PROPERTIES OF WOOD FOR COMBUSTION ANALYSIS

A systematic compilation of 21 different property values of wood and bark fuel was made to facilitate the engineering analysis and modeling of combustion systems. Physical property values vary greatly and properties such as density, porosity, and internal surface area are related to wood species whereas bulk density, particle size, and shape distribution are related to fuel preparation methods. Density of dry wood and bark varies from 300 to 550 kg m-3; bulk density of prepared wood fuel varies from about 160 to 230 kg m-3. Thermal property values such as specific heat, thermal conductivity, and emissivity vary with moisture content, temperature, and degree of thermal degradation by one order of magnitude. The carbon content of wood varies from about 47 to 53% due to varying lignin and extractives content. Mineral content of wood is less than 1%, but it can be over 10 times that value in bark. The composition of mineral matter can vary between and within each tree. Properties that need further investigation are the temperature dependency of thermal conductivity and the thermal emissivity of char-ash. How mineral matter is transformed into various sizes of particulates is not well understood.