Temperature control method for green electricity-to-green ammonia synthesis tower

Abstract

The invention discloses a method for controlling the temperature of a synthesis tower for producing green ammonia by using green electricity, which comprises the following steps of: introducing annular space gas and main line gas from process gas at an outlet of a compressor, introducing the annular space gas into an annular space of the tower wall of the synthesis tower, and controlling the flow of the annular space gas to be stably maintained at a preset value, so that the temperature fluctuation range of a high-pressure shell is less than or equal to 25 DEG C; the preset value is 4%-6% of the total air inflow of 100% loads, and the allowable fluctuation range of the annular gap air flow is smaller than or equal to + / -12.5%. The main line gas function is limited as the main reaction gas flow, and the independently-controlled annular gap gas passage is additionally arranged, so that when the load of the device fluctuates greatly, the annular gap gas flow is kept basically stable, the temperature rise fluctuation range of the high-pressure shell is far lower than that of a traditional process, and fatigue damage caused by alternating thermal stress is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of ammonia synthesis, and in particular relates to a temperature control method for a green electricity-based green ammonia synthesis tower. Background Art

[0002] Traditional ammonia synthesis plants operate in a safe, stable, long-lasting, full, and optimal state to achieve low overall energy consumption and maximize economic benefits. Therefore, they generally require a constant load of around 100%. Furthermore, the plants have limited operational flexibility, with typical design values ranging from 60% to 110%. Fluctuations below 80% are rare, far below the baseline parameter of 1,000 times over the plant's design lifespan, preventing them from failing to achieve their economic targets. Therefore, traditional ammonia synthesis plants do not need to consider the adverse effects of changes in the inlet gas flow rate on the high-pressure shell of the synthesis tower.

[0003] Green electricity such as wind and solar power is volatile and unstable, resulting in very large fluctuations in the device load, which can be as low as 10% and as high as 110%~125%. In addition, the frequency of large fluctuations in the device load is at least once a day. Within the design service life of the device (not less than 15 years), the number of large fluctuations in the device load reaches more than 5,000 times, far exceeding the requirement of GB / T 4732-2024 "Analysis and Design of Pressure Vessels Part 4: Stress Classification Method" that the number of cycles for exemption from fatigue assessment is ≤1,000.

[0004] If a synthesis tower is designed using traditional ammonia synthesis process technology, the mainline gas functions as both mainline gas and annular gap gas. Large flow rate fluctuations can lead to significant temperature fluctuations in the high-pressure shell of the synthesis tower, making it susceptible to fatigue conditions and posing risks to the long-term safe operation of the synthesis tower. For example, CN101182007A discloses an energy-saving ammonia synthesis process that diverts the gas entering the synthesis tower at once, primarily directing 25%-30% of the intake volume into the annular gap. If the total intake volume is unstable, the amount of gas entering the annular gap is also dynamically adjusted, which is detrimental to the stable operation of green ammonia synthesis.

[0005] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the Invention

[0006] The purpose of the present invention is to provide a synthesis tower temperature control method, so as to overcome the defects of the above-mentioned prior art in that green electricity is unstable and the high-voltage shell temperature fluctuates greatly due to large changes in device load.

[0007] To achieve the above-mentioned purpose, the present invention provides a temperature control method for a green electricity-based green ammonia synthesis tower, which includes annular gap gas and main line gas, wherein the annular gap gas and main line gas are process gas from the compressor outlet, and the annular gap gas enters the annular gap of the synthesis tower wall. The annular gap gas flow rate is controlled to be stably maintained at a predetermined value, so that the high-pressure shell temperature fluctuation range is ≤25°C, the predetermined value is 4%~6% of the total air intake at 100% load, and the annular gap gas flow rate is allowed to fluctuate within a range of ≤±12.5%.

[0008] Green electricity primarily refers to electricity generated through the conversion of renewable energy sources such as photovoltaics, wind, hydropower, tidal waves, and biomass. Its core characteristic is that it emits virtually no greenhouse gases or pollutants during the energy production process. This includes clean electricity sources such as solar photovoltaics, onshore and offshore wind power, tidal power, hydropower, and biomass power. This type of electricity, which converts natural energy (such as solar, wind, hydropower, ocean energy, and biomass energy) into electrical energy through technological means, aligns with the global low-carbon development trend and serves as a key energy carrier for achieving the "dual carbon" goals.

[0009] Preferably, in the above technical solution, the synthesis tower includes a high-pressure shell and an internal part sleeved in the high-pressure shell, an annular gap is provided between the high-pressure shell and the internal part, an annular gap gas inlet is provided at the upper part of the high-pressure shell, and a main line gas inlet is provided at the bottom head; the steps include: The annular gap gas enters the annular gap through the annular gap gas inlet, and then flows down along the annular gap and enters the space above the distribution plate of the bottom head of the internal part through the small holes of the tower bottom distribution plate; The main line gas enters the bottom of the synthesis tower through the main line gas inlet, and enters the space above the bottom head distribution plate of the internal part through the small holes of the bottom head distribution plate of the internal part; The annular gap gas flow is controlled to be stably maintained at 5% of the total gas flow, and the allowable fluctuation range is ≤±12.5%; The opening of the main line gas branch valve is fixed after startup and commissioning, and the flow is passively adjusted according to load fluctuations.

[0010] Preferably, in the above technical solution, the annular gap gas and the main line gas maintain independent flow paths before entering the tower bottom distribution plate and the internal bottom head distribution plate, and merge in the cavity surrounded by the tower bottom distribution plate, the internal bottom head distribution plate and the tower bottom heat exchanger.

[0011] Preferably, in the above technical solution, the mainline gas flow rate is a fixed valve opening determined after commissioning and remains unchanged. The mainline gas flow rate is not used as a control method, but is passively controlled by using a fixed opening (determined after commissioning) and then remaining essentially unchanged.

[0012] A temperature control device for a green ammonia synthesis tower for green electricity production adapted to the control method described above, wherein the annular gap gas branch is provided with a flow regulating device for maintaining the flow of the annular gap gas branch constant at 4% to 6% of the total air intake at 100% load.

[0013] Preferably, in the above technical solution, the annular gap between the high-pressure shell and the internals is provided with an annular gap gas inlet at the top and a small hole connected to the tower bottom distribution plate at the bottom; The main line gas inlet at the bottom head of the synthesis tower is connected to the small hole of the distribution plate of the bottom head of the internal part; the annular gap gas and the main line gas come from the process gas at the outlet of the compressor.

[0014] Preferably, in the above technical solution, the aperture of the small holes of the tower bottom distribution plate is Φ10-Φ25, the opening rate is 20%-30%, and the small holes are distributed in concentric circles, and the distance between adjacent circles is 4-6 times the aperture; the aperture of the small holes of the bottom head distribution plate (5) of the internal part is Φ10-Φ25, the opening rate is 20%-30%, and the small holes are distributed in concentric circles, and the distance between adjacent circles is 2-4 times the aperture.

[0015] Preferably, in the above technical solution, the flow regulating device includes a flow meter, a regulating valve and a controller to achieve a flow fluctuation of ≤±5%.

[0016] Preferably, the above technical solution further includes a temperature protection system, which forces the N1 annular gap gas to be fully opened to cool the high-pressure shell when it is detected that the maximum annular gap temperature is greater than the maximum operating temperature of the high-pressure shell.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The temperature fluctuation of the high-pressure shell is significantly reduced: by limiting the function of the main line gas (N2) to the main reaction gas flow and adding an independently controlled annular gap gas (N1) passage, the annular gap gas flow rate remains basically stable when the device load fluctuates greatly, making the temperature rise fluctuation range of the high-pressure shell far lower than that of traditional processes, avoiding fatigue damage caused by alternating thermal stress.

[0018] Enhanced operational stability at low loads: Under low load conditions, the annular gap airflow ratio is significantly increased, ensuring that the bottom heat exchanger maintains effective heat recovery capacity and reduces reliance on external heat compensation.

[0019] Improved fatigue resistance: By stabilizing the annular gap air flow control, the high-pressure casing temperature fluctuation amplitude is always lower than the fatigue assessment critical value, meeting the long-term safe operation requirements under high-frequency load fluctuations (>5,000 times).

[0020] Optimization of green electricity fluctuation adaptability: The annular gap gas flow stabilization mechanism is combined with the passive regulation of the main line gas, so that the synthesis tower can still maintain a stable thermal state of the high-pressure shell when the load changes drastically at the minute level, breaking through the traditional ammonia synthesis unit's dependence on load continuity. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a process flow chart of the present invention; Figure 2 Schematic diagram of the gas path in the synthesis tower of the present invention; Figure 3 It is a schematic diagram of the gas path of the synthesis tower in the prior art.

[0022] In the figure: 1. High-pressure shell; 2. Internals; 3. Annular gap; 4. Tower bottom distribution plate; 5. Internal bottom head distribution plate; 6. No. 1 catalytic bed; 7. Upper interlayer heat exchanger; 8. No. 2 catalytic bed; 9. Lower interlayer heat exchanger; 10. No. 3 catalytic bed; 11. Tower bottom heat exchanger; 12. Distribution baffle; 13. Flow regulating device. DETAILED DESCRIPTION

[0023] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0024] Unless expressly stated otherwise, throughout the specification and claims, the term "comprise" or variations such as "include" or "comprising", etc., will be understood to include the stated elements or components but not to exclude other elements or other components.

[0025] Example 1

[0026] A temperature control device for a green electricity green ammonia synthesis tower comprises: an annular gap 3 between a high-pressure shell 1 and an internal part 2, an annular gap gas inlet at the top, and a small hole at the bottom connected to a tower bottom distribution plate 4; The main line gas inlet at the bottom head of the synthesis tower is connected to the small hole of the bottom head distribution plate 5 of the internal part 2; the annular gap gas branch is provided with a flow regulating device 13 to maintain a constant flow rate at 4% to 6% of the total air intake at 100% load; the annular gap gas and the main line gas come from the process gas after heat exchange at the compressor outlet.

[0027] The aperture of the small hole of the tower bottom distribution plate 4 is Φ10-Φ25, and the opening rate is 20%-30%. The aperture of the small hole of the bottom head distribution plate 5 of the internal part 2 is Φ10-Φ25, and the opening rate is 20%-30%. The small holes are distributed in concentric circles, and the spacing between adjacent circles is 2-4 times the aperture.

[0028] The flow regulating device 13 includes a flow meter, a regulating valve and a controller to achieve flow fluctuation ≤±5%.

[0029] The device is equipped with a temperature protection system. When it detects that the maximum temperature of the annular gap 3 is greater than the maximum operating temperature of the high-pressure shell, the N1 annular gap gas is forced to be fully opened to cool the high-pressure shell.

[0030] The process gas from the compressor outlet after heat exchange is divided into five paths before entering the synthesis tower, namely: 1) N1 annular gap gas - enters the annular gap 3 of the tower wall from the top of the synthesis tower, flows from top to bottom, then enters the small holes of the distribution plate 4 at the bottom of the tower, and then merges with the N2 main line gas to enter the shell side of the heat exchanger to maintain the temperature of the high-pressure shell 1 of the synthesis tower, thereby increasing the operational stability and safety of the synthesis tower.

[0031] 2) N2 main line gas - cold air from the bottom heat exchanger of the synthesis tower, enters the small holes of the bottom head distribution plate of internal part 2 from the bottom head of the synthesis tower, and then merges with the N1 annular gap gas to enter the shell side of the heat exchanger to adjust the process gas temperature out of the synthesis tower to 330-420℃. The cold air out of the bottom heat exchanger enters the zero-meter layer along the central pipe.

[0032] 3) F0 temperature regulating gas - used to adjust the inlet temperature of the catalytic bed 6 of the synthesis tower 1# to 350-370℃ to adapt to different operating conditions of the synthesis tower.

[0033] 4) F1 temperature regulating gas - used to adjust the inlet temperature of the catalytic bed 8 of the synthesis tower 2# to 380~400℃ to adapt to different operating conditions of the synthesis tower.

[0034] 6) F2 temperature regulating gas - used to adjust the inlet temperature of the catalytic bed 10 of the synthesis tower 3# to 380-400℃ to adapt to different operating conditions of the synthesis tower.

[0035] The F1 and F2 temperature-adjusting gases of the upper and lower interlayer heat exchangers 9 entering the synthesis tower and the N2 main line gas and N1 annular gap 3 gas of the bottom heat exchanger 11 shell side respectively exchange heat with the gases after the reaction of the 1# bed, 2# bed and 3# bed, and the temperature rises to 350~380℃. Then, they rise along the central tube to the zero meter of the catalytic bed, and after being adjusted to the appropriate temperature by the f0 cooling gas, they enter the 1# radial catalytic bed to react to 490~510℃, enter the upper interlayer heat exchanger 7 tube side, and after being adjusted to 380~400℃ by the F1 temperature-adjusting gas, they are then discharged from the outside. It enters the 2# catalytic bed 8 along the radial direction from the inside, reacts to 460-480℃, and enters the shell side of the lower interlayer heat exchanger 9. After being adjusted to 380-400℃ by the F2 temperature-regulating gas, it also enters the 3# catalytic bed 10 along the radial direction from the outside to the inside, reacts to 425-450℃, and enters the tube side of the bottom heat exchanger 11. It is cooled to 330-420℃ by the N1 annular gap 3 gas and the N2 main line gas, and then exits the tower. It becomes the reaction gas and enters the heat energy recovery. The circulating gas after cooling and separation of liquid ammonia merges with the fresh gas, is pressurized by the compressor, and enters the synthesis tower after heat exchange.

[0036] The specific adjustment process is: 1) The process gas is divided into five routes: ① N1 annular gap 3 gas, with a basically constant flow rate to ensure small temperature changes in the shell of the ammonia synthesis tower and improve the safety of the high-pressure shell 1; ② F0 temperature-regulating gas, which adjusts the inlet temperature of the first bed layer; ③ F1 temperature-regulating gas, which adjusts the inlet temperature of the second bed layer; ④ F2 temperature-regulating gas, which adjusts the inlet temperature of the third bed layer; ⑤ N2 main line gas, whose valve opening remains unchanged when the device load changes.

[0037] When the load of the device changes from high to low, the opening of the F0 temperature-regulating gas, F1 temperature-regulating gas, and F2 temperature-regulating gas valves becomes smaller, and the N1 annular gap 3 gas flow rate remains unchanged (Note: the proportion of N1 annular gap 3 gas flow rate / total flow rate is small). Therefore, the proportion of N1 annular gap 3 gas + N2 main line gas flow rate increases (as can be seen from Tables 1 and 2, the flow rate proportion increases from 15% to 29%), so that as much reaction heat as possible can be recovered through the third bed outlet heat exchanger under low load, the reaction of the synthesis tower is maintained, and the external heat supply to the synthesis tower is reduced.

[0038] 2) Traditional ammonia synthesis plants operate in a safe, stable, long-term, full, and optimal state to achieve low overall energy consumption and maximize economic benefits. Therefore, they generally require a constant load of around 100%. Furthermore, the plants have limited operational flexibility, typically designed for a range of 60% to 110%. Fluctuations below 80% are rare, far below the baseline of 1,000 load fluctuations within the plant's design lifespan, preventing them from failing to achieve target economic benefits. Therefore, traditional ammonia synthesis plants do not need to consider the adverse effects of changes in the inlet gas flow rate on the reactor shell.

[0039] 3) Improved ammonia synthesis unit (green electricity to green ammonia unit). The operation of the unit needs to adapt to the volatility and instability of green electricity such as wind and solar power. The unit load fluctuates greatly, with a minimum of 10% and a maximum of 110%~125%. In addition, the frequency of large fluctuations in the unit load is at least once a day. Within the design service life of the unit (not less than 15 years), the number of large fluctuations in the unit load reaches more than 5,000 times, far exceeding the requirement of ≤1,000 cycles for exemption from fatigue assessment stipulated in GB / T 4732-2024 "Analysis and Design of Pressure Vessels Part 4: Stress Classification Method".

[0040] If the synthesis tower is designed with traditional ammonia synthesis process technology, the N2 main line gas has the functions of main line gas and annular gap 3 gas. If the flow rate fluctuates greatly, the temperature of the high-pressure shell 1 of the synthesis tower will fluctuate greatly (it can be seen from Tables 1 and 2 that the change in temperature rise is 34.5℃=68.2℃-32.7℃; it can be seen from Tables 1 and 2 that the change in temperature rise is 34.5℃=68.2℃-32.7℃; it can be seen from Tables 1 and 2 that the change in temperature rise is 34.5℃=68.2℃-32.7℃;), and it is easy to operate under fatigue conditions, which brings risks to the long-term safe operation of the synthesis tower.

[0041] If the synthesis tower is designed using an improved ammonia synthesis process technology, the N2 main line gas is limited to the function of the main line gas, and N1 annular gap 3 gas is provided to maintain a basically stable flow rate. This will result in large load changes in the ammonia synthesis unit. However, due to the small fluctuation in the annular gap 3 gas flow rate, the temperature fluctuation of the synthesis tower high-pressure shell 1 is also small (Tables 1 and 2 show that if the N1 flow rate is perfectly regulated, the temperature rise change is 0°C = 100°C - 100°C; Tables 3 and 4 show that if the N1 flow rate is perfectly regulated, the temperature rise change is 0°C = 125°C - 125°C; Tables 5 and 6 show that if the N1 flow rate is perfectly regulated, the temperature rise change is 0°C = 83.3°C - 83.3°C). This allows the synthesis tower high-pressure shell 1 to operate under non-fatigue conditions at all times, bringing benefits to the long-term safe operation of the synthesis tower.

[0042] Table 1 100% load gas flow rate (300,000 tons ammonia synthesis unit benchmark)

[0043] Table 2 10% load gas flow rate (300,000 tons ammonia synthesis unit benchmark)

[0044] Table 3 100% load gas flow rate (300,000 tons ammonia synthesis unit benchmark)

[0045] Table 4 10% load gas flow rate (300,000 tons ammonia synthesis unit benchmark)

[0046] Table 5 100% load gas flow rate (300,000 tons ammonia synthesis unit benchmark)

[0047] Table 6 10% load gas flow rate (300,000 tons ammonia synthesis unit benchmark)

[0048] 4) Flow direction of N1 annular gap 3 gas and N2 main line gas in the improved ammonia synthesis unit (green electricity to green ammonia unit): The N1 annular gap 3 gas flows downward from the annular gap 3 between the high-pressure shell 1 and the internals 2 of the synthesis tower, thereby removing the heat transferred from the internals 2 to the high-pressure shell 1 and preventing the high-pressure shell 1 from overheating; then it enters the bottom cavity of the internals 2 through the small holes in the tower bottom distribution plate 4 and merges with the N2 main line gas; The N2 main line gas enters from the bottom of the synthesis tower, first passes through the distribution baffle 12 and then enters the small holes of the bottom head distribution plate of the internal part 2, and merges with the N1 annular gap 3 gas.

[0049] The gas after the N1 annular gap 3 gas and the N2 main line gas merge enters the tower bottom heat exchanger 11 for heat exchange, and the gas after heat exchange merges with other gases entering the tower and enters the catalyst bed to react.

[0050] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the invention to the precise forms disclosed, and it is apparent that many variations and modifications are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the invention and various options and modifications. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A temperature control method for a green electricity-to-green ammonia synthesis tower, comprising annular gap gas and main line gas, wherein the annular gap gas and main line gas are process gas from a compressor outlet, and the annular gap gas enters the annular gap of the synthesis tower wall, characterized in that: The annular gap air flow is controlled to be stably maintained at a predetermined value so that the high-pressure shell temperature fluctuation range is ≤25°C. The predetermined value is 4%~6% of the total air intake at 100% load, and the annular gap air flow is allowed to fluctuate within ≤±12.5%.

2. The method according to claim 1, wherein: The synthesis tower comprises a high-pressure shell (1) and an internal part (2) sleeved in the high-pressure shell, an annular gap (3) is provided between the high-pressure shell (1) and the internal part (2), an annular gap gas inlet is provided at the upper part of the high-pressure shell (1), and a main line gas inlet is provided at the bottom head; and is characterized in that it comprises the following steps: The annular gap gas enters the annular gap (3) through the annular gap gas inlet, flows downward along the annular gap (3), passes through the small holes of the tower bottom distribution plate (4), and merges with the main line gas entering the small holes of the internal bottom head distribution plate (5) to enter the tower bottom heat exchanger (11) for heat exchange; The main line gas enters the bottom of the synthesis tower through the main line gas inlet, passes through the small holes of the internal bottom head distribution plate (5) and the annular gap gas entering the small holes of the tower bottom distribution plate (4), and enters the tower bottom heat exchanger (11) for heat exchange; The annular gap gas flow is controlled to be stably maintained at 5% of the total gas flow, and the allowable fluctuation range is ≤±12.5%; The opening of the main line gas branch valve is fixed after startup and commissioning, and the flow is passively adjusted according to load fluctuations.

3. The method according to claim 1 or 2, characterized in that: The annular gap gas and the main line gas maintain independent flow paths before entering the tower bottom distribution plate (4) and the internal bottom head distribution plate (5), and merge into a cavity surrounded by the tower bottom distribution plate (4), the internal bottom head distribution plate (5), and the tower bottom heat exchanger (11).

4. The method according to claim 1 or 2, characterized in that: The main line gas flow is the fixed valve opening determined after commissioning and remains unchanged.

5. A temperature control device for a green electricity-based green ammonia synthesis tower adapted to the control method of claim 1, characterized in that: The annular gap air branch is provided with a flow regulating device (13) for maintaining the flow of the annular gap air branch constant at 4% to 6% of the total air intake at 100% load.

6. The device according to claim 5, characterized in that: include: The annular gap (3) between the high-pressure shell (1) and the internal part (2) is provided with an annular gap gas inlet at the top and is connected to the small hole of the tower bottom distribution plate (4) at the bottom; the main line gas inlet at the bottom head of the synthesis tower is connected to the small hole of the internal part bottom head distribution plate (5); the annular gap gas and the main line gas are derived from the process gas at the compressor outlet.

7. The device according to claim 6, characterized in that: The aperture of the small holes of the tower bottom distribution plate (4) is Φ10-Φ25, and the opening rate is 20%-30%; the aperture of the small holes of the internal bottom head distribution plate (5) is Φ10-Φ25, and the opening rate is 20%-30%, and the small holes are distributed in concentric circles, and the spacing between adjacent circles is 2-4 times the aperture.

8. The device according to claim 5, characterized in that: The flow regulating device (13) comprises a flow meter, a regulating valve and a controller, and achieves flow fluctuation ≤±5%.

9. The device according to claim 5, characterized in that: It also includes a temperature protection system. When it is detected that the maximum temperature of the annular gap (3) is greater than the maximum operating temperature of the high-pressure shell, the N1 annular gap gas is forced to be fully opened to cool the high-pressure shell.

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