Torrefaction-assisted oxy-fuel co-combustion of textile dyeing sludge and bamboo residues toward enhancing emission-to-ash desulfurization in full waste circularity

Abstract

Emission-to-ash desulfurization and full waste circularity can be enhanced by the proper selection of multiple wastes and operational conditions. In this context, a new combination of textile dyeing sludge (TDS), bamboo residues (BR), torrefaction, and oxy-fuel (O2/CO2) atmosphere was proposed in this study. Their blend (0.5TDS) torrefied at 250 °C (T250) improved its co-combustion performance by 17.30% based on the comprehensive combustion index (CCI). The CCI value of T250 in the oxy-fuel atmosphere of 20% O2/80% CO2 was about 3.6 times that of the mono-combustion of TDS in the air atmosphere. The co-combustion interaction reduced SO2 emission since the increased alkali metals and alkaline earth metals (especially K) preferentially reacted with S to form sulfate at ≤ 700 °C. Compared to the air mono-combustion of TDS, T250 in 20% O2/80% CO2 reduced SO2 emission (mg/MJ) by 55.09%. With the temperature rise from 700 to 900 °C, K-sulfate was completely transformed into aluminosilicate and released the captured SO2 in which case Ca became the main S-fixing agent. The shift from air to 20% O2/80% CO2 retained sulfate in the bottom ash. Our findings provide new and practical insights into sustainable, efficient, and clean co-combustion and energy utilization.