Multifluid computational fluid dynamics simulation for sawdust gasification inside an industrial scale fluidized bed gasifier

Abstract

Scarcity of fossil fuels, and to fulfill the energy demand of the increasing population, researchers need to shift their attention to the alternative of fossil fuels. It would be impractical and time-consuming to conduct extensive experiments on Fluidized Bed Gasifiers (FBG) of varying fuel types, sizes, geometries and operating conditions. The objective of the current research work is focused on numerical simulation of hydrodynamics behavior and sawdust gasification in an industrial scale FBG using the Eulerian-Eulerian multifluid model. For the accurate prediction of thermal and hydraulic performance (bed voidage, suspension density, pressure drop, heat transfer, and combustion kinetics), one should incorporate the correct parameters in the Computational Fluid Dynamics (CFD) simulation of a fluidized bed gasifier. It includes the multiphase gasification modeling using the Eulerian-Eulerian approach with an user defined heterogeneous reaction kinetics. The adopted CFD methodology is validated with experimental data and extended for the prediction of gasification characteristics of sawdust by incorporating eight heterogeneous (moisture release, volatile cracking, tar cracking, tar oxidation, char combustion, CO₂ gasification, steam gasification, methanation reaction) and five homogeneous oxidation of CO, CH₄, H₂, forward and backward water gas shift (WGS) reactions. In the result section, composition of gasification products is analyzed, along with the hydrodynamics of sawdust and sand phase, heat transfer between the gas, sand and sawdust, reaction rates of different homogeneous and heterogeneous reactions are being analyzed along the height of the domain.