JP2012005931A - Method of operating distillation tower - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of efficiently operating and controlling a distillation tower even when the charge amount of a continuous distillation device is small.SOLUTION: In a continuous distillation device with a heater 2 and a condenser 3 attached to a tower bottom and a tower top, respectively, a distillation tower bottom liquid is introduced into a charge stage or a recovery part when the throughput of a distillation tower 1 is small. Even when the charge liquid amount of the distillation tower is small, a part of the bottom liquid is introduced into the distillation tower charge stage or the recovery part in order to ensure stable operation of the distillation tower, whereby a weeping state of the distillation tower can be prevented by increasing the load of the distillation tower, and increase of steam usage can be reduced.

Description

  The present invention relates to a method for operating a distillation column, and more particularly to a method for efficiently controlling the operation of a distillation column even when the amount of feed (processing amount) of a continuous distillation apparatus is small.

  A distillation tower is a tower-like apparatus used for distillation. In addition to the main part of the distillation tower, the distillation tower is equipped with a heater at the bottom and a condenser at the top. Industrial distillation is carried out continuously when a large amount of treatment is performed. In general, the charged liquid is introduced into the middle part (charged stage) of the distillation column, but the charged liquid may be evaporated by an evaporator and introduced into the distillation column in a gas phase state. The distillation apparatus performs separation operation using the difference in boiling point of substances contained in the feed liquid (raw material), and a distillate rich in low-boiling components can be obtained from the top of the distillation tower, and from the bottom of the tower. A bottoms rich in high-boiling components can be obtained.

  In the distillation column, the vapor distilled from the top of the column is condensed in a condenser and obtained as a liquid. Returning a part of the condensed liquid to the distillation column is called reflux, and for rectification separation, In the distillation column, the reflux liquid flowing down from the upper side and the vapor rising from the lower side must be counter-flowed so that the gas-liquid contact is sufficiently performed. At this time, the components are concentrated by repeating the evaporation and partial condensation of the liquid by the heat of condensation.

  Distillation towers are roughly classified into plate towers and packed towers. The tray tower is a distillation tower in which horizontal shelves (tray) are installed in multiple stages inside the distillation tower. The packed column is a distillation column in which a filler is packed inside the distillation column.

The distillation tower has been designed and manufactured to reduce pressure loss and improve gas-liquid contact efficiency in order to maintain stable operation and increase rectification operation. In consideration of these points, it is necessary to increase the column diameter of the distillation column in order to increase the amount charged (treatment amount) of the distillation column. In that case, in terms of equipment production, the larger the diameter of the distillation column, the larger the initial capital investment amount. Therefore, generally, the column diameter of the distillation column is determined based on the maximum processing amount in order to reduce the capital investment amount.
However, increasing the number of distillation columns as described above inevitably increases the investment recovery risk due to the increase in the initial capital investment.

  When the column diameter of the distillation column is increased, the amount of processing is changed by modifying the equipment inside the distillation column. In such a modification of the equipment inside the distillation tower, it is necessary to stop the operation during the repair period, which is accompanied by a reduction in production. And because the production volume (distillation tower throughput) is increased or decreased according to the customer's demand, it is not easy to frequently modify the equipment inside the distillation tower in response to changes in production due to fluctuations in demand. .

  As a technique for solving such a problem, for example, as in Japanese Patent Publication No. 6-63700 (Patent Document 1), the components in the distillation column are improved from the initial production to prevent a decrease in distillation separation efficiency. There is technology to do. However, the distillation tower using this technique cannot completely prevent the weeping phenomenon, and the weeping phenomenon easily occurs depending on the conditions. For this reason, it is difficult to obtain a high-purity distilled product by a distillation column using this technique.

  As described above, there is a range (stable operation range) in which the distillation column can be operated in a stable state and the required purity of the distillate can be obtained. In the distillation column, when the amount of raw material charged and the reflux ratio are changed, the amount of ascending steam and the amount of descending liquid change in each stage in the distillation column. When the amount of ascending steam is greatly increased, a droplet entrainment phenomenon occurs, and when the amount of ascending steam is greatly decreased, a weeping phenomenon occurs.

  A description will be given using a tray tower as an example. In each stage in the distillation column, when the amount of rising steam and the amount of falling liquid are balanced, there is almost no liquid flowing down from the hole in the tray, and the falling liquid gets over the weir provided in the tray and comes from the downcomer. Flow down. And the vapor | steam which raises the hole of a tray and the falling liquid which flows on a tray contact, vapor-liquid equilibrium is obtained, and distillation is performed. The entrainment phenomenon is a phenomenon in which the descending liquid on the tray is entrained as droplets. In addition, the weeping phenomenon is a phenomenon in which the descending liquid on the tray leaks from the hole of the tray. In general, when the amount of liquid (treatment amount) charged into the distillation column is small, the counter flow rate of gas and liquid at each stage in the distillation column decreases, and a weeping phenomenon occurs. The lower limit of the stable operation range of the distillation column (the lower limit of the throughput of the distillation column) is determined as a distillation load capable of avoiding a decrease in the purity of the distilled product due to such a weeping phenomenon.

  If the amount of liquid fed to the distillation column (processing amount) is small, the distillation separation efficiency will decrease due to the weeping phenomenon. Conventionally, due to hardware measures such as the use of multiple distillation columns and modification of the equipment inside the distillation column. In order to prevent weeping, the stable operation region of the distillation column was changed. Multiple distillation towers means that the distillation tower is designed to have a column diameter that matches the minimum charge (processing amount), and in order to increase the maximum throughput, the number of distillation towers should be multiple and the amount charged should be small. Is a method in which the number of distillation columns to be operated is operated with two or more towers depending on the amount charged when the operation is performed with one tower and the amount to be charged increases.

Remodeling the inside of the distillation tower means arranging the equipment that optimizes the gas-liquid contact area inside the distillation tower according to the amount of liquid (treatment volume) charged to the distillation tower, and achieving a balanced gas-liquid balance. It is a way to maintain and prevent weeping.
Moreover, in order to prevent a weeping phenomenon, there exists a response | compatibility by the operating method of a distillation tower. One is a method for increasing the amount of the reflux liquid in the distillation column, and the other is a method for preparing and supplementing the shorting liquid for the distillation column. These methods increase the amount of ascending steam and the amount of descending liquid at each stage in the distillation column, leading to prevention of the weeping phenomenon, but still have problems.

  That is, the method of increasing the amount of reflux liquid in the distillation column increases the amount of reflux liquid concentrated as a low-boiling component, so that the area of low-boiling components spreads to the distillation column recovery part. The low boiling point component to be removed due to the insufficient number of stages is mixed into the bottoms (high boiling point component), and the purity of the distilled product cannot be obtained.

  In addition, the method of preparing and supplementing the distillation column charge liquid is prepared by mixing the distillation tower distillate obtained by distilling and separating the distillation column charge liquid and the distillation tower distillate to prepare the charge liquid. Since this is a method of adding to the liquid and increasing the amount of liquid charged in the distillation column, a weeping state can be prevented. However, since the distillation column distillate once distilled in the distillation column is distilled again from the top of the distillation column, the amount of energy consumed by the heater of the distillation column increases, and the energy cost per processing amount increases.

Japanese Patent Publication No. 6-63700

 The problem to be solved by the present invention is that there has been no method for increasing or decreasing the production amount without relying on a plurality of distillation columns. Moreover, as a method other than a plurality of distillation towers, there was no other way than simply adapting the equipment inside the distillation tower, and there was no method that could easily increase or decrease the production volume. In addition, it was impossible to obtain a high-purity distilled product while simply increasing or decreasing the production amount.

  Furthermore, the problem to be solved by the present invention is that the purity of the distillate cannot be obtained in the method of increasing the amount of the reflux liquid in the distillation column in order to prevent the weeping phenomenon. And in the method of distilling the distillation tower distillate once distilled from the distillation tower from the top of the distillation tower again, the amount of energy consumed by the heater of the distillation tower increases, and the energy cost per processing amount increases. Was to do.

  In the continuous distillation apparatus in which a heater is attached to the bottom of the column and a condenser is attached to the top of the column, the distillation column can be discharged into the charging stage or the recovery unit when the amount of processing (feeding amount) of the distillation column is small. Is a technology that achieves both stable operation of the distillation column and purity of the distillate.

  In other words, by introducing distillation column bottoms into the distillation column preparation stage or recovery section, the amount of ascending and descending liquids is mainly increased in each stage of the distillation tower recovery section to ensure sufficient gas-liquid contact. Thus, the weeping phenomenon can be prevented. Furthermore, the bottoms of the distillation column are liquids recovered as high-boiling components with high purity by distillation, and even when the bottoms were introduced into the preparation stage or recovery section of the distillation tower, the amount of reflux was increased. It does not cause a decrease in the purity of the distillate (boiler liquid) that occurs in some cases. In addition, since the bottoms of the distillation tower are boiling liquids heated to the boiling point by a heater, even if the bottoms are introduced into the preparation stage or recovery unit of the distillation tower, they are consumed by the heater of the distillation tower. The increase in energy is very small.

  In addition, when the bottoms are introduced into the distillation column concentrating part, the region of the high boiling point component is expanded to the distillation tower concentrating part, and the high boiling point components are mixed in the distillation tower distillate, and the bottoms (distilled product) Cause loss. At this time, it is possible to prevent the high boiling point component from being mixed into the distillation column distillate by increasing the amount of the reflux solution, but the introduced reflux solution (low boiling point component) is distilled from the top of the distillation column. Since it is necessary, the amount of energy consumed by the heater of the distillation tower is increased. Therefore, in the embodiment of the present invention, the bottoms are introduced into the preparation stage or the recovery part of the distillation column.

  As described above, according to the present invention, even when the amount of liquid (treatment amount) in the distillation column is small, a part of the bottoms is introduced into the distillation column preparation stage or the recovery unit in order to ensure stable operation of the distillation column. Thus, the distillation column load can be increased to avoid the weeping state of the distillation column, and the increase in the amount of steam used can be reduced. That is, by implementing the method of the present invention, the lower limit of the throughput (operation load) of the distillation column can be expanded from 70% to 40% of the design capacity, and the distillation column can be efficiently stabilized with a small amount of energy. And is industrially valuable.

  The present invention will be described in more detail with reference to FIG. A continuous distillation apparatus in which a heater 2 is attached to the bottom of the distillation tower 1 and a condenser 3 is attached to the top of the tower is shown. The feed liquid 4 (raw material) to the distillation column 1 is given energy by the heater 2 and is separated by distillation into a low boiling point component and a high boiling point component. A low boiling point component in the charged liquid is distilled as a vapor from the top of the distillation tower and cooled by the condenser 3, and a rectifying operation is performed by introducing a part 5 of the condensed liquid as a reflux liquid into the distillation tower. The high boiling point component in the charged liquid is withdrawn as a bottoms 7 from the bottom of the distillation column. In the present invention, the distillation separation efficiency is adjusted by introducing a part 8 of the bottoms 7 into the charging stage or the recovery unit of the distillation column 1. As long as the distillation apparatus has such a function, the present invention can be applied to any structure, and the shape of the distillation column and the structure or configuration of the components in the distillation column are not particularly limited.

  The method for increasing the amount of the reflux liquid in the distillation column is performed by increasing the reflux liquid 5 in FIG. However, in this method, low boiling point components are mixed in the distillation column bottoms 7 and the purity of the bottoms is lowered. Further, since the low boiling point component to be distilled is further introduced, the amount of energy required for heating and evaporation of the increased reflux liquid is increased in the distillation tower heater 2, and the energy cost per processing amount is increased.

  FIG. 3 shows a method for preparing and supplementing the feed solution for the distillation column. When the amount of distillation column charge (treatment amount) is small, the preparation liquid 10 prepared by mixing the distillation tower bottom liquid 7 and the distillation tower distillate 6 so as to be equivalent to the composition of the preparation liquid is added to the distillation tower preparation liquid 4. To increase the throughput of the distillation tower. However, since the distillation column distillate 6 once separated and distilled in the distillation column is again introduced into the distillation column via the preparation solution 10 and distilled from the top of the distillation column, the distillate used for the preparation The amount of energy required for heating and evaporation is increased in the distillation tower heater 2, and the energy cost per processing amount is increased.

  In the embodiment of FIG. 1, the operation method of FIG. 4 is performed when the charged liquid 4 (raw material) to the distillation column 1 contains a solid content and there is a concern about deterioration of the quality of the distilled product or contamination of the distillation column. By charging the distillation liquid 1 in the vapor state in which almost the entire amount of the charged liquid 4 has been previously evaporated by the evaporator 11, the solids contained in the charged liquid 4 are discharged from the evaporator 11 in the state of a concentrated residual liquid. The In this case, in the method for preparing and supplementing the preparation liquid for the distillation tower as described with reference to FIG. 3, the amount of energy required for re-evaporating the preparation liquid 10 is further increased.

Hereinafter, an embodiment of the present invention will be described with reference to FIG. This example relates to the purification of acetic acid contained in organic solvents.

The feed liquid 4 (raw material) to the distillation column 1 is a mixed solution of an organic solvent containing ethyl acetate and acetic acid, and is distilled and separated into a low boiling point component and a high boiling point component in the distillation column 1. Since this feed liquid 4 contains solids, almost the entire amount is evaporated by the evaporator 11 and introduced into the distillation column 1. The organic solvent which is a low-boiling component in the feed liquid 4 is cooled by the condenser 3 from the top of the distillation column and obtained as a condensate 6, and the acetic acid which is a high-boiling component is withdrawn as a bottoms 7 from the bottom of the distillation column. . And the distillation operation is performed so that the acetic acid purity of the bottoms 7 may become 99.9 wt% or more. The production volume is adjusted according to the amount of feed liquid (raw material) generated. For this reason, the operation load of the distillation column may be almost 100% of the processing capacity, but when the amount of charged liquid is reduced, the operation load of the distillation column may be reduced to 50% of the processing capacity. At this time, it falls below the lower limit of the stable operation range of the distillation column, and a weeping phenomenon occurs, resulting in a decrease in the acetic acid purity of the bottoms as a distilled product.

As an operation method of the distillation tower to avoid this situation, a part of the bottom liquid (introducing liquid) 8 is introduced into the charging stage of the distillation tower 1. In the embodiment, the position where the introduction liquid 8 is introduced into the distillation column 1 is the distillation column preparation stage, but it may be a distillation column recovery section. However, in manufacturing the equipment, the distillation column preparation stage needs to have a wide step interval in order to connect the pipes of the preparation liquid 4 and the introduction liquid 8, so if the introduction positions of the preparation liquid 4 and the introduction liquid 8 are different, The height of the distillation tower increases and the equipment manufacturing cost increases.

The lower limit of the stable operation range of the distillation column is when the reduction in the amount charged (treatment amount) to the distillation column is about 70% of the processing capacity. When the processing capacity is reduced to about 50%, the ratio of the amount of the introduced liquid 8 and the amount of the bottoms 7 obtained as a distilled product is set to 1.4, thereby preventing the weeping phenomenon and the distillation separation efficiency. Can be avoided. At this time, the amount of the reflux liquid is increased to prevent loss of the introduced high boiling point component to the distillate 6. In addition, if the ratio of the introduced liquid 8 and the bottom liquid 7 exceeds 2.0, the amount of the required reflux liquid greatly increases, so the amount of energy consumed by the heater 2 increases and the energy cost increases. It is not preferable.

When the method for increasing the amount of reflux liquid is applied, the amount of the reflux liquid necessary for preventing the weeping phenomenon is 1.2 times that of the method of the present invention, and is consumed by the evaporator 11 and the heater 2. The amount of energy required is about 1.1 times that of the method of the present invention.

In the case of applying the method of preparing and replenishing the feed liquid, in order to evaporate again the liquid 10 prepared from the bottoms distilled and distilled in the distillation column and the distillate in the evaporator 11 and introduce them into the distillation column. The amount of energy consumed by the evaporator 11 and the heater 2 increases according to the amount of the replenished preparation solution 10. When the preparation liquid is replenished so that the processing amount of the distillation column can be 50% to 70% of the processing capacity so as to prevent the weeping phenomenon, the amount of energy consumed in the evaporator 11 and the heater 2 is the same as that of the present invention. It is about 1.2 times that of the method.

FIG. 1 is a schematic view in which an embodiment of the present invention is applied to a general distillation apparatus, Fig. 2 is a schematic diagram showing a conventional distillation apparatus FIG. 3 is a schematic diagram showing an operation method for replenishing a feed liquid with a distilled separation liquid in a conventional distillation apparatus, FIG. 4 is a schematic view of a distillation apparatus in an embodiment of the present invention.

1 ... distillation tower, 2 ... heater, 3 ... condenser, 4 ... feeding liquid, 5 ... refluxing liquid, 6 ... distilled liquid, 7 ... bottom liquid, 8 ... bottom liquid introduced into the distillation tower (introduction Liquid), 9 ... tank for preparing liquid, 10 ... replenisher for charging liquid, 11 ... evaporator, 12 ... residual evaporation liquid

Claims (3)

A continuous distillation apparatus having a heater at the bottom and a condenser at the top of the tower, wherein the distillation tower bottoms are introduced into the charging stage or recovery section of the distillation tower, and the distillation apparatus is operated. 2. The distillation according to claim 1, wherein the ratio of the bottoms of the distillation column introduced into the charging stage or recovery part of the distillation column and the bottoms obtained as a distillate is 0.1 to 2.0. How to operate the device. The operating method of the distillation apparatus of Claim 1 or 2 introduce | transduced into a distillation column in the state of the vapor | steam which the preparation liquid of the distillation column evaporated.