Anyone know how to set up a charcoal-making pit for terra preta production?

[NickB79]

There was a discussion here a few months ago about creating homemade charcoal to use as terra preta to improve soil fertility and tie up carbon in the soil. I was hoping for some advice on creating my own setup.

I'm looking for an easy set-up to make charcoal at my dad's farm. I wanted to set up a charcoal-making pit in the garden, using the abundant supply of dead poplar, maple, and willow branches we have in a mature windbreak 50 yards away. Once the charcoal is finished burning, I planned on pouring a few buckets of hog manure from the barn into the pit and allowing it to compost into the spring. From what I've read, charcoal acts as a sponge the first year in the ground, absorbing nutrients and actually reducing soil fertility before boosting it the second year. Adding the nutrient-rich manure should help offset this effect.

In my mind I envision what is essentially a tee-pee constructed out of bundles of wood, branches and corn stalks, and covered in soil to control air flow to ensure smoldering instead of all-out burning.

Anyone here ever done something like this before? Thanks.

[izquierdista]

1. Here's some pictures

Courtesy of the National Park Service http://www.terragalleria.com/parks/np.death-valley.4.html

The idea is to heap the wood inside the kiln, so that you have a controlled low flow of oxygen to the fire. That way, the heat drives off the volatile compounds in the wood and leaves behind the charcoal. A corbeled dome of plain red bricks would work. You could leave gaps between the bottom courses to allow for combustion air to enter, and shovel dirt onto the gaps if you needed to lower the air flow.

[opihimoimoi]

2. google the bugger....must have lots info re sub matter...yes, just confirmed...loads of info

[HereSince1628]

3. Charcoal is made with heat not combustion.

The idea is to as much as possible turn carbohydrates (CH2O)n into pure carbon and drive off the miscellaneous volatile gases and of course...H2O.

As you make charcoal it will burn into nothing but mineral ash if it gets too much oxygen.

So what you generally want to do is to create a situation where you can heat wood but deny it oxygen.

That can be done by piling up ricks of wood and using combustion to heat the pile, or you can do it in a 55 gallon barrel with a fire underneath (on edit: with a lid of some sort) that works well enough for 55 gallon amounts.

If you use green wood you'll waste a huge amount of wood just driving off the water. Let the wood you are turning into charcoal season.

Ashes from your fire, btw, are rich in some mineral nutrients although they are also very alkaline. Used in green compost, or sprinkled on the garden with some caution and common sense, ashes can be a garden's friend.

[DCKit]

4. OMG, I'm not alone!!!!!

What ^ they said. Any kind of container - or even a pit in the ground - that allows you to limit the air intake.

The idea of "cooking" the charcoal in a 55 gallon barrel would work, but I wonder how much wood it would consume.

I just bought a 27lb, 5gal. bucket of activated charcoal on ebay for $48. Living in an apartment isn't conducive to making charcoal.

I've been using charcoal for several years in my container plants and the pepper plants were monsters this summer and LOADED.

[TheMadMonk]

9. Is that loaded with fruit, or :"locked and loaded" for the Johnny Cash moment.

"Burning ring of fire" that is.

[DCKit]

11. Hundreds of peppers. nt

[TheMadMonk]

12. Just enough for my special sauce.

I "misread" :evilgrin: what I was intending to make, and instead of dropping in 100g of regular chillies, I dropped 100 minced red devils in instead.

To quote a certain working class cook who made it good: "Lovely Jubbly". However, it very definitely came back to haunt you. Particularly when used in place of tomato paste on a pizza bass.

I love my hot, (or is that my endorphins) in case you haven't noticed. :evilgrin:

So does our chihuahua Mishka. Feed her jalepenos and she will shake her head, snort, and go mad with her tongue and then come straight back for another hit. I guess that Mexican blood will tell even when removed from its home by a dozen generations and 10,000 miles of ocean. Good thing 'melange' is fictional because this dog is a major spice addict. Raw or cooked she flat refuses to eat unseasoned meat and has done so from day one.

[TheMadMonk]

5. I just happened to pick up a copy of "Producer Gas for Motor Vehicles" ...

...at a garage sale a week or two ago.

So here's a couple of pages.



If you're at all mechanically inclined, or know someone who is, it should be possible to figure out a way to collect evolved gases (mostly hydrocarbons and hydrogen) and store them for later use. Either to get the next burn going or for winter heating. The biggest hurdle will be making your pit completely gas tight.

This next bit's a bit of an educated guess:

Don't limit yourself to burning just wood. Since for terra preta we don't care about the cleanliness, dustiness, or solidity of our charcoal, pack the gaps with that cow poo, horse poo, any any other reasonably dry organic material. It should give you a start on "charging" your terra preta and increase gas evolution considerably.

(whoopsie: wrong order)
(bloody hell: can't spell either)

[TheMadMonk]

6. Just to add. If can trap and store your gases....

...you don't need a fire to start the pit burning. It can be completely packed cold, sealed and then started by burning the gas mixed with just the right amount of oxygen. Done this way, you'll get close to 100% conversion of wood to charcoal.

A few lengths of small (3/4 inch or so) steel tubing with 3/32 holes drilled at inch intervals in the bottom of the pit should do the trick.

Probably the easiest way would be to lay out a grid of house bricks in the bottom of the pit, set the burners between the bricks and lay a sheet of heavy gauge, 1 inch mesh on the bricks. Wood on top, seal the pit and go.

Get yourself a pyrometer, to monitor the heat of the pit. Ideally the temperature should be about 400 C. If it falls below this, the burners can either be reignited, or used to introduce just enough air to get the temperature back up.

[NickB79]

7. Excellent info! I didn't think about using sheet metal

I don't think I'm gonna be digging a 15-ft pit, but all of that info could be scaled down to the levels I need. And using sheet metal is genius; I was concerned that using dirt to control airflow would smother the embers, but sheet metal (which my dad's farm has plenty of), would work perfectly. Thank you!

[TheMadMonk]

8. The theory, from the same book.

Carbonisation of wood

When wood is heated, the first of its constituents driven off is water, followed by an evolution of gases com-

[TheMadMonk]

10. Must be bored today. Here's a basic schematic for a kiln

An improved version of the Aussie drum kiln. (if it works)

The tower on the right is the same design as the old town gas storage tanks we older folk might remember. Two cylinders, each closed at one end and one slightly smaller in diameter than the other. The larger is filled with water and the other inverted and "sunk" inside the larger. Evolved gases will pass through the bubbler (the hat thingy) and fill the space above the water, lifting the inner cylinder in the process. The weight of the inner cylinder then pushes the gases back to the burner.


Pack with wood. Seal. And charge the storage "tower" with propane for the first burn.
The (air) mixer should be adjusted to maintain a slightly "rich" (oxygen poor) burn.
(a small sealable window can be used to observe the flames. they should be slightly yellowish around the edges.)

It's obviously going to take some experimentation to get it working just right, but it looks theoretically sound.

First problem: dealing with C02 from the burner. Probably the easiest solution is to place the burner completely outside the kiln, and to "cook" the charcoal in a totally oxygen free environment.

Second problem: Too much evolved gases. Quick and dirty solution would be to drill a few holes a few inches the lower rim of the inner storage cylinder to bleed off any excess once it is full. Better would be to make the storage tower large enough to collect all the gases, for burning at a later time.

[madokie]

13. Here you go

http://www.twinoaksforge.com/BLADSMITHING/MAKING%20CHARCOAL.htm

pretty much all the info needed to get started