Mechanisms governing the formation and destruction of NO{sub}x and other nitrogenous species in low NO{sub}x coal combustion systems

摘要

The salient fundamental factors that influence the design of low NO{sub}x burners and of NO{sub}x abatement schemes are reviewed They have been examined through laboratory combustor studies which simulate some of the salient features of practicalsystems while still preserving flexibility and the ability to extract mechanisms. These studies have shown that coal ignition properties and flame attachment to the burner have great influence on coil nitrogen conversion to NO{sub}x in axial turbulentdiffusion flames. They have also shown that distributed air addition is more effective at reducing NO{sub}x formation than simple air-staging, and these results conform to held data from full scale applications.Short time scale phenomena in the ignition zone involve heterogeneous and micro-scale diffusion phenomena, and the total volatile nitrogen released is only partially converted to NO{sub}x even in the presence of excess quantities of oxygen. Micro-mixingalso complicates predictions of short time scale phenomena during reburning. However, for both pulverized coal staged combustion and gas reburning situations long time scale concentration profiles of NO, HCN and NH{sub}3 can he well modelled by the samesimplified kinetic mechanism, which is based on known detailed gas phase reactions and partial equilibrium assumptions.