A simplified mathematical model leading to a closed form of solution is developed for estimation of nitric oxide emission from a coal fired circulating fluidized bed (CFB) furnace. The furnace is divided into two sections: a lower section below and an upper section above the secondary air injection level. Reactions in the cyclone and the return leg are neglected. Furnace dimensions, coal feed rate, coal composition and furnace temperature are inputs to the model which was validated against several pilot scale and commercial units. Experimental results from two pilot plants and two commercial power plants agree with model predictions. A sensitivity analysis was carried out using the model to examine the effect of different operating parameters and coal properties on the overall NO emission from the furnace. It was found that excess air and furnace temperature are most important factors influencing the NO emission level. The primary to secondary air ratio influences the NO emission level reasonably. Properties of coal are other factors which affect the NO emission to a large extent. The model, though it invovles some simplification, predicts the overall emission of NO with a level of accuracy accepted in commercial operation.
On a mis au point un modele mathematique simplifie menant a une forme de solution fermee pour l'estimation de l'emission de bioxyde d'azote d'un four a lit fluidise circulant (CFB) alimente au charbon. Le four est divise en deux sections: une section inferieure sous le niveau d'injection d'air secondaire et une section superieure au-dessus de ce niveau. Les reactions dans le cyclone et la branche de retour sont negligees. Les dimensions du four, la vitesse d'alimentation en charbon, la composition du charbon et la temperature du four sont prises en compte dans le modele, lequel a ete valide par comparaison avec plusieurs unites commerciales ou a l'echelle pilote. Les resultats experimentaux de deux usines pilotes et de deux centrales d'energie electrique commerciales concordent avec les predictions du modele. Une analyse de sensibilite a ete menee a l'aide du modele afin d'etudier l'effet de differentes parametres de fonctionnement et des proprietes du charbon sur l'emission globale de NO du four. Il est apparu que l'exces d'air et la temperature du four etaient des facteurs extrěmement importants influencant le niveau d'emission de NO. Le rapport de l'air primaire a l'air secondaire influence le niveau d'emission de NO raisonnablement. Les proprietes du charbon sont un autre facteur qui influe sur l'emission de NO dans une certaine mesure. Bien qu'il necessite une simplification, le modele predit l'emission globale de NO avec un degre de precision accepte dans les applications commerciales.
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