From all fossil fuels, natural gas has the lowest carbon to hydrogen ratio, which enables Gas Turbines (GTs) running on natural gas to produce electricity with the lowest CO2 emissions per produced kWh. These lower emissions have pushed power production towards natural gas. However, if we want to move towards a carbon clean power production, the carbon in the exhaust must be captured. This leads to a major challenge since the low CO2 concentration in the exhaust of a GT makes carbon capture much more expensive compared to coal fired power production.

The CO2 concentration can be increased by performing Exhaust Gas Recirculation (EGR). However, EGR on GT cycles negatively affects the efficiency. Using the concept of Humid Air Turbine (HAT), we investigate whether the efficiency losses can be compensated by introducing water in the cycle. This paper presents this novel approach by showing the impact of EGR on a flexible humidified micro Gas Turbine (mGT). It is based on results of simulations performed in Aspen® using the Turbec T100 mGT as reference case. Both the dry and wet operation of the Turbec T100 were simulated and validated with experimental results. For improved carbon capture, EGR was simulated in both the dry and the humidified mGT cycle. Simulation results indicate that EGR has no effect on the thermodynamic performance of the mGT and its components (compressor, turbine and recuperator), however efficiency is reduced significantly (up to 3.8% relative at nominal power output) because of additional losses to the fan blower installed to ensure the EGR. Additionally, the cycle performance strongly depends on the degree of cooling of the EGR stream before injection in the compressor inlet. Nevertheless, the simulation results also reveal that mGT humidification increases the total cycle efficiency, entirely compensating the EGR induced losses. Humidifying the mGT with EGR even leads to a higher electric efficiency than the standard mGT cycle, unlocking the idea of carbon capture in mGTs.

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