Pyrolysis of textile dyeing sludge in fluidized bed: Characterization and analysis of pyrolysis products

Abstract

Fluidized bed pyrolysis (FBP) of textile dyeing sludge (DS) was carried out in a benchtop unit. The FBP char (FC) yield decreased and non-condensable gas yield increased with increasing temperature. The minimum FC yield (73.47 wt%) and maximum non-condensable gas yield (24.10 wt%) were found with addition of kaolin at 850 °C. The maximum condensates yield was observed at 650 °C (i.e. 3.52 wt%) without additives. Catalysts reduced condensate yield and promoted decomposition of macromolecules (e.g. siloxane and dichloroacetic acid allyl ester). DS and FC contained small amounts of heavy metals (e.g. Zn, Ni, Pb, Cr and Cu) and a better sulfur retention ability of CaO at higher temperatures (e.g. 650–850 °C) was observed. The surface morphology of FC was improved significantly with increasing temperature and catalysts addition. CO2, CO and CH4 yields in non-condensable gases increased with temperature and the addition of CaO led to the highest yields of CO (5.46 wt%), H2 (0.35 wt%) and CH4 (1.22 wt%) at 850 °C and the lowest yield of CO2 (0.45 wt%) at 450 °C. Higher temperature promoted release of nitrogen, sulfur and chlorine and catalysts promoted release of nitrogen from DS. Kaolin and Ca-bentonite enhanced release of sulfur, whereas CaO showed good sulfur retention capacity.