Kevin,
The objective of the filler is two-fold:
One reason is precisely to reduce the maximum flow of primary air.
Without resistance, too much primary air can race through the loose pile
of biomass, reach too much of the biomass at the same time, and have an
excessive fire without much control. Control simply by a "gate" at the
entrance of the primary air is usually insufficient.
Second reason is that burning embers at the top of loosely packed fuel
can sometimes fall to lower areas of the fuel bed and ignite the raw
fuel there. This defeats the process of the pyrolysis front that
starts at the top and should progress slowly and uniformly downward
through the bed of fuel. That migrating pyrolytic front is THE most
important and distinguishing feature of the TLUD stoves. Ignition at
the top and having updraft are not the single-most defining
characteristics of TLUD stoves (even though that is what the name
says). Maybe I should have called it Migrating Pyrolytic Front
Gasification (or MPFG), but TLUD is the accepted name now. [And Tom
Reed always thanks me for getting away from the Inverted DownDraft (IDD)
name that was not well understood.]
Important note: When the pyrolytic front correctly reaches the bottom
of the batch of fuel, the combustion style changes to be Bottom-Burning
UpDraft (call it BBUD if you must have an acronym, but note that at the
start it was NOT IGNITED or lit at the bottom). And there is no more
migration/movement of a "gas-making" zone.
Also note: When the batch has been pyrolyzed, the burning at the bottom
is "char-gasification" and can be at forge temperatures that can damage
the metal pieces. There is still restricted flow of primary air. The
hot gases go upward. IF additional raw biomass fuel is placed onto the
top of that charcoal, it will be heated, dried, torrified, and
eventually pyrolyzed, giving additional pyrolytic gases that can be
combusted where the incoming secondary air enters. But this is NOT
operating as a TLUD stove (with MPFG). This type of bottom-burning
gasifier is well illustrated by the Oorja stove (former BP, now First
Energy) in India. It has a cast-iron cup in the bottom to protect the
other metal parts, and that cup glows red-hot after continual use.
[Technical note: Stove testing should measure separately the emissions
during each of the different combustion modes instead of just reporting
averages that include emissions from two or more combustion modes. I
think we can do some of that at this summer's Stove Camps at CREEC -
Uganda and at Aprovecho - Oregon-USA where emissions equipment is
available.]
About terminology: A bucket stove or mud stove or Rocket stove and
many others can be ignited at the bottom of a container and they do have
updraft, BUT they are NOT GASIFIER devices. So the designation BLUD is
not relevant. UD and DD and TLUD are designations historically for
gasifiers, which means that the gases are created in one place that is
NOT the same place as the combustion or other use of the gases.
Paul (James, please get this onto the
drtlud.com website in edited format.)
Paul S. Anderson, PhD aka "Dr TLUD"
Email: [email protected] Skype: paultlud Phone: +1-309-452-7072
Website: www.drtlud.com
On 5/6/2013 1:17 AM, Kevin wrote:
Dear Paul
----- Original Message -----
*From:* Paul Anderson <mailto:[email protected]>
*To:* Discussion of biomass cooking stoves
<mailto:[email protected]>
*Cc:* Kevin <mailto:[email protected]> ;
[email protected] <mailto:[email protected]> ; James
S. Schoner <mailto:[email protected]> ; Hugh McLaughlin
<mailto:[email protected]>
*Sent:* Sunday, May 05, 2013 6:33 PM
*Subject:* Re: [Stoves] [biochar] Charcoal as space filler in TLUD
reactors
Kevin,
The "charcoal as filler" is not about consuming the charcoal.
# Sorry, I missed that.
The charcoal is "almost" non-active in the pyrloysis of the new
biomass. This is a discussion about limiting air flows with a
filler that mostly is inactive in environments that are at 650 C
without oxygen.
# Why do you feel it would be advantageous to limit air flow with
an inert filler? If the char was significantly larger or smaller
than the biomass fuel, it could significantly increase pressure
drop through the bed, and would likely reduce maximum flow.
# Thanks.
[ Note that I avoid using the word "inert" in this discussion.]
Best wishes,
Kevin
Paul
Paul S. Anderson, PhD aka "Dr TLUD"
Email:[email protected] Skype: paultlud Phone: +1-309-452-7072
Website:www.drtlud.com
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