[Gasification] woodgas truck report for last night

[John Bertl]

Jim Mason wrote:

>is it really accurate to say that the temp of the reduction zone is not 
>really relevant for tar
cracking?  and that it is really a function of the temp and dimension of the 
cobustion zone.  that all
tar cracking really happens in the combustion zone and anything that makes 
it to the reduction
zone is just going to pass through?   surely reduction zone temp is 
somewhat relevant for this tar
cracking?  after going around lots of peripheral issues, i am now confused 
about a primary issue.
such seems repeated the case with gasification i am finding.

>  so the char bed can remain at the bottom, but likely not hot enough to do 
>much good.  and the
little at the point where the fire runs out of oxygen is not enough or hot 
enough to do much, as
you note.

>the hot reaction zones are in the center of your char, not against any 
>walls  of  a vessel.

--------------------
A point to remember - the reduction zone is where endothermic reactions are 
suppose to occur.
These endothermic reactions slow to the point of not occurring at about 850 
C.  Therefore, one
should consider the char or reaction zone a COLD zone.  Heat is not produced 
here  -  Heat is
ABSORBED here.  All heat to drive the desired reactions must come from the 
oxidation zone and
be carried to the reduction zone by the moving gas.  It is the gases that 
must be hot.  Gases when flowing through material will always take the path 
of least resistance.  When "chunk" material is in a column, the least 
resistance, if steps are not taken to minimize it effects, will always be 
against the vessel walls as there will be more open area there.

As Doug says: Reduction is always immediately beginning at the point the 
fire stops, having
consumed all the oxygen. Even a smoulder well have micro reduction, but only 
incandescent
oxidation temperatures will create the depth of reduction you need.  (Right 
On Doug)

----------------
The gases will begin to cool at the point where oxidation stops and even a 
little bit before because
of radiation.  This is the major reason insulation is important.  Both the 
oxidation and the
reduction zone need to maximize energy to the reaction and not to the 
environment ie. the gasifier
shell or conduction to the pyrolysis zone.  Another point is the oxidation 
needs to be vigorous and
it needs to achieve a high temperature.

-------------------
Jim Mason Wrote
>it is starting to seem to me that insulation is close to as important as  
>many dimension issues.  the
heat loss can be tremendous both internally  and externally.  the temp 
levels of all these reactions
are obviously critical. bad insulation can quickly drop them below what will 
work

-------------------
Duh - You Bet - Right On - You Got It
The smaller the gasifier, the more important this is.

-------------------
Jim Mason Wrote
>the wood is chunk wood and a large reaction area is needed as the total 
>surface area of chunk
wood is low.  if the fuel is granular, the reaction suface is much higher, 
and reaction area volumes
can be much smaller.

---------------------
This is a factor but not as much a factor as air velocity.  Higher 
velocities will handle larger wood
chunks (the granularzation of the material becomes less significant)  the 
same as small wood
chunks or porous chunks at lower velocities.

_________________________________________________________________
Interest Rates near 39yr lows! $430,000 Mortgage for $1,399/mo - Calculate 
new payment 
http://www.lowermybills.com/lre/index.jsp?sourceid=lmb-9632-18466&moid=7581