A method for reducing thermal shock damage to a smelt reduction furnace stack

Abstract

The application discloses a method for reducing thermal shock loss of a flue of a smelting reduction furnace, and belongs to the technical field of smelting reduction ironmaking, and comprises the following steps: rich-methane gas and water vapor are introduced into an inlet end of a flue of the smelting reduction furnace according to a certain proportion, and a reforming reaction occurs between the rich-methane gas and the water vapor and high-temperature carbon dioxide gas generated in the smelting reduction furnace; high-temperature flue gas in the smelting reduction furnace provides energy required by the reforming reaction, and the temperature of the gas in the flue is greatly reduced; after the gas in the flue is continuously cooled, dedusted and purified through a cooling flue, the gas is sprayed into the furnace again or stored for another use. The technical scheme of the application prolongs the service life of flue refractory and the utilization efficiency of flue gas sensible heat, and simultaneously improves the reduction potential and combustion heat value of the flue gas.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of smelting reduction ironmaking, in particular to a method for reducing heat shock loss of flue of smelting reduction furnace. BACKGROUND

[0002] The heat source in the smelting reduction furnace is the secondary combustion zone, the central temperature of which is as high as 2500℃; the coal gas generated by the combustion reaction and the reduction reaction in the furnace has a temperature of about 1500-1700℃ when reaching the top of the furnace, and has the characteristics of large gas volume and high temperature. Due to the intense heat shock of the high-temperature coal gas on the refractory of the furnace top flue and the vaporization cooling flue steel pipe, the service life of the refractory and the steel pipe is greatly shortened, causing frequent damage to the furnace top and the flue, and seriously affecting the operation rate of the smelting reduction furnace. At the same time, a large amount of CO2 contained in the furnace top coal gas causes the reduction potential and the combustion heat value of the coal gas to be reduced, and the efficiency is not high when the coal gas is pre-reduced and utilized. In addition, due to the unsatisfactory heat transfer effect between the upper and lower parts of the furnace, the temperature of the liquid molten iron generated is only 1430-1450℃, which is still far from the reasonable iron temperature of 1500℃, and the overall energy utilization in the smelting reduction furnace is not sufficient. In order to fully utilize the large sensible heat of the flue gas, the existing technology involves a HIsmelt smelting reduction furnace top coal gas treatment process, which uses a flue type vaporization cooling device to recover the waste heat of high-temperature flue gas and reduce the flue gas temperature, and then generates steam by using the waste heat after cyclone dust removal to generate power. This method improves the waste heat recovery efficiency and realizes efficient recovery and utilization of energy. However, this method has little effect on reducing the heat shock loss of the refractory at the inlet of the flue, and at the same time, the process of converting heat energy into steam and then into electric energy has undergone two conversions, resulting in a large energy loss. It also relates to a method for improving the temperature of molten iron in a molten pool, which introduces high-temperature flue gas into the molten pool in a dynamic cycle to transfer the sensible heat of the high-temperature flue gas to the molten iron, thereby improving the temperature of the molten iron. However, the heat source in the smelting reduction furnace is the secondary combustion of CO and H2 generated by coal decomposition, and the method uses the flue gas generated in the furnace, which will cause CO2 accumulation and greatly reduce the reduction efficiency. At the same time, due to the high CO2 gas, more heat will be taken away from the furnace, which may also cause the heat transfer efficiency to continuously decrease with the increase of the cycle time.

[0003] Therefore, there is an urgent need for a simple, reliable, safe and stable, low-cost method that can effectively reduce the heat shock loss of the flue and improve the utilization efficiency of the sensible heat of the flue gas. SUMMARY

[0004] The present application aims to solve the problems of heat shock loss of high-temperature flue gas of the smelting reduction furnace on the flue refractory and the utilization of sensible heat, and provides a method for reducing the heat shock loss of the flue of the smelting reduction furnace, improves the service life of the flue refractory and the utilization efficiency of the sensible heat of the flue gas, and at the same time improves the reduction potential and the combustion heat value of the flue gas.

[0005] To achieve the above object, the present application adopts the following technical solutions:

[0006] A method for reducing the thermal shock loss of a smelting reduction furnace flue, the method comprising:

[0007] S1: methane-rich gas and water vapor are introduced into the inlet end of the flue of the smelting reduction furnace in a certain proportion, and a reforming reaction occurs between the methane-rich gas and water vapor and the high-temperature carbon dioxide gas generated in the smelting reduction furnace;

[0008] S2: The high-temperature flue gas in the smelting reduction furnace provides the energy required for the reforming reaction, and the gas temperature in the flue is greatly reduced;

[0009] S3: After the gas in the flue is cooled, dedusted and purified, it is re-injected into the furnace or stored for other use.

[0010] Further, in S1, the reforming reaction is:

[0011] Further, in S1, the methane-rich gas is natural gas, coal bed gas or coke oven gas, wherein the volume fraction of CH4 in the coke oven gas is not less than 20%. Here, since the endothermic effect of the reforming reaction is low when the CH4 content is low, in order to ensure the rapid cooling effect, the volume fraction of CH4 in the coke oven gas is not less than 20%. Preferably, the volume fraction of CH4 in the coke oven gas is 22-25%.

[0012] Further, in S1, by adjusting the proportion of the introduced methane-rich gas and water vapor, the composition of the dedusted and purified gas can be adjusted.

[0013] Further, in S1, it also includes:

[0014] The methane-rich gas and water vapor are preheated, and the temperature of the preheated methane-rich gas and water vapor when entering the inlet end of the flue is not less than 400℃. The purpose is to reduce the competition of gas-gas heat transfer for endothermic reforming reaction, and to increase the proportion of reforming reaction as much as possible, so as to increase the reforming cooling effect and make the reducing gas content in the product gas as high as possible. Preferably, the temperature of the preheated methane-rich gas and water vapor when entering the inlet end of the flue is 500-600℃.

[0015] Further, in the S3, the flue gas after the reforming reaction continues to be cooled in the cooling flue, and the waste heat is used to preheat the methane-rich gas and water vapor, and the temperature of the flue gas at the outlet of the cooling flue is not lower than 450 DEG C. The reason for selecting this value is to consider the preheating of the methane-rich gas and water vapor, and to increase the reforming reaction heat absorption and cooling and the proportion of the reduction gas after the reforming as much as possible, and the temperature value is slightly higher than 400 DEG C. Preferably, the temperature of the flue gas at the outlet of the cooling flue is 600 DEG C.-700 DEG C.

[0016] Further, the smelting reduction furnace is a HIsmelt smelting reduction furnace, a Hisarna smelting reduction furnace or a flash smelting smelting reduction furnace.

[0017] Further, when the smelting reduction furnace is a HIsmelt smelting reduction furnace, the molar ratio of CH4 to water vapor in the methane-rich gas is 1:1-4:1, and the dust content of the gas after dust removal and purification is not higher than 50 mg / Nm 3 .

[0018] Here, because the CO2 content in the tail gas is high, the methane steam reforming cooling effect is lower than that in the methane dry reforming process, and in order to ensure the cooling effect, the water vapor molar fraction of the HIsmelt smelting reduction furnace is limited to be below 0.5.

[0019] Further, when the smelting reduction furnace is a Hisarna smelting reduction furnace, the molar ratio of CH4 to water vapor in the methane-rich gas is 2:1-4:1, and the dust content of the gas after dust removal and purification is not higher than 15 mg / Nm 3 .

[0020] Here, the water vapor reforming cooling effect is lower than that in the methane dry reforming process, and in order to ensure the cooling effect, the water vapor molar fraction of the Hisarna smelting reduction furnace is limited to be below 0.33.

[0021] Further, when the smelting reduction furnace is a flash smelting smelting reduction furnace, the molar ratio of CH4 to water vapor in the methane-rich gas is 1:1-2:1, and the dust content of the gas after dust removal and purification is not higher than 15 mg / Nm 3 .

[0022] Here, because the CO2 content in the tail gas is low, the water vapor content is appropriately increased to increase the proportion of the methane steam reforming, so that the high-temperature flue is rapidly cooled. In order to ensure the cooling effect, the water vapor molar fraction is in the range of 0.33-0.5.

[0023] The present application has the following advantages:

[0024] The method for reducing the heat shock loss of the smelting reduction furnace has the advantages of simplicity, reliability, safety, stability, low operation cost and high energy efficiency.

[0025] Firstly, the reforming reaction occurs between the methane-rich gas from the flue inlet end and the water vapor and the carbon dioxide generated in the furnace, and the reaction formula is shown in formula (1) and formula (2). The reaction is a strong endothermic reaction, and the heat energy of the high-temperature flue gas is used to promote the reforming reaction, greatly reducing the flue gas temperature and reducing the thermal shock loss of the flue material to the high-temperature flue gas;

[0026]

[0027]

[0028] Secondly, the CO and H2 generated by the reforming reaction are mixed into the flue gas at the top of the furnace, increasing the proportion of reducing gas in the flue gas at the top of the furnace and improving the reduction potential of the flue gas. After the flue gas is dusted and purified, it is re-introduced into the smelting reduction furnace, which promotes the reduction of iron oxides;

[0029] Thirdly, in addition to the reduction effect, the CO and H2 re-introduced into the furnace will also undergo secondary combustion in the furnace, releasing a large amount of heat energy, which plays an important role in increasing the temperature of the molten iron in the iron bath.

[0030] Fourthly, the method provided by the present application only needs to set a device for introducing methane-rich gas at the inlet end of the flue of the smelting reduction furnace, and the cooled, dusted and purified gas is re-introduced into the furnace. Therefore, the existing process equipment does not need to be greatly modified, and the method has good operability and realizability.

[0031] Fifthly, the method provided by the present application has high energy conversion efficiency. The high-temperature physical heat energy in the converter gas is converted into chemical energy by using the thermochemical energy storage technology, and the preheated methane-rich gas is used in combination with the subsequent utilization mode. The total energy recovery efficiency of the whole process is about 50% to 60%, which is much higher than the efficiency (25% to 37%) of the traditional recovery process.

[0032] Sixthly, the method provided by the present application has the characteristics of high cooling efficiency. By using CH4 dry / steam reforming, the high-temperature flue gas (1700 DEG C) can be reduced to about 1000 DEG C in a very short time (<2s), and the rapid cooling amplitude is about 41%. Then the flue gas is further cooled in the subsequent cooling flue.

[0033] Therefore, the present application has important practical and economic significance for improving the service life of the flue material of the smelting reduction furnace, and has good popularization and application value, and the prospect is very promising. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings described below only show some of the embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort based on these drawings.

[0035] Figure 1 The process schematic diagram for reducing the heat shock loss of the HIsmelt smelting reduction furnace is provided for an embodiment of the present application;

[0036] Figure 2 a to Figure 2 d is the computational fluid dynamics simulation result of the HIsmelt smelting reduction furnace and the flue temperature field distribution provided for an embodiment of the present application, wherein, Figure 2 a is the flue temperature diagram of the present situation without using the technical process; Figure 2 b is the flue temperature diagram of embodiment 1; Figure 2 c is the flue temperature diagram of embodiment 2; Figure 2 d is the flue temperature diagram of embodiment 3. DETAILED DESCRIPTION

[0037] In order to better understand the technical solutions of the present application, the embodiments of the present application will be described in detail below with reference to the drawings.

[0038] It should be clear that the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort belong to the scope of protection of the present application.

[0039] The terms used in the embodiments of the present application are only for the purpose of describing the specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0040] Previously, methane dry reforming and methane steam reforming were applied to the chemical production field, which used a large amount of heating process to achieve the purpose of preparing a certain proportion of synthesis gas, such as preparing H2, CO, etc. Due to the existence of barriers between the metallurgical production industry and the chemical production industry, no one has grafted the methane reforming process used in chemical synthesis to the metallurgical production industry. We apply this process to the metallurgical field, and the purpose or effect is different from that. The main purpose is to use the strong endothermic effect of methane reforming to quickly reduce the flue temperature of the smelting furnace to improve the service life of the flue, and at the same time, to achieve the environmental protection benefit of reducing carbon emissions. This has no precedent in the metallurgical production industry.

[0041] The application provides a method for reducing the top-flue thermal shock of a smelting reduction furnace, as shown in the formula, the method introduces preheated methane-rich gas and water vapor into the flue inlet end of the smelting reduction furnace in a certain proportion, the methane-rich gas and the water vapor and the high-temperature carbon dioxide gas generated in the smelting reduction furnace are subjected to a reforming reaction, the reforming reaction is as follows: Figure 1 The high-temperature flue gas provides the energy required by the reforming reaction, greatly reduces the gas temperature in the flue, reduces the thermal washing loss of the flue under high-temperature conditions, and at the same time, increases the content of H2 and CO in the top flue gas, and the flue gas can be sprayed into the furnace again or stored for other use after being cooled and dust-removed and purified in the cooling flue.

[0042] The methane-rich gas is natural gas, coal bed gas or coke oven gas, and the volume fraction of CH4 in the coke oven gas is not less than 20%.

[0043] The proportion of the introduced methane-rich gas and water vapor is adjusted to adjust the composition of the dust-removed and purified gas.

[0044] The temperature of the preheated methane-rich gas and water vapor when entering the flue inlet end is not less than 400 DEG C. For example, the temperature of the preheated methane-rich gas and water vapor when entering the flue inlet end is 500 DEG C.-600 DEG C.

[0045] The gas in the flue after the reforming reaction is continuously cooled in the cooling flue, the waste heat is used for preheating the methane-rich gas and water vapor, and the flue gas temperature at the outlet of the cooling flue is not higher than 450 DEG C. For example, the flue gas temperature at the outlet of the cooling flue is 600 DEG C.-700 DEG C.

[0046] The smelting reduction furnace is a HIsmelt smelting reduction furnace, a Hisarna smelting reduction furnace or a flash smelting smelting reduction furnace.

[0047] The HIsmelt smelting reduction iron process is a process in which non-coking coal is used as the main energy, iron-containing raw materials, coal and flux are directly sprayed into the molten iron pool at the lower part of the smelting reduction furnace by using N2 as the carrier, with the coal being dissolved and cracked in the molten iron pool at high temperature, and the iron oxides in the hot ore fines being rapidly reduced by carbon in the molten pool.

[0048] The method does not use coke, sinter and pellet, greatly reduces the emission of nitrogen oxides, sulfur oxides, carbon dioxide and dioxin, has the advantages of simple process, high resource and energy utilization efficiency, small environmental pollution, etc., and has a very bright application prospect, and has been a research hotspot in the ironmaking industry.

[0049] ​Hisarna process: Hisarna is actually a combination of ULCOS's previously developed Isarna technology and Rio Tinto's HIsmelt smelter technology. Hisarna integrates three new ironmaking technologies: first, the preheating and partial pyrolysis of coal in a reactor; second, the melting and pre-reduction of iron ore in a cyclone melting section; and third, the final reduction and iron production in the bottom molten pool.

[0050] Flash ironmaking: Flash ironmaking can be carried out using reducing gases such as CH4, H2, and CO. When using reducing gases of 50% H2 and 50% CO, the CO2 content in the flue is about 20%, the H2 content is about 48%, the CO content is about 30%, and the temperature reaches as high as 1700℃.

[0051] When the melting reduction furnace is an HISmelt melting reduction furnace: the molar ratio of CH4 to water vapor in the methane-rich gas is 1:1 to 4:1; the dust content of the gas after dust removal and purification is not higher than 50 mg / Nm³. 3 .

[0052] When the melting reduction furnace is a Hisarna melting reduction furnace: the molar ratio of CH4 to water vapor in the methane-rich gas is 2:1 to 4:1; the dust content of the gas after dust removal and purification is not higher than 15 mg / Nm³. 3 .

[0053] When the smelting reduction furnace is a flash ironmaking smelting reduction furnace: the molar ratio of CH4 to water vapor in the methane-rich gas is 1:1 to 2:1; the dust content of the gas after dust removal and purification is not higher than 15 mg / Nm³. 3 .

[0054] Example 1

[0055] It should be noted that the simulation conditions for the HIsmelt melting reduction furnace in Examples 1-3 were set as follows: flue gas temperature 1700℃; flue gas flow rate: 210000 m³ / h. 3 / h; The composition of flue gas in the furnace (by volume fraction) is: 70% CO2, 15% CO, 10% H2, 5% N2; The flow velocity of the natural gas and steam mixture entering the furnace is 5 m / s; There are 2 inlets for the natural gas and steam mixture; The inlet radius is 0.1 m.

[0056] Natural gas and steam are preheated to 400℃, then mixed in a specific ratio (CH4 and H2O molar ratio of 1:1) and introduced into the flue gas inlet. Inside the flue, methane undergoes a reforming reaction with steam and carbon dioxide. This reaction absorbs heat from the flue gas, significantly reducing its temperature. The calculated average gas temperature inside the flue is 879℃, while the temperature at the cooled flue gas outlet is 439℃. After reforming and dust removal, the dust content in the gas is 14 mg / m³. 3 .

[0057] Example 2

[0058] Natural gas and steam are preheated to 450℃, then mixed in a specific ratio (CH4 and H2O molar ratio of 2:1) and introduced into the flue gas inlet. Inside the flue, methane undergoes a reforming reaction with steam and carbon dioxide. This reaction absorbs heat from the flue gas, significantly reducing its temperature. The calculated average gas temperature inside the flue is 822℃, while the temperature at the cooled flue gas outlet is 427℃. After reforming and dust removal, the dust content of the gas is 11 mg / m³. 3 .

[0059] Example 3

[0060] Natural gas and steam are preheated to 500℃, then mixed in a specific ratio (CH4 to H2O molar ratio of 4:1) and introduced into the flue gas inlet. Inside the flue, methane undergoes a reforming reaction with steam and carbon dioxide. This reaction absorbs heat from the flue gas, significantly reducing its temperature. The calculated average gas temperature inside the flue is 793℃, while the temperature at the cooled flue gas outlet is 421℃. After reforming and dust removal, the dust content of the gas is 12 mg / m³. 3 .

[0061] Figure 2 a to Figure 2 d represents the computational fluid dynamics simulation results of the temperature field distribution in the HIsmelt melting reduction furnace and flue gas according to an embodiment of the present invention, wherein... Figure 2 a represents the flue temperature diagram under the current conditions before this technology was used; Figure 2 b is the flue temperature diagram of Example 1; Figure 2 c is the flue temperature diagram of Example 2; Figure 2 Figure d shows the flue gas temperature diagram for Example 3. From... Figure 2 As can be seen from Figure a, without using this technology, the temperature in the molten reduction furnace and flue is approximately 1600℃, which is extremely high and causes significant impact and wear on the high-temperature refractory materials in the flue. However, after using this technology, in Figure 2 In b-2d, it can be seen that the temperature reduction in the upper part of the molten reduction furnace and the flue section is very significant (the flue gas in the upper part of the molten reduction furnace rapidly decreases from a high temperature of 1700℃ to about 1100℃, and is further rapidly cooled in the cooling flue). This technology process... The rapid and significant endothermic nature of the two reforming reactions achieves the goal of reducing thermal shock losses in the molten reduction furnace flue. In this Fluent simulation setting, CO2 content is 70%, which is relatively high. Therefore, comparing Examples 1, 2, and 3, it can be seen that a higher CH4 ratio results in a better cooling effect than a lower ratio. Comparing the simulation results of Examples 1 and 3, the temperature at the flue inlet and the upper region of the molten reduction furnace in Example 3 is reduced by approximately 150°C compared to Example 1.

[0062] Flue exit feature Without the process Example 1 Example 2 Example 3 Flue average temperature (°C) 1690 (inlet) 879 822 793 CH4(%) 0 4 9 13 CO2(%) 70 36 20 12 [ H2(%) ] 10 24 35 39 CO (%) 15 27 31 33 [ H2O (%) ] 0 7 3 2 [N2 (%)] 5 2 2 1

[0063] Table 1. Characteristics of the flue outlet of Examples 1-3 compared to existing technologies that did not use this process.

[0064] The data in the table above clearly shows that the average flue temperature in Examples 1-3 using this technology is significantly lower than that without it. Simultaneously, due to the methane reforming reaction, the CO and H2 content at the flue outlet increases substantially after using this technology. Furthermore, it can be seen that as the proportion of methane in the injected gas increases, the CO and H2 content at the flue outlet also increases, resulting in a greater cooling effect.

[0065] In summary, the technical solution of this application introduces preheated methane-rich gas and water vapor into the flue inlet of the molten reduction furnace. The high-temperature flue gas generated by the HIsmelt molten reduction furnace itself carries the heat for a reforming reaction, significantly reducing the flue gas temperature and mitigating the wear on the flue refractory material caused by high-temperature impact. Simultaneously, the CO and H2 generated by the reforming reaction increase the reduction potential of the flue gas. The purified gas is then reinjected into the furnace, achieving the goal of flue gas recycling. This technical solution achieves full utilization of the thermal and chemical energy of high-temperature flue gas without large-scale modifications to existing equipment, and has advantages such as simplicity, reliability, safety, stability, and low operating costs.

[0066] The foregoing has provided a detailed description of a method for mitigating thermal shock loss in the flue gas of a HISmelt melting reduction furnace, as provided in the embodiments of this application. The descriptions of the embodiments above are merely illustrative of the method and its core concepts; furthermore, those skilled in the art will recognize that variations in specific implementation methods and application scope may occur based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

[0067] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A method for reducing thermal shock loss in the flue gas duct of a molten reduction furnace, characterized in that, The method includes: S1: The methane-rich gas and water vapor are preheated, and the temperature of the preheated methane-rich gas and water vapor when they enter the flue inlet end is not lower than 400°C; they are introduced into the flue inlet end of the molten reduction furnace in a certain proportion, and the methane-rich gas and water vapor undergo a reforming reaction with the high-temperature carbon dioxide gas generated in the molten reduction furnace. S2: The high-temperature flue gas in the molten reduction furnace provides the energy required for the reforming reaction, and the gas temperature in the flue is significantly reduced; S3: After the gas in the flue is further cooled and purified by the cooling flue, it is either injected back into the furnace or stored for later use. The smelting reduction furnace is a Hismelt smelting reduction furnace, a Hisarna smelting reduction furnace, or a flash ironmaking smelting reduction furnace. When the melting reduction furnace is an HISmelt melting reduction furnace: the molar ratio of CH4 to water vapor in the methane-rich gas is 1:1 to 4:1; the dust content of the gas after dust removal and purification is not higher than 50 mg / Nm³. 3 ; When the melting reduction furnace is a Hisarna melting reduction furnace: the molar ratio of CH4 to water vapor in the methane-rich gas is 2:1 to 4:1; the dust content of the gas after dust removal and purification is not higher than 15 mg / Nm³. 3 ; When the smelting reduction furnace is a flash ironmaking smelting reduction furnace: the molar ratio of CH4 to water vapor in the methane-rich gas is 1:1 to 2:1; the dust content of the gas after dust removal and purification is not higher than 15 mg / Nm³. 3 .

2. The method for reducing thermal shock loss in the flue gas duct of a molten reduction furnace according to claim 1, characterized in that, In S1, the reforming reaction is: CH4+CO2↔2H2+2CO, CH4+H2O↔3H2+CO.

3. The method for reducing thermal shock loss in the flue gas duct of a molten reduction furnace according to claim 1, characterized in that, In step S1, the methane-rich gas is natural gas, coalbed methane, or coke oven gas, wherein the volume fraction of CH4 in the coke oven gas is not less than 20%.

4. The method for reducing thermal shock loss in the flue gas duct of a molten reduction furnace according to claim 3, characterized in that, In step S1, the composition of the gas after dust removal and purification is adjusted by changing the ratio of the introduced methane-rich gas and water vapor.

5. The method for reducing thermal shock loss in the flue gas duct of a molten reduction furnace according to claim 1, characterized in that, In step S3, the gas in the flue after the reforming reaction continues to be cooled in the cooling flue, and the residual heat is used to preheat the methane-rich gas and water vapor. The flue gas temperature at the outlet of the cooling flue is not lower than 450°C.

Images