JPS61129092A - Apparatus for controlling air feed amount of aeration tank - Google Patents

Abstract

PURPOSE:To feed an optimum amount of air, by providing not only a dissolved oxygen densitometer to an aeration tank but also a respiration speedometer to each aeration zone and regulating the number of rotations of a blower on the basis of the measured value of the dissolved oxygen densitometer. CONSTITUTION:Org. waste water flowed into the aeration zone 4a of an aeration tank 3 through an inflow pipe 1 is treated with activated sludge in the aeration tank 3 under an optimum condition in the presence of air supplied from a blower 9 through a gas main pipe 8, a distribution pipe 6 and an air diffusion plate 7. The treated waste water is successively flowed down to aeration zones 4a, 4b, 4c and flowed out through an outflow pipe 2 and separated from activated sludge in a sedimentation tank to be discharged out of the system as treated water. DO in the aeration tank 3 is measured by a DO meter 10 and the current signal of the measured value is converted to a voltage signal by a converter 12a to be inputted to a microcomputer 13. The number of rotations of blower 9 is calculated from the deviation of DO with an objective value.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a device for controlling the amount of air supplied to an aeration tank when organic wastewater such as sewage is treated by an activated sludge method.

<Prior Art> In sewage treatment plants and the like that treat organic wastewater using the activated sludge method, the aeration tank blower consumes the largest amount of electricity, which is said to account for approximately 40% of the total electricity consumption of the entire treatment plant. Therefore, when considering energy conservation for the entire treatment plant, it is most effective to reduce the amount of electricity used by the blower, and it is important to control the amount of air supplied to supply only the necessary amount of oxygen without excessive aeration. . For example, [Energy Saving Aeration Handbook, published by Science and Technology Development Center, 1
As shown in "August 1, 1980, pp. 81-98", the air flow is controlled by adjusting it with an on-off valve installed on the suction side of the blower so that the amount of air supplied is a constant ratio to the amount of incoming water. , using the so-called inflow water proportional control method, or installing a dissolved oxygen concentration meter (hereinafter referred to as Do meter) in the aeration tank, and measuring the difference between the target value of dissolved oxygen concentration (hereinafter referred to as DO) and the actual Do value. There is a so-called constant Do control system, in which the DO in the aeration tank is kept constant by adjusting an on-off valve provided on the suction side of the blower or by adjusting the rotational speed of the blower. However, although the inflow water volume proportional control system is the most common system, it focuses only on fluctuations in water volume and does not work at all against fluctuations in water quality. In addition, the constant Do control method adjusts the amount of air supplied in response to fluctuations in water volume and water quality, but since the length of a normal aeration tank is considerably longer than its width, complete mixing cannot be achieved, and the installation position of the DO meter The aeration tank as a whole is subject to considerable variation due to differences in In other words, if a DO meter is installed on the inflow side, the latter stage of the aeration tank will be over-aerated, whereas if it is installed on the outflow side, the first stage of the aeration tank will be under-aerated, which may lead to a decline in treatment function. be.

In order to solve this problem of constant Do control, there is a so-called tapered aeration method in which the installation density of air diffuser plates or air diffuser pipes is lowered from the inflow side to the outflow side.

However, with this tapered aeration method, it is difficult to determine the Cheeverd ratio at the time of design, and even if the ratio is determined after sufficient preliminary research, it is extremely difficult to respond to subsequent changes in water quality itself. be.

<Problems to be Solved by the Invention> The present invention provides continuous control over the entire aeration tank without causing insufficient aeration in the front stage of the aeration tank or overaeration in the latter stage even if the amount and quality of water flowing into the aeration tank fluctuates. The purpose of the present invention is to provide an air supply amount control device for an aeration tank that can supply an optimal amount of air and further saves energy consumption by always maintaining the amount of air supplied in an optimal state. It is.

Means for Solving the Problems> The present invention divides an aeration tank in an activated sludge method to form a plurality of aeration zones, and divides the gas supplied from a blower into a plurality of aeration zones with a control valve attached to each aeration zone. It is an aeration tank that distributes and supplies water to each aeration zone via piping, and a dissolved oxygen concentration meter is installed at any position in the aeration tank, and a respiro rate meter is installed in each aeration zone. The rotational speed of the blower is adjusted based on the measured value, and the required air volume for each corresponding aeration zone is calculated based on the measured value of each respirometer, and then that amount is calculated from the required air volume for each aeration zone. An aeration tank characterized in that the amount of air supplied to each aeration zone is controlled by calculating the opening degree of each control valve that can supply air, and adjusting the opening degree of each control valve based on the calculation result. This invention relates to an air supply amount control device.

The present invention will be explained below based on the drawings.

FIG. 1 is a flow explanatory diagram showing an example of an embodiment of the apparatus of the present invention, in which an aeration tank 3 having an inflow pipe 1 and an outflow pipe 2 is divided into, for example, three parts to form aeration zones 4a, 4b, and 4c. and each aeration zone 4a, 4b.

A distribution pipe 6 having a control valve 5 is attached to each of the distribution pipes 4c, and a large number of air diffuser plates (or air diffuser pipes) 7 are attached to the distribution pipe 6.
Attached. Each distribution pipe 6 is connected to a blower 9 via a main gas pipe 8. On the other hand, place D at any position in the aeration tank 3.
o A total of 10 zones are provided, and each aeration zone 4a, 4b, 4
A respiration rate meter 11 is provided at each of C. The converter 12a in the figure converts the measured value signal of the Do meter 10 or the respiration rate meter 11, for example, a current signal of 4 to 20 mA, into a voltage signal of 0 to 10 cm. The voltage signal is received and converted into a digital signal of θ to 4095, for example, and the output value for controlling the rotation speed of the blower 9 is calculated via the converter 12b1 inverter 14. It is used to calculate the output value of opening degree control.

The converter 12b converts the signal from the microcomputer 13, for example, a voltage signal of 0 to IOV, into a current signal of 4 to 20 mA, and the inverter 14 outputs the signal from the converter 12b, a current signal of 4 to 20 mA, for example. The output is converted into a frequency signal of 20 to 50 Hz, and the output value is input to a part of the motor of the blower 9. Furthermore, since the device of the present invention supplies each aeration zone with the optimum amount of air that matches the respiration rate of activated sludge in each aeration zone, the Do of each aeration zone becomes approximately the same value, and therefore the installation position of the DO meter is Any position in the aeration tank 3 may be used.

<Operation of the invention> The present invention calculates the true oxygen demand required per unit capacity of each aeration zone from the respiration rate of activated sludge,
The optimal amount of air is sent to each aeration zone, and organic wastewater such as sewage that has flowed into the aeration zone 4a of the aeration tank 3 via the inflow pipe 1 is passed through the gas main pipe 8, the distribution pipe 6, Under optimal aeration conditions supplied from the blower 9 via the aeration plate 7, the activated sludge in the aeration tank 3 sequentially flows down to the aeration zones 4a, 4b, 4C, and then flows through the outflow pipe 2. After flowing out and being separated from activated sludge in a settling tank (not shown), it is discharged outside the system as treated water. The optimal aeration conditions for the aeration tank 3 described above are established as follows.

First, the DO in the aeration tank 3 is measured by the DO meter 10, and the current signal of the measured value is converted into a voltage signal by the converter 12a, which is manually input to the microcomputer 13, and the manual value is converted into a digital signal. The target value of DO (usually 1 to 2 l11
r/1) is subjected to PI calculation (proportional integral calculation) or PID calculation (proportional integral differential calculation) to calculate the rotation speed of the blower 9.

Next, the digital signal of the calculated value is converted into a voltage signal and input to the converter 12b, where the voltage signal is converted into a current signal, and the output is further sent to the inverter 14, where the current signal is converted into a frequency signal and the blower -9 to a part of the motor, and controls the rotation speed of the blower -9. Note that if the blower 9 is one that maintains a nearly constant amount of air even if the pressure on the discharge side changes, such as a displacement type (roots type, etc.),
By controlling the rotation speed of the blower 9,
The discharge amount can be effectively controlled.

In addition, each respiration rate meter 11 installed in each aeration zone 4a, 4b, and 4C is used to measure the respiration rate at regular intervals (usually every 0.5 to 6 hours), and the current signal of the measured value is transferred to the converter 12a. The output is converted into a voltage signal and inputted to the microcomputer 13, the input value is converted into a digital signal, and the required air supply amount for each corresponding aeration zone 4a, 4b, 4C is calculated based on the digital signal. The output value of the opening degree of each control valve 5 that can supply the required amount of air is calculated from the required amount of air, and the output calculation result is converted into a voltage signal and input to the converter 12b, where the voltage signal is converted into a current. The signal is converted into a signal and output to each control valve 5, and the opening degree of each control valve 5 is adjusted. The above operation is shown in the flowchart explanatory diagram of FIG. 2.

Further, the opening degree of each control valve 5 described above is calculated according to the following procedure. Here, i indicates each aeration zone, and in the formulas in each procedure below, i=1 is the aeration zone 4a, i=
2 indicates the aeration zone 4b, and i=3 indicates the aeration zone 4C.

[Procedure 1] Input of respiration rate rz (nw/j?-hr) Let the respiration rate of each aeration zone be r, , r, , r3.

[Step 2] Required overall oxygen transfer capacity coefficient K for each aeration zone
Calculation of L-= (1/hr) Kts+” r I/ (Cs Co) KLaz=
r z / (Cs Co)KLa3= r x /
(Cs-Co)C8: Saturation D0 at water temperature in aeration zone (■#) C,: DO target value (■/j Calculate KLat for each aeration zone using the above formula.'
[Step 3] Required air supply amount Qi for each aeration zone (No?/
Calculation of '+min') The relationship between the required air supply amount per diffuser plate and KL, i is as follows:
Since it is a -order function, it is expressed by the following formula.

Q+/N+=A-KL□+B Qt/Nt=A-KLat+B Qz/N: 1=A-Kta2+B A, B: Constant determined by diffuser plate installation water depth and installation density, wastewater properties, water temperature, etc. Ni: Each aeration Step 2 for the number of diffuser plates installed in the zone
Substituting the KLmi of each aeration zone determined by Q = / N t and Q! of each aeration zone. seek.

[Step 4] Calculate the air diffuser plate pressure loss ΔPat (mAq) The relationship between the air supply amount per air diffuser plate and the pressure loss is roughly shown in Figure 3, but these values were determined in advance through experiments. Create a table using
ΔPdi corresponding to N, i.e. ΔP of each aeration zone
Find dl, Δp, tz, and ΔPo.

[Step 5] Pressure loss ΔPa of gas piping to each aeration zone
(wmAq) (7) Calculation Normally ΔPA! It is a very small value compared to , so it is ignored.

[Step 6] Pressure loss ΔPVi (m
Calculation of Aq) Assuming that the water level and the installation water depth of the diffuser plate are the same in each aeration zone, and assuming that the pressure loss of the piping is ignored, the following equation holds true.

ΔPVI+Δpd+=ΔPVt+Δpat=ΔPV3+
ΔPd3 Here, the values of Ql, Qt, and Q3 are compared, and the opening degree of the control valve in the aeration zone with the maximum air supply amount is set to 100%. For example, Q
When l is the maximum, the opening degree of the control valve 5 in the aeration zone 4a is 100%, so ΔPvI becomes approximately O. Therefore, the above equation becomes ΔPv+"'0 ΔPVl=ΔPd1-Δpat 8PV3"Δp□-ΔPd3, and ΔP4□ obtained in step 4 is substituted to calculate Δpvi of each aeration zone.

[Step 7] Determination of the control valve opening degree Di (%) First, determine the flow rate u1 (m
/sec).

u z = Qt/ 60 s z ui = Q3/60 S = S = Cross-sectional area of the distribution pipe 6 of each aeration zone, and generally the pressure loss of the control valve is: ∆P vt = '3z ・(ui''/ 2 g)・
Pe,; Pressure loss coefficient (~) g: Gravitational acceleration (m/sec") ρ: Density of air (kg/rrr) Therefore, ΔPU of aeration zones 4b and 4c is ΔPv*-f3z" ( uz”/2g)・p,
ΔPv+=e+・(ux”/ 2 g)
・f), calculate 82 and e3 from the above formula, and calculate the pressure loss coefficient e4 and the control valve opening, which were created in advance by experiment,
The control valve opening degree is determined from a table showing the relationship (generally shown in FIG. 4).

The opening degree of the control valve 5 obtained in the above manner is, for example, from 0 to
Convert it into a 10V voltage signal and send it to the converter 12b,
Here, the output is converted into a current signal of, for example, 4 to 20 mA, and sent to each control valve 5, and the opening degree of each control valve 5 is adjusted to optimally supply air to each aeration zone.

Next, an example of calculating the opening degree of each control valve 5 will be shown.

[Calculation example]

Aeration zone water temperature = 20°C, Do target value = 1 / l, number of diffuser plates installed: N + = Nz = Ns = 60, diffuser plate installed water depth = 5 m [Step 1] Respiration rate r positive From the 31 measurement value of the input respiration rate meter, r + "30 tag/l - hr rz - 25 mg/l - hr r 3 = 15 tng/It ・hr [Step 2]
Required overall oxygen transfer capacity coefficient K for each aeration zone. The saturated DO of the aeration zone at a calculated water temperature of 20℃ is 8.8■/
l, so KL□=30/(8,8-1) =3.8 (1/hr) Ktaz= 25/(8,8-1) =3.2 (1/hr) KL-3= 15 / (8,81) = 1.9 (1/hr) [Step 3] The calculation constant for the required air supply amount Q for each aeration zone is Q!, where A is 24 and B is 10. / N4= 24 KLII! + 10 Therefore Qr/l'J+#101 N l/llll1nQz/
Nz average 87 Nj! /m1n Ch/ N3# 56 N l /min and Q + = 6.1 N n? / ta inQ!
= 5.2 Nrd/m1nQz=3.4Nm/w
in [Step 4] Calculation of diffuser plate pressure loss Δpa+ From Figure 3, ΔP□=470mAq.

ΔPaz= 390 tfflA q ΔPax= 270 mA q [Step 5] Pressure loss ΔPA of gas piping to each aeration zone
This is a very small value compared to the calculated ΔPdi, so it is ignored.

[Step 6] Calculation of pressure loss ΔPVi to be given to each control valve ΔPv+-〇Δpvt” ΔPaI-tsPaz=8 0
wAqΔPV'l"ΔPa+-8 to pH = 200 m
A q [Step 7] Determination of control valve opening, % If the inner diameter of distribution pipe 6 is 100 am, 5l = 7.8
5XlO-3rrf Therefore u t= h/ 60 s z= 11 m/5ec
usffi Q*/ 60 S 3-7.2 m/se
calso +i1g"ΔPvz' 2 g/ (ut"・P')#
9 es=APvz' 2 g/ (u3" ・ρ) #50 Note that ρ is 1 after taking into account the temperature increase by the blower and the water depth of 5 m.
．． 5kb Therefore, from FIG. 4, DI-IQ 0% Dz-58% D, = 40%, and the opening degree of the control valve 5 can be determined.

<Effects of the Invention> As explained above, according to the apparatus of the present invention, the optimal air supply amount commensurate with the respiration rate of activated sludge in each of the plurality of aeration zones, that is, the rate of organic matter decomposition, can be constantly supplied to each aeration zone. Since the air can be supplied to the aeration tank, even if the amount and quality of the inflowing water fluctuates, the amount of air supplied can be quickly adjusted to the optimum level, and it is also possible to prevent insufficient aeration in the front stage of the aeration tank or overaeration in the latter stage. In addition, it is possible to save energy consumption by always maintaining the air supply amount in an optimal state.

[Brief explanation of the drawing]

Figures 1 to 4 all relate to the device of the present invention; Figure 1 is an explanatory diagram of the control flow, Figure 2 is an explanatory diagram of the flowchart, and Figure 3 is the amount of air supplied per air diffuser plate. FIG. 4 is an explanatory diagram showing the relationship between pressure loss and the opening degree of the control valve. 1...Inflow pipe 2...Outflow pipe 3...Aeration tank 4...Aeration zone 5...Control valve
6...Distribution pipe 7...Diffuser plate
8... Gas main pipe 9... Blower 10... Dissolved oxygen concentration meter (DO meter) 11... Respiration rate meter 12... Converter 13
...Microcomputer 14...Inverter Fig. 3 atmll'll'tsn';'@4 (Nl/a;n)
Figure 4 ei (-) Procedural amendment (voluntary) 1986? Mr. Michibe Uga, Commissioner of the Patent Office, 1, Indication of the case, Patent Application No. 250574, filed in 1982, 2, Name of the invention, Aeration tank air flow control device 3, Person making the amendment Relationship to the case Patent applicant Address: 5-5-16 Hongo, Bunkyo-ku, Tokyo Name:
(440) Organo Co., Ltd. Representative Nagai
Kunio Ii 4, Agent 113 Address 5-5-16 Hongo, Bunkyo-ku, Tokyo −
) Inside Organo Co., Ltd. Name (6376) Patent Attorney Akira Takahashi 1
．． , 812-5151 5. Please correct the following matters in the detailed description of the invention column and drawings [Figure 2] in the specification subject to amendment. 1. On page 6, line 6, the phrase "to the regulating valve 5" is corrected to "to the regulating valve 5." 2. Figure 2 of the drawing is corrected as shown in the attached sheet. Figure 2 above 11i'j control device

Claims (1)

[Claims] An aeration tank in which the aeration tank is divided to form multiple aeration zones, and gas from a blower is distributed and sent to each aeration zone via a distribution pipe with a control valve, and the aeration tank can be placed at any location in the aeration tank. In addition to installing a dissolved oxygen concentration meter in each aeration zone, a respirometer is installed in each aeration zone, and the rotation speed of the blower is adjusted based on the measured value of the dissolved oxygen concentration meter, and the required amount of each aeration zone is determined based on the measured value of each respirator. Calculate the amount of air to be supplied, then calculate the opening degree of each control valve that can supply the required amount of air to each aeration zone, and adjust the opening degree of each control valve based on the calculation result. An air supply amount control device for an aeration tank, characterized in that the amount of air supplied to each aeration zone is controlled by.