Dear Ron,
Paul O.'s comment brought to mind a major difference between ND and FA
(Natural Draft and Forced Air) TLUD stoves.
I think that when the flow of air (?? and the resultant superficial
velocity Sv???) is low, the small combustion at the MPF (migrating
pyrolytic front) is mainly or perhaps nearly 100% of pyrolytic gases
close to where they exit from the biomass that is being heated.
But when the flow of air is higher (as in the FA in the Oorja), it is
possible for the incoming O2 to reach the surface of the newly created
char layer on the outside of each piece of biomass. This would result
in consumption of char DURING the MPF period (which is the foundation of
the TLUD stove operation),
I have not yet read the thesis (I am working in Uganda right now).
Can you or someone try to get the thesis author into this discussion?
And perhaps Dr. Prof. Mukunda also at IISc-Bangalore? And Dr. Tom Reed?
And CONGRATULATIONS to the new Doctor from all of us on the Stoves Listserv.
Paul
Paul S. Anderson, PhD aka "Dr TLUD"
Email: [email protected] Skype: paultlud Phone: +1-309-452-7072
Website: www.drtlud.com
On 6/27/2013 7:03 PM, Paul Olivier wrote:
Ron,
When char is consumed in a fan-powered TLUD, several negative factors
come into play. At the point where char is consumed, hot zones are
created, giving rise to temperatures that are truly brutal on all
types of metal. As a consequence of such high heat, the walls of the
reactor can be degraded in a matter of months, often times, in just a
few weeks.
When char is consumed, the descent of the pyrolitic front is not
uniform. The syngas generally contains a lot of CO2. An inefficiency
in heat transfer is created as energy gets released within the reactor
at a considerable distance from the pot. To compensate for this loss
in heat transfer, the operator might increase the speed of the fan,
and in so doing, make matters worse.
If syngas contains a lot of CO2, I wonder how this affects the
combustion CO and H2 within the syngas. If CO and H2 are diluted with
CO2, do they fully combust when exposed to secondary air? Is there a
link between the presence of CO2 prior to the combustion of the syngas
and the presence of CO after the combustion of the syngas?
When char gets consumed, pockets of ash are created, and they might
easily contain high levels of cristobalite. This is especially true in
the case of rice hulls, which contain high levels of amorphous silica.
When char gets consumed, the quality of the biochar produced is
compromised. Ash is not biochar, and biochar is not ash.
Thanks.
Paul Olivier
On Fri, Jun 28, 2013 at 2:43 AM, <[email protected]
<mailto:[email protected]>> wrote:
Julien and list
1. Thanks very much for providing this cite. I have read most and
find it to be a well done thesis. I wish we had more like it.
2. The concepts of char and TLUDs are in here thoroughly. But
nothing on the idea of a stove designed to make char. All char is
presumed and desired to be consumed.
3. My conclusion (would like to hear more) is that a good case
is made (not intentionally) for NOT consuming the produced char in
a TLUD (this one fan-powered and widely sold in India as the
"Oorja" (started by BP)). Very little gain in overall efficiency
as the char is consumed.
4. A major advance was his study of the importance of ash in this
"char" period as a poor radiator - thereby responsible for
(undesired) high char temperatures.
5. Most everything shown as a function of superficial velocity
(Vs) - with 16-17 cm/sec shown as key dividing point in stove
behavior.. Above which velocity one swtches from char production
to char consumption. I have not seen this before.
For his highly automated fan system, measuring Vs was
apparently not so difficult. Anyone able to give a way to get an
easy estimate of Vs, when there is only natural draft?
6. Quite a bit on the importance of low emissions of CO.
7. Good information on both the experimental and computational
side of top-lit (packed bed) stoves. Not much here for rocket stoves.
Have I got #3 right?
Ron
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Paul A. Olivier PhD
26/5 Phu Dong Thien Vuong
Dalat
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