Model-based investigation of biomass CO2 gasification to biomass-to-X plant utilising dual fluidised bed gasification

Biomass CO 2 gasification enables the generation of CO 2 -binding syngas. A large-scale dual fluidised bed (DFB) system with interconnected circulating fluidised beds is investigated for the biomass-to-X process by using a 1.5D semi-empirical DFB model. Initially, lab-scale bubbling fluidised bed (BFB) gasifier experiments were simulated to validate the chemical reaction model by using a 1D semi-empirical BFB model. The model validation was successful, and the modelling accuracy was sufficient. After the lab-scale study, the dimensioning and modelling of the DFB gasifier concept were conducted. The performance of the CO 2 -blown DFB system was investigated by varying the system's gasifier operating temperature and CO 2 /C parameter. The investigation indicated the preferred gasifier design temperature as 900 °C. High temperatures are required for sufficient activation of chemical reactions converting the CO 2 . The Boudouard reaction was found to be the most important CO 2 -converting reaction. Variation of the CO 2 /C operational parameter indicated CO 2 /C ≤ 1 range is beneficial when the aim is to use the gasifier as part of a biomass-to-X process. The low ratios enable the gasifier to operate under conditions where the forward water-gas shift reaction is favoured, and H 2 is produced. Conversion of CO 2 is limited in the gasifier. Therefore, the CO 2 /C should be selected low to reduce the flow of unconverted CO 2 through the reactor. The maximum CO 2 conversion obtained is 15 % under the studied operating conditions. The results highlight the inherent limitation of CO 2 reactivity, challenges in reactor design and advance the understanding of the physical operation of the CO 2 gasification process. • Biomass CO 2 gasification is investigated by modelling. • Semi-empirical modelling is employed for bubbling and circulating fluidised beds. • A dual fluidised bed concept for a large-scale CO 2 gasification is developed. • Boudouard reaction has a high influence on CO 2 conversion in the DFB system. • Gasifier parameters CO 2 /C ≤ 1 and 900 °C are recommended for biomass-to-X plants.