[Stoves] Mixing char/coke with raw fuels

[Paul S. Anderson]

Andrew, Tom and all,
<<<<snip/edit>>>>

>> [Paul said:] ...there are no sources of pyrolysis gases in that
char [created in the TLUD].
>
> [Andrew]:  There will still be some ...

Yes, but very little, and probably not enough to keep reworking 
(re-heating) the
char to try to extract the final pyrolysis gases.

> [Andrew]:  ...but the char will still burn [in the TLUD], have
> a try, from memory the downward rate of spread of the fire is much
> faster as the fire front only has to heat dry char to its ignition
> temperature.

Because the goal is to ultimately combust pyrolysis gases in the burner, the
mixing of TLUD-char with the new raw fuel is ESSENTIALLY adding a 
"filler" that
must be heated TO THE TEMPERATURE OF THE PYROLYSIS, not to the temperature of
the ignition of the char.  The NEW char that is being created in the pyrolysis
process will reach the char-ignition temperature (in order to sustain the heat
generation to release the pyrolysis gases), and there seems to be little
justification to have additional (the old char) char also come to the ignition
temperature (unless but unlikely that a case can be made that sufficient
pyrolysis gases could be extracted by re-heating the old char).

And the reason for the faster downward rate of the pyrolysis front is 
that there
is less biomass there that needs to be heated for releasing pyrolyisis 
gases. Fast is not good when duration of the fire is important to the 
cook.

But in the case of COAL as the raw fuel,
> [Andrew]:  ... John Davies posted about getting the high sulphur offgas
> from bitumous coal to burn

I believe this above is in reference to his TLUD that burns coal, and that the
next statement below refers to the "Mbuela" coal burning buckets in the South
African townships:

> (in ~2000 he reported people left the stove
> outside to drive off unburnt offgas and only used it once the fossil
> coal was reduced to burning coke)

> [Andrew wrote:]  I found one way to get around the
> problem was a TLUD burn but recycling sifted coke back alongside or on
> top of the fresh coal. Ronal and I had to eat a cold fish supper
> because we stayed outside playing with it too long.

I believe that John Davies was not mixing the coke/char in with the new 
batch of
coal, so what Andrew is describing is extremely interesting.  Please provide
more details about that "coal in TLUD" experiment.  Is there a theoretical
explanation as to why "coal with coke/char" would burn more cleanly than just
the coal alone in a Davies' style TLUD?

Note to "Newcomers":  Do not rush out to put coal into your TLUDs.  
John Davies'
work in 2002 and later is a very special case that I hope will someday make it
into the mainsteam of cookstoves and space heating.  I hope that John 
will tell
us about any activities in the past few years.

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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