[Stoves] Request for help on TLUD operating data

[Julien Winter]

Hi Ron;

I have been working on aspects of this.  I ran some experiments earlier
this summer that showed that burner design had an impact on mass loss
rate.  What was most important, over the range of models I tested, was how
the secondary air was introduced.  I am going to circulate a couple of
summaries of those experiments shortly.

What I wanted was to find a burner that was reasonable reliable over a
range of fuel moisture contents and primary air rates.  What I have chosen
is a conventional burner with circular air holes for secondary air, but the
burner is about 1.2 x the diameter of the TLUD combustion chamber.  There
is a narrow concentrator ring above the secondary air holes with a aperture
the same diameter as the combustion chamber.  The purpose of the ring is to
prevent flamelets rising vertically from the air holes or between air
holes.  These occasional aberrant flamelets can produce smoke.  This
concentrator ring does not function like the traditional ring, which has a
much narrower aperture.

Now I have a burner I am happy with, I have moved on to the more serious
experiment, using a 17 cm diameter, 25 cm tall TLUD.  My objective is to
study TLUD pyrolysis over a range of primary air rates and fuel moisture
contents.  What is crucial for soil scientists using TLUD biochar is the
temperature at which it is produced.  So far, I have not seen much data on
that, so I am getting my own.  What is the maximum temperature of the
flaming pyrolysis; what is the minimum temperature in damp fuel at low
primary air?

I am measuring temperature profiles on two kinds of wood chips and one type
of softwood pellets, over a range of moisture contents, and over a range of
primary air rates.  In the end, I will have a fairly good profile of TLUD
operation.  It is going to take me a month to complete the experiment.

I have attached some sample temperature data.  The plots show the arrival
of the pyrolytic front at depths of 20, 15, 10, and 5 cm above there
grate.  The velocity of the pyrolytic front can be determined by the time
separation between the temperature traces.  One can see that in wood
pellets, the velocity accelerates slightly as the front descends the bed.
The rate of mass loss can be estimated from the velocity, if one assumes
that the proportion of fuel gasified is constant.   At the moment, I
directly measure the mass of TLUD and fuel before ignition, and after the
end or pyrolysis.  I am looking into measuring mass loss more frequently
(but I have a hanging balance, so I must try not to get cooked).

The technique I am using is common in the literature where 'TLUDs' have
been used to model moving grate gasifiers, so there is a lot of data at
superficial velocities in the range of forced draft TLUDs, on up to full
combustion in the fuel bed.  The first paper was by Stubington, JF; Fenton,
H.  1984.  Combustion Characteristics of Dried and Pelletized Bagasse.
Combustion Science and Technology  37: 285-299.  A recent paper was by
Mahapatra, S; Dasappa, S.  2014.  Experiments and analysis of propagation
front under gasification regimes in a packed bed.  Fuel Processing
Technology 121: 83–90.   In between those two dates there must be a dozen
or so papers.   No similar research has been published for ND-TLUDs.  That
is a deficiency I am aiming to fill.

I am planning to circulate the results of my experiment when it is
completed.

Cheers,
Julien.



-- 
Julien Winter
Cobourg, ON, CANADA
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20140813/996556bd/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Temperature_1.pdf
Type: application/pdf
Size: 946234 bytes
Desc: not available
URL: <http://lists.bioenergylists.org/pipermail/stoves_lists.bioenergylists.org/attachments/20140813/996556bd/attachment.pdf>