Performance evaluation of NOx absorption by different denitration absorbents in wet flue gas denitration

Developing efficient denitration absorbents transforming the NOx of flue gas into nontoxic species are critical for wet flue gas denitration (WFGD). Performance of various denitration absorbents and their unique mechanisms were investigated by a laboratory-scale apparatus, and the denitration efficiency was quantified via response surface method. The denitration efficiency were Na2SO3>Na2S>(NH4)2SO3>TEA>KI>Na2S2O3>NaOH>CO(NH2)2>NH3∙H2O>H2O. Na2SO3, Na2S, (NH4)2SO3, TEA, KI and Na2S2O3 removed NO2 by reducing it into NO2− ion, where the denitration efficiency showed positive correlation with reducing ability. The CO(NH2)2 eliminated NO2 by reducing it into nontoxic N2, but the efficiency was limited due to its low reactivity at low temperatures. The alkaline reagents including NaOH and NH3∙H2O promote NOx absorption via acid-base neutralization mechanism leading to both NO2− and NO3− ions formation. For Na2SO3 with highest denitration efficiency, pH significantly affects its efficiency by changing the proportions of its hydrolysate, oxygen weakens the NOx absorption capacity of absorbent by oxidizing SO32− into inert SO42−, and the accumulation of NO2− ions greatly suppresses the denitration efficiency, whereas NO3− ions had negligible effect. The quadratic regression model could accurately quantify and predict the effects of various factors on denitration efficiency.