Decoupling study on volatiles-char interaction during co-pyrolysis of dry/wet torrefied biomass and coal: Influence of pyrolysis temperature

Abstract

Torrefied biomass-coal co-pyrolysis was a promising route to realize high-efficiency utilization of renewable and fossil energy. Volatiles-char interaction during co-pyrolysis impacts char structure and downstream applications. However, the relevant mechanism remains unclear, and thus decoupling study was necessary. In this study, dry/wet torrefied biomass (RST300/RSH300) was prepared at 300 °C using autoclave reactor and fixed-bed reactor, respectively. Decoupled co-pyrolysis experiments were subsequently conducted at different pyrolysis temperatures (600, 700 and 800 °C) using a staged fixed-bed reactor. Furthermore, various structural characterization techniques (SEM, Raman and FTIR) were coupled to explore the pathway influencing the char structure evolution. The decoupling studies of RST/RSH300-BC co-pyrolysis showed that compared to BC char from individual pyrolysis, RST-BC co-pyrolysis led to significantly more surface deposits. In contrast, RSH-BC co-pyrolysis produced BC char with diverse crack morphologies. At all temperatures, the -OH and C=C peak intensities in RSH-BC chars were much higher than in RST-BC chars. The graphitic ordering of BC chars from both co-pyrolysis systems decreased compared to individual pyrolysis, with RSH300-BC showing a more pronounced reduction. The decoupling results of BC-RST/RSH300 revealed that compared to individual RST/RSH chars, co-pyrolyzed RST char had partially blocked cracks at 700 °C and 800 °C. Both co-pyrolyzed RST/RSH300 char showed higher -OH and C-O-C peak intensities. Notably, at 600 °C and 700 °C, the graphitic ordering improved in both co-pyrolyzed RST/RSH300 chars, with RSH chars showing significant enhancement.