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PROCEEDINGS OF ECOS 2016 - THE 29TH INTERNATIONAL CONFERENCE ON EFFICIENCY, COST, OPTIMIZATION, SIMULATION AND ENVIRONMENTAL IMPACT OF ENERGY SYSTEMS JUNE 19-23, 2016, PORTOROŽ, SLOVENIA

Simulation and comparative Thermoeconomic analysis of Central Receiver Concentrated Solar plants using air as heat transfer fluid Andrea Catalanoa , Matteo Rocco c, Claudia Torob , Emanuela Colombo c , Enrico Sciubba a a

Università di Roma “Sapienza”, Department of Mechanical and Aerospace Engineering, via Eudossiana 18, Rome, Italy, e-mail b CNR Institute of Environmental Geology and Geoengineering, Roma Italy, e-mail, c Politecnico di Milano, Milan, Italy, [email protected]

Abstract The latest developments on solar technologies demonstrated that the Solar Central Receiver configuration is the most promising application among Concentrated Solar Plants (CSPs). As an alternative to more traditional working fluids, solar-heated air can also be used in CSPs both as working fluid in a Brayton thermal cycle and to heat water for a Rankine thermal cycle, reducing maintenance operations and providing the power section with a higher degree of flexibility; in this case an auxiliary burner is required to extend the operation during off-sunshine hours without a Thermal Energy Storage. This configuration is adopted in Julich CSP plant, operating in Germany and characterized by a nominal power of 1.5 MW, where air is used as heat transfer fluid in the solar tower and to produce steam for the bottoming Rankine cycle. In this paper, the Julich plant with thermal energy storage has been compared with a hybrid CSP plant using air as working fluidin terms of resources consumption and costs. A thermoeconomic analysis has been performed for all the simulated plants, considering the average year of operation and the same amount of yearly net electricity production. The exergy and exergoeconomic costs of each system product has been derived, and the structure of such costs has been analyzed.

Keywords Concentrated Solar Plant, Process simulation, Thermoeconomic Analysis, Exergy Analysis.

1. Introduction The second half of the twentieth century has seen a rapid and worldwide increase of atmospheric pollution levels, which has forced many countries to invest in eco-friendly energy conversion process. This was the motivation behind the development and industrialization of several lowpollution novel technologies. Concentrated Solar Power (CSP in the following) is one of them and is showing good prospective for electric power productions. The most popular optical reflecting surfaces for CSP applications are parabolic trough [1], dish concentrators [2], linear Fresnel reflectors [3, 4] and solar central receiver [5]: each configuration requires a specific type of receiver. There is a broad agreement across the CSP community that central receiver solar power plants can play an important role in the future of concentrating solar power [6, 7] In a central receiver CSPa field of heliostats concentrates the direct solar irradiation on a high-temperature solar receiver placed atop of a central tower in which the heat transfer medium absorbs (by convection/radiation effects) the reflected and focused solar power and the heat is made available for a downstream power thermal cycle -usually, a Rankine plant. Current solar towers use water/steam, air or molten salt to transport the heat to the heat-exchanger/steam turbine system. Depending on the receiver design and the working fluid, the upper working temperatures can range from 250°C to 1000°C for 1


future plants, although temperatures of around 600°C will be the norm with current molten salt designs. As reported in [8], the performance of this kind of plant is linked to the installed reflecting surface, as in relation (1).

SP =lr ⋅ Sr =lm ⋅ Sm

(1)

In equation (1), SP is the direct irradiation power, I the power irradiation per unit surface and S is the reflective surface; the subscripts m and r refer to mirrors and receiver respectively. Assuming that no losses occur in the concentrator, the ratio between the available mirror surface and the receiver surface is equal to the ratio between the irradiation on the mirrors and that on the receiver. Therefore, the available specific irradiation power for the receiver is much higher than the irradiation available for a single mirror (see relations (2) and (3)).

= Sm ⋅ Sr C

(2)

I r= C ⋅ I m

(3)

The ratio between the total surface of the mirrors and the receiver surface C is called concentration ratio and is an important CSP design variable: a larger C means a higher power available for the combined cycle. The configurations here analyzed are based on a Solar Central Receiver installed upon a central tower where sunrays are reflected; the design of the receiver depends on the heat transfer medium and on the maximum allowable external surface temperature. The heat transfer medium flows through the receiver and absorbs the irradiation power: its sensible heat can then be used either to energize the working fluid in the power cycle via a secondary heat exchanger medium or directly exploited in the power cycle. Molten Salt or Water are generally used as heat transfer media; both can be stored in Thermal Energy Storage tanks to buffer the daily solar energy variations. Molten Salts have some disadvantages though: they need a secondary heat exchanger, have a minimum working temperature (260÷550 °C) and must be evacuated from pipes, tanks or receivers before maintenance operations. Unlike molten salts, water can be directly heated in the receiver to superheated steam without using another medium, which reduces installation and maintenance costs. Figure 1 shows the working principle of a CSP steam plant.

Figure 1 – Central receiver CSP steam plant working principle. Air can be used as medium as well; it has several advantages: it is free, abundant and it is not a polluting substance and, unlike molten salt, it remains in gaseous state at atmospheric temperature. 2


However, in this case an auxiliary burner is needed to extend the operation during off-sunshine hours This paper simulates, analyzes and compares from a thermo-economic point of view two different central receiver CSP plants using air as the main medium fluid: the Julich plant [9] with TES and an hybrid central receiver plant with an auxiliary burner. The performances of the two solar plants have been compared with the ones obtained from a traditional natural gas- fueled combined- cycle power plant to quantify benefits and drawbacks in terms of efficiency, emissions and costs considering the off-design plant operation due to the seasonal changes in solar radiation. The plants simulations were performed using the CAMEL-Pro™ process simulator [10]; this software (CAlculation with Modular ELements) has been developed at the Department of Mechanical and Aerospace Engineering of the University of Roma Sapienza. The main feature of CAMEL is its modularity that enables users to expand the code by adding new components or by modifying the model of the existing ones. The code’s task is the simulation of energy conversion systems, and in particular, thermal power plants. CAMEL-Pro™ is equipped with a library of thermodynamic properties for the calculation of thermo-physical properties of fluids [11]. Models for the calculation of thermodynamic and transport properties of steam and organic fluids are implemented according to [11]. CAMEL has proved itself as a useful tool for both designing a new plant and analyzing the behavior of an existing one[12-15]. In the first chapter the layout and design data of the simulated plants are presented, the second chapter presents the results of the process simulations and the last part of the paper discuss the results obtained by the thermo-economic analysis and comparison.

2. Plants layout, design data and specifications and economics This section presents the layouts, the operative parameters and the specifications of the simulated plants: • Solar Power Tower Julich (J); • Hybrid Concentrated Solar Plant (CSP); • Conventional Combined Cycle Power Plant (CCP); The electric nominal power output has been fixed to 1.5 MW for all the plants. For the simulations a latitude of 31° north (northern African countries) has been chosen. The climate data, such as global irradiance [kW/m2], daylight hours and ambient temperature for the selected area have been obtained from the NASA database [16] and are reported in Table 1. Table 1 – Local climate data [16], where “i” is the monthly Averaged Radiation Incident On An Equator-Pointed Tilted Surface; “di” is the Monthly averaged daylight hours and “Ti” is the Monthly Averaged Temperature. Month i [kW/m2/day] di [h/day] 10.2 Jan 5.07 11 Feb 5.63 11.9 Mar 6.39 13 Apr 7.12 13.8 May 7.77 14.3 Jun 7.58 14.1 Jul 7.83 13.3 Aug 7.68 12.4 Sep 7.15 11.4 Oct 5.68 10.4 Nov 5.12 3

Ti [°C] 11.6 14.1 18.7 23.9 29.9 35.1 37.7 37.1 31.2 25 18.1


Dec

4.55

10

13.1

2.1. Solar Power Tower Julich (J) The Solar Power Tower Julich [9] is a high temperature central receiver plant where the primary cycle working fluid is air at atmospheric pressure that is heated up to temperatures of about 700°C. This solar heat then powers a steam generator, producing steam at 7 bars and 650°C and driving a 1.5 MWel turbine-generator set. A Thermal Energy Storage (TES) is integrated into the power cycle to ensure longer availability of energy production beyond daylight hours; According with [17] the installed TES reaches 2.4 MWth (air temp 680-640°C) during charge and 2,2 MWth during discharge (air temp 680 °C) within 1.5 hours. The layout of the Julich plant is shown in Figure 2.

Figure 2 – Julich Plant layout.

Figure 3 – Julich Plant simulated layout. 4


In Fig 3, the Julich plant layout simulated in CAMEL is represented. Air flows (stream #1) into the CSP plant (with a volumetric central receiver) and is heated absorbing solar energy. This air is then used to produce steam (stream #8) in the HRSG. Downstream the steam generator the water/steam flowline follows all transformations we can find in a normal steam plant, producing electric power (stream #11). During TES charge operation, part of the heated air (stream #5 at 680°C) goes toward to TES. After the HRSG the air passes through a couple of compressor, fed by the steam turbine, to face pressure losses. During discharge the CSP is kept out from the process and air flows from TES hot side (stream #5) and, after the heat exchange at HRSG, get back at TES cold side ( stream #24, 4 kg/s at 120 °C). The charge/discharge operation takes 1,5 h. This layout is under investigation of DLR and no commercial plant uses this kind of process yet. Technical specifications [18] of the Julich plant are shown in Table 2. Table 2 – Julich plant technical specifications Data Number of heliostats Heliostat aperture Reflecting area Heat Transfer Fluid HTF Temp out Storage Turbine power ST Adiabatic Efficiency

Unit m2 m² °C h MWel %

Value 2153 8.2 17 650 Air 680 1.5 1.5 88

The computed values of m,p,T,h and s at all the Julich cycle states are shown in Table 6 and 7 (In appendix A) for the months of August (maximum solar irradiation), December (minimum solar irradiation) and during TES discharging (night hours).

2.2. Hybrid Concentrated Solar Power Plant As explained in the previous paragraph, in the Julich plant a TES system has been installed to ensure longer availability of the production. In order to make the CSP plant more flexible a second option is to replace TES with a gas burner which allows to guarantee the power requirement during night hours and completes the air heating when the solar irradiation is lower. This solution guarantees the plant to works continuously. The layout of this second hybrid (solar-gas fuelled) plant is reported in Fig 4. The air flow (stream #1) is compressed to face pressure drops and then is heated by both the CSP plant and the combustion chamber reaching the temperature of about 600°C (stream #28). This air then powers a steam generator, producing steam at 7 bars and 675°C (stream #6) and driving a 1.5 MWel turbine-generator set. During night hours, the fuel (stream #22) in the auxiliary burner guarantee the electric production (fixed to 1.5MWel). The CSP plant and the combustion chamber work complementarily: during night hours, the CSP is turned off and air heating is obtained by the combustion chamber while during summer, when the solar irradiation is higher, the air is fully heated by the CSP and the combustion chamber is turned off. Technical specifications of the simulated CSP hybrid plant are shown in Table 3. Table 3 – CSP hybrid plant technical specifications Data Number of heliostats Heliostat aperture Reflecting area Heat Transfer Fluid HTF Temp out

Unit m2 m² °C 5

Value 1800 8.2 14760 Air 680


Turbine power ST Adiabatic Efficiency Fuel

MWel % -

1.5 88 CH4

Figure 4 – Hybrid CSP layout The heliostat field has been sized by requiring that in the sunniest month (August) the plant was exclusively powered by solar energy (degree of hybridization equal to zero). Table 8shows the computed values of m,p,T,h and s at all the cycle states for the hybrid CSP plant in August and December. In Figure 5 solar and fuel inputs percentage yearly trends for the hybrid CSP plant are shown. This plant has a hybridization degree that spans from 0 (August and September) to 18% (December). 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Jan

Feb

Mar

Apr

May

Jun

% Fuel

Jul

Aug

Sep

Oct

Nov

% Solar

Figure 5Hybrid CSP input power monthly distribution 6

Dec


2.3. Conventional Combined Cycle Power Plant (CCP) The layout of the traditional natural gas- fueled combined- cycle power plant, simulated and compared to CSP plants, is presented in Figure 1. This power plant has one gas turbine, one compressor, one HRSG, one steam turbine and one surface condenser with a cooling system using water as cooling medium. The total output power is 1.5 MW, 500kW produced by the steam turbine and 1 MW by the gas turbine group.

Figure 6 Natural gas- fuelled combined cycle layout Technical specifications of the simulated combined plant are shown in Table 4. Table 4 Combined cycle technical specifications Data GT Politropic Efficiency ST y Adiabatic Efficienc COMP Politropic Efficiency CC Efficiency TIT (gas) TIT (steam) HRSG Efficiency Fuel

Unit % % % % 1400 700 % -

Value 88 88 85 95 Air 680 95 CH4

2.4. Investment and Operative economic costs of the plants The estimate of plants investment costs has been performed to identify the main cost drivers and calculate the economic cost of the products. Based on the work of Augsburger [19]direct and indirect costs related to the heliostats field, the solar tower and receiver and to power conversion unit has been calculated for the Julich and CSP 7


plants. The obtained results are presented in Table 5 which also includes the investment cost for CCP calculated by the equations in [20]. As a result, the investment cost of the heliostat field accounts for the highest share, with 7.70[M$] for the Julich and 6.58[M$] for the CSP, exceeding about 25% for both. The natural gas average price has been collected from [21]. Once the Total Investment Cost (TIC) (including O&M costs) has been evaluated for all the considered systems, the annual levelized cost is calculated through the capital recovery factor (crf) method in relation (4), based on an estimated plant lifetime n of 20 years and on an interest rate of capitals i of 5%, equal for all the plants. Z inv = TCI ⋅ crf

→

 i (1 + i )n  Z inv = TCI ⋅   n  (1 + i ) − 1 

(4)

Table 5 – Results of the economic cost analysis for all the systems. Components Solar Tower Receiver Heliostats Field Storage Steam Turbine & generator Steam Generator Cooling System Combustion chamber Compressors Gas Turbine Total Investment Cost Annual Levelized Cost

Julich M$ - 2016 1,34 6,82 7,70 2,29 2,95 0,90 6,04 0,00 28,03 2.25

CCP M$ - 2016 1,34 0,03 4,53 0,10 0,77 0,62 5,56 0.45

CSP M$ - 2016 1,34 6,82 6,52 2,95 0,82 6,04 0,22 0,01 24,72 1.98

3. Thermoeconomic analysis According to literature, Thermoeconomic Analysis (TA) can be defined as the joint application of Exergy Analysis as economic principles, and it is widely recognized as an appropriate thermodynamic-based tool for the evaluation of the costs of energy system products and the structure of such costs [22-25]. Thermoeconomic analysis can be adopted to evaluate different types of “costs” [15, 26, 27], and thus it can be distinguished in two main ways: • Exergy Cost Analysis: introduced by Valero through the Exergy Cost Theory (ECT) [28], it aims at evaluating the cost as the amount of exergy required by the system to produce its products (cex, measured in J/J)[24, 29]; • Exergoeconomic Cost Analysis: it based on the same accounting rules and mathematical formulation of the Exergy Cost Analysis. However, it accounts for the economic cost of the system products (ceco, measured in $/J) [30, 31]. Both the methodologies are based on the same accounting structure and cost allocation rules. Beside the cost accounting purposes, one of the main goal of Thermoeconomics is the evaluation of the cost structure of the system products, understanding the cost formation process and thus introducing criteria and indicators for system design optimization [32, 33]. In this section, Thermoeconomic analysis is applied to the above introduced plant configurations considering their average yearly operation as described in section 3. With reference to Figure 7, Thermoeconomic systems for all the considered plants are written at their maximum aggregation 8


level and based on the exergy balance (4), where arrows distinguish among non-renewable (NR) and renewable (R) inlet contributions (F), products (P), losses (L) and exergy destructions (D). ExF , NR ,i + ExF , R ,i = ExP ,i + ExL ,i + ExD ,i

→ ηex =

ExP ,i ExF , NR ,i + ExF , R ,i

(5)

(ExD) ExNR ExR

System i

ExL ExP

Figure 7 – Definition of system basic structure for Thermoeconomic analysis. In order to perform a fair comparison among such different systems, the exergy balance and the thermoeconomic systems take into account the operative conditions in which all the systems produce the same amount of products. With respect to the CCP and the CSP, the operation of the Julich plant is fully dependent by the average monthly insulation: therefore, the Julich plant produces a fixed net amount of electricity of 8834 MWh/y, working at nominal conditions for about 5889 h/y. These values have been assumed as reference for the other two plants. Based on this assumption, the amount of fuel, losses and destructions have been derived and reported in Table 6, as well as their average yearly exergy efficiencies. Table 6 – Results of the yearly operation of each system.

J CCP CSP

Ex_F,NR Ex_F,R Ex_P Ex_L Ex_D MWh/y MWh/y MWh/y MWh/y MWh/y 0 39442 8834 0 30608 23100 0 8834 865 13401 12776 30100 8834 1186 32856

ηex 0.22 0.38 0.21

3.1. Exergy Cost Analysis Derivation of the exergy costs of system products requires the definition of the Thermoeconomic system as in relation (5): beside the exergy balance, the exergy cost balance and the exergy costing principles are written for the generic ith system. Thanks to the exergy costing principle, the exergy cost balance can be rewritten as a function of the total exergy and the specific exergy cost of each inlet and outlet flow of the analyzed system.  ExF , NR + ExF , R = ExP + ExL + ExD  i − th : Cex ,F, NR + Cex ,F, R =Cex , P + Cex , L → cex ,F, NR ExF , NR + cex ,F, R ExF , R =cex , P ExP + cex , L ExL C= c ⋅ Ex ex , j j  ex , j

(6)

To solve the above exergy cost balance, three auxiliary relations are introduced. For all the analyzed systems:

9


• • •

cex,L = 0 – the exergy cost of losses and residues are equal to zero; cex,F,NR = 1 – the exergy cost of non-renewable fuel is equal to their exergy; cex,F,R = 0 – the exergy cost of renewable fuel is equal to zero. This assumption is justified by the fact that renewable resources are not “scarce” resources in an economic sense, and thus their consumption does not represent a cost for society. According to such auxiliary relations, the exergy cost of system product is derived as in relation (6). cex , P ExP = cex ,F, NR ExF , NR

(7)

By substituting the exergy balance (5) into the exergy cost balance (7), the structure of the exergy cost of the product is derived as in relation(8).

cex , P = cex ,F, NR + cex ,F, NR

ExL + ExD Ex  J  − cex ,F, NR R   ExP ExP  J 

(8)

As can be inferred from relation(8), the exergy cost of product is equal to the sum of three contributions: (1) the exergy cost of non-renewable resources, (2) the increase in exergy cost due to irreversibilities and (3) the exergy cost savings due to the use of renewable resources.

3.2. Exergoeconomic Cost Analysis In a dual way with respect to subsection 3.1, derivation of the exergoeconomic costs of system products requires the definition of the Thermoeconomic system as in relation (9): beside the exergy balance, the exergoeconomic cost balance (notice the subscript “eco”) and the exergy costing principles are written for the generic ith system. Again, the exergoeconomic cost balance can be rewritten as function of total exergy and specific exergy cost of each inlet and outlet flow of the analyzed system.

 ExF , NR + ExF , R = ExP + ExL + ExD  i − th : Ceco ,F, NR + Ceco ,F, R = Ceco , P + Ceco , L + Z inv C= c ⋅ Ex eco , j j  eco , j →

(9)

ceco ,F, NR ExF , NR + ceco ,F, R ExF , R + Z= ceco , P ExP + ceco , L ExL inv

To solve the above introduced exergoeconomic cost balance, three auxiliary relations are introduced. For all the analyzed systems: • ceco,L = 0 – losses are discharged into the environment with no additional economic cost; • ceco,NR = cNG – the exergoeconomic cost of non-renewable resources is equal to the specific economic cost of natural gas (in $/kWh); • ceco,R = 0 – the exergoeconomic cost of renewable inlet flows is equal to zero. Renewable resources (i.e. sunlight) are associated with no economic expenses; According to such auxiliary relations, the exergoeconomic cost of system product is derived as in relation (10). = ceco , P ExP ceco ,F, NR ExF , NR + Z inv

(10)

By substituting the exergy balance (5) into the exergy cost balance (10), the structure of the exergy cost of the product is derived as in relation(11).

ceco , P =cNG + cNG

ExL + ExD Z inv Ex + − cNG R ExP ExP ExP

10

 $   kWh 

(11)


With respect to the exergy cost of product(8), the exergoeconomic cost is equal to the sum of four contributions: (1) the economic cost of non-renewable resources, (2) the increase in economic cost due to irreversibilities, (3) the economic cost increase due to the investment and operative costs of the plant and (4) the economic cost savings due to the use of renewable resources.

3.3. Results and discussion Results of Thermoeconomic analyses are reported in Figure 8: total exergy cost (in MWh/y) and exergoeconomic costs (M$/y) of systems products are represented in black diamond. As defined by relations (8) and (11), such costs are represented by the algebraic sum of different contributions, defined by the colored bars. 6,00

0,50 0,40

4,00

ceco,P [$/kWh]

cex,P [J/J]

0,30 2,00 L+D R

0,00

NR -2,00

P

INV

0,20

L+D 0,10

R

0,00

NR P

-0,10 -4,00

-0,20

-6,00

-0,30 J

CCP

CSP

J

CCP

CSP

Figure 8 – Results of Exergy and Exergoeconomic Cost Analyses: decomposition of exergy and exergoeconomic costs of systems products (L+D=Losses and Destructions, R=Renewable, NR=non-renewable, P=Products, INV=investment). Detailed numerical results are reported in Table 8, where exergy and exergoeconomic costs are reported and their components are detailed. Table 7 – Results of Exergy and Exergoeconomic Cost Analyses.

J

CCP

CSP

c_ex kWh/kWh Non-Renewables 1,00 Renewables -4,46 Losses/Destructions 3,46 Plant investment Product 0,00 Non-Renewables 1,00 Renewables 0,00 Losses/Destructions 1,61 Plant investment Product 2,61 Non-Renewables 1,00 Renewables -3,41 Losses/Destructions 3,85 Plant investment Product 1,45 11

c_eco $/kWh 0,04 -0,18 0,14 0,25 0,25 0,04 0,00 0,06 0,05 0,16 0,04 -0,14 0,15 0,22 0,28


Analyzing the obtained results it appears evident that, from the exergy cost perspective, the Julich plant results as the less exergy intensive solution, followed by the CSP and the CCP. Notice that here only non-renewable contributions have been considered. Comparing the two solar plants with the CCP it can be noticed how the exergetic cost of losses and destruction increase has compensated by the increase of the exergetic cost of non renewable generating a global decrease of the exergetic cost of the product, which leads to highlight the different impact of the irreversibilities. From the exergoeconomic cost perspective, the CCP plant results as the less expensive solution, followed by Julich and CSP. The increase of investment costs in J and CSP is not covered by the reduction given by the renewable sources. Analyzing the economic cost structure, the cost of the products could be optimized by reducing both the investment costs and the costs of irreversibilities and losses which have an impact of about 15-20%.

4. Conclusions In this paper, the Julich solar tower plant with thermal energy storage has been simulated and compared with a hybrid concentrated solar power plant using air as working fluid and with a traditional natural gas- fueled combined- cycle power plant to quantify benefits and drawbacks in terms of resources consumption and costs. A thermoeconomic analysis has been performed for all the simulated plants, considering the average year of operation and the same amount of yearly net electricity production. The exergy and exergoeconomic costs of each system product has been derived, and the structure of such costs has been analyzed. Results show that from the exergy cost perspective, the Julich plant results as the less exergy intensive solution, followed by the CSP and the CCP. On the other hand, from the exergoeconomic cost point of view, the CCP plant results as the less expensive solution, followed by Julich and CSP due to the increase of investment costs not covered by the reduction given by the renewable sources. Analyzing the economic cost structure the optimization of the cost of the products for the two solar plants could be reached by reducing the two main costing factors: the investment costs and the costs of irreversibilities and losses.

Appendix A Table 8 – Julich Plant state properties (August, Pel 2 MW on the left; December, Pel 1.6MW on the right). ID 1 2 4 5 8 9 10 13 16 17 18

m p kg/s kPa 11.7 108 11.7 108 11.7 108 0 108 1.85 806 1.85 789.88 11.7 105.84 1.85 5 1.85 5 0 5 202.30 101

T h K kJ/kg 404.0 118.90 954.6 718.85 954.6 718.85 954.6 718.85 306.0 75.93 920.0 3742.43 393.0 107.56 365.5 2611.01 306.0 75.31 306.0 0.00 298.0 41.85

s kJ/kg-K 7.25 8.18 8.18 8.18 0.48 8.25 7.22 8.73 0.48 0.00 0.37

ID 1 2 4 5 8 9 10 13 16 17 18

12

m kg/s 10.72 10.72 10.72 0.00 1.70 1.70 10.72 1.70 1.70 0.00 185.21

p kPa 108.0 108.0 108.0 108.0 806.0 789.9 105.8 5.0 5.0 5.0 101.0

T h K kJ/kg 404.0 118.90 954.1 718.36 954.1 718.36 954.1 718.36 306.0 75.93 920.0 3742.43 393.0 107.56 365.5 2611.01 306.0 75.31 306.0 0.00 298.0 41.85

s kJ/kg-K 7.25 8.18 8.18 8.18 0.48 8.25 7.22 8.73 0.48 0.00 0.37


19 20 23 25 26 27 29

202.30 0 1.85 11.7 11.7 0 11.7

101 101 806 110.1 110.1 110.1 118.3

303.0 298.0 306.1 398.1 398.1 398.1 407.8

62.76 41.85 76.21 112.86 112.86 112.86 122.81

0.43 0.37 0.48 7.23 7.23 7.23 7.23

19 20 23 25 26 27 29

185.21 0.00 1.70 10.72 10.72 0.00 10.72

101.0 101.0 806.0 110.1 110.1 110.1 118.3

303.0 298.0 306.1 398.1 398.1 398.1 407.8

62.76 41.85 76.21 112.86 112.86 112.86 122.81

0.43 0.37 0.48 7.23 7.23 7.23 7.23

Table 9 – The state properties of the computed Julich Plant (TES discharge, Pel 650kW) ID 1 2 4 5 8 9 10 13 16 17 18 19 20 23 25 26 27 29

m kg/s 0 0 4 -4 0.63 0.63 4 0.63 0.63 0 68.93 68.93 0.0 0.63 4 0 4.00 0.0

p kPa 0 0 108.0 108.0 806.0 789.9 105.8 5.0 5.0 5.0 101.0 101.0 101.0 806.0 110.1 110.1 110.1 118.3

T h K kJ/kg 0 0 0 0 952.8 716.76 952.8 716.76 306.0 75.93 920.0 3742.43 393.0 107.56 365.5 2611.01 306.0 75.31 306.0 0.00 298.0 41.85 303.0 62.76 298.0 41.85 306.1 76.21 398.1 112.86 398.1 112.86 398.1 112.86 407.8 122.81

s kJ/kg-K 0 0 8.17 8.17 0.48 8.25 7.22 8.73 0.48 0.00 0.37 0.43 0.37 0.48 7.23 7.23 7.23 7.23

Table 10 – The state properties of the computed hybrid CSP plant (August, mfuel 0; Pel=1.5MW on the left; December mfuel=0.029kg/s; Pel=1.5MW on the right) ID 1 5 6 7 10 13 14 15 16 17 20 23 25 28

m kg/s 9,8 1,73 1,73 9,8 1,73 1,73 0,0 180,22 180,22 0 1,73 9,8 9,8 9,8

p kPa 101,3 806,0 789,9 107,0 5,0 5,0 5,0 101,0 101,0 101,0 806,0 111,4 109,2 109,2

T K 298 306 800 370 306 306 306 298 303 298 306 307 952 952

h kJ/kg 10,2 75,9 3477,0 83,9 2496,0 75,3 0,0 41,9 62,8 41,9 76,2 19,7 716,3 716,3

s kJ/kg-K 6,954 0,476 7,944 7,159 8,386 0,476 0,000 0,365 0,435 0,365 0,477 6,958 8,170 8,170

ID 1 5 6 7 10 13 14 15 16 17 20 23 25 28

Nomenclature 13

m kg/s 9,70 1,73 1,73 9,73 1,73 1,73 0,00 180,24 180,24 0,00 1,73 9,70 9,70 9,73

p kPa 101,3 806,0 789,9 104,9 5,0 5,0 5,0 101,0 101,0 101,0 806,0 109,2 111,4 107,0

T h K kJ/kg 298 10,21 306 75,93 800 3477,03 370 84,39 306 2495,95 306 75,31 306 0,00 298 41,85 303 62,76 298 41,85 306 76,21 827 573,80 307 19,72 952 720,78

s kJ/kg-K 6,95 0,48 7,94 7,20 8,39 0,48 0,00 0,37 0,43 0,37 0,48 8,01 6,96 8,21


ceco economic cost, $/J cex specific exergy cost, J/J h, specific enthalpy, kJ/kg .

m

mass flow rate, kg/s p, pressure, KPa s, specific entropy, kJ/(kgK) T temperature, K Acronyms CC Combustion chamber COMP Compressor crf Capital Recovery Factor CSP Concentrated Solar Power HRSG Heat Recovery Steam Generator GT Gas Turbine ST Steam Turbine TES Thermal Energy Storage Subscripts and superscripts ex Exergy eco Economic

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