Study on NOx emission during corn straw/sewage sludge co-combustion: Experiments and modelling

Abstract

The co-combustion of sewage sludge (SS) and biomass is promising for achieving energy recovery and compensating for individual feedstock disadvantages. However, the emission of nitric oxide (NOx) during this process is of concern, but no relevant study has focused on this. In this study, the release characteristics of NOx during co-combustion of SS and corn straw (CS) were investigated under different mixing ratios, heating rates, and SS moisture contents. The synergetic effect of SS and CS on NOx reduction was determined and quantified. An independently designed one-dimensional unsteady model with a fully implicit scheme was used. The results showed that with the increase in the SS mixing ratio to 20, 40, 60, and 80 wt%, the NOx emission peak values were reduced by 26%, 38%, 35%, and 40%, respectively. The case with a 60 wt% water content of SS was the best choice for NOx reduction. Furthermore, the model could describe the NOx emission trend accurately, especially for CS combustion and SS/CS co-combustion. This study showed effective NOx reduction during SS/CS co-combustion, thereby indicating that co-combustion is beneficial for the disposal of SS. In the future, the mechanism of the synergetic effect of SS and CS will be investigated from a micro point of view by more comprehensive experiments coupled with process parameter simulation.