A sodium carbonate recovery system and a method for recovering sodium carbonate from PTA organic residue using the same

Abstract

The application provides a sodium carbonate recovery system and a method for recovering sodium carbonate from PTA organic residues by using the system. In the system, a dissolving tank A, a filter, an evaporation feed tank, and an evaporator A are sequentially connected; the evaporator A, an evaporator B, and a recovery tank are sequentially connected; the evaporator A, a thickener A, a centrifuge A, and a screw A are sequentially connected, and the screw A is connected with a drying system and the dissolving tank B respectively; the evaporator B, the thickener B, the centrifuge B, and a screw B are sequentially connected, and the screw B is connected with the dissolving tank B; the evaporator A is connected with a condenser A, the condenser A is connected with the dissolving tank A and the dissolving tank B respectively; the evaporator B, a condenser B, and the dissolving tank B are sequentially connected; and the dissolving tank B is connected with a main device system. In the recovery system, not only the sodium carbonate solid is effectively recovered, but also the concentration of the sodium carbonate solution can be flexibly adjusted according to the requirement. Meanwhile, water is fully recycled in the recovery system, resource waste is reduced, and cost is saved.

Description

Technical Field

[0001] This invention relates to the field of PTA preparation residue treatment technology, specifically to a sodium carbonate recovery system and a method for recovering sodium carbonate from PTA organic residue using this system. Background Technology

[0002] Terephthalic acid (PTA) is the most produced dicarboxylic acid and an important organic synthetic monomer in the chemical industry. It is mainly used to produce polyethylene terephthalate (PET) and bottle-grade polyester. At the same time, terephthalic acid can also be used as a plasticizer raw material, making it widely used in industry.

[0003] There are many methods for PTA production, mainly high-temperature liquid-phase oxidation, phthalic anhydride transposition, and toluene oxidative disproportionation. Among them, high-temperature liquid-phase oxidation mainly includes oxidation and hydrorefining processes. To ensure the smooth operation of this method and avoid blockage of equipment and pipelines, it is usually necessary to clean with alkaline solution. The cleaning waste liquid, residues from the oxidation process, and other wastes carried out by leaks and spills on-site and in the system are all discharged into the waste collection pool and are collectively referred to as PTA organic residues. Because these residues have complex compositions and their composition and content vary with the high-temperature oxidation process, this brings difficulties to the comprehensive recycling and utilization of the waste residues.

[0004] By adding sodium carbonate and / or sodium hydroxide to PTA organic residue, the oxidized residue becomes a water-soluble substance, while metals such as cobalt and manganese are converted into precipitates. Separation is achieved through filtration, and the filtrate enters the wastewater system for biochemical treatment to meet discharge standards. This process results in a large waste of organic acids and a large amount of wastewater discharge. Therefore, the effective recovery of sodium carbonate, turning waste into treasure, reducing waste and wastewater discharge, and lowering costs are of great significance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a sodium carbonate recovery system and a method for recovering sodium carbonate from PTA organic residue using this system. The sodium carbonate recovery system is rationally designed, highly practical, and easy to use. This system not only effectively recovers solid sodium carbonate but also allows for flexible adjustment of the sodium carbonate solution concentration according to needs. Furthermore, the system fully recycles water, reducing resource waste and saving costs. The method for recovering sodium carbonate from PTA organic residue is simple, easy to control, and suitable for widespread application. This method not only allows for flexible utilization and collection of sodium carbonate but also effectively collects solid sodium carbonate from the ash residue after PTA organic residue combustion.

[0006] The technical solution of the present invention is as follows:

[0007] A sodium carbonate recovery system includes a dissolving tank A, a pump A, a filter, an evaporation feed tank, a pump B, an evaporator A, a thickener A, a centrifuge A, a screw A, a drying system, a dissolving tank B, a condenser A, a pump C, a vacuum system A, an evaporator B, a refrigeration system, a thickener B, a centrifuge B, a screw B, a vacuum system B, a pump D, a recovery tank, a pump E, a main unit system, and a condenser B;

[0008] Liquid separation process:

[0009] The dissolving tank A is connected to the filter via pump A; the liquid outlet of the filter is connected to the evaporation feed tank, and the evaporation feed tank is connected to the evaporator A via pump B; the supernatant of evaporator A is extracted and connected to evaporator B, and the sodium bromide-rich supernatant of evaporator B is extracted to the recovery tank for impurity removal.

[0010] Solid separation process:

[0011] First stage: Solids are collected from the bottom of evaporator A. Evaporator A is connected to thickener A. Thickener A is connected to centrifuge A. Solids are discharged from centrifuge A to screw A. Screw A is directed to the drying system or to dissolving tank B by controlling the direction of rotation.

[0012] Second stage: Solids are collected from the bottom of evaporator B. Evaporator B is connected to the refrigeration system. The refrigeration system is connected to thickener B. Thickener B is connected to centrifuge B. Solids are discharged from centrifuge B to screw B. Screw B sends the solids to dissolving tank B.

[0013] Evaporation and condensation process:

[0014] First stage: The gas phase of evaporator A is connected to condenser A. The condensate of condenser A is pumped back to dissolving tank A and dissolving tank B by pump C to recover the condensate. The non-condensable gas of condenser A is vacuumed by vacuum system A to control the vacuum level.

[0015] Second stage: Evaporator B is connected to condenser B. The condensate in condenser B is pumped back to dissolving tank B by pump D to recover the condensate. The non-condensable gas in condenser B is controlled by vacuum system B to control the vacuum level.

[0016] Sodium carbonate recycling process:

[0017] Screws A and B deliver solids to dissolving tank B, which is used to dissolve sodium carbonate. The sodium carbonate solution in dissolving tank B is then returned to the main unit system for reuse via pump E.

[0018] Screw A can also send solids to a drying system, where they are dried to obtain sodium carbonate solids, which are then packaged.

[0019] Preferably, pump A is installed on the connecting pipeline between dissolving tank A and filter, and pump B is installed on the connecting pipeline between evaporation feed tank and evaporator A. The arrangement of pumps A and pump B facilitates the smooth transport of slurry and liquid.

[0020] Preferably, pump C is installed at the condensate outlet of condenser A and pump D is installed at the condensate outlet of condenser B. This facilitates the flexible use of condensate produced by the condenser, improves the recycling rate of condensate, reduces water input, and saves energy.

[0021] Preferably, a thickener A is provided upstream of centrifuge A and a thickener B is provided upstream of centrifuge B to improve the solid separation efficiency of centrifuge A and centrifuge B; a screw A is provided downstream of centrifuge A and a screw B is provided downstream of centrifuge B, and the arrangement of screw A and screw B facilitates solid transport.

[0022] Preferably, the screw A is a bidirectional screw, which can control the solid to enter the dissolving tank B by steering, so as to directly dissolve and reuse sodium carbonate; it can also control the solid to enter the drying system to separate dry sodium carbonate.

[0023] Preferably, the screw B is a unidirectional screw that returns low-purity sodium carbonate to the system.

[0024] Preferably, evaporator A is connected to vacuum system A, and evaporator B is connected to vacuum system B, so as to make more effective use of the low-temperature waste heat of the device; evaporator A uses evaporation crystallization to separate sodium carbonate more efficiently; the sodium carbonate solution is evaporated in two stages by evaporator A and evaporator B to increase the concentration of discharged impurities and improve the recovery rate of sodium carbonate.

[0025] Preferably, the solid outlet of the evaporator B is connected to a refrigeration system to recover more sodium carbonate through freeze crystallization.

[0026] Preferably, the filter is a sintered filter to remove insoluble impurities.

[0027] Preferably, the drying device is a rake dryer, which can dry sodium carbonate quickly and efficiently; the filter is a plate and frame filter, which can filter liquids in large quantities.

[0028] A method for recovering sodium carbonate from PTA organic residue using a sodium carbonate recovery system, the process of which is as follows:

[0029] (1) The ash residue obtained after burning PTA organic residue in an incinerator is placed in a dissolving tank A and mixed with water. The mass ratio of ash residue to water is 1:3.0-5.0 to obtain solution A.

[0030] (2) After filtering solution A to remove insoluble solid cobalt, manganese and corrosive ions, solution B containing only sodium carbonate and sodium bromide is obtained.

[0031] (3) Solution B in the evaporation feed tank is pumped into evaporator A by pump B for concentration. When the sodium carbonate concentration in the solution is between 30-33%, the solution is sent to thickener A for further concentration. When the sodium carbonate concentration in the solution is between 58-62%, it enters centrifuge A for solid-liquid separation.

[0032] (4) The solid separated by centrifuge A is selected to be transported to dissolving tank B as needed to prepare a sodium carbonate solution with a concentration of 20-25%; or when the filter cake is transported to the drying system, sodium carbonate solid is obtained.

[0033] (5) The supernatant in evaporator A is drawn into evaporator B for further concentration, recovery of sodium carbonate and increase of impurity concentration;

[0034] (6) The solid in evaporator B is extracted into the refrigeration system to cool down, thereby reducing the solubility of sodium carbonate and precipitating more sodium carbonate.

[0035] (7) The frozen liquid is concentrated by thickener B and then enters centrifuge B for solid-liquid separation.

[0036] (8) The solid is sent to the dissolving tank B via screw B and dissolved to obtain sodium carbonate solution for reuse in the system.

[0037] The PTA organic residue (hereinafter referred to as organic residue) is dissolved in 20-25% sodium carbonate, which effectively reduces the drastic pH fluctuations and the change in valence of cobalt and manganese ions caused by strong alkalinity during the dissolution process of adding sodium hydroxide or a mixture of sodium hydroxide and sodium carbonate in the existing process. This improves the catalytic activity of the cobalt and manganese recovery catalyst. At the same time, the filtrate after separating cobalt and manganese carbonate is dried and incinerated to obtain sodium carbonate, realizing the recycling of sodium carbonate. When it is necessary to dissolve the organic residue, it is fed into the mixing tank using a bidirectional screw conveyor. The condensate from the condenser enters the mixing tank and is mixed with sodium carbonate to make the sodium carbonate solution in the mixing tank between 20-25% for use in dissolving the organic residue.

[0038] Conversely, the solids separated by the centrifuge are collected as filter cakes with a moisture content between 14-16%, and then sent to a drying device to dry, yielding solid sodium carbonate.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] 1. In the sodium carbonate recovery system provided by this invention, the steam produced by the evaporator is condensed by the condenser to obtain condensate. The condensate is used in the dissolving tank to dissolve ash or in the mixing tank to adjust the concentration of the sodium carbonate solution, thereby achieving water recycling, improving water utilization, reducing energy waste, and lowering production costs. By connecting the gas outlet of the evaporator to the shell-side inlet of the condenser, the water recycling rate can be further improved, thereby reducing costs.

[0041] 2. In the sodium carbonate recovery system provided by this invention, the sodium carbonate solution in the evaporator is applied in two separate ways, making the system design more reasonable. When a sodium carbonate solution with a concentration of 20-25% is required, the sodium carbonate solution with a concentration of 58-62% is diluted directly with condensate, shortening the preparation time. By drying solution B, sodium carbonate solid can be collected, which is convenient for collection and storage.

[0042] 3. The sodium carbonate recovery system provided by this invention has the advantages of reasonable design, high practicality and convenient use. In this recovery system, not only is sodium carbonate solid effectively recovered, but the concentration of sodium carbonate solution can also be flexibly adjusted according to needs. At the same time, the system fully recycles water, reducing resource waste and saving costs.

[0043] 4. The method for recovering sodium carbonate from PTA organic residue provided by this invention has the advantages of being simple, easy to control, and suitable for widespread application. This method not only allows for flexible utilization and collection of sodium carbonate, but also effectively collects solid sodium carbonate from the ash residue after the combustion of PTA organic residue.

[0044] 5. In order to improve the recycling rate of sodium carbonate, this invention adopts a combination of steam crystallization and freeze crystallization to recover sodium carbonate.

[0045] 6. In order to effectively utilize the low-temperature waste heat of the device, both stages of the evaporator of this invention adopt a vacuum system. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 This is a schematic diagram of a sodium carbonate recovery system.

[0048] In the diagram, 1-Dissolving tank A, 2-Pump A, 3-Filter, 4-Evaporation feed tank, 5-Pump B, 6-Evaporator A, 7-Thickener A, 8-Centrifuge A, 9-Screw A, 10-Drying system, 11-Dissolving tank B, 12-Condenser A, 13-Pump C, 14-Vacuum system A, 15-Evaporator B, 16-Refrigeration system, 17-Thickener B, 18-Centrifuge B, 19-Screw B, 20-Vacuum system B, 21-Pump D, 22-Recovery tank, 23-Pump E, 24-Main unit system, 25-Condenser B. Detailed Implementation

[0049] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0050] Example 1

[0051] A sodium carbonate recovery system includes a dissolving tank A1, a pump A2, a filter 3, an evaporation feed tank 4, a pump B5, an evaporator A6, a thickener A7, a centrifuge A8, a screw A9, a drying system 10, a dissolving tank B11, a condenser A12, a pump C13, a vacuum system A14, an evaporator B15, a refrigeration system 16, a thickener B17, a centrifuge B18, a screw B19, a vacuum system B20, a pump D21, a recovery tank 22, a pump E23, a main unit system 24, and a condenser B25.

[0052] Liquid separation process:

[0053] Dissolving tank A1 is connected to filter 3 via pump A2; the liquid outlet of filter 3 is connected to evaporation feed tank 4, and evaporation feed tank 4 is connected to evaporator A6 via pump B5; the supernatant of evaporator A6 is extracted and connected to evaporator B15, and the sodium bromide-rich supernatant of evaporator B15 is extracted to recovery tank 22 for impurity removal.

[0054] Solid separation process:

[0055] First stage: Solids are collected from the bottom of evaporator A6. Evaporator A6 is connected to thickener A7. Thickener A7 is connected to centrifuge A8. Solids are discharged from centrifuge A8 to screw A9. Screw A9 is directed to dry system 10 or to dissolving tank B11 by controlling the direction of rotation.

[0056] Second stage: Solids are collected from the bottom of evaporator B15. Evaporator B15 is connected to refrigeration system 16. Refrigeration system 16 is connected to thickener B17. Thickener B17 is connected to centrifuge B18. Solids are discharged from centrifuge B18 to screw B19. Screw B19 sends the solids to dissolving tank B11.

[0057] Evaporation and condensation process:

[0058] First stage: The gas phase of evaporator A6 is connected to condenser A12. The condensate of condenser A12 is pumped back to dissolving tank A1 and dissolving tank B11 by pump C13 to recover the condensate. The non-condensable gas of condenser A12 is vacuumed by vacuum system A14 to control the vacuum level.

[0059] Second stage: The vapor phase of evaporator B15 is connected to condenser B25. The condensate in condenser B25 is pumped back to dissolving tank B11 by pump D21 to recover the condensate. The non-condensable gas in condenser B25 is vacuumed by vacuum system B20 to control the vacuum level.

[0060] Sodium carbonate recycling process:

[0061] Screws A9 and B19 deliver solids to dissolving tank B11, which is used to dissolve sodium carbonate. The sodium carbonate solution in dissolving tank B11 is then returned to the main unit system 24 for reuse via pump E23.

[0062] Screw A9 can also send solids to drying system 10, where they are dried to obtain sodium carbonate solids, which are then packaged.

[0063] In this embodiment, screw A9 is a bidirectional screw, which can control the solid to enter the dissolving tank B11 by steering, so as to realize the direct dissolution and reuse of sodium carbonate; it can also control the solid to enter the drying system 10 by steering to separate dry sodium carbonate;

[0064] Screw B19 is a one-way screw that returns low-purity sodium carbonate back to the system;

[0065] Filter 3 is a sintered filter 3, which removes insoluble impurities;

[0066] The drying device is a rake dryer, which can quickly and efficiently dry sodium carbonate; the filter 3 is a plate and frame filter, which can filter liquids in large quantities.

[0067] Example 2

[0068] A method for recovering sodium carbonate from PTA organic residue using a sodium carbonate recovery system, the process of which is as follows:

[0069] (1) The ash obtained after burning PTA organic residue in an incinerator is placed in a dissolving tank A1 and mixed with water. The mass ratio of ash to water is 1:4.0 to obtain solution A.

[0070] (2) After filtering solution A through filter 3 to remove insoluble solid cobalt, manganese and corrosive ions, solution B containing only sodium carbonate and sodium bromide is obtained.

[0071] (3) Solution B in evaporation feed tank 4 is pumped into evaporator A6 by pump B5 for concentration. When the sodium carbonate concentration in the solution is between 30-33%, the solution is sent to thickener A7 for further concentration. When the sodium carbonate concentration in the solution is between 58-62%, it enters centrifuge A8 for solid-liquid separation.

[0072] (4) The solid separated by centrifuge A8 is selected by screw A9 to be transported to dissolving tank B11 to prepare a sodium carbonate solution with a concentration of 20-25% as needed; or the filter cake is transported to drying system 10 to obtain sodium carbonate solid.

[0073] (5) The supernatant in evaporator A6 is drawn into evaporator B15 for further concentration, recovery of sodium carbonate and increase of impurity concentration;

[0074] (6) The solid in evaporator B15 is extracted to the refrigeration system 16 to cool down in order to reduce the solubility of sodium carbonate and precipitate more sodium carbonate;

[0075] (7) The frozen liquid is concentrated in thickener B17 and then enters centrifuge B18 for solid-liquid separation.

[0076] (8) The solid is sent to the dissolving tank B11 via screw B19 to dissolve and obtain sodium carbonate solution for reuse in the system.

[0077] Example 3

[0078] The difference from Example 2 is that in step (1), the mass ratio of ash to water is 1:3.0, resulting in solution A.

[0079] Example 4

[0080] The difference from Example 2 is that in step (1), the mass ratio of ash to water is 1:5.0, resulting in solution A.

[0081] Examples 2-4 all achieved the reuse of water and sodium carbonate, effectively reducing energy waste and lowering treatment costs.

[0082] Although the present invention has been described in detail with reference to preferred embodiments, it is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the scope of the claims.

Claims

1. A method for recovering sodium carbonate from PTA organic residue using a sodium carbonate recovery system, characterized in that, The process is as follows: (1) The ash residue obtained after burning PTA organic residue in an incinerator is placed in a dissolving tank A and mixed with water. The mass ratio of ash residue to water is 1:3.0-5.0 to obtain solution A. (2) After filtering solution A to remove insoluble solid cobalt, manganese and corrosive ions, solution B containing only sodium carbonate and sodium bromide is obtained. (3) Solution B in the evaporation feed tank is pumped into evaporator A by pump B for concentration. When the sodium carbonate concentration in the solution is between 30-33%, the solution is sent to thickener A for further concentration. When the sodium carbonate concentration in the solution is between 58-62%, it enters centrifuge A for solid-liquid separation. (4) The filter cake separated by centrifuge A is selected to be transported to dissolving tank B to prepare a sodium carbonate solution with a concentration of 20-25% according to the requirements; or when the filter cake is transported to the drying system, sodium carbonate solid is obtained. (5) The supernatant in evaporator A is drawn into evaporator B for further concentration, recovery of sodium carbonate and increase of impurity concentration; (6) The solid in evaporator B is extracted into the refrigeration system to cool down, thereby reducing the solubility of sodium carbonate and causing more sodium carbonate to precipitate; (7) After freezing, the liquid is concentrated by thickener B and then enters centrifuge B for solid-liquid separation; (8) The solid is sent to dissolving tank B via screw B to dissolve and obtain sodium carbonate solution for reuse in the system; The sodium carbonate recovery system includes a dissolving tank A, a filter, an evaporation feed tank, an evaporator A, a thickener A, a centrifuge A, a screw A, a drying system, a dissolving tank B, a condenser A, a vacuum system A, an evaporator B, a thickener B, a centrifuge B, a screw B, a vacuum system B, a recovery tank, a main unit system, and a condenser B. The dissolving tank A is connected to the filter, the liquid outlet of the filter is connected to the evaporation feed tank, and the evaporation feed tank is connected to the evaporator A; the supernatant outlet of the evaporator A is connected to the evaporator B, and the supernatant outlet of the evaporator B is connected to the recovery tank. The solid outlet at the bottom of the evaporator A is connected to the thickener A, the thickener A is connected to the centrifuge A, the centrifuge A is connected to the screw A, and the outlet of the screw A is divided into two paths, one of which is connected to the drying system and the other of which is connected to the dissolving tank B. The solid outlet at the bottom of the evaporator B is connected to the thickener B, the thickener B is connected to the centrifuge B, the centrifuge B is connected to the screw B, and the screw B is connected to the dissolving tank B. The vapor outlet of the evaporator A is connected to the condenser A, and the condensate outlet of the condenser A is divided into two paths, one of which is connected to the dissolving tank A and the other of which is connected to the dissolving tank B. The vapor outlet of the evaporator B is connected to the condenser B, and the condensate outlet of the condenser B is connected to the dissolving tank B. The dissolving tank B is connected to the main device system; Pump A is installed on the connecting pipe between dissolving tank A and filter, and pump B is installed on the connecting pipe between evaporation feed tank and evaporator A; A refrigeration system is provided on the connecting pipe between the solid outlet at the bottom of the evaporator B and the thickener B.

2. The method for recovering sodium carbonate from PTA organic residue using a sodium carbonate recovery system as described in claim 1, characterized in that, Pump C is installed at the condensate outlet of condenser A, and pump D is installed at the condensate outlet of condenser B.

3. The method for recovering sodium carbonate from PTA organic residue using a sodium carbonate recovery system as described in claim 1, characterized in that, A vacuum system A is connected to condenser A; a vacuum system B is connected to condenser B.

4. The method for recovering sodium carbonate from PTA organic residue using a sodium carbonate recovery system as described in claim 1, characterized in that, Pump E is installed on the connecting pipeline between the dissolving tank B and the main unit system.

5. The method for recovering sodium carbonate from PTA organic residue using a sodium carbonate recovery system as described in claim 1, characterized in that, Screw A is a bidirectional screw; screw B is a unidirectional screw.

6. The method for recovering sodium carbonate from PTA organic residue using a sodium carbonate recovery system as described in claim 1, characterized in that, The filter is a sintered filter.

7. The method for recovering sodium carbonate from PTA organic residue using a sodium carbonate recovery system as described in claim 1, characterized in that, The drying system is a rake dryer.

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