NO x formation from ammonia, hydrogen cyanide, pyrrole, and caprolactam under incinerator conditions

Abstract

The oxidation of NH 3, HCN, pyrrole, and caprolactam has been investigated under incinerator conditions. The residence time resolved measurements have been conducted within a ceramic plug flow reactor built up in semi-technical scale. The experiments cover a temperature range from 1100 to 1350 K, and the air equivalence ratio varies between 0.93 and 1.5. A very important aspect is the presence of H 2O and CH 4 under these conditions. In the temperature range investigated, water and methane have an essential influence on the levels of the important radicals H, O, OH, and HO 2 and, thereby, affect the reaction rates of the reaction system. The measurements for the oxidation of ammonia in the presence of methane show a characteristic conversion of ammonia to hydrogen cyanide of about 10% of the initial NH 3 content, occurring at fuel rich and fuel lean conditions. The only reaction path for the generation of HCN in such an extent proceeds via methylamine arising from the reaction of CH 3 with NH 2. Furthermore, with growing temperature a distinct increase in the NO emissions has been observed, with reaction NO + NH 2 ⇔ N 2 + H 2O playing a key role in the NO removal. The experimental concentration profiles have been simulated using a detailed mechanism from the literature with substantial modifications. The kinetic model is able to predict all characteristics of the experiments very well. The experiments for the decomposition of pyrrole and caprolactam reveal that HCN is formed as intermediate species in very high concentrations. The hydrogen cyanide is then partially oxidized to NO. The destruction of pyrrole has been simulated with the modified mechanism for NH 3 and HCN oxidation, extended by a modified model for pyrrole decomposition from the literature. The agreement of experiments and simulations is very good. For the modelling of the destruction of caprolactam, a new mechanism has been derived that reproduces the experimental results very well.