[Terrapreta] new address to the simple kiln

[Philip Small]

Ron:

My understanding is that Folke's design is inverted downdraft (aka top lit
updraft) based on how Folke first described the workings of it to the list.
It was a very brief reference and perhaps my enthusiasm for TLUD (I caught
that from you, actually) caused me to read more into it than Folke intended,
but I am pretty sure Folke is top lighting this beast.  I was especially
persuaded by the clean burn in the photographs with the size fuel shown.
Clean flame isn't the norm with a bottom lit open can.

Folke's design is pioneering in its simplicity and effectiveness.  It
deserves to be extensively promoted.  I wrote it up this weekend into a FAQ
I am working on with some others on the list.  (Ron, please let me know if
the explanation of how gasification works in this context is correct):
2.05 Isn't making a lot of smoke kind of un-neighborly?

Smoke can be a nuisance when it isn't your own. The considerate option when
you are close in to a neighborhood is to use a (nearly) smokeless approach.
In some jurisdictions, generating smoke is more than un-neighborly, its
illegal <http://www.pscleanair.org/actions/woodstoves/opacity.aspx>.
 2.06 What are some nearly smokeless approaches to making charcoal for the
gardener?

*Choose your feedstock wisely.* No matter what technique you use to make
charcoal <http://terrapreta.bioenergylists.org/makingcharcoal>, choosing
uniformly sized, dry woody material produces the highest yields. Uniformity
is one reason that colliers will routinely use coppiced
hardwoods<http://www.fellsanddales.org.uk/trails/greenwood_trails.php#products>
.

*Inverted Downdraft Gasification.* For a cleaner burning configuration,
consider a Top Lit Updraft<http://www.bioenergylists.org/en/taxonomy/term/113>
 (TLUD) technique, also referred to as inverted downdraft gasification.  The
technique looks simple but in reality it involves some fairly sophisticated
principles (PDF <http://www.woodgas.com/Superficial+Velocity.pdf>). That
doesn't prevent success using common materials and dead simple
design<http://www.garlington.biz/Ray/WoodGasStove/>.
Take that same open barrel configuration [described in 2.04], tweak the
design per the aforementioned sophisticated principles, and now light it
from the top instead of the bottom.  This takes a different skill set than
lighting from the bottom but it's also not that difficult to master.  A
little vaseline or ethanol on a cotton ball can work wonders for starting
up. Once the fire gets going, the top layer of wood burns, creating
charcoal, naturally. The heat from the top layer burning warms the wood
below it releasing combustible and noncombustible gases which flow up into
the charcoal layer. Glowingly hot charcoal has a wondrous ability to strip
oxygen molecules from of anything that passes over it, so it converts the
water into hydrogen, and the carbon dioxide into carbon monoxide. These two
gases are flammable.  They join with the other flammable gases released from
the fuel.  These ignite as they mix with air coming into the top of the open
barrel above the charcoal layer. The result is a scrubbed gas-fed flame that
is much more controlled, and which burns substantially cleaner and hotter
than can be achieved with the bottom lit burn barrel.
(Source<http://cbll.net/articles/dev-world-gasification>).
Insufficient oxygen below the combustion zone impedes loss of the charcoal
despite the high temperature flame immediately above it.  This allows
charcoal to build up faster than it is consumed, at least until the
pyrolysis zone reaches the bottom of the fuel column. The downside is that,
while wondrously clean burning in even the simplest configurations, a TLUD
won't achieve its 20-30% charcoal-to-fuel yield potential without tricking
it out to pre-heat and damper the intake. Thankfully, Folke Günther has come
to our rescue.

*Folke Günther's* *simple TLUD-fired Retort.*  A retort works by restricting
the air supply to the target feed stock for the duration of the burn.  An
outside heat source pyrolyzes the retort contents, small openings in the
retort allow wood gas to escape, but restrict the flow of oxygen in.  While
retorts are capable of very high yield efficiency, the open flame used to
fire the retort is not as clean as can be achieved with a gasifier.  In
small retorts, a further inefficiency is that wood gas generated from the
retort can end up blowing by the combustion zone without being burned. Folke
Günther's elegant
solution<http://terrapreta.bioenergylists.org/gunthersimple0408>is to
combine a
TLUD with a retort.  This is easily the simplest, cleanest burning and
highest yielding method we know of to make garden-sized batches of charcoal.

(Source <http://www.holon.se/folke/carbon/simplechar/simplechar.shtml>)





On Tue, May 27, 2008 at 7:58 AM, Ron Larson <rongretlarson at comcast.net>
wrote:

>  Folke:
>
>     1.  I like your advance a lot - and suggest it may have
> considerable merit in third world cooking.  You did an excellent job in the
> photos and explanations. Some questions:
>
> a.  What is the weight yield for char in the interior can?   A typical
> number for charcoal-making stoves is 25%.  Yours could be higher as there is
> no "flaming pyrolysis" (less carbon conversion to CO?) in the interior can.
> b.  What is the ratio of weights for the exterior combustable wood to the
> interior pyrolyzable wood (before the interior can stops pyrolysis gas
> emissions)?  I.e.  What is the minimum mount of exterior fuel required?
> c.  How long did it take before you could see pyrolysis gases coming from
> the interior can?
> d.  How long before the entire pyrolysis operation was completed?
> e.  Have you tried leaves,grasses, and twigs packed tightly in the interior
> can?  These are hard to combust in stoves but still could become valuable
> biochar.
>
> 2.  Some background on how this relates to charcoal-making cookstoves:
>     a.  The "sister" companion stoves list was started about a dozen years
> ago as an offshoot of Tom Miles' Bioenergy list.  Most of our first
> stoves-list discussion was a result of my describing experiments with
> top-lit stoves with controllable primary air supply.  Tom asked me to be the
> first stoves list coordinator, but one will also see some earlier
> charcoal-making discussion in the bioenergy list archives (assuming those
> still exist).
>     b.  I think there must have been some discussion ten-twelve years
> ago of interior cans of the type you describe;  I certainly tried some, and
> they of course worked as you have described.  But I was not doing what you
> have described - as I had my mind fixed on top-lighting.  In those early
> days, we had some discussion of a well-known Indian researcher's (name
> forgotten) efforts to promote an inverse version on yours (a central flame
> within a toroidal outer pyrolysis chamber.  Top loaded - major difficulties
> in sealing.  The design never took off.
>     c.  The top-lit charcoal-making stove has not taken off as I had
> hoped (in later years, for terra preta/biochar reasons).  There are three
> main reasons I think for that failure.
>         -  One is that a top-lit design is strictly batch operated; your
> design overcomes that because you can add more exterior fuel at any time
> With some modifications in your approach, you could add new fuel at the
> bottom rather than the top.  I suppose that one could find a way to replace
> the interior can - maybe even have the second can move down from an early
> higher position (and itself be replaced by a third can).  It would be nice
> if the lower air supply could be made conrollable (commercial versions maybe
> using a speed-controlled fan??   I found that a ceramic conical "plug" in
> circular holes worked pretty well - compared to sliding "windows".
>         - The second is that it is messy to shut down, assuming you have
> finished the cooking job with just the right amount of starting fuel
> (reference problem #1)  Lots of smoke when the pyrolysis front gets to the
> bottom -until you open up the lower primary air supply and start consuming
> the char (which we on this list want to save for soil augmentation).  Your
> design solves that problem also (assuming that you only see minimum noxious
> gases at the end??).
>         -  The third problem is getting the charcoal out after cooking is
> over.  It is hard ( and messy and somewhat dangerous) to extinguish the hot
> charcoal when you have primary and secondary air ports and a flame exit.
> Your design also solves that problem apparently.  As you note, the interior
> can can have a removable bottom "lid".
>
> 3.  This is to urge others to follow Folke's important suggestion about
> being able to cook with this alternative interior-pyrolysis-can design.  I
> spent some months in Ethiopia trying to perfect a charcoal-making design
> (batch type, top-lit, primary (with control) and secondary air supply) for
> the cooking of enjira.  This is a (delicious) thin sourdough flat bread
> cooked on a homemade thick ceramic disk (a "magogo"), of about 60 cm
> diameter.  Has to be one of the most inefficient cooking methods around.  I
> think there is a fair chance that Folke's approach could work there (steel
> (tefloned??) cooking surface being preferred), with this plate maybe sitting
> on top of the interior can.  This might also be applicable (at least
> outdoors) with the la plancha metal cooking surfaces used throughout the
> Spanish-speaking Americas.  There are probably ways to move this indoors
> with a chimney.
>     I emphasize that my main justification for further research by this
> list is charcoal production.  But it is also a way of cutting costs
> (assuming future carbon credits) for the roughly 3 billion of the world's
> population cooking at least part of the time with wood.  (Also of course
> increased food production and use of scrap fuels not otherwise combustible
> and headed at least partly towards unwanted methane.)
>
> 4.  I kick myself for having been too top-lighting centric.
> Congratulations to Folke.
>
> Ron
>
>
>
> ----- Original Message -----
> *From:* folke Günther <folkeg at gmail.com>
> *To:* 'Terra Preta' <terrapreta at bioenergylists.org>
> *Sent:* Monday, May 26, 2008 8:01 PM
> *Subject:* [Terrapreta] new address to the simple kiln
>
>  See http://terrapreta.bioenergylists.org/gunthersimple0508
>
> ---------
>
> A complete description of the simple charring methods for home garden is
> now at http://www.holon.se/folke/carbon/simplechar/simplechar.shtml
> I saw that there is an older address at the terrapreta list. I use it to
> cook the dinner wok at the same time as I am burning the charcoal.
> Sending you a picture of that too asap.
> YS
> FG
>
> --
> NB :Send your mails to folkeg at gmail.com, not to holon.se
> ----------------------------------------
> Folke Günther
> Kollegievägen 19
> 224 73 Lund
> Sweden
> Phone: +46 (0)46 141429
> Cell: +46 (0)709 710306
> URL: http://www.holon.se/folke
> BLOG: http://folkegunther.blogspot.com/
>
> ------------------------------
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-- 
Philip Small, RPSS
Land Profile, Inc. * PO Box 2175 * Spokane, WA 99210
509-844-2944 cell * 509-838-4996 fax * 509-838-9860 office
Profile: http://www.linkedin.com/in/philipsmall
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