[Stoves] Wendlelbo's : Re Large TLUD --- TLUD Stove history

Mon Aug 29 11:43:21 CDT 2011

Dear Paul

I hope you will recall my demonstrating to you a concentrating cone on a
Vesto coal stove with a side chimney in April 2003. You may remember the
unusual shape of the cone top which sat on the top of the combustion
chamber. It was removable. See the attached photo.

It was into this cone shape that John Davies put his secondary air holes fed
by the rising preheating secondary air (a-la-Vesto preheater).

This cone is not necessary as it is possible to generate the same effect by
correctly sizing the air in-feed as per the 2004 Vesto. The incoming
preheated air creates the 'concentration' and gives the same result without
the metal part. This reduces heat lost, lowers the cost and increases the
combustion efficiency (lower CO/CO2 ratio).

The POCA Stove in Maputo (MCS) used the lesson from the Vesto combustion
chamber (125 mm) to create the same thing in a much larger diameter (200mm).
This is possible because the gas flow rate in the POCA is much lower. The
secondary air drifts center-wards over a cone shaped pile of fuel. This pile
shape is also developed automatically by the bowl-shaped combustion area
(very unlike a JIKO which is flat and not removable). The bowl shape and
slope are critical and are based on the surface roughness of the material.
The Malawian all-metal Pulamusa designer copied the POCA idea but without
the understanding of why the slope is what it is, so it does not work as
well as the original.

The fuel can be piled into the POCA and after a while it automatically
creates a pointed cone of coals with secondary are flowing over it injected
horizontally from the periphery. The hot air has a tendency to rise,
creating an inward drifting cone of secondary burn. Under ideal conditions
it creates a 20mm thick conical layer of blue flame hovering over all the
coals, tending to the centre, with the top point just touching the centre of
the pot. The gases then travel outwards radially under the pot giving
maximum heat transfer - about 60% efficient in that condition.

A similar overall effect was achieved by Joao da Concaciao in Maputo with
his locally made mild steel 125mm Vesto combustion chamber in a 10" clay
pipe body. I measured 53-55% system efficiency burning charcoal (water
boiling).

Regards
Crispin

+++++++

Wendelbo in the 1990s and Anderson in 2005 brought together the gases into a
central hole, which seems a more appropriate use of "concentration while
bringing together."

Whatever the name, Reed and Larson missed it and Wendelbo and Anderson got
it right.

The rest of your message (below) gives an excellent description of why
bottom-lit fires are more smokey and harder to control.  If we could now get
more people to read and understand that message (which is the same from the
"early days" or from "present day writings"), we will eventually get the IDD
/ TLUD technology into the minds of the the Stovers and eventually to the
people who use the stoves.

Paul
--
Paul S. Anderson, PhD
Known to some as:  Dr. TLUD    Doc    Professor
Phone (USA): 309-452-7072   SKYPE: paultlud   Email: psanders at ilstu.edu
www.gtz.de/de/dokumente/giz2011-en-micro-gasification.pdf   (Best ref.)

>
>  Anderson wrote:
>> Those stoves only got that TLUD name  
>> in 2005, and were first named "Top-Lit UpDraft" in 2004 in the  
>> Anderson-Reed document at the LAMNET conference - found at the Stoves  
>> website).  From 1985 to 2005 Reed called the technology IDD, for    
>> Inverted DownDraft.)

> Heggie wrote:
> If one considers the strict interpretation of the terms then the IDD
> gasifier is more correct, it implies air control, Top Lit UpDraught can
> be applied to any fire that is toplit and then develops as an updraught
> fire and indeed in the early days of this list its use was explained by a
> person involved with masonry stoves in US domestic buildings. The reasons
> behind it are simple, if one lights a heap of biomass at the bottom the
> small amount of heat initially allows a low temperature burn of the char
> initially formed, most of the fire smoulders and heats the layers above
> to dry then pyrolise them. As things get hotter a flaming region under
> the fuel develops but the offgas is diluted by combustion products, water
> vapour and is quenched by the fuel it is heating up. The fuel:air mix is
> wrong to allow the flame to propagate. Freshly formed char will ignite at
> low temperatures but gases need a flame or to be above their autoignition
> temperatures to burn. Hence lots of smoke until a flame establishes at
> the top. If the fire is top lit all the combustion products are exposed
> to fresh air and a flame as an ignition source without having to pass
> through a mass of cold fuel wood. The only restraints on air supply are
> the natural air movements.
>
> This differs from the gasifier or pyrolyser concept which inherently
> control the air supply to restrict combustion to that necessary to gasify
> ( about 1/6 stoichiometric air for combustion) or pyrolyse ( less still)
> the biomass. Even The initial demo Tom Reed talks of has the shielding of
> the cigarette paper restricting air to that blown from below.
>
> AJH
>
>
>
>
>
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