Energy-saving method and system for producing high-purity ammonia from industrial ammonia

Abstract

The invention provides an energy-saving method and system for producing high-purity ammonia from industrial ammonia. The method comprises five steps of mechanical filtration, vaporization, adsorption deoiling, adsorption dehydration and rectification. The system comprises a precision filter, a rectifying tower, a rectifying tower top cooler, a vaporizer, a superheater, a reboiler, a dealkylation adsorber 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; liquid ammonia exchanges heat with top gas of the rectifying tower to recover energy before being vaporized, so that energy is saved; heat sources of the vaporizer, the superheater and the reboiler all adopt circulating cooling water which is easy to obtain, heat integration with other devices is facilitated, and energy consumption is reduced; the pressure of circulating cooling water is lower than that of a liquid ammonia process side, materials in the heat exchanger cannot pollute products, and the product quality is guaranteed; the superheater is arranged behind the vaporizer, so that the ammonia gas is not easy to dew in the adsorption process, and the adsorption effect is not influenced.

Description

Technical Field

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

[0002] The purification, analysis and research of high-purity ammonia began with Guangming Chemical Research and Design Institute. Guangming Chemical Research Institute and Beijing Oxygen Plant developed 5N electronic grade high-purity ammonia, which passed the departmental-level appraisal in 1984. The purity of the bottled high-purity ammonia produced reached 5N, and the impurity index was: H2O≤5×10 -6 , O2≤2×10 -6 , THC≤1×10 -6 Until 2000, the preparation of high-purity ammonia in China basically remained at the 5N level, and the purity of the product was unstable. The production scale also remained at the level of pilot plants, with an annual output of about 2 to 5 tons.

[0003] In 2010, Linde put into operation the first ultra-pure ammonia production plant in Xiamen, my country, using the Y-tower distillation and purification technology system to achieve a purity of 7N. Subsequently, Air Liquide, Showa Denko, Guangming Chemical Research and Design Institute, etc. established ultra-pure ammonia plants in China, and are gradually occupying the domestic market. The establishment of factories by foreign companies in China has promoted the development of domestic high-purity ammonia technology to a certain extent. 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 the large separation coefficient between NH3 and O2, H2O, CH4, CO, CO2 and the different adsorption capacity of adsorbents for NH3 and impurities. It uses gas-liquid separation, distillation and physical adsorption to remove impurities. In addition, there is also an alloy getter purification technology that can effectively remove impurities such as H2O and O2 in electronic gases. At present, 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 in the gas 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 proposes an energy-saving method for producing high-purity ammonia from industrial ammonia, which includes five steps: mechanical filtration, vaporization, adsorption deoiling, adsorption dehydration, and distillation.

[0009] As a specific embodiment of the present invention, the mechanical filtration step includes removing particulate impurities in liquid ammonia; the liquid ammonia pressure is 0.6 to 1.2 MPag, and the liquid ammonia temperature is -10°C to -5°C.

[0010] As a specific embodiment of the present invention, the vaporization step includes vaporizing all the liquid ammonia into gaseous ammonia and removing trace amounts of oil substances and water; the vaporization temperature is 5 to 30°C.

[0011] As a specific embodiment of the present invention, the adsorption deoiling step includes removing a very small amount of C3 and above hydrocarbons; the temperature of the adsorption deoiling is 30-40°C.

[0012] As a specific embodiment of the present invention, 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.

[0013] 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.

[0014] 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 15-30°C.

[0015] In a second aspect, the present invention provides an energy-saving industrial ammonia production high-purity ammonia system, which includes a mechanical filtration unit, a heat exchange recovery unit, a vaporization unit, an adsorption dehydration and dehydrocarbon removal unit, and a distillation unit;

[0016] The mechanical filtration unit comprises a liquid ammonia buffer tank, a liquid ammonia pressure pump, and a precision filter connected in sequence;

[0017] The heat exchange recovery unit includes a distillation tower top cooler, a reflux tank, and a reflux pump connected in sequence;

[0018] The vaporization unit comprises a vaporizer and a superheater connected in sequence;

[0019] The adsorption dehydration and dehydrogenation unit comprises a dehydrogenation adsorber and a molecular sieve dehydrator connected in sequence;

[0020] The distillation unit comprises a distillation tower;

[0021] The distillation tower top cooler is connected to the upper end of the precision filter;

[0022] The distillation tower top cooler is connected to the upper end of the distillation tower;

[0023] The distillation tower top cooler is connected to the vaporizer;

[0024] The reflux pump is connected to the upper part of the distillation tower;

[0025] The superheater is connected to the dehydrocarbon adsorber;

[0026] The molecular sieve dehydrator is connected to the distillation tower;

[0027] A high-purity ammonia collection device is also provided on the side of the lower section of the distillation tower;

[0028] The bottom of the distillation tower is connected to the liquid ammonia buffer tank through a liquid ammonia return pump.

[0029] As a specific implementation of the present invention, the high-purity ammonia collection device includes an ammonia purity online analyzer, a product tank, and a non-conforming product tank.

[0030] As a specific embodiment of the present invention, the ammonia purity online analyzer is arranged between the product tank and the distillation tower.

[0031] As a specific implementation of the present invention, a first valve is provided between the product tank and the unqualified product tank.

[0032] As a specific implementation of the present invention, the gas outlet end of the product tank is further provided with a passage controlled by a second valve; the passage delivers high-purity ammonia.

[0033] As a specific implementation of the present invention, the first valve and the second valve are both controlled by the ammonia purity online analyzer.

[0034] As a specific implementation of the present invention, the unqualified product tank is connected to the liquid ammonia buffer tank through an unqualified liquid ammonia pump.

[0035] As a specific embodiment of the present invention, a reboiler is provided at the bottom end of the distillation tower; the inlet end and the outlet end of the reboiler are both connected to the bottom end of the distillation tower.

[0036] As a specific embodiment of the present invention, the heat sources of the evaporator, the superheater and the reboiler are all circulating cooling water.

[0037] The above raw materials in the present invention can be prepared in-house or commercially available, and the present invention is not particularly limited thereto.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The process of the present invention can achieve accurate removal of various impurities, which is beneficial to product quality control;

[0040] 2. In the process of the present invention, the liquid ammonia is exchanged with the top gas of the distillation tower before vaporization to recover energy, and the heat is fully integrated, which is beneficial to energy saving;

[0041] 3. In the process of the present invention, the heat sources of the vaporizer, superheater and reboiler are all circulating cooling water, which is easily available and convenient for heat integration with other devices, thus saving energy consumption;

[0042] 4. The circulating cooling water pressure in the process of the present invention is lower than that in the liquid ammonia process, the material in the heat exchanger will not contaminate the product, and the product quality is guaranteed;

[0043] 5. In the process of the present invention, a superheater is provided after the vaporizer, so that ammonia is not easy to condense during the adsorption process, which affects the adsorption effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1The energy-saving industrial ammonia production high-purity ammonia system and flow chart of Example 1 of the present invention;

[0045] Among them, 1-liquid ammonia buffer tank; 2-liquid ammonia booster pump; 3-precision filter; 4-distillation tower top cooler; 5-distillation tower; 6-reflux tank; 7-reflux pump; 8-superheater; 9-vaporizer; 10-dehydrogenation adsorber; 11-molecular sieve dehydrator; 12-reboiler; 13-product tank; 14-unqualified product tank; 15-liquid ammonia return pump; 16-unqualified liquid ammonia pump. DETAILED DESCRIPTION

[0046] The present invention will be further described below in conjunction with specific embodiments, but they do not constitute any limitation to the present invention.

[0047] Example 1

[0048] This embodiment provides an energy-saving method and system for producing high-purity ammonia from industrial ammonia. Figure 1 The specific details are as follows:

[0049] The main equipment of the system of this embodiment includes: 1-liquid ammonia buffer tank; 2-liquid ammonia booster pump; 3-precision filter; 4-distillation tower top cooler; 5-distillation tower; 6-reflux tank; 7-reflux pump; 8-superheater; 9-vaporizer; 10-dehydrogenation adsorber; 11-molecular sieve dehydrator; 12-reboiler; 13-product tank; 14-unqualified product tank; 15-liquid ammonia return pump; 16-unqualified liquid ammonia pump.

[0050] Example 2

[0051] This embodiment adopts the equipment 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:

[0052] 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 1.0MPag by the liquid ammonia booster pump 2 and then enters the precision filter 3 to remove particulate impurities. After the particulate impurities are removed, the liquid ammonia enters the top cooler 4 of the distillation tower to exchange heat with the top gas of the distillation tower 5 to recover the condensation heat of the top gas. At the same time, the temperature of the liquid ammonia rises and enters the vaporizer 9. The liquid ammonia is completely vaporized into gaseous ammonia in the vaporizer 9. Trace amounts of oil substances and water accumulate in the vaporizer and return to the liquid ammonia buffer tank 1 through liquid level control. The heat source of the vaporizer 9 is supplied by circulating cooling water. The saturated gaseous ammonia temperature after vaporization is about 27℃ and enters the superheater 8, so that the gaseous ammonia temperature is superheated to above the saturated temperature by 5℃ to prevent condensation during the adsorption process from affecting the adsorption effect. The heat source of the superheater 8 is recycled cooling water. The temperature of the superheated gaseous ammonia is about 35℃ and enters the dehydrocarbon adsorber 10. The extremely trace amount of C carried in the gaseous ammonia 3 and above hydrocarbons are all adsorbed here, the dehydrocarbon adsorber 10 is a temperature-swing adsorber, which adopts a thermal regeneration process; the gaseous ammonia from which the impurities of hydrocarbons of carbon 3 and above are removed by the dehydrocarbon adsorber 10 enters the molecular sieve dehydrator 11, and the extremely small amount of water carried in the gaseous ammonia is all adsorbed here; the gaseous ammonia after the water is removed enters the distillation section of the distillation tower 5, the operating pressure of the distillation tower is 0.9MPag, and the heat source is provided by the reboiler 12, and the heat source is supplied by circulating cooling water; in the distillation tower, the light components and the heavy components are separated, and the ammonia gas containing the light components at the top of the tower enters the top cooler 4 of the distillation tower for condensation, and the liquid ammonia refluxes to the top of the distillation tower, and the non-condensable light components are discharged; 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 15; a high-purity ammonia product is drawn out from the side of the middle and lower section of the distillation tower and enters the product tank 13, and the external delivery pipeline is provided with an ammonia purity online analyzer and the product tank 13, and a high-purity ammonia product delivery device passing through the buffer tank. When the product analysis is unqualified, the liquid ammonia is sent to the unqualified product tank 14 and returned to the liquid ammonia buffer tank 1 through the unqualified liquid ammonia pump 16.

[0053] In summary, the process of the method for producing high-purity ammonia from industrial ammonia of the present invention includes five steps: mechanical filtration, vaporization, adsorption deoiling, adsorption dehydration, and distillation, 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; before the liquid ammonia is vaporized, the energy is recovered by heat exchange with the top gas of the distillation tower to save energy; the heat source of the vaporizer, superheater and reboiler all adopts circulating cooling water, which is easily available and convenient for heat integration with other devices, saving energy; the pressure of the circulating cooling water 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; a superheater is arranged after the vaporizer, so that the ammonia gas is not easy to condense during the adsorption process, which affects the adsorption effect.

[0054] Any numerical value mentioned in the present invention, if there is only an interval of two units between any minimum value and any maximum value, includes all values ​​from the minimum value to the maximum value each time increasing by one unit. 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 minimum and maximum values ​​are considered to have been disclosed.

[0055] 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. An energy-saving method for producing high-purity ammonia from industrial ammonia, characterized in that: The method comprises five steps: mechanical filtration, vaporization, adsorption deoiling, adsorption dehydration and distillation.

2. The method according to claim 1, characterized in that The mechanical filtration step includes removing particulate impurities in liquid ammonia; the liquid ammonia pressure is 0.6-1.2 MPag, and the liquid ammonia temperature is -10°C--5°C.

3. The method according to claim 1 or 2, characterized in that: The vaporization step includes vaporizing all the liquid ammonia into gaseous ammonia and removing trace amounts of oil substances and water; the vaporization temperature is 5 to 30°C.

4. The method according to any one of claims 1 to 3, characterized in that: The adsorption deoiling step includes removing a very small amount of C3 and above hydrocarbons; the temperature of the adsorption deoiling is 30-40°C.

5. The method according to any one of claims 1 to 4, 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.

6. The method according to any one of claims 1 to 5, characterized in that: The distillation step includes separation of light components and heavy components; the distillation pressure is 0.7-1 MPa.

7. The method according to any one of claims 1 to 6, 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.

8. An energy-saving industrial ammonia production high-purity ammonia system for implementing the method described in any one of claims 1 to 7, characterized in that: The system includes a mechanical filtration unit, a heat exchange recovery unit, a vaporization unit, an adsorption dehydration and dehydrocarbon removal unit, and a distillation unit; The mechanical filtration unit comprises a liquid ammonia buffer tank, a liquid ammonia pressure pump, and a precision filter connected in sequence; The heat exchange recovery unit includes a distillation tower top cooler, a reflux tank, and a reflux pump connected in sequence; The vaporization unit comprises a vaporizer and a superheater connected in sequence; The adsorption dehydration and dehydrogenation unit comprises a dehydrogenation adsorber and a molecular sieve dehydrator connected in sequence; The distillation unit comprises a 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 distillation tower top cooler is connected to the vaporizer; The reflux pump is connected to the upper part of the distillation tower; The superheater is connected to the dehydrocarbon adsorber; The molecular sieve dehydrator is connected to the distillation tower; A high-purity ammonia collection device is also provided on the side of the lower section of the distillation tower; The bottom of the distillation tower is connected to the liquid ammonia buffer tank through a liquid ammonia return pump.

9. The system according to claim 8, characterized in that The system also includes a feeding device, a pressurizing device, a recovery device and a reflux device.

10. The system according to claim 8 or 9, characterized in that The feeding device comprises a liquid ammonia buffer tank; the pressurizing device comprises a liquid ammonia pressurizing pump; the recovery device comprises a defective product tank; and the reflux device comprises a reflux tank.

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