PARAMETRIC STUDY OF N2O FORMATION IN COAL COMBUSTION

A laboratory scale fluidized bed reactor was used to assess the influence of fuel properties and the major process-related parameters on N2O and NO formation during low temperature coal combustion. A set of coals was used, ranging in rank from lignite to anthracite, as well as chars of some of these coals. The results confirm the high N2O emissions (100-400 ppm) suggested for combustion facilities burning nitrogen-containing fuels at temperatures between 923 K and 1273 K. The main parameters that determine N2O formation from fuel nitrogen are the nitrogen content of the coal, temperature and coal rank. Decreasing temperature results in increasing N2O formation and simultaneously decreasing NO formation. Bituminous coals and anthracite coals showed substantially higher N2O yields than low rank coals. Formation of N2O results from the combustion of the volatiles as well as from char combustion. The air/fuel ratio influences N2O yields in particular near stoichiometric combustion conditions, indicating a possible way to N2O reduction.