[Gasification] Gas-o-Fire , adjustable burner

[drew]

Hi Jeff,

   Nice work.   I have had some similar problems with burn back.   From 
my experience in building forges and furnaces I found that just adding a 
bell on the end of the tube and an inner ring made a huge difference in 
creating stable burners that burn quite different gas mixes quite well 
(for example these burners can be adjusted to burn vaporized heating 
oil, propane, or wood gas.    As I understand it the burn back happens 
when the flame propagation speed exceeds the speed the gas is traveling 
up your pipe.   This happens first close to the pipe wall.   Forming a 
bell or flare on the pipe slows down the gas as it is traveling through 
the expanding diameter pipe, this area should "hold" your flame much 
better than a straight pipe but adding a slightly smaller pipe section 
as your flare might help a lot.  The inner pipe will restrict the flow 
causing a local speeding up of the gas especially along the pipe and 
stopping the burn back.  Adding the inner ring (I have used a rolled 
piece of sheet metal) so that it lies just at the base of your flare, 
and sits 1/8" away from the inside of the flare pipe will act like a 
flame barrier.   You could use a screen for the same thing but it sounds 
like you are very close to the right gas velocity.    Interestingly the 
flame propagation speed of hydrogen is much much higher than CO and so 
when you find that the gas is starting to flash back it would be 
reasonable to assume that you have changed the gas composition to a 
higher hydrogen gas. 
   Your flame color is interesting, I found that the more violet or 
purple in my flame the higher the tar content.

In the images I have attached (they are now located at 
http://gasifiers.bioenergylists.org/?q=node/303 , I hope this is the 
proper way to link to them, if not hints would be apreciated) you can 
see my assembly, the gas passes out through the 3/4 pipe from the top of 
the gasifier (mine is a pressurized tlud variant).   The 1.5 pipe burner 
assembly is slipped over that pipe until the end of the 3/4 pipe is just 
past the air in throttle (the vertical 1.5 pipe in the T).   The burner 
is adjusted by first opening the throttle all the way (the vertical pipe 
has a strip of holes drilled in one side of it, with a second piece of 
larger pipe slipped over it, the larger piece of pipe has a section 
removed.   Turning the larger piece of pipe changes the amount of air 
that can get drawn in thus when the most holes are exposed the throttle 
is open (the holes SA is much larger than the id of the pipe).    With 
the throttle open and the gasifier running slide the whole assembly back 
and forth on the 3/4 pipe until some uncombusted gas comes out the 
throttle, then move it back just to the point that no smoke is coming 
out the throttle, mark this location, or tighten up the set screws (the 
set screws combined with the drilled out reducer are what keeps the 3/4 
pipe centered in the 1.5 pipe so tighten carefully leaving the same 
amount of screw protruding).    Now light the gas, it will likely get 
blown out by so I find having a propane torch hand makes this simpler.   
Now by using the throttle you can adjust the air very simply.      I 
have added the 22.5 degree elbow in my assembly to provide better gas 
air mixing, this is standard in most venturi based designs.   It helps a 
lot by providing an opportunity for the gas and air to be throughly 
mixed providing for the most complete combustion.    Using this I feel 
like I got a noticeably shorter much hotter flame.

Using the push compressed air system worked very well for me, and would 
have allowed me to try some syn gas that would have been tricky 
otherwise but could be very dangerous, from CO poisioning, to explosion 
hazard from leaked flamible gas, and possilbe rupture of the pressurized 
vessel.     It is also interesting to note the odd color of the piping 
here, the zinc is oxidizing,  I ground it back from the flare pipe where 
it gets very hot, but the rest of the assembly is still gaining enough 
heat from the gas that it might be dangerous.   I should have used just 
black iron pipe.

Good Luck  and Be Safe

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