Role of thermal intensity on operational characteristics of ultra-low emission colorless distributed combustion

This paper examines the development of ultra-low emission colorless distributed combustion (CDC) for gas turbines, operating at thermal intensity in the range of 5-453 MW/m3 atm. Higher thermal intensity combustors are desirable for increased performance with minimal increase in hardware costs in terms of both weight and volume of gas turbine combustors. Most land based gas turbine combustors operate at thermal intensity of about 15 MW/m3 atm but operation at higher intensity can provide increased performance. Design of high thermal intensity CDC combustor requires control of critical parameters, such as gas recirculation, fuel/oxidizer mixing, air preheats, and residence time distribution characteristics via proper selection of different air and fuel injection configurations to achieve desirable combustion characteristics. Initially, various flow field configurations were investigated at a low thermal intensity of 5 MW/m3 atm. This effort was followed by investigations at higher thermal intensity ranges of 20-40 MW/m3 atm by reducing the combustor volume for a forward flow configuration under more favorable novel non-premixed conditions. Further investigations were performed for a simpler combustor having single injection ports for air and fuel with detailed investigation of various flow field configurations performed at a thermal intensity of 28 MW/m3 atm. Further reduction in combustion volume resulted in thermal intensity of 57 MW/m3 atm. For the flow configurations investigated, reverse cross-flow configuration was found to give more favorable results with air injected from exit end and fuel injected in a cross-flow direction to the air flow. This reverse cross-flow geometry was investigated in detail by further reducing the combustor volume. Air injection diameter was increased to reduce the pressure drop across the combustor. The combustor was investigated at thermal intensity in the range of 53-85 MW/m3 atm. This geometry resulted in 4 ppm NO emission and CO emissions of about 27 ppm under novel non-premixed flow conditions at thermal intensity of 53 MW/m3 atm. The pressure drop at this operational point was less than 5% to meet the conventional combustor requirements. Further reduction in combustor volume resulted in very high thermal intensity in the range of 156-198 MW/m3 atm and at the most desirable operational point NO and CO emissions were 8 ppm and 82 ppm, respectively under novel non-premixed mode at a thermal intensity of 170 MW/m3 atm. Even further reduction in combustor volume resulted in combustor operation at ultra-high thermal intensity of 283-453 MW/m3 atm and at the desirable operating point the NO and CO emissions were 4 ppm and 115 ppm respectively at a thermal intensity of 340 MW/m3 atm. The sequential efforts reveal the possibility of significantly increasing the thermal intensity while still achieving desirable emission levels.