Distributed closed-kiln biochar

Methodology name	Distributed closed-kiln biochar
Version	1.0
Methodology ID	RBW-BCR-DCB-V1.0
Release date	February 6th, 2026
Status	Public consultation

This methodology document outlines the requirements for distributed biochar projects certified under the Rainbow Standard Rules. These projects produce biochar with at smaller scales and with more low-tech methods than for industrial biochar production.

Acknowledgements 🤝

This methodology was developed by Rainbow with valuable input and support from the Rainbow Distributed biochar Working Group members and other expert contributors.

We would like to thank Marc Hernandez Folguera (Planboo), Lorenz Buser (Cotierra), Adrien Humbert (Circonomy), Nando Knodel (Carbon Connect), Daniel Guarin (Carboneers), Isabel Messori (Atmosfair), Abhishek Sharma, Jiwesh Garg, Kaushal Bisht (Varaha), and Gerard Cornelissen (Norwegian Geotechnical Institute) for their insights and contributions throughout the development process.

Note that the Distributed open-kiln biochar methodology and the Distributed closed-kiln biochar methodology have large overlaps with one another. For reference, here are the points of divergence:

Criteria	Difference in requirements for closed and open kilns
Kiln design	Closed Kilns: Must trap and concentrate pyrolysis gases in a separate chimney or chamber, exposing them to oxygen and high temperatures to combust them before emission. Open Kilns: Must be cone-shaped with a minimum 2 m diameter and 1.5 m height.
Photo proof in dMRV	Closed Kilns: no additional requirements Open Kilns: Must provide photos of the pyrolysis process, flame curtain, quenching, and ensure the flame does not exceed 0.5 meters above the biomass.
Maximum production volume per kiln	Closed Kilns: 1,500 m³ of biochar annually. Open Kilns: 500 m³ of biochar annually.
Inputs	Closed Kilns: Must provide energy inputs for any syngas combustion Open Kilns: no additional requirements

Note that this methodology has large overlaps with the Distributed open-kiln biochar methodology. For reference, here are the points of divergence:

Criteria	Difference in requirements for closed and open kilns
Kiln design	Closed Kilns: Must trap and concentrate pyrolysis gases in a separate chimney or chamber, exposing them to oxygen and high temperatures to combust them before emission. Open Kilns: Must be cone-shaped with a minimum 2 m diameter and 1.5 m height.
Photo proof in dMRV	Closed Kilns: no additional requirements Open Kilns: Must provide photos of the pyrolysis process, flame curtain, quenching, and ensure the flame does not exceed 0.5 meters above the biomass.
Maximum production volume per kiln	Closed Kilns: 1,500 m³ of biochar annually. Open Kilns: 500 m³ of biochar annually.
Inputs	Closed Kilns: Must provide energy inputs for any syngas combustion Open Kilns: no additional requirements

Glossary

Kiln	An individual pyrolysis unit that produced biochar. A kiln may be mobile or stationary, used individually or collectively, and open or closed.
Site	A distinct location where a kiln or kilns are operated.
Kiln operator	The individual performing pyrolysis and producing biochar. This includes preparing biomass, loading it into the kiln, surveilling pyrolysis, storing biochar, taking biochar samples, and ensuring durable biochar end use.
Kiln supervisor	Hired by the Project Developer to be the party responsible for ensuring quality of the operations by on-the-ground presence and random visits to kiln operators.
dMRV	A digital platform (application or website) provided by a dMRV provider to allow kiln operators to record and document their operations, ensuring compliance with methodology requirements.
Kiln run	One full pyrolysis process, the operation of one kiln, one batch of biochar produced.
Production batch	Biochar produced under the same conditions regarding kiln type, biomass feedstock, and temperature curve. A production batch has a maximum validity of 6 months or 75 tonnes of biochar, whichever comes first. Key measurements like carbon content and H/C ratio are done once per production batch
Biochar	Material that is rich in stable carbon, produced through the thermal conversion of biomass in a low-oxygen environment
End use application	The way biochar will be used, such as direct application to soil, mixing with compost and application of the mix to soil, mixing with cement for use in concrete.
End use point	The step in the production chain where biochar leaves the direct control of biochar producers, where it is assumed to be incorporated into its final end use application.
Feedstock	The organic material used as the raw input for biochar production, such as wood, agricultural residues, or manure.
Molar H/Corg ratio	The ratio of hydrogen to organic carbon atoms in biochar, used to assess the stability and quality of biochar; lower ratios indicate higher stability.
Production batch ID	A unique identifier for each production batch.
Pyrolysis	Thermal decomposition process that occurs in the absence of oxygen