The conditions that favor the formation of nitrous oxide from char under fluidized bed combustion conditions are shown to be the oxidation of the char to make the nitrogen bound in the heterocyclic rings accessible so that it can react heterogeneously either with oxygen to form NO or with nitric oxide to form N20. This was demonstrated by measurement of the gas composition when a batch of coal particles was introduced into a fluidized sand bed electrically heated to 1023 K. Oxygen and nitric oxide were added to the fluidizing helium gas in varying concentrations. N20 was formed in amounts that increased with increasing NO concentration showing the importance of NO for N20 formation. The N20 concentration, however, fell to zero when the 02 supply was interrupted underlying the essential role of oxygen in freeing the organically bound nitrogen so that it can react with NO to form N20.
NOMENCLATURE
b fractional carbon burnout (ppm/ppm) c molar concentration (ppm) f fraction, fco = Cco/(Cco + Cco2 + Ccn,), fNo = CNO/[(XN/XcXCco + CCO2 + CcH 4)]' fN20 = 2"CN20/[(XN/Xc)(Cco + CCOz + CCn,)] (ppm/ppm) F cumulative fraction (ppm/ppm) r fractional survival Cout/Cir , (ppm/ppm) x molar ratio (mol/mol) t time (s)