Evaluation of reaction mechanisms and emissions of oily sludge and coal co-combustions in O2/CO2 and O2/N2 atmospheres

Oxy-fuel combustion technology presents promising potential for the thermal disposal of hazardous waste to alleviate the global greenhouse effect on the environment and human well-being. In this study, the co-combustion reaction mechanisms and cleaner and efficient performances of oily sludge (OS) and coal in the oxy-fuel (O2/CO2) and air (O2/N2) atmospheres were characterized. With O2 concentration of 21% and at 20 °C/min, the ignition and burnout temperatures of the OS combustion were slightly worse in the oxy-fuel (403 and 531 °C) than air (407 and 535 °C) atmosphere. The rising O2 concentration increased the comprehensive combustion characteristic index from 1.11 × 10−7 to 4.29 × 10−7 in the air atmosphere and 1.02 × 10−7 to 4.10 × 10−7 in the oxy-fuel atmosphere. Based on the master-plots method, the three combustion stages of light oil, heavy oil, and fixed carbon were best described by the three-dimensional diffusion, interfacial reaction, and random nucleation growth models, respectively. The reaction mechanisms were independent of heating rate, O2 concentration, and atmosphere type. The co-combustion interaction between 70% OS and 30% coal reduced NO and SO2 emissions. Our findings can provide new insights into achieving their cleaner and more efficient co-combustion performance and its operational optimization.