Effects of volatile–char interactions on in situ destruction of nascent tar during the pyrolysis and gasification of biomass. Part I. Roles of nascent char

• Volatile–char interactions can result in tar destruction during pyrolysis.
• The effects of char on tar destruction are not proportional to the amount of char.
• O-containing functional groups in char enhance tar destruction.
• Aromatic ring size and substitutional groups in tar are important for tar destruction.

This study aims to investigate the roles of char in the in situ destruction of tar during the volatile–char interactions. Rice straw and water/acid-washed rice straw samples were pyrolysed at 850 °C with controlled extents of volatile–char interactions in a fluidised-bed/fixed-bed reactor. Our results indicate that the amount of tar decreases significantly with increasing extent of volatile–char interactions. The nascent char has a positive effect on tar destruction, although the effect is not proportional to the amount of char. The destruction of tar compounds during the volatile–char interactions varies with the functional groups, ring sizes and ring structures of tar molecules. Washing the raw biomass with water or acid also changes the extent of tar destruction during the volatile–char interactions. Our results indicate that the char structural features such as the O-containing groups on the char surface are an important factor influencing the tar destruction during the volatile–char interactions.