Numerical investigation on the fast pyrolysis of large biomass particles in bubbling beds using the coupled particle-scale and coarse-grained CFD-DEM

Journal article, 2026

The biomass fast pyrolysis in bubbling fluidized beds represents a complex, nonlinear process involving multi-scale spatiotemporal evolution. Due to the high computational cost of the traditional discrete element model (DEM) and the widespread use of thermally thin models, single-scale numerical models are no longer able to meet the current simulation needs. A one-dimensional particle-scale model for directly solving internal heat transfer is constructed in this paper, and it is coupled with coarse-grained (CG) CFD-DEM to provide a high-precision, low-cost multi-scale simulation strategy for the fast pyrolysis of large biomass particles. Here, the CG particle model and DEM are used to model the motion of sand and biomass, respectively. The results indicate that the product yield is closer to the experimental value when considering the intra-particle heat conduction, which is independent of the change in CG ratio (k). Compared with traditional CFD-DEM (k = 1), the processing at k = 2 and 3 can reduce wall-clock time by approximately 86.3% and 96.6%, respectively, while retaining high-fidelity simulation accuracy. Furthermore, the instantaneous evolution details and thermophysical processes of gas-solid phases in the pyrolysis of large biomass particles can be accurately captured, including the migration of the solid phase in axial and radial directions, bubble evolution, biomass residence characteristics, and distribution of particle size, as well as the intra-particle heat conduction, product formation, etc. Future work will prioritize improving the applicability of multi-scale models, with a focus on integrating GPU parallel acceleration technology and detailed pyrolysis reaction kinetics.