Control method for drum type thickener

Abstract

To provide a drum type concentrator which performs control of immediately elevating concentration when a concentrated sludge concentration is low, and gradually lowering concentration when a concentrated sludge concentration is high.SOLUTION: In a concentrator which separates a filtrate from an outer cylindrical screen 2 while transporting a sludge of a concentration chamber 12 by using a screw blade 3 and discharges a concentrated sludge from a discharge port 11 of the concentration chamber 12: a supply amount width a1 is set higher than a supply amount width a2 in advance; when a measured value X of a concentrated sludge concentration is lower than a standard concentrated sludge concentration X0, a supply amount A of a coagulant is stepwisely increased at the supply amount width a1, and when the measured value X of the concentrated sludge concentration is higher than the standard concentrated sludge concentration X0, the supply amount A of the coagulant is stepwisely decreased at the supply amount width a2; in a case where a concentrated sludge concentration is low, the concentration is elevated in early stage, and in a case where the concentrated sludge concentration is high, the concentration is gradually decreased to prevent the concentration from excessively lowering.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an improved control method for a drum thickener that separates filtrate from an external cylindrical screen while transporting sludge generated from wastewater treatment facilities such as sewage, human waste, rural wastewater, and factories using screw blades. [Background technology]

[0002] Conventionally, a drum-type thickener has been known in which a screw shaft is rotatably inserted into a cylindrical screen, sludge supplied inside is transported by the screw shaft, solid-liquid separation is performed by the screen, and the thickened sludge is discharged from a discharge outlet.

[0003] Also, a method for controlling a drum thickener is known in which the addition rate of a flocculant is controlled in accordance with changes in the properties of the supplied sludge and the sludge concentration of the thickened sludge.

[0004] Patent Document 1 discloses an operation control method for a differential speed rotary concentrator that detects the concentration of concentrated sludge and gradually switches the differential rotation speed of the screw shaft and the outer cylindrical screen and the flocculant dosing rate to maintain a constant concentration of the concentrated sludge. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 4427798 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to operate the thickener stably, the concentration of the thickened sludge discharged from the thickener is controlled to be constant. If the concentration of the thickened sludge deviates from the standard concentration, the rate of coagulant addition is increased or decreased to keep the concentration within the standard. However, low concentrations of thickened sludge have a more adverse effect on downstream processes such as transportation and incineration than high concentrations of thickened sludge, so low-concentration thickened sludge in particular needs to be quickly converted to a high concentration.

[0007] Generally, the relationship between the concentrated sludge concentration and the flocculant addition rate is a correlation like a nonlinear logarithmic function that slopes upward to the right. Where the flocculant addition rate is low, the concentrated sludge concentration fluctuates greatly even with a small addition rate, and where the flocculant addition rate is high, the concentrated sludge concentration does not fluctuate much even with a large addition rate.

[0008] Therefore, when the thickened sludge concentration is low and you want to increase it, you need to increase the concentration quickly, so you need to set an addition rate with a large increase.On the other hand, when the thickened sludge concentration is high and you want to decrease the concentration, you need to decrease the concentration carefully, so you need to set an addition rate with a small decrease.

[0009] The technology in Patent Document 1 gradually decreases the flocculant dosing rate when the concentrated sludge concentration increases, and gradually increases the flocculant dosing rate when the concentrated sludge concentration decreases, but there is no mention or suggestion of setting different dosing rates for each step of the dosing rate d that is gradually increased or decreased. Therefore, it is recognized that the increase or decrease range of the dosing rate d is set to the same, which creates risks in the control and response of each concentration.

[0010] The present invention provides a control method for a drum thickener, which controls the amount of flocculant added depending on the concentration of thickened sludge, and which appropriately sets the increase and decrease amounts of the flocculant supply amount individually. [Means for solving the problem]

[0011] The present invention relates to a drum thickener in which a concentration compartment is formed by an external cylindrical screen and a screw shaft around which a screw blade is wound, and filtrate is separated from the external cylindrical screen while the sludge in the concentration compartment is transported by the screw blade, and the concentrated sludge is discharged from the outlet of the concentration compartment. The range between the maximum standard thickened sludge concentration and the minimum standard thickened sludge concentration was set.A standard thickened sludge concentration, a standard supply amount of flocculant, a maximum supply amount which is the maximum value of the standard supply amount, a minimum supply amount which is the minimum value of the standard supply amount, a supply amount range for gradually increasing the flocculant, and a supply amount range for gradually decreasing the flocculant are set, and the supply amount range is set to be larger than the supply amount range. When the measured value of the thickened sludge concentration is within the range of the standard thickened sludge concentration, the operation of the drum thickener is continued. When the measured value of the thickened sludge concentration is lower than the standard thickened sludge concentration, the supply amount of flocculant is increased stepwise by the supply amount range, and this operation is repeated until the measured value of the thickened sludge concentration rises within the range of the standard thickened sludge concentration. When the measured value of the thickened sludge concentration is higher than the standard thickened sludge concentration, the supply amount of flocculant is reduced stepwise by the supply amount range. It's width This operation is repeated until the measured value of the concentrated sludge concentration falls within the range of the standard concentrated sludge concentration, thereby controlling the measured value of the concentrated sludge concentration within the range of the standard concentrated sludge concentration.If the concentrated sludge concentration is low, the concentration is increased early, and if it is high, the concentration is gradually decreased, preventing the concentration from falling too low.

[0012] If the range of the stepwise decrease in the supply amount is set to 80% or less of the range of the stepwise increase in the supply amount, the rate of increase and decrease of the thickened sludge concentration will be well balanced, enabling stable control. [Effects of the Invention]

[0013] The present invention controls the amount of flocculant supplied to stably discharge thickened sludge at a constant concentration from the thickener. In particular, by setting the increase in the amount of flocculant supplied to be greater than the decrease in the amount of flocculant supplied, the concentration can be increased early when the thickened sludge concentration is low, and gradually decreased when the thickened sludge concentration is high, preventing the concentration from decreasing too much. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a longitudinal sectional side view of a drum-type concentrator according to the present invention. [Figure 2] FIG. 10 is a diagram showing the configuration of a drum-type concentrator equipped with a control device. [Figure 3]FIG. 10 is a conceptual diagram of a concentrated sludge concentration measuring device disposed in a sludge receiving tank. [Figure 4] 10 is a flowchart of a drum concentrator control method. DETAILED DESCRIPTION OF THE INVENTION

[0015] The operation control method and operation control device for a drum concentrator according to the present invention will be described in detail with reference to the drawings. Fig. 1 is a vertical cross-sectional side view of a drum concentrator. Drum concentrator 1 has an external cylindrical screen 2 having a filtering surface on its periphery, and a screw shaft 4 around which screw blades 3 are wound is disposed inside the external cylindrical screen 2, forming a concentration chamber 12 between the external cylindrical screen 2 and the screw shaft 4. An inlet flange 5 and an outlet flange 6 are fitted to the ends of the external cylindrical screen 2, and the inlet flange 5 is journaled on the screw shaft 4. An external cylindrical drive shaft 7 connected to the outlet flange 6 is journaled on a bearing 9 supported in a filtrate receiving tank 8. A screw drive shaft 10 connected to the screw shaft 4 is inserted into the external cylindrical drive shaft 7, and each is configured to be independently rotatable.

[0016] An outer cylinder driver 13 and a screw driver 14 are individually linked to the outer cylinder drive shaft 7 of the outer cylinder screen 2 and the screw drive shaft 10 of the screw shaft 4, and rotate the outer cylinder screen 2 and the screw shaft 4 in opposite directions at different speeds.

[0017] Sludge is supplied to the concentration chamber 12 through the supply channel 11 at the front end of the screw shaft 4 via the supply port 11a, and the filtrate is separated from the outer cylindrical screen 2 while the outer cylindrical screen 2 and the screw shaft 4 are rotated in opposite directions, and the concentrated sludge is discharged from the discharge port 6a of the outlet flange 6. By rotating the outer cylindrical screen 2 and the screw shaft 4 at different speeds, the rotation speed of the screw blades 3 is relatively increased, increasing the number of times the filtering surface of the outer cylindrical screen 2 slides in contact. This regenerates the filtering surface of the outer cylindrical screen 2, which is prone to clogging, and promotes the discharge of filtrate, making it possible to treat large volumes of low-concentration sludge.

[0018] Reference numeral 15 denotes a cleaning water pipe arranged along the outer cylindrical screen 2, which sprays high-pressure water onto the screen surface of the clogged outer cylindrical screen 2 to remove clogging from the filtering surface.

[0019] FIG. 2 is a diagram showing the configuration of a drum-type thickener equipped with a control device. The raw liquid to be treated, such as sludge, stored in a sludge storage tank 20 is supplied by a raw liquid supply pump 21 through a raw liquid supply pipe 22 to a flocculation mixing tank 23.

[0020] A chemical supply pipe 27 is connected to the middle of the raw liquid supply pipe 22 between the raw liquid supply pump 21 and the flocculation mixing tank 23. A chemical supply pipe 27 is connected to the raw liquid supply pipe 22. A chemical supply pump 26 supplies the chemical at a chemical flow rate QP from a polymer dissolving tank 25 in which a polymer flocculant is stored. A chemical flow meter 28 is provided in the middle of the chemical supply pipe 27, between the chemical supply pump 26 and the raw liquid supply pipe 22, to measure the chemical flow rate QP.

[0021] The end of the raw liquid supply pipe 22 is connected to the bottom of a closed flocculation mixing tank 23, and sludge with added polymer flocculant is injected into the flocculation mixing tank 23 from below and mixed and stirred with an agitator 29 to produce flocculated slurry. A slurry supply pipe 30 is connected to the top of the flocculation mixing tank 23, and the other end of this slurry supply pipe 30 is connected to the drum thickener 1, and the flocculated slurry is supplied to the supply path 11 of the drum thickener 1 shown in Figure 1 at the tank pressure of the flocculation mixing tank 23. A sludge receiving tank 40 is disposed at the end of the drum thickener 1, and thickened sludge obtained by separating the filtrate in the drum thickener 1 is discharged into the sludge receiving tank 40.

[0022] In this embodiment, the flocculation mixing tank 23 is used as the flocculation device, but other known flocculation devices such as a line mixer can also be used.

[0023] Figure 3 shows a concentrated sludge concentration measuring device installed in a sludge receiving tank, in which a detector 32 connected to a drive motor 31 hangs down from a sludge receiving tank 40 that stores concentrated sludge, and a power detector 34 is connected to a power cable 33 on the output side of the drive motor 31. Fluctuations in the concentration of sludge concentrated in the drum thickener 1 cause fluctuations in the sliding resistance of the detector 32, which changes the amount of power supplied from a power supply 35 to the drive motor 31. The power value of the drive motor 31 is transmitted from the output side power cable 33 to the power detector 34, which detects the sludge concentration as a voltage value. Reference numeral 36 denotes an overflow weir installed in the sludge receiving tank 40 to maintain the water level.

[0024] The thickened sludge concentration measuring device measures the thickened sludge concentration, which increases or decreases depending on the sludge properties. The raw liquor supplied to the drum-type thickener 1 is adjusted so that the thickened sludge concentration X measured by this thickened sludge concentration measuring device becomes the preset standard thickened sludge concentration X0.

[0025] Specifically, a command is given to the chemical supply pump 26 to increase or decrease the chemical flow rate QP, thereby performing constant thickened sludge concentration control operation. In practice, a detection signal measured by the thickened sludge concentration measuring device is sent to the control device 37, which compares and determines the signal, and the control device 37 gives a command to the chemical supply pump 26.

[0026] Control of the chemical flow rate QP by the chemical supply pump 26 mainly affects the floc strength of the flocculated slurry supplied to the drum thickener 1, and the floc strength increases or decreases in proportion to the chemical flow rate QP, and the concentration of the concentrated sludge discharged from the drum thickener 1 also increases or decreases.

[0027] The operation control method according to the present invention is based on adjusting the amount of flocculant supplied to stabilize the concentration of concentrated sludge discharged from the drum concentrator 1. At this time, the flow rate QP of the chemical solution supplied to the raw liquid is controlled so that the concentration is quickly increased when the concentrated sludge concentration is low, and gradually decreased when the concentrated sludge concentration is high.

[0028] When the operation of the drum-type concentrator 1 is started, the concentration of the thickened sludge is measured in real time by the thickened sludge concentration measuring device and sent to the control device 37.

[0029] Generally, when the properties of the influent sludge change and the amount of solids in the treated sludge increases (decreases), the concentration of the thickened sludge discharged from the drum thickener 1 increases (decreases).

[0030] Therefore, the control device of the present invention 37 In the system, the measured value X of the thickened sludge concentration is compared with a preset standard thickened sludge concentration X0, and if the measured value X deviates from the standard thickened sludge concentration X0, a command is given to the chemical supply pump 26 to control the amount of coagulant supplied and increase or decrease the amount of solids in the coagulated slurry.By adjusting the operating load on the drum type thickener 1, the concentration of the thickened sludge discharged from the drum type thickener 1 can be easily maintained at the standard thickened sludge concentration X0.

[0031] The standard thickened sludge concentration X0 can be set with a certain range, and when the measured value X of the thickened sludge concentration is within the set range, normal operation continues with the current state maintained.

[0032] More specifically, if the measured value X of the thickened sludge concentration is lower than the standard thickened sludge concentration X0, the control device 37 issues a command to the chemical supply pump 26 to increase the amount of coagulant supplied. By supplying conditioned sludge with stronger flocs to the drum type thickener 1, the concentration of the thickened sludge discharged from the drum type thickener 1 can be increased.

[0033] On the other hand, if the measured value X of the thickened sludge concentration is higher than the standard thickened sludge concentration X0, the control device 37 issues a command to the chemical supply pump 26 to reduce the amount of coagulant supplied. By supplying conditioned sludge with weakened floc strength to the drum type thickener 1, the concentration of the thickened sludge discharged from the drum type thickener 1 can be reduced.

[0034] Once the supply rate of the chemical supply pump 26 is changed, the thickened sludge concentration is measured after a certain time has elapsed, and the above operation is repeated until the measured value X returns to within the standard thickened sludge concentration X0.

[0035] The supply amount widths a1 and a2 for gradually increasing or decreasing the supply amount of coagulant are set in advance. At this time, the supply amount width a1 for gradually increasing the supply amount is set larger than the supply amount width a2 for gradually decreasing the supply amount, so that the concentration of low-concentration thickened sludge can be increased quickly and the concentration of high-concentration thickened sludge can be carefully reduced.

[0036] Upper and lower limits may be set for the amount of coagulant supplied, and when the upper or lower limit is reached, an alarm may be issued or operation may be automatically stopped so that an investigation can be carried out. [Example]

[0037] FIG. 4 is a flowchart of a control method for a drum concentrator. A. Initial Setup A standard thickened sludge concentration X0 is set for the thickened sludge discharged from the drum-type thickener 1. In this embodiment, the standard thickened sludge concentration X0 is set to have a range between the maximum standard thickened sludge concentration Xmax and the minimum standard thickened sludge concentration Xmin. The flocculant supply amount A0, maximum supply amount Amax, minimum supply amount Amin, stepwise increase range a1 of the supply amount, and stepwise decrease range a2 of the supply amount are set. In this embodiment, the supply amount range a2 is set to 80% or less of the supply amount range a1.

[0038] B. Start of operation Each device is operated at the above-mentioned reference values ​​X0 and A0. In this embodiment, only the amount of coagulant supplied is controlled according to the concentration of the thickened sludge, but the screw shaft 4 or the outer cylindrical screen 2 may also be controlled as necessary.

[0039] C. Comparison of concentrated sludge concentrations The control device 37 compares the concentrated sludge concentration X measured by it with a predetermined reference concentrated sludge concentration X0. As a result of the comparison by the control device 37, when the concentrated sludge concentration X is smaller than the reference concentrated sludge concentration X0 (X < X0), the process proceeds to D in the flowchart, and the supply of the stock solution by the stock solution supply pump 21 is continued. When the concentrated sludge concentration X is larger than the reference concentrated sludge concentration X0 (X0 < X), the process proceeds to G in the flowchart.

[0040] D. Comparison of the maximum supply amount of the flocculant In the above flowchart C, when the concentrated sludge concentration X is smaller than the reference concentrated sludge concentration X0, in order to increase the concentrated sludge concentration, the supply amount A taking into account the supply amount width a1 that is increased step by step to increase the flocculant is compared with the maximum supply amount Amax. When the supply amount A of the flocculant after the change is smaller than the maximum supply amount Amax, the process proceeds to E in the flowchart, and control is performed to increase the supply amount of the flocculant step by step. When the supply amount A of the flocculant after the change is equal to or greater than the maximum supply amount Amax, the process proceeds to F in the flowchart, and control is performed to issue an alarm or automatically stop the operation of the drum type concentrator 1.

[0041] E. Flocculant supply amount (increase) In the above flowchart D, when the supply amount A of the flocculant after the change is smaller than the maximum supply amount Amax, the chemical solution supply pump 26 is adjusted, and control is performed to increase the supply amount of the flocculant by the preset supply amount width a1.

[0042] F. Alarm · Operation stop After a certain period of time has elapsed, the concentrated sludge concentration is measured again, and the above operation is repeated until the measured value X returns within the reference concentrated sludge concentration X0. If the concentrated sludge concentration X does not return within the reference value X0 even when the flocculant reaches the maximum supply amount Amax or the minimum supply amount Amin described later, an alarm is issued or the operation of the drum type concentrator 1 is automatically stopped.

[0043] G. Comparison of the minimum supply amount of the flocculant In the above flowchart C, when the thickened sludge concentration X is greater than the standard thickened sludge concentration X0, the supply amount A taking into account the supply amount range a2 to be gradually reduced is compared with the minimum supply amount Amin in order to reduce the coagulant in order to lower the thickened sludge concentration. If the changed supply amount A of the flocculant is greater than the minimum supply amount Amin, the flow chart moves to H, where control is performed to gradually reduce the supply amount of the flocculant. If the changed supply amount A of the flocculant becomes equal to or less than the minimum supply amount Amin, the flow chart moves to F, where an alarm is issued or the operation of the drum concentrator 1 is automatically stopped.

[0044] H. Flocculant supply amount (decreased) In the above flow chart G, if the changed flocculant supply amount A is greater than the minimum supply amount Amin, the chemical supply pump 26 is adjusted to reduce the flocculant supply amount by a preset supply amount width a2.

[0045] When the amount of coagulant supplied is changed, the thickened sludge concentration is measured again after a certain time has elapsed, and the above operation is repeated until the measured value X returns to within the standard thickened sludge concentration X0.

[0046] In this embodiment, the concentrated sludge concentration measuring device detects the sludge concentration based on the fluctuation of the sliding resistance of the detector, but other known methods can be adopted.

[0047] In this example, the control factors are the supply amount and supply amount range of the flocculant, but the addition rate and addition rate range of the flocculant can also be used in the same way. [Industrial Applicability]

[0048] The drum-type concentrator of the present invention increases the concentration of concentrated sludge early when the concentration is low, and gradually decreases the concentration when the concentration is high to prevent the concentration from decreasing too much. This reduces the amount of low-concentration concentrated sludge discharged, stabilizes the transfer equipment and transfer method to downstream equipment, and subsequent processes such as dehydration, digestion, and drying, and improves overall manageability. [Explanation of symbols]

[0049] 1. Drum type thickener 2 Outer cylinder screen 3 screw blades 4 screw shaft 6a Outlet 12 Concentration chamber X Measured value of concentrated sludge concentration X0 Standard thickened sludge concentration A0 Standard supply amount Amax Maximum supply amount Amin minimum supply amount a1 Supply volume range to be increased in stages a2 Supply volume range to be gradually reduced

Claims

1. A drum thickener in which a concentration chamber (12) is formed by an external cylindrical screen (2) and a screw shaft (4) around which a screw blade (3) is wound, sludge in the concentration chamber (12) is transported by the screw blade (3) while filtrate is separated from the external cylindrical screen (2), and the concentrated sludge is discharged from a discharge port (6a) of the concentration chamber (12), a standard thickened sludge concentration (X0) having a set range between a maximum standard thickened sludge concentration (Xmax) and a minimum standard thickened sludge concentration (Xmin); a standard supply amount (A0) of flocculant; a maximum supply amount (Amax) which is the maximum value of the standard supply amount; a minimum supply amount (Amin) which is the minimum value of the standard supply amount; a supply amount range (a1) by which the flocculant is gradually increased; and a supply amount range (a2) by which the flocculant is gradually decreased, and the supply amount range (a1) is set to be larger than the supply amount range (a2); When the measured value of the thickened sludge concentration (X) is within the range of the standard thickened sludge concentration (X0), the operation of the drum thickener is continued. When the measured value (X) of the thickened sludge concentration is lower than the standard thickened sludge concentration (X0), the amount of the coagulant supplied is increased stepwise by the supply amount width (a1), and this operation is repeated until the measured value (X) of the thickened sludge concentration rises within the range of the standard thickened sludge concentration (X0); If the measured value (X) of the concentrated sludge concentration is higher than the standard concentrated sludge concentration (X0), the amount of coagulant supplied is gradually reduced by the supply amount width (a2), and this operation is repeated until the measured value (X) of the concentrated sludge concentration falls within the range of the standard concentrated sludge concentration (X0); The measured value (X) of the thickened sludge concentration is controlled within the range of the standard thickened sludge concentration (X0). A method for controlling a drum-type concentrator.

2. The stepwise decrease in the supply amount (a2) is set to 80% or less of the stepwise increase in the supply amount (a1).

2. The method for controlling a drum concentrator according to claim 1.

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