Thermal Characteristics, PCDD/F Formation, and PCDD/F Inhibition in the Incineration of Distillation Residue from Chemical and Coal Industries

Distillation residue is an important byproduct in industrial distillation process and was identified as hazardous waste (HW), with an anual production of over 5 million tons in China. Recent experiments found different emission characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in a same hazardous waste incinerator (HWI) due to feeding HWs. Studies on different HWs found that PCDD/Fs concentrations formed from distillation residue were significantly higher than that of other HWs, indicating a risk of PCDD/Fs excessive emission in HWIs when mixed in the feeds. In this study, a comprehensive research on distillation residue was conducted. The distillation residue had low activation energy and lost weight rapidly at 215 °C. Volatiles were mainly pyrolyzed into organics such as chloroneb (C₈H₈Cl₂O₂). Thus PCDD/Fs could be rapidly formed through precursor synthesis. NaSCN and CaO were found with higher inhibition efficiencies (78.7% and 76.3% respectively) on PCDD/Fs concentrations. Different inhibition mechanisms were discussed. CaO better hindered chlorination process and reduced gaseous Cl₂. And NaSCN could effectively reduce the total Cl released and hinder PCDD/Fs formation from precursors. All of these are helpful to further understand comprehensive characteristics of distillation residue and figure out effective PCDD/Fs control measures, in order to optimize the operation conditions in HWIs and reduce the emission pressure of PCDD/Fs in the future.