Wastewater purification methods

Abstract

A wastewater purification method is provided, comprising: supplying a mixed stream to a first tower, wherein the mixed stream comprises wastewater containing water, nitrile monomers and ammonia, and an acid component; condensing the upper discharge stream of the first tower, supplying the condensed stream to a decanter to separate the condensed stream into an aqueous layer and an organic layer, and supplying the components of the organic layer to a second tower; separating by-products from the lower discharge stream of the second tower, and recovering nitrile monomers from the upper discharge stream of the second tower.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2021-0158835, filed on November 17, 2021, and Korean Patent Application No. 10-2022-0081416, filed on July 1, 2022, the entire contents of which are incorporated herein by reference as a part of this specification. Technical Field

[0004] This invention relates to a wastewater purification method, and more particularly, to a method for recovering reusable components from wastewater and reducing the total nitrogen content in wastewater transferred to a wastewater treatment plant during a purification step at the end of a polymerization reaction using nitrile monomers. Background Technology

[0005] Typically, nitrile rubbers can be obtained by using nitrile monomers to manufacture homopolymer or copolymer latexes containing units derived from nitrile monomers. An example of nitrile rubber may include acrylonitrile-butadiene copolymer latexes manufactured by copolymerizing acrylonitrile and 1,3-butadiene.

[0006] The nitrile rubber can be manufactured by emulsion polymerization, which can be a method of polymerizing monomers in solution using a medium. Emulsion polymerization of nitrile rubber can be carried out, for example, using water as a medium, and by adding nitrile monomers alone or by further adding additional monomers for copolymerization with the nitrile monomers, thereby producing homopolymer or copolymer latex comprising units from nitrile monomers.

[0007] After polymerization, the homopolymer or copolymer latex, including units from nitrile monomers, is transferred to a sludge tank. Unreacted material and water may evaporate to the top of the sludge tank and be transferred to a wastewater tank.

[0008] Simultaneously, ammonia is added to the wastewater tank to adjust the pH of the latex, and it can partially evaporate along with the water to the upper part and be transferred to the wastewater tank. In this case, in the wastewater tank, 2 moles of unreacted nitrile monomers react with 1 mole of ammonia to produce trimers, resulting in the loss of nitrile monomers.

[0009] Furthermore, the wastewater remaining after recovering nitrile monomers from the wastewater is transferred to a wastewater treatment plant. Here, because the total nitrogen (TN) content in the wastewater transferred to the treatment plant is very high, a significant amount of money must be invested in wastewater treatment, resulting in a substantial loss in the price competitiveness of latex products under stricter environmental regulations. Summary of the Invention

[0010] Technical issues

[0011] One object of the present invention is to provide a method that can prevent the loss of unreacted nitrile monomers during the manufacturing process of homopolymer or copolymer latex containing nitrile monomer units and reduce the total nitrogen content in wastewater transferred to wastewater treatment plants, thereby solving the problems mentioned in the background art.

[0012] Technical solution

[0013] In one general aspect, the wastewater purification method includes: supplying a mixed stream to a first tower, wherein wastewater comprising water, nitrile monomers, and ammonia is mixed with an acid component; condensing the upper discharge stream of the first tower to form a condensed stream; supplying the condensed stream to a decanter to separate the condensed stream into an aqueous layer and an organic layer; and supplying the components of the organic layer to a second tower; separating byproducts from the lower discharge stream of the second tower; and recovering nitrile monomers from the upper discharge stream of the second tower.

[0014] Beneficial effects

[0015] The wastewater purification method according to the present invention can reduce the loss of unreacted nitrile monomers and can recover and reuse the nitrile monomers during the manufacturing process of homopolymer or copolymer latex containing nitrile monomer units, thereby improving cost competitiveness.

[0016] In addition, it effectively reduces the total nitrogen content in the purified wastewater delivered to the wastewater treatment plant, thereby reducing the cost of wastewater treatment in the wastewater treatment plant, and improving the price competitiveness of latex products under stricter environmental regulations, thereby improving business sustainability and achieving the effects of reducing carbon emissions and carbon taxes. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of a wastewater purification method according to an exemplary embodiment of the present invention.

[0018] Figure 2 and 3 These are process flow diagrams based on the wastewater purification methods in the comparative examples. Detailed Implementation

[0019] The terms and words used in the specification and claims of this invention should not be construed as having a general or dictionary meaning, but should be interpreted as having a meaning and concept that satisfies the technical concept of the invention, based on the inventors' ability to properly define the concepts of the terms in order to best describe the principles of their own invention.

[0020] The term "flow" in this invention can refer to a fluid flow in a process, or it can refer to the fluid itself flowing in a pipe. Specifically, the flow can refer to the fluid itself flowing in the pipes connecting each device, as well as the fluid flow. Furthermore, the fluid can include any one or more components of gas, liquid, and solid.

[0021] In the following text, reference will be made to Figure 1 The invention will be described in more detail in order to provide a better understanding of it.

[0022] According to the present invention, a wastewater purification method is provided. More specifically, the method may include: supplying a mixed stream to a first tower, wherein the mixed stream comprises wastewater containing water, nitrile monomers, and ammonia, and an acid component; condensing the upper discharge stream of the first tower to form a condensed stream, supplying the condensed stream to a decanter to separate the condensed stream into an aqueous layer and an organic layer, and supplying the components of the organic layer to a second tower; separating by-products from the lower discharge stream of the second tower, and recovering nitrile monomers from the upper discharge stream of the second tower.

[0023] According to an exemplary embodiment of the present invention, wastewater may be generated by a manufacturing process of a homopolymer or copolymer latex comprising units derived from nitrile monomers. Specifically, the manufacturing process of a homopolymer or copolymer latex comprising units derived from nitrile monomers may include a polymerization step and a purification step.

[0024] The polymerization step can be carried out via emulsion polymerization. In emulsion polymerization, water can be used as a medium, and polymerization can be carried out by adding a nitrile monomer alone or by adding an additional monomer for copolymerization with the nitrile monomer. For example, the additional monomer may include a conjugated diene monomer.

[0025] The nitrile monomer may include one or more selected from acrylonitrile, methacrylonitrile, fumaronitrile, α-chloronitrile, and α-cyanoethyl acrylonitrile. As a specific example, the nitrile monomer may be acrylonitrile.

[0026] The conjugated diene monomer may include one or more selected from 1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 1,3-pentadiene, and isoprene. As a specific example, the conjugated diene monomer may be 1,3-butadiene.

[0027] This purification step can be a step of separating unreacted material and water from the homopolymer or copolymer latex containing nitrile monomer units after polymerization is completed. Specifically, after polymerization is completed, the homopolymer or copolymer latex containing nitrile monomer units is transferred to a sludge tank, and in the sludge tank, unreacted material and water can evaporate to the top and be transferred to wastewater tank 10.

[0028] Ammonia should be added to the wastewater tank to adjust the pH of the latex. However, during the evaporation of unreacted material and water and their transfer to wastewater tank 10, some ammonia evaporates along with the water and is introduced into wastewater tank 10. This causes 2 moles of unreacted nitrile monomers to react with 1 mole of ammonia in wastewater tank 10 to produce a trimer called 3,3-iminodipropionitrile, resulting in the loss of nitrile monomers.

[0029] Furthermore, after recovering nitrile monomers from wastewater, the remaining wastewater is transferred to wastewater treatment plants. Since trimers typically account for the majority of the total nitrogen content in wastewater, and the total nitrogen content in the wastewater transferred to wastewater treatment plants is very high, a significant amount of money must be invested in wastewater treatment at these plants. Under stricter environmental regulations, the price competitiveness of latex products is reduced.

[0030] Therefore, the present invention aims to provide a method for minimizing the loss of unreacted nitrile monomers and the total nitrogen content in wastewater, thereby reducing the cost of wastewater treatment and improving the price competitiveness of latex products.

[0031] According to an exemplary embodiment of the present invention, wastewater comprising water, nitrile monomers, and ammonia can be supplied to the wastewater tank 10 via wastewater transfer line 11. Furthermore, acid components can be added to the wastewater tank 10 via acid component transfer line 12. The type of acid component is not particularly limited and may include, for example, one or more selected from acetic acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, and cyanic acid. As a specific example, the acid component may be acetic acid.

[0032] A mixed stream comprising water, nitrile monomers and ammonia, can be discharged from wastewater tank 10 and mixed with acid components, and the mixed stream can be supplied to first tower 20.

[0033] The mixed stream can be in a state where wastewater and acidic components are mixed to lower the pH of the wastewater. For example, the pH of the mixed stream can be above 1.5, above 2.5, above 3.5 and below 4.5, below 5, or below 5.5. By adjusting the pH of the mixed stream to the above range, ammonia (NH3) in the mixed stream can be converted into ammonium salt (NH4). + This prevents the formation of trimers due to side reactions between nitrile monomers and ammonia, thereby reducing the loss of nitrile monomers. Furthermore, since trimers of these nitrile monomers constitute a large portion of the total nitrogen content in wastewater, purified wastewater with reduced total nitrogen content by preventing trimer formation can be transferred to a wastewater treatment plant.

[0034] According to an exemplary embodiment of the present invention, a mixed stream can be supplied to a first column 20. In the first column 20, the components of the mixed stream are separated by distillation, with nitrile monomers and byproducts contained in the mixed stream separated to the upper part, and the remaining components separated to the lower part. Here, the byproducts may include dimers of nitrile monomers. Furthermore, the remaining component separated to the lower part of the first column 20 is purified wastewater, and a portion of this component can be heated in a common reboiler 23 and refluxed back to the first column 20, while the remainder can be transferred to a wastewater treatment plant.

[0035] The upper discharge stream from the first column 20 can be condensed in the condenser 21 and subsequently supplied to the decanter 22. Flare gas is discharged from the decanter, and the condensed upper discharge stream from the first column 20 (the condensed stream) can be separated into an aqueous layer and an organic layer. The aqueous layer component separated in the decanter 22 is purified wastewater and can be transferred to a wastewater treatment plant.

[0036] By preventing the formation of trimers of nitrile monomers and separating nitrile monomers and nitrile monomer dimers in the wastewater in the first tower 20, the total nitrogen content in the purified wastewater transferred to the wastewater treatment plant can be reduced. For example, the ratio of the total nitrogen content in the purified wastewater to the total nitrogen content in the wastewater can be 0.25 or more, 0.3 or more, 0.35 or more and 0.5 or less, or 0.55 or less.

[0037] The operating temperature of the first column 20 can be above 80°C, above 90°C, or above 95°C but below 100°C, below 110°C, or below 130°C. Furthermore, the operating pressure of the first column 20 can be above 0.5 bar, above 0.7 bar, or above 0.9 bar but below 1.5 bar, below 2 bar, or below 3 bar. By controlling the operating conditions of the first column 20 within the above ranges, nitrile monomers can be effectively separated to the upper part.

[0038] According to an exemplary embodiment of the present invention, the organic layer components separated from the decanter 22 may include byproducts and nitrile monomers, and may be supplied to a second column 30 to separate the nitrile monomers from the byproducts.

[0039] The second column 30 can separate nitrile monomers and byproducts containing nitrile dimers from the organic layer components separated in the decanter 22 by distillation. Specifically, the nitrile monomers can be recovered from the upper discharge stream, and the byproducts can be separated as the lower discharge stream of the second column 30.

[0040] According to an exemplary embodiment of the present invention, a portion of the lower discharge stream of the second tower 30 can be returned to the second tower 30 via heat exchanger 33, and the remainder of the stream can be discharged.

[0041] The heat exchanger 33 can be, for example, a shell-and-tube heat exchanger. A shell-and-tube heat exchanger can be formed by a cylindrical body, a tubular tube disposed at the center of the body and carrying fluid, and a shell surrounding the tube. The refrigerant or heat medium supplied to the shell can flow while simultaneously contacting the fluid carried through the tube via the outer wall of the tube and exchanging heat with the fluid carried through the tube. Specifically, the lower discharge stream of the second tower 30 is supplied to the tube of the heat exchanger 33 and moves from the inlet to the outlet of the tube. Here, the heat source supplied to the shell moves from the inlet to the outlet of the shell and can exchange heat with the lower discharge stream of the second tower 30 moving in the tube within the outer wall of the tube. Thus, the lower discharge stream of the second tower 30 supplied to the tube can be heated by the heat source in the shell and returned to the second tower 30.

[0042] Simultaneously, when the lower discharge stream of the second tower 30 passes through the heat exchanger 33, the polymerization reaction of the nitrile monomers contained in the lower discharge stream passing through the tube can occur using the heat supplied by the heat source passing through the shell. The polymer produced by the polymerization reaction may cause scaling, in which some of the polymer precipitates and accumulates in the tube. Since scaling hinders the smooth flow of fluid, it adversely affects the entire process.

[0043] Therefore, in this invention, the operating conditions of the second tower 30 and the heat exchanger 33 are controlled, thereby suppressing scaling that occurs in the heat exchanger 33, which allows for stable operation to reduce cleaning time and cost.

[0044] The temperature of the heat source supplied to the shell of heat exchanger 33 can be, for example, above 60°C, above 65°C, or above 70°C and below 80°C, below 85°C, or below 90°C. When the temperature of the heat source is too high, polymerization of nitrile monomers may occur in the outer wall of the pipe through which the discharge stream moves in the lower part of the second tower 30 due to localized temperature rise and the resulting polymer polymerization. Conversely, when the temperature of the heat source is too low, the formation of polymer polymerization can be suppressed, but the size of the heat exchanger required for sufficient heat exchange is increased. This heat source can be, for example, hot water.

[0045] Meanwhile, as described above, a portion of the lower discharge stream from the second tower 30 can be refluxed back to the second tower 30 via the heat exchanger 33, and the remainder of the stream can be discharged. In the reflux pipe that passes through the heat exchanger 33 and refluxes back to the second tower 30, scaling caused by the polymerization of nitrile monomers may occur. To prevent this, the fluid flowing in the reflux pipe must be kept in a liquid state. If the lower discharge stream from the second tower 30, which is in a liquid state in the reflux pipe, is partially evaporated, the polymerization reaction of nitrile monomers at the liquid-gas interface may be accelerated, causing scaling. Therefore, it is necessary to maintain the pressure in the reflux pipe above a certain level.

[0046] Therefore, the pressure in the return line can be maintained above 0.5 bar, above 1 bar, or above 1.5 bar and below 2.5 bar, below 3.0 bar, or below 3.5 bar. Furthermore, to control the pressure range in this way, in an exemplary embodiment of the invention, a pressure regulating valve can be provided in the return line.

[0047] The temperature of the lower part of the second tower 30 can be above 20°C, above 25°C, above 30°C and below 35°C, below 40°C, or below 45°C. By maintaining the temperature of the lower part of the second tower 30 within the above range, the polymerization reaction of nitrile monomers caused by heat can be suppressed, thereby preventing scaling of the heat exchanger.

[0048] The content of nitrile monomers in the lower discharge stream of the second column 30 can be 5% or more by weight, 10% or more by weight, or 15% or more and 20% or less by weight, 30% or less by weight, or 40% or less by weight. Specifically, within the above ranges, a portion of the nitrile monomers can flow out to the lower discharge stream of the second column 30, and in this case, the temperature of the lower part of the second column 30 can be easily maintained.

[0049] According to an exemplary embodiment of the invention, the upper discharge stream of the second column 30 can be condensed in the condenser 31 and subsequently supplied to the reflux tank 32. The upper discharge stream of the second column 30, which has already been condensed in the condenser 31, discharges flare gas to the upper part of the reflux tank 32, and a portion of the lower discharge stream, including nitrile monomers, is returned to the second column 30. The remainder is recovered and can be reused in the polymerization step of the manufacturing process of homopolymers or copolymer latexes containing nitrile monomer units.

[0050] The operating pressure of the second tower 30 can be above 0.15 bar, above 0.2 bar, or above 0.25 bar and below 0.4 bar, below 0.45 bar, or below 0.5 bar. For example, when the operating pressure of the second tower 30 is below the above range, condensation in the condenser 31 may not proceed well, and when the operating pressure is above the above range, the temperature also rises, and thus scaling due to polymers formed by the polymerization of nitrile monomers may occur in the heat exchanger and reflux pipe.

[0051] According to an exemplary embodiment of the present invention, in this wastewater purification method, if necessary, devices such as distillation columns, condensers, reboilers, valves, pumps, separators and mixers may be further installed.

[0052] In the foregoing, the wastewater purification method according to the present invention is described and illustrated in the accompanying drawings. However, the descriptions and illustrations in the drawings are merely for the purpose of understanding the core structure of the present invention, and there are no separately described and illustrated methods and apparatuses that can be suitably applied and used to implement the wastewater purification method according to the present invention, apart from the methods and apparatuses described and illustrated in the foregoing and the accompanying drawings.

[0053] The invention will be described in more detail below by way of examples. However, the following examples are provided to illustrate the invention, and it will be apparent to those skilled in the art that various modifications and changes can be made without departing from the scope and spirit of the invention, and the scope of the invention is not limited thereto.

[0054] Example

[0055] Example 1

[0056] according to Figure 1 The process flow diagram shown illustrates the purification of wastewater discharged during the manufacturing process of acrylonitrile-butadiene copolymer latex.

[0057] Specifically, wastewater (comprising water, acrylonitrile monomer, and ammonia, with a pH of 8) is supplied to wastewater tank 10 via wastewater transfer line 11. Acetic acid is added to wastewater tank 10 via acid component transfer line 12, and the mixed stream discharged from wastewater tank 10 is supplied to the first tower 20. At this point, the total nitrogen content of the wastewater is confirmed to be 6,000 ppm, the pH of the mixed stream is 5.5, and the total nitrogen content is measured using a commercially available total nitrogen (TN) measuring device.

[0058] The upper discharge stream from the first column 20 is condensed in condenser 21 and supplied to decanter 22, where flare gas is discharged. The stream is separated into an aqueous layer and an organic layer. The organic layer component is transferred to the second column 30, while the aqueous layer component is transferred to a wastewater treatment plant as purified wastewater. Furthermore, a portion of the lower discharge stream from the first column 20 is heated using reboiler 23 and subsequently refluxed, with the remainder transferred to a wastewater treatment plant as purified wastewater. At this point, the operating temperature of the first column 20 is 90°C, and the operating pressure is adjusted to 1 bar. Additionally, the total nitrogen content in the purified wastewater is confirmed to be 3,000 ppm.

[0059] The upper discharge stream of the second column 30 is condensed in condenser 31 and then supplied to reflux tank 32. Flare gas is discharged from reflux tank 32, and a portion of the lower discharge stream is refluxed. Nitrile monomers are recovered and reused from the remaining portion. Furthermore, a portion of the lower discharge stream of the second column 30 passes through heat exchanger 33 and is refluxed back to the second column 30, where byproducts are separated from the remaining portion. At this time, the nitrile monomer content in the lower discharge stream of the second column 30 is adjusted to 15% by weight, and the temperature of the warm water supplied to the shell of heat exchanger 33 is 90°C. Additionally, the operating pressure of the second column 30 is adjusted to 0.3 bar, and the temperature at the bottom is maintained at 45°C.

[0060] In this case, scaling in heat exchanger 33 and condenser 31 was suppressed to extend the washing cycle, and the acrylonitrile recovery rate, calculated by the ratio of the acrylonitrile monomer recovered from the upper discharge stream of the second tower 30 to the acrylonitrile monomer content in the wastewater supplied to wastewater tank 10, was confirmed to be 99.9%.

[0061] Example 2

[0062] The operation was carried out in the same manner as in Example 1, except that the content of nitrile monomers in the lower discharge stream of the second tower 30 was controlled to 10% by weight, and the temperature of the lower part of the second tower 30 was controlled to 50°C.

[0063] In this case, it was confirmed that scaling in the heat exchanger 33 was promoted compared to Example 1, thereby shortening the washing cycle.

[0064] Example 3

[0065] The operation is carried out in the same manner as in Example 1, except that the temperature of the warm water supplied to the shell of the heat exchanger 33 is adjusted to 100°C.

[0066] In this case, it was also confirmed that scaling in the heat exchanger 33 was promoted compared to Example 1, thereby shortening the washing cycle.

[0067] Example 4

[0068] The operation is carried out in the same manner as in Example 1, except that the operating pressure of the second tower 30 is controlled at 0.1 bar.

[0069] In this situation, the upper discharge stream of the second tower 30 is not well condensed in the condenser 31, thereby increasing the amount of nitrile monomers lost when the flare gas is discharged from the reflux tank 32.

[0070] Example 5

[0071] The operation was carried out in the same manner as in Example 1, except that the operating pressure of the second tower 30 was controlled at 0.7 bar.

[0072] In this case, it was confirmed that scaling in the condenser 31 was promoted compared to Example 1, thereby shortening the washing cycle.

[0073] Comparative example

[0074] Comparative Example 1

[0075] according to Figure 2 The process flow diagram shown illustrates the purification of wastewater discharged during the manufacturing process of acrylonitrile-butadiene copolymer latex.

[0076] Specifically, wastewater (which includes water, acrylonitrile monomer, and ammonia, and has a pH of 8) is supplied to wastewater tank 10 via wastewater transmission pipeline 11. The wastewater is then discharged from wastewater tank 10 and supplied to the first tower 20. At this point, the total nitrogen content of the wastewater is confirmed to be 6,000 ppm.

[0077] The upper discharge stream from the first column 20 is condensed in condenser 21 and supplied to decanter 22, where flare gas is discharged. The stream is separated into an aqueous layer and an organic layer. Acrylonitrile is recovered from the organic layer component, and the aqueous layer component is transferred to a wastewater treatment plant as purified wastewater. Furthermore, a portion of the lower discharge stream from the first column 20 is heated using reboiler 23 and subsequently refluxed, with the remainder transferred to a wastewater treatment plant as purified wastewater. At this time, the operating temperature of the first column 20 is 90°C, and the operating pressure is adjusted to 1 bar. Moreover, the total nitrogen content of the purified wastewater is confirmed to be 5,000 ppm, and the acrylonitrile recovery rate, calculated as the ratio of the acrylonitrile monomer content recovered from the organic layer component in decanter 22 to the acrylonitrile monomer content in the wastewater supplied to wastewater tank 10, is confirmed to be 30%.

[0078] Furthermore, since the dimer components of nitrile monomers, in addition to acrylonitrile, are also mixed in the organic layer components, the recycled feed stream cannot be reused in the polymerization process.

[0079] Comparative Example 2

[0080] according to Figure 3 The process flow diagram shown illustrates the purification of wastewater discharged during the manufacturing process of acrylonitrile-butadiene copolymer latex.

[0081] Specifically, the procedure is carried out in the same manner as in Example 1, except that acetic acid is not added to wastewater tank 10.

[0082] In this case, the total nitrogen content of the purified wastewater was confirmed to be 5,000 ppm, and the acrylonitrile recovery rate, calculated by the ratio of the content of acrylonitrile monomer recovered from the upper discharge stream of the second tower 30 to the content of acrylonitrile monomer contained in the wastewater supplied to the wastewater tank 10, was confirmed to be 30%.

Claims

1. A wastewater purification method, comprising: The mixed stream is supplied to the first tower, the mixed stream being obtained by mixing wastewater comprising water, nitrile monomers and ammonia with an acid component; The material discharged from the upper part of the first condenser column forms a condensed material stream, which is supplied to a decanter to separate the condensed material stream into an aqueous layer and an organic layer. The components of the organic layer are then supplied to the second column. Byproducts are separated from the lower discharge stream of the second tower, and nitrile monomers are recovered from the upper discharge stream of the second tower. The first tower operates at a pressure of 0.5 bar to 3.0 bar and at a temperature of 80°C to 130°C. The operating pressure of the second tower is 0.15 bar to 0.5 bar. The temperature at the bottom of the second tower is between 20°C and 45°C. The pH of the mixture flow is between 1.5 and 5.

5.

2. The wastewater purification method according to claim 1, wherein, The lower discharge stream from the first tower and the components of the water layer from the decanter are transferred to the wastewater treatment plant as purified wastewater.

3. The wastewater purification method according to claim 1, wherein, The acid component includes one or more selected from acetic acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, and cyanic acid.

4. The wastewater purification method according to claim 1, wherein, The content of nitrile monomers in the lower discharge stream of the second tower is 5% to 40% by weight.

5. The wastewater purification method according to claim 1, wherein, A portion of the discharge stream from the lower part of the second tower passes through a heat exchanger and is returned to the second tower, while byproducts are separated as the remainder of the stream.

6. The wastewater purification method according to claim 5, wherein, A portion of the discharge stream from the lower part of the second tower passes through the tubes of the heat exchanger, and The temperature of the heat source supplied to the shell of the heat exchanger is 60°C to 90°C.

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