Methane fermentation treatment system and method for operating a methane fermentation treatment device

Abstract

To provide a technique capable of detecting and eliminating entanglement of residue in a methane fermentation facility, regardless of the type of the methane fermentation facility.SOLUTION: When the relationship between obtained values of power input density and solid concentration when an agitator 5 installed in a digestion tank 1 is operated at a predetermined rotation speed deviates from a predetermined correlation, a sediment entanglement elimination process, which includes a process of rotating the agitator 5 in reverse for a predetermined time, is repeatedly performed until the relationship between obtained values of power input density and solid concentration reaches the predetermined correlation.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a methane fermentation treatment system and a method for operating a methane fermentation treatment device. [Background technology]

[0002] Methane fermentation (anaerobic fermentation) is widely used to reduce the volume and generate energy from organic waste, such as sludge and biomass generated during wastewater treatment. Methane fermentation is a technology in which organic matter is stored under anaerobic conditions for a certain period of time, and the organic waste is decomposed by anaerobic microorganisms to produce biogas such as methane gas and carbon dioxide. This technology is widely used in wastewater treatment facilities and wastewater treatment facilities throughout Japan. Generally, the main methane fermentation equipment used for methane fermentation includes a methane fermentation tank that stores organic waste and performs methane fermentation, an agitator that mixes and agitates the methane fermentation liquid in the methane fermentation tank, and a heater that heats the methane fermentation liquid.

[0003] Conventionally, a method for understanding and managing the operating state of such methane fermentation equipment is described in Patent Document 1. Patent Document 1 describes a technology that uses the current value and vibration value of the agitator as indicators to detect tangling of residue in the agitator, and reverses the rotation to eliminate the tangling of residue (hereinafter sometimes referred to as residue tangling). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-139714 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the current value and vibration value of the agitator, which indicate sediment entanglement, vary depending on the methane fermentation equipment and the solids concentration of the methane fermentation liquid used, and these values ​​do not necessarily indicate the occurrence of sediment entanglement, so it may be difficult to solve the problem using the conventional methods described above.

[0006] Therefore, an object of the present invention is to provide a methane fermentation treatment system and a method for operating a methane fermentation treatment device that can detect and eliminate entanglement of screen residue in methane fermentation equipment, regardless of the type of methane fermentation equipment. [Means for solving the problem]

[0007] The methane fermentation treatment system disclosed in the present application comprises: a methane fermentation tank equipped with an agitator for subjecting organic waste to methane fermentation to generate biogas; a power input density acquisition means for acquiring a power input density of the agitator; a solid concentration acquisition means for acquiring a solid concentration in the methane fermentation tank; a control means; and The control means If the relationship between the power input density of the agitator and the acquired values ​​of the solids concentration when operated at a predetermined rotation speed deviates from the predetermined correlation, a process of reversing the rotation of the agitator for a predetermined time is repeatedly performed to eliminate sediment entanglement until the relationship between the acquired values ​​becomes the predetermined correlation.

[0008] According to the above configuration, if the acquired relationship between the power input density and the solids concentration deviates from a predetermined correlation, the sediment entanglement can be eliminated by repeating the process of reversing the rotation of the agitator. Generally, the correlation between the power input density of the agitator and the solids concentration is determined depending on the methane fermentation facility and the solids concentration set in the methane fermentation facility. Therefore, by detecting sediment entanglement based on this correlation, it is possible to detect and eliminate sediment entanglement in any methane fermentation facility.

[0009] In addition, in the methane fermentation treatment system disclosed in the present application, a storage means for storing the predetermined correlation, which is a correlation curve obtained in advance and showing the relationship between the power input density of the agitator when the agitator is operated at the predetermined rotation speed and the solid concentration of the methane fermentation liquor in the methane fermentation tank; and The control means If the relationship between the acquired values ​​is not on the correlation curve, the sediment entanglement dissolution process is repeatedly performed until the relationship between the acquired values ​​is on the correlation curve; After the screen residue entanglement elimination process, it may be determined whether or not the power input density of the agitator operated at the predetermined rotation speed is within an appropriate range.

[0010] With this configuration, if the relationship between the acquired power input density and solids concentration is not on the correlation curve, it is possible to detect and resolve the occurrence of sediment entanglement, and even if it is on the correlation curve, it is possible to determine whether it is within the appropriate range. This not only makes it possible to deal with sediment entanglement, but also makes it possible to determine whether the operating condition of the methane fermentation facility is normal.

[0011] In addition, in the methane fermentation treatment system disclosed in the present application, a solid-liquid separator for separating the organic waste to be sent to the methane fermentation tank into solid and liquid; an input concentration measuring means for measuring the solid concentration of the organic waste input into the methane fermentation tank; and The control means After the screen residue entanglement elimination process, if the power input density of the agitator operated at the predetermined rotation speed is outside an appropriate range, it is determined to be abnormal; If an abnormality is determined and the solid concentration measured by the input concentration measuring means is not within a predetermined concentration range, the abnormality may be determined to be an abnormality in the solid concentration, and the operation of the solid-liquid separation device may be adjusted.

[0012] With this configuration, even if the relationship between the power input density of the agitator and the acquired value of the solids concentration returns to the predetermined correlation after the sediment entanglement is resolved, other abnormalities related to sediment entanglement can be detected by determining whether the power input density is outside the appropriate range. Furthermore, if the solids concentration of the organic waste fed into the methane fermentation tank is not within the predetermined concentration range, it can be determined that the other abnormality related to sediment entanglement is an abnormality in the solids concentration, and the abnormality can be addressed by adjusting the operation of the solid-liquid separation device.

[0013] In addition, in the methane fermentation treatment system disclosed in the present application, further comprising a biogas generation amount detection means for detecting the amount of biogas generated in the methane fermentation tank; The control means After the screen residue entanglement elimination process, if the power input density of the agitator operated at the predetermined rotation speed is outside an appropriate range, it is determined to be abnormal; If the detected amount of biogas is not within a predetermined multiplication range relative to the organic waste being fed into the methane fermentation tank, the abnormality may be determined to be an abnormality in the amount of biogas, and the amount of organic waste being fed into the methane fermentation tank may be adjusted.

[0014] With this configuration, even if the relationship between the power input density of the agitator and the acquired value of the solids concentration returns to the predetermined correlation after the sediment entanglement is resolved, other abnormalities in the sediment entanglement can be detected by determining whether the power input density is outside the appropriate range. Furthermore, if the amount of biogas relative to the amount of organic waste being input is not within a predetermined multiplier range, it can be determined that an abnormality has occurred in the activity of the methanogenic bacteria, and the amount of organic waste input can be adjusted to address the abnormality.

[0015] In addition, in the methane fermentation treatment system disclosed in the present application, The methane fermentation tank further includes a temperature measuring means for measuring the temperature of the methane fermentation liquid in the methane fermentation tank. The control means After the screen residue entanglement elimination process, if the power input density of the agitator operated at the predetermined rotation speed is outside an appropriate range, it is determined to be abnormal; If the temperature in the methane fermentation tank is not uniform, the abnormality may be determined to be an abnormality in the temperature in the methane fermentation tank, and the rotation speed of the agitator may be increased.

[0016] With this configuration, even if the sediment entanglement is resolved and the relationship between the power input density of the agitator and the acquired value of the solids concentration returns to the predetermined correlation, other abnormalities in the sediment entanglement can be detected by determining whether the power input density is outside the appropriate range. Furthermore, if the temperature of the methane fermentation liquid is not uniform, it can be determined that there is an abnormality in the temperature inside the methane fermentation tank, and it becomes possible to respond to the abnormality by increasing the rotation speed of the agitator.

[0017] The operating method disclosed in the present application is A method for operating a methane fermentation treatment device for producing biogas by subjecting organic waste to methane fermentation in a methane fermentation tank equipped with an agitator, comprising: Obtaining the power input density of the agitator; Obtaining a solids concentration in the methane fermentation tank; If the relationship between the power input density and the acquired values ​​of the solids concentration of the agitator when operated at a predetermined rotation speed deviates from the predetermined correlation, a process for eliminating sediment entanglement, including a process for rotating the agitator in reverse for a predetermined time, is repeatedly performed until the relationship between the acquired values ​​becomes the predetermined correlation.

[0018] According to the above configuration, if the acquired relationship between the power input density and the solids concentration deviates from a predetermined correlation, the sediment entanglement can be eliminated by repeating the process of reversing the rotation of the agitator. Generally, the correlation between the power input density of the agitator and the solids concentration is determined depending on the methane fermentation facility and the solids concentration set in the methane fermentation facility. Therefore, by detecting sediment entanglement based on this correlation, it is possible to detect and eliminate sediment entanglement in any methane fermentation facility. [Effects of the Invention]

[0019] According to the present invention, it is possible to detect and eliminate entanglement of screen residue in any methane fermentation facility. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is an explanatory diagram showing a methane fermentation treatment system of the present invention. [Figure 2] FIG. 2 is a block diagram showing the functions of a controller of the methane fermentation treatment system of the present invention. [Figure 3] FIG. 1 is a graph showing a correlation curve showing the relationship between the power input density of the agitator of the present invention and the solid concentration of the methane fermentation liquor in the digester. [Figure 4] 10 is a flowchart of an abnormality detection process according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0022] The organic waste to be treated in the treatment method of the present invention includes sewage sludge, human waste sludge, agricultural village wastewater sludge, septic tank sludge, food waste (food biomass) such as kitchen garbage, lignocellulosic waste such as used paper and waste paper, agricultural residues, and livestock manure. These organic wastes may be treated individually or in combination. The treatment of sewage sludge will be described below as an example of the treatment target.

[0023] Figure 1 is a diagram showing a methane fermentation treatment system 100 of the present invention. As shown in Figure 1, the methane fermentation treatment system 100 includes a digester 1 as a methane fermenter that performs methane fermentation treatment on organic waste to produce biogas.

[0024] (Digester tank 1) The digester 1 is a tank that performs anaerobic fermentation treatment on sewage sludge (organic waste). The solids concentration (TS: Total Solids) of the raw sludge supplied to the digester 1 is preferably, for example, 3 to 10%. The digester 1 is operated at 30 to 45°C for a retention time of approximately 15 to 30 days in mesophilic fermentation treatment, and at 50 to 60°C for a retention time of approximately 7 to 20 days in thermophilic fermentation treatment. The digester 1 may be a steel tank or a concrete tank. Thermometers 11, 12, and 13 are attached to the digester 1 to measure the temperatures (sludge temperatures) of the upper, middle, and lower parts of the interior, respectively. The installation positions of thermometers 11, 12, and 13 are not particularly limited as long as they are immersed in the digested sludge (methane fermentation liquid) contained in digester 1, and may be set as appropriate. However, they are preferably installed at ±300 mm from a height 500 mm below the liquid level (storage height) of the digested sludge (methane fermentation liquid), ±300 mm from half the height of the liquid level (storage height) of the digested sludge (methane fermentation liquid), or ±500 mm from a height 1000 mm above the liquid level from the bottom of digester 1. A biogas flowmeter 18 is attached to biogas pipe 17, which discharges biogas generated in digester 1. In this embodiment, the amount of biogas, including by-products such as carbon dioxide, is used as an indicator, but this is not limited thereto. The amount of methane gas generated may also be determined by measuring the concentration of methane gas itself.

[0025] (Agitator 5) An agitator 5 is attached to the digester tank 1 to agitate the sewage sludge introduced into the digester tank 1. FIG. 1 shows the agitator 5 agitating the sludge with multiple stages of blades 5a (impellers) that rotate horizontally. The agitator 5 is driven by, for example, an electric motor 5b. The agitator 5 is generally located in the center of the digester tank 1 in a plan view. The flow of sludge in the digester tank 1 caused by the agitator 5 during normal operation is indicated by arrow D. During normal operation, the rotation of the blades 5a generates a downward flow in the center of the digester tank 1. The rotation direction (forward rotation) of the blades 5a that generates the sludge flow indicated by arrow D is illustrated in FIG. 1 with the symbol F. This downward flow spreads and reverses at the bottom of the digester tank 1, becoming an upward flow. Note that the agitator 5 (blade 5a) may be rotated in the reverse direction. When the agitator 5 is rotated in the reverse direction, the flow of sludge in the digester tank 1 becomes the opposite of that during normal operation. That is, when blades 5a are rotated in the direction opposite to arrow F (reverse rotation), an upward flow is generated in the center of digestion tank 1, and this upward flow spreads and reverses at the top of digestion tank 1, becoming a downward flow. Note that instead of the impeller-type agitator 5 used in this embodiment, other types of agitators, such as screw-type or draft tube agitators, may be used. Note that the power input density of the agitator in the present invention is the value obtained by dividing the power required to rotate the agitator by the volume of digested sludge in the digestion tank.

[0026] Digestion gas is generated in the digester tank 1 by anaerobic fermentation of the sewage sludge. The digestion gas is a gas (biogas) that is approximately 50-60% by volume methane and approximately 40-50% by volume carbon dioxide. The generated digestion gas is extracted from the digester tank 1 and used as fuel for heating the digester tank 1 or as fuel for power generation equipment (not shown). In other words, by subjecting the sewage sludge to anaerobic fermentation treatment, the energy contained in the sewage sludge can be recovered as digestion gas (gas energy).

[0027] (Sludge loading device 2) The sludge feeder 2 is used to feed sludge into the digester tank 1. The sludge feeder 2 has a solid-liquid separator 21, a pretreatment tank 22, a sludge feed pump 23, and a supply pipe 24 that connects the sludge feed pump 23 to the digester tank 1. A supply sludge concentration meter 25 and a sludge flow meter 26 are attached to the supply pipe 24.

[0028] The solid-liquid separator 21, for example, performs a step of separating a portion of the liquid from the sludge introduced from the previous stage. The solid-liquid separator 21 sends the sludge that has been subjected to solid-liquid separation treatment downstream to the pretreatment tank 22. The solid-liquid separator 21 may be, for example, a mechanical thickener such as a belt type, centrifugal type, or screw type, but is not limited to these as long as it can adjust the solid concentration of the sludge.

[0029] The sludge that has been subjected to solid-liquid separation in the solid-liquid separator 21 is sent to the pretreatment tank 22. There are no particular limitations on the pretreatment tank 22 as long as it has the function of storing the sludge that has been subjected to solid-liquid separation, and an agitator may be provided to prevent the sludge that has been subjected to solid-liquid separation in the pretreatment tank 22 from settling. Furthermore, a solubilization treatment may be performed to facilitate the promotion of the digestion treatment in the downstream stage. As a solubilization method, heating is preferred from the viewpoint of effectively utilizing the methane generated by digestion, but various means such as ultrasound, application of high-voltage pulses, introduction of high-pressure gas, supply of ozone, pulverization, addition of acid, addition of alkali, or addition of enzymes may also be used.

[0030] Sewage sludge (organic waste) discharged from the pretreatment tank 22 is fed into the digester tank 1 through a supply pipe 24 by the operation of a sludge supply pump 23. A supply sludge concentration meter 25 measures the solids concentration of the sewage sludge passing through the supply pipe 24. The supply sludge concentration meter 25 may be installed in the supply pipe 24 between the sludge supply pump 23 and the digester tank 1, as shown in FIG. 1, or may be installed inside the pretreatment tank 22 (not shown). Furthermore, a liquid level meter (not shown) may be installed in the digester tank 1 instead of the sludge flow meter 26 that detects the amount of sludge fed into the digester tank 1.

[0031] The supply sludge concentration meter 25 may be an ultrasonic concentration meter, a microwave concentration meter, a near-infrared concentration meter, or the like. In this embodiment, an in-line type is used as an example, and the entire amount of supplied sludge passes through the supply sludge concentration meter 25. Furthermore, the solid concentration of sewage sludge (organic waste) may be measured manually (such as by collecting and weighing sludge and calculating the solid concentration from the difference in mass before and after drying) in addition to measurement by the supply sludge concentration meter 25. The sludge flow meter 26 may be an ultrasonic type, an electromagnetic type, or the like.

[0032] (Warming device 3) The heating device 3 is a device for heating the digested sludge (methane fermentation liquid) introduced into the digester 1. The heating device 3 includes a heat exchanger 3a as a heater, a circulation pump 31, a return pipe 32, and a circulating sludge concentration meter 33 installed in the return pipe 32. The heat exchanger 3a is an indirect heat exchanger that heats the digested sludge. Hot water is supplied to the heat exchanger 3a from a hot water source such as a boiler (not shown). The digested sludge (methane fermentation liquid) withdrawn from the digester 1 by the operation of the circulation pump 31 is heated by indirect contact with the hot water in the heat exchanger 3a, and then returned to the digester 1 from the top of the digester 1 via the return pipe 32 that connects the heat exchanger 3a to the upper and lower parts of the digester 1. In this way, since the sludge in the digestion tank 1 passes through the return pipe 32, the circulating sludge concentration meter 33 installed in the return pipe 32 functions as a solids concentration measuring means for measuring the solids concentration of the sludge in the digestion tank 1. Note that the configuration for measuring the solids concentration of the sludge in the digestion tank 1 is not limited to this. For example, the solids concentration of the sludge in the digestion tank 1 may be measured manually (such as by collecting and weighing the sludge and calculating the solids concentration from the difference in mass before and after drying).

[0033] (Extraction device 8) The extraction device 8 is used to extract sludge from the bottom of the digestion tank 1 to the outside of the tank. The extraction device 8 is composed of an extraction pump 81 and an extraction pipe 82 connected to the extraction pump 81. Note that the sludge may be extracted from the bottom of the digestion tank 1 by gravity flow, for example, by using a telescopic valve.

[0034] (Controller 6) The controller 6, which serves as a control means, automatically controls the operation of the sludge supply pump 23, agitator 5, circulation pump 31, withdrawal pump 81, and solid-liquid separator 21. The controller 6 is connected to each of these devices for data communication, and by transmitting control signals, automatically controls the operation of feeding sludge into the digester tank 1, the operation of the agitator 5, the circulation operation for heating the digested sludge in the digester tank 1, and the operation of withdrawing sludge from the digester tank 1 to the outside. The controller 6 is also connected to a supply sludge concentration meter 25, a sludge flow meter 26, a biogas flow meter 18, and thermometers 11-13 for data communication, and receives output signals from these devices. Although not shown, a sensor (e.g., an ultrasonic displacement meter) is attached to the digester tank 1 to measure the height of sediment accumulated at the bottom of the digester tank 1, and the output signal from this sensor is also received by the controller 6.

[0035] The functions of the controller 6 will be described in more detail with reference to Fig. 2. Fig. 2 is a block diagram showing the functions of the controller 6. As shown in Fig. 2, the controller 6 has a memory unit 61, a power input density determination unit 62, a solid concentration determination unit 63, an agitator control unit 64, an abnormality determination unit 65, a solid-liquid separator control unit 66, an input amount adjustment unit 67, and a temperature determination unit 68.

[0036] The memory unit 61 stores judgment criteria for making various judgments, which will be described later. Specifically, as will be described later with reference to Fig. 3, the memory unit 61 stores a correlation curve, which has been acquired in advance and which shows the relationship between the power input density of the agitator 5 when the agitator 5 is operated at a predetermined rotation speed and the solids concentration of the digested sludge (methane fermentation liquid) in the digester tank 1. In the memory unit 61, appropriate ranges for the power input density of the agitator 5 and the digested sludge in the digester tank 1 are set in this correlation curve, and this is used for various judgments.

[0037] The power input density determination unit 62 has a function of acquiring the power input density from the agitator 5 and determining whether the acquired power input density is within an appropriate range set in the correlation curve. The agitator control unit 64 controls the driving of the electric motor 5b of the agitator 5, and maintains or changes the rotation speed of the blades 5a, changes the rotation direction, etc. The solid concentration determination unit 63 has a function of acquiring the solid concentration from the circulating sludge concentration meter 33 and determining whether the acquired solid concentration is within an appropriate range set in the correlation curve.

[0038] The abnormality determination unit 65 determines whether or not there is an abnormality in the condition of the digested sludge in the digester tank 1 based on the determination results of the power input density determination unit 62 and the solid concentration determination unit 63. The solid-liquid separator control unit 66 adjusts the operation of the solid-liquid separator 21 if the solid concentration measured by the supply sludge concentration meter 25 is not within a predetermined concentration range. The input amount adjustment unit 67 adjusts the amount of sewage sludge input to the digester tank 1 if the amount of biogas detected by the biogas flow meter 18 relative to the amount of sewage sludge (organic waste) input to the digester tank 1 measured by the sludge flow meter 26 is not within a predetermined ratio range. The temperature determination unit 68 controls the agitator control unit 64 to drive the electric motor 5b of the agitator 5 to increase the rotation speed of the agitator 5 if the temperature in the digester tank 1 is not uniform based on signals obtained from the thermometers 11 to 13.

[0039] In this embodiment, the controller 6 includes a so-called computer, including a CPU (Central Processing Unit), an EEPROM (Electrically Erasable and Programmable Read Only Memory) that rewritably stores programs executed by the CPU and data used in these programs, and a RAM (Random Access Memory) that temporarily stores data when the programs are executed. The above-mentioned functional units of the controller 6 are constructed by the cooperation of these hardware and the programs in the EEPROM. In other words, the programs cause the computers included in the methane fermentation processing system 100 to execute the processes included in the various programs, thereby controlling the operation of the methane fermentation equipment (methane fermentation processing device) included in the methane fermentation processing system 100. In this way, the processes and operations of the methane fermentation processing system 100 can be replaced with programs or operating methods for the methane fermentation processing device. The number of computers included in the controller 6 is not limited to one, and functions may be distributed across multiple computers. In other words, there may be multiple controllers. Note that the control performed by the controller 6 (for example, changing the operating conditions) may be performed manually by an operator without using the controller 6 or without providing the controller 6 at all. Furthermore, measurements of the temperature, concentration of the supplied sludge, concentration of the circulated sludge, sludge flow rate, gas flow rate, etc. may be performed manually by an operator, etc. In other words, the operator may control the agitator, various pumps, solid-liquid separator, etc. based on the values ​​of the measuring instruments.

[0040] (for a given correlation) The predetermined correlation indicates a positive correlation between the power input density of the agitator and the solids concentration of the digested sludge in the digester. As the solids concentration of the digested sludge in the digester increases, the power required for agitation also increases accordingly, leading to a positive correlation between the power input density of the agitator and the solids concentration of the digested sludge in the digester. In this embodiment, as shown in FIG. 3, a pre-obtained approximate curve (correlation curve) plotted between the power input density and the solids concentration is used as the predetermined correlation, but is not limited to this. For example, a numerical range of the solids concentration of the digested sludge (methane fermentation liquid) in the digester 1 corresponding to a predetermined power input density of the agitator 5 may be determined, and if the measured solids concentration of the digested sludge (methane fermentation liquid) in the digester 1 does not fall within the numerical range corresponding to the measured power input density of the agitator 5, it may be determined that the correlation is not satisfied. In addition, a numerical range of the power input density of the agitator 5 corresponding to a predetermined solids concentration of the digested sludge (methane fermentation liquid) in the digestion tank 1 may be determined, and if the measured power input density of the agitator 5 is not within the numerical range corresponding to the measured solids concentration of the digested sludge (methane fermentation liquid) in the digestion tank 1, it may be determined that there is no correlation.

[0041] The correlation curve stored in the memory unit 61 will be described in detail with reference to FIG. 3. This correlation curve is data showing the relationship between the power input density of the agitator 5 and the solids concentration of the digested sludge (methane fermentation liquid) in the digester 1, obtained in advance by operating the methane fermentation treatment system 100 or a methane fermentation facility including the same type of digester 1. This correlation curve is data obtained by operating the agitator 5 to maintain the rotation speed. Therefore, this correlation curve shows how the power input density required to maintain the rotation speed of the agitator 5 changes when the solids concentration of the digested sludge in the digester 1 changes. That is, as shown in FIG. 3, correlation curve C shows that the power input density of the agitator 5 required to maintain the rotation speed increases as the solids concentration of the digested sludge increases, and the power input density of the agitator 5 required to maintain the rotation speed decreases as the solids concentration of the digested sludge decreases. For example, the rotation speed is preferably maintained within a range of 10 to 20 rpm.

[0042] An optimum range is set for the correlation curve in the memory unit 61. The optimum range S is determined by determining the desired solids concentration range S based on the sludge digestion efficiency and the amount of biogas generated, and the corresponding optimum range P for the power input density is determined. For example, the upper limit of the optimum solids concentration range S is preferably 6.0%, and the lower limit of the optimum solids concentration range S is preferably 1.0%. Furthermore, the optimum range S may be set to plus or minus 1.0 points relative to the design solids concentration set during the selection of the agitator and the design of the methane fermentation treatment system. Specifically, when the design solids concentration is 3.0%, the optimum range S is 2.0 to 4.0%. For example, the solids concentration of the sludge discharged from the solid-liquid separator 21 is adjusted by the controller 6 (solid-liquid separator control unit 66) so that the solids concentration falls within the optimum range S set for the correlation curve. When sewage sludge is fermented in the digester 1, the solid matter concentration of the digested sludge becomes approximately half of that of the raw sludge due to the decomposition action of methane fermentation bacteria. The solid matter concentration of the sewage sludge detected by the supply sludge concentration meter 25 is preferably, for example, 3 to 10%. Furthermore, for example, the upper limit of the appropriate range P of power input density is 10.0 W / m 3 is preferred, and 5.0 W / m 3 The lower limit of the appropriate range P of the power input density is 0.2 W / m 3 is preferred, and 0.5W / m 3 is more preferred.

[0043] When the methane fermentation treatment system 100 is operated under the same conditions as those used to output the correlation curve, and there is no sediment entanglement or other abnormality, the values ​​of the power input density and solids concentration will both be on the correlation curve and within the appropriate ranges set for the correlation curve. That is, the power input density is within the appropriate range P, and the solids concentration is within the appropriate range S. Here, "on the correlation curve" does not necessarily mean that the relationship between the power input density and the solids concentration exactly matches any point on the correlation curve. For example, it may be within a range of ±20% of the power input density on the correlation curve, or within a range of ±10% of the solids concentration on the correlation curve. The correlation curve may also be configured to be changeable for each facility. In this case, it is preferable that the memory unit 61 stores a correlation curve for each facility, and it is preferable to change the correlation curve to suit the facility.

[0044] For example, if sediment entanglement occurs, an additional load is placed on the agitator 5, causing the power input density to fall outside the appropriate range P, and further causing the relationship between the power input density and the solids concentration value to deviate from the correlation curve. In such a case, the controller 6 determines that sediment entanglement has occurred, and executes control to eliminate the sediment entanglement (seed entanglement elimination process), which includes a process of operating the agitator 5 in reverse rotation.

[0045] Furthermore, for example, if both the power input density and the solid concentration values ​​are outside the appropriate range, i.e., if the power input density is outside the appropriate range P and the solid concentration is outside the appropriate range S, the controller 6 determines that another abnormality has occurred in the methane fermentation treatment equipment even if the relationship between the power input density and the solid concentration values ​​is on a correlation curve.

[0046] In this way, the methane fermentation treatment system 100 can detect the causes of multiple abnormalities based on the correlation curve and the appropriate range P of power input density and the appropriate range S of solids concentration set in the correlation curve. Specific examples of the above-mentioned other abnormalities other than sediment entanglement and how to deal with them will be described with reference to the flowchart in Figure 4.

[0047] Next, a flowchart of the abnormality detection process executed by the controller 6 in the methane fermentation treatment system 100 will be described with reference to Fig. 4. First, the controller 6 determines whether the power input density to the agitator 5 is within the appropriate range P (S1). Specifically, the controller 6 acquires the current power input density from the agitator 5 and determines whether the value is within the appropriate range P set in the stored correlation curve. If the power input density is within the appropriate range P (S1: YES), the controller 6 repeats step S1, for example, at predetermined time intervals.

[0048] On the other hand, if the power input density is not within the appropriate range P (S1: NO), the controller 6 measures the solids concentration of the digested sludge in the digestion tank 1 (S2). Specifically, the controller 6 acquires the current solids concentration of the digested sludge in the digestion tank 1 measured by the circulating sludge concentration meter 33 (S3). The controller 6 then determines whether the relationship between the acquired power input density and the solids concentration is on a correlation curve (S3). If it is determined that the relationship is not on the correlation curve (S3: NO), the controller 6 determines that sediment entanglement has occurred in the agitator 5 and executes a sediment entanglement dissolution process (S4). In this way, the controller 6 measures the solids concentration when the power input density is outside the appropriate range, and executes a sediment entanglement dissolution process when the power input density is outside the correlation curve. The sediment entanglement dissolution process includes reverse rotation of the agitator 5 to dissolve sediment entanglement.

[0049] For example, in the screen residue entanglement process, the controller 6 first stops the forward rotation, waits for a certain period of time, then rotates the agitator 5 in the reverse direction at half the forward rotation speed, stops the agitator 5 for a certain period of time, and then starts the forward rotation again. The controller 6 then transitions the process to step S3, where it again determines whether the relationship between the power input density and the solids concentration is on the correlation curve. If the relationship is not yet on the correlation curve, the screen residue entanglement process of step S4 is repeated. Thus, if the relationship between the power input density and the solids concentration is not on the correlation curve, the screen residue entanglement process, including the process of rotating the agitator 5 in the reverse direction for a predetermined time, is repeatedly executed until the relationship is on the correlation curve. This repetition includes a single execution of the screen residue entanglement process. In other words, it also includes the case where the relationship is on the correlation curve after only the first execution of the screen residue entanglement process. Although not shown, the power input density is acquired again when transitioning to step S3. The solids concentration may or may not be measured when transitioning to this process. For example, the screen residue entanglement dissolution process may be configured to measure the solid matter concentration if a specific time has elapsed since the previous measurement. That is, the previously measured solid matter concentration may be reused. Then, in step S3, the controller 6 again determines whether the relationship between the power input density and the solid matter concentration is on the correlation curve. In this way, after the screen residue entanglement process, it is again determined whether the relationship between the power input density and the solid matter concentration is on the correlation curve. The reverse rotation speed of the agitator 5 is not particularly limited and can be set as appropriate, but is preferably 3 to 10 rpm, more preferably 5 to 8 rpm. It may also be 1 / 2 to 1 / 3 rpm of the rotation speed when the agitator 5 is operated at a predetermined rotation speed, more preferably 1 / 2 rpm. The screen residue entanglement dissolution process may include a process of rotating the agitator 5 in the reverse direction, and is not limited to the above process. For example, the screen residue entanglement dissolution process may include a process of rotating the agitator 5 in the reverse direction multiple times for a predetermined period of time. In this embodiment, the screen residue entanglement dissolution process is performed under the condition that the power input density is not within the appropriate range (NO in step S1), but is not limited to this.

[0050] If it is determined in step S3 that the relationship between the power input density and the solids concentration is on the correlation curve (S3: YES), the controller 6 determines that there is no sediment entanglement (the sediment entanglement has been resolved), and determines whether the values ​​of the power input density and the solids concentration are both within appropriate ranges to determine whether there are any other abnormalities (S5). That is, it is determined whether the power input density is within appropriate range P and whether the solids concentration is within appropriate range S. Therefore, it is determined again whether the power input density is within appropriate range P. Note that, because the power input density and the solids concentration are on the correlation curve, it is determined whether both are within the appropriate range or neither are outside the appropriate range. If both are within the appropriate range (S5: YES), the controller 6 determines that there are no other abnormalities other than sediment entanglement, and proceeds to step S1.

[0051] On the other hand, if neither the power input density nor the solids concentration is within the appropriate range (S5: NO), the controller 6 determines that there is an abnormality other than entanglement of screen residue (S6). The controller 6 then determines whether the input sludge concentration is within the control value (S7). That is, the controller 6 receives a signal from the input sludge concentration meter 25 and determines whether the solids concentration of the sewage sludge being input to the digester 1 is within the control value. As described above, the solids concentration of the sewage sludge input to the digester 1 should be within plus or minus one point of the expected solids concentration of the sewage sludge after solid-liquid separation, which was set when the solid-liquid separation device 21 for solid-liquid separation of the sewage sludge to be input to the digester 1 was selected. For example, if the expected solids concentration is 4.0%, the control value range is 3.0 to 5.0%. If the input sludge concentration is not within the control value (S7: NO), the controller 6 determines that the abnormality determined in step S6 includes an abnormality in the solids concentration (S8). The controller 6 then controls the operation of the solid-liquid separator 21 to adjust the moisture content of the sewage sludge discharged from the solid-liquid separator 21 (S9). The operation of the solid-liquid separator 21 is not particularly limited. However, if the input sludge concentration is higher than the control value, the controller 6 may perform operations such as reducing the amount of polymer coagulant or inorganic coagulant added to the sewage sludge before solid-liquid separation, increasing the belt speed in the case of a belt-type solid-liquid separator, reducing the rotation speed of the screen, inner cylinder, or outer cylinder in the case of a centrifugal solid-liquid separator, or increasing the rotation speed of the screw shaft in the case of a screw-type solid-liquid separator. If the input sludge concentration is lower than the control value, the controller 6 may perform operations such as increasing the amount of polymer coagulant or inorganic coagulant added, reducing the belt speed in the case of a belt-type solid-liquid separator, increasing the rotation speed of the screen, inner cylinder, or outer cylinder in the case of a centrifugal solid-liquid separator, or reducing the rotation speed of the screw shaft in the case of a screw-type solid-liquid separator.

[0052] If the input sludge concentration is within the control value (S7: YES), the controller 6 determines whether the biogas generation unit is equal to or greater than the control value (control value range) (S10). That is, the controller 6 receives a signal from the biogas flow meter 18 and acquires the amount of biogas being generated. The controller 6 also receives a signal from the sludge flow meter 26 and acquires the amount of sewage sludge being input. Then, the controller 6 calculates the biogas generation magnification based on these. The biogas generation magnification is the value obtained by dividing the amount of biogas generated by the amount of sewage sludge (organic waste) input into the digester 1 (methane fermenter), and is expressed in units of no unit or Nm 3 / m 3 , Nm 3 h -1 / m 3 h -1 The lower limit of the control value for the biogas generation ratio is preferably 5 times, more preferably 10 times, and even more preferably 15 times. The lower limit of the control value for the biogas generation unit is 400 Nm 3 / t-VS is preferred, 500Nm 3 / t-VS is more preferable. VS is an abbreviation for Volatile Solids, and is called loss on ignition. It is the amount of material that volatilizes when the evaporation residue remaining after evaporating the material to be treated to dryness at 105 to 110°C is further incinerated at 600°C. If the biogas generation magnification is not equal to or greater than the control value (S10: NO), the controller 6 determines that an abnormality in the amount of biogas is included in the abnormalities determined in step S6 (S11). For example, an abnormality in the amount of biogas may be caused by an abnormality such as a decrease in the activity of methanogens or the progression of their death. The controller 6 then controls the sludge supply pump 23 to temporarily stop or reduce the amount of sludge being fed to the digester 1, thereby adjusting the input load (S12). Since excessive generation of biogas is not a problem, it is preferable, but not limited to, not to detect this as an abnormality. In addition, instead of the biogas generation multiplier, it may be, for example, a value obtained by dividing the amount of biogas by the amount of solids (Total Solid: TS) input into the digester 1, or a value obtained by dividing the amount of methane gas in the biogas by the amount of sewage sludge (organic waste) or the amount of solids in the sewage sludge (organic waste).

[0053] If the biogas generation magnification is equal to or greater than the control value (within the control value range) (S10: YES), the controller 6 receives signals from the thermometers 11-13 and determines whether the temperature in the digester 1 is uniform (S13). If the temperature in the digester 1 is not uniform (S13: NO), the controller 6 determines that the abnormalities determined in step S6 include an abnormality in the temperature of the methane fermentation liquid in the methane fermentation tank (S14). The controller 6 then controls the agitator 5 to increase the rotation speed for a predetermined time (S15). If the temperature in the digester 1 is uniform (S13: YES), the controller 6 proceeds to step S5. Whether the temperature inside the digester 1 is uniform may be determined as not being uniform if there is a difference between the temperatures acquired by each of the thermometers 11-13, or may be determined as not being uniform if the absolute value of the difference between the highest and lowest temperatures acquired by each of the thermometers 11-13 is 1 point or more, and may be determined as being uniform if that absolute value is less than 1 point. Furthermore, it may be determined as not being uniform immediately when the absolute value of the difference between the highest and lowest temperatures acquired by each of the thermometers 11-13 becomes 1 point or more, or may be determined as not being uniform after that absolute value remains 1 point or more for a predetermined period of time, for example, 3 days or more. Furthermore, when the rotation speed of the agitator 5 is increased for a predetermined time, the rotation speed may be increased for a preset time, for example, for one hour or more, and then controlled to be returned to the predetermined rotation speed, or the temperature may be measured with the thermometers 11 to 13 and determined to be uniform as soon as the absolute value of the difference between the highest and lowest temperatures becomes less than one point, or when this value remains less than one point for a certain period of time, for example, one day or more. The degree to which the rotation speed of the agitator 5 is increased is not particularly limited and may be set as appropriate, but is preferably 1.2 to 3 times, and more preferably 1.5 to 2 times the predetermined rotation speed.

[0054] The priority order of the determinations in steps S7, S10, and S13 is not limited to this, and any of the determinations may be performed first.

[0055] (effect) The methane fermentation treatment system 100 of this embodiment includes a digester 1 (methane fermenter) equipped with an agitator 5 that generates biogas by subjecting organic waste to methane fermentation, and a controller 6. The controller 6 acquires the power input density of the agitator 5. The controller 6 acquires the solids concentration in the digester 1 based on a signal from a circulating sludge concentration meter 33. If the relationship between the power input density of the agitator 5 and the acquired value of the solids concentration when operated at a predetermined rotation speed deviates from a predetermined correlation, the controller 6 repeatedly executes a screen entanglement elimination process, which includes a process of rotating the agitator 5 in the reverse direction for a predetermined time, until the relationship between the power input density and the acquired value of the solids concentration achieves the predetermined correlation.

[0056] The methane fermentation treatment system 100 provides the following effects.

[0057] If the obtained relationship between the power input density and the solids concentration deviates from the predetermined correlation, the sediment entanglement can be eliminated by repeating the process of reversing the rotation of the agitator 5. Generally, the correlation between the power input density of the agitator and the solids concentration is determined according to the methane fermentation facility and the solids concentration set in the methane fermentation facility, so by detecting sediment entanglement based on this correlation, it becomes possible to detect and eliminate sediment entanglement in any methane fermentation facility.

[0058] The methane fermentation treatment system 100 also stores a predetermined correlation curve, which indicates the relationship between the power input density of the agitator 5 and the solids concentration in the digester 1 in the methane fermentation tank when the agitator 5 is operated at a predetermined rotational speed. If the relationship between the acquired values ​​of the power input density and the solids concentration deviates from the correlation curve, the controller 6 may repeatedly execute a screen entanglement resolution process until the relationship between these acquired values ​​reverts to the correlation curve. After the screen entanglement resolution process, the controller 6 may determine whether the power input density of the agitator 5 operated at the predetermined rotational speed is within an appropriate range. This configuration detects and resolves the occurrence of screen entanglement when the acquired relationship between the power input density and the solids concentration is not on the correlation curve, and even if it is on the correlation curve, it can determine whether it is within the appropriate range. This not only enables the system to address screen entanglement but also enables the system to determine whether the methane fermentation facility is operating normally.

[0059] The methane fermentation treatment system 100 further includes a solid-liquid separator 21 that separates organic waste sent to the digester 1 into solid and liquid phases, and a supply sludge concentration meter 25 (input concentration measuring means) that measures the solid concentration of the sewage sludge (organic waste) fed to the digester 1. After the screen residue entanglement removal process, the controller 6 determines that an abnormality has occurred if the power input density of the agitator 5 operating at a predetermined rotation speed is outside of the appropriate range. If an abnormality has been determined and the solid concentration measured by the supply sludge concentration meter 25 is not within the predetermined concentration range, the controller 6 may determine that the abnormality is an abnormality in the solid concentration and adjust the operation of the solid-liquid separator 21. With this configuration, even if the relationship between the power input density of the agitator 5 and the acquired solid concentration returns to the predetermined correlation after the screen residue entanglement is removed, other abnormalities related to screen residue can be detected by determining whether the power input density is outside of the appropriate range. Furthermore, if the solids concentration of the sewage sludge fed into the digestion tank 1 is not within the specified concentration range, it can be determined that other abnormalities in the sludge entanglement are due to an abnormality in the solids concentration, and the abnormality can be addressed by adjusting the operation of the solid-liquid separator 21.

[0060] The methane fermentation treatment system further includes a biogas flowmeter 18 (biogas generation amount detection means) that detects the amount of biogas generated in the digester 1. After the screen residue entanglement removal process, the controller 6 determines that an abnormality exists if the power input density of the agitator 5, which is operated at a predetermined rotation speed, is outside of an appropriate range. If the detected amount of biogas is not within a predetermined multiplier range relative to the sewage sludge introduced into the methane fermentation tank, the controller 6 may determine that the abnormality is an abnormality in the amount of biogas and adjust the amount of sewage sludge introduced into the digester 1. With this configuration, even if the relationship between the power input density of the agitator 5 and the acquired value of the solids concentration returns to a predetermined correlation after the screen residue entanglement is removed, other abnormalities related to screen residue can be detected by determining whether the power input density is outside of the appropriate range. Furthermore, if the amount of biogas relative to the introduced sewage sludge is not within a predetermined multiplier range, it can be determined that an abnormality exists in the activity of methanogenic bacteria, and the amount of sewage sludge introduced can be adjusted to address the abnormality.

[0061] The methane fermentation treatment system further includes thermometers 11-13 (temperature measurement means) for measuring the temperature of the digested sludge in the digester 1. After the screen residue entanglement treatment, the controller 6 determines that an abnormality exists if the power input density of the agitator 5, which is operated at a predetermined rotation speed, is outside the appropriate range. If the temperature in the digester 1 is not uniform, the controller 6 may determine that the abnormality is an abnormality in the temperature in the digester 1 and increase the rotation speed of the agitator 5. With this configuration, even if the relationship between the power input density of the agitator 5 and the acquired value of the solids concentration returns to the predetermined correlation after the screen residue entanglement is resolved, other abnormalities related to screen residue entanglement can be detected by determining whether the power input density is outside the appropriate range. Furthermore, if the temperature of the digested sludge is not uniform, it can be determined that an abnormality exists in the temperature in the digester 1, and the abnormality can be addressed by increasing the rotation speed of the agitator 5.

[0062] The present invention is not limited to the above-described embodiment. The configurations of the above-described embodiment can be appropriately combined, and various modifications can be made to the above-described embodiment. For example, the above-described embodiment can be modified as follows.

[0063] For example, in FIG. 4, the determination processes of steps S7, S10, and S13 are not necessarily required, and any one or more of these may be included, or none of them may be included. Furthermore, in this embodiment, if the controller 6 determines that an abnormality exists in the solid matter concentration after the determination of step S7 (S8), the controller 6 may, for example, notify the facility manager or the like of the details of the abnormality. Similarly, the controller 6 may also notify the facility manager or the like of the details of the abnormality if an abnormality is determined in steps S11 and S14. Furthermore, in the flowchart of FIG. 4, any step may be omitted. For example, if the relationship between the acquired values ​​of the power input density and the solid matter concentration in step S3 is on a correlation curve, the controller 6 may proceed to step S1. That is, the controller 6 does not need to perform the processes from step S5 onwards. [Industrial Applicability]

[0064] The method for operating a methane fermentation treatment device and the methane fermentation treatment device of the present invention can be used to decompose and treat various organic wastes, such as sewage sludge, human waste sludge, agricultural village wastewater sludge, septic tank sludge, food waste (food biomass) including raw garbage, construction waste, lignocellulosic wastes such as used paper and discarded paper, agricultural residues, and livestock manure, and to generate methane using the decomposed products as a raw material. [Explanation of symbols]

[0065] 1: Digestion tank (methane fermentation tank) 2: Sludge injection device 3: Warming device 3a: Heat exchanger 4: Return piping 5: Stirrer 5a: Feather 5b: Electric motor 6: Controller 8: Extraction device 11・12・13:Thermometer 17: Biogas pipe 18: Biogas flow meter 21:Solid-liquid separator 22: Pre-treatment tank 23: Sludge supply pump 24: Supply pipe 25: Supply sludge concentration meter 26: Sludge flow meter 31: Circulation pump 32: Return piping 33: Circulating sludge concentration meter 81:Draw pump 82: Drawn pipe

Claims

1. a methane fermentation tank equipped with an agitator for generating biogas by subjecting organic waste to methane fermentation; a power input density acquisition means for acquiring a power input density of the agitator; a solid concentration acquisition means for acquiring a solid concentration in the methane fermentation tank; a control means; a storage means for storing a correlation curve, which is a predetermined correlation and which shows the relationship between the power input density of the agitator when the agitator is operated at a predetermined rotation speed and the solid matter concentration of the methane fermentation liquid in the methane fermentation tank, which has been acquired in advance; and The control means A methane fermentation treatment system that, when the relationship between the power input density of the agitator and the acquired values ​​of the solids concentration when operated at the specified rotation speed deviates from the specified correlation, repeatedly performs a sediment entanglement elimination process, including a process of rotating the agitator in reverse for a specified time, until the relationship between the acquired values ​​becomes the specified correlation.

2. The methane fermentation treatment system according to claim 1, The control means If the relationship between the acquired values ​​is not on the correlation curve, the sediment entanglement dissolution process is repeatedly performed until the relationship between the acquired values ​​is on the correlation curve; The methane fermentation treatment system determines whether or not the power input density of the agitator operated at the predetermined rotation speed is within an appropriate range after the screen residue entanglement treatment.

3. The methane fermentation treatment system according to claim 1 or 2, a solid-liquid separator for separating the organic waste to be sent to the methane fermentation tank into solid and liquid; an input concentration measuring means for measuring the solid concentration of the organic waste input into the methane fermentation tank; and The control means After the screen residue entanglement elimination process, if the power input density of the agitator operated at the predetermined rotation speed is outside an appropriate range, it is determined to be abnormal; If an abnormality is determined and the solid concentration measured by the input concentration measuring means is not within a predetermined concentration range, the methane fermentation treatment system determines that the abnormality is an abnormality in the solid concentration and adjusts the operation of the solid-liquid separation device.

4. The methane fermentation treatment system according to claim 1 or 2, further comprising a biogas generation amount detection means for detecting the amount of biogas generated in the methane fermentation tank; The control means After the screen residue entanglement elimination process, if the power input density of the agitator operated at the predetermined rotation speed is outside an appropriate range, it is determined to be abnormal; If the amount of biogas detected is not within a predetermined multiplication range relative to the amount of organic waste input into the methane fermentation tank, the methane fermentation treatment system determines that the abnormality is an abnormality in the amount of biogas, and adjusts the amount of organic waste input into the methane fermentation tank.

5. The methane fermentation treatment system according to claim 1 or 2, The methane fermentation tank further includes a temperature measuring means for measuring the temperature of the methane fermentation liquid in the methane fermentation tank. The control means After the screen residue entanglement elimination process, if the power input density of the agitator operated at the predetermined rotation speed is outside an appropriate range, it is determined to be abnormal; If the temperature in the methane fermentation tank is not uniform, the methane fermentation treatment system determines that the abnormality is a temperature abnormality in the methane fermentation tank and increases the rotation speed of the agitator.

6. A method for operating a methane fermentation treatment device for producing biogas by subjecting organic waste to methane fermentation in a methane fermentation tank equipped with an agitator, comprising: Obtaining the power input density of the agitator; Obtaining a solids concentration in the methane fermentation tank; a correlation curve that is a predetermined correlation and that shows the relationship between the power input density of the agitator when the agitator is operated at a predetermined rotation speed and the solid matter concentration of the methane fermentation liquid in the methane fermentation tank, which has been acquired in advance; A method for operating a methane fermentation treatment device, which, if the relationship between the power input density of the agitator and the acquired values ​​of the solids concentration when operated at the specified rotation speed deviates from the specified correlation, repeatedly performs a sediment entanglement elimination process, including a process of rotating the agitator in reverse for a specified time, until the relationship between the acquired values ​​becomes the specified correlation.

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