Re: Heating Stoves

[AJH <andrew.heggie@dtn.ntl.com>]

On Fri, 26 Oct 2001 10:19:03 -0600, "Ron Larson"
<ronallarson@qwest.net> wrote:

>
>>
>> How well could they be made to work with green, or semi-green wood
>> chips?
>>
>    (RWL) to Harmon.   I think all (?) of us working with charcoal-making
>stoves (CMS) would caution against any but the dryest woods.  It may even be
>that in humid parts of the world that "dry" wood is not sufficiently dry.
>This could be a major difficulty that I don't believe has been adequately
>explored in actual practice.   (Tom Reed reported on some tests maybe a year
>ago.)  If such stoves were in wide use in humid locations, I guess that the
>next day's fuel would be being dried in racks with the combustion gases or
>with heat radiated radially from the stove itself.  Whether this is a major
>drawback for the CMS remains to be seen.

Ronal I guess you and I will have to disagree on this terminology,
Tom's IDD is preferable to me because it is descriptive, whilst
charcoal may be a byproduct of the idd stove it is not the best way of
yielding charcoal. Here we need to be a bit careful about what we are
calling charcoal, as a charcoal producer I want to maximise my weight
of charcoal from a given weight. There are a number of ways of doing
this, one is to keep the temperature low, this gives a product that
still contains a high amount of volatile material but has lost its
strength and woody character, it is high volatiles charcoal. I have
achieved yield of 45% of dry weight, even though the maximum fixed
carbon is only 35%. The idd stove at best achieves 25%, still highish
volatile charcoal, hence whilst it is better than a crude clamp of wet
wood it is not the route to producing charcoal, please see my further
post on coal burning about reuse of char.

The other means to increasing yield of *carbon* in pyrolysis is
reported in Mike Antal's work where he appears to crack pyrolysis
products back to soot which remains in the char matrix due to the
patented process.



>.
>    (RWL):   I think the emphasis on a CMS should be on the "fact" (still
>needs more proof) that this is the cleanest-burning stove around.  In my new
>view, the charcoal co-product is valuable where people want and are using
>charcoal for whatever reason - but charcoal is now not the reason for
>further development.  If you have no use for charcoal - there are probably
>better (not necessarily cleaner) ways to do your cooking or heating.   I
>still have not seen a good design for combusting the charcoal after making
>it, in the stove that makes it.  Doesn't say it can't be done - but no one
>has yet reported data showing that the efficiency was high nor the output
>readily controlled when the charcoal was consumed in the container in which
>it was manufactured.

Again I think the charcoal can be recycled into an idd burn, it leads
to a dilution of the offgas cv but I hope this is not a problem in
terms of pollutants. As I spouted off before I think Alex demonstrated
the offgas from the idd pyrolysis front is fairly constant, I believe
as long as the fuel is homogeneous that inclusion of char as an
admixture to the charge will maintain constant conditions. Worse case
is that the char must be *quickly* washed free of ash and dried before
reuse.

>    (RWL)   "Last" point -  chips (and lots of other small waste material)
>might still be possible with a natural-draft CMS if configured in the
>"holey" briquette form.  Not enough work reported yet on this combination.

I have burned all sorts of chipped dry garden waste in idd mode and
natural draught once the initial burn has been initiated with a fan.
As Ronal has noted this can be scaled up but a diffuse flame becomes
very difficult to sustain in larger (up to 25cms) diameters. This is
where the various mixers should have an effect, my tallest idd stove
is about 2m high.

AJH

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