Exergoeconomic and thermodynamic analyses of an externally fired combined cycle with hydrogen production and injection to the combustion chamber

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 7 ) 1 e1 2

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Exergoeconomic and thermodynamic analyses of an externally fired combined cycle with hydrogen production and injection to the combustion chamber Anahita Moharamian a, Saeed Soltani a,*, Marc A. Rosen b, S.M.S. Mahmoudi a a

Faculty of Mechanical Engineering, University of Tabriz, 16471 Tabriz, Iran Faculty of Engineering and Applied Science, University of Ontario Institute of Technology, 2000 Simcoe Street North, Oshawa, Ontario, L1H 7K4, Canada

b

article info

abstract

Article history:

A hydrogen production unit is successfully integrated with an externally fired combined cycle

Received 14 February 2017

using biomass fuel. The hydrogen produced in an electrolyzer can be used for other purposes,

Received in revised form

but when there is temporarily no market for it is injected into the combustion chamber of an

31 October 2017

externally fired combined cycle. Injecting hydrogen into the combustion chamber was found

Accepted 21 November 2017

to reduce fuel consumption by almost 27%. Moreover, hydrogen injection decreased the en-

Available online xxx

ergy efficiency and exergy efficiency by 45%, and decreased both the exergy loss and exergy destruction rates. Meanwhile, CO2 emissions decreased by 32%. However, there are some

Keywords:

disadvantages to hydrogen injection, especially from the viewpoint of exergoeconomics. The

Energy and exergy

total unit product cost for the externally fired combined cycle with hydrogen injection is

Exergoeconomic

almost 27% more than the unit without hydrogen injection, although the exergy loss and

Hydrogen

destruction costs decreased with hydrogen injection. The value of the relative cost difference

PEM

with hydrogen injection rises by 40%. Also the exergoeconomic assessment demonstrates

Biomass

that the cost of components (purchase and maintenance) are higher than cost of components'

Gasification

exergy destruction for both cycles, i.e., with and without hydrogen injection. As the compressor pressure ratio increases, optimal points are identified for biomass flow rate, energy and exergy efficiencies, exergy destruction and loss rates, exergy destruction and loss exergy cost rates, total unit product cost and relative cost difference. Crown Copyright © 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. All rights reserved.

Introduction Population growth and industrial development in many countries lead to environment impacts and ecosystem damage to

(e.g., climate change due to greenhouse gas emissions). The use of renewable energy can help mitigate greenhouse gas emissions. Research on renewable energy technologies can improve their capabilities, and environmentally sensitive energy

* Corresponding author. E-mail addresses: [email protected] (A. Moharamian), [email protected] (S. Soltani), [email protected] (M.A. Rosen), [email protected] (S.M.S. Mahmoudi). https://doi.org/10.1016/j.ijhydene.2017.11.136 0360-3199/Crown Copyright © 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. All rights reserved. Please cite this article in press as: Moharamian A, et al., Exergoeconomic and thermodynamic analyses of an externally fired combined cycle with hydrogen production and injection to the combustion chamber, International Journal of Hydrogen Energy (2017), https:// doi.org/10.1016/j.ijhydene.2017.11.136

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Nomenclature C_ c D E_

Cost rate ($/h) Cost per unit exergy ($/GJ) Membrane thickness (mm) Exergy rate (kW) Activation energy of anode (kJ/mol) Eact;a Activation energy of cathode (kJ/mol) Eact;c EFCCH Externally fired combined cycle with PEM electrolyzer EFCCHI Externally fired combined cycle hydrogen injection F Faraday constant (C/mol) G Gibbs free energy (J/mol) H Specific enthalpy HHV Higher heating value (kJ/kg) J Current density (A/m2) Exchange current density (A/m2) J0 ref Ja (A/m2) Pre-exponential factor of anode (A/m2) ref Jc (A/m2) Pre-exponential factor of cathode (A/m2) _ m Mass flow rate (kg/s) LHV Lower heating value (kJ/kg) Pressure at state i (bar) Pi Compressor pressure ratio rp Proton exchange membrane resistance (U) RPEM T Temperature (K) TIT Gas turbine inlet temperature (K) Ẇ Work rate (kW) _ PEM Electrical power required to split water in the W electrolyzer (kW) Reversible potential (V) V0 Anode activation over potential (V) Vact;a Cathode activation over potential (V) Vact;c Ohmic overpotential (V) VOhm X Steam quality Z Investment expense of component ($) Z_ Investment expense rate of component ($/h)

policies can support the utilization of renewable energy. In addition renewable energy mitigates many environmental consequences and enhances energy security for countries which are dependent on imported non-renewable fuels. Therefore non-fossil energy resources such as biomass can be appropriate alternatives to fossil fuels, in large part because biomass resources are scattered throughout the land. Also, biomass, a common material on Earth, has numerous advantages as an energy resource. It can be utilized directly or converted into various energy products such as biofuels [1]. The most common approach of utilizing biomass for energy is its direct combustion with coal [2]. Several technologies such as gasification and pyrolysis exist for converting biomass, but there remain challenges to its widespread use [3,4]. One approach to overcoming the weaknesses of biomass is to utilize it as a fuel in an externally fired gas turbine [5]; a diverse set of methods for doing so have been recommended [6,7]. Biomass

Greek letter h Energy efficiency Isentropic efficiency of compressor his;C Isentropic efficiency of gas turbine his;GT Isentropic efficiency of steam turbine his;T his;pump Isentropic efficiency of pump ε Exergy efficiency s (x) Local ionic PEM conductivity (S/m) Proton conductivity in PEM (S/m) sPEM Water content at cathode-membrane interface lc Water content at anode-membrane interface la l (x) Water content in location x in membrane b Ratio of chemical exergy of organic reaction of biomass Subscripts a Anode act Activation AP Air preheater HRSG Heat recovery steam generator C Cathode Comp Compressor CC Combustion chamber CI Capital investment D Destruction Cond Condenser G Gasifier GT Gas turbine in Inlet condition i Index for thermodynamic state point is Isentropic PEM Proton exchange membrane out Outlet condition 0 Reference OM Operation and maintenance ohm Ohmic ST Steam turbine

based cogeneration systems and power plants have been evaluated in several studies. Al-Sulaiman et al. [8] considered biomass trigeneration using an organic Rankine cycle (ORC), and found advantages to using biomass for trigeneration instead of electrical generation. Soltani et al. [9] demonstrated that biomass can be used without filtering in an externally fired combined cycle (EFCC) and that it has some advantages over internal fired units when utilized in this manner but also has some disadvantages such as low efficiency. Hydrogen is the product of some cogeneration or multigeneration power plants. Hydrogen is not an energy source but rather is an energy carrier. Its use causes little pollution provided it is produced from clean energy sources. Hydrogen has been investigated extensively as an energy carrier that can help address numerous global energy issues, in large part by facilitating the use of renewable energy [10]. One device to produce hydrogen from water is an electrolyzer, which uses

Please cite this article in press as: Moharamian A, et al., Exergoeconomic and thermodynamic analyses of an externally fired combined cycle with hydrogen production and injection to the combustion chamber, International Journal of Hydrogen Energy (2017), https:// doi.org/10.1016/j.ijhydene.2017.11.136

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electricity to split water into H2 and O2. Various types of electrolyzers exist such as alkaline, solid oxide and proton exchange membrane (PEM) [11]. Kalinci et al. [12] proposed a system in which hydrogen is used as an energy storage medium. For environmental reasons, they utilized renewable energy sources for producing the hydrogen. A novel combined cycle was demonstrated by Khalid et al. [13] for which the electricity demand of a residence was satisfied by a combination of solar photovoltaic arrays and a wind turbine. The authors calculated the energy and exergy efficiencies of the system which produces 1523 kg/ year of hydrogen. Yilmaz and Kanoglu [14] integrated geothermal energy with an ORC to produce hydrogen. They applied a PEM electrolyzer which uses the power generated by the ORC to produce hydrogen from water. Typical energy and exergy efficiencies of the total system were reported to be 6.8 and 28.3%. Ahmadi et al. [15] investigated a multi-generation system which includes a biomass combustor, an ORC, a PEM electrolyzer to produce hydrogen and domestic hot water. The overall exergy efficiency of the multi-generation system was found to be 23%. Nami et al. [16] demonstrated that increasing the pinch point (PP) temperature in an evaporator negatively affects the performance of a hydrogen production system. In this study for the first time hydrogen is produced by the following novel cycle: the externally fired combined cycle hydrogen production (EFCCH). The cycle uses biomass as the only fuel for the combined cycle. For the first time the influences of hydrogen injection into the combustion chamber (CC) of the externally fired combined cycle hydrogen injection (EFCCHI) on its thermodynamic and exergoeconomic performance are assessed and compared with the case when there is only hydrogen production and no injection (EFCCH) for being used in the other units. The reason for this study is that sometimes reliable markets are not available for the product hydrogen so one option is to use the hydrogen within the system. Electrical energy produced by the steam turbine is used for the production of hydrogen, and when there is temporarily no market for it.

as the supplementary energy carrier at point 26 along with the natural gas in the CC.

System analysis Thermodynamic and exergoeconomic analyses are performed for the combined system for electrical power and hydrogen production. The combined system has three main parts: steam and gas turbine cycles, biomass combustor and PEM electrolyzer.

Assumptions The combined system operation taken to be at steady state and the assumed parameter values in this paper are listed in Table 1.

Energy equations For a general component of the system with hydrogen production (EFCCH) and injection (EFCCHI), a mass rate balance can be written as follows [23]: X

_ in ¼ m

_ out m

(1)

and an energy rate balance can be written as follows [23]: _ þ W

X

_ in hin ¼ Q_ þ m

X

_ out hout m

(2)

For the EFCCH system, the energy efficiency can be expressed as follows: h¼

_ net;cycle þ m _ 24 LHVH2 W _ fuel LHVfuel þ Q_ 22 m

(3a)

Note that Q_ 22 is the energy used in the hydrogen unit for heating the water to the PEM electrolyzer temperature, and LHVH2 is the lower heating value of the product hydrogen which is not used within the system. For the EFCCHI system, for which no hydrogen is sold, the energy efficiency can be expressed as follows:

System description h¼ The externally fired combined cycle with hydrogen injection (EFCCHI) is shown in Fig. 1. The cycle comprises various processes, such as gas and steam turbine cycles, hydrogen production cycle and biomass gasification unit. Wood as a biomass at point 10 enters the gasifier and with air at point 9 is gasified at point 11. The gasified biomass enters to the CC and combusts with the air which is expanded by the gas turbine. The combusted gas at point 12 is used for heating the air at point 6. In the air preheater, the gas cools to point 13 and the air which is compressed by the compressor is heated to point 7. The thermal energy of the gas at point 13 is extracted for heating the pumped water in steam turbine cycle using a heat recovery steam generator (HRSG). The steam turbine produces electrical power via the generator. Then electrical power is utilized for hydrogen production in a PEM electrolyzer. The product hydrogen is stored in a hydrogen storage tank for later use in other units or

X

_ net;cycle W

_ fuel LHVfuel þ Q_ 22 m

(3b)

Biomass gasification Biomass enters the gasifier at point 10 and air enters at point 9. The wood biomass utilized in this study is composed of C (carbon), H (hydrogen) and O (oxygen), as detailed in Table 2. The chemical reaction for gasification of the biomass (wood), where the chemical formula for the wood based on a single carbon atom is CHxOyNz, follows: CHx Oy Nz þ mH2 O þ lðO2 þ 3:76N2 Þ/aCO þ bN2 þ cH2 þ dCO2 þ eCH4 þ fH2 O (4) For the wood biomass, the following parameters are given in Table 3: moisture content (MC), higher heating value (HHV), lower heat value (LHV), ratio of chemical exergy to the LHV of

Please cite this article in press as: Moharamian A, et al., Exergoeconomic and thermodynamic analyses of an externally fired combined cycle with hydrogen production and injection to the combustion chamber, International Journal of Hydrogen Energy (2017), https:// doi.org/10.1016/j.ijhydene.2017.11.136

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5

Air

Compressor

Gas turbine

17

Air 9 Generator

Biomass

Gasifier 11

7

8

6

Combustion Air preheater

10

chamber

26 22

H2

O2

Thermal energy

12

Heat exchanger

H2O

O2 separation

13 Steam turbine

HRSG

25

Hot water return

21

3

H2O

18 Generator

23

2

O2,H2O PEM electrolyzer

20

14

24

4 Pump

1

16 Hydrogen storage tank

15

19 Condenser

Fig. 1 e Externally fired combined cycle with hydrogen production and injection (EFCCHI). the organic fraction of the biomass (b), and chemical exergy of biomass ðExch biomass Þ.

PEM electrolyzer analysis As seen in Fig. 1, the PEM electrolyzer utilizes the electrical power generated by the steam turbine for producing H2. The

Table 1 e Parameter values. Parameter Air composition P1 (bar) T1 (K) TPEM (K) Cost of biomass ($/GJ) Cost of PEM electrolyzer ($) Cost of natural gas ($/GJ) D (mm) Gasification equivalence Eact;a (kJ/mol) Eact;c (kJ/mol) F (C/mol) Net output power in EFCC and EFCCHI Pressure drop on hot side of preheater (%) Pressure drop on cold side of preheater (%) Pressure drop in combustion chamber ref

Ja (A/m2) ref

Value 79% Nitrogen, 21% Oxygen 1.01 298 353 [17] 2 [18] _ PEM [19] 1000W 9.08 [20] 50 [17] 0.4188 [21] 76 [16] 10 [16] 96,486 [17] 3000 kW 1.5 [18] 3 [18] 0.5 [18] 1.7  105 [16] 4.6  103 [16]

Jc (A/m2) Gas turbine inlet temperature (K) Maximum pressure of steam cycle (kPa) la lc his;Comp

1400 8000 14 [22] 10 [22] 0.87 [18]

his;GT

0.89 [18]

his;ST

0.9 [18]

his;Pump

0.80 [18]

PEM electrolyzer has four main parts: anode, cathode, membrane and voltage ancillary. The heat exchanger in Fig. 1 is used to heat water from ambient temperature to the temperature of the PEM electrolyzer before it enters the electrolyzer. At the cathode the H2 produced cools, decreasing its temperature. At the anode, oxygen is produced from some of the water; the remainder of the water is used in subsequent H2 production cycles. Thermochemical modeling is utilized to examine the exergy and energy flows and conversions in the of PEM electrolyzer. The total energy needed by the PEM electrolyzer is [22,26]: DH ¼ DG þ TDS

(5)

For electrical and thermal energy respectively, DG (Gibb's free energy) and TDS are needed. Values of enthalpy, entropy and Gibb's free energy for H2O, O2 and H2 are obtained from thermodynamic tables. Note that the theoretical energy is the energy for water electrolysis without any losses. The molar flow rate of product H2 and the PEM electrolyzer voltage respectively can be expressed as follows [27,28]: n_ H2 ;out ¼

J ¼ n_ H2 O;reacted 2F

(6)

V ¼ V0 þ Vact;c þ Vact;a þ Vohm

(7)

Table 2 e Characteristics of wood biomass [24]. Parameter

Value

Composition of biomass (% by weight, dry basis) Moisture content C H O LHV (kJ/kg)

20 50 6 44 449,568

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Table 3 e Expressions for selected parameters for wood biomass. Parameter

Formula 18w MC ¼ 25:93þ18w  100 ð%Þ

Moisture content per kmol of wood

1:044þ0:016 HC0:34493 OC ð1þ0:0531 HCÞ 10:4124 OC

Ratio of chemical exergy to the LHV of the organic fraction of the biomass [25] Chemical exergy of biomass [25]

b¼

Higher heating value (HHV) [3] Lower heating value (LHV)

HHVbiomass ¼ 0.34.91C þ 117.83H  10.34O  1.15N þ 10.05S  2.11A LHVbiomass ¼ HHVbiomass  (mhfg)H2O

V0 ¼ 1:229  8:5  104 ðTPEM  298Þ

Ech biomass ¼ b LHV

(8)

E_ in þ

X

_ in exin ¼ m

   1 1  sPEM ½lðxÞ ¼ ½0:5139lðxÞ  326exp 1268 303 T lðxÞ

la  lc x þ lc D

RPEM ¼ 0

(12)

The activation overpotential [15], Vact, can be determined based on J0. These quantities can be expressed as follows: Vact;i ¼

  RT J 1 sinh F 2J0;i

  Eact;i ref J0;i ¼ Ji exp  RT

i ¼ a; c

i ¼ a; c

(16)

out

·

C_ j ¼ cj Е

(11)

Vohm;PEM ¼ JRPEM

Xn  ·  Xn   · C_ j þ Z ¼ Cj j¼1 j¼1

(9)

(10)

dx sPEM ½lðxÞ

(15)

The unit exergy cost of the product can be assessed by an energy economic analysis. In addition exergy costing for various transformations can allow determination of exergy cost rates, as follows [30]:

in

Here, D is the membrane thickness. The Ohmic resistance [15] and the Ohmic overpotential based on Ohm's law, respectively, can be expressed as ZD

_ out exout þ E_ w þ E_ D m

out

in

Here, F, J and V0 denote Faraday constant, current density and reversible potential, respectively. According to Eq. (8), V0 can be determined based on the temperature of the PEM electrolyzer. The local conductivity s(x) [15,29] of the proton exchange membrane and the water content at the position x in membrane l(x) can be written respectively as

X

(13)

(14)

(17)

The product exergy (E_ p) and fuel exergy (E_ f) rates can be related as: cF E_ F þ Z_ ¼ cP E_ P

(18)

Expressions for E_ p and E_ F are provided in Table 5. Costs for each component can be drawn from suitable references and corrected for the analysis year (2017) via the Marshall and Swift equipment cost index [18,19,33]. Reference year cost ¼

ðOriginal costÞ ðReference cost indexÞ Original year cost index

The exergy efficiency for the EFCCH plant can be expressed as: ε¼

_ net;cycle þ E_ 24 W E_ F;cycle þ E_ 22

(19a)

Since in the EFCCHI we do not have available hydrogen, the exergy efficiency for the EFCCHI plant can be written as:

Component energy analyses Table 4 lists the equations which are used in determining for the EFCCHI system the total power output, heat transfer rates, energy rate balances and mass flow rates.

Exergy and thermoeconomic analyses Exergy analysis complements energy analysis by providing additional insights into process performance. Exergy can be separated into four parts: physical, chemical, kinetic and potential. In many circumstances, kinetic and potential exergy terms are small and can be neglected. Chemical exergy must be considered in combustion processes, which typically are highly irreversible chemical reactions. An exergy balance for a general control volume can be written as follows [30e32]:

Table 4 e Definition of energy equation for each of component of proposed system. Component

Energy analysis

Gas turbine

_ Comp ¼ n_ 5 h5  n_ 6 h6 W _ GT ¼ n_ 7 h7  n_ 8 h8 W

Combustion chamber Air preheater HRSG Pump

n_ 8 h8 þ n_ 11 h11 þ n_ 23 h23 ¼ n_ 12 h12 n_ 6 h6  n_ 7 h7 ¼ n_ 13 h13  n_ 12 h12 n_ 13 h13  n_ 14 h14 ¼ n_ 3 h3 n_ 2 h2 _ Pump ¼ n_ 1 h1  n_ 2 h2 W

Steam turbine

_ ST ¼ n_ 3 h3  n_ 4 h4 W

Condenser

n4 h4  n1 h1 ¼ n16 h16  n15 h15

Compressor

PEM electrolyzer Gasifier

·

·

·

·

·

·

·

WPEM ¼ n21 h21  n22 h22 ·

·

·

n9 h9 þ n10 h10  n11 h11

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Table 5 e Exergetic expense rate balance and auxiliary equations of EFCCHI. _ E-fuel

Component

_ E-product

E_ 18 E_ 12  E_ 13

E_ 6  E_ 5 E_ 7  E_ 6

E_ 7  E_ 8 E_ 11 þ E_ 23

E_ 17  E_ 18 E_ 12  E_ 8

E_ 10 þ E_ 9 E_ 13  E_ 14

E_ 11 E_ 3  E_ 2

Condenser

E_ 3  E_ 4 E_ 4  E_ 1

E_ 20 E_ 16  E_ 15

Pump

E_ 19

E_ 2  E_ 1

Compressor Air preheater Gas turbine Combustion chamber Gasifier Heat recovery steam generator Steam turbine

_ net;cycle W ε¼ E_ F;cycle þ E_ 22

(19b)

The total product cost for the EFCCH and EFCCHI plants can then be written as: cp;total ¼

Pnfuel Pnk _ cFueli E_ Fueli i¼1 Zk þ Pnp i¼1_ i¼1 EPi

(20)

Validation The gasification product constituents obtained in the present study are shown in Table 4, where they are compared with results from other studies. The data in Table 6 shows a good agreement among the calculations in this study, for which the biomass has 20% moisture, and experimental results [34] and the Zainal equilibrium model results [35], all of which are considered at 800 C. Fig. 2 shows the comparison of J-V characteristics of PEM for current model and experimental results by Ioroi et al. [36]. It is seen that there is a good agreement between these two results.

Results and discussion Parametric analyses are applied to demonstrate the effects of varying design and operating conditions on the performance of both cycles considered in this study: the externally fired combined cycle with a PEM electrolyzer but without hydrogen injection into the combustion chamber (EFCCH), and the EFCCH cycle with hydrogen injection into the combustion chamber (EFCCHI). The net electrical power output is fixed for

Cost rate balance/auxiliary equation C_ 5 þ Z_ Comp þ C_ 18 C_ 12 þ Z_ AP ¼ C_ 7 þ C_ 13 c12 ¼ c13 _C7 þ Z_ GT ¼ C_ 18 þ C_ 17 þ C_ 8 c17 ¼ c18 C_ 8 þ Z_ cc þ C_ 11 þ C_ 23 ¼ C_ 12 C_ 6 ¼ C_ 6 þ

C_ 9 þ Z_ GþC_ 10 ¼ C_ 11 C_ 2 þ C_ 13 þ Z_ HRSG ¼ C_ 14þC_ 3 c13 ¼ c14 C_ 3 þ Z_ S,T ¼ C_ 4 þ C_ 20 c19 ¼ c20 C_ 4 þ C_ 1 þ

Z_ Cond þ C_ 15 ¼ C_ 1 þ C_ 16 c1 ¼ c4 Z_ Pump þ C_ 19 ¼ C_ 2

both cycles at 3000 kW. The thermodynamic results as parameters vary are evaluated for both systems, focusing on gas turbine inlet temperature and pressure ratio (rp). Output parameters include energy efficiency, steam turbine power output, hydrogen production rate, unit product cost and total exergy destruction rate. Table 7 lists the thermodynamic values for flows of the EFCCHI (non-shaded columns) and EFCCH (shaded columns), when the net power output is 3000 kW, the gas turbine inlet temperature is 1400 K, and the heat recovery steam generator inlet temperature is 960 K. Fig. 3 shows the variations of hydrogen production rate for the EFCCH plant with rp and TIT. With increasing rp, it is observed that the production rate decreases and reaches a minimum point for hydrogen production at an rp of around 11 and then increases. This increase is beneficial for the hydrogen production unit. As TIT increases, the hydrogen production rate declines. This has a negative impact on the hydrogen production rate, due to the decrease in steam turbine net power production with increasing TIT. Increasing TIT raises the gas turbine power output and, for a constant net power output, requires the steam turbine power production to decrease. Fig. 4 shows the variation with rp of the biomass flow rates in the EFCCHI and EFCCH plants. An optimum point for biomass flow rate is observed for both plants, at around rp ¼ 11. Moreover, the effect of hydrogen injection in the EFCCH plant is seen to be favorable, leading to a reduction in fuel consumption of around 27%.

Table 6 e Comparison of gasification constituents. Constituent

H2 CO CH4 CO2 N2 O2

Present model

Experiment

18.01 18.77 0.68 13.84 48.7 0.00

15.23 23.04 1.58 16.42 42.31 1.42

[34]

Zainal equilibrium model [35] 21.06 19.61 0.64 12.01 46.68 0.00

Fig. 2 e Comparison of results for J-V characteristics of PEM for current model and experimental work [36].

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Table 7 e Thermodynamics characteristics at states of the EFCCH and EFCCHI. _ (kg/s) m _ (kg/s) P (bar) P (bar) T (K) State m

T (K) h (kJ/kmol) h (kJ/kmol) s (kJ/kmol K) s (kJ/kmol K) E_ (kW) E_ (kW)

1 2 3 4 5 6 7 8 11 12 13 14 15 16 23 24 25

314.7 315.4 850 314.7 298 608.4 1400 858.4 1073 1554 960 374.3 298.7 308.15 353.2 353.2 353.2

1.193 1.193 1.193 1.193 4.802 4.802 4.802 4.802 1.338 6.14 6.14 6.14 61.146 61.146 0.24 0.01 0.22

1.159 1.159 1.159 1.159 4.941 4.941 4.941 4.941 0.97 5.92 5.92 5.92 59.382 59.38 0.23 0.01 0.22

0.08 80 80 0.08 1.01 10.13 9.83 1.03 1.03 1.02 1.01 1.01 1.01 1.01 1.01 1.01 1.01

0.08 80 80 0.08 1.01 10.13 9.83 1.03 1.03 1.02 1.01 1.01 1.01 1.01 1.01 1.01 1.01

314.7 315.4 850 314.7 298 608.4 1400 858.4 1073 1522 960 373.9 298.7 308.15 353.2 353.2 353.2

3132 3314 64,600 41,742 4.366 9237 35,330 17,100 67514 3892 24327 43438 1889 2642 6035 22,907 4563

3132 3314 64,600 41,742 4.366 9237 35,330 17,100 67514 1252 20227 39190 1889 2642 6035 22,907 4563

10.67 10.79 125.3 133.4 198.6 200.6 227.9 230.6 227.4 255.7 239 208.5 6.61 9.096 19.37 168.2 85.97

10.67 10.79 125.3 133.4 198.6 200.6 227.9 230.6 227.4 255.6 238.2 208.1 6.61 9.096 19.37 168.2 85.97

2.134 11.88 1813 137.7 0 1459 4453 1282 5207 5534 2247 111.9 0 43.26 129.4 1553 65.15

2.07 11.53 1761 133.8 0 1501 4581 1319 3796 5513 2119 45.11 0 42.1 125.7 1509 63.3

TIT (K) 1170

1200

1230

1260

1290

1320

1350

Hydrogen production rate (kmol/hour)

28 (rp)

27

(TIT)

26

25

24

23 4

6

8

10

12

14

16

18

rp

Fig. 4 e Variation of biomass molar flow rate with compressor pressure ratio (rp) for the EFCCH and EFCCHI systems.

Fig. 3 e Hydrogen production rate variation of EFCCH with compressor pressure ratio and gas turbine inlet temperature.

Figs. 5 and 6 illustrate the effects of pressure ratio on the energy and exergy efficiencies for the EFCCHI and EFCCH systems. There are seen to be optimal pressure ratios which lead to maximum energy and exergy efficiencies for both systems. The optimal pressure ratio is seen to be around 12 for the EFCCHI and around 11 for the EFCCH. At the optimum points, the energy efficiency for the EFCCH is about 0.15 higher than the corresponding value for the EFCCHI, and this value is 0.13 when exergy efficiency is considered. Figs. 7 and 8 demonstrate impact of gas turbine inlet temperature on the energy and exergy efficiencies of the EFCCHI and EFCCH plants. Increasing TIT in both plants has a favorable impact on both the energy and exergy efficiencies. When TIT rises from 1100 K to 1400 K, it can be seen that the energy and exergy efficiencies each increase by 0.11 points, for the EFCCHI plant but in the EFCCH the energy efficiency and exergy efficiency increases by 0.06 points. Figs. 9 and 10 show the variations of exergy loss and destruction rates in the EFCCH and EFCCHI plants with

Fig. 5 e Variation of energy and exergy efficiencies with compressor pressure ratio (rp) for the EFCCHI plant. compressor pressure ratio. For both exergy destruction and loss rates there are optimal points (minima), occurring around rp ¼ 12. Hydrogen injection is seen to reduce the exergy loss rate significantly, as expected since in the EFCCHI the gas flow rate is lower based on Table 7. Another interesting result is that, despite the use of hydrogen injection in the EFCCHI, the exergy destruction rate is lower than for the EFCCH.

Please cite this article in press as: Moharamian A, et al., Exergoeconomic and thermodynamic analyses of an externally fired combined cycle with hydrogen production and injection to the combustion chamber, International Journal of Hydrogen Energy (2017), https:// doi.org/10.1016/j.ijhydene.2017.11.136

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Fig. 6 e Variation of energy and exergy efficiencies with compressor pressure ratio (rp) for the EFCCH plant.

Fig. 7 e Variation of energy and exergy efficiencies with gas turbine inlet temperature for the EFCCHI plant.

Fig. 9 e Variation of exergy loss and exergy destruction rates with compressor pressure ratio (rp) for the EFCCHI plant.

Fig. 10 e Variation of exergy loss and exergy destruction rates with compressor pressure ratio (rp) for the EFCCH plant.

Fig. 8 e Variation of energy and exergy efficiencies with gas turbine inlet temperature for the EFCCH plant.

Figs. 11 and 12 show the variations of exergy destruction and exergy loss rates with gas turbine inlet temperature for the EFCCH and EFCCHI plants. Increasing the gas turbine inlet temperature is observed to decrease both the exergy loss and destruction rates. Fig. 13 shows the variations of CO2 mass discharge rate with rp and TIT. Increasing rp leads to an optimum point for both plants in which the optimum value is about 11. Also, increasing TIT decreases the CO2 mass flow rate, which is beneficial environmentally. Note also that hydrogen injection

Fig. 11 e Variation of exergy loss and exergy destruction rates with gas turbine inlet temperature for the EFCCHI plant. leads to a decrease in the CO2 emission of 32%, which is a pronounced advantage for the EFCCHI plant. The variation of the total unit product cost with both compressor pressure ratio and gas turbine inlet temperature are shown in Figs. 14 and 15. For the plants considered, increasing the compressor pressure ratio leads to optimum points for total unit product cost; these occur at around rp ¼ 8 for the EFCCHI and around rp ¼ 6 for the EFCCH. The total unit

Please cite this article in press as: Moharamian A, et al., Exergoeconomic and thermodynamic analyses of an externally fired combined cycle with hydrogen production and injection to the combustion chamber, International Journal of Hydrogen Energy (2017), https:// doi.org/10.1016/j.ijhydene.2017.11.136

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 7 ) 1 e1 2

Fig. 12 e Variation of exergy loss and exergy destruction rates with gas turbine inlet temperature for the EFCCH plant.

Fig. 13 e Variations of CO2 emission rate with rp and TIT for the EFCCHI and EFCCH plants.

Fig. 14 e Variation of total unit product cost for the EFCCHI plant with compressor pressure ratio and gas turbine inlet temperature.

product cost for the EFCCHI is almost 27% higher than the corresponding value for the EFCCH. This is mainly due to the higher cost of the combustion chamber. Furthermore, increasing the gas turbine inlet temperature reduces the total

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Fig. 15 e Variation of total unit product cost of the EFCCH plant with compressor pressure ratio and gas turbine inlet temperature.

Fig. 16 e Effect on rates of exergy loss cost and exergy destruction cost of varying compressor pressure ratio for the EFCCHI plant.

Fig. 17 e Effect on rates of exergy loss cost and exergy destruction cost of varying compressor pressure ratio for EFCCH plant.

unit product cost for both plants, mainly due to the rise of efficiencies and decrease in biomass fuel input rates as gas turbine inlet temperature increases. Variations of exergy loss and destruction cost rates with compressor pressure ratio are shown in Figs. 16 and 17 for the

Please cite this article in press as: Moharamian A, et al., Exergoeconomic and thermodynamic analyses of an externally fired combined cycle with hydrogen production and injection to the combustion chamber, International Journal of Hydrogen Energy (2017), https:// doi.org/10.1016/j.ijhydene.2017.11.136

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EFCCHI and EFCCH plants, respectively. Optimum points are observed for both cost rates. For the EFCCHI and EFCCH plants, this value is around rp ¼ 12. The exergy loss cost rate is higher for the EFCCH plant, even though the trends for the exergy loss cost rates are similar in Figs. 9 and 10. Also, the exergy destruction cost rate is higher for the EFCCH plant, and again

the trends for the exergy destruction cost rate are similar in Figs. 9 and 10. Variations of the exergy destruction and exergy loss cost rates with gas turbine inlet temperature are shown in Figs. 18 and 19 for the EFCCHI and EFCCH plants, respectively.

Fig. 18 e Effect on rates of exergy loss cost and exergy destruction cost of varying gas turbine inlet temperature for the EFCCHI plant.

Fig. 21 e Variation of relative cost difference and exergoeconomic factor with compressor pressure ratio for the EFCCH plant.

Fig. 19 e Effect on rates of exergy loss cost and exergy destruction cost of varying gas turbine inlet temperature for the EFCCH plant.

Fig. 22 e Variation of relative cost difference and exergoeconomic factor with gas turbine inlet temperature for the EFCCHI plant.

Fig. 20 e Variation of relative cost difference and exergoeconomic factor with compressor pressure ratio for the EFCCHI plant.

Fig. 23 e Variation of relative cost difference and exergoeconomic factor with gas turbine inlet temperature for the EFCCH plant.

Please cite this article in press as: Moharamian A, et al., Exergoeconomic and thermodynamic analyses of an externally fired combined cycle with hydrogen production and injection to the combustion chamber, International Journal of Hydrogen Energy (2017), https:// doi.org/10.1016/j.ijhydene.2017.11.136

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Table 8 e Results for exergoeconomic analysis of EFCCHI (left) and EFCCH (right). Component Comp GT CC AP HRSG Pump ST PEM G

c F,k ($/GJ) EFCCHI

c F,k ($/GJ) EFCCH

Z_ k ($/h) EFCCHI

Z_ k ($/h) EFCCH

C_ D;k ($/h) EFCCHI

C_ D;k ($/h) EFCCH

f k (%) EFCCHI

f k (%) EFCCH

6.24 5.97 3.87 5.15 5.15 6.77 6.12 6.77 2

4.32 4.13 2.78 3.58 3.58 4.70 4.25 4.70 2

9.16 19.10 2.01 12.58 12.01 0.34 62.62 44.63 5.27

8.90 18.57 1.96 13.13 12.33 0.35 63.91 45.95 6.51

2.34 3.00 15.48 5.82 6.04 0.05 3.41 0.61 10.75

1.58 2.02 9.57 3.77 4.31 0.04 2.44 0.44 14.74

79.63 86.40 11.52 68.39 66.55 86.19 94.83 98.68 32.90

84.97 90.18 16.98 77.69 74.09 89.91 96.32 99.04 30.64

Increasing gas turbine inlet temperature is observed to decrease both cost rates in both plants. Figs. 20 and 21 illustrate the variation with rp of the relative cost difference and total exergoeconomic factor, for the EFCCH and EFCCHI plants. Increasing rp raises the exergoeconomic factor in both plants, which means the ratio of component cost relative to exergy destruction cost in the system increases. For the relative cost difference there is an optimum point in both plants; these occur for the EFCCHI and EFCCH plants at compressor pressure ratios of approximately 8 and 6, respectively. Note that the relative cost difference value for the EFCCHI is higher than for the EFCCH, indicating the high cost for EFCCHI plant and maybe not economic application for hydrogen production system (EFCCHI) especially in power plants with high amount of power production. Finally exergoeconomic factor for the EFCCHI is higher than the EFCCH and the ranges of exergoeconomic factors for both plants are higher than 50%, indicating the higher value of the system components' costs relative to the exergy destruction cost. The variations of relative cost difference and exergoeconomic factor with gas turbine inlet temperature are shown in Figs. 22 and 23, for the EFCCHI and EFCCH plants, respectively. Increasing the inlet temperature reduces the relative cost difference, which is beneficial. However, the exergoeconomic factor increases in both plants due to the higher cost of components, especially the combustion chamber and gas turbine. Table 8 shows the exergoeconomic analysis for the EFCCHI and EFCCH plants. Based on the exergoeconomic factor components which should be considered for quality decrease are respectively, the PEM, steam turbine, gas turbine, pump, compressor, air preheater, HRSG. Exergoeconomic results for the EFCCHI and EFCCH reveal that with hydrogen injection components exergy destruction cost decrease and consequently their exergoeconomic factor increase except for gasifier.

Conclusion An externally biomass fired combined cycle with hydrogen production (EFCCH) is thermodynamically and exergoeconomically analyzed. Hydrogen is produced by the PEM electrolyzer with electricity from a steam turbine. When there is temporarily no market for hydrogen for comparative

purposes and to quantify the impact of hydrogen injection, the biomass fired cycle with hydrogen injection into the combustion chamber (EFCCHI) is analyzed as well. The key results and the main conclusions drawn from them are as follows:  As compressor pressure increases, a minimum point for hydrogen production rate is observed. The optimum point for biomass flow rate which occurs at a compressor pressure of around 11 in both plants. Similarly, an optimum point for both energy and exergy efficiencies is observed with respect to compressor pressure ratio (at around 12 for EFCCHI and 11 for EFCCH), and for exergy loss and destruction rates (at around 12 for the EFCCHI and the EFCCH). Optimum points for total unit product cost (at a compressor pressure ratio of 8 for the EFCCHI and 6 for the EFCCH), for CO2 emission (at a compressor pressure ratio of 12 for both plants) and for the exergy destruction and loss cost rates (at a compressor pressure ratio of 12 for the EFCCHI and EFCCH). Finally, the exergoeconomic factor increases in both plants as compressor pressure increases, while an optimum point for relative cost difference is observed at a compressor pressure ratio of 8 for the EFCCHI and 6 for the EFCCH.  Increasing the gas turbine inlet temperature results for both plants leads to increased energy and exergy efficiencies as well as lower exergy loss and destruction rates and lower CO2 emission rates, lower exergy loss and destruction cost rates, lower total unit product costs and relative cost differences, and higher exergoeconomic factors.  Compared to the case without hydrogen injection, it is determined that utilizing hydrogen injection reduces fuel consumption by 27%, decreases energy efficiency and exergy efficiency by 45%, reduces exergy loss rate by 78% and exergy destruction rate by 11%, reduces CO2 emission by 32%, increases total unit product cost by 27%, decreases exergy loss and destruction cost rates 78% and 10% respectively, and increases relative cost difference by 40% and exergoeconomic factor by 1%.  Components which should be considered for quality decrease are, respectively, the PEM, steam turbine, gas turbine, pump, compressor, air preheater, HRSG. Also, hydrogen injection increases the exergoeconomic factor of all components except the gasifier.

Please cite this article in press as: Moharamian A, et al., Exergoeconomic and thermodynamic analyses of an externally fired combined cycle with hydrogen production and injection to the combustion chamber, International Journal of Hydrogen Energy (2017), https:// doi.org/10.1016/j.ijhydene.2017.11.136

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Please cite this article in press as: Moharamian A, et al., Exergoeconomic and thermodynamic analyses of an externally fired combined cycle with hydrogen production and injection to the combustion chamber, International Journal of Hydrogen Energy (2017), https:// doi.org/10.1016/j.ijhydene.2017.11.136