Method and device for recovering bromine and sodium from PTA tail gas treatment waste liquid

Abstract

The present invention provides a method and device for recovering bromine and sodium elements from PTA tail gas treatment waste liquid, relates to the technical field of terephthalic acid oxidation waste liquid treatment, and solves the technical problem that PTA waste liquid in the prior art is only discharged through sulfuric acid neutralization and biochemical treatment, which easily causes the loss of high-value materials such as sodium bicarbonate, sodium carbonate and sodium bromide. The recovery method includes concentrating the pretreated waste liquid to form a concentrated liquid; adjusting the pH value of the concentrated liquid to alkaline and evaporating and crystallizing it to obtain sodium carbonate crystals and / or sodium bicarbonate crystals; subjecting the mother liquor after evaporation and crystallization to special nanofiltration treatment to obtain a sodium bromide desalinated water solution; concentrating the sodium bromide desalinated water solution to obtain a high-concentration sodium bromide solution for subsequent evaporation and crystallization or bromine extraction treatment. The present invention can recover the solute in the waste liquid and convert it into a product salt with high economic value, and the remaining waste liquid is also more conducive to subsequent treatment and discharge.

Description

Technical Field

[0001] The invention relates to the technical field of terephthalic acid oxidation waste liquid treatment, and in particular to a method and device for recovering bromine and sodium elements from PTA tail gas treatment waste liquid. Background Art

[0002] PTA (terephthalic acid) is an important chemical raw material, and its production process includes two processes: oxidation and refining. In the oxidation process, the raw material PX (paraxylene) is oxidized, acetic acid is used as a solvent, cobalt acetate and manganese acetate are used as catalysts, and bromide is used as a co-catalyst. After appropriate treatment of the PTA oxidation tail gas, a tail gas treatment waste liquid containing a large amount of sodium bicarbonate and sodium carbonate, sodium bromide, sodium acetate, organic matter and other impurities is obtained.

[0003] At present, this PTA waste liquid cannot be discharged directly because it contains a large amount of pollutants. Instead, it needs to be neutralized by adding a large amount of sulfuric acid and then sent to the biochemical system for treatment to meet the discharge standards. The treatment of PTA tail gas waste liquid mainly stays in the stage of pre-treatment + conditioning + biochemical treatment. This treatment method can meet the national emission standards except bromine. Only appropriate treatment to meet the discharge standards will result in the loss of a large amount of recyclable high-value materials in the waste liquid. PTA waste liquid contains a large amount of sodium bicarbonate, sodium carbonate, sodium bromide and other substances with great economic value. Through appropriate process technology, these substances in the wastewater can be extracted, which can not only obtain considerable economic value, but also reduce energy consumption and reduce carbon dioxide emissions and other environmental benefits. Taking a PTA production unit with an annual output of 2.5 million tons as an example, the tail gas treatment waste liquid generated is about 210m 3 / h, which contains about 4.5 tons of sodium carbonate / sodium bicarbonate and about 0.35 tons of sodium bromide. The economic value of these two items alone exceeds 100 million yuan per year. At the same time, it can reduce the consumption of 33,000 tons of sulfuric acid and the emission of 15,000 tons of carbon dioxide each year.

[0004] Therefore, how to solve the technical problem that PTA waste liquid is discharged only through sulfuric acid neutralization and biochemical treatment in the prior art, which easily causes the loss of high-value materials such as sodium bicarbonate, sodium carbonate and sodium bromide, has become an important technical problem that people in this field need to solve. Summary of the invention

[0005] The object of the present invention is to provide a method and device for recovering bromine and sodium from PTA tail gas treatment waste liquid, which solves the technical problem that PTA waste liquid is discharged only through sulfuric acid neutralization and biochemical treatment in the prior art, which easily causes the loss of high-value materials such as sodium bicarbonate, sodium carbonate and sodium bromide. The preferred technical scheme among the many technical schemes provided by the present invention can produce many technical effects as described below.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The method for recovering bromine and sodium from PTA tail gas treatment waste liquid provided by the present invention comprises:

[0008] Step S1: Concentrating the pretreated waste liquid to form a concentrated liquid;

[0009] Step S2: adjusting the pH value of the concentrated solution to an alkaline state and subjecting the concentrated solution to evaporation and crystallization to obtain sodium carbonate crystals and / or sodium bicarbonate crystals;

[0010] Step S3: subjecting the mother liquor after evaporation and crystallization in step S2 to a special nanofiltration treatment to obtain a sodium bromide desalinated water solution;

[0011] Step S4: Concentrating the sodium bromide freshwater solution in step S3 to obtain a high-concentration sodium bromide solution for subsequent evaporation crystallization or bromine extraction treatment.

[0012] Furthermore, in step S1, the concentration treatment is an electrodialysis treatment, and the electrodialysis treatment includes a primary concentration electrodialysis and a secondary concentration electrodialysis. The concentrated liquid of the primary concentration electrodialysis enters the secondary concentration electrodialysis for treatment, the desalinated liquid of the secondary concentration electrodialysis is returned to the primary concentration electrodialysis for re-treatment, and the desalinated liquid of the primary concentration electrodialysis is sent to a biochemical system for treatment.

[0013] Furthermore, in step S3, before the mother liquor enters the special nanofiltration treatment, step S301 is also included: diluting the mother liquor and adjusting its pH value to an acidic state.

[0014] Furthermore, in step S4, the concentration treatment is a reverse osmosis treatment and / or an electrodialysis treatment, and the produced water of the concentration treatment is returned to the mother liquor in step S301 to be mixed and diluted with the mother liquor.

[0015] Furthermore, in the step S2, the pH value of the concentrated solution is adjusted by adding a strong alkaline substance to adjust the pH value of the concentrated solution to be greater than 10; in the step S301, the pH value of the mother solution is adjusted by adding an acidic substance to adjust the pH value of the mother solution to 3.5-5.

[0016] Furthermore, in step S1, the pretreatment includes softening and filtering treatment, iron and manganese removal treatment and ion exchange treatment.

[0017] The device for recovering bromine and sodium from PTA tail gas treatment waste liquid provided by the present invention is based on the above-mentioned method for recovering bromine and sodium from PTA tail gas treatment waste liquid, and comprises: a first concentration component, used for concentrating the waste liquid; a first evaporation crystallizer, used for evaporating and crystallizing sodium carbonate and / or sodium bicarbonate; a special nanofiltration component, used for separating sodium bromide from the mother liquor output by the first evaporation crystallizer; a second concentration component, used for concentrating the sodium bromide desalination solution; wherein the first concentration component, the first evaporation crystallizer, the special nanofiltration component and the second concentration component are all connected in sequence.

[0018] Furthermore, it also includes a mother liquid tank and a decarbonization tower for diluting and adjusting the pH value of the mother liquid output by the first evaporation crystallizer, the inlet of the mother liquid tank is connected to the mother liquid outlet of the first evaporation crystallizer, the outlet of the mother liquid tank is connected to the decarbonization tower, a defecation port is provided on the mother liquid tank or on the outlet pipeline of the mother liquid tank, and the liquid outlet of the decarbonization tower is connected to the special nanofiltration component.

[0019] Furthermore, the first concentration component includes a primary electrodialyzer and a secondary electrodialyzer which are arranged in communication with each other, and the desalinated liquid outlet of the secondary electrodialyzer is provided with a second reflux pipe which is in communication with the inlet of the primary electrodialyzer.

[0020] Furthermore, the second concentration component includes a reverse osmosis component and / or an electrodialysis component, and the water output outlet of the reverse osmosis component and / or the electrodialysis component is provided with a first reflux pipe connected to the mother liquid tank.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The method for recovering bromine and sodium from PTA tail gas treatment waste liquid provided by the present invention is to first concentrate the solute in the waste liquid, and then treat the concentrated high-salt waste liquid by evaporation and crystallization, so that a large amount of sodium carbonate and / or sodium bicarbonate in the waste liquid can be crystallized to achieve the purpose of recovery. Moreover, the mother liquor formed after evaporation and crystallization contains a large amount of high-value sodium bromide. Sodium bromide can be separated from the mother liquor by special nanofiltration treatment to obtain a sodium bromide desalinated water solution. After further concentration, the high-concentration sodium bromide solution can be directly subjected to bromine extraction or evaporation and crystallization, so as to obtain a high-value and high-purity sodium bromide product. The present invention can recover most of the solutes in the waste liquid and convert them into sodium carbonate and / or sodium bicarbonate product salts and sodium bromide product salts with high economic value, recover more than 90% of the salt, and convert the remaining waste liquid into easily treatable low-salt waste water. The treated desalinated liquid is more conducive to subsequent biochemical system treatment due to the reduced salt content, and the residual bromine concentration in the waste water can also meet the standard, so that the overall waste water can be fully discharged or reused after proper treatment. The present invention can not only recover components with economic value in PTA oxidation tail gas treatment waste liquid and achieve high economic value, but also reduce the consumption of sulfuric acid and the emission of carbon dioxide in the traditional treatment process of PTA oxidation tail gas treatment waste liquid, and has the environmental protection significance of turning waste into treasure, saving energy and reducing emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 It is a schematic flow diagram of a method for recovering bromine and sodium from PTA tail gas treatment waste liquid provided by an embodiment of the present invention;

[0025] Figure 2 It is a schematic diagram of the overall structure of a device for recovering bromine and sodium elements from PTA tail gas treatment waste liquid provided by an embodiment of the present invention;

[0026] Figure 3 is a schematic structural diagram of a first evaporation crystallizer provided in an embodiment of the present invention;

[0027] Figure 4 It is a schematic structural diagram of a second evaporation crystallizer provided in an embodiment of the present invention.

[0028] In the figure, 1-the first concentration component; 2-the first evaporation crystallizer; 3-the special nanofiltration component; 4-the second concentration component; 5-the mother liquor tank; 6-the decarbonization tower; 7-the first electrodialyzer; 8-the second electrodialyzer; 9-the second reflux pipe; 10-the first reflux pipe; 11-the flash tank; 12-the circulation pump; 13-the forced circulation heat exchanger; 14-the salt leg; 15-the washing water inlet; 16-the crystallization outlet; 17-the first centrifuge; 18-the first drying equipment; 19-the second evaporation crystallizer; 20-the second centrifuge; 21-the second drying equipment; 22-the nanofiltration water production tank; 23-the sodium bromide storage tank; 24-the feed inlet. DETAILED DESCRIPTION

[0029] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0030] The object of the present invention is to provide a method and device for recovering bromine and sodium from PTA tail gas treatment waste liquid, which solves the technical problem in the prior art that PTA waste liquid is discharged only through sulfuric acid neutralization and biochemical treatment, which easily causes the loss of high-value materials such as sodium bicarbonate, sodium carbonate and sodium bromide.

[0031] The following is an explanation of the embodiments with reference to the accompanying drawings. In addition, the embodiments shown below do not limit the invention described in the claims. In addition, the entire contents of the configurations shown in the following embodiments are not limited to the solutions required as the invention described in the claims.

[0032] The technical solution of the present invention is described in detail below in conjunction with specific embodiments.

[0033] Embodiment 1:

[0034] Reference Figure 1-2 The method for recovering bromine and sodium from PTA tail gas treatment waste liquid provided in this embodiment comprises:

[0035] Step S1: The pretreated waste liquid is concentrated to form a concentrated liquid, so as to remove other impurities and water in the waste liquid and greatly increase the content of sodium and bromine elements in the waste liquid, so as to improve the processing efficiency of subsequent processes.

[0036] Step S2: adjusting the pH value of the concentrated solution to an alkaline state and subjecting the concentrated solution to evaporation and crystallization to obtain sodium carbonate crystals and / or sodium bicarbonate crystals, so that the sodium carbonate crystals and / or sodium bicarbonate crystals can be fully precipitated under alkaline conditions. It should be noted that during the evaporation and crystallization process, the treatment temperature can be controlled at 70° C.-90° C., and sodium carbonate monohydrate and / or sodium bicarbonate crystals containing crystal water can be obtained. Subsequently, the sodium carbonate monohydrate and / or sodium bicarbonate crystals can be subjected to solid-liquid separation and then dried to obtain sodium carbonate and / or sodium bicarbonate products with a purity of more than 99%.

[0037] Step S3: The mother liquor after evaporation and crystallization in step S2 is subjected to special nanofiltration treatment to obtain a sodium bromide desalination water solution, that is, the mother liquor formed after the concentrated solution is evaporated and crystallized contains a large amount of impurities such as sodium bromide and sodium acetate. The special nanofiltration treatment can very effectively filter the sodium bromide and separate it from other impurities, that is, the produced water after the special nanofiltration treatment contains only sodium bromide, while other impurities are retained in the concentrated water side of the nanofiltration. The impure concentrated water side liquid can be discharged to the subsequent biochemical system for biochemical treatment.

[0038] Step S4: The sodium bromide freshwater solution in step S3 is concentrated to obtain a high-concentration sodium bromide solution, so as to carry out subsequent evaporation crystallization or bromine extraction treatment, that is, the excess water in the sodium bromide freshwater solution can be removed, and the content of sodium bromide in the solution is increased, so as to improve the purification treatment efficiency of the subsequent evaporation crystallization or bromine extraction treatment. It should be noted here that the high-concentration sodium bromide solution can be further treated according to user needs, and evaporation crystallization or bromine extraction treatment can be carried out on it. When it is necessary to carry out evaporation crystallization treatment on the high-concentration sodium bromide solution, it can be sent to an evaporation crystallizer for evaporation crystallization to obtain sodium bromide crystals. After being fixed and separated, the sodium bromide crystals can be further dried to obtain a high-purity sodium bromide product with a purity of more than 98.5%.

[0039] In this way, the present invention sequentially performs primary concentration, evaporation crystallization, special nanofiltration and re-concentration treatment on the waste liquid, that is, the solute in the waste liquid is first concentrated, and the concentrated high-salt waste liquid is subjected to evaporation crystallization treatment, so that a large amount of sodium carbonate and / or sodium bicarbonate in the waste liquid can be crystallized to achieve the purpose of recovery. In addition, the mother liquor formed after evaporation crystallization contains a large amount of high-value sodium bromide, and the sodium bromide can be separated from the mother liquor by special nanofiltration treatment to obtain a sodium bromide desalinated water solution. After further concentration, the high-concentration sodium bromide solution can be directly subjected to bromine extraction or evaporation crystallization, thereby obtaining a high-value and high-purity sodium bromide product. The present invention can recover most of the solutes in the waste liquid and convert them into sodium carbonate and / or sodium bicarbonate product salt and sodium bromide product salt with high economic value, recover more than 90% of the salt, and convert the remaining waste liquid into easy-to-treat low-salt wastewater. The treated desalinated liquid is more conducive to subsequent biochemical system treatment due to the reduced salt content, and the residual bromine concentration in the wastewater can also meet the standard, so that the overall wastewater can be fully discharged or reused after proper treatment. The present invention can recover the economically valuable components in the PTA oxidation tail gas treatment waste liquid and achieve high economic value, while also reducing the consumption of sulfuric acid and the emission of carbon dioxide in the traditional PTA oxidation tail gas treatment waste liquid treatment process, and has the environmental protection significance of turning waste into treasure, energy saving and emission reduction, and solves the technical problem that the PTA waste liquid in the prior art is only discharged through sulfuric acid neutralization and biochemical treatment, which easily causes the loss of high-value materials such as sodium bicarbonate, sodium carbonate and sodium bromide.

[0040] Embodiment 2:

[0041] Reference Figure 1-2Based on Example 1, this embodiment further defines the method for recovering bromine and sodium from PTA tail gas treatment waste liquid. In step S1, the concentration treatment is an electrodialysis treatment, which can appropriately concentrate the waste liquid, and the electrodialysis treatment includes a primary concentration electrodialysis and a secondary concentration electrodialysis, which can concentrate the waste liquid to a greater extent. The concentrated liquid of the primary concentration electrodialysis enters the secondary concentration electrodialysis for treatment, and the desalinated liquid of the secondary concentration electrodialysis is returned to the primary concentration electrodialysis for reprocessing, that is, the solute content in the concentrated liquid of the primary concentration electrodialysis is very high. After the secondary concentration electrodialysis treatment, the secondary desalinated liquid obtained still contains more solutes. Therefore, returning the secondary desalinated liquid to the primary concentration electrodialysis for reprocessing can greatly improve the recovery rate of the solute in the waste liquid and avoid waste. The desalinated liquid from the first-stage concentrated electrodialysis has a low solute content and can be sent to the biochemical system for treatment. With this arrangement, after two-stage electrodialysis treatment, the waste liquid can be divided into two parts. One part can obtain a 5%-15% concentrated liquid, that is, it can concentrate the solute in the waste liquid by more than ten times, and the other part is a 85%-95% desalinated liquid. The solute content in the desalinated liquid is less than 10% of the solute content in the original waste liquid. Due to its low salt content, the desalinated liquid can be directly sent to the biochemical system for biochemical treatment.

[0042] It should be noted that the electrodialysis process (ED) is a process that uses the selective permeability of ion exchange membranes under an external DC electric field to make anions and cations in water migrate in a directional manner, thereby achieving the separation of water and ions in waste liquid. The principle of the electrodialysis process is: an anode and a cathode are respectively set at both ends of the electrodialysis device, and a number of alternating cation exchange membranes and anion exchange membranes are set between the anode and the cathode. The cation exchange membrane only allows cations to pass through, while the anion exchange membrane only allows anions to pass through. When the positive and negative electrodes are energized, a strong electric field will be formed between the positive and negative electrodes, causing the cations in the solution passing through the electric field to move toward the cathode, while the anions move toward the anode. However, due to the alternating arrangement of the anion and cation exchange membranes, a dilute chamber with a reduced ion concentration and a concentrated chamber with an increased ion concentration will inevitably be formed. The electrodialysis device is provided with different flow channels to collect the solutions in the concentrated chamber and the dilute chamber respectively. In this way, the salt water phase separation of each part is achieved, forming a desalinated liquid and a concentrated liquid. The use of electrodialysis (ED) technology can collect most of the solutes in the PTA oxidation tail gas treatment wastewater in the reduced concentrated liquid, reducing the processing load of the subsequent process system. The low-salinity desalinated liquid has lower solutes and can directly enter the biochemical system for treatment.

[0043] Embodiment 3:

[0044] Reference Figure 1-2Based on Example 1, this embodiment further defines the method for recovering bromine and sodium from PTA tail gas treatment wastewater. In step S3, before the mother liquor enters the special nanofiltration treatment, it also includes step S301: diluting the mother liquor and adjusting its pH value to an acidic state, so that the carbonate and / or bicarbonate in the mother liquor can be converted into carbonic acid. Carbonic acid is unstable in water and easily decomposed into water and carbon dioxide. The acidified mother liquor can be decarbonized so that carbon dioxide can be separated from the solution and dispersed into the atmosphere along with the high-speed flowing air, so that the ion balance of carbonate in the water moves toward the direction of generating carbon dioxide, so that the carbonate and / or bicarbonate in the water are removed in the form of carbon dioxide. The chemical balance is as follows: The mother liquor dilution after decarbonization can be subsequently treated by special nanofiltration.

[0045] Furthermore, in step S4, the concentration treatment is reverse osmosis treatment and / or electrodialysis treatment, which can better concentrate the produced water of the special nanofiltration, increase the concentration of sodium bromide therein, and reduce the processing load of the subsequent process. The produced water of the concentration treatment is clean fresh water, which can be partially refluxed to the mother liquor in step S301 to mix and dilute the mother liquor, that is, the mother liquor is directly diluted with the system produced water, which reduces the input waste of external water and is more environmentally friendly. The rest of the clean fresh water can be reused as clean factory water. The high-concentration sodium bromide solution after the concentration treatment can be directly subjected to bromine extraction treatment or evaporation and crystallization treatment.

[0046] Further, in step S2, the pH value of the concentrated solution is adjusted by adding a strong alkaline substance to adjust the pH value of the concentrated solution to be greater than 10, wherein the strong alkaline substance may be, but is not limited to, sodium hydroxide, which can adjust the entire concentrated solution to an alkaline environment, making it easier for sodium carbonate and / or sodium bicarbonate to be fully separated. In step S301, the pH value of the mother liquor is adjusted by adding an acidic substance to adjust the pH value of the mother liquor to 3.5-5, wherein the acidic substance may be, but is not limited to, acetic acid or dilute sulfuric acid, which can convert carbonate and / or bicarbonate in the mother liquor into carbonic acid, which is unstable in water and easily decomposes into water and carbon dioxide.

[0047] As an optional implementation of an embodiment of the present invention, in step S1, pretreatment includes softening filtration treatment, iron and manganese removal treatment and ion exchange treatment to remove excess impurities in the waste liquid, so that the subsequent extraction of sodium carbonate, sodium bicarbonate and sodium bromide is higher in purity.

[0048] Embodiment 4:

[0049] Reference Figure 2The device for recovering bromine and sodium from PTA tail gas treatment waste liquid provided in this embodiment comprises a first concentrating component 1, a first evaporation crystallizer 2, a special nanofiltration component 3 and a second concentrating component 4, wherein the first concentrating component 1 is used for concentrating the waste liquid, the first evaporation crystallizer 2 is used for evaporation crystallization of sodium carbonate and / or sodium bicarbonate, the special nanofiltration component 3 is used for separating sodium bromide from the mother liquor output by the first evaporation crystallizer 2, and the second concentrating component 4 is used for concentrating the sodium bromide desalination solution, wherein the first concentrating component 1, the first evaporation crystallizer 2, the special nanofiltration component 3 and the second concentrating component 4 are all connected in sequence, and in this way, the present invention recovers bromine and sodium from the waste liquid. Based on the properties of the present invention, the waste liquid is initially concentrated by the first concentration component 1 to increase the concentration of the solute therein, and then the concentrated liquid is evaporated and crystallized by the first evaporation crystallizer 2 to crystallize a large amount of sodium carbonate and / or sodium bicarbonate in the waste liquid to achieve the purpose of recycling. The mother liquor after crystallization contains a large amount of high-value sodium bromide, and the sodium bromide can be separated from the mother liquor by the special nanofiltration component 3 to obtain a sodium bromide desalination solution, and then the sodium bromide desalination solution is further concentrated by the second concentration component 4 to obtain a high-concentration sodium bromide solution, and then a high-value sodium bromide product can be obtained by directly extracting bromine or evaporating and crystallizing the high-concentration sodium bromide solution. The device provided by the present invention is used to treat the waste liquid from the treatment of PTA oxidation tail gas, so that most of the solutes in the waste liquid can be recovered and converted into sodium carbonate and / or sodium bicarbonate product salts and sodium bromide product salts with high economic value. More than 90% of the salt is recovered, and the remaining waste liquid is also converted into easy-to-treat low-salt wastewater. The treated desalinated liquid is more conducive to the subsequent biochemical system for treatment due to the reduced salt content, and the residual bromine concentration in the wastewater can also meet the standard, so that the overall wastewater can be fully discharged or reused after proper treatment. While the present invention recovers the economically valuable components in the waste liquid from the treatment of PTA oxidation tail gas and achieves a higher economic value, it can also reduce the consumption of sulfuric acid and the emission of carbon dioxide in the treatment process of the traditional PTA oxidation tail gas treatment waste liquid, and has the environmental protection significance of turning waste into treasure, saving energy and reducing emissions, and solves the technical problem that the PTA waste liquid in the prior art is only discharged through sulfuric acid neutralization and biochemical treatment, which easily causes the loss of high-value materials such as sodium bicarbonate, sodium carbonate and sodium bromide.

[0050] Reference Figure 2-3As an optional implementation of the embodiment of the present invention, the present invention also includes a mother liquid tank 5 and a decarbonization tower 6 for diluting and adjusting the pH value of the mother liquid produced by the first evaporation crystallizer 2. The inlet of the mother liquid tank 5 is connected to the mother liquid outlet of the first evaporation crystallizer 2, so that the mother liquid separated from the first evaporation crystallizer 2 can be stored in the mother liquid tank 5 for further treatment. The outlet of the mother liquid tank 5 is connected to the decarbonization tower 6. A feeding port for adding an acidic substance is provided on the mother liquid tank 5 or on the outlet pipeline of the mother liquid tank 5, so that the acidic substance can be added to adjust the pH value of the diluted mother liquid. The liquid outlet of the decarbonization tower 6 is connected to the special nanofiltration component 3. With such a configuration, the mother liquid separated from the first evaporation crystallizer 2 can be stored in the mother liquid tank 5, the mother liquid can be diluted in the mother liquid tank 5, and the acidic substance can be added through the feeding port to adjust the pH value of the mother liquid to an acidic state, so that the carbonate and / or bicarbonate in the mother liquid can be converted into carbonic acid. Carbonic acid is unstable in water and easily decomposed into water and carbon dioxide. The acidic mother liquor is then transported to the decarbonization tower 6 for decarbonization treatment. Specifically, the decarbonization tower 6 adopts a packing type. The diluted acidified mother liquor enters from the top of the decarbonization tower 6, passes through the water distribution device, and enters the packing layer. A mechanical fan is set at the bottom of the decarbonization tower 6 to introduce air from the bottom of the decarbonization tower 6, and forms an air flow in the opposite direction with the water flow. In the acidified mother liquor, carbonic acid decomposes into carbon dioxide and water, and carbon dioxide is separated from the solution and dispersed into the atmosphere with the high-speed air flow, so that the ion balance of carbonate in the water moves toward the direction of generating carbon dioxide, so that carbonate and / or bicarbonate in the water are removed in the form of carbon dioxide. The decarbonized mother liquor dilution enters the decarbonization water pool at the bottom of the decarbonization tower 6, and is subsequently transferred to the special nanofiltration component 3 for further treatment.

[0051] As an optional implementation mode of an embodiment of the present invention, the first concentrating component 1 includes a primary electrodialyzer 7 and a secondary electrodialyzer 8 which are arranged in communication with each other. The desalinated liquid outlet of the secondary electrodialyzer 8 is provided with a second reflux pipe 9 which is connected to the inlet of the primary electrodialyzer 7. With such an arrangement, the desalinated liquid of the secondary electrodialyzer 8 can flow back to the inlet of the primary electrodialyzer 7 through the second reflux pipe 9 and re-perform the electrodialysis cycle, which can greatly improve the recovery rate of solutes in the waste liquid and avoid waste.

[0052] As an optional implementation of the embodiment of the present invention, the second concentration component 4 includes a reverse osmosis component and / or an electrodialysis component, and the water outlet of the reverse osmosis component and / or the electrodialysis component is provided with a first reflux pipe 10 connected to the mother liquid tank 5. With such an arrangement, the reverse osmosis component and / or the electrodialysis component can efficiently concentrate the sodium bromide desalination solution flowing out of the special nanofiltration component 3, can increase the concentration of the sodium bromide desalination solution to form a high-concentration sodium bromide solution, and can reduce the processing load of the subsequent process. The high-concentration sodium bromide solution can be discharged and stored in the sodium bromide storage tank 23. Moreover, the clean fresh water flowing out of the water outlet of the second concentration component 4 can be refluxed to the mother liquid tank 5 through the first reflux pipe 10 to dilute the mother liquid, that is, the mother liquid is directly diluted with the water produced by this system, reducing the input of external water.

[0053] Reference Figure 2-3 As an optional implementation method of the embodiment of the present invention, the first evaporation crystallizer 2 is a forced circulation crystallization structure. The first evaporation crystallizer 2 includes a feed port 24, a flash tank 11, a circulation pump 12 arranged outside the flash tank 11, and a forced circulation heat exchanger 13. The flash tank 11, the circulation pump 12 and the forced circulation heat exchanger 13 are connected in a ring shape in sequence. The feed port 24 is arranged between the circulation pump 12 and the forced circulation heat exchanger 13. In this way, the concentrated liquid flowing out of the secondary electrodialyzer 8 enters the shell of the first evaporation crystallizer 2 and mixes with the crystallized concentrated liquid. The circulation pump 12 can provide a driving force to make the slurry in the first evaporation crystallizer 2 flow through the forced circulation heat exchanger 13. The heat released by the steam on the shell side of the heat exchanger through condensation provides heat for the circulating crystallization concentrated liquid on the inside of the heat exchange tube, and can heat the temperature of the concentrated liquid to 70-90°C. The water level hydrostatic head of the heat exchanger prevents the liquid in the pipeline from boiling. The first evaporation crystallizer 2 can also be equipped with a vacuum and condensation device to decompress the system. After the concentrated liquid after heat exchange returns to the shell of the crystallizer, flash evaporation will occur due to the pressure reduction, generating water vapor and releasing heat. The generated water vapor escapes from the top of the flash tank 11 and enters the condenser for condensation. If the first evaporation crystallizer 2 adopts MVR evaporation, it enters the steam compressor. The steam compressor consumes electric energy to pressurize the water vapor and then transfers it to the heating chamber of the forced circulation heat exchanger 13 as the heat source of the crystallizer. The condensed water obtained after steam heat exchange can be reused as clean factory water. As the evaporation proceeds, the concentration of the concentrated liquid gradually increases. When the concentrated liquid reaches the crystallization saturation point, sodium carbonate monohydrate and / or sodium bicarbonate precipitate from the concentrated liquid in the crystallizer.

[0054] Furthermore, a salt leg 14 is provided at the lower portion of the flash tank 11, and a washing component for removing impurities from the crystals of sodium carbonate and / or sodium bicarbonate is provided in the salt leg 14, and a washing water inlet 15 and a crystallization discharge port 16 are provided on the salt leg 14. In this way, as the precipitated salt crystals continue to gather, the salt crystals will settle to the salt leg 14, and the salt leg 14 is provided with a countercurrent washing component, so that the water from the washing water inlet 15 can be used to wash the fallen crystallized salt, and the crystallized salt with smaller particles is dissolved by the washing water and moves upward with the water flow, and the salt particles with larger particles fall to the crystallization discharge port 16 at the bottom of the salt leg 14. The crystallization discharge port 16 is connected in sequence with a first thickener for increasing the concentration of the crystals, a first centrifuge 17 for solid-liquid separation, and a first drying device 18 for drying the crystals. In this way, the salt with larger particles at the crystallization discharge port 16 is transferred to the first thickener with the slurry through a pump for thickening, so that the concentration of the crystals in the slurry can reach 20%-50% (apparent solid-liquid ratio), and then enters the first centrifuge 17 for centrifugal separation. Preferably, the first centrifuge 17 can adopt a double-push centrifugal dehydrator, and the feed is a salt slurry with a solid content of 20%-50% (apparent solid-liquid ratio). After centrifugal separation, sodium carbonate monohydrate and / or sodium bicarbonate crystals with a free water content of ≤5% can be obtained. The centrifuged mother liquor separated in the first centrifuge 17 can be returned to the first evaporation crystallizer 2 through a pipeline for continued concentration, and the crystals separated by centrifugation are sent to the first drying device 18 for drying.

[0055] Among them, the first drying equipment 18 mainly includes a fluidized bed dryer with a vibration function, an air heat exchanger, a cyclone separator, a bag dust collector, a blower and an induced draft fan. Sodium carbonate monohydrate and / or sodium bicarbonate containing a certain amount of free water and crystal water enters the vibrating fluidized bed evenly through the dispersion effect of entering the distributor, fully contacts with the hot air after steam heat exchange, and produces fluidization in the fluidized bed dryer. In this state, the crystal water and free water are removed. The removed water enters the cyclone separator and the bag dust collector with the hot air and is discharged to the outside atmosphere. The high-temperature dry salt particles are cooled by low-temperature air heat exchange and flow out from the outlet of the fluidized bed dryer. After drying in the fluidized bed dryer, sodium carbonate and / or sodium bicarbonate product salt with a purity of more than 99% can be obtained.

[0056] Reference Figure 2 and Figure 4As an optional implementation of the embodiment of the present invention, the present invention also includes a second evaporation crystallizer 19 for evaporation and crystallization of a high-concentration sodium bromide solution, which is connected to the second concentration component 4, that is, the second evaporation crystallizer 19 is a sodium bromide evaporation crystallizer, which can perform evaporation and crystallization on a high-concentration sodium bromide solution. The structure of the second evaporation crystallizer 19 is similar to that of the first evaporation crystallizer 2. The second evaporation crystallizer 19 also mainly includes a flash tank 11, a circulation pump 12, a forced circulation heat exchanger 13, a steam heat pump, a steam condenser and a vacuum pump. The high-concentration sodium bromide solution enters the shell of the crystallizer and mixes with the crystallization concentrate. The circulation pump 12 allows the slurry in the crystallizer to flow through the forced circulation heat exchanger 13, where it obtains heat from the steam on the heater shell side. The hydrostatic head of the water level in the discharge pipe of the forced circulation heat exchanger 13 can suppress boiling in the pipe. When the slurry after heat exchange returns to the crystallizer shell, flash evaporation will occur, generating water vapor and releasing heat. The generated water vapor escapes from the top of the flash tank 11 and enters the steam heat pump. After being pressurized by the motive steam jet in the steam heat pump, it enters the heating chamber of the forced circulation heat exchanger 13 as the heat source of the crystallizer. The condensed water obtained after steam heat exchange can be reused as clean factory water.

[0057] Furthermore, the material outlet of the second evaporation crystallizer 19 is connected in sequence to a second thickener for increasing the concentration of the crystals, a second centrifuge 20 for solid-liquid separation, and a second drying device 21 for drying the crystals. With such an arrangement, as evaporation proceeds, the concentration of the concentrated liquid gradually increases. When the concentration of the concentrated liquid reaches the saturation point of sodium bromide crystallization, sodium bromide crystals precipitate from the concentrated brine in the crystallizer. When the crystal ratio in the brine reaches 10%-25% (apparent solid-liquid ratio), the brine can be transferred to the second thickener by a slurry pump for thickening, and after the crystal concentration reaches 20%-50% (apparent solid-liquid ratio), it enters the second centrifuge 20 for centrifugal separation to obtain sodium bromide crystals with a free water content of ≤5%. The centrifuged mother liquor in the second centrifuge 20 can be returned to the second evaporation crystallizer 19 for further concentration, and the sodium bromide crystals separated by centrifugation can be sent to the second drying device 21 for drying, which can further remove the water in the sodium bromide crystals to obtain sodium bromide product salt with a purity of >98.5%.

[0058] Preferably, the second evaporator crystallizer 19 is a TVR evaporator to adapt to the characteristics of high purity and small flow rate of high-concentration sodium bromide solution.

[0059] In the description of the present invention, it should be noted that, unless otherwise specified, "multiple" means two or more than two; the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0060] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0061] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for recovering bromine and sodium from PTA tail gas treatment waste liquid, characterized in that: include: Step S1: Concentrating the pretreated waste liquid to form a concentrated liquid; Step S2: adjusting the pH value of the concentrated solution to an alkaline state and subjecting the concentrated solution to evaporation and crystallization to obtain sodium carbonate crystals and / or sodium bicarbonate crystals; Step S3: subjecting the mother liquor after evaporation and crystallization in step S2 to a special nanofiltration treatment to obtain a sodium bromide desalinated water solution; Step S4: Concentrating the sodium bromide desalination solution in step S3 to obtain a high-concentration sodium bromide solution for subsequent evaporation crystallization or bromine extraction treatment; In step S1, the pretreatment includes softening and filtering treatment, iron and manganese removal treatment and ion exchange treatment; The concentration treatment is an electrodialysis treatment, which includes a primary concentration electrodialysis and a secondary concentration electrodialysis. The concentrated liquid of the primary concentration electrodialysis enters the secondary concentration electrodialysis for treatment, the desalinated liquid of the secondary concentration electrodialysis is sent back to the primary concentration electrodialysis for re-treatment, and the desalinated liquid of the primary concentration electrodialysis is sent to a biochemical system for treatment; In the step S2, the pH value of the concentrated solution is adjusted by adding a strong alkaline substance to adjust the pH value of the concentrated solution to be greater than 10; In step S3, before the mother liquor enters the special nanofiltration treatment, step S301 is also included: diluting the mother liquor and adjusting its pH value to 3.5-5; In step S4, the concentration treatment is reverse osmosis treatment and / or electrodialysis treatment, and the produced water from the concentration treatment is returned to the mother liquor in step S301 to be mixed and diluted with the mother liquor.

2. A device for recovering bromine and sodium from PTA tail gas treatment waste liquid, based on the method for recovering bromine and sodium from PTA tail gas treatment waste liquid as claimed in claim 1, characterized in that: include: A first concentration component (1) is used to concentrate the waste liquid; A first evaporation crystallizer (2), used for evaporating and crystallizing sodium carbonate and / or sodium bicarbonate; A special nanofiltration component (3) is used to separate sodium bromide from the mother liquor produced by the first evaporation crystallizer (2); A second concentrating component (4) is used to concentrate the sodium bromide desalinated water solution; Wherein, the first concentration component (1), the first evaporation crystallizer (2), the special nanofiltration component (3) and the second concentration component (4) are all connected in sequence; It also comprises a mother liquid tank (5) and a decarbonization tower (6) for diluting and adjusting the pH value of the mother liquid produced by the first evaporation crystallizer (2), wherein the inlet of the mother liquid tank (5) is connected to the mother liquid outlet of the first evaporation crystallizer (2), the outlet of the mother liquid tank (5) is connected to the decarbonization tower (6), a destocking port is provided on the mother liquid tank (5) or on the outlet pipeline of the mother liquid tank (5), and the liquid outlet of the decarbonization tower (6) is connected to the special nanofiltration component (3); The first concentration assembly (1) comprises a primary electrodialyser (7) and a secondary electrodialyser (8) which are arranged in communication with each other, and a desalinated liquid outlet of the secondary electrodialyser (8) is provided with a second reflux pipe (9) which is in communication with an inlet of the primary electrodialyser (7); The second concentration component (4) comprises a reverse osmosis component and / or an electrodialysis component, and the water output outlet of the reverse osmosis component and / or the electrodialysis component is provided with a first reflux pipe (10) connected to the mother liquid tank (5).

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