A Numerical Study on Coal-Biomass Co-gasification according to Steam/Fuel Ratio

摘要

Co-gasified biomass and coal can beconsidered a potential fuel base forgasification and offers the advantage of areduction in CO_2 emissions. In addition,use of biomass could contribute to areduction in fossil fuel dependency. In thisstudy, a mixture of woody biomass andcoal was gasified with air and steam todiscuss the molar ratio of H_2, CH_4, CO andCO_2 in the product gas. In addition, theeffect of the mixtures with varying ratio ofsteam/fuel in a wide range onco-gasification behavior was investigatedtaking into account the gasificationbehavior of each feedstock.A comprehensive three-dimensionalsimulation model was developed forco-gasifiers. The co-gasifier wasnumerically modeled by simultaneouslysolving the rate equations for chemicalreactions of the solid and gas phases forcoal and biomass. Three-dimensionalcomputational fluid dynamics (CFD)modeling on gasification performance in anone-stage entrained bed coal and biomassco-gasifier was performed for parametricstudies 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 commercialcode, ANSYS FLUENT 14. The CFDmodeling was conducted by solvingsteady-state Navier–Stokes equations withthe Eulerian–Lagrangian method. Chemicalreactions were solved via theFinite-Rate/Eddy-Dissipation Model forgas phase. Optimal conditions ofsteam/fuel ratio for this study gasifier usingdesign coal and biomass were obtained as0.058. Carbon conversion efficiencies, coldgas efficiencies, exit temperature andspecies mole fractions were also calculatedby CFD modeling.