Gas production apparatus, gas production system, gas production method

Abstract

To provide a gas production apparatus, a gas production system and a gas production method capable of more efficiently producing a product gas containing carbon monoxide from a raw material gas containing carbon dioxide while avoiding a risk of stable procurement of reducing gas.SOLUTION: According to one aspect of the present invention, there is provided a gas production apparatus for producing a product gas containing carbon monoxide from a raw material gas containing carbon dioxide. The gas production apparatus includes at least one reactor accommodating a reducing agent that reduces carbon dioxide upon contact with the raw material gas, and an electromagnetic wave irradiation unit that irradiates the reducing agent in the reactor with electromagnetic waves. The reducing agent contains an oxygen element and exhibits a reducing ability to carbon dioxide by releasing the oxygen element through irradiation with electromagnetic waves.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a gas production device, a gas production system, and a gas production method. [Background technology]

[0002] In recent years, the concentration of carbon dioxide (CO2), a greenhouse gas, has been increasing in the atmosphere. This increase in the concentration of carbon dioxide in the atmosphere contributes to global warming. Therefore, it is important to capture carbon dioxide released into the atmosphere. If the captured carbon dioxide can be converted into valuable substances and reused, a carbon-recycling society can be realized. Furthermore, as a global measure, the Kyoto Protocol of the United Nations Framework Convention on Climate Change stipulates that developed countries must set their own reduction rates for carbon dioxide, the cause of global warming, using 1990 as the base year, and that they must jointly achieve reduction targets within the commitment period.

[0003] To achieve this reduction target, exhaust gases containing carbon dioxide generated from steel mills, smelters, and thermal power plants are also included, and various technological improvements are being made to reduce carbon dioxide emissions in these industries. One example of such a technology is carbon capture and storage (CCS). However, this technology has physical limitations in terms of storage, and is not a fundamental solution. Additionally, for example, a method has been developed in which a raw material gas containing carbon dioxide and a reducing gas containing a reducing substance are alternately brought into contact with a reducing agent containing a metal oxide to produce a product gas containing carbon monoxide (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-54704 Summary of the Invention [Problem to be solved by the invention]

[0005] The method described in Patent Document 1 uses a reducing gas to reduce the reducing agent in an oxidized state. However, since this method uses a reducing gas, there is a risk of procuring the reducing gas. In view of the above circumstances, the present invention provides a gas production apparatus, a gas production system, and a gas production method that can more efficiently produce a product gas containing carbon monoxide from a raw material gas containing carbon dioxide while avoiding the risk of unstable procurement of reducing gas. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided a gas production apparatus for producing a product gas containing carbon monoxide from a raw material gas containing carbon dioxide. The gas production apparatus includes at least one reactor containing a reducing agent that reduces carbon dioxide upon contact with the raw material gas, and an electromagnetic wave irradiation unit that irradiates the reducing agent in the reactor with electromagnetic waves. The reducing agent contains oxygen, and exhibits carbon dioxide reduction ability by releasing the oxygen upon irradiation with electromagnetic waves.

[0007] According to this embodiment, it is possible to more efficiently produce a product gas containing carbon monoxide from a raw material gas containing carbon dioxide while avoiding the risk of unstable procurement of reducing gas. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing the configuration of a gas production system according to a first embodiment. [Figure 2] FIG. 1 is a schematic diagram showing the configuration of a reactor in a first embodiment. [Figure 3] FIG. 10 is a schematic diagram showing the configuration of a gas production system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A gas production apparatus, a gas production system, and a gas production method according to the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings. <<First Embodiment>> First, a gas production system according to a first embodiment will be described. Fig. 1 is a schematic diagram showing the configuration of a gas production system according to the first embodiment. Fig. 2 is a schematic diagram showing the configuration of a reactor in the first embodiment. The gas production system 10 shown in FIG. 1 includes a gas production apparatus 100, an exhaust gas supply unit (raw material gas supply unit) 1 connected to the gas production apparatus 100 and supplying exhaust gas (raw material gas containing carbon dioxide), and an inert gas supply unit 2 supplying inert gas. In this specification, the upstream side with respect to the gas flow direction will also be referred to simply as the "upstream side," and the downstream side will also be referred to simply as the "downstream side."

[0010] The exhaust gas supply unit 1 is not particularly limited, but may be, for example, a CO2 exhaust gas from at least one facility selected from a garbage incineration plant, a paper mill, a cement factory, a steel mill, a smelter, a thermal power plant, an oil refinery, an ethylene cracker, a refinery, and a chemical plant. x Among them, a furnace (for example, a combustion furnace, a blast furnace, or a converter) attached to a steel mill, a smelter, or a thermal power plant is preferable as the exhaust gas supply unit 1. In the furnace, gas containing carbon dioxide is generated (evolved) when the contents are burned, melted, refined, or the like. In the case of a combustion furnace (incinerator) at a waste incineration plant, the contents (waste) include, for example, plastic waste, food waste, municipal solid waste (MSW), discarded tires, biomass waste, household waste (futons, paper), building materials, etc. These wastes may contain one type alone or two or more types.

[0011] In addition to carbon dioxide, exhaust gas usually contains other gas components such as nitrogen, oxygen, carbon monoxide, water vapor, methane, etc. The concentration of carbon dioxide contained in the exhaust gas is not particularly limited, but considering the production cost of the generated gas (efficiency of conversion to carbon monoxide), it is preferably 1% by volume or more, and more preferably 5% by volume or more. Exhaust gas from combustion furnaces at waste incineration plants contains carbon dioxide at 5% to 15% by volume, nitrogen at 60% to 70% by volume, oxygen at 5% to 10% by volume, and water vapor at 15% to 25% by volume.

[0012] Exhaust gas from a blast furnace (blast furnace gas) is a gas generated when pig iron is produced in a blast furnace, and contains carbon dioxide at 5% to 45% by volume, nitrogen at 55% to 60% by volume, carbon monoxide at 10% to 40% by volume, and hydrogen at 1% to 10% by volume. In addition, exhaust gas from a converter (converter gas) is a gas generated when steel is produced in a converter, and contains carbon dioxide at 15% by volume or more and 20% by volume or less, carbon monoxide at 50% by volume or more and 80% by volume or less, nitrogen at 15% by volume or more and 25% by volume or less, and hydrogen at 1% by volume or more and 5% by volume or less. The exhaust gas may be a pure gas containing 100% by volume of carbon dioxide.

[0013] However, if exhaust gas is used, carbon dioxide that has conventionally been emitted into the atmosphere can be effectively utilized, thereby reducing the burden on the environment. Among these, from the viewpoint of carbon circulation, exhaust gas containing carbon dioxide generated in a steel mill or a smelter is preferred. Furthermore, the blast furnace gas and converter gas may be untreated gas discharged from the furnace and used as is, or treated gas after treatment to remove carbon monoxide, etc., may be used. Untreated blast furnace gas and converter gas each have the gas composition described above, and treated gas has a gas composition close to the gas composition shown for the exhaust gas from the combustion furnace. In this specification, all of the above gases (gases before being supplied to the gas manufacturing apparatus 100) are referred to as exhaust gases.

[0014] The inert gas supply unit 2 supplies an inert gas that has no or little reactivity with a reducing agent 4R (described later) that reduces carbon dioxide. Examples of inert gases include inert gases such as nitrogen gas, argon gas, and helium gas. These gases may be used alone or in combination of two or more.

[0015] The gas production apparatus 100 of this embodiment is an apparatus that produces a product gas containing carbon monoxide from exhaust gas (raw material gas) containing carbon dioxide, and mainly comprises a first gas switching unit 3, multiple (two in this embodiment) reactors 4a, 4b, a second gas switching unit 5, and an electromagnetic wave irradiation unit 6. The exhaust gas supply unit 1 is connected to the first gas switching unit 3 via a gas line GL1, and the inert gas supply unit 2 is connected to the first gas switching unit 3 via a gas line GL2. At least one of a temperature control unit that adjusts the temperature of the gas passing through each gas line GL1, GL2, a pressurizing unit that pressurizes the gas, an impurity removal unit that removes impurities from the gas, etc. may be arranged along each gas line GL1, GL2. The first gas switching unit 3 can be configured to include, for example, a branch gas line and a flow path opening and closing mechanism such as a valve provided midway along the branch gas line.

[0016] The first gas switching unit 3 is connected to the inlet ports of reactors 4a and 4b via two gas lines GL3a and GL3b, respectively. The first gas switching unit 3 is configured to be able to switch between the reactors 4a and 4b to which the exhaust gas is supplied. As a result, the exhaust gas supplied from the exhaust gas supply unit 1 passes through the gas line GL1, the first gas switching unit 3, and the gas lines GL3a and GL3b, and is supplied to each of the reactors 4a and 4b. The first gas switching unit 3 is also configured to be able to switch between the reactors 4a and 4b to which the inert gas is supplied. As a result, the inert gas supplied from the inert gas supply unit 2 passes through the gas line GL2, the first gas switching unit 3, and the gas lines GL3a and GL3b, and is supplied to each of the reactors 4a and 4b.

[0017] Each of the reactors 4a, 4b contains a reducing agent that reduces carbon dioxide upon contact with exhaust gas (raw material gas) and is capable of generating carbon monoxide from carbon dioxide (converting carbon dioxide to carbon monoxide). Specifically, as shown in FIG. 2, each of the reactors 4a, 4b is configured as a multi-tubular reactor (fixed-bed reactor) including a plurality of tubular bodies 41, each filled with (containing) a reducing agent 4R, and a housing 42 having an internal space 43 in which the plurality of tubular bodies 41 are housed. Such a multi-tubular reactor can ensure sufficient opportunities for the reducing agent 4R to come into contact with the exhaust gas and inert gas. As a result, the efficiency of converting carbon dioxide to carbon monoxide can be increased.

[0018] Each of the reactors 4a and 4b may be configured as a reactor (that is, a simple reactor) in which the tube body 41 is omitted and the internal space 43 of the housing 42 is filled with the reducing agent 4R. The reducing agent 4R of this embodiment is preferably in the form of, for example, particles (granules), scales, pellets, etc. The reducing agent 4R in such a shape can increase the filling efficiency into the tubular body 41 and can further increase the contact area with the gas supplied into the tubular body 41.

[0019] When the reducing agent 4R is particulate, its volume-average particle size is not particularly limited, but is preferably 1 mm or more and 50 mm or less, and more preferably 1 mm or more and 30 mm or less. In this case, the contact area between the reducing agent 4R and the exhaust gas (carbon dioxide) can be further increased, and the conversion efficiency of carbon dioxide to carbon monoxide can be further improved. In addition, an increase in the passage resistance of the exhaust gas and the inert gas through each of the reactors 4a and 4b can be prevented or suppressed. The particulate reducing agent 4R is preferably a compact produced by tumbling granulation, since this increases the sphericity.

[0020] The reducing agent 4R may be supported on a carrier. The constituent material of the carrier may be any material that is not easily denatured by contact with exhaust gas (oxidizing gas) or by reaction conditions, and examples thereof include carbon materials (graphite, graphene, carbon black, carbon nanotubes, activated carbon, etc.), carbides such as MoC and SiC, zeolites, montmorillonite, oxides such as ZrO, TiO, V, MgO, CeO, AlO, and SiO, and composite oxides containing these.

[0021] Among these, preferred materials for the carrier include SiC, zeolite, montmorillonite, ZrO2, TiO2, V2O5, MgO, Al2O3, SiO2, and composite oxides containing these. Carriers made of such materials are preferred because they do not adversely affect the reaction of the reducing agent 4R and have excellent supporting ability for the reducing agent 4R. Here, the carrier may not be involved in the reaction of the reducing agent 4R and may simply support (hold) the reducing agent 4R, or it may have the property of absorbing electromagnetic waves. In the latter case, it exhibits the effect of supporting the improvement of the efficiency of absorbing electromagnetic waves by the reducing agent 4R, as described below. SiC is preferred as a material for the carrier. An example of a form in which the reducing agent 4R is supported on a carrier is a configuration in which at least a portion of the surface of the carrier is coated with the reducing agent 4R.

[0022] The reducing agent 4R contains an oxygen element, and exhibits the ability to reduce carbon dioxide by releasing the oxygen element when irradiated with electromagnetic waves. The reducing agent 4R preferably contains a complex oxide that has the property of releasing oxygen element when irradiated with electromagnetic waves having a frequency of 300 MHz or more and 20 GHz or less under a temperature environment of 300°C or more and 770°C or less. The reducing agent 4R containing such a complex oxide quickly absorbs the irradiated electromagnetic waves, causing the crystal structure of the complex oxide to vibrate and generate distortion. As a result, the reducing agent 4R can generate oxygen by efficiently releasing oxygen element. Therefore, in this case, the use of a carrier that has the property of absorbing electromagnetic waves can be omitted. The frequency of the electromagnetic waves is preferably 300 MHz or more and 10 GHz or less, and more preferably 300 MHz or more and 5 GHz or less, in which case the efficiency of desorption of oxygen element from the reducing agent 4R (complex oxide) can be sufficiently increased.

[0023] The environmental temperature at which the composite oxide exhibits its ability to release oxygen elements is preferably 400° C. or higher and 750° C. or lower, and more preferably 500° C. or higher and 700° C. or lower. In this case, the composite oxide releases oxygen elements even at a relatively low temperature, resulting in high energy efficiency. Specifically, when the composite oxide is irradiated with electromagnetic waves, it is preferable that the release of oxygen elements begins at a lower temperature than when the composite oxide is heated only by conventional heating, and specifically, the release of oxygen elements begins at a temperature that is 50° C. or more lower, more preferably at a temperature that is 75° C. or more lower, and even more preferably at a temperature that is 100° C. or more lower, thereby further improving the above-mentioned effects. Here, the composite oxide (oxygen generating agent) is heated by irradiation with electromagnetic waves, and this heating may be carried out by irradiation with electromagnetic waves alone, or by both irradiation with electromagnetic waves and heating by conventional heating. Conventional heating refers to heating an object by heat transfer through conduction, convection, and radiation, and examples include electric furnaces and combustion furnaces. The heat source for conventional heating is placed not only outside the container, but also inside the container if necessary.

[0024] Therefore, it is preferable that the reducing agent 4R be used at a temperature lower than the temperature at which the oxygen element begins to desorb from the complex oxide by conventional heating alone while irradiating the electromagnetic waves (hereinafter also referred to as the "desorption initiation temperature"). Specifically, the temperature during use (when irradiating the electromagnetic waves) may be 50°C or more lower than the desorption initiation temperature, 75°C or more lower, or 100°C or more lower. In this case, it is possible to further improve energy efficiency while maintaining a sufficiently high desorption efficiency of the oxygen element from the complex oxide. The upper limit of this temperature is not particularly limited, but is preferably about 150°C lower than the desorption initiation temperature.

[0025] The dielectric loss tangent of the composite oxide is preferably 0.05 or more, more preferably 0.1 or more, even more preferably 0.15 or more, and particularly preferably 0.2 or more. In this case, the composite oxide can quickly absorb electromagnetic waves regardless of frequency. The upper limit of the dielectric loss tangent of the composite oxide is not particularly limited, but is about 0.4. Furthermore, when the dielectric loss tangent of the complex oxide is within the above range, the dielectric constant is preferably 6 or less, more preferably 5 or less, even more preferably 4 or less, particularly preferably 3 or less, and most preferably 2 or less. In this case, the electromagnetic wave absorption ability of the complex oxide is more easily improved. The lower limit of the dielectric constant of the complex oxide is not particularly limited, but is about 1.

[0026] The composite oxide preferably contains at least two elements belonging to the fourth period of the periodic table. Here, examples of elements belonging to the fourth period of the periodic table include potassium (K), calcium (Ca), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), gallium (Ga), germanium (Ge), etc. Among these, calcium (Ca), titanium (Ti), manganese (Mn), iron (Fe), cobalt (Co), and copper (Cu) are preferred as elements belonging to the fourth period of the periodic table.

[0027] The composite oxide preferably contains at least two elements selected from the alkaline earth metals and transition elements. Examples of elements belonging to alkaline earth metals and transition elements include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), silver (Ag), lanthanum (La), cerium (Ce), samarium (Sm), gadolinium (Gd), hafnium (Hf), tantalum (Ta), etc. Among these, preferred elements belonging to alkaline earth metals and transition elements are calcium (Ca), strontium (Sr), titanium (Ti), manganese (Mn), iron (Fe), cobalt (Co), and copper (Cu).

[0028] The composite oxide may have any crystal structure as long as it has a high ability to absorb electromagnetic waves, but it is preferable that the composite oxide has at least one of a perovskite-type crystal structure, a spinel-type crystal structure, and a corundum-type crystal structure. Studies by the present inventors have revealed that composite oxides having the above crystal structures have a high ability to absorb electromagnetic waves. From the above, the composite oxide is x Sr 1-x FeO3 (perovskite type), SrTi x Co 1-x O2.8 (Perovskite and spinel types), Cu x Mn 1-x At least one of Fe2O4 (spinel type and corundum type) is preferred, and Ca 0.2 Sr 0.8 FeO3, SrTi 0.2 Co 0.8 O 2.8 , Cu 0.5 Mn 0.5 It is more preferable that the composite oxide is at least one of Fe2O4. These composite oxides are preferable because they have a sufficiently high ability to release oxygen elements.

[0029] Ca 0.2 Sr 0.8 The temperature at which FeO3 begins to release oxygen elements by conventional heating alone (release initiation temperature) is 370°C, and the temperature at which SrTi x Co 1-x O 2.8 The temperature at which the separation begins is 700°C, and Cu 0.5 Mn 0.5 The temperature at which Fe2O4 begins to separate is 770°C. In each of the reactors 4a and 4b, the reducing agent 4R itself may be used to form a tubular body (cylindrical molded body) 41. Furthermore, a block-shaped or lattice-shaped (e.g., mesh-shaped or honeycomb-shaped) molded body may be prepared using the reducing agent 4R and placed in the housing 42. In these cases, the reducing agent 4R may be omitted as a filler or may be used in combination.

[0030] Among these, a preferred configuration is one in which a mesh body is made of the reducing agent 4R and placed inside the housing 42. In such a configuration, it is possible to prevent an increase in the resistance to passage of the exhaust gas and the inert gas inside each of the reactors 4a and 4b, while also ensuring sufficient opportunities for the reducing agent 4R to come into contact with the exhaust gas and the inert gas. The volumes of the two reactors 4a and 4b are set to be approximately equal to each other and are appropriately set depending on the amount of exhaust gas to be treated (the size of the exhaust gas supply unit 1 and the size of the gas production apparatus 100). The volumes of the two reactors 4a and 4b may be made different depending on the type of exhaust gas, the electromagnetic wave conditions (described later), the performance of the reducing agent 4R, etc.

[0031] Regardless of the configuration of the reactors 4a and 4b described above, it is preferable to design them so as to prevent an increase in the resistance to passage of the exhaust gas and the inert gas. Such a prevention effect can be achieved by appropriately setting the proportion of the reducing agent 4R in the housing 42. Specifically, it can be defined as the proportion of reducing agent 4R (occupancy rate of reducing agent 4R) in the area surrounded by the inner wall of cylindrical body 421 (see Figure 2) of housing 42 (cross-sectional area of ​​internal space 43) in a cross section perpendicular to the longitudinal direction (gas passage direction) of body 421. The occupancy rate of the reducing agent 4R is not particularly limited, but is preferably 25% or more and 85% or less, more preferably 35% or more and 75% or less, and even more preferably 45% or more and 65% or less.

[0032] An electromagnetic wave irradiation unit 6 is disposed on the side of each of the reactors 4a and 4b. The electromagnetic wave irradiation unit 6 irradiates the reducing agent 4R in the reactors 4a and 4b with electromagnetic waves. The electromagnetic waves irradiated from the electromagnetic wave irradiation unit 6 are preferably microwaves. Here, microwaves refer to electromagnetic waves with frequencies between 300 MHz and 300 GHz, and are classified into ultra-high frequency waves (UHF) with frequencies between 300 MHz and 3000 MHz, centimeter waves (SHF) with frequencies between 3 GHz and 30 GHz, millimeter waves (EHF) with frequencies between 30 GHz and 300 GHz, and submillimeter waves (SHF) with frequencies between 300 GHz and 3000 GHz. Among these, the electromagnetic waves are preferably microwaves (ultra-short waves) with a frequency of 300 MHz or more and 3000 MHz or less. Use of ultra-short waves enables the oxygen element to be separated from the reducing agent 4R at a lower temperature. When irradiating microwaves, appropriate measures to prevent radio wave leakage in accordance with the Radio Law are taken.

[0033] According to the above configuration, by switching the gas line (flow path) in the first gas switching unit 3, for example, exhaust gas can be supplied to reactor 4a containing pre-oxidation reducing agent 4R via gas line GL3a, and the post-oxidation reducing agent 4R contained in reactor 4b can be irradiated with electromagnetic waves from electromagnetic wave irradiation unit 6. At this time, the reaction of the following formula 1 proceeds in reactor 4a, and the reaction of the following formula 2 proceeds in reactor 4b.

[0034] In the following formulas 1 and 2, the reducing agent 4R is ABO x-1 This shows an example in which a compound oxide (where A and B are different elements) is included. Equation 1: CO2+ ABO x-1 → CO + ABO x Formula 2: ABO x + Electromagnetic waves → O2+ ABO x-1 Thereafter, the gas line is switched in the opposite direction in the first gas switching section 3, and electromagnetic waves are irradiated, thereby causing the reaction of the above formula 2 to proceed in reactor 4a, and the reaction of the above formula 1 to proceed in reactor 4b. That is, exhaust gas (raw material gas) is alternately supplied to the reactor 4a and the reactor 4b, and electromagnetic waves are alternately irradiated to the reducing agent 4R in the reactor 4a and the reducing agent 4R in the reactor 4b.

[0035] The reactions shown in the above formulas 1 and 2 are endothermic or exothermic depending on the type of composite oxide. Therefore, when the reactions shown in the above formulas 1 and 2 are endothermic reactions, it is preferable that the gas manufacturing apparatus 100 further has a reducing agent heating section (not shown in FIG. 1) that heats the reducing agent 4R when exhaust gas or electromagnetic waves are applied to the reducing agent 4R. By providing such a reducing agent heating section, it is possible to appropriately adjust the temperature when the exhaust gas or electromagnetic waves are reacted with the reducing agent 4R, thereby suitably preventing or suppressing a decrease in the efficiency of converting carbon dioxide to carbon monoxide, and further promoting the regeneration of the reducing agent 4R (release of oxygen element) by irradiation with electromagnetic waves. Even in the case of this endothermic reaction, the reducing agent 4R may be heated by irradiating it with electromagnetic waves, without providing a reducing agent heating section, to prevent or suppress a drop in its temperature.

[0036] On the other hand, when the reactions represented by the above formulas 1 and 2 are exothermic reactions, the gas production apparatus 100 preferably has a reducing agent cooling unit that cools the reducing agent 4R instead of the reducing agent heating unit. By providing such a reducing agent cooling unit, deterioration of the reducing agent 4R can be suitably prevented when the exhaust gas or electromagnetic waves are reacted with the reducing agent 4R, and a decrease in the efficiency of converting carbon dioxide to carbon monoxide can be suitably prevented or suppressed, and regeneration of the reducing agent 4R (release of oxygen element) by electromagnetic wave irradiation can be further promoted. That is, the gas production apparatus 100 is preferably provided with a reducing agent temperature adjusting unit that adjusts the temperature of the reducing agent 4R depending on the type of reducing agent 4R (exothermic reaction or endothermic reaction). The reducing agent temperature adjustment unit may be configured to both heat and cool the reducing agent 4R. In this case, it is possible to appropriately deal with the case where one of the reactions shown in the above formulas 1 and 2 is an endothermic reaction and the other is an exothermic reaction.

[0037] Here, the conversion rate of carbon dioxide to carbon monoxide in the reactors 4a and 4b is preferably 70% or more, more preferably 85% or more, and even more preferably 95% or more. The upper limit of the conversion rate of carbon dioxide to carbon monoxide is usually about 98%. Such a conversion rate can be set by adjusting the type of reducing agent 4R used, the concentration of carbon dioxide contained in the exhaust gas, the frequency of the electromagnetic waves, the output of the electromagnetic waves, the irradiation time of the electromagnetic waves, the temperature of the reactors 4a and 4b, the flow rate (flow velocity) of the exhaust gas into the reactors 4a and 4b, the timing of switching between the supply of the exhaust gas and the irradiation of the electromagnetic waves, etc.

[0038] The outlet ports of the reactors 4a and 4b are connected to a second gas switching unit 5 via gas lines GL4a and GL4b, respectively. The second gas switching unit 5 can be configured to include, for example, a branch gas line and a flow path opening and closing mechanism such as a valve provided midway along the branch gas line. That is, the second gas switching unit 5 is connected to the two reactors 4a, 4b and is capable of switching the flow paths so as to prevent the product gas and the desorbed gas that have passed through the reactors 4a, 4b from joining together. Furthermore, by adjusting the opening of the valve, it is possible to set the passing speed of the produced gas (exhaust gas) and the inert gas (desorbed gas) passing through the reactors 4a and 4b.

[0039] In addition, the second gas switching unit 5 is connected to a generated gas discharge unit 8, which discharges generated gas containing carbon monoxide outside the gas manufacturing apparatus 100 via a gas line GL8, and a separated gas discharge unit 9, which discharges separated gas containing oxygen outside the gas manufacturing apparatus 100 via a gas line GL9. With this configuration, the produced gas discharged from the reactors 4a and 4b passes through the gas lines GL4a and GL4b, the second gas switching unit 5, and the gas line GL8, and is discharged from the produced gas discharge unit 8 to the outside of the gas production apparatus 100. On the other hand, the desorbed gas discharged from the reactors 4a and 4b passes through the gas lines GL4a and GL4b, the second gas switching unit 5, and the gas line GL9, and is discharged from the desorbed gas discharge unit 9 to the outside of the gas production apparatus 100.

[0040] Next, a method of using the gas production system 10 (a gas production method for producing a product gas containing carbon monoxide from a raw material gas (exhaust gas) containing carbon dioxide) will be described. Step [1] First, the gas line (flow path) is switched in the first gas switching unit 3 to connect the exhaust gas supply unit 1 to the reactor 4a and to connect the inert gas supply unit 2 to the reactor 4b. On the other hand, by switching the gas line (flow path) in the second gas switching unit 5, the reactor 4a and the produced gas discharge unit 8 are connected to each other, and the reactor 4b and the desorbed gas discharge unit 9 are connected to each other. Step [2] Next, in this state, the exhaust gas is supplied from the exhaust gas supply unit 1 to the reactor 4a via the gas line GL1 and the gas line GL3a. In the reactor 4a, the exhaust gas is brought into contact with a reducing agent 4R containing an oxygen element, thereby reducing carbon dioxide to obtain a product gas. At this time, the reducing agent 4R is oxidized by contact with carbon dioxide.

[0041] The temperature (heating temperature) of the reducing agent 4R in the reactor 4a in this step [2] is preferably 600°C or higher, more preferably 650°C or higher and 1100°C or lower, and even more preferably 700°C or higher and 1000°C or lower. The pressure in the reactor 4a (reaction pressure) is preferably less than 1 MPaG, more preferably 0.9 MPaG or less, and even more preferably 0.2 MPaG or more and 0.8 MPaG or less. Setting the reaction conditions within the above ranges makes it possible to prevent or suppress, for example, a sudden decrease in the temperature of the reducing agent 4R due to an endothermic reaction when carbon dioxide is converted to carbon monoxide, and therefore makes it possible to more smoothly proceed with the reduction reaction of carbon dioxide in the reactor 4a.

[0042] Step [3] In parallel with the above steps [1] and [2], the reducing agent 4R (the reducing agent oxidized by contact with the exhaust gas in the previous cycle) in the reactor 4b is irradiated with electromagnetic waves from the electromagnetic wave irradiation unit 6. At this time, the reducing agent 4R absorbs the electromagnetic waves, and the crystal structure vibrates, causing distortion and releasing (desorbing) oxygen elements. As a result, a desorbed gas containing oxygen is generated. The output of the electromagnetic waves in this step [3] is not particularly limited, but is preferably 3 The power per unit area is preferably 1 W or more and 10 kW or less, more preferably 10 W or more and 5 kW or less, and even more preferably 100 W or more and 3 kW or less. By irradiating electromagnetic waves with such an output, the efficiency of desorption of oxygen element from the reducing agent 4R (complex oxide) can be further increased.

[0043] The irradiation time of the electromagnetic waves is not particularly limited, but is preferably from 10 seconds to 10 hours, more preferably from 1 minute to 5 hours, and even more preferably from 10 minutes to 2 hours. Such an irradiation time allows the oxygen element to be sufficiently desorbed from the reducing agent 4R. A shorter irradiation time resulting in a larger amount of oxygen element being desorbed from the reducing agent 4R is preferable in terms of being advantageous for industrialization. Furthermore, the temperature (reaction temperature) of the reducing agent 4R in the reactor 4b in this step [3] is preferably 600°C or higher. That is, it is preferable that the reducing agent 4R in the reactor 4b that is irradiated with electromagnetic waves is heated to 600°C or higher. The temperature (reaction temperature) of the reducing agent 4R in the reactor 4b is more preferably 650°C or higher and 1800°C or lower, and even more preferably 700°C or higher and 1400°C or lower. When irradiating with electromagnetic waves, the oxygen element can be efficiently separated from the reducing agent 4R without heating to a high temperature. Furthermore, in this case, since the reducing agent 4R can be heated by irradiating with electromagnetic waves, a separate heating source can be omitted. While the reducing agent 4R is being irradiated with electromagnetic waves, the reaction temperature of the reducing agent 4R may be increased continuously or stepwise. By adjusting the output of the electromagnetic waves within the above range, it is easy to stabilize the rate of increase in the reaction temperature of the reducing agent 4R (rate of temperature increase).

[0044] Step [4] While the above step [3] is continuing (i.e., while the electromagnetic wave irradiation unit 6 is irradiating the reducing agent 4R in the reactor 4b with electromagnetic waves), an inert gas is supplied to the reactor 4b from the inert gas supply unit 2 via the gas line GL2 and the gas line GL3b. As a result, a released gas containing oxygen and the inert gas is discharged from the reactor 4b. Step [5] Next, the produced gas from reactor 4a is discharged to the outside of the gas production apparatus 100 via gas line GL8 and produced gas discharge section 8, and is then supplied to the next step. Meanwhile, the desorbed gas from reactor 4b is discharged to the outside of the gas production apparatus 100 via gas line GL9 and desorbed gas discharge section 9, and is then supplied to the next step. In other words, the produced gas and the desorbed gas are recovered separately. This prevents carbon monoxide and oxygen from coming into contact with each other, and therefore is highly safe.

[0045] Thereafter, by switching the gas line (flow path) in the first gas switching unit 3, the exhaust gas supply unit 1 and the reactor 4b are communicated with each other, and the inert gas supply unit 2 and the reactor 4a are communicated with each other. On the other hand, by switching the gas line (flow path) in the second gas switching unit 5, the reactor 4b and the produced gas discharge unit 8 are communicated with each other, and the reactor 4a and the desorbed gas discharge unit 9 are communicated with each other. Then, with the reactors 4a and 4b switched, the same steps as the above steps [1] to [5] are carried out. In this way, by switching between the reactors 4a and 4b and repeating the above steps [1] to [5] as one cycle multiple times, it is possible to continuously produce the produced gas from the exhaust gas.

[0046] The concentration of carbon monoxide contained in the product gas discharged from product gas discharge section 8 is preferably 80% by volume or more, more preferably 85% by volume or more, even more preferably 90% by volume or more, particularly preferably 95% by volume or more, and may be 100% by volume. The generated gas may be directly supplied to the next step, or may be purified before being supplied to the next step. Examples of subsequent processes include a process for producing valuable substances (e.g., ethanol) from the generated gas by fermentation with microorganisms (e.g., Clostridium), a process for producing steel using the generated gas as a fuel or reducing agent, a process in the field of manufacturing electrical devices, and a process for synthesizing chemicals (phosgene, acetic acid, etc.) using carbon monoxide as a synthetic raw material.

[0047] <<Second embodiment>> Next, a gas production system according to a second embodiment will be described. FIG. 3 is a schematic diagram showing the configuration of a gas production system according to the second embodiment. The gas production system 10 of the second embodiment will be described below, focusing on the differences from the gas production system 10 of the first embodiment, and a description of similar points will be omitted.

[0048] In the second embodiment, a decompression unit 7 for decompressing the inside of each of the reactors 4a and 4b is provided in the gas lines GL4a and GL4b. Specifically, the decompression unit 7 is configured to decompress the inside of the reactors 4a and 4b to which the inert gas is supplied. The pressure reducing section 7 may be configured with a non-positive displacement pump or a positive displacement pump. Examples of non-positive displacement pumps include centrifugal pumps such as volute pumps, turbine pumps, and multi-stage volute pumps, propeller pumps such as axial flow pumps and mixed flow pumps, and viscous pumps such as cascade pumps. On the other hand, examples of positive displacement pumps include reciprocating pumps such as piston pumps, plunger pumps and diaphragm pumps, and rotary pumps such as gear pumps, screw pumps and vane pumps.

[0049] The pressure reducing section 7 can be configured to reduce the pressure inside the reactors 4a, 4b at least either while the inert gas is being supplied to the reactors 4a, 4b or while the supply of the inert gas to the reactors 4a, 4b is stopped after the inert gas has been supplied to the reactors 4a, 4b. With this configuration, the separated gas can be more reliably discharged from the reactors 4a, 4b than when only the inert gas is used. Furthermore, the pressure reducing unit 7 can be configured to reduce the pressure inside the reactors 4a, 4b while the irradiation of the reducing agent 4R in the reactors 4a, 4b with electromagnetic waves from the electromagnetic wave irradiation unit 6 is stopped. That is, the pressure reducing unit 7 can be configured to reduce the pressure inside the reactors 4a, 4b between the time when the irradiation of the electromagnetic waves is stopped and the time when the next irradiation of the electromagnetic waves is started.

[0050] For example, the pressure reducing unit 7 may reduce the pressure inside the reactors 4a, 4b after the electromagnetic wave irradiation is stopped and before the supply of the exhaust gas is started, and discard the remaining part of the desorbed gas discharged from the reactors 4a, 4b. In this case, it is possible to suitably prevent the reaction between carbon monoxide generated from the exhaust gas (carbon dioxide) and oxygen, resulting in high safety. The pressure reducing section 7 is preferably configured to reduce the pressure inside the reactors 4a, 4b to -50 kPaG or less (preferably -70 kPaG or less). The lower limit of the vacuum inside the reactors 4a, 4b is not particularly limited, but is set to an economical value based on the power cost required for reducing the pressure and the unit price of the valuable material (product) finally obtained. This makes it possible to further improve the above-mentioned effects while suppressing increases in costs.

[0051] According to the gas production apparatus, gas production system, and gas production method described above, a reducing gas is not used to reduce an oxidized reducing agent, and therefore a product gas containing carbon monoxide can be produced more efficiently from a raw material gas containing carbon dioxide while avoiding the risk of unstable procurement of the reducing gas. Furthermore, according to the gas production apparatus, etc., the electromagnetic wave absorption ability of the reducing agent is further improved and the efficiency of oxygen element desorption is increased, thereby making it possible to sufficiently reduce the energy consumption required to produce the generated gas compared to the energy consumption required in conventional gas production apparatus, etc., which includes a reducing gas production process. Furthermore, if electromagnetic waves are used to remove oxygen from the reducing agent, energy can be selectively applied to elements other than oxygen contained in the reducing agent, which makes it easier to cause distortion in the crystal structure (crystal lattice). Therefore, it is expected that oxygen will be removed from the reducing agent at a lower temperature than when using conventional heating alone.

[0052] In the above-described embodiment, for example, a PSA device for removing nitrogen as an impurity removal unit may be provided in the gas line GL1. In this case, the removed (separated) nitrogen can be used as at least a part of the inert gas. The PSA device is a pressure swing adsorption separator, and can use, as an adsorbent, porous materials such as activated carbon, zeolite, silica gel, and molecular sieves, or aqueous solutions such as amine solutions. Activated carbon or zeolite is preferably used in the PSA device.

[0053] The gas production system 10 of the second embodiment described above is configured to include both the inert gas supply unit 2 and the pressure reduction unit 7. However, the inert gas supply unit 2 may be omitted and only the pressure reduction unit 7 may be included. In this case, the pressure reduction unit 7 is preferably configured to reduce the pressure inside the reactors 4a, 4b at least one of while the reducing agent 4R in the reactors 4a, 4b is being irradiated with electromagnetic waves and while the irradiation of the electromagnetic waves to the reducing agent 4R in the reactors 4a, 4b is stopped after the electromagnetic waves have been irradiated to the reducing agent 4R in the reactors 4a, 4b. Furthermore, the number of reactors to be installed is not limited to two, but may be one, or may be three or more. That is, the gas production system 10 only needs to include at least one reactor. Furthermore, it may be provided in the following aspects.

[0054] (1) A gas production apparatus for producing a product gas containing carbon monoxide from a raw material gas containing carbon dioxide, the gas production apparatus comprising: at least one reactor containing a reducing agent that reduces the carbon dioxide upon contact with the raw material gas; and an electromagnetic wave irradiation unit that irradiates the reducing agent in the reactor with electromagnetic waves, wherein the reducing agent contains an oxygen element and exhibits reducing ability with respect to the carbon dioxide by releasing the oxygen element upon irradiation with the electromagnetic waves.

[0055] (2) The gas manufacturing apparatus according to (1) above, wherein the gas manufacturing apparatus is configured to supply an inert gas that is not reactive or has poor reactivity with the reducing agent to the reactor while the electromagnetic wave irradiation unit irradiates the reducing agent in the reactor with the electromagnetic waves.

[0056] (3) The gas manufacturing apparatus described in (2) above, further comprising a pressure reducing unit that reduces the pressure inside the reactor, and the pressure reducing unit is configured to reduce the pressure inside the reactor at least one of while the inert gas is being supplied to the reactor and while the supply of the inert gas to the reactor is stopped after the inert gas has been supplied to the reactor.

[0057] (4) The gas production apparatus according to any one of (1) to (3) above, further comprising a pressure reducing section that reduces the pressure inside the reactor.

[0058] (5) In the gas manufacturing apparatus described in (3) or (4) above, the pressure reducing unit is configured to reduce the pressure inside the reactor while the irradiation of the electromagnetic waves from the electromagnetic wave irradiation unit to the reducing agent in the reactor is stopped.

[0059] (6) The gas manufacturing apparatus according to any one of (3) to (5) above, wherein the pressure reducing section is configured to reduce the pressure inside the reactor to a degree of vacuum of -50 kPaG or less.

[0060] (7) In the gas manufacturing apparatus described in any one of (1) to (6) above, the at least one reactor includes a plurality of the reactors, and further includes a first gas switching unit that can switch the reactor to which the raw material gas is supplied.

[0061] (8) In the gas manufacturing apparatus described in (7) above, the first gas switching unit is configured to be able to switch the reactor that supplies an inert gas that is not reactive or has poor reactivity with the reducing agent.

[0062] (9) The gas manufacturing apparatus according to (8) above, further comprising a pressure reducing section that reduces the pressure inside the reactor, and the pressure reducing section is configured to reduce the pressure inside the reactor to which the inert gas is supplied.

[0063] (10) The gas manufacturing apparatus according to (9) above, further comprising a second gas switching unit connected to the plurality of reactors and capable of switching the flow path so as to prevent gases that have passed through each of the reactors from joining together.

[0064] (11) The gas production apparatus according to any one of (1) to (10) above, wherein the reducing agent in the reactor irradiated with the electromagnetic waves is heated to 600°C or higher.

[0065] (12) The gas production apparatus according to any one of (1) to (11) above, wherein the electromagnetic waves are microwaves having a frequency of 300 MHz or more and 3000 MHz or less.

[0066] (13) A gas production system comprising: the gas production apparatus according to any one of (1) to (12) above; and a raw material gas supply unit connected to the gas production apparatus and supplying a raw material gas containing carbon dioxide.

[0067] (14) The gas production system described in (13) above, further comprising an inert gas supply unit connected to the gas production device and supplying an inert gas that is unreactive or poorly reactive with the reducing agent.

[0068] (15) A gas production method for producing a product gas containing carbon monoxide from a raw material gas containing carbon dioxide, the gas production method comprising: a step of reducing the carbon dioxide by bringing the raw material gas into contact with a reducing agent containing oxygen element to obtain the product gas; and a step of irradiating the reducing agent, which has been oxidized by contact with the raw material gas, with electromagnetic waves to release the oxygen element and obtain a released gas containing oxygen.

[0069] (16) The gas production method according to (15) above, further comprising the step of separately recovering the generated gas and the desorbed gas. Of course, this is not the case.

[0070] As described above, various embodiments of the present invention have been described, but these are presented as examples and do not limit the scope of the invention in any way. The novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. Such embodiments and their modifications are intended to be included within the scope and spirit of the invention, as well as within the scope of the inventions and their equivalents as set forth in the claims.

[0071] For example, the gas production apparatus and gas production system of the present invention may each have any other additional configuration compared to the above embodiments, may be replaced with any configuration that performs similar functions, or may have some configurations omitted. Furthermore, the gas production method of the present invention may have any other additional steps compared to the above embodiment, may be replaced with any step that performs a similar function, or may omit some steps. [Explanation of symbols]

[0072] 10: Gas production system 100: Gas production equipment 1: Exhaust gas supply section 2: Inert gas supply section 3: First gas switching section 4a: Reactor 4b: Reactor 41: Body 42: Housing 421: Torso 43: Interior space 4R: Reducing agent 5: Second switching unit 6: Electromagnetic wave irradiation section 7: Pressure reduction section 8: Produced gas discharge section 9: Inert gas exhaust section GL1: Gas line GL2: Gas line GL3a: Gas line GL3b: Gas line GL4a: Gas line GL4b: Gas line GL8: Gas line GL9: Gas line

Claims

1. A gas production apparatus for producing a product gas containing carbon monoxide from a raw material gas containing carbon dioxide, comprising: at least one reactor containing a reducing agent that reduces the carbon dioxide upon contact with the raw material gas; an electromagnetic wave irradiation unit that irradiates the reducing agent in the reactor with electromagnetic waves, The reducing agent contains an oxygen element, and exhibits a reducing ability for the carbon dioxide by releasing the oxygen element when irradiated with the electromagnetic waves.

2. The gas production apparatus according to claim 1, The gas manufacturing apparatus is configured to supply an inert gas that is not reactive or has poor reactivity with the reducing agent to the reactor while the electromagnetic wave irradiation unit irradiates the reducing agent in the reactor with the electromagnetic waves.

3. The gas production apparatus according to claim 2, Further, a pressure reducing unit is provided for reducing the pressure inside the reactor, The gas manufacturing apparatus is configured so that the pressure reduction section reduces the pressure inside the reactor at least one of while the inert gas is being supplied to the reactor and while the supply of the inert gas to the reactor is stopped after the inert gas is supplied to the reactor.

4. The gas production apparatus according to claim 1, The gas production apparatus further comprises a pressure reducing section that reduces the pressure inside the reactor.

5. The gas production apparatus according to claim 3, The gas manufacturing apparatus, wherein the pressure reducing unit is configured to reduce the pressure inside the reactor while the irradiation of the electromagnetic waves from the electromagnetic wave irradiation unit to the reducing agent in the reactor is stopped.

6. The gas production apparatus according to claim 3, The gas production apparatus, wherein the pressure reducing section is configured to reduce the pressure inside the reactor to a degree of vacuum of −50 kPaG or less.

7. The gas production apparatus according to claim 1, the at least one reactor comprises a plurality of the reactors; The gas production apparatus further comprises a first gas switching unit capable of switching the reactor to which the raw material gas is supplied.

8. The gas production apparatus according to claim 7, The gas production apparatus is configured so that the first gas switching unit can also switch the reactor that supplies an inert gas that is not reactive or has poor reactivity with the reducing agent.

9. The gas production apparatus according to claim 8, Further, a pressure reducing unit is provided for reducing the pressure inside the reactor, The gas production apparatus, wherein the pressure reducing section is configured to reduce the pressure inside the reactor to which the inert gas is supplied.

10. The gas production apparatus according to claim 9, The gas production apparatus further comprises a second gas switching unit connected to the plurality of reactors and capable of switching the flow paths so as to prevent the gases that have passed through the reactors from joining together.

11. The gas production apparatus according to claim 1, The gas production device is configured to heat the reducing agent in the reactor irradiated with the electromagnetic waves to 600°C or higher.

12. The gas production apparatus according to claim 1, The gas production device, wherein the electromagnetic waves are microwaves having a frequency of 300 MHz or more and 3000 MHz or less.

13. 1. A gas production system comprising: The gas production apparatus according to any one of claims 1 to 12; a raw material gas supply unit connected to the gas production apparatus and supplying a raw material gas containing carbon dioxide.

14. The gas production system according to claim 13, The gas production system further comprises an inert gas supply unit connected to the gas production device and supplying an inert gas that is unreactive or poorly reactive with the reducing agent.

15. A gas production method for producing a product gas containing carbon monoxide from a raw material gas containing carbon dioxide, comprising the steps of: a step of reducing the carbon dioxide by bringing the raw material gas into contact with a reducing agent containing oxygen element to obtain the product gas; and irradiating the reducing agent, which has been oxidized by contact with the raw material gas, with electromagnetic waves to cause the oxygen element to be desorbed, thereby obtaining a desorbed gas containing oxygen.

16. The gas production method according to claim 15, The gas production method further comprises a step of separately recovering the generated gas and the desorbed gas.

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