Drying biomass as fuel in a combustion process can increase the combustion efficiency, reduce pollution and improve operation. On the other hand, drying biomass is an expensive process that requires huge capital investment and energy input. The difficulty of removing moisture from biomass is affected by many factors such as the moisture content and the size of the solid particles. The level of drying is therefore a very important parameter, which strongly influences the economies of the utilization of biofuel. This study utilizes a mathematical model that incorporates material and energy balances, heat transfer and drying kinetics to determine the optimum drying level of biomass. Drying kinetic based upon the Fick's second law of diffusion is used in the model to determine the energy and capital expenditures for the drying process. Case studies of wood chips drying are presented to demonstrate how the thickness of wood chips affects the optimal drying intensity and the overall economics of the process. (C) 2013 Elsevier Ltd. All rights reserved.