Exhaust Gas Recirculation in DLN F-Class Gas Turbines for Post-Combustion CO₂ Capture

This paper describes experimental work performed at General Electric, Global Research Center to evaluate the performance and understand the risks of using Dry Low NOx (DLN) technologies in Exhaust Gas Recirculation (EGR) conditions. Exhaust Gas Recirculation is viewed as an enabling technology for increasing the CO₂ concentration of the flue gas while decreasing the volume of the post-combustion separation plant and therefore allowing a significant reduction in CO₂ capture cost. A research combustor was developed for exploring the performance of nozzles operating in low O₂ environment at representative pressures and temperatures. A series of experiments in a visually accessible test rig have been performed at gas turbine pressures and temperatures, in which inert gases such as N₂/CO₂ were used to vitiate the fresh air to the levels determined by cycle models. Moreover, the paper will discuss experimental work performed using a DLN nozzle used in GE’s F-class heavy-duty gas turbines. Experimental results using a research combustor operating in partially premixed mode, incorporate the effect of applying EGR on operability, efficiency and emissions performance under conditions of up to 40% EGR. Experiments performed in fully premixed mode using DLN single nozzle combustor revealed that further reductions in NO_x could be achieved and at the same time still complying with CO emissions. While most existing studies concentrate on limitations related to the Minimum Oxygen Concentration (MOC) at the combustor exit, we report the importance of CO₂ levels in the oxidizer. This limitation is as important as the MOC and it varies with the pressure and firing temperatures.