Biomass Steam Gasification: A Comparison of Syngas Composition between a 1-D MATLAB Kinetic Model and a 0-D Aspen Plus Quasi-Equilibrium Model

Abstract

Biomass is one of the most widespread and accessible energy source and steam gasification is one of the most important processes to convert biomass into combustible gases. However, to date the difference of results between the main models used to predict steam gasification producer gas composition have been not analyzed in details. Indeed, gasification, involving heterogeneous reactions, does not reach thermodynamic equilibrium and so thermodynamic models with experimental corrections and kinetic models are mainly applied. Thus, this paper compares a 1-D kinetic model developed in MATLAB, combining hydrodynamics and reaction kinetics, and a 0-D thermodynamic model developed in Aspen Plus, based on Gibbs free energy minimization applying the quasi-equilibrium approach, calibrated by experimental data. After a comparison of the results of the models against experimental data at two S/B ratios, a sensitivity analysis for a wide range of S/B ratios has been performed. The experimental comparison and sensitivity analysis shows that the two models provide sufficiently similar data in terms of the main components of the syngas although the thermodynamic model shows, with increasing S/B, a greater increase of H2 and CO2 and lower decrease of CH4 and CO respect to the kinetic one and the experimental data. Thus, the thermodynamic model, despite being calibrated by experimental data, can be used mainly to analyze global plant performance due to the reduced importance of the discrepancy from a global energy and plant perspective. Meanwhile, the more complex kinetic model should be used when a more precise gas composition is needed and, of course, for reactor design.