.  More holes can be added if needed.
>
> 2.  There is a clear passage for primary air to get to the bottom of 
> the
> vertical hollow core.  If there is too much passage of air, the core 
> might be
> partially closed at the top.  The tube is to end about 2 - 3 cm below 
> the level
> of the ring of secondary air holes.
>
> 3.  Initially, most of the air coming through the pipe will be primary 
> air to
> support the top-lit pyrolysis, even if that air enters the fuel area 
> laterally
> via the lower holes in the tube.  But any excess air at the top will
> essentially be secondary air providing oxygen to the combustion of 
> those
> pyrolysis gases, sustaining a flame in the center of the fuel pile.  
> This is
> the weakest spot for T-LUD combustion, even in the 4-inch fuel 
> containers.  So
> this flame will be a nice addition.
>
> 4.  As the pyrolysis proceeds downward, the top of the tube will be 
> exposed, so
> all air coming out of that end will be secondary air.  This must NOT 
> be an
> excessive amount if we want to avoid a "torch effect" of a tall 
> vertical flame
> rising substantially higher than the flames supported by the lateral 
> secondary
> air holes in the container sides.  Perhaps a "diffuser cap" to spread 
> that
> stream of air out to the sides will be necessary.
>
> 5.  Let's consider the case of when the pyrolysis is about half 
> completed.
>   a.  Any air movement in the lowest holes on the tube is of little 
> consequence
> because other primary air is entering at the bottom.
>   b.  Holes that are in the zone of flaming pyrolysis are either 
> sending extra
> air (with O2) into contact with the hot fuel and hot char (good for 
> keeping the
> center area hot) or there could be some pyrolysis gases coming into 
> the tube via
> those holes, resulting in a flaming combustion of those gases with the 
> rising
> air.  This also is good because it is acting like secondary air that is
> introduced into the heart of the mass of fuel to burn some gases, but
> constrained inside the hollow tube.  This indeed could be the
> flame-holder/spark-plug.
>   c.  Whether the air is going outward through the holes in the tube 
> or if
> gases are going inward into the tube via those holes will be 
> influenced by the
> amount of pressure (forced-air T-LUD) of the primary air AND by the
> constriction or openness of the top of the tube.  Too open at the top 
> means
> fast moving air with gases being sucked into the tube.  Too closed at 
> the top
> means only providing air with O2 outward in to the four main levels 
> (bottom
> with raw fuel, lower middle with flaming pyrolysis, upper middle with 
> char, and
> top with combustoin of pyrolysis gases in the open space because the 
> fuel level
> has shrunk downwards.
>
> This should work.  Needs lots of experimentation.  But success could 
> mean the
> ability to have much larger diameters of T-LUD gasifiers because there 
> could be
> several of these vertical hollow cores in one fuel container (perhaps 
> 60
> centimeters diameter??).
>
> Note:  We already know that large diameter T-LUD will function and 
> create
> substantial quantities of pyrolysis gases.  But the combustors (the 
> burner
> heads) to handle such quantities are not well developed.
>
> Although I like the above concept, I conclude by saying that there 
> might be
> better and easier ways of sustaining the fire and/or other ways to get
> secondary air into the center of the gases (or getting the gases from 
> the
> center out to the mixing areas with the secondary gases)
>
> Paul
> -- 
> Paul S. Anderson, Ph.D., Geography professor - Emeritus
> Telephone:  USA-309-452-7072 (residence and office)
> Internet site:  www.ilstu.edu/~psanders
> For my gasifier stoves info, go to:
> http://bioenergylists.org/contributors#Paul_Anderson
>
>
>
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