Processing method

Abstract

This invention provides a processing method to improve the quality of carbonized products manufactured from organic waste. [Solution] The processing method includes a removal step of removing magnetic material contained in organic waste, and a carbonization step of carbonizing the organic waste from which the magnetic material has been removed.

Description

TECHNICAL FIELD

[0001] The present invention relates to a treatment method for carbonizing organic waste.

BACKGROUND ART

[0002] Conventionally, a treatment method for carbonizing organic waste that has been subjected to fermentation treatment by anaerobic fermentation treatment is known (for example, see Patent Document 1).

[0003] The treatment method described in Patent Document 1 includes an anaerobic fermentation step of subjecting organic waste to anaerobic fermentation treatment, a hydrothermal carbonization step of generating carbonized sludge from dewatered sludge after the anaerobic fermentation step, and a curing step of curing the carbonized sludge generated in the hydrothermal carbonization step. In the hydrothermal carbonization step, the dewatered sludge is subjected to high-temperature and high-pressure treatment in a gas atmosphere containing no oxygen or having a low oxygen concentration. In the curing step, the carbonized sludge is subjected to low-temperature oxidation treatment with an oxygen-containing gas to reduce exothermic and ignitable properties.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

[0004]

PATENT DOCUMENT 1

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] By the way, organic waste includes, for example, food waste (food-based biomass) such as sewage sludge and kitchen garbage, lignocellulosic waste such as waste paper and used paper, agricultural residues, and livestock manure, and is also organic waste contained in sewage such as domestic wastewater and industrial wastewater. Foreign matter such as metals mainly composed of iron may be mixed into these types of organic waste. In that case, the foreign matter is not removed in the hydrothermal carbonization step and carbonized sludge is generated, which may lead to deterioration of the quality of the carbonized product after the curing treatment.

[0006] Therefore, there is a need for processing methods that improve the quality of carbonized products manufactured from organic waste. [Means for solving the problem]

[0007] The processing method according to the present invention is characterized by including a removal step of removing magnetic material contained in organic waste, and a carbonization step of carbonizing the organic waste from which the magnetic material has been removed.

[0008] As mentioned above, organic waste sometimes contains foreign substances such as metals, primarily iron, which can degrade the quality of the carbonized products after carbonization. In particular, magnetic materials such as iron are easily oxidized, so there was a risk of heat generation and ignition when carbonized products were subjected to low-temperature oxidation treatment, or during transportation or storage of the carbonized products.

[0009] Therefore, this method removes magnetic materials contained in organic waste. This reduces the content of magnetic materials in the organic waste, making it possible to produce high-quality carbonized products without adversely affecting the carbonization process in the carbonization stage.

[0010] Thus, this processing method improves the quality of carbonized products manufactured from organic waste.

[0011] Another feature is that it further includes an anaerobic fermentation step in which the organic waste is subjected to anaerobic fermentation treatment prior to the removal step.

[0012] As in this method, by treating organic waste with anaerobic fermentation in the pre-removal stage, the viscosity of the organic waste is reduced, allowing for the smooth removal of magnetic materials contained in the organic waste.

[0013] Another feature is that the removal process involves removing the magnetic material by attracting it to multiple rod-shaped magnets.

[0014] As demonstrated in this method, multiple rod-shaped magnets allow organic waste to pass through the gaps between them while attracting magnetic materials to the magnet surfaces, thus enabling smooth removal of magnetic materials during the transition to the carbonization process.

[0015] Another feature is that the carbonization process involves curing the carbonized material produced by hydrothermal carbonization of the organic waste from which the magnetic material has been removed.

[0016] As described in this method, by treating organic waste from which magnetic materials have been removed with hydrothermal carbonization and then curing the resulting carbonized material, organic waste can be carbonized in an environmentally friendly manner. On the other hand, curing treatment involves low-temperature oxidation of the carbonized material with an oxygen-containing gas, which may cause the magnetic materials to generate heat and ignite. As mentioned above, since the magnetic materials contained in the organic waste have been removed in this method, the curing treatment can be carried out smoothly. [Brief explanation of the drawing]

[0017] [Figure 1] This is a flowchart illustrating the processing method according to this embodiment. [Figure 2] This flowchart shows the removal process in detail according to this embodiment. [Figure 3] This is a flowchart showing the processing method according to another embodiment 1. [Figure 4] This is a flowchart showing the processing method according to another embodiment 2. [Modes for carrying out the invention]

[0018] The following describes embodiments of the treatment method according to the present invention with reference to the drawings. In this embodiment, a treatment method using a treatment system X that performs an anaerobic fermentation process and hydrothermal treatment of organic waste will be described as an example. However, the invention is not limited to the following embodiments, and various modifications are possible without departing from the gist of the invention.

[0019] The organic waste to be treated in the treatment system X of the present embodiment includes sewage sludge, food waste such as garbage (food-based biomass), lignocellulosic waste such as waste paper and used paper, agricultural residues, and livestock manure. Each of these organic wastes may be treated alone, or may be treated in a mixed state. The sludge generated from the water treatment facility 1 that treats sewage as the treatment target will be described as the organic waste. The sewage refers to sewage, industrial effluent, domestic wastewater, factory effluent and the like. Examples of the water treatment facility 1 for treating sewage include a sewage treatment facility for treating sewage, a wastewater treatment facility for treating wastewater, and the like.

[0020] As shown in Figure 1, the treatment system X is provided with a water treatment facility 1, a methane fermentation tank 2 (anaerobic fermentation treatment tank), a magnetic substance remover 3, a dehydrator 4, a hydrothermal treatment device 5, a solid-liquid separator 6, a curing hopper 7, and a gas power generator 22. The treatment system X in the present embodiment only needs to be provided with at least the magnetic substance remover 3 and the hydrothermal treatment device 5, but it is preferable that the treatment system X further includes the methane fermentation tank 2 and the curing hopper 7.

[0021] The water treatment facility 1 treats sewage. As an example, the sewage treatment facility includes a first sedimentation tank that precipitates suspended solids and organic matter contained in sewage and removes the sludge (primary sludge) settled at the bottom, a biological treatment tank that biologically treats and decomposes the organic matter in sewage, and a second sedimentation tank that precipitates the sludge after biological treatment to separate the treated water and the sludge (secondary sludge).

[0022] The methane fermentation tank 2 is a tank that subjects the sludge (an example of organic waste) discharged from the water treatment facility 1 to anaerobic fermentation treatment. Since the methane fermentation tank 2 performs anaerobic fermentation treatment, it is of a sealed type so as to prevent intrusion of outside air containing oxygen and prevent gas from leaking to the outside. The solid content concentration of the sludge fed into the methane fermentation tank 2 is, for example, 3 to 10% by weight. In the methane fermentation tank 2, in the mesophilic fermentation treatment, the temperature is about 30 to 42°C and the residence time is about 15 to 30 days, and in the thermophilic fermentation treatment, the temperature is about 50 to 60°C and the residence time is about 7 to 20 days. The anaerobic fermentation treatment in the present embodiment is a wet methane fermentation treatment.

[0023] The methane fermentation tank 2 generates biogas inside the methane fermentation tank 2 through anaerobic fermentation treatment of sludge. By subjecting sludge to anaerobic fermentation treatment, the energy contained in the sludge can be recovered as gas energy. The biogas is a gas containing approximately 60% by volume of methane and approximately 40% by volume of carbon dioxide. The generated biogas is extracted from the methane fermentation tank 2 via the gas discharge passage 21 and supplied to the gas power generator 22. The biogas supplied to the gas power generator 22 is used as fuel for the gas power generator 22. The biogas may also be used as fuel for heating the methane fermentation tank 2 or the hydrothermal treatment apparatus 5.

[0024] The fermentation residue of the sludge that has undergone anaerobic fermentation treatment in the methane fermentation tank 2 is discharged from the methane fermentation tank 2 to the outside. The fermented sludge discharged from the methane fermentation tank 2 to the outside is supplied to the dehydrator 4. The solid content concentration of the fermented sludge is, for example, 1.5 to 5% by mass. That is, the fermented sludge is a low-viscosity organic waste, and is in a liquid or slurry state that is constituted by a substance other than liquid or slurry high-viscosity organic waste that is difficult to transfer without a rotary positive displacement pump. This low-viscosity organic waste preferably has a viscosity of 0.2 Pa·s or less.

[0025] Organic waste is contained in sewage such as domestic wastewater and industrial wastewater, for example, and foreign matter such as metals mainly composed of iron may be mixed into this sewage. Therefore, in the present embodiment, before the fermented sludge discharged from the methane fermentation tank 2 is supplied to the dehydrator 4, the magnetic substance contained in the fermented sludge is removed by the magnetic substance remover 3.

[0026] As shown in Figure 2, the magnetic material removal machine 3 removes magnetic material by attracting it to a plurality of rod-shaped magnets 31. The magnetic material removal machine 3 comprises a magnet body 3A fixed to a lid portion 33 having a handle 32, with a plurality of rod-shaped magnets 31 arranged at equal intervals in the circumferential direction, and a container 3B that houses the plurality of rod-shaped magnets 31 inside. The magnet body 3A and the container 3B are integrated by fixing the lid portion 33 with a fastening member to a flange portion 35 that protrudes radially outward in an annular shape from the upper end of the container body 34 of the container 3B. A pair of pipes 37 and 38 are provided on both sides of the container body 34, with the downstream pipe 38 being at a higher position than the upstream pipe 37. These pipes 37 and 38 are fixed with fastening members (not shown) to a flange connection portion 34a in the middle of the piping that connects the methane fermentation tank 2 and the dewatering machine 4. Furthermore, the magnetic material removal device 3 may include a device in which magnets are fixed to the inner wall surface of the container or the inner wall surface of the flow path, or a device equipped with a magnetic drum inside the container or flow path, in which a cylindrical drum that rotates around an axis substantially perpendicular to the direction of flow is magnetized on its surface.

[0027] A bypass circuit 39 is provided between the methane fermentation tank 2 and the dewatering machine 4, bypassing the magnetic material removal machine 3. This bypass circuit 39 is equipped with an on-off valve V. A pump P is also provided between the methane fermentation tank 2 and the dewatering machine 4, downstream of the magnetic material removal machine 3 and the bypass circuit 39. By closing the on-off valve V and driving the pump P, the fermentation sludge passes through the gaps between the multiple bar-shaped magnets 31, and the magnetic material contained in the fermentation sludge is attracted to the bar-shaped magnets 31. At this time, since the downstream pipe 38 is at a higher position than the upstream pipe 37, the inconvenience of floating magnetic material being discharged towards the dewatering machine 4 before being attracted to the bar-shaped magnets 31 can be reduced. On the other hand, when removing the magnetic material attracted to the multiple bar-shaped magnets 31, the pump P is stopped, the on-off valve V is opened, the fermentation sludge is allowed to flow through the bypass circuit 39, the lid 33 is removed, and the multiple bar-shaped magnets 31 are washed.

[0028] The dewatering machine 4 is an example of a solid-liquid separation device used to dewater fermentation sludge discharged from the methane fermentation tank 2. The dewatering machine 4 can use any of the following: a belt press dewatering machine, a centrifugal dewatering machine, a screw press dewatering machine, a filter press dewatering machine, a belt concentrator, and a centrifugal concentrator. Of course, the dewatering machine 4 can also be constructed using other types of dewatering machines.

[0029] As shown in Figure 1, the dewatering machine 4 dewaters the fermented sludge to a dewatered sludge with a water content of approximately 80% by mass, for example. The dewatered filtrate separated from the fermented sludge by the dewatering machine 4 is sent to a separation liquid treatment device (not shown). This separation liquid treatment device is, for example, a device that performs acid coagulation and sedimentation treatment on the dewatered filtrate. The dewatered filtrate may be returned to the water treatment facility 1 either via the separation liquid treatment device or directly without going through the separation liquid treatment device.

[0030] Organic waste such as dewatered sludge is supplied to the hydrothermal treatment device 5. The hydrothermal treatment device 5 hydrothermally treats the organic waste such as dewatered sludge, whose moisture content has been reduced by the dewatering machine 4. Hydrothermal treatment can carbonize the dewatered sludge by treating the organic waste such as dewatered sludge at high temperature and high pressure in a gas atmosphere that does not contain oxygen or has a low oxygen concentration, or in a state where oxygen is blocked.

[0031] In the hydrothermal treatment apparatus 5, first, organic waste such as dewatered sludge supplied from the dewatering machine 4 is preheated. The preheated organic waste such as dewatered sludge is subjected to high temperature and high pressure treatment in a reactor (not shown). The reactor is a container that performs high temperature and high pressure treatment in a gas atmosphere that does not contain oxygen or has a low oxygen concentration, or in a state where oxygen is blocked. As an example, the reactor performs high temperature and high pressure treatment on organic waste such as dewatered sludge in a gas atmosphere with an oxygen concentration of 5 volume% or less. This high temperature and high pressure treatment is performed in the reactor of the hydrothermal treatment apparatus 5, and during this treatment, the oxygen concentration inside the reactor is maintained at approximately 0 volume%. Inside the reactor, the carbonized sludge (carbonized slurry) and the organic waste such as dewatered sludge supplied to the reactor are mixed and stirred.

[0032] The reactor is surrounded by a jacket (not shown), through which a heat transfer medium heated by the thermal energy of the waste heat from the gas generator 22 flows. The heat transfer medium heats the sludge slurry inside the reactor to, for example, 200°C. At this time, the pressure inside the reactor is the pressure equivalent to subcritical water corresponding to the temperature inside the reactor, plus the pressure from the gas produced by the decomposition of the components of the material being treated. Note that the temperature of the sludge slurry inside the reactor is not limited to 200°C, but may be any temperature within the range of, for example, 160°C to 250°C. The pressure inside the reactor is set to a gauge pressure of approximately 0.6 MPa to 3 MPa. Therefore, in the hydrothermal treatment apparatus 5, high-temperature and high-pressure treatment is performed when the temperature of organic waste such as dewatered sludge is between 160°C and 250°C, and the pressure inside the reactor is between 0.6 MPa and 3 MPa.

[0033] The carbonized slurry obtained by hydrothermal treatment in the reactor is cooled and supplied to the solid-liquid separator 6. The solid-liquid separator 6 separates the carbonized slurry supplied from the hydrothermal treatment device 5 into solid and liquid components. The solid-liquid separator 6 is a machine that dewaters the carbonized slurry supplied from the hydrothermal treatment device 5. The solid-liquid separator 6 is not particularly limited, but it is preferably a filter press dewatering machine. The carbonized slurry is a state in which finely divided carbonized material is dispersed in water. Therefore, a filter press dewatering machine with a fine mesh and that can obtain a high solid recovery rate even when compressed under high pressure is suitable. Of course, the solid-liquid separator 6 can also be constructed using other dewatering machines, for example, a centrifugal dewatering machine or a screw press dewatering machine can be used.

[0034] The carbonized slurry separated into solid and liquid components in the solid-liquid separator 6 becomes a solid material consisting of, for example, carbonized sludge with a water content of 35% by mass or less. This solid material is supplied to the curing hopper 7, where it is dried by contact with an oxygen-containing gas and subjected to low-temperature oxidation treatment. This reduces the exothermic and flammable nature of the solid material (carbonized sludge), and the resulting carbonized material can be recycled as carbonized products such as fertilizer or solid fuel.

[0035] The decomposition gas generated in the reactor of the hydrothermal treatment device 5 and the odor gas generated in the solid-liquid separator 6 are supplied to a deodorizing device (not shown) for deodorization. The dewatered filtrate discharged from the solid-liquid separator 6 may be refluxed to the methane fermentation tank 2, or it may be subjected to acid coagulation and precipitation treatment in the separation liquid treatment device (not shown) described above.

[0036] (Processing method) The following describes a treatment method for carbonizing organic waste, using Figures 1 and 2.

[0037] As shown in Figure 1, the processing method in this embodiment includes a removal step to remove magnetic material contained in dewatered sludge (an example of organic waste) and a carbonization step to carbonize the dewatered sludge from which the magnetic material has been removed. The processing method may further include an anaerobic fermentation step in which the sludge (an example of organic waste) is subjected to anaerobic fermentation before the removal step. Furthermore, the processing method may include a water treatment step in which wastewater is treated to produce sludge before the anaerobic fermentation step, or a dewatering step in which the fermented sludge from which the magnetic material has been removed is dewatered after the removal step.

[0038] The anaerobic fermentation process generates biogas in the methane fermentation tank 2 through anaerobic fermentation of the sludge. The generated biogas is removed from the methane fermentation tank 2 via the gas discharge channel 21 and supplied to the gas generator 22.

[0039] The removal process involves closing the on-off valve V and driving the pump P, which removes the magnetic material contained in the fermented sludge using the magnetic material remover 3. Specifically, the fermented sludge passes through the gaps between multiple rod-shaped magnets 31, and the magnetic material contained in the fermented sludge is attracted to the rod-shaped magnets 31 (see Figure 2). In the magnetic material remover 3, the multiple rod-shaped magnets 31 allow the fermented sludge to pass through the gaps between them while attracting magnetic material with their surfaces, thus enabling smooth removal of magnetic material during the transition from the anaerobic fermentation process to the carbonization process.

[0040] In the carbonization process, the fermented sludge from which the magnetic material has been removed by the magnetic material removal machine 3 is dewatered by the dewatering machine 4, and the resulting dewatered sludge is treated as organic waste and subjected to hydrothermal treatment in the hydrothermal treatment device 5. Specifically, the fermented sludge from which the magnetic material has been removed by the magnetic material removal machine 3 is dewatered by the dewatering machine 4 to reduce its water content and supplied to the hydrothermal treatment device 5 as dewatered sludge. Alternatively, the fermented sludge treated in the methane fermentation tank 2 without going through the dewatering machine 4 may be supplied to the hydrothermal treatment device 5 as fermented sludge from which the magnetic material has been removed by the magnetic material removal machine 3.

[0041] Furthermore, in the carbonization process, the carbonized slurry obtained by hydrothermal treatment in the reactor of the hydrothermal treatment device 5 is separated into solid and liquid components in the solid-liquid separator 6, resulting in a solid material consisting of carbonized sludge with a water content of, for example, 35% by mass or less. This solid material is supplied to the curing hopper 7, where it is dried by contact with an oxygen-containing gas and subjected to low-temperature oxidation treatment. This reduces the exothermic and flammable nature of the solid material (carbonized sludge), and the resulting carbonized material can be recycled as carbonized products such as fertilizer or solid fuel.

[0042] Incidentally, wastewater may contain foreign substances such as metals, mainly composed of iron, which can degrade the quality of the carbonized product after carbonization in the carbonization process. In particular, magnetic materials such as iron are easily oxidized, so there was a risk of heat generation and ignition when the carbonized product was subjected to low-temperature oxidation treatment, or during the transport or storage of the carbonized product. Therefore, in this embodiment, magnetic materials contained in the fermented sludge treated in the anaerobic fermentation process are removed. This reduces the content of magnetic materials in the dewatered sludge, making it possible to produce high-quality carbonized products without adversely affecting the carbonization process in the carbonization step.

[0043] Furthermore, if the organic waste is subjected to anaerobic fermentation treatment in the stage prior to the removal process, the viscosity of the organic waste is reduced, and the magnetic material contained in the organic waste can be smoothly removed. In addition, if the dewatered sludge from which the magnetic material has been removed is subjected to hydrothermal carbonization treatment in the carbonization process and the resulting carbonized material is cured in the curing hopper 7, the fermented sludge can be carbonized in a way that has a low environmental impact. On the other hand, since the curing treatment involves low-temperature oxidation treatment of the carbonized material with an oxygen-containing gas, there is a risk that the magnetic material will generate heat and ignite. As described above, in this embodiment, since the magnetic material contained in the fermented sludge treated with anaerobic fermentation is removed in the anaerobic fermentation process, the curing treatment can be carried out smoothly.

[0044] (Another Embodiment 1) Hereinafter, another embodiment 1 will be described using Figure 3. In this embodiment, only the differences from the embodiment described above will be explained, and in order to facilitate understanding of the invention, similar components will be denoted by the same reference numerals.

[0045] In this embodiment, the treatment system X has a methane fermentation tank 2 and a hydrothermal treatment device 5 provided in separate systems (different equipment systems). Organic waste such as fermentation sludge transported from the methane fermentation tank 2 in the separate system is supplied to the hydrothermal treatment device 5 via a magnetic material remover 3 (removal process). The other configurations are the same as in the first embodiment, so their description is omitted. In this case as well, the organic waste supplied to the magnetic material remover 3 can be sewage sludge transported from other systems, food waste such as kitchen waste (food biomass), lignocellulosic waste such as recycled paper and waste paper, agricultural residues, and livestock manure. This embodiment also produces the same effects as the embodiment described above. Note that the organic waste supplied to the magnetic material remover 3 is not limited to fermentation sludge, as long as it is low-viscosity organic waste (for example, with a viscosity of 0.2 Pa·s or less).

[0046] (Another Embodiment 2) Hereinafter, another embodiment 2 will be described using Figure 4. In this embodiment, only the differences from the embodiment described above will be explained, and in order to facilitate understanding of the invention, similar components will be denoted by the same reference numerals.

[0047] In this embodiment, the processing system X receives low-viscosity organic waste (for example, with a viscosity of 0.2 Pa·s or less) from a magnetic material remover 3 to a drying device 8 (removal process). The organic waste from which the magnetic material has been removed by the magnetic material remover 3 is dried in the drying device 8 and supplied to a carbonization device 9 as dried sludge, where it is carbonized to produce a carbonized product (carbonization process). The drying device 8 is, for example, a hot air drying furnace that uses combustion exhaust gas or the like as a heat source to dry the organic waste and obtain dried sludge. The carbonization device 9 is, for example, a rotary kiln, a fluidized bed type, or a heating device of heat transfer disk or screw type.

[0048] In this embodiment, since temperature control of the drying apparatus 8 is difficult when low-viscosity organic waste contains metals, mainly iron, the magnetic material remover 3 is placed even further upstream of the drying apparatus 8 than the carbonization apparatus 9. This makes temperature control of the drying apparatus 8 easier, enabling the supply of dried sludge with an appropriate moisture content to the carbonization apparatus 9, and allowing the production of high-quality carbonized products.

[0049] [Other embodiments] (1) The water treatment facility 1 in the above-described embodiment may be omitted. In this case, the organic waste supplied to the methane fermentation tank 2 is transported and brought in from another system. For example, sludge generated at a water treatment facility in a different location may be transported and supplied to the methane fermentation tank 2. (2) The dewatering machine 4 in the above-described embodiment may be omitted. In this case, the organic waste supplied to the hydrothermal treatment device 5 will have a higher water content, but a similar carbonized slurry can be produced by redesigning the hydrothermal treatment device 5 to have a larger capacity, or by increasing the processing time and processing energy in the hydrothermal treatment device 5. (3) The solid-liquid separator 6 in the above-described embodiment may be omitted. In this case, the application is applicable to cases where the low moisture content of the carbide is not required as described above. (4) The gas generator 22 in the above-described embodiment may be omitted. In this case, the biogas may be used as fuel in other equipment, or the biogas may be packed into a tank and distributed. (5) The methane fermentation tank 2 in the above-described embodiment is not particularly limited as long as it is a fermentation tank capable of producing biogas by anaerobic fermentation treatment. [Industrial applicability]

[0050] This invention can be used in a treatment method for carbonizing organic waste. [Explanation of symbols]

[0051] 1: Water treatment equipment, 2: Methane fermentation tank, 3: Magnetic material removal machine, 3A: Magnet, 3B: Container, 4: Dewatering machine, 5: Hydrothermal treatment device, 6: Solid-liquid separator, 7: Curing hopper, 21: Gas discharge channel, 22: Gas generator, 31: Bar magnet, 32: Handle, 33: Lid, 34: Container body, 34a: Flange connection, 35: Flange, 37: Piping, 38: Piping, 39: Bypass, P: Pump, V: On / off valve, X: Treatment system

Claims

1. A removal process to remove magnetic materials contained in organic waste, A processing method comprising a carbonization step of carbonizing the organic waste from which the magnetic material has been removed.

2. The treatment method according to claim 1, further comprising an anaerobic fermentation step of treating the organic waste with anaerobic fermentation in a step prior to the removal step.

3. The removal step is the processing method according to claim 1, wherein the magnetic material is removed by adsorbing it onto a plurality of rod-shaped magnets.

4. The treatment method according to any one of claims 1 to 3, wherein the carbonization step involves curing the carbonized material produced by hydrothermal treatment of the organic waste from which the magnetic material has been removed.

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