Thermodynamic analysis of a gas turbine cycle combined with fuel reforming for solar thermal power generation

Accepted Manuscript Thermodynamic Analysis of a Gas Turbine Cycle Combined with Fuel Reforming for Solar Thermal Power Generation

Mingjiang Ni, Tianfeng Yang, Gang Xiao, Dong Ni, Xin Zhou, Huanlei Liu, Umair Sultan, Jinli Chen, Zhongyang Luo, Kefa Cen PII:

S0360-5442(17)31167-2

DOI:

10.1016/j.energy.2017.06.172

Reference:

EGY 11180

To appear in:

Energy

Received Date:

25 July 2016

Revised Date:

09 May 2017

Accepted Date:

30 June 2017

Please cite this article as: Mingjiang Ni, Tianfeng Yang, Gang Xiao, Dong Ni, Xin Zhou, Huanlei Liu, Umair Sultan, Jinli Chen, Zhongyang Luo, Kefa Cen, Thermodynamic Analysis of a Gas Turbine Cycle Combined with Fuel Reforming for Solar Thermal Power Generation, Energy (2017), doi: 10.1016/j.energy.2017.06.172

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MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1 2 3 4 5 6

Thermodynamic Analysis of a Gas Turbine Cycle Combined with Fuel Reforming for Solar

7

Thermal Power Generation

8 9

Mingjiang Ni1, Tianfeng Yang1, Gang Xiao1*, Dong Ni2, Xin Zhou1, Huanlei Liu1, Umair

10

Sultan1, Jinli Chen1, Zhongyang Luo1, Kefa Cen1

11

1 State

12 13 14

Key Laboratory of Clean Energy Utilization, Zhejiang University, 38 Zheda Road, Hangzhou, 310027, China

2 State

Key Laboratory of Industrial Control Technology, Zhejiang University, 38 Zheda Road, Hangzhou, 310027, China

15 16 17

Correspondence information: Gang Xiao, PhD, Professor

18

State Key Laboratory of Clean Energy Utilization, Zhejiang University, 38 Zheda Road,

19

Hangzhou, 310027, China

20

[email protected], Tel.: +86 571 87953290, fax: +86 571 87951616

21 22 23 24 25

1

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

Thermodynamic Analysis of a Gas Turbine Cycle Combined with Fuel Reforming for Solar

2

Thermal Power Generation

3

Mingjiang Ni1, Tianfeng Yang1, Gang Xiao1,*, Dong Ni2, Xin Zhou1, Huanlei Liu1, Umair Sultan1,

4

Jinli Chen1, Zhongyang Luo1, Kefa Cen1

5

1

State Key Laboratory of Clean Energy Utilization, Zhejiang University, 38 Zheda Road, Hangzhou,

6 7

310027, China 2

State Key Laboratory of Industrial Control Technology, Zhejiang University, 38 Zheda Road,

8 9

Hangzhou, 310027, China Abstract

10

There is insufficient literature about solarized gas turbines that achieved high efficiency and solar

11

share simultaneously. It is because the outlet temperature of a solar receiver is always much lower

12

than a combustor and it is difficult to design a high-efficiency exhaust-heat recovery system except

13

for a complicated Rankine cycle. A solar-assisted chemically recuperated gas turbine system is

14

proposed and expected to achieve a good performance by combining with two-stage fuel-steam

15

reforming. The first stage is a low-temperature reformer, recovering exhaust gas heat, and the second

16

stage is a high-temperature one, absorbing concentrated solar radiation. Thermodynamic analyses

17

and comparisons are conducted. This system is expected to have a competitive thermal efficiency of

18

47.7%, which is 10.6 percentage points higher than that of a solarized gas turbine system without

19

reformers. Meanwhile, it has a solar share of 75.0%, which is 12.8 percentage points higher than that

20

of a solarized gas turbine system with a low-temperature reformer. In the viewpoint of energy level,

21

the two-stage fuel reforming upgrades low-level thermal energy of the turbine exhaust and solar

22

receiver into high-level chemical energy, reducing exergy destruction. The relative upgrade of

23

energy level is 38.2% for turbine exhaust and 17.4% for solar thermal energy.

24 25 26

Keywords: Solar thermal power; Solarized gas turbine; Fuel reforming; Thermodynamic analysis Corresponding author. Tel.: +86 571 87953290, fax: +86 571 87951616; E-mail address: [email protected]

2

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Nomenclature CRGT chemically recuperated gas turbine Ex exergy flow [MW] Exd exergy destruction flow [MW] ExQ heat exergy flow [MW] Exf fuel exergy flow [MW] ex specific exergy [kJ kmol-1] HRSG heat recovery steam generator h specific enthalpy [kJ kmol-1] LHV lower heating value [MJ kg-1] MSR methane steam reformer mf mass flow rate [kg s-1] Q heat flow [MW] R gas constant [kJ kmol-1K-1] solar-assisted chemically SACRGT recuperated gas turbine solar hybrid chemically recuperated SHCRGT gas turbine SHGT solar hybrid gas turbine SMSR solar methane steam reformer SRGT solar reforming gas turbine system s specific entropy [kJ kmol-1 K-1] T temperature [K] W power [MW]

Xj mole fraction of component j Greek symbols ηth thermal efficiency [%] ηex exergy efficiency [%] Ψ solar share [%] ξ exergy destruction rate [%] Δ difference Subscripts and superscripts ch chemical equ equilibrium exh exhaust gas app heat transfer temperature approach f fuel i

into the system

j

component index

mix o ph rad sol 0

mixture out of the system physical radiation solar reference ambient condition

1 2

1. Introduction

3 4

To reduce fossil fuel consumption and CO2 emissions, renewable energies, such as solar energy

5

and wind, are expected to provide the majority of the future energy supply. Solar thermal power

6

technologies have great potential to become a cost-effective, highly efficient and environmentally

7

friendly base-load power supply. Rankine (steam or organic) cycle and Stirling cycles have been

8

developed for solar thermal power generation [1]. Gas turbines are an advanced way to generate

9

power with benefits of compactness, low emissions, high reliability and multi-fuel capability. A

10

solarized gas turbine system is a promising technology for hybrid operation and dispatchability.

11

Several kinds of solarized gas turbine systems have been proposed and tested, which here is

3

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

classified as simple solar hybrid turbine systems (SHGT), solar reforming gas turbine systems

2

(SRGT) and gas turbine systems integrated with low-temperature solar thermal energy.

3 4

1.1. Simple solar hybrid gas turbine systems

5

With the development of high-temperature solar air receivers, solar energy can directly provide a

6

majority of the heat supply for a gas turbine cycle. In the early 1980s, the Electric Power Research

7

Institute of the USA developed a SHGT system [2]. Concentrated solar radiation was used to preheat

8

pressurized air from a compressor before entering a supplementary combustor, as shown in Fig. 1(a).

9

The fuel mass flow of the combustor could be adjusted frequently to maintain a stable turbine inlet

10

temperature (TIT) regardless of the fluctuation of solar irradiation [3]. A pressurized air receiver is a

11

key component of the SHGT system, which works under unstable high-flux radiation and high-

12

temperature conditions. There are two categories of receivers, i.e., tubular receivers and volumetric

13

receivers. The outlet temperature of a tubular receiver with pressurized air is usually less than 800 °C

14

because of the limitation of metallic materials [4]. A quartz window is always adopted in a

15

volumetric receiver to maintain air pressurized. Porous or foam ceramics are used to absorb high flux

16

radiation for heating air up to 1000 °C or higher [5, 6]. Barigozzi et al. [7] used TRANSYS® and

17

Thermoflex® to simulate a SHGT system based on a SGT-750 Siemens turbine. This system could

18

achieve an electric output of 34.3 MW and a thermal efficiency of 38.3% with a solar share of 70.0%

19

on a typical summer day.

20

So far, several pilot projects of solar hybrid gas turbine systems have been developed. An EU-

21

funded project, called SOLGATE, was conducted to determine the feasibility of a solar hybrid gas

22

turbine system [2]. The SOLGATE project had a capacity of 230 kWe, a solar share of close to 70%

23

and a thermal efficiency of 20%. Compressed air was firstly heated by a tubular receiver and then by

24

two volumetric receivers until reaching 960 °C [8]. Another project, named SOLHYCO, aimed to

25

develop a metallic tubular receiver instead of a volumetric receiver to reduce cost [9]. The outlet air

4

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

temperature of the tubular receiver reached 800 °C [10]. SOLUGAS, another EU-funded project and

2

the first solar hybrid gas turbine system with a MW scale, was tested under design and specific

3

conditions to study its operating characteristics. The tubular receiver made of nickel alloy produced

4

pressurized air of up to 800 °C [4]. In addition, the PEGASE project in France is still under

5

development [11], as well as a new solar air turbine system in CSIRO of Australia [12].

6 7

1.2. Solar reforming gas turbine systems

8

Fig. 1(b) displays a SRGT system, where a solar methane steam reformer (SMSR) absorbs solar

9

radiation by an endothermic reaction, and then the reaction product (syngas) enters a combustor.

10

Reforming of hydrocarbons can convert solar energy into chemical forms by endothermic reactions

11

[13-22]. For instance, the caloric value of methane reforming was increased by 28% [23]. Over the

12

past decades, several solar reforming projects have been successfully implemented to upgrade the

13

calorific value of the feeding fuel [23, 24]. Elysia and Mitsos [25] performed an analysis of a

14

combined cycle integrated with solar reforming, and the results indicated that the maximum solar

15

share could reach 20.5% with a thermal efficiency of 47.6%. Tamme et al. [26] used a solar specific

16

receiver-reactor to upgrade fuel in gas turbine systems. The shortcoming of SRGT system is that the

17

solar share is limited to 25%-30% depending on the process conditions. Steam Fuel

Fuel Receiver

Bypass

Solar Energy

Solar Energy

SMSR

Combustor Bypass

Combustor Turbine

Compressor

Turbine

Compressor Generator

18 19

Air

(a)

Generator

Exhaust

Air

(b)

Exhaust

20

Fig. 1. Schematics of a simple solar hybrid gas turbine system (SHGT) (a) and a solar reforming gas

21

turbine system (b).

22

5

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

1.3. Gas turbine systems integrated with low-temperature solar energy

2

Instead of high-temperature solar receivers or methane-steam reforming, some gas turbine systems

3

combined with low-temperature solar thermal energy. Hong et al. [27] proposed a solar turbine

4

system integrated with methanol decomposition in solar parabolic troughs at 200 °C-300 °C, and the

5

solar share was 18% at the design point. Zhang and Liar [28] presented an intercooled chemically

6

recuperated gas turbine cycle using low temperature solar energy to evaporate water in an

7

intercooled gas turbine. A solar share of 20.3% and a thermal efficiency of 45.9% were expected at

8

normal conditions. Livshits and Kribus [29] studied a solar steam injection gas turbine system with a

9

high steam-to-air ratio, where steam was generated by parabolic troughs or linear Fresnel

10

concentrators. The thermal efficiency and solar share of this system could reach 49% and 21%,

11

respectively. An integrated solar combined cycle system (ISCCS) is of a bottoming Rankine cycle

12

with adding solar energy at low temperature [30-34]. The net instantaneous electrical solar share is

13

17.5% at the design point. For a typical meteorological year in California, the annual solar share is

14

9.4% or 5.6% for this system with or without thermal storage, respectively [30]. Although the solar

15

thermal-to-electric efficiency can reach up to 40% [31], the solar share of ISCCS is often less than

16

20%, which is much lower than that of conventional stand-alone solar thermal power plants.

17

Solarized gas turbine systems mentioned above hardly achieve high efficiency and solar share

18

simultaneously. For example, the SHGT system has a high solar share but the thermal efficiency is

19

lower than 40% because of large exhaust gas loss. A straightforward way to improve the efficiency

20

of the SHGT system is to combine it with a bottoming Rankine cycle. However, to fulfill the high

21

efficiencies of combined cycle plants (>50%), the power capacity should be over 50 MW, which is

22

not feasible for a new technology because of the very high investment cost [35]. It is noted that the

23

size of a gas turbine is sufficiently small to be installed on top of a solar tower, while a steam turbine

24

system is so large and complicated that should be installed on the ground. The long pipe system

25

between gas turbine and steam turbine can cause a lot of route loss and increase the cost. It is a

6

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

possible way to establish a solar gas turbine system with both high thermal efficiency and solar share

2

by directly absorbing solar energy and using an alternative way to recover exhaust gas heat instead of

3

a bottoming steam cycle.

4

This study proposes a solar-assisted chemically recuperated gas turbine system (SACRGT)

5

combined with two-stage fuel-steam reforming, which consists of low- and high-temperature fuel

6

reformers. The former is implemented with recovering exhaust gas heat, and the latter absorbs heat

7

from concentrated solar radiation. SACRGT is expected to increase the thermal efficiency and solar

8

share simultaneously by reducing the combustion exergy destruction and recovering low-level

9

thermal energy of the turbine exhaust and solar receiver. In order to have a deep understanding about

10

the performance of SACRGT, thermodynamic analyses are conducted, as well as comparisons with

11

other system configurations.

12 13

2. System description and models

14

SACRGT is compared with a solar hybrid chemically recuperated gas turbine system (SHCRGT)

15

without high-temperature solar reforming and SHGT without fuel reforming. In order to clearly

16

illustrate the performance, energetic and exegetic simulation models are both established. Energetic

17

analysis is mainly based on the first law of thermodynamics and gives concise characteristics.

18

Exergetic analysis accounts for the available energy and thermodynamic irreversibility [36], trying to

19

find out main exergy-destruction processes.

20 21

2.1. System description

22

Fig. 2(a) depicts the SACRGT system, where compressed air from a compressor is first preheated

23

by a solar air receiver and then flows into a combustor. The exhaust gas heat from the turbine is

24

recovered by a low-temperature fuel reforming system in a blue dashed box and a high-temperature

25

fuel reforming system in a red dashed box. The low-temperature fuel reforming system consists of a

7

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

heat recovery steam generator (HRSG) and a methane steam reformer (MSR). The high-temperature

2

fuel reforming system is a solar methane steam reformer (SMSR). The pressurized syngas flows on

3

the tube-side of the MSR filled with nickel-based catalyst pellets, and exhaust gas flows on the shell

4

side [37-43]. Using methane-steam reforming as exhaust heat recuperation has been studied and

5

validated [44-48]. The extent of fuel reforming in MSR is limited due to the exhaust gas temperature,

6

and the fuel conversion is partially completed [49]. Therefore, high-temperature SMSR is added for

7

further reforming, absorbing more solar thermal energy to improve the solar share. As a comparison

8

system, SHCRGT is proposed without SMSR, as shown in Fig. 2 (b). Receiver

Combustor

Receiver Solar Energy

Combustor

Solar Energy Bypass

Bypass Turbine

Compressor Air

Turbine

Compressor Generator

Air

Generator

SMSR Bypass

Solar Energy Water

Water

Water pump

Water pump Exhaust

HRSG

Exhaust

MSR HRSG

Mixer Fuel compressor

Mixer

MSR Fuel compressor

Fuel

9

Fuel

(a) SACRGT

(b) SHCRGT

10

Fig. 2. Schematics of a solar-assisted chemically recuperated gas turbine system (SACRGT) (a) and

11

a solar hybrid chemically recuperated gas turbine system (SHCRGT) (b).

12 13

The reforming systems and gas turbine are compact to be installed on the solar tower, which

14

reduces the cost significantly. Another potential advantage of the SACRGT system is that NOx

15

emissions can be as low as 1 ppm just as a chemically recuperated gas turbine (CRGT) system [50].

16

Steam in the syngas injected into the combustor results in a lower flame temperature, and hydrogen-

17

rich syngas lowers the flammability limit to keep the monoxide formation within an acceptable level

18

[51]. Moreover, SACRGT has a better part-load performance than a simple gas turbine cycle or

19

combined cycle [51], which is important for a solar thermal power system to accommodate 8

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

dispatchability. A comparison analysis is carried out based on energetic and exergetic methods for

2

SACRGT and SHCRGT and SHGT systems.

3 4

2.2. Energetic model

5

The cycle simulations presented in this paper are based on Aspen Plus®, and the thermodynamic

6

properties are calculated using the Redlich-Kwong-Soave model with default binary interaction

7

coefficients [52]. The reactions of methane-steam reforming in the MSR and SMSR can be described

8

by two main equations [17]:

9

CH 4  H 2O  CO  3H 2 ;

10

CO  H 2O  CO2  H 2 ;

0 H 298 K  206.25kJ / mol 0 H 298 K  41.03kJ / mol

(1) (2)

11

The reformers including MSR and SMSR are simulated by the Gibbs reactor, which uses Gibbs free

12

energy minimization to calculate the chemical reaction and phase equilibrium with restricted

13

equilibrium specifications for systems. The chemical equilibrium approach temperature

14

to specify the chemical non-equilibrium at the reformer outlets. At a high temperature, the catalyst

15

activity is high, and the approach temperature difference is small. For a typical reformer using a

16

nickel-based catalyst, the equilibrium approach

17

below 650 °C [51]:

Tequ  43.33(1.0 

To ), 650

is used

is zero above 650 °C and decreases linearly

Tequ  0, To  650C

18 19

Tequ

Tequ

(3)

To  650C

(4)

20

where To is the temperature of the fuel mixture at the reformer outlet. The heat transfer temperature

21

approach of MSR is given by

22

Tapp  Texh  Tout

(5)

23

where Texh is the temperature of the turbine exhaust gas. The syngas composition at the MSR outlet

24

is equal to the equilibrium composition when the temperature is given by 9

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Tequ  Texh  Tapp  Tequ

1

(6)

2

The temperature of the fuel mixture at the SMSR outlet is assumed to be 800 °C, which is limited by

3

the metal tube. The equilibrium temperature of the fuel mixture at the SMSR outlet is set to 800 °C

4

according to Eq. (3).

5

Fig. 3 shows a diagram of the temperature vs. heat transfer for HRSG and MSR, where the

6

minimum temperature approach determines the maximum mass flow rate of water and heat recovery.

7

This value is set to a constant 10 °C in this study. T

Tapp

Exhaust gas

MSR

Tapp Evaporation

CH4 HRSG

Q

8 9

Water

Fig. 3. Diagram of temperature vs. heat transfer for HRSG and MSR.

10 11 12 13

The thermal efficiency of a system is defined as

th 

Wnet Q f  Qsol

(7)

Q f  m f  LHV

(8)

14

where Wnet is the net electric power produced by the system, including the water pump and fuel

15

compressor consumption; Q f is the fuel heat input based on the low heating value (LHV); m f is the

16

fuel mass flow rate and Qsol is the solar heat absorbed in the solar air receiver and SMSR. The solar

17

contribution to the system is described by the solar share, which is given by

18



Qsol Q f  Qsol

10

(9)

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

The temperature of compressed air at the outlet of the solar air receiver is assumed to 1000 °C

2

typically for a volumetric receiver. TIT is assumed to be 1150 °C, which is lower than that in Ref.

3

[53] to ignore the turbine cooling penalty. The air flow rate of the compressor is set to 10 kg/s.

4

Methane is chosen as the raw material for fuel-steam reforming, and dry air is assumed to be a

5

mixture of 21% oxygen and 79% nitrogen. The model parameters are listed in Table 1 [35, 53-55].

6 7

Table 1

8

Simulation parameters. Item

Parameter

Value

Pressure ratio

10-40

Compressor Isentropic efficiency [%]

Combustor

Turbine

Ambient conditions

SMSR

HRSG

MSR

Solar air receiver

89

Air flow rate [kg s-1]

10

Efficiency [%]

100

Pressure drop [%]

3

LHV (methane) [MJ kg-1]

50.04

TIT [K]

1423

Isentropic efficiency [%]

90

Temperature [K]

298.15

Pressure [Pa]

101325

Dry air

21%O2+79%N2

Temperature [K]

1073

Pressure drop [%]

3

Hot side pressure drop [%]

2

Cold side pressure drop [%]

3

Temperature approach [K]

10

Hot side pressure drop [%]

2

Cold side pressure drop [%]

5

Temperature approach [K]

10

Temperature [K]

1273

11

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation

Others

Receiver pressure drop [%]

3

Water pump efficiency [%]

85

Fuel compressor efficiency [%] 85 Mechanical efficiency [%]

99

Generator efficiency [%]

98

1 2 3 4

2.3. Exergetic model For a steady control volume, the exergy balance equations, regardless of kinetic and potential change, can be written as [36]

 Ex   Ex

5

i

Q

  Exo  Wo  Exd

(10)

6

where Exi and Exo are the exergy flow rates at the inlet and outlet of the control volume,

7

respectively, Wo is the work output and Exd is the exergy destruction of the control volume,

8

subscript (0) refers to the reference ambient condition, which is chosen as 298.15 K and 101325 Pa

9

and

10

ExQ

is the heat exergy flow, which is given by

ExQ  (1 

T0 )Qsol T

(11)

11

where T is the working temperature of SMSR or the solar air receiver. The exergy of working

12

stream is composed of physical exergy and chemical exergy, which is given by [36]

13 14 15

ex  ex ph  ex ch

(12)

The physical exergy is calculated as

ex ph  (h  h0 )  T0 ( s  s0 )

(13)

16

where h and s are the specific enthalpy and entropy, respectively. The chemical exergy is important

17

in the combustion and reforming process. The chemical exergy of a mixture stream is given by [56]

18

ch exmix   X j ex chj  RT0  X j LnX j

12

(14)

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Xj

1

where R is the gas constant and

is the mole fraction of each component in the mixture stream.

2

The reference specific chemical exergies of pure chemical substances are listed in Table 2, and the

3

reference ambient air has 100% humidity [57]. Aspen Plus® does not have a built-in exergy analysis

4

function, and the exergy of each stream must be calculated by users according to Eqs. (10)-(14). The

5

enthalpy and entropy of each stream are obtained using Aspen Plus®, and the values of the same

6

stream at the reference ambient condition can be acquired using Aspen Transfer block and Heat

7

Exchanger block specified at the ambient condition. Chemical exergy data are not included in Aspen

8

Plus® and should therefore be calculated according to Eq. (14) and Table 2. The exergy efficiency

9

can be used to assess the reversible performance of each component in the system. For a power

10

consumption component, such as a compressor, water pump or fuel compressor, the exergy

11

efficiency is defined as

ex  

12

Exo   Exi Wi

(15)

13

where Wi is the power input. For a power generation component, such as a turbine, the exergy

14

efficiency is defined as

ex  15 16

Wo  Exi   Exo

For a combustor, the exergy efficiency is defined as

ex   17

Ex f ,mix

18

where

19

efficiency is defined as

Exo   Exi Ex f ,mix

(17)

is the fuel exergy or reformed fuel mixture exergy. For other components, the exergy

ex  20

(16)

 Ex  Ex   Ex o

i

Q

13

(18)

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

The exergy destruction rate is used to describe the percentage of exergy destruction for each

2

component, which is given by

 3

Exd , j

 Ex

(19)

d

Exd , j

and

 Ex

4

where

5

the system, respectively. The exergy efficiency of the whole system is defined as

d

are the exergy destruction of a component and the total exergy destruction of

ex  6

Ex f , ExQ

Wnet Ex f  ExQ

(20)

and Wnet are the fuel exergy input, the solar heat exergy input and the net electricity

7

where

8

output, respectively.

9 10

Table 2

11

Reference specific chemical exergy.

Substance H2O CO H2 O2 N2 CO2 CH4

Specific chemical exergy (kJ kmol1) 11710 275430 238490 3970 720 20140 836510

12 13

3. Results and discussion

14 15

Energetic results are discussed here, mainly including thermal efficiencies, solar shares and net

16

power, for SHGT, SHCRGT and SACRGT. Exergetic analysis is mainly on exergy efficiencies and

17

exergy destruction rates, trying to point out practical strategies for further improvements.

14

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1 2

3.1. Results of energetic analysis

3

Fig. 4 shows the thermal efficiency and solar share variation as a function of pressure ratio. The

4

solar share decreases as the pressure ratio increases because the solar energy absorbed by the

5

receiver decreases, when the compressor outlet temperature of air increases with pressure ratio. The

6

thermal efficiency first increases and then decreases with increasing pressure ratio. The maximum

7

thermal efficiency of SACRGT is approximately 47.7%, which is very close to SHCRGT, and 28.6%

8

higher than SHGT when the pressure ratio is 20. The solar share of SACRGT is 75%, which is

9

similar to SHGT, and 17.1% higher than SHCRGT. The net electricity power of SACRGT and

10

SHCRGT is much higher than that of SHGT, as shown in Fig. 5, which means a higher specific

11

power output. 80

48

75 44

Thermal efficiency--SHGT Thermal efficiency--SHCRGT Thermal efficiency--SACRGT Solar share--SHGT Solar share--SHCRGT Solar share--SACRGT

42 40

70

65

38 36

Solar share (%)

Thermal efficiency (%)

46

60

34 32

55 10

15

20

25

30

35

40

12

Pressure ratio

13

Fig. 4. Thermal efficiencies and solar shares vs. pressure ratio.

14

15

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 5.5

Net power--SHGT Net power--SHCRGT Net power--SACRGT

Net power (MW)

5.0

4.5

4.0

3.5

3.0

2.5 10

15

20

25

30

35

40

Pressure ratio

1 2

Fig. 5. Net power output vs. pressure ratio.

3 4

In SACRGT, the methane consumption rate of MSR decreases and the methane consumption of

5

SMSR increases with increasing pressure ratio, as shown in Fig. 6. At the SMSR outlet, methane-

6

steam reforming is almost completed. Two solar receivers at the solar tower are needed For

7

SACRGT, one for compressed air heating and the other for solar methane-steam reforming (SMSR).

8

Fig. 7 shows the thermal power inputs of the air receiver and SMSR, which is importance for control

9

strategies of heliostats with two concentrating focuses. 6

Methane consumption--MSR Methane comsumption--SMSR

Methane consumption (g/s)

5

4

3

2

1

0 10

10 11

15

20

25

30

35

40

Pressure ratio

Fig. 6. Methane consumption rate of MSR and SMSR vs. pressure ratio.

12 13

16

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 8

Thermal power input--SAR Thermal power input--SMSR

Thermal power input (MW)

7 6 5 4 3 2 1 0 10

15

25

30

35

40

Pressure ratio

1 2

20

Fig. 7. Solar thermal power inputs vs. pressure ratio.

3 4

Additional water is needed for the reforming process in SACRGT and SHCRGT, as shown in Fig.

5

8. The water consumption of SHCRGT and SACRGT is approximately 1 kg/(kW·h) when the

6

pressure ratio is 20, which is still less than evaporative-cooling solar thermal plants, as shown in

7

Table 3 [29, 58]. A condenser may be needed for water recovery especially in water scarce regions.

Water consumption (kg/(kW·h))

1.5

Water consumption--SHCRGT Water consumption--SACRGT

1.4 1.3 1.2 1.1 1.0 0.9 0.8 10

8 9

15

20

25

30

35

Pressure ratio

Fig. 8. Water consumption vs. pressure ratio.

10

17

40

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

Table 3

2

Water consumption of typical thermal power plants. Technology Natural gas combined cycle with evaporative cooling Cola/nuclear with evaporative cooling Parabolic trough with evaporative cooling Linear Fresnel with evaporative cooling Parabolic trough with dry cooling Power tower with dry cooling

Water consumption [kg/(kW·h)] 0.76 1.51-2.84 3.03 3.79 0.30 0.34

3 4

3.2. Results of exergetic analysis

5

Exergetic analysis can determine loss sources and give advice how to improve the system

6

performance. Exergetic analysis is conducted assuming that the pressure ratio is 20, where peak

7

efficiencies are obtained for SACRGT and SHCRGT. Fig. 9(a) shows the exergy efficiencies and

8

exergy destruction rates of the main components in the SHGT system. The exergy efficiency of

9

SHGT is 44.7%. The maximum exergy destruction rate occurs in the exhaust gas, which is 55.2%.

10

Another main exergy destruction cause is the combustor, which has a relatively low exergy

11

efficiency of 74.3%. It is practical to find a way to reduce the exergy destructions of the exhaust gas

12

and combustor, according to the exergy analysis of SHGT. In SHCRGT, exhaust heat is recovered by

13

HRSG and MSR, and the exergy destruction of the exhaust gas decreases significantly compared

14

with SHGT. The exergy efficiency of the SHCRGT system is 55.0%, as shown in Fig. 9(b). The

15

main exergy destruction is from the combustor, although the exergy efficiency is still slightly higher

16

than that of SHGT. The exergy destruction caused by the fuel compressor and water pump is

17

negligible.

18

The low-temperature fuel reforming system (HRSG and MSR) reduces the exergy destructions of

19

the exhaust gas and improves the thermal efficiency of SACRGT, as shown in Fig. 9(c) (without

20

showing the mixer, fuel compressor and water pump). The high-temperature fuel reforming reduces

18

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

the methane consumption (with high level of exergy), and the combustor exergy efficiency of

2

SACRGT is higher than SHCRGT. The overall system exergy efficiency of SACRGT is 57.5%

3

higher than SHCRGT. Exergy efficiency Exergy destruction rate 94.4

55.2 50

80

Exergy efficiency (%)

60

94.7

92.3

90.4

74.3 40

60 30 40 20 14.1

12.3

20

11.5 10

6.8 0.1

0 om C

r so es pr

SA

R om C

or st bu

m co el Fu

0.0

r so es pr

0

s ga st au h Ex

e in rb Tu

Exergy destruction rate (%)

100

(a) 100

Exergy efficiency Exergy destruction rate 36.2

94.4 90.4

99.2

98.7

94.9

92.4

35

90.2

25 60

20.9

40

15

13.4 11.9

10 20

6.7

6.6

5

3.0

0 om C

0.1

r so es pr

SA

R om C

or st bu el Fu

m co

r so es pr

Exergy efficiency (%)

100

94.4

1.2

0.0

p e in m rb pu Tu er at W

SG R H

M

er ix

0.0

m or ef R

(b)

E

as tg us a xh

30

90.1

25

82.8

80

22.1 20

60

14.9

15

13.3 40

10 7.5

7.4 20

3.3 0

5

0

98.8

98.5

94.8

90.4

er

Exergy efficiency Exergy destruction rate

28.4

4

20

r so es pr om C

5 2.1 0.0

R SA

or st bu m o C

e in rb Tu

(c)

SG R H

SR M

Exergy destruction rate (%)

Exergy efficiency (%)

30

77.5

Exergy destruction rate (%)

82.8

80

SR SM

as tg us a h Ex

0

Fig. 9. Exergy efficiency and exergy destruction rates of the SHGT (a), SHCRGT (b) and SACRGT.

19

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

The low- and high-temperature fuel reforming system upgrades energy level from thermal energy

2

into chemical energy. The concept of energy level was proposed by Ishida and Kawamura [59, 60],

3

and used to characterize energy quality of work output, defined by

A

4

ex s  1  T0 h h

(21)

5

The difference between the energy levels of methane and combustion gas causes a lot of exergy

6

destruction in the combustor of SHGT system, as shown in Fig. 10(a). The turbine exhaust is not

7

utilized, although it has high energy level. In the SHCRGT system, the methane raises the energy

8

level of turbine exhaust from thermal energy to chemical energy by low-temperature fuel reforming,

9

as shown in Fig10(b), which reduces the exergy destruction of combustor. As to the SACRGT

10

system, a high-temperature fuel reforming is added after the low-temperature fuel reforming, which

11

further upgrade the solar thermal energy to chemical energy and further reduces the exergy

12

destruction of combustor, as shown in Fig. 10(c). The exergy of methane does not match the

13

combustion in gas turbine systems [27]. However, the methane exergy can act as a drive force to

14

upgrade thermal energy (turbine exhaust and solar thermal energy) to chemical energy. That is the

15

reason why the exergy efficiency of SACRGT is higher than SHGT and SHCRGT. For SACRGT,

16

the relative energy upgrade of energy level is 38.2% for turbine exhaust, and 17.4% for solar thermal

17

energy of SMSR.

18

20

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Combustor 1.0

Methane Combustion gas

Energy level

0.8

Turbine exhaust 0.5

0.3

0.0 1.0

(a) Methane Syngas of MSR Combustion gas

Energy level

0.8

Turbine exhaust Turbine exhaust 0.5

Low-temperature reforming Exhaust

0.3

0.0

1.0

(b) Methane Syngas of MSR Syngas of SMSR Combustion gas

Energy level

0.8

Solar energy of SMSR

Turbine exhaust

Turbine exhaust 0.5

High-temperature reforming

Exhaust

0.3

0.0

1 2

(c) Fig. 10. Cascade utilization of exergy in SHGT (a), SHCRGT (b) and SACRGT (c).

21

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

3.3. Strategies for further improvement

2

According to the exergy analysis, strategies are discussed for further improvement of the

3

SACRGT system. Although the two-stage fuel reforming system decreases the energy level gap

4

between fuel and combustion gas, the exergy destruction in the combustor is still high. Increasing

5

TIT can reduce the combustor exergy destruction. In this study, TIT is set to 1150 °C, while TIT of

6

modern advanced gas turbine is always over 1500 °C [61]. The steam generated from HRSG can also

7

be used to cool the turbine blades and nozzles because steam has better heat transfer performance

8

than air from a compressor, which means higher TIT is allowed. Another suggestion is to increase

9

the isentropic efficiencies of the compressor and turbine, which are over 90% for advanced gas

10

turbines [61]. Intercooling and reheat are also suitable for SACRGT to reduce exergy destruction of

11

compressors and turbines. With the development of solar receivers, high-temperature receivers

12

(>1000 °C) including SMSR and air receivers can be used to further increase the solar share.

13 14

3.4. Modification of mature gas turbines

15

To demonstrate this new idea, it is appropriate to modify a mature gas turbine considering system

16

cost. Old gas turbines with silo-type or side-mounted combustors are easy to connect to a compressor

17

and an additional solar gas receiver, as the necessary gas pipe of the compressor has already been

18

designed. However, most modern gas turbines with annular or can-annular combustors would require

19

a major redesign of the central casing and combustion section to allow redirection of gas flow [3].

20

The combustor also should be modified to allow reformed fuel gas with a high fraction of steam

21

entry and to keep the flame stable. The combustion mechanism of syngas combustion has been

22

studied by many researchers [62-66]. The combustor liner and outer casing should be designed to

23

withstand high-temperature air from a solar air receiver and the fuel mixture from SMSR. With the

24

injection of steam, the mass flow in a turbine is greater than that in a compressor, which could be

25

limited to keep the compressor from experiencing surge. Aero-derivative gas turbines could be better

22

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

suitable for modification because of their greater ability to accommodate increased mass flow [51].

2

The control system also requires modifications to satisfy different operation modes, such as starting,

3

solar hybrid operation, partial load, fuel only operation, shutdown, and safety actions for

4

emergencies. To reach a higher annual solar share, a thermal energy storage system can be added.

5 6

3.5. Comparison with conventional systems

7

Table 4 compares the performance characteristics of SACRGT with other solar thermal power

8

systems. A solar reforming gas turbine system uses the fuel exergy to upgrade the high-temperature

9

solar thermal energy (>600 °C), and a solar turbine system with integration of methanol

10

decomposition [27] uses the fuel exergy to upgrade low-temperature solar thermal energy (200 °C-

11

300 °C). In the viewpoint of energy level or exergy cascade utilization, these two kinds of systems

12

do not take full advantage of fuel exergy. The SACRGT system has two-stage upgrade process with

13

different working temperatures. A low-temperature reforming is used to upgrade the exhaust gas heat

14

and a high-temperature reforming for solar thermal energy upgrade, achieving a high thermal

15

efficiency and solar share simultaneously. The SACRGT is expected to be a promising configuration

16

for future solar tower systems.

17 18

Table 4

19

Characteristics of solar thermal power cycles. System

Thermal power cycle

Solar receiver temperature

Thermal efficiency

Solar share

Parabolic troughs [2]

Rankine steam cycle

400 °C

37%

˃90%

Tower [67, 68]

Rankine steam cycle

560 °C

~42%

˃90%

ISCCS [30]

Bottoming Rankine cycle integrated with solar heat

400 °C

40%

5.6-9.4%

SOLGATE [2]

Simple solar hybrid gas turbine cycle

960 °C

~20%

70%

23

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation

1

a

SOLHYCO [9]

Simple solar hybrid gas turbine cycle

800 °C

28%

23.1%

SOLUGAS [4]

Simple solar hybrid gas turbine cycle

800 °C

38%

--

Siemens turbine model [7]

Simple solar hybrid gas turbine cycle

800-1000 °C

38.3%

70%

Methane reforming [25]

Solar reformed fuel for combined cycle

577-877 °C

47.6%

20.5%

Methanol decomposition [27]

Solar reformed-fuel combined cycle

200-300 °C

35 %

18%

SOLRGT [28]

Solar-driven steam for chemical recuperated cycle

200-250 °C

45.9%

20.3%

Steam injection [29]

Solar-driven steam injection cycle

~200 °C

49%

21%

SHGTa

Simple solar hybrid gas turbine cycle

1000 °C

37.1%

76.1%

SHCRGTa

Solar hybrid chemically recuperated cycle

1000 °C

47.8%

62.2%

SACRGTa

Solar-assisted chemically recuperated cycle

1000 °C

47.7%

75.0%

The results of the present paper.

2 3

4. Conclusion

4 5

This paper proposes a solarized gas turbine system with two-stage fuel reforming, called SACRGT,

6

and energetic and exergetic analyses are performed. The results show that SACRGT has good

7

thermodynamic performance with high thermal efficiency, exergy efficiency and solar share of

8

47.7%, 57.5% and 75.0%, respectively, at the design point. The two-stage fuel reforming upgrades

9

the thermal energy of turbine exhaust and solar energy into chemical energy, thus reducing the

10

exergy loss in the combustor and recovering thermal energy with low energy level. The relative

11

upgrade of energy level is 38.2% for turbine exhaust and 17.4% for solar thermal energy. Practical

24

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

strategies for further improvements of SACRGT are discussed based on exergetic analyses. It is

2

noted that the gas turbine system integrated with reformers is compact, which can be installed on the

3

top of solar tower to reduce energy loss and investment. Moreover, SACGRT is expected to have

4

better part-load performance and low emissions than conventional solar gas turbine systems. A

5

further study on the optimization, off-design performance, annual performance, energy storage

6

system and economic analysis will be presented in the future.

7 8 9 10

Acknowledgements The authors gratefully acknowledge the support from the State's Key Project of Research and Development Plan (NO: 2016YFE0124700).

11 12

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MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 1

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32

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Figure Captions Fig. 1. Schematics of a simple solar hybrid gas turbine system (SHGT) (a) and a solar reforming gas turbine system (b).

Fig. 2. Schematics of a solar-assisted chemically recuperated gas turbine system (SACRGT) (a) and a solar hybrid chemically recuperated gas turbine system (SHCRGT) (b).

Fig. 3. Diagram of temperature vs. heat transfer for HRSG and MSR.

Fig. 4. Thermal efficiencies and solar shares vs. pressure ratio. Fig. 5. Net power output vs. pressure ratio. Fig. 6. Methane consumption rate of MSR and SMSR vs. pressure ratio. Fig. 7. Solar thermal power inputs vs. pressure ratio. Fig. 8. Water consumption vs. pressure ratio.

Fig. 9. Exergy efficiency and exergy destruction rates of the SHGT (a), SHCRGT (b) and SACRGT. Fig. 10. Cascade utilization of exergy in SHGT (a), SHCRGT (b) and SACRGT (c).

33

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Steam Fuel

Fuel Receiver

Bypass

Solar Energy

Solar Energy

SMSR

Combustor Bypass

Combustor Turbine

Compressor

Turbine

Compressor Generator

Air

(a)

Generator

Exhaust

Air

(b)

Exhaust

Fig. 1. Schematics of a simple solar hybrid gas turbine system (SHGT) (a) and a solar reforming gas turbine system (b).

34

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Receiver

Combustor

Receiver Solar Energy

Combustor

Solar Energy Bypass

Bypass Turbine

Compressor Air

Turbine

Compressor Generator

Air

Generator

SMSR Bypass

Solar Energy Water

Water

Water pump

Water pump Exhaust

HRSG

Exhaust

MSR HRSG

Mixer Fuel compressor

Mixer

MSR Fuel compressor

Fuel

Fuel

(a) SACRGT

(b) SHCRGT

Fig. 2. Schematics of a solar-assisted chemically recuperated gas turbine system (SACRGT) (a) and a solar hybrid chemically recuperated gas turbine system (SHCRGT) (b).

35

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation T

Tapp MSR

Exhaust gas

Tapp Evaporation

CH4 HRSG

Water Q

Fig. 3. Diagram of temperature vs. heat transfer for HRSG and MSR.

36

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 80

48

75 44

Thermal efficiency--SHGT Thermal efficiency--SHCRGT Thermal efficiency--SACRGT Solar share--SHGT Solar share--SHCRGT Solar share--SACRGT

42 40

70

65

38 36

60

34 32

55 10

15

20

25

30

35

40

Pressure ratio

Fig. 4. Thermal efficiencies and solar shares vs. pressure ratio.

37

Solar share (%)

Thermal efficiency (%)

46

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 5.5

Net power--SHGT Net power--SHCRGT Net power--SACRGT

Net power (MW)

5.0

4.5

4.0

3.5

3.0

2.5 10

15

20

25

30

35

Pressure ratio Fig. 5. Net power output vs. pressure ratio.

38

40

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 6

Methane consumption--MSR Methane comsumption--SMSR

Methane consumption (g/s)

5

4

3

2

1

0 10

15

20

25

30

35

40

Pressure ratio Fig. 6. Methane consumption rate of MSR and SMSR vs. pressure ratio.

39

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation 8

Thermal power input--SAR Thermal power input--SMSR

Thermal power input (MW)

7 6 5 4 3 2 1 0 10

15

20

25

30

35

Pressure ratio Fig. 7. Solar thermal power inputs vs. pressure ratio.

40

40

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation

Water consumption (kg/(kW·h))

1.5

Water consumption--SHCRGT Water consumption--SACRGT

1.4 1.3 1.2 1.1 1.0 0.9 0.8 10

15

20

25

30

35

Pressure ratio Fig. 8. Water consumption vs. pressure ratio.

41

40

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Exergy efficiency Exergy destruction rate 94.4

55.2 50

80

Exergy efficiency (%)

60

94.7

92.3

90.4

74.3 40

60 30 40 20 14.1

12.3

20

11.5 10

6.8 0.1

0 om C

r so es pr

SA

R om C

or st bu

m co el Fu

0.0

r so es pr

e in rb Tu E

Exergy destruction rate (%)

100

0

as tg us a xh

(a) 100

Exergy efficiency Exergy destruction rate 36.2

94.4 90.4

99.2

98.7

94.9

92.4

35

90.2

30

77.5

25 60

20.9

40

15

13.4 11.9

10 20

6.7

6.6

5

3.0

0 om C

0.1

r so es pr

SA

R om C

or st bu

m co el Fu

r so es pr

100

94.4

1.2

0.0

p e in m rb pu Tu er at W

SG R H

M

er ix

0.0

m or ef R

(b)

E

s ga st au xh

30

90.1

25

82.8

80

0

98.8

98.5

94.8

90.4

er

Exergy efficiency Exergy destruction rate

28.4

Exergy efficiency (%)

20

22.1 20

60

14.9

15

13.3 40

10 7.5

7.4 20

3.3 0

r so es pr om C

5 2.1 0.0

R SA

or st bu m o C

e in rb Tu

(c)

SG R H

SR M

Exergy destruction rate (%)

Exergy efficiency (%)

80

Exergy destruction rate (%)

82.8

SR SM

s ga st u ha Ex

0

Fig. 9. Exergy efficiency and exergy destruction rates of the SHGT (a), SHCRGT (b) and SACRGT.

42

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Combustor 1.0

Methane Combustion gas

Energy level

0.8

Turbine exhaust 0.5

0.3

0.0 1.0

(a) Methane Syngas of MSR Combustion gas

Energy level

0.8

Turbine exhaust Turbine exhaust 0.5

Low-temperature reforming Exhaust

0.3

0.0

1.0

(b) Methane Syngas of MSR Syngas of SMSR Combustion gas

Energy level

0.8

Solar energy of SMSR

Turbine exhaust

Turbine exhaust 0.5

High-temperature reforming

Exhaust

0.3

0.0

(c) Fig. 10. Cascade utilization of exergy in SHGT (a), SHCRGT (b) and SACRGT (c).

43

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Table 1 Simulation parameters. Item

Parameter

Value

Pressure ratio

10-40

Compressor Isentropic efficiency [%]

89

Air flow rate [kg s-1]

10

Efficiency [%]

100

Pressure drop [%]

3

LHV (methane) [MJ kg-1]

50.04

TIT [K]

1423

Isentropic efficiency [%]

90

Temperature [K]

298.15

Pressure [Pa]

101325

Dry air

21%O2+79%N2

Temperature [K]

1073

Pressure drop [%]

3

Hot side pressure drop [%]

2

Cold side pressure drop [%]

3

Temperature approach [K]

10

Hot side pressure drop [%]

2

Cold side pressure drop [%]

5

Temperature approach [K]

10

Solar air

Temperature [K]

1273

receiver

Receiver pressure drop [%]

3

Combustor

Turbine

Ambient conditions

SMSR

HRSG

MSR

44

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Water pump efficiency [%] Others

85

Fuel compressor efficiency [%] 85 Mechanical efficiency [%]

99

Generator efficiency [%]

98

45

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Table 2 Reference specific chemical exergy. Substance

Specific chemical exergy (kJ kmol1)

H2O

11710

CO

275430

H2

238490

O2

3970

N2

720

CO2

20140

CH4

836510

46

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Table 3 Water consumption of typical thermal power plants. Water consumption Technology [kg/(kW·h)] Natural gas combined cycle with 0.76 evaporative cooling Cola/nuclear with evaporative cooling

1.51-2.84

Parabolic trough with evaporative 3.03 cooling Linear Fresnel with evaporative cooling

3.79

Parabolic trough with dry cooling

0.30

Power tower with dry cooling

0.34

47

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation Table 4 Characteristics of solar thermal power cycles. System

Parabolic troughs [2] Tower [67, 68] ISCCS [30]

SOLGATE [2]

SOLHYCO [9]

SOLUGAS [4]

Solar receiver

Thermal

Solar

temperature

efficiency

share

Rankine steam cycle

400 °C

37%

˃90%

Rankine steam cycle

560 °C

~42%

˃90%

400 °C

40%

5.6-9.4%

960 °C

~20%

70%

800 °C

28%

23.1%

800 °C

38%

--

800-1000 °C

38.3%

70%

577-877 °C

47.6%

20.5%

200-300 °C

35 %

18%

200-250 °C

45.9%

20.3%

~200 °C

49%

21%

1000 °C

37.1%

76.1%

Thermal power cycle

Bottoming Rankine cycle integrated with solar heat Simple solar hybrid gas turbine cycle Simple solar hybrid gas turbine cycle Simple solar hybrid gas turbine cycle

Siemens turbine

Simple solar hybrid gas

model [7]

turbine cycle

Methane reforming

Solar reformed fuel for

[25]

combined cycle

Methanol

Solar reformed-fuel

decomposition [27]

combined cycle

SOLRGT [28]

Solar-driven steam for chemical recuperated cycle

Steam injection

Solar-driven steam

[29]

injection cycle

SHGTa

Simple solar hybrid gas

48

MANUSCRIPT Thermodynamic analysis of gas ACCEPTED turbine cycle combined with fuel reforming for solar thermal power generation turbine cycle SHCRGTa

SACRGTa a

Solar hybrid chemically recuperated cycle Solar assisted chemically recuperated cycle

The results of the present paper.

49

1000 °C

47.8%

62.2%

1000 °C

47.7%

75.0%

ACCEPTED MANUSCRIPT

Highlights     

Solarized gas turbine cycle combined with two-stage fuel reforming is proposed. Low temperature reforming by exhaust heat and high temperature by solar energy. Two-stage reforming upgrades energy levels of turbine exhaust and solar energy. Thermodynamic analyses and comparisons with other systems are conducted. The thermal efficiency and solar share can reach 47.7% and 75%, respectively.