CO 2 Capture in a Chemical Looping Combustion Power Plant Evaluated With an Advanced Exergetic Analysis Fontina Petrakopoulou, a,b George Tsatsaronis, a and Tatiana Morosuk a a Technische Universit € at Berlin, Marchstr. 18, 10587 Berlin, Germany; f.petrakopoulou@chemeng.ntua.gr (for correspondence) b National Technical University of Athens, Iroon Polytechneiou 9, 157 73 Athens, Greece Published online 10 September 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ep.11848 CO 2 capture and storage (CCS) is a way to minimize harmful emissions generated from the combustion of fossil fuels in power plants. Measures to increase the thermody- namic efficiency of power plants incorporating CCS can improve their economic viability, as well as reduce the envi- ronmental impact of such applications. Exergy-based analy- ses are tools that aid the evaluation of energy conversion systems and reveal paths to improve them. In this article, an advanced exergetic analysis is applied to a near-zero- emission power plant that incorporates chemical looping combustion. The final goal is to reveal ways toward a more efficient and less polluting operation of the power plant. The objectives of the article further include the quantification of the different parts of the exergy destruction and the demon- stration of the advantages of using such an advanced method. It has been found that most of the exergy destruction of the plant is endogenous and, for the majority of the com- ponents, unavoidable. When calculating the total avoidable exergy destruction caused by each component, it is found that the most important plant component is the reactor unit, followed by the expander and the compressor of the gas tur- bine. Lastly, the potential for improvement is found to lie mainly with the internal operation of the components, while the interactions among the plant components are less signifi- cant. V C 2013 American Institute of Chemical Engineers Environ Prog, 33: 1017–1025, 2014 Keywords: advanced exergetic analysis, CO 2 capture, chemical looping combustion INTRODUCTION Exergy (useful energy) identifies the real sources of ineffi- ciencies in a system, which is the exergy destruction within a component (caused by irreversibility) and the exergy losses (associated with the transfer of exergy to the environment). The energy concept, on the contrary, identifies as thermody- namic inefficiencies only the transfer of energy to the envi- ronment. Therefore, an exergetic analysis can reveal pathways for improving energy conversion systems, whereas energy-based methods can mislead the improvement efforts. Conventional exergy-based analyses provide useful infor- mation about improvements of an energy conversion system from the viewpoint of thermodynamics [1–3]. In conventional exergoeconomic and exergoenvironmental analyses, mone- tary costs and environmental impacts are quantified and assigned to all exergy streams of the plants, as well as to the exergy destruction incurred within each plant component. Although this information is very useful, conventional exergy-based analyses do not identify component interde- pendencies in a thermal system, nor do they quantify the avoidable part of exergy destruction=cost=environmental impact [4]. These limitations of the conventional exergy- based methods are addressed by the so-called advanced exergy-based analyses. Advanced exergy-based methods have been developed as tools to provide further insight into plant improvement and can be extremely useful when complex energy conversion systems are considered (e.g., see Refs. 5, 6). Although rela- tively complex in their application, these methods are very useful in revealing detailed strategies for improving complex energy conversion systems that cannot be obtained with other means. Specifically, with advanced exergy-based analy- ses, the improvement potential and the component interac- tions are revealed and quantified [7–9]. The potential for improvement is determined by separat- ing the exergy destruction within each plant component into avoidable=unavoidable parts [7]. The avoidable part of the exergy destruction is the part that can be eliminated through design and=or operational improvements. The unavoidable part of the exergy destruction per unit of product, ð _ E D = _ E P Þ UN k , is the part that cannot be eliminated because of physical, technological, or economic constraints. These esti- mations are conducted for the foreseeable future, (thus, they are not based on a specific year of operation of each compo- nent), and are somewhat chosen subjectively. The estima- tions assume the best possible operation of the components that leads to maximum efficiency, which is obtained when the investment cost of the component being considered becomes extremely high (Figure 1) [7]. Additionally, the exergy destruction within plant compo- nents can be separated depending on its source: If it is caused by component interactions, it is exogenous, while if it stems exclusively from the operation of the component itself, it is endogenous [8]. Exogenous and endogenous parts are also calculated for the avoidable and unavoidable parts of exergy destruction. In this work, an advanced exergetic analysis is applied to a combined-cycle power plant incorporating oxy-fuel V C 2013 American Institute of Chemical Engineers Environmental Progress & Sustainable Energy (Vol.33, No.3) DOI 10.1002/ep October 2014 1017