Algae cultivation system

Abstract

Regarding an algae cultivation system equipped with a combustion device for burning methane generated in a methane fermentation tank, we provide an algae cultivation system that can reduce NOx emissions with a simple configuration. [Solution] An algae cultivation system comprising: a methane fermentation tank for methane fermentation of biomass; a combustion device for burning the methane generated in the methane fermentation tank; an algae cultivation tank for cultivating algae; and an oxygen supply line configured to supply oxygen generated in the algae cultivation tank to the combustion device.

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 methane fermentation tank for methane-fermenting biomass, a biogas power generation device for generating power using methane generated in the methane fermentation tank, and an algae culture tank for culturing algae.

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, when methane generated in the methane fermentation tank is burned in a combustion device, nitrogen oxides (NOx) are usually generated in the combustion device because air is used to burn methane.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide an algae culture system including a combustion device for burning methane generated in a methane fermentation tank, which can reduce the NOx emission amount with a simple configuration.

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 methane fermentation tank for methane-fermenting biomass, a combustion device for burning methane generated in the methane fermentation tank, an algae culture tank for culturing algae, An oxygen supply line configured to supply oxygen generated in the algae culture tank to the combustion device, It is equipped with. [Effects of the Invention]

[0007] According to at least one embodiment of the present disclosure, an algae cultivation system is provided that includes a combustion device for burning methane generated in a methane fermentation tank, and that is capable of reducing NOx emissions with a simple configuration. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows a schematic configuration of an algae cultivation system 2 according to one embodiment of the present disclosure. [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] 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. The raw material tank 4 is supplied with biomass (first biomass) such as agricultural residues, livestock waste, food waste, forestry residues, or sewage sludge 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. If the first raw material is a flame-retardant biomass such as bamboo or vegetation, it may be pretreated by hydrothermal treatment or the like before being supplied to the raw material tank 4. The raw material tank 4 is also connected to an algae return line 54, which is configured to supply concentrated algae (second biomass), which is a second raw material different from the first raw material, to the raw material tank 4. The inside of the raw material tank 4 may be provided with a stirring device (not shown) for mixing the raw materials.

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

[0013] The methane fermentation tank 6 is composed of, for example, a container containing methane-fermenting bacteria, and ferments biomass supplied from the raw material tank 4 through the raw material supply line 5 to produce biogas containing methane and carbon dioxide. The methane fermentation may be carried out, for example, under anaerobic conditions at a temperature of 30°C to 60°C, preferably 50°C to 60°C.

[0014] The biogas generated in the methane fermentation tank 6 is a mixed gas containing methane and carbon dioxide, and also 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% or more by volume, 45% or more by volume, or 50% or more by volume of methane, and 30% or more by volume, 35% or more by volume, or 40% or more by volume of carbon dioxide. The biogas line 14 connects the methane fermentation tank 6 to 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. The biogas line 14 is equipped with a blower 15 for supplying the biobus discharged from the methane fermentation tank 6 to the carbon dioxide absorption tower 16.

[0015] Meanwhile, the fermentation residue remaining after methane fermentation of 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 to the solid-liquid separator 20 of the post-treatment device 8. The fermentation residue discharged from the methane fermentation tank 6 to the fermentation residue line 18 contains solid components and digestate 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 solid-liquid separator 20. The fermentation residue line 18 is equipped with a pump 19 for pressurizing the fermentation residue discharged from the methane fermentation tank 6 to the solid-liquid separator 20.

[0016] The post-treatment device 8 includes a carbon dioxide absorption tower 16, a solid-liquid separator 20, a digestate storage tank 25, a mixing tank 26, an algae culture tank 28, an oxygen separation tank 30, a solid-liquid separator 32, and an oxygen storage tank 34, etc.

[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). The gas discharged from the carbon dioxide absorption tower 16 to the methane gas line 36 may contain, for example, 80% or more by volume, 85% or more by volume, or 90% or more by volume of methane gas.

[0018] In addition, the gas discharged from the carbon dioxide absorption tower 16 to the methane gas line 36 contains, in addition to methane gas, trace components such as hydrogen sulfide and water vapor. Therefore, in the exemplary form shown in FIG. 1, the methane gas line 36 is provided with a dehumidifier 38 for removing moisture in the gas flowing through the methane gas line 36 and a desulfurization tower 40 for removing hydrogen sulfide in the gas flowing through the methane gas line 36. Further, the dehumidifier 38 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 hydrogen sulfide is removed in the desulfurization tower 40, and then supplied to the gas holder 9 and stored in the gas holder 9.

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

[0020] On the other hand, the carbonated water generated in the carbon dioxide absorption tower 16 is discharged from the carbon dioxide absorption tower 16 to the carbonated water line 42. The carbonated water line 42 connects the carbon dioxide absorption tower 16 and 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. A pump 46 for pumping the carbonated water discharged to the carbonated water line 42 to the mixing tank 26 is provided in the carbonated water line 42.

[0021] In addition, the solid content and the digestate in the fermented residue supplied from the methane fermentation tank 6 to the solid-liquid separation device 20 are separated from each other by the solid-liquid separation device 20. The solid content (the solid content in the fermented residue) discharged from the solid-liquid separation device 20 may be utilized, for example, as compost or the like. The type of the solid-liquid separation device 20 is not particularly limited, and it may be, for example, a centrifuge, a membrane separation device, a screen or a filter, etc. When the solid-liquid separation device 20 is, for example, a membrane separation device, a part of the solid content discharged from the solid-liquid separation device 20 may be returned to the raw material tank 4.

[0022] The digestate (the digestate in the fermented residue) separated from the solid content in the fermented residue by the solid-liquid separation device 20 is discharged from the solid-liquid separation device 20 to the digestate supply line 48. The digestate supply line 48 connects the solid-liquid separation device 20 and the mixing tank 26 and is configured to supply the digestate discharged from the solid-liquid separation device 20 to the mixing tank 26. A digestate storage tank 25 for storing the digestate discharged from the solid-liquid separation device 20 is provided in the digestate supply line 48. A pump 27 for pumping the digestate discharged from the digestate storage tank 25 to the mixing tank 26 is provided between the digestate storage tank 25 and the mixing tank 26 in the digestate supply line 48.

[0023] The mixing tank 26 and the algae culture tank 28 are connected by an algae extraction line 50. The algae extraction line 50 is configured to extract the algae and the culture solution during cultivation from the algae culture tank 28 and supply them to the mixing tank 26. Here, "during cultivation" means, for example, the middle of the cultivation period of the algae in the algae culture tank 28 when the cultivation period of the algae in the algae culture tank 28 is determined. For example, when the cultivation period of the algae in the algae culture tank 28 is determined to be 30 days, it means the time when 30 days have not passed. A pump 55 for pumping the algae and the culture solution extracted from the algae culture tank 28 to the mixing tank is provided in the algae extraction line 50.

[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 culture tank 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 culture tank 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 culture tank 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 culture tank 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 culture tank 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 culture tank 28.

[0026] The algae culture tank 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 them with light in the culture medium. 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 culture tank 28.

[0027] The algae culture tank 28 may be, for example, a tube-type culture tank in which algae are cultured by irradiating light into a tubular reactor, or a flat-panel type culture tank in which algae are cultured by irradiating light into a flat-plate reactor, or a so-called raceway type culture tank in which algae and culture solution are flowed into each of several annular channels and the algae and culture solution in each annular channel are periodically (for example, every day) exchanged with the other annular channels.

[0028] In the algae culture tank 28, algae perform photosynthesis using carbon dioxide in the culture medium to produce oxygen. Also, in the algae culture tank 28, 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 culture tank 28. The waste products discharged from the algae culture tank 28 (algae, water, and oxygen) are supplied to the oxygen separation tank 30.

[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 in the algae culture tank 28 during cultivation (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. The concentration of carbon dioxide in the exhaust gas flowing through the exhaust gas line 70 may be, for example, 30 to 90 volume percent or 50 to 70 volume percent.

[0031] The oxygen separation tank 30 is configured to separate oxygen from algae (algae that have been cultured in the algae culture tank 28 for a predetermined period of time) and water discharged from the algae culture tank 28. The oxygen separation tank 30 and the gas turbine 60 are connected by an oxygen supply line 31, which is configured to supply oxygen discharged from the oxygen separation tank 30 (oxygen generated by photosynthesis of algae in the algae culture tank 28) to the gas turbine 60. The concentration of oxygen in the gas supplied from the oxygen separation tank 30 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 culture tank 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 culture tank 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 culture tank 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] The following describes the effects of the algae cultivation system 2 described above. According to the algae cultivation system 2 described above, an oxygen supply line 31 is provided to supply oxygen generated in the algae cultivation tank 28 to the gas turbine 60. Therefore, compared to the case where methane generated in the methane fermentation tank 6 is burned in the gas turbine 60 using air (when the algae cultivation system 2 does not have an oxygen supply line 31), the amount of nitrogen oxides (NOx) emitted from the gas turbine 60 can be reduced. As a result, a denitrification device to reduce NOx in the exhaust gas of the gas turbine 60 is not required, or if such a denitrification device is provided, the equipment capacity of the denitrification device can be reduced. Thus, an algae cultivation system 2 that can reduce NOx emissions with a simple configuration can be provided.

[0039] Furthermore, since burning methane using high-concentration oxygen in the gas turbine 60 increases the risk of explosion, a first branch line 71 is provided to supply a portion of the exhaust gas from the gas turbine 60 to the oxygen supply line 31. This reduces the oxygen concentration in the gas supplied from the oxygen supply line 31 to the gas turbine 60. As a result, NOx emissions can be reduced with a simple configuration while reducing the risk of explosion.

[0040] Furthermore, the amount of oxygen produced in the algae culture tank 28 is not necessarily constant and fluctuates depending on environmental conditions such as solar radiation and temperature. Therefore, by providing the oxygen storage tank 34 as described above, it is possible to suppress instability in the supply of oxygen to the gas turbine 60. In addition, even if the oxygen demand of the gas turbine 60 fluctuates, it is possible to suppress any surplus or shortage of oxygen supply to the gas turbine 60 in relation to its oxygen demand.

[0041] Furthermore, by removing moisture from the gas flowing through the oxygen supply line 31 using the dehumidifier 35, corrosion of metal parts of the gas turbine 60 caused by moisture supplied from the oxygen supply line 31 and a decrease in combustion efficiency in the gas turbine 60 can be suppressed.

[0042] Furthermore, according to the algae cultivation system 2 described above, carbon dioxide contained in the biogas generated in the methane fermentation tank 6 can be used to produce carbonated water in the carbon dioxide absorption tower 16, and the carbon dioxide contained in that carbonated water can be used to promote the growth of algae in the algae cultivation tank 28. In addition, since the system is equipped with a solid-liquid separator 32 configured to separate algae and water discharged from the algae cultivation tank 28, and a water return line 56 configured to supply the water discharged from the solid-liquid separator 32 to the carbon dioxide absorption tower 16, the water discharged from the algae cultivation tank 28 (used culture solution from which the concentration of carbon dioxide, etc., has decreased due to algae cultivation) can be supplied to the carbon dioxide absorption tower 16 and reused to produce carbonated water in the carbon dioxide absorption tower 16.Therefore, the growth of algae can be promoted by using the carbon dioxide contained in the biogas generated in the methane fermentation tank 6, and the amount of water consumed in the algae cultivation system 2 can be reduced.

[0043] Furthermore, the algae cultivation system 2 described above includes a mixing tank 26 for mixing the digestate discharged from the methane fermentation tank 6 with the carbonated water produced in the carbon dioxide absorption tower 16, and the culture medium supply line 52 supplies the mixture discharged from the mixing tank 26 to the algae cultivation tank 28. Therefore, the nutrients contained in the digestate discharged from the methane fermentation tank 6 (e.g., phosphorus, potassium, ammonia, etc.) and the carbon dioxide contained in the carbonated water produced in the carbon dioxide absorption tower 16 can be used to promote the growth of algae in the algae cultivation tank 28.

[0044] Furthermore, according to the above-described algae cultivation system 2, an algae extraction line 50 is provided to extract a portion of the algae cultivated in the algae cultivation tank 28 and supply it to the mixing tank 26. The digestate discharged from the methane fermentation tank 6, the carbonated water produced in the carbon dioxide absorption tower 16, and the algae supplied from the algae extraction line 50 are mixed in the mixing tank 26 and returned to the algae cultivation tank 28. In this way, the amount of algae in the algae cultivation tank 28 can be maintained at or above a certain level while discharging algae from the algae cultivation tank 28 to the solid-liquid separation device 32.

[0045] Furthermore, the algae cultivation system 2 described above includes a concentrated algae storage tank 12 for storing algae as solid matter discharged from the solid-liquid separation device 32, and an algae return line 54 for supplying the algae stored in the concentrated algae storage tank 12 to the raw material tank 4. Therefore, even if the first raw material for methane fermentation supplied to the methane fermentation tank 6 is temporarily insufficient, the algae stored in the concentrated algae storage tank 12 can be supplied to the methane fermentation tank 6 to compensate for the shortage of the first raw material for methane fermentation. Thus, the production of methane in the methane fermentation tank 6 can be stabilized by utilizing the algae cultivated in the algae cultivation tank 28. Moreover, because it is maintained as a raw material and supplied when needed, rather than being stored as fuel such as SAF (Sustainable Aviation Fuel) or as energy such as electricity and used when needed, there is no waste in energy conversion.

[0046] Furthermore, according to the above-described algae cultivation system 2, since a digestate storage tank 25 is provided in the digestate supply line 48, the digestate storage tank 25 functions as a buffer to absorb the temporary difference between the amount of digestate discharged from the methane fermentation tank 6 and the amount of digestate required for algae cultivation in the algae cultivation tank 28, thereby improving the overall stability and flexibility of the system. In addition, even if the composition of the digestate discharged from the methane fermentation tank 6 fluctuates, the digestate can be temporarily stored in the digestate storage tank 25, thereby homogenizing the composition of the digestate within the digestate storage tank 25. As a result, a digestate with a stable composition can be supplied from the digestate storage tank 25 to the mixing tank 26.

[0047] 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.

[0048] For example, in the embodiment described above, a gas turbine 60 was shown as an example of a combustion device, but the combustion device is not limited to a gas turbine 60. For example, it could be a gas engine or boiler configured to burn methane discharged from the carbon dioxide absorption tower 16. Alternatively, a fuel cell that generates electricity using methane discharged from the carbon dioxide absorption tower 16 and oxygen supplied from the oxygen supply line 31 may be provided.

[0049] Furthermore, although the algae cultivation system 2 described above was equipped with an oxygen separation tank 30, if the algae cultivation tank 28 is a sealed type and an oxygen supply line 31 can be directly connected to the top of the algae cultivation tank 28, allowing the oxygen accumulated at the top of the algae cultivation tank 28 to be directly extracted by the oxygen supply line 31, then the algae cultivation system 2 does not need to be equipped with an oxygen separation tank 30.

[0050] Furthermore, the algae cultivation system 2 does not necessarily have to be equipped with, for example, dehumidifiers 35, 38, desulfurization tower 40, first branch line 71, second branch line 72, etc.

[0051] The contents described in each of the above embodiments can be understood, for example, as follows:

[0052] [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 methane fermentation tank for methane fermentation of biomass (for example, methane fermentation tank 6 mentioned above), A combustion device for burning the methane generated in the methane fermentation tank (for example, the gas turbine 60 described above, or a gas engine or boiler that replaces the gas turbine 60, or a fuel cell), An algal culture tank for cultivating algae (for example, the algal culture tank 28 described above), An oxygen supply line (for example, the oxygen supply line 31 described above) configured to supply oxygen generated in the algae culture tank to the combustion device, It is equipped with.

[0053] According to the algae cultivation system described in [1] above, an oxygen supply line is provided to supply oxygen generated in the algae cultivation tank to the combustion device. Therefore, compared to the case where methane generated in the methane fermentation tank is burned in the combustion device using air (when the algae cultivation system does not have an oxygen supply line), the amount of nitrogen oxides (NOx) emitted from the combustion device can be reduced. As a result, a denitrification device for reducing NOx in the exhaust gas of the combustion device is not required, or if such a denitrification device is provided, the equipment capacity of the denitrification device can be reduced. Thus, an algae cultivation system that can reduce NOx emissions with a simple configuration can be provided.

[0054] [2] In some embodiments, in the algae cultivation system described in [1] above, An exhaust gas line through which the exhaust gas from the combustion device flows (for example, the exhaust gas line 70 described above), A branch line (for example, the first branch line 71 described above) is configured to branch off from the exhaust gas line and connect to the oxygen supply line, and to supply a portion of the exhaust gas flowing through the exhaust gas line to the oxygen supply line, It is equipped with.

[0055] Combusting methane using high-concentration oxygen in a combustion device increases the risk of explosion. Therefore, by providing a branch line as described in [2] above and supplying a portion of the exhaust gas from the combustion device to the oxygen supply line, the oxygen concentration in the gas supplied from the oxygen supply line to the combustion 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.

[0056] [3] In some embodiments, in the algae cultivation system described in [1] or [2] above, The oxygen supply line further includes an oxygen storage tank (for example, the oxygen storage tank 34 described above) for storing oxygen supplied from the algae culture tank.

[0057] The amount of oxygen produced in an algae cultivation tank is not necessarily constant and fluctuates depending on environmental conditions such as solar radiation and temperature. Therefore, by providing an oxygen storage tank as described in [3] above, it is possible to suppress instability in the supply of oxygen to the combustion device. Furthermore, even if the oxygen demand of the combustion device fluctuates, it is possible to suppress any surplus or shortage of oxygen supply to meet the oxygen demand of the combustion device.

[0058] [4] In some embodiments, in the algae cultivation system described in any of [1] to [3] above, The system further includes a dehumidifier (for example, the dehumidifier 35 described above) provided in the oxygen supply line and configured to remove moisture from the gas flowing through the oxygen supply line.

[0059] According to the algae cultivation system described in [4] above, by removing moisture from the gas flowing through the oxygen supply line using a dehumidifier, corrosion of metal parts of the combustion device and a decrease in combustion efficiency caused by moisture supplied from the oxygen supply line can be suppressed.

[0060] [5] In some embodiments, in the algae cultivation system described in any of [1] to [4] above, The system further includes a chiller (for example, the chiller 37 described above) provided in the oxygen supply line and configured to cool the gas flowing through the oxygen supply line.

[0061] According to the algae cultivation system described in [5] above, the density of the gas flowing through the oxygen supply line can be increased by cooling, thereby efficiently supplying oxygen to the combustion device and improving combustion efficiency.

[0062] [6] In some embodiments, in the algae cultivation system described in [4] above, The oxygen supply line is further provided with an oxygen storage tank (for example, the oxygen storage tank 34 described above) for storing oxygen supplied from the algae culture tank, The dehumidifier is installed downstream of the oxygen storage tank in the oxygen supply line.

[0063] The algae cultivation system described in [6] above can stabilize the supply of oxygen to the combustion device for the same reasons as the algae cultivation system described in [3] above, and can suppress any deficiency or excess of oxygen supplied to the combustion device. In addition, by removing moisture from the gas leaving the oxygen storage tank with a dehumidifier, corrosion of metal parts of the combustion device and a decrease in combustion efficiency caused by moisture supplied from the oxygen supply tank can be suppressed.

[0064] [7] In some embodiments, in the algae cultivation system described in [5] above, The oxygen supply line is further provided with an oxygen storage tank (for example, the oxygen storage tank 34 described above) for storing oxygen supplied from the algae culture tank, The chiller is installed downstream of the oxygen storage tank in the oxygen supply line.

[0065] The algae cultivation system described in [7] above can stabilize the supply of oxygen to the combustion device for the same reasons as the algae cultivation system described in [3] above, and can prevent deficiencies or excesses in the supply of oxygen to the combustion device. In addition, the density of the gas leaving the oxygen storage tank can be increased by cooling, allowing for efficient oxygen supply to the combustion device and improving combustion efficiency.

[0066] [8] In some embodiments, in the algae cultivation system described in any of [1] to [7] above, A concentrated algae storage tank (for example, the concentrated algae storage tank 12 described above) for storing the algae cultured in the aforementioned algae culture tank, An algae return line (for example, the algae return line 54 and raw material supply line 5 described above) supplies the algae stored in the concentrated algae storage tank to the methane fermentation tank, It is further equipped with [this feature].

[0067] According to the algae cultivation system described in [8] above, even if there is a temporary shortage of raw materials for methane fermentation supplied to the methane fermentation tank, the shortage can be compensated for by supplying algae stored in the concentrated algae storage tank to the methane fermentation tank. Therefore, the production of methane in the methane fermentation tank can be stabilized by utilizing algae cultivated in the algae cultivation tank.

[0068] [9] An algae culture system according to at least one embodiment of the present disclosure (e.g., the algae culture system 2 described above) A methane fermentation tank for methane fermentation of biomass (for example, methane fermentation tank 6 mentioned above), An algal culture tank for cultivating algae (for example, the algal culture tank 28 described above), A concentrated algae storage tank (for example, the concentrated algae storage tank 12 described above) for storing the algae cultured in the aforementioned algae culture tank, An algae return line (for example, the algae return line 54 and raw material supply line 5 described above) supplies the algae stored in the concentrated algae storage tank to the methane fermentation tank, It is equipped with.

[0069] According to the algae cultivation system described in [9] above, even if there is a temporary shortage of raw materials for methane fermentation supplied to the methane fermentation tank, the shortage can be compensated for by supplying algae stored in the concentrated algae storage tank to the methane fermentation tank. Therefore, the production of methane in the methane fermentation tank can be stabilized by utilizing algae cultivated in the algae cultivation tank. [Explanation of symbols]

[0070] 2. Algae cultivation system 4. Raw material tanks 5. Raw material supply line 6. Methane fermentation tank 8. Post-treatment device 9 Gas holder 10 Energy conversion device 11,19,27,46,53,55,58,62,63 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 culture tank 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 71 First Branch Line 72 Second Branch Line

Claims

1. A methane fermentation tank for methane fermentation of biomass, A combustion device for burning the methane generated in the aforementioned methane fermentation tank, Algae cultivation tanks for cultivating algae, An oxygen supply line configured to supply oxygen generated in the algae culture tank to the combustion device, An algae cultivation system equipped with [the following features].

2. The exhaust gas line through which the exhaust gas from the combustion device flows, A branch line is configured to branch off from the exhaust gas line and connect to the oxygen supply line, and to supply a portion of the exhaust gas flowing through the exhaust gas line to the oxygen supply line, The algae cultivation system according to claim 1, comprising:

3. The algae cultivation system according to claim 1, further comprising an oxygen storage tank provided in the oxygen supply line for storing oxygen supplied from the algae cultivation tank.

4. The algae cultivation system according to claim 1, further comprising a dehumidifier provided in the oxygen supply line and configured to remove moisture from the gas flowing through the oxygen supply line.

5. The algae cultivation system according to claim 1, further comprising a chiller provided in the oxygen supply line and configured to cool the gas flowing through the oxygen supply line.

6. The oxygen supply line is further provided with an oxygen storage tank for storing oxygen supplied from the algae culture tank, The algae cultivation system according to claim 4, wherein the dehumidifier is provided downstream of the oxygen storage tank in the oxygen supply line.

7. The oxygen supply line is further provided with an oxygen storage tank for storing oxygen supplied from the algae cultivation tank, The algae cultivation system according to claim 5, wherein the chiller is provided downstream of the oxygen storage tank in the oxygen supply line.

8. A concentrated algae storage tank for storing the algae cultured in the aforementioned algae culture tank, An algae return line for supplying the algae stored in the concentrated algae storage tank to the methane fermentation tank, The algae cultivation system according to claim 1, further comprising the following:

9. A methane fermentation tank for methane fermentation of biomass, Algae cultivation tanks for cultivating algae, A concentrated algae storage tank for storing the algae cultured in the aforementioned algae culture tank, An algae return line for supplying the algae stored in the concentrated algae storage tank to the methane fermentation tank, An algae cultivation system equipped with [the following features].

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