Thermal and NOx Characteristics of High Performance Oxy Fuel Flames

This paper describes an investigation on the characteristics of oxy-natural gas flames. Experimental investigations were conducted to gain a detailed understanding of oxy-fuel combustion and to develop high performance oxy-fuel flames. The investigation used a semi-industrial scale test furnace with a thermal input of 265 kW and tested various types of flames while monitoring the characteristics of thermal radiation and NOx emission from the flames. A generic burner with an annular oxygen injector and a single-hole gas nozzle in the center was used. A wide range of velocities of gas as well as oxygen was tested to generate various flame characteristics. Gas and oxygen velocity demonstrated a great influence on the radiative heat flux and NOx emission from flames. A lower velocity of oxygen and gas gave a higher total radiative flux with a relatively higher luminous flame and higher NOx emission which was mainly due to air leakage into the furnace. A novel combustion technique was then used based on the results gained from the generic burners. The FDI (fuel direct injection) technique was used, which was already utilized for ultra low NOx emission from high temperature preheated-air combustion. Along with the experimental approach, numerical analysis was made to gain understanding of the flame characteristics. CFD calculation showed an the effect of entrainment of the combustion products into the main stream of the flame on the thermal radiation and NOx characteristics of flames. The results are expected to help the design of optimum high performance oxy-natural gas flames for high temperature processes such as glass melting furnaces.