JPS60125297A - Method for controlling concentration of dissolved oxygen of aeration tank - Google Patents

Abstract

PURPOSE:To rationalize the concn. of dissolved oxygen of an aeration tank, by mounting a parameter determinging operator for determining the parameter of a control system to a linear dissolved oxygen concn. model corresponding to a preset control response characteristic. CONSTITUTION:A dissolved oxygen concn. detector 4 and a thermometer 5 are provided in an aeration tank 1 and an airflow meter 6 is provided to the air blowing pipe in an emitting side. Process amounts x, theta, u detected by these meters are inputted to an electronic calculator 8 through an input apparatus 7 and operation is performed according to a preliminarily mounted program and an air blowing objective value u* is calculated to be outputted as the operation input signal of a blower through an output apparatus 9. The number control order N* of the blower 2 is outputted to a control apparatus and the opening degree order alphaA* of a suction valve 13 to an opening degree control apparatus 11 while the opening degree order alphaB* of an aeration air amount valve 14 to an opening degree control apparatus 12 to control an air blowing amount (u).

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention uses an electronic meter to measure dissolved oxygen concentration in an aeration tank in a wastewater geological process using activated sludge. This relates to method 4 of controlling the target value using the L machine.

[Technical background of the invention and its problems]

In the activated sludge treatment process, the pollutants in the polluted water that flow into the aeration tank after undergoing treatment processes such as sedimentation are decomposed by activated sludge C = which contains aerobic microorganisms in the aeration tank, forming flocs that are easy to settle. do.

The polluted water that has gone through the process in the aeration tank is further processed through the C2 precipitation process (2). A part of the sediment is collected and returned to the aeration tank as dirty sludge (2). sludge is discharged as surplus sludge.

In such an activated sludge treatment process, it is essential to control the dissolved oxygen concentration in the aeration tank. This will lead to a decrease in the efficiency of the process, and if the concentration of dissolved elements in the sludge decreases excessively, it will lead to a decrease in treatment efficiency and an adverse effect on the sludge itself.

For this reason, each treatment plant determines the allowable range of dissolved oxygen concentration based on its own experience, and operates accordingly.

In other words, the target value of the dissolved oxygen concentration set in advance is compared with the detected value detected by the dissolved oxygen concentration detector, and based on the comparison result, the amount of air supplied to the aeration tank, that is, the blower lid is controlled by 1bu. A method is used to control the dissolved oxygen concentration in the aeration tank.

General (- between air flow rate U and dissolved oxygen concentration
1) Find out the relationship between the equations.

1'-=f (u, x(θhaJCI Rr + a
+ n) (1) t Here 42X: Dissolved oxygen concentration in the aeration tank (ppm) U: Air flow rate [mh,)
m) Rr: Oxygen consumption rate (ppm/h) a, n It is a constant specific to the nibrant.

“The above dissolved oxygen concentration

That is, the time change in the dissolved oxygen concentration X is determined by the linear relationship shown in the equation (zl) (2) between the ventilation mu, which is the manipulated variable, and the dissolved oxygen concentration X, which is the controlled variable.

Such a dissolved tR concentration! (On the other hand, conventionally, the deviation, integral, and differential between the target value and the detected value are multiplied by a constant #X, and the sum is the linear proportional integral differential (
PID) control is used, and the dlIlli11 constant is treated as a fixed foot.

However, in reality, as expressed by equation (1), the C object is nonlinear, so it is impossible to obtain a normal and desirable td11 response using the conventional linear control described above.

[Purpose of the invention]

The present invention adjusts control parameters in consideration of the non-linear relationship between air flow rate and dissolved oxygen concentration, and thereby obtains an appropriate control response. The purpose is to provide a degree control method.

[Summary of the invention]

The present invention detects the dissolved oxygen concentration in the aeration tank in the activated sludge treatment process (two steps), compares it with the set target value for the conserved oxygen concentration, and controls the air blowing lid to the aeration tank according to the deviation. Dissolved oxygen concentration in the tank sub-method 42 includes a linear model determination calculation that calculates a linear dissolved oxygen concentration model from the current air flow rate and time changes in dissolved oxygen concentration, and a preset control response characteristic (depending on the The above linear dissolved oxygen concentration model (2) is equipped with a parameter determination calculation for determining the parameters of the control system, and the amount of air blown to the aeration tank is controlled using the i!ill Il system with the above parameters (-, 11j adjusted). Therefore, regardless of the nonlinear characteristics between the air flow rate and the dissolved #concentration rate, this is always done in order to obtain an appropriate control response.

[Embodiments of the invention]

One Embodiment of the Invention - Figure 1 (2).

In FIG. 1, polluted water flows into the aeration tank 14 and after a certain residence time (flows out).

During this time, the air blown by +IA2 (= the air blown from the diffuser pipe 3
Polluted water (=supplied through

- Air [1 (== is provided with a dissolved T11t elementary concentration detector 4 and a temperature 1tt5, and further 6: an air volume meter 6 is provided in the air pipe on the discharge side of the blower.

The process quantities X and θ detected by these ζ2.

U uses the input device 7 to input 4 children It calculation 8 (two people input,
Calculations are performed according to the pre-built-in program, and the air flow target value U* is calculated, and the output device 9t
- is outputted as an operation input signal for sending A+1A.

In other words, the number of air blowers dA2 -- the command N is the number control device #L
To 1O, once control command α of the suction valve 13 of the blower is to open the suction valve 1I419It Directly to 11, the aeration installed at the aeration tank entrance of the blow pipe] A command to open and close both valves 14 * αB are respectively outputted to the control device 12 as the aeration air volume and the control valve, and the blower lid U is thereby controlled.

The following describes the program incorporated in #llE:P Jl*8.

The program is broadly divided into two parts: the first is a program for linearization within the minute changes in the nonlinear model expressed by the equation (1), and WI2 is for controlling from the characteristic values of the model obtained. This is a grogram that determines the parameters.

Dissolve first! How to linearize the cumulative concentration model J@t-Explain.

As shown in the equation (1) above, the air flow fiu and dissolved #lt
Since it has a nonlinear relationship with the yield rate X, in order to apply the classical control theory (2), linearization is necessary.

Now, if the acid range of + control is 42 around the equilibrium point, then the following equation holds true.

x- 1-f(uo, x(su+ xo I Rro la
+ n ) ” 0 (2) t ΔX: Deviation from the dissolved oxygen concentration when the process was at a certain equilibrium point (ppm) uo: Air flow rate when the process was at a certain equilibrium point -
7 o'clock] ΔU: Deviation from the air flow rate when the process is at a certain equilibrium point (26) R, o: Oxygen consumption rate (pI) m/hour when the process is at a certain equilibrium point] ΔR2 : Equilibrium point 1 of the process: Deviation from the oxygen consumption rate (ppm/hour) 9, other symbols are the same as in equation (1).

By ignoring the terms ΔU and ΔX in Equation (3) (2) and substituting Equation (2), Equation (4J) is obtained.

Watari discharge = -1・ΔX + K2' Δll−ΔRr
t4)t However, Ks = Ks (uow a + n) L5)Ks
= Ks (uoe x(Lee X., a, n) (6
1 Therefore, the model is a first-order lag system that experiences disturbances - 1
Ten T.

The gain and time constant aT of the -order lag system are given by the following equations (7) and (8).

K ” K5/′ to 1 = &+ (uo * x (
Li-x, ), a, n) (7) T= 1/Kt= l/
Kt (uo-a, n) (8) In the end, the amount of air blown uo (
mob ), Yakuza Shun J [degrees
Since T is a constant that is unique to the plant and can be set, T can be obtained as a characteristic value of the linear acid concentration model.

Next, a method for automatically adjusting the two I-P jt+lhl harammeters will be explained.

Figure 2 (in 2, 21 is the parameter determination mechanism, n is the aeration tank model, is the PI sub-control system, and ΔXr is the dissolved #R
The target value (ppm) of the deviation ΔX, k, fo is ■-P
IlIu1 wholesale parameter, S is a differential operator.

The system with is a thread with two conjugate complex hexagons and no zero point, and the closed loop transfer function is a four-hole.

Here, ωb(s): Closed-loop transfer function in Fig. 2 ωfl: Natural frequency ζ: Damping coefficient ζE 1-Kfo 2J kKT
Therefore, the conventional method of keeping the intersection frequency constant (: Yoshi control parameter, k.

It is impossible to obtain fo. Therefore, in the present invention, the following guidelines are newly established to make it possible to obtain a desirable response.

Policy 1: Make the damping constant ζ′ constant.

Policy 2: Step change in target value Δxr (2 responses, response overshoot time tp (time to peak
) is constant.

Prepare to realize these two policies.

The step response of the four-hole (closed-loop transfer function of the system) is 1. @
(t, ζ, ω.

What is 1p? Satisfy! 4 small tp-(tp>0).

Under this condition, if ul), u, etc. are solved simultaneously, fo will be found in the IP control parameter.

In other words, ω. =ωm(k, K, T) −(11')ζ=ζ(i
c, fo, K, T) (12') (= put,
The values of ζ and 1p are given by policies 1, 2 (2), and the characteristics T of the target process.

Since K is ・Q, the parameter k of the IP system.

fo is calculated by the following formula.

k = k (K, 'T, ζ, tp) (141f
o' = fo (K, T, ζ, tp) as In the end, the flowchart in Figure 3 (= algorithm as shown) (from the second, the I-P control parameters can be realized by realizing the above policy 1.2) ( -1 Automatic adjustment becomes possible.

In the above algorithm, I-P control (integral-proportional control) is adopted, but the effect can be further enhanced by adding two filters and reducing the noise of the process signal.

In addition to the method of controlling the suction valve of the blower and the method of adjusting the air flow in front of the aeration tank, there are also methods for controlling the blower's suction valve and controlling the blower's discharge valve. Furthermore, if the water temperature does not fluctuate greatly, keeping the saturated dissolved oxygen concentration constant is also an effective method for simplifying the algorithm.

〔Effect of the invention〕

As explained above, according to the present invention (2), a simple algorithm as shown in Figure 3 (Area 2) automatically adjusts the control parameters (2) in response to system fluctuations, and always maintains a desired control response of a degree of dissolved oxygen. As can be obtained (two can be obtained.

The simplicity of the algorithm means that it is highly practical, and the ability to automatically adjust control parameters reduces product test and adjustment time and further improves efficiency.
Obtaining the desired response at all times is effective in eliminating unnecessary or wasteful air blowing, which has a negative impact on the quality of treated water, and in reducing the operation of blowers, which account for the majority of magnetic type blowers in sewage treatment plants.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention, FIG. FIG. 1 @ Air tank 2 Air blower 4 Dissolved oxygen installed detection meter s aL meter 6 Air flow meter 7 Human power device 8 Shoji meter Maiso 9 Output device 10 Number of units IBu control device 11 Suction valve opening degree control device 12 Air volume control valve opening degree i 'li control device 13, 1411
u @ valve 21 Parameter determination mechanism 22L4 gas tank model I-P system (8733) Agent Patent attorney Yoshiaki Inomata (Haga 1
name) Figure 1

Claims (1)

[Claims] Activated sludge treatment process (2) Detect the dissolved oxygen concentration in the aeration tank, compare it with the set target value for the concentration of dissolved oxygen in the bath, and control the air waves to the aeration tank according to the deviation C2 Dissolved oxygen concentration control method in an aeration tank Reinji uses a linear model determination calculation that calculates a linear dissolved oxygen concentration model from the current air flow rate and time changes in dissolved oxygen concentration, and a linear model determination operation that calculates a linear dissolved oxygen concentration model based on the preset control response characteristics 42. The self-linear dissolved oxygen concentration model (equipped with a parameter determination calculation that determines the control system parameters for
6. A method for controlling dissolved oxygen concentration in an aeration tank, comprising controlling the amount of air blown to the aeration tank using a control system.