Simulation of Thermally Thick Wood Particles Combustion with an Eulerian–Lagrangian Method

An Eulerian-Lagrangian approach for the simulation of thermochemical conversion of thermally thick biomass particles is developed. The solid particle is divided into four layers: moist wood, dry wood, char and ash. Heat transfer between adjacent layers is described as occurring at thin interfaces. An intra-particle temperature profile is predicted to calculate the rates of drying, devolatilization and char combustion. The effects of shrinkage on different conversion processes are considered by using a volume shrinkage factor, so that the layer density is updated during the calculation. The particle model is implemented into the CFD (computational fluid dynamics) code OpenFOAM. The biomass particle and the gas phase are two-way coupled, and homogeneous gas phase reactions are solved. The model is validated and evaluated by comparing with experimental data for different particle sizes, shapes, densities and operating conditions. A comprehensive comparison of the effects from coupling the particle conversion model to the gas phase is also performed. The results show that more accurate and realistic boundary conditions, such as the temperature and concentration of the gas phase reactants for the char burning stage, are provided by the coupling.