a new fully thermal coupled distillation column with postfractionator

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Chemical Engineering and Processing 45 (2006) 254–263

A new fully thermally coupled distillation column with postfractionator

Young Han Kim ∗

Department of Chemical Engineering, Dong-A University, 840 Hadan-dong, Saha- gu, Pusan 604-714, Republic of Korea

Received 12 October 2004; received in revised form 17 February 2005; accepted 17 March 2005

Available online 24 October 2005

Abstract

For the improvement of distillation column efficiency, a new system of a fully thermally coupled distillation column is proposed and its

performance is examined with two industrial processes. The system has an extra column called postfractionator and attached to the main column

of an original fully thermally coupled distillation column.The outcome of performance investigation indicates that a 29% energy saving is yielded with fractionation process and a 7% saving with gas

concentration process over the original fully thermally coupled distillation column. The design detail of the new system is explained, and the

increase of distillation column efficiency is discussed. In addition, some considerations on the new column construction, such as arrangement of

distillation column sections and divided wall construction, are discussed here.

© 2005 Elsevier B.V. All rights reserved.

Keywords: Thermally coupled distillation; Energy-efficient distillation; Fractionation process; Gas concentration process; Multi-component distillation

1. Introduction

The application of a fully thermally coupled distillationcolumn has been increasing in a variety of plants of the

world including North America [1–2]. Especially, the prac-

tical application is active in Europe and Japan, where the

demand of energy conservation is larger than other places

because most of crude oil consumed there is imported from other

countries.

For the cost saving in multi-component distillation, many

alternative configurations of complex distillation systems have

been proposed and systematically examined to find the best

selection. Dunnebier and Pantelides [3] proposed an optimal

design technique leading to the configuration of minimum oper-

ating and capital costs among various alternatives for three

and four component distillation systems. A conventional direct

or indirect sequence ternary distillation system was modified

by introducing an additional vapor stream connection between

the first and second columns to improve column efficiency of

the distillation with increased reversibility of distillation in the

second column [4]. Also, alternative configurations of a fully

∗ Tel.: +82 51 200 7723; fax: +82 51 200 7728.

E-mail address: [email protected].

thermally coupled distillation column were proposed by elim-

inating one or two of the four interconnecting streams [5].

Because the vapor transfer between distillation columns causesan operational problem requiring tight pressure control at the

columns, a general framework was introduced for the design of

thermallycoupled distillation columns without anyintercolumn-

vapor transfers [6].

A systematic method to generate possible distillation con-

figurations for multi-component systems was presented using

the state-task network (STN) representation, and a procedure to

derive distinct thermally coupled configurations from the basic

distillation system was introduced by Agrawal [7]. The design

procedure of complex distillation columns with the STN rep-

resentation is explained in detail elsewhere [8]. A variety of

configurations of thermally coupled distillation columns were

demonstrated in practical aspects, and the shortcut design pro-

cedures for simple distillation columns were presented by Shah

[9]. Though many possible configurations of thermally coupled

distillation columns have been proposed, the proposed config-

uration with a postfractionator for ternary separation was not

introduced yet. Even the systematic method for the new con-

figurations utilizing the STN representation does not show the

proposed configuration. The STN representation connects nodes

of feed and products with lines indicating column section, but

the proposed configuration has a connection between two lines,

0255-2701/$ – see front matter © 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.cep.2005.03.013



Y.H. Kim / Chemical Engineering and Processing 45 (2006) 254–263 255

which the existing method does not include as a possible con-

figuration.

At total reflux operation, the liquid composition profile of

trays in a distillation column matches one of equilibrium distil-

lation lines, in which minimum number of trays having perfect

distillation column efficiency is required for the separation. The

structure of the distillation system is called minimum-stage

distillation-column configuration here. Because the column pro-

file of a fully thermally coupled distillation column is simi-

lar to the equilibrium distillation line, high distillation column

efficiency is available from the reduced feed tray mixing and

remixing of intermediate component. The mixing and remixing

are irreversible processes lowering the efficiency [10]. A struc-

tural design procedure based on the minimum-stage distillation-

column configuration has been applied to various systems of

ternary [11–14] and quaternary systems [15,16].

When the composition of intermediate component in feed

is low, the column profile of a prefractionator including the

feed tray composition and that of a main column containing the

composition of side product—having high concentration of theintermediate component—are distant in a fully thermally cou-

pled distillation column [13]. Therefore, interlinking between

the prefractionatorand main column produces large composition

mismatch between two interlinking trays unless a large number

of trays are utilized. In the large tray number system, the com-

position difference between adjacent trays is so small that it is

easy to find the interlinking trays of close compositions. In case

of an industrial application of the fully thermally coupled distil-

lation column in Japan, this problem does not arise because the

composition of intermediate component in feed is high.

The fractionation process for the separation of BTX mix-

ture is one of the largest processes in a petrochemical plant [17].Because the processing amount of the process is large, the effect

of energy saving is significant. Currently, a series of simple dis-

tillation columns separates the products from the process one at

a time, but the beginning two columns can be replaced with a

fully thermally coupled distillation column. The gas concentra-

tion process separating ethane, propane and butane mixture has

a similar structure of separation processes with a large amount

of processing capacity.

In this study, a new configuration of the fully thermally cou-

pled distillation column is proposed to solve the large mismatch

of compositions in interlinking trays to raise thermodynamic

column efficiency by adding a postfractionator to the main col-

umn of an original fully thermally coupled distillation column(the Petlyuk column). By examining thecolumn profiles of a pre-

fractionator andmain column a way of reducing the composition

mismatch is proposed from exploring how the modification of

the original fully thermally coupled distillation column affects

distillation column efficiency. The procedure of structuraldesign

of the proposed system is explained here, and theenergy require-

ment of the system is compared with that of the original fully

thermally coupled distillation column. Two industrial examples

of the fractionation process handling BTX mixture and the gas

concentration process of ethane, propane and butane mixture

are employed in the performance evaluation using a commer-

cial design program, HYSYS.

Fig. 1. A schematic diagram of a fully thermally coupled distillation column.

2. Design procedure

Whereas Fig.1 demonstrates the original fully thermally cou-

pled distillation column, Fig. 2 describes the proposed system

with a postfractionator. The main idea of the proposed modi-

fication is that the middle section separated with two dashed

lines becomes a postfractionator to raise distillation column

Fig. 2. A schematic diagram of the proposedfully thermally coupled distillation

column with postfractionator. Columns I–III are prefractionator, main column

and postfractionator, respectively.



256 Y.H. Kim / Chemical Engineering and Processing 45 (2006) 254–263

Fig. 3. Residue curves in equilibrium distillation of a ternary system.

efficiency. The design procedures of the proposed column are

explained below.

Residue curves of a ternary distillation drawn from the com-

position at a still of equilibrium distillation experiment are

shown in Fig. 3. As noticed from the plot, a ternary system

has many curves connecting two products of the lightest and the

heaviest components depending upon the initial composition of

intermediate component. The residue curves denote the com-

position profile for a packed distillation column in total reflux

operation [18]. Though the residue curves represent the liquid

composition profile of a packed column, it is generally assumed

that they are accurate representations of the profile of a tray col-umn at total reflux [18–20]. In a high reflux ratio distillation, a

column profile including feed composition is close to the base

of the diagram and that containing side product composition is

similar to one of the profiles near to the vertex as illustrated

in Fig. 4. In case of a direct sequence two-column system as

shown in Fig. 5a, the column profile for the first column has

similar shape to one of the curves, but three compositions of its

feed, overhead and bottom products are collinear on the profile

as plotted in Fig. 5b. Therefore, the profile is severely distorted

from the residue curve, which means that the system is far from

perfect distillation column efficiency and requires extra energy

for the irreversible mixing at feed tray and remixing of inter-

mediate component [10]. The column profile (Fig. 5b) of theconventional two-column system is of a practical BTX frac-

tionation process, and the compositions of feed, overhead and

bottom products are indicated in the figure. Losses occur due

to mismatch between the composition of column feed and the

composition on the feed tray. The composition of intermediate

component in the first column increases below the feed tray, but

as moving further down the column, the composition decreases

as illustrated in Fig. 5b. This remixing is a source of inefficiency

in the separation.

The structural design of the proposed fully thermally coupled

distillation column with a postfractionator is derived from the

design of an original fully thermally coupled distillation column

Fig. 4. Column profiles of minimum stage distillation column in BTX fraction-

ation process. The circles and ‘x’ symbols indicate prepractionator and main

column, respectively.

Fig. 5. A schematic diagram of a conventional-direct sequence two-column

system (a) and column profile of the practical two-column system in BTX frac-

tionation process. The circles and ‘x’ symbols indicate first and second columns.

The F, D and B are the compositions of feed, overhead and bottom products,

respectively.




by assigning the middle section including side draw tray—the

section indicated between two dashed lines in Fig. 1—as the

postfractionator. The design procedure of the original fully ther-

mally coupled distillation column is briefly explained here. The

structure of the fully thermally coupled distillation column is

based on the minimum stage distillation column configuration

at total reflux operation, which has perfect distillation column

efficiency. Then, a practical column system is designed by pro-

portionally extending the minimum-stage distillation-column

configuration keeping the high distillation column efficiency.

The design procedure gives a minimum number of trays at total

reflux operation. For a practical distillation column, the tray

number needs to be extended for finite liquid flow. In many field

applications, twice the minimum tray number is employed as

a practical tray number [21]. Therefore, the number of trays in

a practical fully thermally coupled distillation column is set to

twice the minimum. The optimality of this practice for the BTX

fractionation process is examined by comparing the investment

and operational costs for various numbers of the multiplying

factor [17], and it is shown that the factor of two is reasonable.Because not only the total number of trays but feed and side

draw locations are multiplied by two, the distillation column

of minimum tray number is proportionally extended when it is

converted into a practical distillation column. A practical liquid

flow for the practical distillation column is obtained from the

HYSYS simulation to yield the products of given compositions.

Among the residue curves in Fig. 3, two paths including

feed and side product compositions are utilized in the design.

Whereas the composition of side product is equal to the tray liq-

uid composition of side product, feed composition is different

from feed stage composition. For the design of the minimum-

stage distillation-column system, however, the composition of feed tray is assumed to be same to feed composition because

no feed tray mixing is present in an ideal distillation column.

From the feed composition, the composition profile of tray liq-

uid in a prefractionator is yielded from stage-to-stage calculation

using a vapor–liquid equilibrium relation. The VLE is calcu-

lated with the Peng–Robinson equation for both processes. In

the same manner, the profile for a main column is obtained from

the composition of side draw. The computed column profiles

of a prefractionator with feed composition and a main column

with side draw composition in the minimum-stage distillation

column are plotted in Fig. 4. Interlinking trays between the pre-

fractionator and main column are selected from the profiles

for close composition match to minimize mixing. The num-

bers of total trays, feed and side draw locations and interlinking

trays are determined by counting the tray compositions of the

prefractionator and main column evaluated from stage-to-stage

computation. The minimum-stage distillation-column configu-

ration is expanded to a practical column with the factor of two

using a practical design guideline [21], and the result of BTX

fractionation process is summarizedin Table 1. Also Table 2 lists

the computed outcome of gas concentration process. The tables

include the tray numbers of the original fully thermally coupled

distillation column and the proposed fully thermally coupled

distillation column for the same specification of products.

The postfractionator is taken from the middle section of main

column in the original fully thermally coupled distillation col-umn, which has high composition of intermediate component.

In the BTX fractionation process, the section is determined as

the trays of toluene composition between 0.9935 and 0.9939.

Notice that the composition of 0.9939 is that of side product.

For the gas concentration process, the propane compositions are

between 0.9605 and 0.9682. There is little change of compo-

sition in those trays like ones near to a pinch point. The tray

number of the section is 35 for the BTX fractionation process,

and that for the gas concentration process is 14. The tray num-

bers are included in Tables 1 and 2.

The industrial processes of this study handle 18-component

mixture in the BTX fractionation process and 9 componentsin the gas concentration process. The equilibrium computation

with these numbers of components is not easy with an in-house

design program, and therefore a commercial design program,

HYSYS, is employed in this study. When the structural infor-

mation for a distillation system is provided, the computation of

operating variables is straightforward. Otherwise, lots of itera-

Table 1

Tray numbers from structural design and operating conditions in fractionation process

Name Proposed Original

Prefractionator Main Postfractionator Prefractionator Main

Structural

Number of trays 21 54 35 21 89

Feed/side product 15 20 15 62

Interlinking stages 16, 39 (pre) 16, 84

26, 30 (post)

Operating

Feed (kmol/h) 801.8 801.8

Overhead (kmol/h) 86.48 86.85

Bottom (kmol/h) 376.5 377.4

Side (kmol/h) 337.8 337.8

Reflux (kmol/h 340.0 1236 529.8 290.1 1792

Vapor boil-up (kmol/h) 529.2 1169 340.1 492.9 1634

Heat duty (GJ/h) 42.44 59.35

Tray numbers are counted from top.




Table 2

Tray numbers from structural design and operating conditions in gas concentration process

Name Proposed Original

Prefractionator Main Postfractionator Prefractionator Main

Structural

Number of trays 10 41 14 10 55

Feed/side product 6 6 5 23Interlinking stages 5, 29 (pre) 5, 43

12, 17 (post)

Operating

Feed (kmol/h) 269.1 269.1

Overhead (kmol/h) 24.00 24.00

Bottom (kmol/h) 153.2 152.9

Side (kmol/h) 92.41 92.07

Reflux (kmol/h) 230.4 530.2 139.9 200.0 589.8

Vapor boil-up (kmol/h) 319.2 478.4 75.07 278.2 511.9

Heat duty (GJ/h) 6.883 7.361

Tray numbers are counted from top.

tions with differentstructures are necessaryto yield the optimumdesign variables.

3. Results and discussion

A newstructureof fullythermallycoupled distillation column

system is implemented to the fractionation process of a naphtha-

reforming plant for BTX production and the gas concentration

process to produce gas products from gas mixture drawn from

crude distillation, naphtha reformation and naphtha-cracking

processes in a refinery. The feed and product flow rates of both

processes are listed in Tables 3 and 4. In addition, the outcomes

of structural and operational design are given in Tables 1 and 2.The design is compared with the original fully thermally cou-

pled distillation column for the same production. The HYSYS

process diagrams of the proposed fully thermally coupled distil-

lation column for the BTX fractionation and gas concentration

processesare demonstrated in Figs.6and7. Theoperating condi-

tions for the HYSYS simulation are also included in the figures.

An apparent improvement is observed with the reduction of

heat duty of two processes. The fractionation process requires

38% less duty compared with a two-column system, while

an original fully thermally coupled distillation column saves

13%. The gas concentration process consumes 23% less than

Table 3

Flow rates of feed and products in fractionation process with unit of kmol/h

Component Feed Proposed Original

Overhead Bottom Side Overhead Bottom Side

Light

Benzene 87.850 86.472 0.0000 1.7015 86.830 0.0005 0.9308

Dimethyl c-pentane 0.0124 0.0116 0.0000 0.0008 0.0119 0.0000 0.0004

Intermediate

Methyl c-hexane 0.0075 0.0000 0.0000 0.0064 0.0024 0.0000 0.0015

Toluene 338.10 0.0002 2.2289 335.62 0.0033 3.2667 335.65

n-Octane 0.049 0.0000 0.0016 0.0474 0.0000 0.0012 0.0479

Heavy

Ethylbenzene 14.975 0.0000 14.782 0.0971 0.0000 14.712 0.2257

p-Xylene 57.798 0.0000 57.443 0.1046 0.0000 57.379 0.3069

m-Xylene 128.55 0.0000 127.81 0.2043 0.0000 127.69 0.6129

o-Xylene 60.160 0.0000 60.004 0.0149 0.0000 60.088 0.0584

n-Nonane 0.0057 0.0000 0.0057 0.0000 0.0000 0.0057 0.0000

n-Pentyl benzene 0.3300 0.0000 0.3297 0.0000 0.0000 0.3299 0.0000

Methyl-ethyl benzene 26.010 0.0000 25.991 0.0000 0.0000 26.003 0.0000

tri-Methyl benzene 75.950 0.0000 75.919 0.0000 0.0000 75.940 0.0000

Methyl-n-propyl benzene 0.5700 0.0000 0.5698 0.0000 0.0000 0.5700 0.0000

di-Ethyl benzene 0.3300 0.0000 0.3299 0.0000 0.0000 0.3300 0.0000

o-Cymen 4.1200 0.0000 4.1183 0.0000 0.0000 4.1195 0.0000

tetra-Methyl benzene 4.7500 0.0000 4.7491 0.0000 0.0000 4.7497 0.0000

penta-Methyl benzene 2.2389 0.0000 2.2388 0.0000 0.0000 2.2389 0.0000

Total 801.81 86.484 376.52 337.80 86.848 377.43 337.83




Table 4

Flow rates of feed and products in gas concentration process with unit of kmol/h

Component Feed Proposed Original

Overhead Bottom Side Overhead Bottom Side

Light

Methane 0.9879 0.9881 0.0000 0.0000 0.9877 0.0000 0.0000

Ethane 22.966 22.963 0.0000 0.3035 22.918 0.0000 0.0859Propene 0.5729 0.0010 0.0083 0.5302 0.0005 0.0096 0.5474

Intermediate

Propane 92.553 0.0505 3.5812 89.259 0.0849 3.4366 89.116

Heavy

i-Butane 75.866 0.0000 73.894 1.8819 0.0000 73.891 1.7765

1-Butene 3.2506 0.0000 3.2024 0.0442 0.0000 3.1985 0.0472

n-Butane 71.740 0.0000 71.287 0.3912 0.0000 71.207 0.4961

i-Pentane 1.1720 0.0000 1.1717 0.0001 0.0000 1.1720 0.0003

n-Pentane 0.0171 0.0000 0.0171 0.0000 0.0000 0.0171 0.0000

Total 269.13 24.002 153.16 92.410 23.995 152.93 92.069

the conventional two-column system. In the case, the originalfully thermally coupled distillation column consumes 18% less

energy than the two-column system. Note that the total numbers

of trays in the two-column system, original fully thermally

coupled distillation column and proposed fully thermallycoupled distillation column are same. For the examination

of economic benefit from the introduction of postfractionator

to the fully thermally coupled distillation column, utility and

Fig. 6. A HYSYS process diagram and operating conditions of the proposed fully thermally coupled distillation column in BTX fractionation process.




Fig. 7. A HYSYS process diagram and operating conditions of the proposed fully thermally coupled distillation column in gas concentration process.

investment costs are calculated with the formulas given in Kim

and Luyben [22] adopted from Douglas [23]. The steam cost

is 5 US$ per one million Btu, and the column operation is 300

days a year with 7 years of payout period. The detail of cost

calculation result for the original and proposed fully thermally

coupled distillation columns in BTX fractionation and gas

concentration processes is listed in Table 5. In terms of total

cost, cost reductions of 27 and 8% in the BTX fractionation and

gas concentration processes respectively are evaluated for the

proposed column when the cost is compared with the original.

Table 5Results of cost evaluation for the original and proposed fully thermally coupled

distillation columns in BTX fractionation and gas concentration processes

Item BTX fractionation Gas concentration

Proposed Original Proposed Original

Column 1547 1924 633.9 715.8

Tray 262.6 420.3 83.4 107.6

Heat exchanger 1367 1709 412.7 425.4

Total investment 3177 4053 1130 1249

Utility (year) 1448 2025 234.9 251.2

Total (year) 1902 2604 396.3 429.6

Units are in a thousand US$.

In the BTX fractionation process, the purity of side draw

is much higher than that in the gas concentration process to

require largeramount of liquidflow or more numberof trays.The

introduction of a postfractionator in such a system lowers more

the utility demand. In a simple distillation column, increasing

twice the number of trays raises the product purity by an order

of magnitude, i.e., from 0.99 to 0.999. This is not possible for

the side draw in a fully thermally coupled distillation column,

where the compositions of the lightest and heaviest components

are stationary and limit the purity increase of the side draw [1].

Instead, the purity is affected by one minor component in the

simple distillation column. Therefore, the elevation of liquidflow with the purity increase of side draw in the fully thermally

coupled distillation column is much larger than that in the simple

distillation column. Whereas the purity of side draw in the BTX

fractionation process is 0.994, it is 0.968 in the gas concentration

process. As the fractionation process requires higher reflux ratio

than the gas concentration process, energy saving from adopting

the postfractionator is larger in the former.

The profile of tray liquid compositions in the practical BTX

fractionation process is demonstrated in Fig. 8. The plus sym-

bols areof theprefractionator, andthe circles and times symbols,

which are not clearly indicated, are of the main and postfraction-

ator, respectively. The composition of feed is marked with an F.




Fig. 8. Column profile of the proposed distillation column in BTX fractionation

process. The trays of U and L are upper and lower interlinking trays in main

column with prefractionator.

The liquid compositions of upper and lower interlinking trays

in the main column are shown with a U and an L, respectively.

A magnified illustration of the column profile of the postfrac-

tionator is given in Fig. 9, where the times symbols are of the

postfractionator. The U2 and L2 indicate the upper and lower

interlinking tray compositions in the main column. Because the

residue curves in Fig. 3 do not show the curves near the vertex

for high concentration of intermediate component, the column

profiles of the main column and postfractionator as shown in

Fig. 9 are not exhibited there. Yet the difference of the profiles is

apparent. The column profiles of an original fully thermally cou-pled distillation column are more similar to the residue curves

than those of a conventional two-column system. Moreover, the

introduction of the postfractionator to the fully thermally cou-

pled distillation column makes the distribution of its column

Fig. 9. Magnified demonstration of column profile of postfractionator in BTX

fractionation process. The U2 and L2 are upper and lower interlinking trays in

main column with postfractionator.

Fig.10. Column profile of the proposeddistillationcolumnin gas-concentration

process. The trays of U and L are upper and lower interlinking trays in main

column with prefractionator.

profiles much closer to the distribution of the residue curves. A

column profile similar to the residue curve represents a distil-

lation column operated at total reflux [18], which has perfect

distillation column efficiency. This explains that the proposed

fully thermally coupled distillation column requires less energy

than the original fully thermally coupled distillation column.

The column profile of gas concentration process is shown

in Fig. 10. The symbols are same to those used in Fig. 8. The

detailed demonstration around side draw tray is given in Fig. 11.

The profile of the postfractionator is distinguished from that of

the main column, but the distance of peak compositions in two

profiles is shorter than that of the BTX fractionation process.

In other words, the effect of the postfractionator utilization is

smaller as noticed from the comparison of energy consumption.

The construction of the new fully thermally coupled distillation

Fig. 11. Magnified demonstration of column profile of postfractionator in gas

concentration process. The U2 and L2 are upper and lower interlinking trays in

main column with postfractionator.




Fig. 12. Alternative configurations of the proposed distillation system: (a) section changed between main column and postfractionator; (b) full divided wall structure;

(c) divided wall for prefractionator and main column; (d) divided wall for main column and postfractionator; (e) divided wall for prefractionator and postfractionator.

column is more difficult than the original one due to the addi-

tion of a postfractionator, but the effect of energy saving is too

significant to be ignored. As widely applied configuration of a

fully thermally coupled distillation column in field practice, a

divided wall-type column with two walls can be employed and

also a variety of column configurations are available as shown

in Fig. 12. In case of a separate postfractionator system, themiddle section of main column and the postfractionator can be

exchanged for the simple arrangement of vapor flow (Fig. 2a).

The number of trays in the postfractionator is larger than the

middle section to generate more pressure drop, and therefore

the vapor flow through the separate middle section is easier to

manipulate. Adjusting the location of the middle section makes

liquid from and to the main column flown by gravitation. For

the simplicity of column construction several different combina-

tions of columnsectionsare configured in divided wall structure.

A fully combined structure is illustrated in Fig. 12b, and three

combinations of two columns from the prefractionator, maincol-

umn and postfractionator are demonstrated in Fig. 12c–e. In case

that dividing three sections in a column as illustrated in Fig. 12b

is difficult, either the prefractionator or postfractionator can be

separated from the divided main column. Theseparation of post-

fractionator is exhibited in Fig. 12c, and that of prefractionator

isin Fig. 12d.As in Fig. 12a, the middle section of main column

is replaced with the postfractionator in Fig. 12e. The determi-

nation of a configuration from the alternatives depends uponthe difficulty in construction and operation of the column. An

availability of columns not in use also affects the determination.

4. Conclusions

A new structure of a fully thermally coupled distillation

system requiring less energy than an original fully thermally

coupled distillation column is proposed, and its design and per-

formance are explained here. The system has a postfractionator

connected to the main column of the original system.

Because the composition profiles of tray liquid in the pro-

posed system are closer to residue curves than the original fully




thermally coupled distillation column, its distillation column

efficiency is higher than that of the original. Therefore, an addi-

tional energy reduction of 29% for fractionation process and

7% for gas concentration process over the original fully ther-

mally coupled distillation column is yielded from performance

comparison with the HYSYS simulation. The arrangement of

column sections and divided wallconstruction are also discussed

in the viewpoint of column construction and operation.

Acknowledgments

Financial supports from the Korea Energy Management Cor-

poration and the Korea Science and Engineering Foundation

(Grant no. R01-2003-000-10218-0) are gratefully acknowl-

edged.

Appendix A. Nomenclature

B bottom product

D overhead productF feed

L liquid flow rate(kmol/h) orlowerinterlinking traywith

prefractionator

L2 lower interlinking tray with postfractionator

S side product

U upper interlinking tray with prefractionator

U2 upper interlinking tray with postfractionator

V vapor flow rate (kmol/h)

Subscripts

B vapor boil-up

D reflux flow2 flow to and from prefractionator

3 flow to and from postfractionator

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a new fully thermal coupled distillation column with postfractionator

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