[Stoves] Combusting woodgas: was Re: basics: Need different flame-speeds different mixture-procedures?

[Paul S. Anderson]

Dear Martin, Crispin, Jeff and all,

Thank you for your very productive comments.

Jeff wrote:  Forced secondary air is noisy.
Perhaps in some cases because of size of the units and types of 
combustors, but
not in the TLUD units by Reed and by Anderson.

Crispin, what is "The FSP stove..."  P is for Propane?

Quoting "Boll, Martin Dr." <boll.bn at t-online.de>:   (much snipped)
>
> - For wood-gas:
>
> There is a good chance that the flame blows out itself, because the speed of
> the outstreaming woodgas is too high.(Higher than 40cm per second?)
>
> For woodgas the gas-jet _must be_ slow for not blowing out. Therefore the
> turbulence is _far less_.

My observations come from TLUD gasifiers, especially the natural draft version
called the Champion Stove.

A key piece of the stove is the "concentrator disk" that is above the 
container
with the pyrolizing fuel and below the "internal chimney" that give 
draft up to
the level of the pot (so that an external chimney after the pot is not
necessary).

Important to note that the secondary air enters BELOW the concentrator disk,
coming in radially from all sides, and then upward through the (generally) 3
inch (7.5 cm) hole.  Therefore, the secondary air and the combustible 
gases are
mixing even before reaching the hole.

In this case, when operating at the higher heat setting (because of 
more primary
air being allowed to enter at the bottom) it is common to have the base of the
flame a cm or two above the disk.  Good turbulence/mixing/swirling.  It is
possible to put a bluff body into the pathway of the flaming gases, helping to
maintain the flame.

When operating at low heat settings, it is common for the base of the 
secondary
combustion to actually be below the the hole in the disk.  This is not a
problem at all.  The objective of combusting very nearly all of the gases is
accomplished.

If the hole in the disk is too small, the rising pyrolysis gases cannot 
fit fast
enough through the 3 inch hole.  Instead, some escape laterally throught the
small (3 mm or 1/8th inch) gap between the disk and the upper edge of the fuel
container.  That is a poor result.  Hole sizes of 2 inches and smaller were
found to be too small, and of 4 inches diameter or larger to be too big.

Therefore, to answer your question:
> Is this small turbulence big enough to make a comparable good mixture for
> clean burn??

The turbulance is sufficient.  I do not know if it is "small" or not.

> -Even by a normal kitchen gas-burner there is a gas-air premixture. Is this
> premixture not more necessary by a slower jet-speed coming out of the
> nozzle?

I have explained at least one way to accomplish this pre-mixing, and that the
results are excellent.

> I guess:
> There must be at least a jet-blow against a baffle to get a stable flame.

Not required.

You ask several excellent questions for which I do not have answers, but the
questions deserve quality research (such as by graduate students with equiped
laboratories and knowledgeable engineering-type professors).

> -What is the good range of speed for that? -What are good 
> combinations for pressure difference  and diameter of the
> nozzle, for a given gas/woodgas?
>
> -What is the good premixing ratio of woodgas and air? And has the premixing
> air to be preheated? (For: quicker reaction time; and/or no precipitation
> out of the woodgas?)
>
> - Would a static-mixer be helpful te reach a good gas/air mixture with low
> speed instead of a high-speed-jet?

Plea:  I hope that some person or institution will undertake these and other
research questions about woodgas combustion devices for the cookstove 
sizes!!! I will gladly assist with whatever I can contribute. (There is 
no holding back
on information about TLUD experiences.)  But such efforts are far beyond my
resources, time, and interests.  My efforts are to make TLUD technology
functional and acceptable to people who can benefit from these 
cookstoves. Others are needed for the engineering work.  I hope that 
"Engineers Without
Borders" and other qualified persons or entities will discover the academic
(and social) richness that awaits the initial researchers who examine what the
prototype developers have accomplished.  (My current progress in India will be
released at or before ETHOS 2008 in January.)

My bias shows when I say:  Within a short time woodgas technology at the scale
for household usage should be evident as a major and practical advance for
residential cookstoves and diverse biomass fuels.

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



----------------------------------------------------------------
This message was sent using Illinois State University Webmail.