Drying kinetics of wood chips with different thicknesses, initial moisture contents, and wood parts in a fixed-bed vertical forced convection dryer

Small-scale wood chip gasification combined heat and power (CHP) systems can assist Japan in achieving its decarbonisation and local revitalisation goals. However, the high humidity in the country hinders drying wood chips, making continuous gasifier operation challenging. This study investigates the drying rate and water-effective diffusivity of heartwood, sapwood, and black heartwood chips with initial moisture contents of 72.5 %, 40.3 %, and 71.5 %-wb., respectively. The chips had thicknesses ranging from 2.0 to 4.7 mm at drying temperatures ranging from 40 to 80 °C under an airflow of 1.72 L/min in a forced convection dryer. The experimental findings showed that drying characteristics and effective diffusivities of chips with the same thickness were similar across different wood types, indicating minimal impact of wood parts on drying. Drying air temperature and initial moisture content significantly affected drying time. To ensure uniform drying, it is essential to prevent temperature drops in the drying air by using proper insulation, optimising residence time to avoid over-drying, and managing insufficiently dried chips. Among the drying models tested, the Page model provided the best prediction of drying curves with minimal parameters. These results can help design efficient wood chip dryers for CHP systems.