Digestive System

Abstract

To provide a digestion system in which damage to piping caused by the filling of steam used to heat sludge.SOLUTION: The digestion system includes a digestion tank in which organic matter in excess sludge is digested using anaerobic bacteria, a sludge piping through which excess sludge is fed to the digestion tank, and a steam piping through which steam is fed to the excess sludge in the sludge piping, and the sludge piping has a heating section that heats the excess sludge in the sludge piping with steam, and further has a detector that detects the state of excess sludge in the sludge piping, and a control device that determines the mixing state of the excess sludge and steam according to the detection result of the detector.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to digestive systems. [Background technology]

[0002] In a digestion system that anaerobically digests organic matter contained in sludge, a technique has been proposed in which heated sludge is supplied to a digestion tank in order to achieve efficient digestion (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special table 2011-516246 publication Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned digestion system, it is desirable to suppress damage to the piping caused by the accumulation of steam used to heat the sludge. [Means for solving the problem]

[0005] In order to suppress damage to the above-mentioned piping, the digestion system of the present invention comprises a digestion tank in which organic matter in the excess sludge is digested using anaerobic bacteria, a sludge pipe for supplying the excess sludge to the digestion tank, and a steam pipe for supplying steam to the excess sludge in the sludge pipe, the sludge pipe having a heating section for heating the excess sludge in the sludge pipe with the steam, and further comprising a detector for detecting the state of the excess sludge in the sludge pipe, and a control device for determining the mixed state of the excess sludge and the steam based on the detection result by the detector. Effect of the Invention

[0006] According to the extinguishing system of the present invention, it is possible to suppress damage to piping caused by the accumulation of steam used to heat sludge. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a configuration diagram of a fire extinguishing system 100 according to the first embodiment. [Diagram 2] FIG. 2 is a diagram illustrating heating of excess sludge in the first embodiment. [Diagram 3] FIG. 3 is a diagram illustrating the configuration of the detector and the control device. [Figure 4] FIG. 4 is a diagram illustrating the configuration of the detector and the control device. [Diagram 5] FIG. 5 is a diagram illustrating the configuration of the detector and the control device. [Figure 6] FIG. 6 is a diagram illustrating the configuration of the detector and the control device. [Figure 7] FIG. 7 is a diagram illustrating the configuration of the detector and the control device. [Figure 8] FIG. 8 is a diagram illustrating the configuration of the detector and the control device. [Figure 9] FIG. 9 is a diagram illustrating heating of excess sludge in the second embodiment. [Figure 10] FIG. 10 is a diagram illustrating heating of excess sludge in the second embodiment. [Figure 11] FIG. 11 is a diagram illustrating heating of excess sludge in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments.

[0009] [Fire extinguishing system 100 in the first embodiment] First, a description will be given of a fire extinguishing system 100 in the first embodiment. Fig. 1 is a configuration diagram of the fire extinguishing system 100 in the first embodiment.

[0010] As shown in FIG. 1, the digestion system 100 includes a primary sedimentation tank 10, a wastewater treatment device 20, a final sedimentation tank 30, a thickening tank 40, a thickening device 50, a digestion tank 60, and a steam heater 70.

[0011] The primary sedimentation tank 10 separates organic matter and suspended matter contained in the sewage (hereinafter also referred to as the water to be treated) by settling. The primary sedimentation tank 10 then discharges the separated organic matter and suspended matter as primary settled sludge to a thickening tank 40, and discharges the water to be treated from which the organic matter and suspended matter have been separated to a wastewater treatment device 20.

[0012] The wastewater treatment device 20 treats the water to be treated by biological treatment such as the standard activated sludge process or the circulating nitrification denitrification process. Specifically, the wastewater treatment device 20 has, for example, a denitrification tank (not shown) in which anaerobic denitrifying bacteria generate nitrogen from nitrate ions (denitrification), and a nitrification tank (not shown) provided downstream of the denitrification tank in which aerobic nitrifying bacteria nitrify ammonia nitrogen. The wastewater treatment device 20 then discharges the water to be treated into a final sedimentation tank 30.

[0013] The final settling tank 30 separates sludge contained in the water to be treated discharged from the wastewater treatment device 20 by settling, and discharges the separated sludge as activated sludge. The final settling tank 30 supplies a portion of the activated sludge to the thickening device 50 as excess sludge, and returns the activated sludge other than the excess sludge to the wastewater treatment device 20 as returned sludge. The final settling tank 30 also discharges the water to be treated (supernatant) from which the sludge has been separated to a downstream sterilization treatment device (not shown). The sterilization treatment device (not shown) then sterilizes the water to be treated discharged from the final settling tank 30, and, for example, discharges the sterilized treated water.

[0014] The thickening tank 40 thickens, for example, the primary sludge discharged from the primary sedimentation tank 10 and supplies it to the digestion tank 60. Hereinafter, the primary sludge thickened in the thickening tank 40 is also referred to as thickened primary sludge.

[0015] The thickening device 50 thickens, for example, excess sludge discharged from the final settling tank 30 and supplies the sludge to the digestion tank 60. Hereinafter, the excess sludge thickened in the thickening device 50 will also be referred to as thickened excess sludge.

[0016] In the digestion tank 60, for example, anaerobic bacteria in the digestion tank 60 anaerobically digest (decompose) the organic matter in the sludge (hereinafter simply referred to as sludge), including the primary sludge supplied from the thickening tank 40 and the excess sludge supplied from the thickening device 50, through a vital reaction to generate digested sludge. The anaerobic bacteria in the digestion tank 60 generate digestion gases such as methane gas during the digestion process. Note that the temperature of the digested sludge (digestive liquid) in the digestion tank 60 is preferably maintained between 35°C and 40°C (hereinafter, this temperature range is also referred to as the optimum temperature) for example, in order to efficiently promote the vital reaction and improve the digestion rate.

[0017] The steam heater 70 supplies steam (water vapor) to heat the excess sludge before it is supplied to the digestion tank 60. In the digestion tank 60, the excess sludge heated by the steam supplied from the steam heater 70 is used as a heat medium to maintain the temperature of the digested sludge in the digestion tank 60 at an appropriate temperature.

[0018] 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 the excess sludge containing the 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.

[0019] Therefore, in the digestion system 100 of this embodiment, the excess sludge is heated intensively to sufficiently kill the viable bacteria contained in the excess sludge before it is supplied to the digestion tank 60. Then, in the digestion system 100, the temperature of the digested sludge in the digestion tank 60 is maintained at an appropriate temperature by using the heated excess sludge as a heat medium.

[0020] As a result, the digestion system 100 in this embodiment is able to suppress a decrease in digestion rate in the digestion tank 60.

[0021] Note that the primary sludge does not contain a sufficient amount of viable bacteria to cause a decrease in digestion rate, and may not be the main cause of the decrease in digestion rate. Therefore, in the digestion system 100, in order to increase digestion efficiency and achieve energy savings, the primary sludge may not be heated before being supplied to the digestion tank 60. On the other hand, when the primary sludge is also used as a heat medium, the primary sludge may also be heated before being supplied to the digestion tank 60. The heating of excess sludge will be described below.

[0022] [Heating of excess sludge] 2 is a diagram for explaining heating of excess sludge in the first embodiment. Note that, hereinafter, description of the primary settling sludge will be omitted.

[0023] As shown in FIG. 2, the digestion tank 60 includes, for example, a tank body 61 in which digested sludge 1a is accumulated, and piping 62 (hereinafter also referred to as sludge piping 62).

[0024] The piping 62 has a first portion 62a extending along the vertical direction (the vertical direction of the tank body 61), and a second portion 62b and a third portion 62c extending along a direction different from the vertical direction (for example, the horizontal direction of the tank body 61). One end of the first portion 62a communicates with a supply port 61a provided in an upper portion of the tank body 61 via the third portion 62c, and the other end communicates with the second portion 62b. Moreover, one end of the second portion 62b communicates with the first portion 62a, and the other end communicates with the concentrating device 5.

[0025] The extension direction of the first portion 62a does not have to completely coincide with the vertical direction. The pipe 62 does not have to have the third portion 62c. In this case, the first portion 62a may be connected to the supply port 61a by, for example, a joint (not shown).

[0026] Then, the excess sludge (not shown) supplied from the thickening device 50 is transferred (pressurized) by, for example, a pump (not shown) as indicated by the solid arrow in the piping 62 in Fig. 2. Specifically, the excess sludge supplied from the thickening device 50 passes through the second portion 62b, the first portion 62a, and the third portion 62c in this order, and is supplied into the digestion tank 60 from the supply port 61a in the tank body 61.

[0027] 2, the steam heater 70 has a pipe 71 (hereinafter also referred to as steam pipe 71) that communicates with the pipe 62 at a predetermined portion (hereinafter also referred to as heating section 62a1) in the first section 62a and supplies steam to this predetermined portion. Specifically, the pipe 71 supplies steam to the excess sludge located in the heating section 62a1 to heat it.

[0028] Here, in the case where the excess sludge and steam are not sufficiently mixed in the heating section 62a1 such as steam (when steam is not sufficiently injected into the excess sludge), steam may fill the pipe 62. In this case, the filled steam may cause a hammer phenomenon, which may damage the pipe 62. In particular, as shown in Fig. 2, when steam is supplied to the first portion 62a, steam that is not mixed with the excess sludge may rise in the first portion 62a, and may damage, for example, the third portion 62c.

[0029] Therefore, the extinguishing system 100 in this embodiment has a detector that detects the state of excess sludge in the pipe 62, and a control device that determines the mixed state of the excess sludge and steam according to the detection result by the detector. The control device is, for example, a computer device having a CPU (Central Processing Unit) and memory. Specifically, the control device determines the mixed state of the excess sludge and steam according to, for example, the state of the excess sludge detected by the detector and predetermined state information of the excess sludge (for example, predetermined threshold value or range). Then, the control device adjusts, for example, the number of pipes 71 that supply steam to the excess sludge in the pipe 62 according to the determination result.

[0030] In the following, a case will be described in which the detector is installed in the first portion 62a of the piping 62 and the control device determines the mixed state of the excess sludge located in the first portion 62a, but the detector may be installed, for example, in the second portion 62b of the piping 62, and the control device may be one that determines the mixed state of the excess sludge located in the second portion 62b, for example. In other words, it may be one that determines the mixed state of the excess sludge and steam in the horizontal piping. The configurations of the detector and the control device will be described below.

[0031] [Configuration of detector and control device] 3 to 8 are diagrams for explaining the configuration of the detector and the control device. In the following, the explanation will be given on the assumption that there are a plurality of pipes 71 for supplying steam from the steam heater 70 to the first portion 62a.

[0032] [Example of using two flow meters] First, a description will be given of a case where the detector is two flow meters (for example, ultrasonic flow meters) that measure the flow rate of excess sludge in the first portion 62a of the pipe 62. Fig. 3 is a diagram for explaining a configuration in which flow meters 81 and 82 are used as the detector.

[0033] 3, in the first portion 62a, for example, a flow meter 81 (hereinafter also referred to as the first flow meter 81) and a flow meter 82 (hereinafter also referred to as the second flow meter 82) are installed on the downstream side and the upstream side, respectively, of a supply port (not shown) to which steam is supplied from the pipe 71. Note that upstream and downstream mean upstream and downstream in the direction in which the excess sludge flows in the pipe 62. In other words, the flow meter 81 is a flow meter that measures the flow rate of the excess sludge after the steam is supplied, and the flow meter 82 is a flow meter that measures the flow rate of the excess sludge before the steam is supplied.

[0034] The control device 80 acquires values ​​(flow rates of excess sludge in the first portion 62a) detected by the flowmeter 81 and the flowmeter 82 at regular intervals, such as every minute. Then, the control device 80 determines whether or not the difference between the value acquired from the flowmeter 81 and the value acquired from the flowmeter 82 is within a predetermined range (hereinafter also simply referred to as within the predetermined range).

[0035] As a result, if it is determined that the difference between the value obtained from flow meter 81 and the value obtained from flow meter 82 is not within a specified range, the control device 80 determines that the excess sludge and steam are not sufficiently mixed in the first portion 62a.

[0036] That is, when the excess sludge and steam are not sufficiently mixed in the pipe 62, the amount of bubbles generated in the pipe 62 increases. Bubbles are one of the causes of measurement errors of the flowmeter, and when the amount of bubbles generated increases, the possibility of measurement errors of the flowmeter occurring increases, and further, the possibility of the measurement error increasing increases. That is, when bubbles are generated in the pipe 62, the flowmeter 81 that measures the flow rate of the excess sludge after the steam is supplied is highly likely to not accurately measure the flow rate of the excess sludge. On the other hand, the flowmeter 82 that measures the flow rate of the excess sludge before the steam is supplied can be determined to be able to accurately measure the flow rate of the excess sludge regardless of the mixing state of the excess sludge and the steam. Therefore, for example, when the difference between the value acquired from the flowmeter 81 and the value acquired from the flowmeter 82 is large, the control device 80 determines that the flow rate is not accurately measured in the flowmeter 81, and determines that the excess sludge and the steam are not sufficiently mixed.

[0037] On the other hand, if the control device 80 determines that the difference between the value obtained from flow meter 81 and the value obtained from flow meter 82 is within a predetermined range, it determines that the excess sludge and steam are sufficiently mixed in the first portion 62a.

[0038] In other words, if the difference between the value obtained from flowmeter 81 and the value obtained from flowmeter 82 is small, the control device 80 determines that the flow rate is also being measured accurately by flowmeter 81, and determines that no bubbles are occurring in pipe 62 (excess sludge and steam are sufficiently mixed).

[0039] When it is determined that the excess sludge and the steam are not sufficiently mixed, the control device 80 increases, for example, the number of pipes 71 that supply steam to the first portion 62a. Hereinafter, the control in the case where the number of pipes 71 that supply steam to the first portion 62a is increased will be described.

[0040] [Control of pipe 71 that supplies steam] FIG. 4 is a diagram for explaining control of the number of pipes 71 for supplying steam.

[0041] In the example shown in FIG. 4, the first section 62a is provided with two pipes 71 (hereinafter also referred to as pipe 71a and pipe 72b) for supplying steam to the excess sludge.

[0042] For example, when steam is supplied only through pipe 71a, if it is determined that the excess sludge and steam are not sufficiently mixed, the control device 80 performs control so that steam is supplied through pipe 71b in addition to pipe 71a by opening a valve (not shown) attached to pipe 71b. This enables the control device 80 to promote mixing of the excess sludge and steam in the first portion 62a.

[0043] Furthermore, for example, when steam is supplied using pipe 71b, if it is determined that the excess sludge and steam are sufficiently mixed, the control device 80 closes the valve attached to pipe 71b to stop the supply of steam from pipe 71b, and controls the supply of steam to be only from pipe 71a.

[0044] 4, the first portion 62a has two pipes 71, but the first portion 62a may have three or more pipes 71. The multiple pipes 71 may have different steam supply amounts or ejection directions. The multiple pipes 71 may have different steam ejection timings.

[0045] [Example when using one flow meter] Next, a description will be given of a case where the detector is one flow meter that measures the flow rate of excess sludge in the first portion 62a of the pipe 62. Fig. 5 is a diagram illustrating a configuration in which a flow meter 81 is used as the detector.

[0046] As shown in FIG. 5, in the first portion 62a, for example, only a flow meter 81 is installed downstream of a supply port (not shown) to which steam is supplied from the pipe 71.

[0047] Then, the control device 80 determines, for example, whether the value detected by the flow meter 81 is within a predetermined range, and if it determines that the value detected by the flow meter 81 is not within the predetermined range, it determines that the excess sludge and steam are not sufficiently mixed in the first portion 62a.

[0048] That is, for example, if the range of the flow rate of excess sludge when the excess sludge and steam are sufficiently mixed is known, the flow meter 82 may not be installed in the first section 62a of the piping 62. In this case, the control device 80 may determine whether the excess sludge and steam are sufficiently mixed in the first section 62a by determining whether the value detected by the flow meter 81 is within the known range.

[0049] As a result, in the digestion system 100 of this embodiment, it is possible to reduce the number of flow meters used to determine the mixed state of excess sludge and steam.

[0050] The control device 80 may, for example, determine whether or not the difference between values ​​detected by the flowmeter 81 at two different times is within a predetermined range. If it is determined that the difference between the values ​​detected by the flowmeter 81 is not within the predetermined range, the control device 80 may, for example, determine that the excess sludge and steam are not sufficiently mixed in the first portion 62a.

[0051] [Example of using a vibration meter] Next, a description will be given of a case where the detector is a vibrometer that measures vibrations in the first portion 62a of the pipe 62. Fig. 6 is a diagram illustrating a configuration in which a vibrometer 83 is used as the detector.

[0052] As shown in FIG. 6, in the first portion 62a, for example, a vibrometer 83 is installed downstream of a supply port (not shown) to which steam is supplied from the pipe 71.

[0053] Then, the control device 80, for example, determines whether the value detected by the vibration meter 83 is within a predetermined range, and if it determines that the value detected by the vibration meter 83 is not within the predetermined range, it determines that the excess sludge and steam are not sufficiently mixed in the first portion 62a.

[0054] That is, when bubbles are generated in the pipe 62 or when bubbles are in the process of disappearing in the pipe 62, it can be determined that the vibration meter 83 provided downstream of the supply port to which steam is supplied from the pipe 71 measures a vibration that is greater than when no bubbles are generated in the pipe 62. Therefore, for example, when the value acquired from the vibration meter 83 is not within a predetermined range, the control device 80 determines that the excess sludge and steam are not sufficiently mixed.

[0055] As a result, in the extinguishing system 100 of this embodiment, it becomes possible to determine the mixed state of the excess sludge and steam from the state of vibration within the piping 62.

[0056] [Example of using a pressure gauge] Next, a description will be given of a case where the detector is a pressure gauge that measures the pressure in the first portion 62a of the pipe 62. Fig. 7 is a diagram illustrating a configuration in which a pressure gauge 84 is used as the detector.

[0057] As shown in FIG. 7, in the first portion 62a, for example, a pressure gauge 84 is installed downstream of a supply port (not shown) to which steam is supplied from the pipe 71.

[0058] Then, the control device 80 determines, for example, whether the value detected by the pressure gauge 84 is within a predetermined range, and if it determines that the value detected by the pressure gauge 84 is not within the predetermined range, it determines that the excess sludge and steam are not sufficiently mixed in the first portion 62a.

[0059] That is, when bubbles are generated in the pipe 62 or when bubbles are in the process of disappearing in the pipe 62, the pressure gauge 84 provided downstream of the supply port to which steam is supplied from the pipe 71 measures a higher pressure than when bubbles are not generated in the pipe 62, or it can be determined that the pressure fluctuation is large. Therefore, for example, when the value acquired from the pressure gauge 84 is not within a predetermined range, the control device 80 determines that the excess sludge and steam are not sufficiently mixed.

[0060] As a result, in the extinguishing system 100 of this embodiment, it becomes possible to determine the mixed state of the excess sludge and steam from the pressure state within the piping 62.

[0061] [Example of using two thermometers] Next, a description will be given of a case where the detector is two thermometers that measure the temperature of the excess sludge in the first portion 62a of the pipe 62. Fig. 8 is a diagram for explaining a configuration in which thermometer 85 and thermometer 86 are used as the detector.

[0062] 8, in the first portion 62a, for example, a thermometer 85 (hereinafter also referred to as a first thermometer 85) and a thermometer 86 (hereinafter also referred to as a second thermometer 86) are installed downstream of a supply port (not shown) to which steam is supplied from the pipe 71. Specifically, the thermometer 85 and the thermometer 86 are provided at positions at different heights in the first portion 62a, for example.

[0063] Then, the control device 80 determines, for example, whether the difference between the value obtained from thermometer 85 and the value obtained from thermometer 86 is within a predetermined range, and if it determines that the difference between the value obtained from thermometer 85 and the value obtained from thermometer 86 is not within the predetermined range, it determines that the excess sludge and steam are not sufficiently mixed in the first portion 62a.

[0064] That is, when bubbles are generated in the pipe 62, or when bubbles are in the process of disappearing in the pipe 62, it can be determined that there are places where bubbles are generated and places where bubbles are not generated. In this case, it can also be determined that there is temperature unevenness between the places where bubbles are generated and the places where bubbles are not generated. Therefore, for example, when the difference between the value acquired from the thermometer 85 and the value acquired from the thermometer 86 is not within a predetermined range, the control device 80 determines that there is a place where bubbles are generated and that the excess sludge and steam are not sufficiently mixed.

[0065] As a result, in the extinguishing system 100 of this embodiment, it becomes possible to determine the mixed state of excess sludge and steam from the occurrence of temperature unevenness in the piping 62.

[0066] For example, if the temperature range of the excess sludge when the excess sludge and steam are sufficiently mixed is known, only one of the thermometer 85 and the thermometer 86 may be installed in the first section 62a of the piping 62. In this case, the control device 80 may determine whether the excess sludge and steam are sufficiently mixed in the first section 62a by determining whether the value detected by the thermometer 85 or the thermometer 86 is within the known range.

[0067] [Fire extinguishing system 200 according to the second embodiment] Next, a digestion system 200 in the second embodiment will be described. Figures 9 to 11 are diagrams for explaining the heating of excess sludge in the second embodiment. Below, only the points that differ from the digestion system 100 in the first embodiment will be described.

[0068] Specifically, Fig. 9 is a diagram for explaining a state in which excess sludge is intermittently and continuously transferred. The digestion system 200 in this embodiment has a buffer tank 91 (storage tank 91). The buffer tank 91 communicates with a pipe 92 that communicates with the concentrator 50, and temporarily stores the excess sludge that is intermittently transferred from the concentrator 50 to the pipe 92.

[0069] In this case, the excess sludge is transferred intermittently in pipe 92, and then continuously in pipe 62. Intermittent transfer and continuous transfer will be described below with reference to Figures 10(A) and 10(B). In Figures 10(A) and 10(B), the hatched areas show the amount of excess sludge in a schematic manner, and each shows the state when the same amount of excess sludge is transferred.

[0070] The pipes 62 and 92 shown in Fig. 9 may have different pipe diameters. The pipe diameter of the pipe 92 is, for example, 150 mm or more, which is larger than the pipe diameter of the pipe 62. This pipe diameter of 150 mm or more is determined by the design guidelines for sludge treatment equipment. In the following explanation, it is assumed that the pipe diameter of the pipe 92 is 150 mm.

[0071] Next, a case will be described in which excess sludge produced by the thickening device 50 is pumped through a pipe 92 having a pipe diameter of 150 (mm). In a typical sludge treatment facility, the amount of excess sludge produced is small compared to this pipe diameter. Furthermore, if the sludge is not transported at a specified pipe diameter and flow rate or greater, the sludge will settle at the bottom of the pipe, increasing the possibility that the pipe will become clogged with sludge. For this reason, the excess sludge is transported intermittently from the thickening device 50.

[0072] Fig. 10(A) is a graph illustrating the intermittent transfer of excess sludge. The vertical axis indicates the amount of excess sludge transferred, and the horizontal axis indicates time. The generated excess sludge is transferred through a pipe 92 having a diameter of 150 (mm) at a predetermined flow rate and flow rate. Therefore, at regular intervals, a sludge volume V1 of excess sludge is transferred at one time during a period T1 (intermittent transfer). Note that intermittent transfer refers to transfer not only at regular intervals, but also at irregular intervals.

[0073] 10B is a graph illustrating the continuous transfer of excess sludge. The vertical axis indicates the amount of excess sludge being transferred, and the horizontal axis indicates time. For example, excess sludge of a sludge amount V2 is continuously transferred during a period T2.

[0074] Here, when excess sludge of sludge volume V2, which is less than sludge volume V1, is steam heated to a predetermined temperature during the same time period (for example, period T1), the amount of thermal energy required to steam heat the excess sludge of sludge volume V2 is less than the amount of thermal energy required to steam heat the excess sludge of sludge volume V1.

[0075] That is, to steam-heat the amount of excess sludge of sludge volume V1 to a predetermined temperature in one time period T1, more thermal energy is required than to steam-heat the amount of excess sludge of sludge volume V2 to a predetermined temperature in the same time period T1. In order to generate a large amount of thermal energy, i.e., a large amount of steam, it is necessary to enlarge the boiler that generates the steam. However, enlarging the boiler leads to an increase in installation space, installation costs, maintenance costs, fuel use, etc., and therefore it may be difficult to enlarge the boiler.

[0076] Therefore, in the digestion system 200 of this embodiment, the excess sludge is continuously transferred for a predetermined period of time to prevent clogging of the piping and to reduce the amount of excess sludge transferred. To enable such continuous transfer, a buffer tank 91 is provided to temporarily store the excess sludge, and the diameter of the pipe 62 connecting the buffer tank 91 and the digestion tank 60 is made smaller than the above-mentioned 150 (mm). The diameter of the pipe 62 is set to, for example, 60 (mm) to prevent clogging by sludge and to achieve a predetermined flow velocity and flow rate or more.

[0077] Specifically, the excess sludge temporarily stored in the buffer tank 91 is continuously transferred by a pump (not shown), passes through piping 62, and is supplied into the digestion tank 60 from the upper part of the digestion tank 60.

[0078] During this continuous transfer (period T2), unlike the intermittent transfer described with reference to FIG. 10(A), there is no period during which excess sludge is not transferred, and the amount of excess sludge transferred is reduced.

[0079] As described above, by continuously transporting a small amount of excess sludge and heating it with steam during this transport, it is possible to prevent the boiler from becoming large.

[0080] Next, the control device for controlling the amount of steam, the steam temperature, and the amount of excess sludge transported will be described.

[0081] 11 is a diagram illustrating a control device that controls the amount of steam, the steam temperature, and the amount of excess sludge transferred based on various information. The digestion system 200 of this embodiment further includes a control device 90 that controls a pump and a thermometer.

[0082] In the digestion tank 60 shown in Fig. 11 etc., if the temperature of the digestive fluid is not appropriate, the digestion capacity decreases. Therefore, the control device 90 controls the steam heater 70 and the pump 93 so as to maintain the digestion capacity. The control device 90 may be the same control device as the control device 80 described in Fig. 3, or may be a control device different from the control device 80.

[0083] The pump 93 continuously transfers (pressure-feeds) the excess sludge stored in the buffer tank 91 to the digestion tank 60 via the piping 62. Note that the location of the pump 93 in Figure 11 is just one example, and the pump 93 may be located before or after the buffer tank 91.

[0084] The control device 90 controls at least one of the steam heater 70 and the pump 93 so as to maintain the digestion capacity of the digester 60 at a predetermined capacity. The control device 90 controls at least one of the steam heater 70 and the pump 93 based on at least one of the temperatures in the digester 60 and the piping 62, for example.

[0085] Specifically, the temperature inside the digestion tank 60 is preferably the temperature of the digestive liquid. The temperature of the digestive liquid is a factor that directly affects the digestive capacity in the digestion tank 60. Therefore, the control device 90 performs control based on, for example, the temperature of the digestive liquid.

[0086] Furthermore, the temperature inside the pipe 62 is preferably the temperature at the point where the pipe 62 and the digester tank 60 are connected, i.e., the outlet temperature of the pipe 62. The outlet temperature of the pipe 62 can be regarded as the temperature of the excess sludge immediately before it is charged into the digester tank 60. The temperature of the excess sludge is one of the factors that affect the temperature of the digestive liquid in the digester tank 60. Therefore, the control device 90 performs control based on, for example, the outlet temperature.

[0087] The first thermometer 94 is a thermometer that measures the temperature inside the digester 60 (e.g., the temperature of the digestive liquid). The first thermometer 94 transmits the measured temperature to the control device 90. The second thermometer 95 is a thermometer that measures the temperature inside the piping 62 (e.g., the outlet temperature). The second thermometer 95 transmits the measured temperature to the control device 90.

[0088] When the control device 90 predicts that the digestive ability will decrease due to a decrease in temperature of the digestive liquid, it controls at least one of the steam heater 70 and the pump 93 so as to increase the temperature of the digestive liquid. Before describing the specific control of the control device 90, the following four cases will be considered.

[0089] A first case in which the temperature of the digestive fluid measured by the first thermometer 94 is below a first temperature range.

[0090] A second case in which the temperature of the digestive fluid measured by the first thermometer 94 exceeds the first temperature range.

[0091] A third case in which the outlet temperature measured by the second thermometer 95 is below the second temperature range.

[0092] A fourth case in which the outlet temperature measured by the second thermometer 95 exceeds the second temperature range.

[0093] The first temperature range is, for example, a range from 37°C to 40°C, and the second temperature range is, for example, a range from 70°C to 95°C.

[0094] Next, the control of the steam heater 70 will be described. The control device 90 judges one of the above four cases. When the control device 90 judges that at least one of the first case and the third case is occurring, it transmits a control signal to the steam heater 70 to instruct the steam heater 70 to generate steam at a temperature higher than the current temperature and / or in a larger amount and supply the steam to the piping 62 (first portion 62a). When the control device 90 judges that at least one of the second case and the fourth case is occurring, it transmits a control signal to the steam heater 70 to instruct the steam heater 70 to generate steam at a temperature lower than the current temperature and / or in a smaller amount and supply the steam to the piping 62 (first portion 62a).

[0095] The steam heater 70 responds to the control signal to control the temperature and / or amount of steam and supplies it to the pipe 62 (first portion 62a).

[0096] Next, the control of the pump 93 will be described. The control device 90 determines whether the current situation is one of the above four cases. When the control device 90 determines that the current situation is at least one of the first and third cases, it transmits a control signal to the pump 93 to instruct the pump 93 to reduce the amount of excess sludge transferred from the current amount. When the control device 90 determines that the current situation is at least one of the second and fourth cases, it transmits a control signal to the pump 93 to instruct the pump 93 to increase the amount of excess sludge transferred from the current amount.

[0097] In response to the control signal, the pump 93 controls the amount of excess sludge transported and pumps it out.

[0098] The control device 90 may simultaneously control the steam heater 70 and the pump 93, or may control only the steam heater 70 or only the pump 93.

[0099] As described in FIG. 11, it is possible to maintain the digestion capacity by controlling at least one of the steam heater 70 and the pump 93 based on at least one of the temperature of the digestive liquid and the outlet temperature, which affect the digestion capacity.

[0100] According to the present invention described above, the mixed state of the excess sludge and steam is judged, and based on the judgment result, it is determined whether or not to execute a process for promoting the mixing of the excess sludge and steam. Furthermore, since the mixing of the excess sludge and steam can be promoted, damage to the pipe caused by the overflow of steam can be suppressed. As a means for promoting this mixing, for example, a device for changing the steam supply direction of the steam pipe may be provided at a place where the steam pipe and the sludge pipe communicate with each other. In addition, the mixing of the excess sludge and steam may be promoted by using various means such as executing steam supply control such as controlling the steam supply point to supply steam continuously or intermittently, or executing sludge supply control such as slowing down the sludge supply speed or varying the sludge supply speed. [Explanation of symbols]

[0101] 1a: Digested sludge 10: Primary sedimentation tank 20: Sewage treatment equipment 30: Final sedimentation tank 40: Concentrator tank 50: Concentrator 60: Digestion tank 61: Tank body 61a: Supply port 62: Piping 62a: First portion 62a1: Joint portion 62b: Second part 62c: Heating part 70: Steam heater 71: Piping 71a: Piping 72b: Piping 80: Control device 81: Flow meter 82:Flowmeter 83:Vibration meter 84: Pressure gauge 85: Thermometer 86: Thermometer 90: Control device 91: Buffer tank 92: Piping 93: Pump 94: First thermometer 95: 2nd thermometer 100: Mixing clarifier 200: Mixing clarifier

Claims

1. a digestion tank for digesting organic matter in excess sludge using anaerobic bacteria; a sludge pipe for supplying the excess sludge to the digester; a steam pipe for supplying steam to the excess sludge in the sludge pipe, The sludge pipe has a heating unit that heats the excess sludge in the sludge pipe by the steam, and further a detector for detecting a state of the excess sludge in the sludge pipe; A control device that determines the mixed state of the excess sludge and the steam in the sludge pipe based on the detection result by the detector.

2. The fire extinguishing system according to claim 1 , wherein the control device determines the mixed state according to the state of the excess sludge detected by the detector and predetermined state information of the excess sludge.

3. The detector includes a flow meter that measures a flow rate of the excess sludge, The fire extinguishing system according to claim 1 , wherein the control device determines whether the flow rate measured by the flow meter is within a predetermined range.

4. the detector includes a first flow meter and a second flow meter that are respectively installed upstream and downstream of a position where the steam is supplied to the excess sludge and measure a flow rate of the excess sludge; The fire extinguishing system according to claim 1 , wherein the control device determines whether a difference between the flow rate measured by the first flow meter and the flow rate measured by the second flow meter is within a predetermined range.

5. The detector has a vibration meter that measures vibration of the excess sludge, The fire extinguishing system according to claim 1 , wherein the control device determines whether the vibration measured by the vibration meter is within a predetermined range.

6. The detector has a pressure gauge that measures the pressure of the excess sludge, The fire extinguishing system according to claim 1 , wherein the control device determines whether the pressure measured by the pressure gauge is within a predetermined range.

7. The detector has a thermometer that measures the temperature of the excess sludge, The fire extinguishing system according to claim 1 , wherein the control device determines whether the temperature measured by the thermometer is within a predetermined range.

8. Further, the steam pipes are provided in a plurality, The digestion system according to claim 3 , wherein the control device increases the number of the steam pipes that supply the steam to the excess sludge depending on a result of the determination.

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