JPH01304099A - Air flow amount controlling method for aeration tank - Google Patents

Abstract

PURPOSE:To prevent an incorrect control of an aeration tank at a sewage treatment plant, by optimizing a control ratio of a predetermined DO control to flow amount ratio control and effecting switchover to a flow amount ratio control in the case of control failure. CONSTITUTION:A PID controller 10 in a predetermined DO(dissolved oxygen) controlling apparatus D generates a control signal according to the difference between a detection signal from a DO meter 4 and a predetermined value SV. A ratio setting device 9 in a flow amount ratio control apparatus B generates the signal obtained by multiplying the amount of inflowing sewage by a predetermined ratio, a control ration alpha of the predetermined DO control and the flow amount ration control is set in multiplying devices 11 and 13 and an adding device 12, a control signal is sent to a PID controller 7 in response to this control ratio alpha, and the amount of air being sent to an aeration tank 2 is controlled by a control valve 5 and blower 3. In the case of control failure, a switch SW2 is turned off for automatic switchover to the actual control by an inflow amount ratio control apparatus B, whereby the possibility of continued incorrect control can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling the air volume of an aeration tank in a sewage treatment plant or the like.

[Conventional technology]

Fig. 4 is a block diagram showing the control system of the conventional method for controlling the air volume of an aeration tank.
3 indicates the aeration tank, 3 indicates the blower, and 4 indicates the dissolved oxygen concentration (referred to as DO). An amount of air corresponding to the opening degree of the suction valve 5 is blown into the sewage water in the aeration tank 2 by the blower 3 through the blast pipe 1, and as a result, the dissolved oxygen concentration in the sewage water in the aeration tank 2,
That is, the DO value is measured as DOO12.

The opening degree control of the blow valve 5 is selectively performed by three systems: an aeration air volume constant control system Δ, an inflow rate ratio control system B, and a DO constant control system C.

Is the aeration air volume constant? In the 1'l system A, when the changeover switch SW is closed, the air volume setting value (usually the total aeration air volume) is input to the distributor 6, and is distributed to each aeration tank (only one is shown in the drawing) 2. , and outputs its output to the PID controller 7. PAD system? 111t7 outputs the output necessary to make this detected value match the distribution value to the suction valve 5 based on this distribution value and the detection value detected by the wind star meter 8 arranged in the air pipe 1, and Adjust the opening.

In addition, when the changeover switch SW2 is closed, the inflow ratio control system B inputs a value obtained by multiplying the inflow sewage amount by a coefficient to the distributor 6 using the ratio setting device 9, and adjusts the opening of the suction valve 5 in the same manner as in the above process. I do.

Further, the Do constant control system C is selected by closing the changeover switch SW3. The measured value Pv of Do total 4 is PID
It is input to the controller 10. The PID controller 10 outputs to the multiplier 11 a manipulation output MV necessary to match the measured value pv with the DO setting value S color, based on the measured value pv and the DO setting value S color set in advance. Multiplication 2g t 1
outputs a value obtained by multiplying the operation output MV by a preset ratio α to the adder 12. A value obtained by multiplying the output of the ratio setter 9 by (1-α) is input to this adder 12 from a multiplier 13, and the value obtained by adding both is output to the distributor 6, and the same as described above is performed. The opening degree of the suction valve 5 is adjusted accordingly.

Note that the ratio α here is D for the inflow ratio control n system B.
O is the control ratio of constant control rate.

[Problem to be solved by the invention]

By the way, in the conventional method as described above, during control by the commonly used Do constant control system C, for example, DOO12
When a failure occurs or during maintenance of the DO meter 4 system, control cannot be performed using the Do constant control system C, so it is necessary to switch to another inflow ratio control system such as B, but operation continues without knowing that the failure has occurred. In addition to causing inconvenience such as
The ratio α used for constant DO control has to be determined and set based on actual driving conditions, which poses problems such as cumbersomeness.

The present invention has been made in view of the above circumstances, and its purpose is to perform ratio-following constant DO control that combines inflow ratio control and constant DO control, and to automatically perform automatic control when an unfavorable control situation occurs. An object of the present invention is to provide an air volume control method for an aeration tank that can switch to inflow ratio control automatically.

[Means to solve the problem]

The air volume control method for an aeration tank according to the present invention includes:
00-constant control that controls the blowing air volume to maintain a constant DO value in the sewage in the aeration tank, as opposed to inflow rate ratio control that controls the blowing air volume according to the amount of sewage flowing into the aeration tank. The ratio is variable,
A process in which the control ratio is sequentially changed while a predetermined control condition is satisfied, and when the control condition is no longer satisfied, the control ratio is changed to the inflow ratio control. This includes the process of controlling the

[Effect]

According to the present invention, the optimal ratio between flow ratio control n and DO constant control can be automatically determined, and when a control problem occurs, it can be automatically switched to flow ratio control. Become.

〔Example〕

The present invention will be specifically described below based on drawings showing embodiments thereof. FIG. 1 is a block diagram showing a control system for controlling the air volume of an aeration tank according to the present invention.
is the air pipe, 2 is the aeration tank, 3 is the blower, 4
is a dissolved oxygen concentration meter (hereinafter referred to as a DO meter), 5 is a suction valve,
6 is a distributor, 7 is a PID controller, and 8 is an airflow meter.

A blower 3 is connected to the aeration tank 2 through the air pipe 1.
An amount of air corresponding to the opening degree of the suction valve 5 is blown in, and the resulting dissolved oxygen concentration in the sewage in the aeration tank 2 is measured by the DOO 12.

The opening degree control of the suction valve 5 is selectively performed by the aeration air volume constant control system A, the inflow rate ratio control system B, and the ratio follow-up Do constant control system. The aeration air volume constant control system A and the inflow ratio control system B are substantially the same as the conventional method.

That is, the aeration air volume constant control system A is a changeover switch SW.

When closed, the air volume set value, which is the total aeration flow, is input to the distributor 6, and distributed to each aeration tank (only one tank is shown in the drawing) 2, and the distribution value is the PID.
It is output to the controller 7.

Based on the distribution value and the detected value of the air flow meter 8 attached to the blower pipe 1, the PID controller 7 outputs to the suction valve 5 the output necessary to make the detected value match the distribution value, and adjusts the opening of the suction valve 5. I do.

In addition, in the inflow ratio control system B, when the changeover switch SW2 is closed, a value obtained by multiplying the inflow sewage amount by a coefficient is inputted to the distributor 6 by the ratio setting device 9, and in the same process as described above, the value obtained by multiplying the inflow sewage amount by a coefficient is inputted to the
The opening degree is adjusted.

In the ratio follow-up DO constant control system, the changeover switch SW3 is used when the control ratio α is in the fixed mode, and the changeover switch SW is used when the control ratio α is in the variable mode.

are selectively closed, respectively, as follows.

First, the DOO12 measurement value pv is input to the PID controller IO. The PID controller 10 multiplies the operation output Hν required to match the measured value pv with the DO setting value S color based on the measured value Pv and the predetermined DO setting value S color.
Output to 1. The multiplier 11 multiplies the manipulated output MV by the ratio α when the ratio α is set to the fixed mode, that is, when the switch S is closed, and multiplies the value obtained by multiplying the ratio α by the ratio α when the ratio α is set to the variable mode. In other words, when the switch S2 is closed, a value obtained by multiplying the operation output MV by the ratio α that changes from time to time is output to the adder 12.

The adder 12 receives a value obtained by multiplying the output of the ratio setter 9 by 1-α from another multiplier 13 when the ratio α is set to the fixed mode, that is, when the switch S1 is closed. , when the ratio α is set to variable mode, that is, when the switch S2 is closed, a value multiplied by 1-α that changes from time to time is input.

The adder 12 adds the two together and outputs the result to the distributor 6, and adjusts the opening of the suction valve 5 in the same manner as in the other control systems A and B.

When the ratio α is in the fixed mode, the control content is substantially the same as that of the Do constant control system C in the conventional method.

- When the force ratio α is in the variable mode, the setting of the ratio α is performed in the following process. First, the subtracter 14 calculates the measured value p of the DOO12.
v and the DO setting value S color for the PID controller 10 are taken in, the deviation EV (=SV-PV) is calculated, and this is output to the comparator 15. Comparator 15 calculates this deviation EV
is compared with a deviation limit value IEvH1 that has been set and input in advance, and if the conditions of formulas (11 and (21) below are satisfied, a predetermined signal is output.

Ev≧l EV)l I・(11 EV≧l EVHl −(21) Also, the operation output MV of the PID controller 10 is taken into the comparator 16.17, and the comparator 16 inputs it to the preset upper limit. The comparator 17 compares the value MvH with the preset lower limit value MvL, and calculates the following (3+, 441
When 2 is established, respective predetermined signals are output.

MV≧MVH−(3) MV≦gate vL (4) (When formulas 11 to (4) hold true, the deviation EV,
This indicates that the manipulated output MV is in an unfavorable situation for control.

Based on the signals of these comparators 15, 16, and 17, the ratio α is set according to the algorithm shown in FIGS.

(Algorithm for changing ratio α) Figure 2 is an explanatory diagram showing the algorithm for automatically setting ratio α, and the conditions of equations (1) and (3), (2) and (4)
When none of the conditions in the equation are satisfied, in other words, when the system is in a normal state with no unfavorable conditions occurring, both AND circuits 2L22 output low-level signals, and therefore The timers T, , T, do not reach the operating state, and the OR circuit 23 outputs (11,
When at least one of the conditions of equation f3), (2+, and (4) 2) is not satisfied, a low level signal is output, and the NOT circuit 24 outputs a high level signal.

As a result, when the ratio α is set to α1 as the initial value, it is changed to α2 (−α1 +Δα),
Thereafter, α3. α4...” is automatically changed up to n (maximum value).

The order of changing the setting of the ratio α is from α1 to α described above. Instead of changing sequentially until α1
．． α. , α2. It goes without saying that the values may be changed in such a manner that they converge to a predetermined value, such as α, -1, . . . .

On the other hand, if the conditions of equations fl) to (4) are satisfied from the beginning or are satisfied in the middle, in other words, if a problem occurs in control, the information is not shown in FIG. 2 from the NOT circuit 24. , a low level signal will be output, and the ratio α
is not changed, and the ratio α is set according to the algorithm shown in FIG.

(Algorithm when α=0) (11. When the equations (2), (2), and (4) are satisfied, a high-level signal is output from the AND circuits 31 and 32, and the timer T□ , TJ are both in operation, and when each time limit is reached, a signal is output to the OR circuit 33.

The OR circuit 33 connects at least one timer T3 or T4.
When a signal is emitted from, a high level signal is output,
First, set the currently set ratio α value, for example, α,
Then, this value is stored in a storage device (not shown) and the ratio α is set to zero.

As a result, the selector switch S6 is closed, and in FIG. Equal outputs are output to the distributor 6, and control is essentially automatically switched to control by the inflow ratio control system B.

After that, the failure is repaired and (11, (31 formula, (21, (
A state in which both formulas 41 and 41 do not hold, that is, a return to the normal state,
The signals from AND circuits 31 and 32 become low level,
When the timers T, , T4 become inoperable, each 807
High level signals are output from the circuits 34 and 35.

As a result, a high-level signal is output from the ND circuit 36, and the timer T enters the operating state, and the normal state continues for a certain period of time. When the time limit is reached, the value α of the ratio α stored in advance is called. This value α, is the previous value α1−
1 (=α, -Δα), and thereafter returns to the control state before the failure occurred.

〔effect〕

As described above, in the method of the present invention, D
〇 Appropriate control is easily possible because the control ratio α of constant control is automatically updated sequentially, and when an inconvenience occurs in the control state, it can be automatically switched to inflow rate ratio control to prevent inappropriate control. The present invention has excellent effects, such as being able to eliminate the inconvenience of continuing the process.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the control system used in the method of the present invention, Figs. 2 and 3 are explanatory diagrams showing the setting line for the ratio α, and Fig. 4 is a block diagram showing the control system of the conventional method. . ■...Air pipe 2...Aeration tank 3...
・Blower 4...DO meter 5...Suction valve 6...
Distributor 7... PID controller 8... Air flow meter 9...
・Ratio setter 10... PID controller 11... Multiplier 12... Adder 13... Multiplier 14...'
/Ii calculator 15.16.17... Comparator In the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In contrast to inflow rate ratio control, which controls the blowing air volume according to the amount of sewage flowing into the aeration tank, DO constant control controls the blowing air volume to maintain a constant DO value in the sewage in the aeration tank. A step of making the control ratio variable and sequentially changing the control ratio while a predetermined control condition is satisfied, and setting the control ratio to zero when the control condition is no longer satisfied, 1. A method for controlling air volume of an aeration tank, comprising the step of performing control by switching to inflow ratio control.