Bimetal three-bed chemical looping hydrogen production method

Abstract

The invention belongs to the technical field of hydrogen production processes, and discloses a bimetallic three-bed chemical looping hydrogen production method, which adopts a novel bimetallic oxygen carrier to replace Fe2O3 in a traditional three-bed system, thereby breaking through the limitation of traditional thermodynamics and maximally improving the hydrogen production efficiency under the condition that the carbon capture rate is not changed. According to the system, hydrogen is produced by using a redox pair of Fe3O4-FeO / Fe, and energy is provided for the system by using a redox pair of NiO-Ni, Mn3O4-MnO or Cu2O-Cu. By means of the method, energy distribution between the combustion process and the reforming process can be effectively controlled. The thermodynamic limitation is broken through by replacing a single iron-based oxygen carrier with the bimetallic oxygen carrier, and the carbon dioxide is captured in situ while the hydrogen production efficiency is improved. In addition, the bimetal oxygen carrier can also be used for research on hydrogen production from methane, biogas and other fuel gases, and the increasing requirement for clean hydrogen is met.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrogen production processes. Specifically, it relates to a method for hydrogen production by chemical looping with a dual-metal three-bed system. Background Art

[0002] Under the background of global climate governance, the problem of greenhouse gas emissions caused by the fossil energy-dependent industrial system urgently needs to be solved. According to the 2022 annual report of the International Energy Agency, energy-related CO2 emissions have reached a historical peak of 36.8 Gt, of which the contribution rate of industrial processes is 37%. In this context, hydrogen, as a secondary energy carrier with zero-carbon combustion characteristics, its strategic value is becoming increasingly prominent in the process of energy transformation. Compared with traditional fossil fuels, hydrogen fuel not only has the highest mass energy density of 143 MJ·kg-1, but its oxidation process can also achieve zero CO2 emissions, thus showing unique decarbonization advantages in difficult-to-decarbonize fields such as iron and steel metallurgy and chemical synthesis.

[0003] Current hydrogen production technologies can be classified into three systems according to carbon intensity: the grey hydrogen system relies on natural gas reforming or coal gasification processes, with an emission intensity of 9 - 12 kg CO2 / kg H2; the blue hydrogen system can reduce the carbon emission intensity to 3 - 5 kg CO2 / kg H2 by coupling carbon capture, utilization, and storage (CCUS) technologies; while green hydrogen technology relies on renewable energy electrolysis of water, which can theoretically achieve zero carbon emissions throughout the life cycle. Although green hydrogen is regarded as the ultimate solution, its levelized cost is currently still up to 3 - 6 $ / kg, which is 2 - 3 times higher than that of grey hydrogen. This economic bottleneck has prompted the academic community to shift the research focus to transitional solutions - achieving cost-effective balance in blue hydrogen production through CCUS technology optimization.

[0004] As an innovative hydrogen production paradigm, the chemical looping hydrogen production technology is innovative in terms of energy cascade utilization and process intensification. The syngas chemical looping hydrogen production (SCL) system realizes the syngas reforming for hydrogen production and in-situ CO2 capture simultaneously by constructing a reduction-oxidation cycle system and using the lattice oxygen transfer mechanism of the metal oxygen carrier. This process adopts a three-bed reactor configuration and integrates the synergistic mechanism of chemical looping combustion (CLC) and chemical looping reforming (CLR): the Fe2O3 / Fe3O4 redox pair completes the complete oxidation of the fuel in the CLC unit, releasing reaction heat to maintain the self-heating operation of the system; Fe3O4 / FeO undergoes a partial oxidation reaction in the CLR unit to produce hydrogen efficiently through steam reforming. Thermodynamic analysis shows that although a single iron-based oxygen carrier can achieve thermal coupling of the two subsystems, its inherent redox characteristics lead to an imbalance in energy distribution: the heat release of the CLC subsystem (ΔH = -164 kJ / mol) far exceeds the endothermic demand of the CLR (ΔH = +87 kJ / mol), resulting in limited hydrogen production efficiency of the system (η H2 ≤65.7%), and the excess heat energy is usually recovered in the form of combined cycle power generation.

[0005] In view of the above technical bottlenecks, there is an urgent need for a material to replace the single iron-based oxygen carrier to break through the limitations of traditional thermodynamic equilibrium, optimize the distribution ratio of the chemical energy of syngas between hydrogen production and heat supply, and provide a new technical path for improving the hydrogen production efficiency of the SCL system. Summary of the Invention

[0006] The object of the present invention is to address the defects existing in the existing single iron-based three-bed hydrogen production process. NiO·Fe3O4, Mn3O4·Fe3O4 or Cu2O·Fe3O4 bimetallic oxygen carriers are used to replace Fe2O3 for three-bed hydrogen production, breaking through the limitations of traditional thermodynamic equilibrium. By controlling the ratio between Ni, Mn or Cu and Fe, the chemical energy distribution of the syngas in the CLC and CLR processes can be changed. At the same time, NiO·Fe3O4, Mn3O4·Fe3O4 or Cu2O·Fe3O4 bimetallic oxygen carriers have great potential in fuel activation and reaction kinetics improvement. Adding NiO, Mn3O4 or Cu2O can significantly improve the reaction activity of the iron-based oxygen carrier.

[0007] To solve the above technical problems, the present invention is realized through the following technical solutions:

[0008] The present invention provides a bimetallic three-bed chemical looping hydrogen production method, which includes the following steps:

[0009] (1) Introduce syngas and the bimetallic oxygen carrier into a moving bed reduction reactor to carry out a chemical looping combustion reaction and capture CO2 gas;

[0010] (2) Transport the reduced bimetallic oxygen carrier obtained in step (1) to a moving bed oxidation reactor to carry out a chemical looping reforming reaction with water vapor to produce hydrogen, and at the same time, the bimetallic oxygen carrier is partially oxidized;

[0011] (3) Transport the partially oxidized bimetallic oxygen carrier obtained in step (2) to a combustion reactor, and regenerate the oxygen carrier meeting the requirements for entering the reduction reactor by oxidation with fresh air, and the regenerated bimetallic oxygen carrier is carried out of the reactor by high-speed air to a gas-solid separator;

[0012] (4) After gas-solid separation by the gas-solid separator, the bimetallic oxygen carrier re-enters the moving bed reduction reactor to carry out a chemical looping combustion reaction with syngas and is recycled;

[0013] Steps (1), (2), (3) and (4) are repeated cyclically to realize the production of hydrogen from syngas by the bimetallic oxygen carrier based on a three-bed circulation mode.

[0014] Further, the bimetallic oxygen carrier is NiO·Fe3O4 oxygen carrier, Mn3O4·Fe3O4 oxygen carrier or Cu2O·Fe3O4 oxygen carrier.

[0015] Furthermore, the molar ratio of NiO to Fe3O4 in the bimetallic oxygen carrier, the molar ratio of Mn3O4 to Fe3O4 in the bimetallic oxygen carrier, and the molar ratio of Cu2O to Fe3O4 in the bimetallic oxygen carrier are all in the range greater than 0 and less than or equal to 0.5.

[0016] Furthermore, the product after combustion in step (3) is a mixture of Fe3O4 and NiO / Mn3O4 / Cu2O, and there is no Fe2O3.

[0017] Further, the operation mode of the moving bed reduction reactor and the moving bed oxidation reactor is gas-solid countercurrent.

[0018] Further, the temperature of the syngas in step (1) is 400 - 500 °C.

[0019] Further, the temperature of the bimetallic oxygen carrier before being introduced into the moving bed reduction reactor in step (1) is 800 - 900 °C.

[0020] Further, in step (1), the combustion gas is cooled and condensed, and then CO2 is separated and compressed.

[0021] Further, the temperature of the bimetallic oxygen carrier before being introduced into the moving bed oxidation reactor in step (2) is 700 - 800 °C.

[0022] Further, in step (2), the reaction gas is cooled and flash-separated, and then H2 is separated and compressed.

[0023] Further, the temperature of the bimetallic oxygen carrier before being introduced into the combustion reactor in step (3) is 500 - 800 °C.

[0024] Further, the temperature of the fresh air in step (3) is 400 - 600 °C.

[0025] Further, the combustion reactor in step (3) is a fluidized bed reactor.

[0026] The beneficial effects of the present invention are:

[0027] (1) A dual-metal three-bed chemical looping hydrogen production method of the present invention uses NiO·Fe3O4, Mn3O4·Fe3O4, or Cu2O·Fe3O4 as a dual-metal oxygen carrier to replace single Fe2O3, breaking through the thermodynamic limitations of traditional iron-based oxygen carriers in the hydrogen production process, improving the chemical energy distribution, and increasing the hydrogen production efficiency while maintaining the CO2 capture rate unchanged. This system uses the Fe3O4·FeO / Fe redox pair to produce hydrogen and the NiO·Ni, Mn3O4-MnO, or Cu2O-Cu redox pair to provide energy for the system, thereby effectively controlling the energy distribution between the CLC process and the CLR process to achieve self-heating operation.

[0028] (2) A dual-metal three-bed chemical looping hydrogen production method of the present invention can significantly improve the reaction activity of iron-based oxygen carriers by adding NiO, Mn3O4, or Cu2O, and can be used for the research of hydrogen production from other fuel gases such as methane and biogas.

[0029] (3) A dual-metal three-bed chemical looping hydrogen production method of the present invention can use a gas-solid countercurrent moving bed for the reduction reactor and the oxidation reactor; different from the traditional fluidized bed, this flow contact mode is beneficial to heat exchange between the flow streams and reduces the wear of the oxygen carrier. Description of the Drawings

[0030] Figure 1 It is a process flow diagram of the SCL process for the dual-metal oxygen carrier.

[0031] Figure 2 It is a design diagram of the gas-solid countercurrent moving bed reducer.

[0032] Figure 3 It is a diagram of the change in Gibbs free energy of possible reactions of the Ni-Fe dual metal in a three-bed reactor.

[0033] Figure 4 It is a diagram of the change in Gibbs free energy of possible reactions of the Cu-Fe dual metal in a three-bed reactor.

[0034] Figure 5 It is a diagram of the change in Gibbs free energy of possible reactions of the Mn-Fe dual metal in a three-bed reactor.

[0035] Figure 6 It is an analysis diagram of the maximum hydrogen production efficiency at different dual-metal molar ratios and different syngas feed temperatures with the oxygen carrier feed temperature at 800 °C.

[0036] Figure 7 It is an analysis diagram of the maximum hydrogen production efficiency at different dual-metal molar ratios and different syngas feed temperatures with the oxygen carrier feed temperature at 850 °C.

[0037] Figure 8Analysis diagram of the maximum hydrogen production efficiency at different bimetallic molar ratios at an oxygen carrier feed temperature of 900 °C under different syngas feed temperatures. Detailed implementation mode

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with specific embodiments and the accompanying drawings.

[0039] As Figure 1 shown, by adding the bimetallic oxygen carrier (NiO·Fe3O4, Mn3O4·Fe3O4, or Cu2O·Fe3O4) from the top of the gas-solid countercurrent moving bed reactor, a gas-solid countercurrent contact mode is formed with the syngas added from the bottom under the action of its own gravity. During this process, heat transfer and mass transfer processes occur simultaneously. In the gas-solid countercurrent moving bed reduction reactor, the syngas reacts with NiO·Fe3O4, Mn3O4·Fe3O4, or Cu2O·Fe3O4 and is oxidized to produce CO2 and H2O. The composition of the syngas is diverse. The composition of the syngas in the implementation mode is taken as an example in Table 1. The reaction-generated gas can be cooled downstream to facilitate steam condensation and direct carbon dioxide capture under high pressure. For the solid reactants, NiO, Mn3O4, or Cu2O is reduced to Ni, MnO, or Cu, and Fe3O4 is reduced to a mixture of FeO and Fe. Chemical reactions occurring in the gas-solid countercurrent moving bed reduction reactor:

[0040] NiO·Fe3O4 + CO / H2 → NiO·FeO x + CO2 / H2O (1)

[0041] Mn3O4·Fe3O4 + CO / H2 → MnO·FeO x + CO2 / H2O (2)

[0042] Cu2O·Fe3O4 + CO / H2 → Cu·FeO x + CO2 / H2O (3)

[0043] 0 < x < 1.333, ΔH > 0

[0044] In the gas-solid countercurrent moving bed oxidation reactor, steam reacts with FeO x to produce H2. The FeO coming out of the gas-solid countercurrent moving bed reduction reactor x is partially oxidized here, and the chemical reaction:

[0045] Ni·FeO x + H2O → Ni·FeO y + H2 (4)

[0046] MnO·FeO x+H2O → MnO·FeO y +H2 (5)

[0047] Cu·FeO x +H2O → Cu·FeO y +H2 (6)

[0048] x < y ≤ 1.333, ΔH < 0

[0049] Based on the thermodynamic equilibrium between steam and iron / nickel oxides, the variable y cannot exceed 1.333, and nickel remains in its elemental state without being oxidized in the oxidation reactor.

[0050] In the combustion bed reactor, FeO y is re-oxidized by air with Ni, MnO or Cu to form NiO·Fe3O4, Mn3O4·Fe3O4 or Cu2O·Fe3O4. It can be seen from Figures 3 - 5 that Ni, MnO or Cu is preferentially oxidized over Fe3O4 thermodynamically, so Ni, MnO or Cu can be oxidized separately without oxidizing Fe3O4. The chemical reactions occurring in the burner are:

[0051] Ni·FeO y +O2(Air) → NiO·Fe3O4 (7)

[0052] MnO·FeO y +O2(Air) → Mn3O4·Fe3O4 (8)

[0053] Cu·FeO y +O2(Air) → Cu2O·Fe3O4 (9)

[0054] where y ≤ 1.333, ΔH < 0

[0055] This reaction is highly exothermic, and the released heat can be used to provide energy for the entire system. The solid substances from the combustion reactor are transported through a single-phase riser pipe, while the gas-solid separator is used to separate the bimetallic oxygen carriers of NiO·Fe3O4, Mn3O4·Fe3O4 or Cu2O·Fe3O4 and the oxygen-depleted flue gas. The design of the SCL system should ensure that the net heat of reactions (1)-(9) is zero or negative, as shown in the following equation (10).

[0056] (ΔH reducer +ΔH oxidizer +ΔH combustor ) T ≤ 0 (10)

[0057] The relevant reaction models were established using ASPEN Plus software. The gas-solid countercurrent moving bed reduction reactor and the gas-solid countercurrent moving bed oxidation reactor adopt multi-stage series Gibbs reactors, and the construction mode is as Figure 2 shown. The combustion reactor adopts a single-stage Gibbs reactor. By adjusting the molar ratios a, b, or c of NiO, Mn3O4, or Cu2O to Fe3O4, it is possible to improve the hydrogen production efficiency while maintaining the CO2 capture rate unchanged and to maintain the process autothermal operation through internal heat exchange within the system. The possible reactions and heat absorption and release situations inside each reactor are analyzed as Figure 3 , Figure 4 and Figure 5 shown, which are the analyses of heat absorption and release of Ni-Fe, Cu-Fe, and Mn-Fe bimetals respectively.

[0058] Table 1 Composition of syngas

[0059]

[0060]

[0061] Example 1

[0062] 1) 11704 kmol / h of syngas enters the gas-solid countercurrent moving bed reduction reactor from the bottom at 400 °C and 1 atm. The NiO·Fe3O4 oxygen carrier with a molar ratio a of 0.01 enters the gas-solid countercurrent moving bed reduction reactor from the top at 800 °C. The operation mode of the reduction reactor is atmospheric adiabatic operation. The syngas flows from bottom to top, and the NiO·Fe3O4 oxygen carrier moves from top to bottom. The two react in a countercurrent mode, and the NiO·Fe3O4 oxygen carrier oxidizes the syngas into CO2 and H2O.

[0063] 2) The mixture of CO2 and H2O is cooled to 120 °C in a heat exchanger and then fed into a condenser. The condenser temperature is set at 35 °C, which can condense and separate the water in the gas mixture. The remaining carbon dioxide enters a compressor and is pressurized to 153 atm for transportation and storage.

[0064] 3) The solid product Ni·FeO x is discharged from the bottom of the gas-solid countercurrent moving bed reduction reactor at a temperature of about 850 °C and enters the top of the gas-solid countercurrent moving bed oxidation reactor. The operation mode of the oxidation reactor is atmospheric adiabatic operation. 28000 kmol / h of water is heated from room temperature to 112 °C steam and then fed into the gas-solid countercurrent moving bed oxidation reactor from the bottom, and reacts with the oxygen carrier Ni·FeO x in a steam-iron countercurrent reaction to produce H2.

[0065] 4) Subsequently, the mixture of H2 and unreacted steam is cooled to 120 °C in a heat exchanger and then fed into a flash tank. The temperature inside the flash tank is set at 35 °C, where the unreacted water vapor can be condensed into water and separated. The remaining H2 is pressurized to 22 atm in a compressor for transportation and storage.

[0066] 5) The oxygen carrier Ni·Fe3O4 after the reaction is discharged from the bottom of the gas-solid countercurrent moving bed oxidation reactor and enters the combustion reactor to react with air, being re-oxidized to NiO·Fe3O4. Among them, the air is preheated to 500 °C before entering the combustion reactor.

[0067] 6) The products after combustion are fed into a gas-solid separator, where gas-solid separation is carried out. NiO·Fe3O4 is re-transported to the top of the gas-solid countercurrent moving bed reduction reactor, and the air after the oxygen reaction is discharged after heat exchange and cooling.

[0068] Steps 1) - 6) are repeated cyclically to realize hydrogen production from syngas based on the NiO·Fe3O4 oxygen carrier in a three-bed circulation mode.

[0069] Example 2

[0070] According to Example 1, the value of a is changed to 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 respectively. The syngas feed temperatures are 450 and 500 °C respectively, and the oxygen carrier temperatures are 850 and 900 °C respectively. The rest of the operations are the same as those in Example 1.

[0071] Example 3

[0072] 1) 11704 kmol / h of syngas enters the gas-solid countercurrent moving bed reduction reactor from the bottom under the conditions of 400 °C and 1 atm. The Mn3O4·Fe3O4 oxygen carrier with a molar ratio b of 0.01 enters the gas-solid countercurrent moving bed reduction reactor from the top at 800 °C. The operation mode of the reduction reactor is atmospheric adiabatic operation. The syngas flows from bottom to top, and the Mn3O4·Fe3O4 oxygen carrier moves from top to bottom. The two react in a countercurrent mode, and the Mn3O4·Fe3O4 oxygen carrier oxidizes the syngas into CO2 and H2O.

[0073] 2) The mixture of CO2 and H2O is cooled to 120 °C in a heat exchanger and then fed into a condenser. The temperature of the condenser is set at 35 °C, and the water in the gas mixture can be condensed and separated out. The remaining CO2 enters a compressor and is pressurized to 153 atm for transportation and storage.

[0074] 3) The solid product MnO·FeO in the gas-solid countercurrent moving bed reduction reactor xIt is discharged from the bottom of the reactor at a temperature of about 850 °C and enters the top of the gas-solid countercurrent moving bed oxidation reactor. The operation mode of the oxidation reactor is atmospheric pressure adiabatic operation. 28000 kmol / h of water is heated from room temperature to 112 °C steam and then introduced into the bottom of the oxidation furnace, and reacts with the oxygen carrier MnO·FeO x to carry out a steam-iron countercurrent reaction to produce H2.

[0075] 4) Subsequently, the mixture of H2 and unreacted steam is cooled to 120 °C in a heat exchanger and then introduced into a flash tank. The temperature in the flash tank is set at 35 °C, and the unreacted water vapor can be condensed into water and separated. The remaining H2 is pressurized to 22 atm by a compressor for transportation and storage.

[0076] 5) The reacted oxygen carrier MnO·Fe3O4 is discharged from the bottom of the gas-solid countercurrent moving bed oxidation reactor and enters the combustion reactor to react with air and is re-oxidized to Mn3O4·Fe3O4. Among them, the air is preheated to 500 °C before entering the combustion reactor.

[0077] 6) The combustion products are sent to a gas-solid separator where gas-solid separation is carried out. Mn3O4·Fe3O4 is re-transported to the top of the gas-solid countercurrent moving bed reduction reactor, and the air after the oxygen reaction is discharged after heat exchange and cooling.

[0078] Steps 1)-6) are repeated to realize hydrogen production from syngas based on the three-bed circulation mode of the Mn3O4·Fe3O4 oxygen carrier.

[0079] Example 4

[0080] According to Example 3, the value of b is changed to 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 respectively. The syngas feed temperatures are 450 and 500 °C respectively, and the oxygen carrier temperatures are 850 and 900 °C respectively. The rest of the operations are the same as those in Example 3.

[0081] Example 5

[0082] 1) 11704 kmol / h of syngas enters the reduction reactor from the bottom at 400 °C and 1 atm. The oxygen carrier Cu2O·Fe3O4 with a molar ratio c of 0.01 enters from the top at 800 °C. The operation mode of the reduction reactor is atmospheric pressure adiabatic operation. The syngas flows from bottom to top, and the Cu2O·Fe3O4 oxygen carrier moves from top to bottom. The two react in a countercurrent mode, and the Cu2O·Fe3O4 oxygen carrier oxidizes the syngas into CO2 and H2O.

[0083] 2) The mixture of CO2 and H2O is cooled to 120 °C in a heat exchanger and then fed into a condenser. The temperature of the condenser is set at 35 °C, where the water in the gas mixture can be condensed and separated. The remaining carbon dioxide enters a compressor and is pressurized to 153 atm for transportation and storage.

[0084] 3) The solid product Cu·FeO in the reduction reactor x is discharged from the bottom of the reactor at a temperature of about 750 °C and enters the top of the oxidation furnace. The operation mode of the oxidation reactor is atmospheric adiabatic operation. 28000 kmol / h of water is heated from room temperature to 200 °C steam and fed into the bottom of the oxidation furnace, and reacts with the oxygen carrier Cu·FeO x in a countercurrent steam-iron reaction to produce H2.

[0085] 4) Subsequently, the mixture of H2 and unreacted steam is cooled to 120 °C in a heat exchanger and fed into a flash tank. The temperature in the flash tank is set at 35 °C, where the unreacted steam can be condensed into water and separated. The remaining H2 enters a compressor and is pressurized to 22 atm for transportation and storage.

[0086] 5) The oxygen carrier Cu·Fe3O4 after the reaction is discharged from the bottom of the oxidation bed and enters a fluidized bed combustor to react with air and is re-oxidized to Cu2O·Fe3O4. Among them, the air is preheated to 500 °C before entering the combustor.

[0087] 6) The combustion products are fed into a gas-solid separator, where gas-solid separation is carried out. Cu2O·Fe3O4 is re-transported to the top of the reduction reactor, and the air after the oxygen reaction is discharged after heat exchange and cooling.

[0088] Steps 1)-6) are repeated to realize hydrogen production from syngas based on the three-bed circulation mode of the Cu2O·Fe3O4 oxygen carrier.

[0089] Example 6

[0090] According to Example 5, the value of c is changed to 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 respectively. The syngas feed temperatures are 450 and 500 °C respectively, and the oxygen carrier temperatures are 850 and 900 °C respectively. The rest of the operations are the same as in Example 5.

[0091] The examples respectively explored the molar ratio a of the bimetallic oxygen carriers NiO and Fe3O4 (Examples 1-2), the molar ratio b of Mn3O4 and Fe3O4 (Examples 3-4), and the molar ratio c of Cu2O and Fe3O4 (Examples 5-6).

[0092] The results are as Figures 6 - 8As shown in Table 2, under the same operating conditions, when a is 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 respectively, b is 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 respectively, and c is 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 respectively, the cases where the syngas feed temperature is 400, 450, and 500 °C and the oxygen carrier temperature entering the reduction reactor is 800, 850, and 900 °C are discussed respectively.

[0093] Table 2 Influence of Bimetallic Molar Ratio on Maximum Hydrogen Production Efficiency at Different Syngas and Oxygen Carrier Feed Temperatures

[0094]

[0095]

[0096] When a = 0.01, 0.1, 0.2, 0.3, 0.4, and 0.5, NiO in the reduction reactor is preferentially reduced to Ni. Fe3O4 in the reduction reactor can be effectively reduced to Fe / FeO, reaching a low average valence state. And compared with traditional iron-based chemical looping hydrogen production, the maximum hydrogen production efficiency can be improved while ensuring a carbon capture rate of >99%. When a > 0.5, the relative decrease in the content of Fe3O4 leads to a decrease in the amount converted to Fe / FeO. Therefore, under the same steam feed, the maximum hydrogen production efficiency decreases. In addition, the heat released by the complete oxidation of Ni and air will cause the combustion reactor to overheat, shortening the service life of the oxygen carrier. If the gas flow rate is controlled to keep the temperature of the combustion reactor constant, Ni exists in the form of a mixture of unoxidized Ni and NiO. When the high-temperature solid enters the reduction reactor, the average valence state of Ni decreases, preventing it from being completely oxidized to CO2 and H2O in the reduction reactor. The unreacted CO and H2 reduce the carbon capture rate, resulting in waste of syngas.

[0097] When b = 0.01, 0.1, 0.2, 0.3, 0.4, and 0.5, Mn3O4 in the reduction reactor is preferentially reduced to MnO. Fe3O4 in the reduction reactor can be effectively reduced to Fe / FeO, achieving a low average valence state. And compared with traditional iron-based chemical looping hydrogen production, the maximum hydrogen production efficiency can be increased while ensuring a carbon capture rate of >99%. When b > 0.5, the relative decrease in the content of Fe3O4 leads to a decrease in the amount converted to Fe / FeO. Therefore, under the same steam feed, the maximum hydrogen production efficiency decreases. In addition, the heat released by the complete oxidation of MnO and air will cause the combustion reactor to overheat, shortening the service life of the oxygen carrier. If the gas flow rate is controlled to keep the temperature of the combustion reactor constant, Mn exists in the form of a mixture of unoxidized MnO and Mn3O4. When the high-temperature solid enters the reduction reactor, the average valence state of Mn decreases, preventing it from being completely oxidized to CO2 and H2O in the reduction reactor. The unreacted CO and H2 reduce the carbon capture rate, resulting in waste of syngas.

[0098] When c = 0.01, 0.1, 0.2, 0.3, 0.4, and 0.5, Cu2O in the reduction reactor is preferentially reduced to CuO. Fe3O4 in the reduction reactor can be effectively reduced to Fe / FeO, achieving a low average valence state. And compared with traditional iron-based chemical looping hydrogen production, the maximum hydrogen production efficiency can be increased while ensuring a carbon capture rate of >99%. When b > 0.5, the relative decrease in the content of Fe3O4 leads to a decrease in the amount converted to Fe / FeO. Therefore, under the same steam feed, the maximum hydrogen production efficiency decreases. In addition, the heat released by the complete oxidation of Cu and air will cause the combustion reactor to overheat, shortening the service life of the oxygen carrier. If the gas flow rate is controlled to keep the temperature of the combustion reactor constant, Cu exists in the form of a mixture of unoxidized Cu and Cu2O. When the high-temperature solid enters the reduction reactor, the average valence state of Cu decreases, preventing it from being completely oxidized to CO2 and H2O in the reduction reactor. The unreacted CO and H2 reduce the carbon capture rate, resulting in waste of syngas.

[0099] Thus, according to Figures 6 - 8 and Table 2, when the values of a, b, and c are between greater than 0 and less than or equal to 0.5, the maximum hydrogen production efficiency can be effectively increased. When the value > 0.5, the maximum hydrogen production efficiency decreases significantly.

[0100] For the technical solutions disclosed and proposed in the present invention, those skilled in the art can achieve them by referring to the content herein and appropriately changing conditions, routes and other aspects. Although the methods and preparation techniques of the present invention have been described through preferred embodiments, it is obvious that relevant technicians can make changes or re-combinations to the methods and technical routes described herein without departing from the content, spirit and scope of the present invention to achieve the final preparation technique. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all regarded as being included in the spirit, scope and content of the present invention.

Claims

1. A dual-metal three-bed chemical looping hydrogen production method, which includes the following steps: (1) Feed syngas and the dual-metal oxygen carrier into a moving bed reduction reactor to carry out a chemical looping combustion reaction and capture CO2 gas; (2) Transport the reduced dual-metal oxygen carrier obtained in step (1) to a moving bed oxidation reactor to carry out a chemical looping reforming reaction with steam to produce hydrogen, and at the same time, the dual-metal oxygen carrier is partially oxidized; (3) Transport the partially oxidized dual-metal oxygen carrier obtained in step (2) to a combustion reactor, and regenerate the dual-metal oxygen carrier that meets the requirements for entering the reduction bed reactor by being oxidized by fresh air, and the regenerated dual-metal oxygen carrier is carried out of the reactor by high-speed air to a gas-solid separator; (4) After gas-solid separation by the gas-solid separator, the dual-metal oxygen carrier re-enters the moving bed reduction reactor to carry out a chemical looping combustion reaction with syngas and is recycled; Steps (1), (2), (3) and (4) are repeated cyclically to achieve hydrogen production from syngas by the dual-metal oxygen carrier based on a three-bed circulation mode.

2. The method for producing hydrogen by chemical looping with a dual-metal three-bed according to claim 1, characterized in that, The dual-metal oxygen carrier is a NiO·Fe3O4 oxygen carrier, a Mn3O4·Fe3O4 oxygen carrier or a Cu2O·Fe3O4 oxygen carrier; the product after combustion in step (3) is a mixture of Fe3O4 and NiO / Mn3O4 / Cu2O, and there is no Fe2O3.

3. A method for chemical-looping hydrogen production with a dual-metal three-bed according to claim 2, characterized in that, The molar ratio of NiO, Mn3O4 or Cu2O to Fe3O4 in the dual-metal oxygen carrier is greater than 0 and less than or equal to 0.

5.

4. A method for chemical-looping hydrogen production with a dual-metal three-bed according to claim 1, characterized in that, The operation modes of the moving bed reduction reactor and the moving bed oxidation reactor are gas-solid countercurrent.

5. A dual-metal three-bed chemical-looping hydrogen production method according to claim 1, characterized in that, The temperature of the syngas in step (1) is 400 - 500 °C, and the temperature of the dual-metal oxygen carrier before being fed into the moving bed reduction reactor in step (1) is 800 - 900 °C.

6. A dual-metal three-bed chemical looping hydrogen production method according to claim 1, characterized in that, In step (1), the combustion gas is cooled, condensed and separated to obtain CO2 and compressed.

7. A dual-metal three-bed chemical-looping hydrogen production method according to claim 1, characterized in that, The temperature of the dual-metal oxygen carrier before being fed into the moving bed oxidation reactor in step (2) is 700 - 800 °C.

8. A method for hydrogen production by chemical looping with a dual-metal three-bed according to claim 1, characterized in that The reaction gas in step (2) is cooled and flash-separated to obtain H2 and compressed.

9. A dual-metal three-bed chemical-looping hydrogen production method according to claim 1, characterized in that, The temperature of the dual-metal oxygen carrier before being fed into the combustion reactor in step (3) is 500 - 800 °C, and the temperature of the fresh air in step (3) is 400 - 600 °C.

10. A dual-metal three-bed chemical-looping hydrogen production method according to claim 1, characterized in that, The combustion reactor in step (3) is a fluidized bed reactor.

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