A natural gas steam two-stage heat exchange type composite conversion hydrogen production system

Abstract

The application discloses a natural gas water vapor two-stage heat exchange type composite conversion hydrogen production system, which is composed of a pretreatment module, a heat exchange conversion module, a reforming conversion module, a shift reaction module and a pressure swing adsorption (PSA) hydrogen extraction module. The system aims to solve the problems of the existing technology in the natural gas water vapor conversion hydrogen production system, such as a complex conversion section, limited heat exchange conversion efficiency, limited heat transfer conversion depth, small coupling and synergistic effect with the remaining hydrogen production / hydrogen extraction section, and still existing flue gas emission, and can realize energy cascade utilization, high methane conversion depth, system energy self-balancing, and compact and efficient premise of reducing flue gas emission, completely replace the radiant combustion reforming conversion process of SMR, make the heat coupling between each module in the hydrogen production system more reasonable, flexible and close, and the thermal efficiency of the hydrogen production system is as high as 92-98%, the H2 yield is as high as 90% or more, and the system is convenient for prying and miniaturization, and is suitable for hydrogen production in a hydrogenation station.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hydrogen gas preparation in hydrogen energy, and particularly relates to a natural gas steam two-stage heat exchange type composite conversion hydrogen production system. BACKGROUND

[0002] Hydrogen energy is one of the most promising clean energies at present. At present, the hydrogen gas preparation process mainly obtains hydrogen gas from fossil raw materials containing carbon and hydrogen elements through catalytic thermal cracking reforming and carbon-hydrogen separation and discharges CO2 or CO or other pollutants, including natural gas, methanol, coal, heavy oil, biogas and other raw materials. The natural gas steam reforming conversion (abbreviated as "SMR") for preparing "gray hydrogen" is the largest, most mature and lowest cost method for hydrogen production in the world.

[0003] The methods for preparing "gray hydrogen" from natural gas mainly include steam reforming conversion (SMR), partial oxidation reforming (POR), autothermal reforming (ATR) and heat exchange reforming (HTER), and plasma reforming. Among them, the SMR conversion hydrogen production is the most mature and traditional hydrogen production method. The core technology is a reformer or a conversion reactor. Usually, a radiation chamber (section) provides heat to make the conversion temperature required for the catalytic reforming reaction of methane and water vapor in the tube within the furnace reach as high as 700-900°C. Since the column tube type reformer or reactor is limited by the radiation heat transfer mode, the miniaturization of the device is difficult, and a certain amount of natural gas needs to be consumed as fuel gas, and a large amount of excess steam is generated. Therefore, while increasing the consumption of natural gas and flue gas emissions, the H2 yield is also reduced, and the typical conversion thermal efficiency is only about 70%. Therefore, in view of the problems existing in the natural gas or hydrocarbon steam reforming (SMR) hydrogen production, many new technologies have been proposed to completely or partially replace the radiation section in the SMR conversion section in order to reduce the consumption of natural gas fuel and reduce flue gas emissions, improve the thermal efficiency of the hydrogen production process and the yield of H2 product gas, and facilitate the miniaturization of the device. Among them, the series of technologies related to hydrocarbon steam reforming hydrogen production developed by Topsoe Company, a global leader in hydrocarbon steam reforming hydrogen production technology, and its Chinese subsidiary, including natural gas, are the most typical, including US2015 / 0175416A1, CN111433151A, CN101056817A, CN101208264A, CN200480009024.8, CN200580038308.4, CN00106514.9, CN113474282A, etc.

[0004] Topsoe's series of patented typical processes mainly fall into two categories: First, partially replacing the radiative conversion load to improve conversion thermal efficiency. In traditional hydrocarbon steam SMR conversion processes using natural gas as feedstock, Topsoe's Heat Transfer Conversion (HTER) technology fully utilizes the high-temperature process gas from the radiative (section) conversion outlet as the heat source for heat transfer conversion. This heat transfer conversion is performed on the pre-converted gas entering a combustion chamber-less heat transfer conversion section connected in parallel with the SMR converter, thereby reducing the fuel gas consumption of the radiative conversion unit, increasing the yield of H2 product gas, and achieving a conversion thermal efficiency of 70-90% or higher. On average, it can reduce the radiative conversion load by 30%. However, HTER heat transfer conversion still relies on the heat provided by the high-temperature process gas flowing out of the radiative section. To further reduce the SMR conversion load, Haldor Topsoe, in invention patents such as CN113474282A, employs an electric heating conversion or autothermal conversion (ATR) combined with SMR and HTER to form a complex parallel-series conversion furnace / reactor process involving first, second, third, and fourth conversions. This allows the desorbed gas from the PSA-purified H2 process to be used as fuel gas for the combustion-type conversion furnace (SMR), saving natural gas and reducing the SMR conversion load to a maximum of 30%. Simultaneously, by adjusting the proportion of feed gas introduced into each conversion furnace, both the conversion thermal efficiency and H2 product gas yield reach over 90%. Secondly, the high-temperature flue gas exiting one combustion-type conversion furnace is fully utilized as fuel gas for further processing. The fuel gas from one or more parallel combustion reformers, along with the desorbed gas from the subsequent pressure swing adsorption (PSA) purification of H2, and supplemental fuel gas from external air or oxygen-enriched gas, provides heat to each parallel combustion reformer for conversion. This results in the oxygen content in the last high-temperature flue gas exiting the system being less than 0.3% and the flue gas temperature being less than 600°C, demonstrating that the thermal efficiency of the conversion system can reach over 90%. This forms Haldor Topsoe's unique convective heat transfer reforming (HTCR) process, as described in CN101056817A. The arrangement of at least two reforming units significantly reduces the total feed and fuel requirements for producing each volume unit of hydrogen and / or carbon monoxide. Because the amount of combustion air produced per unit of hydrogen is reduced, the amount of steam produced (which is subsequently used as process steam) is also reduced. Therefore, compared to, for example, using only one reformer, the steam:carbon ratio (S / C ratio, defined as the molar ratio of carbon in the steam to that in the hydrocarbon feed) is lower. This brings many benefits, such as reduced total gas flow rate throughout the hydrogen and / or carbon monoxide production unit, resulting in smaller equipment and / or lower pressure drop, etc. The process is in series for the fuel flue gas and in parallel for the feed gas.As the number of parallel combustion converters increases, the thermal efficiency of the conversion system also increases. Meanwhile, the number of converters depends on the amount and composition of fuel leaving the hydrogen and / or carbon monoxide purification unit.

[0005] Haldor Topsoe's series of patents also have some drawbacks. First, the core of all the patented technologies revolves around the heat balance in the natural gas or hydrocarbon steam reforming hydrogen production system, neglecting the depth of natural gas steam reforming or the methane conversion rate. Although the methane conversion rate can reach over 90%, the reformed gas often still contains about 1-8% methane. This is because both convective heat transfer reforming and heat exchange reforming sacrifice a certain degree of conversion depth to improve thermal efficiency, making it difficult to achieve the depth of traditional SMR or autothermal ATR reforming or a methane conversion rate greater than 97-99%. The higher the methane content in the converted gas, the greater the load requirement for the subsequent H2 purification and separation process. Especially when using PSA to purify H2, methane and H2 can easily form a balanced methane hydrogen (3-5% methane, 95-97% H2), which increases the load for H2 separation and extraction by more than 50%. Second, the heat required for heat exchange HTER conversion still depends on the radiant heat obtained from combustion through an external burner, which is carried into the HTER by the high-temperature converted gas to provide heat for its conversion. This will consume fuel gas and generate high-temperature flue gas, which is still cooled by the heat recovery system (HR) before being discharged. Although conventional natural gas fuel gas can be completely replaced by desorbed gas from PSA hydrogen extraction, the large amount of flue gas emissions still has an adverse impact on the environment. Third, to facilitate the adjustment and stabilization of the syngas (converted gas) outlet temperature in the conversion section, ensure the conversion temperature in the burner-free HTER converter, and increase the methane conversion depth, the technology employs more conversion combinations, including first (e.g., electric heating conversion), second (e.g., conversion with burners), third (e.g., HTER converter), or even fourth (e.g., ATR converter) conversion sections, or multiple converters in series (e.g., HTCR with burners), in order to increase the adjustment range of the conversion load of each converter and the methane conversion depth while ensuring improved conversion thermal efficiency. This results in a lengthy and complex conversion process. Fourth, once the conversion combination or process equipment volume is determined, it is necessary to adjust the feed water-to-carbon ratio (e.g.) or the feed gas entering each converter. The composition of the reformed gas, or the water-to-carbon (S / C) ratio or the hydrogen-to-carbon (H2 / CO) ratio, is controlled by adjusting the distribution ratio of the reforming units in order to produce products mainly composed of H2 or CO. This makes the process more complex, and the changes in the reforming load, methane conversion rate, and reformed gas composition are not significant. Ultimately, the yield of H2 or CO product gas is also basically determined. Fifth, Haldor Topsoe's existing HTER patented technology tends to produce reformed gas with a lower H2 / CO ratio. This is because external CO2 is added to the burner-free heat exchanger in parallel with the main reformer to prevent catalyst carbon buildup or equipment corrosion. This prevents CO from undergoing the Boudouard decomposition reaction at high temperatures to produce coke, and also prevents carbon buildup on the reforming catalyst and / or corrosion of equipment materials.Although introducing CO2 to prevent carbon buildup on the conversion catalyst results in a higher CO or H2 production rate per unit volume compared to the traditional steam-introduction process, the reduction in equipment volume due to CO2 addition has limited benefits. Furthermore, it makes it easier for the higher concentration of CO and H2 in the conversion gas to undergo methanation, affecting the catalytic conversion efficiency of the catalyst and increasing the methane content in the conversion gas, thus reducing the H2 yield. In contrast, preventing carbon buildup in the main converter / reformer primarily involves adjusting the steam input, and appropriately introducing CO2 can more easily regulate the conversion gas composition and prevent carbon buildup, while reducing the likelihood of methanation and resulting in a higher methane conversion rate. Sixth, the coupling between the conversion section and other sections of the hydrogen production system is low. Aside from the inherent upstream and downstream connections in the hydrogen production system, these proprietary technologies only use the desorbed gas from the PSA hydrogen extraction section as fuel gas, establishing a connection or coupling with the conversion section. The composition and flow rate of the desorbed gas do not affect the operating conditions of the conversion section or the composition of the conversion gas; only the temperature of the flue gas after combustion is considered.

[0006] In addition to Topsoe's series of patents, other companies have also developed new converter technologies, such as "A heat exchange converter tube bundle" (CN202221901514.0), "A light hydrocarbon to syngas conversion device using high-temperature first-stage converter gas preheating heat exchange conversion" (CN201821176009.8), and "A central tube converter" (CN201921356691.3), etc. These all aim to improve the thermal efficiency of the conversion section, but they differ significantly from Topsoe's technology with heat exchange or heat transfer conversion (HTER or HTCR). Among them, Chengda's patent CN201821176009.8 utilizes the high-temperature syngas flowing out of the SMR conversion section... The pre-converted gas (mixed steam) is heated to approximately 500-600°C by convective heat transfer of the process gas, and then returned to the SMR converter. This improves the conversion thermal efficiency and reduces the amount of high-temperature process gas from the conventional SMR converter that directly enters waste heat utilization to generate steam. This also means further reduction in fuel gas consumption in the SMR conversion section and a further reduction in converter volume under corresponding loads. However, compared to Haldor Topsoe's HTER process, which utilizes high-temperature process gas from SMR, ATR, or other converters to transfer heat with the pre-converted gas and further reforms it in a burner-free HTER converter, its thermal efficiency is not only improved but also the yield of converted gas or H2 is increased. Therefore, these improved SMR conversion patent technologies cannot compare with Haldor Topsoe's series of patents. Summary of the Invention

[0007] To address the shortcomings of existing technologies in natural gas steam reforming hydrogen production systems, such as complex reforming stages, limited heat exchange efficiency, limited heat transfer depth, weak synergy with other hydrogen production / extraction stages, and persistent flue gas emissions, the primary objective of this invention is to provide a radiation combustion reforming process that completely replaces the SMR process while achieving a compact and efficient energy transfer, reforming efficiency, energy balance, and reduced flue gas emissions within the natural gas steam reforming hydrogen production system. This results in more rational, flexible, and tighter heat coupling between the various modules in the hydrogen production system. Specifically, this invention provides a two-stage heat exchange composite reforming hydrogen production system using natural gas steam reforming. The specific technical solution is as follows.

[0008] A natural gas steam two-stage heat exchange composite conversion hydrogen production system is disclosed. This system comprises a feed gas (raw material gas) pretreatment module, a heat exchange conversion module, a reforming conversion module, a shift reaction module, and a pressure swing adsorption (PSA) hydrogen extraction module.

[0009] 1) Pretreatment module, which is arranged to receive feed gas and purify and preheat it to form mixed steam and pre-converted gas that enter its downstream module. It includes: process / material conveying pipelines for materials entering and leaving the module, conveying pumps and / or booster compressors, preheaters and hydrodesulfurization units. Among them, the feed gas natural gas or hydrocarbon-containing feed gas is preheated to the reaction temperature required for hydrodesulfurization by steam or electric heating and then enters the hydrocatalytic desulfurization unit. The hydrogen comes from the downstream PSA hydrogen extraction module. The desulfurization depth needs to meet the specifications of various catalysts in the downstream convective pre-conversion, heat exchange conversion, reforming conversion and shift reaction modules for catalytic conversion or shift reaction. The feed gas after hydrodesulfurization is purified natural gas, which is mixed with a certain proportion of water vapor to form mixed steam and then enters the downstream heat exchange conversion module.

[0010] 2) The heat exchange conversion module is arranged to receive mixed steam and reformed gas and provide pre-converted gas, final converted gas, and / or heat exchange conversion gas. It mainly consists of a convective pre-conversion unit and a heat exchange conversion unit. The mixed steam, as feed gas, enters the tubes of the convective pre-conversion unit and undergoes convective heat transfer with the combined converted gas from the heat exchange conversion unit flowing outside the tubes to obtain the heat required for the pre-conversion reaction. The mixed steam flowing through the tubes thereby removes C5 carbon, which is harmful to downstream natural gas steam heat exchange conversion and reforming. The gas undergoes a partial conversion reaction with water vapor, involving components with C5 or higher carbon atoms, as well as methane and / or light hydrocarbons with C5 or lower carbon atoms, forming pre-converted gas. A portion of this pre-converted gas flows out of the heat exchange conversion module and into the downstream reforming conversion module, while the remaining portion serves as feedstock entering the heat exchange conversion unit and flowing through the tubes (inside) loaded with reforming catalysts for a heat exchange conversion reaction. The heat required for this reaction comes from convective heat transfer with the high-temperature reformed gas flowing outside the tubes from the downstream reforming conversion module. The temperature of the heat exchange conversion reaction is 780~900℃. The high-temperature heat-exchange reformed gas flowing out of the unit tube, and / or a portion thereof, mixes with the reformed gas that has been cooled by convective heat transfer in the heat-exchange reforming unit to form a combined reformed gas. This combined gas enters the convective pre-reformation unit, where it undergoes convective heat transfer with the mixed steam entering the unit. This results in the mixed steam undergoing pre-reformation in the convective pre-reformation unit at a temperature of 450~650℃, higher than the pre-reformation temperature of the traditional SMR process (270~380℃). After convective heat transfer in the convective pre-reformation unit, the combined reformed gas is cooled to 150~350℃ to form the final reformed gas, which then enters the downstream process. The high-temperature heat exchange conversion gas flowing out of the heat exchange conversion unit tubes of the shift reaction module, and / or a portion thereof, is directly mixed with the combined conversion gas cooled by convective heat transfer in the convective pre-conversion unit to form the final conversion gas at a temperature of 150~350℃, which enters the downstream shift reaction module. The ratio of the two streams of the high-temperature heat exchange conversion gas depends on the reaction temperature required for the high-temperature, medium-temperature, low-temperature, medium-high-temperature, or medium-low-temperature shift reaction adopted by the downstream shift reaction module, as well as the content of C5 and above components in the mixed steam and the corresponding temperature required for convective pre-conversion.

[0011] 3) A reforming and conversion module, which is arranged to receive pre-converted gas and combustion gases including oxygen-enriched gas, H2-containing desorbed gas 2 from the downstream PSA hydrogen extraction module, and / or H2 product gas, as well as water vapor that regulates the water-to-carbon ratio (S / C) and hydrogen-to-carbon ratio (H2 / CO) of the reforming and conversion module, and CO2-containing desorbed gas 1 from the downstream PSA hydrogen extraction module, and to provide high-temperature reformed gas flowing into the upstream heat exchanger. It includes a reforming and conversion tube reactor and a hydrogen-oxygen combustion reaction chamber at the top of the tubes, wherein the introduced oxygen-enriched gas reacts with the pre-converted gas and / or desorbed gas 2 in the hydrogen-oxygen combustion reaction chamber. The H2 in the product gas undergoes a hydrogen-oxygen combustion reaction, generating a huge heat of reaction. This heat is directly carried by the reaction gas into the reforming unit, which contains a reforming catalyst tube for reforming. The reforming temperature reaches 850~990℃, and the methane conversion rate is 99~100%. The high-temperature reformed gas flowing out of the reforming reaction flows into the heat exchanger in the upstream heat exchanger module for convective heat transfer, providing the heat required for heat exchanger conversion. The operation of the reforming module is the main means to determine the S / C and H2 / CO ratios in the natural gas steam reforming process.

[0012] 4) Shift reaction module, which is arranged to receive the final converted gas from the heat exchange conversion module and perform a shift reaction to output shift gas. Its function is to react carbon monoxide (CO) and water vapor in the converted gas with a shift reaction bed loaded with medium-high temperature or medium-low temperature shift catalyst to form shift gas with hydrogen (H2) and carbon dioxide (CO2) as the main components. Part of the shift gas is returned to the heat exchange conversion module to regulate the H2 / CO ratio of the heat exchange conversion gas flowing out of the heat exchange conversion module. The heat required by the shift reaction module is directly brought in by the final converted gas from the upstream heat exchange conversion module. The distribution ratio of the two heat exchange conversion gases in the heat exchange conversion module is adapted to the different shift reaction processes carried out by different shift catalysts used in the shift reaction module. Part of the shift gas enters the downstream module - the pressure swing adsorption (PSA) hydrogen extraction module.

[0013] 5) The PSA hydrogen extraction module is arranged to receive shift gas from the shift reaction module, perform decarbonization separation and H2 purification to output product H2 and desorbed gas. The shift gas either directly or after heat exchange with the feedstock natural gas and cooling to 20-80°C enters the PSA hydrogen extraction module. The decarbonization separation section consists of two or more adsorption towers connected in series or parallel, each loaded with a composite adsorbent. Desorbed gas 1 flowing from one of the adsorption towers is used partly to adjust the H2 / CO ratio of the reformed gas flowing from the upstream reforming module, and partly as feedstock gas for CO2 recovery. The flow rate of desorbed gas 1 returning to the reforming module, the order of desorbed gas flow, and the desorption time depend on the design requirements or online adjustment of the reformed gas H2 / CO ratio. The hydrogen-rich gas flowing from one of the adsorption towers enters the H2 purification section, which consists of two or more H2 sections connected in series or parallel, each loaded with a composite adsorbent. The hydrogen-rich gas flowing from one of the adsorption towers has a purity greater than [missing information]. Of the 99.99% pure H2 product gas, a portion is input into the H2 product gas tank or used at the output, a portion is used as hydrogenation gas in the pretreatment module, and a portion is used as supplementary combustion gas in the reforming and conversion module and / or as catalyst activation and adjustment of the H2 / CO ratio in the shift reaction module. The proportion and timing of the H2 product gas used as hydrogenation gas and / or combustion gas and / or for adjusting the H2 / CO ratio depend on the design requirements or online adjustments of the hydrodesulfurization accuracy, oxygen concentration of the oxygen-enriched combustion gas, and H2 / CO ratio. Meanwhile, the desorbed gas 2 flowing out from one of the adsorption towers is partly returned to the reforming and conversion module as combustion gas. The flow rate and H2 concentration of the desorbed gas 2 used as combustion gas must meet the design requirements or online adjustments of the conversion temperature and load of the combustion reforming section of the reforming and conversion module, and are also related to the design requirements or online adjustments of the purity or yield of the product H2. A portion is either directly exported as fuel gas or further recovered from the H2.

[0014] Furthermore, in the aforementioned natural gas steam two-stage heat exchange composite conversion hydrogen production system, the upstream and downstream links between the pretreatment module, heat exchange conversion module, reforming conversion module, shift reaction module, and PSA hydrogen extraction module are formed by splicing and assembling the corresponding pipelines, valves, and equipment interfaces in each module. The combination of each module and its corresponding operation are closely linked, indispensable, and coordinated. Each module includes not only the main units mentioned above, but also other necessary auxiliary equipment, including compressors, transfer pumps, buffer tanks, cooling water, steam tanks, auxiliary pipelines, supports, platforms, and various valves, which are not limited to being placed within their respective modules. The hydrogen production capacity of each hydrogen production system is a minimum of 50 Nm³ / h and a maximum of 5000 Nm³ / h, and multiple systems can be connected in series or parallel to expand the hydrogen production capacity. The operating pressure range of the hydrogen production system is 0.3~3.5 MPa.

[0015] Furthermore, the aforementioned natural gas steam two-stage heat exchange composite conversion hydrogen production system is applicable to hydrocarbon feedstock gases other than natural gas, including alkanes (C5 and below), refinery tail gas, biogas, coal gas, and some alcohols. The system is a skid-mounted integrated unit with a hydrogen production capacity of 50~10,000 Nm3 / h, especially suitable for miniaturized integrated skid-mounted units with a natural gas or biogas steam conversion capacity of less than 1,000 Nm3 / h, used for hydrogen production in hydrogen refueling stations. The biogas steam conversion hydrogen production system requires the addition of a biogas purification and CO2 removal process in the pretreatment module, either after or before hydrodesulfurization. The method used is either a PSA biogas concentration independent unit or coupled with PSA decarbonization in the PSA hydrogen extraction module. The high-concentration CO2 waste gas generated is used in combination with the desorbed gas 1 of the PSA hydrogen extraction module.

[0016] Furthermore, in the aforementioned two-stage heat exchange composite conversion hydrogen production system using natural gas and steam, the heat exchange conversion unit tubes in the heat exchange conversion module are filled with a low-temperature reforming catalyst. This catalyst is a low-temperature reforming catalyst containing nickel / cobalt as the main active component, rare earth metals and their oxides as co-catalyst components, and carbon nanotubes or carbon fibers and alumina, titanium dioxide, or zirconium oxide as the supporting substrate, replacing the high-temperature nickel / nickel-based reforming catalyst. The conversion temperature of the low-temperature reforming catalyst is 450~600℃, while the reforming conversion tubes in the reforming conversion module are filled with high-temperature... The hot nickel / nickel-based reforming catalyst is used in this process. The high-temperature reformed gas flowing from the reforming module first enters the upstream pretreatment module and undergoes convective heat transfer with the ambient-temperature natural gas feedstock, raising the temperature of the feedstock natural gas to the operating temperature required for hydrodesulfurization. After preheating and convective heat transfer, the reformed gas then enters the heat exchanger unit of the heat exchanger module. It flows through the tubes of the heat exchanger unit, which are filled with a low-temperature reforming catalyst, and undergoes convective heat transfer with the pre-reformed gas flowing through the tubes, which are loaded with a low-temperature reforming catalyst bed. This process raises the temperature of the pre-reformed gas within the heat exchanger unit to the required operating temperature for hydrodesulfurization. The reforming catalyst bed provides the heat required for the reforming process. The pre-reformed gas, after undergoing a low-temperature reforming reaction within the tube stack, is completely mixed with the reformed gas exiting after convective heat transfer to form a combined reformed gas. This combined reformed gas then enters the convective pre-reformation unit of the heat exchanger module, where it undergoes convective heat transfer with the mixed steam flowing into the unit. This causes the mixed steam to be heated and undergo a pre-reformation reaction within the tube stack, removing high-hydrocarbon components and partially undergoing a reforming reaction to form pre-reformed gas. The pre-reformation temperature is 280~350℃. A portion of the pre-reformed gas... The gas enters the reforming and conversion module, and a portion of it enters the heat exchange conversion unit of the heat exchange conversion module. The combined reformed gas is further cooled to 160~280℃ after convective heat transfer to form the final reformed gas, which directly enters the downstream shift reaction module for shift reaction. At this time, the shift reaction catalyst is selected as a medium-low temperature shift catalyst. Thus, the heat carried by the high-temperature reformed gas from the reforming and conversion module is utilized in a cascade manner through the pretreatment module and the heat exchange conversion module, so that the thermal efficiency of the natural gas steam reforming hydrogen production system reaches 99~100%, without consuming external energy.

[0017] Furthermore, in the aforementioned natural gas-steam two-stage heat exchange composite conversion hydrogen production system, the reforming conversion module consists of a hydrogen-oxygen combustion reforming conversion unit and a radiant heat reforming conversion unit generated by the combustion of fuel gas and air. Specifically, a combustion chamber is located at the top, side, or bottom of the reforming conversion reactor, which is composed of tubes loaded with nickel / nickel-based reforming catalysts. A portion of the natural gas is used as fuel gas, and air is used as an oxidizer, which is introduced into the combustion chamber for combustion. The resulting high-temperature combustion gas is ejected through nozzles and radiates heat to the tubes, raising the conversion temperature of the reforming catalyst bed within the tubes to 770-950°C. Consequently, a portion of the natural gas used as feedstock enters the preheating unit of the pretreatment module, with its heat source being from the reforming catalyst. The high-temperature flue gas from the combustion of the reforming module is obtained by convective heat transfer between the pre-conversion unit and mixed steam in the heat exchanger reforming module. The preheated feedstock natural gas then enters the hydrodesulfurization unit for desulfurization. The resulting purified natural gas mixes with water vapor to form mixed steam, which enters the pre-conversion unit of the heat exchanger reforming module. There, it undergoes convective heat transfer with the high-temperature flue gas from the reforming module, resulting in pre-converted gas at a temperature of 250-350°C. This pre-converted gas then enters the convective pre-conversion unit of the heat exchanger reforming module, where it undergoes convective heat transfer with the combined reformed gas from the heat exchanger reforming module, forming intermediate pre-converted gas at a temperature of 450-650°C. This intermediate pre-converted gas then enters the heat exchanger reforming unit for the heat exchanger reforming reaction. The heat exchanger reforming unit consists of a tube-and-shell structure. The internal reactor is loaded with a nickel / nickel-based reforming catalyst. The heat exchange conversion reaction temperature is 750~880℃. Gas originating from the reforming module flows through the tubes of the heat exchange conversion unit, convectively transferring heat to the intermediate pre-conversion gas, which is packed with the nickel / nickel-based reforming catalyst bed and flows through the tubes. This provides a heat source for the heat exchange conversion unit. Simultaneously, the heat exchange conversion gas produced after the intermediate pre-conversion gas undergoes reforming reaction within the tubes of the heat exchange conversion unit mixes with the reforming conversion gas flowing outside the tubes after convective heat transfer, forming a combined conversion gas. This combined gas then enters the convective pre-conversion unit of the heat exchange conversion module, where it undergoes convective heat transfer with the pre-conversion gas from the pre-conversion unit. This further heats and pre-converts the pre-conversion gas, forming the intermediate pre-conversion gas. The gas is split into two streams and enters the heat exchange conversion unit of the heat exchange conversion module and the radiative heat reforming conversion unit of the reforming conversion module respectively for reforming conversion. At the same time, the combined conversion gas is cooled to form the final conversion gas, which is further cooled by the heat recovery system (HR). / A portion of the heat exchange conversion gas is mixed with the combined conversion gas from the convection pre-conversion unit through the heat recovery system (HR) to form the final conversion gas. This final conversion gas meets the operating temperature required for the medium-high temperature or medium-low temperature conversion reaction of the downstream conversion reaction module and enters the conversion reaction module. From there, the conversion gas is formed and further cooled by the heat recovery system (HR) to the operating temperature required by the PSA hydrogen extraction module before entering the PSA hydrogen extraction module to obtain a purity of ≥99%.99% of the H2 product gas is produced through a heat recovery system (HR) that generates steam to meet the needs of the hydrogen production system. A portion of the shift gas, which is not cooled by the HR system, is used as regulating gas to adjust the S / C and / or H2 / CO ratios in the heat exchange conversion module. A portion of the H2 product gas from the PSA purification unit of the PSA hydrogen extraction module is returned to the hydrodesulfurization unit in the pretreatment module for hydrodesulfurization of the feedstock natural gas flowing out of the preheating unit. The desorbed gas 2 from the PSA purification unit of the PSA hydrogen extraction module is used as fuel gas to replace or partially replace natural gas in the reforming module. It enters the combustion chamber of the radiant heat reforming unit of the reforming module for combustion, providing a heat source for the reforming module. The desorbed gas 1 from the PSA decarbonization unit of the PSA hydrogen extraction module is partly used, along with steam and intermediate pre-converted gas, as adjusting gas for the S / C and H2 / CO ratios in the reforming module's conversion process; and partly output as feedstock for extracting high-concentration CO2 or as emissions.

[0018] Furthermore, in the aforementioned natural gas steam two-stage heat exchange composite conversion hydrogen production system, the PSA decarbonization and purification units of the PSA hydrogen extraction module are replaced by a rotary pressure swing adsorption system consisting of a multi-channel rotary valve with 7 or more channels and 5 or more adsorption towers. The composite adsorbent packed in the adsorption towers needs to have 10-20% more carbon molecular sieve added. The rotary valve rotation speed is greater than 200 seconds per revolution. Product H2 flows out from one of the adsorption towers, while the desorbed gas 1 and desorbed gas 2 from the original two stages of PSA decarbonization and purification are combined into a single desorbed gas, flowing out from the other adsorption tower. The desorbed gas flowing out in the early and middle stages is used as fuel gas for the reforming conversion module, while the desorbed gas flowing out in the final stage is either used to adjust the S / C ratio and H2 / CO ratio of the reforming conversion module, or as feed gas for producing high-purity CO2, or directly discharged.

[0019] The beneficial effects of this invention are:

[0020] The greatest advantage of this invention is that, under the premise of ensuring a thermal efficiency of 90-97% in natural gas steam reforming, a methane conversion rate of 99%, an H2 product gas purity of greater than 99.99%, and a total yield of greater than 90%, compared with the prior art, the natural gas steam reforming hydrogen production system of this invention completely replaces the traditional radiation reforming conversion. The energy in the system is 100% utilized in stages, with no combustion flue gas generated and no by-product steam. It can also achieve flexible adjustment of the S / C ratio and H2 / CO ratio in the hydrogen production process.

[0021] The most prominent advantage of this invention is that by utilizing the heat carried by the high-temperature reforming gas and the characteristics of the mixed steam entering the heat exchanger conversion module, along with a portion of the pre-converted gas and another portion of the pre-converted gas entering the reforming module requiring heat for pre-conversion, heat exchanger conversion, and reforming, the high-temperature reforming gas flowing out of the reforming module is first passed through the pre-converted gas in the heat exchanger conversion unit for convective heat transfer. The resulting cooled reforming gas is then mixed with the high-temperature heat exchanger conversion gas to form a combined reforming gas with a slightly higher temperature. This combined reforming gas is then convectively heated with the mixed steam in the convective pre-conversion unit. This results in a pre-converted gas temperature higher than that of existing technologies, significantly reducing the load on downstream heat exchanger conversion and reforming, as well as reducing oxygen consumption and PSA hydrogen extraction desorption gas emissions. Simultaneously, by flexibly adjusting the flow rates of the heat exchanger conversion gas into two streams, the temperature of the final reforming gas entering the shift reaction can be adjusted to meet the needs of different shift reaction processes selected in the downstream shift reaction module of the reforming module.

[0022] The hydrogen production system of this invention does not require external transportation of fuels such as natural gas during normal operation. The required fuel gas relies entirely on the desorbed gas from the PSA hydrogen extraction module within the system and external oxygen-enriched gas. This allows all the energy of the by-product steam in the traditional natural gas steam SMR conversion process to be converted into more H2 or converted gas through heat transfer reforming. Furthermore, the materials used to adjust the S / C ratio and H2 / CO ratio during the conversion process also come from within the hydrogen production system. This achieves both heat balance and basic material quality balance in the hydrogen production system, resulting in a significant reduction in the exhaust emissions of the hydrogen production system.

[0023] The hydrogen production system of this invention eliminates the space-consuming radiation reforming conversion method, making it highly suitable for skid-mounted integration. Its equipment has a small footprint and a large hydrogen production capacity within an effective equipment volume, making it particularly suitable for on-site hydrogen production at new energy hydrogen refueling stations. This avoids expensive hydrogen storage and transportation costs and byproduct steam, significantly reducing the fuel cost of hydrogen-powered vehicles. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the process of Embodiment 1 of the present invention.

[0025] Figure 2 This is a schematic diagram of the process of Embodiment 2 of the present invention.

[0026] Figure 3 This is a schematic diagram of the process of Embodiment 3 of the present invention. Detailed Implementation

[0027] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0028] Example 1

[0029] like Figure 1As shown, a natural gas-steam two-stage heat exchange composite conversion hydrogen production system consists of a feed gas (raw material gas) pretreatment module, a heat exchange conversion module, a reforming conversion module, a shift reaction module, and a pressure swing adsorption (PSA) hydrogen extraction module. First, the feed natural gas, a city gas, has a flow rate of 1,000 Nm³ / h, a methane content greater than 95%, and is supplied at normal pressure and temperature. It is conveyed into the pretreatment module, where it is first pressurized to 2.3~2.6 MPa by a compressor and preheated (using steam heating) to 250~260°C before being introduced into the hydrodesulfurization unit. H₂ product gas from the PSA hydrogen extraction module serves as the hydrogen source for the hydrodesulfurization process. The purified feed gas after zinc oxide hydrodesulfurization is mixed with steam to form a mixed steam that enters the heat exchange conversion module. The pre-conversion unit of the block undergoes a pre-conversion reaction. Its heat source is the combined converted gas at the second-highest temperature, flowing from the heat exchange conversion unit of the heat exchange conversion module. This gas undergoes convective heat transfer with mixed steam in the pre-conversion unit, forming pre-converted gas at a temperature of 530-580℃. Of this, 30-40% enters the heat exchange conversion unit of the heat exchange conversion module for reforming, and 60-70% enters the reforming conversion module for reforming. The reforming conversion module's conversion tubes are loaded with a nickel-based reforming catalyst. Oxygen-enriched gas and desorbed gas 2 from the PSA hydrogen extraction module are used as combustion gases and enter the reforming reactor. There, they undergo hydrogen-oxygen combustion and partial oxidation combustion of methane with the 60-70% pre-converted gas entering the reactor. The enormous heat of combustion generated by the or / and complete oxidation combustion reaction is directly carried by the pre-converted gas into the tubes of the reactor for reforming and conversion. This produces high-temperature reformed gas with a temperature as high as 880~920℃, which enters the heat exchange conversion unit of the heat exchange conversion module. Through convection heat transfer, it provides a heat source for the 30~40% pre-converted gas entering the heat exchange conversion unit to carry out the heat exchange conversion reaction in the tubes of the heat exchange conversion unit, which is loaded with a nickel-based reforming catalyst bed. The temperature of the heat exchange conversion reaction is 780~840℃. 70~75% of the heat exchange conversion gas flowing out of the tubes of the heat exchange conversion unit is mixed with the pre-converted gas flowing out of the reforming conversion module at a temperature of 880~920℃ and flowing outside the tubes of the heat exchange conversion unit. The secondary high-temperature reformed gas, after convective heat transfer through the reforming catalyst bed, is mixed to form a combined reformed gas. This combined gas then enters the convective pre-conversion unit of the heat exchanger module and undergoes convective heat transfer with mixed steam. The cooled combined reformed gas flowing out mixes with 25-30% of the heat exchanger gas flowing out of the heat exchanger module's heat exchanger unit to form the final reformed gas, which has a temperature of 120-200℃. This final reformed gas directly enters the medium-low temperature shift reaction unit of the shift reaction module for shift reaction. Simultaneously, an appropriate amount of water vapor is introduced to react with the final reformed gas, ensuring that the resulting shifted gas contains less than 3% CO, less than 0.2% methane and other hydrocarbons, greater than or equal to 80% H2, and less than or equal to 16% CO2.8% of the gas is converted into hydrogen. Of this, approximately 5-6% is returned as regulating gas to the heat exchange conversion unit of the heat exchange conversion module to adjust the S / C ratio and H2 / CO ratio during the heat exchange conversion process. The remainder enters the downstream PSA hydrogen extraction module. Specifically, the converted gas enters from the bottom of one adsorption tower in the PSA decarbonization process, which consists of three fixed-bed adsorption towers filled with composite adsorbents. After adsorption, hydrogen-rich gas flows out from the top of this adsorption tower. Then, it enters from the bottom of one adsorption tower in the PSA purification process, which consists of four fixed-bed adsorption towers filled with composite adsorbents. After adsorption, the hydrogen-rich gas flows out from the top of this adsorption tower as H2 product gas with a purity greater than or equal to 99.99%, which enters the product gas storage tank or is used at a pressure of 2.0-2.4 MPa. 5-8% of this gas is returned as hydrogenated gas to the hydrodesulfurization unit of the pretreatment module for hydrodesulfurization. The remaining two adsorption towers in the PSA decarbonization process... The adsorption towers are respectively in the pressure equalization drop, reverse release, and pressure equalization rise and final charging stages. Desorbed gas 1 flows out from the bottom of an adsorption tower in the reverse release stage. During the first 45-55% of the reverse release, the desorbed gas 1 flowing out is output from the desorbed gas 1 buffer tank and pressurized before returning to the reforming and conversion module. It is then used to adjust the S / C ratio and the H2 / CO ratio of the reformed gas and / or the final converted gas in the reforming and conversion process with water vapor. The remaining desorbed gas 1 in the reverse release is either output as feed gas for extracting high-concentration CO2 or directly emitted. 50-60% of the desorbed gas 2 flowing out from the PSA purification unit is returned to the reforming and conversion module as combustion gas for reforming and conversion reaction, and the remainder is output as fuel gas. Thus, this hydrogen production system achieves over 98% methane conversion rate and 95% H2 yield while relying on multi-stage convective heat transfer within the system to achieve heat self-sufficiency and balance, with no by-product water vapor generation or flue gas emissions.

[0030] Example 2

[0031] like Figure 2As shown, based on Example 1, the heat exchange conversion unit tubes in the heat exchange conversion module are filled with a low-temperature reforming catalyst. This low-temperature reforming catalyst, containing nickel / cobalt as the main active component, rare earth metals and their oxides as co-catalyst components, and a mixture of carbon nanotubes and alumina / titanium oxide / zirconia as the support, replaces the high-temperature nickel / nickel-based reforming catalyst. The conversion temperature of the low-temperature reforming catalyst is 550~600℃, while the reforming conversion tubes in the reforming conversion module are still filled with a high-temperature nickel / nickel-based reforming catalyst. Therefore, from the reforming conversion... The high-temperature reformed gas (880~920℃) flowing out of the module first enters the upstream pretreatment module and undergoes convective heat transfer with the ambient-temperature natural gas feedstock, raising the temperature of the feedstock natural gas to the operating temperature of 250~260℃ required for hydrodesulfurization without steam heating. After preheating and convective heat transfer, the reformed gas then enters the heat exchange conversion unit of the heat exchange conversion module. It flows through the tubes of the heat exchange conversion unit, which are filled with low-temperature reforming catalyst, and undergoes convective heat transfer with the pre-converted gas flowing through the tubes, which are filled with a low-temperature reforming catalyst bed. The low-temperature reforming catalyst bed provides the heat required for reforming. The pre-reformed gas, after undergoing low-temperature reforming in the tubes, is completely mixed with the reformed gas flowing out after convective heat transfer to form a combined reformed gas. This combined gas then enters the convective pre-reformation unit of the heat exchanger module, where it undergoes convective heat transfer with the mixed steam flowing into the unit. This causes the mixed steam to be heated and undergo a pre-reformation reaction within the tubes of the convective pre-reformation unit, removing high-hydrocarbon components and partially undergoing reforming to form pre-reformed gas. The pre-reformation temperature is 300~350℃. The gas flows into the reforming and conversion module, and a portion enters the heat exchange conversion unit of the heat exchange conversion module. The combined conversion gas is further cooled to 160~200℃ after convective heat transfer to form the final conversion gas, which directly enters the downstream shift reaction module for shift reaction. At this time, the shift reaction catalyst is selected as a medium-low temperature shift catalyst. Thus, the heat carried by the high-temperature reforming and conversion gas from the reforming and conversion module is utilized in a cascade manner through the pretreatment module and the heat exchange conversion module, so that the thermal efficiency of the natural gas steam reforming hydrogen production system reaches 99~100%, without consuming external energy.

[0032] Example 3

[0033] like Figure 3As shown, based on Example 1, the reforming conversion module is replaced by a radiative heat reforming conversion unit generated by the combustion of fuel gas and air instead of a hydrogen-oxygen combustion reforming conversion unit. Specifically, a combustion chamber is provided at the top of the reforming conversion reactor, which consists of a tube array loaded with a nickel / nickel-based reforming conversion catalyst. 20-30% of the natural gas is used as fuel gas, and air is used as a combustion aid. The combustion reaction takes place in the combustion chamber, and the resulting high-temperature combustion gas is ejected through nozzles and radiates heat to the tube array, raising the conversion temperature of the reforming conversion catalyst bed inside the tube array to 800-920°C. Thus, 70-80% of the natural gas, used as feed gas, enters the preheating unit of the pretreatment module. Its heat source is the high-temperature flue gas from the combustion in the reforming conversion module, which is then converted in the heat exchange conversion module. The pre-conversion unit of the gas block is obtained by convective heat transfer with mixed steam. The preheated feedstock natural gas enters the hydrodesulfurization unit for desulfurization. The purified natural gas produced is mixed with water vapor to form mixed steam, which enters the pre-conversion unit of the heat exchanger conversion module. It undergoes convective heat transfer with high-temperature flue gas from the reforming conversion module, forming pre-converted gas with a temperature of 250~300℃. It then enters the convective pre-conversion unit of the heat exchanger conversion module, where it undergoes convective heat transfer with the combined conversion gas from the heat exchanger conversion module, forming intermediate pre-converted gas with a temperature of 500~600℃. This intermediate pre-converted gas then enters the heat exchanger conversion unit for heat exchanger conversion reaction. The tubes of the heat exchanger conversion unit are loaded with nickel / nickel-based reforming conversion catalysts, and the heat exchanger conversion reaction... The temperature should be 780~850℃. The intermediate pre-conversion gas, originating from the reforming and conversion module and flowing outside the heat exchanger conversion unit tubes, undergoes convective heat transfer to the intermediate pre-conversion gas, which is packed with a nickel / nickel-based reforming catalyst bed and flows through the tubes. This provides a heat source for the heat exchanger conversion unit. Simultaneously, the heat exchanger conversion gas produced after the intermediate pre-conversion gas undergoes reforming and conversion within the heat exchanger conversion unit tubes mixes with the reforming conversion gas flowing outside the tubes after convective heat transfer to form a combined conversion gas. This combined gas then enters the convective pre-conversion unit of the heat exchanger conversion module, where it undergoes convective heat transfer with the pre-conversion gas from the pre-conversion unit. This further heats and pre-converts the pre-conversion gas, forming intermediate pre-conversion gas, which is then divided into two streams: one with a concentration of 25~35% and the other with a concentration of 6%. 5-75% of the gas undergoes reforming in the heat exchange conversion unit of the heat exchange conversion module and the radiative thermal reforming conversion unit of the reforming conversion module, respectively. Simultaneously, the combined reformed gas is cooled to form the final reformed gas, which is further cooled by the heat recovery system (HR). Meanwhile, approximately 20-30% of the heat exchange conversion gas is mixed with the combined reformed gas from the convection pre-conversion unit via the heat recovery system (HR) to form the final reformed gas. This final reformed gas meets the operating temperature requirements of the downstream shift reaction module for medium-high temperature or medium-low temperature shift reactions and enters the shift reaction module. From there, it forms shifted gas, which is further cooled by the heat recovery system (HR) to the operating temperature required by the PSA hydrogen extraction module before entering the PSA hydrogen extraction module to obtain a purity greater than or equal to 99%.99% of the H2 product gas is used for steam generation by the added heat recovery system (HR) to meet the needs of the hydrogen production system. Approximately 5-7% of the shift gas, which is not cooled by the HR system, is used as regulating gas to adjust the S / C and / or H2 / CO ratios in the heat exchange conversion module. About 5-8% of the H2 product gas from the PSA purification unit of the PSA hydrogen extraction module is returned to the hydrodesulfurization unit in the pretreatment module to hydrodesulfurize the feedstock natural gas flowing out of the preheating unit. The PSA purification unit from the PSA hydrogen extraction module... The desorbed gas 2 from unit 2 replaces the natural gas fuel gas in the reforming module. It enters the combustion chamber of the radiant reforming unit within the reforming module for combustion, providing a heat source for the reforming module. Thus, except for the initial use of natural gas as fuel gas in the hydrogen production system, the system achieves self-sufficiency in fuel gas. Furthermore, 50-60% of the desorbed gas 1 from the PSA decarbonization unit of the PSA hydrogen extraction module, along with water vapor and intermediate pre-converted gas, serves as the S / C and H2 / CO ratio regulating gas in the reforming module's conversion process. The remaining output is used as feedstock for extracting high-concentration CO2.

[0034] Obviously, the embodiments described above are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments described in this invention, all other embodiments obtained by those skilled in the art without creative effort, or structural changes made under the guidance of this invention, that have the same or similar technical solutions as this invention, all fall within the protection scope of this invention.

Claims

1. A natural gas-steam two-stage heat exchange composite conversion hydrogen production system, characterized in that, The hydrogen production system consists of a pretreatment module, a heat exchange conversion module, a reforming conversion module, a shift reaction module, and a PSA hydrogen extraction module. The pretreatment module includes: material conveying pipelines, conveying pumps and / or booster compressors, a preheating unit, and a hydrodesulfurization unit. All natural gas is used as feed gas and enters the preheating unit of the pretreatment module. The pretreatment module receives the natural gas feed gas and steam it to the reaction temperature required for hydrodesulfurization before it enters the hydrodesulfurization unit to form purified natural gas. The purified natural gas is mixed with a certain proportion of water vapor to form mixed steam, which enters the downstream heat exchange conversion module. The hydrogen in the hydrodesulfurization unit comes from the downstream PSA hydrogen extraction module. The desulfurization depth must meet the specifications of various catalysts in the downstream convection preconversion, heat exchange conversion, reforming conversion, and shift reaction modules for catalytic conversion or shift reaction. The heat exchange conversion module includes a convection pre-conversion unit and a heat exchange conversion unit. The heat exchange conversion module receives mixed steam and high-temperature reformed gas from a downstream reforming conversion module. The mixed steam enters the tubes of the convection pre-conversion unit and undergoes convective heat transfer with the combined reformed gas flowing outside the tubes of the heat exchange conversion unit to obtain the heat required for the pre-conversion reaction. This process removes harmful C5 and higher components from the mixed steam, which would otherwise be detrimental to downstream heat exchange conversion and reforming. Additionally, some of the purified natural gas's main components, methane and light hydrocarbons below C5, undergo a pre-conversion reaction with water vapor in the mixed steam to form pre-converted gas. Part of the pre-converted gas flows out of the heat exchange conversion module and into the downstream reforming conversion module, while another part serves as feedstock in the heat exchange conversion unit and flows through a tube containing a reforming catalyst to undergo a heat exchange conversion reaction, forming heat exchange conversion gas. The heat required for the heat exchange conversion reaction comes from the convection with the high-temperature reformed gas flowing outside the tubes. Heat transfer occurs at temperatures of 780-900℃. A portion of the heat transfer gas flowing out of the heat transfer unit tubes mixes with the reformed gas cooled by convective heat transfer in the heat transfer unit to form a combined reformed gas. This combined reformed gas enters the convective pre-conversion unit and undergoes convective heat transfer with the mixed steam entering the convective pre-conversion unit. The temperature at which the mixed steam undergoes pre-conversion in the convective pre-conversion unit is 450-650℃. After convective heat transfer in the convective pre-conversion unit, the combined reformed gas is cooled to 150-350℃ to form the final reformed gas, which enters the downstream shift reaction module. A portion of the heat transfer gas flowing out of the heat transfer unit mixes with the final reformed gas cooled by convective heat transfer in the convective pre-conversion unit and enters the downstream shift reaction module. The ratio of the two portions of the heat transfer gas depends on the reaction temperature required for the medium-high temperature or medium-low temperature shift reaction used in the downstream shift reaction module, as well as the content of C5 and above components in the mixed steam and the corresponding convective pre-conversion temperature. The reforming and conversion module includes a hydrogen-oxygen combustion reforming and conversion unit, which comprises a reforming and conversion tubular reactor and a hydrogen-oxygen combustion reaction chamber above the tubular reactor. The reforming and conversion module receives pre-converted gas, oxygen-enriched gas, hydrogen-containing desorbed gas 2 from the downstream PSA hydrogen extraction module, water vapor for adjusting the water-to-carbon ratio and hydrogen-to-carbon ratio of the reforming and conversion module, and carbon dioxide-containing desorbed gas 1 from the downstream PSA hydrogen extraction module. The high-temperature reformed and conversion gas generated in the reforming and conversion module flows directly into the upstream heat exchange conversion unit, where the introduced oxygen-enriched gas undergoes hydrogen-oxygen combustion reaction. In the room, the pre-converted gas and hydrogen-containing desorbed gas 2 undergo a hydrogen-oxygen combustion reaction, generating a huge heat of combustion. The heat of combustion is directly carried by the gas participating in the reforming reaction into the tubes loaded with the reforming catalyst in the reforming unit for reforming. The reforming temperature reaches 850~990℃, and the methane conversion rate is 99~100%. The high-temperature reformed gas flowing out of the reforming reaction flows directly into the heat exchange conversion unit in the upstream heat exchange conversion module for convective heat transfer, providing the heat required for heat exchange conversion. The shift reaction module is arranged to receive the final converted gas from the heat exchange conversion module and perform a shift reaction to output shift gas. Its function is to react carbon monoxide and water vapor in the final converted gas with a shift reaction bed loaded with medium-high temperature or medium-low temperature shift reaction catalyst to form shift gas with hydrogen and carbon dioxide as the main components. Part of the shift gas is returned to the heat exchange conversion module to adjust the hydrogen-carbon ratio of the heat exchange conversion gas flowing out of the heat exchange conversion module, and part of it enters the downstream PSA hydrogen extraction module. The heat required by the shift reaction module is directly brought in by the final converted gas from the upstream heat exchange conversion module, and the distribution ratio of the two heat exchange conversion gases in the heat exchange conversion module is adjusted to adapt to the shift reaction process corresponding to different shift reaction catalysts in the shift reaction module. The PSA hydrogen extraction module includes a PSA decarbonization unit and a PSA purification unit.

2. The natural gas steam two-stage heat exchange composite conversion hydrogen production system as described in claim 1, characterized in that, The upstream and downstream connections between the pretreatment module, heat exchange conversion module, reforming conversion module, shift reaction module, and PSA hydrogen extraction module are formed by assembling the corresponding pipes, valves, and equipment interfaces in each module. The hydrogen production system also includes one or more auxiliary devices selected from the following: compressor, transfer pump, buffer tank, steam tank, and auxiliary pipelines. The minimum hydrogen production capacity of the hydrogen production system is 50 Nm³. 3 / h, maximum 5000 Nm 3 The operating pressure range of the hydrogen production system is 0.3~3.5MPa per hour.

3. The natural gas steam two-stage heat exchange composite conversion hydrogen production system as described in claim 1, characterized in that, The high-temperature reformed gas flowing out of the reforming module does not directly enter the heat exchanger conversion unit. Instead, it first enters the preheating unit for convective heat transfer, and then enters the heat exchanger conversion unit for convective heat transfer again. The heat exchanger conversion gas flowing out of the heat exchanger conversion unit is not divided into two parts, but is completely mixed with the reformed gas flowing out after convective heat transfer in the heat exchanger conversion unit to form a combined reformed gas. The tubes of the heat exchanger conversion unit in the heat exchanger conversion module are filled with a low-temperature reforming catalyst. The low-temperature reforming catalyst has nickel / cobalt as the main active component and rare earth metals and their oxides as co-catalyst components. The reforming conversion temperature of the low-temperature reforming catalyst is 450~600℃, while the tube reactor of the reforming module is filled with a high-temperature nickel-based reforming catalyst. The high-temperature reformed gas undergoes convective heat transfer with the ambient-temperature natural gas feedstock in the preheating unit, raising the temperature of the natural gas feedstock to the operating temperature required for hydrodesulfurization. The reformed gas after convective heat transfer in the preheating unit then enters the heat exchanger conversion unit of the heat exchanger conversion module and flows through... Outside the tubes of the heat exchange conversion unit, which are filled with low-temperature reforming catalyst, convective heat transfer occurs between the pre-converted gas flowing through the tubes. This provides the heat required for the conversion of the low-temperature reforming catalyst bed within the heat exchange conversion tubes. After undergoing low-temperature reforming reaction within the tubes, the pre-converted gas exits as heat exchange conversion gas. All the heat exchange conversion gas mixes with the reforming gas exiting after convective heat transfer in the heat exchange conversion unit to form a combined conversion gas. The combined conversion gas then enters the convective pre-conversion unit of the heat exchange conversion module, where it undergoes convective heat transfer with the mixed steam flowing into the convective pre-conversion unit. This causes the mixed steam to be heated and undergo a pre-conversion reaction within the tubes of the convective pre-conversion unit, removing high-hydrocarbon components and partially undergoing reforming reaction to form pre-converted gas. The pre-conversion temperature is 280~350℃. After convective heat transfer in the convective pre-conversion unit, the combined conversion gas is cooled to 160~280℃ to form the final conversion gas. The final conversion gas directly enters the downstream shift reaction module for shift reaction. At this point, a medium-low temperature shift catalyst is selected for the shift reaction.

4. The natural gas steam two-stage heat exchange composite conversion hydrogen production system as described in claim 1, characterized in that, Natural gas is not entirely used as fuel gas; a portion enters the preheating unit of the pretreatment module as feed gas, and a portion enters the reforming and conversion module as fuel gas. The heat exchange conversion module includes a pre-conversion unit, a convection pre-conversion unit, and a heat exchange conversion unit. The reforming unit in the reforming module is not a hydrogen-oxygen combustion reforming unit, but a radiative thermal reforming unit. The reforming module receives intermediate pre-reformed gas from the convection pre-reformation unit, natural gas fuel gas, air, hydrogen-containing desorbed gas 2 from the downstream PSA hydrogen extraction module, carbon dioxide-containing desorbed gas 1 from the downstream PSA hydrogen extraction module, and water vapor. The radiative thermal reforming unit includes a reforming reactor composed of tubes loaded with a nickel-based reforming catalyst and a combustion chamber located at the top, side, or bottom of the reforming reactor. Inside the combustion chamber, a portion of the natural gas is used as fuel gas, and air is used as a combustion aid for combustion. The high-temperature combustion gas produced by the combustion reaction is ejected through nozzles and radiates heat to the tubes, thus stimulating the reforming catalyst within the tubes. The conversion temperature of the agent bed reaches 770~950℃. High-temperature flue gas, generated by combustion in the reforming and conversion module, flows into the pre-conversion unit and undergoes convective heat transfer with mixed steam before serving as the heat source for the preheating unit. Natural gas feedstock gas, after preheating in the preheating unit, enters the hydrodesulfurization unit for desulfurization to produce purified natural gas. The purified natural gas mixes with steam to form mixed steam. This mixed steam enters the pre-conversion unit of the heat exchanger conversion module and undergoes convective heat transfer with the high-temperature flue gas from the reforming and conversion module, forming pre-converted gas at a temperature of 250~350℃. This pre-converted gas then enters the convective pre-conversion unit of the heat exchanger conversion module, where it undergoes convective heat transfer with the combined conversion gas from the heat exchanger conversion module, thus achieving pre-conversion... The gas forms intermediate pre-converted gas at a temperature of 450-650℃, which then enters the heat exchange conversion unit for heat exchange conversion reaction. The heat exchange conversion unit's tubes are loaded with nickel-based reforming catalyst, and its heat exchange conversion reaction temperature is 750-880℃. The intermediate pre-converted gas undergoes convective heat transfer with the reformed gas from the reforming module flowing outside the heat exchange conversion unit's tubes, providing a heat source for the heat exchange conversion unit. Simultaneously, the intermediate pre-converted gas undergoes reforming conversion reaction within the heat exchange conversion unit's tubes to produce heat exchange conversion gas. This heat exchange conversion gas mixes with the reformed gas flowing outside the heat exchange conversion unit's tubes after convective heat transfer to form combined conversion gas. This combined conversion gas then enters the convective pre-conversion unit of the heat exchange conversion module, where it reacts with the pre-converted gas from the pre-conversion unit... The converted gas undergoes convective heat transfer, further heating and pre-converting it to form intermediate pre-converted gas. This intermediate pre-converted gas is split into two streams, which enter the heat exchange conversion unit of the heat exchange conversion module and the radiative heat reforming conversion unit of the reforming conversion module, respectively, for reforming conversion. The combined converted gas undergoes convective heat transfer in the convective pre-conversion unit and is then cooled to form the final converted gas. This final converted gas is mixed with a portion of the heat exchange converted gas through a heat recovery system and, after meeting the operating temperature required for the medium-high temperature or medium-low temperature conversion reaction in the downstream conversion reaction module, enters the conversion reaction module. After undergoing the conversion reaction, it forms converted gas. This converted gas is further cooled through the heat recovery system to the operating temperature required for the PSA hydrogen extraction module before entering the PSA hydrogen extraction module to obtain a purity greater than or equal to 99%.99% of the H2 product gas is produced. The added heat recovery system generates steam to meet the needs of the hydrogen production system. A portion of the shift gas, which is not cooled by the heat recovery system, is used as regulating gas to adjust the water-to-carbon ratio and hydrogen-to-carbon ratio in the heat exchange conversion module. A portion of the H2 product gas from the PSA purification unit of the PSA hydrogen extraction module is returned to the hydrodesulfurization unit in the pretreatment module to hydrodesulfurize the natural gas feedstock gas flowing out of the preheating unit. Hydrogen-containing desorbed gas 2 from the PSA purification unit of the PSA hydrogen extraction module partially replaces the natural gas feedstock gas in the reforming module, entering the combustion chamber of the radiant reforming unit to provide a heat source for the reforming module. Carbon dioxide-containing desorbed gas 1 from the PSA decarbonization unit of the PSA hydrogen extraction module is partly used, along with steam and intermediate pre-converted gas, as regulating gas for the water-to-carbon ratio and hydrogen-to-carbon ratio in the reforming module's conversion process; the remaining part is output as feedstock gas for extracting high-concentration CO2 or as emissions.

5. The natural gas steam two-stage heat exchange composite conversion hydrogen production system as described in claim 1, characterized in that, The PSA hydrogen extraction module consists of two units: the PSA decarbonization unit and the PSA purification unit. It employs a rotary pressure swing adsorption system composed of a multi-channel rotary valve with more than 7 channels and more than 5 adsorption towers. The composite adsorbent packed in the adsorption towers needs to contain 10-20% carbon molecular sieve.

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