AN EXPERIMENTAL INVESTIGATION OF THE CONVERSION OF NO TO NO2 AT HIGH-PRESSURE

Unexpectedly high concentrations of NO2 have been noted in stack emiss ions from industrial combustors. NO2 formation has been reported to oc cur through the so-called ''HO2 mechanism'' in which NO combines with HO2 to produce NO2 and OH. In this study, the formation of NO2 was inv estigated at superatmospheric pressures through experiments and comput er modeling. Computer modeling utilized the CHEMKIN chemical kinetics program and a subset of a previously published C-H-O-N system mechanis m. Experimental work was conducted using a high-pressure flow reactor designed and built in the course of the study. The effects of pressure , temperature, and the presence of a NO2-promoting hydrocarbon, methan e, were investigated. It was discovered that as pressure increased fro m 1 atm to 8.5 atm, the rate and amount of No converted to NO2 also in creased. The results also show a temperature ''window'' between approx imately 800 K and 1000 K in which NO to NO2 conversion readily occurre d. The presence of methane was seen to enhance NO conversion to NO2, a nd a ratio of [CH4]/[NO] was found to be a useful parameter in predict ing NO2 formation. Significant NO conversion to NO2 was noted for [CH4 ]/[NO] > 1 at the hydrocarbon injection point. Experimental results va lidated those trends obtained from modeling with a modified C-H-O-N me chanism.