Fundamental study on Chinese herb residue pyrolysis and gasification by combining fluidized bed and fixed bed

The tar and char from a fluidized bed Chinese herb residue (CHR) pyrolysis were cracked and gasified in a fixed char bed. The change in chemical species of tar before and after passing through a fixed char bed was analyzed. The results show that increasing the residence time of tar and pyrolysis gas in the char bed from 0 s to 0.95 s causes a significant decrease in the chemical species containing -OH, C-H, C-O, C=O and C=C groups, but leads to an obvious increase in the aromatic species. Introducing steam into the char bed results in the formation of more species containing aromatic rings, C-O and -OH groups, while adding the oxygen to the atmosphere increases the amount of aromatic components but has little effect on the amount of species containing -OH, C-H, C=O, C=C and C-O. Both steam and oxygen are effective to remove tar from the gasification gas, but the effect of steam is relatively weaker. Introducing steam together with oxygen will have a rather higher tar removal efficiency, and the tar in the producer gas can be ignored.