PTA wastewater high-efficiency treatment system

Abstract

This application belongs to the field of wastewater energy and resource utilization technology, and particularly relates to a high-efficiency PTA wastewater treatment system. The system has a single-layer sleeve in the first-stage evaporator and double-layer sleeves in the second and third-stage evaporators. The concentrated liquid is then sent to an incinerator. The high-temperature flue gas generated by combustion, after dust removal, is sent to the outside of the single-layer sleeve of the first-stage evaporator. The single-layer sleeve contains PTA wastewater. The space between the double-layer sleeves in the second and third-stage evaporators contains PTA wastewater concentrated in the previous stage evaporator. High-temperature flue gas from the previous stage evaporator flows outside the double-layer sleeves, while steam generated in the previous stage evaporator flows in the innermost layer of the double-layer sleeves. The ash from combustion is sent to a dissolving tank for dissolution. The filtered filtrate is sent to a first-stage crystallizer for evaporation and crystallization, where sodium carbonate crystals are precipitated and recovered. The remaining mother liquor is sent to a second-stage crystallizer for cooling and crystallization, where sodium bromide crystals are precipitated and recovered. The remaining mother liquor is returned to the first-stage crystallizer. This application achieves energy and resource utilization of wastewater with high efficiency.

Description

Technical Field

[0001] This application belongs to the field of wastewater energy and resource utilization technology, and in particular relates to a high-efficiency PTA wastewater treatment system. Background Technology

[0002] Terephthalic acid (PTA), an organic compound, is one of the most important bulk organic raw materials, widely used in various sectors of the national economy such as chemical fibers, electronics, light industry, and construction. Currently, PTA is mainly produced using the air oxidation process with para-xylene. The PTA oxidation tail gas produced during this process is an organic waste gas containing various pollutants emitted from the oxidation reactor, and it is the largest source of harmful gas emissions from PTA plants. Therefore, the effluent from the PTA oxidation tail gas scrubbing tower is also a major source of wastewater in PTA chemical plant production. Based on a PTA wastewater production ratio of approximately 1.45, this means that for every ton of PTA produced, 1.45 tons of wastewater require environmental treatment, with the estimated annual PTA wastewater treatment volume reaching hundreds of millions of tons. Therefore, the environmental pressure of waste disposal is gradually increasing for PTA production enterprises.

[0003] PTA wastewater mainly consists of organic compounds such as phthalic acid, p-xylene, methylbenzoic acid, phthalic acid, benzoic acid, methyl acetate, 4-CBA, and acetic acid, as well as inorganic substances such as cobalt, manganese, and bromine. It is characterized by high water content, high salinity, and complex composition, making it a very difficult waste to treat. Sodium bromide, a crucial raw material for PTA production, is expensive. PTA wastewater contains a certain amount of bromide ions, along with a certain amount of sodium salts of organic acids. Recovering the sodium and bromide ions in the form of sodium bromide would improve the overall cost competitiveness of PTA and is a crucial means of improving energy utilization and saving raw material consumption in PTA production. Furthermore, sodium carbonate is consumed in large quantities during PTA production; currently, conventional PTA production requires large-scale external purchases of sodium carbonate as an industrial raw material. Recovering sodium carbonate from PTA wastewater can also achieve the goal of saving resources and reducing PTA production costs.

[0004] Currently, in the PTA industry, methods for separating sodium carbonate and sodium bromide from PTA wastewater include evaporation crystallization, cooling crystallization, and membrane separation. For example, CN112811444B, CN114380441A, and CN113461199A provide methods for crystallization separation and nanofiltration separation. Regardless of the separation method mentioned above, a significant amount of additional energy consumption is required. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a complete process method for the energy and resource utilization of PTA wastewater, which utilizes the high-temperature gas from the incinerator to provide energy for the concentration and separation system, and uses the condensate from the separation system for cooling and crystallization to dissolve alkali and sodium carbonate.

[0006] This application proposes a high-efficiency PTA wastewater treatment system, including a concentration and separation system, an incinerator 5, a dissolving tank 6, a filter 7, a primary crystallizer 4, and a secondary crystallizer 8. The concentration and separation system includes three evaporators connected in sequence. The first-stage evaporator 1 has a single-layer sleeve, while the second-stage evaporators 2 and 3 have double-layer sleeves. The concentrated liquid prepared by the concentration and separation system is sent to the incinerator 5 for combustion. The high-temperature flue gas generated by combustion exchanges heat with air and is then sent to the outside of the single-layer sleeve of the first-stage evaporator 1. PTA wastewater flows inside the single-layer sleeve, while the wastewater flows between the double-layer sleeves in the second-stage evaporators 2 and 3, where the wastewater is concentrated by the evaporation of the previous stage evaporator. After the PTA wastewater, the high-temperature flue gas from the previous stage evaporator flows outside the double-layered pipe, while the steam generated by the heat exchange and evaporation of the PTA wastewater in the previous stage evaporator flows inside the double-layered pipe. The ash produced by combustion is sent to the dissolving tank 6 for dissolution, and the filtered filtrate is sent to the first-stage crystallizer 4. At the same time, the air is also introduced into the first-stage crystallizer 4 after heat exchange with the high-temperature flue gas, providing energy for the evaporation and crystallization of sodium carbonate. The remaining mother liquor after the sodium carbonate crystallization is sent to the second-stage crystallizer 8. Meanwhile, the condensate generated by heat exchange in the third-stage evaporator 3 is also sent to the second-stage crystallizer 8 for cooling and crystallization to precipitate sodium bromide crystals. The remaining mother liquor after the sodium bromide crystallization is returned to the first-stage crystallizer 4 to enter the next cycle.

[0007] Specifically, the operating pressures of the three-stage evaporator are atmospheric pressure, 0.8-0.6 bar, and 0.5-0.3 bar, respectively.

[0008] Specifically, the system also includes an air heater and a dust collector. In the air heater, the air exchanges heat with the high-temperature flue gas generated by the combustion of the incinerator and becomes hot air, which is then sent to the first-stage crystallizer 4. After the high-temperature flue gas is cooled down by heat exchange, it is sent to the dust collector for dust removal and then passes through the first-stage evaporator 1, the second-stage evaporator 2 and the third-stage evaporator 3 in sequence, serving as the heat source for the evaporation of PTA wastewater. Finally, it is sent to the environmental protection system for desulfurization and denitrification before being discharged.

[0009] Specifically, the upper part of the primary crystallizer 4 is equipped with a spray system, and hot air is introduced from the lower part. As the hot air rises, it comes into contact with the sprayed salt mixture to achieve the evaporation and crystallization of sodium carbonate.

[0010] Specifically, natural gas is added to the incinerator for combustion support, the incinerator temperature is controlled at ≥1100℃, and the ash and condensate produced by the incinerator and the condensate produced by the second-stage evaporator 2 are sent to the dissolving tank 6 to dissolve into a saturated solution.

[0011] Specifically, the 60-80°C condensate generated by heat exchange in the third-stage evaporator 3 is sent to the second-stage crystallizer 8 to cool and crystallize NaBr.

[0012] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain the preferred examples of this application.

[0013] The above technical solution has the following advantages or beneficial effects: This application uses an evaporation / cooling crystallization method to separate and recover sodium carbonate and sodium bromide from PTA boiler ash; the high-temperature gas from the incinerator provides energy for the PTA wastewater concentration and separation system and sodium carbonate evaporation and crystallization. The condensate generated in the system is used to dissolve alkali and for cooling crystallization of sodium carbonate. The process is simple, easy to industrialize, and realizes the energy recovery of wastewater. At the same time, the high-purity sodium carbonate and sodium bromide recovered can meet the quality requirements of industrial-grade products, realizing the resource recovery of wastewater and improving the efficiency of the factory. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, those skilled in the art can obtain other drawings based on the provided drawings without any creative effort.

[0015] Figure 1 This is a schematic diagram of a high-efficiency PTA wastewater treatment system according to an embodiment of this application.

[0016] Figure 2 This is a schematic diagram showing the connections of various devices in a high-efficiency PTA wastewater treatment system according to an embodiment of this application.

[0017] Figure 3 This is a structural schematic diagram of the cross-section of a first-stage evaporator according to an embodiment of this application.

[0018] Figure 4 This is a structural schematic diagram of the cross-section of a first-stage evaporator and a second-stage evaporator according to an embodiment of this application.

[0019] Figure 5 This is a schematic diagram of the structure of an air heater according to an embodiment of this application.

[0020] Figure 6 This is a schematic diagram of the structure of a primary crystallizer according to an embodiment of this application.

[0021] Figure 7 This is a schematic diagram of the structure of a secondary crystallizer according to an embodiment of this application.

[0022] Among them, 1-first stage evaporator, 2-second stage evaporator, 3-third stage evaporator, 4-first stage crystallizer, 5-incinerator, 6-dissolving tank, 7-filter, 8-second stage crystallizer. Detailed Implementation

[0023] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely a part of the embodiments of this application and are intended to explain the inventive concept. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0024] The terms "first," "second," etc., used in the description are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of that feature. The term "multiple" means two or more, unless otherwise explicitly specified.

[0025] Unless otherwise explicitly specified and limited, the terms "connected," "connected," etc., used in the description should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments according to the specific circumstances.

[0026] Unless otherwise expressly specified and limited, "above," "below," or "on top of" the second feature can mean that the first and second features are in direct contact or indirect contact through an intermediate medium. Furthermore, "above," "on top of," or "on top of" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. Similarly, "below," "below," or "under" the second feature can mean that the first and second features are in direct contact or indirect contact through an intermediate medium. Furthermore, "below," "below," or "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0027] For clarity, the term "about" is used herein to imply the possibility of variation within an acceptable range of numerical values ​​known to those skilled in the art. According to one specific embodiment, the term "about" as used herein should be interpreted as implying a possible variation of up to 5% above or below any specified value.

[0028] The term "a specific embodiment" as used in the description means that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0029] refer to Figure 1 and Figure 2 One specific embodiment of this application proposes a high-efficiency PTA wastewater treatment system, which includes a concentration and separation system, an incinerator, an air heater, a dust collector, an environmental protection system, a dissolving tank, a filter, a primary crystallizer, and a secondary crystallizer.

[0030] The concentration and separation system includes three-stage evaporators. The high-temperature flue gas generated from the combustion of the concentrated liquid is fed into an air heater, where it exchanges heat with air before being sent to the first-stage evaporator 1 as a heat source for evaporation. The heat in the second-stage evaporator 2 comes from the high-temperature flue gas and steam discharged from the first-stage evaporator 1, and the heat in the third-stage evaporator 3 comes from the high-temperature flue gas and steam discharged from the second-stage evaporator 2. The concentration and separation system evaporates and concentrates the PTA wastewater before sending it to the incinerator 5, where the concentrated liquid is burned to produce ash and high-temperature flue gas. The pressures of the three-stage evaporators are atmospheric pressure, 0.8-0.6 bar, and 0.5-0.3 bar, respectively. All other operating conditions are at atmospheric pressure, and the incinerator temperature is ≥1100℃.

[0031] The condensate generated from heat exchange in the second-stage evaporator 2 and the ash residue from incineration are sent to the dissolving tank 6 to be mixed into a brine solution. Downstream of the dissolving tank 6, it is sequentially connected to a filter 7, a primary crystallizer 4, and a secondary crystallizer 8. In the air heater, air exchanges heat with high-temperature flue gas to become hot air, which is then sent to the primary crystallizer 4 to provide energy for the evaporation and crystallization of sodium carbonate. The condensate at 60-80°C generated from heat exchange in the third-stage evaporator 3 is sent to the secondary crystallizer 8 to cool and crystallize NaBr.

[0032] refer to Figure 3 One specific embodiment of this application proposes a first-stage evaporator 1 for a high-efficiency PTA wastewater treatment system. The first-stage evaporator 1 is equipped with several single-layer sleeves, with PTA wastewater flowing inside the sleeves and high-temperature flue gas flowing outside the sleeves.

[0033] refer to Figure 4A specific embodiment of this application proposes a second-stage evaporator 2 and a third-stage evaporator 3 for a high-efficiency PTA wastewater treatment system. The second-stage evaporator 2 and the third-stage evaporator 3 have the same structure. The evaporator is equipped with several double-layered tubes. The innermost tube of the double-layered tubes carries steam generated by the heat exchange and evaporation of the wastewater from the previous stage. The interlayer carries the concentrated PTA wastewater from the previous stage. The outside of the tubes carries the high-temperature flue gas from the previous stage heat exchange.

[0034] refer to Figure 5 One specific embodiment of this application proposes an air heater for a high-efficiency PTA wastewater treatment system. The high-temperature flue gas generated by combustion in the incinerator 5 is sent into the air heater, where the air exchanges heat with the high-temperature flue gas to become hot air, which is then sent into the primary crystallizer 4.

[0035] refer to Figure 6 One specific embodiment of this application proposes a primary crystallizer 4 for a high-efficiency PTA wastewater treatment system. The upper part of the primary crystallizer 4 is equipped with a spray, and hot air is introduced from the lower part. During the rising process of the hot air, it comes into contact with the sprayed salt mixture to achieve the evaporation and crystallization of sodium carbonate.

[0036] refer to Figure 7 One specific embodiment of this application proposes a secondary crystallizer 8 in a high-efficiency PTA wastewater treatment system. The condensate generated at 60-80°C in the third-stage evaporator 3 cools the secondary crystallizer 8, thereby achieving cooling crystallization of NaBr.

[0037] The process of the high-efficiency PTA wastewater treatment system of this application is as follows: PTA wastewater enters the concentration and separation system. The heat in the first-stage evaporator 1 comes from the high-temperature flue gas discharged from the incinerator 5. The heat in the second-stage evaporator 2 comes from the high-temperature flue gas and steam discharged from the first-stage evaporator 1. The condensate produced after heat exchange and condensation of the steam in the second-stage evaporator 2 is sent to the dissolving tank 6 to dissolve the ash produced by incineration. The heat in the third-stage evaporator 3 comes from the high-temperature flue gas and steam discharged from the second-stage evaporator 2. The condensate at 60-80℃ is sent to the second-stage crystallizer 8 to cool and crystallize NaBr. The concentrated PTA wastewater is sent to the incinerator, which operates at a temperature greater than or equal to 1100℃. Natural gas is added to the incinerator to aid combustion in the wastewater incineration. The high-temperature flue gas produced leaves the incinerator and enters the air heater to exchange heat with air. The hot air is sent to the first-stage crystallizer 4 to provide heat for the evaporation and crystallization of sodium carbonate. High-temperature flue gas is sequentially sent to the concentration and separation system via an air heater and a dust collector to provide heat for PTA wastewater concentration. After leaving the concentration and separation system, it is discharged after desulfurization and denitrification by the environmental protection system. The ash residue at the bottom of the incinerator contains approximately 95% sodium carbonate, 4% sodium bromide, 1% cobalt, manganese, and other substances. The ash residue is sent to the dissolving tank 6, where it is dissolved into a saturated solution by condensate from the second-stage evaporator 2 and then sent to the filter 7. Insoluble cobalt, manganese, etc., are filtered and recovered. Na2CO3 and NaBr solutions enter the first-stage crystallizer 4 for evaporation and crystallization. Sodium carbonate crystals are precipitated and recycled. The remaining mother liquor enters the second-stage crystallizer 8 for cooling and crystallization. NaBr crystals are precipitated and recycled. The remaining mother liquor after NaBr crystallization is returned to the first-stage crystallizer 4 for the next cycle.

[0038] This application employs an evaporation / cooling crystallization method to separate and recover sodium carbonate and sodium bromide from PTA boiler ash. The high-temperature gas from the incinerator provides energy for the PTA wastewater concentration and separation system and the sodium carbonate evaporation and crystallization. The condensate generated in the system is used to dissolve alkali and for the cooling crystallization of sodium carbonate. The process is simple, easy to industrialize, and realizes the energy recovery from wastewater. Simultaneously, the recovered high-purity sodium carbonate and sodium bromide meet the quality requirements of industrial-grade products, realizing the resource recovery of wastewater and improving the plant's efficiency. Example 1

[0039] The PTA wastewater feed rate is 200 L / h, the condensate flow rate of the second-stage evaporator is 20 L / h, the condensate flow rate of the third-stage evaporator is 5 L / h, and the waste liquid entering the incinerator is 15 L / h. High-temperature flue gas is discharged from the top of the incinerator, and ash is discharged from the bottom at a rate of 5 kg / h. The ash consists of 95% sodium carbonate, 4% sodium bromide, and 1% other components. After dissolving in a dissolving tank, the ash is filtered to recover insoluble substances such as cobalt and manganese. Sodium carbonate is evaporated and crystallized in the first-stage evaporator, with approximately 90% of the sodium carbonate crystals precipitating (4.2 kg / h). The mother liquor in the crystallizer enters the second-stage crystallizer for cooling and crystallization, and NaBr crystals (0.16 kg / h) precipitate and are then recycled.

[0040] Although embodiments of this application have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting this application. Various changes and modifications may be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of the claims of this application.

Claims

1. A high-efficiency PTA wastewater treatment system, comprising a concentration and separation system, an incinerator, a dissolving tank, a filter, a primary crystallizer, and a secondary crystallizer, characterized in that: The concentration and separation system comprises three evaporators connected in sequence. The first-stage evaporator has a single-layer sleeve, while the second and third-stage evaporators have double-layer sleeves. The concentrated liquid produced by the concentration and separation system is sent to an incinerator for combustion. The high-temperature flue gas generated from combustion exchanges heat with air and is then sent to the outside of the single-layer sleeve of the first-stage evaporator. PTA wastewater flows inside the single-layer sleeve. The PTA wastewater concentrated by the previous stage evaporator flows between the double-layer sleeves in the second and third-stage evaporators, while the high-temperature flue gas from the previous stage evaporator flows outside the double-layer sleeves. The innermost layer of the double-layer sleeve... The steam generated from the heat exchange and evaporation of PTA wastewater in the first-stage evaporator flows through the system. The ash produced from combustion is sent to a dissolving tank for dissolution. The resulting mixed brine is then sent to a filter for filtration. The filtrate is then sent to the first-stage crystallizer. Simultaneously, air is heated by heat exchange with the high-temperature flue gas and is also introduced into the first-stage crystallizer to provide energy for the evaporation and crystallization of sodium carbonate. The remaining mother liquor after the sodium carbonate crystallization is sent to the second-stage crystallizer. At the same time, the condensate generated from the heat exchange in the third-stage evaporator is also sent to the second-stage crystallizer for cooling and crystallization to precipitate sodium bromide crystals. The remaining mother liquor after the sodium bromide crystallization is returned to the first-stage crystallizer to enter the next cycle.

2. The PTA wastewater high-efficiency treatment system according to claim 1, characterized in that: The operating pressures of the three-stage evaporator are atmospheric pressure, 0.8-0.6 bar, and 0.5-0.3 bar, respectively.

3. The PTA wastewater high-efficiency treatment system according to claim 1, characterized in that: The system also includes an air heater and a dust collector. In the air heater, the air exchanges heat with the high-temperature flue gas generated by the combustion of the incinerator and becomes hot air, which is then sent to the first-stage crystallizer. After the high-temperature flue gas is cooled down by heat exchange, it is sent to the dust collector for dust removal and then passes through the first-stage evaporator, the second-stage evaporator and the third-stage evaporator in sequence, serving as the heat source for the evaporation of PTA wastewater. Finally, it is sent to the environmental protection system for desulfurization and denitrification before being discharged.

4. The PTA wastewater high-efficiency treatment system according to claim 3, characterized in that: The upper part of the primary crystallizer is equipped with a spray system, and hot air is introduced from the lower part. As the hot air rises, it comes into contact with the sprayed salt mixture, resulting in the evaporation and crystallization of sodium carbonate.

5. The PTA wastewater high-efficiency treatment system according to claim 1, characterized in that: Natural gas is added to the incinerator for combustion support. The incinerator temperature is controlled at ≥1100℃. The ash and slag produced by the incinerator and the condensate produced by the second-stage evaporator are sent to the dissolving tank to dissolve into a saturated solution.

6. The PTA wastewater high-efficiency treatment system according to claim 1, characterized in that: The 60-80℃ condensate generated by heat exchange in the third-stage evaporator is sent to the second-stage crystallizer to cool and crystallize NaBr.

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