Multi-effect evaporation process and device for preparing ammonium bifluoride from waste HF acid

Abstract

The invention relates to a multi-effect evaporation process and device for preparing ammonium bifluoride from waste HF acid. Comprising the following steps: performing a falling film absorption process on HF-containing gas in cathode tail gas of a nitrogen trifluoride electrolytic cell to obtain a hydrofluoric acid solution; adding liquid ammonia into the hydrofluoric acid solution, and reacting to obtain an ammonium bifluoride solution; heating the ammonium bifluoride solution and the centrifuged mother liquor to obtain mixed mother liquor; carrying out heating reduced pressure distillation on the mixed mother liquor, and then carrying out primary cooling to obtain ammonium bifluoride crystal mush; secondary steam generated in the evaporation process can be pressurized and then heated to heat the ammonium bifluoride solution; performing centrifugal separation on the ammonium bifluoride crystal slurry to obtain ammonium bifluoride solid, and recycling mother liquor; according to the method, the problem that the additional value is low when hydrofluoric acid serves as a by-product is solved, a complete heat energy cycle is established through the steam compressor, and high-quality ammonium bifluoride is produced with low energy consumption and high efficiency.

Description

Technical Field

[0001] The present application belongs to the technical field of ammonium bifluoride preparation, and specifically relates to a multi-effect evaporation process and device for preparing ammonium bifluoride from waste HF acid. Background Art

[0002] Ammonium bifluoride (NH 4 HF 2 ) is an important inorganic fluoride, widely used in industrial production and fine chemical fields. Its common uses include: ① metal surface treatment, such as chemical polishing and passivation of light metals such as aluminum and magnesium; ② core etchant in glass etching process; ③ used as semiconductor device cleaning agent and photovoltaic silicon wafer surface treatment agent in the electronics industry; ④ as a fluorinating agent to participate in organic synthesis reactions; ⑤ ceramic industry glaze preparation, etc. With the development of new energy, electronic information and other industries, the demand for high-purity ammonium bifluoride continues to grow.

[0003] At present, the mainstream processes for industrial preparation of ammonium bifluoride are divided into two categories: wet process and dry process. Among them, the wet process has a high degree of technical maturity and is the most widely used in the market. Its process path is: high-purity ammonia (≥99.9%) and anhydrous hydrogen fluoride (≥99.9%) or hydrofluoric acid are used as raw materials, and after neutralization reaction, ammonium bifluoride mother liquor is generated, and then the finished product is obtained through preheating, vacuum concentration distillation, cooling crystallization, solid-liquid separation and drying (cyclone separator / fluidized bed) and other processes. However, this process has significant defects: first, the raw materials need to use ultra-high purity gas and liquid, and the procurement cost is high; second, the multi-step solution transfer leads to complex equipment pipelines, and the one-time use of steam heat source causes low energy efficiency (comprehensive energy consumption reaches 200-300kWh / ton of product); third, the crystallization process control relies on experience operation, the level of automation is insufficient, and the stability of product batches is easily affected by human factors. Although the dry process can simplify the process by directly reacting gaseous ammonia with hydrogen fluoride, the intense heat release of the reaction leads to local overheating, and the product is easily encapsulated with impurities. The purity of the obtained ammonium bifluoride is generally less than 98%, which is difficult to meet the needs of high-end applications.

[0004] With the development of society and the demand for environmental protection, many researchers have recovered hydrofluoric acid from production tail gas and used it to produce ammonium bifluoride to achieve resource recycling. Application No. CN202410092637.1 discloses a system and method for generating ammonium bifluoride using fluorine-containing waste acid, which improves the product quality and industrial economy of ammonium bifluoride, reduces the energy consumption of the device, realizes the effective recycling of fluorine resources, avoids the discharge of waste acid, and improves the stability and storage of the product. 3) The cathode tail gas generated during the production process contains a large amount of by-product hydrofluoric acid (HF). The traditional treatment method only sells it as a low-value-added by-product or neutralizes it, failing to achieve efficient resource utilization. A nitrogen trifluoride production line with an annual output of 10,000 tons can recycle about 5,000 tons of waste HF acid with a concentration of ≥30% each year. However, due to the strict requirements of the existing ammonium bifluoride preparation process on the purity of raw materials, this type of by-product acid cannot be directly used to produce high-value ammonium bifluoride products, resulting in waste of resources and loss of economic benefits.

[0005] In summary, the existing methods for preparing ammonium bifluoride have the problems of high cost, complex equipment, high energy consumption and low purity. 3 ) The cathode tail gas produced in the production process contains a large amount of by-product hydrofluoric acid (HF), which is directly neutralized by alkali and is not fully utilized, resulting in a waste of resources. Therefore, the development of a new ammonium bifluoride preparation technology that is low-cost, low-energy consumption and adaptable to industrial by-product hydrofluoric acid has become a technical problem that needs to be solved urgently. Summary of the invention

[0006] Aiming at the problems that the methods for preparing ammonium bifluoride in the prior art are high cost, complex equipment, high energy consumption and low purity, and the cathode tail gas generated in the current nitrogen trifluoride (NF3) production process contains a large amount of by-product hydrofluoric acid (HF), which is directly neutralized by alkali and is not fully utilized, resulting in waste of resources, the present application proposes a multi-effect evaporation process and device for preparing ammonium bifluoride from waste HF acid.

[0007] The technical solution of this application is as follows: On the one hand, the present application provides a multiple-effect evaporation process for preparing ammonium bifluoride from waste HF acid, comprising the following steps:

[0009] Step S1. Preparation and transfer of hydrofluoric acid: The gas containing HF in the cathode tail gas of the nitrogen trifluoride electrolyzer is absorbed by falling film to obtain a hydrofluoric acid solution;

[0010] Step S2. Preparation of ammonium bifluoride solution: adding liquid ammonia to a hydrofluoric acid solution to react to obtain an ammonium bifluoride solution;

[0011] Step S3. Preheating and mixing: mixing the ammonium bifluoride solution obtained in S2 with the mother liquor obtained after centrifugation in S5, and heating them together to obtain a mixed mother liquor;

[0012] Step S4. Evaporation concentration and crystallization: the mixed mother liquor in S3 is distilled under reduced pressure and then preliminarily cooled, and finally recrystallized to obtain ammonium bifluoride slurry;

[0013] Step S5. Centrifugal separation and mother liquor circulation: The ammonium bifluoride slurry in S4 is centrifuged to obtain ammonium bifluoride solid, and the mother liquor is circulated to S3.

[0014] Preferably, the secondary steam generated in the evaporation process in step S4 is used to heat the ammonium bifluoride solution after being pressurized and heated.

[0015] Preferably, the volume fraction of anhydrous HF in the cathode tail gas of the nitrogen trifluoride electrolyzer in step S1 is 10-15%, and the mass concentration of the hydrofluoric acid solution after concentration is 45-60%.

[0016] Preferably, the reaction temperature in step S2 is 55-75° C., the mass concentration of the obtained ammonium bifluoride solution is 35-55%, and the addition of liquid ammonia is stopped when the pH value of the reaction system is 3.0-5.5.

[0017] Preferably, the temperature is raised to 40-60° C. in step S3, and the mass flow ratio of the ammonium bifluoride solution obtained in S2 to the mother liquor after centrifugation in S6 is (3-5):1.

[0018] Preferably, the evaporation pressure in step S4 is -0.05 to -0.09 MPa, the evaporation temperature is 50 to 75° C., and the mass concentration of the ammonium bifluoride solution after evaporation is 55 to 75%; the crystallization temperature is 30 to 50° C., and the pressure is normal pressure.

[0019] Preferably, the secondary steam is pressurized and heated to 70-95°C.

[0020] Preferably, the ammonium bifluoride solid separated in step S5 has a water content of 5 to 25%.

[0021] Preferably, it also includes,

[0022] Step S6. Drying: Dry the ammonium bifluoride solid separated in step S6, and control the drying temperature to be 100-120°C.

[0023] On the other hand, the present application provides a multiple-effect evaporation device for preparing ammonium bifluoride from waste HF acid, comprising a falling film system, a hydrofluoric acid storage tank, a salt solution storage tank, a preheater, an evaporation separator, a precooler, a crystallization kettle, a centrifuge and a drying fluidized bed arranged in sequence along the material flow direction;

[0024] The pipelines between the hydrofluoric acid storage tank and the salt solution storage tank, the salt solution storage tank and the preheater, the evaporation separator and the precooler, and the crystallization kettle and the centrifuge are all provided with a feed pump;

[0025] The salt solution storage tank is also connected to a liquid ammonia adding system for adding liquid ammonia;

[0026] The evaporation separator is also connected to a steam washing tower for washing the steam generated by the evaporation of ammonium hydrofluoride, the steam washing tower is connected to the heat exchanger, and a compressor for compressing and heating the steam is provided on the pipeline between the steam washing tower and the heat exchanger, and the compressor transports the compressed steam to the heat exchanger;

[0027] The heat exchanger is connected to the external heaters of the preheater and the evaporation separator respectively, and is used to perform heat exchange on the external heaters of the preheater and the evaporation separator, and to discharge the secondary steam condensate and tail gas.

[0028] Beneficial effects of this application:

[0029] 1. The present invention realizes the increase of added value of hydrofluoric acid prepared from cathode tail gas HF of nitrogen trifluoride electrolyzer, effectively recovers fluorine element, and prepares the final ammonium bifluoride solid product with water content controlled within 0.5% and main content controlled above 98.5%, which meets the national standard index requirements of superior products, can be used to produce nitrogen trifluoride raw materials, and is conducive to the reduction of raw material cost investment in the production of nitrogen trifluoride.

[0030] 2. The wet preparation process of ammonium bifluoride on the market mostly adopts steam single-effect heat exchange, which consumes a lot of energy and has low heat exchange efficiency. The present invention adopts steam as the initial heat source and establishes a complete heat energy cycle by a steam compressor. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Attached Figure 1 This is a diagram of a preparation device for the multi-effect evaporation preparation process for preparing ammonium bifluoride from waste HF acid of the present application.

[0032] Explanation of the symbols in the accompanying drawings: 1. Falling film system; 2. Hydrofluoric acid storage tank; 3. Salt solution storage tank; 4. Preheater; 5. Evaporation separator; 6. Precooler; 7. Crystallization kettle; 8. Centrifuge 9. Drying fluidized bed; 10. Steam washing tower; 11. Feed pump; 12. Compressor; 13. Fan; 14. Heat exchanger; 15. Liquid ammonia addition system. DETAILED DESCRIPTION

[0034] In order to further explain the technical means and effects adopted by the present application to achieve the predetermined invention purpose, the specific implementation method, structure, characteristics and effects of the present application are described in detail below in combination with the preferred embodiments.

[0035] Example 1

[0036] S1: Preparation and transfer of hydrofluoric acid

[0037] Gas containing 10-15% anhydrous HF is collected from the cathode tail gas of the nitrogen trifluoride electrolytic cell, and the cathode tail gas containing 10-15% anhydrous HF is introduced into a falling film system 1, and hydrofluoric acid with a concentration of 55% is obtained through multi-stage falling film absorption and stored in a hydrofluoric acid storage tank 2, and then the hydrofluoric acid is transferred to a salt solution storage tank 3 through a solution delivery pump.

[0038] By falling film absorption, anhydrous HF is converted into hydrofluoric acid with a certain concentration, which is convenient for subsequent reaction with ammonia to generate ammonium bifluoride. Multi-stage falling film absorption can improve the absorption efficiency and make the hydrofluoric acid concentration reach a range suitable for subsequent reactions. The hydrofluoric acid is transferred to the salt solution storage tank 3 for the next preparation operation.

[0039] S2: Preparation of ammonium bifluoride solution

[0040] Liquid ammonia is added to the salt solution storage tank 3 through the liquid ammonia addition system 15, specifically, the liquid ammonia is transferred to the quantitative tank through the liquid ammonia pump, and then the liquid ammonia is added to the hydrofluoric acid solution in the salt solution storage tank 3 by nitrogen pressurization. The liquid ammonia addition pipe is inserted below the hydrofluoric acid liquid level, and a distributor with a pore size of 3 cm is provided at the bottom of the liquid ammonia addition pipe, so that the liquid ammonia can be evenly dispersed in the hydrofluoric acid solution. The pH value of the mixed solution added with liquid ammonia is 4.5, and the heat generated during the reaction is removed by circulating water, and the reaction temperature is maintained at 60°C, and finally an ammonium bifluoride solution with a mass concentration of 45% is obtained.

[0041] Hydrofluoric acid reacts with liquid ammonia to generate ammonium bifluoride solution. The liquid ammonia feeding tube is inserted below the liquid surface and dispersed through the distributor to make the liquid ammonia and hydrofluoric acid fully contact, improve the reaction efficiency, and avoid uneven reaction caused by excessive local concentration. Controlling the reaction temperature and pH value is to ensure that the reaction can proceed smoothly and at the same time make the generated ammonium bifluoride solution reach the required mass concentration requirement.

[0042] S3: Preheating and mixing

[0043] The initial ammonium bifluoride solution obtained in S2 is transferred to the preheater 4 together with the mother liquor after centrifugation in S6 through the feed pump 11. The external heater of the preheater 4 and the secondary steam condensate are preliminarily heat exchanged through the heat exchanger 14. The preheated mixed mother liquor is heat exchanged with the secondary steam by a forced circulation pump, and enters the evaporation separator 5 after further heating to form a mixed mother liquor. The temperature of the mixed mother liquor is controlled to be 50°C, and the flow ratio of the initial ammonium bifluoride solution and the ammonium bifluoride crystal slurry centrifugal mother liquor is controlled to be 4:1.

[0044] The initial ammonium bifluoride solution and the centrifuged mother liquor are preheated to increase their temperatures, thereby providing favorable conditions for the subsequent evaporation and concentration operations and reducing energy consumption during the evaporation process. At the same time, by controlling the flow ratio and the temperature of the mixed mother liquor, the mixed mother liquor can better adapt to the operating conditions of the evaporation separator 5, thereby ensuring the stable progress of the evaporation and concentration process.

[0045] S4: Evaporation concentration and crystallization

[0046] The mixed mother liquor transferred from S3 to the evaporation separator 5 is heat-exchanged with the shell-side secondary steam by the external heater of the evaporation separator 5 to increase the temperature of the ammonium bifluoride solution. Under the condition of maintaining the pressure of the evaporation separator 5 at -0.07MPa and the evaporation temperature at 65°C, the ammonium bifluoride solution is concentrated to a mass concentration of 65%. The concentrated solution is transferred to the precooler 6 through the feed pump 11 for preliminary cooling, and the temperature of the cooled solution is controlled to 50°C, and then transferred to the crystallization kettle 7 for crystallization, stirred crystallization, the crystallization temperature is controlled at 40°C, the pressure is normal pressure, and the cooling and heat exchange medium of the crystallization kettle 7 is circulating water. In the evaporation process, the flashed secondary steam enters the steam washing tower 10 for washing after sufficient sedimentation and separation, and then the water droplets entrained by the steam are removed by the demister, and the clean secondary steam enters the steam compressor 12.

[0047] By evaporation concentration, the mass concentration of ammonium bifluoride solution is increased to the scope suitable for crystallization, so that the follow-up can obtain ammonium bifluoride crystals. Maintaining a certain evaporation separator 5 pressure and controlling the evaporation temperature is to optimize the evaporation process, improve evaporation efficiency, and ensure that the solution can concentrate under suitable conditions simultaneously. Preliminary cooling and crystallization operation are to separate out ammonium bifluoride from the solution in the form of crystals, to obtain solid products. Secondary steam is handled in order to reclaim its heat, realize the recycling of heat energy, and improve the energy efficiency of the whole process.

[0048] Secondary steam utilization

[0049] The secondary steam after being pressurized and heated by the compressor 12 in step S4 is raised to a temperature of 80° C. and enters the heat exchanger 14 to exchange heat with the ammonium bifluoride solution through the external heater of the preheater 4. The secondary steam tail liquid generated is discharged while the tail gas is discharged from the fan 13.

[0050] The heat of the secondary steam is recovered and used to heat the ammonium bifluoride solution, so as to realize the recycling of heat energy, reduce the energy consumption of the process, improve the energy utilization efficiency, and ensure that the evaporation concentration process can be carried out continuously and stably.

[0051] S5: Centrifugal separation and mother liquor circulation

[0052] The ammonium bifluoride slurry solution obtained in the crystallization kettle 7 in S4 is transferred to the centrifuge 8 through a delivery pump for centrifugal separation to separate the ammonium bifluoride solid and the mother liquor. The ammonium bifluoride solid obtained after separation has a water content of 20%, and the mother liquor with a mass concentration of 70% is circulated to the S3 system through a delivery pump.

[0053] By centrifugal separation, the ammonium bifluoride solid is separated from the slurry solution to obtain a solid product with a high degree of dryness. The mother liquor separated by centrifugation is circulated to the S3 system through a delivery pump in order to make full use of the ammonium bifluoride component in the mother liquor, improve the utilization rate of raw materials, reduce waste emissions, and reduce production costs.

[0054] S6: Drying

[0055] The ammonium bifluoride solid separated from S5 is sent to the drying fluidized bed 9 for drying. The drying temperature is controlled to be 110° C. After testing, the main content is 99.74%, the water content is 0.1%, the ignition residue is 0.05%, the sulfate content is 0.06%, and the ammonium fluorosilicate content is 0.05%.

[0056] Through the drying operation, the water content of the ammonium bifluoride solid is further reduced, so that it meets the product quality requirements, is easy to store and transport, and also meets the quality requirements as a raw material for producing nitrogen trifluoride.

[0057] Example 2

[0058] S1: Preparation and transfer of hydrofluoric acid

[0059] Gas containing 10-15% anhydrous HF is collected from the cathode tail gas of the nitrogen trifluoride electrolyzer, and the cathode tail gas containing 10-15% anhydrous HF is introduced into a falling film system 1, and hydrofluoric acid with a concentration of 45% is obtained through multi-stage falling film absorption and stored in a hydrofluoric acid storage tank 2, and then the hydrofluoric acid is transferred to a salt solution storage tank 3 through a solution delivery pump.

[0060] S2: Preparation of ammonium bifluoride solution

[0061] Liquid ammonia is added to the salt solution storage tank 3 through the liquid ammonia addition system 15, specifically, the liquid ammonia is transferred to the quantitative tank through the liquid ammonia pump, and then the liquid ammonia is added to the hydrofluoric acid solution in the salt solution storage tank 3 by nitrogen pressurization. The liquid ammonia addition pipe is inserted below the hydrofluoric acid liquid level, and a distributor with a pore size of 4 cm is provided at the bottom of the liquid ammonia addition pipe, so that the liquid ammonia can be evenly dispersed in the hydrofluoric acid solution. The pH value of the mixed solution added with liquid ammonia is 3.0, and the heat generated during the reaction is removed by circulating water, and the reaction temperature is maintained at 75°C, and finally an ammonium bifluoride solution with a mass concentration of 35% is obtained.

[0062] S3: Preheating and mixing

[0063] The initial ammonium bifluoride solution obtained in S2 is transferred to the preheater 4 together with the mother liquor after centrifugation in S6 through the feed pump 11. The external heater of the preheater 4 and the secondary steam condensate are preliminarily heat exchanged through the heat exchanger 14. The preheated mixed mother liquor is heat exchanged with the secondary steam by the forced circulation pump, and enters the evaporation separator 5 after further heating to form a mixed mother liquor. The temperature of the mixed mother liquor is controlled to be 60°C, and the flow ratio of the initial ammonium bifluoride solution and the ammonium bifluoride crystal slurry centrifugal mother liquor is controlled to be 3:1.

[0064] S4: Evaporation concentration and crystallization

[0065] The mixed mother liquor transferred from S3 to the evaporation separator 5 is heat-exchanged with the shell-side secondary steam by the external heater of the evaporation separator 5 to increase the temperature of the ammonium bifluoride solution. Under the condition of maintaining the pressure of the evaporation separator 5 at -0.05MPa and the evaporation temperature at 50°C, the ammonium bifluoride solution is concentrated to a mass concentration of 75%. The concentrated solution is transferred to the precooler 6 through the feed pump 11 for preliminary cooling, and the temperature of the cooled solution is controlled to 40°C, and then transferred to the crystallization kettle 7 for crystallization, stirred crystallization, the crystallization temperature is controlled at 50°C, the pressure is normal pressure, and the cooling and heat exchange medium of the crystallization kettle 7 is circulating water. In the evaporation process, the flashed secondary steam enters the steam washing tower 10 for washing after sufficient sedimentation and separation, and then the water droplets entrained by the steam are removed by the demister, and the clean secondary steam enters the steam compressor 12.

[0066] Secondary steam utilization

[0067] Operation: The secondary steam after being pressurized and heated by the compressor 12 in step S4 is raised to 70° C. and enters the heat exchanger 14 to exchange heat with the ammonium bifluoride solution through the external heater of the preheater 4. The secondary steam tail liquid is discharged and the tail gas is discharged from the fan 13 at the same time.

[0068] S5: Centrifugal separation and mother liquor circulation

[0069] The ammonium bifluoride slurry solution obtained in the crystallization kettle 7 in S4 is transferred to the centrifuge 8 through a delivery pump for centrifugal separation to separate the ammonium bifluoride solid and the mother liquor. The ammonium bifluoride solid obtained after separation has a water content of 25%, and the mother liquor with a mass concentration of 65% is circulated to the S3 system through a delivery pump.

[0070] S6: Drying

[0071] The ammonium bifluoride solid separated from S5 is sent to the drying fluidized bed 9 for drying. The drying temperature is controlled to be 120° C. After testing, the main content is 99.69%, the water content is 0.15%, the ignition residue is 0.04%, the sulfate content is 0.02%, and the ammonium fluorosilicate content is 0.1%.

[0072] Example 3

[0073] S1: Preparation and transfer of hydrofluoric acid

[0074] Gas containing 10-15% anhydrous HF is collected from the cathode tail gas of the nitrogen trifluoride electrolytic cell, and the cathode tail gas containing 10-15% anhydrous HF is introduced into a falling film system 1, and hydrofluoric acid with a concentration of 60% is obtained through multi-stage falling film absorption and stored in a hydrofluoric acid storage tank 2, and then the hydrofluoric acid is transferred to a salt solution storage tank 3 through a solution delivery pump.

[0075] S2: Preparation of ammonium bifluoride solution

[0076] Liquid ammonia is added to the salt solution storage tank 3 through the liquid ammonia addition system 15, specifically, the liquid ammonia is transferred to the quantitative tank through the liquid ammonia pump, and then the liquid ammonia is added to the hydrofluoric acid solution in the salt solution storage tank 3 by nitrogen pressurization. The liquid ammonia addition pipe is inserted below the hydrofluoric acid liquid level, and a distributor with a pore size of 2 cm is provided at the bottom of the liquid ammonia addition pipe, so that the liquid ammonia can be evenly dispersed in the hydrofluoric acid solution. The pH value of the mixed solution added with liquid ammonia is 5.5, and the heat generated during the reaction is removed by circulating water, and the reaction temperature is maintained at 55°C, and finally an ammonium bifluoride solution with a mass concentration of 55% is obtained.

[0077] S3: Preheating and mixing

[0078] The initial ammonium bifluoride solution obtained in S2 is transferred to the preheater 4 together with the mother liquor after centrifugation in S6 through the feed pump 11. The external heater of the preheater 4 and the secondary steam condensate are preliminarily heat exchanged through the heat exchanger 14. The preheated mixed mother liquor is heat exchanged with the secondary steam by the forced circulation pump, and enters the evaporation separator 5 after further heating to form a mixed mother liquor. The temperature of the mixed mother liquor is controlled to be 40°C, and the flow ratio of the initial ammonium bifluoride solution and the ammonium bifluoride crystal slurry centrifugal mother liquor is controlled to be 5:1.

[0079] S4: Evaporation concentration and crystallization

[0080] The mixed mother liquor transferred from S3 to the evaporation separator 5 is heat-exchanged with the shell-side secondary steam by the external heater of the evaporation separator 5 to increase the temperature of the ammonium bifluoride solution. Under the condition of maintaining the pressure of the evaporation separator 5 at -0.09MPa and the evaporation temperature at 75°C, the ammonium bifluoride solution is concentrated to a mass concentration of 55%. The concentrated solution is transferred to the precooler 6 through the feed pump 11 for preliminary cooling, and the temperature of the cooled solution is controlled to 60°C, and then transferred to the crystallization kettle 7 for crystallization, stirred crystallization, the crystallization temperature is controlled at 30°C, the pressure is normal pressure, and the cooling and heat exchange medium of the crystallization kettle 7 is circulating water. In the evaporation process, the flashed secondary steam enters the steam washing tower 10 for washing after sufficient sedimentation and separation, and then the water droplets entrained by the steam are removed by the demister, and the clean secondary steam enters the steam compressor 12.

[0081] Secondary steam utilization

[0082] Operation: The secondary steam after being pressurized and heated by the compressor 12 in step S4 is raised to a temperature of 95° C. and enters the heat exchanger 14 to exchange heat with the ammonium bifluoride solution through the external heater of the preheater 4. The secondary steam tail liquid is discharged while the tail gas is discharged from the fan 13.

[0083] S5: Centrifugal separation and mother liquor circulation

[0084] The ammonium bifluoride slurry solution obtained in the crystallization kettle 7 in S4 is transferred to the centrifuge 8 through a delivery pump for centrifugal separation to separate the ammonium bifluoride solid and the mother liquor. The ammonium bifluoride solid obtained after separation has a water content of 5%, and the mother liquor with a mass concentration of 80% is circulated to the S3 system through a delivery pump.

[0085] S6: Drying

[0086] The ammonium bifluoride solid separated from S5 is sent to the drying fluidized bed 9 for drying. The drying temperature is controlled to be 100° C. After testing, the main content is 99.65%, the water content is 0.2%, the ignition residue is 0.02%, the sulfate content is 0.06%, and the ammonium fluorosilicate content is 0.07%.

[0087] The above is only a preferred embodiment of the present application and does not constitute any form of limitation to the present application. Although the present application has been disclosed as a preferred embodiment as above, it is not intended to limit the present application. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present application. However, any modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application are still within the scope of the technical solution of the present application.

Claims

1. A multiple-effect evaporation process for preparing ammonium bifluoride from waste HF acid, characterized in that: The steps include: Step S1. Preparation and transfer of hydrofluoric acid: The gas containing HF in the cathode tail gas of the nitrogen trifluoride electrolyzer is absorbed by falling film to obtain a hydrofluoric acid solution; Step S2. Preparation of ammonium bifluoride solution: adding liquid ammonia to a hydrofluoric acid solution to react to obtain an ammonium bifluoride solution; Step S3. Preheating and mixing: mixing the ammonium bifluoride solution obtained in S2 with the mother liquor obtained after centrifugation in S5, and heating them together to obtain a mixed mother liquor; Step S4. Evaporation concentration and crystallization: the mixed mother liquor in S3 is distilled under reduced pressure and then preliminarily cooled, and finally recrystallized to obtain ammonium bifluoride slurry; Step S5. Centrifugal separation and mother liquor circulation: The ammonium bifluoride slurry in S4 is centrifuged to obtain ammonium bifluoride solid, and the mother liquor is circulated to S3.

2. The multiple-effect evaporation process for preparing ammonium bifluoride from waste HF acid according to claim 1, characterized in that: The secondary steam generated in the evaporation process in step S4 is used to heat the ammonium bifluoride solution after being pressurized and heated.

3. A multiple-effect evaporation process for preparing ammonium bifluoride from waste HF acid according to claim 1, characterized in that: In step S1, the volume fraction of anhydrous HF in the cathode tail gas of the nitrogen trifluoride electrolysis cell is 10-15%, and the mass concentration of the hydrofluoric acid solution after concentration is 45-60%.

4. The multiple-effect evaporation process for preparing ammonium bifluoride from waste HF acid according to claim 1, characterized in that: The reaction temperature in step S2 is 55-75° C., and the mass concentration of the obtained ammonium bifluoride solution is 35-55%. When the pH value of the reaction system is 3.0-5.5, the addition of liquid ammonia is stopped.

5. The multiple-effect evaporation process for preparing ammonium bifluoride from waste HF acid according to claim 1, characterized in that: In step S3, the temperature is raised to 40-60°C, and the mass flow ratio of the ammonium bifluoride solution obtained in S2 to the mother liquor after centrifugation in S6 is (3-5):

1.

6. The multiple-effect evaporation process for preparing ammonium bifluoride from waste HF acid according to claim 1, characterized in that: The evaporation pressure in step S4 is -0.05 to -0.09 MPa, the evaporation temperature is 50 to 75° C., and the mass concentration of the ammonium bifluoride solution after evaporation is 55 to 75%; the crystallization temperature is 30 to 50° C., and the pressure is normal pressure.

7. The multiple-effect evaporation process for preparing ammonium bifluoride from waste HF acid according to claim 2, characterized in that: The secondary steam is pressurized and heated to 70-95°C.

8. The multiple-effect evaporation process for preparing ammonium bifluoride from waste HF acid according to claim 1, characterized in that: The ammonium bifluoride solid separated in step S5 has a water content of 5 to 25%.

9. The multiple-effect evaporation process for preparing ammonium bifluoride from waste HF acid according to claim 1, characterized in that: Also includes, Step S6. Drying: Dry the ammonium bifluoride solid separated in step S6, and control the drying temperature to be 100-120°C.

10. A multiple-effect evaporation process for preparing ammonium bifluoride from waste HF acid according to any one of claims 1 to 9, characterized in that: It comprises a falling film system (1), a hydrofluoric acid storage tank (2), a salt solution storage tank (3), a preheater (4), an evaporation separator (5), a precooler (6), a crystallization kettle (7), a centrifuge (8) and a drying fluidized bed (9) which are arranged in sequence along the material flow direction; A feed pump (11) is provided on the pipelines between the hydrofluoric acid storage tank (2) and the salt solution storage tank (3), the salt solution storage tank (3) and the preheater (4), the evaporation separator (5) and the precooler (6), and the crystallization kettle (7) and the centrifuge (8); The salt solution storage tank (3) is also connected to a liquid ammonia adding system (15) for adding liquid ammonia; The evaporation separator (5) is also connected to a steam washing tower (10) for washing steam generated by evaporation of ammonium hydrofluoride. The steam washing tower (10) is connected to the heat exchanger (14). A compressor (12) for compressing and heating the steam is provided on the pipeline between the steam washing tower (10) and the heat exchanger (14). The compressor (12) transports the compressed steam to the heat exchanger (14). The heat exchanger (14) is connected to the external heaters of the preheater (4) and the evaporation separator (5) respectively, and is used to perform heat exchange with the external heaters of the preheater (4) and the evaporation separator (5), and to discharge the secondary steam condensate, while the tail gas is discharged through the fan (13).

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