A semiempirical model has been developed for predicting coal-derived soot. The main feature of the model is a transport equation for soot mass fraction. Tar prediction options include either an empirical or a transport equation approach, which directly impacts the source term for soot formation. Also, the number of soot particles per unit mass of gas may be calculated using either a transport equation or an assumed average. Kinetics are based on Arrhenius rates taken from published measurements. Radiative properties are calculated as a function of averaged optical constants, predicted gas temperatures, predicted gas densities, and the soot mass fractions. This model has been incorporated into a comprehensive coal modeling code and evaluated based on comparisons with soot, temperature, and NO x measurements for three experimental cases. Accurate predictions of soot yields have been achieved for both laminar and turbulent coal flames. Larger scale turbulent predictions illustrated that inclusion of a soot model changed the local gas temperatures by as much as 300 K and the local NO x concentration by as much as 250 ppm. These predictions demonstrate the necessity for an accurate soot model in coal combustion systems.
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 µm 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.
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