A numerical study on coal-biomass co-gasification according to steam/fuel ratio

Co-gasified biomass and coal can be considered a potential fuel base for gasification and offers the advantage of a reduction in CO₂ emissions. In addition, use of biomass could contribute to a reduction in fossil fuel dependency. In this study, a mixture of woody biomass and coal was gasified with air and steam to discuss the molar ratio of H₂, CH ₄, CO and CO₂ in the product gas. In addition, the effect of the mixtures with varying ratio of steam/fuel in a wide range on co-gasification behavior was investigated taking into account the gasification behavior of each feedstock. A comprehensive three-dimensional simulation model was developed for co-gasifiers. The co-gasifier was numerically modeled by simultaneously solving the rate equations for chemical reactions of the solid and gas phases for coal and biomass. Three-dimensional computational fluid dynamics (CFD) modeling on gasification performance in an one-stage entrained bed coal and biomass co-gasifier was performed for parametric studies with various steam/fuel ratios (0.008, 0.016, 0.025, 0.033, 0.042, 0.05, 0.058, 0.066, 0.075) using a commercial code, ANSYS FLUENT 14. The CFD modeling was conducted by solving steady-state Navier-Stokes equations with the Eulerian-Lagrangian method. Chemical reactions were solved via the Finite-Rate/Eddy-Dissipation Model for gas phase. Optimal conditions of steam/fuel ratio for this study gasifier using design coal and biomass were obtained as 0.058. Carbon conversion efficiencies, cold gas efficiencies, exit temperature and species mole fractions were also calculated by CFD modeling.