Abstract:
Provided is a heat integrated distillation apparatus in which energy efficiency and a degree of freedom in design is higher than a normal distillation column, and in which maintenance of the apparatus is simple. The heat integrated distillation apparatus includes: rectifying column ( 1 ); stripping column ( 2 ) located higher than rectifying column ( 1 ); first pipe ( 23 ) for connecting top part ( 2   c ) of the stripping column with bottom part ( 1   a ) of the rectifying column; and compressor ( 4 ) that compresses vapor from top part ( 2   c ) of the stripping column to feed the compressed vapor to bottom part to ( 1   a ) of the rectifying column. The heat integrated distillation apparatus further includes: heat exchanger ( 8 ) located at the predetermined stage of rectifying column ( 1 ); liquid withdrawal unit ( 2   d ) located at a predetermined stage of stripping column ( 2 ) and configured to remove some liquids from the predetermined stage to the outside of the column; second pipe ( 24 ) for introducing the liquid from liquid withdrawal unit ( 2   d ) to heat exchanger ( 8 ); and third pipe ( 25 ) for introducing, after the liquid has been introduced to heat exchanger ( 8 ) via second pipe ( 24 ), fluids flowing from heat exchanger  8  to a stage directly below liquid withdrawal unit ( 2   d ).

Description:
TECHNICAL FIELD  
       [0001]    The present invention relates to a distillation apparatus that carries out a distillation operation widely applied to many industrial processes, and more particularly to a heat integrated distillation apparatus. 
       BACKGROUND ART  
       [0002]    Distillation separation is an unit operation widely applied to industrial processes in general, but consumes a large amount of energy. In the industrial field, therefore, studies have been conducted on an energy saving distillation systems. Such studies have brought about development of a heat integrated distillation column (hereinafter, HIDiC) as a distillation apparatus that save much energy. 
         [0003]    As shown in  FIG. 1 , a basic system of the HIDiC has a structure where a rectifying section (high-pressure unit) and a stripping section (low-pressure unit) are provided such that they are separate from each other. Operation pressure of the rectifying section is set higher than that of the stripping section so that the operation temperature of the rectifying section can be higher than that of the stripping section. This enables a reduction in the amount of heat that is supplied to a reboiler because heat transfer occurs from the rectifying section to the stripping section when there is a heat-exchange surface therebetween. Heat of the rectifying section moves to the stripping section, and hence the amount of heat that is removed at a condenser can be reduced. As a result, high energy saving distillation apparatus can be achieved. 
         [0004]    In order to put the concept of HIDiC to practical use, a distillation apparatus having a double-pipe structure as discussed in JP2004-16928A has been proposed (hereinafter, Patent Literature 1). 
         [0005]    As shown in  FIG. 2 , this distillation apparatus, which includes a shell  51  and a plurality of tube units  52  installed in the shell  51 , is formed by connecting each tube unit  52  to the shell  51  via upper tube sheet  53   a  and lower tube sheet  53   b.    
         [0006]    Each tube unit  52  has a double-pipe structure. Inner pipe  54  of tube unit  52  is used as a rectifying section while outer pipe  55  surrounding an outer surface of inner pipe  54  is used as a stripping section. Packing (structured packing)  54   a  and  55   a  are placed along the inside of inner pipe  54 , and between the outer pipe  55  and the inner pipe  54 . Refer to  FIG. 3  for tube unit  52 . The plurality of tube units  52  are arranged so that outer walls  65  of outer pipes  55  can come into contact with each other. 
         [0007]    Referring again to  FIG. 2 , liquid inlet of stripping section  56  to supply liquid feed to the outer pipe (stripping section)  55  and vapor outlet of stripping section  57  to discharge vapor from the outer pipe  55  are arranged in an upper part of the shell  51 . 
         [0008]    Above upper tube sheet  53   a , channel  58   a  that communicates only with inner pipe (rectifying section)  54  is formed. An upper end of the outer pipe  55  is not connected to upper tube sheet  53   a  that is to be opened. 
         [0009]    Liquid inlet of rectifying section  59  to supply liquid (reflux) to the inner pipe  54  and vapor outlet of rectifying section  60  to discharge vapor from the inner pipe  54  are arranged in upper channel  58   a.    
         [0010]    Vapor inlet of stripping section  61  to supply vapor to the outer pipe  55  and liquid outlet of stripping section  62  to discharge liquid from the outer pipe  55  are arranged in a lower part of the shell  51 . 
         [0011]    Below lower tube sheet  53   b , channel  58   b  that communicates with inner pipe  54  is formed. A lower end of outer pipe  55  is not connected to lower tube sheet  53   b  that is to be opened. 
         [0012]    Vapor inlet of rectifying section  63  to supply vapor to the inner pipe  54  and liquid outlet of rectifying section  64  to discharge liquid from the inner pipe  54  are arranged in lower channel  58   b.    
         [0013]    In the abovementioned distillation apparatus, liquid feed are supplied through liquid inlet of stripping section  56 , and uniformly distributed to upper of outer pipes  55  of tube units  52 . Among liquid feed supplied to the upper end of outer pipes  55 , liquid descending from outer pipe  55  in being fractionated in the outer pipe  55 , is supplied to the reboiler installed outside of column via liquid outlet of stripping section  62  and is reboiled. Vapor generated by the reboiler enters the column again from vapor inlet of stripping section  61 . The vapor from vapor inlet of stripping section  61  is distributed to a lower surface of outer pipe  55  of each tube unit  52  and ascends in each outer pipe  55 . The liquid that is left without being vaporized is discharged as a product of the column bottom. 
         [0014]    The vapor ascending from the outer pipe  55  in being fractionated, flows to a compressor via vapor outlet of stripping section  57 . The vapor passing through the compressor enters a rectifying section via vapor inlet of rectifying section  63 . The vapor from vapor inlet of rectifying section  63  ascends from the lower surface of each inner pipe  54 . The vapor ascending through inner pipe  54  in being fractionated exits from an upper surface of each inner pipe  54 , and is supplied to the condenser outside of column via vapor outlet of rectifying section  60 . The vapor from the rectifying section is totally or partially condensed by the condenser. When necessary, a part of the condensed liquid is supplied as reflux to inner pipe  54  via rectifying section liquid entrance  59 , while the rest is discharged as a distillate product. 
         [0015]    In this configuration, energy transfer occurs from the rectifying section (inner pipe  54 ) to the stripping section (outer pipe  55 ). Hence, an amount of heat that is supplied at the reboiler and an amount of heat that is removed at the condenser can be reduced, and energy efficiency can be very high. 
         [0016]    However, the heat integrated distillation apparatus having the rectifying section and the stripping section formed into the double-pipe structures as discussed in Patent Literature 1 has the following problems 1) to 6). 
         [0017]    1) The product cannot be obtained with side-cut stream. The side-cutting means that a product is withdrawn as an intermediate distillate product, during a distillation process until an end distillate is acquired from top of column. 
         [0018]    In the distillation apparatus described in Patent Literature 1, the tube units of the double-pipe structures are arranged to come into contact with each other. Moreover, the outer pipes and the inner pipes are equipped with the structured packing As a result, no pipe arrangement can be formed to withdraw any intermediate distillate product from the inner pipe of each tube unit. Consequently, the structure disables side-cutting. 
         [0019]    2) The feed stage where feed stream is provided cannot be optimized. This is because in the rectifying section and the stripping section formed into the double-pipe structures, packing heights thereof are equal, disabling free setting of the number of stages of the rectifying section and the stripping section. 
         [0020]    3) The feed stage cannot be changed so as to meet the feed stream composition. This is because of the structure where free setting of the feeding stage position is disabled as described in 2). 
         [0021]    4) Multi-feed stream (reception of a plurality of feed streams) cannot be dealt with. This is because of the structure where no feed stream can be supplied in the midway of the double-pipes as described in 1). 
         [0022]    5) Maintenance of the apparatus is difficult. The tube units that use the structured packing are densely arranged to be adjacent to each other as described in 1). This disables complete access to the desired tube unit, and maintenance thereof cannot be carried out. 
         [0023]    6) The heat exchanged rate between the rectifying section and the stripping section that uses double-pipes and in which there is no a degree of freedom in design for designing the heat transfer area, depends only on the temperature profile of the distillation column. Hence, in apparatus design, a degree of freedom in design of heat exchanged rate is small. 
         [0024]    Q, the heat exchanged rate between the rectifying section and the stripping section, is represented by Q=U×A×ΔT, where U is an overall heat-transfer coefficient, A is a heat transfer area, and ΔT is a temperature difference between the rectifying section and the stripping section. In the HIDiC using the double-pipe structure, an inner pipe wall surface becomes a heat transfer area. This heat transfer area has a fixed value determined by a structure of the double-pipes. The overall heat-transfer coefficient also has a fixed value determined by the heat transfer structure and fluid physical properties involved in heat exchange. Thus, as can be understood from the heat exchanged rate formula, a heat exchanged rate on design specification can be changed based only on the temperature difference between the rectifying section and the stripping section, which is changed by the operating pressure of the rectifying section and the stripping section. 
       SUMMARY OF INVENTION  
       [0025]    The present invention provides the following heat integrated distillation apparatus to solve the above-mentioned problems. 
         [0026]    According to an aspect of the present invention, a heat integrated distillation apparatus includes: a rectifying column including a trayed section or a packed bed section, which is a column shell used as a rectifying section; a stripping column located higher than the rectifying column and including a trayed section or a packed bed section used as a stripping section; a first pipe for communicating a column top of the stripping column with a column bottom of the rectifying column; and a compressor installed midway in the first pipe and configured to compress vapor from the top of the stripping column and then to feed the compressed vapor to the bottom of the rectifying column. 
         [0027]    The heat integrated distillation apparatus according to an aspect of the present invention further includes: 
         [0028]    a heat exchanger located at a predetermined stage of the rectifying column; 
         [0029]    a liquid withdrawal unit located at a predetermined stage of the stripping column and configured to withdraw a part of liquid from the predetermined stage to the outside of the column; 
         [0030]    a second pipe for introducing the liquid from the liquid withdrawal unit to the heat exchanger; and 
         [0031]    a third pipe for introducing fluids introduced through the second pipe to the heat exchanger and then discharged out of the heat exchanger to a stage directly below the liquid withdrawal unit. 
         [0032]    In the heat integrated distillation apparatus according to the aspect of the present invention, the fluids flow from the stripping column to the heat exchanger of the rectifying column through the second pipe. Heat is removed from the vapor of the rectifying column in the heat exchanger. Then, the heat can be transferred from the rectifying column to the stripping column through the third pipe. The fluids flow from the stripping column to the rectifying column by gravity. The fluids in the heat exchanger are accordingly pushed to flow from the rectifying column to the stripping column. In other words, this heat integrated distillation apparatus employs a thermo-siphon system, and hence no pressure-feeding means such as a pump is necessary for supplying the liquid from the rectifying column to the stripping column located above in a vertical direction. 
         [0033]    According to another aspect of the present invention, a heat integrated distillation apparatus includes: 
         [0034]    a liquid sump unit located at a predetermined stage of the stripping section and configured to hold descending liquid; 
         [0035]    a heat exchanger located in the liquid sump unit of the stripping column; 
         [0036]    a partition plate set in a predetermined position of the rectifying column and configured to apart upper stages and lower stages completely; 
         [0037]    a second pipe for introducing vapor below the partition plate to the heat exchanger; and 
         [0038]    a third pipe for introducing fluids introduced through the second pipe to the heat exchanger and then discharged out of the heat exchanger to an upper side of the partition plate. 
         [0039]    According to the alternative example, the vapor is withdrawn from the rectifying column through the second pipe. The vapor is introduced to the heat exchanger in the stripping column. Then, heat can be transferred from the rectifying column to the stripping column. High-pressure vapor in the rectifying column ascends through the second pipe to the heat exchanger in the stripping column. Liquid condensed from the vapor in the heat exchanger is accordingly pushed out from the stripping column to the third pipe outside the column, and flows to the rectifying column by gravity. Thus, this configuration also necessitates no pressure-feeding means such as a pump. 
         [0040]    With the apparatus configuration according to the first aspect or the second aspect, which transfers heat from the rectifying column to the stripping column by using the second and third pipes, as compared with a distillation apparatus including no such heat transfer configuration, the heat exchanged rate removed from a condenser attached to a top of the rectifying section can be reduced more, and the heat exchanged rate that is supplied to a reboiler attached to the bottom of the stripping column can be reduced more. As a result, a distillation apparatus that is very high in energy efficiency can be provided. 
         [0041]    The rectifying column and the stripping column are configured by using trayed sections or packed bed sections similar to those of a general distillation apparatus. Hence, the apparatus can deal with side cutting or multi-feed stream without the need for any improvement, and it is possible to easily perform maintenance of the apparatus. For the same reason, the number of stages of the rectifying column or the stripping column can be freely set, and a feed stage can be optimized. 
         [0042]    A heat transfer area can be freely set, and hence the heat exchanged rate can be determined without any dependence on the temperature difference between the columns. 
         [0043]    As described above, according to the present invention, energy efficiency is high, side-cutting and setting of a feed stage position can be easily dealt with, and maintenance of the apparatus is easy. 
         [0044]    The apparatus of the present invention has a structure where a degree of freedom in design is high, and hence can be easily accepted by the user side. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0045]      FIG. 1  shows a basic structure of a HIDiC. 
           [0046]      FIG. 2  shows a heat integrated distillation column using a double-pipe structure described in Patent Literature  1 . 
           [0047]      FIG. 3  is a horizontal sectional view showing the double-pipe structure in the distillation column shown in  FIG. 2 . 
           [0048]      FIG. 4  shows an overall configuration of a heat integrated distillation apparatus according to a first embodiment of the present invention. 
           [0049]      FIG. 5  shows a configuration of a liquid withdrawal unit shown in  FIG. 4 . 
           [0050]      FIG. 6  shows a peripheral configuration of a tube-bundle-type heat exchanger located in a rectifying column shown in  FIG. 4 . 
           [0051]      FIG. 7  shows an overall configuration of a heat integrated distillation apparatus according to a second embodiment of the present invention. 
           [0052]      FIG. 8  shows a peripheral configuration of a tube-bundle-type heat exchanger located in a stripping column shown in  FIG. 7 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS  
       [0053]    A general distillation apparatus, which is not an internally heat integrated distillation apparatus, includes a column built in a vertical direction and having a bottom section, a trayed section(or packed bed section), and a top section. At a boundary of feed location, an upper side of the trayed section(or packed bed section) is a rectifying section and a lower side is a stripping section. On the other hand, a heat integrated distillation apparatus according to the present invention has a basic feature in which a stripping section and a rectifying section similar to those described above are separated from each other, a column shell (stripping column) that is use as is the stripping section extending in a vertical direction and a column shell (rectifying column) that is use as the rectifying section extending in the vertical direction are provided, and the stripping column is located higher than the rectifying column. Hereinafter, embodiments of the present invention are described with reference to the drawings. 
       First Embodiment 
       [0054]      FIG. 4  shows an overall configuration of a heat integrated distillation apparatus according to a first embodiment. The heat integrated distillation apparatus according to the embodiment includes rectifying column  1  and stripping column  2  that are located higher than rectifying column  1 . Rectifying column  1  includes column bottom  1   a , trayed section (or packed bed section)  1   b , and top column  1   c . Stripping column  2  also includes column bottom  2   a , trayed section (or packed bed section)  2   b , and top column  2   c.    
         [0055]    Trayed section  1   b  and  2   b  are sections where several horizontal trays are located therein. A tray on which vapor and liquid contact mutually is referred to as a stage. At each stage, gas-liquid contact promotes a mass transfer. As a result, a gas phase having rich in components with higher volatility ascends to an upper stage, while a liquid phase having rich in components with lower volatility descends to a lower stage. Then, gas-liquid contact is executed again with a new liquid phase or gas phase there for further mass transfer. Thus, there are components in rich with higher volatility at a higher stage of the column, there are components in rich with lower volatility at a lower stage, and a distillation operation is accomplished. 
         [0056]    The packed section that can replace the trayed section is a section where a certain packing is installed in the empty column, and gas-liquid contact is executed on its surface. By the same mechanism as that of the trayed column, there are components in rich with higher volatility at a higher part, there are components in rich with lower volatility at a lower part, and a distillation operation is accomplished. 
         [0057]    In  FIG. 4 , trayed sections  1   b  and  2   b  (or packed bed sections) are shown as blank. In reality, however, the abovementioned structures are employed. 
         [0058]    Each of rectifying column  1  and stripping column  2  is described in detail. First, stripping column  2  is described. 
         [0059]    Heater  3  referred to as a reboiler is disposed outside column bottom  2   a  of stripping column  2 , and pipe  21  is provided from a lower space part of column bottom  2   a  through heater  3  to an upper space part of column bottom  2   a . Liquid descending through trayed section  2   b  (or packed bed section) of stripping column  2  accordingly stays at column bottom  2   a . A part of the liquid is heated by heater  3  to become vapor, and returns to column bottom  2   a . From the bottommost part of column bottom  2   a , liquid in rich with lower volatility components is acquired through pipe  22 . 
         [0060]    Column top  2   c  of stripping column  2  is a position for supplying feed stream. Column top  2   c  is connected, via compressor  4 , to column bottom la of rectifying column  1  by using pipe  23 . According to an embodiment, the feed stream is supplied at the top of column  2   c  of stripping column  2 . However, the feed stage can be an arbitrary stage of trayed section  2   b  (or packed bed section). Even when there is a plurality of raw materials, the feed stage can be column top  2   c  of stripping column  2  and other arbitrary stages (including a stage of rectifying column  1 ). 
         [0061]    In addition, trayed section  2   b  (or packed bed section) of stripping column  2  includes liquid withdrawal unit  2   d  at a predetermined stage. As shown in  FIG. 5 , liquid withdrawal unit  2   d  holds liquid  10  descending from an upper part of stripping column  2  at chimney tray for sump  5 , and withdraws a part of liquid  10  from stripping column  2 . Pipe  24  for directing a part of liquid  10  to rectifying column  1  is connected to liquid withdrawal unit  2   d . Pipe  25  from rectifying column  1  is inserted through a shell wall of stripping column  2  into a stage directly below liquid withdrawal unit  2   d . From pipe  25  inserted into the stage directly below liquid withdrawal unit  2   d , fluids having a mixture of vapor  11  and liquid  12  are introduced as described below, and vapor  11  ascends while liquid  12  descends. 
         [0062]    Rectifying column  1  is described. 
         [0063]    One end of pipe  26  is connected to a bottommost part of column bottom  1   a  of rectifying column  1 , while the other end of pipe  26  is connected to pipe  27  for supplying feed materials to column top  2   c  of stripping column  2 . To recycle the liquid staying at column bottom la of rectifying column  1  to column top  2   c  of stripping column  2  located higher than rectifying column  1 , pump  6  is necessary at the midway section of pipe  26 . 
         [0064]    Condenser  7  is equipped outside column top  1  c of rectifying column  1 , and pipe  28  is connected from an upper space part of column top  1   c  to condenser  7 . Thus, vapor that has withdrawn from column top  1   c  of rectifying column  1  is cooled by the condenser  7  to become liquid, and a distillate liquid having components with higher volatility is acquired. A part of the liquid is refluxed to column top  1   c.    
         [0065]    In addition, tube-bundle-type heat exchanger  8  is inserted into a predetermined stage of trayed section  1   b  (or packed bed section) of rectifying column  1 . A parallel tube portion in a U-shaped tube of tube-bundle-type heat exchanger  8  is equipped along chimney tray for sump  9  for temporarily holding a condensed liquid and re-distributing vapor ascending from below. Lower tube portion  8   a  of the parallel tube portion is connected to pipe  24  connected to liquid withdrawal unit  2   d  of stripping column  2 . Upper tube portion  8   b  is connected to pipe  25  that is inserted into the stage directly below liquid withdrawal unit  2   d.    
         [0066]    An operation of tube-bundle-type heat exchanger  8  is described. 
         [0067]    In the apparatus, the pressure and temperature of vapor out of column  2   c  of stripping column  2 , that is to be supplied to column bottom la of rectifying column  1 , is increased by compressor  4 . Vapor  13  (refer to  FIG. 6 ), whose temperature increased, is introduced to column bottom  1   a  of rectifying section  1  where it ascends and comes into contact with the U-shaped tube of tube-bundle-type heat exchanger  8 . In this case, liquid at an arbitrary stage of stripping column  2  is introduced through pipe  24  to lower tube portion  8   a  of heat exchanger  8 . Thus, the liquid in tube portion  8   a  is heated by the heat of vapor  13 , and a part of vapor  13  in contact with tube portion  8   a  is condensed and becomes liquid  14  which descends. Upper tube portion  8   b  of heat exchanger  8  is also heated by the heat of vapor  13 . Thus, the liquid introduced through pipe  24  into heat exchanger  8  changes into fluids having a mixture of a liquid phase and a gas phase while moving from lower tube portion  8   a  to upper tube portion  8   b . The fluids then pass through pipe  25  outside the column to be introduced to the stage directly below liquid withdrawal unit  2   d  of stripping section  2  (refer to  FIG. 4 ). For circulating of such fluids, no pressure-feeding means such as a pump is necessary because the configuration employs the thermo-siphon system. 
         [0068]    In other words, because liquid withdrawal unit  2   d  of stripping column  2  is connected to lower tube portion  8   a  of heat exchanger  8  of rectifying column  1  via pipe  24  and because upper tube portion  8   b  of heat exchanger  8  of rectifying column  1  is connected to the stage directly below liquid withdrawal unit  2   d  of stripping column  2  via pipe  25 , the liquid descends from stripping column  2  to rectifying column  1  by gravity. As a result, gravity causes the fluids to flow from rectifying column  1  to stripping column  2  even when there is no pump. 
         [0069]    As described above, according to the embodiment, the heat can be removed from the vapor in rectifying column  1  by heat exchanger  8 , and transferred from rectifying column  1  to stripping column  2  through pipe  25 . A heat transfer system using pipes  24  and  25  and heat exchanger  8 , as in the case of the embodiment, is configured as if a side condenser is installed at an arbitrary stage of rectifying column  1  and, simultaneously, as if a side reboiler is installed at an arbitrary stage of stripping column  2 . Thus, as compared with a distillation apparatus that includes no such heat transfer system, the amount of heat that has been removed can be reduced at condenser  7  of rectifying column  1 , and the amount of heat that has been supplied can be reduced at reboiler  3  of stripping column  2 . As a result, a high energy saving distillation apparatus can be achieved. 
         [0070]      FIG. 4  shows only one heat transfer system. However, the number of heat transfer systems equivalent to 10 to 30% of the total number of theoretical stages can be installed. Needless to say, the number of heat transfer systems to be installed and locations of the heat exchanger and the pipes can be arbitrarily determined according to a design specification. 
       Second Embodiment 
       [0071]    Next, a second embodiment of the present invention is described. Components similar to those of the first embodiments are described by using similar reference numerals. 
         [0072]      FIG. 7  shows an overall configuration of a heat integrated distillation apparatus according to the second embodiment. The heat integrated distillation apparatus according to the embodiment includes rectifying column  1  and stripping column  2  located higher than rectifying column  1 . Rectifying column  1  includes column bottom  1   a , trayed section (or packed bed section)  1   b , and top column  1   c . Stripping column  2  also includes column bottom  2   a , trayed section (or packed bed section)  2   b , and top column  2   c . A specific configuration of the trayed column or the packed column is similar to that of the first embodiment. 
         [0073]    The embodiment is different from the first embodiment in that tube-bundle-type heat exchanger  8  is located on stripping column  2  side. 
         [0074]    For stripping column  2  according to the embodiment, components (reboiler  3 , and pipes  21 ,  22 ,  23 , and  27 ) belonging to column bottom  2   a  and column top  2   c  are similar to those of the first embodiment as shown in  FIG. 7 . However, components for trayed section  2   b  (or packed bed section) are changed from those of the first embodiment. 
         [0075]    Trayed section  2   b  (or packed bed section) includes liquid sump unit  2   e  at a predetermined stage. Liquid sump unit  2   e  stores a predetermined amount of liquid  10  that has flowed down onto chimney tray for sump  15 , and liquid spilled from chimney tray for sump  15  drops. To dip a U-shaped tube of tube-bundle-type heat exchanger  8  in the liquid stored by liquid sump unit  2   e , tube-bundle-type heat exchanger  8  is inserted into liquid sump unit  2   e  (refer to  FIG. 8 ). Parallel tube portions  8   a  and  8   b  in the U-shaped tube of tube-bundle-type heat exchanger  8  are arranged along chimney tray for sump  15 . 
         [0076]    Pipe  29  (refer to  FIG. 7 ) for feeding fluids from rectifying column  1  to stripping column  2  is connected to upper tube portion  8   b  of the parallel tube portions. Pipe  30  (refer to  FIG. 7 ) for feeding fluids from stripping column  2  to rectifying column  1  is connected to lower tube portion  8   a.    
         [0077]    An operation of heat exchanger  8  at liquid sump unit  2   e  is described. 
         [0078]    In the apparatus, a liquid feed descends from column top  2   c  of stripping column  2  through a trayed or a packed layer. Liquid  10  (refer to  FIG. 8 ) stays at liquid sump unit  2   e  on chimney tray for sump  15  that is located at an arbitrary stage. The U-shaped tube of tube-bundle-type heat exchanger  8  is located in liquid sump unit  2   e , and hence the U-shaped tube is dipped in liquid  10 . In this state, when high-temperature vapor in rectifying column  1  is introduced through pipe  29  into upper tube portion  8   b  of heat exchanger  8 , a part of liquid  10  in contact with the outer walls of tube portions  8   a  and  8   b , where the high-temperature vapor moves, is heated to become vapor  18 , and ascends (refer to  FIG. 8 ). The high-temperature vapor introduced through pipe  29  into heat exchanger  8  changes to fluids that have a mixture of a liquid phase and a gas phase while being moved from upper tube portion  8   b  to lower tube portion  8   a . The fluids are introduced through pipe  30  outside the column to a stage on partition plate  16  of rectifying column  1  described below (refer to  FIG. 7 ). Operation pressure is set lower on partition plate  16  than that below partition plate  16 . This pressure difference causes circulation of the fluids. In such circulation of the fluids, the configuration needs no special pressure-feeding means such as a pump, as in the case of the first embodiment. 
         [0079]    In other words, because a predetermined stage of rectifying column  1  is connected to upper tube portion  8   b  of heat exchanger  8  in stripping column  2  via pipe  29  and because lower tube portion  8   a  of heat exchanger  8  in stripping column  2  is connected to the predetermined stage of rectifying column  1  via pipe  30 , due to the pressure difference between the upper and lower of partition plate  16 , the high-pressure vapor in rectifying column  1  ascends through pipe  29  toward heat exchanger  8  in stripping column  2 . Liquid that is condensed from vapor in heat exchanger  8  is then pushed out from stripping column  2  to pipe  30  that is outside the column, and descends to rectifying column  1  by gravity. Thus, no pressure-feeding means such as a pump is necessary. 
         [0080]    Rectifying column  1  according to the embodiment is described. 
         [0081]    Similarly, for rectifying column  1 , components (condenser  7 , and pipes  23 ,  26 , and  28 ) belonging to column bottom  1   a  and column top  1   c  are similar to those of the first embodiment as shown in  FIG. 7 . However, components for trayed section  1   b  (or packed bed section) are changed from those of the first embodiment. Specifically, the middle section of trayed section  1   b  (or packed bed section) of rectifying column  1  is completely partitioned into upper and lower stages by partition plate  16 . The stage directly below partition plate  16  communicates with pipe  29 . Ascending vapor at this stage is fed, through pipe  29  extending in a vertical direction, to upper tube portion  8   b  of heat exchanger  8  located in liquid sump unit  2   e  of stripping column  2 . 
         [0082]    Pipe  30  from stripping column  2  side is inserted through an outer wall of rectifying column  1  into the upper stage of partition plate  16 . Fluids having a mixture of vapor and liquid are introduced through pipe  30  to the upper stage of partition plate  16 . The vapor ascends while the liquid descends to stay on partition plate  16 . The ascending vapor that has moved to column top  1  c passes through pipe  28  to be cooled by condenser  7 . As a result, a distillate liquid having rich in high volatility components is acquired. 
         [0083]    The two upper and lower stages sandwiching partition plate  16  can be connected to each other via pipe  31  having control valve  17 . The liquid held on partition plate  16  is fed to the lower stage of partition plate  16  by an opening operation of control valve  17  when appropriate. 
         [0084]    As described above, according to the embodiment, by removing the vapor from rectifying column  1  through pipe  29 , and introducing the vapor into heat exchanger  8  in stripping column  2 , heat can be removed from rectifying column  1  to transfer into stripping column  2 . A heat transfer system using pipes  29  and  30  and heat exchanger  8 , as in the case of the embodiment, is configured as if a side condenser is installed at an arbitrary stage of rectifying column  1  and, simultaneously, a side reboiler is installed at an arbitrary stage of stripping column  2 . Thus, as compared with a distillation apparatus that includes no such heat transfer system, the amount of heat that has been removed can be reduced at condenser  7  of rectifying column  1 , and the amount of heat that has been input can be reduced at reboiler  3  of stripping column  2 . As a result, a very high energy saving distillation apparatus can be achieved. 
         [0085]      FIG. 7  shows only one heat transfer system. However, according to the embodiment, as in the case of the first embodiment, the number of heat transfer systems to be installed and the locations of the heat exchanger and the pipes can be arbitrarily determined according to a design specification. 
         [0086]    The heat integrated distillation apparatus according to each of the first and second embodiments is configured by using the trayed column or the packed column similar to that of the general distillation apparatus. This enables side-cutting or multi-feeding without any need to improve the apparatus, and easy maintenance of the apparatus. For the same reason, freedom for setting the numbers of stages for the rectifying column and the stripping column enables optimization of feed stages. In other words, the present invention can solve problems 1) to 5) of the heat integrated distillation apparatus using the double-pipe structure represented by Patent Literature 1. 
         [0087]    According to the embodiment of the present invention, tube-bundle-type heat exchanger  8  is used as the component of the heat transfer system that transfers heat from rectifying column  1  to stripping column  2 . This enables free changing of the heat transfer area A based on a tube design of heat exchanger  8 . Thus, in order to determine the amount of heat that is to be exchanged between rectifying column  1  and stripping column  2 , not only the temperature difference ΔT between rectifying column  1  and stripping column  2  but also the heat transfer area A can be freely set. The present invention can therefore solve problem 6) of the heat integrated distillation apparatus using the double-pipe structure. 
         [0088]    The preferred embodiments of the present invention have been described. However, the embodiments are in no way limitative of the present invention. Needless to say, various changes can be made to the present invention within its technical teachings. 
         [0089]    According to the first and second embodiments, the distillation column includes the heat exchanger. However, the present invention is not limited to this arrangement. The present invention allows the heat exchanger to be installed outside the distillation column as long as heat can be transferred between the fluids of the portion including the stripping column and the fluids of the portion including the rectifying column. For the shape of the heat exchanger, each of the embodiments employs a tube-bundle-type heat exchanger of the U-shape tube only as a general example when the heat exchanger is included in the distillation column. Heat exchangers of other shapes can be used. 
         [0090]    According to each of the embodiments, rectifying column  1  and stripping column  2  are connected to each other in the vertical direction. However, the present invention is not limited to this arrangement. In other words, the present invention includes an arrangement where rectifying column  1  and stripping column  2  are configured separately and independently, and stripping column  2  is located higher than rectifying column  1 . 
       EXPLANATION OF REFERENCE NUMERALS  
       [0091]      1  rectifying column 
         [0092]      1   a  column bottom 
         [0093]      1   b  trayed section (or packed bed section) 
         [0094]      1   c  column top 
         [0095]      2  stripping column 
         [0096]      2   a  column bottom 
         [0097]      2   b  trayed section (or packed bed section) 
         [0098]      2   c  column top 
         [0099]      2   d  liquid withdrawal unit 
         [0100]      2   e  liquid sump unit 
         [0101]      3  heater (reboiler) 
         [0102]      4  compressor 
         [0103]      5  chimney tray for sump 
         [0104]      6  pump 
         [0105]      7  condenser 
         [0106]      8  tube-bundle-type heat exchanger 
         [0107]      5 ,  15  chimney tray for sump 
         [0108]      9  chimney tray for sump 
         [0109]      10 ,  12 ,  14  liquid 
         [0110]      11 ,  13 ,  18  vapor 
         [0111]      16  partition plate 
         [0112]      17  control valve 
         [0113]      21 ,  22 ,  23 ,  24 ,  25 ,  26 ,  27 ,  28 ,  29 ,  30 ,  31  pipe