JPS58216786A - Method for controlling inflow rate of gas for aeration in sewage treatment - Google Patents

Abstract

PURPOSE:To make setting of control elements easy by selecting required air quantities stepwise, and determining the set quantities of control elements beforehand with respect to the pattern combining the selected air quantities. CONSTITUTION:In the stage of operation, process states are detected with dissolved oxygen meters 13A, 13B and sewage flowmeters 17A, 17B at every suitable period, and the set air quantities Qa, Qb in accordance with the required air quantities in said states, are calculated with flow rate processing units 16A, 16B and outputted. A centralized control device 18 receives said quantities, and selects the corresponding pattern from the patterns which are made beforehand by selecting various values of required air quantities stepwise and combining the same. the flow rate control valves 7A, 7B for the larger set air quantities are fully opened by the output thereof, and the other is regulated with an air quantity ratio Qa/Qb. In the case of throttling the air quantity, the process is so controlled that the operation for the control mechanism for the flow rate of blower is made preferential.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling the amount of aeration gas sent to one or more aeration tanks using one or more blowers.

A conventional example of a device using this type of control method is shown in FIG. Here, IA and IB are aeration tanks, and sewage water as treated water is supplied from sewage ports 2A and 2B. In order to supply aeration gas (oxygen or air) to the membrane tanks IA and IB, a plurality of blowers 3A and 3B (two in the figure) are used.
Its discharge side is connected to one collecting pipe 4. Pro 9
3k.

Suction valves 5A and 5B are provided on the suction side of valve 5B for between the blower discharge pressure and electric control. Multiple pipes from collecting pipe 4 (
2) branch pipes 6A and 6B are branched to form aeration tanks IA and IB.
is connected to. Branch pipe 6A.

6B includes flow rate control valves 7A, 7B as an inlet flow rate control mechanism for controlling the flow rate of inlet gas, and air flow meters 8A, 8B.
is provided.

Regarding control, the blower flow control mechanism compares the set value from the pressure gauge 9 and pressure setting device 10 that detects the pressure in the collecting pipe 4 with the detected value from the pressure gauge 9, and adjusts the blower according to the deviation. A pressure regulator 11 is provided which controls the flow rate of the blower by adjusting the opening degrees of suction valves 5A and 5B, which are one element of flow rate control, and keeps the pressure of the collecting pipe 4 constant. Regarding the inlet flow rate control mechanism, the detected values of the airflow meters 8A and 8B are compared with the set values, and the opening degrees of the flow rate control valves 7A and 7B, which are inlet flow rate control elements, are adjusted based on the deviation, thereby controlling the inlet flow rate. Flow rate controllers 12A and 12B are provided to maintain the set value.
Furthermore, dissolved oxygen meters 13A and 15B that detect the amount of dissolved oxygen in the sewage in the aeration tanks IA and IB, and a dissolved oxygen amount setting device 14
The set values from A and 14B are compared with the detected values from dissolved oxygen meters 15A and 15B, and based on the deviation, the flow rate controller 1
Dissolved oxygen amount controllers 15A and 15B are provided to change and adjust the flow rate setting values given to 2A and 12B and perform cascade control.

In this way, the branch path 6A of each aeration tank IA, IB.

An individual inlet flow rate control loop is provided for each of the aeration tanks IA and IB, and these control loops control the amount of air so that the required air volume is obtained for each of the aeration tanks IA and IB. On the other hand, the pressure in the collecting pipe 4 is controlled at a constant level to maintain a slightly higher pressure so that each inlet flow rate control group can independently control the flow rate without mutual interference.

If this constant pressure control is not performed, the pressure inside the collecting pipe 4 will change depending on the opening degree of the seven flow control valves in the branch pipe 6A system, so if the opening degree of the flow control valve 7B is the same, the branch pipe The flow rate of the 6B system will change. Therefore, when the flow rate control valve 7B is adjusted, the flow rate fed into the branch pipe 6A system changes due to a similar phenomenon. In this way, due to mutual interference, the inlet flow rate control loop is not stabilized, and each flow rate control valve 7A, 7
B has the drawback of repeating the opening operation and becoming unstable.

Therefore, in order to stabilize the control, the internal pressure of the collecting pipe 4 must be maintained at a constant high pressure during operation.

As a result, in order to obtain the required air volume, the flow rate control valve 7A is used.

7B must be used to throttle the flow rate. This aperture is Prowa 3A
, when viewed from the 3B side, it has the disadvantage of wasting unnecessary blower power as it acts as a discharge-side throttle.

However, in order to eliminate the disadvantage of levers, the process state is detected, the required air volume is calculated accordingly, and the blower flow rate control mechanism and feed flow rate control mechanism are appropriately controlled (financed) according to the calculated air volume. ), but determining all the side element setting values for a continuous range of required air volume requires complex calculations and many confirmation experiments, which is time-consuming.

The present invention improves this by selecting the necessary air volume in stages and combining them (pre-control f for turns).
It is an object of the present invention to provide a method for controlling the amount of gas fed for sewage treatment aeration in which it is extremely easy to determine the set value by determining the set amount of the Kl cost element.

The present invention includes one or more blowers and one or more aeration tanks, the discharge side of the blower is connected to a collecting pipe, and the aeration tank is connected to a branch pipe branched from the collecting pipe. , configured to feed aeration gas to the aeration tank, the branch pipe is provided with a feed flow rate control mechanism for controlling the flow rate of the feed gas, and the blower is provided with a blower flow rate control mechanism. In a method for controlling the amount of gas fed for sewage treatment aeration in an aeration system for sewage treatment, the required air volume of each aeration tank is selected in stages, combinations of the required air volume stages of each aeration tank are created in advance, and each combination is The set amounts of the control elements for the feed flow rate control and the set amounts of the control elements for the blower flow rate control, which are correspondingly calculated in advance, are stored as patterns in the integrated control mechanism, and the stored patterns are stored in accordance with the treatment process state. This is a method for controlling the amount of gas fed in for sewage treatment aeration, characterized in that the amount of gas fed in for sewage treatment aeration is controlled by the output of the selected pattern.

Embodiments of the present invention will be described using the drawings. In FIG. 2, parts with the same reference numerals as in FIG. 1 have the same structure and function. In this embodiment, there is no inlet flow rate control loop for each branch pipe 6A6B system, and no blower discharge pressure constant control mechanism for keeping the internal pressure of the collecting pipe 4 constant is used. There may be a plurality of collecting pipes 4.

Reference numerals 16A and 16B are set air volume calculators, which detect the detected amount of sewage inflow from sewage flow meters 17A and 17B that detect the amount of sewage inflow, and the dissolved oxygen t from dissolved oxygen meters 15A and 15B.
Based on one or both of the detected values (hereinafter referred to as DO value), the required airflow 1tQa and Qb in that state is calculated and output as a set air volume, and the central control device 1
Send to 8.

In the central control device 18, the required winds tQa and Q are determined in advance.
The various values of b are set in stages as shown in FIG. 3, and the combinations thereof are patterned as shown in FIG. The value of the manipulated variable for adjusting the valve opening degree and the value of the manipulated variable for adjusting the blower flow rate control element of the blower flow rate control mechanism are calculated and stored for each pattern. The blower flow rate control mechanism includes suction valves 5A, 5B, blower inlet vanes, or diffuser vanes (their opening degrees as blower flow rate control elements), or blower 3A,
5B rotation speed control mechanism (blower rotation speed as a blower flow rate control element), blower 5A.

A control system other than the blower discharge side control, such as 3B's number-side mechanism (the number of blowers is the blower flow control element), is selected and applied alone or in combination.

The amount of operation stored in the central control mechanism 18 is such that the opening degree of the flow control valves 7A and 7B is kept as open as possible, that is, at least one is always fully open (not necessarily mechanically fully open). , meaning the maximum opening degree for normal use), and when reducing the air volume, prioritize the operation of the blower flow rate control mechanism.

During operation, dissolved oxygen meters 15A and 15B and sewage flow meter 1 are used to detect process conditions at appropriate control intervals.
7A, 17B, and set air volume Qa, Qb based on the required air volume in that state. Air volume calculators 16A, 1
6B calculates and outputs.

In response to this, the central control device 18 selects the corresponding pattern from the patterns shown in FIG. 4, and depending on its output, the opening degree of the flow control valve 7 or 7B with the larger set air volume is fully opened, and the opening degree of the other one is The distribution ratio is determined according to the landscape ratio Q a /Q b , and Qa+Qb can be obtained by controlling the flow rate by the action between the blower flow rates.

Therefore, the required air volume of the branch pipes 6A and 6B can be stably obtained without mutual interference, and since the flow rate control valve 7B is opened as wide as possible, there is no loss of power. few.

To give an example of the operation of the set air volume calculators 16A and 16B, the deviation between the actual DO value and its set value is calculated by adding, for example, the value outputted by the proportional-to-integral operation and the value obtained by multiplying the sewage inflow amount by a constant. The value is calculated and output as the setting Kf. At this time, the calculation may be performed by adding a dead time element to the sewage inflow amount. As another example, a method of predictive control based on a model of the reaction process of sewage treatment in the aeration tank based on the current actual DO value, sewage inflow amount, and IN pupil may be used.

To explain the stepwise pattern, the set air volume is determined in stages as shown in Figure 3 in approximately proportion to the amount of sewage inflow, and the set air volume is determined in stages according to the actual amount of sewage inflow based on Figure 3. decide. Furthermore, the actual I)0 value and the set value of DO are compared, and the stage of the set air volume determined from the amount of sewage inflow is corrected according to the deviation of the DO value.

In other words, if the actual DO value is smaller than the set value of Do, the set air volume level is revised to a higher air volume level, and if the actual DO value is greater than the set value of Do, the set air volume level is adjusted to a smaller air volume level. Correct it to In the figure, ■ to ■ indicate the stages of the set air volume.The number of stages is arbitrary, but it is about 3 to 10 stages.The control cycle is set after a period of time has elapsed until the effect of the air volume control performed at a certain time becomes fully visible. The control cycle is determined to perform the next air volume control.

This control period may be fixed, but if it is made variable according to the rate of change in the set air volume, even better quality treated sewage can be obtained.

The setting air volume calculators 16A and 16B are normally used in the aeration tank IA of the pot.
, shall be provided for each IB. However, if the calculation of the set air volume for either one can represent the set air volume for the other, it is sufficient to provide a set air volume calculator for either one.

The memory content in the central controller Ifs18 is each set air volume Q.
Although it is possible to store an analog value such that the manipulated variable corresponding to a Qb is output continuously, the set air volume Qa and Qb can be divided into stages (7 stages in this example) as shown in Fig. 4. It is also possible to memorize a pattern in which set values such as the opening of the flow control valves 7A, 7B, the number of blowers 5A, 5B, the opening of the suction valves 5A, 5B, etc. are determined for each combination. good. For example, for a pattern such as Q8:6, Qb=1, the number of blowers is 1, the opening degree of flow control valve 7A is 100cm, the opening degree of 7B is 50qb, the opening degree of suction valve 5A is 95cm, It is determined as follows.

In the above explanation, there are two aeration tanks IA and IB, blower 5A,
Although 3B has two units, it may be one unit or a plurality of three or more units.

Even if the temperature of the air being blown changes, if the air volume control opening and inlet vane opening remain the same, the density of the air will change,
The blower drive electric motor may be overloaded. Therefore, to prevent this, the temperature is detected and the air volume stages in the pattern are corrected.

ADVANTAGE OF THE INVENTION According to the present invention, it is possible to provide a method for controlling the amount of gas injected for sewage aeration, which makes it easy to set control elements and can be performed extremely easily, especially when changing set values, and has extremely great practical effects. It is something.

While the conventional system prevents mutual interference by applying constant wind pressure control in the collecting pipe, the present invention can eliminate mutual interference without constant wind pressure control. Therefore, the opening degree of the flow rate control valve is increased to reduce the pressure loss due to the throttle on the discharge side of the blower, thereby saving energy.

[Brief explanation of drawings]

Fig. 1 is a flowchart of the conventional example, Fig. 2 is a flowchart of the embodiment of the present invention, Fig. 3 is a graph showing the stepwise setting of the set air volume, and Fig. 4 is a graph showing the combination pattern of the two set air volume. It is a graph. IA, IB...Aeration tank, 2A, 2B...Sewage inlet,
3A'1-6B... Prower, 4... Collecting pipe, 5A,
5B... Suction valve, 6A, 6B... Branch pipe, 7A,
7B...Flow rate control valve, 8A, 8B...Air flow meter, 9
...Pressure gauge, 10...Pressure setting device, 11...Pressure regulator, 12A, 12B...Flow regulator, 13A, 1
5B...Dissolved oxygen meter, 14A. 14B...Dissolved oxygen amount setting device, 15A, 15B...
Dissolved oxygen f controller, 16A, 16B... Setting air volume calculator, 17A, 17B... Sewage flow cap meter, 18... Central control device. Patent applicant: Ebara Corporation

Claims (1)

[Claims] t. One or more blowers and one or more aeration tanks, the discharge side of the blower is connected to a collecting pipe, and the aeration tank is a branch pipe branched from the collecting pipe. connected to the aeration tank to supply aeration gas to the aeration tank,
The branch pipe is provided with an inlet flow rate control mechanism for controlling the flow rate of the inlet gas, and the blower is provided with a blower flow rate control mechanism for supplying gas for sewage treatment aeration in an aeration system for sewage treatment. In the volume control method, the required air volume of each aeration tank is selected in stages, combinations of the required air volume stages of each aeration tank are created in advance, and control elements on the feed flow rate side calculated in advance corresponding to each combination are selected. The set amount and the set amount of the control element of the blower flow lid control are stored in the integrated control mechanism as a putter, and the stored pattern is selected according to the treatment process state, and the feed amount is controlled by the output of the pattern. A method for controlling the amount of gas fed in for sewage treatment aeration.