JP2022155990A - Digestion system - Google Patents

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

The present invention relates to the digestive system.

In a digestion system for anaerobic digestion of organic matter contained in sludge, a technique has been proposed for supplying heated sludge to a digestion tank in order to achieve efficient digestion (see Patent Document 1).

Japanese Patent Publication No. 2011-516246

In the digestion system as described above, it is desired to suppress a decrease in digestibility due to fluctuations in the amount of sludge supplied.

In order to suppress the above-described decrease in digestibility, the digestion system in the present invention includes a digestion tank that digests organic matter in excess sludge with anaerobic bacteria, a sludge pipe that supplies the excess sludge to the digestion tank, and the sludge pipe. a first steam pipe for supplying steam to the excess sludge inside and a second steam pipe for supplying steam to the digestion tank, wherein the sludge pipe supplies the steam supplied from the first steam pipe and a heating unit for heating the excess sludge in the sludge pipe.

According to the digestion system of the present invention, it is possible to suppress a decrease in digestibility due to fluctuations in the amount of sludge supplied.

FIG. 1 is a configuration diagram of a digestion system 100 according to the first embodiment. FIG. 2 is a diagram illustrating heating of excess sludge in the first embodiment. FIG. 3 is a diagram illustrating control of the amount of steam supplied by the control device 80. As shown in FIG. FIG. 4 is a diagram illustrating heating of excess sludge in the second embodiment. FIG. 5 is a diagram illustrating heating of excess sludge in the second embodiment. FIG. 6 is a diagram illustrating heating of excess sludge in the third embodiment. FIG. 7 is a diagram illustrating heating of excess sludge in the fourth embodiment. FIG. 8 is a diagram illustrating heating of excess sludge in the fourth embodiment. FIG. 9 is a diagram illustrating heating of excess sludge in the fourth embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, such an embodiment does not limit the technical scope of the present invention.

[Digestion system 100 in the first embodiment]
First, the digestion system 100 in the first embodiment will be described. FIG. 1 is a configuration diagram of a digestion system 100 according to the first embodiment.

The digestion system 100, as shown in FIG. have

The primary sedimentation tank 10 sediments and separates organic matter and suspended matter contained in sewage (hereinafter also referred to as untreated water). The primary sedimentation tank 10 discharges the separated organic matter and suspended matter as primary sedimentation sludge to the thickening tank 40 , and discharges the water to be treated from which the organic matter and suspended matter are separated to the sewage treatment apparatus 20 .

The sewage treatment apparatus 20 treats the water to be treated by a biological treatment such as a standard activated sludge method or a circulating nitrification/denitrification method. Specifically, the sewage treatment apparatus 20 includes, for example, a denitrification tank (not shown) that generates nitrogen from nitrate ions by anaerobic denitrification bacteria (denitrification), and a denitrification tank that is provided after the denitrification tank to and a nitrification tank (not shown) for nitrifying ammonia nitrogen with nitrifying bacteria. The sewage treatment apparatus 20 then discharges the water to be treated to the final sedimentation tank 30 .

The final sedimentation tank 30 precipitates and separates sludge contained in the water to be treated discharged from the sewage treatment apparatus 20, and discharges the separated sludge as activated sludge. In the final sedimentation tank 30, part of the activated sludge is supplied to the thickener 50 as excess sludge, and the activated sludge other than the excess sludge is returned to the sewage treatment system 20 as return sludge. In addition, the final sedimentation tank 30 discharges the water to be treated (supernatant liquid) from which the sludge has been separated to a subsequent sterilization apparatus (not shown). Thereafter, a sterilization device (not shown) sterilizes the water to be treated discharged from the final sedimentation tank 30, and discharges the sterilized treated water, for example.

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

The thickening device 50 , for example, thickens the excess sludge discharged from the final sedimentation tank 30 and supplies it to the digestion tank 60 . Hereinafter, the excess sludge thickened in the thickener 50 is also referred to as thickened excess sludge.

Digestion tank 60 is, for example, sludge (hereinafter simply referred to as sludge) containing initial sedimentation sludge supplied from thickening tank 40 and excess sludge supplied from thickening device 50 by anaerobic bacteria in digestion tank 60. Digested sludge is produced by anaerobic digestion (decomposition) of organic matter through life reactions. The anaerobic bacteria in the digestion tank 60 produce digestion gas such as methane gas during digestion. In addition, the temperature of the digested sludge (digestive liquid) in the digestion tank 60 is, for example, between 35° C. and 40° C. (hereinafter referred to as the temperature is also called the optimum temperature).

The steam heater 70 supplies steam (water vapor) to the surplus sludge before it is supplied to the digestion tank 60 to heat it. 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.

That is, one of the causes of the decrease in digestibility in the digestion tank 60 is the large amount of bacteria living in the surplus sludge. If surplus 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.

Therefore, in the digestion system 100 of the present embodiment, the surplus sludge is intensively heated at the stage before the surplus sludge is supplied to the digestion tank 60, so that the living bacteria group contained in the surplus sludge is sufficiently removed. annihilate. 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.

As a result, the digestion system 100 according to the present embodiment can suppress a decrease in digestibility in the digestion tank 60 .

The primary sedimentation sludge does not contain enough viable bacteria to cause a decrease in digestibility, and may not be the main cause of a decrease in digestibility. Therefore, in the digestion system 100, in order to improve digestion efficiency and save energy, the initial settling sludge may not be heated before being supplied to the digestion tank 60. On the other hand, when the initial settling sludge is also used as a heat medium, the initial settling sludge may also be heated before it is supplied to the digestion tank 60 . The heating of excess sludge will be described below.

[Heating surplus sludge]
FIG. 2 is a diagram illustrating heating of excess sludge in the first embodiment. In addition, the description of the initial sedimentation sludge is omitted below.

As shown in FIG. 2, the digestion tank 60 has, for example, a tank body 61 for depositing digested sludge 1a, and a pipe 62 (hereinafter also referred to as sludge pipe 62).

The pipe 62 has a first portion 62a extending in the vertical direction (the vertical direction of the tank body 61), a second portion 62b extending in a direction different from the vertical direction (for example, the horizontal direction of the tank body 61), and and a third portion 62c. One end of the first portion 62a communicates with a supply port 61a provided in the upper portion of the tank body 61 via a third portion 62c, and the other end communicates with the second portion 62b. The second portion 62b communicates with the first portion 62a at one end and with the concentrator 5 at the other end.

Note that the extending direction of the first portion 62a does not have to be completely aligned with the vertical direction. Alternatively, the pipe 62 may not have the third portion 62c. In this case, the first portion 62a may communicate with the supply port 61a by, for example, a joint (not shown).

Excess sludge (not shown) supplied from the concentrator 50 is transferred (pumped) by, for example, a pump (not shown) as indicated by the solid line arrow in the pipe 62 in FIG. Specifically, the excess sludge supplied from the thickener 50 passes through the second portion 62b, the first portion 62a and the third portion 62c in order, and is supplied into the digestion tank 60 from the supply port 61a in the tank body 61. .

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) for supplying steam. .

The pipe 71 communicates with the pipe 62 at a predetermined portion (hereinafter also referred to as a heating portion 62a1) of the first portion 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.

A pipe 72 supplies steam to the digester 60 . Specifically, the pipe 72 directly supplies steam to the digested sludge 1a deposited in the digestion tank 60 to heat it.

That is, the amount of surplus sludge supplied to the digestion tank 60 (the amount of surplus sludge passing through the pipe 62) fluctuates due to a variety of factors such as a temporary population increase such as the holding of an event and the weather. Then, for example, when the amount of steam supplied to the surplus sludge is constant, a decrease in the supply amount of the surplus sludge may raise the temperature of the surplus sludge in the heating section 62a1 and instantaneously boil it. Due to this boiling, the sludge in the pipe 62 is scorched, and the carbide or the like strongly adheres to the inner wall of the pipe 62 (so-called sticking), which may clog the pipe 62 . In addition, steam is unevenly distributed in the pipe due to a decrease in the amount of surplus sludge supplied, and as a result, even if the sludge does not boil, the pipe 62 is damaged due to the occurrence of the hammer phenomenon due to this uneven distribution of steam. sometimes.

On the other hand, for example, a method of preventing boiling of the excess sludge by reducing the amount of steam supplied to the excess sludge is conceivable.

However, in this case, the heat energy for heating the digested sludge 1a deposited in the digestion tank 60 is insufficient, and it may become impossible to maintain the temperature of the digested sludge 1a at an appropriate temperature.

Therefore, in the digestion system 100 of the present embodiment, for example, in addition to the pipe 71 that supplies steam to the excess sludge located in the pipe 62, steam is directly applied to the digested sludge 1a deposited in the digestion tank 60. A supply pipe 72 is provided. In the digestion system 100, by using the pipes 71 and 72, respectively, for example, supply of steam to excess sludge and supply of steam to the digested sludge 1a are performed in parallel.

Specifically, in the digestion system 100, by using the piping 71, the excess sludge is steamed to the extent that it does not boil the excess sludge and is necessary to sufficiently kill the living bacteria group contained in the excess sludge. supply to In the digestion system 100, along with this supply, by using the piping 72, it is necessary to prevent boiling of excess sludge in the steam that needs to be supplied to maintain the digested sludge 1a in the digestion tank 60 at an appropriate temperature. The steam that is not supplied to the excess sludge is directly supplied to the digestion tank 60 (digested sludge 1a).

More specifically, for example, when the flow rate of excess sludge in the first portion 62a (the amount of excess sludge supplied to the digestion tank 60) decreases, the operator should, for example, turn on the valves attached to the pipes 71 and 72 (not shown) is opened and closed so that the amount of steam supplied using the pipes 71 and 72 is constant (the amount necessary to maintain the digested sludge 1a at an appropriate temperature). is used to reduce the amount of steam supplied to the excess sludge, and the piping 72 is used to increase the amount of steam supplied to the digested sludge 1a.

As a result, the digestion system 100 of the present embodiment can prevent excess sludge in the pipe 62 from being excessively heated and can maintain the digested sludge 1a in the digestion tank 60 at an appropriate temperature.

On the other hand, for example, when the flow rate of excess sludge in the first portion 62a increases, the operator opens and closes the valves attached to the pipes 71 and 72, for example, by using the pipes 71 and 72. The pipe 71 is used to increase the amount of steam supplied to the surplus sludge, and the pipe 72 is used to decrease the amount of steam supplied to the digested sludge 1a so that the amount of steam to be supplied is constant.

As a result, the digestion system 100 in the present embodiment can sufficiently heat the surplus sludge even when the surplus sludge supply amount is increased, and the living bacteria contained in the surplus sludge can be removed. enough to kill it.

The digestion system 100 may have a control device for controlling 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 memory. The control of the amount of steam supplied by the control device will be described below.

[Control of steam supply]
FIG. 3 is a diagram illustrating control of the amount of steam supplied by the control device 80. As shown in FIG.

In the example shown in FIG. 3, the first portion 62a of the pipe 62 is provided with a flowmeter 81 for measuring the flow rate of excess sludge.

Then, the control device 80 acquires the value detected by the flowmeter 81 (the flow rate of the excess sludge in the first portion 62a) at regular timing such as every minute, and according to the acquired value, the pipe 71 is used to adjust the amount of steam supplied to the excess sludge and the pipe 72 is used to adjust the amount of steam supplied to the digested sludge 1a.

Specifically, for example, when the value obtained from the flow meter 81 is less than a threshold value (hereinafter also referred to as a first threshold value), the control device 80 controls valves (not shown) attached to the pipes 71 and 72. By opening and closing the pipe 71 and the pipe 72, the amount of steam supplied to the excess sludge is reduced using the pipe 71 so that the amount of steam supplied using the pipe 71 and the pipe 72 is constant, and the pipe 72 is used. to increase the amount of steam supplied to the digested sludge 1a. In this case, the controller 80 determines the amount of steam supplied to the excess sludge so that the smaller the value obtained from the flow meter 81, the smaller the amount of steam supplied to the excess sludge. good.

On the other hand, for example, when the value obtained from the flow meter 81 is equal to or greater than a threshold (hereinafter also referred to as a second threshold), the control device 80 opens and closes valves (not shown) attached to the pipes 71 and 72. etc., the amount of steam supplied to the excess sludge is increased using the pipe 71 so that the amount of steam supplied using the pipe 71 and the pipe 72 is constant, and the pipe 72 is used to digest Reduce the amount of steam supplied to the sludge 1a. In this case, the controller 80 determines the amount of steam supplied to the excess sludge so that the larger the value obtained from the flow meter 81, the larger the amount of steam supplied to the excess sludge. good. Note that the second threshold is a threshold corresponding to a value greater than the first threshold. Also, the first threshold and the second threshold may be, for example, the same value.

[Digestion system 200 in the second embodiment]
Next, the digestion system 200 in the second embodiment will be explained. 4 and 5 are diagrams illustrating heating of excess sludge in the second embodiment. Only the differences from the digestion system 100 in the first embodiment will be described below.

As shown in FIG. 4, the pipe 62 in the fire extinguishing system 200 includes, for example, a first portion 62a, a second portion 62b, a third portion 62c, a fourth portion 62d extending in the vertical direction, and a and a fifth portion 62e extending along a different direction (eg, horizontal direction). One end of the fourth portion 62d communicates with a supply port 61b (hereinafter also referred to as an introduction portion 61b) provided in the lower portion of the tank body 61 via a fifth portion 62e, and the other end communicates with the first portion 62a. do. The first portion 62a and the fourth portion 62d form a straight pipe, for example, by connecting the lower end of the first portion 62a and the upper end of the fourth portion 62d.

Note that the extending direction of the fourth portion 62d does not have to be completely aligned with the vertical direction. Also, the pipe 62 may not have the fifth portion 62e. In this case, the fourth portion 62d may communicate with the supply port 61b through a joint (not shown).

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

Then, for example, when the flow rate of excess sludge in the first portion 62a is less than the threshold (hereinafter also referred to as the third threshold), the operator opens the partition 62f as shown in FIG. A portion of the digested sludge 1a deposited in the digestion tank 60 is supplied to the heating section 62a1.

That is, in the digestion system 200 of the present embodiment, for example, when the supply amount of excess sludge is reduced, the excess sludge is excessively heated by supplying digested sludge 1a (digested sludge 1a at an appropriate temperature) to the heating unit 62a1. to prevent

As a result, the fire extinguishing system 200 according to the present embodiment can prevent, for example, the occurrence of a hammer phenomenon in the pipe 62 and the adhesion of carbides and the like to the inner wall of the pipe 62, thereby preventing the pipe 62 from being damaged or clogged. It becomes possible to prevent the occurrence of

Thereafter, for example, when the flow rate of excess sludge in the first portion 62a further decreases, the operator increases the supply amount of digested sludge 1a to the heating section 62a1. In this case, the control device 80 determines the amount of digested sludge 1a supplied to the heating unit 62a1 so that, for example, the smaller the flow rate of the excess sludge in the first portion 62a, the greater the amount of digested sludge 1a supplied to the heating unit 62a1. It may be something to do.

On the other hand, for example, when the flow rate of excess sludge in the first portion 62a increases within the range of less than the third threshold, the operator reduces the supply amount of digested sludge 1a to the heating section 62a1. In this case, the control device 80 determines the amount of digested sludge 1a supplied to the heating unit 62a1 so that, for example, the amount of digested sludge 1a supplied to the heating unit 62a1 decreases as the flow rate of excess sludge in the first portion 62a increases. It may be something to do.

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

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

On the other hand, the operator may alternately heat the surplus sludge and the digested sludge 1a in the heating section 62a1, for example. That is, for example, when the temperature of the surplus sludge has risen to a predetermined temperature (for example, about 80° C.) by heating with steam, the operator puts in the digested sludge 1a, thereby transferring the surplus sludge to the tip of the pipe 62. The digested sludge 1a may be placed in the heating unit 62a1 and heated. In this case, after the digested sludge 1a is introduced, new excess sludge is supplied from the thickening device 50, whereby the digested sludge 1b located in the heating unit 62a1 is pushed out to the tip of the pipe 62 and heated. Heating of new excess sludge in the portion 62a1 is started.

Thereby, in the digestion system 200, even when the digested sludge 1a is supplied to the pipe 62, it is possible to sufficiently kill the living bacteria group contained in the surplus sludge.

As with the digestion system 100, the digestion system 200 also controls 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. There may be.

Further, the control device 80 may use the value detected by the flowmeter 81, for example, to control the opening/closing of the partition portion 62f and adjust the amount of digested sludge 1a supplied to the heating portion 62a1.

[Digestion system 300 in the third embodiment]
Next, the digestion system 300 in the third embodiment will be explained. FIG. 6 is a diagram illustrating heating of excess sludge in the third embodiment. Only differences from the digestion system 100 in the first embodiment and the digestion system 200 in the second embodiment will be described below.

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

In the digestion system 300, excess sludge is supplied to the liquid phase portion of the digested sludge 1a in the digestion tank 60 by supplying excess sludge to the digestion tank 60 from the supply port 61c.

That is, the liquid phase portion of the digested sludge 1 a below the digestion tank 60 has a higher pressure than the gas phase portion of the digested sludge 1 a 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 increased to It becomes higher than the pressure in the pipe 62 communicating with (the supply port 61a in the digestion system 100 described in FIG. 2 and the like). Therefore, the boiling temperature of excess sludge near heating section 62a1 of digestion system 300 is higher than the boiling temperature of excess sludge near heating section 62a1 of digestion system 100 .

Therefore, in the digestion system 300 of the present embodiment, by supplying excess sludge to the liquid phase portion of the digested sludge 1a in the digestion tank 60, for example, the temperature of the excess sludge exceeds 100°C near the heating unit 62a1. Even if the sludge is heated up to , it becomes possible to supply the excess sludge to the digestion tank 60 without boiling it, and it is possible to prevent the piping 62 from being damaged or clogged due to the boiling of the excess sludge.

As with the digestion system 100, the digestion system 300 also controls 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. There may be. In addition, the digestion system 300, like the digestion system 200, may also supply the digested sludge 1a to the heating unit 62a1.

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. Then, the digestion system 300 may, for example, supply excess sludge from the supply port 61a as needed in addition to supplying the excess sludge from the supply port 61c.

[Digestion system 400 in the fourth embodiment]
Next, the digestion system 400 in the fourth embodiment will be explained. 7 to 9 are diagrams explaining heating of excess sludge in the fourth embodiment. Only 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 below.

Specifically, FIG. 7 is a diagram schematically illustrating a state in which excess sludge is intermittently and continuously transferred. Digestion system 400 in the present embodiment has buffer tank 91 (storage tank 91). The buffer tank 91 communicates with a pipe 92 that communicates with the concentrator 50 and temporarily stores surplus sludge intermittently transferred from the concentrator 50 to the pipe 92 .

In this case, the excess sludge is intermittently transferred in the pipe 92 and then continuously transferred in the pipe 62 . Intermittent transfer and continuous transfer will be described below with reference to FIGS. 8(A) and 8(B). In FIGS. 8(A) and 8(B), the hatched areas schematically show the amount of excess sludge, and each schematically shows the state when the same amount of excess sludge is transferred. there is

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 . The numerical value of the pipe diameter of 150 (mm) or more is a numerical value determined by the design guideline of the sludge treatment facility. In the following description, it is assumed that the pipe diameter of the pipe 92 is 150 (mm).

Next, a description will be given of a case in which excess sludge produced by the thickener 50 is pressure-fed through a pipe 92 having a pipe diameter of 150 (mm). In general sludge treatment facilities, the amount of excess sludge generated is small compared to this pipe diameter. Moreover, when sludge is not transferred at a pipe diameter and flow rate of a predetermined value or more, the sludge settles at the bottom of the pipe, and as a result, the possibility of clogging the pipe with sludge increases. Therefore, excess sludge is intermittently transferred from the thickener 50 .

FIG. 8(A) is a graph illustrating intermittent transfer of excess sludge. The vertical axis indicates the amount of surplus sludge transferred, and the horizontal axis indicates time. The generated excess sludge is transferred through a pipe 92 having a pipe diameter of 150 (mm) at a predetermined flow rate and flow rate. Therefore, the surplus sludge of the sludge amount V1 is transferred at a time (intermittent transfer) at regular intervals during the period T1. It should be noted that the intermittent transfer means not only constant intervals, but also transfer at irregular intervals.

Moreover, FIG. 8(B) is a graph diagram explaining the continuous transfer of excess sludge. The vertical axis indicates the amount of surplus sludge transferred, and the horizontal axis indicates time. For example, the excess sludge of the sludge amount V2 is continuously transferred during the period T2.

Here, in the same time (for example, period T1), when steam-heating the excess sludge of the sludge amount V2 which is smaller than the sludge amount V1 to a predetermined temperature, the thermal energy required when steam-heating the excess sludge of the sludge amount V2 The amount is smaller than the amount of thermal energy required when steam-heating the surplus sludge of the sludge amount V1.

That is, in order to steam-heat the excess sludge amount of the sludge amount V1 to the predetermined temperature at once during the period T1, a larger amount of steam is required than when the excess sludge amount of the sludge amount V2 is steam-heated to the predetermined temperature during the same period T1. heat energy is required. In order to generate a lot of heat energy, that is, a large amount of steam, it is necessary to enlarge the size of the boiler that generates the steam. However, increasing the size of the boiler leads to an increase in installation space, installation costs, maintenance costs, fuel consumption, and the like, so it may be difficult to increase the size of the boiler.

Therefore, in the digestion system 400 of the present embodiment, the excess sludge is continuously transferred during a predetermined period in order to suppress clogging of the pipes and reduce the amount of transferred excess sludge. In order to enable such continuous transfer, a buffer tank 91 for temporarily storing surplus sludge is provided, and the pipe diameter of the pipe 62 connecting the buffer tank 91 and the digestion tank 60 is made smaller than the aforementioned 150 (mm). The pipe diameter of the pipe 62 is set to, for example, 60 (mm) in order to prevent clogging by sludge and to maintain a predetermined flow velocity and flow rate or more.

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

During this continuous transfer (period T2), unlike the intermittent transfer described with reference to FIG. 8(A), there is no period in which excess sludge is not transferred, and the transfer amount of excess sludge is reduced.

As described above, by continuously transferring a small amount of surplus sludge and heating it with steam during this transfer, it is possible to suppress the enlargement of the boiler.

Next, a control device for controlling the amount of steam, the temperature of steam and the transfer amount of excess sludge will be described.

FIG. 9 is a diagram for explaining a control device that controls the amount of steam, the temperature of steam, and the transfer amount of excess sludge based on various information. The digestion system 400 of this embodiment further includes a controller 90 that controls the pump and thermometer.

In the digestion tank 60 shown in FIG. 9 and the like, if the temperature of the digested liquid is not appropriate, the digestion capacity is lowered. Therefore, the controller 90 controls the steam heater 70 and the pump 93 so that the digestion capacity is maintained. Note that the control device 90 may be the same control device as the control device 80 described with reference to FIG. 3, or may be a control device different from the control device 80 .

The pump 93 continuously transfers (pumps) the surplus sludge stored in the buffer tank 91 to the digestion tank 60 through the pipe 62 . The arrangement position of the pump 93 in FIG. 9 is an example, and the pump 93 may be arranged before or after the buffer tank 91 .

The controller 90 controls at least one of the steam heater 70 and the pump 93 so that the digestion capacity of the digestion tank 60 is maintained at a predetermined level. The controller 90 controls at least one of the steam heater 70 and the pump 93 based on at least one of the temperature in the digestion tank 60 and the temperature in the pipe 62, for example.

Specifically, the temperature in the digestion tank 60 is preferably the temperature of the digested juice. The temperature of the digestive fluid is a factor that directly affects the digestive capacity of the digester 60 . Therefore, the control device 90 performs control based on, for example, the temperature of the digestive juice.

The temperature inside the pipe 62 is preferably the temperature at the point where the pipe 62 and the digestion tank 60 are connected, that is, the temperature at the outlet of the pipe 62 . The outlet temperature of the pipe 62 can be regarded as the temperature of the surplus sludge just before it is introduced into the digestion tank 60 . The temperature of excess sludge is one of the factors that affect the temperature of the digestive liquid in the digestion tank 60 . Therefore, the control device 90 performs control based on, for example, the outlet temperature.

The first thermometer 94 is a thermometer that measures the temperature inside the digestion tank 60 (for example, the temperature of the digested juice). 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 pipe 62 (for example, the outlet temperature). The second thermometer 95 transmits the measured temperature to the control device 90 .

When the control device 90 predicts that the digestive juice will decrease in digestive capacity due to the decrease in the temperature of the digestive juice, it controls at least one of the steam heater 70 and the pump 93 so as to increase the temperature of the digestive juice. Before describing the specific control of the control device 90, four cases are assumed below.

A first case where the temperature of the digestive juice measured by the first thermometer 94 is equal to or lower than the first temperature range.

A second case where the temperature of the digestive fluid measured by the first thermometer 94 exceeds the first temperature range.

A third case where the outlet temperature measured by the second thermometer 95 is equal to or lower than the second temperature range.

A fourth case where the outlet temperature measured by the second thermometer 95 exceeds the second temperature range.

The first temperature range is, for example, 37°C to 40°C, and the second temperature range is, for example, 70°C to 95°C.

Next, control over the steam heater 70 will be described. The control device 90 determines one of the above four cases. When the control device 90 determines that it is at least one of the first and third cases, the control device 90 generates steam having a temperature higher than the current temperature and/or a large amount of steam and supplies it to the pipe 62 (first portion 62a). A control signal is sent to the steam heater 70 directing it to supply. In addition, when the controller 90 determines that it is at least one of the second case and the fourth case, the control device 90 generates a lower temperature and/or a smaller amount of steam than the current temperature to ) to the steam heater 70 .

Then, the steam heater 70 responds to the control signal to control the temperature and/or amount of steam and supply it to the pipe 62 (first portion 62a).

Next, control over the pump 93 will be described. The control device 90 determines whether it is one of the above four cases. When the control device 90 determines that it is at least one of the first case and the third case, it sends a control signal to the pump 93 to instruct the excess sludge transfer amount to be less than the current transfer amount. do. Further, when the control device 90 determines that it is at least one of the second and fourth cases, the control device 90 sends a control signal to the pump 93 to instruct the transfer amount of surplus sludge to be larger than the current transfer amount. Send to

Then, the pump 93 responds to the control signal to control the transfer amount of the surplus sludge and pump it.

The control device 90 may control the steam heater 70 and the pump 93 at the same time, or may control only the steam heater 70 or only the pump 93 .

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 juice and the outlet temperature, as described in FIG. Digestion can be maintained.

According to the present invention described above, even if the amount of surplus sludge supplied fluctuates due to various factors such as season, temporary population increase (for example, holding an event), weather, etc., the temperature of the digestive juice can be maintained at a desired temperature. Since it can be maintained within the range, it is possible to suppress the decrease in digestibility due to fluctuations in the amount of sludge supplied. In addition, according to the present invention described above, since it is possible to suppress the damage and clogging of the piping, as a result, the surplus sludge is smoothly supplied to the digestion tank, so that the reduction of the digestibility can be suppressed.

1a: Digested sludge 10: Primary sedimentation tank 20: Sewage treatment equipment 30: Final sedimentation tank 40: Concentration tank 50: Concentration equipment 60: Digestion tank 61: Tank body 61a: Supply port 61b: Supply port 61c: Supply port 62: Piping 62a: first portion 62a1: heating portion 62b: second portion 62c: third portion 62d: fourth portion 62e: fifth portion 62f: partition portion 70: steam heater 71: piping 72: piping 80: control device 81: Flowmeter 90: Control device 91: Buffer tank 92: Piping 93: Pump 94: First thermometer 95: Second thermometer 100: Mixed turbidity removal device 200: Mixed turbidity removal device 300: Mixed turbidity removal device

Claims (7)

a digestion tank that digests organic matter in excess sludge with anaerobic bacteria;
A sludge pipe that supplies the excess sludge to the digestion tank;
a first steam pipe that supplies steam to the excess sludge in the sludge pipe;
a second steam pipe that supplies steam to the digestion tank;
The digestion system, wherein 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. 2. The digestion system according to claim 1, wherein said heating section is located in a portion of said sludge pipe extending along the vertical direction of said digestion tank. 2. The method according to claim 1, further comprising a control device for controlling at least one of the amount of steam supplied to the excess sludge in the sludge pipe and the amount of steam supplied to the digestion tank according to the amount of supply of the excess sludge. Digestive system as described. a digestion tank that digests organic matter in excess sludge with anaerobic bacteria;
A sludge pipe that supplies the excess sludge to the digestion tank;
a steam pipe that supplies steam to the excess sludge in the sludge pipe;
The sludge pipe,
a heating unit that heats the excess sludge in the sludge pipe with the steam;
A digestion system having an introduction section for introducing digested sludge in the digestion tank to the heating section. 5. The digestion system according to claim 4, further comprising a control device for controlling the supply amount of said digested sludge to be introduced into said heating unit according to the supply amount of said excess sludge. a digestion tank that digests organic matter in excess sludge with anaerobic bacteria;
A sludge pipe that supplies the excess sludge to the digestion tank;
and a steam pipe that supplies steam to the excess sludge in the sludge pipe, wherein the sludge pipe is
a heating unit that heats the excess sludge in the sludge pipe with the steam;
and an input unit for inputting the surplus sludge into the liquid phase of the digested sludge in the digestion tank. 7. The digestion system according to claim 6, further comprising a controller for controlling the amount of excess sludge supplied to said liquid phase according to the temperature of said excess sludge heated in said heating unit.

Images