JP6948677B2 - Low boiling point substance recovery device and recovery method - Google Patents

Description

The present invention relates to a recovery device and a recovery method for separating and recovering a low boiling point substance from wastewater containing a low boiling point substance such as ammonia.

A steam stripping method is known as a method for separating and removing ammonia-containing wastewater. A general ammonia recovery device using this steam stripping method is provided with a distillation column for steam stripping, and the ammonia-containing steam discharged from the top of the distillation column is fractionated by a condenser to generate condensed water. It is returned to the top of the distillation column as a reflux liquid, and the remaining concentrated ammonia-containing vapor is supplied to the absorption column, absorbed by water, and taken out as recovered ammonia water.

By the way, the steam stripping method used in such an ammonia recovery device is a method of directly blowing steam into the bottom of a distillation column, and since a large amount of steam is used, the running cost is high and the processing cost is required to be reduced. ing. On the other hand, in this method, almost the same amount of water vapor containing ammonia as the input water vapor is generated, but in order to use this as a reflux liquid to the top of the distillation column and a recovered ammonia liquid, it was installed at the top of the column. It needs to be cooled by a heat exchanger (condenser), and the energy is disposable.

In order to solve such a problem, a method has been proposed in which steam discharged from the top of a distillation column is compressed by a steam compressor and heat is recovered by a reboiler to reduce the amount of steam (the following patent documents). 1). In addition, make-up water is supplied to a condenser that fractionates the ammonia-containing steam discharged from the top of the distillation tower, and the make-up water is heat-exchanged with the ammonia-containing steam to evaporate, and is guided to a steam compressor for compression. A configuration has been proposed in which the temperature is raised and reused as steam (see Patent Document 2 below).

Japanese Unexamined Patent Publication No. 2002-28637 Japanese Unexamined Patent Publication No. 2004-114209

In the conventional example disclosed in Patent Documents 1 and 2 above, energy saving is achieved and running cost is reduced by effectively utilizing the heat of the ammonia-containing steam discharged from the top of the distillation column.

However, in such a conventional configuration including at least a distillation column, a heat exchanger (reboiler or condenser: these reboilers or condensers correspond to the evaporator of the present application), and a steam compressor, further energy saving can be achieved. There has been a demand for a low boiling point substance recovery device.

The present invention has been conceived in view of the above problems, and an object of the present invention is to provide a low boiling point substance recovery device and a recovery method in which energy saving is effectively achieved.

In order to achieve the above object, the invention according to claim 1 is to bring a stock solution containing a low boiling point substance into contact with steam for heating, separate the low boiling point substance from the stock solution, gasify it, and use it as steam containing the low boiling point substance. Heat exchange between water and a distillation tower that stores treated water from which low boiling point substances have been removed from the undiluted solution at the bottom of the tower, and steam containing low boiling point substances discharged from the top of the distillation tower. As a result, the steam containing the low boiling point substance is fractionated to concentrate the steam containing the low boiling point substance, and the water is evaporated and discharged as steam, and the steam discharged from the evaporator is compressed. In a low boiling point substance recovery device having at least a compression device that raises the temperature, guides the steam that has been compressed and heated to the distillation tower, and uses it as steam for heating used in the distillation tower, the bottom of the distillation tower. It is characterized by being further provided with a preheater which is provided in the middle of a discharge line for discharging the treated water stored in the steamer to the outside and heats the water used in the evaporator by exchanging heat with the treated water in advance. do.

According to the above configuration, the water used in the evaporator is preheated, so that energy saving at the time of heat exchange in the evaporator can be achieved .
As the "low boiling point substance", alcohols such as ammonia and methanol, ketones such as acetone, and esters such as methyl acetate can be applied.
As "water", pure water, soft water, ion-exchanged water and the like can be applied.

The invention according to claim 2 is the low boiling point substance recovery device according to claim 1, which takes in steam containing a low boiling point substance after being fractionated by the evaporator, cools the steam, and removes water. Te you, further comprising a rectifying column to further enrich the vapor containing low-boiling substances.

According to the above configuration, an evaporator and a concentration tower arranged after the evaporator are provided, and the ammonia-containing vapor discharged from the distillation tower is concentrated at a predetermined height by two-step concentration by the evaporator and the concentration tower. It is possible to generate a vapor containing a low boiling point substance having a concentration (for example, 20 wt% or more). With such a configuration, it is possible to prevent the load on the compression device from becoming too large as compared with the configuration in which the compressor concentrates to a predetermined high concentration (for example, 20 wt% or more) by itself. As a result, it is possible to obtain a recovery device capable of saving energy and producing a steam containing a low boiling point substance having a high concentration (for example, 20 wt% or more) .

In a desirable embodiment , the low boiling point substance recovery device according to claim 2 , wherein the storage liquid stored in the bottom of the concentration tower is provided in the middle of a circulation line leading to the top of the column, and flows through the circulation line. Depending on the heat exchanger that exchanges heat with the cooling water to cool the stored liquid, the temperature sensor that detects the temperature of the stored liquid stored in the bottom of the concentrating tower, and the detection result of the temperature sensor. it characterized by and a control valve for adjusting the flow rate of the coolant passing through the heat exchanger.

According to the above configuration, the opening degree of the control valve is controlled according to the detection result of the temperature sensor, and the flow rate of the cooling water passing through the heat exchanger is adjusted. As a result, the stored liquid (condensed liquid of low boiling point substance-containing vapor) stored at the bottom of the concentrating tower is cooled to a predetermined temperature and sprayed to obtain a predetermined high concentration (for example, 20 wt% or more) of ammonia-containing vapor. Can be generated.

According to a third aspect of the invention, a low-boiling substance recovery apparatus according to claim 1 or 2, wherein the compression device includes you and a plurality of steam compressor is configured by connecting in parallel.

Fourth aspect of the present invention, a recovery device of the low boiling substance according to claim 1, characterized in that said low-boiling substance is ammonia.

In the invention according to claim 5 , the steam for heating is blown into the distillation tower, the steam for heating is brought into contact with the stock solution containing the low boiling point substance, the low boiling point substance is separated from the stock solution and gasified to obtain steam containing the low boiling point substance. The first step of storing the treated water from which the low boiling point substance has been removed from the undiluted solution at the bottom of the distillation tower while discharging from the top of the distillation tower, and the low boiling point substance discharged from the top of the distillation tower are included. By exchanging heat between steam and water in an evaporator, the steam containing the low boiling point substance is fractionated to concentrate the steam containing the low boiling point substance, and the water is evaporated and discharged as steam. A third step of compressing and raising the temperature of steam discharged from the evaporator in a compressor, guiding the compressed and heated steam to the distillation tower, and using it as steam for heating used in the distillation tower. In the method for recovering a low boiling point substance having at least It is characterized in that it heats by exchanging heat with the treated water in advance.
According to the above configuration, the water used in the evaporator is preheated, so that energy saving at the time of heat exchange in the evaporator can be achieved .

The invention according to claim 6 is the method for recovering a low boiling point substance according to claim 5, wherein steam containing the low boiling point substance after being fractionated by the evaporator is taken in, and the vapor is cooled to remove water. It is characterized by further comprising a fourth step of further concentrating the steam containing the low boiling point substance in the concentrating tower.
According to the above configuration, a method for recovering a low boiling point substance can be constructed in which a low boiling point substance can be recovered at a high concentration and energy saving is achieved.

According to the present invention, energy saving can be effectively achieved.

The whole block diagram of the ammonia recovery apparatus which concerns on embodiment. Enlarged view near the evaporator. Enlarged view near the enrichment tower.

Hereinafter, the present invention will be described in detail based on the embodiments. In the following embodiment, as the low boiling point substance recovery device, an ammonia recovery device in which ammonia-containing wastewater is used as a stock solution and ammonia is separated and removed from the ammonia-containing wastewater and recovered will be described as an example. As the low boiling point substance, in addition to ammonia, alcohols such as methanol, ketones such as acetone, and esters such as methyl acetate can also be applied.

(Embodiment)
FIG. 1 is an overall configuration diagram of an ammonia recovery device according to an embodiment. The ammonia recovery device (corresponding to the low boiling point substance recovery device of the present invention) 1 includes a distillation tower 2 in which steam for heating is blown to perform steam stripping, and ammonia-containing steam and water discharged from the top of the distillation tower 2. Evaporator 3 that exchanges heat to evaporate water, a compression device 4 that compresses and raises the temperature of steam discharged from the evaporator 3 and discharges it to the distillation tower 2 as steam for heating, and ammonia concentrated by the evaporator 3. The concentration tower 5 that takes in the contained steam, cools the steam to remove water, and raises the concentration of the ammonia-containing steam to a high concentration (for example, 20 wt% or more), and the ammonia-containing steam from the concentration tower 5 absorbs the water. It includes a first absorption tower 6 that produces recovered ammonia water having a predetermined concentration, and a second absorption tower 7 that prevents uncondensed ammonia-containing vapor in the first absorption tower from being discharged to the outside. Here, to explain the outline of the features of the ammonia recovery device 1 according to the first embodiment, the evaporator 3 and the concentration tower 5 arranged after the evaporator 3 are provided and discharged from the distillation tower 2. The ammonia-containing steam is configured so that a predetermined high concentration (for example, 20 wt% or more) of ammonia water can be recovered by two-step concentration by the evaporator 3 and the concentration tower 5.

Hereinafter, the specific configuration of the ammonia recovery device 1 including the above-mentioned characteristic configuration will be described.
A multi-stage distillation column 2 may be used, and the distillation column 2 is not limited to this, and a non-multi-stage distillation column 2 may be used. That is, a shelf column or a packed column can be used for the distillation column 2. The undiluted solution (ammonia-containing wastewater) is supplied to the top of the distillation column 2 via the undiluted solution supply pipe L1. The pH of the stock solution may be adjusted in advance.

The heating steam from the steam ejector 10 is supplied to the bottom of the distillation column 2 via the heating steam supply pipe L3. The bottom of the distillation column 2 is a heat recovery tank 1 via a pipe L4.
It is connected to No. 1, and the stored liquid (low-concentration ammonia water) at the bottom of the tower is supplied to the heat recovery tank 11 via the pipe L2. The steam ejector 10 is a steam compression means for sucking and compressing steam, and a steam supply pipe L5 and heat through which steam supplied from a high-pressure steam source (not shown) such as a boiler flows to the steam suction side 10a. A steam recycling pipe L6 extending from the recovery tank 11 is connected. With such a configuration, the stored liquid in the heat recovery tank 11 is flash-evaporated, sucked and compressed by the steam ejector 10, mixed with the steam from the steam supply pipe L5, and used as heating steam at the bottom of the distillation column 2. Is blown into. In this way, the stored liquid in the heat recovery tank 11 is flash-evaporated and reused as a part of the heating steam, so that heat can be recovered.

A discharge pipe L7 for discharging treated water (for example, low-concentration ammonia water of 30 ppm or less) is connected to the bottom of the heat recovery tank 11, and the treated water discharge pump P1 is connected on the discharge pipe L7. And three heat exchangers H1, H2 and H3 are provided. The heat exchanger H1 is a water heater that heats water by exchanging heat between water and treated water. The water heated by the heat exchanger H1 is supplied to the bottom of the evaporator 3 via the water supply pipe L8. The heat exchanger H2 is a stock solution preheater that heats the stock solution in advance by exchanging heat between the stock solution and the treated water. The undiluted solution preheated by the heat exchanger H2 is supplied to the top of the distillation column 2 via the undiluted solution supply pipe L1. The heat exchanger H3 is a cooler that cools the treated water by exchanging heat between the cooling water and the treated water. The treated water cooled by the heat exchanger H3 is discharged to the outside of the system via the discharge pipe L7.
The heat exchangers H1, H2, and H3 are located on the discharge pipe L7 on the downstream side of the treated water discharge pump P1 and are installed in the following order. That is, on the discharge pipe L7, the heat exchanger H1 is installed on the upstream side of the heat exchanger H2. By installing in such an order, the amount of heat given from the treated water to the water is the largest, so that energy saving can be achieved in the evaporator 3 that heats the water. Further, since the reason for installing the heat exchanger H3 is to cool the treated water, the heat exchanger H3 is installed on the downstream side of the heat exchangers H1 and H2.

The evaporator 3 is composed of a horizontal tube type evaporator 12, and includes a spreader 13 and an indirect heater 14. The type is not limited to the horizontal tube type, and for example, an evaporation can of a thin film flow (vertical tube) type or the like may be used. As shown in FIG. 2, the indirect heater 14 includes a heat transfer tube group 15 composed of one or a plurality of horizontal heat transfer tubes, and a pair of left and right headers 16A and 16B. Further, the bottom of the evaporation can 12 is a storage portion 17 for storing water supplied through the pipe L8. The stored liquid (water) of the storage unit 17 is supplied by the circulation pump P2 to the spreader 13 provided at the upper part in the evaporation can 12 via the pipe L9, and is supplied from the spreader 13 to the outer surface of the heat transfer tube group 15. After spraying toward the evaporative can, it is configured to circulate by flowing down to the lower storage portion 17 in the evaporation can 12.

The header 16B is connected to the top of the distillation column 2 via a steam supply pipe L10, and the top steam (steam containing ammonia) discharged from the top of the distillation column 2 passes through the steam supply pipe L10 to the header. It is guided to 16B and further circulates in the heat transfer tube group 15. Here, the pressure of the evaporator 3 is lower than the pressure of the steam at the top of the column, so that the circulating liquid (water) sprayed by the sprayer 13 evaporates in a thin film on the surface of the heat transfer tube group 15 and becomes steam. Occurs. This water vapor is supplied to the compression device 4. Here, the principle of vaporizing water in the evaporator 3 will be described in more detail. In the evaporator 3, the pressure on the outside of the heat transfer tube containing the water to be heated is higher than that of the top steam (inside the heat transfer tube) which is the heating source. Because it is low, water evaporates. The pressure difference is generated by the compressor 4 (specifically, the steam compressors 18 and 19). This is because the outside of the evaporator heat transfer tube connected to the suction side of the compression device 4 is low, and the pressure inside the distillation column 2 connected to the discharge side of the compression device 4 and thus the steam at the top of the column is high. In addition, the steam supplied from the steam ejector 10 also raises the pressure in the distillation column 2 and contributes to the evaporation of the water in the evaporator 3.
Further, the condensed water (low-concentration ammonia water) that has flowed and condensed in the heat transfer tube group 15 is stored in the header 16A, and is driven by the condensed water pump P3 to be a reflux liquid through the tube L11 at the top of the distillation column 2. Returned to. The remaining surplus steam (concentrated ammonia-containing steam) is discharged to the top of the concentration tower 5 via the pipe L12.

The compressor 4 includes two steam compressors 18 and 19, and these steam compressors 18 and 19 are configured by connecting the bottom of the distillation column 2 and the top of the evaporation can 10 in parallel. That is, the inlet side 18a of the steam compressor 18 is connected to the upper part of the evaporation can 12 via the pipe L15, and the outlet side 18b of the steam compressor 18 is connected to the bottom of the distillation column 2 via the pipe L15. .. The inlet side 19a of the steam compressor 19 is connected to the upper part of the evaporation can 10 via a branch pipe L17 branched from the pipe L5, and the outlet side 19b of the steam compressor 19 is connected to the bottom of the distillation column 2 via the pipe L18. It is connected.

Here, as the steam compressors 18 and 19, roots type steam compressors having a large maximum differential pressure are used. However, in the present invention, not only the roots type steam compressor but also a turbo type steam compressor, a screw type steam compressor, a vane type steam compressor, or any other steam compressor may be used. Further, although the compressor 4 is composed of two steam compressors 18 and 19 in the present embodiment, it may be composed of one steam compressor or three or more steam compressors.

The concentration tower 5 is composed of a spray-type scrubber. The stored liquid (condensate) stored in the bottom of the concentrating tower 5 flows through the spray pipe (corresponding to the circulation line of the present invention) L20, is guided to the top of the tower, and is sprayed into the top of the tower. It has become. A circulation pump P4 and a heat exchanger H4 are provided in the middle of the spray tube L20. The stored liquid flowing through the spray tube L20 is heat-exchanged with the cooling water in the heat exchanger H4 to be cooled. As shown in FIG. 3, a control valve V1 is provided in the pipe L21 through which the cooling water flows, and the opening degree is controlled by the temperature sensor T that detects the temperature of the stored liquid stored in the bottom of the concentrating tower 5. There is. That is, the opening degree of the control valve V1 is controlled according to the detection result of the temperature sensor T, and the flow rate of the cooling water passing through the heat exchanger H4 is adjusted. Thereby, by cooling the stored liquid (condensate) to a predetermined temperature and spraying it, it is possible to generate a predetermined high concentration (for example, 20 wt% or more) of ammonia-containing vapor.

Further, as shown in FIG. 2, the spray pipe L20 is branched in the middle, and the branched branch pipe L22 is connected to the top of the distillation column 2. A control valve V2 is provided in the middle of the branch pipe L22. Further, as shown in FIG. 2, the concentrating tower 5 is provided with a liquid level sensor S1 for detecting the liquid level of the stored liquid. The liquid level sensor S has a level switch S1a for detecting the upper limit set level and a level switch S1b for detecting the lower limit set level. The liquid level sensor S1 controls the opening degree of the control valve V2 so that the stored liquid is maintained at a predetermined liquid level and the stored liquid that overflows the predetermined liquid level is returned to the top of the distillation column 2. It has become.

The first absorption tower 6 is composed of a spray type scrubber similar to the concentration tower 5, and the spray pipe L23 through which the stored liquid of the first absorption tower 6 circulates has a circulation pump P5 and a heat exchanger H5. Is provided. In the heat exchanger H5, the stored liquid flowing through the spray pipe L23 and the cooling water exchange heat, and the stored liquid is cooled. The cooled storage liquid is sprayed onto the high-concentration (for example, 20 wt% or more) ammonia-containing vapor taken in from the concentration tower 5 via the pipe L24 to condense and recover the ammonia-containing vapor, and collect the recovered ammonia water. Generate. The spray pipe L23 is branched in the middle, and the recovered ammonia water is discharged to the outside of the system via the branched branch pipe L25.

The second absorption tower 7 is composed of a spray type scrubber similar to the first absorption tower 6, and water is supplied to the bottom of the second absorption tower 7 via a pipe L30 and stored in the bottom of the tower. Water is sprayed from the top of the tower through the spray pipe L31 by driving the circulation pump P6. Between the first absorption tower 6 and the second absorption tower 7, a pipe L32 that guides the uncondensed ammonia-containing vapor in the first absorption tower 6 to the top of the second absorption tower 7 and the inside of the second absorption tower 7 A pipe L33 for returning the condensed water of the above to the first absorption tower 6 is provided. Further, an exhaust pipe L34 for exhausting the vapor from which ammonium has been removed is provided at the top of the second absorption tower 7.
In FIGS. 1 to 3, L40 is a cooling water supply pipe, L41 is a pipe branched from the cooling water supply pipe L40, and L21 is a pipe branched from the cooling water supply pipe L40. A heat exchanger H5 is provided, a heat exchanger H2 is provided on the tube L41, and a heat exchanger H4 is provided on the tube L21.

Next, the processing operation of the ammonia recovery device 1 having the above configuration will be described. Steam stripping is performed in the distillation column 2 by blowing steam for heating. That is, in the distillation tower 2, the undiluted solution is brought into contact with steam for heating, ammonia is separated from the undiluted solution, gasified, and discharged from the top of the column as steam containing ammonia, and low-concentration ammonia water from which ammonia is removed from the undiluted solution (for example). 30 ppm or less) is stored at the bottom of the tower as treated water.

The ammonia-containing steam discharged from the top of the distillation tower 2 is guided to the header 16B through the steam supply pipe L10, and further circulates in the heat transfer tube group 15, thereby circulating by the spreader 13. The liquid (water) evaporates into a thin film on the surface of the heat transfer tube group 15, and water vapor is generated. This steam is supplied to the steam compressors 18 and 19. On the other hand, the condensed water (low-concentration ammonia water) that has flowed and condensed in the heat transfer tube group 15 is stored in the header 16A, returned to the top of the distillation column 2 as a reflux liquid via the tube L11, and the remaining surplus steam. (Concentrated ammonia-containing vapor) is supplied to the concentration column 5 via the tube L12.

In the steam compressors 18 and 19, the supplied steam is compressed and raised in temperature and charged into the bottom of the distillation column 2 as steam for heating. As a result, the amount of steam for heating supplied from the steam supply pipe L3 for heating can be reduced, and energy saving can be achieved.

On the other hand, in the concentrating tower 5, the opening degree of the control valve V1 is controlled according to the detection result of the temperature sensor T, and the flow rate of the cooling water passing through the heat exchanger H4 is adjusted. As a result, the stored liquid (condensate) cooled to a predetermined temperature is sprayed from the top of the concentrating tower 5, and the ammonia-containing vapor is fractionated, so that a predetermined high concentration (for example, 20 wt% or more) of ammonia-containing vapor is produced. Generated. The entire amount of the condensate is returned to the top of the distillation column 2 as a reflux liquid. As described above, the concentration tower 5 takes in the ammonia-containing vapor after the evaporation by the evaporator 3, removes water, and further concentrates the vapor containing ammonia, so that the evaporator 3 alone has a predetermined high concentration ( For example, it is possible to prevent the load of the steam compressors 18 and 19 from becoming too large as compared with the configuration of concentrating up to 20 wt% or more). As a result, energy saving can be achieved and a high concentration (for example, 20 wt% or more) of ammonia-containing vapor can be generated.

Next, in the first absorption tower 6, the ammonia-containing vapor guided from the concentration tower 5 via the tube L24 is condensed by the configuration in which the stored liquid at the bottom of the column is sprayed from the top of the column through the spray tube L23. Ammonia recovered water containing a high concentration of ammonia (recovered ammonia water) is produced. In the second absorption tower 7, a small amount of uncondensed ammonia gas remaining in the first absorption tower 6 is guided through the pipe L32, and water supplied from outside the system is sprayed from the top of the tower through the spray pipe L31. Uncondensed ammonia gas is absorbed by the configuration. The water that has absorbed ammonia is returned to the condensate of the first absorption tower 6. As a result, uncondensed ammonia gas is prevented from being discharged to the outside. The gas from which ammonia has been removed is exhausted from the exhaust pipe L34.

(Other matters)
(1) In the above embodiment, the configuration has been described as supplying "water" to the evaporator 3 and the second absorption tower 7, but the "water" is specifically pure water, soft water, or ion-exchanged water. Etc. can be applied.

(2) Further, for reference, in the case of a configuration in which the steam of the distillation column is directly compressed and used as a heat source of the distillation column (for example, Patent Document 1 etc.), the steam of the distillation column is directly compressed. , There is a possibility of corrosion due to contained substances, and there is a possibility of corrosion or leakage at the seal part. On the other hand, in the case of the configuration in which water is evaporated by an evaporator and directly used in the distillation column as in the present invention, the steam (steam) directly used in the distillation column does not contain the contained substance, so that it is contained. It is possible to prevent the occurrence of corrosion and leakage due to substances.

The present invention can be applied to a recovery device and a recovery method for separating and recovering a low boiling point substance from wastewater containing a low boiling point substance such as ammonia.

1: Ammonia recovery device 2: Distillation tower 3: Evaporator 4: Compressor 5: Concentration tower 6: First absorption tower 7: Second absorption tower 18, 19: Steam compressor

Claims (6)

A process in which the undiluted solution containing a low boiling point substance is brought into contact with steam for heating, the low boiling point substance is separated from the undiluted solution, gasified, discharged from the top of the column as steam containing the low boiling point substance, and the low boiling point substance is removed from the undiluted solution. A distillation tower that stores water at the bottom of the tower,
By exchanging heat between water and steam containing a low boiling point substance discharged from the top of the distillation tower, the steam containing the low boiling point substance is fractionated, and the steam containing the low boiling point substance is concentrated. , An evaporator that evaporates the water and discharges it as steam,
A low boiling point substance having at least a compression device that compresses and raises the temperature of steam discharged from the evaporator, guides the compressed and heated steam to the distillation column, and uses it as heating steam used in the distillation column. In the recovery device of
A preheater provided in the middle of a discharge line for discharging treated water stored in the bottom of the distillation column to the outside, and heats the water used in the evaporator by exchanging heat with the treated water in advance .
A low boiling point substance recovery device characterized by being further equipped with. It is characterized by further provided with a concentration tower that takes in steam containing a low boiling point substance after being fractionated by the evaporator, cools the steam to remove water, and further concentrates the steam containing the low boiling point substance. The device for recovering a low boiling point substance according to claim 1. The low boiling point substance recovery device according to claim 1 or 2, wherein the compressor is configured by connecting a plurality of steam compressors in parallel. The device for recovering a low boiling point substance according to any one of claims 1 to 3, wherein the low boiling point substance is ammonia. Steam for heating is blown into the distillation tower, the steam for heating is brought into contact with the undiluted solution containing the low boiling point substance, the low boiling point substance is separated from the undiluted solution, gasified, and discharged from the top of the distillation tower as steam containing the low boiling point substance. At the same time, the first step of storing the treated water from which the low boiling point substance was removed from the undiluted solution at the bottom of the distillation tower, and
By exchanging heat between water and steam containing a low boiling point substance discharged from the top of the distillation tower in an evaporator, the steam containing the low boiling point substance is fractionated and the steam containing the low boiling point substance is concentrated. The second step of evaporating the water and discharging it as steam.
The third step of compressing and raising the temperature of the steam discharged from the evaporator in a compressor, guiding the compressed and heated steam to the distillation column, and using it as the heating steam used in the distillation column.
In the method of recovering low boiling point substances having at least
The water used in the evaporator is preheated by heat exchange with the treated water by a preheater provided in the middle of the discharge line for discharging the treated water stored in the bottom of the distillation tower to the outside. A method for recovering a low boiling point substance. Further provided with a fourth step of taking in the steam containing the low boiling point substance after the evaporation by the evaporator, cooling the steam to remove water, and further concentrating the steam containing the low boiling point substance in the concentrating tower. The method for recovering a low boiling point substance according to claim 5.

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