JPH03258400A - Dissolved oxygen concentration control apparatus - Google Patents

Abstract

PURPOSE:To stably control the concn. of dissolved oxygen in an aeration tank and to save energy by calculating the opening degree command of an induction valve based on a means for inferring the delivery pressure command of a blower, the inferred blower delivery pressure command, opening degree of the blower suction valve and measured delivery pressure value and controlling the opening degree. CONSTITUTION:An airflow valve control part 15 and an induction control part 13 are weakly connected by a means for inferring a delivery pressure command. Since this connection consists of a delicate balance between the blower delivery pressure and opening degree of an airflow control valve and further the DO value as the input variable of the opening degree of the airflow control valve depends on a biochemical reaction, fuzzy elements are increased, and accordingly the pressure and opening degree are balanced by fuzzy inference. Consequently, the frequency of operating and stopping the blower is controlled, the concn. of dissolved oxygen in the aeration tank is stably controlled, the blower delivery pressure is controlled to avoid an unnecessary pressure loss, and hence energy is saved. A highly reliable controller is provided in this way.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention is an improvement of a dissolved oxygen concentration control device that controls the dissolved oxygen concentration in an aeration tank in an activated sludge treatment process so that it reaches a target value. Regarding.

(Prior Art) In a sewage treatment process using activated sludge, it is required to control the dissolved oxygen concentration in an aeration tank to a predetermined value. For this reason, control is performed to detect the dissolved oxygen concentration (hereinafter referred to as DO value) in the aeration tank and adjust the aeration air volume so that the Do value becomes a target value.

FIG. 7 is a block diagram showing an example of the configuration of this type of conventional dissolved oxygen concentration control device.

In FIG. 7, sewage accumulated in the aeration tank 1 is aerated by air sent out from a plurality of blowers 2 (2-1 to 2-N). In addition, a suction valve 3 (3-
1 to 3-N) are attached, and a discharge pressure gauge 4 is installed on the discharge side. The air that has passed through the pressure gauge 4 is guided into the aeration tank 1 via an airflow control valve 5 that adjusts the aeration airflow and an airflow meter 6 that detects the aeration airflow.

On the other hand, a dissolved oxygen concentration meter (hereinafter referred to as a DO meter) 7 is installed in the aeration tank 1.

The detection signals from a total of 7 are used to adjust the Do value in the aeration tank 1 to the target DO.
It is supplied to the DO control unit 8 which calculates and outputs the aeration air volume to obtain the value. And D.

In the control unit 8, when the Do target value X is set, this target value value qr
We are looking for (t).

εd (t)-X, -X (t)...(1)
Δqr (t) - to 1 (ε8 (t) - ε, (1 - τ) ten τ・ε
, (t)/T, l ... (2) q, (
t) -q, (t - τ) 1Δq, (t) ... (3) where, K,, T,: control parameter τ: control period target aeration air volume value q obtained by equation (3) , (t) is the aeration air IL supplied to the air volume control H9 and detected by the air volume meter 6.
q(t) and the valve opening U (t) of the air volume control valve 5, the valve opening target value U,
We are looking for (t).

εQ (t)-q-(t) Q (t)...
〈4) ΔU, (t) −, (ε, (t) − εQ (−τ) + τ・εQ
(t) /Tq) ... (5) U, (t) -U, (t - τ) + ΔU, (t) ... (6) where, K,, T: control parameter and air volume The air volume control valve 5 is adjusted so that the valve opening U (t) of the control valve 5 becomes the valve opening target value U, ct obtained in (6), and thereby the Do value in the aeration tank 1 is adjusted. is controlled so that it becomes the target DO value X.

However, in this method of controlling the O value, since the aeration air volume is regulated by the valve opening degree of the air volume control valve 5, the air pressure at the inlet of the air volume control valve 5, that is, the discharge pressure of each blower 2, cannot be controlled. Must be held at a constant value. Therefore, the detection signal from the discharge pressure gauge 4 is transmitted to the discharge pressure control section 10.
The valve opening degree of each discharge valve 3 is adjusted so that this detection signal becomes equal to the discharge pressure target value. In addition, the operation and stopping of each blower 2 is controlled by a number control unit 11 that determines the number of blowers 2 in operation as the discharge pressure changes.

As a result, the discharge pressure of each blower 2 is maintained at a predetermined value, and the Do value in the aeration tank 1 is stably controlled.

However, in such a conventional dissolved oxygen concentration control device, during a transient response in which the Do value in the aeration tank 1 changes rapidly, the aeration air volume fluctuates greatly, so the blower 2
In order to maintain the discharge pressure at a constant value, the number of operating blowers 2 was frequently changed. Furthermore, in terms of power consumption, pressure must be maintained at a high level, and power is wasted due to pressure loss.

(Problems to be Solved by the Invention) As described above, in the conventional dissolved oxygen concentration control device, the DO
Because the number of blowers in operation fluctuated frequently during transient response, the number of times the blowers were started and stopped was greater than necessary.

For this reason, there have been problems in that the lifespan of the blower and the motor that drives the blower is significantly shortened, and excessive effort is required for maintenance and the like.

Therefore, it is possible to consider a method of controlling the aeration air volume to a constant value without sub-controlling the DO value.
Since it is not possible to follow fluctuations in the value, the aeration air volume must be set to an excessive value, which results in unnecessary power consumption, which is impractical.

The purpose of the present invention is to stably control the dissolved oxygen concentration in the aeration tank while suppressing the frequency of operation and stop of the blower, and to save energy by controlling the blower discharge pressure to avoid unnecessary pressure loss. The object of the present invention is to provide an extremely reliable dissolved oxygen concentration control device capable of controlling the concentration of dissolved oxygen.

[Structure of the Invention] (Means for Solving the Problem) In order to achieve the above object, the dissolved oxygen concentration in the aeration tank is reduced by controlling the amount of aeration air to at least one aeration tank in the activated sludge treatment process. In the dissolved oxygen concentration control device that controls the aeration air volume to a target value, the first invention detects the valve opening degree of an air volume control valve that adjusts the aeration air volume to the aeration tank, the air volume target value, and the aeration air volume to the aeration tank. Based on the aeration air volume output from the air flow meter,
Discharge pressure target value inference means for inferring the discharge pressure target value of the blower by fuzzy inference, the blower discharge pressure target value inferred by the discharge pressure target value inference means, and the valve opening of the suction valve that adjusts the blower discharge pressure. and a suction valve control means for controlling the valve opening of the suction valve by calculating a valve opening target value of the suction valve based on the measured value of the discharge pressure of the blower, and a second In the invention, outputs are obtained from a dissolved oxygen concentration meter and a thermometer provided in the aeration tank, an airflow meter that measures the amount of aeration air supplied to the aeration tank, and a flowmeter that measures the flow rate of sewage flowing into the aeration tank. a required air volume calculation means that calculates the required aeration air volume according to a predetermined calculation formula based on the dissolved oxygen concentration, tank internal temperature, aeration air volume, and sewage flow rate; and the dissolved oxygen concentration output from the dissolved oxygen concentration meter, respectively; Based on the preset target dissolved oxygen concentration,
a concentration adjustment means for calculating a target value of aeration air volume in the aeration tank;
a number increase/decrease determination means for determining whether the blower is a bottle stand or a mounting base based on the required aeration air volume calculated by the required air volume calculation means and the aeration air volume target value calculated by the concentration adjustment means; and a number control means for controlling operation or stopping of the blowers based on the determination result.

(Function) In the dissolved oxygen concentration control device according to the first invention, the air volume valve is opened as much as possible to prevent unnecessary power consumption due to pressure loss. The air volume control valve control, which controls the DO constant, and the suction valve control, which controls the blower discharge pressure to a constant level, are independent so that they do not interfere with each other, but from the perspective of energy saving, it is important to avoid unnecessary increases in pressure. Therefore, the air volume valve control system and the suction control system are weakly coupled by the discharge pressure target value inference means, which is a feature of the present invention. This connection is made up of a delicate balance between the blower discharge pressure and the air volume control valve opening.
Moreover, the DO value, which is a human-shaped variable of the air volume control valve opening, is highly ambiguous because it depends on biochemical reactions.
By balancing pressure and valve opening using fuzzy reasoning, energy savings can be achieved in a stable state.

In addition, in the dissolved oxygen concentration control device according to the second invention, in determining the increase or decrease in the number of blowers, the number of operating blowers is determined based on the Do value in the aeration tank, the temperature, and the flow rate of sewage flowing into the aeration tank. There is.

If it is estimated that the amount of aeration air sufficient to satisfy the amount of oxygen required by the aeration tank can be secured, the number of operating units will not be increased or decreased even if the discharge pressure of the blowers suddenly changes. As a result, the number of times the blower starts and stops can be significantly reduced.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a configuration example when the dissolved oxygen concentration control device according to the present invention is applied to an activated sludge treatment process.

In Figure 1, aeration tank 1 (1-1-K
), wastewater flowing in from the upstream process is accumulated and aerated with air sent out from a plurality of blowers 2 (2-1 to 2-N).

Suction valves 3 (3-1 to 3-N) are attached to the air inlet pipe of each blower 2 in order to adjust the discharge pressure of the blower 2, and the valve opening of each suction valve 3 is Valve control section 13
The alignment is controlled by Further, a discharge pressure gauge 4 is installed on the discharge side of the blower 2. The air that has passed through the discharge pressure gauge 4 is then passed through the air volume control valves 5 (5-1 to 5-K) provided for each aeration 11 and the air volume meters 6 (6-1 to 6-K). , are supplied to each aeration tank 1.

In addition, a flow meter 18 is installed in the wastewater supply pipe to the aeration tank 1, and a dissolved oxygen concentration meter (hereinafter referred to as a Do meter) 7 (7-1 to 7-K) and a temperature meter are installed in each aeration tank 1. Total 19 (1
9-1 to 19-K) are installed, and the detected flow rate signal y, temperature signal θ1 to θ, DO signal X1 to
X1 is supplied to the dissolved oxygen concentration control device 12 via the man-machine/process interface 23. Furthermore, the valve opening signal Uh of each suction valve 3 and the discharge pressure gauge 4 described above are
The pressure signal h1 detected by the valve opening signal U1~UK% of each air volume control valve 5 and the air volume signal q detected by each air volume meter 6
, ~Qx are similarly supplied to the dissolved oxygen concentration control device 12 via the man-machine/process interface 23.

On the other hand, as shown in FIG.
is the DO value X at time t of each aeration tank 1, (t) ~
Based on the deviation between x (t) and the preset DO target value X, the aeration air volume target value Q,1 (t
) to q*K(t), and based on this, the valve opening target value U, 1 (t) of each air volume control valve 5.
~ U,k (t).

Further, a discharge pressure target value inference device that fuzzy infers a discharge pressure target value h7 of the blower 2 so that the air volume control valve 5 opens as much as possible based on the air volume control valve opening degree, the air volume signal, and the aeration air volume target value. It is equipped with 21. Furthermore, the corrected discharge pressure target value (t), the valve opening degree Uh (t) of the suction valve 3, and the measured discharge pressure value h (t) of the blower 2 are added.
The suction valve control section 13 calculates and outputs a valve opening target value Uh, (1) of the suction valve 3 based on the above.

On the other hand, dissolved oxygen concentration X1 to XK in each aeration tank, temperature θ,
~θ. , and a required air volume calculation unit 17 that calculates the required aeration air volume for each aeration tank based on the sewage inflow flow rate y;
o A number increase/decrease determination unit 20 that determines whether to increase or install the blowers 2 based on the aeration air volume target value that is the output from the adjustment unit 16 and the required aeration air volume that is the output from the required air volume calculation unit 17; , a number control section 14 that controls operation or stopping of the blower 2, that is, the number of blowers 2, based on a determination signal from the number increase/decrease determination section 20. Furthermore, it is equipped with an energy saving method 22 that stores if-t ben rules to be referred to when performing fuzzy inference on the discharge pressure target value in the discharge pressure target value inference device 21, and a man-machine/process interface 23. Rules can be added and modified through the .

Next, the operation of the dissolved oxygen concentration control device configured as above will be explained using FIGS. 2 to 6.

In FIG. 1, when sewage flows into each aeration tank and aeration is started by air sent from the blower 2, a DO value XX(1) is detected in a certain aeration tank 1-,
It is supplied to the DO adjustment section 16 of the dissolved oxygen concentration control device 12 via the man-machine/process interface 23 .

In the Do adjustment section 16, when the DO target value X is set,
The aeration air volume target value q, k (t) for each aeration tank 1 is calculated by the same procedure as the above-mentioned equations (1) to (3), and this is supplied to the air volume control valve controller 15. In addition, the air volume control valve control unit 15 is given the aeration air volume QK% detected by the air flow meter 6- and the valve opening degree UK of the air volume control valve 5-, so that the above-mentioned (4) to (6) The valve opening target value U, k (t) for the air volume control valve 5- is determined by the same procedure as in the equation. Based on this result, the air volume control valve 5-K
is adjusted, and the aeration air volume is controlled.

Next, in the discharge pressure target value inference device 21, D.

The aeration air volume target value q for each aeration tank 1, which is the output from the adjustment unit 16, is the total sum of *(t) q, l-1-1(t)-Σq,k(t)-1, and the air flow meter. Aeration air volume qk for each aeration tank 1 obtained from 6
Based on the sum q, """ (t)-Σ qh (t)-1 of (t) and the opening degree Uk (t) of the air volume control valve 5, it is given to the suction valve control unit 13 by fuzzy reasoning. A pressure target value is deduced.

This point will be specifically explained using FIGS. 2 and 3.

In Figure 2, the opening degree ψ of the air volume control 5 is set to 0% when the valve is in the fully open position as shown in the figure, and the direction of the arrow is positive in the same figure, and the degree of closure is expressed as a percentage. shall be taken as a thing. In addition, the maximum closing degree ψ■
Let aX be the degree of closure of 100%.

That is, as pre-processing for the fuzzy inference, the fuzzy input variables, the total air volume target value deviation q@@I', and the air volume control valve opening degree ψ' are calculated using equations (7) and (8).

q meeting・t −(q l o“l q , I O“l )
/α ... (7) ψ1−ψ/β
(8) Here, α, β: normalization coefficients Next, the pressure correction amount D1 is fuzzy inferred using a known fuzzy inference calculation formula. Then, the obtained pressure correction amount D' and the previous pressure target value, (-Δt)
Based on this, the pressure target value (f) is determined by equation (9).

h, (f) -h, (-Δt) (1'+kD')...(9
) k: correction amount coefficient Δt: control period In addition, since it is necessary to generate a swirling flow in the aeration tank, the aeration air volume shall be limited so as not to fall below the lower limit value q, ml''. , ψ in equation (8) is selected from the aeration series with the maximum degree of closure.

Figure 3 shows 1f-then referred to in fuzzy inference.
- It is a figure showing an example of a rule table.

In FIG. 3, 0 to 100% is a fuzzy set indicating the degree of air flow control valve closure, NB, NM, NS.

Z, PS, PM, and PB are each NB (negative and large),
NM (negative and medium), Z (zero: 1), PS (positive and small),
This is a fuzzy set indicating PM (positive and medium) and PB (positive and large).

An example of the rule is shown below.

if (total air volume target value deviation) is NB and
(Air volume control valve closing degree) 's20% then (Pressure target value) '5PBif (Total air volume target value deviation) 's Z and (Air volume control valve closing degree) 1s60% then (Pressure target value) is NM Figure 3 The rule table shown below indicates that the air volume control valve closing degree is approximately 2.
It is written to save energy by maintaining it at the 0% position.

FIGS. 4 and 5 are diagrams each showing an example of a membership function representing a fuzzy set.

The fuzzy inference method performs a fuzzy operation based on the rules stored in the energy saving plan 22 based on the membership function of the rule condition part, the membership function of the conclusion part, and the input value to make the result fuzzy. A method is used in which a set is created, the maximum value of this composite ambiguous set is used as an output function, and the center of gravity of this output composite function is used as the output of fuzzy inference.

Specifically, for each rule, a fuzzy set is created with the minimum value of the membership function in the condition part as a weighting coefficient and the maximum value of the membership function in the conclusion part as a weighting coefficient for the input value, and all The sum of the fuzzy sets obtained by each rule is the composite fuzzy set, the maximum value of the composite fuzzy set is the output composite function, the center of gravity of this output composite function is calculated by equation (10), and this value is Let be the fuzzy inference value.

D'-1:: : B" (x) X xdx/ f-
::B''(x)dx-(10)Dl :Fuzzy inference value It is possible to achieve significant energy savings.

On the other hand, in FIG. 1, the required air volume calculation section 17 uses the formula (
A mathematical model of the DO process shown in 11) has been set.

dX (t) /d t -a-q' fXs -X (t))R・
-... (11) a, n Nibrant-specific constants see ] The oxygen respiration rate R1 in the second term on the right side of equation (11) is an element that indicates the amount of oxygen required by the aeration tank, and this equation (11) is determined by the difference between the oxygen supply amount and the oxygen supply amount. DO value
This shows that the amount of change in (t) is determined.

Then, in the required air volume calculation section 17, the given DO value
From (t), find the saturated DO value X from the time change dX (t)/dt and the water temperature θ, substitute these values, aeration air volume q, and DO value Estimated oxygen respiration rate R1 using a method such as
is required.

Furthermore, since the oxygen respiration rate R1 is approximately proportional to the wastewater inflow rate y, the estimated oxygen respiration rate R1 is changed in proportion to the fluctuation in the wastewater flow rate y.

Thus, R, -R1(y) in formula (1).

X-X, and when the Do value is controlled to a steady state, the rate of change in the Do value is dX(t)/dt-O. A target value q is determined.

Q"-(R1/a CXa-XI) l"'-(
12) Next, the number increase/decrease determination unit 20 calculates the total air volume target value q5 obtained by the required air volume calculation unit 17 and the aeration air volume target value q for each aeration tank 1 obtained by the DOm node 16.
Total air volume target value q from +k (f), ""' (
t) - Σ q 1m (t), it is determined whether to add -1 aircraft 2 or to mount the aircraft 2 on the air blower. As shown in FIG. 6, the final determination is made by a combination of a determination based on the target air volume total amount and a determination based on the required air volume. In this case, the individual determinations are divided into adding, maintaining, and placing a platform at a certain setting level. The number of operating units determined here is calculated based on the DO value in each aeration tank 1, temperature, and wastewater inflow flow rate, so it is estimated that the aeration air volume sufficient to satisfy the oxygen demand can be secured. In this case, the number of operating units will not be increased or decreased even if the discharge pressure suddenly changes.

In this way, when it is estimated that the required aeration air volume for each aeration tank can be secured, the blower 2 is not started and stopped unnecessarily, and the number of times the blower 2 is started and stopped is significantly reduced. , As a result, the life of the blower 2 is extended,
Maintenance work is reduced.

As described above, in the dissolved oxygen concentration control device of this embodiment, the amount of electric power consumed by the blower 2 can be significantly reduced, and air can be stably supplied to the aeration tank 1. This makes it possible to significantly reduce the number of times the system starts and stops.

Thereby, the life of the blower 2 can be significantly extended, and work such as maintenance can be reduced.

In the above example, the number of operating blowers 2 was determined based on the flow rate of sewage flowing into the aeration tank 1 and the temperature inside the aeration tank 1. Since these factors are almost constant, they can also be treated as constants. It is possible.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to stably control the dissolved oxygen concentration in the aeration tank while suppressing the frequency of operation and stop of the blower, and to control the blower discharge pressure so that unnecessary pressure loss does not occur. An extremely reliable dissolved oxygen concentration control device that can save energy can be provided.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the dissolved oxygen concentration control device according to the present invention applied to an activated sludge treatment process, and FIG. 2 is a diagram for explaining the action of the air volume control valve in the embodiment. FIG. 3 is a diagram showing a fuzzy rule table which is an example of the discharge pressure target value inference device in the same embodiment, and FIGS. 4 and 5 are examples of fuzzy division of the input/output variable space by membership functions in the same embodiment. FIG. 6 is a diagram showing an example of a determination table for determining whether to increase or decrease the blower, and FIG. 7 is a block diagram showing an example of the configuration of a conventional dissolved oxygen concentration control device. 1... Aeration tank, 2... Blower, 3... Suction valve, 4
...Discharge pressure gauge, 5...Air volume control valve, 6...Air flow meter, 7...DO meter, 8...Do regulator, 9...Air volume regulator, 10...Discharge pressure Controller, 11... Number controller, 12... Dissolved oxygen concentration control device, 13... Suction valve control section, 14... Number control section, 15... Air volume control valve control section, 16. ... pO adjustment section, 17 ... required air volume calculation section, 18 ... flow meter, 19 ... thermometer, 20
. . . Number increase/decrease determination unit, 21 . . . Discharge pressure target value device, 22 . a Patent attorney Patent attorney Takehiko Suzue Air volume control valve closing degree ψ Fig. 4-0,2 α2 0.4 0.6 Fig. 5 0.8 1.0 1.2 Determination by required air volume

Claims (2)

[Claims] (1) A dissolved oxygen concentration control device that controls the dissolved oxygen concentration in the aeration tank to a target value by controlling the amount of aeration air to at least one aeration tank in an activated sludge treatment process, comprising: Based on the valve opening degree of the air volume control valve that adjusts the air volume, the air volume target value, and the aeration air volume output from the air flow meter that detects the aeration air volume to the aeration tank, the blower discharge pressure target value is determined by fuzzy reasoning. discharge pressure target value inference means for inferring the discharge pressure target value, the blower discharge pressure target value inferred by the discharge pressure target value inference means, the valve opening degree of the suction valve that adjusts the discharge pressure of the blower, and the measurement of the discharge pressure of the blower. A dissolved oxygen concentration control device comprising: suction valve control means for controlling the valve opening degree of the suction valve by calculating a valve opening degree target value of the suction valve based on the value. (2) A dissolved oxygen concentration control device that controls the dissolved oxygen concentration in the aeration tank to a target value by controlling the amount of aeration air to at least one aeration tank in the activated sludge treatment process, comprising: a device installed in the aeration tank; Dissolved oxygen concentration outputted from a dissolved oxygen concentration meter, a thermometer, an airflow meter that measures the amount of aeration air supplied to the aeration tank, and a flowmeter that measures the flow rate of sewage flowing into the aeration tank, and the tank a required air volume calculation means that calculates the required aeration air volume according to a predetermined calculation formula based on the internal temperature, the aeration air volume, and the sewage flow rate; and the dissolved oxygen concentration output from the dissolved oxygen concentration meter, and a preset target dissolved oxygen concentration. Based on oxygen concentration and
a concentration adjusting means for calculating an aeration air volume target value in the aeration tank; and a concentration adjusting means for calculating an aeration air volume target value in the aeration tank; a number increase/decrease determination means for determining whether to increase or decrease the number of fans; and a number control means for controlling operation or stop of the blower based on a determination result by the number increase/decrease determination means. Dissolved oxygen concentration control device.