System and method for producing hydrogen through ammonia decomposition

Abstract

The invention relates to the field of hydrogen production through ammonia decomposition, and discloses a system and a method for producing hydrogen through ammonia decomposition. The ammonia decomposition hydrogen production system comprises a hydrogen preparation unit, a residual ammonia recovery and separation unit and a hydrogen purification unit, and the hydrogen preparation unit, the residual ammonia recovery and separation unit and the hydrogen purification unit are connected with one another through pipelines; the hydrogen preparation unit comprises an ammonia decomposition reactor, and the ammonia decomposition reactor is used for carrying out ammonia decomposition reaction on raw material ammonia gas to obtain product gas; the system further comprises a heat exchange unit, and the heat exchange unit is used for conducting heat exchange on the product gas and the raw material ammonia gas. The residual ammonia recovery and separation unit comprises a temperature swing adsorption device, and the temperature swing adsorption device is used for adsorbing unreacted ammonia gas to obtain cracked gas; the hydrogen purification unit comprises a membrane separator and a pressure swing adsorption device; the membrane separator is used for separating and purifying the pyrolysis gas to obtain hydrogen-nitrogen mixed gas and crude hydrogen; and the pressure swing adsorption device is used for purifying the crude hydrogen to obtain hydrogen and desorbed gas. The system is high in hydrogen yield and small in occupied area.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogen production by decomposing ammonia, and in particular to a system and method for producing hydrogen by decomposing ammonia. Background Art

[0002] As a green, low-carbon, and abundant secondary energy source, hydrogen energy is gradually becoming an important carrier of global energy transformation and development. At the same time, hydrogen energy is a clean, carbon-free energy source. With the rapid development of fuel cell vehicles in the future, the demand for hydrogen energy will also increase rapidly. However, at present, the development of the hydrogen energy industry still faces certain problems. The problem is that my country's fossil resources and renewable energy are unevenly distributed, and the regional imbalance between hydrogen sources and hydrogen use scenarios is particularly prominent. To solve this problem, the use of distributed hydrogen production technology can realize hydrogen production directly at hydrogen refueling stations, thereby reducing hydrogen costs and reducing transportation safety risks.

[0003] The advantages of developing distributed hydrogen production technology using ammonia as a liquid hydrogen storage medium lie in its ease of liquefaction, the availability of a mature transportation network, high hydrogen storage density, and the carbon-free nature of its decomposition products. However, this method also faces challenges. Due to limited skid space, the hydrogen produced by ammonia decomposition cannot be generated at high yields through pressure swing adsorption alone. Furthermore, ammonia as a raw material poses toxicity concerns. If ammonia is not completely decomposed, directly removing the ammonia from the exhaust gas poses a safety hazard. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems existing in the prior art and provide a system and method for producing hydrogen by decomposing ammonia, which is efficient, energy-saving, safe and environmentally friendly, has a high hydrogen yield and occupies a small area.

[0005] To achieve the above objectives, the present invention provides, in a first aspect, a system for producing hydrogen by decomposing ammonia, wherein the system comprises a hydrogen production unit, a residual ammonia recovery and separation unit, and a hydrogen purification unit, wherein the hydrogen production unit, the residual ammonia recovery and separation unit, and the hydrogen purification unit are interconnected by pipelines;

[0006] The hydrogen production unit includes an ammonia decomposition reactor, which is used to perform an ammonia decomposition reaction on the raw ammonia to obtain product gas;

[0007] The system further includes a heat exchange unit, which is used to exchange heat between the product gas and the raw ammonia gas;

[0008] The residual ammonia recovery and separation unit includes a temperature swing adsorption device, which is used to adsorb unreacted ammonia to obtain cracked gas;

[0009] The hydrogen purification unit includes a membrane separator and a pressure swing adsorption device;

[0010] The membrane separator is used to separate and purify the cracked gas to obtain hydrogen-nitrogen mixed gas and crude hydrogen;

[0011] The pressure swing adsorption device is used to purify crude hydrogen to obtain product hydrogen and desorption gas.

[0012] A second aspect of the present invention provides a method for producing hydrogen by decomposing ammonia, wherein the method is performed in the system described in the first aspect, and wherein the method comprises:

[0013] S1. The raw ammonia gas enters the ammonia decomposition reactor of the hydrogen production unit through the heat exchange unit to undergo ammonia decomposition reaction to obtain product gas;

[0014] S2, the product gas enters the temperature swing adsorption device of the residual ammonia recovery and separation unit to adsorb unreacted ammonia to obtain cracked gas;

[0015] S3, the cracked gas enters the membrane separator of the hydrogen purification unit for separation and purification to obtain hydrogen-nitrogen mixed gas and crude hydrogen;

[0016] S4. The crude hydrogen enters the pressure swing adsorption device of the hydrogen purification unit for purification to obtain product hydrogen and desorption gas.

[0017] The system provided by the present invention uses a heat exchange unit to utilize the product gas of ammonia decomposition to exchange heat with the raw ammonia gas, thereby reducing heat loss and achieving energy saving through internal circulation heat exchange.

[0018] The system provided by the present invention uses a membrane separator coupled with a pressure swing adsorption device to purify hydrogen, thereby improving the hydrogen yield under skid-mounted conditions with limited space, while controlling the by-product to nitrogen, which can be directly discharged without pollution.

[0019] The system of the present invention preferably adopts a method of back-flushing the desorption gas obtained from the hydrogen purification system into the temperature swing adsorption device to purify the hydrogen that is not fully separated for a second time, thereby improving the hydrogen yield. At the same time, the unreacted ammonia re-enters the temperature swing adsorption device for secondary absorption, thereby avoiding the pollution of ammonia emissions to the environment.

[0020] The system provided by the present invention adopts a membrane separator coupled process to obtain a hydrogen-nitrogen mixed gas. Preferably, high-purity nitrogen is produced through a catalytic oxidation unit to increase the value of by-products. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the system of the present invention.

[0022] Description of Reference Numerals

[0023] 1-Liquid Ammonia Electrifier 2-Ammonia Purifier

[0024] 3-Heat exchange unit 31-First heat exchange inlet

[0025] 32-first heat exchange outlet 33-second heat exchange inlet

[0026] 34-Second heat exchange outlet 4-Ammonia decomposition reactor

[0027] 5- Temperature swing adsorption device 6- Membrane separator

[0028] 61-First Exit 62-Second Exit

[0029] 7-pressure swing adsorption device 71-third outlet

[0030] 72-Fourth outlet 8-First buffer tank

[0031] 81-First entrance 82-Second entrance

[0032] 9-Second buffer tank 10-Third buffer tank

[0033] 11-Fourth buffer tank 12-First compressor

[0034] 13-Second compressor DETAILED DESCRIPTION

[0035] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0036] Unless otherwise defined, the technical terms used herein have the same meanings as those commonly understood by those skilled in the art to which this application belongs; the use of relevant terms herein is only for describing specific embodiments and is not intended to limit the present invention.

[0037] In the description of the present invention, the term "and / or" is used to describe a logical relationship between objects, indicating that three possible relationships exist. For example, A and / or B means: A exists, B exists, and both A and B exist. Furthermore, the character " / " generally indicates that the objects are in a logical "or" relationship.

[0038] In the present invention, terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship of quantity, priority or sequence between these entities or operations.

[0039] Without further restrictions, in the present invention, the words "include", "comprise", "have" or other similar expressions used in sentences are intended to cover non-exclusive inclusion. These expressions do not exclude the presence of additional elements in the process, method or product including the elements, so that the process, method or product including a series of elements may include not only those limited elements, but also other elements not explicitly listed, or also include elements inherent to such process, method or product.

[0040] In the present invention, expressions such as "greater than," "less than," and "exceed" are understood to exclude the number itself; expressions such as "above," "below," and "within" are understood to include the number itself. Furthermore, in the description of the embodiments of the present invention, "multiple" means two or more (including two), and similar expressions related to "multiple," such as "multiple groups" and "multiple times," are also understood in this manner, unless otherwise specifically defined.

[0041] In the description of the embodiments of the present invention, the space-related expressions used, such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "vertical", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicate the orientation or position relationship based on the orientation or position relationship shown in the specific embodiments or drawings, and are only for the convenience of describing the specific embodiments of the present invention or facilitating the reader's understanding, and do not indicate or imply that the device or component referred to must have a specific position, a specific orientation, or be constructed or operated in a specific orientation, and therefore cannot be understood as limiting the embodiments of the present invention.

[0042] Unless otherwise expressly specified or limited, in the description of the embodiments of the present invention, the terms "installed", "connected", "connected", "fixed", "set", etc. used should be understood in a broad sense. For example, the "connection" can be a fixed connection, a detachable connection, or an integrated setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal connection between two elements or the interaction relationship between two elements. For those skilled in the art of the technology to which the present invention belongs, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0043] The present invention provides a system for producing hydrogen by decomposing ammonia, such as Figure 1 As shown, the system includes a hydrogen preparation unit, a residual ammonia recovery and separation unit and a hydrogen purification unit, and the hydrogen preparation unit, the residual ammonia recovery and separation unit and the hydrogen purification unit are interconnected by pipelines;

[0044] The hydrogen production unit includes an ammonia decomposition reactor 4, which is used to perform an ammonia decomposition reaction on the raw ammonia gas to obtain product gas;

[0045] The system further includes a heat exchange unit 3, which is used to exchange heat between the product gas and the raw ammonia gas;

[0046] The residual ammonia recovery and separation unit includes a temperature swing adsorption device 5, which is used to adsorb unreacted ammonia to obtain cracked gas;

[0047] The hydrogen purification unit includes a membrane separator 6 and a pressure swing adsorption device 7;

[0048] The membrane separator 6 is used to separate and purify the cracked gas to obtain hydrogen-nitrogen mixed gas and crude hydrogen;

[0049] The pressure swing adsorption device 7 is used to purify crude hydrogen to obtain product hydrogen and desorption gas.

[0050] The system provided by the present invention uses a heat exchange unit to utilize the product gas of ammonia decomposition to exchange heat with the raw ammonia gas, thereby reducing heat loss and achieving energy saving through internal circulation heat exchange.

[0051] The system provided by the present invention uses a pressure swing adsorption device coupled with a membrane separator to purify hydrogen, thereby improving the hydrogen yield under skid-mounted conditions with limited space, while controlling the by-product to nitrogen, which can be directly discharged without pollution.

[0052] The system provided by the present invention adopts a membrane separator coupled process to obtain a hydrogen-nitrogen mixed gas. Preferably, high-purity nitrogen can be produced through a catalytic oxidation unit, thereby increasing the value of by-products.

[0053] In the present invention, membrane separation coupled with pressure swing adsorption is adopted to obtain crude hydrogen containing a large amount of hydrogen and a small amount of nitrogen through a membrane separator, and then the hydrogen purity in the crude hydrogen is improved to the technical index through a pressure swing adsorption device. Preferably, the separated analyzed gas re-enters the residual ammonia separation and recovery unit and the hydrogen purification unit, and the hydrogen in the unanalyzed gas is further separated and purified for a second time, thereby improving the hydrogen recovery rate while ensuring the purity of the hydrogen.

[0054] In the present invention, the form of the ammonia raw material used in the ammonia decomposition reaction is not particularly limited. Preferably, ammonia gas is used to gasify the ammonia source liquid ammonia to obtain the raw material and further improve the efficiency of hydrogen production from ammonia decomposition. Preferably, the hydrogen production unit further includes a liquid ammonia electrifier 1, which is used to gasify the ammonia source liquid ammonia into ammonia gas.

[0055] In order to purify ammonia and improve the efficiency of hydrogen production by ammonia decomposition, the hydrogen production unit preferably further includes an ammonia purifier 2, which is used to purify ammonia to obtain raw ammonia.

[0056] In the present invention, ammonia purification refers to trace amounts of water and oil in the raw ammonia. The present invention does not particularly limit the specific operating methods and conditions for ammonia purification, and those skilled in the art can select them according to actual needs.

[0057] In the present invention, there is no particular limitation on the arrangement of the liquid ammonia electrifier and the ammonia purifier, as long as the gasification and purification of the raw liquid ammonia can be achieved. Preferably, the liquid ammonia electrifier 1 and the ammonia purifier 2 are connected in series through a pipeline. According to a specific embodiment of the present invention, the inlet of the liquid ammonia electrifier 1 is connected to the external ammonia source, the outlet of the liquid ammonia electrifier 1 is connected to the inlet of the ammonia purifier 2, and the outlet of the ammonia purifier 2 is connected to the inlet of the ammonia decomposition reactor 3. In the above manner, the external ammonia source liquid ammonia enters the liquid ammonia electrifier for gasification to obtain ammonia gas, the ammonia gas enters the ammonia purifier for purification to obtain raw ammonia gas, and the raw ammonia gas enters the ammonia decomposition reactor for ammonia decomposition reaction.

[0058] In the present invention, to improve the efficiency of the ammonia decomposition reaction, the ammonia decomposition reactor 4 is preferably loaded with an ammonia decomposition catalyst. The present invention does not specifically limit the type of ammonia decomposition catalyst. Preferably, the ammonia decomposition catalyst comprises a metal active component, a promoter, and an alumina support. The present invention does not specifically limit the type of active metal. Preferably, the metal active component comprises Ru and a non-precious metal component, wherein the non-precious metal component is selected from at least one of Mn, Fe, Co, Ni, and Cu. The present invention does not specifically limit the type of promoter. Preferably, the promoter is selected from at least one of CeO2, MgO, CuO, CaO, and La2O3. The present invention does not specifically limit the content of the various components in the ammonia decomposition catalyst. Preferably, based on the total weight of the ammonia decomposition catalyst, the Ru content is 0.1-2.5% by weight, the non-precious metal content as oxide is 0.1-10% by weight, the promoter content is 2-8% by weight, and the alumina support content is 69.5-97.8% by weight.

[0059] In the present invention, there is no particular limitation on the preparation method of the ammonia decomposition catalyst, and all conventional methods defined in the art are applicable to the present invention.

[0060] In the present invention, to improve the energy utilization rate of the ammonia decomposition hydrogen production system and reduce its energy consumption, thereby achieving energy conservation, the heat exchange unit 3 is preferably provided with a first heat exchange inlet 31, a first heat exchange outlet 32, a second heat exchange inlet 33, and a second heat exchange outlet 34. In the present invention, the heat exchange unit is preferably provided by a heat exchanger, which is schematically illustrated in the present invention.

[0061] In the present invention, according to a specific embodiment of the present invention, as Figure 1 As shown, preferably, the outlet of the ammonia purifier 2 is connected to the first heat exchange inlet 31, the first heat exchange outlet 32 ​​is connected to the inlet of the ammonia decomposition reactor 4, the outlet of the ammonia decomposition reactor 4 is connected to the second heat exchange inlet 33, and the second heat exchange outlet 34 is connected to the inlet of the temperature swing adsorption device 5. Through the above embodiment, the product gas at the outlet of the ammonia decomposition reactor 4 exchanges heat with the raw ammonia gas discharged from the first heat exchange outlet 32 ​​when passing through the second heat exchange inlet 33, so that the temperature of the raw ammonia gas can reach the decomposition temperature more quickly to carry out the decomposition reaction, while saving energy consumption and realizing heat circulation within the system.

[0062] In the present invention, the temperature swing adsorption device can simultaneously adsorb unreacted ammonia in the product gas and residual ammonia in the analysis gas, as well as perform secondary purification of hydrogen that is not fully separated. The present invention preferably adopts two methods to achieve the above effects.

[0063] According to a specific embodiment of the present invention, the inlet of the temperature swing adsorption device 5 is connected to the outlet of the ammonia decomposition reactor 4. Through this preferred embodiment, unreacted ammonia in the ammonia decomposition reaction can be adsorbed to absorb residual ammonia.

[0064] In the present invention, the method of back-flushing the desorption gas obtained from the hydrogen purification system into the temperature swing adsorption device is adopted to purify the hydrogen that is not fully separated for a second time, thereby increasing the hydrogen yield. At the same time, the unreacted ammonia re-enters the temperature swing adsorption device for secondary absorption, thereby avoiding the pollution of ammonia emissions to the environment. According to another specific embodiment of the present invention, the inlet of the temperature swing adsorption device 5 is connected to the third outlet 71 of the pressure swing adsorption device 7. Through the above preferred embodiment, the desorption gas is back-flushed into the temperature swing adsorption device, and the desorption gas is mixed with the cracking gas and circulated in the entire reaction system to recover the residual ammonia, thereby avoiding the pollution of ammonia emissions to the environment. By re-entering the separated desorption gas into the residual ammonia separation and recovery unit and the hydrogen purification unit, the hydrogen in the undesorption gas is further separated and purified, thereby improving the hydrogen recovery rate while ensuring the purity of the hydrogen.

[0065] In the present invention, in order to achieve the recycling of unreacted ammonia, a temperature swing adsorption device is used to adsorb the unreacted ammonia and temporarily store the unreacted ammonia in the temperature swing adsorption device. The subsequent desorption gas is backflushed and mixed with the cracking gas for secondary adsorption. Preferably, the temperature swing adsorption device 5 is provided with an adsorption bed and a regeneration bed, and the adsorption bed and the regeneration bed are connected in parallel. It should be noted that the adsorption bed and the regeneration bed are used alternately. After the adsorbent in the adsorption bed is saturated with adsorption, the inlet of the temperature swing adsorption device 5 is switched to the inlet of the regeneration bed, and the outlet of the temperature swing adsorption device 5 is switched to the outlet of the regeneration bed. After the cracking gas and the desorption gas are mixed, residual ammonia is absorbed, and no ammonia is emitted during the entire process. Parallel connection means that there is no logistics exchange between the adsorption bed and the regeneration bed, but they have the same source of product gas, thereby forming multi-bed parallel processing, further improving the processing capacity of the temperature swing adsorption device. According to a specific embodiment of the present invention, the product gas enters the adsorption bed in the temperature swing adsorption device 5 for adsorption. After the adsorbent in the adsorption bed is saturated with adsorption, it is switched to be used as a regeneration bed and regenerated by back-flushing with regenerated hydrogen. After the regeneration is completed, the adsorption bed is waited for to be saturated with adsorption, and the two are switched again, and the cycle is repeated.

[0066] In the present invention, a buffer tank is usually provided to achieve buffering and temporary storage of gas in each process. Preferably, the system further includes a first buffer tank 8, a second buffer tank 9, a third buffer tank 10 and a fourth buffer tank 11.

[0067] In the present invention, preferably, the system further comprises a first compressor 12 and a second compressor 13. In the present invention, there is no particular limitation on the arrangement of the first compressor and the second compressor, and those skilled in the art can select them according to actual needs.

[0068] In the present invention, in order to better improve the recovery rate and purity of hydrogen and prepare high-purity nitrogen feed gas, the crude hydrogen obtained from the membrane separator 6 is passed into the pressure swing adsorption device 7 for purification to obtain product hydrogen and desorption gas, and the desorption gas is then passed together into the residual ammonia absorption system and the hydrogen purification unit for secondary hydrogen recovery. According to a specific embodiment of the present invention, the first outlet 61 of the membrane separator 6 is connected to the inlet of the fourth buffer tank 11, the outlet of the fourth buffer tank 11 is connected to the inlet of the second compressor 13, the outlet of the second compressor 13 is connected to the inlet of the pressure swing adsorption device 7, and the third outlet 71 of the pressure swing adsorption device 7 is connected to the second inlet 82 of the first buffer tank 8. Through the above embodiment, the crude hydrogen is pressurized and then transported to the pressure swing adsorption device 7 for purification. The analyzed gas re-enters the first buffer tank 8 and is mixed with the cracked gas for secondary hydrogen-nitrogen separation. The final product hydrogen is collected from the fourth outlet 72 of the pressure swing adsorption device 7, and the by-product hydrogen-nitrogen mixed gas is output from the second outlet 62 of the membrane separator 6. This allows the hydrogen and nitrogen in the product to be better separated and purified, thereby improving the hydrogen yield.

[0069] In the present invention, to ensure ammonia emissions, the cracked gas from the ammonia decomposition reactor undergoes residual ammonia absorption, and the desorbed gas from the pressure swing adsorption unit undergoes a secondary residual ammonia absorption. According to one embodiment of the present invention, the second heat exchange outlet 34 of the heat exchanger 3 is connected to the first inlet 81 of the first buffer tank 8, the third outlet 71 of the pressure swing adsorption unit 7 is connected to the second inlet 82 of the first buffer tank 8, and the outlet of the first buffer tank 8 is connected to the inlet of the temperature swing adsorption unit 5. This method enables cyclic absorption of residual ammonia in the system, preventing ammonia emissions.

[0070] In the present invention, in order to achieve the recycling of unreacted ammonia, a temperature swing adsorption device is used to adsorb the unreacted ammonia, thereby achieving effective utilization of ammonia. Preferably, the adsorption bed and the regeneration bed are each independently filled with an adsorbent.

[0071] In the present invention, the range of adsorbents is relatively wide, and any adsorbent conventionally defined in the art is applicable to the present invention. Preferably, the adsorbent is selected from at least one of molecular sieves, activated carbon, silica gel, and alumina.

[0072] In the present invention, there is no particular limitation on the type of membrane separator, and all membrane separators conventionally defined in the art are applicable to the present invention.

[0073] In the present invention, there is no particular limitation on the type of membrane used in the membrane separator. Preferably, the membrane used in the membrane separator 6 is an inorganic membrane and / or an organic membrane.

[0074] In the present invention, there is no particular limitation on the type of inorganic membrane. Preferably, the inorganic membrane is selected from at least one of a ceramic membrane, a glass membrane, a metal membrane, and a molecular sieve membrane.

[0075] In the present invention, there is no particular limitation on the type of organic membrane. Preferably, the organic membrane is made of polysulfone and / or polyimide.

[0076] In the present invention, there is no particular limitation on the property parameters of the membrane, and those skilled in the art can select them according to actual conditions.

[0077] In the present invention, the system preferably further comprises a catalytic oxidation unit for catalytically oxidizing the hydrogen-nitrogen mixture to produce high-purity nitrogen as a byproduct. In the system provided by the present invention, the hydrogen-nitrogen mixture is passed through the catalytic oxidation unit to produce high-purity nitrogen, thereby improving the separation and purification of hydrogen and nitrogen in the product, increasing hydrogen yield, and enhancing the value of the byproduct.

[0078] In the present invention, preferably, the system also includes an auxiliary unit, which includes a gas collection pipe, an air supply pipeline, a ventilation system, a power distribution system and a PLC control system. The auxiliary unit is used to control and connect in series the hydrogen preparation unit, the residual ammonia recovery and separation unit, the hydrogen purification unit and the heat exchange unit.

[0079] A second aspect of the present invention provides a process for producing hydrogen by decomposing ammonia, wherein the process is carried out in the system described in the first aspect, and wherein the process comprises:

[0080] S1, the raw ammonia gas enters the ammonia decomposition reactor 4 of the hydrogen production unit through the heat exchange unit 3 to undergo ammonia decomposition reaction to obtain product gas;

[0081] S2, the product gas enters the temperature swing adsorption device 5 of the residual ammonia recovery and separation unit to adsorb unreacted ammonia to obtain cracked gas;

[0082] S3, the cracked gas enters the pressure swing adsorption device membrane separator 6 of the hydrogen purification unit for separation and purification to obtain hydrogen and crude hydrogen as hydrogen-nitrogen mixed gas products;

[0083] S4, the crude hydrogen desorption gas enters the pressure swing adsorption device 7 of the hydrogen purification unit for purification to obtain product hydrogen and desorption gas.

[0084] The process provided by the present invention, carried out in the aforementioned system, can improve the hydrogen yield while improving the purity of the hydrogen, and can realize the ammonia decomposition hydrogen production reaction within the limited space of the skid-mounted system, thereby realizing the preparation of fuel cell-grade hydrogen. The entire process has no residual ammonia emissions, truly achieving zero pollution.

[0085] In the present invention, the range of conditions for the ammonia decomposition reaction is relatively wide. Preferably, in step S1, the temperature of the ammonia decomposition reaction is 480-600°C.

[0086] In the present invention, other conditions involved in the ammonia decomposition reaction are not particularly limited, and those skilled in the art may select them according to actual needs.

[0087] In the present invention, preferably, the method further comprises transporting the ammonia source liquid ammonia to the liquid ammonia electrifier 1 and the ammonia purifier 2 of the hydrogen preparation unit in sequence for gasification and purification to obtain raw ammonia gas.

[0088] In the present invention, to avoid residual ammonia emission and achieve residual ammonia absorption, the method preferably further comprises: returning the desorption gas in step S4 to step S2 to be mixed with the cracking gas, and then conveying it to the temperature swing adsorption device 5 for secondary adsorption.

[0089] In the present invention, catalytic oxidation in the hydrogen-nitrogen mixed gas can improve the high-value utilization of by-products. Preferably, the method further comprises: conveying the hydrogen-nitrogen mixed gas in step S3 to a catalytic oxidation unit for catalytic oxidation to obtain high-purity nitrogen as a by-product.

[0090] In the present invention, the range of conditions for temperature swing adsorption is relatively wide, and those skilled in the art can select according to actual conditions. Preferably, the inlet pressure of the pressure swing adsorption device 7 is 1500-2300 KPa.

[0091] In the present invention, the range of membrane separation conditions is relatively wide, and those skilled in the art can select according to actual conditions. Preferably, the inlet pressure of the membrane separator 6 is 1500-2300 KPa.

[0092] In the present invention, preferably, the purity of the hydrogen produced by the method provided by the present invention meets the hydrogen technical index requirements specified in GB / T37244-2018 "Hydrogen Fuel for Proton Exchange Membrane Fuel Cell Vehicles".

[0093] According to a specific embodiment of the present invention, the ammonia decomposition hydrogen production process is as follows Figure 1 In the system shown, the raw liquid ammonia is vaporized in the liquid ammonia electric vaporizer 1, and then passes through the ammonia purifier 2 to remove impurities. The raw liquid ammonia enters the first heat exchange inlet 31 of the heat exchange unit 3. After heat exchange in the heat exchange unit 3, it flows out from the first heat exchange outlet 32 ​​and enters the ammonia decomposition reactor 4 for ammonia decomposition reaction. The resulting product gas flows out from the second heat exchange inlet 33 of the heat exchange unit 3, enters the heat exchange unit, and then flows out through the second heat exchange outlet 34. The product gas then enters the first inlet 81 of the first buffer tank 8 and then enters the temperature swing adsorption device 5 to adsorb unreacted ammonia to obtain cracked gas. The cracked gas is then pressurized in the second buffer tank 9 and the first compressor 12, and then passes through the third buffer tank 10 to enter the membrane separator 6 for separation. Crude hydrogen and a hydrogen-nitrogen mixed gas are respectively obtained from the first outlet 61 and the second outlet 62 of the membrane separator 6. The hydrogen-nitrogen mixed gas is transported to the catalytic oxidation unit for catalytic oxidation to obtain high-purity nitrogen as a by-product. The crude hydrogen is pressurized by the fourth buffer tank 11 and the second compressor 13 and then enters the pressure swing adsorption device 7. The decomposed gas and the product hydrogen are obtained from the third outlet 71 and the fourth outlet 72 of the pressure swing adsorption device 7 respectively. The decomposed gas enters the temperature swing adsorption device 5 again through the second inlet 82 of the first buffer tank 8 to carry out the above cycle for purification and separation.

[0094] The present invention will be described in detail below through examples.

[0095] To illustrate the system and method provided by the present invention, the following examples are schematically illustrated by simulation experiments, specifically using ASPEN software to simulate and illustrate the continuous progress of the ammonia decomposition reaction.

[0096] Example 1

[0097] According to Figure 1 In the system shown, the raw liquid ammonia (mass flow rate: 121.4 kg / h) is vaporized by the liquid ammonia electric vaporizer 1, and then passes through the ammonia purifier 2 to remove impurities. The raw liquid ammonia enters the first heat exchange inlet 31 of the heat exchange unit 3, undergoes heat exchange from 30°C to 330°C in the heat exchange unit 3, and then flows out from the first heat exchange outlet 32 ​​to enter the ammonia decomposition reactor 4, where the ammonia decomposition reaction is carried out at 550°C. The obtained product gas (ammonia mass flow rate: 0.4 kg / h; nitrogen mass flow rate: 99.5 kg / h; hydrogen mass flow rate: 21.5 kg / h) flows out from the second heat exchange inlet 33 of the heat exchange unit 3, undergoes heat exchange to 40°C, and then flows out from the second heat exchange outlet 33 of the heat exchange unit 3. The crude hydrogen (nitrogen mass flow rate: 2.0 kg / h; hydrogen mass flow rate: 21.4 kg / h) and the hydrogen-nitrogen mixed gas (nitrogen mass flow rate: 99.6 kg / h; hydrogen mass flow rate: 1.1 kg / h) are respectively obtained from the first outlet 61 and the second outlet 62 of the membrane separator 6. The hydrogen-nitrogen mixed gas is transported to the catalytic oxidation unit for catalytic oxidation to obtain high-purity nitrogen as a by-product. The crude hydrogen is pressurized to 1800 kPa by the fourth buffer tank 11 and the second compressor 13 and enters the pressure swing adsorption device 7. Desorption gas (nitrogen mass flow rate: 2.1 kg / h; hydrogen mass flow rate: 1.0 kg / h) and product hydrogen (mass flow rate: 20.4 kg / h) are respectively obtained from the third outlet 71 and the fourth outlet 72 of the pressure swing adsorption device 7. The desorption gas enters the temperature swing adsorption device 5 again through the second inlet 82 of the first buffer tank 8 to undergo the above-mentioned cycle for purification and separation. The final product hydrogen has a purity of 99.999% and a recovery rate of 95.3% (calculated based on the ratio of the mass of the product hydrogen to the mass of hydrogen atoms in the raw liquid ammonia).

[0098] The system of the present invention recovers residual ammonia by circulating the analytical gas, thereby avoiding environmental pollution caused by ammonia emissions.

[0099] According to an embodiment of the present invention, ammonia is used as a raw material for hydrogen production. Ammonia is easy to decompose and has a high decomposition rate, is low in cost, is easy to store, is not prone to safety accidents such as explosions, and the products after the reaction are clean and environmentally friendly and will not cause air pollution. In addition, the heat obtained from the ammonia decomposition reaction is recycled and utilized, thereby reducing the energy loss of the system. In addition, the device for producing fuel cell-grade hydrogen by decomposing ammonia uses a membrane separator coupled with a pressure swing adsorption device to purify the hydrogen, thereby improving the hydrogen recovery rate under skid-mounted conditions with limited space, and at the same time controlling the by-product to be a hydrogen-nitrogen mixed gas, which can be used to prepare high-purity nitrogen. Finally, the device for producing fuel cell-grade hydrogen by decomposing ammonia uses a desorption gas circulation method of the pressure swing adsorption device to recover residual ammonia, thereby avoiding environmental pollution caused by ammonia emissions.

[0100] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A system for producing hydrogen by decomposing ammonia, characterized in that: The system comprises a hydrogen preparation unit, a residual ammonia recovery and separation unit and a hydrogen purification unit, wherein the hydrogen preparation unit, the residual ammonia recovery and separation unit and the hydrogen purification unit are interconnected through pipelines; The hydrogen preparation unit comprises an ammonia decomposition reactor (4), and the ammonia decomposition reactor (4) is used to carry out an ammonia decomposition reaction on the raw ammonia to obtain a product gas; The system further comprises a heat exchange unit (3), wherein the heat exchange unit (3) is used to perform heat exchange between the product gas and the raw ammonia gas; The residual ammonia recovery and separation unit comprises a temperature swing adsorption device (5), and the temperature swing adsorption device (5) is used to adsorb unreacted ammonia to obtain cracked gas; The hydrogen purification unit comprises a membrane separator (6) and a pressure swing adsorption device (7); The membrane separator (6) is used to separate and purify the cracked gas to obtain a hydrogen-nitrogen mixed gas and crude hydrogen; The pressure swing adsorption device (7) is used to purify crude hydrogen to obtain product hydrogen and decomposed gas.

2. The system according to claim 1, wherein: The hydrogen preparation unit further comprises a liquid ammonia electrifier (1), and the liquid ammonia electrifier (1) is used to gasify the ammonia source liquid ammonia into ammonia gas. Preferably, the hydrogen preparation unit further comprises an ammonia purifier (2), and the ammonia purifier (2) is used to purify ammonia to obtain raw ammonia.

3. The system according to claim 1 or 2, wherein: The inlet of the temperature swing adsorption device (5) is in communication with the outlet of the ammonia decomposition reactor (4); and / or the inlet of the temperature swing adsorption device (5) is in communication with the first outlet (71) of the pressure swing adsorption device (7); Preferably, the temperature swing adsorption device (5) is provided with an adsorption bed and a regeneration bed, and the adsorption bed and the regeneration bed are connected in parallel; Preferably, the adsorption bed and the regeneration bed are each independently filled with an adsorbent; Preferably, the adsorbent is selected from at least one of molecular sieves, activated carbon, silica gel and alumina.

4. The system according to any one of claims 1 to 3, wherein: The membrane used in the membrane separator (6) is an inorganic membrane and / or an organic membrane; Preferably, the inorganic membrane is selected from at least one of a ceramic membrane, a glass membrane, a metal membrane and a molecular sieve membrane; Preferably, the material of the organic film is polysulfone and / or polyimide.

5. The system according to any one of claims 1 to 4, wherein: The system also includes a catalytic oxidation unit, which is used to catalytically oxidize the hydrogen-nitrogen mixed gas to obtain high-purity nitrogen as a by-product.

6. A method for producing hydrogen by decomposing ammonia, wherein: The method is performed in a system according to any one of claims 1 to 5, wherein the method comprises: S1, the raw ammonia gas enters the ammonia decomposition reactor (4) of the hydrogen production unit through the heat exchange unit (3) to undergo an ammonia decomposition reaction to obtain a product gas; S2, the product gas enters the temperature swing adsorption device (5) of the residual ammonia recovery and separation unit to adsorb unreacted ammonia to obtain cracked gas; S3, the cracked gas enters the membrane separator (6) of the hydrogen purification unit for separation and purification to obtain a hydrogen-nitrogen mixed gas and crude hydrogen; S4, the crude hydrogen enters the pressure swing adsorption device (7) of the hydrogen purification unit for purification to obtain product hydrogen and desorption gas.

7. The method according to claim 6, wherein: In step S1, the temperature of the ammonia decomposition reaction is 480-600°C.

8. The method according to claim 6 or 7, wherein: The method further comprises transporting the ammonia source liquid ammonia to the liquid ammonia electrifier (1) and the ammonia purifier (2) of the hydrogen preparation unit in sequence for gasification and purification to obtain raw ammonia gas.

9. The method according to any one of claims 6 to 8, wherein: The method further comprises: returning the decomposed gas in step S4 to step S2 to be mixed with the cracked gas, and then conveying the mixed gas to a temperature swing adsorption device (5) for secondary adsorption; Preferably, the method further comprises: conveying the hydrogen-nitrogen mixed gas in step S3 to a catalytic oxidation unit for catalytic oxidation to obtain high-purity nitrogen as a by-product.

10. The method according to any one of claims 6 to 9, wherein: The inlet pressure of the pressure swing adsorption device (7) is 1500-2300 KPa. Preferably, the inlet pressure of the membrane separator (6) is 1500-2300 KPa.

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