Fire hazard analysis of Mediterranean Genista Salzmannii: Pyrolysis and kinetic characterization

Abstract

The present article aims to enhance the understanding of the solid-state thermal degradation behavior and pyrolysis kinetics of Mediterranean Genista Salzmannii Needles (GSN) to support wildland fire research. In fact, proximate, ultimate and microstructural analyses were performed to characterize forest fuel-based material. In addition, a thermogravimetric system coupled with Fourier Transform Infrared spectrometry (TG-FTIR) was used to analyze the pyrolytic behavior and the evolved gaseous products. Experiments included testing both grinded and intact (cut GSN) forms of GSN, which can provide reliable information for pyrolysis models. Slow (20 and 40 °C/min) and quasi-fast (60, 80 and 100 °C/min) heating rates were applied for the TG-FTIR experiments, in order to get close from the actual conditions of wildland fires (preheating/smoldering and flame region, respectively). Furthermore, the kinetic triplet was determined at five heating rates by means of two iso-conversional methods (Flynn–Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS)) coupled with one model fitting method (Coats Redfern). A numerical simulation was applied to adequately estimates these parameters. The analysis findings revealed that GSN has a high content of volatile and carbon. The rapid pyrolysis zone (200–600 °C) was considered as the main stage of mass loss. The cut GSN was characterized by a higher mass loss rate compared to the grinded GSN. The dominant gases released during pyrolysis were CO2, CO bond, CC bond, CH and/or CO bond, aliphatic C-H (existence of CH4) and H2O. Moreover, kinetic analysis between 180 and 650 °C revealed that the average apparent activation energy (Eα) derived from FWO and KAS of the cut GSN (206.7, 242.2 and 376.6 kJ/mol for stage 1, 2 and 3, respectively) was slightly higher than those of grinded GSN (176.9, 203.7 and 360.1 kJ/mol for stage 1, 2 and 3, respectively). The different Eα distribution was mainly due to the compact physical structure of the cut GSN. The thermal decomposition of hemicellulose (0.05 < α < 0.35) and cellulose (0.35 < α < 0.75) were best described by the random nucleation and nuclei growth mechanisms (A1/3 and A1/2, respectively). Char formation (α > 0.75) was the most complex process and was found to be consistent with the high-order reaction model. Finally, the simulated data of conversion based on the obtained kinetic triplet exhibited a good agreement with the experimental data.