Modeling the Drying and Heat Treatment of Lignocellulosic Biomass: 2D Effects Due to the Product Anisotropy

Due to a thermal degradation of the cell wall constituents, mild pyrolysis (treatment at temperature levels in the range 200–300°C) significantly changes the biomass properties, which is desirable for energy or material purposes. However, due to exothermic reactions, industrial plants must overcome serious problems such as thermal runaway and internal checking to obtain a relevant and homogeneous final product quality. To understand these problems at a fundamental level, a computational model is proposed here that couples the thermal decomposition of cellulose, hemicelluloses, and lignin components with the heat and mass transfer phenomena. The simulations performed were undertaken with the macroscopic behavior of wood in mind, including its strong anisotropy, which is reflected in the values of the permeability. Our results focus on the effect that the longitudinal direction of the board has on the treatment homogeneity. In addition, they highlight that higher initial moisture contents induce delayed treatment, which inevitably results in lower treatment homogeneity.