Microwave pyrolysis of textile dyeing sludge in a continuously operated auger reactor: Condensates and non-condensable gases

Abstract

This paper investigated an auger pyrolyser under microwave irradiation using textile dyeing sludge (DS) as the feedstock. Microwave power, temperature, auger speed, gas velocity and addition of catalysts were studied. In terms of ICP-MS, Cu and As concentrations in condensates, depending on pyrolysis temperatures, exceeded the wastewater discharge standard in China. The condensate and oil yields reached maximum (i.e. 12.86 wt% and 0.84 wt%, respectively) at 650 °C. The content of aromatic compounds in the oil increased as temperature increased, up to 88.38% (GC-MS area) at 750 °C. Heterocyclic aromatic compounds containing nitrogen accounted for 20%–58% of the pyrolysis oil. Addition of catalysts such as CaO and Fe decreased pyrolysis oil yield and increased the content of H2. The H2 content increased from 25.39v% without catalyst to 64.17v% with addition of 30 wt% CaO. The electricity consumption was 0.80–2.64 kWh/kg wet sludge from 450 to 750 °C and auger speed range of 1–9 rpm. Higher auger speeds and lower temperatures led to lower electricity consumption.