Evaluation on the oxy-fuel combustion behavior of dried sewage sludge

• The oxy-fuel combustion behavior of dried sewage sludge was detected.
• The comprehensive performance indices of sewage sludge were determined.
• Dominant combustion mechanisms around two main peaks were evaluated.
• Kinetic compensation effects were revealed in key burning stages of sewage sludge.

The combustion behavior of sewage sludge under oxy-fuel condition was evaluated based on a thermal analysis technique. At heating rates of 20–80 K min−1, the ignition temperatures of the sewage sludge were between 250 and 300 °C under air and three O2/CO2 atmospheres (oxygen contents of 21%, 30% and 40%). The burning process of the sewage sludge in air was very similar to 30%O2/70%CO2 atmosphere. The ignition and burnout temperatures of the sewage sludge decreased with increasing oxygen contents in O2/CO2 atmospheres. The average comprehensive performance indices of the sewage sludge in 40%O2/60%CO2 atmosphere were about 2 times more than that in 21%O2/79%CO2 atmosphere. Moreover, the ignition and comprehensive performance indices of the sample sharply rose up with increasing heating rates. The ignition and comprehensive performance indices of the sewage sludge in 30%O2/70%CO2 atmosphere at 80 K min−1 were about 4 times and 6 times more than that at 20 K min−1. The kinetic parameters in four combustion stages around two peaks were evaluated based on the Coats–Redfern method coupled with Ozawa–Flynn–Wall equation. There were certain kinetic compensation effects for both main combustion stages and different oxygen contents in oxy-fuel.