[Stoves] Nozzles for TLUDs Re: venturi system -ratios of air and gas?

[Crispin Pemberton-Pigott]

Dear Friends

 

Alex English is too polite to toot his own horn but he showed me a natural draft corn pellet burner with exactly this sort of riser, venturi and stack a few years ago (2007?). He used vanes to induce a vortex and the diameter of the throat was surprisingly small. It was the first time I had seen a CO concentration of 6 ppm in the exhaust. 

 

Because I can’t quickly find a photo of it, I will toss in one of his pellet burners. This one is used to heat his house – natural draft with a horizontal version of what you guys are talking about.

 



 

Julian that photo is great. What a monster.

 

Regards

Crispin

 

 

 

Hi Paul, Frans and all;

When you talk of Kevin Adair's nozzle, are I assume you describing a hourglass riser above the concentrator ring?  Something like the hourglass comes to mind following Frans' comments on the coanda effect.  However, I expect that the dominant force at the bottom of the hourglass would be buoyancy, straight up.

A rough type of 'hourglass' venturi burner was invented by Dave Yarrow (ca. 2013) for barrel type TLUDs.  I built one myself, and it roars.  I have attached a couple of photos

1) shows the whole unit.  There is a 130 L reactor barrel inside the 200 L barrel, so secondary air was being preheated, and passed over the top of the 130 L barrel where woodgas ignited under the concentrator.  The flame then went up into the chimney burner.

2) shows the bottom of the chimney burner, which constricts to accelerate the gases, then expands.  Where it expands, there are tertiary air holes that are cut at an angle to get rotational turbulence (supposedly).  The idea is to create a bit of a venturi suction for the tertiary air.  

This unit is designed for a high gasification rate.  At low gasification rates, the flame is below the concentrator.  I haven't done any more work on this idea, because I have been focusing attention at on the initial mixing of woodgas and secondary air.  I have yet to move upstream.

I don't have this unit any more.  I gave it to a friend who lives in the countryside, and does not fear being shut down by the town's fire department.

 

 

Of course, anything said about a natural draft, wood gas burner is dependent on the supply rate of woodgas, because that can change its mode of operation (as above).  The big problem for any burner is to get it to work over a wide range of woodgas supply rates.  What works great at a medium gasification rate, can be the cause of smoke at a high gasification rate.  

Premixing air and woodgas under natural draft would be a nice thing to achieve.  The challenge under natural draft is to get the flow of the mixture to be faster than the flame speed of H2, CO, CH4, so there is no flash back.  We may be able to achieve that at higher gasification rates.  At low rates, the flame will likely flash back to the top of the char, which may not be a bad thing for low turndown.

Cheers,

Julien.

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