Eventos Anais de eventos
ENCIT 2022
19th Brazilian Congress of Thermal Sciences and Engineering
THERMODYNAMIC ANALYSIS OF THE INFLUENCE OF CARBON DIOXIDE AS DILUENT IN OXY-FUEL COMBUSTION GAS TURBINES
Submission Author:
Antonio Gallego , SP , Brazil
Co-Authors:
Rafael Pinho Furtado, Antonio Gallego, Silvia Azucena Nebra de Perez, André Vilela, Reynaldo Palacios
Presenter: Reynaldo Palacios
doi://10.26678/ABCM.ENCIT2022.CIT22-0238
Abstract
Oxy-fuel combustion is an important technology to reduce carbon dioxide emissions in thermal power plants like boilers and gas turbines. The use of oxy-fuel in gas turbines implies substituting air for oxygen with carbon dioxide or water in the dilution process in the combustion process. The substitution of carbon dioxide and water as working fluid, that is, the carbon dioxide would replace the air, the usual working fluid. The gas properties of this working fluid differ significantly from those of a conventional air-breathing gas turbine; hence, the gas turbine must be designed accordingly. The combustion with nearly pure oxygen can reach temperatures around 2500 °C, much higher than the thermal capacity of the materials employed in combustors and turbines. Then, to control the combustion chamber temperature, the oxygen is diluted with a portion of flue gas. The flue gas produced is composed mainly of carbon dioxide and water vapour. They were making it possible to separate the water from the flue gas by condensation and avoiding more complex separation processes, such as chemical absorbents, which is the main advantage of oxy-fuel technology. On the other hand, the nearly pure oxygen stream, containing about 90-99.5 mol%, is produced in an air separation unit, which has a high energy consumption and penalizes the power plant efficiency. In this work, two oxy-fuel gas cycles were analyzed among those present in the literature: the semi-closed oxy-fuel combined cycle (SCOC-CC) and the E-Matiant. The main objective of the analysis is to identify the advantages and disadvantages of these cycles utilizing the first and second laws of thermodynamics and the theory of exergy cost, thereby helping to determine the influence of using CO2 as diluent in oxy-fuel combustion and the sources of the cycle’s thermodynamic inefficiencies. The energy efficiency of the SCOC-CC and E-Matiant are, respectively, 49.14% and 47.65%. The exergy efficiency is 46.94% for the SCOC-CC and 53.79% for the E-Matiant. In comparison to a conventional combined cycle, these cycles are less efficient, but they have the great advantage of capturing all the carbon dioxide produced in the combustion, which makes them attractive from an environmental perspective.
Keywords
Oxy-fuel, SCOC-CC, CO2 capture, Exergoeconomic analysis, Exergy analysis.
