(345d) Bi-Objective Optimization of an Integrated Natural Gas Combined Cycle (NGCC) and Post Combustion Carbon Capture (PCCC) System: Efficiency Penalty Versus Cost of CO2 Avoided

Generation of electricity through fossil fuel power plants has a significant impact on greenhouse gas (GHG) emissions, especially with the projected increase in global energy demand. Therefore, reducing GHG emissions is crucial to mitigate climate change, and effective strategies must be adopted. However, decarbonizing power plants is an energy-intensive process that results in substantial power loss and increased electricity cost. According to the literature, integrating a natural gas combined cycle (NGCC) power plant with post-combustion carbon capture (PCCC) unit results in an efficiency penalty between 9% and 14%. To address this challenge, researchers have explored various strategies to reduce the efficiency penalty of the integration system. Among these strategies are heat integration, heat intensification, installation of a vapor-compression refrigeration cycle, and modifications to the process configuration, all of which have been proven to reduce the efficiency penalty. Nonetheless the economic feasibility of the proposed processes remains uncertainty in many of the studies. This study proposes the development of a bi-objective optimization model to minimize the efficiency penalty and the cost of CO2 avoided of the integrated system. An equation-based model of a 727 MW NGCC is developed in gPROMS^© and a rate-based simulation of the PCCC is developed in Aspen Plus, both of which are validate. To perform the optimization in the integrated system, the rigorous PCCC simulation is approximated by a surrogate model. Thus, NGCC and PCCC are represented by a mathematical model, and the base case integration has an efficacy penalty of 8.83% and a cost of CO2 avoided of 90.6 $/tonneCO2. An optimization problem was formulated with the following decision variables: exhaust gas recycling (EGR) ratio, steam extraction site, lean solvent load, and absorber and stripper length-to-diameter ratio. The results show that a further reduction in the efficiency penalty of the integrated system causes an increase in the cost of CO2 avoided. In other words, the efficient penalty and the cost of CO2 avoided are inversely proportional. The minimum efficient penalty and cost of CO2 avoided are 7.5% and 74.3 $/tonneCO2, which is a significant improvement compared to the base case. Overall, the study underlines the importance of evaluating the economic feasibility of the proposed system, as well as demonstrated the power and capability of surrogate model in representing a rigorous rate-based capture simulation.