This article reports on an investigation of a comprehensive mathematical model for biomass combustion within the one-dimensional model framework. The model takes into account different thermochemical processes, e.g., moisture evaporation, pyrolysis, heterogeneous char reactions, intra-particle heat and mass transfer, and changes in thermo-physical properties. Different approaches to model the various processes involved in the thermochemical conversion of biomass are discussed, and a sensitivity study is carried out to investigate the performance of sub-models for the drying process. The comprehensive model is used to investigate the effect of moisture diffusion and vapor condensation inside the particle pores. The model is evaluated under different conditions, and satisfactory comparison of the model results with experimental data and model results from other researchers is observed.