Experimental investigation of the emissions and performance of a micro gas turbine setup with enhanced EGR

Exhaust gas recirculation (EGR) is investigated to reduce the amine-based carbon capture penalty of combined cycle gas turbines by the reduction in mass flow rate and the increase in CO2 concentration permitted by the semi-closed cycle. Furthermore, EGR is one of the best pathways to reduce NOx emissions. While many numerical investigations have been performed in literature, there is a clear lack of full-scale experimental investigations on a real gas turbine. To answer that need, an MTT EnerTwin®, micro gas turbine has been modified and equipped with an external EGR loop allowing to apply recirculation rates up to flameout. Within the wide spectrum of EGR fraction, the composition of the exhaust gases and the combined heat and power production has been measured. While EGR effectively allows to reach a dry CO2 concentration up to 7.9%, decrease NOx emissions and slightly improve the combined thermal and electrical production (due to the higher specific heat capacity of the working fluid, when applying EGR, and low recirculation temperature), CO emissions are the main limiting factor before flameout is reached. However, the results observed at low pressure (3–5 bar and TIT of 950 °C for mGT) cannot be directly transposed at high pressure (15–20 bar and TIT of 1300–1400 °C for industrial GT) due to the sensitivity of NOx formation chemistry to pressure and temperature levels. The significant differences between mGTs and industrial GTs make complex any comparisons and emulations between those two scales. Extrapolating the results from mGTs to industrial GTs thus present some limitations and further investigations need to be done to understand the impact of pressure on the NOx and CO production. Nevertheless, EGR has been characterized experimentally on a mGT and identified as a clear potential pathway to carbon neutrality by improving post combustion capture efficiency owing to the gain in CO2 concentration.