Report from the Field

Don Morrison reports: "The 55 gal reservoir is just the right volume for quenching the coals from the 5' kiln by raking and spraying. I also liked the ease of tipping the kiln and dumping by one person with cable attached to handle and 4-wheeler.

Flame Carbonizers for Biochar: In Practice and Theory

Here's a presentation I gave at the Char Production Gathering at Aprovecho in August. Tried to compile everything I have learned about Flame Cap Kilns and other simple carbonizers for making biochar.

Checklist for a Biochar Burn

Here's a checklist of things you need to consider when planning a biochar burn:

• You need a water source, first of all, both for safety and for quenching the char. 
• Several shovels and rakes for spreading and cooling the char when it's done.
• Old steel roofing material is helpful for spreading and cooling the char without getting dirt or other contamination.
• Dry wood. A moisture meter is helpful. It's not very efficient to use wood that is more than 20% moisture. 
• Safety - Helpers should all have leather gloves and wear cotton or wool clothing that won't melt. These piles can put out a lot of heat! It is good for at least one person to have a fire helmet and a face shield. 
• You may need to get a burn permit from the local officials. 
• Ignition - I use a propane weed burner type torch for ignition, but all you need is a match if you have plenty of dry kindling. Light it on the top. 
• Make sure the kindling is somewhat densely packed so it will sustain a flame and allow the flame to move down to the lower layers. It seems slow to start but pretty soon you'll find the whole pile is ablaze. 
• Use a wind screen if conditions are breezy. Even if wind is not a factor, a wind screen will help hold in heat for a safer and more efficient biochar burn.

Start Your Flame Cap Kiln with a Top Lit Open Burn

Here is a series of pictures showing how we get a good start in the pyramid kiln by stacking a pile of wood in the kiln and lighting it from the top. It burns down to coals pretty quickly and gets the burn off to a good start by providing a nice, deep bed of coals that can really put out the heat for the first layer of wood.

We call a pyramid, cone, pit or tube an Open Fire Kiln.

We call an open burn pile that you light from the top (so it burns up the smoke and is clean) a Top-Lit Open Burn. You can read my article about open burning of forest fuel load reduction piles here:

Learning to Burn and Make Biochar, Not Smoke. Kelpie Wilson. Tree Care Industry Magazine. February 2014.

Build an open stack of wood with kindling on top. Light the top.

Heat transfers by radiation to the layer of wood below the flame.

Most of the wood in the stack is now charred. It only took about 15 minutes.

All the wood from the stack is now charred, and the pile has collapsed.

Now we have added the first layer on the bed of coals. We will continue adding a new layer as the old one chars.