Production process

Biochar is produced through pyrolysis, which means heating to high temperatures under oxygen-poor conditions.

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Production methods

There are many different manufacturing methods of biochar depending on your wishes. Both for manufacturing on a large and small scale.


Pyrolys temperature inpact

The structure and composition of biochar are affected by the production temperatures, and thus also its properties.

Production process

Manufacture by pyrolysis

Organic material is needed for the production of biochar. The lower the moisture content, the less energy for drying is generally consumed in the process. At hobby level, dry wood fits well, such as firewood, wood chips or pellets. On a larger scale, from a resource and climate point of view, the use of residues is to prefer.

The biochar is produced by drying and heating the organic material to 300-1000 °C in an oven without air supply. Volatile substances such as methane, hydrogen, and carbon monoxide are departing. Left in solid form will be biochar in the form of charcoal (when heating wood) or in the form of black coal (when heated by straw or similar materials). Heating in an oxygen-poor environment is called Pyrolysis. The very word pyrolysis originates from the Greek pyro for "fire" and lysis for "separate".

After the pyrolysis step in the process, the biochar can be treated to obtain the desired properties. Depending on the use, you can moisten, atomize and/or activate the biochar in different ways. Before use in cultivation, it is often loaded with nutrition and microbes.


Production methods


Manufacturing - on a small and large scale

Today biochar is manufactured on a small scale at many places. In gardening and self-catering, there are lots of examples of simple methods of manufacturing. One of the easier ways to create biochar is to burn branches and twigs in a pit, a so-called open pit. Methods that use sheet metal barrels or other vessels are also common and relatively simple for manufacturing on hobby level.

See examples of open pit. (eng)

For larger scale manufacturing, methods with continuous flow of the material are more commonly used, for example through a transport screw.

There are some manufacturers of biochar in Sweden, which has larger facilities based on the continuous method:

Skånefrö manufactures ETC certified biochar in a pyrolysis machine from Pyreg.

Stockholm Exergi recycles biomaterials from garden waste.

Hjelmsäters Property and ETC solar park have pyrolysis machines from Biomacon.

RESET is another manufacturer of modern pyrolysis plants.

Pyrolysis temperature

Different temperatures in the manufacturing process

The temperature under the pyrolysis affects the structure and composition of the biochar, which in turn gives the biochar different properties.

As the figure shows (blue curve), the amount of finished biochar decreases when the pyrolysis temperature is increased, although the change is relatively small at temperatures above 600-700 °C. This is because some slightly heavier substances e.g. wooden oils transition to gaseous form and evaporate from the material only at higher temperatures.

The ability of biochar to suck or adsorb (red curve) also changes depending on pyrolysis temperature. The highest ability is given at about 600 °C as shown in the figure.

The curves in the figure apply to a certain type of biomass and it can generally vary within large spans, but the basic relationships apply most of the time.

Roughly speaking, about two kg of dried biomass is required to produce one kg biochar.

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