Digestive System

Abstract

To provide a digestion system that can suppress the decrease in digestion rate accompanying the fluctuation in sludge feed rate.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, a first steam piping through which steam is fed to the excess sludge in the sludge piping, and a second steam piping through which steam is fed to the digestion tank, and the sludge piping has a heating section that heats the excess sludge in the sludge piping with steam fed from the first steam piping.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to the digestive system. [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 digestion system as described above, it is desirable to suppress the decrease in digestion rate that occurs due to fluctuations in the amount of sludge supplied. [Means for solving the problem]

[0005] In order to suppress the above-mentioned decrease in digestion rate, the digestion system of the present invention comprises a digestion tank in which the organic matter in the excess sludge is digested by anaerobic bacteria, a sludge piping for supplying the excess sludge to the digestion tank, a first steam piping for supplying steam to the excess sludge in the sludge piping, and a second steam piping for supplying steam to the digestion tank, and the sludge piping has a heating section that heats the excess sludge in the sludge pipe with the steam supplied from the first steam pipe. Effect of the Invention

[0006] According to the digestion system of the present invention, it is possible to suppress a decrease in digestion rate that occurs due to fluctuations in the amount of sludge supplied. [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 for explaining control of the steam supply amount by the control device 80. As shown in FIG. [Figure 4] FIG. 4 is a diagram illustrating heating of excess sludge in the second embodiment. [Diagram 5] FIG. 5 is a diagram illustrating heating of excess sludge in the second embodiment. [Figure 6] FIG. 6 is a diagram illustrating heating of excess sludge in the third embodiment. [Figure 7] FIG. 7 is a diagram illustrating heating of excess sludge in the fourth embodiment. [Figure 8] FIG. 8 is a diagram illustrating heating of excess sludge in the fourth embodiment. [Figure 9] FIG. 9 is a diagram illustrating heating of excess sludge in the fourth 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] As shown in FIG. 2, the steam heater 70 has, for example, a pipe 71 (hereinafter also referred to as a first steam pipe 71) and a pipe 72 (hereinafter also referred to as a second steam pipe 72) which supply steam.

[0028] The pipe 71 communicates with the pipe 62 at a predetermined portion (hereinafter also referred to as a 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.

[0029] The pipe 72 supplies steam to the digestion tank 60. Specifically, the pipe 72 supplies steam directly to the digested sludge 1a accumulated in the digestion tank 60 to heat it.

[0030] That is, the supply amount of excess sludge supplied to the digester 60 (the amount of excess sludge passing through the pipe 62) varies due to various factors such as a temporary increase in population due to an event being held, weather, etc. Then, for example, when the supply amount of steam to the excess sludge is constant, a decrease in the supply amount of excess sludge may cause the temperature of the excess sludge in the heating section 62a1 to rise and instantaneously boil. Due to this boiling, the sludge in the pipe 62 may burn, and carbonized matter or the like may firmly adhere to the inner wall of the pipe 62 (so-called adhesion), and the pipe 62 may be clogged. In addition, a decrease in the supply amount of excess sludge may cause steam to be unevenly distributed in the pipe, and as a result, even if the sludge does not boil, damage may occur in the pipe 62 due to the uneven distribution of steam, which may cause the hammer phenomenon.

[0031] In response to this, for example, a method of preventing the excess sludge from boiling may be considered, by reducing the amount of steam supplied to the excess sludge.

[0032] In this case, however, there may be a shortage of thermal energy for heating the digested sludge 1a accumulated in the digestion tank 60, making it impossible to maintain the temperature of the digested sludge 1a at an appropriate temperature.

[0033] Therefore, in the digestion system 100 of this embodiment, for example, in addition to the pipe 71 that supplies steam to the excess sludge located in the pipe 62, a pipe 72 that supplies steam directly to the digested sludge 1a accumulated in the digestion tank 60 is provided. Then, in the digestion system 100, by using each of the pipes 71 and 72, for example, the supply of steam to the excess sludge and the supply of steam to the digested sludge 1a are performed in parallel.

[0034] Specifically, in the digestion system 100, steam that is not enough to boil the excess sludge but is necessary to sufficiently kill the viable bacteria contained in the excess sludge is supplied to the excess sludge by using the pipe 71. In addition to this supply, the digestion system 100 uses the pipe 72 to directly supply to the digestion tank 60 (digested sludge 1a) the steam that needs to be supplied to maintain the digested sludge 1a in the digestion tank 60 at an appropriate temperature, but that is not supplied to the excess sludge due to the need to prevent the excess sludge from boiling.

[0035] More specifically, for example, if the flow rate of excess sludge in the first section 62a (the amount of excess sludge supplied to the digester tank 60) decreases, an operator, for example, opens and closes valves (not shown) attached to pipes 71 and 72, thereby reducing the amount of steam supplied to the excess sludge using pipe 71 and increasing the amount of steam supplied to the digested sludge 1a using pipe 72 so that the amount of steam supplied using pipes 71 and 72 remains constant (the amount necessary to maintain the digested sludge 1a at an appropriate temperature).

[0036] As a result, the digestion system 100 in this embodiment is able to maintain the digested sludge 1a in the digestion tank 60 at an appropriate temperature while preventing the excess sludge in the piping 62 from being overheated.

[0037] On the other hand, for example, if the flow rate of excess sludge in the first section 62a increases, the operator increases the amount of steam supplied to the excess sludge using pipe 71 and decreases the amount of steam supplied to the digested sludge 1a using pipe 72, for example, by opening and closing valves attached to pipes 71 and 72, so that the amount of steam supplied using pipes 71 and 72 remains constant.

[0038] As a result, the digestion system 100 in this embodiment is able to sufficiently heat the excess sludge even when the supply amount of excess sludge increases, making it possible to sufficiently kill the viable bacterial groups contained in the excess sludge.

[0039] The digestion system 100 may have a control device that controls the amount of steam supplied to the excess sludge and the amount of steam supplied to the digested sludge 1a. The control device is, for example, a computer device having a CPU (Central Processing Unit) and a memory. The control of the amount of steam supplied by the control device will be described below.

[0040] [Controlling the amount of steam supply] FIG. 3 is a diagram for explaining control of the steam supply amount by the control device 80. As shown in FIG.

[0041] In the example shown in FIG. 3, a flow meter 81 is installed in the first portion 62a of the pipe 62 to measure the flow rate of the excess sludge.

[0042] The control device 80 then acquires the value detected by the flow meter 81 (the flow rate of excess sludge in the first section 62a) at regular intervals, such as every minute, and adjusts the amount of steam supplied to the excess sludge using piping 71 and the amount of steam supplied to the digested sludge 1a using piping 72 based on the acquired value.

[0043] Specifically, for example, when the value acquired from the flowmeter 81 is less than a threshold value (hereinafter also referred to as a first threshold value), the control device 80 opens and closes valves (not shown) attached to the pipes 71 and 72, etc., to reduce the amount of steam supplied to the excess sludge using the pipe 71 and increase the amount of steam supplied to the digested sludge 1a using the pipe 72 so that the amount of steam supplied using the pipes 71 and 72 remains constant. In this case, the control device 80 may determine the amount of reduction in the steam supplied to the excess sludge, for example, so that the smaller the value acquired from the flowmeter 81, the less the amount of steam supplied to the excess sludge.

[0044] On the other hand, for example, when the value acquired from the flowmeter 81 is equal to or greater than the threshold value (hereinafter also referred to as the second threshold value), the control device 80 increases the amount of steam supplied to the excess sludge using the pipe 71 and decreases the amount of steam supplied to the digested sludge 1a using the pipe 72, so that the amount of steam supplied using the pipes 71 and 72 is constant, by opening and closing valves (not shown) attached to the pipes 71 and 72, for example. In this case, the control device 80 may determine the increase in the amount of steam supplied to the excess sludge, for example, so that the amount of steam supplied to the excess sludge increases as the value acquired from the flowmeter 81 increases. The second threshold value is a threshold value corresponding to a value greater than the first threshold value. Also, the first threshold value and the second threshold value may be, for example, the same value.

[0045] [Fire extinguishing system 200 according to the second embodiment] Next, a digestion system 200 in the second embodiment will be described. Figures 4 and 5 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.

[0046] As shown in Fig. 4, the piping 62 in the digestion system 200 has, for example, a first portion 62a, a second portion 62b, and a third portion 62c, as well as a fourth portion 62d extending vertically and a fifth portion 62e extending in a direction different from the vertical direction (for example, a horizontal direction). One end of the fourth portion 62d is connected to a supply port 61b (hereinafter also referred to as an introduction portion 61b) provided in a lower portion of the tank body 61 via the fifth portion 62e, and the other end is connected to the first portion 62a. The first portion 62a and the fourth portion 62d form a straight piping by, for example, connecting the lower end of the first portion 62a to the upper end of the fourth portion 62d.

[0047] The extension direction of the fourth portion 62d does not have to completely coincide with the vertical direction. The pipe 62 does not have to have the fifth portion 62e. In this case, the fourth portion 62d may be connected to the supply port 61b by a joint (not shown).

[0048] Furthermore, the pipe 62 has, for example, a partition 62f that can be opened and closed between the first section 62a and the fourth section 62d. The partition 62f controls the amount of the digested sludge 1a accumulated in the digestion tank 60 that is supplied to the heating section 62a1. When a portion of the digested sludge 1a accumulated in the digestion tank 60 is supplied to the heating section 62a1, the supply is performed by, for example, a pump (not shown) provided in the fifth section 62e. That is, the supply amount of the digested sludge 1a is adjusted by the partition 62f and this pump.

[0049] Then, for example, when the flow rate of excess sludge in the first section 62a falls below a threshold value (hereinafter also referred to as the third threshold value), the operator opens the partition section 62f, as shown in Figure 5, to supply a portion of the digested sludge 1a accumulated in the digestion tank 60 to the heating section 62a1.

[0050] That is, in the digestion system 200 of this embodiment, for example, when the supply amount of excess sludge decreases, excessive heating of the excess sludge is prevented by supplying digested sludge 1a (digested sludge 1a at an appropriate temperature) to the heating section 62a1.

[0051] As a result, the fire extinguishing system 200 in this embodiment can, for example, prevent the occurrence of the hammer phenomenon in the piping 62 and the adhesion of carbonized matter and the like to the inner walls of the piping 62, thereby making it possible to prevent damage to or blockage of the piping 62.

[0052] Thereafter, for example, if the flow rate of excess sludge in the first portion 62a further decreases, the operator increases the amount of digested sludge 1a supplied to the heating portion 62a1. In this case, the control device 80 may determine the amount of digested sludge 1a supplied to the heating portion 62a1 such that the amount of digested sludge 1a supplied to the heating portion 62a1 increases as the flow rate of excess sludge in the first portion 62a decreases.

[0053] On the other hand, for example, when the flow rate of excess sludge in the first portion 62a increases within a range below the third threshold, the operator reduces the amount of digested sludge 1a supplied to the heating portion 62a1. In this case, the control device 80 may determine the amount of digested sludge 1a supplied to the heating portion 62a1 such that the amount of digested sludge 1a supplied to the heating portion 62a1 decreases as the flow rate of excess sludge in the first portion 62a increases.

[0054] Furthermore, for example, when the flow rate of the excess sludge in the first portion 62a increases to or above the third threshold, the operator stops the supply of the digested sludge 1a to the heating portion 62a1, for example, by closing the partition portion 62f.

[0055] When the digested sludge 1a is supplied to the heating unit 62a1, the operator may, for example, heat the excess sludge and the digested sludge 1a simultaneously in the heating unit 62a1. That is, the operator may, for example, heat the mixed sludge in which the excess sludge and the digested sludge 1a are mixed in the heating unit 62a1.

[0056] On the other hand, the operator may alternately heat the excess sludge and the digested sludge 1a in the heating section 62a1, for example. That is, the operator may, for example, push the excess sludge to the forward part of the piping 62 by inputting the digested sludge 1a as the temperature of the excess sludge rises to a predetermined temperature (for example, about 80°C) by heating with steam, and place the input digested sludge 1a in the heating section 62a1 for heating. In this case, after the input of the digested sludge 1a, new excess sludge is supplied from the concentrating device 50, so that the digested sludge 1b located in the heating section 62a1 is pushed to the forward part of the piping 62, and heating of the new excess sludge in the heating section 62a1 is started.

[0057] As a result, in the digestion system 200, even when the digested sludge 1a is supplied to the pipe 62, it is possible to sufficiently kill the viable bacteria contained in the excess sludge.

[0058] In addition, like the digestion system 100, the digestion system 200 may also be configured to control the amount of steam supplied to the excess sludge and the amount of steam supplied to the digested sludge 1a by using piping 71 and piping 72.

[0059] Furthermore, the control device 80 may use values ​​detected by the flow meter 81, for example, to control the opening and closing of the partition section 62f and adjust the amount of digested sludge 1a supplied to the heating section 62a1.

[0060] [Fire extinguishing system 300 according to the third embodiment] Next, the digestion system 300 in the third embodiment will be described. Fig. 6 is a diagram for explaining heating of excess sludge in the third embodiment. Below, only the points different from the digestion system 100 in the first embodiment and the digestion system 200 in the second embodiment will be described.

[0061] Unlike the digestion system 100, the third section 62c in the digestion system 300 has one end communicating with a supply port 61c (hereinafter also referred to as the input section 61c) provided near the vertical center of the tank body 61, and the other end communicating with the first section 62a. The supply port 61c is provided at a height corresponding to the liquid phase portion of the digested sludge 1a in the digestion tank 60.

[0062] In the digestion system 300, excess sludge is supplied to the digestion tank 60 through the supply port 61c, thereby supplying the excess sludge to the liquid phase portion of the digested sludge 1a in the digestion tank 60.

[0063] That is, the liquid phase portion of the digested sludge 1a below the digestion tank 60 has a higher pressure than the gas phase portion of the digested sludge 1a above the digestion tank 60. Therefore, the pressure in the pipe 62 communicating with the supply port 61c provided at a height corresponding to the liquid phase portion of the digested sludge 1a is higher than the pressure in the pipe 62 communicating with the supply port 61a (the supply port 61a in the digestion system 100 described in FIG. 2 and the like) provided at a height corresponding to the gas phase portion of the digested sludge 1a. Therefore, the boiling temperature of the excess sludge near the heating unit 62a1 of the digestion system 300 is higher than the boiling temperature of the excess sludge near the heating unit 62a1 of the digestion system 100.

[0064] Therefore, in the digestion system 300 of this embodiment, by supplying excess sludge to the liquid phase portion of the digested sludge 1a in the digestion tank 60, it is possible to supply the excess sludge to the digestion tank 60 without boiling it, even if the excess sludge is heated to a temperature exceeding 100°C near the heating section 62a1, for example, thereby making it possible to prevent damage and blockage of the piping 62 due to the boiling of the excess sludge.

[0065] Similarly to the digestion system 100, the digestion system 300 may also control the amount of steam supplied to the excess sludge and the amount of steam supplied to the digested sludge 1a by using the pipes 71 and 72. Similarly to the digestion system 200, the digestion system 300 may also supply the digested sludge 1a to the heating section 62a1.

[0066] Furthermore, the digestion system 300 may have, for example, a pipe 62 communicating with the supply port 61a (the pipe 62 described in FIG. 2 and the like) in addition to the pipe 62 communicating with the supply port 61c. The digestion system 300 may also supply excess sludge from the supply port 61a as necessary, in addition to the supply of excess sludge from the supply port 61c.

[0067] [Fire extinguishing system 400 according to the fourth embodiment] Next, a digestion system 400 in the fourth embodiment will be described. Figures 7 to 9 are diagrams for explaining the heating of excess sludge in the fourth embodiment. Below, only the differences from the digestion system 100 in the first embodiment, the digestion system 200 in the second embodiment, and the digestion system 300 in the third embodiment will be described.

[0068] Specifically, Fig. 7 is a diagram for explaining a state in which excess sludge is intermittently and continuously transferred. The digestion system 400 in this embodiment has a buffer tank 91 (storage tank 91). The buffer tank 91 communicates with a pipe 92 that communicates with the concentrating device 50, and temporarily stores the excess sludge that is intermittently transferred from the concentrating device 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 8(A) and 8(B). In Figures 8(A) and 8(B), the hatched areas show the amount of excess sludge in a schematic manner, and each shows a schematic state when the same amount of excess sludge is transferred.

[0070] The pipes 62 and 92 shown in Fig. 7 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. 8(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] 8(B) 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 excess sludge volume V1 to a predetermined temperature in one go in a period T1, more thermal energy is required than to steam-heat the excess sludge volume V2 to a predetermined temperature in the same period T1. 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 400 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 rate 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. 8(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] 9 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 400 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. 9 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 (pumps) 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 9 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 to be transferred 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. 9, 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 fluid and the outlet temperature, which affect the digestion capacity.

[0100] According to the present invention described above, even if the supply amount of excess sludge fluctuates due to various factors such as the season, temporary population increase (e.g., holding of an event), weather, etc., the temperature of the digestive liquid can be maintained within a desired temperature range, thereby suppressing a decrease in digestion rate due to fluctuations in the supply amount of sludge. Furthermore, according to the present invention described above, damage to and blockage of piping can be suppressed, and as a result, excess sludge can be smoothly supplied to the digestion tank, thereby suppressing a decrease in digestion rate. [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 61b: Supply port 61c: Supply port 62: Piping 62a: First part 62a1: Heating part 62b: 2nd part 62c: 3rd part 62d: 4th part 62e: 5th part 62f: Partition 70: Steam heater 71: Piping 72: Piping 80: Control device 81: Flow meter 90: Control device 91: Buffer tank 92: Piping 93: Pump 94: 1st thermometer 95: 2nd thermometer 100: Mixing clarifier 200: Mixing clarifier 300: 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 first steam pipe for supplying steam to the excess sludge in the sludge pipe; A second steam pipe for supplying steam to the digester, the sludge pipe has a heating unit that heats the excess sludge in the sludge pipe with the steam supplied from the first steam pipe, The digestion system further has a control device that controls the amount of steam supplied from the first steam pipe to the excess sludge in the sludge pipe and the amount of steam supplied from the second steam pipe to the digestion tank in accordance with the amount of the excess sludge supplied.

2. The digestion system according to claim 1 , wherein the heating section is located in a portion of the sludge pipe that extends vertically along the digestion tank.

3. 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 is a heating unit that heats the excess sludge in the sludge pipe by the steam; A digestion system having an introduction section that introduces digested sludge in the digestion tank to the heating section.

4. A digestion system as described in claim 3, wherein the introduction section circulates the digested sludge between the digester tank and the sludge piping.

5. The digestion system according to claim 3 , further comprising a control device that controls the amount of digested sludge supplied to the heating section in response to the amount of excess sludge supplied.

6. 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 is a heating unit that heats the excess sludge in the sludge pipe by the steam; A digestion system having an input section that inputs the excess sludge into the liquid phase of the digested sludge in the digestion tank.

7. A digestion system as described in Claim 6, wherein the feeding section feeds the excess sludge into the liquid phase, thereby increasing the pressure in the sludge piping higher than when the excess sludge is fed into the gas phase of the digested sludge in the digester tank.

8. The digestion system according to claim 6 , further comprising a control device that controls the amount of the excess sludge supplied to the liquid phase in accordance with the temperature of the excess sludge heated in the heating section.

Images