[Stoves] on gasifying palm kernel shells

Fri Aug 23 23:41:02 CDT 2013

Alex,

Perhaps getting a blue flame depends both on what is happening within the
reactor (temperature, AER and moisture) and within the burner (secondary
and tertiary air/gas mixing). If a dirty gas is produced within the
reactor, even the best burner will not be able to burn this gas correctly.
I have seen several rice hull gasifiers that produce a clean gas, but the
supply of air at the burner was so poorly done. This results in a very poor
transfer of heat to the pot.

Thanks.
Paul Olivier

On Sat, Aug 24, 2013 at 9:00 AM, Alex English <english at kingston.net> wrote:

>  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/
>
>
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-- 
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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