A laminar entrained flow reactor has been designed for studying the chemistry of fast biomass pyrolysis. This is the first of two papers on the reaction system. Peak heating rates in the reactor are on the order of 10(4) K/s. The reactor is capable of interfacing with a molecular beam mass spectrometer for rapid analysis of gas phase chemistry. Computational fluid dynamic simulations are used to predict an accurate time-temperature profile for the reactants and to better understand the internal processes in the reactor. Predicted and measured reaction rates compare favorably for a gas phase reaction standard. Particle devolatilization is modeled to help understand the tradeoff between heat transport and kinetic control of the pyrolysis rate. Biomass and cellulose particles below about 50 mum are expected to be sufficiently small to avoid heat transport pyrolysis control, and thus allow study of kinetically controlled pyrolysis in this reactor. This paper is the first of two, and describes the characterization of the entrained flow reactor and methodologies developed for determining quantitative kinetic measurements. The second paper describes the application of these techniques to the study of cellulose pyrolysis at high heating rates.