Smokeless (sootless) combustion of vegetable oil

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  • #26
chemisttree
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So, have you given up on the wick/precipitator idea? Is cleaning the precipitator from time to time a problem? For your burner, how do you intend to use it? Is that purpose likely for a device that uses the blue swirl? Blue swirl needs a long chimney. For a precipitator equipped device?
 
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Well... an electrostatic precipitator suitable for this application should be designed, of course. And it should be effective, in the sense that it must capture more than 99% of the input soot. Cleaning the elements would not be too big a problem as long as "from time to time" is not once in a day or the like... I guess that burning a potentially smokey substance as oil - even vegetable, not mineral - would release quite a good deal of soot. As I mentioned in a previous post, the automatic cleaning systems used in big industrial precipitators are not suitable for such small (almost minuscule) designs. I haven't done experiments with the blue whirls yet, of course. But from what I could read about it, I think that the blue whirl is an extremely efficient, clean, simple, and "elegant" combustion regime. It's very close to perfection by very own nature. No cleaning systems, no electricity, no moving parts. And there is also another factor I didn't mention before. When you burn vegetable oils in the usual ways, you don't get just soot: you get odour , too. And you can't get rid of odours with just an electrostatic precipitator: you need other devices, like carbon filters or scrubbers, all devices that are either too complex or need scheduled replacement of parts. On the other hand, blue whirl attain a virtually perfect combustion. In the words of @Baluncore:
the blue whirl will rapidly vaporise the low molecular weight fraction on the surface, while breaking larger molecules into medium sizes that might normally have become smoke. [...] It seems the blue whirl takes medium weight molecules into the base flow, sorts, delays and processes them by weight, until they have reacted completely and are released as CO2 and H2O in the exhaust.
It seems that the blue whirl has the ability to break any molecule down to smaller and smaller molecules, and those molecules are not allowed to escape (presumable courtesy of the bright ring) until everything has been reduced to CO2 and H2O. In other words, what cannot burn is left as floating, cold tar, while all can burn is burned down to CO2 and H2O : odourless. Without noise, electricity, filters or the like. I cannot imagine anything more perfect nor more elegant.
 
  • #28
Baluncore
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I think there is a limitation due to using water as the fluid bed to the whirl. That limits pyrolysis of the heavier products to the boiling point of water, 100°C. It sets an upper limit to the molecular weight of the available reactants.

It might be possible to add something to the water, such as methanol, or maybe an acid, which could reduce recombination of pyrolysis products, and so avoid forming a hydroxide sludge.

Maybe raise the boiling point by adding salt to make a brine bed. Salt selection could also change the colour of the flame.
 
  • #29
chemisttree
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Well... an electrostatic precipitator suitable for this application should be designed, of course. And it should be effective, in the sense that it must capture more than 99% of the input soot. Cleaning the elements would not be too big a problem as long as "from time to time" is not once in a day or the like... I guess that burning a potentially smokey substance as oil - even vegetable, not mineral - would release quite a good deal of soot. As I mentioned in a previous post, the automatic cleaning systems used in big industrial precipitators are not suitable for such small (almost minuscule) designs. I haven't done experiments with the blue whirls yet, of course. But from what I could read about it, I think that the blue whirl is an extremely efficient, clean, simple, and "elegant" combustion regime. It's very close to perfection by very own nature. No cleaning systems...
Nothing was mentioned about the need to clean or not to except the mention of changing water. Soot IS produced, btw. Have you read the source you posted? It specifically states that wicks are not likely to be able to reproduce the whirl. Tests were conducted over a flat stainless surface and the whirl was observed so there is no absolute requirement for the water pool. No mention of pyrolysis. Combustion is believed to be via vaporization only which argues against the formation of thick, viscous and dark liquids via pyrolysis. No evidence given about the mechanism of fuel vaporization other than vaporization. A variety of low boiling fuels (ethanol, acetone, iso-octane, n-heptane and cyclohexane) were studied. None with low volatility like olive oil.

It’s a cool report but you are barking up the wrong tree I’m afraid.

You still haven’t described the purpose of the burner you want to build.

Have you read the source you posted?
 
  • #30
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Hello, sorry for the delay in writing, I've been quite busy with my job and various neverending chores ?:)
@chemisttree you quite stole my thoughts :oldwink: I have read the part where they say that blue whirls can be produced also over a flat metal surface. It makes sense since, at least in my limited mind of a non-engineer, the only significant difference between water and flat metal (or even glass) would probably be that water allows the fuel to move in and all around virtually frictionless, not the same with metal or glass. Vapour from the water bed does not seem to play any part in the dynamics of the whirl. I have a feeling (just a gut feeling, no equations here :oldbiggrin: ) that the frictionless movements of fuel on water should yeld a more stable and reliable blue whirl in comparison to metal or glass (especially with denser fuels, like oils), but probably no big differences in fundamental mechanics here.
It specifically states that wicks are not likely to be able to reproduce the whirl
I never thought to get a blue whirl from a wick... I mentioned wicks in my opening post only because, at that time, I had never heard a thing about blue whirls. Just that.
Soot IS produced, btw
My understanding is that soot is produced just as an "imperfection", so to speak, if and when the blue whirl is unstable (transient yellow hue/streaks). As long as it is stable, both in colour and shape/motion, soot does not seem to be produced, or maybe just in molecular amounts.
I have collected a total of 6 papers on the blue whirl so far (even one in Spanish, ¡olé! :oldbiggrin: ), I haven't read them completely yet, due to lack of time, but I think I haven't missed any of the basics.
I think there is a limitation due to using water as the fluid bed to the whirl. That limits pyrolysis of the heavier products to the boiling point of water, 100°C. It sets an upper limit to the molecular weight of the available reactants.
I don't know... as I mentioned before, water does not seem to play any significant role in the mechanics of the blue whirl, except maybe for allowing the smoothest possible movements of the fuel "puddle". The fuel feeding the whirl is drawn from the surface of the fuel puddle, i.e. from the fuel-air interface: there is more fuel, not water, directly below the fuel being sucked up/vaporized. But I may be perfectly wrong here.
 

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