Advanced exergy and exergoeconomic analyses of a cascade absorption heat transformer for the recovery of low grade waste heat

Energy Conversion and Management 205 (2020) 112392

Contents lists available at ScienceDirect

Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman

Advanced exergy and exergoeconomic analyses of a cascade absorption heat transformer for the recovery of low grade waste heat

T

Yinglong Wanga,c, Yigang Liua, Xiaobin Liua, Wanxiang Zhanga, Peizhe Cuia, Mengxiao Yua, ⁎ Zhiqiang Liub, Zhaoyou Zhua,c, Sheng Yangb,d, a

College of Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, People’s Republic of China School of Energy Science and Engineering, Central South University, Changsha 410083, People’s Republic of China c Shandong Collaborative Innovation Center of Eco-Chemical Engineering, Qingdao University of Science and Technology, Qingdao 266042, People’s Republic of China d Key Laboratory of Low-Carbon Conversion Science & Engineering, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201203, People’s Republic of China b

A R T I C LE I N FO

A B S T R A C T

Keywords: Absorption heat transformer Advanced exergy analysis Advanced exergoeconomic analysis Exergy destruction rate Cost rate

For utilizing industrial low grade waste heat, a cascade absorption heat transformer is proposed in this paper. Conventional and advanced exergy and exergoeconomic analyses are used to determine the cause and avoidable degree of the exergy destruction and cost rates of the components. The analysis results show that only 21.28% of the exergy destruction rates are avoidable by improvement, while 80.2% of the investment cost rates are from the components themselves. Moreover, the advanced exergoeconomic factor shows that the optimization priority of the LiBr absorber, NH3 condenser, and NH3 absorber is different from that indicated by the conventional method. Improvement suggestions for each component are given based on the analysis. Moreover, the influence of the parameters, footprint, and control strategy on the system are also studied. These analyses have a significant effect on optimizing the components in the system.

1. Introduction According to a recent report, the worldwide energy consumption in 2018 increased by 317% compared with that in 1949 [1]. The statistical data show that the per capita global energy consumption has increased to 3104 kW per year [2]. Faced with such a rapid growth in energy consumption, responding to this problem becomes increasingly important. Industry is the most energy-consuming sector, accounting for 37% of the world's total energy consumption [3]. Half of this energy is lost as low grade waste heat, which results in the increase in production costs [4]. This has led to crises in energy and CO2 emissions [5]. The use of waste heat has become a crucial issue [6]. The absorption heat transformer (AHT) is an important future technology for energy utilization in the 21st century [7]. Low grade waste heat can be converted into a small amount of high quality heat energy through this method. In the process, more than 50% of the waste heat can be recovered by providing only a small amount of mechanical energy [8]. The AHT consists of a generator, absorber, evaporator, condenser, heat exchanger, pump, and valve [9]. The waste heat is absorbed by the generator, and the high grade energy is produced in the absorber. Because of its excellent energy-saving and environmental

⁎

friendliness, it has been widely studied by researchers. Liu et al. [10] studied a single stage absorption heat transformer (SSAHT) driven by solar energy. They determined the optimal design conditions of the system by the ratio method. Under these conditions, the output heat per day is 1318 kWh. Mahmoudi et al. [11] carried out a multi-objective optimization of an SSAHT from the perspective of thermodynamics and economy. The optimal temperatures of evaporator, condenser, and absorber are 86.51 °C, 39.03 °C, and 123.1 °C, respectively. Wang et al. [12] designed a double absorption heat transformer (DAHT) for a CO2 capture process, which improved the exergy efficiency of the system by 1.85% and reduced the cost by 10.7 $/t-CO2. Yari et al. [13] studied a double stage absorption heat transformer (DSAHT), which improved the maximum temperature rise by 18%–27%. The highest thermodynamic efficiency of the system is 0.451. The double lift absorption heat transformer (DLAHT) designed by Lubis et al. [14] can produce steam of higher than 170 °C with the hot water of 84 °C and with a maximum coefficient of performance (COP) of 0.3. By adding additional heat exchangers, Donnellan et al. [15] designed a triple absorption heat transformer (TAHT). The exergy destruction of the system was reduced by 28% and the COP increased by 16%. Advanced exergy analysis is a method to determine the

Corresponding author at: School of Energy Science and Engineering, Central South University, Changsha 410083, People’s Republic of China (S. Yang). E-mail address: [email protected] (S. Yang).

https://doi.org/10.1016/j.enconman.2019.112392 Received 2 September 2019; Received in revised form 6 November 2019; Accepted 7 December 2019 0196-8904/ © 2019 Elsevier Ltd. All rights reserved.

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

Nomenclature

UN,EX

Ċ c Ė e f h I i M ṁ N P Q̇ Ṙ

Subscripts

r s T t V Ẇ x y Ż z

exergy cost rate ($/h) unit exergy cost ($/GJ) exergy rate (kW) standard chemical exergy (kJ/mol) exergoeconomic factor specific enthalpy (kJ/kg) investment cost ($) interest rate (%) price index mass flow rate (kg/s) system life (year) pressure (kPa) heat transfer rate(kW) total cost rate ($/h) revised factor specific entropy (kJ/kg·K) temperature (K) annual working hour (h) equipment size power (kW) mass concentration exergy destruction ratio investment cost rate ($/h) mole fraction

ABS b CON ce cw D EVA e ele F GEN H HE i in L LiBr m NH3 out P PUM p r t tot VAL 0 1, 2, 3

Greek symbols

ε ϕ η α

exergy efficiency (%) maintenance factor isentropic efficiency (%) capital recovery factor

unavoidable exogenous

absorber base equipment condenser cold energy cooling water destruction evaporator actual equipment electricity fuel generator high heat exchanger component i inlet low LiBr/H2O system material NH3/H2O system outlet product pump pressure revised temperature total valve standard state state points

Superscripts

Abbreviations

AV AV,EN AV,EX adv ch EN EX ph UN UN,EN

AHT CAHT CEPCI COP DAHT DLAHT DSAHT SSAHT TAHT

avoidable avoidable endogenous avoidable exogenous advanced chemical endogenous exogenous physical unavoidable unavoidable endogenous

absorption heat transformer cascade absorption heat transformer chemical economic plant cost index coefficient of performance double absorption heat transformer double lift absorption heat transformer double stage absorption heat transformer single stage absorption heat transformer triple absorption heat transformer

(1.3$/h) and exergoeconomic factor (85.88%) came from the absorber and turbine, respectively. Gungor et al. [20] applied this method to the gas engine heat pump. They found that 74% of the energy destruction in the system is avoidable, and the maximum potential for improvement comes from the condenser. Esfahani et al. [21] designed the heat pump desalination process and carried out an advanced exergy analysis. Through optimization, exergy efficiency can be increased by 4.75%, while total product cost rate can be reduced by 33%. In addition, many researchers have applied this method to new energy conversion processes and cogeneration projects. In this work, a new cascade absorption heat transformer (CAHT) for the recovery of low grade waste heat was first proposed. Then, a process description, model, simulation, and assumption were made. Next, an energy analysis and conventional and advanced exergy and exergoeconomic analyses were carried out. Finally, the influence of the parameters on the CAHT was studied.

irreversibility and inefficiency of the components in energy conversion processes. In this method, endogenous, exogenous, and avoidable and unavoidable exergy destruction constitute the total exergy destruction of the system. The endogenous part is caused by the component itself, while the exogenous part is created by the influence of other components on it [16]. Moreover, due to the limitation of technique and economic conditions, exergy destruction can be divided into two parts: avoidable and unavoidable [17]. Researchers have applied advanced exergy analysis methods to many processes. Bagheri et al. [18] applied the advanced exergy analysis method to an absorption refrigeration cycle and optimized the system by the golden section method. Under the conditions for the highest exergy efficiency, the unavoidable part accounts for 66% of the total exergy destruction. Mehrpooya and Mousavi [19] studied a Kalina cycle driven by solar power using an advanced exergoeconomic analysis. They found that the highest exergy destruction was 94.44 kW, which occurred in the heater. The highest exergy destruction cost rate

2

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

2. Method

quantitatively and qualitatively, the change in design attributes of the two subsystems is studied when the division temperature changes. The condenser temperature and low pressure are representative of the LiBr AHT design variables, while the design variables of the NH3 AHT are high pressure and low pressure. As can be seen from Fig. 4, with the increase in division temperature, all four design variables show a linear growth trend. Among these variables, the growth rate of the lowpressure NH3 is increasingly slower, while the growth rates of the other three variables are basically unchanged. The input and output data of the CAHT simulation are listed in Tables 3 and 4, respectively.

2.1. Process description CAHT is a new DSAHT with two different working fluids. Although researchers have developed many new working fluids for AHT, only NH3/H2O and LiBr/H2O are currently used in industry [22]. Using these two working fluids, a new CAHT was established for the recovery of the waste heat of 90–150 °C in this study. Fig. 1 is the temperature rise principle of the CAHT. The waste heat includes the low temperature part of 90–136 °C (TL) and the high temperature part of 136–150 °C (TH). TL was increased to above 136 °C by an NH3 AHT, and then used together with TH in an LiBr AHT to produce high quality energy at 158 °C. The low-temperature heat generated by the LiBr AHT returns to the NH3 AHT for supplying energy. The entire CAHT process is shown in Fig. 2. On the left side is the LiBr AHT, which is the main part of the system. The lean LiBr solution is heated in the LiBr generator, and the steam generated at the top of the LiBr generator is condensed in the LiBr condenser. The released heat is used to drive the NH3 evaporator. After being pressurized by the pump, the water enters the LiBr evaporator and evaporates after obtaining heat energy from the NH3 absorber. The steam generated in the LiBr evaporator enters the LiBr absorber to generate a large amount of heat for the production of low-pressure steam. The rich LiBr solution from the LiBr generator is pressurized by the pump and heat exchanged with the lean LiBr solution from the absorber. Finally, the lean LiBr solution produced by the LiBr absorber is heated in the LiBr heat exchanger and returned to the LiBr generator. On the right side is the NH3 AHT, which is the auxiliary part of the system. The rich NH3 solution is heated by waste heat in the NH3 generator, and the NH3 produced is condensed in the NH3 condenser. The NH3 liquid goes to the NH3 evaporator after being pressurized by the pump. In the NH3 evaporator, the NH3 liquid is gasified by the energy from the waste heat, and then it enters the NH3 absorber to provide heat for the LiBr evaporator. The lean NH3 solution produced is pumped into the NH3 heat exchanger to exchange heat with the rich NH3 solution from the NH3 absorber. Then, it enters the NH3 absorber to absorb the NH3 gas. The rich NH3 solution in the absorber is returned to the NH3 generator through the NH3 heat exchanger and valve to complete the cycle.

2.3. Assumptions The specific assumptions are listed below [26,27]. 1. The whole system is operated under steady-state conditions. 2. The variations in kinetic and potential energy are ignored. 3. The pressure drop is neglected in all components except for pumps and valves. 4. The heat transfer to the environment is neglected for all components. Fig. 5 is the flowsheet of system modeling equations. The parameters of the CAHT analysis are given in Table 5. In the following sections, more details will be provided for this analysis. 2.4. Energy analysis The energy analysis is carried out by the following equations [28]. Table 6 shows the energy analysis results of the CAHT.

Mass balance: ∑ ṁ = 0

(1)

̇ =0 Material balance: ∑ mx

(2)

Energy balance: ∑ Q̇ +

∑ Ẇ

+

∑ mḣ = 0

(3)

2.5. Exergy analysis 2.5.1. Conventional exergy analysis An exergy analysis can determine the thermodynamic irreversibility in the components. The exergy rate is calculated by the following formula. The standard chemical exergy of the components is illustrated in Table 7.

2.2. Process simulation The CAHT has been simulated in Aspen Plus in this work. For the NH3 AHT, the property method of the simulation is PSRK [23]. For the LiBr AHT, ELECNRTL is chosen as the property method, and the parameters are calculated and corrected according to the experimental data [24]. The parameters of the LiBr AHT are given in Table 1. To verify the accuracy of the models, we compared them with the work of Kurem and Horuz [25]. The results in Table 2 show that the deviations of the two models are only 0.4% and 0.2%, which proves that the models are accurate. In addition to the verification of model accuracy, a sensitivity analysis of the influence of the system modeling parameter uncertainty on the prediction results is also conducted. The division temperature of the heat source is an important parameter that is directly related to the heat production efficiency of the CAHT. Fig. 3 shows the relationship between the COP and division temperature. With the increase in division temperature, the COP of the LiBr AHT increases quickly, and then increases slowly, while the COP of the NH3 AHT decreases slowly with the increase in division temperature. The total COP of the CAHT increases first and then decreases, and the peak value appears when the division temperature is 136 °C. Therefore, the division temperature of the system is chosen as 136 °C. To determine the coupling relationship between the two systems

E ̇ = E ̇ ph + E ̇ ch

(4)

The physical exergy rate can be calculated by Eq. (5) [29].

158°C

TH (136-150°C)

LiBr AHT

TL (90-136°C)

NH3 AHT

90°C Fig. 1. Temperature rise principle of the CAHT. 3

T (level)

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

Lean LiBr solution H2O Rich LiBr solution Lean NH3 solution NH3 Rich NH3 solution Heat stream Low-pressure steam 158°C 9

19 8 5

10

LiBr pump 2

2

LiBr heat exchanger

6

·

1

4 LiBr Valve 3

18 17 NH3 evaporator NH 3 pump 4 NH3 absorber

15

LiBr evaporator 7 LiBr absorber

LiBr condenser

NH3 heat exchanger 20 11 NH3 Valve 14 NH3 pump 3

LiBr pump 1 LiBr generator

12

NH3 condenser

16

NH3 reboiler

NH3 generator 13

90°C-136°C

136°C-150°C

Heat source Fig. 2. Entire CAHT process. Table 1 Property parameters of the LiBr AHT. Parameters GMELCC-1 GMELCC-1 GMELCD-1 GMELCD-1

Molecule i or Electrolyte i H2O Li+/Br– H2O Li+/Br–

Molecule j or Electrolyte j +

–

Li /Br H2O Li+/Br– H2O

Values 7.16759 –1.41076 –4803.4 K –854.7 K

Table 2 Comparison of the model in this work and the reference work. Parameters

Data of Kurem and Horuz

Present study

Data type

TGEN-LiBr TCON-LiBr TABS-LiBr COPLiBr TGEN-NH3 TCON-NH3 TABS-LiBr COPNH3

90.0 °C 30.0 °C 110.0 °C 0.497 85.0 °C 30.0 °C 110.0 °C 0.483

90.0 °C 30.0 °C 110.0 °C 0.499 85.0 °C 30.0 °C 110.0 °C 0.482

Input Input Input Output Input Input Input Output

Deviation (%)i

0.4%

Fig. 3. Sensitivity analysis of the division temperature on the COP. 0.2%

E ̇ ph = ṁ [(hi − h 0 ) − T0 (si − s0 )]

EN

∑ z i ei

EḊ , k = EḊ , k + EḊ , k

(6)

UN EḊ refers to the irreversibility part that is not eliminated due to AV technological and economic constraints [33]. EḊ refers to the irreversibility ̇ part that can be reduced. The calculation basis is shown in Table 9. ED is equal to the sum of UN AV EḊ and EḊ .

EN

The exergy destruction rate (EḊ ) can be calculated by the following formula.

EḊ = EḞ − EṖ =

̇ ∑ Eiṅ − ∑ Eout

T + ∑ Q̇ ⎛1 − 0 ⎞ + T⎠ ⎝

∑ Ẇ

can be found in Ref. [32]. EḊ is

(5)

The chemical exergy rate can be calculated by Eq. (6) [30].

E ̇ ch =

EX

calculation methods for EḊ and EḊ EX EN equal to the sum of EḊ and EḊ .

UN

EX

AV

EḊ , k = EḊ , k + EḊ , K

(8)

(9)

Based on the above work, EḊ is divided in more detail [34]. UN , EN EḊ is the part of the unavoidable irreversibility that cannot be decreased due to the limitation of technique and economy conditions from the component itself. It can be calculated as below:

(7)

Table 8 lists the exergy equations for the components of the CAHT. 2.5.2. Advanced exergy analysis EX EN Advanced exergy analysis divides the EḊ into four parts: EḊ , EḊ , EX UN EN AV EḊ and EḊ [31]. EḊ is caused by the component itself. EḊ refers to the irreversibility caused by other components in the process. The

UN , EN

EḊ , k

̇ , k UN EN ED ⎞⎟ = EṖ , k ⎛⎜ ̇ ⎝ EP, k ⎠

(10)

UN , EX EḊ is the part of the unavoidable irreversibility that cannot be

4

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

Fig. 4. Influence of the division temperature on the design variables of the two systems. Table 3 Input data of the CAHT simulation. Components

Models

Specifications

LiBr generator

Flash 2 (V-DRUM1)Heater

LiBr condenser LiBr evaporator LiBr absorber LiBr heat exchanger LiBr valve LiBr pump NH3 generator NH3 condenser

Heater Heater Heater HeatX (GEN-HT) Valve 2 Pump (ICON1) Radfrac (FRACT1)-

NH3 NH3 NH3 NH3 NH3

Heater Heater HeatX (GEN-HT) Valve 2 Pump (ICON1)

Duty = 0 kW, Pressure = 84 kPa Pressure = 84 kPa, Temperature = 403.2 K Vapor fraction = 0, Pressure = 84 kPa Vapor fraction = 1, Pressure = 275 kPa Vapor fraction = 0, Pressure = 275 kPa Hot inlet-cold outlet temperature difference = 10.0 K Outlet pressure = 84 kPa Discharge pressure = 275 kPa Distillate rate = 1410 kg/h Reflux ratio = 0.15 Condenser = Total Vapor fraction = 1, Pressure = 4550 kPa Vapor fraction = 0, Pressure = 4550 kPa Hot inlet-cold outlet temperature difference = 10.0 K Outlet pressure = 1570 kPa Discharge pressure = 4550 kPa

evaporator absorber heat exchanger valve pump

Table 4 Simulation results of the CAHT. Stream number

T (°C)

P (kPa)

m (kg/h)

h (kJ/kg)

s (kJ/kg K)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

127.7 130.0 130.0 130.2 157.1 94.9 95.0 130.7 167.1 143.4 89.3 92.3 92.3 93.9 126.7 40.4 44.8 84.4 136.7 108.8

84.00 84.00 84.00 235.00 235.00 84.00 275.00 275.00 275.00 275.00 1570.00 1570.00 1570.00 4550.00 4550.00 1570.00 4550.00 4550.00 4550.00 4550.00

6865.00 294.46 6570.54 6570.54 6570.54 294.46 294.46 294.46 6865.00 6865.00 13155.30 1410.00 11745.30 11745.30 11745.30 1410.00 1410.00 1410.00 13155.30 13155.30

−10061.27 −13237.16 −9842.84 −9842.48 −9785.22 −15583.21 −15582.54 −13241.27 −10006.15 −10061.03 −9735.96 −2871.40 −10536.79 −10527.10 −10369.74 −3863.80 −3835.27 −2714.07 −9601.39 −9741.89

−4.28 −1.81 −4.20 −3.97 −4.00 −8.18 −8.17 −2.36 −4.13 −4.11 −9.06 −6.65 −9.18 −9.17 −8.76 −10.80 −10.75 −7.58 −8.75 −9.10

UN , EX

UN UN , EN = EḊ , k − EḊ , k

AV , EN

EḊ

H2O (%mass)

Li+ (%mass)

Br- (%mass)

0.04 0.00 0.04 0.04 0.04 0.00 0.00 0.00 0.04 0.04

0.44 0.00 0.46 0.46 0.46 0.00 0.00 0.00 0.44 0.44

0.50 1.00 0.44 0.44 0.44 1.00 1.00 1.00 0.50 0.50

0.52 1.00 0.50 0.50 0.50 1.00 1.00 1.00 0.52 0.52 0.50 0.00 0.56 0.56 0.56 0.00 0.00 0.00 0.50 0.50

reduced by optimizing the component itself. It can be calculated as below:

reduced owing to the limitation of technique and economy conditions in other equipment. It can be calculated as below:

EḊ , k

NH3 (%mass)

AV , EN

EḊ , k

(11)

EN UN , EN = EḊ , k − EḊ , k

AV , EX

EḊ

is the part of the avoidable irreversibility that can be 5

(12)

is the part of the avoidable irreversibility that can be

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

Fig. 5. Flowsheet of system modeling equations.

2.6. Exergoeconomic analysis

reduced by optimizing other equipment. It can be calculated as below: AV , EX

EḊ , k

AV AV , EN = EḊ , k − EḊ , k

2.6.1. Conventional exergoeconomic analysis In exergoeconomic analysis, the exergy destruction cost rate (CḊ ) and investment cost rate (Z ̇ ) are calculated as indicators.

(13)

6

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

Table 5 Parameters of the CAHT analysis. Parameter

T0 (°C)

P0 (kPa)

cTH ($/GJ)

cTL ($/GJ)

cele ($/GJ)

i (%)

N (year)

t (h)

ϕ (-)

Value

25.0

101.3

4.66

3.65

19.31

15

10

8000

1.06

The cost rates are given by Eqs. (14) and (15) [35].

Table 7 Standard chemical exergy of the components.

cP,k EṖ , k = cF , k EḞ , k + Zk̇

(14)

CṖ , k = CḞ , k + Zk̇

(15)

Components

Li

Br

N

H

O

NH3

H2O

e (kJ/mol)

371.96

34.33

0.34

117.64

1.97

336.69

8.62

CḊ can be calculated as follows [36]. CḊ , k = cF , k EḊ , k

Table 8 Exergy analysis equations of the CAHT.

(16)

According to Smith [37], the investment cost of equipment can be calculated by the following formula. Table 10 lists the specific parameters.

V Ie = Ib ⎛ e ⎞ V ⎝ b⎠ ⎜

M

Equations of exergy analysis

LiBr generator

̇ EḊ , GEN − LiBr = E1̇ + QGEN − LiBr 1 −

LiBr condenser

̇ − liquid EḊ , CON − LiBr = E2̇ − E6̇ − ΔENH 3

LiBr evaporator

⎟

(17)

LiBr absorber LiBr heat exchanger LiBr pump 1

(18)

LiBr pump 2

The cost data was converted from 2000 to 2018 through the chemical economic plant cost index (CEPCI). The value of the CEPCI in 2000 was 394.1, while in 2018 it was 638.1 [39].

Ie,2018 = Ie,2000

LiBr valve NH3 generator

NH3 evaporator

(19)

NH3 absorber

The capital recovery factor (α ) can be calculated by the following formula.

i (1 + i) N α= (1 + i) N − 1

ϕαIb

Ve M Vb

( )

8000

NH3 heat exchanger NH3 pump 3

(20)

×

CEPCI2018 × rm rp rt CEPCI2000

⎟

̇ − E13 ̇ − E12

̇ + Q̇EVA − NH ⎛1 − EḊ , EVA − NH3 = E17 3 ⎝

T0 ⎞ TEVA − NH3 ⎠

̇ − E18

⎟

̇ + E18 ̇ − E19 ̇ − Q̇ ABS − NH ⎛1 − EḊ , ABS − NH3 = E15 3 ⎝ ̇ + E19 ̇ − E15 ̇ − E20 ̇ EḊ , HE − NH = E14 3

̇ + ẆPUM 3 − NH − E14 ̇ EḊ , PUM 3 − NH3 = E13 3

NH3 pump 4

̇ + ẆPUM 4 − NH − E17 ̇ EḊ , PUM 4 − NH3 = E16 3

NH3 valve

̇ − E11 ̇ EḊ , VAL − NH3 = E20

(21)

LiBr generator LiBr condenser

ṁ 1 = ṁ 2 + ṁ 3 ̇ ṁ 1 x1 = ṁ 3 x3QGEN − LiBr = ṁ 2 h2 + ṁ 3 h3 − ṁ 1 h1 ̇ QCON − LiBr = ṁ 6 h 6 − ṁ 2 h2

LiBr evaporator

Q̇EVA − LiBr = ṁ 8 h8 − ṁ 7 h7

LiBr absorber

ṁ 9 = ṁ 5 + ṁ 8ṁ 9 x 9 = ṁ 5 x5Q̇ ABS − LiBr = ṁ 5 h5 + ṁ 9 h9 − ṁ 8 h8 ṁ 5 h5 − ṁ 4 h4 = ṁ 10 h10 − ṁ 9 h9 ẆPUM1 − LiBr = ṁ 4 h4 − ṁ 3 h3 ẆPUM 2 − LiBr = ṁ 7 h7 − ṁ 6 h6 ṁ 10 = ṁ 1ṁ 10 x10 = ṁ 1 x1 ̇ ṁ 11 = ṁ 12 + ṁ 13ṁ 11 x11 = ṁ 12 x12 + ṁ 13 x13QGEN − NH3 = ṁ 12 h12 + ṁ 13 h13 − ṁ 11 h11

NH3 evaporator

̇ QCON − NH3 = ṁ 16 h16 − ṁ 12 h12 Q̇EVA − NH = ṁ 18 h18 − ṁ 17 h17

NH3 absorber

ṁ 19 = ṁ 18 + ṁ 15ṁ 19 x19 = ṁ 15 x15 + ṁ 18 x18Q̇ ABS − NH3 = ṁ 19 h19 − ṁ 15 h15 − ṁ 18 h18

NH3 heat exchanger NH3 pump 3

ṁ 15 h15 − ṁ 14 h14 = ṁ 20 h20 − ṁ 19 h19 ẆPUM 3 − NH3 = ṁ 14 h14 − ṁ 13 h13

NH3 pump 4

ẆPUM 4 − NH3 = ṁ 17 h17 − ṁ 16 h16

NH3 valve

ṁ 20 = ṁ 11ṁ 20 x20 = ṁ 11 x11

3

7

− E8̇

T0 ⎞ TGEN − NH3 ⎠

Equations of energy analysis

NH3 condenser

T0 ⎞ TABS − NH3 ⎠

3

̇ ̇ + QGEN EḊ , GEN − NH3 = E11 − NH3 ⎛1 − ⎝ ̇ ̇ ̇ ̇ ED, CON − NH3 = E12 − E16 − ΔEcw

Components

LiBr valve NH3 generator

2

EḊ , PUM1 − LiBr = E3̇ + ẆPUM1 − LiBr − E4̇ EḊ , PUM 2 − LiBr = E6̇ + ẆPUM 2 − LiBr − E7̇ ̇ − E1̇ EḊ , VAL − LiBr = E10

Table 6 Mass/material/energy equations of the CAHT.

LiBr pump 2

) − Ė − Ė

̇ EḊ , HE − LiBr = E4̇ + E9̇ − E5̇ − E10

Table 11 lists the cost rate equations of the CAHT.

LiBr heat exchanger LiBr pump 1

T0 TGEN − LiBr

⎜

In summary, Z ̇ of the CAHT can be calculated as follows:

Zk̇ =

EḊ , EVA − LiBr = E7̇ + Q̇ ABS − NH3 ⎛1 − ⎝ ̇ EḊ , ABS − LiBr = E5̇ + E8̇ − E9̇ − ΔElps

⎜

NH3 condenser

CEPCI2018 CEPCI2000

( ⎜

On this basis, the cost is corrected by material-, pressure-, and temperature-revised factors [38].

Ir = Ie rm rp rt

Components

T0 ⎞ TABS − NH3 ⎠ ⎟

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

Table 9 Ideal, unavoidable, and real conditions of components in the CAHT.

Table 11 Equations for the exergoeconomic analysis of the CAHT.

Components

Ideal conditions

Unavoidable conditions

Real conditions

LiBr generator LiBr condenser LiBr evaporator LiBr absorber LiBr heat exchanger LiBr pump LiBr valve NH3 generator NH3 condenser NH3 evaporator NH3 absorber NH3 heat exchanger NH3 pump NH3 valve

ΔT = 0 K ΔT = 0 K ΔT = 0 K ΔT = 0 K ΔT = 0 K η = 100% η = 100% ΔT = 0 K ΔT = 0 K ΔT = 0 K ΔT = 0 K ΔT = 0 K η = 100% η = 100%

ΔT = 0.25 ΔT = 0.25 ΔT = 0.25 ΔT = 0.25 ΔT = 0.25 η = 95% η = 96% ΔT = 0.25 ΔT = 0.25 ΔT = 0.25 ΔT = 0.25 ΔT = 0.25 η = 95% η = 96%

ΔT = 6 K ΔT = 10 K ΔT = 10 K ΔT = 10 K ΔT = 10 K η = 90% η = 90% ΔT = 6 K ΔT = 10 K ΔT = 10 K ΔT = 10 K ΔT = 10 K η = 90% η = 90%

K K K K K

K K K K K

Components

Cost rate equations

LiBr generator

̇ − GEN − LiBr = C2̇ + C3̇ ̇ C1̇ + ZGEN − LiBr + CQ

LiBr condenser

̇ − liquid ̇ C2̇ + ZCON − LiBr = C6̇ + CNH 3

LiBr evaporator

̇ − ABS − NH = C8̇ ̇ − LiBr + CQ C7̇ + ZEVA 3

LiBr absorber

̇ ̇ − LiBr = C9̇ + Clps C5̇ + C8̇ + ZABS

LiBr heat exchanger

̇ ̇ − LiBr = C5̇ + C10 C4̇ + C9̇ + ZHE ̇ − PUM1 − LiBr = C4̇ ̇ C3̇ + ZPUM 1 − LiBr + CW ̇ − PUM 2 − LiBr = C7̇ ̇ C6̇ + ZPUM 2 − LiBr + CW

LiBr pump 1 LiBr pump 2 LiBr valve

̇ + ZVAL ̇ − LiBr = C1̇ C10 ̇ + ZGEN ̇ − GEN − LiBr = C12 ̇ + C13 ̇ ̇ C11 − NH3 + CQ ̇ + ZCON ̇ + Ccw ̇ ̇ C12 − NH = C16

NH3 generator NH3 condenser

3

NH3 evaporator

̇ + ZEVA ̇ − EVA − NH = C18 ̇ ̇ − NH + CQ C17 3 3 ̇ + C18 ̇ + ZABS ̇ + CQ ̇ − ABS − NH ̇ − NH = C19 C15 3 3 ̇ + C19 ̇ + ZHE ̇ + C20 ̇ ̇ − NH = C15 C14

NH3 absorber NH3 heat exchanger

3

NH3 pump 3 NH3 pump 4

2.6.2. Advanced exergoeconomic analysis EX EN Ċ and Ċ are calculated by: EN CḊ , k EX CḊ , k

NH3 valve

=

EN cF , k EḊ , k

(22)

=

EX cF , k EḊ , k

(23) EN

EX

CḊ , k = cF , k EḊ , k = CḊ , k + CḊ , k

UN , EN

Zk̇

(24)

EX

EN = Zk̇ − Zk̇

(27) AV

CḊ , k = cF , k EḊ , k = CḊ , k + CḊ , k

̇ EN

̇ EX

̇ UN

UN , EN

UN , EN

UN , EN

− Zk̇

(33)

AV , EN

= cF , k EḊ , k

AV , EN

= Zk̇

AV , EN

EN

(34)

UN , EN

− Zk̇

(35)

AV , EX

(29)

AV , EX CḊ and Z ̇ are the parts of the avoidable inefficiency that can be reduced by optimizing other equipment and is calculated as below.

̇ AV

= cF , k EḊ , k

UN

AV , EN

Zk̇

C , C , C , and C are combined in more detail [41]. UN , EN CḊ and Z ̇UN , EN are the parts of the unavoidable inefficiency that cannot be reduced due to the limitation of technique and economy conditions in the component itself and can be expressed as follows. CḊ , k

= Zk̇

CḊ , k

is determined by considering the inefficiency of the component [40]. The calculation is based on Table 9. The formula is listed below:

= Zk̇ −

UN , EX

(32)

and Z ̇ are the parts of the avoidable inefficiency that can be decreased by optimizing the component itself. The calculation is as follows.

(28)

UN Zk̇

(31)

UN , EX

AV , EN CḊ

UN Zk̇

AV Zk̇

= cF , k EḊ , k

Zk̇

AV AV CḊ , k = cF , k EḊ , k UN

UN , EX

CḊ , k

UN Ċ and Ċ AV are calculated by:

(26)

UN Ż EN = EṖ , k ⎜⎛ k ⎟⎞ ̇ ⎝ EP, k ⎠

and Z ̇UN , EX are the parts of the unavoidable inefficiency that cannot be reduced owing to the limitation of technique and economy conditions in other equipment and can be formulated as follows.

(25)

UN UN CḊ , k = cF , k EḊ , k

3

UN , EX CḊ

EN The calculation of Z ̇ and Z ̇ EX is based on Ref. [17], and the formula is listed below:

Zk̇

̇ + ZPUM ̇ − PUM 3 − NH = C14 ̇ ̇ C13 3 − NH3 + CW 3 ̇ + ZPUM ̇ − PUM 4 − NH = C17 ̇ ̇ C16 − NH3 + CW 3 ̇ + ZVAL ̇ ̇ − NH = C11 C20

AV , EN

AV , EN = cF , k EḊ , k

AV , EX

= Zk̇

CḊ , k Zk̇

(30)

EX

(36)

UN , EX

− Zk̇

(37)

Table 10 Specific component parameters in the CAHT. Components

Capacity measures

Base sizes

Size ranges

Base costs

Price index

rm

rp

rt

LiBr generator LiBr condenser LiBr evaporator LiBr absorber LiBr heat exchanger LiBr pump LiBr valve NH3 distillation column NH3 sieve trays NH3 condenser NH3 evaporator NH3 absorber NH3 heat exchanger NH3 pump NH3 valve

Volume Area Area Volume Area Power Diameter Mass Diameter Area Area Volume Area Power Diameter

5.0 m3 80 m2 80 m2 5.0 m3 80 m2 4 kW 0.3 m 8.0 t 0.5 m 80 m2 80 m2 0.1 m3 80 m2 4 kW 0.3 m

5–200 m3 80–4000 m2 80–4000 m2 5–200 m3 80–4000 m2 4–700 kW 0.3–3 m 8–300 t 0.5–4 m 80–4000 m2 80–4000 m2 0.1–20 m3 80–4000 m2 4–700 kW 0.3–3 m

1.15 × 104 $ 3.28 × 104 $ 3.28 × 104 $ 1.15 × 104 $ 3.28 × 104 $ 9.84 × 103 $ 1.80 × 103 $ 6.5 × 104 $ 6.56 × 103 $ 3.28 × 104 $ 3.28 × 104 $ 4.92 × 103 $ 3.28 × 104 $ 9.84 × 103 $ 1.80 × 103 $

0.53 0.68 0.68 0.53 0.68 0.55 0.97 0.89 0.91 0.68 0.68 0.53 0.68 0.55 0.97

1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 2.40 1.00 1.00 1.00

1.60 2.00 2.00 2.00 2.00 2.00 2.00 1.02 1.02 1.02 1.02 1.00 1.02 1.02 1.02

1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00

8

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

Table 12 Specific data of the conventional exergy and exergoeconomic analyses. Components

EḞ (kW)

EṖ (kW)

EḊ (kW)

cF ($/GJ)

cP ($/GJ)

CḊ ($/h)

Z ̇ ($/h)

ε (%)

yD (%)

f (%)

̇ ($/h) Rtot

LiBr generator LiBr condenser LiBr evaporator LiBr absorber LiBr heat exchanger LiBr pump 1 LiBr pump 2 LiBr valve NH3 generator NH3 condenser NH3 evaporator NH3 absorber NH3 heat exchanger NH3 pump 3 NH3 pump 4 NH3 valve

362.16 391.24 517.62 489.16 1233.70 6.55 0.55 222.13 573.47 1624.80 725.75 619.90 1267.07 315.91 87.31 295.60

206.42 368.04 498.03 447.53 1163.68 3.08 0.14 211.15 405.10 1297.71 686.33 517.62 1141.05 191.71 31.39 270.21

155.74 23.20 19.59 41.63 70.02 3.47 0.41 10.98 168.37 327.09 39.42 102.28 126.02 124.20 55.92 25.39

4.66 8.18 8.70 9.04 4.80 19.31 19.31 4.62 3.65 5.17 6.47 6.84 3.72 19.31 19.31 3.49

8.18 8.70 9.04 9.88 5.09 41.07 75.86 4.86 5.17 6.47 6.84 8.19 4.13 31.82 53.71 3.82

2.61 0.68 0.61 1.35 1.21 0.24 0.03 0.18 2.21 6.09 0.92 2.52 1.69 8.63 3.89 0.32

1.29 1.36 1.31 1.63 1.98 1.10 0.28 0.20 8.77 2.60 2.12 4.24 2.65 4.74 2.34 0.28

57.00 94.07 96.22 91.49 94.32 47.02 25.45 95.06 70.64 79.87 94.57 83.50 90.05 60.69 35.95 91.41

12.04 1.79 1.51 3.22 5.41 0.27 0.03 0.85 13.01 25.28 3.05 7.91 9.74 9.60 4.32 2.02

33.05 66.56 68.03 54.64 62.09 82.03 90.82 52.25 79.86 29.92 69.80 62.76 61.10 35.43 37.53 46.74

3.90 2.04 1.92 2.99 3.19 1.34 0.31 0.38 10.98 8.69 3.04 6.76 4.34 13.37 6.22 0.60

Table 13 Exergy destruction rate of each component in the CAHT. Components

EḊ (kW)

EḊ (kW)

EḊ (kW)

EḊ (kW)

EḊ (kW)

EḊ

LiBr generator LiBr condenser LiBr evaporator LiBr absorber LiBr heat exchanger LiBr pump 1 LiBr pump 2 LiBr valve NH3 generator NH3 condenser NH3 evaporator NH3 absorber NH3 heat exchanger NH3 pump 3 NH3 pump 4 NH3 valve

155.74 23.20 19.59 41.63 70.02 3.47 0.41 10.98 168.37 327.09 39.42 102.28 126.02 124.20 55.92 25.39

119.19 5.36 16.56 33.09 16.69 3.01 0.36 9.38 138.19 59.41 31.96 84.36 26.90 109.31 50.09 21.96

36.55 17.84 3.03 8.54 53.33 0.46 0.05 1.60 30.18 267.68 7.46 17.92 99.12 14.89 5.83 3.43

124.13 18.78 12.94 27.26 55.85 2.86 0.33 8.69 140.69 262.14 23.73 70.92 100.98 102.42 45.66 20.93

31.61 4.42 6.65 14.37 14.17 0.61 0.08 2.29 27.68 64.95 15.69 31.36 25.04 21.78 10.26 4.46

96.32 4.11 10.79 21.37 13.53 2.54 0.29 7.36 116.35 44.03 18.78 59.68 22.53 91.16 41.27 18.59

EN

EX

UN

EṖ , k EḊ , k εk = =1− EḞ , k EḞ , k

=

AV , EN

Ṙtot

(38)

UN

AV , EX

EḞ , k − EḊ , k − EḊ , k

yD, k =

EḊ , k EḊ , tot

y adv D, k =

EḊ , K EḊ , tot

AV , EN

EḊ

(kW)

22.87 1.25 5.77 11.72 3.16 0.47 0.07 2.02 21.84 15.38 13.18 24.67 4.37 18.15 8.82 3.38

AV , EX

EḊ

(kW)

8.74 3.17 0.88 2.65 11.01 0.14 0.01 0.28 5.84 49.57 2.51 6.68 20.67 3.63 1.44 1.09

AV , EN

= Zk̇

(44) AV , EN

+ CḊ , k

(45)

3. Results and discussion 3.1. Conventional exergy and exergoeconomic analyses of CAHT

(39)

The specific data of the conventional exergy and exergoeconomic analyses are given in Table 12. The total EḊ of the system is 1293.73 kW. Among the system parts, the EḊ of the NH3 condenser is the highest (327.09 kW), accounting for 25.28% of the total. These EḊ are mainly caused by cooling water. Apart from the NH3 condenser, the generators of the LiBr and NH3 AHT have higher EḊ , with the values of 168.37 kW and 155.74 kW. The highest CḊ comes from NH3 pump 3 (8.63 $/h). This is because of its high loss of electricity. In addition, components with high Z ̇ values are the NH3 generator (8.77 $/h), NH3 pump 3 (4.74 $/h), and NH3 absorber (4.24 $/h) in order. It can be ̇ ) have a great found that the components with a high total cost (Rtot impact on the CAHT. This means that the NH3 pump 3 (13.37 $/h) and NH3 generator (10.98 $/h) have the greatest impact. The exergoeconomic factor ( f ) is used to evaluate the influence of CḊ and Z ̇ on the system. A high f means that Z ̇ has a great influence, while a low f means that CḊ has an obvious effect. Therefore, CḊ of the LiBr generator, NH3 condenser, NH3 pumps, and NH3 valve should be decreased, while Z ̇ of the other components needs more consideration.

(40)

EN , AV

(41)

The exergoeconomic factor represents the influence of the thermodynamic performance and economic performance on the components. It can be calculated as below.

Zk̇ Zk̇ + CḊ , k

f kAV , EN =

27.81 14.67 2.15 5.89 42.32 0.32 0.04 1.33 24.34 218.11 4.95 11.24 78.45 11.26 4.39 2.34

(kW)

EṖ , k

The formulas for calculating the exergy destruction ratio are listed below.

fk =

UN , EX

EḊ

̇ = Zk̇ + CḊ , k Rtot

Exergy efficiency refers to the ratio of product exergy to feed exergy. It can be calculated by the following formulas:

ified

(kW)

The total cost rate can be calculated as below.

2.7. Performance criteria

εk, mod

UN , EN

AV

AV , EN Zk̇ AV , EN ̇ AV , EN Zk̇ + CD,k

(42)

(43) 9

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

Fig. 6. Distribution of the exergy destruction rate for each component in the CAHT. Table 14 Exergy destruction cost rate of each component in the CAHT. Components

CḊ ($/h)

CḊ ($/h)

CḊ ($/h)

CḊ ($/h)

CḊ ($/h)

CḊ

LiBr generator LiBr condenser LiBr evaporator LiBr absorber LiBr heat exchanger LiBr pump 1 LiBr pump 2 LiBr valve NH3 generator NH3 condenser NH3 evaporator NH3 absorber NH3 heat exchanger NH3 pump 3 NH3 pump 4 NH3 valve

2.61 0.68 0.61 1.35 1.21 0.24 0.03 0.18 2.21 6.09 0.92 2.52 1.69 8.63 3.89 0.32

2.00 0.16 0.52 1.07 0.29 0.21 0.03 0.15 1.81 1.11 0.75 2.08 0.36 7.60 3.49 0.28

0.61 0.52 0.09 0.28 0.92 0.03 0.00 0.03 0.40 4.98 0.17 0.44 1.33 1.03 0.41 0.04

2.08 0.55 0.40 0.88 0.97 0.20 0.02 0.14 1.85 4.88 0.55 1.75 1.35 7.12 3.18 0.26

0.53 0.13 0.21 0.47 0.24 0.04 0.01 0.04 0.36 1.21 0.37 0.77 0.34 1.51 0.71 0.06

1.61 0.12 0.34 0.69 0.23 0.18 0.02 0.12 1.53 0.82 0.44 1.47 0.30 6.33 2.87 0.23

EN

EX

UN

AV

10

UN , EN

($/h)

UN , EX

CḊ

0.47 0.43 0.07 0.19 0.73 0.02 0.00 0.02 0.32 4.06 0.12 0.28 1.05 0.78 0.31 0.03

($/h)

AV , EN

CḊ

0.38 0.04 0.18 0.38 0.05 0.03 0.01 0.03 0.29 0.29 0.31 0.61 0.06 1.26 0.61 0.04

($/h)

AV , EX

CḊ

0.15 0.09 0.03 0.09 0.19 0.01 0.00 0.00 0.08 0.92 0.06 0.16 0.28 0.25 0.10 0.01

($/h)

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

Table 15 Investment cost rate of the CAHT components. Components

Z ̇ ($/h)

Z ̇ EN ($/h)

Z ̇ EX ($/h)

Z ̇UN ($/h)

Z ̇ AV ($/h)

Z ̇UN , EN ($/h)

Z ̇UN , EX ($/h)

Z ̇ AV , EN ($/h)

Z ̇ AV , EX ($/h)

LiBr generator LiBr condenser LiBr evaporator LiBr absorber LiBr heat exchanger LiBr pump 1 LiBr pump 2 LiBr valve NH3 generator NH3 condenser NH3 evaporator NH3 absorber NH3 heat exchanger NH3 pump 3 NH3 pump 4 NH3 valve

1.29 1.36 1.31 1.63 1.98 1.10 0.28 0.20 8.77 2.60 2.12 4.24 2.65 4.74 2.34 0.28

1.12 0.86 0.97 1.38 1.31 0.97 0.23 0.17 7.76 1.67 1.59 3.63 1.73 4.01 2.03 0.24

0.17 0.50 0.34 0.25 0.67 0.13 0.05 0.03 1.01 0.93 0.53 0.61 0.92 0.73 0.31 0.04

1.16 0.98 0.88 1.43 1.61 0.87 0.22 0.15 7.82 1.83 1.31 3.88 2.16 3.78 2.01 0.22

0.13 0.38 0.43 0.20 0.37 0.23 0.06 0.05 0.95 0.77 0.81 0.36 0.49 0.96 0.33 0.06

1.01 0.61 0.66 1.22 1.04 0.76 0.19 0.13 6.97 1.16 0.97 3.34 1.39 3.34 1.76 0.20

0.15 0.37 0.22 0.21 0.57 0.11 0.03 0.02 0.85 0.67 0.34 0.54 0.77 0.44 0.25 0.02

0.11 0.25 0.31 0.16 0.27 0.21 0.04 0.04 0.79 0.51 0.62 0.29 0.34 0.67 0.27 0.04

0.02 0.13 0.12 0.04 0.10 0.02 0.02 0.01 0.16 0.26 0.19 0.07 0.15 0.29 0.06 0.02

Fig. 7. Distribution of the investment cost rate of the CAHT components.

11

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

Fig. 8. Advanced exergy and exergoeconomic analyses results of the CAHT.

Fig. 9. Conparsion of the conventional and advanced exergy destruction rate results.

The results for CḊ are listed in Table 14. Since CḊ is calculated by EḊ , the distribution of CḊ would be alike to EḊ . Therefore, the figure of CḊ is omitted in this work. The results for Z ̇ are given in Table 15 and Fig. 7. It can be found that the proportion of the gray part is the largest, which means that most of the unavoidable costs are caused by the components themselves. The NH3 evaporator (29.21%) and LiBr evaporator (23.75%) AV , EN have the highest Z ̇ . For the other components, reducing Z ̇ is more difficult. The results for EḊ , CḊ , and Z ̇ of the whole system are shown in Fig. 8. As can be seen from the figure, 56.10% of the EḊ in the system is EX EN EN EḊ , and 43.90% is EḊ . These results mean that the effect of EḊ is EX ̇ important, and ED also cannot be ignored. At the same time, 21.28% of the EḊ (12.14% endogenous and 9.14% exogenous) can be avoided.

3.2. Advanced exergy and exergoeconomic analyses of the CAHT The results of EḊ are given in Table 13 and Fig. 6. It can be found that the NH3 condenser (66.68% unavoidable and 15.51% avoidable), NH3 heat exchanger (62.25% unavoidable and 16.40% avoidable), LiBr condenser (63.23% unavoidable and 13.66% avoidable), and LiBr heat EX exchanger (60.44% unavoidable and 15.72% avoidable) have high EḊ . EN For generators, evaporators, absorbers, pumps, and valves, EḊ acAV counts for a larger proportion of the total. The high EḊ occurs in the NH3 evaporator (33.43% endogenous and 6.36% exogenous), LiBr evaporator (29.45% endogenous and 4.49% exogenous), and LiBr absorber (28.15% endogenous and 6.37% exogenous). For these components, it is more likely that theEḊ can be reduced, while this may be more difficult for other components. 12

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

Fig. 10. Comparison of the conventional and advanced exergy destruction cost rate results.

Fig. 11. Comparison of the conventional and advanced investment cost rate results.

Therefore, in the process of reducing EḊ , both the component itself and the interaction between components should be considered. The middle part of Fig. 8 is about CḊ . The main reason for the difference between this part and EḊ is that the price of electricity far exceeds the value of waste heat. The outcomes on the right side of Fig. 8 show that 80.41% AV of the Z ̇ comes from the component itself. In addition, Z ̇ is only ̇ 17.84%. Therefore, it is difficult to optimize Z . The conventional and advanced exergy and exergoeconomic analyses results are shown in Fig. 9. The NH3 condenser has the highest EḊ AV , EN AV , EN (25.28%), but its EḊ is only 1.19%. EḊ for the NH3 absorber and LiBr generator are 1.91% and 1.77%, respectively. Thus, the improvement of NH3 absorber and LiBr generator takes a priority over to that of NH3 condenser. Fig. 10 shows that the highest CḊ comes from the NH3 pump 3, followed by the NH3 condenser and NH3 pump 4. It can be found that

AV , EN AV , EN the CḊ of the pumps are higher. On the contrary, the CḊ of other components are lower. Therefore, the NH3 pumps and condenser need to be improved first. Fig. 11 shows that the Z ̇ of the NH3 AHT is significantly higher than that of the LiBr AHT. This is mainly due to the large flow rate of the NH3 AV , EN AHT. The highest Z ̇ and Z ̇ come from the NH3 generator. This proves that their Z ̇ can be reduced to a certain extent. The optimization should focus more on the NH3 AHT. Table 16 shows the comparisons of the conventional and advanced performance criteria results. The ε of the advanced method is obviously higher than that of the conventional method. In addition, the advanced ̇ . For f , method also gives the endogenous avoidable parts of yD and Rtot the two methods present some different results. For the LiBr absorber, NH3 condenser, and NH3 absorber, the two methods have the opposite

13

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

Table 16 Comparison of the conventional and advanced performance criteria results. Components

ε (%)

yD (%)

f (%)

̇ ($/h) Rtot

εmodified (%)

y adv D (%)

f AV , EN (%)

̇ Rtot

LiBr generator LiBr condenser LiBr evaporator LiBr absorber LiBr heat exchanger LiBr pump 1 LiBr pump 2 LiBr valve NH3 generator NH3 condenser NH3 evaporator NH3 absorber NH3 heat exchanger NH3 pump 3 NH3 pump 4 NH3 valve

57.00 94.07 96.22 91.49 94.32 47.02 25.45 95.06 70.64 79.87 94.57 83.50 90.05 60.69 35.95 91.41

12.04 1.79 1.51 3.22 5.41 0.27 0.03 0.85 13.01 25.28 3.05 7.91 9.74 9.60 4.32 2.02

33.05 66.56 68.03 54.64 62.09 82.03 90.82 52.25 79.86 29.92 69.80 62.76 61.10 35.43 37.53 46.74

3.90 2.04 1.92 2.99 3.19 1.34 0.31 0.38 10.98 8.69 3.04 6.76 4.34 13.37 6.22 0.60

90.03 99.66 98.85 97.45 99.73 86.76 66.67 99.05 94.88 98.83 98.12 95.45 99.62 91.35 78.07 98.77

1.77 0.10 0.45 0.91 0.24 0.04 0.01 0.16 1.69 1.19 1.02 1.91 0.34 1.40 0.68 0.26

22.28 87.17 63.30 29.63 83.18 86.59 88.65 54.73 73.38 64.04 66.84 32.29 85.30 34.69 30.55 48.45

0.49 0.29 0.49 0.54 0.32 0.24 0.05 0.07 1.08 0.80 0.93 0.90 0.40 1.93 0.88 0.08

AV , EN

($/h)

Table 17 Strategies for decreasing the exergy destruction cost rate. Components

LiBr generator LiBr condenser LiBr evaporator LiBr absorber LiBr heat exchanger LiBr pump 1 LiBr pump 2 LiBr valve NH3 generator NH3 condenser NH3 evaporator NH3 absorber NH3 heat exchanger NH3 pump 3 NH3 pump 4 NH3 valve

Categories of exergy destruction cost rate ($/h)

Focused part

CḊ

CḊ

CḊ

CḊ

2.61 0.68 0.61 1.35 1.21 0.24 0.03 0.18 2.21 6.09 0.92 2.52 1.69 8.63 3.89 0.32

0.53 0.13 0.21 0.47 0.24 0.04 0.01 0.04 0.36 1.21 0.37 0.77 0.34 1.51 0.71 0.06

0.38 0.04 0.18 0.38 0.05 0.03 0.01 0.03 0.29 0.29 0.31 0.61 0.06 1.26 0.61 0.04

0.15 0.09 0.03 0.09 0.19 0.01 0.00 0.00 0.08 0.92 0.06 0.16 0.28 0.25 0.10 0.01

AV

AV , EN

Possible strategies Strategy A

AV , EX

EN EX EN EN/EX EX EN EN EN EN EX EN EN/EX EX EN EN EN

Strategy C

√ √ √ √

√ √

√

√ √ √ √ √ √ √ √ √ √

Strategy A: increase the efficiency of the component or replace with an effective component. Strategy B: increase the efficiency of components other than this one. Strategy C: increase the efficiency of the whole system.

Fig. 12. Influence of generator temperature on the LiBr AHT and NH3 AHT.

14

Strategy B

√ √ √

√

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

Fig. 13. Influence of high pressure on the LiBr AHT and NH3 AHT.

Fig. 14. Influence of low pressure on the LiBr AHT and NH3 AHT.

unchanged. This is mainly due to the significant influence of low pressure on the condenser and generator of the LiBr AHT. However, due to the limitation of the heat source, the influence on the NH3 AHT is not obvious. In addition to the above parameters, the influence of potential limitations such as the footprint and control strategy on the system is also considered. For the NH3 AHT, the footprint of NH3 will significantly affect the temperature rise effect on the system. The more NH3 that leaves the upper part of the generator, the higher the temperature rise effect. Similarly, for the LiBr AHT, the higher the LiBr content in the bottom of the generator, the worse the effect of heat production. For the control strategy, the liquid level, temperature, and pressure controls are mainly considered. In the single stage AHT, changing the parameters will affect the temperature, pressure, and liquid level of each stream in the system. For the cascade system, if the parameters of any single AHT change, the control of the other AHT will change. Therefore, the comprehensive control of temperature, pressure, and liquid level, combined with other effective control schemes, will be our future research direction.

priority. The above shows the significant impact of the advanced method on performance criteria. AV The strategies (A, B, and C) for decreasing CḊ are shown in Table 17. Depending on which parts of the components need to be focused on, different strategies are identified.

3.3. Parametric study The influence of generator temperature, high pressure, and low pressure on the EḊ is studied in this part. In addition, the footprint and control strategy of the system are also discussed. Fig. 12 shows the influence of the generator temperature on the LiBr AHT and NH3 AHT. It can be found that the decreasing trend of EḊ is different with the increase in generator temperature. When the LiBr generator temperature increases in the range of 130–136 °C, the LiBr EḊ decreases rapidly. However, when it is in the range of 136–144 °C, the LiBr EḊ decreases very slowly. The same effect occurs in the NH3 ANT with a demarcation point of 92 °C. This shows that increasing the generator temperature can significantly reduce its EḊ . Fig. 13 shows the influence of high pressure on the LiBr AHT and NH3 AHT. With the increase in high pressure, EḊ increases continuously. This is due to the increase in the heat transfer rate of the absorber and evaporator on the high pressure side. TheEḊ of the two AHTs show different trends in the results of the effect of low pressure in Fig. 14. The EḊ of the LiBr AHT shows a growing trend, while the EḊ of the NH3 AHT remains basically

4. Conclusions In this study, a conventional and advanced exergy and exergoeconomic analyses of the proposed system were conducted. The main conclusions from the present study are summarized as follows: 15

Energy Conversion and Management 205 (2020) 112392

Y. Wang, et al.

1. The advanced analysis results show that 21.28% of the exergy destruction rate, 21.07% of the exergy destruction cost rate, and 17.84% of the investment cost rate are avoidable. Additionally, 56.10%, 65.94%, and 80.2% of them are endogenous. 2. The conventional analysis results cannot show the improvement of the component. For example, the highest exergy destruction rate comes from the NH3 condenser (327.09 kW), while the advanced analysis results show that 80.14% of it is unavoidable. 3. The results of the advanced and conventional analyses are not always identical. The exergoeconomic factors show that the LiBr absorber, NH3 condenser, and NH3 absorber have the opposite priority from the two methods. 4. Higher exergy destruction and cost rates come from the NH3 cycle, which indicates that the improvement of this part should be given priority. 5. Based on the analysis results, strategy B is used for condensers and heat exchangers, while strategy A is used for other components. In addition, strategy C is used in heat exchangers and the NH3 evaporator. 6. The influence of generator temperature and low pressure on the system exergy destruction rate does not show a standard linearity. In addition, footprint and control strategy are also crucial to the system.

[11] Mahmoudi SMS, Salehi S, Yari M, Rosen M. Exergoeconomic performance comparison and optimization of single-stage absorption heat transformers. Energies 2017;10(4):532. [12] Wang D, Li S, Liu F, Gao L, Sui J. Post combustion CO2 capture in power plant using low temperature steam upgraded by double absorption heat transformer. Appl Energ 2018;227:603–12. [13] Yari M, Salehi S, Mahmoudi SMS. Three-objective optimization of water desalination systems based on the double-stage absorption heat transformers. Desalination 2017;405:10–28. [14] Lubis A, Giannetti N, Yamaguchi S, Saito K, Inoue N. Experimental performance of a double-lift absorption heat transformer for manufacturing-process steam generation. Energ Convers Manage 2017;148:267–78. [15] Donnellan P, Byrne E, Cronin K. Internal energy and exergy recovery in high temperature application absorption heat transformers. Appl Therm Eng 2013;56(1–2):1–10. [16] Salehzadeh A, Saray RK, JalaliVahid D. Investigating the effect of several thermodynamic parameters on exergy destruction in components of a tri-generation cycle. Energy 2013;52:96–109. [17] Anvari S, Saray RK, Bahlouli K. Conventional and advanced exergetic and exergoeconomic analysis applied to a tri-generation cycle for heat, cold and power production. Energy 2015;91:925–39. [18] Bagheri BS, Shirmohammadi R, Mahmoudi SMS, Rosen MA. Optimization and comprehensive exergy-based analysis of a parallel flow double-effect water-lithium bromide absorption refrigeration system. Appl Therm Eng 2019;152:643–53. [19] Mehrpooya M, Mousavi SA. Advanced exergoeconomic assessment of a solar-driven Kalina cycle. Energ Convers Manage 2018;178:78–91. [20] Gungor A, Tsatsaronis G, Gunerhan H, Hepbasli A. Advanced exergoeconomic analysis of a gas engine heat pump (GEHP) for food drying processes. Energ Convers Manage 2015;91:132–9. [21] Esfahani IJ, Lee S, Yoo C. Evaluation and optimization of a multi-effect evaporation–absorption heat pump desalination based conventional and advanced exergy and exergoeconomic analyses. Desalination 2015;359:92–107. [22] Donnellan P, Cronin K, Byrne E. Recycling waste heat energy using vapour absorption heat transformers: a review. Renew Sust Energ Rev 2015;42:1290–304. [23] Kiepe J, Horstmann S, Fischer K, Gmehling J. Application of the PSRK model for systems containing strong electrolytes. Ind Eng Chem Res 2004;43(20):6607–15. [24] Johnston X.X.X.I.I. SM. The Boiling and Freezing Points of Concentrated Aqueous Solutions, and the Question of the Hydration of the Solute. Earth Env Sci T R So 1908;45(4):855–84. [25] Kurem E, Horuz I. A comparison between ammonia-water and water-lithium bromide solutions in absorption heat transformers. Int Commun Heat Mass 2001;28(3):427–38. [26] Grossman G, Wilk M. Advanced modular simulation of absorption systems. Int J Refrig 1994;17(4):231–44. [27] She X, Yin Y, Xu M, Zhang X. A novel low-grade heat-driven absorption refrigeration system with LiCl–H2O and LiCl–H2O working pairs. Int J Refrig 2015;58:219–34. [28] Cui P, Yu M, Liu Z, Zhu Z, Yang S. Energy, exergy, and economic (3E) analyses and multi-objective optimization of a cascade absorption refrigeration system for lowgrade waste heat recovery. Energ Convers Manage 2019;184:249–61. [29] Mehrpooya M, Gharagheizi F, Vatani A. Thermoeconomic analysis of a large industrial propane refrigeration cycle used in NGL recovery plant. Int J Energ Res 2009;33(11):960–77. [30] Yang S, Qian Y, Yang S. Development of a Full CO2 Capture process based on the rectisol wash technology. Ind Eng Chem Res 2016;55(21):6186–93. [31] Açıkkalp E, Aras H, Hepbasli A. Advanced exergoeconomic analysis of an electricity-generating facility that operates with natural gas. Energ Convers Manage 2014;78:452–60. [32] Morosuk T, Tsatsaronis G. A new approach to the exergy analysis of absorption refrigeration machines. Energy 2008;33(6):890–907. [33] Vatani A, Mehrpooya M, Palizdar A. Advanced exergetic analysis of five natural gasliquefaction processes. Energ Convers Manage 2014;78:720–37. [34] Kelly S, Tsatsaronis G, Morosuk T. Advanced exergetic analysis: approaches for splitting the exergy destruction into endogenous and exogenous parts. Energy 2009;34(3):384–91. [35] Mehrpooya M, Ansarinasab H. Advanced exergoeconomic evaluation of single mixed refrigerant natural gas liquefaction processes. J Nat Gas Sci Eng 2015;26:782–91. [36] Lazzaretto A, Tsatsaronis G. SPECO: a systematic and general methodology for calculating efficiencies and costs in thermal systems. Energy 2006;31(8):1257–89. [37] Smith R. Chemical process design and integration. John Wiley; 2005. [38] Sun H, Qiu L. Comparison with ammonia absorption refrigeration technique and compression refrigerationcraft in economic efficiency. Chem Eng 2006;125(2):49–50. [39] Hou S, Cao S, Yu L, Zhou Y, Wu Y, Zhang F. Performance optimization of combined supercritical CO2 recompression cycle and regenerative organic Rankine cycle using zeotropic mixture fluid. Energ Convers Manage 2018;166:187–200. [40] Tsatsaronis G, Park MH. On avoidable and unavoidable exergy destructions and investment costs in thermal systems. Energ Convers Manage 2002;43:1259–70. [41] Alavi O, Mostafaeipour A, Qolipour M. Analysis of hydrogen production from wind energy in the southeast of Iran. Int J Hydrogen Energ 2016;41(34):15158–71.

Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work is supported by the National Natural Science Foundation of China (No. 21776145), National Natural Science Foundation of China (No. 21676152), National Natural Science Foundation of China (No. 21808117), National Natural Science Foundation of China (No. 51676209), Talent Fund of Shandong Collaborative Innovation Center of Eco-Chemical Engineering (XTCXQN03), State Key Laboratory Base of Eco-chemical Engineering (STHG1803), and Foundation of Key Laboratory of Low-Carbon Conversion Science & Engineering (No. KLLCCSE-201907, SARI, CAS). References [1] Wang Q, Hu YJ, Hao J, Lv N, Li TY, Tang BJ. Exploring the influences of green industrial building on the energy consumption of industrial enterprises: a case study of Chinese cigarette manufactures. J Clean Prod 2019;231:370–85. [2] Löschel A, Managi S. Recent advances in energy demand analysis—insights for industry and households. Resour Energy Econ 2019;56:1–5. [3] Abdelaziz EA, Saidur R, Mekhilef S. A review on energy saving strategies in industrial sector. Renew Sust Energ Rev 2011;15(1):150–68. [4] Lassagne O, Gosselin L, Désilets M, Iliuta MC. Techno-economic study of CO2 capture for aluminum primary production for different electrolytic cell ventilation rates. Chem Eng J 2013;230:338–50. [5] Wang Y, Liu X, Kraslawski A, Gao J, Cui P. A novel process design for CO2 capture and H2S removal from the syngas using ionic liquid. J Clean Prod 2019;213:480–90. [6] Yu M, Cui P, Wang Y, Liu Z, Zhu Z, Yang S. Advanced exergy and exergoeconomic analysis of cascade absorption refrigeration system driven by low grade waste heat. ACS Sustain Chem Eng 2019;7:16843–57. [7] Horuz I, Kurt B. Absorption heat transformers and an industrial application. Renew Energ 2010;35(10):2175–81. [8] Donnellan P, Byrne E, Oliveira J, Cronin K. First and second law multidimensional analysis of a triple absorption heat transformer (TAHT). Appl Energ 2014;113:141–51. [9] Wakim M, Rivera-Tinoco R. Absorption heat transformers: Sensitivity study to answer existing discrepancies. Renew Energ 2019;130:881–90. [10] Liu F, Sui J, Liu T, Jin H. Energy and exergy analysis in typical days of a steam generation system with gas boiler hybrid solar-assisted absorption heat transformer. Appl Therm Eng 2017;115:715–25.

16