Abstract
Most of the water network design strategies considering regeneration and recycling are using the assumptions that the processes are isothermal and steady state. However, almost all of the available processes have temperature change from the inlets to the outlets of the units. Moreover, to maintain the process units’ temperature under the specified limit, additional heat exchangers are usually required. The traditional approach of designing water network and heat exchanger network are usually made separately. It is reasonable to expect that a simultaneous design procedure of water network and heat exchanger network that considers process temperature change may result in a better design option. In this work, systematic design of non-isothermal water networks with regeneration and recycling is proposed. Superstructure model with non-linear programming (NLP) model is developed accordingly to incorporate all possible networks. Regeneration units and heat exchangers are introduced to achieve the specified contaminant requirements and temperature limits of each process unit. The superstructure model is enhanced with regeneration unit model by considering the removal ratio of contaminants. As opposed to the traditional model, the novel heat exchanger model in this work is constructed separately for the heating side and the cooling side to increase further flexibility to the original model. The overall model is optimized simultaneously to achieve feasible heat exchange network and optimal configuration. The total annual cost (TAC) and global equivalent cost (GEC) are considered as the objective function to represent the economic benefits of the given case study. Several case studies are provided to demonstrate the effectiveness of the proposed design strategy.
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Abbreviations
- \( {\displaystyle \begin{array}{l}{P}_1,{P}_2,{P}_3,\dots \in P\\ {}{P}_1,{P}_2,{P}_3,\dots \in {P}^{\hbox{'}}\\ {}{P}_1,{P}_2,{P}_3,\dots \in {P}^{\hbox{'}\hbox{'}}\end{array}} \) :
-
P ≠ P'and P' ≠ P'' (Process)
- \( {\displaystyle \begin{array}{l}{R}_1,{R}_2,{R}_3,\dots \in R\ \\ {}{R}_1,{R}_2,{R}_3,\dots \in {R}^{\hbox{'}}\\ {}{R}_1,{R}_2,{R}_3,\dots \in {R}^{\hbox{'}\hbox{'}}\end{array}} \) :
-
R ≠ R'and R' ≠ R'' (Regeneration)
- \( {\displaystyle \begin{array}{l}{Eh}_1,{Eh}_2,{Eh}_3,\dots \in Eh\\ {}{Eh}_1,{Eh}_2,{Eh}_3,\dots \in {Eh}^{\hbox{'}}\\ {}{Eh}_1,{Eh}_2,{Eh}_3,\dots \in {Eh}^{\hbox{'}\hbox{'}}\end{array}} \) :
-
Eh ≠ Eh'and Eh' ≠ Eh'' (Exchanger heating side)
- \( {\displaystyle \begin{array}{l}{Ec}_1,{Ec}_2,{Ec}_3,\dots \in Eh\\ {}{Ec}_1,{Ec}_2,{Ec}_3,\dots \in {Eh}^{\hbox{'}}\\ {}{Ec}_1,{Ec}_2,{Ec}_3,\dots \in {Eh}^{\hbox{'}\hbox{'}}\end{array}} \) :
-
Ec ≠ Ec'and Ec' ≠ Ec'' (Exchanger cooling side)
- C1, C2, C 3, … ∈ C :
-
Component
- Un ∈ P, R, Eh, Ec :
-
Units
- Hu 1, Hu 2, Hu 3, … ∈ Hu :
-
Hot utility
- Cu 1, Cu 2, Cu 3, … ∈ Cu :
-
Cold utility
- in:
-
Input condition
- out:
-
Output condition
- f :
-
Fresh water
- w :
-
Waste water
- M C,P :
-
Amount of contaminant C generated by the process P (g/h)
- \( {C}_{\max C,P}^{in} \) :
-
Limiting inlet concentration C of process P (ppm)
- \( {C}_{\max C,P}^{out} \) :
-
Limiting outlet concentration C of process P (ppm)
- PR C,R :
-
Removal ratio of contaminant C in regeneration R
- PHD P :
-
Heat duty of process P (kW)
- RHD R :
-
Heat duty of regeneration R (kW)
- T f :
-
Temperature of freshwater inlet
- \( {T}_{\max P}^{in} \) :
-
Maximum for limit inlet temperature of process P (°C)
- \( {T}_{\min P}^{in} \) :
-
Minimum for limit inlet temperature of process P (°C)
- \( {T}_{\max P}^{out} \) :
-
Maximum for limit outlet temperature of process P (°C)
- \( {T}_{\min P}^{out} \) :
-
Minimum for limit outlet temperature of process P (°C)
- \( {T}_{\max \mathrm{R}}^{in} \) :
-
Maximum limit for inlet temperature of regeneration R (°C)
- \( {T}_{\min \mathrm{R}}^{in} \) :
-
Minimum limit for inlet temperature of regeneration R (°C)
- \( {T}_{\max \mathrm{R}}^{out} \) :
-
Maximum limit for outlet temperature of regeneration R (°C)
- \( {T}_{\min \mathrm{R}}^{out} \) :
-
Minimum limit for outlet temperature of regeneration R (°C)
- \( {C}_{\max C}^w \) :
-
Maximum limit for concentration of contaminant C in waste flow (ppm)
- \( {T}_{\max T}^w \) :
-
Maximum limit for temperature of waste flow (°C)
- C Fw :
-
Cost of fresh water
- C Hu,Un :
-
Cost of hot utility
- C Cu,Un :
-
Cost of cold utility
- \( {T}_{Hu, Un}^{in} \) :
-
Inlet temperature of hot utility
- \( {T}_{Cu, Un}^{in} \) :
-
Inlet temperature of cold utility
- \( {T}_{Hu, Un}^{out} \) :
-
Outlet temperature of cold utility
- Cp :
-
Heat capacity of water
- C fixed :
-
Fixed charges for heat exchangers and utility units
- C area :
-
Area cost coefficient for heat exchangers and utility units
- U Eh,Ec,hu,cu :
-
Overall heat transfer coefficients for hot stream, cold stream, and heat exchanger
- H :
-
Hours of plant operation
- T f :
-
Inlet temperature of fresh water
- \( {T}_{\max T}^w \) :
-
Maximum limit for temperature of wastewater stream
- α:
-
Regeneration cost factor
- β :
-
Wastewater cost factor
- γ :
-
Minimum temperature difference of the heat exchangers’ inlet and outlet
- λ:
-
Exponent parameter for area cost
- NEh,Ec :
-
Number of heat exchanger
- NHu,Un :
-
Number of hot utility
- N Cu,Un :
-
Number of cold utility
- \( {F}_P^f \) :
-
Flowrate from fresh water to process P (t/h)
- \( {F}_R^f \) :
-
Flowrate from fresh water to regeneration R (t/h)
- \( {F}_{Eh}^f \) :
-
Flowrate from fresh water to exchanger heating side Eh (t/h)
- \( {F}_{Ec}^f \) :
-
Flowrate from fresh water to exchanger cooling side Ec (t/h)
- F P→P' :
-
Flowrate from process P to process P’ (t/h)
- F R→R' :
-
Flowrate from regeneration R to regeneration R’ (t/h)
- F Eh→Eh' :
-
Flowrate from exchanger heating side Eh to exchanger heating side Eh’ (t/h)
- F Ec→Ec' :
-
Flowrate from exchanger cooling side Ec to exchanger cooling side Ec’ (t/h)
- F P→R :
-
Flowrate from process P to regeneration R (t/h)
- F P→Eh :
-
Flowrate from process P to exchanger heating side Eh (t/h)
- F P→Ec :
-
Flowrate from process P to exchanger cooling side Ec (t/h)
- F R→P :
-
Flowrate from regeneration R to process P (t/h)
- F R→Eh :
-
Flowrate from regeneration R to exchanger heating side Eh (t/h)
- F R→Ec :
-
Flowrate from regeneration R to exchanger cooling side Ec (t/h)
- F Eh→P :
-
Flowrate from exchanger heating side Eh to process P (t/h)
- F Eh→R :
-
Flowrate from exchanger heating side Eh to regeneration R (t/h)
- F Eh→Ec :
-
Flowrate from exchanger heating side Eh to exchanger cooling side Ec (t/h)
- F Ec→P :
-
Flowrate from exchanger cooling side Ec to process P (t/h)
- F Ec→R :
-
Flowrate from exchanger cooling side Ec to regeneration R (t/h)
- F Ec→Eh :
-
Flowrate from exchanger cooling side Ec to exchanger heating side Eh (t/h)
- \( {F}_P^w \) :
-
Flowrate from process P to discharge (t/h)
- \( {F}_R^w \) :
-
Flowrate from regeneration R to discharge (t/h)
- \( {F}_{Eh}^w \) :
-
Flowrate from exchanger heating side Eh to discharge (t/h)
- \( {F}_{Ec}^w \) :
-
Flowrate from exchanger cooling side Ec to discharge (t/h)
- \( {C}_{C,P}^{in} \) :
-
Inlet concentration C of process P (ppm)
- \( {C}_{C,P}^{out} \) :
-
Outlet concentration C of process P (ppm)
- \( {C}_{C,R}^{in} \) :
-
Inlet concentration C of regeneration R (ppm)
- \( {C}_{C,R}^{out} \) :
-
Outlet concentration C of regeneration R (ppm)
- C C,Eh :
-
Inlet concentration C of exchanger heating side Eh (ppm)
- C C,Ec :
-
Inlet concentration C of exchanger cooling side Ec (ppm)
- \( {C}_C^w \) :
-
Concentration C of wastewater (ppm)
- \( {T}_P^{in} \) :
-
Inlet temperature of process P (°C)
- \( {T}_P^{out} \) :
-
Outlet temperature of process P (°C)
- \( {T}_R^{in} \) :
-
Inlet temperature of regeneration R (°C)
- \( {T}_R^{out} \) :
-
outlet temperature of regeneration R (°C)
- \( {T}_{Eh}^{in} \) :
-
Inlet temperature of exchanger heating side Eh (°C)
- \( {T}_{Eh}^{out} \) :
-
outlet temperature of exchanger heating side Eh (°C)
- \( {T}_{Ec}^{in} \) :
-
Inlet temperature of exchanger cooling side Ec (°C)
- \( {T}_{Ec}^{out} \) :
-
Outlet temperature of exchanger cooling side Ec (°C)
- T w :
-
Temperature of wastewater (°C)
- \( {Q}_P^{in} \) :
-
Inlet heat duty of process P inlet using hot utility (ton.°C.CP/h)
- \( {Q}_R^{in} \) :
-
Inlet heat duty of regeneration R using hot utility (ton.°C.CP/h)
- \( {Q}_{Eh}^{in} \) :
-
Inlet heat duty of exchanger heating side Eh using hot utility (ton.°C.CP/h)
- \( {Q}_{Ec}^{in} \) :
-
Inlet heat quality of exchanger cooling side Ec using hot utility (ton.°C.CP/h)
- \( {T}_{Hu, Un}^j \) :
-
Temperature for unit before heated by hot utility
- \( {T}_{Hu, Un}^k \) :
-
Temperature for unit after heated by hot utility
- \( {T}_{Cu, Un}^j \) :
-
Temperature for unit before cooled by cold utility
- \( {T}_{Cu, Un}^k \) :
-
Temperature for unit after cooled by cold utility
- ΔT Eh,Ec :
-
Temperature difference of the mixing exchangers’ inlet and outlet
- ΔT Hu,Un :
-
Temperature difference of the hot utility’ inlet and outlet
- ΔT Cu,Un :
-
Temperature difference of the cold utility’ inlet and outlet
- Q Eh,En :
-
The exchanged energy by the heat exchanger
- A Eh,Ec :
-
Heat transfer area of mixing heat exchanger
- A Hu,Un :
-
Heat transfer area of hot utility
- A Cu,Un :
-
Heat transfer area of cold utility
- \( {D}_P^{in} \) :
-
Removal heat duty in process P inlet using cooling utility (ton.°C.CP/h)
- \( {D}_R^{in} \) :
-
Removal heat duty in regeneration R inlet using cooling utility (ton.°C.CP/h)
- \( {D}_{Eh}^{in} \) :
-
Removal heat duty in exchanger heating side Eh inlet using cooling utility (ton.°C.CP/h)
- \( {D}_{Ec}^{in} \) :
-
Removal heat duty in exchanger cooling side Ec inlet using cooling utility (ton.°C.CP/h)
- \( {D}_w^{in} \) :
-
Removal heat in exchanger cooling side Ec inlet using cooling utility (ton.°C.CP/h)
- Cannual :
-
Annual cost (M$)
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Acknowledgments
The authors wish to thank the anonymous reviewers for the useful comments that helped improve the readability of this work. The research was partially supported by the Ministry of Science and Technology, Taiwan under contract no. MOST 106-2221-E-005-095-, the 105科技部補助大專校院延攬特殊優秀人才 award, and a grant from National Chung-Hsing University 10617003G 新進教師經費補助.
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Cheng, WH., Adi, V.S.K. Simultaneous Optimization of Non-Isothermal Design of Water Networks with Regeneration and Recycling. Process Integr Optim Sustain 2, 183–203 (2018). https://doi.org/10.1007/s41660-018-0045-2
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DOI: https://doi.org/10.1007/s41660-018-0045-2