Method for recovering a sulfolane waste stream containing potassium chloride

Abstract

The present application relates to the field of petrochemical industry, in particular to a method for recovering potassium chloride-containing sulfolane wastewater. In view of the problem that the prior art cannot simultaneously separate and extract potassium chloride and sulfolane from the sulfolane wastewater containing potassium chloride, the potassium chloride in the wastewater is brought to a relatively stable state through falling film evaporation, and then the potassium chloride is precipitated and the sulfolane is condensed to achieve effective recovery of the potassium chloride and the sulfolane, so that the purity of the recovered sulfolane is greater than or equal to 99.8%, the recovery rate is greater than or equal to 98%, and the recovery rate of the potassium chloride is greater than or equal to 98%. The content of each component in the preheated liquid is determined, and the falling film evaporation temperature and time are set according to the determination results, so that the preliminary treatment liquid quickly reaches the set potassium chloride content, and the distilled water obtained by evaporation is recovered for preheating of the wastewater mother liquor, thereby effectively reducing the energy consumption of the whole process.

Description

Technical Field

[0001] The invention relates to the field of petrochemical industry, and in particular to a method for recovering sulfolane wastewater containing potassium chloride. Background Art

[0002] Sulfolane is a versatile solvent with excellent performance. In addition to its use as an aromatics extraction solvent, it can also be used as a purifier for natural gas, synthetic feed gas, and gas refineries, a solvent for polymer spinning and casting, and a solvent for various organic reactions. It is widely used in reactions such as halogenation, hydrogenation, hydration, hydrolysis, dehydration, sulfonation, diazotization, and polymerization, and is an important chemical raw material. Sulfolane-containing wastewater generated by chemical processes contains high levels of sulfolane. Direct discharge not only pollutes the environment but also wastes resources. Therefore, efficient and energy-saving recovery of sulfolane from sulfolane wastewater is a much-needed new technology for wastewater resource utilization and harmlessness.

[0003] Currently, the main treatment methods for sulfolane wastewater include four-effect distillation, biochemical methods, and extraction methods. The four-effect distillation method volatilizes the water in the sulfolane wastewater through distillation to recover the sulfolane. However, due to the extremely high latent heat of vaporization of water, the entire distillation process consumes a lot of energy. Furthermore, high temperatures can easily cause side reactions such as sulfolane ring opening. The biochemical method treats sulfolane wastewater through biodegradation. However, after degradation, the sulfolane cannot be recovered, resulting in a waste of resources. The extraction method effectively separates the sulfolane by adding an extractant. However, this method has high extraction temperature requirements. Excessively high or low extraction temperatures are not conducive to sulfolane recovery. Furthermore, the extractant needs to be separated later, increasing the processing difficulty.

[0004] At the same time, the above methods can only separate sulfolane. In fact, the sulfolane wastewater solution also contains other recyclable components, such as potassium chloride. The existing technology cannot achieve the simultaneous recycling of potassium chloride and sulfolane.

[0005] Above, a wastewater treatment method capable of simultaneously recycling potassium chloride and sulfolane is proposed. Summary of the Invention

[0006] Based on the above problems, an object of the present invention is to provide a method for recovering potassium chloride-containing sulfolane wastewater, which can simultaneously recover potassium chloride and sulfolane in the sulfolane wastewater.

[0007] Another object of the present invention is to provide a recovery device for recovering sulfolane wastewater containing potassium chloride.

[0008] In a first aspect, the present invention relates to a method for recovering sulfolane wastewater containing potassium chloride, the method comprising the following steps:

[0009] preheating the waste liquid mother liquor to obtain a preheated liquid;

[0010] The density and conductivity of the preheating liquid are measured to determine the mass percentages of potassium chloride, sulfolane and water therein;

[0011] The preheated liquid is subjected to falling film evaporation to obtain water vapor and preliminary treatment liquid;

[0012] Separating the preliminary treated liquid to obtain potassium chloride and evaporation liquid;

[0013] The evaporated liquid is subjected to secondary condensation to recover sulfolane and water;

[0014] in,

[0015] The falling film evaporation temperature is set according to the mass percentage of potassium chloride; its advantage is to improve the evaporation efficiency and shorten the evaporation time;

[0016] The mass percentage of potassium chloride in the preliminary treatment liquid is 5%-7%.

[0017] Furthermore, the water vapor obtained by the falling film evaporation is used to preheat the waste liquid mother liquor. This has the advantage that the water vapor can be reused, which can save energy.

[0018] Preferably, the separation is performed by performing a first heating evaporation on the preliminary treatment liquid to precipitate a first potassium chloride, and collecting the first evaporated liquid, and then performing a second heating evaporation on the first evaporated liquid to precipitate a second potassium chloride and collecting the second evaporated liquid; the second evaporated liquid is the final evaporated liquid, and the first potassium chloride and the second potassium chloride precipitated by the two heating evaporations are combined to form the final precipitated potassium chloride.

[0019] Preferably, the first heating evaporation temperature is 122-125° C., the second heating evaporation starting temperature is 142-145° C., and the heating is continued until the evaporation ends at a temperature of 192-195° C. This has the advantage of improving the recovery rate of potassium chloride.

[0020] Preferably, in the two-stage condensation, the temperature of the first stage condensation is 120-130° C., and the temperature of the second stage condensation is 50-60° C. The advantage of separating sulfolane and water by two-stage condensation is that the recovery rate of sulfolane is improved.

[0021] In a second aspect, the present invention relates to a recovery device for use in recovering sulfolane waste liquid containing potassium chloride, which can utilize any of the above methods.

[0022] The equipment preferably includes a plate and frame heat exchanger 1 for preheating, a density meter 2 and a conductivity meter 3 for determining the content of potassium chloride, sulfolane and water in the preheating liquid; a falling film evaporator 4 for falling film evaporation, a separation device 5 for precipitating potassium chloride and collecting evaporated liquid, and a condenser 6 for secondary condensation.

[0023] Further, the separation device comprises a salt precipitation heater I 501, a salt precipitation heater II 502 for collecting precipitated potassium chloride, and an evaporator I 503, an evaporator II 504 for collecting evaporated liquid. The advantage is to improve the recovery rate of potassium chloride.

[0024] Further, the condenser comprises a primary condenser 601 and a secondary condenser 602.

[0025] Further, the water vapor evaporated by the falling film evaporator 4 is delivered to the plate and frame heat exchanger 1 as its heat source. The advantage is to reduce energy consumption.

[0026] The beneficial effects of the present application are:

[0027] The present application aims at the problem that the prior art cannot realize the simultaneous separation and extraction of potassium chloride and sulfolane from sulfolane waste liquid containing potassium chloride. The potassium chloride in the waste liquid is brought to a relatively stable state by falling film evaporation, and then the potassium chloride is precipitated and sulfolane is condensed to realize effective recovery of potassium chloride and sulfolane. The purity of the recovered sulfolane is ≥99.8%, the recovery rate is ≥98%, and the recovery rate of potassium chloride is ≥98%.

[0028] The present application determines the content of each component in the preheated liquid by density and conductivity measurement, and sets the falling film evaporation feed temperature according to the mass percentage of potassium chloride in the measurement result, controls the preliminary treatment liquid to quickly reach the set potassium chloride content, and recovers the distilled water obtained by evaporation for preheating of the waste liquid mother liquor, effectively reducing the energy consumption of the whole process. BRIEF DESCRIPTION OF DRAWINGS

[0029] ATTACHED Figure 1 : Recovery equipment for recovering sulfolane waste liquid containing potassium chloride. DETAILED DESCRIPTION

[0030] The present application will be specifically described below by examples. It is necessary to point out here that the following examples are only used to further illustrate the present application and cannot be understood as limiting the protection scope of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application according to the content of the present application.

[0031] As a kind of excellent multi-effect solvent, the component types and contents of sulfolane waste liquid are usually not fixed, so the prior art generally only focuses on the recovery of single component of sulfolane when recovering sulfolane, and other components are treated as waste, which causes waste and harm to the environment.

[0032] The present application is directed to a specific sulfocarbamide waste liquid obtained in the actual production process of the applicant (the waste liquid is obtained in the production of a specific material, and the components in the sulfocarbamide waste liquid are relatively fixed, and the main components in the waste liquid are potassium chloride, sulfocarbamide and moisture. The sulfocarbamide waste liquid treatment method disclosed in the prior art can only realize the recovery of sulfocarbamide, and does not involve the recovery and purification of potassium chloride. In view of this, the applicant proposes a recovery method for sulfocarbamide wastewater containing potassium chloride and a corresponding supporting equipment, which can simultaneously realize the efficient recovery of potassium chloride and sulfocarbamide.

[0033] In the first embodiment of the present application, a recovery method for sulfocarbamide wastewater containing potassium chloride is disclosed, which comprises the following steps:

[0034] The preheated mother liquor of the waste liquid is obtained; the density and conductivity of the preheated liquid are determined to determine the mass percentage of potassium chloride, sulfocarbamide and water therein; the preheated liquid is subjected to falling film evaporation to obtain water vapor and a preliminary treatment liquid; the preliminary treatment liquid is separated to obtain potassium chloride and an evaporation liquid; the evaporation liquid is subjected to secondary condensation to recover sulfocarbamide and water; wherein the falling film evaporation temperature is set according to the mass percentage of potassium chloride; the advantage is to improve the evaporation efficiency and shorten the evaporation time; the mass percentage of potassium chloride in the preliminary treatment liquid is 5%-7%, for example, 5%, 5.5%, 6%, 6.5%, 7%, preferably 5%.

[0035] In the above embodiment, the main components (in terms of mass percentage) of the waste liquid mother liquor are 1-5% of potassium chloride, 35-40% of water and 60-65% of sulfocarbamide; the density and conductivity of the preheated liquid are determined to determine the specific content of the three components in the mother liquor, so as to determine the temperature of the next falling film evaporation.

[0036] The method for determining the specific content of the three components in the waste liquid mother liquor is summarized by the applicant according to a large number of directional determinations. The specific method is as follows: first, the density and conductivity of a plurality of mixtures with known mass percentages of potassium chloride, sulfocarbamide and water are determined to form a standard comparison table; then, the density and conductivity of the waste liquid mother liquor are determined and compared with the standard comparison table to obtain the specific values of each component in the waste liquid mother liquor. Those skilled in the art can obtain the standard comparison table according to the above disclosed specific operation method, and the present application will not be described in detail, only some specific comparison values are disclosed. For example, when the density is 1.2740 g / cm 3 , the conductivity is 0.22130 S / cm, and the mass percentage of each component in the preheated liquid can be determined as follows: water 35.2%, sulfocarbamide 60.3% and potassium chloride 4.5%; when the density is 1.2796 g / cm 3, the conductivity is 0.25581 S / cm, the mass percentage of each component of the preheating liquid can be determined as follows: water 32.5%, sulfocarbamide 62.7%, and potassium chloride 4.8%; when the measured density is 1.2682 g / cm 3 , the conductivity is 0.20977 S / cm, the mass percentage of each component of the preheating liquid can be determined as follows: water 33.0%, sulfocarbamide 63.0%, and potassium chloride 4.0%; when the measured density is 1.2773 g / cm 3 , the conductivity is 0.25471 S / cm, the mass percentage of each component of the preheating liquid can be determined as follows: water 34.0%, sulfocarbamide 61.0%, and potassium chloride 5.0%; when the measured density is 1.2897 g / cm 3 , the conductivity is 0.30585 S / cm, the mass percentage of each component of the preheating liquid can be determined as follows: water 34%, sulfocarbamide 60.0%, and potassium chloride 6.0%.

[0037] It should be noted that the above specific values are determined to confirm the next falling film evaporation temperature, and the specific method for determining the falling film evaporation temperature is as follows: determining a reference value of the mass percentage of potassium chloride, if the mass percentage of potassium chloride in the preheating liquid is lower than the reference value, the falling film evaporation temperature is increased, and if the mass percentage of potassium chloride in the preheating liquid is higher than the reference value, the falling film evaporation temperature is decreased. The reference value of the mass percentage of potassium chloride and the range of the falling film evaporation temperature can be adjusted and determined by a person skilled in the art according to the specific equipment processing capacity, energy consumption, and processing time. The present application only discloses some preferred embodiments. Preferably, the reference value of the mass percentage of potassium chloride is set to 3%, when the content is lower than 3%, the falling film evaporation temperature is 90°C, and when the content is higher than 3%, the falling film evaporation temperature is 87°C. It can be understood that a person skilled in the art can select the reference value of the mass percentage of potassium chloride according to the actual production efficiency and equipment processing capacity, for example, the reference line can also be set to 4%, 4.5%, etc., not higher than 5%. The purpose of setting the reference value of the mass percentage of potassium chloride and the falling film processing temperature in the present application is to maintain the mass percentage of potassium chloride in the range of 5%-7% after falling film processing on the basis of ensuring the falling film processing speed, and to improve the processing efficiency.

[0038] It can be understood that the above falling film evaporation is to retain sulfocarbamide with a larger molecular weight in the preliminary processing liquid through the filtering effect of the molecular film, so as to evaporate only water.

[0039] The above embodiment can realize efficient recovery of potassium chloride and sulfolane in the potassium chloride-containing sulfolane waste liquid, so that the content of sulfolane in the treated waste water is ≤100 mg / L, and the content of potassium chloride is ≤50 mg / L; the purity of the recovered sulfolane is ≥99.8%, the moisture content is ≤0.005%, and the recovery rate is ≥98%; the recovery rate of potassium chloride is ≥98%, and the purity of the obtained potassium chloride meets the requirements of the first-class product of type II in GB6549-2011 "Potassium Chloride".

[0040] In another preferred embodiment, the water vapor obtained by falling film evaporation is used to preheat the waste liquid mother liquor. The water vapor obtained by falling film evaporation contains high heat energy, and its use for preheating the waste liquid mother liquor can preheat the temperature of the waste liquid mother liquor, increase the heating rate and heating time during falling film evaporation, so as to realize the reuse of water vapor, achieve the purpose of providing efficiency and reducing energy consumption.

[0041] In another preferred embodiment, the separation is first heating evaporation of the preliminary treated liquid, precipitation of first potassium chloride, and collection of first evaporation liquid, and then second heating evaporation of the first evaporation liquid, precipitation of second potassium chloride, and collection of second evaporation liquid; the second evaporation liquid is the final evaporation liquid, and the sum of the first potassium chloride and the second potassium chloride is the final potassium chloride.

[0042] In another preferred embodiment, the first heating evaporation temperature is 122-125℃, for example 122℃, 123℃, 124℃, or 125℃, the second heating evaporation starting temperature is 142-145℃, for example 142℃, 143℃, 144℃, or 145℃, and the temperature at the end of evaporation is 192-195℃, for example 192℃, 193℃, 194℃, or 195℃. The advantage is to improve the recovery rate of potassium chloride.

[0043] It can be understood that the above separation can also only include first heating evaporation. When the separation method is first heating evaporation, the heating starting temperature is 122-125℃, for example 122℃, 123℃, 124℃, or 125℃, and the temperature at the end of evaporation is 192-195℃, for example 192℃, 193℃, 194℃, or 195℃. Similarly, it can also achieve the purpose of precipitating potassium chloride and recovering evaporation liquid.

[0044] In another preferred embodiment, the temperature of the first stage condensation is 120-130°C, preferably 120°C, 121°C, 122°C, 123°C, 124°C, 125°C, 126°C, 127°C, 128°C, 129°C, 130°C, and the temperature of the second stage condensation is 50-60°C, for example 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C, 60°C. The sulfolane and water are separated by the second stage condensation, which has the advantage of increasing the recovery of sulfolane.

[0045] In the above embodiments, the components collected by the two stages of condensation are different. The temperature of the evaporated liquid after the second heating is about 190°C, at which time the evaporated liquid contains sulfolane and water. The temperature of the first stage condensation is 120-130°C, at which time the water does not condense, so the first stage condensation is mainly used to collect sulfolane. The temperature of the second stage condensation is reduced to 50-60°C, which is mainly used to collect water. Such a staged condensation increases the purity and yield of sulfolane.

[0046] The second embodiment of the present application relates to a recovery device used for recovering sulfolane waste liquid containing potassium chloride, which can be used to operate any of the above methods.

[0047] Figure 1 A recovery device used for recovering sulfolane waste liquid containing potassium chloride is schematically shown, which includes a plate heat exchanger 1 for preheating, a densimeter 2 and a conductivity meter 3 for determining the content of potassium chloride, sulfolane and water in the preheated liquid, a falling film evaporator 4 for falling film evaporation, a separation device 5 for precipitating potassium chloride and collecting evaporated liquid, and a condenser 6 for second stage condensation. The device is used for recovering sulfolane waste liquid containing potassium chloride, achieving efficient recovery of potassium chloride and sulfolane.

[0048] In another preferred embodiment, the separation device includes a salt precipitation heater I 501, a salt precipitation heater II 502 for collecting precipitated potassium chloride, and an evaporator I 503, an evaporator II 504 for collecting evaporated liquid. The advantage is that the recovery rate of potassium chloride is improved by secondary separation. It can be understood that the separation device can also only include a salt precipitation heater I 501 and an evaporator I 503.

[0049] In another preferred embodiment, the condenser includes a first stage condenser 601 and a second stage condenser 602. The separate collection of sulfolane and water is achieved by staged condensation, which improves the purity and recovery rate of sulfolane.

[0050] In another preferred embodiment, the water vapor evaporated by the falling film evaporator 4 is used as the heat source of the plate and frame heat exchanger 1. The advantage is to reduce energy consumption. The water vapor obtained by falling film evaporation contains high heat energy, and the use of the water vapor for preheating the mother liquor of the waste liquid can preheat the mother liquor of the waste liquid to 50±2℃, shorten the heating time during falling film evaporation, and thus realize the reuse of the water vapor, improve the efficiency, and reduce the energy consumption.

[0051] In another preferred embodiment, the potassium chloride content in the preliminary treatment liquid after evaporation of the falling film evaporator is 5%-7%, and the potassium chloride content >7% will not be conducive to the loosening of the preliminary treatment liquid to the next unit, and will cause the blockage of the delivery port.

[0052] The following will disclose specific embodiments of the present application, and the corresponding examples will prove the technical effects of the present application.

[0053] Embodiment 1

[0054] According to the method of the present application, the mother liquor of the waste liquid is input into the plate and frame heat exchanger 1 through the mother liquor tank for preheating to obtain preheated liquid.

[0055] The preheated liquid is measured by the densimeter 2 and the conductivity meter 3, and the density of the preheated liquid is 1.274 g / cm 3 , the conductivity is 0.2213 S / cm, and the mass percentage of each component in the preheated liquid is determined by the standard control table: water 35.2%, sulfolane 60.3%, and potassium chloride 4.5%.

[0056] The preheated liquid is input into the falling film evaporator 4 for falling film evaporation, the set potassium chloride mass percentage is 3%, the potassium chloride mass percentage in the preheated liquid is 4.5%, the set falling film evaporation temperature is 87℃, the evaporation is carried out until the potassium chloride mass percentage is 5%, the preliminary evaporation liquid and water vapor are obtained, and the water vapor is returned to the plate and frame heat exchanger 1 for preheating.

[0057] The preliminary evaporation liquid is input into the separation device 5, the temperature of the salt separation heater I 501 is set to 123℃, and the heating is continued to 194℃, the potassium chloride is precipitated, and the evaporation liquid is recovered in the evaporator I 503, and at this time, the temperature of the evaporation liquid is about 190℃;

[0058] The evaporation liquid is input into the condenser 6, the temperature of the first-stage condensation 601 is set to 125℃, the sulfolane is condensed and recovered, the temperature of the second-stage condensation 602 is set to 55℃, and the water is condensed and recovered.

[0059] The purity of the sulfolane recovered in this embodiment is 99.85%, the water content is ≤0.005%, and the potassium chloride content is ≤50 mg / L; the sulfolane recovery rate is ≥98%, and the potassium chloride recovery rate is ≥98%. The content of sulfolane in the treated waste water is 68 mg / L, and the content of potassium chloride is 32 mg / L.

[0060] Example 2

[0061] By adopting the method of the present invention, the waste liquid mother liquid is input into the plate-frame heat exchanger 1 through the mother liquid tank for preheating to obtain preheated liquid;

[0062] The density of the preheating liquid was measured by density meter 2 and conductivity meter 3, and the density was 1.2897 g / cm 3 , the conductivity is 0.30585S / cm, and the mass percentages of the components in the preheating liquid are determined by the standard reference table as follows: water 34%, sulfolane 60.0%, potassium chloride 6.0%;

[0063] The preheating liquid is fed into the falling film evaporator 4 for falling film evaporation. The potassium chloride mass percentage benchmark is set to 3%, the potassium chloride mass percentage in the preheating liquid is 6.0%, and the falling film evaporation temperature is set to 87°C. The preheating liquid is evaporated to a potassium chloride mass percentage of 7% to obtain a preliminary evaporated liquid and water vapor. The water vapor is returned to the plate and frame heat exchanger 1 for preheating.

[0064] The preliminary evaporated liquid is input to the separation device 5, the temperature of the salt precipitation heater I 501 is set to 123°C, and it is continuously heated to 195°C to precipitate potassium chloride. The evaporated liquid 1 is recovered in the evaporator I 503, and the evaporated liquid 1 is input to the salt precipitation heater II 502 for heating. The initial temperature is set to 143°C and it is continuously heated to the terminal temperature of 195°C to precipitate potassium chloride. The potassium chloride precipitated twice is combined to obtain the final potassium chloride, and the evaporated liquid is recovered. At this time, the evaporating liquid temperature is about 190°C;

[0065] The evaporating liquid is input to the condenser 6, set the primary condensation temperature 601 to 128 ℃, condensation recovery sulfolane, and then set the secondary condensation temperature 602 to 52 ℃, condensation recovery water;

[0066] The sulfolane recovered in this embodiment has a purity of 99.84%, a moisture content of ≤0.005%, and a chloride content of ≤50 mg / L. The sulfolane recovery rate is ≥98%, and the potassium chloride recovery rate is ≥98%. The sulfolane content in the treated wastewater is 67 mg / L, and the potassium chloride content is 35 mg / L.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for recovering sulfolane waste liquid containing potassium chloride, the method comprising the following steps: preheating the waste liquid mother liquor to obtain a preheated liquid; The density and conductivity of the preheating liquid are measured to determine the mass percentages of potassium chloride, sulfolane and water therein; The preheated liquid is subjected to falling film evaporation to obtain water vapor and preliminary treatment liquid; Separating the preliminary treated liquid to obtain potassium chloride and evaporation liquid; The evaporated liquid is subjected to secondary condensation to recover sulfolane and water; in, The falling film evaporation temperature is set according to the mass percentage of potassium chloride; The mass percentage of potassium chloride in the preliminary treatment liquid is 5%-7%; The separation comprises performing a first heating evaporation on the preliminary treatment liquid to precipitate a first potassium chloride, collecting the first evaporated liquid, and then performing a second heating evaporation on the first evaporated liquid to precipitate a second potassium chloride, and collecting the second evaporated liquid; the second evaporated liquid is the final evaporated liquid, and the first potassium chloride and the second potassium chloride precipitated by the two heating evaporations are combined to obtain the final precipitated potassium chloride; The first heating evaporation temperature is 122-125°C, the second heating evaporation starting temperature is 142-145°C, and the heating is continued. The temperature at the end of evaporation is 192-195°C.

2. The recycling method according to claim 1, wherein: The water vapor obtained by the falling film evaporation is used to preheat the waste liquid mother liquor.

3. The recycling method according to claim 1, wherein: In the two-stage condensation, the temperature of the first stage condensation is 120-130°C, and the temperature of the second stage condensation is 50-60°C.

4. An apparatus for operating the method according to any one of claims 1 to 3, the apparatus comprising a plate and frame heat exchanger (1) for preheating, a density meter (2) and a conductivity meter (3) for determining the contents of potassium chloride, sulfolane and water in the preheating liquid; a falling film evaporator (4) for falling film evaporation, a separation device (5) for precipitating potassium chloride and collecting evaporated liquid, and a condenser (6) for secondary condensation.

5. The device according to claim 4, wherein: The separation device comprises a salt precipitation heater I (501) and a salt precipitation heater II (502) for collecting precipitated potassium chloride, and an evaporator I (503) and an evaporator II (504) for collecting evaporated liquid.

6. The device according to claim 4, wherein: The condenser includes a primary condenser (601) and a secondary condenser (602).

7. The device according to claim 4, wherein: The water vapor evaporated by the falling film evaporator (4) is transported to the plate and frame heat exchanger (1) as its heat source.

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