Stoving system and heating control method

Abstract

To provide a digestion system and heating control method to control a temperature in a tank.SOLUTION: A system includes a tank for digesting excess sludge, a first piping for supplying excess sludge to the tank, a second piping for circulating the digested sludge in the tank to and from outside the tank, a heater for heating at least one of the excess sludge in the first piping and the digested sludge in the second piping by means of a fluid, and a controller for controlling at least one of heating of the excess sludge in the first piping by the heater and heating of the digested sludge in the second piping by the heater based on the supply status of excess sludge to the tank and the temperature inside the tank.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a fire extinguishing system and a method for controlling heat. [Background technology]

[0002] In a digestion system having a tank (hereinafter also referred to as a digestion tank) for digesting the material to be treated (for example, organic matter contained in primary sludge and excess sludge), a technology has been proposed that achieves efficient digestion of the material to be treated by maintaining the temperature inside the tank at an appropriate temperature (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2011-516246 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-described extinguishing system, it is desirable to control the temperature of the material to be treated that is put into the tank so that the temperature inside the tank is at an appropriate level. [Means for solving the problem]

[0005] The digestion system of the present disclosure comprises a tank for digesting excess sludge, a first pipe for supplying the excess sludge to the tank, a second pipe for circulating the digested sludge in the tank between the tank and the outside, a heater for heating at least one of the excess sludge in the first pipe and the digested sludge in the second pipe using a fluid, and a control device for controlling at least one of the heating of the excess sludge in the first pipe by the heater and the heating of the digested sludge in the second pipe by the heater based on the supply status of the excess sludge to the tank and the temperature in the tank. [Effects of the Invention]

[0006] The fire extinguishing system and heating control method of the present disclosure allows for control of the temperature within the tank. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram illustrating the configuration of a processing system 1000 according to the first embodiment. [Figure 2] FIG. 2 is a diagram illustrating a specific example of adjusting the temperature of digested sludge in the digestion tank 60. [Figure 3] FIG. 3 is a diagram illustrating a specific example of adjusting the temperature of digested sludge in the digestion tank 60. [Figure 4] FIG. 4 is a diagram illustrating a specific example of adjusting the temperature of digested sludge in the digestion tank 60. [Figure 5] FIG. 5 is a diagram illustrating a specific example of adjusting the temperature of digested sludge in the digestion tank 60. [Figure 6] FIG. 6 is a diagram illustrating the hardware configuration of the control device 90. As shown in FIG. [Figure 7] FIG. 7 is a diagram illustrating the function of the control device 90. [Figure 8] FIG. 8 is a flowchart illustrating the temperature control process in the first embodiment. [Figure 9] FIG. 9 is a flowchart illustrating the temperature control process in the first embodiment. [Figure 10] FIG. 10 is a diagram illustrating the temperature control process in the first modified example. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, such descriptions should not be interpreted in a limiting sense, and do 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 the present disclosure. Furthermore, different embodiments can be combined as appropriate.

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

[0010] The treatment system 1000 in this embodiment is, for example, a water treatment system that treats liquid such as sewage (hereinafter also referred to as water to be treated).

[0011] 1, the treatment 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 thickener 40, a thickener 50, and a digestion system 100. More specifically, the digestion system 100 includes, for example, a tank 60 (hereinafter also referred to as the digestion tank 60), a heater 70, and a cooler 80.

[0012] The primary sedimentation tank 10 separates, for example, organic and other contaminants (e.g., solid organic matter) contained in the water to be treated. The separated contaminants (hereinafter also referred to as primary sludge) are then discharged to a concentration device 40 by, for example, a pump (not shown). The water to be treated after the separation of contaminants by sedimentation is then discharged to a digestion tank 60 by, for example, a pump (not shown).

[0013] The reaction tank 20 is a tank that treats the water to be treated by biological treatment such as the standard activated sludge method. Specifically, the reaction tank 20 decomposes organic matter (e.g., soluble organic matter) contained in the water to be treated, for example, by microorganisms (hereinafter also referred to as activated sludge) propagated in the reaction tank 20. 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 by, for example, a pump (not shown).

[0014] The final settling tank 30, for example, separates and discharges activated sludge contained in the water to be treated discharged from the reaction tank 20. A portion of the settled and separated activated sludge (hereinafter also referred to as excess sludge) is discharged to the thickening device 50 by, for example, a pump (not shown). Another portion of the settled and separated activated sludge (hereinafter also referred to as returned sludge) is returned to the reaction tank 20 by, for example, a pump (not shown). The water to be treated (supernatant) after separation of the activated sludge is discharged to a downstream sterilization treatment device (not shown), for example, by a pump (not shown). Thereafter, the sterilization treatment device sterilizes the water to be treated discharged from the final settling tank 30, and the sterilized treated water is discharged into a river or the like.

[0015] The thickening device 40 thickens, for example, the primary sludge discharged from the primary sedimentation tank 10. The thickened primary sludge is then discharged into the digestion tank 60 by, for example, a pump (not shown). Furthermore, the liquid separated from the primary sludge by thickening is returned to the primary sedimentation tank 10 by, for example, a pump (not shown).

[0016] The thickening device 50 thickens, for example, excess sludge discharged from the final settling tank 30. The thickened excess sludge is then discharged to the digestion tank 60 by, for example, a pump (not shown). Furthermore, the liquid separated from the excess sludge by the thickening is returned to the final settling tank 30 by, for example, a pump (not shown).

[0017] In the digestion tank 60, for example, anaerobic bacteria in the digestion tank 60 anaerobically digest (decompose) organic matter contained in the primary sludge supplied from the thickener 40 and the excess sludge supplied from the thickener 50 through a biological reaction, producing digested sludge. The anaerobic bacteria in the digestion tank 60 produce digestion gases such as methane gas (hereinafter simply referred to as digestion gas) during the digestion process. Note that the temperature of the digested sludge (digestion liquid) in the digestion tank 60 is preferably maintained between 35°C and 39°C (hereinafter this temperature range is also referred to as the optimum temperature) in order to efficiently promote the biological reactions and improve the digestion rate.

[0018] The heater 70 heats, for example, excess sludge before it is supplied to the digestion tank 60. Specifically, the heater 70 is, for example, a heat exchanger that heats the excess sludge with a fluid (for example, a fluid such as hot water) before it is supplied to the digestion tank 60. Note that, although the following description will be given assuming that the heater 70 is a heat exchanger, this is not limiting. Specifically, the heater 70 may be, for example, a steam heater that supplies steam (water vapor) to the excess sludge before it is supplied to the digestion tank 60 to heat it.

[0019] The cooler 80 cools, for example, the excess sludge after being heated by the heater 70 (excess sludge before being supplied to the digestion tank 60). Specifically, the cooler 80 is, for example, a heat exchanger that cools the excess sludge after being heated by the heater 70 using a fluid (for example, a fluid such as cooling water).

[0020] In the treatment system 1000, for example, excess sludge heated by the heater 70, or excess sludge heated by the heater 70 and then cooled by the cooler 80, is supplied to the digestion tank 60.

[0021] As a result, in the treatment system 1000, the temperature of the digested sludge in the digestion tank 60 is maintained at an appropriate temperature by using, for example, excess sludge heated by the heater 70, or excess sludge heated by the heater 70 and then cooled by the cooler 80, as a heat medium.

[0022] That is, one of the causes of the decrease in digestion rate in the digestion tank 60 is the large amount of bacteria living in the excess sludge. If excess sludge containing living bacteria is directly supplied to the digestion tank 60, the anaerobic bacteria in the digestion tank 60 may not be able to sufficiently decompose (digest) the bacteria.

[0023] Therefore, in the digestion system 100 of this embodiment, for example, before the excess sludge is supplied to the digestion tank 60, the excess sludge is intensively heated by the heater 70, thereby sufficiently killing the living bacteria contained in the excess sludge. Then, the digestion system 100 maintains the temperature of the digested sludge in the digestion tank 60 at an appropriate temperature by, for example, using the heated excess sludge as a heat medium.

[0024] Furthermore, in this embodiment, the digestion system 100, for example, adjusts the temperature of the excess sludge supplied to the digestion tank 60 by cooling the excess sludge using the cooler 80 after it has been heated by the heater 70 as necessary, thereby accurately adjusting the temperature of the digested sludge in the digestion tank 60.

[0025] As a result, the digestion system 100 in this embodiment can, for example, suppress a decrease in digestion rate in the digestion tank 60.

[0026] Furthermore, in the digestion system 100 of this embodiment, for example, when excess sludge is not being supplied to the digestion tank 60, the digested sludge in the digestion tank 60 is circulated between the inside and outside of the digestion tank 60 as needed. The digestion system 100 then adjusts the temperature of the digested sludge to be resupplied into the digestion tank 60 by, for example, heating the digested sludge discharged outside the digestion tank 60 using a heater 70 or cooling it using a cooler 80, thereby accurately adjusting the temperature of the digested sludge in the digestion tank 60.

[0027] As a result, the digestion system 100 of this embodiment can suppress a decrease in the digestion rate in the digestion tank 60, even when, for example, excess sludge is not supplied to the digestion tank 60. A specific example of adjusting the temperature of the digested sludge in the digestion tank 60 will be described below.

[0028] Note that the primary sludge does not contain a sufficient amount of viable bacteria to cause a decrease in digestibility, and may not be the main cause of the decrease in digestibility. Therefore, in the digestion system 100, for example, the primary sludge supplied from the thickener 40 (the primary sludge before being supplied to the digestion tank 60) may not be heated. On the other hand, if the primary sludge supplied from the thickener 40 is also used as a heat medium in the digestion tank 60, the digestion system 100 may also heat the primary sludge supplied from the thickener 40 (the primary sludge before being supplied to the digestion tank 60).

[0029] Furthermore, the digestion system 100 may be one that adjusts (heats or cools) the temperature of the excess sludge to which the primary sludge has been added, for example.

[0030] Furthermore, in the digestion system 100, for example, when excess sludge is not being supplied to the digestion tank 60, the temperature of the digested sludge to which the primary settling sludge has been added may be adjusted (heated or cooled).

[0031] [Specific example of temperature adjustment of digested sludge in digestion tank 60] 2 to 5 are diagrams illustrating specific examples of adjusting the temperature of digested sludge in the digestion tank 60. Note that the positions and numbers of pipes and valves shown in Figures 2 to 5 are merely examples and are not limited to these.

[0032] First, a specific example of the case where the temperature of the digested sludge in the digestion tank 60 is increased by using excess sludge (when the temperature of the digested sludge in the digestion tank 60 is lower than the optimum temperature) will be described.

[0033] The excess sludge supplied from the thickening device 50 is temporarily stored in a storage tank (not shown). Then, as shown in FIG. 2, the excess sludge is supplied to the heater 70 via a pipe L1 by, for example, a pump P1. The pipe L1 is, for example, a pipe connecting the thickening device 50, a storage tank provided downstream of the thickening device 50, and the heater 70 provided downstream of the storage tank. The excess sludge heated by the heater 70 is then supplied to the digestion tank 60 by, for example, the pump P1 via a portion of the pipe L2, a portion of the pipe L4, and a portion of the pipe L3 (bypassing the cooler 80). The pipe L2 is, for example, a pipe connecting the heater 70 and the cooler 80, the pipe L3 is, for example, a pipe connecting the cooler 80 and the digestion tank 60, and the pipe L4 is, for example, a pipe connecting the pipe L2 and the pipe L3. Hereinafter, the pipe L1 (which may be a part of the upstream side of the heater 70), the pipe L2, the pipe L3, and the pipe L4 will also be collectively referred to as the first pipe.

[0034] That is, in the digestion system 100, for example, when it is necessary to raise the temperature of the digested sludge in the digestion tank 60, the excess sludge heated by the heater 70 (excess sludge after the bacterial groups have been sufficiently killed) is supplied to the digestion tank 60 without being cooled by the cooler 80.

[0035] This allows the digestion system 100 to supply excess sludge to the digestion tank 60 at a temperature that can raise the temperature of the digested sludge in the digestion tank 60, for example.

[0036] 2, the case where excess sludge heated by the heater 70 bypasses the cooler 80 has been described, but the present invention is not limited to this. Specifically, for example, when the cooler 80 is stopped (when no fluid is supplied to the cooler 80), the excess sludge may be supplied to the digestion tank 60 via the cooler 80.

[0037] Next, a specific example of a case where the temperature of the digested sludge in the digestion tank 60 is lowered by using excess sludge (when the temperature of the digested sludge in the digestion tank 60 exceeds the optimum temperature) will be described.

[0038] As shown in Fig. 3, the excess sludge supplied from the thickening device 50 is supplied to the heater 70 via a pipe L1 by, for example, a pump P1. The excess sludge heated by the heater 70 is then supplied to the cooler 80 via a pipe L2 by, for example, a pump P1. The excess sludge cooled by the cooler 80 is then supplied to the digestion tank 60 via a pipe L3 by, for example, a pump P1.

[0039] That is, in the digestion system 100, for example, when it is necessary to lower the temperature of the digested sludge in the digestion tank 60, the excess sludge heated by the heater 70 (excess sludge after the bacterial groups have been sufficiently killed) is cooled by the cooler 80 before being supplied to the digestion tank 60.

[0040] This allows the digestion system 100 to supply excess sludge to the digestion tank 60 at a temperature that can lower the temperature of the digested sludge in the digestion tank 60, for example.

[0041] Next, a specific example of raising the temperature of digested sludge in digestion tank 60 when excess sludge is not being supplied to digestion tank 60 will be described.

[0042] As shown in Figure 4, the digested sludge in the digestion tank 60 is supplied to the heater 70 by, for example, pump P2 via pipe L5 and a portion of pipe L1. Pipe L5 is, for example, a pipe that connects the digestion tank 60 and pipe L1. The digested sludge heated by the heater 70 is then supplied to the digestion tank 60 by, for example, pump P2 via a portion of pipe L2, pipe L4, and a portion of pipe L3 (bypassing the cooler 80).

[0043] That is, in the digestion system 100, for example, when excess sludge is not being supplied to the digestion tank 60 and it is necessary to raise the temperature of the digested sludge in the digestion tank 60, the digested sludge in the digestion tank 60 is temporarily discharged outside the digestion tank 60 and heated (directly heated), and the heated digested sludge is then supplied back to the digestion tank 60.

[0044] This makes it possible for the digestion system 100 to raise the temperature of the digested sludge in the digestion tank 60, even when, for example, excess sludge is not being supplied to the digestion tank 60 (when there is not enough excess sludge in the storage tank to supply to the digestion tank 60). In other words, for example, the digestion system 100 can adjust the temperature of the digested sludge in the digestion tank 60 so that it falls within an appropriate temperature range, regardless of whether excess sludge is being supplied to the digestion tank 60 or not.

[0045] 4, a case has been described in which the digested sludge heated by the heater 70 is circulated while bypassing the cooler 80, but this is not limiting. Specifically, for example, when the cooler 80 is stopped (when no fluid is supplied to the cooler 80), the digested sludge may be circulated via the cooler 80.

[0046] Next, a specific example of lowering the temperature of digested sludge in digestion tank 60 when excess sludge is not being supplied to digestion tank 60 will be described.

[0047] As shown in Fig. 5, the digested sludge in the digestion tank 60 is supplied to the cooler 80 by, for example, pump P2 via part of pipe L5, pipe L6, and part of pipe L2 (bypassing the heater 70). Pipe L6 is, for example, a pipe that connects pipe L5 and pipe L2. The digested sludge cooled by the cooler 80 is then supplied to the digestion tank 60 by, for example, pump P2 via pipe L3. Hereinafter, pipe L1 (which may be a part upstream of the heater 70), pipe L2, pipe L3, pipe L4, pipe L5, and pipe L6 will be collectively referred to as the second pipe.

[0048] That is, in the digestion system 100, for example, when excess sludge is not being supplied to the digestion tank 60 and it is necessary to lower the temperature of the digested sludge in the digestion tank 60, the digested sludge in the digestion tank 60 is temporarily discharged outside the digestion tank 60 and cooled (directly cooled), and the cooled digested sludge is then supplied again to the digestion tank 60.

[0049] This makes it possible for the digestion system 100 to lower the temperature of the digested sludge in the digestion tank 60, even when, for example, excess sludge is not being supplied to the digestion tank 60 (when there is not enough excess sludge in the storage tank to supply to the digestion tank 60). In other words, for example, the digestion system 100 can adjust the temperature of the digested sludge in the digestion tank 60 to an appropriate temperature, regardless of whether excess sludge is being supplied to the digestion tank 60 or not.

[0050] 5, a case has been described in which the digested sludge supplied from the digestion tank 60 is circulated while bypassing the heater 70, but this is not limiting. Specifically, for example, when the heater 70 is stopped (when no fluid is supplied to the heater 70), the digested sludge may be circulated via the heater 70.

[0051] Furthermore, in the above example, the pipes through which the digested sludge passes (pipes L1, L2, L3, L4, L5, and L6) share some of the same pipes as the pipes through which the excess sludge passes (pipes L1, L2, L3, and L4), but this is not limited to this. Specifically, the pipes through which the digested sludge passes may be, for example, pipes different from the pipes through which the excess sludge passes (pipes that do not share some of the same pipes as the pipes through which the excess sludge passes).

[0052] 2 etc., a case will be described in which valve V1 is provided in pipe L1 closer to pump P1 (upstream) than the junction with pipe L5, valve V2 is provided in pipe L2 closer to cooler 80 (downstream) than the branch point with pipe L4, valve V3 is provided in pipe L4, valve V4 is provided in pipe L5 closer to pipe L1 (downstream) than the branch point with pipe L6, and valve V5 is provided in pipe L6, but this is not limiting. Specifically, valve V1 may be provided upstream of pump P1, for example.

[0053] [Control device 90 in the first embodiment] Next, the configuration of the control device 90 in the first embodiment will be described. Fig. 6 is a diagram illustrating the hardware configuration of the control device 90. Fig. 7 is a diagram illustrating the functions of the control device 90.

[0054] As shown in FIG. 6, the treatment system 1000 has a control device 90 that executes a process for controlling the temperature of the digested sludge in the digestion tank 60 (hereinafter, also simply referred to as a temperature control process).

[0055] 6, the control device 90 is, for example, an electrical device having an electronic circuit. Specifically, the control device 90 is, for example, a computer device having a CPU 901 which is a processor, a memory 902, a communication device 903, and a storage medium 904. Each unit is connected to each other via, for example, a bus 905.

[0056] The storage medium 904 has, for example, a program storage area (not shown) that stores a program 910 for performing the temperature control process. The storage medium 904 also has, for example, an information storage area 930 that stores information used when performing the temperature control process. Specifically, the information storage area 930 stores, for example, a set point variable (SV) for the heating temperature of the excess sludge by the heater 70 and an SV for the cooling temperature of the excess sludge by the cooler 80. The storage medium 904 may be, for example, a hard disk drive (HDD) or a solid state drive (SSD).

[0057] The CPU 901 performs temperature control processing by executing a program 910 loaded into the memory 902 from the storage medium 904, for example.

[0058] The communication device 903 accesses an operation terminal (not shown) through which an operator inputs necessary information, for example, via a network (not shown) such as the Internet.

[0059] 7, the control device 90 acquires the temperature (i.e., the temperature of the digested sludge in the digestion tank 60) measured by, for example, a thermometer T attached to the digestion tank 60. Thereafter, the control device 90 performs a temperature control process, for example, by using the acquired temperature.

[0060] The electronic circuitry of the control device 90 may be, for example, a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). The temperature control process may be executed by, for example, the FPGA or the ASIC.

[0061] [Temperature Control Process in the First Embodiment] Next, a description will be given of the temperature control process in the first embodiment. Figures 8 and 9 are flow charts illustrating the temperature control process in the first embodiment.

[0062] [Temperature control process when excess sludge is supplied to digestion tank 60] First, a description will be given of the temperature control process when excess sludge is supplied to the digestion tank 60. Figure 8 is a flowchart illustrating the temperature control process when excess sludge is supplied to the digestion tank 60.

[0063] In the following, we will explain the state at the start of the temperature control process, where valve V1 is open, valve V2 is closed, valve V3 is open, valve V4 is closed, and valve V5 is closed, as shown in Figure 2.

[0064] 8, the control device 90 waits until it is time to execute the temperature control process (hereinafter also referred to as the process execution time) (NO in step S10 in FIG. 8). The process execution time may be, for example, every hour.

[0065] Then, when the time to execute the treatment arrives (YES in step S10 in FIG. 8), the control device 90 acquires, for example, the temperature measured by a thermometer T (the temperature of the digested sludge in the digestion tank 60) (step S11 in FIG. 8). Specifically, the control device 90 acquires, for example, the temperature measured by the thermometer T.

[0066] Then, when it is determined that the temperature measured by the thermometer T is higher than the threshold value Tg (YES in step S11 of FIG. 8), the control device 90 acquires, for example, the heating temperature of the excess sludge by the heater 70. The threshold value Tg may be, for example, a temperature included in the optimum temperature range (for example, 37°C).

[0067] Specifically, the control device 90 acquires, for example, the heating temperature (SV value) of the excess sludge by the heater 70 from the information storage area 930. In addition, the control device 90 acquires, for example, the heating temperature (SV value) of the excess sludge by the heater 70 directly from a device (not shown) that supplies a fluid to the heater 70. Hereinafter, the device that supplies a fluid to the heater 70 will also be simply referred to as a supply device.

[0068] As a result, when it is determined that the heating temperature of the excess sludge by the heater 70 exceeds the threshold value T1 (YES in step S12 of FIG. 8), the control device 90 performs control (hereinafter also referred to as first temperature reduction control) to lower the heating temperature of the excess sludge by the heater 70 to a predetermined temperature (hereinafter also referred to simply as the predetermined temperature) (step S13 of FIG. 8). The threshold value T1 is, for example, a temperature higher than the minimum temperature to which the excess sludge needs to be heated (hereinafter also referred to as the minimum heating temperature), and the difference from the minimum heating temperature is smaller than the predetermined temperature. The minimum heating temperature is, for example, the minimum temperature (e.g., 60°C) required to sufficiently kill the viable bacteria contained in the excess sludge.

[0069] Specifically, in this case, the control device 90 controls the supply device, for example, by reducing the flow rate of the fluid supplied to the heater 70, so that the heating temperature of the excess sludge by the heater 70 is reduced by a predetermined temperature. More specifically, the control device 90 controls the supply device, for example, to reduce the SV value for the heating temperature of the excess sludge by a predetermined temperature. In this case, the control device 90 may store a new SV value for the heating temperature of the excess sludge in the information storage area 930, for example.

[0070] In other words, in this case, even if the heating temperature of the excess sludge by the heater 70 is to be lowered by a predetermined temperature, the control device 90 determines that the heating temperature of the excess sludge by the heater 70 will not reach the minimum heating temperature, and performs the first temperature reduction control.

[0071] This enables the control device 90 to, for example, lower the temperature of the excess sludge supplied to the digestion tank 60, thereby lowering the temperature of the digested sludge in the digestion tank 60.

[0072] On the other hand, if it is determined that the heating temperature of the excess sludge by the heater 70 does not exceed the threshold value T1 (NO in step S12 of Figure 8), the control device 90 performs control (hereinafter also referred to as second temperature reduction control) to cool the excess sludge after it has been heated by the heater 70 using the cooler 80 (step S14 of Figure 8).

[0073] Specifically, in this case, as shown in Figure 3, the control device 90 controls, for example, to open valve V2 and close valve V3, thereby controlling the supply of excess sludge from the heater 70 to the cooler 80. Then, the control device 90 controls, for example, the cooler 80 to cool the excess sludge after it has been heated by the heater 70, thereby supplying the excess sludge after it has been cooled by the cooler 80 to the digestion tank 60.

[0074] That is, in this case, for example, when the heating temperature of the excess sludge by the heater 70 is lowered by a predetermined temperature, the control device 90 determines that the heating temperature of the excess sludge by the heater 70 reaches the minimum heating temperature (below the minimum heating temperature), and performs the second temperature reduction control instead of the first temperature reduction control.

[0075] As a result, the control device 90 can lower the temperature of the excess sludge supplied to the digestion tank 60, even if it is not possible to lower the heating temperature of the excess sludge by the heater 70, and can therefore lower the temperature of the digested sludge in the digestion tank 60.

[0076] In addition, the control device 90 similarly acquires the heating temperature of the excess sludge by the heater 70, for example, when it determines that the temperature measured by the thermometer T does not exceed the threshold value Tg (NO in step S11 in Figure 8).

[0077] As a result, if it is determined that the heating temperature of the excess sludge by the heater 70 does not exceed the threshold value T2 (NO in step S15 of FIG. 8), control is performed to increase the heating temperature of the excess sludge supplied to the heater 70 by a predetermined temperature (hereinafter also referred to as second temperature increase control) (step S17 of FIG. 8). The threshold value T2 is, for example, a temperature lower than a predetermined reference temperature (hereinafter also referred to as the heating reference temperature), and the difference between the threshold value T2 and the heating reference temperature is smaller than the predetermined temperature. The heating reference temperature is, for example, a temperature (e.g., 75°C) that is determined in advance based on constraints on the maximum temperature of the fluid supplied to the heater 70, etc.

[0078] Specifically, the control device 90 controls the supply device, for example, by increasing the flow rate of the fluid supplied to the heater 70, so that the heating temperature of the excess sludge by the heater 70 increases by a predetermined temperature. More specifically, the control device 90 controls the supply device, for example, to increase the SV value for the heating temperature of the excess sludge by a predetermined temperature. In this case, the control device 90 may store a new SV value for the heating temperature of the excess sludge in the information storage area 930, for example.

[0079] In other words, in this case, even if the heating temperature of the excess sludge by the heater 70 is increased by a predetermined temperature, the control device 90 determines that the heating temperature of the excess sludge by the heater 70 does not reach the heating reference temperature, and performs second temperature increase control.

[0080] This enables the control device 90 to, for example, increase the temperature of the excess sludge supplied to the digestion tank 60, thereby increasing the temperature of the digested sludge in the digestion tank 60.

[0081] On the other hand, if it is determined that the heating temperature of the excess sludge by the heater 70 exceeds the threshold value T2 (YES in step S15 of Figure 8), the control device 90 performs control (hereinafter also referred to as first temperature increase control) to, for example, increase the heating temperature of the excess sludge supplied to the heater 70 to the maximum temperature (step S16 of Figure 8).

[0082] Specifically, in this case, the control device 90 controls the supply device so that the heating temperature of the excess sludge by the heater 70 is maximized, for example, by maximizing the flow rate of the fluid supplied to the heater 70. More specifically, the control device 90 controls the supply device so that the SV value for the heating temperature of the excess sludge is maximized, for example.

[0083] In the above example, the case where step S12 is performed when the temperature measured by thermometer T is above threshold value Tg and step S15 is performed when the temperature measured by thermometer T is not above threshold value Tg has been described, but the present invention is not limited to this. Specifically, the control device 90 may perform step S12 when the temperature measured by thermometer T is above a threshold value included in the appropriate temperature range (hereinafter also referred to as a first upper threshold value), and may perform step S15 when the temperature measured by thermometer T is below a threshold value included in the appropriate temperature range and lower than the first upper threshold (hereinafter also referred to as a first lower threshold value).

[0084] [Temperature Control Process When Excess Sludge is Not Supplied to Digestion Tank 60] Next, a description will be given of the temperature control process when excess sludge is not supplied to the digestion tank 60. Figure 9 is a flowchart illustrating the temperature control process when excess sludge is not supplied to the digestion tank 60.

[0085] In the following, we will explain the state at the start of the temperature control process, where valve V1 is closed, valve V2 is closed, valve V3 is open, valve V4 is open, and valve V5 is closed, as shown in Figure 4.

[0086] As shown in FIG. 9, the control device 90 waits until the processing execution time comes (NO in step S20 in FIG. 9), for example.

[0087] Then, when the time to execute the treatment arrives (YES in step S20 in FIG. 8), the control device 90 acquires, for example, the temperature measured by a thermometer T (the temperature of the digested sludge in the digestion tank 60) (step S21 in FIG. 9). Specifically, the control device 90 acquires, for example, the temperature measured by a thermometer T.

[0088] If it is determined that the temperature measured by the thermometer T is below the threshold value T3 (hereinafter also referred to as the second lower threshold value) (YES in step S21 in FIG. 9), the control device 90 performs control (hereinafter also referred to as circulation temperature increase control) to heat the digested sludge discharged from the digestion tank 60 using the heater 70 (step S22 in FIG. 9). The threshold value T3 may be, for example, a threshold value included in the range of optimum temperatures.

[0089] Specifically, as shown in Figure 4, the control device 90, for example, heats the digested sludge discharged from the digestion tank 60 using a heater 70, and then supplies the digested sludge heated by the heater 70 back to the digestion tank 60.

[0090] That is, for example, when excess sludge is not supplied to the digestion tank 60 and the temperature of the digested sludge in the digestion tank 60 cannot be adjusted (raised) by using the excess sludge, the control device 90 discharges the digested sludge from the digestion tank 60 and directly heats it. Also, for example, when the control device 90 has performed control (first temperature increase control or second temperature increase control) to heat the excess sludge supplied to the digestion tank 60 but has not been able to raise the temperature of the digested sludge in the digestion tank 60 to within the appropriate temperature range, the control device 90 discharges the digested sludge from the digestion tank 60 and directly heats it.

[0091] On the other hand, if it is determined that the temperature measured by the thermometer T is not below the threshold value T3 (NO in step S21 in FIG. 9), the control device 90 determines, for example, whether the temperature measured by the thermometer T is below a threshold value T4 (hereinafter also referred to as a second upper limit threshold value) (step S23 in FIG. 9). The threshold value T4 may be, for example, a threshold value included in the range of optimum temperatures and higher than the threshold value T3.

[0092] As a result, if it is determined that the temperature measured by the thermometer T is not below the threshold value T4 (NO in step S23 of Figure 9), the control device 90 performs control (hereinafter also referred to as circulation temperature reduction control) to cool the digested sludge discharged from the digestion tank 60 using the cooler 80 (step S24 of Figure 9).

[0093] Specifically, in this case, as described in Figure 5, the control device 90 controls, for example, to open valves V2 and V5 and close valves V3 and V4, thereby controlling the supply of digested sludge from the digestion tank 60 to the cooler 80. Then, the control device 90, for example, causes the cooler 80 to cool the digested sludge circulating between the inside and outside of the digestion tank 60, and causes the digested sludge cooled by the cooler 80 to be supplied again to the digestion tank 60.

[0094] That is, for example, when excess sludge is not being supplied to the digestion tank 60 and the temperature of the digested sludge in the digestion tank 60 cannot be adjusted (lowered) by using the excess sludge, the control device 90 discharges the digested sludge from the digestion tank 60 and cools it directly. Also, for example, when the control device 90 has performed control (first temperature reduction control or second temperature reduction control) to cool the excess sludge supplied to the digestion tank 60 but has not been able to lower the temperature of the digested sludge in the digestion tank 60 to within an appropriate temperature range, the control device 90 discharges the digested sludge from the digestion tank 60 and cools it directly.

[0095] The control device 90, for example, acquires the amount of excess sludge in a storage tank that temporarily stores the excess sludge supplied from the concentration device 50, and switches between excess sludge supply control (hereinafter also simply referred to as supply control) that supplies excess sludge to the digestion tank 60, and circulation control (hereinafter also simply referred to as circulation control) that circulates the digested sludge in the digestion tank 60.

[0096] Specifically, for example, when the amount of excess sludge stored in the storage tank is equal to or greater than a predetermined amount (for example, 10 percent of the storage tank's allowable storage capacity), the control device 90 controls the opening and closing of each valve to execute supply control (see FIGS. 2 and 3). Then, the control device 90 stores control information (hereinafter also simply referred to as control information) indicating that supply control will be executed in the memory 902 or the information storage area 930.

[0097] On the other hand, for example, when the amount of excess sludge stored in the storage tank is less than a predetermined amount, the control device 90 controls the opening and closing of each valve to perform circulation control (see FIGS. 4 and 5). Then, the control device 90 stores control information indicating that circulation control will be performed in the memory 902 or the information storage area 930.

[0098] Then, the control device 90 switches between executing the process described in Fig. 8 and executing the process described in Fig. 9 based on, for example, control information stored in the memory 902 or the information storage area 930. That is, for example, when the control information indicates that supply control is to be executed, the control device 90 executes the process described in Fig. 8. On the other hand, for example, when the control information indicates that circulation control is to be executed, the control device 90 executes the process described in Fig. 9.

[0099] [Temperature Control Process in the First Modification] Next, a modified example of the temperature control process in the first embodiment (hereinafter also referred to as the first modified example) will be described. Fig. 10 is a diagram for explaining the temperature control process in the first modified example.

[0100] The fire extinguishing system 100 may, for example, not include the cooler 80, as shown in FIG.

[0101] Then, for example, if the control device 90 determines in step S12 of Figure 8 that the heating temperature of the excess sludge by the heater 70 does not exceed the threshold value T1 (NO in step S12 of Figure 8), instead of step S14 of Figure 8 (second temperature reduction control), it may perform control to set the heating temperature of the excess sludge supplied to the heater 70 to the minimum temperature.

[0102] Specifically, in this case, the control device 90 controls the supply device so that the heating temperature of the excess sludge by the heater 70 is minimized, for example, by minimizing the flow rate of the fluid supplied to the heater 70. More specifically, the control device 90 controls the supply device so that the SV value for the heating temperature of the excess sludge is minimized, for example.

[0103] This allows the fire extinguishing system 100 in the first modified example to perform temperature control processing with, for example, a simple configuration.

[0104] Thus, the digestion system 100 of this embodiment includes, for example, a digestion tank 60 that digests excess sludge, a first pipe that supplies the excess sludge to the digestion tank 60, a second pipe that circulates the digested sludge in the digestion tank 60 between the inside and outside of the digestion tank 60, a heater 70 that heats at least one of the excess sludge in the first pipe and the digested sludge in the second pipe with a fluid, and a control device 90 that controls at least one of the heating of the excess sludge in the first pipe by the heater 70 and the heating of the digested sludge in the second pipe by the heater 70 based on the supply status of excess sludge to the digestion tank 60 and the temperature inside the digestion tank 60. The heater 70 may be provided, for example, in the first pipe.

[0105] Specifically, for example, when excess sludge is supplied to the digestion tank 60 via the first pipe and the temperature inside the digestion tank 60 is below the first lower threshold, the control device 90 controls the heater 70 to increase the heating temperature of the excess sludge in the first pipe.

[0106] Furthermore, for example, when digested sludge is circulated between the inside and outside of the digestion tank 60 via the second pipe and the temperature inside the digestion tank 60 is below a second lower threshold, the control device 90 controls the heater 70 to heat the digested sludge in the second pipe. More specifically, for example, when excess sludge is not being supplied to the digestion tank 60, the control device 90 determines whether the temperature inside the digestion tank 60 is below the second lower threshold. Then, for example, if the control device 90 determines that the temperature inside the digestion tank 60 is below the second lower threshold, the control device 90 circulates digested sludge between the inside and outside of the digestion tank 60 via the second pipe and controls the heater 70 to heat the digested sludge in the second pipe.

[0107] Furthermore, the control device 90 includes, for example, a cooler 80 that cools at least one of the excess sludge in the first pipe and the digested sludge in the second pipe using a fluid, and controls at least one of the cooling of the excess sludge in the first pipe by the cooler 80 and the cooling of the digested sludge in the second pipe by the cooler 80 based on the supply status of excess sludge to the digestion tank 60 and the temperature inside the digestion tank 60. The cooler 80 may be provided in, for example, the second pipe.

[0108] Specifically, for example, when excess sludge is supplied to the digestion tank 60 via the first pipe and the temperature inside the digestion tank 60 exceeds a first upper limit threshold, the control device 90 controls the cooler 80 to cool the excess sludge inside the first pipe. Even more specifically, when the control device 90 determines that the temperature inside the digestion tank 60 exceeds the first upper limit threshold, the control device 90 controls the heater 70 to lower the heating temperature of the excess sludge inside the first pipe, depending on the heating temperature of the excess sludge inside the first pipe by the heater 70, or controls the cooler 80 to cool the excess sludge inside the first pipe.

[0109] Furthermore, for example, when digested sludge is circulated between the inside and outside of the digestion tank 60 via the second pipe and the temperature inside the digestion tank 60 exceeds a second upper limit threshold, the control device 90 controls the cooler 80 to cool the digested sludge in the second pipe. More specifically, for example, when excess sludge is not being supplied to the digestion tank 60, the control device 90 determines whether the temperature inside the digestion tank 60 exceeds the second upper limit threshold. Then, for example, if the control device 90 determines that the temperature inside the digestion tank 60 exceeds the second upper limit threshold, the control device 90 circulates digested sludge between the inside and outside of the digestion tank 60 via the second pipe and controls the cooler 80 to cool the digested sludge in the second pipe.

[0110] This allows the digestion system 100 to adjust the temperature of the digested sludge in the digestion tank 60 so that it falls within an appropriate temperature range, regardless of whether excess sludge is being supplied to the digestion tank 60. This makes it possible for the digestion system 100 to suppress, for example, a decrease in the digestion rate in the digestion tank 60.

[0111] [Temperature Control Process in the Second Modification] Next, another modified example of the temperature control process in the first embodiment (hereinafter also referred to as a second modified example) will be described.

[0112] The control device 90 may, for example, calculate the amount of heat (hereinafter also referred to as the required amount of heat) required to raise the temperature of the excess sludge to a predetermined target temperature (hereinafter also simply referred to as the target temperature) by using the amount (estimated amount) of excess sludge supplied to the digestion tank 60 and the temperature of the excess sludge supplied to the digestion tank 60 (the temperature of the excess sludge before it is heated by the heater 70).

[0113] The control device 90 may then calculate the heating temperature of the excess sludge (the heating temperature of the excess sludge by the heater 70) required to supply the required amount of heat to the excess sludge, for example, by using the calculated required amount of heat and the amount of excess sludge supplied to the digestion tank 60. Thereafter, the control device 90 may control the flow rate of the fluid supplied to the heater 70, for example, so that the heating temperature of the excess sludge becomes the calculated value.

[0114] This enables the control device 90 to, for example, calculate (predict) the heating temperature of excess sludge that will bring the temperature inside the digestion tank 60 to a target temperature before or while the excess sludge is being supplied to the digestion tank 60. Therefore, the control device 90 can more accurately adjust the temperature inside the digestion tank 60 by, for example, controlling the heater 70 according to the calculated heating temperature. Furthermore, the control device 90 can, for example, reduce the frequency with which the digested sludge is circulated inside the digestion tank 60 (circulation temperature increase control and circulation temperature decrease control).

[0115] Furthermore, when digestion of primary sludge (for example, primary sludge supplied from the thickening device 40 described in Figure 1) is also performed in the digestion tank 60, the control device 90 may calculate the required heat quantity by, for example, using the amount (predicted amount) of excess sludge supplied to the digestion tank 60, the temperature of the excess sludge supplied to the digestion tank 60 (the temperature of the excess sludge before being heated by the heater 70), the amount (predicted amount) of primary sludge supplied to the digestion tank 60, and the temperature of the primary sludge supplied to the digestion tank 60.

[0116] As a result, even when primary settling sludge is supplied to the digestion tank 60, the control device 90 can calculate (predict) the heating temperature of the excess sludge that will enable the temperature inside the digestion tank 60 to reach the target temperature before or during the supply of the excess sludge to the digestion tank 60.

[0117] The above calculations can utilize various data such as the flow rate and temperature of excess sludge, the temperature of the digested sludge in the digestion tank 60, the capacity of the digestion tank 60, the specific heat and specific gravity of the sludge, etc.

[0118] In this way, the control device 90 in this modified example calculates the amount of heat required to raise the temperature of the excess sludge supplied to the digestion tank 60 to a target temperature based on, for example, the amount of excess sludge supplied to the digestion tank 60 and the temperature of the excess sludge supplied to the digestion tank 60 before heating by the heater 70, and determines the heating temperature of the excess sludge in the first pipe by the heater 70 based on the calculated amount of heat.

[0119] This allows the control device 90 in this modified example to, for example, adjust the temperature inside the digestion tank 60 with greater precision.

[0120] The control device 90 may, for example, supply the required amount of heat to the excess sludge by controlling both the flow rate of the fluid supplied to the heater 70 and the flow rate of the fluid supplied to the cooler 80. That is, for example, when the amount of heat supplied to the excess sludge by the heater 70 exceeds the required amount of heat, the control device 90 may supply the excess sludge to the cooler 80 to cool the excess sludge, thereby controlling the amount of heat supplied to the excess sludge to be the required amount of heat.

[0121] Furthermore, the control device 90 may perform circulation temperature increase control, for example, when it is not possible to supply all of the required heat to the excess sludge, to heat the digested sludge in the digestion tank 60. Furthermore, the control device 90 may perform circulation temperature decrease control, for example, when more heat than is required is supplied to the excess sludge, to cool the digested sludge in the digestion tank 60.

[0122] Furthermore, when the temperature of the heating fluid (heat medium) supplied to the heater 70 is equal to or lower than a predetermined threshold value (hereinafter simply referred to as the predetermined threshold value), the control device 90 may, for example, temporarily stop the supply of at least any one of excess sludge and digested sludge (hereinafter also referred to as the sludge to be heated) to the heater 70. Then, for example, when the temperature of the fluid exceeds the predetermined threshold value, the control device 90 may resume the supply of the sludge to be heated to the heater 70. [Explanation of symbols]

[0123] 10: Primary sedimentation tank 20: Sewage treatment plant 30: Final settling tank 40: Thickener 50: Concentrator 60: Digestion tank 70: Heater 80: Cooler 90: Control device 100: Fire extinguishing system 901:CPU 902:Memory 903: Communication device 904: Storage medium 905: Bus 910: Program 930: Information storage area 1000: Processing system L1: Piping L2: Piping L3: Piping L4: Piping L5: Piping L6: Piping P1: Pump P2: Pump T: Thermometer V1: Valve V2: Valve V3: Valve V4: Valve V5: Valve

Claims

1. a tank for digesting excess sludge; a first pipe for supplying the excess sludge to the tank; a second pipe for circulating the digested sludge in the tank between the tank and the outside; a heater that heats at least one of the excess sludge in the first pipe and the digested sludge in the second pipe by a fluid; a control device that controls at least one of the heating of the excess sludge in the first pipe by the heater and the heating of the digested sludge in the second pipe by the heater based on the supply status of the excess sludge to the tank and the temperature in the tank, A digestion system in which the control device circulates the digested sludge between the inside and outside of the tank via the second piping when the excess sludge is not supplied to the tank via the first piping.

2. The digestion system described in claim 1, wherein the control device controls the heater to increase the heating temperature of the excess sludge in the first pipe when the excess sludge is supplied to the tank through the first pipe and the temperature in the tank is below a first lower threshold.

3. The digestion system described in claim 1, wherein the control device controls the heater to heat the digested sludge in the second pipe when the digested sludge circulates between the inside and outside of the tank via the second pipe and the temperature in the tank is below a second lower threshold.

4. a tank for digesting excess sludge; a first pipe for supplying the excess sludge to the tank; a second pipe for circulating the digested sludge in the tank between the tank and the outside; a heater that heats at least one of the excess sludge in the first pipe and the digested sludge in the second pipe by a fluid; a control device that controls at least one of the heating of the excess sludge in the first pipe by the heater and the heating of the digested sludge in the second pipe by the heater based on the supply status of the excess sludge to the tank and the temperature in the tank, The control device A digestion system in which, when the excess sludge is not supplied to the tank through the first pipe and the temperature inside the tank is below a second lower threshold, the digested sludge is circulated between the inside and outside of the tank through the second pipe, and the heater is controlled to heat the digested sludge in the second pipe.

5. a tank for digesting excess sludge; a first pipe for supplying the excess sludge to the tank; a second pipe for circulating the digested sludge in the tank between the tank and the outside; a heater that heats at least one of the excess sludge in the first pipe and the digested sludge in the second pipe by a fluid; a control device that controls at least one of the heating of the excess sludge in the first pipe by the heater and the heating of the digested sludge in the second pipe by the heater based on the supply status of the excess sludge to the tank and the temperature in the tank; Further, a cooler is provided that cools at least one of the excess sludge in the first pipe and the digested sludge in the second pipe using a fluid, A digestion system in which the control device controls at least one of the cooling of the excess sludge in the first pipe by the cooler and the cooling of the digested sludge in the second pipe by the cooler based on the supply status of the excess sludge to the tank and the temperature in the tank.

6. The digestion system described in claim 5, wherein the control device controls the cooler to cool the excess sludge in the first pipe when the excess sludge is supplied to the tank through the first pipe and the temperature in the tank exceeds a first upper limit threshold.

7. The digestion system described in claim 6, wherein when the temperature in the tank exceeds the first upper limit threshold, the control device controls the heater to lower the heating temperature of the excess sludge in the first pipe, depending on the heating temperature of the excess sludge in the first pipe by the heater, or controls the cooler to cool the excess sludge in the first pipe.

8. The digestion system described in claim 5, wherein the control device controls the cooler to cool the digested sludge in the second pipe when the digested sludge circulates between the inside and outside of the tank via the second pipe and the temperature in the tank exceeds a second upper limit threshold.

9. The control device A digestion system as described in claim 8, wherein when the excess sludge is not supplied to the tank through the first pipe and when the temperature inside the tank exceeds the second upper threshold, the digested sludge is circulated between the inside and outside of the tank through the second pipe, and the cooler is controlled to cool the digested sludge in the second pipe.

10. The control device calculating an amount of heat required to raise the temperature of the excess sludge supplied to the tank to a target temperature based on the amount of excess sludge supplied to the tank and the temperature of the excess sludge supplied to the tank before being heated by the heater; The digestion system according to claim 1 , wherein the heating temperature of the excess sludge in the first pipe by the heater is determined based on the calculated amount of heat.

11. a tank for digesting excess sludge; a first pipe for supplying the excess sludge to the tank; a second pipe for circulating the digested sludge in the tank between the tank and the outside; a heater that heats at least one of the excess sludge in the first pipe and the digested sludge in the second pipe by a fluid; a control device that controls at least one of the heating of the excess sludge in the first pipe by the heater and the heating of the digested sludge in the second pipe by the heater based on the supply status of the excess sludge to the tank and the temperature in the tank, The control device When the excess sludge is supplied to the tank through the first pipe and the temperature in the tank is lower than a first lower threshold, the heating temperature of the excess sludge in the first pipe by the heater is controlled to be increased; A digestion system in which the digested sludge circulates between the inside and outside of the tank via the second piping, and when the temperature inside the tank is below a second lower threshold, the heater is controlled to heat the digested sludge in the second piping.

12. A heating control method for a digestion system having a tank for digesting excess sludge, a first pipe for supplying the excess sludge to the tank, a second pipe for circulating the digested sludge in the tank between the tank and the outside, and a heater for heating at least one of the excess sludge in the first pipe and the digested sludge in the second pipe with a fluid, comprising: based on the supply status of the excess sludge to the tank and the temperature in the tank, controlling at least one of heating of the excess sludge in the first pipe by the heater and heating of the digested sludge in the second pipe by the heater; A heating control method in which, in the control process, when the excess sludge is not supplied to the tank through the first piping, the digested sludge is circulated between the inside and outside of the tank through the second piping.

Images