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Can I make biochar in a lidded roasting pan in the oven?

 
pollinator
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Hi all. I have made biochar in a BBQ outside using a retort made of an old turkey roaster. It chinked like fine china and didn't smell, and didn't kill my compost or my garden beds, so I think I did okay for my first time round.

My question is this: if I take a turkey roaster, fill it with wood scraps, seal the lid on (with clay from outside), and put it in my oven, on refractory brick, for an autoclean cycle, will it do the trick? If so, I know how I am going to stack functions during my next kitchen clean!

-CK
 
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Hey Chris-

Apparently combustible gasses start to be released from wood at about 300c or about 570f, which is what we want to happen when liberating resins from wood leaving behind carbon, and I know I can set my oven to 550, but I have no idea how hot my ovens self clean cycle gets. I know in an outdoor drum style retort, these gasses ignite from the surrounding fire when they seep out of the drum containing the wood. All I can suggest is experiment and give it a try, hopefully without blowing up your oven! Maybe the danger factor should limit char making to the outdoors?
 
Chris Kott
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Yeah, good call. I was thinking about my old oven, which heated using natural gas. I would have routed a pressure-relief valve to direct the off-gassing back down to the burner like I did in the BBQ. With an electric oven though...

My landlord would love that.

-CK
 
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I think I wouldn't try that experiment.  I've cooked charcoal in our wood stove with a steam table pan with a loose lid.  As the wood cooks it gives off wood gas which burns as it escapes under the lid.  

I am assuming some pressure builds up to cause that gas to leave the wood.  So I suspect your turkey pan would become pressurized and likely still leak the wood gas.  Then once a flammable gas is in your very hot oven it would probably ignite.  The oven may be able to contain the fire but I'm not sure it would look the same after.

If you do try it, keep a fire extinguisher close by
 
pollinator
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Not only is there the fire hazard mentioned by others, but there could by a carbon monoxide danger as well.
 
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Please, please, please do not do this Chris!!!  If you do it should be in an oven you don't care about and outside away from anything that you care about.  The pyrolysis gases that form would be poisonous to you and very likely might ignite.  They will build pressure and they will get out of the roaster pan and into the oven.  I would not be surprised if the oven explodes.

I love Biochar, but you've got to stay safe.  It's easy to make up a large batch of Biochar in a fire pit.  You can find info on that online.  If you don't I can write up a description for you when I have a little more time.  Until then promise you won't do this in your oven!
 
pollinator
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As others have mentioned, the gases released are potentially harmful. On top of that the gases contain all sorts of resinous compounds (think "sticky gloop") that will condense as soon as they hit a cool surface, given that they are not actually combusting in the oven itself. That will cause nothing but trouble in your vents etc...
 
Chris Kott
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Great responses, thank you all.

What really started me thinking about this was a pile of chicken bones I can't put in the compost, but would love to put in my garden.

What if I just used chicken bones?

-CK
 
Michael Cox
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You won't end up with biochar - although the old "terra preta" soils did contain all sorts of charred material - bones, wood, baked clay etc... That is not to say it won't be a reasonable soil amendment, it just isn't the same product.
 
pollinator
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Chris, I have had a couple pretty good explosions making biochar outside in a retort.  I'm all about experimenting, but I may skip that one :)
 
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