Kemcyklisk förgasning för produktion av bioflygbränsle med negativa emissioner

Forskningsprojekt, 2021 – 2023

The objective of this project was to develop a sustainable and cost-effective route for producing biofuels for transport, particularly aviation fuels. Current thermochemical biomass-to-fuel pathways are too expensive, but the proposed concept, chemical looping gasification (CLG), has the potential to significantly lower costs.

CLG uses two interconnected fluidized-bed reactors and a circulating metal oxide oxygen carrier, such as iron sand, to transfer oxygen between reactors while avoiding direct contact between air and fuel. This produces a nitrogen-free gasification gas that can be upgraded to liquid fuels.

Experiments were conducted in a small batch fluidized bed, a continuous 10 kW CLG unit, and the Chalmers gasifier (1–4 MW). Batch tests showed that iron sand, despite its low oxygen transport capacity, has sufficient reactivity toward both gaseous and solid fuels. Additional studies on interactions between potassium salts and iron-based oxygen carriers found that conversion degree had little influence; potassium from carbonate and sulfate generally diffused into the oxygen carriers.

In the 10 kW facility, straw and forest residues were successfully gasified, although recurring bed agglomeration was observed and requires further investigation. No agglomeration occurred in the batch reactor or in the large-scale Chalmers gasifier.

Large-scale tests in the Chalmers gasifier were carried out over three days in December 2023. Gasifier operation was stable throughout, with temperatures between 821 and 843 °C and no signs of agglomeration or attrition. Results demonstrated clear potential for CLG with iron sand at larger scale. Compared with ilmenite and quartz sand, iron sand provided relatively high CO and H₂ yields, while tar levels were lower than with quartz sand, although still higher than desired.

The project also included process optimization, simulation, and techno-economic analysis of the biomass-to-biojet-fuel value chain.

Overall, the results show that CLG is a promising technology for syngas production and subsequent biojet fuel synthesis. Iron sand appears to be an attractive oxygen carrier due to its low cost, adequate reactivity, and stability. However, mechanisms leading to agglomeration and defluidization must be further investigated before commercial deployment.