SO2 and NOx emissions from sludge combustion in a CO2/O2 atmosphere

Abstract

Incineration for the disposal of sludge is drawing increased attention, and SO2 and NOx are the main secondary pollutants produced during the incineration process. Process control during incineration is the most reasonable method to reduce the production of secondary gaseous pollutants. In this study, batch combustion tests of sludge were carried out in CO2/O2 and N2/O2 atmospheres to investigate SO2 and NOx emissions. The emissions were characterized by different temperatures, varying oxygen concentrations in the feed gas and two atmospheres. The results showed that the maximum value and appearance time of the peak of SO2 concentration curve were affected by temperature. In CO2/O2 and 80%N2/20%O2 atmospheres, the average SO2 concentration increased from 650°C to 750°C, while at 800°C the transformation rate of sulfur in the sludge was nearly 100%. At the same temperature, the average SO2 concentration in the N2/O2 atmosphere was higher than that in the CO2/O2 atmosphere. The maximum value and peak shape of the NOx concentration curve changed with temperature. Specifically, the average NOx concentration increased from 550°C to 650°C and declined from 650°C to 950°C. As the oxygen concentration increased, the average SO2 and NOx concentration also increased. The difference in the NOx emission between the 80%N2/20%O2 and 80%CO2/20%O2 atmosphere was significant when the temperature was lower than 750°C, but not at 750–950°C. Overall, the results of this study indicate that sludge combustion under a 80%CO2/20%O2 atmosphere might simultaneously reduce SO2 and NOx emissions.