Fuel synthesis system

Abstract

The present invention provides a fuel synthesis system that can simplify the system configuration and further improve system efficiency. [Solution] A fuel synthesis system that generates fuel using exhaust gas, comprising: an oxygen removal device that removes oxygen contained in the exhaust gas; and a SOEC located downstream of the oxygen removal device, which co-electrolyzes carbon dioxide and water in the exhaust gas to produce carbon monoxide and hydrogen.

Description

Technical Field

[0001] The present invention relates to a fuel synthesis system.

Background Art

[0002] In order to achieve a carbon-neutral society, technologies for reusing carbon dioxide contained in exhaust gas discharged from factories and the like and reducing the amount of carbon dioxide emissions have attracted attention.

[0003] Among them, a solid oxide electrolysis cell (SOEC) can convert carbon dioxide and water into fuels such as carbon monoxide and hydrogen, respectively, and thus has an affinity for the problem of reducing carbon dioxide emissions. Therefore, various fuel synthesis systems equipped with SOEC have been proposed so far (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Generally, when constructing a system for supplying carbon dioxide contained in exhaust gas to SOEC for electrolysis into carbon monoxide, temperature control of the exhaust gas and treatment of gas components other than carbon dioxide contained in the exhaust gas become problems.

[0007] For example, when separating and recovering carbon dioxide from exhaust gas, a carbon dioxide separator using the amine absorption method is typically employed. However, the water content in typical exhaust gas reduces the concentration of the amine absorbent in the carbon dioxide separator, negatively impacting its carbon dioxide separation function. Therefore, the water content in the exhaust gas must be removed before passing it through the carbon dioxide separator.

[0008] Furthermore, carbon dioxide separators lose their recovery efficiency at high temperatures. Therefore, exhaust gas must be sufficiently cooled before passing through the carbon dioxide separator.

[0009] Thus, conventional systems have the problem of requiring additional equipment to process the various components contained in the exhaust gas, which complicates the system. Furthermore, conventional systems have the problem of not being able to fully utilize the heat of the high-temperature exhaust gas, which limits the improvement of system efficiency.

[0010] This invention has been made in view of the above background, and aims to provide a fuel synthesis system that can simplify the system configuration and further improve system efficiency. [Means for solving the problem]

[0011] The present invention relates to a fuel synthesis system that generates fuel using exhaust gas, An oxygen removal device that removes oxygen contained in exhaust gas, A SOEC is positioned downstream of the oxygen removal device and co-electrolyzes carbon dioxide and water in the exhaust gas to produce carbon monoxide and hydrogen, A fuel synthesis system having the following characteristics is provided. [Effects of the Invention]

[0012] The present invention provides a fuel synthesis system that simplifies the system configuration and can further improve system efficiency. [Brief explanation of the drawing]

[0013] [Figure 1] This is a diagram schematically showing a configuration example of a fuel synthesis system according to an embodiment of the present invention. [Figure 2] This is a diagram schematically showing a configuration example of a fuel synthesis system according to another embodiment of the present invention. [Figure 3] This is a diagram schematically showing a configuration example of a conventional fuel synthesis system.

Mode for Carrying Out the Invention

[0014] Hereinafter, an embodiment of the present invention will be described.

[0015] As described above, in a conventional system equipped with an SOEC, it is necessary to remove the water contained in the exhaust gas before the exhaust gas is supplied to the carbon dioxide separator. Also, it is necessary to lower the exhaust gas temperature before the exhaust gas is supplied to the carbon dioxide separator.

[0016] However, when such measures are taken, the system becomes complicated, and the heat contained in the exhaust gas cannot be effectively utilized, making it difficult to improve the system efficiency.

[0017] The inventors of the present application have intensively studied countermeasures for such problems regarding conventional fuel synthesis systems. And the inventors of the present application have noticed that if the exhaust gas can be directly administered to the SOEC without being treated, the carbon dioxide and water contained in the exhaust gas can be co-electrolyzed, and high system efficiency can be obtained with a simple system configuration.

[0018] However, oxygen contained in normal exhaust gas has a problem of deteriorating (oxidizing) the components of the SOEC, especially the electrodes. In this regard, the inventors of the present application have noticed that if the oxygen contained in the exhaust gas can be removed at the previous stage of the SOEC, such problems can also be solved, leading to the present invention.

[0019] That is, in one embodiment of the present invention, A fuel synthesis system that generates fuel using exhaust gas, an oxygen removal device that removes oxygen contained in the exhaust gas, an SOEC disposed downstream of the oxygen removal device, which co-electrolyzes carbon dioxide and water in the exhaust gas to produce carbon monoxide and hydrogen, is provided.

[0020] The fuel synthesis system according to an embodiment of the present invention includes an oxygen removal device. This oxygen removal device has a function of removing oxygen contained in the exhaust gas. Therefore, in the fuel synthesis system according to an embodiment of the present invention, when the exhaust gas is supplied to the SOEC, the problem that the components of the SOEC are deteriorated by the oxygen contained in the exhaust gas can be avoided.

[0021] In addition, the oxygen removal device can operate even at a high temperature, for example, 500°C to 900°C. Therefore, high-temperature exhaust gas can be directly introduced into the oxygen removal device.

[0022] Also, in the fuel synthesis system according to an embodiment of the present invention, by passing the exhaust gas through the oxygen removal device, an oxygen-free exhaust gas containing carbon dioxide and water (hereinafter referred to as "treated gas") can be obtained.

[0023] This treated gas can be directly supplied to the SOEC. Also, on the SOEC side, carbon dioxide and water contained in the treated gas can be co-electrolyzed to produce carbon monoxide and hydrogen.

[0024] Due to such an effect, in one embodiment of the present invention, a fuel synthesis system that can simplify the system configuration and further improve the system efficiency can be provided.

[0025] (Fuel synthesis system according to an embodiment of the present invention) Hereinafter, referring to the drawings, the fuel synthesis system according to an embodiment of the present invention will be described in more detail.

[0026] Figure 1 schematically shows one example configuration of a fuel synthesis system according to one embodiment of the present invention.

[0027] As shown in Figure 1, a fuel synthesis system 100 according to one embodiment of the present invention (hereinafter referred to as the "first system") includes an exhaust gas source 110, a heater 120, an oxygen removal device 130, and an SOEC 140. Note that the heater 120 is not an essential component and may be omitted if unnecessary, such as when the exhaust gas temperature is sufficiently high.

[0028] Furthermore, the first system 100 may also have a first heat exchanger 150 and / or a second heat exchanger 160.

[0029] The following describes each component.

[0030] (Exhaust gas source 110) In the first system 100, exhaust gas is supplied from an exhaust gas source 110. The exhaust gas source 110 is not limited to, but may be, for example, various factories (e.g., steel mills, oil refineries, glass factories, and cement factories), or a thermal power plant, etc.

[0031] Generally, exhaust gases contain carbon dioxide (CO2), oxygen (O2), water (H2O), and nitrogen (N2) as their main gases. These may have the following compositions, for example: CO2: 0 vol% ~ 30 vol% (for example, 10 vol%) H2O: 0 vol% ~ 40 vol% (for example, 30 vol%) O2: 0 vol%~20 vol% (e.g., 5 vol%~10 vol%), N2: 0 vol% to 80 vol% (for example, 50 vol% to 55 vol%).

[0032] However, the gas composition of the exhaust gas varies depending on the exhaust gas source 110, so the above is merely one example.

[0033] In addition to the main gases mentioned above, normal exhaust gases also contain trace amounts of SO2.x and NO x These include, among others. However, it is well known that these trace gases have been removed by conventional equipment. Therefore, we will not explain the trace gas components any further here.

[0034] (First heat exchanger 150 / Second heat exchanger 160) A first heat exchanger 150 is located downstream of the exhaust gas source 110.

[0035] The first heat exchanger 150 has the role of raising the temperature of the exhaust gas supplied from the exhaust gas source 110. Therefore, if the temperature of the exhaust gas supplied from the exhaust gas source 110 is sufficiently high, the first heat exchanger 150 may be omitted.

[0036] A second heat exchanger 160 is positioned downstream of the first heat exchanger 150.

[0037] The second heat exchanger 160 has the role of further increasing the temperature of the exhaust gas discharged from the first heat exchanger 150. Therefore, if the temperature of the exhaust gas supplied from the first heat exchanger 150 (or exhaust gas source 110) is sufficiently high, the second heat exchanger 160 may be omitted.

[0038] The heat source for the first heat exchanger 150 and the second heat exchanger 160 is the high-temperature gas produced by the electrolytic reaction in SOEC140, which will be described later.

[0039] (Heater 120) A heater 120 is positioned downstream of the first heat exchanger 150 and the second heat exchanger 160.

[0040] The heater 120 has the role of raising the exhaust gas discharged from the second heat exchanger 160 (or, if not present, the first heat exchanger 150 or exhaust gas source 110) to a desired temperature. For example, the temperature of the exhaust gas discharged from the heater 120 is in the range of 500°C to 900°C.

[0041] As mentioned above, if the temperature of the exhaust gas before it is introduced into the subsequent oxygen removal device 130 is sufficiently high, the heater 120 may be omitted.

[0042] (Oxygen removal device 130) Downstream of the heater 120, an oxygen removal device 130 is positioned.

[0043] The oxygen removal device 130 has the role of removing oxygen from the components contained in the exhaust gas. The oxygen removal device 130 is composed of, for example, an oxygen pump.

[0044] The operating temperature of the oxygen removal device 130 varies depending on the oxygen removal device 130 used. For example, if the oxygen removal device 130 is an oxygen pump, the oxygen removal device 130 operates at 500°C to 900°C.

[0045] The exhaust gas discharged from the oxygen removal device 130, i.e., the "treated gas," contains nitrogen, carbon dioxide, and water as its main components.

[0046] (SOEC140) SOEC140 is responsible for electrolyzing the oxygen-free treatment gas discharged from the oxygen removal device 130.

[0047] In particular, the processed gas contains a large amount of residual carbon dioxide and water. Therefore, in SOEC140, carbon dioxide and water are co-electrolyzed.

[0048] The SOEC140 operates at temperatures between 500°C and 900°C.

[0049] (operation) Next, we will briefly describe the operation of the first system 100 having the configuration described above.

[0050] First, exhaust gas is discharged from the exhaust gas source 110.

[0051] The temperature of the exhaust gas discharged from the exhaust gas source 110 is not particularly limited, but is, for example, 0°C or higher. Preferably, the temperature of the exhaust gas is 25°C or higher.

[0052] The exhaust gas is heated by the first heat exchanger 150 and the second heat exchanger 160, if necessary. The exhaust gas may also be heated by the heater 120, either in addition to or separately from these.

[0053] As a result, the temperature of the exhaust gas immediately before it is supplied to the oxygen removal device 130 is raised to a range of 500°C to 900°C.

[0054] Next, the high-temperature exhaust gas is supplied to the oxygen removal device 130. Here, the oxygen gas in the exhaust gas is removed, and an oxygen-free treated gas is generated.

[0055] The temperature of the processed gas discharged from the oxygen removal device 130 is, for example, in the range of 500°C to 900°C.

[0056] Next, the processing gas is supplied to SOEC140.

[0057] In the SOEC140, carbon dioxide and water contained in the process gas undergo co-electrolysis. This generates carbon monoxide and hydrogen on the cathode side, while oxygen is generated on the anode side.

[0058] The operating temperature range for SOEC140 is, for example, 500°C to 900°C.

[0059] Furthermore, since the processing gas does not contain oxygen, even if the processing gas is supplied to the cathode of SOEC140, deterioration (oxidation) of the components is unlikely to occur.

[0060] Next, the high-temperature carbon monoxide and hydrogen generated on the cathode side are supplied to the first heat exchanger 150 as needed, where they are heat-exchanged with the exhaust gas supplied from the exhaust gas source 110. Subsequently, the carbon monoxide and hydrogen are stored in the storage device 170 as combustion energy for the generated gas.

[0061] Meanwhile, the oxygen generated on the anode side of SOEC140 is supplied to the second heat exchanger 160 as needed, and heat is exchanged with the exhaust gas supplied from the exhaust gas source 110.

[0062] Thus, in the first system 100, the process gas can be supplied directly to the SOEC 140, allowing for the electrolysis of carbon dioxide and water with a simple system configuration. Furthermore, in the first system 100, the heat from the exhaust gas source 110 and the heat contained in the generated gas from the SOEC 140 can be effectively utilized, significantly increasing system efficiency.

[0063] (Fuel synthesis system according to another embodiment of the present invention) Next, with reference to Figure 2, a fuel synthesis system according to another embodiment of the present invention will be described.

[0064] Figure 2 schematically shows an example configuration of a fuel synthesis system according to another embodiment of the present invention.

[0065] As shown in Figure 2, this fuel synthesis system (hereinafter referred to as the "second system") 200 has the same configuration as the first system 100 described above. Therefore, in Figure 2, devices similar to the first system 100 are given reference numerals that add 100 to the reference numerals of the devices shown in Figure 1.

[0066] For example, the second system 200 includes an exhaust gas source 210, a first heat exchanger 250, a second heat exchanger 260, an SOEC 240, and a storage device 270.

[0067] However, the configuration of the oxygen removal device 230 in the second system 200 differs from that of the first system 100. Specifically, in the second system 200, the oxygen removal device 230 is selected from a solid oxide fuel cell (SOFC) and a molten carbonate fuel cell (MCFC). Hereinafter, the oxygen removal device 230 in the second system 200 will also be referred to as the "fuel cell (230)".

[0068] Furthermore, in the second system 200, the aforementioned heater 120 is usually omitted.

[0069] The operating temperature of fuel cell 230 varies depending on the type of fuel cell used. For example, if fuel cell 230 is an SOFC, it operates at 500°C to 900°C. Furthermore, if fuel cell 230 is an MCFC, it operates at 500°C to 700°C.

[0070] When using such a second system 200, the exhaust gas heated in the first heat exchanger 250 / second heat exchanger 260 is supplied to the cathode (oxygen electrode) 230-C of the fuel cell 230.

[0071] Meanwhile, a fuel gas such as hydrogen is supplied to the anode (fuel electrode) 230-A of the fuel cell 230, resulting in an electrochemical reaction within the fuel cell 230 that generates electricity and water.

[0072] Therefore, the fuel cell 230 can be used as an oxygen removal device for exhaust gas.

[0073] Subsequently, the exhaust gas from which oxygen has been consumed within the fuel cell 230 is supplied to the SOEC 240, where co-electrolysis of carbon dioxide and hydrogen occurs.

[0074] Furthermore, the oxygen gas produced in SOEC240 may be supplied to the second heat exchanger 260 for heat recovery. In addition, all or part of the fuel produced in SOEC240 may be supplied to the anode 230-A of the aforementioned fuel cell 230 and used as fuel gas. Moreover, any fuel not used in the reaction in fuel cell 230 is supplied to the first heat exchanger 250 for heat recovery and then stored in the storage device 270.

[0075] Thus, the same effects as the first system 100 can be obtained in the second system 200 as in the first system 100.

[0076] In other words, the second system 200 can supply oxygen-free carbon dioxide and water to the SOEC 240 with a simple system configuration, and can co-electrolyze carbon dioxide and water. Furthermore, the second system 200 can effectively utilize the heat from the exhaust gas source 210, as well as the heat contained in the generated gas from the SOEC 240, thereby significantly increasing system efficiency.

[0077] An embodiment of the present invention has been described above, using the first system 100 and the second system 200 as examples.

[0078] However, these are merely examples, and it will be apparent to those skilled in the art that a fuel synthesis system according to one embodiment of the present invention may have other configurations.

[0079] For example, in the second system 200, an oxygen pump may be placed downstream of the fuel cell 230. In this case, residual oxygen not used in the reaction at the cathode 230-C of the fuel cell 230 can be reliably removed using the oxygen pump. Also, in the first system 100 and the second system 200, the oxygen recovered by heat in the second heat exchangers 160 and 260 may be recovered and stored without being exhausted.

[0080] Other changes may also be anticipated. [Examples]

[0081] An embodiment of the present invention will be described below. In the following description, Examples 1 to 7 are examples, and Examples 11 and 12 are comparative examples.

[0082] (Example 1) The system efficiency was evaluated based on the fuel synthesis system 100 shown in Figure 1 above. The following operating conditions were assumed for each device during the evaluation. An oxygen pump was used as the oxygen removal device 130.

[0083] <Exhaust gas source 110> Exhaust gas temperature: 25℃ Exhaust gas composition: Carbon dioxide = 1.0 mol / s (10 vol%), O2 = 0.5 mol / s (5 vol%), H2O = 3.0 mol / s (30 vol%), N2 = 5.5 mol / s (55 vol%) <First heat exchanger 150> Heat exchanger temperature efficiency upper limit: 0.9 Exhaust gas inlet temperature: 25℃ Exhaust gas outlet temperature: 647℃ Inlet temperature of supply gas (fuel gas produced from SOEC140): 850°C Supply gas (fuel gas produced from SOEC140) outlet temperature: 108℃ <Second heat exchanger 160> Heat exchanger temperature efficiency upper limit: 0.9 Exhaust gas inlet temperature: 647℃ Exhaust gas outlet temperature: 675℃ Inlet temperature of supply gas (oxygen gas from SOEC140): 850°C Supply gas (oxygen gas from SOEC140) outlet temperature: 667°C <Heater 120> Energy input: 66.0 kW Exhaust gas inlet temperature: 675℃ Exhaust gas outlet temperature: 850℃ <Oxygen removal device 130> Energy input: 37.6 kW Operating temperature: 850℃ The oxygen pump removes oxygen gas to a concentration of 0.1 vol%. Oxygen pump operating voltage; sum of oxygen pump Nernst voltage and overvoltage (assuming 100mV) Exhaust gas inlet temperature: 850℃ Processing gas outlet temperature: 850℃ <soec140> Energy input: 797.1 kW Operating temperature: 850℃ Generated gas temperature: 850°C.

[0084] The calculation of system efficiency is performed using the following equation (1) described in Non-Patent Document 1. System efficiency η = (Energy of combustion of generated gas E1) / (Energy input E2) (1) I used it.

[0085] In Example 1, the system efficiency η = (912.4kW / (66.0kW + 37.6kW + 797.1kW) × 100 = 101.3%) That was the case.

[0086] (Example 2) System efficiency was evaluated using the same method as in Example 1. However, in Example 2, the following operating conditions were assumed for each device.

[0087] <Exhaust gas source 110> Exhaust gas temperature: 25℃ Exhaust gas composition: Carbon dioxide = 1.0 mol / s (10 vol%), O2 = 1.0 mol / s (10 vol%), H2O = 3.0 mol / s (30 vol%), N2 = 5.0 mol / s (50 vol%) <First heat exchanger 150> Exhaust gas inlet temperature: 25℃ Exhaust gas outlet temperature: 646℃ Inlet temperature of supply gas (fuel gas produced from SOEC140): 850°C Supply gas (fuel gas produced from SOEC140) outlet temperature: 108℃ <Second heat exchanger 160> Exhaust gas inlet temperature: 646℃ Exhaust gas outlet temperature: 673℃ Inlet temperature of supply gas (oxygen gas from SOEC140): 850°C Supply gas (oxygen gas from SOEC140) outlet temperature: 666°C <Heater 120> Energy input: 66.8kW Exhaust gas inlet temperature: 673℃ Exhaust gas outlet temperature: 850℃ <Oxygen removal device 130> Energy input: 81.6 kW Operating temperature: 850℃ Exhaust gas inlet temperature: 850℃ Processing gas outlet temperature: 850℃ <soec140> Energy input: 796.3 kW Operating temperature: 850℃ Generated gas temperature: 850°C.

[0088] The calculation showed that the system efficiency η = (912.4kW) / (66.8kW + 81.6kW + 796.3kW) × 100 = 96.6%.

[0089] (Example 3) System efficiency was evaluated using the same method as in Example 1. However, in Example 3, the following operating conditions were assumed for each device.

[0090] <Exhaust gas source 110> Exhaust gas temperature: 300℃ Exhaust gas composition: Carbon dioxide = 1.0 mol / s (10 vol%), O2 = 1.0 mol / s (10 vol%), H2O = 3.0 mol / s (30 vol%), N2 = 5.0 mol / s (50 vol%) <First heat exchanger 150> Exhaust gas inlet temperature: 300℃ Exhaust gas outlet temperature: 705℃ Inlet temperature of supply gas (fuel gas produced from SOEC140): 850°C Supply gas (fuel gas produced from SOEC140) outlet temperature: 355℃ <Second heat exchanger 160> Exhaust gas inlet temperature: 705℃ Exhaust gas outlet temperature: 724℃ Inlet temperature of supply gas (oxygen gas from SOEC140): 850°C Supply gas (oxygen gas from SOEC140) outlet temperature: 719°C <Heater 120> Energy input: 47.8kW Exhaust gas inlet temperature: 724℃ Exhaust gas outlet temperature: 850℃ <Oxygen removal device 130> Energy input: 81.6 kW Operating temperature: 850℃ Exhaust gas inlet temperature: 850℃ Processing gas outlet temperature: 850℃ <soec140> Energy input: 796.3 kW Operating temperature: 850℃ Generated gas temperature: 850°C.

[0091] The calculation showed that the system efficiency η = (912.4kW) / (47.8kW + 81.6kW + 796.3kW) × 100 = 98.6%.

[0092] (Example 4) System efficiency was evaluated using the same method as in Example 1. However, in Example 4, the following operating conditions were assumed for each device.

[0093] <Exhaust gas source 110> Exhaust gas temperature: 500℃ Exhaust gas composition: Carbon dioxide = 1.0 mol / s (10 vol%), O2 = 1.0 mol / s (10 vol%), H2O = 3.0 mol / s (30 vol%), N2 = 5.0 mol / s (50 vol%).

[0094] <First heat exchanger 150> Exhaust gas inlet temperature: 500℃ Exhaust gas outlet temperature: 754℃ Inlet temperature of supply gas (fuel gas produced from SOEC140): 850°C Supply gas (fuel gas produced from SOEC140) outlet temperature: 535℃ <Second heat exchanger 160> Exhaust gas inlet temperature: 754℃ Exhaust gas outlet temperature: 767℃ Inlet temperature of supply gas (oxygen gas from SOEC140): 850°C Supply gas (oxygen gas from SOEC140) outlet temperature: 763°C <Heater 120> Energy input: 31.9kW Exhaust gas inlet temperature: 767℃ Exhaust gas outlet temperature: 850℃ <Oxygen removal device 130> Energy input: 81.6 kW Operating temperature: 850℃ Exhaust gas inlet temperature: 850℃ Processing gas outlet temperature: 850℃ <soec140> Energy input: 796.3 kW Operating temperature: 850℃ Generated gas temperature: 850°C.

[0095] The calculation showed that the system efficiency η = (912.4kW) / (31.9kW + 81.6kW + 796.3kW) × 100 = 100.3%.

[0096] (Example 5) The system efficiency was evaluated based on the fuel synthesis system 200 shown in Figure 2 above. The following operating conditions were assumed for each device during the evaluation. A SOFC was used as the oxygen removal device 230.

[0097] <Exhaust gas source 210> Exhaust gas temperature: 25℃ Exhaust gas composition: Carbon dioxide = 1.0 mol / s (10 vol%), O2 = 0.5 mol / s (5 vol%), H2O = 3.0 mol / s (30 vol%), N2 = 5.5 mol / s (55 vol%) <First heat exchanger 250> Heat exchanger temperature efficiency upper limit: 0.9 Exhaust gas inlet temperature: 25℃ Exhaust gas outlet temperature: 587℃ Inlet temperature of supply gas (anode exhaust gas from fuel cell 230): 850°C Supply gas (anode exhaust gas from fuel cell 230) outlet temperature: 108℃ <Second heat exchanger 260> Heat exchanger temperature efficiency upper limit: 0.9 Exhaust gas inlet temperature: 587℃ Exhaust gas outlet temperature: 623℃ Inlet temperature of supply gas (oxygen gas from SOEC240): 850°C Supply gas (oxygen gas from SOEC240) outlet temperature: 613℃ <Heater> Required energy input: 85.1 kW However, since the heat generated by the SOFC (combustion energy required to produce hydrogen to remove oxygen (285.8kW) - energy equivalent to the amount of electricity generated from the SOFC (135.1kW) = 150.8kW) can be effectively utilized, it will not be used.

[0098] <Fuel cell 230> Generated voltage: 0.7V Net combustion energy of the generated gas = Combustion energy of the generated gas (912.4 kW) from SOEC - Combustion energy required for hydrogen production to remove oxygen (285.8 kW) = 626.5 kW Net input energy = Energy input to SOEC (772.7kW) - Energy equivalent to power generated from SOFC (135.1kW) = 637.6kW Operating temperature: 850℃ Exhaust gas inlet temperature: 850℃ Processing gas outlet temperature: 850℃ <soec240> Energy input: 772.7kW Operating temperature: 850℃ Generated gas temperature: 850°C.

[0099] The calculation showed that the system efficiency η = (626.5kW) / (637.6kW) × 100 = 98.3%.

[0100] (Example 6) System efficiency was evaluated using the same method as in Example 5. However, in Example 6, the following operating conditions were assumed for each device.

[0101] <Exhaust gas source 210> Exhaust gas temperature: 300℃ Exhaust gas composition: Carbon dioxide = 1.0 mol / s (10 vol%), O2 = 0.5 mol / s (5 vol%), H2O = 3.0 mol / s (30 vol%), N2 = 5.5 mol / s (55 vol%).

[0102] <First heat exchanger 250> Exhaust gas inlet temperature: 300℃ Exhaust gas outlet temperature: 666℃ Inlet temperature of supply gas (anode exhaust gas from fuel cell 230): 850°C Supply gas (anode exhaust gas from fuel cell 230) outlet temperature: 355°C <Second heat exchanger 260> Exhaust gas inlet temperature: 666℃ Exhaust gas outlet temperature: 691℃ Inlet temperature of supply gas (oxygen gas from SOEC240): 850°C Supply gas (oxygen gas from SOEC240) outlet temperature: 684°C <Heater> Required energy input: 60.1 kW However, since the heat generated by the SOFC (combustion energy required to produce hydrogen to remove oxygen (285.8kW) - energy equivalent to the amount of electricity generated from the SOFC (135.1kW) = 150.8kW) can be effectively utilized, it will not be used.

[0103] <Fuel cell 230> Net combustion energy of the generated gas = Combustion energy of the generated gas (912.4 kW) from SOEC - Combustion energy required for hydrogen production to remove oxygen (285.8 kW) = 626.5 kW Net input energy = Energy input to SOEC (772.7kW) - Energy equivalent to power generated from SOFC (135.1kW) = 637.6kW Operating temperature: 850℃ Exhaust gas inlet temperature: 850℃ Processing gas outlet temperature: 850℃ <soec240> Energy input: 772.7kW Operating temperature: 850℃ Generated gas temperature: 850°C.

[0104] The calculation showed that the system efficiency η = (626.5kW) / (637.6kW) × 100 = 98.3%.

[0105] (Example 7) The system efficiency was evaluated using the same method as in Example 5. However, in Example 7, an MCFC was used as the oxygen removal device 230. In addition, the following operating conditions were assumed for each device.

[0106] <Exhaust gas source 210> Exhaust gas temperature: 300℃ Exhaust gas composition: Carbon dioxide = 1.0 mol / s (10 vol%), O2 = 0.5 mol / s (5 vol%), H2O = 3.0 mol / s (30 vol%), N2 = 5.5 mol / s (55 vol%).

[0107] <First heat exchanger 250> Heat exchanger temperature efficiency upper limit: 0.9 Exhaust gas inlet temperature: 300℃ Exhaust gas outlet temperature: 532℃ Inlet temperature of supply gas (anode exhaust gas from fuel cell 230): 650°C Supply gas (anode exhaust gas from fuel cell 230) outlet temperature: 335°C <Second heat exchanger 260> Heat exchanger temperature efficiency upper limit: 0.9 Exhaust gas inlet temperature: 532℃ Exhaust gas outlet temperature: 576℃ Inlet temperature of supply gas (oxygen gas from SOEC240): 850°C Supply gas (oxygen gas from SOEC240) outlet temperature: 564°C <Heater> Required energy input: 102.1 kW However, since the calorific value of the MCFC (combustion energy required to produce hydrogen to remove oxygen (285.8kW) - energy equivalent to the amount of electricity generated from the MCFC (135.1kW) = 150.8kW) can be effectively utilized, it will not be used.

[0108] <Fuel cell 230> Generated voltage: 0.7V Net combustion energy of the generated gas = Combustion energy of the generated gas (912.4 kW) from SOEC - Combustion energy required for hydrogen production to remove oxygen (285.8 kW) = 626.5 kW Net input energy = Energy input to SOEC (772.7kW) - Energy equivalent to power generated from MCFC (135.1kW) = 637.6kW Operating temperature: 650℃ Exhaust gas inlet temperature: 650℃ Processing gas outlet temperature: 650℃ <soec240> Energy input: 772.7kW Operating temperature: 850℃ Generated gas temperature: 850°C.

[0109] The calculation showed that the system efficiency η = (626.5kW) / (637.6kW) × 100 = 98.3%.

[0110] (Example 11) We evaluated the system efficiency assuming a conventional fuel synthesis system.

[0111] Figure 3 shows a schematic representation of the system configuration used.

[0112] As shown in Figure 3, this fuel synthesis system (hereinafter referred to as the "conventional system") 300 includes an exhaust gas source 310, a carbon dioxide separation and recovery device 312, a water tank (including a pump) 375, a steam generator 379, a mixer 355, and an SOEC 340. The conventional system 300 also includes a first heat exchanger 350 and a second heat exchanger 360.

[0113] The exhaust gas sources 310 and SOEC340 are the same as the exhaust gas sources 110 and SOEC140 in the first system 100 described above. Therefore, a detailed explanation is omitted here.

[0114] On the other hand, the carbon dioxide separation and recovery device 312 has the function of separating and recovering carbon dioxide contained in the exhaust gas discharged from the exhaust gas source 310 by amine absorption. Therefore, of the exhaust gas supplied to the carbon dioxide separation and recovery device 312, only carbon dioxide is supplied to the downstream first heat exchanger 350.

[0115] It is undesirable to supply exhaust gas containing water to the carbon dioxide separation and recovery unit 312. This is because the water in the exhaust gas lowers the concentration of the amine absorbent in the carbon dioxide separation and recovery unit 312, adversely affecting the carbon dioxide separation function. For this reason, although not shown in Figure 3, a device to remove water from the exhaust gas is installed upstream of the carbon dioxide separation and recovery unit 312.

[0116] The first heat exchanger 350 has the role of heating the carbon dioxide supplied from the carbon dioxide separation and recovery device 312 by utilizing the heat of the high-temperature oxygen gas generated from SOEC 340. Therefore, heated carbon dioxide is discharged from the first heat exchanger 350.

[0117] Meanwhile, the steam generator 379 has the role of converting water stored in the water tank 375 and supplied by the pump into steam. The generated steam is supplied to the second heat exchanger 360.

[0118] The second heat exchanger 360 has the role of heating the steam generated in the steam generator 379 by utilizing the heat of the high-temperature fuel gas (carbon monoxide + hydrogen) produced from the SOEC 340. Therefore, heated steam is discharged from the second heat exchanger 360.

[0119] The carbon dioxide discharged from the first heat exchanger 350 and the steam discharged from the second heat exchanger 360 are mixed in the mixer 355 to produce a mixed gas. If necessary, the mixed gas may be further heated here.

[0120] The mixed gas, combined in mixer 355, is supplied to SOEC 340, where carbon dioxide and water vapor are co-electrolyzed.

[0121] The hydrogen and carbon monoxide produced by electrolysis are supplied to the second heat exchanger 360, where heat is recovered and then stored in the storage device 370. Meanwhile, the high-temperature oxygen produced in SOEC 340 is supplied to the first heat exchanger 350, where heat is recovered.

[0122] In evaluating the system efficiency compared to the conventional system 300, the following operating conditions were assumed for each device.

[0123] <Exhaust gas source 310> Exhaust gas temperature: 25℃ Exhaust gas composition: Carbon dioxide = 1.0 mol / s (10 vol%), O2 = 0.5 mol / s (8 vol%), H2O = 3.0 mol / s (30 vol%), N2 = 5.5 mol / s (55 vol%) <Carbon dioxide separation and recovery device 312> Energy input: 88kW (equivalent to 2 GJ / ton-CO2 using the highest performance amine absorbent) Exhaust gas inlet temperature: 25℃ Exhaust gas outlet temperature: 25℃ <First heat exchanger 350> Exhaust gas inlet temperature: 25℃ Exhaust gas outlet temperature: 767.5℃ Inlet temperature of supply gas (oxygen gas from SOEC340): 850°C Supply gas (oxygen gas from SOEC140) outlet temperature: 186.7℃ <Steam Generator 379> Energy input: 149.5kW Water inlet temperature: 25℃ Water vapor outlet temperature: 200℃ <Second heat exchanger 360> Exhaust gas inlet temperature: 200℃ Exhaust gas outlet temperature: 785℃ Inlet temperature of supply gas (fuel gas produced from SOEC340): 850°C Supply gas (fuel gas produced from SOEC140) outlet temperature: 338.3℃ <Mixer 355> Energy input: 12.8kW Carbon dioxide inlet temperature: 767.5℃ Water vapor inlet temperature: 785℃ Mixed gas outlet temperature: 850℃ <soec340> Energy input: 823.2kW Operating temperature: 850℃ Generated gas temperature: 850°C.

[0124] The calculation showed that the system efficiency η = (912.43kW) / (88kW + 149.5kW + 12.8kW + 823.2kW) × 100 < 85%.

[0125] (Example 12) The system efficiency was evaluated using the same method as in Example 11. However, in Example 12, the following exhaust gas composition was assumed.

[0126] Exhaust gas composition: Carbon dioxide = 1.0 mol / s (10 vol%), O2 = 1.0 mol / s (10 vol%), H2O = 3.0 mol / s (30 vol%), N2 = 5.0 mol / s (50 vol%).

[0127] The calculation showed that the system efficiency η = (912.43kW) / (88kW + 149.5kW + 12.8kW + 823.2kW) × 100 < 85%.

[0128] Table 1 below summarizes the conditions used and the calculated system efficiency for each example system.

[0129] [Table 1] Table 1 shows that the systems in Examples 1 to 7 have significantly improved system efficiency η compared to the systems in Examples 11 to 12.

[0130] (Aspects of the present invention) The embodiments of the present invention are described below.

[0131] (Aspect 1) A fuel synthesis system that uses exhaust gas to produce fuel, An oxygen removal device that removes oxygen contained in exhaust gas, A SOEC is positioned downstream of the oxygen removal device and co-electrolyzes carbon dioxide and water in the exhaust gas to produce carbon monoxide and hydrogen, A fuel synthesis system having the following features.

[0132] (Aspect 2) The fuel synthesis system according to embodiment 1, wherein the oxygen removal device comprises at least one of an oxygen pump, a solid oxide fuel cell (SOFC), and a molten carbonate fuel cell (MCFC).

[0133] (Aspect 3) The exhaust gas is discharged from the exhaust gas source, The fuel synthesis system according to embodiment 1 or 2, wherein the exhaust gas discharged from the exhaust gas source contains carbon dioxide in the range of 0 vol% to 30 vol%, water in the range of 0 vol% to 40 vol%, oxygen in the range of 0 vol% to 20 vol%, and nitrogen in the range of 0 vol% to 80 vol%.

[0134] (Aspect 4) The fuel synthesis system according to embodiment 3, wherein the exhaust gas source is various production plants or thermal power plants.

[0135] (Appendix 5) The fuel synthesis system according to embodiment 3 or 4, wherein the exhaust gas discharged from the exhaust gas source is 0°C or higher.

[0136] (Aspect 6) Furthermore, the oxygen removal device has a heat exchanger upstream of it. The fuel synthesis system according to any one of embodiments 3 to 5, wherein the heat exchanger heats the exhaust gas from the exhaust gas source with heat from the SOEC.

[0137] (Aspect 7) Furthermore, the fuel synthesis system according to any one of embodiments 1 to 6, further comprising a heater for heating the exhaust gas upstream of the oxygen removal device. [Explanation of Symbols]

[0138] 100 Fuel Synthesis System (System 1) 110 Exhaust gas sources 120 Heater 130 Oxygen Removal Device 140 SOEC 150 First heat exchanger 160 Second heat exchanger 170 Storage equipment 200 Fuel Synthesis System (Second System) 210 Exhaust gas sources 230 Oxygen removal device (fuel cell) 230-A Anode 230-C Cathode 240 SOEC 250 First heat exchanger 260 Second heat exchanger 270 Storage equipment 300 Fuel Synthesis System (Conventional System) 310 Exhaust gas sources 312 Carbon Dioxide Separation and Recovery System 340 SOEC 350 First heat exchanger 355 Mixer 360 Second heat exchanger 370 Storage equipment 375 Aquariums 379 Steam Generator

Claims

1. A fuel synthesis system that uses exhaust gas to produce fuel, An oxygen removal device that removes oxygen contained in exhaust gas, A SOEC is located downstream of the oxygen removal device, and co-electrolyzes carbon dioxide and water in the exhaust gas to produce carbon monoxide and hydrogen, A fuel synthesis system having the following features.

2. The fuel synthesis system according to claim 1, wherein the oxygen removal device comprises at least one of an oxygen pump, a solid oxide fuel cell (SOFC), and a molten carbonate fuel cell (MCFC).

3. The exhaust gas is discharged from the exhaust gas source, The fuel synthesis system according to claim 1, wherein the exhaust gas discharged from the exhaust gas source contains carbon dioxide in the range of 0 vol% to 30 vol%, water in the range of 0 vol% to 40 vol%, oxygen in the range of 0 vol% to 20 vol%, and nitrogen in the range of 0 vol% to 80 vol%.

4. The fuel synthesis system according to claim 3, wherein the exhaust gas source is various production plants or thermal power plants.

5. The fuel synthesis system according to claim 3, wherein the exhaust gas discharged from the exhaust gas source is 0°C or higher.

6. Furthermore, the oxygen removal device has a heat exchanger upstream of it. The fuel synthesis system according to claim 3, wherein the heat exchanger heats the exhaust gas from the exhaust gas source with heat from the SOEC.

7. Furthermore, the fuel synthesis system according to claim 1, further comprising a heater for heating the exhaust gas upstream of the oxygen removal device.

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