A low-temperature, low-pressure ammonia synthesis device and a renewable energy ammonia synthesis system

Abstract

The present invention discloses a low-temperature, low-pressure ammonia synthesis device and a renewable energy ammonia synthesis system. The low-temperature, low-pressure ammonia synthesis device includes a reactor outer tube, a raw gas inlet pipe, and a product gas outlet pipe. The reactor outer tube is provided with multiple catalyst frames, each of which is provided with a catalyst bed. An annular gas channel I is formed between the reactor outer tube and the catalyst frames, one end of which is connected to the raw gas inlet pipe. A central tube is provided within the catalyst bed, one end of which is connected to the product gas outlet pipe, and the other end is sealed and placed at the bottom of the bottom catalyst bed and connected to the bottom catalyst frame. A heat exchange tube bundle is arranged in the bottom catalyst frame, forming a one-way airflow channel that is connected in series between the catalyst frames. The product gas is discharged from the product gas outlet pipe through the central tube. The ammonia synthesis device of the present invention can perform efficient heat transfer, achieve accurate bed temperature control, facilitate the ammonia synthesis reaction, and has the advantages of energy saving and consumption reduction. The operating temperature range of the ammonia synthesis device is 300°C to 450°C, and the pressure range is 0.1MPa to 10MPa.

Description

Technical Field

[0001] The present invention relates to the technical field of clean energy conversion and storage, and in particular to a low-temperature and low-pressure ammonia synthesis device and a renewable energy ammonia synthesis system. Background Art

[0002] my country's renewable energy power generation industry, including wind and solar power, is currently experiencing rapid growth. However, these renewable energy sources are subject to significant fluctuations due to seasonality and weather conditions, making them incompatible with relatively stable electricity demand. Therefore, exploring new applications for renewable energy sources, which are difficult to connect to the grid, holds significant economic and social benefits.

[0003] Hydrogen production through water electrolysis can achieve large-scale, efficient consumption of renewable energy. Using hydrogen as an energy carrier can improve energy system resilience and enable energy redistribution across regions. However, due to its low density and difficulty in liquefying, currently more mature high-pressure hydrogen storage methods require 35-70 MPa, consuming significant compression work, and possessing a mass hydrogen storage density of only approximately 5%, resulting in high hydrogen storage and transportation costs.

[0004] Ammonia is one of the most basic chemical raw materials in modern industrial and agricultural production. It has the advantages of easy liquefaction, high volumetric energy density, no carbon emissions, non-flammability and high safety. It is expected to be used as an efficient hydrogen carrier in the new energy field to solve the bottleneck problem of hydrogen storage and transportation.

[0005] Modern industrial ammonia synthesis typically uses the Haber-Bosch process, where hydrogen and nitrogen are introduced into a high-temperature, high-pressure reactor for a catalytic reaction to produce ammonia. Traditionally, hydrogen is produced through the catalytic gasification / reforming of fossil fuels coupled with a water-gas shift reaction.

[0006] Currently, various synthetic ammonia reactors are only suitable for large-scale synthetic ammonia industry. They have high operating temperatures and pressures, high energy consumption, complex synthesis routes, multiple equipment, and large-scale installations, which limit the distributed, miniaturized application and flexible exploration of synthetic ammonia technology in the field of renewable energy. Summary of the Invention

[0007] The present invention aims to solve the problems of existing ammonia synthesis reaction devices and systems, such as high operating temperature and pressure, high energy consumption, complex synthesis routes, multiple equipment, and large device scale, and to provide an efficient and compact low-temperature and low-pressure ammonia synthesis device and a renewable energy ammonia synthesis system.

[0008] The present invention adopts the following technical solutions:

[0009] A low-temperature, low-pressure ammonia synthesis device comprises a reactor outer tube, the reactor outer tube being provided with a raw gas inlet pipe and a product gas outlet pipe, the reactor outer tube being provided with a central tube, n catalyst frames, and a cooling tank, wherein n ≥ 2, a unidirectional airflow channel being formed between the catalyst frames, and a first catalyst bed containing an ammonia synthesis catalyst being provided in each catalyst frame; the central tube being located at the circumferential center of the catalyst frame and penetrating the catalyst frame, one end of the central tube being connected to the product gas outlet pipe, the other end of the central tube being closed and disposed in the bottommost catalyst frame, the lower portion of the side wall of the central tube portion located at the bottommost catalyst frame being provided with a plurality of air holes circumferentially arranged. , the air holes are connected to the catalyst frame of the lowest layer; the cooling tank is located below the catalyst frame of the lowest layer, and a plurality of heat exchange tube bundles circumferentially passing through the interior of the catalyst frame of the lowest layer are arranged in the catalyst frame of the lowest layer, one end of each heat exchange tube bundle is respectively connected to the cooling tank, and the other end thereof is connected to the heat exchange tube outlet; the raw gas enters the uppermost catalyst frame through the raw gas inlet tube for the first ammonia synthesis reaction, and the mixture after the reaction passes through each catalyst frame in sequence through the unidirectional airflow channel, and finally enters the catalyst frame of the lowest layer, and after heat exchange and catalysis, the final product is discharged from the product gas outlet pipe; the heat exchange medium in each heat exchange tube bundle absorbs the reaction heat from the catalyst frame and is discharged from the heat exchange tube outlet.

[0010] The catalyst frames are arranged in an upper and lower spaced relationship within the outer tube of the reactor, and an annular airflow channel I is formed between the outer tube of the reactor and each of the catalyst frames; the lower end of the central tube is closed and arranged inside the lowest catalyst frame, the catalyst frame located at the lowest is connected to the central tube, and an annular airflow channel II is formed between the remaining catalyst frames and the central tube, and the annular airflow channel II is connected to the annular airflow channel I through the catalyst frame; after the raw gas undergoes an ammonia synthesis reaction through the uppermost catalyst frame, the reaction mixture passes through the catalyst frame below it in turn to undergo at least one ammonia synthesis reaction, and the final product is discharged from the product gas outlet pipe.

[0011] There are three catalyst frames, which are the first catalyst frame, the second catalyst frame and the third catalyst frame from top to bottom. The gas flow direction in the first catalyst frame and the second catalyst frame is radial, and the gas flow direction in the third catalyst frame is axial. The annular gap airflow channel II located on the inner part of the first catalyst frame is connected to the annular gap airflow channel II located on the inner part of the second catalyst frame, and the annular gap airflow channel I located on the outer part of the second catalyst frame is connected to the annular gap airflow channel I located on the outer part of the third catalyst frame.

[0012] A heat exchange chamber is provided between the second catalyst frame and the third catalyst frame. The upper part of the heat exchange chamber is closed, and the lower part is connected with the third catalyst frame, and a mixed gas inlet connected with the heat exchange chamber is provided at the bottom of the annular gap airflow channel I on the side part of the second catalyst frame; the heat exchange chamber is provided with the heat exchange tube bundle, the upper end of the heat exchange tube bundle passes through the heat exchange chamber and is connected with the heat exchange tube outlet, and the lower end passes downward through the third catalyst frame and is connected with the cooling tank; the raw gas enters the annular gap airflow channel I from the raw gas inlet pipe, and radially enters the first catalyst frame for preliminary ammonia synthesis reaction, and the reaction mixture I passes through the annular gap airflow channel II and radially enters the second catalyst frame for further reaction, and the reaction mixture II enters the heat exchange chamber through the annular gap airflow channel I and the mixed gas inlet in turn for heat exchange, and then enters the third catalyst frame for further heat exchange and reaction, and the final product is discharged from the product gas outlet pipe.

[0013] The outer cylinder of the reactor is also provided with a 1# auxiliary line air inlet pipe and a 2# auxiliary line air inlet pipe. After the synthetic ammonia product gas discharged from the product gas outlet pipe is liquefied and the liquid ammonia is separated, the remaining gas can be used as circulating gas to enter the synthetic ammonia device from the raw gas inlet pipe, the 1# auxiliary line air inlet pipe and the 2# auxiliary line air inlet pipe respectively; the 1# auxiliary line air inlet pipe is connected to the annular gap air flow channel II located on the inner side of the first catalyst frame, and the circulating gas entering from the 1# auxiliary line air inlet pipe is mixed with the mixture I and heat exchange is performed; the 2# auxiliary line air inlet pipe is connected to the annular gap air flow channel I located on the outer side of the second catalyst frame, and the circulating gas entering from the 2# auxiliary line air inlet pipe is mixed with the mixture II and heat exchange is performed.

[0014] A second catalyst bed containing a catalytic combustion catalyst is also provided in the annular gap airflow channel between the first catalyst frame and the annular gap airflow channel I. The second catalyst bed is arranged close to the first catalyst frame and is used to remove oxygen from the raw gas entering from the raw gas inlet pipe.

[0015] A plurality of heat exchange tube bundles passing through the interior of the third catalyst frame are arranged in the third catalyst frame, one end of each heat exchange tube bundle is connected to the cooling tank, and the other end is connected to the heat exchange tube outlet; the cooling tank is located below the interior of the outer tube of the reactor, one end of the cooling tank is connected to the coolant inlet pipe, and the other end is connected to the heat exchange tube bundle.

[0016] The outer cylinder of the reactor is a double-cavity structure.

[0017] One end of the heat exchange tube bundle away from the cooling tank is connected to the heat exchange tube bundle through the heat exchange tube outlet, and the medium after heat exchange passes through the heat exchange tube bundle and is discharged from the heat exchange tube outlet.

[0018] A plurality of baffles are provided inside the third catalyst frame. After the catalytic reaction in the second catalyst frame, the mixture II passes through the heat exchange chamber and enters the third catalyst frame. After the axial and radial reactions in the third catalyst frame through the baffles, the mixture III enters the central tube through a plurality of air holes opened on the bottom tube wall of the central tube and is discharged from the product gas outlet pipe.

[0019] The ammonia synthesis catalyst in the first catalyst bed is one of an Fe-based catalyst, a Ni-based catalyst, and a Ru-based catalyst, and the carrier is one or more of activated carbon, alumina, magnesium oxide, cerium dioxide, and barium oxide; the active component of the catalytic combustion catalyst in the second catalyst bed is one or more of Pd, Pt, and Sn, and the carrier is one or more of alumina, molecular sieve, zirconium oxide, cerium oxide, etc.; the heat exchange medium in the cooling tank is one of molten salt, high-pressure cold water, and supercritical CO2.

[0020] The present invention also provides a renewable energy ammonia synthesis system, comprising the above-mentioned ammonia synthesis device, a water electrolysis device, a nitrogen source supply device, an ammonia separation device, a preheater and an ammonia condensation group, wherein the hydrogen outlet of the water electrolysis device and the nitrogen outlet of the nitrogen source supply device are connected to the raw gas inlet pipe of the ammonia synthesis device, the raw hydrogen and nitrogen are mixed through the pipeline and enter the ammonia synthesis device through the raw gas inlet pipe for ammonia synthesis, the product gas outlet pipe of the ammonia synthesis device is connected to the ammonia separation device, the ammonia separation device has two outlets, namely a liquid outlet and an exhaust port, the liquid outlet is connected to an external storage tank, and the exhaust port is connected to the raw gas inlet pipe, the ammonia in the ammonia mixed gas synthesized in the ammonia synthesis device is condensed, liquefied and separated in the ammonia separation device, wherein the liquid ammonia enters the external storage tank through the liquid outlet for storage, and the unliquefied gas is preheated as circulating gas by the preheater and enters the ammonia synthesis device from the raw gas inlet pipe.

[0021] The synthetic ammonia device is provided with a 1# auxiliary line air inlet pipe and a 2# auxiliary line air inlet pipe. The 1# auxiliary line air inlet pipe is connected to the annular gap air flow channel II located on the inner part of the first catalyst frame, and the 2# auxiliary line air inlet pipe is connected to the annular gap air flow channel I located on the outer part of the second catalyst frame; the exhaust port on the ammonia separation device is divided into three pipelines, which are respectively connected to the raw gas inlet pipe, the 1# auxiliary line air inlet pipe and the 2# auxiliary line air inlet pipe, and the circulating gas enters the synthetic ammonia device through the raw gas inlet pipe, the 1# auxiliary line air inlet pipe and the 2# auxiliary line air inlet pipe respectively.

[0022] The system further comprises a power supply mechanism, which is electrically connected to the water electrolysis device and provides electrical energy for the water electrolysis device to electrolyze water.

[0023] The power supply mechanism is one or more of photovoltaic, wind power, hydropower, and tidal power generation.

[0024] The power supply mechanism can also be electrically connected to an external power grid via an inverter.

[0025] The nitrogen source providing device is a membrane separation device or a pressure swing adsorption device that uses air separation to supply nitrogen.

[0026] The ammonia condensation group includes a water cooler and an ammonia cooler arranged in series, the inlet of the water cooler is connected to the product gas outlet pipe, and the outlet of the ammonia cooler is connected to the inlet of the ammonia separation device; the exhaust port of the ammonia separation device is connected to the circulation machine and the circulating oil separator in sequence, and then connected to the raw gas inlet pipe, 1# auxiliary line inlet pipe and 2# auxiliary line inlet pipe respectively.

[0027] The circulating machine and the circulating oil separator are electrically connected to the inverter respectively, and electric energy is provided to the circulating machine and the circulating oil separator through the power supply mechanism or the external power grid.

[0028] The working pressure of the water electrolysis device is 0.1MPa-10MPa, and the working temperature is ≤90°C.

[0029] The ratio of the raw gas to the circulating gas introduced into the raw gas inlet pipe is 1:(1.5-4), and the ratio of the circulating gas introduced into the raw gas inlet pipe, the 1# auxiliary line air inlet pipe and the 2# auxiliary line air inlet pipe is (70-88):(5-10):(7-20).

[0030] The technical solution of the present invention has the following advantages:

[0031] A. Existing ammonia synthesis technologies primarily operate at 450°C-500°C and 20MPa-30MPa, suitable for large-scale, centralized industrial ammonia synthesis based on traditional fossil fuels. To address the application of renewable energy, the ammonia synthesis industry needs to develop towards miniaturization and distributed production, requiring low-temperature and low-pressure ammonia synthesis technology. This invention provides a low-temperature, low-pressure ammonia synthesis unit based on Fe and Ni catalysts operating in the temperature range of 300°C-450°C and the pressure range of 0.1MPa-10MPa.

[0032] B. The low-temperature, low-pressure ammonia synthesis unit of the present invention achieves efficient heat transfer, offering energy savings and cost reductions. The heat exchange tube bundle passes through the bottom third catalyst frame and extends into a cooling tank, which provides a continuous cooling source for the heat exchange tube bundle. The heat from the catalytic reaction in the third catalyst frame is exchanged with the heat exchange tube bundle, achieving heat transfer. A heat exchange chamber is provided between the second and third catalyst frames. Mixture II, after the reaction in the second catalyst frame, first enters the heat exchange chamber for heat exchange with the heat exchange tube bundle, facilitating the ammonia synthesis reaction and achieving energy savings and cost reductions. Compared to traditional adiabatic and isothermal reactors, the ammonia synthesis reaction unit provided by the present invention utilizes a combination of multi-stage bed quenching, phase change heat transfer, and radial and axial flow, resulting in more precisely controlled bed temperature, more efficient heat exchange, high conversion efficiency, minimal pressure loss, and high energy efficiency.

[0033] C. Hydrogen produced by water electrolysis contains a high concentration of O2, which can affect the activity and stability of the ammonia synthesis reaction. To address this issue, the present invention installs a catalytic combustion catalyst outside the uppermost radial flow bed to convert O2 in the device into H2O. The catalyst includes, but is not limited to, one or more of Pd, Pt, and Sn-based catalysts, thereby achieving efficient oxygen removal. The selected ammonia synthesis catalyst has good water resistance, and the reaction is virtually unaffected by H2O.

[0034] D. In the renewable energy ammonia synthesis system of the present invention, renewable energy includes but is not limited to photovoltaic, wind power, hydropower, tidal power generation, etc., and can choose between grid-connected and off-grid modes: in the grid-connected mode, renewable energy is connected to the grid within the capacity allowed by the grid, and excess electricity is used for electrolysis of water to produce hydrogen. When renewable energy power is insufficient, grid power can also be used to meet basic production needs, especially by utilizing valley electricity prices to improve economic efficiency; in the off-grid mode, all renewable energy power is used for electrolysis of water to produce hydrogen to synthesize ammonia.

[0035] E. The electrolysis of water in the present invention is operated at a pressure of 0.1-10 MPa, which matches the pressure of the ammonia synthesis process. There is no need to additionally pressurize the hydrogen. Compared with the prior art, the present invention can omit the pressurization process between the electrolysis of water and the synthesis of ammonia, that is, no compressor and supporting equipment are required. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the specific embodiments of the present invention, the following will briefly introduce the drawings required for use in the specific embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 This is a schematic diagram of the overall structure of the low-temperature and low-pressure ammonia synthesis device of the present invention;

[0038] Figure 2 Schematic diagram of the overall structure of the renewable energy ammonia synthesis system.

[0039] The following are marked in the figure:

[0040] 1-Synthetic ammonia unit

[0041] 11 - Feed gas inlet pipe; 12 - Reactor outer cylinder; 13 - Coolant inlet pipe; 14 - Product gas outlet pipe; 15 - Center pipe; 16 - Catalyst frame, 160 - First catalyst bed, 161 - First catalyst frame, 1611 - Second catalyst bed, 162 - Second catalyst frame, 163 - Third catalyst frame, 1631 - Baffle; 17 - Cooling tank; 18 - Heat exchange tube bundle; 19 - Heat exchange tube outlet; 20 - Heat exchange chamber, 201 - Mixed gas inlet;

[0042] a-annular gap airflow channel I, b-annular gap airflow channel II, c-1# auxiliary line air intake pipe, d-2# auxiliary line air intake pipe;

[0043] 2-water electrolysis device; 3-nitrogen source supply device; 4-ammonia separation device, 41-liquid outlet, 42-exhaust port; 5-preheater; 6-ammonia condensation group, 61-water cooler, 62-ammonia cooler; 7-external storage tank; 8-power supply mechanism, 81-inverter; 9-circulator; 10-circulating oil separator. DETAILED DESCRIPTION

[0044] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0045] like Figure 1As shown, the present invention provides a low-pressure ammonia synthesis apparatus 1, comprising a reactor outer cylinder 12, provided with a feed gas inlet pipe 11 and a product gas outlet pipe 14. A central tube 15, n catalyst frames 16, and a cooling tank 17 are housed within the reactor outer cylinder 12, where n ≥ 2. A unidirectional airflow channel is formed between the catalyst frames 16, and each catalyst frame 16 is provided with a first catalyst bed 160 containing an ammonia synthesis catalyst. The central tube 15 is located at the circumferential center of the catalyst frame 16 and extends through the catalyst frame 16. One end of the central tube 15 communicates with the product gas outlet pipe 14, while the other end is sealed and disposed within the bottommost catalyst frame 16. The portion of the central tube 15 located at the bottommost catalyst frame 16 has a plurality of circumferentially defined air holes on its lower sidewall, which communicate with the bottommost catalyst frame 16. A cooling tank 17 is located below the bottom catalyst frame 16. Several heat exchange tube bundles 18 circumferentially extend through the bottom catalyst frame 16. Each heat exchange tube bundle 18 is connected to the cooling tank 17 at one end and to a heat exchange tube outlet 19 at the other end. The feed gas enters the top catalyst frame 16 through the feed gas inlet pipe 11 for the initial ammonia synthesis reaction. After the reaction, the mixture passes through each catalyst frame 16 in sequence via a unidirectional airflow channel before entering the bottom catalyst frame 16. After heat exchange and catalysis, the final product is discharged through the product gas outlet pipe 14. The coolant in the heat exchange tube bundle 18 absorbs the reaction heat from the bottom catalyst frame 16 and is discharged through the heat exchange tube outlet 19. The low-temperature, low-pressure ammonia synthesis unit of the present invention enables efficient heat transfer and preheating of the feed gas, resulting in energy savings and reduced consumption. The heat exchange tube bundle passes through the bottom catalyst frame. The catalyst reaction heat within the bottom catalyst frame is exchanged with the coolant within the heat exchange tube bundle, achieving heat transfer. The reaction mixture exchanges heat with the coolant through the heat exchange tube bundle, facilitating the ammonia synthesis reaction and achieving energy savings and cost reductions. Compared to traditional adiabatic and isothermal reactors, the ammonia synthesis reaction unit provided by the present invention utilizes multi-stage bed quenching, phase change heat transfer, and radial flow to achieve more precisely controlled bed temperature, more efficient heat exchange, high conversion efficiency, minimal pressure loss, and high energy efficiency.

[0046] Furthermore, catalyst frames 16 are arranged vertically within the reactor outer tube 12, forming an annular airflow channel Ia between the reactor outer tube 12 and each catalyst frame 16. The lower end of the central tube 15 is sealed and located within the bottommost catalyst frame 16. The bottommost catalyst frame 16 is in communication with the central tube 15, while the remaining catalyst frames 16 each form an annular airflow channel IIb between them. The annular airflow channels IIb are connected to the annular airflow channel Ia through the catalyst frames 16. After the feed gas undergoes an ammonia synthesis reaction in the topmost catalyst frame 16, the post-reaction mixture passes through the catalyst frames 16 below it, undergoing at least one ammonia synthesis reaction. The final product is then discharged through the product gas outlet pipe 14.

[0047] There are preferably three catalyst frames 16, which are the first catalyst frame 161, the second catalyst frame 162 and the third catalyst frame 163 from top to bottom. The gas flows in the first catalyst frame 161 and the second catalyst frame 162 in a radial direction, and the gas flows in the third catalyst frame 163 in an axial direction. The annular gap airflow channel Ⅱb located on the inner part of the first catalyst frame 161 is connected to the annular gap airflow channel Ⅱb located on the inner part of the second catalyst frame 162, and the annular gap airflow channel Ⅰa located on the outer part of the second catalyst frame 162 is connected to the annular gap airflow channel Ⅰa located on the outer part of the third catalyst frame 163.

[0048] A heat exchange chamber 20 is provided between the second catalyst frame 162 and the third catalyst frame 163. The upper portion of the heat exchange chamber 20 is sealed, and its lower portion communicates with the third catalyst frame 163. A mixed gas inlet 201, communicating with the heat exchange chamber 20, is provided at the bottom of the annular airflow channel Ia outside the second catalyst frame 162. A heat exchange tube bundle 18 is provided within the heat exchange chamber 20. The upper end of the heat exchange tube bundle 18 passes through the heat exchange chamber 20 and communicates with the heat exchange tube outlet 19. The lower end of the heat exchange tube bundle 18 passes downward through the third catalyst frame 163 and communicates with the cooling tank 17. The raw gas enters the annular gap airflow channel Ia from the raw gas inlet pipe 11, and radially enters the first catalyst frame 161 for preliminary ammonia synthesis reaction. After the reaction, the mixture I passes through the annular gap airflow channel IIb and radially enters the second catalyst frame 162 for further reaction. After the reaction, the mixture II enters the heat exchange chamber 20 through the annular gap airflow channel Ia and the mixed gas inlet 201 in sequence for heat exchange, and then enters the third catalyst frame 163 for further heat exchange and reaction. The final product is discharged from the product gas outlet pipe 14.

[0049] In addition, the reactor outer tube 12 is equipped with a 1# auxiliary gas inlet pipe c and a 2# auxiliary gas inlet pipe d. After the synthetic ammonia product gas discharged from the product gas outlet pipe 14 is liquefied and separated into liquid ammonia, the remaining gas can be used as recycle gas to enter the ammonia synthesis unit through the feed gas inlet pipe 11, the 1# auxiliary gas inlet pipe c, and the 2# auxiliary gas inlet pipe d, respectively. The 1# auxiliary gas inlet pipe c communicates with the annular gap flow channel IIb located inside the first catalyst frame 161. The recycle gas entering from the 1# auxiliary gas inlet pipe c mixes with the mixture I and undergoes heat exchange. The 2# auxiliary gas inlet pipe d communicates with the annular gap flow channel Ia located outside the second catalyst frame 162. The recycle gas entering from the 2# auxiliary gas inlet pipe d mixes with the mixture II and undergoes heat exchange. A second catalyst bed 1611 containing a catalytic combustion catalyst is also provided in the annular gap airflow channel between the first catalyst frame 161 and the annular gap airflow channel Ia. The second catalyst bed 1611 is arranged close to the first catalyst frame 161 and is used to remove oxygen in the raw gas entering from the raw gas inlet pipe 11.

[0050] The end of the heat exchange tube bundle 18 away from the cooling tank 17 is connected to the heat exchange tube bundle 18 via the heat exchange tube outlet 19. The medium after heat exchange passes through the heat exchange tube bundle 18 and is discharged from the heat exchange tube outlet 19. A plurality of baffles 1631 are provided within the third catalyst frame 163. After the catalytic reaction in the second catalyst frame 162, the mixture II passes through the heat exchange chamber 20 and enters the third catalyst frame 163. After the mixture III undergoes an axial and radial reaction within the third catalyst frame 163 through the baffles 1631, it enters the central tube 15 through a plurality of air holes provided in the bottom wall of the central tube 15 and is discharged through the product gas outlet pipe 14.

[0051] Furthermore, the ammonia synthesis catalyst in the first catalyst bed 160 of the outer tube of the reactor is one of an Fe-based catalyst, a Ni-based catalyst, and a Ru-based catalyst, and the carrier is one or more of activated carbon, alumina, magnesium oxide, cerium dioxide, and barium oxide; the hydrogen produced by electrolysis of water to produce hydrogen contains a high concentration of O2, which will affect the activity and stability of the ammonia synthesis reaction. To address this problem, the present invention provides a second catalyst bed 1611 between the first catalyst frame 161 and the annular gap airflow channel Ia to convert O2 in the device into H20. The catalyst includes but is not limited to one or more of Pd, Pt, and Sn-based catalysts, and the carrier is one or more of alumina, molecular sieve, zirconium oxide, cerium oxide, etc., thereby achieving efficient deoxygenation.

[0052] During use, a feed gas composed of a mixture of hydrogen and nitrogen (containing less than 0.2% oxygen) enters the device through the feed gas inlet pipe 11. The feed gas first flows through the second catalyst bed 1611 in the annular gap flow channel Ia between the outer tube 12 of the reactor, where oxygen and hydrogen react to form H2O. The gas then enters the first catalyst frame 161 for the first stage of ammonia synthesis. After the gas flows radially within the bed, the reaction mixture I enters the annular gap flow channel IIb and mixes with the recycle gas from the 1# auxiliary line inlet pipe c to control the temperature of the reaction gas flow before entering the second catalyst frame 162 to continue the second stage of ammonia synthesis. The reacted mixture II enters the annular gap airflow channel Ia and is mixed with the circulating gas coming in from the 2# auxiliary line air inlet pipe d to control the temperature before entering the heat exchange chamber 20. The mixture II exchanges heat with the heat exchange tube bundle 18 in the heat exchange chamber 20 and then enters the third catalyst frame 163. Under the action of the baffle 1631, the ammonia synthesis reaction is carried out in the radial direction of the third catalyst frame 163, and heat is exchanged with the heat exchange tube bundle 18 in the third catalyst frame 163 during the flow process. The final product enters the central tube 15 through the air holes at the bottom of the central tube 15 and leaves the ammonia synthesis device 1 from the product gas outlet pipe 14.

[0053] When in use, the coolant can be selected from molten salt, high-pressure water, and supercritical CO2. The coolant enters the cooling tank 17 through the coolant inlet pipe 13, and enters the heat exchange tube bundle 18 after being buffered in the cooling tank 17, and then passes through the third catalyst frame 163 and the heat exchange cavity 20. The cooling medium gradually absorbs the heat released by the synthetic ammonia in the bed and is finally discharged from the heat exchange tube outlet 19.

[0054] like Figure 2 As shown, the present invention also provides a renewable energy ammonia synthesis system, comprising the above-mentioned ammonia synthesis unit 1, a water electrolysis unit 2, a nitrogen source supply unit 3, an ammonia separation unit 4, a preheater 5 and an ammonia condensation group 6. The hydrogen outlet of the water electrolysis unit 2 and the nitrogen outlet of the nitrogen source supply unit 3 are connected to the raw gas inlet pipe 11 of the ammonia synthesis unit 1. The raw hydrogen and nitrogen are mixed through the pipeline and then enter the ammonia synthesis unit 1 through the raw gas inlet pipe 11 for ammonia synthesis. The product gas outlet pipe 14 of the ammonia synthesis unit 1 is connected to the ammonia separation unit 4. The ammonia separation unit 4 has two outlets, namely a liquid outlet 41 and an exhaust port 42. The liquid outlet 41 is connected to the external storage tank 7, and the exhaust port 42 is connected to the raw gas inlet pipe 11. Ammonia in the ammonia mixed gas synthesized in the ammonia synthesis unit 1 is condensed, liquefied and separated in the ammonia separation unit 4. The liquid ammonia enters the external storage tank 7 through the liquid outlet 41 for storage. The unliquefied gas is used as circulating gas and is preheated by the preheater 5 before entering the ammonia synthesis unit 1 through the raw gas inlet pipe 11.

[0055] Ammonia synthesis unit 1 is equipped with a 1# auxiliary air inlet pipe c and a 2# auxiliary air inlet pipe d. The 1# auxiliary air inlet pipe c communicates with an annular air flow channel IIb located inside the first catalyst frame 161, while the 2# auxiliary air inlet pipe d communicates with an annular air flow channel Ia located outside the second catalyst frame 162. The exhaust port 42 on the ammonia separation unit 4 is divided into three pipes, connected to the feed gas inlet pipe 11, the 1# auxiliary air inlet pipe c, and the 2# auxiliary air inlet pipe d, respectively. Recycled gas enters the ammonia synthesis unit 1 through the feed gas inlet pipe 11, the 1# auxiliary air inlet pipe c, and the 2# auxiliary air inlet pipe d, respectively. The ratio of feed gas to recycle gas introduced into the feed gas inlet pipe 11 is 1:1.5-4. The ratio of recycle gas introduced into the feed gas inlet pipe 11, the 1# auxiliary air inlet pipe c, and the 2# auxiliary air inlet pipe d is (70-88):(5-10):(7-20).

[0056] The system also includes a power supply mechanism 8, which is electrically connected to the water electrolysis device 2 and provides electrical energy for the water electrolysis device 2 to electrolyze water. The power supply mechanism 8 can be one or more of photovoltaic, wind, hydropower, and tidal power generation. The power supply mechanism 8 can also be electrically connected to an external power grid via an inverter 81. In the renewable energy ammonia synthesis system of the present invention, renewable energy includes, but is not limited to, photovoltaic, wind, hydropower, and tidal power generation. Photovoltaic power is integrated into a DC-DC converter, while wind and hydropower are integrated into an AC-DC converter. These are then combined with grid power passing through the inverter 81 into a single bus, which is then driven by the DC-DC converter to operate the high-voltage water electrolysis device 2. Renewable energy access can be divided into two modes: off-grid and on-grid. In the off-grid mode, all renewable energy power is used for water electrolysis to produce hydrogen and ammonia. In the on-grid mode, renewable energy is integrated into the grid within the grid's permitted capacity, and excess power is used for water electrolysis to produce hydrogen. When renewable energy power is insufficient, grid power can be used to meet basic hydrogen production needs. In particular, off-peak electricity prices can be utilized to improve the economic efficiency of the system process and balance renewable energy power with grid load.

[0057] The nitrogen source providing device 3 is a membrane separation device or a pressure swing adsorption device that uses air separation to supply nitrogen. The water after external purification is pressurized by a compressor and sent to the high-pressure water electrolysis device 2 to decompose into hydrogen and oxygen. The hydrogen and the nitrogen generated by the air separation nitrogen supply device are mixed in a certain proportion to form a synthetic ammonia raw gas, which is sent to the synthetic ammonia section at the back end. The water electrolysis of the present invention operates at a pressure of 0.1-10MPa, which matches the pressure of the synthetic ammonia process. There is no need to additionally pressurize the hydrogen. Compared with the prior art, the present invention can omit the pressurization process between the electrolysis of water and the synthesis of ammonia, that is, no compressor and supporting equipment are required. Both the water electrolysis and the air separation nitrogen supply device can produce high-purity oxygen as a by-product, and the hydrogen in the synthetic ammonia raw gas can also come from industrial by-product hydrogen.

[0058] In addition, the ammonia condenser group 6 includes a water cooler 61 and an ammonia cooler 62 arranged in series. The inlet of the water cooler 61 is connected to the product gas outlet pipe 14, and the outlet of the ammonia cooler 62 is connected to the inlet of the ammonia separation unit 4. The exhaust port 42 of the ammonia separation unit 4 is connected in sequence to the circulation unit 9 and the circulating oil separator 10, and then to the feed gas inlet pipe 11, the 1# auxiliary line inlet pipe c, and the 2# auxiliary line inlet pipe d. Part of the gas at the outlet of the ammonia separation unit 4 is discharged as purge gas, and part of it is passed through the circulation unit 9 and the circulating oil separator 10 as circulating gas, and then enters the ammonia synthesis unit through the feed gas inlet pipe 11, the 1# auxiliary line inlet pipe, and the 2# auxiliary line inlet pipe d, thereby controlling the temperature distribution within the unit. The circulation unit 9 and the circulating oil separator 10 are each electrically connected to the inverter 81, which provides power to the circulation unit 9 and the circulating oil separator 10 via the power supply unit 8 or the external power grid.

[0059] The hydrogen produced by water electrolysis in this invention does not require deoxygenation or dehydration. Nitrogen can be derived from on-site air separation or directly purchased liquid nitrogen. If on-site air separation is used, membrane separation technology, pressure swing adsorption, cryogenic technology, etc. can be used. Oxygen in the hydrogen-nitrogen feed gas can be removed in the ammonia synthesis unit, thereby appropriately reducing the oxygen content requirement for the ammonia synthesis feed gas. Ammonia separation technologies that can be used include, but are not limited to, one or more of ammonia cooling separation, ammonia adsorption separation, and ammonia absorption separation.

[0060] The entire system of the present invention can not only efficiently synthesize ammonia under low temperature and low pressure conditions, but also produce high-purity oxygen as a by-product, and has the characteristics of high energy efficiency and high economic benefits.

[0061] Experimental Example 1:

[0062] Ammonia synthesis unit level:

[0063] The hydrogen-nitrogen volume ratio of the raw gas entering the pipe is 3:1, the pressure is 10 MPa, and the temperature is 380°C;

[0064] The space velocity of the three first catalyst beds from top to bottom is: 10000h -1 5000h -1 5000h -1 ;

[0065] Second catalyst bed space velocity: 15000h -1 ;

[0066] The bed inlet temperature of the first and second catalyst frames is controlled at 380°C, and the bed temperature in the third catalyst frame is controlled at 400°C;

[0067] The coolant entering the coolant pipe is high-pressure water with a pressure of 11 MPa and a temperature of 25°C;

[0068] The temperature at the outlet of the heat exchange tube is 320°C;

[0069] The ammonia concentration at the outlet of the product gas outlet pipe is 21.4%.

[0070] System process level:

[0071] In the grid-connected mode, renewable energy is connected to the grid within the capacity allowed by the grid, and excess electricity is used to electrolyze water to produce hydrogen. When renewable energy power is insufficient, grid power can also be used to meet basic production needs, especially by utilizing valley electricity prices to improve economic efficiency, and it can also play a role in regulating the balance between renewable energy power and grid load.

[0072] The working pressure of the water electrolysis device is 10MPa, the working temperature is 80℃, and the purity of the hydrogen produced is 99.5%;

[0073] The purity of nitrogen obtained by air membrane separation is 99.999%;

[0074] The volume ratio of hydrogen and nitrogen in the feed gas is 3:1, and the ratio of feed gas to recycle gas is 1:2.5;

[0075] The distribution ratio of circulating gas is: 70% for raw gas inlet pipe, 15% for 1# auxiliary line inlet pipe, and 15% for 2# auxiliary line inlet pipe;

[0076] The synthetic ammonia pressure is 10MPa.

[0077] Experimental Example 2:

[0078] Ammonia synthesis unit level:

[0079] The hydrogen-nitrogen volume ratio of the raw gas entering the pipe is 2.5:1, the pressure is 7 MPa, and the temperature is 380°C;

[0080] The space velocity of the three first catalyst beds from top to bottom is: 10000h -1 5000h -1 5000h -1 ;

[0081] Second catalyst bed space velocity: 15000h -1 ;

[0082] The bed inlet temperature of the first and second catalyst frames is controlled at 380°C, and the bed temperature in the third catalyst frame is controlled at 400°C;

[0083] The coolant entering the coolant pipe is supercritical CO2, with a pressure of 8 MPa and a temperature of 25°C;

[0084] The temperature at the heat exchange tube outlet is 295°C;

[0085] The ammonia concentration at the outlet of the product gas outlet pipe is 18.27%.

[0086] System process level:

[0087] The working pressure of the water electrolysis device is 7.5MPa, the working temperature is 80℃, and the purity of the hydrogen produced is 99%;

[0088] Air separation uses pressure swing adsorption technology to obtain nitrogen with a purity of 99.999%;

[0089] The volume ratio of hydrogen and nitrogen in the feed gas is 3:1, and the ratio of feed gas to recycle gas is 1:3.5;

[0090] The distribution ratio of circulating gas is: 80% for raw gas inlet pipe, 10% for 1# auxiliary line inlet pipe, and 10% for 2# auxiliary line inlet pipe;

[0091] The synthetic ammonia pressure is 7MPa.

[0092] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A low-temperature, low-pressure ammonia synthesis device, comprising a reactor outer cylinder, the reactor outer cylinder being provided with a feed gas inlet pipe and a product gas outlet pipe, characterized in that: The reactor outer cylinder is provided with a central tube, n catalyst frames and a cooling tank, wherein n is greater than or equal to 2, and a unidirectional airflow channel is formed between the catalyst frames, and a first catalyst bed containing an ammonia synthesis catalyst is provided in each catalyst frame; The central tube is located at the circumferential center of the catalyst frame and passes through the catalyst frame. One end of the central tube is connected to the product gas outlet pipe, and the other end is closed and disposed in the bottom catalyst frame. A plurality of air holes are circumferentially formed on the lower portion of the side wall of the central tube portion located at the bottom catalyst frame, and the air holes are in conduction with the bottom catalyst frame. The cooling tank is located below the catalyst frame at the bottom layer. A plurality of heat exchange tube bundles are arranged in the catalyst frame at the bottom layer and pass through the interior thereof in a circumferential direction. One end of each heat exchange tube bundle is connected to the cooling tank, and the other end thereof is connected to the heat exchange tube outlet. The raw gas enters the top catalyst frame through the raw gas inlet pipe to perform the first ammonia synthesis reaction. After the reaction, the mixture passes through each catalyst frame in sequence through the unidirectional airflow channel and finally enters the bottom catalyst frame. After heat exchange and catalysis, the final product is discharged from the product gas outlet pipe. The catalyst frames are arranged in an upper and lower spaced relationship within the reactor outer tube, and an annular airflow channel I is formed between the reactor outer tube and each of the catalyst frames; the lower end of the central tube is closed and disposed within the lowermost catalyst frame, the lowermost catalyst frame is in communication with the central tube, and an annular airflow channel II is formed between the remaining catalyst frames and the central tube, and the annular airflow channel II is in communication with the annular airflow channel I through the catalyst frame; There are three catalyst frames, which are the first catalyst frame, the second catalyst frame and the third catalyst frame from top to bottom; a heat exchange cavity is provided between the second catalyst frame and the third catalyst frame, the upper part of the heat exchange cavity is closed, and the lower part is connected with the third catalyst frame, and a mixed gas inlet connected with the heat exchange cavity is provided at the bottom of the annular gap airflow channel I on the outer part of the second catalyst frame; the heat exchange tube bundle is provided in the heat exchange cavity, the upper end of the heat exchange tube bundle passes through the heat exchange cavity and is connected with the heat exchange tube outlet, and the lower end passes downward through the third catalyst frame and is connected with the cooling tank.

2. The low-temperature, low-pressure ammonia synthesis device according to claim 1, characterized in that: The gas flow direction in the first catalyst frame and the second catalyst frame is radial, and the gas flow direction in the third catalyst frame is axial. The annular gap airflow channel II located on the inner part of the first catalyst frame is connected to the annular gap airflow channel II located on the inner part of the second catalyst frame, and the annular gap airflow channel I located on the outer part of the second catalyst frame is connected to the annular gap airflow channel I located on the outer part of the third catalyst frame.

3. The low-temperature, low-pressure ammonia synthesis device according to claim 2, characterized in that: The outer cylinder of the reactor is also provided with a 1# auxiliary line air inlet pipe and a 2# auxiliary line air inlet pipe, and the synthetic ammonia product gas discharged from the product gas outlet pipe is liquefied to separate the liquid ammonia; The 1# auxiliary air intake pipe is connected to the annular air flow channel II located on the inner side of the first catalyst frame, and the recycle gas entering from the 1# auxiliary air intake pipe is mixed with the mixture I and undergoes heat exchange; the 2# auxiliary air intake pipe is connected to the annular air flow channel I located on the outer side of the second catalyst frame, and the recycle gas entering from the 2# auxiliary air intake pipe is mixed with the mixture II and undergoes heat exchange; A second catalyst bed containing a catalytic combustion catalyst is also provided in the annular gap airflow channel between the first catalyst frame and the annular gap airflow channel I. The second catalyst bed is arranged close to the first catalyst frame and is used to remove oxygen from the raw gas entering from the raw gas inlet pipe.

4. The low-temperature, low-pressure ammonia synthesis device according to claim 3, characterized in that: The end of the heat exchange tube bundle away from the cooling tank is connected to the heat exchange tube bundle through the heat exchange tube outlet, and the medium after heat exchange passes through the heat exchange tube bundle and is discharged from the heat exchange tube outlet; A plurality of baffles are provided inside the third catalyst frame. After the catalytic reaction in the second catalyst frame, the mixture II passes through the heat exchange chamber and enters the third catalyst frame. After the axial and radial reactions in the third catalyst frame through the baffles, the mixture III enters the central tube through a plurality of air holes opened on the bottom tube wall of the central tube and is discharged from the product gas outlet pipe.

5. The low-temperature, low-pressure ammonia synthesis device according to claim 4, characterized in that: The ammonia synthesis catalyst in the first catalyst bed is one of an Fe-based catalyst and a Ni-based catalyst, and the carrier is one or more of activated carbon, alumina, magnesium oxide, cerium dioxide, and barium oxide; the active component of the catalytic combustion catalyst in the second catalyst bed is one or more of Pd, Pt, and Sn, and the carrier is one or more of alumina, molecular sieve, zirconium oxide, and cerium oxide; the heat exchange medium in the cooling tank is one of molten salt, high-pressure cold water, and supercritical CO2.

6. A renewable energy ammonia synthesis system, characterized in that: A method of synthesizing ammonia comprising: providing a low-temperature, low-pressure ammonia synthesis device according to any one of claims 1 to 5, a water electrolysis device, a nitrogen source supply device, an ammonia separation device, a preheater, and an ammonia condensation group, wherein the hydrogen outlet of the water electrolysis device and the nitrogen outlet of the nitrogen source supply device are connected to a raw gas inlet pipe of the ammonia synthesis device, the raw hydrogen and nitrogen are mixed through a pipeline and then enter the ammonia synthesis device through the raw gas inlet pipe for ammonia synthesis, the product gas outlet pipe of the ammonia synthesis device is connected to the ammonia separation device, the ammonia separation device has two outlets, namely a liquid outlet and an exhaust port, the liquid outlet is connected to an external storage tank, and the exhaust port is connected to the raw gas inlet pipe, the ammonia in the ammonia mixed gas synthesized in the ammonia synthesis device is condensed, liquefied, and separated in the ammonia separation device, wherein the liquid ammonia enters the external storage tank for storage through the liquid outlet, and the unliquefied gas is preheated as circulating gas in the preheater and then enters the ammonia synthesis device from the raw gas inlet pipe.

7. The renewable energy ammonia synthesis system according to claim 6, characterized in that: The synthetic ammonia device is provided with a 1# auxiliary line air inlet pipe and a 2# auxiliary line air inlet pipe. The 1# auxiliary line air inlet pipe is connected to the annular gap air flow channel II located on the inner part of the first catalyst frame, and the 2# auxiliary line air inlet pipe is connected to the annular gap air flow channel I located on the outer part of the second catalyst frame; the exhaust port on the ammonia separation device is divided into three pipelines, which are respectively connected to the raw gas inlet pipe, the 1# auxiliary line air inlet pipe and the 2# auxiliary line air inlet pipe, and the circulating gas enters the synthetic ammonia device through the raw gas inlet pipe, the 1# auxiliary line air inlet pipe and the 2# auxiliary line air inlet pipe respectively.

8. The renewable energy ammonia synthesis system according to claim 7, characterized in that: The system further includes a power supply mechanism, which is electrically connected to the water electrolysis device to provide electrical energy for the water electrolysis device to electrolyze water; The nitrogen source providing device is a membrane separation device or a pressure swing adsorption device that uses air separation to supply nitrogen.

9. The renewable energy ammonia synthesis system according to claim 8, characterized in that: The ammonia condensation group includes a water cooler and an ammonia cooler arranged in series, the inlet of the water cooler is connected to the product gas outlet pipe, and the outlet of the ammonia cooler is connected to the inlet of the ammonia separation device; the exhaust port of the ammonia separation device is connected in sequence to a circulating machine and a circulating oil separator, and then respectively connected to the raw gas inlet pipe, the 1# auxiliary line inlet pipe, and the 2# auxiliary line inlet pipe; The circulating machine and the circulating oil separator are electrically connected to the inverter respectively, and the circulating machine and the circulating oil separator are provided with electric energy through the power supply mechanism or the external power grid.

10. The renewable energy ammonia synthesis system according to claim 9, characterized in that: The ratio of the raw gas to the circulating gas introduced into the raw gas inlet pipe is 1:(1.5-4), and the ratio of the circulating gas introduced into the raw gas inlet pipe, the 1# auxiliary line air inlet pipe and the 2# auxiliary line air inlet pipe is (70-88):(5-10):(7-20).

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