Conversion Mechanism of Organic Components during the Eucalyptus Biomass Pyrolysis Process Based on the Multispectral Association Method

Abstract

It is important to understand the transformation mechanism of the pyrolysis process, which is a crucial method for thermally utilizing solid fuels. In this work, multispectral association technology was employed to measure the pyrolysis process of biomass (eucalyptus) and investigate the spatiotemporal characteristics of its gas−solid products. We utilized tunable diode laser absorption spectroscopy (TDLAS) to quantitatively measure the gases produced during the pyrolysis process (CH 4 , H 2 O), which reflects the progress of the pyrolysis. Laser-induced breakdown spectroscopy (LIBS) was used to qualitatively measure characteristic elements such as C, C 2 , and H in the gas phase, revealing the product conversion trends. In addition, Raman spectroscopy was used to provide information about the molecular structure and functional group changes in biomass pyrolysis char. The evolving pattern of the Raman spectrum revealed that biomass char exhibits high reactivity during the dehydration and devolatilization stage, with a swift detachment of the methyl functional group. TDLAS and LIBS measurements revealed that a substantial amount of methane was produced, accompanied by the initial release peaks of the C and C 2 spectrum. During the secondary cracking stage, the reactivity and the rate of functional group detachment of biomass char gradually diminished. Methane production is relatively low in this stage, and the second-release peaks in the C and C 2 spectra might be associated with other organic gases generated through tar cracking. In addition, through multispectral association measurements on the samples with varying moisture content, it was found that moisture would increase the reactivity and the rate of functional group detachment of the biomass char, resulting in an increase in methane yield. Moreover, the spatial distribution characteristics of TDLAS and LIBS above the samples revealed that moisture facilitates the cracking of tar, resulting in the production of small molecular gases.