Algae cultivation system

Abstract

This invention provides an algae cultivation system capable of extracting high concentrations of oxygen from algae cultivation tanks. [Solution] An algae cultivation system comprising a first algae cultivation tank and at least one carbon dioxide storage container for storing a gas containing carbon dioxide, wherein the first algae cultivation tank includes a ceiling wall, the lower part of each of the at least one carbon dioxide storage containers is immersed in the culture medium inside the first algae cultivation tank, an opening is formed at the lower end of each of the at least one carbon dioxide storage containers that opens downward, and a liquid level of the culture medium is formed inside each of the at least one carbon dioxide storage containers at a position above the opening.

Description

Technical Field

[0001] The present disclosure relates to an algae culture system.

Background Art

[0002] Patent Document 1 discloses an algae culture system including a biogas power generation device that generates electricity using biogas generated in a methane fermentation tank, and an algae culture tank that cultures algae using carbon dioxide generated in the biogas power generation device.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the algae culture system described in Patent Document 1, the gas containing carbon dioxide generated in the biogas power generation device is introduced into the space above the liquid level of the culture solution in the algae culture tank (the space between the light-transmitting cover of the algae culture tank and the culture solution). Therefore, in this space, the gas containing carbon dioxide supplied from the biogas power generation device and the oxygen generated in the algae culture tank are mixed, and it has been difficult to extract high-concentration oxygen from the algae culture tank.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide an algae culture system capable of extracting high-concentration oxygen from an algae culture tank.

Means for Solving the Problems

[0006] To achieve the above object, an algae culture system according to at least one embodiment of the present disclosure includes a first algae culture tank for storing algae and a culture solution for culturing the algae, The first algae culture tank is provided with at least one carbon dioxide storage container for storing gas containing carbon dioxide, Equipped with, The first algae culture tank includes a ceiling wall, The lower part of each of the at least one carbon dioxide storage containers is immersed in the culture medium inside the first algae culture tank. Each of the lower ends of the at least one carbon dioxide storage container has an opening that opens downwards, Inside each of the at least one carbon dioxide storage containers, the liquid level of the culture medium is formed at a position above the opening. [Effects of the Invention]

[0007] According to at least one embodiment of the present disclosure, an algae cultivation system is provided that is capable of extracting high concentrations of oxygen from an algae cultivation tank. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram shows a schematic configuration of an algae cultivation system 2 according to one embodiment. [Figure 2] Figure 1 schematically shows an example of the algae cultivation apparatus 28 of the algae cultivation system 2. [Figure 3] Figure 2 is a schematic diagram showing the longitudinal cross-section of each algae culture tank 74 and the carbon dioxide storage container 75. [Figure 4] This figure shows a modified example of the algae cultivation apparatus 28. [Figure 5] This figure shows another variation of the algae cultivation apparatus 28. [Figure 6] Figure 5 shows a longitudinal cross-section of the algae cultivation apparatus 28, specifically the algae cultivation tank 74, the carbon dioxide storage container 75, and the oxygen recovery tower 90. [Figure 7] This figure shows yet another modified example of the algae cultivation apparatus 28. [Modes for carrying out the invention]

[0009] Hereinafter, several embodiments of this disclosure will be described with reference to the attached drawings. However, the dimensions, materials, shapes, relative arrangements, etc., of the components described or shown in the drawings as embodiments are not intended to limit the scope of the invention, but are merely illustrative examples. For example, expressions describing relative or absolute arrangements such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial" should not only strictly describe such arrangements, but also describe states of relative displacement with tolerances or angles or distances that allow for the same function to be achieved. For example, expressions such as "identical," "equal," and "homogeneous" that describe things being in an equal state not only describe a state of being strictly equal, but also describe a state in which there is a tolerance or a difference that is sufficient to achieve the same function. For example, expressions describing shapes such as squares or cylinders shall not only represent geometrically precise shapes such as squares or cylinders, but also shapes that include protrusions, chamfers, etc., to the extent that the same effect can be achieved. On the other hand, expressions such as "to possess," "to be equipped with," "to have," "to include," or "to have" a single component are not exclusive expressions that exclude the existence of other components.

[0010] <Example of the overall configuration of an algae cultivation system> Figure 1 is a diagram showing a schematic configuration of an algae cultivation system 2 according to one embodiment. As shown in Figure 1, the algae cultivation system 2 includes a raw material tank 4, a methane fermentation tank 6, a post-treatment device 8, a gas holder 9, an energy conversion device 10, and a concentrated algae storage tank 12, etc.

[0011] The raw material tank 4 stores biomass which is the raw material for methane fermentation. Biomass (first biomass) such as agricultural residues, livestock waste, food waste, forestry residues or sewage sludge, etc. is supplied to the raw material tank 4 as the first raw material for methane fermentation. The moisture content of the first raw material may be, for example, 50% or more, 70% or more, or 90% or more. When this first raw material is a flame-retardant biomass such as bamboo or vegetation, etc., pretreatment such as hydrothermal treatment may be performed on the flame-retardant biomass before it is supplied to the raw material tank 4. Also, an algae return line 54 described later is connected to the raw material tank 4, and the algae return line 54 is configured to be able to supply concentrated algae (second biomass) as a second raw material different from the first raw material to the raw material tank 4. A stirring device (not shown) for mixing the raw materials may be provided inside the raw material tank 4.

[0012] The raw material tank 4 and the methane fermentation tank 6 are connected by a raw material supply line 5, and the raw material supply line 5 is configured to supply the biomass (biomass containing at least one of the above first raw material and second raw material) discharged from the raw material tank 4 to the methane fermentation tank 6. A pump 11 for pumping the biomass discharged from the raw material tank 4 to the methane fermentation tank 6 is provided in the raw material supply line 5.

[0013] The methane fermentation tank 6 is constituted by, for example, a container containing methane-fermenting bacteria, and methane-ferments the biomass supplied from the raw material tank 4 through the raw material supply line 5 to generate biogas containing methane and carbon dioxide. Note that the methane fermentation may be performed, for example, under anaerobic conditions at 30°C or more and 60°C or less, preferably 50°C or more and 60°C or less.

[0014] The biogas generated in the methane fermentation tank 6 is a mixed gas containing methane and carbon dioxide, and as other components, it contains trace components such as hydrogen sulfide and water vapor. The biogas generated in the methane fermentation tank 6 is discharged from the methane fermentation tank 6 to the biogas line 14. The biogas discharged from the methane fermentation tank 6 to the biogas line 14 may contain, for example, 40% by volume or more, 45% by volume or more, or 50% by volume or more of methane, and 30% by volume or more, 35% by volume or more, or 40% by volume or more of carbon dioxide. The biogas line 14 connects the methane fermentation tank 6 and the carbon dioxide absorption tower 16 of the post-treatment device 8. The biogas line 14 is configured to supply the biogas discharged from the methane fermentation tank 6 to the carbon dioxide absorption tower 16. A blower 15 for supplying the biogas discharged from the methane fermentation tank 6 to the carbon dioxide absorption tower 16 is provided in the biogas line 14.

[0015] On the other hand, the fermentation residue remaining after methane fermentation of the biomass in the methane fermentation tank 6 is discharged from the methane fermentation tank 6 to the fermentation residue line 18. The fermentation residue line 18 connects the methane fermentation tank 6 and the solid-liquid separation device 20 of the post-treatment device 8. The fermentation residue discharged from the methane fermentation tank 6 to the fermentation residue line 18 contains a solid component and a digestion liquid as a liquid component. The fermentation residue line 18 is configured to supply the fermentation residue discharged from the methane fermentation tank 6 to the fermentation residue line 18 to the solid-liquid separation device 20. A pump 19 for pressure-feeding the fermentation residue discharged from the methane fermentation tank 6 to the solid-liquid separation device 20 is provided in the fermentation residue line 18.

[0016] The post-treatment device 8 includes a carbon dioxide absorption tower 16, a solid-liquid separation device 20, a digestion liquid storage tank 25, a mixing tank 26, an algae cultivation device 28, a solid-liquid separation device 32, an oxygen storage tank 34, and the like.

[0017] As described above, biogas is supplied to the carbon dioxide absorption tower 16 from the methane fermentation tank 6 through the biogas line 14. The carbon dioxide absorption tower 16 is configured to produce carbonated water by dissolving the carbon dioxide contained in the biogas in water through gas-liquid contact between the biogas supplied from the methane fermentation tank 6 and water. Since methane in biogas is less soluble in water than carbon dioxide, most of the methane in the biogas is discharged from the carbon dioxide absorption tower 16 to the methane gas line 36 without dissolving in water. The internal pressure of the carbon dioxide absorption tower 16 may be set to a pressure higher than atmospheric pressure to promote the dissolution of carbon dioxide in water. The methane gas line 36 connects the carbon dioxide absorption tower 16 to the energy conversion device 10 (in the illustrated example, the gas turbine 60 provided in the energy conversion device 10). The methane gas discharged from the carbon dioxide absorption tower 16 to the methane gas line 36 is stored in a gas holder 9 for storing methane gas and then supplied to the energy conversion device 10 (in the illustrated example, the gas turbine 60 provided in the energy conversion device 10).

[0018] The gas discharged from the carbon dioxide absorption tower 16 to the methane gas line 36 contains trace components other than methane gas, such as hydrogen sulfide and water vapor. Therefore, in the exemplary configuration shown in Figure 1, the methane gas line 36 is equipped with a dehumidifier 38 for removing moisture from the gas flowing through the methane gas line 36, and a desulfurization tower 40 for removing hydrogen sulfide from the gas flowing through the methane gas line 36. The dehumidifier 38 also includes a chiller 39 for cooling the gas flowing through the methane gas line 36. The gas discharged from the carbon dioxide absorption tower 16 to the methane gas line 36 is cooled by the chiller 39 in the dehumidifier 38 to remove moisture, and then hydrogen sulfide is removed in the desulfurization tower 40 before being supplied to the gas holder 9 and stored in the gas holder 9.

[0019] In the illustrated exemplary embodiment, the energy conversion device 10 includes a gas turbine 60 (combustion device) and a generator 61 connected to the gas turbine 60. Methane gas exiting the gas holder 9 is supplied to the gas turbine 60 as fuel by a blower 63 installed between the gas holder 9 and the gas turbine 60 in the methane gas line 36. The gas turbine 60 burns the methane gas supplied from the carbon dioxide absorption tower 16 through the methane gas line 36 to produce combustion gas, converts the energy of the combustion gas into rotational energy for the turbine, transmits the rotational energy to the generator 61, and causes the generator 61 to generate electricity. An exhaust gas line 70 is connected to the gas turbine 60, and the combustion gas produced by burning methane gas in the gas turbine 60 is discharged into the exhaust gas line 70 as exhaust gas from the gas turbine 60.

[0020] Meanwhile, the carbonated water produced in the carbon dioxide absorption tower 16 is discharged from the carbon dioxide absorption tower 16 into the carbonated water line 42. The carbonated water line 42 connects the carbon dioxide absorption tower 16 to the mixing tank 26. The carbonated water line 42 is configured to supply the carbonated water discharged from the carbon dioxide absorption tower 16 to the mixing tank 26. The carbonated water line 42 is equipped with a pump 46 for pressurizing the carbonated water discharged into the carbonated water line 42 and sending it to the mixing tank 26.

[0021] Furthermore, the solid components in the fermentation residue supplied from the methane fermentation tank 6 to the solid-liquid separator 20 and the digestate are separated from each other by the solid-liquid separator 20. The solid components discharged from the solid-liquid separator 20 (solid components in the fermentation residue) may be used, for example, as compost. The type of solid-liquid separator 20 is not particularly limited, but may be a centrifuge, membrane separator, screen or filter, for example. If the solid-liquid separator 20 is a membrane separator, for example, a portion of the solid components discharged from the solid-liquid separator 20 may be returned to the raw material tank 4.

[0022] The digestate separated from the solid components in the fermentation residue by the solid-liquid separator 20 (digestate in the fermentation residue) is discharged from the solid-liquid separator 20 to the digestate supply line 48. The digestate supply line 48 connects the solid-liquid separator 20 to the mixing tank 26 and is configured to supply the digestate discharged from the solid-liquid separator 20 to the mixing tank 26. The digestate supply line 48 is provided with a digestate storage tank 25 for storing the digestate discharged from the solid-liquid separator 20. Between the digestate storage tank 25 and the mixing tank 26 in the digestate supply line 48, there is a pump 27 for pressurizing the digestate discharged from the digestate storage tank 25 to the mixing tank 26.

[0023] The mixing tank 26 and the algae cultivation apparatus 28 are connected by an algae extraction line 50, which is configured to extract partially cultivated algae and culture solution from the algae cultivation apparatus 28 and supply them to the mixing tank 26. "Partially cultivated" means, for example, in the middle of the cultivation period for algae in the algae cultivation apparatus 28, if the cultivation period for algae in the algae cultivation apparatus 28 is set to 30 days, and means the point in time when 30 days have not yet elapsed. The algae extraction line 50 is equipped with a pump 55 for pressurizing the algae and culture solution extracted from the algae cultivation apparatus 28 to the mixing tank.

[0024] The mixing tank 26 is configured to mix carbonated water (carbonated water produced in the carbon dioxide absorption tower 16) supplied from the carbon dioxide absorption tower 16 through the carbonated water line 42, digestate (digestate discharged from the methane fermentation tank 6) supplied from the digestate storage tank 25 through the digestate supply line 48, and algae and culture medium supplied from the algae cultivation device 28 through the algae extraction line 50, and to store and discharge this mixture. The mixing tank 26 mixes the carbonated water supplied from the carbon dioxide absorption tower 16 through the carbonated water line 42, the digestate supplied from the digestate storage tank 25 through the digestate supply line 48, and the culture medium supplied from the algae cultivation device 28 through the algae extraction line 50 to produce a new culture medium (a culture medium with a higher carbon dioxide concentration than the culture medium supplied via the algae extraction line 50, and with added nutrients such as nitrogen, phosphorus, and potassium contained in the digestate), and stores the mixture of this new culture medium and the algae supplied from the algae cultivation device 28 through the algae extraction line 50 and discharges it to the culture medium supply line 52.

[0025] The mixing tank 26 and the algae cultivation apparatus 28 are connected by a culture medium supply line 52, which is configured to supply the algae and culture medium discharged from the mixing tank 26 to the algae cultivation apparatus 28. The culture medium supply line 52 is equipped with a pump 53 for pressurizing the algae and culture medium discharged from the mixing tank 26 to the algae cultivation apparatus 28.

[0026] The algae cultivation apparatus 28 contains algae and culture medium supplied from the mixing tank 26 through the culture medium supply line 52, and is configured to cultivate the algae by irradiating the algae in the culture medium with light. Since this culture medium contains carbon dioxide contained in the carbonated water produced in the carbon dioxide absorption tower 16 and nutrients (e.g., phosphorus, potassium, ammonia, etc.) contained in the digestate discharged from the methane fermentation tank 6, the carbon dioxide and nutrients in the culture medium can be used to promote the growth of algae in the algae cultivation apparatus 28.

[0027] Each of the algae culture apparatus 28 may include, as will be described later, a flat-panel culture tank in which algae contained in a flat-plate reactor are cultured by irradiating them with light, or it may include a closed-type raceway culture tank in which algae and culture solution are flowed through, for example, an annular channel or a meandering channel.

[0028] In each of the algae cultivation devices 28, algae perform photosynthesis using carbon dioxide in the culture medium to produce oxygen. In addition, nutrients in the culture medium (e.g., phosphorus, potassium, ammonia, etc.) are absorbed by the algae and used for their growth, so water (culture medium with reduced concentrations of carbon dioxide and the above nutrients), algae, and oxygen are discharged from the algae cultivation device 28. The oxygen discharged from the algae cultivation device 28 is supplied to the gas turbine 60 through the oxygen supply line 31, which will be described later. The algae and water discharged from the algae cultivation device 28 are supplied to the oxygen separation tank 30 through the discharge line 29.

[0029] In Figure 1, labels a, b, and c within the diamonds indicate the connection points of the corresponding lines, as described below. In the illustrated exemplary configuration, the exhaust gas line 70 is configured to supply exhaust gas from the gas turbine 60 to algae being cultivated in the algae cultivation apparatus 28 (see label b above). In the illustrated example, the exhaust gas line 70 is configured to supply exhaust gas from the gas turbine 60 to algae that have been cultivated for a shorter period than the algae extracted from the algae extraction line 50.

[0030] In the illustrated exemplary embodiment, the algae cultivation system 2 also includes a first branch line 71. The first branch line 71 branches off from the exhaust gas line 70 and connects to the oxygen supply line 31, functioning as an exhaust gas recirculation line that supplies a portion of the exhaust gas flowing through the exhaust gas line 70 to the oxygen supply line 31. In some embodiments, the algae cultivation system 2 may also include a second branch line 72 that branches off from the exhaust gas line 70 and connects to the carbon dioxide absorption tower 16 (see label c above). In this case, by supplying a portion of the exhaust gas flowing through the exhaust gas line 70 to the carbon dioxide absorption tower 16 from the second branch line 72, the carbon dioxide contained in the exhaust gas can be used to produce carbonated water in the carbon dioxide absorption tower 16.

[0031] The algae cultivation apparatus 28 and the gas turbine 60 are connected by an oxygen supply line 31, which is configured to supply oxygen discharged from the algae cultivation apparatus 28 (oxygen generated by photosynthesis of algae in the algae cultivation apparatus 28) to the gas turbine 60. The concentration of oxygen in the gas discharged from the algae cultivation apparatus 28 to the oxygen supply line 31 may be, for example, 30 to 90 volume percent or 50 to 70 volume percent.

[0032] In the illustrated exemplary configuration, the oxygen supply line 31 is equipped with, in order from upstream in the direction of oxygen flow, a vacuum blower 33, an oxygen storage tank 34, a dehumidifier 35, and a blower 45.

[0033] The vacuum blower 33 supplies oxygen from the oxygen separation tank 30 to the oxygen storage tank 34. The oxygen storage tank 34 stores the oxygen supplied from the oxygen separation tank 30 (oxygen supplied from the algae cultivation device 28). The dehumidifier 35 cools the gas flowing through the oxygen supply line 31 (oxygen that has left the oxygen storage tank 34) with the chiller 44 and removes moisture from the gas. The oxygen from which moisture has been removed by the dehumidifier 35 is supplied to the gas turbine 60 by the blower 45 and used in the combustion of methane gas in the gas turbine 60.

[0034] The solid-liquid separation device 32 is configured to separate the algae discharged from the oxygen separation tank 30 from the water (i.e., the algae discharged from the algae cultivation device 28 from the water). The type of solid-liquid separation device 32 is not particularly limited, but may be a centrifuge, membrane separator, screen, or filter, for example.

[0035] The solid-liquid separator 32 and the carbon dioxide absorption tower 16 are connected by a water return line 56. A portion of the water discharged from the solid-liquid separator 32 is supplied to the carbon dioxide absorption tower 16 through the water return line 56. The remaining water discharged from the solid-liquid separator 32 (the portion of the water discharged from the solid-liquid separator 32 that is not supplied to the carbon dioxide absorption tower 16) is discharged outside the system. The water return line 56 is equipped with a pump 58 for pressurizing water from the solid-liquid separator 32 to the carbon dioxide absorption tower 16.

[0036] The solid-liquid separation device 32 and the concentrated algae storage tank 12 are connected by an algae discharge line 59. Algae (concentrated algae) discharged from the solid-liquid separation device 32 are supplied to the concentrated algae storage tank 12 through the algae discharge line 59 and stored in the concentrated algae storage tank 12. In this way, the concentrated algae storage tank 12 stores algae cultivated in the algae cultivation device 28. The algae discharge line 59 is equipped with a pump 62 for pressurizing the algae from the solid-liquid separation device 32 to the concentrated algae storage tank 12.

[0037] The concentrated algae storage tank 12 and the raw material tank 4 are connected by an algae return line 54. The algae (concentrated algae) discharged from the concentrated algae storage tank 12 are supplied to the raw material tank 4 through the algae return line 54 (see label a above). The algae return line 54 is equipped with a pump 63 for pressurizing the algae from the concentrated algae storage tank 12 to the raw material tank 4.

[0038] <Example of algae cultivation system configuration> Figure 2 is a schematic diagram showing an example of the algae cultivation apparatus 28 of the algae cultivation system 2 shown in Figure 1. In Figure 2, the arrangement of multiple algae cultivation tanks 74 and multiple carbon dioxide storage containers 75 of the algae cultivation apparatus 28 is schematically shown in plan view. Figure 3 is a schematic diagram showing the longitudinal cross-section of each algae cultivation tank 74 and carbon dioxide storage container 75 in Figure 2.

[0039] In the exemplary configurations shown in Figures 2 and 3, the algae cultivation apparatus 28 includes a plurality of algae cultivation tanks 74, a plurality of carbon dioxide storage containers 75, a pressurizing fan 80, and a gas holder 81.

[0040] Each of the multiple algae culture tanks 74 is configured as a container for storing algae and a culture medium for culturing the algae. In the exemplary configurations shown in Figures 2 and 3, each of the algae culture tanks 74 is a hollow, roughly rectangular reactor (a so-called flat-panel culture tank).

[0041] In the exemplary configuration shown in Figure 2, multiple algae culture tanks 74 are arranged in series in the direction of the culture medium flow (the direction of algae flow), and two adjacent algae culture tanks 74 are connected by an algae transfer line 83 for transferring algae and culture medium. In the exemplary configuration shown, the algae culture apparatus 28 has four algae culture tanks 74, but the number of algae culture tanks 74 in the algae culture apparatus 28 is not particularly limited and may be, for example, one, two, three, or five or more.

[0042] A culture medium supply line 52 is connected to the algae culture tank 74 located at the uppermost position in the flow direction of the culture medium among the multiple algae culture tanks 74, and algae and culture medium are supplied to this uppermost algae culture tank 74 from the culture medium supply line 52. The algae and culture medium cultivated in the uppermost algae culture tank 74 are supplied to the next algae culture tank 74 through the algae transfer line 83. Each of the algae transfer lines 83 is equipped with a pump 94 for sending algae and culture medium to the next algae culture tank 74. The algae and culture medium supplied from the culture medium supply line 52 are cultured in each of the multiple algae culture tanks 74 as they pass through them sequentially, and the algae and water (culture medium with reduced concentrations of carbon dioxide and the above nutrients) discharged from the algae culture tank 74 located at the lowermost position in the flow direction of the culture medium among the multiple algae culture tanks 74 to the discharge line 29 are supplied to the solid-liquid separation device 32 described above.

[0043] In the exemplary configuration shown in Figure 2, each of the multiple carbon dioxide storage containers 75 is provided in a one-to-one correspondence with each of the multiple algae cultivation tanks 74, and the exhaust gas line 70 described above branches into multiple branch lines 70a to 70d, each connected to one of the multiple carbon dioxide storage containers 75.

[0044] The pressurizing fan 80 and the gas holder 81 are installed in the exhaust gas line 70. The gas holder 81 is located downstream of the pressurizing fan 80 in the exhaust gas line 70, and the pressurizing fan 80 pressurizes the exhaust gas (gas containing carbon dioxide) from the gas turbine 60 and supplies it to the gas holder 81. The gas holder 81 stores the exhaust gas from the gas turbine 60 supplied from the exhaust gas line 70. The exhaust gas (gas containing carbon dioxide) from the gas turbine 60 that leaves the gas holder 81 is supplied to each of the multiple carbon dioxide storage containers 75 through the exhaust gas line 70. The concentration of carbon dioxide in the exhaust gas supplied to the gas holder 81 and the multiple carbon dioxide storage containers 75 through the exhaust gas line 70 may be, for example, 30 to 90 volume percent or 50 to 70 volume percent.

[0045] Since the configurations of each of the multiple algae culture tanks 74 and each of the multiple carbon dioxide storage containers 75 are identical, the following explanation will use Figure 3 to describe the common configurations of each of the multiple algae culture tanks 74 and each of the multiple carbon dioxide storage containers 75. As shown in Figure 3, the algae culture tank 74 includes a ceiling wall 74a, side walls 74b (four side walls in a rectangular parallelepiped algae culture tank 74), and a bottom wall 74c. The algae culture tank 74 may have, for example, a transparent ceiling wall 74a and side walls 74b, or the entire algae culture tank 74 may be transparent. In the illustrated exemplary embodiment, a carbon dioxide storage container 75 is inserted and fixed into an opening 76 provided in the ceiling wall 74a, and the opening 76 is closed by the carbon dioxide storage container 75. In the illustrated exemplary embodiment, since the algae culture tank 74 is installed at an inclination with respect to the horizontal plane H, the ceiling wall 74a and bottom wall 74c are inclined with respect to the horizontal plane H, and a pair of opposing side walls 74b1 and 74b2 of the side walls 74b are inclined with respect to the vertical plane V. An oxygen outlet 84 is formed in the ceiling wall 74a at a position P2 between the upper end P1 of the ceiling wall 74a and the carbon dioxide storage container 75, for discharging oxygen that accumulates in the space S between the ceiling wall 75a and the culture medium inside the algae culture tank 74. The oxygen outlet 84 is connected to an oxygen supply line 31, which supplies the oxygen discharged from the oxygen outlet 84 to the gas turbine 60 (see Figure 1). The gas turbine 60 uses the oxygen supplied from the oxygen supply line 31 to burn methane gas as described above.

[0046] The carbon dioxide storage container 75 is located in the upper part 74u of the algae culture tank 74. The carbon dioxide storage container 75 is connected to the exhaust gas line 70 and is configured to store exhaust gas containing carbon dioxide supplied from the exhaust gas line 70. The lower part 75d of the carbon dioxide storage container 75 is immersed in the culture medium inside the algae culture tank 74. An opening 77 that opens downward is formed at the lower end 75e of the carbon dioxide storage container 75. Inside the carbon dioxide storage container 75, the liquid level 78 of the culture medium that has entered through the opening 77 is formed above the opening 77.

[0047] The carbon dioxide storage container 75 includes a top wall 75a and side walls 75b (four side walls in the case of a rectangular carbon dioxide storage container 75). The top wall 75a and side walls 75b of the carbon dioxide storage container 75 may be transparent. The carbon dioxide storage container 75 does not have a bottom wall, and the opening 77 is formed by the lower edge 79 of the side wall 75b. The top wall 75a of the carbon dioxide storage container 75 is located above the top wall 74a of the algae culture tank 74, and the side walls 75b of the carbon dioxide storage container 75 extend from the top wall 75a through the opening 76 in the top wall 74a of the algae culture tank 74 to the interior of the algae culture tank 74, and are immersed in the culture medium inside the algae culture tank 74.

[0048] In the configuration shown in Figures 2 and 3, the liquid level 78 of the culture medium is formed inside the carbon dioxide storage container 75 at a position above the opening 77. Therefore, the carbon dioxide inside the carbon dioxide storage container 75 can be dissolved into the culture medium from the liquid level 78 and diffused throughout the culture medium inside the algae culture tank 74, thereby promoting the growth of algae using carbon dioxide.

[0049] Therefore, compared to cases where carbon dioxide is directly supplied to the space S above the liquid surface 85 of the culture medium inside the algae culture tank 74 (the space outside the carbon dioxide storage container 75), or where carbon dioxide bubbles are released into the culture medium from a nozzle or the like inside the algae culture tank 74, this method suppresses the increase in carbon dioxide concentration in the space S above the liquid surface 85 of the culture medium inside the algae culture tank 74, allowing high concentrations of oxygen produced by algae photosynthesis to accumulate in that space S. Consequently, it becomes possible to extract high concentrations of oxygen from the oxygen outlet 84 of the algae culture tank 74.

[0050] Furthermore, in the configuration shown in Figures 2 and 3, a pressurizing fan 80 is provided to pressurize the exhaust gas supplied to the carbon dioxide storage container 75. As a result, the pressure of the exhaust gas inside the gas holder 81 and the exhaust gas inside the carbon dioxide storage container 75 are higher than the pressure in the space S. Consequently, the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 is lower than the liquid level 85 of the culture medium outside the carbon dioxide storage container 75 inside the algae culture tank 74. Therefore, the rate of dissolution of carbon dioxide into the culture medium inside the carbon dioxide storage container 75 can be increased, and the rate at which carbon dioxide in the culture medium inside the carbon dioxide storage container 75 diffuses into the culture medium outside the carbon dioxide storage container 75 can be increased. Thus, the concentration of carbon dioxide in the culture medium inside the algae culture tank 74 can be increased, thereby enhancing the effect of promoting algae growth.

[0051] Since the system is equipped with an exhaust gas line 70 configured to supply exhaust gas discharged from the gas turbine 60 (see Figure 1) to a carbon dioxide storage container 75, the carbon dioxide contained in the exhaust gas discharged from the gas turbine 60 can be used to promote the growth of algae.

[0052] Furthermore, since the system is equipped with an oxygen supply line 31 configured to supply oxygen-containing gas produced by photosynthesis of algae in the algae cultivation apparatus 28 to the gas turbine 60, the oxygen produced in the algae cultivation apparatus 28 can be used for fuel combustion in the gas turbine 60. As a result, nitrogen oxide emissions can be reduced compared to when the gas turbine 60 burns fuel using air (when the algae cultivation system 2 is not equipped with an oxygen supply line 31).

[0053] Furthermore, burning fuels such as methane using high concentrations of oxygen increases the risk of explosion. However, by providing the first branch line 71 as described above and supplying a portion of the exhaust gas from the gas turbine 60 to the oxygen supply line 31, the oxygen concentration in the gas supplied from the oxygen supply line 31 to the gas turbine 60 can be reduced. This makes it possible to provide an algae cultivation system 2 that reduces NOx emissions with a simple configuration while reducing the risk of explosion.

[0054] In some embodiments, the height of the liquid level 78 (see Figure 3) of the culture medium inside each of the multiple carbon dioxide storage containers 75 may differ for each algae culture tank 74 (each carbon dioxide storage container 75). For example, when comparing two of the multiple algae culture tanks 74, the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 in the algae culture tank 74 located relatively downstream in the flow direction of the culture medium (second algae culture tank) may be higher than the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 in the algae culture tank 74 located relatively upstream in the flow direction of the culture medium (first algae culture tank).

[0055] In this case, for example, the position of the liquid level 78 of the culture solution inside the carbon dioxide storage container 75 may be made different for each algae culture tank 74 (each carbon dioxide storage container 75) by making the diameter of the pipes constituting each of the multiple branch lines 70a to 70d in the exhaust gas line 70 different for each algae culture tank 74. For example, when comparing two of the multiple algae culture tanks 74, the diameter of the branch line 70b connected to the carbon dioxide storage container 75 provided in the algae culture tank 74 (second algae culture tank) located relatively downstream in the flow direction of the culture solution may be made smaller than the diameter of the branch line 70a connected to the carbon dioxide storage container 75 provided in the algae culture tank 74 (first algae culture tank) located relatively upstream in the flow direction of the culture solution.

[0056] This makes it possible to lower the pressure of the exhaust gas inside the carbon dioxide storage container 75 located in the algae culture tank 74 (second algae culture tank) that is relatively downstream in the flow direction of the culture medium than the pressure of the exhaust gas inside the carbon dioxide storage container 75 located in the algae culture tank 74 (first algae culture tank) that is relatively upstream in the flow direction of the culture medium. As a result, as described above, the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 located in the algae culture tank 74 (second algae culture tank) that is relatively downstream can be raised higher than the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 located in the algae culture tank 74 (first algae culture tank) that is relatively upstream in the flow direction of the culture medium.

[0057] In the later stages of algal cultivation, the growth rate of algae tends to decrease compared to the early stages of cultivation. In this regard, as described above, by raising the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 located in the relatively downstream algal cultivation tank 74 higher than the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 located in the relatively upstream algal cultivation tank 74 in the direction of culture medium flow, the diffusion rate of carbon dioxide from the carbon dioxide storage container 75 into the culture medium of the downstream algal cultivation tank 74 can be made slower than the diffusion rate of carbon dioxide from the carbon dioxide storage container 75 into the culture medium of the upstream algal cultivation tank 74. As a result, the algae in each algal cultivation tank 74 can be efficiently grown at an appropriate carbon dioxide concentration according to the growth stage of the algae.

[0058] In some embodiments, as shown in Figure 4, for example, a pressure regulating valve 95 may be provided in each of the multiple branch lines 70a to 70d in the exhaust gas line 70. In this case, when comparing two of the multiple algae culture tanks 74, the valve opening of the pressure regulating valve 95 provided in the branch line 70b corresponding to the algae culture tank 74 (second algae culture tank) located relatively downstream in the flow direction of the culture medium may be smaller than the valve opening of the pressure regulating valve 95 corresponding to the algae culture tank 74 (first algae culture tank) located relatively upstream in the flow direction of the culture medium.

[0059] As a result, the pressure of the exhaust gas inside the carbon dioxide storage container 75 located in the algae culture tank 74 (second algae culture tank) that is relatively downstream in the flow direction of the culture medium can be made lower than the pressure of the exhaust gas inside the carbon dioxide storage container 75 located in the algae culture tank 74 (first algae culture tank) that is relatively upstream in the flow direction of the culture medium. Therefore, as described above, the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 located in the algae culture tank 74 (second algae culture tank) that is relatively downstream can be made higher than the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 located in the algae culture tank 74 (first algae culture tank) that is relatively upstream in the flow direction of the culture medium. Thus, algae in multiple algae culture tanks 74 can be efficiently grown at an appropriate carbon dioxide concentration according to the growth stage of the algae.

[0060] Figure 5 is a schematic diagram showing another example of the algae cultivation apparatus 28 in the algae cultivation system 2 shown in Figure 1. In Figure 5, the arrangement of the algae cultivation tank 74, carbon dioxide storage container 75, and oxygen recovery tower 90 of the algae cultivation apparatus 28 is schematically shown in plan view. Figure 6 is a diagram showing a longitudinal cross-section of the algae cultivation tank 74, carbon dioxide storage container 75, and oxygen recovery tower 90 of the algae cultivation apparatus 28 shown in Figure 5.

[0061] In some embodiments, as shown in Figure 5, the algae culture tank 74 may be a raceway-type algae culture tank 74 in which algae and culture medium are flowed through a meandering channel or annular channel (a meandering channel 87 in the illustrated example) to cultivate the algae. The algae culture tank 74 shown in Figure 5 includes a plurality of linear channel sections 87a that extend in a straight line in a plan view, and a plurality of return channel sections 87b that redirect the flow of the culture medium by 180°, and the linear channel sections 87a and return channel sections 87b are arranged alternately along the flow of the culture medium.

[0062] In the exemplary configurations shown in Figures 5 and 6, the algae cultivation apparatus 28 includes a plurality of carbon dioxide storage containers 75 provided in the algae cultivation tank 74. Each of the plurality of carbon dioxide storage containers 75 is provided in a one-to-one correspondence with each of the plurality of linear flow channels 87a. In the illustrated example, at the upstream end 88 of each carbon dioxide storage container 75 in the direction of the culture medium flow of the algae cultivation tank 74, the width W of the carbon dioxide storage container 75 in the direction perpendicular to the culture medium flow direction decreases as it moves upstream in the culture medium flow direction.

[0063] As shown in Figure 6, the lower part 75d of each carbon dioxide storage container 75 is immersed in the culture medium inside the algae culture tank 74, and an opening 77 that opens downwards is formed at the lower end 75e of each carbon dioxide storage container 75. In addition, inside each carbon dioxide storage container 75, the liquid level 78 of the culture medium that has entered through the opening 77 is formed at a position above the opening 77.

[0064] Each of the carbon dioxide storage containers 75 is located in the upper part 74u of the algae culture tank 74. Multiple openings 76 are formed in the ceiling wall 74a of the algae culture tank 74, and each of the carbon dioxide storage containers 75 is inserted into and fixed into the corresponding opening 76, with each opening 76 being blocked by the corresponding carbon dioxide storage container 75. Each of the carbon dioxide storage containers 75 is connected to the exhaust gas line 70 and is configured to store gas containing carbon dioxide supplied from the exhaust gas line 70.

[0065] Each carbon dioxide storage container 75 includes a top wall 75a and side walls 75b (in the example shown in Figure 5, five side wall sections arranged in a pentagonal shape in plan view). Each carbon dioxide storage container 75 does not have a bottom wall, and the opening 77 is formed by the lower edge 79 of the side wall 75b. The top wall 75a of each carbon dioxide storage container 75 is located above the top wall 74a of the algae culture tank 74, and the side walls 75b of each carbon dioxide storage container 75 extend from the top wall 75a through the corresponding opening 76 in the top wall 74a of the algae culture tank 74 into the interior of the algae culture tank 74, and are immersed in the culture medium inside the algae culture tank 74.

[0066] In the configurations shown in Figures 5 and 6, as in the embodiments shown in Figures 2 to 4, the liquid level 78 of the culture medium is formed above the opening 77 inside the carbon dioxide storage container 75. Therefore, the carbon dioxide inside the carbon dioxide storage container 75 can be dissolved into the culture medium from the liquid level 78 and diffused throughout the culture medium inside the algae culture tank 74, thereby promoting the growth of algae using carbon dioxide.

[0067] Therefore, compared to cases where carbon dioxide is directly supplied to the space S above the liquid surface 85 of the culture medium inside the algae culture tank 74 (the space outside the carbon dioxide storage container 75), or where a nozzle is installed in the culture medium and carbon dioxide bubbles are released into the culture medium from the nozzle, this method suppresses the increase in carbon dioxide concentration in the space S above the liquid surface 85 of the culture medium inside the algae culture tank 74, and allows high concentrations of oxygen produced by algae photosynthesis to accumulate in the space S above. Consequently, it becomes possible to extract high concentrations of oxygen from the algae culture tank 74.

[0068] In the illustrated example, the algae cultivation apparatus 28 includes an oxygen recovery tower 90 located downstream of the algae cultivation tank 74 in the direction of the culture medium flow. An oxygen supply line 31 is connected to the upper part of the oxygen recovery tower 90, and a discharge line 29 is connected to the lower part of the oxygen recovery tower 90. The algae cultivated in the algae cultivation tank 74 and water (culture medium with reduced concentrations of carbon dioxide and the above nutrients) flow into the oxygen recovery tower 90. The algae and water in the oxygen recovery tower 90 are discharged from the oxygen recovery tower 90 to the discharge line 29 and supplied to the solid-liquid separator 32 by a pump 91 located in the discharge line 29. In addition, high-concentration oxygen accumulated in the space S above the liquid surface 85 of the culture medium inside the algae cultivation tank 74 flows into the oxygen recovery tower 90, is discharged from the upper part of the oxygen recovery tower 90 to the oxygen supply line 31, and supplied to the oxygen storage tank 34.

[0069] Furthermore, in the configurations shown in Figures 5 and 6, a pressurizing fan 80 is provided to pressurize the exhaust gas supplied to the carbon dioxide storage container 75. As a result, the pressure of the exhaust gas inside the gas holder 81 and the exhaust gas inside the carbon dioxide storage container 75 are higher than the pressure in the space S. Consequently, the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 is lower than the liquid level 85 of the culture medium outside the carbon dioxide storage container 75 inside the algae culture tank 74. Therefore, the rate of dissolution of carbon dioxide into the culture medium inside the carbon dioxide storage container 75 can be increased, and the rate at which carbon dioxide in the culture medium inside the carbon dioxide storage container 75 diffuses into the culture medium outside the carbon dioxide storage container 75 can be increased. Thus, the concentration of carbon dioxide in the culture medium inside the algae culture tank 74 can be increased, thereby enhancing the effect of promoting algae growth.

[0070] In some embodiments, as shown in Figure 7, for example, the heights of the culture medium liquid levels 78 (see Figure 3) inside each of the multiple carbon dioxide storage containers 75 provided in the algae culture tank 74 may differ from each other. For example, when comparing two of the multiple carbon dioxide storage containers 75, the position of the culture medium liquid level 78 inside the carbon dioxide storage container 75 located relatively downstream in the flow direction of the culture medium (second carbon dioxide storage container) may be higher than the position of the culture medium liquid level 78 inside the carbon dioxide storage container 75 located relatively upstream in the flow direction of the culture medium (first carbon dioxide storage container).

[0071] In this case, as shown in Figure 7, for example, a pressure regulating valve 95 may be provided in each of the multiple branch lines 70a to 70d in the exhaust gas line 70. In this case, when comparing two of the carbon dioxide storage containers 75, the valve opening of the pressure regulating valve 95 provided in the branch line 70b corresponding to the carbon dioxide storage container 75 located relatively downstream in the flow direction of the culture medium may be made smaller than the valve opening of the pressure regulating valve 95 corresponding to the carbon dioxide storage container 75 located relatively upstream in the flow direction of the culture medium.

[0072] As a result, the pressure of the exhaust gas inside the carbon dioxide storage container 75 located relatively downstream in the flow direction of the culture medium can be made lower than the pressure of the exhaust gas inside the carbon dioxide storage container 75 located relatively upstream in the flow direction of the culture medium. Therefore, as described above, the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 located relatively downstream can be made higher than the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 located relatively upstream in the flow direction of the culture medium.

[0073] As described above, in the later stages of the algal cultivation period, the growth rate of the algae tends to decrease compared to the early stages of the cultivation period. In this regard, as described above, by raising the position of the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 located relatively downstream in the flow direction of the culture medium to the position of the liquid level 78 inside the carbon dioxide storage container 75 located relatively upstream in the flow direction of the culture medium, the diffusion rate of carbon dioxide from the downstream carbon dioxide storage container 75 to the culture medium can be made slower than the diffusion rate of carbon dioxide from the carbon dioxide storage container 75 in the upstream algal cultivation tank 74 to the culture medium. As a result, the algae in each algal cultivation tank 74 can be efficiently grown at an appropriate carbon dioxide concentration according to the growth stage of the algae.

[0074] In some embodiments, in the configuration shown in Figure 6, the positions of the liquid level 78 of the culture medium inside each of the multiple carbon dioxide storage containers 75 may be made different by varying the diameter of the piping that constitutes each of the multiple branch lines 70a to 70d in the exhaust gas line 70 for each carbon dioxide storage container 75. For example, when comparing two of the multiple carbon dioxide storage containers 75, the diameter of the branch line 70b connected to the carbon dioxide storage container 75 located relatively downstream in the flow direction of the culture medium may be made smaller than the diameter of the branch line 70a connected to the carbon dioxide storage container 75 located relatively upstream in the flow direction of the culture medium.

[0075] As a result, the pressure of the exhaust gas inside the carbon dioxide storage container 75 located relatively downstream in the flow direction of the culture medium can be made lower than the pressure of the exhaust gas inside the carbon dioxide storage container 75 located relatively upstream in the flow direction of the culture medium. Therefore, as described above, the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 located relatively downstream in the flow direction of the culture medium can be made higher than the liquid level 78 of the culture medium inside the carbon dioxide storage container 75 located relatively upstream. Thus, the algae in the algae culture tank 74 can be efficiently grown at an appropriate carbon dioxide concentration according to the growth stage of the algae.

[0076] This disclosure is not limited to the embodiments described above, but also includes modified forms of the embodiments described above, as well as forms that combine these forms as appropriate.

[0077] For example, in the embodiments shown in Figures 2 and 3, the algae cultivation apparatus 28 was equipped with a plurality of algae cultivation tanks 74 connected in series in the direction of the culture medium flow. However, if a plurality of algae cultivation tanks 74 connected in series in the direction of the culture medium flow is considered as one set, the algae cultivation apparatus 28 may be equipped with a plurality of sets arranged in parallel in the direction of the culture medium flow.

[0078] Furthermore, in the embodiments shown in Figures 5 and 6, the algae cultivation apparatus 28 comprises one algae cultivation tank 74 equipped with multiple carbon dioxide storage containers 75. However, if one set consists of an algae cultivation tank 74 equipped with multiple carbon dioxide storage containers 75, the algae cultivation apparatus 28 may comprise multiple sets.

[0079] Furthermore, in some embodiments shown in Figures 1 to 7, a gas turbine 60 is shown as an example of a combustion device included in the energy conversion device 10. However, the combustion device is not limited to a gas turbine 60, and may be, for example, a gas engine or boiler configured to burn methane discharged from the carbon dioxide absorption tower 16. In this case, the exhaust gas line 70 may be configured to supply the exhaust gas from the gas engine or boiler to each of the carbon dioxide storage containers 75. Alternatively, the energy conversion device 10 may be, for example, a fuel cell that generates electricity using hydrogen obtained by reforming methane discharged from the carbon dioxide absorption tower 16. In this case, the exhaust gas line 70 may be configured to supply gas containing carbon dioxide generated by the reforming of methane to the carbon dioxide storage container 75.

[0080] Furthermore, while some embodiments shown in Figures 1 to 7 illustrate a configuration in which gas containing carbon dioxide discharged from the energy conversion device 10 is supplied to the carbon dioxide storage container 75, the algae cultivation system 2 does not necessarily have to be equipped with the energy conversion device 10, and the carbon dioxide supply source for supplying gas containing carbon dioxide to each of the carbon dioxide storage containers 75 may be only the gas holder 81 that stores carbon dioxide.

[0081] Furthermore, although the algae cultivation apparatus 28 shown in Figure 5 was equipped with an oxygen recovery tower 90, the algae cultivation system 2 does not need to be equipped with an oxygen recovery tower 90 if, for example, the algae cultivation tank 74 is a sealed type and the oxygen supply line 31 can be directly connected to the top of the algae cultivation tank 74 to directly extract the oxygen that accumulates at the top of the algae cultivation tank 74 via the oxygen supply line 31.

[0082] Furthermore, in some embodiments shown in Figures 3 and 6, the liquid level 78 of the culture solution inside the carbon dioxide storage container 75 is shown to be lower than the liquid level 85 of the culture solution outside the carbon dioxide storage container 75 inside the algae culture tank 74. However, in other embodiments, the liquid level 78 of the culture solution inside the carbon dioxide storage container 75 may be at the same height as the liquid level 85 of the culture solution outside the carbon dioxide storage container 75 inside the algae culture tank 74.

[0083] The contents described in each of the above embodiments can be understood, for example, as follows:

[0084] [1] An algae culture system according to at least one embodiment of the present disclosure (e.g., the algae culture system 2 described above) A first algal culture tank (for example, the algal culture tank 74 described above) for storing algae and a culture medium for culturing the algae, The first algae culture tank is provided with at least one carbon dioxide storage container (for example, the carbon dioxide storage container 75 described above) for storing gas containing carbon dioxide, Equipped with, The first algae culture tank includes a ceiling wall (for example, the ceiling wall 74a described above), The lower part of each of the at least one carbon dioxide storage containers (for example, the lower part 75d described above) is immersed in the culture medium inside the first algae culture tank. Each of the lower ends of the at least one carbon dioxide storage container (for example, the lower end 75e described above) has an opening (for example, the opening 77 described above) that opens downwards. Inside each of the at least one carbon dioxide storage containers, the liquid level of the culture medium (for example, the liquid level 78 described above) is formed at a position above the opening.

[0085] According to the algae cultivation system described in [1] above, the liquid level of the culture medium is formed above the opening inside each of the at least one carbon dioxide storage containers. Therefore, the carbon dioxide inside each of the at least one carbon dioxide storage containers can be dissolved into the culture medium from the liquid level and diffused throughout the culture medium inside the first algae cultivation tank, thereby promoting algae growth using carbon dioxide. For this reason, compared to, for example, directly supplying carbon dioxide to the space above the liquid level of the culture medium inside the first algae cultivation tank (the space outside the carbon dioxide storage containers) or releasing gas bubbles containing carbon dioxide into the culture medium from a nozzle or the like provided inside the first algae cultivation tank, it is possible to suppress the increase in the concentration of carbon dioxide in the space above the liquid level of the culture medium inside the first algae cultivation tank (the space outside the carbon dioxide storage containers), and to accumulate high concentrations of oxygen produced by algae photosynthesis in that space. Therefore, it is possible to extract high concentrations of oxygen from the first algae cultivation tank.

[0086] [2] In some embodiments, in the algae cultivation system described in [1] above, Each of the at least one carbon dioxide storage containers includes a ceiling wall (e.g., the ceiling wall 75a described above) and a side wall (e.g., the side wall 75b described above).

[0087] According to the algae cultivation system described in [2] above, gas containing carbon dioxide stored in the space enclosed by the ceiling wall and side walls can be dissolved into the culture medium inside the carbon dioxide storage container, and the effects described in [1] above can be obtained with a simple configuration.

[0088] [3] In some embodiments, in the algae cultivation system described in [2] above, The ceiling wall of each of the at least one carbon dioxide storage vessel is located above the ceiling wall of the first algae culture tank.

[0089] The algae cultivation system described in [3] above allows for a larger volume of space for storing carbon dioxide in each of the at least one carbon dioxide storage containers compared to the case where the ceiling wall of each of the at least one carbon dioxide storage containers is at the same height as or below the ceiling wall of the first algae cultivation tank. This stabilizes the concentration of carbon dioxide in the culture medium in the first algae cultivation tank and promotes the growth of algae.

[0090] [4] In some embodiments, in the algae cultivation system described in any of [1] to [3] above, The ceiling wall of the first algae culture tank is inclined with respect to the horizontal plane.

[0091] According to the algae cultivation system described in [4] above, the oxygen that accumulates above the liquid surface of the culture medium inside the first algae cultivation tank can be biased to one side in the horizontal direction (towards the upper end of the ceiling wall), making it easier to recover oxygen from the first algae cultivation tank.

[0092] [5] In some embodiments, in the algae cultivation system described in [4] above, An oxygen outlet (e.g., the oxygen outlet 84 described above) for discharging oxygen from inside the first algae culture tank is formed in the ceiling wall of the first algae culture tank at a position between the upper end of the ceiling wall of the first algae culture tank (e.g., position P1 described above) and the carbon dioxide storage container.

[0093] According to the algae cultivation system described in [5] above, oxygen that is biased to one side in the horizontal direction (towards the upper end of the ceiling wall) inside the first algae cultivation tank can be easily discharged from the oxygen outlet.

[0094] [6] In some embodiments, in the algae cultivation system described in any of [1] to [5] above, At the upstream end of each of the at least one carbon dioxide storage containers in the flow direction of the culture medium of the first algae culture tank (for example, the upstream end 88 described above), the width of the carbon dioxide storage container in a direction perpendicular to the flow direction (for example, the width W described above) decreases as it moves upstream in the flow direction.

[0095] According to the algae cultivation system described in [6] above, it is possible to suppress the obstruction of algae movement within the algae cultivation tank by the carbon dioxide storage tank.

[0096] [7] In some embodiments, in the algae cultivation system described in any of [1] to [6] above, The at least one carbon dioxide storage container includes a plurality of carbon dioxide storage containers provided in the first algae culture tank, The lower part of each of the plurality of carbon dioxide storage containers (for example, the lower part 75d described above) is immersed in the culture solution inside the first algae culture tank. Each of the plurality of carbon dioxide storage containers has an opening (for example, the opening 77 described above) that opens downward at its lower end (for example, the lower end 75e described above). Inside each of the plurality of carbon dioxide storage containers, a liquid level of the culture medium (for example, the liquid level 78 described above) is formed at a position above the opening.

[0097] According to the algae cultivation system described in [7] above, the liquid surface of the culture medium is formed above the opening inside each of the multiple carbon dioxide storage containers. As a result, the gas containing carbon dioxide inside each of the multiple carbon dioxide storage containers dissolves from the liquid surface into the culture medium and diffuses throughout the culture medium inside the first algae cultivation tank, thereby promoting algae growth using carbon dioxide. Therefore, compared to, for example, supplying carbon dioxide directly to the space above the liquid surface of the culture medium inside the first algae cultivation tank, or releasing gas bubbles containing carbon dioxide from a nozzle or the like provided inside the first algae cultivation tank, it is possible to suppress the rise in carbon dioxide concentration in the space above the liquid surface of the culture medium inside the first algae cultivation tank (the space outside the multiple carbon dioxide storage containers), and to accumulate high-concentration oxygen produced by the algae in that space above. Consequently, it becomes possible to extract high-concentration oxygen from the first algae cultivation tank.

[0098] [8] In some embodiments, in the algae cultivation system described in any of [7] above, The aforementioned plurality of carbon dioxide storage containers are A first carbon dioxide storage container (for example, the carbon dioxide storage container 75 located at the uppermost upstream position in the flow direction of the culture medium (right side in Figure 7) among the four carbon dioxide storage containers 75 in Figure 7), where the liquid level of the culture medium is formed at a first position above the opening, A second carbon dioxide storage container (for example, the carbon dioxide storage container 75 downstream of the first carbon dioxide storage container among the four carbon dioxide storage containers 75 in Figure 7) is located downstream of the first carbon dioxide storage container in the flow direction of the culture medium of the first algae culture tank, and the liquid level of the culture medium is formed at a position above the first position. Includes.

[0099] In the later stages of algal cultivation, the growth rate of the algae tends to decrease compared to the earlier stages of cultivation. In this regard, the algal cultivation system described in [8] above allows the diffusion rate of carbon dioxide from the second carbon dioxide storage container downstream to the culture medium in the first algal cultivation tank to be slower than the diffusion rate of carbon dioxide from the first carbon dioxide storage container upstream to the culture medium in the first algal cultivation tank. As a result, the algae in the first algal cultivation tank can be efficiently grown at an appropriate carbon dioxide concentration according to the growth stage of the algae.

[0100] [9] In some embodiments, in the algae cultivation system described in any of [1] to [8] above, A second algae culture tank (for example, an algae culture tank 74 downstream of the first algae culture tank 74 in Figure 2) for storing the algae and culture medium discharged from the first algae culture tank (for example, an algae culture tank 74 located upstream of the four algae culture tanks 74 in Figure 2), The second algae culture tank is provided with at least one carbon dioxide storage container (for example, the carbon dioxide storage container 75 described above) for storing gas containing carbon dioxide, Furthermore, The second algae culture tank includes a ceiling wall (for example, the ceiling wall 74a described above), The lower part of each of the at least one carbon dioxide storage containers provided in the second algae culture tank (for example, the lower part 75d described above) is immersed in the culture medium inside the second algae culture tank. At the lower end of each of the at least one carbon dioxide storage containers provided in the second algae culture tank (for example, the lower end 75e described above), an opening (for example, the opening 77 described above) that opens downward is formed. Inside each of the at least one carbon dioxide storage containers provided in the second algae culture tank, the liquid level of the culture medium (for example, the liquid level 78 described above) is formed at a position above the opening. The liquid level of the culture medium inside each of the at least one carbon dioxide storage containers provided in the second algae culture tank is higher than the liquid level of the culture medium inside each of the at least one carbon dioxide storage containers provided in the first algae culture tank.

[0101] In the later stages of algal cultivation, the growth rate of algae tends to decrease compared to the early stages of cultivation. In this regard, the algal cultivation system described in [9] above allows the diffusion rate of carbon dioxide from the carbon dioxide storage container into the culture medium of the second algal cultivation tank downstream in the flow direction of the culture medium to be slower than the diffusion rate of carbon dioxide from the carbon dioxide storage container into the culture medium of the first algal cultivation tank upstream. As a result, algae in the first algal cultivation tank and algae in the second algal cultivation tank can be efficiently grown at an appropriate carbon dioxide concentration according to the growth stage of the algae.

[0102]

[10] In some embodiments, in the algae cultivation system described in any of [1] to [9] above, An energy conversion device that emits exhaust gas containing carbon dioxide (for example, the energy conversion device 10 described above), An exhaust gas line (for example, the exhaust gas line 70 described above) configured to supply the exhaust gas discharged from the energy conversion device to the carbon dioxide storage container, It is further equipped with [this feature].

[0103] According to the algae cultivation system described in

[10] above, the carbon dioxide contained in the exhaust gas discharged from the energy conversion device can be used to promote the growth of algae.

[0104]

[11] In some embodiments, in the algae cultivation system described in

[10] above, The system further includes an oxygen supply line (for example, the oxygen supply line 31 described above) configured to supply the oxygen-containing gas generated in the first algae culture tank to the energy conversion device.

[0105] According to the algae cultivation system described in

[11] above, the oxygen produced in the first algae cultivation tank can be used in the energy conversion device. Therefore, if the energy conversion device is, for example, a combustion device that burns fuel, nitrogen oxide emissions can be reduced compared to when the fuel is burned using air (when the algae cultivation system does not have an oxygen supply line).

[0106]

[12] In some embodiments, in the algae cultivation system described in

[11] above, The system further includes a branch line (for example, the first branch line 71 described above) that branches off from the exhaust gas line and connects to the oxygen supply line, and is configured to supply a portion of the exhaust gas flowing through the exhaust gas line to the oxygen supply line.

[0107] When a high concentration of oxygen is used in an energy conversion device to burn fuels such as methane, the risk of explosion increases. Therefore, as described in

[12] above, by providing a branch line to supply a portion of the exhaust gas from the energy conversion device to an oxygen supply line, the oxygen concentration in the gas supplied from the oxygen supply line to the energy conversion device can be reduced. This makes it possible to provide an algae cultivation system that reduces NOx emissions with a simple configuration while reducing the risk of explosion.

[0108]

[13] In some embodiments, in the algae cultivation system described in any of

[10] to

[12] above, The system further includes a gas holder (for example, the gas holder 81 described above) provided between the energy conversion device and the carbon dioxide storage container in the exhaust gas line, and configured to store the exhaust gas.

[0109] According to the algae cultivation system described above

[13] , carbon dioxide can be stably supplied to the carbon dioxide storage container even if the operating state of the energy conversion device changes, thereby enabling stable growth of algae.

[0110]

[14] In some embodiments, in the algae cultivation system described in any of [1] to

[13] above, A gas holder (for example, the gas holder 81 described above) that stores the gas containing carbon dioxide, A gas line (for example, the exhaust gas line 70 described above) configured to supply the gas containing carbon dioxide stored in the gas holder to the at least one carbon dioxide storage container, It is equipped with.

[0111] According to the algae cultivation system described above

[14] , carbon dioxide can be stably supplied to the carbon dioxide storage container, thereby enabling stable growth of algae.

[0112]

[15] In some embodiments, in the algae cultivation system described in any of [1] to

[14] above, A gas line (for example, the exhaust gas line 70 described above) configured to supply the gas containing carbon dioxide to the at least one carbon dioxide storage container, A pressurizing device (for example, the pressurizing fan 80 described above) is provided in the gas line and pressurizes the gas containing carbon dioxide, It is equipped with.

[0113] According to the algae cultivation system described in

[15] above, the pressure of the exhaust gas inside the carbon dioxide storage container can be increased, making the liquid level of the culture medium inside the carbon dioxide storage container lower than the liquid level of the culture medium outside the carbon dioxide storage container inside the algae cultivation tank. This allows for a faster dissolution rate of carbon dioxide into the culture medium inside the carbon dioxide storage container, and also allows for a faster diffusion rate of carbon dioxide from the culture medium inside the carbon dioxide storage container to the culture medium outside the carbon dioxide storage container. Consequently, the concentration of carbon dioxide in the culture medium inside the algae cultivation tank can be increased, thereby enhancing the effect of promoting algae growth. [Explanation of Symbols]

[0114] 2. Algae cultivation system 4. Raw material tanks 5. Raw material supply line 6. Methane fermentation tank 8. Post-treatment device 9.81 Gas holder 10 Energy conversion device 11,19,27,46,53,55,58,62,63,91,94 pumps 12 Concentrated Algae Storage Tank 14 Biogas Line 15,45,63 Blower 16. Carbon dioxide absorption tower 18 Fermentation Residue Line 20,32 Solid-liquid separation equipment 25 Digestive fluid storage tank 26 Mixing tank 28 Algae cultivation equipment 29 Discharge line 30 Oxygen Separation Tanks 31. Oxygen supply line 33 Vacuum blower 34 Oxygen storage tank 35,38 Dehumidifier 36 Methane gas line 39,44 Chiller 40 Desulfurization tower 42. Carbonated Water Line 48 Digestive fluid supply line 50 Algae Extraction Lines 52 Culture medium supply line 54 Algae Removal Line 56 Water return line 59 Algae discharge line 60 Gas Turbine 61 Generators 70 Exhaust gas line 70a, 70b, 70c, 70d branch line 71 First Branch Line 72 Second Branch Line 74 Algae culture tank 74a, 75a Ceiling and walls 74b,75b side wall 74b1,74b2 Side wall part 74c bottom wall 74u upper part 75 Carbon dioxide storage containers 75d lower part 75e bottom end 76,77 Opening 78,85 liquid level 79 Lower edge 80 Pressurized Fan 83 Algae Transfer Line 84 Oxygen outlet 87 Meandering Channels 87a Straight channel section 87b Folding channel section 88 Upstream end 90 Oxygen recovery tower 95 Pressure regulating valve

Claims

1. A first algae culture tank for storing algae and a culture medium for culturing the algae, The first algae culture tank is provided with at least one carbon dioxide storage container for storing gas containing carbon dioxide, Equipped with, The first algae culture tank includes a ceiling wall, The lower part of each of the at least one carbon dioxide storage containers is immersed in the culture medium inside the first algae culture tank. Each of the lower ends of the at least one carbon dioxide storage container has an opening that opens downwards, An algae cultivation system in which, inside each of the at least one carbon dioxide storage containers, the liquid level of the culture medium is formed at a position above the opening.

2. The algae cultivation system according to claim 1, wherein each of the at least one carbon dioxide storage vessels includes a ceiling wall and side walls.

3. The algae cultivation system according to claim 2, wherein the ceiling wall of each of the at least one carbon dioxide storage vessels is located above the ceiling wall of the first algae cultivation tank.

4. The algae cultivation system according to claim 1, wherein the ceiling wall of the first algae cultivation tank is inclined with respect to the horizontal plane.

5. The algae cultivation system according to claim 4, wherein an oxygen outlet for discharging oxygen from inside the first algae cultivation tank is formed in the ceiling wall of the first algae cultivation tank at a position between the upper end of the ceiling wall of the first algae cultivation tank and the carbon dioxide storage container.

6. The algae cultivation system according to claim 1, wherein at the upstream end of each of the at least one carbon dioxide storage containers in the flow direction of the culture medium of the first algae cultivation tank, the width of the carbon dioxide storage container in a direction perpendicular to the flow direction decreases as it moves upstream in the flow direction.

7. The at least one carbon dioxide storage container includes a plurality of carbon dioxide storage containers provided in the first algae culture tank, The lower part of each of the plurality of carbon dioxide storage containers is immersed in the culture solution inside the first algae culture tank. Each of the aforementioned plurality of carbon dioxide storage containers has an opening that opens downwards at its lower end. The algae cultivation system according to claim 1, wherein the liquid level of the culture medium is formed inside each of the plurality of carbon dioxide storage containers at a position above the opening.

8. The aforementioned plurality of carbon dioxide storage containers are A first carbon dioxide storage container in which the liquid level of the culture medium is formed at a first position above the opening, A second carbon dioxide storage container is located downstream of the first carbon dioxide storage container in the flow direction of the culture medium in the first algae culture tank, and the liquid level of the culture medium is formed at a position above the first position. The algae cultivation system according to claim 7, comprising:

9. A second algae culture tank for storing the algae and culture medium discharged from the first algae culture tank, The second algae culture tank is provided with at least one carbon dioxide storage container for storing gas containing carbon dioxide, Furthermore, The aforementioned second algae culture tank includes a ceiling wall, The lower part of each of the at least one carbon dioxide storage containers provided in the second algae culture tank is immersed in the culture medium inside the second algae culture tank. Each of the at least one carbon dioxide storage containers provided in the second algae culture tank has an opening that opens downwards at its lower end, Inside each of the at least one carbon dioxide storage containers provided in the second algae culture tank, the liquid level of the culture medium is formed at a position above the opening. The algae cultivation system according to claim 1, wherein the liquid level of the culture medium inside the at least one carbon dioxide storage container provided in the second algae cultivation tank is higher than the liquid level of the culture medium inside the at least one carbon dioxide storage container provided in the first algae cultivation tank.

10. An energy conversion device that emits exhaust gas containing carbon dioxide, An exhaust gas line configured to supply the exhaust gas discharged from the energy conversion device to the carbon dioxide storage container, The algae cultivation system according to claim 1, further comprising the following:

11. The algae cultivation system according to claim 10, further comprising an oxygen supply line configured to supply the oxygen-containing gas generated in the first algae cultivation tank to the energy conversion device.

12. The algae cultivation system according to claim 11, further comprising a branch line configured to branch off from the exhaust gas line and connect to the oxygen supply line, thereby supplying a portion of the exhaust gas flowing through the exhaust gas line to the oxygen supply line.

13. The algae cultivation system according to claim 10, further comprising a gas holder provided between the energy conversion device and the carbon dioxide storage container in the exhaust gas line and configured to store the exhaust gas.

14. A gas holder for storing the aforementioned gas containing carbon dioxide, A gas line configured to supply the gas containing carbon dioxide stored in the gas holder to the at least one carbon dioxide storage container, The algae cultivation system according to claim 1, further comprising the following:

15. A gas line configured to supply the gas containing carbon dioxide to the at least one carbon dioxide storage container, A pressurizing device provided in the gas line for pressurizing the gas containing carbon dioxide, The algae cultivation system according to claim 1, further comprising the following:

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