Hydrogen production device

Abstract

Provided is a technology that makes it possible to reduce the amount of carbon dioxide emitted during production of hydrogen. This hydrogen production device comprises: a detonation-type combustion furnace that uses supplied hydrogen and supplied oxidation gas to cause detonation; and a decomposition furnace that thermally decomposes supplied hydrocarbon to generate hydrogen and carbon, wherein one furnace among the detonation-type combustion furnace and the decomposition furnace is formed in a cylindrical shape extending in the longitudinal direction, and is provided inside the other furnace formed in a tubular shape extending in the longitudinal direction.

Description

Hydrogen production equipment

[0001] This application is based on Japanese Patent Application No. 2023-136570, filed on August 24, 2023, the contents of which are incorporated herein by reference.

[0002] The use of hydrogen is expected to achieve carbon neutrality. Methane pyrolysis is sometimes used as a method for producing hydrogen. ４ →C+2H ２ Pulse methane pyrolysis (PMP) is known as one of the hydrogen production methods (see, for example, Patent Document 1). PMP is a method of heating methane by mixing combustion exhaust gas from intermittent methane deflagration with raw methane.

[0003] Japanese Patent Application Laid-Open No. 2022-094918

[0004] In PMP, carbon dioxide is emitted when hydrogen is produced, so there is room for further improvement in terms of reducing carbon dioxide emissions when hydrogen is produced.

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to one aspect of the present invention, there is provided a hydrogen production apparatus. This hydrogen production apparatus includes a detonation combustion furnace that generates detonation using supplied hydrogen and an oxidizing gas, and a decomposition furnace that thermally decomposes supplied hydrocarbons to produce hydrogen and carbon, wherein one of the detonation combustion furnace and the decomposition furnace is formed in a cylindrical shape extending in the longitudinal direction and is provided inside the other furnace that is formed in a tubular shape extending in the longitudinal direction. With this aspect of the hydrogen production apparatus, hydrogen is produced by heating and thermally decomposing hydrocarbons using detonation or combustion gases generated by detonation, thereby reducing carbon dioxide emissions during hydrogen production.

[0007] (2) In the hydrogen production apparatus described in (1) above, hydrogen and oxidizing gas may be supplied to the detonation combustion furnace from one end in the longitudinal direction, and hydrocarbons may be supplied to the cracking furnace from the other end in the longitudinal direction. This configuration of the hydrogen production apparatus allows the flow directions of the hydrogen and oxidizing gas to be opposite to the flow direction of the hydrocarbons. This increases the efficiency of heat exchange between the detonation combustion furnace and the cracking furnace.

[0008] (3) In the hydrogen production apparatus described in (1) or (2), a portion of the hydrogen produced in the decomposition furnace may be supplied to the detonation combustion furnace. This configuration of the hydrogen production apparatus eliminates the need to externally supply hydrogen as fuel for detonation.

[0009] (4) In the hydrogen production apparatus according to any one of (1) to (3), the one furnace may be the detonation combustion furnace. In this hydrogen production apparatus, the high-temperature detonation combustion furnace is provided inside the decomposition furnace, which can suppress heat loss and, as a result, can suppress a decrease in hydrogen production efficiency.

[0010] (5) In the hydrogen production apparatus according to any one of (1) to (4), hydrocarbons may be supplied to the cracking furnace from above in a vertical direction, and the cracking furnace may discharge the generated hydrogen and carbon from below in a vertical direction. According to this hydrogen production apparatus, the generated solid carbon can be removed from below in a vertical direction, thereby preventing a decrease in the recovery efficiency of carbon as a by-product.

[0011] The present disclosure can be realized in various forms, for example, a method for producing hydrogen, a system for producing hydrogen, an apparatus for producing carbon, a system for producing carbon, an apparatus for producing hydrogen and carbon, a method for producing hydrogen and carbon, a system for producing hydrogen and carbon, etc.

[0012] The present invention relates to a hydrogen production system and a hydrogen production method, and more particularly to a hydrogen production apparatus and a hydrogen production method.

[0013] FIG. 1 is a schematic diagram illustrating the schematic configuration of a hydrogen production system 200 including a hydrogen production apparatus 100 according to an embodiment of the present disclosure. The hydrogen production apparatus 100 (hereinafter also referred to as "apparatus 100") in the present disclosure produces hydrogen and carbon from hydrocarbons by thermally decomposing the hydrocarbons. This thermal decomposition is known as methane thermal decomposition. In methane thermal decomposition, when the hydrocarbon is methane, an overall reaction represented by the following formula (1) occurs: CH ４ →C+2H ２ ...(1)

[0014] As shown in the above formula (1), methane pyrolysis produces hydrogen and carbon. Therefore, methane pyrolysis does not produce carbon dioxide when hydrogen is produced. Therefore, according to the device 100 of this embodiment, carbon dioxide emissions during the hydrogen production process can be eliminated, thereby reducing carbon dioxide emissions. The hydrocarbon feedstock is not particularly limited, but examples include methane, ethane, propane, butane, pentane, etc. Alternatively, a mixed gas containing methane as the main component and ethane, propane, butane, pentane, etc., or a mixed gas containing ethane, propane, butane, pentane, etc. as the main component may be used. From the viewpoint of availability, natural gas containing methane as the main component is preferred as the hydrocarbon feedstock. In addition to conventional natural gas, unconventional natural gases such as shale gas, tight gas, coalbed methane, and methane hydrate can also be used.

[0015] 2 is an explanatory diagram schematically illustrating the configuration of a hydrogen production apparatus 100. The apparatus 100 of the present disclosure includes a detonation combustion furnace 10 and a cracking furnace 20. In this embodiment, the detonation combustion furnace 10 is formed in a columnar shape extending in the longitudinal direction, and the cracking furnace 20 is formed in a tubular shape extending in the longitudinal direction. The detonation combustion furnace 10 is provided inside the cracking furnace 20. In other words, the detonation combustion furnace 10 is inserted radially inside the cracking furnace 20. Therefore, the detonation combustion furnace 10 and the cracking furnace 20 are arranged in a substantially concentric shape. Note that the cross-sectional shapes of the detonation combustion furnace 10 and the cracking furnace 20 are not limited to being substantially circular, and may be polygonal shapes such as polygons close to circles.

[0016] The detonation combustion furnace 10 generates detonation therein using the supplied hydrogen and oxidizing gas. In this specification, "detonation" refers to a phenomenon in which a shock wave generated during combustion and a combustion wave propagate together at supersonic speed. The oxidizing gas is not particularly limited, but examples thereof include oxygen and air containing oxygen. The hydrogen used as fuel supplied to the detonation combustion furnace 10 may be a mixed gas of hydrogen and hydrocarbon. The detonation combustion furnace 10 is provided with a first supply section 12 and a first discharge section 14.

[0017] The first supply unit 12 is provided at one end in the longitudinal direction of the detonation combustion furnace 10. Hydrogen and oxidizing gas are supplied from the first supply unit 12 into the interior of the detonation combustion furnace 10. In this embodiment, the first supply unit 12 corresponds to a through-hole formed in the end face in the longitudinal direction of the detonation combustion furnace 10. It is preferable that a plurality of such through-holes are formed in a row at approximately equal intervals along the circumferential direction on the end face of the detonation combustion furnace 10, but they may also be formed in a row at any intervals, or there may be only one through-hole.

[0018] The detonation combustion furnace 10 of this embodiment is provided with a pre-detonator (not shown) located near the first supply section 12. The pre-detonator is formed with a smaller diameter than the detonation combustion furnace 10 and explodes a mixture of hydrogen and oxidizing gas to generate a detonation wave, which propagates into the detonation combustion furnace 10. The pre-detonator makes it possible to easily generate and propagate a detonation wave inside the detonation combustion furnace 10. The oxidizing gas used in the pre-detonator is preferably oxygen from the viewpoint of increasing the efficiency of detonation generation. Note that the pre-detonator may be omitted and a detonation wave may be generated by an ignition source with high energy, such as an electric spark, or detonation may be initiated by transitioning from a deflagration wave to a detonation wave.

[0019] The first discharge section 14 is provided at the other longitudinal end of the detonation combustion furnace 10. Steam generated by combustion is discharged from the first discharge section 14. In this embodiment, the first discharge section 14 is formed at the longitudinal end of the detonation combustion furnace 10. In this embodiment, the first discharge section 14 has a reduced diameter section 15 and a tapered section 16. The reduced diameter section 15 is connected to the detonation combustion furnace 10 and has a diameter smaller than that of the detonation combustion furnace 10. The presence of the reduced diameter section 15 makes it possible to slow down the discharge rate of high-temperature steam discharged from the detonation combustion furnace 10. The tapered section 16 is connected to the reduced diameter section 15 and is tapered so that its diameter increases in a direction away from the detonation combustion furnace 10. At least one of the reduced diameter section 15 and the tapered section 16 may be omitted. That is, the diameter of the first discharge section 14 may be approximately constant, may be approximately the same as the diameter of the detonation type combustion furnace 10, or may be smaller or larger than the diameter of the detonation type combustion furnace 10.

[0020] As indicated by the thin arrows in FIG. 2 , within the detonation combustion furnace 10 of this embodiment, rotational detonation occurs in a region relatively close to the first supply section 12 in the longitudinal direction. In the following description, for convenience, the region within the detonation combustion furnace 10 where detonation occurs will also be referred to as the "detonation region 18," and the other regions will also be referred to as the "combustion gas region 19." When the supplied fuel is hydrogen and the oxidizing gas is oxygen, the temperature within the detonation region 18 is expected to be approximately 3000°C to 3500°C. When the supplied fuel is hydrogen and the oxidizing gas is air, the temperature within the detonation region 18 is expected to be approximately 2000°C to 2500°C. As the temperature within the detonation combustion furnace 10 moves from the detonation region 18 toward the first discharge section 14 in the longitudinal direction, i.e., as the temperature moves away from the detonation region 18, the temperature within the detonation combustion furnace 10 decreases due to heat exchange with the cracking furnace 20.

[0021] The cracking furnace 20 has a cylindrical external shape surrounding the detonation combustion furnace 10. The cracking furnace 20 generates hydrogen and carbon by thermally cracking at least a portion of the hydrocarbons supplied thereto using the heat from the detonation combustion furnace 10. The cracking furnace 20 is provided with a second supply section 22 and a second discharge section 24.

[0022] The second supply section 22 is provided at the other longitudinal end of the cracking furnace 20. In other words, the second supply section 22 is provided on the side of the detonation combustion furnace 10 where the first discharge section 14 is formed in the longitudinal direction of the apparatus 100. The hydrocarbon feedstock is supplied from the second supply section 22 to the inside of the cracking furnace 20. In this embodiment, the second supply section 22 corresponds to a through-hole formed in the end face of the cracking furnace 20 in the longitudinal direction. It is preferable that a plurality of such through-holes are formed in a row at approximately equal intervals along the circumferential direction on the end face of the cracking furnace 20, but they may be formed in a row at any intervals, or there may be only one through-hole.

[0023] The second discharge section 24 is provided at one end in the longitudinal direction of the cracking furnace 20. In other words, the second discharge section 24 is provided on the side of the apparatus 100 where the first supply section 12 of the detonation combustion furnace 10 is formed in the longitudinal direction. Hydrogen and carbon produced by pyrolysis and hydrocarbons remaining without pyrolysis are discharged from the second discharge section 24. In this embodiment, the second discharge section 24 corresponds to a through-hole formed in the end face of the cracking furnace 20 in the longitudinal direction. It is preferable that a plurality of such through-holes are formed in a row at approximately equal intervals along the circumferential direction on the end face of the cracking furnace 20, but they may also be formed in a row at any intervals, or there may be only one through-hole.

[0024] The internal temperature of the cracking furnace 20 increases due to heat exchange with the detonation combustion furnace 10. Relatively low-temperature hydrocarbons supplied from the second supply section 22 are preheated by heat exchange with the combustion gas region 19, and when they reach the region surrounding the detonation region 18, they are further heated and thermally decomposed. In the following description, for convenience, the region inside the cracking furnace 20 where the temperature at which hydrocarbons thermally decompose is reached is also referred to as the "thermal decomposition region 28," and the other regions are also referred to as the "preheating region 29." In the preheating region 29, the temperature gradually increases from the second supply section 22 side toward the thermal decomposition region 28 side in the longitudinal direction, preheating the hydrocarbons. The temperature of the thermal decomposition region 28 is expected to be approximately 900°C to 1700°C. From the viewpoint of improving hydrogen yield, the temperature of the thermal decomposition region 28 is preferably 1000°C or higher, more preferably 1100°C or higher, and even more preferably 1200°C or higher. In the longitudinal direction of the device 100, the boundary position between the pyrolysis region 28 and the preheating region 29 does not have to coincide with the boundary position between the detonation region 18 and the combustion gas region 19. Note that, although the device 100 of the present disclosure is made of alumina, it is not limited to ceramic materials such as alumina, and may be made of any heat-resistant material, such as silicon carbide.

[0025] According to the apparatus 100 of the present disclosure, hydrogen is produced by thermally decomposing hydrocarbons using high-temperature detonation, and therefore, it is expected that carbon dioxide will not be substantially generated. As a result, carbon dioxide emissions during hydrogen production can be reduced. Furthermore, according to the apparatus 100 of the present disclosure, since hydrocarbons are thermally decomposed at high temperatures using detonation, the use of a catalyst for the thermal decomposition of hydrocarbons can be omitted. As a result, the inclusion of catalyst-derived components in the carbon produced as a by-product can be suppressed, thereby producing high-purity carbon. Furthermore, according to the apparatus 100 of the present disclosure, the detonation-type combustion furnace 10 and the decomposition furnace 20 are separate. Therefore, compared to an apparatus using a method in which the produced hydrogen and combustion exhaust gases (carbon dioxide, nitrogen, oxygen, water, etc.) are mixed and discharged, such as a pulse methane pyrolysis (PMP) method, separation of hydrogen from a mixed gas containing multiple components can be omitted.

[0026] As described above, in this embodiment, hydrogen and oxidizing gas are supplied to the detonation combustion furnace 10 from the first supply unit 12 provided at one end of the longitudinal direction, and hydrocarbons are supplied to the cracking furnace 20 from the second supply unit 22 provided at the other end of the longitudinal direction. Therefore, in the apparatus 100 of this embodiment, the flow direction of hydrogen and oxidizing gas is opposite to the flow direction of hydrocarbons. This improves heat exchange efficiency, thereby preventing a decrease in hydrogen production efficiency. Furthermore, in the apparatus 100 of this embodiment, the high-temperature detonation combustion furnace 10 is provided inside the cracking furnace 20, thereby preventing heat loss and, as a result, preventing a decrease in hydrogen production efficiency. Furthermore, since the detonation combustion furnace 10 in the apparatus 100 of this embodiment utilizes a so-called rotary detonation mechanism, the process of purging the interior of the combustion furnace with nitrogen or the like after detonation occurs can be omitted.

[0027] As shown in FIG. 1 , a hydrogen production system 200 (hereinafter also referred to as "system 200") in this embodiment includes a hydrogen production apparatus 100, a carbon separation apparatus 80, and a hydrogen separation apparatus 90. The carbon separation apparatus 80 is provided downstream of the second discharge section 24 of the cracking furnace 20. The carbon separation apparatus 80 separates carbon from the hydrogen, carbon, and hydrocarbons discharged from the second discharge section 24. The specific configuration of the carbon separation apparatus 80 is not particularly limited, and may be configured to include, for example, a filter that traps carbon, such as a dust collection filter. The mixed gas of hydrogen and hydrocarbons separated by the carbon separation apparatus 80 is supplied to the hydrogen separation apparatus 90. The hydrogen separation apparatus 90 separates the mixed gas of hydrogen and hydrocarbons into hydrogen and hydrocarbons. The specific configuration of the hydrogen separation apparatus 90 is not particularly limited, and may be configured to include, for example, a mesh-like member having gaps formed therein that allow only hydrogen molecules to pass through.

[0028] In the system 200 of this embodiment, the following formulas (2) to (4) hold true. In the formulas and in FIG. 1, α represents the methane conversion rate, and β represents the amount of hydrogen used for combustion. CH ４ →2αH ２ + (1-α) CH ４ +αC...(2) βH ２ +β / 2×O ２ →βH ２ O...(3) 2α-β>0...(4)

[0029] Here, the reaction heat of the above formula (2) is −74.8 × α [kJ / mol ＣＨ４ ], and the reaction heat of the above formula (3) is 241.8 × β [kJ / mol Ｈ２ Therefore, if all the combustion heat of detonation is used for thermal decomposition, the system 200 is established when β≧0.3α. Therefore, under ideal conditions, ４ to 1.7 mol H ２ is generated.

[0030] In this embodiment, the hydrogen separated in the hydrogen separation device 90 is supplied to the detonation combustion furnace 10. That is, in this embodiment, a portion of the hydrogen produced in the cracking furnace 20 is supplied to the detonation combustion furnace 10. With this configuration, it is possible to omit the external supply of hydrogen as detonation fuel, thereby making the detonation combustion furnace 10 self-contained. It should be noted that, in addition to the hydrogen produced in the cracking furnace 20, when a mixed gas of the generated hydrogen and the remaining hydrocarbons that have not been cracked is discharged from the cracking furnace 20, the mixed gas of hydrogen and hydrocarbons may be supplied to the detonation combustion furnace 10. Furthermore, in this embodiment, the hydrocarbons separated in the hydrogen separation device 90 are supplied to the cracking furnace 20. With this configuration, the remaining hydrocarbons that have not been thermally cracked can be reused, thereby suppressing a decrease in hydrogen production efficiency. Furthermore, in this embodiment, the device 100 is arranged so that its longitudinal direction is approximately vertical. Therefore, hydrocarbons are supplied to the cracking furnace 20 from above in the vertical direction, and the cracking furnace 20 discharges the generated hydrogen and carbon from below in the vertical direction. With this configuration, solid carbon can be extracted from below in the vertical direction, and therefore a decrease in the efficiency of recovering carbon as a by-product can be suppressed.

[0031] B. Other Embodiments: In the hydrogen production apparatus 100 in the above embodiment, the detonation combustion furnace 10 is provided inside the cracking furnace 20. However, one of the detonation combustion furnace 10 and the cracking furnace 20 may be formed in a cylindrical shape extending in the longitudinal direction and provided inside the other furnace formed in a tubular shape extending in the longitudinal direction. Therefore, the cylindrical cracking furnace 20 may be provided inside the tubular detonation combustion furnace 10. In other words, the cylindrical cracking furnace 20 may be inserted radially inside the tubular detonation combustion furnace 10.

[0032] In the hydrogen production apparatus 100 in the above embodiment, hydrogen and oxidizing gas are supplied to the detonation combustion furnace 10 from one end in the longitudinal direction, and hydrocarbons are supplied to the cracking furnace 20 from the other end, but the present disclosure is not limited to this. The hydrogen production apparatus 100 may also be configured such that hydrogen and oxidizing gas are supplied to the detonation combustion furnace 10 and hydrocarbons are supplied to the cracking furnace 20 from one end in the longitudinal direction. According to such a configuration, the detonation region 18, which has become excessively hot, can be cooled by the hydrocarbons supplied at a relatively low temperature.

[0033] Although the hydrogen production device 100 in the above embodiment is based on the so-called rotary detonation, it may also use the so-called pulse detonation. With pulse detonation, hydrogen and oxidizing gas are intermittently supplied to the detonation combustion furnace, which can suppress a decrease in energy efficiency. Furthermore, with pulse detonation, it is possible to relatively lower the temperature of the high-temperature water vapor generated by combustion before discharging it.

[0034] The hydrogen production apparatus 100 in the above embodiment is merely an example and can be modified in various ways. In order to prevent the temperature around the detonation combustion furnace 10 from becoming excessively high, a solvent such as water may be flowed around the detonation combustion furnace 10 to remove heat and thereby lower the temperature. Furthermore, the temperature of the hydrocarbons supplied in the second supply section 22 of the cracking furnace 20 may be raised in advance by boiling the solvent. This configuration is applicable to both an embodiment in which the cracking furnace 20 is provided inside the detonation combustion furnace 10 and an embodiment in which the detonation combustion furnace 10 is provided inside the cracking furnace 20.

[0035] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0036] A simulation of the temperature distribution in a hydrogen production device was performed. Methane was used as the hydrocarbon and air was used as the oxidizing gas. The temperature and pressure behind the detonation were calculated based on the Chapman-Jouguet (CJ) theory, a one-dimensional detonation theory. The CJ temperature, CJ pressure, and gas composition were calculated using the web version of NASA CEA (https: / / cearun.grc.nasa.gov / ). Using the calculated CJ temperature, CJ pressure, and gas composition as inflow conditions, the temperature distribution was obtained using an original simulation solver created in Python.

[0037] FIG. 3 is an explanatory diagram showing the simulation results of the example. In FIG. 3, a cross-sectional schematic diagram of the hydrogen production apparatus 100 is shown, along with the corresponding positions of the temperature distribution and gas concentration distribution in the longitudinal direction. In FIG. 3, the first supply section 12 of the detonation combustion furnace 10 and the second discharge section 24 of the cracking furnace 20 are shown on the left side of the page, and the second supply section 22 of the cracking furnace 20 and the first discharge section 14 of the detonation combustion furnace 10 are shown on the right side of the page. That is, in the detonation combustion furnace 10, gas flows from the left to the right of the page, and in the cracking furnace 20, gas flows from the right to the left of the page. For convenience, the temperature distribution and gas concentration distribution are shown with arrows in the curved lines to indicate the direction of gas flow.

[0038] The results shown in FIG. 3 reveal the following. The hydrogen and oxidizing gas supplied from the first supply section 12 (shown on the left side of the drawing) to the interior of the detonation combustion furnace 10 formed a detonation wave and reached a high temperature of 2000°C or higher. In the detonation combustion furnace 10, the temperature gradually decreased from the first supply section 12 toward the first discharge section 14 due to heat exchange with the hydrocarbons in the cracking furnace 20. Furthermore, the hydrogen concentration decreased due to combustion, and in the combustion gas region 19, the hydrogen concentration reached nearly 0%. The hydrocarbons supplied at room temperature from the second supply section 22 (shown on the right side of the drawing) to the interior of the cracking furnace 20 gradually increased in temperature due to heat exchange with the detonation combustion furnace 10 from the second supply section 22 toward the second discharge section 24. The hydrocarbon concentration in the preheating region 29 was nearly 100%. The hydrocarbons that reached the temperature at which pyrolysis occurred were pyrolyzed, thereby decreasing the hydrocarbon concentration.

[0039] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in each embodiment corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0040] DESCRIPTION OF SYMBOLS 10...detonation type combustion furnace, 12...first supply section, 14...first discharge section, 15...diameter reduction section, 16...tapered section, 18...detonation region, 19...combustion gas region, 20...cracking furnace, 22...second supply section, 24...second discharge section, 28...thermal decomposition region, 29...preheating region, 80...carbon separation device, 90...hydrogen separation device, 100...hydrogen production device, 200...hydrogen production system

Claims

1. A hydrogen production apparatus comprising: a detonation type combustion furnace that generates detonation using supplied hydrogen and an oxidizing gas; and a decomposition furnace that thermally decomposes supplied hydrocarbons to produce hydrogen and carbon, wherein one of the detonation type combustion furnace and the decomposition furnace is formed in a cylindrical shape extending in the longitudinal direction and is provided inside the other furnace that is formed in a tubular shape extending in the longitudinal direction.

2. A hydrogen production apparatus as claimed in claim 1, wherein hydrogen and oxidizing gas are supplied to the detonation type combustion furnace from one end in the longitudinal direction, and hydrocarbons are supplied to the decomposition furnace from the other end in the longitudinal direction.

3. The hydrogen production apparatus according to claim 1 or 2, wherein a portion of the hydrogen produced in the decomposition furnace is supplied to the detonation type combustion furnace.

4. The hydrogen production apparatus according to claim 1 or 2, wherein the one of the furnaces is a detonation type combustion furnace.

5. A hydrogen production apparatus according to claim 1 or 2, wherein the decomposition furnace is supplied with hydrocarbons from above in a vertical direction, and the decomposition furnace discharges generated hydrogen and carbon from below in a vertical direction.