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 <[email protected]> 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/ > > > _______________________________________________ > Stoves mailing list > > to Send a Message to the list, use the email > [email protected] > > to UNSUBSCRIBE or Change your List Settings use the web > pagehttp://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/ > > > -- 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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