Fractional conversion of char N to no in an entrained flow reactor

Abstract

Char samples have been produced, under oxidative pyrolysis conditions, from Australian bituminousand subbituminous coals under high heating rate conditions in an entrained flow reactor. The samples were collected, characterized, and stored under iner gas. The chars were then combusted in the entrained flow reactor, using Ar/O2 mixtures (to eliminate thermal NOx formation and to enable determination of formed N2), and the amounts of NO and N2 produced were determined for a range of temperatures and residence times. The fractional conversion of NO to nitrogen-containing products was determined from the NO and N2 measurements. This is the first time this technique has been applied at this scale to determine the selectivity of char N conversion to NO. It is not possible to discern significant differences between the four chars studied. The results show that, under stoichiometric conditions (=1), char N will be released at a rate determined by the char burnout. An overall fractional conversion of char N to NO of 0.5±0.1 for =1 represents a reasonable summary of the data. Under fuel-lean conditions, fractional conversions as high as 0.7–0.8 are observed, while under fuel-rich conditions, fractional conversions as low as 0.3–0.4 are observed. These results include chars prepared from parent coals with N contents ranging from 1.07 to 2.20 wt. % (dry ash-free basis) and coal types including subbituminous and bituminous. The implications for predictive methods and modeling of NOx emissions are discussed.