Thermal conversion processes of biomass and its residues are considered as a great alternative for sustainable development of the energy sector. Thermal processes like pyrolysis and gasification lead to produce solid, liquid or gas components which can be used not only in the power engineering, but also in chemistry technologies. This work presents CFD investigation of fast pyrolysis of red oak in a free fall reactor. The Euler – Euler multiphase model has been proposed for biomass pyrolysis. The reactor domain has been described as a heterogenous mixture of reacting woody particles and gaseous phase. Primary tars, light-weight gas components and nitrogen are contained in a homogenous mixture of gas phase. A lumped, multistage kinetic scheme has been applied to describe the thermal conversion of red oak particles into volatiles and char. In CFD calculations it was assumed that biomass is built by three main components: cellulose, hemicellulose and lignin. Numerical studies of biomass pyrolysis was conducted at 823 K at constant flow rate of nitrogen. Received products were designed into three groups: solid (char/unreacted components), primary tars and non-condensable gases. This study was focused on the prediction of products creation. The distribution of products in reactor zone was presented, too. Numerical results were validated by empirical results.