A staged flue gas heat utilization device and method for hydrogen production from natural gas

Abstract

The present invention discloses a segmented flue heat utilization device and method for hydrogen production from natural gas, which relates to the field of hydrogen production from natural gas. The device includes a mixed gas preheater, a first natural gas preheater, a second natural gas preheater, a flue gas waste heat boiler, a burner, an air preheater, an induced draft fan and a chimney. The method includes: S1 the high-temperature flue gas exchanges heat through the mixed gas preheater; S2 the flue gas exchanges heat through the first natural gas preheater; S3 the flue gas is heated by the burner; S4 the flue gas exchanges heat through the flue gas waste heat boiler; S5 the flue gas exchanges heat through the second natural gas preheater; S5 the flue gas exchanges heat through the air preheater and is discharged through the induced draft fan and the chimney; after a series of heat exchanges, the high-temperature flue gas is cooled to slightly higher than the dew point temperature to prevent dew point corrosion of the flue gas, and the heat is fully recovered and utilized. The air is preheated through the air preheater and then enters the burner for combustion, reducing the consumption of natural gas fuel; the regulation and control of the device's flue gas discharge temperature and rich steam production are achieved through the burner.

Description

Technical Field

[0001] The present invention relates to the field of hydrogen production from natural gas, and particularly to a segmented flue heat utilization device and method for hydrogen production from natural gas. Background Art

[0002] As a mature hydrogen production method, hydrogen production technology from natural gas has the advantages of low cost and significant scale effect under the current upsurge of hydrogen energy utilization. Research and development of more advanced new process technologies for hydrogen production from natural gas are important guarantees for solving cheap hydrogen sources and an inevitable choice for the long-term development of hydrogen production devices from natural gas. However, hydrogen production devices from natural gas are devices with overcapacity. During normal production, there will be surplus steam. For small devices, the surplus steam is generally used for deaeration of acidic water inside the device. For large devices, due to the large amount of surplus steam generated, steam balance needs to be carried out with the whole plant. Summary of the Invention

[0003] The purpose of the present invention is to design a segmented flue heat utilization device and method for hydrogen production from natural gas to solve the above problems.

[0004] The present invention achieves the above purpose through the following technical solutions:

[0005] A segmented flue heat utilization device for hydrogen production from natural gas, where high-temperature flue gas enters the flue from a reformer for hydrogen production from natural gas, including:

[0006] A mixed gas preheater; the gas outlet of the mixed gas preheater is connected to the gas inlet of the reforming tubes in the reformer;

[0007] A first natural gas preheater; the natural gas outlet of the first natural gas preheater is connected to the gas inlet of the mixed gas preheater;

[0008] A second natural gas preheater; the natural gas outlet of the second natural gas preheater is connected to the natural gas inlet of the first natural gas preheater;

[0009] A flue gas waste heat boiler; the steam outlet of the flue gas waste heat boiler is connected to the gas inlet of the mixed gas preheater;

[0010] A burner for heating the flue gas flowing from the reformer to the flue gas waste heat boiler;

[0011] An air preheater, the air outlet of the air preheater is connected to the gas inlet of the burner;

[0012] An induced draft fan, the gas inlet of the induced draft fan is connected to the flue, and the gas outlet of the induced draft fan is connected to the gas inlet of the burner;

[0013] The chimney has its air inlet connected to the air outlet of the induced draft fan. After the high-temperature flue gas enters the flue, it sequentially passes through the mixed gas preheater, the first natural gas preheater, the burner, the flue gas waste heat boiler, the second natural gas preheater, and the air preheater, and finally the low-temperature flue gas is discharged through the induced draft fan and the chimney.

[0014] Further, the burner includes a plurality of burner heads distributed in a ring, and the direction of the burner heads is perpendicular to the flow direction of the flue gas.

[0015] Further, the burner also includes an installation chamber, a support member, and a gas mixing chamber. Both the gas mixing chamber and the flue are fixedly installed in the installation chamber through the support member. The flue is arranged in the gas mixing chamber, and the burner heads are annularly installed in the flue. The gas inlets of the burner heads are connected to the gas mixing chamber, and the combustion directions of the burner heads all face the central axis of the flue. The support member is filled with refractory castable.

[0016] Further, the burner also includes a fuel gas feed pipe and a sleeve. The fuel gas feed pipe is arranged inside the sleeve. The air inlets of the sleeve are respectively connected to the air outlet of the air preheater and the air outlet of the induced draft fan. The air outlets of the fuel gas feed pipe and the sleeve are both connected to the gas mixing chamber. The ignition end of the igniter of the burner is arranged inside the gas mixing chamber.

[0017] Further, the conversion tubes on the reformer include flexible elements for maintaining the internal seal of the conversion tubes and the furnace body of the reformer. The lower ends of the flexible elements are fixedly connected to the pipe orifices at the top of the furnace body for passing through the conversion tubes. The lower ends of the conversion tubes are fixedly installed at the bottom of the furnace body. The upper ends of the conversion tubes sequentially pass through the pipe orifices at the top of the furnace body and the flexible elements, and the upper ends of the conversion tubes are fixedly connected to the upper pigtail pipe joints.

[0018] Further, the flexible element is an expansion joint. The lower end of the expansion joint is fixedly connected to the pipe orifice at the top of the furnace body. The upper ends of the conversion tubes sequentially pass through the pipe orifices at the top of the furnace and the expansion joint, and the inside of the expansion joint is filled with high-temperature ceramic fiber blankets.

[0019] A method for heat utilization of a segmented flue in hydrogen production from natural gas includes the following steps:

[0020] S1. The high-temperature flue gas coming out of the reformer enters the flue and undergoes the first heat exchange with natural gas and steam through the mixed gas preheater. After the natural gas and steam are heated, they enter the conversion tubes.

[0021] S2. The flue gas after the first heat exchange undergoes the second heat exchange with natural gas through the first natural gas preheater. After the natural gas is heated, it enters the air inlet of the mixed gas preheater.

[0022] S3. The flue gas after the second heat exchange is heated by the burner.

[0023] S4. The heated flue gas exchanges heat with water for the third time through the flue gas waste heat boiler, and the steam generated by the flue gas waste heat boiler enters the air inlet of the mixed gas preheater.

[0024] S5. The flue gas after the third heat exchange exchanges heat with natural gas through the second natural gas preheater for the fourth time. After the natural gas is heated up, it enters the natural gas inlet of the first natural gas preheater.

[0025] S5. The flue gas after the fourth heat exchange finally exchanges heat with air through the air preheater for the last time. After the temperature is reduced, the temperature is slightly higher than the dew point temperature. Finally, the cooled flue gas is extracted by the induced draft fan. Most of the flue gas is discharged through the chimney, and the other part enters the air inlet of the sleeve in the burner.

[0026] Further, in S1, the temperature range of the flue gas after the first heat exchange is 560 - 600 °C, and the temperature ranges of natural gas and steam are 560 - 600 °C; in S2, the temperature range of the flue gas after the second heat exchange is 360 - 400 °C, and the temperature range of natural gas is 320 - 360 °C; in S4, the temperature range of the flue gas after the third heat exchange is 200 - 240 °C; in S5, the temperature range of the flue gas after the fourth heat exchange is 160 - 200 °C.

[0027] The beneficial effects of the present invention are as follows: The high-temperature flue gas coming out of the reformer is cooled to slightly higher than the dew point temperature through the mixed gas preheater, the second natural gas preheater, the flue gas waste heat boiler, the first natural gas preheater and the air preheater, which not only prevents the dew point corrosion of the flue gas, but also fully recovers and utilizes the heat. The air is preheated by the air preheater and then enters the burner for combustion, reducing the consumption of natural gas fuel, and making the consumption of the natural gas hydrogen production device reach 0.391; through the burner, the regulation and control of the flue gas discharge temperature and the rich steam production amount are realized. When the natural gas hydrogen production device is initially operated, the burner is turned on. In the initial stage of operation, the steam generated by the flue gas waste heat boiler is faster than that without the burner by 6 hours, and the initial reduction time is greatly advanced. The catalyst is switched from nitrogen heating to steam heating in advance, the nitrogen heating time of the catalyst is shortened, and the service life of the catalyst is extended. When the device operates normally, the flue gas auxiliary burner provides heat, and the by-product steam production amount of the device increases, which is more conducive to the overall steam balance of the device. The increased steam can be used to heat tap water for use, the original coal-fired boiler is cancelled, the overall energy consumption is saved, and the environment is also protected. Brief Description of the Drawings

[0028] Figure 1 is a schematic structural diagram of a natural gas hydrogen production sectionalized flue gas heat utilization device of the present invention;

[0029] Figure 2 is a schematic structural diagram of a burner in a natural gas hydrogen production sectionalized flue gas heat utilization device of the present invention;

[0030] Figure 3 It is a schematic structural diagram of a conversion tube in a segmented flue heat utilization device for hydrogen production from natural gas according to the present invention;

[0031] Figure 4 It is a schematic flow diagram of a method for segmented flue heat utilization in hydrogen production from natural gas according to the present invention;

[0032] Among them, the corresponding reference numerals are:

[0033] 1 - Installation chamber, 2 - Gas mixing chamber, 3 - Air outlet, 4 - Ignition gun, 5 - Fuel gas feed pipe, 6 - Outlet of induced draft fan, 7 - Refractory castable, 8 - Support member, 9 - Reformer, 10 - Flue gas waste heat boiler, 11 - Mixed gas preheater, 12 - First natural gas preheater, 13 - Burner, 14 - Air preheater, 15 - Second natural gas preheater, 16 - Induced draft fan, 17 - Chimney, 18 - Conversion tube, 19 - Expansion joint, 20 - Bottom of furnace body, 21 - Top of furnace body, 22 - High-temperature ceramic fiber blanket, 23 - Upper pigtail pipe joint. Specific embodiments

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and shown in the accompanying drawings here can be arranged and designed in various different configurations.

[0035] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the present invention claimed, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0036] It should be noted that: similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0037] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "left", "right", etc. is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed during use, or the orientation or positional relationship commonly understood by those skilled in the art. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0038] In addition, terms such as "first", "second", etc. are only used for distinguishing descriptions and cannot be construed as indicating or implying relative importance.

[0039] In the description of the present invention, it should also be noted that unless otherwise clearly specified and defined, terms such as "arrangement", "connection", etc. should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0040] The following will describe in detail the specific embodiments of the present invention with reference to the accompanying drawings.

[0041] As Figure 1 shown, a segmented flue gas heat utilization device for hydrogen production from natural gas, high-temperature flue gas enters the flue from a reformer 9 for hydrogen production from natural gas, including:

[0042] A mixed gas preheater 11; the gas outlet of the mixed gas preheater 11 is communicated with the gas inlet of a reforming tube 18 in the reformer 9;

[0043] A first natural gas preheater 12; the natural gas outlet of the first natural gas preheater 12 is communicated with the gas inlet of the mixed gas preheater 11;

[0044] A second natural gas preheater 15; the natural gas outlet of the second natural gas preheater 15 is communicated with the natural gas inlet of the first natural gas preheater 12;

[0045] A flue gas waste heat boiler 10; the steam outlet of the flue gas waste heat boiler 10 is communicated with the gas inlet of the mixed gas preheater 11;

[0046] A burner 13 for heating the flue gas flowing from the reformer 9 to the flue gas waste heat boiler 10;

[0047] An air preheater 14, the air outlet 3 of the air preheater 14 is communicated with the gas inlet of the burner 13;

[0048] An induced draft fan 16, the gas inlet of the induced draft fan 16 is communicated with the flue, and the gas outlet 6 of the induced draft fan 16 is communicated with the gas inlet of the burner 13;

[0049] A chimney 17, the gas inlet of the chimney 17 is communicated with the gas outlet 6 of the induced draft fan 16; after the high-temperature flue gas enters the flue, it sequentially passes through the mixed gas preheater 11, the first natural gas preheater 12, the burner 13, the flue gas waste heat boiler 10, the second natural gas preheater 15, and the air preheater 14, and finally the low-temperature flue gas is discharged through the induced draft fan 16 and the chimney 17.

[0050] As Figure 2 shown, the burner 13 includes a plurality of burner heads distributed in a ring shape, and the direction of the burner heads is perpendicular to the flow direction of the flue gas.

[0051] As Figure 2 shown, the burner 13 further includes an installation chamber 1, a support member 8, and a gas mixing chamber. The gas mixing chamber and the flue are both fixedly installed in the installation chamber 1 through the support member 8. The flue is arranged in the gas mixing chamber. The burner heads are annularly installed in the flue. The gas inlets of the burner heads are communicated with the gas mixing chamber. The combustion directions of the burner heads all face the central axis of the flue. The support member 8 is filled with refractory castable.

[0052] As Figure 2 shown, the burner 13 further includes a fuel gas feed pipe 5 and a sleeve. The fuel gas feed pipe 5 is arranged in the sleeve. The air inlets of the sleeve are respectively communicated with the air outlet 3 of the air preheater 14 and the outlet 6 of the induced draft fan 16. The outlet of the fuel gas feed pipe 5 and the outlet of the sleeve are both communicated with the gas mixing chamber. The ignition end of the igniter 4 of the burner 13 is arranged inside the gas mixing chamber.

[0053] The air is preheated by the air preheater 14 and then enters the burner 13 for air distribution and combustion, reducing the consumption of natural gas fuel and making the consumption of the natural gas hydrogen production device reach 0.391.

[0054] Through the action of the burner 13, the steam balance of the whole plant of the natural gas hydrogen production device can be solved. At the same time, part of the low-temperature flue gas is mixed with air and sent into the gas mixing cavity through the induced draft fan 16. Due to the heat absorption of the flue gas and the dilution of the oxygen concentration, the combustion speed and the furnace temperature are reduced, so the thermal NOX is reduced, which can be reduced by 30 - 50%, making the natural gas hydrogen production device more energy-saving and environment-friendly.

[0055] When the hydrogen production equipment starts initially, the burner 13 is turned on, and the burner head burns and heats the flue gas in the flue gas passage. The flue gas is heated, and the high-temperature flue gas exchanges heat with the flue gas waste heat boiler 10, increasing the steam production and the steam production speed of the device. During the initial operation, it can reduce the initial operation time of the device, reduce the steam passivation time of the catalyst, extend the service life of the catalyst, greatly increase the self-production of steam, and achieve the purpose of heating the self-produced steam by itself. Through tests, it is proved that when the natural gas flow rate is 10 Nm3 / h, the burner 13 provides 80,000 Kcal / h of heat. In the initial operation, the flue gas waste heat boiler 10 generates steam 6 hours faster than without the burner 13, and the reduction time is greatly advanced. The catalyst switches from nitrogen heating to steam heating in advance, the nitrogen heating time of the catalyst is shortened, and the service life of the catalyst is extended; when the natural gas hydrogen production equipment operates normally, the burner 13 provides heat, and the by-product steam volume of the natural gas hydrogen production equipment increases, which is more conducive to the overall steam balance of the device. When the natural gas hydrogen production equipment operates normally, it is also possible to choose whether to continue to use the burner 13 to burn and heat the flue gas according to the actual steam demand situation.

[0056] Since the burner head of the burner 13 faces the axial axis direction of the flue gas passage, the flame of such a burner 13 is short and rigid during combustion. Under the condition of ensuring the utilization of flue gas heat, the flame will not contact the heat exchange tubes of the flue gas waste heat boiler 10, causing damage to the flue gas waste heat boiler 10.

[0057] When the device operates normally, the burner 13 provides heat, and the by-product steam volume increases, which is more conducive to the overall steam balance of the device. The increased steam can be used to heat tap water for use, canceling the original coal-fired boiler, saving the overall energy consumption, and protecting the environment.

[0058] As Figure 3 shown, the conversion tubes 18 on the reformer 9 include flexible elements for maintaining the sealing performance inside the furnace body of the reformer 9 and the conversion tubes 18. The lower end of the flexible element is fixedly connected to the pipe orifice on the top of the furnace body 21 for passing through the conversion tubes 18. The lower ends of the conversion tubes 18 are fixedly installed at the bottom of the furnace body. The upper ends of the conversion tubes 18 sequentially pass through the pipe orifice on the top of the furnace body 21 and the flexible element, and the upper ends of the conversion tubes 18 are fixedly connected to the upper pigtail pipe joint 23.

[0059] As Figure 3 shown, the flexible element is an expansion joint 19. The lower end of the expansion joint 19 is fixedly connected to the pipe orifice on the top of the furnace body 21. The upper ends of the conversion tubes 18 sequentially pass through the pipe orifice on the furnace top and the expansion joint 19, and the inside of the expansion joint 19 is filled with high-temperature ceramic fiber blankets 22.

[0060] When installing the conversion tube 18, first pre-stretch and fix the conversion tube 18 downward, and use a fixed flange to fixedly connect it to the bottom 20 of the furnace body of the reformer 9. The upper end of the conversion tube 18 sequentially passes through the pipe orifice of the top 21 of the furnace body of the reformer 9 and the expansion joint 19 from bottom to top, and the upper end of the conversion tube 18 is fixedly connected to the upper pigtail pipe joint 23. When installing the expansion joint 19, it is pre-compressed, and its pre-compression amount is greater than the maximum change amount of the conversion tube 18. The inside of the expansion joint 19 is filled with a high-temperature ceramic fiber blanket 22. The expansion joint 19 can effectively solve the problem of thermal expansion and contraction of the conversion tube 18. At the same time, the combination of the expansion joint 19 and the high-temperature ceramic fiber blanket 22 can effectively ensure the sealing problem between the reformer 9 and the conversion tube 18. At the same time, the high-temperature ceramic fiber blanket 22 also has a heat preservation effect, which can keep the conversion tube 18 warm, avoid air leakage in the reformer 9, and cause an increase in energy consumption. At the same time, since the expansion joint 19 can be fixed to the top 21 of the furnace body of the reformer 9 only through a flange, a large amount of steel structures are effectively avoided, and the operation space on the top of the reformer 9 is liberated to a great extent.

[0061] As Figure 4 shown, a method for heat utilization of a segmented flue for hydrogen production from natural gas includes the following steps:

[0062] S1. The high-temperature flue gas coming out of the reformer 9 enters the flue and undergoes the first heat exchange with natural gas and steam through the mixed gas preheater 11. The flue gas temperature drops to 560 - 600 °C, and the natural gas and steam are heated to 560 - 600 °C and then enter the conversion tube 18;

[0063] S2. The flue gas after the first heat exchange undergoes the second heat exchange with natural gas through the first natural gas preheater 12. The flue gas temperature drops to 360 - 400 °C, and the natural gas is heated to 320 - 360 °C and then enters the air inlet of the mixed gas preheater 11;

[0064] S3. The flue gas after the second heat exchange is heated by the burner 13;

[0065] S4. The heated flue gas undergoes the third heat exchange with water through the flue gas waste heat boiler 10. The flue gas temperature drops to 200 - 240 °C, and the steam generated by the flue gas waste heat boiler 10 enters the air inlet of the mixed gas preheater 11;

[0066] S5. The flue gas after the third heat exchange undergoes the fourth heat exchange with natural gas through the second natural gas preheater 15. The flue gas temperature drops to 160 - 200 °C, and the natural gas is heated and then enters the natural gas inlet of the first natural gas preheater 12;

[0067] S6. The flue gas after the fourth heat exchange finally exchanges heat with air through the air preheater 14 for the last time. After cooling, the temperature is slightly higher than the dew point temperature. Finally, the cooled flue gas is extracted by the induced draft fan 16. Most of the flue gas is discharged through the chimney 17, and the other part enters the air inlet of the sleeve in the burner 13.

[0068] The technical solution of the present invention is not limited to the limitations of the above specific embodiments. Any technical deformation made according to the technical solution of the present invention falls within the protection scope of the present invention.

Claims

1. A staged flue gas heat utilization device for hydrogen production from natural gas. High-temperature flue gas enters the flue from a reformer for hydrogen production from natural gas. It is characterized in that Comprising: Mixed gas preheater; The outlet of the mixed gas preheater is communicated with the inlet of the conversion tubes in the reformer; First natural gas preheater; the natural gas outlet of the first natural gas preheater is communicated with the inlet of the mixed gas preheater; Second natural gas preheater; the natural gas outlet of the second natural gas preheater is communicated with the natural gas inlet of the first natural gas preheater; Flue gas waste heat boiler; the steam outlet of the flue gas waste heat boiler is communicated with the inlet of the mixed gas preheater; Burner for heating the flue gas flowing from the reformer to the flue gas waste heat boiler; Air preheater, the air outlet of the air preheater is communicated with the inlet of the burner; Induced draft fan, the inlet of the induced draft fan is communicated with the flue, and the outlet of the induced draft fan is communicated with the inlet of the burner; Chimney, the inlet of the chimney is communicated with the outlet of the induced draft fan; the high-temperature flue gas enters the flue and sequentially passes through the mixed gas preheater, the first natural gas preheater, the burner, the flue gas waste heat boiler, the second natural gas preheater and the air preheater, and finally the low-temperature flue gas is discharged through the induced draft fan and the chimney; The burner further includes an installation chamber, a support member and a gas mixing chamber. The gas mixing chamber and the flue are both fixedly installed in the installation chamber through the support member. The flue is arranged in the gas mixing chamber. The burner head is annularly installed in the flue. The gas inlet of the burner head is communicated with the gas mixing chamber. The combustion directions of the burner heads all face the central axis of the flue. The support member is filled with refractory castable; The burner further includes a fuel gas feed pipe and a sleeve. The fuel gas feed pipe is arranged in the sleeve. The inlet of the sleeve is respectively communicated with the air outlet of the air preheater and the outlet of the induced draft fan. The outlet of the fuel gas feed pipe and the outlet of the sleeve are both communicated with the gas mixing chamber. The ignition end of the igniter of the burner is arranged inside the gas mixing chamber.

2. The segmented flue heat utilization device for hydrogen production from natural gas according to claim 1, wherein, The burner includes a plurality of burner heads distributed annularly, and the directions of the burner heads are perpendicular to the flow direction of the flue gas.

3. A staged flue gas heat utilization device for hydrogen production from natural gas according to any one of claims 1-2, characterized in that, The conversion tubes on the reformer include flexible elements for maintaining the internal seal of the conversion tubes and the furnace body of the reformer. The lower end of the flexible element is fixedly connected to the pipe orifice on the top of the furnace body for passing through the conversion tubes. The lower ends of the conversion tubes are all fixedly installed at the bottom of the furnace body. The upper ends of the conversion tubes sequentially pass through the pipe orifice on the top of the furnace body and the flexible element, and the upper ends of the conversion tubes are fixedly connected to the upper pigtail pipe joint.

4. A staged flue gas heat utilization device for hydrogen production from natural gas according to claim 3, characterized in that, The flexible element is an expansion joint. The lower end of the expansion joint is fixedly connected to the pipe orifice on the top of the furnace body. The upper ends of the conversion tubes sequentially pass through the pipe orifice on the top of the furnace and the expansion joint. The inside of the expansion joint is filled with high-temperature ceramic fiber blanket.

5. A method for segmented flue gas heat utilization in hydrogen production from natural gas, which is applied to a segmented flue gas heat utilization device for hydrogen production from natural gas as described in any one of claims 1-4, characterized in that, Including the following steps: S1. The high-temperature flue gas coming out of the reformer enters the flue and exchanges heat with natural gas and steam for the first time through the mixed gas preheater. After the natural gas and steam are heated, they enter the conversion tubes; S2. The flue gas after the first heat exchange exchanges heat with natural gas for the second time through the first natural gas preheater. After the natural gas is heated, it enters the inlet of the mixed gas preheater; S3. The flue gas after the second heat exchange is heated through the burner; S4. The heated flue gas exchanges heat with water for the third time through the flue gas waste heat boiler. The steam generated by the flue gas waste heat boiler enters the inlet of the mixed gas preheater; S5. The flue gas after the third heat exchange undergoes a fourth heat exchange with natural gas through the second natural gas preheater. After the natural gas is heated up, it enters the natural gas inlet of the first natural gas preheater. S6. The flue gas after the fourth heat exchange finally undergoes a final heat exchange with air through the air preheater. After the temperature drops, it is slightly higher than the dew point temperature. Finally, the cooled flue gas is extracted by the induced draft fan. Most of the flue gas is discharged through the chimney, and the other part enters the inlet of the middle sleeve of the burner.

6. A method for segmented flue gas heat utilization in hydrogen production from natural gas according to claim 5, characterized in that, In S1, the temperature range of the flue gas after the first heat exchange is 560 - 600 °C, and the temperature range of the natural gas and steam is 560 - 600 °C; in S2, the temperature range of the flue gas after the second heat exchange is 360 - 400 °C, and the temperature range of the natural gas is 320 - 360 °C; in S4, the temperature range of the flue gas after the third heat exchange is 200 - 240 °C, and in S5, the temperature range of the flue gas after the fourth heat exchange is 160 - 200 °C.

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