[Stoves] on gasifying palm kernel shells

[Alex English]

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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