Method and system for producing high-purity ammonia from industrial ammonia

Abstract

The invention provides a method and a system for producing high-purity ammonia from industrial ammonia. The method comprises four steps of low-temperature cooling, mechanical filtration, rectification and adsorption dehydration. The system comprises a liquid ammonia cooler, a precision filter, a rectifying tower, a rectifying tower top cooler, a reboiler and a molecular sieve dehydrator. According to the method and the system, various impurities are accurately removed, the product quality control is facilitated, and meanwhile, whether a certain process is bypassed or not can be determined according to the actual impurity condition of the raw material, so that the energy consumption is reduced; energy is recovered through low-temperature cooling and top gas heat exchange of the rectifying tower, heat is fully integrated, and energy conservation is facilitated; a heat source of the reboiler of the rectifying tower adopts circulating cooling water which is easy to obtain and is convenient to integrate with heat of other devices, so that energy consumption is reduced; the evaporative condenser is arranged between the upper tower and the lower tower of the rectifying tower, so that heat exchange efficiency is high and energy is saved; gas ammonia of the tower top cooler of the rectifying tower is lower than that of liquid ammonia, materials in the heat exchanger cannot pollute products, and product quality is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of petrochemical industry, and in particular relates to a method and system for producing high-purity ammonia from industrial ammonia. Background Art

[0002] Purification, analysis and research of high-purity ammonia, developed 5N electronic grade high-purity ammonia, and passed the appraisal. The purity of the bottled high-purity ammonia produced is 5N, and the impurity index is: H 2 O≤5×10 -6 , O 2 ≤2×10 -6 , THC≤1×10 -6 The preparation of high-purity ammonia basically remains at the 5N level, and the product purity is unstable. The production scale also remains at the level of a pilot plant, with an annual output of about 2 to 5 tons.

[0003] After the optimization of process technology in recent years, my country has continuously optimized the ultra-pure ammonia process on the basis of absorbing advanced foreign technological achievements, solved the problems in the original process, and can maintain the purity of ultra-pure ammonia at 7N.

[0004] High-purity ammonia purification technology mainly includes chemical method and physical method. Chemical method refers to the method of removing impurities through chemical reaction; physical method is based on NH 3 Same as O 2 , H 2 O、CH 4 ,CO,CO 2 There is a large separation factor and adsorbent for NH 3 Different from the impurity adsorption capacity, the impurities are removed by gas-liquid separation, distillation and physical adsorption. In addition, there is an alloy getter purification technology that can effectively remove H in electronic gas. 2 O, O 2 Impurities such as chlorinated hydrocarbons are present in the ammonia. Currently, this method is only used in terminal purification devices for electronic gases. The application of this technology in purification processes requires further research and improvement of catalysts. The physical method generally uses the large difference in water concentration between the vapor and liquid phases of ammonia for separation.

[0005] At present, there are several different production processes for high-purity ammonia, which can be roughly classified into: complete distillation type, filtration adsorption distillation type and complete filtration adsorption type. Compared with the three processes, the complete filtration adsorption production process is relatively simple, but its current production quality is relatively low, and the product quality is determined by the purifier; the process of production based on distillation is more complicated than the process of production based on purifier adsorption. The production process needs to control the process parameters to make the product meet the requirements, but the quality of production based on distillation will be more stable; the product quality and process complexity of the filtration adsorption distillation process are between the above two processes. The main domestic high-purity ammonia production companies are: Indesai Electronics Co., Ltd., Dalian Free Trade Zone Kelide Chemical Technology Development Co., Ltd., and Suzhou Jinhong Gas Co., Ltd. It is reported that all three companies can produce ultra-pure ammonia with a purity of 7N.

[0006] The main problems existing in the existing technology are: the pure distillation process for producing high-purity ammonia is relatively difficult to separate due to the association of polar molecular water and ammonia, and requires continuous heat and cold sources, resulting in high energy consumption and unreliable product quality; industrial liquid ammonia directly enters the vaporizer, and the condensation heat at the top of the distillation tower is not recovered, resulting in insufficient energy utilization; the operating pressure on the medium side of the common materials of the vaporizer, the distillation tower reboiler, and the distillation tower top condenser is unclear, and there is a problem of trace leakage of common materials to the liquid ammonia side due to long-term operation of the heat exchanger, resulting in substandard product quality. Summary of the invention

[0007] In order to solve the problems of high operating cost and insufficient energy utilization in the prior art, the present invention proposes an energy-saving industrial ammonia production high-purity ammonia process, which adopts adsorption plus distillation to fully utilize the process heat and optimize the operating conditions.

[0008] In a first aspect, the present invention provides a method for producing high-purity ammonia from industrial ammonia, which comprises four steps of cryogenic cooling, mechanical filtration, distillation, and adsorption and water removal.

[0009] The sources of impurities in industrial liquid ammonia include impurities carried by raw hydrogen and nitrogen, as well as possible pollution caused by catalysts, pipelines, equipment, etc. The main impurity gases in raw hydrogen are hydrogen, water, carbon monoxide, carbon dioxide, and hydrocarbons (mainly carbon 1 and carbon 2), and the main impurity gases in raw nitrogen are nitrogen, oxygen, and rare gases. In addition, there are metal particles that may be produced by catalysts, equipment, and pipelines, and oil impurities (C3 and above) that may be produced by compressors. Among them, water is a polar molecule and has a greater association force with ammonia. Hydrogen, nitrogen, carbon monoxide, carbon dioxide, oxygen, argon, carbon 1, and carbon 2 are light components relative to ammonia, and water and C3 and above are heavy components relative to ammonia.

[0010] As a specific embodiment of the present invention, the temperature of the low temperature cooling is -30 to -15°C; and the pressure is 1 to 1.5 MPa.

[0011] As a specific embodiment of the present invention, the mechanical filtration step includes removing particulate impurities in liquid ammonia; the liquid ammonia pressure is 1 to 1.5 MPa, and the liquid ammonia temperature is -30 to -15°C.

[0012] As a specific embodiment of the present invention, the distillation step includes separation of light components and heavy components; the distillation pressure is 0.7-1 MPa.

[0013] As a specific embodiment of the present invention, the distillation step also includes condensing the light component ammonia gas, refluxing the liquid ammonia, and removing the non-condensable light components; the condensation temperature is 15 to 30°C.

[0014] In a second aspect, the present invention provides a system for producing high-purity ammonia from industrial ammonia, comprising a cryogenic cooling unit, a mechanical filtration unit, an adsorption dehydration unit, and a distillation unit;

[0015] The low temperature cooling unit comprises a liquid ammonia pressure pump and a liquid ammonia cooler connected in sequence;

[0016] The mechanical filtration unit includes precision filters connected in sequence;

[0017] The adsorption dehydration unit includes a molecular sieve dehydrator;

[0018] The distillation unit comprises a distillation tower and a distillation tower top cooler; an evaporative condenser is arranged between the upper tower and the lower tower of the distillation tower;

[0019] The distillation tower top cooler is connected to the upper end of the precision filter;

[0020] The distillation tower top cooler is connected to the upper end of the distillation tower;

[0021] The molecular sieve dehydrator is connected to the distillation tower.

[0022] As a specific embodiment of the present invention, the system further comprises a feeding device and a reflux device.

[0023] As a specific implementation of the present invention, the feeding device includes a liquid ammonia buffer tank; the liquid ammonia buffer tank is connected to a liquid ammonia booster pump.

[0024] As a specific embodiment of the present invention, the reflux device includes a reflux pump and a reflux tank; the reflux pump is connected to the upper part of the distillation tower and is connected to the reflux tank.

[0025] As a specific embodiment of the present invention, a high-purity ammonia collection device is further provided on the side of the lower section of the distillation tower.

[0026] As a specific implementation of the present invention, the high-purity ammonia collection device includes an ammonia purity online analyzer, a product tank, a substandard product tank, and a substandard liquid ammonia pump.

[0027] As a specific embodiment of the present invention, the ammonia purity online analyzer is arranged between the liquid ammonia buffer tank and the distillation tower.

[0028] As a specific implementation of the present invention, a first valve is provided between the liquid ammonia buffer tank and the unqualified product tank.

[0029] As a specific embodiment of the present invention, the gas outlet end of the liquid ammonia buffer tank is further provided with a passage controlled by a second valve;

[0030] As a specific embodiment of the present invention, the passage delivers high-purity ammonia.

[0031] As a specific implementation of the present invention, the first valve and the second valve are both controlled by the ammonia purity online analyzer.

[0032] As a specific implementation of the present invention, the unqualified product tank is connected to the feed buffer tank through an unqualified liquid ammonia pump.

[0033] As a specific embodiment of the present invention, a reboiler is provided at the bottom end of the distillation tower.

[0034] As a specific embodiment of the present invention, the inlet end and the outlet end of the reboiler are both connected to the bottom end of the distillation tower.

[0035] As a specific implementation of the present invention, the heat source of the distillation tower reboiler is circulating cooling water.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The process of the present invention includes four processes: low temperature cooling, mechanical filtration, distillation, and adsorption and dehydration, which can achieve accurate removal of various impurities, which is beneficial to product quality control. At the same time, it can be determined whether to bypass a certain process according to the actual impurity situation of the raw materials to reduce energy consumption;

[0038] 2. In the process of the present invention, low temperature cooling and heat exchange of distillation tower top gas are used to recover energy, and the heat is fully integrated, which is beneficial to energy saving;

[0039] 3. In the process of the present invention, the heat source of the distillation tower reboiler adopts circulating cooling water, which is easily available and convenient for heat integration with other devices, thus saving energy consumption;

[0040] 4. In the process of the present invention, an evaporative condenser is arranged between the upper tower and the lower tower of the distillation tower, so that the heat exchange efficiency is high and energy-saving;

[0041] 5. In the process of the present invention, the gas ammonia in the top cooler of the distillation tower is lower than that in the liquid ammonia process side, the material in the heat exchanger will not contaminate the product, and the product quality is guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The system and flow chart for producing high-purity ammonia from industrial ammonia according to Example 1 of the present invention;

[0043] Among them, 1-liquid ammonia buffer tank; 2-liquid ammonia booster pump; 3-liquid ammonia cooler; 4-precision filter; 5-feed preheater; 6-liquid ammonia return pump; 7-distillation tower; 8-evaporative condenser; 9-reboiler; 10-distillation tower top cooler; 11-reflux tank; 12-reflux pump; 13-product tank; 14-molecular sieve dehydrator; 15-unqualified product tank; 16-unqualified liquid ammonia pump. DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with specific embodiments, but they do not constitute any limitation to the present invention.

[0045] Example 1

[0046] This embodiment provides a method and system for producing high-purity ammonia from industrial ammonia, combined with Figure 1 The specific details are as follows:

[0047] The main equipment of the system in this embodiment includes: 1-liquid ammonia buffer tank; 2-liquid ammonia booster pump; 3-liquid ammonia cooler; 4-precision filter; 5-feed preheater; 6-liquid ammonia return pump; 7-distillation tower; 8-evaporative condenser; 9-reboiler; 10-distillation tower top cooler; 11-reflux tank; 12-reflux pump; 13-product tank; 14-molecular sieve dehydrator; 15-unqualified product tank; 16-unqualified liquid ammonia pump.

[0048] Example 2

[0049] This embodiment adopts the system provided in Example 1 to carry out the method and process of producing high-purity ammonia from industrial ammonia, and the specific details are as follows:

[0050] Industrial liquid ammonia with a pressure of 0.4MPag and a temperature of -7℃ first enters the liquid ammonia buffer tank 1 for temporary storage. The liquid ammonia at the bottom of the buffer tank is pressurized to about 1.2MPag by the liquid ammonia booster pump 2 and then enters the liquid ammonia cooler 3. After cooling to -20℃, it enters the precision filter 4 to remove particulate impurities, lubricating oil and most of the water. The liquid ammonia then enters the distillation tower 7. The distillation tower is divided into an upper tower and a lower tower. The operating pressure of the lower tower of the distillation tower is 0.9MPag. The heat source is provided by the reboiler 9. In the lower tower of the distillation tower, the light component and the heavy component are separated. The gas phase flow out of the tower top passes through the molecular sieve dehydrator 14, dehydrated, and then enters the evaporative condenser at the bottom of the lower tower. 8. The gaseous ammonia is cooled in the evaporative condenser 8. In the upper tower, the ammonia gas containing light components enters the top cooler 10 of the distillation tower, is condensed by the low-temperature gaseous ammonia in the shell side of the liquid ammonia cooler, and then goes to the reflux tank 11. The liquid ammonia in the reflux tank 11 is refluxed to the top of the distillation tower through the reflux pump 12, and the non-condensable light components are discharged. The gaseous ammonia heated by the feed preheater 5 enters the distillation tower 7; the liquid ammonia containing trace heavy components at the bottom of the tower is returned to the liquid ammonia buffer tank 1 through the liquid ammonia return pump 6; a stream of high-purity ammonia product is drawn out from the side of the middle and lower section of the distillation tower, and the external delivery pipeline is equipped with an ammonia purity online analyzer and a product tank 13, and a high-purity ammonia product delivery device passing through the product tank 13. When the product analysis is unqualified, the liquid ammonia is sent to the unqualified product tank 15, and is sent back to the liquid ammonia buffer tank 1 through the unqualified liquid ammonia pump 16.

[0051] In summary, the process of the method for producing high-purity ammonia from industrial ammonia of the present invention includes four processes: low-temperature cooling, mechanical filtration, distillation, and adsorption and dehydration, which can achieve accurate removal of various impurities, which is beneficial to product quality control. At the same time, it can be determined whether to bypass a certain process to reduce energy consumption according to the actual impurity situation of the raw materials; in the process of the present invention, low-temperature cooling and heat exchange of the distillation tower top gas recover energy, and the heat is fully integrated, which is beneficial to energy saving; in the process of the present invention, the heat source of the distillation tower reboiler adopts circulating cooling water, which is easily available and convenient to integrate with the heat of other devices, saving energy consumption; in the process of the present invention, an evaporative condenser is arranged between the upper tower and the lower tower of the distillation tower, and the heat exchange efficiency is high and energy-saving; in the process of the present invention, the gas ammonia of the top cooler of the distillation tower is lower than that of the liquid ammonia process side, the material in the heat exchanger will not contaminate the product, and the product quality is guaranteed.

[0052] Any numerical value mentioned in the present invention includes all values ​​that increase by one unit each time from the lowest value to the highest value if there is only an interval of two units between any minimum value and any maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, time, etc. is declared to be 50-90, in this specification it means that 51-89, 52-88... and 69-71 and 70-71 are specifically listed. For non-integer values, 0.1, 0.01, 0.001 or 0.0001 can be appropriately considered as a unit. These are just some specially specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed lowest and highest values ​​are considered to have been disclosed.

[0053] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Although the present invention described therein relates to specific methods, materials and embodiments, it does not mean that the present invention is limited to the specific examples disclosed therein, on the contrary, the present invention can be extended to all other methods and applications with the same functions.

Claims

1. A method for producing high-purity ammonia from industrial ammonia, characterized in that: The method comprises four steps: low temperature cooling, mechanical filtration, distillation and adsorption dehydration.

2. The method according to claim 1, characterized in that The temperature of the low temperature cooling is -30 to -15°C; the pressure is 1 to 1.5 MPa.

3. The method according to claim 1 or 2, characterized in that: The mechanical filtration step includes removing particulate impurities in liquid ammonia; the liquid ammonia pressure is 1 to 1.5 MPa, and the liquid ammonia temperature is -30 to -15°C.

4. The method according to any one of claims 1 to 3, characterized in that: The distillation step includes separation of light components and heavy components; the distillation pressure is 0.7-1 MPa.

5. The method according to any one of claims 1 to 4, characterized in that: The distillation step also includes condensing the light component ammonia gas, refluxing the liquid ammonia, and removing the non-condensable light components; the condensation temperature is 15 to 30°C.

6. The method according to any one of claims 1 to 5, characterized in that: The adsorption dehydration step includes removing trace amounts of water carried in the gaseous ammonia; the temperature of the adsorption dehydration is 30-40°C.

7. A system for producing high-purity ammonia from industrial ammonia for implementing the method described in any one of claims 1 to 6, characterized in that: It includes a cryogenic cooling unit, a mechanical filtration unit, an adsorption dehydration unit and a distillation unit; The low temperature cooling unit comprises a liquid ammonia pressure pump and a liquid ammonia cooler connected in sequence; The mechanical filtration unit includes precision filters connected in sequence; The adsorption dehydration unit includes a molecular sieve dehydrator; The distillation unit comprises a distillation tower and a distillation tower top cooler; an evaporative condenser is arranged between the upper tower and the lower tower of the distillation tower; The distillation tower top cooler is connected to the upper end of the precision filter; The distillation tower top cooler is connected to the upper end of the distillation tower; The molecular sieve dehydrator is connected to the distillation tower.

8. The system according to claim 7, characterized in that The system also includes a feeding device, and a reflux device; The feeding device comprises a liquid ammonia buffer tank; the liquid ammonia buffer tank is connected to a liquid ammonia pressure pump; The reflux device includes a reflux pump and a reflux tank; the reflux pump is connected to the upper part of the distillation tower and is connected to the reflux tank; A high-purity ammonia collecting device is also provided on the side of the lower section of the distillation tower.

9. The system according to claim 7 or 8, characterized in that: The high-purity ammonia collection device includes an ammonia purity online analyzer, a product tank, a substandard product tank, and a substandard liquid ammonia pump; the substandard product tank is connected to the liquid ammonia buffer tank via the substandard liquid ammonia pump.

Images