An apparatus for purifying liquid ammonia by rectification

Abstract

This invention provides a liquid ammonia distillation and purification device, which combines a distillation column and a water washing column to control temperature and pressure under relatively mild conditions. The distillation column removes heavy component impurities from the raw material, while the water washing column removes light component impurities. This allows for high-volume production while achieving higher product purity, reaching 99.99999%. Furthermore, this invention utilizes a condenser to condense and liquefy part of the gaseous ammonia for recycling, enabling multiple distillations and ensuring that the product quality meets the requirements for ultrapure ammonia. The saturated ammonia water in the water washing column can also be reused, making it more energy-efficient and environmentally friendly.

Description

Technical Field

[0001] This utility model relates to the field of liquid ammonia purification technology, specifically to a liquid ammonia distillation and purification device. 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. In recent years, with the gradual depletion of global energy resources such as oil and environmental pollution, and the impact of the greenhouse effect on the climate, countries around the world are vigorously developing clean energy and energy-saving technologies, focusing on a low-carbon economy.

[0003] Against this backdrop, my country's solar cells, semiconductor light-emitting devices, and related industries have experienced rapid development. The manufacturing process requires large quantities of ultrapure ammonia as a nitrogen source. In particular, the higher the purity of the ammonia used in wafer growth, the lower the power consumption and the greater the luminous 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 for high-quality ultrapure ammonia is a technical problem that needs to be solved in this field. Utility Model Content

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology, meet the actual needs, and provide an ultrapure ammonia preparation equipment. 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 utility model 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. 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 beneficial effects of this utility model are as follows:

[0013] 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%.

[0014] 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.

[0015] 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

[0016] Figure 1 Schematic diagram of the device of this utility model.

[0017] Figure 2 This utility model has a process flow diagram.

[0018] 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

[0019] The embodiments of this utility model will be described in detail below with reference to the examples. The following examples are only used to illustrate this utility model and should not be regarded as limiting the scope of this utility model.

[0020] Example 1

[0021] This utility model 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 separator 7.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Example 2

[0029] use Figure 1 The device shown works as follows:

[0030] 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;

[0031] 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.

[0032] 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.

[0034] The liquid ammonia flowing out of the condenser is returned to the distributor;

[0035] 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.

[0036] The liquid ammonia separated by the ammonia separator is returned to the water washing tower.

[0037] 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℃.

[0038] 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.

[0039] 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.

[0040] Table 1 Metal impurity content of the product in Example 2

[0041]

Claims

1. A liquid ammonia distillation and purification apparatus, characterized in that, It 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 column (6) connected to the pressure reducing valve (8), and a heat exchanger (6-3) and ammonia separator II (7) connected to the water washing column (6). 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). 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). 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 circulating pump, and the heat exchanger (6-3) is connected to the sprayer (6-1). 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). The ammonia separator 2 (7) has a liquid ammonia outlet and an ammonia outlet for 7N grade ammonia gas at its rear end, and the liquid ammonia outlet is connected to a sprayer (6-1); the evaporator (1) has an industrial grade liquid ammonia inlet at its front end.

2. The liquid ammonia distillation and purification apparatus according to claim 1, characterized in that, The evaporator (1), distillation column (4), coil (4-2), water washing column (6), ammonia separator one (2), ammonia separator two (7), condenser (5) and heat exchanger (6-3) are made of 304, 316L or PTFE.

3. The liquid ammonia distillation and purification apparatus according to claim 1, characterized in that, The evaporator (1) and coil (4-2) are made of 304 stainless steel, the distillation column (4) is made of 316L stainless steel, and the water washing tower, ammonia separator, condenser and heat exchanger are all made of 304+PTFE stainless steel.

4. The liquid ammonia distillation and purification apparatus according to claim 1, characterized in that, The pressure reducing valve (8) is a special valve for ammonia.

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