Energy-saving concentration and crystallization device and process for ammonium chloride solution

Abstract

The invention relates to the technical field of monopotassium phosphate production, in particular to an energy-saving concentration and crystallization device and process for an ammonium chloride solution. S2, oil-water separation; s3, purifying and size mixing; s4, filtering; s5, multi-effect evaporation and concentration; according to the method, efficient demulsification is achieved by innovatively adopting a centrifugal separator, organic phase entrainment is greatly reduced, and follow-up pollution is avoided from the source. Aiming at the problem of low-boiling-point solvent recovery, high-vacuum low-temperature evaporation and condensation technologies are integrated, and low-temperature efficient separation and cyclic utilization of organic matters are realized. A multi-effect / MVR concentration system is combined, solvent recovery and ammonium chloride solution concentration are synchronously completed, and the advantages of low-temperature operation, high efficiency and energy conservation are achieved. Through synergistic reaction of mother liquor and stock solution, waste is treated by waste, metal impurities are effectively removed, equipment scaling is prevented, long-period stable operation of a system is guaranteed, and finally a high-purity ammonium chloride product is obtained. The whole device has the advantages of low energy consumption, low cost and high purity.

Description

Technical Field

[0001] This invention relates to the field of potassium dihydrogen phosphate production technology, and in particular to an energy-saving concentration and crystallization device for ammonium chloride solution and its process. Background Technology

[0002] The process of preparing potassium dihydrogen phosphate (MKP) from wet-process phosphoric acid and potassium chloride via organic amine extraction is considered a promising production route due to its low raw material costs and avoidance of by-products. This process typically involves key steps such as extraction, back-extraction, crystallization, and solvent recovery. However, several technical challenges remain to be addressed in the actual industrial application of this technology, seriously affecting the stable operation of the system, product quality, and economic benefits.

[0003] First, the entrainment and contamination problems in the extraction system are prominent. During the phase separation process of extraction and back-extraction, due to the certain solubility of light white oil, higher alcohols, and other additives in the ammonium chloride aqueous phase, coupled with the kinetic stability of the phase separation interface, a certain degree of oil-water mixing inevitably occurs. This results in the entrainment of the oil phase in the aqueous phase, forming a small amount of "oil-in-water" (O / W) emulsion. This entrainment causes continuous loss of organic extractants, increasing production costs; at the same time, the entrained organic phase entering subsequent processes will contaminate the product potassium dihydrogen phosphate, leading to an increase in its organic impurity content and affecting product purity.

[0004] Secondly, the enrichment and separation of impurity ions pose a significant challenge. Because the raw material, wet-process phosphoric acid, contains various metallic impurities such as iron, aluminum, calcium, and magnesium, during the extraction process, the organic amine extractant, while primarily extracting phosphoric acid, also co-extracts small amounts of iron, aluminum, and other impurity ions. In the back-extraction stage, a 2% dilute ammonia solution is used as the back-extraction agent. The resulting ammonium phosphate solution is used for MKP production, while the co-extracted impurity ions may be concentrated and eluted during the extractant reactivation stage. Currently, ammonium chloride solution is commonly used to reactivate the extractant. During this process, these metallic impurity ions react with phosphate and ammonium ions to generate a mixed-type insoluble phosphate colloidal suspension containing up to 0.5% phosphate and water-insoluble matter (SS).

[0005] The mixed ammonium chloride waste liquid has a complex composition, high viscosity, and is extremely difficult to separate into solid and liquid components. Its treatment has become a bottleneck in the entire process: on the one hand, the ammonium chloride and valuable phosphate contained therein are difficult to recover effectively, resulting in resource waste and reduced yield; on the other hand, the high water insoluble matter and colloidal substances easily cause scaling and blockage of equipment and pipelines, forcing the system to be shut down frequently for cleaning, which seriously restricts the continuous and stable operation capability of the unit.

[0006] Therefore, developing a new process that can effectively solve the problems of organic phase entrainment loss, overcome the problem of impurity ion enrichment, and achieve efficient recycling of resources in waste liquid is crucial for promoting the industrial application of organic amine extraction technology for producing potassium dihydrogen phosphate. Summary of the Invention

[0007] The purpose of this invention is to provide an energy-saving ammonium chloride solution concentration and crystallization device and its process.

[0008] The solution of the present invention is: An energy-saving concentration and crystallization process for ammonium chloride solution includes the following steps: S1. Back-extraction: An ammonium chloride-ammonia solution with a mass concentration of 5%–15% and a free ammonia concentration of 1.5%–3% is used as the back-extraction agent to react with the extractant to generate an ammonium chloride stock solution. The pH of the ammonium chloride stock solution is 7.0–8.0. The extractant is a mixed solvent of organophosphate ammonium salt (R•H3PO4) and organoammonium chloride salt (R•HCl). The ammonium chloride-ammonia solution, as the back-extraction agent, reacts with the organic phase loaded with phosphoric acid and impurities—the extractant. After the reaction, phosphate ions and impurity anions are separated from the extractant, generating an ammonium chloride stock solution and restoring the activity of the organic extractant (R). S2. Oil-water separation: The ammonium chloride solution is centrifuged to remove the extractant entrained in the ammonium chloride emulsion and return it to the extraction system for recycling, thus obtaining an aqueous ammonium chloride solution; most of the organic phase is removed. S3. Purification and slurry preparation: The ammonium chloride aqueous solution is mixed with the ammonium chloride crystallization mother liquor and liquid ammonia, and the mixture is stirred to obtain a feed solution. The pH of the feed solution is adjusted to 8.0-8.5 to precipitate metal impurity ions. S4. Filtration: The liquid is filtered to obtain a clear ammonium chloride mixture, wherein the solid content of the clear ammonium chloride mixture is ≤0.01%. S5. Multi-effect evaporation and concentration: The clarified ammonium chloride mixture is preheated and concentrated at least twice; wherein... The first-effect evaporation is carried out under a vacuum of -50 to -45 kPa and a temperature of 60 to 65 °C. The vapor phase produced by evaporation is condensed, and the condensate is separated into oil and water. The recovered organic fusel alcohol is returned to the extraction process. The first-effect evaporation yields an ammonium chloride solution with a concentration of 15% to 20%, which is then further concentrated in the second effect. After the second-effect evaporation, a concentrated ammonium chloride solution with a concentration of 40-45% and a specific gravity of 1.34-1.38 is obtained. S6. Cooling, crystallization and separation: The concentrated ammonium chloride solution is transported to a cooling crystallizer and cooled to below 40°C to precipitate ammonium chloride crystals, obtaining a crystal slurry; the crystal slurry is centrifuged to separate solid ammonium chloride product and ammonium chloride crystallization mother liquor, which is returned to step S3 for recycling.

[0009] As a preferred technical solution, the stripping agent in step S1 is an ammonium chloride-ammonia solution with a mass concentration of 10% and a free ammonia concentration of 3%.

[0010] As a preferred technical solution, centrifugal separation in step S2 is performed using a centrifuge, and centrifugal separation in step S6 is performed using a centrifuge.

[0011] As a preferred technical solution, the pH of the ammonium chloride crystallization mother liquor is 5.3.

[0012] As a preferred technical solution, in step S5, the condensate generated by the first-effect evaporation is cooled to below 40°C and then subjected to gravity sedimentation for oil-water separation.

[0013] The present invention also discloses an energy-saving concentration and crystallization device for ammonium chloride solution, including a back-extraction recovery system, wherein the ammonium chloride stock solution tank of the back-extraction recovery system is connected to the feed inlet of a centrifuge via a pump; The organic phase outlet of the centrifuge is connected to the extractant collection tank, and the aqueous phase outlet of the centrifuge is connected to the ammonium chloride reaction tank. The ammonium chloride reaction tank is equipped with a mother liquor inlet and a liquid ammonia inlet; the ammonium chloride reaction tank is connected to the feed inlet of the filter via a pump, and the filtrate outlet of the filter is connected to the ammonium chloride stock solution tank; The outlet of the ammonium chloride stock solution tank is connected to the inlet of the preheater via a pump; the outlet of the preheater is connected to the inlet of the multi-effect evaporation system; and the shell-side outlet of the preheater is connected to the condensate tank of the oil-water separator. The multi-effect evaporation system includes at least two evaporation units, namely a first-effect evaporation unit and a second-effect evaporation unit; The first-effect evaporation unit includes a first-effect heater, a first-effect separation chamber, a first-effect separator, and a first-effect forced circulation pump. The shell-side inlet of the first-effect heater is connected to the steam outlet of the steam compressor via a pipe. The shell-side outlet of the first-effect heater is connected to the shell-side inlet of the preheater via a pipe. The tube-side inlets of the first-effect heater are connected to the outlet of the first-effect forced circulation pump and the outlet of the preheater, respectively. The outlet of the first-effect heater is connected to the inlet of the first-effect separation chamber. The vapor phase outlet of the first-effect separation chamber is connected to the first-effect separator. The outlet of the first-effect separation chamber is connected to the inlet of the first forced circulation pump. The outlet of the first separator is connected to the cooler of the oil-water separation device. The second-effect evaporation unit includes a second-effect heater, a second-effect separation chamber, a second-effect separator, and a second forced circulation pump. The tube-side inlet of the second-effect heater is connected to the outlet of the first separation chamber via the pump; the tube-side outlet of the second-effect heater is connected to the inlet of the second-effect separation chamber via the second forced circulation pump; the gas phase outlet of the second-effect separation chamber is connected to the second-effect separator; the outlet of the second-effect separation chamber is connected to the tube-side inlet of the second-effect heater; and the outlet of the second-effect separation chamber is connected to the inlet of the stirred crystallizer of the cooling crystallization system via the pump. The cooling crystallization system includes a stirred crystallizer, a crystallization cooler, a cooling crystallization circulation pump, and a crystallization discharge pump. The circulation port of the stirred crystallizer is connected to the inlet of the crystallization cooler through the cooling crystallization circulation pump. The discharge port of the crystallization cooler is connected to the inlet of the stirred crystallizer. The discharge port of the stirred crystallizer is connected to the inlet of the centrifuge through the crystallization discharge pump. The liquid phase outlet of the centrifuge is connected to the ammonium chloride mother liquor tank, the outlet of the ammonium chloride mother liquor tank is connected to the mother liquor inlet of the ammonium chloride reaction tank through a pump, and the solid phase outlet of the centrifuge is sent out through a conveyor.

[0014] As a preferred technical solution, the operating conditions of the first-effect evaporation unit are set to a vacuum degree of -50 kPa and a temperature of 65°C.

[0015] As a preferred technical solution, the oil-water separation device includes a cooler, a vacuum pump, a condensate tank, a gravity settling separation tank, and an organic phase collection tank. The inlet of the cooler is connected to the outlet of the first-effect separator, the condensate outlet of the cooler is connected to the condensate tank, the gas phase outlet of the cooler is connected to the vacuum pump, the condensate tank is connected to the inlet of the gravity settling separation tank via the pump, and the overflow outlet of the gravity settling separation tank is connected to the organic phase collection tank.

[0016] As a preferred technical solution, the crystallization cooler is an external circulating crystallization cooler.

[0017] Advantages of this invention: 1. This invention features a highly efficient demulsification and separation process, significantly reducing organic phase entrainment losses. This invention innovatively employs an extraction centrifuge for primary separation of the severely emulsified ammonium chloride back-extraction solution, effectively breaking the oil-water emulsion state and significantly reducing the organic extractant content in the ammonium chloride solution from an A / O ratio of 1000:7.5 to 1000:1, greatly minimizing organic solvent entrainment losses. This not only directly reduces the replenishment cost of expensive extractants during production but also prevents contamination of the organic phase in the subsequent ammonium chloride evaporation and crystallization process, ensuring the purity and quality of the final ammonium chloride product.

[0018] 2. Innovative integration of low-temperature concentration and solvent recovery technologies to achieve closed-loop recycling of organic matter and system balance. Addressing the industry pain point of difficulty in recovering low-boiling-point and slightly soluble solvents in composite extractants, this invention features a unique combined process of "high-vacuum low-temperature evaporation + condensation recovery." By significantly lowering the boiling point of the organic solvent under high-vacuum conditions, it can evaporate from the aqueous phase at low temperatures (e.g., 65°C), avoiding the damage to the extractant's activity caused by high temperatures. The evaporated organic gas phase is efficiently recovered into a liquid state via a low-temperature condensation system and returned to the extraction system for recycling. This technology solves the problem of continuously increasing organic matter content in ammonium chloride solutions, ultimately affecting the stable operation of the system, achieving efficient recovery and recycling of organic solvents, forming a resource closed loop, and significantly reducing the cost of treating waste gas, wastewater, and solid waste.

[0019] 3. The multi-effect / MVR integrated concentration system combines high efficiency, energy saving, and low-temperature separation advantages. The low-temperature concentration and MVR (mechanical vapor recompression) technology integrated system developed in this invention is an innovative solution. The front-end low-temperature effect prioritizes the evaporation and separation of volatile organic solvents, completing the primary purification of the solvent with low energy consumption; the back-end MVR effect efficiently concentrates the ammonium chloride solution after organic matter removal, fully utilizing the high thermal efficiency advantage of MVR technology. The entire system simultaneously achieves the two core objectives of "solvent separation" and "solution concentration," combining the dual advantages of low-temperature operation to protect materials and high efficiency and energy saving, with operating costs far lower than traditional multi-effect evaporation.

[0020] 4. Synergistic purification and impurity removal ensure crystallization quality and long-term stable system operation. This invention cleverly utilizes the phosphorus content of the back-extraction solution and the low acidity of the crystallization mother liquor. By comprehensively reacting the mother liquor, the raw solution, and a small amount of liquid ammonia, a synergistic purification effect of "treating waste with waste" is achieved. After the reaction, the solution pH rises to 8.0, causing iron, aluminum, calcium, magnesium, and other metal cations to completely form insoluble phosphate precipitates and be effectively removed. This process fundamentally eliminates the risk of scale formation and equipment blockage by impurity ions during evaporation and crystallization, greatly improving the online operating time of the evaporator. At the same time, it yields ammonium chloride crystals with higher purity and better stability, providing a key guarantee for the long-term, stable, and continuous operation of the entire potassium dihydrogen phosphate production system. Attached Figure Description

[0021] 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, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0022] Figure 1 This is a flow chart of the process of the present invention; 1-Ammonium chloride stock solution tank; 2-Centrifuge; 3-Extractant collection tank; 4-Ammonium chloride reaction tank; 5-Filter; 6-Ammonium chloride stock solution tank; 7-Preheater; 8-Condensate tank; 9-First-effect heater; 10-First-effect separation chamber; 11-First-effect separator; 12-First-effect forced circulation pump; 13-Cooler; 14-Second-effect heating gas; 15-Second-effect separation chamber; 16-Second-effect separator; 17-Second-effect forced circulation pump; 18-Stirred crystallizer; 19-Crystallization cooler; 20-Cooling crystallization circulation pump; 21-Crystallization discharge pump; 22-Centrifuge; 23-Ammonium chloride mother liquor tank; 24-Vacuum pump; 25-Gravity sedimentation separation tank; 26-Organic phase collection tank. Detailed Implementation

[0023] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0024] Example 1: An energy-saving concentration and crystallization process for ammonium chloride solution includes the following steps: S1. Back-extraction: An ammonium chloride-ammonia solution with a mass concentration of 10% and a free ammonia concentration of 3% is used as the back-extraction agent to react with the extractant to generate ammonium chloride stock solution. The extractant is a mixed solvent of organophosphate ammonium salt and organoammonium chloride salt. The ammonium chloride-ammonia solution, as the back-extraction agent, reacts with an organic phase extractant loaded with phosphate and impurities (the organic phase extractant is composed of TOA, N235, cycloalkanes KN4016, and isooctanol in a mass ratio of 5:2:2:1, with a phase O / A ratio of 1:1). After the reaction, phosphate and impurity anions are separated from the extractant, generating ammonium chloride stock solution (the ammonium chloride stock solution contains 8-10% chloride ions, 2.5-3% P2O5, 1-1.5% K2O, and has a pH of 7.5) and restoring the activity of the organic extractant (R). S2. Oil-water separation: The ammonium chloride solution is centrifuged at 1000 rpm / min for 5 minutes. The extractant entrained in the ammonium chloride solution emulsion is removed and returned to the extraction system for recycling. An ammonium chloride aqueous solution is obtained. Most of the organic phase is removed. After separation, the content of organic phase (A / O) entrained in the ammonium chloride aqueous solution is reduced to below 1000:1.

[0025] S3. Purification and slurry preparation: Mix the ammonium chloride aqueous solution with the ammonium chloride crystallization mother liquor and liquid ammonia at a mass ratio of 6:2:0.05, stir for 30 minutes to allow metal impurity ions to precipitate. Monitor the pH value of the reaction solution online during the process. When the pH of the solution reaches 8.0-8.3, proceed to the next step. S4. Filtration: The liquid is filtered to obtain a clear ammonium chloride mixture, wherein the solid content of the clear ammonium chloride mixture is ≤0.01%. S5. Multi-effect evaporation and concentration: The clarified ammonium chloride mixture is preheated and concentrated through at least two effects of evaporation; wherein... The first-effect evaporation is carried out under a vacuum of -50 kPa and a temperature of 65°C. The vapor phase produced by evaporation is condensed, and the condensate is separated into oil and water. The recovered organic fusel alcohol is returned to the extraction process. The first-effect evaporation yields a 20% concentration of ammonium chloride solution, which is then further concentrated in the second effect. After the second evaporation, a concentrated ammonium chloride solution with a concentration of 42% and a specific gravity of 1.36 was obtained. S6. Cooling, Crystallization, and Separation: The concentrated ammonium chloride solution is fed to a cooling crystallizer and cooled to below 40°C to precipitate ammonium chloride crystals, yielding a crystal slurry. The crystal slurry is centrifuged to separate solid ammonium chloride product and ammonium chloride crystallization mother liquor. The ammonium chloride crystallization mother liquor is returned to step S3 for recycling. The ammonium chloride crystallization mother liquor has a chloride ion content of 18-20%, a P2O5 content of 8-10%, and a K2O content of 3.5-5%. The pH of the ammonium chloride crystallization mother liquor is 5.0-5.3.

[0026] In step S2, centrifugal separation is performed using a centrifuge; in step S6, centrifugal separation is performed using a centrifuge.

[0027] In step S5, the condensate produced by the first-effect evaporation is cooled to below 40°C and then subjected to gravity sedimentation for oil-water separation.

[0028] Example 2: An energy-saving concentration and crystallization process for ammonium chloride solution includes the following steps: S1. Back-extraction: An ammonium chloride-ammonia solution with a mass concentration of 5% and a free ammonia concentration of 1.5% is used as the back-extraction agent to react with the extractant to generate an ammonium chloride stock solution with a pH of 7.0. The extractant is a mixed solvent of organophosphate ammonium salt and organoammonium chloride salt. The ammonium chloride-ammonia solution, as the back-extraction agent, reacts with the organic phase loaded with phosphate and impurities—the extractant. After the reaction, phosphate ions and impurity anions are separated from the extractant, generating an ammonium chloride stock solution and restoring the activity of the organic extractant (R). S2. Oil-water separation: The ammonium chloride solution is centrifuged to remove the extractant entrained in the ammonium chloride emulsion and return it to the extraction system for recycling, thus obtaining an aqueous ammonium chloride solution; most of the organic phase is removed. S3. Purification and slurry preparation: The ammonium chloride aqueous solution is mixed with the ammonium chloride crystallization mother liquor and liquid ammonia, and the mixture is stirred to obtain a feed solution. The pH of the feed solution is adjusted to 8.0 to precipitate the metal impurity ions. S4. Filtration: The liquid is filtered to obtain a clear ammonium chloride mixture, wherein the solid content of the clear ammonium chloride mixture is ≤0.01%. S5. Multi-effect evaporation and concentration: The clarified ammonium chloride mixture is preheated and concentrated through at least two effects of evaporation; wherein... The first-effect evaporation is carried out under a vacuum of -50 kPa and a temperature of 65°C. The vapor phase produced by evaporation is condensed, and the condensate is separated into oil and water. The recovered organic fusel alcohol is returned to the extraction process. The first-effect evaporation yields a 20% concentration of ammonium chloride solution, which is then further concentrated in the second effect. After the second-effect evaporation, a concentrated ammonium chloride solution with a concentration of 40% and a specific gravity of 1.34 was obtained. S6. Cooling, crystallization and separation: The concentrated ammonium chloride solution is transported to a cooling crystallizer and cooled to below 40°C to precipitate ammonium chloride crystals, obtaining a crystal slurry; the crystal slurry is centrifuged to separate solid ammonium chloride product and ammonium chloride crystallization mother liquor, which is returned to step S3 for recycling.

[0029] In step S2, centrifugal separation is performed using a centrifuge; in step S6, centrifugal separation is performed using a centrifuge.

[0030] The pH of the ammonium chloride crystallization mother liquor is 5.3.

[0031] In step S5, the condensate produced by the first-effect evaporation is cooled to below 40°C and then subjected to gravity sedimentation for oil-water separation.

[0032] Example 3: An energy-saving concentration and crystallization process for ammonium chloride solution includes the following steps: S1. Back-extraction: An ammonium chloride-ammonia solution with a mass concentration of 15% and a free ammonia concentration of 3% is used as the back-extraction agent to react with the extractant to generate an ammonium chloride stock solution with a pH of 8.0. The extractant is a mixed solvent of organophosphate ammonium salt and organoammonium chloride salt. The ammonium chloride-ammonia solution, as the back-extraction agent, reacts with the organic phase loaded with phosphate and impurities—the extractant. After the reaction, phosphate ions and impurity anions are separated from the extractant, generating an ammonium chloride stock solution and restoring the activity of the organic extractant (R). S2. Oil-water separation: The ammonium chloride solution is centrifuged to remove the extractant entrained in the ammonium chloride emulsion and return it to the extraction system for recycling, thus obtaining an aqueous ammonium chloride solution; most of the organic phase is removed. S3. Purification and slurry preparation: The ammonium chloride aqueous solution is mixed with the ammonium chloride crystallization mother liquor and liquid ammonia, and the mixture is stirred to obtain a feed solution. The pH of the feed solution is adjusted to 8.0 to precipitate the metal impurity ions. S4. Filtration: The liquid is filtered to obtain a clear ammonium chloride mixture, wherein the solid content of the clear ammonium chloride mixture is ≤0.01%. S5. Multi-effect evaporation and concentration: The clarified ammonium chloride mixture is preheated and concentrated through at least two effects of evaporation; wherein... The first-effect evaporation is carried out under a vacuum of -50 kPa and a temperature of 65°C. The vapor phase produced by evaporation is condensed, and the condensate is separated into oil and water. The recovered organic fusel alcohol is returned to the extraction process. The first-effect evaporation yields a 20% concentration of ammonium chloride solution, which is then further concentrated in the second effect. After the second-effect evaporation, a concentrated ammonium chloride solution with a concentration of 45% and a specific gravity of 1.38 was obtained. S6. Cooling, crystallization and separation: The concentrated ammonium chloride solution is transported to a cooling crystallizer and cooled to below 40°C to precipitate ammonium chloride crystals, obtaining a crystal slurry; the crystal slurry is centrifuged to separate solid ammonium chloride product and ammonium chloride crystallization mother liquor, which is returned to step S3 for recycling.

[0033] In step S2, centrifugal separation is performed using a centrifuge; in step S6, centrifugal separation is performed using a centrifuge.

[0034] The pH of the ammonium chloride crystallization mother liquor is 5.3.

[0035] In step S5, the condensate produced by the first-effect evaporation is cooled to below 40°C and then subjected to gravity sedimentation for oil-water separation.

[0036] Example 4: An energy-saving concentration and crystallization process device for ammonium chloride solution includes a back-extraction recovery system for regenerating the extractant and generating ammonium chloride stock solution. The ammonium chloride stock solution tank 1 of the back-extraction recovery system is connected to the feed inlet of a centrifuge 2 via a pump for receiving the ammonium chloride stock solution and performing oil-water separation. The organic phase outlet of the centrifuge 2 is connected to the extractant collection tank 3, and the aqueous phase outlet of the centrifuge 1 is connected to the ammonium chloride reaction tank 4. The ammonium chloride reaction tank 4 is equipped with a mother liquor inlet and a liquid ammonia inlet; the ammonium chloride reaction tank 4 is connected to the feed inlet of the filter 5 via a pump, and the filtrate outlet of the filter 5 is connected to the ammonium chloride stock solution tank 6; the filter 5 is used for solid-liquid separation of the purified liquid. The outlet of the ammonium chloride stock solution tank 6 is connected to the inlet of the preheater 7 via a pump; the outlet of the preheater 7 is connected to the inlet of the multi-effect evaporation system; and the shell-side outlet of the preheater 7 is connected to the condensate tank 8 of the oil-water separation device. The multi-effect evaporation system includes at least two evaporation units, namely a first-effect evaporation unit and a second-effect evaporation unit, which are connected by a pump. The first-effect evaporation unit includes a first-effect heater 9, a first-effect separation chamber 10, a first-effect separator 11, and a first-effect forced circulation pump 12. The shell-side inlet of the first-effect heater 9 is connected to the steam outlet of the steam compressor via a pipe, and the shell-side outlet of the first-effect heater 9 is connected to the shell-side inlet of the preheater 7 via a pipe. The tube-side inlet of the first-effect heater 9 is connected to the outlet of the first-effect forced circulation pump 12 and the outlet of the preheater 7, respectively. The outlet of the first-effect heater 9 is connected to the inlet of the first-effect separation chamber 10. The vapor phase outlet of the first-effect separation chamber 10 is connected to the first-effect separator 11, and the outlet of the first-effect separation chamber 10 is connected to the inlet of the first forced circulation pump 12. The outlet of the first separator 11 is connected to the cooler 13 of the oil-water separation device. The second-effect evaporation unit includes a second-effect heater 14, a second-effect separation chamber 15, a second-effect separator 16, and a second forced circulation pump 17. The tube-side inlet of the second-effect heater 14 is connected to the outlet of the first separation chamber 15 via the pump; the tube-side outlet of the second-effect heater 14 is connected to the inlet of the second-effect separation chamber 15 via the second forced circulation pump 17; the gas phase outlet of the second-effect separation chamber 15 is connected to the second-effect separator 16; the outlet of the second-effect separation chamber 15 is connected to the tube-side inlet of the second-effect heater 14; and the outlet of the second-effect separation chamber 15 is connected to the inlet of the stirred crystallizer 18 of the cooling crystallization system via the pump. The cooling crystallization system includes a stirred crystallizer 18, a crystallization cooler 19, a cooling crystallization circulation pump 20, and a crystallization discharge pump 21. The circulation port of the stirred crystallizer 18 is connected to the inlet of the crystallization cooler 19 through the cooling crystallization circulation pump 20. The discharge port of the crystallization cooler 19 is connected to the inlet of the stirred crystallizer 18. The discharge port of the stirred crystallizer 18 is connected to the inlet of the centrifuge 22 through the crystallization discharge pump 21. The liquid outlet of the centrifuge 22 is connected to the ammonium chloride mother liquor tank 23, and the outlet of the ammonium chloride mother liquor tank 23 is connected to the mother liquor inlet of the ammonium chloride reaction tank 4 via a pump. The solid phase outlet of the centrifuge 22 is discharged via a conveyor. The centrifuge 22 is used to separate the crystal slurry, and the solid phase outlet yields the ammonium chloride product.

[0037] The operating conditions of the first-effect evaporation unit are set to a vacuum of -50 kPa and a temperature of 65°C.

[0038] The oil-water separation device includes a cooler 13, a vacuum pump 24, a condensate tank 8, a gravity settling separation tank 25, and an organic phase collection tank 26. The inlet of the cooler 13 is connected to the outlet of the first-effect separator 11. The condensate outlet of the cooler 13 is connected to the condensate tank 8. The gas phase outlet of the cooler 13 is connected to the vacuum pump 24. The condensate tank 8 is connected to the inlet of the gravity settling separation tank 25 via the pump. The overflow outlet of the gravity settling separation tank 25 is connected to the organic phase collection tank 26.

[0039] The crystallizer 19 is an external circulating crystallizer that can cool the material to 40°C.

[0040] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. An energy-saving concentration and crystallization process for ammonium chloride solution, characterized in that, Includes the following steps: S1. Back-extraction: An ammonium chloride-ammonia solution with a mass concentration of 5%–15% and a free ammonia concentration of 1.5%–3% is used as the back-extraction agent to react with the extractant to generate an ammonium chloride stock solution with a pH of 7.0–8.

0. The extractant is a mixed solvent of organophosphate ammonium salt and organoammonium chloride salt. S2. Oil-water separation: The ammonium chloride solution is centrifuged to remove the extractant entrained in the ammonium chloride emulsion and returned to the extraction system for recycling, thus obtaining an ammonium chloride aqueous solution. S3. Purification and slurry preparation: Mix the ammonium chloride aqueous solution with the ammonium chloride crystallization mother liquor and liquid ammonia, stir and react to obtain the slurry, and adjust the pH of the slurry to 8.0-8.5; S4. Filtration: The liquid is filtered to obtain a clear ammonium chloride mixture, wherein the solid content of the clear ammonium chloride mixture is ≤0.01%. S5. Multi-effect evaporation and concentration: The clarified ammonium chloride mixture is preheated and concentrated at least twice; wherein... The first-effect evaporation is carried out under a vacuum of -50 to -45 kPa and a temperature of 60 to 65 °C. The vapor phase produced by evaporation is condensed, and the condensate is separated into oil and water. The recovered organic fusel alcohol is returned to the extraction process. The first-effect evaporation yields an ammonium chloride solution with a concentration of 15% to 20%, which is then further concentrated in the second effect. After the second-effect evaporation, a concentrated ammonium chloride solution with a concentration of 40-45% and a specific gravity of 1.34-1.38 is obtained. S6. Cooling, crystallization and separation: The concentrated ammonium chloride solution is transported to a cooling crystallizer and cooled to below 40°C to precipitate ammonium chloride crystals, obtaining a crystal slurry; the crystal slurry is centrifuged to separate solid ammonium chloride product and ammonium chloride crystallization mother liquor, which is returned to step S3 for recycling.

2. The energy-saving concentration and crystallization process for ammonium chloride solution as described in claim 1, characterized in that: The stripping agent mentioned in step S1 is an ammonium chloride-ammonia solution with a mass concentration of 10% and a free ammonia concentration of 3%.

3. The energy-saving concentration and crystallization process for ammonium chloride solution as described in claim 1, characterized in that: The centrifugal separation is performed using a centrifuge.

4. The energy-saving concentration and crystallization process for ammonium chloride solution as described in claim 1, characterized in that: In step S5, the condensate produced by the first-effect evaporation is cooled to below 40°C and then subjected to gravity sedimentation for oil-water separation.

5. An apparatus for an energy-saving concentration and crystallization process of ammonium chloride solution as described in any one of claims 1 to 4, characterized in that: Includes a back-extraction system, wherein the ammonium chloride stock solution tank of the back-extraction system is connected to the feed inlet of a centrifuge via a pump; The organic phase outlet of the centrifuge is connected to the extractant collection tank, and the aqueous phase outlet of the centrifuge is connected to the ammonium chloride reaction tank. The ammonium chloride reaction tank is equipped with a mother liquor inlet and a liquid ammonia inlet; the ammonium chloride reaction tank is connected to the feed inlet of the filter via a pump, and the filtrate outlet of the filter is connected to the ammonium chloride stock solution tank; The outlet of the ammonium chloride stock solution tank is connected to the inlet of the preheater via a pump; the outlet of the preheater is connected to the inlet of the multi-effect evaporation system; and the shell-side outlet of the preheater is connected to the condensate tank of the oil-water separator. The multi-effect evaporation system includes at least two evaporation units, namely a first-effect evaporation unit and a second-effect evaporation unit; The first-effect evaporation unit includes a first-effect heater, a first-effect separation chamber, a first-effect separator, and a first-effect forced circulation pump. The shell-side inlet of the first-effect heater is connected to the steam outlet of the steam compressor via a pipe. The shell-side outlet of the first-effect heater is connected to the shell-side inlet of the preheater via a pipe. The tube-side inlets of the first-effect heater are connected to the outlet of the first-effect forced circulation pump and the outlet of the preheater, respectively. The outlet of the first-effect heater is connected to the inlet of the first-effect separation chamber. The vapor phase outlet of the first-effect separation chamber is connected to the first-effect separator. The outlet of the first-effect separation chamber is connected to the inlet of the first forced circulation pump. The outlet of the first separator is connected to the cooler of the oil-water separation device. The second-effect evaporation unit includes a second-effect heater, a second-effect separation chamber, a second-effect separator, and a second forced circulation pump. The tube-side inlet of the second-effect heater is connected to the outlet of the first separation chamber via the pump; the tube-side outlet of the second-effect heater is connected to the inlet of the second-effect separation chamber via the second forced circulation pump; the gas phase outlet of the second-effect separation chamber is connected to the second-effect separator; the outlet of the second-effect separation chamber is connected to the tube-side inlet of the second-effect heater; and the outlet of the second-effect separation chamber is connected to the inlet of the stirred crystallizer of the cooling crystallization system via the pump. The cooling crystallization system includes a stirred crystallizer, a crystallization cooler, a cooling crystallization circulation pump, and a crystallization discharge pump. The circulation port of the stirred crystallizer is connected to the inlet of the crystallization cooler through the cooling crystallization circulation pump. The discharge port of the crystallization cooler is connected to the inlet of the stirred crystallizer. The discharge port of the stirred crystallizer is connected to the inlet of the centrifuge through the crystallization discharge pump. The liquid phase outlet of the centrifuge is connected to the ammonium chloride mother liquor tank, the outlet of the ammonium chloride mother liquor tank is connected to the mother liquor inlet of the ammonium chloride reaction tank through a pump, and the solid phase outlet of the centrifuge is sent out through a conveyor.

6. The apparatus for energy-saving concentration and crystallization process of ammonium chloride solution as described in claim 5, characterized in that: The operating conditions of the first-effect evaporation unit are set to a vacuum degree of -50 to -45 kPa and a temperature of 60 to 65 °C.

7. The apparatus for energy-saving concentration and crystallization process of ammonium chloride solution as described in claim 5, characterized in that: The oil-water separation device includes a cooler, a vacuum pump, a condensate tank, a gravity settling separation tank, and an organic phase collection tank. The inlet of the cooler is connected to the outlet of the first-effect separator, the condensate outlet of the cooler is connected to the condensate tank, the gas inlet of the cooler is connected to the vacuum pump, the condensate tank is connected to the inlet of the gravity settling separation tank via the pump, and the overflow outlet of the gravity settling separation tank is connected to the organic phase collection tank.

8. The apparatus for energy-saving concentration and crystallization process of ammonium chloride solution as described in claim 5, characterized in that: The crystallization cooler is an external circulating crystallization cooler.

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