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  • 8/19/2019 Fibonacci Search for Optimal Feed Location

    1/14

    This article was downloaded by: [University of Sydney]On: 30 December 2014, At: 05:20Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House37-41 Mortimer Street, London W1T 3JH, UK

    Chemical Engineering CommunicationsPublication details, including instructions for authors and subscription information:

    http://www.tandfonline.com/loi/gcec20

    FIBONACCI SEARCH FOR OPTIMAL FEED LOCATIONJ.C. WANG

    a

    a Engineering Department , Union Carbide Chemicals and Plastics , P.O. Box 8361, South

    Charleston, WV, 25303

    Published online: 24 Apr 2007.

    To cite this article: J.C. WANG (1980) FIBONACCI SEARCH FOR OPTIMAL FEED LOCATION, Chemical EngineeringCommunications, 4:6, 651-663, DOI: 10.1080/00986448008935937

    To link to this article: http://dx.doi.org/10.1080/00986448008935937

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    Chern.Eng. Commun. Vol.4, pp. 651-663

    0098-6445/80/0406-0651S04.50/0

    < lGordon and Breach, Science Publishers Inc., 1980

    Printed in the U.S.A.

    FIBONACCI SEARCH FOR OPTIMAL

    FEED LOCATION

    J e WANG*

    Union Carbide Chemicals and Plastics,

    Engineering Department,

    P.o.  ox 8361, South Charleston, WV 25303

     Received

     uly

    23,1979; infinal

    form

    October 11,1979)

    A Fibonacci search technique is used in conjunction with a rigorous multicomponent distillation computer

    module to find the opt ima l feed location within a sect ion

    o

    a disti llat ion column. The funct ion to be

    minimized can be one of the following:

     keycomponentratiodifference

     reflux

    ratio or reboiler ratio

     condenser

    dutyor reboilerduty

     his technique has been used successfully in the relocation

    o

    feed stages

    o

    many existing distillation

    columns and thus saved energy consumption. We shall describe this technique with a sample problem.

    INTRODUCTION

    Feed location is an important factor in the design of a new disti llation column or in

    evaluat ing the performance of an existing column. A mislocated feed not only can

    seriously impair separation efficiency but also affect the energy consumption. The

    subject of optimal feed location has been studied by many investigators.

    McCabe and

    Thiele, ' Gil li land,' and others define the optimum feed stage based on matching the

    ratio of the light and heavy key components in the feed and on the feed stage. Scheibel

    and Montross, Floyd and Hipkin;'

    and

    Maas,' have developed procedures to find

    the

    opt imum feed stage that produces the maximum separations. Shipman ' gave a

    criterion of the optimal feed stage based on the minimization of the entropy

    production. Although his approach is thermodynamica lly sound, the method is

    difficult to apply and has not much practical value. Recently, Waller and Gustafsson

    t reated the feed stage problem in their opt imizat ion of the steady state distiIJation

    operation.

    Distillation processes are the most energy intensive operation in the petroleum and

    petrochemical industries. Prengle, et at, reported that up to 40 of the energy

    consumed in a petrochemical plant is taken by the distillation columns.   is therefore

    more logical to define the optimal feed location based on the energy consumption.

    Luyben has given such a cri ter ion by stating  The minimum energy consumption is

    achieved in a column with a fixed number of total t rays when not only

    X

    D

    and

    X

    B

    are

    held at their specified values but also the feed is introduced onto the optimum feed

     Dr.

    Wang isnowwith Simulation Science, Inc., 1400 N. Harbor Blvd., Fullerton, CA 92635.

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    652

    J.C.

    WANG

    tray. In this

    paper

    we shall show

    that the

    energy consumption of a distillation column

    with a fixed

    number of

    stages for a specified

    separation

    is an unimodal function or the

    feed

    stage

    location. This function can be

    evaluated

    by using a

    steady

    state

    computer

    simulation program.

    The

    problem of finding

    the

    optimal feed location is then to search

    for

    the min imum

    point of this function. A Fibonacci search procedure is then

    developed for solving this problem.

    The

    procedure is simple

    and

    can be readily

    incorporated into any distillation simulation program.

    THE

    SIMULATION

    MODULE

    Ever since the invention of the digital computer, numerous methods have been

    proposed for

    the computer

    solution of

    the

    distillation problem.   is beyond

    our

    scope to

    review

    the

    various methods in this paper. By selecting some

    of the

    methods we have

    developed a sophisticated

    computer

    program not only for disti llat ion

    bu t

    also for

    absorption (with or without reboiler)

    and

    liquid-liquid extraction.

    These

    operations

    can be classif ied as the Multicomponent

    Multistage

    Separation

    Processes and there

    fore we have des ignated

    our

    program as

    the MMSP

    program. The program is

    modular

    and

    it consists of various subprograms.

    These

    include

    the thermodynamics

    subprograms, the

    mathematical

    subprograms, the initiation subprograms,

    and the

    separation subprograms. It

    can

    also be readily incorporated to

    any

    process flowsheet

    s imulator such as Union

    Carbide s IPES (Integrated  ro ess Engineering System)

    program. The

    input can

    either

    come from

    the

    standard

    8

    1

    2

    x

    II data

    sheets or from

    a stored file.

    The output can either

    be printed or s tored in a file to be used for column

    design

    programs

    such as

    our APT   ll

    Purpose   ray program. Figure I shows

    the

    information flow

    of

    such a program system.

    The

    methods used in

    the MMSP program

    are:

    The Wang-Hcnkc

    method

    (DSTLWH)

    for distillation;

    the

    Sujata s Sum

    Rate '

    method

    (DSTLSR)

    for absorb

    ers or liquid-liquid extractors; and

    the

    Block Tridiagonal

    matrix

    method (DSTLBT)

    developed by

    Naphthali and

    Sandholrn

    and

    modified by

    Tang.

     

    In

    the

    last method,

    the

    MESH (Material

    Balance, Equilibrium,

    Summation,

    and Heat

    balance)

    equa-.

    tions are solved simultaneously using the

    Newton

    Raphson technique. The MESH

    equations

    are arranged

    in such a way

    t ha t t he Jacobian matrix

    is in a simple block

    tridiagonal form. Using this method, var ious top

    and

    bottom specifications can be

    made.

    These

    include condenser

    and

    reboiler

    temperature,

    condenser

    and

    reboiler

    heat

    duty, reflux

    and

    reboiler ratio,

    and

    most importantly,

    the product

    purities in

    terms of

    mole fraction, moles, or percent recovery

    of

    the key components.

    For

    the

    design problems of

    determining the

    stage

    and

    reflux

    requirements

    in a

    disti llat ion column for a specified key

    component

    separation, we employed

    VanWin

    kle s

    shortcut

    method

    (SHTCUT). The number

    of equil ibrium stages are first

    computed from

    SHTCUT

    and

    the

    reflux

    requirement and

    energy consumption

    are

    computed by use of the Block Tridiagonal matrix method (DSTLBT).

    The MMSP program

    has been used within Union Carbide for the simulat ion,

    design, control studies,

    and

    energy

    audit

    of

    many

    distillation columns, absorbers,

    and

    liquid-liquid extractors. The column

    can

    be a simple one with one feed

    and

    two

    product s or a complex one with multiple feeds, multip le s idedraws,

    and

    multiple

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    Ul

     

    8

    ~

    «

    z

    ~

    o

    0::

     

    J:

    I

    z

    «

    J:

    u

    OPTIMAL

    FEED

    LOCATION

    PHYSICAL

    PROPERTY

    rFEED AND COLUMN

    INPUT DATA FORMS

    INPUT DATA FORMS

    HYSICAL

    PROPERTY

    ~ D T

    FEED AND

    COLUMN

    DATASET

     PP-COMMON

    BANK

    INPUT DATA SET

    ~

    -.

    THERMODYNAMICS

    -

     

    COLUMN INITIATION

    SUBPROGRAMS

    -

    SUBPROGRAMS

    MATHEMATICAL

    I

    UBPROGRAMS

    EPARATION SUBPROGRAMS

    ,

     

    GFLASH

    XFLASH

    SHTCUT

    DSTLBT

    DSTLSR

    DSTLWH

     

    ROCESS FLOWSHEET

    STAND ALONE PROGRAM

    \ S

      S

    ~

    PROBLEMSL

    OR PROP. \

    FILES

    t

     

    P R I N T R

    TRAY DESIGN

    PROGRAM

    O U T P U T

      P T ~ L L PURPOSE TRAY

    FIGURE

    I I nfo rma ti on flow for MMSP simulation and design.

    653

    Ul

    m

    s

     i

    >

    Ul

    Ul

    tl

    o

    0::

    D.

     

    z

     

    J:

    U

    interstage heaters or coolers).

    The

    mi xtu re to be s ep ar at ed can be of any de gre e of

    nonideality ranging from those obeying Raoult s law to highly nonideal systems such

    as azeotropes. We have incorporated in

    our

    Thermodynamics Subprogram Library a

    spectrum of equilibrium models. These include Chao Seader correlation, Robinson

    Chao correlation, Poynting correction, and others for liquid phase fugacity; Redlich

    Kister, Regulat Solution, NRTL Wilson equation, Margules, and Uniquac for liquid

    activity coefficients; Redlich-Kwong, Second Virial, Prausnitz-Chueh modified

  • 8/19/2019 Fibonacci Search for Optimal Feed Location

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    654 J.C. WANG

    Redlich-Kwong and other equa tions of state to compute vapor phase fugacity

    coefficient and vapor

    enthalpy departure

    We also

    can

    use the BWR Starling BWR

    and

    Soave modified Redlich-Kwong equation to

    calculate

    K-values

    and

    enthalpy

    departures for hydrocarbon mixtures. The data required for all these models can be

    retrieved from a comprehensive Data Bank in which the pure component physical

    properties of more

    than

    1000 compounds

    are

    stored.

    The

    MMSP

    program is used for the evaluat ion of the energy consumption of the

    dist il la tion column as a function of the location of the main feed stream. The input

    data

    to the program include:

    • total

    number

    of stages including condenser and reboiler

    • feed conditions, rates and compositions

    • sided raw locations and rates, if any

    • purity specifications in terms of mole fraction or percent recovery of the

    specified components in the distillate and bottom products

    • the codes to indicate the models selected for calcu lat ing the K-values

    and

    the

    enthalpies. The pure component data can be retr ieved from the Data Bank

    bu t

    binary interaction

    parameters

    must be supplied in the input sheets.

    Most of the input data items listed above are provided with the item numbers in the

    data sheets. Any of these items can be changed by supplying its item number and its

    new value. At the end of each case, the computed resul ts are stored on the computer.

    The

    program will then proceed to read the

    change

    cards, change the values of the

    specified items, and perform the computation for the new case. Since the new case

    starts with a converged solution of the previous case, the new case converges very fast.

    Finally, the resul ts of all the cases

    are

    printed in a single output.

    This

    change case

    procedure can be overseen by a control subrou tine such as the one described in this

    paper for the optimal feed location.

    The

    output

    from the program includes the column profiles of stage temperatures

    internal vapor

    and

    liquid rates , the stage vapor

    and

    liquid compositions

    and

    the

    following items which are related to the energy consumption of the distillation

    column:

    • the reflux rat io or reflux rate,

    • the reboi ler rat io or reboiler vapor rate

    • the condenser

    duty

    • the reboiler duty.

      addition the following two items related to

    matching

    the compositions in the feed

    and

    on the feed

    stage can

    also be computed:

    • the absolute value of the difference between the key components

    ratio

    in the feed

    and that on the feed stage, i.e.,

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    OPTIM L

    FEED LO TION

    655

    • the sum of the absolute values of the difference between the feed composition and

    the feed stage composition for all the components.

    where Z - feed composition, m.f.;

     

    feed stage composition, m.f. Subscripts i for the

    ith component, l for the light key,   for the heavy key.

    EFFE T

    OF

    FEED LO TION

    ON

    DISTILL TION

    To show the effect of the feed stage location on the performance of the distillation

    column, let us consider the problem of benzene-toluene-xylene separation. As shown in

    Fig. 2, 100 Kg molesjhr of the mixture is fed to a distillation column to be separated to

    a disti llate containing 0.01 mole of toluene and a bottom product containing 0.01

    mole

     

    of benzene. A shortcut calculation indicated

    that

    40 stages are required at a

    reflux ratio equal to 1.2 times the minimum. Therefore, 42 stages including condenser

    and reboiler are used in the rigorous calculation. The stages are numbered from top to

    bottom with the condenser as the first s tage and the reboiler as the 42nd stage. The

    effect of the feed stage in the middle section of the column (Stage 16 to

    Stage

    29) is to

    be studied by using the change case procedure.

    The simulation was done by using the Block Tridiagonal matrix method with the

    purity specifications for

    the

    distillate (0.0001 rn.f. of toluene) and the bottom product

    (0.0001 m.f. of benzene). The Wang-Henke method was used for initiating the column

    profiles to be used in the base case. The Chao-Seader correlation' was used to

    calculate the K-values and the Yen-Alexander correlation was used for calculating

    the vapor and liquid enthalpies. All the physical properties required were retrieved

    from the Data Bank. The computed results are plotted in Figure 3. The smoothed

    curves for the fourteen case studies with feed stage at 16 to 29 include the values of   l

    k

    and   l the reflux ratio, the reboiler ratio, the condenser duty, and the reboiler duty.

    These results show clearly that all the quantities listed are unimodal functions of the

    feed stage location with only one minimum point within

    the

    section of the column. It

    was also noticed

    that

    the minimum points for all the quantit ies with the exception of

      l

    k

    fall on the same point. This has been true for all the problems we have encountered.

    Therefore, the criterion of optimal feed stage based on the matching of the key

    component ratio is not correct. The criterion based on the energy consumption should

    be used. Since the energy consumption is related to the reflux rate, the boil-up rate,

    the condenser duty, arid the reboiler duty, the optimal feed location can also be defined

    as the one that minimized one of these quantities (or the weighted sum of these

    quantities). The optimal feed location problem can then be determined by applying a

    unidimensional search technique.

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    656

    p 101

    KPA

    F, 100 Kc;MoL.ES /HR

    S TU RED L IQ U ID I

      T 364

    0

    K

    BENzENE, 0.6 M.F.]

    TOL.UENE, 0.3

    _XVL.ENE, 0. 1

      e WANG

    ___

    3 _

    16

     

    8

    ~ I t K G M o L E S

    HR

    0,0001

    MIF.j

    TOL.UENE,

    0.7499

      VL.ENE

    1

    0.2500

    FIGURE 2 The sample problem.

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    1. 4

    i.a

    OPTIMAL

    FEEO

    LOCATION

    5. 5 t \ \ 4 ~

    4 4

    . ~ I _ _ _ I _ l

    0

    5

    4 t - - t - ~ - ; - -

    ...

    0

    0(

    III

    J:

    5 •3 t l l

    II:

    III

    5 • 2 r t t \ ~ I _ _

    III

    o

    Z

    ~

    5. 1 r - - ~ t - \ - - t _ _ - _ : ~ - I _ _ ~ r _ _ -

    c

    5.0

    +-+----11--+-++

    II:

    III

    : 4.

    9   t I l 1 ~

    o

    lD

    III

    0::4.

    8

    r \ f \ ~

    III

    U

    1. 2

    4.6

    II:

    III

    1.0

    4. 5

    c

    0.8

    4.4

    0(

    l:t:

    0

     

    i

    0.4

    z

    o

    E

    0.2

    rJl

    o

    L

      0.0

    29 28 27

    NUMBER

    FIGURE 3 Effect of feed stage on distillatiion (benzene-toluene-xylene separation).

    THE SEARCH ALGORITHM

    657

    0

    i=

    0(

    0::

    3.7

    II:

    III

    J

    3. 6

    0

    lD

    III

    0::

    3.5

    1.8

    1.7

    ~

    0::

    1. 6

    s

    i o

    5

    ,

    0::

    x

    ::I

    J

    II

    III

    0::

    There are various methods for the search of the minimum point of a function. One of

    these is the graphical method that we just described in the previous section. Beveridge

    and Schechter,' Wilde,19 and others have reviewed one dimensional search techniques.

    Himmelblau' and Beveridge and Schechter ' compare the efficiency of the various

    unidimensional search techniques. They show that the Golden Search and the

    Fibonacci Search are the two most efficient methods. Since the Fibonacci search

  • 8/19/2019 Fibonacci Search for Optimal Feed Location

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    658

    J.e. WANG

    t echn ique is based on the Fibonacci

    numbers

    it is especia lly convenient for integer

    search problems such as our optimal feed stage problem.   this case, the Fibonacci

    number

    F

    is the

    number

    of s tages within a sect ion of columns in which

    the

    optimal

    feed stage lies and n is the required number of function evaluat ions column

    simulations .

    Using the Fibonacci search technique, we have developed a computational proce

    dure for locating the

    optimum

    feed stage with a section of the distillation column. The

    function to be minimized can be one of the following:

    1 = s,  I  Zlk

    -

     X

    lk

      · the key ratio difference

    .

    Zhk X

     

    I

    z, -  X; iF I The

    composition difference

      R

    /

    D the reflux ratio

    1 V

    /

    B the boilup ratio

    1

    Qc the condenser

    heat duty

    1 = QR, the reboiler heat

    duty

     1

    2

    3

    4

    5

    6

    where

    J

    F indicates the feed stage number.

    The computational procedure for the

    optimal

    feed stage

    search

    algorithm includes

    the following steps:

     t p

    I

    Supply the input

    data

    for

    the

    column simulation except

    the

    feed

    stage

    location.

    The

    data requirements are outlined in the previous section. Also specify the function to be

    minimized.

     t p

    2

    Specify the section of the co lumn to be

    searched

    by giving the

    stage

    number J F near

    the column top and the stage number

    J

    F

    b

    near the bottom.

    The

    difference between

    J

    F

    b

    and J F

    must be a Fibonacci

    number F• Then

    find

    the

    number

    of

    function evaluations

    n corresponding to F from the table of Fibonacci number Table I .

     t p

    3

    Determine the first two stage numbers to be checked as follows:

    JF - JF + F _

    2

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    Step 4

    OPTIM L

    FEED LOC TION

    T LE I

    The First Fibonacci Numbers

    n

     

    0

     

    I I

    2 2

    3

    3

    4 5

    5 8

    6 13

    7

    21

    8

    34

    9

    55

    10 89

    11

    144

    12

    233

    13 377

    659

    Eva lu at e the function to be minimiz ed as

    I

    and

    12

    c orr esp on di ng to the feed s ta ge

    numbers

    JF

    and

    JF

    2

    by performing the column simulation with the purity specifica-

    tions for the top and bottom product streams. Also set the search number I   2.

     t p 5

    Checkj vs./2 If

    II

    < 2 go to Step 6 otherwise set:

    and evaluate a new

    12

    corresponding to the new

    JF

    2

    by p erf or min g the column

    simulation then go to Step 7.

     t p 6

    Set

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    660

    J.C. WANG

    and

    evaluate

    a new   corresponding to

    the

    new

     

    I

    by performing

    t he column

    simulation.

     t p 7

    Update

    the search

    counter

    I as

    I

    =

    I  

    I

     t p

    8

    Cheek

    I vs. n If I = n stop the i teration and go to

    output.

    Otherwise

    repeat Step

    5

    through

    Step

    8.

    This procedure has been programmed into

    the

    MMSP

    program

    as

    the fBSRCH

    subprogram. The

    results from all the column simulations

    are

    stored and printed in

    the

    final

    output

    along with

    the

    column profiles corresponding to

    the

    optimal feed

    stage

    location.

    These

    results including

     

    reflux ratio, reboiler

    rate

    condenser

    duty

    reboiler

    duty number

    of iterations used in

    the

    column simulation,

    and the

    convergence

    of the column simulations are printed in

    tabular

    form.

    APPLICATION

     

    THE

    SEARCH PROCEDURE

    We shall i llustrate

    the f ibonacci

    search procedure by applying it to

    the

    sample

    problem

    of

    benzene-toluene-xylene

    separation

    discussed previously.

    The

    section

    of the

    column between stage 16

    and

    29 was

    searched

    for

    the

    optimal feed

    stage

    location

    that

    produces the

    minimum

    reboiler heat duty.

    The

    total

    number

    of stages within

    the

    section is

    the fibonacci number

    13.

    from

    Table

    I we found

    that

    n

    -

    6

    and

    therefore a

    maximum

    of

    six 6 column simulations were required.

    The search

    procedure was

    started

    as follows.

    figure

    4 is

    the

    graphical representation of this procedure.

    The

    first two feed stages to be checked were

     

    I

     

    JF F

    n

    _

    =

    16

     

    5 = 21

    JF

    2

    = JF F

    n

    _

    I 16

     

    8 - 24

    Column

    simulations using

    DSTLBT

    were performed with these two feed stages.

    The

    corresponding reboiler duties were

    obtained

    as:

      4.7702

    GJ/hr

      = 4.5997

    GJ/hr

    Since  

    >

     

    the minimum

    point

    must

    lie in

    the

    section between

    stage

    21 to

    stage

    29.

    Therefore

    we eliminated

    the

    section from

    stage

    16 to

    stage

    21 from

    further

    consideration.

    We then

    followed

    Step

    5 to set

    the

    top limit

    of the

    new section as

    JF

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    OPTIMAL F EE D L OC AT IO N

    661

    1\

    \

    \

    I

    \

    --_.

    II

    \

    _. -

    -- _

    ..-

    i

     

    ..

    -.-

      _ _

    --- -

     

    f-- -

    /

    I

    1\

    i

    z

    J

    Q

    \

     

    ;

    /

    I

    ,

    \

    .J

    {

    lJJ

    a

    1/

    t:

    i:

     

    I-

     

    /

     

    \

     

    6

    r

    V

    .

    -

    SECOND

    ,

    5 ELIMINATION J

     

    -

    1 IRST

    ELIMINATION

    _

    JF .

    JFz JF.

    JF ,

    4

      (MIN)

    I

    3

    I

    29

    28

    27

    26 25

    24

    23

    22 21

    20

    19 18

    I

    5. 4

    4 .

    4.

    5. 5

    5. 6

    5. 7

    5. 8

    5. 9

    4

    (JF. i

    It: 4 .

    g 4. 7

    lJJ

    .It: 4.

    e

    5. 3

    ~ 5

    FEED ST GE NUM ER

    FIGURE 4 Graphical representation of the Fibonacci search procedure.

    JF - 21. We also

    s tf

    -

    f2

    - 4.5997 GJ/hr, and JF - J

    2

    24. A new

    J

    2

    was

    obtained as

    J

    2

    J

    t

    +

    J

    b

    - JF

    =

    21 + 29 - 24 - 26

    Another column simulation with feed stage at 26 was performed. The reboiler duty

    was obtained as

    f

    4.7046 GJ

    /hr

    Since

    f

    <

    f2

    the optimal feed location must lie above stage 26. The column section

    between stage 26 and stage 29 was eliminated from further consideration. Following

    Step 6 we set J

    b

    - 26 /2 f - 4.5997

    GJ/hr,

    and J - JF 24. A new JF was

    obtained as

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    662 J.e. WANG

    J

    I

    = JF +

    J

    b

    -

    J

    -

    21 + 26 - 24   23

    The

    column simulation with

    J

    I

    23 yielded

    the

    reboiler

    duty

    II

    -

    4.6242

    GJ/hr

    Since f

    >

    I the minimum point must lie in the section from stage 24 to

    stage

    26. The

    section to be searched was finally reduced to three stages. The reboiler duties

    corresponding to two of these stages as feed

    stage

     24 and 26 were already obtained.

    The

    final column simulation performed with feed

    stage J

    F

    I

    - 25 yielded a reboi ler

    duty II = 4.6168 GJ /hr

    This

    was larger

    than

    the reboiler duty  I 4.5997 obtained

    for feed stage JF = 24. Therefore the opt imal feed location was found to be

    stage

    24

    from the top.

    Table

    II lists the results obta ined from the MMSP program for the above search

    procedure. The total

    number

    of column simulations used in this search procedure was

    5 as compared to 13 used in the case study. In

    Table

     

    we compared the

    computer

    times used and the

    computer

    costs for these two procedures. An IBM

    370/168

    computer

    was used for the simulations.

    The advantage

    of using the Fibonacci

    Search

    procedure becomes more obvious when larger numbers of stages are in the section to

    be searched.

    TABLE II

    Results of Fibonacci Search Applied to the Sample Problem

    Feed Reflux Boilup Condenser Duty Reboiler Duty

    Stage No.

    a,

    a, Ratio   tio GJjhr GJjhr

    2\ 0 31\6 0 \024

    1.4771

    3.5292

    4.6349 4.7702

    26 0 6\80

    0 \789 1.4417 3 48\4 4.5703 4.7056

    23

    0.0695 0.0610

    1.3983

    3.42\ 0 4.4887 4.6242

    25

    0.3422 0.0986 1.3942 3.4156

    4.4818

    4.6\68

    24 0.\088

    0.0589

    \.3838 3 40\3

    4.4625 4.5977

    TABLE III

    Comparison etween Fibonacci Search and Case Study

     ibon cci

    Search

    Case Study

    No of Column Simulations 5

    \3

    Total No. of Iterations

     DSTLBT 20

    50

    Total CPU Time. Sec.

     IBM 370/168

    3.27 8.78

    Total Cost.  

    Printing   CPU

    4.36 20.00

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    CONCLUSION

    OPTIMAL FEED LOCATION

    663

    A computational procedure using the Fibonacci search technique has been developed

    for the location of the opt imal feed

    stage

    within a section of the column such that the

    min imum energy consumption of the distillation column can be achieved.

    The

    procedure is simple

    and

    can be readily incorpora ted into

    any

    rigorous distillation

    simulat ion module. This procedure has been used in Union

    Carbide

    for relocation of

    the feed stage in many existing columns. During 1978 over 25,000 column simulations

    have been performed by use of the MMSP

    computer

    program. Eight percent of these

    simulat ions used the Fibonacci search procedure for opt imal feed location. Most of

    them were for feed

    stage

    relocation in existing disti llat ion columns to reduce energy

    consumption in the plants. The saving of energy cost was estimated to be over a million

    dollars per year.

    LITERATURE CITED

     

    Beveridge, G.S.G .. and Schechter, R.S., Optimization Theory and Practice. McGraw-Hili Book Co..

    1970.

    2. Chao, K.C.. and Seader, J.D.,  A General Correlation of Vapor-Liquid Equilibrium in Hydrocarbon

    Mixtures, A./.Ch.E. Journal,

    1,598

    (1961).

    3. Floyd, E.R., and Hipkin, H.G., Locating Feed Trays in Fractionators, Ind. Eng. Chem., 55 (6), 34

    (1963). .

    4. Gilliland, E.R.. Multicomponent

    Rectification-Optimum

    Feed Plate Composition, Ind. Eng.

    Chern.. 32, 918 (1940).

    5. Himmelblau. D.M., Applied Nonlinear Programming, McGraw-Hili BookCo., 1972.

    6. Luyben, W.L.,

     Steady-State

    Energy Conservation Aspects of Distillation Control System Design,

    Ind. Eng. Chem. Fundamentals, 14 (4), 321 (1975).

    7. Maas, J .H.,  Optimum Feed Stage Location in Multicomponent Distillations, Chern. Eng., April 16,

    1973, page 96.

    8. McCabe, W.L., and Thiele, E.W., Ind. Eng. Chem.,

    17,605

    (1925).

    9. Naphtali, L.M., and Sandholm, D.P. , Multicomponent Separation Calculation by Linearization,

    A./.Ch.E. Journal, 17

     1),148

    (1971).

    10. Prengle, H.W., Crump, J.R., Fang, e.S., Frupa, M., Henley, J. , and Worley, T., Potential for Energy

    Conservation of Industrial Operation in Texas, Final Report on Project

    SID-10,

    Governor s Energy

    Advisory Council, The State of Texas (1974).

    II . Scheibel, E.G., and Montross, C.F.,

     Optimum

    Feed

    Tray

    in Multicomponent Distillation Calcula

    tions, Ind. Eng. Chem.. 401 (8), 1398 (1948).

    12. Shipman, e.W.,  On the Optimum Choice of Feed

    Stage

    in Staged Equilibrium Processes, A.I.Ch.E.

    Journal, 18

     6),1253

    (1972).

    13. Sujata, A.D., Absorber-Stripper Calculation Made Easier,

    Hydrocarbon Processing and Pet. Ref.

    40  12),137 (1961).

    14. Tang, Y.P., Multicomponent Distillation Calculation by Newton s Method, Union Carbide Chemi

    cals and rlastics. Engineering Department Report.

    June 7,1972.

    15. Union Carbide Chemicals and Plastics,  User s Manual for the Integrated Process Engineering

    System 1976.

    16. Waller, K.V., and Gustafsson, T.K., On Optimal Steady-State Operation in Distillation, Ind. Eng.

    Chern. Process Des. Dev., 17 (3), 313 (1978).

    17. Wang,

    J.e.

    and Henke, G.E., Tridiagonal Matrix for Distillation, Hydrocarbon Processing, 45 (8),

    155 (1966). .

    18. Wang, J.e.,  User s Manual for Simulation of Multicomponent Multistage Separatian Processes,

    Union Carbide Chemicals and Plastics, Engineering Department, 1977.

    19. Wilde, DJ.,  Optimum Seeking Method, Prentice Hall, Inc., Englewood, N.J., 1964.

    20. VanWinkle , M., and Todd, W.G.,

     Optimum

    Fractionator Design by Simple Graphical Methods,

    Chern. Eng.. September

    20,1971,

    pp. 136-148.

    21. Yen, L.e., and Alexander, R.E., Estimation of Vapor and Liquid Enthalpies, A.I.Ch.E. Journal. II

     2),334 (1965).