JPS62121610A - Control method of sludge concentration meter in gravity type sludge condenser tank - Google Patents

Abstract

PURPOSE:To facilitate the control of a gravity thickener, by converting the output of a sludge-concentration meter for sludge fed to a condenser tank to a relative value of solid concentration based on the output of a sludge- concentration meter for sludge to be discharged. CONSTITUTION:Sewave sludge 2 is fed intermittently at predetermined intervals to a condenser tank 1 through a sludge feed pipe 3. And feed quantity of sludge is measured by a flowmeter 4 and concentration of solid in sludge is measured by an ultrasonic type sludge-concentration meter 5, the resultant measurement thereof is stored in a storage-operation control device 6. The height of the accumulation of concentrated sludge 7 precipitated and accumulated in the condenser tank 1 is measured by means of a sludge interface level meter 8. When a predetermined condition of concentrated sludge has been satisfied, a motor-operated valve 10 of a discharge pipe 9 is opened to discharge a part of the concentrated sludge 7, while discharge quantity and concentration of solids in discharged sludge is measured by a flowmeter 11 and ultrasonic type sludge-concentration meter 12 respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for managing a 7η mud depth meter disposed in a gravity-type sludge thickening tank used in a sewage treatment plant or the like.

[Conventional technology]

In order to properly operate gravity-type sludge thickening tanks (hereinafter simply referred to as thickening tanks) used in sewage treatment plants, it is necessary to reduce the solids contained in the sludge supplied to the thickening tank and the sludge discharged from the thickening tank. It is necessary to measure the concentration of sludge using a sludge concentration meter and operate the thickening tank based on the measurement results.

These measured values include the volume of sludge supplied to the thickening tank and the volume of sludge deposited in the thickening tank, which are measured separately, as well as the amount of sludge loaded into the thickening tank and the amount of sludge discharged from the thickening tank. Alternatively, it is used each time to manage the time that sludge remains in the fibrillation tank. The lη mud concentration n1 used here does not directly measure the ratio of the mass of solids contained in the l'j mud to the mass of the sludge, but rather The amount absorbed or reflected by solids in sludge is measured, and the relationship between the amount of absorption or reflection determined in advance and the concentration of solids in sludge is used to indirectly measure the amount absorbed or reflected by solids in sludge. The objective is to find out the solid concentration of

[Problem that the invention seeks to solve]

However, in the case of thickening tanks in sewage treatment plants, the properties of the sludge that is the object of measurement, such as the particle size distribution and color of the solids, are not constant. In many cases, it becomes impossible to accurately measure the solids concentration using the determined relational expression at a later date.

Therefore, when using the solids concentration value in sludge as an index for thickening tank management as described above, the relationship between the output value of the sludge concentration meter and the solids concentration should be checked frequently and corrected. It is necessary to do so.

However, in order to directly measure the concentration of solids in sludge, a certain amount of sludge is collected, its mass or volume is measured, and then the collected sludge is completely reduced to solid and liquid by means such as filtration, centrifugation, or heating. It is necessary to separate, measure the mass of the separated solid content, and calculate the ratio to the previously measured amount of collected sludge. This work requires manpower and a lot of time, so it is expensive and cannot be carried out on a large scale (1).Due to the problems of this direct measurement, This makes it difficult to actually carry out accurate management.

For example, in order to maintain a substantially constant amount of accumulated sludge in the thickening tank, the amount of solids in the supplied sludge and the amount of solids in the discharged sludge should always be equal. Therefore, if control is performed so that the sludge 1) output amount becomes the amount expressed by the following formula (11), the accumulated sludge in the thickening tank should be retained in a substantially constant amount.

V, = C, ·Vf /C,...-11) However, both the sludge supply to the thickening tank and the sludge discharge from the thickening tank are intermittent operations, and each symbol indicates the following.

V: Current discharge amount (nr) C7: Average solids concentration of sludge supplied from the previous discharge to the current discharge (g/rrr) ■,: From the previous discharge to the current discharge sludge supply amount (rrr) Cu: Average solids concentration of sludge discharged this time (g/
rd) However, for the reasons mentioned above, it is difficult to accurately measure C, , C, each time it is supplied and discharged.

Therefore, such a control method has not been widely used so far.

Therefore, the present invention provides a method for controlling the operation of a gravity thickening tank used in a sewage treatment plant based on the solids concentration of sludge.
The purpose is to perform operational control of the thickening tank without any hindrance even if the relationship between the solids concentration of the target sludge and the meter output value deviates from the initial relationship.

[Means for solving problems]

In order to achieve the purpose of the method for managing a sludge concentration needle in a gravity-type sludge thickening tank according to the present invention, the first sludge concentration d1. A sludge interface meter that measures the position of the interface between the sludge and supernatant liquid deposited in the sludge thickening tank, and a second sludge concentration meter that indirectly measures the solid matter concentration in the sludge discharged from the sludge thickening tank. The value of the volume of sludge deposited in the sludge thickening tank, which can be determined from the measurement of the sludge interface meter installed in the gravity-type sludge thickening tank, 1111 + the value of the volume of sludge discharged from the JJI mud bay shrinking tank, 2nd Convert the indicated value of the first sludge concentration meter to the solid concentration using the values of the solid matter concentration in the discharged sludge obtained by the sludge concentration meter III and the volume of the sludge supplied to the sludge thickening tank. It is characterized by constantly updating the conversion formula.

〔Example〕

Next, the present invention will be specifically explained with reference to embodiments shown in the drawings.

FIG. 1 is a flowchart in this embodiment.

Sewage sludge 2 to be concentrated is intermittently supplied to the thickening tank 1 via a sludge supply pipe 3 at preset time intervals. At this time, the sludge supply amount is measured by the flow meter 4, and the solid matter concentration in the sludge is measured by the ultrasonic sludge lacquer meter 5, and the measurement results are stored in the storage calculation control device 6. Solids settled from the supplied lη mud in the thickening tank 1 are deposited in the tank as thickened sludge 7. The height of the pile is measured by a sludge interface meter 8. Preset concentration
When the sludge υ1 discharge conditions are satisfied (for example, when the amount of sludge in the tank exceeds a certain amount, when the scheduled discharge time has arrived, etc.), the discharge pipe 9
The electric valve 10 opens and a portion of the thickened sludge 7 is discharged.

At this time, the concentrated sludge 7 is discharged while measuring the discharge amount and the solid matter concentration in the discharged sludge using the flow meter 11 and the ultrasonic sludge concentration meter 12, respectively.

The feature of the present invention is that the output value of the sludge concentration meter 5 for thickening tank supplied sludge is changed to a relative fixed solids concentration value based on the output value of the sludge concentration meter 12 for discharged sludge by the procedure described below. This makes it easier to manage gravity thickeners, which was considered difficult with the prior art.

■ First, before operating the equipment shown in Figure 1, check the sludge concentration meter 5.
12 is calibrated using a conventional method, and the immediate relationship between the solid matter concentration in the sludge and the meter output value is obtained as shown in the following equations (2) and (3).

Cf-a, xr...(2) cu =
au-xl+ ... (31 However, Ct, Cu: supply sludge, l ,,: Conversion coefficient■ Start supplying sludge to the gravity type sludge thickening tank 1.

fIIl in general sewage treatment plants? As in the case of the i-tank, in this embodiment as well, tm i1? Sludge supply to the i tank + sludge discharge from the fM shrinkage tank is performed intermittently. During the period from the start of sludge supply until the first sludge discharge, the volume of sludge intermittently supplied into the thickening tank 1 (which can be measured with the flowmeter 4) and the solids calculated by formula (2) The product of solid matter concentration is determined for each feeding of sludge (sludge).Furthermore, the cumulative value is determined by the storage arithmetic and control device 6 and is stored as the volumetric solid matter amount G in the tank.

That is, G←−G+Cf・・・・(4) However, 11.: Volume of sludge supplied in one supply operation −: Meaning of substituting the result on the right side into the left side The first 4fi of G is O ■ When the predetermined conditions for sludge discharge, such as the arrival of the scheduled discharge time, are met, the height of the sludge 7 accumulated in the thickening tank 1 is measured by the sludge interface meter 8, and this measured value and The volume of the accumulated sludge 7 is calculated from the internal structure of the thickening tank, and the result is stored in the storage calculation control device 6.

■ Next, the discharge of sludge from the thickening tank 1 is started, and the output value of the concentration meter 12, the value of the solid matter concentration in the discharged sludge obtained by equation (3), and the value stored in the storage calculation device 6 are used. Then, the correction coefficient K is calculated according to the following equation (5).

V-C.

K-□...(5) However, V: Volume of accumulated sludge calculated from the height of sludge accumulation Cu: Discharge determined by equation (3)? 'i Solids concentration of mud ■ The value obtained by multiplying this correction coefficient K by the above-mentioned G and the conversion coefficient af in equation (2), that is, -G and -ay
are G and af after correction.

G←−K・G・・・・・・(6) a, ←−to−
al...(7)■ After the sludge discharge operation is completed, G is replaced with new G by further subtracting the product of the discharged sludge volume and its solids concentration. That is, G←−G−Cu−V, ...−・+81 However, vu: Volume of sludge discharged in one discharge operation■ After that, the volume of sludge in the supplied sludge until the start of the next discharge operation For the solids concentration of Solids of internally deposited sludge 1
The value of 1G is calculated according to the above equation (4).

■ From then on, repeat the steps below.

The above is the operating procedure of the present invention.

[Experiment example]

Next, in order to prove the effectiveness of the present invention, the results of an experiment conducted using the apparatus shown in FIG. 1 will be described.

1 Experiment 1. − First, N
I41i! Control was performed to maintain the amount of accumulated sludge in the tank almost constant.

That is, in the apparatus shown in FIG. 1, sludge 2 was continuously supplied to the thickening tank 1, and the volume and solids concentration of the supplied sludge were measured using a flow meter 4 and a concentration meter 5, respectively. Starting from when the height of the sludge accumulated in tank 1' reaches about 2 times the depth of thickening tank 1, the water is removed every hour to maintain the amount of accumulated sludge in thickening tank 1 almost constant. 2 (Sludge discharge was carried out in accordance with 11.

At this time, changes over time in the position of the accumulated sludge in the tank as measured by the sludge interface meter 8 are shown in FIG.

If the measured value by the meter is correct and the amount of solids bathed together with the separated liquid 13 is negligible, the amount of solids discharged from the thickening tank l should be equal to the amount of solids supplied since the previous discharge. , the amount of accumulated sludge should also be approximately constant. However, this is not actually the case. The reason for this is thought to be that the conversion coefficient a, which converts the densitometer output to the solids concentration, has changed as described below.

Changes in this conversion coefficient a are shown in Figures 3+a) and 3(b).
It is clearly expressed in l. That is, Fig. 3 (a
When using an ultrasonic densitometer to measure the solids concentration in the supplied sludge, 1. 1 in l'j mud prepared before implementing the control described in l-. This is a regression equation between the depth of the sludge and the current output value obtained when the sludge is supplied to the dth concentration of sludge. During the control period, the value corresponding to Cf in equation (11) is the current output value of the ultrasonic concentration meter converted based on this regression equation.

Further, FIG. 3 Tbl is a regression equation between the solid matter concentration in the sludge and the current value of the densitometer, which was created in the same manner as in FIG. 3(a) after the above control is completed. As is clear from this figure, the regression coefficient has changed during the control period.

1 Experiment 2. - Next, by applying the present invention, Experiment 1. The same purpose of control was carried out. That is, the sludge 2 was continuously supplied to the thickening tank 1 shown in FIG. 1, and the volume and solids concentration of the supplied sludge were measured using a flow meter 4 and a concentration meter 5, respectively. Further, the height of the sludge 7 deposited in the tank was measured using a sludge interface meter 8.

Starting from the time when the height of the sludge accumulated in this tank reaches approximately 2 the depth of the thickening tank 1, the amount calculated to be equal to the amount of sludge supplied during the past hour is calculated every hour. Sludge was discharged from thickening tank 1 at a discharge rate such that: The control equation at this time is exactly the same as equation (1). However, the conversion formula for the concentration of solids in the sludge supplied to the thickening tank 1 and the amount of solids in the sludge deposited in the tank were corrected by the method of the present invention each time the sludge was discharged from the thickening tank 1.

As clearly shown in FIG. 4, when this method was used, the desired control became possible.

The above is an example that is relatively easy to understand among concentration tank control methods. In addition, by applying this invention, the control of the sludge retention time in the thickening tank, which has been difficult to control accurately due to the measurement of sludge concentration, can be achieved accurately and easily. be able to do it.

〔Effect of the invention〕

As explained above, when using the management method of the present invention,
Measuring sludge concentration is accurate and easy to see. Therefore, it has become possible to accurately manage the sludge that remains in the thickening tank, and it has also become possible to control the sludge residence time with high precision.

[Brief explanation of drawings]

Figure 1 shows an example of the equipment used to carry out the method of the present invention, Figure 2 shows changes over time in conventional accumulated sludge, and Figure 3 shows the relationship between solids concentration and densitometer output. FIG. 4 shows changes over time in accumulated sludge modified by the method of the present invention. 1: Thickening tank 2: Sludge 3: Sludge supply pipe 4: Flow meter 5: Sludge concentration meter 6: Memory calculation control device 7: Thickened sludge 8: Interface meter 9: Discharge pipe 10: Electric valve 11: Flow meter 12: Sludge Concentration meter 13: Separated liquid

Claims (1)

[Claims] 1. A first sludge concentration meter that indirectly measures the concentration of solids in sludge supplied to a sludge thickening tank; A sludge interface meter that measures the position and a second sludge concentration meter that indirectly measures the solids concentration in the sludge discharged from the sludge thickening tank are installed in the gravity sludge thickening tank, and the measured values of the sludge interface meter are installed. Estimated value of volume of sludge deposited in the sludge thickening tank, value of volume of sludge discharged from the sludge thickening tank, estimated value of solids concentration in discharged sludge obtained by the second sludge concentration meter, and sludge Sludge concentration in a gravity type sludge thickening tank, characterized in that a conversion formula for converting the indicated value of the first sludge concentration meter into solid matter concentration is constantly updated using the value of the volume of sludge supplied to the thickening tank. How to manage your meter.