Method for producing synthetic fuel

Abstract

To provide a method for producing a synthetic fuel capable of reducing carbon dioxide emissions into the atmosphere.SOLUTION: There is provided a method for producing a synthetic fuel which comprises: a gasification step (G) of gasifying a waste product by reacting with oxygen and water at a high temperature; a carbon dioxide separation step (S) of separating carbon dioxide from a gasified gas (1) produced in the step (G); an FT synthesis step of subjecting a synthesis gas (2) in which carbon dioxide is separated in the step (S) to Fischer-Tropsch synthesis to produce a synthesis fuel and further comprises a carbon dioxide electrolysis step (E) of electrolyzing carbon dioxide separated in the step (S) to produce an electrolysis gas (3) containing carbon monoxide and carbon dioxide, wherein the electrolysis gas (3) produced in carbon dioxide electrolysis step (E) is supplied to the carbon dioxide separation step (S) to separate carbon dioxide from the gasified gas (1) and the electrolysis gas (3).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing synthetic fuels such as SAF (Sustainable aviation fuel) and diesel fuel from waste such as biomass, and more particularly to a method for producing synthetic fuels that can reduce the amount of carbon dioxide emitted into the atmosphere during the gasification of waste with oxygen and water at high temperature.

Background Art

[0002] Conventionally, there has been known a technique for gasifying waste such as woody biomass and MSW (Municipal Solid Waste) with oxygen and water at high temperature in a gasification furnace, and synthesizing the obtained carbon monoxide and hydrogen by Fischer-Tropsch (FT) synthesis to produce synthetic fuel.

[0003] FIG. 2 is a flowchart showing an example of each step of a conventional method for producing synthetic fuel. The method shown in FIG. 2 includes a gasification step (G) in which waste such as woody biomass and MSW is reacted with oxygen and water at high temperature to produce a gasification gas (1) containing carbon dioxide, carbon monoxide, and hydrogen, a carbon dioxide separation step (S) in which carbon dioxide is separated from the gasification gas (1) produced in the gasification step (G), and an FT synthesis step in which a synthesis gas (2) (a gas containing carbon monoxide and hydrogen) from which carbon dioxide has been separated in the carbon dioxide separation step (S) is subjected to FT synthesis to produce synthetic fuel. In this conventional method, the carbon dioxide separated in the carbon dioxide separation step (S) is usually discharged into the atmosphere.

[0004] In addition, as a method for producing synthetic fuel using carbon dioxide as one of the raw materials, for example, there is a method described in Patent Document 1. Patent Document 1 discloses a process in which carbon dioxide and water are co-electrolyzed in a synthesis gas generation cell (solid oxide electrolysis cell) to be converted into carbon monoxide and hydrogen, and then this is converted into hydrocarbon fuel in a catalytic reactor.

[0005] The reaction equations for producing synthetic fuels such as SAF from waste such as biomass by FT synthesis are represented as follows. C p H q +pH2O → pCO+(p+(q / 2))H2(1) CO+H2O ←→ CO2+H2(2) nCO+(2n+1)H2→ C n H 2n+2 +nH2O (3)

[0006] The above reaction equation (1) represents the reaction of producing carbon monoxide (CO) and hydrogen gas (H2) by partially burning or steam gasifying waste. And the reaction equation (3) represents the reaction of producing synthetic fuel (C n H 2n+2 ) from carbon monoxide (CO) and hydrogen gas (H2). The amount of hydrogen gas (H2) used relative to the amount of carbon monoxide (CO) used is 2 times or more (2n + 1). On the other hand, as represented by the reaction equation (2), a shift reaction occurs between carbon monoxide and water (CO + H2O) and carbon dioxide and hydrogen gas (CO2 + H2). As a result, when the production amount of carbon monoxide (CO) is large, the production amount of hydrogen gas (H2) decreases, and conversely, when the production amount of hydrogen gas (H2) is large, the production amount of carbon monoxide (CO) decreases. Therefore, when increasing the production amount of hydrogen gas (H2) to 2 times or more the production amount of carbon monoxide, the production amount of carbon monoxide (CO) decreases accordingly. Moreover, the production amount of carbon dioxide (CO2) discharged into the atmosphere increases.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] In the conventional method shown in FIG. 2, the carbon dioxide separated in the carbon dioxide separation step (S) is usually discharged into the atmosphere. However, discharging a large amount of carbon dioxide, which is one of the greenhouse gases, into the atmosphere is not preferable from the viewpoint of preventing global warming. Therefore, the present inventor has studied an effective recycling method for carbon dioxide in order to reduce the amount of carbon dioxide discharged into the atmosphere.

[0009] That is, an object of the present invention is to provide a method for producing a synthetic fuel capable of reducing the amount of carbon dioxide discharged into the atmosphere.

Means for Solving the Problems

[0010] As a result of intensive studies to achieve the above object, the present inventor has found that it is very effective to combine steps such as a carbon dioxide electrolysis step with the conventional method shown in FIG. 2 and recycle carbon monoxide generated by electrolysis as a raw material for Fischer-Tropsch synthesis, and has completed the present invention. That is, the present invention is specified by the following matters.

[0011] [1] A gasification step (G) of reacting waste, oxygen, and water at a high temperature to gasify them and generate a gasified gas (1) containing carbon dioxide, carbon monoxide, and hydrogen, A carbon dioxide separation step (S) of separating carbon dioxide from at least the gasified gas (1) generated in the gasification step (G), A Fischer-Tropsch synthesis step of Fischer-Tropsch synthesizing a synthesis gas (2) from which carbon dioxide has been separated in the carbon dioxide separation step (S) to generate a synthetic fuel, In a method for producing a synthetic fuel having further having a carbon dioxide electrolysis step (E) of electrolyzing carbon dioxide separated in the carbon dioxide separation step (S) to generate an electrolysis gas (3) containing carbon monoxide and carbon dioxide, A method for producing a synthetic fuel, characterized in that the electrolysis gas (3) generated in the carbon dioxide electrolysis step (E) is supplied to the carbon dioxide separation step (S) to separate carbon dioxide from the gasified gas (1) and the electrolysis gas (3).

[0012] [2] Further, it has a water electrolysis step (WE) of electrolyzing water to generate oxygen and hydrogen, supplies the generated hydrogen to the FT synthesis step, and supplies the generated oxygen to the gasification step (G). The method for producing synthetic fuel according to [1].

[0013] [3] Further, it has an oxygen separation step of separating oxygen from air, and supplies the separated oxygen to the gasification step (G). The method for producing synthetic fuel according to [1] or [2].

[0014] [4] An improved method for reducing the amount of carbon dioxide discharged into the atmosphere in an existing synthetic fuel production facility, A gasification device (g) that gasifies waste by reacting it with oxygen and water at a high temperature to generate a gasification gas (1) containing carbon dioxide, carbon monoxide, and hydrogen, A carbon dioxide separation device (s) that separates carbon dioxide from at least the gasification gas (1) generated in the gasification device (g), An FT synthesis device that Fischer-Tropsch synthesizes the synthesis gas (2) from which carbon dioxide has been separated in the carbon dioxide separation device (s) to generate synthetic fuel, For an existing synthetic fuel production facility having, Add a carbon dioxide electrolysis device (e) that electrolyzes the carbon dioxide separated in the carbon dioxide separation device (s) to generate an electrolysis gas (3) containing carbon monoxide and carbon dioxide, Supply the electrolysis gas (3) generated in the carbon dioxide electrolysis device (e) to the carbon dioxide separation device (s), and separate carbon dioxide from the gasification gas (1) and the electrolysis gas (3). An improved method for a synthetic fuel production facility.

[0015] [5] Further, add a water electrolysis device (we) that electrolyzes water to generate oxygen and hydrogen, supply the generated hydrogen to the FT synthesis device, and supply the generated oxygen to the gasification device (g). The improved method for a synthetic fuel production facility according to [4].

Advantages of the Invention

[0016] In the present invention, since a part of the carbon dioxide that was conventionally discharged into the atmosphere is reduced to carbon monoxide in the carbon dioxide electrolysis step (E) and recycled as a raw material for FT synthesis, the amount of carbon dioxide discharged into the atmosphere can be reduced.

[0017] Furthermore, it is preferable to supply hydrogen generated by electrolyzing water to the FT synthesis step. Thereby, the shortage of hydrogen in the raw material gas in the FT synthesis step can be compensated. In this case, the molar amount of hydrogen generated by electrolyzing water and supplied to the FT synthesis step is preferably 2 times or more the molar amount of carbon monoxide in the electrolysis gas (3). Thereby, the composition balance of the raw material gas in the FT synthesis step becomes suitable.

[0018] Furthermore, it is also preferable to supply oxygen generated by electrolyzing water to the gasification step (G). By using this oxygen for gasifying waste, the load on the oxygen separation step can be reduced.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0020] FIG. 1 is a flowchart showing an example of each step of the method for producing a synthetic fuel of the present invention. Hereinafter, each step will be described.

[0021] [Oxygen Separation Step] The oxygen separation step shown in FIG. 1 is a step of separating oxygen from air. The oxygen separated in this oxygen separation step is supplied to the gasification step (G) described later.

[0022] As a method for separating oxygen from air in this oxygen separation step, typically, a method (Vacuum Pressure Swing Adsorption (VPSA) method) of adsorbing gases other than oxygen in air (such as nitrogen) onto an adsorbent (e.g., synthetic zeolite) by adjusting the pressure to obtain high-purity oxygen gas can be mentioned. The adsorbed gases other than oxygen (such as nitrogen) may be discharged into the atmosphere. Regarding the specific reaction conditions, types of adsorbents, and reaction apparatus configurations, known conditions, types, and configurations related to oxygen separation technology can be adopted without limitation.

[0023] In the present invention, it is preferable to use the above-described VPSA step as one of the steps for obtaining oxygen to be supplied to the gasification step (G). However, the present invention is not limited thereto. Instead of the VPSA step, high-purity oxygen gas may be obtained by other known methods (such as cryogenic separation method) and supplied to the gasification step (G). Although the VPSA step is often advantageous in terms of economy, for example, in a small-scale plant, the cryogenic separation method may be more advantageous in terms of economy.

[0024] [Gasification step (G)] The gasification step (G) shown in FIG. 1 is a step of reacting waste, oxygen, and water at a high temperature to gasify them and generate a gasification gas (1) [CO2 / CO / H2] containing carbon dioxide, carbon monoxide, and hydrogen. The gasification gas (1) [CO2 / CO / H2] generated in this gasification step (G) is supplied to the carbon dioxide separation step (S) described later.

[0025] As a method for reacting waste, oxygen, and water at a high temperature to gasify them in this step (G), typically, a method of supplying waste, oxygen, and water to a gasification furnace (melting furnace) and reacting them at a predetermined temperature and pressure can be mentioned. Regarding the specific reaction conditions and reaction apparatus configurations, known conditions and configurations related to gasification technology can be adopted without limitation. For example, the reaction temperature is usually 700°C or higher, preferably 800°C to 1200°C.

[0026] In the gasification process (G), the waste used as a raw material is, for example, lignocellulosic biomass or MSW (Municipal Solid Waste). However, the present invention is not limited thereto. For example, waste such as herbaceous biomass and PKS (Palm Kernel Shell) can also be used.

[0027] [Carbon dioxide separation process (S)] The carbon dioxide separation process (S) shown in FIG. 1 is a process for separating carbon dioxide from the gasification gas (1) [CO2 / CO / H2] generated in the gasification process (G) and the electrolysis gas (3) [CO2 / CO] generated in the carbon dioxide electrolysis process (E) described later.

[0028] The carbon dioxide separated in this carbon dioxide separation process (S) is not discharged into the atmosphere but is supplied to the carbon dioxide electrolysis process (E) described later for recycling. As a result, the amount of carbon dioxide discharged into the atmosphere can be reduced.

[0029] On the other hand, the synthesis gas after carbon dioxide is separated, that is, the synthesis gas (2) [CO / H2] containing carbon monoxide and hydrogen, is supplied as a raw material for synthetic fuel to the FT synthesis process described later.

[0030] As a method for separating carbon dioxide from the gasification gas (1) and the electrolysis gas (3) in this process (S), typically, a chemical absorption method is exemplified in which carbon dioxide is absorbed by an absorption liquid such as an amine in an absorption process and carbon dioxide is separated by heating the absorption liquid in a regeneration process. Regarding the specific reaction conditions and reaction apparatus configuration, known conditions and configurations related to carbon dioxide separation technology can be adopted without limitation.

[0031] [Carbon dioxide electrolysis process (E)] The carbon dioxide electrolysis process (E) shown in FIG. 1 is a process for electrolyzing the carbon dioxide separated in the carbon dioxide separation process (S) to generate an electrolysis gas (3) [CO / CO2] containing carbon monoxide and carbon dioxide. The electrolysis gas (3) [CO / CO2] generated in this carbon dioxide electrolysis process (E) is returned to the carbon dioxide separation process (S).

[0032] The carbon dioxide electrolysis step (E) is typically a step of reducing a part of carbon dioxide to carbon monoxide by electrolysis. Therefore, the electrolysis gas (3) [CO / CO2] produced is typically a mixed gas of carbon monoxide produced by reduction and carbon dioxide that has not been reduced. Regarding the specific electrolysis conditions and the configuration of the electrolysis apparatus, known conditions and configurations related to carbon dioxide electrolysis technology can be adopted without limitation.

[0033] This step of reducing a part of carbon dioxide to carbon monoxide by electrolysis has the advantage that, compared with the method described in Patent Document 1 (a method of converting carbon dioxide and water into carbon monoxide and hydrogen by co-electrolysis at a high temperature (500 °C or higher) in a solid oxide electrolysis cell), electrolysis can be carried out at a low temperature (less than 100 °C), and there is no problem of performance degradation due to the adhesion of precipitated carbon to the electrode.

[0034] Then, by returning the electrolysis gas (3) produced in the carbon dioxide electrolysis step (E) to the carbon dioxide separation step (S), carbon monoxide in the electrolysis gas (3) [CO / CO2] becomes a part of the raw material for synthetic fuel.

[0035] It is preferable to discharge a part of the carbon dioxide after being treated in the carbon dioxide electrolysis step (E) to the atmosphere. The reason is to prevent the accumulation of inert gases such as nitrogen in the system. However, the amount of carbon dioxide discharged to the atmosphere in this step is extremely small compared with the amount discharged in the conventional method shown in FIG. 1 (that is, the total amount of carbon dioxide separated in the carbon dioxide separation step (S)). Therefore, according to the present invention, the amount of carbon dioxide discharged can be sufficiently reduced compared with the conventional method.

[0036] In the carbon dioxide electrolysis step (E), it is preferable to use electric power generated by renewable energy (renewable energy power). Renewable energy is energy that always exists in nature, such as sunlight, wind power, geothermal energy, and hydroelectric power, and is characterized by not emitting carbon dioxide during power generation. Using this renewable energy power in the carbon dioxide electrolysis step (E) is in line with the object of the present invention to reduce the amount of carbon dioxide emissions.

[0037] [Water electrolysis step (WE)] The water electrolysis step (WE) shown in FIG. 1 is a step of electrolyzing water to generate oxygen and hydrogen. Regarding the specific electrolysis conditions and electrolysis apparatus configuration in this step (WE), known conditions and configurations related to water electrolysis technology can be adopted without limitation.

[0038] In the water electrolysis step (WE), the generated hydrogen is supplied to the FT synthesis step described later. Thereby, the shortage of hydrogen in the raw material gas in the FT synthesis step can be compensated. The molar amount of hydrogen generated in the water electrolysis step (WE) and supplied to the FT synthesis step is preferably 2 times or more the molar amount of carbon monoxide in the electrolysis gas (3). Thereby, the composition balance of the raw material gas in the FT synthesis step becomes suitable.

[0039] On the other hand, the oxygen generated in the water electrolysis step (WE) is supplied to the gasification step (G). By using this oxygen for the gasification of waste, the load on the oxygen separation step can be reduced.

[0040] In the water electrolysis step (WE), similar to the case of the carbon dioxide electrolysis step (E) described above, it is preferable to use electric power generated by renewable energy.

[0041] In the present invention, it is preferable to use the water electrolysis step (WE) described above as one of the steps for generating hydrogen to be supplied to the FT synthesis step. However, the present invention is not limited thereto. Instead of the water electrolysis step (WE), hydrogen may be generated by other known methods and supplied to the FT synthesis step.

[0042] [FT Synthesis Process] The FT synthesis process shown in Fig. 1 is a process of synthesizing a synthesis gas (2) from which carbon dioxide has been separated in a carbon dioxide separation step (S), that is, a synthesis gas (2) [CO / H2] containing carbon monoxide and hydrogen by Fischer-Tropsch (FT) synthesis to produce a synthetic fuel.

[0043] Fischer-Tropsch (FT) synthesis is a synthesis method for obtaining synthetic fuels (gases and liquid hydrocarbons) from carbon monoxide and hydrogen by a catalytic reaction. As the catalyst, iron or cobalt compounds are usually used. Regarding the specific reaction conditions, types of catalysts, and reaction apparatus configurations in this FT synthesis, known conditions, types, and configurations related to FT synthesis technology can be adopted without limitation.

[0044] By this FT synthesis process, SAF (Sustainable aviation fuel) and other synthetic fuels can be obtained. Examples of other synthetic fuels include kerosene, diesel, and naphtha. Also, the gas fraction generated during synthesis is either used as fuel gas or burned in a flare or the like and released into the atmosphere as off-gas.

[0045] [Method for Improving Manufacturing Equipment of Synthetic Fuel] The method for manufacturing a synthetic fuel of the present invention described above can be implemented by newly constructing all the apparatuses for carrying out each step. However, it can also be implemented by adding a carbon dioxide electrolyzer and, if necessary, other apparatuses (for example, a water electrolyzer) to existing manufacturing equipment.

[0046] That is, the method for improving the manufacturing equipment of synthetic fuel of the present invention is a method for reducing the amount of carbon dioxide discharged into the atmosphere in the equipment of the existing synthetic fuel manufacturing equipment. The method includes gasifying waste, oxygen, and water by reacting them at a high temperature to generate a gasification gas (1) containing carbon dioxide, carbon monoxide, and hydrogen in a gasification device (g); a carbon dioxide separation device (s) for separating carbon dioxide from at least the gasification gas (1) generated in the gasification device (g); and an FT synthesis device for Fischer-Tropsch synthesizing a synthesis gas (2) from which carbon dioxide has been separated in the carbon dioxide separation device (s) to produce synthetic fuel. For the existing synthetic fuel manufacturing equipment having these components, a carbon dioxide electrolysis device (e) is added to electrolyze the carbon dioxide separated in the carbon dioxide separation device (s) to generate an electrolysis gas (3) containing carbon monoxide and carbon dioxide. The electrolysis gas (3) generated in the carbon dioxide electrolysis device (e) is supplied to the carbon dioxide separation device (s), and the method is characterized by separating carbon dioxide from the gasification gas (1) and the electrolysis gas (3).

[0047] Furthermore, in this improvement method, it is preferable to add a water electrolysis device (we) for electrolyzing water to generate oxygen and hydrogen, and supply the generated hydrogen to the FT synthesis device. In this case, the molar amount of hydrogen generated by the water electrolysis device (we) supplied to the FT synthesis device is preferably not less than twice the molar amount of carbon monoxide in the electrolysis gas (3). It is also preferable to supply the oxygen generated by the water electrolysis device (we) to the gasification device (g).

[0048] Adding devices such as a carbon dioxide electrolysis device to the existing manufacturing equipment in this way is advantageous in terms of equipment cost compared to the case of newly constructing all the equipment. Furthermore, by effectively using the carbon dioxide that was previously discharged in the existing manufacturing equipment, the production amount of synthetic fuel can be increased.

Industrial Applicability

[0049] The present invention is very useful from the viewpoint of preventing global warming because it recycles carbon dioxide generated when producing synthetic fuel from waste and can reduce the amount of carbon dioxide discharged into the atmosphere.

Explanation of Signs

[0050] (G) Gasification process (S) Carbon dioxide separation process (E) Carbon dioxide electrolysis process (WE) Water electrolysis process

Claims

1. A gasification step (G) in which waste, oxygen, and water are reacted at a high temperature to be gasified to produce a gasified gas (1) containing carbon dioxide, carbon monoxide, and hydrogen; A carbon dioxide separation step (S) in which carbon dioxide is separated from at least the gasified gas (1) produced in the gasification step (G); An FT synthesis step in which a synthesis gas (2) from which carbon dioxide has been separated in the carbon dioxide separation step (S) is subjected to Fischer-Tropsch synthesis to produce a synthetic fuel; In a method for producing a synthetic fuel having: Further comprising a carbon dioxide electrolysis step (E) in which carbon dioxide separated in the carbon dioxide separation step (S) is electrolyzed to produce an electrolyzed gas (3) containing carbon monoxide and carbon dioxide; A method for producing a synthetic fuel, characterized in that the electrolyzed gas (3) produced in the carbon dioxide electrolysis step (E) is supplied to the carbon dioxide separation step (S) to separate carbon dioxide from the gasified gas (1) and the electrolyzed gas (3).

2. The method for producing a synthetic fuel according to claim 1, further comprising a water electrolysis step (WE) in which water is electrolyzed to produce oxygen and hydrogen, the produced hydrogen is supplied to the FT synthesis step, and the produced oxygen is supplied to the gasification step (G).

3. The method for producing a synthetic fuel according to claim 1 or 2, further comprising an oxygen separation step in which oxygen is separated from air, and the separated oxygen is supplied to the gasification step (G).

4. An improved method for reducing the amount of carbon dioxide discharged into the atmosphere from an existing synthetic fuel production facility, A gasification device (g) in which waste, oxygen, and water are reacted at a high temperature to be gasified to produce a gasified gas (1) containing carbon dioxide, carbon monoxide, and hydrogen; A carbon dioxide separation device (s) for separating carbon dioxide from at least the gasified gas (1) produced in the gasification device (g); An FT synthesis device for subjecting a synthesis gas (2) from which carbon dioxide has been separated in the carbon dioxide separation device (s) to Fischer-Tropsch synthesis to produce a synthetic fuel; For an existing synthetic fuel production facility having: Adding a carbon dioxide electrolysis device (e) that electrolyzes carbon dioxide separated in the carbon dioxide separation device (s) to produce an electrolyzed gas (3) containing carbon monoxide and carbon dioxide; An improved method for a synthetic fuel production facility, characterized in that the electrolyzed gas (3) produced in the carbon dioxide electrolysis device (e) is supplied to the carbon dioxide separation device (s) to separate carbon dioxide from the gasified gas (1) and the electrolyzed gas (3).

5. Furthermore, an improved method for a synthetic fuel production facility according to claim 4, wherein a water electrolysis device (we) that electrolyzes water to generate oxygen and hydrogen is added, the generated hydrogen is supplied to a FT synthesis device, and the generated oxygen is supplied to a gasification device (g).

Images