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<div class="moz-cite-prefix">Paul,<br>
I am told that flame colour is linked to gas species and
temperature. Yes I have seen blue flames from charcoal fires.
However the bottom or base of a candle flame in earth's gravity is
also blue. That is a hydrocarbon combustion flame not a CO
combustion flame. It is due to excellent mixing with oxygen.
Convection due to gravity creates a column separation between gas
fuels and the surrounding oxygen/air. In zero gravity the candle
flame is a blue dome. Inject air into a candle flame in earth's
gravity and you can turn it blue. The same is , or can be, true
for pyrolysis gasses from a TLUD. However turning it blue is
somewhat misleading. What we are also doing is eliminating the
dominant colours of yellow and orange by not giving soot a chance
to form and glow.<br>
<br>
I have achieved blue flames with wood pellets in a TLUD when the
maximum process temperature in the descending reaction zone was
500C +/- . I don't know the answer to your question but I suggest
there are other possible explanations.<br>
<br>
Alex<br>
<br>
<br>
<br>
On 23/08/2013 8:48 PM, Paul Olivier wrote:<br>
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<div>Yesterday I received some palm kernel shells
from Malaysia, and proceeded to run them through
my 150 TLUD of only a 25 cm height.<br>
<br>
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The gasification of the palm kernel shells looked
like this:<br>
<a moz-do-not-send="true"
href="http://www.youtube.com/watch?v=IDFHPjLx08A&feature=youtu.be">http://www.youtube.com/watch?v=IDFHPjLx08A&feature=youtu.be</a><br>
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I am not so happy with this result: too much of an
orange flame.<br>
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<div>But I am not sure of the moisture content of
these shells, and I doubt that they were in the
ideal 10 to 12% range.<br>
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When I mixed in some rice hulls with the palm kernel
shells, the flame looked like this:<br>
<a moz-do-not-send="true"
href="http://www.youtube.com/watch?v=N_sI4zKUuq8&feature=youtu.be">http://www.youtube.com/watch?v=N_sI4zKUuq8&feature=youtu.be</a><br>
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This represents a remarkable improvement in flame color.<br>
<br>
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I am trying to understand why rice hulls have they effect
that they have, either when processed alone or in
conjunction with some other material. There is the initial
combustion reaction that provides a lot of heat to the
process. This reaction gives rise to a lot of CO2. But the
water gas reaction, the water shift reaction and the
methane reaction do not convert this CO2 into CO. It
appears that there is only one reaction that can do this:
the Boudouard reaction where C + CO2 gives CO.<br>
<br>
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Let us suppose that if the biomass is at 10% moisture
content and if the AER is at 0.3, the temperature at the
combustion reaction reaches 800 C or more. According to what
I have been able to understand from Tom Miles, it is at this
temperature that the Boudouard kicks in. But if the gas
expands quickly and cools off after the combustion reaction,
the Boudouard reaction will not take place. So we end up
with a dirty gas full of CO2.<br>
<br>
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But if rice hull char situated above the gasification front
provides a lot of resistance to the flow of gas and does not
allow the gas to expand and quickly cool off, then it could be
possible for the Boudouard reaction to take place, even in a
small TLUD. When CO burns, it does so with a blue flame, and
if enough CO is present in the gas, the flame color is a rich
blue.<br>
<br>
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<div>If there are relatively large spaces into between the palm
kernel shell char above the combustion zone, the gas quickly
expands and cools off: no Boudouard reaction and a lot of
dirty gas is produced.<br>
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Does this make sense?<br>
<br>
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<div>Thanks.<br>
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<div>Paul Olivier<br>
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<div>-- <br>
Paul A. Olivier PhD<br>
26/5 Phu Dong Thien Vuong<br>
Dalat<br>
Vietnam<br>
<br>
Louisiana telephone: 1-337-447-4124 (rings
Vietnam)<br>
Mobile: 090-694-1573 (in Vietnam)<br>
Skype address: Xpolivier<br>
<a moz-do-not-send="true"
href="http://www.esrla.com/" target="_blank">http://www.esrla.com/</a>
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