# Distributed closed-kiln biochar | **Methodology name** | Distributed closed-kiln biochar | | -------------------- | ------------------------------- | | **Version** | 1.0 | | **Methodology ID** | RBW-BCR-DCB-V1.0 | | **Release date** | April 24th, 2026 | | **Status** | In use | This methodology document outlines the requirements for distributed biochar projects certified under the [Rainbow Standard Rules](https://docs.rainbowstandard.io/rainbow-standard-documents/rainbow-standard-rules). These projects produce biochar at smaller scales per kiln run, and with more low-tech and mid-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 ](https://docs.rainbowstandard.io/methodologies/distributed-open-kiln-biochar)methodology and the [Distributed closed-kiln biochar](https://docs.rainbowstandard.io/methodologies/distributed-closed-kiln-biochar) methodology have large overlaps with one another. For reference, here are the points of divergence:

Criteria	Open kiln requirement	Closed kiln requirement
Kiln design	Must be cone-shaped with a flame-curtain design to reliably combust pyrolysis gases at the rim.	Must trap and concentrate pyrolysis gases in a separate chimney or chamber, exposing them to oxygen and high temperatures to combust them before emission.
Biochar pollutants	Not required to provide PAH content of biochar.	Must provide PAH content of biochar.
Methane measurement techniques	Must use the carbon mass balance method only.	May use either carbon mass balance or volumetric flow × concentration to measure methane emissions.
Eligible biomass	Must also justify that the specific biomass type, preparation, and particle size are appropriate for flame-curtain operation.	May use any eligible biomass provided it meets the requirements.
Photo proof in dMRV	Must provide photos of the clean pyrolysis process, flame curtain, quenching.	No photos required of the clean pyrolysis process and flame curtain.
Inputs	No energy inputs expected during pyrolysis, no additional data requirements.	Must provide energy inputs for any syngas combustion.

## 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 third-party dMRV provider other than Rainbow, 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 200 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.
Bone-dry biochar	Biochar with a moisture content of 0%, typically measured immediately after exiting the kiln before any water is added during quenching.
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/C_org 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
Quenching	The process of rapidly cooling biochar immediately after pyrolysis to stop combustion and minimize methane emissions.
Site Composite Pile	A growing pile of biochar subsamples accumulated by the Kiln Operator over the course of a Production Batch. After each kiln run, a defined quantity of biochar is set aside and added to this pile. One Site Composite Pile is maintained per site per Production Batch.
Site Composite Sample	A representative sample of biochar taken from the thoroughly mixed Site Composite Pile once the Production Batch is complete. Site Composite Samples from all sites within the same Production Batch are combined to form the Production Batch Composite Pile.
Production Batch Composite Pile	A combined pile of Site Composite Samples collected from all sites contributing to the same Production Batch. The pile is thoroughly mixed by the Kiln Supervisor before a representative sample is taken for laboratory analysis.
Production Batch Representative Sample	The final representative sample taken from the mixed Production Batch Composite Pile and sent to an accredited laboratory for measurement of organic carbon content, permanence indicators (H/Corg ratio and/or inertinite content), and, once per year, environmental pollutants.

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