Note: Before you can make the charcoal, you have to locate and prepare the stuff you are going to burn. This “stuff” is commonly referred to as feedstock. This is a very important part of the process and requires some study, practice and the right tools to make sure your burn won’t be interrupted or compromised. We have a detailed guide on preparing and managing feedstock here.
CharCone charcoal burn checklist:
- Feedstock – You will need 8-12 cubic feet of prepared feedstock to do a complete burn (ending up with a cone almost filled with charcoal). Do not underestimate this part of the process – this is quite a lot of stuff and takes a good deal of time to prepare properly. Make sure you have enough feedstock at hand and ready to go or you could find yourself running about late in the burn, looking for more (this seems to happen quite a lot). Either that or you will just have a shorter burn with less charcoal.
- Tools – All of the tools you will be using should be at hand. Once the burn gets going it will require almost your full attention and you will not have time (without consequence) to go search for needed tools. Go here for more complete tool information and checklist.
- Water – Make sure your quenching water is drawn and ready. Also have water (or other beverages) for refreshment.
- Food – if you are planning to do any cooking, all of you food should be prepped and ready to cook.
- Safety – A water hose ready to spray or a fire extinguisher should be nearby. A burn kit or other first aid should be at hand.
Make sure your CharCone is properly assembled and the rim shield is locked in place. The cap should be tightened over the drain and the whole system should be on level, solid ground with any combustibles a safe distance away.
Getting started and building the raft
It is important to start the charcoal making process from a good base of burning embers and a preheated cone. To accomplish this the raft technique seems to work best. It entails building a stack of smaller (6″-8″ L) sticks in the cone to form a “chimney”. The raft is then filled with light, very flammable kindling (a little accelerant is permitted here as well) and lit from the top. It will catch quickly and you will soon have a pile of burning wood at the bottom of your CharCone. Tamp it down a bit if needed and get ready to add the first layer.
The layering technique – key to making charcoal in the CharCone
Adding the feedstock in many light layers is the secret to making charcoal in an open kiln. It works on a “flame cap” or “flame curtain” principal whereby the fire burns only at the top (3-6″) of the fuel stack. The fire on top consumes most of the available oxygen (limited by the design of the kiln) and the wood deeper down does not “combust” but still keeps on “cooking”. It is still over 500F or hotter down there, hot enough to release volatile gases and water vapor. Those gasses feed and are consumed by the fire as well. This process (the transformation of organic material though elevated temperature and in the absence of oxygen) is call pyrolysis and is the essence of how charcoal is made.
The trick is, you have to keep the flame going on top without smothering the fire or even causing it to stall enough to create smoke. That means putting the next layer on at the right time, in the right quantity and of the appropriate weight. It takes a little practice to develop this skill and there are other factors such as ambient conditions, feedstock moisture levels, etc. but once you get the hang of it, it flows pretty easy and becomes an engaging challenge.
The layering technique in a nutshell: Wait until the previous layer starts to ash over, then add the next layer being mindful of keeping the flame burning cleanly.
One more fact about the fire dynamics: the CharCone is designed to create a horizontal vortex of air currents to recirculate the combustion gases and smoke back into the fire for cleaner processing and emissions. It achieves this by the shape, slope and depth of the container and by the rim shield, which acts as wind shield but also creates a convection current by heating the air between it and the cone. Ironically, the smokeless result of all this makes it hard to notice the vortex current, but if you look closely, you can see the odd wisp of smoke and even the flames curl inwards.
The first layer
Start by tossing on a few smaller sticks that you know will burn well. Gradually keep adding more until the flames decrease. Now wait until the flame recovers a bit and then try evening out the layer by filling in the uncovered gaps. Let the flame fully recover and wait until the entire layer has caught fire. When a light layer of ash appears on a good portion of it, start adding the next layer immediately.
If you’ve sorted your feedstock, you can mix in some the thicker pieces at the beginning (they need the longer time to cook). Go easy at first – you don’t want the fire to get smothered or weak. Always have some small kindling or light tinder on hand to keep the flames going if need be.
Keeping it going and finishing the burn
Repeat the layering process until the bowl is nearly full.
At the end you will have to alter the technique slightly. As the burn finishes, there is much less time for the topmost layers to complete the pyrolysis process. To help this along, you can add some very small kindling or even dried leaves to keep the flames going without creating another true layer.
Finally, you quench the fire and all of the charcoal to end the process. There a both dry and wet quenching techniques.
The dry quench – In dry quenching you must seal the entire vessel so no air can get in. Without any oxygen, the entire system will extinguish. This has its advantages in that when cooled the charcoal will be dry and ready for further processing or its next use. It also eliminates the need for water, a processed resource that adds to the carbon cost of the operation. However, we do not recommend the dry quench method. Dry quenching has one very strong disadvantage – safety. Charcoal in the center of the kiln, even though not visibly on fire is still “burning”. If even just a little oxygen is present (a small leak in the system or ending the quench too early), the coals would not be fully extinguished and could easily reignite when exposed to oxygen after emptying. There have been numerous cases of this exact thing happening with backyard kettle grills. Think of the “ashes” in your home fireplace able to reignite a fire the next morning. You can never be sure that a dry quenched fire is completely “out”.
The wet quench – If you want to be sure that the fire is completely extinguished, soak it with water. This can be done in two ways; 1) quenching from the top – simply adding water from a hose or watering can, or 2) quenching from the bottom by attaching a hose and letting it fill from the bottom up. There are advantages and disadvantages to each method but either way you are assured of a complete quench. This disadvantages of wet quenching in general is the use of water and fact that the char now is a bit saggy and may have to be dried before further processing. The CharCone is fitted with a drain at the bottom and a hose adapter is available for bottom quenching. After the wet quench is complete the drain can be opened and the excess water drained off. Capture it if you can and use it for watering your plants. The pH will be quite high though (10-12) so be sure your soil or plants can tolerate it.
Crushing the charcoal (optional at this stage)
While the charcoal is still in the cone you have a great opportunity to crush it. If you are intending to mix it in with soil for growing plants or vegetables this is an important step and will need to be done eventually. Of all the steps in making biochar, this is one that does not have too many easy options. You need to get the particle size down to 1/4″ or less ideally and that is not easy at all. So while you ave it in the cone (think mortar) get and old baseball bat (think pestle) and pound away. It can be tedious work but it doesn’t take that long, is great upper body exercise, and I actually think it’s fun.
Removal and storage
After quenching, draining and optionally crushing the charcoal you are now ready to remove it from the cone. First, unlock the rim shield and remove it. Method #1 – lay out a 9′ x 9′ tarp in front of the cone. Carefully tip the cone so that it spills out onto the tarp shovel out all of the charcoal onto the tarp. Spread it out for drying, cover it up for later processing or remove it to another container. Method #2 – simply shove the charcoal out of the cone and into a metal pail (you will need a 10-20 gallon pail) with a tight closing lid. This is excellent long-term storage but also you will now be 100% sure that the fire is OUT and the container or anything else will not catch fire.