Multi-stage coupling chemical looping hydrogen production device and method

Abstract

The invention provides a multistage coupling chemical looping hydrogen production device. The multistage coupling chemical looping hydrogen production device comprises a first-section reducer, a water vapor oxidation hydrogen production device, a second-section reducer, a methane converter and an air oxidizer, identical first oxygen carriers are arranged in the first-section reducer and the water vapor oxidation hydrogen production device, and identical second oxygen carriers are arranged in the second-section reducer, the methane converter and the air oxidizer; the methane converter is connected with the first-section reducer and is used for conveying synthesis gas after methane conversion to the first-section reducer; the second-section reducer is connected with the methane converter and is used for refluxing carbon dioxide or water vapor or both to the methane converter; the first-section reducer is connected with the second-section reducer and is used for conveying reduction tail gas containing carbon monoxide or hydrogen or the carbon monoxide and the hydrogen to the second-section reducer. Therefore, the invention provides the multistage coupling chemical looping hydrogen production device and method which can realize energy self-sustaining and do not need external energy input.

Description

Technical Field

[0001] The present invention relates to a novel hydrogen production device and method, and particularly to a device and method for water splitting hydrogen production by using multistage coupled chemical looping conversion. Background Art

[0002] As a clean energy source, hydrogen does not produce pollutants such as CO2 during use, so it is considered to be one of the important energy sources for achieving the global "carbon neutrality" goal in the future. However, hydrogen usually exists in the form of compounds such as H2O or C n H m in nature, etc., so additional energy is required to extract it from the compound to prepare hydrogen.

[0003] One of the main application scenarios of hydrogen is hydrogen fuel cells, which have very high requirements for the purity of hydrogen, usually above 99.9%. Therefore, efficiently and safely preparing high-purity hydrogen is the key issue for the large-scale application of hydrogen energy and the direction of joint efforts in this field.

[0004] The chemical looping hydrogen production process is a brand-new hydrogen production technology. Tsinghua University has been committed to the research in this field for many years and applied for a patent for invention named "A Process and Application for Reforming Coupled Chemical Looping of Methane-Containing Combustible Gas to Prepare High-Purity Hydrogen" with the application number 202110963317.5 in 2021 (which has now been transferred to the applicant of this patent). This patent (Patent Document 1) discloses a device for preparing high-purity hydrogen, including a reforming reactor, a hydrogen production reactor and a controller. The hydrogen production reactor contains an oxygen carrier, the reforming reactor contains a reforming catalyst, the controller controls the gas entering the hydrogen production reactor, and the controller is used to switch the gas entering the hydrogen production reactor so that three chemical reactions, namely the oxygen carrier reduction reaction, the steam hydrogen production reaction and the oxygen carrier oxidation reaction, are completed in the hydrogen production reactor. The controller controls the three reactions to cycle, so as to obtain high-purity hydrogen while reducing the carbon deposition of the oxygen carrier volume and being able to completely capture carbon dioxide to prevent greenhouse gas emissions.

[0005] However, Patent Document 1 does not deeply discuss the heat balance problem of the overall system.

[0006] Specifically, in the three reaction stages of chemical looping hydrogen production, the oxygen carrier reduction reaction is an endothermic reaction or a heat balance process, and the oxygen carrier steam oxidation hydrogen production reaction and the oxygen carrier air deep oxidation reaction are exothermic processes. The total heat release of the latter two is > the total heat absorption of the methane reforming conversion reaction. From the perspective of the total heat balance, the whole process heat matching can be carried out to achieve energy self-sufficiency. However, there are the following problems in practice.

[0007] (1) During the chemical-looping hydrogen production process, the heat generated by the two exothermic reactions will accumulate in the oxygen carrier bed in large quantities. It is necessary to remove the heat accumulated in the bed through a heat-carrying medium and then transfer the heat in the heat-carrying medium to the reforming reactor through a heat exchange system, which requires a relatively complex heat exchange system to achieve.

[0008] (2) To achieve a high methane conversion rate, the methane reforming process needs to be carried out at a reaction temperature > 800 °C, and this process is a strongly endothermic reaction. To form a sufficient heat transfer temperature difference inside and outside the reactor, a heat supply source at a higher temperature (> 1100 °C) is required (usually using the thermal radiation heating of a burner flame); to avoid the sintering of the oxygen carrier, it is necessary to control the temperature of the oxygen carrier bed < 950 °C at the end of the two exothermic reactions in the chemical-looping hydrogen production process. When removing the heat accumulated in the reaction through a heat-carrying medium, the final temperature of the heat-carrying medium when it flows out of the reactor is usually < 920 °C, which has a large gap with the required heat source temperature of 1100 °C, resulting in a small temperature difference (ΔT = 920 - 800 = 120 °C) between the heat-carrying medium temperature and the methane reforming reaction temperature, and it is impossible to fully conduct the heat released during the chemical-looping hydrogen production reaction process to the methane reforming process, thus affecting the overall efficiency in some cases.

[0009] More specifically, as Figure 1 shown, there are four reaction stages in the original "chemical-looping hydrogen production using methane-containing fuel gas as raw material" process disclosed in Patent Document 1, namely, ① methane reforming, ② oxygen carrier reduction, ③ oxygen carrier steam oxidation to produce hydrogen, and ④ oxygen carrier air oxidation. Among them, the three reaction processes of ② oxygen carrier reduction, ③ oxygen carrier steam oxidation to produce hydrogen, and ④ oxygen carrier air oxidation are carried out cyclically.

[0010] The above ① methane reforming is a strongly endothermic process that requires a large amount of high-quality heat supply, while ④ oxygen carrier air oxidation is a strongly exothermic process that can release a large amount of heat. However, since most of the heat released during the oxygen carrier air oxidation process is absorbed by the oxygen carrier material in the reactor (the oxygen carrier itself is a metal oxide with a large heat capacity), most of the heat released in this process is stored in the oxygen carrier bed after the reaction (70 - 90%), and it cannot directly supply heat to the strongly endothermic methane reforming at the front end; if the heat in the oxygen carrier bed is removed through a gaseous heat-conducting medium, on the one hand, a series of complex heat exchange systems need to be added, and on the other hand, the temperature of the heat-conducting gas medium used to remove the heat in the bed cannot meet the heating requirements of methane reforming.

[0011] Patent Document 1: Publication No. CN113753857A (Patent Application No. CN202110963317.5) Summary of the Invention

[0012] In view of this, the main object of the present invention is to provide a multi-stage coupled chemical looping hydrogen production device and method that can achieve energy self-sustainment and does not require external energy input.

[0013] To more clearly illustrate the present invention, the following first describes the process by which the R & D team of this patent decoupled and improved the structure from the structure of the above-mentioned patent document 1 to obtain the structure of the present invention in order to achieve the above object.

[0014] (1) Decoupling of the three-process chemical cycle

[0015] First of all, the R & D team of this patent hopes to effectively couple the oxygen carrier air oxidation process with the methane reforming and conversion process by inventing a certain method, and directly use the heat released by the oxygen carrier air oxidation process to supply heat to the methane reforming and conversion process without passing through a gas heat transfer medium or other heat exchange methods.

[0016] The R & D team of this patent found through painstaking research that in the original chemical looping hydrogen production process, the oxygen carrier reduction stage is a coupled process of several reactions, namely:

[0017] Change in the state of the oxygen carrier: Process ② Fe2O3 → Fe3O4 → FeO → Fe;

[0018] And (Process ③ + Process ④) actually occurred in the reverse process of Process ②: The change in the state of the oxygen carrier during the steam oxidation process is: Process ③ Fe → FeO → Fe3O4; The change in the state of the oxygen carrier during the oxygen carrier air oxidation process: Process ④ Fe3O4 → Fe2O3;

[0019] If the original oxygen carrier reduction stage (Process ②) is decoupled and split into two steps by means of thermodynamic control, it can be decoupled and split as follows, specifically as Figure 2 shown:

[0020] Process ② = Process ⑤ + Process ⑥

[0021] Process ⑤: First-stage reduction of the oxygen carrier Fe2O3 → Fe3O4

[0022] Process ⑥: Second-stage reduction of the oxygen carrier Fe3O4 → FeO → Fe

[0023] If the initial state of the oxygen carrier in the reactor is Fe2O3, by controlling the CO / CO2 molar ratio and H2 / H2O molar ratio in the reducing gas, according to the limitations in reaction thermodynamics, Fe2O3 can only be reduced to Fe3O4 (for example: below 800 °C, if the CO / CO2 molar ratio in the reducing gas < 33 / 67, Fe2O3 can only form Fe3O4). After reduction, the oxygen carrier is oxidized with air, then Process ④ and Process ⑤ can separately constitute an oxidation-reduction cycle (that is, the "second-stage chemical looping reaction cycle" referred to in the present invention):

[0024] Oxygen carrier reduction: Process ⑤ Fe2O3 → Fe3O4

[0025] Oxygen carrier oxidation: Process ④ Fe3O4 → Fe2O3

[0026] This redox cycle includes the strongly exothermic air oxidation process in the original chemical-looping hydrogen production process. At the same time, since the initial state of the oxygen carrier and the highest valence state after air oxidation are both Fe2O3, according to the thermodynamic equilibrium, as long as there is unreacted Fe2O3 in the reactor, the gas phase at the outlet of the reduction reactor will be all CO2 and H2O. The reduction gas can be controlled not to penetrate the reactor by controlling the reduction time. After simple water removal from the tail gas, CO2 can be separated in situ to obtain high-purity CO2.

[0027] If the initial state of the oxygen carrier in the reactor is controlled to be Fe3O4, under certain reduction gas composition conditions, the oxygen carrier can be reduced to FeO (e.g., at 800 °C, CO / CO2 molar ratio > 33 / 67), or further reduced to Fe (e.g., at 800 °C, CO / CO2 molar ratio > 65 / 35). After reduction, steam is used for oxidation, then Process ③ and Process ⑥ can also form an independent redox cycle (referred to as the first-stage chemical-looping reaction cycle):

[0028] Oxygen carrier reduction: Process ⑥ Fe3O4 → FeO → Fe

[0029] Oxygen carrier oxidation: Process ③ Fe → FeO → Fe3O4

[0030] This redox cycle includes the hydrogen production process by steam oxidation in the original chemical-looping hydrogen production process. And during the oxygen carrier reduction process of this cycle, since the initial state of the oxygen carrier in the reactor and the highest valence state after steam oxidation are both Fe3O4, according to the thermodynamic equilibrium characteristics, as long as there is still unreacted Fe3O4 in the reactor, the reduction tail gas flowing out of the reactor is the equilibrium concentration under this condition (e.g., at 800 °C, in the presence of Fe3O4, the equilibrium molar composition of CO / CO2 is 33 / 67).

[0031] Through the above two independent redox cycles and their respective thermodynamic and chemical equilibrium characteristics, the reduction tail gas of the first-stage chemical-looping reaction cycle can be used as the reduction raw material gas for the second-stage chemical-looping reaction cycle.

[0032] (2) Decoupled chemical-looping coupling methane reforming

[0033] By decoupling the three processes of the original chemical-looping hydrogen production, namely "reduction - steam oxidation - air oxidation", the air oxidation process can be separated from the hydrogen production process and form a separate chemical cycle (i.e., the "second-stage chemical-looping reaction cycle" referred to in the present invention), which provides the possibility for heat coupling between the strongly exothermic air oxidation process and the strongly endothermic methane reforming process.

[0034] The R & D team of this patent hopes to directly utilize the heat released and accumulated in the oxygen carrier bed during the air oxidation process in the second-stage chemical-looping reaction cycle for the strongly endothermic methane reforming reaction (i.e., Process ①). Three conditions also need to be created: (a) the heat released during the air oxidation process > the heat absorbed during the methane reforming process; (b) Process ① can share a reactor with the chemical cycle composed of Process ⑤ and Process ④ and can be switched cyclically. (c) The oxygen carrier used in the chemical-looping cycle of Process ④ + Process ⑤ can provide a catalytic effect for methane reforming in a certain state during the cycle.

[0035] To meet conditions (a) + (b), Process ① needs to be incorporated into the new chemical-looping cycle composed of "Process ④ + Process ⑤"; the oxygen carrier state that meets condition (c) generally exists in the form of elemental metal, so Process ① needs to be placed after Process ⑤ and it is necessary to ensure that Process ⑤ is an exothermic reaction or a heat balance reaction. Based on the above analysis, the R & D team of this patent proposed the following two-stage chemical-looping reaction cycle coupling methane reforming hydrogen production process, specifically as Figure 3 shown in (the new process).

[0036] To achieve the ultimate objective of the present invention, the present invention provides a multistage coupled chemical-looping hydrogen production device, characterized in that the multistage coupled chemical-looping hydrogen production device includes a first-stage chemical-looping reaction unit and a second-stage chemical-looping reaction unit. The first-stage chemical-looping reaction unit includes a first-stage reducer and a steam oxidation hydrogen producer, and these two parts can be mutually converted according to the reaction stage and the whole cycle is repeated. The second-stage chemical-looping reaction unit includes a second-stage reducer, a methane converter, and an air oxidizer, and these three parts can be mutually converted according to the reaction stage and the whole cycle is repeated. The same first oxygen carrier is provided in the first-stage reducer and the steam oxidation hydrogen producer. The first oxygen carrier changes into metallic elementary substance or metal oxides with different chemical valences at each reaction stage, and the metal has multiple chemical valences. The same second oxygen carrier is provided in the second-stage reducer, the methane converter, and the air oxidizer. The second oxygen carrier changes into metallic elementary substance or metal oxides with different chemical valences at each reaction stage, and the metallic elementary substance corresponding to the second oxygen carrier plays a catalytic role in the methane conversion reaction in the methane conversion reactor. The methane converter is connected to the first-stage reducer for delivering the syngas after methane conversion to the first-stage reducer. The second-stage reducer is connected to the methane converter for refluxing carbon dioxide or steam or both to the methane converter. The first-stage reducer is connected to the second-stage reducer for delivering the reduction tail gas containing carbon monoxide or hydrogen or both to the second-stage reducer.

[0037] In a preferred embodiment, the first oxygen carrier contains an active component, and optionally contains a sub-active component or an inactive component or both. The active component is Fe3O4, and the sub-active component is one or more of MoO3, GeO2, WO3, Mn2O3, ZnO, CeO2. The inactive component can be one or more of Al2O3, MgO, ZrO2, Y2O3, MgO, MgAl2O4, CaAl2O4, TiO2, CaO.

[0038] As an alternative, the first oxygen carrier does not contain an active component, contains a sub-active component, and optionally contains an inactive component. The sub-active component is one or more of MoO3, GeO2, WO3, Mn2O3, ZnO, CeO2. The inactive component can be one or more of Al2O3, MgO, ZrO2, Y2O3, MgAl2O4, CaAl2O4, TiO2, CaO.

[0039] In a preferred embodiment, in the first oxygen carrier, the content of the active component is 50-95 wt.%, the content of the sub-active component is 0-5 wt.%, and the content of the inactive component is 5-50 wt.%.

[0040] In a preferred embodiment, the first oxygen carrier comprises Fe3O4 as the active ingredient and Al2O3 or MgO as the inactive ingredient.

[0041] In a preferred embodiment, the composition of the first-stage oxygen carrier is 75 wt.% of Fe3O4 as the active ingredient and 25 wt.% of Al2O3 as the inactive ingredient, or the composition of the first-stage oxygen carrier is 80 wt.% of Fe3O4 as the active ingredient and 20 wt.% of MgO + Al2O3 as the inactive ingredient.

[0042] In a preferred embodiment, the second oxygen carrier comprises an active ingredient, and optionally comprises a sub-active ingredient or an inactive ingredient or both. The active ingredient is one or more of NiO, CuO, ZnO, the sub-active ingredient is one or more of Fe2O3, CeO2, Co3O4, Mn2O3, and the inactive ingredient can be one or more of ZrO2, MgO, Y2O3, MgAl2O4, CaAl2O4, CaO, Al2O3, TiO2.

[0043] As an alternative, the second oxygen carrier does not contain an active ingredient, contains a sub-active ingredient, and optionally contains an inactive ingredient. The sub-active ingredient is one or more of Fe2O3, CeO2, Co3O4, Mn2O3, and the inactive ingredient can be one or more of ZrO2, MgO, Y2O3, MgAl2O4, CaAl2O4, CaO, Al2O3, TiO2.

[0044] In a preferred embodiment, in the second oxygen carrier, the content of the active ingredient is 8 wt.% to 40 wt.%, the content of the sub-active ingredient is 0 to 5 wt.%; the content of the inactive ingredient is 60 wt.% to 92 wt.%.

[0045] In a preferred embodiment, the second oxygen carrier comprises NiO as the active ingredient.

[0046] In a preferred embodiment, the composition of the second oxygen carrier is 18 wt.% of NiO as the active ingredient and 82 wt.% of MgAl2O4 as the inactive ingredient, or the composition of the second oxygen carrier is 18 wt.% of NiO as the active ingredient and 82 wt.% of CaAl2O4 as the inactive ingredient.

[0047] The present invention also provides a multistage coupled chemical looping hydrogen production method, which is characterized by using the multistage coupled chemical looping hydrogen production device and comprising the following steps:

[0048] Device startup and oxygen carrier and reactor preparation step, in which the device is started up, and the above-mentioned first oxygen carrier is filled into the two reactors corresponding to the first-stage chemical looping reaction unit respectively, and the second oxygen carrier is filled into the three reactors corresponding to the second reaction chain unit respectively;

[0049] Reactor pretreatment step, in which the above-mentioned total five reactors are heated up respectively, and the system is adjusted as a whole to be suitable for the following reactions by means of pre-reduction and pre-oxidation in cooperation, that is: the two reactors corresponding to the first-stage chemical looping reaction unit are switched between each other and the first-stage reduction reaction and steam oxidation hydrogen production reaction are cyclically repeated, and the three reactors corresponding to the second-stage chemical looping reaction unit are switched between each other and the second-stage reduction reaction, methane reforming reaction and air oxidation reaction are cyclically repeated;

[0050] Methane reforming step, introducing methane-containing combustible gas into the methane reformer, which first mixes with the reduction tail gas partially recycled from the second-stage reducer, and then methane reacts with the mixed gas containing CO2 or H2O or both under the catalysis of elemental metal to carry out the methane reforming reaction, and makes full use of the heat already stored in the oxygen carrier in the air oxidation step to generate syngas containing components of CO, H2, CO2, and H2O and enter the first-stage reducer of the first-stage chemical looping reaction unit;

[0051] Air oxidation step, after the methane reforming reaction is completed, the reactor is switched to the state of the air oxidizer and the air oxidation process is carried out, that is, air or oxygen is introduced into the air oxidizer to oxidize the elemental metal state oxygen carrier to the high-valence state and a large amount of reaction heat is released, and most of this reaction heat is stored in the oxidized oxygen carrier bed layer in advance for the reaction heat required in the subsequent methane reforming process;

[0052] Second-stage reduction step, after the air oxidation is completed, the reactor is switched to the state of the second-stage reducer and the second-stage reduction process is carried out, that is, the remaining CO and H2 in the first-stage reduction tail gas reduce the second oxygen carrier in the second-stage reducer from the high-valence oxide state to the elemental state, and at the same time CO and H2 are completely oxidized to CO2 and H2O, and by controlling and adjusting the switching time to ensure that the second-stage reduction process does not penetrate, so that all the second-stage reduction tail gas is CO2 and H2O, and a part of the tail gas is refluxed to the methane reformer and mixed with the methane-containing fuel gas to carry out the methane reforming reaction, and the remaining part is heat recovered and then H2O is condensed to obtain high-purity CO2 and carry out CO2 capture;

[0053] The first-stage reduction step: Introduce the syngas containing CO and H2 generated by the methane converter into the first-stage reducer, and reduce the sub-high-valent metal oxide state of the first oxygen carrier to the low-valent metal oxide or metallic element by CO and H2 in the syngas. The syngas is partially oxidized by the chemical-looping oxygen carrier in the first stage to generate a mixed gas containing unreacted remaining CO, H2, as well as CO2 and H2O, namely the first-stage reduction tail gas, which is then returned to the second-stage reducer in the second-stage chemical-looping reaction unit;

[0054] The steam oxidation hydrogen production step: Pass steam into the steam oxidation hydrogen producer to oxidize the low-valent metal oxide oxygen carrier or metallic element generated in the first-stage reduction step to the sub-high-valent oxidation state, and simultaneously produce high-purity hydrogen.

[0055] In a preferred embodiment, 70-93% of the heat generated by the oxidation reaction in the air oxidizer is accumulated in the bed of the second oxygen carrier, and then 55-85% of the heat generated by the oxidation reaction in the air oxidizer is used for the endothermic requirement of the methane conversion reaction.

[0056] In a more preferred embodiment, 80-93% of the heat generated by the oxidation reaction in the air oxidizer is accumulated in the bed of the second oxygen carrier, and then 70-85% of the heat generated by the oxidation reaction in the air oxidizer is used for the endothermic requirement of the methane conversion reaction.

[0057] In a further preferred embodiment, 85-91% of the heat generated by the oxidation reaction in the air oxidizer is accumulated in the bed of the second oxygen carrier, and then 70-79% of the heat generated by the oxidation reaction in the air oxidizer is used for the endothermic requirement of the methane conversion reaction.

[0058] In a preferred embodiment, the initial filled oxidation state of the first oxygen carrier is different from the metal oxidation state during the repeated cycle process.

[0059] In a preferred embodiment, the metal oxidation state of the first oxygen carrier during the repeated cycle process is Fe3O4, and the initial filled oxidation state is Fe2O3.

[0060] In a preferred embodiment, the methane-containing combustible gas is natural gas, biogas, coalbed methane or petroleum gas, but is not limited thereto.

[0061] Among them, when the methane-containing combustible gas is biogas, the typical concentration of methane is 40-60 vol.%, but is not limited thereto.

[0062] As described above, through the multi-stage coupled chemical looping hydrogen production device and method of the present invention, by adjusting reaction conditions such as the initial valence state of the oxygen carrier and the gas-phase composition of the reducing gas inlet, the two exothermic reaction stages of the oxygen carrier steam oxidation hydrogen production reaction and the oxygen carrier air deep oxidation reaction can be separated from the three-reaction stage cycle system, and each separately forms a "reduction-oxidation" reaction cycle of two reaction stages with the corresponding decoupled reduction reaction process. Its essence is to decouple the original three-reaction stages of chemical looping hydrogen production, change the heat removal method in the chemical looping hydrogen production process and the heat transfer method with the methane reforming and conversion process, and realize direct heat transfer and utilization.

[0063] The first "reduction-oxidation" cycle needs to include two reaction stages of "oxygen carrier reduction - oxygen carrier steam oxidation hydrogen production", which can produce partially oxidized first-stage tail gas for use in the second-stage reduction after the first-stage reduction, and produce hydrogen in the oxygen carrier steam oxidation stage.

[0064] The second "reduction-oxidation" cycle includes two reaction stages of "oxygen carrier reduction - oxygen carrier air deep oxidation reaction". The ultimate goal is to use the large amount of heat released in the oxygen carrier air oxidation reaction stage to supply the strong endothermic demand of the methane conversion reaction process. However, as mentioned before, if the heat in the oxygen carrier bed is removed from the reactor to supply the demand of the methane conversion reactor, it is necessary for the heat transfer medium to conduct heat exchange, which has problems such as complex system, mismatching of heat source temperature and heat exchange temperature difference; and if a suitable metal oxygen carrier is selected, while realizing the "reduction-oxidation" cycle, it has the catalytic performance for methane conversion. In this way, the heat accumulated in the bed after the oxygen carrier air oxidation can be directly used for the strong endothermic reaction of methane conversion, without the heat transfer medium and complex heat exchange process, and the energy direct matching supply and utilization of the two processes can be realized. The present invention perfectly solves this problem through the above technical solutions.

[0065] Therefore, the present invention can provide a multi-stage coupled chemical looping hydrogen production device and method that realizes energy self-sustainment and does not require external energy input. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 is a schematic structural diagram showing the chemical looping hydrogen production process of Comparative Document 1.

[0067] Figure 2 is a schematic diagram showing the decoupling process of the chemical looping hydrogen production process of the present invention.

[0068] Figure 3 is a schematic diagram showing the decoupling process of the chemical looping hydrogen production process of the present invention and the new process.

[0069] Figure 4 is a schematic structural diagram showing the multi-stage coupled chemical looping hydrogen production device of the embodiment of the present invention.

[0070] Figure 5 is a flowchart of the multi-stage coupled chemical-looping hydrogen production method representing an embodiment of the present invention.

[0071] Figure 6 is a timing schematic diagram of the reactions at each stage of the first-stage chemical-looping reaction cycle of the present invention.

[0072] Figure 7 is a timing schematic diagram of the reactions at each stage of the second-stage chemical-looping reaction cycle of the present invention. Detailed Embodiments

[0073] Next, in conjunction with the accompanying drawings, the detailed embodiments of the present invention will be described in detail. It should be clear, however, that those skilled in the art should understand that the present invention is not limited to these specific embodiments, but rather, various equivalent changes, modifications, or substitutions can be made to the present invention without departing from its basic idea and gist. Therefore, the scope of protection of the present invention should include these equivalent changes, modifications, or substitutions and be determined according to the scope defined by the appended claims, rather than relying solely on the specific embodiments described herein.

[0074] Figure 4 is a schematic structural diagram of the multi-stage coupled chemical-looping hydrogen production device representing an embodiment of the present invention. Figure 5 is a flowchart of the multi-stage coupled chemical-looping hydrogen production method representing an embodiment of the present invention.

[0075] Figure 6 is a timing schematic diagram of the reactions at each stage of the first-stage chemical-looping reaction cycle of the present invention.

[0076] Figure 7 is a timing schematic diagram of the reactions at each stage of the second-stage chemical-looping reaction cycle of the present invention. Next, first, according to Figure 4 , the structure of the multi-stage coupled chemical-looping hydrogen production device and the related reactions in the embodiments of the invention will be described. Second, according to Figure 5 , Figure 6 , Figure 7 , the multi-stage coupled chemical-looping hydrogen production method in the embodiments of the present invention will be described.

[0077] (Overall Structure of the Multi-Stage Coupled Chemical-Looping Hydrogen Production Device)

[0078] As Figure 4 shown, the multi-stage coupled chemical-looping hydrogen production device of the present invention includes a first-stage chemical-looping reaction unit represented by the upper frame in the figure and a second-stage chemical-looping reaction unit represented by the lower frame.

[0079] The first-stage chemical-looping reaction unit includes a first-stage reducer and a steam oxidation hydrogen producer, and these two parts can be converted into each other according to the reaction stage.

[0080] In both the first-stage reducer and the steam oxidation hydrogen generator, a metal oxide (denoted by metal N) is provided as the oxygen carrier in the reduction-oxidation reaction (hereinafter referred to as the "first oxygen carrier"). The metal N must be a metal with multiple valence states, and the initial state of the first oxygen carrier can be an oxide of metal N. For example, it can be a sub-high-valence metal oxide. Further, when N is Fe, it can be Fe3O4. However, its initial state can be a metal oxide state with other valences. For example, when N is Fe, the initial state of the first oxygen carrier can be Fe2O3.

[0081] The first oxygen carrier contains an active component, and can optionally contain a sub-active component or an inactive component, or contain both a sub-active component and an inactive component. Among them, the active component can be Fe3O4, but is not limited thereto; the sub-active component can be one or more of MoO3, GeO2, WO3, Mn2O3, ZnO, CeO2; the inactive component can be one or more of Al2O3, ZrO2, Y2O3, MgO, MgAl2O4, CaAl2O4, TiO2, CaO. Here, the main role of the active component is to carry out the oxidation-reduction reaction cycle and obtain pure hydrogen through the steam oxidation reaction; the main role of the sub-active component is to enhance and stabilize the role of the active component; the main role of the inactive component is to make the characteristics of the oxygen carrier more stable, avoid sintering, and construct a stable pore structure, etc.

[0082] As an alternative, the first oxygen carrier may not contain an active component, only contain a sub-active component, and optionally contain an inactive component. The sub-active component is one or more of MoO3, GeO2, WO3, Mn2O3, ZnO, CeO2, and the inactive component can be one or more of Al2O3, MgO, ZrO2, Y2O3, MgAl2O4, CaAl2O4, TiO2, CaO. The reason for not using the above sub-active component as the active component in the present invention is to consider many factors such as cost. If cost and other factors are not considered, or under special conditions, those skilled in the art can completely not use the active component and only use the sub-active component.

[0083] The first oxygen carrier can be prepared by high-temperature solid-state reaction calcination of the active component, sub-active component or inactive component. Among them, the content of the active component is 50-95 wt.%, the content of the sub-active component is 0-5 wt.%; the content of the inactive component is: 5-50 wt.%, the high-temperature calcination temperature is 750°C-1150°C, and the average particle size of the formed oxygen carrier is 1 mm-10 mm.

[0084] The first stage reducer and the steam oxidation hydrogen generator can realize the mutual switching of the functions of the two reaction units by using multiple pipelines and valves arranged on the pipelines in a manner similar to that described in Patent Document 1. For example, when the two reactors corresponding to the first stage reducer and the steam oxidation hydrogen generator are defined as reactor D and reactor E ( Figure 6 ), initially the reactor D realizes the function of the first-stage reducer and the reactor E realizes the function of the steam oxidation hydrogen producer, but after the pipeline is switched by the valve, the reactor D realizes the function of the steam oxidation hydrogen producer and the reactor E realizes the function of the first-stage reducer.

[0085] The multi-stage coupled chemical chain hydrogen production device of the present invention may also include a controller, which controls or monitors each pipeline, valve, temperature, pressure, etc. in the device, and performs control and adjustment at any time. For example, it can switch the input and output of gases, switch the reactions of each reactor according to the reaction stage, transfer or recover heat or energy, capture carbon dioxide, cool water vapor, etc.

[0086] Next, the reactions occurring in the first-stage reducer and the steam oxidation hydrogen generator are described.

[0087] After the system is preheated and the circulation starts, the synthesis gas containing CO and H2 produced by the methane converter described below is introduced into the first stage reducer, and the secondary high-valent metal oxide state (such as Fe3O4) is reduced to low-valent metal oxide or metal element (such as FeO, Fe in iron-based oxygen carrier) by CO and H2 in the synthesis gas. Due to the thermodynamic limitation of the chemical chain reaction, the synthesis gas is partially oxidized by the first stage oxygen carrier to generate a mixed gas containing CO and H2 that are not completely reacted, as well as CO2 and H2O (first stage reduction tail gas), which then returns to the second stage chemical chain reaction unit to reduce the second stage oxygen carrier. Among them, the reduction reaction temperature in the first stage reducer is 400-915℃.

[0088] The reaction in the first stage reducer is (first stage reduction) the following process⑥:

[0089] N represents a metal element, a, b, i represent numbers (0<i<b)

[0090] N a O b +iCO / H2→N a O b-i +iCO2 / H2O

[0091] N a O b +bCO / H2→aN+bCO2 / H2O

[0092] N a Ob-i +(b - i)CO / H₂ → aN + (b - i)CO₂ / H₂O

[0093] When the first oxygen carrier is Fe, the reduction process of the oxygen carrier in process ⑥ is Fe₃O₄ → FeO → Fe.

[0094] In addition, in the steam oxidation hydrogen generator (which is actually the reactor after the reduction reaction in the first - stage reducer mentioned above), steam is introduced to oxidize the oxygen carrier of the low - valence metal oxide or the metal - element oxygen carrier produced by the first - stage reduction to the sub - high - valence oxidation state, and hydrogen is generated simultaneously. For example, when the metal N corresponding to the first oxygen carrier is Fe, the Fe element (or Fe / FeO) in the oxygen carrier is oxidized to Fe₃O₄. Among them, the reduction reaction temperature in the steam oxidation hydrogen generator is 450 - 900 °C.

[0095] The steam oxidation reaction in the steam oxidation hydrogen generator is process ③ as follows:[[]]

[0096] N represents a metal element, and a, b, and i represent numbers (0 < i < b)

[0097] aN + bH₂O → N a O b + bH₂

[0098] N a O b-i + iH₂O → N a O b + iH₂

[0099] aN + (b - i)H₂O → N a O b-i +(b - i)H₂

[0100] When the first oxygen carrier is an oxide of Fe, the steam oxidation process of the oxygen carrier in process ③ is Fe → FeO → Fe₃O₄

[0101] Next, each reactor in the second - stage chemical - looping reaction unit will be described. As Figure 4 shown, the second - stage chemical - looping reaction unit includes a second - stage reducer, a methane converter, and an air oxidizer, and these three parts can be converted with each other according to the reaction stage.

[0102] The second - stage reducer, the methane converter, and the air oxidizer are all provided with a metal oxide (represented by metal M) as the oxygen carrier in the redox reaction (hereinafter referred to as the "second oxygen carrier"). This metal M must be selected as a metal that can play a catalytic role in the methane conversion reaction and should be a metal that can store heat sufficiently through the redox reaction.

[0103] The second oxygen carrier contains an active component, and may selectively contain a sub-active component or an inactive component, or contain both a sub-active component and an inactive component.

[0104] Among them, the active component can be one or more of NiO, CuO, ZnO, preferably consisting only of NiO, but not limited thereto; the sub-active component can be one or more of Fe2O3, CeO2, Co3O4, Mn2O3; the inactive component can be one or more of ZrO2, MgO, Y2O3, MgAl2O4, CaAl2O4, CaO, Al2O3, TiO2. Here, the main function of the active component is to carry out the redox cycle, release heat and store heat during the air oxidation process, and play a catalytic role during the methane reforming reaction after reduction; the main function of the sub-active component is to enhance and stabilize the active component, and the main function of the inactive component is to make the reaction of the second oxygen carrier more stable, avoid sintering, achieve a reasonable pore structure, and achieve a better heat storage structure, etc.

[0105] As an alternative, the second oxygen carrier does not contain an active component, contains a sub-active component, and selectively contains an inactive component. The sub-active component is one or more of Fe2O3, CeO2, Co3O4, Mn2O3, and the inactive component can be one or more of ZrO2, MgO, Y2O3, MgAl2O4, CaAl2O4, CaO, Al2O3, TiO2. The reason why the above sub-active component is not used as an active component in the present invention is to consider many factors such as cost. If cost and other factors are not considered, or under special conditions, those skilled in the art can completely not use the active component and only use the sub-active component.

[0106] The second oxygen carrier can be prepared by high-temperature solid-state reaction calcination of the active component, sub-active component or inactive component. Among them, the total content of the active component is 8wt.% - 40wt.%, the total content of the sub-active component is 0 - 5wt.%, the total content of the inactive component is 60wt.% - 92wt.%, the high-temperature calcination temperature is 550°C - 1250°C, and the average particle size of the oxygen carrier after forming is 1mm - 8mm.

[0107] The second-stage reducer, methane reformer and air oxidizer can, according to the method described in the similar patent document 1, use multiple pipelines and valves arranged on the pipelines to realize the mutual switching of the functions of the three reaction units. For example, when the three reactors corresponding to the second-stage reducer, methane reformer and air oxidizer are defined as reactor B, reactor A and reactor C (see Figure 7) After the system is preheated and enters the circulation system, initially, reactor A functions as a methane converter, reactor B functions as a second-stage reducer, and reactor C functions as an air oxidizer. However, after switching the pipeline through the valve, reactor A functions as an air oxidizer, reactor B functions as a methane converter, and reactor C functions as a second-stage reducer. Next, after switching the pipeline through the valve again, reactor A functions as a second-stage reducer, reactor B functions as an air oxidizer, and reactor C functions as a methane converter. And so on, repeating in a cycle.

[0108] Next, the reactions occurring in the second-stage reducer, methane converter, and air oxidizer will be described.

[0109] After the overall system is preheated and the cycle starts, in the methane converter, combustible gas containing methane is introduced. It first mixes with a part of the recycled tail gas from the second-stage reduction, and the mixed gas first undergoes a methane conversion reaction. In the methane conversion reaction stage, the second oxygen carrier in the reactor has been pre-reduced to the elemental metal state and heat has been accumulated in the oxygen carrier bed. Methane entering the system reacts with possible components such as CO2, or H2O, or a mixture of CO2 and H2O under the catalysis of the elemental metal to undergo a methane conversion reaction (process ①), and the heat already accumulated in the oxygen carrier is fully utilized to generate syngas containing components of CO, H2, CO2, and H2O (referred to as "syngas"), which enters the first-stage reducer of the first chemical looping reaction unit. Among them, the reaction temperature range in the methane converter is 500°C to 1050°C.

[0110] The possible methane conversion reaction in the methane converter is as follows in process ①:

[0111]

[0112]

[0113] When the first oxygen carrier is an oxide of Ni, the oxygen carrier remains unchanged as elemental Ni in process ①.

[0114] After the methane conversion reaction is completed, the temperature of the oxygen carrier and the bed decreases to 400 - 700°C. At this time, the reactor is switched to the state of the air oxidizer through the controller and the air oxidation process (process ④) is carried out. That is, air or oxygen is introduced into the air oxidizer, and the oxygen oxidizes the elemental metal state oxygen carrier to the high valence state and releases a large amount of heat. The reaction heat is mostly accumulated in the bed of the oxidized oxygen carrier to store heat in advance for the reaction heat required in the subsequent methane conversion process. Among them, the reaction temperature of the air oxidation process in the first chemical looping reaction unit is 400 - 950°C.

[0115] The reaction carried out in the air oxidizer is Process ④ as follows:

[0116] xM + 1 / 2yO₂ → M x O y

[0117] When the first oxygen carrier is an oxide of Ni, the change of the oxygen carrier in Process ④ is Ni → NiO.

[0118] After the air oxidation is completed, the reactor is switched to the state of the second-stage reducer through the controller and the second-stage reduction process (Process ⑤) is carried out. The remaining CO and H₂ in the tail gas of the first-stage reduction reduce the second oxygen carrier of the second chemical chain from the high-valent oxide state to the elemental state. The heat released by the reaction is accumulated in the oxygen carrier bed. This part of the heat, together with the heat accumulated in the oxygen carrier during the previous air oxidation process, can provide the heat required for the reaction in the next-stage methane conversion process. At the same time, CO and H₂ are completely oxidized to CO₂ and H₂O, and the switching time is adjusted through the controller to ensure that the second-stage reduction process does not penetrate (that is, no CO or H₂ flows out); all of the second-stage reduction tail gas is CO₂ and H₂O. According to specific requirements, a part of the tail gas (CO₂ and H₂O) can be refluxed to the methane conversion stage of the second chemical chain, mixed with the methane-containing fuel gas, and then enter the methane conversion reactor. The remaining part is used to recover heat, and after condensing H₂O in it, high-purity CO₂ can be obtained for CO₂ capture. The reaction temperature of the oxygen carrier reduction process in the second chemical chain reaction unit is 450 - 1000 °C.

[0119] (Description of the multi-stage coupled chemical looping hydrogen production method)

[0120] Next, the multi-stage coupled chemical looping hydrogen production method using the multi-stage coupled chemical looping hydrogen production device of the present invention will be described.

[0121] As Figure 5 shown, when using the multi-stage coupled chemical looping hydrogen production device of the present invention for the hydrogen production process, first, the device startup and the preparation of the oxygen carrier and the reactor are required. Specifically, in the five reactors (A / B / C / D / E) of the multi-stage coupled chemical looping hydrogen production device, the above-mentioned first oxygen carrier is filled into the two reactors D and E corresponding to the first chemical chain reaction unit, and the second oxygen carrier is filled into the reactors A / B / C corresponding to the second reaction chain unit. Among them, the initial filled oxidation state of the oxygen carrier can be the metal oxide in the oxidation state during the actual cycle process, or other metal oxides in the oxidation state. For example, although the form of the first oxygen carrier in the two reactors D and E corresponding to the first chemical chain reaction unit after the cycle starts is Fe₃O₄, the initially filled oxide can be Fe₂O₃.

[0122] Next, heat up all five reactors (A / B / C / D / E) to the specified temperature.

[0123] After the oxygen carriers in the 3 reactors (A / B / C) of the second-stage chemical looping unit are pre-reduced, introduce H2 into the 3 reactors (A / B / C) to start the pre-reduction of the oxygen carriers. When all reactors complete the pre-reduction, introduce air into one of the reactors A for air oxidation and heat storage. When the reactor A that has completed air oxidation and heat storage is switched to H2 reduction and continues to accumulate heat; at the same time, another reactor B conducts air oxidation.

[0124] After the reactor A that has completed hydrogen reduction and heat storage starts to introduce combustible gas containing CH4 for methane conversion and produce syngas containing CO and H2; at the same time, the reactor B is switched to oxygen carrier reduction, and the reducing gas comes from the reduction tail gas of the first-stage chemical looping unit (containing penetrated CO and H2); at the same time, the reactor C conducts air oxidation.

[0125] The reactor A that has completed methane conversion is switched to the air oxidation process for air oxidation, heat generation and heat storage; the reactor B is switched to methane conversion; the reactor C is switched to the oxygen carrier reduction process.

[0126] After the reactor A completes air oxidation, it is switched to the oxygen carrier reduction process; after the reactor B completes methane conversion, it is switched to the air oxidation process; at this time, the reactor C is switched to the methane conversion process.

[0127] The subsequent process of the second-stage chemical looping unit is cyclically switched among the 3 reactors (A / B / C).

[0128] On the other hand, the syngas enters the reactor D in the 2 reactors (D / E) of the first-stage chemical looping unit to reduce the first oxygen carrier provided therein, and the reduction tail gas (containing penetrated CO and H2) returns to enter the reactor in the reduction state in the second-stage chemical looping unit (the second-stage reducer) to reduce the second oxygen carrier therein.

[0129] The reactor D that has completed the reduction of the first oxygen carrier is switched to the steam oxidation hydrogen production process and completes the steam oxidation hydrogen production reaction. At the same time, the reactor E introduces syngas for the first oxygen carrier reduction reaction. Next, the reactor D that has completed the oxygen carrier steam oxidation hydrogen production is switched to oxygen carrier reduction, and the reactor E that has completed reduction is switched to steam oxidation hydrogen production, and the above cycle process is repeated.

[0130] Figure 6 It is a timing schematic diagram showing the reactions at each stage of the first-stage chemical looping reaction cycle of the present invention. As Figure 6As shown, reactors D and E are heated up together during the start-up preparation stage, and then enter the waiting state (waiting for the second chemical looping unit to complete preheating and pre-reduction). After that, only reactor D is reduced during the first cycle (cycle 1-1). After the reduction is completed, reactor D is switched to steam oxidation, and reactor E is reduced. Then, reactors D and E are switched between steam oxidation reaction and the first-stage reduction reaction and repeated in a cycle.

[0131] Figure 7 It is a timing diagram showing the reactions at each stage of the second chemical looping reaction cycle of the present invention. As Figure 7 shown, reactors A / B / C are heated up together during the start-up preparation stage, and then co-pre-reduced. Then, reactor A is oxidized, and then reactor A is reduced while reactor B is oxidized. After that, starting from the first cycle (cycle 2-1), reactors A / B / C are switched to each other and the three reaction processes of methane conversion, reduction, and oxidation are repeated in a cycle.

[0132] According to the device and method of the present invention, 70-93%, preferably 80-93%, more preferably 85-91% of the heat generated by the oxidation reaction in the air oxidizer is accumulated in the bed layer of the second oxygen carrier. Furthermore, finally, 55-85%, preferably 70-85%, more preferably 70-79% of the heat generated by the oxidation reaction in the air oxidizer is used for the endothermic demand of the methane conversion reaction. Thus, the present invention can achieve an energy self-sustaining multi-stage coupled chemical looping hydrogen production device and method without external energy input.

[0133] (Example 1)

[0134] Next, Example 1 of the present invention will be described. In this example, the multi-stage coupled chemical looping hydrogen production device of the present invention described above is used, and the multi-stage coupled chemical looping hydrogen production method of the present invention described above is used to produce high-purity hydrogen. The specific parameters are as follows:

[0135] First-stage chemical looping reactor: 2 reactors, each reactor loaded with 120 kg of the first-stage oxygen carrier

[0136] Composition of the first-stage oxygen carrier: Active ingredient 55 wt.%: Fe2O3; Inactive ingredient 45 wt.%: ZrO2

[0137] Second-stage chemical looping reactor: 3 reactors, each reactor loaded with 200 kg of the second-stage oxygen carrier,

[0138] Composition of the second-stage oxygen carrier: Active ingredient 18 wt.%: NiO, Inactive ingredient of the oxygen carrier 82 wt.%: CaAl2O4

[0139] Methane-containing fuel gas raw material: biogas (60 vol.% CH4, 40 vol.% CO2), flow rate 34 Nm 3 / h

[0140] Methane conversion (Process ①): Bed temperature 550 - 950 °C, syngas composition (molar ratio): CO / CO2 / H2 / H2O / CH4 = 47 / 4 / 44.5 / 4.2 / 0.3, syngas outlet temperature 250 °C, syngas flow rate 88 Nm 3 / h

[0141] First-stage reduction (Process ⑥): Bed temperature 700 - 850 °C, first-stage reduction tail gas composition (molar ratio): CO / CO2 / H2 / H2O = 17 / 34 / 16 / 33, tail gas temperature 230 °C

[0142] Second-stage reduction (Process ⑤): Bed temperature 850 - 950 °C, second-stage reduction tail gas composition (molar ratio): CO2 / H2O = 51 / 49, tail gas temperature 180 °C

[0143] First-stage oxidation (Process ③): Bed temperature 600 - 850 °C, steam oxidation outlet gas phase composition (molar ratio): H2 / H2O = 46 / 54, crude hydrogen temperature 175 °C, after further heat recovery and cooling, product hydrogen composition: H2 / H2O = 99.99 / 0.01, product hydrogen flow rate: 58 Nm 3 / h

[0144] Second-stage oxidation (Process ④): Bed temperature 550 - 900 °C, oxidation tail gas outlet composition: N2, tail gas temperature 160 °C

[0145] The endothermic heat of the methane conversion reaction in Process ①: 187 - 225 MJ / h; the exothermic heat of the second-stage air oxidation reaction in Process ④: 380 - 405 MJ / h, where 80 - 90% of the heat is accumulated in the oxygen carrier bed of the second-stage chemical looping reactor, and 55 - 70% of the heat can be used to meet the endothermic heat demand of the methane conversion reaction in Process ①.

[0146] (Example 2)

[0147] Next, the specific Example 2 of the present invention will be described. In this example, the multi-stage coupled chemical looping hydrogen production device of the present invention described above is used, and the multi-stage coupled chemical looping hydrogen production method of the present invention described above is used to produce high-purity hydrogen. The specific parameters are as follows:

[0148] First-stage chemical looping reactor: 2 reactors, each reactor loaded with 210 kg of first-stage oxygen carrier

[0149] Composition of the first-stage oxygen carrier: Active ingredient 80 wt.%: Fe2O3; Inactive ingredient 20%: MgAl2O4 + ZrO2

[0150] Second - stage chemical looping reactor: 3 reactors, each reactor is loaded with 600 kg of the second - stage oxygen carrier,

[0151] Composition of the second - stage oxygen carrier: Active ingredient 12 wt.%: NiO, Inactive ingredient of the oxygen carrier 88 wt.%: MgAl2O4

[0152] Methane - containing fuel gas feedstock: Biogas (55 vol.% CH4, 45 vol.% CO2), flow rate 108 Nm 3 / h

[0153] Methane conversion (Process ①): Bed temperature 550 - 950 °C, Composition of the syngas produced (molar ratio): CO / CO2 / H2 / H2O / CH4 = 45 / 4.5 / 46 / 4 / 0.5, Syngas outlet temperature 240 °C, Syngas flow rate 280 Nm 3 / h

[0154] First - stage reduction (Process ⑥): Bed temperature 700 - 850 °C, Composition of the first - stage reduction tail gas (molar ratio): CO / CO2 / H2 / H2O = 16.5 / 33.5 / 15 / 35, Tail gas temperature 220 °C

[0155] Second - stage reduction (Process ⑤): Bed temperature 850 - 950 °C, Composition of the second - stage reduction tail gas (molar ratio): CO2 / H2O = 50 / 50, Tail gas temperature 170 °C

[0156] First - stage oxidation (Process ③): Bed temperature 600 - 850 °C, Composition of the gas phase at the outlet of steam oxidation (molar ratio): H2 / H2O = 48 / 52, Crude hydrogen temperature 170 °C, After further heat recovery and cooling, Composition of the product hydrogen: H2 / H2O = 99.992 / 0.008, Product hydrogen flow rate: 148.5 Nm 3 / h

[0157] Second - stage oxidation (Process ④): Bed temperature 550 - 900 degrees Celsius, Composition of the oxidation tail gas at the outlet (molar ratio): N2, Tail gas temperature 165 °C

[0158] Endothermic heat of the methane conversion reaction in Process ①: 544.5 - 655 MJ / h; Exothermic heat of the second - stage air oxidation reaction in Process ④: 738 - 795 MJ / h, among which 86 - 93% of the heat is accumulated in the oxygen - carrier bed of the second - stage chemical looping reactor, and 73 - 85% of the heat can be used to meet the endothermic heat demand of the methane conversion reaction in Process ①.

[0159] (Example 3)

[0160] Next, Example 3 of the present invention will be described. In this example, the multi-stage coupled chemical-looping hydrogen production device of the present invention described above is used, and the multi-stage coupled chemical-looping hydrogen production method of the present invention described above is used to produce high-purity hydrogen. The specific parameters are as follows:

[0161] First-stage chemical-looping reactor: 2 reactors, each reactor loaded with 50 kg of the first-stage oxygen carrier

[0162] Composition of the first-stage oxygen carrier: Active ingredient 80 wt. %: Fe3O4; Inactive ingredient 20%: Al2O3

[0163] Second-stage chemical-looping reactor: 3 reactors, each reactor loaded with 160 kg of the second-stage oxygen carrier,

[0164] Composition of the second-stage oxygen carrier: Active ingredient 16 wt. %: NiO, Inactive ingredient of the oxygen carrier 84 wt. %: CaAl2O4

[0165] Methane-containing fuel gas raw material: Natural gas, flow rate 15 Nm 3 / h

[0166] Methane conversion (Process ①): Bed temperature 550 - 950 °C, Composition of the syngas produced (molar ratio): CO / CO2 / H2 / H2O / CH4 = 46.2 / 4 / 45.5 / 4.1 / 0.2, Syngas outlet temperature 260 °C, Syngas flow rate 62 Nm 3 / h

[0167] First-stage reduction (Process ⑥): Bed temperature 700 - 850 °C, Composition of the first-stage reduction tail gas (molar ratio): CO / CO2 / H2 / H2O = 17 / 32 / 18 / 323, Tail gas temperature 221 °C

[0168] Second-stage reduction (Process ⑤): Bed temperature 850 - 950 °C, Composition of the second-stage reduction tail gas (molar ratio): CO2 / H2O = 49 / 51, Tail gas temperature 172 °C

[0169] First-stage oxidation (Process ③): Bed temperature 600 - 850 °C, Composition of the gas phase at the outlet of steam oxidation (molar ratio): H2 / H2O = 45.2 / 54.8, Crude hydrogen temperature 182 °C. After further heat recovery and cooling, Composition of the product hydrogen: H2 / H2O = 99.99 / 0.01, Product hydrogen flow rate: 36.8 Nm 3 / h

[0170] Second-stage oxidation (Process ④): Bed temperature 550 - 900 degrees Celsius, Composition of the oxidation tail gas at the outlet (molar ratio): N2, Tail gas temperature 135 °C

[0171] Process ①: The endothermic methane conversion reaction is 137 - 165 MJ / h; Process ④: The exothermic second-stage air oxidation reaction is 270 - 291 MJ / h, of which 85 - 91% of the heat is accumulated in the oxygen carrier bed of the second-stage chemical looping reactor, and 70 - 79% of the heat can be used to meet the endothermic demand of the methane conversion reaction in Process ①.

[0172] (Heat conversion result)

[0173] According to the results of Examples 1, 2, and 3 above, the relationship between the heat released by the second-stage air oxidation reaction, the percentage of the heat released accumulated in the oxygen carrier bed of the second-stage chemical looping reactor, and the percentage of the heat finally used to meet the endothermic demand of the methane conversion reaction is as follows.

[0174]

[0175] According to the device and method of the present invention, 70 - 93%, preferably 80 - 93%, more preferably 85 - 91% of the heat generated by the oxidation reaction in the air oxidizer is accumulated in the bed of the second oxygen carrier. Furthermore, finally, 55 - 85%, preferably 70 - 85%, more preferably 70 - 79% of the heat generated by the oxidation reaction in the air oxidizer is used to meet the endothermic demand of the methane conversion reaction.

[0176] In summary, the process of the present invention adopts a novel structure, which can efficiently couple the strong exothermic air oxidation process in the chemical looping process with the methane catalytic conversion process. Most of the heat released after air oxidation is stored in the reactor bed. Subsequently, the oxygen carrier is reduced to the metallic elemental state through a slightly exothermic oxygen carrier reduction process, and heat is continuously stored in the reactor. Then, it is switched to the methane conversion process. The oxygen carrier that has been reduced to the metallic elemental state has the catalytic ability for methane conversion, and at the same time, the heat accumulated in the previous two processes can directly supply the heat required for the strongly endothermic methane conversion reaction.

[0177] Thus, by decoupling the three-reaction-stage cyclic chemical looping hydrogen production process in the single existing technology, splitting it into two different chemical looping reaction processes, and coupling them with the methane conversion process, using the heat generated by the air oxidation in one of the chemical looping processes to directly supply the methane conversion process, self-heating methane conversion to produce syngas from methane-containing fuel gas under oxygen-free conditions can be achieved, and hydrogen production by steam oxidation of the oxygen carrier can be carried out. The entire process does not require external separate heating measures, does not require the use of heat transfer media and complex heat exchange systems, and can achieve the self-maintenance effect of heat within the system.

[0178] (Vocabulary specified in this patent)

[0179] Multistage coupled chemical looping hydrogen production device

[0180] The first-stage chemical looping reaction unit

[0181] The second chemical looping reaction unit

[0182] The first reducer, steam oxidation hydrogen generator

[0183] The second reducer, methane converter, air oxidizer

[0184] The first oxygen carrier, the second oxygen carrier, methane-containing combustible gas, syngas, reduction tail gas, active ingredient, sub-active ingredient, inactive ingredient

[0185] The first reduction reaction, steam oxidation hydrogen production reaction

[0186] The second reduction reaction, methane conversion reaction, air oxidation reaction are switched and cycled repeatedly (reaction)

[0187] The first reduction step, steam oxidation hydrogen production step

[0188] The second reduction step, methane conversion step, air oxidation step, the first chemical looping reaction cycle, the second chemical looping reaction cycle

Claims

1. A multi-stage coupled chemical chain hydrogen production device, characterized in that: The multi-stage coupled chemical chain hydrogen production device comprises a first-stage chemical chain reaction unit and a second-stage chemical chain reaction unit. The first stage chemical chain reaction unit includes a first stage reducer and a water vapor oxidation hydrogen generator, and these two parts can be mutually converted and the whole cycle can be repeated according to the reaction stage; The second stage chemical chain reaction unit includes a second stage reducer, a methane converter, and an air oxidizer, and these three parts can be mutually converted and repeated in a whole cycle according to the reaction stage; The same first oxygen carrier is arranged in the first stage reducer and the water vapor oxidation hydrogen generator, and the first oxygen carrier changes into a metal element or a metal oxide with different chemical valences in each reaction stage, and the metal has multiple valences; The same second oxygen carrier is arranged in the second-stage reducer, the methane converter and the air oxidizer, the second oxygen carrier changes into a metal element or a metal oxide with different chemical valence at each reaction stage, and the metal element corresponding to the second oxygen carrier acts as a catalyst in the methane conversion reaction in the methane conversion reactor; The methane converter is connected to the first stage reducer and is used to deliver the synthesis gas converted from methane to the first stage reducer; The second stage reducer is connected to the methane converter and is used to reflux carbon dioxide or water vapor or both to the methane converter; The first-stage reducer is connected to the second-stage reducer and is used to transport reduction tail gas containing carbon monoxide or hydrogen or both to the second-stage reducer.

2. The multi-stage coupled chemical chain hydrogen production device according to claim 1, characterized in that: The first oxygen carrier comprises an active ingredient and optionally comprises a secondary active ingredient or an inactive ingredient or both. The active ingredient is Fe3O4, The secondary active ingredients are one or more of MoO3, GeO2, WO3, Mn2O3, ZnO, CeO2, The inactive ingredient may be one or more of Al2O3, MgO, ZrO2, Y2O3, MgAl2O4, CaAl2O4, TiO2, CaO.

3. The multi-stage coupled chemical chain hydrogen production device according to claim 2, characterized in that: The first oxygen carrier does not contain an active ingredient, contains a secondary active ingredient, and selectively contains an inactive ingredient, The secondary active ingredients are one or more of MoO3, GeO2, WO3, Mn2O3, ZnO, CeO2, The inactive ingredient may be one or more of Al2O3, MgO, ZrO2, Y2O3, MgAl2O4, CaAl2O4, TiO2, CaO.

4. The multi-stage coupled chemical chain hydrogen production device according to claim 2, characterized in that: In the first oxygen carrier, the content of active components is 50-95wt.%, the content of secondary active components is 0-5wt.%, and the content of inactive components is 5-50wt.%.

5. The multi-stage coupled chemical chain hydrogen production device according to claim 2, characterized in that: The first oxygen carrier contains Fe3O4 as the active component and Al2O3 or MgO as the inactive component.

6. The multi-stage coupled chemical looping hydrogen production device according to claim 5, wherein the composition of the first-stage oxygen carrier is 75 wt.% of Fe3O4 as the active component and 25 wt.% of Al2O3 as the inactive component, or the composition of the first-stage oxygen carrier is 80 wt.% of Fe3O4 as the active component and 20 wt.% of MgO + Al2O3 as the inactive component.

7. The multi-stage coupled chemical looping hydrogen production device according to claim 1, wherein the second oxygen carrier contains an active component, and optionally contains a sub-active component or an inactive component or both, the active component is one or more of NiO, CuO, ZnO, the sub-active component is one or more of Fe2O3, CeO2, Co3O4, Mn2O3, the inactive component can be one or more of ZrO2, MgO, Y2O3, MgAl2O4, CaAl2O4, CaO, Al2O3, TiO2.

8. The multi-stage coupled chemical looping hydrogen production device according to claim 1, wherein the second oxygen carrier does not contain an active component, contains a sub-active component, and optionally contains an inactive component, the sub-active component is one or more of Fe2O3, CeO2, Co3O4, Mn2O3, the inactive component is one or more of ZrO2, MgO, Y2O3, MgAl2O4, CaAl2O4, CaO, Al2O3, TiO2.

9. The multi-stage coupled chemical looping hydrogen production device according to claim 7, wherein in the second oxygen carrier, the content of the active component is 8 wt.% to 40 wt.%, the content of the sub-active component is 0 to 5 wt.%; the content of the inactive component is 60 wt.% to 92 wt.%.

10. The multi-stage coupled chemical looping hydrogen production device according to claim 7, wherein the second oxygen carrier contains NiO as the active component.

11. The multi-stage coupled chemical looping hydrogen production device according to claim 7, wherein the composition of the second oxygen carrier is 18 wt.% of NiO as the active component and 82 wt.% of MgAl2O4 as the inactive component, or the composition of the second oxygen carrier is 18 wt.% of NiO as the active component and 82 wt.% of CaAl2O4 as the inactive component.

12. A multi-stage coupled chemical looping hydrogen production method, wherein the multi-stage coupled chemical looping hydrogen production device described in any one of claims 1 to 11 is used, and the method includes the following steps: Device startup and oxygen carrier and reactor preparation step, in this step, start the device, and respectively fill the above-mentioned first oxygen carrier into the two reactors corresponding to the first-stage chemical looping reaction unit, and fill the second oxygen carrier into the three reactors corresponding to the second reaction chain unit respectively; Reactor pre-treatment step, in which the above-mentioned total of five reactors are respectively heated up, and the system as a whole is adjusted to be suitable for the following reactions by means of a combination of pre-reduction and pre-oxidation, that is: the two reactors corresponding to the first-stage chemical looping reaction unit are switched between each other and the first-stage reduction reaction and steam oxidation hydrogen production reaction are cyclically repeated, and the three reactors corresponding to the second-stage chemical looping reaction unit are switched between each other and the methane reforming reaction, air oxidation reaction and second-stage reduction reaction are cyclically repeated; Methane reforming step, introducing methane-containing combustible gas into the methane reformer, which first mixes with the reduction tail gas partially recycled from the second-stage reducer, and then methane reacts with a mixed gas containing CO2 or H2O or both under the catalysis of elemental metal to carry out the methane reforming reaction, and fully utilizes the heat already stored in the oxygen carrier in the air oxidation step to generate syngas containing CO, H2, CO2, and H2O components and enter the first-stage reducer of the first-stage chemical looping reaction unit; Air oxidation step, after the methane reforming reaction is completed, switch the reactor to the state of the air oxidizer and carry out the air oxidation process, that is, introduce air or oxygen into the air oxidizer to oxidize the elemental metal state oxygen carrier to the high-valent state, and at the same time release a large amount of reaction heat, and most of this reaction heat is stored in the bed layer of the oxidized oxygen carrier in advance for the reaction heat required for the subsequent methane reforming process; Second-stage reduction step, after the air oxidation is completed, switch the reactor to the state of the second-stage reducer and carry out the second-stage reduction process, that is, the remaining CO and H2 in the first-stage reduction tail gas reduce the second oxygen carrier in the second-stage reducer from the high-valent oxide state to the elemental state, and at the same time CO and H2 are completely oxidized to CO2 and H2O, and by controlling and adjusting the switching time to ensure that the second-stage reduction process does not penetrate, so that all the second-stage reduction tail gas is CO2 and H2O, and a part of the tail gas is refluxed to the methane reformer and mixed with the methane-containing fuel gas to carry out the methane reforming reaction, and the remaining part recovers heat and then condenses H2O therein to obtain high-purity CO2 and carry out CO2 capture; First-stage reduction step, introducing the syngas containing CO and H2 generated by the methane reformer into the first-stage reducer, reducing the sub-high-valent metal oxide state of the first oxygen carrier to the low-valent metal oxide or elemental metal by CO and H2 in the syngas, and the syngas is partially oxidized by the first-stage chemical looping oxygen carrier to generate a mixed gas containing unreacted remaining CO, H2, and CO2, H2O, that is, the reduction tail gas, and then return it to the second-stage reducer of the second-stage chemical looping reaction unit; Steam oxidation hydrogen production step, introducing steam into the steam oxidation hydrogen producer to oxidize the low-valent metal oxide oxygen carrier or elemental metal generated in the first-stage reduction step to the sub-high-valent oxidation state, and at the same time produce high-purity hydrogen.

13. The multi-stage coupled chemical looping hydrogen production method according to claim 12, wherein 70% to 93% of the heat generated by the oxidation reaction in the air oxidizer is accumulated in the bed of the second oxygen carrier, and then 55% to 85% of the heat generated by the oxidation reaction in the air oxidizer is used for the endothermic requirement of the methane reforming reaction.

14. The multistage coupled chemical-looping hydrogen production method according to claim 12, wherein 80% to 93% of the heat generated by the oxidation reaction in the air oxidizer is accumulated in the bed of the second oxygen carrier, and then 70% to 85% of the heat generated by the oxidation reaction in the air oxidizer is used for the endothermic requirement of the methane reforming reaction.

15. The multistage coupled chemical-looping hydrogen production method according to claim 12, wherein 85% to 91% of the heat generated by the oxidation reaction in the air oxidizer is accumulated in the bed of the second oxygen carrier, and then 70% to 79% of the heat generated by the oxidation reaction in the air oxidizer is used for the endothermic requirement of the methane reforming reaction.

16. The multistage coupled chemical-looping hydrogen production method according to claim 12, wherein The initial filling oxidation state of the first oxygen carrier is different from the metal oxidation state during the repeated cycle.

17. The multistage coupled chemical-looping hydrogen production method according to claim 16, wherein The metal oxidation state of the first oxygen carrier during the repeated cycle is Fe3O4, and the initial filling oxidation state is Fe2O3.

18. The multistage coupled chemical-looping hydrogen production method according to claim 12, wherein The methane-containing combustible gas is natural gas, biogas, coalbed methane or petroleum gas.

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