JP7497242B2 - Gas production device, gas production system, and gas production method - Google Patents

Description

The present invention relates to a gas production device, a gas production system, and a gas production method.

In recent years, the concentration of carbon dioxide ( _CO2 ), a type of greenhouse gas, in the atmosphere has been increasing. The increase in the concentration of carbon dioxide in the atmosphere contributes to global warming. Therefore, it is important to capture carbon dioxide emitted into the atmosphere, and if the captured carbon dioxide can be converted into valuable substances and reused, a carbon circulation society can be realized.
As a global policy, the Kyoto Protocol of the United Nations Framework Convention on Climate Change stipulates that each developed country must set its own reduction rate for carbon dioxide, the cause of global warming, using 1990 as a base year, and that they must jointly achieve reduction targets within the commitment period.

In order to achieve the reduction target, exhaust gas containing carbon dioxide generated from steel mills, smelters, and thermal power plants is also included, and various technological improvements have been made to reduce carbon dioxide in these industries. One example of such a technology is _CO2 capture and storage (CCS). However, this technology has physical limitations in terms of storage, and is not a fundamental solution.
In addition, for example, Patent Document 1 discloses a technology for converting carbon dioxide into a valuable substance. Specifically, the document discloses a production apparatus for producing carbon monoxide from carbon dioxide by using cerium oxide containing zirconium.

Patent No. 5858926

However, according to the inventors' study, the invention described in Patent Document 1 is an invention for specifying a metal oxide that effectively converts carbon dioxide into carbon monoxide. Patent Document 1 only discloses conceptual or general information on the conditions and equipment for producing carbon monoxide, as shown in the drawings, and it was found that further technical improvements are necessary to produce carbon monoxide industrially.
Therefore, an object of the present invention is to provide a gas production apparatus (i.e., an industrially advantageous production apparatus), a gas production system, and a gas production method that can continuously and stably produce a product gas containing carbon monoxide from a raw material gas containing carbon dioxide.

This objective is achieved by the present invention described below.

(1) A gas production apparatus of the present invention is a gas production apparatus that produces a product gas containing carbon monoxide by contacting a raw material gas containing carbon dioxide with a reducing agent containing a metal oxide that reduces the carbon dioxide,
a raw material gas supply unit for supplying the raw material gas;
a reducing gas supply unit that supplies a reducing gas containing a reducing substance that reduces the reducing agent that has been oxidized by contact with the carbon dioxide;
a reaction section including a plurality of reactors each connected to the raw material gas supply section and the reducing gas supply section, and the reducing agent disposed in the reactors, the reaction section being capable of switching between the raw material gas and the reducing gas supplied to each of the reactors;
a gas junction section for merging the gases that have passed through the reactor to generate a mixed gas;
a reducing agent temperature adjusting unit that adjusts a temperature of the reducing agent when the reducing agent is brought into contact with the raw material gas or the reducing gas,
Each of the reactors includes a plurality of tubes each filled with the reducing agent, and a housing that houses the plurality of tubes;
The reducing agent temperature control unit is characterized by comprising a medium to be supplied to a space defined by the multiple tubes and the housing, a transfer device to transfer the medium to the space, and a heating device to heat the medium or a cooling device to cool the medium.

(2) In the gas production apparatus of the present invention, it is preferable that the reducing agent temperature adjustment unit is a reducing agent heating unit that heats the reducing agent when the reducing agent is brought into contact with the source gas or the reducing gas.
(3) In the gas production apparatus of the present invention, it is preferable that the reducing agent heating unit includes a first heat exchanger that exchanges heat between the mixed gas and the medium before being supplied to the space of the reactor.

(4) In the gas production apparatus of the present invention, it is preferable that the reducing agent heating section includes a second heat exchanger that exchanges heat between the medium after passing through the space of the reactor and at least one of the raw material gas and the reducing gas before being supplied to the reactor.
(5) In the gas production apparatus of the present invention, it is preferable that the metal oxide contains at least one metal element selected from the group consisting of metal elements belonging to Groups 3 to 12.

(6) The gas production system of the present invention comprises:
a raw material gas generating unit that generates a raw material gas containing carbon dioxide;
The gas production apparatus of the present invention is provided,
The gas production apparatus is characterized in that it is connected to the raw material gas generation unit via the raw material gas supply unit.

(7) A gas production method of the present invention includes contacting a raw material gas containing carbon dioxide with a reducing agent containing a metal oxide that reduces the carbon dioxide to produce a product gas containing carbon monoxide, the method comprising the steps of:
preparing a plurality of reactors each having the reducing agent disposed therein, the raw material gas, and a reducing gas containing a reducing substance that reduces the reducing agent oxidized by contact with the carbon dioxide;
by switching the reactors to which the raw material gas and the reducing gas are supplied, the raw material gas and the reducing gas are alternately brought into contact with the reducing agent in each of the reactors to convert the carbon dioxide into carbon monoxide, and then the oxidized reducing agent is reduced;
The gases that have passed through the reactor are combined to generate a mixed gas;
When recovering the mixed gas as the product gas as it is or by purifying the carbon monoxide from the mixed gas,
When the raw material gas or the reducing gas is brought into contact with the reducing agent, a temperature-controlled medium is supplied to a space partitioned from the reducing agent in each of the reactors, thereby adjusting the temperature of the reducing agent.

(8) In the gas production method of the present invention, when the raw material gas or the reducing gas is brought into contact with the reducing agent, it is preferable to heat the reducing agent by supplying the heated medium to the space of each of the reactors.

According to the present invention, it is possible to efficiently and continuously produce a product gas containing carbon monoxide from a raw gas containing carbon dioxide. In particular, in the present invention, a reducing agent temperature control unit is provided to adjust the temperature of the reducing agent, so that the temperature can be maintained at a target temperature depending on the type of reaction between the raw gas or reducing gas and the reducing agent, and it is possible to suitably prevent or suppress a decrease in the conversion efficiency of carbon dioxide to carbon monoxide and promote the regeneration of the reducing agent by the reducing gas. In addition, the reducing agent temperature control unit is configured to supply a temperature-controlled medium to a space partitioned from the reducing agent in a multi-tube reactor to heat or cool the reducing agent, so that, for example, renewable energy can be used as a power source for the reducing agent temperature control unit, in which case the reducing agent can be safely heated or cooled while reducing the burden on the environment.

1 is a schematic diagram illustrating one embodiment of a gas production system according to the present invention. FIG. 2 is a cross-sectional view showing a schematic configuration of the reactor in FIG. 1. FIG. 2 is a schematic diagram showing a configuration of an exhaust gas heating unit in FIG. 1 . FIG. 2 is a schematic diagram showing a configuration of a reducing agent heating unit. FIG. 11 is a schematic diagram showing another configuration of the reducing agent heating unit. 1 is a schematic diagram showing a configuration in the vicinity of a connection portion between a gas production apparatus and a furnace according to the present invention. FIG. 2 is a schematic diagram showing another embodiment of the gas production system of the present invention. FIG. 8 is a cross-sectional view showing a schematic configuration of the refiner shown in FIG. 7 .

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.
FIG. 1 is a schematic diagram showing one embodiment of the gas production system of the present invention, FIG. 2 is a cross-sectional view showing a schematic configuration of the reactor of FIG. 1, and FIG. 3 is a schematic diagram showing the configuration of the exhaust gas heating section of FIG. 1.
The gas production system 100 shown in FIG. 1 includes a furnace (raw material gas generation section) 20 that generates exhaust gas (raw material gas) containing carbon dioxide, and a gas production apparatus 1 connected to the furnace 20 via a connection section 2.
In this specification, the upstream side with respect to the gas flow direction is also simply referred to as the "upstream side", and the downstream side is also simply referred to as the "downstream side".

The furnace 20 is not particularly limited, but may be, for example, a furnace attached to a steelworks, a smelter, or a thermal power plant, and preferably includes a combustion furnace, a blast furnace, a converter, etc. In the furnace 20, exhaust gas is generated (generated) when the contents are burned, melted, refined, etc.
In the case of a combustion furnace (incinerator) in 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 be contained alone or in combination of two or more types.

Exhaust gas usually contains, in addition to carbon dioxide, 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 in consideration of the production cost of the generated gas (conversion efficiency to carbon monoxide), it is preferably 1 vol% or more, and more preferably 5 vol% or more.
Exhaust gas from the combustion furnace in a waste incineration plant contains 5 to 15 volume % carbon dioxide, 60 to 70 volume % nitrogen, 5 to 10 volume % oxygen, and 15 to 25 volume % water vapor.

Exhaust gas from a blast furnace (blast furnace gas) is a gas generated when producing pig iron in a blast furnace, and contains 10 to 15 volume % carbon dioxide, 55 to 60 volume % nitrogen, 25 to 30 volume % carbon monoxide, and 1 to 5 volume % hydrogen.
In addition, exhaust gas from a converter (converter gas) is a gas generated when steel is produced in the converter, and contains 15 to 20 volume % carbon dioxide, 50 to 60 volume % carbon monoxide, 15 to 25 volume % nitrogen, and 1 to 5 volume % hydrogen.
The raw material gas is not limited to exhaust gas, and a pure gas containing 100% by volume of carbon dioxide may be used.

However, if exhaust gas is used as the raw material gas, carbon dioxide that has conventionally been discharged into the atmosphere can be effectively utilized, and the burden on the environment can be reduced. Among these, from the viewpoint of carbon circulation, exhaust gas containing carbon dioxide generated in a steelworks or a smelter is preferred.
In addition, the blast furnace gas and converter gas may be untreated gas discharged from the furnace as it is, or may be treated gas after treatment to remove carbon monoxide, for example. The untreated blast furnace gas and converter gas each have the gas composition described above, and the treated gas has a gas composition close to the gas composition shown in the exhaust gas from the combustion furnace. In this specification, all of the above gases (gases before being supplied to the gas production device 1) are referred to as exhaust gas.

<Overall composition>
The gas production apparatus 1 produces a product gas (synthetic gas) containing carbon monoxide by contacting exhaust gas (raw material gas containing carbon dioxide) discharged from the furnace 20 and supplied via the connection part 2 with a reducing agent containing a metal oxide that reduces the carbon dioxide contained in the exhaust gas.
The gas manufacturing apparatus 1 mainly includes a connection section 2, a reducing gas supply section 3, two reactors 4a, 4b, a gas line GL1 connecting the connection section 2 to each of the reactors 4a, 4b, a gas line GL2 connecting the reducing gas supply section 3 to each of the reactors 4a, 4b, and a gas line GL4 connected to each of the reactors 4a, 4b.
In this embodiment, the connection part 2 constitutes a raw material gas supply part that supplies the exhaust gas to the reactors 4a and 4b.
If necessary, pumps for transferring gas may be provided at predetermined positions along the gas lines GL1, GL2, and GL4. For example, when the pressure of the exhaust gas is adjusted to a relatively low level in the compression section 6 described below, the gas can be transferred smoothly within the gas production apparatus 1 by providing the pumps.

One end of the gas line GL1 is connected to the connection unit 2. Meanwhile, the other end of the gas line GL1 is connected to the inlet ports of the reactors 4a and 4b in the reaction unit 4 via the gas switching unit 8 and two gas lines GL3a and GL3b.
With this configuration, the exhaust gas supplied from the furnace 20 via the connection part 2 passes through the gas line GL1 and is supplied to each of the reactors 4a, 4b.
The gas switching unit 8 can be configured to include, for example, a branch gas line and a flow passage opening and closing mechanism such as a valve provided midway along the branch gas line.

As shown in Fig. 2, each of the reactors 4a and 4b is a multi-tube reactor (fixed-bed reactor) including a plurality of tubes 41 each filled with a reducing agent 4R and a housing 42 containing the plurality of tubes 41. Such a multi-tube reactor can ensure sufficient opportunities for the reducing agent 4R to come into contact with the exhaust gas and the reducing gas. As a result, the production efficiency of the generated gas can be improved.
The reducing agent 4R of the present embodiment is preferably in the form of, for example, particles (granules), flakes, pellets, etc. The reducing agent 4R in such a shape can increase the efficiency of filling the pipe 41, and can further increase the contact area with the gas supplied into the pipe 41.
When the reducing agent 4R is particulate, its volume average particle size is not particularly limited, but is preferably 1 to 50 mm, and more preferably 3 to 30 mm. 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. Similarly, regeneration (reduction) of the reducing agent 4R by a reducing gas containing a reducing substance can also be performed more efficiently.
The particulate reducing agent 4R is preferably a compact produced by rolling granulation, since this increases the sphericity.

The reducing agent 4R may be supported on a carrier. The constituent material of the carrier is not particularly limited as long as it is difficult to be modified depending on the exhaust gas (raw material gas) and reaction conditions, and examples thereof include carbon materials (graphite, graphene, etc.), zeolite, montmorillonite, SiO ₂ , ZrO ₂ , TiO ₂ , V ₂ O ₅ , MgO, alumina (Al ₂ O ₃ ), silica, and composite oxides of these materials. Among these, zeolite, montmorillonite, SiO ₂ , ZrO ₂ , TiO ₂ , V ₂ O ₅ , MgO, alumina (Al ₂ O ₃ ), silica, and composite oxides of these materials are preferred. A carrier made of such a material is preferred in that it does not adversely affect the reaction of the reducing agent 4R and has excellent supporting ability for the reducing agent 4R. Here, the carrier does not participate in the reaction of the reducing agent 4 R, but simply supports (holds) the reducing agent 4 R. One example of such a form is a configuration in which at least a part of the surface of the carrier is coated with the reducing agent 4 R.

The metal oxide (oxygen carrier) contained in the reducing agent 4R is not particularly limited as long as it can reduce carbon dioxide, but it preferably contains at least one type selected from metal elements belonging to groups 3 to 12, more preferably contains at least one type selected from metal elements belonging to groups 4 to 12, and even more preferably contains at least one type of titanium, vanadium, iron, copper, zinc, nickel, manganese, chromium, cerium, etc., and is particularly preferably a metal oxide or composite oxide containing iron. These metal oxides are useful because they have particularly good efficiency in converting carbon dioxide to carbon monoxide.

In each of the reactors 4a and 4b, the tube (cylindrical molded body) 41 may be made of the reducing agent 4R (metal oxide) itself. Furthermore, a molded body having a block shape, a lattice shape (for example, a mesh shape, a honeycomb shape), or the like may be made of the reducing agent 4R and placed in the housing 42. In these cases, the reducing agent 4R as a filler may be omitted or may be used in combination.
Among these, a preferred configuration is one in which a mesh body is made of the reducing agent 4R and placed in the housing 42. In the case of such a configuration, it is possible to prevent an increase in the passage resistance of the exhaust gas and the reducing gas in each of the reactors 4a, 4b, while also ensuring sufficient opportunities for the reducing agent 4R to come into contact with the exhaust gas and the reducing gas.
The volumes of the two reactors 4a, 4b are set to be approximately equal to each other, and are appropriately set according to the amount of exhaust gas to be treated (the size of the furnace 20 and the size of the gas production device 1).

In the gas line GL1, a concentration adjusting section 5, a compression section 6, a minor component removing section 7, and an exhaust gas heating section (raw material gas heating section) 10 are provided in this order from the connection section 2 side.
The concentration adjusting unit 5 adjusts the concentration of carbon dioxide contained in the exhaust gas to increase (in other words, to concentrate carbon dioxide). The exhaust gas also contains unnecessary gas components such as oxygen. By increasing the concentration of carbon dioxide contained in the exhaust gas with the concentration adjusting unit 5, the concentrations of the unnecessary gas components contained in the exhaust gas can be relatively lowered. This makes it possible to prevent or suppress the unnecessary gas components from adversely affecting the efficiency of conversion of carbon dioxide to carbon monoxide by the reducing agent 4R.
The concentration adjusting unit 5 is preferably configured with an oxygen removing device that removes oxygen contained in the exhaust gas. This makes it possible to reduce the amount of oxygen brought into the gas production apparatus 1 (i.e., adjust the concentration of oxygen contained in the exhaust gas to be lower). This makes it possible to move the gas composition of the exhaust gas away from the explosion range and prevent the exhaust gas from igniting. In addition, since the oxygen removing device in the gas production apparatus 1 consumes a large amount of electric energy, it is effective to use electricity as a renewable energy source as described below.

In this case, the concentration of oxygen contained in the exhaust gas is preferably adjusted to less than 1% by volume, more preferably less than 0.5% by volume, and even more preferably less than 0.1% by volume, based on the total volume of the exhaust gas, thereby making it possible to more reliably prevent the exhaust gas from igniting.
The oxygen removal device for removing oxygen contained in exhaust gas can be constructed using one or more of a low-temperature separation type (cryogenic type) separator, a pressure swing adsorption (PSA) type separator, a membrane separation type separator, a temperature swing adsorption (TSA) type separator, a chemical absorption type separator, a chemical adsorption type separator, etc.
In addition, the concentration adjusting unit 5 may adjust the carbon dioxide concentration to a high level by adding carbon dioxide to the exhaust gas.

The compression section 6 increases the pressure of the exhaust gas before it is supplied to the reactors 4a and 4b. This increases the amount of exhaust gas that can be treated at one time in the reactors 4a and 4b. This further improves the efficiency of converting carbon dioxide into carbon monoxide in the reactors 4a and 4b.
The compression section 6 can be composed of, for example, a volumetric compressor such as a centrifugal compressor or an axial flow compressor, a reciprocating compressor, a diaphragm compressor, a single screw compressor, a twin screw compressor, a scroll compressor, a rotary compressor, a rotary piston type compressor, or a slide vane type compressor, a Roots blower (two-blade blower) capable of handling low pressure, a centrifugal blower, or the like.

Among these, from the viewpoint of easiness in increasing the scale of the gas production system 100, it is preferable that the compression section 6 be configured with a centrifugal compressor, and from the viewpoint of reducing the manufacturing costs of the gas production system 100, it is preferable that the compression section 6 be configured with a reciprocating compressor.
The pressure of the exhaust gas after passing through the compression section 6 is not particularly limited, but is preferably 0 to 1 MPaG, more preferably 0 to 0.5 MPaG, and even more preferably 0.01 to 0.5 MPaG. In this case, the efficiency of converting carbon dioxide to carbon monoxide in the reactors 4a and 4b can be further improved without increasing the pressure resistance of the gas production apparatus 1 more than necessary.

The minor component removal section 7 removes minor components (such as trace amounts of unnecessary gas components) contained in the exhaust gas.
The fine component removal section 7 can be composed of at least one type of treatment device selected from the group consisting of a gas-liquid separator, a guard reactor, and a scrubber (absorption tower).
When multiple treatment devices are used, the order of arrangement of the devices is arbitrary, but when a gas-liquid separator and a protective device are used in combination, it is preferable to arrange the gas-liquid separator upstream of the protective device. In this case, the efficiency of removing trace components from the exhaust gas can be further increased, and the service life (life) of the protective device can be extended.

The gas-liquid separator separates, for example, condensed water (liquid) generated when the exhaust gas is compressed in the compression section 6 from the exhaust gas. In this case, unnecessary gas components remaining in the exhaust gas are also dissolved in the condensed water and removed.
The gas-liquid separator can be configured, for example, as a simple container, a swirl-flow separator, a centrifugal separator, a surface tension separator, etc. Among these, it is preferable that the gas-liquid separator is configured as a simple container, since it has a simple configuration and is inexpensive, etc. In this case, a filter that allows the passage of gas but prevents the passage of liquid may be disposed at the gas-liquid interface in the container.
In this case, a liquid line may be connected to the bottom of the container, and a valve may be provided on the way. With this configuration, the condensed water stored in the container can be discharged to the outside of the gas production apparatus 1 through the liquid line by opening the valve.
The liquid line may be connected to a tank 30, which will be described later, so that the discharged condensed water can be reused.

The exhaust gas from which condensed water has been removed in the gas-liquid separator may be configured to be supplied to, for example, a protector.
Such a protector preferably includes a substance capable of capturing trace components (inactivating components) contained in the exhaust gas that reduce the activity of the reducing agent 4R upon contact with the reducing agent 4R.
According to this configuration, when exhaust gas passes through the protector, the substance in the protector reacts (captures) with the inactivated components, thereby preventing or suppressing the exhaust gas from reaching the reducing agent 4R in the reactors 4a and 4b, thereby protecting the exhaust gas (i.e., preventing a decrease in activity). Therefore, it is possible to prevent or suppress a drastic decrease in the efficiency of conversion of carbon dioxide to carbon monoxide by the reducing agent 4R due to the adverse effect of the inactivated components.

Such a substance may be a substance having a composition contained in the reducing agent 4R that reduces the activity of the reducing agent 4R by contacting with an inactivating component, specifically, a metal oxide that is the same as or similar to the metal oxide contained in the reducing agent 4R. Here, a similar metal oxide refers to a metal oxide that contains the same metal element but has a different composition, or a metal oxide that contains different types of metal elements but belongs to the same group in the periodic table of the elements.
The inactivating component is preferably at least one selected from sulfur, mercury, a sulfur compound, a halogen compound, an organic silicone, an organic phosphorus, and an organic metal compound, and more preferably at least one selected from sulfur and a sulfur compound. If such an inactivating component is removed in advance, it is possible to effectively prevent the activity of the reducing agent 4R from decreasing rapidly.
The above-mentioned substance may be any substance whose activity is reduced by the same component as the inactivating component of the reducing agent 4R, and metal oxides such as iron oxide and zinc oxide are preferred because of their excellent ability to capture the inactivating components.

The protective device can be configured in such a way that a mesh material is placed within a housing and particles of the above-mentioned material are placed on the mesh material, or that a honeycomb-shaped filter member or a cylindrical or granular molded body made of the above-mentioned material is placed within the housing.
In particular, when the protective device is placed between the compression section 6 (gas-liquid separator) and the exhaust gas heating section 10, it is possible to improve the efficiency of removing inactivated components while preventing deterioration of the above-mentioned substances due to heat.

The exhaust gas heating section 10 heats the exhaust gas before it is supplied to the reactors 4a and 4b. By preheating the exhaust gas before the reaction (before reduction) in the exhaust gas heating section 10, the conversion (reduction) reaction of carbon dioxide to carbon monoxide by the reducing agent 4R can be further promoted in the reactors 4a and 4b.
The exhaust gas heating section 10 can be composed of, for example, an electric heater 101 and a heat exchanger (economizer) 102 as shown in FIG.
The heat exchanger 102 is configured by bending a part of the piping constituting the gas line GL4 (see below) that discharges the gas (mixed gas) after passing through the reactors 4a and 4b, and bringing it close to the piping constituting the gas line GL1. With this configuration, the heat of the high-temperature gas (mixed gas) after passing through the reactors 4a and 4b is used to heat the exhaust gas before being supplied to the reactors 4a and 4b by heat exchange, so that the heat can be effectively utilized.

The heat exchanger 102 can be configured, for example, as a jacket type heat exchanger, an immersed coil type heat exchanger, a double-pipe type heat exchanger, a shell-and-tube type heat exchanger, a plate type heat exchanger, a spiral type heat exchanger, or the like.
In addition, in the exhaust gas heating section 10, either the electric heater 101 or the heat exchanger 102 may be omitted.
In the exhaust gas heating section 10, a combustion furnace or the like can be used instead of the electric heater 101. However, if the electric heater 101 is used, electricity (electrical energy) as a renewable energy source can be used as the power source, so that the burden on the environment can be reduced.
As the renewable energy, electric energy utilizing at least one selected from photovoltaic power generation, wind power generation, hydroelectric power generation, wave power generation, tidal power generation, biomass power generation, geothermal power generation, solar heat, and geothermal heat can be used.

In addition, an exhaust gas line may be branched off from the gas line GL1 upstream of the exhaust gas heating section 10 (for example, between the gas-liquid separator and the protector midway through the microcomponent removal section 7), and a vent section provided outside the gas manufacturing apparatus 1 may be connected to the end of the exhaust gas line.
In this case, a valve is preferably provided in the exhaust gas line.
If the pressure in the gas production device 1 (gas line GL1) rises more than necessary, a valve can be opened to discharge (release) part of the exhaust gas from the vent through the exhaust gas line, thereby preventing damage to the gas production device 1 due to an increase in pressure.

One end of the gas line GL2 is connected to the reducing gas supply unit 3. On the other hand, the gas line GL2 is connected to the inlet ports of the reactors 4a and 4b provided in the reaction unit 4 via a gas switching unit 8 and two gas lines GL3a and GL3b, respectively.
The reducing gas supply unit 3 supplies a reducing gas containing a reducing substance that reduces the reducing agent 4R oxidized by contact with carbon dioxide. The reducing gas supply unit 3 in this embodiment is composed of a hydrogen generation device that generates hydrogen by electrolysis of water, and a tank (reducing gas raw material storage unit) 30 that stores water and is outside the gas production apparatus 1 is connected to this hydrogen generation device. With this configuration, the reducing gas containing hydrogen (reducing substance) supplied from the hydrogen generation device (reducing gas supply unit 3) passes through the gas line GL2 and is supplied to each of the reactors 4a, 4b.
The hydrogen generation device can generate a large amount of hydrogen relatively cheaply and easily. Another advantage is that the condensed water generated in the gas production device 1 can be reused. Since the hydrogen generation device consumes a large amount of electric energy in the gas production device 1, it is effective to use electricity as a renewable energy source as described above.

The hydrogen generating device may be a device that generates by-product hydrogen. In this case, a reducing gas containing by-product hydrogen is supplied to each of the reactors 4a and 4b. Examples of devices that generate by-product hydrogen include devices that electrolyze a sodium chloride aqueous solution, devices that steam reform petroleum, and devices that manufacture ammonia.
Also, the gas line GL2 may be connected via a connection part to a coke oven outside the gas production apparatus 1 so that the exhaust gas from the coke oven is used as the reducing gas. In this case, the connection part constitutes a reducing gas supply part. This is because the exhaust gas from the coke oven is mainly composed of hydrogen and methane, and contains 50 to 60 volume % hydrogen.
A reducing gas heating section 11 is provided in the gas line GL2. This reducing gas heating section 11 heats the reducing gas before it is supplied to the reactors 4a and 4b. By preheating the reducing gas before reaction (before oxidation) in the reducing gas heating section 11, the reduction (regeneration) reaction of the reducing agent 4R by the reducing gas in the reactors 4a and 4b can be further promoted.

The reducing gas heating section 11 can be configured in the same manner as the above-mentioned exhaust gas heating section 10. The reducing gas heating section 11 is preferably configured with only an electric heater, only a heat exchanger, or a combination of an electric heater and a heat exchanger, and more preferably configured with only a heat exchanger, or a combination of an electric heater and a heat exchanger.
If the reducing gas heating section 11 is equipped with a heat exchanger, the heat of the high-temperature gas (e.g., mixed gas) after passing through the reactors 4a, 4b can be used to heat the reducing gas by heat exchange before being supplied to the reactors 4a, 4b, thereby enabling effective use of heat.

According to the above configuration, by switching the gas line (flow path) in the gas switching unit 8, for example, exhaust gas can be supplied via gas line GL3a to reactor 4a containing pre-oxidized reducing agent 4R, and reducing gas can be supplied via gas line GL3b to reactor 4b containing post-oxidized reducing agent 4R. 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.
In the following formulas 1 and 2, the metal oxide contained in the reducing agent 4R is iron oxide (FeO_x-1) is shown as an example.
Formula 1: CO₂+ FeO_x-1 →CO + FeO_x
Formula 2: H₂+ FeO_x→ H₂O + FeO_x-1
Then, by switching the gas line in the opposite direction in the gas switching unit 8, the reaction of the above formula 2 can be carried out in the reactor 4a, and the reaction of the above formula 1 can be carried out in the reactor 4b.

The reactions shown in the above formulas 1 and 2 are both endothermic reactions. For this reason, the gas production device 1 preferably further includes a reducing agent heating section (not shown in FIG. 1 ) that heats the reducing agent 4R when the exhaust gas or reducing gas is brought into contact with the reducing agent 4R (i.e., when the exhaust gas or reducing gas reacts with the reducing agent 4R).
By providing such a reducing agent heating section, the temperature in the reaction between the exhaust gas or reducing gas and the reducing agent 4R can be maintained at a high temperature, thereby preferably preventing or suppressing a decrease in the conversion efficiency of carbon dioxide to carbon monoxide, and further promoting the regeneration of the reducing agent 4R by the reducing gas.

However, depending on the type of reducing agent 4R, the reactions shown in the above formulas 1 and 2 may be exothermic reactions. In this case, the gas production device 1 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, it is possible to suitably prevent deterioration of the reducing agent 4R during the reaction between the exhaust gas or reducing gas and the reducing agent 4R, suitably prevent or suppress a decrease in the conversion efficiency of carbon dioxide to carbon monoxide, and further promote regeneration of the reducing agent 4R by the reducing gas.
In other words, the gas production device 1 is preferably provided with a reducing agent temperature adjustment unit that adjusts the temperature of the reducing agent 4R depending on the type of reducing agent 4R (exothermic reaction or endothermic reaction).
A suitable configuration of the reducing agent temperature adjustment section will be described in detail later.

The outlet ports of the reactors 4a and 4b are connected to branch gas lines GL4a and GL4b, respectively, which join at a gas junction J4 to form the gas line GL4. In addition, valves (not shown) are provided midway along the branch gas lines GL4a and GL4b, as necessary.
For example, by adjusting the opening of the valve, the passing speed of the exhaust gas and the reducing gas passing through the reactors 4a, 4b (i.e., the treatment speed of the exhaust gas by the reducing agent 4R and the treatment speed of the reducing agent 4R by the reducing gas) can be set.
In this embodiment, the reactors 4 a, 4 b and the gas switching unit 8 constitute the reaction unit 4 .

With this configuration, the gases (mainly carbon monoxide and water vapor in this embodiment) that have passed through each of the reactors 4a, 4b are mixed by merging at the gas junction J4, and after a mixed gas (junction gas) is generated, it passes through a single gas line GL4.
Therefore, by changing the flow path switching state (open/closed state of the valve) of the gas switching unit 8 to perform different reactions in the reactors 4a and 4b, it is possible to continuously produce the mixed gas, and ultimately the product gas can also be continuously produced. In addition, since the same reaction is repeatedly performed alternately in the reactors 4a and 4b, the concentration of carbon monoxide contained in the mixed gas can be stabilized, and as a result, the concentration of carbon monoxide contained in the product gas can also be stabilized.
Therefore, the above-described gas production apparatus 1 (gas production system 100) can continuously and stably produce carbon monoxide from carbon dioxide, which is industrially advantageous.

On the other hand, if the gas junction J4 is not provided, it becomes necessary to shut off the gas switching unit 8 (close the valve once) when switching the gas to be supplied, and each of the reactors 4a and 4b must be of a batch type, which results in a long time for producing carbon monoxide, poor conversion efficiency, and is industrially disadvantageous.
In addition, the components of the gas discharged from each of the reactors 4a and 4b differ every time the gas supply is switched, which makes the post-treatment process of the gas discharged from each of the reactors 4a and 4b complicated.
Here, it is usually preferable to adjust the concentration of carbon monoxide contained in the mixed gas to a specific range (a predetermined volume % relative to the entire mixed gas). If this concentration is too low, it tends to be difficult to obtain a product gas containing a high concentration of carbon monoxide, although this depends on the performance of the gas purification section 9 described below. On the other hand, even if the concentration is increased beyond the upper limit, no further increase in the effect of increasing the concentration of carbon monoxide contained in the final product gas cannot be expected.

A generated gas discharge part 40 that discharges the generated gas to the outside of the gas production apparatus 1 is connected to the end of the gas line GL4 opposite to the reactors 4a, 4b.
Further, a gas purification section 9 is provided in the middle of the gas line GL4.
In the gas purification unit 9, carbon monoxide is purified from the mixed gas and a product gas containing a high concentration of carbon monoxide is recovered. Note that, if the concentration of carbon monoxide in the mixed gas is sufficiently high, the gas purification unit 9 may be omitted.
The gas purification section 9 can be composed of at least one type of treatment device selected from the group consisting of a cooler, a gas-liquid separator, a gas separator, a separation membrane, and a scrubber (absorption tower).
When multiple treatment devices are used, the order of arrangement of the devices may be arbitrary, but when a cooler, a gas-liquid separator, and a gas separator are used in combination, it is preferable to arrange them in this order, which can further increase the efficiency of purifying carbon monoxide from the mixed gas.

The cooler cools the mixed gas, which produces condensed water (liquid).
Such a cooler can be configured to include a jacket-type cooling device in which a jacket is disposed around a pipe for passing a refrigerant, a multi-tube cooling device having a configuration similar to that of the reactors 4a and 4b (see FIG. 2) in which the mixed gas passes through a tube and the refrigerant passes around the tube, an air fin cooler, or the like.

The gas-liquid separator separates condensed water generated when the mixed gas is cooled by the cooler from the mixed gas. At this time, the condensed water has the advantage that it can dissolve and remove unnecessary gas components (especially carbon dioxide) remaining in the mixed gas.
The gas-liquid separator can be configured similarly to the gas-liquid separator of the fine component removing section 7, and can preferably be configured as a simple container. In this case, a filter that allows the passage of gas but prevents the passage of liquid may be disposed at the gas-liquid interface in the container.
In this case, a liquid line may be connected to the bottom of the container, and a valve may be provided on the way. With this configuration, the condensed water stored in the container can be discharged (released) to the outside of the gas production apparatus 1 through the liquid line by opening the valve.

Furthermore, it is preferable to provide a drain trap downstream of the valve in the liquid line. With this, even if the valve malfunctions and carbon monoxide or hydrogen flows into the liquid line, the carbon monoxide or hydrogen can be stored in the drain trap and prevented from being discharged outside the gas production apparatus 1. Instead of or together with this drain trap, a function for detecting valve malfunction and a redundancy measure in case of valve malfunction may be provided.
The liquid line may be connected to the tank 30 described above so as to reuse the discharged condensed water.

The gas separator may be configured using one or more of the following: a low-temperature separation type (cryogenic type) separator, a pressure swing adsorption (PSA) type separator, a membrane separation type separator, a temperature swing adsorption (TSA) type separator, a separator using a porous coordination polymer (PCP) in which a metal ion (e.g., copper ion) and an organic ligand (e.g., 5-azidoisophthalic acid) are composited, and a separator using amine absorption.
A valve may be provided between the gas-liquid separator and the gas separator in the gas line GL4. In this case, the processing speed of the mixed gas (the production speed of the generated gas) can be adjusted by adjusting the opening of the valve.

In this embodiment, the concentration of carbon monoxide contained in the mixed gas discharged from the gas-liquid separator is 75 to 90% by volume with respect to the entire mixed gas.
Therefore, in fields where a product gas containing a relatively low concentration of carbon monoxide (75 to 90% by volume) can be used, the carbon monoxide can be directly supplied to the next process without being purified from the mixed gas, i.e., a gas separator can be omitted.
Such fields include, for example, the field of synthesizing valuable substances (e.g., ethanol, etc.) from generated gas by fermentation with microorganisms (e.g., Clostridium, etc.), the field of producing steel using generated gas as a fuel or reducing agent, the field of producing electric devices, and the field of synthesizing chemicals (phosgene, acetic acid, etc.) using carbon monoxide as a synthetic raw material.

On the other hand, in fields where it is necessary to utilize a product gas containing carbon monoxide at a relatively high concentration (more than 90% by volume), carbon monoxide is purified from the mixed gas to obtain a product gas containing carbon monoxide at a high concentration.
Such fields include, for example, a field in which the generated gas is used as a reducing agent (blast furnaces), a field in which the generated gas is used as fuel to generate electricity by thermal power, a field in which the generated gas is used as a raw material to manufacture chemicals, and a field in which the generated gas is used as fuel for fuel cells.

Next, the use (operation) of the gas production system 100 will be described.
[1] First, the gas lines (flow paths) are switched in the gas switching unit 8 to communicate the connection unit 2 with the reactor 4a and to communicate the reducing gas supply unit 3 with the reactor 4b.
[2] Next, in this state, the supply of exhaust gas from the furnace 20 via the connection part 2 is started.
The exhaust gas supplied from the furnace 20 is usually at a high temperature of 50 to 300° C., but is cooled to 30 to 50° C. before reaching the concentration adjusting section 5 .

[3] Next, the exhaust gas passes through an oxygen remover (concentration adjuster 5), which removes oxygen from the exhaust gas and increases the concentration of carbon dioxide contained in the exhaust gas.
[4] The exhaust gas then passes through compression section 6, which increases the pressure of the exhaust gas.
[5] Next, the exhaust gas passes through the fine component removal section 7. This removes condensed water generated when the exhaust gas is compressed in the compression section 6 and inactive components that reduce the activity of the reducing agent 4R from the exhaust gas.

[6] Next, the exhaust gas passes through the exhaust gas heating section 10. This causes the exhaust gas to be heated.
[7] Next, the exhaust gas is supplied to the reactor 4a. In the reactor 4a, the carbon dioxide in the exhaust gas is reduced to carbon monoxide by the reducing agent 4R. At this time, the reducing agent 4R is oxidized.
The heating temperature of the exhaust gas in the above step [6] is preferably 300 to 700° C., more preferably 450 to 700° C., further preferably 600 to 700° C., and particularly preferably 650 to 700° C. If the heating temperature of the exhaust gas is set within the above range, for example, a sudden decrease in temperature of the reducing agent 4R due to an endothermic reaction when carbon dioxide is converted to carbon monoxide can be prevented or suppressed, and the reduction reaction of carbon dioxide in the reactor 4a can proceed more smoothly.

[8] In parallel with the above steps [2] to [7], water (reducing gas raw material) is supplied from the tank 30 to the hydrogen generation device (reducing gas supply unit 3), and hydrogen is generated from the water.
[9] Next, the reducing gas containing hydrogen passes through the reducing gas heating section 11. This causes the reducing gas to be heated.
[10] Next, the reducing gas is supplied to the reactor 4b. In the reactor 4b, the reducing agent 4R in an oxidized state is reduced (regenerated) by the reducing gas (hydrogen).
The heating temperature of the reducing gas in the above step [9] is preferably 300 to 700° C., more preferably 450 to 700° C., further preferably 600 to 700° C., and particularly preferably 650 to 700° C. If the heating temperature of the reducing gas is set within the above range, for example, a sudden decrease in temperature of the reducing agent 4R due to an endothermic reaction when reducing (regenerating) the reducing agent 4R in an oxidized state can be prevented or suppressed, so that the reduction reaction of the reducing agent 4R in the reactor 4b can proceed more smoothly.

Here, when the heating temperature of the exhaust gas by the exhaust gas heating unit 10 is X [°C] and the heating temperature of the reducing gas by the reducing gas heating unit 11 is Y [°C], |X-Y| (i.e., the absolute value of the difference between X and Y) preferably satisfies a relationship of 0 to 25, more preferably satisfies a relationship of 0 to 20, and even more preferably satisfies a relationship of 0 to 15. In other words, the heating temperature X of the exhaust gas and the heating temperature Y of the reducing gas may be the same or slightly different. If X and Y are set so as to satisfy the above relationship, the conversion of carbon dioxide to carbon monoxide and the reduction of the reducing agent 4R by the reducing gas can be proceeded in a good balance.
In addition, when the heating temperature X of the exhaust gas and the heating temperature Y of the reducing gas are made different, the amount of heat required for the reduction reaction of the reducing agent 4R by the reducing gas tends to be larger than the amount of heat required for the reduction reaction of carbon dioxide by the reducing agent 4R, so it is preferable to set the heating temperature Y of the reducing gas higher than the heating temperature X of the exhaust gas.

In this embodiment, the timing of switching the gas lines in the gas switching unit 8 (i.e., the timing of switching between the exhaust gas and the reducing gas supplied to the reactors 4a, 4b) is preferably set to Condition I: when a predetermined amount of exhaust gas is supplied to the reactor 4a or 4b, or Condition II: when the conversion efficiency of carbon dioxide to carbon monoxide falls below a predetermined value. In this way, the reactors 4a, 4b are switched before the conversion efficiency of carbon dioxide to carbon monoxide drops significantly, so that the concentration of carbon monoxide contained in the mixed gas can be increased and stabilized.
To detect condition II, gas concentration sensors may be disposed near the inlet and outlet ports of the reactors 4a and 4b, respectively. The conversion efficiency of carbon dioxide to carbon monoxide can be calculated based on the detection values of the gas concentration sensors.

In addition, from the viewpoint of further stabilizing the concentration of carbon monoxide contained in the mixed gas, it is preferable to set the amount of exhaust gas supplied to the reactors 4a and 4b and the amount of reducing gas supplied to the reactors 4a and 4b as close as possible. Specifically, when the amount of exhaust gas supplied to the reactors 4a and 4b is P [mL/min] and the amount of reducing gas supplied to the reactors 4a and 4b is Q [mL/min], it is preferable that P/Q satisfies a relationship of 0.9 to 2, and more preferably a relationship of 0.95 to 1.5. If the amount of exhaust gas supplied P is too large, depending on the amount of reducing agent 4R in the reactors 4a and 4b, the amount of carbon dioxide discharged from the reactors 4a and 4b tends to increase without being converted to carbon monoxide.

The predetermined amount in the above condition I is preferably an amount of 0.01 to 3 moles, and more preferably an amount of 0.1 to 2.5 moles, of carbon dioxide per mole of the metal element having the largest mass ratio in the reducing agent 4R.
The predetermined value in the above condition II is preferably 50 to 100%, more preferably 60 to 100%, and even more preferably 70 to 100%. The upper limit of the predetermined value may be 95% or less, or may be 90% or less.
In either case, it is possible to switch between the reactors 4a and 4b before the conversion efficiency of carbon dioxide to carbon monoxide drops drastically, and as a result, a mixed gas containing a high concentration of carbon monoxide can be stably obtained, and therefore a product gas containing a high concentration of carbon monoxide can also be produced.

The supply amount Q of the reducing gas (reducing substance) is preferably 0.1 to 3 moles of hydrogen per mole of the metal element having the largest mass ratio in the reducing agent 4R, and more preferably 0.15 to 2.5 moles. Even if the supply amount Q of the reducing gas is increased beyond the upper limit, no further increase in the effect of reducing the oxidized reducing agent 4R can be expected. On the other hand, if the supply amount Q of the reducing gas is too small, the reduction of the reducing agent 4R may be insufficient depending on the amount of hydrogen contained in the reducing gas.
The pressure of the reducing gas supplied to the reactors 4a and 4b may be atmospheric pressure or pressurized (approximately the same as that of the exhaust gas).

[11] Next, the gases that have passed through the reactors 4a and 4b are joined together to generate a mixed gas. At this point, the temperature of the mixed gas is usually 600 to 650° C. If the temperature of the mixed gas at this point is within the above range, it means that the temperature inside the reactors 4a and 4b is maintained at a sufficiently high temperature, and it can be determined that the conversion of carbon dioxide to carbon monoxide by the reducing agent 4R and the reduction of the reducing agent 4R by the reducing gas are proceeding efficiently.
[12] Next, the mixed gas is cooled to 100 to 300° C. before reaching the gas purification section 9.
[13] Next, the mixed gas passes through the gas purification unit 9. This removes, for example, the generated condensed water and carbon dioxide dissolved in the condensed water. As a result, carbon monoxide is purified from the mixed gas, and a product gas containing a high concentration of carbon monoxide is obtained.
The temperature of the resulting product gas is 20 to 50°C.
[14] Next, the produced gas is discharged from the produced gas discharge section 40 to the outside of the gas production apparatus 1 and is used for the next process.

<Configuration of reducing agent heating unit (reducing agent temperature adjustment unit)>
FIG. 4 is a schematic diagram showing a configuration of the reducing agent heating unit, and FIG. 5 is a schematic diagram showing another configuration of the reducing agent heating unit.
The reducing agent heating section 12 shown in FIG. 4 includes a medium to be supplied to a space 43 defined by a plurality of tubes 41 and a housing 42 in the multi-tube reactors 4a and 4b shown in FIG. 2, a transfer device 121 that transfers the medium to the space 43, and a heating device 122 that heats the medium.

The reducing agent heating section 12 of this configuration example includes a circulating medium line ML1 connected to each of the reactors 4a and 4b, and the medium line ML1 is filled with a medium. The medium line ML1 branches along the way, then connects to each of the reactors 4a and 4b, and then merges again to form a single line. A transfer device 121 and a heating device 122 are disposed along the combined medium line ML1.
According to this configuration, the medium heated by the heating device 122 is supplied to the space 43 of the reactors 4a, 4b when circulating through the medium line ML1. This causes the reducing agent 4R to be indirectly heated through the tube 41. In addition, the heating temperatures of the reducing agent 4R in the two reactors 4a, 4b can be set to be approximately equal.
The heating temperature of the reducing agent 4R is preferably 300 to 700° C., and more preferably 650 to 700° C. If the heating temperature is too high, the reducing agent 4R tends to deteriorate and become less active, although this depends on the type of metal oxide constituting the reducing agent 4R. On the other hand, if the heating temperature is too low, it tends to take a long time to produce a product gas containing a high concentration of carbon monoxide.

The medium may be a gas, a liquid (including a viscous liquid), or the like.
The heating device 122 can be composed of only an electric heater, or can be composed of an electric heater and a heat exchanger similar to that described in the exhaust gas heating section 10 .
According to the latter configuration, the heat of the high-temperature gas after passing through the reactors 4a, 4b is utilized to heat the medium by heat exchange before being supplied to the reactors 4a, 4b, thereby enabling effective use of heat.
When a gas is used as the medium, the transfer device 121 may be configured with a blower, and when a liquid is used as the medium, the transfer device 121 may be configured with a pump.
The reducing agent heating unit 12 may be configured with an electric heater instead of using a medium (heating gas). In this case, heating by the electric heater may be performed on the housing 42 of the reactors 4a and 4b, or may be performed separately on the tube 41 filled with the reducing agent 4R.

The reducing agent heating section 12 shown in FIG. 5 includes a non-circulating medium line ML2, and is configured to use the air (gas) as the medium.
In this configuration example, a transfer device 121 (blower), a first heat exchanger 123, and a heating device 124 composed of an electric heater are arranged in this order from the atmospheric supply port side of the medium line ML2, and a second heat exchanger 125 is arranged on the atmospheric exhaust port side.
It is preferable that the first heat exchanger 123 and the second heat exchanger 125 each have a configuration similar to that of the heat exchanger 102 .
The first heat exchanger 123 exchanges heat between the gas (e.g., mixed gas) that has passed through the inside of the tubes 41 of the reactors 4a and 4b and the atmosphere before being supplied to the space 43 of the reactors 4a and 4b. On the other hand, the second heat exchanger 125 exchanges heat between the atmosphere that has passed through the space 43 of the reactors 4a and 4b and the exhaust gas before being supplied to the reactors 4a and 4b.

The heat of the high-temperature gas or the atmosphere (medium) after passing through the reactors 4a, 4b is used to heat the atmosphere (medium) or exhaust gas before being supplied to the reactors 4a, 4b by heat exchange, thereby making it possible to effectively utilize heat.
In addition, instead of being configured to exchange heat with the exhaust gas before being supplied to the reactors 4a, 4b, the second heat exchanger 125 may be configured to exchange heat with the reducing gas before being supplied to the reactors 4a, 4b, or may be configured to exchange heat with both the exhaust gas and the reducing gas before being supplied to the reactors 4a, 4b.
In addition, according to the configuration example shown in FIG. 5, the temperature of the medium contacting the transport device 121 is lower than in the configuration example shown in FIG. 4, so there is an advantage that a relatively inexpensive transport device with low heat resistance can be used.

Here, if a combustion furnace or the like is used to heat the reactors 4a and 4b (reducing agent 4R), it becomes necessary to burn fuel to maintain the heating temperature (reaction temperature) of the reducing agent 4R, which generates carbon dioxide, which must be released into the atmosphere.
In contrast, by configuring the reducing agent heating section 12 as shown in Figures 4 and 5, electricity (electrical energy) as renewable energy as described above can be used as the power source for the transfer device 121 and the heating devices 122 and 124, thereby reducing the burden on the environment.
Another advantage is that the possibility of ignition of combustible gas present in the gas production apparatus 1 can be more reliably reduced.

As described above, when the reaction caused by the reducing agent 4R is an exothermic reaction, the reducing agent temperature adjustment unit can be configured as a reducing agent cooling unit. In this case, for example, in the configuration shown in Figures 4 and 5, the first heat exchanger 123 and the second heat exchanger 125 can be omitted, and the heating devices 122 and 124 can be changed to cooling devices. Examples of cooling devices include jacket-type cooling devices and multi-tube cooling devices. In this case, too, it is preferable to set the cooling temperature of the reducing agent 4R (temperature after temperature adjustment) to the same range as described above.

<Configuration near the connection part>
FIG. 6 is a schematic diagram showing the configuration of the vicinity of the connection part (raw material gas supply part) between the gas production apparatus of the present invention and the furnace.
As shown in Fig. 6, the furnace 20 is provided with a chimney 21 for discharging exhaust gas into the atmosphere. One end of a gas line 23 is connected to a branching portion 22 midway along the height of the chimney 21. The other end of the gas line 23 is connected to a connection portion 2 of the gas production device 1.

6, a cooling section 13 is provided between the connection section 2 and the concentration adjusting section 5. The cooling section 13 includes a cooling device 131 and a container 132 connected to the cooling device 131. The cooling device 131 can be configured as a jacket-type cooling device or a multi-tube-type cooling device as described above.
Since the exhaust gas supplied from the furnace 20 contains oxidizing gas components (SO _x , HCl, etc.) in addition to water vapor, it is preferable to condense the water vapor together with the oxidizing gas components by cooling in the cooling section 13 and remove them as condensed water (acidic aqueous solution) in which the oxidizing gas components are dissolved. This makes it possible to suitably prevent corrosion of the piping that constitutes the gas line GL1.
In this configuration example, an acidic aqueous solution is generated by cooling the exhaust gas with the cooling device 131, and this acidic aqueous solution is stored in the container 132 and separated from the exhaust gas. In addition, a filter that allows the passage of gas but prevents the passage of liquid may be disposed at the gas-liquid interface in the container 132.
In such a configuration, the distance (L1 in FIG. 6) between the branching portion 22 and the cooling device 131 is not particularly limited, but is preferably 10 m or less, and more preferably 1 to 5 m. By setting the distance L1 within the above range, it is possible to prevent the generation of condensed water (acidic aqueous solution) in which acid gas is dissolved, in unintended locations in the gas line GL1, and more reliably prevent corrosion of the piping that constitutes the gas line GL1.

Furthermore, when the gas production system 100 is installed in a cold region, for example, depending on the distance L2 between the furnace 20 and the gas production device 1, condensed water may be generated in the middle of the gas line 23 and may even freeze. This may cause the piping that constitutes the gas line 23 to break.
Therefore, in order to prevent such trouble, it is preferable to heat the exhaust gas in the gas line 23. The heating temperature may be any temperature at which freezing does not occur, but is preferably equal to or higher than the acid dew point temperature (e.g., 120° C.), and more preferably 120 to 150° C. This makes it possible to prevent damage to the pipes constituting the gas line 23, while also suitably preventing corrosion of the pipes due to the generation of condensed water in which acid gas is dissolved.
In order to heat the exhaust gas in the gas line 23, for example, an electric heating wire (heater) may be wound around the piping constituting the gas line 23. For the purpose of corrosion resistance, a resin-lined pipe made of a corrosion-resistant resin material (for example, a fluororesin material) may be used instead of a heater.
In this configuration example, the container 132 may be omitted, if necessary.

In the above embodiment, exhaust gas has been described as a representative example of a raw material gas, but as described above, the raw material gas is not limited to exhaust gas as long as it is a gas containing carbon dioxide. Therefore, in the above embodiment, the various processing conditions for the exhaust gas (including the pressure of compression by the compression section 6, the heating temperature before supplying to the reactors 4a and 4b, the amount of supply to the reactors 4a and 4b, etc.) can be similarly applied to other raw material gases.

By using the gas production apparatus 1 and the gas production system 100 as described above, a product gas containing carbon monoxide can be produced from a raw material gas containing carbon dioxide.
<Gas production method>
The gas production method of the present embodiment is a method for producing a product gas containing carbon monoxide by contacting the exhaust gas (raw material gas) with the reducing agent 4R, and includes the steps of: I: preparing a plurality of reactors 4a, 4b in which the reducing agent 4R is disposed, and exhaust gas and a reducing gas containing hydrogen (reducing substance) that reduces the reducing agent 4R oxidized by contact with carbon dioxide; II: by switching between the reactors 4a, 4b for supplying the exhaust gas and the reducing gas, the reducing agent 4R is alternately brought into contact with the exhaust gas and the reducing gas in each of the reactors 4a, 4b to produce a carbon monoxide-containing product gas. After converting oxidized carbon into carbon monoxide, the oxidized reducing agent 4R is reduced; III: the gases that have passed through the reactors 4a, 4b are joined together to generate a mixed gas; IV: the mixed gas is recovered as is or as a product gas by purifying carbon monoxide from the mixed gas. When the reducing agent 4R is brought into contact with the exhaust gas or reducing gas, a temperature-controlled medium is supplied to a space partitioned from the reducing agent 4R in each of the reactors 4a, 4b to adjust the temperature of the reducing agent 4R (heat or cool the reducing agent 4R).

＜Product＞
The product gas produced using the gas production apparatus 1 and the gas production system 100 generally has a carbon monoxide concentration of 60 vol % or more, preferably 75 vol % or more, and more preferably 90 vol % or more.
Furthermore, the generated gas as described above can be used in fields such as the synthesis of valuable substances (e.g., ethanol, etc.) by fermentation with microorganisms (e.g., Clostridium, etc.), the production of steel using it as a fuel or reducing agent, the production of electric devices, the production of chemicals (phosgene, acetic acid, etc.) using carbon monoxide as a synthetic raw material, the use of it as a reducing agent (blast furnaces), the use of it as a fuel for thermal power generation, and the use of it as a fuel in fuel cells, etc.

In the above-described gas production system 100 (gas production apparatus 1), the gases passing through the reactors 4a and 4b are joined together immediately after passing through the reactors 4a and 4b, but various treatments may be performed before joining together. That is, at least one type of treatment device can be provided in the middle of the branch gas lines GL4a and GL4b for any purpose.
Next, the gas production system 100 having such a configuration will be described.
FIG. 7 is a schematic diagram showing another embodiment of the gas production system of the present invention, and FIG. 8 is a cross-sectional view showing a schematic configuration of the purifier of FIG.
Hereinafter, the gas production system 100 shown in FIG. 7 will be described, focusing on the differences from the gas production system 100 shown in FIG. 1, and a description of the similar points will be omitted.
7 further includes purifiers 14a, 14b provided in the branch gas lines GL4a, GL4b. That is, the purifiers 14a, 14b are connected downstream of the corresponding reactors 4a, 4b, and the gases that have passed through the reactors 4a, 4b and the purifiers 14a, 14b in sequence are joined at a gas junction J4.

8, each of the purifiers 14a, 14b is configured as a multi-tube type purification device including a plurality of separation tubes 141 and a housing (purifier body) 142 that houses the plurality of separation tubes 141. According to such a multi-tube type purification device, it is possible to ensure a sufficient opportunity for the gas that has passed through the reactors 4a, 4b to come into contact with the separation tubes 141.
Each of the purifiers 14a, 14b is preferably configured to be capable of at least one of separating water (oxide of the reducing substance) and hydrogen (reducing substance) generated by contact with the reducing agent 4R, and separating carbon monoxide and carbon dioxide. In particular, the separation tube 141 is preferably configured to allow water (water vapor) or carbon monoxide to pass through its wall and separate it from hydrogen or carbon dioxide.

In this embodiment, the water and carbon monoxide that permeate the separation tube 141 are discharged from the purifiers 14a and 14b to the branch gas lines GL4a and GL4b. On the other hand, the reducing gas (unreacted hydrogen) and exhaust gas (unreacted carbon dioxide) that pass through the separation tube 141 are discharged to the gas lines GL14a and GL14b connected to the housing 142 (space 143).
These gas lines GL14a and GL14b may be connected to the gas lines GL1 and GL2, respectively, so that unreacted hydrogen and carbon dioxide can be reused.
The gas discharged to the branch gas lines GL4a and GL4b may contain gas components other than water or carbon monoxide, and the gas discharged to the gas lines GL14a and GL14b may contain gas components other than hydrogen or carbon dioxide.

In addition, the separation of carbon monoxide and carbon dioxide, and the separation of water and hydrogen can also be achieved by cooling the gas discharged from each reactor 4a, 4b by utilizing the difference in condensation (liquefaction) temperature. However, in this case, when the separated gas components are used at a high temperature downstream of the reactors 4a, 4b (for example, when used in the heat exchanger 102), they need to be heated again, resulting in a waste of thermal energy. In contrast, the purifiers 14a, 14b can perform the separation operation of the gas components at a high temperature (for example, 200 to 500°C), so that the temperature of the separated gas components is unlikely to decrease, which can contribute to a reduction in thermal energy in the overall production of the generated gas.
In addition, from the standpoint of more reliably preventing a decrease in the temperature of the gas components after separation by the refiners 14a and 14b, a heating device (e.g., an irradiation device that irradiates microwaves) for heating the separation tube 141 may be provided.

As described above, gas at a relatively high temperature is discharged from each of the reactors 4a and 4b. Therefore, it is preferable that the separation tube 141 has heat resistance. This can prevent the separation tube 141 from being altered or deteriorated.
The separation tube 141 is preferably made of a metal, an inorganic oxide, or a metal organic framework (MOF). In this case, it is easy to impart excellent heat resistance to the separation tube 141. Examples of the metal include titanium, aluminum, copper, nickel, chromium, cobalt, and alloys containing these. Examples of the inorganic oxide include silica and zeolite. Examples of the metal organic framework include a structure of zinc nitrate hydrate and terephthalic acid dianion, and a structure of copper nitrate hydrate and trimesic acid trianion. When a metal is used, the separation tube 141 is preferably made of a porous material having a porosity of 80% or more.

The separation tube 141 is preferably made of a porous body having continuous pores (pores penetrating the tube wall) in which adjacent pores are connected to each other. With the separation tube 141 having such a configuration, the permeability of water or carbon monoxide can be increased, and separation of water and hydrogen and/or separation of carbon monoxide and carbon dioxide can be performed more smoothly and reliably.
The porosity of the separation tube 141 is not particularly limited, but is preferably 5 to 95%, more preferably 10 to 90%, and even more preferably 20 to 60%. This makes it possible to prevent the mechanical strength of the separation tube 141 from decreasing excessively while maintaining a sufficiently high permeability to water or carbon monoxide.
The shape of the separation tube 141 is not particularly limited, and examples thereof include a cylindrical shape, a rectangular shape, and a rectangular tube shape such as a hexagon.

From the viewpoint of improving the handleability of the gas after merging at the gas junction J4 (preventing ignition) and maintaining high production efficiency of the generated gas, it is effective to remove unreacted hydrogen.
That is, as shown in FIG. 8, it is preferable to configure the system so that water is moved from hydrogen (H ₂ ) and water (H ₂ O) that have passed through reactors 4 a and 4 b to a space 143 in a housing 142 via a separation tube 141 .
In this case, the average pore diameter of the separation cylinder 141 is preferably 600 pm or less, and more preferably 400 to 500 pm, so that the efficiency of separating water and hydrogen can be further improved.
The space 143 within the housing 142 may be depressurized or a carrier gas (sweep gas) may be passed through the space 143. Examples of the carrier gas include an inert gas such as helium or argon.

Moreover, it is preferable that separation tube 141 has hydrophilic properties. If separation tube 141 has hydrophilic properties, the affinity of water to separation tube 141 increases, and water can more easily pass through separation tube 141.
Methods for imparting hydrophilicity to separation tube 141 include a method of improving the polarity of separation tube 141 by changing the ratio of metal elements in the inorganic oxide (e.g., increasing the Al/Si ratio), a method of coating separation tube 141 with a hydrophilic polymer, a method of treating separation tube 141 with a coupling agent having a hydrophilic group (polar group), a method of subjecting separation tube 141 to plasma treatment, corona discharge treatment, etc.
Furthermore, the surface potential of the separation cylinder 141 may be adjusted to control its affinity for water.

On the other hand, when separation of carbon monoxide and carbon dioxide is given priority in separation tube 141, and when separation of water and hydrogen and separation of carbon monoxide and carbon dioxide are both performed simultaneously, the constituent material, porosity, average pore size, degree of hydrophilicity or hydrophobicity, surface potential, etc. of separation tube 141 can be set in an appropriate combination.
The refiner may be provided midway along the gas line GL4, between the gas junction J4 and the gas refinement unit 9.
In addition, when the purifiers 14a and 14b are provided, the gas purifying section 9 may be omitted.

Although the gas production apparatus, the gas production system, and the gas production method of the present invention have been described above, the present invention is not limited to these.
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-mentioned embodiments, may be replaced with any configuration that performs a similar function, or some configurations may be omitted.
Moreover, in the gas production method of the present invention, a step for any purpose may be added to the above embodiment.

In the above embodiment, a gas containing hydrogen has been described as a representative reducing gas. However, the reducing gas may be a gas containing at least one selected from hydrocarbons (e.g., methane, ethane, acetylene, etc.) and ammonia as a reducing substance instead of or in addition to hydrogen.
In the above embodiment, the heat exchanger is configured to exchange heat between the exhaust gas (raw material gas), the reducing gas or the heating medium before being supplied to the reactor and the mixed gas. However, a heat exchanger configured to exchange heat with the gas discharged from each reactor and before being made into the mixed gas may be adopted.

100...gas production system 1...gas production device 2...connection section 3...reducing gas supply section 4...reaction section 4a, 4b...reactor 41...tube body, 42...housing, 43...space, 44...partition section, 4R...reducing agent 5...concentration adjustment section 6...compression section 7...trace component removal section 8...gas switching section 9...gas purification section 10...exhaust gas heating section 101...electric heater, 102...heat exchanger 11...reducing gas heating section 12...reducing agent heating section 121...transfer device, 122...heating device, 123...first heat exchanger, 124...electric heater,
125...Second heat exchanger 13...Cooling section 131...Cooling device, 132...Container 14a, 14b...Refiner 141...Separation tube, 142...Housing, 143...Space 20...Furnace 21...Chimney, 22...Branch section, 23...Gas line 30...Tank 40...Produced gas discharge section GL1...Gas line GL2...Gas line GL3a, GL3b...Gas line GL4...Gas line GL4a, GL4b...Branch gas line, J4...Gas junction GL14a, GL14b...Gas line L1...Separation distance L2...Separation distance

Claims (5)

A gas production apparatus for producing a product gas containing carbon monoxide by contacting a raw material gas containing carbon dioxide with a reducing agent containing a metal oxide that reduces the carbon dioxide, the apparatus comprising:
a raw material gas supply unit for supplying the raw material gas;
a reducing gas supply unit that supplies a reducing gas containing a reducing substance that reduces the reducing agent that has been oxidized by contact with the carbon dioxide;
a reaction section including a plurality of reactors each connected to the raw material gas supply section and the reducing gas supply section, and the reducing agent disposed in the reactors, the reaction section being capable of switching between the raw material gas and the reducing gas supplied to each of the reactors;
a gas junction section for merging the gases that have passed through the reactor to generate a mixed gas;
a reducing agent heating unit that heats the temperature of the reducing agent when the reducing agent is brought into contact with the raw material gas or the reducing gas,
Each of the reactors includes a plurality of tubes each filled with the reducing agent, and a housing that houses the plurality of tubes;
The reducing agent heating unit comprises a medium to be supplied to a space defined by the plurality of tubes and the housing, a transfer device to transfer the medium to the space, a heating device to heat the medium, and a first heat exchanger to exchange heat between the mixed gas and the medium before being supplied to the space of the reactor . 2. The gas manufacturing apparatus according to claim 1, wherein the reducing agent heating unit is provided with a second heat exchanger that exchanges heat between the medium after passing through the space of the reactor and at least one of the raw material gas and the reducing gas before being supplied to the reactor. 3. The gas production apparatus according to claim 1 , wherein the metal oxide contains at least one metal element selected from the group consisting of metal elements belonging to groups 3 to 12. a raw material gas generating unit that generates a raw material gas containing carbon dioxide;
The gas production apparatus according to any one of claims 1 to 3 ,
The gas production system is characterized in that the gas production apparatus is connected to the raw material gas generation unit via the raw material gas supply unit. 1. A gas production method for producing a product gas containing carbon monoxide by contacting a raw material gas containing carbon dioxide with a reducing agent containing a metal oxide that reduces the carbon dioxide, comprising:
preparing a plurality of reactors each having the reducing agent disposed therein, the raw material gas, and a reducing gas containing a reducing substance that reduces the reducing agent oxidized by contact with the carbon dioxide;
by switching the reactors to which the raw material gas and the reducing gas are supplied, the raw material gas and the reducing gas are alternately brought into contact with the reducing agent in each of the reactors to convert the carbon dioxide into carbon monoxide, and then the oxidized reducing agent is reduced;
The gases that have passed through the reactor are combined to generate a mixed gas;
When recovering the mixed gas as the product gas as it is or by purifying the carbon monoxide from the mixed gas,
When the raw material gas or the reducing gas is brought into contact with the reducing agent, a heated medium is supplied to a space partitioned from the reducing agent in each of the reactors, thereby heating the temperature of the reducing agent;
2. A method for producing a gas, comprising the steps of: heating the medium by a heating device and exchanging heat between the mixed gas and the medium before it is fed into the space of the reactor .

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