Methane fermentation treatment method and methane fermentation treatment facility

Abstract

To efficiently produce biogas in a methane fermentation tank by maintaining organic waste at a desired temperature for a desired time while suppressing an increase in the size and cost of equipment.SOLUTION: The method includes a step of at least partially heating the C1 and C2 of the organic wastes, and a step of supplying the C1 and C2 of the organic wastes including those heated in the step to a methane fermentation tank 33. The heating unit 31 heats the C2 of organic wastes and supplies the heated C2 to the constant temperature tank 32, the constant temperature tank 32 retains the C2 of organic wastes while maintaining the temperature of the C2 of organic wastes, and the constant temperature tank 32 returns at least a part of the soil of organic wastes to the heating unit 31.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a methane fermentation treatment method and a methane fermentation treatment facility for producing biogas by subjecting organic waste to methane fermentation treatment. [Background technology]

[0002] For example, methane fermentation (anaerobic fermentation) is widely used to reduce the volume of organic waste generated in wastewater treatment, such as sludge and biomass, and to generate energy. Methane fermentation is a technology in which organic waste is stored under anaerobic conditions for a certain period of time, and the action of anaerobic microorganisms decomposes the organic waste to produce biogas such as methane gas and carbon dioxide. This technology is widely used in waste treatment facilities and wastewater treatment facilities in Japan.

[0003] A methane fermentation facility that performs methane fermentation is primarily equipped with a methane fermentation tank that stores organic waste and performs methane fermentation, an agitator that agitates the methane fermentation liquid in the methane fermentation tank, and a heating device that heats the methane fermentation liquid.

[0004] In order to increase the efficiency of biogas recovery, a method has been used in which organic waste for methane fermentation is heated and solubilized before undergoing methane fermentation treatment (see, for example, Patent Documents 1 and 2). By heating the organic waste for methane fermentation, persistent substances in the organic waste are solubilized, increasing the amount of biogas generated.

[0005] In Patent Document 1, organic waste is heated in a heat exchanger and held at 150 to 200°C for 20 to 90 minutes. In Patent Document 2, organic waste is heated in a heat exchanger, then mixed with air from an air compressor and held at 60 to 80°C for 60 to 120 minutes. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 57-107299 [Patent Document 2] Japanese Patent Application Publication No. 58-95600 Summary of the Invention [Problem to be solved by the invention]

[0007] In both Patent Documents 1 and 2, the organic waste is heated in a heat exchanger, but in order to heat the organic waste to the desired temperature, it is necessary to increase the capacity of the heat exchanger, which leads to an increase in the size of the equipment and costs. In order to maintain the organic waste at the desired temperature for the desired time, it is also necessary to increase the capacity of the maintenance equipment, etc., which leads to significant problems of an increase in the size of the equipment and costs.

[0008] Furthermore, the organic waste supplied to the heat exchanger varies in temperature, flow rate, and other conditions. Therefore, for example, if the temperature of the organic waste supplied to the heat exchanger is low or the flow rate of the organic waste supplied to the heat exchanger is high, simply heating the organic waste in the heat exchanger may not be enough to heat the organic waste to the desired temperature range, or conversely, it may be overheated beyond the desired temperature range. For this reason, if the capacity or capability of the heat exchanger is increased, the problems of increased equipment size and cost become more pronounced.

[0009] In view of this situation, a main object of the present invention is to provide a methane fermentation treatment method and methane fermentation treatment facility that can efficiently produce biogas in a methane fermentation tank by maintaining organic waste at a desired temperature for a desired period of time while suppressing increases in the size and cost of the facility. [Means for solving the problem]

[0010] A first characteristic configuration of the present invention is a methane fermentation treatment method for producing biogas by subjecting organic waste to methane fermentation treatment in a methane fermentation tank, a heating step of heating at least a portion of the organic waste; a supply step of supplying the organic waste, including that which has been subjected to the heating step, to the methane fermentation tank; In the heating step, a first heating step of heating the organic waste in a heating unit and supplying the organic waste to a thermostatic bath; a second heating step of maintaining the temperature of the organic waste in the thermostatic bath; and a third heating step of removing at least a portion of the organic waste from the thermostatic bath and returning it to the heating unit. The organic waste is maintained at a target temperature for heating for a set heating time or longer.

[0011] According to this configuration, the heating step can thermally solubilize at least a portion of the organic waste, increasing the amount of biogas produced in the methane fermentation tank and enabling efficient biogas production.

[0012] Furthermore, in the heating process, the organic waste is not simply heated in a heating unit such as a heat exchanger. Instead, the first, second, and third heating steps are performed sequentially, allowing the organic waste to be heated and retained while circulating between the heating unit and the thermostatic chamber. Therefore, even if a small-capacity heating unit or thermostatic chamber is used, the organic waste can be maintained at the heating target temperature for at least the heating set time, thereby preventing the equipment from becoming too large and increasing costs. Furthermore, regardless of the various conditions of the organic waste, such as the temperature and flow rate received in the heating process, the temperature of the organic waste can be accurately heated to the heating target temperature and appropriately maintained at that heating target temperature for at least the heating set time. This allows for effective thermal solubilization of the organic waste, thereby enabling more efficient and effective biogas generation in the methane fermentation tank.

[0013] A second characteristic configuration of the present invention is a method for treating a wastewater treatment plant, comprising the steps of: providing a first organic waste and a second organic waste that is more difficult to decompose than the first organic waste; In the heating step, the second organic waste is the object to be heated, In the supply step, the first organic waste is supplied to the methane fermentation tank without undergoing the heating step, and the second organic waste is supplied to the methane fermentation tank after undergoing the heating step.

[0014] According to this configuration, the second organic waste, which is more difficult to decompose than the first organic waste, is subjected to a heating process and then supplied to the methane fermentation tank in the supply process. Therefore, the second organic waste can be thermally solubilized by the heating process, and the amount of biogas produced in the methane fermentation tank can be increased, allowing for efficient biogas production.

[0015] Moreover, in the heating step, it is only necessary to heat the second organic waste, and the volume of the object to be heated can be reduced, which allows for a more compact device and energy conservation.

[0016] A third characteristic feature of the present invention is that a temperature adjustment step is performed in which the temperature of the methane fermentation liquid containing organic waste supplied to the methane fermentation tank is adjusted to a target temperature for methane fermentation by a temperature adjustment unit.

[0017] According to this configuration, in the temperature adjustment process, the temperature of the methane fermentation liquid can be adjusted to the target temperature for methane fermentation, so that the methane fermentation process in the methane fermentation tank can be carried out suitably and biogas can be produced efficiently in the methane fermentation tank.

[0018] In a fourth characteristic configuration of the present invention, the heating unit heats the organic waste by exchanging heat between the organic waste and a heating medium in a heat exchanger, the temperature adjustment unit adjusts the temperature of the methane fermentation liquid by exchanging heat between the methane fermentation liquid and a temperature adjustment heat medium in the heat exchanger, The heat exchanger is configured to be freely switchable between a heating state in which the organic waste is heated by receiving the supply of the heating heat medium, and a temperature control state in which the temperature of the methane fermentation liquid is controlled by receiving the supply of the temperature control heat medium.

[0019] According to this configuration, when the first heating step in the heating step is performed, the heat exchanger can be switched to a heating state to heat the organic waste in the heat exchanger. When the temperature adjustment step is performed, the heat exchanger can be switched to a temperature adjustment state to adjust the temperature of the methane fermentation liquid. In this way, a common heat exchanger can be used for the first heating step and the temperature adjustment step, which simplifies the configuration.

[0020] A fifth characteristic configuration of the present invention is a method for producing a waste material by a method comprising the steps of: performing a cooling step in which the organic waste heated in the heating step is cooled in a cooling section; In the supplying step, the organic waste, including that which has been subjected to the cooling step, is supplied to the methane fermentation tank; the heating unit heats the organic waste by exchanging heat between the organic waste and a heating medium in a heat exchanger; the cooling unit cools the organic waste by exchanging heat between the organic waste and a cooling heat medium in the heat exchanger; The heat exchanger is configured to be freely switchable between a heating state in which the organic waste is heated by receiving the heating heat medium, and a cooling state in which the organic waste is cooled by receiving the cooling heat medium.

[0021] According to this configuration, when the first heating step in the heating step is performed, the heat exchanger can be switched to a heating state to heat the organic waste. When the cooling step is performed, the heat exchanger can be switched to a cooling state to cool the organic waste. In this way, a common heat exchanger can be used for the first heating step and the cooling step, thereby simplifying the configuration.

[0022] A sixth characteristic configuration of the present invention is a methane fermentation treatment facility for producing biogas by subjecting organic waste to methane fermentation treatment in a methane fermentation tank, a heating step execution unit that performs a heating step of heating at least a portion of the organic waste; a supply process execution unit that carries out a supply process of supplying the organic waste, including that which has been subjected to the heating process, to the methane fermentation tank, The heating process execution unit a first heating step execution unit that performs a first heating step of heating the organic waste in a heating unit and supplying the organic waste to a thermostatic bath; a second heating step execution unit that performs a second heating step of maintaining the temperature of the organic waste in the thermostatic bath; a third heating step execution unit that performs a third heating step of removing at least a portion of the organic waste from the thermostatic bath and returning it to the heating unit, The first heating step is performed by the first heating step executing unit, the second heating step is performed by the second heating step executing unit, and the third heating step is performed by the third heating step executing unit, and the organic waste is maintained at the heating target temperature for a heating set time or longer.

[0023] According to this configuration, as with the first characteristic configuration, the heating step can thermally solubilize at least a portion of the organic waste, increasing the amount of biogas produced in the methane fermentation tank and enabling efficient biogas production. Moreover, in the heating step, the organic waste is not simply heated in a heating unit such as a heat exchanger, but rather the first heating step, the second heating step, and the third heating step are performed sequentially, allowing the organic waste to be heated and retained while circulating between the heating unit and the thermostatic bath. Therefore, even if small-capacity heating units and thermostatic baths are used, the organic waste can be maintained at the heating target temperature for at least the heating set time, regardless of the various conditions of the organic waste, such as the temperature and flow rate, received in the heating step, thereby preventing the equipment from becoming too large and the costs from increasing. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram showing an overall schematic configuration of a wastewater treatment facility according to a first embodiment. [Figure 2] FIG. 10 is a diagram showing a heating unit and a temperature adjusting unit in a second embodiment. [Figure 3] FIG. 10 is a diagram showing a heating unit and a cooling unit in a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0025] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a methane fermentation treatment method and a wastewater treatment facility to which a methane fermentation treatment facility according to the present invention is applied will be described with reference to the drawings. [First embodiment] As shown in Figure 1, this wastewater treatment facility 1 is a facility that treats organic wastewater such as sewage and wastewater containing organic matter. The wastewater treatment facility 1 is equipped with a wastewater treatment system (sewage treatment system) 2, a sludge treatment system 3 (corresponding to a methane fermentation treatment facility) that subjects organic waste to methane fermentation treatment (anaerobic digestion treatment), and a biogas utilization system 4.

[0026] In Figure 1, the routes through which the raw organic wastewater A1, treated water A2, sludge B1-B3, organic waste C1 and C2, and methane fermentation liquid D flow are indicated by thick lines, the routes through which the biogas E flows are indicated by dotted lines, the routes through which the heating heat transfer medium F flows are indicated by thin lines (with some bypass routes exceptionally shown by dotted lines), and the routes through which the cooling heat transfer medium G flows are indicated by dashed lines.

[0027] As shown by the bold lines in Figure 1, the wastewater treatment system 2 is equipped with, in order from upstream in the flow direction of raw organic wastewater A1, a primary sedimentation tank 21, a biological treatment tank 22, and a final sedimentation tank 23. The raw water A1 first flows into the primary sedimentation tank 21, where suspended matter and solids that tend to settle are settled and removed. Next, in the biological treatment tank 22, organic matter and other contaminants in the raw water A1 are decomposed and removed by the action of microorganisms. Finally, activated sludge is settled in the final sedimentation tank 23, and the clean supernatant water is discharged as treated water A2.

[0028] The raw sludge settled and removed in the primary settling tank 21 is sent as primary settling sludge B1 to a first thickener 24 (for example, a mechanical thickener such as a screw thickener, centrifugal thickener, or flotation thickener, or a gravity thickener such as a gravity thickener tank) where it is thickened to a solids concentration of, for example, about 2 to 10%. A portion of the activated sludge settled and removed in the final settling tank 23 is returned to the biological treatment tank 22 as returned sludge B2, and the remaining excess sludge B3 is sent to a second thickener 25 (for example, a mechanical thickener such as a screw thickener, centrifugal thickener, or flotation thickener) where it is thickened to a solids concentration of, for example, about 2 to 10%.

[0029] As shown by the thick line in Figure 1, the sludge treatment system 3 receives organic wastes C1 and C2 from the wastewater treatment system 2 and subjects the organic wastes C1 and C2 to methane fermentation to produce biogas E. The organic waste includes a first organic waste C1 and a second organic waste C2 that is more difficult to decompose than the first organic waste C1. The sludge treatment system 3 receives primary sludge B1 from the first thickener 24 as the first organic waste C1, and receives excess sludge B3 from the second thickener 25 as the second organic waste C2. In this way, the organic waste from the wastewater treatment system 2 is supplied to the sludge treatment system 3 in a separated state as the first organic waste C1 and the second organic waste C2. The volume ratio of the first organic waste C1 to the second organic waste C2 is not particularly limited and may be set as appropriate, but it is preferable to set it to, for example, C1:C2 = 1.5:1, so that there is more first organic waste C1 than second organic waste C2.

[0030] The sludge treatment system 3 is equipped with a heating unit 31, a thermostatic tank 32, a methane fermentation tank 33, and a supply unit 34 that supplies the first organic waste C1 and the second organic waste C2 to the methane fermentation tank 33. As shown by the thick lines in Figure 1, the supply unit 34 supplies the first organic waste C1 and the second organic waste C2 to the methane fermentation tank 33 using a first supply path 35 that supplies the first organic waste C1 and a second supply path 36 that supplies the second organic waste C2.

[0031] The second supply path 36 is provided with, in order from the upstream side in the flow direction of the second organic waste C2, a heating unit 31 and a thermostatic bath 32. A first pump P1 and a first on-off valve K1 are provided, from the upstream side, in a portion of the second supply path 36 between the thermostatic bath 32 and the methane fermentation tank 33. A first circulation path 37 is provided which branches off from between the first pump P1 and the first on-off valve K1 in the second supply path 36 and is connected to a portion upstream of the heating unit 31, and which returns at least a portion of the second organic waste C2 in the thermostatic bath 32 to the heating unit 31. A second on-off valve K2 is provided midway along the first circulation path 37.

[0032] The second supply path 36 is provided with a first flow rate sensor R1 that detects the flow rate of the second organic waste C2 being supplied to the thermostatic bath 32, and a second flow rate sensor R2 that detects the flow rate of the second organic waste C2 being removed from the thermostatic bath 32 by the first pump P1. The thermostatic bath 32 is provided with a first temperature detection sensor T1 that detects the temperature of the second organic waste C2 inside the thermostatic bath 32.

[0033] The heating unit 31 heats the second organic waste C2 supplied from the second concentrator 25. In the thermostatic bath 32, the second organic waste C2 heated by the heating unit 31 is retained while maintaining its temperature.

[0034] The methane fermentation tank 33 receives the first organic waste C1 from the first supply line 35 and the second organic waste C2 from the second supply line 36, and performs methane fermentation treatment (anaerobic digestion treatment) of a methane fermentation liquid D containing the first organic waste C1 and the second organic waste C2 through the action of anaerobic bacteria such as acid-producing bacteria and methanogens. The methane fermentation tank 33 is equipped with an agitator (not shown) that agitates the methane fermentation liquid D in the methane fermentation tank 33. Heat insulating material or the like can be provided on the outer wall or the like of the methane fermentation tank 33 to prevent a drop in the temperature of the methane fermentation liquid D.

[0035] The methane fermentation tank 33 is provided with a second circulation path 38 that removes the methane fermentation liquid D in the methane fermentation tank 33, circulates it, and returns it to the methane fermentation tank 33. In the middle of the second circulation path 38, a second pump P2 and a temperature adjustment unit 39 that adjusts the temperature of the methane fermentation liquid D are arranged in this order from the upstream side in the flow direction of the methane fermentation liquid D. The methane fermentation tank 33 is provided with a second temperature detection sensor T2 that detects the temperature of the methane fermentation liquid D.

[0036] The digested sludge produced by the methane fermentation process in the methane fermenter 33 is supplied to a dehydration facility (not shown) where it is dehydrated, and then transported by a transport vehicle such as a truck to a treatment plant outside the wastewater treatment facility 1. Although not shown, the dehydrated separated liquid separated from the digested sludge during the dehydration process is returned to the inlet side of the primary sedimentation tank 21 as return water.

[0037] The biogas utilization system 4 utilizes the biogas E produced by the methane fermentation treatment in the sludge treatment system 3, and is equipped with a generator 41 driven by a gas engine.

[0038] The biogas E from the methane fermentation tank 33 is supplied as fuel to a gas engine that drives a generator 41. The electricity generated by the generator 41 may be used within the wastewater treatment facility 1 or may be sold to an electric power company.

[0039] The operation of the sludge treatment system 3 will be described below, and the methane fermentation treatment method according to the present invention will also be described.

[0040] In this wastewater treatment facility 1, organic waste from a wastewater treatment system 2 is separated into a first organic waste C1 and a second organic waste C2 and supplied to a sludge treatment system 3. In the sludge treatment system 3, a heating step is carried out in which the second organic waste C2, which is more difficult to decompose than the first organic waste C1, is heated in a heating unit 31, thereby maintaining the second organic waste C2 at a heating target temperature for a heating set time or longer, thereby thermally solubilizing the second organic waste C2. In contrast, the first organic waste C1 does not pass through the heating unit 31 and does not undergo the heating step in the heating unit 31.

[0041] As shown by the thin line in Fig. 1, the heating section 31 is composed of a heat exchanger to which a heating heat medium F, such as hot water, is circulated and supplied via a heating heat medium circulation path 5. In the heating section 31, the second organic waste C2 is heated by heat exchange between the heating heat medium F and the second organic waste C2. The heating section 31 is not limited to one equipped with a heat exchanger, and various heating devices can be used as long as they are capable of heating the second organic waste C2.

[0042] The heating medium F is generated, for example, by recovering exhaust heat from a gas engine for driving a generator 41, and the heating medium F generated in the heating medium circulation path 5 is circulated and supplied to the heating section 31.

[0043] In order to maintain the second organic waste C2 at the heating target temperature for at least the heating set time, a heating step is carried out in which the second organic waste C2 is heated in the heating unit 31. However, depending on various conditions such as the temperature and flow rate of the second organic waste C2, it may not be possible to heat the second organic waste C2 to the heating target temperature by simply heating it once in the heating unit 31, so the heating unit 31 must have a large capacity and capability, which leads to an increase in the size of the equipment and an increase in costs.

[0044] Therefore, in this embodiment, the heating process is performed in a form in which a first heating process, a second heating process, and a third heating process are performed, and the second organic waste C2 is maintained at a heating target temperature for at least a heating set time. The heating target temperature can be set to, for example, 50 to 75°C, and the heating set time can be set to 5 to 30 minutes, but the heating target temperature and heating set time can be appropriately changed to suit the conditions under which the amount of biogas generated is maximized.

[0045] In the first heating step, the second organic waste C2 is heated in the heating section 31 by the first heating step execution section and supplied to the thermostatic bath 32. In the heating section 31, the second organic waste C2 (see the thick line in FIG. 1) supplied via the second supply path 36 is heat exchanged with the heating heat medium F (see the thin line in FIG. 1) circulated and supplied via the heating heat medium circulation path 5 to heat the second organic waste C2, and the heated second organic waste C2 is supplied to the thermostatic bath 32 via the second supply path 36. The first heating step execution section is made up of the second supply path 36, the heating section 31, the heating heat medium circulation path 5, etc.

[0046] In the second heating step, the second heating step performing unit maintains the temperature of the second organic waste C2 supplied and causes it to stay in the thermostatic bath 32. The second heating step performing unit is made up of the thermostatic bath 32 and the like.

[0047] In the third heating step, the third heating step execution unit removes at least a portion of the second organic waste C2 from the thermostatic bath 32 and returns it to the heating unit 31. By switching the first on-off valve K1 to a closed state and the second on-off valve K2 to an open state and operating the first pump P1, at least a portion of the second organic waste C2 is removed from the thermostatic bath 32, and the removed second organic waste C2 is supplied through the first circulation path 37 to a portion of the second supply path 36 upstream of the heating unit 31, and returned to the heating unit 31. The third heating step execution unit is made up of the first on-off valve K1, the second on-off valve K2, the first pump P1, the first circulation path 37, etc.

[0048] In the heating step, a first heating step and a second heating step are performed, and whether or not a third heating step is performed is determined depending on whether or not the temperature of the second organic waste C2 in the thermostatic chamber 32 has reached the target heating temperature. If the temperature detected by the first temperature detection sensor T1 provided in the thermostatic chamber 32 is below the target heating temperature, a control unit (not shown) or the like switches the first on-off valve K1 to a closed state and the second on-off valve K2 to an open state, and operates the first pump P1 to perform the third heating step.

[0049] In the third heating step, the first pump P1 is not simply operated, but the rotation speed of the first pump P1 is controlled so as to adjust the flow rate of the second organic waste C2 removed from the thermostatic bath 32 in accordance with the flow rate of the second organic waste C2 supplied to the thermostatic bath 32. For example, a control unit or the like (not shown) controls the rotation speed of the first pump P1 so that the flow rate detected by the second flow sensor R2 corresponds to the flow rate detected by the first flow sensor R1.

[0050] In this way, by repeatedly performing the first heating step, the second heating step, and the third heating step, it is possible to heat the second organic waste C2 to the heating target temperature, for example, even if the temperature of the supplied second organic waste C2 is low. Moreover, even if the temperature of the second organic waste C2 drops during transport through the second supply path 36 or in the thermostatic bath 32, it is possible to precisely maintain the second organic waste C2 at the heating target temperature for at least the heating set time by performing the third heating step and then performing the first and second heating steps again while fine-tuning the temperature.

[0051] The supply process execution unit carries out a supply process in which the first organic waste C1 and the second organic waste C2, including waste that has undergone the heating process, are supplied to the methane fermentation tank 33. In this embodiment, the first organic waste C1 that has not been heated in the heating unit 31 and therefore not undergone the heating process is supplied to the methane fermentation tank 33 via a first supply path 35, and the second organic waste C2 that has been heated in the heating unit 31 and undergone the heating process is supplied to the methane fermentation tank 33 via a second supply path 36. The supply process execution unit is made up of the first supply path 35, the second supply path 36, etc.

[0052] A first organic waste C1 that has not been heated in the heating section 31 and has not undergone a heating process, and a second organic waste C2 that has been heated in the heating section 31 and undergone a heating process are supplied to the methane fermentation tank 33, and a methane fermentation liquid D containing the first organic waste C1 and the second organic waste C2 is subjected to a methane fermentation process.

[0053] In order to carry out methane fermentation treatment in the methane fermenter 33, it is necessary to adjust the temperature of the methane fermentation liquid D in the methane fermenter 33 to a target temperature for methane fermentation (for example, 34°C to 39°C, preferably 37°C). The target temperature for methane fermentation is, for example, 30°C to 45°C, preferably 35°C to 40°C, and more preferably 37°C, and is used to carry out methane fermentation treatment at a medium temperature. However, the target temperature is not limited to this temperature range. For example, methane fermentation treatment can also be carried out at a high temperature by setting the target temperature for methane fermentation to 50°C to 60°C, preferably 54°C to 57°C, and more preferably 55°C.

[0054] Therefore, in this embodiment, the temperature adjustment execution unit performs a temperature adjustment process in which the temperature of the methane fermentation liquid D is adjusted to the target temperature for methane fermentation by the temperature adjustment unit 39. When the temperature detected by the second temperature detection sensor T2 provided in the methane fermentation tank 33 deviates from the target temperature for methane fermentation, the temperature adjustment process is performed to maintain the temperature of the methane fermentation liquid D in the methane fermentation tank 33 at the target temperature for methane fermentation.

[0055] In the temperature adjustment step, a control unit (not shown) or the like operates the second pump P2 and circulates the methane fermentation liquid D through the second circulation path 38 with the temperature adjusted by the temperature adjustment unit 39. The temperature adjustment unit 39 is composed of a heat exchanger to which temperature adjustment heat media F, G are circulated and supplied, and adjusts the temperature of the methane fermentation liquid D by exchanging heat between the temperature adjustment heat media F, G and the methane fermentation liquid D. The temperature adjustment unit 39 is not limited to one equipped with a heat exchanger, and various temperature adjustment devices can be applied as long as they are capable of adjusting the temperature of the second organic waste C2. The temperature adjustment execution unit is composed of the second pump P2, the temperature adjustment unit 39, the second circulation path 38, etc.

[0056] When the temperature detected by the second temperature detection sensor T2 is lower than the target temperature for methane fermentation, a control unit (not shown) or the like supplies a heating heat medium F as a temperature-adjusting heat medium to the temperature adjustment unit 39 through the heating heat medium circulation path 5 (see the thin line in FIG. 1) and operates the second pump P2. In this case, the methane fermentation liquid D in the methane fermentation tank 33 is taken out to the second circulation path 38 and supplied to the temperature adjustment unit 39, where the methane fermentation liquid D is heated by heat exchange with the heating heat medium F, and the heated methane fermentation liquid D is returned to the methane fermentation tank 33.

[0057] Conversely, when the temperature detected by the second temperature detection sensor T2 is higher than the target temperature for methane fermentation, a control unit (not shown) or the like supplies a cooling heat medium G, which serves as a heat medium for temperature adjustment, from a cold source (not shown) to the temperature adjustment unit 39 through the cooling heat medium circulation path 6 (see the dashed dotted line in FIG. 1), and operates the second pump P2. In this case, the methane fermentation liquid D in the methane fermentation tank 33 is taken out to the second circulation path 38 and supplied to the temperature adjustment unit 39, where the methane fermentation liquid D is cooled by heat exchange with the cooling heat medium G, and the cooled methane fermentation liquid D is returned to the methane fermentation tank 33.

[0058] In this way, the supply mode of the temperature adjustment heat medium to the temperature adjustment unit 39 can be freely switched between a heating state in which a heating heat medium F is supplied through the heating heat medium circulation path 5, as shown by the thin line in Fig. 1, and a cooling state in which a cooling heat medium G is supplied through the cooling heat medium circulation path 6, as shown by the dashed-dotted line in Fig. 1. When the temperature detected by the second temperature detection sensor T2 is lower than the target temperature for methane fermentation and the methane fermentation liquid D is to be heated, the state is switched to the heating state, and conversely, when the temperature detected by the second temperature detection sensor T2 is higher than the target temperature for methane fermentation and the methane fermentation liquid D is to be cooled, the state is switched to the cooling state.

[0059] The heating heat medium circulation path 5 is equipped with a heating section 31 used in the heating step and a temperature adjustment section 39 used in the temperature adjustment step. The target temperature for heating is generally set to a temperature higher than the target temperature for methane fermentation, and therefore the heating section 31 and the temperature adjustment section 39 are arranged in this order from the upstream side in the flow direction of the heating heat medium F. In this way, while the heating heat medium circulation path 5 is equipped with both the heating section 31 and the temperature adjustment section 39, heating to the target temperature for heating can be performed in the heating section 31 as well, and heating to the target temperature for methane fermentation can also be performed in the temperature adjustment section 39.

[0060] Incidentally, in the heating heat medium circulation path 5, the temperature adjustment unit 39 can be bypassed and the heating heat medium F can be circulated, as shown by the dotted line in Fig. 1. For example, when temperature adjustment is not performed by the temperature adjustment unit 39, the temperature adjustment unit 39 can be bypassed and the heating heat medium F can be returned to the generator 41.

[0061] Second Embodiment Since this second embodiment is an alternative embodiment of the heating unit 31 and the temperature adjustment unit 39 in the first embodiment, the following description will focus on the heating unit 31 and the temperature adjustment unit 39 with reference to Fig. 2. The other configurations are the same as those in the first embodiment, so the same reference numerals are used and the description will be omitted.

[0062] In the first embodiment, as shown in Fig. 1, the heat exchanger in the heating section 31 and the heat exchanger in the temperature adjustment section 39 are provided separately. In contrast to this, in the second embodiment, as shown in Fig. 2, the heat exchanger in the heating section 31 and the heat exchanger in the temperature adjustment section 39 are configured as a common heat exchanger 7. Incidentally, in Fig. 2, for the second organic waste C2 and the methane fermentation liquid D, the paths through which they flow are indicated by thick lines, and the paths through which they do not flow are indicated by thin lines. As with Fig. 1, for the heating heat medium F and the cooling heat medium G, the path for the heating heat medium F is indicated by thin lines, and the path for the cooling heat medium G is indicated by dashed dotted lines, and which path the heat medium flows through is distinguished by the arrows.

[0063] The common heat exchanger 7 is configured to be freely switchable by a control unit (not shown) or the like among a first heating state shown in Fig. 2(A), a second heating state shown in Fig. 2(B), and a cooling state shown in Fig. 2(C). In the first heating state (corresponding to the heating state) shown in Fig. 2(A), the common heat exchanger 7 functions as a heating unit 31, and in the second heating state and cooling state (corresponding to the temperature adjustment state) shown in Figs. 2(B) and 2(C), the common heat exchanger 7 functions as a temperature adjustment unit 39.

[0064] In order to supply the second organic waste C2 or the methane fermentation liquid D to the common heat exchanger 7, as shown on the left side of FIG. 2, a second supply path 36 for passing the second organic waste C2 and a second circulation path 38 for passing the methane fermentation liquid D are connected to the upstream side of the heat exchanger 7 in a state where they converge, and the second supply path 36 and the second circulation path 38 are connected to the downstream side of the heat exchanger 7 in a state where they branch off.

[0065] Upstream of the heat exchanger 7 (lower left side in each of FIGS. 2(A)-(C)), a third on-off valve K3 is disposed in the second supply path 36, and a fourth on-off valve K4 is disposed in the second circulation path 38. Downstream of the heat exchanger 7 (upper left side in each of FIGS. 2(A)-(C)), a fifth on-off valve K5 is disposed in the second supply path 36, and a sixth on-off valve K6 is disposed in the second circulation path 38.

[0066] In order to supply the heating heat medium F or the cooling heat medium G to the common heat exchanger 7, as shown on the right side in each of Figures 2(A) to 2(C), the heating heat medium circulation path 5, through which the heating heat medium F flows, and the cooling heat medium circulation path 6, through which the cooling heat medium G flows, are connected to the upstream side of the heat exchanger 7 in a state where they converge, and the heating heat medium circulation path 5 and the cooling heat medium circulation path 6 are connected to the downstream side of the heat exchanger 7 in a state where they branch off.

[0067] Upstream of the heat exchanger 7 (upper right in each of FIGS. 2A-2C), a seventh on-off valve K7 is disposed in the heating heat medium circulation path 5, and an eighth on-off valve K8 is disposed in the cooling heat medium circulation path 6. Downstream of the heat exchanger 7 (lower right in FIG. 2), a ninth on-off valve K9 is disposed in the heating heat medium circulation path 5, and a tenth on-off valve K10 is disposed in the cooling heat medium circulation path 6.

[0068] 2(A), when the heat exchanger 7 is made to function as the heating section 31, a control section (not shown) switches the third on-off valve K3, fifth on-off valve K5, seventh on-off valve K7, and ninth on-off valve K9 to an open state and switches the other on-off valves to a closed state, thereby switching to a first heating state. In the first heating state, the second organic waste C2 and the heating medium F are supplied to the heat exchanger 7, thereby causing heat exchange between the second organic waste C2 and the heating medium F, and heating the second organic waste C2.

[0069] When the heat exchanger 7 is made to function as the temperature adjustment unit 39 to heat the methane fermentation liquid D, a control unit (not shown) switches the fourth on-off valve K4, the sixth on-off valve K6, the seventh on-off valve K7, and the ninth on-off valve K9 to an open state and switches the other on-off valves to a closed state, thereby switching to a second heating state, as shown in Fig. 2(B). In the second heating state, the methane fermentation liquid D and the heating heat medium F are supplied to the heat exchanger 7, thereby causing heat exchange between the methane fermentation liquid D and the heating heat medium F, and heating the methane fermentation liquid D.

[0070] When the heat exchanger 7 is made to function as the temperature adjustment unit 39 to cool the methane fermentation liquid D, a control unit (not shown) switches the fourth on-off valve K4, the sixth on-off valve K6, the eighth on-off valve K8, and the tenth on-off valve K10 to an open state and switches the other on-off valves to a closed state, thereby switching to a cooling state, as shown in Fig. 2(C). In the cooling state, the methane fermentation liquid D and a cooling heat medium G are supplied to the heat exchanger 7, thereby causing heat exchange between the methane fermentation liquid D and the cooling heat medium G, and cooling the methane fermentation liquid D.

[0071] In this way, by separately setting a heating period in which the heat exchanger 7 is switched to the first heating state and functions as the heating section 31, and a temperature adjustment period in which the heat exchanger 7 is switched to the second heating state or the cooling state and functions as the temperature adjustment section 39, depending on various conditions such as required timing, it is possible to perform both the heating process using the heating section 31 and the temperature adjustment process using the temperature adjustment section 39 while using a common heat exchanger 7.

[0072] Third Embodiment This third embodiment adds a cooling step to the first embodiment, in which the second organic waste C2 heated in the heating step is cooled in a cooling section, so the following description will focus on the cooling step, with reference to Figure 3. The other components are the same as those in the first embodiment, so the same reference numerals will be used and a description will be omitted.

[0073] In the third embodiment, as shown in Fig. 3, a cooling step is carried out in which the second organic waste C2 heated in the heating step is cooled in a cooling section 40, and the heat exchanger in the heating section 31 and the heat exchanger in the cooling section 40 are provided as a common heat exchanger 8. Incidentally, in Fig. 3, as in Fig. 1, the path of the heating heat medium F is shown by a thin line, and the path of the cooling heat medium G is shown by a dashed dotted line, and which path the heat medium flows through is distinguished by the arrow.

[0074] A second supply path 36, through which the second organic waste C2 flows, is provided with, in order from the upstream side in the flow direction of the second organic waste C2, a heat exchanger 8 and a thermostatic bath 32. As in the first embodiment, a first pump P1 is provided in the second supply path 36 downstream of the thermostatic bath 32, and a first circulation path 37 branches off from the downstream side of the first pump P1.

[0075] The heat exchanger 8 is configured to be freely switched between a heating state shown in Fig. 3(A) and a cooling state shown in Fig. 3(B) by a control unit (not shown) etc. In the heating state shown in Fig. 3(A), the heat exchanger 7 functions as a heating unit 31, and in the cooling state shown in Fig. 3(B), the heat exchanger 8 functions as a cooling unit 40.

[0076] In order to supply the heating heat medium F or the cooling heat medium G to the heat exchanger 8, as shown in FIG. 3, a heating heat medium circulation path 5 through which the heating heat medium F flows and a cooling heat medium circulation path 6 through which the cooling heat medium G flows are connected to the upstream side of the heat exchanger 8 (to the left of the heat exchanger 8 in each of FIGS. 3(A) and 3(B)) in a confluence state, and the heating heat medium circulation path 5 and the cooling heat medium circulation path 6 are connected to the downstream side of the heat exchanger 8 (to the right of the heat exchanger 8 in FIG. 2) in a branch state. Incidentally, for the cooling heat medium circulation path 6, for example, the temperature adjustment unit 39 in FIG. 1 and the heat exchanger 8 in FIG. 3 are provided in parallel, so that the cooling heat medium G can be circulated and supplied to the heat exchanger 8. Furthermore, a cooling heat medium circulation path that circulates and supplies the cooling heat medium G from a cold source to the heat exchanger 8 can be provided in addition to the cooling heat medium circulation path 6 in FIG. 1.

[0077] An eleventh on-off valve K11 is disposed in the heating heat medium circulation path 5 and a twelfth on-off valve K12 is disposed in the cooling heat medium circulation path 6 on the upstream side of the heat exchanger 8 (on the left side of the heat exchanger 8 in each of FIGS. 3(A) and 3(B)). A thirteenth on-off valve K13 is disposed in the heating heat medium circulation path 5 and a fourteenth on-off valve K14 is disposed in the cooling heat medium circulation path 6 on the downstream side of the heat exchanger 8 (on the right side of the heat exchanger 8 in each of FIGS. 3(A) and 3(B)).

[0078] When the heat exchanger 8 is made to function as the heating section 31, as shown in Fig. 3(A), a control section (not shown) switches the eleventh on-off valve K11 and the thirteenth on-off valve K13 to an open state and switches the other on-off valves to a closed state, thereby switching to a heating state. In the heating state, the second organic waste C2 and the heating medium F are supplied to the heat exchanger 7, thereby causing heat exchange between the second organic waste C2 and the heating medium F, and heating the second organic waste C2.

[0079] When the heat exchanger 8 is made to function as the cooling section 40, as shown in Fig. 3(B), a control section (not shown) switches the twelfth on-off valve K12 and the fourteenth on-off valve K14 to an open state and switches the other on-off valves to a closed state, thereby switching to a cooling state. In the cooling state, the second organic waste C2 and the cooling heat medium G are supplied to the heat exchanger 7, thereby causing heat exchange between the second organic waste C2 and the cooling heat medium G and cooling the second organic waste C2.

[0080] In this way, by separately setting a heating period in which the heat exchanger 8 is switched to a heating state and functions as the heating section 31, and a cooling period in which the heat exchanger 8 is switched to a cooling state and functions as the cooling section 40, depending on various conditions such as required timing, it is possible to carry out both a heating process using the heating section 31 and a cooling process using the cooling section 40 while using the same heat exchanger 8. For example, a heating period can be set for the heating timing in which a heating process is carried out in which the second organic waste C2 is maintained at the heating target temperature for at least the heating set time, and a cooling period can be set for the cooling timing after the second organic waste C2 has been maintained at the heating target temperature for at least the heating set time.

[0081] In the third embodiment, a cooling process is carried out in which the second organic waste C2 heated in the heating process is cooled in the cooling section 40. Referring to FIG. 1, in the supply process, the first organic waste C1 is supplied to the methane fermentation tank 33 via the first supply path 35, and the second organic waste C2 that has undergone the cooling process is supplied to the methane fermentation tank 33 via the second supply path 36, and the organic wastes C1 and C2, including the waste that has undergone the cooling process, are supplied to the methane fermentation tank 33.

[0082] Here, when cooling the second organic waste C2 in the cooling unit 40, the temperature at which the target cooling temperature is set can be changed as appropriate. For example, the target cooling temperature can be set to a temperature equivalent to the target temperature for methane fermentation, using the target temperature for methane fermentation as a reference, or the target cooling temperature can be set so that the methane fermentation liquid D in the methane fermentation tank 33 reaches the target temperature for methane fermentation. In this way, when the target cooling temperature is set so that the methane fermentation liquid D in the methane fermentation tank 33 reaches the target temperature for methane fermentation, the second circulation path 38, the temperature adjustment unit 39, etc. in Figure 1 can be omitted.

[0083] [Another embodiment] Other embodiments of the present invention will be described below. Note that the configurations of the embodiments described below are not limited to being applied independently, but can also be applied in combination with the configurations of other embodiments.

[0084] (1) In the above embodiment, the first organic waste C1 is the primary settling sludge B1, and the second organic waste C2, which is more difficult to decompose than the first organic waste C1, is the excess sludge B3. However, the nature of the first organic waste and the second organic waste can be changed as appropriate. For example, the first organic waste can be food waste such as prepared food scraps, and the second organic waste can be oxidation ditch sludge or woody or plant biomass such as thinnings or rice straw.

[0085] (2) In the above embodiment, the organic waste is separated into first organic waste C1 and second organic waste C2 based on their hardiness, and the second organic waste C2 is the target of heating in the heating step. Alternatively, the organic waste may not be separated into first organic waste C1 and second organic waste C2, and some or all of the organic waste may be the target of heating in the heating step.

[0086] (3) In the above embodiment, the first organic waste C1 is supplied to the methane fermentation tank 33 via the first supply path 35, and the second organic waste C2 is supplied to the methane fermentation tank 33 via the second supply path 36, and the first organic waste C1 and the second organic waste C2 are separately supplied to the methane fermentation tank 33. Alternatively, for example, the first organic waste C1 can be mixed with the second organic waste C2 that has been subjected to the heating step, and the mixture can be supplied to the methane fermentation tank 33.

[0087] In the third embodiment, a cooling process is performed in which the second organic waste C2 heated in the heating process is cooled in the cooling section 40, so that the first organic waste C1 can be mixed with the second organic waste C2 before it is cooled in the cooling section 40, or the first organic waste C1 can be mixed with the second organic waste C2 after it has been cooled in the cooling section 40. [Explanation of symbols]

[0088] 7 Heat exchanger 8 Heat exchanger 31 Heating section 32 Constant temperature bath 33 Methane fermentation tank 39 Temperature adjustment section 40 Cooling section C1 First organic waste C2 Secondary organic waste D. Methane fermentation liquid E. Biogas F Heating medium G Cooling heat medium

Claims

1. A methane fermentation treatment method for producing biogas by subjecting organic waste to methane fermentation in a methane fermentation tank, comprising: a heating step of heating at least a portion of the organic waste; a supply step of supplying the organic waste, including that which has been subjected to the heating step, to the methane fermentation tank; In the heating step, a first heating step of heating the organic waste in a heating unit and supplying the organic waste to a thermostatic bath; a second heating step of maintaining the temperature of the organic waste in the thermostatic bath; and a third heating step of removing at least a portion of the organic waste from the thermostatic bath and returning it to the heating unit. The methane fermentation treatment method comprises maintaining the organic waste at a target heating temperature for a set heating time or longer.

2. The organic waste includes a first organic waste and a second organic waste that is more difficult to decompose than the first organic waste, In the heating step, the second organic waste is the object to be heated, 2. The methane fermentation treatment method according to claim 1, wherein in the supply step, the first organic waste is supplied to the methane fermentation tank after not undergoing the heating step, and the second organic waste is supplied to the methane fermentation tank after undergoing the heating step.

3. 3. The methane fermentation treatment method according to claim 1, further comprising a temperature adjustment step of adjusting the temperature of the methane fermentation liquid containing organic waste supplied to the methane fermentation tank to a target temperature for methane fermentation by a temperature adjustment unit.

4. the heating unit heats the organic waste by exchanging heat between the organic waste and a heating medium in a heat exchanger; the temperature adjustment unit adjusts the temperature of the methane fermentation liquid by exchanging heat between the methane fermentation liquid and a temperature adjustment heat medium in the heat exchanger, 4. The methane fermentation treatment method according to claim 3, wherein the heat exchanger is configured to be freely switched between a heating state in which the organic waste is heated by receiving the supply of the heating heat medium, and a temperature control state in which the methane fermentation liquid is temperature-controlled by receiving the supply of the temperature control heat medium.

5. a cooling step in which the organic waste heated in the heating step is cooled in a cooling section; In the supplying step, the organic waste, including that which has been subjected to the cooling step, is supplied to the methane fermentation tank; the heating unit heats the organic waste by exchanging heat between the organic waste and a heating medium in a heat exchanger; the cooling unit cools the organic waste by exchanging heat between the organic waste and a cooling heat medium in the heat exchanger; 3. The methane fermentation treatment method according to claim 1, wherein the heat exchanger is configured to be switchable between a heating state in which the organic waste is heated by receiving the heating heat medium, and a cooling state in which the organic waste is cooled by receiving the cooling heat medium.

6. In a methane fermentation treatment facility that produces biogas by subjecting organic waste to methane fermentation in a methane fermentation tank, a heating step execution unit that performs a heating step of heating at least a portion of the organic waste; a supply process execution unit that carries out a supply process of supplying the organic waste, including that which has been subjected to the heating process, to the methane fermentation tank, The heating process execution unit a first heating step execution unit that performs a first heating step of heating the organic waste in a heating unit and supplying the organic waste to a thermostatic bath; a second heating step execution unit that performs a second heating step of maintaining the temperature of the organic waste in the thermostatic bath; a third heating step performing unit that performs a third heating step of removing at least a portion of the organic waste from the thermostatic bath and returning it to the heating unit; A methane fermentation treatment facility that maintains the organic waste at a heating target temperature for a heating set time or longer by performing a first heating process by the first heating process execution unit, a second heating process by the second heating process execution unit, and a third heating process by the third heating process execution unit.

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