Effects of air preheating on emissions of NO, HCN and NH3 from a two-stage combustion

Abstract

The purpose of this study is to investigate the effects of air preheating on the emissions of NO, HCN and NH 3 from an ordinary single-stage combustion and a two-stage combustion, with the hope of finding an ideal combustion method which can realize both energy savings and NO x reduction. Two approaches were used to carry out this study. One approach was a computer simulation on the basis of an extended Zeldovich mechanism which was aimed at a priori estimation of air preheating effects on thermal NO. The second approach was a series of experiments using a small-scale two-stage combustor, which was intended to check the simulated results and to investigate the behavior of fuel NO, HCN and NH 3 in a two-stage combustion. The following results were obtained: o 1) Air preheating up to 300°C increased emissions of thermal NO from ordinary single stage city gas combustion by a factor of three in the experiments and by a factor of four in the computer simulation. In contrast to these findings, emissions of thermal NO and fuel NO from the two stage combustion, where the primary air ratio was less than 0.8, were not significantly increased by 300°C air preheating. 2) The concentration of hydrocarbon and HCN which might be an intermediate product during the conversion process from NH 3 to NO was decreased 50% in the primary stage of the two-stage combustion by preheating the primary air to 300°C. Therefore, air preheating had a positive effect on the reduction of hydrocarbon and HCN at the primary stage.