NO FORMATION AND REDUCTION IN FLAMES WITH HIGH FEED GAS OXYGEN CONCENTRATIONS
Conference contribution, 2017
Experiments from previous work performed at Chalmers University of Technology have shown tendencies for high NOX reduction during oxy-fuel combustion of propane at feed gas oxygen concentrations in the range 35 to 40 vol. %. In recent experiments the same tendency has been observed also for oxygen enriched air combustion where the NO reduction is onset already at oxygen concentrations around 30 vol. % for new burner conditions. It is not anticipated, and it has so far not been possible, that this effect is only due to homogenous reburning effects. The present paper discusses the related chemistry and results from ongoing work that seeks to find a better description of the reduction sequence related to high feed gas oxygen fractions. What has been found so far is a possible link between increased oxygen concentration, temperature and soot formation that could influence the NO formation. This will be discussed in this work based on experimental observation from a 100 kW combustion unit as well as some kinetic modelling. The latter part includes both homogenous gas phase nitrogen chemistry as well as soot formation. These two models are, however, kept separate.
The increased amount of soot observed at high inlet oxygen concentrations, together with higher reaction activity for gas phase species of importance, for both NOX formation and soot production (e.g. hydrocarbon radicals and acetylene), supports the theory of the high NOX reduction found at high oxygen concentration to be – at least partly – due to soot-NOX interactions.