Solubilization device, organic waste treatment system, and treatment method

Abstract

The present invention is characterized by comprising: a heat solubilization tank (11) that performs heat solubilization treatment on sludge; a steam supply device (4) that supplies steam to the sludge in the heat solubilization tank (11); a gas discharge pipe (31) that discharges a gas in the heat solubilization tank (11) to the solubilized sludge (W4) discharged from the heat solubilization tank (11); a pressure sensor (32) that measures the pressure inside the heat solubilization tank (11); a pressure control valve (31a) that opens and closes the gas discharge pipe (31); and a pressure control means (33) that adjusts the opening degree of the pressure control valve (31a) such that the measured value of the pressure sensor (32) reaches a target value.

Description

Solubilization device, organic waste treatment system and treatment method

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

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

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

[0004] JP-T-2003-500208 A JP-A-2007-117801 A JP-A-2009-148650 A JP-T-2011-516246 A Japanese Patent No. 6159573

[0005] In thermal solubilization treatment, it is preferable to maintain the temperature in the thermal solubilization tank at a predetermined set temperature. However, when thermal solubilization treatment is performed continuously in the thermal solubilization tank, heat is transferred in and out as sludge is supplied and discharged, 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 inflow. However, fine adjustment of the amount of steam inflow is difficult and may fluctuate more than necessary, so even if the amount of steam inflow is changed to adjust the temperature in the thermal solubilization tank, there is a risk that the temperature will not be stable.

[0006] An object of the present invention is to provide a solubilization device, an organic waste treatment system, and a treatment method that can maintain a constant temperature inside a thermal solubilization tank.

[0007] The solubilization apparatus of the present invention, which solves these problems, comprises a thermal solubilization tank that performs thermal solubilization treatment on sludge, a steam supply device that supplies steam to the sludge in the thermal solubilization tank, a gas exhaust pipe that exhausts gas from the thermal solubilization tank to the solubilized sludge discharged from the thermal solubilization tank, a pressure sensor that measures the pressure in the thermal solubilization tank, a pressure control valve that opens and closes the gas exhaust pipe, and pressure control means that adjusts the opening of the pressure control valve so that the measurement value of the pressure sensor becomes a target value.

[0008] The organic waste treatment method of the present invention also includes a steam supply step of supplying steam as a heat source into a thermal solubilization tank in which sludge is subjected to thermal solubilization treatment, a measurement step of measuring the pressure inside the thermal solubilization tank, and a pressure control step of opening and closing a pressure control 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 discharge pipe based on the measured pressure in the thermal solubilization tank, thereby maintaining a constant pressure in the thermal solubilization tank. In other words, according to the present invention, the saturated water vapor pressure in the gas phase in the thermal solubilization tank can be maintained constant, thereby maintaining the temperature in the gas phase at a temperature corresponding to the saturated water vapor pressure, thereby reducing variations in the thermal solubilization treatment. Furthermore, the gas (exhaust heat) discharged to the outside of the thermal solubilization tank through the gas discharge pipe is supplied to the solubilized sludge discharged from the thermal solubilization tank, thereby heating the solubilized sludge and thereby reducing energy consumption during the digestion treatment of the solubilized sludge.

[0010] When the thermal solubilization tank is provided with an outlet pipe for discharging the solubilized sludge, it is preferable that the gas exhaust pipe be connected to the outlet pipe, which allows the solubilized sludge to be heated efficiently.

[0011] The solubilization apparatus preferably includes a level sensor that measures a physical quantity correlated with the liquid level of the sludge in the thermal solubilization tank, a level adjustment valve that opens and closes the outlet pipe, and a level control means that adjusts the aperture of the level adjustment valve so that the measurement value of the 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 device and a digestion tank for performing digestion treatment on the solubilized sludge.

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

[0014] 1 is a process flow diagram of an organic waste treatment system; FIG. 2 is a cross-sectional view of a solubilization device; FIG. 3 is another process flow diagram of an organic waste treatment system;

[0015] (Treatment System 1) The configuration of an organic waste treatment system 1 according to the present invention will be described with reference to Figure 1. The organic waste treatment system 1 comprises a solubilization apparatus 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 apparatus 2. The organic waste treatment system 1 of this embodiment also comprises a digested sludge storage tank 5 that stores the organic waste (sludge W2) that has been digested in the digestion tank 3, a sludge dehydrator 6 that dehydrates the sludge W2 sent from the digested sludge storage tank 5 to produce 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 for pre-treating the dewatered sludge W3, a thermal solubilization tank 11 for thermal solubilization of the treated sludge W5 discharged from the mixing pot 12, a steam supply device 4 for supplying steam to the sludge in the thermal solubilization tank 11 and the mixing pot 12, a gas exhaust pipe 31 for exhausting gas from the tank 11, and a pressure control valve 31a for opening and closing 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 control valve 31a so that the measurement value of the pressure sensor 32 becomes the target value, an outlet pipe 24 that discharges the solubilized sludge W4 from the thermal solubilization tank 11, a liquid level sensor 34 that measures a physical quantity correlated with 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 the 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, kitchen garbage, livestock manure, etc. In the digester 3, the organic waste W1 undergoes methane fermentation (digestion treatment) using anaerobic methane fermentation bacteria. The operating temperature of the digester 3 is set appropriately 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 supply device 4. The steam supply 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. 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 (composed 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 the digested sludge storage tank 5. A portion of the sludge W2 stored in the digested sludge storage tank 5 is sent to a sludge dehydrator 6. The sludge dehydrator 6 may be, for example, a centrifugal dehydrator (decanter), a screw compression dehydrator, or a belt press dehydrator. The dehydrated filtrate discharged from the sludge dehydrator 6 is sent to a water treatment system (not shown). The dehydrated sludge W3 dehydrated by the sludge dehydrator 6 is combined with the remainder of the sludge W2 discharged from the digested sludge storage tank 5 and then sent by a sludge pump P through a dehydrated sludge supply pipe 7 to the solubilizer 2. The solubilizer 2 thermally solubilizes the dehydrated sludge W3 continuously introduced into the solubilizer 2, and the treated solubilized sludge W4 is returned to the digester 3 through 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 dehydrator 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 dehydrator 6. The residence time of the sludge in the solubilization device 2 is, for example, about 10 to 60 minutes.

[0019] (Solubilization Apparatus 2) Next, the configuration of the solubilization apparatus 2 will be described in detail with reference to Figure 2. In the solubilization apparatus 2 of this embodiment, pretreatment of dewatered sludge W3 is performed 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 this 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 the circumferential surface thereof.

[0021] The pot body 14 has a large diameter in the center and gradually narrows toward 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 pipe 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 pipe 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, and they are inserted into the pot body 14 so as to be offset from each other in the axial direction of the pot body 14 and extend in a direction perpendicular to the axial direction of the pot body 14. The tip of the steam pipe 15 is fitted into a steam pipe support portion 16 recessed in 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 generally 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 within the drain pipe 18. The discharge nozzle 20 is composed of a tubular 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 of the pot body 14. The upper end of the discharge nozzle 20 is formed with 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 and not open. A plurality of small-diameter nozzle holes 23 are drilled around the upper end (discharge end) of the large-diameter discharge nozzle 20 at equal intervals in the circumferential direction. That is, the plurality of nozzle holes 23 are formed at equal intervals around the axis O of the thermal solubilization tank 11. The diameter of the nozzle holes 23 is, for example, approximately 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 reflux 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 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 sends a control signal to the drive unit 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 a target value. In other words, the pressure of the gas phase 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 become 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 therefore the temperature in the gas phase can be kept at a temperature corresponding to the saturated water vapor pressure.

[0029] The steam supply device 4 of this embodiment includes, in addition to the mixing pot 12 and the steam pipe 15, a steam injection pipe 25 that supplies high-temperature steam S2 into the thermal solubilization tank 11. The steam injection pipe 25 is attached to the peripheral wall near the bottom of the thermal solubilization tank 11. The steam injection pipe 25 is perforated with a plurality of steam injection holes 26. The diameter of the steam injection holes 26 is approximately 6 millimeters.

[0030] (Method for Treating 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 in which steam generated in the steam boiler of the steam supply device 4 is supplied as a heat source into the solubilization device 2 (thermal solubilization tank 11 and mixing pot 12). After the pressure inside the thermal solubilization tank 11 reaches a predetermined pressure, dewatered sludge W3 is introduced into the solubilization device 2, and thermal solubilization is initiated within a predetermined temperature range.

[0032] For convenience, the temperatures of the high-temperature steams S1 and S2 supplied from the steam supply device 4 are set to approximately the same temperature. 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. As a result of tests conducted by the inventors under these temperature conditions, it has been confirmed that 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 ton / hr, more preferably 0.15 to 0.35 ton / hr, per ton of dewatered sludge W3, and by 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 approximately "high-temperature steam S1:high-temperature steam S2 = 7:3."

[0033] Furthermore, the total amount of high-temperature steam S1 and S2 supplied to the thermal solubilization tank 11 is preferably slightly more than the amount necessary to heat 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 100% by mass, the increment is 3% by mass to 50% by mass.

[0034] The dewatered sludge W3 transported through the dewatered sludge supply pipeline 7 is directly mixed in the mixing pot 12 with high-temperature steam S1 injected from the steam injection holes 17 of the steam pipe 15, thereby heating the dewatered sludge and adding steam condensed water, thereby reducing 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 with 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 transported to the digester 3.

[0035] The measurement step is a step of continuously measuring the pressure of the gas phase 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 aperture of the pressure control valve 31a so that the pressure of the gas phase 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 aperture of the pressure control valve 31a is increased to release the gas (gas containing water vapor) in the thermal solubilization tank 11 through the gas exhaust pipe 31 to the outlet pipe 24. When the pressure in the thermal solubilization tank 11 falls below the target value, the aperture of the pressure control 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 in 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 the temperature of the gas phase in the thermal solubilization tank 11 can be maintained within a predetermined temperature setting range (e.g., 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 discharge pipe 31 based on the measured pressure of the gas phase in the thermal solubilization tank 11, thereby maintaining a constant pressure in the thermal solubilization tank 11. Furthermore, the gas (exhaust heat) discharged to the outside of the thermal solubilization tank 11 through the gas discharge pipe 31 is supplied to the solubilized sludge W4 discharged from the thermal solubilization tank 11, thereby heating the solubilized sludge W4 and ultimately reducing the amount of energy consumed for heating the digestion tank 3.

[0038] In addition, 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 heat loss is minimal 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 maintain a constant liquid level in the thermal solubilization tank 11 by adjusting the opening of the liquid level control valve 24a, which reduces the occurrence of variations in the thermal solubilization treatment.

[0040] (Modification) Figure 3 shows a modification of the treatment flow of the organic waste treatment system 1. In this treatment flow, newly treated organic waste W1 is first dehydrated in a sludge dehydrator 6. Dehydrated sludge W3 is sent to the solubilization apparatus 2 via a dehydrated sludge supply pipeline 7. Solubilized sludge W4 that has been thermally solubilized in the solubilization apparatus 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 digester 3, and digestion gas G is sent to the steam supply device 4. The digested sludge is either recovered externally or returned to the solubilization apparatus 2. The steam supply device 4 generates high-temperature steam using the digestion gas G as fuel and supplies it to the solubilization apparatus 2.

[0041] Although the embodiment of the present invention has been described above, appropriate design modifications 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 can be released into the digestion tank 3.

[0042] REFERENCE SIGNS LIST 1 Treatment system 2 Solubilization device 3 Digestion tank 4 Steam supply device 7 Dewatered sludge supply line 11 Thermal solubilization 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 solubilization apparatus comprising: 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 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. The solubilization apparatus according to claim 1, further comprising an outlet pipe for discharging the solubilized sludge from the thermal solubilization tank, the gas exhaust pipe being connected to the outlet pipe.

3. The solubilization apparatus according to claim 2, characterized in that it comprises a liquid level sensor that measures a physical quantity correlated with 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 adjustment valve so that the measurement value of the liquid level sensor becomes a target value.

4. An organic waste treatment system comprising: a solubilization apparatus 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 method for treating organic waste comprising: 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.

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