2D Modeling and Simulation of Pyrolysis of a Thermally Thick Biomass Particle

A transient 2D kinetic-heat transfer model incorporating primary and secondary reactions is proposed to investigate the effect of reactor temperature and particle length/diameter (L/D) ratio on the pyrolysis behavior and validate it with the experimental results. The RMS error between the experimental and the model predictions are found to be 0.36–1.89% for 2D model and 13.00–13.11% for 1D model at reactor temperatures 723–798 K and L/D of 1.0. This uncderscores the necessity for the use of the 2D model in place of the 1D model, particularly at the lower L/D ratio. Temporal propagation of temperature and mass fractional residue profiles at different locations of the pyrolyzing casuarina (Casuarina equisetifolia) biomass particle is analyzed. At a high L/D (~6), two symmetric hot spots are found to appear at two axial end faces, which gradually merge to form a dumbbell-shaped hot spot near the central core. For a low L/D (~1), a symmetrical, concentric, elliptical, shell-shaped hot spot appears at a short distance from the outer surface, which quickly propagates toward the center, eventually merging into a sphere at the particle center. It is estimated that for a 0.0254 m diameter particle at the reactor temperature of 673 K, the optimal residence time is 10 min for L/D = 1, while it is 17 min for L/D = 2.