oil tank for biochar kiln?

Hello folks. I have a great deal of honeysuckle in piles around our property and have been contemplating turning it into biochar. We already had one such large fire and have noticed the soil hasn't recovered in two years, leading us to the idea of an above ground kiln. We have acquired a 250 gallon fuel oil tank, the type often converted to a smoker, and were hoping to cut it and put a hinge on it in a way that would allow us to sell or gift it as a smoker in the future, but are realizing we may have bitten off more than we can chew as far as this process. Here's the deal:

It seems like it could be very dangerous to cut it, either with a torch or even with a sawzall, without purging the vapors from inside. This seems like it would be very smelly and rude to neighbors and nesting birds. My partner gets headaches very easily from such things and we have an asthmatic cat as well. Is there any way to mitigate this effect?

The other question involves the safety of the resulting biochar for chickens and soil. Would we need to throw away or burn without quenching the first, or even second batch to make sure there weren't any possible contaminants? I figure the hydrocarbons burn but could there be trace heavy metals etc? I know when people make smokers they just burn one super hot fire without any meat in there to deal with this. Maybe the air purge already helps?

We're also considering whether its all too much. We also are reserving the option of simply piling what we can't convert to firewood into a pile in the overgrown alley for the power company contractors to take in a few years(we'd probably receive it back as woodchips), as much of it was from us doing their job anyway. Either way just trying to get a picture of what this might look like to make a good decision. Any thoughts would be greatly appreciated. Thank you!

I think that the structure could show some promise.  Many people have creatively redesigned different kinds of structures to make them work for biochar.  

I am concerned about the fuel still in the tank.  It seems like there should be some way of moving it into your own oil tank or someone else's, instead of spilling it or just burning it without using it.

John S
PDX OR

It sounds like you have taken on more of a challenge than you were expecting. There is nothing wrong with changing your mind and taking a different approach.

It may be easier to sell the tank for cash, and turn the previous burn area into more of a trench for biochar production. If you do the latter, please make sure you dig out all roots etc., which can act like a fuse and carry your fire elsewhere.

Residual fuel and vapours: Any liquids should be drained and collected. Vapour for diesel and home heating oil isn't nearly as flammable as gasoline, but caution is wise. Putting the output of a blower (like a bathroom fan with an extension duct) in the tank for a day should help settle things out. You could also hire/swap with a welder who has a better sense of the risk.

Heavy metals: I am not aware of these being added to home heating oil. Other anti-gel, anti-fuel-separation and anti-corrosion chemicals probaby were. After a first burn to flare off the hydrocarbons, scrubbing the inside with a strong, hot TSP solution would help remove residues. This is is even said to be effective with old drums that held leaded gasoline.

My 2c.

I belive heating oil is basically diesel and diesel isn't volatile like gasoline.
That bring said , if I wanted to cut a tank and was afraid of igniting the residual contents, I would fill the tank up with water, and get to cutting.
If you are concerned about using electric tools so close to water, drain down to just below the cut line, and then get to cutting.
Even just a sprinkler set up inside the tank could mitigate the possibility of any ignition.


Instead of making char with the first burn, maybe use nice dry fuel and burn it hot and fast as possible.
You might want to  protect the ground underneath by elevating the kiln on concrete blocks or metal legs.
My own kiln is a 50 gallon water tank with a long notch cut out of one side, I do wish I had a lid for it.


If you can get the company to turn the branches into woodchips, I would do that AND cut more for making  biochar in the 250 gallon retort.
The chips should work well in a TLUD charcoal retort.
TLUDs take less tending, and its easier to tap into their process heat for cooking, etc.