FORMATION CHARACTERISTICS AND MECHANISMS OF N2O IN BUBBLING FLUIDIZED-BED COAL COMBUSTION

Characteristics and mechanisms of N2O formation/destruction in bubblin g fluidized-bed coal combustion were studied experimentally and theore tically. Combustion experiments were carried out to find the influence of bed temperature, combustion stoichiometry, coal type and feeding m ethod of coal particles on N2O formation. To obtain get a deeper under standing of the mechanisms of N2O formation/destruction, the homogeneo us volatile combustion in the freeboard were simulated numerically. Th e effect of bed temperature, combustion stoichiometry and volatile-N s pecies on N2O formation and the controlling reactions of N2O formation /destruction are analyzed. This study finds that N2O concentration inc reases with decreasing bed temperature and with increasing combustion stoichiometry. On the other hand, NO concentration changes little agai nst bed temperature, but increases with increasing combustion stoichio metry. N2O seems to be mainly formed from the volatile matter combusti on. HCN and NH3, evolved as volatile-N species, strongly contribute to form N2O as well as NO. Especially, HCN contributes more to forming N 2O than does NH3. On the other hand, H radicals produced by the oxidat ion reactions of CO and H-2 promote the destruction of N2O.