Liquid ammonia rectification and purification device and method

Abstract

According to the liquid ammonia rectification and purification device and method, the rectification tower and the water washing tower are combined, the temperature and the pressure are controlled under mild conditions, heavy component impurities in raw materials are removed through the rectification tower, and light component impurities are removed through the water washing tower; on one hand, large-flow production can be met, and on the other hand, higher product purity can be achieved, and the purity reaches 99.99999%. Besides, part of gas ammonia is condensed, liquefied and recycled by virtue of a condenser, and multiple times of rectification are realized, so that the product quality is ensured to meet the requirement of an ultra-pure ammonia product; saturated ammonia water in the water washing tower can be recycled, so that the device is more energy-saving and environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of liquid ammonia purification, and in particular to a liquid ammonia rectification and purification device and method. Background Art

[0002] Ultrapure ammonia is widely used in the electronics, chemical, metallurgy and other industries, especially in the semiconductor industry. Ultrapure ammonia is one of the key raw materials for the preparation of semiconductor silicon nitride thin films, and the purity of ammonia will directly affect the quality of silicon nitride materials. Ultrapure ammonia, as a nitrogen source for the LED electronics industry, can be used in the manufacture of thin-film solar cells and can be used in combination with silane and ultrapure argon.

[0003] In the manufacturing process, a large amount of ultra-pure ammonia is needed as a nitrogen source, especially in the growth process of wafers. The higher the purity of ammonia used, the lower the power consumption and the greater the luminous intensity. Therefore, the production of ultra-pure ammonia will have broad market prospects in the future.

[0004] At present, the commonly used production methods of ultra-pure ammonia are adsorption, distillation, or a combination of adsorption and distillation. However, this method has high energy consumption and large tail gas emissions, and it is difficult to purify to a high purity. Therefore, providing a continuous production system and process control method for high-quality ultra-pure ammonia is a technical problem that needs to be solved in the field. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art, meet the actual needs, and provide a method for preparing ultra-pure ammonia. The present invention first gasifies the raw liquid ammonia, then performs a distillation and purification process, and finally absorbs the ammonia gas with ultra-pure water to obtain ammonia water. The process is simple and reliable, easy to implement, and can effectively ensure the purity of the finished liquid ammonia.

[0006] The invention provides a liquid ammonia distillation and purification device, comprising a distillation tower, the top of the distillation tower is connected to a condenser, the condenser is connected to a pressure reducing valve, the pressure reducing valve is connected to a water washing tower, and the water washing tower is connected to a heat exchanger and an ammonia-liquid separator.

[0007] The front end of the distillation tower is connected to a compressor, the compressor is connected to an ammonia-liquid separator 1, and the ammonia-liquid separator is connected to an evaporator.

[0008] The distillation tower is provided with a coil and a distributor, the coil is located at the bottom of the distillation tower, and the distributor is located at the top of the distillation tower; the coil is connected to a reboiler outside the distillation tower.

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

[0010] The ammonia outlet at the top of the distillation tower is connected to the front end of the condenser, and 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 tower, water washing tower, ammonia liquid separator 1, ammonia liquid separator 2, condenser and heat exchanger are made of one or more of 304, 316L or PTFE; preferably, the evaporator and coil are made of 304 material, the distillation tower is made of 316L material, the water washing tower, ammonia liquid separator, condenser and heat exchanger are all made of 304+PTFE material; the pressure reducing valve is a special valve for ammonia.

[0012] The present invention also provides a method for distilling and purifying liquid ammonia, comprising the following steps: S1. Industrial-grade liquid ammonia is converted into gaseous ammonia by the evaporator, and the gaseous ammonia is then initially filtered by the ammonia-liquid separator; S2. The gaseous ammonia after preliminary filtration is pressurized by a compressor and introduced from the bottom of the distillation tower. During the rising process of the gaseous ammonia, the gaseous ammonia conducts mass and heat transfer with the liquid ammonia flowing down from the distributor at the top of the tower. Finally, the gaseous ammonia flows out from the top of the tower into the condenser; S3. The gaseous ammonia flowing out of the condenser enters from the lower section of the water scrubber after being reduced in pressure by the pressure reducing valve, and flows toward the top of the tower, where it contacts in reverse direction with the saturated ammonia water sprayed from the top of the tower. The gaseous ammonia is extracted from the top of the water scrubber, and the gas phase separated by the ammonia-liquid separator II is high-purity ammonia gas.

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

[0014] The saturated ammonia water in the water washing tower flows downward into the bottom of the water washing tower, is pumped into the heat exchanger through a circulation 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-liquid separator 2 flows back to the water washing tower for spraying; The temperature of the saturated ammonia water sprayed by the sprayer is 20-30°C.

[0015] The internal temperature of the distillation tower is 5-15°C, and the pressure is 0.8-0.9MPa; preferably 10°C, 0.9MPa; the internal temperature of the water washing tower is 13-23°C, and the pressure is 0.1-0.4MPa; preferably 18°C, 0.2MPa.

[0016] The working temperature of the evaporator is 40-50°C; the working temperature of the condenser is 7-12°C; the flow rate of liquid ammonia in the distributor is 90kg / h; the flow rate of saturated ammonia water in the sprinkler is 160kg / h; and the working temperature of the heat exchanger is 7-12°C.

[0017] Regularly add ultrapure water from the ultrapure water inlet, remove part of the saturated ammonia water at the bottom of the water washing tower, and prepare new saturated ammonia water.

[0018] The beneficial effects of the present invention are as follows: 1. This ultra-pure ammonia continuous production system adopts a combination of a distillation tower and a water washing tower. On the one hand, it can meet the large-flow production. On the other hand, according to the impurity components in the raw materials, the distillation tower removes the heavy components, and the water washing tower removes the light components, which can achieve a higher product purity of 99.99999%.

[0019] 2. When the double-tower process technology of distillation tower and water washing tower is selected, part of the gaseous ammonia can be condensed and liquefied with the help of heat exchanger, and recycled to achieve the effect of multiple distillations. At the same time, the distillation process is ensured to be fully effective, thereby ensuring that the product quality meets the requirements of ultra-pure ammonia products.

[0020] 3. Saturated ammonia water only needs to be added once when the machine is started for the first time, and no replenishment is required during the subsequent production process, which is energy-saving and environmentally friendly; it can be discharged during the start-up and shutdown process and replaced regularly. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0022] Figure 2 Process flow chart of the present invention.

[0023] Explanations in the figure: 1. Evaporator, 2. Ammonia-liquid separator 1, 3. Compressor, 4. Distillation tower, 5. Condenser, 6. Water washing tower, 7. Ammonia-liquid separator 2, 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 DESCRIPTION

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

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

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

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

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

[0029] The ammonia outlet at the top of the distillation tower 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 the pressure reducing valve 8, and the liquid ammonia outlet is connected to the distributor 4-3.

[0030] The evaporator 1, coil 4-2, distillation tower 4, water washing tower 6, ammonia liquid separator 1 2, ammonia liquid separator 2 7, 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 material, the distillation tower 4 is made of 316L material, the water washing tower 6, ammonia liquid separator 1 2, ammonia liquid separator 2 7, condenser 5 and heat exchanger 6-3 are all made of 304+PTFE material; the pressure reducing valve 8 adopts a special valve for ammonia.

[0031] Ultrapure water is regularly added from the ultrapure water inlet 6-2, part of the saturated ammonia water at the bottom of the water washing tower 6 is removed, and new saturated ammonia water is prepared. Liquid ammonia at the bottom of the distillation tower 4 is regularly discharged.

[0032] Example 2 use Figure 1 The specific working process of the device shown is as follows: S1. Industrial-grade liquid ammonia is converted into gaseous ammonia by the evaporator, and the gaseous ammonia is then initially filtered by the ammonia-liquid separator; S2. The gaseous ammonia after preliminary filtration is pressurized by the compressor and introduced from the bottom of the distillation tower. During the rising process of the gaseous ammonia, it conducts mass and heat transfer with the liquid ammonia (temperature is 20°C) flowing down from the distributor at the top of the tower. Finally, the gaseous ammonia flows out from the top of the tower and enters the condenser; The liquid ammonia flowing to the bottom of the distillation tower is vaporized again by heating the coil. The coil contains a 40°C ethylene glycol aqueous solution, and the heat is provided by the reboiler.

[0033] S3. The gaseous ammonia flowing out of the condenser is reduced in pressure to 0.2MPa by the pressure reducing valve and then enters the lower section of the water scrubber and flows toward the top of the tower. It contacts the saturated ammonia water (temperature is 20℃) sprayed down by the tower top sprayer in reverse direction. The gaseous ammonia is extracted from the top of the water scrubber and the gas phase separated by the ammonia liquid separator is high-purity ammonia gas. The liquid ammonia flowing out of the condenser flows back to the distributor; The saturated ammonia water in the water scrubber flows downward into the bottom of the water scrubber, is pumped into the heat exchanger through a circulation 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-liquid separator 2 is refluxed to the water washing tower.

[0034] Among them, the internal temperature of the distillation tower is 10℃ and the pressure is 0.9MPa; the internal temperature of the water washing tower is 18℃ and the pressure is 0.2MPa; the working temperature of the evaporator is 40℃; the working 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; the working temperature of the heat exchanger is 7℃.

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

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

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

[0038] Comparative Example 1 The difference from Example 2 is that the pressure reducing valve from the distillation tower to the water scrubber is reduced to 0.5 MPa before entering the water scrubber, and the internal temperature of the water scrubber is 18°C ​​and the pressure is 0.5 MPa; the rest is the same as Example 2. The results of the metal impurity content of ammonia water are shown in Table 2.

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

Claims

1. A liquid ammonia distillation and purification device, characterized in that: The distillation tower (4) comprises a condenser (5) connected to the top of the distillation tower (4), the condenser (5) is connected to a pressure reducing valve (8), the pressure reducing valve (8) is connected to a water washing tower (6), and the water washing tower (6) is connected to a heat exchanger (6-3) and a second ammonia liquid separator (7).

2. A liquid ammonia distillation and purification device according to claim 1, characterized in that: The front end of the distillation tower (4) is connected to a compressor (3), the compressor (3) is connected to an ammonia-liquid separator (2), and the ammonia-liquid separator (2) is connected to an evaporator (1).

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

4. A liquid ammonia distillation and purification device according to claim 1, characterized in that: The water washing tower (6) is provided with an ultrapure water inlet (6-2), and a sprayer (6-1) is provided inside the water washing tower (6); the bottom of the water washing tower (6) is connected to the heat exchanger (6-3) via a circulation pump, and the heat exchanger (6-3) is connected to the sprayer (6-1); the ammonia outlet at the top of the distillation tower (4) is connected to the front end of the condenser (5), and the rear end of the condenser (5) is provided with an ammonia outlet and a liquid ammonia outlet, the ammonia outlet is connected to the pressure reducing valve (8), and the liquid ammonia outlet is connected to the distributor (4-3).

5. A method for purifying liquid ammonia by distillation, characterized in that: The following steps are involved: S1. Industrial-grade liquid ammonia is converted into gaseous ammonia by the evaporator, and the gaseous ammonia is then initially filtered by the ammonia-liquid separator; S2. The gaseous ammonia after preliminary filtration is pressurized by a compressor and introduced from the bottom of the distillation tower. During the rising process of the gaseous ammonia, the gaseous ammonia conducts mass and heat transfer with the liquid ammonia flowing down from the distributor at the top of the tower. Finally, the gaseous ammonia flows out from the top of the tower into the condenser; S3. The gaseous ammonia flowing out of the condenser enters from the lower section of the water scrubber after being reduced in pressure by the pressure reducing valve, and flows toward the top of the tower, where it contacts in reverse direction with the saturated ammonia water sprayed from the top of the tower. The gaseous ammonia is extracted from the top of the water scrubber, and the gas phase separated by the ammonia-liquid separator II is high-purity ammonia gas.

6. A method for purifying liquid ammonia by distillation according to claim 5, characterized in that: The liquid ammonia flowing out of the condenser is refluxed to the distributor; the liquid ammonia at the bottom of the distillation tower is vaporized again by heating the coil, the coil contains ethylene glycol aqueous solution at 40-50°C, and the heat is provided by the reboiler; The temperature of the liquid ammonia flowing down the distributor is 20-30°C.

7. A method for purifying liquid ammonia by distillation according to claim 5, characterized in that: The saturated ammonia water in the water washing tower flows downward into the bottom of the water washing tower, is pumped into the heat exchanger through a circulation 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-liquid separator 2 flows back to the water washing tower for spraying; The temperature of the saturated ammonia water sprayed by the sprayer is 20-30°C.

8. A method for purifying liquid ammonia by distillation according to claim 5, characterized in that: The internal temperature of the distillation tower is 5-15°C, and the pressure is 0.8-0.9MPa; preferably 10°C, 0.9MPa; the internal temperature of the water washing tower is 13-23°C, and the pressure is 0.1-0.4MPa; preferably 18°C, 0.2MPa.

9. A method for purifying liquid ammonia by distillation according to claim 5, characterized in that: The working temperature of the evaporator is 40-50°C; the working temperature of the condenser is 7-12°C; the flow rate of liquid ammonia in the distributor is 90kg / h; the flow rate of saturated ammonia water in the sprinkler is 160kg / h; and the working temperature of the heat exchanger is 7-12°C.

10. A method for purifying liquid ammonia by distillation according to any one of claims 6 or 7, characterized in that: The evaporator, distillation tower, coil, water scrubber, ammonia liquid separator 1, ammonia liquid separator 2, condenser and heat exchanger are made of one or more of 304, 316L or PTFE; Preferably, the evaporator and coil are made of 304 material, the distillation tower is made of 316L material, and the water washing tower, ammonia liquid separator, condenser and heat exchanger are all made of 304+PTFE material; The pressure reducing valve adopts a special valve for ammonia.

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