Integrating Turbine Blade Cooling With Exhaust Gas Recirculation for Enhanced Carbon Capture in Combined Cycle Gas Turbine

In this paper, we present the investigation towards the feasibility of turbine blade cooling using Exhaust Gas from the Exhaust Gas Recirculation (EGR) in Combined Cycle Gas Turbine (CCGT) power plants for enhanced carbon capture (CC). The study has been performed due to the need to develop more economical solutions for carbon capture in current CCGTs during the transition towards net zero. Commercially mature CCGTs are the most efficient technology for power generation through fossil fuels and are widely used due to their higher flexibility, reliability and lower emissions compared to other power generation technologies. Post-combustion CC offers a solution to reduce CO2 emissions from CCGTs. However, the low CO2 concentration in exhaust gas results in a high CC energy demand, leading to high operating costs (OPEX), and the large volumetric exhaust flow rate requires large CC equipment and, thus, high capital costs (CAPEX). Based on theoretical studies, it is generally accepted that EGR should be applied in current CCGTs to reduce exhaust flow and increase its exhaust CO2 concentration. However, as EGR reduces oxygen concentration at the combustor inlet, the allowable recirculation of exhaust gas is limited by the minimum oxygen content required in the combustor to avoid flame instability and carbon monoxide emission. In this study, we explore an innovative approach that uses exhaust gas for cooling the turbine blade, referred to as exhaust gas cooling (EGC), as a potential solution for further increasing the CO2 concentration in the exhaust and reducing exhaust mass flow without impact on combustion, leading to smaller CC units and lower CC energy consumption in existing utility-scale CCGTs, which are currently cooled using compressor bleed air. An H-class Mitsubishi M701JAC power plant with three pressure level reheat bottoming cycle is modelled in WTEMP (Web-based Thermo-Economic Modular Program) software, a modular cycle analysis tool developed at the University of Genova. Carbon capture from the exhaust gas is performed using a Monoethanolamine (MEA) CC unit, modelled in Aspen Plus V14. A fraction of recirculated exhaust gas, compressed by an auxiliary EGC compressor, is used for cooling the turbine blades and the remaining is mixed with inlet air before gas turbine intake. Simulations were performed while maintaining an oxygen concentration of 16% (by mol.) at the combustor inlet. The impact of EGR-based turbine cooling on CCGT full load performance is evaluated in terms of efficiency and CC plant penalty. Results showed that, compared to conventional EGR, for the same O2 fraction at the combustor inlet, replacing compressor bleed air with exhaust gas for turbine cooling can increase the EGR ratio from 0.35 to 0.40 and reduce the exhaust mass flow by 91.2 kg/s (14.4%) in an H-class CCGT, leading to an increase in CO2 exhaust concentration by 15.32%. As a result, the size of the CC columns and their heat consumption were slightly reduced. With EGC, the power plant efficiency also increased by around 2%, mainly due to the use of exhaust gas with high specific heat for cooling. Therefore, the study demonstrates a novel concept that can be implemented in current CCGT power plants for enhanced carbon capture.