The report gives results of an experimental investigation of coal pyrolysis and oxidation, and char oxidation to determine the effects of temperature and fuel/oxygen equivalence ratio on the conversion of coal-nitrogen to NOx. Experiments involved a laboratory laminar flow furnace under conditions representing pulverized coal combustors; i.e., heating rates of 1000 to 1 million K/sec, temperatures of 1000 to 2100 K, and residence times of 2 to 1000 milliseconds. The devolatilization experiments showed that no nitrogen loss occurred until 10 to 15% of the coal had been devolatilized, consistent with the hypothesis that coal-nitrogen is contained mostly in heterocyclic rings. Nitrogen was completely removed from the char by prolonged heating at above 1750 K, implying that nitrogen does not form condensed stable structures at pulverized flame temperatures, as does carbon. After initial fracture, loss of nitrogen and total weight loss are linearly correlated with a nitrogen-to-carbon slope of 1.25 to 1.5. Volatile nitrogen compounds accounted for the major fraction of NOx produced from coal-nitrogen, especially at high temperatures and low fuel/oxygen equivalence ratios. The results suggest that low NOx emissions from pulverized coal combustion are favored by a two-stage design: the first stage operated fuel-rich at high temperature; the second, fuel-lean at low temperature.

Grant no. R803242, task no. 2, program element no. EHE624A. Issued Aug. 1978. Includes bibliographical references (pages 172-176).