Gas separation system, purified synthesis gas production system, and liquid fuel production system

Abstract

This system reduces carbon dioxide levels and supplies gas with high hydrogen and carbon monoxide content. [Solution] The gas separation system is a gas separation system that receives a supply synthesis gas containing hydrogen, carbon monoxide, and carbon dioxide, and separates the separation gas containing carbon dioxide to produce purified synthesis gas of hydrogen and carbon monoxide, comprising: a first separation membrane that receives the supply synthesis gas and separates it into a first separation gas containing carbon monoxide and carbon dioxide and a second separation gas containing hydrogen; and a second separation membrane that receives the first separation gas separated by the first separation membrane and separates it into a third separation gas containing carbon monoxide and a fourth separation gas containing carbon dioxide, and combines the second separation gas and the third separation gas to produce the purified synthesis gas.

Description

[[Technical Field]]

[0001] The present disclosure relates to a gas separation system, a purified syngas production system, and a liquid fuel production system. [[Background Art]]

[0002] Biomass has attracted attention as a new resource for synthesizing hydrocarbon fuels. For example, Patent Document 1 discloses a technique for synthesizing hydrocarbon fuels using this type of biomass. In Patent Document 1, a solid oxide hydrogen electrolyzer is used to generate syngas consisting of hydrogen gas and carbon monoxide gas, which is then supplied to a liquid fuel synthesis apparatus. In the liquid fuel synthesis apparatus, FT crude oil is produced through FT synthesis based on the Fischer-Tropsch process (FT process). [[Prior Art Documents]] [[Patent Documents]]

[0003] [[Patent Document 1]] Japanese Patent No. 6999213 [[Summary of the Invention]] [[Problems to be Solved by the Invention]]

[0004] By the way, when syngas generated by a solid oxide hydrogen electrolyzer is directly supplied to FT synthesis, carbon dioxide (carbonic acid gas) that has not been completely converted in the solid oxide hydrogen electrolyzer is supplied to the apparatus that performs FT synthesis. As a result, the component ratio of the syngas is not suitable for FT synthesis, which may reduce efficiency when producing liquid fuel. This is also the case when syngas generated by reverse water-gas shift reaction is directly supplied to FT synthesis. Therefore, it is desired to reduce the content of carbon dioxide and supply a gas with high content rates of hydrogen and carbon monoxide.

[0005] This disclosure is made to address the above-mentioned needs and aims to provide a gas separation system, a purified synthesis gas production system, and a liquid fuel production system that can reduce the carbon dioxide content and supply gas with a high hydrogen and carbon monoxide content. [Means for solving the problem]

[0006] To solve the above problems, the gas separation system according to the present disclosure is a gas separation system to which a supply synthesis gas containing hydrogen, carbon monoxide, and carbon dioxide is supplied, and a separation gas containing carbon dioxide is separated to produce purified synthesis gas of hydrogen and carbon monoxide, comprising: a first separation membrane to which the supply synthesis gas is supplied and separated into a first separation gas containing carbon monoxide and carbon dioxide and a second separation gas containing hydrogen; and a second separation membrane to which the first separation gas separated by the first separation membrane is supplied and separated into a third separation gas containing carbon monoxide and a fourth separation gas containing carbon dioxide, and the second separation gas and the third separation gas are combined to produce the purified synthesis gas.

[0007] Furthermore, the purified synthesis gas production system relating to this disclosure comprises a gas separation system and a supply synthesis gas generation system that generates the supply synthesis gas supplied to the gas separation system.

[0008] Furthermore, the liquid fuel production system according to this disclosure includes the gas separation system and an FT synthesis unit that performs Fischer-Tropsch synthesis with the purified synthesis gas discharged from the gas separation system to produce liquid hydrocarbons. [Effects of the Invention]

[0009] According to the gas separation system, purified synthesis gas production system, and liquid fuel production system of this disclosure, it is possible to reduce the carbon dioxide content and supply gases with high hydrogen and carbon monoxide content. [Brief explanation of the drawing]

[0010] [Figure 1] This is an overall configuration showing a liquid fuel production system according to the first embodiment. [Figure 2] This is an overall configuration diagram showing a liquid fuel production system according to the second embodiment. [Modes for carrying out the invention]

[0011] Hereinafter, embodiments for implementing the gas separation system, refined synthesis gas production system, and liquid fuel production system according to this disclosure will be described with reference to the attached drawings. However, this disclosure is not limited to these embodiments.

[0012] <First Embodiment> (Liquid fuel production system) The liquid fuel production system 1 is a system for synthesizing hydrocarbon fuel, which is a fuel, using biomass as a raw material. The liquid fuel production system 1 of this embodiment comprises a biomass power generation system 2, a carbon dioxide capture device 3, a supply synthesis gas generation system 4, a gas separation system 6, a second drain water discharge unit 8, and an FT synthesis system 9. Furthermore, the supply synthesis gas generation system 4 and the gas separation system 6 constitute a refined synthesis gas production system 75.

[0013] The biomass power generation system 2 is configured to generate electricity using biomass, a reusable organic resource, as fuel. The biomass power generation system 2 generates steam by burning biomass in a biomass boiler (not shown), and uses the generated steam to drive a turbine (not shown) to generate electricity. The biomass power generation system 2 emits exhaust gas G, which is produced when biomass is burned.

[0014] The carbon dioxide recovery unit 3 separates and recovers gaseous carbon dioxide (CO2) contained in the exhaust gas G using an absorbent liquid such as an amine. The carbon dioxide recovery unit 3 recovers carbon dioxide from the exhaust gas G supplied from the biomass power generation system 2. The carbon dioxide recovery unit 3 supplies the recovered carbon dioxide (carbon dioxide) to the synthesis gas production system. The carbon dioxide recovery unit 3 also supplies the exhaust gas G from which carbon dioxide has been separated to external equipment such as a chimney.

[0015] The supply synthesis gas generation system 4 uses carbon dioxide supplied from the carbon dioxide recovery device 3 to generate supply synthesis gas Gs containing hydrogen (H2), carbon monoxide (CO), and carbon dioxide. The supply synthesis gas generation system 4 of this embodiment generates supply synthesis gas Gs using a solid oxide electrolysis cell (SOEC). Specifically, the supply synthesis gas generation system 4 of this embodiment includes a water vapor supply line 41, a water supply pump 42, a water vapor generation unit 43, a carbon dioxide supply line 44, a carbon dioxide heating unit 45, an air supply line 46, an air heating unit 47, an SOEC unit 48, an oxygen recovery line 49, an oxygen cooling unit 50, a gas recovery line 51, a first gas cooling unit 52, a second gas cooling unit 53, a gas circulation line 54, and a drain water discharge unit 55.

[0016] The steam supply line 41 supplies steam S and carbon dioxide (carbonic acid gas) to the SOEC unit 48. The steam supply line 41 connects the SOEC unit 48 to an external water source (not shown).

[0017] The water supply pump 42 is connected to the steam supply line 41. The water supply pump 42 pumps water W from the water source and circulates it through the steam supply line 41 towards the steam generation unit 43.

[0018] The steam generator 43 heats water W that has flowed through the steam supply line 41 to generate steam S. The steam generator 43 is arranged on the steam supply line 41 at a downstream position closer to the SOEC unit 48 than the water supply pump 42. The steam generator 43 is, for example, a boiler or a heat exchanger.

[0019] The carbon dioxide supply line 44 supplies carbon dioxide fed from the carbon dioxide recovery device 3 into the feed synthesis gas generation system 4. The carbon dioxide supply line 44 connects the carbon dioxide recovery device 3 and the steam supply line 41. The carbon dioxide supply line 44 is connected between the steam generator 43 and the SOEC unit 48 so as to join the steam supply line 41.

[0020] The carbon dioxide heating unit 45 heats carbon dioxide that has flowed through the carbon dioxide supply line 44. The carbon dioxide heating unit 45 is arranged midway along the carbon dioxide supply line 44. The carbon dioxide heating unit 45 is, for example, a boiler or a heat exchanger.

[0021] The air supply line 46 supplies air A to the SOEC unit 48. The air supply line 46 connects the SOEC unit 48 to a region facing outside air external to the feed synthesis gas generation system 4.

[0022] The air heating unit 47 heats air A that has flowed through the air supply line 46. The air heating unit 47 is arranged midway along the air supply line 46. The air heating unit 47 is, for example, a boiler or a heat exchanger.

[0023] The SOEC unit 48 electrolyzes the supplied high-temperature steam S to produce hydrogen and oxygen, and also co-electrolyzes the high-temperature steam S and carbon dioxide to produce carbon monoxide, hydrogen and oxygen. In addition, part of the electric power P obtained from the biomass power generation system 2 is supplied to the SOEC unit 48. In the SOEC unit 48, a gas G1 containing the produced hydrogen and carbon monoxide, unreacted residual carbon dioxide, and steam S is generated, and is discharged to the gas recovery line 51. Further, in the SOEC unit 48, the produced oxygen-containing gas is discharged to an oxygen recovery line 49.

[0024] The oxygen recovery line 49 is supplied with the oxygen-containing gas discharged from the SOEC unit 48. The oxygen recovery line 49 connects the SOEC unit 48 to a device that requires oxygen outside the supply syngas generation system 4.

[0025] The oxygen cooling unit 50 cools the gas flowing through the oxygen recovery line 49. The oxygen cooling unit 50 is disposed in the middle of the oxygen recovery line 49. The oxygen cooling unit 50 is, for example, a heat exchanger. The heat recovered by the oxygen cooling unit 50 is supplied to an air heating unit 47 and used for heating air A.

[0026] The gas recovery line 51 supplies the gas G1 containing hydrogen, carbon monoxide, carbon dioxide, and steam S produced in the SOEC unit 48 to a drain water discharge unit 55. The gas recovery line 51 connects the SOEC unit 48 and the drain water discharge unit 55.

[0027] The first gas cooling unit 52 cools the gas G1 flowing through the gas recovery line 51. The first gas cooling unit 52 is disposed in the middle of the gas recovery line 51. The first gas cooling unit 52 is, for example, a heat exchanger. The heat T1 recovered by the first gas cooling unit 52 is supplied to a steam generation unit 43 and used for generating (superheating) the high-temperature steam S.

[0028] The second gas cooling section 53 further cools the gas G1 that has been cooled in the first gas cooling section 52. The second gas cooling section 53 is located in the middle of the gas recovery line 51. The second gas cooling section 53 is located downstream of the first gas cooling section 52, closer to the drain water discharge section 55. The second gas cooling section 53 is, for example, a heat exchanger. The heat T2 recovered in the second gas cooling section 53 is supplied to the steam generation section 43 and used to generate (superheat) high-temperature steam S.

[0029] The gas circulation line 54 returns a portion of the gas G1 that has flowed through the gas recovery line 51 to the water vapor supply line 41. The gas circulation line 54 connects a portion of the gas recovery line 51 to a portion of the water vapor supply line 41. The gas circulation line 54 is connected to the gas recovery line 51 between the first gas cooling section 52 and the second gas cooling section 53. The gas circulation line 54 is connected to the water vapor supply line 41 between the confluence point of the carbon dioxide supply line 44 and the water vapor supply line 41 and the SOEC section 48. Therefore, the gas circulation line 54 combines a portion of the gas G1 that has been cooled in the first gas cooling section 52 but not yet cooled in the second gas cooling section 53 with the water vapor S and carbon dioxide before they are supplied to the SOEC section 48.

[0030] The drain water discharge section 55 is supplied with gas G1 that has been cooled by flowing through the gas recovery line 51. The drain water discharge section 55 discharges water vapor S, which has been cooled during the process of flowing through the gas recovery line 51, as drain water. The drain water discharge section 55 also discharges supply synthesis gas Gs, which is the gas from which water vapor S (drain water) has been removed from the gas containing hydrogen, carbon monoxide, carbon dioxide, and water vapor S, and which contains hydrogen, carbon monoxide, and carbon dioxide.

[0031] The gas separation system 6 receives the supply synthesis gas Gs, separates the separated gas containing carbon dioxide, and produces purified synthesis gas RG with a high content of hydrogen and carbon monoxide. The supply synthesis gas Gs discharged from the drain water discharge section 55 of the supply synthesis gas generation system 4 is supplied to the gas separation system 6. The gas separation system 6 of this embodiment includes a synthesis gas supply line 61, a first separation membrane 62, a first separated gas flow line 63, a second separation membrane 64, a second separated gas flow line 65, a separated gas compressor 66, a separated gas cooling section 67, a third separated gas flow line 68, a fourth separated gas flow line 69, and a hydrogen recovery line 70.

[0032] The synthesis gas supply line 61 supplies the supplied synthesis gas Gs from the drain water discharge section 55 to the first separation membrane 62. The synthesis gas supply line 61 connects the drain water discharge section 55 and the first separation membrane 62.

[0033] The supply synthesis gas Gs is supplied to the first separation membrane 62. The first separation membrane 62 separates the supply synthesis gas Gs into a first separation gas SG1 containing carbon monoxide and carbon dioxide, and a second separation gas SG2 containing hydrogen. The first separation gas SG1 contains almost no hydrogen and has a high content of carbon monoxide and carbon dioxide. The second separation gas SG2 contains almost no carbon monoxide and carbon dioxide and has a high content of hydrogen. The first separation membrane 62 is designed to be impermeable to carbon dioxide but permeable to hydrogen. Therefore, the first separation membrane 62 separates carbon dioxide and carbon monoxide, which has a larger molecular size than carbon dioxide, from the supply synthesis gas Gs. The first separation membrane 62 is designed to be capable of separating gases at high pressure (higher than atmospheric pressure). Examples of the first separation membrane 62 include metal membranes formed from metal materials, organic (polymer) membranes such as hollow fiber membranes formed from polymer materials, and ceramic membranes that can be used even at high temperature and high pressure.

[0034] The first separation gas distribution line 63 is supplied with the first separation gas SG1 discharged from the first separation membrane 62. The first separation gas distribution line 63 connects the first separation membrane 62 and the second separation membrane 64.

[0035] The first separation gas SG1, separated by the first separation membrane 62, is supplied to the second separation membrane 64. The second separation membrane 64 separates the first separation gas SG1 into a third separation gas SG3 containing carbon monoxide and a fourth separation gas SG4 containing carbon dioxide. The third separation gas SG3 contains almost no carbon dioxide and has a high carbon monoxide content. The fourth separation gas SG4 contains almost no carbon monoxide and has a high carbon dioxide content. The second separation membrane 64 is designed to be impermeable to carbon monoxide but permeable to carbon dioxide. In other words, the molecular size of permeable particles is smaller in the first separation membrane 62 compared to the second separation membrane 64. Therefore, the second separation membrane 64 separates carbon dioxide from the first separation gas SG1. The second separation membrane 64 is designed to separate gases at high pressure (higher than atmospheric pressure). Examples of the second separation membrane 64 include metal films formed from metal materials, organic (polymer) films such as hollow fiber films formed from polymer materials, and ceramic films that can be used even at high temperatures and pressures.

[0036] The second separation gas flow line 65 is supplied with the second separation gas SG2 discharged from the first separation membrane 62. The second separation gas flow line 65 connects the first separation membrane 62 to an external device (second drain water discharge section 8) of the synthesis gas supply line 61. In the second separation gas flow line 65, the third separation gas SG3 containing carbon monoxide is added to the flowing second separation gas SG2 to produce purified synthesis gas RG, which is then discharged.

[0037] The separation gas compressor 66 compresses the second separation gas SG2 separated by the first separation membrane 62. The separation gas compressor 66 compresses the second separation gas SG2 before the third separation gas SG3 joins it. The separation gas compressor 66 is located in the middle of the second separation gas flow line 65. The separation gas compressor 66 is, for example, a compressor.

[0038] The separation gas cooling unit 67 cools the second separation gas SG2 that has flowed through the second separation gas flow line 65. The separation gas cooling unit 67 cools the second separation gas SG2 that has been compressed by the separation gas compressor 66. The separation gas cooling unit 67 is located in the middle of the second separation gas flow line 65. The separation gas cooling unit 67 is located downstream of the separation gas compressor 66, closer to the second drain water discharge unit 8, with the separation gas compressor 66 sandwiched between the separation membrane 62 and the separation gas cooling unit 67. The separation gas cooling unit 67 is, for example, a heat exchanger. The heat T3 recovered in the separation gas cooling unit 67 is supplied to the steam generation unit 43 and used to generate (superheat) high-temperature steam S.

[0039] The third separation gas flow line 68 is supplied with the third separation gas SG3 discharged from the second separation membrane 64. The third separation gas flow line 68 connects the second separation membrane 64 and the second separation gas flow line 65. The third separation gas flow line 68 is connected to the second separation gas flow line 65 at a position downstream of the separation gas cooling unit 67, closer to the second drain water discharge unit 8. By connecting to the second separation gas flow line 65, the third separation gas flow line 68 merges the third separation gas SG3, which contains carbon monoxide, with the second separation gas SG2, which has been cooled in the separation gas cooling unit 67. As a result, purified synthesis gas RG is generated at the point where the second separation gas flow line 65 and the third separation gas flow line 68 merge.

[0040] The fourth separation gas distribution line 69 is supplied with the fourth separation gas SG4 discharged from the second separation membrane 64. The fourth separation gas distribution line 69 returns the fourth separation gas SG4 discharged from the second separation membrane 64 to the supply synthesis gas generation system 4. The fourth separation gas distribution line 69 connects the second separation membrane 64 to the carbon dioxide supply line 44. The fourth separation gas distribution line 69 is connected to the carbon dioxide supply line 44 at an upstream position closer to the carbon dioxide recovery device 3 relative to the carbon dioxide heating unit 45. By being connected to the carbon dioxide supply line 44, the fourth separation gas distribution line 69 combines the fourth separation gas SG4 discharged from the second separation membrane 64 with the carbon dioxide supplied from the carbon dioxide recovery device 3.

[0041] The hydrogen recovery line 70 supplies a portion of the gas that has flowed through the second separation gas distribution line 65 to the FT synthesis system 9. The hydrogen recovery line 70 supplies the second separation gas SG2, which has been separated by the first separation membrane 62 and is not yet compressed by the separation gas compressor 66, to the hydrocracking section 97 of the FT synthesis system 9, which will be described later. The hydrogen recovery line 70 is connected to the second separation gas distribution line 65 midway through it. The hydrogen recovery line 70 is connected to the second separation gas distribution line 65 between the first separation membrane 62 and the separation gas compressor 66.

[0042] In the second drain water discharge section 8, water is separated from the purified synthesis gas RG and the drain water is discharged. The purified synthesis gas RG from which the water has been separated is then supplied to the FT synthesis system 9.

[0043] The FT synthesis system 9 synthesizes hydrocarbon fuel, which is a liquid fuel, from purified synthesis gas RG containing carbon monoxide and hydrogen by a Fischer-Tropsch (FT) synthesis reaction. The FT synthesis system 9 of this embodiment includes a purified synthesis gas supply line 91, an FT synthesis section 92, a first fuel supply line 93, a first separation section 94, a second fuel supply line 95, an off-gas circulation line 96, a hydrocracking section 97, a third fuel supply line 98, a second separation section 99, a fourth fuel supply line 100, a tail gas circulation line 101, and a distillation purification section 102.

[0044] The purified synthesis gas supply line 91 supplies purified synthesis gas RG to the FT synthesis unit 92. In this embodiment, the purified synthesis gas supply line 91 supplies purified synthesis gas RG from which water has been separated at the second drain water discharge unit 8. The purified synthesis gas supply line 91 connects the second drain water discharge unit 8 and the FT synthesis unit 92.

[0045] The FT synthesis unit 92 produces a liquid first fuel F1 containing liquid hydrocarbons by carrying out an FT synthesis reaction using purified synthesis gas RG containing carbon monoxide. In addition to the target product, hydrocarbon fuel, the first fuel F1 contains carbon dioxide and water vapor as by-products. The first fuel F1 produced in the FT synthesis unit 92 is supplied to the first fuel supply line 93.

[0046] The first fuel supply line 93 supplies the first fuel F1, produced in the FT synthesis unit 92, to the first separation unit 94. The first fuel supply line 93 connects the FT synthesis unit 92 and the first separation unit 94.

[0047] The first separation unit 94 separates off-gas OG containing carbon dioxide and excess water from the first fuel F1 to produce the second fuel F2. The second fuel F2 produced in the first separation unit 94 is supplied to the second fuel supply line 95. The off-gas OG produced in the first separation unit 94 is supplied to the off-gas circulation line 96.

[0048] The second fuel supply line 95 supplies the second fuel F2, generated in the first separation unit 94, to the hydrocracking unit 97. The second fuel supply line 95 connects the first separation unit 94 and the hydrocracking unit 97.

[0049] The off-gas circulation line 96 supplies off-gas OG, which contains carbon dioxide discharged from the first separation unit 94, to the biomass power generation system 2. The off-gas circulation line 96 connects the first separation unit 94 to the biomass power generation system 2 (e.g., a biomass boiler). The off-gas circulation line 96 returns carbon dioxide discharged from the FT synthesis system 9 to the biomass power generation system 2.

[0050] The hydrocracking unit 97 hydrocrackings the second fuel F2, which contains liquid hydrocarbons of the wax fraction with a high number of carbon atoms, using hydrogen gas to reduce its carbon number. In this hydrocracking reaction, a catalyst and heat are used to produce low molecular weight hydrocarbons with a low number of carbon atoms. In this type of hydrocracking, heavy components are converted into lamp oil and diesel fuel. The hydrocracking unit 97 produces a third fuel F3 containing the hydrocracking liquid hydrocarbons. The third fuel F3 produced in the hydrocracking unit 97 is supplied to the third fuel supply line 98.

[0051] The third fuel supply line 98 supplies the third fuel F3 produced in the hydrocracking unit 97 to the second separation unit 99. The third fuel supply line 98 connects the hydrocracking unit 97 and the second separation unit 99.

[0052] The second separation unit 99 separates hydrogen-containing tail gas TG and water from the third fuel F3 to produce the fourth fuel F4. The fourth fuel F4 produced in the second separation unit 99 is supplied to the fourth fuel supply line 100. The tail gas TG produced in the second separation unit 99 is supplied to the tail gas circulation line 101.

[0053] The fourth fuel supply line 100 supplies the fourth fuel F4, produced in the second separation unit 99, to the distillation and purification unit 102. The fourth fuel supply line 100 connects the second separation unit 99 and the distillation and purification unit 102.

[0054] The tail gas circulation line 101 supplies the tail gas TG containing hydrogen discharged from the second separation unit 99 to the hydrocracking unit 97. The tail gas circulation line 101 connects the second separation unit 99 and the hydrocracking unit 97. The distillation and refining unit 102 fractionally distills and rectifies the fourth fuel F4 to produce naphtha, kerosene, and diesel fuel as products.

[0055] (Effects and Benefits) In the gas separation system 6 of this first embodiment, supply synthesis gas Gs produced in the supply synthesis gas generation system 4 is supplied, and purified synthesis gas RG is produced by the first separation membrane 62 and the second separation membrane 64. Specifically, in the first separation membrane 62, the supply synthesis gas Gs is separated into a first separation gas SG1 containing carbon monoxide and carbon dioxide, and a second separation gas SG2 containing hydrogen. Furthermore, in the second separation membrane 64, the first separation gas SG1 is separated into a third separation gas SG3 containing carbon monoxide and a fourth separation gas SG4 containing carbon dioxide. As a result, in the gas separation system 6, carbon monoxide and carbon dioxide are first removed from the supply synthesis gas Gs by the first separation membrane 62. Then, carbon dioxide is removed from the carbon monoxide and carbon dioxide by the second separation membrane 64, and the remaining carbon monoxide is combined with hydrogen. In this way, purified synthesis gas RG with a high content of hydrogen and carbon monoxide is produced by removing the carbon dioxide contained in the supply synthesis gas Gs. As a result, the gas separation system 6 can supply gas with reduced carbon dioxide content and a high concentration of hydrogen and carbon monoxide.

[0056] In particular, in this embodiment, the purified synthesis gas RG discharged from the gas separation system 6 is supplied to the FT synthesis section 92 of the liquid fuel production system 1. In other words, the purified synthesis gas RG is used to produce the first fuel F1 containing liquid hydrocarbons through the FT synthesis reaction. In this way, carbon dioxide (CO2) remaining in the supply synthesis gas Gs generated in the supply synthesis gas generation system 4 is removed in the gas separation system 6, so that purified synthesis gas RG with a high content of hydrogen and carbon monoxide, which is suitable for FT synthesis, can be used in the FT synthesis section 92. Therefore, the conversion rate of FT synthesis in the FT synthesis section 92 can be improved. As a result, the amount of unreacted gas in the FT synthesis section 92 is reduced, the generation of off-gas OG is suppressed, and the yield of liquid hydrocarbons can be increased. Therefore, the unit cost can be improved when producing naphtha, kerosene, and diesel fuel, which are the products of the liquid fuel production system 1.

[0057] Furthermore, by utilizing the first separation membrane 62 and the second separation membrane 64 in the gas separation system 6, highly reactive substances such as carbon monoxide can be stably removed compared to when using an absorbent liquid such as an amine. In addition, impurities generated during separation can be reduced compared to when using an absorbent liquid, and hydrogen, carbon monoxide, and carbon dioxide can be separated in a highly pure state. Moreover, stable separation performance can be maintained even if the supply synthesis gas Gs to be separated is at high pressure or if there are variations in the composition ratio of the supply synthesis gas Gs when it is supplied.

[0058] Furthermore, in the gas separation system 6, a portion of the second separated gas SG2, which is produced by separating the supplied synthesis gas Gs by the first separation membrane 62, is recovered by the hydrogen recovery line 70 and supplied to the hydrocracking unit 97, which is an external device of the gas separation system 6. Therefore, highly pure hydrogen that has not been compressed or cooled can be supplied to equipment that requires hydrogen, such as the hydrocracking unit 97. Moreover, in this embodiment, the second separated gas SG2 containing hydrogen is supplied to the hydrocracking unit 97 of the FT synthesis system 9, which synthesizes hydrocarbon fuel by the FT synthesis reaction. Therefore, the FT synthesis system 9 does not require the installation of equipment (PSA) that generates hydrogen by pressure fluctuation adsorption using an adsorbent, for example. Thus, the FT synthesis system 9 can be manufactured with a simpler configuration and at a lower cost.

[0059] Furthermore, in the gas separation system 6, the second separated gas SG2 flowing through the second separated gas distribution line 65 is compressed by the separation gas compressor 66 and then cooled in the separation gas cooling unit 67. The separation gas cooling unit 67 recovers a portion of the heat generated from cooling the second separated gas SG2 and supplies it to the steam generation unit 43 located outside the gas separation system 6. Therefore, the heat generated from cooling the second separated gas SG2 can be reused in heating equipment that requires high temperatures, such as the steam generation unit 43. Consequently, the supply synthesis gas generation system 4 does not require the installation of equipment to supply a high-temperature heating medium to the steam generation unit 43, or the required equipment capacity can be reduced. Therefore, the supply synthesis gas generation system 4 can be manufactured with a simpler configuration and at a lower cost.

[0060] Furthermore, the fourth separation gas SG4 separated by the second separation membrane 64 is supplied to the carbon dioxide supply line 44 via the fourth separation gas distribution line 69. In other words, the fourth separation gas SG4, which has a high carbon dioxide content that is unwanted in the purified synthesis gas RG, is recovered to the carbon dioxide supply line 44 without being discharged to the outside. By being returned to the carbon dioxide supply line 44, the fourth separation gas SG4 is supplied to the SOEC unit 48 located outside the gas separation system 6. Therefore, by reusing the fourth separation gas SG4 separated in the gas separation system 6 in the SOEC unit 48, the emission of carbon dioxide into the atmosphere can be suppressed. Also, the fourth separation gas SG4 is a gas contained in the gas G1 discharged from the SOEC unit 48. Therefore, even if the carbon dioxide originally supplied to the SOEC unit 48 is not all converted and is discharged there, the unconverted carbon dioxide will return to the SOEC unit 48. Therefore, the allowable amount of carbon dioxide that can be discharged without conversion in the SOEC unit 48 increases. Consequently, the load on the SOEC unit 48 can be easily adjusted according to the balance of the entire system. This allows for a simpler configuration of the equipment around the SOEC unit 48.

[0061] Furthermore, a purified synthesis gas production system 75 is configured, comprising a gas separation system 6 and a supply synthesis gas generation system 4 that generates supply synthesis gas Gs to the gas separation system 6. In particular, in this embodiment, the purified synthesis gas production system 75 includes a supply synthesis gas generation system 4 having an SOEC section 48. Therefore, even in plants where an FT synthesis system 9 has already been set up, a configuration capable of generating purified synthesis gas RG can be installed.

[0062] <Second Embodiment> Next, a liquid fuel production system 1A of a second embodiment of the present disclosure will be described. In the second embodiment described below, components common to the first embodiment are denoted by the same reference numerals in the figures and their descriptions are omitted. The liquid fuel production system 1A of the second embodiment differs from the first embodiment in that it does not utilize SOEC in the supply synthesis gas generation system 4A.

[0063] As shown in Figure 2, the supply synthesis gas generation system 4A of the second embodiment generates hydrogen by electrolysis and produces supply synthesis gas Gs by a reverse shift reaction using the generated hydrogen. Specifically, the supply synthesis gas generation system 4A of the second embodiment includes a water electrolysis unit 56, a hydrogen supply line 41A, a carbon dioxide supply line 44A, a carbon dioxide heating unit 45, a reverse shift reaction unit 57, a gas recovery line 51A, a gas cooling unit 52A, a gas circulation line 54A, and a drain recovery line 59.

[0064] The water electrolysis unit 56 generates hydrogen and oxygen by electrolyzing water W. Water W is supplied to the water electrolysis unit 56 from an external water source (not shown). The hydrogen generated in the water electrolysis unit 56 is discharged into the hydrogen supply line 41A. In addition, a portion of the electricity P obtained from the biomass power generation system 2 is supplied to the water electrolysis unit 56.

[0065] The hydrogen supply line 41A supplies hydrogen to the reverse shift reaction unit 57. In this embodiment, the hydrogen supply line 41A supplies hydrogen and carbon dioxide (carbonic acid gas) to the reverse shift reaction unit 57. The hydrogen supply line 41A connects the water electrolysis unit 56 and the reverse shift reaction unit 57.

[0066] In the second embodiment, the carbon dioxide supply line 44A connects the carbon dioxide recovery device 3 and the hydrogen supply line 41A. The carbon dioxide supply line 44A is connected to the hydrogen supply line 41A between the water electrolysis unit 56 and the reverse shift reaction unit 57.

[0067] The reverse shift reaction unit 57 generates carbon monoxide from the supplied carbon dioxide and hydrogen through a reverse shift reaction. In the reverse shift reaction unit 57, gas G1 is produced, which contains carbon monoxide and unreacted residual carbon dioxide and hydrogen, and is discharged to the gas recovery line 51A.

[0068] In the second embodiment, the gas recovery line 51A supplies gas G2, which contains hydrogen, carbon monoxide, carbon dioxide, and water vapor S produced in the reverse shift reaction unit 57, to the drain water discharge unit 55A. The gas recovery line 51A connects the reverse shift reaction unit 57 and the drain water discharge unit 55A.

[0069] The gas cooling unit 52A cools the gas G2 that has flowed through the gas recovery line 51A. The gas cooling unit 52A is located in the middle of the gas recovery line 51A. The gas cooling unit 52A is, for example, a heat exchanger. The heat T4 recovered in the gas cooling unit 52A is supplied to the carbon dioxide heating unit 45 and used to generate (superheat) high-temperature carbon dioxide gas. In the second embodiment, the heat T3 recovered in the separated gas cooling unit 67 is also supplied to the carbon dioxide heating unit 45 and used to generate (superheat) high-temperature carbon dioxide gas.

[0070] The gas circulation line 54A returns a portion of the gas G2 that has flowed through the gas recovery line 51A back to the carbon dioxide supply line 44A. The gas circulation line 54A connects a point in the middle of the gas recovery line 51A with a point in the middle of the carbon dioxide supply line 44A. The gas circulation line 54A is connected to the gas recovery line 51A at an upstream position closer to the reverse shift reaction unit 57 than the gas cooling unit 52A. The gas circulation line 54A is connected to the carbon dioxide supply line 44A at an upstream position closer to the carbon dioxide recovery device 3 than the carbon dioxide heating unit 45. Therefore, the gas circulation line 54A combines a portion of the gas G2 before it is cooled in the gas cooling unit 52A with the carbon dioxide before it is supplied to the reverse shift reaction unit 57.

[0071] The drain water discharge section 55A is supplied with gas G2 that has been cooled by flowing through the gas recovery line 51A. The drain water discharge section 55A discharges the water in the gas G2 that has been cooled during the process of flowing through the gas recovery line 51A as drain water. The drain water discharge section 55A also discharges the supply synthesis gas Gs, which contains hydrogen, carbon monoxide, and carbon dioxide, and is the gas from which the drain water has been removed from gas G2, which contains hydrogen, carbon monoxide, carbon dioxide, and water vapor S.

[0072] The drain recovery line 59 recovers the drain water discharged from the drain water discharge section 55A and supplies it to the water electrolysis section 56. Furthermore, in this embodiment, the drain recovery line 59 also recovers the drain water discharged from the second drain water discharge section 8 and supplies it to the water electrolysis section 56.

[0073] (Effects and Benefits) In this second embodiment, unlike the first embodiment, the supply synthesis gas production system 4A has a reverse shift reaction unit 57 instead of a SOEC unit 48. In other words, the purified synthesis gas production system 75A of the second embodiment includes a supply synthesis gas production system 4A having a reverse shift reaction unit 57. Thus, even if the equipment that produces the supply synthesis gas Gs is different, the same effects as in the first embodiment can be obtained.

[0074] (Other embodiments) Although embodiments of this disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and may include design changes and the like that do not depart from the gist of this disclosure.

[0075] It should be noted that the liquid fuel production system 1,1A is not limited to the configuration of this embodiment, as long as it can synthesize hydrocarbon fuel using biomass as a raw material. For example, the liquid fuel production system 1,1A does not need to have a carbon dioxide capture device 3.

[0076] Furthermore, the supply synthesis gas generation systems 4 and 4A are not limited to the configuration of this embodiment, as long as they can generate supply synthesis gas Gs. For example, the supply synthesis gas generation systems 4 and 4A do not need to have gas circulation lines 54 and 54A. However, it is preferable that the supply synthesis gas generation systems 4 and 4A have an SOEC section 48 and a reverse shift reaction section 57.

[0077] Furthermore, the gas separation system 6 only needs to have a first separation membrane 62 and a second separation membrane 64, and other structures are not limited to the configuration of this embodiment. For example, the gas separation system 6 does not need to have a hydrogen recovery line 70.

[0078] Furthermore, the FT synthesis system 9 only needs to have an FT synthesis unit 92, and other configurations are not limited to the configuration of this embodiment. For example, the FT synthesis system 9 may have only an FT synthesis unit 92, and other equipment may be arranged separately.

[0079] Furthermore, the first separation membrane 62 and the second separation membrane 64 are not limited to being arranged as single devices, as in this embodiment. For example, the first separation membrane 62 and the second separation membrane 64 may be configured as multiple separation membranes arranged in series or in parallel.

[0080] Furthermore, the purified synthesis gas RG produced in the gas separation system 6 is not limited to being used for FT synthesis as in this embodiment. The purified synthesis gas RG produced in the gas separation system 6 can be supplied to systems that utilize gas with a low carbon dioxide content and a high hydrogen and carbon monoxide content. Therefore, the purified synthesis gas RG may be supplied, for example, to a methanation system that synthesizes methane.

[0081] <Note> The gas separation system 6, the refined synthesis gas production systems 75, 75A, and the liquid fuel production systems 1, 1A described in each embodiment can be understood, for example, as follows.

[0082] (1) The gas separation system 6 according to the first embodiment is a gas separation system 6 to which a supply synthesis gas Gs containing hydrogen, carbon monoxide, and carbon dioxide is supplied, and the separation gas containing carbon dioxide is separated to produce purified synthesis gas RG of hydrogen and carbon monoxide, comprising: a first separation membrane 62 to which the supply synthesis gas Gs is supplied and separates into a first separation gas SG1 containing carbon monoxide and carbon dioxide and a second separation gas SG2 containing hydrogen; and a second separation membrane 64 to which the first separation gas SG1 separated by the first separation membrane 62 is supplied and separates into a third separation gas SG3 containing carbon monoxide and a fourth separation gas SG4 containing carbon dioxide, and the second separation gas SG2 and the third separation gas SG3 are combined to produce the purified synthesis gas RG.

[0083] With this configuration, in the gas separation system 6, carbon monoxide and carbon dioxide are first removed from the supply synthesis gas Gs by the first separation membrane 62. Then, carbon dioxide is removed from the carbon monoxide and carbon dioxide by the second separation membrane 64, and the remaining carbon monoxide is combined with hydrogen. In this way, purified synthesis gas RG is produced, in which carbon dioxide contained in the supply synthesis gas Gs is removed and the hydrogen and carbon monoxide content is high. As a result, the gas separation system 6 can supply gas with reduced carbon dioxide and a high hydrogen and carbon monoxide content.

[0084] (2) The gas separation system 6 according to the second embodiment is the gas separation system 6 of (1), further comprising a compressor for compressing the second separated gas SG2 that has been separated by the first separation membrane 62 and before it is joined with the third separated gas SG3, and supplying a portion of the second separated gas SG2 before it is compressed by the compressor to an external device from between the first separation membrane 62 and the compressor.

[0085] This configuration allows for the supply of highly pure, uncompressed hydrogen to external equipment that requires it.

[0086] (3) The gas separation system 6 according to the third embodiment is the gas separation system 6 of (2), further comprising a cooling unit for cooling the second separated gas SG2 compressed by the compressor, the cooling unit recovers a portion of the heat generated by cooling the second separated gas SG2, and supplies a portion of the recovered heat to an external device.

[0087] With this configuration, the heat generated by cooling the second separation gas SG2 can be reused in heating equipment that requires high temperatures.

[0088] (4) The gas separation system 6 according to the fourth embodiment is any one of the gas separation systems 6 described in (1) to (3), wherein the second separation membrane 64 supplies the fourth separation gas SG4 to an external device.

[0089] With this configuration, the fourth separation gas SG4, which has a high carbon dioxide content and is unwanted in the purified synthesis gas RG, is recovered by external equipment without being discharged to the outside. Therefore, by reusing the fourth separation gas SG4 separated by the gas separation system 6 in external equipment, the emission of carbon dioxide into the atmosphere can be suppressed.

[0090] (5) The purified synthesis gas production system 75, 75A according to the fifth embodiment comprises one gas separation system 6 from any one of (1) to (4) and supply synthesis gas production systems 4, 4A that produce the supply synthesis gas Gs supplied to the gas separation system 6.

[0091] With this configuration, even in plants where the FT synthesis system 9 is already set up, a configuration capable of generating purified synthesis gas RG can be installed.

[0092] (6) The purified synthesis gas production system 75 according to the sixth embodiment is the purified synthesis gas production system 75 of (5), wherein the supply synthesis gas production systems 4, 4A include a SOEC section 48 that receives carbon dioxide and water W, generates hydrogen using a solid oxide electrolytic cell, and discharges the supply synthesis gas Gs.

[0093] (7) The purified synthesis gas production system 75A according to the seventh embodiment is the purified synthesis gas production system 75A of (5), wherein the supply synthesis gas production systems 4, 4A include a reverse shift reaction section 57 to which hydrogen and carbon dioxide are supplied and carbon monoxide is produced by a reverse shift reaction and the supply synthesis gas Gs is discharged.

[0094] (8) A liquid fuel production system 1, 1A according to the eighth embodiment, a purified synthesis gas production system 75, 75A which is one of (5) to (7), and an FT synthesis unit 92 which produces liquid hydrocarbons by performing Fischer-Tropsch synthesis with the purified synthesis gas RG discharged from the gas separation system 6.

[0095] With this configuration, the purified synthesis gas RG is used to produce liquid hydrocarbons in the FT synthesis reaction. In this way, carbon dioxide (CO2) remaining in the supply synthesis gas Gs produced in the supply synthesis gas generation systems 4 and 4A is removed by the gas separation system 6, so that purified synthesis gas RG with a high content of hydrogen and carbon monoxide, which is suitable for FT synthesis, can be used in the FT synthesis unit 92. Therefore, the conversion rate of FT synthesis in the FT synthesis unit 92 can be improved. As a result, the amount of unreacted gas in the FT synthesis unit 92 is reduced, the generation of off-gas OG is suppressed, and the yield of liquid hydrocarbons can be increased. [Explanation of Symbols]

[0096] 1.1A Liquid Fuel Production System 2. Biomass power generation system G exhaust gas 3. Carbon dioxide capture device 4. 4A Supply Synthesis Gas Generation System 41. Steam supply line 42 Water supply pump 43. Steam generation section 44,44A Carbon dioxide supply line 45 Carbon dioxide heating section 46 Air supply line 47 Air heating section 48 SOEC Department 49. Oxygen recovery line 50 Oxygen Cooling Unit 51, 51A Gas Recovery Line 52 Gas First Cooling Section 53 Second gas cooling section 54,54A Gas circulation line 55, 55A Drain water discharge section W water S Water vapor A air Gs supply synthesis gas 6. Gas Separation System 61 Synthesis gas supply line 62 First separation membrane 63. First Separation Gas Distribution Line 64 Second separation membrane 65 Second Separation Gas Distribution Line 66 Separation gas compressor 67 Separation gas cooling section 68 Third Separation Gas Distribution Line 69. Fourth Separation Gas Distribution Line 70 Hydrogen recovery line SG1 First Separation Gas SG2 Second Separation Gas SG3 Third Separation Gas SG4 Fourth Separation Gas RG (Refined Synthesis Gas) 75,75A Refined Synthesis Gas Production System 8. Second drain water discharge section 9 FT synthesis system 91. Purified synthesis gas supply line 92 FT synthesis section 93 First Fuel Supply Line 94 First separation section 95 Second fuel supply line 96 Off-gas circulation line 97 Hydrocracking section 98 Third Fuel Supply Line 99 Second separation section 100 Fourth Fuel Supply Line 101 Tail gas circulation line 102 Distillation and Purification Section F1 Daiichi Fuel F2 secondary fuel F3 tertiary fuel F4 fourth fuel OG Off-gas TG tail gas 41A Hydrogen supply line 52A Gas Cooling Section 56 Water electrolysis section 57 Reverse shift reaction section 59 Drain recovery line

Claims

1. A gas separation system is provided which a supply synthesis gas containing hydrogen, carbon monoxide, and carbon dioxide is supplied, and a separation gas containing carbon dioxide is separated to produce purified synthesis gas of hydrogen and carbon monoxide, The supply synthesis gas is supplied to a first separation membrane that separates it into a first separation gas containing carbon monoxide and carbon dioxide, and a second separation gas containing hydrogen. The first separation gas separated by the first separation membrane is supplied to a second separation membrane, which separates it into a third separation gas containing carbon monoxide and a fourth separation gas containing carbon dioxide. A gas separation system that combines the second separated gas and the third separated gas to produce the purified synthesis gas.

2. The system further comprises a compressor for compressing the second separated gas, which has been separated by the first separation membrane and is not yet combined with the third separated gas, The gas separation system according to claim 1, wherein a portion of the second separated gas before it is compressed by the compressor is supplied to an external device from between the first separation membrane and the compressor.

3. The system further includes a cooling unit for cooling the second separated gas compressed by the compressor, The gas separation system according to claim 2, wherein the cooling unit recovers a portion of the heat generated from cooling the second separated gas and supplies a portion of the recovered heat to an external device.

4. The gas separation system according to claim 1 or 2, wherein the second separation membrane supplies the fourth separation gas to an external device.

5. A gas separation system according to claim 1 or 2, A purified synthesis gas production system comprising a supply synthesis gas generation system that generates the supply synthesis gas supplied to the gas separation system.

6. The purified synthesis gas production system according to claim 5, wherein the supply synthesis gas production system comprises a SOEC section to which carbon dioxide and water are supplied, hydrogen is produced using a solid oxide electrolytic cell, and the supply synthesis gas is discharged.

7. The purified synthesis gas production system according to claim 5, further comprising a reverse shift reaction section to which hydrogen and carbon dioxide are supplied and carbon monoxide is produced by a reverse shift reaction, and the supplied synthesis gas is discharged.

8. A purified synthesis gas production system according to claim 5, A liquid fuel production system comprising an FT synthesis unit that produces liquid hydrocarbons by performing Fischer-Tropsch synthesis with the purified synthesis gas discharged from the gas separation system.

Images