Method for automatically adjusting hydrogen-nitrogen ratio in synthesis ammonia production
By establishing multiple control loop relationships in the synthesis ammonia production process, the automatic adjustment of the hydrogen-nitrogen ratio is achieved, the problem of low manual adjustment accuracy is solved, the adjustment accuracy and production efficiency are improved, and resource waste and production costs are reduced.
Patent Information
- Application Number
- CN202510394056.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-31
- Publication Date
- 2025-06-10
AI Technical Summary
In the existing synthetic ammonia production process, the control of the hydrogen-nitrogen ratio depends on manual adjustment, resulting in low adjustment accuracy and prone to the imbalance of the hydrogen-nitrogen ratio.
By establishing the PID single-loop regulation relationship between the purified gas flowmeter and the regulating valve, the ratio control loop relationship between the nitrogen flowmeter and the purified gas flowmeter, the ratio control loop relationship between the hydrogen analysis table and the refined nitrogen valve, and the cascade circuit relationship between the inlet pressure of the inlet press and the steam speed of the regulating press, the automatic adjustment of the hydrogen-nitrogen ratio is achieved.
It improves the accuracy of the adjustment of the hydrogen-nitrogen ratio, reduces the working intensity of the operator, improves production efficiency, ensures the stable operation of the synthesis unit, and reduces resource waste and production costs.
Smart Images
Figure CN120117629A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of synthetic ammonia, and in particular to a method for automatically adjusting the hydrogen-nitrogen ratio in synthetic ammonia production. Background Art
[0002] Ammonia is an important chemical product, widely used in fertilizer, pesticide, plastic, fuel and medicine industries. The main production processes of ammonia include coal gasification, shift, low-methanol (low-temperature methanol washing), PSA hydrogen extraction (pressure swing adsorption hydrogen extraction), liquid nitrogen washing and synthetic ammonia, through which raw coal is converted into synthetic ammonia.
[0003] The hydrogen-nitrogen ratio is a key control parameter in the production of synthetic ammonia, and the rationality of its value directly affects the efficiency of ammonia synthesis and the stability of the system. When the hydrogen-nitrogen ratio is at the optimal ratio, it can not only increase the chemical reaction rate and increase the ammonia production per unit time, but also maintain the stability of the raw gas flow of the synthesis system, thereby ensuring that the system pressure is stable within the process index range and extending the continuous operation cycle of the synthesis unit. In the existing synthetic ammonia production process, the control of the hydrogen-nitrogen ratio mainly depends on the manual adjustment of the valve opening on the gas transmission pipeline. Specifically, the purified gas from the low-methane process is divided into two routes, one is sent to PSA to extract pure hydrogen, and the other is sent to liquid nitrogen washing and nitrogen preparation. At present, the opening of the pneumatic valve on the PSA pipeline is mainly adjusted manually to adjust the gas volume to PSA and liquid nitrogen washing. When the opening of the pneumatic valve is increased, the gas volume to PSA increases, and the gas volume to liquid nitrogen washing and nitrogen preparation decreases; when the opening of the pneumatic valve is closed, the gas volume to PSA decreases, and the gas volume to liquid nitrogen washing and nitrogen preparation increases.
[0004] However, the above-mentioned method of adjusting the hydrogen-nitrogen ratio has the following problems during actual use: 1. The above-mentioned adjustment method is manually adjusted, which is too dependent on the experience of the operator, and is prone to the situation where the hydrogen-nitrogen ratio is out of balance due to the operator's lack of experience; 2. Affected by the volume and pressure of the purified gas entering the liquid nitrogen washing cold box, as well as the volume and pressure of the synthesis gas leaving the liquid nitrogen washing cold box, the pressure of the medium-pressure nitrogen entering the liquid nitrogen washing boundary area is prone to change. Even a small change in the pressure of the medium-pressure nitrogen will cause a large fluctuation in the flow rate of the medium-pressure nitrogen entering the liquid nitrogen washing, and ultimately lead to an imbalance in the hydrogen-nitrogen ratio of the synthesis gas. Summary of the invention
[0005] The invention provides a method for automatically adjusting the hydrogen-nitrogen ratio in synthetic ammonia production, so as to solve the technical problems in the prior art that the adjustment precision of the hydrogen-nitrogen ratio is low and the imbalance of the hydrogen-nitrogen ratio is easy to occur when the hydrogen-nitrogen ratio is manually adjusted.
[0006] In order to solve the above problems, the method for automatically adjusting the hydrogen-nitrogen ratio in synthetic ammonia production provided by the present invention adopts the following technical scheme:
[0007] An automatic adjustment method for the hydrogen-nitrogen ratio in ammonia synthesis production, comprising the following steps:
[0008] S1: Establish relationships: Establish a PID single-loop adjustment relationship between the purified gas flowmeter installed on the inlet pipeline of the liquid nitrogen wash cold box and the regulating valve installed on the PSA pipeline, and a ratio control loop relationship with the nitrogen flowmeter installed on the medium-pressure nitrogen pipeline. Establish a ratio control loop relationship between the hydrogen analyzer installed on the synthesis gas pipeline of the liquid nitrogen wash cold box and the accurately metered nitrogen valve installed on the medium-pressure nitrogen pipeline. Establish a cascade loop relationship between the inlet pressure of the synthesis compressor on the synthesis gas pipeline and the steam turbine speed of the synthesis compressor;
[0009] S2: Front-end control: When leaving the low-temperature methanol washing process, when the purified gas flowmeter monitors fluctuations in the total amount of purified gas, the regulating valve automatically adjusts its opening to preferentially ensure the gas volume and pressure for nitrogen distribution in the liquid nitrogen wash;
[0010] S3: Middle-end control: When the ratio between the purified gas flowmeter and the nitrogen flowmeter exceeds or is less than the set value range, the air separation unit connected to the medium-pressure nitrogen pipeline automatically adjusts the delivery volume of medium-pressure nitrogen;
[0011] S4: End control: When the hydrogen percentage measured by the hydrogen analyzer exceeds or is less than its set range, the opening of the accurately metered nitrogen valve is adjusted accordingly;
[0012] S5: Terminal control: When the pressure measured by the inlet pressure gauge of the synthesis compressor exceeds or is less than its set range, the steam turbine speed of the synthesis compressor is automatically increased or decreased to ensure the stability of the synthesis gas pressure.
[0013] The beneficial effects of the automatic adjustment method for the hydrogen-nitrogen ratio in ammonia synthesis production provided by the present invention are:
[0014] During the ammonia synthesis production process, the control of the hydrogen-nitrogen ratio mainly relies on manually adjusting the opening of the valves on the gas transmission pipeline by workers. This adjustment method is too dependent on the experience of workers, and it is easy to cause the imbalance of the hydrogen-nitrogen ratio due to the lack of experience of the operating workers. Moreover, affected by the gas volume and pressure of the purified gas entering the liquid nitrogen wash cold box, as well as the gas volume and pressure of the synthesis gas leaving the liquid nitrogen wash cold box, the pressure of the medium-pressure nitrogen entering the liquid nitrogen wash boundary area is likely to change, resulting in the imbalance of the hydrogen-nitrogen ratio of the synthesis gas;
[0015] In this application, by establishing a PID single-loop regulation relationship between the regulating valve of the pipeline to PSA and the purified gas entering the liquid nitrogen wash cold box, a ratio control loop relationship between the medium-pressure nitrogen flow rate entering the liquid nitrogen wash cold box and the purified gas flow rate entering the liquid nitrogen wash cold box, a ratio control loop relationship between the percentage of hydrogen in the syngas exiting the liquid nitrogen wash cold box and the precision nitrogen distribution valve, and a cascade loop relationship between the inlet pressure of the synthesis compressor installed on the syngas pipeline and the steam turbine speed of the synthesis compressor, the automatic adjustment of the opening degrees of each valve can be achieved without the need for operators to control the valves, which improves the automation level and the adjustment precision of the hydrogen-nitrogen ratio, reduces the working intensity of the operators, and improves the production efficiency.
[0016] Through the above settings, the present invention realizes the automatic adjustment of the opening degrees of each valve, improves the automation level and the adjustment precision of the hydrogen-nitrogen ratio, plays a positive role in stabilizing the safe, stable, long-term, full-load and excellent operation of the synthesis unit, and reduces the waste of resources caused by the syngas produced being sent to the flare system for combustion due to the hydrogen-nitrogen ratio of the syngas not meeting the requirements, saves the production cost of synthetic ammonia, promotes the refined management of synthetic ammonia production, and effectively solves the technical problems of low adjustment precision of manually adjusting the hydrogen-nitrogen ratio and easy occurrence of hydrogen-nitrogen ratio imbalance in the prior art.
[0017] Further, the regulating valve is a pneumatic regulating valve.
[0018] Further, for each increase in the opening degree of the pneumatic regulating valve, the flow rate of the purified gas increases by 300 - 600 Nm 3 / h.
[0019] Further, in the PID single-loop regulation relationship, the proportional term P is 30, the integral term I is 30, and the derivative term D is 0.
[0020] Further, the value range of the ratio between the purified gas flowmeter and the nitrogen flowmeter is 3.22 - 3.40.
[0021] Further, in step S1, the hydrogen analyzer is an on-line analyzer, and a ratio control loop relationship is established between the percentage content of hydrogen measured by the on-line analyzer and the precision nitrogen distribution valve.
[0022] Beneficial effects: The on-line analyzer can monitor the percentage content of hydrogen in the syngas in real time and continuously, and has high precision and reliability, which is convenient for timely adjusting the flow rate of medium-pressure nitrogen, optimizing the production process of synthetic ammonia, and improving the production efficiency and the quality of synthetic ammonia.
[0023] Further, the value range of the percentage content of hydrogen measured by the on-line analyzer is 0.9 - 1.1.
[0024] Further, there is a direct proportional relationship between the inlet pressure of the inlet and combination press and the steam turbine speed of the combination press.
[0025] Further, the set value range of the inlet pressure gauge of the inlet and combination press is 5.05 - 5.45 MPa.
[0026] Further, a syngas pressure gauge is installed on the syngas pipeline, and the pressure change measured by the syngas pressure gauge is consistent with the pressure change trend measured by the inlet pressure gauge of the inlet and combination press. Description of the Drawings
[0027] By referring to the following detailed description with reference to the drawings, the above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood. In the drawings, several embodiments of the present invention are shown in an exemplary rather than restrictive manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein:
[0028] Figure 1 is a flowchart of the automatic adjustment method for the hydrogen-nitrogen ratio in ammonia synthesis production provided by the present invention;
[0029] Figure 2 is a schematic structural diagram of the automatic adjustment system for the hydrogen-nitrogen ratio in ammonia synthesis production provided by the present invention.
[0030] Description of the Reference Numerals:
[0031] 1. Liquid nitrogen wash cold box; 2. Purified gas flowmeter; 3. PSA pipeline; 4. Pneumatic control valve; 5. Medium-pressure nitrogen pipeline; 6. Nitrogen flowmeter; 7. Syngas pipeline; 8. On-line analyzer; 9. Precision nitrogen distribution valve; 10. Inlet pressure gauge of the inlet and combination press; 11. Combination press; 12. Syngas pressure gauge; 13. Low-temperature methanol wash tower; 14. Outlet pipeline; 15. Purified gas pipeline; 16. Pressure gauge; 17. Steam turbine speed controller. Detailed Embodiments
[0032] The principles and spirit of the present invention will be described in detail below with reference to several representative embodiments of the present invention.
[0033] Examples of the automatic adjustment method for the hydrogen-nitrogen ratio in ammonia synthesis production provided by the present invention:
[0034] The chemical formula of ammonia is NH 3, is a colorless gas with a strong pungent odor. Ammonia is often used as the main raw material for manufacturing nitrogen fertilizers in agriculture, such as urea, ammonium nitrate, ammonium phosphate, etc., which plays an important role in increasing crop yields; it is often used as a refrigerant in industrial refrigeration and is widely used in fields such as food refrigeration and cold chain logistics; it is commonly used in the production of various chemical products in chemical raw materials, such as nitric acid, explosives, dyes, and plastics; in the field of clean energy, it can be used as a carrier of hydrogen energy, producing hydrogen through cracking for use in fuel cells or directly as a fuel; in the environmental protection industry, ammonia water can be used for wastewater treatment, adjusting the pH value, or removing heavy metal particles.
[0035] Ammonia synthesis production is an important chemical industrial process. Its main purpose is to directly synthesize ammonia (NH 3 ) by combining nitrogen and hydrogen under high temperature, high pressure, and the action of a catalyst. Ammonia is the main raw material for the fertilizer industry and basic organic chemical industry. The main raw materials for producing ammonia include natural gas, light oil, heavy oil, coal, etc. These raw materials can be made into crude raw material gas containing hydrogen and nitrogen through specific conversion technologies.
[0036] The production process of ammonia synthesis usually includes three steps: raw material gas preparation, raw material gas purification, and ammonia synthesis. Among them, in the raw material gas preparation process, for solid raw materials (such as coal and coke), the gasification method is usually used to produce synthesis gas. Residual oil can obtain synthesis gas by non-catalytic partial oxidation. For gaseous hydrocarbons and naphtha, the two-stage steam reforming method is used in industry to produce synthesis gas; in the raw material gas purification process, the crude raw material gas contains impurities other than hydrogen and nitrogen, such as carbon monoxide (CO), sulfides, carbon dioxide (CO 2 ), etc., and needs to be purified. The purification process includes a conversion process (converting CO into CO 2 and H 2 ), a desulfurization and decarbonization process, and a gas refining process; in the ammonia synthesis process, first, the purified hydrogen-nitrogen mixed gas is compressed to high pressure, and then a synthesis reaction occurs under the action of a catalyst to generate ammonia gas.
[0037] During the normal production process of ammonia synthesis, when the gas volume of the purified gas entering the liquid nitrogen wash cold box changes, in order to stabilize the ratio of H 2 and N 2 , the on-site control personnel of the liquid nitrogen wash need to frequently manually adjust the regulating valve and the precise nitrogen distribution valve. When the gas volume of the purified gas entering the liquid nitrogen wash cold box becomes larger, in order to stabilize the ratio of H 2 and N 2 , the on-site control personnel of the liquid nitrogen wash will increase the opening of the precise nitrogen distribution valve, which will ultimately cause the gas volume sent to the synthesis process to exceed the designed gas volume, resulting in an increase in the pressure of the synthesis system. After the synthesis process still shows no obvious effect after adjusting the speed of the synthesis compressor and adjusting the anti-surge, etc., the excess synthesis gas will be sent to the flare system for combustion, resulting in a great waste of resources and an increase in production costs.
[0038] When the gas volume of the purified gas entering the liquid nitrogen wash cold box decreases, to stabilize the ratio of H 2 and N 2 the central control personnel of the liquid nitrogen wash will adjust the opening degree of the precision nitrogen valve smaller, which will ultimately lead to the gas volume going to the synthesis process being lower than the designed gas volume, resulting in a decrease in the synthesis system pressure. When the rotational speed of the synthesis is reduced and still cannot meet the designed pressure and gas volume of the compressor inlet system, it will cause the compressor to stop, ultimately affecting normal production.
[0039] The above situation not only increases the labor intensity of the central control personnel, but also easily causes frequent fluctuations in the synthesis gas volume and the hydrogen-nitrogen ratio in the liquid nitrogen wash process, which will also impact the stable operation of the synthesis unit. In severe cases, it may cause the compressor to stop, ultimately affecting normal production.
[0040] Therefore, based on the above problems existing in the control of the hydrogen-nitrogen ratio in the existing synthetic ammonia production process, an automatic adjustment method for the hydrogen-nitrogen ratio in synthetic ammonia production is proposed.
[0041] As Figure 1 shown, the automatic adjustment method for the hydrogen-nitrogen ratio in synthetic ammonia production includes the following steps:
[0042] S1: Establish relationships: Establish a PID single-loop regulation relationship between the purified gas flowmeter installed on the inlet pipeline of the liquid nitrogen wash cold box and the regulating valve installed on the PSA pipeline, a ratio control loop relationship with the nitrogen flowmeter installed on the medium-pressure nitrogen pipeline, establish a ratio control loop relationship between the hydrogen analyzer installed on the synthesis gas pipeline of the liquid nitrogen wash cold box and the precision nitrogen valve installed on the medium-pressure nitrogen pipeline, and establish a cascade loop relationship between the inlet pressure of the compressor inlet on the synthesis gas pipeline and the steam turbine speed of the compressor;
[0043] S2: Front-end control: When leaving the low-temperature methanol wash process, when the purified gas flowmeter monitors fluctuations in the total purified gas volume, the regulating valve automatically adjusts the opening degree to give priority to ensuring the gas volume and pressure for nitrogen distribution in the liquid nitrogen wash;
[0044] S3: Middle-end control: When the ratio between the purified gas flowmeter and the nitrogen flowmeter exceeds or is less than the set value range, the air separation unit connected to the medium-pressure nitrogen pipeline automatically adjusts the delivery volume of the medium-pressure nitrogen;
[0045] S4: End control: When the hydrogen percentage measured by the hydrogen analyzer exceeds or is less than its set range, the opening degree of the precision nitrogen valve is adjusted accordingly;
[0046] S5: Terminal control: When the pressure measured by the inlet pressure gauge of the compressor inlet exceeds or is less than its set range, the steam turbine speed of the compressor is automatically increased or decreased to ensure the stability of the synthesis gas pressure.
[0047] Regarding the front-end control. In this embodiment, the regulating valve is a pneumatic regulating valve. For each increase in its opening degree, the flow rate of the purified gas increases by 300 - 600 Nm 3 / h; in other embodiments, the regulating valve is an electromagnetic regulating valve or an electric regulating valve.
[0048] In this embodiment, in the PID single-loop regulation relationship, the proportional term P is 30, the integral term I is 30, and the differential term D is 0. PID single-loop regulation is the most basic and classic control method in industrial control. Its core is to dynamically adjust the output of the controller through the coordinated action of three parameters: proportional (P), integral (I), and differential (D), so that the controlled variable (such as temperature, pressure, flow rate, etc.) is stabilized near the set value. Among them, the role of proportional control is to output the control quantity proportionally according to the magnitude of the deviation. The larger the deviation, the stronger the control action, and the response speed is fast, which can quickly reduce the deviation; the role of integral control is to integrate the deviation. The integral term is proportional to the duration of the deviation, which is used to eliminate the static error and improve the control accuracy; the role of differential control is to output the control quantity according to the rate of change of the deviation, which is used to predict the change trend of the deviation and perform correction in advance, which can improve the dynamic performance of the system, reduce the overshoot, and improve the stability of the system.
[0049] Regarding the middle-end control. The value range of the ratio between the purified gas flowmeter and the nitrogen flowmeter is 3.22 - 3.40. The ratio control loop is a control strategy widely used in industrial production processes. Its core lies in regulating the proportional relationship between two or more variables to ensure the stability of the production process and the product quality.
[0050] Regarding the end control. In this embodiment, the hydrogen analyzer is an on-line analyzer. A ratio control loop relationship is established between the powder content of hydrogen measured by the on-line analyzer and the fine-tuning nitrogen valve. The value range of the percentage content of hydrogen measured by the on-line analyzer is 0.9 - 1.1. The on-line analyzer measures the percentage content of hydrogen in the syngas based on the differences in the thermophysical properties of the components in the mixed gas, especially the significantly higher thermal conductivity of hydrogen compared to other common gases. It has high precision and high reliability, and can more accurately achieve the control of the hydrogen-nitrogen ratio in ammonia synthesis.
[0051] Regarding terminal control. A cascade control loop is an advanced control strategy composed of two or more controllers in series, where the output of one controller serves as the setpoint of another controller. This structure enables the system to respond more quickly and accurately to external disturbances and internal parameter changes, improving control accuracy and stability. In the method for automatically adjusting the hydrogen-nitrogen ratio in ammonia synthesis provided by the present invention, there is a direct proportional relationship between the inlet pressure of the synthesis compressor and the steam turbine speed of the synthesis compressor. A synthesis gas pressure gauge is installed on the synthesis gas pipeline, and the pressure change measured by the synthesis gas pressure gauge is consistent with the pressure change trend measured by the inlet pressure gauge of the synthesis compressor. In this embodiment, the set value range of the inlet pressure gauge of the synthesis compressor is 5.05 - 5.45 MPa.
[0052] It should be noted that in the method for automatically adjusting the hydrogen-nitrogen ratio in ammonia synthesis provided by the present invention, unless otherwise specified, the synthesis compressor mentioned refers to the synthesis compressor.
[0053] In front-end control, by stabilizing the flow rate and pressure of the purified gas entering the liquid nitrogen wash cold box at the front end, precise control of the hydrogen-nitrogen ratio can be achieved. This mainly addresses the problem that when the flow rate of the purified gas entering the liquid nitrogen wash cold box changes due to fluctuations in the flow rate of the purified gas coming out of the low-temperature methanol wash process, and the flow rates to and into the liquid nitrogen wash cannot be adjusted quickly and effectively, resulting in an imbalance in the hydrogen-nitrogen ratio of the synthesis gas. Since the flow rate of the purified gas coming out of the low-temperature methanol wash process is affected by the previous process (such as changes in coal slurry concentration, shift reaction efficiency, etc.), the flow rate will fluctuate within a certain range. By establishing a PID single-loop control relationship between the opening of the purified gas flow meter and the pneumatic control valve, the opening of the pneumatic control valve can be automatically adjusted when the total flow rate of the purified gas coming out of the low-temperature methanol wash process fluctuates, giving priority to ensuring the flow rate and pressure of the gas going to the liquid nitrogen wash cold box, and ultimately achieving precise control of the hydrogen-nitrogen ratio at the front end.
[0054] In mid-end control, by stabilizing the flow rate and pressure of the medium-pressure nitrogen entering the liquid nitrogen wash cold box in the mid-end, precise control of the hydrogen-nitrogen ratio is achieved. This mainly addresses the problem that when the pressure of the medium-pressure nitrogen entering the liquid nitrogen wash process fluctuates, causing a large flow rate fluctuation and resulting in an imbalance in the hydrogen-nitrogen ratio of the synthesis gas. A ratio control loop relationship is established between the nitrogen flow meter installed on the medium-pressure nitrogen pipeline and the purified gas flow meter, and the ratio range is set. Since the flow rate of the purified gas entering the liquid nitrogen wash cold box has been subject to PID single-loop control in the front-end control and its value has stabilized, the ratio control loop relationship between the nitrogen flow meter and the purified gas flow meter can ensure the stability of the flow rate and pressure of the medium-pressure nitrogen entering the liquid nitrogen wash cold box.
[0055] The end control mainly aims at the problem of inaccurate hydrogen-nitrogen ratio in the syngas sent to the synthesis process. A ratio control loop relationship is established between the on-line analyzer installed on the syngas pipeline out of the liquid nitrogen wash cold box and the precision nitrogen distribution valve. When the nitrogen percentage monitored by the on-line analyzer fluctuates, the opening of the precision nitrogen distribution valve will be adjusted accordingly.
[0056] The terminal control mainly aims at the problem that the medium-pressure nitrogen pressure and flow rate entering the liquid nitrogen wash area are easily affected by the syngas pressure out of the liquid nitrogen wash. Since the pressure change measured by the syngas pressure gauge is consistent with the pressure change trend measured by the inlet pressure gauge of the synthesis compressor, therefore, by establishing a cascade loop relationship between the inlet pressure of the synthesis compressor and the steam turbine speed of the synthesis compressor, and the inlet pressure of the synthesis compressor is used as the main parameter of the cascade loop relationship, while the steam turbine speed of the synthesis compressor is used as the secondary parameter of the cascade loop relationship, the stability of the inlet pressure of the synthesis compressor can be ensured by automatically adjusting the speed of the steam turbine of the synthesis compressor, indirectly realizing the stability of the syngas pressure of the liquid nitrogen wash cold box, so as to more precisely control the hydrogen-nitrogen ratio.
[0057] In summary, by continuously adjusting the purified gas volume and pressure, medium-pressure nitrogen gas volume and pressure, the opening of the precision nitrogen distribution valve, and the system pressure at the front end, middle end, end, and terminal, the automatic and precise control and adjustment of the hydrogen-nitrogen ratio in the synthetic ammonia production process can be achieved.
[0058] As Figure 2 shown, the automatic hydrogen-nitrogen ratio adjustment system for synthetic ammonia production adopted by the automatic hydrogen-nitrogen ratio adjustment method for synthetic ammonia production provided by the present invention includes a low-temperature methanol wash tower 13, a liquid nitrogen wash cold box 1, and a synthesis compressor 11 arranged in sequence from left to right.
[0059] Among them, the outlet of the low-temperature methanol wash tower 13 is connected with an outlet pipeline 14. The end of the outlet pipeline 14 is connected with a PSA pipeline 3 and a purified gas pipeline 15. A purified gas flowmeter 2 and a pressure gauge 16 for measuring the medium-pressure nitrogen pressure entering the liquid nitrogen wash cold box 1 are installed on the purified gas pipeline 15. A pneumatic regulating valve 4 is installed on the PSA pipeline 3. The outlet of the liquid nitrogen wash cold box 1 is connected with a synthesis gas compressor through a synthesis gas pipeline 7. An on-line analyzer 8, a synthesis gas pressure gauge 12, and an inlet pressure gauge 10 of the synthesis compressor are installed on the synthesis gas pipeline 7 from left to right in sequence. The synthesis compressor 11 is equipped with a steam turbine speed controller 17.
[0060] The medium-pressure nitrogen entering the liquid nitrogen wash cold box 1 is divided into two paths, one for rough nitrogen distribution and the other for washing nitrogen.
[0061] In addition, the automatic hydrogen-nitrogen ratio adjustment system for ammonia synthesis production further includes an air separation unit (not shown in the figure) for storing medium-pressure nitrogen. The outlet of the air separation unit is connected to a medium-pressure nitrogen pipeline 5. The end of the medium-pressure nitrogen pipeline 5 is respectively connected to a liquid nitrogen wash cold box 1 and a synthesis gas pipeline 7. A pressure gauge 16 for measuring the nitrogen pressure in the medium-pressure nitrogen pipeline 5, a nitrogen flow meter 6 for measuring the gas volume of the medium-pressure nitrogen entering the liquid nitrogen wash cold box 1, and a precision nitrogen distribution valve 9 for controlling the delivery of medium-pressure nitrogen to the synthesis gas pipeline 7 are installed on the medium-pressure nitrogen pipeline 5.
[0062] Based on the above description of this specification, those skilled in the art can also understand the following terms used, such as terms indicating orientation or position relationship, such as "upper", "lower", "front", "rear", "left", "right", "width", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or position relationship shown in the drawings of this specification. It is only for the purpose of facilitating the description of the solution of the present invention and simplifying the description, rather than explicitly or implicitly indicating that the device or element involved must have the specific orientation, be constructed and operate in the specific orientation. Therefore, the above terms of orientation or position relationship cannot be understood or interpreted as a limitation to the solution of the present invention.
[0063] In addition, in the description of this specification, the meaning of "a plurality of" is at least two, such as two, three or more, etc., unless otherwise specifically and clearly defined.
Claims
1. A method for automatically adjusting the hydrogen-nitrogen ratio in synthetic ammonia production, characterized in that: The steps include: S1: Establish relationships: Establish a PID single-loop regulation relationship between the purge gas flowmeter installed on the inlet pipeline of the liquid nitrogen cold-washing box and the regulating valve installed on the PSA pipeline, and a ratio control loop relationship between the nitrogen flowmeter installed on the medium-pressure nitrogen pipeline, establish a ratio control loop relationship between the hydrogen analyzer installed on the synthesis gas pipeline of the liquid nitrogen cold-washing box and the fine nitrogen valve installed on the medium-pressure nitrogen pipeline, and establish a cascade loop relationship between the inlet pressure of the combined compressor installed on the synthesis gas pipeline and the turbine speed of the combined compressor; S2: Front-end control: When leaving the low-Methane process, when the purge gas flow meter detects that the total purge gas volume fluctuates, the regulating valve automatically adjusts the opening to give priority to ensuring the volume and pressure of liquid nitrogen washing and nitrogen distribution; S3: Mid-end control: When the ratio between the purge gas flowmeter and the nitrogen flowmeter exceeds or is less than the set value range, the air separation unit connected to the medium-pressure nitrogen pipeline automatically adjusts the delivery volume of the medium-pressure nitrogen; S4: Terminal control: When the hydrogen percentage measured by the hydrogen analyzer exceeds or is less than the set range, the opening of the fine nitrogen valve will be adjusted automatically; S5: Terminal control: When the pressure measured by the inlet pressure gauge of the compressor exceeds or is less than the set range, the compressor turbine speed is automatically increased or decreased to ensure the stability of the synthesis gas pressure.
2. The method for automatically adjusting the hydrogen-nitrogen ratio in synthetic ammonia production according to claim 1, characterized in that: The regulating valve is a pneumatic regulating valve.
3. The method for automatically adjusting the hydrogen-nitrogen ratio in synthetic ammonia production according to claim 2, characterized in that: The pneumatic regulating valve increases its opening by 300-600 Nm per time. 3 / h.
4. The method for automatically adjusting the hydrogen-nitrogen ratio in synthetic ammonia production according to any one of claims 1 to 3, characterized in that: In the PID single-loop regulation relationship, the proportional term P is 30, the integral term I is 30, and the differential term D is 0.
5. The method for automatically adjusting the hydrogen-nitrogen ratio in synthetic ammonia production according to any one of claims 1 to 3, characterized in that: The ratio between the purified gas flow meter and the nitrogen flow meter ranges from 3.22 to 3.
40.
6. The method for automatically adjusting the hydrogen-nitrogen ratio in synthetic ammonia production according to any one of claims 1 to 3, characterized in that: In the step S1, the hydrogen analysis table is an online analysis table, and a ratio control loop relationship between the percentage content of hydrogen measured by the online analysis table and the nitrogen fine-mixing valve is established.
7. The method for automatically adjusting the hydrogen-nitrogen ratio in synthetic ammonia production according to claim 6, characterized in that: The percentage of hydrogen measured by the online analysis table ranges from 0.9 to 1.
1.
8. The method for automatically adjusting the hydrogen-nitrogen ratio in synthetic ammonia production according to any one of claims 1 to 3, characterized in that: There is a positive proportional relationship between the inlet pressure of the compressor and the rotation speed of the steam turbine of the compressor.
9. The method for automatically adjusting the hydrogen-nitrogen ratio in synthetic ammonia production according to claim 8, characterized in that: The setting value range of the inlet pressure gauge of the inlet press is 5.05~5.45MPa.
10. The method for automatically adjusting the hydrogen-nitrogen ratio in synthetic ammonia production according to claim 8, characterized in that: A synthesis gas pressure gauge is installed on the synthesis gas pipeline, and the pressure change measured by the synthesis gas pressure gauge is consistent with the pressure change trend measured by the inlet pressure gauge of the synthesis compressor.