Predictive one step kinetic model of coal pyrolysis for CFD applications

This work’s aim is the development of a simplified kinetic model for coal devolatilization, suitable for CFD applications. The detailed model of coal devolatilization, already developed and tested against a very large set of experiments and conditions, is too large to be implemented and used inside a CFD code. An automatic procedure is developed to estimate the kinetic parameters and stoichiometric coefficients of a one step model. An optimization technique manages to minimize an objective function which measures the distance between the simple one step kinetic mechanism and the results of the detailed model of coal volatilization. The results show that rate parameters can be expressed as function of the coal rank, or better of its carbon content. Despite its simplicity, the one step model is able to characterize not only the weight loss, but also the relative yields of gaseous species (CO, H2O, CO2, H2, C2H4, HCN, H2S), tar species and char. The coal database discussed in this work includes 13 coals of different elemental composition, from lignite to anthracite. The agreement of the one step model with the detailed model of coal volatilization is satisfactory for both evolution rates and cumulative values. Finally, it is important to newly underline that the proposed model, based on the detailed model, is predictive and only needs the coal elemental composition (coal rank) as an input. Two sets of correlation for the distribution of the nitrogen and sulfur compounds into solid, tar and gas phases are also proposed.