Introduction to Exergoeconomic and Exergoenvironmental Analyses

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Tehnishe Universität Berlin Introdution to

Environment Oshawa, Canada April, 30 - May 4,

1 Tehnishe Universität Berlin Introdution to Exergoeonomi and Exergoenvironmental Analyses George Tsatsaronis The Summer Course on Exergy and its Appliation for Better Environment Oshawa, Canada April, 30 - May 4, 202 tsatsaronis@iet.tu-berlin.de

2 System Improvement - 2 Design improvement of an energy onversion system means the seletion of the struture and the design parameters (the deision variables) of the system to minimize the total ost (environmental impat) of the system produts (over the entire lifetime of the system) under boundary onditions assoiated with available materials, finanial resoures, environmental protetion and government regulation as well as with the safety, reliability, operability, maintainability, and availability of the system. In a truly improved system, the magnitude of every signifiant thermodynami ineffiieny (exergy destrution and exergy loss) is ustified by onsiderations related to investment and operating osts as well as to environmental impat or is imposed by at least one of the above boundary onditions.

3 System Improvement Engineers involved in the design of energy onversion systems want, after they have developed a first worable design, and in order to improve this design, to now the answers to the following questions: Where do thermodynami ineffiienies in the system our, how high are they, and what auses them? What measures or alternative designs would improve the effiieny of the overall energy-onversion system? How high is the required total investment and the purhased equipment osts (environmental impat) of the most important system omponents? How muh do the thermodynami ineffiienies ost (have environmental impat) the system operator? What measures would improve the ost (environmental) effetiveness of the overall system? Exergy analysis Eonomi analysis or L C A Exergoeonomi (environmental) analysis

4 4 Exergoeonomi Analysis

5 Exergoeonomis: Definition - 5 Exergoeonomis applied to design improvement (optimization) represents a unique ombination of exergy analysis and ost analysis, to provide the designer of an energy onversion system with information not available through onventional energy, exergy, or ost analyses, but ruial to the design of a ost-effetive system. A thermodynami improvement, whih aims at minimizing the thermodynami ineffiienies, represents a sub-ase of the general ase of design improvement. The formulation of a mathematial model for an optimization problem is always one of the most important and sometimes the most diffiult tas in an optimization study.

6 Exergoeonomis: Definition The obetive of exergoeonomi optimization is to minimize the sum of apital-investment related osts, fuel osts and operating and maintenane expenses for the overall plant (to find the appropriate trade-offs mainly between the first two groups). Deisions are made, however, at the plant omponent level.

7 Exergoeonomis: Thermodynamis and Eonomis - 7 Exergoeonomis is based on the following three onnetions between thermodynamis and eonomis: An exergy destrution represents in the design of a new energy onversion system not only a thermodynami ineffiieny but also an opportunity to redue the investment ost assoiated with this system. Exergy is the only rational basis for assigning monetary values to the interations that an energy onversion system experienes with its surroundings and to the soures of thermodynami ineffiienies within the system. The ost of exergy destrution is, in general, different for eah omponent and depends on the relative position of the omponent within the energy onversion system.

8 Z E Exergoeonomis: Thermodynamis and Eonomis - 2 CI P, An exergy destrution represents in the design of a new energy onversion system not only a thermodynami ineffiieny but also an opportunity to redue the investment ost assoiated with the system being analyzed. 8 E E D, P,

9 Exergoeonomis: Thermodynamis and Eonomis - 3 The Exergy Costing priniple states that exergy is the only rational basis for assigning monetary values to the interations an energy system experienes with its surroundings and to the thermodynami ineffiienies within the system. Mass, energy or entropy should not be used for assigning the above mentioned monetary values beause their exlusive use results in misleading onlusions. Aording to the exergy-osting priniple, the ost stream ( C ) assoiated with an exergy stream ( E ) is given by 9 [ /s] C E [ /J]x[J/s] where stream E represents the average ost per exergy unit of the

10 Exergoeonomis: Exergy Costing 0 Costs of exergy transfers assoiated with heat and wor C C Q W Q W E Q W Cost rate assoiated with a stream of matter C m E PH PH CH CH T T M M CH CH e e m e e e PH E PH CH E CH, Q, and W denote average osts per unit of exergy (for example, /GJ )

11 Exergoeonomis: Cost Calulation osts are nown for all entering streams alulate osts of existing streams using ost balanes and auxiliary equations

12 Exergoeonomis: Cost Balane - 2 C C,,in 2,,in C n,,in 2 n -th system omponent Z Z CI Z OM 2 m C,, C 2,, out out C m,, out Cost balane applied to the -th system omponent n C,,in m CI OM Z Z C,,out n E Z E,in m,out

13 Exergoeonomis: Cost Balane C C,,in 2,,in C n,,in 2 n -th system omponent Z Z CI Z OM 2 m C,, C 2,, out out C m,, out Cost balane applied to the -th system omponent P, E P, F, E F, Z A fuel and a produt are defined for eah omponent of a system.

14 Exergoeonomis: Auxiliary Equations - 4 osts are nown for all entering streams alulate osts of existing streams using ost balanes and auxiliary equations In general, if there are N e exergy streams exiting the omponent being onsidered, we need to formulate (N e ) auxiliary equations (based on so-alled F and P rules).

15 Exergoeonomis: Auxiliary Equations F Equations The total ost assoiated with the removal of exergy from an exergy stream in a omponent is equal to the ost at whih the removed exergy was supplied to the same stream in upstream omponents The exergy differene of this stream between inlet and outlet is onsidered in the definition of fuel for the omponent.

16 Exergoeonomis: Auxiliary Equations P Equations Eah exergy unit is supplied to any stream assoiated with the produt of a omponent at the same average ost P, This ost an be alulated diretly from the ost balane and the F equations.

17 Heat Transfer - 7 Hot stream C P C F 4 Q E Q 3 C C Z C 2 HE 3 C4 2 Cold stream F C E 4 4 C E 3 3 T T 0

18 8 Heat Transfer - 4 SG Z C C C C C C C C C P C F E E C C E E C C p E E C C E C E C

19 Compressor, Pump, or Fan 9 Compressor with ooling air extrations 2 W 3 air ompressed air 4 5 ooling air e e e e e e e e e e e e P 3 3 CM E Z E E E E P C F C

20 Turbine or Expander 20 Expander with ooling air supply 4 5 ooling air C P C F ombustion produts W 3 C 3 Z EX C C4 C5 C2 2 F C E 2 2 C E C E 4 4 C E 5 5

21 Combustion Chamber 2 fuel oxidant gaseous reation produts 2 3 solids 4 C P C F C C Z C 3 2 CC C4 C E 4 4 C E

22 Exergoeonomis: Variables - 22 Cost balanes P, P,tot E E P, P,tot F, F,tot E E F, F,tot Z Z tot C L,tot Average ost of fuel and produt for the -th omponent F, F,tot C E C E F, F, Average ost of fuel and produt for the overall system F,tot F,tot C D, F, E P, P,tot D, C E C E P, Cost rate assoiated with exergy destrution P, P,tot P,tot

23 Exergoeonomis: Cost Soures 23 The real ost soures in an energy onversion system are: apital investment for eah omponent operating and maintenane expenses Z Z CI Z OM ost of exergy destrution C D, F, ost of exergy loss from the overall system (th stream reeted to the environment) C L,tot E D, E

24 Component Evaluation 24 The evaluation of system omponents from the exergoeonomi viewpoint is based, in addition to the exergy E based variables and, on D, the ost of exergy destrution and on the apital investment ost., C D, The sum of these two osts determines the eonomi importane of the omponent being onsidered. y D, Z C D, Z

25 Component Optimization 25 Z E CI P, Z E CI P, opt C E D, P, opt 45 o C E D, P,

26 Exergoeonomis: Variables Relative ost differene between the average ost per exergy unit of produt and average ost per exergy unit of fuel r P, F, F, F, E F, D, E P, Z F, Z E P, Exergoeonomi fator f Z Z C D, Z Z F, E D,

27 Exergoeonomis: Variables The alulation of some exergoeonomi variables might be assoiated with some arbitrariness. However, exergy-based methods are pratial methods that allow engineers to extrat useful onlusions. Auray is of seondary importane. Therefore, the riterion for aepting or reeting new variables should be whether the information provided by them helps engineers to develop ideas and solutions that annot be suggested by other variables.

28 28 Exergoenvironmental Analysis

29 Exergoenvironmental Analysis - 29 An exergoenvironmental analysis rests on the notion that exergy is the only rational basis for assigning, not only monetary values, but also values of environmental impat to the transport of energy and to the thermodynami ineffiienies within the omponents. We refer to this priniple as exergoenvironmental osting.

30 Exergoenvironmental Analysis An exergoenvironmental analysis onsists of three steps: The first step is an exergy analysis. The seond step onsists of an LCA onduted for (a) eah relevant system omponent, and (b) all relevant input streams to the overall system. In the third step, the environmental impat obtained from the LCA is assigned to the exergy streams in the system. The most important omponents from the eologial point of view (having the highest total environmental impat within the system) are identified.

31 Environmental Impat Balane 3 Y PF B B,,in B 2,,in B n,,in 2 n -th system omponent 2 m B,, out B 2,, out B m,, out b P, E P, b F, E F, Y B PF Y Y CO Y OM Y DI The omponent-related environmental impat B PF b m m i PF i i,out i,in Formation of pollutants, e.g., CO, CO 2, N 2 O, NO x and SO x

32 Life Cyle Assessment 32 The total system used to ondut the LCA inludes the supply of the input streams, espeially the fuel, and the full life yle of omponents. Inventories of elementary flows i.e., onsumption of natural resoures and energy as well as emissions - are ompiled following the guidelines of international standard approahes. An impat assessment is performed using an environmental indiator (e.g., the Eo-indiator 99, whih is based on the definition of three damage ategories, human health, eosystem quality and natural resoures). The result is expressed as Eo-indiator points (pts).

33 33 Appliation to a Simple Gas-Turbine System

34 Simple gas-turbine system: Appliation - 34

35 Simple gas-turbine system: Appliation E D,CC E F,CC E P, CC E 3 E4 E2 E D,AC E W F,AC AC E P,AC E 2 E E D,GT E F,GT E P,GT E E W 4 5 GT 72.76

36 Simple gas-turbine system: Appliation Air ompressor Combustion hamber Expander

37 Simple gas-turbine system: Appliation

38 Simple gas-turbine system: Appliation Exergy analysis Exergoeonomi analysis Eonomi analysis

39 Simple gas-turbine system: Appliation Y CC 34mPts / h E D, CC E 3 E4 E2 E D,AC W AC E 2 E E D,GT E E W 4 GT 5 Y AC 82mPts / h Y AC 394mPts / h

Simple gas-turbine system: Appliation - 7 40

40 Simple gas-turbine system: Appliation Exergy analysis Exergoenvironmental analysis

41 Conlusions 4 The exergy-based methods enable engineers to alulate the flow of exergy, ost and environmental impat through the plant identify the real soures of thermodynami ineffiienies, osts, and environmental impats alulate the ost and the environmental impat assoiated with exergy destrution at the omponent level deide about well ustified design hanges With these methods a plant an be analyzed in a onsistent way from the viewpoint of thermodynamis, eonomis and environmental impat, and the onnetions between thermodynamis and eonomis as well as between thermodynamis and LCA are revealed The onnetions between environmental impat on one side and thermodynamis or eonomis on the other side still need to be studied.

42 Introdution: Exergy-based Methods 42 Exergoeonomi analysis Exergoenvironmental analysis Exergy analysis Eonomi analysis Life yle assessment Exergoeonomi evaluation Iterative improvement Exergoeonomi evaluation Iterative improvement

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