Coupled reactor and particle model of biomass drying and pyrolysis in a bubbling fluidized bed reactor

Abstract

A comprehensive single particle model of biomass drying and pyrolysis is coupled with an ideal reactor model of a bubbling fluidized bed with nitrogen as the fluidizing gas. To predict biomass pyrolysis products yield and composition under steady-state operation, a two-step biomass pyrolysis kinetic mechanism is adopted with primary pyrolysis described by two different reaction kinetic schemes: (a) Three parallel first-order reactions producing primary pyrolysis products (non-condensable gas, tar/bio-oil and char), and (b) a detailed solid state kinetics mechanism based on multiple reactions of lignin, cellulose, and hemicellulose contents of two specific types of biomass (poplar and lodgepole pine). Secondary pyrolysis is modeled by two parallel reactions describing homogeneous thermal cracking of tar to non-condensable gas and char. In addition to the yields of pyrolysis products often modeled as lumped species, this model addresses an existing gap of knowledge in predicting the proportions of major compounds in the pyrolysis gas based on a few simplifying assumptions and CHO elemental balances. This predictive model is a useful tool to relate biomass pyrolysis products yield and composition to process operating parameters such as biomass ultimate analysis, reactor temperature, gas residence time, mean solids residence time inside the reactor, as well as biomass particle size and moisture content. Model predictions for the two kinetic schemes are in good agreement with available experimental data from the literature.