$NO_x$ reduction by selective non-catalytic reduction in a pilot scale reactor

Abstract

The present study entails a systematic experimental investigation and a kinetic model development of selective non- catalytic reduction of $NO_x$ by ammonia, urea, and hydrazine which is thought to be a successful replacement of ammonia or urea. The effects of urea molar ratio to NO, reaction temperature and additives (polyethylene oxide (PEO), CO, $C_3H_8$, MeOH and EtOH) on NO reduction in flue gas have been determined in a pilot-scale flow reactor (0.2 m-ID × 6.0 m-high). The flow rate of the flue gas was varied from 50 to 100 N㎥/hr. The inlet concentration of NO in the reactor was varied between 250 and 350 ppm and the outlet concentration of NO was measured at the injection temperature range of 700K-1373K at 50K intervals. During the experiments, the molar ratio of urea solution (5% w/w) to NO was varied from 1.0 to 2.5 and that of oxygen was varied in the range of 3 to 5%. Significant NO reduction begins to occur at a reaction temperature of approximately 1223K, and ammonia emission rapidly decreases with increasing the reaction temperature. As the temperature increases to approximately 1273K, the maximum NO reduction can be attained. At temperatures above 1273K, NO reduction decreases with increasing temperature and ammonia emission is negligible. The temperature range in which the effective NO reduction occurs is called ``temperature window``. The molar ratios of urea to NO does not affect the temperature window but the degree of NO reduction increases to 80% with increasing the molar ratio of urea to NO up to 2.0. Among the tested additives, CO additive has the greatest effect with respect to the shift of effective temperature window and alcohol additives have the least effect. The effect of reaction temperature and CO additive on the $N_2H_4 - NO_x$ reaction is determined with 12 % w/w $O_2$. The experimental procedure was basically the same as those of the urea process. The outlet concentration of NO was measured at the injection temperature ra...