Flexible ammonia synthesis process

Abstract

This invention discloses a flexible ammonia synthesis process. The feed gas, after preheating, enters a temperature-controlled ammonia synthesis tower, where it reacts under the action of a catalyst. After the reaction, the gas recovers heat energy through an outlet waste boiler, undergoes multi-stage cooling, and then enters an ammonia separator. Liquid ammonia is obtained at the bottom, while the non-condensable gas at the top is pressurized by a circulating compressor and returned to the inlet of the temperature-controlled ammonia synthesis tower. In the tower, the feed gas enters through the feed gas inlet and passes radially from the outside in through a distribution plate, catalyst bed section I, another distribution plate, and catalyst bed section II, undergoing heat exchange and reaction simultaneously. The reacting gases converge at the center and are then exited through the reaction gas outlet at the bottom. This invention features a simple process, easy control, low equipment investment and operating costs, energy saving and consumption reduction, high reaction efficiency, relaxed reaction conditions, and the bed is less prone to overheating or temperature loss under high loads. The system can maintain stable operation even with fluctuations in feed gas flow rate of 0–120%.

Description

Technical Field

[0001] This invention belongs to the field of renewable energy and clean energy conversion, and specifically relates to a flexible ammonia synthesis process. Background Technology

[0002] my country's synthetic ammonia industry emits 219 million tons of CO2, with coal-based synthetic ammonia, accounting for 75% of the total, emitting 4.2 tons of CO2 per ton of NH3. Developing new processes to reduce the overall energy consumption of traditional synthetic ammonia plants is beneficial for reducing carbon emissions. The use of renewable energy to electrolyze water to produce hydrogen, followed by a green hydrogen-green ammonia process for storage, transportation, and conversion, has shown promising application prospects.

[0003] Currently, my country's renewable energy sources such as wind and solar power are developing rapidly. However, renewable energy power generation is characterized by intermittency and volatility, making it difficult to integrate renewable electricity into the grid on a large scale. Furthermore, the hydrogen produced by water electrolysis also exhibits volatility. Therefore, to achieve stable production of green hydrogen and green ammonia, the ammonia synthesis unit must be able to withstand wide load fluctuations.

[0004] Currently, most industrial ammonia synthesis plants, both domestically and internationally, employ multi-stage adiabatic interlayer heat exchange ammonia synthesis towers. These towers typically have multiple catalyst layers with heat exchangers between them, resulting in a highly complex reactor structure, difficult maintenance, and high equipment costs. Furthermore, the reaction pressure in ammonia synthesis towers is usually between 15 MPaG and 20 MPaG, leading to high energy consumption. In particular, the stacked arrangement of the beds within the reactor makes it easy for issues such as bed connections, sealing, thermal stress, and gas transport to cause a decrease in net ammonia value, and even risks like bed overheating and reaction runaway, especially during low-load fluctuations in the feed gas flow. This limits their application in green ammonia applications.

[0005] Patent CN115893446 discloses a multi-bed isothermal ammonia synthesis reactor with built-in multi-stage radial catalyst beds and a water-controlled reactor structure at the end, which reduces the height of the equipment. However, the gas flow on the shell and tube side inside the reactor is complex, the bed resistance is high, and the multiple cold gas pipes can easily cause uneven gas mixing, especially under low load fluctuations. At the same time, the steam pressure level produced by the water heat transfer tube bundle reaches 12 MPaG, resulting in high equipment cost.

[0006] Patent CN113461027 discloses a low-pressure ammonia synthesis tower and a renewable energy low-pressure ammonia synthesis system. The reactor outer sleeve is fitted with multiple catalyst frames, and each catalyst frame contains a catalyst bed. This structure is conducive to efficient heat transfer and preheating of raw material gas. However, the reactor is equipped with two auxiliary gas inlet pipes, which makes the structure complex and prone to overheating.

[0007] Patent CN202410264234.0 discloses a flexible control system and control method for synthesizing green ammonia, which adds an ammonia cracking unit. When operating at low load, the ammonia cracking unit is started to produce raw gas, but this significantly increases the complexity of the device and the energy consumption of operation.

[0008] Patent CN202410021111.4 discloses a system for dynamically synthesizing green ammonia from new energy sources and its operation method, including an ammonia synthesis tower and multiple ammonia synthesis regulating towers. When the output of the new energy source fluctuates and decreases, causing the load of the ammonia synthesis tower to drop to 10-50%, the synthesized ammonia gas is returned to the ammonia synthesis tower through the first ammonia synthesis regulating tower to maintain the normal operation of the tower. When the load of the first ammonia synthesis regulating tower drops to 10-50%, the ammonia synthesis tower stops operating, and the synthesized ammonia gas is returned to the first ammonia synthesis regulating tower through the second ammonia synthesis regulating tower to maintain the normal operation of the tower.

[0009] Patent CN201710325686.5 describes a low-pressure ammonia synthesis process in which the mixed gas exiting the first ammonia synthesis tower enters the second ammonia synthesis tower filled with ruthenium-based catalyst for secondary ammonia synthesis. This process uses two ammonia synthesis reactors, requires heat exchangers to transfer heat externally, and does not maximize the efficiency of the catalyst.

[0010] Patent CN202310675830.3 discloses a green ammonia synthesis system and method. By connecting the outlet of the syngas compressor to the heat exchanger, connecting the heat exchanger to the outlet pipeline of the ammonia synthesis tower, and connecting the water cooler and the cold exchanger to the inlet of the syngas compressor, a flexible adjustment link is formed, providing a flexible and adjustable load ammonia synthesis process. However, the flexible load adjustment is only possible within the range of 10% to 100%.

[0011] Patent CN202310092638.1 discloses a molten salt heat transfer ammonia synthesis process, in which molten salt is pumped into the shell side of an ammonia synthesis tower using a molten salt circulation pump, and a mixed gas enters the tube side from the top of the ammonia synthesis tower. Under the action of a catalyst, hydrogen and nitrogen in the mixed gas undergo an ammonia synthesis reaction, and the heat released by the reaction is removed by the molten salt in the shell side. However, the reaction pressure still needs to be 10-15 MPaG, and it is not possible to flexibly adjust the load under large-scale load changes. Summary of the Invention

[0012] The purpose of this invention is to solve the above-mentioned technical problems and provide a flexible ammonia synthesis process that is simple, easy to control, has low equipment investment and operating costs, saves energy and reduces consumption, has high reaction efficiency, allows for relaxed reaction conditions, is not prone to bed overheating or loss of temperature under high load, and can maintain stable system operation even under fluctuations of 0-120% in the raw material flow rate.

[0013] The technical solution of this invention is as follows: the raw gas is preheated and then enters the temperature-controlled ammonia synthesis tower to react under the action of a catalyst. After the reaction, the gas recovers heat energy through the outlet waste boiler, and then enters the ammonia separation tank after multi-stage cooling. Liquid ammonia product is obtained at the bottom, and the non-condensable gas at the top is returned to the inlet of the temperature-controlled ammonia synthesis tower after being pressurized by the circulating compressor.

[0014] The temperature-controlled ammonia synthesis tower has a raw material gas inlet at the top and a reaction gas outlet at the bottom. The tower contains two radially connected catalyst bed sections, Section I and Section II. Distribution plates are installed at the inlets of both sections. Section I, located on the outer layer, is filled with an iron-based ammonia synthesis catalyst and has multiple heat exchange tubes. Section II, located on the inner layer, is filled with a Ru-based ammonia synthesis catalyst and also has multiple heat exchange tubes. The raw material gas enters the tower through the raw material gas inlet and passes radially from the outside in through the distribution plate, Section I, the distribution plate, and Section II, undergoing heat exchange and reaction simultaneously. The reaction gas converges at the center and exits through the reaction gas outlet at the bottom. The temperature-controlled medium in the heat exchange tubes is heat transfer oil or molten salt.

[0015] The core-to-core distance of the heat exchange tubes in section I of the catalyst bed is 45–60 mm, and the wall-to-wall distance of the heat exchange tubes in section II of the catalyst bed is 50–80 mm.

[0016] The radial thickness of catalyst bed section I is 2 / 3 to 4 / 5 of the total radial thickness of the catalyst bed, and the radial thickness of catalyst bed section II is 1 / 5 to 1 / 3 of the total radial thickness of the catalyst bed.

[0017] The inlet temperature of the temperature-controlled ammonia synthesis tower is 320–380℃, the outlet temperature of catalyst bed I is 300–420℃, the outlet temperature of catalyst bed II is 300–400℃, and the reaction pressure is 7.0–13.5 MPaG.

[0018] The Ru-based ammonia synthesis catalyst uses rare earth modified carbon material as a support and Ru-rare earth dual components as active components.

[0019] The preparation method of the Ru-based ammonia synthesis catalyst is as follows:

[0020] (1) Preparation of rare earth modified carbon material carrier Supp-M: Rare earth precursors were loaded onto a carbon material carrier by impregnation to obtain rare earth modified carbon material powder Supp-F. Then, Supp-F powder was placed on a partition plate inside a reactor by hydrothermal induction. The reactor was heated to 150-210℃ and treated for 8 hours to obtain powder Supp-S. Supp-S was then treated at 300-350℃ for 4 hours under a hydrogen atmosphere to obtain rare earth modified carbon material carrier Supp-M. The rare earth carrier loading amount accounts for 0.001-0.010 times the specific surface area of ​​the carbon material carrier. The rare earth precursor is two or three of lanthanum nitrate, yttrium nitrate, cerium nitrate, and scandium nitrate.

[0021] (2) Preparation of Ru-rare earth dual-active component ammonia synthesis catalyst: Ru and rare earth active components were prepared into a precursor solution. Ru-rare earth was loaded onto rare earth modified carbon material support Supp-M by vacuum ultrasonic impregnation method, and then calcined to obtain Ru-rare earth dual-active component ammonia synthesis catalyst. The mass ratio of Ru to rare earth active component was 0.003:1 to 0.05:1; the mass ratio of Ru to rare earth modified carbon material support Supp-M was 0.001:1 to 0.005:1; the rare earth active component was one of lanthanum nitrate, yttrium nitrate, cerium nitrate, and scandium nitrate.

[0022] In the preparation method of the catalyst, the calcination conditions in step (2) are as follows: first, calcination is carried out at 150-300℃ using a H2 / Ar mixed gas atmosphere, then at 300-350℃ using an O2 / N2 atmosphere, and finally at 350-50℃ using an air atmosphere.

[0023] The preheating process of the raw gas includes: the raw gas is preheated by inlet and outlet heat exchangers and reaction gas heaters in sequence and then sent to the temperature-controlled ammonia synthesis tower; the reaction gas exiting the controlled synthesis tower recovers heat energy through the outlet waste boiler and then enters the ammonia separation tank after multi-stage cooling; the multi-stage cooling process includes the reaction gas exchanging heat with the raw gas through inlet and outlet heat exchangers and then being further cooled by water coolers and cold exchangers, and finally entering the ammonia cryotherm for deep cooling.

[0024] The non-condensable gas at the top of the ammonia separator first exchanges heat with the reaction gas through a cold exchanger, then is pressurized by a circulating compressor, and then mixed with the raw material gas before being preheated by the inlet and outlet heat exchangers and the reaction gas heater before being sent to the temperature-controlled ammonia synthesis tower.

[0025] When the raw material gas flow rate is between 11% and 120% load, the temperature-controlled medium exiting the temperature-controlled ammonia synthesis tower is sent to the steam generator to produce high-pressure steam, and then returned to the temperature-controlled ammonia synthesis tower via the temperature-controlled medium storage tank. When the raw material gas flow rate is between 0 and 10% load, the temperature-controlled medium exiting the temperature-controlled ammonia synthesis tower enters the temperature-controlled medium storage tank via the bypass of the steam generator, and is then returned to the temperature-controlled ammonia synthesis tower.

[0026] The control medium exiting the temperature-controlled medium storage tank is divided into two streams. The first stream enters the temperature-controlled ammonia synthesis tower to transfer heat, and the second stream enters the reaction gas heater to preheat the raw material gas before returning to the temperature-controlled medium storage tank.

[0027] When the raw material gas flow rate is between 31% and 110% of the load, the flow rate of the second temperature control medium is 3% to 8% of the total flow rate; when the raw material gas flow rate is between 0 and 30% of the load, the flow rate of the second temperature control medium is 30% to 40% of the total flow rate.

[0028] When the feed gas flow rate is between 31% and 120% load, all the reaction gas enters the inlet and outlet waste boilers to produce high-pressure steam; when the feed gas flow rate is between 0 and 30% load, 70% to 90% of the reaction gas bypasses the outlet waste boiler, and the remainder enters and exits the waste boilers.

[0029] A flow regulation loop is installed at the circulating compressor. When the raw material gas flow rate is 0-10% at low load, 81-100% of the non-condensable gas is introduced into the flow regulation loop of the circulating compressor for circulation, and the remaining non-condensable gas is introduced into the circulating compressor to maintain low load operation. When the raw material gas flow rate is 11-20% at load, all the non-condensable gas is introduced into the circulating compressor.

[0030] When the raw gas flow rate is running at 0-10% load, the temperature control medium storage tank heats the incoming control medium.

[0031] To address the problems existing in the background technology, the inventors made the following improvements:

[0032] 1) Improvements were made to the arrangement and heat exchange method of the catalyst bed in the temperature-controlled ammonia synthesis tower: On the one hand, considering the characteristics of the ammonia synthesis reaction, which has a high inlet nitrogen concentration and a large amount of heat release, while the outlet nitrogen concentration is low and the heat release is small, two radially connected catalyst bed sections, Section I and Section II, were set up. Compared with the axially arranged adiabatic interlayer heat exchange structure, the equipment structure is simpler, the manufacturing cost is lower, and the feed gas is introduced into the catalyst bed from the outer periphery to the center, resulting in a larger introduction area, more uniform distribution, higher reaction efficiency, and higher reactor heat transfer efficiency. On the other hand, the outer catalyst bed section I is filled with conventional iron-based ammonia synthesis catalysts, such as the pre-reduction catalyst produced by Clariant. These catalysts are low in cost, have suitable activity, and are suitable for feed gas with high nitrogen concentration and large heat release. Combined with a closer tube-to-heater spacing and a temperature control medium, bed temperature runaway can be effectively avoided. The inner catalyst bed section II is filled with a low-temperature, high-activity Ru-based ammonia synthesis catalyst. These catalysts can exhibit good ammonia synthesis performance at lower temperatures and concentrations, improving the single-pass conversion rate. This radial double-layer catalyst bed structure can minimize costs while improving single-pass conversion rate and net ammonia value at the outlet. Furthermore, the feed gas does not require an additional auxiliary inlet; instead, it enters the temperature-controlled ammonia synthesis process in a single stream from the top, greatly reducing the difficulty of control.

[0033] 2) The second stage is filled with a low-temperature, high-activity Ru-based ammonia synthesis catalyst. This type of catalyst is particularly preferred for its Ru-rare earth dual-active component composition. It can be prepared using the aforementioned method. It uses rare earth-modified carbon material as a support and Ru-rare earth dual components as the active components. It possesses a stable nano-interface structure and surface defect sites. Utilizing the electron-rich structure of the carbon support and the oxygen vacancies of the rare earth elements, the coupled effects of both are beneficial for activating N2 molecules and improving the catalyst's low-temperature activity. It exhibits excellent ammonia synthesis performance under low-pressure (7.0–13.5 MPaG) and low-temperature (350–380℃) reaction conditions, with a single-pass ammonia net value at the outlet reaching 25–34%. Furthermore, the radial thickness of the first stage of the catalyst bed is greater than that of the second stage, which adapts to high loads, ensures reaction efficiency, and further reduces catalyst costs.

[0034] 3) To address the issue of wide load fluctuations (0-120%) in upstream feed gas as described in the background technology, in addition to improvements to the temperature-controlled ammonia synthesis tower, the inventors have also implemented several control measures to achieve flexible ammonia synthesis, including:

[0035] The temperature control medium uses heat transfer oil or molten salt, and a bypass of the steam generator is provided. When the raw material gas flow rate is between 11% and 120% load, the temperature control medium exiting the temperature-controlled ammonia synthesis tower is sent to the steam generator to produce high-pressure steam, and then returned to the temperature-controlled ammonia synthesis tower via the temperature control medium storage tank. When the raw material gas flow rate is between 0 and 10% load, the heat of reaction is relatively small, and the temperature control medium exiting the temperature-controlled ammonia synthesis tower enters the temperature control medium storage tank via the bypass of the steam generator, without producing high-pressure steam, and is directly returned to the temperature-controlled ammonia synthesis tower.

[0036] The control medium exiting the temperature-controlled medium storage tank is divided into two streams. The first stream enters the temperature-controlled ammonia synthesis tower for heat transfer, and the second stream enters the reaction gas heater to preheat the feed gas before returning to the temperature-controlled medium storage tank. When the reaction load is between 31% and 110%, the second stream of temperature-controlled medium maintains a flow rate of 3% to 8% of the total flow rate. When the reaction gas load increases, the flow rate of the temperature-controlled medium can be directly increased to better adapt to fluctuations in the ammonia synthesis operating conditions. When the reaction load is between 0% and 30%, the flow rate of the second stream of temperature-controlled medium is 30% to 40% of the total flow rate to control the preheating of the reaction gas to reach the reactor inlet temperature, avoiding the impact on catalyst performance during low-load operation and improving catalyst lifespan.

[0037] A bypass is set up for the outlet waste heat boiler. When operating at 0-30% load, most of the reaction gas goes through the bypass of the outlet waste heat boiler to avoid affecting the bed inlet temperature at low load. When operating at 31%-120% load, most of the reaction gas inlet and outlet waste heat boilers produce high-pressure steam.

[0038] A flow regulation loop is installed at the circulating compressor. When the raw material gas flow rate is 0-10% at low load, the circulating compressor maintains low load operation. At the same time, non-condensable gas with a flow rate of 81-100% is introduced into the flow regulation loop of the circulating compressor for circulation.

[0039] The temperature-controlled medium storage tank is equipped with a heating device. When the raw material gas flow rate is between 0-10% load, the temperature-controlled medium storage tank heats the incoming temperature-controlled medium. The temperature of the temperature-controlled medium can be flexibly controlled according to the reaction temperature requirements of the temperature-controlled ammonia synthesis tower to adapt to low-load operation.

[0040] 4) The reactant gas is introduced into the outlet waste boiler to produce high-pressure steam, and then into the inlet and outlet heat exchangers to preheat the feed gas. The reactant gas is also introduced into the cold exchanger to preheat the non-condensable gas. The temperature control medium exiting the reactor is introduced into the steam generator to produce high-pressure steam, and a portion of the temperature control medium is introduced into the reactant gas heater to preheat the feed gas. Through multiple multi-stage heat exchangers, sufficient waste heat recovery is achieved, effectively saving energy and reducing operating costs.

[0041] In summary, the process of this invention is extremely simple, with low equipment investment and operating costs. It can fully adapt to a wide range of raw material gas load fluctuations from 0% to 120% while using a single feed stream, offering great operational flexibility. The system can maintain a constant temperature even at zero load, and when restarting, the process gas can be directly introduced to the target load, greatly simplifying load adjustment operations. The ammonia synthesis reaction pressure can be 7.0–13.5 MPaG, equipment investment can be reduced by more than 30%, operating costs can be reduced by 15%, the reactor has a high single-pass conversion rate, and the single-pass ammonia net value at the outlet reaches 25–34%, demonstrating significant energy-saving and consumption-reducing effects.

[0042] Instruction manual illustrations

[0043] Figure 1 This is a process flow diagram of the present invention.

[0044] Figure 2 This is a schematic diagram of the structure of a temperature-controlled ammonia synthesis tower.

[0045] Among them, R101 is the temperature-controlled ammonia synthesis tower, E101 is the inlet and outlet heat exchanger, E102 is the reaction gas heater, E103 is the outlet waste boiler, E104 is the water cooler, E105 is the cold exchanger, E106 is the ammonia cryocooler, E108 is the bypass cooler, E201 is the steam generator, E301 is the ammonia refrigeration station, V101 is the steam drum, V102 is the ammonia separator, and V201 is the temperature-controlled medium storage tank. A is the bypass of the steam generator, B is the bypass of the outlet waste boiler, and C is the flow regulation loop.

[0046] 1 is the feed gas inlet; 2 is the temperature control medium outlet; 3 is the tower wall; 4 is the distribution plate; 5 is the distribution plate; 6 is the catalyst bed section II; 7 is the catalyst bed section I; 8 is the temperature control medium inlet; 9 is the reaction gas outlet; 10 is the heat exchange tube. Detailed Implementation

[0047] The process of the present invention will be further explained below with reference to the accompanying drawings:

[0048] Example 1: Ru-Rare Earth Dual-Active Component Ammonia Synthesis Catalyst

[0049] (1) Preparation of rare earth modified carbon material carrier Supp-M: The rare earth precursor was loaded onto the carbon material carrier by impregnation method to obtain rare earth modified carbon material powder Supp-F. Then, the powder Supp-F was placed on the inner plate of the reactor by hydrothermal induction method. The reactor was heated to 210℃ and treated for 8h to obtain powder Supp-S. Then, Supp-S was treated at 320℃ for 4h under hydrogen atmosphere to obtain rare earth modified carbon material carrier Supp-M (1). The rare earth carrier loading amount accounts for 0.001 times the specific surface area of ​​the carbon material carrier. The rare earth precursor is lanthanum nitrate and yttrium nitrate.

[0050] (2) Preparation of Ru-rare earth dual-active component ammonia synthesis catalyst: Ru and rare earth active components were prepared into a precursor solution. Ru-rare earth was loaded onto rare earth modified carbon material support Supp-M by vacuum ultrasonic impregnation. Then, it was calcined under the following conditions: first, calcined at 150-300℃ in an H2 / Ar mixed atmosphere, then calcined at 300-350℃ in an O2 / N2 atmosphere, and finally calcined at 350-50℃ in an air atmosphere to obtain Ru-rare earth dual-active component ammonia synthesis catalyst. The mass ratio of Ru to rare earth active component was 0.003:1; the mass ratio of Ru to rare earth modified carbon material support Supp-M was 0.005:1; and the rare earth active component was lanthanum nitrate.

[0051] Example 2: Ru-Rare Earth Dual-Active Component Ammonia Synthesis Catalyst

[0052] (1) Preparation of rare earth modified carbon material carrier Supp-M: Rare earth precursors were loaded onto carbon material carriers by impregnation method to obtain rare earth modified carbon material powder Supp-F. Then, Supp-F powder was placed on the inner baffle of the reactor by hydrothermal induction method. The reactor was heated to 150℃ and treated for 8h to obtain powder Supp-S. Supp-S was then treated at 300℃ for 4h under hydrogen atmosphere to obtain rare earth modified carbon material carrier Supp-M. The rare earth carrier loading amount accounts for 0.010 times the specific surface area of ​​the carbon material carrier. The rare earth precursors are yttrium nitrate, cerium nitrate, and scandium nitrate.

[0053] (2) Preparation of Ru-rare earth dual-active component ammonia synthesis catalyst: Ru and rare earth active components were prepared into a precursor solution. Ru-rare earth was loaded onto rare earth modified carbon material support Supp-M by vacuum ultrasonic impregnation. Then, it was calcined under the following conditions: first, calcined at 150-300℃ in an H2 / Ar mixed atmosphere, then calcined at 300-350℃ in an O2 / N2 atmosphere, and finally calcined at 350-50℃ in an air atmosphere to obtain Ru-rare earth dual-active component ammonia synthesis catalyst. The mass ratio of Ru to rare earth active component was 0.05:1; the mass ratio of Ru to rare earth modified carbon material support Supp-M was 0.002:1; and the rare earth active component was one of yttrium nitrate.

[0054] Example 3: Ru-Rare Earth Dual-Active Component Ammonia Synthesis Catalyst

[0055] (1) Preparation of rare earth modified carbon material carrier Supp-M: Rare earth precursors were loaded onto carbon material carriers by impregnation method to obtain rare earth modified carbon material powder Supp-F. Then, Supp-F powder was placed on the inner baffle of the reactor by hydrothermal induction method. The reactor was heated to 190℃ and treated for 8h to obtain powder Supp-S. Supp-S was then treated at 350℃ for 4h under hydrogen atmosphere to obtain rare earth modified carbon material carrier Supp-M. The rare earth carrier loading amount accounts for 0.0018 times the specific surface area of ​​the carbon material carrier. The rare earth precursor is yttrium nitrate or cerium nitrate.

[0056] (2) Preparation of Ru-rare earth dual-active component ammonia synthesis catalyst: Ru and rare earth active components were prepared into a precursor solution. Ru-rare earth was loaded onto rare earth modified carbon material support Supp-M by vacuum ultrasonic impregnation. Then, it was calcined under the following conditions: first calcination at 150-300℃ in H2 / Ar mixed atmosphere, then calcination at 300-350℃ in O2 / N2 atmosphere, and finally calcination at 350-50℃ in air atmosphere to obtain Ru-rare earth dual-active component ammonia synthesis catalyst. The mass ratio of Ru to rare earth active component was 0.01:1; the mass ratio of Ru to rare earth modified carbon material support Supp-M was 0.005:1; and the rare earth active component was scandium nitrate.

[0057] Structure of temperature-controlled ammonia synthesis tower:

[0058] See also Figure 2 The temperature-controlled ammonia synthesis tower has a raw material gas inlet 1 at the top and a reaction gas outlet 9 at the bottom. Two radially connected catalyst bed sections, section I 7 and section II 6, are installed inside the tower. Distribution plates 4 and 5 are installed at the inlets of both sections, with channels of φ2 to φ5 mm evenly distributed on the distribution plates. Section I 7 is located on the outer layer and is filled with iron-based ammonia synthesis catalyst, and has multiple heat exchange tubes 10 with a core-to-core distance of 45 to 60 mm. Section II 6 is located on the inner layer and is filled with Ru-based ammonia synthesis catalyst, and has multiple heat exchange tubes 10 with a core-to-core distance of 50 to 80 mm. The raw material gas enters the tower through the raw material gas inlet 1 and passes radially from the outside to the inside, sequentially through distribution plate 4, section I 7, distribution plate 5, and section II 6, undergoing heat exchange and reaction simultaneously. The reaction gas converges at the center and is then exited through the reaction gas outlet 9 at the bottom. The temperature-controlled medium in the heat exchange tubes is heat transfer oil or molten salt. The lower end of the heat exchange tube is connected to the temperature control medium inlet 8, and the upper end is connected to the temperature control medium outlet 2.

[0059] The radial thickness of catalyst bed section I is 2 / 3 to 4 / 5 of the total radial thickness of the catalyst bed, and the radial thickness of catalyst bed section II is 1 / 5 to 1 / 3 of the total radial thickness of the catalyst bed.

[0060] Process Example:

[0061] See also Figure 1 and Figure 2 The feed gas (composed of a mixture of 75% hydrogen and 25% nitrogen by volume) from the upstream process is preheated sequentially through inlet and outlet heat exchangers E101 and reaction gas heater E102 before being fed into the temperature-controlled ammonia synthesis tower R101. In the temperature-controlled ammonia synthesis tower R101, the feed gas enters the tower through feed gas inlet 1 and flows downwards along the outer wall of the tower, simultaneously passing from the outside to the inside through distribution plate 4, catalyst bed section I 7, distribution plate 5, and catalyst bed section II 6. Simultaneously, heat is transferred through the heat exchange tubes during the reaction. The reaction gas converges at the center and is then exited through the reaction gas outlet 9 at the bottom. The temperature-controlled medium in the heat exchange tubes is heat transfer oil. The inlet temperature of the temperature-controlled ammonia synthesis tower E101 is controlled at 320–380°C, the outlet temperature of catalyst bed section I is 300–420°C, the outlet temperature of catalyst bed section II is 300–400°C, and the reaction pressure is 7.0–13.5 MPaG.

[0062] The reaction gas exiting the controlled synthesis tower R101 recovers heat energy and produces by-product steam through the outlet waste boiler E103. After being cooled by heat exchange with the raw material gas through the inlet and outlet heat exchangers E101, it is further cooled by the water cooler E104 and the cold exchanger E105 before entering the ammonia cryocooler E106 for deep cooling. Finally, it enters the ammonia separator V102 for gas-liquid separation, and liquid ammonia product is obtained at the bottom. The non-condensable gas at the top first exchanges heat with the reaction gas through the cold exchanger E105, then is pressurized by the circulating compressor C201, and then mixed with the raw material gas. After being preheated by the inlet and outlet heat exchangers E101 and the reaction gas heater E102, it is sent to the temperature-controlled ammonia synthesis tower R101.

[0063] Considering that the feed gas load of upstream processes varies from 0-120%, the specific flexible control measures are as follows:

[0064] When the raw material gas flow rate is between 11% and 120% load, the temperature-controlled medium exiting the temperature-controlled ammonia synthesis tower R101 is sent to the steam generator E201 to produce high-pressure steam, and then returned to the temperature-controlled ammonia synthesis tower R101 via the temperature-controlled medium storage tank V201. When the raw material gas flow rate is between 0 and 10% load, the temperature-controlled medium exiting the temperature-controlled ammonia synthesis tower R101 enters the temperature-controlled medium storage tank V201 via the bypass A of the steam generator, and is then returned to the temperature-controlled ammonia synthesis tower R101.

[0065] The control medium exiting the temperature-controlled medium storage tank V201 is divided into two streams. The first stream enters the temperature-controlled ammonia synthesis tower R101 for heat transfer, and the second stream enters the reaction gas heater E102 to preheat the raw material gas before returning to the temperature-controlled medium storage tank V201. The specific control measures are as follows: when the raw material gas flow rate is between 31% and 110% of the load, the flow rate of the second temperature-controlled medium is 3% to 8% of the total flow rate; when the raw material gas flow rate is between 0 and 30% of the load, the flow rate of the second temperature-controlled medium is 30% to 40% of the total flow rate.

[0066] When the feed gas flow rate is between 31% and 120% load, all the reaction gas enters the inlet and outlet waste boiler E103 to produce high-pressure steam; when the feed gas flow rate is between 0 and 30% load, 70% to 90% of the reaction gas flow rate passes through the bypass B of the outlet waste boiler, and the remainder enters and exits the inlet and outlet waste boiler E103.

[0067] A flow regulation loop C is set at the circulating compressor. When the raw material gas flow rate is 0-10% at low load, 81-100% of the non-condensable gas is introduced into the flow regulation loop C of the circulating compressor for circulation, and the remaining non-condensable gas is introduced into the circulating compressor C201 to maintain low load operation. When the raw material gas flow rate is 11-120% at load, all the non-condensable gas is introduced into the circulating compressor C201.

[0068] When the raw gas flow rate is between 0-10% load, the temperature control medium storage tank V201 (equipped with a heating device) heats the incoming control medium to meet the temperature control requirements in the temperature control ammonia synthesis tower R101. When the raw gas flow rate is between 11-120% load, the heating stops.

[0069] The boiler feedwater of the waste boiler E103 at the reactor outlet is dynamically adjusted. When the load is 0-30%, the opening of the boiler feedwater of the waste boiler E103 at the outlet is reduced, and the amount of by-product steam is reduced to avoid affecting the bed inlet temperature at low load. When the load is 31%-120%, the boiler feedwater valve of the waste boiler E103 at the outlet is opened wider, and the amount of by-product steam is increased to make reasonable use of the heat released by the reaction.

[0070] In Process Examples 1-3 of the above-described process embodiments, the catalyst bed I section is filled with iron-based ammonia synthesis catalyst (pre-reduction catalyst produced by Clariant). The catalyst bed II section is replaced with the corresponding three catalysts in the three embodiments. The reaction conditions and results are shown in Table 1. Comparative Examples 1 and 2 are the same as Process Example 1. The specific differences are shown in Table 1.

[0071] Table 1

[0072]

[0073] As can be seen from process examples 1 to 3, by using a temperature-controlled ammonia synthesis tower and the catalysts of examples 1 to 3, the net ammonia value can reach 23.8% and the high value can reach 32.2% under the corresponding reaction conditions. When operating at 0-120% load for peak shaving, the temperature of the entire bed is relatively stable.

[0074] In Comparative Example 1, the ammonia tower outlet temperature reached 430°C and the pressure was as high as 15 MPaG, while the net ammonia value at the outlet was only 19.5%, which was significantly lower than that in Process Example 1. The equipment investment and energy consumption of the equipment were higher, and when running at a low load of 10%, the bed was prone to cross-temperature conditions.

[0075] In Comparative Example 2, if the II-stage bed is filled with the same catalyst as the I-stage bed, under the same reaction conditions as in Process Example 1, the net ammonia value at the outlet is only 18.3%, which is lower than in Process Example 1, and the low-temperature control effect of the temperature-controlled ammonia synthesis tower is not effectively utilized.

Claims

1. A flexible ammonia synthesis process, characterized in that, The raw gas is preheated and then enters the temperature-controlled ammonia synthesis tower. Under the action of the catalyst, the gas reacts. After the reaction, the gas recovers heat energy through the outlet waste boiler and then enters the ammonia separation tank after multi-stage cooling. Liquid ammonia product is obtained at the bottom, and the non-condensable gas at the top is returned to the inlet of the temperature-controlled ammonia synthesis tower after being pressurized by the circulating compressor. The temperature-controlled ammonia synthesis tower has a raw material gas inlet at the top and a reaction gas outlet at the bottom. The tower contains two radially connected catalyst bed sections, Section I and Section II. Distribution plates are installed at the inlets of both sections. Section I, located on the outer layer, is filled with an iron-based ammonia synthesis catalyst and has multiple heat exchange tubes. Section II, located on the inner layer, is filled with a Ru-based ammonia synthesis catalyst and also has multiple heat exchange tubes. The raw material gas enters the tower through the raw material gas inlet and passes radially from the outside in through the distribution plate, Section I, the distribution plate, and Section II, undergoing heat exchange and reaction simultaneously. The reaction gas converges at the center and exits through the reaction gas outlet at the bottom. The temperature-controlled medium in the heat exchange tubes is heat transfer oil or molten salt. The raw material gas is preheated by inlet and outlet heat exchangers and reaction gas heaters before being sent to the temperature-controlled ammonia synthesis tower. The reaction gas exiting the temperature-controlled ammonia synthesis tower recovers heat energy through the outlet waste boiler and then enters the ammonia separation tank after multi-stage cooling. The multi-stage cooling process includes the reaction gas exchanging heat with the raw material gas through inlet and outlet heat exchangers, then being further cooled by water coolers and cold exchangers, and finally entering the ammonia cryotherm for deep cooling. When the raw material gas flow rate is between 11% and 120% load, the temperature-controlled medium exiting the temperature-controlled ammonia synthesis tower is sent to the steam generator to produce high-pressure steam, and then returned to the temperature-controlled ammonia synthesis tower via the temperature-controlled medium storage tank. When the raw material gas flow rate is between 0 and 10% load, the temperature-controlled medium exiting the temperature-controlled ammonia synthesis tower enters the temperature-controlled medium storage tank via the bypass of the steam generator, and is then returned to the temperature-controlled ammonia synthesis tower.

2. The flexible ammonia synthesis process as described in claim 1, characterized in that, The core-to-core distance of the heat exchange tubes in section I of the catalyst bed is 45–60 mm, and the wall-to-wall distance of the heat exchange tubes in section II of the catalyst bed is 50–80 mm.

3. The flexible ammonia synthesis process as described in claim 1, characterized in that, The radial thickness of catalyst bed section I is 2 / 3 to 4 / 5 of the total radial thickness of the catalyst bed, and the radial thickness of catalyst bed section II is 1 / 5 to 1 / 3 of the total radial thickness of the catalyst bed.

4. The flexible ammonia synthesis process as described in claim 3, characterized in that, The inlet temperature of the temperature-controlled ammonia synthesis tower is 320–380℃, the outlet temperature of catalyst bed I is 300–420℃, the outlet temperature of catalyst bed II is 300–400℃, and the reaction pressure is 7.0–13.5 MPaG.

5. The flexible ammonia synthesis process as described in claim 1, characterized in that, The Ru-based ammonia synthesis catalyst uses rare earth modified carbon material as a support and Ru-rare earth dual components as active components.

6. The flexible ammonia synthesis process as described in claim 5, characterized in that, The preparation method of the Ru-based ammonia synthesis catalyst is as follows: (1) Preparation of rare earth modified carbon material carrier Supp-M: Rare earth precursors were loaded onto carbon material carriers by impregnation to obtain rare earth modified carbon material powder Supp-F. Then, powder Supp-F was placed on the inner baffle of the reactor and treated again by hydrothermal induction. The reactor was heated to 150-210℃ and treated for 8 hours to obtain powder Supp-S. Then, Supp-S was treated at 300-350℃ for 4 hours under hydrogen atmosphere to obtain rare earth modified carbon material carrier Supp-M. The rare earth carrier loading amount accounts for 0.001-0.010 times the specific surface area of ​​the carbon material carrier. The rare earth precursor is two or three of lanthanum nitrate, yttrium nitrate, cerium nitrate, and scandium nitrate. (2) Preparation of Ru-rare earth dual-active component ammonia synthesis catalyst: Ru and rare earth active components were prepared into a precursor solution. Ru-rare earth was loaded onto rare earth modified carbon material support Supp-M by vacuum ultrasonic impregnation. Then, the Ru-rare earth dual-active component ammonia synthesis catalyst was obtained by programmed temperature calcination. The mass ratio of Ru to rare earth active component was 0.003:1 to 0.05:1; the mass ratio of Ru to rare earth modified carbon material support Supp-M was 0.001:1 to 0.005:1; the rare earth active component was one of lanthanum nitrate, yttrium nitrate, cerium nitrate, and scandium nitrate.

7. The flexible ammonia synthesis process as described in claim 6, characterized in that, In the preparation method of the catalyst, the programmed temperature calcination conditions in step (2) are as follows: first, calcination is carried out at 150-300℃ using an H2 / Ar mixed gas atmosphere, then at 300-350℃ using an O2 / N2 atmosphere, and finally at 350-50℃ using an air atmosphere.

8. The flexible ammonia synthesis process as described in claim 1, characterized in that, The non-condensable gas at the top of the ammonia separator first exchanges heat with the reaction gas through a cold exchanger, then is pressurized by a circulating compressor, and then mixed with the raw material gas before being preheated by the inlet and outlet heat exchangers and the reaction gas heater before being sent to the temperature-controlled ammonia synthesis tower.

9. The flexible ammonia synthesis process as described in claim 1, characterized in that, The control medium exiting the temperature-controlled medium storage tank is divided into two streams. The first stream enters the temperature-controlled ammonia synthesis tower to transfer heat, and the second stream enters the reaction gas heater to preheat the raw material gas before returning to the temperature-controlled medium storage tank.

10. The flexible ammonia synthesis process as described in claim 9, characterized in that, When the raw material gas flow rate is between 31% and 120% of the load, the flow rate of the second temperature control medium is 3% to 8% of the total flow rate; when the raw material gas flow rate is between 0 and 30% of the load, the flow rate of the second temperature control medium is 30% to 40% of the total flow rate.

11. The flexible ammonia synthesis process as described in claim 1, characterized in that, When the feed gas flow rate is between 31% and 120% load, all the reaction gas enters the inlet and outlet waste boilers to produce high-pressure steam; when the feed gas flow rate is between 0 and 30% load, 70% to 90% of the reaction gas flow rate bypasses the outlet waste boiler, and the remainder enters and exits the waste boilers.

12. The flexible ammonia synthesis process as described in claim 1, characterized in that, A flow regulation loop is installed at the circulating compressor. When the raw material gas flow rate is 0-10% at low load, 81-100% of the non-condensable gas is introduced into the flow regulation loop of the circulating compressor for circulation, and the remaining non-condensable gas is introduced into the circulating compressor to maintain low load operation. When the raw material gas flow rate is 11-120% at load, all non-condensable gas is introduced into the circulating compressor.

13. The flexible ammonia synthesis process as described in claim 10, characterized in that, When the raw gas flow rate is running at 0-10% load, the temperature control medium storage tank heats the incoming control medium.

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