Ammonia-hydrogen combustion-ammonia decomposition hydrogen production-fuel cell coupling system

Abstract

The utility model discloses an ammonia hydrogen combustion-ammonia decomposition hydrogen production-fuel cell coupling system which comprises a liquid ammonia storage device, a gasifier, a first heat exchanger, a second heat exchanger, an ammonia decomposition reactor, a membrane separation purifier, a combustor and a fuel cell. The system realizes multi-stage preheating of ammonia gas through the first heat exchanger and the second heat exchanger, so that the energy efficiency is improved; ammonia gas in the ammonia decomposition reactor is decomposed into hydrogen and nitrogen, high-temperature product mixed gas serves as a heat source of the second heat exchanger, and energy is further recycled; the membrane separation purifier adopts a selective hydrogen permeation membrane to efficiently separate hydrogen, so that the hydrogen purity is improved; hydrogen prepared by ammonia decomposition is used for fuel cell power generation, and gradient utilization and efficient conversion of energy are achieved. In addition, a combustor is introduced into the system, residual gas, external air and hydrogen are used for combustion, heat is supplied to the ammonia decomposition reaction, and stable operation of the system under different working conditions can be guaranteed by adjusting the proportion and flexibly controlling the temperature and strength of the combustion reaction.

Description

Technical Field

[0001] The utility model relates to the technical field of hydrogen energy, and particularly relates to an ammonia-hydrogen combustion-ammonia decomposition hydrogen production-fuel cell coupling system. Background Technique

[0002] With the transformation of the global energy structure and the enhancement of environmental protection awareness, hydrogen energy, as a clean, efficient, and renewable energy source, is considered an important part of the future energy system. However, the preparation, storage, and transportation of hydrogen have always been key technical problems restricting its wide application. Traditional hydrogen production methods such as steam reforming and electrolysis of water have various deficiencies in terms of energy consumption, cost, and environmental friendliness. Therefore, it is of great significance to explore and develop new, efficient, and environmentally friendly hydrogen production and utilization technologies.

[0003] In this context, ammonia, as a potential hydrogen carrier, has gradually attracted the attention of researchers due to its high hydrogen content (about 17.6%), easy liquefaction for storage and transportation, and the ability to be prepared by renewable energy sources (such as hydropower and wind power). Ammonia decomposition hydrogen production technology, as a new hydrogen production method, has significant advantages such as clean and efficient, convenient storage, and wide application. Through the ammonia decomposition reaction, ammonia can be efficiently converted into hydrogen and nitrogen under relatively low temperature and pressure conditions, and the hydrogen can be directly used in fields such as fuel cells. The major technical requirement in the current ammonia-hydrogen technology field is to integrate the power systems formed by the hydrogen production system and the fuel cell system to form skid-mounted and mobile equipment, so that it can be used in application scenarios such as ships, heavy trucks, and miniaturized energy storage devices.

[0004] However, currently restricted by the system integration and the technical level of key components, ammonia decomposition hydrogen production technology and hydrogen-oxygen fuel cell technology still face some challenges in practical applications, such as high reaction temperature, large energy consumption, and complex systems. In order to further improve the efficiency and economy of ammonia decomposition hydrogen production and expand its application fields, researchers have begun to explore combining ammonia decomposition hydrogen production technology with other technologies to form a coupling system. Content of the Utility Model

[0005] Aiming at the deficiencies of the prior art, the utility model provides an ammonia-hydrogen combustion-ammonia decomposition hydrogen production-fuel cell coupling system, aiming to provide heat energy for the ammonia decomposition reaction through the heat generated by ammonia-hydrogen combustion, reducing energy consumption; at the same time, using the hydrogen produced by ammonia decomposition for fuel cell power generation to achieve cascaded utilization and efficient conversion of energy. This system integrates multiple links such as liquid ammonia storage and gasification, ammonia-hydrogen combustion, ammonia decomposition hydrogen production, hydrogen purification, and fuel cell power generation, forming a closed-loop energy conversion and utilization system.

[0006] The utility model adopts the following technical solutions:

[0007] The utility model provides an ammonia hydrogen combustion - ammonia decomposition hydrogen production - fuel cell coupling system, which includes a liquid ammonia storage device, a vaporizer, a second heat exchanger, an ammonia decomposition reactor, a membrane separation and purification device, and a fuel cell; the liquid ammonia storage device is communicated with the vaporizer and is used for vaporizing liquid ammonia into ammonia gas; the second heat exchanger includes a second cold heat exchange gas channel and a second hot heat exchange gas channel, the ammonia decomposition reactor includes an ammonia decomposition reaction ammonia gas channel and an ammonia decomposition reaction flue gas channel, the membrane separation and purification device includes a purified gas channel and a residual gas channel, the outlet of the vaporizer is communicated with the inlet of the second cold heat exchange gas channel, and the outlet of the second cold heat exchange gas channel is communicated with the inlet of the ammonia decomposition reaction ammonia gas channel, and the ammonia gas after heat exchange by the second heat exchanger is introduced into the ammonia decomposition reactor for ammonia decomposition; the outlet of the ammonia decomposition reaction ammonia gas channel is communicated with the inlet of the second hot heat exchange gas channel, and the outlet of the second hot heat exchange gas channel is communicated with the inlet of the purified gas channel, and the product mixed gas after decomposition by the ammonia decomposition reactor is used as the heat exchange medium of the second heat exchanger to exchange heat with the ammonia gas passing through the second cold heat exchange gas channel and then is introduced into the membrane separation and purification device for hydrogen purification; the outlet of the purified gas channel is communicated with the negative electrode of the fuel cell to provide fuel hydrogen for the fuel cell.

[0008] The system further includes a first heat exchanger and a burner. The first heat exchanger includes a first cold heat exchange gas channel and a first hot heat exchange gas channel. The outlet of the vaporizer is communicated with the inlet of the first cold heat exchange gas channel, and the outlet of the first cold heat exchange gas channel is communicated with the second cold heat exchange gas channel, and the ammonia gas vaporized by the vaporizer is subjected to the first heat exchange and temperature rise through the first heat exchanger; the outlet of the residual gas channel is communicated with the inlet of the burner, the outlet of the burner is communicated with the inlet of the ammonia decomposition reaction flue gas channel, the outlet of the ammonia decomposition reaction flue gas channel is communicated with the inlet of the first hot heat exchange gas channel, and the high - temperature flue gas generated by the ignition and combustion of the mixed gas in the burner provides heat energy for the ammonia decomposition reaction in the ammonia decomposition reactor, and the remaining heat is used for heat exchange of the ammonia gas passing through the first heat exchanger.

[0009] The separation membrane for purification in the membrane separation and purification device is a hydrogen - selective permeable membrane, which can efficiently separate hydrogen from other gases.

[0010] Preferably, the separation membrane in the membrane separation and purification device adopts one of a metal vanadium or a metal niobium alloy membrane.

[0011] Preferably, the ammonia decomposition reactor is a fixed - bed reactor, and an ammonia decomposition catalyst is filled in the ammonia gas channel of the ammonia decomposition reactor. The reactant ammonia gas flow enters the ammonia gas channel of the ammonia decomposition reactor after flowing out of the second heat exchanger and flows through the ammonia decomposition catalyst to be converted into decomposition products to obtain hydrogen and nitrogen.

[0012] The burner contains an ignition device. Under appropriate fuel flow rate and air flow rate, after successful ignition and stable operation of the device, the air flow rate is 4 to 30 times the ammonia flow rate flowing into the ammonia decomposition reactor. Whether the fuel combustion state is normal is judged by whether the temperature at the burner outlet is not lower than 640 °C.

[0013] The purified hydrogen flowing out of the membrane separation and purification device can be introduced into the hydrogen tank after being cooled to near room temperature by the radiator. The hydrogen in the hydrogen tank and the compressed air generated by the air compressor flow into the negative electrode and the positive electrode of the fuel cell at a certain flow rate respectively, and the fuel cell can start working and output electric work externally.

[0014] The system further includes a radiator and a hydrogen tank. The outlet of the purified gas channel is successively connected in series with the radiator and the hydrogen tank to cool and collect the purified hydrogen. The outlet of the hydrogen tank is communicated with the negative electrode of the fuel cell.

[0015] The system further includes an air compressor. The outlet of the air compressor is divided into two paths, one path is communicated with the inlet of the burner, and the other path is communicated with the positive electrode of the fuel cell.

[0016] The outlet of the air compressor, the outlet of the hydrogen tank, the outlet of the vaporizer, the outlet of the second heat exchange hot gas channel and the outlet of the residual gas channel can be simultaneously communicated with the inlet of the burner through pipelines to provide fuel gas and combustion-supporting gas for the burner. The outlet of the first heat exchange hot gas channel is communicated with the flue gas processor for purifying the discharged flue gas.

[0017] The system further includes a nitrogen tank. The outlet pipeline of the liquid ammonia storage device and the outlet pipeline of the nitrogen tank converge and are communicated with the inlet of the vaporizer.

[0018] The technical solution of the present utility model has the following advantages:

[0019] A. Through the continuous gasification, heat exchange, decomposition of ammonia to produce hydrogen and the utilization of the fuel cell of the present utility model, the effective conversion of ammonia to hydrogen is realized, and the generated hydrogen is used for fuel cell power generation, improving the overall energy utilization efficiency.

[0020] B. To achieve system integration and miniaturization, the present utility model has made a creative design in the sharing of equipment units. For example, the hydrogen gas tank supplied to the negative electrode of the fuel cell also serves two other functions: providing starting fuel for igniting the burner and providing storage space for the hydrogen gas products decomposed from the purified ammonia. The existence of this hydrogen gas tank also has an air flow buffering effect. Even if the air flow from the outlet of the purifier fluctuates to a certain extent with the fluctuations of the process conditions, the air flow supplied to the fuel cell can be relatively stable. Similarly, the air compressor, which is the source of oxygen supply, also serves two functions simultaneously: supplying air to the positive electrode of the fuel cell and to the burner. The design methods of the air compressor and the hydrogen gas tank fully reflect the characteristics of system function coupling.

[0021] C. From the technical characteristics of the device and the process characteristics of the ammonia decomposition reaction, since the ammonia decomposition reaction needs to be carried out at high temperature and the reaction itself is an endothermic reaction, therefore, the heat required to make the equipment work stably mainly includes the heat absorbed by the reaction, the heat absorbed by the vaporization of liquid ammonia, the heat required to heat the gaseous ammonia from a temperature near room temperature to the reaction temperature, the heat required to maintain the temperature of the reactor and the catalyst, and the natural heat dissipation generated by the contact between the pipeline, the cavity and the outside. Except that the vaporization of liquid ammonia can absorb heat from the environment at normal temperature and pressure, all other heat that needs to be absorbed needs to be provided by the heat of the flue gas generated by the combustion process in the burner from the source. Combustion heating is a simple, efficient and space-saving heating method. Except for the burner itself as the heat source, the reactor requires the highest temperature. However, for simple heat exchange, the overall energy utilization rate is difficult to be satisfactory. In order to improve the energy utilization rate, this case designs a two-stage ammonia heat exchanger, enabling the higher-temperature flue gas to conduct two heat exchanges, and at the same time, the product gas also conducts one heat exchange, corresponding to preheating the ammonia gas before entering the reactor more fully.

[0022] D. In terms of temperature and pressure matching, the preferred operating temperature of the metal separation membrane of the present utility model is 300 - 400 °C, and the temperature in the reactor is preferably 440 - 580 °C. It can be seen from this that the temperature and pressure ranges of the product gas after passing through the second heat exchanger will have good matching with the operating temperature range of the metal separation membrane. Especially for the preferred reaction temperature and pressure ranges, they have good matching with the temperature and pressure ranges where the alloy membrane has good separation performance. This enables the alloy membrane to simplify the process and save the overall energy consumption without further process change operations such as heating and pressurizing the product gas when performing gas separation and purification.

[0023] E. The overall design of the present utility model is compact, integrating multiple links such as liquid ammonia storage, vaporization, heat exchange, ammonia decomposition to produce hydrogen, hydrogen purification, and fuel cell power generation, realizing the continuous conversion from raw materials to electric energy, and improving the integration degree and automation level of the system.

[0024] F. The utility model can flexibly control the temperature and intensity of the combustion reaction by adjusting the proportions of hydrogen, air, and ammonia in the burner, and further adjust the conditions of the ammonia decomposition reaction, ensuring the stable operation of the system under different working conditions.

[0025] G. The utility model makes full use of the characteristics of the working temperature and pressure of the ammonia decomposition to hydrogen production reaction, making it suitable for using non-precious metal alloy membranes for hydrogen purification. The use of non-precious metal alloy membranes greatly reduces the cost of the separation membrane compared with palladium-based membranes. On the other hand, compared with the commonly used pressure swing adsorption separation method, for the same hydrogen separation flux in the utility model, the weight and volume of the alloy membrane are greatly reduced, which is of great significance for the miniaturization, modularization, and mobility of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific embodiments of the utility model, the drawings required for the specific embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the utility model. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 It is a schematic diagram of the overall structure of the ammonia-hydrogen combustion - ammonia decomposition to hydrogen production - fuel cell coupling system.

[0028] The labels in the figure are as follows:

[0029] 1 - Liquid ammonia storage device; 2 - Vaporizer; 3 - First heat exchanger, 31 - First cold air heat exchange channel, 32 - First hot air heat exchange channel; 4 - Second heat exchanger, 41 - Second cold air heat exchange channel, 42 - Second hot air heat exchange channel; 5 - Ammonia decomposition reactor, 51 - Ammonia decomposition reaction ammonia channel, 52 - Ammonia decomposition reaction flue gas channel; 6 - Membrane separation and purification device, 61 - Purified gas channel, 62 - Residual gas channel; 7 - Burner; 8 - Air compressor; 9 - Radiator; 10 - Hydrogen tank; 20 - Flue gas processor; 30 - Nitrogen tank; 40 - Fuel cell. SPECIFIC EMBODIMENTS

[0030] The technical solutions of the utility model will be clearly and completely described below with reference to the drawings. Obviously, the described embodiments are some embodiments of the utility model, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the utility model without creative efforts belong to the scope of protection of the utility model.

[0031] As Figure 1As shown in the figure, this embodiment provides a hydrogen production system by coupling ammonia combustion and ammonia decomposition, which includes a liquid ammonia storage device 1, a vaporizer 2, a first heat exchanger 3, a second heat exchanger 4, an ammonia decomposition reactor 5, a membrane separation and purification device 6, and a fuel cell 40. The liquid ammonia storage device 1 is connected to the vaporizer 2 and is used to vaporize liquid ammonia into ammonia gas. The first heat exchanger 3 includes a first cold heat exchange gas channel 31 and a first hot heat exchange gas channel 32. The second heat exchanger 4 includes a second cold heat exchange gas channel 41 and a second hot heat exchange gas channel 42. The ammonia decomposition reactor 5 includes an ammonia decomposition reaction ammonia gas channel 51 and an ammonia decomposition reaction flue gas channel 52. The membrane separation and purification device 6 includes a purified gas channel 61 and a residual gas channel 62. The outlet of the vaporizer 2 is connected to the inlet of the first cold heat exchange gas channel 31, and the outlet of the first cold heat exchange gas channel 31 is connected to the inlet of the second cold heat exchange gas channel 41, so as to perform the first heat exchange and temperature rise on the ammonia gas vaporized by the vaporizer 2 through the first heat exchanger 3. The outlet of the second cold heat exchange gas channel 41 is connected to the inlet of the ammonia decomposition reaction ammonia gas channel 51, and the ammonia gas after heat exchange through the second heat exchanger 4 is introduced into the ammonia decomposition reactor 5 for ammonia decomposition. The outlet of the ammonia decomposition reaction ammonia gas channel 51 is connected to the inlet of the second hot heat exchange gas channel 42, and the outlet of the second hot heat exchange gas channel 42 is connected to the inlet of the purified gas channel 61. The product mixed gas decomposed by the ammonia decomposition reactor 5 is used as the heat exchange medium of the second heat exchanger 4 to exchange heat with the ammonia gas passing through the second cold heat exchange gas channel 41 and then introduced into the membrane separation and purification device 6 for hydrogen purification. The membrane separation and purification device 6 includes at least one inlet, two outlets and contains a metal alloy separation membrane inside. The gas channel through which the gas entering from the inlet passes through the separation membrane and flows out from one of the outlets is the purified gas channel 61, while the gas channel through which the gas that does not pass through the separation membrane and flows out from the other outlet is the residual gas channel 62. The membrane separation and purification device 6 is separated by the metal alloy separation membrane for purification. The gas passing through the separation membrane is the purified gas, and the gas that does not pass through the separation membrane enters the residual gas channel 62 as the residual gas. The outlet of the purified gas channel 61 is connected to the negative electrode of the fuel cell 40 to provide fuel hydrogen for the fuel cell 40. Through the continuous vaporization, heat exchange, decomposition and hydrogen production of ammonia gas and the utilization of the fuel cell, the present utility model realizes the effective conversion of ammonia gas to hydrogen gas, and uses the generated hydrogen gas for fuel cell power generation, improving the overall energy utilization efficiency.

[0032] Furthermore, the system further includes a burner 7. The outlet of the residual gas passage 62 is communicated with the inlet of the burner 7, the outlet of the burner 7 is communicated with the inlet of the ammonia decomposition reaction flue gas passage 52, and the outlet of the ammonia decomposition reaction flue gas passage 52 is communicated with the inlet of the first heat exchange hot gas passage 32. After the high-temperature flue gas generated by the ignition and combustion of the mixed gas in the burner 7 provides heat energy for the ammonia decomposition reaction in the ammonia decomposition reactor 5, the remaining heat is used for heat exchange of ammonia gas through the first heat exchanger 3. The utility model realizes the efficient recovery and utilization of energy through multi-stage heat exchange between the heat generated in the ammonia decomposition process and the heat generated in the combustion process. In particular, the ammonia gas entering the ammonia decomposition reactor is preheated by the high-temperature flue gas generated by combustion, reducing energy consumption and improving the overall thermal efficiency of the system.

[0033] The separation membrane for purification in the membrane separation and purification device 6 is a hydrogen-selective permeable membrane, which can efficiently separate hydrogen from other gases. Specifically, the separation membrane of the membrane separation and purification device 6 adopts a metal vanadium or metal niobium alloy membrane, and the alloy material can be expressed as, M1 x M2 y M3 z ; where M1 represents metal V or Nb, or both, M2 represents one or more of metals W, Mo, Ta, and M3 represents one of Cr, Mn, Ti, Al, Y, Ma, La, Sr, Ba, Ce; the subscripts x, y, z respectively represent the molar fractions corresponding to the atoms of elements M1, M2, M3, where x is 0.87 to 0.96, y is 0.03 to 0.13, z is 0.005 to 0.01, and x + y + z = 1.00; M1 and M2 form a solid solution, and the role of M3 is a deoxidizing alloying element. In this embodiment, the separation membrane in the membrane separation and purification device 6 adopts a metal vanadium-niobium alloy membrane, and the specific material can be expressed as V 0.80 Nb 0.12 Mo 0.05 Cr 0.03 . The working temperature of the separation membrane is 240 to 640 °C, preferably 300 - 400 °C; the working pressure, that is, the gas pressure entering the membrane separator is >0.2 MPa, preferably 0.4 - 1.2 MPa; it should be noted that the process parameters of the separation process outside the above working temperature and pressure do not mean that the hydrogen separation and purification completely fails, but may lead to one or more situations such as reduced purification efficiency, reduced hydrogen purity, and faster damage to the separation membrane.

[0034] The ammonia decomposition reactor 5 uses a fixed-bed reactor. The ammonia decomposition catalyst is filled in the ammonia gas channel of the reactor. The reactant ammonia gas flow enters the ammonia gas channel 51 of the reactor after flowing out of the second heat exchanger 4 and flows through the ammonia decomposition catalyst, and is converted into decomposition products to obtain hydrogen and nitrogen. Inside the ammonia decomposition reactor 5, when the device is operating stably, the process conditions are as follows: The ammonia decomposition catalyst uses an iron-based catalyst, a ruthenium-based catalyst, or a mixture of the two types of catalysts; after the device operates stably, the reaction conditions of the reactor are as follows: The working temperature is 340-840 °C, preferably 440-580 °C; the gas pressure inside the reactor is controlled at 0.2-3 MPa, preferably 0.5-1.5 MPa; the ammonia gas space velocity is 100-10000 h -1 , preferably 1400-6000 h -1 .

[0035] The purified hydrogen flowing out of the membrane separation and purification device 6 has a purity of not less than 99.99%; the hydrogen production rate calculated based on this part of hydrogen can reach 60-86%.

[0036] The system also includes a radiator 9 and a hydrogen tank 10. The radiator 9 and the hydrogen tank 10 are connected in series in sequence at the outlet of the purified gas channel 61, which are used for cooling and collecting the purified hydrogen; the outlet of the hydrogen tank 10 is connected to the negative electrode of the fuel cell 40.

[0037] The system also includes an air compressor 8. After the air compressor 8 compresses the air in the atmosphere, it can output compressed air. The compressed air outlet is divided into two paths. One path is connected to the inlet of the burner 7, and the other path is connected to the positive electrode of the fuel cell 40. The outlet of the air compressor 8, the outlet of the hydrogen tank 10, the outlet of the vaporizer 2, the outlet of the second heat exchange hot gas channel 42, and the outlet of the residual gas channel 62 can be simultaneously connected to the inlet of the burner 7 through pipelines to provide fuel gas and combustion-supporting gas for the burner 7. The outlet of the first heat exchange hot gas channel 32 is connected to the flue gas processor 20, which is used for purifying the discharged flue gas. The utility model can flexibly control the temperature and intensity of the combustion reaction by adjusting the proportions of hydrogen, air, and ammonia in the burner, and further adjust the conditions of the ammonia decomposition reaction to ensure the stable operation of the system under different working conditions.

[0038] The burner 7 contains an ignition device. Under appropriate fuel flow rate and air flow rate, after successful ignition and when the device is operating stably, the air flow rate is 4-30 times the ammonia gas flow rate flowing into the ammonia decomposition reactor; whether the fuel combustion state is normal is judged by whether the temperature at the outlet of the burner is not less than 640 °C.

[0039] The purified hydrogen gas flowing out of the membrane separation purifier 6 can be introduced into the hydrogen gas tank 10 after being cooled to near room temperature by the radiator 9. The hydrogen gas in the hydrogen gas tank 10 and the compressed air generated by the air compressor 8 are respectively fed into the negative electrode and the positive electrode of the fuel cell 40 at a certain flow rate, and the fuel cell can start working and output electric work externally.

[0040] The system further includes a nitrogen gas tank 30. The outlet pipeline of the liquid ammonia storage device 1 converges with the outlet pipeline of the nitrogen gas tank 30 and is connected to the inlet of the vaporizer 2.

[0041] It should be further noted that before the system reaches stable operation, it needs to include a startup stage. The main purpose is to adjust the materials and equipment at or below room temperature to reach a stable operation state. It should be noted that since the initial state of the system is not limited, the startup method to achieve stable operation has great flexibility. Therefore, the startup method of the system and the initial state at startup are not within the protection scope of this application. However, to further clarify the working method of the system, this application gives a conventional method of starting the system from the normal room temperature state.

[0042] Open the nitrogen gas tank 30 to drive out the air in the gas path through which the subsequent liquid ammonia passes, such as the vaporizer 2, the first heat exchanger 3, the second heat exchanger 4, and the ammonia decomposition reactor 5, to avoid the explosion risk caused by the possible mixing of air and fuel. After driving for a period of time, close the nitrogen gas tank and open the ammonia source 1 so that the liquid ammonia flows downstream after passing through the vaporizer 2. Open the air compressor 8 so that the generated compressed air enters the burner 7 and the positive electrode of the fuel cell 40 respectively and reaches the set flow rate; then open the hydrogen gas tank 10 so that hydrogen gas enters the burner 7, ignite the burner 7 and observe the temperature of the flue gas at the outlet of the burner 7. If the outlet flue gas temperature continuously reaches above 640 °C, it is considered that the ignition purpose is achieved. Thereafter, under the heating of the outlet flue gas, the material temperatures of the two heat exchangers, the ammonia decomposition reactor 5, and the membrane separation purifier 6 start to rise and gradually reach the target process parameters. Technicians can decide whether to use the ammonia gas from the outlet of the vaporizer 2 to the inlet of the burner 7 as further fuel according to the material situation and temperature change. When the residual gas passage 62 shows the generation of air flow and continuously supplies fuel to the burner 7, technicians can gradually reduce the hydrogen gas at the outlet of the hydrogen gas tank 10 until it is completely closed. When the temperature, pressure, and flow rate in the ammonia decomposition reactor 5 reach the target process conditions, it is considered that the system startup is completed and enters the stable operation state. At this time, the nitrogen gas tank 30, the ammonia gas pipeline from the vaporizer 2 to the burner 7, and the hydrogen gas pipeline from the hydrogen gas tank 10 to the burner 7 are all in the closed state.

[0043] To achieve system integration and miniaturization, the present utility model has made a creative design in the sharing of equipment units. For example, the hydrogen tank supplied to the negative electrode of the fuel cell also serves two other functions: providing starting fuel for igniting the burner and providing storage space for the hydrogen products decomposed from the purified ammonia. The existence of this hydrogen tank also has an air flow buffering effect. Even if the air flow from the outlet of the purifier fluctuates to a certain extent with the fluctuations of the process conditions, the air flow supplied to the fuel cell can be relatively stable. Similarly, the air compressor, which is the source of oxygen supply, also serves two functions simultaneously: supplying air to the positive electrode of the fuel cell and to the burner. The design methods of the air compressor and the hydrogen tank fully reflect the characteristics of system function coupling.

[0044] From the technical characteristics of the device and the process characteristics of the ammonia decomposition reaction, since the ammonia decomposition reaction needs to be carried out at high temperature and the reaction itself is an endothermic reaction, therefore, to make the equipment work stably, the heat to be provided mainly includes the heat absorbed by the reaction, the heat absorbed by the vaporization of liquid ammonia, the heat required to heat gaseous ammonia from a temperature near room temperature to the reaction temperature, the heat required to maintain the temperature of the reactor and the catalyst, and the natural heat dissipation generated by the contact of the pipeline, cavity with the outside. Except that the vaporization of liquid ammonia can absorb heat from the environment at normal temperature and pressure, all other heat to be absorbed needs to be provided by the heat of the flue gas generated by the combustion process in the burner from the source. Combustion heating is a simple, efficient and space-saving heating method. Except for the burner itself as the heat source, the reactor requires the highest temperature. However, for simple heat exchange, the overall energy utilization rate is difficult to be satisfactory. To improve the energy utilization rate, this case designs a two-stage ammonia heat exchanger, enabling the higher-temperature flue gas to conduct two heat exchanges, and at the same time, the product gas also conducts one heat exchange, corresponding to a relatively sufficient preheating of the ammonia before entering the reactor.

[0045] In terms of temperature and pressure matching, the preferred operating temperature of the metal separation membrane of the present utility model is 300 - 400 °C, and the temperature in the reactor is preferably 440 - 580 °C. It can be seen from this that the temperature and pressure ranges of the product gas after passing through the second heat exchanger will have good matching with the operating temperature range of the metal separation membrane. Especially for the preferred reaction temperature and pressure ranges, they have good matching with the temperature and pressure ranges where the alloy membrane has good separation performance. This enables the alloy membrane to simplify the process and save the overall energy consumption without further process change operations such as heating and pressurizing the product gas when performing gas separation and purification.

[0046] Advantages of using non-precious metal membrane separators:

[0047] It is an obvious common sense in this field that the purity of hydrogen significantly affects the quality or value of hydrogen products. For example, one of the requirements for the purity of hydrogen in a low-temperature hydrogen-oxygen fuel cell is that the purity is not less than 99.99%. Therefore, the hydrogen produced by chemical reactions usually requires a purification process to greatly improve the value of hydrogen products. For the commonly used hydrogen purification methods, the relatively mature ones are mainly the metal membrane separation method and the pressure swing adsorption method (PSA) based on pressure swing adsorption technology.

[0048] The PSA method utilizes the different adsorption capacities of porous materials such as molecular sieves for different gas molecules, as well as the different values of adsorption, desorption capacities, and rates under variable pressure. Through multiple variable pressure operations, some substance molecules (usually impurity molecules) in the raw material gas are adsorbed on the porous material while more target gas molecules are desorbed, thereby realizing the purification of the target gas. The pressure swing adsorption method is technically mature, and the gas can be purified to a high purity according to the purity requirements. Its disadvantage is that the device is too large and heavy, suitable for factory sites, and it is very difficult to be applied to mobile, skid-mounted, and modular equipment.

[0049] The metal membrane separation method utilizes the screening effect of the metal lattice for substances of different sizes and different chemical affinity abilities at a certain temperature, allowing the target gas molecules to pass through the metal membrane faster while the impurity molecules cannot pass through or pass through more slowly. Its advantages are high separation efficiency per unit mass of the equipment, strong chemical selectivity, and the device is easy to be miniaturized and lightweight. The current main disadvantage is that there are not many optional material types and the cost is relatively high. Especially for the currently relatively widely used palladium metal membrane, due to the precious metal property of the material and the high processing cost, the use cost of the palladium membrane is relatively high.

[0050] The present utility model makes full use of the characteristics of the working temperature and pressure of the ammonia decomposition hydrogen production reaction, making it suitable for using a non-precious metal alloy membrane for hydrogen purification. Using a non-precious metal alloy membrane, compared with the palladium-based membrane, the cost of the separation membrane is greatly reduced; on the other hand, compared with the commonly used pressure swing adsorption separation method, for the same hydrogen separation flux in the present utility model, the weight and volume are greatly reduced, which is of great significance for the miniaturization, modularization, and mobility of the device.

[0051] Example 1:

[0052] Using the system as Figure 1 shown, after startup, the stable operation conditions and effects are as follows:

[0053] The separation membrane in the membrane separation purifier 6 adopts a metal vanadium-niobium alloy membrane, and the specific material can be expressed as V 0.80 Nb 0.12 Mo 0.05 Cr 0.03 .

[0054] The operating temperature of the separation membrane is 430 °C; the operating pressure is 0.7 MPa. The ammonia decomposition catalyst is an iron-based catalyst, a type of fused iron catalyst. After the device operates stably, the reaction conditions of the reactor are as follows: the operating temperature is 540 - 580 °C; the gas pressure inside the reactor is 0.7 MPa; the ammonia gas space velocity is 4400 h -1 , and the volume of the filled catalyst is 2.5 L.

[0055] The burner 7 contains an ignition device. At appropriate fuel flow rates and air flow rates, after successful ignition and when the device operates stably, the air flow rate is 12 times the ammonia gas flow rate flowing into the ammonia decomposition reactor; the temperature at the burner outlet remains near 740 °C.

[0056] The purified hydrogen gas flowing out from the membrane separation and purification device 6, after analysis and measurement, its purity is not less than 99.99%; the hydrogen production rate calculated based on this part of hydrogen gas is 68.0%.

[0057] The fuel cell 40 is a low-temperature stack hydrogen-oxygen fuel cell with a rated power of 10 kW. After opening the hydrogen tank 10 and the air compressor 8 and setting the hydrogen and air flow rates according to the fuel cell operating requirements, the fuel cell can output 10 kW of electric power. After the device operates stably, keeping the hydrogen gas flow continuously supplement the hydrogen source of the hydrogen tank 10 through the purification channel 61 of the membrane separator and the radiator 9, the fuel cell can continuously output 10 kW of electric power.

[0058] For some conventional technical operations in the fields described in this application, such as the control, measurement, and adjustment of temperature, pressure, and flow rate inside components, burner ignition, selection of heat exchangers and radiators, measurement of hydrogen purity or gas components, tail gas treatment, etc., the specific implementation methods and selection of design instrument types are not limited, as long as the process condition objectives can be achieved.

[0059] The above fixed-bed reactor is a common type of reactor in this field or the chemical engineering field. Its main feature is that the catalyst is filled in the reactor, and the raw material gas passes through the catalyst bed layer at a certain temperature, pressure, and flow rate to form reaction products. In this case, the ammonia gas flowing out from the second heat exchanger enters the reactor and forms product nitrogen and hydrogen after passing through the catalyst.

[0060] Due to the heat effect of the reaction inside the fixed-bed reactor and the uneven heating of the heat source, the temperature of the catalyst bed layer inside the reactor, usually called the reaction temperature, is often not uniform at different spatial points and is usually a temperature range. Typically, the temperature difference at different points can be in the range of 10 - 40 °C.

[0061] "Gas space velocity" is a commonly used technical term in the technical route of fixed-bed reactors, referring to the volume of gas flowing through a unit volume of catalyst per unit time under standard conditions, and its unit is commonly h-1.

[0062] Physical quantities such as reaction conversion rate, yield, gas purity, etc. are calculated by the measurement and calculation methods recognized in the field.

[0063] The fuel cell described in this application refers to a hydrogen-oxygen fuel cell. Preferably, the fuel at the negative electrode is high-purity hydrogen, and the positive electrode uses air as the oxygen source. Those skilled in the art should know that hydrogen-oxygen fuel cells have relatively high requirements for hydrogen purity, which need to reach not less than 99.99% (v / v).

[0064] The overall design of the present utility model is compact, integrating multiple links such as liquid ammonia storage, gasification, heat exchange, ammonia decomposition to produce hydrogen, hydrogen purification, and fuel cell power generation, realizing continuous conversion from raw materials to electric energy, and improving the integration degree and automation level of the system.

[0065] What is not described in the present utility model is applicable to the prior art.

[0066] Obviously, the above embodiments are only examples for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or variations derived therefrom are still within the protection scope of the present utility model.

Claims

1. A coupled system of ammonia-hydrogen combustion - ammonia decomposition for hydrogen production - fuel cell, characterized in that, It includes a liquid ammonia storage device (1), a vaporizer (2), a second heat exchanger (4), an ammonia decomposition reactor (5), a membrane separation and purification device (6), and a fuel cell (40); the liquid ammonia storage device (1) is communicated with the vaporizer (2) and is used for vaporizing liquid ammonia into ammonia gas; the second heat exchanger (4) includes a second heat exchange cold gas channel (41) and a second heat exchange hot gas channel (42), the ammonia decomposition reactor (5) includes an ammonia decomposition reaction ammonia gas channel (51) and an ammonia decomposition reaction flue gas channel (52), the membrane separation and purification device (6) includes a purified gas channel (61) and a residual gas channel (62), the outlet of the vaporizer (2) is communicated with the inlet of the second heat exchange cold gas channel (41), and the outlet of the second heat exchange cold gas channel (41) is communicated with the inlet of the ammonia decomposition reaction ammonia gas channel (51) to introduce the ammonia gas after heat exchange by the second heat exchanger (4) into the ammonia decomposition reactor (5) for ammonia decomposition; the outlet of the ammonia decomposition reaction ammonia gas channel (51) is communicated with the inlet of the second heat exchange hot gas channel (42), and the outlet of the second heat exchange hot gas channel (42) is communicated with the inlet of the purified gas channel (61). The product mixed gas after decomposition by the ammonia decomposition reactor (5) is used as the heat exchange medium of the second heat exchanger (4) to exchange heat with the ammonia gas passing through the second heat exchange cold gas channel (41) and then is introduced into the membrane separation and purification device (6) for hydrogen purification; the outlet of the purified gas channel (61) is communicated with the negative electrode of the fuel cell (40) to provide fuel hydrogen for the fuel cell (40).

2. The coupled system of ammonia-hydrogen combustion - ammonia decomposition for hydrogen production - fuel cell according to claim 1, characterized in that, The system further includes a first heat exchanger (3) and a burner (7). The first heat exchanger (3) includes a first heat exchange cold gas channel (31) and a first heat exchange hot gas channel (32). The outlet of the vaporizer (2) is communicated with the inlet of the first heat exchange cold gas channel (31), and the outlet of the first heat exchange cold gas channel (31) is communicated with the second heat exchange cold gas channel (41) to heat up the ammonia gas vaporized by the vaporizer (2) through the first heat exchanger (3) for the first time; the outlet of the residual gas channel (62) is communicated with the inlet of the burner (7), the outlet of the burner (7) is communicated with the inlet of the ammonia decomposition reaction flue gas channel (52), and the outlet of the ammonia decomposition reaction flue gas channel (52) is communicated with the inlet of the first heat exchange hot gas channel (32). The high-temperature flue gas generated by the ignition and combustion of the mixed gas in the burner (7) provides heat energy for the ammonia decomposition reaction in the ammonia decomposition reactor (5), and the remaining heat is used for heat exchange of the ammonia gas passing through the first heat exchanger (3).

3. The coupled system of ammonia-hydrogen combustion - ammonia decomposition for hydrogen production - fuel cell according to claim 2, characterized in that, The separation membrane for purification in the membrane separation and purification device (6) is a hydrogen-selective permeable membrane, which can efficiently separate hydrogen from other gases.

4. The coupled system of ammonia-hydrogen combustion - ammonia decomposition for hydrogen production - fuel cell according to claim 3, characterized in that, The separation membrane in the membrane separation and purification device (6) is a metal vanadium alloy membrane structure or a metal niobium alloy membrane structure.

5. The coupled system of ammonia-hydrogen combustion - ammonia decomposition for hydrogen production - fuel cell according to claim 1, characterized in that, The ammonia decomposition reactor (5) is a fixed bed reactor. An ammonia decomposition catalyst is filled in the ammonia gas passage of the ammonia decomposition reactor (5). The reactant ammonia gas stream flows out of the second heat exchanger (4) and then enters the ammonia gas passage of the ammonia decomposition reactor (5), and flows through the ammonia decomposition catalyst to be converted into decomposition products to obtain hydrogen and nitrogen.

6. The coupled system of ammonia-hydrogen combustion - ammonia decomposition for hydrogen production - fuel cell according to claim 3, characterized in that, The system further includes a radiator (9) and a hydrogen gas tank (10). The outlet of the purified gas passage (61) is sequentially connected in series with the radiator (9) and the hydrogen gas tank (10) in sequence for cooling and collecting the purified hydrogen gas; the outlet of the hydrogen gas tank (10) is communicated with the negative electrode of the fuel cell (40).

7. The coupled system of ammonia-hydrogen combustion - ammonia decomposition for hydrogen production - fuel cell according to claim 6, characterized in that, The system further includes an air compressor (8). The outlet of the air compressor (8) is divided into two paths. One path is communicated with the inlet of the burner (7), and the other path is communicated with the positive electrode of the fuel cell (40).

8. The coupled system of ammonia-hydrogen combustion - ammonia decomposition for hydrogen production - fuel cell according to claim 7, characterized in that, The outlet of the air compressor (8), the outlet of the hydrogen gas tank (10), the outlet of the vaporizer (2), the outlet of the second heat exchange hot gas passage (42), and the outlet of the residual gas passage (62) can be simultaneously connected to the inlet of the burner (7) through pipelines to provide fuel gas and combustion-supporting gas for the burner (7); the outlet of the first heat exchange hot gas passage (32) is communicated with the flue gas processor (20) for purifying the discharged flue gas.

9. The coupled system of ammonia-hydrogen combustion - ammonia decomposition for hydrogen production - fuel cell according to claim 8, characterized in that, The system further includes a nitrogen gas tank (30). The outlet pipeline of the liquid ammonia storage device (1) and the outlet pipeline of the nitrogen gas tank (30) converge and then are communicated with the inlet of the vaporizer (2).

Images