Solubilization device, organic waste treatment system and treatment method

Abstract

The present invention is characterized by comprising a thermal solubilization tank (11) for performing a thermal solubilization treatment on sludge, a steam supplying device (4) for supplying steam to the sludge in the thermal solubilization tank (11), a gas exhaust pipe (31) for exhausting gas in the thermal solubilization tank (11) to solubilized sludge (W4) discharged from the thermal solubilization tank (11), a pressure sensor (32) for measuring the pressure in the thermal solubilization tank (11), a pressure regulating valve (31a) for opening and closing the gas exhaust pipe (31), and a pressure control means (33) for adjusting the aperture of the pressure regulating valve (31a) so that the measurement value of the pressure sensor (32) becomes a target value.

Description

[Technical field]

[0001] The present invention relates to a solubilization device, an organic waste treatment system, and a treatment method. [Background technology]

[0002] Anaerobic digestion using anaerobic organisms is known as a method for treating organic waste such as food waste, livestock manure, and sewage sludge. In this anaerobic digestion process, organic waste such as sludge is put into a digestion tank and is fermented into methane through solubilization, hydrolysis, and acid fermentation, and the solids are decomposed into methane gas and carbon dioxide, reducing the volume of the solids. The methane gas is used as energy.

[0003] Before the anaerobic digestion process, the sludge may be subjected to a thermal solubilization process. The thermal solubilization process is a process in which the sludge (organic waste) is heated to a predetermined temperature to hydrolyze the solid content. For example, Patent Documents 1 to 5 describe a technique for thermally solubilizing the sludge by supplying high-temperature steam to the sludge. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2003-500208 [Patent Document 2] JP 2007-117801 A [Patent Document 3] JP 2009-148650 A [Patent Document 4] Special Publication No. 2011-516246 [Patent Document 5] Patent No. 6159573 Summary of the Invention [Problem to be solved by the invention]

[0005] In the thermal solubilization treatment, it is preferable to maintain the temperature in the thermal solubilization tank at a predetermined set temperature. However, when the thermal solubilization treatment is continuously performed in the thermal solubilization tank, heat is transferred in and out with the supply and discharge of sludge, making it difficult to maintain a constant temperature. When sludge is heated with steam, the temperature can be adjusted by changing the amount of steam that flows in. However, since it is difficult to finely adjust the amount of steam that flows in, and the amount of steam that flows in may fluctuate more than necessary, there is a risk that the temperature will not be stable even if the amount of steam that flows in is changed in order to adjust the temperature in the thermal solubilization tank.

[0006] An object of the present invention is to provide a solubilization device, an organic waste treatment system, and a treatment method that are capable of maintaining a constant temperature inside a thermal solubilization tank. [Means for solving the problem]

[0007] The solubilization apparatus of the present invention, which solves such problems, comprises a thermal solubilization tank for performing a thermal solubilization treatment on sludge, a steam supplying device for supplying steam to the sludge in the thermal solubilization tank, a gas exhaust pipe for exhausting gas in the thermal solubilization tank to the solubilized sludge discharged from the thermal solubilization tank, a pressure sensor for measuring the pressure in the thermal solubilization tank, a pressure regulating valve for opening and closing the gas exhaust pipe, and a pressure control means for adjusting the opening of the pressure regulating valve so that the measurement value of the pressure sensor becomes a target value.

[0008] In addition, the organic waste treatment method of the present invention includes a steam supplying step of supplying steam as a heat source into a thermal solubilization tank in which a thermal solubilization treatment is performed on sludge, a measuring step of measuring the pressure inside the thermal solubilization tank, and a pressure control step of opening and closing a pressure regulating valve to release gas inside the thermal solubilization tank into an outlet pipe through which solubilized sludge discharged from the thermal solubilization tank flows.

[0009] According to the present invention, the gas (gas phase gas) in the thermal solubilization tank is discharged to the outside of the thermal solubilization tank through the gas exhaust pipe based on the measured pressure in the thermal solubilization tank, so that the pressure in the thermal solubilization tank can be kept constant. In other words, according to the present invention, the saturated water vapor pressure in the gas phase in the thermal solubilization tank can be kept constant, so that the temperature in the gas phase can be kept at a temperature corresponding to the saturated water vapor pressure, and thus the thermal solubilization treatment is less likely to vary. In addition, the gas (exhaust heat) discharged to the outside of the thermal solubilization tank through the gas exhaust pipe is supplied to the solubilized sludge discharged from the thermal solubilization tank, so that the solubilized sludge can be heated, and thus it is possible to reduce the amount of energy consumed when digesting the solubilized sludge.

[0010] When an outlet pipe for discharging the solubilized sludge from the thermal solubilization tank is provided, it is preferable that the gas exhaust pipe is connected to the outlet pipe. In this way, the solubilized sludge can be heated efficiently.

[0011] It is preferable that the solubilization apparatus comprises a liquid level sensor that measures a physical quantity correlated to the liquid level of the sludge in the thermal solubilization tank, a liquid level adjustment valve that opens and closes the outlet pipe, and a liquid level control means that adjusts the opening of the liquid level control valve so that the measurement value of the liquid level sensor becomes a target value. In this way, the liquid level in the solubilization tank can be kept constant, making it less likely that variations will occur in the thermal solubilization treatment.

[0012] The organic waste treatment system of the present invention comprises the solubilization apparatus and a digestion tank for carrying out a digestion treatment on the solubilized sludge. Effect of the Invention

[0013] According to the present invention, variation in the thermal solubilization treatment is less likely to occur, and it is possible to reduce the amount of energy consumed when digesting solubilized sludge. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a process flow diagram of an organic waste treatment system. [Diagram 2] FIG. 2 is a cross-sectional view of the solubilization device. [Diagram 3] FIG. 11 is another processing flow diagram of the organic waste processing system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] (Processing System 1) The configuration of an organic waste treatment system 1 according to the present invention will be described with reference to Fig. 1. The organic waste treatment system 1 is configured to include a solubilization device 2 that thermally solubilizes dewatered sludge W3, and a digestion tank 3 that digests solubilized sludge W4 that has been thermally solubilized in the solubilization device 2. Furthermore, the organic waste treatment system 1 of this embodiment includes a digested sludge storage tank 5 that stores organic waste (sludge W2) that has been digested in the digestion tank 3, a sludge dewatering machine 6 that dehydrates the sludge W2 sent from the digested sludge storage tank 5 to generate dewatered sludge W3, and means for transporting sludge (dewatered sludge supply pipe 7, return pipe 8, sludge pump P, etc.).

[0016] The solubilization apparatus 2 includes a mixing pot 12 that performs pretreatment on the dewatered sludge W3, a thermal solubilization tank 11 that performs thermal solubilization treatment on the treated sludge W5 discharged from the mixing pot 12, a steam supplying device 4 that supplies steam to the sludge in the thermal solubilization tank 11 and the mixing pot 12, a gas exhaust pipe 31 that exhausts gas from the tank 11, and a pressure control valve 31a that opens and closes the gas exhaust pipe 31. As shown in Figure 2, the solubilization apparatus 2 of this embodiment is equipped with a pressure sensor 32 that measures the pressure in the thermal solubilization tank 11, a pressure control means 33 that adjusts the opening of the pressure regulating valve 31a so that the measurement value of the pressure sensor 32 becomes a target value, an outlet pipe 24 that discharges solubilized sludge W4 from the thermal solubilization tank 11, a liquid level sensor 34 that measures a physical quantity correlated to the liquid level of the sludge in the thermal solubilization tank 11, a liquid level control valve 24a that opens and closes the outlet pipe 24, and a liquid level control means 35 that adjusts the opening of the liquid level control valve 24a so that the measurement value of the liquid level sensor 34 becomes a target value.

[0017] The treatment flow of the organic waste treatment system 1 will be described with reference to Figure 1. First, organic waste W1 to be newly treated is fed into the digester 3. Examples of the organic waste W1 include organic sludge such as sewage sludge and septic tank sludge, food waste, raw garbage, livestock manure, etc. In the digester 3, the organic waste W1 is subjected to methane fermentation (digestion treatment) by anaerobic methane fermentation bacteria. The operating temperature of the digester 3 is appropriately set taking into consideration the type of methane fermentation bacteria, doubling time, etc. As a result of methane fermentation, mainly CH 4 , CO 2 A digestion gas G consisting of the above is generated, and a part or all of it is sent to the steam boiler of the steam supplying device 4. The steam supplying device 4 generates high-temperature steam using this digestion gas G as fuel and supplies it to the thermal solubilization tank 11 and the mixing pot 12 of the solubilization device 2. Note that instead of using a steam boiler, the digestion gas G may be supplied to a digestion gas generator to generate electricity, and high-temperature steam recovered from the exhaust heat of the digestion gas generator (comprised of a digestion gas engine and a generator) may be supplied to the thermal solubilization tank 11 and the mixing pot 12.

[0018] The organic waste (sludge W2) digested in the digester 3 is stored in a digested sludge storage tank 5. A portion of the sludge W2 stored in the digested sludge storage tank 5 is sent to a sludge dewatering machine 6. The sludge dehydrator 6 is composed of, for example, a centrifugal dehydrator (decanter), a screw compression type dehydrator, a belt press dehydrator, etc. The dehydrated filtrate discharged from the sludge dehydrator 6 is sent to a water treatment system (not shown). The dewatered sludge W3 dewatered by the sludge dewaterer 6 is combined with the remainder of the sludge W2 discharged from the digested sludge storage tank 5, and then discharged by the sludge pump P through the dewatered sludge supply pipeline 7 to the solubilization device 2. The solubilization device 2 thermally solubilizes the dewatered sludge W3 that is continuously fed into the solubilization device 2, and the treated solubilized sludge W4 is returned to the digestion tank 3 via a return pipe 8. It is also possible that the entire amount of sludge W2 is sent from the digested sludge storage tank 5 to the sludge dewatering machine 6. It is also possible that the digested sludge storage tank 5 is not provided, and the sludge W2 is sent directly from the digestion tank 3 to the sludge dewatering machine 6. The residence time of the sludge in the solubilization device 2 is, for example, about 10 to 60 minutes.

[0019] (Solubilizer 2) Next, the configuration of the solubilization device 2 will be described in detail with reference to FIG. In the solubilization apparatus 2 of this embodiment, pretreatment of the dewatered sludge W3 is carried out in the mixing pot 12, and the treated sludge W5 treated in the mixing pot 12 is subjected to thermal solubilization treatment in the thermal solubilization tank 11. The steam supplying device 4 of the present embodiment supplies steam to the sludge in the thermal solubilization tank 11 and also supplies steam to the dewatered sludge W3 in the mixing pot 12.

[0020] The mixing pot 12 is connected to the downstream end of the dewatered sludge supply pipeline 7. The mixing pot 12 is configured to include a substantially cylindrical pot body 14 disposed as part of the dewatered sludge supply pipeline 7, and a steam pipe 15 inserted into the pot body 14 from its peripheral surface.

[0021] The pot body 14 is formed with a large diameter in the center and gradually tapers to a smaller diameter near the upper and lower ends. A flange 13 at one end (lower end) of the pot body 14 is bolted to a flange of the dewatered sludge supply pipeline 7. The opening diameter at the lower end of the pot body 14 is approximately the same as the inner diameter of the dewatered sludge supply pipeline 7, and the opening diameter at the upper end is approximately the same as the inner diameter of the lower end of the discharge nozzle 20 described below. In this embodiment, two steam pipes 15 are provided, which are offset from each other in the axial direction of the pot body 14 and inserted into the inside of the pot body 14 so as to extend in a direction perpendicular to the axial direction of the pot body 14. The periphery of the tip of the steam pipe 15 is fitted inside a steam pipe support portion 16 recessed into the inner peripheral surface of the pot body 14.

[0022] The thermal solubilization tank 11 is a sealed cylindrical body. The set pressure (target value) of the gas phase in the thermal solubilization tank 11 is about 0.2 MPa to 1.0 MPa, preferably 0.5 MPa to 0.8 MPa, and the set temperature is 120°C to 180°C, preferably 150°C to 170°C.

[0023] A large-diameter drain pipe 18 is attached coaxially to the lower end of the thermal solubilization tank 11, and a discharge nozzle 20 is coaxially disposed inside this drain pipe 18. The discharge nozzle 20 is made of a pipe member with an open lower end, and is connected to the upstream end of the mixing pot 12. A flange 21 at the lower end of the discharge nozzle 20 is bolted to a flange 22 at the upper end side of the pot body 14. The upper end of the discharge nozzle 20 is formed to have a slightly larger diameter than the pipe diameter near the lower end, and is disposed at the bottom of the thermal solubilization tank 11. The upper end of the discharge nozzle 20 is closed without opening. A plurality of small-diameter nozzle holes 23 are drilled at equal intervals in the circumferential direction around the upper end (discharge end) of the discharge nozzle 20 formed with a large diameter. That is, the plurality of nozzle holes 23 are formed at equal intervals around the axis O of the thermal solubilization tank 11). The hole diameter of the nozzle holes 23 is, for example, about 15 millimeters.

[0024] An outlet pipe 24 for discharging the solubilized sludge W4 to the outside is attached to the peripheral wall of the thermal solubilization tank 11. The outlet pipe 24 constitutes a part of the return pipeline 8. A liquid level control valve 24a for opening and closing the outlet pipe 24 is attached to the outlet pipe 24. The liquid level control valve 24a is, for example, an air-operated ball valve.

[0025] A liquid level sensor 34 is attached to the side of the thermal solubilization tank 11. The liquid level sensor 34 measures a physical quantity correlated with the liquid level of the sludge in the solubilization device 2. The liquid level sensor 34 in this embodiment is of a differential pressure type, and includes a sensor that measures the pressure of the gas phase in the thermal solubilization tank 11, and a sensor that measures the pressure of the liquid phase (sludge) in the thermal solubilization tank 11. The measurement result of the liquid level sensor 34 is output to the liquid level control means 35.

[0026] The liquid level control means 35 adjusts the opening degree of the liquid level adjustment valve 24a in accordance with the measurement value of the liquid level sensor 34, and adjusts the liquid level to a target value. The liquid level control means 35 transmits a control signal to the drive section of the liquid level adjustment valve 24a.

[0027] A gas exhaust pipe 31 and a pressure sensor 32 are attached to the top of the thermal solubilization tank 11. One end of the gas exhaust pipe 31 is connected to the top of the thermal solubilization tank 11, and the other end of the gas exhaust pipe 31 is connected to the outlet pipe 24. A pressure control valve 31a that opens and closes the gas exhaust pipe 31 is attached to the gas exhaust pipe 31. The pressure control valve 31a is, for example, an air-operated control valve.

[0028] The pressure sensor 32 measures the pressure of the gas phase in the thermal solubilization tank 11. The measurement result of the pressure sensor 32 is output to the pressure control means 33. The pressure control means 33 adjusts the opening of the pressure regulating valve 31a so that the measurement value of the pressure sensor 32 becomes the target value. In other words, the pressure of the gas phase part in the thermal solubilization tank 11 is controlled by the pressure control means 33. By controlling the measurement value of the pressure sensor 32 to a target value (set pressure), the saturated water vapor pressure in the gas phase in the thermal solubilization tank 11 can be kept constant, and the temperature in the gas phase can be kept at a temperature corresponding to the saturated water vapor pressure.

[0029] The steam supplying device 4 of this embodiment includes a steam injection pipe 25 that supplies high-temperature steam S2 into the thermal solubilization tank 11, in addition to the mixing pot 12 and the steam pipe 15. The steam injection pipe 25 is attached to the peripheral wall near the bottom of the thermal solubilization tank 11. A plurality of steam injection holes 26 are drilled in the steam injection pipe 25. The steam injection holes 26 have a hole diameter of about 6 mm.

[0030] (Method of Disposal of Organic Waste) Next, a method for treating organic waste will be described. The method for treating organic waste includes a supplying step, a measuring step, and a control step.

[0031] The supply step is a step of supplying steam generated in a steam boiler of the steam supplying device 4 as a heat source into the solubilization device 2 (thermal solubilization tank 11 and mixing pot 12). After the inside of the thermal solubilization tank 11 reaches a predetermined pressure, the dewatered sludge W3 is put into the solubilization device 2, and thermal solubilization is started at a predetermined temperature range.

[0032] The temperatures of the high-temperature steams S1 and S2 supplied from the steam supply device 4 are set to approximately the same temperature for convenience. If the set temperature of the gas phase in the thermal solubilization tank 11 is 160°C, the temperatures of the high-temperature steams S1 and S2 are set to approximately 175 to 180°C, which is slightly higher than the set temperature. As a result of testing by the inventor under these temperature conditions, it was confirmed that the sludge can be effectively thermally solubilized by supplying the high-temperature steams S1 and S2 at a total rate of 0.1 to 0.4 tons / hr, more preferably 0.15 to 0.35 tons / hr, for 1 ton of dewatered sludge W3, and setting the calorific value per unit time of the high-temperature steam S1 to the mixing pot 12 to be greater than the calorific value per unit time of the high-temperature steam S2 to the thermal solubilization tank 11, preferably at a ratio of about "high-temperature steam S1:high-temperature steam S2=7:3".

[0033] Moreover, the total amount of high-temperature steam S1 and S2 supplied to the thermal solubilization tank 11 is preferably a little more than the amount necessary for heating the dewatered sludge W3 to be supplied, taking into consideration heat radiation and exhaust from the thermal solubilization tank 11 and the gas exhaust pipe 31a. Specifically, when the amount of high-temperature steam necessary for heating is taken as 100% by mass, the increment is 3% by mass to 50% by mass.

[0034] The dewatered sludge W3 conveyed through the dewatered sludge supply pipeline 7 is directly mixed with the high-temperature steam S1 injected from the steam injection holes 17 of the steam pipe 15 in the mixing pot 12, whereby the dewatered sludge W3 is heated and given steam condensed moisture, thereby decreasing its viscosity. The temperature of the dewatered sludge W3 in the dewatered sludge supply pipeline 7 is approximately 25 to 35°C. The sludge whose viscosity has been reduced in the mixing pot 12 is fed as treated sludge W5 into the thermal solubilization tank 11 through the discharge nozzle 20. The treated sludge W5 fed into the thermal solubilization tank 11 is thermally solubilized by the high-temperature steam S2 injected from the steam injection holes 26 of the steam injection pipe 25, and after a predetermined residence time, is discharged from the outlet pipe 24 and conveyed to the digestion tank 3.

[0035] The measurement step is a step of continuously measuring the pressure of the gas phase part in the thermal solubilization tank 11 by the pressure sensor 32. The measured value of the pressure sensor 32 is sent to the pressure control means 33.

[0036] The control step is a step of controlling the opening degree of the pressure regulating valve 31a so that the pressure of the gas phase part in the thermal solubilization tank 11 measured in the measurement step becomes a target value. When the pressure in the thermal solubilization tank 11 exceeds the target value, the opening degree of the pressure regulating valve 31a is increased to release the gas (gas containing water vapor) in the thermal solubilization tank 11 to the outlet pipe 24 via the gas exhaust pipe 31. When the pressure in the thermal solubilization tank 11 falls below the target value, the opening degree of the pressure regulating valve 31a is reduced or fully closed to increase the pressure in the thermal solubilization tank 11. By controlling the pressure in the gas phase part of the thermal solubilization tank 11 to become the target value, the saturated water vapor pressure in the thermal solubilization tank 11 can be maintained at a predetermined value, and therefore the temperature of the gas phase part in the thermal solubilization tank 11 can be maintained within a predetermined temperature setting range (for example, 165±2°C).

[0037] According to the solubilization apparatus 2 described above, the gas (gas containing water vapor) in the thermal solubilization tank 11 is discharged to the outside of the thermal solubilization tank 11 through the gas exhaust pipe 31 based on the measured pressure of the gas phase in the thermal solubilization tank 11, so that the pressure in the thermal solubilization tank 11 can be kept constant. In addition, the gas (exhaust heat) discharged to the outside of the thermal solubilization tank 11 through the gas exhaust pipe 31 is supplied to the solubilized sludge W4 discharged from the thermal solubilization tank 11, so that the solubilized sludge W4 can be heated, and thus the amount of energy consumed for heating the digestion tank 3 can be reduced.

[0038] In this embodiment, the gas (exhaust heat) from the thermal solubilization tank 11 is supplied to the solubilized sludge W4 in the outlet pipe 24, so that the heat loss is small and the solubilized sludge W4 can be efficiently heated. In other words, the solubilized sludge W4 can be used as a heat source for the digestion tank 3.

[0039] Furthermore, the solubilization device 2 can keep the liquid level in the thermal solubilization tank 11 constant by adjusting the opening of the liquid level control valve 24a, so that variations in the thermal solubilization treatment are less likely to occur.

[0040] (Modification) Figure 3 shows a modified example of the treatment flow of the organic waste treatment system 1. In this treatment flow, organic waste W1 to be newly treated is first dehydrated in a sludge dewatering machine 6. Dehydrated sludge W3 is sent to the solubilization device 2 via a dehydrated sludge supply pipeline 7. Solubilized sludge W4 that has been thermally solubilized in the solubilization device 2 is continuously sent to the digester 3 via a flash tank 9 and a cooler 10. The solubilized sludge W4 undergoes methane fermentation in the digestion tank 3, and digestion gas G is sent to the steam supplying device 4. The digested sludge is either recovered outside or returned to the solubilization device 2. The steam supplying device 4 generates high-temperature steam using the digestion gas G as fuel and supplies it to the solubilization device 2.

[0041] Although the embodiment of the present invention has been described above, appropriate design changes are possible within the scope of the present invention. For example, the gas exhaust pipe 31 may be connected to the digestion tank 3 so that the gas in the thermal solubilization tank 11 is released into the digestion tank 3. [Explanation of symbols]

[0042] 1 Processing System 2 Solubilization device 3 Digestion tank 4 Steam supply device 7. Dewatered sludge supply pipe 11. Heat-solubilizing tank 12 Mixing Pot 24 Outlet pipe 31 Gas exhaust pipe 32 Pressure Sensor 33 Pressure control means 34 Liquid level sensor 35 Liquid level control means S1, S2 High temperature steam W1 Organic waste W3 Dewatered sludge W4 Solubilized sludge W5 Treated sludge

Claims

1. a thermal solubilization tank for performing thermal solubilization treatment on the sludge; A steam supplying device that supplies steam to the sludge in the thermal solubilization tank; a gas exhaust pipe for exhausting gas from the thermal solubilization tank to the solubilized sludge discharged from the thermal solubilization tank; a pressure sensor for measuring a pressure in the thermal solubilization tank; a pressure control valve for opening and closing the gas exhaust pipe; and a pressure control means for adjusting the opening of the pressure regulating valve so that the measurement value of the pressure sensor becomes a target value.

2. An outlet pipe for discharging the solubilized sludge from the thermal solubilization tank is provided, 2. The solubilization apparatus according to claim 1, wherein the gas exhaust pipe is connected to the outlet pipe.

3. a liquid level sensor for measuring a physical quantity correlated with the liquid level of the sludge in the thermal solubilization tank; a liquid level control valve that opens and closes the outlet pipe; 3. The solubilization apparatus according to claim 2, further comprising a liquid level control means for adjusting an opening degree of the liquid level control valve so that a measurement value of the liquid level sensor becomes a target value.

4. A solubilization device according to any one of claims 1 to 3, and a digestion tank for carrying out a digestion treatment on the solubilized sludge.

5. a steam supplying step of supplying steam as a heat source into a thermal solubilization tank in which the sludge is subjected to a thermal solubilization treatment; A measuring step of measuring a pressure in the thermal solubilization tank; a pressure control step of opening and closing a pressure regulating valve to release gas in the thermal solubilization tank into an outlet pipe through which solubilized sludge discharged from the thermal solubilization tank flows.