Energy 138 (2017) 920e928 Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy An exergy-based study on the relationship between costs and environmental impacts in power plants * Yolanda Lara a, Fontina Petrakopoulou b, Tatiana Morosuk c, , Alicia Boyano c, d, 1, George Tsatsaronis c a Research Centre for Energy Resources and Consumption, Zaragoza, Spain b University Carlos III of Madrid, Spain c Technische Universitat€ Berlin, Germany2 d European Commission, Joint Research Centre, Sevilla, Spain article info abstract Article history: Exergy-based (exergetic, exergoeconomic and exergoenvironmental) analyses, are used for designing, Received 21 December 2016 assessing and improving energy conversion systems. In an exergoeconomic analysis, thermodynamic Received in revised form inefficiencies e represented by exergy destruction e are used in combination with investment costs to 10 June 2017 calculate the “cost-optimal” layout of a plant. Analogously, in an exergoenvironmental analysis, the aim is Accepted 13 July 2017 to minimize the total environmental impact of a plant. Until today exergoeconomic and exergoenvir- Available online 14 July 2017 onmental analyses have been used as separate and distinct tools and the improvement of a plant has been considered in terms of the reduction of either costs or environmental impact. To simultaneously Keywords: Exergy analysis decrease the investment costs and the component-related (manufacturing or construction-related) Exergoeconomic analysis environmental impacts, their relationship with exergy destruction must be studied in parallel. This Exergoenvironmental analysis paper examines the relationship between exergoeconomic and exergoenvironmental data under various plant operating conditions. A combined-cycle power plant is analyzed and options for a simultaneous improvement from the thermodynamic, economic and environmental viewpoints are discussed. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction The environmental impacts of equipment and of real thermo- dynamic inefficiencies, their relation and interdependencies In the last decades, interest in complex analytical methods that and simultaneously include energy (exergy), economic, and environ- Actions that could decrease the cost(s) of the overall product(s), mental considerations has been growing. Such methods reveal: while, at the same time, enhancing the efficiency, and decreasing the environmental impact of the evaluated energy The thermodynamic performance of systems and the individual conversion system. processes that cause the real thermodynamic inefficiencies, The economic expenditures linked to equipment and the real An exergoeconomic analysis has been applied to numerous thermodynamic inefficiencies, their relations and energy conversion systems; different approaches for the exer- interdependencies, goeconomic analysis have been discussed [1e3], and a review of publications related to the application of exergoeconomic analysis to cogeneration systems has been published [4]. * Corresponding author. Furthermore, different approaches that combine exergetic and E-mail addresses: [email protected] (Y. Lara), [email protected] environmental analyses have been developed: the cumulative (F. Petrakopoulou), [email protected] (T. Morosuk), alicia.boyano- exergy consumption [5,6], the exergoecological analysis [7], the [email protected] (A. Boyano), [email protected] extended exergy accounting [8,9], the environomic analysis [10] (G. Tsatsaronis). 1 The views expressed in the paper are purely those of the authors and may not and the exergoenvironmental analysis [11]. These methods have be considered under any circumstance as an official position of the European been applied to various energy conversion systems, while the Commission. methods cumulative exergy consumption and extended exergy 2 www.energietechnik.tu-berlin.de, www.ebr.tu-berlin.de. http://dx.doi.org/10.1016/j.energy.2017.07.087 0360-5442/© 2017 Elsevier Ltd. All rights reserved. Y. Lara et al. / Energy 138 (2017) 920e928 921 Nomenclature Z cost associated with investment expenditures (V) B environmental impact associated with an exergy Greek symbols stream (Points) time rate b environmental impact per unit of exergy (Points/J) D difference C cost associated with an exergy stream (V) ε exergetic efficiency c cost per unit of exergy (V/J) h isentropic efficiency E exergy (J) l stoichiometric amount of air e specific exergy (J/kg) jjth stream Subscripts kkth component D refers to exergy destruction m mass (kg) F fuel p pressure (bar) P product T temperature (С) tot refers to the total system Y construction-of-component-related environmental impact (Points) accounting can also be applied to countries. It should be noted that Refs. [17e21]). some publications use the term exergoenvironmental analysis to merely indicate the environmental impact of CO ,NO and other 2 x 2.2. Exergoeconomic analysis pollutants, while at the same time ignoring the exergy destruction- related environmental impact. Sometimes, the environomic anal- An exergoeconomic analysis reveals the origin, magnitude and ysis is reported as an exergoenvironmental analysis. Only the use of location of costs of thermodynamic inefficiencies in energy con- precisely defined terms [12] eliminates this confusion. version systems. The analysis is realized at the component level of a There are publications that discuss the application of the three system and shows the relative cost importance the components analyses, i.e. exergetic, economic and environmental, conducted constituting the structure under examination, as well as alternative independently. For example, in Refs. [13,14]: (a) the exergetic solutions for enhancing the cost effectiveness of the overall system. analysis discusses only the value of the exergetic efficiency of the The exergoeconomic methodology [3,21] includes: overall system, (b) the economic analysis abbreviates to the cost of the generated electricity as a function of some economic input data, _ _ _ (a) A cost balance for each plant component, C ; ¼ C ; þ Z or and (c) the environmental analysis abbreviates to the value of P k F k k _ ¼ _ þ _ _ _ cP;kEP;k cF;kEF;k Zk. In these equations CP;k and CF;k are emitted CO2. Another group of publications (e.g., Refs. [15,16]) deals with the application of an evolutionary algorithm that finds the the cost rates of fuel and product, cP;k and cF;k are the asso- _ surface of optimal solutions defined by three objective functions ciated costs per unit of exergy and Zk represents the sum of associated with energetic, economic and environmental aspects. the cost rates associated with capital investment (CI) and Further improvements to energy conversion systems from the & & _ ¼ _CI þ _OM operating maintenance (O M) costs: Zk Zk Zk . thermodynamic, economic, and environmental viewpoints are e obtained with the aid of advanced exergy-based methods [17 19]. In this work, we assume that These include (a) an advanced exergetic analysis, (b) an advanced exergoeconomic analysis, and (c) an advanced exergoenvir- _OM (a) when the plant design is varied, the contribution of Zk re- onmental analysis. All these analyses have a similar methodological _ mains constant, and, thus, any changes in the Zk are linked to _CI background. changes in the capital investment cost Z , and (b) the fi k One of the rst attempts to combine these two exergy-based auxiliary cost equations are based on the P and F rules, as methods is reported in Ref. [20]. In this work we investigate explained in Ref. [3]. methods to improve an energy conversion system by simulta- neously decreasing costs and environmental impacts. It should be Exergoeconomic variables that can be used to improve the noted that it is not our purpose to assign costs to environmental overall performance of component k in an iterative optimization impacts (or vice versa) because this process is still arbitrary. The are the cost rate associated with its exergy destruction results from the performed environmental (Life cycle assessment, _ ¼ _ _CI þ _ LCA) and cost analyses are obtained independent from one another. CD;k cF;kED;k and its total cost rate, i.e., the sum (Zk CD;k). Other variables of the exergoeconomic analysis are given in many publi- e 2. Exergy-based analyses cations (e.g., Refs [3,17 21]). 2.1. Exergetic analysis 2.3. Exergoenvironmental analysis The exergetic balance and exergetic efficiency of a component k, Analogous to the exergoeconomic analysis, an exergoenvir- _ _ based on its exergy rates of fuel and product (EF;k and EP;k) [1,3,21] onmental analysis reveals the origin and magnitude of environ- _ _ mental impacts of thermodynamic inefficiencies in energy _ ¼ _ þ _ ε ¼ EP;k ¼ À ED;k _ are EF;k EP;k ED;k and k _ 1 _ , respectively. ED;k is the EF;k EF;k conversion systems [11]. The exergoenvironmental analysis is also total exergy destruction within the component. realized at the component level of a system and shows the relative More variables, as well as details related to the methodology of importance of the components with respect to their environmental the exergetic analysis can be found in numerous publications (e.g., impact, as well as alternative solutions for reducing the 922 Y. Lara et al. / Energy 138 (2017) 920e928 environmental impact of the overall system. In general, there are two possibilities for quarters I and II: An exergoenvironmental analysis combines a Life Cycle Assessment (LCA) with an exergetic analysis. For the purpose of the _ = _ The values of ED;k EP;k decrease with increasing values of work presented here, the LCA is realized using the life cycle impact _CI= _ _CO= _ assessment method Eco-indicator 99 [22], as this is the method Zk EP;k (line 1), or with decreasing values of Yk EP;k (line 3), or _ = _ _CI= _ employed in the reference case [24]. With this method, a one- The values of ED;k EP;k increase with increasing values of Zk EP;k dimensional characterization indicator is obtained and used in a _CO _ (line 2), or with decreasing values of Y =E (line 4).