A multi-stage preheating heat exchange device for hydrogen production from ammonia

Abstract

The present application relates to hydrogen energy preparation technical field, specifically, it relates to a kind of multistage preheating for hydrogen production of ammonia heat exchange device, it includes box and heat exchanger being arranged in box, the heat exchanger has the combustion passage for ammonia and air mixture gas combustion heat release and the decomposition passage for hydrogen production of ammonia decomposition, first gas pipe and second gas pipe are provided on the box, the first gas pipe and the second gas pipe are all connected with the combustion passage of the heat exchanger;In the multistage preheating for hydrogen production of ammonia heat exchange device in this application, by setting electric heating mechanism and ignition catalyst, only need to heat the smaller volume ignition catalyst to ammonia ignition temperature when starting, the high-temperature flue gas generated by its combustion heats the larger volume heat exchanger to working temperature, avoid direct electric heating to heat exchanger, reduce the power consumption of starting stage.

Description

Technical Field

[0001] This invention relates to the field of hydrogen production technology, and more specifically, to a multi-stage preheating heat exchange device for hydrogen production from ammonia. Background Technology

[0002] Hydrogen energy is a clean and efficient secondary energy source, but its large-scale application is constrained by storage and transportation challenges. At room temperature and pressure, hydrogen has an extremely low volumetric energy density; even when compressed to 35 MPa, its energy storage per unit volume is far lower than that of traditional fuels. This results in large, costly storage tanks and poses risks of leakage and explosion. Therefore, finding safe, efficient, and economical methods for hydrogen storage and transportation is a key bottleneck for the development of the hydrogen energy industry.

[0003] Ammonia (NH3) has a high hydrogen content of up to 17.6%, low production costs, and can be liquefied at around 2 MPa at room temperature. The volumetric energy density of liquid ammonia is about 3 to 4 times that of high-pressure hydrogen. Ammonia has a mature storage and transportation system, and its combustion does not emit carbon dioxide, making it widely recognized as a highly promising hydrogen carrier. However, ammonia cannot be used directly in proton exchange membrane fuel cells, as it would poison the catalyst and lead to performance degradation; it must first be decomposed into hydrogen.

[0004] Currently, the main method used is high-temperature thermochemical decomposition: 2NH3⇌N2 + 3H2. This reaction is strongly endothermic. In practical industrial applications, to balance the reaction rate and conversion rate of ammonia decomposition, the temperature usually needs to be maintained at around 700℃. This process typically uses a heat exchange device for heating. However, existing heat exchange devices have the following shortcomings: First, the startup energy consumption is high. Ammonia is burned inside the heat exchanger to provide heat, but the combustion of ammonia requires the temperature inside the device to reach above 220°C to proceed stably. The current practice is to use an external electric heating mechanism to preheat the entire heat exchanger, but the device is large in size, and heating to 220°C requires too much electricity, resulting in high startup costs.

[0005] Secondly, repeated heating after shutdown and cleaning results in additional energy consumption. After the heat exchange unit has been running for a period of time, impurities gradually accumulate in the internal flow channels used for ammonia combustion, affecting heat exchange efficiency and requiring shutdown for disassembly and cleaning. After cleaning and resumption of operation, the unit temperature has dropped to room temperature (below 220°C), making it impossible to directly introduce ammonia for ignition and combustion. The electric heating mechanism must be restarted for reheating, resulting in repeated electricity consumption and further increasing operating costs. Summary of the Invention

[0006] The purpose of this invention is to provide a multi-stage preheating heat exchange device for ammonia-to-hydrogen production. This device utilizes a preheating component and a combustion catalytic component. The high-temperature flue gas generated by the combustion in the combustion catalytic component preheats the heat exchanger, avoiding direct electric heating of the entire heat exchanger. Furthermore, the combustion catalytic component is continuously kept warm through a reflux channel, enabling rapid restart after shutdown. This solves the problems of high start-up energy consumption and reliance on repeated electric heating for restarting in existing devices.

[0007] To achieve the above objectives, a multi-stage preheating heat exchange device for ammonia to hydrogen production includes a housing and a heat exchanger disposed within the housing. The heat exchanger has a combustion channel for the combustion and heat release of a mixture of ammonia and air and a decomposition channel for the decomposition of ammonia to hydrogen production. The housing is provided with a first gas supply pipe and a second gas supply pipe, both of which are connected to the combustion channel of the heat exchanger. An electric heating mechanism and an ignition catalyst are sequentially arranged along the gas flow direction of the first gas pipeline. The electric heating mechanism is used to heat the ignition catalyst, which contains an ammonia ignition catalyst to ignite the ammonia gas mixed with air. The second gas delivery pipe is used to directly deliver the ammonia-air mixture to the combustion channel of the heat exchanger; It also includes a return pipe, one end of which is connected to the combustion channel outlet of the heat exchanger, and the other end is connected to the first gas supply pipe. It is used to guide part of the flue gas after combustion in the heat exchanger back to the ignition catalyst to maintain the temperature of the ignition catalyst so that when the device is restarted, the heat exchanger can be reheated to the working temperature through the ignition catalyst.

[0008] In the above technical solution, the ignition catalyst is preheated by an electric heating mechanism until it reaches the ammonia ignition temperature. Then, a mixture of ammonia and air is introduced and combusted within the ignition catalyst. The resulting high-temperature flue gas heats the heat exchanger to its ignition temperature. Subsequently, the gas supply is switched to the second gas pipe, allowing the mixed gas to combust directly within the heat exchanger, releasing heat to provide heat for the ammonia decomposition to produce hydrogen. Simultaneously, a return pipe guides a portion of the high-temperature flue gas from the heat exchanger back to the ignition catalyst, continuously heating and maintaining its temperature. Therefore, when the heat exchanger needs to be shut down and reassembled for cleaning, the ignition catalyst remains above its ignition temperature due to the return flue gas insulation. There is no need to restart the electric heating mechanism; simply introducing the mixed gas directly into the first gas pipe achieves rapid restart, effectively reducing startup energy consumption and operating costs.

[0009] Based on this, the heat exchanger includes a plurality of first heat exchange plates and second heat exchange plates that are alternately bonded together in sequence; A flue gas passage is provided on the side of the first heat exchange plate facing the second heat exchange plate, and the inner wall of the flue gas passage is coated with an ammonia ignition catalyst. A decomposition channel is provided on the side of the second heat exchanger away from the first heat exchanger, and the inner wall of the decomposition channel is coated with an ammonia decomposition catalyst. The box is equipped with an inlet and an outlet that communicate with the decomposition channel.

[0010] Based on this, both the electric heating mechanism and the ignition catalyst have a housing; The electric heating mechanism has a honeycomb heating plate inside its outer shell and electrodes connected to the honeycomb heating plate on its outer shell. The outer shell of the ignition catalyst is equipped with a metal honeycomb component, and the inner wall of the metal honeycomb component is coated with an ammonia ignition catalyst, so that the mixture of ammonia and air undergoes a catalytic combustion reaction at a preset temperature.

[0011] Based on this, the ammonia ignition catalyst is a rare earth-based catalyst, used to enable the mixture of ammonia and air to burn at a temperature above 220°C. The ammonia decomposition catalyst is a platinum-based catalyst used to decompose ammonia at temperatures above 700°C.

[0012] Based on this, an electric valve is installed on the return pipe to control the opening and closing of the gas path inside the return pipe, so that the return flue gas can flow continuously or intermittently through the ignition catalyst.

[0013] In another technical solution, multiple scraper rings are provided on the inner wall of each flue gas passage, and the scraper rings are arranged at equal intervals along the length of the flue gas passage. Multiple scraper rings are fixed together on a base plate, which is slidably installed in a groove opened in the side wall of the second heat exchange plate, and the sliding direction is parallel to the length direction of the flue gas channel. A connecting frame is fixedly connected to one end of multiple substrates; It also includes a drive component for moving the substrate.

[0014] The drive component can adopt the following structure: The driving component includes a memory spring; one end of the memory spring is fixed to the side wall of the connecting frame, and the other end is fixed to the side wall of the housing and located at the connection point between the first air supply pipe and the housing. By intermittently heating the ignition catalyst, the temperature of the gas flowing through the memory spring changes alternately between hot and cold. The memory spring contracts or extends with the temperature change, thereby driving the substrate to slide back and forth along the slide groove. During the reciprocating movement, the scraper ring scrapes off the impurities attached to the inner wall of the flue gas channel.

[0015] This solution utilizes the heat generated by the device itself during operation as the driving force, eliminating the need for additional active drive components such as electric push rods. This simplifies the structure, reduces manufacturing costs, and minimizes power consumption during operation.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This multi-stage preheating system is used in a heat exchanger for ammonia-to-hydrogen production. By incorporating an electric heating mechanism and a ignition catalyst, during startup, only the smaller ignition catalyst needs to be heated to the ammonia ignition temperature. The high-temperature flue gas generated by its combustion then heats the larger heat exchanger to its operating temperature, avoiding direct electric heating of the heat exchanger and reducing power consumption during startup. Simultaneously, a reflux pipe guides a portion of the high-temperature flue gas from the heat exchanger back to the ignition catalyst for continuous heating and insulation. When the heat exchanger is shut down for cleaning or other reasons and reassembled, there is no need to restart the electric heating mechanism; simply introducing a mixture of ammonia and air allows for re-ignition and combustion, further reducing energy consumption and operational complexity.

[0017] 2. This multi-stage preheating is used in the heat exchange unit for ammonia-to-hydrogen production. Because the reflux pipe continuously returns high-temperature flue gas to the ignition catalyst, the temperature of the ignition catalyst is maintained above 220℃. This insulation measure not only helps reduce energy consumption during restart but also allows the high-temperature gas flowing through the ignition catalyst to heat the memory spring. When the ambient-temperature mixed gas delivered by the second gas pipe flows through the memory spring, the memory spring is alternately heated and cooled. The deformation generated by this thermal cycle drives the cleaning mechanism to clean impurities adhering to the inner wall of the flue gas passage. No additional power source is required, which simplifies the structure and reduces operating costs. Attached Figure Description

[0018] Figure 1 This is a three-dimensional schematic diagram of the overall structure of the present invention; Figure 2 This is a cross-sectional schematic diagram of the overall structure of the present invention; Figure 3 This is a schematic cross-sectional view of the electric heating mechanism and the ignition catalyst of the present invention; Figure 4 This is a schematic diagram of the combustion catalytic converter of the present invention; Figure 5 This is a schematic diagram of the heat exchanger of the present invention; Figure 6 This is a schematic diagram of the working state of the ignition catalyst of the present invention; Figure 7 This is a schematic diagram of the scraper ring of the present invention; Figure 8 This is a schematic diagram of the substrate structure of the present invention; Figure 9 This is a schematic diagram of the working state of the scraper ring of the present invention; Figure 10 This is a schematic diagram of the working state of the memory spring of the present invention.

[0019] The meanings of the labels in the diagram are as follows: 100. Housing; 101. Partition; 102. Opening; 103. Inlet; 104. Outlet; 105. Exhaust port; 106. Diverter; 110. Heat exchanger; 111. First heat exchange fin; 112. Second heat exchange fin; 113. Flue gas passage; 114. Inlet end; 115. Exhaust end; 120. First gas supply pipe; 121. Return port; 130. Second gas supply pipe; 140. Electric heating mechanism; 141. Honeycomb heating plate; 142. Electrode; 150. Ignition catalyst; 151. Outer shell; 152. Metal honeycomb component; 160. Return pipe; 161. Electric valve; 170. Scraper ring; 171. Base plate; 172. Connecting frame; 173. Memory spring. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0023] In the process of producing hydrogen from ammonia via high-temperature thermochemical decomposition, a heat exchange device is required to provide heat for the decomposition reaction. For example... Figure 1 and Figure 2 As shown, the heat exchange device includes a housing 100 and a heat exchanger 110 disposed inside the housing 100.

[0024] Combination Figure 5The heat exchanger 110 is composed of multiple vertically placed plates stacked together, with the sidewalls of adjacent plates touching each other to form a heat exchange channel. For ease of explanation, the description will take the adjacent first heat exchange plate 111 and the second heat exchange plate 112 as examples.

[0025] The first heat exchange plate 111 is recessed inward on the side facing the second heat exchange plate 112 to form multiple flue gas channels 113. These channels 113 are arranged parallel to each other in the horizontal direction, and the ends of each channel 113 penetrate the edge of the first heat exchange plate 111. This allows gas to flow in from one end of the flue gas channel 113 and out from the other end when the first and second heat exchange plates 111 and 112 are in contact with each other. The inner wall of the flue gas channel 113 is coated with an ammonia combustion catalyst (e.g., a rare earth-based catalyst). When a mixture of ammonia and air flows through the flue gas channel 113, a catalytic combustion reaction occurs under the action of the catalyst, releasing heat and heating the first and second heat exchange plates 111 and 112 to approximately 700°C.

[0026] The second heat exchanger 112 is recessed inward on the side opposite to the first heat exchanger 111 to form a decomposition channel. The bottom end of the decomposition channel penetrates the bottom edge of the second heat exchanger 112 to form an air inlet 114, and the top end penetrates the top edge of the second heat exchanger 112 to form an exhaust end 115. The inner wall of the decomposition channel is coated with an ammonia decomposition catalyst (e.g., a platinum-based or rhodium-based noble metal catalyst) to catalyze the high-temperature thermal decomposition reaction of ammonia. During assembly, the first heat exchanger 111 and the second heat exchanger 112 are used as a basic unit. Multiple basic units are stacked and then fastened together with bolts to form a complete heat exchanger 110.

[0027] Combination Figure 2 The housing 100 has partitions 101 at the bottom and top, forming a heat exchange chamber for accommodating the heat exchanger 110. The top partition 101 is attached to the top of the heat exchanger 110, and the bottom partition 101 is attached to the bottom of the heat exchanger 110 to prevent gas leakage. The partitions 101 have openings 102 corresponding to the decomposition channels of the heat exchanger 110.

[0028] by Figure 2 The indicated direction is for reference only. The left end of the heat exchange chamber is connected to a first gas supply pipe 120 for conveying a mixture of ammonia and air, and the right end is connected to an exhaust port 105 for discharging flue gas. The mixing ratio of ammonia and air is automatically controlled by a PID controller. The mixed gas enters the heat exchange chamber through the first gas supply pipe 120, and then enters the flue gas passage 113. Under the action of the ammonia ignition catalyst coated on the inner wall of the flue gas passage 113, a combustion reaction occurs, releasing heat and heating the heat exchanger 110 to approximately 700°C. The flue gas after combustion is discharged through the exhaust port 105. At this point, the heat exchanger 110 has reached the required temperature, providing a heat source for subsequent ammonia decomposition to produce hydrogen.

[0029] The inlet 103 at the bottom of the housing 100 is connected to the air inlet 114 via the port 102, and the outlet 104 at the top is connected to the exhaust outlet 115 via the port 102. Pure ammonia gas (excluding air) is introduced into the housing 100 through the bottom inlet 103, and then enters the decomposition channel through the port 102 and the air inlet 114. Inside the decomposition channel, the ammonia gas undergoes a high-temperature thermochemical decomposition reaction under the catalytic action of the ammonia decomposition catalyst, generating hydrogen and nitrogen. The resulting mixed gas then passes through the exhaust outlet 115 and the port 102, and is finally discharged from the top outlet 104 to supply subsequent equipment.

[0030] However, although the ammonia ignition catalyst coated on the inner wall of the flue gas passage 113 can reduce the combustion temperature of the ammonia-air mixture, the ignition temperature is still above 220°C. To achieve this ignition temperature, the heat exchanger 110 needs to be preheated. If an external electric heating method is used to heat the heat exchanger 110 to above 220°C, a large amount of electricity is required due to the large size of the heat exchanger 110. To reduce the power consumption during the start-up phase, the present invention sequentially arranges an electric heating mechanism 140, an ignition catalyst 150, and a second gas supply pipe 130 at one end of the first gas supply pipe 120 connecting to the housing 100, wherein the ignition catalyst 150 is located on the side of the electric heating mechanism 140 closer to the housing 100, and the second gas supply pipe 130 is located on the side of the ignition catalyst 150 closer to the housing 100.

[0031] The electric heating mechanism 140 can heat up to approximately 400°C after being connected to a DC power supply. During the startup phase, air is first introduced into the first gas supply pipe 120. The air is heated as it flows through the electric heating mechanism 140, and then continues to flow through the ignition catalyst 150, heating it to the ammonia ignition temperature (approximately 220°C). The ignition catalyst 150 contains an ammonia ignition catalyst. Once the ignition catalyst 150 reaches its ignition temperature, a mixture of ammonia and air is introduced into the first gas supply pipe 120. This mixture ignites under the action of the catalyst as it flows through the ignition catalyst 150, raising its temperature to approximately 700°C. The high-temperature flue gas generated by combustion flows through the heat exchanger 110, heating it to approximately 220°C, thus bringing the heat exchanger 110 to the ammonia ignition temperature.

[0032] Subsequently, the process is switched to introducing a mixture of ammonia and air into the second gas supply pipe 130. The mixture flows directly through the heat exchanger 110 and burns inside the heat exchanger 110, further heating the heat exchanger 110 to the temperature required for ammonia decomposition (approximately 700°C).

[0033] Furthermore, the present invention also includes a return pipe 160, which guides part of the flue gas after combustion in the heat exchanger 110 back to the first gas supply pipe 120, allowing the flue gas to flow through the ignition catalyst 150 and continuously heat the ignition catalyst 150. In this way, the ignition catalyst 150 remains heated throughout the entire operation. When it is necessary to shut down and disassemble the heat exchanger 110 for cleaning, simply reassemble the heat exchanger 110 after cleaning. At this time, the ignition catalyst 150 remains near the ignition temperature under the action of the flue gas returning through the return pipe 160. When restarting, there is no need to activate the electric heating mechanism 140; simply introduce a mixture of ammonia and air into the first gas supply pipe 120, and it will ignite in the ignition catalyst 150. The resulting flue gas will reheat the heat exchanger 110 to its operating temperature.

[0034] Specifically, refer to Figure 3 The first gas supply pipe 120 has a two-section structure, consisting of a front section and a rear section. The front section connects to the gas supply mechanism to receive gas; the rear section connects to the housing 100 to deliver gas into the housing 100. An electric heating mechanism 140 and an ignition catalyst 150 are installed between the front and rear sections.

[0035] Both the electric heating mechanism 140 and the ignition catalyst 150 have a housing 151, which are interconnected. The housing 151 near the front end is connected to the first gas supply pipe 120, and the housing 151 near the rear end is connected to the first gas supply pipe 120. A honeycomb heating plate 141 is disposed inside the housing 151 of the electric heating mechanism 140, and an electrode 142 connected to the honeycomb heating plate 141 is disposed outside the housing 151. When the electrode 142 is connected to a DC power supply, it can heat the honeycomb heating plate 141 to a predetermined temperature (e.g., 400°C), thereby heating the flowing air and subsequently heating the ignition catalyst 150 to approximately 220°C. A metal honeycomb element 152 (its structure is referenced...) is disposed inside the housing 151 of the ignition catalyst 150. Figure 4 The inner wall of the metal honeycomb component 152 is coated with an ammonia ignition catalyst (such as a rare earth-based catalyst), which enables the mixture of ammonia and air to undergo catalytic combustion at about 220°C.

[0036] The second gas supply pipe 130 is connected to the first gas supply pipe 120 at the rear. After the mixture of ammonia and air is transported through the second gas supply pipe 130, it can directly enter the box 100 and flow into the flue gas passage 113 of the heat exchanger 110.

[0037] In addition, such as Figures 1-3As shown, a diversion port 106 is provided on one side of the exhaust port 105 in the housing 100, and a return port 121 is provided on the first gas supply pipe 120 at the front. One end of the return pipe 160 is connected to the diversion port 106, and the other end is connected to the return port 121, which is used to guide part of the flue gas after combustion in the housing 100 back to the first gas supply pipe 120 at the front.

[0038] As an alternative, one end of the return pipe 160 can also be connected between the electric heating mechanism 140 and the ignition catalyst 150, so that the return flue gas flows directly through the ignition catalyst 150 without passing through the electric heating mechanism 140, which can also achieve continuous heating and heat preservation of the ignition catalyst 150.

[0039] When working, refer to Figure 6 First, the power supply to the electric heating mechanism 140 is turned on to heat it up. Then, air is introduced into the first air inlet pipe 120, flowing sequentially through the electric heating mechanism 140, the ignition catalyst 150, and the heat exchanger 110, finally exiting through the exhaust port 105. The air is heated as it flows through the electric heating mechanism 140, and the heated gas, upon passing through the ignition catalyst 150, heats the ignition catalyst 150 to approximately 220°C.

[0040] Subsequently, the power supply to the electric heating mechanism 140 is turned off, and the mixture of ammonia and air (refer to the solid arrow inside the first gas supply pipe 120) is delivered to the front first gas supply pipe 120 in proportion. When the mixture flows through the ignition catalyst 150, it ignites at 220°C under the action of the ammonia ignition catalyst inside the ignition catalyst 150, raising the temperature of the ignition catalyst 150 itself to approximately 700°C. The flue gas generated by combustion (refer to the dashed arrow inside the first gas supply pipe 120) enters the heat exchange chamber through the rear first gas supply pipe 120, and flows through the heat exchanger 110 through the flue gas passage 113, heating the heat exchanger 110 to approximately 220°C.

[0041] Next, the mixture of ammonia and air is switched to the second gas supply pipe 130 for delivery. The mixture enters the heat exchange chamber directly through the second gas supply pipe 130 and flows into the flue gas passage 113. Under the action of the ammonia ignition catalyst on the inner wall of the flue gas passage 113, it is burned, further heating the heat exchanger 110 to about 700°C. The gas after combustion is discharged through the exhaust port 105.

[0042] Then, pure ammonia gas (excluding air) is introduced into the housing 100 through the bottom inlet 103, and then enters the decomposition channel through the outlet 102 and the air inlet 114. Inside the decomposition channel, the ammonia gas undergoes a high-temperature thermochemical decomposition reaction under the catalytic action of the ammonia decomposition catalyst to produce hydrogen and nitrogen. The resulting mixed gas then passes through the exhaust end 115 and the outlet 102, and is finally discharged from the top exhaust port 104 to supply subsequent equipment.

[0043] Meanwhile, a portion of the flue gas discharged from flue gas passage 113 flows back to the first gas supply pipe 120 via return pipe 160, passing through electric heating mechanism 140 and ignition catalyst 150. The residual heat of the flue gas is used to raise the temperature of ignition catalyst 150 to approximately 500°C, maintaining it at a standby temperature of approximately 500°C. When it is necessary to shut down and disassemble the heat exchanger 110 for cleaning, cleaning and reassembly can be completed within the time window during which the ignition catalyst 150 naturally cools from 500°C to 220°C. After reassembly, there is no need to reconnect the power supply to electric heating mechanism 140; a mixture of ammonia and air can be directly introduced into the first gas supply pipe 120, and the residual heat of ignition catalyst 150 can be used to restart the combustion process, achieving rapid restart.

[0044] In addition, an electric valve 161 is installed on the return pipe 160 to control the opening and closing of the gas passage inside the return pipe 160, allowing the return flue gas to flow continuously or intermittently through the ignition catalyst 150. By controlling the intermittent opening and closing of the electric valve 161, the disturbance of the return flue gas to the system airflow distribution can be reduced while ensuring that the temperature of the ignition catalyst 150 is maintained above the ammonia ignition temperature. At the same time, the risk of trace impurities carried during the return process accumulating in the ignition catalyst 150 is reduced.

[0045] To reduce the adhesion of impurities in the flue gas to the inner wall of the flue gas passage 113 and extend the cleaning cycle, such as Figure 7 and Figure 8 As shown, the present invention provides multiple scraper rings 170 on the inner wall of each flue gas passage 113, with each scraper ring 170 equidistantly arranged along the length of the flue gas passage 113. The multiple scraper rings 170 are jointly fixed on a base plate 171, which is slidably mounted in a groove formed in the side wall of the second heat exchange plate 112, with the sliding direction parallel to the length of the flue gas passage 113. Figure 8 As shown, a small gap (e.g., 0.1 to 0.5 mm) is left between the outer ring of the scraper ring 170 and the inner wall of the flue gas passage 113 to avoid damaging the catalyst coating, and its internal space is for flue gas to pass through.

[0046] When working, refer to Figure 9 The drive substrate 171 moves, causing the scraper ring 170 to move from... Figure 9 The solid line position moves to the dashed line position. During the movement, the thicker impurities attached to the side wall of the flue gas channel 113 are scraped off. The scraped-off impurities are blown out of the flue gas channel 113 by the flue gas flow.

[0047] In terms of the drive structure, one end of multiple substrates 171 can extend out of the side wall of the heat exchanger 110, and the extended ends can be fixed together by a connecting frame 172. At this time, the substrates 171 can be moved by an active drive component such as an electric push rod.

[0048] In addition to the active drive method, a memory spring 173 can also be used to drive the connecting frame 172. For example... Figure 8 As shown, at least one memory spring 173 is fixedly connected to the side wall of the connecting frame 172. The other end of the memory spring 173 is fixed to the side wall of the housing 100 near the first air supply pipe 120 and is located at the connection between the first air supply pipe 120 and the housing 100.

[0049] The shape memory spring 173 can be made of a nickel-titanium hafnium (NiTiHf) based high-temperature shape memory alloy. This alloy, by adding hafnium (Hf) to a nickel-titanium (NiTi) binary alloy to replace part of the titanium (Ti), increases the martensitic transformation temperature of the alloy from the conventional below 100°C, meeting the operating requirements of the shape memory spring 173 in this design: contraction in a high-temperature flue gas environment of approximately 500°C and elongation in a mixed gas environment at room temperature (approximately 20–25°C). For example, a nickel-titanium hafnium alloy with a hafnium content of 20 at.%–25 at.% (such as Ni50.3Ti29.7Hf20) can be selected, and the phase transformation temperature of this composition system can cover the operating range of approximately 500°C.

[0050] For detailed working principles, please refer to... Figure 10 When the electric valve 161 opens and the flue gas in the return pipe 160 enters the first gas supply pipe 120, the flue gas heats the ignition catalyst 150 and flows into the heat exchange chamber through the second gas supply pipe 120, contacting the memory spring 173. The memory spring 173 contracts upon heating, pulling the base plate 171 to move via the connecting bracket 172. When the electric valve 161 closes and the flue gas return is interrupted, only a mixture of ammonia and air at room temperature (transported via the second gas supply pipe 130) flows through the memory spring 173. Since its temperature is much lower than the flue gas temperature, the memory spring 173 returns to its extended state, pushing the base plate 171 back to its original position. During the reciprocating movement of the base plate 171, the scraper ring 170 continuously scrapes off impurities adhering to the sidewall of the flue gas passage 113.

[0051] As another implementation, when the temperature of the ignition catalyst 150 is higher than 220°C, the mixture of ammonia and air can also be delivered to the first gas supply pipe 120. The mixture is burned at the ignition catalyst 150, and the flue gas generated by the combustion flows through the memory spring 173, which can also cause the memory spring 173 to contract when heated, thereby driving the scraper ring 170.

[0052] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A multi-stage preheating heat exchange device for ammonia-to-hydrogen production, comprising a housing (100) and a heat exchanger (110) disposed within the housing (100), wherein the heat exchanger (110) has a combustion channel for the heat release from the combustion of a mixture of ammonia and air and a decomposition channel for the decomposition of ammonia to produce hydrogen, characterized in that, The housing (100) is provided with a first gas supply pipe (120) and a second gas supply pipe (130), both of which are connected to the combustion channel of the heat exchanger (110). An electric heating mechanism (140) and an ignition catalyst (150) are sequentially arranged along the gas flow direction of the first gas pipe (120). The electric heating mechanism (140) is used to heat the ignition catalyst (150). The ignition catalyst (150) contains an ammonia ignition catalyst, which is used to ignite and burn the ammonia gas mixed with air flowing through it. The second gas delivery pipe (130) is used to directly deliver the ammonia-air mixture to the combustion channel of the heat exchanger (110); It also includes a return pipe (160), one end of which is connected to the combustion channel outlet of the heat exchanger (110), and the other end is connected to the first gas supply pipe (120), which is used to guide part of the flue gas after combustion in the heat exchanger (110) back to the ignition catalyst (150) to maintain the temperature of the ignition catalyst (150) so that when the device is restarted, the heat exchanger (110) can be reheated to the working temperature through the ignition catalyst (150); The heat exchanger (110) includes a plurality of first heat exchange plates (111) and second heat exchange plates (112) that are alternately attached in sequence. A flue gas passage (113) is provided on the side of the first heat exchange plate (111) facing the second heat exchange plate (112), and the inner wall of the flue gas passage (113) is coated with an ammonia ignition catalyst. The second heat exchange plate (112) is provided with a decomposition channel on the side away from the first heat exchange plate (111), and the inner wall of the decomposition channel is coated with an ammonia decomposition catalyst. The box (100) is provided with an inlet (103) and an outlet (104) that are connected to the decomposition channel. Both the electric heating mechanism (140) and the ignition catalyst (150) have a housing (151). The electric heating mechanism (140) has a honeycomb heating plate (141) inside its outer shell (151) and an electrode (142) connected to the honeycomb heating plate (141) on its outer side. The outer shell (151) of the ignition catalyst (150) is provided with a metal honeycomb component (152), and the inner wall of the metal honeycomb component (152) is coated with an ammonia ignition catalyst, so that the mixture of ammonia and air undergoes a catalytic combustion reaction at a preset temperature. Each of the flue gas passages (113) has multiple scraper rings (170) on its inner wall, and each scraper ring (170) is arranged at equal intervals along the length of the flue gas passage (113). Multiple scraper rings (170) are fixed together on a base plate (171). The base plate (171) is slidably installed in a groove opened in the side wall of the second heat exchange plate (112), and the sliding direction is parallel to the length direction of the flue gas channel (113). A connecting frame (172) is fixedly connected to one end of multiple substrates (171). It also includes a drive component for moving the substrate (171).

2. The multi-stage preheating heat exchanger for ammonia-to-hydrogen production according to claim 1, characterized in that, The ammonia ignition catalyst is a rare earth-based catalyst, used to enable the combustion of a mixture of ammonia and air at a temperature above 220°C. The ammonia decomposition catalyst is a platinum-based catalyst used to decompose ammonia at temperatures above 700°C.

3. The multi-stage preheating heat exchanger for ammonia-to-hydrogen production according to claim 1, characterized in that, One end of the return pipe (160) is connected to the outlet of the flue gas passage (113), and the other end is connected to the first gas supply pipe (120).

4. The multi-stage preheating heat exchanger for ammonia-to-hydrogen production according to claim 3, characterized in that, The portion of the return pipe (160) that connects to the first gas supply pipe (120) is located between the electric heating mechanism (140) and the ignition catalyst (150), or on the side of the electric heating mechanism (140) away from the ignition catalyst (150).

5. The multi-stage preheating heat exchanger for ammonia-to-hydrogen production according to claim 1, characterized in that, The return pipe (160) is equipped with an electric valve (161) for controlling the opening and closing of the gas passage inside the return pipe (160), so that the return flue gas can flow continuously or intermittently through the ignition catalyst (150).

6. The multi-stage preheating heat exchanger for ammonia-to-hydrogen production according to claim 1, characterized in that, The driving component includes a memory spring (173); one end of the memory spring (173) is fixed to the side wall of the connecting frame (172), and the other end is fixed to the side wall of the housing (100), and is located at the connection between the first air supply pipe (120) and the housing (100); By intermittently heating the ignition catalyst (150), the temperature of the flow through the memory spring (173) is changed, and the temperature change is used to drive the memory spring (173) to move the substrate (171).

7. The multi-stage preheating heat exchanger for ammonia-to-hydrogen production according to claim 6, characterized in that, The memory spring (173) is made of nickel-titanium hafnium-based high-temperature shape memory alloy.

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