COAL-NITROGEN RELEASE AND NOX EVOLUTION IN AIR-STAGED COMBUSTION

Experiments on an electrically heated entrained flow combustion reacto r were carried out in order to test the air-staging behavior of four b ituminous coals of industrial interest. Through measurements of gaseou s nitrogen-containing species profiles (NO, HCN) and sampling of char particles at different conversion levels, a study was elaborated about the impact of process parameters and coal type on NO formation and re duction, as well as on the nitrogen fate during the course of combusti on. While the air-staging abatement efficiency was observed to be corr elated with the volatile-nitrogen release from the coal, the presented analysis reveals that the contribution of char-nitrogen release canno t be neglected. This study shows that nitrogen release rates change si gnificantly during the various phases of combustion, also revealing th e effect of the operating conditions on the release rates. A simple co mputational modeling has been carried out in order to estimate the rel ative influence of the process parameters on char-nitrogen conversion into NO in the burnout zone. The results exhibit the influence of the NO concentration level in the gas phase as one possible explanation of the differences exhibited by the coals. The comparison of experimenta l data and the computational modeling also displays the necessity of a more detailed kinetic approach to describe char-nitrogen evolution by computer codes for the optimization of staged combustion processes.