In order to study the effect of flue gas recirculation (FGR) by primary air mixed with FGR or nitrogen on NO x emissions in a fixed total primary air flow rate, the bed temperature, stoichiometric oxygen ratio in the combustion chamber, and excess oxygen ratio were investigated in a pilot-scale vortexing fluidized-bed combustor (VFBC). As a result, the NO x emissions could effectively be decreased with FGR in the VFBC. The lower NO x emissions were attributed to the fact that the FGR allows NO x to enter the reactor again with the chance of being reduced and that the FGR contains more CO 2 to suppress NO x formation or promote NO x reduction through its conversion to CO by reaction with char.

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Performance of a CO boiler has a detrimental influence on the operation and production of related industries. In a previous study, we have presented a numerical study of the influence of refractory thickening on the heat transfer and fluid flow in a CO boiler. In this paper, the influence of refractory thickening on the reacting flow and DeNOx effect in a CO boiler is discussed. It is found that refractory thickening can reduce the temperature and the skin friction in the DeNOx section. Furthermore, NOx formation in the DeNOx section is also alleviated by refractory thickening.

This study investigates numerically the NOx reduction by SNCR in a CO boiler. The combustion and fluid flow in the FPC CO boiler is examined with emphasis on the influence of the injection position of reducing agent on NOx reduction. Simulation results indicate that NOx is formed mainly in the high temperature region near the boiler inlet where the mixing caused by swirler is strong. Among the reducing agent injection positions investigated, the boiler inlet has the best NOx reduction efficiency, while 0.5m behind the boiler inlet is the worst. When reducing agent is injected from the boiler inlet, a NOx reduction efficiency of 51% is achieved if default amount of reducing agent is injected. When reducing agent is injected from 3.6m behind the boiler inlet, the NOx reduction efficiency is 14% for default amount of reducing agent. The injection position of reducing agent has a siginificant influence on the NOx reduction efficiency. Better injection positions for NOx reduction should be where reducing agent can pass through a region where temperature is suitable for the SNCR reaction or residence time of reducing agent in the SNCR reaction region can be longer, e.g., the boiler inlet or the downstream region of the oxidizer lower portion where recirculation exists.