Towards a carbon clean micro gas turbine: Carbon capture penalty reduction using exhaust gas recirculation

The massive deployment of Renewable Energy (RE) over the last 10 years is putting a severe constraint on classical thermal power production. Indeed, the inherent highly intermittent and uncertain character of RE in combination with the lacking storage capacity of batteries (especially for medium to long term) is requiring a high flexibility from the classic thermal power production to ensure grid stability. Small-scale thermal production in Decentralized Energy Systems (DESs), like micro Gas Turbines (mGTs), offer high potential to provide the necessary flexibility. However, if we want to move towards a carbon neutral society by 2050, these units cannot emit any greenhouse gases. In this regard, applying post-combustion carbon capture (CC) offers a solution. However, the very lean mGT operating conditions results in low CO2 concentration in flue gases. This negatively affects the CO2 capture cost given the higher carbon capture penalty. Performing Exhaust Gas Recirculation (EGR) is a way to increase the CO2 content in the flue gases, and thus potentially decreasing the CC energy penalty. Nevertheless, applying EGR impacts negatively the mGT performance, due to losses induced by additional equipments to ensure the EGR, the higher inlet gas temperature as well as the changing working fluid composition. In view of this, the impact of EGR on the mGT-CC system still needs to be analyzed. In this respect, this work aims to investigate the performance of an mGT, namely the Turbec T100, coupled with a typical chemical absorption plant, where the absorbent is a 30wt% aqueous monoethanolamine (MEA) solution, for various EGR ratio using Aspen Plus. Simulation results show that adding CC to an mGT strongly reduces the electrical efficiency. from 29.5% to 15.1% due to the low CO2 concentration in mGT flue gases (1.7 vol.%). The increase of this CO2 concentration up to 4.4 vol.%, by performing EGR, showed an efficiency increase up to 22.5%. Moreover, a high EGR ratio induces a smaller flue gas flow rate, that reduce the size, and thus the cost of the CC equipment's.