Earth Pit Kiln

Fire in a pit – the start of an earth pit kiln. This would then be covered by layers and layers of fresh biomass that is allowed to char (“pyolyze”) but not burn to ash.

One of the simplest ways of turning biomass into charcoal is the “earth pit kiln”. It turns out that it also gives a very clean burn that allows for the production of high-quality biochar. It is less useful for making traditional charcoal. This is because most of the volatiles (gases, liquids, tars, etc. - basically, pyrolysis oil) are driven off and burned by this method and therefore lost from the energy content.

A similar type of pyrolysis is achieved by the more sophisticated Kon-Tiki Kiln.

One of the downsides of the earth pit kiln is that the surrounding soil may soak up a lot of heat. This is especially a problem if the soil is very cold or moist. Then the temperature at the bottom of the burn may remain too low for optimal biochar production (should be at least 400-450C°, better to have higher temperature well above 550-600°C). This may not be a problem if you are charring a large amount of material and if the burn lasts a long time: then the surrounding soil can heat up sufficiently. The Kon-Tiki Kiln avoids this whole problem.

In addition to char production, the heat generated in the pit kiln can be used for other products, such as pottery and other ceramics. These products may or may not be comparable in quality to those from a dedicated firing.

Links

• Video: “Cone Pit Biochar in 15 minutes”
• “How to Make Biochar with Only a Match”
• “Biochar Burn Demonstration”
• BioEnergy Lists: “Earth Pit Kiln”
• (Mother Earth News) “Firing Pottery in a Pit Kiln”