Comparative evaluation of power plants with CO2 capture. Thermodynamic, economic and environmental performance

CCS (Carbon Capture and Sequestration) in the energy sector is seen as a bridge technology for CO2 mitigation, due to the ever-growing environmental impact of anthropogenic-emitted greenhouse gases. In this work, eight power plant concepts using CO2 capture technologies are assessed based on their efficiency, economic feasibility and environmental footprint. Exergy-based analyses are used for evaluating the considered power plants through comparison with a reference plant without CO2 capture. While conventional exergy-based analyses provide important information that can lead to improvements in plant performance, additional insight about individual components and the interactions among equipment can aid further assessment. This led to the development of advanced exergy-based analyses, in which the exergy destruction, as well as the associated costs and environmental impacts are split into avoidable/unavoidable and endogenous/exogenous parts. Based on the avoidable parts, the potential for improvement is revealed, while based on the endogenous/exogenous parts, the component interactions are obtained. Among the examined plants with CO2 capture, the most efficient are those working with oxy-fuel technology. An exergoeconomic analysis shows a minimum increase in the relative investment cost (in Euro/kW) of 80% for the conventional approach (chemical absorption) and an increase of 86% for the oxy-fuel plant with chemical looping combustion. The latter shows a somewhat decreased environmental impact when compared to that of the reference plant. On the contrary, the plant with chemical absorption results in a higher environmental penalty due to its high efficiency penalty. Therefore, accepting that all assumptions and data related to the calculations of the environmental impacts are reliable, efficiency improvement seems to be a more significant factor in potentially decreasing a plant's environmental impact. With advanced exergy-based analyses, interdependencies among components are identified, and the real potential for cost- and environmental-related improvement is revealed. A common trend for all plants examined is that most thermodynamic inefficiencies are caused by the internal operation of the components. Additionally, avoidable quantities are generally found to be low for components with high costs and environmental impacts, leaving a relatively narrow window of improvement potential.