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Energy 141 (2017) 1555e1568

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Energy

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Synthesis of energy efficient chilled and cooling water network byintegrating waste heat recovery refrigeration system

Wai Mun Chan a, Yik Teeng Leong b, Ji Jinn Foo a, Irene Mei Leng Chew a, *

a School of Engineering, Monash University Malaysia, Jalan Lagoon Selatan, 47500 Bandar Sunway, Selangor, Malaysiab School of Engineering, Taylor’s University, No.1 Jalan Taylor’s, 47500 Subang Jaya, Selangor Darul Ehsan, Malaysia

a r t i c l e i n f o

Article history:Received 15 April 2017Received in revised form6 November 2017Accepted 8 November 2017Available online 9 November 2017

Keywords:Absorption refrigerationHeat integrationMultiple waste heatsVapor compression refrigerationEco-industrial parks

* Corresponding author.E-mail address: Irene.chew@monash.edu (I.M.L. C

https://doi.org/10.1016/j.energy.2017.11.0560360-5442/© 2017 Elsevier Ltd. All rights reserved.

a b s t r a c t

Vapor compression refrigeration system (VCRS) is the conventional technology that uses electricity togenerate chilled water for process cooling and air conditioning. On the other hand, there are variousalternative green technologies that use waste heat to drive refrigeration system. In current industrialpractices, abundant amounts of waste heat in the form of steam, hot water and flue gas remain untappedand are wasted. Absorption refrigeration system (ARS) is the alternative green technology that couldrecover those waste heats to produce cooling utility. In previous works, the integration of chilled andcooling water network within an Eco-Industrial Park (EIP) has been proven to be more cost effective thanindividual plant. However, the network is configured with VCRS which is an energy intensive technology.In this paper, ARS is integrated with VCRS to synthesize an energy efficient chilled and cooling waternetwork using superstructure optimization approach. To further enhance energy efficiency, secondarywaste heat recovery is proposed. Results shown the proposed ARS-VCRS integrated network has reducedthe CO2 emission and the overall costs by 53% and 21% compared to VCRS alone. The minimum coolingduty and waste heat in the EIP for ARS-VCRS installation are determined through sensitivity analysis.

© 2017 Elsevier Ltd. All rights reserved.

1. Introduction

Chilled water is a common utility used widely in various in-dustrial processes such as food preservation, room cooling insemiconductor industries, freeze-drying process in pharmaceuticalindustries and etc. Chilled water can be supplied by vaporcompression refrigeration system (VCRS), absorption refrigerationsystem (ARS) or adsorption refrigeration system (ADS). The con-ventional method using VCRS may inflict high electricity cost tomany industries. According to Marques et al. [1], the energy usedfor refrigeration operation accounts for 17% of the worldwideelectricity usage. In an effort to reduce the electricity consumption,thermally driven refrigeration systems such as ARS and ADS havereceived much attention owing to the ability to recover waste heatfor chilled water production. An ARS can be driven not only by highor medium grade thermal heat, such as high pressure steam or hotflue gas, but also by thermal energy such as solar, biogas frombiomass and hot water [2]. However, crystallization may takesplace in ARS when the refrigeration solution temperature is too low

hew).

[3]. As compared to ARS, an ADS is able to utilize lower temperaturewaste heat and avoid crystallization problems, but its coefficient ofperformance is lower and large volume is required for the adsor-bent [4]. Due to these factors, ADS will not be the focus in thispaper.

Many literature have been carried out to study the energy sav-ings potential that accrue from ARS application in various pro-cesses. Bruno et al. [5] proposed the integration of ARS into anolefin plant raw gas drying process driven by waste heat fromquench oil, it is reported that the proposed network is able torecover 12,807 MWh of waste heat for ARS, and reduce the CO2emission by 720 t CO2/y. Trygg and Amiri [6] presented a model forthe ARS integration into a combined heating and power (CHP).Based on the results, the cooling cost is reduced by 170%, as theelectricity generation from CHP can be sold instead of using it forVCRS. Kalinowski et al. [7] demonstrated the application of ARS inthe liquefied natural gas recovery process, utilizing the high tem-perature exhaust gas generated from the gas turbine, it is reportedthat 5.2 MW of waste heat could be recovered from a 9 MW elec-tricity generation process to drive the ARS, which led to 1.9 MWreduction in electricity consumption for the overall refrigerationsystem. Al-Alili et al. [8] developed a model to study the

Nomenclature

Setsfi;…; iNsourcesg is a set of process sources Ifj;…; jNsinks

g is a set of process sinks Jfp;…; pNplants

g is a set of plants Pfk;…; kARSg is a set of absorption refrigeration system K

ParametersdminSi 2Ip

F Lower limit for return chilled water flowrate (kg/s)dmaxSi 2 Ip

F Upper limit for return chilled water flowrate (kg/s)dminSi 2 Jp

F Lower limit for supply chilled water flowrate (kg/s)dmaxSi 2Jp

F Upper limit for supply chilled water flowrate (kg/s)dminT Minimum temperature limit (�C)dmaxT Maximum temperature limit (�C)dmaxSRS Maximum cooling capacity per chiller unit (RT)dmaxFCT Maximum chilled water flowrate per cooling tower

unit (kg/s)dmaxAHEX

Maximumheat transfer area per unit of heat exchanger(m2)

r Density of water (kg/m3)v Velocity of water in the interplant piping (m/s)a Cooling tower performance coefficientb Percentage loss of circulating water in cooling towerlHS Latent heat of steam (kJ/kg)hP Pump efficiencycP W Specific heat capacity of water (kJ/kg

C)cP FG Specific heat capacity of flue gas (kJ/kg

C)CFG Flue gas treatment cost unit (US$/kg SO2)CHS Steam purchase cost unit (US$/kg)CHW Hot water purchase cost unit (US$/kg)CINIT Initial capital cost (US$/unit)CINCR AS Incremental capital cost of ARS (US$/RT)CINCR VS Incremental capital cost of VCRS (US$/RT)CINCR CT Incremental capital cost of cooling tower (US$/m3)CINCR HEX Incremental capital cost of heat exchanger (US$/m2)CAIR CT Capital cost of cooling tower related to air intake

flowrate (US$/kg air)COP Coefficient of performancee CO2 emission factor (kg CO2/kWh)H Height (m)Ka Annualized factor for capital cost calculationsLp Length of interplant piping (m)ta Annual operating hours (hr)TCWI RS Cooling water inlet temperature to refrigeration

system (�C)TCWO RS Cooling water outlet temperature from refrigeration

system (�C)Ti Source temperature (�C)Tj Sink temperature (�C)TIN FG ARS flue gas inlet temperature (�C)TIN HS ARS steam inlet temperature (�C)TIN HW ARS hot water inlet temperature (�C)TOUT FG ARS flue gas outlet temperature (�C)TOUT2 FG Heat exchanger flue gas outlet temperature (�C)TOUT HS ARS steam outlet temperature (�C)TOUT HW ARS hot water outlet temperature (�C)win Cooling tower inlet air mass fraction (kg water/kg dry

air)wout Cooling tower outlet air mass fraction (kg water/kg dry

air)wSO2

Concentration of SO2 in flue gas (ppm)

UAVG Average heat transfer coefficient (W/m2

C)

Continuous variablesDTLMTD Log-mean temperature differenceAHEX Heat transfer area (m2)ACCT Area of condenser cooling tower mass transfer (m2)CAPAS Capital cost of ARS (US$/year)CAPVS Capital cost of VCRS (US$/year)CAPCCT Capital cost of condenser cooling tower (US$/year)CAPCT Capital cost of individual plant cooling tower (US$/

year)CAPPCp Capital cost of interplant piping (US$/year)E CO2 emission (kg CO2/year)FCW AS;k Cooling water flowrate of ARS (kg/s)FCW VS Cooling water flowrate of VCRS (kg/s)FCW RS Cooling water flowrate from overall refrigeration

system (kg/s)Fi Total source flowrate (kg/s)Fj Total sink flowrate (kg/s)Fi;j Water flowrate from source to sink (kg/s)FR CT;i Return water flowrate from source to individual plant

cooling tower (kg/s)FR VS;i Return water flowrate from source to centralized VCRS

(kg/s)FR AS;i Return water flowrate from source to centralized ARS

(kg/s)FS CT ;j Supply water flowrate from individual plant cooling

tower to sink (kg/s)FS VS;j Supply water flowrate from centralized VCRS to sink

(kg/s)FS AS;j Supply water flowrate from centralized ARS to sink

(kg/s)FR AS;k Return chilled water to individual ARS (kg/s)FFG Sum flowrate of flue gas from all plants (kg/s)FHS Sum flowrate of steam from all plants (kg/s)FHW Sum flowrate of hot water from all plants (kg/s)FRHW AS;k¼3 Hot water recycle flowrate (kg/s)FDHW AS;k¼3 Hot water discharge flowrate (kg/s)FFG AS;k¼1 Flue gas flowrate to flue gas ARS (kg/s)FHS AS;k¼2Steam flowrate to steam ARS (kg/s)FHW AS;k¼3 Hot water flowrate to hot water ARS (kg/s)FFG EX Unwanted flue gas flowrate (kg/s)FHS EX Unwanted steam flowrate (kg/s)FHW EX Unwanted hot water flowrate (kg/s)FAIR CCT Condenser cooling tower air intake flowrate (kg/s)FBLD CCT Condenser cooling tower blowdown water flowrate

(kg/s)FDRF CCT Condenser cooling tower drifted water flowrate (kg/s)FEVP CCT Condenser cooling tower evaporates flowrate (kg/s)IFG Flue gas treatment cost (US$/year)IHS Steam purchase cost (US$/year)IHW Hot water purchase cost (US$/year)Kx Cooling tower mass transfer coefficient (kW/m2 C)MCCT Merkel’s number of condenser cooling towerNAS Quantity of ARS unitNCT Quantity of individual plant cooling tower unitNCCT Quantity of condenser cooling tower unitNVS Quantity of VCRS unitPC VS Power consumption by VCRS compressor (kW)PF Power consumption by cooling tower fan (kW)PP Power consumption by water pump (kW)SAS;k Cooling capacity of ARS (RT)QAC AS;k Heat withdrawn from ARS absorber-condenser (kW)

W.M. Chan et al. / Energy 141 (2017) 1555e15681556

QEV AS;k Heat absorbed to ARS evaporator (kW)QWH AS;k Waste heat energy for individual ARS (kW)QHEX Heat transfer in heat exchanger (kW)TR CT ;i Return water temperature from source to individual

plant cooling tower (�C)TR VS;i Return water temperature from centralized VCRS to

sink (�C)TR AS;i Returnwater temperature from centralized ARS to sink

(�C)TS CT ;j Supply water temperature from individual plant

cooling tower to sink (kg/s)TS VS;j Supply water temperature from centralized VCRS to

sink (kg/s)

TS AS;j Supply water temperature from centralized ARS to sink(kg/s)

VCT Fill volume of individual plant cooling tower (m3)VCCT Fill volume of condenser cooling tower (m3)

Binary variablesZR AS;i Binary variable to determine the existence of a pipeline

from plant p to the centralized ARSZS AS;j Binary variable to determine the existence of a pipeline

from the centralized ARS to plant pZR AS;i Binary variable to determine the existence of a pipeline

from plant p to the centralized VCRSZS AS;j Binary variable to determine the existence of a pipeline

from the centralized VCRS to plant p

W.M. Chan et al. / Energy 141 (2017) 1555e1568 1557

performance of a 10 kW solar driven single effect ARS, the reportedelectricity consumption and CO2 emission is 47% and 12 t/y lesserthan VCRS, taken into consideration the electricity required forARS’s hot water heater and pump. Salmi et al. [9] developed asteady state thermodynamic model for the application of ARS uti-lizing waste heat generated from the main engine of a ship, it isestimated that the ARS integration could reduce the electricityconsumption by 70% compared to VCRS, which yields approxi-mately 46.8 t/y of fuel. Kwak et al. [10] proposed a modeling anddesign framework to study the economic performance of ARS uti-lizing low grade waste heat as heat source. It is reported that theARS is less profitable compared to VCRS due to high capital cost, butthe energy savings can outweigh the capital cost if the requiredduty becomes greater. Nonetheless, in order to justify this concept,an approach is required to determine the minimum duty inachieving the capital-energy trade-off.

On the other hand, hybrid refrigeration systems that combinesVCRS and ARS have been studied. Han et al. [11] proposed a hybridabsorption-compression refrigeration system driven by mid tem-peraturewaste heat, the coefficient of performance of the proposedsystem is 41.9% higher than that of ARS. Jain et al. [12] developed athermodynamic model for cascaded vapor compression-absorptionrefrigeration system, the reported coefficient of performance is155% higher with respect to VCRS. Although these hybrid refriger-ation systems have shown improvements in the coefficient ofperformance, they will not be considered in this study as they arestill in the research stage. Aside from the types of refrigerationsystem selection, the operating parameters are crucial in opti-mizing chilled water system. Many studies have investigated therelationship between refrigeration system performance and itsoperating parameters, such as the chilled water return temperature[13], chilled water supply temperature and flowrate [14]. Besides,various design frameworks are presented to synthesize an opti-mum chilled water network system. Lee et al. [15] performed amathematical optimization for a chilled water network, which aimsto minimize chilled water usage by including all possible networkconfiguration into superstructure and simultaneously reducing thenetwork complexity. Foo et al. [16] presented the targeting anddesign of chilled water networks based on pinch analysis, the tar-geting technique employed graphical and algebraic tools to deter-mine the minimum chilled water flowrate.

Most of the literature suggested that the implementation ofwaste heat recovery technology such as ARS could lead toremarkable reduction in electricity consumption and carbon foot-print. However, the implementation of green technology is alwaysdone at the expense of higher capital investment cost [17]. One ofthe approaches to overcome the high capital investment cost is to

ensure the cooling duty and thewaste heat sources are significantlylarge to achieve the economies of scale. This can be done throughthe formation of EIP to promote the exchange of materials, energy,water, and by-products among the participating plants [18]. Theindustrial symbiosis relationship in the EIP offers attractive eco-nomic and environment advantages to further enhance the overallenergy savings and carbon reduction. Various articles studied onthe utilization of waste heat and the optimization of waste heatrecovery network within an EIP. Chae et al. [19] analyzed the in-dustrial energy consumption and proposed an energy strategy foran EIP utilizing waste steam and waste water, which can be usedsolely or mixed to supply low pressure steam or hot water for otherplants. It is reported that the optimized network with minimumcost consumes more waste steam thanwaste water, as waste steamhas greater heat quality. Hip�olito-Valencia et al. [20] presented amathematical model integrating both ARS and CHP in an EIP,allowing both intraplant and interplant heat integration. Besides,the capital cost, operating cost, and the sale of excess electricitygenerated from the CHP have been considered in the evaluation ofoverall costs. Chew et al. [21] performed pinch analysis for total siteheat integration on the hot and cold streams in the participatingplants to maximize the overall energy savings. Zhang et al. [22]proposed a waste heat recovery network within an EIP toimprove the overall energy efficiency by promoting interplantsharing of hot streams. Abdul Aziz et al. [23] developed a frame-work for low CO2 industrial site planning to explore the potentialfor total site heat recovery using heat exchangers and CHP. Hassibaet al. [24] presented a network that recover different grades ofwaste steam generated from an EIP for electricity and hot watergeneration through CHP. Nonetheless, the aforementioned worksfocused on the waste heat recovery from a single waste heat type, aresearch gap remains to analyze the various types waste heat asheat source during the integration of ARS and VCRS in the chilledwater network system within an EIP, and to apply direct heatintegration between the different waste heat types to improve theenergy efficiency.

The previous work from Leong et al. [25] developed an MINLPmodel that involves the superstructure of a chilled and coolingwater network in an EIP, the network is integrated with centralizedVCRS to generate chilled water for the participating plants. It isreported that a centralized VCRS with cooling water integrationgave the lowest total annual cost compared to individual plantVCRS. In this paper, the authors extend the previous work byconsidering the recovery of process waste heat to minimize elec-tricity usage. With that, this work focuses on the synthesis of anenergy efficient chilled and cooling water network with integrationof the centralized ARS-VCRS. The purpose of this network is to

W.M. Chan et al. / Energy 141 (2017) 1555e15681558

maximize energy savings through the utilization of different wasteheat types generated from an EIP, typically waste hot water andsteam from process heating; waste hot flue gas from gas engine,furnace and boiler exhaust.

2. Problem statement

Given a set of industrial plants p2 P, each of which is desired toreduce the environmental impact by converting process waste heatto valuable resources. These participating plants are intended torecover waste heat in a centralized ARS-VCRS within an EIP (Fig. 1).Each participating plant has its own set of process cooling demands(sinks j 2 J) and return streams (sources i 2 I) with predefinedtemperatures and flowrates. Given also the available waste heat (k2 K) with predefined temperature and specific heat capacitywithin the EIP. Three different waste heats in the form of flue gas,steam and hot water are used to drive the ARS. It is intended tosynthesize a cost optimal chilled and cooling water networks withintegrated waste heat recovery system, hence the objective func-tion in this work is to minimize overall annual cost. Sensitivityanalysis is carried out to evaluate the capital-energy trade-off forARS-VCRS installation by targeting the minimum waste heat andcooling demand.

3. The optimization model

In this section, the mathematical modeling equations developedfor the scenario analysis are demonstrated. Themodeling equationsfor individual plant cooling tower and VCRS are adopted fromLeong et al. [25], the contents that are presented in this sectionincludes the modeling equation for overall chilled and coolingwater network, ARS, secondary waste heat recovery network(direct heat integration on ARS waste heat streams), condensercooling tower, overall cost calculations and objective function forthe scenario analysis.

The proposed network configuration is as shown in Fig. 1, acentralized ARS-VCRS is integrated into the chilled and coolingwater network in order to supply chilled water for the three plantsin the EIP (Plant A, Plant B, and Plant C). It is notable that thecentralized VCRS are integrated along with ARS instead of beingreplaced by ARS because the waste heat may be insufficient tosustain the entire chilled and cooling water network capacity. Asidefrom that, each plant is assumed to have an individual coolingtower for the process water.

PLANT A

PLANT B PLANT C

ARS-VCRS

Fig. 1. Schematic of the proposed centralized ARS-VCRS configuration.

3.1. Overall chilled and cooling water network

The overall chilled and cooling water network consists of threeplants in an EIP. The cooling water source is from individual plantcooling tower whereas the chilled water is supplied by thecentralized ARS-VCRS. The mass and energy balance equations forsource and sinks are shown in Eqs. (1)e(6) and the temperatureconstraints are presented in Eqs. (7)e(12).

� Xj 2 J

Fi;j�þ FR CT;i þ FR VS;i þ FR AS;i ¼ Fi ci 2Ip;cp2 P

(1)

� Xj 2 J

Fi;jTi�þ FR CT ;iTR CT;i þ FR VS;iTR VS;i þ FR AS;iTR AS;i

¼ FiTi ci 2Ip;cp2 P (2)

� Xi 2 I

Fi;j�þ FS CT;j þ FS VS;j þ FS AS ¼ Fj cj 2Jp; cp2P (3)

� Xi 2 I

Fi;jTi�þ FS CT ;jTS CT þ FS VS;jTS VS þ FS AS;jTS AS

¼ FjTj cj 2Jp; cp2P (4)

Xi 2 I

FR AS;i ¼Xj 2 J

FS AS;j (5)

Xi 2 I

FR AS;i ¼Xk 2 K

FR AS;k (6)

dminTR CT;i

� TR CT;i � dmaxTR CT;i

(7)

dminTR VS;i

� TR VS;i � dmaxTR VS;i

(8)

dminTR AS;i

� TR AS;i � dmaxTR AS;i

(9)

dminTS CT

� TS CT � dmaxTS CT

(10)

dminTS VS

� TS VS � dmaxTS VS

(11)

dminTS AS

� TS AS � dmaxTS AS

(12)

where Fi;j is the flowrate from source to sink. FR CT;i, FR VS;i, andFR AS;i is the return flowrate to cooling tower, VCRS, and ARS; FS CT;j,FS VS;j, and FS AS;j is the supply flowrate from cooling tower, VCRSand ARS to sink; Fi and Fj is the total source and sink flowrate; Tiand Tj is the source and sink temperature; TR CT ;i, TR VS;i, and TR AS;iis the return temperature from source to cooling tower, VCRS andARS; TS CT ;j, TS VS;j, and TS AS;j is the supply temperature fromcooling tower, VCRS and ARS to sink; FR AS;k is the return chilledwater flowrate to individual ARS, k defines a set of different types ofARS (k ¼ 1, k ¼ 2, and k ¼ 3 represents flue gas ARS, steam ARS, andhot water ARS, respectively). The return and supply temperature ofcooling tower, VCRS, and ARS are constrained by a minimumtemperature limit, dmin

T , and maximum temperature limit, dmaxT . The

values of the limits are shown in Table 1. Note that the coolingtower in this section refers to the individual plant cooling tower,the modeling equations for condenser cooling tower will be pre-sented in section 3.4.

Table 1Parameter values for the optimization model.

Parameter Value Parameter Value

dminSi 2Ip

F 0.5 kg/s CINIT AS;k¼1 495,000 US$

dmaxSi 2 Ip

F 1000 kg/s CINIT AS;k¼2 495,000 US$

dminSi 2Jp

F 0.5 kg/s CINIT AS;k¼3 385,000 US$

dmaxSi 2Jp

F 1000 kg/s CINIT VS 275,000 US$

dminTR CT;i

35 �C CINIT CT 31,185 US$

dmaxTR CT;i

75 �C CINIT PC 250 US$

dminTR VS;i

15 �C CINIT HEX 3000 US$

dmaxTR VS;i

25 �C CINCR PC 7200 US$/m2

dminTR AS;i

15 �C CINCR AS;k¼1 450 US$/rt

dmaxTR AS;i

25 �C CINCR AS;k¼2 450 US$/rt

dminTS CT

15 �C CINCR AS;k¼3 350 US$/rt

dmaxTS CT

25 �C CINCR VS 250 US$/rt

dminTS VS

5 �C CINCR HEX 68 US$/m2

dmaxTS VS

8 �C CINCR CT 1606 US$/m3

dminTS AS

5 �C CAIR CT 1097.5 US$/(kg dry air/s)

dmaxTS AS

8 �C COPAS;k¼1 1.4

dmaxSRS

3300 RT COPAS;k¼2 1.4

dmaxFCT

750 kg/s COPAS;k¼3 0.7

dmaxAHEX

1000 m2 COPVS 4.0

r 1000 kg/m3 H 10 mv 1 ms-1 Ka 0.256a 0.0105 Lp 300 mb 0.002 ta 7920 h/ylHS 2258 kJ/kg TCWI RS 30 �ChP 0.82 TCWO RS 38 �CcP W 4.18 kJ/kg�C TIN FG 480 �CcP FG 1.02 kJ/kg�C TIN HS 170 �CCFG 1.00 US$/kg SO2 TIN HW 152 �CwSO2

500 ppm flue gas TOUT FG 95 �CCHS 4.40 US$/kg steam TOUT HS 95 �CCHW 0.05 US$/m3 TOUT HW 85 �Cg 9.81 m/s2 wIN 0.005 kg-water/kg-dry-airUAVG 250 W/m2�C wOUT 0.02 kg-water/kg-dry-air

W.M. Chan et al. / Energy 141 (2017) 1555e1568 1559

3.2. Absorption refrigeration system (ARS)

The types of refrigerants that are commonly used in ARS areNH3-H2O and LiBr-H2O. As compared to LiBr-H2O ARS, NH3-H2OARS can supply chilled water at very low temperature (below 0 C),but it has a lower coefficient of performance and the refrigerantammonia is toxic [26]. Since the minimum temperature of chilledwater in this paper is 5 �C which is within the typical temperaturerange of chilled water [27], LiBr-H2O ARS is selected for the model.The inlet/outlet temperature for flue gas, steam, and hot water aredefined according to the temperature setting stated in ShuangLiangH2O-LiBr ARS [28], which is 480 �C/170 �C, 152 �C/95 �C, and 95 �C/85 �C, respectively. The maximum capacity of a chiller is 3300refrigeration tons (RT). Besides, according to the temperaturerequirement, a single effect ARS is selected for hot water, whiledouble effect ARS is selected for steam and hot flue gas [29]. Thecoefficient of performance is 0.7 single effect ARS and 1.4 for doubleeffects ARS, respectively [30]. In this paper, the refrigerant pumpwork in the ARS is assumed negligible because it is relativelyinsignificant compared to the heat input [31].

The modeling equations for ARS waste heat utilization areshown as follow:

QWH AS;k¼1 ¼ FFG AS;k¼1cP FG�TIN FG � TOUT FG

�(13)

QWH AS;k¼2 ¼ FHS AS;k¼2�lHS þ cP W

�TIN HS � TOUT HS

��(14)

QWH AS;k¼3 ¼ FHW AS;k¼3cP W�TIN HW � TOUT HW

�(15)

FFG ¼X

p 2 P

FFG;p (16)

FHS ¼X

p 2 P

FHS;p (17)

FHW ¼X

p 2 P

FHW ;p (18)

FFG ¼ FFG AS;k¼1 þ FFG EX (19)

FHS ¼ FHS AS;k¼2 þ FHS EX (20)

FHW ¼ FHW AS;k¼3 þ FHW EX (21)

where QWH AS;k¼1, QWH AS;k¼2, and QWH AS;k¼3 is the energyrequired to operate flue gas, steam and hot water ARS, these wasteheat energy are absorbed into the system through the generator;cP W and cP FG is the specific heat capacity of water and flue gas; lHSis the latent heat of steam; TIN FG, TIN HS, and TIN HW is the inlettemperature of flue gas, steam and hot water ARS; TOUT FG, TOUT HS,and TOUT HW is the outlet temperature of flue gas, steam and hotwater ARS; FFG, FHS, and FHW is the summation of flue gas, steamand hot water flowrate collected from each plants; FFG AS;k¼1,FHS AS;k¼2, and FHW AS;k¼3 is the flue gas, steam and hot waterflowrate used for its individual ARS operation; FFG EX , FHS EX , andFHW EX are the unwanted extra waste heat.

The total energy balance for ARS operation including theabsorber, condenser, generator, evaporator are presented in Eqs.(22)e(29). Eqs. (30) and (31) depict the power consumption ofprocess water pump.

QAC AS;k ¼ QWH AS;k þ QEV AS;k ck2K (22)

QWH AS;k ¼QEV AS;k

COPAS;kck2K (23)

QEV AS;k ¼ FR AS;k cP W�TR AS;i � TS AS;j

�ck2K (24)

SAS;k ¼ 0:285�QEV AS;k

�ck2K (25)

NAS;k ¼ ROUNDUP�SAS;k

.dmaxSRS

�ck2K (26)

NAS ¼Xk 2 K

NAS;k (27)

QAC AS;k ¼ FCW AS;k cP W�TCWO RS � TCWI RS

�ck2K (28)

FCW AS ¼Xk 2 K

FCW AS;k (29)

PP AS;k ¼FR AS;kHRSg1000hP AS

ck2K (30)

W.M. Chan et al. / Energy 141 (2017) 1555e15681560

PP AS ¼Xk 2 K

PP AS;k (31)

where COPAS;k is the individual ARS’s coefficient of performance(COP); HRS is the height of the refrigeration system; hP AS is thewater pump efficiency; PP AS;k is the power consumption of waterpump by each type of ARS; PP AS is the total water pump powerconsumption from overall ARS; QAC AS;k is the heat withdrawn fromARS absorber-condenser operation; QEV AS;k is the heat required forevaporator of the ARS; TCWI RS and TCWO RS is the inlet and outlettemperature of cooling water for the refrigeration system; FCW AS;kis the coolingwater flowrate required for the individual ARS; SAS;k isthe cooling capacity expressed in RT; NAS;k is the unit quantity foreach type of ARS; NAS is the total quantity of ARS. dmax

SRS is themaximum capacity per chiller unit; g is the gravitationalacceleration.

To determine the existence of the pipelines between thecentralized ARS and plant P, the constraints are formulated asfollow:

Xi 2 Ip

FR AS;i � dminSi 2Ip

FR AS;iZR AS;i � 0 cp2P (32)

Xi 2 Ip

FR AS;i � dmaxSi 2 Ip

FR AS;iZR AS;i � 0 cp 2P (33)

Xi 2 Jp

FS AS;j � dminSi 2Jp

FS AS;jZS AS;j � 0 cp2P (34)

Xi 2 Jp

FS AS;j � dmaxSi 2Jp

FS AS;jZS AS;j � 0 cp2P (35)

where dminSi 2Ip

FR AS;i and dmaxSi 2 Ip

FR AS;i is the lower and upper limit ofARS return chilled water flowrate; dmin

Si 2JpFars;j and dmax

Si 2JpFars;j is the

lower and upper limit of ARS supply chilled water flowrate; ZR AS;i isthe binary variable to determine the existence of pipeline fromplant p to the centralized ARS; ZS AS;j is the binary variable todetermine the existence of pipeline from the centralized ARS chillerto plant p. Note that for VCRS, the modeling equations are similar toEqs. (22)e(35), except the cooling water is only require forcondenser operation and QWH AS;k is replaced with electricity en-ergy for compressor operation in the VCRS, PC VS.

Flue gas ARS

Steam ARS

Hot water ARS

Flue gas inletT=480 C

Flue gT=

Steam inletT=152 C

SteacondeT=9

Hot water inletT=95 C

Hot wT=

Fig. 2. Proposed secondary was

3.3. Secondary waste heat recovery network

According to the temperature setting of ARS waste heat outlet asmentioned in section 3.2, the flue gas outlet temperature is 170 �C,the steam condensate outlet temperature is 95 �C, and the hotwater outlet temperature is 85 �C. The temperature difference be-tween waste heat outlet streams offers the opportunity forapplying heat integration to enhance energy savings. Namely, asecondary waste heat recovery network is introduced (Fig. 2). Asshown, the hot water outlet stream acts as an ARS recycle stream toretrieve thermal energy from flue gas outlet and steam condensateoutlet. A heat exchanger is used to transfer the heat from flue gasoutlet to the recycle stream. Whereas for steam condensate outlet,since it has a similar medium as the hot water inlet, it can be feddirectly to the recycle stream.

In order to model the secondary waste heat recovery network,the hot water outlet stream is first separated into two streams, hotwater recycle and hot water discharge (Eq (36)). The hot waterrecycle then enters the heat exchanger as a cold stream with fluegas outlet as the hot stream, the area and unit quantity of heatexchangers are evaluated accordingly (Eqs. (37)e(40)).

FHW AS;k¼3 ¼ FRHW AS;k¼3 þ FDHW AS;k¼3 (36)

QHEX ¼ FFG AS;k¼1cP;water�TOUT FG � TOUT2 FG

�(37)

QHEX ¼ FRHW AS;k¼3cP;water�TIN HW � TOUT HW

�(38)

AHEX ¼ QHEX=ðUAVGDTLMTDÞ (39)

NHEX ¼ ROUNDUP�AHEX

.dmaxAHEX

�(40)

where FRHW AS;k¼3 is the hot water recycle flowrate; FDHW AS;k¼3 isthe hot water discharge flowrate; QHEX is the heat transfer betweenthe hot stream and cold stream; TOUT2 FG is the temperature of fluegas discharge from secondary waste heat recovery network;DTLMTDis the log-mean temperature difference; UAVG is the average heattransfer coefficient for gas-water heat transfer; AHEX is the mini-mum heat transfer required; NHEX is the number of heat exchanger;dmaxAHEX

is the maximum heat transfer area for a commercial heatexchanger.

Finally, the hot water recycle will mixed with the steam

HEX

as outlet170 C

mnsate5 C

ater outlet85 C

Hot waterdischargeT=85 C

Flue gas dischargeT=100 C

Hot waterrecycleT=85 C

Hot waterrecycleT=95 C

Secondary waste heat recovery

te heat recovery network.

W.M. Chan et al. / Energy 141 (2017) 1555e1568 1561

condensate and the ARS hot water inlet. In order to incorporatethese changes into the model, Eq (13) is modified to Eq (42).

FRHWI AS;k¼3 ¼ FRHW AS;k¼3 þ FHS AS;k¼2 þ FHW AS;k¼3 (41)

QWH AS;k¼3 ¼ FRHWI AS;k¼3cP W�TIN HW � TOUT HW

�(42)

where FRHWI AS;k¼3 is the new ARS hot water inlet flowrate if sec-ondary waste heat recovery network is considered.

3.4. Condenser cooling tower network

Cooling tower is required for chiller because heat rejection isneeded for the condenser operation in VCRS, and for the absorber-condenser operation in ARS. In this paper, a cooling tower networkis shared by both ARS and VCRS as they require similar return andsupply cooling water temperature (Fig. 3). The difference betweentemperature for the cooling water inlet and outlet for thecondenser is limited to 8

C, with an inlet temperature of 30

C andoutlet temperature of 38 �C, as crystallization of refrigerant mightoccur if the inlet temperature of cooling water is too low [32]. Themaximum flowrate for cooling tower with the mentioned tem-perature setting is 750 kg/s [33].

The cooling tower in this section refers to the refrigerationsystem. The modeling equation Eqs. (43)e(45) are used to deter-mine the flowrate of air intake and evaporates as a function of inletair humidity, condenser cooling water flowrate and the tempera-ture range [34]. Eqs. (46)e(53) are adopted from Leong et al. [25],which are used to determine the fan and pump power consump-tion, fill volume and makeup water flowrate.

FCW RS ¼ FCW AS þ FCW VS (43)

FEVP CCT ¼ 0:00153FCW RS�TCWO RS � TCWI RS

�(44)

FAIR CCT ¼ FEVP CCT

ð1�wOUT ÞðwOUT �wINÞ(45)

FBLD CCT ¼ FEVP CCT

CC � 1(46)

FDRF CCT ¼ bFCW RS (47)

Ev

Cooling waterRefrigerant

Compressor

Condenser

Expansionvalve

Evaporator

VCRS

Fig. 3. Condenser cooli

FMUP CCT ¼ FEVP CCT þ FBLD CCT þ FDRF CCT (48)

KxACCT ¼ 2:95�FCW RS

�0:26�FAIR CCT�0:72 (49)

MCCT ¼�

FCW RS

FAIR CCT

�0:5(50)

VCCT ¼ MCCTFCW RS

KxACCT(51)

PF CCT ¼ aFCW RScP W�TCWO RS � TCWI RS

�(52)

PP CCT ¼ FCW RSHCTg1000hP CCT

(53)

NCCT ¼ ROUNDUP�FCW RS

.dmaxFCT

�(54)

where FCW RS is the total cooling water flowrate for the overallcondenser system; FCW VS is the cooling water flowrate for VCRS;FEVP CCT is the flowrate of cooling tower evaporates. FAIR CCT is theair intake flowrate; FBLD CCT is the blowdown water flowrate; CC isthe cycle of concentration; wout and win is the humidity of theoutlet and inlet air; FDRF CCT is the drift loss flowrate; b is the per-centage of loss on circulating water. Kx is the mass transfer coeffi-cient; ARCT is the mass transfer area of cooling tower; MCCT is theMerkel’s number; VCCT is the cooling tower fill volume; PF CCT andPP CCT is the cooling tower’s fan and water pump power con-sumption; a is the cooling tower performance coefficient; hP CCT isthe water pump efficiency; HCT is the height of cooling tower; NRCTis the quantity of cooling tower; dmax

FCT is the maximum flowrate perunit of cooling tower. Note that the modeling equation for indi-vidual plant cooling tower is similar to Eq (43) e (54).

3.5. Cost equations

According to Peter et al. [35], the purchase cost of an equipmentincreases with its capacity, and it is accounted for only 15%e40% ofits total capital investment cost. The rests include initial capitalcosts for installation, instrumentation and controls, piping, elec-trical equipment, buildings, services, yard improvements and lands.A large size equipment is often more economical compared tomultiple smaller size equipment with similar total capacity,

Absorber

Generator

Condenser

aporator

Cooling tower

ARS

ng tower network.

W.M. Chan et al. / Energy 141 (2017) 1555e15681562

because the initial capital costs can be reduced. To include theinitial capital cost factor in the modeling, the initial capital costs ofrefrigeration system is based on the quantity of chiller unit and isassumed 60% of the total capital cost for a medium size refrigera-tion system. The initial capital cost for the remaining technologiesare obtained from the literature mentioned below. The modelingequation for the capital cost calculations are as follow:

CAPAS ¼ Ka�CINITASNAS þ CINCRAS

SAS�

(55)

CAPVS ¼ Ka�CINIT VSNVS þ CINCR VSSVS

�(56)

CAPHEX ¼ Ka�CINIT HEX NHEX þ CINCR HEXAHEX

�(57)

CAPCCT ¼ Ka�CINIT CT NCCT þ CINCR CTVCCT þ CAIR CTFAIR CCT

�(58)

CAPCT ¼ Ka�CINIT CT NCT þ CINCR CTVCT þ CAIR CTFAIR CT

�(59)

CAPPCp ¼ Ka�CINIT PC

�ZR VS;i þ ZS VS;j þ ZR AS;i þ ZS AS;j

��

cp2 P

(60)

where CAPAS, CAPVS, CAPHEX, CAPCCT , CAPCT , CAPPCp is the capitalcost for ARS, VCRS, heat exchanger, condenser cooling tower, in-dividual plant cooling tower, and interplant piping; Ka is theannualized factor for capital cost calculations; CINIT and CINCR rep-resents the initial and incremental capital cost factor; CAIR CT is thefixed cost parameter of the cooling tower based on air mass flow-rate, FAIR; VCT and VCCT is the fill volume of individual plant coolingtower and condenser cooling tower; Lp is the length of the inter-plant piping; r and v is the density and velocity of water. The sourceof capital costs for ARS and VCRS is Englemen [36], cooling towerand piping cost are obtained from Leong et al. [25]. The capital costof heat exchangers are fitted using data from Peter et al. [35].

The operating costs that are considered in this paper include theelectricity cost for cooling tower and VCRS operations, makeupwater cost for cooling tower, treatment cost for flue gas to removecorrosive components, and the purchase cost of waste steam andhot water from the plants. The modeling equations for thesecomponents are shown as follow:

Table 2Water limiting data for Plants A, B, and C [25].

Plant Sink, j Flowrate, Fj (kg/s) Temperature, Tj (�C)

A SK-A1 360 5SK-A2 400 12SK-A3 120 20SK-A4 320 25

B SK-B1 210 5SK-B2 260 17SK-B3 300 24

C SK-C1 400 8SK-C2 380 16

Total 2750

OPCccwn; ¼ ta�CELCTAP þ CW

�FMUP RCT þ FMUP CT

�þ IFG þ IHSþ IHW

�(61)

TAP ¼X

p 2 P

�PF CT þ PP CT

� þ PC VS þ PP VS þ PP AS þ PF CCT

þ PP CCT

(62)

IFG ¼ taFFG AS;k¼1wSO2CFG (63)

IHS ¼ taFHS AS;k¼2CHS (64)

IHW ¼ taFHW AS;k¼3CW (65)

where ta is the annual operating hours; IFG is the treatment cost offlue gas; IHS and IHW is the purchase cost of steam and hot waterfrom the individual plant; PF CT and PF CCT stands for the powerconsumption by individual plant and condenser cooling tower fan;CFG, CHS, and CHW is the cost unit for flue gas, steam and hot water;wSO2

is the concentration of SO2, which has a value of 500 ppmaccording to Min et al. [37]. The treatment cost of flue gas is ob-tained from Cichanowicz [38]. The purchase cost of water andsteam is set according to utilities costs in Peter et al. [35]. Thecapital cost units and operating cost units are summarized inTable 1.

3.6. Objective function

The objective function used for the superstructure optimizationis to minimize the total annualized cost, TAC. The full equation forthe objective function is shown as follow:

minðTACÞ ¼ CAPCT þ CAPCCT þ CAPVCRSþ CAPHEX þ CAPARS

þ CAPPC þ OPCccwn

(66)

The definition of each cost component is discussed in section3.5. Scenario 1 adopted the superstructure from Leong et al. [25],where the chilled and cooling water network contains centralizedVCRS without the consideration of waste heat, the term of CAPARSand CAPHEX can be taken out from the objective function. Scenario2 considers only centralized ARS with VCRS, hence CAPHEX is

Source, i Flowrate, Fi (kg/s) Temperature, Ti (�C)

SR-A1 250 11SR-A2 280 20SR-A3 340 35SR-A4 80 58SR-A5 200 65SR-A6 50 70

SR-B1 100 10SR-B2 160 28SR-B3 280 48SR-B4 230 65

SR-C1 200 12SR-C2 100 35SR-C3 480 45

2750

Table 3Waste heat profile for each participating plant.

Plant Hot water flowrate, FFG AS;k¼1 (kg/s) Steam flowrate, FHS AS;k¼2 (kg/s) Flue gas flowrate, FHW AS;k¼3 (kg/s)

A 205.0 1.0 12.0B 180.0 0.8 8.0C 10.0 0.2 2.0

W.M. Chan et al. / Energy 141 (2017) 1555e1568 1563

removed from the objective function. For scenario 3, secondarywaste heat recovery network is included, thus the exact Eq. (66) isused as the objective function.

Aside from cost performance, the total CO2 emission of theoverall chilled and cooling water network is evaluated using themodeling equation as follow:

E ¼ TAP � e (67)

where E is CO2 emission and e is the emission factor with value of0.7488 kg CO2/kWh [39].

Finally, the necessary values for the entire optimization modelincluding the parameters, capital cost units, operating cost units,maximum limit and minimum limit for the variables mentionedabove are summarized in Table 1.

4. Scenario analysis

Three scenarios are investigated in this section. Scenario 1 isadopted from Leong et al. [25], where centralized VCRS is used, itrepresents the synthesis of a conventional chilled and coolingwater network which uses only electricity in the chilled watergeneration. Scenario 2 illustrates the proposed centralized ARS-VCRS which maximizes the reutilizing of the available processwaste heat, before considering the use of fresh electricity in thechilled water generation. Scenario 3 proposed to further promotethe energy efficiency of waste heat recovery by introducing sec-ondary waste heat recovery network, as shown in Fig. 2.

The stream data for process sinks and sources used for thisscenario analysis are given in Table 2, which determines the coolingdemand and supply needed for the overall EIP. The waste heatprofile for each of the participating plants is predefined in Table 3.The proposed superstructure as shown in Fig. 1 is formulated asMINLP models. The MINLP formulation considers the interactionsbetween the process sinks and sources, the waste heat supply, thecentralized ARS-VCRS, and the individual plant cooling towers. ThisMINLP model is solved by using LINGO v16.0 with an integralbranch-and-bound Global Solver. The quality of the chilled andcooling water (i.e., pollutant composition) from the industrial plantin this EIP is not analyzed in this paper. Hence, the mixing of chilledand cooling water sources is not considered. The optimization re-sults for the scenario analysis is discussed in the aspect of overallnetwork performance. Sensitivity analysis is carried out to study

Table 4Overall results.

Parameters Unit

Total annual cost (USD x 106)Overall capital cost (USD x 106)Overall operating cost (USD x 106)VCRS capacity (RT)Flue gas ARS capacity (RT)Steam ARS capacity (RT)Hot water ARS capacity (RT)Overall waste heat reduction (MW)Electricity consumption (MW)CO2 emission (t CO2/h)

the capital-energy trade-off and then to determine the minimumwaste heat amount and cooling demand for ARS-VCRS installation.

4.1. Overall network performance

In this section, the overall network performance of an EIP isevaluated in economic and environmental aspect. The networkcomplexity and the potential for future EIP expansion for eachscenario are also discussed accordingly.

The economic performance is evaluated based on overall annualcost consisting of operating cost and capital cost. The incurred costsfor each scenario are summarized in Table 4. From Table 4, scenario1 has the highest overall annual cost (9.89 � 106 USD), followed byscenario 2 (8.04 � 106 USD) and scenario 3 (7.81 � 106 USD).However, the capital cost in Scenario 3 is the highest (3.56 � 106

USD). The capital cost of scenario 3 is slightly higher than scenario 2(3.55 � 106 USD) because it incurred higher capital cost forinstalling high capacity of ARS to integrate the secondary wasteheat recovery network. Besides, the installation of heat exchangerin scenario 3 contributes in high capital cost. Scenario 2 has ahigher capital cost compared to scenario 1 due to the installation ofARS, which is more expensive compared to VCRS. On the otherhand, scenario 2 (4.49� 106 USD) has a lower overall operating costthan scenario 1 (7.03 � 106 USD) because the utilization of wasteheat has reduced the electricity consumption, hence decreasing theelectricity cost. Scenario 3 has the lowest operating cost of4.25 � 106 USD because the secondary waste heat recoverynetwork enhances the overall energy efficiency. Despite having thehighest capital cost in scenario 3, the overall annual cost is thelowest as the operating cost savings obtained from the utilization ofwaste heat is able to outcompete the expenses. Nonetheless, thehigh capital cost in scenario 3 may cause many small and mediumenterprises to refrain from the implementation due to the financialconstraint. In that, EIP can take on the advantage of symbioticrelationship between big enterprises and small and medium en-terprises, where big enterprises can contribute in financial supportwhile the small and medium enterprises can provide waste heatsupply.

The ARS integration in scenario 2 has recovered 26 MWof wasteheat, and reduced the electricity consumption from 12 MW (sce-nario 1) to 6.2 MW. The integration of secondary waste heat re-covery network in scenario 3 further enhanced the waste heatrecovery to 29 MW and lowered the electricity consumption to

Scenario 1 Scenario 2 Scenario 3

9.89 8.04 7.812.86 3.55 3.567.03 4.49 4.259784 2190 16800 2970 29700 1876 18760 2750 32600 26,000 29,00012.0 6.2 5.89.2 4.6 4.3

W.M. Chan et al. / Energy 141 (2017) 1555e15681564

5.8 MW. Note that the reduction in electricity consumption is lowerthan the amount of waste heat being recovered, this is due to thehigher coefficient of performance in VCRS compared to ARS.Moreover, electricity consumption of any operation is directlyassociated with its carbon footprint, as electricity generation ismainly dependent upon the burning of fossil fuels. The carbonfootprint is the lowest in scenario 3 (4.3 t CO2/h), followed byscenario 2 (4.6 t CO2/h), and scenario 1 (9.2 t CO2/h). Withincreasing evidence that climate change is mainly contributed byhuman activities, governments have taken actions such as incor-porating sustainable development into policy making and imple-menting carbon tax. Eventually, industries strive to reduce theircarbon footprint and achieve carbon neutrality with strategies suchas investing in renewable energy or upgrading to a higher energyefficiency process. In that, the implementation of scenario 3 canreduce further the efforts required to achieve carbon neutrality, asthe CO2 emission in scenario 3 is 53% lower than scenario 1. Asidefrom that, waste heat is subjected to a discharge temperature range,discharging beyond the range could potentially impact the envi-ronment [40]. In this aspect, scenario 3 stands out from the restbecause the integration of ARS with secondary waste heat recoverynetwork utilizes the waste heat to a much lower temperature,

SR.A1 (11 C)

SR.A2 (20 C)

SR.A3 (35 C)

SR.A4 (58 C)

SR.A5 (65 C)

SR.A6 (70 C)

SK.A1(5 C)

SR.A2(12 C)

SK.A3(20 C)

SK.A4(25 C)

SK.B1(5 C)

SK.B2(17 C)

SK.B3(24 C)

MCT,

SR.B1 (10 C)

SR.B2 (28 C)

SR.B3 (48 C)

SR.B4 (65 C)

SR.C1 (12 C)

SR.C2 (35 C)

SR.C3 (45 C)

SK.C1(8 C)

SK.C2(16 C)

MCT,C

MV

250 kg/s

120 kg/s 160 kg/s

120 kg/s

130 kg/s

20 kg/s

40 kg/s360 kg/s

210 kg/s 220 kg/s 30 kg/s

40 kg/s 120 kg/s

50 kg/s 230 kg/s

230 kg/s

171 kg/s

19 kg/s 76 kg/s

480 kg/s

T=43 C556 kg/

229 kg/s 361 kg/s

100 kg/s

Plant B

Plant C

Plant A

29 kg/s

4 kg/s

Electricity

LEGEND:

Process waterCondenser cooling waterChilled water

Fig. 4. Chilled and cooling wat

hence reducing the cooling duty required to achieve the dischargetemperature range.

The chilled and cooling water network of scenario 1 is shown inFig. 4, all the return chilled water streams from the plants are sentto only VCRS. Since VCRS is fully driven by electricity, it has a morestable supply compared to waste heat. Electricity interruption isnormally backup by emergency standby generator, which is astandard practice across industries. The main concerning parame-ters in this scenario are only the flowrate and temperature ofchilled water return and supply. For scenario 2 (Fig. 5), the chilledand cooling water network is integrated with waste heat recoverynetwork for ARS operation, which contributes to networkcomplexity. Since waste heat supply is susceptible to process up-sets, the resulting fluctuations will disrupt the overall chilled watersystem if precautionary measures are absent. In that, a larger ca-pacity of VCRS may be needed to cover for moments with insuffi-cient waste heat. Another option is to employ thermal energystorage to attenuate the fluctuations. Monitoring and controls be-tween the parameters of chilled water system and each individualplant waste heat streams are necessary, to ensure any fluctuationscan be detected and acted upon. On the other hand, scenario 3(Fig. 6) has a more complex network than scenario 2, as the former

MCT,A

MVCRS,A

B

MVCRS.B

CoolingTower C

CRS,C

220 kg/s

80 kg/s

200 kg/s

50 kg/s

T=56 C460 kg/s

s

T=52 C550 kg/s

T=5 C380 kg/s

T=15 C210 kg/s

T=15 C

T=15 C

T=15 C

T=5 C229 kg/s

T=15 C229 kg/s

T=5 C210 kg/s

VCRS x 3(9784 Refrigerant

Tons)

T=5 C210 kg/s

T=15 C380 kg/s

CoolingTower B

Centralized CoolingHub

CoolingTower A

196 kg/s

CoolingTower X 2

T=30 C1280 kg/s

T=38 C1280 kg/s

Electricity8888 kWh

er network for scenario 1.

SR.A1 (11 C)

SR.A2 (20 C)

SR.A3 (35 C)

SR.A4 (58 C)

SR.A5 (65 C)

SR.A6 (70 C)

SK.A1(5 C)

SR.A2(12 C)

SK.A3(20 C)

SK.A4(25 C)

MCT,A

MASC,A

SK.B1(5 C)

SK.B2(17 C)

SK.B3(24 C)

MCT,B

SR.B1 (10 C)

SR.B2 (28 C)

SR.B3 (48 C)

SR.B4 (65 C)

MVCC.B

SR.C1 (12 C)

SR.C2 (35 C)

SR.C3 (45 C)

SK.C1(8 C)

SK.C2(16 C)

MCT,CCoolingTower C

MASC,C

250 kg/s

120 kg/s 160 kg/s

120 kg/s 220 kg/s

80 kg/s

200 kg/s

50 kg/s

130 kg/s

20 kg/s

40 kg/s360 kg/s

210 kg/s220 kg/s 30 kg/s

40 kg/s 120 kg/s

50 kg/s 230 kg/s

230 kg/s

T=56 C460 kg/s

171 kg/s

19 kg/s 76 kg/s

480 kg/s

T=43 C556 kg/s

229 kg/s 361 kg/s

100 kg/s

Flue gas ARS x 1(2970 Refrigerant

Tons)

T=52 C550 kg/s

T=15 C248 kg/s

T=5 C248 kg/s

T=5 C380 kg/sT=15 C

T=15 C

T=15 C

T=15 C229 kg/s

T=5 C210 kg/s

HP steam ARS x 1(1876 Refrigerant

Tons)

Hot water ARS x 1(2750 Refrigerant

Tons)

T=5 C183 kg/s

T=5 C72 kg/s

T=5 C230 kg/s

T=5 C157 kg/s

CoolingTower B

Centralized Cooling Hub

CoolingTower A

Plant B

Plant C

Plant A

T=15 C72 kg/s

T=15 C131 kg/s

29 kg/s

4 kg/s

196 kg/s

VCRS x 1(2190 Refrigerant

Tons)

T=15 C157 kg/s

T=15 C183 kg/s

T=15 C230 kg/s

T=5 C131 kg/s

CoolingTower x 3

T=30 C1838 kg/s

T=38 C1838 kg/s

T=30 C547 kg/s

T=30 C659 kg/s

T=30 C286 kg/s

T=30 C346 kg/s

T=38 C547 kg/s

T=38 C659 kg/s

T=38 C286 kg/s

T=38 C346 kg/s

Electricity2284 kWh

Hot water inletT=95 C295 kg/s

Hot water outletT=95 C295 kg/s

Flue gas inletT=480 C22 kg/s

Flue gas outletT=170 C22 kg/s

HP steam inletT=152 C2 kg/s

Steam condensateT=90 C2 kg/s

T=15 C210 kg/s

T=15 C27 kg/s

T=5 C27 kg/s

ElectricityHot waterSteam

LEGEND:

Hot flue gasProcess waterCondenser cooling waterChilled water

Fig. 5. Chilled and cooling water network for scenario 2.

W.M. Chan et al. / Energy 141 (2017) 1555e1568 1565

network is integratedwith secondarywaste heat recovery network,which comprised of an additional heat exchanger and a waste heatrecycle stream to hot water ARS. The quality of waste heat recyclestream must be monitored carefully as it has a direct effect on theARS performance. Since the parameters of waste heat recyclestream are associated with ARS waste heat outlet streams, aproperly designed control system is required specifically for thesecondary waste heat recovery network to determine the optimumrecycle ratio based on the parameters of waste heat outlet streams.

The future expansion of scenario 1 is limited by its overrelianceon electricity usage. Since the main energy source for electricitygeneration is fossil fuel, which is in the midst of scarcity, theimplementation of scenario 1 will not assist the EIP development inthe long run because it lacks the solution to reduce dependency onelectricity consumption. Scenario 2 exhibits greater expansionpotential compared to scenario 1, as the centralized cooling hub inscenario 2 comprised of both VCRS and ARS, which can accom-modate any types of waste heat generated by other plants in future

expansion. Besides, the price of electricity is predicted to raise inthe near future [41], which means the operating cost savings ob-tained from ARS can potentially increase alongside the develop-ment of EIP. These factors combined with the ability of ARS to causeremarkable reduction in carbon footprint have enhanced the futureexpansion potential of scenario 2. For scenario 3, the energy savingsobtained from secondary waste heat recovery network is propor-tional to the amount of waste heat, this makes scenario 3 moreappealing in the aspect of future expansion, as the increase inwasteheat amount is a predictable phenomenon when an EIP expands.Besides, it is also anticipated that the waste heats generated fromthe future participating plants may have temperature lower thanthe specification temperature limit for ARS waste heat input.Instead of disregarding these waste heats, they can be sent directlyto the secondary waste heat recovery network to enhance energyefficiency of the overall network without affecting the performanceof ARS. In brief, scenario 3 has themost significant future expansionpotential as it comprised of both ARS and secondary waste heat

Chilled water

SR.A1 (11 C)

SR.A2 (20 C)

SR.A3 (35 C)

SR.A4 (58 C)

SR.A5 (65 C)

SR.A6 (70 C)

SK.A1(5 C)

SR.A2(12 C)

SK.A3(20 C)

SK.A4(25 C)

MCT,A

MASC,A

SK.B1(5 C)

SK.B2(17 C)

SK.B3(24 C)

MCT,B

SR.B1 (10 C)

SR.B2 (28 C)

SR.B3 (48 C)

SR.B4 (65 C)

MVCC.B

SR.C1 (12 C)

SR.C2 (35 C)

SR.C3 (45 C)

SK.C1(8 C)

SK.C2(16 C)

MCT,CCoolingTower C

MASC,C

250 kg/s

120 kg/s 160 kg/s

120 kg/s 220 kg/s

80 kg/s

200 kg/s

50 kg/s

130 kg/s

20 kg/s

40 kg/s360 kg/s

210 kg/s 220 kg/s 30 kg/s

40 kg/s 120 kg/s

50 kg/s 230 kg/s

230 kg/s

T=56 C460 kg/s

171 kg/s

19 kg/s 76 kg/s

480 kg/s

T=43 C556 kg/s

229 kg/s 361 kg/s

100 kg/s

Flue gas ARS x 1(2970 Refrigerant

Tons)

T=52 C550 kg/s

T=15 C248 kg/s

T=5 C248 kg/s

T=5 C380 kg/sT=15 C

T=15 C

T=15 C

T=5 C229 kg/s

T=15 C229 kg/s

T=5 C210 kg/s

HP steam ARS x 1(1876 Refrigerant

Tons)

Hot water ARS x 1(3260 Refrigerant

Tons)

T=5 C141 kg/s

T=5 C273 kg/s

T=5 C157 kg/s

CoolingTower B

Centralized Cooling Hub

CoolingTower A

Plant B

Plant C

Plant A

T=15 C72 kg/s

T=15 C132 kg/s

29 kg/s

4 kg/s

196 kg/s

VCRS x 1(1680 Refrigerant

Tons)

T=15 C157 kg/s

T=15 C141 kg/s

T=15 C273 kg/s

T=5 C132 kg/s

CoolingTower x 3

T=30 C1894 kg/s

T=38 C1894 kg/s

T=30 C547 kg/s

T=30 C781 kg/s

T=30 C220 kg/s

T=30 C347 kg/s

T=38 C547 kg/s

T=38 C781 kg/s

T=38 C220 kg/s

T=38 C347 kg/s

Electricity2284 kWh

Hot water inletT=95 C295 kg/s

Hot water outletT=95 C349 kg/s

Flue gas inletT=480 C22 kg/s

Flue gas outletT=170 C22 kg/s

HP steam inletT=152 C2 kg/s

Steam condensateT=95 C2 kg/s

ElectricityHot waterSteam

LEGEND:

Hot waterrecycleT=95 C52 kg/s

Flue gasdischargeT=100 C22 kg/s

T=5 C72 kg/s

T=5 C69 kg/s

Hot waterdischargeT=95 C297 kg/s

T=15 C210 kg/s

T=15 C69 kg/s

T=15 C380 kg/s

Hot flue gasProcess waterCondenser cooling water

Fig. 6. Chilled and cooling water network for scenario 3.

W.M. Chan et al. / Energy 141 (2017) 1555e15681566

recovery network. However, its implementation can only be justi-fied in an EIP, where the various types of waste heat are abundantlyavailable, as it is difficult to achieve the waste heat types andamount for the case of individual plant.

Overall, the proposed ARS-VCRS with secondary waste heat

recovery network excels in the aspect of energy efficiency andfuture EIP expansion potential, it reflects the ultimate objective ofEIP development, where the participating plants collaborate to seekfor cost and environmental benefits, as well as business excellence.Furthermore, its implementation can improve the sustainability of

W.M. Chan et al. / Energy 141 (2017) 1555e1568 1567

participating plants and assist them in fulfilling corporate socialresponsibility. Nevertheless, it has contributed to a more complexnetwork which increases susceptibility towards process failure;and subjected to a relatively high capital cost which impacts thefinancial viability of its implementation.

4.2. Sensitivity analysis for ARS-VCRS installation

The sensitivity analysis is carried out by focusing on one type ofARS-VCRS at a time. In this analysis, the amount of each type ofwaste heat is reduced gradually until only VCRS is preferred in theEIP, the waste heat amount and cooling duty of ARS-VCRS duringthis trade-off are recorded as the minimum benchmarks andtabulated in Table 5. By comparing the minimum benchmarks tothe waste heat profile in Table 3, Plant C is found to have deficitwaste heat where the amount is insufficient for ARS-VCRS instal-lation. Therefore, the waste heat will be disregarded in the case ofindividual plant cooling hub. On the other hand, the rest of theplants have sufficient waste heat for ARS-VCRS installation, whichprovides the options of joining the centralized cooling hub orestablishing their individual plant cooling hub. That being said, theaction of disuniting will affect the overall EIP network performance,as there will be issues of deficit or excess waste heat which lead towastage. In order to attract those with sufficient or excess wasteheat, game theory can be employed to allocate costs and benefitsaccording to the participants’ contributions [42]. Aside from that,the information in Table 5 also serves as the minimum benchmarkfor ARS-VCRS during operation. Operating the ARS-VCRS below thebenchmark will result in potential financial loss due to the inabilityto overcome the capital instalment. Therefore, EIP managementmust anticipate any events that can trigger waste heat shortage orreduction in cooling demand, and propose correspondingcountermeasures.

5. Conclusion

In this paper, a chilled and cooling water superstructure inte-grated with centralized ARS-VCRS utilizing various types of wasteheat within an EIP is developed, the superstructure is formulatedand solved as MINLP models. This paper analyzed the overallnetwork performance of the centralized ARS-VCRS, which isimportant for decision making in an EIP. Although centralized ARS-VCRS has a more complex piping network, it actually improved theeconomic and environmental performance and future expansionpotential for the EIP. The proposed secondary waste heat recoveryhas further enhanced the energy efficiency of the overall chilledand cooling water network, led to 53% reduction in electricityconsumption and CO2 emission. This paper also identified theminimum cooling duty and waste heat amount for ARS-VCRSinstallation using sensitivity analysis. The main contribution ofthis paper is to show that heat integration causes the centralizedARS-VCRS to be more economically feasible and brings industriescloser to clean production. For future improvement, further utili-zation of the waste heat can be studied, as there is energyremaining in the discharged waste. For instance, hot water can be

Table 5Sensitivity analysis for each refrigeration system.

Refrigeration system Minimum waste heatamount (kg/s)

Minimum coolingduty (RT)

Steam ARS-VCRS 0.4 kg/s 400Flue gas ARS-VCRS 3.0 kg/s 400Hot water ARS-VCRS 20.0 kg/s 700

sent to an adsorption chiller that can utilize lower temperature hotwater. Furthermore, other factors such as environmental impact,connectivity and network reliability may come into the equationduring decision making. Therefore, multiple objective optimiza-tions can be employed for multiple criteria.

Acknowledgement

The authors would like to acknowledge the financial supportfrom Monash University Malaysia (Higher Degree by ResearchScholarships).

References

[1] Marques C, Davies G, Maidment GG, Evans J, Wood I. The use of phase changematerials in domestic refrigerator applications. The Institute of Refrigeration;2013. www.ior.org.uk. [Accessed 13 June 2017].

[2] Cai D, He G, Tian Q, Tang W. Thermodynamic analysis of a novel air-coolednon-adiabatic absorption refrigeration cycle driven by low grade energy.Energy Convers Manag 2014;86:537e47.

[3] Gilani SI-u-H, Ahmed MSMS. Solution crystallization detection for double-effect LiBr-H2O steam absorption chiller. Energy Procedia 2015;75(Supple-ment C):1522e8.

[4] Wang R, Wang L, Wu J. Introduction. Adsorption refrigeration technology.John Wiley & Sons, Singapore Pte. Ltd; 2014. p. 1e22.

[5] Bruno JC, Vidal A, Coronas A. Improvement of the raw gas drying process inolefin plants using an absorption cooling system driven by quench oil wasteheat. Energy Convers Manag 2006;47(1):97e113.

[6] Trygg L, Amiri S. European perspective on absorption cooling in a combinedheat and power system e a case study of energy utility and industries inSweden. Appl Energy 2007;84(12):1319e37.

[7] Kalinowski P, Hwang Y, Radermacher R, Al Hashimi S, Rodgers P. Applicationof waste heat powered absorption refrigeration system to the LNG recoveryprocess. Int J Refrig 2009;32(4):687e94.

[8] Al-Alili A, Islam MD, Kubo I, Hwang Y, Radermacher R. Modeling of a solarpowered absorption cycle for Abu Dhabi. Appl Energy 2012;93:160e7.

[9] Salmi W, Vanttola J, Elg M, Kuosa M, Lahdelma R. Using waste heat of ship asenergy source for an absorption refrigeration system. Appl Therm Eng2017;115:501e16.

[10] Kwak D-H, Binns M, Kim J-K. Integrated design and optimization of technol-ogies for utilizing low grade heat in process industries. Appl Energy 2014;131:307e22.

[11] Han W, Sun L, Zheng D, Jin H, Ma S, Jing X. New hybrid absorp-tionecompression refrigeration system based on cascade use of mid-temperature waste heat. Appl Energy 2013;106:383e90.

[12] Jain V, Kachhwaha SS, Sachdeva G. Thermodynamic performance analysis of avapor compressioneabsorption cascaded refrigeration system. Energy Conv-ers Manag 2013;75(Supplement C):685e700.

[13] Chan KT, Yu FW. Applying condensing-temperature control in air-cooledreciprocating water chillers for energy efficiency. Appl Energy 2002;72(3):565e81.

[14] Thu K, Saththasivam J, Saha BB, Chua KJ, Srinivasa Murthy S, Ng KC. Experi-mental investigation of a mechanical vapour compression chiller at elevatedchilled water temperatures. Appl Therm Eng 2017;123:226e33.

[15] Lee J-Y, Chen C-L, Wen T-L, Ng DKS, Foo DCY, Wang T-C. Synthesis and designof chilled water networks using mathematical optimization. Appl Therm Eng2013;58(1e2):638e49.

[16] Foo DCY, Ng DKS, Leong MKY, Chew IML, Subramaniam M, Aziz R, et al.Targeting and design of chilled water network. Appl Energy 2014;134:589e99.

[17] Law R, Harvey A, Reay D. Opportunities for low-grade heat recovery in the UKfood processing industry. Appl Therm Eng 2013;53(2):188e96.

[18] Chertow MR. “Uncovering” industrial symbiosis. J Ind. Ecol 2007;11(1):11e30.[19] Chae SH, Kim SH, Yoon S-G, Park S. Optimization of a waste heat utilization

network in an eco-industrial park. Appl Energy 2010;87(6):1978e88.[20] Hip�olito-Valencia BJ, Lira-Barrag�an LF, Ponce-Ortega JM, Serna-Gonz�alez M,

El-Halwagi MM. Multiobjective design of interplant trigeneration systems.AIChE J 2014;60(1):213e36.

[21] Chew KH, Kleme�s JJ, Wan Alwi SR, Manan ZA. Process modifications tomaximise energy savings in total site heat integration. Appl Therm Eng2015;78:731e9.

[22] Zhang C, Zhou L, Chhabra P, Garud SS, Aditya K, Romagnoli A, et al. A novelmethodology for the design of waste heat recovery network in eco-industrialpark using techno-economic analysis and multi-objective optimization. ApplEnergy 2016;184:88e102.

[23] Abdul Aziz E, Wan Alwi SR, Lim JS, Abdul Manan Z, Kleme�s JJ. An integratedPinch Analysis framework for low CO2 emissions industrial site planning.J Clean Prod 2017;146:125e38.

[24] Hassiba RJ, Al-Mohannadi DM, Linke P. Carbon dioxide and heat integration ofindustrial parks. J Clean Prod 2017;155(Part 1):47e56.

W.M. Chan et al. / Energy 141 (2017) 1555e15681568

[25] Leong YT, Tan RR, Chew IML. Superstructural approach to the synthesis offree-cooling system through an integrated chilled and cooling water network.Process Saf Environ Prot 2016;103(Part B):273e90.

[26] Kurem E, Horuz I. A comparison between ammonia-water and water-lithiumbromide solutions in absorption heat transformers. Int Commun Heat MassTransf 2001;28(3):427e38.

[27] Leong YT, Tan RR, Aviso KB, Chew IML. Fuzzy analytic hierarchy process andtargeting for inter-plant chilled and cooling water network synthesis. J CleanProd 2016;110:40e53.

[28] ShuangLiang. Absorption chiller product catalogue. Jiangsu Shuangliang Air-Conditioning Equipment Co., Ltd.; 2009. p. 17e20. 31-6, 44e45.

[29] Xu ZY, Wang RZ, Wang HB. Experimental evaluation of a variable effectLiBrewater absorption chiller designed for high-efficient solar cooling system.Int J Refrig 2015;59:135e43.

[30] Shirazi A, Taylor RA, White SD, Morrison GL. A systematic parametric studyand feasibility assessment of solar-assisted single-effect, double-effect, andtriple-effect absorption chillers for heating and cooling applications. EnergyConvers Manag 2016;114:258e77.

[31] Srikhirin P, Aphornratana S, Chungpaibulpatana S. A review of absorptionrefrigeration technologies. Renew Sustain Energy Rev 2001;5(4):343e72.

[32] Xu Y-j, Zhang S-j, Xiao Y-h. Modeling the dynamic simulation and control of asingle effect LiBreH2O absorption chiller. Appl Therm Eng 2016;107:1183e91.

[33] Super tower industries. 2017. www.supertower.com.sg/products/downloads/Catalogue.pdf. [Accessed 19 July 2017].

[34] Castro MM, Song TW, Pinto JM. Operational cost minimization in cooling

water systems. Braz J Chem Eng 2000;17:649e58.[35] Peter M, Timmerhaus K, West R. Plant design and economics for chemical

engineers. fifth ed. New York: Mcgraw-Hill; 2004.[36] Englemen R. Commercial building applications for fuel cell gas turbine hy-

brids: analysis of absorption cooling potential using exhaust heat. 2005. www.lti-global.com/pdfs/HybridEnergy.pdf. [Accessed 21 June 2017].

[37] Min H-K, Ahmad T, Kim K-Y, Oh K-J, Lee S-S. Mercury adsorption character-istics of sulphur-impregnated activated carbon pellets for the flue gas con-dition of a cement-manufacturing process. Adsorpt Sci Technol 2015;33(3):251e62.

[38] Cichanowicz JE. Current capital cost and cost effectiveness of power plantemissions control technologies. 2010. www.publicpower.org/files/pdfs/uargscr_fgdfinal.pdf. [Accessed 21 June 2017].

[39] Brande M. Electricity-specific emission factors for grid electricity. 2011. www.ecometrica.com/assets/Electricity-specific-emission-factors-for-grid-electricity.pdf. [Accessed 3 June 2017].

[40] Madden N, Lewis A, Davis M. Thermal effluent from the power sector: ananalysis of once-through cooling system impacts on surface water tempera-ture. Environ Res Lett 2013;8(3), 035006.

[41] Energy Information Adminstration. Annual energy outlook 2017 with Pro-jections to 2040. 2017. https://www.eia.gov/outlooks/aeo. [Accessed 3 June2017].

[42] Tan RR, Andiappan V, Wan YK, Ng RTL, Ng DKS. An optimization-basedcooperative game approach for systematic allocation of costs and benefits ininterplant process integration. Chem Eng Res Des 106: 43e58.