WO2013105342A1 - Evaporator, evaporation system, and evaporation method - Google Patents

Abstract

The present invention relates to an evaporator that includes: a plurality of heating tubes; an upper tube plate that supports the plurality of heating tubes with spaces therebetween; and a first dispersion plate provided above the upper tube plate. On the first dispersion plate are provided two or more liquid through holes constituted such that a starting material liquid passes through and two or more gas through holes constituted such that a gas passes through. Viewed from the direction that the plurality of heating tubes extend, the plurality of liquid through holes is formed in positions that overlap regions in the upper tube plate in which the heating tubes are not provided and the plurality of gas through holes is formed in positions that overlap regions in which the plurality of heating tubes is provided. The plurality of heating tubes has protruding parts that protrude from the upper surface of the upper tube plate. According to the present invention, an evaporator in which blockage in the heat tubes can be suppressed and evaporation of a starting material liquid can be carried out smoothly is provided.

Description

Evaporation apparatus, evaporation system, and evaporation method

The present invention relates to an evaporation apparatus, an evaporation system, and an evaporation method.
This application claims priority based on Japanese Patent Application No. 2012-004130 filed in Japan on January 12, 2012, the contents of which are incorporated herein by reference.

An evaporation apparatus described in Patent Document 1 is known as an evaporation apparatus that evaporates a raw material liquid. The evaporation apparatus of Patent Document 1 is a vertical down-flowing liquid film heat exchanger having a plurality of heat transfer tubes. In this evaporator, the raw material liquid is flown into the plurality of heat transfer tubes, and the film of the raw material liquid is formed on the inner wall surfaces of the plurality of heat transfer tubes. The raw material liquid is configured to evaporate.

Japanese Patent Laid-Open No. 2002-284752

In the evaporation apparatus of Patent Document 1, in order to suppress the residue of the raw material liquid remaining on the inner wall surfaces of the plurality of heat transfer tubes, the raw material liquid film is formed on the inner wall surfaces of the plurality of heat transfer tubes. The liquid is evaporating. In the process, the raw material liquid is supplied to the plurality of heat transfer tubes together with the solvent, but some gas is used as a medium. The raw material liquid and the gas are supplied in parallel to the liquid film heat exchanger under the vertical flow. In this case, the thickness of the film of the raw material liquid on the inner wall surfaces of the plurality of heat transfer tubes varies depending on the arrangement of the raw material liquid and the gas supply unit. When the thickness of the raw material liquid film is reduced, the inner wall surface of the heat transfer tube may be exposed due to evaporation of the raw material liquid. When the inner wall surface is exposed, the residue of the raw material liquid remains on the exposed inner wall surface, which may cause clogging of the heat transfer tube.

The present invention has been made in view of such circumstances, and by forming a good falling liquid film, it is possible to suppress clogging of the heat transfer tube and to smoothly evaporate the raw material liquid. An object is to provide an apparatus, an evaporation system, and an evaporation method.

In order to achieve the above object, an aspect of the evaporation apparatus of the present invention is provided above a plurality of heat transfer tubes, a tube plate that supports the plurality of heat transfer tubes with a space therebetween, and the tube plate. A first dispersion plate, and the first dispersion plate has a plurality of liquid passage holes through which the raw material liquid passes when viewed from the extending direction of the plurality of heat transfer tubes. And a plurality of vent holes through which gas passes are formed at positions overlapping the plurality of heat transfer tubes, and the plurality of heat transfer tubes are formed on the upper surface of the tube plate. It has the protrusion part which protrudes from.

In one aspect of the present invention, a portion of the surface of the first dispersion plate on the tube plate side where the liquid passage hole is formed is provided with a nozzle protruding from the surface to the tube plate side. Features.

In one embodiment of the present invention, an inflow portion for allowing the raw material liquid and the gas to flow toward the first dispersion plate is provided.

In one aspect of the present invention, one or more dispersion plates are provided between the first dispersion plate and the inflow portion, and a plurality of the raw material liquids from the inflow portion are passed through the dispersion plate. Are formed, and at least a plurality of the liquid passage holes of the dispersion plate disposed immediately above the first dispersion plate are seen from the extending direction of the plurality of heat transfer tubes. The dispersion plate is arranged at a position not overlapping with the plurality of vent holes.
The one or more dispersion plates are preferably four or less.

In one aspect of the present invention, a housing portion is provided for housing the tube plate and the first dispersion plate, and a second dispersion plate is provided between the inflow portion and the first dispersion plate. A plurality of liquid passage holes through which the raw material liquid from the inflow portion flows into the liquid passage holes formed in the first dispersion plate; and the inflow port. A plurality of ventilation pipes through which gas from a portion passes, a gap is formed between an outer peripheral portion of the second dispersion plate and an inner wall surface of the storage portion, and the second The plurality of vent pipes of the dispersion plate are arranged concentrically when viewed from the extending direction of the plurality of heat transfer tubes, and the plurality of vent pipes of the second dispersion plate are on the inflow portion side. The second dispersion plate has a notch on the center side.

In one aspect of the present invention, the apparatus has a transfer mechanism for transferring the raw material liquid flowing out from the plurality of heat transfer tubes to the inflow portion.

In one aspect of the present invention, a groove is formed at the tip of the protruding portion.

In one aspect of the present invention, the area of the heat transfer tube is larger than the area of the air holes of the first dispersion plate when viewed from the extending direction of the heat transfer tube.

In one aspect of the present invention, the center of the heat transfer tube coincides with the center of the vent hole of the first dispersion plate when viewed from the extending direction of the heat transfer tube.

In one embodiment of the present invention, the raw material liquid contains cyclohexanone oxime.

One aspect of the evaporation system of the present invention includes an evaporation device, a pump for circulating a part of the residue of the source gas generated by the evaporation device to the evaporation device, and a vacuum distillation for distilling the remaining part of the residue And a condenser for condensing the raw material distilled off by the vacuum distillation apparatus.

One aspect of the evaporation method of the present invention is that the evaporation apparatus is used to heat and evaporate the raw material liquid, and the residue after obtaining the raw material gas is distilled under a pressure lower than the pressure at the time of heat evaporation. The raw material gas contained in the residue is recovered by condensing the raw material gas distilled off by distillation.
One aspect of the evaporation method of the present invention is an evaporation method for evaporating a mixed solution of cyclohexanone oxime and a solvent for diluting the cyclohexanone oxime, wherein the solvent is alcohol, and the entire evaporation surface in the evaporator is at least cyclohexanone oxime. The amount of cyclohexanone oxime flowing down at the lower end of the evaporation surface in the evaporator is 170 kg per unit length (m) of the lower end of the evaporation surface so that the mixture becomes wet at 1060 torr. The evaporation is performed at a reduced pressure of 1.4 kPa to 10 kPa.

That is, the present invention relates to the following.
(1) a plurality of heat transfer tubes;
A tube plate configured to support the plurality of heat transfer tubes spaced apart from each other;
A first dispersion plate provided above the tube plate,
The first dispersion plate is provided with two or more liquid passage holes configured to pass the raw material liquid and two or more vent holes configured to pass the gas, and the plurality of heat transfer tubes As viewed from the extending direction, the plurality of liquid passage holes are formed at positions where the heat transfer tubes of the tube plate are not provided, and the plurality of vent holes are provided with the plurality of heat transfer tubes. It is formed at a position that overlaps the area that is
The plurality of heat transfer tubes have a protruding portion configured to protrude from an upper surface of the tube plate.
(2) The first dispersion plate is provided with a nozzle on the tube plate side surface of the first dispersion plate,
The nozzle protrudes in the tube plate side direction from the tube plate side surface of the first dispersion plate,
The evaporation apparatus according to (1), wherein the nozzle is provided in a portion of the surface on the tube plate side of the first dispersion plate where the liquid passage hole is formed.
(3) The evaporation apparatus according to (1) or (2), further including an inflow portion configured to allow the raw material liquid and the gas to flow toward the first dispersion plate.
(4) One or more dispersion plates are provided between the first dispersion plate and the inflow portion,
The one or more dispersion plates are provided with a plurality of liquid passage holes configured to pass the raw material liquid from the inflow portion,
Among the one or more dispersion plates, at least a plurality of liquid passage holes of the dispersion plate disposed immediately above the first dispersion plate are the first dispersion as viewed from the extending direction of the plurality of heat transfer tubes. The evaporator according to (3), wherein the evaporator is disposed at a position overlapping a region where a plurality of ventilation holes of the plate are not provided.
(5) Furthermore, it has an accommodating part configured to accommodate the tube sheet and the first dispersion plate,
Between the inflow portion and the first dispersion plate, a second dispersion plate is provided,
The second dispersion plate has a plurality of liquid passage holes configured to allow the raw material liquid from the inflow portion to flow toward the liquid passage holes formed in the first dispersion plate, and the inflow A plurality of vent pipes configured to pass gas from the section, and
A gap is formed between the outer peripheral portion of the second dispersion plate and the inner wall surface of the housing portion,
The plurality of ventilation pipes of the second dispersion plate are arranged concentrically as viewed from the extending direction of the plurality of heat transfer pipes,
The plurality of vent pipes of the second dispersion plate have notches on the inflow portion side and on the central portion side of the second dispersion plate (3) or ( The evaporation apparatus as described in 4).
(6) In addition, any one of (3) to (5), further comprising a transfer mechanism configured to transfer the raw material liquid flowing out from the plurality of heat transfer tubes to the inflow portion. The evaporation apparatus according to one.
(7) The evaporation apparatus according to any one of (1) to (6), wherein a groove is formed at a tip of the protrusion.
(8) Of the two or more heat transfer tubes, the area of the heat transfer tube is larger than the area of the vent hole of the first dispersion plate provided immediately above the extension direction of the heat transfer tube. The evaporator according to any one of (1) to (7), wherein
(9) The center of the heat transfer tube is coincident with the center of the vent hole of the first dispersion plate provided immediately above, as viewed from the extending direction of the heat transfer tube ( The evaporation apparatus according to any one of 1) to (8).
(10) The evaporation apparatus according to any one of (1) to (9), wherein the raw material liquid contains cyclohexanone oxime.
(11) The evaporation apparatus according to any one of (1) to (10);
A pump configured to circulate a part of the residue of the source gas generated by the evaporator to the evaporator;
A vacuum still configured to distill the remainder of the residue;
A condenser configured to condense the raw material distilled off by the vacuum distillation apparatus;
An evaporation system characterized by comprising:
(12) When the evaporation apparatus according to any one of (1) to (10) is used to heat-evaporate the raw material liquid and obtain a raw material gas, the residue remaining after the heat-evaporation is performed. An evaporation method, wherein a raw material liquid contained in the residue is recovered by condensing a raw material gas distilled by distillation under a pressure lower than a pressure.
(13) The raw material liquid is a mixed liquid of cyclohexanone oxime and a solvent for diluting the same, and the solvent is alcohol, so that the entire evaporation surface in the evaporator is at least wet with cyclohexanone oxime. In addition, the mixed liquid is evaporated at a pressure of 1060 torr or less, and the amount of cyclohexanone oxime flowing down at the lower end of the evaporation surface in the evaporator is evaporated at 170 kg / hour or more per meter which is the unit length of the lower end of the evaporation surface, The evaporation method according to (12), wherein the distillation is performed under a reduced pressure of 1.4 kPa to 10 kPa.

According to one aspect of the present invention, when the raw material liquid and the gas are evaporated in a vertically flowing liquid film heat exchanger, the clogging of the heat transfer tube is suppressed by forming a favorable falling liquid film. It is possible to provide an evaporation apparatus, an evaporation system, and an evaporation method that can smoothly evaporate the raw material liquid.

It is a schematic diagram which shows the evaporation apparatus which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the arrangement | positioning state of the several ventilation hole in the 1st dispersion | distribution board of the evaporator which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the evaporation apparatus which concerns on 2nd Embodiment of this invention. It is a schematic diagram which shows the arrangement | positioning state of the several ventilation pipe | tube in the 2nd dispersion | distribution board of the evaporation apparatus which concerns on 2nd Embodiment of this invention. It is a schematic diagram which shows the arrangement | positioning state of two or more vent pipes in the 2nd dispersion | distribution board of the evaporation apparatus which concerns on 2nd Embodiment of this invention. It is a schematic diagram which shows the modification of the protrusion part of a heat exchanger tube. It is a schematic diagram which shows the modification of the protrusion part of a heat exchanger tube. It is a schematic diagram which shows the modification of the protrusion part of a heat exchanger tube. It is a schematic diagram which shows an example of an evaporation system.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.
In all the following drawings, the dimensions and ratios of the respective constituent elements are appropriately changed in order to make the drawings easy to see. In the following description and drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant description is omitted.

(First embodiment)
FIG. 1 is a longitudinal sectional view showing an evaporator 1 according to a first embodiment of the present invention.
As shown in FIG. 1, the evaporator 1 includes a plurality of heat transfer tubes 2, an upper tube plate 3, a lower tube plate 4, a first dispersion plate 5, a dispersion plate 6, a storage unit 7, a tower A bottom 8, a raw material liquid supply pipe (inflow part) 9, a gas supply pipe (inflow part) 10, and a heat medium supply pipe 11 are configured.

In the evaporation apparatus 1, the gas from the gas supply pipe 10 passes through the plurality of vent holes 52 and enters the plurality of heat transfer tubes 2 in a state where the film of the raw material liquid is formed on the inner wall surfaces of the plurality of heat transfer tubes 2. The plurality of heat transfer tubes are heated by a heat medium to evaporate the raw material liquid.

A disc-shaped upper tube plate 3 and a lower tube plate 4 are connected to the lower portion of the accommodating portion 7. A plurality of heat transfer tubes 2 are supported on the upper tube plate 3 and the lower tube plate 4 at intervals. The plurality of heat transfer tubes 2 have projecting portions 2 a that project from the upper surface of the upper tube sheet 3. The first dispersion plate 5 is provided above the upper tube plate 3 inside the housing portion 7.

FIG. 2 is a schematic diagram showing an arrangement state of the plurality of vent holes 52 in the first dispersion plate 5 of the evaporation apparatus 1. FIG. 2 is a plan view of the first dispersion plate 5. For convenience, the accommodating portion 7 is indicated by a broken line.
As shown in FIG. 2, the accommodating portion 7 is circular in plan view. The first dispersion plate 5 is formed with a plurality of liquid passage holes 51 through which the raw material liquid passes and a plurality of vent holes 52 through which gas passes. The shape of the liquid passage hole 51 is circular in plan view. The shape of the vent hole 52 is circular in plan view. In the plan view, the first dispersion plate 5 has the air holes 52 alternately arranged so that one air hole 52 is positioned between the two liquid holes 51. The arrangement state of the plurality of vent holes 52 shown in the present embodiment is an example, and the present invention is not limited to this, and various arrangement states can be adopted.

Referring back to FIG. 1, the plurality of liquid passage holes 51 are arranged at positions overlapping the region where the heat transfer tubes 2 of the upper tube plate 3 are not provided when viewed from the extending direction of the plurality of heat transfer tubes 2. Each liquid passage hole 51 is located above the upper tube sheet 3 in the approximate center between two adjacent heat transfer tubes 2. It is sufficient that the liquid does not directly enter the heat transfer tube 2 from each liquid flow hole 51, and each liquid flow hole 51 may be biased at the center between the two adjacent heat transfer tubes 2.

The first dispersion plate 5 is provided with a nozzle 51a on the surface of the upper tube plate 3 side. The nozzle 51 a protrudes from the surface of the first dispersion plate 5 in the direction of the upper tube sheet 3. The nozzle 51 a is provided in a portion where the liquid passage hole 51 is formed on the surface of the first dispersion plate 5 on the upper tube plate 3 side.

The plurality of vent holes 52 are arranged at positions overlapping with regions where the plurality of heat transfer tubes 2 are provided when viewed from the extending direction of the plurality of heat transfer tubes 2. The distance between the lower ends of the plurality of vent holes 52 and the upper ends of the plurality of heat transfer tubes 2 (interval in the extending direction of the heat transfer tubes 2) is, for example, 1/50 to 1 / The size is in the range of 5. Preferably, the distance between the lower ends of the plurality of vent holes 52 and the upper ends of the plurality of heat transfer tubes 2 is set to a size in the range of 1/30 to 1/10 with respect to the inner diameter of the housing portion 7.

The shape of the heat transfer tube 2 is circular as seen from the extending direction of the plurality of heat transfer tubes 2, similarly to the shape of the vent hole 52. The inner diameter of the heat transfer tube 2 is, for example, in the range of 20 mm to 100 mm. Preferably, the inner diameter of the heat transfer tube 2 is in the range of 35 mm to 70 mm.

The shape of the air holes 52 and the heat transfer tubes 2 when viewed from the extending direction of the plurality of heat transfer tubes 2 is not limited to a circle, and various shapes such as an ellipse can be adopted. However, in order to allow the gas to pass smoothly, the shape of the vent hole 52 and the heat transfer tube 2 when viewed from the extending direction of the plurality of heat transfer tubes 2 is preferably circular.

The center of the vent hole 52 coincides with the center of the heat transfer tube 2 provided immediately above, as viewed from the extending direction of the heat transfer tube 2.
The center of the vent hole 52 provided immediately above may be slightly deviated from the center of the heat transfer tube 2 when viewed from the extending direction of the heat transfer tube 2. In other words, each of the plurality of vent holes 52 only needs to be disposed at a position overlapping with a region where each of the plurality of heat transfer tubes 2 is provided when viewed from the extending direction of the plurality of heat transfer tubes 2.

The area of the heat transfer tube 2 is larger than the area of the vent hole 52 provided immediately above the heat transfer tube 2 when viewed from the extending direction. The area when the plurality of heat transfer tubes 2 are viewed from the extending direction of the plurality of heat transfer tubes 2 is not limited to the area larger than the area of the vent hole 52 provided immediately above the heat transfer tubes 2, It may be the same area as the area of the vent hole 52 provided in the. That is, the area when the plurality of heat transfer tubes 2 are viewed from the extending direction of the plurality of heat transfer tubes 2 may be an area equal to or larger than the area of the vent hole 52 provided immediately above the heat transfer tubes 2.
Further, the area when the two or more heat transfer tubes 2 are viewed from the extending direction of the two or more heat transfer tubes 2 is less than twice the area of the vent hole 52 provided immediately above the area. preferable.

The raw material liquid supply pipe 9 is connected to the upper side wall of the housing part 7. The gas supply pipe 10 is connected to the upper wall of the housing part 7. The dispersion plate 6 is provided between the raw material liquid supply pipe 9 and the gas supply pipe 10 and the first dispersion plate 5.

The dispersion plate 6 is formed with a plurality of liquid separation holes 61 for separating the raw material liquid from the raw material liquid supply pipe 9. In FIG. 1, the plurality of liquid separation holes 61 are arranged at positions overlapping the plurality of liquid passage holes 51 when viewed from the extending direction of the plurality of heat transfer tubes 2, but are not limited thereto. The plurality of liquid separation holes 61 may be disposed at positions that do not overlap with the plurality of vent holes 52 when viewed from the extending direction of the plurality of heat transfer tubes 2.

A nozzle 61 a that protrudes from the surface to the first dispersion plate 5 side is provided in a portion where the liquid separation holes 61 are formed on the surface of the dispersion plate 6 on the first dispersion plate 5 side.

Although there is a gap 62 between the outer peripheral portion of the dispersion plate 6 and the inner wall surface of the accommodating portion 7, the present invention is not limited to this. The evaporator 1 only needs to be configured so that the gas from the gas supply pipe 10 flows below the dispersion plate 6 and flows into the plurality of heat transfer tubes 2.

In this embodiment, a mixed liquid of cyclohexanone oxime and a solvent for diluting the cyclohexanone oxime is used as a raw material liquid. The mixed liquid is supplied to the evaporator 1 through the raw material liquid supply pipe 9.

As the solvent, a solvent having a boiling point lower than that of cyclohexanone oxime and capable of dissolving and diluting cyclohexanone oxime can be used. Examples thereof include saturated alcohols having 1 to 8 carbon atoms selected from methanol, ethanol, propanol, tertiary butanol, 1-hexanol, 1-octanol, and the like. Among these, methanol or ethanol is preferable. The mixing ratio of cyclohexanone oxime and the solvent is preferably about 100: 1 to 1:10 by weight.

Further, when the mixed liquid is transferred to the evaporator 1 through the raw material liquid supply pipe 9, simultaneously, a lower alcohol such as methanol and an inert gas such as nitrogen gas are introduced into the evaporator 1 from the gas supply pipe 10. It is preferable.

Also, nitrogen gas is used as an inert gas. The inert gas is not limited to nitrogen gas, and various inert gases can be used.

The heat medium supply pipe 11 is connected to the lower side wall of the housing portion 7. The heat medium supply pipe 11 allows the heat medium to flow toward the outer wall surface of the heat transfer tube 2. For example, steam or the like is used as the heat medium.

In the evaporation apparatus 1 of the present embodiment, the raw material liquid from the raw material liquid supply pipe 9 flows into the heat transfer tube 2, and a film of the raw material liquid is formed on the inner wall surfaces of the plurality of heat transfer tubes 2. In this state, the outer wall surfaces of the plurality of heat transfer tubes 2 are heated by the heat medium from the heat medium supply pipe 11 to evaporate the raw material liquid.
Hereinafter, the manner in which the raw material liquid and the gas flow in the storage unit 7 in the evaporation apparatus 1 will be described with reference to FIG.

As shown in FIG. 1, the raw material liquid from the raw material liquid supply pipe 9 passes through the liquid separation holes 61 of the dispersion plate 6 and flows into the liquid passage holes 51 formed in the first dispersion plate 5. The The raw material liquid that has flowed toward the liquid flow hole 51 flows into a region of the upper tube plate 3 where the heat transfer tube 2 is not provided. The raw material liquid that has flowed into the region overflows and flows into the plurality of heat transfer tubes 2. Thereby, it will be in the state (what is called a wet wall state) in which the film | membrane of the raw material liquid was formed in the inner wall surface of the some heat exchanger tube 2. FIG.

On the other hand, the heat medium from the heat medium supply pipe 11 flows into the outer wall surfaces of the plurality of heat transfer tubes 2.
Thereby, a some heat exchanger tube is heated.

The gas from the gas supply pipe 10 passes through a gap 62 between the outer peripheral portion of the dispersion plate 6 and the inner wall surface of the accommodating portion 7 and is directed to a plurality of vent holes 52 formed in the first dispersion plate 5. Inflow. The gas that has flowed toward the vent hole 52 flows into the heat transfer tube in a state where a film of the raw material liquid is formed on the inner wall surfaces of the plurality of heat transfer tubes 2.

¡The amount of liquid flowing down at the lower ends of the heat transfer tubes 2 shall be more than the minimum allowable load. Here, the minimum allowable load or more is caused to flow down from the lower ends of the plurality of heat transfer tubes 2 an amount of non-evaporated material solution that is more than the amount that a film of the raw material solution is always formed on all inner wall surfaces of the plurality of heat transfer tubes 2. Means that. That is, even when the raw material liquid flowing on the inner wall surface of the plurality of heat transfer tubes 2 is evaporated by managing the amount of flowing down liquid at the lower end of the plurality of heat transfer tubes 2 to be more than the minimum allowable load, The state in which the film of the raw material liquid is formed is maintained.

For example, when cyclohexanone oxime is supplied as a raw material liquid, in order to maintain a state in which a liquid film is formed on the inner wall surface of the heat transfer tube 2, the flow rate of the raw material liquid at the lower end of the inner wall surface of the heat transfer tube 2 is The unit wall length at the lower end of the inner wall surface is 170 kg / hour or more, preferably 170 to 1700 kg / hour, more preferably 340 to 680 kg / hour.

In addition, when cyclohexanone oxime is supplied as a raw material liquid, the pressure at which the mixed liquid is evaporated is preferably 1060 torr or less. When the pressure is higher than 1060 torr, the cyclohexanone oxime may be deteriorated. Preferably, the mixed solution is evaporated in the range of 760 torr (atmospheric pressure) to 1000 torr.

In addition, when cyclohexanone oxime is supplied as a raw material liquid, the temperature at which the mixed liquid is evaporated is preferably in the range of 130 ° C. or higher and 170 ° C. or lower. The evaporated gas obtained by the evaporator 1 is taken out to the tower bottom 8 through the heat transfer tube 2.

According to the evaporator 1 of the present embodiment, the first dispersion plate 5 is provided with the plurality of liquid passage holes 51 and the heat transfer tubes 2 of the upper tube plate 3 when viewed from the extending direction of the plurality of heat transfer tubes 2. A plurality of vent holes 52 are formed at positions overlapping with the plurality of heat transfer tubes 2, while being formed at positions overlapping with the regions not formed. As a result, the raw material liquid from the raw material liquid supply pipe 9 passes through the liquid passage hole 51 and flows into the region where the heat transfer tubes 2 of the upper tube plate 3 are not provided, and flows into the plurality of heat transfer tubes 2. The With the raw material liquid film formed on the inner wall surfaces of the plurality of heat transfer tubes 2, the gas from the gas supply pipe 10 passes through the plurality of vent holes 52 and flows into the plurality of heat transfer tubes 2. Further, the raw material liquid from the raw material liquid supply pipe 9 is prevented from flowing directly into the plurality of heat transfer tubes 2. Furthermore, in order to restrict | limit the flow direction of the gas from the gas supply piping 10, gas flows smoothly into the inside of the some heat exchanger tube 2. FIG. Therefore, the film thickness of the raw material liquid formed on the inner wall surfaces of the plurality of heat transfer tubes 2 can be made uniform.
The thickness of the film of the raw material liquid formed on the inner wall surfaces of the plurality of heat transfer tubes varies depending on the arrangement of the gas and raw material liquid supply units. When the thickness of the raw material liquid film is reduced, the inner wall surface of the heat transfer tube may be exposed due to evaporation of the raw material liquid. When the inner wall surface is exposed, the residue of the raw material liquid remains on the exposed inner wall surface, which may cause clogging of the heat transfer tube.
On the other hand, in the present embodiment, when viewed from the extending direction of the plurality of heat transfer tubes 2, the plurality of liquid passage holes 51 are arranged at positions that overlap with the region of the upper tube plate 3 where the heat transfer tubes 2 are not provided. In addition, since the plurality of vent holes 52 are arranged at positions overlapping the plurality of heat transfer tubes 2, the thickness of the raw material liquid film formed on the inner wall surface of the plurality of heat transfer tubes 2 changes. It is suppressed. Further, an unevaporated raw material liquid in an amount equal to or more than the amount that a film of the raw material liquid is always formed on all inner wall surfaces of the plurality of heat transfer tubes 2 is caused to flow down from the lower ends of the plurality of heat transfer tubes 2. Thereby, even if the raw material liquid flowing on the inner wall surface of the heat transfer tube 2 is evaporated, the inner wall surface is not exposed and the raw material liquid residue does not remain. Therefore, clogging of the heat transfer tube can be suppressed, and the raw material liquid can be smoothly evaporated.

Further, a nozzle 51a is provided in a portion where the liquid passage hole 51 is formed on the surface of the first dispersion plate 5 on the upper tube plate 3 side. For this reason, compared with the case where the nozzle 51a is not provided, the raw material liquid which passed the liquid flow hole 51 becomes easy to flow into the area | region where the heat exchanger tube 2 of the upper tube plate 3 is not provided. Thereby, it is suppressed that the raw material liquid which passed the liquid flow hole 51 flows along the surface at the side of the upper tube sheet 3 of the 1st dispersion plate 5, and dripping. Therefore, the raw material liquid is prevented from flowing directly into the plurality of heat transfer tubes 2. Therefore, it is possible to maintain a state in which a uniform film of the raw material liquid is formed on the inner wall surfaces of the plurality of heat transfer tubes 2.

Further, a nozzle 61a is provided at a portion where the liquid separation hole 61 is formed on the surface of the dispersion plate 6 on the first dispersion plate 5 side. For this reason, compared with the case where the nozzle 61 a is not provided, the raw material liquid that has passed through the liquid separation hole 61 is likely to flow toward the liquid passage hole 51 formed in the first dispersion plate 5. Thereby, it is suppressed that the raw material liquid which passed the liquid separation hole 61 flows along the surface at the side of the 1st dispersion plate 5 of the dispersion plate 6, and dripping. Therefore, the raw material liquid is prevented from flowing directly into the plurality of heat transfer tubes 2. Therefore, it is possible to maintain a state in which a uniform film of the raw material liquid is formed on the inner wall surfaces of the plurality of heat transfer tubes 2.

Further, the gas from the gas supply pipe 10 passes through the gaps 62, passes through the plurality of vent holes 52, and flows into the plurality of heat transfer tubes. Thereby, since the flow direction of the gas from the gas supply pipe 10 is restricted, the gas flows smoothly into the plurality of heat transfer tubes 2. Therefore, it is possible to maintain a state in which a uniform film of the raw material liquid is formed on the inner wall surfaces of the plurality of heat transfer tubes 2 in the process in which the gas flows inside the plurality of heat transfer tubes 2. Therefore, clogging of the heat transfer tube can be suppressed, and the raw material liquid can be smoothly evaporated.

Further, the area of the heat transfer tube 2 is larger than the area of the vent hole 52 as viewed from the extending direction of the heat transfer tube 2. Therefore, the gas that has passed through the vent hole 52 easily flows into the heat transfer tube 2. If the area of the heat transfer tube 2 is smaller than the area of the vent hole 52 when viewed from the extending direction of the heat transfer pipe 2, the gas that has passed through the vent hole 52 flows into the outside of the heat transfer pipe 2, The flow of the raw material liquid on the tube plate 3 may be disturbed. When the flow of the raw material liquid on the upper tube plate 3 is disturbed, the thickness of the raw material liquid film formed on the inner wall surface of the heat transfer tube 2 changes.
On the other hand, in this embodiment, since the area of the heat transfer tube 2 is larger than the area of the vent hole 52 when viewed from the extending direction of the heat transfer tube 2, the gas that has passed through the vent hole 52 passes through the heat transfer pipe 2. Inflow to the outside of the is suppressed. Thereby, it is suppressed that the flow of the raw material liquid on the upper tube sheet 3 is disturbed. Therefore, it can suppress that the thickness of the film | membrane of the raw material liquid formed in the inner wall face of the heat exchanger tube 2 changes.

Further, the center of the heat transfer tube 2 coincides with the center of the vent hole 52 when viewed from the extending direction of the heat transfer tube 2. As a result, the gas that has passed through the vent hole 52 easily flows into the heat transfer tube 2. That is, the gas that has passed through the vent hole 52 is prevented from flowing into the outside of the heat transfer tube 2. Thereby, it is suppressed that the flow of the raw material liquid on the upper tube sheet 3 is disturbed. Therefore, it can suppress that the thickness of the film | membrane of the raw material liquid formed in the inner wall face of the heat exchanger tube 2 changes.

In the evaporation apparatus of the present embodiment, cyclohexanone oxime is used as the raw material liquid, but this is not a limitation. In addition to this, various raw material liquids in which a residue of the raw material liquid may remain during evaporation can be used.

Further, in the evaporation apparatus of the present embodiment, only one dispersion plate 6 is provided on the first dispersion plate 5, but this is not limitative. For example, one or two or more dispersion plates 6 may be provided on the first dispersion plate 5. Moreover, the nozzle 61a may be provided in the dispersion plate 6, and the nozzle 61a does not need to be provided.

(Second Embodiment)
FIG. 3 is a longitudinal sectional view showing an evaporation apparatus 1A according to the second embodiment of the present invention, corresponding to FIG. As shown in FIG. 3, the evaporation apparatus 1 </ b> A according to the present embodiment is provided with a second dispersion plate 12 instead of the dispersion plate 6, and the second raw material liquid flowing out from the plurality of heat transfer tubes 2 is used. It differs from the evaporation apparatus 1 which concerns on the above-mentioned 1st Embodiment by the point which has the transfer mechanism 13 made to transfer above the dispersion plate 12. FIG. Since the other points are the same as the above-described configuration, the same elements as those in FIG.

As shown in FIG. 3, in the evaporation apparatus 1 </ b> A, a second dispersion plate 12 is provided between the raw material liquid supply pipe 9 and the gas supply pipe 10 and the first dispersion plate 5. The second dispersion plate 12 has a plurality of liquid passage holes 121 through which the raw material liquid from the raw material liquid supply pipe 9 flows toward the liquid passage holes 51 formed in the first dispersion plate 5, and the gas supply pipe 10. A plurality of vent pipes 122 through which gas from The plurality of liquid passage holes 121 are arranged at positions that do not overlap with the plurality of vent holes 52 when viewed from the extending direction of the plurality of heat transfer tubes 2.

FIG. 4A and FIG. 4B are schematic views showing an arrangement state of a plurality of vent pipes 122 in the second dispersion plate 12 of the evaporator 1A. 4A is a plan view of the second dispersion plate 12. For convenience, the accommodating portion 7 is indicated by a broken line, and the cutout portion 122a of the vent pipe 122 is indicated by a two-dot chain line. FIG. 4B is a perspective view of the second dispersion plate 12.

As shown in FIG. 4A, the second dispersion plate 12 is formed with a plurality of liquid passage holes 121 through which the raw material liquid passes and a plurality of vent pipes 122 through which the gas passes. The shape of the liquid passage hole 121 is circular in plan view. The shape of the vent pipe 122 is circular in plan view. In the plan view, six vent pipes 122 are concentrically arranged on the second dispersion plate 12. The number of arrangement of the ventilation pipes 122 shown in the present embodiment is an example, and is not limited to this, and various arrangement numbers can be adopted.

A gap 123 exists between the outer peripheral portion of the second dispersion plate 12 and the inner wall surface of the accommodating portion 7. The area of the gap 123 is preferably 5% to 40% of the cross-sectional area of the accommodating portion 7, and more preferably 10 to 30%.
The total area of the openings of the plurality of ventilation pipes 122 of the second dispersion plate 12 is an area in the range of 30% to 70% of the area of the gap 123. The total area of the openings of the plurality of ventilation pipes 122 of the second dispersion plate 12 is preferably 40 to 60% of the area of the gap 123.

The plurality of ventilation pipes 122 have a notch 122 a on the gas supply pipe 10 side and on the central part side of the second dispersion plate 12. The notch 122a is a straight line connecting the center CP2 of the vent pipe 122 and the center CP1 of the second dispersion plate 12 as viewed from the extending direction of the heat transfer pipe 2 (plan view), and the circumference of the vent pipe 122. Among the two intersection points P1 and P2, the intersection point P1 closer to the center CP1 of the second dispersion plate 12 is arranged to be the midpoint of the arc AR of the notch 122a.
The central angle θ of the notch with respect to the arc AR is desirably, for example, 90 ° to 270 °, and more preferably about 150 to 210 °.

3 and 4B, the upper end of the ventilation pipe 122 protrudes upward from the upper end of the side wall of the second dispersion plate 12. As shown in FIG. In the longitudinal cross-sectional view of FIG. 3, the length H2 of the notch 122a in the vertical direction is desirably about 10% to 80%, more preferably about 20 to 50% with respect to the total length H1 of the vent pipe 122.

As described above, the presence of the vent pipe 122 having the notch 122a on the gas supply pipe 10 side suppresses the generation of a strong gas flow in the gap 123 at the outer peripheral portion, thereby suppressing the adverse effect on the liquid flow. Can do.

Returning to FIG. 3, a nozzle 121 a that protrudes from the surface to the first dispersion plate 5 side is formed in a portion of the surface of the second dispersion plate 12 on the first dispersion plate 5 side where the liquid passage holes 121 are formed. Is provided.

A gap 123 exists between the outer peripheral portion of the second dispersion plate 12 and the inner wall surface of the accommodating portion 7.
The evaporator 1 </ b> A is configured such that the gas from the gas supply pipe 10 passes through the gap 123, passes through the plurality of vent holes 52, and flows into the plurality of heat transfer tubes 2.

The transfer mechanism 13 has a transfer pipe 131 and a pump 132. In the evaporator 1 </ b> A, one end of a transfer pipe 131 is connected to the bottom of the tower bottom 8. The other end of the transfer pipe 131 is connected to the raw material liquid supply pipe 9.

In order to maintain the state in which the liquid film is formed on the inner wall surface of the heat transfer tube 2, it is necessary to set the amount of the raw material liquid flowing down at the lower end of the inner wall surface of the heat transfer tube 2 to a predetermined amount or more. Therefore, the raw material liquid may pass through the heat transfer tube 2 without evaporating and drop on the tower bottom 8 in some cases. The raw material liquid (non-evaporated liquid) is supplied to the pump 132 through the transfer pipe 131 from the tower bottom 8. A part of the non-evaporated liquid is supplied again into the container 7 by the pump 132 through the transfer pipe 131 and the raw material liquid supply pipe 9.
In this way, the unevaporated liquid is circulated. The supplied non-evaporated liquid passes through the liquid passage hole 121 of the second dispersion plate 12, passes through the liquid passage hole 51 of the first dispersion plate 5, and is not provided with the heat transfer tube 2 of the upper tube plate 3. It flows into the region and flows into the plurality of heat transfer tubes 2.

According to the evaporation apparatus 1 </ b> A of the present embodiment, the second dispersion plate 12 is provided, and the plurality of vent pipes 122 are concentrically arranged when viewed from the extending direction of the plurality of heat transfer pipes 2. Therefore, compared with the case where the plurality of ventilation pipes 122 are randomly arranged, the gas flow from the gas supply pipe 10 is suppressed from being biased to a part in the housing portion 7, and is uniform throughout the housing portion 7. become.
Therefore, the gas from the gas supply pipe 10 is uniformly supplied to the first dispersion plate 5 through the gap 123 and the vent pipe 122 in the outer peripheral portion of the second dispersion plate 12, and the gas flow direction is limited, The gas flows smoothly into the plurality of heat transfer tubes 2. Therefore, it is possible to maintain a state in which a uniform film of the raw material liquid is formed on the inner wall surfaces of the plurality of heat transfer tubes 2.

Further, since the transfer mechanism 13 is provided, a part of the unevaporated liquid can be again used for evaporation.

In the said embodiment, the groove | channel may be formed in the front-end | tip of the protrusion part of a heat exchanger tube.
FIG. 5A to FIG. 5C are schematic views showing modifications of the projecting portion of the heat transfer tube.

For example, as shown in FIG. 5A, a V-shaped groove 2Ab may be formed at the tip of the protrusion 2Aa of the heat transfer tube 2A.
Moreover, as shown to FIG. 5B, the U-shaped groove | channel 2Bb may be formed in the front-end | tip of protrusion part 2Ba of the heat exchanger tube 2B.
Moreover, as shown to FIG. 5C, the concave groove | channel 2Cb may be formed in the front-end | tip of the protrusion part 2Ca of the heat exchanger tube 2C.

When the groove is not formed at the tip of the projecting portion of the heat transfer tube, the height of the tip of the projecting portion of each heat transfer tube is made the same in order to uniformly distribute the raw material liquid to the plurality of heat transfer tubes. There is a need. On the other hand, when the groove is formed at the tip of the projecting portion of the heat transfer tube, the required degree of manufacturing accuracy and installation accuracy of the heat transfer tube is reduced in uniformly distributing the raw material liquid to the plurality of heat transfer tubes. .

(Evaporation system)
FIG. 6 is a schematic diagram illustrating an example of an evaporation system.
As shown in FIG. 6, the evaporation system 100 includes an evaporator 1, a pump 101, a vacuum distillation apparatus 102, and a condenser 103.

The evaporation system 100 collects the raw material from the mixture of the raw material unevaporated liquid and the tar content derived from the raw material, which has not been evaporated by the evaporation device 1, and reuses it in the evaporation device 1.

The raw material liquid L1 is sent to the storage unit through the raw material liquid supply pipe. In the supply process, the solvent L2 is supplied from the solvent supply pipe, and the raw material liquid L1 and the solvent L2 are mixed.
The mixed gas of the gas G1 and the solvent gas G2 is sent to the accommodating part through the gas supply pipe.

In the state where the film of the raw material liquid is formed on the inner wall surfaces of the plurality of heat transfer tubes, the heat transfer tubes are heated by the heat medium H to evaporate the raw material liquid. Thereby, evaporation gas (cyclohexanone oxime gas) G3 is obtained. At the same time, a mixture of the raw material liquid and the high boiling point component is obtained as the residue C. The heat source of the heat medium H is not particularly limited and may be arbitrarily selected from known ones.

A part of the residue C (raw material non-evaporated liquid) C1 is again supplied and circulated by the pump 101 through the transfer pipe and the raw material liquid supply pipe into the accommodating portion.

The remaining portion of residue C (or the remaining portion of residue C) C2 is supplied to vacuum distillation apparatus 102 and distilled. For example, when the raw material liquid is cyclohexanone oxime, the distillation is preferably performed at a distillation temperature of 90 to 135 ° C. under a reduced pressure of 1.4 kPa to 10 kPa (absolute pressure). As a result, the low-boiling component A containing the raw material is distilled off, and the high-boiling component T that is a distillation residue is discharged.

The low boiling point component A containing the distilled off raw material is led to the condenser 103 and condensed. As a result, the low-boiling component A1 containing the condensed raw material is recovered and the uncondensed low-boiling component A2 is discharged. The low-boiling component A1 containing the recovered raw material is supplied and circulated again through the transfer pipe and the raw material liquid supply pipe into the accommodating portion.

According to one aspect of the present invention, it is possible to suppress clogging of heat transfer tubes and tarring of raw materials, to smoothly evaporate raw material liquid and recover raw materials that have not been evaporated, and to efficiently evaporate raw materials. The evaporation apparatus 1 and the evaporation system 100 can be provided.

The preferred embodiments according to the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to these examples. Various shapes, combinations, and the like of the constituent members shown in the above-described examples are examples, and various modifications can be made based on design requirements and the like without departing from the gist of the present invention.

Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto.

Example 1
The raw material liquid was evaporated in a circulating manner to an evaporator equipped with a heat transfer tube having an inner diameter of 50 mm and a length of 6 m. As the raw material liquid, a mixed liquid of cyclohexanone oxime and a solvent for diluting the cyclohexanone oxime was used. Methanol was used as the solvent. Nitrogen gas was used as the gas. The first dispersion plate was used as the dispersion plate, and the number of stages of the dispersion plate was one (see FIG. 1). The main operating conditions are as follows.
-Circulation rate of non-evaporated liquid: 140 (140 to 150) kg / hour / main-Methanol liquid supply amount per heat transfer tube: 0.85 (0.825 to 0.875) kg / hour / main-Transmission Methanol gas supply amount per heat tube: 50 (50-52.5) kg / hour / main ・ Nitrogen gas supply amount per heat transfer tube: 5% of methanol gas supply amount
Evaporation temperature: 140-160 ° C
Operating pressure: 950 torr or less As a result, clogging of the heat transfer tube was not observed until the amount of cyclohexanone oxime evaporated per heat transfer tube = 95T.

Example 2
The raw material liquid was evaporated in a circulating manner to an evaporator equipped with a heat transfer tube having an inner diameter of 50 mm and a length of 6 m. As the raw material liquid, a mixed liquid of cyclohexanone oxime and a solvent for diluting the cyclohexanone oxime was used. Methanol was used as the solvent. Nitrogen gas was used as the gas. The first dispersion plate and the second dispersion plate were used as the dispersion plates, and the number of stages of the dispersion plates was two. Moreover, the nozzle was installed in the part in which the liquid separation hole of the 1st dispersion plate was formed (refer FIG. 3). The main operating conditions are as follows.
-Circulation rate of non-evaporated liquid: 140 (140 to 150) kg / hour / main-Methanol liquid supply amount per heat transfer tube: 0.85 (0.825 to 0.875) kg / hour / main-Transmission Methanol gas supply amount per heat tube: 55 (49-58) kg / hour / main ・ Nitrogen gas supply amount per heat transfer tube: 5% of methanol gas supply amount
Evaporation temperature: 140-160 ° C
Operating pressure: 950 torr or less As a result, clogging of the heat transfer tube was not observed until the amount of cyclohexanone oxime evaporated per heat transfer tube = 100T.

According to the present invention, when the raw material liquid and the gas are evaporated in the vertical flow-down liquid film heat exchanger, by forming a good flow-down liquid film, clogging of the heat transfer tube is suppressed, and Since an evaporation apparatus, an evaporation system, and an evaporation method capable of smoothly performing evaporation can be provided, it is extremely useful in the industry.

DESCRIPTION OF SYMBOLS 1,1A, 1B ... Evaporator, 2, 2A, 2B, 2C ... Heat transfer tube, 2a, 2Aa, 2Ba, 2Ca ... Projection part, 2Ab, 2Bb, 2Cb ... Groove, 3 ... Upper tube sheet (tube sheet), 5 5A, 5B ... first dispersion plate, 6 ... dispersion plate, 7 ... accommodating section, 9 ... raw material liquid supply pipe (inflow part), 10 ... gas supply pipe (inflow part), 12 ... second dispersion plate, DESCRIPTION OF SYMBOLS 13 ... Transfer mechanism, 51 ... Liquid passage hole, 51a ... Nozzle, 52 ... Vent hole, 62 ... Crevice, 100 ... Evaporation system, 101 ... Pump, 102 ... Vacuum distillation apparatus, 103 ... Condenser, 121 ... Liquid passage hole, 122 ... Vent pipe, 122a ... Notch

Claims (13)

A plurality of heat transfer tubes;
A tube plate configured to support the plurality of heat transfer tubes spaced apart from each other;
A first dispersion plate provided above the tube plate,
The first dispersion plate is provided with two or more liquid passage holes configured to pass the raw material liquid and two or more vent holes configured to pass the gas, and the plurality of heat transfer tubes As viewed from the extending direction, the plurality of liquid passage holes are formed at positions where the heat transfer tubes of the tube plate are not provided, and the plurality of vent holes are provided with the plurality of heat transfer tubes. It is formed at a position that overlaps the area that is
The plurality of heat transfer tubes have a protruding portion configured to protrude from an upper surface of the tube plate. In the first dispersion plate, a nozzle is provided on the tube plate side surface of the first dispersion plate,
The nozzle protrudes in the tube plate side direction from the tube plate side surface of the first dispersion plate,
2. The evaporation apparatus according to claim 1, wherein the nozzle is provided in a portion of the surface of the first dispersion plate on the tube plate side where the liquid passage hole is formed. The evaporation apparatus according to claim 1, further comprising an inflow portion configured to allow the raw material liquid and the gas to flow toward the first dispersion plate. One or more dispersion plates are provided between the first dispersion plate and the inflow portion,
The one or more dispersion plates are provided with a plurality of liquid passage holes configured to pass the raw material liquid from the inflow portion,
Among the one or more dispersion plates, at least a plurality of liquid passage holes of the dispersion plate disposed immediately above the first dispersion plate are the first dispersion as viewed from the extending direction of the plurality of heat transfer tubes. The evaporator according to claim 3, wherein the evaporator is disposed at a position overlapping a region where a plurality of air holes of the plate are not provided. Furthermore, it has an accommodating part configured to accommodate the tube sheet and the first dispersion plate,
Between the inflow portion and the first dispersion plate, a second dispersion plate is provided,
The second dispersion plate has a plurality of liquid passage holes configured to allow the raw material liquid from the inflow portion to flow toward the liquid passage holes formed in the first dispersion plate, and the inflow A plurality of vent pipes configured to pass gas from the section, and
A gap is formed between the outer peripheral portion of the second dispersion plate and the inner wall surface of the housing portion,
The plurality of ventilation pipes of the second dispersion plate are arranged concentrically as viewed from the extending direction of the plurality of heat transfer pipes,
5. The plurality of vent pipes of the second dispersion plate have notches on the inflow portion side and on the center portion side of the second dispersion plate. The evaporation apparatus according to 1. 6. The apparatus according to claim 3, further comprising a transfer mechanism configured to transfer the raw material liquid flowing out from the plurality of heat transfer tubes to the inflow portion. Evaporation device. The evaporation apparatus according to any one of claims 1 to 6, wherein a groove is formed at a tip of the protrusion. Of the two or more heat transfer tubes, the area of the heat transfer tube is larger than the area of the vent holes of the first dispersion plate provided immediately above the extension direction of the heat transfer tube. The evaporation apparatus according to any one of claims 1 to 7, wherein: The center of the heat transfer tube coincides with the center of the vent hole of the first dispersion plate provided immediately above the heat transfer tube when viewed from the extending direction thereof. The evaporation apparatus according to any one of claims 8 to 9. The evaporation apparatus according to any one of claims 1 to 9, wherein the raw material liquid contains cyclohexanone oxime. An evaporator according to any one of claims 1 to 10;
A pump configured to circulate a part of the residue of the source gas generated by the evaporator to the evaporator;
A vacuum still configured to distill the remainder of the residue;
A condenser configured to condense the raw material distilled off by the vacuum distillation apparatus;
An evaporation system characterized by comprising: A pressure lower than the pressure at the time of heat evaporation of the residue remaining after the raw material liquid is heated and evaporated using the evaporation apparatus according to any one of claims 1 to 10. The evaporation method is characterized in that the raw material liquid contained in the residue is recovered by condensing the raw material gas distilled by distillation underneath and distillation. The raw material liquid is a mixed liquid of cyclohexanone oxime and a solvent for diluting the same, the solvent is alcohol, and the entire evaporation surface in the evaporator is at least wet with cyclohexanone oxime. The mixture was evaporated at a pressure of 1060 torr or less, and the amount of cyclohexanone oxime flowing down at the lower end of the evaporation surface in the evaporator was evaporated at 170 kg / hr or more per unit length of the lower end of the evaporation surface. The evaporation method according to claim 12, which is performed under a reduced pressure of 1.4 kPa to 10 kPa.

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