[Stoves] Ph.D. Thesis on TLUD Stoves.

[Tom Miles]

Paul,

 

The typical impact of higher CO2 is to reduce combustion temperatures and
make producer gas combustion less stable.  As dilution increases and
temperatures decrease in upper regions I would expect to see an increase in
unburned CO. You should be able to measure differences with a small probe
and thermocouple.  

 

Tom

 

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of
Paul Olivier
Sent: Thursday, June 27, 2013 5:04 PM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Ph.D. Thesis on TLUD Stoves.

 

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, <rongretlarson at comcast.net> 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
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Dalat
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