Distillation apparatus and distillation method

Abstract

To provide a distillation apparatus that can efficiently separate a low-boiling solvent.SOLUTION: A distillation apparatus, which separates a low-boiling solvent from mixed liquid including the low-boiling solvent, a high-boiling solvent and salt, is provided with: a distillation tower in which the low-boiling solvent is evaporated from the mixed liquid and concentrated liquid in which concentration of the high-boiling solvent increases is stored in a lower part thereof; a condensing line having a capacitor which flows out vapor of the low-boiling solvent from an upper side of the distillation tower and condenses the vapor of the low-boiling solvent; a first reheating line which has a first extraction pump that extracts the concentrated liquid from the distillation tower and a first heat exchanger that heats the concentrated liquid extracted by the first extraction pump without evaporating the low-boiling solvent, through which the concentrated liquid heated by the first heat exchanger is refluxed to the distillation tower; and a second reheating line which has a second extraction pump that extracts the concentrated liquid from the distillation tower and a second heat exchanger that heats the concentrated liquid extracted by the second extraction pump to evaporate the low-boiling solvent, through which the concentrated liquid condensed by the second heat exchanger and the vapor of the low-boiling solvent is refluxed to the distillation tower.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a distillation apparatus and a distillation method. [Background technology]

[0002] A distillation apparatus for separating a low-boiling solvent from a mixture containing a low-boiling solvent and a high-boiling solvent can be configured to evaporate the low-boiling solvent from the mixture in a distillation column, condense the low-boiling solvent vapor flowing out from the top of the distillation column in a condenser, and extract a concentrated liquid stored in the bottom of the distillation column, reheat it in a reheater (reboiler), and then reflux it to the distillation column. A typical reheater is a multi-tube (shell-and-tube) heat exchanger having multiple heat transfer tubes arranged vertically. The concentrated liquid flowing down the heat transfer tubes is heated by a heat medium such as steam supplied to the outside of the heat transfer tubes (see, for example, Patent Document 1). In such a multi-tube down-flow heat exchanger, the low-boiling solvent evaporates inside the heat transfer tubes, and the concentrated liquid with an increased concentration of the high-boiling solvent and the low-boiling solvent vapor are refluxed to the distillation column. In other words, by using a multi-tube downflow heat exchanger, it is not necessary to evaporate the low boiling point solvent from the concentrated liquid inside the distillation column, and therefore the low boiling point solvent can be evaporated relatively efficiently. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-240482 Summary of the Invention [Problem to be solved by the invention]

[0004] The mixed liquid to be distilled may contain salt, which can cause a problem of reduced heat transfer coefficient due to scaling caused by salt precipitation on the inner surface of the heat transfer tube. In particular, when the concentrated liquid boils inside the heat transfer tube, salt scaling on the inner surface of the heat transfer tube is extremely accelerated. Therefore, in order to increase the capacity of the distillation apparatus, it is desirable to increase the heat transfer area of the multi-tube downflow heat exchanger. However, increasing the size of the multi-tube downflow heat exchanger increases the cost and installation space of the distillation apparatus.

[0005] In view of the above circumstances, an object of the present invention is to provide a distillation apparatus and a distillation method that can efficiently separate low-boiling point solvents. [Means for solving the problem]

[0006] (1) A distillation apparatus according to one aspect of the present invention is a distillation apparatus for separating a low-boiling solvent from a mixed liquid containing a low-boiling solvent, a high-boiling solvent, and a salt, the distillation apparatus comprising: a distillation column for evaporating the low-boiling solvent from the mixed liquid and storing a concentrated liquid having an increased concentration of the high-boiling solvent at a lower portion; a condensation line for causing vapor of the low-boiling solvent to flow out from an upper portion of the distillation column and having a condenser for condensing the vapor of the low-boiling solvent; a first withdrawal pump for extracting the concentrated liquid from the distillation column; a first reheat line for refluxing the concentrated liquid heated in the first heat exchanger to the distillation column; a second withdrawal pump for extracting the concentrated liquid from the distillation column; and a second reheat line for refluxing the concentrated liquid concentrated in the second heat exchanger and vapor of the low-boiling point solvent to the distillation column. The second reheat line has a second heat exchanger for heating the concentrated liquid extracted by the second withdrawal pump to evaporate the low-boiling point solvent.

[0007] (2) The distillation apparatus of (1) above may further include a control device that adjusts the amount of heat supplied to the second heat exchanger so as to maintain a constant temperature of the concentrated liquid inside the distillation column.

[0008] (3) In the distillation apparatus of (1) or (2) above, the first heat exchanger may be a welded plate heat exchanger.

[0009] (4) In the distillation apparatus according to any one of (1) to (3) above, the second heat exchanger may be a multi-tube downflow heat exchanger.

[0010] (5) A distillation apparatus according to one embodiment of the present invention is a distillation method for separating a low-boiling solvent from a mixture containing a low-boiling solvent, a high-boiling solvent, and a salt, the method comprising the steps of: supplying the mixture to a distillation column that evaporates the low-boiling solvent and stores a concentrated liquid having an increased concentration of the high-boiling solvent in the lower part; discharging vapor of the low-boiling solvent from the upper part of the distillation column and condensing the vapor of the low-boiling solvent; withdrawing the concentrated liquid from the distillation column, heating the concentrated liquid in a first heat exchanger that does not evaporate the low-boiling solvent, and then refluxing the concentrated liquid to the distillation column; and withdrawing the concentrated liquid from the distillation column, heating the concentrated liquid in a second heat exchanger that evaporates the low-boiling solvent, and refluxing the concentrated liquid concentrated by evaporation of the low-boiling solvent and the vapor of the low-boiling solvent to the distillation column.

[0011] (6) In the distillation method of (5) above, the low-boiling point solvent may be water, and the high-boiling point solvent may be at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.

[0012] (7) The distillation method according to claim 5 or 6, wherein the salt is at least one selected from the group consisting of sodium chloride, sodium sulfate, and sodium hydroxide.

[0013] (8) In the distillation method according to any one of (5) to (7), the amount of heat per heat transfer area of the heat medium supplied to the second heat exchanger per hour is 60 MJ / m 2 / h or less may be used. [Effects of the Invention]

[0014] According to the present invention, low boiling point solvents can be separated efficiently. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing the configuration of a distillation apparatus according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig. 1 is a diagram showing the configuration of a distillation apparatus 1 according to one embodiment of the present invention.

[0017] The distillation apparatus 1 of this embodiment is an apparatus for carrying out one embodiment of the distillation method of the present invention, and separates a low-boiling solvent from a mixture containing a low-boiling solvent, a high-boiling solvent, and a salt. The distillation apparatus 1 includes a distillation column 10, a condensation line 20, a first reheat line 30, a second reheat line 40, and a control device 50.

[0018] In this application, the terms "low-boiling solvent" and "high-boiling solvent" refer to the relative boiling points of the two solvents and do not limit the absolute temperature range of the boiling points. In other words, a "low-boiling solvent" refers to a solvent that evaporates and separates, and a "high-boiling solvent" refers to a solvent that remains without evaporating. Each term may include multiple solvents. A typical example of a low-boiling solvent is water, and a typical example of a high-boiling solvent is at least one selected from the group consisting of dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and dimethylacetamide (DMAC). A "salt" may be unavoidably contained in a mixed liquid, for example, when the mixed liquid is industrial wastewater, or may be intentionally added to suppress thermal decomposition of the solvent. For example, when the high-boiling solvent is dimethyl sulfoxide, at least one selected from the group consisting of sodium chloride, sodium sulfate, and sodium hydroxide may be used as the "salt" added to suppress thermal decomposition of the high-boiling solvent.

[0019] The distillation column 10 is a vessel into which a mixed liquid is introduced. The low-boiling solvent is evaporated from the mixed liquid within the distillation column, and a concentrated liquid containing an increased concentration of high-boiling solvent and salt due to the evaporation of the low-boiling solvent is stored in the lower part. The distillation column 10 is preferably configured to operate at a pressure lower than atmospheric pressure so that the low-boiling solvent can be evaporated at a lower temperature. The distillation column 10 may have a first packing 11 in the middle of its height to promote the evaporation of the low-boiling solvent from the mixed liquid, and the mixed liquid may be introduced so as to be sprayed over the first packing 11. The distillation column 10 may also be configured to allow the condensed liquid of the separated low-boiling solvent to be refluxed, or may have a second packing 12 above the first packing 11 to promote the evaporation of the refluxed low-boiling solvent, and the condensed liquid of the low-boiling solvent may be refluxed so as to be sprayed over the second packing 12. The distillation column 10 may also have a temperature sensor 13 to detect the temperature of the concentrated liquid stored in the lower part.

[0020] The condensation line 20 allows the low-boiling-point solvent vapor to flow out from the top of the distillation column 10 and condenses and recovers the low-boiling-point solvent vapor. For this purpose, the condensation line 20 has a condenser 21 that condenses the low-boiling-point solvent vapor. The condensation line 20 may also have a receiving tank 22 that temporarily stores the condensate and a condensate pump 23 that returns the condensate to the distillation column 10 or sends it to the outside. The condenser 21 is formed from a heat exchanger that exchanges heat between the low-boiling-point solvent vapor and a refrigerant, and generates a negative pressure by condensing the low-boiling-point solvent vapor. This draws the vapor inside the distillation column 10 into the condensation line 20, reducing the pressure inside the distillation column 10 to a pressure lower than atmospheric pressure.

[0021] The first reheat line 30 includes a first withdrawal pump 31 that extracts the concentrated liquid from the distillation column 10 and a first heat exchanger 32 that heats the concentrated liquid extracted by the first withdrawal pump 31 without evaporating the low-boiling solvent. The concentrated liquid heated by the first heat exchanger 32 is then refluxed to the distillation column 10. Note that "without evaporation" means that there is no substantial increase in the amount of vapor in the first heat exchanger 32. This does not exclude, for example, slight bubbles due to cavitation or micro-level evaporation and condensation at the equilibrium liquid surface. A welded plate-type heat exchanger is preferably used as the first heat exchanger 32, as it has a large heat transfer area relative to its volume, can increase the flow rate of the concentrated liquid inside, and thus prevents the boiling of the low-boiling solvent in the concentrated liquid. Steam or the like can be used as a heat medium for heating the concentrated liquid.

[0022] The second reheat line 40 includes a second withdrawal pump 41 that extracts the concentrated liquid from the distillation column 10 and a second heat exchanger 42 that heats the concentrated liquid extracted by the second withdrawal pump 41 to evaporate the low-boiling solvent. The concentrated liquid and low-boiling solvent vapor heated by the second heat exchanger 42 are refluxed to the distillation column 10. The second reheat line 40 preferably refluxes the concentrated liquid and low-boiling solvent vapor between the first packing 11 and the liquid surface of the concentrated liquid in the distillation column 10. This allows the low-boiling solvent vapor to rise through the first packing 11 and come into contact with the newly supplied mixed liquid, facilitating the evaporation of the low-boiling solvent from the mixed liquid. A multi-tube downflow heat exchanger is preferably used as the second heat exchanger 42, as it does not apply pressure to the concentrated liquid and therefore can efficiently evaporate the low-boiling solvent. Steam or the like can be used as a heat medium to heat the concentrated liquid.

[0023] The control device 50 adjusts the amount of heat supplied to the second heat exchanger 42, i.e., the amount of heat medium supplied, so as to maintain a constant temperature of the concentrated liquid inside the distillation column 10 detected by the temperature sensor 13. The control device 50 may be configured, for example, by a PID controller, a programmable controller, or the like. In order to prevent scaling of the second heat exchanger 42, the amount of heat per heat transfer area of the heat medium supplied to the second heat exchanger per hour is set to an upper limit (for example, 60 MJ / m) that is set so as to prevent boiling of the low-boiling point solvent inside the second heat exchanger 42. 2 / h). The amount of heat supplied to the first heat exchanger 32 can be set to a constant value that is preset so that the amount of heat supplied to the second heat exchanger 42 can be kept below the upper limit. In this way, by providing a constant amount of heat to the concentrated liquid using the first heat exchanger 32, which does not evaporate the low-boiling-point solvent, and by maintaining a constant temperature of the concentrated liquid inside the distillation column 10 using the second heat exchanger 42, which evaporates the low-boiling-point solvent, it is possible to prevent a decrease in performance of the second heat exchanger 42 due to salt scaling. Therefore, the distillation apparatus 1 has a large distillation capacity, and even when a large amount of low-boiling-point solvent is separated, the separation capacity is not easily reduced, enabling stable distillation, thereby enabling efficient separation of the low-boiling-point solvent from the mixed liquid.

[0024] As is clear from the above description, one embodiment of the distillation method of the present invention that can be implemented in distillation apparatus 1 is a distillation method for separating a low-boiling solvent from a mixture containing a low-boiling solvent, a high-boiling solvent, and a salt. The distillation method includes the steps of: evaporating the low-boiling solvent and supplying the mixture to distillation column 10, which stores a concentrated liquid with an increased concentration of the high-boiling solvent at the bottom; condensing the low-boiling solvent vapor by flowing the low-boiling solvent vapor from the top of distillation column 10; withdrawing the concentrated liquid from distillation column 10, heating it in first heat exchanger 32, which does not evaporate the low-boiling solvent, and then refluxing it to distillation column 10; and withdrawing the concentrated liquid from distillation column 10, heating it in second heat exchanger 42, which evaporates the low-boiling solvent, and refluxing the concentrated liquid and low-boiling solvent vapor back to distillation column 10. These steps are performed in parallel during steady-state operation.

[0025] The above-described distillation apparatus 1 and distillation method use a first heat exchanger 32 that can be made relatively small because it is configured not to evaporate low-boiling-point solvents, and a second heat exchanger 42 that can be made relatively large because it evaporates low-boiling-point solvents, in combination, thereby reducing equipment costs and installation space while increasing the separation capacity of low-boiling-point solvents from the mixed liquid.

[0026] Although the present invention has been described above with reference to an embodiment, it is not limited to the above embodiment and various modifications and variations are possible. For example, the temperature sensor may be provided upstream of the second reheat line. Furthermore, the flow paths for discharging the low-boiling solvent and concentrated liquid from the distillation apparatus may be configured to allow them to flow by gravity without passing through the first and second withdrawal pumps. [Explanation of symbols]

[0027] 1. Distillation apparatus 10 Distillation tower 11 First filler 12 Second filler 13 Temperature Sensor 20 Condensation Line 21 Condenser 22 Receiving Tank 23 Condensate Pump 30 First Reheat Line 31 First withdrawal pump 32 1st heat exchanger 40 Second Reheat Line 41 Second withdrawal pump 42 Second heat exchanger 50 Control device

Claims

1. A distillation apparatus for separating a low boiling point solvent from a mixed liquid containing a low boiling point solvent, a high boiling point solvent, and a salt, comprising: a distillation column that evaporates the low-boiling point solvent from the mixed liquid and stores a concentrated liquid having an increased concentration of the high-boiling point solvent in a lower portion thereof; a condensation line through which the vapor of the low boiling point solvent flows from the top of the distillation column and which has a condenser for condensing the vapor of the low boiling point solvent; a first reheat line including a first withdrawal pump that withdraws the concentrated liquid from the distillation column and a first heat exchanger that heats the concentrated liquid withdrawn by the first withdrawal pump without evaporating the low-boiling point solvent, and which refluxes the concentrated liquid heated by the first heat exchanger to the distillation column; a second reheat line including a second withdrawal pump that withdraws the concentrated liquid from the distillation column and a second heat exchanger that heats the concentrated liquid withdrawn by the second withdrawal pump to evaporate the low-boiling point solvent, and which refluxes the concentrated liquid concentrated in the second heat exchanger and the vapor of the low-boiling point solvent back to the distillation column; A distillation apparatus comprising:

2. The distillation apparatus according to claim 1, further comprising a control device that adjusts the amount of heat supplied to the second heat exchanger so as to maintain a constant temperature of the concentrated liquid inside the distillation column.

3. 3. The distillation apparatus according to claim 1, wherein the first heat exchanger is a welded plate heat exchanger.

4. 3. The distillation apparatus according to claim 1, wherein the second heat exchanger is a multi-tube downflow heat exchanger.

5. A distillation method for separating a low boiling point solvent from a mixture containing a low boiling point solvent, a high boiling point solvent, and a salt, comprising: a step of evaporating the low-boiling point solvent from the mixed liquid and supplying the mixed liquid to a distillation column in which a concentrated liquid having an increased concentration of the high-boiling point solvent is stored at the bottom; allowing the vapor of the low boiling point solvent to flow out from an upper portion of the distillation column and condensing the vapor of the low boiling point solvent; withdrawing the concentrated liquid from the distillation column, heating the concentrated liquid in a first heat exchanger that does not evaporate the low-boiling point solvent, and then refluxing the concentrated liquid to the distillation column; withdrawing the concentrated liquid from the distillation column, heating the concentrated liquid in a second heat exchanger that evaporates the low-boiling point solvent, and refluxing the concentrated liquid concentrated by evaporation of the low-boiling point solvent and the vapor of the low-boiling point solvent back into the distillation column; A distillation method comprising:

6. the low boiling point solvent is water, 6. The distillation method according to claim 5, wherein the high-boiling point solvent is at least one selected from the group consisting of dimethyl sulfoxide, dimethylformamide, and dimethylacetamide.

7. 7. The distillation method according to claim 5, wherein the salt is at least one selected from the group consisting of sodium chloride, sodium sulfate, and sodium hydroxide.

8. The amount of heat per heat transfer area of the heat medium supplied to the second heat exchanger per hour is 60 MJ / m ２ The distillation method according to claim 5 or 6, wherein the distillation rate is 1000 kJ / h or less.

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