Thermodynamic and Exergy Analysis of Energy-Integrated Distillation


Thermodynamic and Exergy Analysis of Energy-Integrated Distillation...

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Thermodynamic and Exergy Analysis of EnergyIntegrated Distillation Technologies Focusing on Dividing-Wall Columns with Upper and Lower Partitions Ariella Janka Tarjani, Andras Jozsef Toth, Tibor Nagy, Eniko Haaz, Nora Valentinyi, Anita Andre, Daniel Fozer, and Peter Mizsey Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b04247 • Publication Date (Web): 23 Feb 2018 Downloaded from http://pubs.acs.org on February 24, 2018

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Thermodynamic and Exergy Analysis of Energy-Integrated Distillation Technologies Focusing on Dividing-Wall Columns with Upper and Lower Partitions Ariella Janka Tarjani1,*, Andras Jozsef Toth1, Tibor Nagy1, Eniko Haaz1, Nora Valentinyi1, Anita Andre1, Daniel Fozer1 and Peter Mizsey1,2 1

Department of Chemical and Environmental Process Engineering, Faculty of Chemical Technology and Biotechnology, Budapest University of Technology and Economics P.O. Box 1521, Budafoki Street 8, H-1111, Budapest, Hungary

2

Department of Fine Chemicals and Environmental Technologies, University of Miskolc, Egyetemvaros, H-3515 Miskolc, Hungary

Abstract This study continues our research about dividing-wall distillation columns (DWCs) with upper and lower partitions1. Thermodynamic efficiencies and heat demands are investigated to offer a more complex point of view about distillation technologies. Rigorous simulations of nine distillation systems are completed and the results are evaluated. Among the separation systems there are conventional direct and indirect distillation systems and energy-integrated ones, that is, DWCs with upper and lower partition, columns with side stripper or side rectifier, the fully thermally coupled distillation column (FTCDC), the sloppy system, and a direct sequence with backward heat integration (DQB) are examined using three different alcohol mixtures. Results are obtained from rigorous simulations using exergy analysis. Thermodynamic efficiencies are in agreement with the expectations based on previous researches. Based on the thermodynamic efficiencies and heat demands the direct sequence with backward heat integration proved to be the most suitable distillation technology for the mixtures examined. The DWC with upper partition shows also promising behavior. Keywords exergy analysis, thermodynamic efficiency, energy-integrated distillation, dividing-wall column 1. Introduction Distillation is a well-known separation tool applied in several industrial sectors such as crude oil processing, pharmaceutical industry, solvent regeneration and waste water treatment. Being such a relevant technology, it is a great concern to find more competent column designs2. The ideal distillation column with no irreversible change and no entropy loss is the reversible distillation column proposed by Fonyó3. However, constructing the ideal column would require an infinite number of plates and many other impossible installations that would make it an unrealizable structure. Several energy-integrated distillation technologies have been introduced over the years bringing operating columns closer to the behavior of a reversible distillation column. These energy-integrated column designs are usually compared by energy efficiency, greenhouse gas emission, heat demand and cost estimation. Kencse and Mizsey4 have investigated the direct sequence with backward heat-integration (DQB), the fully thermally coupled distillation column (FTCDC) introduced by Petlyuk5 in 1965 and the sloppy system with forward heat-integration. Their study concludes that the heat-integrated structures have the highest energy efficiency and the DQB structure has the most favorable CO2 equivalent emission. Internally heat-integrated systems have been studied by Olujic6 and it proved to be competitive to a vapor recompression system. Heat-integrated columns also

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suppress both the FTCDC and conventional distillation columns in an economic study7. Single columns with side products also have favorable costs and efficiency but heat-integration overcomes in this case as well8. The FTCDC shows an energy saving in a range between 10 and 50% compared to the conventional distillation sequence but for separating certain hydrocarbon mixtures FTCDC columns are not recommended. Hernandez et al.9 have investigated the FTCDC structure along with six alternative constructions and found resembling thermodynamic efficiencies. Continuing research toward energy-efficient distillation dividing-wall columns (DWCs) have been suggested by Kaibel10 in 1987. DWCs proved to be superior to conventional distillation sequences and more than 100 applications are known due to the predicted 30% investment and energy cost reduction11, 12 . Energy and cost needs can be reduced further by applying large number of trays as it improves both thermodynamic efficiency and controllability of DWCs as Serra et al.13 reported. Optimal design of DWCs can also improve their energy efficiency. Using the V-min diagram introduced by Halvorsen et al.14, minimum energy requirement can be determined based only on feed data. Following the overall process synthesis concept15 it is vital to consider thermodynamic, economic and controllability results simultaneously. In our previous study1 controllability properties of conventional distillation sequences and DWCs with upper and lower partition (Figures 1 and 2) have been examined through the separation of ternary alcohol mixtures. Conventional technologies proved to have favorable controllability results in case of the studied mixtures. However, dividing-wall column with lower partition (DWCL) has similar controllability properties to the corresponding conventional structure. It seems more reboilers improve controllability as vapor ascends faster than liquid descends. DWCs with upper and lower partitions reported to be incapable of the same energy saving as the DWC with a middle section but investment cost of the second column are still avoided12. Continuing the study, thermodynamic performances of DWCs with upper and lower partitions are to be investigated to find out if these thermally-coupled systems also have a trade-off between controllability and energy efficiency as it is reported on other similar systems12, 16.

Figure 1. Dividing-Wall Column with Upper partition (DWCU)1

Figure 2. Dividing-Wall Column with Lower partition (DWCL)1

In this paper DWCs are compared with conventional and energy-integrated distillation technologies making it a total of nine systems investigated. The comparison is based on thermodynamic efficiency and heat demand. Case studies are carried out using three ternary alcohol mixtures with different

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separation indices. Efficiencies are determined by conventional exergy analysis based on the results of the 27 rigorous simulations completed in Aspen Plus.

2. Exergy Analysis Exergy analysis is a capable tool for designing, optimizing and improving different thermodynamic systems. It is widely used in several industrial sectors like paper mills, aluminum and iron foundries, chemical and petrochemical industries, sugar and cement processing as a recent review presents17. It is proved that these sectors have a promising future in reducing their energy consumption. Exergy analysis can support this improvement by revealing unknown losses. This concept is also encouraged by the modern lean management as Haragovics and Mizsey18 have introduced. Their study presents how lean philosophy draws attention to inflexibility and hidden losses making industrial chemical processes inefficient and shows how exergy analysis helps reveal these potentials. Exergy analysis can also predict results of economic studies by examining the thermodynamic efficiency of the system19. The method of exergy analysis is considered well-established as it is based on the two main laws of thermodynamics20. Based on the first law an energy balance can be applied to every energy system. However, the second law states that not all the heat energy can be converted to useful work thus an exergy balance provides more adequate results. Exergy is the maximum available energy in datum conditions as it proceeds to a dead state21 thus is shows the quantity and quality of energy22. In the case of distillation, exergy analysis shows how much of the invested heat can be transformed to separation work and how much irreversible loss is generated. In this study distillation technologies are compared by their heat demand and thermodynamic efficiencies. Enthalpy balances give information about the energy wastes while thermodynamic efficiencies show the rate of heat conversion and separation work. The related equations have been set by Seader and Henley23. The thermodynamic efficiency can be calculated with equation (1):

η=

W W + Ex

(1)

where W [kW] is the separation work and Ex [kW] is the exergy loss. The separation work can be determined with equation (2):

W = n  ∙ Ex − n  ∙ Ex

(2)

Ex = H − T ∙ S

(3)

Ex = T ∙ ΔS

(4)





where n [kmol/h] is the mole flow and Ex [kJ/kmol] is the specific exergy of the streams calculated by equation (3): where H [kJ/kmol] is the molar enthalpy, T [K] is the temperature of the environment fixed at 283 K and S [kJ/kmol·K] is the molar entropy of the streams. On the other hand, exergy loss or irreversibility can be calculated from the irreversible entropy loss in equation (4): where ΔS [kW/K] produced by the exergy balance in equation (5):

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ΔS = n  ∙ S + 

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Q   Q !" − n  ∙ S + T  T!" 

(5)

where Q   and Q !" [kW] are the heat flows while T  and T!" [K] are the temperatures in the condensator and the reboiler respectively. There are several other definitions for thermodynamic efficiency as Cornelissen gathered24. Simple efficiency is the ratio of the outgoing and the incoming exergy flow while rational efficiency is the ratio of the desired and used exergy. Both these definitions can be used for the introduced equations (1-5). Fundamentally similar definition of energetic efficiency has been proposed by Fonyo3. In equation (6) efficiency is calculated as the ratio of Δ S$ [kW/K] the entropy used by the separation process and Δ S% [kW/K] the invested entropy.

η=

Δ S$ Δ S%

(6)

Invested entropy has a familiar definition in equation (7):

Δ S% =

Q   Q !" − T  T!"

(7)

Entropy needed for separating components is calculated by equation (8):

Δ S$ = −R 'D x,* ∙ ln,γ,* ∙ x,* . + W x,/ ∙ ln,γ,/ ∙ x,/ . − F x,1 ∙ ln,γ,1 ∙ x,1 .2 





(8)

where R is the ideal gas constant 8.314 kJ/kmol K, D, W and F [kmol/h] are the mole flows of the distillate, the bottom product and the feed respectively, x is the mole fraction and γ is the activity coefficient of components. Using this equation makes calculations less rigorous as it highly depends on γ values.

Recently exergy analysis has been applied for several technological improvements. Lumin et al.25 implemented exergy analysis for the assessment of a novel different pressure thermally coupled distillation technology. Yang et al.26 have used exergy consumption and exergy loss to compare a new five-stage flash CO2 capture technology with the Rectisol process. Xu et al.27 have proposed a general methodology for the process synthesis of refrigeration systems using exergy-temperature charts combined with exergy analysis. Another recent approach is the advanced exergy analysis28. In advanced exergy analysis different forms of inefficiencies are differed as avoidable and unavoidable ones. Avoidable or endogenous inefficiencies can be reeducated by technological improvements but unavoidable or exogenous exergy destructions are caused by component interactions which cannot be lowered by such upgrade29. 3. Case Studies Rigorous simulations are carried out using RadFrac columns in Aspen Plus V8.0 according to the design procedure presented by Luyben30. Design parameters are determined by using a subroutine calculating the objective function Total Annual Cost (TAC) adopting the philosophy of Douglas31. As the same utility and capital cost prices have been applied, cost-ratios of the examined schemes are constant32.

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Studied systems include the conventional distillation sequence for separating a ternary mixture. These systems consist of two traditional columns with a single feed, distillate and bottom product. Figures 3 and 4 are showing the two possible alternatives, direct and indirect sequences.

Figure 3. Conventional Direct System (CDS) 1

Figure 4. Conventional Indirect System (CIS) 1

In the case of modeling DWCs, no built-in module is available in Aspen Plus therefore thermodynamically equivalent representations of the DWCU and DWCL systems are used (Figures 5 and 6)33. These designs are claimed to be similar to the ones in Figures 1 and 2 although the wall has significant effect on the heat balance in a favorable way making these models to be a worst scenario in terms of thermodynamic efficiency. Suphanit et al.34 have studied the influence of the wall on Petlyuk and Kaibel columns and concluded that some further energy savings can be achieved when heat transfer is allowed through certain places of the wall.

Figure 5. Partially coupled direct configuration1

Figure 6. Partially coupled indirect configuration1

Similar to the models in Figures 5 and 6 there are distillation systems with side columns. In this study the direct side rectifier (Figure 7) and the indirect side stripper (Figure 8) systems are examined. These side columns lack one of their heat exchangers and their operation is supported by the main column through the vapor-liquid equilibrium stream connecting them. These distillation systems are considered common in the crude industry.

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Figure 7. Side Rectifier system 35

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Figure 8. Side Stripper system (SS)

The next studied distillation system is the Petlyuk configuration in Figure 9. This structure also consists of two columns, a main column and a prefractionator. The main design criteria for the Petlyuk system is the optimal fractional recovery of the middle component defined by equation (9): 7 36

β=

α5 − α6 α7 − α6

(9)

where 8 is the volatility of the components. Using optimal fractional recovery, flow rates of the prefractionator can be calculated where the energy demand of the system is minimal. The top product of the prefractionator is defined by equation (10):

V  − L = a + β ∙ b

(10)

L  − V = c + >1 − β@ ∙ b

(11)

where V  is the vapor flow from the top, L is the liquid flow into the top, a and b is the amount of component A and B in the feed stream respectively. The bottom product is calculated with a similar method in equation (11): where L  is the liquid flow from the bottom, A is the vapor flow into the bottom and c is the amount of component C in the feed stream. Determined design parameters are also used for the similar sloppy system in Figure 10.

Figure 9. Petlyuk configuration

Figure 10. Sloppy system

The last examined technology is the most promising one in the literature, the heat-integrated columns in Figure 11. This constitution is based on the conventional direct sequence in Figure 3 but the bottom of the first column is heated by the vapor of the second column. Operating such a system requires a higher pressure in the second column, therefore a pump has to be installed on the BC stream.

Figure 11. Direct sequence with backwards heat integration (DQB)

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As it was mentioned before, three ternary alcohol mixtures are used in the simulations identical to the ones in our previous study1. Components, relative volatilities (αB @ and the ease of separation is listed in Table 1 for each mixture. Separation indices (SI) are calculated with equation (12):

SI = Table 1. Mixtures used in the simulations1 Mixture 1 2 3

A Ethanol Ethanol Methanol

B N-Propanol N-Propanol T-Butanol

C N-Butanol I-Butanol N-Butanol

α75 α56

αAC 8,47 5,52 17,87

(12)

αBC 3,00 1,96 6,07

αAB 2,82 2,82 2,95

SI 0,94 1,44 0,49

In the case of Mixture 1 the separation index shows similar ease of separation for A/B and B/C cuts. B/C cut is harder in Mixture 2 and A/B cut is harder in Mixture 3. The feed stream is equimolar in each case, it contains 33 kmol/h A, 34 kmol/h B and 33 kmol/h C. Product purities are always 95 mol% and their pressure and temperature are identical to those of the feed stream. In case of exergy analysis, it is vital to define the strict boundaries of the systems investigated. System boundaries contain the drawn structures in Figures 3 to 11 and the product coolers to achieve the mentioned identical state to the feed stream. 4. Results Figures 12 to 14 contain the calculated thermodynamic efficiencies and heat demands of the studied systems. Thermodynamic efficiencies are between 5 and 30% which is a typical range for distillation technologies. Two methods of calculation are shown on the charts. The so called Total Site method that assumes a heat cascade around the distillation system and the so called Stand-alone system where the distillation system is a single system and utilities should be applied8. In the case of the Total site, therefore, heat can be delivered and/or utilized at any temperature level but in the case of the Stand-alone distillation systems the temperatures are that of the utilities temperature. As utilities, steam and cooling water are applied and their temperature values are 283 K and 433 K, respectively. In Total Site Mode all heat exchangers have their own temperatures. Heat duties of the reboilers, condensers and product coolers are shown separately.

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Mixture 1 Thermodynamic efficiency (%)

25 Total Site Integration Stand-alone Mode

20 15 10 5 0 CDS

DQB DWCU

SR

CIS DWCL

SS

Petlyuk Sloppy

Product coolers [kW] Condenser duty [kW] Reboiler duty [kW]

8000 Heat demand [kW]

7000 6000 5000 4000 3000 2000 1000 0 CDS

DQB DWCU SR

CIS DWCL

SS

Petlyuk Sloppy

Figure 12. Thermodynamic efficiencies and heat demands of the studied systems for Mixture 1

Mixture 2 25 Thermodynamic efficiency (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Total Site Integration Stand-alone Mode

20 15 10 5 0 CDS

DQB DWCU

SR

CIS DWCL

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SS

Petlyuk Sloppy

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Product coolers [kW] Condenser duty [kW] Reboiler duty [kW]

12000 Heat demand [kW]

10000 8000 6000 4000 2000 0 CDS

DQB DWCU SR

CIS DWCL

SS

Petlyuk Sloppy

Figure 13. Thermodynamic efficiencies and heat demands of the studied systems for Mixture 2

Mixture 3 25 Thermodynamic efficiency (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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Total Site Integration Stand-alone Mode

20 15 10 5 0 CDS

DQB DWCU

SR

CIS DWCL

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SS

Petlyuk Sloppy

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Product coolers [kW] Condenser duty [kW] Reboiler duty [kW]

10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0

Heat demand [kW]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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CDS

DQB DWCU

SR

CIS DWCL

SS

Petlyuk Sloppy

Figure 14. Thermodynamic efficiencies and heat demands of the studied systems for Mixture 3

Results of the exergy analysis show that direct distillation structures are thermodynamically more efficient than the corresponding indirect sequence. As only A and B components have to be vaporized once in direct structures, thus less energy is needed to separate mixtures than using indirect technologies where component B has to be vaporized twice. However, the different ease of separation can result in quite different reflux ratios resulting that indirect separation becomes more competitive that the direct one. The reason of inefficiencies can be due also to the so called remixing effect. That phenomenon has been studied by Triantafyllou, Smith37 and Annakou, Mizsey7. Among the studied distillation technologies heat-integrated DQB has the highest thermodynamic efficiency in case of every mixture. However, heat demand of the system is similar to the conventional direct sequence. This anomaly is caused by the difference in the pressure profiles of the second columns as for heat-integration it is necessary to increase the pressure in the second column to be able to heat the first one. The higher pressure usually results in a higher energy consumption than that of the optimal pressure case. In Figures 12 to 14 Petlyuk configuration has low thermodynamic efficiencies and high heat demands making it a not recommended system for separating these alcohol mixtures. Application of the Petlyuk system is highly dependent on the mixture to be separated and the product purity descriptions as it is stated in a previous study.7 Turns out that Petlyuk columns are not competitive with the other examined energy-integrated technologies in this case. Although DWCs and Petlyuk systems have similar properties, DWCs proved to be more efficient in this study. However, there is one case with mixture 3 where DWCU happens to show higher heat demand than Petlyuk. This example confirms that SI has a significant impact on the results and mixtures with different SI values have to be examined to get a credible result over a wide range. Even in this case thermodynamic efficiency of the DWCU proves to be a slightly higher thus DWCs are more attractive than Petlyuk columns.

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As for the least competent technology, Petlyuk, Sloppy and conventional indirect systems prove to have the lowest thermodynamic efficiencies among the studied energy-integrated technologies. Direct sequences are usually considered more efficient except when mixtures with SI < 1 are considered. Supporting this theory, in case mixture 3 several indirect structures prove to have a higher thermodynamic efficiency than the corresponding direct alternatives.

5. Conclusions Energy-integrated distillation technologies are studied and compared using conventional exergy analysis. Thermodynamic efficiencies and heat demands of the nine examined technologies are determined by Aspen Plus simulations. Three different alcohol mixtures are separated in the case studies making a total of 27 simulations. Results show that heat-integration has the highest thermodynamic efficiency among the studied distillation technologies. DWCU and DWCL columns prove to be thermodynamically more efficient than the Petlyuk system. Along with Petlyuk, conventional indirect and sloppy systems prove to be the least efficient ones. Continuing our previous study, controllability results are discussed together with the founding of exergy analysis. Conventional distillation columns have more favorable controllability features than those of the DWCs with upper and lower partitions, but the thermodynamic results prove these DWCs to be more energy efficient technology than conventional distillation columns. Among these DWCs, DWCL has more promising controllability results as it has more reboilers. However, direct structures (DWCU) prove to have higher thermodynamic efficiencies than indirect ones (DWCL) as all components are vaporized once if no extreme reflux rations there are. The different advantages of DWCU and DWCL columns indicate that there is a trade-off between thermodynamic efficiency and controllability considering these energy-integrated systems.

Author information Corresponding Author *E-mail: [email protected] Notes: The authors declare no competing financial interest.

Acknowledgments This paper was supported by the János Bolyai Research Scholarship of Hungarian Academy of Sciences, OTKA 112699 and FIEK GINOP-2.3.4-15-2016-00004. Nomenclature A B C CDS

most volatile component middle component least volatile component conventional direct distillation sequence

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CIS D DQB DWC DWCL DWCU Ex Ex F H I L n Q S SI SR SS T T TAC V W W α αB β ΔS η

conventional indirect distillation sequence distillate mole flow [kmol/h] direct distillation sequence with backwards heat integration dividing-wall column dividing-wall column with lower partition dividing-wall column with upper partition specific exergy of streams [kJ/kmol] exergy loss or anergy [kW] feed mole flow [kmol/h] molar enthalpy of streams [kJ/kmol] irreversibility [kJ/kmol] liquid flow [kmol/h] mole flow [kmol/h] heat flow [kW] molar entropy of streams [kJ/kmol·K] separation index distillation column with side rectifier distillation column with side stripper temperature [K] temperature of the environment [K] total annual cost vapor flow [kmol/h] bottom product molt flow [kmol/h] separation work [kW] volatility of components relative volatility optimal fractional recovery of the middle component in Petlyuk columns irreversible entropy production [kW/K] thermodynamic efficiency

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22. Yang, Q.; Qian, Y.; Wang, Y.; Zhou, H.; Yang, S., Development of an Oil Shale Retorting Process Integrated with Chemical Looping for Hydrogen Production. Industrial & Engineering Chemistry Research 2015, 54, (23), 6156-6164. 23. Seader, J. D. H., E. J.; Roper, D. K., Separation Process Principles. Wiley: 2013. 24. Cornelissen, R. L. Thermodynamics and sustainable development. University of Twente, Enschede, The Netherlands, 1997. 25. Li, L.; Sun, L.; Wang, J.; Zhai, J.; Liu, Y.; Zhong, W.; Tian, Y., Design and Control of Different Pressure Thermally Coupled Reactive Distillation for Methyl Acetate Hydrolysis. Industrial & Engineering Chemistry Research 2015, 54, (49), 12342-12353. 26. Yang, S.; Qian, Y.; Yang, S., Development of a Full CO2 Capture Process Based on the Rectisol Wash Technology. Industrial & Engineering Chemistry Research 2016, 55, (21), 6186-6193. 27. Xu, C.; Zhang, J.; Dinh, H.; Xu, Q., Process Synthesis of Mixed Refrigerant System for Ethylene Plants. Industrial & Engineering Chemistry Research 2017, 56, (28), 7984-7999. 28. Erbay, Z.; Hepbasli, A., Application of conventional and advanced exergy analyses to evaluate the performance of a ground-source heat pump (GSHP) dryer used in food drying. Energy Conversion and Management 2014, 78, 499-507. 29. Fu, P.; Wang, N.; Wang, L.; Morosuk, T.; Yang, Y.; Tsatsaronis, G., Performance degradation diagnosis of thermal power plants: A method based on advanced exergy analysis. Energy Conversion and Management 2016, 130, 219-229. 30. Luyben, W. L., Distillation Design and Control Using AspenSimulation. John Wiley & Sons: New York, 2013. 31. Douglas, J. M., Conceptual design of chemical processes. McGraw Hill: New York, 1988. 32. Mizsey, P.; Hau, N. T.; Benko, N.; Kalmar, I.; Fonyo, Z., Process control for energy integrated distillation schemes. Computers & Chemical Engineering 1998, 22, S427-S434. 33. Rong, B.-G., Synthesis of dividing-wall columns (DWC) for multicomponent distillations—A systematic approach. Chemical Engineering Research and Design 2011, 89, (8), 1281-1294. 34. Suphanit, B.; Bischert, A.; Narataruksa, P., Exergy loss analysis of heat transfer across the wall of the dividing-wall distillation column. Energy 2007, 32, (11), 2121-2134. 35. Gómez-Castro, F. I.; Rodríguez-Ángeles, M. A.; Segovia−Hernández, J. G.; Hernández, S.; Gutiérrez-Antonio, C.; Briones-Ramírez, A.; Uribe Ramírez, A. R., Analysis of Dynamic Performance for Multiple Dividing Wall Distillation Columns. Industrial & Engineering Chemistry Research 2013, 52, (29), 9922-9929. 36. Rév, E.; Emtir, M.; Szitkai, Z.; Mizsey, P.; Fonyó, Z., Energy savings of integrated and coupled distillation systems. Computers & Chemical Engineering 2001, 25, (1), 119-140. 37. Triantafyllou, C.; Smith, R., The design and optimization of fully thermally coupled distillation columns. Chemical Engineering Research and Design 1992, 70, Part A, 118.

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