Assessments and analysis of lumped and detailed pyrolysis kinetics for biomass torrefaction with particle-scale modeling

Abstract

A one-dimensional model with consideration of internal and external heat transfer, particle shrinkage, moisture evaporation, and pyrolysis kinetics is developed to predict biomass torrefaction behaviors. Three different kinetic schemes (i.e. a lump kinetic scheme and two detailed kinetic schemes (Andrés Anca-Couce and IngwaldObernberger, 2016, and Debiagi et al., 2018) are evaluated to find the suitable pyrolysis kinetics for biomass torrefaction process. The modeling results are compared with single beechwood particle torrefaction experiments. The results show that the detailed kinetic scheme proposed by Debiagi et al. shows the best performance among the three kinetic schemes, and it can correctly predict particle shrinkage, particle conversion, mass loss history, and biochar C/H/O compositions, while the lump kinetic scheme underestimates torrefaction rates and particle shrinkage degree at low temperature conditions (280–370 °C), and the kinetic scheme proposed by Andrés and Ingwald underestimates carbon concentration and overestimates the oxygen concentration of torrefied wood at high temperature conditions (370, 400, and 430 °C). Therefore, the kinetic scheme of Debiagi et al. is considered to be the most promising kinetics in particle-scale modeling of the torrefaction process. A sensitivity analysis is also performed to evaluate the effects of modeling parameters on modeling results as well as study the control mechanism of torrefaction process. The results show that modeling results are significantly influenced by parameters involved with external and external heat transfer related, boundary conditions, and reaction rate, indicating torrefaction process of large particles is controlled by both internal and external heat transfer, and kinetics.