On a serious note, you don't want additional air feed at the bottom, you want it all to be rushing down the feed tube to keep the fire from drafting up - that is a significant amount of fuel and you really don't want to get it burning back at you. I have seen a recommendation from Peter van den Berg that the 1:2:4 standard J-tube proportions could be based on between 0.7 and 1.3 times nominal diameter (9-16"), and the 6' feed tube is way over that base, as well as wanting a 24' riser to balance it. I would recommend no more than a 3' feed tube which should draft okay with the rest of your dimensions and the increased ferocity I would expect from more than doubling the cross section of the system over an 8".
Is this to be outdoors?
You really need the riser at least 3x and preferably 4x the feed tube height to get and keep the draft going the right way. I think you would do as well to skip the long burn tunnel and use maybe a half barrel or less fitted to the vertical ones. There is a limit to how long the flame zone needs to be, and you will have so much riser length that all of the combustion can happen there. I think that would make it significantly easier to start the draft.
You described a 12" liner with 18" drums around it, packed with refractory. This goes inside the 55 gallon drums, with air space?? I don't see the point of insulating around the big drums. Are you intending to have the downdraft in the space between the small and big drums? Or just shooting the heat up into the air?
My plan is for this thing to be outside.
I decided to just bury it instead of fooling with a bunch of refractory and other nonsense. Plain old earth is FREE
I figure weld the barrels together and bury 'em and light that sucker on fire. If it works like I hope, I'll re-visit it and install
piping and benches to turn it into an outside burn/hangout area with a cozy heated bench
That answers my question. So the riser should be three (possibly four) barrels instead of two. I know there's some sort of ratio but I nosed through the Ianto Evans/
Leslie Jackson book and I wasn't confident with my design. I know it's important to have enough heat in the riser to get a complete burn.
So you would design it with...
TWO barrels for your fuel/feed
a half-barrel for your burn tunnel
and three stacked barrels for the riser
If you really want to put 8' long sticks in this thing, since it is outdoors and burning sticks falling out is not such a hazard, you might add a collar a couple of feet above the top of the barrel to keep the long sticks upright and feeding down. A 6' long feed tube is just dangerous in my opinion. It will also be a significant pain to keep clean.
What are your plans for keeping or draining water out of the bottom of this thing?
That extra high heat riser is something i've been thinking about as well.
Without burning whole 8 foot limbs, i have been cutting that size fuel and then burning 1' and less sections in a normal size 8 " feed tube, 1" to 3" dia pieces and would really like to see the efficiency go up. Seems like the thicker the wood, the less efficient the burn- cooler temps and less complete combustion= more smoke
Of course my application is inside and needed for heat/ hot water, so an extra barrel height would jeopardize my ceiling.
also, if you use refractory cement or clay for your insulation, you may want to consider sawdust or perlite mixed in to add insulative value and increase efficiency/ draw as well,
This will take every ounce of my mental strength! All for a tiny ad:
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