Kinetic Model of Steam Gasification of Biomass in a Bubbling Fluidized Bed Reactor

摘要

A simple kinetic model is developed for biomass gasification in a bubbling fluidized bed (BFB) with steam as the fluidizing gas. The biomass pyrolysis is described by a two-step kinetic model in which the primary pyrolysis is modeled by three parallel first-order reactions producing noncondensable gas, tar (bio-oil), and char, and the secondary pyrolysis is modeled by a first-order reaction representing homogeneous thermal cracking of tar. In addition to the yields of pyrolysis products that are often modeled as lumped species, the proportions of major compounds in the pyrolysis gas are predicted based on CHO elemental balances. By incorporating homogeneous and heterogeneous biomass gasification reactions, a seamless kinetic model of a BFB gasifier is developed. An ideal reactor model is used for the BFB gasifier assuming perfectly mixed solids and plug flow of the gas phase. This predictive model is a useful tool to relate biomass gasification product yields and composition to key process operating parameters such as biomass ultimate analysis, reactor temperature, and steam-to-biomass ratio. Predictions of the gasifier model are in good agreement with experimental data from the literature.