Paul,
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.
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.
Alex
On 23/08/2013 8:48 PM, Paul Olivier wrote:
Yesterday I received some palm kernel shells from Malaysia, and
proceeded to run them through my 150 TLUD of only a 25 cm height.
The gasification of the palm kernel shells looked like this:
http://www.youtube.com/watch?v=IDFHPjLx08A&feature=youtu.be
I am not so happy with this result: too much of an orange flame.
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.
When I mixed in some rice hulls with the palm kernel shells, the flame
looked like this:
http://www.youtube.com/watch?v=N_sI4zKUuq8&feature=youtu.be
This represents a remarkable improvement in flame color.
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.
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.
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.
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.
Does this make sense?
Thanks.
Paul Olivier
--
Paul A. Olivier PhD
26/5 Phu Dong Thien Vuong
Dalat
Vietnam
Louisiana telephone: 1-337-447-4124 (rings Vietnam)
Mobile: 090-694-1573 (in Vietnam)
Skype address: Xpolivier
http://www.esrla.com/
_______________________________________________
Stoves mailing list
to Send a Message to the list, use the email address
[email protected]
to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
for more Biomass Cooking Stoves, News and Information see our web site:
http://stoves.bioenergylists.org/
_______________________________________________
Stoves mailing list
to Send a Message to the list, use the email address
[email protected]
to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org
for more Biomass Cooking Stoves, News and Information see our web site:
http://stoves.bioenergylists.org/
