Gradient ammonia decomposition fixed bed reactor system for tail gas waste heat utilization

Abstract

The utility model discloses a gradient ammonia decomposition fixed bed reactor system for tail gas waste heat utilization. The gradient ammonia decomposition fixed bed reactor system comprises a liquid ammonia storage tank, a shell-and-tube heat exchanger, a gradient catalyst reactor, a tail gas detection device and an ammonia gas detector. According to the gradient type ammonia decomposition fixed bed reactor system provided by the utility model, on one hand, the gradient type catalyst bed layer is arranged in the ammonia decomposition reactor based on the basic principle that ammonia decomposition reaction is strong in heat absorption, so that the compounding of multi-system catalysts is realized, the temperature requirements in different use scenes can be matched, and the gradient design enables the reaction to be advanced step by step; catalyst sintering caused by local overheating is reduced, and complete decomposition of ammonia is ensured; and on the other hand, compared with traditional ammonia decomposition reaction equipment, by arranging the shell-and-tube heat exchanger between the liquid ammonia storage tank and the gradient type catalyst reactor, heat energy of high-temperature tail gas can be efficiently utilized, the energy utilization efficiency is remarkably improved, energy consumption is reduced, and economic benefits are improved.

Description

Technical Field

[0001] This utility model belongs to the field of ammonia decomposition hydrogen production technology, specifically relating to a gradient ammonia decomposition fixed-bed reactor system for utilizing waste heat from tail gas. Background Technology

[0002] Ammonia decomposition for hydrogen production is an important method for hydrogen production. Due to its advantages such as readily available raw materials, safe storage and transportation, and mild reaction conditions, it has been widely used in fuel cells, the electronics industry, and the metallurgical industry in recent years. However, traditional ammonia decomposition reactor systems still have some problems and bottlenecks: for example, traditional fixed-bed reactors often use a single catalyst (such as a nickel-based catalyst), which is difficult to adapt to the activity requirements of different temperature ranges in the ammonia decomposition reaction. This leads to catalyst deactivation due to problems such as carbon deposition and sintering, resulting in short service life, high replacement frequency, and increased operating costs. Furthermore, the ammonia decomposition reaction is a strongly endothermic reaction, and traditional reactors rely on continuous external heating. The direct emission of high-temperature exhaust gas (typically 600-800℃) causes a significant waste of thermal energy, resulting in high system energy consumption and poor economic efficiency. Therefore, there is an urgent need to develop a high-efficiency, energy-saving ammonia decomposition reactor system to meet the needs of industrial applications. Summary of the Invention

[0003] To address the limitations of traditional ammonia decomposition reactors, such as their single reaction system and high energy consumption, the purpose of this invention is to provide a gradient ammonia decomposition fixed-bed reactor system that utilizes waste heat from tail gas. Through gradient catalyst design, efficient waste heat recovery, and intelligent temperature control technology, the system significantly improves ammonia decomposition efficiency, reduces energy consumption, and ensures safe and stable operation.

[0004] To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0005] A gradient ammonia decomposition fixed-bed reactor system for utilizing waste heat from tail gas includes: a liquid ammonia storage tank, a shell-and-tube heat exchanger, a gradient catalyst reactor, a tail gas detection device, and an ammonia detector for detecting whether ammonia leakage has occurred in the gradient catalyst reactor; wherein:

[0006] Liquid ammonia storage tanks are used to supply pure ammonia;

[0007] The working principle of a shell-and-tube heat exchanger is indirect heat transfer through the tube walls, utilizing the counter-current flow of hot and cold fluids in the tube side and shell side, as well as the disturbance of baffles to enhance heat transfer efficiency. Specifically, the hot and cold fluids in the tube side (inside the tubes) and shell side (outside the tubes) indirectly transfer heat through the metal tube walls, with the tube walls acting as an indirect barrier to achieve heat exchange. In this application, when the high-temperature exhaust gas flows in the shell side, heat is transferred through the tube walls to the low-temperature ammonia gas inside the tubes, thus achieving temperature regulation.

[0008] The outlet of the liquid ammonia storage tank is connected to the tube-side inlet of the shell-and-tube heat exchanger; the tube-side outlet of the shell-and-tube heat exchanger is connected to the top inlet of the gradient catalyst reactor; the bottom outlet of the gradient catalyst reactor is connected to the shell-side inlet of the shell-and-tube heat exchanger; the shell-side outlet of the shell-and-tube heat exchanger is connected to the tail gas detection device; high-temperature tail gas is introduced into the shell side of the shell-and-tube heat exchanger, and raw material ammonia is introduced into the tube side. The ammonia is preheated by the waste heat of the tail gas, and the raw material ammonia enters the reactor after being preheated by the heat exchanger, thus realizing the purpose of utilizing the waste heat of the tail gas.

[0009] A gradient catalyst reactor includes a shell, an ammonia decomposition reactor located inside the shell, and a temperature control component for controlling the temperature of the ammonia decomposition reactor. The ammonia decomposition reactor includes a shell, within which a gradient catalyst bed is installed. The gradient catalyst bed consists of an upper bed plate, a middle bed plate, and a lower bed plate installed sequentially from top to bottom within the shell. Catalysts with progressively increasing catalytic activity temperatures are placed on the upper, middle, and lower bed plates. This design is based on the fact that the ammonia decomposition reaction (2NH3→3H2+N2) is a strongly endothermic reaction, and different active sites of different catalysts can be matched to different temperature ranges. For example, a highly active Ru-based catalyst is used in the low-temperature range (400-500℃) to accelerate the initial decomposition of ammonia; a Ni-based catalyst is used in the medium-temperature range (550-650℃) to prevent carbon deposition of intermediate products; and an Fe-based catalyst is used in the high-temperature range (650-750℃) to ensure complete ammonia decomposition. The gradient design allows the reaction to proceed step-by-step, reducing catalyst sintering caused by localized overheating.

[0010] The ammonia detector is installed at the flange interface and catalyst bed inspection port in the ammonia decomposition reactor. When the NH3 concentration is detected to be ≥10ppm, the ammonia feed valve is shut off in conjunction with the detector.

[0011] As a preferred technical solution, the temperature control component includes a zoned heating device and a temperature measuring device. The zoned heating device consists of three sets of heaters installed inside the outer casing and used to heat the catalyst on the upper, middle, and lower bed plates, respectively. The temperature measuring device includes three high-temperature resistant optical windows installed on the outer casing, corresponding to the positions of the catalyst on the upper, middle, and lower bed plates, and multiple infrared sensors. Each infrared sensor corresponds to a temperature zone in the gradient catalyst reactor, and the infrared sensors can monitor the temperature of each layer in the gradient catalyst reactor in real time through the high-temperature resistant optical windows. More preferably, the three sets of heaters are silicon carbide rod electric heaters, with each layer's power independently adjustable from 0-5kW; the high-temperature resistant optical windows are sapphire optical windows, which have excellent temperature resistance properties, ensuring the safety and stability of the device during use.

[0012] As a preferred technical solution, the outlet of the liquid ammonia storage tank is connected to the tube-side inlet of the shell-and-tube heat exchanger via pipe one; pipe one is equipped with an ammonia feed valve; the tube-side outlet of the shell-and-tube heat exchanger is connected to the top inlet of the gradient catalyst reactor via pipe two, which is equipped with an overpressure protector to ensure the safe operation of the device; the bottom outlet of the gradient catalyst reactor is connected to the shell-side inlet of the shell-and-tube heat exchanger via pipe three; the shell-side outlet of the shell-and-tube heat exchanger is connected to the tail gas detection device via pipe four; pipe four is equipped with an exhaust valve; the exhaust port of the exhaust valve is connected to pipe five; the outlet of pipe five extends into the absorbent liquid. Pipe five is a venting pipe, its function being to release the gas in the pipe into pipe five when the overpressure protector detects excessively high pressure in the system, connecting it to the alkaline absorbent liquid, which is a 5%-10% NaOH solution.

[0013] As a preferred technical solution, a heat-insulating buffer layer is installed at the bottom of the upper, middle, and lower bed boards. The heat-insulating buffer layer is preferably ceramic fiber felt with a thickness of 10-20 mm, and the interlayer temperature difference is controlled to ≤20℃ to reduce interlayer heat conduction. More preferably, the upper, middle, and lower bed boards are all porous titanium alloy gas distribution plates.

[0014] As a preferred technical solution, the exhaust gas detection device is an online gas chromatograph, which is used to analyze the composition of the gas passing through the gradient catalyst bed and determine the ammonia decomposition effect.

[0015] As a preferred technical solution, the ammonia decomposition reactor system further includes a PLC controller, which is connected to the heater, infrared sensor, ammonia detector, online gas chromatograph, and overpressure protector. The PLC controller is pre-programmed with the following control logic: dynamically adjusting the heating power based on the NH3 concentration data from the online gas chromatograph; triggering an alarm and reducing the heating power when the infrared temperature measurement module detects that the temperature of a certain layer exceeds a set threshold (upper layer > 500℃, middle layer > 650℃, lower layer > 750℃); and urgently cutting off the ammonia supply and initiating pressure relief when the overpressure protector activates.

[0016] This utility model has the following beneficial effects:

[0017] This invention provides a gradient ammonia decomposition fixed-bed reactor system for utilizing waste heat from tail gas. On one hand, based on the fundamental principle that ammonia decomposition is strongly endothermic, a gradient catalyst bed is set within the ammonia decomposition reactor, achieving the composite of multiple catalyst systems. This allows for matching the temperature requirements of different application scenarios, and the gradient design ensures the reaction proceeds step-by-step, reducing catalyst sintering caused by localized overheating and guaranteeing complete ammonia decomposition. On the other hand, compared to traditional ammonia decomposition equipment, by setting a shell-and-tube heat exchanger between the liquid ammonia storage tank and the gradient catalyst reactor, the thermal energy of the high-temperature tail gas can be efficiently utilized, significantly improving energy utilization efficiency, reducing energy consumption, and increasing economic benefits. Attached Figure Description

[0018] Figure 1 A schematic diagram of the gradient ammonia decomposition fixed-bed reactor system for waste heat utilization of tail gas provided by this utility model;

[0019] Figure 2 This is a schematic diagram of the structure of an ammonia decomposition reactor;

[0020] Figure reference numerals: 1-Liquid ammonia storage tank, 2-Shell-tube heat exchanger, 201-Tube-side inlet, 202-Tube-side outlet, 203-Shell-side inlet, 204-Shell-side outlet, 3-Gradient catalyst reactor, 301-Shell shell, 302-Shell shell, 303-Upper bed plate, 304-Middle bed plate, 305-Lower bed plate, 306-Catalyst, 307-Insulation buffer layer, 308-Heater, 309-High-temperature resistant optical window, 310-Infrared sensor, 4-Tail gas detection device, 5-Ammonia detector, 6-Pipeline 1, 7-Feed valve, 8-Pipeline 2, 9-Overpressure protector, 10-Pipeline 3, 11-Pipeline 4, 12-Exhaust valve, 13-Pipeline 5, 14-PLC controller, 15-Absorbent liquid. Detailed Implementation

[0021] The present invention will be further described below with reference to the embodiments and accompanying drawings, so that those skilled in the art can better understand and implement the present invention. However, the embodiments are not intended to limit the present invention.

[0022] In the description of this utility model, it should be understood that the terms "upper," "middle," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the 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 of this utility model. The terms "one," "two," "three," and "four," etc., used in this utility model do not represent a specific order, but are merely used for distinguishing names.

[0023] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0024] refer to Figure 1 and Figure 2 A gradient ammonia decomposition fixed-bed reactor system for utilizing waste heat from tail gas includes: a liquid ammonia storage tank 1, a shell-and-tube heat exchanger 2, a gradient catalyst reactor 3, a tail gas detection device 4, and an ammonia detector 5 for detecting whether ammonia leakage has occurred in the gradient catalyst reactor. The ammonia detector is arranged at the flange interface and the catalyst bed inspection port in the ammonia decomposition reactor. When an NH3 concentration ≥10ppm is detected, the ammonia feed valve is closed. The tail gas detection device 4 is an online gas chromatograph.

[0025] The outlet of the liquid ammonia storage tank 1 is connected to the tube-side inlet 201 of the shell-and-tube heat exchanger; the tube-side outlet 202 of the shell-and-tube heat exchanger is connected to the top inlet of the gradient catalyst reactor; the bottom outlet of the gradient catalyst reactor is connected to the shell-side inlet 203 of the shell-and-tube heat exchanger; the shell-side outlet 204 of the shell-and-tube heat exchanger is connected to the tail gas detection device 4; high-temperature tail gas is introduced into the shell side of the shell-and-tube heat exchanger 2, and raw material ammonia is introduced into the tube side. The ammonia is preheated by the waste heat of the tail gas. The raw material ammonia enters the reactor after being preheated by the heat exchanger, thereby achieving the purpose of utilizing the waste heat of the tail gas.

[0026] The gradient catalyst reactor 3 includes a shell 301, an ammonia decomposition reactor located inside the shell, and a temperature control component for controlling the temperature of the ammonia decomposition reactor. The shell 302 of the ammonia decomposition reactor is made of 310S stainless steel with a wall thickness of 12mm and a design pressure resistance of 2.5MPa. It is equipped with a detachable gradient catalyst bed with a total height of 1200mm and a diameter of 300mm. The gradient catalyst bed includes an upper bed plate 303, a middle bed plate 304, and a lower bed plate 305 installed in the shell from top to bottom. Catalysts with progressively increasing catalytic activity temperatures are placed on the upper bed plate 303, the middle bed plate 304, and the lower bed plate 305, respectively. In practice, the upper bed plate is filled with a low-temperature active catalyst, such as Ru / CeO2 (active temperature 400-500℃), with a thickness of 300mm; the middle bed plate is filled with a medium-temperature composite catalyst, such as Ni / MgO (active temperature 550-650℃), with a thickness of 400mm; and the lower bed plate is filled with a high-temperature catalyst, such as Fe / Al2O3 (active temperature 650-750℃), with a thickness of 500mm. Each bed plate is a porous titanium alloy gas distribution plate with a pore size of 0.8mm and an open porosity between 30-50%, and the surface is coated with an Al2O3-Y2O3 anti-oxidation coating. A 20mm thick ceramic fiber felt heat insulation buffer layer is set between the layers to ensure that the temperature difference between the layers is 10-15℃.

[0027] The temperature control component includes a zoned heating device and a temperature measuring device. The zoned heating device consists of three sets of heaters 308, which are installed inside the outer casing and are used to heat the catalyst on the upper, middle, and lower bed plates, respectively. In a preferred embodiment, all three sets of heaters are silicon carbide rod electric heaters, with each layer having an independently adjustable power of 0-5kW. Specifically, the power is 3kW for the upper layer, 4kW for the middle layer, and 5kW for the lower layer, and can be adjusted independently. The temperature measuring device includes three high-temperature resistant optical windows 309 installed on the outer casing, corresponding to the positions of the catalyst on the upper, middle, and lower bed plates, respectively, and multiple infrared sensors 310. Each infrared sensor 310 corresponds to a temperature zone in the gradient catalyst reactor, and the infrared sensors can monitor the temperature of each layer in the gradient catalyst reactor in real time through the high-temperature resistant optical windows. The high-temperature resistant optical windows are sapphire optical windows, which have excellent temperature resistance properties, ensuring the safety and stability of the device during use.

[0028] In one embodiment, the outlet of the liquid ammonia storage tank 1 is connected to the tube-side inlet 201 of the shell-and-tube heat exchanger via pipe 6; pipe 6 is equipped with an ammonia feed valve 7; the tube-side outlet 202 of the shell-and-tube heat exchanger is connected to the top inlet of the gradient catalyst reactor via pipe 8, which is equipped with an overpressure protector 9 to ensure the safe operation of the device; the bottom outlet of the gradient catalyst reactor is connected to the shell-side inlet 203 of the shell-and-tube heat exchanger via pipe 10; the shell-side outlet 204 of the shell-and-tube heat exchanger is connected to the tail gas detection device 4 via pipe 11; pipe 11 is equipped with an exhaust valve 12; the exhaust port of the exhaust valve is connected to pipe 13; the outlet of pipe 13 extends into the absorbent liquid 15. Pipeline 5.13 is a venting pipeline. Its function is to vent gas into pipeline 5 when the overpressure protector detects that the pressure in the system is too high. The gas is then connected to the alkaline absorption liquid, which is a 5%-10% NaOH solution.

[0029] The waste heat recovery process is as follows: Raw ammonia enters the tube side of a shell-and-tube heat exchanger from a liquid ammonia storage tank. After being preheated to 350-400°C by the high-temperature tail gas in the shell side, it enters through the top inlet of the reactor. The preheated ammonia gas then passes through three catalyst beds to complete the decomposition reaction, generating a mixed high-temperature tail gas containing 75% H2 and 25% N2. The high-temperature tail gas is then cooled to below 200°C in the shell side of the heat exchanger before being discharged.

[0030] The ammonia detector and overpressure protector in the gradient ammonia decomposition fixed bed reactor system provided by this utility model are safety protection systems. When the ammonia detector detects an NH3 concentration ≥10ppm, or when the system pressure exceeds 2.2MPa, the ammonia feed valve is closed and the gas is released into the absorbent liquid for absorption.

[0031] The gradient ammonia decomposition fixed-bed reactor system provided by this utility model has the following process flow for ammonia decomposition: First, pure ammonia is supplied through a liquid ammonia storage tank. The ammonia gas passes sequentially through the tube-side inlet and tube-side outlet of a shell-and-tube heat exchanger, and after being heated, enters the ammonia decomposition reactor. The gas flow passes from top to bottom through three catalyst beds at different temperatures. The temperature of each catalyst bed is precisely controlled by an electric heater and an infrared temperature control system. The gas passing through the catalyst beds is analyzed for gas composition using online gas chromatography, and then discharged after heat exchange in a shell-and-tube heat exchanger.

[0032] The gradient ammonia decomposition fixed-bed reactor system provided by this utility model allows for temperature control of the gradient catalyst bed through manual operation or automatic control via a PLC controller. In manual operation, the temperature data of the catalyst in each bed layer is obtained by observing the infrared sensor, and the operating power of the heaters at corresponding positions in each layer is manually adjusted to bring each layer to the preset operating temperature. In automatic control via the PLC controller, the PLC controller is connected to the heaters, infrared sensors, and an online gas chromatograph, and the heating power is dynamically adjusted based on the NH3 concentration data from the online gas chromatograph. When the infrared sensor detects that the temperature of a certain layer exceeds a set threshold (upper layer > 500℃, middle layer > 650℃, lower layer > 750℃), an alarm is triggered and the heating power is reduced. Furthermore, the PLC controller can be connected to the feed valve, ammonia detector, and overpressure protector. When excessive external ammonia concentration or excessive system pressure is detected, the ammonia feed valve is closed, and the gas is released into the absorbent liquid for absorption. Specifically, the PLC program is preset as follows: turn on the lower layer electric heating to the target temperature, and after the infrared temperature measurement stabilizes, start the middle layer and upper layer heating in sequence; when the temperature of each layer reaches the set value, slowly open the ammonia feed valve; the online gas chromatograph is set to automatically inject samples every 5 minutes to analyze the tail gas components.

[0033] Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. All other embodiments obtained by those skilled in the art based on the embodiments of this utility model without inventive effort are within the scope of protection of this utility model.

Claims

1. A gradient ammonia decomposition fixed-bed reactor system for utilizing waste heat from tail gas, characterized in that, include: Liquid ammonia storage tank, shell-and-tube heat exchanger, gradient catalytic reactor, tail gas detection device, and ammonia detector for detecting ammonia leakage in the gradient catalytic reactor; wherein: The outlet of the liquid ammonia storage tank is connected to the tube-side inlet of the shell-and-tube heat exchanger; the tube-side outlet of the shell-and-tube heat exchanger is connected to the top inlet of the gradient catalyst reactor; the bottom outlet of the gradient catalyst reactor is connected to the shell-side inlet of the shell-and-tube heat exchanger; and the shell-side outlet of the shell-and-tube heat exchanger is connected to the exhaust gas detection device. The gradient catalyst reactor includes a shell, an ammonia decomposition reactor located inside the shell, and a temperature control component for controlling the temperature of the ammonia decomposition reactor. The ammonia decomposition reactor includes a shell, and a gradient catalyst bed is installed inside the shell. The gradient catalyst bed includes an upper bed plate, a middle bed plate, and a lower bed plate installed from top to bottom inside the shell. Catalysts with progressively increasing catalytic activity temperatures are placed on the upper, middle, and lower bed plates, respectively.

2. The gradient ammonia decomposition fixed-bed reactor system according to claim 1, characterized in that, The temperature control assembly includes a zone heating device and a temperature measuring device. The zone heating device consists of three sets of heaters installed inside the outer shell and used to heat the catalyst on the upper, middle, and lower bed plates, respectively. The temperature measuring device includes three high-temperature resistant optical windows installed on the outer shell, corresponding to the positions of the catalyst on the upper, middle, and lower bed plates, respectively, as well as multiple infrared sensors. Each infrared sensor corresponds to a temperature zone in the gradient catalyst reactor, and the infrared sensors can monitor the temperature of each layer in the gradient catalyst reactor in real time through the high-temperature resistant optical windows.

3. The gradient ammonia decomposition fixed-bed reactor system according to claim 2, characterized in that, All three sets of heaters are silicon carbide rod electric heaters.

4. The gradient ammonia decomposition fixed-bed reactor system according to claim 2, characterized in that, The high-temperature resistant optical window is a sapphire optical window.

5. The gradient ammonia decomposition fixed-bed reactor system according to any one of claims 1 to 4, characterized in that, The outlet of the liquid ammonia storage tank is connected to the tube-side inlet of the shell-and-tube heat exchanger via a pipe; an ammonia feed valve is installed on pipe one; the tube-side outlet of the shell-and-tube heat exchanger is connected to the top inlet of the gradient catalyst reactor via a pipe two, and an overpressure protector is installed on pipe two; the bottom outlet of the gradient catalyst reactor is connected to the shell-side inlet of the shell-and-tube heat exchanger via a pipe three; the shell-side outlet of the shell-and-tube heat exchanger is connected to the tail gas detection device via a pipe four; an exhaust valve is installed on pipe four; the exhaust port of the exhaust valve is connected to pipe five; the outlet of pipe five extends into the absorbent liquid.

6. The gradient ammonia decomposition fixed-bed reactor system according to any one of claims 1 to 4, characterized in that, The bottom of the upper, middle, and lower bed boards are all equipped with heat-insulating buffer layers.

7. The gradient ammonia decomposition fixed-bed reactor system according to any one of claims 1 to 4, characterized in that, The upper, middle, and lower bed plates are all porous titanium alloy gas distribution plates.

8. The gradient ammonia decomposition fixed-bed reactor system according to claim 1, characterized in that, The exhaust gas detection device is an online gas chromatograph.

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