Influence of volatiles-char interaction during torrefied biomass and coal co-pyrolysis on char structure: Comparison of different decoupling studies

Abstract

Co-pyrolysis of torrefied biomass and coal was a potential path to achieve the high-efficiency and large-scale co-utilization of these two carbonaceous feedstocks. Interaction between volatiles and char was an inevitable reaction during co-pyrolysis, and thus impacts the char structure. This work was aimed to conducting a comparison of different decoupling studies to make a clearer understanding of this interaction. Torrefied biomass is prepared at 200, 250, and 300 °C (RST200–300) in a fixed bed reactor, followed by co-pyrolysis with coal (BC) and coal char (BCC) at various ratios. RST-BC co-pyrolysis reduces oxygen-containing functional groups on the BCC surface, with the total amount decreasing from 33.1 % to 30.0 %, and decreases the C-O-C peak intensity of decoupled BCC. Compared with single BCC, co-pyrolysis of RST200/250-BC at 3:1 ratio increases C-O content by 3.5 % and 3.1 %, respectively. RST200-BC co-pyrolysis enhances the order degree of BCC, while RST250/300-BC co-pyrolysis reduce it. RST-BCC co-pyrolysis increases the C-O-C peak intensity on the BCC surface, but this effect is diminished for RST prepared at higher temperatures. During RST200/250-BCC co-pyrolysis, the order degree of decoupled BCC decreases, but RST300-BCC co-pyrolysis shows a converse effect. The impact of volatiles on the carbon structure evolution of coal char enhances with increasing RST ratios. For RST-BC/BCC co-pyrolysis, the C-C content on BCC surface increased, particularly for RST200 at a 3:1 ratio, with C-C content increased by 3.5 % and 3.4 %. These findings suggest that volatiles interactions during co-pyrolysis reduce oxygen-containing groups on the BCC surface and alter its ordered structure.