A method and system for producing low-pressure aqueous ammonia
By using a low-pressure ammonia production method and heat exchange and dehydration pressurization technology, the problems of high equipment material and energy consumption in high-pressure synthetic ammonia production have been solved, achieving efficient and low-cost ammonia production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ALLY HI TECH CO LTD
- Filing Date
- 2023-09-08
- Publication Date
- 2026-06-12
AI Technical Summary
In existing ammonia production processes, the temperature and pressure of the ammonia synthesis reaction are high, resulting in high equipment material and energy consumption, and low reaction efficiency.
The low-pressure ammonia production method involves heat exchange between the raw material gas and the product gas before and after the ammonia synthesis reaction. The raw material gas is heated by an exothermic reaction while the product gas is cooled, eliminating the need for a cooling liquid chemical section. The ammonia synthesis pressure is reduced to 5-8 MPa. Dehydration and pressurization modules are installed to control gas purity, thereby achieving efficient ammonia synthesis reaction and ammonia preparation.
It reduced equipment investment costs and energy consumption, simplified the process, improved reaction efficiency, and ensured that the ammonia synthesis reaction proceeded efficiently within a stable pressure range, thus achieving efficient production of ammonia water.
Smart Images
Figure CN117247027B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of ammonia synthesis technology, and specifically to a method and system for producing low-pressure ammonia water. Background Technology
[0002] Ammonia water (NH3·H2O), also known as ammonia solution, is a solution of ammonia in water and is an important chemical raw material. Industrially, ammonia water is mainly produced by synthesizing ammonia gas from hydrogen and nitrogen, and then reacting the ammonia gas with water through a hydration reaction.
[0003] The existing ammonia water production process mainly includes: (I) Ammonia synthesis: gaseous nitrogen and gaseous hydrogen are reacted under the conditions of catalyst and temperature of 400~500℃ and pressure of 15~25MPa. After the reaction, separation and post-treatment are carried out to remove impurities and improve the purity of ammonia; (II) Ammonia water preparation: ammonia gas is passed into water to undergo a hydration reaction to realize the absorption of ammonia gas to generate ammonia water; the ammonia water is separated to remove impurities and unreacted gases; then the ammonia water is concentrated and further purified to obtain qualified ammonia water.
[0004] Currently, the temperature of industrial ammonia synthesis reactions is typically 400-500℃, and the pressure is 15-25MPa. These high temperatures and pressures place high demands on the equipment materials, thickness, size, floor space, and safety measures of the ammonia synthesis system. Furthermore, it also suffers from high energy consumption and low reaction efficiency. Summary of the Invention
[0005] To address the shortcomings of the existing technologies, this invention provides a low-pressure ammonia water production method and system. The process of this method and system is simple. It achieves heating of the raw material gas and cooling of the product gas by exchanging heat between the raw material gas and the product gas before and after the ammonia synthesis reaction, thus eliminating the step of cooling and liquefying the ammonia after synthesis. Moreover, the pressure of the synthesized ammonia is lower than that of traditional ammonia water production, which reduces the overall pressure level of the device, thereby reducing equipment investment costs and lowering operating energy consumption.
[0006] To achieve the above objectives, the present invention provides a method for producing low-pressure ammonia water, comprising the following steps:
[0007] Step S1: Mix hydrogen and nitrogen in a certain proportion and then pressurize them;
[0008] Step S2: The pressurized mixed gas is dehydrated.
[0009] Step S3: The dehydrated mixed gas is heated by heat exchange, and the heated mixed gas undergoes a catalytic reaction to synthesize ammonia gas under a pressure of 3-15 MPa to obtain crude ammonia mixed gas.
[0010] Step S4: The crude ammonia mixture is cooled by heat exchange with the dehydrated mixture, and the cooled crude ammonia mixture is washed with water to generate ammonia water.
[0011] In one embodiment of this application, it further includes:
[0012] Step S5: The gas discharged after water washing in step S4 is recovered, and the recovered gas is pressurized and then mixed with the raw material gas for dehydration treatment.
[0013] In one embodiment of this application, in step S1, the O2 content in the mixed gas of hydrogen and nitrogen is less than 5 ppm.
[0014] In one embodiment of this application, the dehydration treatment includes a coarse dehydration treatment and a fine dehydration treatment. The coarse dehydration treatment uses a gas-liquid separator, and the fine dehydration treatment uses temperature-switching adsorption dehydration.
[0015] The mixed gas after fine dehydration treatment contains less than 5 ppm H2O, less than 100 ppm gaseous NH3, and less than 20 ppm total CO and CO2.
[0016] In one embodiment of this application, one or more of the following are also included:
[0017] In step S3, the dehydrated mixed gas is heated to 320-350°C via heat exchange;
[0018] In step S3, the catalyst used for the catalytic reaction to synthesize ammonia is an iron-based catalyst or a ruthenium-based catalyst, the reaction pressure is 5-8 MPa, the system pressure drop is controlled within 0.5 MPa during the reaction, and the temperature of the obtained crude ammonia mixture is 380-450℃.
[0019] In step S5, the crude ammonia mixture is cooled to below 40°C via heat exchange.
[0020] The present invention also provides a low-pressure ammonia water production system, characterized in that it includes a raw material gas production module, a first pressurization module, a dehydration module, an ammonia synthesis module and a water washing module connected in sequence;
[0021] It also includes a heat exchange module, which is connected to the outlet end of the dehydration module and the inlet end of the ammonia synthesis module, and is also connected to the outlet end of the ammonia synthesis module and the gas inlet end of the water washing module.
[0022] in:
[0023] The raw material gas production module is used to provide hydrogen and nitrogen.
[0024] The first pressurization module mixes and pressurizes the hydrogen and nitrogen provided by the raw material gas production module;
[0025] The dehydration module is used to remove moisture from the mixed gas after being pressurized by the first pressurization module;
[0026] The heat exchange module heats the mixed gas after it has been dehydrated by the dehydration module;
[0027] The ammonia synthesis module uses the high-pressure mixed gas heated by the heat exchange module to undergo a catalytic reaction to synthesize ammonia gas; the synthesized crude ammonia mixed gas is then cooled by heat exchange through the heat exchange module.
[0028] The water washing module washes the cooled crude ammonia mixture with water to synthesize ammonia water.
[0029] In one embodiment of this application, a second pressurization module is further included. The second pressurization module is connected to the gas outlet end of the water washing module and the inlet end of the dehydration module, and pressurizes the gas discharged from the water washing module before discharging it to the dehydration module for recycling.
[0030] In one embodiment of this application, the dehydration module includes a coarse dehydration unit and a fine dehydration unit connected in sequence.
[0031] In one embodiment of this application, the raw gas production module includes a water electrolysis production unit and an air separation unit.
[0032] In one embodiment of this application, a deoxygenation unit is further included, which is disposed between the raw material gas production module and the first pressurization module; the hydrogen and nitrogen produced by the raw material gas production module are deoxygenated by the deoxygenation unit in proportion.
[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0034] 1. The low-pressure ammonia water production method and system of the present invention has a simple process. It uses heat exchange between the raw material gas and the product gas (i.e., crude ammonia mixture) before and after the ammonia synthesis reaction to heat the raw material gas and cool the product gas by utilizing the exothermic reaction of ammonia synthesis. The product gas (crude ammonia mixture) is directly washed with water after cooling to generate ammonia water, which eliminates the process of cooling, liquefying and separating after ammonia synthesis. Moreover, the pressure of ammonia synthesis is lower than that of ammonia synthesis in traditional ammonia water production, which reduces the pressure level of the overall device, reduces equipment investment costs and energy consumption.
[0035] 2. This invention incorporates dehydration, and through coarse dehydration and fine dehydration steps, removes free water sequentially, controlling the content of H2O, gaseous NH3, CO, and CO2 in the mixed gas. This ensures that the subsequent ammonia synthesis reaction proceeds smoothly and efficiently under a low-pressure environment. The obtained crude ammonia mixture is cooled (below 40°C) and then directly liquefied and separated by demineralized water washing. There is no need to cool the crude ammonia mixture to liquefaction (-20°C) and perform ammonia separation, which simplifies the process and reduces equipment investment and energy consumption.
[0036] 3. The low-pressure ammonia water production method and system of the present invention, since the ammonia synthesis reaction is an exothermic and volume-reducing reaction, controls the pressure of the ammonia synthesis module within the range of 5-8 MPa through the first and second pressurization modules, and controls the temperature within the range of 320-350℃ through heat exchange to carry out a continuous and efficient ammonia synthesis reaction. The crude ammonia mixture gas after the reaction is cooled by heat exchange with the raw material gas, and the synthesized ammonia water is directly washed with water; the washed gas is recovered and recycled to ensure that the raw material gas is fully utilized; the entire production process does not require additional heat energy after startup, and the system can achieve ammonia synthesis and ammonia water preparation under a relatively low pressure. This method and system have low requirements for equipment pressure levels, which can reduce equipment costs. During operation, the raw material gas and the circulating gas are pressurized by two pressurization modules respectively, which can effectively reduce operating power and energy consumption; the heat energy of the crude ammonia mixture gas is recovered and reused, reducing the investment in the cooling section of the ammonia synthesis equipment.
[0037] 4. Two booster modules / processes are set up. The recovered circulating gas is boosted by the second booster module, which can effectively reduce the energy consumption required for boosting and adapt to the large volume of recovered circulating gas in this process. It can also better control the pressure of the ammonia synthesis section and ensure that the system pressure drop is controlled within 0.5MPa during the reaction process, so that the ammonia synthesis reaction can be carried out efficiently within a stable pressure range. Attached Figure Description
[0038] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0039] Figure 1 This is a schematic diagram of the low-pressure ammonia water production method in an embodiment of the present invention.
[0040] Figure 2 This is a schematic diagram of the low-pressure ammonia water production system in an embodiment of the present invention.
[0041] Figure label:
[0042] 1. Raw material gas production module; 11. Water electrolysis production unit; 12. Air separation unit; 13. Deoxygenation unit;
[0043] 2. First booster module;
[0044] 3. Dehydration module; 31. Coarse dehydration unit; 32. Fine dehydration unit;
[0045] 4. Second booster module;
[0046] 5. Ammonia synthesis module;
[0047] 6. Water washing module;
[0048] 7. Heat exchange module. Detailed Implementation
[0049] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.
[0050] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
[0051] Example 1
[0052] like Figure 1 As shown in the figure, this invention provides a method for producing low-pressure ammonia water, which includes the following steps:
[0053] Step S1: Mix the raw materials hydrogen and nitrogen in a certain proportion and then compress and pressurize them;
[0054] Step S2: Dehydrate the pressurized mixed gas from step S1.
[0055] Step S3: The mixed gas after dehydration in step S2 is heated by heat exchange, and the heated mixed gas is subjected to catalytic reaction to synthesize ammonia gas under a pressure of 3-15 MPa to obtain crude ammonia mixed gas.
[0056] In step S4, the crude ammonia mixture obtained in step S3 is heat-exchanged with the aforementioned dehydrated mixture, the crude ammonia mixture is cooled, and the cooled crude ammonia mixture is washed with water to generate ammonia water.
[0057] Preferably, the method further includes: step S5, recovering the gas discharged during the water washing process in step S4, and then pressurizing the recovered gas and mixing it with the pressurized raw material mixed gas in step S1 for dehydration treatment.
[0058] Preferably, in step S1, hydrogen is obtained through a hydrogen production process, preferably hydrogen with a purity of 99.8% (V / V%) or higher obtained through water electrolysis; nitrogen is obtained through an air separation process, preferably nitrogen with a purity of 99.9% (V / V%) or higher obtained through pressure swing adsorption or cryogenic separation of air. The ratio of hydrogen to nitrogen is approximately 3:1, and the O2 content in the hydrogen and nitrogen mixture is controlled to be less than 5 ppm, preferably less than 1 ppm; if the O2 content in the hydrogen and nitrogen mixture is greater than 5 ppm, the hydrogen and nitrogen mixture is chemically deoxygenated to ensure that the O2 content is less than 5 ppm. After controlling the O2 content to be less than 5 ppm, the hydrogen and oxygen mixture is compressed and pressurized.
[0059] In step S2, the dehydration process includes coarse dehydration and fine dehydration. The coarse dehydration is performed using a gas-liquid separator to remove most of the free water from the mixed gas. The fine dehydration uses temperature-switched adsorption dehydration to remove water and impurities. During fine dehydration, the H2O content in the mixed gas should be controlled to be less than 5 ppm, preferably less than 1 ppm; the gaseous NH3 content should be controlled to be less than 100 ppm; and the total CO and CO2 content should be controlled to be less than 20 ppm. By controlling the purity of the mixed gas after fine dehydration, a good foundation can be provided for the subsequent smooth and efficient catalytic reaction to synthesize ammonia under low-pressure conditions, and the post-processing steps after ammonia synthesis can be reduced.
[0060] In one embodiment, the recycled gas recovered during the washing process is pressurized and mixed with the mixed gas after coarse dehydration, and then subjected to fine dehydration together. That is, the recovered recycled gas is mixed with the raw material mixed gas after coarse dehydration and before fine dehydration (not shown in the figure), which can effectively reduce the amount of gas required for dehydration, ensuring gas quality while reducing the equipment operating load. Of course, the recovered recycled gas can also be mixed with the pressurized mixed gas from step S1 and subjected to both coarse and fine dehydration (e.g., ...). Figure 2 As shown in the figure, this can effectively ensure the dehydration effect.
[0061] In step S3, the mixed gas (including the recovered circulating gas) after dehydration treatment in step S2 is heated by heat exchange with the crude ammonia mixed gas discharged after the catalytic reaction to synthesize ammonia. The heating temperature is controlled at about 320-350℃. The heated mixed gas enters the ammonia synthesis module and undergoes catalytic reaction to synthesize ammonia gas under the conditions of temperature of 350-450℃ and pressure of 3-15MPa.
[0062] The preferred temperature for ammonia synthesis is controlled within the range of 350-450℃, and the reaction pressure is controlled within the range of 3-8MPa; the temperature of the crude ammonia mixture discharged after the reaction is 380-450℃.
[0063] Further optimization of the ammonia synthesis process by controlling the reaction pressure at 5-8 MPa and the system pressure drop within 0.5 MPa during the reaction ensures a more stable and efficient ammonia synthesis and subsequent ammonia production.
[0064] In step S4, the crude ammonia mixture obtained from the ammonia synthesis reaction at a temperature of 380-450℃ exchanges heat with the dehydrated mixture through a heat exchange module. This achieves cooling of the crude ammonia mixture and heating of the raw material mixture (including the recovered circulating gas), controlling the temperature of the cooled crude ammonia mixture to be below 40℃. The cooled crude ammonia mixture then enters a water washing module (such as a water washing absorption tower) for washing and recovery with demineralized water to obtain ammonia water. The ammonia content in the gas discharged during the water washing process is controlled to be below 200ppm, and the concentration of the obtained ammonia water can reach 27% or higher. The washed ammonia water is discharged to an ammonia water storage tank for storage. The ammonia water concentration can be adjusted to the required level by adding demineralized water or using the condensate generated from the dehydration treatment (coarse dehydration treatment and fine dehydration treatment) in step S2, such as adjusting the ammonia water concentration to 5%-20% for irrigation.
[0065] Example 2
[0066] like Figure 2 As shown, this embodiment of the invention also provides a low-pressure ammonia water production system, which is applicable to the low-pressure ammonia water production method described in Embodiment 1. The system includes a raw material gas production module 1, a first pressurization module 2, a dehydration module 3, a synthetic ammonia module 5, and a water washing module 6 connected in sequence. It also includes a heat exchange module 7, the heating channel of which is connected to the outlet end of the dehydration module 3 and the inlet end of the synthetic ammonia module 5, and the cooling channel of which is connected to the outlet end of the synthetic ammonia module 5 and the gas inlet end of the water washing module.
[0067] The feedstock gas production module 1 is used to provide hydrogen and nitrogen. Preferably, the feedstock gas module 1 includes a water electrolysis production unit 11 and an air separation unit 12. The water electrolysis production unit 11 produces hydrogen through water electrolysis, with the hydrogen purity controlled at 99.8% (V / V%) or higher. The air separation unit 12 separates air using pressure swing adsorption or cryogenic separation, providing nitrogen with a purity of 99.9% (V / V%) or higher. The hydrogen and nitrogen provided by the feedstock gas production module 1 are then sent to the subsequent first pressurization module 2.
[0068] The first pressurization module 2 is a compressor used to mix and pressurize the hydrogen and nitrogen provided by the raw material gas production module 1 (water electrolysis production unit 11 and air separation unit 12). The pressurized mixed gas is then sent to the dehydration module 3.
[0069] The dehydration module 3 is used to thoroughly remove moisture from the pressurized mixed gas. Preferably, the dehydration module 3 includes a coarse dehydration unit 31 and a fine dehydration unit 32 arranged sequentially. The coarse dehydration unit 31 can be a gas-liquid separator to remove free water from the mixed gas. The fine dehydration unit 32 uses a temperature-switching adsorption dehydration device for dehydration and impurity removal. Through temperature-switching adsorption dehydration, the H2O content in the mixed gas can be reduced to below 5 ppm, or even controlled to below 1 ppm, while simultaneously reducing the gaseous NH3 content to below 100 ppm and the total CO and CO2 content to below 20 ppm. The dehydrated mixed gas then enters the heat exchange module 7 for heat exchange and heating.
[0070] The ammonia synthesis module 5 is an ammonia synthesis tower. The mixed gas in the heat exchange module 7 should be heated to the temperature required for ammonia synthesis to ensure rapid catalytic reaction after entering the ammonia synthesis module 5. After the catalytic reaction, ammonia gas is generated in the ammonia synthesis module 5, and a crude ammonia mixture is obtained and discharged. This crude ammonia mixture enters the cooling channel of the heat exchange module 7 for heat exchange and cooling. Specifically, the high-temperature crude ammonia mixture exchanges heat with the lower-temperature dehydrated mixed gas, achieving heat recovery, cooling, and heating of the dehydrated mixed gas.
[0071] The cooled crude ammonia mixture enters water washing module 6 for ammonia water synthesis. Water washing module 6 is a water washing absorption tower. The cooled crude ammonia mixture undergoes water washing and absorption with demineralized water, causing the ammonia to dissolve in the water and form ammonia water. The obtained ammonia water is discharged to an ammonia water storage tank for concentration maintenance and adjustment.
[0072] In one embodiment, a second pressurization module 4 is also included. The second pressurization module 4 is also a compressor. Its inlet is connected to the gas outlet of the water washing module 6, and its outlet is connected to the inlet of the dehydration module 3. This module pressurizes the gas discharged from the water washing module 6 and discharges it to the dehydration module 3 for recycling. Specifically, the outlet of the water washing absorption tower is connected to the dehydration module 3 after passing through the second pressurization module 4. The undissolved gas (mainly hydrogen and nitrogen) after water washing is pressurized and discharged to the dehydration module 3 to mix with the raw material gas for dehydration and recycling, thereby improving the utilization rate of the raw material gas. Preferably, the outlet of the second pressurization module 4 is connected after the coarse dehydration unit 11 and before the fine dehydration unit 12, meaning the recycled gas is mixed with the coarsely dehydrated raw material gas and then subjected to fine dehydration.
[0073] In one embodiment, a deoxygenation unit 13 is also provided. The deoxygenation unit 13 is disposed between the raw material gas production module 1 and the first pressurization module 2, and is used to deoxygenate the hydrogen and nitrogen gas provided by the raw material gas production module 11 after mixing in a certain proportion, so as to ensure the purity of the raw material gas.
[0074] The dehydration module 3 (coarse dehydration unit 31 and fine dehydration unit 32) is equipped with pipelines connected to the washing module and / or ammonia storage tank for recovering the condensate generated during the dehydration process. The condensate is used for washing synthetic ammonia or for diluting and adjusting the concentration of ammonia.
[0075] In the working process, hydrogen produced by water electrolysis unit 11 and nitrogen produced by air separation unit 12 are mixed at a hydrogen to nitrogen ratio of approximately 3:1. After mixing, the mixture undergoes chemical deoxygenation treatment in deoxygenation unit 13 to control the O2 content in the mixed gas to 5 ppm or less, preferably to 1 ppm or less. The deoxygenated mixed gas is then compressed and pressurized by the first pressurization module 2. After pressurization, it is mixed with the circulating gas recovered by water washing module 6 and pressurized by the second pressurization module 4, and then enters the dehydration module 3 for coarse dehydration and fine dehydration in sequence. (The circulating gas recovered by the water washing module 6 and pressurized by the second pressurization module 4 can also be mixed with the raw material mixed gas after coarse dehydration, and then subjected to fine dehydration together), so that the H2O content in the mixed gas is reduced to below 5 ppm, preferably below 1 ppm, while the gaseous NH3 content is controlled to be reduced to below 100 ppm, and the total CO and CO2 content is reduced to below 20 ppm; the mixed gas after dehydration is heated to about 320-350°C by the heat exchange module 7, and then sent to the ammonia synthesis module 5. In the synthesis tower, hydrogen and nitrogen react to produce ammonia under catalytic reactions with iron-based or ruthenium-based catalysts at a temperature of 350-450℃ and a pressure of 5-8 MPa (the system pressure drop of the ammonia synthesis module 5 needs to be controlled within 0.5 MPa during the ammonia synthesis process). The ammonia gas discharged after the reaction in the ammonia synthesis module 5 is a mixture of hydrogen and nitrogen, which is the crude ammonia mixture. The temperature of the crude ammonia mixture discharged from the ammonia synthesis module 5 is approximately 380-450℃. This crude ammonia mixture undergoes heat exchange with the dehydrated mixture in the heat exchange module 7 to recover heat energy. The mixture is cooled while being heated after dehydration. The crude ammonia mixture, cooled by heat exchange module 7, enters the water washing absorption tower of water washing module 6, where it comes into counter-current contact with demineralized water sprayed from top to bottom. This process absorbs the ammonia to generate ammonia water, controlling the ammonia content at the gas outlet of the water washing absorption tower to be less than 200 ppm. The gas discharged from the water washing absorption tower is used as recovered gas, pressurized by the second pressurization module 4, and then discharged to the dehydration module 3 for recycling. The ammonia water obtained from water washing module 6 is discharged to an ammonia water storage tank for storage or diluted to the required concentration for later use. The ammonia water concentration synthesized by the above process can reach 27% or higher, and the unit energy consumption for ammonia water synthesis is significantly reduced compared to traditional processes (15-25 MPa).
[0076] In summary, the low-pressure ammonia water production method and system of this application achieves heat recovery and cooling of the crude ammonia mixture by exchanging heat with the dehydrated raw material gas and the recovered circulating gas, while heating the raw material gas and the recovered circulating gas to the temperature required for the ammonia synthesis reaction, so that the ammonia synthesis reaction can be carried out continuously and efficiently.
[0077] The ammonia synthesis reaction is exothermic and involves volume reduction. This application utilizes a first and a second pressurization module to control the pressure of the ammonia synthesis module within the range of 5-8 MPa. Through heat exchange, the temperature is controlled within the range of 320-350℃, enabling continuous and efficient ammonia synthesis. The resulting crude ammonia mixture is cooled by heat exchange with the raw material gas. The synthesized ammonia water is then directly washed with water, and the washed gas is recovered and recycled, ensuring full utilization of the raw material gas. No additional heat energy is required after the entire production process begins, and the system maintains a relatively low pressure to achieve ammonia synthesis and ammonia water preparation. This method and system have low requirements for equipment pressure levels, reducing equipment costs. During operation, the raw material gas and circulating gas are pressurized by two separate pressurization modules, effectively reducing operating power and energy consumption. The heat energy of the crude ammonia mixture is recovered and reused, reducing the investment in cooling equipment for the ammonia synthesis process.
[0078] In addition, two pressurization modules / processes are set up. The recovered circulating gas is pressurized by the second pressurization module 4, which can effectively reduce the energy consumption required for pressurization and adapt to the situation of large volume of recovered circulating gas in this process. It can also better control the pressure of the ammonia synthesis section, ensure that the ammonia synthesis reaction is carried out within a stable pressure range, and control the system pressure drop within 0.5MPa during the reaction process.
Claims
1. A method for producing low-pressure aqueous ammonia, characterized by, Includes the following steps: Step S1: Hydrogen and nitrogen are mixed in a certain proportion and then pressurized through the first pressurization module; Step S2: The pressurized mixed gas is dehydrated; the dehydration treatment includes coarse dehydration treatment and fine dehydration treatment. The coarse dehydration treatment uses a gas-liquid separator, and the fine dehydration treatment uses temperature-switched adsorption dehydration. Step S3: The dehydrated mixed gas is heated to 320-350℃ by heat exchange, and the heated mixed gas undergoes a catalytic reaction to synthesize ammonia gas under a pressure of 3-15MPa to obtain crude ammonia mixed gas. Step S4: The crude ammonia mixture is cooled by heat exchange with the dehydrated mixture to below 40°C. The cooled crude ammonia mixture is then washed with water to generate ammonia water. Step S5: The gas discharged after water washing in step S4 is recovered. The recovered gas is pressurized by the second pressurization module and then dehydrated together with the raw material mixed gas.
2. The low-pressure aqueous ammonia production method according to claim 1, characterized by, In step S1, the O2 content in the mixed gas of hydrogen and nitrogen is less than 5 ppm.
3. The method for producing low-pressure ammonia water according to claim 1, characterized in that, The mixed gas after fine dehydration treatment contains less than 5 ppm H2O, less than 100 ppm gaseous NH3, and less than 20 ppm total CO and CO2.
4. The method for producing low-pressure ammonia water according to claim 1, characterized in that, In step S3, the catalyst used for the catalytic reaction to synthesize ammonia is an iron-based catalyst or a ruthenium-based catalyst, the reaction pressure is 5-8 MPa, the system pressure drop is controlled within 0.5 MPa during the reaction, and the temperature of the obtained crude ammonia mixture is 380-450℃.
5. A low-pressure ammonia water production system, characterized in that, It includes a raw material gas production module, a first pressurization module, a dehydration module, a synthetic ammonia module, and a water washing module connected in sequence; It also includes a heat exchange module and a second pressurization module, wherein the heat exchange module is connected to the outlet end of the dehydration module and the inlet end of the ammonia synthesis module, and is also connected to the outlet end of the ammonia synthesis module and the gas inlet end of the water washing module. The second pressurization module is connected to the gas outlet of the water washing module and the inlet of the dehydration module. It pressurizes the gas discharged from the water washing module and discharges it to the dehydration module for recycling. in: The raw material gas production module is used to provide hydrogen and nitrogen. The first pressurization module mixes and pressurizes the hydrogen and nitrogen provided by the raw material gas production module; The dehydration module includes a coarse dehydration unit and a fine dehydration unit connected in sequence, used to remove moisture from the mixed gas pressurized by the first pressurization module; The heat exchange module heats the mixed gas after it has been dehydrated by the dehydration module; The ammonia synthesis module uses the high-pressure mixed gas heated by the heat exchange module to undergo a catalytic reaction to synthesize ammonia gas; the synthesized crude ammonia mixed gas is then cooled by heat exchange through the heat exchange module. The water washing module washes the cooled crude ammonia mixture with water to synthesize ammonia water.
6. The low-pressure ammonia water production system according to claim 5, characterized in that, The raw material gas production module includes a water electrolysis production unit and an air separation unit.
7. The low-pressure ammonia water production system according to claim 5 or 6, characterized in that, It also includes a deoxygenation unit, which is located between the raw material gas production module and the first pressurization module; the hydrogen and nitrogen produced by the raw material gas production module are deoxygenated by the deoxygenation unit in proportion.