An apparatus and method for purifying liquid ammonia by rectification

Abstract

The application provides a liquid ammonia rectification purification device and method, which combines a rectification tower and a water washing tower, controls temperature and pressure in relatively mild conditions, removes heavy component impurities in raw materials by the rectification tower, and removes light component impurities by the water washing tower. On one hand, the application can meet large flow production, and on the other hand, the application can reach higher product purity, and the purity reaches 99.99999%. In addition, the application condenses and liquefies part of gaseous ammonia by means of a condenser, recycles and utilizes, realizes multiple rectifications, and thus ensures that product quality meets the requirements of ultra-pure ammonia products. The saturated ammonia water in the water washing tower can also be recycled, and the application is more energy-saving and environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of liquid ammonia purification technology, specifically to a liquid ammonia distillation purification apparatus and method. Background Technology

[0002] Ultrapure ammonia has wide applications in the electronics, chemical, and metallurgical industries, especially in the semiconductor industry. Ultrapure ammonia is one of the key raw materials for preparing semiconductor silicon nitride thin films, and the purity of ammonia directly affects the quality of silicon nitride materials. As a nitrogen source in the LED electronics industry, ultrapure ammonia can be used in the manufacture of thin-film solar cells and can be used in combination with silane and ultrapure argon.

[0003] The manufacturing process requires a large amount of ultrapure ammonia as a nitrogen source. Especially during wafer growth, higher purity ammonia results in lower power consumption and greater luminescence intensity. Therefore, the production of ultrapure ammonia has a promising market prospect in the future.

[0004] Currently, the commonly used methods for producing ultrapure ammonia are adsorption, distillation, or a combination of both. However, these methods are energy-intensive, produce large amounts of exhaust gas, and are difficult to purify to very high purity. Therefore, providing a continuous production system and process control method for high-quality ultrapure ammonia is a technical problem that needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art, adapt to practical needs, and provide a method for preparing ultrapure ammonia. This invention adopts a process of first vaporizing the raw material liquid ammonia, then performing distillation and purification, and finally absorbing the ammonia gas with ultrapure water to obtain ammonia water. The process is simple, reliable, easy to implement, and can effectively ensure the purity of the finished liquid ammonia.

[0006] This invention provides a liquid ammonia distillation and purification device, including a distillation column, a condenser connected to the top of the distillation column, a pressure reducing valve connected to the condenser, a water washing column connected to the pressure reducing valve, and a heat exchanger and an ammonia separator connected to the water washing column.

[0007] The front end of the distillation column is connected to a compressor, the compressor is connected to an ammonia separator, and the ammonia separator is connected to an evaporator.

[0008] The distillation column is equipped with a coil and a distributor inside. The coil is located at the bottom of the distillation column, and the distributor is located at the top of the distillation column. The coil is connected to the reboiler outside the distillation column.

[0009] The water washing tower is equipped with an ultrapure water inlet and a sprayer inside; the bottom of the water washing tower is connected to a heat exchanger via a circulating pump, and the heat exchanger is connected to the sprayer.

[0010] The ammonia outlet at the top of the distillation column is connected to the front end of the condenser. The rear end of the condenser is provided with an ammonia outlet and a liquid ammonia outlet. The ammonia outlet is connected to a pressure reducing valve, and the liquid ammonia outlet is connected to a distributor.

[0011] The evaporator, coil, distillation column, water washing column, ammonia separator I, ammonia separator II, condenser, and heat exchanger are made of one or more of 304, 316L, or PTFE; preferably, the evaporator and coil are made of 304, the distillation column is made of 316L, and the water washing column, ammonia separator, condenser, and heat exchanger are all made of 304+PTFE; the pressure reducing valve is an ammonia-specific valve.

[0012] The present invention also provides a method for purifying liquid ammonia by distillation, comprising the following steps: S1. Industrial-grade liquid ammonia is converted into gaseous ammonia by an evaporator, and the gaseous ammonia is then preliminarily filtered by an ammonia-liquid separator; S2. After preliminary filtration, the gaseous ammonia is pressurized by the compressor and introduced from the bottom of the distillation column. During the upward process, the gaseous ammonia undergoes mass and heat transfer with the liquid ammonia flowing down from the top distributor. Finally, the gaseous ammonia flows out from the top of the column and enters the condenser. S3. The gaseous ammonia flowing out of the condenser is depressurized by the pressure reducing valve and enters the lower section of the water washing tower. It flows towards the top of the tower and comes into countercurrent contact with the saturated ammonia water sprayed down by the top sprayer. The gaseous ammonia is collected from the top of the water washing tower and the gas phase separated by the ammonia liquid separator is high-purity ammonia.

[0013] The liquid ammonia flowing out of the condenser is returned to the distributor; the liquid ammonia at the bottom of the distillation column is re-vaporized by heating the coil, which contains an ethylene glycol aqueous solution at 40-50°C, and the heat is provided by the reboiler. The temperature of the liquid ammonia flowing down from the distributor is 20-30℃.

[0014] The saturated ammonia water inside the water washing tower flows downward into the bottom of the tower, is pumped into the heat exchanger by the circulating pump for heat exchange and cooling, and then enters the sprayer at the top of the tower to participate in the circulation; the liquid ammonia separated by the ammonia separator II flows back to the water washing tower for spraying. The temperature of the saturated ammonia water sprayed by the sprayer is 20-30℃.

[0015] The internal temperature of the distillation column is 5~15℃ and the pressure is 0.8~0.9MPa; preferably 10℃ and 0.9MPa; the internal temperature of the water washing column is 13~23℃ and the pressure is 0.1~0.4MPa; preferably 18℃ and 0.2MPa.

[0016] The evaporator operates at a temperature of 40-50℃; the condenser operates at a temperature of 7-12℃; the liquid ammonia flow rate of the distributor is 90 kg / h; the saturated ammonia flow rate of the sprayer is 160 kg / h; and the heat exchanger operates at a temperature of 7-12℃.

[0017] Regularly replenish ultrapure water from the ultrapure water inlet, remove some of the saturated ammonia water from the bottom of the water washing tower, and prepare fresh saturated ammonia water.

[0018] The beneficial effects of this invention are as follows: 1. This ultrapure ammonia continuous production system adopts a combination of a distillation tower and a water washing tower. On the one hand, it can meet the needs of large-volume production. On the other hand, based on the impurities in the raw materials, the distillation tower removes heavy components and the water washing tower removes light components, so as to achieve higher product purity, reaching 99.99999%.

[0019] 2. When using the dual-tower process technology of distillation tower and water washing tower, a heat exchanger can be used to condense and liquefy part of the gaseous ammonia for recycling, achieving the effect of multiple distillations. At the same time, it ensures that the distillation process is fully and effectively, thereby ensuring that the product quality meets the requirements of ultrapure ammonia products.

[0020] 3. Saturated ammonia water only needs to be added once during the initial startup, and no replenishment is required in subsequent production processes, which is energy-saving and environmentally friendly; it can be discharged during startup and shutdown processes and replaced periodically. Attached Figure Description

[0021] Figure 1 Schematic diagram of the device of the present invention.

[0022] Figure 2 Process flow diagram of this invention.

[0023] The diagram is labeled as follows: 1. Evaporator, 2. Ammonia Separator I, 3. Compressor, 4. Distillation Column, 5. Condenser, 6. Water Washing Tower, 7. Ammonia Separator II, 8. Pressure Reducing Valve, 4-1. Reboiler, 4-2. Coil, 4-3. Distributor, 6-1. Sprayer, 6-2. Ultrapure Water Inlet, 6-3. Heat Exchanger. Detailed Implementation

[0024] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0025] Example 1 The present invention provides a liquid ammonia distillation and purification device, including a distillation column 4, a condenser 5 connected to the top of the distillation column 4, a pressure reducing valve 8 connected to the condenser 5, a water washing column 6 connected to the pressure reducing valve 8, a heat exchanger 6-3 connected to the water washing column 6, and an ammonia liquid separator 7.

[0026] The front end of the distillation column 4 is connected to the compressor 3, the compressor 3 is connected to the ammonia separator 2, and the ammonia separator 2 is connected to the evaporator 1.

[0027] The distillation column 4 is equipped with a coil 4-2 and a distributor 4-3 inside. The coil 4-2 is located at the bottom of the distillation column 4, and the distributor 4-3 is located at the top of the distillation column 4. The coil 4-2 is connected to the reboiler 4-1 outside the distillation column 4.

[0028] The water washing tower 6 is equipped with an ultrapure water inlet 6-2, and a sprayer 6-1 is installed inside the water washing tower 6; the bottom of the water washing tower 6 is connected to a heat exchanger 6-3 via a circulating pump, and the heat exchanger 6-3 is connected to the sprayer 6-1.

[0029] The ammonia outlet at the top of the distillation column 4 is connected to the front end of the condenser 5. The rear end of the condenser 5 is provided with an ammonia outlet and a liquid ammonia outlet. The ammonia outlet is connected to a pressure reducing valve 8, and the liquid ammonia outlet is connected to a distributor 4-3.

[0030] The evaporator 1, coil 4-2, distillation column 4, water washing column 6, ammonia separator 1, ammonia separator 2, condenser 5, and heat exchanger 6-3 are made of one or more of 304, 316L, or PTFE; preferably, the evaporator 1 and coil 4-2 are made of 304, the distillation column 4 is made of 316L, and the water washing column 6, ammonia separator 1, ammonia separator 2, condenser 5, and heat exchanger 6-3 are all made of 304+PTFE; the pressure reducing valve 8 is an ammonia-specific valve.

[0031] Regularly replenish ultrapure water from ultrapure water inlet 6-2, drain some of the saturated ammonia water from the bottom of water washing tower 6, and prepare fresh saturated ammonia water. Regularly drain the liquid ammonia from the bottom of distillation tower 4.

[0032] Example 2 use Figure 1 The device shown works as follows: S1. Industrial-grade liquid ammonia is converted into gaseous ammonia by an evaporator, and the gaseous ammonia is then preliminarily filtered by an ammonia-liquid separator; S2. After preliminary filtration, the gaseous ammonia is pressurized by the compressor and introduced from the bottom of the distillation column. During the upward movement of the gaseous ammonia, it undergoes mass and heat transfer with the liquid ammonia (temperature 20℃) flowing down from the top distributor of the column. Finally, the gaseous ammonia flows out from the top of the column and enters the condenser. The liquid ammonia flowing to the bottom of the distillation column is re-vaporized by heating the coil, which contains an aqueous solution of ethylene glycol at 40°C. The heat is provided by the reboiler.

[0033] S3. The gaseous ammonia flowing out of the condenser is reduced to 0.2MPa by the pressure reducing valve and then enters the lower section of the water washing tower and flows towards the top of the tower. It comes into countercurrent contact with the saturated ammonia water (temperature 20℃) sprayed down by the top sprayer. The gaseous ammonia is collected from the top of the water washing tower and the gas phase separated by the ammonia liquid separator is high-purity ammonia. The liquid ammonia flowing out of the condenser is returned to the distributor; The saturated ammonia water inside the water washing tower flows downward into the bottom of the tower, is pumped into the heat exchanger by the circulating pump for heat exchange and cooling, and then enters the sprayer at the top of the tower to participate in the circulation. The liquid ammonia separated by the ammonia separator is returned to the water washing tower.

[0034] The internal temperature of the distillation column is 10℃ and the pressure is 0.9MPa; the internal temperature of the water washing column is 18℃ and the pressure is 0.2MPa; the operating temperature of the evaporator is 40℃; the operating temperature of the condenser is 7℃; the flow rate of liquid ammonia in the distributor is 90kg / h; the flow rate of saturated ammonia water in the sprayer is 160kg / h; and the operating temperature of the heat exchanger is 7℃.

[0035] Industrial grade liquid ammonia: feed rate 160 kg / h; ammonia content ≥ 99.9%, moisture ≤ 0.1%, oil content ≤ 5 mg / kg, iron content ≤ 1 mg / kg.

[0036] The obtained high-purity ammonia gas was diluted with ultrapure water to prepare ammonia water with a mass fraction of 25%. The content of various metal impurities was less than 10 ppt. The results are shown in Table 1. The process produced no secondary pollution.

[0037] Table 1 Metal impurity content of the product in Example 2

[0038] Comparative Example 1 Unlike Example 2, the pressure of the pressure reducing valve at the distillation column entering the water washing tower was reduced to 0.5 MPa before entering the water washing tower. The internal temperature of the water washing tower was 18°C, and the pressure was 0.5 MPa; otherwise, it was the same as Example 2. The results of the ammonia water metal impurity content are shown in Table 2.

[0039] Table 2. Metal impurity content of Comparative Example 1 .

Claims

1. A method for purifying liquid ammonia by distillation, characterized in that, Includes the following steps: S1. Industrial-grade liquid ammonia is converted into gaseous ammonia by an evaporator, and the gaseous ammonia is then preliminarily filtered by an ammonia-liquid separator; S2. After preliminary filtration, the gaseous ammonia is pressurized by the compressor and introduced from the bottom of the distillation column. During the upward process, the gaseous ammonia undergoes mass and heat transfer with the liquid ammonia flowing down from the top distributor. Finally, the gaseous ammonia flows out from the top of the column and enters the condenser. S3. The gaseous ammonia flowing out of the condenser is reduced to 0.2MPa by the pressure reducing valve and then enters the lower section of the water washing tower and flows towards the top of the tower. It comes into countercurrent contact with the saturated ammonia water sprayed down by the top sprayer. The gaseous ammonia is collected from the top of the water washing tower and the gas phase separated by the second ammonia separator is high-purity ammonia. The high-purity ammonia gas has a purity of ≥99.99999%, and both metal and silicon impurities are <10ppt. The internal temperature of the distillation column is 10℃ and the pressure is 0.9MPa; the internal temperature of the water washing column is 18℃ and the pressure is 0.2MPa; the operating temperature of the evaporator is 40℃; the operating temperature of the condenser is 7℃; the flow rate of liquid ammonia in the distributor is 90kg / h; the flow rate of saturated ammonia water in the sprayer is 160kg / h; and the operating temperature of the heat exchanger is 7℃. The liquid ammonia flowing out of the condenser is returned to the distributor; the liquid ammonia at the bottom of the distillation column is re-vaporized by heating the coil, which contains an ethylene glycol aqueous solution at 40°C, and the heat is provided by the reboiler; the liquid ammonia flowing down from the distributor is at a temperature of 20°C. The saturated ammonia water inside the water washing tower flows downward into the bottom of the tower, is pumped into the heat exchanger by the circulating pump for heat exchange and cooling, and then enters the sprayer at the top of the tower to participate in the circulation; the liquid ammonia separated by the ammonia separator flows back to the water washing tower for spraying; the temperature of the saturated ammonia water sprayed by the sprayer is 20°C.

2. The liquid ammonia distillation purification method according to claim 1, characterized in that, The evaporator, distillation column, coil, water washing tower, ammonia separator I, ammonia separator II, condenser and heat exchanger are made of one or more of 304, 316L or PTFE.

3. The liquid ammonia distillation purification method according to claim 2, characterized in that, The evaporator and coils are made of 304 stainless steel, the distillation column is made of 316L stainless steel, and the water washing tower, ammonia separator I, ammonia separator II, condenser and heat exchanger are all made of 304+PTFE stainless steel; the pressure reducing valve is a special valve for ammonia.

4. A method for purifying liquid ammonia by distillation according to any one of claims 1-3, characterized in that, The purification process is carried out in a liquid ammonia distillation unit, which includes a distillation column (4), a condenser (5) connected to the top of the distillation column (4), a pressure reducing valve (8) connected to the condenser (5), a water washing tower (6) connected to the pressure reducing valve (8), and a heat exchanger (6-3) and an ammonia separator (7) connected to the water washing tower (6). The ammonia outlet at the top of the distillation column (4) is connected to the front end of the condenser (5). The rear end of the condenser (5) is provided with an ammonia outlet and a liquid ammonia outlet. The ammonia outlet is connected to a pressure reducing valve (8). The water washing tower (6) is provided with an ultrapure water inlet (6-2), and the interior of the water washing tower (6) is provided with a sprayer (6-1); the bottom of the water washing tower (6) is connected to a heat exchanger (6-3) via a circulating pump, and the heat exchanger (6-3) is connected to the sprayer (6-1); the rear end of the ammonia separator II (7) is provided with an ammonia gas outlet and a liquid ammonia outlet, and the liquid ammonia outlet is connected to the sprayer (6-1).

5. The liquid ammonia distillation purification method according to claim 4, characterized in that, The front end of the distillation column (4) is connected to the compressor (3), the compressor (3) is connected to the ammonia separator (2), and the ammonia separator (2) is connected to the evaporator (1).

6. The liquid ammonia distillation purification method according to claim 4, characterized in that, The distillation column (4) is equipped with a coil (4-2) and a distributor (4-3) inside. The coil (4-2) is located at the bottom of the distillation column (4), and the distributor (4-3) is located at the top of the distillation column (4). The coil (4-2) is connected to the reboiler (4-1) outside the distillation column (4).

7. The liquid ammonia distillation purification method according to claim 4, characterized in that, The liquid ammonia outlet at the rear end of the condenser (5) is connected to the distributor (4-3).

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