[Stoves] Comments about T-LUDs

[Kevin Chisholm]

Dear Paul

Thanks for the interesting comments on TLUD's...

To inquire further on one thought... "Is the J Stove a gasifier?"

In the past, effort was expended to define gasification and gasifiers, to 
little avail. Biomass combustion is not possible without gasification. To 
employ the terms "gasify", "gasifier". "gasification"  in connection with 
"biomass combustion" is redundant, and therefore unnecessary.

The reality is that any stove is a gasifier stove, because they all employ a 
process for conversion of a solid (or liquid) into a gas, so that combustion 
is possible. A "wheeled automobile", a "winged aircraft", and a "gasifier 
stove", would all seem to be in the same league. Are there any automobiles 
that don't have wheels, aircraft that don't have wings, or stoves that are 
not gasifiers?

In general, it appears that "gasifiers are devices that convert solids or 
liquids into gases for consumption elsewhere." Clearly, Doug Williams 
gasifiers are "gasifiers". One can ask the following questions about such a 
gasifier:
" How is the gas going to be used? Is it going to be used for an engine, for 
direct combustion, or as a feed to a chemical process?"
"How far will the gas be piped or ducted to the point of use?"

Similarly, an updraft gasifier producing a cold tarry gas suitable for 
combustion in one or more burners is also a "gasifier". Since the gas is 
very dirty, requiring extensive cleaning for engine use, and since it could 
not be transported very far without plugging and maintenance problems, it is 
clearly a different kind of gasifier. However, there is the clear and 
distinct similarity that there is definitely a purposeful separation zone 
where no combustion is taking place, and where combustion would be 
detrimental to the intent of the device or system

On the other hand, it appears that stoves are devices that want to convert 
the fuel into a gas, and complete the combustion process as quickly and 
completely as possible.

Consider an open bonfire... it converts the fuel to a gas, and burns the 
gases above the fuel bed. It could perhaps be defined as a "close coupled 
gasifier combustion system." If a box was put around the bonfire, then it 
could perhaps be called a "close coupled gasifier stove". However, the prime 
purpose of both of these systems is immediate combustion, while true 
gasifiers have remote gas utilization of the gas as their design intent.

The key differentiating issue between a "stove" and a "gasifier" would seem 
to be: "Is the intent of the design to permit utilization of the gas at a 
significant distance from the point of generation?"

If this is the key issue, then a "close coupled gasifier stove" is a stove 
system, and not a gasifier system.

Does this hang together for you?

Best wishes,

Kevin



----- Original Message ----- 
From: "Paul S. Anderson" <psanders at ilstu.edu>
To: "AJH" <list at sylva.icuklive.co.uk>
Cc: <stoves at listserv.repp.org>
Sent: Friday, October 06, 2006 2:06 AM
Subject: Re: [Stoves] Comments about T-LUDs


...del...
***************************
Next topic is the ¡§J¡¨ stove, starting with comments by Tom Reed and by 
AJH:

Tom Reed wrote:
The "J" stove, developed about 1984 by Mike Antal at U. Hawaii and Peter
Verhaart (?) in the Netherlands is a VERY simple true downdraft
gasifier.  I hope this gets comments from both on the origins and maybe
some pictures of the J stove.  The J stove probably formed my
development of the TLUD in 1985.

AJH wrote in reference to the above note:
Peter has posted to us about his downdraught barbecue stove so I think
you are right. Also when Elsen was making his chardust he used just
such an approach as a pyrolyser and flare.

The thing that strikes me about both down draught and top lit
updraught (alias inverted down draught o.k. Martin ;-)) is that the
incoming air keeps the mass of fuel outside the active zone cool, so
this limits how much fuel is undergoing reaction at any one moment
without the need to add fuel in Paul's trickle feed fashion.

Paul replies:
A.  For clarification, I only described and named the ¡§trickle fuel¡¨ or
¡§trickle feed¡¨ way of adding fuel.  I was not the first to use that 
method,
and I certainly am not advocating it and do not want it attributed to me.

B.  I want to question whether or not a ¡§J¡¨ stove is a gasifier.  My
¡§test¡¨
of what is a gasifier revolves around the creation of the combustible gases
SEPARATELY IN TIME AND PLACE from the combustion of those gases.  The
separation can be as little as fractions of seconds and only millimeters of
space, but those separations are identifiable.  And in practice, it should 
be
possible for the gasification (gas-making) stage to be sustainable WITHOUT
combustion of the created gased (resulting in a smoky mess), but the whole
process is controlled and the combustion can be re-ignited or
extinguished with
only a modest effort.  Simply to have smoldering tips of sticks in a J-stove
would not be sufficient to show the sustained gas-making function necessary 
to
qualify as a gasifier.  But use of a fan to assure continuing flow of 
primary
would be allowed and, in fact, be necessary for the gasifier to function 
when
the combustion was extinguished and the draft from the chimney is weak or
absent.

The key issue, as I see it, is in the physical nature of the fuel mass and 
the
ability of the primary air to pass through the fuel with appropriate
resistance
to maintain a zone of pyrolysis or char gasification.

If the fuel is a collection of loose sticks, IMHO the result will be a 
rather
traditional fire that burns the sticks without meeting the above stated
requirement of separation of gas creation from gas combustion.

If, on the other hand, the fuel is like a pile of woodchips as used in the
WoodGas CampStove and other T-LUD gasifiers, I believe that the J-stove 
could
be operational as a gasifier of some sort (DD or IDD or ¡§J-DD¡¨ as in
¡§J-stove-DownDraft¡¨), especially if some provision for entry of
secondary air
is made for combustion of the created gases.

In the case of Peter V.¡¦s barbecue stove, it might operate either way.  I 
do
not know about Elsen¡¦s device.  And maybe Tom can tell us more about what 
he
saw in 1984 with Mike Antal in Hawaii.  I do know that the gigantic
¡§J¡¨ style
burner in the building where we had Stove Camp 2005 on the Aprovecho
Campus was
operated with loose sticks and did sustain a nice traditional fire that
was not
being operated like a gasifier.

************************