Thermodynamic analysis of oxy-fuel gas cycles for CO2 capture
With the need to reduce the emission of greenhouse gases, several technologies have been developed aiming to increase efficiency and to reduce the emission of carbon dioxide (CO2) in thermal power systems. One of the proposals for mitigating CO2 emissions and CO2 capture is the oxy-fuel combustion technology. In this technology, combustion takes place in the presence of a stream with high concentration of oxygen (greater than 90 mol% of O2), in such a way that the combustion products are a stream composed mainly of water and CO2 and other impurities present in the oxygen stream and in the fuel. One of the advantages of oxy-combustion is the ease to remove water from flue gases, which can be removed by condensation. On the other hand, to obtain oxygen, an air separation unit is required, which has high energy consumption and penalizes the efficiency of power plants with oxy-fuel combustion. In these systems an efficiency decrease in the range of 10% is expected. In this work, 3 oxy-fuel gas cycles were chosen among those present in the literature for a comparative analysis: semi-closed oxy-fuel combined cycle (SCOC-CC), Clean Energy Systems (CES) and E-Matiant. These thermodynamic cycles were modeled in the EES. As the efficiency of power systems is also an important factor for the mitigation of CO2 emissions, it was proposed to maximize the energy efficiency of these cycles through particle swarm optimization. The comparative analysis has as main objective to find the advantages and disadvantages of the 3 cycles, taking into account the first and second analysis of thermodynamics. Results show that the optimal efficiency found by the optimization algorithm for the SCOC-CC cycle is 7.43 percentage points lower than a reference plant (conventional combined cycle), the optimal efficiency found for the E-Matiant cycle is 9.35 percentage points lower than the reference plant and the optimal efficiency found for the CES cycle is 10.74 percentage points lower than the reference plant.