Study on the gas-solid flow and reaction characteristics of oxy-fuel co-firing of coal and biomass in a pressurized fluidized bed by 3D Eulerian-Lagrangian modelling

The oxy-fuel co-firing of coal and biomass in a pressurized fluidized bed (POFB), which integrates the benefits of pressurized oxy-fuel combustion, fluidized bed technology, and biomass as a carbon-neutral fuel, has been identified as a promising and innovative approach for low-cost CO₂ capture and environmentally friendly waste disposal. However, experimentation and numerical simulations remain both challenging and limited. In this study, a 3D Eulerian-Lagrangian model based on the MP-PIC scheme was further developed, and was validated through our continuously running 10 kW_th POFB tests. The effects of the combustion pressure (P) on gas–solid flow and reaction characteristics were analysed. The results showed that the model accurately predicted flow structure, temperature, and composition of CO₂, CO, O₂, NO, N₂O, and SO₂, under both atmospheric and pressurized combustion. When P increased, the POFB operated under both the CH mode (i.e., unchanged flow structure and heat input) and IH mode (i.e., unchanged local apparent gas velocity but increased heat input) constructed favourable gas–solid flow and chemical reaction conditions. Notably, increasing P under the IH mode enhanced the uniformity of the particle distribution along the axial direction and radial ring-core structure. The results demonstrated that increasing P not only led to a better temperature distribution and higher CO₂ concentration in the flue gas but also reduced pollutants emissions. Overall, this study advanced the development of numerical models and obtained a series of results that are difficult to achieve through experiments, offering valuable support for the design, optimisation, and scaling up of POFB.