Emission Characteristics of Nitrous and Nirogen Oxides from a Bubbling Fluidized-Bed Coal Combustion and Comparison with the results from a Circulating Fluidized-Bed Combustion

Abstract

The effects of operating conditions, air staging, limestone feed and coal types on N₂O and NOx emissions were examined using an experimental bubbling fluidized-bed combustor. N₂O emission level increased with decreasing in bed temperature and increasing in residual oxygen concentration and superficial gas velocity. Both of air staging and limestone feed into the bed were effective for reduction of N₂O emission. In general, N₂O emission increased with nitrogen content in coal, though no reasonable correlation has been found between NOx emissions and the nitrogen content.
The emission levels of N₂O and NOx from the bubbling combustion were compared with those from circulating combustion, which was reported previously. Although total emissions of N₂O and NOx from both types of combustion were almost same level, N₂O emission from the bubbling combustion showed lower level than that from the circulating combustion. The reason for the difference in the emission levels of N₂O and NOx from both types of combution was qualitatively discussed to take into account both differences in flow dynamics of bubbling and circulating beds and in chemical reactions under heterogeneous and homogeneous systems.