Ammonium sulfate and monoammonium phosphate mixed solution evaporative crystallization salt separation treatment system

Abstract

The utility model discloses an ammonium sulfate and monoammonium phosphate mixed solution evaporative crystallization salt separation treatment system which comprises a preheating unit, an ammonium sulfate evaporation concentration unit, an ammonium sulfate evaporation crystallization unit, a recovery heat exchange unit, an ammonium sulfate post-treatment unit, a monoammonium phosphate cooling crystallization unit, a monoammonium phosphate post-treatment unit and a carnallite treatment unit. According to the technical scheme adopted by the utility model, a mixed solution containing ammonium sulfate and monoammonium phosphate is subjected to combined treatment, so that qualified ammonium sulfate crystal salt, monoammonium phosphate crystal salt and mixed salt can be obtained, and the by-product benefit of a wastewater treatment system can be effectively improved.

Description

Technical Field

[0001] This utility model belongs to the field of high-salt wastewater evaporation and salt separation technology, specifically relating to a mixed solution of ammonium sulfate and monoammonium phosphate for evaporation, crystallization and salt separation treatment. Background Technology

[0002] The production process of lithium iron phosphate (LFP) batteries can be simplified as follows: first, iron phosphate is produced; then, iron phosphate is sintered with lithium carbonate, glucose, etc., to produce lithium iron phosphate. The production of iron phosphate generates a large amount of wastewater. Depending on the raw materials used, the production process of iron phosphate can be broadly divided into the ammonia method and the sodium method. The main difference is that the ammonia method uses ammonia water, while the sodium method uses sodium hydroxide. Due to increased competition in the iron phosphate industry in recent years, manufacturers tend to favor the lower-cost ammonia method. The ammonia method for iron phosphate production produces mother liquor and wash water containing ammonium sulfate, which may contain a small amount of monoammonium phosphate. After pretreatment and membrane concentration, the mother liquor is sent to an evaporation and crystallization system to produce ammonium sulfate byproducts for sale, while the distilled water is reused and miscellaneous salts are shipped out.

[0003] Currently, the main process for treating ferric phosphate and ammonium sulfate wastewater is "pretreatment + reverse osmosis + evaporation crystallization". Generally, the reverse osmosis process concentrates the wastewater's TDS (Total Dissolved Solids) to about 15%, and this portion of the wastewater is then sent to the evaporation crystallization system. Conventional evaporation crystallization systems produce ammonium sulfate as a byproduct, but rarely can they separate the salts to produce monoammonium phosphate. Therefore, when the phosphate content in the wastewater increases, the quality of the ammonium sulfate byproduct inevitably fails to meet external sales standards, and the amount of impurities increases, reducing the byproduct revenue for ferric phosphate producers, which is unacceptable in the current economic environment.

[0004] In view of this, providing a process for the separate crystallization of monoammonium phosphate, improving the stability of ammonium sulfate byproduct quality, reducing the amount of mixed salts produced, and realizing the evaporation, crystallization, and salt separation of ammonium sulfate and monoammonium phosphate has become an urgent problem to be solved at this stage. Utility Model Content

[0005] The purpose of this invention is to provide a salt separation system for the evaporation and crystallization of a mixture of ammonium sulfate and monoammonium phosphate, in order to solve the aforementioned problems existing in the prior art.

[0006] To achieve the above objectives, this utility model adopts the following technical solution: a system for evaporating, crystallizing, and separating salts from a mixture of ammonium sulfate and monoammonium phosphate, comprising:

[0007] The preheating unit is used to preheat the raw water containing a mixture of ammonium sulfate and monoammonium phosphate.

[0008] An ammonium sulfate evaporation and concentration unit is used to evaporate and concentrate raw water to obtain a concentrated solution with a TDS value of 450 mg / L-500 mg / L.

[0009] An ammonium sulfate evaporation and crystallization unit is used to evaporate and crystallize a concentrated solution to obtain a concentrated salt slurry with a solid content of 5%-15%.

[0010] The heat recovery unit is used to pressurize and heat the steam discharged from the ammonium sulfate evaporation and concentration unit and the ammonium sulfate evaporation and crystallization unit, and then transport the pressurized and heated steam to the ammonium sulfate evaporation and concentration unit and the ammonium sulfate evaporation and crystallization unit.

[0011] An ammonium sulfate post-treatment unit is used to centrifuge concentrated salt slurry to obtain ammonium sulfate and ammonium sulfate mother liquor; an ammonium sulfate mother liquor reflux pipe is provided between the ammonium sulfate post-treatment unit and the ammonium sulfate evaporation and crystallization unit, and the ammonium sulfate mother liquor reflux pipe is used to return the ammonium sulfate mother liquor to the ammonium sulfate evaporation and crystallization unit.

[0012] The monoammonium phosphate cooling crystallization unit is used to cool and crystallize ammonium sulfate mother liquor to obtain a salt slurry.

[0013] The monoammonium phosphate post-treatment unit is used to centrifuge the salt slurry to obtain monoammonium phosphate and ammonium phosphate mother liquor; an ammonium phosphate mother liquor reflux pipe is provided between the monoammonium phosphate post-treatment unit and the monoammonium phosphate cooling crystallization unit, the ammonium phosphate mother liquor reflux pipe is used to return the ammonium phosphate mother liquor to the monoammonium phosphate cooling crystallization unit;

[0014] The mixed salt processing unit is used to dry the ammonium phosphate mother liquor transported from the monoammonium phosphate post-processing unit to obtain mixed salts.

[0015] As an optional implementation of the above technical solution, the preheating unit includes a feed tank, a water pump, a distilled water preheater, and a steam preheater connected in sequence. The feed tank is used to store raw water. The distilled water preheater has a first heat exchange chamber for inputting distilled water to preheat the raw water for the first time. The steam preheater has a second heat exchange chamber for inputting steam to preheat the raw water for the second time.

[0016] As an optional implementation of the above technical solution, both the distilled water preheater and the steam preheater are plate heat exchangers.

[0017] As an optional embodiment of the above technical solution, the ammonium sulfate evaporation and concentration unit includes a falling film evaporator, a falling film circulation pump, a falling film separator, and a falling film transfer pump. The falling film circulation pump is used to circulate the raw water in the falling film evaporator to obtain concentrated liquid in the falling film evaporator. The falling film separator is used to separate the gas generated by the falling film evaporator. The separated liquid is returned to the falling film evaporator, and the separated steam is transported to the recovery heat exchange unit. The falling film transfer pump is used to transport the concentrated liquid to the ammonium sulfate post-treatment unit.

[0018] As an optional embodiment of the above technical solution, the ammonium sulfate evaporation and crystallization unit includes a forced circulation crystallization separator, a forced circulation evaporator, a forced circulation pump, and an ammonium sulfate discharge pump. The forced circulation crystallization separator and the forced circulation evaporator are connected by the forced circulation pump. The forced circulation pump is used to circulate the concentrate in the forced circulation crystallization separator, so that the concentrate forms ammonium sulfate crystals in the forced circulation evaporator, and the ammonium sulfate crystals are returned to the forced circulation crystallization separator to obtain a concentrated salt slurry. The steam generated by the forced circulation crystallization separator is used to transport to the heat recovery and heat exchange unit, and the ammonium sulfate discharge pump is used to transport the concentrated salt slurry to the ammonium sulfate post-treatment unit.

[0019] As an optional embodiment of the above technical solution, the heat recovery unit includes a compressor, a gas scrubbing tower, a condensate tank, and a condensate pump; the gas scrubbing tower is used to receive the steam discharged from the ammonium sulfate evaporation and concentration unit and the ammonium sulfate evaporation and crystallization unit; the compressor is used to pressurize and heat the gas conveyed by the gas scrubbing tower, and to convey the pressurized and heated steam to the ammonium sulfate evaporation and concentration unit and the ammonium sulfate evaporation and crystallization unit; the condensate tank is used to receive the condensate discharged from the ammonium sulfate evaporation and concentration unit and the ammonium sulfate evaporation and crystallization unit; and the condensate pump is used to convey the condensate from the condensate tank to the first heat exchange chamber of the distilled water preheater.

[0020] As an optional embodiment of the above technical solution, the ammonium sulfate post-processing unit includes an ammonium sulfate thickener, an ammonium sulfate centrifuge, an ammonium sulfate mother liquor tank, and an ammonium sulfate mother liquor pump. The ammonium sulfate thickener, the ammonium sulfate centrifuge, and the ammonium sulfate mother liquor tank are connected in sequence. The ammonium sulfate centrifuge is used to centrifuge the concentrated salt slurry to obtain ammonium sulfate and ammonium sulfate mother liquor. The ammonium sulfate mother liquor tank is used to store the ammonium sulfate mother liquor. The input end of the ammonium sulfate mother liquor pump is connected to the ammonium sulfate mother liquor tank. One output end of the ammonium sulfate mother liquor pump is connected to the ammonium sulfate evaporation and crystallization unit through the ammonium sulfate mother liquor reflux pipe. The other output end of the ammonium sulfate mother liquor pump is connected to the monoammonium phosphate cooling and crystallization unit.

[0021] As an optional embodiment of the above technical solution, the monoammonium phosphate cooling crystallization unit includes a low-temperature flash crystallizer, a flash circulation pump, a steam condenser, a vacuum pump, and a phosphate discharge pump. The vacuum pump is used to draw negative pressure into the flash crystallizer, so that the ammonium sulfate mother liquor inside the low-temperature flash crystallizer flashes and crystallizes under negative pressure to obtain a salt slurry. The flash circulation pump is used to circulate the ammonium sulfate mother liquor inside the flash crystallizer to flash-cool it. The steam condenser is used to cool the steam generated by the flash crystallizer. The phosphate discharge pump is used to transport the salt slurry in the low-temperature flash crystallizer to the monoammonium phosphate post-processing unit.

[0022] As an optional embodiment of the above technical solution, the monoammonium phosphate post-processing unit includes an ammonium phosphate thickener, an ammonium phosphate centrifuge, an ammonium phosphate mother liquor tank, and an ammonium phosphate mother liquor pump; the ammonium phosphate thickener, the ammonium phosphate centrifuge, and the ammonium phosphate mother liquor tank are connected in sequence; the ammonium phosphate centrifuge is used to centrifuge the salt slurry to obtain monoammonium phosphate and ammonium phosphate mother liquor; the ammonium phosphate mother liquor tank is used to store the ammonium phosphate mother liquor; the input end of the ammonium phosphate mother liquor pump is connected to the ammonium phosphate mother liquor tank; one output end of the ammonium phosphate mother liquor pump is connected to the monoammonium phosphate cooling and crystallization unit through the ammonium phosphate mother liquor reflux pipe; and the other output end of the ammonium phosphate mother liquor pump is connected to the mixed salt processing unit.

[0023] As an optional embodiment of the above technical solution, the mixed salt processing unit includes a mother liquor dryer, which is a scraper drum dryer or a rake dryer. The mother liquor dryer is used to dry the ammonium phosphate mother liquor and output mixed salt.

[0024] The beneficial effects of this utility model are as follows:

[0025] The technical solution adopted in this utility model is to combine the treatment of a mixed solution containing ammonium sulfate and monoammonium phosphate to obtain qualified ammonium sulfate crystals, monoammonium phosphate crystals and mixed salts, which can effectively improve the by-product efficiency of the wastewater treatment system. Attached Figure Description

[0026] Figure 1 This is a flowchart of a salt separation system for evaporation and crystallization of a mixture of ammonium sulfate and monoammonium phosphate in one embodiment of this utility model;

[0027] Figure 2 This is a schematic diagram of the connection structure of the preheating unit, the ammonium sulfate evaporation and concentration unit, the ammonium sulfate evaporation and crystallization unit, the heat recovery and exchange unit, and the ammonium sulfate post-treatment unit in one embodiment of this utility model.

[0028] Figure 3 This is a schematic diagram of the connection structure of the monoammonium phosphate cooling crystallization unit, the monoammonium phosphate post-treatment unit, and the miscellaneous salt treatment unit in one embodiment of this utility model.

[0029] In the diagram: 1-Preheating unit; 2-Ammonium sulfate evaporation and concentration unit; 3-Ammonium sulfate evaporation and crystallization unit; 4-Heat recovery unit; 5-Ammonium sulfate post-treatment unit; 6-Monoammonium phosphate cooling and crystallization unit; 7-Monoammonium phosphate post-treatment unit; 8-Miscellaneous salt treatment unit;

[0030] 11-Feed box; 12-Water pump; 13-Distilled water preheater; 14-Steam preheater;

[0031] 21-Falling film evaporator; 22-Falling film circulating pump; 23-Falling film separator; 24-Falling film transfer pump;

[0032] 31-Forced circulation crystallizer; 32-Forced circulation evaporator; 33-Forced circulation pump; 34-Ammonium sulfate discharge pump;

[0033] 41-Compressor; 42-Air scrubber; 43-Condensate tank; 44-Condensate pump;

[0034] 51-Ammonium sulfate thickener; 52-Ammonium sulfate centrifuge; 53-Ammonium sulfate mother liquor tank; 54-Ammonium sulfate mother liquor pump;

[0035] 61-Low-temperature flash crystallizer; 62-Flash circulation pump; 63-Steam condenser; 64-Vacuum pump; 65-Ammonium phosphate discharge pump;

[0036] 71-Ammonium phosphate thickener; 72-Ammonium phosphate centrifuge; 73-Ammonium phosphate mother liquor tank; 74-Ammonium phosphate mother liquor pump;

[0037] 81-Mother liquor dryer. Detailed Implementation

[0038] like Figures 1-3 As shown, this embodiment provides a salt separation system for evaporation and crystallization of a mixture of ammonium sulfate and monoammonium phosphate, which includes: a preheating unit 1, an ammonium sulfate evaporation and concentration unit 2, an ammonium sulfate evaporation and crystallization unit 3, a heat recovery and exchange unit 4, an ammonium sulfate post-treatment unit 5, a monoammonium phosphate cooling and crystallization unit 6, a monoammonium phosphate post-treatment unit 7, and a miscellaneous salt treatment unit 8.

[0039] The preheating unit 1 includes a feed tank 11, a water pump 12, a distilled water preheater 13, and a steam preheater 14. A mixture of ammonium sulfate and monoammonium phosphate is fed into the feed tank 11 as raw water. The raw water is then pumped by the water pump 12 into the distilled water preheater 13 and the steam preheater 14. The distilled water preheater 13 has a first heat exchange chamber for receiving distilled water to preheat the raw water initially. The steam preheater 14 has a second heat exchange chamber for receiving steam to preheat the raw water a second time. The raw water is generally preheated to 90-100°C. Both the distilled water preheater 13 and the steam preheater 14 use plate heat exchangers.

[0040] The ammonium sulfate evaporation and concentration unit 2 includes a falling film evaporator 21, a falling film circulating pump 22, a falling film separator 23, and a falling film transfer pump 24. The falling film evaporator 21 is a shell-and-tube heat exchanger with two interfaces: a hot side and a cold side. The hot side is compressor outlet steam or live steam, and the cold side is circulating liquid. The medium on the hot side is high-temperature steam, which heats the heat exchange tubes of the falling film evaporator to transfer heat to heat the circulating liquid on the cold side. The temperature of the steam on the hot side is about 105°C, and the temperature of the circulating liquid on the cold side is about 90°C. In this example, the falling film circulating pump 22 draws the circulating liquid from the bottom of the falling film evaporator 21 and returns it to the top of the evaporator 21, entering the cold side of the evaporator. The wastewater undergoes heat exchange and evaporation with the hot-side steam in the heat exchange tubes, requiring the concentrated liquid to be free of crystalline salts. Generally, after the concentrated wastewater reaches a TDS of 45%-50%, it is transported to the ammonium sulfate evaporation and crystallization unit 3 via the falling film transfer pump 24. The falling film transfer pump 24 typically operates at a variable frequency, its operating frequency interlocked with the liquid level in the ammonium sulfate evaporation and crystallization unit 3. The secondary steam generated from evaporation and concentration enters the falling film separator 23, which has a built-in demister. The secondary steam after passing through the falling film separator 23 enters the gas scrubbing tower 42 in the recovery heat exchange unit 4. The condensate generated after heat exchange on the hot side of the falling film evaporator 21 is discharged to the condensate tank 43 in the recovery heat exchange unit 4, and then transported by the condensate pump 44 to the first heat exchange chamber of the distilled water preheater 13 to preheat the raw water, achieving energy recovery.

[0041] The ammonium sulfate evaporation and crystallization unit 3 includes a forced circulation crystallization separator 31, a forced circulation evaporator 32, a forced circulation pump 33, and an ammonium sulfate discharge pump 34. A falling film transfer pump 24 delivers 45-50% concentrated liquid to the crystallization separator 31. The liquid circulates and exchanges heat in the forced circulation evaporator 32 via the forced circulation pump 33, and after heating, it flashes and evaporates in the crystallization separator 31 to achieve ammonium sulfate crystallization. The forced circulation evaporator 32 is a shell-and-tube heat exchanger with two interfaces: a hot side and a cold side. The hot side receives compressor outlet steam or live steam, while the cold side receives circulating liquid. The medium on the hot side is high-temperature steam, which heats the heat exchange tubes of the forced circulation evaporator 32 to transfer heat to heat the circulating liquid on the cold side. The steam temperature on the hot side is approximately 105°C, and the circulating liquid temperature on the cold side is approximately 97°C. In this example, the forced circulation pump 33 is an axial flow pump with a design head of 2.8~4m and an outlet pressure of 0.25~0.32MPa. The outlet of the forced circulation pump 33 is connected to the cold side of the forced circulation evaporator 32. After heat exchange, it returns to the forced circulation crystallizer 31 for flash crystallization. The secondary steam generated at the top enters the gas scrubbing tower 42 in the recovery heat exchange unit 4. The concentrated salt slurry (solid content 5%~15%) at the bottom of the crystallizer 31 is transported to the post-ammonium sulfate post-treatment unit 5 via the ammonium sulfate discharge pump 34.

[0042] The heat recovery unit 4 includes a compressor 41, a gas scrubbing tower 42, a condensate tank 43, and a condensate pump 44. The compressor 41 is a centrifugal steam compressor that pressurizes and heats the secondary steam generated by the falling film evaporator 21 and the forced circulation evaporator 32 to increase its calorific value. The steam is then returned to the falling film separator 23 and the forced circulation crystallizer 31 as a heat source for evaporation, concentration, and crystallization of the circulating liquid. The secondary steam generated by the falling film separator 23 and the forced circulation crystallizer 31 is defoamed by the gas scrubbing tower 42 before entering the compressor 41, which increases the temperature of the secondary steam by 18-20°C. The secondary steam exiting the compressor 41 returns to the falling film evaporator 21 and the forced circulation evaporator 32 for heat exchange and condensation before entering the condensate tank 43. The condensate is then pumped by the condensate pump 44 to the first heat exchange chamber of the distilled water preheater 13 to exchange heat with the raw water. After the condensate temperature drops to 50-60°C, it is discharged outside the system. If a lower condensate temperature is required, consider adding a condensate cooling plate, which can further reduce the condensate temperature to below 45℃.

[0043] The ammonium sulfate post-processing unit 5 includes an ammonium sulfate thickener 51, an ammonium sulfate centrifuge 52, an ammonium sulfate mother liquor tank 53, and an ammonium sulfate mother liquor pump 54. The ammonium sulfate thickener 51 is equipped with a stirrer to increase the solid-liquid ratio of the concentrated salt slurry. One end of the thickener is connected to the ammonium sulfate discharge pump 34 of the ammonium sulfate evaporation and crystallization unit, and the other end is connected to the ammonium sulfate centrifuge 52. The ammonium sulfate centrifuge 52 is a solid-liquid separation device, which can be a two-stage pusher centrifuge, a horizontal screw centrifuge, etc. It can centrifuge and dehydrate ammonium sulfate to a moisture content of 3%~5%. Generally, the wet salt after centrifugation will be dried again in a fluidized bed dryer to a moisture content of less than 0.5% to obtain ammonium sulfate. After centrifugation, the ammonium sulfate mother liquor flows by gravity to the ammonium sulfate mother liquor tank 53, and is then transported to the ammonium sulfate strong circulation crystallization separator 31 by the ammonium sulfate mother liquor pump 54. When the monoammonium phosphate content in the mother liquor rises to the set concentration, the ammonium sulfate mother liquor pump 54 transports the ammonium sulfate mother liquor to the low-temperature flash crystallizer 61 in the monoammonium phosphate post-treatment unit 6 for low-temperature flash crystallization.

[0044] The monoammonium phosphate cooling crystallization unit 6 includes a low-temperature flash crystallizer 61, a flash circulation pump 62, a steam condenser 63, a vacuum pump 64, and a phosphate discharge pump 65. The vacuum pump 64 draws negative pressure into the low-temperature flash crystallizer 61, and the ammonium sulfate mother liquor pump 54 transports the high-temperature ammonium sulfate mother liquor (temperature 95~100℃) to the low-temperature flash crystallizer 61. Under negative pressure conditions, flash crystallization occurs. Since the solubility of monoammonium phosphate decreases rapidly with decreasing temperature, monoammonium phosphate is crystallized and produced in the low-temperature flash crystallizer 61. In this example, the flash circulation pump 62 is an axial flow pump with a head of 2.5~3.5m. It extracts the circulating liquid from the low-temperature flash crystallizer 61 and returns it to the crystallizer to circulate and flash-cool the mother liquor. The generated secondary steam is cooled by the steam condenser 63, which is a shell-and-tube heat exchanger. The hot side inlet is for secondary steam, and the hot side outlet is connected to the vacuum pump 64. The cold side is circulated with circulating water. After the secondary steam is condensed in the steam condenser 63, it enters the condensate tank. The remaining tail gas is extracted by the vacuum pump 64 and discharged into the atmosphere. The brine slurry in the low-temperature flash crystallizer 61 is discharged to the ammonium phosphate thickener 71 in the monoammonium phosphate post-treatment unit 7 via the ammonium phosphate discharge pump 65.

[0045] The monoammonium phosphate (MAP) post-processing unit 7 includes a MAP thickener 71, a MAP centrifuge 72, a MAP mother liquor tank 73, and a MAP mother liquor pump 74. The MAP thickener 71 is equipped with a stirrer to increase the solid-liquid ratio of the concentrated MAP slurry. One end of the thickener is connected to the MAP mother liquor pump 74 of the MAP cooling and crystallization unit, and the other end is connected to the MAP centrifuge 72. The MAP centrifuge 72 is a solid-liquid separation device, and can be a two-stage pusher centrifuge, a horizontal screw centrifuge, a scraper centrifuge, etc. It can centrifuge and dehydrate MAP to a moisture content of 3%~5%. Generally, the centrifuged wet salt will be further dried and dehydrated in a fluidized bed dryer to a moisture content of less than 0.5%, yielding MAP. After centrifugation, the ammonium phosphate mother liquor flows by gravity to the ammonium phosphate mother liquor tank 73, and is then transported by the ammonium phosphate mother liquor pump 74 to the low-temperature flash crystallizer 61 of the monoammonium phosphate cooling crystallization unit 6. When the content of impurities in the ammonium phosphate mother liquor rises to the design concentration, the ammonium phosphate mother liquor pump 74 transports the ammonium phosphate mother liquor to the impurities treatment unit 8.

[0046] The mixed salt processing unit 8 includes a mother liquor dryer 81; the mother liquor dryer 81 is a scraper drum dryer or a rake dryer. After the ammonium phosphate mother liquor enters the mother liquor dryer 81, the mother liquor dryer 81 dries the ammonium phosphate mother liquor and outputs mixed salt.

[0047] This invention provides a system for the evaporation, crystallization, and salt separation of a mixture of ammonium sulfate and monoammonium phosphate: the mixture, used as raw water, is heated to 90-100°C after passing through a distilled water preheater 13 and a steam preheater 14. The preheated raw water then enters a falling film evaporator 21, where it is concentrated at 90°C. After the raw water is concentrated to a TDS of 40-45%, it is transported to an ammonium sulfate crystallizer 31 via a falling film transfer pump 24. The raw water is heated to approximately 97°C in the crystallizer 31 to produce ammonium sulfate crystals, which are then transported to an ammonium sulfate thickener 51 via an ammonium sulfate discharge pump 24. After passing through an ammonium sulfate centrifuge... After centrifugation, ammonium sulfate wet salt is obtained. The ammonium sulfate mother liquor after centrifugation is returned to the ammonium sulfate crystallizer 31 via the ammonium sulfate mother liquor pump 54. When the concentration of monoammonium phosphate reaches the design value, the mother liquor is transported to the low-temperature flash crystallizer 61 via the ammonium sulfate mother liquor pump 54. The monoammonium phosphate slurry produced by low-temperature crystallization is transported to the ammonium phosphate thickener 71 via the ammonium phosphate discharge pump 65. After passing through the ammonium phosphate centrifuge 72, monoammonium phosphate wet salt is obtained. When the content of impurities in the ammonium phosphate mother liquor rises to the design concentration, the ammonium phosphate mother liquor pump 74 transports the ammonium phosphate mother liquor to the mother liquor dryer 81 in the impurity salt treatment unit to obtain impurity salt. The technical solution adopted by this utility model is for the combined treatment of mixed liquids containing ammonium sulfate and monoammonium phosphate, which can obtain qualified ammonium sulfate crystals, monoammonium phosphate crystals, and mixed salts, and can effectively improve the by-product efficiency of wastewater treatment systems.

[0048] The workflow of the above-mentioned ammonium sulfate and monoammonium phosphate mixed solution evaporation crystallization salt separation treatment system includes the following steps:

[0049] (1) Preheat the raw water containing the mixture of ammonium sulfate and monoammonium phosphate to 90~100℃;

[0050] (2) The evaporation temperature of the ammonium sulfate evaporation and concentration unit 2 and the ammonium sulfate evaporation and crystallization unit 3 is set to 80-85℃. The secondary steam enters the compressor 41 after being defoamed by the gas scrubbing tower 42.

[0051] (3) The ammonium sulfate evaporation and concentration unit 2 and the ammonium sulfate evaporation and crystallization unit 3 generate secondary steam (steam temperature 80-85℃). After being heated by the compressor 41, the secondary steam temperature is raised to 100-105℃ and then returned to the falling film evaporator 21 and the forced circulation evaporator 32 to exchange heat with the circulating liquid.

[0052] (4) After the ammonium sulfate is evaporated and concentrated, the concentration of the mixture reaches 45%-50%. Then it is discharged to the ammonium sulfate evaporation and crystallization unit 3 to produce ammonium sulfate salt. After passing through the post-treatment unit, the wet ammonium sulfate salt and centrifugal mother liquor are produced. The ammonium sulfate mother liquor is discharged to the monoammonium phosphate cooling and crystallization unit 6. Due to the decrease in temperature, the solubility of monoammonium phosphate decreases. Monoammonium phosphate is cooled to 40°C and then crystallized (freezing crystallization can be considered when the concentration of monoammonium phosphate is high). After passing through the post-treatment unit, the wet monoammonium phosphate salt and centrifugal mother liquor are produced.

[0053] (5) The centrifuged mother liquor of monoammonium phosphate is discharged to the mother liquor dryer 81. The mother liquor dryer 81 is a scraper drum dryer or a rake dryer. After the mother liquor enters the mother liquor dryer 81, it produces mixed salts.

[0054] Compared with existing technologies, this invention can stably produce monoammonium phosphate byproducts by evaporating and crystallizing ammonium sulfate, cooling and crystallizing monoammonium phosphate, and drying the mother liquor to produce impurities. It can also ensure the stability of the quality of ammonium sulfate byproducts, reduce the amount of impurities, and increase the economic benefits of the byproducts ammonium sulfate and monoammonium phosphate.

[0055] In this description of the utility model, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. They can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art will understand the specific meanings of these terms in this utility model. Furthermore, the specific features and structures described in the embodiments are included in at least one implementation method. Those skilled in the art can combine features from different implementation methods without contradiction. The scope of protection of this utility model is not limited to the specific implementation methods described above. Based on the basic technical concept of this utility model, implementation methods that can be conceived by those skilled in the art without creative effort are all within the scope of protection of this utility model.

Claims

1. A system for evaporating, crystallizing, and separating salts from a mixture of ammonium sulfate and monoammonium phosphate, characterized in that, include: The preheating unit (1) is used to preheat the raw water containing a mixture of ammonium sulfate and monoammonium phosphate. Ammonium sulfate evaporation and concentration unit (2) is used to evaporate and concentrate raw water to obtain a concentrated solution with a TDS value of 450 mg / L-500 mg / L. Ammonium sulfate evaporation and crystallization unit (3) is used to evaporate and crystallize the concentrate to obtain a concentrated salt slurry with a solid content of 5%-15%. The heat recovery unit (4) is used to pressurize and heat the steam discharged from the ammonium sulfate evaporation and concentration unit (2) and the ammonium sulfate evaporation and crystallization unit (3), and to transport the pressurized and heated steam to the ammonium sulfate evaporation and concentration unit (2) and the ammonium sulfate evaporation and crystallization unit (3); Ammonium sulfate post-treatment unit (5) is used to centrifuge concentrated salt slurry to obtain ammonium sulfate and ammonium sulfate mother liquor; an ammonium sulfate mother liquor reflux pipe is provided between the ammonium sulfate post-treatment unit (5) and the ammonium sulfate evaporation and crystallization unit (3), and the ammonium sulfate mother liquor reflux pipe is used to return the ammonium sulfate mother liquor to the ammonium sulfate evaporation and crystallization unit (3); The monoammonium phosphate cooling crystallization unit (6) is used to cool and crystallize the ammonium sulfate mother liquor to obtain a salt slurry. The monoammonium phosphate post-treatment unit (7) is used to centrifuge the salt slurry to obtain monoammonium phosphate and ammonium phosphate mother liquor; an ammonium phosphate mother liquor reflux pipe is provided between the monoammonium phosphate post-treatment unit (7) and the monoammonium phosphate cooling crystallization unit (6), and the ammonium phosphate mother liquor reflux pipe is used to return the ammonium phosphate mother liquor to the monoammonium phosphate cooling crystallization unit (6); The mixed salt processing unit (8) is used to dry the ammonium phosphate mother liquor conveyed by the monoammonium phosphate post-processing unit (7) to obtain mixed salt.

2. The ammonium sulfate and monoammonium phosphate mixed solution evaporation crystallization salt separation treatment system according to claim 1, characterized in that, The preheating unit (1) includes a feed tank (11), a water pump (12), a distilled water preheater (13), and a steam preheater (14) connected in sequence. The feed tank (11) is used to store raw water. The distilled water preheater (13) has a first heat exchange chamber for inputting distilled water to preheat the raw water once. The steam preheater (14) has a second heat exchange chamber for inputting steam to preheat the raw water a second time.

3. The ammonium sulfate and monoammonium phosphate mixed solution evaporation crystallization salt separation treatment system according to claim 2, characterized in that, Both the distilled water preheater (13) and the steam preheater (14) are plate heat exchangers.

4. The ammonium sulfate and monoammonium phosphate mixed solution evaporation crystallization salt separation treatment system according to claim 1, characterized in that, The ammonium sulfate evaporation and concentration unit (2) includes a falling film evaporator (21), a falling film circulation pump (22), a falling film separator (23), and a falling film transfer pump (24). The falling film circulation pump (22) is used to circulate the raw water of the falling film evaporator (21) to obtain concentrated liquid in the falling film evaporator (21). The falling film separator (23) is used to separate the gas generated by the falling film evaporator (21). The separated liquid is returned to the falling film evaporator (21), and the separated steam is transported to the recovery heat exchange unit (4). The falling film transfer pump (24) is used to transport the concentrated liquid to the ammonium sulfate post-treatment unit (5).

5. The ammonium sulfate and monoammonium phosphate mixed solution evaporation crystallization salt separation treatment system according to claim 1, characterized in that, The ammonium sulfate evaporation and crystallization unit (3) includes a forced circulation crystallization separator (31), a forced circulation evaporator (32), a forced circulation pump (33), and an ammonium sulfate discharge pump (34). The forced circulation crystallization separator (31) and the forced circulation evaporator (32) are connected by the forced circulation pump (33). The forced circulation pump (33) is used to circulate the concentrate in the forced circulation crystallization separator (31), so that the concentrate forms ammonium sulfate crystals in the forced circulation evaporator (32), and the ammonium sulfate crystals are returned to the forced circulation crystallization separator (31) to obtain a concentrated salt slurry. The steam generated by the forced circulation crystallization separator (31) is used to transport to the recovery heat exchange unit (4), and the ammonium sulfate discharge pump (34) is used to transport the concentrated salt slurry to the ammonium sulfate post-treatment unit (5).

6. The ammonium sulfate and monoammonium phosphate mixed solution evaporation crystallization salt separation treatment system according to claim 2, characterized in that, The heat recovery unit (4) includes a compressor (41), a gas scrubbing tower (42), a condensate tank (43), and a condensate pump (44). The gas scrubbing tower (42) is used to receive the steam discharged from the ammonium sulfate evaporation and concentration unit (2) and the ammonium sulfate evaporation and crystallization unit (3). The compressor (41) is used to pressurize and heat the gas transported by the gas scrubbing tower (42) and transport the pressurized and heated steam to the ammonium sulfate evaporation and concentration unit (2) and the ammonium sulfate evaporation and crystallization unit (3). The condensate tank (43) is used to receive the condensate discharged from the ammonium sulfate evaporation and concentration unit (2) and the ammonium sulfate evaporation and crystallization unit (3). The condensate pump (44) is used to transport the condensate from the condensate tank (43) to the first heat exchange chamber of the distilled water preheater (13).

7. The ammonium sulfate and monoammonium phosphate mixed solution evaporation crystallization salt separation treatment system according to claim 1, characterized in that, The ammonium sulfate post-processing unit (5) includes an ammonium sulfate thickener (51), an ammonium sulfate centrifuge (52), an ammonium sulfate mother liquor tank (53), and an ammonium sulfate mother liquor pump (54). The ammonium sulfate thickener (51), the ammonium sulfate centrifuge (52), and the ammonium sulfate mother liquor tank (53) are connected in sequence. The ammonium sulfate centrifuge (52) is used to centrifuge the concentrated salt slurry to obtain ammonium sulfate and ammonium sulfate mother liquor. The ammonium sulfate mother liquor tank (53) is used to store the ammonium sulfate mother liquor. The input end of the ammonium sulfate mother liquor pump (54) is connected to the ammonium sulfate mother liquor tank (53). One output end of the ammonium sulfate mother liquor pump (54) is connected to the ammonium sulfate evaporation crystallization unit (3) through the ammonium sulfate mother liquor reflux pipe. The other output end of the ammonium sulfate mother liquor pump (54) is connected to the monoammonium phosphate cooling crystallization unit (6).

8. The ammonium sulfate and monoammonium phosphate mixed solution evaporation crystallization salt separation treatment system according to claim 1, characterized in that, The monoammonium phosphate cooling crystallization unit (6) includes a low-temperature flash crystallizer (61), a flash circulation pump (62), a steam condenser (63), a vacuum pump (64), and a phosphate discharge pump (65). The vacuum pump (64) is used to draw negative pressure into the low-temperature flash crystallizer (61) so that the ammonium sulfate mother liquor inside the low-temperature flash crystallizer (61) flash crystallizes under negative pressure to obtain a salt slurry. The flash circulation pump (62) is used to circulate the ammonium sulfate mother liquor inside the low-temperature flash crystallizer (61) to flash cool it down. The steam condenser (63) is used to cool down the steam generated by the low-temperature flash crystallizer (61). The phosphate discharge pump (65) is used to transport the salt slurry in the low-temperature flash crystallizer (61) to the monoammonium phosphate post-processing unit (7).

9. The ammonium sulfate and monoammonium phosphate mixed solution evaporation crystallization salt separation treatment system according to claim 1, characterized in that, The monoammonium phosphate post-processing unit (7) includes an ammonium phosphate thickener (71), an ammonium phosphate centrifuge (72), an ammonium phosphate mother liquor tank (73), and an ammonium phosphate mother liquor pump (74). The ammonium phosphate thickener (71), the ammonium phosphate centrifuge (72), and the ammonium phosphate mother liquor tank (73) are connected in sequence. The ammonium phosphate centrifuge (72) is used to centrifuge the salt slurry to obtain monoammonium phosphate and ammonium phosphate mother liquor. The ammonium phosphate mother liquor tank (73) is used to store the ammonium phosphate mother liquor. The input end of the ammonium phosphate mother liquor pump (74) is connected to the ammonium phosphate mother liquor tank (73). One output end of the ammonium phosphate mother liquor pump (74) is connected to the monoammonium phosphate cooling crystallization unit (6) through the ammonium phosphate mother liquor return pipe. The other output end of the ammonium phosphate mother liquor pump (74) is connected to the miscellaneous salt processing unit (8).

10. The ammonium sulfate and monoammonium phosphate mixed solution evaporation crystallization salt separation treatment system according to claim 1, characterized in that, The mixed salt processing unit (8) includes a mother liquor dryer (81), which is a scraper drum dryer or a rake dryer. The mother liquor dryer (81) is used to dry the ammonium phosphate mother liquor and output mixed salt.

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