JP4584849B2 - Flocculant injection amount control method and control controller - Google Patents

Description

  The present invention relates to a control method of a water treatment facility for injecting a flocculant into raw water and aggregating impurities such as organic matter in the raw water and filtering, and more particularly to a method and a control controller for controlling the amount of flocculant injected into raw water. .

  When a membrane filtration device is installed in a water treatment facility that treats raw water with the property of changing water quality, such as surface water, and when flocculant is injected into the raw water to agglomerate impurities such as organic matter, aggregation is performed. It is important to appropriately control the injection amount of the agent. If the injection amount of the flocculant is insufficient, the flocculence is poor and the quality of the filtered water is deteriorated. If the injection amount of the flocculant is too large, the flocs are easily broken and the membrane is rapidly blocked. It progresses, and the membrane differential pressure rises in a short time and falls into the process.

  As a method for controlling the injection amount of the flocculant in the conventional membrane filtration process, there is a method described in Patent Document 1 in which the injection amount is changed so that the differential pressure increase rate matches the reference value. Patent Document 2 describes that a flocculant is injected according to the flow rate of raw water, although it is not a membrane filtration device.

Japanese Patent Laid-Open No. 10-15307 Japanese Unexamined Patent Publication No. 07-112103

When the amount of flocculant injection is controlled so that the rate of increase in the differential pressure matches a predetermined reference value, increasing the number of water pumps increases the amount of organic matter to be processed compared to the case of one water pump. For this reason, the amount of the flocculant injected is insufficient, and there is a possibility that poor aggregation occurs. In addition, when the rate of increase in differential pressure when organic substances, impurities, etc. are completely agglomerated when the amount of water supplied to the membrane filtration device is the maximum, if the water supply amount does not reach the maximum water supply amount Also, the amount of organic matter, impurities, etc. sent to the membrane filtration device is reduced. Therefore, even if they are completely agglomerated, the rate of increase in the differential pressure does not reach the reference value of the rate of increase in the differential pressure determined for the case where the water supply amount is maximum. At this time, if the flocculant injection amount is controlled so that the rate of increase in the differential pressure coincides with a predetermined reference value, the flocculant injection amount may be excessive.

  An object of the present invention is to enable a membrane filtration operation in a stable state even when the inlet inflow amount or the number of water pumps varies.

  In order to solve the above problem, in order to detect the state of the membrane filtration device in addition to the rate of increase in the differential pressure, the inlet inflow amount of the membrane filtration device may be taken into consideration. Therefore, the differential pressure of the membrane filtration device and the inlet inflow amount of the membrane filtration device are measured, and the flocculant injection amount is controlled in consideration of the fluctuation of the inlet inflow amount.

Specifically, a flocculant injection amount control method in a device for injecting a flocculant into raw water to form a floc floc, supplying raw water containing the formed floc floc to a membrane filtration device, and filtering the raw water, The amount of raw water flowing into the filtration device is detected, and the rate of increase in the pressure difference between the inlet side and the outlet side of the membrane filtration device is detected. The amount of flocculant injected based on the detected amount of flow in and the pressure difference To control.

  When the detected inflow amount changes, the flocculant injection amount may be changed by an amount proportional to the change in inflow amount. Further, the amount of the flocculant injected at the start of operation is desirably set in advance based on the concentration of organic matter in the raw water and the inflow amount.

  By setting the amount of the flocculant injected at the start of operation to a preset amount based on the concentration of organic matter in the raw water and the inflow amount, the organic matter, impurities, etc. in the raw water can be sufficiently agglomerated. Furthermore, if the inflow rate fluctuates, if the amount of flocculant injected is changed by an amount proportional to the change in inflow rate, even if the inflow amount fluctuates, organic matter, impurities, etc. in the raw water will be sufficiently agglomerated and flocked. be able to.

  According to the present invention, the membrane filtration device can be operated in a stable state even if the amount of raw water inflow into the membrane filtration device varies.

  FIG. 1 shows an overall configuration of a water treatment facility according to an embodiment of the present invention. The illustrated water treatment facility includes a raw water tank 1 into which surface water flows, a coagulation tank 2 for temporarily storing raw water taken from the raw water tank 1, a coagulant tank 3 disposed in connection with the coagulation tank 2, A suction header 25 connected to the outlet side of the coagulation tank 2, three water pumps 4 connected to the suction header 25 in parallel with each other, and a discharge side of the three water pumps 4 are connected in common. The discharge header 26, the membrane filtration device 5 connected to the discharge header 26 by the inflow pipe 27, the outflow pipe 28 connected to the output side of the membrane filtration device 5, and the inflow pipe 27. An inflow flow meter 7, a differential pressure meter 6 connected to an inflow pipe 27 and an outflow pipe 28 on the downstream side of the inflow amount flow meter 7 to measure and output the differential pressure between them, and the differential pressure gauge 6 and the inflow amount flow meter 7. Coagulant injected from coagulant tank 3 into coagulation tank 2 with output as input A controller 8 for controlling the amount, is configured to include a display device 13 connected to the controller 8.

  In the above water treatment facility, raw water taken from the raw water tank 1 and containing organic substances and impurities to be aggregated (hereinafter referred to as organic substances) is temporarily stored in the coagulation tank 2, and the coagulant tank 3 supplies the coagulant to the coagulant tank 2. Is injected and added. A flocculant injection amount control means (not shown) is provided on the flocculant outlet side of the flocculant tank 3, and the organic matter in the raw water is agglomerated by injecting and adding the flocculant to the agglomeration tank 2. To form aggregated floc. The raw water containing the coagulation floc in the coagulation tank 2 is sent to the membrane filtration device 5 by the water pump 4 and filtered. The raw water filtered by the membrane filtration device 5 becomes clean water and is discharged from the outflow pipe 28.

  The output signals of the differential pressure gauge 6 that measures the difference between the inlet pressure and the outlet pressure of the membrane filtration device 5 and the inflow amount flow meter 7 that measures the inlet flow rate of the membrane filtration device 5 are sent to the controller 8, and the control controller 8 controls the amount of the coagulant injected from the coagulant tank 3 into the coagulation tank 2 by using the output signals of the differential pressure meter 6 and the inflow amount flow meter 7 through the injection amount control means.

FIG. 2 shows the configuration of the controller 8. The control controller 8 includes a calculation unit 10 that performs calculation processing on data obtained from the measuring device 9 such as the differential pressure gauge 6 and the inflow amount flow meter 7, and a processing result of the calculation unit 10 as input. And a control unit 11 that issues an operation command to the operation device 12. The computing unit 10 stores the concentration data of the raw water, the data of the coagulant injection amount corresponding to the inlet flow rate of the membrane filtration device (hereinafter simply referred to as the flow rate), and the differential pressure increase rate data at that time. Has been. The display device 13 displays the calculation result of the controller 8, the state of the device, and the like, and the facility operator can also perform monitoring control using the display device 13. The controller 8 can set the concentration of organic matter or the like in the raw water, and the calculation unit 10 calculates the differential pressure increase rate based on the differential pressure input from the differential pressure gauge 6. At the same time, a calculation process according to the set density is performed.

  FIG. 3 shows a data processing flow of the controller 8. Prior to the start of facility operation, data obtained from the measuring device 9 such as the differential pressure gauge 6 and the inflow amount flowmeter 7 and a relation table that defines the relationship between the set concentration and the flocculant injection amount are read (procedure 14). Is done. When the operation is started, reception of data of the differential pressure gauge 6 and the inflow flowmeter 7 (procedure 15) is performed at predetermined time intervals. Next, based on the received data, the flocculant injection amount is determined with reference to the read relation table (procedure 16). Based on the determined flocculant injection amount, a control signal to the operating device is generated and output (procedure 17). In the above procedure, the flocculant injection amount is determined with reference to the read relation table. However, the coagulant injection amount can be obtained from the measuring device 9 such as the differential pressure gauge 6 and the inflow amount flowmeter 7 even if it is not necessarily the relation table. The relationship between the data and the flocculant injection amount may be defined using mathematical expressions and graphs.

  FIG. 4 shows a procedure for determining the flocculant injection amount when the number of water pumps is increased. Each water pump 4 is a pump of the same capacity that is operated at a constant speed. When the number of water pumps increases (procedure 18), the inflow amount at the inlet of the membrane filtration device increases in proportion to the increase in the number (procedure 19). This increases the number of organic substances to be treated (procedure 20). At this time, the flocculant injection amount is increased in proportion to the number of pumps (procedure 21). When sufficient coagulant is injected to form coagulation flocs, the number of coagulation flocs increases in proportion to the number of water pumps (procedure 22). As a result, the number of flocculated flocs removed by the membrane filtration device is increased and the membrane is blocked. That is, as the number of pumps increases or the inlet inflow increases, the amount of flocculant injected increases proportionally, and the differential pressure increase rate increases accordingly (procedure 23).

  When organic matter in the raw water is agglomerated by the injected flocculant and becomes flocculent floc and filtered by the membrane filtration device, the aggregated floc that accumulates on the entrance side of the membrane increases with the passage of time, and the difference between the filtration devices The pressure rises. The rate of increase in the differential pressure is determined by the amount of coagulation floc deposited on the entrance side of the film per time, that is, the concentration of organic matter and the inflow when the injection amount of the coagulant is appropriate. In other words, once the concentration of organic matter and the amount of inflow are determined, the flocculant injection amount is adjusted so that the rate of increase in the differential pressure becomes a preset value corresponding to the concentration of organic matter and the amount of inflow. The flocculant injection amount can be set. This means that when the flocculant injection amount is set to an appropriate state for a certain inflow amount, even if the inflow amount fluctuates, the inflow amount does not change unless the concentration of organic matter, etc. This means that the flocculant injection amount should be changed in proportion.

  At the start of the operation of the membrane filtration device, the controller 8 injects a preset flocculant injection amount according to the concentration of organic matter and the inflow amount, but the subsequent increase rate of the differential pressure is a preset value. If smaller than this, it is determined that the flocculant injection amount is insufficient, and the operation is performed to increase the flocculant injection amount by a predetermined amount.

  On the other hand, when the amount of the flocculant injected is excessive, as described above, the generated flocculent flocs are liable to collapse and the membrane pores are easily clogged. That is, when an excessive amount of flocculant is injected beyond the appropriate amount of flocculant, the rate of increase in the differential pressure is greater than the rate of increase in the differential pressure set in advance corresponding to the concentration of organic matter and the amount of inflow. Become. That is, when the differential pressure increase rate is greater than the preset differential pressure increase rate, the controller 8 operates to reduce the coagulant injection amount by a predetermined amount.

When the concentration of organic matter in the raw water does not change, the relationship between the inflow rate of the membrane filtration device inlet and the appropriate flocculant injection amount is plotted on the horizontal axis, and the appropriate flocculant injection amount is plotted on the vertical axis. These are shown in FIG. The straight line S ₁ indicates the amount of the flocculant injected corresponding to the inflow amount for the raw water having a standard concentration of organic matter, etc., and m, 2 m, and 3 m on the vertical axis indicate the concentration K of the standard concentration of organic matter. Are the initial setting values of the flocculant injection amount in the case of the inflow amounts f ₁ , f ₂ , and f ₃ , and the points f ₁ m, f ₂ m, and f ₃ m on the straight line S ₁ are respectively In addition, the amount of the flocculant injection necessary and sufficient for aggregating the organic matter contained in the raw water is shown. Linear S ₂ shows the case of a low concentration L than the concentration is the standard concentration K of organic substances or the like contained in the raw water, the straight line S ₃ rather than concentration the standard concentration K of organic substances or the like contained in the raw water The case of high concentration M is shown.

FIG. 6 shows the relationship between the flow rate at the inlet of the membrane filtration device, the differential pressure increase rate, and the coagulant injection amount, which is the relationship for determining the control amount in FIG. FIG. 6 shows the data of the flocculant injection amount for the raw water having a standard concentration of organic matter, etc., and the differential pressure increase rate is shown on the horizontal axis and the flocculant injection amount is shown on the vertical axis. It is. The slanted lines in the figure indicate lines f ₁ , f ₂ , and f ₃ with a constant flow rate into the membrane filtration device, and the lines f ₁ , f ₂ , and f ₃ indicate the case where _one , _two , and _three water pumps are operated. The inflow of each is shown.

The vertical axes m ₀ , 2 m ₀ , and 3 m ₀ are the flocculant injection amount initial setting values for the inflow amounts f ₁ , f ₂ , and f ₃ , respectively, and the points f ₁ m, f ₂ m, and f ₃ m is a point that indicates a sufficient amount of the flocculant injection necessary for aggregating the organic matter contained in the raw water, and the differential pressure increase rate when the necessary and sufficient amount of the flocculant is injected. v, 2v, and 3v are shown.

The lines f ₁ , f ₂ , and f ₃ are straight lines on the upper and lower sides of the point f ₁ m, the point f ₂ m, and the point f ₃ m in the figure, but the points f ₁ m, f ₂ m, and f ₃ m On the upper side of the figure, the curve has a gentle slope starting from the point f ₁ m, the point f ₂ m, and the point f ₃ m. This indicates that the flocculant injection amount becomes excessive with respect to the inflow amount, and as a result, the formed floc flocs are apt to collapse and the differential pressure increases rapidly.

Incidentally, the point represented by f 3 _m, the concentration of organic matter in the three water pumps showed differential pressure increase rate 3v when the raw water standard concentration is water, planned differential pressure increases as the membrane filtration unit It is the upper limit of speed, in other words, the differential pressure increase speed. If the differential pressure increase rate is higher than this, that is, if the concentration of organic substances contained in the raw water is higher than the standard concentration, the frequency of backwashing increases and the filtration efficiency increases. Since it decreases and is not preferable, the inflow is reduced.

As shown in FIG. 5, the point f ₁ m, the point f ₂ m, and the point f ₃ m are arranged on the straight line S ₁ and are represented by the points f ₁ m, f ₂ m, and f ₃ m. The agent injection volume is proportional to the inflow volume. Therefore, the flocculant injection amount may be changed in proportion to the inflow amount. In the present embodiment, three inflow pumps of the same specification with a constant flow rate are used, and the inflow amount is changed by controlling the number of units. Therefore, in FIG. 6, three lines f ₁ , f ₂ , f indicating the inflow amount are used. ₃ is shown, by the rotation speed control or the like, even when the steplessly inflow changes, likewise, be varied along the straight line S ₁ in proportion to coagulant injection amount inflow Good.

In linear S ₂ in FIG. 5, since the concentration of organic substances or the like contained in the raw water is lower than the standard concentration, even in the inflow f _3, coagulant injection amount remains 2m _0, the differential pressure increase rate, It is stored at a differential pressure increase speed 2v represented by a point f ₂ m in FIG. In linear S ₃ in FIG. 5, higher than concentrations the standard concentration of organic matter contained in the raw water, varying the coagulant injection amount in accordance with the inflow, coagulant injection amount inflow f ₂ There has been reached 3m _0. As a result, flocs are formed increases rapidly, with inflow f _2, it reaches the differential pressure increase rate 3v represented by point f _{3 m} in FIG. When the differential pressure increase speed 3v is detected, the controller 8 stops further increase of the inflow amount.

  The data shown in FIG. 5 and the data shown in FIG. 6 are stored in the calculation unit 10 of the controller 8 so as to be readable using the organic substance concentration and the inflow amount as keys.

  The display device 13 displays the organic matter concentration of raw water being processed and the raw water inlet inflow amount, the flocculant injection amount, and the differential pressure increase rate during operation.

  Hereinafter, the procedure during operation will be described.

  Prior to the start of operation, the concentration of organic matter in the raw water is set in the calculation unit 10 of the controller 8. In addition, the number of operating pumps is set. When the operation is started, the calculation unit 10 of the controller 8 selects the flocculant injection amount with reference to the data shown in FIG. 5 based on the set organic substance concentration and the detected inflow amount. Based on the selected flocculant injection amount, the control unit 11 outputs a control signal to the injection amount control means to inject the selected amount of the flocculant into the flocculant tank 2.

  After the operation is started, the calculation unit 10 of the controller 8 reads the output data of the inflow amount flow meter 7 and the differential pressure gauge 6 at a predetermined sampling interval, and calculates the inflow amount and the differential pressure increase rate. The calculation unit 10 compares the calculated differential pressure increase rate with the differential pressure increase rate v, 2v, or 3v corresponding to the inflow amount shown in FIG. 6, and when the calculated differential pressure increase rate is low, The flocculant injection amount is increased by a predetermined amount, and when the calculated differential pressure increase rate is high, the flocculant injection amount is decreased by a predetermined amount.

  When the amount of the flocculant injected is increased or decreased, after a time when a delay in the response of the differential pressure increase rate is expected, the differential pressure increase rate is detected, and the detected differential pressure increase rate is shown in FIG. The above procedure is repeated in comparison with the differential pressure increasing speed v, 2 v, or 3 v corresponding to the indicated inflow amount.

  If the calculated differential pressure increase speed is within the allowable range with respect to the differential pressure increase speed v, 2v, or 3v corresponding to the inflow amount shown in FIG. 6, the operation is continued as it is.

  When a change in the inflow amount is detected during operation, the calculation unit 10 of the control controller 8 sets the flocculant injection amount obtained by increasing or decreasing the flocculant injection amount by an amount proportional to the fluctuation amount of the inflow amount. The control unit 11 outputs a control signal to the injection amount control means based on the signal input from the calculation unit 10 to increase or decrease the flocculant injection amount.

  As shown in the procedure of FIG. 4, if the amount of flocculant injected is increased in proportion to the increase in the number of inlet inflows or the number of water pumps as the number of inlet inflows or the number of water pumps increases, it can be controlled efficiently. Results are obtained.

  Furthermore, the following results are also obtained from the above results. First, even when the number of pumps is one, the inlet inflow amount varies when the number of water pumps is variable, so that the present invention is also applicable to this case. Secondly, when there are multiple water pumps at a fixed speed, the differential pressure increase rate is proportional to the number of units, so the inlet flow rate can also be predicted, so it can be controlled without the flow rate flow meter 7. It is possible to remove the inflow flow meter.

It is a block diagram which shows the structure of the water treatment facility which concerns on embodiment of this invention. It is a block diagram which shows the structural example of the control controller shown in FIG. It is a flowchart which shows the procedure which determines the coagulant | flocculant injection amount when the number of water pumps is increased. It is a figure which shows a series of factors until determining the coagulant | flocculant injection amount at the time of increasing the number of water pumps. It is a figure which shows notionally the relationship between a membrane filtration apparatus inlet inflow amount, the coagulant | flocculant injection amount, and organic matter etc. density | concentration of raw | natural water. It is a figure which shows notionally the relationship between a membrane filtration apparatus inlet inflow amount, the coagulant | flocculant injection amount, and a differential pressure | voltage rise rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Coagulation tank 3 Coagulant tank 4 Water supply pump 5 Membrane filtration device 6 Differential pressure meter 7 Inflow amount flow meter 8 Control controller 9 Measuring device 10 Calculation unit 11 Control unit 12 Operation device 13 Display device 25 Suction header 26 Discharge header 27 Inflow pipe 28 Outflow pipe

Claims (3)

Injected to form an aggregated floc flocculant raw water, the raw water containing the formed floc a coagulant injection amount control method of filtering is supplied to membrane filtration apparatus, raw water to the membrane filtration unit Coagulant injection that detects the inflow amount and detects the rate of increase in the pressure difference between the inlet side and the outlet side of the membrane filtration device and controls the amount of coagulant injection based on the detected rate of increase in the inflow rate and pressure difference In the amount control method , the coagulant injection amount control method is characterized in that the amount of coagulant injection at the start of operation is set in advance based on the concentration of organic matter in the raw water and the inflow amount .   2. The flocculant injection amount control method according to claim 1, wherein when the detected inflow amount changes, the flocculant injection amount is changed by an amount proportional to the fluctuation of the inflow amount. Method. Injecting a coagulant into raw water, a controller for controlling the coagulant injection amount in an apparatus for filtering and supplying to the membrane filtration apparatus at a water pump raw water containing the generated flocs, to raw water coagulant The injection amount is determined in advance according to the combination of the increase rate of the differential pressure of the membrane filtration device and the number of water pumps , or is determined in advance according to the combination of the increase rate of the differential pressure and the inflow amount of raw water . Characterized in that it has means for controlling based on any one of the amounts, and means for controlling the injection amount of the flocculant at the start of operation to a preset amount based on the concentration of organic matter in the raw water and the inflow amount. control controller.

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