Formation of Oxides of Nitrogen in Pulverized Coal Combustion

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Abstract
Nitrogen oxides are a potential atmospheric pollutant. Their formation and decomposition were studied in an experimental pulverized-coal-fired furnace. The concentration of nitrogen oxides (NOx) was a maximum in the combustion zone and decreased as the combustion gas cooled. At a coal burning rate of 2 Ib/hr and 22% excess air, reduction of nitrogen oxides was obtained by selective secondary-air distribution. With 105% cf the stoichiometric air fed to the coal-combustion zone and 17% additional air fed just beyond the flame front, 62% reduction of NOx occurred with good combustion efficiency. Lowering the quantity of excess air lowered the NOx concentration, but at the expense of combustion efficiency. When 22% excess air was fed to the primary combustion zone, NOx concentration in the effluent was 550 ppm and carbon in the fly ash 2.0%. With 5% excess air, the NOx concentration fell to 210 ppm and carbon in the fly ash rose to 13.8%. With stoichiometric combustion the NOx was 105 ppm a reduction of 81 %, and the carbon was 42.3%. Recirculation of combustion gas was not an effective means of lowering NOx formation.

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