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New Intensified Heat Integration of Vapor Recompression Assisted Dividing Wall column Lianghua Xu, Murong Li, Xiaohong Yin, and Xigang Yuan Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b03802 • Publication Date (Web): 25 Jan 2017 Downloaded from http://pubs.acs.org on February 1, 2017

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Industrial & Engineering Chemistry Research

New

Intensified

Heat

Integration

of

Vapor

Recompression Assisted Dividing Wall column Lianghua Xu * 1, Murong Li 1, Xiaohong Yin 1, Xigang Yuan 2 1. College of Chemical and Chemical Engineering, Tianjin University of Technology, Tianjin 300384, China 2 State Key Laboratory of Chemical Engineering, Tianjin University, Tianjin 300072, China ABSTRACT: The energy efficiency of dividing wall column (DWC) can be improved by the vapor recompression (VRC) technology, but large temperature difference between the overhead and bottom of the DWC limits the application of VRC. In order to fully recover the heat generated by the VRC under large compression ratio, new intensified heat integrations of the VRC assisted DWC are provided in this paper. In the intensified configurations, the reboiler condensed liquid is used to vaporize the side liquid stream in an intermediate reboiler(IR), the overhead vapor is preheated by the subcooled liquid. The best IR position can be gotten by the aid of the column grand composite curves (CGCC) of the DWC. Three separation cases with different ESI values are simulated to validity the energy capacity of the intensified configurations, the results show that the intensified heat integration technolgy can significantly improve the energy efficiency of the DWC with large temperature difference between the overhead and the bottom. 1. INTRODUCTION

1

ACS Paragon Plus Environment


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Distillation is the most widely applied separation technology in chemical industry, but its energy consumption is always high. Heat integration technology is the main approach to improve the energy efficiency of distillation system,1 the well-known ones include divided wall column (DWC), vapor recompression (VRC) and internally heat internally integrated distillation column (HIDiC).2 As a fully thermal coupled distillation arrangement, DWC combines the prefractionor and the main column into one shell to separate multicomponent mixture. Compared to the conventional column sequence, about 30% of energy and capital cost will be saved by DWC.3–5 However, the energy efficiency of DWC is not always high because all the heat can be only added to the bottom reboiler at the highest temperature and removed from the top condenser at the lowest temperature.6,7 The extreme energy consumption can be reduced by the heat integration technology such as VRC technology. The conventional VRC has high energy efficiency with small temperature span across the column and large heat duty.8 But for the DWC, the temperature difference between the overhead and bottom is always large because three products are extracted from the same one column. The large temperature difference problem is the main challenge for VRC to be implemented in DWC. Chew9 provided the multi-stage vapor recompressors assisted DWC configuration, but the compressor cost is so expensive that its number must be limited. The VRC with side heat exchanger configurations have been applied in the conventional distillation and reaction distillation for separating the wide boiling mixture.10–12 Navarro-Amoros7 and Lee13 provided the side VRC assisted DWC 2


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configurations, in which the VRC is connected with the DWC by in side stage. Although the compressor ratio will be reduced in these configurations, but on one hand, the flow can’t be totally extracted from the side stage, their energy capacities are limited, on the other hand, large extraction liquid or vapor amount will affect the normal separation in the column. The same problems are appeared in the reactive dividing wall column, azeotropic dividing wall column and extractive dividing wall column.14, 15 We combine the advantages of conventional VRC and side VRC technologies into one DWC, provide the intensified heat integration of VRC assisted DWC configuration. In the intensified configurations, the conventional VRC is added between the overhead and bottom of the DWC to recover the heat of overheat vapor as much as possible, the high temperature condensed liquid from the bottom reboiler is used to vaporize the side liquid in an intermediate reboiler. Compared with the conventional VRC assisted DWC, the intensified configurations have the intermediate reboiler, both of the reboiler and condenser duties can be further reduced. Compared with the side VRC assisted DWC, the intensified configurations have few side withdrawn flow, the separation efficiency of the column can’t be affected significantly. To realize the heat integration in the IR, enough temperature difference between two heat exchanged streams is necessary, so the IR position should be chosen carefully. First, the position should be located in the intermediate reboiler region of the DWC. Second, the side liquid temperature should be as low as possible to get 3



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large heat transfer drive force. The side product stage is the very suitable position, on one hand, the temperature of this stage is lower than the stripping section stage, on the other, the composition of liquid on this stage is purer than other side liquid flows, the influence of intermediate reboiler to the stage separation efficiency is lower. For the DWC, either intermediate reboiler or intermediate condenser may be installed in the side product stage because it is the connection of the rectifying and stripping sections of the DWC, but one of them is effective to reduce the energy consumption of the DWC. 7 In this paper, we provide a direct approach to design the intensified heat integration of VRC assisted DWC configurations. The column grand composite curves (CGCC) of the DWC are used to determine the best IR position. In the following, firstly, the strategies of the intensified heat integration are described in detail, then the simulation method and economic analyze for the configurations are carried out, and then the energy capabilities of the intensified heat integration are validated in three separation cases, some conclusions are finally given. 2. INTENSIFIED HEAT INTEGRATION CONFIGURATIONS The standard VRC assisted DWC configuration (SVRC-DWC) is shown in Figure 1(a), the overhead vapor is compressed to a higher temperature to vaporize the bottom liquid, and then becomes the saturated condensed liquid in the reboiler, the condensed liquid should be depressed to the top pressure by the throttle valve (TV) before returning to the top of DWC. In this process, partial saturated vapors will be condensed in the isentropic compressor and partial saturated liquid will be flashed in 4


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the TV, so the overhead vapor must be preheated by a heater and the flashed vapor must be fully condensed by a cooler. When the compression ratio(CR) is small, the heat duties of the heater and cooler can be ignored, but under large CR, these heat duties will become large and even reduce the energy efficiency of VRC significantly. The waste heat generated by the VRC can be recovered by intensifying the heat integration between the VRC and DWC. In order to intensify the heat integration between the VRC and DWC, a retrofitted VRC assisted DWC configuration (REVRC-DWC, shown in Figure 1(b)) is first achieved. In this configuration, the flashed stream directly return to the top of column, part of the flashed vapor is used to heat the bottom liquid, and the remained vapor is condensed by the top condenser. By this modification, the recovered heat from the overhead vapor is increased and the cooler duty is reduced. Based on the REVRC-DWC configuration, the intensified heat integration between VRC and DWC is achieved. The high temperature condensed liquid is used to vaporize side liquid in an intermediate reboiler(IR), then the condensed liquid become subcooled. The subcooled liquid is not easy to be flashed in the depression process compared with the saturated liquid, so the amount of flashed vapor generated in the TV is reduced, then both of condenser and reboiler duties can be decreased. This heat integration configuration is named as HI-VRC-DWC and shown in Figure1(c). Based on the HI-VRC-DWC configuration, the subcooled liquid from IR can be used to preheat the overhead vapor. So the condenser duty and the hot utility of the heater can be further reduced. This intensified heat integration configuration is named 5



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as IHI-VRC-DWC and shown in Figure 1(d). 3. SIMULATION AND ECNOMIC ESTIMATION METHODS 3.1 Optical design of the DWC. The typical DWC configuration is shown in Figure 2(a), NT1 and NT2 represent the stage numbers of main column and prefractionator respectively, NF, NS, NL and NV represent the feed stage, side product stage, liquid connection stage and vapor connection stage respectively.16 rL and rV are defined as the liquid and vapor splits from the main column to the prefractionator respectively. Five independent structure variables ( NT1, NT2, NF, NS, NL or NV) and five operating variables ( rL, rV,, side product rate (S), the distillate rate (W), reflux ratio(R) or the reboiler duty(QR)) 17-18 are first estimated by the shortcut method based on the Fenske-Underwood-Gilliland-Kirkbride equations. Then the rigorous simulation and optimization of the DWC are performed by Aspen Plus V7.3TM. In order to get the converged results rapidly, a thermodynamics equivalent configuration (provided by Navarro et al

19

) is adopted and shown in Figure 2(b). The saturated

vapor (D1) and liquid streams (W1) plus the corresponding heat streams substitute the vapor and liquid connection streams respectively. This equivalent model avoids complex iterations and has high accuracy. The minimum total annual cost (TAC) is adopted as the optimization goal to optimize all design variables of the DWC. The detailed optimization procedure is shown in Figure 3. 3.2 Simulation of the intensified configurations. After getting the results of the DWC, the VRC assisted DWC configurations are simulated. In all configurations, the 6


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adiabatic efficiency of the compressor is set by 75%, and the electric drive efficiency of the compressor is assumed as 90%. First, the simulation of the SVRC-DWC and REVRC-DWC configurations are carried out. Next, the column grand composite curve (CGCC)20 of the DWC is generated for simulating the HI-VRC-DWC configuration. In this paper, we choose the stage-enthalpy (S-H) profile to determine the IR position. In the S-H profile, the region between the ideal and actual enthalpy profiles is divided into two parts by the pinch point. The above part represents the intermediate reboiler region and the below part represents intermediate condenser region.21 If the side product stage is in the intermediate reboiler region, it is chosen as the IR position. If the side product stage is in the intermediate condenser region, the IR position should be chosen from the stripping section. In this condition, the optimal IR position can be achieved by sensitivity analysis and the middle stage of the stripping section is chosen as the initial IR position. In order to realize the heat integration, the flowrate of the side liquid is gradually increased from a little value (5 kmol/h for example), and the flowrates of the overhead vapor and the bottom liquid are decreased correspondingly. The final flowrates of the side liquid and other streams are achieved until the logarithmic temperature difference of the IR is down to 10 oC. If the temperature of subcooled liquid from the IR is high enough, the subcooled liquid can preheat the overhead vapor. Then the simulation of the IHI-VRC-DWC configuration can be achieved. In the simulation of each configuration, the vapor and liquid split ratios are varied to get the minimum TAC. 7



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3.3 Economic estimation. The total annual cost (TAC) is chosen as the optimization and evaluation parameters in this paper, which is the sum of operating cost and annualized capital cost of the configurations. The operating cost is calculated by CAPCOST22, which is the summation of electricity (16.8 $/GJ), low pressure steam (13.28 $/GJ) or high pressure steam (14.19 $/GJ) and cooling water (0.354 $/GJ) for a year containing 8322 operating hours. The cost equipment estimating formulas are given by Olujic23, the M&S index is updated to 1468.6 in 2012.15 The column shell and tray costs of DWC are added by a penalty of 50% because of the complex internal structure of the DWC. The overall heat transfer coefficient is specified as 1.0 kW/(m2·oC) for the reboiler and 0.8 kW/(m2·oC) for the condenser and other heat exchangers. The calculation formula of annualized capital cost is taken from reference 7. 4. RESULTS AND DISCUSSION The energy capacities of the configurations are validated in three cases, which are (1) n-pentane/n-hexane/n-heptane mixture, (2) i-pentane/n-pentane/n-hexane mixture and (3) benzene/toluene/ethylbenzene mixture, their ESI values are 1.04, 0.47 and 1.26 successively.

17, 24

Soave−Redlich−Kwong (SRK) equation (for case 1 and 2) and

Peng–Robinson (PR) equation (for case 3) are selected to predict their thermodynamic properties respectively.17,

25

In three cases, the key component recovery in each

product is specified as 98%, the design pressure is chosen to ensure the use of cooling water in the condensers. 4.1 Case1. The simulation results of the DWC and its S-H profile are shown in 8


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Figure 4 (a) and (b), Figure 4 (a) indicates that the temperature difference between the o

overhead and the bottom is high up to 64.8 C. So the compression ratio (CR) should be regulated to 5.9 to meet the heat transfer demand in SVRC-DWC configurations as shown in Fig.5 (a). Under so large CR condition, large amount of condensed liquid flashed in the TV, so the cooler must provide 1466 kW duty to fully condense the flashed vapor. Figure 5(b) shows the simulation results of REVRC-DWC configuration, in which the cooler is replaced by the condenser. The compressed vapor flowrate is increased to provide all the reboiler duty, so the trim-reboiler is saved. Meanwhile, the condense duty is decreased from 1466 kW to 994 kW. But the compressor duty and the heater duty are increased to some extent. Figure 4 (b) shows the side product stage is in the intermediate condenser region, so the IR position of the HI-VRC-DWC configuration must be chosen from the stripping section. Figure 5(c) shows the simulation results of HI-VRC-DWC configuration, it indicates that the optimal IR position is located at stage 36, which is nearer to the bottom stage than the side product stage. The temperature difference between the reboiler condensed liquid and the side liquid is 24.2 oC, limited side liquid (62 kmol/h) is withdrawn from stage 36. But the energy saving of the intensified configuration is significant, we can see that 529kW of reboiler duty is provided by the IR, the top condenser duty is deceased from 994 kW to 771 kW, and the compressor duty is decreased from 916 kW to 752 kW. Figure 5(c) shown that the temperature of the condense liquid out of the IR is 113.2 9



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o

C, much higher than that of the overheat vapor (TD=57.2oC), it can preheat the

overhead vapor. So the IHI-VRC-DWC configuration is achieved and its simulation results are shown in Figure 5(d). In this configuration, 275 kW of heat is recovered from the heater and the same amount of duty is saved in the condenser. The energy consumption and cost estimation of each configuration are listed in Table 1. It shows that 53.8% and 63.5% of operating cost are saved in the HI-VRC-DWC and IHI-VRC-DWC configurations respectively. Without the intensified heat integration, 0.5% of TAC is saved in the SVRC-DWC configuration. After intensified heat integration, the TAC savings are up to 16.9% and 25.3% in HI-VRC-DWC and IHI-VRC-DWC respectively. 4.2 Case 2. The design results of the DWC and its S-H profile are shown in Figure 6 (a) and (b). Figure 6 (a) indicates the temperature difference between the overhead and the bottom is 42.3 oC which is smaller than that in case 1. So the CR of compressor is regulated to 3.9 in the SVRC-DWC configuration as shown Figure 7 (a). It shows that the compressor and the cooler duties are still very high because the flowrate of overhead vapor is large. The simulation results of REVRC-DWC configuration are shown in figure 7(b). Because part of flashed vapor from the TV is used to vaporize the bottom liquid, the condense duty is reduced from 2401 kW to 1691 kW and the trim-reboiler is saved. Figure 6 (b) indicates that the side product stage is in the IR region, and can be selected as the IR position. The simulation of HI-VRC-DWC configuration is achieved and shown in Fig. 7(c). Because the ESI value of this case is 0.47 and the IR 10


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position is located at the side product stage, the temperature difference between the reboiler condensed liquid and the side liquid is high up to 45 oC. In this situation, 228kmol/h of liquid is withdrawn from the side product stage, about 1583kW of bottom reboiler duty is saved. Meanwhile, the amount of flashed vapor from the TV is largely reduced, so the condenser and the compressor duties are reduced significantly. Figure 7 (c) shows that the temperature of subcooled liquid from the IR (63.9 oC) is much higher than the overhead temperature (49.3oC), so the simulation of IHI-VRC-DWC configuration can be achieved. The results are shown in Figure 7(d), which indicates that 303 kW heat is recovered in the heater, and the same amount of condenser duty is saved. Energy consumption and cost estimation of each configuration are listed in Table 2. We can see that the operating cost savings of HI-VRC-DWC and IHI-VRC-DWC configurations are high up to 72.7% and 77.6% respectively, which are much higher than that (50.4% ) of SVRC-DWC configuration. 44.8% and 48.6% of TAC are saved in HI-VRC-DWC and IHI-VRC-DWC configurations, which are much larger than that (24.8%) in SVRC configuration. Compared with case 1, the energy efficiency of the intensified configuration is much higher in this case, because more amount of liquid is withdrawn from the side product stage. 4.3 case 3. One of the applications for the DWC in industry is the separation of benzene, toluene and ethylbenzene, so we choose this mixture to validate the energy capacity of the proposed configurations. The optimal design results of the DWC and its S-H profile are shown in Figure 8 (a) and (b). We can see that the side product 11



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stage is located in the side condenser resign, the IR position of the HI-VRC-DWC and IHI-VRC-DWC configurations must be chosen from the stripping section. The simulation results of the four configurations are shown in Figure 9 (a) ~ (d). Figure 9 (c) shown that the IR is located in stage 42. Because the ESI value of this case is 1.26 and the IR position is located in the stripping section, the temperature difference between the reboiler condensed liquid and the side liquid is 23.8 oC, limited amount (56kmol/h) of the side liquid is withdrawn from stage 42. So the saved heat by the IR is the least in three cases. However, large amount of the reboiler, condenser and compressor duties are still saved in the HI-VRC-DWC and IHI-VRC-DWC configurations. The detailed energy consumption and costs of each configuration are listed in Table 3, we can see that the large amounts of operating cost and TAC are saved in HI-VRC-DWC and IHI-VRC-DWC configurations. The intensified heat integration of the VRC assisted DWC is still very effective in this case. 5. Conclusion Two kinds of new intensified heat integration of VRC assisted DWC configurations, HI-VRC-DWC and IHI-VRC-DWC are provided in this paper. In both configurations, the condensed liquid from the bottom reboiler is used to vaporize the side liquid in the intermediate reboiler. The intensified heat integrations concentrate the advantages of the conventional VRC and the side VRC technologies and can be achieved by the aid of the S-H profiles of the DWC. Three separation cases show that the intensified heat integrations can significantly improve the energy efficiency of the DWC with large 12


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temperature difference between the overhead and the bottom. It is clear that the intensified heat integration technology is not always effective. When the temperature difference between the condensed liquid and the side liquid is very small, there is no enough large driving force of heat exchange in the intermediate reboiler. In this situation, the standard VRC can be applied into the DWC configuration. AUTHOR INFORMATION Corresponding Author *Tel.: +86 022-60214259. Fax: +86 022-60214258. E-mail: [email protected] The authors declare no competing financial interest. ACKNOWLEDGMENTS The research is financially supported by the National Science Foundation of China (21406170), the State Key Laboratory of Chemical Engineering (SKL-ChE-15B04), and Tianjin Municipal Education Commission (20140509). NOMENCLATURE Comp = compressor CGCC = column grand composite curve CR = compression ratio D =distillate product DWC =dividing wall column F=feed of distillation 13



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H= enthalpy of distillation stage HIDiC = internally heat integrated distillation column HI-VRC-DWC= intensified heat integration of VRC assisted DWC configuration IHI-VRC-DWC= improved HI-VRC-DWC configuration IR = intermediate reboiler L= liquid flowrate N= number of stage QC = condenser duty QComp= compression duty QH= heater duty QIR= intermediate reboiler duty QR= bottom reboiler heat R= reflux ratio REVRC-DWC = retrofitted VRC assisted DWC S= side product SVRC-DWC= standard VRC assisted DWC rL = fraction of the liquid from the main column to the prefractionator rv=fraction of the vapor from the main column to the prefractionator TAC= total annual cost TD = distillate product temperature Tin = the temperature of the hot inlet stream in the heat exchanger tin= the temperature of the cold inlet stream in the heat exchanger 14


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Tout= the temperature of the hot outlet stream in the heat exchanger tout= the temperature of the cold outlet stream in the heat exchanger TS = side product temperature TW= bottom product temperature TV = throttle valve V= vapor flowrate VRC = vapor recompression W= bottom product x=mole composition of feed and product

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Analysis, Synthesis and Design of Chemical Processes. 4th ed. Upper Saddle River, NJ: Prentice Hall, 2012. (23) Olujic, Z.; Sun, L.; de Rijke, A.; Jansens, P. J., Conceptual Design of an Internally Heat Integrated Propylene-Propane Splitter. Energy. 2006, 31(15), 3083–3096. (24) Ramirez-Corona, N.; Jimenez-Gutierrez, A.; Castro-Aguero, A.; Rico-Ramirez, V. Optimum Design of Petlyuk and Divided-Wall Distillation Systems Using a Shortcut Model. Chem. Eng. Res .Des. 2010, 88(10), 1405–1418. (25) Premkumar, R.; Rangaiah, G. P. Retrofitting conventional column systems to dividing-Wall Columns. Chem. Eng. Res. Des. 2009, 87 (1), 47–60.

18


Page 18 of 31

Page 19 of 31

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


Figures in the article

Heater

Comp

Condenser

D

Comp

Heater

D

Cooler S

F

S

F

TV

TV

Reboiler

W

Reboiler

W

Trim-reboiler

(a) Condenser

(b)

Heater

Comp

Comp

Heater

Condenser

D D TV

TV

S

F

S F IR IR

Reboiler

W

Reboiler

W

(c)

(d)

Figure 1. Schematic diagrams of the (a)SVRC-DWC; (b)REVRC-DWC; (c)HI-VRC-DWC and (d)IHI-VRC-DWC

19



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

QC

D

R

Page 20 of 31

D

NL rL F

NT2

NT1

NF NS

D1 S

S

F

rV

W1 NV W W

-QR

(a)

(b)

Figure 2. (a) DWC configuration and (b) the equivalent configuration of DWC

20


Page 21 of 31

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


Start

Given NT1

Given NT2

Given NF, NS, NV and NV

Vary R, S, W to achieve thre product sepcifications

Vary rL, rV to get minimum QR

Is QR minimized with fixed NF, NS, NL and NV

No

Yes Calculate TAC

No

Is TAC minimized with fixed NT2 Yes

No

Is TAC minimized with fixed NT1 Yes Get the optimal parameters:NT1, NT2, NF, NS, NV, NV, rL and rV

End

Figure 3. Optimization procedure of the DWC

21



P=2 bar R=1.874 QC=2421 kW D=121.0 kmol/h n-pentane: 0.99 n-hexane: 0.01 o TD=57.9 C

1 7 17 F=300 kmol/h n-pentane: 0.40 n-hexane: 0.20 n-heptane: 0.40 o TF=79.9 C

17

S=62.6 kmol/h n-hexane: 0.92 n-pentane: 0.01 n-heptane: 0.07 TS=93.7oC

31

51

Reboiler Ideal profile Actual profile

41

Stage

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

Page 22 of 31

31 Pinch point

21

Side product stage

11 1

51

Condenser 0

QR=2683 kW

500

W=116.4 kmol/h n-heptane: 0.99 n-hexane: 0.01 TW=122.7 oC

(a)

1000 1500 2000 Enthalpy (KW)

2500

3000

(b)

Figure 4. (a) simulation results of the DWC and (b) S-H profile of the main column of DWC in case 1

22


Page 23 of 31

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


P=2 bar R=1.874

QH =223 kW

D

S

17

17

P=2 bar R=1.874

QC =994 kW

D

1 7

F

CR=5.90 QComp= 610 kW

QH =336 kW

1 7 S

17

17

F QC =1466 kW

TV

TV

31

31

51

51 QR=1782 kW

W

QR=2683 kW

W

V=348kmol/h QTR=901 kW

V=523kmol/h L=316kmol/h

L=210kmol/h

(a)

QC =771kW

P=2 bar R=1.889

D

F

(b)

QH =275kW


QC =496kW

1 7

17

P=2 bar R=1.889

D

17

31 36

1 7

W

CR=5.90 QComp= 752kW

QH=275kW

TV

TV

S

F

17

QIR=529kW o L=62kmol/h Tin=132.8 C o o tin=108.6 C Tout=113.2 C

17

31 36

o

51


QIR=529kW o L=62kmol/h Tin=132.8 C o o tin=108.6 C Tout=113.2 C o

tout=113.9 C L=256kmol/h

S

51 QR=2174 kW V=429 kmol/h

W

(c)

tout=113.9 C QR=2174 kW L=256kmol/h

V=429 kmol/h

(d)

Figure 5. simulation results of the (a) SVRC-DWC, (b) REVRC-DWC, (c) HI-VRC-DWC and (d) IHI-VRC-DWC in case1

23



P=2 bar R=6.236 QC=5610kW D=116.3 kmol/h i-pentane: 0.99 n-pentane: 0.01 o TD=49.3 C

1 52

96 77 Stage

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

Page 24 of 31

60 F=300 kmol/h i-pentane: 0.40 n-pentane: 0.20 n-hexane: 0.40 o TF=63.6 C

Reboiler Side product stage

Ideal profile Actual profile

58 39

S=62.7 kmol/h i-pentane: 0.07 n-pentane: 0.92 n-hexane: 0.01 TS=57.7 oC

86 95 99

QR=5711 kW

20 1

W=121.0kmol/h n-hexane: 0.99 n-pentane: 0.01 o TW=91.6 C

Pinch point

Condenser 0 1000 2000 3000 4000 5000 6000 Enthalpy Deficit (KW)

(a)

(b)

Figure 6. (a) simulation results of the DWC and (b) S-H profile of the main column of the DWC in case 2

24


Page 25 of 31

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



P=2 bar R=6.236 QH =341 kW

D

1

D

52 F


P=2 bar R=6.236 QC =1691kW QH =422 kW

1

QC=2401 kW

52

60

F

60 TV

TV S

86

S

86

95

V=845 kmol/h

95

99

V=1048kmol/h

99 QR=4653 kW

W

W

QR=5711 kW

L=600kmol/h

QTR=1058 kW

L=736.5kmol/h

(a) QC =1183 kW

P=2 bar R=6.245

D

(b) CR=3.90 QComp= 978 kW

QH =303 kW

QC =880 kW

1

P=2 bar R=6.245

D

52

TV

60

F

S 86 95 99 W

o

tin=57.7 C L=228kmol/h o tout=57.8 C

TV

60

QIR=1583 kW o Tin=102.7 C o Tout=63.9 C

S

V=751kmol/h

86

tin=57.7oC

95

L=228kmol/h tout=57.8oC

99 L=535 kmol/h


1

52 F

QH=303kW

QR=4148 kW W

(a)

L=535kmol/h

QIR=1583 kW Tin=102.7oC Tout=63.9oC V=751kmol/h QR=4148 kW

(b)

Figure 7. simulation results of the (a) SVRC-DWC, (b) REVRC-DWC, (c) HI-VRC-DWC and (d) IHI-VRC-DWC in case 2

25



P=1.75 bar R=3.709 QC=3908 kW D=100.8 kmol/h Benzene: 0.98 Toluene: 0.02 TD=100.2 oC

1 7

61

Reboiler

51

Ideal profile Actual profile

41

18 24 F=300 kmol/h Benzene: 0.33 Toluene: 0.33 Ethylbene: 0.34 TF=124.2 oC

38

S=98.9 kmol/h Toluene: 0.96 Benzene: 0.01 Ethylbene: 0.03 TS=134.0oC

Stage

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

Page 26 of 31

31 21

Side product stage

11 1

58

QR=4064 kW

Pinch point

Condenser 0

W=100.3 kmol/h Ethylbene: 0.98 Toluene: 0.02 TW=157.8 oC

1000

2000 3000 Enthalpy (KW)

4000

Figure 8. (a) simulation results of the DWC and (b) S-H profile of the main column of the DWC in case 3

26


Page 27 of 31

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


P=1.75 bar R=3.709


QH =86 kW

QC =955 kW

D

1 7 S

18

D

24

TV 38

TV

58

58 QR=3355 kW V=478kmol/h

W QTR=709 kW

QR=4064 kW V=580kmol/h

W L=427kmol/h

L=353kmol/h

(a) QC=821kW

CR=4.60 QComp=880kW

QC =729kW

1 7

P=1.75bar R=3.758

D

18 F

(b)

P=1.75bar QH=92kW R=3.758

D

S

L=56kmol/h o tin=144.3 C

QH=92kW

CR=4.60 QComp=880kW

TV 18

F

42

1 7

TV

24 38

S

18 F

38

CR=4.60 QComp=1000 kW

1 7

QC =1463 kW

24

F

P=1.75 bar QH =104 kW R=3.709

S

24

QIR=528kW Tin=168.1oC Tout=148.3oC

38 42

L=56kmol/h o tin=144.3 C

QIR=528kW Tin=168.1oC Tout=148.3oC

o

58 W

tout=148.9 C 58 L=375kmol/h

QR=3582kW V=510kmol/h

W

(c)

tout=148.9oC L=375kmol/h

QR=3582kW V=510kmol/h

(d)

Figure 9. simulation results of the (a) SVRC-DWC, (b) REVRC-DWC, (c) HI-VRC-DWC and (d) IHI-VRC-DWC in case 3

27



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

Page 28 of 31

Tables in the article Table 1. Comparison of Estimated Operating and Capital Costs in Case 1 Items

DWC

SVRC-DWC

REVRC-DWC

HI-VRC-DWC

IHI-VRC-DWC

Condenser duty (kW)

2421

0.0

994

771

496

0.0

1466

0.0

0.0

0.0

Cost of cooling water ($/y)

25700

15500

10500

8200

5200

Reboiler duty (kW) (steam-heated)

2683

901

0.0

0.0

0.0

Reboiler duty (kW) (compressed vapor-heated)

0.0

1782

2683

2174

2174

Intermediate reboiler duty (kW)

0.0

0.0

0.0

529

529

1140600

383000

0.0

0.0

0.0

Heater duty (kW)

0.0

223

336

275

275

Cost of low pressure steam ($/y)

0.0

88720

133700

109410

0.0

Compressor duty (kW)

0.0

610

916

752

752

Cost of electricity ($/y)

0.0

341000

512000

421000

421000

1166300

828220

656200

538610

426200

0.0

29.0

43.7

53.8

63.5

Column

668075

668075

668075

668075

668075

Trays

54290

54290

54290

54290

54290

Top condenser

189174

0.0

106057

89937

67499

0.0

136511

0.0

0.0

0.0

108634

248355

328462

278969

278969

Trim-reboiler

0.0

53427

0.0

0.0

0.0

Intermediate reboiler

0.0

0.0

0.0

110637

110637

Heater

0.0

16449

21409

18602

28777

Compressor

0.0

2064832

2881831

2451393

2451393

Total capital cost ($)

1381356

3603122

4421307

4033086

4020823

TAC ($/y)

1372163

1365193

1315107

1139661

1025423

0.0

0.5

4.2

16.9

25.3

Cooler duty (kW)

Cost of medium pressure steam($/y)

Operating cost ($/y) Operating cost saving (%) Capital cost ($)

Cooler Reboiler

TAC saving (%)

28


Page 29 of 31

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


Table 2. Comparison of Estimated Operating and Capital Costs in Case 2 Items

DWC

SVRC-DW C

REVRC-DWC

HI-VRC-DWC

IHI-VRC-DWC

Condenser duty (kW)

5610

0.0

1691

1183

880

0.0

2401

0.0

0.0

0.0


59000

25500

17900

12600

9400


5711

1058

0.0

0.0

0.0


0.0

4653

5711

4148

4148


0.0

0.0

0.0

1583

1583

2428000

449800

0.0

0.0

0.0

Heater duty (kW)

0.0

341

422

303

303


0.0

135700

167900

120550

0.0


0.0

1101

1364

978

978


0.0

616000

763000

547000

547000

2487000

1227000

948800

680150

556400

0.0

50.7

61.5

72.7

77.6

Column

1608994

1608994

1608994

1608994

1608994

Trays

185029

185029

185029

185029

185029

Top condenser

427939

0.0

196299

155543

128414

0.0

242726

0.0

0.0

0.0

135878

417737

479989

396713

396713

Trim-reboiler

0.0

45419

0.0

0.0

0.0


0.0

0.0

0.0

143761

143761

Heater

0.0

19831

22927

18602

121603

Compressor

0.0

3351042

3994496

3040830

3040830


3254852

6767790

7384746

6446484

6522356

TAC ($/y)

2972071

2235604

2049349

1640870

1528427

0.0

24.8

31.0

44.8

48.6

Cooler duty (kW)


Operating cost ($/y) Operating cost saving (%) Capital cost ($)

Cooler Reboiler

TAC saving (%)

29



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

Page 30 of 31

Table 3. Comparison of Estimated Operating and Capital Costs in Case 3 Items

DWC

SVRC-DWC

REVRC-DWC

HI-VRC-DWC

IHI-VRC-DWC

Condenser duty (kW)

3908

0.0

955

821

729

0.0

1463

0.0

0.0

0.0


41000

15500

10100

8700

7700


4064

709

0.0

0.0

0.0


0.0

3355

4064

3582

3582


0.0

0.0

0.0

528

528

1728000

301400

0.0

0.0

0.0

Heater duty (kW)

0.0

86

104

92

92


0.0

34220

41380

36600

0.0


0.0

825

1000

880

880


0.0

461000

559000

492000

492000

1769000

812120

610480

537300

499700

0.0

54.1

65.5

69.6

71.8

Column

980816

980816

980816

980816

980816

Trays

92566

92566

92566

92566

92566

Top condenser

136200

0.0

54440

49492

45820

0.0

69100

0.0

0.0

0.0

247433

353982

405834

373861

373861

Trim-reboiler

0.0

79513

0.0

0.0

0.0


0.0

0.0

0.0

119111

119111

Heater

0.0

17758

19831

12638

14090

Compressor

0.0

2644883

3096808

2788625

2788625


1993706

4775309

5186986

4953800

4951580

TAC ($/y)

2066122

1523784

1383497

1275565

1237634

0.0

26.2

33.0

38.3

40.1

Cooler duty (kW)


Operating cost ($/y) Operating cost saving (%) Capital cost($)

Cooler Reboiler

TAC saving (%)

30


Page 31 of 31

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


Table of Contents Graphic Heater

Comp

Condenser

D

Comp

Heater

D

Cooler S

F

S

F

TV

TV

Reboiler

W

Reboiler

W

Trim-reboiler

(a) Condenser

(b)

Heater

Comp

Comp

Heater

Condenser

D D TV

TV

S

F

S F IR IR

Reboiler

W

Reboiler

W

(c)

(d)

Schematic diagrams of the (a)SVRC-DWC; (b)REVRC-DWC; (c)HI-VRC-DWC and (d)IHI-VRC-DWC

31


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