A Simplified Pyrolysis Model of a Biomass Particle Based on Infinitesimally Thin Reaction Front Approximation

Abstract

This paper presents a simplified model for prediction of pyrolysis of a biomass particle. The main assumptions include (1) decomposition of virgin material in an infinitesimal thin reaction front at a constant pyrolysis temperature, (2) constant thermophysical properties throughout the process, (3) negligible effect of volatiles flow. The formulation is presented for various stages of thermally thin and thermally thick slab particles. In each phase, the energy conservation is applied for the particle in a simple enthalpy balance form and the enthalpy of particle is computed at a volumetric mean temperature. The accuracy of this new model has been examined by comparing the predictions with various experiments of slab particles found in the literature as well as the predictions of a comprehensive model, in terms of mass loss rate, surface and internal temperatures, and conversion time. The results show that the model prediction is qualitatively and quantitatively in a satisfactory agreement with measured values. Comparing the outcome of the simplified model and a comprehensive model in terms of the conversion time of beech and spruce wood particles at high external heat fluxes reveals fair agreement between these two models. These multiple validations indicate that the presented model can be employed in design codes for practical applications. Typical numerical results are further presented to highlight the effect of the prescribed pyrolysis temperature on mass loss rate and surface temperature of both thermally thick and thin particles. The extension of the model for other particle shapes is outlined.