Fundamental investigation on the Fuel-NOx emission of the oxy-fuel combustion with a tubular flame burner

Abstract

The Fuel-NOx emission from the oxy-fuel combustion has been experimentally investigated using CH4/O2/CO2 mixture as a model of the oxy-fuel combustion with FGR, and using NH3 as a model of fuel-N. With a tubular flame burner, effects of the oxygen concentration, fuel-N concentration, equivalence ratio and the preheating temperature have been systematically investigated. Results showed that, under the non-preheating conditions, Fuel-NOx concentrations were strongly dependent on the oxygen concentrations and the equivalence ratio. However, with increasing preheating temperature, the NOx concentration approached to the same values for all O2 concentration conditions, and hence, the effects of O2 concentration became less by the preheating. It was also found that relatively large amount of NO2 was emitted in the fuel-lean condition when both of O2 concentration and the preheating temperature were low. NO2 was decreased with increase in the oxygen concentration and in the preheating temperature, however, at least 45ppm NO2 was detected in the experiment, which was 5–7% of NOx. The effects of the preheat temperature on the Fuel-NOx were also analyzed with 1-D flame speed model. Results showed that, preheating under the low O2 concentration condition led to an evident increase of the O radical in contrast to the limitation of the H radical formation in the oxy-fuel combustion. This resulted in the increase of the HNO and eventually NO concentration. On the other hand, under the high O2 concentration conditions, NOx was not increased by the preheating, because the preheating led to an increase of H radical as well as O radical. The increase of the H radical attributed to the enhancement of the NH radical formation which resulted in the reduction of the HNO, and hence, the saturated NO concentrations.