Evaluation of novel process configurations for coproduction of LNG and NGL using advanced exergoeconomic analysis

Applied Thermal Engineering 115 (2017) 885–898

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Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng

Research Paper

Evaluation of novel process configurations for coproduction of LNG and NGL using advanced exergoeconomic analysis Hojat Ansarinasab a,⇑, Mehdi Mehrpooya b a b

Faculty of Energy Systems Engineering, Petroleum University of Technology (PUT), Iran Renewable Energies Department, Faculty of New Sciences and Technologies, University of Tehran, Tehran, Iran

h i g h l i g h t s
Advanced exergoeconomic analysis is applied on two processes for co-production of LNG/NGL.
Cost of investment is divided into avoidable/unavoidable and endogenous/exogenous.
Results show that interactions between the components is not considerable.

a r t i c l e

i n f o

Article history: Received 3 August 2016 Revised 3 January 2017 Accepted 6 January 2017 Available online 9 January 2017 Keywords: Liquefaction process Advanced exergy analysis Advanced exergoeconomic analysis Exergy destruction cost Investment cost

a b s t r a c t Advanced exergoeconomic analysis is applied on two novel process configurations for co-production of LNG and NGL. Dual mixed refrigerant (DMR) and mixed fluid cascade (MFC) refrigeration systems are used for supplying the required refrigeration. Based on the avoidable cost of exergy destruction in DMR process configuration, C-300 compressor with 504.43 ($/h) and in MFC process configuration, C200A compressor with 251.05 ($/h) should be modified first. Based on the avoidable endogenous/exogenous part, three strategies are proposed for reducing exergy destruction cost in the process components. Cost of exergy destruction and investment in most of the process components are endogenous. So interactions among the components in these processes is not strong. Investment cost of turbo expander and compressors are unavoidable due to technological and economic limits while air coolers and heat exchangers have potential for improvement. Cost of exergy destruction of the air coolers and heat exchangers are unavoidable while turbo expander and compressors are avoidable. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction Liquefied natural gas (LNG) operating condition is 161 °C at 101 kPa [1]. But there are impurities in natural gas that should be separated. Natural gas liquids (NGL) are extracted for added value and as a main feed in the petrochemical processes [2]. LNG production and NGL recovery are cryogenic processes so refrigeration system is the most important part in both of them. Increasing the level of integration is logical to increase the efficiency and to decrease the capital and operating costs [3]. The produced residue gas in NGL recovery plants leaves the demethanizer tower at about 100 °C so is can be used for supplying a part of the required refrigeration in the process before flowing to the pipeline. The main idea of integrated NGL and LNG process configurations is using outlet low temperature gas from the demethanizer tower

⇑ Corresponding author. E-mail address: [email protected] (H. Ansarinasab). http://dx.doi.org/10.1016/j.applthermaleng.2017.01.019 1359-4311/Ó 2017 Elsevier Ltd. All rights reserved.

straightly to the liquefaction unit as inlet feed. With integration of NGL recovery and LNG processes total cost decreases and efficiency increases [4]. Required refrigeration in nonintegrated processes is provided by separated heat exchangers and cycles, while in integrated processes, refrigeration is supplied from the shared refrigeration cycles and devices, In other words it is obvious that NGL and LNG processes are series plants. Integrated hydrocarbon recovery processes are investigated by stochastic optimization methods [5]. In this study operating condition and process configuration are considered as continuous and discrete decision variables respectively. Benefits of integration have been attracted companies to design integrated systems. In another paper a currently in operation ethane recovery plant is optimized by shuffled frog leaping optimization algorithm [6]. The results show that by adjusting the operating variables, ethane recovery can be increased up to 18%. Fluor Technologies indicates that by integration of LNG and NGL processes 10% of the required energy is saved [7]. LNG production

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Nomenclature c C_ E_ f _ m P r T y Z_

unit exergy cost ($/Gj) exergy cost rate ($/h) exergy rate (kW) exergoeconomic factor (%) flow rate (kg mole/h) pressure (bar) relative cost difference (%) temperature (C) exergy destruction ratio capital investment cost flow rate ($/h)

Greek letters e exergy efficiency D gradient Superscripts AV avoidable EN endogenous EX exogenous tot total UN unavoidable Subscripts D destruction

capacity of ConocoPhillips integrated process is almost 7% more, while it requires same power [2]. Four integrated LNG and NGL process configuration is proposed which are different in the NGL recovery section [8]. A novel integrated process configuration for NGL/LNG production is introduced. This process uses two mixed refrigerant cycles to provide the required refrigeration [9]. LNG and NGL processes are costly and consume high amount of energy. This will show the necessity of a techno-economic evaluation for such processes. Many researchers has utilized conventional exergy and exergoeconmic analysis methods on the refrigeration cycles to determine the improvement potential. Energy and exergy optimization is performed for cogeneration plant consisting of an Otto cycle [10], Brayton cycle [11] and irreversible Carnot heat engine [12]. Energy and exergy analysis of internal combustion engine fueled with diesel and natural gas are presented [13]. Thermodynamic and exergy analysis are carried out for heat engine and combined cogeneration systems with steam and gas turbines [14,15]. A hybrid power cycle using solar energy and cold energy of LNG is evaluated by exergy analysis [16]. The results show that the most exergy lost is related to the air preheater, combustion chamber and boiler. An integrated combined cooling heating and power process is investigated by exergy analysis method [17]. A currently in operation is investigated by advanced exergy analysis method [18]. The results show that the exergy destruction is related to the air coolers. Cryogenic helium extraction from natural gas processes are evaluated by advanced exergy analysis method [19]. The results show that the compressors have the lowest exergy destruction. Cryogenic air separation processes are investigated by exergy analysis method. In [20] one column configuration and in [21] two column configuration are considered. In both of them cold energy of LNG is used as the cold sources in the process. A novel hydrocarbon recovery process with auto-refrigeration system is analyzed by exergy method [22]. Exergy analysis is applied to refrigeration cycles in ethylene and propylene production processes. Rate of exergy destruction in the process can be decreased by adjusting

F k P tot c

fuel kth component production total critical

Abbreviations AC air cooler C compressor C3MR C3 precooled mixed refrigerant D flash drum DMR dual mixed refrigerant E multi stream heat exchanger LNG liquefied natural gas MFC mixed fluid cascade MIX mixer NG natural gas NGL natural gas liquid P pump SMR single mixed refrigerant T demethanizer tower TE turbo expander V expansion valve

the operating conditions of the cycles [23]. A new parameter is introduced for evaluation of the integration level in the hydrocarbon recovery processes. This parameter is defined based on the exergy concept [24]. Exergy analysis of the cascade refrigeration cycles used for natural gas liquefaction is investigated [25]. Exergy analysis is applied to multistage cascade low temperature refrigeration systems utilized in olefin plants [26]. Exergy analysis of absorption refrigeration machines is presented by a new method [27]. The exergy analysis of a hydrogen liquefaction system is considered [28]. An integrated natural gas liquids (NGL) and liquefied natural gas (LNG) processes is investigated by exergy and exergoeconomic analysis methods [29]. Exergoeconomic analysis is performed on the process for the coproduction of liquefied natural gas (LNG) and natural gas liquids (NGL) based on the mixed fluid cascade (MFC) refrigeration systems, as one of the most important and popular natural gas liquefaction processes [30]. Exergoeconomic analysis is carried out for single mixed refrigerant natural gas liquefaction processes [31]. PRICO liquefaction process is analyzed by exergy-based methods [32]. Exergy and exergoeconomic analyses on product recovery and separation systems of natural gas plant is performed [33]. A large industrial propane refrigeration cycle is analyses by thermoeconomic analysis method [34]. Conventional exergy and exergoeconomic analysis does not useful to determine the origin of irreversibilities and compute improvement potential. Advanced exergy and advanced exergoeconomic analysis are important tools to recognize sources of irreversibility and determine interactions among the process components. Advanced exergy analysis is applied on a hybrid fuel cell power plant [35]. The results show that the most portion of the exergy destruction is avoidable (more than 65%). An industrial propane refrigeration cycle is investigated by the advanced exergy analysis method [18]. The results shows that 59.61% of the exergy is lost in the unavoidable form in all components. Advanced exergy analysis on five conventional LNG processes is done [36]. Power plant

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system and a vaporization liquefied natural gas are analyzed by advanced exergy method [37]. Advanced exergy analysis on a cascade refrigeration system for liquefaction of natural gas is performed [38]. Advanced exergoenvironmental and advanced exergy methods are studied on a natural-gas regasification plant [39]. A tri-generation cycle is optimized using advanced exergoeconomic concepts [40]. By optimization, the total costs rate is reduced about 26%. A two stage hybrid absorption compression refrigeration system is evaluated by exergoeconomic analysis [41]. Advanced exergoeconomic analysis is carried out for three multi stage mixed refrigerant liquefaction processes. They are propane precooled mixed refrigerant (C3MR), dual mixed refrigerant (DMR) and mixed fluid cascade (MFC). Results show that interactions between the process components is not considerable [42]. Advanced exergoeconomic analysis is studied on two single mixed refrigerant (SMR) processes. The results show that investment costs and exergy destruction costs in most of the process components are endogenous [43]. Advanced exergoeconomic analysis is performed on a building heating system [44]. The results show that cost of exergy destruction in the distribution and generation stages is exogenous and in the emission stage is endogenous. Conventional and advanced exergoeconomic analyses is used for a geothermal district heating systems [45]. The results show that cost rate related to the components is avoidable. Advanced exergoeconomic analysis is studied on a novel process for production of LNG by using a single effect absorption refrigeration cycle [46]. Advanced exergoeconomic analysis gives more information for investment and exergy destruction cost with more sense about the processes. In this study, advanced exergoeconomic analysis is performed on two novel integrated processes for coproduction of LNG and NGL. For providing the required refrigeration in the processes, double mixed refrigerant (DMR) and mixed fluid cascade (MFC) processes are used. These process configurations have not been investigated by conventional and advanced exergoeconomic analysis so the results are novel and would be valuable. Also their performance are investigated by economic parameters. 2. Process description 2.1. Dual mixed refrigerant (DMR) process configuration Process flow diagram (PFD) of DMR process configuration is presented in Fig. 1. As can be seen, Liquefaction system and NGL recovery are done in one process. Operating conditions of DMR configuration stream are presented in Table 1. 2.1.1. NGL recovery section In both of processes, NGL recovery section are the same, however operating condition in this processes is different. Therefore the NGL recovery section is described in this section only. Cleaned natural gas feed enters the process at 63 bar and 37 °C. Natural gas is cooled in two steps. At first, Natural gas temperature is reduced to 3 °C in E-101 heat exchanger and is cooled to 33 °C in E-102 heat exchanger. Then, the two-phase flow enters D-101 separator. A portion of gas product in D-101 separator, enters E-103 heat exchanger and is subcooled to 88 °C. Then, stream 114 enters the V-101 and T-101 demethanizer tower respectively. Another portion of gas product in D-101 separator, flows to TE-101 turbo expander. Next, stream 109 follows to the demethanizer tower. Also, the liquid product in D-101 separator is spilled into two parts. Stream 108 enters the V-102 and T-101 demethanizer tower respectively. Another portion, is subcooled in E-103 heat exchanger to 50 °C and enters the V-103 valve. In demethanizer tower, there is no need to have a reboiler, because side streams 1, 2,

887

and 3 enter the heat exchangers E-101 and E-102 to provide the required heat for stripping volatile component from the produced NGL. 2.1.2. Liquefaction section Stream 112 (Lean gas) that leaves the demethanizer tower at 25 bar and 97 °C enters the LNG section. Next, it is pressurized via compressor C-101 and follows to the E-103 heat exchanger and is cooled to 128 °C. The liquefied natural gas is subcooled to 160 °C in E-104 heat exchanger while its pressure is reduced to the atmospheric pressure in V-104 valve. Then, the two-phase flow enters D-102 separator where the liquid product is extracted. 2.1.3. Refrigeration system Double mixed refrigerant (DMR) process has high efficiency in addition of simplicity. This process have two refrigerant cycles (Precooling and Liquefaction). The precooling cycle (cycle 200) provides the required cold utility for E-101 and E-102 heat exchangers. The liquefaction cycle (cycle 300) provides the required cold utility for E-103 and E-104 heat exchangers.
Cycle 200 (Precooling Cycle): Mixed refrigerant (stream 200), is divided to two streams as it passes through E-101 heat exchanger. Temperature of a portion of it decreases after passing through V-201 valve, and returns to E-101 heat exchanger for cooling. The second portion passes through E-102 heat exchanger and V-2 valve and returns to E-102 heat exchanger and provides cooling load for E-102 exchanger. Outlet refrigerant from E-102 heat exchanger is pressurized in C-201 compressor and combines with outlet refrigerant from E-101 heat exchanger. Then, stream 210 enters the C-202 compressor and AC-201 air cooler respectively.
Cycle 300 (Liquefaction Cycle): The outlet stream from AC-301 is cooled in two steps by E-101 and E-102 heat exchangers, respectively. Then, is separated to liquid and vapor phases in D-301 separator. Gas product in D-301 separator, is cooled in two steps by E-103 and E-104 heat exchangers, respectively. Then, enters the V-302 valve and returns to E-104 heat exchanger. Liquid product in D-301 separator, is cooled in E-103 heat exchanger and passes through V-301 valve and combines with outlet refrigerant from E-104 heat exchanger and returns to E103 heat exchanger. Then, outlet refrigerant from E-103 heat exchanger enters to C-301 compressor and AC-301 air cooler respectively. 2.2. Mixed fluid cascade (MFC) process configuration This process configuration is based on the mixed fluid cascade system. Process flow diagram of MFC process configuration is presented in Fig. 2. As can be seen, Liquefaction system and NGL recovery are done in one PFD. Structure of liquefaction and NGL recovery sections of the MFC process are the same as DMR process. MFC process includes three refrigeration cycles (precooling, middle and liquefaction) and subsequently has a high production capacity. Precooling cycle (cycle 400) provides the required cold utility in E101 and E-102 heat exchangers. The middle cycle (cycle 200) and liquefaction cycle (cycle 300) provide the required cold utility in E-103 and E-104 heat exchangers respectively. Red1, blue and green lines show the process flow diagram of 400, 300 and 200 cycle, respectively (Fig. 2). Operating conditions of the streams are presented in Table 2.

1 For interpretation of color in Fig. 2, the reader is referred to the web version of this article.

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313 AC-301

312

C-301 211

210

D-301

C-201

310

Mix-301

C-202

204

305 V-201

200

306 Mix-202

AC-201

300

209

203 201

208

202 Tee-201

207

121

V-301

V-302

311

302

V-202

304 206

205

309

301

Feed gas

V-104

307

101 E-101

308

303 118

105

119

E-104

120

D-102

E-103

E-102

LNG side3 113

108 Tee-102 102 103

116 107

C-101

114

TE-101 112

D-101

115 V-101 109 V-102

104 Tee-101

108

V-103

110

117

T-101

Side3R side2R

side2 side1R

side1

NGL

Fig. 1. Process flow diagram of the DMR configuration [47].

Table 1 Thermodynamic data for DMR configuration material streams. Stream No.

T (°C)

P (bar)

_ (kmol/h) m

E_ (kW)

c ($/GJ)

Stream No.

T (°C)

P (bar)

_ (kmol/h) m

E_ (kW)

c ($/GJ)

Feed 101 102 103 104 105 106 107 108 109 110 112 113 114 115 116 117 118 119 120 121 200 201 202 203 204 205 206

37.00 3.00 33.00 33.00 33.00 33.00 33.00 33.00 33.00 69.81 53.44 97.37 37.30 88.00 97.78 50.00 38.62 128.00 160.10 162.54 162.54 36.85 0.05 0.05 2.86 31.77 0.05 33.15

63.09 63.09 63.09 63.09 63.09 63.09 63.09 63.09 63.09 26.00 25.00 25.00 63.09 63.09 25.00 63.09 25.50 63.00 63.00 1.01 1.01 19.20 19.20 19.20 7.60 7.60 19.20 19.20

18,000 18,000 18,000 15,728 2272 6291 9437 682 1590 9437 682 15,115 15,115 6291 6291 682 1590 15,115 15,115 15,115 492 22,000 22,000 13,800 13,800 13,800 8200 8200

6,135,673 6,135,883 6,138,050 4,019,697 2,118,353 1,607,879 2,411,818 635,505 1,482,847 2,408,644 635,469 3,547,880 3,551,850 1,612,592 1,611,999 635,635 1,482,439 3,572,127 3,581,967 3,579,616 105,449 12,683,966 12,684,567 7,956,683 7,956,301 7,952,569 4,727,884 4,729,165

19.59 19.60 19.63 19.63 19.63 19.63 19.63 19.63 19.63 19.63 19.65 19.69 19.73 19.81 19.82 19.64 19.63 20.08 20.23 20.24 20.24 96.61 96.61 96.61 96.62 96.62 96.61 96.62

207 208 209 210 211 300 301 302 303 304 305 306 307 308 309 310 311 312 313 Side Side Side Side Side Side NGL LNG

34.54 1.62 42.43 35.76 84.09 35.00 0.15 33.15 33.15 128.45 134.06 33.15 128.45 160.15 166.57 140.94 135.17 43.84 143.66 12.81 35.00 48.25 0.00 10.33 0.00 28.05 162.54

3.00 3.00 7.60 7.60 19.20 48.60 48.60 48.60 48.60 48.60 3.00 48.60 48.60 48.60 3.00 3.00 3.00 3.00 48.60 25.00 25.00 25.00 25.00 25.00 25.00 25.00 1.01

8200 8200 8200 22,000 22,000 25,000 25,000 25,000 17,538 17,538 17,538 7462 7462 7462 7462 7462 25,000 25,000 25,000 2700 2700 2700 2700 2700 2700 2885 14,623

4,728,841 4,720,797 4,725,514 12,678,064 12,691,786 8,792,332 8,793,581 8,798,502 7,054,849 7,074,269 7,071,654 1,743,654 1,754,801 1,759,739 1,758,667 1,742,290 8,813,717 8,752,045 8,800,704 2,091,508 2,092,180 1,898,569 1,896,922 2,129,250 2,129,463 2,587,971 3,474,166

96.62 96.62 96.58 96.60 96.55 73.41 73.42 73.44 73.44 73.46 73.49 73.44 73.49 73.55 73.60 73.60 73.51 73.51 73.33 96.62 96.62 96.62 96.62 96.62 96.62 19.69 20.24

3. Numerical implementation In order to carry out process simulation and the thermodynamic calculations Peng-Robinson (PR) and Peng-Robinson-Stryjek-Vera

1 1R 3 3R 2 2R

(PRSV) equations of state can be obtained for each part the process (LNG liquefaction and NGL recovery). In this study PRSV is used for simulation in Aspen HYSYS software. The original Peng-Robinson equation of state provides accurate vapor pressure prediction for

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309

307

308

AC-302

AC-301 C-301

C-302 207

208

200

C-202

AC-202

300

411

Mix-401

C-401

C-402

408

V-401

400

306

C-201

AC-201

410

409

AC-401

205

206

407

405

406

121 404

Tee-401 201 301 101

E-101

V-301

204

305

403

402

401 Feed gas

V-201

V-402

203

202 302

118

105 107

E-102

303

V-104 E-104

119

120

D-102

E-103 LNG 108

113

Tee-102 102

103

116

C-100

114

TE-101

112

D-101

V-101

115

109

104

108 Tee-101

V-102

V-103 117

110

T-101

Side3R side2R side2

side1R

side1

NGL

Fig. 2. Process flow diagram of the MFC configuration [47].

Table 2 Thermodynamic data for MFC configuration material streams. Stream No.

T (°C)

P (bar)

_ (kmol/h) m

E_ (kW)

c ($/GJ)

Stream No.

T (°C)

P (bar)

_ (kmol/h) m

E_ (kW)

c ($/GJ)

Feed 101 102 103 104 105 106 107 108 109 110 112 113 114 115 116 117 118 119 120 121 200 201 202 203 204 205 206 207 208

37.00 3.00 30.00 30.00 30.00 30.00 30.00 30.00 30.00 65.13 62.86 96.95 36.72 88.00 97.38 50.00 47.88 85.20 162.50 162.74 162.74 35.00 3.00 27.00 81.50 90.99 29.72 67.63 35.00 77.90

63.09 63.09 63.09 63.09 63.09 63.09 63.09 63.09 63.09 26.00 25.00 25.00 63.00 63.09 25.00 63.09 25.50 63.00 63.00 1.01 1.01 27.90 27.90 27.90 27.90 3.10 3.10 15.00 15.00 27.90

18,000 18,000 18,000 16,550 1449 6620 9930 435 1015 9930 435 15,595 15,595 6620 6620 435 1015 15,595 15,595 15,595 280 19,000 19,000 19,000 19,000 19,000 19,000 19,000 19,000 19,000

4,996,763 4,996,945 4,998,823 4,309,499 689,324 1,723,800 2,585,699 206,797 482,527 2,582,263 206,801 3,661,497 3,665,625 1,728,834 1,728,219 206,857 482,354 3,675,985 3,697,653 3,695,246 59,006 8,043,713 8,045,217 8,049,792 8,058,378 8,056,898 8,019,264 8,037,947 8,037,115 8,045,129

19.75 19.75 19.79 19.80 19.80 19.80 19.80 19.80 19.80 19.80 19.82 19.88 19.92 19.98 19.99 19.81 19.80 20.10 20.45 20.46 20.46 78.21 78.25 78.27 78.28 78.29 78.29 78.22 78.23 78.20

300 301 302 303 304 305 306 307 308 309 400 401 402 403 404 405 406 407 408 409 410 411 Side 1 Side 2 Side 3 Side1R Side 2R Side 3R NGL LNG

35.00 3.00 27.00 85.20 159.00 166.85 89.56 53.70 35.00 48.50 40.00 8.80 8.80 22.00 29.38 1.25 8.80 0.34 33.58 35.34 37.99 81.86 17.74 7.88 54.08 35.00 0.00 15.00 28.40 162.74

29.00 29.00 29.00 29.00 29.00 3.50 3.50 25.00 25.00 29.00 16.90 16.90 16.90 16.90 3.00 3.00 16.90 6.70 6.70 6.70 6.70 16.90 25.00 25.00 25.00 25.00 25.00 25.00 25.00 1.01

12,500 12,500 12,500 12,500 12,500 12,500 12,500 12,500 12,500 12,500 27,400 27,400 10,910 10,910 10,910 10,910 16,490 16,490 16,490 27,400 10,910 27,400 2300 2300 2300 2300 2300 2300 2404 15,315

3,174,436 3,174,538 3,175,193 3,186,058 3,205,684 3,204,369 3,160,635 3,173,431 3,173,265 3,174,542 16,573,397 16,573,117 6,599,004 6,600,236 6,599,788 6,590,999 9,974,113 9,973,578 9,970,113 16,566,503 6,596,395 16,583,671 1,188,394 1,138,270 1,037,425 1,188,352 1,137,840 1,036,461 1,334,987 3,636,239

74.64 74.65 74.66 74.69 74.72 74.75 74.75 74.64 74.64 74.64 104.35 104.35 104.35 104.35 104.36 104.36 104.35 104.35 104.35 104.34 104.31 104.27 104.35 104.36 104.36 104.35 104.36 104.36 19.88 20.46

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hydrocarbons in the 6–10 carbon number range. It is defined as follows:

P¼

RT



a

ð1Þ

t  b t  ðt þ bÞ þ bðt  bÞ

where

analysis. Exergy destruction is calculated based on the difference between the fuel exergy rate and the product exergy rate (relation 1). Exergy efficiency is defined as ratio of product exergy rate to fuel exergy rate (relation 2). Ratio of exergy destruction is calculated by relation 3 [51]:

E_ D ¼ E_ F  E_ P


 a ¼ 0:457235R2 T 2c =Pc a

ð7Þ

ð2Þ E_

and

b ¼ 0:077796RT c =P c

ð3Þ

Soave used the following correlation for a,

h


i2 a ¼ 1 þ k 1  T 0:5 R

ð4Þ

where k is considered to be a function of the acentric factor x only. Stryject and Vera [48] modified the functional dependence of the k parameter. A major improvment in the prediction capability is achieved with the following simple expression for k:


 k ¼ ko þ k1 1 þ T 0:5 ð0:7  T R Þ R

ð5Þ

where

ko ¼ 0:378893 þ 1:4897153x  0:171318x2 þ 0:0196554x3 ð6Þ k1 is a characteristic parameter of the pure component. The k1 values for a wide variety of pure compounds are available in Ref. [49]. After simulation and applying energy balance results are shown in Table 3. 4. Methodology 4.1. Conventional exergy and exergoeconomic analyses We can called the exergy as the maximum work potential that can be obtained from a system that its final state is in equilibrium with the environment [50]. An exergy analysis permits us to determine the irreversibilities in a system. Exergy efficiency, exergy destruction and the ratio of exergy destruction are three variables which are calculated from exergy

e ¼ _P EF yD ¼

or

E_

e ¼ 1  _D EF

ð8Þ

E_ D;k _EF;tot

ð9Þ

Scope of exergoeconomic analyses is determining the relationship between the economics principles and exergy analyses. Calculation of the exergy cost is usually along with balanced costs and is separately given for each component. Cost balance for the process components can be written as follows [52]:

cP;k E_ P;k ¼ cF;k E_ F;k þ Z_ tot k

ð10Þ

C_ P;k ¼ C_ F;k þ Z_ tot k

ð11Þ

where cP,k is unit average exergy cost of product and cF,k is unit average exergy cost of fuel and Z_ tot shows the cost rate associated with the operating and maintenance and capital investment expenses. For some of the equipment with more than one output flow, there is more than one unknown parameter, so some auxiliary equations should be defined based on the laws of P and F [53]. The cost balance and auxiliary equations of the process components are shown in Tables 4 and 5. Cost of exergy destruction which is related to exergy destruction, exergoeconomic factor and relative cost difference are parameters that can be gained from the exergoeconomic analyses as follows [54]:

C_ D;k ¼ cF;k E_ D;k

ð12Þ

cP;k  cF;k cF;k

ð13Þ

r¼

Table 3 Main equipment power consumption, specific power and coefficient of performance. Process

MFC Power(kW)a

Component name

Power(kW)a

Compressors

C-101 C-201 C-202 C-301 TE-101

5839.84 6201.84 17388.45 59800.44 2126.27

C-101 C-201 C-202 C-301 C-302 C-401 C-402 TE-101

6064.86 24107.69 10203.72 16807.21 1664.71 7123.01 21791.78 2319.30

Air coolers

AC-201 AC-301

1537.12 225.50

AC-201 AC-202 AC-301 AC-302 AC-401

92.60 1393.89 299.75 232.81 4851.01

Mass flows (kg/h)

Specific power (kW h/kg LNG) COP a

DMR Component name

Mechanical efficiency = 0.75.

Feed LNG NGL

440069.66 236974.31 194736.50

351916.90 248388.30 98673.99

0.375 2.70

0.371 3.02

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H. Ansarinasab, M. Mehrpooya / Applied Thermal Engineering 115 (2017) 885–898 Table 4 Main and auxiliary equations for DMR configuration. Component

Equation

E-1A

C_ 300 þ C_ 200 þ C_ 203 þ C_ feed þ C_ side1 þ Z_ E1A ¼ C_ 301 þ C_ 201 þ C_ 204 þ C_ 101 þ C_ side1R C_ 203 E_ 203

¼

C_ 204 C_ side1 ; E_ 204 E_ side1

¼

C_ side1R E_ side1R

_ C_ feed ; CE_ 101  _ 101 E feed

¼

C_ 201 C_ 200 E_ 201 E_ 200

¼

C_ 301 C_ 300 E_ 301 E_ 300

Component

Equation

V-1

C_ 114 ¼ C_ 115 C_ 108 ¼ C_ 117

V-2

C_ 301 þ C_ 205 þ C_ 207 þ C_ 101 þ C_ side2 þ C_ side3 þ Z_ E1B ¼ C_ 302 þ C_ 206 þ C_ 208 þ C_ 102 þ C_ side2R þ C_ side3R

V-4

C_ side2 E_ side2

V-200

C_ 110 ¼ C_ 116 C_ 119 ¼ C_ 120 C_ 202 ¼ C_ 203

V-201

C_ 206 ¼ C_ 207

V-300 V-301

C_ 308 ¼ C_ 309 C_ 304 ¼ C_ 305

MIX-200

C_ 209 þ C_ 204 ¼ C_ 210

MIX-300 C-100

C_ 305 þ C_ 310 ¼ C_ 311 C_ 112 þ C_ W þ Z_ C100 ¼ C_ 113

C-200A

C_ 208 þ C_ W þ Z_ C200A ¼ C_ 209

C_ 120 þ Z_ D1 ¼ C_ 121 þ C_ LNG

C-200B

C_ 121 E_ 121

C-300

C_ 210 þ C_ W þ Z_ C200B ¼ C_ 211 C_ 312 þ C_ W þ Z_ C300 ¼ C_ 313

AC-200

C_ 211 þ C_ W þ Z_ AC200 ¼ C_ 200

C_ 102 þ Z_ D2 ¼ C_ 103 þ C_ 104

AC-300

C_ 103 E_ 103

TEE-100

C_ 313 þ C_ W þ Z_ AC300 ¼ C_ 300 C_ 103 ¼ C_ 105 þ C_ 106

V-3 E-1B

E-2

D-2

_

side3

_

_

207

side3R

_

_

208

102

_

_

101

206

_

_

205

302

301

_

_

_

_

_

_

_

_

_

_

_

C 105 C 113 C 107 C 303 C 306 ¼ CE_ 312 ; CE_ 114  ¼ CE_ 118  ¼ CE_ 116  ¼ CE_ 304  ¼ CE_ 307  E_ E_ E_ E_ E_ 312

114

105

118

113

116

107

304

303

307

306

C_ 307 þ C_ 309 þ C_ 118 þ Z_ E3 ¼ C_ 308 þ C_ 310 þ C_ 119 C_ 309 E_ 309

D-1

_

side2R

C_ 306 þ C_ 303 þ C_ 311 þ C_ 105 þ C_ 113 þ C_ 107 þ Z_ E2 ¼ C_ 307 þ C_ 304 þ C_ 312 þ C_ 114 þ C_ 118 þ C_ 116 C_ 311 E_ 311

E-3

_

C 101 C 205 C 301 ¼ CE_ side2R ; CE_ side3 ¼ CE_ side3R ; CE_ 207 ¼ CE_ 208 ; CE_ 102  ¼ CE_ 206  ¼ CE_ 302  E_ E_ E_

¼

C_ 310 C_ 119 C_ 118 ; E_ 310 E_ 119 E_ 118

¼

C_ 308 C_ 307 E_ 308 E_ 307

_

¼ CE_ LNG LNG

_

¼ CE_ 104 104

C_ 107 E_ 107

D-300

C_ 302 þ Z_ D300 ¼ C_ 303 þ C_ 306 C_ 303 E_ 303

_

TEE-101

¼ CE_ 306

C_ 106  C_ W þ Z_ TE100 ¼ C_ 109 C_ 106 E_ 106

C_ 104 ¼ C_ 107 þ C_ 108

_

TEE-200

¼ CE_ 109

205

C_ 201 ¼ C_ 202 þ C_ 205 _

¼ CE_ 106 106

C_ 115 þ C_ 117 þ C_ 109 þ C_ 110 þ C_ side1R þ C_ side2R þ C_ side3R þ Z_ T101 ¼ C_ 112 þ C_ side1 þ C_ side2 þ C_ side3 þ C_ NGL C_ 203 E_ 203

fk ¼

_

¼ CE_ 205

109

C_ 105 E_ 105

T-101

108

306

C_ 202 E_ 202

TE-100

_

¼ CE_ 108

_

_

_

_

_

_

¼ CE_ side1 ; CE_ 112 ¼ CE_ NGL ; CE_ 207 ¼ CE_ side3 ¼ CE_ side2 side1

112

NGL

207

side3

side2

Z_ k _Z k þ C_ D;k

ð14Þ

4.2. Advanced exergy and exergoeconomic analyses Conventional exergy analysis determines location and magnitude of irreversibilities in an energy system. But this analysis does not useful to determine the origin of irreversibilities and compute improvement potential. Therefore, sources of irreversibilities and interactions among the process components can only be determined by advanced exergy analysis. The main idea of advanced exergy analysis is categorizing the exergy destruction or irreversibility of the process components. The endogenous/exogenous parts give information about the origin of the irreversibility. The part of exergy destruction of the kth component is produced by itself is endogenous E_ EN and the part of exergy destruction is D;k

related to the induced destruction from the remaining components is exogenous E_ EX . In this study, engineering (graphical) method (it D;k

is an accurate method to calculate endogenous exergy destruction) [55] is used. To calculate endogenous exergy destruction we have to draw a leaner (y = ax + b) diagram (Fig. 3). According to the leaner diagram, x, y and b are the total exergy destruction of the other process components, total exergy destruction of the process and endogenous exergy destruction of the kth component, respectively. The avoidable/unavoidable parts give information about the removing ability of exergy destruction of the component. Unavoidable exergy destruction E_ UN is due to technological and economic D;k

limitations. This means that avoidable exergy destruction E_ AV D;k can be reduced by technological improvements. Four different parts of irreversibility can be presented by dividing unavoidable and avoidable to exogenous and endogenous parts. Table 6 (column three) presents the equations used to carry out the advanced exergy analyses of under consideration processes. The main idea of advanced exergoeconomic analysis is dividing the cost of exergy destruction and investment cost of the process components into endogenous/exogenous parts and avoidable/unavoidable parts. Fig. 4 is described a clear model for splitting the total cost of kth component. The endogenous part means cost of kth component when operates with its real efficiency while other components operate ideally. For calculation of exogenous part for each component, endogenous part is subtracted from the total real investment cost and the real exergy destruction cost. In addition by splitting the exergy destruction cost rate and the investment cost rate of the component into its unavoidable and avoidable parts, a feasible economic potential for improving the kth component can be recognized. Table 7 shows the operating conditions which are assumed to calculate the avoidable/unavoidable investment costs. Costs related to the internal operating conditions and the component interactions are distinguished by separating the unavoidable exogenous and the avoidable exogenous parts of the kth component. Table 6 (column four and five) presents the equations used to carry out the advanced exergy analyses of under consideration processes. To comparison of the evaluated results between the conventional and advanced methods, modified exergeoconomic factor

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H. Ansarinasab, M. Mehrpooya / Applied Thermal Engineering 115 (2017) 885–898

Table 5 Main and auxiliary equations for MFC configuration. Component

Equation

E-1A

C_ 300 þ C_ 200 þ C_ 400 þ C_ 407 þ C_ feed þ C_ side1 þ Z_ E1A ¼ C_ 301 þ C_ 201 þ C_ 401 þ C_ 101 þ C_ 408 þ C_ side1R

Component

Equation

V-1 V-2

C_ 114 ¼ C_ 115 C_ 108 ¼ C_ 117

V-3

C_ 110 ¼ C_ 116

C_ 101 þ C_ 301 þ C_ 201 þ C_ 402 þ C_ 404 þ C_ side2 þ C_ side3 þ Z_ E1B ¼ C_ 102 þ C_ 302 þ C_ 202 þ C_ 403 þ C_ 405 þ C_ side2R þ C_ side3R

V-4

C_ side2 E_ side2

V-100

C_ 119 ¼ C_ 120 C_ 406 ¼ C_ 407

V-101

C_ 403 ¼ C_ 404

V-200 V-300

C_ 203 ¼ C_ 204 C_ 304 ¼ C_ 305

C-100

C_ 112 þ C_ W þ Z_ C100 ¼ C_ 113

C-200A C-200B

C_ 205 þ C_ W þ Z_ C200A ¼ C_ 206 C_ 207 þ C_ W þ Z_ C200B ¼ C_ 208

C-300A

C_ 306 þ C_ W þ Z_ C300A ¼ C_ 307

C_ 120 þ Z_ D1 ¼ C_ 121 þ C_ LNG

C-300B

C_ 121 E_ 121

C-400A

C_ 308 þ C_ W þ Z_ C300B ¼ C_ 309 C_ 405 þ C_ W þ Z_ C400A ¼ C_ 410

C-400B

C_ 409 þ C_ W þ Z_ C400B ¼ C_ 411

C_ 102 þ Z_ D2 ¼ C_ 103 þ C_ 104

AC-200A

C_ 103 E_ 103

AC-200B

C_ 206 þ C_ W þ Z_ AC200A ¼ C_ 207 C_ 208 þ C_ W þ Z_ AC200B ¼ C_ 200

C_ 407 E_ 407

E-1B

¼

C_ 408 C_ side1 ; E_ 408 E_ side1

_

¼

C_ side1R E_ side1R

_

_ C_ feed ; CE_ 101  _ 101 E feed

_

_

¼

C_ 201 C_ 200 E_ 201 E_ 200

_

¼

C_ 301 C_ 300 E_ 301 E_ 300

_

_

¼

C_ 401 C_ 400 E_ 401 E_ 400

_

_

_

_

_

_

C 101 C 201 C 301 C 402 ¼ CE_ side2R ; CE_ side3 ¼ CE_ side3R ; CE_ 404 ¼ CE_ 405 ; CE_ 102  ¼ CE_ 202  ¼ CE_ 302  ¼ CE_ 403  E_ E_ E_ E_ side2R

side3

404

side3R

405

102

101

202

201

302

301

403

402

C_ 113 þ C_ 302 þ C_ 202 þ C_ 204 þ C_ 107 þ C_ 105 þ Z_ E2 ¼ C_ 118 þ C_ 303 þ C_ 203 þ C_ 205 þ C_ 114 þ C_ 116

E-2

C_ 204 E_ 204

_

_

_

_

_

_

_

_

_

_

_

C 113 C 107 C 105 C 202 C 302 ¼ CE_ 205 ; CE_ 118  ¼ CE_ 116  ¼ CE_ 114  ¼ CE_ 203  ¼ CE_ 303  E_ E_ E_ E_ E_ 205

118

113

116

107

114

105

203

202

303

302

C_ 303 þ C_ 305 þ C_ 118 þ Z_ E3 ¼ C_ 304 þ C_ 306 þ C_ 119

E-3

C_ 305 E_ 305

D-1

D-2

TE-100

_

_

_

_

_

C 118 C 303 ¼ CE_ 306 ; CE_ 119  ¼ CE_ 304  E_ E_ 306

119

118

304

303

_

¼ CE_ LNG LNG

_

¼ CE_ 104 104

AC-300A

C_ 307 þ C_ W þ Z_ AC300A ¼ C_ 308

C_ 106  C_ W þ Z_ TE100 ¼ C_ 109

AC-300B

C_ 106 E_ 106

AC-400

C_ 309 þ C_ W þ Z_ AC300B ¼ C_ 300 C_ 411 þ C_ W þ Z_ AC400 ¼ C_ 400

MIX-1

C_ 408 þ C_ 410 ¼ C_ 409

TEE-101

C_ 104 ¼ C_ 107 þ C_ 108

_

¼ CE_ 109 109

C_ 103 ¼ C_ 105 þ C_ 106

TEE-100

C_ 105 E_ 105

_

C_ 107 E_ 107

¼ CE_ 106 106

C_ 115 þ C_ 117 þ C_ 109 þ C_ 110 þ C_ side1R þ C_ side2R þ C_ side3R þ Z_ T101 ¼ C_ 112 þ C_ side1 þ C_ side2 þ C_ side3 þ C_ NGL

T-101

C_ 407 E_ 407

_

_

_

_

_

404

side2

side3

112

NGL

108

C_ 401 ¼ C_ 402 þ C_ 406 C_ 402 E_ 402

_

¼ CE_ side1 ; CE_ 404 ¼ CE_ side2 ¼ CE_ side3 ; CE_ 112 ¼ CE_ NGL side1

TEE-102

_

¼ CE_ 108 _

¼ CE_ 406 406

ĖF,tot - ĖP,tot

C_ AV;EN ¼ C_ AV;EN þ Z_ AV;EN tot D;k k

5. Results and discussion

ε =const. k

5.1. Conventional exergy and exergoeconomic analysis

ĖN ĖD,k

Ė D,others Fig. 3. Illustration of the engineering method [19].


 AV;EN , modified exergy efficiency (emodified ) and total operating fk
 AV;EN _ cost C tot are introduced. These parameters are formulated as follows [47]:

E_

P;k emodified ¼ _ EF;k  E_ UN  E_ AV;EX D;k

AV;EN

fk

¼

ð17Þ

Z_ AV;EN k _C AV;EN þ Z_ AV;EN D;k k

ð15Þ

D;k

ð16Þ

Results of conventional exergy and exergoeconomic analysis of DMR and MFC processes are presented in Table 8. For both processes, the highest irreversibility is related to compressors C-301 (11,141 kW) and C-201 (5423 kW), respectively. Exergy efficiency and total exergy destruction rate of the DMR process are 43.66% 26,788 kW respectively. Exergy efficiency and total exergy destruction rate of the MFC process are 53.83% and 22,272 kW respectively. Results of the exergoeconomic analysis for DMR configuration process show that the highest exergoeconomic factor is related to the compressor C-201 which equals 57.37%, while E-104 heat exchanger has the smallest exergoeconomic factor (0.21). In this process, the largest relative cost difference is related to the demethanizer tower T-101 and the smallest relative cost difference is related to E-102 heat exchanger. In addition, E-103 heat exchanger with 1583 $/h and TE-101 turbo expander with 44.59 $/h have the maximum and minimum exergy destruction costs respectively. Results of MFC process show that the highest exergoeconomic factor is related to the compressor C-302 which equals 69.53%, while E-104 heat exchanger has the smallest exergoeconomic factor (0.66). In this process, the largest relative cost difference is related to the demethanizer tower T-101 and the smallest relative cost difference is related to the air cooler AC-301. In addition, E-103 heat

893

H. Ansarinasab, M. Mehrpooya / Applied Thermal Engineering 115 (2017) 885–898 Table 6 Equations used for advanced exergy and exergoeconomic analysis [56]. TERM

Definition

Splitting the exergy destruction

Splitting the exergy destruction costs

Splitting the investment costs

Endogenous

Exergy destruction and cost rate within component k associated with the operation of the component itself Exergy destruction and cost rate within component k caused by the remaining components Exergy destruction and cost rate that cannot be avoided

E_ EX D;k Calculated by engineering

_ EN C_ EN D;k ¼ c F:k ED;k

_ EN Z_ EN k ¼ EP;k

Exergy destruction and cost rate that can be avoided Unavoidable exergy destruction and cost rate within component k associated with the operation of the component itself Unavoidable exergy destruction and cost rate within component k caused by the remaining components Avoidable exergy destruction and cost rate within component k associated with the operation of the component itsel Avoidable exergy destruction and cost rate within component k caused by the remaining components

_ _ UN E_ AV D;k ¼ ED;k  ED;k

Exogenous

Unavoidable Avoidable Unavoidable endogenous

Unavoidable exogenous

Avoidable endogenous

Avoidable exogenous

method [55] _ _ EN E_ EX D;k ¼ ED;k  ED;k

_ E_ UN D;k ¼ EP;k



E_ D;k E_ P;k

E_ UN;EN ¼ E_ EN P;k D;k

UN



E_ D;k E_ P;k

UN


real Z_ E_ P

k

_ EX C_ EX D;k ¼ c F:k ED;k

_ _ EN Z_ EX k ¼ Zk  Zk

_ UN C_ UN D;k ¼ c F:k ED;k

_ Z_ UN k ¼ EP;k

_ AV C_ AV D;k ¼ c F:k ED;k

_ _ UN Z_ AV k ¼ Zk  Zk

C_ UN;EN ¼ cF:k E_ UN;EN D;k D;k

Z_ UN;EN ¼ E_ EN P;k k


UN Z_ E_ P

k


UN Z_ E_ P

k

_ UN;EN E_ UN;EX ¼ E_ UN D;k  ED;k D;k

C_ UN;EX ¼ cF:k E_ UN;EX D;k D;k

_ UN;EN Z_ UN;EX ¼ Z_ UN k  Zk k

_ UN;EN ¼ E_ EN E_ AV;EN D;k  ED;k D;k

;EN C_ AV;EN ¼ cF:k E_ AV D;k D;k

_ UN;EN Z_ AV;EN ¼ Z_ EN k  Zk k

_ AV;EN E_ AV;EX ¼ E_ AV D;k  ED;k D;k

C_ AV;EX ¼ cF:k E_ AV;EX D;k D;k

_ UN;EX Z_ AV;EX ¼ Z_ EX k  Zk k

Ċtot,k

+

Ċ D,k

Ż D,k

UN,ĖN Ċ D,k

+

UN,ĖN Ż D,k

+

ĖN Ċ D,k

UN,ĖX Ċ D,k

UN Ċ D,k

ĖN Ż D,k

UN,ĖX Ż D,k

UN Ż D,k

ĖX Ċ D,k

AV,ĖN Ċ D,k

AV Ċ D,k

ĖX Ż D,k

AV,ĖN Ż D,k

AV Ż D,k

+

+ +

+

AV,ĖX Ċ D,k

+

+ +

+

AV,ĖX Ż D,k

Fig. 4. Division of the exergy cost associated with capital investment and exergy destruction.

Table 7 Assumptions for the advanced exergoeconomic analysis. Component

Z_ UN (operating conditions or % Z_ k )

Compressor [57] Turbo expander [58] Multi stream heat exchanger [58] Air cooler [58]

90% 80% DTmin = 0.5 °C, DP = DPreal DTmin = 5 °C, DP = DPreal

exchanger with 768.9 $/h and AC-301 air cooler with 19.36 $/h have the maximum and minimum exergy destruction costs respectively. 5.2. Advance exergy and exergoeconomic analysis Results of advanced exergy analysis of DMR and MFC processes are presented in Table 9. The results were obtained by using

engineering (graphical) method [55]. The engineering method is based on the conventional exergy analysis results. In these processes, portion of endogenous exergy destruction is higher than the exogenous part, except T-101 turbo expander. Therefore interactions among the process components is not considerable. In DMR and MFC processes, the difference between the exogenous and endogenous exergy destruction of the C-301 and C-402 compressors is rather high. As can be seen in both processes, exergy destruction of the compressors and turbo expander are avoidable while air coolers and heat exchangers exergy destruction are unavoidable. In DMR process, according to the avoidable endogenous exergy destruction, C-301 and C-202 compressors should be considered respectively. Also, in MFC process, according to the avoidable endogenous exergy destruction, C-201, C-301 and C-402 compressors should be considered respectively.

894

H. Ansarinasab, M. Mehrpooya / Applied Thermal Engineering 115 (2017) 885–898

Table 8 Results of exergy and exergoeconomic analysis of DMR and MFC configuration process. Component

E_ F (kW)

E_ p (kW)

E_ D (kW)

cF ($/Gj)

cP ($/Gj)

C_ D ($/h)

Z_ ($/h)

e (%)

yD (%)

r (%)

f (%)

DMR process C-101 C-201 C-202 C-301 TE-101 AC-201 AC-301 E-101 E-102 E-103 E-104 T-101

5839.84 6201.84 17388.45 59800.44 3173.80 44295.85 70367.73 73801.28 52069.41 102815.13 11211.54 3876.93

3970.24 4717.37 13722.14 48659.09 2126.27 39252.39 64915.59 72147.52 51041.62 96831.55 9611.62 1938.76

1869.60 1484.47 3666.31 11141.35 1047.53 5043.46 5452.14 1653.76 1027.79 5983.59 1599.92 1938.17

19.72 19.72 19.72 19.72 11.82 19.72 19.72 96.62 96.62 73.51 73.60 96.62

38.57 34.28 30.43 27.54 19.72 22.47 21.41 98.85 98.60 78.08 85.88 193.95

132.73 105.40 260.31 791.03 44.59 358.08 387.10 575.23 357.50 1583.47 423.91 674.16

136.65 141.86 268.80 578.11 15.84 29.98 7.85 5.21 5.59 8.01 0.89 5.19

67.98 76.06 78.91 81.37 66.99 88.61 92.25 97.76 98.03 94.18 85.73 51.00

2.10 1.67 4.13 12.54 1.18 5.68 6.14 1.86 1.16 6.73 1.80 2.18

95.57 73.82 54.31 39.63 66.77 13.92 8.57 2.31 2.05 6.21 16.68 100.74

50.73 57.37 50.80 42.22 26.21 7.73 1.99 0.90 1.54 0.50 0.21 0.76

MFC process C-101 C-201 C-202 C-301 C-302 C-401 C-402 TE-101 AC-201 AC-202 AC-301 AC-302 AC-401 E-101 E-102 E-103 E-104 T-101

6064.86 24107.69 10203.72 16807.21 1664.71 7123.01 21791.78 3436.58 34692.36 41759.66 27265.42 28369.27 45649.91 86933.37 63269.78 86243.61 42867.07 3433.61

4127.75 18684.55 8014.84 12796.40 1277.25 5396.43 17167.90 2319.30 33998.51 40924.47 26992.76 28085.58 43823.91 84998.91 61831.40 83515.65 40427.75 1717.03

1937.11 5423.14 2188.88 4010.81 387.46 1726.58 4623.88 1117.28 693.85 835.19 272.65 283.69 1825.99 1934.46 1438.37 2727.97 2439.32 1716.58

19.72 19.72 19.72 19.72 19.72 19.72 19.72 11.93 19.72 19.72 19.72 19.72 19.72 104.35 104.36 78.29 74.75 104.35

38.39 30.34 31.80 31.61 39.35 33.99 30.05 19.72 20.15 20.15 19.94 19.96 20.58 106.75 106.81 80.88 79.29 209.51

137.52 384.99 155.39 284.74 27.50 122.57 328.26 48.00 49.26 59.29 19.36 20.14 129.63 726.71 540.38 768.91 656.41 644.85

139.90 329.15 193.15 263.19 62.76 154.56 310.20 17.00 3.78 3.78 1.65 3.78 6.91 8.21 5.32 8.51 4.39 5.19

68.06 77.50 78.55 76.14 76.72 75.76 78.78 67.49 98.00 98.00 99.00 99.00 96.00 97.77 97.73 96.84 94.31 50.01

2.10 5.87 2.37 4.34 0.42 1.87 5.01 1.21 0.75 0.90 0.29 0.31 1.98 2.09 1.56 2.96 2.64 1.86

94.67 53.84 61.26 60.31 99.55 72.34 52.38 65.23 2.20 2.17 1.09 1.20 4.39 2.30 2.35 3.30 6.07 100.78

50.43 46.09 55.42 48.03 69.53 55.77 48.58 26.15 7.13 5.99 7.85 15.80 5.06 1.12 0.97 1.09 0.66 0.80

Table 9 Advanced exergy destruction rates of processes. Component

E_ D (kW)

E_ EN D;k (kW)

E_ EX D;k (kW)

E_ UN D;k (kW)

E_ AV D;k (kW)

E_ AV;EN (kW) D;k

E_ AV;EX (kW) D;k

E_ UN;EN (kW) D;k

E_ UN;EX (kW) D;k

DMR process C-101 C-201 C-202 C-301 TE-101 AC-201 AC-301 E-101 E-102 E-103 E-104

1869.60 1484.47 3666.31 11141.35 1047.53 5043.46 5452.15 1653.76 1027.79 5983.59 1599.92

1002.07 950.08 2738.32 8416.65 459.32 3242.57 3667.60 927.58 537.41 3338.66 872.93

867.53 534.39 927.99 2724.70 588.22 1800.89 1784.54 726.18 490.38 2644.93 726.99

588.40 504.92 1274.18 4036.63 350.74 3530.42 3816.50 1157.63 719.45 4188.51 1119.94

1281.20 979.55 2392.13 7104.72 696.79 1513.04 1635.64 496.13 308.34 1795.08 479.98

686.70 626.92 1786.65 5367.21 305.53 972.77 1100.28 278.27 161.22 1001.60 261.88

594.50 352.63 605.48 1737.51 391.27 540.27 535.36 217.85 147.11 793.48 218.10

315.37 323.15 951.67 3049.44 153.79 2269.80 2567.32 649.30 376.19 2337.06 611.05

273.03 181.77 322.51 987.19 196.95 1260.62 1249.18 508.33 343.27 1851.45 508.89

MFC process C-101 C-201 C-202 C-301 C-302 C-401 C-402 TE-101 AC-201 AC-202 AC-301 AC-302 AC-401 E-101 E-102 E-103 E-104

1937.11 5423.14 2188.88 4010.81 387.47 1726.58 4623.88 1117.28 693.85 835.19 272.65 283.69 1826.00 1934.46 1438.37 2727.97 2439.32

1123.50 4679.25 1380.30 3238.67 303.00 908.75 3864.00 287.26 610.00 751.63 187.96 199.02 1418.08 1527.62 1026.58 2329.07 2037.53

813.62 743.90 808.58 772.14 84.46 817.83 759.88 830.01 83.85 83.57 84.69 84.67 407.92 406.83 411.80 398.90 401.79

610.24 1886.85 757.76 1397.01 131.56 584.26 1604.56 374.50 485.69 584.64 190.86 198.58 1278.20 1354.12 1006.86 1909.58 1707.52

1326.87 3536.29 1431.12 2613.80 255.91 1142.32 3019.33 742.78 208.15 250.56 81.80 85.11 547.80 580.34 431.51 818.39 731.80

769.57 3051.22 902.46 2110.60 200.12 601.24 2523.14 190.98 183.00 225.49 56.39 59.71 425.42 458.29 307.97 698.72 611.26

557.31 485.08 528.66 503.20 55.78 541.08 496.19 551.80 25.15 25.07 25.41 25.40 122.38 122.05 123.54 119.67 120.54

353.93 1628.03 477.84 1128.06 102.88 307.52 1340.87 96.29 427.00 526.14 131.57 139.32 992.65 1069.34 718.60 1630.35 1426.27

256.31 258.82 279.92 268.95 28.68 276.75 263.69 278.21 58.69 58.50 59.28 59.27 285.54 284.78 288.26 279.23 281.25

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H. Ansarinasab, M. Mehrpooya / Applied Thermal Engineering 115 (2017) 885–898

Results of advanced exergoeconomic analysis of DMR and MFC configuration processes are shown in Tables 10 and 11. Results are obtained from splitting the exergy destruction cost of the process components (Table 10). As can be seen, portion of endogenous

exergy destruction cost is higher than the exogenous part in all components except T-101 turbo expander. Therefore interactions among the process components is not considerable. Exergy destruction cost of air coolers and heat exchangers are unavoidable

Table 10 Advanced exergy destruction cost rates of processes. Component

C_ D ($/h)

C_ EN D;k ($/h)

C_ EX D;k ($/h)

C_ UN D;k ($/h)

C_ AV D;k ($/h)

($/h) C_ AV;EN D;k

C_ AV;EX ($/h) D;k

C_ UN;EN ($/h) D;k

C_ UN;EX ($/h) D;k

DMR process C-101 C-201 C-202 C-301 TE-101 AC-201 AC-301 E-101 E-102 E-103 E-104

132.74 105.40 260.31 791.04 44.59 358.09 387.10 575.23 357.50 1583.47 423.91

71.15 67.46 194.42 597.58 19.55 230.22 260.40 322.64 186.93 883.53 231.29

61.59 37.94 65.89 193.45 25.04 127.86 126.70 252.59 170.57 699.94 192.62

41.78 35.85 90.47 286.60 14.93 250.66 270.97 402.66 250.25 1108.43 296.74

90.96 69.55 169.84 504.43 29.66 107.43 116.13 172.57 107.25 475.04 127.17

48.76 44.51 126.85 381.07 13.01 69.07 78.12 96.79 56.08 265.06 69.39

42.21 25.04 42.99 123.36 16.66 38.36 38.01 75.78 51.17 209.98 57.79

22.39 22.94 67.57 216.51 6.55 161.16 182.28 225.85 130.85 618.47 161.90

19.39 12.91 22.90 70.09 8.38 89.50 88.69 176.81 119.40 489.96 134.84

MFC process C-101 C-201 C-202 C-301 C-302 C-401 C-402 TE-101 AC-201 AC-202 AC-301 AC-302 AC-401 E-101 E-102 E-103 E-104

137.52 385.00 155.39 284.74 27.51 122.57 328.26 48.00 49.26 59.29 19.36 20.14 129.63 726.71 540.38 768.91 656.41

79.76 332.19 97.99 229.92 21.51 64.51 274.31 12.34 43.31 53.36 13.34 14.13 100.67 573.88 385.67 656.47 548.29

57.76 52.81 57.40 54.82 6.00 58.06 53.95 35.66 5.95 5.93 6.01 6.01 28.96 152.83 154.71 112.43 108.12

43.32 133.95 53.80 99.18 9.34 41.48 113.91 16.09 34.48 41.50 13.55 14.10 90.74 508.70 378.27 538.24 459.48

94.20 251.05 101.60 185.56 18.17 81.10 214.35 31.91 14.78 17.79 5.81 6.04 38.89 218.01 162.11 230.67 196.92

54.63 216.61 64.07 149.84 14.21 42.68 179.12 8.21 12.99 16.01 4.00 4.24 30.20 172.16 115.70 196.94 164.49

39.56 34.44 37.53 35.72 3.96 38.41 35.23 23.71 1.79 1.78 1.80 1.80 8.69 45.85 46.41 33.73 32.44

25.13 115.58 33.92 80.08 7.30 21.83 95.19 4.14 30.31 37.35 9.34 9.89 70.47 401.72 269.97 459.53 383.80

18.20 18.37 19.87 19.09 2.04 19.65 18.72 11.95 4.17 4.15 4.21 4.21 20.27 106.98 108.29 78.70 75.68

Table 11 Advanced investment costs rates of processes. Component

Z_ k ($/h)

Z_ EN k ($/h)

Z_ EX k ($/h)

Z_ UN ($/h) k

Z_ AV k ($/h)

Z_ AV;EN ($/h) k

Z_ AV;EX ($/h) k

Z_ UN;EN ($/h) k

Z_ UN;EX ($/h) k

DMR process C-101 C-201 C-202 C-301 TE-101 AC-201 AC-301 E-101 E-102 E-103 E-104

136.65 141.86 268.80 578.11 15.84 29.98 7.85 5.21 5.59 8.01 0.89

73.24 90.79 200.76 436.73 6.95 19.27 5.28 2.92 2.92 4.47 0.49

63.41 51.07 68.04 141.38 8.89 10.71 2.57 2.29 2.67 3.54 0.40

122.99 127.67 241.92 520.30 12.67 13.49 3.53 2.34 2.52 3.60 0.40

13.67 14.19 26.88 57.81 3.17 16.49 4.32 2.87 3.07 4.41 0.49

7.32 9.08 20.08 43.67 1.39 10.60 2.90 1.61 1.61 2.46 0.27

6.34 5.11 6.80 14.14 1.78 5.89 1.41 1.26 1.47 1.95 0.22

65.92 81.71 180.69 393.06 5.56 8.67 2.38 1.32 1.32 2.01 0.22

57.07 45.96 61.23 127.24 7.12 4.82 1.16 1.03 1.20 1.59 0.18

MFC process C-101 C-201 C-202 C-301 C-302 C-401 C-402 TE-101 AC-201 AC-202 AC-301 AC-302 AC-401 E-101 E-102 E-103 E-104

139.90 329.15 193.15 263.19 62.76 154.56 310.20 17.00 3.78 3.78 1.65 3.78 6.91 8.21 5.32 8.51 4.39

81.14 284.00 121.80 212.52 49.08 81.35 259.22 4.37 3.32 3.40 1.14 2.65 5.37 6.48 3.80 7.27 3.67

58.76 45.15 71.35 50.67 13.68 73.21 50.98 12.63 0.46 0.38 0.51 1.13 1.54 1.73 1.52 1.24 0.72

125.91 296.24 173.84 236.87 56.48 139.10 279.18 13.60 1.70 1.70 0.74 1.70 3.11 3.69 2.39 3.83 1.98

13.99 32.92 19.32 26.32 6.28 15.46 31.02 3.40 2.08 2.08 0.91 2.08 3.80 4.52 2.93 4.68 2.41

8.11 28.40 12.18 21.25 4.91 8.13 25.92 0.87 1.83 1.87 0.63 1.46 2.95 3.57 2.09 4.00 2.02

5.88 4.51 7.14 5.07 1.37 7.32 5.10 2.53 0.25 0.21 0.28 0.62 0.85 0.95 0.84 0.68 0.40

73.03 255.60 109.62 191.27 44.17 73.21 233.30 3.50 1.50 1.53 0.51 1.19 2.41 2.92 1.71 3.27 1.65

52.88 40.63 64.22 45.60 12.31 65.89 45.88 10.10 0.21 0.17 0.23 0.51 0.69 0.78 0.69 0.56 0.33

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Table 12 Comparison of the evaluated results between the exergy and exergoeconomic analyses for the conventional and advanced methods. Component

Conventional

Advanced

e (%)

f (%)

C_ tot ($/h)

e modified (%)

f

DMR process C-101 C-201 C-202 C-301 TE-101 AC-201 AC-301 E-101 E-102 E-103 E-104

67.98 76.06 78.91 81.37 66.99 88.61 92.25 97.76 98.03 94.18 85.73

50.73 57.37 50.80 42.22 26.21 7.73 1.99 0.90 1.54 0.50 0.21

269.39 247.26 529.11 1369.15 60.43 388.07 394.95 580.44 363.09 1591.48 424.80

85.25 88.27 88.48 90.07 87.44 97.58 98.33 99.62 99.69 98.98 97.35

13.06 16.94 13.66 10.28 9.65 13.31 3.58 1.63 2.79 0.92 0.38

56.08 53.59 146.93 424.74 14.40 79.67 81.02 98.40 57.69 267.52 69.65

MFC process C-101 C-201 C-202 C-301 C-302 C-401 C-402 TE-101 AC-201 AC-202 AC-301 AC-302 AC-401 E-101 E-102 E-103 E-104

68.06 77.50 78.55 76.14 76.72 75.76 78.78 67.49 98.00 98.00 99.00 99.00 96.00 97.77 97.73 96.84 94.31

50.43 46.09 55.42 48.03 69.53 55.77 48.58 26.15 7.13 5.99 7.85 15.80 5.06 1.12 0.97 1.09 0.66

277.42 714.15 348.54 547.93 90.27 277.13 638.46 65.00 53.04 63.07 21.01 23.92 136.54 734.92 545.70 777.42 660.80

84.29 85.96 89.88 85.84 86.45 89.98 87.19 92.39 99.46 99.45 99.79 99.79 99.04 99.46 99.50 99.17 98.51

12.93 11.59 15.97 12.42 25.68 16.01 12.64 9.63 12.33 10.46 13.52 25.60 8.90 2.03 1.77 1.99 1.21

62.75 245.01 76.25 171.09 19.12 50.82 205.04 9.08 14.82 17.88 4.63 5.70 33.15 175.73 117.79 200.94 166.50

AV,EN

($/h) C_ AV;EN tot

(%)

Table 13 Strategies for reducing avoidable cost of exergy destruction. Process

DMR process

MFC process

a b c

Component

Cost of exergy destruction categories ($/h) C_ D

C_ AV D;k

C_ AV;EN D;k

C_ AV;EX D;k

C-101 C-201 C-202 C-301 TE-101 AC-201 AC-301 E-101 E-102 E-103 E-104

132.74 105.4 260.31 791.04 44.59 358.09 387.1 575.23 357.5 1583.47 423.91

90.96 69.55 169.84 504.43 29.66 107.43 116.13 172.57 107.25 475.04 127.17

48.76 44.51 126.85 381.07 13.01 69.07 78.12 96.79 56.08 265.06 69.39

42.21 25.04 42.99 123.36 16.66 38.36 38.01 75.78 51.17 209.98 57.79

C-101 C-201 C-202 C-301 C-302 C-401 C-402 TE-101 AC-201 AC-202 AC-301 AC-302 AC-401 E-101 E-102 E-103 E-104

137.52 385 155.39 284.74 27.51 122.57 328.26 48 49.26 59.29 19.36 20.14 129.63 726.71 540.38 768.91 656.41

94.2 251.05 101.6 185.56 18.17 81.1 214.35 31.91 14.78 17.79 5.81 6.04 38.89 218.01 162.11 230.67 196.92

54.63 216.61 64.07 149.84 14.21 42.68 179.12 8.21 12.99 16.01 4 4.24 30.2 172.16 115.7 196.94 164.49

39.56 34.44 37.53 35.72 3.96 38.41 35.23 23.71 1.79 1.78 1.8 1.8 8.69 45.85 46.41 33.73 32.44

The part should be focused

Possible strategies to reduce cost of exergy destruction Strategy Aa

Strategy Bb

EN./EX. EN./EX. EN. EN./EX. EN./EX. EN. EN. EN./EX. EN./EX. EN./EX. EN./EX.

* * * * * * * * * * *

* *

EN./ EX EN. EN. EN. EN. EN./EX. EN. EX. EN. EN. EN./EX. EN./EX. EN. EN. EN. EN. EN.

* * * * * * *

Strategy A: improving the efficiency of the kth component or replacing the component with efficient devices. Strategy B: improving the efficiency of the remaining components. Strategy C: structural optimization of the overall system.

* * * * * * * * *

Strategy Cc

* *

*

* * * *

* * * *

*

*

*

*

*

*

* *

*

H. Ansarinasab, M. Mehrpooya / Applied Thermal Engineering 115 (2017) 885–898

due to technological and economic limitations while turbo expander and compressors have potential for improvement. In DMR and MFC processes, according to the avoidable endogenous exergy destruction cost, C-301 and C-201 compressors should be considered respectively. Results obtained from splitting the investment cost of the process components are shown in Table 11. Similar to the exergy destruction cost, cost of investment is endogenous for all components except T-101 turbo expander. As can be seen in this table, the difference between the exogenous and endogenous investment cost of the compressors is higher than the other components. Investment cost of the turbo expander and compressors are unavoidable due to technological and economic limitations while air coolers and heat exchangers have potential for improvement. After calculation of the investment costs and exergy destruction costs for the process components next step will be comparison of the process components before and after modification. The main performance parameters selected for comparison are exergoeconomic factor, exergy efficiency and total costs. Results obtained from comparison of the conventional and advanced analyses for DMR process are presented in Table 12. As can be seen, modified exergy efficiency is higher than the exergy efficiency for each component. Based on the total costs, C-301 compressor, E-103 heat exchanger and C-202 compressor should be modified, respectively. E-104 heat exchanger and C-201 compressor have the minimum and maximum exergoeconomic factor in both advanced and conventional exergoeconomic analyses, respectively. Results obtained from comparison of the conventional and advanced analyses for MFC process are presented in Table 12. Similar to the DMR, in this process modified exergy efficiency is higher than the exergy efficiency for each component. Based on the total costs, C-201, C402 compressors and E-103 heat exchanger should be modified, respectively. E-104 heat exchanger and C-302 compressor have the minimum and maximum exergoeconomic factor in both advanced and conventional exergoeconomic analyses, respectively. Next step will be improving efficiency of the process by using strategies for reducing cost of exergy destruction. According to the avoidable endogenous part, two strategies are proposed as follows:
Improving efficiency of the components.
Replacing the component with an efficient one. Also, based on the avoidable exogenous part, two strategies proposed as below:
Improving the efficiency of the remaining components.
Structural optimization of the overall system. Strategies for reducing avoidable exergy destruction cost are presented in Table 13. Exergy destructions cost in the process components except TE-101 turbo expander which is related to MFC process are endogenous. Therefore, strategy A cannot be used for TE-101 turbo expander. Some components have high avoidable endogenous and exogenous part of exergy destruction cost. Therefore, strategies B and C should be used in the same time for these components. 6. Conclusions In this study, advanced exergoeconomic analysis was performed on two novel integrated processes for coproduction of LNG and NGL. For providing the required refrigeration in the processes, double mixed refrigerant (DMR) and mixed fluid cascade (MFC) process are used. Result of exergy analysis show that exergy efficiency of the DMR process is 43.66% and its total exergy

897

destruction rate is 26,788 kW. Also, exergy efficiency of the MFC process is 53.83% and its total exergy destruction rate is 22,272 kW. This value is considerable comparing to the similar cases. According to the results of conventional exergoeconomic analysis, E-103 heat exchanger (1583.47 $/h) and E-103 heat exchanger (768.91 $/h) have the maximum exergy destruction cost in DMR and MFC processes, respectively. This heat exchanger plays effective role in the integration of the LNG and NGL processes. So improving its performance can affect the process efficiency significantly. The results gained from the advanced exergy and exergoeconomic analysis are as below:
Cost of exergy destruction and investment in most of the process components are endogenous. Therefore, interactions among the components in these processes is not strong.
Investment cost of the turbo expander and compressors are unavoidable due to technological and economic limitations while air coolers and heat exchangers have potential for improvement.
Cost of exergy destruction of the air coolers and heat exchangers are unavoidable while turbo expander and compressors are avoidable.
Exergy destruction cost in most of the process components are endogenous. Therefore, strategy A is useful for reducing the exergy destruction cost.

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