The advantages of reheated and intercooled gas turbines for combined cycles with post-combustion CO2 capture and storage

Abstract

This study investigates the efficiency and economic performance achievable by combined cycles with post-combustion CO₂ capture, employing different strategies to increase the concentration of CO₂ in the flue gases. These expedients include reheating in the gas turbine expansion, intercooling of the compression, and supplementary firing at the inlet of the heat recovery steam generator. The power block is modelled by using GS, a software developed at Politecnico di Milano, and the models are calibrated against data from commercial gas turbines. The amine-based CO₂ capture and compression system are simulated with a validated model implemented in Aspen Plus software. The analysis shows that, compared to the standard H-class combined cycle, reheating and intercooling slightly improve the efficiency with and without CO₂ capture (rising from 63% to 63.6-64.4% without capture and from 55.5% to 56.1-57.1% with CO₂ capture). A further important advantage of reheating and intercooling is the significant (up to 10%) decrease in the plants' specific investment cost ($/kW), especially for CO₂ capture plants. The best option for efficiency and costs involves a combination of intercooling and reheating, achieving a 4.5% reduction in the cost of electricity compared to the H-class standard cycle. The introduction of supplementary firing, in addition to reheating, further lowers the specific plant cost but negatively impacts efficiency and the cost of electricity.