METHOD FOR OPERATING METHANE FERMENTATION TREATMENT APPARATUS AND METHANE FERMENTATION TREATMENT APPARATUS

Abstract

To provide a technique capable of easily eliminating bubbles generated in a methane fermentation tank without installing a new piping in a gas phase part in the methane fermentation tank.SOLUTION: A method for operating a methane fermentation treatment apparatus 101 which comprises: a methane fermentation tank 1 for anaerobically fermenting an organic waste; bubble detection means 12 for detecting bubbles generated in the methane fermentation tank 1; a circulation piping 8 through which a fermentation liquid in the methane fermentation tank 1 is circulated; and a heat exchanger 7 that is provided in the circulation piping 8 to heat the fermentation liquid flowing through the circulation piping 8. When bubbles of the fermentation liquid are detected by the bubble detection means 12, the temperature of the fermentation liquid in the methane fermentation tank 1 is increased higher than that during a normal operation by the heat exchanger 7.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] In methane fermentation tanks where anaerobic fermentation of organic waste is performed, the fermentation liquid inside the tank may foam during processing. If foaming is severe, the foam interface may rise and the foam may get mixed into the biogas recovery pipe. If foam gets mixed into the recovery pipe, it may damage the downstream biogas equipment. For example, Patent Documents 1 and 2 describe techniques to prevent foaming in methane fermentation tanks.

[0003] The technology described in Patent Document 1 relates to an antifoaming agent supplying device. An antifoaming agent storage tank is provided above a methane fermentation tank that performs anaerobic treatment. The antifoaming agent in the antifoaming agent storage tank is supplied to the methane fermentation tank.

[0004] In Patent Document 2, a pipe through which hot water from a boiler flows, or a pipe through which warm water generated by utilizing the exhaust heat of a biogas utilization device flows, is provided in the gas phase of a methane fermentation tank. The hot water from the boiler or the warm water generated by utilizing the exhaust heat of the biogas utilization device heats bubbles that are generated in the gas phase, thereby reducing the viscosity of the bubbles and making them easier to break. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6378957 [Patent Document 2] Patent No. 5166337 Summary of the Invention [Problem to be solved by the invention]

[0006] When only an antifoaming agent is used as a foaming countermeasure using an antifoaming agent injection device as described in Patent Document 1, there is a problem that the cost of chemicals (antifoaming agent cost) increases. In addition, when a large amount of antifoaming agent is used, there is another problem that the fermentation liquid is diluted by the antifoaming agent.

[0007] On the other hand, the technology described in Patent Document 2 can reduce the amount of antifoaming agent used. However, the technology described in Patent Document 2 requires the installation of piping through which hot water or warm water flows in the gas phase of the methane fermentation tank, which makes the gas phase of the methane fermentation tank complicated. In addition, measures to prevent corrosion of the piping are also required.

[0008] An object of the present invention is to provide a technique that can easily destroy foam generated inside a methane fermentation tank without installing new piping in the gas phase section inside the methane fermentation tank. [Means for solving the problem]

[0009] The method of operating a methane fermentation treatment apparatus disclosed in the present application is a method of operating a methane fermentation treatment apparatus comprising a methane fermentation tank for anaerobic fermentation treatment of organic waste, a foaming detection means for detecting foam generated inside the methane fermentation tank, a circulation pipe for circulating the fermentation liquid in the methane fermentation tank, and a heat exchanger provided in the circulation pipe for heating the fermentation liquid flowing through the circulation pipe, characterized in that when foaming in the fermentation liquid is detected by the foaming detection means, the temperature of the fermentation liquid in the methane fermentation tank is raised by the heat exchanger above the temperature during normal operation.

[0010] The main causes of foaming include an increase in the viscosity of the fermentation liquid, contamination with foaming substances from organic waste, and secretion of foaming substances from microorganisms. When the amount of foaming substances in the fermentation liquid increases or the viscosity of the fermentation liquid increases, foaming is more likely to occur. When the temperature of the fermentation liquid increases, the viscosity of the fermentation liquid decreases and the foaming substances become more easily dispersed. This makes the fermentation liquid less likely to foam. Also, when the viscosity is low, the bubbles are more likely to disappear. An example of a foaming substance is fat or oil. According to the operating method configured as above, by increasing the temperature of the fermentation liquid in the methane fermentation tank, it is possible to easily eliminate the bubbles generated inside the methane fermentation tank.

[0011] When foaming in the fermentation liquid is no longer detected by the foaming detection means, the temperature of the fermentation liquid in the methane fermentation tank may be returned to the temperature during normal operation.

[0012] If the temperature of the fermentation liquid is constantly high, it may cause problems with methane fermentation (anaerobic fermentation treatment of organic waste). When foaming in the fermentation liquid is no longer detected by the foaming detection means, the temperature of the fermentation liquid can be returned to the temperature during normal operation to prevent problems with methane fermentation.

[0013] The temperature of the fermentation liquid in the methane fermentation tank may be increased by the heat exchanger to a temperature higher than that during normal operation, and then after a predetermined time has elapsed, the temperature of the fermentation liquid in the methane fermentation tank may be returned to the temperature during normal operation.

[0014] With this configuration, even if foaming of the fermentation liquid continues to be detected, the temperature of the fermentation liquid returns to the normal operating temperature after a certain time has elapsed, making it possible to avoid a state in which the temperature of the fermentation liquid is constantly high, thereby more reliably preventing any impediments to methane fermentation.

[0015] The circulation piping may include a first withdrawal pipe for withdrawing the fermentation liquid from the bottom of the methane fermentation tank, a second withdrawal pipe for withdrawing the fermentation liquid from the top of the methane fermentation tank, and a return piping for returning the fermentation liquid to the top of the methane fermentation tank, and during normal operation, the fermentation liquid may be withdrawn from the bottom of the methane fermentation tank using the first withdrawal pipe, and when the temperature of the fermentation liquid in the methane fermentation tank is raised by the heat exchanger to a temperature higher than that during normal operation, the fermentation liquid may be withdrawn from the top of the methane fermentation tank using the second withdrawal pipe.

[0016] Bubbles accumulate near the surface of the fermentation liquid. Bubbles are also more likely to occur near the surface of the fermentation liquid. The surface of the fermentation liquid is located at the top of the methane fermentation tank. If the fermentation liquid is withdrawn from the top of the methane fermentation tank, heated, and returned to the top of the methane fermentation tank, the temperature near the surface of the fermentation liquid can be raised more quickly than if the fermentation liquid is withdrawn from the bottom of the methane fermentation tank, heated, and returned to the top of the methane fermentation tank. By quickly raising the temperature near the surface of the fermentation liquid, any bubbles that occur are easily eliminated in a short time. In addition, since there is no need to heat the entire tank, the impact on methane fermentation can be reduced.

[0017] Furthermore, since the fermentation liquid containing a large amount of foam flows through the circulation pipe, a defoaming effect can be expected due to the foam breaking down during the process of flowing through the circulation pipe.

[0018] The present application also discloses a methane fermentation treatment device, which includes a methane fermentation tank for anaerobic fermentation of organic waste, a foaming detection means for detecting foam generated inside the methane fermentation tank, a circulation pipe for circulating the fermented liquid in the methane fermentation tank, and a heat exchanger provided in the circulation pipe for heating the fermented liquid flowing through the circulation pipe, and further includes a control device for increasing the temperature of the fermented liquid in the methane fermentation tank by the heat exchanger above the temperature during normal operation when foaming in the fermented liquid is detected by the foaming detection means.

[0019] When the temperature of the fermentation liquid rises, the viscosity of the fermentation liquid decreases, and the dispersibility of the fermentation liquid and the foaming substances contained therein increases, making the fermentation liquid less likely to foam. Furthermore, when the dispersibility of the foaming substances is high, the foam that has formed also tends to disappear. As described above, according to the methane fermentation treatment device configured as above, by raising the temperature of the fermentation liquid in the methane fermentation tank, it is possible to easily destroy the foam that has formed inside the methane fermentation tank. Furthermore, foaming countermeasure operations can be performed automatically.

[0020] The control device may be configured to return the temperature of the fermentation liquid in the methane fermentation tank to the temperature during normal operation when foaming in the fermentation liquid is no longer detected by the foaming detection means.

[0021] If the temperature of the fermentation liquid is constantly high, there is a risk that this will cause problems with methane fermentation. When foaming in the fermentation liquid is no longer detected by the foaming detection means, the temperature of the fermentation liquid can be returned to the temperature during normal operation to prevent problems with methane fermentation.

[0022] The control device may be configured to raise the temperature of the fermentation liquid in the methane fermentation tank above the temperature during normal operation by the heat exchanger, and then, after a predetermined time has elapsed, return the temperature of the fermentation liquid in the methane fermentation tank to the temperature during normal operation.

[0023] With this configuration, even if foaming of the fermentation liquid continues to be detected, the temperature of the fermentation liquid returns to the normal operating temperature after a certain time has elapsed, making it possible to avoid a state in which the temperature of the fermentation liquid is constantly high, thereby more reliably preventing any impediments to methane fermentation.

[0024] The circulation piping may include a first withdrawal pipe for withdrawing the fermentation liquid from the bottom of the methane fermentation tank, a second withdrawal pipe for withdrawing the fermentation liquid from the top of the methane fermentation tank, and a return piping for returning the fermentation liquid to the top of the methane fermentation tank, and the control device may be configured to withdraw the fermentation liquid from the bottom of the methane fermentation tank using the first withdrawal pipe during normal operation, and to withdraw the fermentation liquid from the top of the methane fermentation tank using the second withdrawal pipe when the temperature of the fermentation liquid in the methane fermentation tank is raised by the heat exchanger to a temperature higher than that during normal operation.

[0025] When the fermentation liquid is withdrawn from the top of the methane fermentation tank, heated, and returned to the top of the methane fermentation tank, the temperature near the surface of the fermentation liquid can be raised more quickly than when the fermentation liquid is withdrawn from the bottom of the methane fermentation tank, heated, and returned to the top of the methane fermentation tank. The rapid rise in temperature near the surface of the fermentation liquid makes it easier for generated bubbles to disappear in a short time.

[0026] Furthermore, since the fermentation liquid containing a large amount of foam flows through the circulation pipe, a defoaming effect can be expected due to the foam breaking down during the process of flowing through the circulation pipe. Effect of the Invention

[0027] According to the present invention, a technique can be provided that can easily destroy bubbles generated inside a methane fermentation tank without installing new piping in the gas phase section inside the methane fermentation tank. [Brief description of the drawings]

[0028] [Figure 1] 1 is a diagram showing a methane fermentation treatment apparatus according to a first embodiment of the present invention. [Diagram 2] FIG. 4 is a diagram showing a methane fermentation treatment apparatus according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0030] (First embodiment) As shown in FIG. 1, a methane fermentation treatment apparatus 101 includes a methane fermentation tank 1, an agitator 2, a heating device 3, an extraction device 4, and a controller 5 (control device).

[0031] The methane fermentation tank 1 is a tank for anaerobic fermentation of organic waste such as sewage sludge and food waste. The methane fermentation tank 1 is, for example, a concrete tank. The methane fermentation tank 1 may also be a steel tank. The methane fermentation tank 1 is provided with an agitator 2, a heating device 3, an extraction device 4, and the like.

[0032] The agitator 2 is for agitating the sludge (organic waste, fermentation liquid) put into the methane fermentation tank 1. In this embodiment, the agitator 2 is configured to agitate the sludge (fermentation liquid) with multiple stages of blades 2a (impellers) rotating in a horizontal direction. The drive source of the agitator 2 is, for example, an electric motor 2b. The agitator 2 is disposed in the center of the methane fermentation tank 1 in a plan view. The rotation of the blades 2a generates a downward flow in the center of the methane fermentation tank 1. The downward flow spreads at the bottom of the methane fermentation tank 1, reverses, and becomes an upward flow. The blades 2a of the agitator 2 may be rotated in the reverse direction. When the blades 2a are rotated in the reverse direction, an upward flow is generated in the center of the methane fermentation tank 1, and the upward flow spreads at the top of the methane fermentation tank 1, reverses, and becomes a downward flow. The agitator 2 may also be disposed at a position shifted from the center of the methane fermentation tank 1 in a plan view. Furthermore, the stirrer may be a draft tube type stirrer or a gas stirring type stirrer.

[0033] Hereinafter, the sludge in the methane fermentation tank 1 will be referred to as the fermentation liquid. The heating device 3 is for heating (warming) the fermentation liquid in the methane fermentation tank 1. The heating device 3 is equipped with a circulation pump 6, a heat exchanger 7, and a circulation pipe 8. The temperature of the fermentation liquid in the tank is made uniform by stirring the fermentation liquid with the agitator 2.

[0034] The circulation pipe 8 is a pipe for circulating the fermentation liquid in the methane fermentation tank 1. The circulation pipe 8 is provided outside the methane fermentation tank 1. The circulation pipe 8 can be divided into an extraction pipe 8a for extracting the fermentation liquid from the bottom of the methane fermentation tank 1 on the upstream side of the heat exchanger 7, and a return pipe 8b for returning the fermentation liquid to the upper part of the methane fermentation tank 1 on the downstream side of the heat exchanger 7. A circulation pump 6 is disposed in the path of the extraction pipe 8a, and an extraction valve 13 is disposed upstream of the circulation pump 6a in the path of the extraction pipe 8a. The extraction valve 13 may be an automatic valve capable of remote control or a manual valve. In addition, when the extraction valve 13 is controlled to open and close by the controller 5, the extraction valve 13 is an automatic valve capable of remote control. In the case where the extraction valve 13 is opened and closed only manually by an operator, the extraction valve 13 may be a manual valve.

[0035] The heat exchanger 7 is an indirect heat exchanger that heats the fermentation liquid flowing through the circulation pipe 8. Hot water is supplied to the heat exchanger 7 from a boiler 9. The fermentation liquid drawn from the bottom of the methane fermentation tank 1 is heated by indirect contact with hot water in the heat exchanger 7, and then returned to the methane fermentation tank 1 from the top of the methane fermentation tank 1. The heating device 3 also contributes to stirring the fermentation liquid in the methane fermentation tank 1. The heat source for heating the fermentation liquid is not limited to the hot water from the boiler 9. For example, hot water may be obtained from the exhaust heat of a biogas generator or from a sludge incineration facility, and the hot water may be used as the heat source for heating the fermentation liquid. A heat medium other than hot water may also be used. For example, heat oil or steam may be used as the heat medium.

[0036] The fermentation liquid in the methane fermentation tank 1 is heated (warmed) by the heating device 3 and stirred by the agitator 2. Biogas generated by anaerobic fermentation in the methane fermentation tank 1 is extracted from the methane fermentation tank 1 through a gas recovery pipe (not shown). The gas recovery pipe is connected to the upper surface of the methane fermentation tank 1. The biogas is, for example, a gas that is about 60% by volume methane and about 40% by volume carbon dioxide. The biogas extracted from the methane fermentation tank 1 is used as fuel for the boiler 9 or as fuel for a power generation facility (not shown).

[0037] The extraction device 4 is for extracting the fermentation residue in the methane fermentation tank 1 from the bottom of the methane fermentation tank 1 to the outside of the tank. The extraction device 4 is provided with an extraction pump 10 and an extraction pipe 11.

[0038] According to the guidelines of the Japan Sewage Works Association, for example, the methane fermenter 1 is operated at a temperature of about 30 to 37°C for a retention time of about 20 to 30 days in mesophilic fermentation treatment, and at a temperature of about 50 to 55°C for a retention time of about 10 to 15 days in high temperature fermentation treatment.

[0039] Here, the fermentation liquid may foam inside the methane fermentation tank 1. When sludge containing components that cause foaming is put into the methane fermentation tank 1, or when some environmental change occurs while the components are present in the methane fermentation tank 1, bubbles may suddenly appear and grow in a short time. In particular, when the sludge contains a large amount of oils and fats, highly viscous bubbles are likely to form. This type of foam is difficult to break, and the bubbles increase rapidly within a short period of time, resulting in sudden foaming. When foaming is severe, the foam interface rises and the bubbles get mixed into the gas recovery pipe, and the fermentation liquid may then break and flow out of the gas recovery pipe.

[0040] The main causes of foaming in the fermentation liquid are the increase in viscosity of the fermentation liquid and the dispersibility of foaming substances due to secretions from organic waste and microorganisms. When the viscosity increases or the dispersibility of the foaming substance is low, the fermentation liquid is prone to foaming. When the viscosity decreases or the dispersibility of the foaming substance is high, the fermentation liquid is less likely to foam. In addition, when the dispersibility of the foaming substance is low, the generated bubbles are difficult to disappear, and when the dispersibility of the foaming substance is high, the generated bubbles are easy to disappear. To increase the dispersibility of the foaming substance and reduce the viscosity of the fermentation liquid, the temperature of the fermentation liquid is increased. Therefore, the methane fermentation treatment device 101 of this embodiment is provided with a foaming detection means 12 in the methane fermentation tank 1 and a controller 5 (control device) for controlling the temperature of the fermentation liquid.

[0041] The foaming detection means 12 is an instrument for detecting foam generated inside the methane fermentation tank 1. As the foaming detection means 12, a capacitance type level gauge, an electrode type level gauge, an ultrasonic type level gauge, or the like is used. The foaming detection means 12 may be attached to the top surface of the methane fermentation tank 1, or may be attached to the side surface of the upper part of the methane fermentation tank 1. In addition to the foaming detection means 12, a liquid level gauge (not shown) for detecting the liquid level WL of the methane fermentation tank 1 is attached to the methane fermentation tank 1.

[0042] The foaming detection means 12 and the controller 5 are connected by a cable, and a detection signal from the foaming detection means 12 is input to the controller 5 via the cable. The controller 5 controls the boiler 9 and the like.

[0043] The controller 5 is configured to control, when foaming detection means 12 detects foaming of the fermentation liquid in the methane fermenter 1, to raise the temperature of the fermentation liquid by the heat exchanger 7 above the temperature during normal operation.

[0044] When foaming is not occurring in the methane fermentation tank 1, or when foaming is occurring but the amount of foam is small, the foaming detection means 12 detects the liquid level of the fermentation liquid in the methane fermentation tank 1, and the controller 5 receives a signal of the detected liquid level WL. When foaming occurs in the methane fermentation tank 1 and the foam grows, the foam interface rises due to the large number of bubbles that swell up. When the foaming detection means 12 detects a foam interface higher than the liquid level WL and the controller 5 receives a signal of the detected interface level, the controller 5 performs the following control. Note that when foaming of the fermentation liquid in the methane fermentation tank 1 is detected by the foaming detection means 12, it means when the foaming detection means 12 detects a foam interface at a height that is a predetermined level or higher than the liquid level WL.

[0045] The controller 5 controls the boiler 9 so as to raise the temperature of the fermentation liquid in the methane fermentation tank 1 by the heat exchanger 7 to a temperature higher than that during normal operation. Here, the above temperature (the temperature during normal operation) is the preset operating temperature of the methane fermentation tank 1. The temperature in the methane fermentation tank 1 is measured by a thermometer (not shown) provided in the methane fermentation tank 1 for the temperature of the fermentation liquid in the tank or the temperature of the heated fermentation liquid, and the flow rate of the warm water supplied from the boiler 9 to the heat exchanger 7 is adjusted so that this temperature becomes the set temperature (for example, 37°C to 39°C). When the controller 5 detects foaming of the fermentation liquid, it adjusts the amount of warm water of the boiler 9 so that the temperature of the fermentation liquid after heating becomes higher than that during normal operation (for example, 40 to 45°C). Instead of directly measuring the temperature in the methane fermentation tank 1, the temperature of the fermentation liquid after heating may be measured in the pipe (measured at the return pipe 8b portion constituting the circulation pipe 8), and the temperature of the methane fermentation tank 1 may be estimated.

[0046] When the controller 5 raises the temperature of the fermentation liquid, it increases the flow rate of the warm water supplied from the boiler 9 to increase the amount of heat supplied from the heat exchanger 7 to the circulated fermentation liquid. As a result, warm water with a larger flow rate than during normal operation is supplied from the boiler 9 to the heat exchanger 7. The fermentation liquid drawn from the bottom of the methane fermentation tank 1 is heated in the heat exchanger 7 by indirect contact with the large flow rate of warm water from the boiler 9. The heated fermentation liquid returns into the methane fermentation tank 1 from the upper part of the methane fermentation tank 1. As a result, the temperature of the fermentation liquid in the methane fermentation tank 1 rises. Thereby, the viscosity of the fermentation liquid becomes lower or the dispersibility of the foaming substance increases, and the generated bubbles are likely to disappear. Also, the fermentation liquid is less likely to foam. From the above, according to the methane fermentation treatment apparatus 101, it is possible to easily defoam the bubbles generated inside the methane fermentation tank 1 without installing a new pipe in the gas phase part in the methane fermentation tank 1.

[0047] Also, when the temperature of the fermentation liquid in the methane fermentation tank 1 rises, the reaction rate of anaerobic fermentation may be improved. Furthermore, the viscosity of the fermentation liquid decreases, and the stirring efficiency by the stirrer 2 also improves.

[0048] Incidentally, without using the controller 5 or without providing the controller 5, an operator may detect foaming of the fermentation liquid in the methane fermentation tank 1 by the foaming detection means 12, and when foaming is detected, the operator may manually raise the temperature of the fermentation liquid in the methane fermentation tank 1 to a temperature higher than that during normal operation by the heat exchanger 7. That is, the operator may manually perform the control performed by the controller 5. Incidentally, the operator may also manually perform the control performed by the controller 5 described later, such as the control when foaming of the fermentation liquid is no longer detected. The operator performs manual control, for example, as follows. The operator detects foaming of the fermentation liquid in the methane fermentation tank 1 from the detection value of the foaming detection means 12. The detection value of the foaming detection means 12 is displayed, for example, on an electrical panel (not shown). The operator empirically knows (detects) the presence or absence of foaming in the methane fermentation tank 1 based on the detection value of the foaming detection means 12. Incidentally, if a sight window is provided in the methane fermentation tank 1, the presence or absence of foaming may be detected by visually checking through the sight window. When an operator detects foaming occurring in the methane fermentation tank 1, the flow rate of hot water supplied from the boiler 9 is increased, and the fermentation liquid flowing through the circulation pipe 8 is heated by the heat exchanger 7 with hot water at a flow rate greater than that during normal operation.

[0049] When the foaming state of the fermentation liquid subsides due to the disappearance of foam and the reduction in new foaming, and foaming in the fermentation liquid is no longer detected by the foaming detection means 12, the controller 5 returns the temperature of the fermentation liquid in the methane fermentation tank 1 to the temperature during normal operation. That is, the controller 5 returns the flow rate of hot water supplied from the boiler 9 to its original value (reducing it to the flow rate during normal operation) and returns the set value of the temperature of the fermentation liquid after heating to its original value (returning it to the temperature during normal operation). When it is not necessary to heat the fermentation liquid, such as in summer in the case of mesophilic fermentation treatment, the controller 5 controls the boiler 9 to stop or the supply of hot water to the heat exchanger 7 is stopped, or manually by an operator. When it is necessary to heat the fermentation liquid, the operation of the boiler 9 continues as is.

[0050] If the temperature of the fermentation liquid is constantly high, there is a risk of it interfering with methane fermentation (anaerobic fermentation treatment of organic waste). When foaming in the fermentation liquid is no longer detected by the foaming detection means 12, the temperature of the fermentation liquid in the methane fermenter 1 can be returned to the temperature during normal operation to prevent any interference with methane fermentation.

[0051] The controller 5 may be configured to control the temperature of the fermentation liquid in the methane fermentation tank 1 to return to the temperature during normal operation after a predetermined time has elapsed after the temperature of the fermentation liquid in the methane fermentation tank 1 has been raised above the temperature during normal operation by the heat exchanger 7. As described above, when heating of the fermentation liquid is not required, such as in summer in the case of mesophilic fermentation treatment, the boiler 9 is stopped or the supply of hot water to the heat exchanger 7 is stopped under the control of the controller 5 or manually by an operator. When heating of the fermentation liquid is required, the operation of the boiler 9 is continued as is.

[0052] According to the above control, even if foaming of the fermentation liquid continues to be detected, the temperature of the fermentation liquid returns to the normal operating temperature after a predetermined time has elapsed, so it is possible to avoid a state in which the temperature of the fermentation liquid is constantly high, and as a result, it is possible to more reliably prevent any impediments to methane fermentation.

[0053] Second embodiment 2 is a diagram showing a methane fermentation treatment device 102 according to a second embodiment of the present invention. The difference between the methane fermentation treatment device 101 of the first embodiment and the methane fermentation treatment device 102 of the second embodiment is that, in the second embodiment, when foaming of the fermentation liquor in the methane fermenter 1 is detected by the foaming detection means 12, the circulation piping 8 is switched to perform an operation in which the vicinity of the liquid surface of the fermentation liquor is preferentially circulated and heated (circulated heated). The same symbols are used for devices common to the methane fermentation treatment device 101 of the first embodiment and the methane fermentation treatment device 102 of the second embodiment.

[0054] The circulation pipe 8 constituting the methane fermentation treatment device 102 of the second embodiment includes, as a pipe for drawing the fermentation liquid from inside the methane fermentation tank 1, a drawing pipe 8a (hereinafter referred to as a first drawing pipe 8a) for drawing the fermentation liquid from the bottom of the methane fermentation tank 1, and a second drawing pipe 8c for drawing the fermentation liquid from the upper part of the methane fermentation tank 1. The upstream end of the second drawing pipe 8c is connected to the upper part of the side of the methane fermentation tank 1. The downstream end of the second drawing pipe 8c is connected to the first drawing pipe 8a between the circulation pump 6 and the drawing valve 13. A second drawing valve 14 is disposed upstream of the second drawing pipe 8c. The second drawing valve 14 may be an automatic valve that can be remotely operated, or may be a manual valve.

[0055] In the second embodiment, the withdrawal valve 13 will be referred to as the first withdrawal valve 13. When the first withdrawal valve 13 and the second withdrawal valve 14 are controlled to be opened and closed by the controller 5, the first withdrawal valve 13 and the second withdrawal valve 14 are automatic valves that can be remotely operated. When the first withdrawal valve 13 and the second withdrawal valve 14 are opened and closed only manually by an operator, the first withdrawal valve 13 and the second withdrawal valve 14 may be manual valves.

[0056] In the second embodiment, the temperature inside the methane fermentation tank 1 is measured by a thermometer (not shown) installed inside the tank, which is the same as in the first embodiment. However, although there is no particular restriction on the position of the thermometer in the first embodiment, in the second embodiment, it is preferable to measure the temperature of the upper layer of the methane fermentation tank 1. For this reason, it is preferable to install the thermometer at a height within 1 / 2, more preferably within 1 / 4, of the fermentation liquid depth from the liquid surface.

[0057] During normal operation, when the fermentation liquid is heated by the heat exchanger 7 and returned to the upper part of the methane fermentation tank 1 using the return pipe 8b, the controller 5 controls the withdrawal of the fermentation liquid from the bottom of the methane fermentation tank 1 using the first withdrawal pipe 8a. This control is the same in the methane fermentation treatment device 101 of the first embodiment. The controller 5 supplies hot water from the boiler 9 to the heat exchanger 7 at the flow rate during normal operation. The controller 5 changes the first withdrawal valve 13 from closed to open, and operates the circulation pump 6. At this time, the second withdrawal valve 14 is closed.

[0058] On the other hand, when the temperature of the fermentation liquid in the methane fermentation tank 1 is raised by the heat exchanger 7 to a temperature higher than that during normal operation, the controller 5 controls the withdrawal of the fermentation liquid from the upper part of the methane fermentation tank 1 using the second withdrawal pipe 8c. The controller 5 increases the amount of hot water supplied compared to that during normal operation, and supplies hot water from the boiler 9 to the heat exchanger 7. The controller 5 changes the second withdrawal valve 14 from closed to open, and changes the first withdrawal valve 13 from open to closed (switching of withdrawal valves 13·14). The withdrawal valves 13·14 may be switched after increasing the amount of hot water supplied, or the withdrawal valves 13·14 may be switched before increasing the amount of hot water supplied.

[0059] As a result, hot water is supplied from the boiler 9 to the heat exchanger 7 at a flow rate greater than that during normal operation. The fermentation liquid is extracted from the upper part of the methane fermentation tank 1 by the second extraction pipe 8c. The extracted fermentation liquid is heated in the heat exchanger 7 by indirect contact with hot water at a flow rate greater than that during normal operation. The heated fermentation liquid returns to the methane fermentation tank 1 from the upper part of the methane fermentation tank 1.

[0060] In the methane fermentation tank 1, bubbles accumulate near the liquid surface of the fermentation liquid. Also, bubbles are likely to occur near the liquid surface of the fermentation liquid. The liquid surface of the fermentation liquid is located near the upper part of the methane fermentation tank 1. When the fermentation liquid is drawn from the upper part of the methane fermentation tank 1, heated, and returned to the upper part of the methane fermentation tank 1, the temperature near the liquid surface of the fermentation liquid can be raised more quickly than when the fermentation liquid is drawn from the bottom of the methane fermentation tank 1, heated, and returned to the upper part of the methane fermentation tank 1. The temperature near the liquid surface of the fermentation liquid rises quickly, so that the generated bubbles are easily vanished in a short time. In addition, the fermentation liquid containing a large amount of bubbles flows through the circulation pipe 8, and a vanishing effect due to the vanishing of bubbles during the process of flowing through the circulation pipe 8 can be expected. Furthermore, a vanishing effect due to the vanishing of bubbles by the circulation pump 6 can be expected. In addition, the upper part of the fermentation liquid in the methane fermentation tank 1 is preferentially heated, and the influence of the heating is relatively less likely to reach the lower part of the fermentation liquid in the methane fermentation tank 1. Therefore, it is easy to return the temperature of the fermentation liquid to the temperature during normal operation.

[0061] The level (position, height) of the suction port 15 of the second withdrawal pipe 8c is preferably between the liquid level WL of the fermentation liquid and 50 cm, preferably 100 cm, below the liquid level WL of the fermentation liquid. This makes it possible to quickly increase the temperature near the liquid level of the fermentation liquid and to withdraw fermentation liquid containing a large amount of bubbles from the methane fermentation tank 1. The level of the suction port 15 of the second withdrawal pipe 8c refers to the level of the bottom of the piping portion extending horizontally at the upstream end of the second withdrawal pipe 8c.

[0062] 2, the return port 16 of the return pipe 8b and the suction port 15 of the second withdrawal pipe 8c are disposed on the same side with respect to the agitator 2. The suction port 15 of the second withdrawal pipe 8c may be disposed on the opposite side to the return port 16 of the return pipe 8b with respect to the agitator 2. This makes it possible to prevent the fermentation liquor discharged from the return pipe 8b from being immediately sucked into the second withdrawal pipe 8c, and makes it possible to more quickly increase the temperature near the liquid surface of the fermentation liquor.

[0063] In the above embodiment, in order to raise the temperature of the fermentation liquid in the methane fermenter 1 above the temperature during normal operation, the flow rate of hot water supplied from the boiler 9 to the heat exchanger 7 is increased compared to that during normal operation. The method of raising the temperature of the fermentation liquid is not limited to this. For example, the temperature of the hot water may be adjusted by changing (increasing) the temperature of the boiler 9 or an alternative heat source, or the set temperature of the heat source such as the boiler 9 (set temperature of the hot water) may be kept constant and the flow rate of the fermentation liquid circulated by the circulation pump 6 may be reduced below that during normal operation.

[0064] In addition, although the sludge extraction pipe (extraction pipe 8a) is provided at the bottom of the fermentation tank in the first embodiment, it may be provided at the top of the fermentation tank. In other words, the sludge may be extracted from the top of the methane fermentation tank 1, heated by the heat exchanger 7, and then returned to the top of the methane fermentation tank 1.

[0065] The present invention is not limited to the above-described embodiment. The configurations of the above-described embodiment may be appropriately combined, or various modifications may be made to the above-described embodiment. [Explanation of symbols]

[0066] 1: Methane fermentation tank 5: Controller (control device) 7: Heat exchanger 8: Circulation piping 8a: Drawn tube (first drawn tube) 8b: Return pipe 8c: Second drawn tube 12: Foam detection means 101, 102: Methane fermentation treatment equipment

Claims

1. a methane fermentation tank for anaerobic fermentation of organic waste; A foam detection means for detecting foam generated inside the methane fermentation tank; A circulation pipe for circulating the fermentation liquid in the methane fermentation tank; A heat exchanger provided in the circulation pipe for heating the fermentation liquid flowing through the circulation pipe; A method for operating a methane fermentation treatment apparatus comprising: When foaming in the fermentation liquid is detected by the foaming detection means, the temperature of the fermentation liquid in the methane fermentation tank is increased by the heat exchanger to a temperature higher than that during normal operation. A method for operating a methane fermentation treatment device.

2. The method for operating a methane fermentation treatment apparatus according to claim 1, When foaming in the fermentation liquid is no longer detected by the foaming detection means, the temperature of the fermentation liquid in the methane fermentation tank is returned to the temperature during normal operation. A method for operating a methane fermentation treatment device.

3. The method for operating a methane fermentation treatment apparatus according to claim 1, After the temperature of the fermentation liquid in the methane fermentation tank is increased by the heat exchanger to a temperature higher than that during normal operation, when a predetermined time has elapsed, the temperature of the fermentation liquid in the methane fermentation tank is returned to the temperature during normal operation. A method for operating a methane fermentation treatment device.

4. The method for operating a methane fermentation treatment apparatus according to any one of claims 1 to 3, The circulation piping is A first withdrawal pipe for withdrawing a fermentation liquid from the bottom of the methane fermentation tank; a second withdrawal pipe for withdrawing the fermentation liquid from the upper part of the methane fermentation tank; A return pipe for returning the fermentation liquid to the upper part of the methane fermentation tank; Equipped with During normal operation, the first withdrawal pipe is used to withdraw the fermentation liquid from the bottom of the methane fermentation tank; When the temperature of the fermentation liquid in the methane fermentation tank is increased by the heat exchanger to a temperature higher than that during normal operation, the fermentation liquid is drawn out from the upper part of the methane fermentation tank using the second drawing pipe. A method for operating a methane fermentation treatment device.

5. a methane fermentation tank for anaerobic fermentation of organic waste; A foam detection means for detecting foam generated inside the methane fermentation tank; A circulation pipe for circulating the fermentation liquid in the methane fermentation tank; A heat exchanger provided in the circulation pipe for heating the fermentation liquid flowing through the circulation pipe; A methane fermentation treatment device comprising: and a control device that, when foaming in the fermentation liquid is detected by the foaming detection means, increases the temperature of the fermentation liquid in the methane fermentation tank by the heat exchanger above the temperature during normal operation. Methane fermentation treatment equipment.

6. The methane fermentation treatment device according to claim 5, When foaming in the fermentation liquid is no longer detected by the foaming detection means, the control device returns the temperature of the fermentation liquid in the methane fermentation tank to a temperature during normal operation. Methane fermentation treatment equipment.

7. The methane fermentation treatment device according to claim 5, The control device increases the temperature of the fermentation liquid in the methane fermentation tank by the heat exchanger above the temperature during normal operation, and then returns the temperature of the fermentation liquid in the methane fermentation tank to the temperature during normal operation after a predetermined time has elapsed. Methane fermentation treatment equipment.

8. In the methane fermentation treatment device according to any one of claims 5 to 7, The circulation piping is A first withdrawal pipe for withdrawing a fermentation liquid from the bottom of the methane fermentation tank; a second withdrawal pipe for withdrawing the fermentation liquid from the upper part of the methane fermentation tank; A return pipe for returning the fermentation liquid to the upper part of the methane fermentation tank; Equipped with The control device, during normal operation, draws out the fermentation liquid from the bottom of the methane fermentation tank using the first withdrawal pipe, and when the temperature of the fermentation liquid in the methane fermentation tank is raised higher than the temperature during normal operation by the heat exchanger, draws out the fermentation liquid from the upper part of the methane fermentation tank using the second withdrawal pipe. Methane fermentation treatment equipment.

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