Digestive system and temperature control method

Abstract

This invention provides a digestion system and temperature control method that allow for easy control of the temperature inside a tank. [Solution] The system comprises a digester tank for digesting sludge, a first pipe for supplying sludge to the digester tank, a storage tank communicating with the first pipe for storing the sludge supplied to the digester tank, a second pipe for supplying excess sludge to the storage tank, a heater provided in the second pipe for heating the excess sludge in the second pipe with a first fluid, and a control device that controls at least one of the supply of excess sludge to the heater and the supply of the first fluid to the heater based on the temperature related to digestion.

Description

Technical Field

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[0001] The present disclosure relates to a digestion system and a temperature control method.

Background Art

[0002] In a digestion system having a tank (hereinafter also referred to as a digestion tank) for digesting a material to be treated (for example, organic substances contained in primary sediment and excess sludge), a technique has been proposed to realize efficient digestion of the material to be treated by maintaining the temperature in the tank at an appropriate temperature (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the digestion system as described above, for example, it is desired to easily control the temperature in the tank so that the temperature in the tank is maintained at an appropriate temperature. [[ID=3​​​​​​​​​​​​According to the digestion system and temperature control method described herein, it becomes possible to easily control the temperature inside the tank. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a diagram illustrating the configuration of the processing system 1000 in the first embodiment. [Figure 2] Figure 2 is a diagram illustrating the configuration of the temperature control system 100 in the first embodiment. [Figure 3] Figure 3 is a diagram illustrating the hardware configuration of the control device 200 in the first embodiment. [Figure 4] Figure 4 is a diagram illustrating the functions of the control device 200 in the first embodiment. [Figure 5] Figure 5 is a flowchart illustrating the temperature control process in the first embodiment. [Figure 6] Figure 6 illustrates the configuration of the temperature control system 100 in the first modified example. [Figure 7] Figure 7 illustrates the configuration of the temperature control system 100 in a second modified example. [Modes for carrying out the invention]

[0008] Embodiments of this disclosure will be described below with reference to the drawings. However, this description should not be interpreted as limiting, and will not limit the subject matter described in the claims. Furthermore, various changes, substitutions, and modifications can be made without departing from the spirit and scope of this disclosure. Different embodiments can also be combined as appropriate.

[0009] [Processing system 1000 in the first embodiment] First, the processing system 1000 in the first embodiment will be described. Figure 1 is a diagram illustrating the configuration of the processing system 1000 in the first embodiment.

[0010] The processing system 1000 in this embodiment is a water treatment system that processes liquids such as sewage (hereinafter also referred to as treated water).

[0011] Specifically, as shown in Figure 1, the processing system 1000 includes, for example, a primary sedimentation tank 10, a tank 20 (hereinafter also referred to as the reaction tank 20), a final sedimentation tank 30, a concentration device 40, a concentration device 50, a tank 60 (hereinafter also referred to as the digestion tank 60), a temperature control system 100, and a control device 200. Hereafter, the processing system 1000 will also be referred to as the digestion system 1000.

[0012] The primary sedimentation tank 10 separates pollutants such as organic matter (e.g., solid organic matter) contained in the water to be treated by sedimentation. The separated pollutants (hereinafter also called primary sludge) are then discharged to the concentration device 40 by a pump (not shown), for example. The water to be treated after the sedimentation of pollutants has been performed is then discharged to the reaction tank 20 by a pump (not shown), for example.

[0013] The reaction tank 20 is a tank that treats the water to be treated by biological treatment, such as the standard activated sludge process. Specifically, the reaction tank 20 uses microorganisms (hereinafter also called activated sludge) cultivated in the reaction tank 20 to decompose organic matter (e.g., dissolved organic matter) contained in the water to be treated. After the organic matter has been decomposed by the activated sludge, the water to be treated is discharged from the reaction tank 20 to the final sedimentation tank 30, for example, by overflow.

[0014] The final sedimentation tank 30, for example, separates and discharges the activated sludge contained in the treated water discharged from the reaction tank 20. A portion of the separated activated sludge (hereinafter also referred to as excess sludge) is discharged to the concentration device 50 by a pump (not shown), for example. Another portion of the separated activated sludge (hereinafter also referred to as return sludge) is returned to the reaction tank 20 by a pump (not shown), for example. Furthermore, the treated water after the separation of activated sludge is discharged to a subsequent sterilization device (not shown) by overflow, for example. The sterilization device then sterilizes the treated water discharged from the final sedimentation tank 30, for example, and discharges the sterilized treated water into a river, etc.

[0015] The concentration device 40 concentrates, for example, the primary sludge discharged from the primary sedimentation tank 10. The concentrated primary sludge is then discharged to the digester tank 60 by, for example, a pump (not shown). The liquid separated from the primary sludge by concentration is returned to the primary sedimentation tank 10 by, for example, a pump (not shown).

[0016] The concentration device 50 concentrates, for example, the excess sludge discharged from the final sedimentation tank 30. The concentrated excess sludge is then discharged to the digester tank 60 by, for example, a pump (not shown). The liquid separated from the excess sludge by concentration is returned to the final sedimentation tank 30 by, for example, a pump (not shown).

[0017] The digester 60, for example, uses anaerobic bacteria within the digester 60 to anaerobically digest (decompose) organic matter contained in the sludge (hereinafter simply referred to as sludge), including the primary sedimentation sludge supplied from the concentration unit 40 and the excess sludge supplied from the concentration unit 50, through biological reactions to produce digested sludge. Specifically, the anaerobic bacteria in the digester 60 produce digester gases (hereinafter simply referred to as digester gases), such as methane gas, during the digestion process. It is preferable to maintain the temperature of the digested sludge (digested liquid) in the digester 60 between 35°C and 39°C (hereinafter referred to as the optimal temperature) in order to efficiently promote biological reactions and improve the digestion rate.

[0018] The temperature adjustment system 100 adjusts, for example, the temperature of excess sludge before it is supplied to the digestion tank 60. Specifically, the temperature adjustment system 100 heats, for example, the excess sludge before it is supplied to the digestion tank 60. Hereinafter, the temperature adjustment system 100 will be described.

[0019] [Temperature adjustment system 100 in the first embodiment] FIG. 2 is a diagram for explaining the configuration of the temperature adjustment system 100 in the first embodiment.

[0020] As shown in FIG. 2, the temperature adjustment system 100 in the present embodiment includes, for example, a heater 110, a buffer tank 120 (hereinafter also referred to as a storage tank 120), a pump P1, a pump P2, and a pump P3.

[0021] The pump P1 is provided, for example, upstream of the branch point with the line L3 in the line L1, supplies at least a part of the excess sludge supplied from the concentration device 50 to the heater 110, and further supplies the excess sludge heated by the heater 110 to the buffer tank 120. The line L1 is a pipe that communicatively connects the concentration device 50, the heater 110, and the buffer tank 120 in this order. And in the line L1, for example, at a position between the branch point with the line L3 and the heater 110, a valve V1 capable of adjusting the flow rate of the excess sludge supplied to the line L1 (heater 110) is provided. Hereinafter, the line L1 will also be referred to as the second pipe.

[0022] The pump P2 is provided, for example, in the line L2, and supplies the primary sedimentation sludge supplied from the concentration device 40 to the buffer tank 120. The line L2 is a pipe that communicatively connects the concentration device 40 and the buffer tank 120. And in the line L2, for example, a valve V2 capable of adjusting the flow rate of the primary sedimentation sludge in the line L2 is provided.

[0023] The buffer tank 120 is, for example, connected to line L1 and line L2, and is a tank that temporarily stores at least one of the excess sludge supplied from the thickening device 50 via line L1 and the primary sedimentation sludge supplied from the thickening device 40 via line L2. Specifically, the buffer tank 120 is, for example, a tank with a smaller capacity than the digestion tank 60.

[0024] Pump P3 is installed, for example, in line L4 and supplies sludge stored in buffer tank 120 to digester tank 60. Line L4 is, for example, piping connecting buffer tank 120 and digester tank 60. Line L4 is also provided with, for example, valve V4 that can adjust the flow rate of sludge in line L4. Hereinafter, line L4 will also be referred to as the first piping.

[0025] The following explanation will describe the case in which the buffer tank 120 stores both the excess sludge supplied from the thickening device 50 and the primary sedimentation sludge supplied from the thickening device 40, but it is not limited to this case. Specifically, for example, only the excess sludge supplied from the thickening device 50 may be supplied to the buffer tank 120. In this case, the primary sedimentation sludge supplied from the thickening device 40 may be supplied directly to the digestion tank 60, for example.

[0026] The heater 110 heats the excess sludge supplied from the concentration device 50 via line L1, for example. Specifically, the heater 110 is a heat exchanger that heats the excess sludge with a fluid that is a heat transfer medium, such as steam (hereinafter also referred to simply as the fluid or first fluid). The fluid may be a fluid that circulates between a heat source device (not shown) capable of heating the fluid and the heater 110. The excess sludge heated by the heater 110 is then supplied to the buffer tank 120 via line L1, for example.

[0027] Furthermore, line L1 is provided with, for example, line L3, which bypasses the heater 110. Line L3 is, for example, piping that connects the position between pump P1 and heater 110 in line L1 with the position between heater 110 and buffer tank 120 in line L1. In other words, line L3 is, for example, piping that connects the inlet side of heater 110 with the outlet side of heater 110. Line L3 is provided with, for example, valve V3 that can adjust the amount of excess sludge supplied to line L3. Hereinafter, line L3 will also be referred to as the third piping.

[0028] In other words, the processing system 1000 in this embodiment can supply at least a portion of the excess sludge supplied from the concentration device 50 to the buffer tank 120 without supplying it to the heater 110. To put it another way, the processing system 1000 in this embodiment can supply at least a portion of the excess sludge supplied via line L1 to the buffer tank 120 without heating it in the heater 110. Specifically, the processing system 1000 in this embodiment can supply at least a portion of the excess sludge supplied from the concentration device 50 to the buffer tank 120 without supplying it to the heater 110 by supplying at least a portion of the excess sludge supplied from the concentration device 50 to line L3 by pump P1, for example.

[0029] Therefore, the processing system 1000 in this embodiment can adjust the temperature of the sludge stored in the buffer tank 120 by adjusting the amount of excess sludge that bypasses the heater 110 (the amount of excess sludge supplied to line L3), thereby adjusting the amount of heat supplied to the excess sludge supplied from the concentration device 50. Specifically, the processing system 1000 in this embodiment can control the temperature of the sludge in the buffer tank 120 to an appropriate temperature by adjusting the amount of heat supplied to the excess sludge supplied from the concentration device 50. Consequently, the processing system 1000 in this embodiment can control the temperature of the digested sludge in the digester tank 60 to an appropriate temperature by sequentially supplying the sludge in the buffer tank 120 (sludge that has been adjusted to an appropriate temperature) to the digester tank 60.

[0030] As a result, the processing system 1000 in this embodiment can easily adjust the temperature of the digested sludge in the digester tank 60, and can easily control the temperature of the digested sludge in the digester tank 60 to maintain it at an appropriate temperature. Therefore, the processing system 1000 in this embodiment can suppress, for example, a decrease in the digestion rate in the digester tank 60.

[0031] Specifically, for example, if the capacity of the buffer tank 120 is smaller than the capacity of the digester tank 60, the temperature of the sludge in the buffer tank 120 can be adjusted more quickly and with greater precision than the temperature of the sludge in the digester tank 60. Therefore, in this embodiment, the processing system 1000 adjusts the temperature of the sludge in the digester tank 60 more precisely than when excess sludge or initial sedimentation sludge is directly supplied to the digester tank 60 (i.e., when the processing system 1000 does not have a buffer tank 120), by adjusting the temperature of the sludge in the buffer tank 120 before supplying it to the digester tank 60.

[0032] Furthermore, in this embodiment, the processing system 1000 allows for the installation of an agitator (not shown) in the buffer tank 120 to agitate the sludge for the purpose of adjusting its temperature, by performing sludge temperature adjustment in the buffer tank 120. Therefore, for example, if the capacity of the buffer tank 120 is smaller than the capacity of the digester tank 60, the processing system 1000 in this embodiment can reduce the size of the agitator and the power required to operate the agitator compared to when sludge temperature adjustment is performed in the digester tank 60.

[0033] The following description will focus on the case where the temperature of the sludge in the buffer tank 120 is controlled to reach an appropriate temperature, but is not limited to this. Specifically, for example, if the temperature of the digested sludge in the digester tank 60 is above the appropriate temperature, the treatment system 1000 may adjust the temperature of the sludge in the buffer tank 120 to be below the appropriate temperature, and further supply the sludge adjusted to be below the appropriate temperature from the buffer tank 120 to the digester tank 60. Alternatively, for example, if the temperature of the digested sludge in the digester tank 60 is below the appropriate temperature, the treatment system 1000 may adjust the temperature of the sludge in the buffer tank 120 to be above the appropriate temperature, and further supply the sludge adjusted to be above the appropriate temperature from the buffer tank 120 to the digester tank 60.

[0034] Furthermore, each of line L1 and line L2 may be equipped with, for example, an excess sludge concentration meter (not shown) for measuring the concentration of excess sludge flowing through line L1, and a primary sedimentation sludge concentration meter (not shown) for measuring the concentration of primary sedimentation sludge flowing through line L2.The treatment system 1000 may, for example, use the concentration of excess sludge measured by the excess sludge concentration meter and the concentration of primary sedimentation sludge measured by the primary sedimentation sludge concentration meter to calculate the concentration of sludge in the buffer tank 120 (sludge supplied to the digester tank 60), and further use the calculated concentration to calculate (predict) the amount of digester gas generated in the digester tank 60.

[0035] [Control device 200 in the first embodiment] Next, the control device 200 in the first embodiment will be described. Figure 3 is a diagram illustrating the hardware configuration of the control device 200 in the first embodiment. Figure 4 is a diagram illustrating the functions of the control device 200 in the first embodiment.

[0036] The control device 200 performs, for example, control over the temperature adjustment of the excess sludge supplied to the digester tank 60 (hereinafter also referred to as temperature adjustment control).

[0037] Specifically, the control device 200 is, for example, an electronic device having an electronic circuit, as shown in Figure 3. More specifically, the control device 200 is a computer device having, for example, a CPU 201 which is a processor, a memory 202, a communication device 203, and a storage medium 204. Each part is connected to the others, for example, via a bus 205.

[0038] The storage medium 204 has, for example, a program storage area (not shown) for storing a program 210 for performing temperature control. The storage medium 204 also has, for example, an information storage area 230 for storing information used when performing temperature control. The storage medium 204 may be, for example, an HDD (Hard Disk Drive) or an SSD (Solid State Drive).

[0039] The CPU 201 performs temperature control, for example, by executing a program 210 loaded into memory 202 from storage medium 204.

[0040] The communication device 203 accesses, for example, an operating terminal (not shown) used by an operator to input necessary information via a network (not shown), such as the Internet.

[0041] Then, as shown in Figure 4, the control device 200 acquires the temperature measured by a thermometer T attached to the buffer tank 120 (i.e., the temperature of the sludge in the buffer tank 120). Subsequently, the control device 200 performs temperature control, for example, by using the acquired temperature.

[0042] The electronic circuitry of the control device 200 may be, for example, an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit). Furthermore, the temperature control may be performed, for example, by the FPGA or ASIC.

[0043] [Temperature control process in the first embodiment] Next, the temperature control process in the first embodiment will be described. Figure 5 is a flowchart illustrating the temperature control process in the first embodiment. The following description will assume that temperature adjustment control is performed automatically by the control device 200, but is not limited to this. Specifically, temperature adjustment control may be performed manually by an operator, for example.

[0044] The control device 200 waits, for example, until it is time to perform temperature control (hereinafter also referred to as the control execution time). The control execution time may be, for example, at regular intervals such as every minute.

[0045] Then, for example, when the control execution time arrives, the control device 200 acquires the temperature measured by the thermometer T (the temperature of the digested sludge in the buffer tank 120) (step S1 in Figure 5).

[0046] Next, the control device 200 determines, for example, whether the temperature obtained in step S1 satisfies predetermined conditions (hereinafter also simply referred to as predetermined conditions) (step S2 in Figure 5).

[0047] As a result, for example, if it is determined that the temperature obtained in step S1 satisfies a predetermined condition (YES in step S2 of Figure 5), the control device 200 adjusts the temperature of the sludge in the buffer tank 120 (step S3 of Figure 5).

[0048] On the other hand, if, for example, the control device 200 determines that the temperature obtained in step S1 does not meet the predetermined conditions (NO in step S2 in Figure 5), the control device 200 does not perform step S3.

[0049] Specifically, for example, if the control device 200 determines that the temperature obtained in step S1 is below a predetermined lower threshold (hereinafter also simply referred to as the lower threshold), the control device 200 determines that a predetermined condition is met and performs control to increase the amount of excess sludge supplied to the heater 110 (control to decrease the amount of excess sludge not supplied to the heater 110) by performing control to increase the opening degree of valve V1 and control to decrease the opening degree of valve V3. The lower threshold may be, for example, a temperature corresponding to the lower limit of the appropriate temperature.

[0050] In other words, if the control device 200 determines, for example, that the temperature obtained in step S1 is below a lower threshold, it increases the amount of excess sludge heated by the heater 110, thereby raising the temperature of the excess sludge supplied to the buffer tank 120.

[0051] In this case, the control device 200 may, for example, perform control to increase the opening degree of valve V1 as the temperature obtained in step S1 decreases. Alternatively, the control device 200 may, for example, perform control to decrease the opening degree of valve V3 as the temperature obtained in step S1 decreases.

[0052] Furthermore, for example, if the control device 200 determines that the temperature obtained in step S1 is below a lower threshold, it may determine that a predetermined condition is met and, along with controlling the opening degree of valves V1 and V3, or in lieu of controlling the opening degree of valves V1 and V3, it may perform at least one of the following: increasing the amount of fluid supplied to the heater 110, or increasing the temperature of the fluid supplied to the heater 110.

[0053] In other words, if the control device 200 determines, for example, that the temperature obtained in step S1 is below a lower threshold, it may increase the temperature of the excess sludge supplied to the buffer tank 120 by increasing the amount of fluid used to heat the excess sludge in the heater 110, or by increasing the temperature of the fluid used to heat the excess sludge in the heater 110.

[0054] In this case, the control device 200 may, for example, increase the amount of fluid as the temperature obtained in step S1 decreases. Alternatively, the control device 200 may, for example, increase the temperature of the fluid as the temperature obtained in step S1 decreases.

[0055] Furthermore, for example, if the control device 200 determines that the temperature obtained in step S1 exceeds a predetermined upper threshold (hereinafter also simply referred to as the upper threshold), the control device 200 determines that a predetermined condition is met and performs control to reduce the amount of excess sludge supplied to the heater 110 (control to increase the amount of excess sludge not supplied to the heater 110) by performing at least one of the following: reducing the opening degree of valve V1 or increasing the opening degree of valve V3. The upper threshold may, for example, be a temperature corresponding to the upper limit of the appropriate temperature. Also, the upper threshold may, for example, be the same threshold as the lower threshold.

[0056] In other words, if the control device 200 determines, for example, that the temperature obtained in step S1 exceeds an upper threshold, it reduces the amount of excess sludge heated by the heater 110, thereby lowering the temperature of the excess sludge supplied to the buffer tank 120.

[0057] In this case, the control device 200 may, for example, perform control to decrease the opening degree of valve V1 as the temperature obtained in step S1 increases. Alternatively, the control device 200 may, for example, perform control to increase the opening degree of valve V3 as the temperature obtained in step S1 increases.

[0058] Furthermore, for example, if the control device 200 determines that the temperature obtained in step S1 exceeds the upper threshold, it may determine that a predetermined condition is met and, along with controlling the opening degree of valves V1 and V3, or instead of controlling the opening degree of valves V1 and V3, perform at least one of the following: control to reduce the amount of fluid supplied to the heater 110, or control to lower the temperature of the fluid supplied to the heater 110.

[0059] In other words, if the control device 200 determines, for example, that the temperature obtained in step S1 exceeds an upper threshold, it may reduce the temperature of the excess sludge supplied to the buffer tank 120 by reducing the amount of fluid used to heat the excess sludge in the heater 110, or by lowering the temperature of the fluid used to heat the excess sludge in the heater 110.

[0060] In this case, the control device 200 may, for example, decrease the amount of fluid as the temperature obtained in step S1 increases. Alternatively, the control device 200 may, for example, decrease the temperature of the fluid as the temperature obtained in step S1 decreases.

[0061] As described above, the processing system 1000 in this embodiment includes, for example, a digester 60 for digesting sludge, a line L4 for supplying sludge to the digester 60, a buffer tank 120 communicating with line L4 and storing the sludge supplied to the digester 60, a line L1 for supplying excess sludge to the buffer tank 120, a heater 110 provided in line L1 for heating the excess sludge in line L1 with a fluid, and a control device 200 that controls at least one of the supply of excess sludge to the heater 110 and the supply of fluid to the heater 110 based on the temperature related to digestion. The temperature related to digestion is, for example, a temperature related to digestion such as the temperature inside the buffer tank 120 (the temperature of the sludge inside the buffer tank 120).

[0062] Specifically, the processing system 1000 in this embodiment includes, for example, a line L3 provided in line L1 that connects the inlet and outlet sides of the heater 110. More specifically, in the processing system 1000 in this embodiment, line L3 is, for example, piping that bypasses the heater 110.

[0063] Furthermore, in the processing system 1000 of this embodiment, the control device 200 controls, for example, at least one of the supply of excess sludge to the heater 110 and the supply of fluid to the heater 110 so that the temperature of the sludge in the buffer tank 120 falls within a predetermined range. The predetermined range is, for example, a range corresponding to an appropriate temperature.

[0064] As a result, the processing system 1000 in this embodiment can easily adjust the temperature of the digested sludge in the digester tank 60, and can easily control the temperature of the digested sludge in the digester tank 60 to maintain it at an appropriate temperature. Therefore, the processing system 1000 in this embodiment can suppress, for example, a decrease in the digestion rate in the digester tank 60.

[0065] Specifically, for example, if the capacity of the buffer tank 120 is smaller than the capacity of the digester tank 60, the temperature of the sludge in the buffer tank 120 can be adjusted more quickly and with greater precision than the temperature of the sludge in the digester tank 60. Therefore, in this embodiment, the processing system 1000 adjusts the temperature of the sludge in the digester tank 60 more precisely than when excess sludge or initial sedimentation sludge is directly supplied to the digester tank 60 (i.e., when the processing system 1000 does not have a buffer tank 120), by adjusting the temperature of the sludge in the buffer tank 120 before supplying it to the digester tank 60.

[0066] The control device 200 may, for example, control the opening degree of valves V1 and V3, control the amount of fluid supplied to the heater 110, and control the temperature of the fluid supplied to the heater 110, depending on the amount of excess sludge supplied from the concentration device 50 (amount per unit time).

[0067] In other words, in the treatment system 1000, for example, there may be increases or decreases in the amount of excess sludge supplied to the concentration device 50, malfunctions of equipment such as the concentration device 50, or blockages of piping such as line L1. In these cases, for example, the amount of excess sludge supplied from the concentration device 50 changes. Therefore, the control device 200 may, for example, perform control in response to changes in the amount of excess sludge supplied from the concentration device 50.

[0068] Specifically, the control device 200 may, for example, when the amount of excess sludge supplied from the thickening device 50 increases, perform at least one of the following: increase the opening of valve V1 or decrease the opening of valve V3. Furthermore, the control device 200 may, for example, when the amount of excess sludge supplied from the thickening device 50 increases, perform at least one of the following: increase the amount of fluid supplied to the heater 110 or increase the temperature of the fluid supplied to the heater 110.

[0069] Furthermore, the control device 200 may, for example, perform at least one of the following: reduce the opening of valve V1 or increase the opening of valve V3 when the amount of excess sludge supplied from the thickening device 50 decreases. Also, the control device 200 may, for example, perform at least one of the following: reduce the amount of fluid supplied to the heater 110 or lower the temperature of the fluid supplied to the heater 110 when the amount of excess sludge supplied from the thickening device 50 decreases.

[0070] Furthermore, line L1 may include, for example, another buffer tank (not shown) located between the concentration device 50 and the pump P1. This other buffer tank may, for example, temporarily store excess sludge supplied from the concentration device 50. In addition, the pump P1 may, for example, supply at least a portion of the excess sludge stored in the other buffer tank to the heater 110. This allows the control device 200 to more flexibly adjust, for example, the amount of excess sludge supplied to the heater 110 (amount supplied per unit time) and the timing of the supply.

[0071] [Temperature control system 100(1) in a modified example] Next, we will describe the temperature control system 100 in the first modified example. Figure 6 is a diagram illustrating the configuration of the temperature control system 100 in the first modified example. The differences from the temperature control system 100 in the first embodiment will be described below.

[0072] As shown in Figure 6, the temperature control system 100 in this modified example has, for example, line L5 and valve V5 instead of line L3 and valve V3 in the temperature control system 100 of the first embodiment. Also, as shown in Figure 6, the temperature control system 100 in this modified example has, for example, valve V6 instead of valve V1 in the temperature control system 100 of the first embodiment.

[0073] Line L5 is, for example, a pipe that connects the location between the heater 110 and the buffer tank 120 in line L1 to the location between the pump P1 and the heater 110 in line L1. In other words, line L5 is, for example, a pipe that connects the outlet side of the heater 110 to the inlet side of the heater 110 (i.e., a pipe that can supply excess sludge that has been heated in the heater 110 back to the heater 110). Line L5 is provided with, for example, a valve V5 that can adjust the flow rate of excess sludge supplied to line L5. Hereinafter, line L5 will also be referred to as the third pipe.

[0074] Furthermore, line L1 is provided with a valve V6 that can adjust the flow rate of excess sludge supplied to line L1 (buffer tank 120), for example, at a position between the branching point of line L5 and the buffer tank 120.

[0075] In other words, the treatment system 1000 in this modified example can be further heated, for example, by supplying at least a portion of the excess sludge heated by the heater 110 back to the heater 110. To put it another way, the treatment system 1000 in this modified example can be repeatedly heated in the heater 110 by, for example, circulating at least a portion of the excess sludge supplied via line L1.

[0076] Therefore, for example, if heating the excess sludge supplied from the concentration device 50 once by the heater 110 is insufficient to raise the temperature of the sludge in the buffer tank 120 to a suitable temperature, the treatment system 1000 in this modified example further heats at least a portion of the excess sludge that has been heated by the heater 110 by supplying it to the heater 110 again.

[0077] Specifically, if the control device 200 determines, for example, that the temperature obtained in step S1 is below a lower threshold, it determines that a predetermined condition is met and performs control to increase the amount of excess sludge supplied back to the heater 110 (control to decrease the amount of excess sludge supplied to the buffer tank 120) by performing control to increase the opening of valve V5 and control to decrease the opening of valve V6.

[0078] In other words, if the control device 200 determines, for example, that the temperature obtained in step S1 is below a lower threshold, it increases the amount of excess sludge to be reheated by the heater 110, thereby raising the temperature of the excess sludge supplied to the buffer tank 120.

[0079] More specifically, if the control device 200 determines, for example, that the temperature obtained in step S1 is below a lower threshold, it may calculate the amount of heat that needs to be supplied by excess sludge to bring the buffer tank 120 to an appropriate temperature (hereinafter also referred to as the first heat amount) by using the temperature obtained in step S1 and the amount of excess sludge supplied from the thickening device 50 (the amount of excess sludge that is scheduled to be supplied from the thickening device 50). In this case, the control device 200 may also calculate the amount of heat that can be supplied to the excess sludge by heating it once in the heater 110 (hereinafter also referred to as the second heat amount). If, for example, the second heat amount is less than the first heat amount, the control device 200 may reheat at least a portion of the excess sludge supplied from the thickening device 50 by opening the valve V5, which was previously fully closed. On the other hand, for example, if the second heat quantity is greater than or equal to the first heat quantity, the control device 200 may not perform the control to open the valve V5, which is normally closed, and may not reheat the excess sludge supplied from the concentrating device 50.

[0080] Furthermore, if the control device 200 determines, for example, that the temperature obtained in step S1 exceeds an upper limit threshold, it determines that a predetermined condition is met and performs control to reduce the amount of excess sludge supplied back to the heater 110 (control to increase the amount of excess sludge supplied to the buffer tank 120) by performing at least one of the following: reducing the opening degree of valve V5 or increasing the opening degree of valve V6.

[0081] In other words, if the control device 200 determines, for example, that the temperature obtained in step S1 exceeds an upper threshold, it reduces the amount of excess sludge to be reheated by the heater 110, thereby lowering the temperature of the excess sludge supplied to the buffer tank 120.

[0082] More specifically, the control device 200 may, for example, perform control to fully close the valve V5 if it determines that the temperature acquired in step S1 exceeds an upper threshold.

[0083] Thus, the processing system 1000 in this modified example includes, for example, a line L5 provided in line L1 that connects the inlet and outlet sides of the heater 110. Specifically, in the processing system 1000 in this modified example, line L5 is, for example, a pipe that supplies (returns) at least a portion of the excess sludge after heating by the heater 110 back to the heater 110.

[0084] As a result, in this modified example, even when the amount of excess sludge supplied from the concentration device 50 is small, and heating all of the excess sludge supplied from the concentration device 50 once with the heater 110 is insufficient to raise the temperature of the sludge in the buffer tank 120 to an appropriate level, the treatment system 1000 can raise the temperature of the sludge in the buffer tank 120 to an appropriate level by reheating at least a portion of the excess sludge that has been heated by the heater 110. Therefore, in this modified example, the treatment system 1000 can maintain the temperature of the digested sludge in the digester tank 60 at an appropriate level, for example, and suppress a decrease in the digestion rate in the digester tank 60.

[0085] In this modified example, the processing system 1000 may further include, for example, the line L3, valve V3, and valve V1 described in the first embodiment.

[0086] [Temperature control system 100(2) in modified example] Next, we will describe the temperature control system 100 in the second modified example. Figure 7 is a diagram illustrating the configuration of the temperature control system 100 in the second modified example. Below, we will explain the differences from the temperature control system 100 in the first embodiment.

[0087] As shown in Figure 7, the temperature control system 100 in this modified example further includes, in addition to the components of the temperature control system 100 in the first embodiment, a line L6 and a pump P4.

[0088] Line L6 is a pipe to which a heat transfer fluid (hereinafter also referred to simply as fluid or second fluid) such as hot water or cooling water is supplied, with at least a portion of it located within the buffer tank 120. Specifically, at least a portion of line L6 (the portion of line L6 located within the buffer tank 120) is a heat transfer tube to which the fluid is supplied, provided, for example, on at least one of the walls or bottom of the buffer tank 120. More specifically, at least a portion of line L6 (the portion of line L6 located within the buffer tank 120) is provided, for example, to extend along the inner wall or inner bottom of the buffer tank 120. Line L6 is also provided with a valve V7 capable of adjusting the amount of fluid flowing through it. Hereinafter, line L6 will also be referred to as the temperature control section L6.

[0089] Pump P4 is installed, for example, outside the buffer tank 120 in line L6, and heats or cools the sludge in the buffer tank 120 by causing the fluid to flow within line L6.

[0090] The fluid flowing through line L6 may, for example, be introduced by pump P4 from one end of line L6 located outside the buffer tank 120, flow through the buffer tank 120, and then discharged from the other end of line L6 located outside the buffer tank 120.

[0091] Furthermore, line L6 may be, for example, a pipe circulating between the buffer tank 120 and other equipment (not shown) located outside the buffer tank 120. Other equipment could be, for example, a heat source for heating the fluid or a cooling device for cooling the fluid. In this case, the fluid flowing through line L6 may be circulated between the buffer tank 120 and the other equipment by, for example, a pump P4.

[0092] In other words, the processing system 1000 in this modified example can heat the sludge in the buffer tank 120 by, for example, introducing hot water into the line L6.

[0093] Therefore, in this modified example, if the amount of excess sludge supplied from the concentration device 50 is small, and even if all of the excess sludge supplied from the concentration device 50 is heated by the heater 110, the temperature of the sludge in the buffer tank 120 cannot be raised to a suitable temperature, the processing system 1000 can further heat the sludge in the buffer tank 120 by circulating hot water in line L6.

[0094] Furthermore, in this modified example, the processing system 1000 can cool the sludge in the buffer tank 120 by, for example, circulating cooling water within line L6.

[0095] Therefore, in this modified example, the processing system 1000 can cool the sludge in the buffer tank 120 by circulating cooling water in line L6, even if, for example, the temperature of the excess sludge supplied from the concentration device 50 is high and not all of the excess sludge supplied from the concentration device 50 is heated by the heater 110, and the temperature of the sludge in the buffer tank 120 is above the appropriate temperature.

[0096] Specifically, if the control device 200 determines, for example, that the temperature obtained in step S1 is below a lower threshold, it determines that a predetermined condition is met and performs control to increase the amount of excess sludge supplied to the heater 110 (control to decrease the amount of excess sludge not supplied to the heater 110) by performing control to increase the opening of valve V1 and control to decrease the opening of valve V3. Furthermore, if the control device 200 determines that the temperature obtained again in step S1 is below a lower threshold despite having performed control to increase the opening of valve V1 and control to decrease the opening of valve V3, it increases the opening of valve V7 and supplies hot water to line L6. More specifically, if the control device 200 determines that the temperature obtained again in step S1 is below a lower threshold despite having performed control to fully open valve V1 and fully close valve V3, it increases the opening of valve V7 and supplies hot water to line L6.

[0097] Furthermore, if the control device 200 determines, for example, that the temperature obtained in step S1 exceeds the upper limit threshold, it determines that a predetermined condition is met and performs control to reduce the amount of excess sludge supplied to the heater 110 (control to increase the amount of excess sludge not supplied to the heater 110) by performing control to reduce the opening of valve V1 and control to increase the opening of valve V3. Then, if the control device 200 determines that the temperature obtained again in step S1 exceeds the upper limit threshold despite having performed control to reduce the opening of valve V1 and control to increase the opening of valve V3, it increases the opening of valve V7 and supplies cooling water into line L6. More specifically, if the control device 200 determines that the temperature obtained again in step S1 exceeds the upper limit threshold despite having performed control to fully close valve V1 and fully open valve V3, it increases the opening of valve V7 and supplies cooling water into line L6.

[0098] Thus, in the processing system 1000 of this modified example, a line L6 is provided in the buffer tank 120 for heating or cooling the sludge in the buffer tank 120 with a fluid.

[0099] As a result, in this modified version, even if, for example, the amount of excess sludge supplied from the concentration device 50 is small and heating the excess sludge supplied from the concentration device 50 by the heater 110 is insufficient to raise the temperature of the sludge in the buffer tank 120 to an appropriate temperature, the processing system 1000 in this modified version can further heat the sludge in the buffer tank 120 with hot water to raise the temperature of the sludge in the buffer tank 120 to an appropriate temperature. Therefore, in this modified version, the processing system 1000 can, for example, maintain the temperature of the digested sludge in the digester tank 60 at an appropriate temperature, thereby suppressing a decrease in the digestion rate in the digester tank 60.

[0100] Furthermore, in this modified example, even if the temperature of the excess sludge supplied from the concentration device 50 (the temperature of the excess sludge before heating by the heater 110) is high and the temperature of the sludge in the buffer tank 120 exceeds the appropriate temperature, the processing system 1000 in the buffer tank 120 can be cooled with cooling water to lower the temperature of the sludge in the buffer tank 120 to the appropriate temperature. Therefore, even in this case, the processing system 1000 in this modified example can maintain the temperature of the digested sludge in the digester tank 60 at the appropriate temperature, and suppress the decrease in the digestion rate in the digester tank 60.

[0101] In the above example, the case in which line L6 and pump P4 in this modified example are further provided in the temperature control system 100 of the first embodiment has been described, but the invention is not limited to this. Specifically, line L6 and pump P4 in this modified example may be, for example, further provided in the temperature control system 100 of the first modified example. [Explanation of symbols]

[0102] 10: Primary sedimentation tank 20: Reaction tank 30: Final sedimentation tank 40: Concentration unit 50: Concentrator 60: Digestion tank 100: Temperature control system 110: Heater 200: Control unit 201: CPU 202: Memory 203: Communication device 204: Storage medium 205: Bus 210: Program 230: Information storage area 1000: Processing System L1: Line L2: Line L3: Line L4: Line L5: Line L6: Line P1: Pump P2: Pump P3: Pump P4: Pump T: Thermometer V1: Valve V2: Valve V3: Valve V4: Valve V5: Valve V6: Valve V7: Valve

Claims

1. A digester tank for digesting sludge, A first pipe for supplying the sludge to the digester tank, A storage tank which is in communication with the first pipe and stores the sludge supplied to the digestion tank, A second pipe for supplying excess sludge to the aforementioned storage tank, A heater provided in the second pipe, which heats the excess sludge in the second pipe with the first fluid, A digestion system comprising a control device that controls at least one of the following based on the temperature related to digestion: the supply of the excess sludge to the heater and the supply of the first fluid to the heater.

2. Furthermore, the second piping is provided with a third piping that connects the inlet side and the outlet side of the heater, The digestion system according to claim 1, wherein the control device controls the supply of the excess sludge to the third pipe.

3. The digestion system according to claim 1, wherein the control device controls at least one of the supply of the excess sludge to the heater and the supply of the first fluid to the heater so that the temperature of the sludge in the storage tank falls within a predetermined range.

4. The digestion system according to claim 1, wherein the storage tank has a temperature control unit for heating or cooling the sludge in the storage tank with a second fluid.

5. A method for controlling the temperature in a digestion system comprising: a digestion tank for digesting sludge; a first pipe for supplying the sludge to the digestion tank; a storage tank communicating with the first pipe and storing the sludge supplied to the digestion tank; a second pipe for supplying excess sludge to the storage tank; and a heater provided in the second pipe for heating the excess sludge in the second pipe with a first fluid, wherein the system comprises: A temperature control method that controls at least one of the following: the supply of the excess sludge to the heater and the supply of the first fluid to the heater, based on the temperature related to the digestion.

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