Predicting the pyrolysis of single biomass particles based on a time and space integral method

Abstract

The objective of this paper is to present a simple pyrolysis model to capture the main characteristics of the decomposition of a thermally thin particle at high temperatures corresponding to those found in the furnace of coal/biomass power plants. To achieve this goal, it is assumed that pyrolysis begins soon after the surface of the particle has reached a certain pyrolysis temperature, and proceeds according to a shrinking (unreacted) core model with an infinitesimal reaction front. The formulation of various stages including initial heating, pre-pyrolysis heating, pyrolysis and post-pyrolysis heating is carried out based on a time and space integral method which allows one to describe the energy conservation equation in an algebraic form. Two different treatments are presented for the pyrolysis stage. The first formulation assumes separate temperature profiles for char and biomass regions (double-temperature profile), whereas in the second treatment only one profile is considered for the temperature throughout the particle (single-temperature profile). Of particular interest is the latter approach that leads to simple relationships for predicting the duration of various stages, enabling one to predict the mass loss history. The accuracy of both methods is examined by comparing their predictions with recent experimental data reported in the literature as well as the prediction of comprehensive pyrolysis models. Satisfactory agreement is achieved indicating that both pyrolysis models based on double- and single-temperature profiles can be used with sufficient accuracy for engineering purposes.