Effects of Inlet Air Temperature and Steam Addition on the Realization of MILD Combustion for Humid Air Turbine

Abstract

MILD (Moderate or Intense Low-oxygen Dilution) combustion is a promising technology with low emissions and low noise. In this paper, a simplified chemical reactor network (CRN) based on the MILD combustion of methane was established to investigate the effects of inlet air temperature and steam addition on the realization of MILD combustion for humid air turbine (HAT). The results show that for the three typical conditions of the HAT cycle, the most suitable main combustion zone temperature is about 1700 K, which is most conducive to the realization of MILD combustion. The influence of steam dilution on the threshold recirculation ratio can be neglected, but it will increase the ignition delay time until reaching the critical value of steam content, which is beneficial to the complete mixing of flue gas and unburnt reactants. When the inlet air temperature increases from 381 K to 881 K, the threshold recirculation ratio for MILD combustion decreases by 70%. The influence of the inlet air temperature on the threshold recirculation ratio for MILD combustion is dominant compared to the steam content. An atmospheric experiment of MILD combustor with parallel-jet arrangement was performed to study the effect of steam content on the realization of MILD combustion. For the adiabatic flame temperature of 1650- 1900 K, the NOx emissions are below 3 ppm (at 15% O2, dry) when the steam content varies from 0 to 0.2 kg/kg. For the steam content of 0.2 kg/kg, the reaction is widely distributed. The ultra-low emissions and distributed reaction zone shows the characteristics of MILD combustion.