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

Characteristics and mechanisms of N2O formation/destruction in bubbling fluidized-bed coal combustion were studied experimentally and theoretically. Combustion experiments were carried out to find the influence of bed temperature, combustion stoichiometry, coal type and feeding method of coal particles on N2O formation. To obtain get a deeper understanding of the mechanisms of N2O formation/destruction, the homogeneous volatile combustion in the freeboard were simulated numerically. The effect of bed temperature, combustion stoichiometry and volatile-N species on N2O formation and the controlling reactions of N2O formation/destruction are analyzed. This study finds that N2O concentration increases with decreasing bed temperature and with increasing combustion stoichiometry. On the other hand, NO concentration changes little against bed temperature, but increases with increasing combustion stoichiometry. N2O seems to be mainly formed from the volatile matter combustion. HCN and NH3, evolved as volatile-N species, strongly contribute to form N2O as well as NO. Especially, HCN contributes more to forming N2O than does NH3. On the other hand, H radicals produced by the oxidation reactions of CO and H-2 promote the destruction of N2O.