Ammonia synthesis process and system

Abstract

The invention relates to an ammonia synthesis process and system, and the process comprises the following steps: under the action of a catalyst, carrying out ammonia synthesis reaction in a reactor by taking hydrogen and nitrogen as raw materials to generate ammonia gas; wherein an ammonia gas adsorbent is arranged in the reactor, and the ammonia gas is in contact with the ammonia gas adsorbent, so that the ammonia gas is adsorbed. According to the ammonia synthesis process in one embodiment, the ammonia gas adsorbent is arranged in the reactor, so that the ammonia gas generated by the synthesis reaction is continuously adsorbed by the adsorbent, the concentration of the product ammonia gas in the reactor is reduced, the forward proceeding of the synthesis reaction is promoted, and the conversion rate of the raw material gas is improved.

Description

Technical Field

[0001] The invention relates to the synthesis of ammonia, and in particular to a synthesis process of ammonia with high conversion rate. Background Art

[0002] Ammonia is one of the most widely produced and used chemicals in the world. In addition to the research on catalysts, how to efficiently separate ammonia from synthesis gas is also an important topic and an important link involving increasing production and energy saving. In the synthesis process of ammonia, the concentration of ammonia in the synthesis gas is generally 10-20% due to the limitation of reaction equilibrium. At present, the condensation method is generally used in industry to liquefy and separate ammonia from synthesis gas, and the remaining gas is mixed with fresh raw gas as circulating gas and sent back to the synthesis tower for further reaction. However, the efficiency of physical condensation is low, and about 3% of ammonia will still remain in the circulating gas, resulting in a large amount of ammonia product being wasted, reducing the net value of ammonia and increasing the circulation volume of the circulating machine. In addition, the residual ammonia returned to the synthesis tower with the circulating gas will also be unfavorable to the balanced conversion of the raw gas, so that the energy consumption of the entire ammonia synthesis process still needs to be reduced.

[0003] On the other hand, green ammonia is a small-scale synthetic ammonia supporting wind and solar hydrogen production projects. Compared with traditional large-scale synthetic ammonia, it has the characteristics of unstable gas source and fewer professional operators. Traditional synthetic ammonia is generally produced in chemical parks with complete supporting facilities; while green ammonia is small in scale and has no supporting chemical parks, which requires adjustments to the green ammonia synthesis process based on the traditional process. Summary of the invention

[0004] In order to overcome at least one defect of the above-mentioned prior art, in the first aspect, an embodiment of the present invention provides an ammonia synthesis process, comprising: under the action of a catalyst, carrying out a synthetic ammonia reaction in a reactor with hydrogen and nitrogen as raw materials to generate ammonia; wherein an ammonia adsorbent is arranged in the reactor, so that the ammonia is brought into contact with the ammonia adsorbent to adsorb the ammonia.

[0005] In a second aspect, an embodiment of the present invention provides a composition for synthesizing ammonia, comprising a catalyst for synthesizing ammonia and an ammonia adsorbent.

[0006] In a third aspect, an embodiment of the present invention provides an ammonia synthesis system, comprising:

[0007] One or more reactors for carrying out a reaction for synthesizing ammonia and performing adsorption treatment on the ammonia;

[0008] A raw gas device, used to provide the reactor with raw gas for reaction;

[0009] A circulating gas pipeline, used for circulating the unreacted gas in the reactor back to the raw gas device;

[0010] A flushing gas pipeline for supplying flushing gas to the reactor; and

[0011] An ammonia recovery device for collecting ammonia obtained by desorption treatment.

[0012] In one embodiment of the ammonia synthesis process of the present invention, by arranging an ammonia adsorbent in the reactor, the ammonia generated by the synthesis reaction is continuously adsorbed by the adsorbent, reducing the concentration of the product ammonia in the reactor, promoting the forward progress of the synthesis reaction, and increasing the conversion rate of the feed gas. Description of the Drawings

[0013] The drawings are only for the purpose of showing specific embodiments and are not considered to be a limitation of the present invention. Among them:

[0014] Figure 1 is a schematic structural diagram of an ammonia synthesis system according to an embodiment of the present invention;

[0015] The description of the reference numerals is as follows:

[0016] 10. First reaction tower; 11. First intake valve; 12. First outlet valve; 13. First nitrogen valve; 14. First ammonia recovery valve; 20. Second reaction tower; 21. Second intake valve; 22. Second outlet valve; 23. Second nitrogen valve; 24. Second ammonia recovery valve; 30. Circulation gas pipeline; 40. Flushing gas pipeline; 51. Nitrogen pipeline; 52. Hydrogen pipeline; 61. Heat exchanger; 62. Booster; 63. Liquid ammonia collection tank. Detailed Embodiments

[0017] Typical embodiments embodying the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various changes in different embodiments, all of which do not depart from the scope of the present invention, and the description therein is essentially for illustrative purposes and not for limiting the present invention.

[0018] An embodiment of the present invention provides an ammonia synthesis process, including: under the action of a catalyst, using hydrogen and nitrogen as feed gases to carry out an ammonia synthesis reaction in a reactor to generate ammonia; wherein, an ammonia adsorbent is arranged in the reactor to bring ammonia into contact with the ammonia adsorbent for adsorbing ammonia.

[0019] In one embodiment, the reaction temperature for synthesizing ammonia from hydrogen and nitrogen can be 150 - 400 °C, such as 180 °C, 200 °C, 220 °C, 250 °C, 280 °C, 300 °C, 320 °C, 350 °C, 380 °C; the reaction pressure can be 1 - 10 MPa, such as 2 MPa, 5 MPa, 6 MPa, 8 MPa.

[0020] In one embodiment, during the desorption process, the temperature of the reactor is 200 - 500 °C, such as 250 °C, 300 °C, 350 °C, 400 °C, 450 °C; and the pressure is 0 - 1 MPa, such as 0.1 MPa, 0.2 MPa, 0.5 MPa, 0.8 MPa.

[0021] In one embodiment, the hydrogen for synthesizing ammonia can be obtained from electrolytic water for hydrogen production, and the nitrogen can be obtained from PSA air for nitrogen production. Hydrogen and nitrogen can be mixed in a ratio (such as 3:1), pressurized by a compressor, and then introduced into the reactor for reaction. The reactor can be heated by electricity to raise the temperature. Further, the raw material gas containing hydrogen and nitrogen can be pressurized to 5 - 10 MPa and then introduced into the reactor.

[0022] In one embodiment, since the ammonia produced by the reaction is continuously absorbed by the ammonia adsorbent, the ammonia content (volume content) of the reactor gas (synthesis gas) during the reaction process is maintained below 0.1 vol%.

[0023] In one embodiment, inside the reactor, the ammonia adsorbent and the catalyst can be arranged in a mixed manner. For example, the adsorbent particles and the catalyst particles are mixed evenly and then loaded into the corresponding device of the reactor; or the ammonia adsorbent and the catalyst are arranged in a stacked manner. Arranging the ammonia adsorbent and the catalyst adjacent to each other is beneficial to the adsorption of ammonia.

[0024] In one embodiment, one or more layers of catalyst and one or more layers of ammonia adsorbent are arranged in the reactor. The multiple layers of catalyst and the multiple layers of ammonia adsorbent can be arranged in an alternating stacked manner; preferably, the catalyst layer is located above the ammonia adsorbent layer, so that the gas first contacts the catalyst for reaction and then contacts the ammonia adsorbent layer. That is, in the top - down direction (or the gas flow direction), it can be that the first - layer catalyst is located on the first - layer adsorbent, the first - layer adsorbent is located on the second - layer catalyst, and the second - layer catalyst is located on the second - layer adsorbent. As the reaction proceeds, the adsorbent is saturated layer by layer from top to bottom. During the whole process, the ammonia content in the reactor gas is maintained below 0.1 vol%, and the equilibrium concentration cannot be reached, which promotes the reaction to proceed in the direction of ammonia synthesis. Further, the height ratio of the multiple catalyst layers to the multiple adsorbent layers can be 1:(1 - 2), such as 1:1, 1:1.5, 1:2.

[0025] In one embodiment, the ammonia adsorbent includes one or more of the halides of alkali metals and alkaline earth metals; further, the ammonia adsorbent can be the halides of calcium, magnesium, barium, and lithium. For example, the ammonia adsorbent can be magnesium chloride, calcium chloride, or a mixture of the two.

[0026] In one embodiment, the catalyst can be an existing catalyst for synthesizing ammonia from hydrogen and ammonia. Further, the catalyst is preferably a catalyst for low-temperature ammonia synthesis. For example, the catalyst includes iron element and / or ruthenium element.

[0027] In one embodiment, the catalyst can be one or more of iron, ruthenium and their complexes, such as an iron-based catalyst.

[0028] In one embodiment, the volume ratio of the catalyst to the ammonia adsorbent is 1:(1-2), such as 1:1, 1:1.5, 1:2.

[0029] In one embodiment, the feed gas includes hydrogen and nitrogen. During operation, the feed gas is introduced into the reactor to carry out the ammonia synthesis reaction under the action of the catalyst. The generated ammonia will be adsorbed by the ammonia adsorbent. Therefore, the content of ammonia in the syngas during the reaction process is extremely low. The gas discharged from the reactor mainly contains hydrogen and nitrogen, which can be returned to the feed gas device as recycle gas for reuse. As the reaction and adsorption proceed, the content of ammonia in the syngas gradually increases. When the ammonia content in the syngas is greater than 0.1% by volume, the ammonia synthesis reaction is stopped, and the ammonia adsorbed on the ammonia adsorbent is desorbed.

[0030] In one embodiment, multiple reactors are used for continuous ammonia synthesis. The multiple reactors include a first reactor and a second reactor; the ammonia synthesis reaction and the desorption treatment of the ammonia adsorbent can be alternately carried out in the first reactor and the second reactor respectively. In addition, the switching period can be determined according to the adsorption and desorption time, and a medium-temperature pressure swing adsorption process is adopted.

[0031] In one embodiment, the desorption treatment (or desorption regeneration) of ammonia can be carried out by means of pressure reduction and vacuum pumping. Further, nitrogen can be used to flush the inside of the reactor to further purge the ammonia in the reactor after the desorption treatment and reduce the ammonia residue. Still further, after the desorption treatment is completed, a nitrogen-hydrogen mixed gas can be introduced into the reactor for pressurization to carry out the next reaction and desorption.

[0032] One embodiment of the present invention provides a composition for ammonia synthesis, including the above-mentioned catalyst for ammonia synthesis and the above-mentioned ammonia adsorbent.

[0033] Refer to Figure 1 As shown, one embodiment of the present invention provides an ammonia synthesis system for carrying out the above synthesis process, including:

[0034] One or more reactors for carrying out the ammonia synthesis reaction and adsorbing ammonia;

[0035] A feed gas device for providing the feed gas for the reactor to carry out the reaction;

[0036] A recycle gas pipeline 30 for recycling the unreacted gas in the reactor back to the raw material gas device;

[0037] A purge gas pipeline 40 for supplying purge gas to the reactor; and

[0038] An ammonia recovery device for collecting the ammonia obtained from the desorption treatment.

[0039] In one embodiment, the reactor is a reaction tower or a synthesis tower.

[0040] In one embodiment, the multiple reactors include a first reaction tower 10 and a second reaction tower 20. The first reaction tower 10 and the second reaction tower 20 are respectively connected to the raw material gas device, the recycle gas pipeline 30, the purge gas pipeline 40, and the ammonia recovery device.

[0041] In one embodiment, a first intake valve 11 is provided between the raw material gas device and the first reaction tower 10 for controlling the entry and cut-off of the raw material gas into the first reaction tower 10. Correspondingly, a second intake valve 21 is provided between the raw material gas device and the second reaction tower 20 for controlling the entry and cut-off of the raw material gas into the second reaction tower 20.

[0042] In one embodiment, a first outlet valve 12 is provided between the recycle gas pipeline 30 and the first reaction tower 10 to enable the flow and cut-off of the gas between the first reaction tower 10 and the recycle gas pipeline 30. The unreacted gas discharged from the first reaction tower 10 can be returned to the raw material gas device through the recycle gas pipeline 30. Correspondingly, a second outlet valve 22 is provided between the recycle gas pipeline 30 and the second reaction tower 20.

[0043] In one embodiment, the raw material gas device includes a nitrogen gas pipeline 51 and a hydrogen gas pipeline 52 for respectively supplying nitrogen and hydrogen. A first nitrogen valve 13 and a second nitrogen valve 23 are respectively provided between the nitrogen gas pipeline 51 and the first reaction tower 10 and the second reaction tower 20 to respectively enable the flow and cut-off of the gas between the nitrogen gas pipeline 51 and the first reaction tower 10 and the second reaction tower 20.

[0044] In one embodiment, a first ammonia recovery valve 14 and a second ammonia recovery valve 24 are respectively provided between the ammonia recovery device and the first reaction tower 10 and the second reaction tower 20 to respectively enable the flow and cut-off of the passage between the ammonia recovery device and the first reaction tower 10 and the second reaction tower 20.

[0045] In one embodiment, the ammonia recovery device includes a heat exchanger 61, a booster 62, and a liquid ammonia collection tank 63 connected in sequence. The first ammonia recovery valve 14 can be disposed between the first reaction tower 10 and the heat exchanger 61, and the second ammonia recovery valve 24 can be disposed between the second reaction tower 20 and the heat exchanger 61.

[0046] In one embodiment, during operation, the first intake valve 11 is opened to allow the raw material gas to enter the first reaction tower 10 for reaction. During the reaction, the ammonia generated is continuously adsorbed by the ammonia adsorbent in the first reaction tower 10, and the unreacted raw material gas returns to the raw material gas device as recycle gas through the recycle gas pipeline. When the ammonia content in the recycle gas at the outlet of the first reaction tower 10 is greater than 0.1% by volume, it indicates that the ammonia adsorbent in the first reaction tower 10 has been saturated with adsorption. The first intake valve 11 is closed, and the second intake valve 21 is opened to switch the raw material gas to be introduced into the second reaction tower 20, so that the synthesis reaction proceeds in the second reaction tower 20;

[0047] On the other hand, the first reaction tower 10 is depressurized, and ammonia is completely desorbed by vacuum pumping. The desorbed ammonia is heat-exchanged and cooled through the heat exchanger 61 and pressurized and liquefied by the booster 62 to liquefy the ammonia, and finally the liquefied ammonia is collected by the liquid ammonia collection tank 63. After the desorption is complete, a mixed gas of hydrogen and nitrogen is further introduced into the first reaction tower 10 to pressurize the first reaction tower 10 to prepare for the next ammonia adsorption.

[0048] In one embodiment, the ammonia synthesis reaction is an exothermic reaction. From a thermodynamic perspective, low temperature (e.g., 150 - 400 °C) and high pressure (e.g., 1 - 10 MPa) are beneficial for the forward generation of NH3, and low temperature and high pressure are also beneficial for the process of the adsorbent adsorbing ammonia.

[0049] In one embodiment of the ammonia synthesis process of the present invention, by using a catalyst and an ammonia adsorbent in combination, the product ammonia is almost immediately adsorbed as it is generated, reducing the ammonia concentration in the synthesis gas, thereby increasing the conversion rate of the reactants and the production rate of the product, and further reducing the production energy consumption and cost.

[0050] In one embodiment of the ammonia synthesis process of the present invention, the coupling of catalysis and ammonia adsorption is beneficial to a certain extent for the reaction temperature of ammonia synthesis to develop towards milder conditions, so that the reaction temperature can be lower than that of traditional ammonia synthesis at the same ammonia conversion rate; for example, the reaction temperature of traditional ammonia synthesis is 380 - 450 °C and the pressure is 10 - 20 MPa; while the reaction temperature of one embodiment of the ammonia synthesis process of the present invention can be 150 - 400 °C and the pressure can be 1 - 10 MPa.

[0051] A process for synthesizing ammonia according to an embodiment of the present invention can achieve continuous ammonia production by using two reactors, omitting the ammonia separation step. Under the same reaction conditions, the net ammonia conversion rate of this process can increase by 3% compared with the traditional ammonia synthesis tower + separation process.

[0052] A process for synthesizing ammonia according to an embodiment of the present invention has a simple process, is convenient for integration with a new energy system, and reduces the operation difficulty of new energy systems such as the green ammonia system. Specifically, the forward development of the ammonia synthesis reaction is promoted by coupling the catalytic process with ammonia adsorption, improving the conversion rate of ammonia. On the one hand, the integration of the reaction and separation process simplifies the overall process; on the other hand, the temperature and pressure for ammonia synthesis under the action of adsorption enhancement can be further reduced, which is more conducive to adapting to the volatility of the gas source.

[0053] Hereinafter, the ammonia synthesis process according to an embodiment of the present invention will be further described in conjunction with the accompanying drawings and specific embodiments. Among them, the ammonia net value is the ammonia content in the gas at the reactor outlet minus the ammonia content in the inlet gas.

[0054] Example 1

[0055] Using calcium chloride as the ammonia adsorbent and an iron-based catalyst for the ammonia synthesis process, wherein the catalyst and the ammonia adsorbent are arranged in multiple layers, and the catalyst layer and the ammonia adsorbent layer are arranged alternately, and their volume ratio is 1:1. The ammonia catalyst and the adsorbent are stacked in layers in the first reaction tower 10 and the second reaction tower 20, and the ammonia synthesis, adsorption process, and desorption process are alternately carried out in the two towers according to the foregoing steps. The temperature in the tower during the reaction is 300 °C, and the pressure is 10 MPa. The temperature in the tower during the desorption process is 300 °C, and the pressure is 0.1 MPa.

[0056] Finally, the ammonia net value of the reaction tower is measured to be 12%.

[0057] Example 2

[0058] Using a mixture of calcium chloride and magnesium chloride as the ammonia adsorbent and an iron-based catalyst for the ammonia synthesis process, wherein the catalyst and the ammonia adsorbent are arranged in multiple layers, and the catalyst layer and the ammonia adsorbent layer are arranged alternately, and their volume ratio is 1:1. The ammonia catalyst and the adsorbent are stacked in layers in the first reaction tower 10 and the second reaction tower 20, and the ammonia synthesis, adsorption process, and desorption process are alternately carried out in the two towers according to the foregoing steps. The temperature in the tower during the reaction is 300 °C, and the pressure is 10 MPa. The temperature in the tower during the desorption process is 300 °C, and the pressure is 0.1 MPa.

[0059] Finally, the ammonia net value of the reaction tower is measured to be 14%.

[0060] Comparative Example 1

[0061] In this example, the synthesis of ammonia is carried out by traditional processes. Using an iron-based ammonia synthesis catalyst, the ammonia synthesis reaction is carried out at 300 °C and a pressure of 10 MPa, and the net ammonia value is 7%.

[0062] Unless otherwise specified, the terms used in this invention have the meanings commonly understood by those skilled in the art.

[0063] The embodiments described in this invention are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Those skilled in the art can make various other substitutions, changes and improvements within the scope of this invention. Therefore, this invention is not limited to the above embodiments and is only defined by the claims.

Claims

1. A process for ammonia synthesis, comprising: Under the action of a catalyst, a reaction for synthesizing ammonia is carried out in a reactor using hydrogen and nitrogen as raw materials to produce ammonia gas; wherein, an ammonia adsorbent is arranged in the reactor so that the ammonia gas contacts with the ammonia adsorbent to adsorb the ammonia gas.

2. The ammonia synthesis process according to claim 1, wherein, The catalyst and the ammonia adsorbent are arranged in a mixed manner, or the catalyst and the ammonia adsorbent are arranged in a stacked manner.

3. The ammonia synthesis process according to claim 2, wherein, Multiple layers of the ammonia adsorbent and multiple layers of the catalyst are arranged in the reactor, and the multiple layers of the ammonia adsorbent and the multiple layers of the catalyst are arranged in an alternating stacked manner.

4. The ammonia synthesis process according to claim 1, wherein, The ammonia adsorbent includes one or more of halides of alkali metals and alkaline earth metals; and / or, The catalyst includes iron element and / or ruthenium element.

5. The ammonia synthesis process according to claim 1, wherein, The volume ratio of the catalyst to the ammonia adsorbent is 1:(1 - 2); and / or, The reaction temperature for synthesizing ammonia is 150 - 400 °C, and the reaction pressure is 1 - 10 MPa; and / or, The ammonia adsorbent includes one or more of halides of calcium, magnesium, barium, and lithium.

6. The ammonia synthesis process according to claim 1, wherein, When the ammonia content in the reactor gas is greater than 0.1% by volume, the reaction for synthesizing ammonia is stopped, and the ammonia adsorbent adsorbed with ammonia is subjected to ammonia desorption treatment; and / or, The ammonia adsorbent includes calcium chloride and / or magnesium chloride.

7. The ammonia synthesis process according to claim 6, wherein, Multiple reactors are used for continuous synthesis of ammonia. The multiple reactors include a first reactor and a second reactor; the reaction for synthesizing ammonia and the desorption treatment are alternately carried out in the first reactor and the second reactor respectively.

8. A composition for ammonia synthesis, comprising a catalyst for ammonia synthesis and an ammonia adsorbent.

9. An ammonia synthesis system, comprising: One or more reactors for carrying out the reaction of synthesizing ammonia gas and adsorbing the ammonia gas; A raw material gas device for providing the raw material gas for the reactor to carry out the reaction; A circulating gas pipeline for circulating the gas that has not reacted in the reactor back to the raw material gas device; A flushing gas pipeline for providing flushing gas for the reactor; And An ammonia recovery device for collecting the ammonia obtained from the desorption treatment.

10. The ammonia synthesis system according to claim 9, wherein, The reactor is a reaction tower or a synthesis tower; and / or, The ammonia recovery device includes a heat exchanger, a booster, and a liquid ammonia collection tank.

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