Synergistic interactions between lignite and biomass during co-pyrolysis from volatile release, kinetics, and char structure

Abstract

One of the most efficient techniques to achieve efficient utilization of both is coal and biomass co-pyrolysis. Despite a great deal of recent research on the co-pyrolysis process, it is still unknown how biomass affects the co-pyrolysis's synergistic effect and how volatiles interact. This study uses a thermogravimetric analyzer to examine the weight loss law of co-pyrolysis of wheat straw, rice straw, and bamboo powder with various amounts of Zhundong coal. According to the findings, there is a strong positive interaction, a mild positive interaction, and a negative interaction when three different types of biomass (wheat straw, rice straw, bamboo straw) are co-pyrolysis with Zhundong coal. The interaction between wheat straw and Zhundong coal is the strongest when the mass ratio of wheat straw to Zhundong coal is 6: 4. Using a thermogravimetric-infrared spectrometer, the changes in volatile functional groups during co-pyrolysis are investigated. It is discovered that adding wheat straw decreased the amount of CO2 produced by Zhundong coal pyrolysis. Regarding the mechanism of co-pyrolysis, the alkali and alkaline earth metals (AAEMs) on the surface of biochar catalyze the pyrolysis of Zhundong coal, while the “hydrogen donor” and “free radical donor” generated by biomass pyrolysis inhibited the cross-linking and polymerization of macromolecular volatiles produced by Zhundong coal pyrolysis. The activation energy of the mass ratio of wheat straw to Zhundong coal = 6: 4 sample is calculated by three model-free methods. The co-pyrolysis process's average activation energy is determined to be between 175.95 and 194.18 kJ/mol. Through scanning electron microscopy, it is found that the morphology of co-pyrolysis carbon is significantly different from that of single pyrolysis carbon. The porous structure of biochar promotes the secondary cracking of heavy volatiles produced by coal pyrolysis, while the cracking of volatiles further promotes the development of the pore structure of biochar.