Accuracy Improvement of Numerical Simulation of a Hydraulics with Wood Pellet Combustion Operating in a Full-Loop Circulating Fluidized Bed Combustor

Three-dimensional computational fluid dynamics (CFD) modeling of the hydrodynamic characteristics for the various sand particle sizes (10 mm, 250 mm, 482 mm, 750 mm, 1000 mm, and the actual PSD (particle size distribution)) in a 0.1 MW_th pilot scale full-loop circulating fluidized bed combustor (CFBC) was numerically investigated with a commercial CFD code, ANSYS FLUENT. Those were clearly validated with actual CFBC operating data. As the result, the sand particle size of the actual PSD were in good agreement. In order to accurately simulate wood pellet combustion, kinetic parameters for activation energy (E_a) and pre-exponential factor (A) for wood pellet decomposition and char combustion were obtained from lab-scale TGA experiments with wood pellet sample actually used for CFBC operation. The CFD modeling on wood pellet combustion were conducted with the selected sand particle size of actual PSD with improved char combustion model using the user-defined function (UDF) reflected kinetic parameters. The CFD modeling results were carefully compared with actual CFBC operating results. Therefore, our CFD simulation results for the concentrations of gas species (N₂, CO₂, O₂, SO₂, CO, NO, and N₂O) at the gas exit in the cyclone were also in good agreement with the actual CFBC operating data. The accuracy improvements were increased from 1.9 times to 2.5 times due to our improved char combustion model using the UDF.