A pilot scale system and a computer model have been developed to evaluate the performances of a novel straw pyrolyzer based on direct (convective) heating. A horizontal cylindrical reactor is continuously fed from the end by straw, while hot gas enters through holes distributed along the lateral surface. The model includes the unsteady, two-dimensional conservation equations of heat and mass transfer for the solid and the gas phase, the generalized Darcy law and a multi-step devolatilization mechanism. Numerical simulations have been carried out to investigate the influences of gas temperature and gas to straw ratio. It was found that the key parameter for high conversion of straw to volatile products and char is the solid residence time. Predicted and measured conversion efficiencies compared well.