Rigorous Comparative Study of Energy-Integrated Distillation Schemes

Ind. Eng. Chem. Res. 1996, 35, 1877-1885

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Rigorous Comparative Study of Energy-Integrated Distillation Schemes Omar Annakou and Peter Mizsey* Department of Chemical Engineering, Technical University of Budapest, H-1521 Budapest, Hungary

This paper presents results of a rigorous study and comparison of conventional and energyintegrated distillation schemes for the separation of ternary mixtures. The major part of this work is devoted to the design and simulation of the fully thermally coupled distillation column (Petlyuk or Kaibel column) with particular emphasis on the question of the fractional recovery of the middle component in the prefractionator and as a consequence the internal recycle streams. A comparative economic parametric study is carried out for three different distillation schemes: conventional sequences, heat-integrated columns, and the fully thermally coupled distillation column. The heat-integrated columns show the best economic features over the other two schemes except the few cases when the concentration of the middle component in the feed is high and the A/B split is more difficult than the B/C split. In such rare cases the fully thermally coupled distillation column proves to be the cheapest solution. In the cases of sharp separations the heat-integrated scheme is always the most economical solution. 1. Introduction Distillation columns are the most widely used separation units in the petrochemical and chemical industries. In order to reduce their significant energy consumption there have been several successful developments by the use of process and energy integration techniques. A possible way is the integration of conventional distillation columns into the remainder of the process (e.g., Smith and Linnhoff, 1988; Mizsey and Fonyo, 1990). If this integration is limited or impossible, the operation of the distillation columns should be investigated and/ or energy-integrated solutions between the individual columns and nonconventional arrangements should be considered such as heat integration, thermocoupling, and heat pumping (Meszaros and Fonyo, 1986; Mizsey and Fonyo, 1992; Annakou and Mizsey, 1995). The aim of these energy-integrated schemes is cost saving by less energy consumption. The successful schemes are usually compared to the conventional arrangements as well as to other energy-integrated alternatives. The selection from the several energy-integrated solutions is usually based on economic features. One of the early works in this area is the study of Tedder and Rudd (1978), who have analyzed the economic features of eight distillation schemes for the separation of ideal ternary mixtures. These distillation schemes include conventional direct and indirect sequences, sidestream strippers, sidestream rectifiers, etc. However, the fully thermally coupled distillation column (FTCDC) known as the Petlyuk column or dividing wall column (Petlyuk et al., 1965; Kaibel, 1987) has not been included (Figure 1c,d). They have found that the regions of economic optimality for various designs depend on the ternary mixtures separated, but changes in the feed composition have characteristic effects on the total annual costs. Kaibel (1987) has introduced a different arrangement of the FTCDC by using only one distillation column with the vertical partition known as the dividing wall column. Kaibel has concluded that the typical energy savings of such a column compared to conventional distillation arrangements is 20-35%. * Author to whom correspondence should be addressed. Fax: +36 1 463 3197. Email: [email protected].

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Fidkowski and Krolikowski (1986, 1987) have studied ideal ternary solutions and selected the fractional recovery of the middle component in the top product of the prefractionator as a decision variable. They have also compared the FTCDC to conventional sequences and other thermally coupled schemes shown in Figure 1. They have developed an optimization procedure for FTCDC aiming at minimizing the vapor flow rate from the system’s reboiler. They have used the Underwood method for calculating minimum vapor flow rates, and they have not considered the number of theoretical plates. For the optimal fractional recovery of the middle component in the top product of the prefractionator, they have used the formula based on the relative volatilities introduced by Treybal (1968). They have found that the FTCDC is the least energy-consuming scheme. However, they have indicated that rigorous methods must be used for design purposes. Glinos and Malone (1988) have studied ternary mixtures and sharp separation for several distillation alternatives including sidestream strippers, sidestream rectifiers, a prefractionator, and a Petlyuk column. In all cases they have focused on optimality regions in terms of the minimum total vapor rate generated by the reboilers. On the basis of this optimality measure, they have developed approximate designs for the complex columns and compared them to the conventional direct and indirect sequences. For the FTCDC they have suggested that the multiple solutions can be easily bounded and the optimal solution is one that minimizes the total vapor flow rate in the whole system. Carlberg and Westerberg (1989) have studied the thermally coupled columns using the vapor flow rate as bases. They have indicated that the recovery of the middle component in the prefractionator is not an independent variable because it depends on the recoveries of the light and heavy components. Rev (1990) has developed a model for designing distillation columns with a single distributing component. He has studied the FTCDC and emphasized the importance of the distribution of the middle component. He has derived analytical expressions for the limiting flow rates in the FTCDC to determine the optimal fractional recovery or “balanced split” of the middle component. His analytical © 1996 American Chemical Society

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Ind. Eng. Chem. Res., Vol. 35, No. 6, 1996

Figure 1. Different arrangements of thermally coupled distillation columns.

expression for the optimal fractional recovery, however, is different from that of Treybal (1968) and Fidkowski and Krolikowski (1986). His work is a theoretical one with no case studies. Triantafyllou and Smith (1992) have presented a shortcut design procedure for the FTCDC. They have recognized that the flow rates in the main column are not independent of the vapor flow fed to the prefractionator. They have compared the dividing wall column to the conventional arrangement and found that about 30% of the total cost can be saved. The vapor flow in the main column is not independent of the vapor flow fed to the prefractionator, and the specifications of the recoveries of the light and the heavy components in the prefractionator determine the vapor and liquid drawoff rates. Triantafyllou and Smith (1992) have also emphasized the basic principle of Petlyuk et al. (1965) that in the case of the FTCDC there is no remixing effect in the system, which would be a source of inefficiency in the separation, on the contrary to simple distillation columns separating a ternary mixture.

It can be concluded from the review of the previous works that the question of the vapor and liquid drawoff rates, that is, the internal recycle streams in the FTCDC, has not been resolved, yet. Most of these studies are based on shortcut methods and are for sharp separations. None of the previous studies has included the heat-integrated columns and tried to compare their performance to the fully thermally coupled distillation column. The present study is an attempt to address the unanswered questions. 2. Aim of This Work The aim of this work is to investigate energyintegrated distillation schemes and compare them to each other and to the best conventional distillation scheme (Figure 2) used for the separation of ternary mixtures. The energy-integrated schemes studied (Figures 3 and 4) are heat-integrated distillation columns and the fully thermally coupled distillation column (FTCDC). Particular emphasis of this work is devoted to solve the design questions of the FTCDC.

Ind. Eng. Chem. Res., Vol. 35, No. 6, 1996 1879

Figure 2. Conventional distillation schemes for the separation of ternary mixtures.

Figure 3. Heat integration for the direct separation sequence.

3. Systems Studied 3.1. Conventional Distillation Scheme. In the case of the separation of ternary mixtures, the conventional schemes consist of two columns (columns with one feed and two products). These schemes are known as direct and indirect sequences (Figure 2). 3.2. Heat-Integrated Distillation Scheme. Heat integration is an important method for conserving energy in the chemical process industries. Heat integration of two columns, which is also called the match of two columns, is based on the idea of utilizing the overhead vapor of one column to provide its heat content for boiling up a second column. Two solutions of the heat integration are considered for each separation sequence. Figure 3 shows them in the case of the direct separation sequence. In the first scheme the first column boils up the second one, called forward match, and the opposite solution is the reverse match. 3.3. Fully Thermally Coupled Distillation Column. In the case of thermocoupling a part of the heat needed for the separation is provided through material flows. Figure 1 shows several arrangements which utilize thermocoupling to cover a part of the heat required for separation. The fully thermally coupled distillation column (Figure 1c) has been known for more than a half-century, and theoretical studies have shown that it can save about 30% of energy compared to conventional schemes (Brugma, 1942; Petlyuk et al., 1965). In the case of the dividing wall column, also known as the Kaibel column, Figure 1d (Kaibel, 1987; Triantafyllou and Smith, 1992)

from the point of mathematical modeling the column is practically identical to the Petlyuk column if we neglect the heat transfer across the dividing wall or insulate it (Lestak et al., 1994). Figure 4 shows the model of the FTCDC with the variables and streams studied. The first column is the so-called prefractionator without condenser and reboiler, and the second column is known as the main column with condenser and reboiler. The columns are connected by liquid and vapor streams (two feed streams, two side draw-off streams). 4. Design and Simulation of the FTCDC Due to the recycle streams between the two columns, the design of such complex columns becomes a difficult task compared to conventional arrangements. To design and simulate the FTCDC system shown in Figure 4, several quantities must be determined: (1) number of theoretical trays in the prefractionator, (2) number of theoretical trays in the main column, (3) internal recycle streams, liquid stream draw-off from the main column to the prefractionator (L21), and vapor stream draw-off from the main column to the prefractionator (V21), (4) reflux ratio in the main column, (5) tray locations for all feed streams, side draw-off streams, and side product stream. For such a design problem two major approaches of the process syntheses are in use: the hierarchical approach (e.g., Douglas, 1985, 1988) and the algorithmic approach (Grossmann, 1989; Viswanathan and Gross-

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Figure 5. Three-column model to represent FTCDC.

Figure 4. Streams and variables of the fully thermally coupled distillation column (FTCDC) modeled.

mann, 1993). The two major approaches can also be combined (Mizsey and Fonyo, 1990). In our work we apply the tools of the hierarchical approach. We start the solution by shortcut design procedures to estimate the number of theoretical trays, location of the feed trays and draw-off trays, and the reflux ratio. In the next step of the design the system is to be investigated by rigorous modeling and changes should be made according to the desired performance. Figure 5 shows a simplified model of the FTCDC in which three columns are used to represent the whole system. One is the prefractionator (column 1) and the other two columns (columns 2 and 3) are for the separation of A/B and B/C, respectively. This simplified three-column model has been already used by Carlberg and Westerberg (1989) and Triantafyllou and Smith (1992) as the basis for shortcut design. 4.1. Design Model for the Prefractionator. First, the prefractionator is to be designed as a separate unit. In the prefractionator it is supposed that the most volatile component (A) of the ternary mixture (A, B, C) is only in the top product and the heaviest component (C) is only in the bottom product. The middle component (B) distributes between the top and bottom products. This distribution is influenced by the number of theoretical trays in the prefractionator and the internal recycle streams of the FTCDC. Having determined these design parameters, the net top product (V12 - L21) and the net bottom product (L12 - V21) of the prefractionator can be estimated. The net top product is:

V12 - L21 ) A + βB

(1)

and the net bottom product is:

L12 - V21 ) C + (1 - β)B

(2)

where β is the fractional recovery of the middle component in the top product and ranges between 0 and 1:

β)

DFxDF,B FFxFF,B

(3)

The optimal fractional recovery of the middle component where the energy consumed by the FTCDC is minimal has been defined by Treybal (1968) in terms of the relative volatilities and also used by Fidkowski and Krolikowski (1986) for saturated liquid feed:

β* )

RB - RC RA - RC

(4)

β*, also called the balanced fractional recovery, is used to estimate the flow rates in the prefractionator and also the internal recycle streams. The prefractionator is modeled as a separate column with a ternary feed mixture and two product streams defined by eqs 1 and 2. Figure 6 shows the prefractionator shortcut model. In this model a partial condenser and partial reboiler are assumed. On the basis of this model and the mass balance, the internal recycle streams, the number of theoretical trays in the prefractionator, and the feed tray location can be estimated. 4.2. Design Model for the Main Column. Figure 5 shows a shortcut model for designing the main column. This model consists of two simple columns, column 2 and column 3. Column 2 is a simple binary column splitting the net feed stream of A + βB into two products: A and B. Column 3 is also a simple binary distillation column separating the net feed stream of C + (1 - β)B into two products: B and C. On the basis of this model, the number of theoretical trays (the sum of theoretical trays of column 2 and column 3), reflux ratio, and feed tray locations for both columns can be estimated. The tray locations for the draw-off streams are adjacent to the feed tray for both columns. These appropriate tray locations have a paramount importance in the optimal operation of the FTCDC (and also the


Figure 6. Shortcut model for the prefractionator.

conventional columns) because irreversible losses occur in distillation operations due to mismatches between the composition of the column feed and the composition on the feed plate. The shortcut model calculates the optimal feed tray location by the Kirkbride relationship (Kirkbride, 1944). The determination of the reflux is a crucial point of the design. On the basis of the results obtained by the simulation of column 2 and column 3, the reflux flow rate of that column is selected which is higher and that will be the reflux flow rate of the main column. 4.3. Combined Approach for Design and Simulation of the FTCDC. For the design and simulation of the FTCDC the steps discussed can be outlined in a combined approach shown in Figure 7. This approach starts by calculating the feed temperature TF for a saturated liquid feed and then the balanced fractional recovery (β*) using eq 4. The next step is to solve the prefractionator using the shortcut model already mentioned. From the prefractionator model the number of theoretical trays for the prefractionator NP and the internal recycle streams can be estimated. The optimal feed tray locations meet the requirement that the streams from the prefractionator (V12 and L12) are fed to the plates of the main column whose corresponding compositions (vapor or liquid) most closely approximate the feed compositions. As far as the feed streams from the main column to the prefractionator are concerned, the streams of the other phase (liquid or vapor, respectively) of the feed plates in the main column are selected (L21 and V21) which are, by definition, in equilibrium with the feed streams from the prefractionator since these feed streams are already optimally located. The main column is represented by columns 2 and 3 in Figure 5. The number of theoretical trays in the main column NM can be estimated by the sum of the number of theoretical trays in column 2 (N2) and column 3 (N3), and the reflux flow rate and the reflux ratio are also determined according to the design model. The final step is the rigorous simulation of the FTCDC, and appropriate changes can be made according to the performance desired by altering the operating variables (e.g., checking the right tray locations for the draw-off and feed streams, proper reflux ratio).

Figure 7. Combined approach for design and simulation of the FTCDC. Table 1. Ternary Mixtures Studied mixture

RA

RB

RAB

SI

β*

pentane-hexane-heptane isopentane-pentane-hexane butane-isopentane-pentane

7.38 3.62 2.95

2.67 2.78 1.3

2.76 1.3 2.26

1.03 0.47 1.74

0.26 0.68 0.154

Table 2. Product Purity Specifications

case

product purity specifications (%), A)B)C

1 2 3

99 95 90

Table 3. Feed Compositions case

feed composition A/B/C

1 2 3 4

33/34/33 80/10/10 10/80/10 10/10/80

5. Case Studies Three different ternary mixtures of different eases of separation at four different feed compositions and three different product purity specifications are investigated (Tables 1-3). The ease of separation can also be characterized by the separation index (SI):

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Figure 8. Annual cost and reboiler duty versus β for mixture 1.

Figure 9. Annual cost and reboiler duty versus β for mixture 2.

SI ) RAB/RBC

(5)

In mixture 1 A/B separation is almost as B/C separation (SI ∼ 1). In mixture 2 A/B separation is more difficult than B/C separation (SI < 1). In mixture 3 B/C separation is more difficult than A/B separation (SI > 1). A professional simulation package, PROCESS, is used for the shortcut and rigorous modeling of the distillation schemes studied (Simulation Sciences, Inc., 1985a,b). The rigorous model of the package also sizes the equipment. The total cost is selected as an objective function. The installation cost is calculated by the PROCESS cost functions. The equipment cost calculations have adjustments for construction material type, installation cost, and operating conditions (pressure and temperature). The calculation is based on the size of the equipment item, e.g., diameter, height, volume, number of theoretical trays. The utility prices are shown in Table 4. The project life is 10 years.

Table 4. Utility Costs utility

cost

electricity cooling water low-pressure steam medium-pressure steam high-pressure steam

0.10 US$/kwh 0.31 US$/thousand of US gallons 13.00 US$/ton 16.00 US$/ton 20.00 US$/ton

6. Investigation of the Fractional Recovery in the FTCDC A comprehensive parametric study is performed to investigate the role of the fractional recovery on the energy consumption and the total annual cost of the FTCDC. The FTCDC is rigorously simulated at several fractional recovery values within the range of 0 < β < 1 and also at the balanced fractional recovery (β*). 6.1. Results of the Fractional Recovery Study. Figures 8-10 show the plots of the annual total cost and the reboiler duty versus the fractional recovery for the three ternary mixtures. Table 5 shows the balanced


Figure 10. Annual cost and reboiler duty versus β for mixture 3. Table 5. Fractional Recovery Values mixture

β*

βp

1 2 3

0.26 0.68 0.154

0.26 0.70 0.15

fractional recovery and the optimal fractional recovery obtained by the parametric study. The balanced fractional recoveries calculated by eq 4 are close to the values obtained by the parametric study (βp). The optimal fractional recoveries βp are taken from the plots of the objective function, i.e., the annual total cost versus β. The plots of the reboiler duty versus β indicate the energy consumption of the FTCDC at different values of the fractional recovery and clearly show the proportionality of the total cost to the energy consumption represented by the reboiler duty. These results obtained by rigorous simulations show the importance of the fractional recovery that have already been discussed in previous works. Stupin (1971) has arbitrarily set the vapor and liquid flows from the main column to the prefractionator. Chavez et al. (1986) have found multiple solutions for a Petlyuk separation system over a range of reflux ratios. Glinos and Malone (1988) have also reported that there might be an infinite number of solutions for the fractional recovery of the middle component and for the quantity of vapor fed to the prefractionator from the main column, but these solutions can be bounded by an upper and a lower vapor rate determined for the possible splits (A/BC, AB/BC, AB/C) in the prefractionator. Our results also indicate the importance of the fractional recovery and its role in determining the internal recycle streams for better economic performance of the FTCDC. The fractional recovery and as a following the internal recycle streams should not be arbitrarily selected. They are very important design parameters and should be determined to obtain the optimal economic performance of the FTCDC. The claim that the FTCDC is a flexible system and can handle various quantities for recycle streams for the same separation is true. However, this can be done only on the expenses of more energy consumption which implies higher cost values.

Figure 11. Composition profile of the middle component in the main column for the FTCDC.

7. Comparative Economic Parametric Study of the Different Distillation Schemes A comparative study is performed for the three different distillation schemes: (1) the conventional sequences (direct and indirect), (2) the heat-integrated columns, (3) the FTCDC. As a part of the parametric study, the optimal feed tray locations and the proper reflux ratios are also studied and tuned by rigorous tools. In the case of the FTCDC, Figure 11 shows an example for the composition profile of component B in the main column for the mixture 1, equimolar feed composition, purity 99% case. The feed trays and feed compositions are also indicated. According to the composition profile, the feeds are properly located in this case. Among the 33 FTCDC cases studied there are such cases where according to the rigorous simulation the locations of the feed trays can be shifted. These shifts mean 3-4 theoretical trays at the most and a change in the total cost of less than 1%. Since our aim is also the comparison of the three distillation schemes to determine the optimal range of their use, the same procedure is followed for the conventional scheme as well. The change of the cost is also less than 1%. As a consequence, this final tuning by rigorous simulation, which carefully should be done in the case of individual column design, does not influence our conclusions. 7.1. Results of the Comparative Economic Parametric Study. The results for the three different

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Table 6. For Feed Composition 33/34/33 purity mixture % conventional 1 2 3

99 95 90 99 95 90 99 95 90

8.0 7.11 6.68 16.4 14.84 13.83 19.6 18.0 14.61

HI 6.17 5.04 4.76 14.2 12.9 12.2 17.7 16.44 12.46

conv. HI FTCDC seq seq. match 6.66 5.9 5.53 19.0 13.7 12.4 18.9 16.53 14.27

D D D D D D D D D

D D D D D D D D D

R R R R R R R R R

Table 7. For Feed Composition 80/10/10 mixture 1 2 3

purity % conventional 99 95 90 99 95 90 99 95 90

6.75 5.6 5.27 21.8 12.35 8.14 22.9 10.7 9.77

HI

FTCDC

conv. seq

5.83 4.88 4.85 21.3 11.7 8.1 18.6 10.38 9.93

6.2 5.43 5.1 24.1 13.16 9.7 23.4 14.29 10.75

D D D D D D D D D

H seq. match D D D D D D D D D

R R R R R R R R R



9.51 7.33 6.06 22.3 15.13 12.68 19.98 15.25 13.06

HI

FTCDC

6.56 5.14 5.29 15.35 14.4 11.92 17.21 13.46 6.97

7.4 5.68 5.47 17.3 11.2 8.6 21.4 14.26 8.88

conv. HI seq seq. match D D D D D D D D D

D D D D D D D D D

R R R R R R R R R



conv. HI seq seq. match

HI

FTCDC

7.73 5.2

5.5 4.55

5.61 4.3

ID ID

ID ID

F F

11.1 9.45

9.7 9.3

10.1 9.33

D D

D D

R R

19.1 13.87

16.7 11.92

20.4 15.14

ID ID

ID ID

F F

separation schemes obtained by rigorous simulations are shown in Tables 6-9. The total costs are shown in 105 US$/year at a feed flow rate of 100 kg‚mol/h, and the equipment is always sized for the sharpest purity specification; that is, the different product purities are satisfied by varying the operational parameters (e.g., feed tray locations, reflux ratios). The number of the theoretical plates ranges from 20 to 95 according to the difficulty of the separation problems. The reflux ratios outline the difficulty of the separation problems, and from the 99 cases studied, as examples, the equimolar feed and 99% purity cases are selected (conventional scheme column 1, column 2, and FTCDC): mixture 1 (1.5, 1.8, and 3.2), mixture 2 (8.2, 1.7, and 14), and mixture 3 (2.2, 11, and 15). The portion of the utility cost in the total cost ranges from 75 to 81% in the case of the conventional scheme, it is between 60 and 74% in the case of the heatintegrated scheme, and in the case of the FTCDC it is between those of the conventional and heat-integrated schemes. The optimal conventional separation sequence (D ) direct sequence, ID ) indirect sequence), the optimal heat-integrated sequence (HI), and the type of

match sequence (F ) heat-integrated forward match, R ) heat-integrated reverse match) are indicated. According to the comparison of the total cost calculated by rigorous simulations, the heat-integrated schemes are always more economical than the conventional distillation. The FTCDC shows considerable energy savings in several cases compared to the cheapest conventional scheme. However, it can be competitive with the heat-integrated schemes in only those few cases when the concentration of the middle component in the feed is high and the A/B split is harder than B/C split (mixture 2, feed composition (10/80/10), product purity specification 95% and 90%; Table 8). This result of our rigorous parametric study is in agreement with the theoretical predictions of Glinos and Malone (1988). 8. Conclusions Three different ternary distillation schemes, the conventional distillation schemes, the heat-integrated schemes, and the fully thermally coupled distillation column, are studied by rigorous modeling and compared to each other on the basis of the total cost. Three mixtures with different eases of separation are investigated at four different feed compositions and three different product purity specifications. For the design of the fully thermally coupled distillation column a combined procedure combining the shortcut and rigorous methods is presented. Particular emphasis is given to the determination of the optimal fractional recovery of the middle component in the prefractionator and the internal recycle flows between the main column and the prefractionator. The results of this investigation show that the optimal fractional recovery can be determined on the basis of the relative volatilities. The internal recycle streams are also important design parameters, and they should also be determined for the optimal performance. The economic comparisons of the three distillation schemes show that the heat-integrated scheme is always more economical than the best conventional scheme. The FTCDC shows considerable energy savings in several cases compared to the conventional systems. The energy savings of the two energy-integrated structures range between 10 and 50%. The FTCDC can be competitive with the heat-integrated schemes only in those few cases when the concentration of the middle component in the feed is high and the A/B split is harder than B/C split. The thermally coupled distillation column is not recommended when the composition of the least volatile component is the highest in the feed. In the cases of sharp separations the heat-integrated scheme is always the most economical solution. Nomenclature A ) lightest component B ) middle component C ) heaviest component DF ) distillate product flow rate, kg‚mol/h FF ) feed flow rate, kg‚mol/h L12 ) liquid flow from the prefractionator to the main column L21 ) liquid draw-off from the main column to the prefractionator LR ) reflux flow rate in the main column, kg‚mol/h LR2 ) reflux flow rate in column 2 of the simplified model, kg‚mol/h LR3 ) reflux flow rate in column 3 of the simplified model, kg‚mol/h

Ind. Eng. Chem. Res., Vol. 35, No. 6, 1996 1885 N ) number of theoretical trays N2 ) number of theoretical trays in column 2 of the simplified model N3 ) number of theoretical trays in column 3 of the simplified model NM ) number of theoretical trays in the main column NP ) number of theoretical trays in the prefractionator q ) feed thermal condition SI ) separation index TF ) feed temperature V12 ) vapor flow from the prefractionator to the main column V21 ) vapor draw-off from the main column to the prefractionator x ) liquid composition xDF,B ) composition of the middle component (B) in the distillate product stream xFF,B ) composition of the middle component (B) in the feed stream y ) vapor composition R ) relative volatility β ) fractional recovery of the middle component β* ) balanced fractional recovery of the middle component βp ) optimal fractional recovery obtained by the parametric study

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Grossmann, I. E. MINLP Optimization Strategies and Algorithmic for Process Synthesis. Proceedings of FOCAPD’89, Snowmass, CO, July 1989. Kaibel, G. Distillation Columns with Vertical Partitions. Chem Eng. Technol. 1987, 10, 92-98. Kirkbride, C. G. Pet. Refin. 1944, 23, 32. Lestak, F.; Smith, R.; Dhole, V. Heat Transfer Across the Dividing Wall of Dividing Wall Columns. Trans. Inst. Chem. 1994, 72, 639-644. Meszaros, I.; Fonyo, Z. A New Bounding Strategy for Synthesising Distillation Schemes with Energy Integration. Comput. Chem. Eng. 1986, 10, 545-550. Mizsey, P.; Fonyo, Z. Toward a More Realistic Process Synthesiss The Combined Approach. Comput. Chem. Eng. 1990, 14 (11), 1213-1236. Mizsey, P.; Fonyo, Z. Energy Integrated Distillation System Design Enhanced by Heat Pumping, Distillation and Absorption. Inst. Chem. Eng. 1992, B69-76. Petlyuk, F. B.; Platonov, V. M.; Slavinskii, D. M. Thermodynamically Optimal Method for Separating Multicomponent Mixtures. Int. Chem. Eng. 1965, 5 (3), 555-561. Rev, E. The Constant Heat Transport Model and Design of Distillation Columns with One Single Distributing Component. Ind. Eng. Chem. Res. 1990, 29, 1935-1943. Simulation Sciences Inc. PROCESS Reference Manual; SimSci: Fullerton, 1985a; pp 8.1-8.5. Simulation Sciences Inc. PROCESS Reference Manual; SimSci: Fullerton, 1985b; pp 9.1-9.32. Smith, R.; Linnhoff, B. The Design of Separators in the Context of Overall Processes. Chem. Eng. Res. Des. 1988, 66, 195-228. Stupin, W. J. The Separation of Multicomponent Mixtures in Thermally Coupled Distillation Systems. Ph.D. Dissertation, University of Southern California, Los Angeles, CA, 1971. Tedder, D. W.; Rudd, D. F. Parametric Studies in Industrial Distillation. AIChE J. 1978, 24, 303-315. Treybal, R. E. Mass Transfer Operations, 2nd ed.; McGraw-Hill: New York, 1968. Triantafyllou, C.; Smith, R. The design and Optimisation of Fully Thermally Coupled Distillation Columns. Trans. Inst. Chem. 1992, 70, 118-132. Viswanathan, J.; Grossmann, I. E. Optimal Feed Locations and Number of Trays for Distillation Columns with Multiple Feeds. Ind. Eng. Chem. Res. 1993, 32, 2942-2949.

Received for review July 17, 1995 Revised manuscript received February 15, 1996 Accepted March 14, 1996X IE950445+

X Abstract published in Advance ACS Abstracts, May 1, 1996.

Rigorous Comparative Study of Energy-Integrated Distillation Schemes

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