1. New generation Line-Focusing Solar Power Plants with Molten Salt as Heat Transfer Fluid and Supercritical Carbon Dioxide Brayton Power Cycles
Luis Coco-Enríquez
Javier Muñoz-Antón
Grupo de Investigaciones Termoenergéticas
Universidad Politécnica de Madrid

2. Contents Introduction. State of the art.
Innovative Plant configuration MS+sCO2 Brayton power cycle.
Reference Plant configuration DSG+Rankine power cycle.
Modeling Assumptions.
Simulation methodology.
Main Results.
Conclusions.
Future Work.
Main References.
Detailed Results.

3. Introduction
There are TWO promising Technologies under development in solar power plants:
Direct Molten Salt Heat Transfer Fluid, in line focusing solar collectors (Parabolic PTC or Linear Fresnel LF), for replacing Syntetic Oils (Dowtherm, Therminol VP1, etc), and increasing turbine inlet temperature (TIT).
- Supercritical Carbon Dioxide (s-CO2) Brayton power cycles, for reducing Balance Of Plant equipments dimensions and increasing net plant efficiency.
For gaining synergies, both technologies are integrated in the same plant layout:
Direct Molten Salt + Supercritical Carbon Dioxide Brayton power cycle
PTC or LF
collectors
with MS
sCO2 Brayton
power cycle
Heat
Exchanger
Thermal Energy
Solar Energy
Thermal Energy
Electriciy 1

4. State of the art: Direct Molten Salts as Heat Transfer Fluid
Rankine cycle
Molten Salt HTF
Oil HTF
Rankine cycle
Synthetic Oil as HTF (Legacy)
TIT limitation 390ºC, therrmal oil degradation.
Solar Energy Generating Systems (SEGS)
solar plants net efficiency ~37%.
TWO heat exchangers required (TES, BOP).
High TES volume due to low temperature
difference between cold and hot tank.
Direct Molten Salt as HTF (State of the Art)
TIT up to 550ºC.
Net plants efficiency up to ~40%.
- Only ONE heat exchanger between SF and BOP.
2.5 times reduction of volume storage tanks.
Great interest for this technology for industrial solutions deployment. Several Demostration plants
operating: Archimedes Solar (PTC), Novatec (LF) 2

5. State of the art: Receivers
for Direct Molten Salt as HTF
1. Receiver features:
- Molten salts corrosion resistance, austenitic stainless steel (AISI 316Ti).
- Selective coating optimized up to 550 °C for minimizing radiative heat losses.
2. Examples of Direct Molten Salt comercial receivers:
- Archimede Solar Energy, HCEMS-11.
- Scott PTR70 Advance, the 4th Generation. 3

6. State of the art: Receivers
for Direct Molten Salt as HTF
3. Receiver design for Linear Fresnel solar collectors depending on temperature
level of application:
J. F. Feldhoff, et al., DLR & CIEMAT “Status and first results of the DUKE project –Component qualification of new receivers and collectors”. SolarPaces 2013.
4. Heat Losses Correlations:
- Parabolic Trough: Q = ΔT ΔT NREL 2009 experiment
Q = ΔT ΔT DUKE project results paper
- Linear Fresnel: Q = 1.06 ΔT ΔT NOVATEC for DSG boiling
Q = 0.15 ΔT ΔT NOVATEC for DSG superheated 4

7. State of the art: sCO2 Brayton power cycles
sCO2 Advantages:
High density working fluid at Compressor and Turbine inlet, improving Turbomachines isentropic efficiency and reducing equipments dimensions, volume, footprint and the associated BOP civil work.
No environmental impacts no toxicity ,and low cost working fluid.
Single phase power cycle reduces operational control system complexity and design.
Higher flexibility and more rapid response under transitory conditions (variable DNI,
plant startup, local shadowing, etc)
sCO2 disadvantages:
sCO2 under high pressure and temperature (550ºC, 250 bar) requires high alloy
materials (like SS347, etc) to overcome corrosion, increasing final equipments cost.
Huge heat energy exchanged requiring advanced HX design (PCHE).
BOP equipments not yet commercially developed.
Back up fossil boilers are not yet design. 5

8. Innovative Plant Configuration
For gaining synergies, both technologies are integrated in the same plant layout:
Direct Molten Salt + Supercritical Carbon Dioxide Brayton power cycle 6

9. Innovative Plant configuration: sCO2 Brayton power cycles
SB: Simple Brayton cycle, with ReHeating
RC: Recompression cycle RC, with ReHeating 7

10. Innovative Plant configuration: sCO2 Brayton power cycles
PCRC: Partial Cooling and Recompression, with ReHeating
RCMCI: Recompression Main Compression Intercooling , with ReHeating 8

11. Reference Plant Configuration: DSG with subcritical Rankine cycle
DSG with Recirculation Mode
Rankine Power Cycle
DIRECT
REHEATING 9

12. Reference Plant Configuration: DSG with subcritical Rankine cycle
Advantages:
Turbines technology widely validated and under development for Fossil Fuel Power
plants. Main example Ultra Supercritical Fossil Power Plants.
BOP HX(feed-water heaters) are manufactured with low cost material (Carbon Steel).
SF receiver low cost material (Carbon Steel).
No HXs between SF and BOP; two Direct ReHeating stages in the power cycle.
Disadvantages:
Complex control system for transitory operational conditions, with two steam
generation modes under industrial development (Recirculation mode and Once-
Through mode).
Bigger steam turbines dimensions and footprint in relation to sCO2 turbomachinery,
and associated BOP civil work.
TES design complexity due to steam-liquid water phase change. 10

13. Modeling Assumptions (Design Point)
Solar Power plant Location parameters:
Receiver:
Location:
Dagget,CA, USA.
DNI:
986 W/m2
Ambient temperature:
25 ºC
Outer Diameter:
70 mm
Wall Thickness:
4.191 mm
Material:
Stainless steel
Linear Fresnel collectors:
Parabolic collectors:
Collector type:
SuperNova 1 (Novatec)
Optical Efficiency:
0.67 (boiling)
0.647 (superheating)
Collector type:
EuroTrough II
Optical Efficiency:
0.75
Heat Transfer Fluid:
Molten Salt
60%NaNO3+40%KNO3 11

14. Modeling Assumptions (Design Point)
Rankine Power cycle:
sCO2 Brayton Power cycle:
HP Turbine:
2 stages:
87.7 bar; 36 bar
IP Turbine:
3 stages: 16.5 bar;
10.34 bar; 6.18 bar
LP Turbine:
4 stages: 5.17 bar; 3.04bar; 1.17 bar;
0.37 bar
Turbine Efficiency:
85%
Condenser Pressure:
0.08 bar
Generator Efficiency:
98.23% (Design-Point)
Auxiliary BOP:
0.01% (Gross Power)
TTD:
5 ºC
DCA:
Deaerator pressure:
6.17 bar
Turbine Efficiency:
93%
Compressor Efficiency:
89%
HX Effectiveness:
95%
No HX Pressure Drop
Turbine Inlet Temperature :
550ºC
Turbine Inlet Pressure:
250 bar
Reheating Pressure:
173 bar
Compressor Inlet :
32 ºC
Compressor Inlet Pressure:
74 bar
Splitting fraction:
71% and 29%
Auxiliary BOP
(ACHE fan and others):
0.01%(Gross power)
Generator Efficiency:
98.23 (Design-Point) 12

15. Simulation Methodology
Thermoflow 23 software heat balances simulation.
Modeling capabilities and accuracy validated with Korea Advanced Institute of Science
and Technology (KAIST), reference: “Computational analysis of supercritical CO2
Brayton cycle power conversion system for fusion reactor.
sCO2 thermodynamic properties were calculated with REFPROP software,
developed by National Institute of Standards and Technology (NIST).
Turbines and compressors modeled with isentropic efficiencies (η) to consider real gas
behavior.
Recuperators were modeled as counter-flow and via the effectiveness number-of
transfer units (ε-NTU) method, subdividing the heat exchangers according to the
finite differences method to take into account sCO2 properties variations.
No pressure drops in HXs neither heat looses. 13

16. Conclusions
MS+sCO2 Brayton power plants net efficiencies are higher than DSG+Rankine plants thanks to supercritical fluid properties, with higher energy density and higher turbomachines isentropic efficiency.
For the design-point, TIT=550ºC, Recompression cycle net efficiency is 46.84% and with a DSG+Rankine plant configuration, net efficiency is 40.24% (with one Direct ReHeating stage).
As a general rule, for TIT<500ºC, RCMCI plant configuration provides the highest net plant efficiency, and for TIT>500ºC, RC plant configuration is the optimum.
We confirmed One ReHeating stage increases net plant efficiency between % in Brayton solar power plants. And this value is very constrained by the pressure drop in Reheating heat exchanger and by pressure drop in the Reheating solar field.
MS Receiver Heat Losses were estimated and compared with DSG plant. As a general conclusion, heat losses in MS receiver are higher than in DSG receiver mainly due to different temperatures profiles along pipes, due to working fluids different specific heat capacity at constant pressure (Cp), and different heat energy transfer physical phenomeno, (no phase change, no latent heat, and no boiling in supercritical fluids). 20

17. Conclusions
Better net plant efficiency was also translated into SF effective aperture area savings. Comparing MS+RC with DSG+Rankine plants configurations for a fixed net power output and similar turbine inlet conditions, SF area savings are 6% with PTC and 10% with LF, in terms of SF land area savings 13.5% PTC and 23.76% LF (550ºC TIT with ReHeating).
MS+sCO2 plant SF capital investment cost is not competitive with DSG+Rankine plant solution because MS receiver material cost (stainless steel) is much higher than DSG receivers made of carbon steel.
Shell & Tubes heat exchangers were assessed as a feasible and competitive alternative to PCHE in Primary Heat Exchanger (“main Boiler”); with sCO2 flowing in tubes side and MS in the shell-side. Molten salt HeatTransfer Coefficient in shell side is higher (~3800 W/m2 ºC) than sCO2 (~1425 W/m2ºC). However, shell & tube heat exchanger type are not advisable for recuperators heat exchangers detailed design. 21

18. Future Works
MS receiver heat looses more accurate correlations should be obtained from real Direct Molten Salt Demo projects to validate our analysis.
MS receivers material (Austenitic stainless steel) cost should be optimised in
comparison with DSG Carbon steel receiver pipes:
a) Developing new Solar Salts chemical compositions with lower corrosion behaviour.
b) Anodes or impressed current cathodic protection, internal painting or internal
coating tubes, etc. Find similarities in corrosion protection of “Marine” structures.
Thermal Energy Storage System (with two Molten Salt tanks) will be integrated in the
plant design to warranty a dispachable energy source. Also Fossil Fuel Boiler or Gas Turbine integration could be other alternatives for increasing annual plant performance.
Other HTF (DSG, VP1, Ethane, SF6, etc) could be combined with MS and sCO2 Brayton power cycles in terms of reducing final plant capital investment cost and increase net plant efficiency.
Material and manufacturing equipment cost should be optimized for confirming the
“Supremacy” of MS+sCO2 Brayton power plants in comparison with DSG+Rankine plants. 22

19. Final Conclusion
We confirmed that with the actual Material and Manufacturing BOP equipments Cost, the innovative sCO2 Brayton solar plants are not the only competitive solution for increasing net plant efficiency and for reducing final energy cost; Subcritical and Supercritical water Rankine solar plants could also play also an important role in the future generation solar power plants. 23

20. THANK YOU VERY MUCH FOR YOUR ATTENTION !!!
$$$,
Nobel,
Etc.
Fussion … … … …
Solar (PETE + sCO2)
Solar (sCO2, sWater, sHTFs)
Solar (Rankines) 24

21. Main references
[1] A.Maccari, Archimede Solar Energy. “Archimede Solar Energy Molten Salt Parabolic Trough
Demo Plant: A Step Ahead Towards the New Frontiers of CSP”. SolarPaces 2014.
[2] F. Matino, Archimede Solar Energy “Molten Salt Receivers Operated on Parabolic Trough Demo
Plant and in Laboratory Conditions”. SolarPaces 2014.
[3] G.Morin, Novatec Solar GmbH. “Molten Salt as Heat Transfer Fluid in a Linear Fresnel Collector
Comercial Application Backed by Demonstration ”. SolarPaces 2014.
[4] F.Burkholder and C.Kutscher “Heat Loss Testing of Schott’s 2008 PTR70 Parabolic Trough
Receiver”. Report NREL/TP , May 2009.
[5] Novatec Solar, “SAM Linear Fresnel solar boiler model”, NREL SAM Conference 2013.
[6] EPRI. Electric Power Research Institute. G8 Cleaner Fossil Fuels Workshop. Stu Dalto, Director,
Generation, IEA Secretariat, Paris France, January, 2008.“Boiler material for USC pulverized
coal (PC) Plants”.
[7] Burhanuddin Halimi, Kune Y. Suh, “Computational analysis of supercritical CO2 Brayton cycle
power conversion system for fusion reactor”. Elsevier, Energy Conversion and Management
63 (2012) 24

22. Main references
[8] Steven A. Wright, Thomas M. Conboy, and Gary E. Rochau, “Overview of supercritical CO2 power cycle development at Sandia National Laboratories”, October 25-27, 2011 Columbus, Ohio, Sandia National Lab.
[9] Craig Turchi et al.. “10 MW Supercritical CO2 Turbine Test”. National Renewable Laboratory USA, report nº DE-EE , January 2014.
[10] A. G. Fernández Díaz-Carralero, F.J. Pérez Trujillo, M.P. Hierro de Bengoa. “Estudios Físico-Químicos y de corrosión a elevada temperatura para el diseño de nuevos fluidos almacenadores
de energía en centrales solares de concentración”. Universidad Complutense de Madrid, Facultad
de Ciencias Químicas, Departamento Ciencia de Materiales e Ingeniería Metalúrgica, Madrid 2013. 25

23. Results: Net Plant Efficiency (Solar Power Plant without ReHeating)
For TIT<500ºC, RCMCI configuration
is the optimum one in terms of net plant
efficiency, above DSG+Rankine 1.5%-3.5%.
For TIT> 500ºC, RC plant configuration is
the optimum sCO2 plant design.
For TIT=550ºC MS+RC sCO2 efficiency is
45.12% higher than DSG+Rankine about
5%-6.5%.
For TIT=400ºC the RCMCI configuration
performance was 36.65% higher than DSG
Rankine plant with ~35%.
TIT (ºC)
DSG+Rankine
Effc.Net
(%)
MS+SB UA
(MW/ºC)
MS+RC
Eff.Net
MS+PCRC
MS+RCMCI
400
34.98
32.26
11.3
35.3
21.2
34.27
16.27
36.65
19.5
450
36.21
34.91
11.7
39.1
21.7
37.01
16.4
39.74
19.4
500
37.34
37.21
11.6
42.33
21.6
39.45
16.6
42.47
550
38.39
39.24
11.65
45.12
21.5
41.66
16.9
44.9
19.8 14

24. Results: Net Plant Efficiency (Solar Power Plant with ReHeating)
As main reference Legacy solar Oil plants with TIT 390ºC and reheating, net plant efficiency ~37%.
For TIT=400ºC, Brayton power cycle increases efficiency up to 37.76% (for RC configuration) and 38.64% for RCMCI configuration.
For TIT=550ºC, sCO2 net plant efficiency with RC configuration is 46.81% versus 40.81% with Rankine cycles.
For similar net plant efficiencies RCMCI configuration always requires less heat exchangers conductance (UA) than RC configuration.
TIT
(ºC)
DSG+Rankine
(One DRH)
Effc.Net(%)
DSG+Rankine (Two DRH)
MS+SB
Eff.Net
(%)
UA (MW/ºC)
MS+RC
MS+PCRC
Effc.Net
MS+PCRC UA (MW/ºC)
MS+
RCMCI
UA MW/ºC
400
36.52
37.19
33.89
11.66
37.76
20.84
36.81
16.73
38.64
18.81
450
37.83
38.46
36.37
41.26
21.03
39.47
17.10
41.57
19.05
500
39.1
39.53
38.53
11.78
44.26
21.09
41.89
16.63
44.16
19.37
550
40.24
40.81
40.45
11.93
46.81
21.10
44.03
17.05
46.48
19.8 15

25. Results: Unitary Power Output (Solar Power Plant without ReHeating)
For translating net power efficiency improvement into SF aperture area savings, we defined:
Unitary Power Output = Net Power Output (kW) / SF aperture area (m2).
In the graph above are compared PTC versus LF solar collectors required aperture area for a fixed power output.
For TIT < 500ºC the optimum Solar Power Plant configuration is PTC MS + RCMCI (minimum SF effective aperture area for a fixed net power output). 16

26. Results: Unitary Power Output (Solar Power Plant with ReHeating)
ReHeating improves Unitary Power Output, for example in the RC configuration:
For PTC ~1.35% (from kW/m2 toó kW/m2) and for LF ~ 1.58% (from kW/m2 toó kW/m2).
At TIT=550ºC, with PTC MS+RC configuration, SF effective aperture area saving ~6% in comparison with PTC DSG+Rankine, and SF land area saving 13.5%.
With LF MS+RC configuration, SF effective aperture area saving ~10% in comparison with LF DSG+Rankine, and SF land area saving 23.76%. 17

27. Results: Solar Field Capital Cost (Solar Power Plant without ReHeating)
Design Point conditions: 55 Mwe Net Power Plant Output, 550ºC TIT
Solar power plant Technology
LF DSG
Rankine
LF MS SB
LF MS RC
LF MS
PCRC
RCMCI
Receiver Material CS SS
SF aperture area (m2)
256780
256377
224113
241858
225029
SF capital cost (Mill. USD)
61.52
89.22
77.99
84.16
78.31
PTC DSG
PTC MS SB RC
215855
225964
197838
213358
198791
81.12
113.23
99.138
106.92
99.62
Net plant efficiency (%)
38.4
39.3
45.16
41.71
44.94
Unitary cost data:
LF DSG:
USD/m2
LF MS:
300 USD/m2
PTC DSG:
324 USD/m2
PTC MS:
432 USD/m2
Installation
multiplier: 1.16
Note: Unitary cost data taken from Thermoflow software
Optimum net plant efficiency with RC Brayton plant (45.16%).
Lowest Effective Aperture area SF is obtained with RC Brayton Plant ( m2).
LF with DSG provides the SF most cost competitive technical solution (61.52 Mill.USD).
Brayton power cycles net plant efficiency not translated in lower SF capital investment cost
due to MS receivers material (Stainless Steel) cost.
Heat tracing requirements in MS SF should be added to this cost analysis. 18

28. Results: Solar Field Capital Cost (Solar Power Plant with ReHeating)
Design Point conditions: 55 Mwe Net Power Plant Output, 550ºC TIT
Solar power plant Technology
LF DSG
Rankine
(One DRH)
(Two DRH)
LF MS SB
LF MS RC
PCRC
RCMCI
Receiver Material CS SS
SF aperture area (m2)
244028
245674
253191
220426
238041
221603
SF Capital Cost (Mill. USD)
58.47
58.86
88.11
76.71
82.84
77.12
LF SG
PTC MS
207858
206331
223690
195071
210285
196000
SF capital cost (Mill. USD)
78.12
77.55
112.09
97.75
105.37
98.22
Net plant efficiency (%)
40.24
40.81
40.45
46.81
43.12
46.48
Note: Unitary cost data taken from Thermoflow software.
DRH integration in line focusing DSG solar plants with Rankine power cycles, increases net plant efficiency ~2.4% , from 38.4% to 40.81% for Two DRH stages, and reduces SF capital investment cost ~4.5%. (At Design Point).
ReHeating integration in line focusing MS solar plants with sCO2 Brayton power cycles, increases net plant efficiency ~ 1.6%, from 45.2% to 46.8% for the RC configuration, and reduces SF capital investment cost ~1.5%, for RC configuration. (At Design Point) 19

29. Results: Unitary Power Output (Solar Power Plant without ReHeating)
TIT (ºC)
PTC DSG
Rankine
Unitary
Power
(W/m2)
PTC MS+SB
UA (MW/ºC)
PTC MS+RC UA
(MW/ºC)
PTC MS+PCRC
PTC MS+RCMCI
400
235.24
215.08
11.3
235.03
21.2
228.27
16.27
243.90
19.5
450
242.9
229.03
11.7
255.89
21.7
242.47
16.4
259.98
19.4
500
249.5
238.58
11.6
270.20
21.6
252.45
16.6
271.07
550
254.96
243.57
11.65
278.16
21.5
257.85
16.9
276.89
19.8
TIT (ºC)
LF DSG
Rankine
Unitary
Power
(W/m2)
LF MS+SB
UA (MW/ºC)
LF MS+RC UA
(MW/ºC)
LF MS+PCRC
LF MS+RCMCI
400
196.69
184.87
11.3
201.97
21.2
196.19
16.27
209.61
19.5
450
203.28
197.97
11.7
221.20
21.7
209.59
16.4
224.76
19.4
500
209.15
207.91
11.6
235.62
21.6
220.06
16.6
236.38
550
214.28
214.75
11.65
245.62
21.5
227.51
16.9
244.50
19.8 26

30. Results: Unitary Power Output (Solar Power Plant with ReHeating)
TIT
(ºC)
PTC DSG
Rankine
(One DRH)
Unitary
Power
(W/m2)
Rankine (Two DRH )
PTC MS SB
UA (MW/ºC)
PTC MS RC
PTC MS RC
PTC MS PCRC
PTC MS PCRC UA (MW/ºC)
PTC MS RCMCI
PTC MS RCMCI
UA (MW/ºC)
400
245.10
249.06
224.27
11.66
249.24
20.84
243.34
16.73
255.18
18.81
450
252.83
256.26
236.12
266.75
21.03
255.86
17.10
269.01
19.05
500
259.62
261.43
243.47
11.78
277.81
21.09
258.52
16.63
277.65
19.37
550
264.77
266.78
245.97
11.93
282.01
21.10
261.59
17.05
280.69
19.8
TIT
(ºC)
LF DSG
Rankine
(One DRH)
Unitary
Power
(W/m2)
Rankine (Two DRH )
LF MS SB
UA (MW/ºC)
LF MS RC
LF MS RC
LF MS PCRC
LF MS PCRC UA (MW/ºC)
LF MS RCMCI
LF MS RCMCI
UA (MW/ºC)
400
207.08
207.25
192.02
11.66
209.37
20.84
208.18
16.73
218.27
18.81
450
214.03
213.52
203.59
229.96
21.03
220.50
17.10
231.83
19.05
500
220.19
219.37
212.05
11.78
242.08
21.09
225.17
16.63
241.84
19.37
550
225.47
224.00
217.33
11.93
249.57
21.10
231.17
17.05
248.23
19.8 27

31. Results: Heat Exchangers Capital Cost (Solar Power Plant without ReHeating)
Design Point conditions: 55 Mwe Net Power Plant Output, 550ºC TIT
Solar power plant Technology
DSG
Rankine
MS+SB
MS+RC
MS+PCRC
MS+RCMCI
LTR (MWth) -
154.11
85.35
35.62
64.536
HTR (MWth)
98.27
145.61
PHX (MWth)
140.28
122.01
132.05
ACHE (MWth)
83.52
65.27
75.33
65.822
PCHE unitary cost (USD/kW) [X] 92
Target PCHE unitary cost (USD/kW)
46.20
64.04
71.85
69.04
Total HX Capital Cost (Mill. USD)
17.46
34.77
34.12
35.75
35.20
Notes:
Rankine cycles HX unitary cost data from Thermoflow software.
Brayton power cycles HX unitary cost data from Sandia National Lab.
- Rankine power cycles HX lowest Total Cost (17.46 Millo. USD)
- PCHE material required for sCO2 fluid is Austenitic stainless steel AISI 347.
- Rankine cycles HX material is Carbon Steel much cheaper than austenitic stainless steel.
Feed-Water Heaters are much cheaper than Recuperators due to material, sizes and higher water
condensation heat transfer coeficcients.
Target PCHE unitary cost were calculated for obtaining similar HX total cost with both power cycle
technologies (Rankine and Brayton). 28

32. Results: Heat Exchangers Capital Cost (Solar Power Plant without ReHeating)
Design Point conditions: 55 Mwe Net Power Plant Output, 550ºC TIT
Rankine Plant HX Total Cost details:
Feed-Water Heaters 1 to 5 (Mill. USD)
1.19
Deaerator (Mill. USD)
0.40
ACC (Mill. USD)
15.87
Total HX Capital Cost (Mill. USD)
17.46
Notes:
Rankine cycles HX unitary cost data from Thermoflow software.
- Rankine power cycles HX lowest Total Cost (17.46 Millo. USD)
- PCHE material required for sCO2 fluid is Austenitic stainless steel AISI 347.
- Rankine cycles HX material is Carbon Steel much cheaper than austenitic stainless steel.
Feed-Water Heaters are much cheaper than Recuperators due to material, sizes and higher water
condensation heat transfer coeficcients.
Target PCHE unitary cost were calculated for obtaining similar HX total cost with both power cycle
technologies (Rankine and Brayton). 29

33. Results: Heat Exchangers Capital Cost (Solar Power Plant with ReHeating)
Design Point conditions: 55 Mwe Net Power Plant Output, 550ºC TIT
Solar power plant Technology
DSG
Rankine (One DRH)
Rankine (Two DRH)
MS+SB
MS+RC
MS+PCRC
MS+RCMCI
LTR (MWth) -
83.829
35.94
63.659
HTR (MWth)
112.44
155.94
PHX (MWth)
87.263
103.35
92.398
ACHE (MWth)
26.507
30.445
24.43
26.154
PCHE unitary cost (USD/kW) [X]
79.423
60.932
70.99
61.761
Target PCHE unitary cost
(USD/kW) 92
Total HX Capital Cost (Mill. USD)
16.26
15.91
35.13
34.49
35.44
Notes:
Rankine cycles HX unitary cost data from Thermoflow software.
Brayton power cycles HX unitary cost data from Sandia National Lab. 30

34. Results: Heat Exchangers Capital Cost (Solar Power Plant with ReHeating)
Design Point conditions: 55 Mwe Net Power Plant Output, 550ºC TIT
DSG Rankine (One DRH)
DSG Rankine (Two DRH)
Rankine Plant HX Total Cost details:
Feed-Water Heaters 1 to 5 (Mill. USD)
1.095
1.082
Deaerator (Mill. USD)
0.362
0.355
ACC (Mill. USD)
14.81
14.472
Total HX Capital Cost (Mill. USD)
16.26
15.91
Notes:
Rankine cycles HX unitary cost data from Thermoflow software. 31

35. Results: Receiver Heat Losses (for LF solar collectors)
Receiver Heat losses differs in all the technologies studied due to different temperature profiles along receivers. Main reasons are:
Parabolic and Fresnel collectors different aperture area and optical real performance.
- Different HTF properties (Water & MS).
- Differences between Water and MS Specific Heat Capacity at constant pressure (Cp).
- Water boiling at a constant saturation temperature.
- Others...
Heat Looses correlations for LF collectors:
Q= 1.06 ΔT ΔT4 (boiling) ;
Q= 0.15 ΔT ΔT4 (superheated or MS)
Heat Looses correlation for PTC collectors:
Q = ΔT ΔT4
Heat Losses in LF solar collectors:
TIT<500ºC:
MS+sCO2 < DSG+Rankine
TIT>500ºC:
MS+sCO2 >≈ DSG+Rankine
Heat Losses in PTC solar collectors:
TIT<500ºC:
MS+sCO2 >DSG+Rankine
TIT>500ºC:
MS+sCO2 >>DSG+Rankine 32

36. Results: Receiver Heat Losses (for LF solar collectors)
Plant without ReHeating
Plant with ReHeating
Due to lack of more accurate information heat looses correlations for direct molten salt receivers were based on recent experiments provided by NREL and Novatec, not from real Demonstration Projects. 33

37. Results: Receiver Heat Losses (for LF solar collectors)
Plant configuration WithOut ReHeating
TIT
(ºC)
LF DSG
Rankine
(MWth)
LF MS SB RC
PCRC
RCMCI
400
5.69
2.72
2.60
2.64
2.54
450
6.17
4.25
4.00
4.12
3.97
500
6.80
6.55
6.12
6.36
6.11
550
7.64
9.96
9.23
9.64
9.25
Heat Losses in LF solar collectors:
TIT<500ºC:
MS+sCO2 < DSG+Rankine
TIT>500ºC:
MS+sCO2 >≈ DSG+Rankine
Plant configuration With ReHeating
TIT
(ºC)
LF DSG
Rankine
(One DRH)
(MWth)
(Two DRH)
LF MS SB RC
PCRC
RCMCI
400
4.93
4.92
3.13
2.998
2.95
2.89
450
5.55
5.65
4.91
4.64
4.63
4.53
500
6.36
6.62
7.59
7.10
7.17
6.98
550
7.48
8.00
11.53
10.73
11.02
10.61 34

38. Results: Receiver Heat Losses (for PTC solar collectors)
Plant without ReHeating
Plant with ReHeating
Due to lack of more accurate information heat looses correlations for direct molten salt receivers were based on recent experiments provided by NREL and Novatec, not from real Demonstration Projects. 35

39. Results: Receiver Heat Losses (for PTC solar collectors)
Plant configuration WithOut ReHeating
TIT
(ºC)
PTC DSG
Rankine
(MWth)
PTC MS SB RC
PCRC
RCMCI
400
2.67
4.07
3.89
3.95
3.80
450
3.24
6.41
6.03
6.22
5.98
500
4.05
9.98
9.32
9.68
9.30
550
5.22
15.37
14.29
14.91
14.33
Heat Losses in PTC solar collectors:
TIT<500ºC:
MS+sCO2 >DSG+Rankine
TIT>500ºC:
MS+sCO2 >>DSG+Rankine
Plant configuration With ReHeating
TIT
(ºC)
PTC DSG
Rankine
(One DRH)
(MWth)
(Two DRH)
PTC MS SB RC
PCRC
RCMCI
400
2.64
2.79
4.69
4.49
4.42
4.33
450
3.40
3.68
7.41
7.01
7.00
6.84
500
4.52
4.997
11.60
10.87
11.09
10.69
550
6.14
6.95
17.94
16.72
17.14
16.52 36

40. Results: Shell & Tubes PHX and RHX detailed design
Design Point conditions: 55 Mwe Net Power Plant Output, 550ºC TIT
Shell Length (m)
Shell Diameter (m)
Cost
(USD/
per Unit)
Qty. (Uds.)
Total Cost
(USD)
Heat
(kW)
Unitary Cost (USD/kW)
Aptubes
(bar)
Apshell RC
PHX
12.86
1.141 6
87174
94.2
0.1299
0.4956
RHX
8.759
1.349
30420
226.6
0.06
0.1415
PCRC
12.17
1.005
103218
61.3
0.133
0.6962
7.688
1.215
876287
24414
215.35
0.0561
0.1554
RCMCI
12.04
1.057
92244
73.3
0.1277
0.6074
7.983
1.255
946542
26130
217.35
0.0571
0.1405
Notes:
PCHE unitary costs 92 USD/kW.
Shell&Tubes material AISI347.
It was confirmed 500 kPa pressure drops in PHX and RHX decrease net plant efficiency ~1,5% in RC from 46.84% to 45.31%, as stated by Dostal 2004.
- Shell & Tubes HX pressure drops (sCO2 tube side) are lower than in PCHE. Pressure drop impact in the net plant efficiency could be calculated in future works. 37

41. UA cost increasing (USD) UA cost increasing (USD)
Results: Fixed UA & Plant Efficiency (Solar Power Plant With ReHeating)
Design Point conditions: 55 Mwe Net Power Plant Output, 550ºC TIT
PCRC Brayton Power cycle
SB (SB) Power cycle SF
aperture area (m2) UA
(MW/K)
Net Eff.
(%)
SF cost savings (USD)
UA cost increasing (USD)
Net Savings (USD)
253190
3.2
40.49 0   0
246435
4.0
41.71
850904
242236
5.0
42.51
521100
422844
240147
6.0
42.91
257700
208940
239122
7.0
43.12
126600
102772
SF aperture area (m2)
UA (MW/K)
Net Eff. (%)
SF costs savings (USD)
UA cost increasing (USD)
Net Savings (USD)
238041
7.486
43.16  0
237378 8
43.29
198900
162100
235816 10
43.61
468600
378072
234971 12
43.79
253500
204556
234459 14
43.90
153600
123884
234113 16
43.97
103800
83468
233857 18
44.03
76800
61988 38

42. Results: Fixed UA & Plant Efficiency (Solar Power Plant Without ReHeating)
Design Point conditions: 55 Mwe Net Power Plant Output, 550ºC TIT
Main assumptions:
Fixed Heat Exchanger conductances UA
(LTR, HTR, PHX, RHX, ACHE).
Increase LTR and HTR conductances UA.
Heat Transfer Coefficients not varied in HX despite UA increments.
Results:
- SF area savings due to UA increasings
Higher UA requires higher HX capital cost.
Higher UA reduce SF capital cost.
Recompression with Main
Compression Intercooling (RCMCI)
SF aperture area (m2)
UA (MW/K)
Net
Eff. (%)
SF capital cost savings (USD)
UA cost increasing (USD)
Net Savings (USD)
221601
10.9
46.52
221269
11.5
46.62
99600
72000
220150
15.5
46.98
132000
91888
219610
19.5
47.16
69900
48280
219282
23.5
47.26
41700
27624
219175
25.5
47.3
32100
11684
20416
Recompression (RC) Brayton cycle
SF aperture area (m2)
UA (MW/K)
Net Effi. (%)
SF cost savings (USD)
UA cost increasing (USD)
Net Savings (USD)
220427
12.439
46.84
219636
13.5
47.09
237300
166184
217747
17.5
47.71
233400
160168
216793
21.5
48.03
120000
82280
216285
25.5
48.19
64800
44192 39