Comprehensive CFD modelling of solar fast pyrolysis of beech wood pellets

Abstract

The present work focuses on the study of the solar pyrolysis of beech wood pellets. The biomass degradation process was modelled in the CFD (Computational Fluid Dynamics) platform ANSYS FLUENT 14.0. The results of simulations were compared to experimental tests conducted in a lab-scale solar reactor in order to validate the CFD model. The biomass pyrolysis was carried out at temperatures ranging from 600 to 2000 °C, at two heating rates: 10 and 50 °C/s. This new 2D single particle model represents a significant improvement of previous simpler version, not only because it allows monitoring the evolution of gas speciation but also because its formulation enables to deal with different types of biomass feedstock. The model structure comprises a multi-step complex kinetic framework that involves competitive reactions –including secondary tar reaction- along with rigorous heat and mass (species) transport inside the particle. On this basis, char, tar and gas predicted yields are compared with experimental data. In addition, the gas composition (CH4, CO, CO2, H2and CxHy) is also compared. CFD results are in good agreement with the experimental values, validating this approach as a useful tool to predict the products yields and their composition when pyrolyzing biomass particles. Furthermore, the model can be used when modelling any process where pyrolysis occurs and it can even be easily coupled to any reactor scale model.