Simulation of pyrolysis and combustion of pine wood using two-step reaction scheme

Abstract

This study developed a simulation framework employing a two-step decomposition model approach in Fire dynamic Simulator (FDS). The kinetic parameters for the two-step decomposition approach were determined through experimental thermogravimetry analysis (TGA). TGA in the temperature range of 298– 1073K at four different heating rates of 5, 10, 15 and 20 K/min were performed. Two regions were detected from the iso-conversional plot of pine indicating with average activation energy Ea values of 171 kJ/mol and 251 kJ/mol in the conversion range of 1–25% and 25–85% respectively were obtained. The activation energy values were used to determine the material degradation mechanism using the Criados masterplots. The results showed that the pyrolysis process of pine wood can be described by three-dimensional diffusion reaction mechanism (Jander equation). Corresponding values of pre-exponential factors were calculated using compensation effect with lnA values ranging from 12-23 s-1.The kinetic parameters determined from TGA were subsequently utilized to simulate the TGA experiments in FDS. The proposed simulation approach demonstrated better agreement of simulation and experimental data of TGA when compared to the traditional single-step approach. Single-step reaction scheme did not accurately reproduce the required attributes of the DTG curve i.e., onset of decomposition, peak location and peak magnitude when compared with two-step reaction scheme. In order to further validate the proposed model, a cone calorimeter simulation model was developed wherein kinetic parameters obtained through single-step and two-step decomposition were simultaneously studied with corresponding experimental data for three different irradiation levels. It was observed that single-step reaction scheme predicts early time to ignition and underestimates the second peak HRR than two-step reaction scheme. The proposed simulation approach results in better predictions and is expected to lead to improved simulation-based research in the area of fire engineering.