FUEL-GAS INJECTION TO REDUCE N2O EMISSIONS FROM THE COMBUSTION OF COAL IN A FLUIDIZED-BED

A laboratory-scale, fluidized-bed reactor (29 mm i.d.) has been used f or experiments in which a stream of simulated combustion gases is pass ed through a countercurrent flame of either methane or propane. The ef fects of N2O concentration and bed temperature on N2O reduction have b een analyzed. Additionally, the effects of NO, SO2, O-2, and carrier g as (N-2 or He) in the inlet stream have been studied. An attempt to es tablish whether N2O decomposition in the flame proceeds via radical or thermal mechanisms was carried out by assuming an ideal reaction mode l in the flame. Up to 99% N2O decomposition was achieved at a gas/oxyg en equivalence ratio of 0.83 (12 vol.% O-2) and a total flow rate of 1 L/min, for both methane and propane injected into the reactor. The an alyses indicate that NOx is formed in the flame mainly via a ''prompt NO'' mechanism. Metallic surfaces can alter the N2O chemistry, either enhancing (empty reactor) or inhibiting (flame) N2O decomposition. Bot h NO and SO2 play a minor role in the decomposition of N2O, and so doe s the carrier gas, though in this case, N-2 can produce considerable a mounts of NOx under particular circumstances. Under the conditions use d, thermal decomposition accounts for only around 10% of the high N2O conversions achieved in the flame, radical mechanisms playing a major role.