Nitrogen conversion during the homogeneous and heterogeneous stages of sludge steam gasification: Synergistic effects of Fenton's reagent and CaO conditioner

Abstract Fenton’s reagent (Fe 2+  + H 2 O 2 ) and CaO are the conditioners during sludge dewatering, which also showed abilities in NO x precursors control during drying and pyrolysis process that we have found before. This study further refined the effects of conditioners on homogeneous and heterogeneous processes during sludge steam gasification using a self-designed decoupling reactor. The results show that compared with raw sludge, the NH 3 and HCN yields of conditioned sludge decreased by 13.71–17.67 mL/g and 17.77–23.45 mL/g at 873–1073 K respectively. 50.59–98.76% of decrement attributed to the synergistic effect of conditioners on volatiles homogeneous reforming, owing to the less NH 3 , HCN and tar-N yields in devolatilization product as well as the indirect enhancement of HCN hydrolysis. Fenton’s reagent added alone exhibited a significant effect on volatiles heterogeneous reforming. During the interaction between volatiles and char, iron salts could catalyze the nitrile-N and pyrrole-N in char conversion to stable indoles in tar and inhibited the hydrolysis of amine-N to release NH 3 . Calcium salts also showed a certain capability on the co-decomposition of quaternary-N in char and indoles/quinolones in tar to harmless N 2 . Thus, the combination of Fenton’s reagent and CaO can complementarily reduce the emission of NO x precursors at each stage of gasification.