# Analysis of an Integrated Solar Combined Cycle with Recuperative Gas Turbine and Double Recuperative and Double Expansion Propane Cycle

^{1}

^{2}

^{*}

## Abstract

**:**

## 1. Introduction

_{2}(sCO

_{2}) cycle as the bottoming cycle, where the gas turbine also included reheating, in addition to intercooling and recuperation. The authors compared toluene and isobutene for the ORC and concluded that isobutene had a better performance.

_{2}and the bottoming cycle was an ORC.

## 2. Configurations

#### 2.1. Conventional CC

#### 2.2. Conventional ISCC

_{th}PTC solar field that heats a thermal oil. Then, the thermal oil is directed to a solar steam generator (SSG) to evaporate water at the high-pressure level of the HRSG. Therefore, the SSG works in parallel with the high-pressure evaporator of the heat recovery steam generator. The configuration is depicted in Figure 2. Design parameters are presented in previous Table 1. Table 2 shows the data of the PTC solar field.

#### 2.3. CCGT-R-DRDE and ISCC-R-DRDE Configurations

_{main}). The second heating line is heated (from 2 to 6) in a recuperator fed by steam coming from the outlet of the main turbine. The vapor generated in the recuperator is expanded in a secondary turbine (VT

_{secondary}). Finally, the vapor at the exit of the secondary turbine is directed to a secondary recuperator, which slightly preheats the fluid of the main heating line (from 2 to 2a in Figure 3). The scheme of the cycle and the temperature–entropy (T-s) diagram are shown in Figure 3.

## 3. Methodology

#### 3.1. Simulation at Nominal Conditions

_{R,GT}), at the air side, is calculated as below [25]:

^{2}is considered. Provided the nominal mass flow rate recommended inside the troughs (Table 2), the local PTC efficiency (η

_{PTC,l}) can be estimated with the following expression [30]:

_{th}for the ISCC configuration (11 loops of 39 modules) and 15 MW

_{th}for the ISCC-R-DRDE one (8 loops of 50 modules).

#### 3.2. Simulation at Off-Design Operation

^{2}is required to ensure a correct collector cooling.

#### 3.3. Annual Performance

#### 3.4. Merit Numbers

_{f}is the fuel mass flow, and H

_{c}is the lower heating value of the fuel (natural gas, 48.000 kJ/kg).

_{ise}), which assesses the individual contribution of each heat source according to the irreversibility associated with each heat source:

_{ise}is:

_{inv}, LC

_{O&M}, and LC

_{f}are the levelized cost of equipment acquisition, operating/maintenance and fuel, respectively, and E

_{yearly}is the yearly energy production. Economic parameters used for the LCOE calculation are shown in Table 3.

_{ise}) is used as follows:

## 4. Results and Discussion

#### 4.1. Performance of Reference Configurations without Solar Contribution

#### 4.2. Performance of the Reference ISCC

#### 4.3. Performance of ISCC-R-DRDE

#### 4.4. Daily and Yearly Operation

^{2}. For all configurations, the maximum power is obtained during the morning due to the low ambient temperature. As expected, the power rate and fuel consumption (E

_{f}) of the configurations using recuperative GT are lower than those obtained for the non-recuperative configurations.

_{tot}) and fuel consumption for all configurations in Almeria and Las Vegas. It can be observed that configurations with recuperative GT and DRDE bottoming cycle require lower yearly fuel consumption than that of the non-recuperative GTs, although they generate lower energy. Figure 7b shows the heat rate (that relates fuel consumption to energy production). It can be observed that the heat rate is lower for the configurations based on the DRDE cycle. Thus, they are advisable from a thermodynamic perspective. In addition, one can observe that solar integration leads to lower heat rates in Las Vegas than in Almeria thanks to the higher annual irradiation, whereas combined cycles with no solar integration achieve lower heat rates in Almeria due to lower mean temperatures.

## 5. Conclusions

## Supplementary Materials

## Author Contributions

## Funding

## Conflicts of Interest

## Nomenclature

Acronyms | |

CC | Combined cycle |

CCGT | Combined cycle gas turbine |

CCGT-R-DRDE | CCGT with recuperative GT and DRDE cycle |

CSP | Concentrating solar power |

DRDE | Double recuperative double expansion |

GT | Gas turbine |

HP | High pressure |

HRSG | Heat recovery steam generator |

HRVG | Heat recovery vapor generator |

HTF | Heat transfer fluid |

ISCC | Integrated solar combined cycle |

ISCC-R-DRDE | ISCC with recuperative GT and DRDE cycle |

LP | Low pressure |

O&M | Operation and maintenance |

ORC | Organic Rankine cycle |

PTC | Parabolic trough collectors |

SSG | Solar steam generator |

ST | Steam turbine |

SVG | Solar vapor generator |

TMY | Typical meteorological year |

VT | Vapor turbine |

Symbols | |

C | Cost of energy (€·J^{−1}) |

DNI | Direct normal irradiation (W·m^{−2}) |

E | Energy (J) |

h | Hour (h) |

H_{c} | Lower heating value (J·kg^{−1}) |

HR | Heat rate (-) |

IAM | Incidence angle modifier (-) |

LC | Levelized cost (€) |

LCOE | Levelized cost of energy (€·J^{−1}) |

ṁ | Mass flow rate (kg·s^{−1}) |

n | Yearly frequency (-) |

p | Pressure (Pa) |

P | Power (W) |

$\dot{Q}$ | Thermal power (W) |

t | Time (s) |

T | Temperature (K) |

U | Overall heat transfer coefficient (W·K^{−1}·m^{−2}) |

UA | Thermal conductance (W·K^{−1}) |

Greek letters | |

Δ | Increment |

ε | Effectiveness (-) |

ξ | Pressure drop (-) |

η | Efficiency (-) |

Subscripts | |

amb | Ambient |

exh | Exhaust gas |

f | Fuel |

gt | Gas turbine |

inv | Investment |

ise | Internal solar-to-electricity |

l | Length coordinate |

max | Maximum |

R | Recuperator |

sol | Solar |

st | Steam turbine |

tot | Total |

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**Figure 3.**Layout of the double recuperative double expansion (DRDE) cycle (

**a**) and its T-s diagram (

**b**) [24].

Gas Turbine | |

Ambient conditions | 15 °C, 1 bar |

Compressor pressure ratio | 16:1 |

Air mass flow rate | 210 kg/s |

Turbine inlet temperature | 1227 °C |

Efficiency of combustion chamber | 95% |

Steam Cycle HRSG | |

Steam temperature | 545 °C |

HP/LP pressure | 90 bar/5 bar |

Pinch points | 10 °C |

Approach points | 20 °C |

LP temperature difference | 10 °C |

DRDE Cycle HRVG | |

Vapor temperature | 370 °C |

Pressure | 170 bar |

Pinch point | 10 °C |

Mechanical efficiency | 98% |

Subject | Data |
---|---|

Outer and inner tube diameter | 0.07/0.065 m |

Outer and inner glass envelope diameter | 0.115/0.109 m |

Module and mirror length | 12.27/11.9 m |

Intercept factor | 92% |

Reflectivity of mirrors | 92% |

Transmissivity of glass | 94.5% |

Absorptivity of tubes | 94% |

Optical efficiency (peak) | 75% |

Thermal emissivity | 4.795·10^{−2} + 2.331·10^{−4}·T (°C) |

Maximum oil mass flow rate recommended | 7.725 kg/s |

Subject | Cost |
---|---|

PTC cost | 200 €/m^{2} |

Land cost | 2 €/m^{2} |

Specific cost for the power block [34,38] | (466.1 + 113900/P[MW]) €/kW |

Steam turbine cost variation [39] | (0.207·ΔP[MW]) M€ |

Gas turbine recuperator * [40] | (2861·A^{0.59}[m^{2}]) $ |

SSG^{+} [3] | (−7·10^{−4}·A^{2}[m^{2}] + 126.9·A[m^{2}] + 7770.4) € |

Combined cycle O/M cost | 17.9 €/(year·kW) |

Solar field O/M cost | 9 €/(year·m^{2}) |

Surcharge for construction, engineering, and contingencies | 10% |

O/M equipment cost percentage of investment | 1% |

Interest rate | 4% |

Fuel escalation rate | 2.5% |

O/M escalation rate | 1% |

Natural gas | 0.0232 €/kWh |

Life | 25 years |

Tamb (°C) | Configuration | P_{CC} (MW) | P_{GT} (MW) | P_{ST,VT} (MW) | HR | η | η_{GT} | η_{ST,VT} | T_{exh,GT} (°C) | p_{max} (bar) |
---|---|---|---|---|---|---|---|---|---|---|

0 | CCGT | 137.7 | 99.0 | 38.7 | 1.85 | 54.1% | 38.9% | 34.7% | 558 | 90.6 |

CCGT-R-DRDE | 122.1 | 96.9 | 25.2 | 1.78 | 56.3% | 44.7% | 29.5% | 435 | 169.4 | |

15 | CCGT | 124.8 | 87.7 | 37.1 | 1.88 | 53.2% | 37.4% | 34.0% | 575 | 90 |

CCGT-R-DRDE | 109.3 | 85.8 | 23.5 | 1.82 | 55.1% | 43.2% | 28.4% | 450 | 169.1 | |

30 | CCGT | 109.0 | 73.8 | 35.2 | 1.93 | 51.9% | 35.2% | 33.3% | 598 | 88.6 |

CCGT-R-DRDE | 93.5 | 72.1 | 21.4 | 1.88 | 53.2% | 41.0% | 27.3% | 468 | 165.5 |

Tamb (°C) | Irradiation (W/m^{2}) | P_{CC} (MW) | P_{GT} (MW) | P_{ST,VT} (MW) | ṁ_{f}·H_{c} (MW) | Q_{sol,net} (MW) | η | HR | η_{ise} | p_{max} (bar) |
---|---|---|---|---|---|---|---|---|---|---|

0 | 0 | 136.7 | 99.0 | 37.7 | 255 | 0 | 53.7% | 1.86 | - | 75 |

15 | 0 | 123.9 | 87.7 | 36.2 | 234 | 0 | 52.9% | 1.89 | - | 75 |

30 | 0 | 108.2 | 73.8 | 34.4 | 210 | 0 | 51.5% | 1.94 | - | 73 |

0 | 850 | 142.7 | 99.0 | 44.1 | 255 | 16.1 | 52.8% | 1.78 | 40.6% | 91 |

15 | 850 | 130.1 | 87.7 | 42.4 | 234 | 16.1 | 52.0% | 1.80 | 38.8% | 90 |

30 | 850 | 114.4 | 73.8 | 40.5 | 210 | 16.1 | 50.6% | 1.84 | 36.6% | 89 |

Tamb (°C) | Irradiation (W/m^{2}) | P_{CC} (MW) | P_{GT} (MW) | P_{ST,VT} (MW) | ṁ_{f}·H_{c} (MW) | Q_{sol,net} (MW) | η | HR | η_{ise} | p_{max} (bar) |
---|---|---|---|---|---|---|---|---|---|---|

0 | 0 | 121.9 | 96.9 | 25.0 | 217 | 0 | 56.2% | 1.78 | - | 117 |

15 | 0 | 108.9 | 85.8 | 23.0 | 198 | 0 | 54.8% | 1.82 | - | 116 |

30 | 0 | 92.7 | 72.1 | 20.6 | 176 | 0 | 52.8% | 1.90 | - | 114 |

0 | 850 | 126.9 | 96.9 | 30.7 | 217 | 15.3 | 54.9% | 1.70 | 38.9% | 161 |

15 | 850 | 114.4 | 85.8 | 28.6 | 198 | 15.3 | 53.5% | 1.73 | 38.2% | 153 |

30 | 850 | 98.2 | 72.1 | 26.1 | 176 | 15.3 | 51.4% | 1.79 | 35.0% | 151 |

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## Share and Cite

**MDPI and ACS Style**

Rovira, A.; Abbas, R.; Muñoz, M.; Sebastián, A.
Analysis of an Integrated Solar Combined Cycle with Recuperative Gas Turbine and Double Recuperative and Double Expansion Propane Cycle. *Entropy* **2020**, *22*, 476.
https://doi.org/10.3390/e22040476

**AMA Style**

Rovira A, Abbas R, Muñoz M, Sebastián A.
Analysis of an Integrated Solar Combined Cycle with Recuperative Gas Turbine and Double Recuperative and Double Expansion Propane Cycle. *Entropy*. 2020; 22(4):476.
https://doi.org/10.3390/e22040476

**Chicago/Turabian Style**

Rovira, Antonio, Rubén Abbas, Marta Muñoz, and Andrés Sebastián.
2020. "Analysis of an Integrated Solar Combined Cycle with Recuperative Gas Turbine and Double Recuperative and Double Expansion Propane Cycle" *Entropy* 22, no. 4: 476.
https://doi.org/10.3390/e22040476