[Stoves] on gasifying palm kernel shells

[Paul Olivier]

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/
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