2-D CFD modeling of gasification of a large biomass char particle in CO2 environment

Abstract

There is a dearth in the literature of simple but robust models for gasification of large biomass particles that can address all important aspects of the reaction. A transient two-dimensional single-particle model of biomass gasification in the CO2 environment was developed in this work that incorporates chemical kinetics and heat transfer resistances, mass transfer inside the particle and boundary layer, non-equimolar counter diffusion including Knudsen diffusion, spatiotemporal variation in specific char surface area and thermophysical properties. The model was validated extensively with experimental results. Detailed simulation was carried out at reactor temperatures of 923–1123 K) using COMSOL Multiphysics software for two biomass samples – casuarina and acacia. Simulated conversion, reaction rate, temperature and gas composition profiles revealed that the reactions initially followed a shrinking core model, shifting subsequently to a shrinking reactive core model. Sensitivity analysis identified the sensitivities of process parameters as: reactor temperature > particle diameter (constant length) > initial specific char surface area > porosity > pore parameter > particle diameter (constant volume). Casuarina was found to be a more reactive and better-suited biomass than acacia for gasification applications. The work has furnished important guidelines for selecting suitable biomass type and process parameters to design an appropriate gasifier for industrial use.