Hydrogen production system

Abstract

To provide a new hydrogen production system capable of efficiently producing hydrogen while considering the influence on the environment.SOLUTION: A hydrogen production system includes a metal oxide reactor 10 filled with a nickel-supported cerium oxide-titanium oxide catalyst, a shift reactor 20 filled with a shift catalyst and into which a gas flowing out of the metal oxide reactor 10 flows, and a separator 30 that separates carbon dioxide from the gas flowing out of the shift reactor 20 to take out hydrogen, in which a part of the carbon dioxide separated by the separator 30 flows into the metal oxide reactor 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hydrogen production system. [Background technology]

[0002] Carbon dioxide reduction, which recycles carbon dioxide, a greenhouse gas, into a useful resource, has attracted attention. For example, Non-Patent Document 1 discloses a method using metal oxides to reduce carbon dioxide to obtain carbon monoxide (Non-Patent Document 1). Carbon monoxide, obtained by reducing carbon dioxide, can be used for, for example, the production of chemical raw materials and the heat treatment of metals. However, because its industrial uses are limited, it is necessary to convert it into a more useful energy medium.

[0003] On the other hand, hydrogen is attracting attention as a next-generation energy source because it does not produce carbon dioxide. Known systems for producing hydrogen while being environmentally friendly include a method in which hydrogen is produced in a steam methane reformer or a coal gasifier, and then the carbon monoxide obtained together with the hydrogen is introduced into a shift reactor to produce more hydrogen (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2023-550152 [Patent Document 2] Patent No. 5781368 [Non-patent literature]

[0005] [Non-Patent Document 1] Chongyan Ruan et al., Energy Environmental Science, 2 , 2019, 767. Summary of the Invention [Problem to be solved by the invention]

[0006] The methods described in Patent Documents 1 and 2 can produce hydrogen, a clean energy source. However, in light of the increasing demand for hydrogen in recent years, there is a need to produce hydrogen more efficiently while taking into account its impact on the environment. The present invention has been made in view of the above circumstances, and provides a new hydrogen production system that can efficiently produce hydrogen while taking into consideration the impact on the environment. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention employs the following configuration. [1] A hydrogen production system comprising: a metal oxide reactor packed with a nickel-supported cerium oxide-titanium oxide catalyst; a shift reactor packed with a shift catalyst and into which gas flowing out from the metal oxide reactor flows; and a separation device that separates carbon dioxide from the gas flowing out from the shift reactor to extract hydrogen, wherein a portion of the carbon dioxide separated by the separation device flows into the metal oxide reactor. [2] The hydrogen production system according to [1], wherein a portion of the gas flowing out from the shift reactor, in addition to a portion of the carbon dioxide separated by the separation device, flows into the metal oxide reactor. [3] The hydrogen production system according to [1] or [2], wherein in addition to the gas flowing out from the metal oxide reactor, the gas flowing out from the steam methane reformer flows into the shift reactor. [4] The hydrogen production system according to [1] or [2], wherein in addition to the gas flowing out from the metal oxide reactor, the gas flowing out from the autothermal reformer flows into the shift reactor. [5] The hydrogen production system according to [1] or [2], wherein in addition to the gas flowing out from the metal oxide reactor, the gas flowing out from the partial oxidation reformer flows into the shift reactor. [6] The hydrogen production system according to [1] or [2], wherein in addition to the gas flowing out from the metal oxide reactor, the gas flowing out from the coal gasification furnace flows into the shift reactor. [7] The hydrogen production system according to any one of [1] to [6], wherein the ratio of the amount of hydrogen to the total amount of hydrogen and carbon dioxide in the total gas flowing into the metal oxide reactor is 1 to 50%. [Effects of the Invention]

[0008] According to the hydrogen production system of the present invention, hydrogen can be produced efficiently while taking into consideration the impact on the environment. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of a hydrogen production system according to a first embodiment. [Figure 2] FIG. 1 is a diagram illustrating a schematic diagram of an embodiment of a separation device. [Figure 3] FIG. 10 is a diagram schematically illustrating another embodiment of the separation device. [Figure 4] FIG. 1 is a schematic configuration diagram of a hydrogen production system according to a second embodiment. [Figure 5] FIG. 10 is a schematic configuration diagram of a hydrogen production system according to a third embodiment. [Figure 6] This is the model used in the simulation. DETAILED DESCRIPTION OF THE INVENTION

[0010] In this specification and claims, a numerical range expressed by "to" means a numerical range in which the numbers before and after "to" are the lower and upper limits. The amounts and proportions of each gas are based on the volume at standard conditions (101,325 Pa, 0°C).

[0011] First Embodiment A hydrogen production system according to a first embodiment of the present invention will be described with reference to FIG. The hydrogen production system of this embodiment includes a metal oxide reactor 10, a shift reactor 20, and a separation device 30.

[0012] The hydrogen production system of this embodiment forms a circulation flow path in which gas flowing out from the metal oxide reactor 10 flows into the shift reactor 20, gas flowing out from the shift reactor 20 flows into the separation device 30, and a portion of the carbon dioxide separated in the separation device 30 flows into the metal oxide reactor 10, and the hydrogen separated in the separation device 30 is recovered.

[0013] [Metal oxide reactor] The metal oxide reactor 10 is filled with a nickel-supported cerium oxide-titanium oxide catalyst (hereinafter sometimes referred to as "thermal catalyst"). When the thermal catalyst is heated, oxygen inside is removed, creating oxygen vacancies, which then deprive the catalyst of oxygen, and the catalyst has a reducing effect. Therefore, when carbon dioxide is introduced into the metal oxide reactor 10 under heating, carbon dioxide is reduced to carbon monoxide.

[0014] It is preferable to introduce hydrogen together with carbon dioxide into the metal oxide reactor 10. The hydrogen supply source may be a part of the gas flowing out from the shift reactor 20 described below, a part of the hydrogen flowing out from the separation device 30, or any other source. When hydrogen is introduced together with carbon dioxide, the reaction of formula (1) based on oxygen vacancies and the reverse shift reaction shown in formula (2) occur.

[0015] CO2 → CO (1) CO2 + H2 → CO + H2O (2) The ratio of the amount of carbon monoxide obtained by reduction to the amount of carbon dioxide introduced (hereinafter sometimes referred to as "reduction rate") tends to increase as the amount of hydrogen introduced together with carbon dioxide increases.

[0016] However, since increasing the amount of hydrogen introduced increases the amount of hydrogen consumed in the metal oxide reactor 10, it is not preferable to introduce a large amount of hydrogen. The ratio of the amount of hydrogen to the total amount of introduced carbon dioxide and hydrogen (hereinafter sometimes referred to as "hydrogen introduction rate") is preferably 1 to 50%, more preferably 5 to 40%, and even more preferably 10 to 30%.

[0017] The thermal catalyst can be produced by preparing CeO2-TiO2 using the coprecipitation method, then supporting Ni by impregnation, and then pulverizing it. CeO2 has the property of removing oxygen from its lattice at high temperatures. Furthermore, by combining TiO2 with CeO2, the bond between the cerium atom and the oxygen atom is weakened, making it easier to remove oxygen. Ni acts as a catalyst that lowers the energy barrier between the reactions of formula (1) and (2) above.

[0018] The molar ratio of cerium to titanium [Ce:Ti] in CeO2-TiO2 is preferably 0.1 to 10: 1, and more preferably 1 to 4: 1. The amount of supported nickel is preferably 0.1 to 20 mass % of CeO2-TiO2, and more preferably 0.5 to 10 mass %.

[0019] The average particle size of the thermal catalyst after pulverization is preferably 1 to 1,000 nm, more preferably 10 to 500 nm, where the average particle size is the average particle size on a mass basis calculated from the specific surface area and density. When the average particle size of the thermal catalyst is equal to or less than the upper limit of the above-mentioned preferred range, the specific surface area increases, and the reaction of formula (1) becomes possible even at a low reaction temperature.

[0020] The reaction temperature in the metal oxide reactor 10 is preferably 300 to 1,600°C, and more preferably 500 to 1,200°C. By setting the reaction temperature at or above the lower limit of the above-mentioned preferred range, the reaction of formula (1) can be sufficiently promoted. On the other hand, by setting the reaction temperature at or below the upper limit of the above-mentioned preferred range, the crystal structure upon firing can be easily maintained, cycle stability can be improved, and a good reduction rate can be maintained for a long period of time.

[0021] The pressure during the reaction in the metal oxide reactor 10 is preferably from atmospheric pressure to 5.0 MPa g, more preferably from atmospheric pressure to 4.0 MPa g. If the pressure is increased in the upstream stage of the metal oxide reactor 10 so that the pressure during the reaction is near the upper limit of the above-mentioned preferred range, the temperature of the reaction gas can be increased, and additional input energy can be reduced.

[0022] A nickel-supported cerium oxide-titanium oxide catalyst with oxygen vacancies can be expressed as "Ni / Ce2Ti2O7" when the molar ratio of cerium to titanium [Ce:Ti] is 1:1. A nickel-supported cerium oxide-titanium oxide catalyst without oxygen vacancies can be expressed as "Ni / CeO2TiO2" when the molar ratio of cerium to titanium [Ce:Ti] is 1:1.

[0023] A thermal catalyst that has lost its oxygen vacancies can be regenerated to have oxygen vacancies by heating. The heating temperature during regeneration is preferably 300 to 1,600°C, and more preferably 500 to 1,200°C.

[0024] By setting the heating temperature during regeneration at or above the lower limit of the above-mentioned preferred range, oxygen vacancies can be sufficiently restored, while by setting the heating temperature at or below the upper limit of the above-mentioned preferred range, the crystal structure upon firing can be easily maintained, cycle stability can be improved, and a good reduction rate can be maintained for a long period of time. There are no particular conditions for the pressure during regeneration of the metal oxide reactor 10 .

[0025] It is preferable to use solar heat or exhaust heat to heat the metal oxide reactor 10 to the temperature required for use or regeneration, but any shortfall can be made up by a heater or the like. A preferred method for utilizing the exhaust heat is to use a heat exchanger such as the gas / gas heat exchanger of the second embodiment described below.

[0026] To continuously carry out the reaction in the metal oxide reactor 10, for example, as shown schematically in FIG. 2, a first reaction vessel 11 and a second reaction vessel 12 are prepared, and the second reaction vessel 12 is used while the thermal catalyst layer (first packed layer 13) of the first reaction vessel 11 is being regenerated, and the first reaction vessel 11 is used while the thermal catalyst layer (second packed layer 14) of the second reaction vessel 12 is being regenerated.

[0027] During regeneration under heating, the thermal catalyst in the first packed bed 13 changes from "Ni / CeO2TiO2" to "Ni / Ce2Ti2O7", for example, and the released oxygen can be removed by pushing it out with an inert gas. The thermal catalyst of the second packed bed 14 in use under heating changes, for example, from "Ni / Ce2Ti2O7" to "Ni / CeO2TiO2," and converts the incoming carbon dioxide and hydrogen into carbon monoxide and water.

[0028] Also, as shown in FIG. 3, for example, a cylindrical reaction vessel 15 may be separated into a first chamber 18 and a second chamber 19 by a partition wall 17 that divides the reaction vessel 15 along its diameter, and the thermal catalyst layer (packed layer 16) may be made rotatable between the first chamber 18 and the second chamber 19. It should be noted that the partition walls 17 have portions 17a that divide the packed bed 16 in half, and are separated from the partition walls 17 above and below the packed bed 16, and can rotate together with the packed bed 16.

[0029] The right-hand portion of the packed bed 16, which has rotated to become the first chamber 18 side, is being regenerated under heating, and the thermal catalyst in that portion changes, for example, from "Ni / CeO2TiO2" to "Ni / Ce2Ti2O7," and the released oxygen can be removed by pushing it out with an inert gas. The left-hand side portion of the packed bed 16, which has rotated to become the second chamber 19 side, is in use under heating, and the thermal catalyst in that portion changes, for example, from "Ni / Ce2Ti2O7" to "Ni / CeO2TiO2," and converts the incoming carbon dioxide and hydrogen into carbon monoxide and water. In FIG. 3, the gas flows in the first chamber 18 and the second chamber 19 in the same direction, but they may flow in opposite directions (counterflow).

[0030] [Shift reactor] The shift reactor 20 is filled with a shift catalyst. Any known shift catalyst can be used. In the shift reactor 20, a shift reaction of the following formula (3) occurs.

[0031] CO + H2O → CO2 + H2 (3) The water used in the reaction of formula (3) can be supplied from the water produced by formula (2) in the metal oxide reactor 10, but if this is insufficient, it may be supplied directly to the shift reactor 20 from a separate source.

[0032] It is preferable to use two or more shift reactors as the shift reactor 20, each packed with a shift catalyst having different temperature characteristics, etc. A typical shift reactor 20 is equipped with a high-temperature shift reactor packed with a shift catalyst that can withstand high temperatures on the upstream side of the gas stream and a low-temperature shift reactor packed with a shift catalyst suitable for use at low temperatures on the downstream side. If necessary, a bypass line may be provided to return a part of the gas flowing out from any one of the shift reactors to the upstream side.

[0033] The reason for providing two stages of shift reactors 20, one for high temperature and one for low temperature, is that when the carbon monoxide concentration is high, a large amount of heat is generated during the reaction. That is, gas with a high carbon monoxide concentration is first reacted in a high-temperature shift catalyst, which has a high heat resistance, and then cooled in a cooler and reacted in a low-temperature shift catalyst, which has a low catalyst heat resistance limit temperature. In addition, to prevent the shift reaction from proceeding all at once, multiple high-temperature shift reactors may be provided.

[0034] High-temperature shift catalysts that can withstand high temperatures include iron-chromium catalysts, while low-temperature shift catalysts suitable for use at low temperatures include copper-zinc catalysts. The operating temperature of the high-temperature shift catalyst is about 300 to 500°C, and the operating temperature of the low-temperature shift catalyst is about 180 to 290°C. To obtain a high shift reaction rate, the shift reaction must be carried out at a low temperature. However, a high-temperature shift catalyst has a wider operating temperature range than a low-temperature shift catalyst, which is advantageous for operational control.

[0035] The pressure during the reaction in the shift reactor 20 is set so that the water introduced does not condense, i.e., so that the water can remain in a gaseous (vapor) state. The specific preferred pressure depends on the temperature.

[0036] [Separation device 30] The separation device 30 is a device that separates carbon dioxide from the gas flowing out of the shift reactor 20 and extracts hydrogen. Methods for separating carbon dioxide from mixed gases include chemical absorption, physical adsorption, and membrane separation.

[0037] 1 shows a separation device 30 including a carbon dioxide absorption tower 31 and a carbon dioxide regeneration tower 32. The carbon dioxide absorption tower 31 is a chemical absorption tower in the case of a chemical absorption method, and is a physical absorption tower in the case of a physical adsorption method. Hereinafter, a detailed description will be given of an example in which the separation device 30 is based on the amine absorption method using an amine absorption liquid for the chemical absorption method.

[0038] In the amine absorption method, the carbon dioxide in the gas is selectively absorbed by the amine absorbing solution in the carbon dioxide absorption tower 31 by countercurrently contacting the inflowing gas with the amine absorbing solution. The amine absorbing solution that has absorbed the carbon dioxide is then transferred to the carbon dioxide regeneration tower 32. In the carbon dioxide regeneration tower 32, steam is supplied to the attached reboiler to heat and regenerate the amine absorbing solution, and the carbon dioxide is separated from the amine absorbing solution. The amine absorbing solution from which the carbon dioxide has been separated is cooled in a heat exchanger and a cooler, and then supplied to the carbon dioxide absorption tower 31 again.

[0039] The hydrogen from which carbon dioxide has been separated in the separator 30 is purified as necessary and then recovered. The purification method typically involves the use of a pressure swing adsorption unit, but cryogenic separation may be used in place of or in addition to the pressure swing adsorption unit.

[0040] A portion of the carbon dioxide separated in the separator 30 is supplied to the metal oxide reactor 10. Since the gas (carbon dioxide) flowing out of the separator 30 has a reduced pressure, it may be compressed by a compressor 40 to a pressure suitable for the metal oxide reactor 10 before being supplied to the metal oxide reactor 10. The remaining carbon dioxide is processed using known carbon dioxide capture and storage (CCS) technology.

[0041] Second Embodiment A hydrogen production system according to a second embodiment of the present invention will be described with reference to Fig. 4. In Fig. 4, the same components as those in the first embodiment are denoted by the same reference numerals as in Fig. 1, and detailed description thereof will be omitted.

[0042] The hydrogen production system of this embodiment includes a reformer 50 in addition to the same components as those in FIG. 1, and in addition to the gas flowing out from the metal oxide reactor 10, the gas flowing out from the reformer 50 also flows into the shift reactor 20. Furthermore, in addition to a portion of the carbon dioxide separated in the separator 30, a portion of the gas flowing out from the shift reactor 20 flows into the metal oxide reactor 10.

[0043] A part of the carbon dioxide separated in the separation device 30 is compressed by a first compressor 41, and a part of the gas flowing out from the shift reactor 20 is compressed by a second compressor . The gases that have been pressurized are joined together and introduced into a gas / gas heat exchanger 44, where they are heated by heat exchange with the gas that has flowed out of the metal oxide reactor 10.

[0044] In this embodiment, an example of a method for purifying hydrogen is shown, in which a pressure swing adsorption device 51 is used. In order to increase the purity of hydrogen, the off-gas coming out of the pressure swing adsorption device 51 is combined with the fuel gas and used to heat the reformer 50. In the case of a steam methane reforming method in which the reformer 50 is a steam methane reformer, the desulfurized natural gas is introduced into the reformer 50, and the reforming reaction of the following formula (4) occurs. CH4 + H2O → CO + 3H2 (4)

[0045] In the case of an autothermal reforming method in which the reformer 50 is an autothermal reformer, desulfurized natural gas is introduced into the reformer 50, and in addition to the reforming reaction of the above formula (4), a partial oxidation reaction of the following formula (5) occurs. 2CH4 + O2 → 2CO + 4H2 (5) In the autothermal reforming method, the heat generated by the partial oxidation reaction of the above formula (5) is utilized for the endothermic steam reforming reaction of the above formula (4), and reforming is carried out without an external heat supply.

[0046] In the case of a partial oxidation method in which the reformer 50 is a partial oxidation type reformer, the desulfurized natural gas is introduced into the reformer 50, and the partial oxidation reaction of the above formula (5) occurs. In the partial oxidation method, the necessary heat is provided by the heat generated by the partial oxidation reaction of the above formula (5).

[0047] The reformer 50 is often used together with the shift reactor 20 to further produce hydrogen from the carbon monoxide generated by formula (4). Therefore, the system of this embodiment can be constructed by essentially simply adding the metal oxide reactor 10 and its peripheral devices to an existing hydrogen production system using the reformer 50.

[0048] Third Embodiment A hydrogen production system according to a third embodiment of the present invention will be described with reference to Fig. 5. In Fig. 5, components similar to those in the first or second embodiment are denoted by the same reference numerals as in Figs. 1 and 4, and detailed descriptions thereof will be omitted.

[0049] The hydrogen production system of this embodiment includes a coal gasification furnace 60 in addition to the same components as those in FIG. 1 , and in addition to the gas flowing out from the metal oxide reactor 10, the gas flowing out from the coal gasification furnace 60 also flows into the shift reactor 20. The gas flowing out from the coal gasifier 60 is purified by a gas purification facility, and is heat exchanged in a gas / gas heat exchanger 64 before being introduced into the shift reactor 20.

[0050] FIG. 5 shows a gas purification facility that includes a first water washing tower 61, a COS converter 63, a second water washing tower 62, and a desulfurization facility 70. The desulfurization equipment 70 shown includes a desulfurization tower 71 and a regeneration tower 72 . In this embodiment, in order to increase the purity of the recovered hydrogen, purification equipment such as a pressure swing adsorption device can be used, as in the second embodiment.

[0051] The coal gasifier 60 is often used together with the shift reactor 20 to further produce hydrogen from carbon monoxide that is generated together with hydrogen. Therefore, the system of this embodiment can be constructed by essentially simply adding the metal oxide reactor 10 and its peripheral devices to an existing hydrogen production system that uses a coal gasifier 60. [Example]

[0052] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0053] <Preparation of thermal catalyst> After preparing CeO2-TiO2 (Ce:Ti=4:1, molar ratio) using the coprecipitation method, 5 wt% of Ni was supported on the CeO2-TiO2 by the impregnation method.Then, it was ground in a 0.5 mm diameter bead mill at 3884 rpm for 30 minutes to obtain a thermal catalyst.

[0054] <Experimental Example> [Experimental Methods and Results] Carbon dioxide reduction experiments were carried out on the obtained thermal catalyst, and the reduction rate depending on the hydrogen introduction rate was investigated. In the carbon dioxide reduction experiment, as a pretreatment, a U-shaped quartz tube filled with 0.02 g of the synthesized thermal catalyst was placed in an oven at 900°C, and helium was flowed through the U-shaped quartz tube at 30 mL / min for 10 minutes.

[0055] Next, while the oven was maintained at 900°C, a reduction treatment was carried out by flowing a mixed gas of carbon dioxide and hydrogen in a specified ratio, instead of helium, into the U-shaped quartz tube at 15 mL / min. The composition of the outflowing gas was analyzed using a mass spectrometer, and the ratio of the carbon monoxide concentration to the total concentration of carbon dioxide and carbon monoxide was taken as the reduction rate.

[0056] The combination of the above pretreatment and reduction treatment was counted as one cycle, and 50 cycles were repeated, and the average reduction rate for the 50 cycles was calculated. As a result, when the hydrogen introduction rate of the mixed gas was 20% (CO2: 12 mL / min, H2: 3.0 mL / min), the average reduction rate was 39%. In addition, when the hydrogen introduction rate of the mixed gas was 30% (CO2: 10.5 mL / min, H2: 4.5 mL / min), the average reduction rate was 55%.

[0057] [Consideration] When the hydrogen introduction rate is 20%, the average reduction rate is 39%, so 4.68 mL / min (12 x 0.39) of hydrogen is obtained from 12 mL / min of carbon dioxide. On the other hand, 3.0 mL / min of hydrogen is thought to be consumed by the reverse shift reaction. Therefore, the increased hydrogen production rate using the U-shaped quartz tube filled with the thermal catalyst is 1.68 mL / min (4.68 - 3.0).

[0058] When the hydrogen introduction rate is 30%, the average reduction rate is 55%, so 5.775 mL / min (10.5 x 0.55) of hydrogen is obtained from 10.5 mL / min of carbon dioxide. On the other hand, 4.5 mL / min of hydrogen is thought to be consumed by the reverse shift reaction. Therefore, the increased hydrogen production rate using the U-shaped quartz tube filled with the thermal catalyst is 1.275 mL / min (5.775 - 4.5).

[0059] From the above, it was found that hydrogen production can be increased even with a hydrogen introduction rate of 30%, but that hydrogen production can be increased more efficiently with a hydrogen introduction rate of 20%. The increase in production is believed to be due to a reduction effect caused by oxygen vacancies in the thermal catalyst taking away oxygen.

[0060] <Calculating energy efficiency> [Simulation and Results] Simulations were performed to determine the degree of energy efficiency with which the system of the present invention, which uses a metal oxide reactor 10 in addition to a reformer 50 and a shift reactor 20, can increase hydrogen production when the hydrogen introduction rate is 20%, compared to when hydrogen is produced using only a reformer 50 and a shift reactor 20. The reformer 50 was a steam methane reformer.

[0061] The simulation was performed according to the model shown in Fig. 6. In Fig. 6, the same components as those in the second embodiment are denoted by the same reference numerals as in Fig. 4, and their description will be omitted. In the model of Fig. 6, a steam generator 43 and a preheater 45 are added to the components of the second embodiment. In the simulation, a physical absorption model was adopted for the carbon dioxide separation device.

[0062] In the steam generator 43, heat is exchanged between the water and the high-temperature gas flowing out from the metal oxide reactor 10, thereby evaporating the water. In the preheater 45, heat is exchanged between the obtained steam and the gas before it flows into the gas / gas heat exchanger 44. As a result, the gas that has been heated to a certain extent is introduced into the gas / gas heat exchanger 44.

[0063] According to this model, the increased hydrogen production amount and required additional energy were calculated under the following conditions using Aspen Plus V14, a process simulation software manufactured by AspenTech Japan Co., Ltd.

[0064] 1. The desulfurized natural gas is subjected to steam methane reforming (SMR) in the reformer 50 (CH4 + H2O ⇒ CO + 3H2). 2. Gas flowing out of the reformer (flow rate: approx. 460,000 Nm 3 / h) is passed through the shift reactor 20 to cause a shift reaction (CO+H2O⇒CO2+H2).

[0065] 3. Gas branched from the shift reactor 20 (flow rate: approximately 370,000 Nm 3 / h) is separated into carbon dioxide gas and hydrogen gas in a separator 30. The separated hydrogen gas (flow rate: about 300,000 Nm 3 / h) is purified in the pressure swing adsorption device 51 and produced as pure hydrogen (approximately 230,000 Nm 3 / h). 4. The off-gas (flow rate: approximately 70,000 Nm) that comes out to increase the purity in the pressure swing adsorption device 51 3 / h) The fuel is combined with the heating fuel in the reformer 50 and combusted.

[0066] 5. The gas (approximately 1,000 Nm) branched from the shift reactor 20 3 / h) and the gas (approximately 3,000 Nm 3 / h, approximately 5% of the carbon dioxide recovered in the separation device 30) is compressed to 2.6 MPag and 0.07 MPag to 3.5 MPag in compressors 42 and 41, respectively. 6. The gas pressurized by the compressors 42 and 41 is heated to 900°C by heat exchange in the preheater 45 and the gas / gas heat exchanger 44, and by a heater. It is then introduced into the metal oxide reactor 10, where carbon dioxide is reduced to carbon monoxide.

[0067] 7. The remaining gas (flow rate: about 70,000 Nm3) after being branched and sent to the first compressor 41 from the gas flowing out of the separator 30 3 / h) is recovered as carbon dioxide. 8. Outlet gas of metal oxide reactor 10 (flow rate: approximately 4,000 Nm 3 / h) is heat exchanged in a steam generator 43 and a gas / gas heat exchanger 44, and then introduced before the shift reactor 20 and merged with the gas after the outlet of the reformer 50.

[0068] In addition, the gas flowing out from shift reactor 20 has the pressure, temperature, and composition shown in Table 1, the gas flowing out from separation device 30 has the pressure, temperature, and composition shown in Table 2, and the gas flowing out from pressure swing adsorption device 51 has the pressure, temperature, and composition shown in Table 3. Here, the pressure, temperature, and composition in Tables 1 to 3 are the results obtained by simulation based on the pressure, temperature, and composition of natural gas described in the literature (NATIONAL ENERGY TECHNOLOGY LABORATORY, "COMPARISON OF COMMERCIAL, STATE OF THE ART, FOSSIL BASED HYDROGEN PRODUCTION TECHNOLOGIES" April 12, 2022) and the flow rates described in Tables 1 to 3.

[0069] [Table 1]

[0070] [Table 2]

[0071] [Table 3]

[0072] The flow rate of the gas flowing from the shift reactor 20 to the metal oxide reactor 10 is 1,090 Nm 3 / h, and the flow rate of gas flowing from the separator 30 into the metal oxide reactor 10 is 2,999 Nm 3 / h, the ratio of the amount of hydrogen to the total amount of hydrogen and carbon dioxide in all gases flowing into the metal oxide reactor 10 (hydrogen introduction rate) becomes about 20%.

[0073] The flow rate of gas flowing out of the pressure swing adsorption device 51 was calculated using Aspen Plus V14 and was found to be 228,090 Nm 3 / h, and the amount of hydrogen obtained per hour is 228,045 Nm3 of pure hydrogen. 3 / h. On the other hand, when the entire amount of gas flowing out of the shift reactor 20 is sent to the separator 30 and the carbon dioxide separated from hydrogen in the separator 30 is not sent to the metal oxide reactor 10 but is entirely recovered as carbon dioxide, the flow rate of the gas flowing out of the pressure swing adsorption unit 51 is calculated using Aspen Plus V14 and is found to be 227,779 Nm 3 / h, and the amount of hydrogen obtained per hour is 227,734 Nm3 of pure hydrogen. 3 / h. As a result, the hydrogen production increase due to the addition of a route via the metal oxide reactor 10 is 311 Nm 3 / h was calculated.

[0074] In addition, this increased production volume of 311 Nm 3 The additional energy required per hour to obtain this was as follows. Note that utilities such as steam and water and the endothermic reaction due to carbon dioxide reduction were not taken into account.

[0075] The total energy required to pressurize the air from 0.07 MPa to 3.5 MPa in the first compressor 41 and the energy required to pressurize the air from 2.6 MPa to 3.5 MPa in the second compressor 42: 442.5 kW. The energy of the electric heater that compensates for the portion that cannot be heated by heat exchange when heating the gas flowing into the metal oxide reactor 10 to 900°C: 972.8 kW. Increase in facility energy consumption due to increased circulation gas volume (5%): 363.7kW. Total: 1779kW.

[0076] [Consideration] From the above results, it can be seen that, according to the present invention, by adding the process via the metal oxide reactor 10, an additional energy of 1779 kW can be used to produce 311 Nm per hour. 3of hydrogen production, i.e., 5.7kW / Nm 3 This suggests that hydrogen production can be increased using approximately the same amount of energy as hydrogen production using water electrolysis. Therefore, it has been found that the present invention makes it possible to increase blue hydrogen production with efficiency comparable to that of hydrogen production by water electrolysis, by simply investing in additional equipment, such as the metal oxide reactor 10 and its related equipment. [Explanation of symbols]

[0077] 10 Metal Oxide Reactor 20 Shift reactor 30 Separation device 31 Carbon dioxide absorption tower 32 Carbon dioxide regeneration tower 40 Compressor 4 43 Steam Generator 44 Gas / gas heat exchanger 45 Preheater 50 Reformer 51 Pressure Swing Adsorption Device 60 Coal Gasifier 64 Gas / Gas Heat Exchanger 70 Desulfurization equipment

Claims

1. A hydrogen production system comprising: a metal oxide reactor packed with a nickel-supported cerium oxide-titanium oxide catalyst; a shift reactor packed with a shift catalyst and into which gas flowing out from the metal oxide reactor flows; and a separation device that separates carbon dioxide from the gas flowing out from the shift reactor to extract hydrogen, wherein a portion of the carbon dioxide separated by the separation device flows into the metal oxide reactor.

2. The hydrogen production system according to claim 1 , wherein a portion of the gas flowing out from the shift reactor, in addition to a portion of the carbon dioxide separated by the separation device, flows into the metal oxide reactor.

3. 3. The hydrogen production system according to claim 1, wherein in addition to the gas flowing out from the metal oxide reactor, the gas flowing out from the steam methane reformer flows into the shift reactor.

4. 3. The hydrogen production system according to claim 1, wherein in addition to the gas flowing out from the metal oxide reactor, the gas flowing out from the autothermal reformer flows into the shift reactor.

5. 3. The hydrogen production system according to claim 1, wherein in addition to the gas flowing out from the metal oxide reactor, the gas flowing out from the partial oxidation reformer flows into the shift reactor.

6. 3. The hydrogen production system according to claim 1, wherein in addition to the gas flowing out from the metal oxide reactor, a gas flowing out from a coal gasifier flows into the shift reactor.

7. 3. The hydrogen production system according to claim 1, wherein the ratio of the amount of hydrogen to the total amount of hydrogen and carbon dioxide in all gases flowing into the metal oxide reactor is 1 to 50%.

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