Kurkela E., Kurkela M., Tuomi S., Hiltunen I., 2024, Development of Flexible Fluidised-bed Gasification Process for
Co-production of Synthesis Gas and Biochar, Chemical Engineering Transactions, 109, 157-162 DOI:10.3303/CET24109027

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Researchers from the VTT Technical Research Centre of Finland have developed a flexible fluidized-bed gasification process capable of producing both biochar and high-quality synthesis gas. This process, part of the FlexSNG project, operates in two distinct modes: co-production of biochar and synthesis gas, which can be converted to biomethane, and maximizing syngas production.

Three test runs using a Circulating Fluidized-Bed (CFB) gasifier identified optimal conditions for both operation modes. The gasifier setup included a fluidized-bed gasifier, hot gas filter, and catalytic reformer. Two gasifier designs were tested: a conventional CFB and a modified Bubbling Circulating Fluidized-Bed (BCFB), the latter combining features of bubbling and circulating fluidized beds to enhance flexibility.

Fluidized-bed reactors are favored for biomass and waste gasification due to their stability and uniform temperature distribution. The FlexSNG project initially hypothesized that CFB gasifiers lacked flexibility for biochar production. However, the BCFB design, featuring primary and secondary feeds of gasification agents, proved to offer better flexibility and efficiency. It uses a mix of coarse and fine bed materials to stabilize the bed and optimize tar decomposition.

Test results showed stable operation and easy switching between different biomass feedstocks with minimal operational issues. The CFB gasifier achieved high carbon conversion efficiencies but produced minimal biochar. In contrast, the BCFB gasifier demonstrated higher biochar yields but faced challenges with fine particle attrition and unstable operation without external bed material.

Further development will involve a pressurized CFB gasification test rig to enhance biochar yields and improve gasifier stability. This work highlights the potential of flexible gasification processes in advancing biomass conversion technologies, supported by funding from the EU’s Horizon 2020 program and Canadian research funds.