JPS58122089A - Controlling system for air quantity in aeration tank - Google Patents

Abstract

PURPOSE:To supply optimum quantity of oxygen by providing a control loop for concn. of dissolved oxygen in an aeration tank and a control loop of the air quantity to be supplied into the aeration tank, and a selecting means which selects the smaller control output of either of said two control outputs. CONSTITUTION:The measured value D of a DO meter installed in an aeration tank 1 is subjected to PID operation so as to be made coincident with the set value S4 of DO given from the outside and an operated value M of air quantity is outputted. An upper and lower limit limiter 6 for air quantity limits an operated value K of air quantity within the range determined by an upper limit set value LL for air quantity and a lower limit set value LD for air quantity given from the outside and outputs the same as a set value S5 of air quantity. The value M outputted from a DO loop controller 5 is limited within the prescribed range consisting of an upper limit limiter 11 for air magnification constituted of a multiplier 9 and an upper limit limiter 10 for air quantity and the limiter 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air amount control device for an aeration tank (also referred to as an aeration tank) used when purifying sewage by the so-called activated sludge method in a sewage treatment plant or the like. In general, this type of control not only supplies the necessary oxygen to the activated sludge in the aeration tank, but also controls the amount of air to the minimum required from the perspective of energy conservation, and does not require frequent setting changes. It is desirable that the control be such that only

By the way, the purpose of the flash tank in the activated sludge process is
Activated sludge supplies the amount of oxygen necessary to biologically decompose the organic matter that flows in. In other words, by sending compressed air to the aeration tank and stirring it, oxygen in the air is dissolved. It is something that

However, it is necessary for activated sludge! 1! The cumulative i- is the water quality of the inflowing sewage, the water jlL- or the water temperature, and the activated sludge OS.
Therefore, as a simple and continuous measurement method to measure whether or not the oxygen or air required for activated sludge is being sufficiently supplied, the continuous meter 1114 is A possible indicator is the dissolved acid *C in the aeration tank, hereinafter abbreviated as simple KDO. ) #There is a degree.

That is, in general, excess or deficiency of the amount of oxygen or air - f
Since it appears as a change in iDO#, it can be considered that when the DO concentration is low, the air amount is insufficient and the amount of air is insufficient, and when the Do concentration is high, the air amount is excessive.

FIG. 1 is a block diagram showing such a general constant control method.

In the figure, 1 is an aeration tank, 2 is a flow meter that measures the flow rate of sewage flowing into the aeration tank, 3 is a control valve, 4 is an air flow needle, and 5 is a DO loop controller consisting of a PID @ moderator) E!
−? , s is above the air volume setting value.

The upper and lower air volume limits are determined by the air volume controller, 7 is an air volume loop controller consisting of a PID controller, and 8 is a DO meter. That is, the DO meter 8 is installed in the aeration tank, and the air amount set value S1 is determined by performing j9PID calculation using the controller c2-75 so that the measured value matches the set value 80.
This becomes the set value S2 of the air amount control loop via the air amount upper and lower limit j ivy 6. The air amount control loop controller 7 performs PID calculation so that the air amount measurement value F matches the set value S2, and closes the control valves 3t-#a. The air volume upper limiter (LU) prevents activated sludge flocs from collapsing due to excessive air flow, while the lower air volume limiter (LD
) Id ml is provided to maintain minimum stirring power.

However, this conventional method has the following drawbacks.

(1) Energy loss is large.

The reason is not clear, but when both the quality and quantity of inflowing sewage decrease, or when a DO measurement obstruction 'X' flows in, the DO measurement value drops significantly below the set value, causing the air volume to increase. (At the sewage treatment plant, this condition occurs almost every day from midnight until early morning.) In this case, with the conventional control device, if there is a positive deviation between the DO measurement value and the set value, the air amount will be adjusted to the upper limit setting value of the air amount upper limiter (see 6 in Figure 1). L of
(see U) increases at t and maintains its value. However, of this amount of air, the amount of air above a certain value is excess air, and therefore the blower that supplies the air wastes electricity. Considering that approximately 40% of this energy is consumed by the blower, and that this excess air wastes p energy, saving energy is a huge social benefit! This is a big drawback in these days when it is almost foggy.

f2) Special measures are required when maintaining the Do needle.

In general, regular maintenance is essential for the water quality needle.In the conventional method, while the DO meter is being maintained (once every few days), the signal is "0"] and the apparent DO measurement. Since the value is significantly lower than the set value, the control operation similar to that described in (1) will be performed, and power will be wasted. To avoid this, for example, special measures must be added to the control system to maintain the status quo during DO meter maintenance! occurs. This K requires some kind of logic circuit, but that circuit is not necessarily simple.

(3) ODO where it is difficult to back up when the Do needle is abnormal
If the needle becomes abnormal, DO control using that value becomes impossible, so in such a case, the power to the DO meter is usually cut off and inspection and repair are performed. During this time, the signal remains at "0", and the phenomenon is similar to (2). However, the backup method in this case is different from (2).

The reason for this is that missing measurements due to DO meter maintenance are short-lived but often occur for a long time, while missing measurements due to abnormal DO needles are less frequent but last for a long time. This is because the methods naturally need to be different.

In addition, as a backup method in case of DO meter abnormality, (a
Possible methods include preparing multiple Do meters, (C) providing separate backup loops, and (C) having the operator manually adjust the air volume in the event of an abnormality. On the other hand, as another method, the ratio R1 of the amount of air supplied to the aeration tank and the amount of sewage flowing into the aeration tank Q, that is, the ratio R1, that is, A/Q, is controlled to a predetermined value. There is also a control method that does this.

FIG. 2 is a block diagram showing such a control method. In the figure, 1 to 4 and 7 are similar to those shown in 1E), and 9 is a multiplier. The ratio R as described above is set in the multiplier 9. In addition, since the inflow sewage pressure 1[Q is given from the flow meter 2, the multiplier 9 multiplies these (RXQ), and this The result is given as a set value of the air amount controller 27. Therefore, the controller 7 controls the control valve 3 so that a total of 51-g of air measured by the air indicator 4 matches the set value S5). Control quantity. This control method is based on the viewpoint that the amount of oxygen required by activated sludge is proportional to the amount of sewage inflow, and is also called the constant blast magnification control method.

Although it is unfortunate as mentioned above that the amount of oxygen required for activated sludge varies greatly depending on the S degree and activity of activated sludge, this method performs control simply based on the amount of sewage inflow. Therefore, when the activated sludge temperature is low, or when the inflowing sewage is diluted by the mixing of rainwater, etc.
Even if this amount of air is not normally required, more air than necessary is supplied based on the amount of inflow, which has the disadvantage of wasting energy. This invention was made in view of the above. , the purpose is as follows: @ Ge) Control the amount of air to maintain the DO concentration in the aeration tank at the set value, and add an appropriate amount of acid volume to the activated sludge in the aeration tank. supply.

(b) Suppress the supply of excess air using a simple method and increase the energy saving effect.

□ At the time of Do meter maintenance and when the Do meter is abnormal, it is possible to automatically perform appropriate backup using a simple method.

(2) The flexibility of plant operation is increased by allowing the user to freely select either the Do constant control method, the constant air magnification control method, or a combination control method depending on the plant situation at that time.

A of this invention! #Fine is a Do constant control loop that keeps the DOIa degree of the atomization tank constant, and a value obtained by multiplying the measured amount of wastewater flowing into the atomization tank by a predetermined multiplier, which is used as the air volume setting value for the aeration tank. A constant air magnification control loop is provided to control the air volume, and the smaller of the control outputs of these loops is used as a set value for the lower constant air volume control loop to control the air volume. . In addition, it has been proven that even if the amount of supplied air is reduced in this way, it does not affect the processing efficiency in any way.The actual Jlfl of this invention will be explained below with reference to the drawings. ◎ Figure aIa 1 is a block diagram showing an embodiment of the present invention. FIG.

As is clear from the same figure, the control method according to the present invention is a good format in which the control methods shown in FIGS. 1 and 2 are combined. In addition, 10 is the air amount upper limit 9i], and 11 is the air magnification upper limiter. l, Do loop control S, air tank l
The measured value of the Do meter installed at D is given from the outside.
A PID calculation is performed so as to match the O set value 811, and the air amount set value is output.

Multiplier 9Fi, measured value Q of the amount of sewage flowing into the aeration tank 1,
It is multiplied by the air magnification upper limit setting fiRtr given from the outside and output as the air amount upper limit calculation value QXRυ. The air amount upper limiter 10 outputs the smaller one of the air amount calculation value M and the air amount upper limit calculation value QXRU to the air amount upper and lower limit limiter 6 as the air amount calculation value. The air amount upper/lower limit limiter 6 converts the air amount calculation value K into an air amount upper limit set value LU given from the outside and an air amount lower limit setting 11.
LD and output as an air amount setting value (calculated value) S5. Air volume loop control 27
Vi, 5PID calculation is performed so that the measured value F of the 9 air indicator 4 installed in the air piping matches the air amount setting @ 85, and the air amount control valve 3 installed in the air piping is opened/closed. The air amount calculation value M output from the Tsuma, p, Do loop controller 25 is calculated by the multiplier 9 and the air amount upper limiter 10.
Figure 4 is a characteristic diagram for explaining the control operation range according to the present invention. It is. The figure shows the air volume setting value (calculated value) 85
This diagram shows the range of values obtained for and p in relation to the measured value Q of sewage inflow.
O constant control is performed, air magnification constant control is performed at the boundary of straight @ It is a diagram. In this embodiment, a low selector 12 is provided, and the air amount calculation value M, which is the output of the DO loop controller) H-45, and the air amount calculation @[QX
The % feature is that the smaller one of R and R is selected by the low selector 12, the selected value is limited by the air amount upper and lower limiter 6, and this is output on the hole as the calculated air value s5. However, since it is basically the same as that shown in FIG. 3, and the control operation range is also performed as shown in FIG. 4, the details will be omitted.

In addition, in Fig. 3 or Fig. 5, the air magnification setting value R
By setting sufficiently large values for U and H, Do
The area where constant control is possible becomes as shown by the diagonal line in Figure 6, and the function of the constant air magnification control loop becomes virtually meaningless.As a result, it becomes the same as in Figure 1, and constant control becomes possible. . Furthermore, FIG. 6 is a ninth characteristic diagram similar to FIG. 4, which explains the range of the set value of the air amount when the set value of the air magnification is made sufficiently large. On the other hand, by setting a value sufficiently larger than the DO set value 54KDO measurement value, the DO
The function of the constant control loop becomes virtually meaningless.
As shown in the figure, constant air magnification control is possible. In addition, the 79th
FIG. 6 is a ninth characteristic diagram similar to FIG. 6, illustrating the range in which the air amount setting value can be adjusted when the DO setting value is sufficiently increased. For these reasons, in this invention, a single DO
It can be seen that constant temperature@ or single constant air magnification control and combination control of these are possible. That is, in the actual operation 111111 of the sewage treatment process,
Since it is required to use constant DO control, constant air doubling control, and combination control of these depending on various conditions such as the state of the plant, the state of inflowing sewage, or the weather, it is necessary to use the set value as in this invention. It can be said that it is a very big advantage that the control method can be freely selected depending on the selection of the control method. Therefore, this invention
By simply combining the constant DO control method and the constant air magnification control method, the present invention achieves superior effects that go beyond simply increasing the energy saving effect.

In addition, in FIG. 3, while the air magnification constant control is being performed by the selection operation of the air amount upper limiter lO,
As shown by the dotted line in the same figure, a command is sent from the IJ fimitter 1 to the upper PID controller 25, and when the controller 5 receives this command, the integral term of the PID calculation is maintained at its initial state. By doing so, it is possible to quickly return to DO control.

Similarly, while the air magnification constant control is being performed by the selection operation of the low selector 2 at 2 in FIG. 5, when this command t- is received, if the integral item of the PID calculation is maintained in the initial state, the return to DOffijlN can be carried out promptly.

As described above, according to the present invention, the measured value of 009 degrees in the aeration tank is maintained at the set value within a range not limited by the limiter 6°11, etc., and an appropriate amount of oxygen is supplied to the activated sludge in the aeration tank. This is because a feedback control loop (closed loop) for the DO concentration is configured. As a precaution, when both the quality and quantity of inflowing sewage decrease, or when substances interfering with Do measurement flow in, the air amount calculation value output from Do loop controller)-c2-1 increases. Then, the air magnification upper limiter 11 or selector 12 automatically shifts to air magnification constant control, and after that, the amount of air corresponding to the amount of inflowing sewage is supplied until the DO measurement value reaches the set value again, and the excess air is supplied. is suppressed 0 This ninth, above (1) to (3)
This method has the advantage of preventing the energy loss as described in section 2, does not require any special measures during maintenance of the DO meter, and makes it easy to shift to /< pull-up control when the DO meter is abnormal.

[Brief explanation of the drawing]

The eleventh factor is a block diagram showing a conventional example of an air amount control method in an aeration tank, and the second factor is a block diagram showing another conventional example.
FIG. 3 is a block diagram showing an embodiment of the present invention, and FIG. 4 is a characteristic diagram for explaining the control operation according to the present invention.
The figure is a block diagram showing another Mei J1flll of the present invention. FIGS. 6 and 7 are characteristic diagrams showing the case where various setting values in FIG. 4 are changed. Symbol explanation 1... Aeration tank, 2... Flow meter, 3... Air amount control valve, 4... Air position needle, 5... DO loop controller, 6... Air amount upper and lower limits IJ Mitter, 7... Air amount loop controller, 8... DO needle, 9... Multiplier, 10... Air amount upper limiter, 11-- Air magnification upper limiter, 12... Low selector agent Patent Attorney Akio Namiki Agent Patent Attorney Kiyoshi Matsuzaki 1's 3°'2 Figure 35! ! I-1 JIEJ Figure 5 Water pollution 1 total Gl jl (Q) Figure 5 #! 6 Figure 7 Figure 7 Drought〉To the circle)i↑Sacrilegejode (Q)

Claims (1)

[Claims] An aeration tank that is equipped with an air volume constant control loop that controls the air volume of the aeration tank to a predetermined value so that the air volume of the aeration tank that receives air supply and processes the inflowing sewage using the activated sludge method. In the control system, a first control loop measures the oxygen concentration dissolved in the aeration tank and controls it to a nuclear dissolved oxygen degree t-predetermined value, and measures the amount of sewage flowing into the aeration tank. and a second control loop that controls the amount of air supplied to the aeration tank by setting a value obtained by multiplying the measured amount of sewage by a predetermined multiplier as an air amount setting value necessary for the aeration tank; A selection means is provided for selecting one of the smaller control outputs of the second control loop, and the output from the selection means is used as a set value for the constant air amount control loop to control the air amount in the aeration tank. This is the air volume control method for the aeration tank.